SLEW APPARATUS OF A WORKING MACHINE

Description

FIELD

The field of the disclosure is working machines having a slew apparatus, for example excavators, backhoe loaders, telehandlers, etc.

BACKGROUND

It is known for certain kinds of working machines to be equipped with a slew apparatus which enables the upper part of the machine, typically including the operator cab and tool platform, to be rotated about a vertical axis of the machine relative to the lower part, which typically includes an undercarriage with wheels, tracks and/or legs. Such apparatus enables a working machine to operate without having to reposition itself. One example of such a machine would be an excavator digging a trench, in which case the excavator can be positioned adjacent to the trench location where it can be secured in place, usually by means of extendable legs, and the operator can then use the excavator shovel to dig the trench and use the slew apparatus to rotate the shovel and cab relative to the excavator undercarriage to dump earth removed from the trench in a location spaced from the trench. In another example, a telehandler can be positioned in one location, for example to lift a load from high shelving, then rotated using the slew to allow the telehandler to be driven along a path between shelving in order to deliver the load to another location. Those are two, non-limiting examples of many known applications of slew apparatuses on working machines.

Existing slew apparatuses typically comprise a rotating slew frame, which carries all of the upper parts of the working machine, e.g., operator cab and tool platform, which frame is rotatably mounted to the lower part of the working machine. The lower part of the vehicle has a ring gear with inwardly projecting gear teeth and the rotating frame has a ring bearing arranged outside the ring gear and a planet gear arranged inside the ring gear, with teeth that interdentate with the ring gear teeth. The planet gear is usually driven in rotation by a hydraulic motor, enabling the rotating frame to be driven in rotation relative to the ring gear. In another arrangement, the ring gear has outwardly projecting gear teeth and then the planet gear is arranged to the exterior of the ring gear.

There is an increasing inclination in the field of working machines to replace hydraulic motors with electric motors. Integration of electric motors presents new mounting and packaging challenges, which the present teachings seek to address.

SUMMARY

The present teachings provide a slew apparatus of a working machine according to the appended claims.

An aspect of the teachings provides a slew apparatus of a working machine comprising a slew frame, an electric motor mounting element mounted to the slew frame and an electric motor mounted to the electric motor mounting element for driving the slew apparatus in rotation. The electric motor has a drive axis defining an axial direction and a radial direction normal to the axis, and a drive output shaft extending from one axial end thereof. The electric motor mounting element comprises a body configured to receive the electric motor and at least three mounting legs. Each leg projects radially from the body so as to define a free end spaced from the body and each leg defines a mounting portion, at the respective free end thereof, and configured to effect fastening of the electric motor mounting element to the slew frame so as to mount the electric motor to the slew frame. Each mounting portion is spaced radially outwardly from the perimeter of the electric motor when viewed in the axial direction thereof.

By providing a three-legged mounting element where the legs project radially from the electric motor body, the motor can be mounted to the frame so as to resist the torque reaction created when it drives the frame in rotation and the projection of the legs facilitates access to mount (and demount) the motor to the frame.

Each mounting portion may comprise a mounting aperture arranged to receive a fastener to effect fastening of the electric motor mounting element to the slew frame. That allows bolts to pass through the mounting apertures to secure the motor to the frame.

The legs may be substantially equal in radial length. In that way, the legs resist the torque reaction created when the motor drives the frame in rotation equally. Alternatively, the legs may have different radial lengths. Different leg length allows the selection of different radial locations for the mounting apertures which may be necessary on particular machines, e.g., to allow for the placement of other components on the frame.

The legs may be respectively evenly spaced about the body when viewed in the axial direction. That ensures an even distribution of the force required to resist the reactive torque moment created when the motor drives the frame in rotation.

