WO2021045129A1

WO2021045129A1 - Piston for engine

Info

Publication number: WO2021045129A1
Application number: PCT/JP2020/033341
Authority: WO
Inventors: 英之藤田
Original assignee: ヤマハ発動機株式会社
Priority date: 2019-09-05
Filing date: 2020-09-02
Publication date: 2021-03-11
Also published as: JP6952220B2; JPWO2021045129A1

Abstract

At least one of a pair of piston skirt parts (27) of a piston (25) for an engine has recesses (29) at both ends in the circumferential direction thereof, and the outer circumferential surface (28) of the piston skirt part (27) has a sliding surface (28a) as well as a stepped surface (29a) and a facing surface (29b) that form the recesses (29). The sliding surface (28a) forms an oil film between the sliding surface (28a) and the inner wall surface (15f) of a cylinder hole (17a). The stepped surface (29a) is connected to the sliding surface (28a) and constitutes a step formed at a depth at which the oil film between the sliding surface (28a) and the inner wall surface (15f) of the cylinder hole (17a) can be cut. The facing surface (29b) is connected to the stepped surface (29a) and faces the inner wall surface (15f) of the cylinder hole (17a). As a result thereof, it is possible to reduce sliding resistance when the pair of piston skirt parts (27) are deformed and increase the lengths in the circumferential direction of the outer circumferential surfaces (28) of the pair of piston skirt parts (27) and the flexibility of design of the oil film area to be secured.

Description

Engine piston

The present invention relates to an engine piston having a pair of piston skirts.

The engine piston is housed in a cylinder hole formed inside the cylinder part of the engine. The engine piston is provided so as to be able to reciprocate through the cylinder hole. The engine piston has a pair of piston skirts that receive pressure from the inner wall surface of the cylinder hole when reciprocating. The inner wall surface of the cylinder hole and the outer peripheral surface of the pair of piston skirts facing the inner wall surface of the cylinder hole are lubricated with engine oil.

Engine pistons are required to reduce the weight of a pair of piston skirts in order to speed up reciprocating motion. Further, the piston for an engine is required to reduce the sliding resistance. Therefore, Patent Document 1 makes the length of one of the pair of piston skirts in the circumferential direction shorter than the length of the other in the circumferential direction. As a result, the area of the oil film between the piston skirt portion and the inner wall surface of the cylinder hole is reduced to reduce friction. Further, in Patent Document 1, the radius of curvature of the piston skirt portion having a short circumferential length is made smaller than the radius of curvature of the piston skirt portion having a long circumferential length. As a result, even if the pair of piston skirts are deformed under high temperature conditions during engine operation, the circumferential direction is larger than the gap at the angle θ of the piston skirts, which have a long circumferential length and relatively low rigidity. The sliding resistance is reduced by ensuring a large gap at the angle θ of the piston skirt portion, which has a short length and relatively high rigidity.

Japanese Unexamined Patent Publication No. 2002-317691

In Patent Document 1, in order to secure a gap between both ends of the piston skirt portion and the inner wall surface of the cylinder at the time of deformation, (A) a length in the circumferential direction of the other rather than the length of one of the pair of piston skirt portions in the circumferential direction. The length is long. However, if the length of the piston skirt portion in the circumferential direction is increased, the area of the oil film formed between the inner wall surface of the cylinder hole and the outer peripheral surfaces of the pair of piston skirt portions becomes large, and the sliding resistance becomes large. Therefore, in Patent Document 1, in order to suppress sliding resistance, (B) the radius of curvature of the piston skirt portion having a short circumferential length is reduced. However, the area of the oil film formed between the inner wall surface of the cylinder hole and the piston skirt portion tends to change due to changes in operating conditions and the like. If the area of the oil film is to be secured even if the operating conditions change, the length of the outer peripheral surface of the piston skirt portion in the circumferential direction cannot be shortened. That is, in order to secure the area of the oil film even if the operating conditions change, the length of the outer peripheral surface of the piston skirt portion in the circumferential direction must be increased. In this way, it is necessary to design the length of the outer peripheral surface of the piston skirt portion in the circumferential direction and the area of the oil film to be secured so as to reduce the sliding resistance at the time of deformation, which has been proposed in Patent Document 1. In the means (A) and (B), since the area of the oil film changes depending on the operating conditions and the like, the length of the outer peripheral surface of the piston skirt portion in the circumferential direction and the degree of freedom in designing the area of the oil film are low.

The present invention makes it possible to reduce the sliding resistance when the pair of piston skirts are deformed, while increasing the degree of design freedom in the circumferential length of the outer peripheral surfaces of the pair of piston skirts and the area of the oil film to be secured. It is an object of the present invention to provide an engine piston having a pair of piston skirt portions.

The inventors of the present application reduce the sliding resistance when the pair of piston skirts are deformed, and increase the degree of freedom in designing the length of the outer peripheral surface of the pair of piston skirts in the circumferential direction and the area of the oil film to be secured. We examined the configuration that can be used. In Patent Document 1, the outer peripheral surfaces of the pair of piston skirts and the inner wall surface of the cylinder hole are lubricated with engine oil. That is, the engine oil enters the gap formed between the outer peripheral surfaces of the pair of piston skirts and the inner wall surface of the cylinder hole. An oil film is formed by the engine oil in the gap formed between the outer peripheral surfaces of the pair of piston skirts and the inner wall surface of the cylinder hole. Therefore, when the pair of piston skirts reciprocate in the cylinder axis direction, the oil film formed in the gap between the outer peripheral surface of the pair of piston skirts and the inner wall surface of the cylinder hole forms the pair of piston skirts. Sliding resistance is generated. When the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction is shortened, the sliding resistance due to the oil film generated on the pair of piston skirts is reduced. On the other hand, when the pair of piston skirts reciprocate in the cylinder axis direction, they come into contact with the inner wall surface of the cylinder hole to receive a load from the inner wall surface of the cylinder hole. The pair of piston skirts are preferably deformed with respect to the load received from the inner wall surface of the cylinder hole. When the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction is shortened, the rigidity of the pair of piston skirts is increased, and the pair of piston skirts are less likely to be deformed. Therefore, in order to reduce the rigidity of the pair of piston skirts, it is conceivable to increase the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction. However, if the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction is increased, the sliding resistance due to the oil film generated on the pair of piston skirts increases. That is, in order to adjust the rigidity of the pair of piston skirts, it is required to increase the degree of freedom in designing the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction. In this way, in order to reduce the sliding resistance of the pair of piston skirts, it is considered to increase the degree of freedom in designing the length of the outer peripheral surface of the pair of piston skirts in the circumferential direction and the area of the oil film to be secured. Be done.

The pair of piston skirts having different radii of curvature in Patent Document 1 are composed of curved surfaces having a plurality of curvatures. Since the pair of piston skirts of Patent Document 1 has a curved surface having a plurality of curvatures, operating conditions such as the size of the gap, the viscosity of the engine oil, the temperature of the engine oil, and the speed of reciprocating movement of the piston. The area of the oil film changes due to such factors. Regarding the pair of piston skirts of Patent Document 1, it is difficult to determine the relationship between the circumferential length of the outer peripheral surface and the oil film area. Therefore, the inventors of the present application can form recesses with steps at both ends of the pair of piston skirts, and cut the oil film between the outer peripheral surface of the piston skirt and the inner wall surface of the cylinder hole. It was found that the position where the oil film cuts is determined by the possible step, and the area of the oil film is unlikely to change depending on the operating conditions. Originally, there is a gap between the outer peripheral surface of the piston skirt and the inner wall surface of the cylinder hole. Therefore, by forming a recess having a step on the outer peripheral surface, even if the step is a slight step, the gravity of the engine oil itself becomes larger than the surface tension with respect to the engine oil existing in the recess, and the piston at the step. The oil film between the outer peripheral surface of the skirt portion and the inner wall surface of the cylinder hole can be cut. Then, in order to adjust the rigidity of the pair of piston skirts, even if the length of the outer peripheral surface of the pair of piston skirts in the circumferential direction is increased or decreased, the length of the concave portion in the circumferential direction is adjusted. By doing so, the length of the sliding surface in the circumferential direction, which is the surface excluding the recesses on the outer peripheral surface, which forms an oil film with the inner wall surface of the cylinder hole, can be freely designed. As a result, the inventors of the present application can freely design the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction according to the required rigidity, and can freely design the area of the oil film to be secured. I found that I could do it. That is, if recesses having steps are formed at both ends of the pair of piston skirts, and the steps are made into steps that can cut an oil film between the outer peripheral surface of the piston skirt and the inner wall surface of the cylinder hole, the deformation occurs. It has been found that it is possible to increase the degree of freedom in designing the area of the oil film that secures the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction while reducing the sliding resistance at the time. Moreover, by forming recesses with steps at both ends of the pair of piston skirts, it is possible to secure a gap between the pair of piston skirts and the inner wall surface of the cylinder hole at both ends. Further, the inventors of the present application set the step to be a slight step that cuts an oil film between the outer peripheral surface of the piston skirt portion and the inner wall surface of the cylinder hole, so that cracks due to stress concentration do not occur in the step. I found that.

(1) The engine piston of the present invention is arranged in a columnar cylinder hole formed inside the cylinder portion of the engine, and the cylinder hole is provided so as to be reciprocally movable in the direction of the cylinder axis, which is the axis of the cylinder hole. A piston head portion forming a part of a combustion chamber formed inside the cylinder portion, and (a) being connected to the piston head portion and provided so as to be reciprocally movable in the cylinder axis direction, and the cylinder axis. The first piston skirt portion having an arc shape along the inner wall surface of the cylinder hole when viewed in a direction, and between the outer peripheral surface of the first piston skirt portion and the inner wall surface of the cylinder hole. The first piston skirt portion is formed with a gap through which engine oil can enter, and (b) is connected to the piston head portion and is provided so as to be reciprocally movable in the cylinder axis direction and in the cylinder axis direction. The second piston skirt portion has an arcuate shape along the inner wall surface of the cylinder hole, and is between the outer peripheral surface of the second piston skirt portion and the inner wall surface of the cylinder hole. A pair of cylinder skirts including the second cylinder skirt, and both ends of the piston head and the pair of cylinder skirts in the circumferential direction are connected to each other and a gap through which engine oil can enter is formed. A pair of ribs in which a conrod that transmits the reciprocating movement of the piston head portion and the pair of piston skirt portions in the cylinder axis direction as a rotational force of the crank shaft of the engine is oscillatingly connected via a piston pin. An engine piston including a portion, wherein at least one of the first piston skirt portion and the second piston skirt portion is the circumference of at least one of the first piston skirt portion and the second piston skirt portion. The first piston skirt portion or the second piston skirt portion having recesses provided so as to be recessed toward the cylinder axis in the radial direction of the cylinder hole orthogonal to the cylinder axis at both ends in the direction. At least one outer peripheral surface of the piston skirt portion includes a sliding surface that forms an oil film between the cylinder hole and the inner wall surface of the cylinder hole due to engine oil that has entered between the cylinder hole and the inner wall surface of the cylinder hole. Two surfaces forming a recess, (i) connected to the sliding surface and arranged along the radial direction of the cylinder hole and the axial direction of the cylinder, and the diameter of the cylinder hole. In the direction, a stepped surface forming a step formed at a depth capable of cutting an oil film between the sliding surface and the inner wall surface of the cylinder hole, and (ii) connected to the stepped surface. It is characterized by including a facing surface which is arranged along the circumferential direction of the cylinder hole and the cylinder axis direction and faces the inner wall surface of the cylinder hole.

