Internal combustion engine

Abstract

To inhibit wear of a piston in an offset crank mechanism.SOLUTION: An internal combustion engine includes a piston 20 and a crank shaft. One of directions that are orthogonal to both of a center axis C of the piston 20 and a rotation axis of the crank shaft is referred to as a first direction X1 and a direction opposite to the first direction X1 is referred to as a second direction X2. The rotation axis of the crank shaft is located at a position offset from the center axis C of the piston 20 in the first direction X1. The piston 20 has a third ring groove 203 and multiple oil holes 210. The oil holes 210 are arranged in a circumferential direction centered on the center axis C of the piston 20. When viewed from a direction along the center axis C of the piston 20, a total of minimum passage cross-sectional areas of the oil holes 210 located at the second direction X2 side relative to the center axis C of the piston 20 is larger than a total of minimum passage cross-sectional areas of the oil holes 210 located at the first direction X1 side relative to the center axis C of the piston 20.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] The internal combustion engine described in Patent Document 1 includes a crankshaft, a piston, and a connecting rod. The piston is cylindrical with a central axis. The piston reciprocates inside a cylinder bore, which is a cylindrical space. A first end of the connecting rod is connected to the piston. The crankshaft is connected to a second end of the connecting rod opposite to the first end. When the piston reciprocates, the motion is transmitted to the crankshaft via the connecting rod. The reciprocating motion of the piston is then converted into a rotational motion by the crankshaft.

[0003] Furthermore, the rotation axis of the crankshaft described in Patent Document 1 is not positioned on the central axis of the piston. Specifically, the rotation axis of the crankshaft is positioned at a position offset from the central axis of the piston in a direction perpendicular to both the rotation axis of the crankshaft and the central axis of the piston. In other words, the position of the crankshaft is offset from the central axis of the piston. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2008-116006 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of a crank structure that is offset from the center axis of the piston as described in Patent Document 1, friction is greater at certain points on the piston than at other points, which can lead to wear of the piston. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides an internal combustion engine including a cylindrical piston that reciprocates within a cylinder bore, a connecting rod having a first end connected to the piston, and a crankshaft that is connected to a second end of the connecting rod and converts the reciprocating motion of the piston into a rotational motion, wherein when one of directions perpendicular to both a central axis of the piston and a rotational axis of the crankshaft is defined as a first direction and a direction opposite to the first direction is defined as a second direction, the rotational axis of the crankshaft is positioned at a position shifted in the first direction with respect to the central axis of the piston, the piston has a ring groove recessed in its outer peripheral surface and extending in a ring shape centered on a central axis of the piston, and a plurality of oil holes penetrating from the inner peripheral surface of the piston to the ring groove, the oil holes are arranged side by side in a circumferential direction centered on the central axis of the piston, and when viewed from a direction along the central axis of the piston, a sum of the smallest flow path cross-sectional areas of the oil holes located on a second direction side of the central axis of the piston is larger than a sum of the smallest flow path cross-sectional areas of the oil holes located on a first direction side of the central axis of the piston.

[0007] In the above configuration, when oil is supplied to the inner peripheral surface of the piston, the oil reaches the outer peripheral surface of the piston through the oil hole. The amount of oil supplied to the outer peripheral surface of the piston is greater on the second direction side relative to the central axis than on the first direction side. In other words, piston wear can be effectively reduced in a situation where the friction of the piston on the second direction side is large due to the offset of the crankshaft. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing the positional relationship between a piston and a crankshaft of an internal combustion engine according to a first embodiment. [Diagram 2] FIG. 2 is a partial plan view of the piston of the first embodiment. [Diagram 3] FIG. 3 is a schematic end view taken along line 3-3 in FIG. [Figure 4] FIG. 4 is a schematic end view of a piston of the internal combustion engine according to the second embodiment. [Diagram 5] FIG. 5 is a schematic end view of a piston of an internal combustion engine according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] First Embodiment A first embodiment of the present invention will now be described. As shown in Fig. 1, the internal combustion engine 10 has a cylinder bore 11. The cylinder bore 11 is a cylindrical space. One side of the cylinder bore 11 is open to a crankcase. Although not shown in the figure, the internal combustion engine 10 is provided with an oil jet that supplies oil into the cylinder bore 11 from the crankcase side.

