JPH11200947A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To preferably suppress an increase in hammering sound of a piston and an increase in friction. SOLUTION: A piston 11 is provided with a piston head part 21 and a piston skirt part 22 extending in the lower part of the piston head part 21 which are respectively made of an aluminum alloy. A combustion chamber composed of a deep bowl type recessed part 24 is provided on the top surface of the piston head part 21. A partition wall 25 between the bottom wall of this recessed part (combustion chamber) 24, that is, the recessed part 24 and the inside space of the piston skirt part 22 is formed with a heat resistant steel with heat resistance higher than that of the aluminium alloy. The heat resistant steel as the partition wall 25 is connected to the piston head part 21 while it is cast into the piston 11. The partition wall 25 has thickness t1 which is thinner than the thickness t2 of the partition wall 58 of a conventional piston 51 which is completely made of aluminium alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine suitable for use in a direct injection type internal combustion engine capable of directly injecting fuel into a cylinder.

[0002]

2. Description of the Related Art In general, in a piston used in a direct injection type internal combustion engine, a fuel injected from a fuel injection valve is collected as a combustible mixture near a spark plug to perform stratified combustion. Is provided with a combustion chamber having a predetermined concave shape (see, for example, JP-A-8-35429). FIG. 7 shows a cross-sectional structure of a conventional piston used in such a direct injection type internal combustion engine.

As shown in FIG. 7, a piston 51 made of an aluminum alloy has a substantially disc-shaped piston head 53 having a top surface formed in a substantially triangular cross section and a deep dish-shaped recess 52 provided therein. , A hollow piston skirt 54 extending below the piston head 53. A pin boss 55 is formed on the inner wall surfaces of the piston head 53 and the piston skirt 54, and a connecting rod (connecting rod) 56 is rotatably connected to the pin boss 55 via a piston pin 57. The connecting rod 56 has a pin boss portion with its outer peripheral edge secured with a predetermined clearance C1 between the bottom wall of the concave portion 52, that is, the lower surface of the partition 58 between the concave portion 52 and the inner space of the piston skirt portion 54. 55. The partition wall 58 is formed with a minimum thickness t2 that can withstand the pressure and temperature in the combustion chamber.

[0004]

By the way, in the piston 51 having the combustion chamber having the concave portion 52 on the top surface, the clearance C1 between the piston 51 and the connecting rod 56 is ensured, and the pressure resistance and heat resistance through the partition wall 58 are secured. Therefore, the height from the axis of the piston pin 57 to the upper end of the outer peripheral surface of the piston 51, that is, the compression height h2, has to be naturally increased in the mode shown in FIG. . For this reason, the piston 51
As the weight increases, the center of gravity also moves in a direction away from the piston pin 57, and as a result, inconveniences such as an increase in piston tapping noise and an increase in friction are caused.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a piston for an internal combustion engine capable of suitably suppressing an increase in piston tapping sound and an increase in friction. is there.

[0006]

According to a first aspect of the present invention, there is provided a piston for an aluminum alloy internal combustion engine having a combustion chamber of a predetermined shape having a concave portion on a top surface. The gist of the present invention is that a partition for separating the bottom of the combustion chamber and the gap between the connecting rods is formed of heat-resistant steel.

[0007] According to such a configuration, when the partition is formed with a minimum necessary thickness that can withstand the pressure and temperature in the combustion chamber, it is possible to form the partition thinner than when the partition is formed of an aluminum alloy. Become. Therefore, the increase in the weight of the piston can be suppressed, and the compression height of the piston can be reduced, so that the center of gravity of the piston can be brought closer to the piston pin.

[0008] According to a second aspect of the present invention, in the piston for an internal combustion engine according to the first aspect, the partition wall is formed in a state where a plate material made of the heat-resistant steel is cast into the piston. This is the gist.

According to such a configuration, the joining property between the partition wall made of heat-resistant steel and the piston made of aluminum alloy can be suitably improved. In the invention according to claim 3, in an aluminum alloy internal combustion engine piston having a combustion chamber of a predetermined shape having a concave portion on a top surface,
The gist of the present invention is that a partition separating the bottom surface of the combustion chamber and a gap between the connecting rods and an inner wall surface of the combustion chamber are formed of heat-resistant steel.

