Piston, engine and vehicle

Abstract

To provide a piston, an engine and a vehicle capable of improving friction while suppressing noise of a piston.SOLUTION: A piston according to one embodiment of the present disclosure is arranged in a cylinder. The piston has an outer surface shape in which an outer peripheral surface at one end side in a first direction protrudes more toward a thrust side toward an anti-thrust side.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to pistons, engines, and vehicles. [Background technology]

[0002] In engines used in vehicles such as automobiles and trucks, the cylinder bores formed in the cylinder section of the cylinder block, etc., are subject to significant deformation due to the tightening of head bolts and thermal loads. This deformation increases friction loss with the pistons arranged inside the cylinder section, which can lead to a deterioration in fuel efficiency. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-145861 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, the piston skirt profile is symmetrical on the thrust side and anti-thrust side. During the piston's upward stroke, the piston's position makes it difficult for an oil film to form on the anti-thrust side, resulting in greater friction loss on the piston skirt during the upward stroke than during the downward stroke. Therefore, if the upper piston skirt profile is moved inward and the diameter is reduced to avoid increased friction loss, the secondary piston motion increases, resulting in a deterioration in noise performance due to slap.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a piston, an engine, and a vehicle that can suppress piston noise and improve friction. [Means for solving the problem]

[0006] A piston according to one embodiment of the present disclosure is a piston arranged in a cylinder, and the outer peripheral surface at one end side in a first direction has an outer surface shape that protrudes more toward the thrust side than toward the anti-thrust side when viewed from the first direction. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a piston, an engine, and a vehicle that can suppress piston noise and improve friction. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram showing a vehicle according to a first embodiment of the present invention; [Figure 2] 1 is an explanatory diagram showing a schematic configuration of an engine according to a first embodiment of the present invention. [Figure 3] FIG. 2 is an explanatory view showing the shape of a piston according to the first embodiment of the present invention. [Figure 4] 4 is a graph showing the profiles of piston skirts according to the first embodiment of the present invention and a comparative example. [Figure 5] 10 is a graph showing a simulation result of friction loss of a piston skirt according to a comparative example. [Figure 6] FIG. 10 is an explanatory diagram showing the state of an oil film on a piston skirt according to a comparative example. [Figure 7] 10 is a graph showing the results of a simulation of the relationship between the crank angle of a piston and the area on the skirt where high shear stress acts due to sliding, according to a comparative example. [Figure 8] 5A and 5B are explanatory diagrams showing the relationship between the swinging motion of the piston during thermal expansion and the oil film according to the embodiment. [Figure 9] 6 is a graph showing a simulation result of friction loss of a piston skirt according to an embodiment. [Figure 10] FIG. 4 is an explanatory diagram showing the state of an oil film on a piston skirt according to the embodiment. [Figure 11]4 is a graph showing FMEP (Friction Mean Effective Pressure) due to sliding between a cylinder bore and a piston skirt in an embodiment and a comparative example. [Figure 12] 6 is a graph showing noise characteristics of cylinder blocks according to an embodiment and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] The configurations of a vehicle 1, an engine 2, and a piston 13 according to an embodiment of the present disclosure will be described below with reference to the drawings. FIG. 1 is an explanatory diagram showing a vehicle according to an embodiment of the present disclosure, and FIG. 2 is an explanatory diagram showing a schematic configuration of an engine. FIG. 3 is an explanatory diagram showing the shape of the piston according to this embodiment, and FIG. 4 is a graph showing the profiles of piston skirts according to this embodiment and a comparative example. In the drawings, X, Y, and Z respectively represent three directions that are perpendicular or intersect with each other. Note that in each drawing, the configuration is enlarged, reduced, or omitted as appropriate for ease of explanation. In this embodiment, an example is shown in which a first direction along the direction of reciprocation of the piston 13 is the Z axis, a second direction in which the cylinder portion 11 is aligned is the Y axis, and a third direction along the thrust and anti-thrust sides is aligned along the X axis.

[0010] 1, a vehicle 1 includes an engine 2, a transmission 3, and, for example, four or more wheels 4. When a piston 13 of the engine 2 of the vehicle 1 is driven, driving force is transmitted to the wheels 4 via the transmission 3.

[0011] The engine 2 includes a cylinder block 10 having a plurality of cylinder portions 11, a piston 13 housed within the cylinder block 10, and a crankshaft 14 provided below the piston 13 within the cylinder block 10.

[0012] The cylinder block 10 according to this embodiment is a multi-cylinder in-line engine in which multiple cylinders are arranged in series. The cylinder block 10 is a so-called closed deck type in which a cylinder head is fastened and fixed to the opening side of a cylinder section 11 by head bolts.

[0013] The cylinder block 10 has, at its upper portion, a plurality of cylinder portions 11, which are a plurality of cylindrical spaces that open to one side in the first direction. A crankshaft 14 is housed in the lower portion of the cylinder block 10.

