JOINT MECHANISM FOR CONSTRUCTION MACHINE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from Japanese Patent Application Serial No. 2024-159109 (filed on Sep. 13, 2024), the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to a joint mechanism for a construction machine.

BACKGROUND

Japanese Patent Application Publication No. 2002-88796 (“the '796 Publication”) discloses an excavator including a vehicle body, a boom, an arm, and a bucket. The boom is coupled to the front end of the vehicle body. The boom can rotate up and down relative to the vehicle body. The arm is coupled to the distal end of the boom. The arm can rotate up and down relative to the boom. The bucket is coupled to the distal end of the arm. The bucket can rotate up and down relative to the arm. In the techniques such as those disclosed in the '796 Publication, it is desirable to reduce the burden on joints, such as the coupling portion between the boom and arm or the coupling portion between the arm and bucket, for example.

SUMMARY

One aspect provides a joint mechanism for a construction machine. The joint mechanism comprises: a drive unit including an electric motor, the drive unit being configured to output torque; a first member including a first coupling wall and a second coupling wall that are aligned in an axial direction along a rotation axis of the torque output by the drive unit; a second member at least partially located between the first coupling wall and the second coupling wall in the axial direction; and a coupling member that couples the first coupling wall and the second member so as to allow relative rotation in a circumferential direction around the rotation axis, wherein the drive unit couples the second coupling wall and the second member so as to allow relative rotation in the circumferential direction.

Another aspect provides a joint mechanism for a construction machine. The joint mechanism comprises: a drive unit including an electric motor, the drive unit being configured to output torque; a first member; and a second member aligned with the first member in an axial direction along a rotation axis of the torque output by the drive unit, wherein the drive unit includes a base portion and an output portion, the base portion being fixed to the second member, the output portion being fixed to the first member so as to be rotatable in a circumferential direction around the rotation axis relative to the base portion, and wherein the output portion has a spline groove formed along the rotation axis, and the output portion is fixed to the first member via the spline groove.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view schematically showing an excavator.

FIG. 2 is a sectional view schematically showing a first joint mechanism.

FIG. 3 is a sectional view schematically showing a second joint mechanism.

FIG. 4 is a sectional view schematically showing a third joint mechanism.

FIG. 5 is a sectional view schematically showing a modification example of the joint mechanism.

FIG. 6 is a sectional view schematically showing a modification example of the joint mechanism.

FIG. 7 is a sectional view schematically showing a modification example of the joint mechanism.

FIG. 8 is a sectional view schematically showing a modification example of the joint mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A joint mechanism for a construction machine according to one embodiment will now be described with reference to the appended drawings. The drawings may show the components in an enlarged manner for the sake of better intelligibility. The dimensions of the components and the ratios thereof in the drawings may be different from those of the actual components, and among the drawings. In this specification, the reference signs may be omitted in collectively explaining components having the same name used in multiple joint mechanisms.

Overall Configuration

As shown in FIG. 1, an excavator 10, serving as a construction machine, includes a vehicle body 12 and a pair of traveling units 14. The vehicle body 12 houses various mechanisms, devices, and parts necessary to operate the excavator 10. The vehicle body 12 may optionally include a seat for accommodating an operator. The pair of traveling units 14 are provided at the left and right sides across the vehicle body 12. The traveling units 14 each include a traveling crawler and an operating mechanism that circles the crawler.

The excavator 10 includes a support member 60, a boom 30, and an arm 40. The excavator 10 also includes a bucket 50 as an attachment. The support member 60 is positioned in front of the vehicle body 12. The support member 60 includes a support member body 62 and walls for coupling the support member body 62 to the boom 30. The support member body 62 is coupled to the vehicle body 12.

The boom 30 is coupled to the support member 60. The boom 30 includes a boom body 31 and walls for coupling the boom body 31 to the support member 60 and the arm 40. The boom body 31 is shaped like an elongated plate or column. For example, the boom body 31 is bent at a midpoint in its longitudinal direction. The boom body 31 can rotate about the first rotation axis 21J relative to the support member 60. The first rotation axis 21J extends in a direction orthogonal to an imaginary axis extending in the top-bottom direction of the vehicle body 12. The first rotation axis 21J is the central axis of the torque output by a first drive unit 101, which is described later.

The arm 40 is coupled to the end of the boom body 31 opposite to the coupling point to the vehicle body 12. The arm 40 includes an arm body 41 and walls for coupling the arm body 41 to the boom 30 and the bucket 50. The arm body 41 is shaped like an elongated plate or column. The arm body 41 can rotate about the second rotation axis 22J relative to the boom 30. The second rotation axis 22J is substantially parallel to the first rotation axis 21J. The second rotation axis 22J is the central axis of the torque output by a second drive unit 102, which is described later.

The bucket 50 is coupled to the end of the arm 40 opposite to the coupling point to the boom 30. The bucket 50 includes a bucket body 51 and walls for coupling the bucket body 51 to the arm 40. The bucket body 51 is shaped like a box having an opening. The bucket body 51 can rotate about the third rotation axis 23J relative to the arm 40. The third rotation axis 23J is substantially parallel to the first rotation axis 21J. The third rotation axis 23J is the central axis of the torque output by a third drive unit 103, which is described later.

<First Joint Mechanism>

The following describes a first joint mechanism 21, which is the mechanism that couples the support member 60 and the boom 30. As shown in FIG. 2, the excavator 10 includes a first drive unit 101, a first brake unit 130, a pin 71, and a cover 72 in a first coupling portion that couples the support member 60 and the boom 30. The first joint mechanism 21 in this embodiment includes these components, as well as the support member 60 and the boom 30, which are coupled to each other. The support member 60 is the first member in the first joint mechanism 21. The boom 30 is the second member in the first joint mechanism 21. The pin 71 is the coupling member in the first joint mechanism 21. In FIG. 2, some of the components of the first joint mechanism 21 are shown in plan view not in sectional view.

As shown in FIG. 2, in the first coupling portion, the support member body 62 and the boom body 31 are located on one side and the other side across the first rotation axis 21J. The end surface 62A of the support member body 62 and the first end surface 31A of the boom body 31 are opposed to each other across the first rotation axis 21J. The first end surface 31A of the boom body 31 is the end surface of the long-shaped boom body 31 closer to the vehicle body 12. With respect to a first axial direction along the first rotation axis 21J, the dimension of the end surface 62A of the support member body 62 is larger than the dimension of the first end surface 31A of the boom body 31. Hereafter, in the description of the first joint mechanism 21, one of the two directions along the first rotation axis 21J will be referred to as the first direction A1, and the other as the second direction A2. The end of the end surface 62A of the support member body 62 on the first direction A1 side is located on the first direction A1 side relative to the end of the first end surface 31A of the boom body 31 on the first direction A1 side. The end of the end surface 62A of the support member body 62 on the second direction A2 side is located on the second direction A2 side relative to the end of the first end surface 31A of the boom body 31 on the second direction A2 side.

The support member 60 includes a first coupling wall 64 and a second coupling wall 66 as components for coupling the support member body 62 to the boom body 31. The first coupling wall 64 protrudes from the end surface 62A of the support member body 62 toward the boom body 31. Specifically, the first coupling wall 64 protrudes from the end of the end surface 62A of the support member body 62 on the first direction A1 side. The first coupling wall 64 is shaped like a plate. In the first axial direction, the first coupling wall 64 has a connecting end, connected to the end surface 62A, and a protruding end opposite to the connecting end. In the first axial direction, the entirety of the first coupling wall 64 from the connecting end to the protruding end is located at substantially the same position as the end of the end surface 62A on the first direction A1 side. The protruding end of the first coupling wall 64 is located on the boom body 31 side of the first rotation axis 21J. The first rotation axis 21J passes through the principal surface of the first coupling wall 64. The principal surface of the first coupling wall 64 is substantially orthogonal to the first rotation axis 21J. The “principal surface” as used herein is the surface with the largest area among the outer surfaces of a plate-like object. The first coupling wall 64 has a through hole 64A. The through hole 64A extends through the first coupling wall 64 in the first axial direction. The central axis of the through hole 64A substantially coincides with the first rotation axis 21J.

The second coupling wall 66 protrudes from the end surface 62A of the support member body 62 toward the boom body 31. Specifically, the second coupling wall 66 protrudes from the end of the end surface 62A of the support member body 62 on the second direction A2 side. The second coupling wall 66 has the same shape and dimensions as the first coupling wall 64. Thus, the second coupling wall 66 is shaped like a plate. In the first axial direction, the second coupling wall 66 has a connecting end, connected to the end surface 62A, and a protruding end opposite to the connecting end. In the first axial direction, the entirety of the second coupling wall 66 from the connecting end to the protruding end is located at substantially the same position as the end of the end surface 62A on the second direction A2 side. The second coupling wall 66 is aligned with the first coupling wall 64 in the first axial direction. Like the first coupling wall 64, the second coupling wall 66 is located at a position through which the first rotation axis 21J passes. The principal surface of the second coupling wall 66 is substantially orthogonal to the first rotation axis 21J. The second coupling wall 66 has a through hole 66A. The through hole 66A will be detailed later.

The boom 30 includes a first connecting wall 33 and a second connecting wall 35 as components for coupling the boom body 31 to the support member body 62. The first connecting wall 33 protrudes from the first end surface 31A of the boom body 31 toward the support member body 62. Specifically, the first connecting wall 33 protrudes from the end of the first end surface 31A on the first direction A1 side. The first connecting wall 33 is shaped like a plate. In the first axial direction, the first connecting wall 33 has a connecting end, connected to the first end surface 31A, and a protruding end opposite to the connecting end. In the first axial direction, the entirety of the first connecting wall 33 from the connecting end to the protruding end is located at substantially the same position as the end of the first end surface 31A on the first direction A1 side. The protruding end of the first connecting wall 33 is located on the support member body 62 side of the first rotation axis 21J. The first rotation axis 21J passes through the principal surface of the first connecting wall 33. The principal surface of the first connecting wall 33 is substantially orthogonal to the first rotation axis 21J. In the first axial direction, the first connecting wall 33 is located between the first coupling wall 64 and the second coupling wall 66. The first connecting wall 33 is located immediately adjacent to the first coupling wall 64. There is a small gap between the first connecting wall 33 and the first coupling wall 64. The first connecting wall 33 has a through hole 33A. The through hole 33A extends through the first connecting wall 33 in the first axial direction. The central axis of the through hole 33A substantially coincides with the first rotation axis 21J. The diameter of the through hole 33A is substantially equal to the diameter of the through hole 64A in the first coupling wall 64 of the support member 60.

The second connecting wall 35 protrudes from the first end surface 31A of the boom body 31 toward the support member body 62. Specifically, the second connecting wall 35 protrudes from the end of the first end surface 31A on the second direction A2 side. The second connecting wall 35 has the same shape and dimensions as the first connecting wall 33. Thus, the second connecting wall 35 is shaped like a plate. In the first axial direction, the second connecting wall 35 has a connecting end, connected to the first end surface 31A, and a protruding end opposite to the connecting end. In the first axial direction, the entirety of the second connecting wall 35 from the connecting end to the protruding end is located at substantially the same position as the end of the first end surface 31A on the second direction A2 side. Like the first connecting wall 33, the second connecting wall 35 is located at a position through which the first rotation axis 21J passes. The principal surface of the second connecting wall 35 is substantially orthogonal to the first rotation axis 21J. The second connecting wall 35 is aligned with the first connecting wall 33 in the first axial direction. In the first axial direction, the second connecting wall 35 is located between the first connecting wall 33 and the second coupling wall 66 of the support member 60. The second connecting wall 35 is separated from both the first connecting wall 33 and the second coupling wall 66. In the first axial direction, the distance between the second connecting wall 35 and the first connecting wall 33 is larger than the distance between the second connecting wall 35 and the second coupling wall 66. In FIG. 2, the distance between the second connecting wall 35 and the second coupling wall 66 is shown exaggeratedly large. The second connecting wall 35 has a through hole 35A. The through hole 35A extends through the second connecting wall 35. The central axis of the through hole 35A substantially coincides with the first rotation axis 21J. The diameter of the through hole 35A is larger than the diameter of the through hole 33A in the first connecting wall 33.