According to such a configuration, in addition to the partition walls, the heat resistance of the inner wall surface of the combustion chamber is maintained high. Therefore, the occurrence of cracks and melting on the inner wall surface of the combustion chamber due to exposure to high temperatures is also suitably suppressed.

According to a fourth aspect of the present invention, in the piston for an internal combustion engine according to the third aspect, the partition wall and the inner wall surface of the combustion chamber are formed by casting a material made of the heat-resistant steel into the piston. It is the gist that it is formed in a state.

According to such a configuration, it is possible to suitably enhance the jointability between the partition wall made of heat-resistant steel and the inner wall surface of the combustion chamber and the piston made of aluminum alloy.

[0013]

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG.

As shown in FIG. 1, a piston 11 is provided in a cylinder block 2 of an engine 1 as an internal combustion engine so as to be able to reciprocate, and the piston 11 is connected to an output shaft of the engine 11 via a connecting rod (connecting rod) 12. Is connected to the crankshaft 13. The reciprocating movement of the piston 11 is converted into rotation of the crankshaft 13 by the connecting rod 12. On the side of the crankshaft 13 facing the connecting rod 12, a balance weight 13a for balancing the rotation of the crankshaft 13 is provided.

A cylinder head 4 is provided at an upper end of the cylinder block 2 via a gasket 3, and a combustion chamber 14 is formed between the cylinder head 4 and the piston 11. The cylinder head 4 is provided with an intake port 5 and an exhaust port 6 which communicate with the combustion chamber 14, and the intake port 5 and the exhaust port 6 have:
An intake valve 7 and an exhaust valve 8 are provided, respectively. The intake valve 7 and the exhaust valve 8 are driven to open and close by a cam (not shown) to communicate and shut off the intake port 5 and the combustion chamber 14 and the exhaust port 6 and the combustion chamber 14, respectively. A spark plug 9 is disposed in the cylinder head 4 so as to be exposed to the combustion chamber 14, and a fuel injection valve 10 is disposed in the combustion chamber 14 near the intake port 5.

On the other hand, as shown in FIG. 2A, the piston 11 has a substantially disk-shaped piston head 21 having a triangular cross section at the top, and a hollow extending below the piston head 21. And a piston skirt portion 22 having a shape. The piston head portion 21 and the piston skirt portion 22 are made of a lightweight aluminum alloy having excellent thermal conductivity and have a predetermined rigidity.

Three piston rings 23 are mounted on the outer peripheral surface of the piston head 21. In addition, a combustion chamber including a deep dish-shaped recess 24 is provided on the top surface of the piston head 21. The bottom wall of the concave portion (combustion chamber) 24, that is, the partition wall 25 that separates the concave portion 24 from the inner space of the piston skirt portion 22, is formed of heat-resistant steel having higher heat resistance than an aluminum alloy, for example, a titanium-based heat-resistant alloy. ing. This partition wall 25 is in a state of being cast into the piston 11, whereby the piston head portion 2 is formed.
1. That is, the piston 11 is
5 is formed by positioning and fixing a plate made of heat resistant steel in the mold of the piston 11 and pouring and solidifying a molten aluminum alloy into the mold.

A pin boss 26 is formed below the partition 25 in the piston head 21.
The connecting rod 12 is rotatably connected to the pin boss 26 via a piston pin 27. Note that the connecting rod 12 is connected to the pin boss portion 26 in a state where the outer peripheral edge of the connecting rod 12 has a predetermined clearance C1 between it and the lower surface of the partition wall 25.

Incidentally, in the piston according to the present embodiment, the partition wall 25 made of the heat-resistant steel is formed with a thickness t1 as shown in FIG. 2 (a). This partition 2
5 is set to a thickness that can withstand the pressure and temperature in the combustion chamber 14 including the concave portion 24, but since the partition wall 25 has higher heat resistance than an aluminum alloy, FIG.
The partition 5 of the conventional piston 51 shown in comparison with FIG.
8 is formed thinner than the thickness t2. Therefore,
The height from the axis of the piston pin 27 to the upper end of the outer peripheral surface of the piston 11, that is, the compression height h1, is also:
It is lower than the compression height h2 of the conventional piston 51 by the height h3 corresponding to the difference between the thicknesses t1 and t2.

As described above, in the piston 11, the compression height is reduced by the thickness of the partition wall 25, and the center of gravity of the piston 11 approaches the piston pin 27 side. Further, if the entire piston 11 is formed of heat-resistant steel, the weight of the piston 11 is increased.
Since only 5 is made of heat-resistant steel and the partition wall 25 is formed thin, an increase in the weight of the piston 11 is also suppressed.

