Piston of internal combustion engine

Abstract

To solve a problem of excessively high temperature of an outer edge part of a combustion chamber.SOLUTION: A piston of an internal combustion engine includes: a cylindrical piston body; and a top surface member 31 attached to the piston body. The top surface member 31 has a lower heat conductivity than the piston body, and has a higher hardness than the piston body. The top surface member 31 has a disk part 32, a circular part 33, and a connection part 35. The disk part 32 closes an opening of the piston body. The circular part 33 is positioned on an outside of the disk part 32. Also, the circular part 33 is exposed from an outer peripheral surface of the piston body. The connection part 35 connects an outer peripheral edge of the disk part 32 and an inner peripheral edge of the circular part 33 through the piston body in a radial direction. The plurality of connection parts 35 are present in a circumferential direction about a center axis CA of the piston body. The piston body is in contact with the connection part 35 in the circumferential direction.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a piston of an internal combustion engine. This piston includes a piston body made of aluminum and a low heat conduction member made of a titanium alloy. The low heat conduction member is attached to the piston body. The low heat conduction member constitutes a part including the center of the top surface of the piston.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a piston such as that of Patent Document 1, it is conceivable to configure not only the center of the top surface of the piston but also the entire top surface of the piston with a low heat conductivity member. Thereby, the strength of the outer edge portion of the top surface of the piston can be improved. However, in this case, the heat of the outer edge portion of the combustion chamber partitioned by the cylinder head and the top surface of the piston is difficult to be transmitted to the piston. As a result, the temperature of the outer edge portion of the combustion chamber may become excessively high, which may cause knocking of the piston or the like.

Means for Solving the Problems

[0005] To solve the above problems, the present invention provides a cylindrical piston body, and a top member attached to the piston body, having a lower thermal conductivity and a higher hardness than the piston body. The top member includes a disc portion that closes the opening of the piston body, an annular portion that is located outside the disc portion and exposed from the outer peripheral surface of the piston body, and a connecting portion that penetrates the piston body in the radial direction centered on the central axis of the piston body to connect the outer peripheral edge of the disc portion and the inner peripheral edge of the annular portion. A plurality of connecting portions exist in the circumferential direction centered on the central axis of the piston body, and the piston body is a piston of an internal combustion engine that contacts the connecting portions in the circumferential direction.

Advantages of the Invention

[0006] Since the heat of the outer edge portion of the combustion chamber can be transmitted to the piston body through the annular portion and the connecting portion, the temperature of the outer edge portion of the combustion chamber is less likely to become excessively high.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0008] Hereinafter, an embodiment in which the piston of the present invention is applied to an internal combustion engine will be described with reference to FIGS. 1 and 2. <Schematic Configuration of Internal Combustion Engine> As shown in FIG. 1, the internal combustion engine 10 includes a plurality of cylinders 11, an intake passage 12, and an exhaust passage 13. In FIG. 1, one cylinder 11 is shown as a representative.

[0009] The air cylinder 11 is a cylindrical space partitioned by a cylinder block and a cylinder head. The intake passage 12 is a flow passage for intake air supplied to the air cylinder 11. The downstream end of the intake passage 12 is connected to the air cylinder 11. The exhaust passage 13 is a flow passage for the air-fuel mixture after combustion, that is, exhaust gas. The upstream end of the exhaust passage 13 is connected to the air cylinder 11.

[0010] The internal combustion engine 10 includes an intake valve 14, an exhaust valve 15, and a spark plug 16. The intake valve 14 opens and closes the connection point between the downstream end of the intake passage 12 and the air cylinder 11. The exhaust valve 15 opens and closes the connection point between the upstream end of the exhaust passage 13 and the air cylinder 11. Further, the exhaust valve 15 opens and closes in conjunction with the intake valve 14. The tip of the spark plug 16 faces into the air cylinder 11. The spark plug 16 ignites the air-fuel mixture of intake air and fuel in the air cylinder 11.

