JPH112155A - Piston structure - Google Patents

Abstract

(57) [Problem] To provide a piston structure capable of reducing slap noise. SOLUTION: In a piston structure for an internal combustion engine, a balance member 10 having a specific gravity larger than a base material of a piston 1 is provided below a piston pin center A of a piston skirt portion 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure of a piston used in an internal combustion engine.

[0002]

2. Description of the Related Art In some cases, a relief is formed on the top surface of a piston to avoid interference with intake and exhaust valves. Especially,
On the top of the piston used for diesel engines,
A combustion chamber recess forming part of the combustion chamber is formed.
These are often formed eccentrically with respect to the piston center, in which case the center of gravity of the piston moves from the center line of the piston. When such a piston moves up and down in a cylinder, a moment is generated with respect to the center of the piston pin on the piston center line due to inertia acting on the position of the center of gravity of the piston near the position of the vertical dead center of the piston. There was a problem that a slap sound was generated upon collision.

In order to reduce the slap noise, there is known a technique called piston pin offset in which the center of the piston pin is offset from the center line of the piston to the thrust side. In addition, the center of gravity of the cast iron ring is changed by changing the cross-sectional area of the cast iron ring forming the ring groove while being integrally cast into the piston, thereby correcting the center of gravity of the piston on the piston center line. The technology is also known.

[0004]

However, with the above-described piston pin offset technique and the technique of correcting the center of gravity of the piston on the center line of the piston, it is difficult to sufficiently reduce the slap noise, and the noise due to the slap noise is large. There is a point. In particular, the moment acting on the center of gravity of the piston near the top and bottom dead center of the piston differs between an idle state (at low rotation) where the influence of combustion pressure is large and a high rotation and high load state where the influence of inertia force is large. An optimum center of gravity position is required in the state. Therefore, it is difficult to achieve both reduction of the slap noise in the idling state and the high rotation / high load state, and it is desired to reduce the slap noise over the entire operation range of the engine.

Therefore, an object of the present invention is to provide a piston structure that can reduce slap noise.

[0006]

According to a first aspect of the present invention, in a piston structure for an internal combustion engine, a balance member having a larger specific gravity than a base material of a piston is provided below a center of a piston pin of a piston skirt. With this configuration, the center of gravity of the piston is lowered, and the center of gravity of the piston approaches the center of the piston pin.

According to a second aspect of the present invention, in a piston structure for an internal combustion engine, a balance member having a larger specific gravity than a base material of the piston is provided on a thrust side of a piston skirt portion. Moves to the thrust side of the piston.

According to a third aspect of the present invention, in the piston structure for an internal combustion engine, a balance member having a specific gravity larger than that of the base material of the piston is provided below the center of the piston pin of the piston skirt and on the thrust side. Configuration
This configuration lowers the center of gravity of the piston,
The center of gravity of the piston moves to the thrust side of the piston.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a piston used in a diesel engine as an internal combustion engine, and reference numeral 2 denotes
1 shows a cylinder accommodating a piston 1. The piston 1 is cast from an aluminum alloy, and mainly includes a head portion 3, a skirt portion 4, a piston ring 5, and a pin boss portion 7 that supports a piston pin 6.

A combustion chamber recess 8 which forms a part of the combustion chamber is formed on the top surface 3a of the head portion 3. Since the fuel injection nozzle (not shown) is arranged to avoid interference with the intake and exhaust valves, the combustion chamber recess 8 is provided eccentrically to the right with respect to the piston center line A in the figure. Inside the head portion 3, a space 9 for cooling the piston 1, particularly the head portion 3, is formed in an annular shape so as to cover the outer periphery of the combustion chamber recess 8. The center 6a of the piston pin 6 is located on the piston center line A.

A metal ring 10 is provided on the outer periphery of the lower part of the skirt 4 as a balance member. The ring 10 is formed of a material having a specific gravity greater than that of the base material (aluminum alloy) of the piston 1, and is integrally cast when the piston 1 is cast. In the present embodiment, the ring 10 is formed from Ni-resist which is a nickel-containing cast iron. The specific gravity of the niresist is approximately 9, which is larger than the specific gravity of the aluminum alloy (approximately 3).

The ring 10 is formed by gradually changing its cross-sectional area so that the cross-sectional area on the left side is larger than the cross-sectional area on the right side in the figure. That is, the cross-sectional area of the ring 10 cast on the thrust side of the piston 1 is larger than the cross-sectional area of the ring 10 cast on the opposite thrust side. Here, the thrust side of the piston 1 refers to the side where the piston 1 contacts the wall surface 2a of the cylinder 2 during the expansion stroke.
In the figure, it is the left side of the piston 1.