The slew apparatus may comprise a ring bearing having a ring bearing mounting defining a circumference, the electric motor mounting element being mounted such that the electric motor mounting element body is arranged within the circumference and at least one leg projects radially outside the circumference so that the mounting portion on that leg is outside the circumference. By extending the leg outside the circumference of the ring bearing, the greater length of the leg allowed by that arrangement reduces the load on the mounting when resisting the reactive torque moment created when the motor drives the frame in rotation. Optionally, more than one leg projects radially outside the circumference. Alternatively, in the case where the ring gear has outwardly projecting gear teeth and the planet gear is arranged to the exterior of the ring gear, the electric motor mounting element is mounted such that the electric motor mounting element body is arranged outside the circumference and at least one leg projects radially inside the circumference so that the mounting portion on that leg is inside the circumference.

The electric motor mounting element body is optionally generally circular when viewed in the axial direction so as to minimize the footprint of the body by generally matching the shape of the electric motor and to reduce the potential for stress concentrations.

Each mounting aperture may be surrounded by a collar projecting axially from the respective leg. Each collar may having an axial depth less than the thickness of the slew frame and may project from the face of the electric motor mounting element which abuts the frame and the frame has respective frame apertures which are greater in diameter than the outer diameter of the collars. When the electric motor mounting element is mounted on the frame, the collars may be received in the frame apertures so as to locate the electric motor mounting element prior to mounting of the electric motor mounting element to the frame. Alternatively, or in addition, the collars may project from the face of the electric motor mounting element which faces away from the frame and those collars may have an internal diameter which allows a mounting tool, such as a bolt gun, to be received in the collars so as to facilitate assembly of the electric motor mounting element to the frame.

The electric motor may include a gear apparatus at the drive output end thereof, the gear apparatus being configured to receive the drive output shaft of the electric motor and step down the drive output to a lower revolution, higher torque gear output shaft. In that way, the motor itself provides an output shaft configured at the appropriate torque and rotational speed to drive the frame in rotation. Electric motors typically provide high speed, low torque output so providing a gear apparatus on the motor itself removes the need for additional components and simplifies installation. The gear apparatus may comprise a gear lubricant port and the electric motor may be arranged on the electric motor mounting element such that the legs are circumferentially spaced from the port, when viewed in the axial direction. The electric motor may have at least one radially projecting portion to receive an electrical or fluid connection port

and the motor is optionally arranged on the electric motor mounting element such that the legs are circumferentially spaced from the projecting portion, when viewed in the axial direction. In that way, pipework to supply lubricant to the gear apparatus or an electrical power supply to the motor does not interfere with access to the mounting apertures.

Optionally, the body of the electric motor mounting element does not project radially beyond the perimeter of the electric motor, when viewed in the axial direction. That ensures that the body takes up the minimum amount of space on the frame.

Another aspect of the teachings provides a slew apparatus of a working machine comprising: a slew frame; a slew bearing mounted to the slew frame; and an electric motor assembly mounted to the slew frame. The slew bearing comprises a ring bearing defining a circumference and a bearing axis, the bearing axis defining an axial direction of the apparatus and a line from the bearing axis to the circumference defining a radial direction of the apparatus. The electric motor assembly comprises an electric motor and an electric motor mounting, the electric motor defining a motor drive axis, the electric motor having an axial length and a motor diameter which are specified to provide an electric motor rated to drive the slew bearing in rotation. The slew bearing and electric motor assembly are arranged on the slew frame such that the motor drive axis is inside the ring bearing circumference and extends substantially parallel to the axial direction and the motor drive axis is located radially closer to the ring bearing circumference than the ring bearing axis. The axial length and diameter of the electric motor, and the configuration of the electric motor mounting are configured such that a space is defined between the radially innermost part of the electric motor and the ring bearing axis.

The axial length and overall diameter of electric motors determine its power output, torque capability and shaft speed. A larger diameter motor can accommodate larger windings and magnets whilst a longer motor provides more space for additional windings. The overall dimensions of the motor are constrained by the space available on the frame, between the frame and the underside, typically, of the operator cab, in terms of motor length and packaging of other components on the frame, in terms of motor diameter. By tuning the selection of motor length versus motor diameter, whilst providing a motor rated to perform the task of rotating the slew frame, a space can be provided around the center of the ring bearing axis. That allows for the passage of, e.g., wiring or hydraulic pipes through that space.