According to this configuration, at least one of the first piston skirt portion and the second piston skirt portion has recesses provided at both ends of at least one of the first piston skirt portion and the second piston skirt portion in the circumferential direction. The recess is provided so as to be recessed toward the cylinder axis in the radial direction of the cylinder hole orthogonal to the cylinder axis. That is, the recess is provided so as to be recessed from the sliding surface of the first piston skirt portion or the second piston skirt portion. Further, at least one outer peripheral surface of the first piston skirt portion or the second piston skirt portion has a sliding surface, a stepped surface, and a facing surface. The sliding surface forms an oil film between the sliding surface and the inner wall surface of the cylinder hole due to the engine oil that has entered between the sliding surface and the inner wall surface of the cylinder hole. The stepped surface and the facing surface form recesses. The stepped surface is connected to the sliding surface and is arranged along the radial direction of the cylinder hole and the axial direction of the cylinder, and can cut an oil film between the sliding surface and the inner wall surface of the cylinder hole in the radial direction of the cylinder hole. It constitutes a step formed at a depth that can be achieved. The facing surface is connected to the stepped surface and is arranged along the circumferential direction of the cylinder hole and the cylinder axis direction, and faces the inner wall surface of the cylinder hole. Therefore, the facing surface does not form an oil film with the inner wall surface of the cylinder hole. When the pair of piston skirts reciprocate in the cylinder axis direction, no oil film is formed in the recesses between the pair and the inner wall surface of the cylinder hole. That is, a state in which the recessed space is filled with engine oil cannot be maintained. The recessed space is a space formed between the stepped surface and the facing surface of the recess and the inner wall surface of the cylinder hole.

The step formed by the step surface of the recess is a step capable of cutting an oil film between the inner wall surface of the cylinder hole and at least one of the sliding surfaces of the first piston skirt portion or the second piston skirt portion. Originally, there is a gap between the sliding surfaces of the pair of piston skirts and the inner wall surface of the cylinder hole. Therefore, by forming a recess forming a step on the outer peripheral surface, even if the step is a slight step, the gravity of the engine oil itself becomes larger than the surface tension with respect to the engine oil existing in the recess, and the pair of pistons. It is possible to cut an oil film between the sliding surface of the skirt portion and the inner wall surface of the cylinder hole. Therefore, the position where the oil film is cut is determined between the inner wall surface of the cylinder hole and the outer peripheral surface of at least one of the first piston skirt portion and the second piston skirt portion. Since the sliding surface on the outer peripheral surface of at least one of the first piston skirt portion and the second piston skirt portion and the oil film on the inner wall surface of the cylinder hole are cut off at the stepped surface, the area of the oil film is unlikely to change depending on operating conditions and the like. In order to adjust the rigidity of at least one of the first piston skirt portion and the second piston skirt portion, the length of at least one of the outer peripheral surfaces of the first piston skirt portion or the second piston skirt portion in the circumferential direction is increased. Even if it is shortened or shortened, the length of the sliding surface in the circumferential direction can be freely designed by adjusting the length of the facing surface of the recess in the circumferential direction. As a result, the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction can be freely designed according to the required rigidity, and the area of the oil film to be secured can be freely designed. That is, recesses having steps are formed at both ends of the pair of piston skirts, and the steps cut the oil film on the sliding surfaces of the pair of piston skirts. It is possible to increase the degree of freedom in designing the length of the outer peripheral surface of the piston skirt portion in the circumferential direction and the area of the oil film to be secured. Moreover, by forming recesses with steps at both ends of the pair of piston skirts, it is possible to secure a gap between the pair of piston skirts and the inner wall surface of the cylinder hole at both ends. Further, if the step is a slight step that cuts an oil film between the inner wall surface of the cylinder hole and the sliding surface of the pair of piston skirts, cracks due to stress concentration do not occur in the step.

As described above, the engine piston having the pair of piston skirts of the present invention can reduce the sliding resistance when the pair of piston skirts are deformed, and the length of the outer peripheral surface of the pair of piston skirts in the circumferential direction. It is possible to increase the degree of freedom in designing the area of the oil film to be secured.

(2) From one aspect of the present invention, the engine piston of the present invention preferably has the following configuration in addition to the configuration of (1) above.
The recesses are both ends in the circumferential direction of the first piston skirt portion, both ends in the circumferential direction of the second piston skirt portion, or both ends in the circumferential direction of the first piston skirt portion and the second piston skirt. It is provided at both ends in the circumferential direction of the portion.

According to this configuration, the engine piston of the present invention can change the arrangement of the recesses provided in the pair of piston skirts. By changing the arrangement of the recesses provided in the pair of piston skirts, the sliding resistance of the pair of piston skirts due to the oil film of the engine oil can be adjusted. By changing the arrangement of the recesses provided in the pair of piston skirts, the sliding resistance at the time of deformation of the pair of piston skirts can be reduced, and the length of the outer peripheral surfaces of the pair of piston skirts in the circumferential direction. And the degree of freedom in designing the area of the oil film to be secured can be increased.

(3) From one aspect of the present invention, the engine piston of the present invention preferably has the following configuration in addition to the above configuration (1) or (2).
The pair of rib portions are connected to the first end portion of the first piston skirt, which is one end portion in the circumferential direction of the inner peripheral surface of the first piston skirt portion, and the inner circumference of the second piston skirt portion. The first rib portion connected to the first end portion of the second piston skirt, which is one end portion in the circumferential direction of the surface, and the other end portion in the circumferential direction of the inner peripheral surface of the first piston skirt portion. 1 With a second rib portion connected to the second end portion of the piston skirt and connected to the second end portion of the second piston skirt which is the other end portion in the circumferential direction of the inner peripheral surface of the second piston skirt portion. When viewed in the radial direction passing through the recess, the recess includes the first end of the first piston skirt, the first end of the second piston skirt, and the second end of the first piston skirt. Or, it is provided so as to overlap at least one of the second end portions of the second piston skirt.

According to this configuration, the pair of rib portions has a first rib portion and a second rib portion. The first rib portion is connected to the first end portion of the first piston skirt, which is one end portion in the circumferential direction of the inner peripheral surface of the first piston skirt portion. Further, the first rib portion is connected to the first end portion of the second piston skirt, which is one end portion in the circumferential direction of the inner peripheral surface of the second piston skirt portion. The second rib portion is connected to the second end portion of the first piston skirt, which is the other end portion in the circumferential direction of the inner peripheral surface of the first piston skirt portion when viewed in the cylinder axis direction. Further, the second rib portion is connected to the second end portion of the second piston skirt, which is the other end portion in the circumferential direction of the inner peripheral surface of the second piston skirt portion. Here, in the first piston skirt portion and the second piston skirt portion, the rigidity of the portion connected to the first rib portion and the second rib portion becomes relatively large. On the other hand, the recess is the first end of the first piston skirt, the first end of the second piston skirt, the second end of the first piston skirt, or the second when viewed in the radial direction of the cylinder hole passing through the recess. It is provided so as to overlap at least one of the second ends of the piston skirt. That is, in the first piston skirt portion and the second piston skirt portion, the first end portion of the first piston skirt, the first end portion of the second piston skirt, the second end portion of the first piston skirt, or the second end portion having relatively high rigidity. A recess is provided in at least one of the second ends of the two-piston skirt. As a result, the diameter is at least one of the first end of the first piston skirt, the first end of the second piston skirt, the second end of the first piston skirt, or the second end of the second piston skirt, which have relatively high rigidity. At the positions arranged in the direction, a large gap that does not form an oil film can be secured between the piston skirt portion and the inner wall surface of the cylinder hole. That is, in the pair of piston skirts, the first end of the first piston skirt, the first end of the second piston skirt, the second end of the first piston skirt, or the second end, which have relatively high rigidity and are relatively hard to deform. By providing a recess in a position where it is aligned radially with at least one of the second ends of the piston skirt, a large gap that does not form an oil film is secured between the piston skirt and the inner wall surface of the cylinder hole, and the inside of the cylinder hole is secured. It is possible to make it difficult to receive a load from the wall surface.

(4) According to one aspect of the present invention, the engine piston of the present invention preferably has the following configuration in addition to the configuration of any one of (1) to (3) above.
The piston head portion, the pair of piston skirt portions, and the pair of rib portions are formed by casting or forging, and the stepped surface and the facing surface of the recess are not removed.

According to this configuration, the piston head portion, the pair of piston skirt portions and the pair of rib portions are formed by casting or forging. Further, the stepped surface and the facing surface of the recess are surfaces that have not been removed. The removal process means that the process is performed by a processing method such as lathe processing, milling processing, or polishing processing. Removal processing means cutting and processing the material. This facilitates the molding of the recesses in the pair of piston skirts. Further, the length of the concave portion in the circumferential direction can be adjusted to facilitate the design of the length of the sliding surface in the circumferential direction.

(5) From one aspect of the present invention, the engine piston of the present invention preferably has the following configuration in addition to the configuration of any one of (1) to (4) above.
The stepped surface and the facing surface of the recess are formed by a removal process.

According to this configuration, the stepped surface and the facing surface of the recess are formed by removal processing. This facilitates the molding of the recesses in the pair of piston skirts. This makes it easier to adjust the circumferential length of the recess and design the circumferential length of the sliding surface.

(6) According to one aspect of the present invention, the engine piston of the present invention preferably has the following configuration in addition to the configuration of any one of (1) to (5) above.
The crankshaft is characterized in that its central axis is arranged at a position where it does not pass through the cylinder axis.

According to this configuration, the engine in which the engine piston is arranged is a so-called offset crank type engine having a crankshaft whose central axis is arranged at a position where it does not pass through the cylinder axis. In an offset crank engine, the timing of the top dead center of the crankshaft and the timing of the top dead center of the piston do not match. Therefore, it is possible to make a difference between the stroke time of the compression stroke and the stroke time of the expansion stroke, and it is possible to expand the piston earlier or to lengthen the time that the piston stays at the top dead center after ignition. Further, an engine that is not an offset crank type is an engine having a crankshaft whose central axis is arranged at a position passing through a cylinder axis. In the offset crank type engine, the load acting on the pair of piston skirts in the expansion stroke is reduced as compared with the non-offset crank type engine. In the offset crank type engine 10, even if the load acting on the pair of piston skirts 27 is reduced in the expansion stroke, the length of the outer peripheral surfaces 28 of the pair of piston skirts 27 in the circumferential direction is increased from the viewpoint of rigidity design. It may not be possible to make it smaller. Even in such a case, by adjusting the arrangement of the recesses and the circumferential length of the facing surfaces of the recesses 29, the circumferential length of the outer peripheral surfaces of the pair of piston skirts and the area of the oil film to be secured Can be designed.

[Definition of terms]
In the present invention and the present specification, the engine to which the "engine piston" is applied includes a 4-stroke engine. Further, in the present invention and the present specification, the engine to which the "engine piston" is applied includes a two-stroke engine. In the present invention and the present specification, the engine to which the "engine piston" is applied includes a gasoline engine. Further, in the present invention and the present specification, the engine to which the "engine piston" is applied includes a diesel engine. The engine to which the "engine piston" is applied includes a so-called offset crank type engine having a crankshaft whose central axis is arranged so as not to pass through the cylinder axis. Further, an engine to which the "engine piston" is applied includes an engine having a crankshaft whose central axis is arranged at a position passing through a cylinder axis. In the present invention and the present specification, the engine to which the "engine piston" is applied includes a wet sump type engine. In the present invention and the present specification, the engine to which the "engine piston" is applied includes a dry sump type engine. In the present invention and the present specification, the engine to which the "engine piston" is applied includes a water-cooled engine and an air-cooled engine. In the present invention and the present specification, the engine to which the "engine piston" is applied includes a single cylinder engine and a multi-cylinder engine. Further, the engine having the engine piston of the present invention may be applied to a saddle-mounted vehicle. The saddle-type vehicle to which the present invention is applied includes a motorcycle, a tricycle, a four-wheel buggy (ATV: All Terrain Vehicle), a watercraft, a snowmobile, and the like. Further, the engine having the engine piston of the present invention may be applied to a vehicle other than a saddle-type vehicle. For example, an engine having an engine piston of the present invention may be applied to a four-wheeled vehicle or a ship.

In the present invention and the present specification, the "engine piston" is formed of a metal or a composite material of metal and resin. Further, in the "engine piston", the piston head portion, the pair of piston skirt portions, and the pair of rib portions may be integrally molded, or may be molded together after being molded as separate bodies. The "engine piston" may include a step manufactured by casting or forging, may include a step manufactured by a 3D printer, or may include a step manufactured by machining.