[0010] The internal combustion engine 10 also includes a piston 20, a connecting rod 21, and a crankshaft 30. The piston 20 is generally cylindrical. In a direction along a central axis C of the piston 20, one end of the piston 20 opposite the crankcase is closed. The space defined by the end face of the piston 20 and the inner wall surface of the cylinder bore 11 is a combustion chamber in which a mixture of fuel and air is burned. The piston 20 reciprocates within the cylinder bore 11 in a direction along the central axis C.

[0011] The connecting rod 21 is generally rod-shaped. Here, the dimension of the connecting rod 21 in a direction perpendicular to the extension direction is defined as the width direction. Here, the width dimension of the connecting rod 21 increases overall from the first end to the second end. The first end of the connecting rod 21 is connected to the piston 20.

[0012] The crankshaft 30 is bent multiple times. That is, the crankshaft 30 is crank-shaped. Although not shown, the crankshaft 30 has a crank journal. The crank journal rotates around the rotation axis LC. The crankshaft 30 also has a crank pin 31. The crank pin 31 is connected to the second end of the connecting rod 21. The crank pin 31 rotates on a circular trajectory P centered on the rotation axis LC in accordance with the reciprocating motion of the piston 20. The crank journal of the crankshaft 30 rotates in accordance with the rotation of the crank pin 31. That is, the crankshaft 30 converts the reciprocating motion of the piston 20 into a rotational motion. In FIG. 1, the trajectory P of the crank pin 31 is illustrated by a two-dot chain line.

[0013] An axis perpendicular to both the rotation axis LC of the crankshaft 30 and the central axis C of the piston 20 is defined as an orthogonal axis X. One of the directions along the orthogonal axis X is defined as a first direction X1, and the opposite direction to the first direction X1 is defined as a second direction X2. Here, the rotation axis LC of the crankshaft 30 is located at a position shifted in the first direction X1 with respect to the central axis C in the direction along the orthogonal axis X. That is, the position of the crankshaft 30 is offset with respect to the central axis C of the piston 20. When the piston 20 moves from the top dead center to the bottom dead center, the crankshaft 30 rotates so that the crank pin 31 passes on the second direction X2 side as viewed from the rotation axis LC. That is, the crankshaft 30 rotates clockwise in FIG. 1.

[0014] 2, the piston 20 has three ring grooves 200. The three ring grooves 200 are a first ring groove 201, a second ring groove 202, and a third ring groove 203. Each ring groove 200 is recessed in the outer circumferential surface 20A of the piston 20. Each ring groove 200 extends in an annular shape centered on the central axis C of the piston 20.

[0015] When the end face of the piston 20 farthest from the crankshaft 30 in the direction along the central axis C is defined as the top face 20B, the first ring groove 201 is located closest to the top face 20B among the three ring grooves 200. The second ring groove 202 is located on the opposite side of the first ring groove 201 to the top face 20B of the piston 20. The third ring groove 203 is located on the opposite side of the second ring groove 202 to the top face 20B of the piston 20. Piston rings are fitted in the first ring groove 201, the second ring groove 202, and the third ring groove 203. Note that the piston rings are not shown in the drawings.

[0016] As shown in Fig. 3, the piston 20 has a plurality of oil holes 210. Each oil hole 210 penetrates from the inner circumferential surface 20C of the piston 20 to the third ring groove 203. The axis along which each oil hole 210 extends is perpendicular to the central axis C. The flow passage cross section of each oil hole 210 is substantially circular. Each oil hole 210 has a constant flow passage cross-sectional area regardless of location.

[0017] In this embodiment, the piston 20 has eight oil holes 210. When viewed from a direction along the central axis C of the piston 20, the eight oil holes 210 are arranged at equal intervals in the circumferential direction around the central axis C of the piston 20.

