Piston cooling structure

Abstract

To provide a piston cooling structure with excellent cooling efficiency without complicating the manufacture of a piston.SOLUTION: A piston cooling structure 10 cools a piston 12 that reciprocates within a cylinder that is approximately parallel to the ground when installed, and that has a skirt part 16 that surrounds a back surface part 15 of a piston head 14. The piston cooling structure has an oil jet device that sprays oil toward the back surface part 15 of the piston head 14, and a first inclined part 24 that is inclined downward toward the back surface part 15 of the piston head 14 is provided in at least a lower region of the inside surface of the skirt part 16 of the piston 12 when installed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a piston cooling structure, and more particularly to a piston cooling structure that uses oil to cool a piston used in a cylinder that is installed approximately parallel to the ground. [Background technology]

[0002] For example, in a reciprocating piston internal combustion engine, an oil jet device built into the bottom of the cylinder block of the internal combustion engine sucks up oil stored in an oil pan and sprays it onto the back side of the piston head in order to cool the piston.

[0003] Figures 4 and 5 show a conventional piston cooling structure 100 as an example. Figure 4 is a front view, and Figure 5 is a bottom view. However, Figures 4(b) and 5(b) show the inside of the piston 12 in a see-through manner. The piston 12 reciprocates approximately parallel to the ground, as indicated by arrow A. Note that the cylinder is omitted to simplify the drawings. A connecting rod 20 is connected to the piston 12 by fitting a piston pin 18 into a piston boss 19 provided on a piston skirt portion 16. The connecting rod 20 is also connected to a crankshaft (not shown).

[0004] Next, the flow of oil for cooling the piston 12 will be described. Oil from an oil jet device (not shown) is sprayed onto the piston head back surface 15 of the reciprocating piston 12 via a nozzle 22 arranged near the piston 12. In Figures 4(b) and 5(b), the sprayed oil is indicated by the reference numeral 23. The oil jet device is linked to the movement of the crankshaft, and is configured to spray the oil 23 as the crankshaft rotates. The spray speed of the oil 23 from the nozzle 22 changes according to the rotation of the crankshaft, and the spray speed of the oil 23 increases as the rotation speed of the crankshaft increases.

[0005] 6 shows how the oil 23 bounces when it is injected. The oil 23 is injected from the nozzle 22 and hits the piston head back surface 15 of the piston 12, but the piston head back surface 15 is generally flat. Therefore, the oil 23 injected from the nozzle 22 bounces off the piston head back surface 15, and the rebounded oil 23-1 is scattered outside the piston 12. Therefore, the cooling efficiency of the piston 12 is lower than the theoretical value.

[0006] In recent years, with the increasing power output of engines, there has been a demand for improving the cooling efficiency of pistons. For example, Patent Document 1 discloses a piston in which grooves are formed on the back surface of the piston head, and injected oil is retained in these grooves to improve the cooling efficiency of the piston head.

[0007] Patent Document 2 discloses a piston structure in which oil is injected onto the back surface of a slanted engine piston via a hole formed in a connecting rod to cool the piston, and the piston structure is equipped with a flow control plate with a hole inside the piston skirt through which the connecting rod can pass. Because the engine is slanted, the injected oil forms a temporary oil reservoir below the slanted flow control plate, thereby improving the cooling efficiency of the piston. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-285192 [Patent Document 2] Japanese Utility Model Application Publication No. 59-058723 Summary of the Invention [Problem to be solved by the invention]

[0009] Pistons used in internal combustion engines are manufactured by pouring molten material into a mold. Therefore, in order to ensure the internal space inside the piston, a mold that fits the internal space must be created and then cast out.

[0010] The grooves on the back surface of the piston head of Patent Document 1 are formed, for example, by processing the piston head using a cutting tool such as a cutter with a cutting edge after molding, or by providing a core for forming the grooves when casting the piston.

[0011] The flow control plate in Patent Document 2 is fabricated separately and attached after the piston head is fabricated, which requires additional man-hours to fabricate the flow control plate and attach it to the piston.

[0012] That is, forming a groove or oil reservoir for retaining oil in the internal space of the piston increases the cooling efficiency of the piston, but makes the work of manufacturing the piston complicated and time-consuming.

[0013] The present invention has been made in view of the above problems, and an object of the present invention is to provide a piston cooling structure that has good cooling efficiency without complicating the manufacturing process of the piston. [Means for solving the problem]

[0014] In order to achieve the above object, a piston cooling structure according to one embodiment of the present invention comprises: A piston cooling structure including: a piston that, in an installed state, reciprocates within a cylinder that is approximately parallel to the ground and has a skirt portion that surrounds a back surface of a piston head; and an oil jet device that injects oil toward the back surface of the piston head of the piston, The piston skirt has a first inclined portion that slopes downward toward the back surface of the piston head, at least in a lower region of the inner surface of the piston skirt in the installed state.