In the present invention and the present specification, the "cylinder axis direction" is the direction of the axis of the cylinder hole. The axis of the cylinder hole is the cylinder axis and is a straight line passing through the center of the cylinder hole. The cylinder axis is not a line segment existing only in the region where the cylinder hole exists, but a straight line extending infinitely. The cylinder axis direction is a direction along the direction in which the piston head portion and the pair of piston skirt portions reciprocate in the cylinder hole. In the present invention and the present specification, the "diameter direction of the cylinder hole" is a direction orthogonal to the axis of the cylinder hole. In the present invention and the present specification, the "depth of the step in the radial direction of the cylinder hole" is centered on the cylinder axis through the outer peripheral edge of the step surface in a straight line orthogonal to the cylinder axis. It is the length between the intersection of the circles and the intersection of the circles centered on the cylinder axis that passes through the inner peripheral end of the stepped surface.

In the present invention and the present specification, the "pair of piston skirt portions" are the first piston skirt portion and the second piston skirt portion. The circumferential length of the first piston skirt portion and the circumferential length of the second piston skirt portion may be the same or different. The circumferential length of the first piston skirt portion may be longer or shorter than the circumferential length of the second piston skirt portion. The length of the first piston skirt portion in the cylinder axis direction and the length of the second piston skirt portion in the cylinder axis direction may be the same or different. The length of the first piston skirt portion in the cylinder axis direction may be longer or shorter than the length of the second piston skirt portion in the cylinder axis direction.

In the present invention and the present specification, the "pair of rib portions" are the first rib portion and the second rib portion. The first rib portion and the second rib portion are the distances between the intersection of the inner peripheral surface of the first rib portion and the piston pin in the axial direction of the piston pin and the intersection of the inner peripheral surface of the second rib portion and the piston pin. Is configured to be the same as or different from the length of the inner peripheral surface of the first piston skirt portion in the axial direction of the piston pin. The inner peripheral surface of the first rib portion is a surface facing the second rib portion of the first rib portion. The first rib portion and the second rib portion are the distances between the intersection of the inner peripheral surface of the first rib portion and the piston pin in the axial direction of the piston pin and the intersection of the inner peripheral surface of the second rib portion and the piston pin. The distance between the second rib portion and the intersection of the piston pin axis may be longer or shorter than the length of the inner peripheral surface of the first piston skirt portion in the piston pin axis direction. It is composed of. The first rib portion and the second rib portion are the distances between the intersection of the inner peripheral surface of the first rib portion and the piston pin in the axial direction of the piston pin and the intersection of the inner peripheral surface of the second rib portion and the piston pin. Is configured to be the same as or different from the length of the inner peripheral surface of the second piston skirt portion in the axial direction of the piston pin. The first rib portion and the second rib portion are the distances between the intersection of the inner peripheral surface of the first rib portion and the piston pin in the axial direction of the piston pin and the intersection of the inner peripheral surface of the second rib portion and the piston pin. However, the length may be longer or shorter than the length of the inner peripheral surface of the second piston skirt portion in the axial direction of the piston pin. The length of the first rib portion in the cylinder axis direction and the length of the second rib portion in the cylinder axis direction may be the same or different. The length of the first rib portion in the cylinder axis direction may be longer or shorter than the length of the second rib portion in the cylinder axis direction.

In the present invention and the present specification, the "sliding surface of the first piston skirt portion" refers to the first piston skirt portion that faces the inner wall surface of the cylinder hole and forms an oil film between the inner wall surface of the cylinder hole. It is a face. The sliding surface is formed in a shape along the inner wall surface of the cylinder hole. The sliding surface may be configured with one curvature. For example, the sliding surface may be configured to be parallel to the inner wall surface of the cylinder hole. Further, the sliding surface may be configured to have a plurality of different curvatures. For example, the sliding surface may be configured such that both ends in the circumferential direction form an arc having a larger curvature than the central portion in the circumferential direction. "The oil film between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole" means that the gap between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole is filled with engine oil. This means that the paired piston skirts are configured to be held while reciprocating in the cylinder axis direction. The state in which engine oil is filled between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole is defined as at least both ends of the sliding surface of the first piston skirt in the circumferential direction and the inner wall surface of the cylinder hole. The gap between them is filled with engine oil. When the gap between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole is filled with engine oil, between the entire sliding surface of the first piston skirt and the inner wall surface of the cylinder hole. The gap is filled with engine oil. The "sliding surface of the first piston skirt portion" may have a dent recessed in the radial direction at a position other than the circumferential end of the sliding surface of the first piston skirt portion. Specifically, the dent at a portion other than the circumferential end of the sliding surface of the first piston skirt may be a dent filled with engine oil or a dent not filled with engine oil. Good. When the gap between the sliding surface and the inner wall surface of the cylinder hole is filled with engine oil, the sliding surface has a recess in a portion other than the circumferential end of the sliding surface of the first piston skirt. The gap between the whole and the inner wall surface of the cylinder hole is filled with engine oil. Further, when the gap between the sliding surface of the first piston skirt portion and the inner wall surface of the cylinder hole is filled with engine oil, at least both ends of the sliding surface of the first piston skirt portion in the circumferential direction and the cylinder hole It also includes a state in which the gap between the inner wall surface of the piston is filled with the engine oil and a part of the space between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole is not filled with the engine oil. .. A part of the space between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole is, for example, air bubbles contained in the engine oil or a dent not filled with the engine oil. The "sliding surface of the second piston skirt portion" is the same as the "sliding surface of the first piston skirt portion". The "oil film between the sliding surface of the second piston skirt and the inner wall surface of the cylinder hole" is the same as the "oil film between the sliding surface of the first piston skirt and the inner wall surface of the cylinder hole". ..

In the present invention and the present specification, the "circumferential length of the sliding surface of the first piston skirt portion" is the circumferential length of the sliding surface of the first piston skirt portion when viewed in the cylinder axis direction. That's right. The circumferential direction referred to in the present invention means a circumferential direction centered on the cylinder axis. The "circumferential length of the outer peripheral surface of the first piston skirt portion" is the circumferential length of the sliding surface of the first piston skirt portion and the circumferential length of the recess when viewed in the cylinder axis direction. Is the total of. That is, the "length in the circumferential direction of the outer peripheral surface of the first piston skirt portion" is the circumferential direction of the arc extending from the sliding surface of the first piston skirt portion by the amount of the recess when viewed in the cylinder axis direction. Is the length of. The "sliding surface of the second piston skirt portion" is the same as the "sliding surface of the first piston skirt portion". The “length in the circumferential direction of the outer peripheral surface of the second piston skirt portion” is also the same as the “length in the circumferential direction of the outer peripheral surface of the first piston skirt portion”.

In the present invention and the present specification, the "step surface" constitutes a step connected to the sliding surface and formed at a depth capable of cutting an oil film between the sliding surface and the inner wall surface of the cylinder hole. It is a surface to do. The connecting portion between the stepped surface and the sliding surface is formed by a corner portion having an apex protruding in the radial direction when viewed in the cylinder axis direction. Alternatively, the connecting portion between the stepped surface and the sliding surface is formed by a curved portion having no apex protruding in the radial direction when viewed in the cylinder axis direction. The stepped surface is arranged along the radial direction of the cylinder hole and the direction of the cylinder axis. The stepped surface is parallel to the radial direction of the cylinder hole. Alternatively, the stepped surface is inclined with respect to the radial direction of the cylinder hole. That is, the stepped surface is a surface that intersects the radial straight line of the cylinder hole passing through the cylinder axis in the range of an angle of −45 degrees or more and 45 degrees or less when viewed in the cylinder axis direction. The stepped surface is parallel to the cylinder axis direction. Alternatively, the stepped surface is inclined with respect to the cylinder axis direction. That is, the stepped surface is a surface that intersects the cylinder axis within an angle range of −45 degrees or more and 45 degrees or less when viewed in the radial direction of the cylinder hole. The stepped surface is a flat surface. Alternatively, the stepped surface is a curved surface. Alternatively, the stepped surface is a curved surface and a flat surface. In the present invention and the present specification, the "opposing surface" is a surface connected to a stepped surface and facing the inner wall surface of the cylinder hole. The connecting portion between the stepped surface and the facing surface is formed by a corner portion having an apex recessed in the radial direction when viewed in the cylinder axis direction. Alternatively, the connecting portion between the stepped surface and the facing surface is formed by a curved portion having no apex recessed in the radial direction when viewed in the cylinder axis direction. The facing surfaces are arranged along the circumferential direction of the cylinder hole and the cylinder axis direction. The facing surface is parallel to the circumferential direction of the cylinder hole. Alternatively, the facing surface is inclined with respect to the circumferential direction of the cylinder hole. That is, the facing surfaces are surfaces that intersect with respect to the circumferential direction of the cylinder hole within a range of an angle of −45 degrees or more and 45 degrees or less when viewed in the cylinder axis direction. The facing surface is parallel to the cylinder axis direction. Alternatively, the facing surface is inclined with respect to the cylinder axis direction. That is, the facing surface is a surface that intersects the cylinder axis in the range of an angle of −45 degrees or more and 45 degrees or less when viewed in the circumferential direction of the cylinder hole. The facing surface is a curved surface. Alternatively, the facing surface is a flat surface. Alternatively, the facing surfaces are flat and curved. The facing surface does not form an oil film with the inner wall surface of the cylinder hole. In the present invention and the present specification, "the facing surface does not form an oil film with the inner wall surface of the cylinder hole" means that all of the facing surfaces are reciprocated while the pair of piston skirts reciprocate in the cylinder axis direction. Means that does not form an oil film with the inner wall surface of the cylinder hole. That is, in the present invention and the present specification, "the facing surface does not form an oil film with the inner wall surface of the cylinder hole" means that while the pair of piston skirts reciprocate in the cylinder axis direction, it is instantaneous. The facing surface may include forming an oil film with the inner wall surface of the cylinder hole. Further, in the present invention and the present specification, "the facing surface does not form an oil film with the inner wall surface of the cylinder hole" means that the facing surface while the pair of piston skirts reciprocate in the cylinder axis direction. It may include forming an oil film with the inner wall surface of the cylinder hole in a part of the cylinder hole. As a result, the recess is in a state where the engine oil is filled in the recess space formed between the stepped surface and the facing surface of the recess and the inner wall surface of the cylinder hole when the piston skirt portion reciprocates in the cylinder axis direction. Is formed unretainable. That is, the recess is formed so that the recess space is not maintained in the state of being filled with the engine oil while the piston skirt portion reciprocates in the cylinder axis direction. That is, in the present invention and the present specification, "the facing surface does not form an oil film with the inner wall surface of the cylinder hole" means a recessed space while the pair of piston skirts reciprocate in the cylinder axis direction. Means that the state filled with engine oil is not maintained. More specifically, the recessed space is a space formed between the stepped surface and the facing surface of the recess and the inner wall surface of the cylinder hole facing the facing surface of the recess.

Here, the phrase "the recess is formed so that the recess space cannot be held in a state where the engine oil is filled" includes that the recess is formed so that the recess space is in the following state, for example. The first state is a state in which at least a part of the recessed space is instantaneously filled with engine oil while the pair of piston skirts reciprocate in the cylinder axis direction. For example, while the pair of piston skirts reciprocate in the cylinder axis direction, a part of the engine oil adhering to the inner wall surface of the cylinder hole may momentarily flow into the recessed space. In this case, the recessed space is momentarily filled with engine oil. Even if such a state occurs, all or part of the engine oil in the recessed space is immediately discharged to the outside of the recessed space. The second state is that the engine oil adheres to the surface of the recess and the engine oil separated from the engine oil adhered to the stepped surface and / or the facing surface of the recess adheres to the inner wall surface of the cylinder hole. This is a state in which the pair of piston skirts are held while reciprocating in the cylinder axis direction. The third state is a state in which there is almost no engine oil in the recessed space while the pair of piston skirts reciprocate in the cylinder axis direction. The state in which the engine oil is substantially absent in the recessed space includes a state in which the engine oil is thinly adhered to the stepped surface and the facing surface of the recessed portion and the engine oil is thinly adhered to the inner wall surface of the cylinder hole.

In the present invention and the present specification, "removal processing" means processing by scraping a material by a processing method such as lathe processing, milling processing, or polishing processing.

In the present invention and the present specification, the end portion of a certain component means a portion where the end portion of the component and the vicinity portion thereof are combined.

In the present invention and the present specification, the direction along the A direction is not limited to the direction parallel to the A direction. The direction along the A direction includes a direction inclined in a range of ± 45 ° with respect to the A direction. This definition also applies when a straight line follows the A direction. The direction A does not point to a specific direction. The A direction can be replaced with a vertical direction, a vertical direction, a front-back direction, or a left-right direction.