[0018] Assume that an imaginary line VL is drawn perpendicular to the central axis C and parallel to the rotation axis LC of the crankshaft 30. At this time, two oil holes 210 are located on the imaginary line VL. In other words, these two oil holes 210 are bisected by the imaginary line VL. Furthermore, three oil holes 210 are located on the first direction X1 side of the central axis C, i.e., on the first direction X1 side of the imaginary line VL. And three oil holes 210 are located on the second direction X2 side of the imaginary line VL.

[0019] Assuming that it is viewed from a direction along the central axis C of the piston 20. In this case, the flow passage cross-sectional area of ​​each of the three oil holes 210 located on the second direction X2 side with respect to the imaginary line VL is larger than the flow passage cross-sectional area of ​​each of the three oil holes 210 located on the first direction X1 side with respect to the imaginary line VL. In addition, the flow passage cross-sectional areas of the two oil holes 210 located on the imaginary line VL are both the same as the flow passage cross-sectional area of ​​the oil hole 210 located on the second direction X2 side with respect to the imaginary line VL.

[0020] Assume that the piston 20 is divided into a first direction X1 side and a second direction X2 side by the imaginary line VL. In this case, the total flow passage cross-sectional area of ​​the oil holes 210 on the first direction X1 side of the piston 20 is three times the flow passage cross-sectional area of ​​the small oil holes 210 plus one time the flow passage cross-sectional area of ​​the large oil holes 210. On the other hand, the total flow passage cross-sectional area of ​​the oil holes 210 on the second direction X2 side of the piston 20 is four times the flow passage cross-sectional area of ​​the large oil holes 210. Therefore, the total flow passage cross-sectional area of ​​the oil holes 210 located on the second direction X2 side with respect to the imaginary line VL is larger than the total flow passage cross-sectional area of ​​the oil holes 210 located on the first direction X1 side with respect to the imaginary line VL.

[0021] <Operation of the First Embodiment> Combustion in the internal combustion engine 10 causes the piston 20 to reciprocate inside the cylinder bore 11. In response to the reciprocating movement of the piston 20, the crankshaft 30 rotates about a rotation axis LC. At this time, the second end of the connecting rod 21 rotates on a trajectory P in the clockwise direction in FIG.

[0022] As described above, the rotation axis LC of the crankshaft 30 is offset in the first direction X1 with respect to the central axis C of the piston 20. As a result, when the connecting rod 21 moves toward the cylinder bore 11, that is, during the compression stroke of combustion, the piston 20 is strongly pressed in the second direction X2. Therefore, the friction of the piston 20 on the second direction X2 side with respect to the central axis C is greater than that on the first direction X1 side.

[0023] Furthermore, the internal combustion engine 10 injects oil into the cylinder bore 11 from the crankcase side by an oil jet (not shown). The injected oil adheres to the inner circumferential surface 20C of the piston 20. The oil then flows down the inner circumferential surface 20C of the piston 20 to reach the oil hole 210, and then reaches the outer circumferential surface 20A of the piston 20 via the oil hole 210.

[0024] <Advantages of the First Embodiment> (1-1) In the above embodiment, the oil holes 210 located on the second direction X2 side with respect to the imaginary line VL have a larger flow passage cross-sectional area than the oil holes 210 located on the first direction X1 side. Therefore, the total flow passage cross-sectional area of ​​the oil holes 210 located on the second direction X2 side with respect to the imaginary line VL is larger than the total flow passage cross-sectional area of ​​the oil holes 210 located on the first direction X1 side. In other words, the amount of oil passing through the oil holes 210 is greater on the second direction X2 side with respect to the imaginary line VL than on the first direction X1 side. This makes it possible to effectively reduce wear of the piston 20 in a situation where the friction of the piston 20 on the second direction X2 side with respect to the imaginary line VL is large.

[0025] (1-2) In the above embodiment, the difference in the flow passage cross-sectional area of ​​the oil hole 210 can change the lubrication performance between the first direction X1 side and the second direction X2 side with respect to the central axis C. Therefore, without changing the arrangement of the oil hole 210, a difference in lubrication performance can be generated between the first direction X1 side and the second direction X2 side of the piston 20.