[0011] The internal combustion engine 10 includes a piston 20 and an oil jet 17. As a whole, the piston 20 is cylindrical with one end closed. Therefore, the piston 20 has a straight central axis CA. The structure of the piston 20 will be described later. The closed end of the piston 20 faces the intake passage 12 and the exhaust passage 13 side. Hereinafter, the surface of the piston 20 facing the intake passage 12 and the exhaust passage 13 side will be referred to as the top surface 20A. Also, among the two directions along the central axis CA, the side in the direction in which the piston 20 moves toward the intake passage 12 and the exhaust passage 13 side is called the top dead center side, and the opposite side is called the bottom dead center side. The top surface 20A of the piston 20 and the inner surface of the wall partitioning the air cylinder 11 define a combustion chamber R.

[0012] The piston 20 is reciprocally movable within the air cylinder 11 along the central axis CA of the piston 20. Although not shown in the figure, the piston 20 is connected to the crankshaft via a connecting rod. These connecting rod and crankshaft convert the linear reciprocating motion of the piston 20 into a rotational motion.

[0013] The oil jet 17 is located on the bottom dead center side with respect to the piston 20. The oil jet 17 is supplied with engine oil from an oil pump (not shown). The tip of the oil jet 17 faces the piston 20. Therefore, as indicated by the dashed arrow in FIG. 1, the oil jet 17 injects engine oil toward the piston 20. The engine oil injected onto the piston 20 lubricates and cools the piston 20. That is, the engine oil functions as a lubricant and a cooling medium. Note that in FIG. 1, only one oil jet 17 is shown, but there may be a plurality of oil jets 17.

[0014] <Regarding the piston> As shown in FIG. 1, the piston 20 includes a piston body 21. The piston body 21 is cylindrical. Therefore, both the top dead center side and the bottom dead center side of the piston body 21 are open. The material of the piston body 21 is an aluminum alloy.

[0015] The piston body 21 includes a cooling groove 22, a first ring groove 23, and a second ring groove 24. The cooling groove 22 is recessed from the end face on the bottom dead center side of the piston body 21 toward the top dead center side. The cooling groove 22 extends over 360 degrees around the central axis CA. That is, the cooling groove 22 extends in an annular shape. Note that the engine oil injected from the oil jet 17 also adheres to the inner surface of the cooling groove 22.

[0016] The first ring groove 23 is recessed from the outer peripheral surface of the piston body 21 toward the central axis CA. The first ring groove 23 is located on the top dead center side with respect to the bottom surface on the top dead center side of the cooling groove 22. Therefore, the internal space of the first ring groove 23 is not connected to the internal space of the cooling groove 22. The first ring groove 23 extends over 360 degrees around the central axis CA. That is, the first ring groove 23 extends in an annular shape.

[0017] The second ring groove 24 is recessed from the outer peripheral surface of the piston body 21 toward the central axis CA. The second ring groove 24 is located on the top dead center side with respect to the first ring groove 23. The second ring groove 24 extends annularly, similarly to the first ring groove 23. Although illustration is omitted, known piston rings are fitted into these first ring groove 23 and second ring groove 24.

[0018] The piston body 21 further includes an outer concave portion 25 and an inner concave portion 26. The outer concave portion 25 is recessed from the outer peripheral surface of the piston body 21 toward the central axis CA. The outer concave portion 25 is located on the top dead center side with respect to the second ring groove 24. The outer concave portion 25 extends over 360 degrees around the central axis CA. That is, the outer concave portion 25 extends annularly.

[0019] The inner concave portion 26 is recessed from the inner peripheral surface of the piston body 21 toward the outer peripheral surface side. The inner concave portion 26 is disposed at the same position as the outer concave portion 25 in the direction along the central axis CA. That is, the inner concave portion 26 is disposed at a position facing the outer concave portion 25. Note that the bottom surface of the inner concave portion 26 does not reach the bottom surface of the outer concave portion 25. The inner concave portion 26 extends annularly, similarly to the outer concave portion 25.

