Internal combustion engine

Abstract

To reduce a friction force when a piston slides on a sliding surface, and suppress deterioration of work efficiency in an internal combustion engine.SOLUTION: An internal combustion engine 1 comprises a piston 30, a cylinder 12 having a sliding surface 13 on which the piston 30 slides, and a piston pin 38 that connects the piston 30 to a connecting rod. The sliding surface 13 is shaped so that an inner diameter of an axial central part 14c is larger than an inner diameter of an upper end part 14a, and a center of the piston pin 38 is located at a center of the piston 30.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] The piston of an internal combustion engine is connected to a connecting rod by a piston pin. By the way, in order to reduce the impact force acting on the sliding surface of the cylinder by the skirt portion of the piston when the piston moves up and down, the center of the piston pin is offset from the center of the piston (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the center of the piston pin is offset from the center of the piston, the force with which the piston is pressed against the sliding surface of the cylinder increases, so that the frictional force increases and the expansion period of the piston becomes shorter, resulting in a decrease in the work efficiency of the internal combustion engine.

[0005] Therefore, the present invention has been made in view of these points, and an object thereof is to reduce the frictional force when the piston slides on the sliding surface and to suppress a decrease in the work efficiency of the internal combustion engine.

Means for Solving the Problems

[0006] In one aspect of the present invention, there is provided an internal combustion engine including a piston, a cylinder having a sliding surface on which the piston slides, and a piston pin connecting the piston and a connecting rod. The sliding surface has a shape in which the inner diameter at the central portion in the axial direction is larger than the inner diameter at the upper end portion on the top dead center side of the piston, and the center of the piston pin is located at the center of the piston.

[0007] Further, the central portion of the sliding surface may have a convexly curved shape. Further, the upper end portion may face the entire outer peripheral surface of the piston located at the top dead center.

[0008] Further, the sliding surface has a lower end portion on the bottom dead center side of the piston, and the inner diameter of the central portion may be larger than the inner diameter of the lower end portion. Further, the length of the upper end portion in the axial direction may be larger than the length of the lower end portion in the axial direction.

[0009] Further, the piston has a skirt portion and a ring member provided on the peripheral surface of the piston for scraping off lubricating oil adhering to the sliding surface. The cylinder includes a thrust region against which the skirt portion is pressed when the piston descends. The skirt portion includes a first opposing portion facing the thrust region, and a hole having a predetermined depth into which the lubricating oil scraped off by the ring member flows is provided at the center in the circumferential direction of the first opposing portion.

[0010] Further, the piston has a skirt portion and a ring member provided on the peripheral surface of the piston for scraping off lubricating oil adhering to the sliding surface. The cylinder includes an anti-thrust region against which the skirt portion is pressed when the piston ascends. The skirt portion includes a second opposing portion facing the anti-thrust region, and a hole having a predetermined depth into which the lubricating oil scraped off by the ring member flows is provided at the center in the circumferential direction of the second opposing portion.

[0011] Further, the lubricating oil flowing into and retained in the hole portion may flow out to the skirt portion when the piston moves up and down.

[0012] Further, the skirt portion may be located below the hole portion in the vertical direction of the piston and may have a communication groove communicating with the hole portion.

Advantages of the Invention

[0013] According to the present invention, it is possible to reduce the frictional force when the piston slides on the sliding surface and to suppress a decrease in the work efficiency of the internal combustion engine.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0015] <Configuration of Internal Combustion Engine> FIG. 1 is a schematic diagram showing the configuration of the internal combustion engine 1. The internal combustion engine 1 is, for example, a direct injection engine. The internal combustion engine 1 includes a cylinder block 10, a cylinder head 20, and a piston 30.

[0016] The cylinder block 10 has a cylinder 12 that houses a piston 30 so that the piston 30 can reciprocate, and a crankcase 16 that houses a crankshaft 35. The cylinder block 10 is configured by integrating the cylinder 12 and the crankcase 16. An oil pan 18 that stores lubricating oil is attached to the crankcase. The cylinder 12 has a sliding surface 13 on which the piston 30 slides.