In the present invention and the present specification, at least one of A, B, or C is either A, B, C, A and B, B and C, A and C, or A and B and C. ..

In the present invention, including, comprising, having and their derivatives are used intended to include additional items in addition to the listed items and their equivalents. ing. The terms mounted, connected and coupled are used in a broad sense. Specifically, it includes not only direct mounting, connection and coupling, but also indirect mounting, connection and coupling. Moreover, connected and coupled are not limited to physical or mechanical connections / connections. They also include direct or indirect electrical connections / couplings.

Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by those skilled in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be construed to have meanings consistent with their meaning in the context of the relevant technology and the present disclosure, and are idealized or over-formed. It is not interpreted in a specific sense.

In the present specification, the term "favorable" is non-exclusive. "Preferable" means "preferable, but not limited to". In the present specification, the configuration described as "preferable" exhibits at least the above-mentioned effect obtained by the above-mentioned configuration (1). Also, as used herein, the term "may" is non-exclusive. "May" means "may be, but is not limited to". In the present specification, the configuration described as "may" exerts at least the above-mentioned effect obtained by the above-mentioned configuration (1).

If the number of components is not clearly specified in the claims and is displayed in the singular when translated into English, the present invention may have a plurality of the components. .. Further, the present invention may have only one of these components.

The present invention does not limit the combination of configurations from the other viewpoints described above with each other.
Prior to discussing embodiments of the invention in detail, it should be understood that the invention is not limited to the details of component configuration and arrangement described in the following description or illustrated in the drawings. The present invention is possible in other embodiments as well as in various modified embodiments. In addition, the present invention can be carried out by appropriately combining modified examples described later.

The engine piston of the present invention allows the design of the circumferential length of the outer peripheral surfaces of the pair of piston skirts and the area of the oil film to be secured while allowing the sliding resistance when the pair of piston skirts to be deformed to be reduced. The degree can be increased.

It is a figure which shows typically the piston for an engine which concerns on 1st Embodiment. It is a schematic cross-sectional view which looked at the piston for engine which concerns on 1st Embodiment in the direction of the cylinder axis. It is sectional drawing which shows typically the state of the engine oil between the pair of piston skirts of the engine piston which concerns on 1st Embodiment, and the inner wall surface of a cylinder hole. It is a schematic diagram which enlarged the concave part of the piston for engine which concerns on 1st Embodiment, and looked at the cylinder axis direction. It is a schematic view which looked at the piston for engine which concerns on 1st Embodiment in the radial direction of a cylinder hole. It is a schematic cross-sectional view which looked at the piston for engine which concerns on 2nd Embodiment in the cylinder axis direction. It is a schematic view which enlarged the concave part of the piston for engine which concerns on 3rd Embodiment, and looked at the cylinder axis direction. FIG. 5 is a schematic view of an engine including an engine piston according to a sixth embodiment as viewed in the radial direction of a cylinder hole.

<First Embodiment>
Hereinafter, the first embodiment of the present invention will be described with reference to FIGS. 1 to 5. FIG. 1 is a cross-sectional view of the engine piston according to the first embodiment seen in the radial direction of the cylinder hole orthogonal to the cylinder axis and a cross-sectional view of the engine piston according to the first embodiment seen in the cylinder axis direction. .. As shown in FIG. 1, the engine piston 25 includes a piston head portion 26, a pair of piston skirt portions 27, and a rib portion 31. The engine piston 25 is arranged inside the cylinder portion 15 of the engine 10.

The piston head portion 26 is arranged in a cylinder hole 17a formed inside the cylinder portion 15 of the engine 10. The cylinder hole 17a has a columnar shape. The piston head portion 26 is provided so that the cylinder hole 17a can be reciprocated in the cylinder axis 15X direction, which is the direction of the axis. The piston head portion 26 constitutes a part of the combustion chamber 15a formed inside the cylinder portion 15 of the engine 10. The combustion chamber 15a is composed of a substantially hemispherical surface centered on the direction of the axis 15X (hereinafter, referred to as the cylinder axis 15X) of the cylinder hole 17a. The piston head portion 26 is provided so that the cylinder hole 17a can be reciprocated in the cylinder axis 15X direction. That is, the engine piston 25 is provided so that the cylinder hole 17a can be reciprocated in the cylinder axis 15X direction. The engine piston 25 of the first embodiment is applied to, for example, an engine of a motorcycle. The engine piston 25 of the first embodiment is arranged so that the piston head portion 26 is on the top and the pair of piston skirt portions 27 is on the bottom in the vertical direction of the vehicle. Further, the engine piston 25 of the first embodiment has an engine 10 so that the cylinder axis 15X direction is parallel to the vertical direction of the vehicle or is inclined in a range of −90 degrees or more and 90 degrees or less with respect to the vertical direction of the vehicle. Is placed in.

The piston head portion 26 is provided in a columnar shape. The piston head portion 26 is arranged so that the direction of the axis X25 (hereinafter, referred to as the piston axis 25X direction) is along the cylinder axis 15X direction. Specifically, the piston head portion 26 is arranged so that the piston axis 25X substantially coincides with the cylinder axis 15X direction. When the engine piston 25 reciprocates in the cylinder axis 15X direction, the piston head portion 26 moves slightly in the cylinder hole 17a in the radial direction orthogonal to the cylinder axis 15X. The piston head portion 26 is arranged so that its outer peripheral surface faces the inner wall surface 15f of the cylinder hole 17a. One or more annular grooves (not shown) are formed on the outer peripheral surface of the piston head portion 26. An annular compression ring (not shown) and / or an annular oil ring (not shown) are provided in the annular groove of the piston head portion 26. The compression ring and the oil ring are configured to come into contact with the inner wall surface 15f of the cylinder hole 17a. The compression ring and the oil ring are configured to be slidable on the inner wall surface 15f of the cylinder hole 17a as the engine piston 25 reciprocates in the cylinder axis 15X direction. The compression ring and the oil ring prevent the engine oil in the cylinder hole 17a from entering the combustion chamber 15a. A part of the combustion chamber 15a is formed by the upper surface of the piston head portion 26, which is the uppermost surface in the cylinder axis 15X direction. In the following description of the configuration of the engine piston 25 alone, the piston head portion 26 will be described on the premise that the engine piston 25 is arranged so that the piston axis 25X coincides with the cylinder axis 15X direction. doing. That is, in the following description of the configuration of the engine piston 25 alone, the cylinder axis 15X can be replaced with the piston axis 25X.

The pair of piston skirt portions 27 includes the first piston skirt portion 27A and the second piston skirt portion 27B. The first piston skirt portion 27A and the second piston skirt portion 27B are connected to the piston head portion 26. Specifically, the upper ends of the first piston skirt portion 27A and the second piston skirt portion 27B are connected to the lower surface of the piston head portion 26. The first piston skirt portion 27A and the second piston skirt portion 27B are arranged on the lower surface of the piston head portion 26 so as to be separated from each other. That is, the positions of the first piston skirt portion 27A and the positions of the second piston skirt portion 27B are different when viewed in the cylinder axis 15X direction. The first piston skirt portion 27A and the second piston skirt portion 27B are provided so as to be reciprocating in the cylinder axis 15X direction. The first piston skirt portion 27A and the second piston skirt portion 27B have an arc shape along the inner wall surface 15f of the cylinder hole 17a when viewed in the cylinder axis 15X direction. Specifically, when viewed in the cylinder axis 15X direction, the shapes of the first piston skirt portion 27A and the second piston skirt portion 27B are arcuate shapes centered on the cylinder axis 15X. The central angle of the arc-shaped first piston skirt portion 27A centered on the cylinder axis 15X is the same as the central angle of the arc-shaped second piston skirt portion 27B centered on the cylinder axis 15X. Even if the first piston skirt portion 27A is formed so that both ends in the circumferential direction have a linear shape along the cylinder axis 15X when viewed in the radial direction of the cylinder hole 17a orthogonal to the cylinder axis 15X. It may or may not be formed. Even if the second piston skirt portion 27B is formed so that both ends in the circumferential direction have a linear shape along the cylinder axis 15X when viewed in the radial direction of the cylinder hole 17a orthogonal to the cylinder axis 15X. It may or may not be formed. The crankshaft 47 may be arranged so that the axis Lc direction of the crankshaft 47 (hereinafter referred to as the crankshaft Lc direction) passes through the cylinder axis 15X, or the crankshaft Lc does not pass through the cylinder axis 15X. May be placed in. A substantially arc-shaped gap CL through which the engine oil LO can enter is formed between the outer peripheral surface 28A of the first piston skirt portion 27A and the inner wall surface 15f of the cylinder hole 17a. A substantially arc-shaped gap CL is formed between the outer peripheral surface 28B of the second piston skirt portion 27B and the inner wall surface 15f of the cylinder hole 17a so that the engine oil LO can enter. The gap CL is a minute arc-shaped gap when viewed in the cylinder axis 15X direction.

For example, the engine oil LO pressurized by a pump (not shown) is injected toward the inner wall surface 15f of the cylinder hole 17a and the lower surface of the piston head portion 26 of the engine piston 25. The pump may be driven by the driving force of the engine or may be driven by electric power. The injected engine oil LO adheres to the inner wall surface 15f. The piston head portion 26, the first piston skirt portion 27A, and the second piston skirt portion 27B of the engine piston 25 reciprocate in the cylinder axis 15X direction. Due to the reciprocating movement of the engine piston 25, the engine oil LO adhering to the inner wall surface 15f enters the gap CL between the outer peripheral surface 28A of the first piston skirt portion 27A and the inner wall surface 15f of the cylinder hole 17a. Similarly, due to the reciprocating movement of the engine piston 25, the engine oil LO adhering to the inner wall surface 15f enters the gap CL between the outer peripheral surface 28B and the inner wall surface 15f of the second piston skirt portion 27B. In this way, the outer peripheral surface 28A, the outer peripheral surface 28B, and the inner wall surface 15f are lubricated by the engine oil LO.

The pair of rib portions 31 are connected to both ends of the piston head portion 26 and the pair of piston skirt portions 27 in the circumferential direction. The upper ends of the pair of rib portions 31 are connected to the lower surface of the piston head portion 26. The pair of rib portions 31 are a first rib portion 31A and a second rib portion 31B. More specifically, the first rib portion 31A has a first boss portion 32A. The second rib portion 31B has a second boss portion 32B. The first boss portion 32A and the second boss portion 32B are arranged in the order of the first boss portion 32A, the cylinder axis 15X, and the second boss portion 32B when viewed in the radial direction of the cylinder hole 17a orthogonal to the cylinder axis 15X. It is provided in. The first boss portion 32A is provided in the central portion of the first rib portion 31A. Further, the second boss portion 32B is provided at the central portion in the circumferential direction of the second rib portion 31A. A columnar pin hole 33 into which the piston pin 45 can be inserted is formed in the first boss portion 32A. The second boss portion 32B is formed with a columnar pin hole 33 into which the piston pin 45 can be inserted. The shaft of the pin hole 33 of the first boss portion 32A and the pin hole 33 of the second boss portion 32B are formed in the first boss portion 32A and the second boss portion 32B so that their respective axes coincide with each other. The axis of each pin hole 33 is parallel to the crank axis Lc direction. The axis of each pin hole 33 does not have to be parallel to the crank axis Lc direction. The piston pin 45 is inserted into the pin hole 33 of the first boss portion 32A and the pin hole 33 of the second boss portion 32B. The piston pin 45 is made of, for example, a metal or a composite material of metal and resin, and is formed in a cylindrical shape or a columnar shape. The connecting rod 46 is swingably connected to the pair of rib portions 31 via the piston pin 45. The connecting rod 46 transmits the reciprocating movement of the piston head portion 26 and the pair of piston skirt portions 27 in the cylinder axis 15X direction as the rotational force of the crankshaft 47. The crankshaft 47 is included in the engine 10. More specifically, the piston pin 45 is inserted into a columnar hole provided at the upper end of the connecting rod 46 to support the connecting rod 46. That is, the piston pin 45 is inserted into the hole of the connecting rod 46, the pin hole 33 of the first boss portion 32A, and the pin hole 33 of the second boss portion 32B. Therefore, the connecting rod 46 is swingably connected to the pin hole 33 of the first rib portion 31A and the pin hole 33 of the second rib portion 31B around the axis of the piston pin 45. That is, the first rib portion 31A and the second rib portion 31B are swingably connected to the connecting rod 46 via the piston pin 45. The connecting rod 46 is rotatably provided on the crankshaft 47. More specifically, the lower end of the connecting rod 46 is connected to an eccentric shaft 48 (see FIG. 8) included in the crankshaft 47, and is swingably connected around the central axis of the eccentric shaft 48. The central axis of the eccentric shaft 48 deviates from the central axis of the crankshaft 47. The eccentric shaft 48 rotates around the central axis of the crankshaft 47. That is, the lower end of the connecting rod 46 is rotatably connected to the crankshaft 47 around the central axis of the crankshaft 47. When the lower end of the connecting rod 46 connected to the eccentric shaft 48 rotates around the central axis of the crankshaft 47, the connecting rod 46 reciprocates in the cylinder axis 15X direction while swinging around the central axis of the eccentric shaft 48. Then, the engine piston 25 connected to the upper end of the connecting rod 46 reciprocates in the cylinder axis 15X direction.