The slew apparatus may further comprise a hydraulic equipment package, a hydraulic valve block and a battery all mounted to the slew frame.

In that case, the hydraulic equipment package, hydraulic valve block and battery are each optionally mounted toward the periphery of the frame and may together delimit a generally central space, the electric motor assembly being mounted to the slew frame in the generally central space. Arranging the hydraulics and battery in this way balances the load on the frame.

The slew frame may comprise a first diagonal rib, a second diagonal rib oriented on an intersecting line with respect to the first diagonal rib and a cross rib oriented to intersect both diagonal ribs such that the ribs delimit a substantially triangular or trapezoidal inner space. In such a case, the electric motor is optionally mounted to the slew frame within the inner space defined by the ribs and/or the hydraulic equipment package, hydraulic valve block and battery are each optionally mounted to the frame outside the inner space defined by the ribs. The hydraulic equipment package may be mounted to the frame adjacent to the first diagonal rib and/or the hydraulic valve block may be mounted to the frame adjacent to the second diagonal rib and/or the heat exchanger may be mounted to the frame adjacent to the cross rib. Arranging the equipment on the frame adjacent to the ribs supports the equipment in a structurally beneficial way.

Optionally, the hydraulic equipment package, hydraulic valve block and battery delimit a substantially trapezoidal central space bounded on three sides by the hydraulic equipment package, hydraulic valve block and battery and open on a fourth side, the electric motor being mounted to the frame within the trapezoidal central space, the electric motor having at least one radially projecting portion to receive an electrical or fluid connection port, the radially projecting portion extending from the electric motor towards the open fourth side of the trapezoidal central space. The radially projecting portion optionally extends from the electric motor towards a point on the open fourth side of the trapezoidal central space adjacent to the hydraulic equipment package. In such an arrangement, a hydraulic return valve may be mounted to the frame, optionally arranged between the electric motor and the open fourth side of the trapezoidal central space.

Where the frame has first, second and cross ribs, which delimit three sides of a trapezoidal inner space, the fourth side being open, the frame may have front and rear ends, the open fourth side being arranged toward the front end of the frame, the electric motor being mounted to the slew frame within the inner space defined by the ribs, a hydraulic return valve being mounted to the frame between the electric motor and the open fourth side.

Arranging the hydraulic return valve in this position allows for a more convenient arrangement of routes for hydraulic hoses to and from the return valve.

Where the frame has a front end and a rear end, and the ring bearing defines a slew axis between the front and rear ends, the motor is optionally arranged towards the front end of the frame relative to the slew axis, i.e., forward of the slew axis.

The electric motor has an axial length, which is measured from the surface of the slew frame on which the motor is mounted to the upper face of the motor, spaced from the frame, and a radial width, which is the maximum diameter of the motor along the axial length. The axial length is optionally greater than the radial width of the motor. By utilizing the available axial length of the motor, given the available space above the frame, to meet the power rating requirement of the motor, the footprint of the motor is minimized.

The ratio of the axial length of the electric motor to the radial width of the electric motor may be in the range 1.1:1 to 1.5:1. The axial length of the electric motor may be in the range 250 to 350mm. The radial width of the electric motor may be in the range 166 to 318mm.

In a further aspect of the teachings, there is provided a working machine having a cab for an operator and a slew apparatus as described in either of the foregoing aspects, the cab being arranged above the slew apparatus.

In that way, a working machine is provided with an electrically driven slew apparatus having the aforementioned advantages.

The cab may have a cab floor with a cavity being defined between the underside of the cab floor and the slew frame, the cavity having a height measured between the underside of the cab floor and the upper face of the slew frame and the height of the cavity is optionally in the range 300 to 400mm, further optionally 310 to 330mm. That cavity height allows the electric motor to be accommodated without elevating the cab too high. The underside of the cab floor may include sound deadening material and the height of the cavity, in such a case, is thus measured between the lowermost extent of the sound deadening material and the upper face of the slew frame.

The electric motor is optionally arranged in the cavity with a clearance between the upper face of the motor and the underside of the cab floor of 50-70mm, further optionally 60mm. That clearance allows sufficient space above the motor to allow for the passage, for example, of an electrical power line without interference with the cab or motor.

