JPH0667838U - Piston structure of internal combustion engine - Google Patents

Abstract

(57) [Summary] [Objective] By making the amount of tilting of the piston as small as possible, it is possible to suppress the generation of a large hammering sound due to the piston lap and to reduce the amount of blow-by gas generated. [Structure] A thick portion 24 is provided from an upper end portion 20c to a lower end portion 20d on an inner surface of a thrust side side wall 20b of a skirt portion 20 in which a piston 12 tilts during an expansion stroke of an engine and receives a thrust force from a thrust side inner surface 11b of a cylinder 11. The rigidity is set such that the upper and lower end portions 20c and the lower end portion 20d are substantially equal to each other by being formed so as to be gradually increased in the direction.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to improvement of a piston structure of an internal combustion engine.

[0002]

[Prior art]

 As is well known, for example, a piston of an internal combustion engine for an automobile tilts during one cycle because a lateral force of a connecting rod, a gas pressure during an expansion stroke, and a moment around a piston pin act due to an inertial force. Then, it reciprocates while being pressed against the inner surfaces of the thrust and anti-thrust cylinders. For this reason, the lower end of the skirt portion of the piston tends to locally have high surface pressure.

That is, as shown in FIG. 8, for example, when the piston 1 descends from the top dead center position to the bottom dead center side through the connecting rod 2 due to gas pressure during the expansion stroke, the piston 1 moves to the piston pin 3 A clockwise moment is generated around the center of the piston 1. As a result, the piston 1 tilts and the crown 4 on the anti-thrust side or the upper end of the side wall 6b on the anti-thrust side contacts the anti-thrust side inner surface 5a of the cylinder 5, while the skirt The thrust side wall 6a of the portion 6 moves to the bottom dead center side while contacting the thrust side inner surface 5b of the cylinder 5. Therefore, on the crown portion 4 side of the piston 1, the surface pressure against the inner surface of the cylinder 5 can be sufficiently suppressed by the piston ring 7, but the lower end portion of the skirt portion 6 has the thrust side wall 6a and the anti-thrust side wall. 6b tends to locally cause high surface pressure.

Therefore, for example, in the technique disclosed in Japanese Utility Model Laid-Open No. 64-21239, the skirt portion 6 is formed by making the thickness of the skirt portion 6 thinner than the thickness of the anti-thrust side sidewall 6b. The rigidity of the thrust side wall 6a is set low. As a result, when the thrust-side side wall 6a is pressed against the thrust-side inner surface 5b of the cylinder 5, the thrust-side side wall 6a is easily deformed to reduce the contact pressure by increasing the contact area.

[0005]

[Problems to be solved by the device]

 However, in the above-mentioned conventional piston structure, the thickness of the thrust side wall 6a is made thinner than the anti-thrust side side wall 6b of the skirt part 6, so that the skirt part 6 during the expansion stroke is as described above. Although the surface pressure of the thrust side wall 6a becomes low due to the large deformation of the piston 1, the amount of tilting of the piston 1 increases due to the large deformation of the thrust side wall 6a. Therefore, the piston slap with respect to the inner surfaces 5a and 5b of the cylinder 5 immediately after the top dead center becomes large, and there is a possibility that a violent impact or a large hammering sound may be generated.

Further, since the tilting amount of the piston 1 becomes large, the outer diameter of the piston crown portion 4 must be set to be relatively small. Therefore, the clearance (land clearance C) between the outer peripheral surface of the piston crown portion 4 and the inner surface of the cylinder 5 becomes large. As a result, the amount of gas leaking from the combustion chamber into the crankcase, that is, the so-called blow-by gas amount increases, the amount of unburned HC generated increases, and exhaust emission performance deteriorates.

[0007]

[Means for Solving the Problems]

 The present invention has been devised in view of the above conventional problems. The invention of claim 1 is a piston structure of an internal combustion engine that reciprocates in a cylinder, wherein the piston tilts at least during an expansion stroke of the engine. The side wall of the skirt portion on the side that receives the thrust force from the inner surface of the cylinder is formed so that the thickness gradually increases from the upper end portion to the lower end portion of the skirt portion, and the thick portion has a circumferential direction in the skirt portion. The feature is that the length is set up and down almost uniformly.

According to a second aspect of the present invention, in a piston structure of an internal combustion engine that reciprocates in a cylinder, a side wall of a skirt portion on a side that receives the thrust force extends from a lower end portion of the skirt portion to a vicinity of an upper end portion thereof. It is characterized in that the side wall on the thrust side in the circumferential direction of the skirt portion is gradually tapered from the upper end portion to the lower end portion.

According to a third aspect of the present invention, in a piston structure of an internal combustion engine that reciprocates in a cylinder, the side wall of the skirt portion on the side that receives the thrust force is located on both sides of the skirt portion centerline between the pin boss portions. The pin boss is formed so that the thickness is gradually increased over the side portion, and the thickness distribution in the vertical direction of the thick portion is set to be gradually wider from the upper end side to the lower end side of the skirt portion. Is characterized by.

