Piston

Abstract

The present invention provides a piston that slides inside a cylinder liner, the piston comprising a top land, a top ring, a second land, a second ring, and a third land, in that order from the top dead center side in the sliding direction. A lateral surface of the third land is located farther outward than a lateral surface of the top land in the radial direction of the piston. The lateral surface of the third land is located farther inward than a lateral surface of the second land in the radial direction of the piston.

Description

piston

[0001] The present disclosure relates to a piston.

[0002] The piston is provided with a top land, a second land, a third land, and a skirt in this order from the top dead center side in the sliding direction of the piston. A top ring is provided in the groove between the top land and the second land. A second ring is provided in the groove between the second land and the third land. An oil ring is provided in the groove between the third land and the skirt.

[0003] In conventional pistons, the side of the third land, the side of the top land, and the side of the second land are located farthest from the liner (cylinder liner) that houses the piston (see, for example, Patent Document 1). By locating the third land farthest from the liner in this way, piston scuffing (hereinafter simply referred to as scuffing in this specification) in which the piston gets caught on the liner is suppressed.

[0004] Japanese National Publication No. 6-34152

[0005] Conventional pistons have a large gap between the third land and the liner, which makes it easy for the second ring to float, which increases the amount of blow-by gas.

[0006] An object of the present disclosure is to provide a piston that can reduce the amount of blow-by gas.

[0007] The piston according to the present disclosure is a piston that slides within a cylinder liner and comprises, in order from the top dead center side in the sliding direction, a top land, a top ring, a second land, a second ring, and a third land, with the side of the third land being positioned radially outward of the piston than the side of the top land, and the side of the third land being positioned radially inward of the piston than the side of the second land.

[0008] With this piston, by placing the third land closer to the liner than the top land, the pressure on the bottom dead center side of the second ring can be reduced, suppressing second ring lift. Furthermore, by placing the second ring closer to the liner than the third land, piston scuffing can be suppressed.

[0009] 1 is a structural diagram of a piston according to an embodiment of the present disclosure, and FIG. 2 is a graph showing a simulated side profile of a piston according to an embodiment of the present disclosure.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following description, the direction in which the piston 1 slides will be referred to as the sliding direction, the side on which the top dead center of the piston 1 is located will be referred to as the top dead center side, and the side on which the bottom dead center of the piston 1 is located will be referred to as the bottom dead center side.

[0011] As shown in Figure 1, a piston 1 is rotatably supported on a crankshaft 4 via a connecting rod 2. The piston 1 is housed in a liner (cylinder liner) 6 fixed to a cylinder of an engine 3, and rotates the crankshaft 4 by reciprocating along the liner 6 between top dead center and bottom dead center. Oil is stored in a crankcase 8 that houses the crankshaft 4. The engine 3 in this embodiment is a diesel engine.

[0012] The piston 1 includes a top land 11, a top ring 12, a second land 13, a second ring 14, a third land 15, an oil ring 16, and a skirt 17. The piston 1 has a substantially cylindrical shape and is formed by aluminum casting, aluminum forging, or the like.

[0013] The top land 11 is located closest to the top dead center and is the portion of the piston 1 facing the combustion chamber 10. The side surface 11a of the top land 11 widens radially outward toward the bottom dead center in the sliding direction. That is, the side surface 11a of the top land 11 is wider radially outward at the end of the bottom dead center than at the end of the top dead center. A top ring groove 11b is provided between the top land 11 and the second land 13. An annular top ring 12 is housed in the top ring groove 11b. The top ring 12 contacts the liner 6 and seals the gap between the combustion chamber 10 and the crankcase 8. The top ring 12 maintains an oil film formed between the liner 6 and the top ring 12 and prevents oil from entering the combustion chamber 10.

[0014] The second land 13 is a portion of the piston 1 adjacent to the top land 11 on the bottom dead center side, with the top ring groove 11b in between. The side surface 13a of the second land 13 is wider radially outward from the piston 1 at the bottom dead center end than at the top dead center end. A second ring groove 13b is provided between the second land 13 and the third land 15. An annular second ring 14 is housed in the second ring groove 13b. Like the top ring 12, the second ring 14 contacts the liner 6 and seals the gap between the combustion chamber 10 and the crankcase 8. Like the top ring 12, the second ring 14 maintains the oil film formed between the liner 6 and the top ring 12 and prevents oil from entering the combustion chamber 10.

