PISTON AND INTERNAL COMBUSTION ENGINE

Description

TECHNICAL FIELD

Cross-Reference to Related Applications

The present application claims priority to Japanese Patent Application number 2024-123013, filed on Jul. 30, 2024 contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present disclosure relates to a piston and an internal combustion engine. A piston of an internal combustion engine is provided with a cooling cavity through which lubricating oil flows within a piston head, in order to cool the piston head, which reaches a high temperature (see Japanese Unexamined Patent Application Publication No. 2019-39340). Lubricating oil flowing through the cooling cavity is discharged from a discharge port communicating with the cooling cavity and falls into an oil pan in a lower portion of the internal combustion engine.

In order to reduce friction or the like that occurs when the piston slides relative to the cylinder, an oil film of lubricating oil is formed on an inner wall surface of the cylinder. Although it can be proposed to supply the lubricating oil discharged from the discharge port to the inner wall surface of the cylinder in order to maintain the oil film, since the discharge port is located away from the inner wall surface of the cylinder, it is difficult to direct the lubricating oil discharged from the discharge port toward the inner wall surface of the cylinder.

BRIEF SUMMARY OF THE INVENTION

The present disclosure has been made in view of these points, and its object is to effectively utilize lubricating oil discharged from a cooling cavity.

A first aspect of the present disclosure provides a piston that reciprocates within a cylinder, the piston including: a piston head having a combustion chamber formed on a top surface; a cooling portion formed in an annular cavity inside the piston head and through which lubricating oil flows; a discharge port that communicates with the cooling portion and discharges lubricating oil from the cooling portion to a lower side of the piston head; and a skirt portion extending downward from a lower end portion of an outer periphery of the piston head, wherein the skirt portion includes a flow path portion that is formed in an inner peripheral surface opposite to an outer peripheral surface facing the cylinder, and through which lubricating oil discharged from the discharge port flows along the inner peripheral surface.

A second aspect of the present disclosure provides an internal combustion engine including: a cylinder; and a piston that reciprocates within the cylinder, wherein the piston includes: a piston head having a combustion chamber formed on a top surface; a cooling portion formed in an annular cavity inside the piston head and through which lubricating oil flows; a discharge port that communicates with the cooling portion and discharges lubricating oil from the cooling portion to a lower side of the piston head; and a skirt portion extending downward from a lower end portion of an outer periphery of the piston head, among which the skirt portion includes a flow path portion that is formed in the inner peripheral surface opposite to an outer peripheral surface facing the cylinder, and through which lubricating oil discharged from the discharge port flows along the inner peripheral surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of an internal combustion engine 1 according to an embodiment.

FIG. 2 is a schematic view showing an internal configuration of a piston 30.

FIG. 3 is a cross-sectional view taken along a line I-I of FIG. 2.

FIG. 4 is a view of the piston 30 as seen from below.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present disclosure will be described through exemplary embodiments, but the following exemplary embodiments do not limit the invention according to the claims, and not all of the combinations of features described in the exemplary embodiments are necessarily essential to the solution means of the invention.

<Configuration of an Internal Combustion Engine>

FIG. 1 is a schematic diagram illustrating a configuration of an internal combustion engine 1 according to one embodiment. Here, the internal combustion engine 1 is mounted on a vehicle such as a truck, but is not limited thereto, and may be mounted on, for example, a ship.

The internal combustion engine 1 is, for example, a diesel engine. The internal combustion engine 1 is a power source that generates power for causing a vehicle to travel by burning and expanding an air-fuel mixture of intake air in a combustion chamber 2. The internal combustion engine 1 includes a cylinder block 10, a cylinder head 20, a piston 30, a crankshaft 60, and an injection portion 70.

The cylinder block 10 includes a cylinder 12 that houses the piston 30 in a manner allowing the piston 30 to reciprocate, and a crankcase 16 that houses the crankshaft 60. An oil pan 18 that reserves lubricating oil is attached to the crankcase 16.

The cylinder head 20 is provided to an upper portion of the cylinder block 10. The cylinder head 20 includes an injector 22, an intake valve 25, and an exhaust valve 26. The injector 22 injects fuel into the combustion chamber 2 defined by a top surface of the piston 30, an inner wall surface 13 of the cylinder 12, and the cylinder head 20. The intake valve 25 opens and closes to introduce fresh air from an intake port 23 into the combustion chamber 2. The exhaust valve 26 opens and closes to guide exhaust gas from the combustion chamber 2 into an exhaust port 24.