[0026] <Second embodiment> Next, a second embodiment of the internal combustion engine 10 will be described. The internal combustion engine 10 of the second embodiment is different from the internal combustion engine 10 of the first embodiment in the configuration related to the oil hole 210. The other configurations are the same as those of the first embodiment. Below, the parts related to the oil hole 210 will be described, and the description of the same configuration as the first embodiment will be simplified or omitted.

[0027] As shown in FIG. 4, the piston 20 has a plurality of oil holes 210. Each oil hole 210 penetrates from the inner circumferential surface 20C of the piston 20 to the third ring groove 203. The axis along which each oil hole 210 extends is perpendicular to the central axis C. The flow passage cross section of each oil hole 210 is substantially circular. In this embodiment, the flow passage cross section areas of all the oil holes 210 are the same. Furthermore, each oil hole 210 has a constant flow passage cross section area regardless of location.

[0028] In this embodiment, the piston 20 has ten oil holes 210. When viewed from a direction along the central axis C of the piston 20, the ten oil holes 210 are arranged in a circumferential direction around the central axis C of the piston 20.

[0029] Assume that an imaginary line VL is drawn that is perpendicular to the central axis C and parallel to the rotation axis LC of the crankshaft 30. In this case, two oil holes 210 are located on the imaginary line VL. Also, one oil hole 210 is located on the first direction X1 side of the imaginary line VL. And seven oil holes 210 are located on the second direction X2 side of the imaginary line VL. The seven oil holes 210 located on the second direction X2 side are aligned at equal intervals in the circumferential direction around the central axis C of the piston 20.

[0030] Assume that the piston 20 is divided into the first direction X1 side and the second direction X2 side by the imaginary line VL. In this case, the total of the flow passage cross-sectional areas of the oil holes 210 on the first direction X1 side of the piston 20 is twice the value of the flow passage cross-sectional area of ​​the oil holes 210. Also, the total of the flow passage cross-sectional areas of the oil holes 210 on the second direction X2 side of the piston 20 is eight times the value of the flow passage cross-sectional area of ​​the oil holes 210. As described above, the flow passage cross-sectional areas of the oil holes 210 are the same. Therefore, the total of the flow passage cross-sectional areas of the oil holes 210 located on the second direction X2 side with respect to the imaginary line VL is larger than the total of the flow passage cross-sectional areas of the oil holes 210 located on the first direction X1 side with respect to the imaginary line VL.

[0031] <Effects of the second embodiment> (2-1) In the above embodiment, the number of oil holes 210 located on the second direction X2 side with respect to the imaginary line VL is greater than the number of oil holes 210 located on the first direction X1 side. Therefore, the total flow path cross-sectional area of ​​the oil holes 210 located on the second direction X2 side with respect to the central axis C is greater than the total flow path cross-sectional area of ​​the oil holes 210 located on the first direction X1 side. Therefore, similar to the effect described in (1-1), wear of the piston 20 can be reduced.

[0032] (2-2) In the above embodiment, the difference in the arrangement of the oil holes 210 can change the lubrication performance between the first direction X1 side and the second direction X2 side with respect to the central axis C. Therefore, without changing the shape of the oil holes 210, a difference in lubrication performance can be generated between the first direction X1 side and the second direction X2 side of the piston 20.

[0033] <Example of change> The above-described embodiments may be modified as follows: The above-described embodiments and the following modifications may be combined and implemented within the scope of technical compatibility.

[0034] The number of ring grooves 200 in the piston 20 can be changed as appropriate. As long as the piston 20 has at least one ring groove 200, the configurations relating to the oil hole 210 in each of the above embodiments can be applied.

[0035] The oil hole 210 may penetrate to any of the ring grooves 200. That is, the oil hole 210 may penetrate to the first ring groove 201 or the second ring groove 202. Furthermore, the piston 20 may have an oil hole 210 penetrating to the first ring groove 201 or the second ring groove 202, in addition to the oil hole 210 penetrating to the third ring groove 203.