[0020] As shown in FIG. 1, the piston 20 includes a top surface member 31 attached to the piston body 21. As shown in FIG. 2, the top surface member 31 is generally disc-shaped as a whole. The material of the top surface member 31 is stainless steel. Therefore, the thermal conductivity of the top surface member 31 is lower than the thermal conductivity of the piston body 21. Also, the hardness of the top surface member 31 is greater than the hardness of the piston body 21. Here, the hardness referred to is Vickers hardness.

[0021] The top surface member 31 further includes a disc portion 32, an annular portion 33, and a connecting portion 35. These disc portion 32, annular portion 33, and connecting portion 35 are integrally formed. As shown in FIG. 1, the disk portion 32 is disk-shaped. The outer edge of the disk portion 32 fits into the inner concave portion 26 of the piston body 21. As a result, the disk portion 32 closes the opening on the top dead center side in the piston body 21. Also, the surface of the disk portion 32 on the top dead center side is located slightly on the bottom dead center side with respect to the end surface of the piston body 21 on the top dead center side. And the surface of the disk portion 32 on the top dead center side, together with the end surface of the piston body 21 on the top dead center side, constitutes the top surface 20A of the piston 20. Specifically, the surface of the disk portion 32 on the top dead center side constitutes the central portion of the top surface 20A of the piston 20.

[0022] The inner diameter of the annular portion 33 is larger than the outer shape of the disk portion 32. Also, the outer diameter of the annular portion 33 is the same as the outer diameter of the piston body 21. The annular portion 33 is located outside the disk portion 32. The disk portion 32 fits into the outer concave portion 25 of the piston body 21. Therefore, the outer peripheral surface of the disk portion 32 is exposed from the outer peripheral surface of the piston body 21.

[0023] The annular portion 33 has a third ring groove 34. The third ring groove 34 is recessed from the outer peripheral surface of the annular portion 33 toward the central axis CA. The third ring groove 34 extends annularly in the same manner as the first ring groove 23. Although not shown, a known piston ring is fitted into the third ring groove 34.

[0024] As shown in FIG. 2, the connecting portion 35 connects the outer peripheral edge of the disk portion 32 and the inner peripheral edge of the annular portion 33. That is, the connecting portion 35 penetrates the piston body 21 in the radial direction centered on the central axis CA. There are eight connecting portions 35 at equal intervals in the circumferential direction centered on the central axis CA. As a result, the top member 31 has eight through holes 31H that penetrate the top member 31 in the direction along the central axis CA between the adjacent connecting portions 35 in the circumferential direction. In FIG. 2, only some of the eight connecting portions 35 and the eight through holes 31H are labeled.

[0025] As shown in FIG. 1, within each through-hole 31H, there exists a portion of the piston body 21 that is sandwiched between the bottom surface of the outer concave portion 25 and the bottom surface of the inner concave portion 26. Therefore, the piston body 21 is in contact with each connecting portion 35 in the circumferential direction centered on the central axis CA.

[0026] <Operation of this Embodiment> When the air-fuel mixture burns in the combustion chamber R, the temperature of the top surface 20A of the piston 20 rises. The central portion of the top surface 20A is composed of the top surface member 31 with relatively low thermal conductivity. Therefore, the heat preservation of the top surface 20A of the piston 20 is enhanced. Thus, it is possible to prevent a decrease in combustion efficiency due to a decrease in the temperature of the combustion chamber R.

[0027] <Effects of this Embodiment> (1) According to the above embodiment, the annular portion 33 with high hardness has the third ring groove 34. Therefore, even if the piston ring fitted in the third ring groove 34 rubs against the annular portion 33, excessive wear of the annular portion 33 can be prevented.

