JP2001140695A - Piston structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide piston structure capable of preventing a cylinder liner from early wearing and improving durability. SOLUTION: In piston structure in which a recessed section 20 for a combustion chamber 7 is provided in a piston top section 16, the recessed section 20 is formed while deviating from the center line L of a piston and a cut buck section E in a top land section d forming the outer periphery of the piston top section 16 in the same deviating direction B.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston structure of an internal combustion engine, and more particularly, to a piston structure having a concave portion serving as a combustion chamber at the top of the piston.

[0002]

2. Description of the Related Art An internal combustion engine burns fuel supplied to its combustion chamber to generate high-temperature, high-pressure combustion gas. At this time, a piston receives a gas pressure received from the combustion gas through a connecting rod and applies a torque to a crankshaft. Tell as. When such an engine is driven, the piston swings around the piston pin with respect to the connecting rod, and at this time, the piston reciprocates while transmitting lateral 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. Wear resistance is required, and it is also necessary to easily achieve weight reduction with high speed and good thermal conductivity, and it is often manufactured from an aluminum alloy.

[0003] In order to enable lean operation and non-lean operation according to the required output, a direct injection type internal combustion engine capable of performing direct fuel injection timing to a combustion chamber in an intake stroke or a compression stroke. It has been known. The piston used in this in-cylinder injection type internal combustion engine has a recess formed in 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. Sometimes, fuel injection is performed, ignition is performed by a spark plug, and lean combustion is enabled.

[0004]

In the case of such an in-cylinder injection type internal combustion engine, the recess is formed so as to be deviated from the center of the piston, and a part of the periphery of the recess is formed on a land which forms the outer periphery of the top of the piston. Closely deployed. As described above, since the concave portion, that is, the combustion chamber is close to the land portion, hard and thick carbon easily adheres or adheres to the land portion on the concave side with time, and the accumulated carbon is swung by the piston. , Causing hard deposits, which rub against the cylinder liner and can cause excessive wear at an early stage.
An object of the present invention is to provide a piston structure that can prevent early wear of a cylinder liner and improve durability based on the above-mentioned problems.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, in a piston structure having a concave portion serving as a combustion chamber at the top of the piston, the concave portion is deviated from the center of the piston. A cutback portion is formed on a land portion that is formed and is located in the same deflection direction and forms an outer peripheral edge of the piston top. As described above, the cutback portion is formed in the portion located in the deviation direction, and a relatively large gap is formed therein, thereby facilitating the invasion of the flame into the gap. For this reason, the carbon generated in the cutback portion can be easily burned by the flame, and it is possible to prevent the accumulation of carbon on the land portion and the formation of hard accumulation, thereby suppressing early wear of the cylinder liner, The durability of the cylinder liner can be improved, and the amount of blow-by gas can be reduced.

Preferably, the piston structure is provided in a direct injection type internal combustion engine. In the case of this in-cylinder injection type internal combustion engine, fuel is sprayed in the intake stroke in an operation range other than the lean operation range, and the ratio of the sprayed fuel entering the gap between the land and the cylinder liner is high. A cutback portion was formed in the portion located in the position direction, a relatively large gap was formed therein, and the penetration of the flame into this gap was facilitated. Therefore, the carbon generated in the cutback can be easily burned by the flame, the early wear of the cylinder liner can be suppressed, the durability of the cylinder liner can be improved, and the amount of blow-by gas can be reduced.

[0007]

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.

The engine 2 includes a cylinder head 4 with a head cover 3, a lower cylinder block 5, a crankcase (not shown) and a crank cover (not shown) which are stacked in this order and integrated to form a body outer portion. Engine 2
Of the cylinder block 5 and a cylinder liner 6 in which the piston 1 is inserted, and a combustion chamber 7 sandwiched between the piston 1 and the inner wall 401 of the cylinder head 4.
And a pair of intake / exhaust ports 8, 9 communicable with the combustion chamber 7.
(Only one side is shown), a pair of intake and exhaust valves 11 and 12 (only one side is shown) for opening and closing these intake and exhaust ports, a valve train (not shown) for driving these, and a reciprocating motion of the piston 1. A crankshaft (not shown) and a connecting rod 13 for converting the rotational motion into a rotational motion are provided.

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 front side) is provided on one side of the vertical plane. 8) is provided on the other side with a pair of exhaust ports 9 (only the near side is shown). The combustion chamber 7 formed in the cylinder head 4
Is formed as a wedge-shaped recess long in the direction perpendicular to the paper surface, and an intake port 8 opened and closed by an intake valve 11 on a left portion of the inner wall 401 forming the wedge-shaped recess, and is opened and closed by an exhaust valve 12 on a right portion. Exhaust ports 9 are respectively formed. 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 cylinder liner 6 is, as shown in FIG.
Is formed in a substantially perfect circular shape, and the piston 1 fitted to the
The piston rings r1 and r2 and the oil ring r0 (see FIG. 4) provided on the outer peripheral portion are in sliding contact with each other.