[0015] The third land 15 is a portion of the piston 1 adjacent to the second land 13 on the bottom dead center side, with the second ring groove 13b in between. In this embodiment, the side surface 15a of the third land 15 is formed straight along the sliding direction of the piston 1, with its top dead center-side end and bottom dead center-side end. An oil ring groove 15b is provided between the third land 15 and the skirt 17. An annular oil ring 16 is housed in the oil ring groove 15b. Like the top ring 12 and second ring 14, the oil ring 16 contacts the liner 6 and seals the gap between the combustion chamber 10 and the crankcase 8. Similarly to the top ring 12 and second ring 14, the oil ring 16 maintains the oil film formed between the liner 6 and the top ring 12 and prevents oil from entering the combustion chamber 10. The oil ring 16 also collects excess oil adhering to the liner 6 and returns the oil to the crankcase 8 via an oil passage (not shown) in the piston 1.

[0016] The skirt 17 is a portion of the piston 1 adjacent to the third land 15 on the bottom dead center side with the oil ring groove 15b in between. A side surface 17a of the skirt 17 is longer in the sliding direction than the top land 11, the second land 13, and the third land 15.

[0017] Fig. 2 is a graph showing simulated profiles of the side surface 11a of the top land 11 (see Fig. 1), the side surface 13a of the second land 13 (see Fig. 1), the side surface 15a of the third land 15 (see Fig. 1), and the side surface 17a of the skirt 17 (see Fig. 1). More specifically, Fig. 2 is a graph showing the distance from the liner 6 to the side surface 11a of the top land 11, the side surface 13a of the second land 13, the side surface 15a of the third land 15, and the side surface 17a of the skirt 17. The graph shown by the solid line in Fig. 2 is the profile of the piston 1 of the present disclosure, and the graph shown by the dashed line in Fig. 2 is the profile of a conventional piston disclosed as a comparative example.

[0018] Point A in Figure 2 indicates the position of the end of the side surface 11a of the top land 11 on the top dead center side. Point B indicates the position of the end of the side surface 11a of the top land 11 on the bottom dead center side. Point C indicates the position of the end of the side surface 13a of the second land 13 on the top dead center side. Point D indicates the position of the end of the side surface 13a of the second land 13 on the bottom dead center side. The solid line E indicates the position of the side surface 15a of the third land 15. Point F indicates the position of the end of the side surface 17a of the skirt 17 on the top dead center side. Point G indicates the position of the end of the side surface 17a of the skirt 17 on the bottom dead center side.

[0019] As shown by the solid lines at points B and E in Figure 2, in the piston 1, the side surface 15a of the third land 15 is positioned radially outward of the piston 1 relative to the bottom dead center end of the side surface 11a of the top land 11. By bringing the side surface 15a of the third land 15 closer to the liner 6 than the side surface 11a of the top land 11, the pressure on the bottom dead center side of the second ring 14 can be reduced, thereby suppressing lifting of the second ring 14. When the second ring 14 floats toward the top dead center, a gap is generated between the second ring groove 13b and the second ring 14, through which blow-by gas passes. The piston 1 of the present disclosure suppresses lifting of the second ring 14, thereby suppressing the generation of this gap and realizing a reduction in the amount of blow-by gas.

[0020] An imaginary line X1 connecting points A and B in Figure 2 indicates an extension of the side surface 11a of the top land 11. As shown in Figure 2, the side surface 15a of the third land 15 is located radially outward from the extension of the side surface 11a of the top land 11. This ensures that the side surface 15a of the third land 15 is always located radially outward from the bottom dead center end of the side surface 11a of the top land 11, even when the piston 1 rotates counterclockwise or clockwise and the posture of the piston 1 is tilted with respect to the sliding direction of the piston 1. As a result, floating of the second ring 14 can be more reliably suppressed.

[0021] As shown by the solid lines at points D and E in Figure 2, the side surface 15a of the third land 15 is located radially inward of the piston 1 relative to the side surface 13a of the second land 13. By positioning the side surface 13a of the second land 13 closer to the liner 6 than the side surface 15a of the third land 15, scuffing of the piston 1 due to the third land 15 can be suppressed.

[0022] The imaginary line X2 in Fig. 2 indicates an extension plane of the profile of the top dead center side of the side surface 17a of the skirt 17 toward the top dead center. As shown by the imaginary line X2 in Fig. 2, at least a portion of the side surface 13a of the second land 13 is located on an extension plane of the profile of the top dead center side of the side surface 17a of the skirt 17 toward the top dead center. Furthermore, in this embodiment, the side surface 13a of the second land 13 is formed so as to substantially coincide with the extension plane of the profile of the side surface 17a of the skirt 17 toward the top dead center.

