internal combustion engine

Abstract

To efficiently cool down a piston by oil while providing a piston of high strength and light weight.SOLUTION: An internal combustion engine includes nozzle (21) for supplying oil toward a back side of a piston (14) from a crank case (16), wherein a pair of pin bosses (32) in which a piston pin hole (32h) is formed, a pair of piston skirts (33) that face in a direction perpendicular to an axial line (C1) of the piston pin hole (32h), and a connection rib (37) connecting the pin boss (32) and the piston skirt (33) are provided on a back side of a piston head (31) of the piston (14). Reinforcement ribs (41a, 41b) connecting the pair of pin bosses (32) within a width of the pair of pin bosses (32) are provided on the back side of the piston head (31). The reinforcement ribs (41a, 41b) each have a recessed part (41x) that recesses on the piston head (31) side from the axial line (C1) of the piston pin hole (32h).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an internal combustion engine. [Background technology]

[0002] A known internal combustion engine for a saddle-ride vehicle such as a motorcycle is equipped with an oil jet nozzle that supplies oil from the crankcase toward the back side of the piston, and the back side of the piston is provided with a pair of pin bosses in which piston pin holes are formed, and a pair of piston skirts that face each other in a direction perpendicular to the axis of the piston pin holes (for example, Patent Document 1). Patent Document 1 describes a piston that has a rib provided on the IN side (intake port side) of the pin boss. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-137003 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, if the piston is reinforced by providing ribs as exemplified in Patent Document 1 and the piston is made thinner, it becomes easier to obtain a piston that is both strong and lightweight. However, in the case of a configuration in which the piston is cooled by an oil jet as described in Patent Document 1, it is difficult for the oil from the nozzle to pass over the ribs, making it difficult to uniformly cool the back surface of the piston over a wide area. The present invention has been made in view of the above circumstances, and has as its object to provide a piston that is strong and lightweight while effectively cooling the piston with oil. [Means for solving the problem]

[0005] In an internal combustion engine having a nozzle for supplying oil from a crankcase toward a back side of a piston, the back side of the piston being provided with a pair of pin bosses in which a piston pin hole is formed, a pair of piston skirts facing each other in a direction perpendicular to the axis of the piston pin hole, and a connecting rib connecting the pin bosses and the piston skirts, the back side of the piston head is provided with a reinforcing rib connecting the pair of pin bosses within the width of the pair of pin bosses, and the reinforcing rib has a recessed portion recessed toward the piston head side relative to the axis of the piston pin hole. the reinforcing rib includes a first reinforcing rib extending parallel to the axis of the piston pin hole or in a direction that can be considered to be parallel, and a second reinforcing rib connecting both ends of the first reinforcing rib to the pair of pin bosses and increasing in height the farther away from the first reinforcing rib, the first reinforcing rib and the second reinforcing rib are connected by a gently curved shape, the first reinforcing rib extends with a constant width and height along the axis of the piston pin hole, the piston is provided with oil return holes that are spaced apart in the circumferential direction and connect to an oil ring groove provided in the piston, the first reinforcing rib and the second reinforcing rib are formed closer to the piston head than a piston skirt side end of the oil ring groove, and are provided at positions that do not overlap with the oil return holes in a side cross-sectional view that is along the axis of the piston pin hole and passes through the cylinder axis of a cylinder section that accommodates the piston An internal combustion engine is provided. [Effects of the Invention]