[0017] The cylinder head 20 is provided on the top of the cylinder block 10. The cylinder head 20 is fixed to the cylinder block 10 with bolts. The cylinder head 20 has an injector 22, an intake port 23, an exhaust port 24, an intake valve 25, and an exhaust valve 26. The injector 22 injects fuel into a combustion chamber 2 defined by the top surface of the piston 30, the sliding surface 13 of the cylinder 12, and the cylinder head 20. The intake port 23 is an intake port that introduces fresh air into the combustion chamber 2. The exhaust port 24 is an exhaust port that guides exhaust gas from the combustion chamber 2. The intake valve 25 introduces fresh air from the intake port 23 into the combustion chamber 2 by opening and closing. The exhaust valve 26 guides exhaust gas from the combustion chamber 2 to the exhaust port 24 by opening and closing.

[0018] The piston 30 slides on the sliding surface 13 of the cylinder 12 when reciprocating between the top dead center and the bottom dead center. Lubricating oil is supplied to the sliding surface 13 to form an oil film. A plurality of ring members are provided on the outer periphery of the upper part of the piston 30 to seal the combustion gas and maintain the oil film at a predetermined thickness. The ring members are provided in each of the ring grooves 31a, 31b, and 31c (see FIG. 2) formed on the outer periphery of the piston 30. The ring member provided in the ring groove 31c is an oil ring that scrapes off the lubricating oil adhering to the sliding surface 13.

[0019] The piston 30 has a piston pin 38. The piston pin 38 connects the piston 30 and the connecting rod 36. The connecting rod 36 connects the piston 30 and the crankshaft 35, and converts the reciprocating motion of the piston 30 into the rotational motion of the crankshaft 35. In the present embodiment, the center of the piston pin 38 is located at the center of the piston 30.

[0020] A skirt portion 32 is provided at the lower part of the piston 30. When the piston 30 reciprocates between the top dead center and the bottom dead center, the skirt portion 32 of the piston 30 is pressed against the sliding surface 13 of the cylinder 12. The sliding surface 13 of the cylinder 12 includes a thrust region against which the skirt portion 32 is pressed when the piston 30 descends from the top dead center to the bottom dead center, and an anti-thrust region against which the skirt portion 32 is pressed when the piston 30 ascends from the bottom dead center to the top dead center.

[0021] FIG. 2 is a schematic diagram for explaining the thrust region and the anti-thrust region of the cylinder 12. In FIG. 2, for convenience of explanation, the cylinder 12 is shown in an unfolded state. Also, the piston 30 shown in the upper left of FIG. 2 is located at the top dead center. The horizontal axis of the developed view of the cylinder 12 indicates the developed angle of the cylinder 12, and the vertical axis indicates the height of the cylinder 12. "Th" shown in FIG. 2 means the thrust side, "ATh" means the anti-thrust side, "Front" means the front side of the piston 30, and "Rear" means the rear side of the piston 30.

[0022] The position where the developed angle of FIG. 2 is 180° is the central position in the circumferential direction of the thrust region, and the position where the developed angle is 0° is the central position in the circumferential direction of the anti-thrust region. The thrust region is a region within a predetermined angle range (for example, in the range of 135° to 225°) centered on 180° of the developed angle. The anti-thrust region is a region within a predetermined angle range (for example, in the ranges of 0° to 45° and 315° to 360°) centered on 0° (360°) of the developed angle.

[0023] <Details of the sliding surface of the cylinder> FIG. 3 is a schematic diagram showing the shape of the sliding surface 13 of the cylinder 12. The shape of the sliding surface 13 shown in FIG. 3 is the shape in the longitudinal section of the cylinder 12. In FIG. 3, for convenience of explanation, the difference between the inner diameter of the central portion 14c and the inner diameter of the upper end portion 14a (lower end portion 14b) is shown larger than the actual one.

