PISTON AND INTERNAL COMBUSTION ENGINE

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent Application number 2024-123014, filed on Jul. 30, 2024 contents of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Technical Field

The present disclosure relates to a piston and an internal combustion engine. Lubricating oil is supplied to an internal combustion engine in order to reduce friction generated by sliding between components. However, lubricating oil may adhere to an inner peripheral surface of a piston. For example, in Japanese Unexamined Patent Application Publication No 2015-25424, lubricating oil scattered from a crankshaft adheres to an inner peripheral surface of a skirt of a piston and flows along the inner peripheral surface.

Meanwhile, it has been proposed to supply lubricating oil adhered to an inner peripheral surface of a skirt to an inner wall surface of a cylinder in order to retain an oil film of lubricating oil on the inner wall surface of the cylinder. However, in the above-described technique, the lubricating oil flows downward along the inner peripheral surface of the skirt, making it difficult to retain the oil film on 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 adhered to an inner peripheral surface of a skirt portion.

A first aspect of the present disclosure provides a piston that reciprocates within a cylinder, the piston including: a skirt portion extending downward from a lower end portion of an outer circumference of a piston head; and a coupling portion coupled to a crankshaft that converts reciprocating motion into rotational motion via a connecting rod, wherein the skirt portion includes a convex portion that protrudes toward the coupling portion from a lower portion of an inner peripheral surface opposite to an outer peripheral surface facing the cylinder, the convex portion being capable of retaining lubricating oil.

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 skirt portion extending downward from a lower end portion of an outer circumference of a piston head; and a coupling portion coupled to a crankshaft that converts reciprocating motion into rotational motion via a connecting rod, among which the skirt portion includes a convex portion that protrudes toward the coupling portion from a lower portion of an inner peripheral surface opposite to an outer peripheral surface facing the cylinder, the convex portion being capable of retaining lubricating oil.

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 schematic view illustrating a state in which lubricating oil is retained by a convex portion 50 when the piston 30 is positioned at a bottom dead center.

FIG. 4 is a schematic view illustrating a state in which the lubricating oil is retained by the convex portion 50 when the piston 30 moves from the bottom dead center to a top dead center.

FIG. 5 is a schematic view illustrating a state in which the lubricating oil is retained by the convex portion 50 when the piston 30 is positioned at the top dead center.

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 5.

FIG. 2 is a schematic view showing the internal configuration of the piston 30. The piston 30 shown in FIG. 2 is positioned at the bottom dead center. 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 convex 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 a 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 on 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 description.

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 a coupling portion 35 (piston pin), is the thrust region, and the portion on the right side, as seen from the coupling portion 35, 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. In other words, the discharge path 45 connects the cooling portion 40 and the discharge port 44. 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 discharge port 44 is formed on the inner peripheral surface 37 of the skirt portion 36A, and the lubricating oil, which has flowed through the discharge path 45, adheres to the inner peripheral surface 37. 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 order to smoothly rotate the crankshaft 60, lubricating oil is supplied to the crankshaft 60, and the lubricating oil adheres to the crankshaft 60. Specifically, the lubricating oil adheres to an outer peripheral surface of a balance weight 61 of the crankshaft 60. In this case, when the crankshaft 60 rotates in conjunction with reciprocating motion of the piston 30, the lubricating oil adhered to the outer peripheral surface of the balance weight 61 scatters toward the inner peripheral surface 37 of the skirt portion 36 (for example, the lubricating oil scatters in a direction D1 indicated by a broken line in FIG. 2), and adheres to the inner peripheral surface 37. In particular, when the piston 30 is positioned near the bottom dead center, the lubricating oil adhered to the outer peripheral surface of the balance weight 61 is more likely to adhere to the inner peripheral surface 37 located near the balance weight 61.

In the present embodiment, in order to effectively utilize the lubricating oil adhered to the inner peripheral surface 37 of the skirt portion 36 (here, the skirt portion 36A on the thrust region side of the inner wall surface 13), the convex portion 50 that retains the lubricating oil flowing along the inner peripheral surface 37 is provided on the inner peripheral surface 37 of the skirt portion 36A. The convex portion 50 is formed so as to protrude in the direction normal to the inner peripheral surface 37. Specifically, the convex portion 50 is formed so as to face the central axis C (FIG. 2) of the piston 30. The convex portion 50 protrudes from a lower portion of the inner peripheral surface 37 of the skirt portion 36A toward the coupling portion 35.

FIG. 3 is a schematic view illustrating a state in which the lubricating oil is retained by the convex portion 50 when the piston 30 is positioned at the bottom dead center. FIG. 4 is a schematic view illustrating a state in which the lubricating oil is retained by the convex portion 50 when the piston 30 moves from the bottom dead center to the top dead center. FIG. 5 is a schematic view illustrating a state in which the lubricating oil is retained by the convex portion 50 when the piston 30 is positioned at the top dead center. When the piston 30 reciprocates, the convex portion 50 protruding from the inner peripheral surface 37 retains lubricating oil (for example, lubricating oil scattered from the crankshaft 60 and adhered to the inner peripheral surface 37) flowing along the inner peripheral surface 37. For example, when the piston 30 moves from the bottom dead center to the top dead center, the convex portion 50 retains the lubricating oil flowing along the inner peripheral surface 37, as shown in FIG. 3. When the piston 30 is positioned at the bottom dead center, downward inertial forces increase and the lubricating oil more easily flows along the inner peripheral surface 37, but since the convex portion 50 protrudes from the inner peripheral surface 37, the convex portion 50 can retain the lubricating oil, as shown in FIG. 3. In addition, when the piston 30 moves from the bottom dead center to the top dead center, the downward inertial forces decrease compared to in the case where the piston 30 is positioned at the bottom dead center, and thus the convex portion 50 can retain the lubricating oil, as shown in FIG. 4.