[0006] This allows for a strong and lightweight piston, while still allowing the piston to be effectively cooled by oil. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view of an internal combustion engine according to an embodiment of the present invention, taken along the axial direction of a crankshaft. [Figure 2] FIG. [Figure 3] FIG. [Figure 4] FIG. 4 is a view taken along the line IV-IV in FIG. 3. [Figure 5] FIG. 4 is a cross-sectional view of FIG. 3 . [Figure 6] FIG. 10 is a diagram showing a reinforcing rib of a first modified example together with the surrounding configuration. [Figure 7] FIG. 10 is a diagram showing a reinforcing rib of a second modified example together with the surrounding configuration. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] [Embodiment Mode] FIG. 1 is a cross-sectional view of an internal combustion engine 10 according to an embodiment of the present invention, taken along the axial direction of a crankshaft 11. As shown in FIG. The internal combustion engine 10 is a four-stroke engine mounted on a saddle-ride vehicle such as a motorcycle. The internal combustion engine 10 accommodates a piston 14 in a cylinder section 13 of an engine block. One end of a connecting rod 15 is connected to the piston 14 via a piston pin 14p. The internal combustion engine 10 accommodates a crankshaft 11 connected to the other end of the connecting rod 15 in a crankcase 16. A cylinder sleeve (also referred to as a cylinder liner) 13s is press-fitted into the cylinder section 13, although the cylinder sleeve 13s may not be press-fitted. Furthermore, one end of the connecting rod 15 corresponds to the "small end of the connecting rod 15," and the other end of the connecting rod 15 corresponds to the "big end of the connecting rod 15."

[0010] A cylinder head 17 is connected to the upper surface of the cylinder portion 13, and a combustion chamber 18 is formed between the cylinder head 17 and the piston 14. The cylinder head 17 is formed with an intake port 19 and an exhaust port 20 that open to the combustion chamber 18. The cylinder head 17 is also provided with an intake valve 19v that opens and closes the intake port 19, and an exhaust valve 20v that opens and closes the exhaust port 20. In FIG. 1, the intake port 19 is indicated by "IN" and the exhaust port 20 is indicated by "EX."

[0011] The internal combustion engine 10 is provided with a nozzle 21 that supplies oil from the crankcase 16 toward the back side of the piston 14. The nozzle 21 is a nozzle for an oil jet (also called a piston jet), and spraying oil from the nozzle 21 promotes cooling of the piston 14 and lubrication of various parts. The nozzle 21 sprays oil toward an area on the exhaust port 20 side (EX side) behind the piston 14. The oil sprayed from the nozzle 21 is engine oil. Note that the nozzle 21 shown in FIG. 1 and the figures described below is a schematic illustration, and the position of the nozzle 21, etc., is not limited to the configuration shown in the figures.

[0012] With respect to the cylinder axis L0 passing through the center of the cylinder section 13, the intake port 19 side of the internal combustion engine 10 is located at the rear side of the internal combustion engine 10 and at the rear side of the vehicle body, and the exhaust port 20 side is located at the front side of the internal combustion engine 10 and at the front side of the vehicle body. However, the position and shape of each port 19, 20, etc. may be changed as appropriate depending on the arrangement of the internal combustion engine 10, for example, the intake port 19 side may be located above the internal combustion engine 10 and above the vehicle body, and the exhaust port 20 side may be located below the internal combustion engine 10 and below the vehicle body. Furthermore, the vehicle equipped with the internal combustion engine 10 is not limited to a saddle-ride vehicle, and may be any vehicle. Furthermore, the internal combustion engine 10 may be used for purposes other than vehicle applications.

[0013] In Figure 1 and the figures described below, the axis passing through the center of the piston pin 14p is indicated by the symbol C1, and the axis passing through the center of the crankshaft 11 is indicated by the symbol C2. In the following explanation, directions will basically be explained based on the state in Figure 1. Furthermore, when explaining directions and areas based on the intake port 19 and the exhaust port 20, the intake port 19 side may be referred to as the "IN side," and the exhaust port 20 side may be referred to as the "EX side."