[0036] The flow passage cross-sectional area may change midway through each oil hole 210. In this case, if the sum of the minimum flow passage cross-sectional areas of the oil holes 210 located on the second direction X2 side is greater than the sum of the minimum flow passage cross-sectional areas of the oil holes 210 located on the first direction X1 side, the above effect (1-1) or (2-1) can be obtained.

[0037] In each of the above embodiments, the sum of the flow path cross-sectional areas of the oil holes 210 located on the second direction X2 side with respect to the virtual line VL needs to be greater than the sum of the flow path cross-sectional areas of the oil holes 210 located on the first direction X1 side.

[0038] For example, in the first embodiment, the number of oil holes 210 located on the first direction X1 side with respect to the virtual line VL may be greater than the number of oil holes 210 located on the second direction X2 side. Even in this case, if the flow passage cross-sectional area of ​​each oil hole 210 located on the second direction X2 side is large, the total flow passage cross-sectional area of ​​the oil holes 210 located on the second direction X2 side can be made large.

[0039] Similarly, for example, in the second embodiment, the flow path cross-sectional area of ​​one oil hole 210 located on the first direction X1 side with respect to the virtual line VL may be larger than the flow path cross-sectional area of ​​one oil hole 210 located on the second direction X2 side. Even in this case, if there are a large number of oil holes 210 located on the second direction X2 side, the total flow path cross-sectional area of ​​the oil holes 210 located on the second direction X2 side can be made larger.

[0040] Regardless of the flow passage cross-sectional area of ​​the oil hole 210, a difference in lubrication performance can be generated between the first direction X1 side and the second direction X2 side of the piston 20. Specifically, as in the above-described embodiments, one of the directions perpendicular to both the central axis C of the piston 20 and the rotation axis LC of the crankshaft 30 is defined as a first direction X1, and the direction opposite to the first direction X1 is defined as a second direction X2. In this case, by supplying more oil to the second direction X2 side of the central axis C of the piston 20 than to the first direction X1 side, the above-described problem that the piston 20 may be worn can be solved.

[0041] As a configuration for solving such a problem, for example, an example shown in FIG. 5 can be given. In the example shown in FIG. 5, the axis along which the oil hole 210 located on the second direction X2 side with respect to the central axis C extends is inclined with respect to the central axis C of the piston 20. This oil hole 210 extends linearly. And, the opening of the oil hole 210 on the inner circumferential surface 20C side of the piston 20 is located closer to the top surface 20B side of the piston 20 than the opening on the third ring groove 203 side. That is, the oil hole 210 descends toward the third ring groove 203. On the other hand, the axis along which the oil hole 210 located on the first direction X1 side with respect to the central axis C extends is perpendicular to the central axis C.

[0042] According to the configuration of this modified example, oil passes through the oil holes 210 located on the second direction X2 side according to the inclination more easily than through the oil holes 210 located on the first direction X1 side with respect to the central axis C. The amount of oil passing through the oil holes 210 on the second direction X2 side increases to the extent that the oil passes through them more easily. This makes it possible to effectively reduce wear of the piston 20 in a situation where friction of the piston 20 on the second direction X2 side with respect to the central axis C is large.

[0043] In the modification shown in FIG. 5, the axis of the oil hole 210 located on the first direction X1 side with respect to the central axis C may be inclined with respect to the central axis C of the piston 20. Even in this case, if the inclination of the axis of the oil hole 210 located on the second direction X2 side with respect to the central axis C is steep, the amount of oil passing through the oil hole 210 on the second direction X2 side can be increased. Specifically, the first imaginary line is a virtual line connecting the center of the opening on the inner circumferential surface 20C side of the piston 20 and the center of the opening on the outer circumferential surface 20A side of the piston in the oil hole 210 located on the first direction X1 side with respect to the central axis C. Similarly, the second imaginary line is a virtual line connecting the center of the opening on the inner circumferential surface 20C side of the piston 20 and the center of the opening on the outer circumferential surface 20A side of the piston in the oil hole 210 located on the second direction X2 side with respect to the central axis C. In this case, if the angle formed by the second virtual line and the central axis C on the crankshaft 30 side is smaller than the angle formed by the first virtual line and the central axis C on the crankshaft 30 side, the amount of oil passing through the oil hole 210 on the second direction X2 side can be increased.