[0014] In this embodiment, the multiple cylinder sections 11 are arranged along a second direction, which is the extension direction of the crankshaft 14. A piston 13 is arranged inside each cylinder section 11 so as to be able to reciprocate along the first direction. The inner wall surface of the cylinder section 11 forms a cylinder bore (bore section) 20, which serves as a sliding surface for the piston.

[0015] Here, if the reciprocating direction of the piston 13 is defined as a first direction and the direction perpendicular to the first direction and in which the crankshaft 14 extends is defined as a second direction, one side in a third direction perpendicular to the first and second directions is defined as the thrust side, and the other side is defined as the anti-thrust side. For example, when the piston 13 reciprocates in the first direction, a so-called oscillating motion occurs in each cylinder portion 11, in which the piston 13 tilts, causing the piston 13 to hit the inner wall of the cylinder portion 11 and receive lateral pressure. At this time, the direction in which the piston 13 receives lateral pressure when it is subjected to a load due to combustion immediately after top dead center is defined as the thrust side, and the opposite direction is defined as the anti-thrust side.

[0016] A cylinder head is disposed on the cylinder block 10, facing the cylinder block 10, with a gasket interposed therebetween. For example, the cylinder head has bolt holes through which head bolts pass, and is fastened onto the cylinder block 10 by the head bolts.

[0017] The crankshaft 14 is disposed in an accommodation space formed in the lower part of the cylinder block, and is disposed along a second direction that is perpendicular to the direction of the cylinder axis along which the piston 13 reciprocates.

[0018] 3, the piston 13 has a top portion on which a piston ring is provided on the upper side, and a piston skirt 31 (piston skirt) below the area of ​​the top portion where the piston ring is provided. The piston 13 is connected to the crankshaft 14, and reciprocates in the first direction within the cylinder portion 11 as the crankshaft 14 rotates.

[0019] 3 and 4 show the profile of the outer shape of the piston skirt 31 of the piston 13. In Fig. 3, the profile SL of Comparative Example 1, in which the outer shape of the piston skirt 31 is configured symmetrically, is shown by a dashed line, and the profile PL of the outer shape of the piston 13 according to Example 1 of this embodiment is shown by a solid line.

[0020] In this embodiment, the piston skirt 31 has an elliptical shape, with its dimensions on the thrust side and anti-thrust side larger than those in directions perpendicular to the thrust and anti-thrust directions. As shown in the profile in Fig. 3, the piston skirt 31 is configured so that its widths on the thrust side and anti-thrust side are particularly enlarged near the midpoint in the height direction, which is the direction of movement. That is, the piston skirt 31 has an enlarged portion 311, where its width dimension along the thrust and anti-thrust directions is greatest, near the midpoint in the first direction, which is the direction of reciprocating movement.

[0021] The outer shape of piston skirt 31 is asymmetrical between the thrust side and the anti-thrust side. That is, the outer peripheral surface of piston skirt 31 at its upper end has an outer surface shape that protrudes more toward the thrust side than toward the anti-thrust side when viewed from the first direction. Specifically, the shape of piston skirt 31 has a profile in which the outer shape shifts upward from enlarged portion 311, where the width is greatest, to upper end 312, with the outer shape shifting inward on the anti-thrust side and outward on the thrust side. That is, in the upper region from enlarged portion 311 to upper end 312, the outer shape on the anti-thrust side is set to be more inward than the outer shape on the thrust side.

[0022] Moreover, the piston skirt 31 is configured symmetrically in the lower region from the expanded portion 311 to the lower end portion 313.

[0023] That is, the piston skirt 31 of the piston 13 according to this embodiment has a shape in which the upper side is biased more toward the thrust side than the lower side. In addition, the bias becomes larger from the enlarged portion 311 toward the upper end portion 312.

[0024] Generally, the piston sliding speed increases when the piston is near the midpoint of its reciprocating motion in the cylinder section 11. The friction generated between the piston skirt and the bore, which is the sliding surface of the inner wall of the cylinder section 11, increases as the piston sliding speed increases. Therefore, when the piston reciprocates within the cylinder section, the skirt friction increases when the piston is near the midpoint of its reciprocating motion. For example, the piston skirt friction tends to increase where the piston sliding speed is highest.

[0025] Figure 5 is a graph showing the results of a simulation of piston skirt friction loss in a comparative example. The vertical axis represents friction loss, and the horizontal axis represents crank angle. The analysis conditions were a rated point (maximum output point) of 2860 rpm (FL), and a piston pin offset of +1 mm.

[0026] As shown in Figure 5, the piston in the comparative example rises during the intake stroke between crank angles 720 and 900°, and then descends from top dead center. Between crank angles 720 and 900°, the piston tilts toward the thrust side, generating friction on the thrust side. Then, during the exhaust stroke, the piston rises again from bottom to top between crank angles 900 and 1080°, and then descends again until crank angle 1080°. The peak between crank angles 900 and 1080° is the upstroke. At this time, friction occurs on the anti-thrust side, and is at its maximum.

[0027] Figure 6 is an explanatory diagram showing the state of the oil film on the piston skirt in a comparative example. Comparing the bottom diagram of Figure 6, it can be seen that the oil film on the thrust side is thicker than the oil film on the anti-thrust side. The top diagram shows that the oil film pressure is high and the oil film is thick.