[0014] Fig. 2 is a side view of the piston 14. Fig. 3 is a side cross-sectional view of the piston 14. Fig. 4 is a view taken along the line IV-IV in Fig. 3, and Fig. 5 is a cross-sectional view taken along the line VV in Fig. 3. As shown in Figures 2 to 4, piston 14 includes a substantially disk-shaped piston head 31, a pair of pin bosses 32 in which piston pin holes 32h are formed, and a pair of piston skirts 33 provided on both ends (IN side and EX side) of piston pin hole 32h in a direction perpendicular to the axis of piston pin hole 32h. Valve relief surfaces 31a, 31b are provided on the ceiling surface of piston head 31 to avoid contact with exhaust valve 20v and intake valve 19v. Piston pin hole 32h connects piston 14 and connecting rod 15 by inserting piston pin 14p through it while connecting rod 15 is positioned. The axis of piston pin hole 32h coincides with axis C1 of piston pin 14p, and is therefore referred to as "axis C1 of piston pin hole 32h" or "axis C1."

[0015] 3, the pair of pin bosses 32 have a shape that widens toward the piston head 31. More specifically, each pin boss 32 has a shape that widens in the left-right direction in FIG. 3 from a position corresponding to the axis C1 of the piston pin hole 32h toward the piston head 31 above.

[0016] 2 and 3, a plurality of ring grooves 34a, 34b, and 34c into which a plurality of piston rings are fitted are provided on the side surface of the piston head 31. The first ring groove 34a located at the top is a top ring groove into which a top ring is fitted. The second ring groove 34b below the first ring groove 34a is a second ring groove 34b into which a second ring is fitted. Furthermore, the third ring groove 34c below the second ring groove 34b is an oil ring groove into which an oil ring is fitted. As shown in FIG. 3, each piston skirt 33 is provided with oil return holes 35 spaced apart in the circumferential direction, the oil return holes 35 being connected to the third ring groove 34c, which is an oil ring groove.

[0017] 4, the piston 14 is integrally provided with a plurality of connecting ribs 37 that connect each pin boss 32 to each piston skirt 33. The pair of pin bosses 32 has a shape that widens toward the piston head 31, and the widened portions are connected to each piston skirt 33 via the connecting ribs 37. Therefore, the pin bosses 32 and piston skirt 33 can be reinforced by the connecting ribs 37. The piston 14 of this configuration is formed to be symmetrical with respect to a plane passing through the axis C1 of the piston pin hole 32h. Therefore, the pin bosses 32 and the connecting ribs 37 also have bilaterally symmetrical shapes with respect to the plane passing through the axis C1. Note that any part of the piston 14 may have a shape that is not bilaterally symmetrical with respect to the plane passing through the axis C1.

[0018] As shown in FIGS. 3 and 4, reinforcing ribs 41a and 41b that connect at least one pair of pin bosses 32 are integrally provided on the back surface of the piston head 31. 3, the reinforcing ribs 41a, 41b are provided at an interval within the width W1 of the pair of pin bosses 32. As shown in Figures 3 and 4, one reinforcing rib 41a is formed as a rib that connects one end of at least one pair of pin bosses 32 in the IN-EX direction (EX-side end portions). The other reinforcing rib 41b is formed as a rib that connects the other end of at least one pair of pin bosses 32 in the IN-EX direction (IN-side end portions). Here, the IN-EX direction is the direction in which the intake port 19 and the exhaust port 20 are aligned, and is a term used appropriately by those skilled in the art. Note that the IN-EX direction of the pin boss 32 can also be expressed as the width direction of the pin boss 32, or as the direction perpendicular to the axis C1 of the pin boss 32, etc. These reinforcing ribs 41a and 41b are symmetrical with respect to a plane passing through the axis C1, and therefore, the rib 41a will be mainly described in detail below, and a duplicated description of the rib 41b will be omitted.