[0024] The cylinder 12 is a cylindrical cylinder bore, and the sliding surface 13 is the inner wall surface of the cylinder. As shown in FIG. 3, the sliding surface 13 has a barrel shape in which the center in the axial direction of the cylinder 12 bulges. The sliding surface 13 includes an upper end portion 14a, a lower end portion 14b, and a central portion 14c.

[0025] The upper end portion 14a is a region on one end side (upper end side) in the axial direction of the cylinder 12 (in other words, the sliding direction of the piston 30) (see FIG. 2). When the piston 30 is at the top dead center, the upper end portion 14a faces the entire outer peripheral surface of the piston 30.

[0026] The lower end portion 14b is a region on the other end side (lower end side) in the axial direction of the cylinder 12 (see FIG. 2), and faces the entire outer peripheral surface of the piston 30 when the piston 30 is at the bottom dead center. The inner diameter d2 of the lower end portion 14b is the same as the inner diameter d1 of the upper end portion 14a. However, it is not limited to this, and the inner diameter d2 of the lower end portion 14b may be different from the inner diameter d1 of the upper end portion 14a.

[0027] The central portion 14c is a region between the upper end portion 14a and the lower end portion 14b in the axial direction of the cylinder 12 (see FIG. 2). When the piston 30 reciprocates between the top dead center and the bottom dead center, the central portion 14c may contact the skirt portion 32 of the piston 30.

[0028] The inner diameter d3 of the central portion 14c is larger than the inner diameters of both axial ends of the sliding surface 13 (that is, the inner diameter d1 of the upper end portion 14a and the inner diameter d2 of the lower end portion 14b). As a result, the sliding surface 13 has a barrel-shaped configuration with a bulge at the axial center. Since the inner diameter d1 of the upper end portion 14a is smaller than the inner diameter d3, the gap between the skirt portion 32 and the upper end portion 14a can be reduced. Therefore, the impact force when the skirt portion 32 slides on the upper end portion 14a can be reduced. Since the inner diameter d3 of the central portion 14c is large, the gap between the skirt portion 32 and the central portion 14c can be increased when the piston 30 moves between the top dead center and the bottom dead center. Therefore, the frictional force when the skirt portion 32 slides on the central portion 14c can be reduced. The inner diameter d3 of the central portion 14c is, as an example, 0.05% to 0.3% larger than the inner diameter d1 of the upper end portion 14a.

[0029] In the above, it is assumed that the inner diameter d3 of the central portion 14c is larger than the inner diameter d2 of the lower end portion 14b, but it is not limited to this. For example, the inner diameter d2 of the lower end portion 14b may be the same size as or larger than the inner diameter d3 of the central portion 14c. Even in this case, since the gap between the skirt portion 32 and the central portion 14c can be increased, the frictional force when the skirt portion 32 slides on the central portion 14c can be reduced.

[0030] The central portion 14c has a convexly curved shape. Specifically, the central portion 14c has an arcuately curved shape as shown in FIG. 3. The central portion 14c may be curved with a predetermined curvature. The central portion 14c is connected between the upper end portion 14a and the lower end portion 14b without a step.

[0031] The axial length h3 of the central portion 14c is larger than the axial length h1 of the upper end portion 14a and the axial length h2 of the lower end portion 14b. Specifically, the axial length h3 of the central portion 14c is longer than the sum of the axial length h1 of the upper end portion 14a and the axial length h2 of the lower end portion 14b. As a result, the central portion 14c where the gap with the skirt portion 32 becomes large can be provided over a wide range in the axial direction, and the frictional force acting from the skirt portion 32 on the central portion 14c can be reduced.

[0032] The axial length h1 of the upper end portion 14a is longer than the axial length h2 of the lower end portion 14b. In this case, since the area of the upper end portion 14a, which is narrower than the central portion 14c, becomes larger, it becomes easier to suppress the amount of piston head vibration of the piston 30 near top dead center. Note that the present invention is not limited to the above, and for example, the axial length h1 of the upper end portion 14a may be the same as the axial length h2 of the lower end portion 14b.