The piston 30 reciprocates within the cylinder 12. When the piston 30 reciprocate between a top dead center and a bottom dead center, the piston 30 slides on the inner wall surface 13 of the cylinder 12. The lubricating oil is supplied to the inner wall surface 13 to form an oil film. Since the oil film is formed on the inner wall surface 13, frictional force when the piston 30 slides on the inner wall surface 13 can be reduced. A detailed configuration of the piston 30 will be described later.

The crankshaft 60 is coupled to the piston 30 via a connecting rod (hereinafter referred to as “con rod”) 62. The crankshaft 60 converts reciprocating motion of the piston 30 into rotational motion.

The injection portion 70 injects the lubricating oil toward the piston 30. For example, when the piston 30 is positioned at the bottom dead center, the injection portion 70 injects lubricating oil upward toward the piston 30 positioned above. Specifically, the injection portion 70 injects lubricating oil upward toward an inlet 42 (FIG. 2) of the piston 30 so that the lubricating oil is supplied to a cooling portion 40 (FIG. 2) of the piston 30.

<Internal Configuration of the Piston>

An internal configuration of the piston 30 will be described with reference to FIGS. 2 to 4.

FIG. 2 is a schematic view showing the internal configuration of the piston 30. FIG. 3 is a cross-sectional view taken along a line I-I of FIG. 2. FIG. 4 is a view of the piston 30 as viewed from below. As illustrated in FIG. 2, the piston 30 includes a piston head 32, a coupling portion 35, a skirt portion 36, the cooling portion 40, the inlet 42, a discharge port 44, and a groove portion 50.

The piston head 32 is a cylindrical portion formed at an upper portion of the piston 30. At the center of a top surface of the piston head 32, a cavity 33 that is recessed with respect to the top surface is provided. The cavity 33, together with the cylinder 12 and the cylinder head 20, forms the combustion chamber 2 (FIG. 1) in which fuel and air combust. Fuel is injected into the cavity 33 from the injector 22 (FIG. 1). A groove 34, in which a piston ring is mounted, is formed in an outer peripheral surface of the piston head 32. The piston ring serves to seal combustion gas and to maintain the oil film on the inner wall surface 13 of the cylinder 12 at a predetermined thickness. In FIG. 2, the piston ring is omitted for convenience of explanation.

Here, the coupling portion 35 is a piston pin, and couples the piston 30 and the con rod 62. The coupling portion 35 is cylindrically shaped and fits into a pin hole of the piston 30. The coupling portion 35 is disposed to extend from the front to the rear of the plane of FIG. 2.

The skirt portion 36 is a lower portion of the piston 30. The skirt portion 36 extends downward from a lower end of the outer periphery of the piston head 32. The skirt portion 36 is cylindrically shaped. The skirt portion 36 is provided to suppress tilting of the piston 30 within the cylinder 12. The skirt portion 36 is formed so that its thickness decreases toward a lower end 39.

The skirt portion 36 is provided around the entire circumference of the piston 30, but only on portions facing a thrust region and an anti-thrust region of the inner wall surface 13 of the cylinder 12. The thrust region of the inner wall surface 13 is a region in which the skirt portion 36 slides as the piston 30 moves from the top dead center to the bottom dead center. The anti-thrust region of the inner wall surface 13 is a region in which the skirt portion 36 slides as the piston 30 moves from the bottom dead center to the top dead center. In FIG. 2, the portion on the left side, as seen from the piston 30, is the thrust region, and the portion on the right side, as seen from the piston 30, is the anti-thrust region.

The skirt portion 36 includes a skirt portion 36A located on the left side of the coupling portion 35 and a skirt portion 36B located on the right side of the coupling portion 35. The skirt portion 36A faces the thrust region while the skirt portion 36B faces the anti-thrust region. The skirt portions 36A and 36B are arranged symmetrically with respect to the coupling portion 35.

The cooling portion 40 is a lubrication path, lubricated by the lubricating oil, for cooling the piston head 32, which reaches a high temperature. The cooling portion 40 is formed in an annular cavity inside the piston head 32. The cavity serves as a cooling cavity through which lubricating oil flows. The cooling portion 40 is formed to surround the periphery of the cavity 33.