[0044] The technical ideas that can be derived from the above-described embodiments and modifications will be described below. an internal combustion engine comprising: a cylindrical piston that reciprocates within a cylinder bore; a connecting rod having a first end connected to the piston; and a crankshaft that is connected to a second end of the connecting rod and converts the reciprocating motion of the piston into a rotational motion, wherein when one of directions perpendicular to both a central axis of the piston and a rotational axis of the crankshaft is defined as a first direction and a direction opposite to the first direction is defined as a second direction, the rotational axis of the crankshaft is located at a position shifted in the first direction with respect to the central axis of the piston, the piston is recessed in an outer circumferential surface of the piston, and has a ring groove that extends annularly about the central axis of the piston and a front end of the piston that extends from an inner circumferential surface of the piston and a plurality of oil holes which penetrate to the ring groove, the oil holes being arranged in a row in a circumferential direction around a central axis of the piston, wherein when a virtual line connecting the center of an opening on the inner circumferential surface of the piston and the center of an opening on the outer circumferential surface of the piston in the oil holes located on a first direction side of the central axis of the piston is defined as a first virtual line, and a virtual line connecting the center of an opening on the inner circumferential surface of the piston and the center of an opening on the outer circumferential surface of the piston in the oil holes located on a second direction side of the central axis of the piston is defined as a second virtual line, an angle formed by the second virtual line and the central axis on the crankshaft side is smaller than an angle formed by the first virtual line and the central axis on the crankshaft side. [Explanation of symbols]

[0045] C…Central axis line LC: Rotation axis X1…first direction X2…Second direction 10. Internal combustion engine 11…Cylinder bore 20…Piston 30…Crankshaft 200…Ring groove 203…3rd ring groove 210…Oil hole

Claims

[Claim 1] A cylindrical piston that reciprocates within a cylinder bore; a connecting rod having a first end connected to the piston; a crankshaft connected to a second end of the connecting rod for converting the reciprocating motion of the piston into a rotary motion; An internal combustion engine comprising: When one of directions perpendicular to both the central axis of the piston and the rotational axis of the crankshaft is defined as a first direction, and a direction opposite to the first direction is defined as a second direction, a rotation axis of the crankshaft is shifted in the first direction with respect to a central axis of the piston, The piston has a ring groove recessed in an outer peripheral surface of the piston and extending in an annular shape centered on a central axis of the piston, and a plurality of oil holes penetrating from an inner peripheral surface of the piston to the ring groove, The oil holes are arranged in a line in a circumferential direction around a central axis of the piston, When viewed from a direction along the central axis of the piston, The sum of the minimum flow passage cross-sectional areas of the oil holes located on the second direction side with respect to the central axis of the piston is the oil passage cross-sectional area is larger than the sum of the minimum flow passage cross-sectional areas of the oil holes located on a first direction side with respect to a central axis of the piston, an opening of the oil hole on the inner peripheral surface side, the opening being located on the second direction side with respect to a central axis of the piston, is located closer to the top surface side of the piston than an opening of the oil hole on the ring groove side, When a virtual line connecting the center of the opening on the inner circumferential surface side and the center of the opening on the ring groove side of the oil hole located on a first direction side with respect to the central axis of the piston is defined as a first virtual line, and a virtual line connecting the center of the opening on the inner circumferential surface side and the center of the opening on the ring groove side of the oil hole located on a second direction side with respect to the central axis of the piston is defined as a second virtual line, An angle on the crankshaft side and the second direction side among the angles formed between the second virtual line and the central axis on a virtual plane including the second virtual line and the central axis is smaller than an angle on the crankshaft side and the first direction side among the angles formed between the first virtual line and the central axis on a virtual plane including the first virtual line and the central axis. Internal combustion engine.

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