As described above, since the space 9 and the ring 10 are provided in the piston 1, respectively,
, That is, the center of gravity of the piston 1 can be brought closer to the center 6a of the piston pin, and since the cross-sectional area on the left side of the ring 10 is larger than the cross-sectional area on the right side, the center of gravity of the piston 1 is The piston 1 can move to the left (thrust side) in the drawing.

In FIG. 1, the center of gravity of the piston 1 before the space 9 and the ring 10 are provided in the piston 1 is shown with respect to the center line A of the piston because the combustion chamber recess 8 is eccentric to the right in the figure. It is eccentric to the middle and to the left (indicated by G1). On the other hand, the center of gravity of the piston 1 after the space 9 and the ring 10 are respectively provided in the piston 1 moves to a position indicated by a reference sign G2 in the drawing. That is, assuming that the vertical direction of the piston 1 is the X direction and the thrust-anti-thrust direction of the piston 1 is the Y direction, the center of gravity G1 of the piston 1
By moving the space 9 and the ring 10 in the piston 1 respectively, the space 9 and the ring 10 move by the movement amount X1 in the X direction and by the movement amount Y1 in the Y direction, and move to the center of gravity G2. The vertical direction of the piston 1 means the center 6a of the piston pin.
And the direction parallel to the piston center line A, and the thrust-anti-thrust direction of the piston 1 is a direction orthogonal to the piston pin center 6a and passing through the thrust side and the anti-thrust side of the piston 1. It is.

Accordingly, when the center of gravity of the piston 1 approaches the center 6a of the piston pin, the distance from the center 6a of the piston pin to the center of gravity of the piston 1 decreases from L1 to L2. Of the piston 1 collides with the cylinder wall surface, and the slap noise can be reduced. In particular, since the ring 10 is made of niresist having a specific gravity greater than the specific gravity of the piston 1, it is possible to prevent the piston 1 from being enlarged and to lower the center of gravity of the piston 1.

In the above-described embodiment, a space 9 is provided above the piston 1 and a ring 10 is provided on the piston 1 in order to lower the center of gravity of the piston 1, that is, to bring the center of gravity of the piston 1 closer to the center 6a of the piston pin. It was provided at the bottom. However, in order to lower the center of gravity of piston 1,
A method of providing a space 9 above the piston 1 and a method of forming a ring 10
May be provided only below the piston 1. Although the center of gravity of the piston 1 can be lowered by either method, the method of providing the space 9 above the piston 1 limits the size (capacity) of the space 9 because the strength of the head portion 2 is maintained. There is
When the ring 10 is provided below the piston 1, the weight of the piston 1 increases. Therefore, by providing both the space 9 and the ring 10 in the piston 1 as in the above-described embodiment, the center of gravity of the piston 1 can be lowered, and the weight increase of the piston 1 can be minimized.

Further, since the center of gravity of the piston 1 moves to the thrust side, the piston speed immediately before the piston 1 collides with the wall surface 2a of the cylinder 2 is reduced, and the impact is alleviated and the collision force is reduced. Slap sound can be reduced. The reduction of the collision force will be described with reference to FIG. In the figure, the left side is the thrust side of the piston 1 in the figure.

As shown in FIG. 2A, in the compression stroke,
The piston 1 rises inside the cylinder 2 while contacting the wall surface 2a of the cylinder 2 on the opposite thrust side. Next, FIG.
Immediately after the piston 1 reaches the top dead center,
Both the anti-thrust side and the thrust side of the piston 1 descend while maintaining a state in which the piston 1 is not pressed by the wall surface 2a of the cylinder 2, and as shown in FIG. Middle, tilt in the direction of arrow B,
The lower end of the skirt portion 4 on the thrust side of the piston 1 collides with the wall surface 2a of the cylinder 2. At this time, piston 1
Is small, the piston speed immediately before the piston 1 collides with the wall surface 2a of the cylinder 2 is reduced.

Further, as shown in FIG. 2D, during the expansion stroke, the combustion pressure applied to the top surface 3a of the head portion 3 and the lower end of the piston 1 on the thrust side are changed to the wall surface 2a of the cylinder 2.
The piston 1 tilts in the direction of the arrow C in the figure around the center 6a of the piston pin, and the upper end of the skirt portion 4 on the thrust side of the piston 1 collides with the wall surface 2a of the cylinder 2. At this time, the piston speed immediately before the piston 1 collides with the wall surface 2a of the cylinder 2 is reduced, and the impact of the piston 1 on the wall surface 2a of the cylinder 2 is reduced, so that the collision force is reduced. Can be reduced. In the drawings, reference numeral 11 denotes a connecting rod.