The inlet 42 communicates with the cooling portion 40 and is an opening for introducing lubricating oil into the cooling portion 40. The inlet 42 is provided in a lower portion of the piston head 32 and communicates with the cooling portion 40 via an introduction path 43. The introduction path 43 is formed in the piston head 32 along the vertical direction. The inlet 42 is located at a lower end, which is a distal end of the introduction path 43. The inlet 42 is formed in a portion of the piston head 32 facing the anti-thrust region of the inner wall surface 13 of the cylinder 12.

The inlet 42 guides the lubricating oil, which is injected by the injection portion 70 (FIG. 1) when the piston 30 is at the bottom dead center, to the cooling portion 40. The inlet 42 is formed at a position where the injection portion 70 is located directly below it when the piston 30 is positioned at the bottom dead center. The lubricating oil introduced into the cooling portion 40 from the inlet 42 circulates in the cavity of the cooling portion 40.

The discharge port 44 communicates with the cooling portion 40 and is an opening for discharging the lubricating oil flowing through the cooling portion 40. The discharge port 44 is provided in the lower portion of the piston head 32 and communicates with the cooling portion 40 via a discharge path 45. The discharge port 44 is formed in the piston head 32 along the vertical direction. The discharge port 44 is located at a lower end, which is a distal end of the discharge path 45. The discharge port 44 is formed in a portion of the piston head 32 facing the thrust region of the inner wall surface 13 of the cylinder 12.

The discharge port 44 discharges the lubricating oil, which has flowed from the cooling portion 40 through the discharge path 45, to the lower side of the piston head 32. The lubricating oil flowing through the cooling portion 40 flows into the discharge path 45, for example, when the piston 30 moves from the bottom dead center to the top dead center.

In the present embodiment, in order to effectively utilize the lubricating oil discharged from the discharge port 44, the skirt portion 36 (here, the skirt portion 36A on the thrust region side of the inner wall surface 13) has a flow path portion that directs the lubricating oil discharged from the discharge port 44 from the back surface (inner peripheral surface 37) side of the skirt portion 36A toward the inner wall surface 13 of the cylinder 12. Specifically, the flow path portion is a flow path that supplies the lubricating oil discharged from the discharge port 44 between the thrust region of the inner wall surface 13 of the cylinder 12 and the skirt portion 36A, when the piston 30 descends. Therefore, since a large amount of lubricating oil is supplied between the thrust region of the inner wall surface 13 and the skirt portion 36A, an oil film having a large thickness is formed in the thrust region. As a result, it is possible to suppress frictional force when the skirt portion 36A slides against the thrust region of the inner wall surface 13 during the descent of the piston 30.

In the present embodiment, the flow path portion is a groove portion 50 formed in the inner peripheral surface 37 that is opposite to the outer peripheral surface 38 of the skirt portion 36A facing the cylinder 12. The groove portion 50 allows the lubricating oil discharged from the discharge port 44 to flow along the inner peripheral surface 37. Specifically, the lubricating oil discharged from the discharge port 44 flows along the groove portion 50 due to intermolecular forces and inertial forces. As the lubricating oil flows along the groove portion 50 (the lubricating oil flows as indicated by an arrow D in FIG. 2), the lubricating oil is more likely to adhere to the inner wall surface 13 of the cylinder 12. As a result, it is possible to suppress the lubricating oil discharged from the discharge port 44 from falling into the oil pan 18 (FIG. 1) without being utilized.

The groove portion 50 is formed in the inner peripheral surface 37 up to the lower end 39 of the skirt portion 36A. As a result, the lubricating oil more easily flows along the groove portion 50 to the lower end 39 of the skirt portion 36A, due to intermolecular forces and inertial forces. This facilitates the movement of the lubricating oil from the lower end 39 to the inner wall surface 13 of the cylinder 12, making the lubricating oil more likely to adhere to the inner wall surface 13.

In the present embodiment, since the thickness of the skirt portion 36A is small, the groove portion 50, which serves as the flow path portion, is formed in the inner peripheral surface 37 of the skirt portion 36A. In particular, having the groove portion 50 also provided up to the lower end 39 of the skirt portion 36A makes it easier for the lubricating oil to move from the lower end 39 to the inner wall surface 13 of the cylinder 12.

