JP3921317B2 - Piston structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piston structure of an internal combustion engine, and more particularly to a piston structure in which a concave portion serving as a combustion chamber is provided at the top of a piston.
[0002]
[Prior art]
The internal combustion engine burns fuel supplied to the combustion chamber to generate high-temperature and high-pressure combustion gas, and at that time, the piston receives the gas pressure received from the combustion gas as a rotational force through the connecting rod to the crankshaft. When such an engine is driven, the piston swings around the piston pin with respect to the connecting rod, and at that time, the piston slides back and forth while transmitting a side pressure to the inner wall of the cylinder liner via the piston top and skirt. For this reason, the piston as a whole is required to have sufficient mechanical strength, and its upper surface is required to have sufficient heat resistance than being exposed to high temperature and pressure, and in particular, the piston outer peripheral wall is more resistant to sliding than the cylinder inner wall. Abrasion is required, and it is easy to reduce the weight as the speed increases, and it is also necessary to have good thermal conductivity, and it is often manufactured from an aluminum alloy.
[0003]
By the way, in order to enable a lean operation and a non-lean operation according to a required output, a cylinder injection type internal combustion engine capable of performing the timing of direct fuel injection into the combustion chamber in the intake stroke or the compression stroke is known. ing. The piston used in this in-cylinder injection type internal combustion engine has a recess formed on the top surface of the piston top, and a relatively small combustion chamber can be formed by the recess and the inner wall on the cylinder head side. Sometimes fuel is injected and ignited with a spark plug to enable lean combustion.
[0004]
[Problems to be solved by the invention]
In the case of such an in-cylinder internal combustion engine, the recess is formed deviating from the center of the piston, and a part of the periphery of the recess is disposed close to a land portion that forms the outer periphery of the top of the piston. In this way, since the recess, that is, the combustion chamber is close to the land portion, the hard and thick carbon tends to stick or adhere to the land portion on the recess side with time. And can be hardened to form a hard deposit that can rub the cylinder liner and cause excessive wear early.
An object of the present invention is to provide a piston structure capable of preventing early wear of a cylinder liner and improving durability based on the above-described problems.
[0005]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, according to the invention of claim 1, in the piston structure in which a concave portion serving as a combustion chamber is provided at the top of the piston, the concave portion is formed by being deviated from the center of the piston. and to form a cutback portion cut away by a predetermined distance than approximately 1/3 of the area only other than the deflection direction region on the land portion forming the outer peripheral edge of the piston crown.
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 entry of the flame into the gap. For this reason, the carbon generated in the cutback part can be easily burned by the flame, the stagnant carbon is prevented from adhering to the land part, and a hard stagnant product can be prevented, and early wear of the cylinder liner is suppressed, The durability of the cylinder liner can be improved, and the amount of blow-by gas can be reduced.
[0006]
Preferably, the piston structure is provided in a cylinder 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 operating region other than the lean operating region, and the ratio of the sprayed fuel entering the gap between the land portion and the cylinder liner is high. A cut-back portion was formed in a portion located in the lateral direction, a relatively large gap was formed therein, and flame entry into the gap was facilitated. For this reason, 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]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a piston 1 employing a piston structure as an embodiment of the present invention. The piston 1 is mounted on a direct injection internal combustion engine (hereinafter simply referred to as the engine 2). The engine 2 is a four-cycle, four-valve type, in-line four-cylinder, but the configuration of each cylinder is the same. Here, the piston 1 of one cylinder will be mainly described.
[0008]
The engine 2 includes a cylinder head 4 with a head cover 3, a cylinder block 5 below the cylinder head 5, a crankcase and a crank cover (not shown) that are stacked in this order and integrated to form a main body outline. Inside the main body of the engine 2, a cylinder liner 6 that is 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) capable of communicating with each other, a pair of intake / exhaust valves 11 and 12 (only one side is shown) for opening and closing these intake / exhaust ports, and driving these There are provided a valve system (not shown), a crankshaft (not shown), a connecting rod 13 and the like that convert the reciprocating motion of the piston 1 into a rotational motion.
[0009]
It is assumed that the cylinder head 4 is provided with a vertical plane (not shown) including the cylinder axis L along the center of the cylinder liner 6, and a pair of intake ports (only the front side is shown) on one side of the vertical plane. 8 is provided with a pair of exhaust ports 9 (only the front side is shown) on the other side. An inner wall 401 formed on the cylinder head 4 and opposed to the combustion chamber 7 is formed as a wedge-shaped recess that is long in the direction perpendicular to the paper surface. An intake port 8 that is opened and closed by the intake valve 11 is formed on the left side of the inner wall 401 that forms the wedge-shaped recess. The exhaust port 9 that is opened and closed by the exhaust valve 12 is formed in the right part. Further, a spark plug 14 is mounted at a substantially central position of the inner wall 401 forming the wedge-shaped recess, and an injector 15 is mounted on the cylinder outer peripheral portion of the intake port 8.