[0028] Figure 7 is a graph showing the results of a simulation of the relationship between the crank angle of a piston in a comparative example and the area on the skirt where high shear stress acts due to sliding. In Figure 7, the vertical axis shows area and the horizontal axis shows crank angle. Figure 7 shows that the area increases during the upward stroke. At this time, the area on which shear stress acts becomes larger, resulting in greater friction.

[0029] FIG. 8 is an explanatory diagram showing the relationship between thermal expansion, oscillation angle, and oil film of a piston according to an embodiment. FIG. 8 shows the inclination of the piston 13 and the state of the oil film relative to the shape of the bore 20. In FIG. 8, on the thrust side, the piston 13 descends while tilting counterclockwise due to side force caused by combustion pressure. Therefore, as shown by the hatching, an oil film forms in the gaps that open downward. On the other hand, on the anti-thrust side, the piston ascends while tilting clockwise. Therefore, an oil film forms in the gaps that open upward. That is, if the profile of the piston skirt 31 is such that the upper side protrudes toward the thrust side, an oil film is likely to form on the lower side on the thrust side. On the anti-thrust side, the gaps that open upward, which is the direction of travel, are small, making it difficult for an oil film to form. Therefore, friction is high on the anti-thrust side during ascent. Therefore, from FIG. 8, it can be said that the required shapes of the piston skirt on the thrust side and the anti-thrust side differ depending on the attitude of the piston 13 and the direction of oil inflow.

[0030] Figure 9 is a graph showing the results of a simulation of friction loss with the piston skirt in the embodiment and the comparative example. Figure 9 shows that friction can be reduced where friction loss is at its maximum. The analysis conditions are the rated point (maximum output point): 2860 rpm FL, piston: pin offset +1 mm, the same analysis conditions as the comparative example.

[0031] Fig. 10 is an explanatory diagram showing the state of the oil film on the piston skirt according to the embodiment, which shows that a thicker oil film is formed in the embodiment than in the comparative example.

[0032] FIG. 11 is a graph showing the friction mean effective pressure (FMEP) due to sliding between the cylinder bore and piston skirt in the embodiment and the comparative example. FIG. 11 shows a simulation of the friction between the piston and the sliding surface when the piston 13 strokes, with the cylinder bore 20 deformed by thermal loads, head bolt tightening loads, and other factors during actual operation. The simulation conditions are the same for the comparative example and the embodiment. As can be seen from the graph in FIG. 11, the FMEP in the embodiment is almost half that of the comparative example. These data demonstrate that the piston 13 in the embodiment reduces friction with the cylinder bore 20. Therefore, the piston 13 can reduce friction and deformation compared to the comparative example, which has a symmetrical profile. FIG. 12 is a graph showing acceleration amplitude as a noise characteristic of the cylinder block 10 in the embodiment and the comparative example. The measurement position is, for example, the acceleration at the degeneration point at the top of the cylinder block 10.

[0033] 11 shows that the piston 13 according to the embodiment has reduced friction compared to Comparative Example 1. Also, FIG. 12 shows no deterioration in noise performance (NV performance). That is, as shown in FIGS. 11 and 12, the piston 13 according to the embodiment is expected to have lower friction than Comparative Example 1 by forming the piston skirt 31 so that the upper side thereof protrudes toward the thrust side. Furthermore, by adjusting the shape of the piston 13 in this way, it is possible to expect performance improvements without making expensive investments in processing equipment, etc.

[0034] As described above, with the piston 13 according to this embodiment, the piston skirt 31 is shaped so that its upper portion on the thrust side juts outward and its upper portion on the anti-thrust side recedes inward, thereby promoting oil film formation and reducing friction, thereby suppressing noise and improving engine performance.

[0035] The present invention is not limited to the above embodiment. For example, the detailed shape of the profile can be changed as appropriate. Furthermore, the number of cylinders 11 arranged and the specific shape and arrangement of each component are not limited to those described above and can be changed as appropriate.

[0036] Although one embodiment of the present disclosure has been described above in detail, the present invention is not limited to the above embodiment and can be appropriately modified, improved, etc. The present invention is defined by the claims and includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0037] 1...vehicle, 2...engine, 3...transmission, 4...wheel, 10...cylinder block, 11...cylinder portion, 13...piston, 14...crankshaft, 20...cylinder bore (bore), 31...piston skirt, 311...enlarged portion, 312...upper end, 313...lower end.

Claims

1. A piston disposed within a cylinder, A piston having an outer peripheral surface at one end side in a first direction that has an outer surface shape that protrudes more toward the thrust side than toward the anti-thrust side.

2. A plurality of pistons according to claim 1; a cylinder block in which a plurality of cylinder portions in which the pistons are disposed are formed; An engine.

3. A plurality of the cylinder portions are formed side by side, 3. The engine according to claim 2, wherein one side in a direction intersecting a direction in which the plurality of cylinder portions are arranged is the thrust side, and the other side is the anti-thrust side.

4. A vehicle comprising the engine of claim 3.

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