JP2003161203A - Piston for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively supply lubricant to a relief groove 22 recessed on a bearing surface 14 and to reduce the weight of a pin boss part 15. <P>SOLUTION: The pin boss part 15 integrally ties a piston head 11 including a piston crown surface 12 with an approximately cylindrical part 13 formed with the bearing surface 14 for inserting a piston pin. The relief groove 22 recessed on the bearing surface 14 along the peripheral surface of the piston pin is arranged within an upper half area R of the piston crown surface 12 in the bearing surface 14. Prolongations 24 along thrust side edges 23a of the pin boss 15 are made to intersect with the relief groove 22 in an axial view of the piston pin. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston preferably used in a reciprocating internal combustion engine for automobiles.

[0002]

2. Description of the Related Art A piston of an internal combustion engine generally has a structure in which a piston head including a piston crown surface and a cylindrical portion having a bearing surface through which a piston pin is inserted are integrally connected by a pin boss portion. ing. The bearing surface has been increased in surface pressure due to the reduction of the pressure receiving area due to the recent downsizing and weight reduction of pistons, but on the other hand, it is very difficult to supply lubricating oil in a layout. It is a part of the piston friction part where lubrication is extremely difficult. In order to improve the lubrication state between the bearing surface and the piston pin, a relief groove is provided in the bearing surface of the cylindrical portion as disclosed in Japanese Patent Laid-Open No. 10-18908, and the relief groove is formed. A technique for supplying lubricating oil to the gap between the piston pin and the bearing surface via the above is known.

[0003]

Among the above bearing surfaces,
In the upper half region near the piston crown surface, a particularly strong load acts near the compression top dead center, so that there is a great need for lubrication. Therefore, it is desirable to arrange the relief groove in this upper half region. However, general engines except horizontally opposed engines are mounted on the vehicle with the piston crown side facing up substantially vertically, so it is difficult to introduce lubricating oil into the relief grooves arranged in the upper half area. It is difficult to secure the desired lubrication performance. If the strength of the piston pin is increased to compensate for such a lack of lubrication performance, an increase in cost cannot be avoided. Further, if an oil groove or oil hole for guiding the lubricating oil to the relief groove is formed in the cylindrical portion or the pin boss portion, it is necessary to perform processing for forming this oil groove or oil hole, which also increases cost and lowers strength. I will invite you.

The present invention has been made in view of the above problems, and an object thereof is to provide a novel piston for an internal combustion engine capable of improving the lubrication performance between the piston pin and the bearing surface with a simple structure. I am trying.

Another object of the piston according to the present invention is to reduce the weight and save the material while ensuring necessary strength and rigidity.

[0006]

A piston of an internal combustion engine according to the present invention includes a piston head portion including a piston crown surface, a substantially cylindrical cylindrical portion having a bearing surface through which a piston pin is inserted, and the piston. It has a pin boss portion that connects the head portion and the cylindrical portion, and a relief groove that is recessed in the bearing surface and extends along the outer peripheral surface of the piston pin, and the relief groove is the piston crown surface in the cylindrical portion. It is located in the upper half of the area. The internal combustion engine described above is typically a diesel engine or a gasoline engine used in an automobile. The piston is generally formed integrally with each part by using a material such as an aluminum alloy that is lightweight and has a low coefficient of thermal expansion. The relief grooves have, for example, a shape that is recessed from the bearing surface in a substantially semi-circular shape in cross section, and a pair of left and right relief grooves are provided as viewed in the axial direction of the piston pin.