[0019] As shown in Fig. 4, the reinforcing ribs 41a, 41b are formed in a rib shape that extends parallel to the axis C1 with the same width within the width of the pin boss 32 when viewed from below the piston 14 shown in Fig. 4. Furthermore, these reinforcing ribs 41a, 41b are arranged on either side of the axis C1, on the IN side and the EX side. Note that the width of the reinforcing ribs 41a, 41b may be changed as appropriate. As shown in Figure 5, the reinforcing rib 41a includes a first reinforcing rib 41x that extends parallel to the axis C1 of the piston pin hole 32h in a side view of the piston 14, and a second reinforcing rib 41y that connects both ends of the first reinforcing rib 41x to a pair of pin bosses 32 and that increases in height as it moves away from the first reinforcing rib 41x. First reinforcing rib 41x constitutes the recessed portion (which can also be called a valley portion) of reinforcing rib 41a that is recessed most toward the piston head 31 relative to axis C1 of piston pin hole 32h. Second reinforcing rib 41y constitutes a rib that protrudes further toward the piston pin hole 32h (the opposite side of piston head 31) than first reinforcing rib 41x. These reinforcing ribs 41x and 41y form reinforcing rib 41a as a rib that forms an arch shape that protrudes toward the back of piston head 31.

[0020] By forming the rib in such an arch shape, the reinforcing rib 41a and the pin bosses 32 are connected over a wide area, and a low recessed portion (corresponding to the first reinforcing rib 41x) can be provided between the pair of pin bosses 32. As shown in Fig. 3, when oil is supplied from the nozzle 21 to the exhaust side behind the piston 14, the low-height first reinforcing rib 41x makes it easier for the oil to climb over the reinforcing rib 41a. This allows the oil to flow smoothly from the exhaust side to the intake side of the piston 14, as shown by arrow D in Fig. 3. Therefore, the oil that cools the exhaust side of the piston 14 can be used to cool the intake side of the piston 14.

[0021] FIG. 5 is a schematic enlarged view of the region α where the reinforcing rib 41a and the pin boss 32 are connected. As shown in this figure, the first reinforcing rib 41x and the second reinforcing rib 41y are connected by a gently curved surface shape Sa, and the second reinforcing rib 41y and the pin boss 32 are also connected by a gently curved surface shape Sb. This prevents stress concentration at the boundaries between the first reinforcing rib 41x, the second reinforcing rib 41y, and the pin boss 32, and allows oil to flow smoothly through the boundaries. The curved surface shape Sa is a shape that connects the first reinforcing rib 41x and the second reinforcing rib 41y with a concave curved surface, and the curved surface shape Sb is a shape that connects the second reinforcing rib 41y and the pin boss 32 with a concave curved surface. However, the curved surfaces Sa and Sb may be changed as appropriate as long as oil can flow smoothly through the boundaries.

[0022] 3, the reinforcing rib 41a and the back surface of the piston head 31 are also connected by a gently curved surface Sc. This prevents stress concentration at the boundary between the reinforcing rib 41a and the piston head 31 and allows oil to flow smoothly along each boundary. Note that the curved surface Sc is a concave curved surface that connects the reinforcing rib 41a and the back surface of the piston head 31, but the curved surface Sc may be changed as appropriate as long as oil can flow smoothly along the boundary. Furthermore, since the reinforcing rib 41b has the same shape as the reinforcing rib 41a, the same effect as that obtained by the reinforcing rib 41a can be obtained.

[0023] 2, internal combustion engine 10 of this embodiment includes nozzle 21 that supplies oil from crankcase 16 toward the back side of piston 14, and is provided on the back side of piston head 31 with a pair of pin bosses 32 in which piston pin holes 32h are formed, a pair of piston skirts 33 that face each other in a direction perpendicular to axis C1 of piston pin hole 32h, and a connecting rib 37 that connects pin bosses 32 and piston skirt 33. Furthermore, reinforcing ribs 41a, 41b that connect the pair of pin bosses 32 within width W1 of pair of pin bosses 32 are provided on the back side of piston 14, and reinforcing ribs 41a, 41b have first reinforcing ribs 41x that form recesses that are recessed toward piston head 31 relative to axis C1 of piston pin hole 32h.