[0033] Incidentally, it has been found that by offsetting the center of the piston pin 38 from the center of the piston 30, the impact force acting on the sliding surface 13 (specifically, the central portion in the axial direction of the sliding surface 13) from the skirt portion 32 during the expansion stroke can be reduced. On the other hand, in the present embodiment, the center of the piston pin 38 is located at the center of the piston 30 (not offset), and the central portion 14c of the sliding surface 13 has a barrel-shaped configuration that bulges.

[0034] FIG. 4 is a schematic diagram for explaining the relationship between the piston 30 and the sliding surface 13 in the present embodiment. Note that in FIG. 4, due to the temperature rise of the cylinder block 10 caused by combustion in the internal combustion engine 1, the fastening force of the bolts fixing the cylinder block 10 and the cylinder head 20, etc., the shape of the sliding surface 13 is deformed. Further, state A1 in FIG. 4 shows the piston 30 located at top dead center, and state A2 shows the piston 30 during descent. In the present embodiment, since the sliding surface 13 has a barrel-shaped configuration, as shown in state A2, the gap between the skirt portion 32 and the central portion 14c becomes larger, and the frictional force exerted by the skirt portion 32 on the central portion 14c during the compression stroke and the expansion stroke can be reduced.

[0035] Also, in the present embodiment, since the inner diameter of the upper end portion 14a is smaller than the inner diameter of the central portion 14c, as shown in state A1 of FIG. 4, the amount of piston 30's wobbling (tilting) near top dead center becomes smaller. Therefore, when the piston 30 with a small wobbling amount moves from top dead center to bottom dead center (expansion stroke), as shown in state A2, the skirt portion 32 easily comes into contact with the central portion 14c in parallel, so that the impact force acting on the central portion 14c by the skirt portion 32 (specifically, the thrust region Th of the sliding surface 13) can be reduced. Thus, in the present embodiment, even if the center of the piston pin 38 is not offset from the center of the piston 30, the impact force acting on the sliding surface 13 from the skirt portion 32 can be reduced.

[0036] FIG. 5 is a schematic diagram for explaining a comparative example. In the comparative example, the center of the piston pin 38 is offset from the center of the piston 30. When the center of the piston pin 38 is offset, as shown in state B1, when the piston 30 reciprocates, the force with which the piston 30 is pressed against the sliding surface 13 by the rotational moment increases, so that the frictional force increases and the expansion period of the piston 30 becomes shorter, resulting in a decrease in the work efficiency of the internal combustion engine 1. Further, when the piston 30 located at top dead center is in an inclined state at top dead center, the combustion gas in the combustion chamber easily flows between the piston 30 and the sliding surface 13, and the soot deposited on the outer peripheral surface of the piston 30 (specifically, the top land) increases. On the other hand, in the present embodiment, since the center of the piston pin 38 is not offset, the frictional force when the piston 30 slides on the sliding surface 13 can be reduced, and it is possible to prevent the expansion period from becoming shorter, so that a decrease in the work efficiency of the internal combustion engine 1 can be suppressed. Also, as shown in state A2 of FIG. 4, since it is possible to suppress an increase in the inclination of the piston 30 located at top dead center, it is possible to suppress the deposition of soot on the outer peripheral surface of the piston 30.

[0037] In the above description, the sliding surface 13 has been described as having a barrel shape shown in FIG. 3 as an example. However, the shape of the sliding surface 13 may be such that it becomes a barrel shape during the operation of the internal combustion engine 1 in consideration of the influence of the temperature rise of the cylinder block 10, the tightening force of the bolts fixing the cylinder block 10 and the cylinder head 20, etc. Also, in the above description, the cross section of the sliding surface 13 has been assumed to be a circle, but it is not limited to this. For example, the sliding surface 13 may be an ellipse with the thrust region and the anti-thrust region as the major axis. Since the skirt portion 32 of the piston 30 slides on the thrust region and the anti-thrust region of the sliding surface 13, making the sliding surface 13 an ellipse facilitates reducing the frictional force exerted by the skirt portion 32 on the sliding surface 13.