FIG. 2 illustrates the collision of the piston 1 with the cylinder 2 during the expansion stroke (top dead center). However, when the piston 1 is at the bottom dead center (at the start of the exhaust stroke or the compression stroke), the piston 1 The collision of 1 with the cylinder 2 is in a state opposite to the state described with reference to FIG. 2, and the slap sound at this time is larger than the conventional slap sound. However, comparing the slap noise during the expansion stroke of the piston 1 with the slap noise at the bottom dead center, the combustion force is applied to the piston 1 during the expansion stroke, so that the collision force of the piston 1 against the cylinder 2 becomes lower dead center. The slap sound during the expansion stroke is much larger than the slap sound at the bottom dead center. Therefore, in order to reduce the slap sound, it is most effective to reduce the slap sound during the expansion stroke.

For example, conventionally, the slap sound at the time of the expansion stroke is 100, and the slap sound at the bottom dead center is 6
Assuming that the slap sound at the time of the expansion stroke is reduced to 80 and the slap sound at the bottom dead center becomes 70, the conventional slap sound is reduced to 100 by the configuration of the present embodiment. Since the slap sound can be substantially reduced.

Next, the movement amounts X1 and Y1 of the center of gravity of the piston 1 in the X and Y directions will be described. The amount of movement of the center of gravity of the piston 1 in each direction can be obtained by the simulation analysis shown in FIG. This simulation is performed when the center of gravity of the piston 1 is moved in each direction when the engine operating state is an idle state (during low rotation) and when the engine operating state is a high rotation / high load state. FIG. 3A and FIG. 3B show the analysis results of the collision force of the piston 1 against the wall surface 2a of the cylinder 2 during the expansion stroke. 3 (a) and 3 (b), the X-axis indicates the amount of movement of the center of gravity (mm) of the piston 1 in the vertical direction, the Y-axis indicates the amount of movement of the center of gravity (mm) in the thrust-anti-thrust direction of the piston 1, and the Z-axis. The piston 1 is on the wall 2a of the cylinder 2
Shows the collision force (kg) at the time of collision. 3A and 3B, the piston 1 before the space 9 and the ring 10 are provided on the piston 1.
Are indicated by G1.

As is clear from FIGS. 3A and 3B,
By lowering the position of the center of gravity of the piston 1, that is, by bringing the position of the center of gravity of the piston 1 closer to the center 6a of the piston pin, the collision force is reduced. 3B, the collision force is reduced by moving the position of the center of gravity of the piston 1 toward the thrust side and lowering the position of the center of gravity of the piston 1.

From the above simulation results, in order to reduce the slap noises in the idle state and the high rotation / high load state, the position of the center of gravity of the piston 1 is lowered, that is, the position of the center of gravity of the piston 1 is set to the center of the piston pin. It is clear that it is effective to approach 6a, and it is also effective to move the position of the center of gravity of the piston 1 to the thrust side. Therefore, the size (capacity) of the space 9, the weight of the ring 10, and the cross-sectional area of the ring 10 are determined based on the simulation result. That is, the size (capacity) of the space 9, the weight of the ring 10, and the cross-sectional area of the ring 10 are determined so that the center of gravity of the piston 1 moves to a predetermined center of gravity position obtained from the simulation result.

FIGS. 4A and 4B show the case where the center of gravity of the piston 1 is at the reference position (the center of gravity G1 in FIG. 1).
The idle state and the high rotation speed between the case where it is above the reference position and the case where it is below the reference position.
The result of having measured each slap sound in a high load state is shown. Note that the measurement of the slap sound was performed approximately 1 minute from the engine.
m. In FIGS. 4A and 4B,
The frequency of the slap sound (Hz) is set on the horizontal axis, and the noise level of the slap sound (dB (A)) is set on the vertical axis. In the figure, a dashed line D1 indicates a measurement result when the center of gravity of the piston 1 is at the reference position, and a broken line D2 indicates a measurement result when the center of gravity of the piston 1 is above the reference position.
Numeral 3 indicates the measurement results when the center of gravity of the piston 1 is below the reference position. FIG. 4 (a), (b)
As is clear from FIG. 7, when the center of gravity of the piston 1 is below the reference position (D3), the noise level of the slap sound is lower than the noise level of the reference position over substantially the entire frequency range.