[0024] According to this configuration, the piston 14 can be reinforced by the connecting rib 36 and the reinforcing ribs 41a, 41b, allowing the piston head 31 and other components to be made thinner, thereby reducing the weight of the piston 14. Furthermore, oil supplied to the back side of the piston 14 can easily overcome the reinforcing ribs 41a, 41b, particularly the first reinforcing rib 41x, making it easier for the oil to uniformly cool the back side of the piston 14 over a wide area. This allows the piston 14 to be effectively cooled by the oil while still achieving a high strength and lightweight design. Furthermore, because the piston 14 can more easily achieve the strength required, it is also possible to increase the degree of freedom in the shape of the piston 14.

[0025] 3, the pair of pin bosses 32 are formed in a shape that widens toward the piston head 31. With this configuration, the widened portions of the pin bosses 32 are reinforced with the reinforcing ribs 41a, 41b, thereby effectively increasing the strength of the pin bosses 32 and their surrounding areas. This makes it easier to obtain a high-strength, lightweight piston 14.

[0026] 5, the reinforcing ribs 41a, 41b are formed in an arch shape that protrudes toward the rear of the piston head 31. This configuration allows oil to easily move over the reinforcing ribs 41a, 41b, which is advantageous for cooling the piston 14. Furthermore, since the reinforcing ribs 41a, 41b and the pin boss 32 are connected by the gently curved surface shape Sb, stress concentration at the boundary between the reinforcing ribs 41a, 41b and the pin boss 32 can be suppressed, which is advantageous for increasing the strength of the piston 14 and also makes it less likely that the flow of oil will be obstructed.

[0027] The reinforcing ribs 41a, 41b include a first reinforcing rib 41x extending parallel to the axis C1 of the piston pin hole 32h and a second reinforcing rib 41y extending away from the back of the piston head 31 as the distance from both ends of the first reinforcing rib 41x increases, and the first reinforcing rib 41x and the second reinforcing rib 41y are connected by a gently curved surface shape Sa. This configuration allows oil to easily climb over the first reinforcing rib 41x, and the second reinforcing rib 41y can enhance the reinforcing effect of the reinforcing ribs 41a, 41b. Furthermore, stress concentration at the boundary between the first reinforcing rib 41x and the second reinforcing rib 41y can be suppressed, which is advantageous for increasing the strength of the piston 14 and also makes it less likely to impede the flow of oil. Note that first reinforcing rib 41x is not limited to a shape extending parallel to axis C1 of piston pin hole 32h, and may be a rib shape extending in a direction that can be regarded as parallel to axis C1 of piston pin hole 32h. Furthermore, the shapes of each of ribs 41x, 41y may be changed as appropriate.

[0028] 4, the reinforcing ribs 41a, 41b include a reinforcing rib 41a connecting one ends of at least one pair of pin bosses 32 in the inlet-exit direction and a reinforcing rib 41b connecting the other ends of at least one pair of pin bosses 32 in the inlet-exit direction, and each reinforcing rib 41a, 41b is arranged parallel to the axis C1 of the piston pin hole 32h. With this configuration, the pin boss 32 can be efficiently reinforced by the multiple reinforcing ribs 41a, 41b, making it easier to obtain a piston 14 that is stronger and lighter.

[0029] 4 and 5, the first reinforcing rib 41x extends with a constant width and height along the axis C1 of the piston pin hole 32h. This configuration makes it easier to equalize the temperature distribution of the first reinforcing rib 41x, and makes it easier to properly cool the piston 14 through contact between the first reinforcing rib 41x and oil.

[0030] 3, the reinforcing ribs 41a, 41b are connected to the back surface of the piston head 31 by a gently curved surface Sc. This configuration allows oil to flow smoothly at the boundaries between the reinforcing ribs 41 and the piston head 31, and also suppresses stress concentration at the boundaries, making it easier to obtain a stronger and lighter piston 14.

[0031] 3, the reinforcing ribs 41a, 41b are formed closer to the piston head 31 than the piston skirt side end of the oil ring groove 34c provided in the piston 14. With this configuration, the reinforcing ribs 41a, 41b do not get in the way when drilling the oil return hole 35, improving workability in drilling the hole and increasing the degree of freedom in arranging the oil return hole 35.