As shown in FIGS. 2 (1) to (3), the shapes of the first piston skirt portion 27A and the second piston skirt portion 27B, which are the pair of piston skirt portions 27, may be the same. As shown in FIG. 2 (4), the shapes of the first piston skirt portion 27A and the second piston skirt portion 27B may be different. That is, the circumferential length of the first piston skirt portion 27A and the circumferential length of the second piston skirt portion 27B may be the same or different. The circumferential length of the first piston skirt portion 27A may be longer or shorter than the circumferential length of the second piston skirt portion 27B. Further, although not shown, the length of the first piston skirt portion 27A and the length of the second piston skirt portion 27B may be the same or different in the cylinder axis 15X direction. The length of the first piston skirt portion 27A in the cylinder axis 15X direction may be longer or shorter than the length of the second piston skirt portion 27B in the cylinder axis 15X direction.

As shown in FIGS. 2 (1) and 2 (4), the first rib portion 31A and the second rib portion 31B may be formed in a straight line. Alternatively, as shown in FIG. 2 (2), the first rib portion 31A and the second rib portion 31B may be formed so that the central portion thereof is recessed toward the cylinder axis 15X. Alternatively, as shown in FIG. 2 (3), the first rib portion 31A and the second rib portion 31B may be formed so that the central portion thereof is separated from the cylinder axis 15X. Specifically, as shown in FIG. 2 (1), the first rib portion 31A and the second rib portion 31B are formed with the inner peripheral surface of the first rib portion 31A and the piston pin 45 in the axial direction Lp direction of the piston pin 45. The distance between the intersection of the two ribs 31B and the intersection of the inner peripheral surface of the second rib portion 31B and the piston pin 45 is the same as the length of the inner peripheral surface of the first piston skirt portion 27A in the axis Lp direction of the piston pin 45. It is configured to be. Further, as shown in FIGS. 2 (2) to (4), the first rib portion 31A and the second rib portion 31B are the inner peripheral surface of the first rib portion 31A and the piston pin in the axis Lp direction of the piston pin 45. The distance between the intersection with 45 and the intersection of the inner peripheral surface of the second rib portion 31B and the piston pin 45 is the length of the inner peripheral surface of the first piston skirt portion 27A in the axis Lp direction of the piston pin 45. Configured differently. For example, as shown in FIG. 2 (2), the first rib portion 31A and the second rib portion 31B are the intersections of the inner peripheral surface of the first rib portion 31A and the piston pin 45 in the axial direction Lp direction of the piston pin 45. , The distance between the inner peripheral surface of the second rib portion 31B and the intersection of the piston pin is configured to be longer than the length of the inner peripheral surface of the first piston skirt portion 27A in the axis Lp direction of the piston pin 45. .. Further, for example, as shown in FIGS. 2 (3) and 2 (4), the first rib portion 31A and the second rib portion 31B are the inner peripheral surface of the first rib portion 31A and the piston in the axis Lp direction of the piston pin 45. The distance between the intersection with the pin 45 and the intersection between the inner peripheral surface of the second rib portion 31B and the piston pin is shorter than the length of the inner peripheral surface of the first piston skirt portion 27A in the axis Lp direction of the piston pin 45. It is configured as follows.

As shown in FIG. 2 (1), the first rib portion 31A and the second rib portion 31B have an intersection of the inner peripheral surface of the first rib portion 31A and the piston pin 45 in the axial direction Lp direction of the piston pin 45, and the piston pin 45. The distance between the inner peripheral surface of the second rib portion 31B and the intersection of the piston pin 45 is configured to be the same as the length of the inner peripheral surface of the second piston skirt portion 27B in the axis Lp direction of the piston pin 45. Will be done. Further, as shown in FIGS. 2 (2) to (4), the first rib portion 31A and the second rib portion 31B are the inner peripheral surface of the first rib portion 31A and the piston pin in the axis Lp direction of the piston pin 45. The distance between the intersection with 45 and the intersection of the inner peripheral surface of the second rib portion 31B and the piston pin 45 is the length of the inner peripheral surface of the second piston skirt portion 27B in the axis Lp direction of the piston pin 45. Configured differently. For example, as shown in (2) and (4) of FIG. 2, the first rib portion 31A and the second rib portion 31B are the inner peripheral surface of the first rib portion 31A and the piston pin in the axis Lp direction of the piston pin 45. The distance between the intersection with 45 and the intersection of the inner peripheral surface of the second rib portion 31B and the piston pin 45 is based on the length of the inner peripheral surface of the second piston skirt portion 27B in the axis Lp direction of the piston pin 45. It is configured to be long. Further, for example, as shown in FIG. 2 (3), the first rib portion 31A and the second rib portion 31B are formed with the inner peripheral surface of the first rib portion 31A and the piston pin 45 in the axial direction Lp direction of the piston pin 45. The distance between the intersection of the two ribs 31B and the intersection of the inner peripheral surface of the second rib portion 31B and the piston pin 45 is shorter than the length of the inner peripheral surface of the second piston skirt portion 27B in the axis Lp direction of the piston pin 45. It is composed of.

As shown in FIG. 1, at least one of the first piston skirt portion 27A and the second piston skirt portion 27B has a recess 29. Although the recess 29 is shown in a size that is easy to see in FIGS. 1 to 8, the size of the recess 29 can be changed in various ways as long as it is described in the claims of the present invention. The recesses 29 are provided at both ends of the outer peripheral surface 28A of the first piston skirt portion 27A or at least one of the second piston skirt portions 27B in the circumferential direction. In FIG. 1, recesses 29 are provided at both ends of the outer peripheral surface 28A of the first piston skirt portion 27A in the circumferential direction and at both ends of the outer peripheral surface 28B of the second piston skirt portion 27B in the circumferential direction. Specifically, the first piston skirt portion 27A has recesses 29A1 and 29A2 at both ends in the circumferential direction thereof. The second piston skirt portion 27B has recesses 29B1 and 29B2 at both ends in the circumferential direction thereof.

The outer peripheral surface 28 (28A, 28B) of at least one of the first piston skirt portion 27A or the second piston skirt portion 27B having the recess 29 is a sliding surface 28a and a stepped surface which is two surfaces forming the recess 29. Includes 29a and facing surface 29b. The sliding surface 28a is formed in a shape along the inner wall surface 15f of the cylinder hole 17a. The sliding surface 28a may be configured with one curvature. For example, the sliding surface 28a may be configured to be parallel to the inner wall surface 15f of the cylinder hole 17a. Further, the sliding surface 28a may be configured to have a plurality of different curvatures. For example, the sliding surface 28a may be configured such that both ends in the circumferential direction form an arc having a larger curvature than the central portion in the circumferential direction. The gap CL includes a gap between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a. The sliding surface 28a forms an oil film between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a due to the engine oil LO that has entered between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a. That is, when the gap CL between at least one of the sliding surfaces 28a of the pair of piston skirts 27 and the inner wall surface 15f of the cylinder hole 17a is filled with the engine oil LO, the pair of piston skirts 27 are cylinders. It is configured to be held while reciprocating in the 15X direction of the axis.

The recess 29 is provided so as to be recessed toward the cylinder axis 15X in the radial direction of the cylinder hole 17a orthogonal to the cylinder axis 15X. That is, the radial length of the cylinder hole 17a from the facing surface 29b of the recess 29 to the cylinder axis 15X is the radial length of the cylinder hole 17a from the sliding surface 28a of the first piston skirt portion 27A to the cylinder axis 15X. Shorter than that. The stepped surface 29a is connected to the sliding surface 28a. The step surface 29a is arranged along the radial direction of the cylinder hole 17a and the cylinder axis 15X direction. The step surface 29a constitutes a step formed at a depth capable of cutting an oil film between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a in the radial direction of the cylinder hole 17a. The facing surface 29b is connected to the stepped surface 29a. The facing surface 29b is arranged along the circumferential direction of the cylinder hole 17a and the cylinder axis 15X direction, and faces the inner wall surface 15f of the cylinder hole 17a. The gap CL includes a gap between the stepped surface 29a and the facing surface 29b and the inner wall surface 15f of the cylinder hole 17a. Therefore, the facing surface 29b does not form an oil film between the facing surface 29b and the inner wall surface 15f of the cylinder hole 17a. Specifically, in the cylinder axis 15X direction, the lengths of the recesses 29A1 and 29A2 are the same as the length of the sliding surface 28a of the first piston skirt portion 27A. In the cylinder axis 15X direction, the lengths of the recesses 29B1 and 29B2 are the same as the length of the sliding surface 28a of the second piston skirt portion 27B. The recesses 29A1 and 29A2 communicate with the cylinder hole 17a on the lower end surface of the first piston skirt portion 27A. The recesses 29B1 and 29B2 communicate with the cylinder hole 17a on the lower end surface of the second piston skirt portion 27B.

Based on FIG. 3, the state of the engine oil LO between the pair of piston skirt portions 27 and the inner wall surface 15f of the cylinder hole 17a will be described. The recesses 29 in FIG. 3 correspond to the recesses 29A1, 29A2, 29B1 and 29B2 in FIG. 1, and the description thereof will be omitted. As shown in FIG. 3, an oil film is formed between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a. The stepped surface 29a of the recess 29 cuts an oil film formed between the inner wall surface 15f of the cylinder hole 17a and the sliding surface 28a. Therefore, the facing surface 29b of the recess 29 does not form an oil film with the inner wall surface 15f of the cylinder hole 17a. Therefore, while the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction, all of the facing surfaces 29b do not form an oil film with the inner wall surface 15f of the cylinder hole 17a. While the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction, the facing surface 29b may momentarily form an oil film between the pair of piston skirts 27 and the inner wall surface 15f of the cylinder hole 17a. Further, while the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction, an oil film may be formed on a part of the facing surface 29b with the inner wall surface 15f of the cylinder hole 17a. That is, the recess 29 is formed so that the recess space SP cannot be held in a state where the engine oil LO is filled when the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction. The recess space SP is a space formed between the stepped surface 29a and the facing surface 29b of the recess 29 and the inner wall surface 15f of the cylinder hole 17a.

Here, the configuration of the recessed space SP will be described in detail with reference to FIG. As shown by the one-point chain line in FIG. 3, the outer peripheral end of the stepped surface 29a of the recess 29 in the radial direction of the cylinder hole 17a and the plane parallel to the radial direction of the cylinder hole 17a are assumed to be the first virtual plane PL1. As shown by the alternate long and short dash line in FIG. 3, a plane that passes through the outer peripheral end of the facing surface 29b of the recess 29 in the circumferential direction and is parallel to the first virtual plane PL1 is assumed to be the second virtual plane PL2. It is assumed that a plane including the lower surface of the piston head portion 26 and orthogonal to the cylinder axis 15X is a third virtual plane (not shown). A plane that passes through the lower end of the recess 29 and is orthogonal to the cylinder axis 15X is assumed to be a fourth virtual plane (not shown). The space surrounded by the first virtual plane PL1, the second virtual plane PL2, the third virtual plane, the fourth virtual plane, the stepped surface 29a, the facing surface 29b, and the inner wall surface 15f is the recessed space SP. The shape of the recessed space SP is a columnar shape long in the cylinder axis 15X direction. The length of the recess space SP in the cylinder axis 15X direction is the same as the length of the pair of piston skirts 27 in the cylinder axis 15X direction.