[0038] <Configuration of skirt portion of piston> When the sliding surface 13 has a barrel shape as described above, the gap between the central portion 14c of the sliding surface 13 and the skirt portion 32 becomes large, and lubricating oil is likely to be retained on the surface of the skirt portion 32. In particular, in the present embodiment, as will be described below, since the configuration is such that the lubricating oil scraped by the oil ring, which is a ring member, can be supplied to the skirt portion 32, it becomes easy to retain the lubricating oil on the skirt portion 32. When lubricating oil is retained on the skirt portion 32, vibrations and noises during the reciprocating motion of the piston 30 can be reduced.

[0039] FIG. 6 is a schematic diagram showing the configuration of the piston 30. FIG. 7 is a cross-sectional view taken along line I-I of FIG. 6. Note that FIG. 6 shows the piston 30 obtained by rotating the piston 30 shown in FIG. 2 by 90 degrees in the circumferential direction. On the outer peripheral surface of the piston 30, a hole portion 40 is provided through which the lubricating oil scraped by the ring member, which is an oil ring, flows in. The hole portion 40 is provided at the center in the circumferential direction of the opposing portion (first opposing portion) that opposes the thrust region of the cylinder 12 of the skirt portion 32. Specifically, the hole portion 40 is provided at the upper center in the circumferential direction of the first opposing portion.

[0040] The hole portion 40 is adjacent to the ring groove 31c. The hole portion 40 is formed to have a predetermined depth from the outer peripheral surface of the piston 30 as shown in FIG. 7. The depth of the hole portion 40 is greater than the depth of the ring groove 31c. However, the hole portion 40 is not a hole penetrating the piston 30, but a blind hole. Therefore, the lubricating oil scraped by the ring member is likely to be held in the hole portion 40.

[0041] The lubricating oil flowing into and held in the hole portion 40 flows out of the hole portion 40 when the piston 30 moves up and down. For example, the lubricating oil held in the hole portion 40 flows out onto the surface of the skirt portion 32 when the piston 30 moves up or down. That is, the lubricating oil held in the hole portion 40 is supplied to the surface of the skirt portion 32. In particular, since the hole portion 40 is provided at the upper center in the circumferential direction of the first opposing portion, the lubricating oil held in the hole portion 40 is likely to be supplied to a wide range of the first opposing portion. As a result, the amount of lubricating oil held in the portion of the surface of the skirt portion 32 facing the thrust region increases.

[0042] The skirt portion 32 is located below the hole portion 40 in the vertical movement direction of the piston 30 and has a communication groove 42 communicating with the hole portion 40. The communication groove 42 is located at the upper part of the surface of the skirt portion 32. The communication groove 42 is a groove formed such that the portion between the hole portion 40 and the skirt portion 32 is inclined as shown in FIG. 7. The communication groove 42 serves as a flow path for the lubricating oil held in the hole portion 40 to flow to the surface of the skirt portion 32 (specifically, the region R shown in FIG. 6). Therefore, by providing the communication groove 42, the lubricating oil is likely to be supplied to the region R of the skirt portion 32. The region R of the skirt portion 32 is a region that is likely to come into contact with the thrust region of the sliding surface 13 when the piston 30 moves downward.

[0043] The shape of the communication groove 42 is a fan shape as shown in FIG. 6 here. However, it is not limited to this, and the shape of the communication groove 42 may be a triangular shape. In the case of such a fan shape or triangular shape, since the width of the communication groove 42 becomes narrower toward the tip, the lubrication in the communication groove 42 easily flows to the skirt portion 32.

[0044] In addition, in the present embodiment, a hole 40 is also provided at the center in the circumferential direction of the opposing portion (second opposing portion) that faces the anti-thrust region of the cylinder 12 of the skirt portion 32. Specifically, the hole 40 is provided at the upper center in the circumferential direction of the second opposing portion. Further, a communication groove 42 that communicates with the hole 40 is provided. That is, the hole 40 and the communication groove 52 are provided at intervals of 180 degrees in the circumferential direction of the outer peripheral surface of the piston 30. Thereby, lubricating oil is supplied to the portions of the skirt portion 32 that face the thrust region and the anti-thrust region. In other words, lubricating oil is supplied to the portion of the skirt portion 32 that is likely to come into contact with the cylinder 12.