[0032] 4, two reinforcing ribs 41a, 41b are arranged parallel to each other within the width of the pin boss 32. This configuration allows the reinforcing ribs 41a, 41b to be provided so as to avoid one end of the connecting rod 15, and the multiple reinforcing ribs 41a, 41b can enhance the reinforcing effect. Therefore, the gap between the connecting rod 15 and the piston 14 can be reduced while enhancing the reinforcing effect.

[0033] The above-described embodiment shows one aspect of the present invention, and the present invention is not limited to the above-described embodiment, and the configuration of details, etc. may be changed as appropriate. FIG. 6 is a diagram showing a reinforcing rib 41a of the first modified example together with the surrounding structure. The reinforcing rib 41a of the first modified example differs from the above embodiment in that, in a side cross-sectional view perpendicular to the axis C1 of the piston pin hole 32h, the center PT of the reinforcing rib 41a (corresponding to the position overlapping with the cylinder axis L0) forms the point that is most recessed toward the piston 14, and the rib height gradually increases with increasing distance from this center PT, so that the entire reinforcing rib 41a is formed in a convex arc-shaped arch shape.

[0034] The height of the rib at and around the position PT is set to an appropriate height that allows oil from the nozzle 21 to flow smoothly from the EX side to the IN side of the piston 14. The position PT and its surrounding area correspond to the "recessed portion recessed toward the piston head (31) from the axis (C1) of the piston pin hole (32h)" of the present invention. In the first modified example, similar to the above embodiment, various effects can be obtained, such as the ability to promote cooling of the piston 14 by oil while obtaining a high-strength, lightweight piston 14. In the first modified example, the reinforcing rib 41a can be easily formed into a smoother shape with fewer steps, which is expected to have the effect of further suppressing localized stress concentration on the reinforcing rib 41a and allowing oil to flow more smoothly. In the first modified example, the reinforcing rib 41a and the pin boss 32 are also connected by a gently curved surface shape Sb, and the reinforcing rib 41a and the reinforcing rib 41b have the same shape.

[0035] FIG. 7 is a diagram showing a reinforcing rib 41a of the second modified example together with the surrounding structure. The second modified example differs from the first modified example in that the center PT of the reinforcing rib 41a is formed at a position that coincides with the back surface of the piston head 31. With this configuration, the rib height of the reinforcing rib 41a is zero at the position PT, and the rib height of the reinforcing rib 41a in the surrounding area is also reduced. This makes it less likely that the reinforcing rib 41a will obstruct the flow of oil, making it possible to further promote cooling of the piston 14 by the oil.

[0036] In the second modified example, the reinforcing rib 41a and the pin boss 32 are also connected by a gently curved surface shape Sb, and the reinforcing rib 41a and the reinforcing rib 41b have the same shape. As shown in these modified examples, the height and shape of the reinforcing ribs 41 a, 41 b may be changed as appropriate. Furthermore, the reinforcing ribs 41 a, 41 b may not have the same shape, and the number of reinforcing ribs 41 a, 41 b may be one, three, or more, as long as it is possible to obtain a high-strength, lightweight piston 14 and promote cooling of the piston 14 by oil.

[0037] Furthermore, the connection position between the connecting rib 37 and the pin boss 32 may be inside, outside, or in the middle of the pin boss 32 when viewed from the direction of the axis C1 of the piston pin 14p. The connection position between the connecting rib 37 and the piston skirt 33 may be at either end of the piston skirt 33 or at a position shifted inward from either end. The piston 14 may be manufactured by any known method, such as gravity casting, die casting, or forging. The internal combustion engine 10 to which the present invention is applicable may be either a water-cooled engine or an air-cooled engine.

[0038] [Configuration supported by the above embodiment] The above embodiment supports the following configurations.