As shown in FIGS. 1 to 4, the piston 1 has a piston top 16 facing the combustion chamber 7, a skirt 17 facing the cylinder liner 6, and a lower portion which is an inner side wall of the piston top 16. And a pair of pin boss portions 19 protruding. As shown in FIG.
Ring grooves 22 and 23 for a plurality of piston rings r1 and r2 and ring grooves 3 for an oil ring r0
0s are formed in this order at predetermined intervals in the vertical direction. The symbol g indicates an oil drain hole.

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 smoothly reverse the intake air descending and flowing through the intake port 8 substantially along the cylinder axis L, and the reverse tumble flow TF
It is formed to flow as. The raised portion 21 forms a wedge-shaped protrusion such that the upper surface thereof uniformly faces the inner wall 401 forming the wedge-shaped recess, and the recess 2 is formed on the surface facing the intake port 12.
0, the inclined wall f is formed on the side facing the exhaust port 13, and the longitudinal direction A of the engine main body is formed at the center.
(See FIG. 3). In addition,
The bent ridge e has a straight shape at both ends and a concave portion 2 at the middle.
It is formed as a curved peak portion where 0 and the inclined wall surface f intersect.
By adopting such a shape, when the piston 2 moves to the compression top dead center TDC (the position shown by the solid line in FIG. 1), air from the gap sandwiched between the inclined wall surface f and the inner wall 401 forming the wedge-shaped concave portion. Is pushed out as a squish flow SF to the concave portion 20 side beyond the peak portion e, and the reverse flow of the reverse tumble flow TF can be promoted.

As shown in FIG. 3, the piston top 16 has its concave portion 20 deviated from the piston center line L, which coincides with the cylinder axis, in the deflection direction B, which is one side wall of the cylinder block 5, in plan view. Formed and the recess 20
Is made to face the spark plug 14 at the center of the piston.
Thereby, the fuel flowing together with the reverse tumble flow TF in the concave portion 20 can be relatively easily guided to the ignition plug 14, and the ignition can be facilitated.

As shown in FIGS. 2 and 3, one side of the cylinder block 5 on the top land portion d of the piston 1 in the direction B of deviation of the recess 20 has a smaller area than the other areas. A cutback portion E in which the top land portion d was cut off by the interval α was formed. Here, the cutback portion E is formed on the top land portion d of the piston 1 and in a region approximately one third of the top land portion d, and is configured to cover all regions where the relative distance from the recess 20 is relatively small. Such a piston 1
Of the piston 1 and the inner wall surface 6 of the cylinder liner 6
01 has a relatively large t2 at the cutback portion E, and a relatively small t1 at a portion other than the cutback portion E.
(<T2).

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 into the cylinder during the compression stroke or the intake stroke according to the operating range, and the piston 1
Immediately before the compression top dead center TDC, the mixture in the combustion chamber 7 is ignited by the ignition plug 14 and proceeds to the combustion stroke. 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 in the intake stroke injection operation range, the piston 1 is moved to the bottom dead center B during the intake stroke.
When the fuel injection valve 15 is in the operating range where the fuel injection valve 15 is not opposed to the concave portion 20 on the DC position side, fuel spray is performed.
The fuel spray is diffused to almost the entire area of the combustion chamber 7, and this is stirred by the reverse tumble flow TF. After compression in the compression stroke, an ignition process is performed, and the process proceeds to the combustion stroke. In this intake stroke injection operation region, a part of the fuel spray tends to enter the gap between the top land portion d and the inner wall surface 601 of the cylinder liner due to the reverse tumble flow TF. And carbon tend to stick.

Further, when the engine 2 is in the compression stroke injection operation range, in the compression stroke, that is, when the piston 1 is in the up position, and when the fuel injection valve 15 is in the operation range opposed to the recess 20, the fuel spray is generated. When formed, the combustion chamber 7 in which most of the fuel spray is covered by the recess 20 and the inner wall 401 forming a wedge-shaped recess
The gas is swirled and stirred, and the ignition process is performed after the compression stroke, and the process proceeds to the combustion stroke. In this compression stroke injection operation range,
Although the fuel spray from the fuel injection valve 15 is sprayed relatively efficiently into the concave portion 20, a part of the fuel spray also enters the gap between the top land portion d and the inner wall surface 601 of the cylinder liner. At the beginning, the spray is easily scattered outside the concave portion 20, and also in this case, the fuel or carbon tends to stick to the top land portion d with time.