According to a first aspect of the invention, an extension line extending along a thrust direction side edge of the pin boss portion intersects with the relief groove or is located above the piston above the relief groove when viewed in the axial direction of the piston pin. It is characterized by passing through. That is, the side surface of the pin boss portion in the thrust direction is located above the piston in relation to the relief groove. The thrust direction corresponds to a direction orthogonal to both the axial direction of the piston pin and the reciprocating direction of the piston. The upper side of the piston corresponds to the direction in which the reciprocating piston moves toward the combustion chamber. According to the present invention, the lubricating oil that flows down the piston along the surface of the pin boss portion is favorably introduced into the relief groove, so that the pin boss portion and the cylindrical portion have a simple structure without intentionally providing an oil hole or the like. The lubricity between the piston pin and the bearing surface can be effectively improved.

Preferably, the extension line extends substantially linearly and is inclined so as to approach the center of the piston from the piston head toward the cylindrical portion. That is, when viewed in the axial direction of the piston pin, the pin boss portion has a substantially inverted triangular shape that contracts downward in the piston. Therefore, typically, the lower root portion of the pin boss portion that is connected to the cylindrical portion is smaller than the outer diameter of the cylindrical portion, and the vicinity of the proximal portion has a concave shape, which reduces weight and saves material. Can be planned. Further, by setting the base portion on the upper side of the pin boss portion connected to the piston head portion to be sufficiently large (for example, equal to or larger than the diameter of the cylindrical portion), the strength and rigidity required for the pin boss portion can be secured.

More preferably, a communication passage is formed in the piston head for communicating the ring groove into which the oil ring is fitted and the piston internal space facing the pin boss. In this case, the lubricating oil scraped up from the cylinder wall surface by the oil ring is sufficiently supplied to the pin boss portion via the ring groove and the communication passage, so that the lubricity around the piston pin is further improved.

According to a second aspect of the present invention, a pair of thrust side surfaces of the pin boss portion are inclined so that they approach each other as they go from the piston head portion to the cylindrical portion,
It is characterized in that it is smoothly connected to the outer periphery of the cylindrical portion at a position above the piston with respect to the relief groove.
According to the present invention, the lubricating oil that flows down the piston along the surface of the pin boss portion is favorably introduced into the relief groove, so that the lubricity between the piston pin and the bearing surface can be improved. In addition, since the pin boss portion typically has an inverted triangular shape in which the width becomes narrower toward the cylindrical portion, it is possible to reduce the weight and save the material while securing the necessary strength and rigidity as described above. be able to.

[0011]

According to the present invention, the lubrication performance between the piston pin and the bearing surface is effective while having a simple structure that does not intentionally require an oil supply hole or groove in the pin boss portion or the cylindrical portion. Can be improved.

Further, it becomes possible to reduce the weight of the pin boss portion while ensuring the necessary strength and rigidity of the pin boss portion.

[0013]

1 and 2 show a piston of an internal combustion engine according to a first embodiment of the present invention. The piston 10 has a substantially disk-shaped piston head 11 having a piston crown surface 12 facing the combustion chamber, and a substantially cylindrical cylindrical portion 13 having a bearing surface 14 into which a piston pin (not shown) is inserted. It has a pin boss portion 15 that integrally connects the piston head portion 11 and the cylindrical portion 13, and is integrally formed of a lightweight metal material such as an aluminum alloy.

On the outer peripheral surface of the land portion 16 which constitutes the outer peripheral portion of the piston head 11, three ring grooves 17, 18 and 19 into which the piston ring is fitted are recessed. Upper 2
A compression ring that mainly prevents the combustion gas in the combustion chamber from leaking to the lower side of the piston is attached to the ring grooves 17 and 18, and the lowermost ring groove 19 mainly scrapes the lubricating oil from the cylinder wall surface. An oil ring for adjusting the thickness of the lubricating oil film is attached. A skirt portion 20 is formed extending from the land portion 16 toward the lower side of the piston.