[0039] (Configuration 1) An internal combustion engine including a nozzle that supplies oil from a crankcase toward a back side of a piston, and the back side of a piston head of the piston is provided with a pair of pin bosses in which a piston pin hole is formed, a pair of piston skirts that face each other in a direction perpendicular to the axis of the piston pin hole, and a connecting rib that connects the pin bosses and the piston skirts, and the back side of the piston head is provided with a reinforcing rib that connects the pair of pin bosses within the width of the pair of pin bosses, and the reinforcing rib has a recess that is recessed toward the piston head relative to the axis of the piston pin hole. This configuration makes it possible to obtain a piston that is strong and lightweight, while also promoting cooling of the piston by oil.

[0040] (Configuration 2) The internal combustion engine according to configuration 1, wherein the reinforcing rib has an arch shape that protrudes toward the rear of the piston head. This configuration allows the oil to easily move over the reinforcing ribs, which is advantageous for cooling the piston.

[0041] (Configuration 3) The internal combustion engine according to configuration 1 or 2, wherein the reinforcing rib and the pin boss are connected by a gently curved surface. This configuration can suppress stress concentration at the boundary between the reinforcing rib and the pin boss, which is advantageous for increasing the strength of the piston and also makes it less likely to impede the flow of oil.

[0042] (Configuration 4) An internal combustion engine described in any one of configurations 1 to 3, wherein the reinforcing rib includes a first reinforcing rib extending parallel to the axis of the piston pin hole or in a direction that can be considered to be parallel, and a second reinforcing rib connecting both ends of the first reinforcing rib to the pair of pin bosses and increasing in height as it moves away from the first reinforcing rib, and the first reinforcing rib and the second reinforcing rib are connected by a gently curved shape. This configuration allows oil to easily climb over the first reinforcing rib, and the second reinforcing rib enhances the reinforcing effect of the reinforcing rib. It also reduces stress concentration at the boundary between the first and second reinforcing ribs, which is advantageous for increasing the strength of the piston and making it less likely to impede the flow of oil.

[0043] (Configuration 5) An internal combustion engine according to any one of Configurations 1 to 4, wherein the reinforcing ribs include a reinforcing rib connecting at least one end of the pair of pin bosses in the IN-EX direction and a reinforcing rib connecting at least the other end of the pair of pin bosses in the IN-EX direction, and each reinforcing rib is disposed parallel to the axis of the piston pin hole. According to this configuration, the pin boss can be efficiently reinforced by the multiple reinforcing ribs, making it easier to obtain a piston that is stronger and lighter in weight.

[0044] (Configuration 6) The internal combustion engine according to configuration 4, wherein the first reinforcing rib extends along the axis of the piston pin hole with a constant width and height. According to this configuration, the temperature distribution of the first reinforcing rib can be more easily equalized, and the piston can be more easily cooled appropriately due to contact between the first reinforcing rib and the oil.

[0045] (Configuration 7) The internal combustion engine according to any one of configurations 1 to 6, wherein the reinforcing rib and the back surface of the piston head are connected by a gently curved surface. This configuration allows oil to flow smoothly at the boundary between the reinforcing rib and the piston head, and also suppresses stress concentration at the boundary, making it easier to obtain a piston that is stronger and lighter.

[0046] (Configuration 8) An internal combustion engine according to any one of configurations 1 to 7, wherein the piston includes an oil ring groove and an oil return hole provided in the oil ring groove, and the reinforcing rib is formed closer to the piston head than the piston skirt side end of the oil ring groove. According to this configuration, the reinforcing rib does not get in the way when drilling the oil return hole, improving the workability of drilling the hole and increasing the degree of freedom in arranging the oil return hole.

[0047] (Configuration 9) The internal combustion engine according to any one of configurations 1 to 8, wherein the reinforcing ribs are arranged in two parallel rows within the width of the pin boss. This configuration makes it possible to reduce the gap between the connecting rod and the piston while enhancing the reinforcing effect of the reinforcing rib.