[0015] With this configuration, the oil sprayed from the oil jet device bounces off the back surface of the piston head. However, after bouncing, some of the oil that would previously have flowed directly outside the piston is caught by the first inclined portion. That is, because the first inclined portion slopes downward toward the back surface of the piston head, at least some of the rebounded oil is caught on the first inclined portion and flows back to the back surface of the piston head. The oil then accumulates on the first inclined portion while also contacting the back surface of the piston head. Therefore, the sprayed and scattered oil can further cool the piston on the first inclined portion. That is, the sprayed oil can be used efficiently to cool the piston, improving the cooling efficiency of the oil spray.

[0016] Furthermore, since it can be formed by adding only the simple structure of the inclined portion, the manufacturing process is not complicated. [Effects of the Invention]

[0017] The piston cooling structure of the present invention allows the injected oil to be used efficiently to cool the piston with a simple configuration without complicating manufacturing, thereby improving piston cooling efficiency and enabling the engine to handle higher power outputs. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a schematic perspective view of a piston according to an embodiment of the piston cooling structure of the present invention; [Figure 2] This is an explanatory diagram of oil splashing inside the piston shown in Figure 1, with the inside of the piston shown in perspective. [Figure 3] 2 is an explanatory diagram of an oil reservoir in the piston shown in FIG. 1, with the inside of the piston shown in perspective. [Figure 4] 4(a) and 4(b) are schematic front views of a conventional piston cooling structure, with the inside of the piston shown in a see-through manner. [Figure 5]5(b) is a schematic bottom view of a conventional piston cooling structure, with the inside of the piston shown in perspective. [Figure 6] 1 is an explanatory diagram illustrating a problem of a conventional piston cooling structure. DETAILED DESCRIPTION OF THE INVENTION

[0019] The piston cooling structure according to an embodiment of the present invention will be described in detail below with reference to the drawings. In this embodiment, a plurality of cylinders are installed substantially parallel to the ground in an installed state, and one of a plurality of pistons reciprocating within each cylinder is shown.

[0020] FIG. 1 shows an embodiment of a piston cooling structure of the present invention, and shows a schematic configuration of a piston.

[0021] As shown in the figure, the piston 12 has a piston head portion 14 and a skirt portion 16 that extends outward from a piston head back surface portion 15, which is the back surface of the piston head portion 14, to surround the back surface portion 15 of the piston head portion 14 and form an internal space 13 therein. In this embodiment, the internal space 13 of the skirt portion 16 is generally cylindrical and extends at an angle downward to the piston head back surface portion 15. The piston head portion 14 is formed with a plurality of grooves 17 into which pressure rings, oil rings, etc. are fitted. The skirt portion 16 is formed with a piston boss 19 into which a piston pin 18 is fitted. The piston pin 18 is inserted into the tip end of a connecting rod 20, and the connecting rod 20 is connected to the piston 12 by fitting the piston pin 18 into the piston boss 19. The piston head back surface portion 15 is formed flat.

[0022] As described above, the first inclined portion 24 that slopes downward toward the piston head back surface portion 15 is configured with an inclined surface that forms the internal space 13. In other words, the lower region of the inclined surface forms the first inclined portion 24. In this embodiment, the first inclined portion 24 is an inclined surface that has a substantially semicircular cross section.

[0023] The second inclined portion 26 facing the first inclined portion 24 is configured in the upper region of the inclined surface that forms the internal space 13.

[0024] The first inclined portion 24 and the second inclined portion 26 extend substantially parallel to each other, but it is sufficient that the distance between them at least becomes smaller toward the piston head back surface portion 15. In other words, the substantially cylindrical internal space 13 may be formed into a slightly tapered, substantially truncated cone shape.

[0025] Due to the formation of the above-mentioned substantially cylindrical internal space 13, the thickness of the skirt portion 16 on the ground side in the installed state gradually increases in the direction away from the piston head back surface portion 15. On the other hand, the thickness of the side opposite to the ground side decreases in the direction away from the piston head back surface portion 15.

[0026] The distance between the first inclined portion 24 and the second inclined portion 26 narrows toward the piston head back surface portion 15, which facilitates the formation of the skirt portion 16 during the manufacturing of the piston 12. In other words, the removal of the skirt portion 16 from the mold during the casting process can be easily performed by a so-called oblique casting operation, and the manufacturing process does not become complicated.