As shown in FIG. 3, the cylinder liner 6 has an inner wall surface 601 formed in a substantially circular shape, and piston rings r1 and r2 and an oil ring r0 (see FIG. 3) provided on the outer peripheral portion of the piston 1 fitted thereto. 4) is in sliding contact.
[0010]
As shown in FIGS. 1 to 4, the piston 1 protrudes below a piston top 16 facing the combustion chamber 7, a skirt 17 facing the cylinder liner 6, and a lower wall that is an inner wall of the piston top 16. And a pair of pin boss portions 19. As shown in FIG. 2, a plurality of ring grooves 22 and 23 for piston rings r1 and r2 and a ring groove 30 for oil ring r0 are spaced apart from each other in the vertical direction on the outer peripheral wall of the piston top 16 in this order. Formed. Note that the symbol g indicates an oil drain hole.
[0011]
The piston top 16 has a recess 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 as a reverse tumble flow TF. The raised portion 21 has a wedge-shaped protrusion whose upper surface uniformly faces the inner wall 401 forming a wedge-shaped recess, and is formed by biasing the recess 20 on the side facing the intake port 12, An inclined wall surface f is formed on the opposite surface side, and a bent ridge portion e continuous in the longitudinal direction A (see FIG. 3) of the engine body is formed in the center. The bent ridge portion e is formed as a curved ridge portion in which both end portions are straight and the intermediate portion intersects the concave portion 20 and the inclined wall surface f. By adopting such a shape, when the piston 2 moves to the compression top dead center TDC (position indicated 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 recess. 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.
[0012]
As shown in FIG. 3, the piston top portion 16 is formed by biasing the concave portion 20 in the displacement direction B that is one side wall side of the cylinder block 5 from the piston center line L side that coincides with the cylinder axis in a plan view. In addition, the piston center side periphery of the recess 20 is opposed to the spark plug 14. Thereby, the fuel which flows with the reverse tumble flow TF in the recess 20 can be guided to the spark plug 14 relatively easily, and ignition can be facilitated.
[0013]
As shown in FIG. 2 and FIG. 3, on the top land portion d of the piston 1 and on one side surface portion of the cylinder block 5 that is the displacement direction B of the recess 20, the space α is more than the other region. A cutback portion E in which the top land portion d was cut out was formed. Here, the cut-back portion E is formed on the top land portion d of the piston 1 in an approximately 略 region thereof, and is configured to cover all regions having a relatively small relative distance from the recess 20. By fitting and inserting such a piston 1 into the cylinder liner 6, the gap between the top land portion d of the piston 1 and the inner wall surface 601 of the cylinder liner 6 becomes a relatively large t2 at the cut back portion E, and the cut back portion A relatively small t1 (<t2) is obtained at a portion other than E.
[0014]
Such an engine 2 receives the intake air from the intake port during the intake stroke, compresses the intake air as a reverse tumble flow TF during the compression stroke, compresses the fuel, and sprays fuel into the cylinder during the compression stroke or the intake stroke depending on the operating range. The piston 1 is ignited by the spark plug 14 immediately before the compression top dead center TDC, 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 as a rotational force from each pin boss portion 19 to the crankshaft (not shown) via the piston pin 24 and the connecting rod 13.
[0015]
When such an engine 2 is in the intake stroke injection operation region, during the intake stroke, that is, when the piston 1 is on the bottom dead center BDC position side and the fuel injection valve 15 is in the operation region not facing the recess 20, A fuel spray is formed, and in this case, the fuel spray is diffused almost over the entire combustion chamber 7, which is stirred by the reverse tumble flow TF, subjected to an ignition process after compression in the compression stroke, and proceeds to the combustion stroke. In this intake stroke injection operation region, a part of the fuel spray easily enters 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 tends to stick.