[0028] On the other hand, since the thermal conductivity of the annular portion 33 is relatively low, the heat of the outer edge portion in the combustion chamber R is difficult to be transmitted to the piston 20. If the temperature of the outer edge portion in the combustion chamber R becomes excessively high, it will cause knocking of the piston 20 and the like. In this regard, in the above embodiment, the piston body 21 also exists within the through-hole 31H of the top surface member 31, and the piston body 21 is in contact with the connecting portion 35 even in the circumferential direction. Therefore, the temperature of the outer edge portion in the combustion chamber R can be transmitted to the piston body 21 through the annular portion 33 and the connecting portion 35. And the piston body 21 itself is cooled by the engine oil from the oil jet 17. In this way, since the heat dissipation route from the outer edge portion of the combustion chamber R is ensured, it is possible to prevent the temperature of the outer edge portion in the combustion chamber R from becoming excessively high.

[0029] (2) The disc portion 32, the annular portion 33, and the connecting portion 35 of the above-described embodiment are integrally formed. Therefore, the work of combining or fixing them to each other is unnecessary. That is, the top member 31 can be manufactured simply.

[0030] <Modified Example> This embodiment can be implemented with the following modifications. This embodiment and the following modified examples can be implemented in combination with each other within a technically non - conflicting range.

[0031] · The shape of the connecting portion 35 in the top member 31, and thus the shape of the through - hole 31H, can be changed as appropriate. For example, in the top member 131 shown in FIG. 3, the shape of the through - hole 131H is circular in plan view. Even with such a shape of the through - hole 131H, the same effects as those described in (1) and (2) above can be obtained. Also, not limited to the shape of the through - hole 131H illustrated in FIG. 3, for example, the through - hole 31H of the top member 31 may have a shape that is long in the radial direction centered on the central axis CA. Note that the shape of the connecting portion 35 may be adjusted according to the shape of the through - hole 31H.

[0032] · The number of the connecting portions 35 in the top member 31 may be plural. Note that even when the number of the connecting portions 35 is changed, the same number of through - holes 31H as the number of the connecting portions 35 exist. · The shape of the cooling groove 22 in the piston body 21 does not matter. Specifically, the cross - sectional shape of the cooling groove 22 when the piston body 21 is viewed in cross - section in a cross - section including the central axis CA does not matter. Also, the cooling groove 22 may exist intermittently in the circumferential direction centered on the central axis CA.

[0033] · Further, one or more fins may protrude from the inner surface of the cooling groove 22. By the presence of such fins, the contact area with respect to the engine oil injected from the oil jet 17 increases. Thereby, the piston body 21 can be effectively cooled.

[0034] ·The surface of the disc portion 32 on the top dead center side may be flush with the end face of the piston body 21 on the top dead center side. In this case, the end faces of the connecting portion 35 and the annular portion 33 on the top dead center side also constitute the top surface 20A.

[0035] ·The material of the piston body 21 is not limited to aluminum alloy. Also, as long as the condition that the thermal conductivity is lower and the hardness is greater than that of the piston body 21 is satisfied, the material of the top member 31 is not limited to stainless steel.

Explanation of reference numerals

[0036] 21…piston body 31…top member 32…disc portion 33…annular portion 35…connecting portion

Claims

[Claim 1] A cylindrical piston body; a top surface member attached to the piston body, the top surface member having a lower thermal conductivity than the piston body and a higher hardness than the piston body; The top surface member is a disk portion that closes the opening of the piston body; a ring portion located outside the disk portion and exposed from an outer circumferential surface of the piston body; a connecting portion that penetrates the piston body in a radial direction about a central axis of the piston body and connects an outer peripheral edge of the disk portion and an inner peripheral edge of the annular portion, The connecting portion is present in a plurality of parts in a circumferential direction around a central axis of the piston body, The piston body is in contact with the connecting portion in the circumferential direction. Piston of an internal combustion engine.

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