JP2001152963A - Piston structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston structure capable of reducing its weight sufficiently. SOLUTION: In a piston structure having an outward opening part 18 which is formed in the outer peripheral part of a piston 1, and a pin boss part 19 which is formed at the center side of the piston 1 more than the outward opening part and in the inner wall of a piston-top part 16, a hollow part 27 is provided to open in a part of a piston head 16 opposite to the outward opening part 18, and in the orthogonal surface of the center line L of the piston in the hollow part 27, a cross-sectional shape in the opening position h1 is more extended to the center side of the piston than that in the hole back position h2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston structure for an internal combustion engine, and more particularly, to an outer peripheral portion of a piston body, wherein an outwardly open portion is formed, and a pin boss portion is disposed on the piston center side from the outwardly open portion. And a piston structure integrally formed on the inner wall of the piston top.

[0002]

2. Description of the Related Art An internal combustion engine burns fuel supplied into its combustion chamber to generate high-temperature, high-pressure combustion gas. At this time, a pressing force received from the combustion gas by a piston is applied to a crankshaft via a connecting rod by a rotational force. Tell as. in this case,
The piston swings around the piston pin with respect to the connecting rod when the engine is driven. At this time, the piston reciprocates while transmitting side pressure to the inner wall of the cylinder liner via the piston top and the skirt. For this reason, the piston is required to have sufficient mechanical strength as a whole, and the upper surface is required to have sufficient heat resistance to be exposed to high temperature and high pressure. In particular, the outer peripheral wall of the piston is more resistant to sliding contact with the inner wall of the cylinder. Since they are required to have abrasion properties, and are also required to have a light weight and thermal conductivity, they are often manufactured from an aluminum alloy.

[0003] Also, structurally, it is advantageous to reduce the weight of the piston as much as possible to increase the speed of the engine, and it is desirable to reduce the wear of the cylinder liner by reducing the lateral pressure. In the disclosed piston, a straight hole is provided on the lower wall side of the piston top to reduce the weight.

[0004]

There is known an in-cylinder injection type internal combustion engine capable of adjusting the timing of direct fuel injection into a combustion chamber in order to enable rich operation and lean operation according to the required output. I have. The piston used in this in-cylinder injection type internal combustion engine has a recess formed on the upper surface of the top of the piston, and a relatively small capacity combustion chamber can be formed by the recess and the inner wall on the cylinder head side. Go to
It enables lean burn.

[0005] In the case where the concave portion is provided at the top of the piston, the shape of the top of the piston becomes larger than that of a normal piston, resulting in an increase in weight.
That is, the piston pin is easily displaced from the piston pin toward the top of the piston, and the heat dissipation is also easily reduced as the shape is increased. As described above, the piston used in the in-cylinder injection type internal combustion engine, which has a relatively large piston top and is likely to cause an increase in weight, reduces the amount of wear on the cylinder liner by reducing the side pressure, especially for coping with an increase in engine speed. Therefore, it is desired to sufficiently reduce the weight of the piston.
As disclosed in Japanese Patent No. 5874, it is not possible to achieve a sufficient weight reduction only by providing a straight hole from the opening to the deepest portion. In particular, it is desired to reduce the weight as much as possible for a piston used in an in-cylinder injection type internal combustion engine, which has a relatively large piston top and tends to increase the weight. An object of the present invention is to provide a piston structure that can achieve a sufficient weight reduction based on the above-mentioned problems.

[0006]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, an outwardly opening portion formed on an outer peripheral portion of a piston and an inner wall of a top portion of the piston closer to the center of the piston than the outwardly opening portion. In a piston structure having a pin boss portion formed, a hollow portion that opens toward the outward opening portion is provided at a portion of the piston top portion facing the outward opening portion, and the hollow portion is formed in a plane orthogonal to the piston center line. Has a cross section extending from the opening position toward the center of the piston at a position deep inside the hole. As described above, when the cross-sectional shape of the hollow portion in a plane orthogonal to the piston center line is formed so as to expand from the opening position to the center side of the piston at the hole deep position, the hollow portion is large compared to the opening cross-sectional area. The piston can be formed into a cavity having a spatial volume, the weight of the piston can be sufficiently reduced, the side pressure caused by the swinging motion of the piston can be reduced, and the amount of blow-by gas and slap noise of an internal combustion engine employing this piston can be reduced.

[0007] Preferably, a concave portion serving as a combustion chamber and a raised portion located on the outer peripheral side of the piston concave portion with respect to the concave portion are formed at the top of the piston, and the deepest portion of the hollow portion may be formed in the raised portion. . In this case, it is possible to sufficiently reduce the weight of the piston which has a concave portion and a protruding portion near the concave portion, and the top of the piston is relatively likely to cause an increase in weight. It is possible to sufficiently reduce oil consumption (LOC), blow-by gas amount, slap noise, and friction loss of an internal combustion engine, for example, a direct injection internal combustion engine.

[0008]

FIG. 1 shows a piston 1 employing a piston structure according to one embodiment of the present invention. This piston 1 is a cylinder injection type internal combustion engine (hereinafter simply referred to as engine 2).
Attached). Although the engine 2 is a four-cycle, four-valve type in-line four-cylinder engine, the configuration of each cylinder is the same. Here, the piston 1 of one cylinder will be mainly described. In the engine 2, a cylinder head 4 with a head cover 3, a cylinder block 5 thereunder, a crankcase and a crank cover (not shown) are stacked in this order and integrated to form a body outer portion. Inside the main body of the engine 2, a cylinder liner 6 which is a part of the cylinder block 5 and in which the piston 1 is inserted, a combustion chamber 7 sandwiched between the piston 1 and the inner wall 401 of the cylinder head 4, and a combustion chamber 7 A pair of intake / exhaust ports 8 and 9 (only one side is shown) that can communicate with the air conditioner, a pair of intake / exhaust valves 11 and 12 (only one side is shown) for opening and closing these intake / exhaust ports, and drive these And a not-shown crankshaft and a connecting rod 13 for converting the reciprocating motion of the piston 1 into rotational motion.

Here, it is assumed that the cylinder head 4 has a vertical plane (not shown) including the cylinder axis L extending along the center of the cylinder liner 6, and a pair of intake ports ( (Only the near side is shown) 8
On the other side a pair of exhaust ports 9 (only the near side is shown)
Respectively. The inner wall 401 formed in the cylinder head 4 and facing the combustion chamber 7 is formed as a wedge-shaped recess which is long in the direction perpendicular to the plane of the drawing.
An intake port 8 opened and closed by an intake valve 11 is located on the left side of
An exhaust port 9 opened and closed by an exhaust valve 12 is formed on the right side portion. Further, a spark plug 14 is mounted at a substantially central position of the inner wall 401 forming a wedge-shaped concave portion, and an injector 15 is mounted at a portion of the intake port 8 on the outer peripheral side of the cylinder. The piston 1 fitted to the cylinder liner 6 reciprocates between a top dead center TDC position shown by a solid line and a bottom dead center BDC position (not shown).

As shown in FIGS. 1 to 5, the piston 1 has a piston top 16 facing the combustion chamber 7, a skirt 17 facing the cylinder liner 5, and a part of the skirt 17 retreats toward the center of the piston. The piston includes an outward recessed portion formed as an outward opening portion, and a pair of pin boss portions projecting below a lower wall which is an inner side wall of the piston top portion. The piston top 16 has a concave portion 20 and a raised portion 21 formed on the upper surface thereof. The concave portion 20 and the raised portion 21 are formed so as to smoothly reverse the intake air that has flowed down through the intake port 8 substantially along the cylinder axis L, and to flow it as a reverse tumble flow TF. The raised portion 21 forms a wedge-shaped projection such that the upper surface thereof uniformly faces the inner wall 401 forming a wedge-shaped recess, and the recess 20 is formed so as to be biased toward the surface facing the intake port 12. An inclined wall f is formed on the side facing the surface 13, and a bent ridge e that is continuous in the longitudinal direction A of the engine body (see FIG. 3) is formed at the center. The bent ridge e has a straight shape at both ends, and an intermediate portion is formed as a curved ridge in which the recess 20 and the inclined wall f intersect. For this reason, when the piston 2 moves to the top dead center TDC, air from the gap sandwiched by the inclined wall f and the inner wall 401 forming the wedge-shaped recess passes over the peak e and forms the squish flow SF toward the recess 20. Extruded, reverse tumble flow TF
Inversion flow can be promoted.

As shown in FIG. 2, the piston top 16 has a plurality of ring grooves 22 and 23 for a piston ring and a ring groove 30 for an oil ring formed on its outer peripheral wall 161 at predetermined intervals in the vertical direction. They are formed separately. The symbol g indicates an oil drain hole. As shown in FIGS. 4 and 5, a pin boss portion 17 protrudingly formed on a lower wall surface which is an inner wall surface of the piston top portion 16 has a bearing shape, and a pair of pin boss portions 17 is formed in a longitudinal direction A (see FIG. 3) of the engine body. These ends are located on the center side of the piston with a gap C between the outer peripheral edge of the piston and face the outward recess 18 serving as an outward opening forming a space of the gap C.

As shown in FIG. 4, the skirt portion 17 constituting the lower side of the piston 1 body has a deformed cylindrical shape, that is, a skirt main portion 171 extending downward from the outer peripheral wall portion 161 as it is. A pin boss opposing portion 172 which is curved toward the center of the piston and is integrally connected to an intermediate portion of the pin boss portion 19 in the longitudinal direction so as to avoid the outward recessed portion 18 from the peripheral main portion 171. Here, the peripheral main portions 171 opposed to each other can slide on the cylinder liner 6, and are formed so that the side pressure received by the piston 1 can be transmitted to the cylinder liner 6 from the sliding surface. The pin boss opposing portion 172 connects the peripheral main portions 171 provided to oppose each other to enhance their rigidity and also can reinforce the pin boss portion 17. A downward wall f1 facing the outward recess 18 at the lower wall of the piston top 16
Each of the hollow portions 27 is formed to open toward the outward concave portion 18, that is, downward.

The cross section of the hollow portion 27 in a plane (not shown) orthogonal to the piston center line L coinciding with the cylinder axis is substantially flat near the opening position h1 as shown in FIGS. At the deepest portion of the hole depth position h2 reaching the inside of the protruding portion 21, it is formed in a substantially elliptical shape (shown by a broken line in FIG. 4) larger than the opening position h1 side. That is, at the deepest portion of the hole depth position h2, the cross-sectional shape on the opening position h1 side indicates that
The central inner wall surface f2 is formed so as to extend toward the central side which is the piston center line L side by the width α, and both side widths in the circumferential direction of the piston are also increased by β. Here, as is apparent from FIG. 5, the raised portion 21 has a sufficient space in the vertical direction, which is the longitudinal direction of the piston, between the raised portion 21 and the pin boss portion 19, and has a predetermined vertical width k above the pin boss portion 19. Is secured so that the input received by the pin boss portion 17 is dispersed, so that there is no problem in terms of strength even if the hollow deepest portion is provided on the upper side. Thereby, the opening position h is located at the hole depth position h2.
The hollow deepest portion whose cross-sectional shape is sufficiently larger than that of the first embodiment is provided, and the weight of the piston can be sufficiently reduced. Since the inner wall surface f3 of the hollow portion 27 on the outer peripheral edge side of the piston is close to the ring grooves 22, 23, and 30, the position is set in consideration of securing the strength of the portion, and furthermore, the position of the core during casting is set. The inclination angle δ is set to facilitate extraction.

The engine 2 receives the intake air from the intake port during the intake stroke, and supplies the intake air to the reverse tumble flow T during the compression stroke.
The fuel is sprayed from the fuel injection valve 15 in the compression stroke or the intake stroke according to the lean operation range or the operation range other than the lean operation range, and the piston 1 is compressed immediately before the compression top dead center TDC. The mixture is ignited by a spark plug 14 and proceeds to a combustion process. The resultant force of the combustion gas pressure received by the piston top 16 in the combustion stroke is output from each pin boss 19 as a rotational force to the crankshaft (not shown) via the piston pin 24 and the connecting rod 13.

When the engine 2 is driven, the piston 1 receives the gas pressure received at the top 16 of the piston 2 so that the piston pin 24 maintains sufficient rigidity above the pin boss 19 from a position where a predetermined vertical width k is secured. Can communicate. When this piston slides, the connecting rod 1
3 changes the angle of inclination, and the side pressure generated at that time changes the peripheral main portion 171 of the skirt portion 17 sliding in the cylinder liner 6.
Through the cylinder liner 6. In this case, the piston top 16 is formed with a hollow portion 27, and in particular,
The raised portion 21 is sufficiently lightened to the vicinity of the concave portion 20 to achieve weight reduction.