The lubricating oil that is retained by the convex portion 50 when the piston 30 moves to the top dead center moves from the convex portion 50 to the inner wall surface 13 of the cylinder 12 and adheres to the inner wall surface 13 as the piston 30 moves from the top dead center to the bottom dead center. In particular, since upward inertial forces increase when the piston 30 is positioned at the top dead center, the lubricating oil retained by the convex portion 50 moves from the convex portion 50 to the thrust region of the inner wall surface 13 and adheres thereto, as shown in FIG. 5. Because the lubricating oil adhered to the thrust region forms an oil film, it becomes possible to suppress friction when the piston 30 slides in the thrust region of the skirt portion 36A during its movement toward the bottom dead center.

The convex portion 50 protrudes from the inner peripheral surface 37 in the horizontal direction. Because the convex portion 50 protrudes in the horizontal direction, the convex portion 50 can more easily retain the lubricating oil that flows vertically downward along the inner peripheral surface 37 of the skirt portion 36A. In particular, the convex portion 50 can more easily retain the lubricating oil even when the piston 30 is positioned at the bottom dead center.

The convex portion 50 protrudes from a lower end of the skirt portion 36A toward the coupling portion 35. When the convex portion 50 is provided at the lower end of the skirt portion 36A, the lubricating oil retained by the convex portion 50 can more easily move to the inner wall surface 13 of the cylinder 12 adjacent in the radial direction of the piston 30. As a result, the lubricating oil flowing along the inner peripheral surface 37 of the skirt portion 36A can be adhered to the inner wall surface 13 to form an oil film. However, the present disclosure is not limited thereto, and the convex portion 50 may instead be formed at a position spaced upward from the lower end of the skirt portion 36A.

The height of the protruding portion 50 in the protruding direction (hereinafter, also referred to as protrusion height) is set to be smaller than the thickness of the skirt portion 36A. For example, the protrusion height of the convex portion 50 is 5 mm. As a result, compared to the case in which the protrusion height of the convex portion 50 is larger than the thickness of the skirt portion 36A, the lubricating oil retained by the convex portion 50 can more readily move to the inner wall surface 13 of the cylinder 12, thereby increasing the amount of lubricating oil adhering to the inner wall surface 13.

The convex portion 50 is formed along the circumferential direction at the lower portion of the inner peripheral surface 37 of the skirt portion 36A. For example, the convex portion 50 is formed to extend from one end to the other end in the circumferential direction of the lower portion of the inner peripheral surface 37 of the skirt portion 36A. As an example, the convex portion 50 is formed such that the angle formed between (i) a first line connecting one end of the inner peripheral surface 37 to the center of the piston 30 and (ii) a second line connecting the other end of the inner peripheral surface 37 to the center of the piston 30 is 60 degrees. In this case, the convex portion 50 can retain the lubricating oil flowing along the inner peripheral surface 37 of the skirt portion 36A over a wide area.

The convex portion 50 is located in a portion of the inner peripheral surface 37 of the skirt portion 36A corresponding to the thrust region of the inner wall surface 13 of the cylinder 12. For example, the length of the convex portion 50 in the circumferential direction is the same as the length of the thrust region of the inner wall surface 13 in the circumferential direction. In this case, the lubricating oil that moves from the convex portion 50 to the inner wall surface 13 adheres to a wide area in the circumferential direction of the thrust region, so that the oil film can be formed in a wide area of the thrust region. However, the present disclosure is not limited thereto, and the length of the convex portion 50 in the circumferential direction may be larger than the length of the inner wall surface 13 in the circumferential direction of the thrust region.

The convex portion 50 is located below the discharge port 44 in the vertical direction. In this case, the convex portion 50 can retain the lubricating oil discharged from the discharge port 44. In particular, the convex portion 50 can retain the lubricating oil that is discharged from the discharge port 44 and falling along the inner peripheral surface 37. Thus, the lubricating oil discharged from the discharge port 44 can be effectively utilized without falling into the oil pan 18.

Although the cooling portion 40 is provided in the piston head 32 of the piston 30 in the above description, the present disclosure is not limited thereto, and the cooling portion 40 does not need to be provided in the piston head 32. Even in this case, it is significant to have the convex portion 50 on the inner peripheral surface 37 of the skirt portion 36A, in that the convex portion 50 can retain the lubricating oil that has moved from the outer peripheral surface of the crankshaft 60 while it is rotating and adhered to the inner peripheral surface 37 of the skirt portion 36.

Effects of the Embodiment

The piston 30 according to the present embodiment has the skirt portion 36A extending downward from the lower end portion of the outer periphery of the piston head 32, and a coupling portion 35 coupled to a crankshaft that converts reciprocating motion into rotational motion via the connecting rod. The skirt portion 36A has the convex portion 50 that protrudes from the lower portion of the inner peripheral surface 37 toward the coupling portion 35 and can retain the lubricating oil.

In this way, when the piston 30 reciprocates, the lubricating oil flowing along the inner peripheral surface 37 is retained by the convex portion 50 protruding from the lower portion of the inner peripheral surface 37. The lubricating oil retained by the convex portion 50 then moves from the convex portion 50 to the inner wall surface 13 (specifically, the thrust region) of the cylinder 12, and the oil film of the lubricating oil can be formed on the inner wall surface 13. As a result, the lubricating oil adhered to the inner peripheral surface 37 of the skirt portion 36A 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.