In this embodiment, the skirt portion 20 is partially located at a position corresponding to the thrust direction P1 (direction orthogonal to both the axial direction P2 of the piston pin and the reciprocating direction P3 of the piston) in which a strong side thrust force acts. And is provided at a total of two locations so as to cut out a part of the cylindrical shape. The circumferential ends of both skirts 20 are connected to each other by reinforcing ribs 21 extending in a flat plate shape along the thrust direction P1. Each reinforcing rib 21
It integrally projects from the lower surface of the piston head portion 11 to the lower side of the piston, and near the center thereof, the pin boss portion 15 described above.
And the cylindrical portion 13 are integrally connected, and also have a function of reinforcing the pin boss portion 15 and the cylindrical portion 13. That is, the pin boss portion 15 projects downward from the lower surface of the piston head 11 toward the piston in the same manner as the reinforcing rib 21, and integrally projects from the reinforcing rib 21 toward the piston center.

The bearing surface 14 of the cylindrical portion 13 is formed with two relief grooves 22 which are further recessed radially outward from the bearing surface 14. The relief groove 22 has a substantially semi-circular cross-sectional shape and extends along the axial direction of the bearing surface 14, and has a function of introducing lubricating oil into the gap between the outer periphery of the piston pin and the bearing surface 14. The relief groove 22 is formed on the bearing surface 14
Above all, it is arranged in this region R so as to surely lubricate the upper half region R close to the piston crown surface 12 (upper side of the piston) where a strong load acts near the compression top dead center. The region R is a region above the piston (upper side in FIG. 1) of the thrust direction reference line L1 extending in the thrust direction P1 through the center of the bearing surface 14.

The pair of thrust-direction side surfaces 23 of the pin boss portion 15 are tapered and linearly inclined toward each other toward the cylindrical portion 13 from the piston head 11.
It is smoothly connected to the outer peripheral surface of the cylindrical portion 13 at a position closer to the piston head 11 (upper side of the piston) than the relief groove 22. That is, the pin boss portion 15 has a substantially inverted triangular shape in which the width gradually decreases toward the lower side of the piston when viewed in the axial direction of the piston pin.

When viewed in the piston pin axial direction shown in FIG. 1, an extension line 24 linearly extended along the thrust direction side edge 23a formed by the thrust direction side surface 23 of the pin boss portion 15 is a relief groove. It is set to intersect with 22. Therefore, as the piston 10 reciprocates, the lubricating oil that flows down along the surface of the pin boss portion 15 including the thrust-direction side surface 23 drops into the cylindrical portion 13.
Via the axial side surface 25 of the relief groove 2 of the cylindrical portion 13.
2 well supplied. In addition, the thrust side surface 23
Is formed in a plane shape substantially along the piston pin direction P2, so that most of the thrust direction side surface 23 corresponds to the thrust direction side edge 23a.

Unlike the present embodiment, the extension line 2 is seen in the piston pin axial direction as in the comparative example shown in FIG.
When 4'is set so as to pass below the relief groove 22 ', the pin boss portion 15' is different from that of the present embodiment.
Also, the amount of the lubricating oil flowing down along the surface of the cylindrical portion 13 ′ and supplied to the relief groove 22 ′ is reduced, and the lubricity thereof is deteriorated.

Furthermore, in the present embodiment, the width in the thrust direction of the lower root portion 27 connected to the cylindrical portion 13 in the pin boss portion 15 is set to be smaller than the diameter ΔD in the thrust direction of the cylindrical portion 13. Therefore, in the vicinity of the base portion 27 on the lower side, a concave portion 28 which is depressed with respect to the outer periphery of the cylindrical portion 13 is provided, and the weight of the piston 10 and the material saving are achieved by the concave portion 28. be able to. Further, in the pin boss portion 15, the upper root portion 29 that smoothly connects to the piston head portion 11 is set to be larger than the thrust direction diameter ΔD. By making the upper root portion 29 sufficiently large in this way, it is possible to secure the strength and rigidity required for the pin boss portion 15 while reducing the weight of the pin boss portion 15 as described above.