The phrase "the recess 29 is formed so that the recess space SP cannot be held in a state where the engine oil LO is filled" includes that the recess 29 is formed so that the recess space SP is, for example, in the following state. The first state is a state in which at least a part of the recessed space SP is instantaneously filled with the engine oil LO while the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction. For example, while the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction, a part of the engine oil LO adhering to the inner wall surface 15f of the cylinder hole 17a may momentarily flow into the recess space SP. In this case, the recessed space SP may be instantaneously filled with the engine oil LO. Even if such a state occurs, the engine oil LO in the recessed space SP is immediately discharged downward from the recessed space SP due to gravity, as shown by the shape of the ellipse or the circle in FIG. 3 (1). .. Then, the engine oil LO adheres to the stepped surface 29a and the facing surface 29b of the recess 29, and the engine oil LO separated from the engine oil LO adhering to the stepped surface 29a and the facing surface 29b of the recess 29 is inside the cylinder hole 17a. It is in a state of being attached to the wall surface 15f. In the second state, as shown in FIG. 3 (2), the engine oil LO adheres to the stepped surface 29a and / or the facing surface 29b of the recess 29, and adheres to the stepped surface 29a and the facing surface 29b of the recess 29. The state in which the engine oil LO separated from the engine oil LO adheres to the inner wall surface 15f of the cylinder hole 17a is held while the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction. The third state is a state in which the engine oil LO is almost absent in the recessed space SP, as shown in FIG. 3 (3). The state in which the engine oil LO is almost nonexistent in the recess space SP means that the engine oil LO is thinly adhered to the stepped surface 29a and the facing surface 29b of the recess 29, and the engine oil LO is thinly adhered to the inner wall surface 15f of the cylinder hole 17a. Includes thin adhesion.

The recess 29 is formed by a stepped surface 29a and a facing surface 29b. The step surface 29a is arranged along the radial direction of the cylinder hole 17a and the cylinder axis 15X direction. The stepped surface 29a is a flat surface, a curved surface, or a curved surface and a flat surface. The stepped surface 29a is a surface that intersects the radial straight line of the cylinder hole 17a passing through the cylinder axis 15X in an angle range of −45 degrees or more and 45 degrees or less when viewed in the cylinder axis 15X direction. As shown in FIGS. 4 (1) to (3), the stepped surface 29a is parallel to the radial direction of the cylinder hole 17a. Alternatively, as shown in FIGS. 4 (4) to (5), the stepped surface 29a is inclined with respect to the radial direction of the cylinder hole 17a. As shown in FIGS. 4 (1) to (6), the connecting portion between the stepped surface 29a and the sliding surface 28a is formed by a corner portion having an apex protruding in the radial direction when viewed in the cylinder axis 15X direction. .. Alternatively, as shown in FIG. 4 (7), the connecting portion between the stepped surface 29a and the sliding surface 28a is formed by a curved portion having no apex protruding in the radial direction when viewed in the cylinder axis 15X direction. ..

The stepped surface 29a is a surface that intersects the cylinder axis 15X within an angle range of −45 degrees or more to 45 degrees or less when viewed in the radial direction of the cylinder hole 17a passing through the stepped surface 29a. As shown in FIG. 5 (1), the stepped surface 29a is parallel to the cylinder axis 15X direction when viewed in the radial direction of the cylinder hole 17a passing through the stepped surface 29a. Alternatively, as shown in FIGS. 5 (2) and 5 (3), the step surface 29a is inclined with respect to the cylinder axis 15X direction when viewed in the radial direction of the cylinder hole 17a passing through the step surface 29a. Therefore, as shown in FIG. 5 (2), the length of the upper end of the facing surface 29b is longer than the length of the lower end when viewed in the radial direction of the cylinder hole 17a passing through the facing surface 29b. As shown in FIG. 5 (3), the length of the upper end of the facing surface 29b is shorter than the length of the lower end when viewed in the radial direction of the cylinder hole 17a passing through the facing surface 29b.

The facing surface 29b is arranged along the circumferential direction of the cylinder hole 17a and the cylinder axis 15X direction. The facing surface 29b is a flat surface, a curved surface, or a curved surface and a flat surface. The facing surface 29b is a surface that intersects the circumferential direction of the cylinder hole 17a within an angle range of −45 degrees or more and 45 degrees or less when viewed in the cylinder axis 15X direction. As shown in FIGS. 4 (1), (4) and (5), the facing surface 29b is parallel to the circumferential direction of the cylinder hole 17a. Alternatively, as shown in FIGS. 4 (2) and (3), the facing surface 29b is inclined with respect to the circumferential direction of the cylinder hole 17a. As shown in FIGS. 4 (1) to (5) and (7), the connecting portion between the stepped surface 29a and the facing surface 29b is a corner portion having a vertex recessed in the radial direction when viewed in the cylinder axis 15X direction. It is formed. Alternatively, as shown in FIG. 4 (6), the connecting portion between the stepped surface 29a and the facing surface 29b is formed by a curved portion having no apex recessed in the radial direction when viewed in the cylinder axis 15X direction.

The facing surface 29b is a surface that intersects the cylinder axis 15X within an angle range of −45 degrees or more and 45 degrees or less when viewed in the circumferential direction of the cylinder hole 17a. As shown in FIG. 5 (4), the facing surface 29b is parallel to the cylinder axis 15X direction. Alternatively, as shown in FIGS. 5 (5) and 5 (6), the facing surface 29b is inclined with respect to the cylinder axis 15X direction.

The plurality of recesses 29 provided at at least one of the two ends of the pair of piston skirts 27 may have any one configuration shown in FIG. 4, or any two configurations shown in FIG. It may be a combination. In FIG. 5, a plurality of recesses 29 provided at at least one of the two ends of the pair of piston skirts 27 are configured to be symmetrical with respect to the cylinder axis 15X. However, the plurality of recesses 29 provided at at least one of the two ends of the pair of piston skirts 27 are not configured symmetrically with respect to the cylinder axis 15X, and even if any two of FIGS. 5 are combined. Good.

The engine piston 25 of the first embodiment has the following effects.

At least one of the first piston skirt portion 27A and the second piston skirt portion 27B is provided on at least one of the outer

peripheral surfaces

28A and 28B of the first piston skirt portion 27A or the second piston skirt portion 27B in the circumferential direction. It has a recess 29 to be provided. The recess 29 is provided so as to be recessed toward the cylinder axis 15X in the radial direction of the cylinder hole 17a orthogonal to the cylinder axis 15X. That is, the recess 29 is provided so as to be recessed from the sliding surface 28a of the first piston skirt portion 27A or the second piston skirt portion 27B. Further, at least one of the outer peripheral surfaces 28 (28A, 28B) of the first piston skirt portion 27A or the second piston skirt portion 27B has a sliding surface 28a, a stepped surface 29a, and an facing surface 29b. The sliding surface 28a forms an oil film between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a due to the engine oil LO that has entered between the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a. The stepped surface 29a and the facing surface 29b form a recess 29. The step surface 29a is connected to the sliding surface 28a and is arranged along the radial direction of the cylinder hole 17a and the cylinder axis 15X direction, and the sliding surface 28a and the inner wall surface 15f of the cylinder hole 17a are arranged in the radial direction of the cylinder hole 17a. It constitutes a step formed at a depth that can cut the oil film between them. The facing surface 29b is connected to the stepped surface 29a and is arranged along the circumferential direction of the cylinder hole 17a and the cylinder axis 15X direction, and faces the inner wall surface 15f of the cylinder hole 17a. The facing surface 29b does not form an oil film with the inner wall surface 15f of the cylinder hole 17a. When the pair of piston skirts 27 reciprocate in the cylinder axis 15X direction, no oil film is formed in the recess 29 with the inner wall surface 15f of the cylinder hole 17a.

The step formed by the step surface 29a of the recess 29 cuts an oil film between the inner wall surface 15f of the cylinder hole 17a and at least one of the sliding surfaces 28a of the first piston skirt portion 27A or the second piston skirt portion 27B. It is a step that can be made. Originally, there is a gap CL between the sliding surface 28a of the pair of piston skirts 27 and the inner wall surface 15f of the cylinder hole 17a. Therefore, by forming the recess 29 forming the step on the outer peripheral surface 28, the gravity of the engine oil LO itself is larger than the surface tension of the engine oil LO existing in the recess 29 even if the step is a slight step. Therefore, the oil film between the sliding surface 28a of the pair of piston skirts 27 and the inner wall surface 15f of the cylinder hole 17a can be cut. Therefore, the position where the oil film is cut between the inner wall surface 15f of the cylinder hole 17a and the outer peripheral surface 28 of at least one of the first piston skirt portion 27A or the second piston skirt portion 27B is determined. Since the oil film on the sliding surface 28a of at least one of the outer peripheral surfaces 28 of the first piston skirt portion 27A or the second piston skirt portion 27B and the inner wall surface 15f of the cylinder hole 17a is cut off at the stepped surface 29a, the area of the oil film operates. It is hard to change depending on the conditions. In order to adjust the rigidity of at least one of the first piston skirt portion 27A or the second piston skirt portion 27B, in the circumferential direction of at least one of the outer peripheral surfaces 28 of the first piston skirt portion 27A or the second piston skirt portion 27B. Even if the length is increased or decreased, the length of the sliding surface 28a in the circumferential direction can be freely designed by adjusting the length of the facing surface 29b of the recess 29 in the circumferential direction. As a result, the length of the outer peripheral surfaces 28 of the pair of piston skirts 27 in the circumferential direction can be freely designed according to the required rigidity, and the area of the oil film to be secured can be freely designed. That is, recesses 29 having steps are formed at both ends of the pair of piston skirts 27, and the steps cut the oil film on the sliding surfaces 28a of the pair of piston skirts 27, thus reducing the sliding resistance during deformation. At the same time, it is possible to increase the degree of freedom in designing the length of the outer peripheral surfaces 28 of the pair of piston skirts 27 in the circumferential direction and the area of the oil film to be secured. Moreover, by forming recesses with steps at both ends of the pair of piston skirts 27, it is possible to secure a gap between the pair of piston skirts and the inner wall surface of the cylinder hole at both ends. Further, if the step is a slight step that cuts an oil film between the inner wall surface 15f of the cylinder hole 17a and the sliding surface 28a of the pair of piston skirts 27, a crack is generated in the step due to stress concentration. do not do.

As described above, the engine piston 25 having the pair of piston skirts 27 of the first embodiment has the outer circumference of the pair of piston skirts 27 while allowing the sliding resistance of the pair of piston skirts 27 at the time of deformation to be reduced. The design freedom of the circumferential length of the surface 28 and the area of the oil film to be secured can be increased.

<Second Embodiment>
Hereinafter, the engine piston 25 according to the second embodiment of the present invention will be described with reference to FIG. The engine piston 25 of the second embodiment has the following configurations in addition to the configurations of the first embodiment.

The recesses 29 are provided at both ends of the first piston skirt portion 27A in the circumferential direction and at both ends of the second piston skirt portion 27B in the circumferential direction. That is, the first piston skirt portion 27A has recesses 29A1 and 29A2 at both ends in the circumferential direction thereof. The second piston skirt portion 27B has recesses 29B1 and 29B2 at both ends in the circumferential direction thereof.

Alternatively, the recesses 29 are provided at both ends of the first piston skirt portion 27A in the circumferential direction. That is, the first piston skirt portion 27A has recesses 29A1 and 29A2 at both ends in the circumferential direction thereof. The second piston skirt portion 27B is not provided with the recesses 29B1 and 29B2.

Alternatively, the recesses 29 are provided at both ends of the second piston skirt portion 27B in the circumferential direction. That is, the second piston skirt portion 27B has recesses 29B1 and 29B2 at both ends in the circumferential direction thereof. The first piston skirt portion 27A is not provided with the recesses 29A1 and 29A2.

The engine piston 25 of the second embodiment has the following effects in addition to the effect of the engine piston 25 of the first embodiment.