[0016]
Further, when the engine 2 is in the compression stroke injection operation region, fuel spray is formed in the compression stroke, that is, when the piston 1 is at the time of ascent and the fuel injection valve 15 is in the operation region facing the recess 20. In this case, most of the fuel spray is swirled and stirred in the combustion chamber 7 covered with the concave portion 20 and the inner wall 401 forming the wedge-shaped concave portion, and after the compression stroke, an ignition process is performed and proceeds to the combustion stroke. In this compression stroke injection operation region, the fuel spray from the fuel injection valve 15 is sprayed relatively efficiently into the recess 20, but a part of the spray is again formed between the top land portion d and the inner wall surface 601 of the cylinder liner. Particularly, in the initial stage of injection, the spray is likely to be scattered outside the recess 20, and in this case as well, the fuel and carbon tend to adhere to the top land portion d over time.
[0017]
However, in the piston 1 used in the engine 2, a cutback portion E is provided in a portion located in the displacement direction B of the concave portion 20, which is a position where carbon is relatively easily generated, and a relatively large gap t2 is provided here. Formed. For this reason, the fuel and carbon adhering to the top land part d can be easily burned by the flame that has entered the gap t2, and the stagnant carbon adheres to the top land part d in the entire engine operating range. Can be prevented from being generated.
For this reason, the engine 2 equipped with the piston 1 does not progress in wear of the cylinder liner in proportion to the passage of operating time as in the conventional engine, and is provided with a cut-back portion E to generate a hard debris. Therefore, the wear of the cylinder liner hardly progresses even with the passage of operating time. For this reason, the engine 2 equipped with the piston 1 can improve the durability of the cylinder liner 6 and can also reduce the amount of blow-by gas.
[0018]
The piston 1 used in the engine 2 of FIG. 1 has a cut-back portion E along the same piston center line L as the cylinder axis on the top land portion d on the displacement direction B side of the recess 20. Instead, it may be configured as shown in FIGS. The pistons 1a and 1b here can be attached to the engine 2 instead of the piston 1 of FIG.
[0019]
The piston 1a shown in FIG. 5 (a) is cut out by a distance α1 from other regions when forming the cut-back portion E on the top land portion d on the side of the displacement direction B of the concave portion 20 (see FIG. 4). A top land portion d having a conical surface fc shape was formed. In this case, the top land portion d having a conical surface fc shape can facilitate the intrusion of the flame, the fuel and carbon adhering to the top land portion d can be easily burned, and the decrease in the hole depth of the piston ring r1 can be relatively suppressed. Can do. The piston 1b shown in FIG. 5 (b) forms a cutback portion E which is cut out by a distance α2 in the top land portion d, and also in the second land portion d2 in the same region as the cutback portion E. Formed. In this case, the fuel and carbon that have reached the second land portion d2 side can be combusted, and it is possible to prevent stagnant carbon from adhering to the top land portion d and the second land portion d2 to generate hard stagnant deposits. Early wear of the inner wall surface 601 is more reliably suppressed, the durability of the cylinder liner 6 can be further improved, and the amount of blow-by gas can be more reliably reduced.
[0020]
The piston 1 in FIG. 1 was mounted on an engine 2 that is a cylinder injection type internal combustion engine, but is not limited to this, and is not limited to this. In these cases, the same effect as the piston 1 of FIG. 1 can be obtained.
[0021]
【The invention's effect】
As described above, a first aspect of the invention, on the land portion of the piston, the recess is a portion positioned deflection direction displaced from the piston central above only in the region of approximately 1/3 on the land portion A cut-back portion cut out by a predetermined interval from a region other than the deviation direction was formed, and a relatively large gap was formed therein, thereby facilitating the entry of the flame into the gap. For this reason, carbon generated in the cut-back portion can be burned, stagnant carbon is prevented from adhering to the land portion, and hard stagnant deposits are prevented, and early wear of the cylinder liner is suppressed. Durability can be improved and the amount of blow-by gas can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a main part of an engine to which a piston structure as one embodiment of the present invention is applied.
FIG. 2 is an enlarged side view of the piston in FIG.
FIG. 3 is a plan view of the piston in FIG. 1;
4 is an enlarged side sectional view of the piston in FIG. 1. FIG.
5 is a cross-sectional view of a main part of a piston that can be used in place of the piston of FIG. 1. FIG. 5 (a) shows a first modification, and FIG. 5 (b) shows a second modification.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Piston 2 Engine 16 Piston top part 7 Combustion chamber 20 Recess d Top land part B Deflection direction E Cutback part L Piston centerline

Claims (1)

In the piston structure provided with a recess that becomes a combustion chamber at the top of the piston,
The recess is formed offset from the piston center, a predetermined distance from approximately 1/3 of the area only other than the deflection direction region on the land portion forming an outer peripheral edge of the piston crown a same deviation direction Piston structure characterized by forming a cut-back part that is notched only.

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