However, in the piston 1 used in the engine 2, a cutback portion E is provided at a portion of the concave portion 20 which is located in the deflection direction B, where carbon is relatively easily generated.
And a relatively large gap t2 is formed here. For this reason, in the entire operation range of the engine, the fuel and carbon adhering to the top land portion d can be easily burned by the flame that has entered the gap t2, and the accumulated carbon adheres to the top land portion d and the hard accumulated material Is prevented from being generated. Therefore, unlike the conventional engine, the engine 2 equipped with the piston 1 does not wear the cylinder liner in proportion to the elapse of the operation time, and the cut-back portion E is provided to generate hard deposits. Is eliminated, so that the wear of the cylinder liner hardly progresses even after the operation time elapses. Therefore, the engine 2 equipped with the piston 1 can improve the durability of the cylinder liner 6 and can reduce the blow-by gas amount.

The piston 1 used in the engine 2 shown in FIG.
A cutback portion E is formed on the top land portion d on the side of the deflection direction B of the concave portion 20 along the same piston center line L as the cylinder axis, but instead of this, FIGS. 5A and 5B
May be configured as shown in FIG. The piston 1a here,
1b can be mounted on the engine 2 instead of the piston 1 in FIG. 1, and the description of the overlapping portion is omitted.

The piston 1a shown in FIG.
In forming the cutback portion E on the top land portion d on the side of the deflection direction B in FIG. 4 (see FIG. 4), the top land portion d having a conical surface fc shape is formed by cutting out the other region by an interval α1. did. In this case, the top land portion d having a conical surface fc shape facilitates the invasion of the flame, easily combusts the fuel and carbon adhering thereto, and relatively suppresses the decrease in the hole depth of the piston ring r1. Can be. The piston 1b shown in FIG.
In addition to forming the cutback portion E which is cut out by the interval α2, the cutback portion E is also formed in the second land portion d2.
A cutback portion E2 was formed in the same region as that of FIG. In this case, the fuel and carbon reaching the second land portion d2 can be burned, and the top land portion d and the second land portion d can be burned.
2 can be prevented from being deposited on the inner surface of the cylinder liner 6 and hard deposits can be generated, early wear of the inner wall surface 601 of the cylinder liner 6 can be more reliably suppressed, and the durability of the cylinder liner 6 can be further improved. As a result, the amount of blow-by gas can be reduced more reliably.

The piston 1 shown 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 1 is provided with a concave portion deviated to the outer peripheral side at the top of the piston. The present invention can be applied to various engines, and in these cases, the same operation and effect as the piston 1 of FIG. 1 can be obtained.

[0021]

As described above, according to the first aspect of the present invention, a cutback portion is formed in a portion of the land of the piston where the concave portion is located in the direction of deviation from the center of the piston. A large gap was formed to facilitate the penetration of the flame into this gap. For this reason, the carbon and the like generated in the cutback portion can be burned, and the accumulation of carbon on the land portion is prevented from forming a hard accumulation, the premature wear of the cylinder liner is suppressed, and the cylinder liner is prevented from being worn. Durability can be improved, and the amount of blow-by gas 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 an enlarged side sectional view of a piston in FIG. 1;

5A and 5B are cross-sectional views of main parts of a piston that can be used in place of the piston of FIG. 1, wherein FIG. 5A is a first modified example, and FIG.
A modified example will be described.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piston 2 Engine 16 Piston top part 7 Combustion chamber 20 Depression d Top land part B Deflection direction E Cutback part L Piston center line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideki Miyamoto 5-33-8 Shiba, Minato-ku, Tokyo / Inside Mitsubishi Motors Corporation (72) Inventor Kiyoshi Hatano 5-33-8 Shiba, Minato-ku, Tokyo・ Mitsubishi Motor Industry Co., Ltd. (72) Hideo Nakai, Inventor 5-33-8 Shiba, Minato-ku, Tokyo ・ Mitsubishi Motor Industry Co., Ltd. -Mitsubishi Motors Corporation (72) Inventor Tomoyuki Imai 5-33-8 Shiba, Minato-ku, Tokyo-Mitsubishi Motors Corporation F-term (reference) 3G023 AA11 AA15 AB03 AC05 AD02 AD06 AE02 AF01 AG02

Claims (1)

[Claims] 1. A piston structure in which a recess serving as a combustion chamber is provided at the top of a piston, wherein the recess is formed so as to be deviated from the center of the piston, and has a direction of the same deviation and forms an outer peripheral edge of the top of the piston. A piston structure characterized by forming a cut-back portion on the piston.