The arrangement of the recesses 29 provided in the pair of piston skirts 27 of the engine piston 25 can be changed. By changing the arrangement of the recesses 29 provided in the pair of piston skirts 27, the sliding resistance of the pair of piston skirts 27 due to the oil film of the engine oil LO can be adjusted. By changing the arrangement of the recesses 29 provided in the pair of piston skirts 27, the sliding resistance at the time of deformation of the pair of piston skirts 27 can be reduced, and the outer peripheral surfaces 28 of the pair of piston skirts 27. It is possible to increase the degree of freedom in designing the length in the circumferential direction and the area of the oil film to be secured.

<Third Embodiment>
Hereinafter, the engine piston 25 according to the third embodiment of the present invention will be described with reference to FIGS. 6 and 7. The engine piston 25 of the third embodiment has the following configurations in addition to the configurations of the first embodiment or the second embodiment.

As shown in FIG. 6, the pair of rib portions 31 are a first rib portion 31A and a second rib portion 31B. One end of the first rib portion 31A is connected to the first end portion 27A1 of the first piston skirt, which is one end in the circumferential direction of the inner peripheral portion of the first piston skirt portion 27A. The other end of the first rib portion 31A is connected to the first end portion 27B1 of the second piston skirt, which is one end in the circumferential direction of the inner peripheral portion of the second piston skirt portion 27B. One end of the second rib portion 31B is connected to the second end portion 27A2 of the first piston skirt, which is the other end portion in the circumferential direction of the inner peripheral portion of the first piston skirt portion 27A. The other end of the second rib portion 31B is connected to the second end portion 27B2 of the second piston skirt, which is the other end portion in the circumferential direction of the inner peripheral portion of the second piston skirt portion 27B.

As shown in FIG. 7 (1), the recess 29A1 overlaps with the first end portion 27A1 of the first piston skirt when viewed in the radial direction D1 of the cylinder hole 17a passing through the recess 29A1. Although not shown, the recess 29A2 also overlaps with the second end 27A2 of the first piston skirt when viewed in the radial direction of the cylinder hole 17a passing through the recess 29A2. Although not shown, the recess 29B1 also overlaps with the first end 27B1 of the second piston skirt when viewed in the radial direction of the cylinder hole 17a passing through the recess 29B1. Although not shown, the recess 29B2 also overlaps with the second end 27B2 of the second piston skirt when viewed in the radial direction of the cylinder hole 17a passing through the recess 29B2.

In the engine piston 25, when at least one of the recesses 29A1, 29A2, 29B1 and 29B2 is viewed in the radial direction passing through the recesses 29A1, 29A2, 29B1 and 29B2, the first end portion 27A1 of the first piston skirt, It may be provided so as to overlap the first end portion 27B1 of the second piston skirt, the second end portion 27A2 of the first piston skirt, and the second end portion 27B2 of the second piston skirt.

Further, as shown in FIG. 7 (2), in the engine piston 25 of the first embodiment or the second embodiment, when the recess 29A1 is viewed in the radial direction D1 of the cylinder hole 17a passing through the recess 29A1. It may be configured so as not to overlap with the first end portion 27A1 of the first piston skirt. Although not shown, the recess 29A2 also does not have to overlap the first piston skirt second end 27A2 when viewed in the radial direction D2 of the cylinder hole 17a passing through the recess 29A2. Although not shown, the recess 29B1 also does not have to overlap with the first end 27B1 of the second piston skirt when viewed in the radial direction D3 of the cylinder hole 17a passing through the recess 29B1. Although not shown, the recess 29B2 also does not have to overlap with the second end 27B2 of the second piston skirt when viewed in the radial direction D4 of the cylinder hole 17a passing through the recess 29B2.

The engine piston 25 of the third embodiment exerts the following effects in addition to the effects of the engine piston 25 of the first embodiment or the second embodiment.

In the engine piston 25 of the third embodiment, the pair of rib portions 31 has a first rib portion 31A and a second rib portion 31B. One end of the first rib portion 31A is connected to the first end portion 27A1 of the first piston skirt portion 27A of the first piston skirt portion 27A. The other end of the first rib portion 31A is connected to the first end portion 27B1 of the second piston skirt portion 27B of the second piston skirt portion 27B. One end of the second rib portion 31B is connected to the second end portion 27A2 of the first piston skirt portion 27A of the first piston skirt portion 27A. The other end of the second rib portion 31B is connected to the second end portion 27B2 of the second piston skirt portion 27B of the second piston skirt portion 27B. Here, in the first piston skirt portion 27A and the second piston skirt portion 27B, the rigidity of the portions connected to the first rib portion 31A and the second rib portion 31B becomes relatively large. In other words, the rigidity of the first piston skirt first end 27A1, the second piston skirt first end 27B1, the first piston skirt second end 27A2, and the second piston skirt second end 27B2 becomes relatively large. ..

On the other hand, the recess 29A1 overlaps with the portion of the first rib portion 31A connected to the first end portion 27A1 of the first piston skirt when viewed in the radial direction D1 passing through the recess 29A1. The recess 29A2 overlaps the portion of the second rib portion 31B connected to the second end portion 27A2 of the first piston skirt when viewed in the radial direction D2 passing through the recess 29A2. The recess 29B1 overlaps with a portion of the first rib portion 31A connected to the first end portion 27B1 of the second piston skirt when viewed in the radial direction D3 passing through the recess 29B1. The recess 29B2 overlaps the portion of the second rib portion 31B connected to the second end portion 27B2 of the second piston skirt when viewed in the radial direction D4 passing through the recess 29B2. Alternatively, in the engine piston 25, when at least one of the recesses 29A1, 29A2, 29B1 and 29B2 is viewed radially through the recesses 29A1, 29A2, 29B1 and 29B2, the first piston skirt first end 27A1 and It overlaps the first end portion 27B1 of the second piston skirt, the second end portion 27A2 of the first piston skirt, and the second end portion 27B2 of the second piston skirt. That is, in the first piston skirt portion 27A and the second piston skirt portion 27B, the first piston skirt portion 27A1 having relatively high rigidity, the second piston skirt first end portion 27B1, and the first piston skirt second end portion Recesses 29A1, 29A2, 29B1 and 29B2 are provided in at least one of 27A2 and the second end 27B2 of the second piston skirt. As a result, the diameters of the first piston skirt first end 27A1, the second piston skirt first end 27B1, the first piston skirt second end 27A2, and the second piston skirt second end 27B2, which have relatively high rigidity. At the positions arranged in the direction, a large gap that does not form an oil film can be secured between the pair of piston skirt portions 27 and the inner wall surface 15f of the cylinder body 17. That is, in the first piston skirt portion 27A and the second piston skirt portion 27B, the first piston skirt first end portion 27A1, the second piston skirt first end portion 27B1, and the first piston skirt second end portion having relatively high rigidity. An oil film is formed between the pair of piston skirts 27 and the inner wall surface 15f of the cylinder hole 17a by providing the recess 29 at a position where it is radially aligned with at least one of 27A2 and the second end 27B2 of the second piston skirt. It is also possible to secure a large gap CL that does not receive a load from the inner wall surface 15f of the cylinder body 17.

<Fourth Embodiment>
Hereinafter, the engine piston 25 according to the fourth embodiment of the present invention will be described. The engine piston 25 of the fourth embodiment includes the following configurations in addition to the configurations of any of the first to third embodiments.

The engine piston 25 is made of, for example, a metal or a composite material of metal and resin. The piston head portion 26, the pair of piston skirt portions 27, and the pair of rib portions 31 are, for example, integrally molded or separately molded and then molded together.

The engine piston 25 is manufactured by casting or forging. After the casting or forging step, the outer peripheral surface 28A of the first piston skirt portion 27A and the sliding surface 28a of the outer peripheral surface 28B of the second piston skirt portion 27B may be formed by a removal process. The sliding surface 28a may be a surface that has not been removed. The stepped surface 29a and the facing surface 29b of the recess 29 have not been removed. That is, the stepped surface 29a and the facing surface 29b of the recess 29 are surfaces that have not been removed. Here, the surface that has not been removed is a surface that has not been removed by lathe processing, milling processing, polishing processing, or the like.

The engine piston 25 of the fourth embodiment exerts the following effects in addition to the effects of the engine piston 25 of any of the first to third embodiments.

The engine piston 25 of the fourth embodiment includes a piston head portion 26, a pair of piston skirt portions 27, and a pair of rib portions 31. That is, the piston head portion 26, the pair of piston skirt portions 27, and the pair of rib portions 31 are made of metal. The engine piston 25 is formed by casting or forging. That is, the piston head portion 26, the pair of piston skirt portions 27, and the pair of rib portions 31 are formed by casting or forging. The stepped surface and the facing surface of the recess 29 are surfaces that have not been removed. This facilitates the molding of the recesses 29 in the pair of piston skirts 27. Further, the length of the recess 29 in the circumferential direction can be adjusted to facilitate the design of the length of the sliding surface 28a in the circumferential direction.

<Fifth Embodiment>
Hereinafter, the engine piston 25 according to the fifth embodiment of the present invention will be described. The engine piston 25 of the fifth embodiment includes the following configurations in addition to the configurations of any of the first to third embodiments.

The engine piston 25 is made of, for example, a metal or a composite material of metal and resin. The piston head portion 26, the pair of piston skirt portions 27, and the pair of rib portions 31 are, for example, integrally molded or separately molded and then molded together. ..

The engine piston 25 is manufactured, for example, by casting or forging. The engine piston 25 may be manufactured by, for example, a 3D printer or may be manufactured by machining. After a step such as casting or forging, the outer peripheral surface 28A of the first piston skirt portion 27A and the sliding surface 28a of the outer peripheral surface 28B of the second piston skirt portion 27B may be formed by a removal process. The sliding surface 28a may be a surface that has not been removed. After the casting or forging process, the stepped surface 29a and the facing surface 29b of the recess 29 are formed by a removal process.

The engine piston 25 of the fifth embodiment exerts the following effects in addition to the effects of the engine piston 25 of any of the first to third embodiments.

The engine piston 25 of the fifth embodiment is made of metal. The engine piston 25 includes a piston head portion 26, a pair of piston skirt portions 27, and a pair of rib portions 31. That is, the piston head portion 26, the pair of piston skirt portions 27, and the pair of rib portions 31 are made of metal. The engine piston 25 is formed by casting or forging. That is, the piston head portion 26, the pair of piston skirt portions 27, and the pair of rib portions 31 are formed by casting or forging. Further, the stepped surface 29a and the facing surface 29b of the recess 29 are formed by the removal process. This facilitates the molding of the recesses 29 in the pair of piston skirts 27. This makes it easier to adjust the circumferential length of the recess 29 and design the circumferential length of the sliding surface 28a.

<Sixth Embodiment>
Hereinafter, the engine piston 25 according to the sixth embodiment of the present invention will be described with reference to FIG. The engine piston 25 of the sixth embodiment includes the following configurations in addition to the configurations of any of the first to fifth embodiments. Here, as an example of the engine 10, a 4-stroke engine applied to a motorcycle will be described. A 4-stroke engine is an engine that repeats an intake stroke, a compression stroke, a combustion stroke (expansion stroke), and an exhaust stroke for each cylinder. The left-right direction, the up-down direction, and the front-rear direction in the following description are all directions based on the motorcycle on which the engine 10 is mounted. However, these directions are the directions when a motorcycle having at least one front wheel and at least one rear wheel is placed on a horizontal ground. That is, in the description of the specific example of the present embodiment, the front-rear direction, the left-right direction, and the up-down direction are the front-rear direction of the vehicle, the left-right direction of the vehicle, and the up-down direction of the vehicle as seen from the rider riding the motorcycle 1, respectively. That is. Further, the arrows F, arrow B, arrow U, arrow D, arrow L, and arrow R in each drawing of the present application represent the forward direction, the rear direction, the upward direction, the downward direction, the left direction, and the right direction, respectively. ..

As shown in FIG. 8, the engine 10 has a crankcase portion 16, a cylinder portion 15, an engine piston 25, a connecting rod 46, and a crankshaft 47.