[0027] Next, the cooling effect of the piston cooling structure of the present invention will be described. Oil for cooling the piston 12 is stored in an oil pan (not shown). This oil is sucked up by an oil jet device (not shown) built into the bottom of the cylinder block of the internal combustion engine and sprayed toward the piston head back surface 15, thereby cooling the piston 12.

[0028] For this oil injection, an oil injection nozzle 22 is attached near the reciprocating piston 12.

[0029] The injection speed of the oil 23 injected from the nozzle 22 changes according to the rotation of the crankshaft (not shown) to which the connecting rod 20 is connected, and as the rotation speed of the crankshaft increases, the injection speed of the oil 23 also increases. In other words, when the engine rotates at high speed and the temperature of the piston 12 becomes high, the oil 23 is injected forcefully toward the back surface 15 of the piston head 14.

[0030] 2 shows the behavior of the injected oil, and as shown in the figure, oil 23 injected from nozzle 22 hits the piston head back surface 15 and bounces back (white arrow 23-1). The bounced back oil 23-1 is received by the inclined surface of first inclined portion 24, and a portion of it is further bounced back (white arrow 23-2). Because first inclined portion 24 is inclined toward the back surface 15 of the piston head portion 14, oil 23-2 received by or bounced back from first inclined portion 24 gathers and accumulates at the lowest part of first inclined portion 24.

[0031] FIG. 3 shows the state of the accumulated oil 23-3. As can be seen from the figure, the oil 23-3 remains in contact with the piston head back surface 15, and can absorb heat from the piston head portion 14.

[0032] Therefore, in the past, oil 23-1 that was sprayed from the nozzle 22 and bounced off the piston head back surface 15 flowed directly out of the skirt portion 16, but oil 23-2 that bounces off the first inclined portion 24 of the piston 12 can be retained on the first inclined portion 24 and can be used effectively to cool the piston 12.

[0033] The heat generated in the piston 12 by the engine running is absorbed by the injected oil 23 and further by the oil 23-3 accumulated on the first inclined portion 24, so that the piston 12 is cooled effectively.

[0034] Since the cylinder 12 reciprocates at high speed, the accumulated oil 23-3 absorbs heat while in contact with the piston head back surface 15 while the piston 12 moves from top dead center to bottom dead center, and when the piston 12 reaches the lower fulcrum and moves to top dead center, the oil that has absorbed the heat is released to the outside of the cylinder 12. Then, with the next piston movement, new oil is sprayed and accumulated.

[0035] In this way, the heat absorption effect of the oil 23-3 accumulated in the skirt portion 16, which is not present in conventional configurations, allows the piston 12 to be cooled efficiently by the oil 23, and can also be used for engines with higher output.

[0036] The present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, although the internal space of the skirt portion 16 is cylindrical, it may have other shapes, such as a rectangular prism.

[0037] In addition, in the embodiment, the skirt portion 16 surrounding the piston head back surface portion 15 is configured to be cylindrical (tubular) as a whole, but this is not limited to this, and it is not necessary to form the entire skirt portion 16 in a cylindrical shape as long as it can form at least the first inclined portion 24 and can form a wall portion for attaching the connecting rod 18. [Explanation of symbols]

[0038] 10, 100 Piston cooling structure 12 pistons 13 Interior Space 14 Piston head 15 Back side of piston head 16 Skirt Club 17 Groove 18 Piston pin 19 Piston boss 20 Connecting rod 22 nozzles 23 Oil 23-1, 23-2 Splashed oil 23-3 Stagnant oil 24 1st inclined portion 26 Second inclined portion

Claims

1. In a piston cooling structure for cooling a piston that, in an installed state, reciprocates within a cylinder that is substantially parallel to the ground and has a skirt portion that surrounds a back surface of a piston head, an oil jet device for injecting oil toward the back surface of the piston head; a piston skirt portion provided in at least a lower region of the inner surface of the piston in the installed state with a first inclined portion that slopes downward toward the back surface of the piston head.

2. 2. The piston cooling structure according to claim 1, wherein a second inclined portion is provided in an upper region of the skirt portion of the piston facing the lower region, the second inclined portion having an inclined surface whose distance from the inclined surface of the first inclined portion decreases at least toward the back surface of the piston head.

3. The piston skirt portion is formed in a cylindrical shape extending from the back surface portion of the piston head, The internal space of the cylindrical skirt portion extends downward from the open end to the back surface of the piston head.

3. The piston cooling structure according to claim 2, wherein the piston is formed into a generally cylindrical space extending at an angle, the first inclined portion being formed on a lower inner surface of the cylindrical skirt portion that forms the generally cylindrical space, and the second inclined portion being formed on an upper inner surface of the cylindrical skirt portion that forms the cylindrical space.

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