[0045] <Effects in the present embodiment> In the internal combustion engine 1 of the above-described embodiment, the sliding surface 13 of the cylinder 12 has a shape in which the inner diameter of the central portion 14c is larger than the inner diameter of the upper end portion 14a. And the center of the piston pin 38 is located at the center of the piston 30. Thereby, the gap between the skirt portion 32 and the central portion 14c of the sliding surface 13 becomes larger, and the frictional force that the skirt portion 32 acts on the central portion 14c during the compression stroke and the expansion stroke can be reduced. Further, since the center of the piston pin 38 is located at the center of the piston 30, it is possible to prevent the expansion period of the piston 30 from becoming short, so that a decrease in the work efficiency of the internal combustion engine 1 can be suppressed.

[0046] As described above, the present invention has been described using embodiments. However, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist. For example, all or part of the device can be configured by functionally or physically dispersing and integrating it in any unit. Also, new embodiments resulting from any combination of a plurality of embodiments are included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination have the effects of the original embodiments combined.

Description of reference numerals

[0047] 1 Internal combustion engine 12 Cylinder 13 Sliding surface Upper end portion of 14a Lower end portion of 14b Central portion of 14c 30 Piston 32 Skirt portion 38 Piston pin 40 Hole portion 42 Communication groove

Claims

1. A piston, a cylinder having a sliding surface on which the piston slides, a piston pin connecting the piston and the connecting rod, and comprising: The sliding surface has a shape in which the inner diameter of the central portion in the axial direction is larger than the inner diameter of the upper end portion on the top dead center side of the piston, The piston has a skirt portion and a ring member provided in a ring groove on the circumferential surface of the piston for scraping lubricating oil adhering to the sliding surface, The cylinder includes a thrust region against which the skirt portion is pressed when the piston descends, The skirt portion includes a first facing portion facing the thrust region, At the center in the circumferential direction of the first facing portion, a hole portion having a depth larger than the depth of the ring groove and into which the lubricating oil scraped by the ring member flows is provided, The skirt portion is located below the hole portion in the vertical direction of the piston and has a communication groove communicating with the hole portion, The communication groove is formed in a fan shape such that the space between the hole portion and the surface of the skirt portion is inclined, The lubricating oil flowing into and held in the hole portion flows out to the skirt portion when the piston moves up and down, An internal combustion engine.

2. A piston, a cylinder having a sliding surface on which the piston slides, a piston pin connecting the piston and the connecting rod, and comprising: The sliding surface has a shape in which the inner diameter of the central portion in the axial direction is larger than the inner diameter of the upper end portion on the top dead center side of the piston, The piston has a skirt portion and a ring member provided in a ring groove on the circumferential surface of the piston for scraping lubricating oil adhering to the sliding surface, The cylinder includes an anti-thrust region against which the skirt portion is pressed when the piston ascends. The skirt portion includes a second opposing portion facing the anti-thrust region. A hole portion with a depth greater than the depth of the ring groove is provided at the center in the circumferential direction of the second opposing portion, into which the lubricating oil scraped by the ring member flows. The skirt portion is located below the hole portion in the ascending and descending direction of the piston and has a communication groove communicating with the hole portion. The communication groove is formed in a fan shape such that the space between the hole portion and the surface of the skirt portion is inclined. The lubricating oil flowing into and held in the hole portion flows out to the skirt portion when the piston ascends and descends. Internal combustion engine.

3. The central portion of the sliding surface has a convexly curved shape. The internal combustion engine according to claim 1 or 2.

4. The sliding surface has a lower end portion on the bottom dead center side of the piston. The inner diameter of the central portion is larger than the inner diameter of the lower end portion. The internal combustion engine according to claim 1 or 2.

5. The length of the upper end portion in the axial direction is larger than the length of the lower end portion in the axial direction. The internal combustion engine according to claim 4.

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