The cylinder portion 15 has a cylinder body 17, a cylinder head 18, and a head cover 19. The cylinder portion 15 is configured by connecting the cylinder body 17, the cylinder head 18, and the head cover 19 in this order. The cylinder portion 15 of Specific Example 1 is made of metal. That is, the cylinder body 17, the cylinder head 18, and the head cover 19 are made of metal. The cylinder body 17 and the cylinder head 18 correspond to the cylinder portion 15 of the present invention. The cylinder axis 15X direction is a direction along the vertical direction. For example, the engine 10 is provided in a motorcycle so that the cylinder axis 15X direction is a direction along the vertical direction.

The crankcase portion 16 is configured to be connected to the cylinder body 17 of the cylinder portion 15. The crankcase portion 16 accommodates the crankshaft 47 and the connecting rod 46. The engine oil LO is stored in the lower part of the internal space of the crankcase portion 16. The crankshaft 47 is rotatably provided on the crankcase portion 16. As shown in FIG. 8 (1), in the engine 10 which is not an offset crank type, the crankshaft 47 is arranged at a position where the crankshaft line Lc passes through the cylinder axis line 15X. As shown in FIG. 8 (2), in the offset crank type engine 10 in which the engine piston 25 of the sixth embodiment is arranged, the crankshaft 47 is arranged at a position where the crankshaft line Lc does not pass through the cylinder axis line 15X. Will be done. The engines 10 in which the engine pistons 25 of the first to fifth embodiments are arranged are the non-offset crank type engine 10 shown in FIG. 8 (1) and the offset crank type engine shown in FIG. 8 (2). Includes 10.

The engine 10 has an intake valve 35, an exhaust valve 36, an intake passage portion 38, and an exhaust passage portion 39. The cylinder head 18 is provided with an intake port 15b for communicating the combustion chamber 15a and the cylinder head intake passage portion 15d, which will be described later. The cylinder head 18 is provided with an exhaust port 15c for communicating the combustion chamber 15a and the cylinder head exhaust passage portion 15e, which will be described later. The cylinder head 18 has a cylinder head intake passage portion 15d connected to the intake port 15b. The cylinder head 18 has a cylinder head exhaust passage portion 15e connected to the exhaust port 15c, so that the intake valve 35 has an axis line extending backward along the intake port 15b and the cylinder head intake passage portion 15d. Is placed in. The intake valve 35 opens and closes the intake port 15b by reciprocating along its axis. The intake valve 35 opens and closes the intake port 15b to communicate and shut off the combustion chamber 15a and the cylinder head intake passage portion 15d. The exhaust valve 36 is arranged at the exhaust port 15c and the cylinder head exhaust passage portion 15e so that its axes are directed in the forward direction while being along the vertical direction. The exhaust valve 36 opens and closes the exhaust port 15c by reciprocating along its axis. The exhaust valve 36 opens and closes the exhaust port 15c to communicate and shut off the combustion chamber 15a and the cylinder head exhaust passage portion 15e. The intake passage portion 38 is connected to the cylinder head intake passage portion 15d. The exhaust passage portion 39 is connected to the cylinder head exhaust passage portion 15e. A throttle valve (not shown) is arranged inside the intake passage portion 38.

The intake valve 35 and the crankshaft 47 are interlocked with each other via an interlocking mechanism (not shown). Similarly, the exhaust valve 36 and the crankshaft 47 are interlocked with each other via an interlocking mechanism (not shown).

The fuel injection device (not shown) is arranged in the cylinder head intake passage portion 15d or the intake passage portion 38, and performs a fuel injection operation in the combustion stroke. When the fuel injection operation is executed, the fuel injection device injects fuel. In the intake stroke, the cylinder head intake passage portion 15d and the intake passage portion 38 introduce an air-fuel mixture containing air and fuel into the combustion chamber 15a. The ignition device (not shown) is arranged in the combustion chamber 15a and performs an ignition operation in the combustion stroke. When the ignition operation is executed, the ignition device ignites the air-fuel mixture in the combustion chamber 15a. In the compression stroke, the engine piston 25 compresses the air-fuel mixture in the combustion chamber 15a. In the exhaust stroke, the cylinder head exhaust passage portion 15e and the exhaust passage portion 39 discharge the burned exhaust gas to the outside of the combustion chamber 15a.

The fuel injection device repeatedly executes the fuel injection operation. The igniter repeatedly executes the ignition operation. That is, the engine 10 repeats the intake stroke, the compression stroke, the combustion stroke, and the exhaust stroke. As a result, in each cylinder of the engine 10, the engine piston 25 reciprocates through the cylinder hole 17a along the cylinder axis 15X. Then, the connecting rod 46 transmits the reciprocating movement of the engine piston 25 as a rotational force of the crankshaft 47 via the piston pin 45. The rotation of the crankshaft 47 causes the engine 10 to generate power. The power of the engine 10 is transmitted to the rear wheels, which are the driving wheels of the motorcycle, via a transmission (not shown). The crankshaft 47 may be connected to a starter motor (not shown). The starter motor rotates the crankshaft 47. The rotational force of the crankshaft 47 is transmitted to the engine piston 25 by the connecting rod 46, and the engine piston 25 reciprocates along the cylinder axis 15X.

The engine piston 25 reciprocates through the cylinder hole 17a in the cylinder axis 15X direction while slightly moving in the radial direction of the cylinder hole 17a. When the first piston skirt portion 27A and the second piston skirt portion 27B reciprocate in the cylinder axis 15X direction, the sliding surface 28a of the first piston skirt portion 27A becomes an inner wall surface 15f and / or the second piston skirt portion 27B. The sliding surface 28a of the above comes into contact with the inner wall surface 15f. For example, in the compression stroke and the exhaust stroke, when the first piston skirt portion 27A reciprocates in the cylinder axis 15X direction, the sliding surface 28a of the first piston skirt portion 27A comes into contact with the inner wall surface 15f. Further, for example, in the intake stroke and the combustion stroke, when the second piston skirt portion 27B reciprocates in the direction of the cylinder axis 15X, the sliding surface 28a of the second piston skirt portion 27B comes into contact with the inner wall surface 15f.

The engine piston 25 of the sixth embodiment exerts the following effects in addition to the effects of the engine piston 25 of any one of the first to fifth embodiments.

The engine 10 in which the engine piston 25 of the sixth embodiment is arranged is a so-called offset crank type engine 10 having a crankshaft 47 arranged at a position where its central axis Lc does not pass through the cylinder axis 15X. In the offset crank type engine, the timing of the top dead center of the crankshaft 47 and the timing of the top dead center of the piston do not match. Therefore, it is possible to make a difference between the stroke time of the compression stroke and the stroke time of the expansion stroke, and it is possible to expand the piston earlier or to lengthen the time that the piston stays at the top dead center after ignition. Further, the engine 10 which is not an offset crank type is an engine 10 having a crankshaft 47 arranged at a position where its central axis Lc passes through a cylinder axis 15X. In the offset crank type engine 10, the load acting on the pair of piston skirt portions 27 in the expansion stroke is reduced as compared with the engine 10 which is not the offset crank type. In the offset crank type engine 10, even if the load acting on the pair of piston skirts 27 is reduced in the expansion stroke, the length of the outer peripheral surfaces 28 of the pair of piston skirts 27 in the circumferential direction is increased from the viewpoint of rigidity design. It may not be possible to make it smaller. Even in such a case, the length of the outer peripheral surfaces 28 of the pair of piston skirts 27 in the circumferential direction is secured by adjusting the arrangement of the recesses 29 and the length of the facing surfaces of the recesses 29 in the circumferential direction. The area of the oil film can be designed.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and specific examples thereof, and various modifications can be made as long as they are described in the claims.

10: Engine, 15: Cylinder part, 15a: Combustion chamber, 15f: Inner wall surface, 15X: Cylinder axis, 17a: Cylinder hole, 25: Piston for engine, 26: Piston head part, 27: Pair of piston skirt parts, 27A : 1st piston skirt part, 27A1: 1st end part of 1st piston skirt, 27A2: 2nd end part of 1st piston skirt, 27B: 2nd piston skirt part, 27B1: 1st end part of 2nd piston skirt, 27B2: Second piston skirt second end, 28, 28A, 28B: outer peripheral surface, 29, 29A1, 29A2, 29B1, 29B2: recess, 29a: stepped surface, 29b: facing surface, 31: pair of rib portions, 31A: first 1 rib part, 31B: 2nd rib part, 46: conrod, 47: crank shaft, CL: gap, LO: engine oil

Claims

It is arranged in a columnar cylinder hole formed inside the cylinder portion of the engine, and the cylinder hole is provided so as to be reciprocating in the direction of the cylinder axis, which is the axis thereof, and a combustion chamber formed inside the cylinder portion. And the piston head part that forms a part of
(A) A th-order which is connected to the piston head portion and is provided so as to be reciprocally movable in the cylinder axis direction, and the shape when viewed in the cylinder axis direction is an arc shape along the inner wall surface of the cylinder hole. The first piston skirt portion, which is a one-piston skirt portion and in which a gap through which engine oil can enter is formed between the outer peripheral surface of the first piston skirt portion and the inner wall surface of the cylinder hole, and ( b) A th-order which is connected to the piston head portion and is provided so as to be reciprocally movable in the cylinder axis direction, and the shape when viewed in the cylinder axis direction is an arc shape along the inner wall surface of the cylinder hole. A pair of two-piston skirt portions including the second piston skirt portion in which a gap through which engine oil can enter is formed between the outer peripheral surface of the second piston skirt portion and the inner wall surface of the cylinder hole. With the piston skirt
A crankshaft that is connected to both ends of the piston head portion and the pair of piston skirt portions in the circumferential direction, and that the engine has reciprocating movement of the piston head portion and the pair of piston skirt portions in the cylinder axis direction. A pair of ribs, in which the connecting rod transmitted as rotation is oscillatingly connected via a piston pin,
It is an engine piston equipped with
At least one of the first piston skirt portion and the second piston skirt portion
At both ends of the first piston skirt portion or at least one of the second piston skirt portions in the circumferential direction, the first piston skirt portion is provided so as to be recessed toward the cylinder axis in the radial direction of the cylinder hole orthogonal to the cylinder axis. Has a recess and
The outer peripheral surface of at least one of the first piston skirt portion or the second piston skirt portion having the recess is
A sliding surface that forms an oil film between the cylinder hole and the inner wall surface of the cylinder hole due to engine oil that has entered between the cylinder hole and the inner wall surface of the cylinder hole.
Two surfaces forming the recess, (i) connected to the sliding surface and arranged along the radial direction of the cylinder hole and the axial direction of the cylinder, and the sliding in the radial direction of the cylinder hole. A stepped surface forming a step formed at a depth capable of cutting an oil film between the moving surface and the inner wall surface of the cylinder hole, and (ii) the circumference of the cylinder hole connected to the stepped surface. A piston for an engine, which is arranged along the direction and the direction of the cylinder axis, and includes a facing surface facing the inner wall surface of the cylinder hole.
The recess is
Both ends of the first piston skirt in the circumferential direction,
Both ends of the second piston skirt in the circumferential direction, or
The engine piston according to claim 1, wherein the first piston skirt portion is provided at both ends in the circumferential direction and the second piston skirt portion is provided at both ends in the circumferential direction.
The pair of ribs
It is connected to the first end of the first piston skirt, which is one end in the circumferential direction of the inner peripheral surface of the first piston skirt, and one of the circumferential directions of the inner peripheral surface of the second piston skirt. The first rib part connected to the first end part of the second piston skirt, which is the end part,
It is connected to the second end of the first piston skirt, which is the other end of the inner peripheral surface of the first piston skirt in the circumferential direction, and the other end of the inner peripheral surface of the second piston skirt in the circumferential direction. Including a second rib portion connected to the second end portion of the second piston skirt, which is an end portion,
The recess is the first end of the first piston skirt, the first end of the second piston skirt, the second end of the first piston skirt, or the recess when viewed in the radial direction through the recess. The engine piston according to claim 1 or 2, wherein the second piston skirt is provided so as to overlap at least one of the second end portions.
The piston head portion, the pair of piston skirt portions, and the pair of rib portions are formed by casting or forging, and the stepped surface and the facing surface of the recess are not removed. The engine piston according to any one of claims 1 to 3.
The engine piston according to any one of claims 1 to 3, wherein the stepped surface and the facing surface of the recess are formed by a removal process.
The engine piston according to any one of claims 1 to 5, wherein the crankshaft is arranged at a position where the central shaft does not pass through the cylinder axis.