[0048] (Configuration 10) The internal combustion engine according to any one of configurations 1 to 9, wherein the pair of pin bosses have a shape that widens toward the piston head. According to this configuration, the expanded portion of the pin boss is reinforced with the reinforcing rib, thereby effectively increasing the strength of the pin boss and its surrounding area. [Explanation of symbols]

[0049] 10 Internal combustion engine 11 Crankshaft 12 Engine block 13 Cylinder section 14 Piston 14p Piston pin 15 Connecting rod 16 Crankcase 17 Cylinder head 18 Combustion chamber 19 Intake port 19v intake valve 20 exhaust port 20v exhaust valve 21 nozzles 31 Piston head 32 Pin boss 32h Piston pin hole 33 Piston skirt 34c 3rd ring groove (oil ring groove) 35 Oil return hole 36,37 Connecting rib 41a, 41b Reinforcement rib 41x First Reinforcement Rib 41y Second reinforcing rib C1 axis L0 Cylinder axis Sa,Sb,Sc curved shape

Claims

1. An internal combustion engine including a nozzle (21) for supplying oil from a crankcase (16) toward a back side of a piston (14), and provided on a back side of a piston head (31) of the piston (14) with a pair of pin bosses (32) in which a piston pin hole (32h) is formed, a pair of piston skirts (33) facing each other in a direction perpendicular to an axis (C1) of the piston pin hole (32h), and a connecting rib (37) connecting the pin bosses (32) and the piston skirts (33), Reinforcing ribs (41 a, 41 b) are provided on the back of the piston head (31) within the width of the pair of pin bosses (32) to connect the pair of pin bosses (32), The reinforcing ribs (41a, 41b) have recessed portions (41x) recessed toward the piston head (31) from the axis (C1) of the piston pin hole (32h), The reinforcing ribs (41a, 41b) include a first reinforcing rib (41x) extending parallel to or in a direction that can be considered parallel to an axis (C1) of the piston pin hole (32h), and a second reinforcing rib (41y) connecting both ends of the first reinforcing rib (41x) to the pair of pin bosses (32) and increasing in height as it moves away from the first reinforcing rib (41x), The first reinforcing rib (41x) and the second reinforcing rib (41y) are connected by a gently curved surface shape, The first reinforcing rib (41x) extends along the axis (C1) of the piston pin hole (32h) with a constant width and height, The piston (14) has oil return holes (35) spaced apart in the circumferential direction and connected to an oil ring groove (34c) provided in the piston (14), The first reinforcing rib (41x) and the second reinforcing rib (41y) are formed closer to the piston head (31) than the piston skirt side end of the oil ring groove (34c), and are provided at positions that do not overlap with the oil return hole (35) in a side cross-sectional view that is along the axis (C1) of the piston pin hole (32h) and passes through the cylinder axis (L0) of the cylinder portion (13) that houses the piston (14). Internal combustion engine.

2. The reinforcing ribs (41a, 41b) have an arch shape that protrudes toward the rear of the piston head (31).

2. The internal combustion engine according to claim 1.

3. The reinforcing ribs (41a, 41b) and the pin bosses (32) are connected by a gently curved surface.

2. The internal combustion engine according to claim 1.

4. The reinforcing ribs (41a, 41b) include a reinforcing rib (41a) that connects at least one end of the pair of pin bosses (32) in the intake-exit direction, and a reinforcing rib (41b) that connects at least the other end of the pair of pin bosses (32) in the intake-exit direction, Each of the reinforcing ribs (41a, 41b) is disposed parallel to the axis (C1) of the piston pin hole (32h). An internal combustion engine according to any one of claims 1 to 3.

5. The reinforcing ribs (41a, 41b) and the back surface of the piston head (31) are connected by a gently curved surface. An internal combustion engine according to any one of claims 1 to 3.

6. At least two of the reinforcing ribs (41a, 41b) are arranged parallel to each other within the width of the pair of pin bosses (32).

5. The internal combustion engine according to claim 4.

7. The pair of pin bosses (32) are shaped to widen toward the piston head (31). An internal combustion engine according to any one of claims 1 to 3.

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