The pin 71 is positioned to extend from the first coupling wall 64 of the support member 60 to the first connecting wall 33 of the boom 30. Specifically, the pin 71 is located inside the through hole 64A in the first coupling wall 64 and the through hole 33A in the first connecting wall 33. The pin 71 extends through the through hole 64A in the first coupling wall 64 and the through hole 33A in the first connecting wall 33. The pin 71 is shaped like a circular column. The central axis of the pin 71 substantially coincides with the first rotation axis 21J. The diameter of the pin 71 is substantially equal to the diameter of the through hole 64A in the first coupling wall 64. Since the pin 71 extends through both the through hole 64A in the first coupling wall 64 and the through hole 33A in the first connecting wall 33, the pin 71 couples the first coupling wall 64 and the first connecting wall 33. The outer surface of the pin 71 is in sliding contact with the inner surface of the through hole 64A in the first coupling wall 64. Similarly, the outer surface of the pin 71 is in sliding contact with the inner surface of the through hole 33A in the first connecting wall 33. As a result, the pin 71 supports the first coupling wall 64 and the first connecting wall 33 so as to allow relative rotation. At the same time, the pin 71 couples the first coupling wall 64 and the first connecting wall 33 so as to allow relative rotation in the circumferential direction around the first rotation axis 21J. A bearing may be placed between the through hole 64A in the first coupling wall 64 and the pin 71. Similarly, another bearing may be placed between the through hole 33A in the first connecting wall 33 and the pin 71. These bearings may be rolling bearings or plain bearings. When a bearing is placed for each through hole, the diameter of the pin 71 or the through hole should be adjusted appropriately.

The cover 72 is located opposite the first connecting wall 33 with respect to the first coupling wall 64. The cover 72 is shaped like a circular plate, for example. The principal surface of the cover 72 faces the principal surface of the first coupling wall 64. The diameter of the cover 72 is larger than the diameter of the through hole 64A in the first coupling wall 64. The cover 72 closes the through hole 64A. In this embodiment, the cover 72 is fixed to the pin 71. For example, the cover 72 and the pin 71 are formed integrally. The cover 72 is fixed to the first coupling wall 64 by bolts B.

The first drive unit 101 is located between the second coupling wall 66 of the support member 60 and the first connecting wall 33 of the boom 30 in the first axial direction. The first drive unit 101 includes an electric motor 110 and a speed reducer 120. In FIG. 2, the boundary between the electric motor 110 and the speed reducer 120 is represented by a single dotted line for convenience.

The electric motor 110 is the drive source for the first drive unit 101. The electric motor 110 is electrically connected to a battery (not shown). The electric motor 110 includes a housing 112 and an output shaft 114. The housing 112 is shaped like a circular tube. The central axis of the housing 112 substantially coincides with the first rotation axis 21J. The housing 112 is fixed to the second connecting wall 35 of the boom 30 via a fixing structure of the speed reducer 120, which is described later. The housing 112 is located on the first direction A1 side relative to the second connecting wall 35. Specifically, the housing 112 is located between the first connecting wall 33 and the second connecting wall 35 in the first axial direction. The housing 112 constitutes the base portion in the first drive unit 101.

The output shaft 114 is located inside the housing 112. The output shaft 114 is shaped like a circular column. The central axis of the output shaft 114 substantially coincides with the first rotation axis 21J. The output shaft 114 is rotatable relative to the housing 112. The output shaft 114 rotates in the circumferential direction around the first rotation axis 21J. The output shaft 114 can rotate in both forward and reverse directions upon power supply to the housing 112. In other words, the output shaft 114 can output torque in both forward and reverse directions with respect to the circumferential direction around the first rotation axis 21J. In the first axial direction, both ends of the output shaft 114 protrude outside the housing 112.

The speed reducer 120 is positioned on the second direction A2 side relative to the electric motor 110. The speed reducer 120 includes a case 122, a speed reduction mechanism 123, and an output member 124. The case 122 is shaped like a circular tube. The central axis of the case 122 substantially coincides with the first rotation axis 21J. The end surface of the case 122 on the first direction A1 side is fixed to the end surface of the housing 112 of the electric motor 110 on the second direction A2 side. For example, flange walls protrude from both the outer circumferential surface of the housing 112 and the outer circumferential surface of the case 122. These flange walls are bolted together to fix the housing 112 and the case 122 to each other. In the first axial direction, the case 122 is located at substantially the same position as the second connecting wall 35 of the boom 30. The case 122 is located inside the through hole 35A in the second connecting wall 35. The case 122 extends through the second connecting wall 35. The outer diameter of the case 122 is substantially equal to the diameter of the through hole 35A in the second connecting wall 35. The case 122 is fixed to the second connecting wall 35. For example, the speed reducer 120 includes a flange wall protruding from the outer circumferential surface of the case 122. This flange wall is bolted to the second connecting wall 35, such that the case 122 is fixed to the second connecting wall 35.

The speed reduction mechanism 123 is located inside the case 122. The speed reduction mechanism 123 is coupled to the output shaft 114 of the electric motor 110. The speed reduction mechanism 123 multiplies the torque output from the output shaft 114 of the electric motor 110 with a predetermined ratio and outputs the resulting torque to the output member 124. The speed reduction mechanism 123 may be of, for example, an eccentric oscillation gear type or planetary gear type. The speed reduction mechanism 123 can be of any type as long as it is capable of multiplying the torque from the electric motor 110 and outputting the resulting torque.

The output member 124 protrudes from the inside of the case 122 toward the second direction A2 side relative to the case 122. The output member 124 is shaped like a circular column. The central axis of the output member 124 constitutes the first rotation axis 21J. Although not shown, the output member 124 is rotatably supported inside the case 122 by a rolling bearing, for example. The output member 124 is rotatable relative to the case 122 and thus to the housing 112 of the electric motor 110. The output member 124 rotates in the circumferential direction around the first rotation axis 21J. Specifically, the output member 124 rotates in the circumferential direction around the first rotation axis 21J relative to the base portion. The output member 124 is fixed to the second coupling wall 66 of the support member 60. This fixing structure will be described later. The output member 124 constitutes the output portion of the first drive unit 101.

As described above, the housing 112 of the electric motor 110 and the case 122 of the speed reducer 120 are fixed to the second connecting wall 35 of the boom 30. On the other hand, the output member 124 of the speed reducer 120 is fixed to the second coupling wall 66 of the support member 60. In addition, the output member 124 of the speed reducer 120 rotates in the circumferential direction around the first rotation axis 21J relative to the case 122 of the speed reducer 120. Thus, the first drive unit 101 outputs torque for relative rotation of the second connecting wall 35 and the second coupling wall 66 in the circumferential direction around the first rotation axis 21J.

As described above, the pin 71 couples the first coupling wall 64 of the support member 60 and the first connecting wall 33 of the boom 30. The first drive unit 101 couples the second coupling wall 66 of the support member 60 and the second connecting wall 35 of the boom 30. Thus, the boom 30 is coupled to the first coupling wall 64 of the support member 60 via the pin 71 and also coupled to the second coupling wall 66 of the support member 60 via the first drive unit 101.

The following describes the fixing structure between the output member 124 of the speed reducer 120 and the second coupling wall 66 of the support member 60. As a prerequisite for this fixing structure, the second coupling wall 66 has the through hole 66A. The through hole 66A extends through the second coupling wall 66 in the first axial direction. The central axis of the through hole 66A substantially coincides with the first rotation axis 21J. A plurality of spline teeth 66S protrude from the inner surface of the through hole 66A. The plurality of spline teeth 66S are arranged at equal intervals in the circumferential direction around the first rotation axis 21J. The spline teeth 66S extend along the first rotation axis 21J. In the first axial direction, the spline teeth 66S extend over the entire distance between the opposite ends of the second coupling wall 66. On the other hand, a plurality of spline grooves 124S are formed in the outer circumferential surface of the portion of the output member 124 of the speed reducer 120 that is exposed from the case 122. The plurality of spline grooves 124S are arranged at equal intervals in the circumferential direction around the first rotation axis 21J. The spline grooves 124S extend along the first rotation axis 21J. In other words, the spline grooves 124S are formed along the first rotation axis 21J. The spline grooves 124S extend to the end of the output member 124 on the second direction A2 side. The depth of the spline grooves 124S shown in FIG. 2 is set for convenience. The same applies to spline grooves in other drawings.

The output member 124 of the speed reducer 120 is fixed to the second coupling wall 66 by spline coupling. Specifically, the output member 124 of the speed reducer 120 is located inside the through hole 66A in the second coupling wall 66. The spline teeth 66S of the second connecting wall 66 are fitted in the spline grooves 124S of the output member 124. As a result, the output member 124 is fixed to the second coupling wall 66. Thus, the output member 124 is fixed to the second coupling wall 66 via the spline grooves 124S. A cover may be used to close the opening of the through hole 66A in the second coupling wall 66 on the opposite side to the speed reducer 120.

The first brake unit 130 is located opposite the speed reducer 120 with respect to the electric motor 110. In other words, in the first axial direction, the first brake unit 130 is located between the electric motor 110 and the first connecting wall 33 of the boom 30. The first brake unit 130 is fixed to the housing 112 of the electric motor 110. For example, flange walls protrude from the outer circumferential surfaces of both the first brake unit 130 and the housing 112 of the electric motor 110. These flange walls are bolted together to fix the first brake unit 130 and the housing 112 of the electric motor 110 to each other. The first brake unit 130 is coupled to the output shaft 114 of the electric motor 110. The first brake unit 130 is electrically connected to a battery (not shown). When supplied with power from the battery, the first brake unit 130 does not apply a braking force to the output shaft 114 of the electric motor 110. Therefore, at this time, the output shaft 114 of the electric motor 110 can rotate freely. On the other hand, when the power supply from the battery is cut off, the first brake unit 130 applies a braking force to the output shaft 114. Thus, the first brake unit 130 prohibits the output shaft 114 of the electric motor 110 from rotating.

The following describes an example of the procedure for coupling the components of the first joint mechanism 21. First, the operator positions the support member 60 and the boom 30 in alignment. Specifically, the operator positions the support member 60 and the boom 30 so that the through hole 64A in the first coupling wall 64 of the support member 60 and the through hole 33A in the first connecting wall 33 of the boom 30 are coaxial. The operator then attaches the first drive unit 101 to the walls. Specifically, the operator first puts the case 122 of the speed reducer 120 through the through hole 35A in the second connecting wall 35 of the boom 30. The operator then inserts the output member 124 of the speed reducer 120 into the through hole 66A in the second coupling wall 66 of the support member 60. Thus, the operator accomplishes spline coupling between the output member 124 of the speed reducer 120 and the second coupling wall 66. The operator then fixes the case 122 of the speed reducer 120 to the second connecting wall 35. In addition, the operator fixes the housing 112 of the electric motor 110 to the case 122 of the speed reducer 120. The operator then fixes the first brake unit 130 to the housing 112 of the electric motor 110. The operator then puts the pin 71 through the through hole 64A in the first coupling wall 64 of the support member 60 and the through hole 33A in the first connecting wall 33 of the boom 30. The operator then fixes the cover 72, which is integrated with the pin 71, to the first coupling wall 64. In the above-described manner, the components are coupled together. The procedure for coupling the components described above is an example, and the procedure for coupling the components can be modified as needed.