FIG. 5 shows the result of measuring the change in the slap sound when the center of gravity of the piston 1 is moved up and down from the reference position (the center of gravity G1 in FIG. 1). The measurement of the slap sound was performed at a position approximately 1 m away from the engine. As is clear from FIG. 5, when the center of gravity of the piston 1 is below the reference position, the noise level of the slap sound is lower than the noise level of the reference position.

In FIG. 1, instead of the ring 10, a balance member indicated by reference numeral 15 may be provided only on the thrust side of the skirt portion 4. A material having a specific gravity larger than that of the base material of the piston 1 is used for the balance member 15 as in the above-described embodiment. Further, instead of the ring 10, a balance member having a specific gravity larger than that of the base material of the piston may be provided at symmetrical positions with respect to the center line of the piston pin of the skirt. At this time, by increasing the balance member on the thrust side of the piston, the center of gravity of the piston can be moved to the thrust side.

In the above-described embodiment, the center of gravity of the piston 1 does not coincide with the center 6a of the piston pin.
Since the center of gravity of the piston 1 coincides with the center 6a of the piston pin, the moment acting on the piston 1 is minimized.
It is desirable to match. However, in practice, the increase in the weight of the piston 1 is limited, and moving the center of gravity of the piston 1 to the thrust side is also effective in reducing the slap noise. Do not match.

In the above-described embodiment, the center of gravity of the piston 1 is moved to the thrust side with respect to the center 6a of the piston pin. By moving to the side, a state corresponding to the conventional piston pin offset to the thrust side can be created, and in this case, the slap noise can be reduced similarly to the conventional piston pin offset.

Further, the case where the present invention is applied to a piston used in a diesel engine has been described.
Similar effects can be obtained even when the present invention is applied to a piston used in a gasoline engine.

[0031]

As described above, according to the first aspect of the present invention,
According to the invention of the above, since the center of gravity of the piston is lowered and the center of gravity of the piston approaches the center of the piston pin, the distance from the center of the piston pin to the center of gravity of the piston is shortened, and the moment force acting on the position of the center of gravity of the piston during the expansion stroke is reduced. As a result, the collision force at which the piston collides with the cylinder wall surface is reduced, and the slap noise can be reduced. Further, the slap noise in the idle state (during low rotation) and the high rotation / high load state can also be reduced, and the slap noise can be reduced over the entire operating range of the engine.

According to the second aspect of the present invention, the center of gravity of the piston moves to the thrust side, so that the piston speed immediately before the piston collides with the cylinder wall surface is reduced, and the collision force of the piston against the cylinder wall surface is reduced. Therefore, the slap sound can be reduced.

According to the third aspect of the present invention, the center of gravity of the piston lowers and the center of gravity of the piston moves toward the thrust side of the piston. Therefore, during the expansion stroke, the piston speed immediately before the piston collides with the cylinder wall surface decreases. Since the impact force of the piston on the cylinder wall is reduced, the slap noise can be effectively reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a piston showing a piston structure of the present invention.

2A and 2B are schematic diagrams for explaining a collision of a piston with a cylinder wall surface, wherein FIG. 2A shows a compression stroke, FIG. 2B shows a state immediately after the piston reaches a top dead center, and FIG. (D) shows a state in which it has collided with the cylinder wall surface, and (d) shows a state during the expansion stroke.

3A and 3B are characteristic diagrams obtained by a simulation analysis for finding an optimum center of gravity of a piston, wherein FIG. 3A shows a case where the engine operation state is idle, and FIG. 3B shows a case where the engine operation state is high rotation and high load. Are respectively shown.

FIGS. 4A and 4B are characteristic diagrams in which respective slap sounds are measured when the center of gravity of the piston is moved up and down from a reference position, wherein FIG. 4A shows a case where the engine operation state is idle, and FIG. The cases of rotation and high load are shown respectively.

FIG. 5 is an explanatory diagram of a measurement result of a slap sound change amount when the center of gravity of a piston is moved up and down from a reference position.

[Explanation of symbols]

 Reference Signs List 1 piston 2 cylinder 4 skirt 6 piston pin 6a piston pin center 9 space 10 ring (balance member) A piston center line G1, G2 center of gravity

Claims (3)

[Claims] 1. A piston structure for an internal combustion engine, wherein a balance member having a larger specific gravity than a base material of the piston is provided below a center of a piston pin of a piston skirt portion. 2. A piston structure for an internal combustion engine, wherein a balance member having a larger specific gravity than a base material of the piston is provided on a thrust side of a piston skirt portion. 3. A piston structure for an internal combustion engine, wherein a balance member having a specific gravity greater than that of a base material of the piston is located below a center of a piston pin of a piston skirt.
A piston structure provided on the thrust side.