Lubricating oil is appropriately scraped up according to the rotation of the crankshaft and is supplied to the pin boss portion 15 and the cylindrical portion 13, but in order to supply the lubricating oil more reliably, it is preferably shown in FIG. Thus, the oil jet 30 for injecting the lubricating oil from below the piston 10 toward the inside of the piston is arranged in the cylinder block or the like.

3 and 4 show a second embodiment of the present invention. It should be noted that substantially the same constituent elements as those of the first embodiment described above are designated by the same reference numerals, and redundant description will be appropriately omitted. Inside the piston head portion 11 (land portion 16), a lowermost ring groove 19 to which an oil ring is attached,
An internal space of the piston 10 in which the pin boss portion 15 exists,
A plurality of communication passages 31 communicating with each other are intermittently provided in the circumferential direction. The communication passage 31 has an outlet to the internal space of the piston disposed near the upper root portion 29 of the pin boss portion 15 and is inclined so as to substantially follow the thrust-direction side surface 23 of the pin boss portion 15. In other words, the base portion 29 on the upper side of the pin boss portion 15 projects radially outward to the vicinity of the outlet of the communication passage 31. In this case, the lubricating oil adhering to the cylinder wall surface is sufficiently supplied to the surface of the pin boss portion 15 via the ring groove 19 and the communication passage 31, so that the lubricating performance of the piston pin is further improved.

Further, as shown in FIG. 4, the extension line 24 extending along the thrust direction side edge 23a of the pin boss portion 15 in the axial direction of the piston pin has the relief groove 22 as in the first embodiment. It does not intersect with, and passes above the relief groove 22 above the piston. Even in this case, as in the first embodiment, most of the lubricating oil flowing down the surface of the pin boss portion 15 is satisfactorily supplied to the relief groove 22, and its lubricity is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a piston of an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a bottom view corresponding to the piston of FIG. 1 seen from the lower side of the piston.

FIG. 3 is a sectional view showing a piston of an internal combustion engine according to a second embodiment of the present invention.

FIG. 4 is an enlarged view of a main part of FIG.

FIG. 5 is an enlarged view of a main part of a piston according to a comparative example.

[Explanation of symbols]

10 ... Piston 11 ... Piston head 12 ... Piston crown 13 ... Cylindrical part 14 ... Bearing surface 15 ... Pin boss 19 ... Ring groove 22 ... Relief groove 23a ... Side edge in thrust direction 24 ... extension line 31 ... Passage

Claims (4)

[Claims] 1. A piston head including a piston crown surface, a substantially cylindrical cylindrical portion having a bearing surface through which a piston pin is inserted, a pin boss portion connecting the piston head and the cylindrical portion, and the bearing. And a relief groove extending along the outer peripheral surface of the piston pin, the relief groove of the internal combustion engine being arranged in the upper half region of the piston crown surface side in the cylindrical portion. In the piston, the extension line extending along the thrust direction side edge of the pin boss portion intersects with the relief groove or passes above the relief groove above the piston in the axial direction of the piston pin. Internal combustion engine piston. 2. The internal combustion engine according to claim 1, wherein the extension line extends substantially linearly and is inclined so as to approach the center of the piston from the piston head toward the cylindrical portion. Piston. 3. A communication passage is formed in the piston head, the communication groove communicating with a ring groove into which an oil ring is fitted and a piston inner space facing the pin boss portion. Or the piston of the internal combustion engine according to 2. 4. A piston head portion including a piston crown surface, a substantially cylindrical cylindrical portion having a bearing surface through which a piston pin is inserted, a pin boss portion connecting the piston head portion and the cylindrical portion, and the bearing. And a relief groove extending along the outer peripheral surface of the piston pin, the relief groove of the internal combustion engine being arranged in the upper half region of the piston crown surface side in the cylindrical portion. In the piston, the pair of thrust side surfaces of the pin boss portion are inclined so as to approach each other from the piston head toward the cylindrical portion, and at the position on the piston upper side of the relief groove to the outer periphery of the cylindrical portion. Internal combustion engine pistons characterized by a smooth connection.