The first joint mechanism 21 is configured as described above. In the first joint mechanism 21, when the output shaft 114 of the electric motor 110 in the first drive unit 101 rotates, the output member 124 of the speed reducer 120 outputs torque in accordance with that rotation. The output of this torque causes the second connecting wall 35 of the boom 30 to rotate around the first rotation axis 21J relative to the second coupling wall 66 of the support member 60. Accordingly, the boom 30 rotates relative to the support member 60. At this time, the pin 71 acts as the axis of relative rotation between the first coupling wall 64 of the support member 60 and the first connecting wall 33 of the boom 30.

<Second Joint Mechanism>

The following describes a second joint mechanism 22, which is the mechanism that couples the boom 30 and the arm 40. As shown in FIG. 3, the excavator 10 includes a second drive unit 102, a second brake unit 132, a first pin 81, a second pin 82, a first cover 83, and a second cover 84 in a second coupling portion that couples the boom 30 and the arm 40. The second joint mechanism 22 includes these components, as well as the boom 30 and the arm 40, which are coupled to each other. The boom 30 is the first member in the second joint mechanism 22. The arm 40 is the second member in the second joint mechanism 22. The first pin 81 is the first coupling member in the second joint mechanism 22, and the second pin 82 is the second coupling member in the second joint mechanism 22. In FIG. 3, some of the components of the second joint mechanism 22 are shown in plan view not in sectional view.

As shown in FIG. 3, in the second coupling portion, the boom body 31 and the arm body 41 are located on one side and the other side across the second rotation axis 22J. The second end surface 31B of the boom body 31 and the first end surface 41A of the arm body 41 are opposed to each other across the second rotation axis 22J. The second end surface 31B of the boom body 31 is the end surface of the long-shaped boom body 31 opposite to the first end surface 31A. The first end surface 41A of the arm body 41 is the end surface of the long-shaped arm body 41 closer to the boom 30. Hereafter, in the description of the second joint mechanism 22, one of the two directions along the second rotation axis 22J will be referred to as the first direction B1, and the other as the second direction B2.

The end of the boom body 31 that is closer to the arm body 41 protrudes toward the first direction B1 relative to the main portion 31M of the boom body 31. As a result, with respect to a second axial direction along the second rotation axis 22J, the dimension of the second end surface 31B of the boom body 31 is larger than the dimension of the main portion 31M of the boom body 31. Contrary to the boom body 31, the end of the arm body 41 that is closer to the boom body 31 protrudes toward the second direction B2 relative to the main portion 41M of the arm body 41. As a result, with respect to the second axial direction, the dimension of the first end surface 41A of the arm body 41 is larger than the dimension of the main portion 41M of the arm body 41. With respect to the second axial direction, the dimensions of the first end surface 41A of the arm body 41 is substantially equal to the dimensions of the second end surface 31B of the boom body 31. In addition, with respect to the second axial direction, the dimension of the main portion 41M of the arm body 41 is substantially equal to the dimension of the main portion 31M of the boom body 31.

With the dimensional relationship described above, the boom body 31 and arm body 41 are arranged as follows. In the second axial direction, the main portion 31M of the boom body 31 and the main portion 41M of the arm body 41 are located at substantially the same position. Since the end of the boom body 31 protrudes toward the first direction B1, the end of the second end surface 31B of the boom body 31 on the first direction B1 side is located on the first direction B1 side relative to the end of the first end surface 41A of the arm body 41 on the first direction B1 side. On the other hand, since the end of the arm body 41 protrudes toward the second direction B2, the end of the first end surface 41A of the arm body 41 on the second direction B2 side is located on the second direction B2 side relative to the end of the second end surface 31B of the boom body 31 on the second direction B2 side.

The boom 30 includes a first coupling wall 37 and a second coupling wall 39 as components for coupling the boom body 31 to the arm body 41. The first coupling wall 37 protrudes from the second end surface 31B of the boom body 31 toward the arm body 41. Specifically, the first coupling wall 37 protrudes from the end of the second end surface 31B on the first direction B1 side. The first coupling wall 37 is shaped like a plate. In the second axial direction, the first coupling wall 37 has a connecting end, connected to the second end surface 31B, and a protruding end opposite to the connecting end. In the second axial direction, the entirety of the first coupling wall 37 from the connecting end to the protruding end is located at substantially the same position as the end of the second end surface 31B on the first direction B1 side. The protruding end of the first coupling wall 37 is located on the arm body 41 side of the second rotation axis 22J. The second rotation axis 22J passes through the principal surface of the first coupling wall 37. The principal surface of the first coupling wall 37 is substantially orthogonal to the second rotation axis 22J. The first coupling wall 37 has a through hole 37A. The through hole 37A extends through the first coupling wall 37 in the second axial direction. The central axis of the through hole 37A substantially coincides with the second rotation axis 22J.

The second coupling wall 39 protrudes from the second end surface 31B of the boom body 31 toward the arm body 41. Specifically, the second coupling wall 39 protrudes from the end of the second end surface 31B on the second direction B2 side. The second coupling wall 39 has the same shape and dimensions as the first coupling wall 37. Thus, the second coupling wall 39 is shaped like a plate. In the second axial direction, the second coupling wall 39 has a connecting end, connected to the second end surface 31B, and a protruding end opposite to the connecting end. In the second axial direction, the entirety of the second coupling wall 39 from the connecting end to the protruding end is located at substantially the same position as the end of the second end surface 31B on the second direction B2 side. Like the first coupling wall 37, the second coupling wall 39 is located at a position through which the second rotation axis 22J passes. The principal surface of the second coupling wall 39 is substantially orthogonal to the second rotation axis 22J. The second coupling wall 39 is aligned with the first coupling wall 37 in the second axial direction. The second coupling wall 39 has a through hole 39A. The through hole 39A extends through the second coupling wall 39 in the second axial direction. The central axis of the through hole 39A substantially coincides with the second rotation axis 22J. The diameter of the through hole 39A is substantially equal to the diameter of the through hole 37A in the first coupling wall 37.

The arm 40 includes a first connecting wall 43 and a second connecting wall 44 as components for coupling the arm body 41 to the boom body 31. The first connecting wall 43 protrudes from the first end surface 41A of the arm body 41 toward the boom body 31. Specifically, the first connecting wall 43 protrudes from the end of the first end surface 41A on the first direction B1 side. The first connecting wall 43 is shaped like a plate. In the second axial direction, the first connecting wall 43 has a connecting end, connected to the first end surface 41A, and a protruding end opposite to the connecting end. In the second axial direction, the entirety of the first connecting wall 43 from the connecting end to the protruding end is located at substantially the same position as the end of the first end surface 41A on the first direction B1 side. The protruding end of the first connecting wall 43 is located on the boom body 31 side of the second rotation axis 22J. The second rotation axis 22J passes through the principal surface of the first connecting wall 43. The principal surface of the first connecting wall 43 is substantially orthogonal to the second rotation axis 22J. In the second axial direction, the first connecting wall 43 is located between the first coupling wall 37 and the second coupling wall 39 of the boom 30. The first connecting wall 43 is located immediately adjacent to the first coupling wall 37. There is a small gap between the first connecting wall 43 and the first coupling wall 37. The first connecting wall 43 has a through hole 43A. The through hole 43A extends through the first connecting wall 43 in the second axial direction. The central axis of the through hole 43A substantially coincides with the second rotation axis 22J. The diameter of the through hole 43A is substantially equal to the diameter of the through hole 37A in the first coupling wall 37 of the boom 30.

The second connecting wall 44 protrudes from the first end surface 41A of the arm body 41 toward the boom body 31. Specifically, the second connecting wall 44 protrudes from the end of the first end surface 41A on the second direction B2 side. The second connecting wall 44 has the same shape and dimensions as the first connecting wall 43. Thus, the second connecting wall 44 is shaped like a plate. In the second axial direction, the second connecting wall 44 has a connecting end, connected to the first end surface 41A, and a protruding end opposite to the connecting end. In the second axial direction, the entirety of the second connecting wall 44 from the connecting end to the protruding end is located at substantially the same position as the end of the first end surface 41A on the second direction B2 side. Like the first connecting wall 43, the second connecting wall 44 is located at a position through which the second rotation axis 22J passes. The principal surface of the second connecting wall 44 is substantially orthogonal to the second rotation axis 22J. In the second axial direction, the second connecting wall 44 is located opposite the first connecting wall 43 with respect to the second coupling wall 39 of the boom 30. The second connecting wall 44 is located immediately adjacent to the second coupling wall 39. There is a small gap between the second connecting wall 44 and the second coupling wall 39. The second connecting wall 44 has a through hole 44A. The through hole 44A extends through the second connecting wall 44 in the second axial direction. The central axis of the through hole 44A substantially coincides with the second rotation axis 22J. The diameter of the through hole 44A is substantially equal to the diameter of the through hole 43A in the first connecting wall 43.

The first pin 81 is positioned to extend from the first coupling wall 37 of the boom 30 to the first connecting wall 43 of the arm 40. Specifically, the first pin 81 is located inside the through hole 37A in the first coupling wall 37 and the through hole 43A in the first connecting wall 43. The first pin 81 extends through the through hole 37A in the first coupling wall 37 and the through hole 43A in the first connecting wall 43. The first pin 81 is shaped like a circular column. The central axis of the first pin 81 substantially coincides with the second rotation axis 22J. The diameter of the first pin 81 is substantially equal to the diameter of the through hole 43A in the first connecting wall 43. Since the first pin 81 extends through both the first coupling wall 37 and the first connecting wall 43, the first pin 81 couples the first coupling wall 37 and the first connecting wall 43. The outer surface of the first pin 81 is in sliding contact with the inner surface of the through hole 37A in the first coupling wall 37. Similarly, the outer surface of the first pin 81 is in sliding contact with the inner surface of the through hole 43A in the first connecting wall 43. As a result, the first pin 81 supports the first coupling wall 37 and the first connecting wall 43 so as to allow relative rotation. At the same time, the first pin 81 couples the first coupling wall 37 and the first connecting wall 43 so as to allow relative rotation in the circumferential direction around the second rotation axis 22J. As in the first joint mechanism 21, a bearing may be placed between the inner surface of the through hole 37A in the first coupling wall 37 and the first pin 81. Similarly, another bearing may be placed between the inner surface of the through hole 43A in the first connecting wall 43 and the first pin 81.

The first cover 83 is located opposite the first connecting wall 43 with respect to the first coupling wall 37. The first cover 83 is shaped like a circular plate, for example. The principal surface of the first cover 83 faces the principal surface of the first coupling wall 37. The diameter of the first cover 83 is larger than the diameter of the through hole 37A in the first coupling wall 37. The first cover 83 closes the through hole 37A. In this embodiment, the first cover 83 is fixed to the first pin 81. For example, the first cover 83 and the first pin 81 are formed integrally. The first cover 83 is fixed to the first coupling wall 37 by bolts B.

The second pin 82 is positioned to extend from the second coupling wall 39 of the boom 30 to the second connecting wall 44 of the arm 40. Specifically, the second pin 82 is located inside the through hole 39A in the second coupling wall 39 and the through hole 44A in the second connecting wall 44. The second pin 82 extends through the through hole 39A in the second coupling wall 39 and the through hole 44A in the second connecting wall 44. The second pin 82 is shaped like a circular column. The central axis of the second pin 82 substantially coincides with the second rotation axis 22J. The diameter of the second pin 82 is substantially equal to the diameter of the through hole 39A in the second coupling wall 39. Since the second pin 82 extends through both the second coupling wall 39 and the second connecting wall 44, the second pin 82 couples the second coupling wall 39 and the second connecting wall 44. The outer surface of the second pin 82 is in sliding contact with the inner surface of the through hole 39A in the second coupling wall 39. Similarly, the outer surface of the second pin 82 is in sliding contact with the inner surface of the through hole 44A in the second connecting wall 44. As a result, the second pin 82 supports the second coupling wall 39 and the second connecting wall 44 so as to allow relative rotation. At the same time, the second pin 82 couples the second coupling wall 39 and the second connecting wall 44 so as to allow relative rotation in the circumferential direction around the second rotation axis 22J. As with the first pin 81, a bearing may be placed between the inner surface of the through hole 39A in the second coupling wall 39 and the second pin 82. Similarly, another bearing may be placed between the inner surface of the through hole 44A in the second connecting wall 44 and the second pin 82.

The second cover 84 is located opposite the second coupling wall 39 with respect to the second connecting wall 44. The second cover 84 is shaped like a circular plate, for example. The principal surface of the second cover 84 faces the principal surface of the second connecting wall 44. The diameter of the second cover 84 is larger than the diameter of the through hole 44A in the second connecting wall 44. The second cover 84 closes the through hole 44A. In this embodiment, the second cover 84 is fixed to the second pin 82. For example, the second cover 84 and the second pin 82 are formed integrally. The second cover 84 is fixed to the second connecting wall 44 by bolts B.

In the second axial direction, the second drive unit 102 is located between the first connecting wall 43 of the arm 40 and the second coupling wall 39 of the boom 30. The second drive unit 102 is configured in substantially the same manner as the first drive unit 101. Therefore, the second drive unit 102 is only briefly described in the following. The second drive unit 102 includes an electric motor 110 and a speed reducer 120. The electric motor 110 includes a housing 112 and an output shaft 114 rotatable relative to the housing 112. The speed reducer 120 includes a case 122 fixed to the housing 112 of the electric motor 110, a reduction mechanism 123 for multiplying the torque of the electric motor 110, and an output member 124 for outputting the torque from the reduction mechanism 123 to the outside. The housing 112 of the electric motor 110 constitutes the base portion in the second drive unit 102. The output member 124 of the speed reducer 120 constitutes the output portion of the second drive unit 102. In the second drive unit 102, the second rotational axis 22J replaces the first rotational axis 21J in the first drive unit 101 as the central axis of the torque output by the output member 124. In other words, the central axis of the output member 124 of the speed reducer 120 in the second drive unit 102 constitutes the second rotation axis 22J. In addition, the output member 124 of the speed reducer 120 rotates in the circumferential direction around the second rotation axis 22J relative to the case 122 of the speed reducer 120 and thus to the housing 112 of the electric motor 110. Further description of the configuration of the second drive unit 102 is omitted. The components of the second drive unit 102 shown in FIG. 3 that function in the same or substantially the same manner as the corresponding components of the first drive unit 101 shown in FIG. 2 are denoted by the same reference signs as in FIG. 2.

The second drive unit 102 is fixed to the first connecting wall 43 of the arm 40 and the second coupling wall 39 of the boom 30. Specifically, the housing 112 of the electric motor 110 is fixed to the first connecting wall 43 via the second brake unit 132. This fixing structure will be described later. The output member 124 of the speed reducer 120 is fixed to the second coupling wall 39. For example, the speed reducer 120 includes a flange wall 124F protruding from the output member 124. The flange wall 124F is fixed to the second coupling wall 39 by bolts B, thereby fixing the output member 124 to the second coupling wall 39. Unlike the first drive unit 101, the output member 124 of the second drive unit 102 does not have spline grooves 124S.

As described above, the housing 112 of the electric motor 110 is fixed to the first connecting wall 43 of the arm 40. On the other hand, the output member 124 of the speed reducer 120 is fixed to the second coupling wall 39 of the boom 30. In addition, the output member 124 of the speed reducer 120 rotates in the circumferential direction around the second rotation axis 22J relative to the case 122 of the speed reducer 120 and thus to the housing 112 of the electric motor 110. Thus, the second drive unit 102 outputs torque for relative rotation of the first connecting wall 43 and the second coupling wall 39 in the circumferential direction around the second rotation axis 22J.

As described above, the first pin 81 couples the first coupling wall 37 of the boom 30 and the first connecting wall 43 of the arm 40. The second drive unit 102 couples the second coupling wall 39 of the boom 30 and the first connecting wall 43 of the arm 40. Thus, the first connecting wall 43 of the arm 40 is coupled to the first coupling wall 37 of the boom 30 via the first pin 81 and also coupled to the second coupling wall 39 of the boom 30 via the second drive unit 102.

The second brake unit 132 is located on the first direction B1 side relative to the second drive unit 102. The second brake unit 132 is located between the first connecting wall 43 of the arm 40 and the electric motor 110 of the second drive unit 102. The second brake unit 132 is fixed to the housing 112 of the electric motor 110. The second brake unit 132 functions in the same manner as the first brake unit 130. The second brake unit 132 is also fixed to the first connecting wall 43 of the arm 40. For example, the second brake unit 132 includes a flange wall 132F. The flange wall 132F is fixed to the first connecting wall 43 by bolts B, thereby fixing the second brake unit 132 to the first connecting wall 43. At the same time, the electric motor 110 of the second drive unit 102, which is fixed to the second brake unit 132, is also fixed to the first connecting wall 43.

The following describes an example of the procedure for coupling the components of the second joint mechanism 22. First, the operator positions the boom 30 and the arm 40 in alignment. Specifically, the operator positions the boom 30 and the arm 40 so that the through hole 37A in the first coupling wall 37 of the boom 30 and the through hole 43A in the first connecting wall 43 of the arm 40 are coaxial. The operator then fixes the second drive unit 102 to the first connecting wall 43 of the arm 40 and the second coupling wall 39 of the boom 30. Specifically, the operator first places the speed reducer 120 of the second drive unit 102 between the first connecting wall 43 and the second coupling wall 39. The operator then fixes the output member 124 of the speed reducer 120 to the second coupling wall 39. The operator then fixes the housing 112 of the electric motor 110 to the case 122 of the speed reducer 120. The operator then fixes the second brake unit 132 to the housing 112 of the electric motor 110. The operator then fixes the second brake unit 132 to the first connecting wall 43 of the arm 40. The operator then puts the first pin 81 through the through hole 37A in the first coupling wall 37 of the boom 30 and the through hole 43A in the first connecting wall 43 of the arm 40. The operator then fixes the first cover 83, which is integrated with the first pin 81, to the first coupling wall 37. The operator then puts the second pin 82 through the through hole 44A in the second connecting wall 44 of the arm 40 and the through hole 39A in the second coupling wall 39 of the boom 30. The operator then fixes the second cover 84, which is integrated with the second pin 82, to the second connecting wall 44. In the above-described manner, the components are coupled together. The procedure for coupling the components described above is an example, and the procedure for coupling the components can be modified as needed.

The second joint mechanism 22 is configured as described above. In the second joint mechanism 22, when the output shaft 114 of the electric motor 110 in the second drive unit 102 rotates, the output member 124 of the speed reducer 120 outputs torque in accordance with that rotation. The output of this torque causes the first connecting wall 43 of the arm 40 to rotate around the second rotation axis 22J relative to the second coupling wall 39 of the boom 30. Accordingly, the boom 30 and the arm 40 rotate relative to each other. At this time, the first pin 81 supports the relative rotation between the first coupling wall 37 of the boom 30 and the first connecting wall 43 of the arm 40. Similarly, the second pin 82 supports the relative rotation between the second coupling wall 39 of the boom 30 and the second connecting wall 44 of the arm 40.

<Third Joint Mechanism>

The following describes a third joint mechanism 23, which is the mechanism that couples the arm 40 and the bucket 50. As shown in FIG. 4, the excavator 10 includes a third drive unit 103, a third brake unit 133, a pin 91, and a cover 92 in a third coupling portion that couples the arm 40 and the bucket 50. The third joint mechanism 23 includes these components, as well as the arm 40 and the bucket 50, which are coupled to each other. The bucket 50 is the first member in the third joint mechanism 23. The arm 40 is the second member in the third joint mechanism 23. The third brake unit 133 is the specific member in the third joint mechanism 23. The pin 91 is the coupling member in the third joint mechanism 23. In FIG. 4, some of the components of the third joint mechanism 23 are shown in plan view not in sectional view.

As shown in FIG. 4, in the third coupling portion, the bucket body 51 and the arm body 41 are located on one side and the other side across the third rotation axis 23J. The end surface 51A of the bucket body 51 and the second end surface 41B of the arm body 41 are opposed to each other across the third rotation axis 23J. The end surface 51A of the bucket body 51 is one of the outer surfaces of the bucket body 51, which is shaped like a box. The second end surface 41B of the arm body 41 is the end surface of the long-shaped arm body 41 opposite to the first end surface 41A. With respect to a third axial direction along the third rotation axis 23J, the dimension of the end surface 51A of the bucket body 51 is larger than the dimension of the second end surface 41B of the arm body 41. Hereafter, in the description of the third joint mechanism 23, one of the two directions along the third rotation axis 23J will be referred to as the first direction C1, and the other as the second direction C2. The end of the end surface 51A of the bucket body 51 on the first direction C1 side is located on the first direction side relative to the end of the second end surface 41B of the arm body 41 on the first direction C1 side. The end of the end surface 51A of the bucket body 51 on the second direction C2 side is located on the second direction C2 side relative to the end of the second end surface 41B of the arm body 41 on the second direction C2 side.

The bucket 50 includes a first coupling wall 53 and a second coupling wall 55 as components for coupling the bucket body 51 to the arm body 41. The first coupling wall 53 protrudes from the end surface 51A of the bucket body 51 toward the arm body 41. Specifically, the first coupling wall 53 protrudes from the end of the end surface 51A on the first direction C1 side. The first coupling wall 53 is shaped like a plate. In the third axial direction, the first coupling wall 53 has a connecting end, connected to the end surface 51A, and a protruding end. In the third axial direction, the entirety of the first coupling wall 53 from the connecting end to the protruding end is located at substantially the same position as the end of the end surface 51A on the first direction C1 side. The protruding end of the first coupling wall 53 is located on the arm body 41 side of the third rotation axis 23J. The third rotation axis 23J passes through the principal surface of the first coupling wall 53. The principal surface of the first coupling wall 53 is substantially orthogonal to the third rotation axis 23J.

The second coupling wall 55 protrudes from the end surface 51A of the bucket body 51 toward the arm body 41. Specifically, the second coupling wall 55 protrudes from the end of the end surface 51A on the second direction C2 side. The second coupling wall 55 has the same shape and dimensions as the first coupling wall 53. Thus, the second coupling wall 55 is shaped like a plate. In the third axial direction, the second coupling wall 55 has a connecting end, connected to the end surface 51A, and a protruding end opposite to the connecting end. In the third axial direction, the entirety of the second coupling wall 55 from the connecting end to the protruding end is located at substantially the same position as the end of the end surface 51A on the second direction C2 side. The second coupling wall 55 is aligned with the first coupling wall 53 in the third axial direction. Like the first coupling wall 53, the second coupling wall 55 is located at a position through which the third rotation axis 23J passes. The principal surface of the second coupling wall 55 is substantially orthogonal to the third rotation axis 23J. The second coupling wall 55 has a through hole 55A. The through hole 55A extends through the second coupling wall 55 in the third axial direction. The central axis of the through hole 55A substantially coincides with the third rotation axis 23J.

The arm 40 includes a specific connecting wall 47 as a component for coupling the arm body 41 to the bucket body 51. The specific connecting wall 47 protrudes from the second end surface 41B of the arm body 41 toward the bucket body 51. Specifically, the specific connecting wall 47 protrudes substantially from the middle of the second end surface 41B in the third axial direction. The specific connecting wall 47 is shaped like a plate. In the third axial direction, the specific connecting wall 47 has a connecting end, connected to the second end surface 41B, and a protruding end opposite to the connecting end. In the third axial direction, the entirety of the specific connecting wall 47 from the connecting end to the protruding end is located at substantially the same position as the middle of the second end surface 41B. The protruding end of the specific connecting wall 47 is located on the bucket body 51 side of the third rotation axis 23J. The third rotation axis 23J passes through the principal surface of the specific connecting wall 47. The principal surface of the specific connecting wall 47 is substantially orthogonal to the third rotation axis 23J. In the third axial direction, the specific connecting wall 47 is located between the first coupling wall 53 and the second coupling wall 55. Specifically, in the third axial direction, the specific connecting wall 47 is located substantially at the middle between the first coupling wall 53 and the second coupling wall 55. The specific connecting wall 47 has a through hole 47A. The through hole 47A extends through the specific connecting wall 47 in the third axial direction. The central axis of the through hole 47A substantially coincides with the third rotation axis 23J.

In the third axial direction, the third drive unit 103 is located between the first coupling wall 53 and the second coupling wall 55 of the bucket 50. The third drive unit 103 is configured in substantially the same manner as the first drive unit 101. Therefore, the third drive unit 103 is only briefly described in the following. The third drive unit 103 includes an electric motor 110 and a speed reducer 120. The electric motor 110 includes a housing 112 and an output shaft 114 rotatable relative to the housing 112. The speed reducer 120 includes a case 122 fixed to the housing 112 of the electric motor 110, a reduction mechanism 123 for multiplying the torque of the electric motor 110, and an output member 124 for outputting the torque from the reduction mechanism 123 to the outside. The housing 112 of the electric motor 110 constitutes the base portion in the third drive unit 103. The output member 124 constitutes the output portion of the third drive unit 103. In the third drive unit 103, the third rotational axis 23J replaces the first rotational axis 21J in the first drive unit 101 as the central axis of the torque output by the output member 124. In other words, the central axis of the output member 124 of the speed reducer 120 in the third drive unit 103 constitutes the third rotation axis 23J. In addition, the output member 124 of the speed reducer 120 rotates in the circumferential direction around the third rotation axis 23J relative to the case 122 of the speed reducer 120 and thus to the housing 112 of the electric motor 110. Further description of the configuration of the third drive unit 103 is omitted. The components of the third drive unit 103 shown in FIG. 4 that function in the same or substantially the same manner as the corresponding components of the first drive unit 101 shown in FIG. 2 are denoted by the same reference signs as in FIG. 2.

The third drive unit 103 is fixed to the specific connecting wall 47 of the arm 40. Specifically, the housing 112 of the electric motor 110 is located inside the through hole 47A in the specific connecting wall 47. The housing 112 extends through the through hole 47A. The diameter of the housing 112 is substantially equal to the diameter of the through hole 47A. The central axis of the housing 112 substantially coincides with the third rotation axis 23J. The housing 112 is fixed to the specific connecting wall 47. For example, the housing 112 is fixed to the specific connecting wall 47 by bolts, using an L-shaped fitting or the like. The housing 112 may have a flange wall protruding from the outer circumferential surface of the housing 112. The flange wall may be fixed to the specific connecting wall 47 by bolts. Since the housing 112 of the electric motor 110 is fixed to the specific connecting wall 47, the case 122 of the speed reducer 120 is also fixed to the specific connecting wall 47.

The third drive unit 103 is fixed to the second coupling wall 55 of the bucket 50. Specifically, the output member 124 of the speed reducer 120 is fixed to the second coupling wall 55 of the bucket 50 by spline coupling. Specifically, the output member 124 has a plurality of spline grooves 124S, as in the first drive unit 101. The plurality of spline grooves 124S are arranged at equal intervals in the circumferential direction around the third rotation axis 23J. The spline grooves 124S extend along the third rotation axis 23J. The spline grooves 124S extend to the end of the output member 124 on the first direction C1 side. The second coupling wall 55 of the bucket 50 has the through hole 55A as a component for receiving the spline grooves 124S. The central axis of the through hole 55A substantially coincides with the third rotation axis 23J. A plurality of spline teeth 55S protrude from the inner surface of the through hole 55A. The plurality of spline teeth 55S are arranged at equal intervals in the circumferential direction around the third rotation axis 23J. The spline teeth 55S extend along the third rotation axis 23J. In the third axial direction, the spline teeth 55S extend over the entire distance between the opposite ends of the second coupling wall 55. The output member 124 of the speed reducer 120 is located inside the through hole 55A. The spline teeth 55S of the through hole 55A are fitted into the spline grooves 124S of the output member 124. As a result, the output member 124 is fixed to the second coupling wall 55. Thus, the output member 124 is fixed to the second coupling wall 55 via the spline grooves 124S. A cover may be used to close the opening of the through hole 55A in the second coupling wall 55 on the opposite side to the speed reducer 120. In FIG. 4, the gap between the case 122 of the speed reducer 120 and the second coupling wall 55 is shown exaggeratedly large.

As described above, the housing 112 of the electric motor 110 and the case 122 of the speed reducer 120 are fixed to the specific connecting wall 47 of the arm 40. On the other hand, the output member 124 of the speed reducer 120 is fixed to the second coupling wall 55 of the bucket 50. In addition, the output member 124 of the speed reducer 120 rotates in the circumferential direction around the third rotation axis 23J relative to the case 122 of the speed reducer 120. Thus, the third drive unit 103 outputs torque for relative rotation of the specific connecting wall 47 and the second coupling wall 55 in the circumferential direction around the third rotation axis 23J. At the same time, the third drive unit 103 couples the specific connecting wall 47 and the second coupling wall 55.

The third brake unit 133 is located on the first direction C1 side relative to the third drive unit 103. The third brake unit 133 is located between the first coupling wall 53 of the bucket 50 and the electric motor 110 of the third drive unit 103. The third brake unit 133 is also located between the first coupling wall 53 and the specific connecting wall 47 of the arm 40. The third brake unit 133 is fixed to the housing 112 of the electric motor 110. The third brake unit 133 functions in the same manner as the first brake unit 130. The third brake unit 133 is fixed to the first coupling wall 53 of the bucket 50. For example, the third brake unit 133 may have a flange wall 133F similar to that of the second brake unit 132. The flange wall 133F is fixed to the first coupling wall 53 by bolts B, thereby fixing the third brake unit 133 to the first coupling wall 53.

As described above, the third brake unit 133 is fixed to the first coupling wall 53 of the bucket 50 and the housing 112 of the electric motor 110. The housing 112 is fixed to the specific connecting wall 47. Thus, the third brake unit 133 is interposed between the first coupling wall 53 and the specific connecting wall 47.

The pin 91 is positioned to extend from the first coupling wall 53 of the bucket 50 to the third brake unit 133. The pin 91 is shaped like a circular column. The central axis of the pin 91 substantially coincides with the third rotation axis 23J. The diameter of the pin 91 is substantially equal to the diameter of the through hole 53A in the first coupling wall 53. The pin 91 extends through the through hole 53A in the first coupling wall 53 and is also inserted into the third brake unit 133. Thus, the pin 91 couples the first coupling wall 53 and the third brake unit 133. The outer surface of the pin 91 is in sliding contact with the inner surface of the through hole 53A in the first coupling wall 53. The portion of the pin 91 that is located inside the third brake unit 133 is rotatably supported, for example, by a rolling bearing 133G. As a result, the pin 91 supports the first coupling wall 53 and the third brake unit 133 so as to allow relative rotation. At the same time, the pin 91 couples the first coupling wall 53 and the third brake unit 133 so as to allow relative rotation in the circumferential direction around the third rotation axis 23J. A bearing may be placed between the inner surface of the through hole 53A in the first coupling wall 53 and the pin 91.

As described above, the pin 91 couples the first coupling wall 53 of the bucket 50 and the third brake unit 133. The third brake unit 133 is coupled to the specific connecting wall 47 of the arm 40 via the electric motor 110 of the third drive unit 103. Thus, the pin 91 couples the first coupling wall 53 and the specific connecting wall 47. In a different view, the specific connecting wall 47 is connected to the first coupling wall 53 of the bucket 50 via the electric motor 110, the third brake unit 133, and the pin 91. On the other hand, the specific connecting wall 47 is coupled to the second coupling wall 55 of the bucket 50 via the third drive unit 103. Thus, the specific connecting wall 47 and thus the arm 40 is coupled to both the first coupling wall 53 and the second coupling wall 55 of the bucket 50.

The cover 92 is located opposite the specific connecting wall 47 with respect to the first coupling wall 53. The cover 92 is shaped like a circular plate, for example. The principal surface of the cover 92 faces the principal surface of the first coupling wall 53. The diameter of the cover 92 is larger than the diameter of the through hole 53A in the first coupling wall 53. The cover 92 closes the through hole 53A. In this embodiment, the cover 92 is fixed to the pin 91. For example, the cover 92 and the pin 91 are formed integrally. The cover 92 is fixed to the first coupling wall 53 by bolts B.

The following describes an example of the procedure for coupling the components of the third joint mechanism 23. First, the operator positions the bucket 50 and the arm 40 in alignment. Specifically, the operator positions the bucket 50 and the arm 40 so that the through hole 53A in the first coupling wall 53 of the bucket 50 and the through hole 47A in the specific connecting wall 47 of the arm 40 are coaxial. The operator then fixes the third drive unit 103 to the second coupling wall 55 of the bucket 50 and the specific connecting wall 47 of the arm 40. Specifically, the operator first places the speed reducer 120 of the third drive unit 103 between the specific connecting wall 47 and the second coupling wall 55. The operator then inserts the output member 124 of the speed reducer 120 into the through hole 55A in the second coupling wall 55. Thus, the operator accomplishes spline coupling between the output member 124 of the speed reducer 120 and the second coupling wall 55. The operator puts the electric motor 110 through the specific connecting wall 47 of the arm 40 from the first direction C1 side. The operator then fixes the housing 112 of the electric motor 110 to the specific connecting wall 47, and the operator also fixes the housing 112 of the electric motor 110 to the case 122 of the speed reducer 120. Further, the operator places the third brake unit 133 between the electric motor 110 and the first coupling wall 53 of the bucket 50. The operator then fixes the third brake unit 133 to the electric motor 110 and the first coupling wall 53. The operator then inserts the pin 91 into the first coupling wall 53 and the third brake unit 133. The operator then fixes the cover 92, which is integrated with the pin 91, to the first coupling wall 53. In the above-described manner, the components are coupled together. The procedure for coupling the components described above is an example, and the procedure for coupling the components can be modified as needed.

The third joint mechanism 23 is configured as described above. In the third joint mechanism 23, when the output shaft 114 of the electric motor 110 in the third drive unit 103 rotates, the output member 124 of the speed reducer 120 outputs torque in accordance with that rotation. The output of this torque causes the second coupling wall 55 of the bucket 50 to rotate around the third rotation axis 23J relative to the specific connecting wall 47 of the arm 40. Accordingly, the arm 40 and the bucket 50 rotate relative to each other. At this time, the pin 91 supports the relative rotation between the first coupling wall 53 of the bucket 50 and the third brake unit 133 and thus the third drive unit 103.

Operation and Effects of Embodiment

(1) Suppose that, in the third joint mechanism 23 shown in FIG. 4, the bucket 50 is rotated relative to the arm 40. At this time, the walls coupling the bucket 50 to the arm 40 are subjected to a first load, which is a load corresponding to the weight of the bucket 50 and the excavated material excavated by the bucket 50, and is a circumferential load around the third rotation axis 23J. In this embodiment, the bucket 50 is coupled to the arm 40 via the two walls, the first coupling wall 53 and the second coupling wall 55. Therefore, the first load is distributed between the first coupling wall 53 and the second coupling wall 55. In other words, in this embodiment, the first load can be shared between two walls, the first coupling wall 53 and the second coupling wall 55, thus reducing the burden per wall for coupling.

When the bucket 50 rotates relative to the arm 40 or when the bucket 50 strikes a material to be excavated, the bucket 50 may act to move in any direction orthogonal to the third rotation axis 23J, as indicated by the arrow U in FIG. 4, for example. This action is referred to as the orthogonal action. The pin 91 extends through the first coupling wall 53 of the bucket 50. The pin 91 receives the first coupling wall 53 when the bucket 50 performs the orthogonal action. Specifically, the pin 91, and thus the bearing 133G supporting the pin 91, is responsible for absorbing the load acting on the first coupling wall 53. Since the pin 91 receives this load, the impact can be reduced which acts on the output member 124 of the speed reducer 120 from the second coupling wall 55 as the bucket 50 performs the orthogonal action.

Although the third joint mechanism 23 is mentioned here as the example, the same applies to the first joint mechanism 21 and the second joint mechanism 22. For example, in the first joint mechanism 21 shown in FIG. 2, the support member 60 is coupled to the boom 30 by two walls, the first coupling wall 64 and the second coupling wall 66. This reduces the burden on the coupling walls, compared to the case where the support member 60 is coupled to the boom 30 by a single wall, for example. In the first joint mechanism 21, the first coupling wall 64 is coupled to the first connecting wall 33 of the boom 30 by the pin 71. For example, when the boom 30 and thus the first connecting wall 33 acts in any direction orthogonal to the first rotation axis 21J, the pin 71 receives the first connecting wall 33. Since the pin 71 receives the first connecting wall 33, the impact can be reduced which acts on the second drive unit 102 from the second connecting wall 35.

(2) In the third joint mechanism 23 shown in FIG. 4, the arm 40 has only one wall, constituted by the specific connecting wall 47, for coupling to the bucket 50. In this case, the structure of the arm 40 can be simplified compared to a configuration with multiple walls for coupling, for example. Further, in the third axial direction, the specific connecting wall 47 is located substantially at the middle between the first coupling wall 64 and the second coupling wall 66. Since the specific connecting wall 47 is located substantially at the middle between the first coupling wall 64 and the second coupling wall 66, the force supporting the bucket 50 is equalized in the third axial direction. This stabilizes the support condition of the bucket 50.

(3) In the first joint mechanism 21 shown in FIG. 2, the boom 30 has two walls, the first connecting wall 33 and the second connecting wall 35, for coupling to the support member 60. The first connecting wall 33 and the second connecting wall 35 separately support the pin 71 and the first drive unit 101. In this way, since the pin 71 and the first drive unit 101 are supported by separate walls, the load acting on the pin 71 and the load acting on the first drive unit 101 can be released independently. Therefore, for example, when the boom 30 acts in any direction orthogonal to the first rotation axis 21J, the load received by the pin 71 is not transmitted to the first drive unit 101. This contributes to reduction of the burden on the first drive unit 101.

(4) In the first joint mechanism 21 shown in FIG. 2, the housing 112 of the electric motor 110 is located between the first connecting wall 33 and the second connecting wall 35 of the boom 30. Further, the first connecting wall 33 and the second connecting wall 35 of the boom 30 are located between the first coupling wall 64 and the second coupling wall 66 of the support member 60. Thus, in the first axial direction, the housing 112 of the electric motor 110, and thus the entire electric motor 110, is doubly sandwiched between walls on both sides. In this case, the electric motor 110 is not exposed to the outside in the first axial direction. This arrangement is suitable for protecting the electric motor 110 because earth and sand are less likely to fall onto the electric motor 110.

(5) As to the third joint mechanism 23 shown in FIG. 4, the bucket 50 will be more frequently detached for maintenance, for example, than the arm 40 or the boom 30. Therefore, it is desirable to minimize the number of steps required to attach and detach the bucket 50 to and from the arm 40. In this regard, the third joint mechanism 23 includes only one pin 91 as a coupling member that supports the bucket 50 and the arm 40 so as to allow relative rotation. If there are multiple pins coupling the bucket 50 and the arm 40, the number of steps required to mount the pins will increase with the number of pins. By contrast, this embodiment includes only one pin 91, which minimizes the number of steps required to attach or detach the bucket 50 to or from the arm 40 in terms of the attachment or detachment of the pin.

(6) In the second joint mechanism 22 shown in FIG. 3, the boom 30 has two walls, the first coupling wall 37 and the second coupling wall 39, for coupling to the arm 40. The arm 40 has the first connecting wall 43 that pairs with the first coupling wall 37, and the second connecting wall 44 that pairs with the second coupling wall 39. The first pin 81 extends through the first coupling wall 37 and the first connecting wall 43. The second pin 82 extends through the second coupling wall 39 and the second connecting wall 44. Thus, the second joint mechanism 22 includes two pins as coupling members. In this case, for example, when the arm 40 acts to move in any direction orthogonal to the second rotation axis 22J, both the first pin 81 and the second pin 82 receive this action of the arm 40. Thus, the burden on each of the first pin 81 and the second pin 82 can be reduced. At the same time, the presence of the two pins for receiving the impact can reduce the impact reaching the second drive unit 102.

(7) In the third joint mechanism 23 shown in FIG. 4, the output member 124 of the speed reducer 120 is fixed to the second coupling wall 55 of the bucket 50 by spline coupling. With the spline coupling, the output member 124 of the speed reducer 120 needs only to be moved in the third axial direction relative to the second coupling wall 55 to fix the speed reducer 120 to the second coupling wall 55. Therefore, in the configuration of this embodiment, which uses the spline coupling, the speed reducer 120 can be easily attached to the second coupling wall 55 and thus to the bucket 50. The same applies to attachment of the speed reducer 120 to the second coupling wall 66 in the first joint mechanism 21 shown in FIG. 2. In the configuration of this embodiment, the detachment work can also be simplified as is the attachment work described above.

As described below, when the output member 124 of the speed reducer 120 and the second coupling wall 55 are fixed together using the spline coupling, the torque of the output member 124 can be securely transmitted to the second coupling wall 55. The surfaces of the spline grooves 124S of the output member 124 that face in the circumferential direction around the third rotation axis 23J are herein referred to as the side surfaces. Similarly, the surfaces of the spline teeth 55S of the second coupling wall 55 that face in the above circumferential direction are referred to as the side surfaces. The side surfaces of the spline grooves 124S and the side surfaces of the spline teeth 55S face each other. At the same time, the side surfaces of the spline grooves 124S are in contact with the side surfaces of the spline teeth 55S. Suppose that the output member 124 now rotates in the above circumferential direction. The torque is transmitted from the side surfaces of the spline grooves 124S to the side surfaces of the spline teeth 55S. The second coupling wall 55 rotates with the spline teeth 55S. As in the third joint mechanism 23 mentioned here as an example, the torque output by the output member 124 of the speed reducer 120 can also be reliably transmitted to the second coupling wall 66 in the first joint mechanism 21 shown in FIG. 2.

Modification Examples

The above embodiment can be modified as described below. The above embodiment and the following modification examples can be implemented in combination to the extent where they are technically consistent to each other.

As to the first joint mechanism 21, the way of forming the spline grooves 124S of the output member 124 of the speed reducer 120 is not limited to the example in the above embodiment. The portion of the outer circumferential surface of the output member 124 other than the portion having the irregularities related to the spline coupling is referred to as the general surface. In forming the spline grooves 124S in the outer circumferential surface of the output member 124, a plurality of spline teeth may protrude from the general surface. The spline teeth adjacent to each other may define a spline groove 124S. As with the first joint mechanism 21 mentioned here as an example, the third joint mechanism 23 is also susceptible to other ways of forming the spline grooves 124S than in the example in the above embodiment.

The method of fixing two components at various points in the first joint mechanism 21 is not limited to the examples in the above embodiment. Any method is acceptable as long as two components can be fixed together. For example, means other than spline coupling may be used in fixing the output member 124 of the speed reducer 120 to the second coupling wall 66 of the support member 60. As with the first joint mechanism 21 mentioned above, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other methods of fixing two components than in the examples in the above embodiment.

If the spline coupling is not used in fixing two components, the configuration related to the spline coupling may be eliminated. Specifically, the spline grooves 124S may be eliminated from the output member 124 of the speed reducer 120, and the spline teeth 66S may be eliminated from the second coupling wall 66 of the support member 60.

As to the first joint mechanism 21, the cover 72 and the pin 71 need not be fixed to each other. If the cover 72 and the pin 71 are not fixed to each other, a cover should be provided on the second direction A2 side of the first connecting wall 33 to close the through hole 33A in the first connecting wall 33. This cover and the cover 72 prevent the pin 71 from coming off from the through hole 64A in the first coupling wall 64 and the through hole 33A in the first connecting wall 33. In this case, the pin 71 still functions as a shaft member that supports the relative rotation between the first coupling wall 64 and the first connecting wall 33. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to the configuration in which the cover and the pin are not fixed to each other.

As to the first joint mechanism 21, it is not required that the pin 71 extend through the first coupling wall 64 and the first connecting wall 33. For example, in the first axial direction, the pin 71 may extend from the middle of the through hole 64A in the first coupling wall 64 to the middle of the through hole 33A in the first connecting wall 33. Even in this case, the pin 71 extends from the first coupling wall 64 to the first connecting wall 33, and thus the pin 71 can still support the first coupling wall 64 and the first connecting wall 33 so as to allow relative rotation. Further, in connecting the first coupling wall 64 and the first connecting wall 33 so as to allow relative rotation, the following coupling members may be employed in place of the pin 71. A coupling member shaped like a circular column may protrude from the side surface of the first connecting wall 33 on the first direction A1 side, and a recess may be provided in the side surface of the first coupling wall 64 on the second direction A2 side to receive the coupling member. In this case, the central axis of the coupling member should substantially coincide with the central axis of the torque output by the first drive unit 101. Even in such configuration, this coupling member can support the first coupling wall 64 and the first connecting wall 33 so as to allow relative rotation. Thus, the coupling member is not limited to the examples in the above embodiment. Any coupling member is acceptable that is able to couple the first coupling wall 64 and the first connecting wall 33 so as to allow relative rotation around the central axis of the torque output by the first drive unit 101. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other configuration of the coupling member than in the example in the above embodiment.

As to the first joint mechanism 21, the position of the first drive unit 101 relative to the second connecting wall 35 in the first axial direction is not limited to the example in the above embodiment. Specifically, it is not required that the base portion of the first drive unit 101 be located between the first connecting wall 33 and the second connecting wall 35. For example, as will be described later for the modification shown in FIG. 5, the base portion may be located on the second direction A2 side relative to the second connecting wall 35. As with the first joint mechanism 21, the third joint mechanism 23 is also susceptible to other location of the third drive unit 103 in the third axial direction relative to the specific connecting wall 47 than in the example in the above embodiment. The entire second drive unit 102 may be located on the second direction C2 side relative to the specific connecting wall 47, as will be described later for the modification shown in FIG. 7.

As to the first joint mechanism 21, the walls to which the base portion and the fixed portion of the first drive unit 101 are fixed are not limited to the examples in the above embodiment. For example, the wall to which the base portion of the first drive unit 101 is fixed and the wall to which the output portion of the same is fixed may be swapped, unlike the example in the above embodiment. Specifically, the housing 112 of the electric motor 110 may be fixed to the second coupling wall 66 of the support member 60, while the output member 124 of the speed reducer 120 may be fixed to the second connecting wall 35 of the boom 30. In the first drive unit 101, the base portion should be fixed to one of the second coupling wall 66 and the second connecting wall 35, and the output portion should be fixed to the other of the second coupling wall 66 and the second connecting wall 35. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to the configuration in which the wall to which the base portion is fixed and the wall to which the output portion is fixed are swapped, unlike the example in the above embodiment.

In the case where the output portion of the first drive unit 101 is fixed to the second connecting wall 35 as in the above modification example, any method is acceptable to fix the output portion to the second connecting wall 35. For example, the output portion may be fixed to the second connecting wall 35 by spline coupling or other methods. The same applies to the second drive unit 102 and the third drive unit 103.

As to the first joint mechanism 21, the configuration of the first drive unit 101 is not limited to the example in the above embodiment. The first drive unit 101 may be configured in any manner as long as it includes the electric motor 110 and can output torque around a specific rotation axis. This specific axis corresponds to the first rotation axis 21J in the above embodiment. For example, in the first drive unit 101, the output shaft 114 of the electric motor 110 and the reduction mechanism 123 of the speed reducer 120 may be connected via an impact mitigation mechanism. The impact mitigation mechanism can transmit the rotation of the output shaft 114 of the electric motor 110 to the reduction mechanism 123 and also mitigate the impact transmitted from the reduction mechanism 123 to the output shaft 114 of the electric motor 110. For example, the impact mitigation mechanism may be made of a rubber or plastic component. For example, the impact mitigation mechanism may be constituted by a spring. In the first drive unit 101, the shape of the housing 112 of the electric motor 110 may be different from the example in the above embodiment. The shape of the case 122 of the speed reducer 120 may be different from the example in the above embodiment. The first drive unit 101 may be embodied without the speed reducer 120. When the first drive unit 101 is embodied without the speed reducer 120, the output shaft 114 of the electric motor 110 outputs torque to the outside of the first drive unit 101. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other configuration of the drive unit than in the example in the above embodiment. The drive unit may be configured in any manner as long as it includes an electric motor and can output torque around a specific rotation axis.

As to the first joint mechanism 21, the treatment of the component that constitutes the base portion of the first drive unit 101 is not limited to the example in the above embodiment. The base portion may be constituted by any component that does not itself output power but supports the rotation of the output portion. For example, in addition to the housing 112 of the electric motor 110, the case 122 of the speed reducer 120 may be treated as the base portion. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other treatment of the base portion than in the example in the above embodiment.

Similar to the above modification example regarding the base portion, the treatment of the component that constitutes the output portion of the first drive unit 101 is not limited to the example in the above embodiment. The output portion may be constituted by any component that rotates relative to the base portion and outputs torque to the outside of the first drive unit 101. For example, when the first drive unit 101 is embodied without the speed reducer 120, the output shaft 114 of the electric motor 110 constitutes the output portion. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other treatment of the output portion than in the example in the above embodiment.

In the first joint mechanism 21, the first brake unit 130 is not necessarily required. The same applies to the second joint mechanism 22 and the third joint mechanism 23. In the first joint mechanism 21, the location of the first coupling wall 64 and the second coupling wall 66 relative to the support member body 62 is not limited to the example in the above embodiment. Specifically, in the first axial direction, the first coupling wall 64 may be located at any position within the end surface 62A of the support member body 62. For example, in the first axial direction, the first coupling wall 64 may be located near the middle of the end surface 62A of the support member body 62. Similarly, in the first axial direction, the second coupling wall 66 may be located at any position within the end surface 62A of the support member body 62. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other location of the coupling walls relative to the body of the first member than in the example in the above embodiment.

In the first joint mechanism 21, it is not required that the first coupling wall 64 and the second coupling wall 66 have the same shape and dimensions. The shape and dimensions of the first coupling wall 64 may be suitably designed so that it can be located at a position through which the first rotation axis 21J passes. The same applies to the second coupling wall 66. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other shapes and dimensions of the coupling walls than in the example in the above embodiment.

In the first joint mechanism 21, the location of the first connecting wall 33 and the second connecting wall 35 relative to the boom body 31 is not limited to the example in the above embodiment. Specifically, in the first axial direction, the first connecting wall 33 may be located at any position within the end surface 31A of the boom body 31. Similarly, in the first axial direction, the second connecting wall 35 may be located at any position within the end surface 31A of the boom body 31. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other location of the connecting walls relative to the second member than in the example in the above embodiment.

In the first joint mechanism 21, it is not required that the first connecting wall 33 and the second connecting wall 35 have the same shape and dimensions. The shape and dimensions of the first connecting wall 33 may be suitably designed so that it can be located at a position through which the first rotation axis 21J passes. The same applies to the second coupling wall 35. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to other shapes and dimensions of the connecting walls than in the example in the above embodiment.

In the first joint mechanism 21, the configuration of the coupling in the above embodiment may be applied with the support member and the boom interchanged. In other words, in the first joint mechanism 21, the configuration of the walls provided on the boom and the support member may be changed so that the boom constitutes the first member and the support member constitutes the second member. Specifically, the boom includes a first coupling wall and a second coupling wall that are aligned in the first axial direction. On the other hand, the support member includes a first connecting wall located between the first coupling wall and the second coupling wall in the first axial direction, and a second connecting wall located between the first connecting wall and the second coupling wall. The first coupling wall of the boom is coupled to the first connecting wall of the support member by a coupling member, and the second coupling wall of the boom is coupled to the second connecting wall of the support member by the first drive unit 101. As with the first joint mechanism 21 mentioned here as an example, the second joint mechanism 22 and the third joint mechanism 23 are also susceptible to the configuration in which the first member and the second member are interchanged and configured for the joint mechanism.

The configuration of the coupling applied to the first joint mechanism 21 may be applied to other parts of the excavator 10 than the coupling portion between the support member 60 and the boom 30. For example, the same configuration may be applied to the coupling portion between the boom 30 and the arm 40, or the coupling portion between the bucket 50 and the arm 40. As with the first joint mechanism 21 mentioned here as an example, the configuration of the second joint mechanism 22 and the third joint mechanism 23 are also applicable to other parts than in the example in the above embodiment.

As described for the above embodiment, in the first joint mechanism 21, the first member includes two coupling walls aligned in the direction along a specific rotation axis. The second member includes two connecting walls aligned in the direction along the specific rotation axis. The two connecting walls are located between the two coupling walls. The following describes two examples of configuration different than in the above embodiment for coupling the first member and the second member, including such walls, by a coupling member and a drive unit so as to allow relative rotation. The two examples described here are focused on the coupling portion between the bucket 50 and the arm 40. The bucket 50 and the arm 40 are coupled so as to be rotatable relative to each other around the third rotation axis 23J shown in FIG. 1.

The first example is now described with reference to FIG. 5. The first example differs from the example in FIG. 2 in that the location of the drive unit relative to the second connecting wall is modified, and in that the base portion of the drive unit is fixed to the second coupling wall while the output portion is fixed to the second connecting wall. In FIG. 5, the same reference signs as in FIGS. 1 to 4 are used for the components that function in the same or substantially the same manner as the corresponding components shown in FIGS. 1 to 4. In addition, the description of FIG. 5 will be omitted or simplified, as appropriate, for the components that function in the same or substantially the same manner as the corresponding components in the first joint mechanism 21.

The joint mechanism 223 shown in FIG. 5 includes a first member constituted by the bucket 50 and a second member constituted by the arm 40. The bucket 50 and the arm 40 are located on one side and the other side across the third rotation axis 23J. The first coupling wall 253 and the second coupling wall 255 protrude from the end surface 51A of the bucket body 51. The first coupling wall 253 and the second coupling wall 255 are aligned in the third axial direction. The second coupling wall 255 is located on the second direction C2 side relative to the first coupling wall 253. The first coupling wall 253 and the second coupling wall 255 are located near the middle of the end surface 51A of the bucket body 51 in the third axial direction.

On the other hand, the first connecting wall 233 and the second connecting wall 235 protrude from the second end surface 41B of the arm body 41. The first connecting wall 233 and the second connecting wall 235 are aligned in the third axial direction. The first connecting wall 233 is located between the first coupling wall 253 and the second coupling wall 255 of the bucket 50. The second connecting wall 235 is located between the first connecting wall 233 and the second coupling wall 255 of the bucket 50. In the example shown in FIG. 5, the first connecting wall 233 and the second connecting wall 235 are separated in the third axial direction. However, the first connecting wall 233 and the second connecting wall 235 may be integrated together.

The first coupling wall 253 of the bucket 50 and the first connecting wall 233 of the arm 40 are coupled by the pin 71 so as to be rotatable relative to each other. Specifically, the pin 71 extends through a through hole 253A in the first coupling wall 253 of the bucket 50 and a through hole 233A in the first connecting wall 233 of the arm 40.

The second coupling wall 255 of the bucket 50 and the second connecting wall 235 of the arm 40 are coupled by the drive unit 104. In the drive unit 104, the case 122 of the speed reducer 120 is located on the second direction C2 side relative to the second coupling wall 255. The case 122 is fixed to the second coupling wall 255 via a flange wall 122F protruding from the outer circumferential surface of the case 122. The electric motor 110 is located on the second direction C2 side relative to the speed reducer 120. Thus, unlike the example in FIG. 2, the case 122 of the speed reducer 120 and the housing 112 of the electric motor 110 are not located in the space between the first connecting wall 233 and the second connecting wall 235, but are exposed to the outside. A brake unit 134 is located on the second direction C2 side relative to the electric motor 110. The brake unit 134 is fixed to the housing 112 of the electric motor 110. The brake unit 134 functions in the same manner as in the above embodiment.

The output member 124 of the speed reducer 120 extends through the through hole 255A in the second coupling wall 255 of the bucket 50. The output member 124 can slide along the inner surface of the through hole 255A. The end of the output member 124 on the first direction C1 side is located inside the through hole 235A in the second connecting wall 235 of the arm 40. Inside the through hole 235A, the spline grooves 124S of the output member 124 engage with the spline teeth 235S formed in the through hole 235A. Thus, the output member 124 is spline-coupled to the second connecting wall 235 via the spline grooves 124S. In addition, the output member 124 rotates in the circumferential direction around the third rotation axis 23J relative to the case 122 of the speed reducer 120 and thus to the housing 112 of the electric motor 110.

Thus, in the example shown in FIG. 5, the housing 112 of the electric motor 110, which constitutes the base portion of the drive unit 104, is fixed to the second coupling wall 255. On the other hand, the output member 124 of the speed reducer 120, which constitutes the output portion of the drive unit 104, is fixed to the second connecting wall 235. When the electric motor 110 is driven, the second connecting wall 235 fixed to the output member 124 and the second coupling wall 255 fixed to the housing 112 of the electric motor 110 rotate relative to each other in the circumferential direction around the third rotation axis 23J.

In the example shown in FIG. 5, the electric motor 110 and even the speed reducer 120 are exposed to the outside. In such configuration, it is easy to attach or detach the electric motor 110 and the speed reducer 120 to or from the second coupling wall 255. Therefore, the maintenance work is simple.

The second example is now described with reference to FIG. 6. The second example differs from the example shown in FIG. 2 in that the second member includes three connecting walls. In FIG. 6, the same reference signs as in FIGS. 1 to 5 are used for the components that function in the same or substantially the same manner as the corresponding components shown in FIGS. 1 to 5. In addition, the description of FIG. 6 will be omitted or simplified, as appropriate, for the components that function in the same or substantially the same manner as the corresponding components in the first joint mechanism 21.

As with the example shown in FIG. 5, the joint mechanism 330 shown in FIG. 6 includes a first member constituted by the bucket 50 and a second member constituted by the arm 40. The bucket 50 and the arm 40 are located on one side and the other side across the third rotation axis 23J. The first coupling wall 353 and the second coupling wall 355 protrude from the end surface 51A of the bucket body 51. The first coupling wall 353 and the second coupling wall 355 are aligned in the third axial direction. The second coupling wall 355 is located on the second direction C2 side relative to the first coupling wall 353.

On the other hand, three connecting walls, a first connecting wall 333, a second connecting wall 335, and a third connecting wall 337, protrude from the second end surface 41B of the arm body 41. The first connecting wall 333, the second connecting wall 335, and the third connecting wall 337 are aligned in the third axial direction. The first connecting wall 333, the second connecting wall 335, and the third connecting wall 337 are separated from one another in the third axial direction. The first connecting wall 333 is located between the first coupling wall 353 and the second coupling wall 355 of the bucket 50. The second connecting wall 335 is located between the first connecting wall 333 and the second coupling wall 355 of the bucket 50. The third connecting wall 337 is located between the second connecting wall 335 and the second coupling wall 355. Thus, the third connecting wall 337 is located opposite the first connecting wall 333 with respect to the second connecting wall 335.

The first coupling wall 353 of the bucket 50 and the first connecting wall 333 of the arm 40 are coupled by the pin 71 so as to be rotatable relative to each other. Specifically, the pin 71 extends through a through hole 353A in the first coupling wall 353 of the bucket 50 and a through hole 333A in the first connecting wall 333 of the arm 40.

The second connecting wall 335 of the arm 40 and the second coupling wall 355 of the bucket 50 are coupled by the drive unit 104. Specifically, the housing 112 of the electric motor 110 is located inside the through hole 335A in the second connecting wall 335. The housing 112 extends through the through hole 335A. The housing 112 is fixed to the second connecting wall 335. The brake unit 134 is located on the first direction C1 side relative to the housing 112. On the other hand, the speed reducer 120 is located on the second direction C2 side relative to the housing 112. The output member 124 of the speed reducer 120 extends through the through hole 337A in the third connecting wall 337. The output member 124 can slide along the inner surface of the through hole 337A. The end of the output member 124 on the second direction C2 side reaches the second direction C2 side relative to the third connecting wall 337. The end of the output member 124 on the second direction C2 side is located inside the through hole 355A in the second coupling wall 355. Inside the through hole 355A, the spline grooves 124S of the output member 124 engage with the spline teeth 355S formed in the through hole 355A. Thus, the output member 124 is spline-coupled to the second coupling wall 355 via the spline grooves 124S. The output member 124 rotates in the circumferential direction around the third rotation axis 23J relative to the case 122 of the speed reducer 120 and thus to the housing 112 of the electric motor 110. Therefore, when the electric motor 110 is driven, the second coupling wall 355 fixed to the output member 124 and the second connecting wall 335 fixed to the housing 112 of the electric motor 110 rotate relative to each other in the circumferential direction around the third rotation axis 23J. The portion of the output member 124 that extends through the third connecting wall 337, for example, may be constituted by the impact mitigation mechanism described above. Thus, the output member 124 does not have to be made entirely of one member in the third axial direction, but may be made of different materials or members connected together.

In the configuration shown in FIG. 6, the drive unit 104 is supported by three walls: the second coupling wall 355 of the bucket 50, the second connecting wall 335 of the arm 40, and the third connecting wall 337 of the arm 40. Therefore, the burden of supporting the drive unit 104 can be distributed among the walls. Thus, the burden on each wall can be reduced. In the configuration shown in FIG. 6, the output member 124 of the drive unit 104 extends through the third connecting wall 337. This has the following advantages. As described for the effects of the above embodiment, when the bucket 50 rotates relative to the arm 40 or when the bucket 50 strikes a material to be excavated, the bucket 50 may act to move in any direction orthogonal to the third rotation axis 23J, as indicated by the arrow V in FIG. 6, for example. With such action of the bucket 50, the output member 124 of the speed reducer 120, together with the second coupling wall 355, may also act to move in any direction orthogonal to the third rotation axis 23J. The third connecting wall 337, through which the output member 124 extends, can receive such action of the output member 124. This reduces the impact reaching the electric motor 110.

In the configuration in which the second member includes three connecting walls as described above, the third connecting wall 337 may be located opposite the second connecting wall 335 with respect to the second coupling wall 355 of the bucket 50. On top of that, the drive unit 104 may be coupled to the third connecting wall 337.

As described for the above embodiment, in the second joint mechanism 22, the first member includes two coupling walls aligned in the direction along a specific rotation axis. The second member includes two connecting walls aligned in the direction along the specific rotation axis. One of the two connecting walls is located between the two coupling walls, while the other is located outside of the two coupling walls. In coupling the first member and the second member, including such walls, by the drive unit and the two coupling members so as to allow relative rotation, the overall configuration of the first member and the second member may be modified from the example in the above embodiment. For example, as to the second joint mechanism 22 of the above embodiment, the dimension of the main portion 31M of the boom body 31 and the dimension of the second end surface 31B of the boom body 31 in the second axial direction may be substantially the same. As to the second joint mechanism 22 of the above embodiment, the second end surface 31B of the boom body 31 may extend toward the second direction B2 relative to the main portion 31M of the boom body 31. Although the boom 30 is mentioned here as an example, the overall shape of the arm 40 may be modified.

As to the third joint mechanism 23, the specific member is not limited to the brake unit. Further, it is not required to interpose the specific member between the specific connecting wall 47 and the first coupling wall 53 in a configuration in which the second member has only one connecting wall, as in the third joint mechanism 23.

As described for the above embodiment, in the third joint mechanism 23, the first member includes two coupling walls aligned in the direction along a specific rotation axis. On the other hand, the second member includes the specific connecting wall located between the two coupling walls in the direction along the specific rotation axis. With reference to FIG. 7, the following describes an example of configuration different than in the above embodiment for coupling the first member and the second member, including such walls, by a coupling member and a drive unit so as to allow relative rotation. The joint mechanism 23A shown in FIG. 7 differs from the example shown in FIG. 4 in that the pin 91 directly couples the first coupling wall 53 and the specific connecting wall 47.

Specifically, in the joint mechanism 23A, the specific connecting wall 47 protrudes from the end of the second end surface 41B of the arm body 41 on the first direction C1 side. In the third axial direction, the specific connecting wall 47 is located immediately adjacent to the first coupling wall 53 of the bucket 50. In the third axial direction, there is a small gap between the specific connecting wall 47 and the first coupling wall 53. The pin 91 extends through the through hole 53A in the first coupling wall 53 and the through hole 47A in the specific connecting wall 47. The pin 91 supports the first coupling wall 53 and the specific connecting wall 47 so as to allow relative rotation.

On the other hand, the third brake unit 133 is located on the second direction C2 side relative to the specific connecting wall 47. The third brake unit 133 is fixed to the specific connecting wall 47 via the flange wall 133F. The third drive unit 103 is located on the second direction C2 side relative to the third brake unit 133. The housing 112 of the electric motor 110 in the third drive unit 103 is fixed to the third brake unit 133. Thus, the housing 112 is fixed to the specific connecting wall 47 via the third brake unit 133. On the other hand, the output member 124 of the speed reducer 120 is fixed to the second coupling wall 55 of the bucket 50 via the spline grooves 124S, as in the third joint mechanism 23 in the above embodiment. In FIG. 7, the same reference signs as in FIGS. 1 to 6 are used for the components that function in the same or substantially the same manner as the corresponding components shown in FIGS. 1 to 6, and redundant description of such components are omitted.

In the joint mechanism 23A shown in FIG. 7, the arm 40 has only one wall, constituted by the specific connecting wall 47, for coupling to the bucket 50. Therefore, the structure of the arm 40 in the example shown in FIG. 7 can be simplified, as in (2) above, compared to a configuration with multiple walls for coupling, for example. In addition, the third joint mechanism 23A shown in FIG. 7 includes only one pin 91 as a coupling member that supports the bucket 50 and the arm 40 so as to allow relative rotation. Therefore, as in (5) above, the number of steps required to attach or detach the bucket 50 to or from the arm 40 can be minimized in terms of the attachment or detachment of the pin.

As to the configuration shown in FIG. 7, the first coupling wall 53 may be eliminated from the bucket 50, along with the pin 91 extending through the first coupling wall 53. Thus, the bucket 50, or the first member, has only one coupling wall 55, as in the joint mechanism 350 shown in FIG. 8. The coupling wall 55 is coupled to the specific connecting wall 47 of the arm 40, or the second member, by the drive unit 103. As described above, the housing 112 of the electric motor 110 is fixed to the specific connecting wall 47 via the brake unit 133. Thus, the base portion of the drive unit is fixed to the second member. However, it is not required that the brake unit 133 be interposed between the base portion and the second member. On the other hand, the output member 124 of the speed reducer 120 is fixed to the coupling wall 55 by spline coupling. Thus, the output portion is fixed to the first member by spline coupling. In FIG. 8, the same reference signs as in FIGS. 1 to 7 are used for the components that function in the same or substantially the same manner as the corresponding components shown in FIGS. 1 to 7, and redundant description of such components are omitted.

In the techniques as disclosed in the '796 Publication for example, it is required to simplify the work of assembling each component in the joints, such as the coupling portion between a boom and an arm or the coupling portion between an arm and a bucket, for example. In this respect, the configuration shown in FIG. 8 utilizes spline coupling as the structure for fixing the output member 124 of the speed reducer 120 to the coupling wall 55. With the spline coupling, as described in (7) above, it is only necessary to insert the output member 124 into the through hole 55A in the coupling wall 55, in order to fix the output member 124 to the coupling wall 55. Thus, the work of fixing the output member 124 to the coupling wall 55 is simple.

In the configuration where the bucket 50 has only one coupling wall 55, as in the example shown in FIG. 8 described above, the location of the coupling wall 55 relative to the bucket body 51 in the third axial direction is not limited to the example shown in FIG. 8, but can be modified as needed. Similarly, the location of the specific connecting wall 47 relative to the arm body 41 in the third axis direction is not limited to the example shown in FIG. 8, but can be modified as needed. In the joint mechanism 350 shown in FIG. 8, the wall to which the base portion of the drive unit 103 is fixed and the wall to which the output portion of the same is fixed may be swapped. In this case, the arm 40 should be treated as the first member, and the specific connecting wall 47 in FIG. 8 should be treated as the coupling wall. At the same time, the bucket 50 should be treated as the second member, and the coupling wall 55 in FIG. 8 should be treated as the connecting wall. In other words, the base portion of the drive unit is fixed to the first member, and the output portion of the same is fixed to the second member. Thus, in the configuration in which the first member has only one coupling wall, the first member is not limited to an attachment such as the bucket 50. As the first member is changed from the attachment, the second member, which is coupled to the first member, is also changed. The coupling structure in which the first member has only one coupling wall may be applied to other parts of the excavator 10 than the coupling portion between the bucket 50 and the arm 40.

The overall configuration of the excavator 10 is not limited to the example in the above embodiment. For example, an attachment other than the bucket may be used. The attachment may be any device, mechanism, or apparatus that is effective in various operations using the excavator 10. Further, the excavator 10 may include two components coupled rotatably, not in the configuration with the boom 30, the arm 40, and the attachment. The various joint mechanisms described for the above embodiment may be applied to the coupling portion between such two components.

The construction machine to which the various joint mechanisms described for the above embodiment are applied is not limited to the excavator 10. The various joint mechanisms described for the above embodiment and its modification examples can be applied to any kind of construction machine to reduce the burden on the joints.

The foregoing embodiment describes a plurality of physically separate constituent parts. They may be combined into a single part, and any one of them may be divided into a plurality of physically separate constituent parts. Irrespective of whether or not the constituent parts are integrated, they are acceptable as long as they are configured to solve the problems.

A technical idea that can be grasped from the above embodiment and its modification examples is described in the following. A joint mechanism for a construction machine, comprising: a drive unit including an electric motor, the drive unit being configured to output torque; a first member including a first coupling wall and a second coupling wall that are aligned in a direction along a rotation axis of the torque output by the drive unit; a second member at least partially located between the first coupling wall and the second coupling wall in the direction along the axial direction; a specific member interposed between the first coupling wall and the second member; and a coupling member that couples the first coupling wall and the specific member so as to allow relative rotation in a circumferential direction around the rotation axis, wherein the drive unit couples the second coupling wall and the second member, and allows relative rotation of the second coupling wall and the second member in the circumferential direction around the rotation axis.