BRIEF DESCRIPTION OF DRAWINGS

Examples will now be described by way of example only with reference to the accompanying figures, in which:

FIG. 1 is a side elevation of a working machine having a slew apparatus according to the teachings hereof.

FIG. 2 is an enlarged view of part of the working machine of FIG. 1,

FIG. 3 is a perspective view of a slew apparatus according to the teachings,

FIG. 4 is a plan view from above of the slew apparatus of FIG. 3,

FIG. 5 is a plan view from below of the slew apparatus of FIGS. 3 and 4,

FIG. 6 is a view similar to FIG. 4 but with some components omitted for clarity but including hydraulic hoses and electric wiring harnesses,

FIG. 7 is an enlarged side section of the slew apparatus showing the clearance between the motor and the cab floor,

FIG. 8 is an enlarged perspective view of the electric motor and mounting of the slew apparatus of FIGS. 3 to 7 with other features omitted for clarity,

FIG. 9 is an enlarged perspective view of the electric motor mounted to the slew frame with other features omitted for clarity, and

FIG. 10 is a perspective view of a known slew apparatus including a hydraulic motor.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various examples and the teachings. However, those skilled in the art will understand that: the present teachings may be practiced without these specific details or with known equivalents of these specific details; that the present teachings are not limited to the described examples; and, that the present teachings may be practiced in a variety of alternative examples. It will also be appreciated that well known methods, procedures, components, and systems may not have been described in detail.

References to vertical and horizontal in the present disclosure should be understood to be in relation to the machine when stood on horizontal ground in a non-working condition. The term axial is generally used in relation to the longitudinal axis of the machine. The term width is generally used in relation to the longitudinal length, that is, transverse to the length.

The inventors have determined that replacing hydraulic motors with electric motors can reduce the overall load on the working machine hydraulic system and removes the need for pipework to connect the hydraulic motor to the hydraulic system. However, in order to provide an equivalent power output, electric motors tend to be longer in their axial extent and/or wider in their radial extent than an equivalent hydraulic motor. That can pose a difficulty in fitting the electric motor into space previously occupied by the hydraulic motor as the space above the motor is much more limited so may be unavailable, e.g., to route hydraulic pipes or wiring harnesses. Also, the wider diameter of the electric motor means that the bolt locations used to secure the hydraulic motor to the frame may be obscured by the body of the electric motor. The arrangements illustrated and described in the present disclosure address the problems presented by these factors.

With reference to FIGS. 1 and 2, a working machine 1, in this case in the form of a tracked mini-excavator, comprises an undercarriage 2 and a superstructure 3. The undercarriage 2 includes a set of tracks 4 driven by the working machine power plant (not shown). The superstructure 3 includes an operator cab 5 and a shovel arm assembly 6. The superstructure 3 is mounted to the under carriage 2 by means of a slew apparatus 7.

The slew apparatus 7 is shown in more detail in FIGS. 3-6.

With reference to FIGS. 3-6, the slew apparatus comprises a rotating frame 10, having a nose end 12 and a tail end 14. The working machine’s superstructure 3 is mounted to the rotating frame 10 in such a way that an operator in the cab 5 faces in the direction of the front end 12.

The undercarriage 2 of the working machine 1 carries an upwardly projecting ring gear 16. The rotating frame 10 has a large circular recess generally centrally located which receives a ring bearing 18 sized to fit around the ring gear 16 in sliding, rotational contact. The ring gear 16 and ring bearing 18 are best illustrated in FIG. 5. The ring gear 16 and ring bearing 18 define a slew axis S (see FIG. 2) of the slew apparatus 7, about which the rotating frame 10 rotates. As shown in FIG. 2, the cab 5 has a cab floor, the level of the underside of which (taking into account any sound deadening material) is shown by the broken line C. The upper face of the frame 10 is shown by the dot-dash line F.