Further, since the heat-resistant steel serving as the partition wall 25 is joined in a state of being cast into the piston 11 made of an aluminum alloy, the joining property of these materials can be maintained high. In particular, if a material having a thermal expansion coefficient close to that of an aluminum alloy is selected as the heat-resistant steel, the combustion chamber 14
Even if the partition wall 25 and the piston 11 are thermally expanded by the heat inside, the possibility that the joint surface between the partition wall 25 and the piston 11 is damaged due to a difference in thermal expansion between them is also suppressed.

As described in detail above, according to the piston of the first embodiment, the following effects can be obtained. -It is possible to preferably suppress an increase in piston tapping noise and an increase in friction due to an increase in the weight of the piston 11 and movement of the center of gravity.

The joining property between the partition wall 25 made of heat-resistant steel and the piston 11 made of aluminum alloy can be kept high. As shown in FIG. 3, in order to mount the conventional piston 51 for an internal combustion engine on the engine 61, the deck height DH2 of the cylinder block 62 constituting the internal combustion engine is replaced by a general flat top piston. Than the deck height of the engine cylinder block using
It is necessary to form the piston 51 higher by the increase of the compression height. Therefore, when the piston 51 is used, a cylinder block of an engine using a general piston having a flat top cannot be applied,
Requires significant design changes. Therefore, the productivity of the entire engine 61 deteriorates. Moreover, the cylinder block 62
If the deck height DH2 is increased, the size of the entire engine 61 may be increased, and the mounting space may have to be changed.

It is also conceivable to mount the piston 51 on the engine 61 by shortening the length of the connecting rod 56 without changing the deck height DH2 of the cylinder block 62. However, when the piston 51 is at the bottom dead center position in the manner shown in FIG.
1 must not interfere with the balance weight 63a provided on the crankshaft 63, and for that purpose, a predetermined clearance C2 must be secured between the pin boss 55 and the balance weight 63a.
Therefore, the length of the connecting rod 56 cannot be easily reduced.

In this regard, in the internal combustion engine piston according to the above-described embodiment, the compression height of the piston 11 is set to the compression height of the general flat-top piston (see FIG. 4B) as shown in FIG. It can be set to the same height as. In this case, the deck height DH1 of the cylinder head 2 shown in FIG. 1 may be the same height as the deck height of a cylinder block of an engine using a general flat top piston, and this flat top piston is used. The cylinder block of the engine can be applied as it is. Therefore, it is not necessary to change the design of the cylinder block 2, and the productivity of the entire engine 1 is improved, and the entire engine can be made more compact than the conventional engine using the piston 51.

(Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to FIG. Note that, in the present embodiment, the same or corresponding elements as those in the first embodiment are denoted by the same reference numerals in the drawings, and a detailed description of those elements will be omitted.

As shown in FIG. 5, a wall 25a extending from a partition wall 25 made of the above-mentioned heat-resistant steel is joined to the entire inner wall surface of the concave portion (combustion chamber) 24 of the piston 11.
Note that the heat-resistant steel material forming the partition wall 25 and the wall portion 25a is also cast in the piston 11 as in the first embodiment.

In the piston 11, a wall 25 made of heat-resistant steel is formed on the entire inner wall surface of the recess (combustion chamber) 24.
By joining a, the heat resistance of the entire inner wall surface of the recess 24 is maintained high. Therefore, the occurrence of cracks on the inner wall surface of the concave portion 24 and the melting of the inner wall surface due to exposure to a high temperature can be suitably suppressed. In particular, at the periphery of the opening end of the concave portion 24, heat tends to hardly escape and the temperature tends to be high.
Such a structure is effective, and a precise design is not required for the shape of the periphery of the opening end of the concave portion 24.
1 as a whole can be easily designed.

As described in detail above, according to the second embodiment, the following effects can be obtained in addition to the effects of the first embodiment. The occurrence of cracks on the inner wall surface of the recess (combustion chamber) 24 and the melting of the inner wall surface can be suppressed.

Since the shape of the peripheral portion of the opening end of the recess (combustion chamber) 24 does not need to be precisely designed, the entire piston 11 can be easily designed. Each of the above embodiments can be modified and implemented as follows.

