JP2008008170A - Piston structure for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the weight of a piston while improving the weight balance of the piston. <P>SOLUTION: A crown part 5 has a shape in which an intake side thereof is relatively heavier than an exhaust side thereof across a piston pin boss part 26. A recess 30 opened downward is formed in an upper area of a side wall part 25 on a lower surface of a land part 20 of the piston 1. Two ribs 31 extending between the land part 20 and the side wall part 25 are formed in the recess part 30. The intake side rib 31a is formed thicker and the exhaust side rib 31b is formed thinner across the piston pin boss part 26. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piston structure for an engine that is fitted into a cylinder to define a combustion chamber.

  Patent Document 1 discloses a typical example of a piston. The piston has a crown part that forms a combustion shape and a land part that has an outer peripheral surface depending from the outer peripheral edge of the crown part, and a plurality of seal rings and oil rings are accommodated on the outer peripheral surface of the land part. The circumferential groove is formed. The piston also has a pair of skirt portions that hang downward from the land portion, and a piston pin boss portion formed on a sidewall portion that connects the pair of skirt portions, and is formed in the piston pin boss portion. A piston pin penetrating the small end of the connecting rod is inserted into the pin hole.

  The piston is fitted in the cylinder of the engine and reciprocates. If the right and left weight balance around the piston pin is inappropriate, smooth reciprocation in the cylinder is hindered. .

Patent Document 2 discloses a piston in which a central portion of the upper surface of the crown portion is projected and a part of the upper surface is greatly depressed so that a tumble flow is generated in the combustion chamber. Since the crown portion of the piston is a main element that defines the shape of the combustion chamber, many proposals have been made regarding the shape of the upper surface. These proposals include the intention to respond to environmental demands for further reduction in fuel consumption by increasing engine combustion efficiency to prevent global warming.
JP 2001-295696 A JP 2001-241426 A

  However, the idea regarding the shape of the crown part of the piston is aimed at optimizing the combustion of the engine, and as a result of this idea, it is possible to hinder the right and left weight balance of the piston centering on the piston pin Including sex. By the way, in order to reduce the fuel consumption of automobiles, efforts are constantly made to reduce the weight of each automobile part, and this is no exception for pistons.

  The present invention has been devised under such a background, and the object of the present invention is to make it difficult to ensure the weight balance of the piston when designing the piston, for example, by devising the shape of the crown or the like. It is an object of the present invention to provide an engine piston structure that can contribute to weight reduction of the piston while improving the weight balance.

According to the present invention, the above technical problem is
A piston that is reciprocally fitted to a cylinder to define a combustion chamber of the engine,
A crown that forms the shape of the combustion chamber;
A land portion having an outer peripheral surface depending from the outer peripheral edge of the crown portion, and a seal ring, a seal ring accommodating groove for accommodating the oil ring, and a land portion having an oil ring accommodating groove formed on the outer peripheral surface;
A pair of skirt portions depending downward from the land portion;
Sidewall portions connecting the pair of skirt portions;
In the piston structure of the engine provided with the piston pin boss part formed in the sidewall part,
The crown portion has a structure in which the one side is unbalanced in weight compared to the other side around the piston pin boss portion,
On the lower surface of the land portion, a depression opened downward is formed in an upper region of the sidewall portion,
In the recess, the land portion and the sidewall portion are connected and the piston pin boss portion is sandwiched between at least two ribs,
The first rib located on the relatively light weight side of the crown portion with respect to the piston pin boss portion is set to be heavier than the second rib located on the heavy side. This is accomplished by providing an engine piston structure.

  That is, according to the present invention, not only is it possible to reduce the weight of the piston by forming a recess in the lower surface of the land portion and providing a rib in the recess, but the rib in the recess can be connected to the piston pin boss portion. At least two of them are sandwiched, and the relative weights of the ribs located on one side and the other side are made different so that the ribs having different weights can be unloaded on the weight surface of the crown portion according to the shape of the crown portion. Balance can be suppressed.

  In a preferred embodiment of the present invention, the first rib located on the relatively light side of the crown is formed thicker than the second rib located on the heavy side. In this way, by changing the thickness of the rib, it is possible to suppress the above-described imbalance in the weight surface of the crown portion, and further, the oil ring housing groove and the piston pin boss are further added to the thick rib. By forming the oil supply hole communicating with the pin hole of the part, the oil supply passage of the oil ring housing groove can be efficiently arranged.

  As a preferred example of the shape of the crown part to which the present invention can be applied, the crown part has a ring-shaped part protruding upward on the upper surface of the crown part, and a central recess surrounded by the ring-shaped part, An example is a piston in which the ring-shaped part has shapes with different heights on one side and the other side with the piston pin boss part as the center. As will be described later, this piston can change the combustion mode of the engine to “late centroid combustion”, thereby realizing a high compression ratio while preventing knocking.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIGS. 1-7 shows the piston of an Example, FIG. 8 shows the example which can improve the knocking-proof performance of an engine by employ | adopting the form of the crown part of the piston of an Example.

  For convenience of explanation, referring first to FIG. 8, the piston 1 of the embodiment is fitted in a cylinder 2 of a gasoline engine, and the reciprocating motion of the piston 1 is connected to a crankshaft (not shown) via a connecting rod (not shown). (Not shown) and output as rotational motion by this crankshaft.

  The combustion chamber 4 of the engine is defined by the shape of the crown portion 5 of the piston 1 and the surface shape of the cylinder head 6, and the combustion chamber 4 adopts a conventionally known pent roof type. Reference numeral 7 indicates an exhaust port, 8 indicates an intake port, and the exhaust port 7 and the intake port 8 are opened and closed at predetermined timings synchronized with the rotation of the crankshaft by the exhaust valve 9 and the intake valve 10, respectively. . Further, the exhaust port 7 and the intake port 8 are disposed on one side and the other side of the pent roof type combustion chamber 4 which are inclined, and a spark plug 11 is disposed at a substantially intermediate portion between the exhaust port 7 and the intake port 8. Yes.

  The crown portion 5 of the piston 1 has a ring-shaped portion 15 sandwiched between the outer peripheral edge portion 13 and the central portion 14 and raised upward when viewed in plan. That is, in the crown portion 5 of the piston 1, the outer peripheral edge portion 13 and the central portion 14 located on the outer peripheral side sandwiching the ring-shaped portion 15 protruding upward form a recess. Then, the exhaust-side portion 15a and the intake-side portion 15b are relatively low on the entire circumference of the ring-shaped portion 15, and the boundary portion 15c between the exhaust-side and intake-side is relatively high. Preferably, the exhaust side portion 15a is shaped to be higher than the intake side portion 15b. Therefore, the ring-shaped portion 15 protruding upward is preferably designed such that the height dimension increases in the order of the intake side portion 15b, the exhaust side portion 15a, and the boundary portion 15c (intake side portion 15b <exhaust side portion. 15a <boundary portion 15c).

  FIG. 8 illustrates a state in which the piston 1 is located near the top dead center. As can be understood from FIG. 8, in the ring-shaped portion 15 of the piston 1, the exhaust side portion 15 a Compared to the side portion 15b, the space (d1 <d2) of the combustion chamber 4 can be narrowed.

  By adopting the above-described shape of the crown portion 5 of the piston 1, the outer peripheral edge portion 13 of the crown portion 5 constitutes a secondary combustion space. When a flame kernel is formed in the combustion chamber 4 by ignition of the spark plug 11 facing the central recess 14 of the piston 1, the combustion proceeds while the flame surface spreads in a substantially spherical shape, and the pressure in the combustion chamber 4 is increased. It rises rapidly (expansion stroke). Then, the piston 1 is pushed down by the increased in-cylinder pressure. Combustion in this expansion stroke will be described. Combustion at a relatively low speed in the main combustion period of the previous period (a period in which 10% to less than 50% of the main combustion period in which 10% to 90% of the fuel mass burns) In the later main combustion period (a period in which 50% or more and less than 90% of the fuel mass burns), combustion is performed at a relatively high speed. In this way, by adopting the shape of the crown portion 5 described above, it is possible to achieve a combustion mode mainly consisting of the late main combustion period (such a combustion mode is referred to as “late-stage center-of-gravity combustion”). ).

  More specifically, a relatively large raised exhaust side portion of the ring-shaped portion 15 is formed between the first recess (center recess) constituting the central portion 14 of the crown portion 5 and the outer peripheral edge portion 13 on the exhaust side. The combustion chamber 4 is narrowed by 15a (d1). Therefore, in the process in which the flame kernel formed in the central recess 14 of the crown portion 5 spreads in a substantially concentric spherical shape, the ring-shaped portion 15 receives a kind of squeezing action, and under this influence, the flame is propagated in the outer circumferential direction. Is suppressed. For this reason, the combustion speed in the central recess 14 of the crown portion 5 is kept relatively low (the first main combustion period). When the flame surface (front line of flame propagation) exceeds the ring-shaped portion 15, the flame propagates at a relatively high speed in the outer peripheral edge portion 13 of the crown portion 5 (late main combustion period).

  As described above, in the ring-shaped portion 15, the exhaust side portion 15 a facing the high temperature exhaust valve 9 is raised relatively larger than the intake side portion 15 b facing the relatively low temperature intake valve 10. is there. The advantage of this configuration is that the flame propagation to the exhaust side of the entire region of the crown portion 5 of the piston 1 proceeds relatively rapidly and the flame propagation to the intake side becomes relatively slow. The purpose is to suppress the occurrence of a non-uniform combustion rate. And by adopting the shape of the above-mentioned crown portion 5 and realizing the late center-of-gravity type combustion, it is possible to realize a high compression ratio while preventing knocking.

  1, 2, 3, and the like, the piston 1 has a land portion 20 having an outer peripheral surface depending from the outer peripheral edge of the crown portion 5, as in the prior art, and an outer periphery of the land portion 20. Seal ring receiving grooves 21, 22 and an oil ring receiving groove 23 are formed on the surface. Further, the piston 1 has a pair of skirt portions 24, 24 that hang downward from the land portion 20, and a piston pin boss portion 26 formed on a sidewall portion 25 that connects the pair of skirt portions 24, 24 together. . Each of the pair of piston pin boss portions 26 is formed with a pin hole 27 into which a piston pin (not shown) located on the same axis is inserted.

  In connection with the above-described shape of the crown 5 of the piston 1, the exhaust side with the axis L (FIG. 4) between the pair of pin holes 27 and 27 can be understood with reference to FIG. And the intake side are different in shape, and if only the crown portion 5 is noted, the exhaust side is heavier than the intake side.

  As best understood with reference to FIGS. 6 and 7, a depression 30 is formed on the lower surface of the land portion 20 so as to open downward in an upper region of the sidewall portion 25. As best understood from FIG. 2, the recess 30 is disposed obliquely so as to approach the center of the piston as it goes upward, that is, as it goes deeper. As shown in FIGS. 1 and 5, a plurality of ribs 31 extending between the land portion 20 and the sidewall portion 25 and connecting both the portions 20 and 25 are formed in the recess 30. In the illustrated embodiment, a pair is formed on the left and right with the piston pin boss portion 26 interposed therebetween.

  Of the plurality of ribs 31 included in one recess 30, the first rib 31a located on the intake side is a relatively thick rib, and the second rib 31b located on the exhaust side is a relatively thin rib. The first rib 31a on the intake side, which is relatively light in weight due to the shape of the crown part 5, is set so as to be relatively heavier than the second rib 31b on the relatively heavy exhaust side. Has been. That is, in relation to the shape of the crown portion 5 described above, the crown portion 5 has a shape in which the intake side is relatively heavier than the exhaust side across the piston pin boss portion 26. Accordingly, the first rib 31a located on the intake side is made heavier (for example, thicker) than the second rib 31b located on the exhaust side, so that the crown portion associated with the shape of the crown portion 5 described above is obtained. The weight imbalance at 5 can be improved. That is, the imbalance of the weight balance accompanying the shape of the crown part 5 can be suppressed by the weight difference between the first rib 31a and the second rib 31b.

  When the relatively thick first rib 31a located on the intake side is designed to be thick, an oil supply passage 32 that leads to the oil ring housing groove 23 is provided using the thick shape. It may be. The oil supply passage 32 communicates with the pin hole 27 of the piston pin boss portion 26. The oil supply passage 32 includes a horizontal hole 32a that extends through the first rib 31a, and a vertical hole 32b that penetrates the piston pin boss portion 26 from the bottom surface through the boss portion 26 and communicates with the horizontal hole 32a described above. The oil supply passage 32 is constituted by the horizontal hole 32a and the vertical hole 32b.

  As described above, when the weight balance of the crown portion 5 is obstructed as a result of devising the shape of the crown portion 5 of the piston 1 to improve the fuel combustibility, for example, the weight of the piston 1 is reduced. A plurality of ribs 31 in the recess 30 provided for this purpose are used to design the rib 31a of the portion of the rib 31 where the weight balance is relatively light, typically thick, while the weight balance The weight balance of the piston 1 can be improved by designing the rib 31b at a portion where the weight is relatively heavy to be small (for example, thin).

  When the first rib 31a of the piston 1 is designed to be thick, an oil supply passage 32 that leads from the oil ring housing groove 23 to the pin hole 27 of the piston pin boss portion 26 is formed using the thick rib 31a. Thus, the oil supply passage provided in the oil ring housing groove 23 can be efficiently arranged.

The side view which looked at the piston of the Example from the piston pin boss | hub part side. The side view which looked at the piston of the Example from the skirt part side. The perspective view which looked at the piston of the Example from the exhaust side. The perspective view which looked at the piston of the Example from the intake side. The bottom view which looked at the piston from the bottom. Sectional drawing along the VI-VI line of FIG. The figure which looked at the cross-section of FIG. 6 from diagonally. Sectional drawing for demonstrating the combustion chamber shape formed by the piston fitted to the cylinder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston 2 Cylinder 4 Combustion chamber 5 Piston crown part 7 Exhaust port 8 Intake port 11 Spark plug 14 Center part (central recess)
DESCRIPTION OF SYMBOLS 15 Ring-shaped part 15a Exhaust side part of a ring-shaped part 15b Intake side part of a ring-shaped part 20 Land part 21,22 Seal ring accommodation groove 23 Oil ring accommodation groove 24 Skirt part 25 Side wall part 26 Piston pin boss part 27 Pin hole 30 Hollow 31 rib 31a first rib (intake side: wall thickness)
31b 2nd rib (exhaust side: thin)
32 Oil supply passage

Claims (3)

A piston that is reciprocally fitted to a cylinder to define a combustion chamber of the engine,
A crown that forms the shape of the combustion chamber;
A land portion having an outer peripheral surface depending from the outer peripheral edge of the crown portion, and a seal ring, a seal ring accommodating groove for accommodating the oil ring, and a land portion having an oil ring accommodating groove formed on the outer peripheral surface;
A pair of skirt portions depending downward from the land portion;
Sidewall portions connecting the pair of skirt portions;
In the piston structure of the engine provided with the piston pin boss part formed in the sidewall part,
The crown portion has a structure in which the one side is unbalanced in weight compared to the other side around the piston pin boss portion,
On the lower surface of the land portion, a depression opened downward is formed in an upper region of the sidewall portion,
In the recess, the land portion and the sidewall portion are connected and the piston pin boss portion is sandwiched between at least two ribs,
The first rib located on the relatively light weight side of the crown portion with respect to the piston pin boss portion is set to be heavier than the second rib located on the heavy side. The piston structure of the engine. The first rib located on the relatively light side of the crown is formed thicker than the second rib located on the heavy side;
The engine piston structure according to claim 1, wherein an oil supply hole communicating with the oil ring housing groove and a pin hole of the piston pin boss portion is formed in the first rib.   A ring-shaped portion protruding upward from the upper surface of the crown portion; and a central recess surrounded by the ring-shaped portion, wherein the ring-shaped portion has one side and the other side centered on the piston pin boss portion. The piston structure of the engine according to claim 1, wherein the piston structures have different shapes.

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