With reference to FIG. 3, the rotating frame 10 mounts a hydraulic equipment package 20, an electrical battery pack 22, a hydraulic valve block 24, a hydraulic return valve 26 and an electric motor assembly 28. A kingpost carrier 30, for mounting the tool, dig end or shovel arm (or excavator end/excavating arm) 6 to the frame 10, extends from approximately the mid-point of the nose end 12 of the frame 10. Tool mounting brackets 32, 34 extend from opposite sides of the nose end 12 of the rotating frame 10.

As best shown in FIG. 4, the rotating frame 10 is generally circular in shape, truncated at the front end 12. A bulkhead 36 extends across the nose end 12 and the kingpost carrier 30 extends from the bulkhead 36. A first diagonal rib 38 extends from the rear face of the bulkhead 36 from approximately the position of one edge of the kingpost carrier 30. The first diagonal rib 38 extends rearwardly of the frame at an oblique angle relative to the fore and aft direction of the frame 10. A second diagonal rib extends from the rear face of the bulkhead 36 approximately from the position of the opposite edge of the kingpost carrier 30 when viewed from above. The second diagonal rib extends rearwardly of the frame at an oblique angle relative to the fore and aft direction of the frame and divergent from the first diagonal rib 38. A cross rib 42 extends at right angles to a fore and aft direction of the frame, positioned slightly rearwardly of the slew axis S of the frame 10. The cross rib 42 passes over the second diagonal rib 40 and meets the first diagonal rib 38, so that the first and second diagonal ribs 38, 40 and cross rib 42 form a structural “A” frame. The first and second diagonal ribs 38, 40 continue beyond the cross rib 42 to the rear end 14 of the frame 10.

The bulkhead 36, first and second diagonal ribs 38, 40 and cross rib 42 delimit a trapezoidal central space in which the electric motor 28 is located.

As best shown in FIG. 4, the hydraulic equipment package 20 is arranged on the frame 10 outside, and adjacent to, the first diagonal rib 38. The battery pack 22 is arranged at the rear of the frame, immediately behind and adjacent to the cross rib 42. The hydraulic block 24 is arranged on the frame 10 outside and adjacent to the second diagonal rib 40. That arrangement distributes the weight of the equipment on the frame evenly around the frame with respect to the slew axis. The arrangement of the battery pack 22 towards the rear 14 of the frame 10 counterbalances the weight of the tool arm 6 carried by the kingpost carrier 30.

The hydraulic equipment package 20 includes a hydraulic pump, an inverter and a hydraulic tank (not shown).

As shown in FIG. 6, a heat exchanger 44 of a cooling system for the vehicle hydraulics is arranged towards the rear end 14 of the frame 10 outside the second diagonal rib 40 with respect to the slew axis.

The electric motor 28 is arranged in the trapezoidal central space on the frame 10, forward of the slew axis S, between the slew axis and the first diagonal rib 38. The hydraulic return valve 26 is arranged between the electric motor 28 and the kingpost carrier 30 approximately at the intersection of the first diagonal rib 38 and the bulkhead 36.

An aperture 46 is formed in the rotating frame 10 around the slew axis S, amongst other things, to allow for the passage of hydraulic hoses, for example hoses to supply hydraulic power to hydraulic motors driving the working machine tracks.

Referring to FIGS. 5 and 9, the general position of the electric motor 28 relative to the slew axis S can be seen. The position of the electric motor in terms of its radial distance from the slew axis S is determined by the size of the output gear of the electric motor, which will be described in more detail below.

As best shown in FIG. 8, the electric motor assembly 28 comprises an electric motor part 48 and a transmission part 50. The electric motor part 48 and transmission part 50 are both generally cylindrical. The electric motor part 48 is mounted on top of the transmission part 50. The electric motor part includes an electric motor with an electric motor output shaft (not shown) on an electric motor drive axis. The electric motor output shaft passes into the transmission part 50. The transmission part includes gear assembly (not shown) which receives the relatively high speed, low torque input from the electric motor output shaft and converts that into a relatively low speed, higher torque transmission output shaft. The transmission output shaft carries an output gear wheel 52 which can be seen in FIG. 5. The motor 28 further comprises an electrical power input port 54, which extends from the end of the electric motor 28 which is spaced from the transmission, from a position generally central of the electric motor, radially of the electric motor with respect to the electric motor drive axis M and extending beyond the outer peripheral edge of the cylindrical electric motor assembly 28. The transmission part 50 includes a port 55 for receiving lubricant. The lubricant port 55 is arranged angularly spaced, when viewed from above, with respect to the electrical power input port 54.