[0010]

[Action]

 According to the invention of each of the above-mentioned constitutions, the rigidity of the thrust side wall of the skirt portion is gradually increased by, for example, gradually increasing the wall thickness from the upper end portion toward the lower end portion. The rigidity of the upper end connected to the land and the lower end of the free end are substantially the same. Therefore, the amount of vertical deformation of the thrust side wall of the skirt during the expansion stroke is small and substantially uniform. Therefore, the amount of tilting of the piston immediately after top dead center can be made as small as possible. As a result, it is possible to sufficiently suppress the generation of a loud tapping sound due to the piston slap, prevent the wear of the cylinder by lowering the pressing force of the lower end of the skirt against the thrust-side inner surface of the cylinder, and the land clearance is also possible. It can be made as small as possible.

[0011]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of a piston structure of an internal combustion engine according to the first aspect of the present invention. The piston 12 reciprocating in a cylinder 11 in a cylinder block is made of an aluminum alloy material. Ring grooves 17, 18, and 19 for fitting and holding three piston rings 14, 15, and 16 are formed on the outer periphery of a ring land portion 12a formed in a substantially circular surface and below the crown portion 13 for receiving combustion gas. In addition, the skirt portion 20 is coupled to the lower portion of the ring land portion 12a. A pair of pin boss portions 23 that support the piston pin 22 through the pin hole 21 are provided to face each other at a substantially central position inside.

Further, in the skirt portion 20, for example, the side wall 20a on the anti-thrust side where the crown portion 13 is pressed against the inner surface 11a on the anti-thrust side of the cylinder 11 immediately after the top dead center during the expansion stroke is formed to have a uniform thickness. On the other hand, the thick side wall 24 is formed on the inner surface of the thrust side wall 20b. That is, the thick portion 24 is gradually thickened from the skirt upper end portion 20c side near the ring groove 19 to the lower end portion 20d at an inclination angle θ of about 2 ° to 10 °, and at the same time, The width in the circumferential direction is set to a predetermined width. Therefore, the rigidity of the skirt portion 20 on the thrust side gradually increases from the upper end portion 20c to the lower end portion 20d due to the thick portion 24, whereby the relative thrust of the thrust side upper and lower end portions 20c, 20d. The rigidity is almost the same.

Therefore, according to this embodiment, during the expansion stroke of the engine, the piston 12 tilts rightward in the drawing immediately after the top dead center, and the anti-thrust side 13a of the crown portion 13 becomes the anti-thrust side of the cylinder 11. The lower end portion 20d, which is the free end side of the thrust side wall 20b of the skirt portion 20 that hits the inner surface 11a, contacts the thrust side inner surface 11b of the cylinder 11. At this time, as described above, the lower end portion 20d has high rigidity due to the thick portion 24, and has substantially the same rigidity as the vicinity of the upper end portion 20c which is connected to the ring land portion 12a and has high rigidity. Since this is ensured, the amount of compressive deformation of the lower end portion 20d of the thrust side wall 20b when hitting the thrust side inner surface 11b of the cylinder 11 is suppressed to a small amount, and the amount of deformation is uniform with the upper end portion 20c side. Therefore, the amount of tilting of the piston 12 rightward immediately after the top dead center can be made as small as possible. As a result, the generation of a loud hammering sound due to the piston slap is sufficiently suppressed, and the pressure contact force of the lower end portion 20d with respect to the thrust-side inner surface 11b of the cylinder 11 is reduced to prevent the occurrence of wear.

Moreover, since the tilting amount of the piston 12 can be reduced, the outer diameter dimension of the crown portion 13 can be increased as much as possible, and therefore the land clearance C can be reduced. Therefore, blow-by gas from the combustion chamber 25 into the crankcase is prevented, and the amount of unburned HC generated can be reduced.

2 to 4 show an embodiment according to the invention of claim 2, wherein the thickness of the thrust side wall 20b of the skirt portion 20 of the piston 12 is gradually reduced from the upper end portion 20c to the lower end portion 20d. While being formed, the length in the circumferential direction is set to be gradually tapered from the upper end 20c to the lower end 20d. That is, the circumferential length Sb of the lower end portion 20d is set to be gradually shorter than the circumferential length Sa of the upper end portion 20c. As a result, the supporting rigidity of the skirt portion on the lower end portion 20d side in the circumferential direction gradually increases, and becomes substantially the same as that on the upper end portion 20c side. The thickness of the skirt portion 20 on the anti-thrust side and the length in the circumferential direction are set to be the same for the upper and lower end portions 20e 1 and 20f 2 as shown in FIGS.

Therefore, also in this embodiment, the same operational effect as the embodiment according to the invention of claim 1 can be obtained without increasing the weight of the piston.