As a result, since the position of the center of gravity can be relatively close to the vicinity of the piston pin 24, the swinging operation of the piston 1 around the piston pin 24 can be reduced, and the lateral pressure can be kept low. For this reason, it is possible to suppress an increase in friction with respect to the cylinder liner 6, an increase in the amount of carbide adhering, and an increase in LOC. Can be achieved. Further, when the piston 1 is lowered, the oil scraped from the cylinder liner 6 flows into the hollow portion h2 from the opening position h1 into the hollow portion 27 when the piston 1 rises. The oil that has flowed into 27 can cool the raised portion 21.

In the above description, the piston 1 has the hollow portions 27 formed in the pair of outwardly recessed portions 18 of the piston top 16 respectively. Instead, the piston 1a is replaced with a piston 1a as shown in FIGS. You may comprise. This piston 1
a can be mounted on the engine 1 instead of the piston 1 in FIG.
The description of the overlapping part is omitted. The piston 1a has a pair of hollow portions 27a formed at the piston top 16a, and the two hollow portions 27a are connected to each other by a pair of curved oil passages 2a.
The cooling channels 29 communicate with each other at 8 to form an annular cooling channel 29 in plan view as a whole. In this case, the outer peripheral wall 161a of the piston top 16a is formed to be relatively thick, and the curved oil passage 28 is formed at this portion. In addition, a downward opening 281 is formed in a plurality of appropriate places of each curved oil passage 28,
Similarly to the opening of the hollow portion 27, these downward openings 281 can sufficiently supply and discharge oil when the piston 1a is raised and lowered.

The piston 1a also has the same operation and effect as the piston 1 of FIG. 1, and in particular, the heat radiation characteristics of the piston 1 can be further improved and the increase in weight can be suppressed. In the piston 1 of FIG. 1, a part of the skirt 17 is retracted toward the center of the piston to form an outward recess 18 as an outward open space, but in some cases, the pin boss facing portion 172 of the skirt 17 is eliminated. The piston may be formed only as the peripheral main portion 171. In this case, a not-shown piston is provided with an outward notch as an outward opening portion, and a hollow portion is formed on a lower wall surface on the piston top side opposed to the notch. In this case, the same operation and effect as the piston 1 of FIG. 1 can be obtained. The piston 1 in FIG. 1 is mounted on the engine 2 which is a direct injection type internal combustion engine, but is not limited to this. The piston is a normal piston having a flat top, or a cavity is formed on the flat piston top. The present invention can also be applied to a piston of a recessed diesel engine. In these cases, the same operation and effect as the piston 1 of FIG. 1 can be obtained.

[0019]

As described above, according to the first aspect of the present invention, the cross-sectional shape of the hollow portion on the plane perpendicular to the center line of the piston is formed so as to expand from the opening position to the center of the piston at the hole deep position. Therefore, in this case, the hollow portion can be formed as a cavity having a large space volume in comparison with the opening cross-sectional area, the weight of the piston and the position of the center of gravity can be sufficiently reduced, and the side pressure due to the swinging motion of the piston is reduced. The blow-by gas amount, slap noise and friction loss of an internal combustion engine employing a piston can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an essential part of an engine to which a piston structure according to an embodiment of the present invention is applied.

FIG. 2 is an enlarged side view of a piston in FIG.

FIG. 3 is a plan view of a piston in FIG. 1;

FIG. 4 is a sectional view taken along line XX of FIG. 2;

FIG. 5 is a sectional view taken along line YY of FIG. 2;

FIG. 6 is an enlarged plan view of a piston to which a piston structure according to a second embodiment of the present invention is applied.

FIG. 7 is a side sectional view of the piston of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston 2 Engine 16 Piston top part 18 Outward open part (outward concave part) 19 Pin boss part 27 Hollow part h1 Open position h2 Hole deep position L Piston center line

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideki Miyamoto 5-33-8 Shiba, Minato-ku, Tokyo / Inside Mitsubishi Motors Corporation (72) Inventor Hideo Nakai 5-33-8 Shiba, Minato-ku, Tokyo・ F-term in Mitsubishi Motors Corporation (reference) 3G023 AA11 AB03 AC05 AD02 AD08

Claims (1)

[Claims] 1. A piston structure having an outwardly opening portion formed on an outer peripheral portion of a piston and a pin boss portion formed on an inner wall of a piston top portion on the center side of the piston from the outwardly opening portion, wherein the outwardly opening portion of the piston top portion is provided. A hollow portion that opens toward the outward opening portion is provided at a portion facing the portion, and a cross-sectional shape of the hollow portion on a plane orthogonal to the piston center line extends toward the center of the piston at a position deeper than the opening position. A piston structure characterized by the following.