As shown in FIG. 4, the bulkhead 36 of the front end 12 of the rotating frame 10 terminates short of the side of the frame, on which side is located the hydraulic equipment pack 20. The first diagonal rib 38 has a portion 38a which has a lower height than the reminder of the rib, the lower height portion 38a being arranged substantially adjacent to the bulkhead 36. The space defined at the end of the bulkhead 36 and by the lower height portion 38a of the first diagonal rib 38 provides an open side of the, otherwise bounded, trapezoidal central section. When it is mounted on the frame 10, the electric motor assembly 28 is oriented angularly in such a way that the electrical power input port 54 extends towards the reduced height portion of the first diagonal rib 38 and towards the space beyond the end of the bulkhead 36 and thus towards the open side of the trapezoidal central section (see FIG. 9).

The position of the electric motor assembly 28 with respect to the slew axis S and with respect to the first and second diagonal ribs 38, 40 and the cross rib 42, creates two main hydraulic hose pathways H1, H2 within the trapezoidal central section, the first hose pathway H1 being defined between the body of the electric motor assembly 28 and the cross rib 42 and the second hose pathway H2 being defined between the electric motor assembly 28 and the second diagonal rib 40. The main hose pathways H1, H2 are best illustrated in FIG. 4.

FIG. 6 shows the hydraulic hose lines which run between the hydraulic equipment package 20, the hydraulic valve block 24, the tool arm 6, the hydraulic return valve 26, the undercarriage 2 of the working machine and the heat exchanger 44 of a cooling system. A first set of hoses 68 run from the hydraulic equipment package 20 to the hydraulic valve block 24 via main hose pathway H1. A second set of hoses 70 run from the hydraulic valve block 24 to the tool arm 6 via main hose pathway H2 and an opening in the bulkhead 36. A third set of hoses 72 run from the hydraulic valve block 24 through the main hose pathway H2 and down through the central aperture 46 in the frame to the undercarriage 2. A single return hose 74 passes from the hydraulic valve block 24 to the hydraulic return valve 26, the hose 74 running substantially parallel to the bulkhead. Inlet and return cooling hoses 76 run from the hydraulic return valve 26 to the heat exchanger 44, the hoses 76 running in the space between the electric motor assembly 28 and the first diagonal rib 38 and then turning to run in the main hose pathway H1 to the heat exchanger 44.

The electric motor assembly 28 is mounted to an electric motor mounting 56 which, in turn, is mounted to the rotating frame 10.

The electric motor mounting 56 comprises a substantially circular body 58, which is marginally greater in diameter than the electric motor assembly 28 and which has an aperture formed centrally thereof to allow passage of the transmission output shaft. An annular pilot hub 59 depends from the body 58 around the output shaft aperture. Three mounting legs 60 extend radially from the circular body 58, each leg 60 being equally angularly spaced from the other two. Each leg 60 projects beyond the periphery of the electric motor assembly 28, when viewed from above, which allows easier access for tools on installation. Each leg includes an aperture 62 formed through the respective free end thereof, which aperture 62 allows for the passage of

a fastener, such as a nut and bolt therethrough. The frame 10 has corresponding apertures 66 formed therethrough.

In the electric motor mounting 56 shown in the figures, each leg 60 is of equal length. However, the legs may be of unequal lengths. The legs 60 may have an irregular angular spacing. For example, instead of each leg being spaced at 120 degrees to its neighbors, two legs may be spaced at 90 degrees with respect to each other and one at 135 degrees to the others. Also, more than three legs may be provided.