5 to 7 show an embodiment of the invention of claim 3, in which the thickness of the upper and lower end portions 20c and 20d of the skirt portion on the thrust side side wall 20b in the circumferential direction is changed. The upper and lower rigidity is changed.

That is, the circumferential wall thickness of the skirt portion 20 between the pin boss portions 23 of the piston 12 is uniform on the anti-thrust side, but different on the thrust side between the upper and lower end portions 20c, 20d. is there. That is, as shown in FIGS. 5 and 6, it is formed such that the thickness gradually increases from the center line X between the pin boss portions 23 and 23 to the side portions of the pin boss portions 23 and 23, and the thick portion The thickness of the upper end portion 20c in the circumferential direction from the side of the pin boss portion 23 in the center line X direction between the pin boss portions 23, 23 is the thick portion 26 in the range of the arc length Lb. On the other hand, the lower end portion 20d is formed in the thick portion 27 in the range of the arc length La which is longer than Lb in the circumferential direction from the pin boss portion 23 in the center line X direction, and is formed from the upper end portion 20c side. The thickness distribution of the thick-walled portions 26, 27 up to the vicinity of the lower end portion 20d side is widened toward the end. Therefore, the upper end portion 20c and the lower end portion 20d have substantially the same rigidity. Therefore, this embodiment can also obtain the same operational effect as each embodiment.

Therefore, the generation of hammering sound due to the piston slap can be further suppressed, and the land clearance can be reduced to further improve the emission performance.

The present invention is not limited to the configuration of the above-described embodiment, but as a means for changing the rigidity of the upper and lower end portions 20c, 20d of the skirt portion 20, a core material having a changed wall thickness is embedded inside. It is also possible to do.

[0022]

[Effect of device]

 As is clear from the above description, according to the piston structure of the internal combustion engine according to the inventions of claims 1 to 3, the rigidity of the skirt portion which receives the thrust force from the inner surface of the cylinder due to the tilting of the piston during the expansion stroke of the engine is achieved. However, since it is set to be gradually increased from the upper end portion to the lower end portion, the rigidity of the entire side wall on the thrust side becomes substantially the same in the vertical direction. Therefore, when the thrust force is applied from the inner surface of the cylinder, the vertical deformation amount of the skirt portion on the thrust side is small and substantially uniform. Therefore, the amount of tilting of the piston can be made as small as possible. As a result, the generation of a large hammering sound due to the piston slap is suppressed, and the pressure contact force of the skirt portion with respect to the thrust side inner surface of the cylinder is reduced to prevent the occurrence of wear. Further, the production of blow-by gas, that is, the production of unburned HC due to the reduction of land clearance can be reduced.

[Brief description of drawings]

1 is a sectional view of an essential part showing an embodiment of the invention of claim 1;

FIG. 2 is a side view of a piston showing an embodiment according to the invention of claim 2;

3 is a sectional view taken along the line AA of FIG.

FIG. 4 is another side view of the piston showing the second embodiment.

FIG. 5 is an A- of FIG. 7 showing an embodiment according to the invention of claim 3;
A line sectional view.

6 is a sectional view taken along line BB of FIG.

FIG. 7 is a vertical cross-sectional view of the piston of this embodiment.

FIG. 8 is a schematic view showing the operation of a conventional piston immediately after top dead center.

[Explanation of symbols]

 11 ... Cylinder 11b ... Thrust side inner surface 12 ... Piston 20 ... Skirt portion 20a ... Anti-thrust side sidewall 20b ... Thrust side sidewall 20c ... Thrust side upper end 20d ... Thrust side lower end 23 ... Pin boss 24, 26, 27 ... Thick wall Department

Claims (3)

[Scope of utility model registration request] 1. In a piston structure of an internal combustion engine that reciprocates in a cylinder, at least during an expansion stroke of the engine,
The side wall of the skirt portion on the side where the piston tilts and receives the thrust force from the inner surface of the cylinder is formed so that the thickness gradually increases from the upper end portion to the lower end portion of the skirt portion, and the skirt of the thick portion A piston structure for an internal combustion engine, characterized in that the length in the circumferential direction is set substantially vertically. 2. In a piston structure of an internal combustion engine that reciprocates in a cylinder, the side wall of the skirt portion on the side that receives the thrust force gradually becomes thicker from the lower end of the skirt to the vicinity of the upper end. The piston structure of the internal combustion engine, wherein the length of the thrust side wall in the circumferential direction of the skirt portion is gradually shortened from the upper end to the lower end. 3. In a piston structure of an internal combustion engine that reciprocates in a cylinder, the side wall of the skirt portion on the side that receives the thrust force extends from the skirt center line side between both pin boss portions to the side portions of both pin boss portions. Piston of an internal combustion engine, characterized in that the thickness distribution in the vertical direction of the thick portion is gradually widened from the upper end side to the lower end side of the skirt portion. Construction.