The groove portion 50 is formed in the inner peripheral surface 37 to extend from the upper end to the lower end of the skirt portion 36A. This makes it possible to increase the amount of lubricating oil flowing through the groove portion 50. As a result, a large amount of lubricating oil adheres to the inner wall surface 13 of the cylinder 12 from the lower end of the skirt portion 36A, and the thickness of the oil film increases.

The thickness of the skirt portion 36A decreases from the upper end toward the lower end 39 of the skirt portion 36A. Therefore, the distance between the bottom surface of the groove portion 50 and the outer peripheral surface 38 of the skirt portion 36A decreases toward the lower end 39 of the skirt portion 36A. As a result, since the radial distance of the cylinder 12 between the lower end 39 of the skirt portion 36A and the inner wall surface 13 is short, the lubricating oil flowing along the bottom surface of the groove portion 50 more easily moves from the lower end of the skirt portion 36A to the inner wall surface 13 of the cylinder 12.

The groove portion 50 is a groove portion in which the inner peripheral surface 37 of the skirt portion 36A is recessed along the axial direction of the piston 30. Here, the depth of the groove portion 50 is constant, and is approximately the same as the diameter of the discharge port 44, for example. On the other hand, the width (width L shown in FIG. 3) of the groove portion 50 in the orthogonal direction perpendicular to the vertical direction increases toward the lower end of the skirt portion 36A. Therefore, the groove portion 50 has a trapezoidal shape, as shown in FIG. 3. Although the depth of the groove portion 50 is constant in the above description, the depth of the groove portion 50 is not limited to being constant and may vary.

The width of the lower end of the groove portion 50 in the orthogonal direction is set to be the same as the width of the inner wall surface 13 in the circumferential direction of the thrust region, for example. In this way, the lubricating oil discharged from the discharge port 44 more easily adheres to the entire thrust region of the inner wall surface 13. Consequently, the thickness of the oil film in the thrust region of the inner wall surface 13 increases, making it possible to reduce the frictional force when the skirt portion 36A slides in the thrust region of the inner wall surface 13 as the piston 30 moves from the top dead center to the bottom dead center.

The groove portion 50 is connected to the discharge path 45. This facilitates the lubricating oil flowing through the discharge path 45 to flow along the groove portion 50. In addition, the width of the groove portion 50 in the orthogonal direction perpendicular to the vertical direction is larger than the diameter of the discharge port 44. As a result, since the area of the groove portion 50 through which the lubricating oil flows can be widened, most of the lubricating oil flowing through the discharge path 45 more easily flows along the groove portion 50.

In the above description, the groove portion 50 is the flow path portion through which the lubricating oil discharged from the discharge port 44 flows along the inner peripheral surface 37 of the skirt portion 36A. However, the present disclosure is not limited thereto, and for example, a hole portion provided so as to penetrate through the skirt portion 36A along the inner peripheral surface 37 may be the flow path portion. Even in such a case, the lubricating oil discharged from the discharge port 44 can still be directed to the inner wall surface 13 of the cylinder 12.

Effects of the Present Embodiment

The piston 30 according to the present embodiment includes a discharge port 44 that discharges lubricating oil from the communicating cooling portion 40 to the lower side of the piston head 32, and the skirt portion 36A that extends downward from the lower end portion of the outer periphery of the piston head 32. The skirt portion 36A is formed on the inner peripheral surface 37, which is opposite to the outer peripheral surface 38 facing the cylinder 12, and includes the groove portion 50 that serves as the flow path portion through which the lubricating oil discharged from the discharge port 44 flows along the inner peripheral surface 37. As a result, the lubricating oil discharged from the discharge port 44 flows along the groove portion 50 formed in the inner peripheral surface 37 of the skirt portion 36A and moves from the skirt portion 36A to the inner wall surface 13 of the cylinder 12, thereby forming the oil film of the lubricating oil on the inner wall surface 13. Accordingly, the lubricating oil discharged from the discharge port 44 can be effectively utilized.

The present disclosure is explained based on the exemplary embodiments. The technical scope of the present disclosure is not limited to the scope explained in the above embodiments and it is possible to make various changes and modifications within the scope of the disclosure. For example, all or part of the device can be configured with any unit which is functionally or physically dispersed or integrated. Further, new exemplary embodiments generated by arbitrary combinations of them are included in the exemplary embodiments. Further, effects of the new exemplary embodiments brought by the combinations also have the effects of the original exemplary embodiments.