As shown in FIG. 8 in broken lines, each leg may optionally include a mounting collar 78 which surrounds and extends upwardly from each mounting aperture 62. The mounting collar 78 defines a bore which has a diameter greater than the diameter of the mounting aperture, the bore diameter being just larger than the diameter of a tool head which is used to tighten a bolt passing through the mounting aperture 62. Also, each leg may optionally include a locating collar 80, which surrounds and extends downwardly from each mounting aperture 62. The outer diameter of the locating collar 80 is just smaller than that of the frame apertures 66. In that way, when the mounting 56 is arranged on the frame, the locating collars drop into the frame apertures to locate the mounting in the correct position prior to securing the mounting to the frame by means of bolts passing through the mounting apertures 62.

The body 58 has an annular collar 64 extending therefrom and arranged to receive the lower portion of the transmission part 50 of the electric motor assembly 28. The collar 64 has a flange 65 around its upper edge which receives motor mounting bolts 67, by which the motor 28 is secured to the motor mounting 56.

The rotating frame 10 includes a mounting plate 82 (see FIG. 9) which is substantially the same shape as the body 58 of the mounting 56 and through which the frame apertures 66 pass. The plate 82 is welded to the frame 10 and is provided to reinforce the frame to assist in supporting the mass of the motor 28 and to act as a guide on installation. The frame 10 itself also includes a scallop portion 88 which encroaches into the otherwise circular central aperture 46 (see FIG. 5), which scallop portion 88 supports part of the body 58 of the electric motor mounting 56.

As shown in FIG. 5, when the mounting 56 is arranged on the frame 10, the annular pilot hub 59 passes through an aperture in the frame 10 and the mounting apertures 62 in two of the mounting legs 60 (and thus the corresponding apertures 66 in the frame 10) lie inside the circumference of the ring bearing 18 and the mounting aperture of one of the mounting legs 60

(and its corresponding frame aperture) lies outside the circumference of the ring bearing 18. That mounting configuration helps to resist the reacted torque created when the electric motor assembly 28 is driving the rotating frame 10 in rotation.

When it is mounted on the mounting 56, the electric motor assembly 28 is arranged such that the power input port 54 and the lubricant port 55 are angularly spaced from the legs 60 of the mounting 56.

As best shown in FIGS. 2 and 7, the cab 5 is arranged generally centrally with respect to the frame 10 so that the cab floor level C is directly above the electric motor assembly 28 when it is fitted to the frame 10. The electric motor assembly 28 is dimensioned such that a clearance is provided above it, beneath the cab floor level C. Typically, the distance between the upper face level F of the frame 10 and the cab floor underside level C is in the range 300mm to 400mm, or 310mm to 330mm. As such, in order to provide a desired clearance of 50-70mm between the top of the electric motor assembly 28 and the cab floor level C, the axial length of the electric motor assembly 28, measured from the upper face of the rotating frame 10, is 250mm to 300mm.

As discussed above, the height and diameter of the electric motor assembly 28 is a significant factor in determining the power output and torque capacity of the electric motor assembly 28. In the examples shown, the axial length of the motor and the diameter are selected so as to be able to drive the rotating frame in rotation using a transmission output gear which is a small as possible. That, in turn, enables the electric motor assembly 28 to be mounted such that the drive axis M of the electric motor is radially closer to the ring bearing circumference than the slew axis S. In order to achieve the necessary power output and torque capacity, whilst maintaining the above-described clearance above the motor assembly, the diameter of the electric motor assembly 28 is in the range 166mm to 318mm.

The combination of the selection of the electric motor assembly axial length and diameter allows for the aforementioned clearance and the use of a sufficiently small transmission output gear wheel allows offsetting of the motor assembly 28 relative to the slew axis S and thus provide the above-described main hose pathways H1, H2. Generally, the ratio of the axial length of the electric motor to the radial width of the electric motor is in the range 1.1: to 1.5:1.

By contrast, and as illustrated in FIG. 9, the known hydraulic slew motor HSM is smaller both in height and diameter, such that hoses may be routed above the motor HSM.

Consequently, the position of the motor HSM is not constrained by the need to provide hose pathways.

The one or more examples are described above by way of example only and it will be appreciated that the variations are possible without departing from the scope of protection afforded by the appended claims.