[0023] The skirt 17 primarily functions to prevent tilting of the piston 1. By locating a portion of the side surface 13a of the second land 13 on the extension of the side surface 17a of the skirt 17, tilting of the piston 1 can be prevented by using not only the skirt 17 but also the second land 13. In the piston 1 of the present disclosure, the third land 15 is closer to the liner 6 than in conventional pistons. However, as described above, the skirt 17 and the second land 13 are used to stabilize the posture of the piston 1, which prevents scuffing caused by the third land 15.

[0024] Furthermore, the piston 1 of the present disclosure is formed so that the side surface 13a of the second land 13 coincides with the extension surface of the profile of the side surface 17a of the skirt 17 toward the top dead center, thereby making the posture of the piston 1 more stable.

[0025] The shape of the side surface 17a of the skirt 17 is such that it is positioned radially inward of the piston 1 as it moves from the middle of the piston 1 in the sliding direction toward the top dead center and bottom dead center. The imaginary line X3 in FIG. 2 is a line extending from point F toward the bottom dead center in the sliding direction. As shown by points F and G in FIG. 2, the shape of the side surface 17a of the skirt 17 is such that the end of the side surface 17a on the bottom dead center side is positioned radially inward of the piston 1 relative to the end of the side surface 17a on the top dead center side. As shown in the graph of the comparative example in FIG. 2, in a conventional piston, the end of the side surface 17a on the bottom dead center side is positioned radially outward of the piston 1 relative to the end of the side surface 17a on the top dead center side, thereby preventing the piston from tilting. In such a conventional piston, the contact area between the skirt and the liner tends to be large, which tends to increase frictional resistance. The shape of the side surface 17a of the skirt 17 of the present disclosure is such that the end of the side surface 17a on the bottom dead center side is positioned radially inward of the piston 1 relative to the end of the side surface 17a on the top dead center side. This narrows the lower end of the skirt 17 radially inward. This reduces the contact area between the liner 6 and the side surface 17a of the skirt 17, thereby reducing frictional resistance. Meanwhile, as described above, the skirt 17 and the second land 13 are used to prevent the piston 1 from tilting, which makes it easier to stabilize the posture of the piston 1. When the posture of the piston 1 is stabilized, it is easier to prevent the second ring 14 from floating. As a result, this piston 1 can further reduce the amount of blow-by gas.

[0026] As described above, according to the present disclosure, it is possible to provide a piston 1 capable of reducing the amount of blow-by gas.

[0027] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the invention. In particular, the multiple modifications described in this specification can be combined as needed.

[0028] For example, in the above embodiment, the engine 3 is a diesel engine, but the piston 1 may be a piston 1 used in a gasoline engine.

[0029] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0030] This application is based on a Japanese patent application (Patent Application No. 2023-203291) filed on November 30, 2023, the contents of which are incorporated herein by reference.

[0031] 1 Piston 6 Liner 11 Top land 11a Side 12 Top ring 13 Second land 13a Side 14 Second ring 15 Third land 15a Side 16 Oil ring 17 Skirt 17a Side

Claims

1. A piston that slides within a cylinder liner, In order from the top dead center side in the sliding direction, there are a top land, a top ring, a second land, a second ring, and a third land. Equipped with a side surface of the third land is located radially outward of the piston relative to a side surface of the top land, and a side surface of the third land is located radially inward of the piston relative to a side surface of the second land, a skirt disposed closer to the bottom dead center in the sliding direction than the third land; a part of a side surface of the second land is located on an extension plane obtained by extending a shape of the side surface of the skirt on a top dead center side in the sliding direction toward the top dead center, a side surface of the second land is disposed along an extension surface obtained by extending the shape of the side surface of the skirt on the top dead center side in the sliding direction toward the top dead center side; piston.

2. The side surface of the top land widens radially outward toward the bottom dead center in the sliding direction, A side surface of the third land is located radially outward from an extension surface of a side surface of the top land. The piston of claim 1.

3. The shape of the side surface of the skirt is such that the end portion on the bottom dead center side is positioned radially more inward than the end portion on the top dead center side of the piston.

3. The piston according to claim 1 or 2.