In the above embodiments, the heat-resistant steel which becomes the partition wall 25 or the wall 25a is joined to the piston head 21 in a state of being cast into the piston 11. 21 may be press-fitted.

[0032] Particularly in the second embodiment, the wall portion 25a
The joint surface between the heat-resistant steel material and the piston head portion 21 may be formed in a saw blade shape, for example, as shown in FIG. If you do this,
The contact area of the joining surface increases, and the thermal conductivity and joining property between the materials can be improved. In addition,
The shape of such a joint surface is not limited to the saw blade shape.
In short, any shape may be used as long as it has one or a plurality of engaging concave and convex surfaces and the contact area of the joining surfaces increases.

While the embodiments have been described above, technical ideas other than the claims that can be grasped from the embodiments will be described below together with their effects. (1) In the piston for an internal combustion engine according to any one of claims 1 to 4, the partition wall has a wall thickness such that a compression height of the piston is equal to a compression height of a piston having a flat top surface. A piston for an internal combustion engine characterized by being made.

In this way, a cylinder block of an internal combustion engine on which a general flat-top piston is mounted can be applied as the cylinder block of the internal combustion engine on which the piston is mounted.

(2) In the piston for an internal combustion engine according to claim 3 or claim 4 or (1), one or more joint surfaces between the heat-resistant steel material constituting the inner wall surface of the combustion chamber and the piston are provided. A piston for an internal combustion engine, characterized in that the piston has an engaging uneven surface.

In this way, the contact area between the heat-resistant steel material and the piston made of an aluminum alloy is increased, and the heat conductivity and the jointability thereof can be further improved.

[0037]

According to the first aspect of the present invention, the compression height of the piston can be reduced, the increase in the weight of the piston can be suppressed, and the center of gravity can be made closer to the piston pin side. it can. Therefore, it is possible to preferably suppress an increase in piston hitting sound, an increase in friction, and the like.

According to the second aspect of the present invention, it is possible to preferably improve the joining property between the partition wall made of heat-resistant steel and the piston made of aluminum alloy. According to the third aspect of the present invention, it is possible to prevent the inner wall surface of the concave portion from being cracked or melted by being exposed to a high temperature.

According to the fourth aspect of the present invention, it is possible to preferably improve the jointability between the partition wall made of heat-resistant steel and the inner wall surface of the combustion chamber and the piston made of an aluminum alloy.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an internal combustion engine equipped with a piston according to a first embodiment.

FIG. 2 is a schematic cross-sectional view showing the piston of the embodiment and a conventional piston in comparison.

FIG. 3 is a schematic cross-sectional view of an internal combustion engine equipped with a conventional piston.

FIG. 4 is a schematic cross-sectional view showing the piston of the first embodiment in comparison with a general flat-top piston.

FIG. 5 is a schematic sectional view of an internal combustion engine equipped with a piston according to a second embodiment.

FIG. 6 is a schematic sectional view showing the structure of a piston according to yet another embodiment.

FIG. 7 is a schematic sectional view showing the structure of a conventional piston.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine (internal combustion engine), 2 ... Cylinder head, 11
... piston, 12 ... connecting rod, 14 ... combustion chamber, 24 ... recess (combustion chamber), 25 ... partition wall, 25a ... wall part.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02F 3/00 302 F02F 3/00 302Z F16J 1/01 F16J 1/01

Claims (4)

[Claims] 1. A piston for an internal combustion engine made of an aluminum alloy having a combustion chamber of a predetermined shape having a concave portion on a top surface, wherein a partition wall separating a bottom surface of the combustion chamber and a gap between a connecting rod is formed of heat-resistant steel. A piston for an internal combustion engine, characterized in that: 2. The piston for an internal combustion engine according to claim 1, wherein the partition wall is formed in a state in which a plate material made of the heat-resistant steel is cast in the piston. . 3. A piston for an internal combustion engine made of an aluminum alloy having a combustion chamber of a predetermined shape having a concave portion on a top surface thereof, wherein a partition separating a bottom surface of the combustion chamber and a gap between a connecting rod and an inner wall surface of the combustion chamber are provided. Made of heat-resistant steel. 4. The piston for an internal combustion engine according to claim 3, wherein the partition and the inner wall surface of the combustion chamber are formed in a state where a material made of the heat-resistant steel is cast into the piston. A piston for an internal combustion engine, characterized in that: