JP2013024164A - Piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston capable of preventing an increase in engine noise and a deterioration in piston endurance reliability caused by a collision of a retaining ring when an upper piston returns to a high-compression position from a low-compression position.SOLUTION: The upper piston 2 is urged upward with respect to a lower piston 1 by a belleville spring 9, the separation of the upper piston 2 from the lower piston 1 is prevented by the retaining ring 10, and knocking is suppressed by displacing the upper piston 2 downward while deflecting the belleville spring 9 when in-cylinder pressure increases. A protrusion 6 is protrusively formed on the undersurface of the upper piston 2 and slidably fitted into a fitting part 5 on the lower piston 1 to form a damper chamber 7. When the upper piston 2 is displaced upward by a decrease in in-cylinder pressure, the upper piston 2 is gradually displaced by making air flow into the damper chamber 7 via a clearance between the protrusion 6 and the fitting part 5.

Description

  The present invention relates to an engine piston, and more particularly to a variable compression ratio piston capable of varying a compression ratio in accordance with an in-cylinder pressure.

As is well known, an increase in the compression ratio of the engine leads to an improvement in thermal efficiency, but also causes knocking. Knocking causes serious troubles such as engine breakage. For this reason, in the engine design stage, in general, the compression ratio is set slightly lower than the knocking limit in order to reliably suppress knocking. This fact means that there is room for further increasing the compression ratio of the engine to contribute to the improvement of thermal efficiency, and various techniques that focus on this point have been proposed (for example, see Patent Document 1).
The technique described in Patent Document 1 relates to a variable compression ratio piston, and is configured by dividing a piston into a lower piston and an upper piston. The lower piston is connected to the crankshaft side via a connecting rod, and the upper piston is fitted on the top (combustion chamber side) of the lower piston so that the piston can reciprocate in the axial direction of the piston. A disc spring is interposed between the lower piston and the upper piston to urge the upper piston in the reduction direction of the combustion chamber volume (increase direction of the compression ratio), and a retaining ring provided on the inner periphery of the upper piston. Is brought into contact with the top of the lower piston from below to prevent the upper piston from being separated from the lower piston by the biasing force of the disc spring. Hereinafter, the position of the upper piston at this time is referred to as a high compression position.

  In the combustion stroke of the engine, the in-cylinder pressure suddenly increases and then decreases with the progress of combustion in the cylinder, and the disc spring always receives the in-cylinder pressure via the upper piston. The disk spring bends when it reaches just before knocking occurs in the cylinder due to the increase in the cylinder pressure, and the upper piston is displaced in the direction of expansion of the combustion chamber volume (in the direction of decreasing the compression ratio), so that knocking is suppressed. . Hereinafter, the position of the upper piston at this time is referred to as a low compression position. Thus, knocking is always suppressed by the displacement of the upper piston in accordance with the in-cylinder pressure, so that the compression ratio at the high compression position can be set near the knocking limit in order to improve thermal efficiency.

US Pat. No. 5,755,192

However, in the technique disclosed in Patent Document 1, a problem occurs when the upper piston returns from the low compression position to the high compression position as the in-cylinder pressure decreases.
In other words, when the in-cylinder pressure decreases, the upper piston receives a biasing force of the disc spring and is suddenly displaced from the low compression position toward the high compression position, and in the high compression position, the retaining ring collides with the top of the lower piston. Regulate the position of the upper piston. For this reason, a hitting sound is generated by the collision of the retaining ring, which causes an increase in noise during engine operation, and also has a problem of adversely affecting the durability reliability of the piston.
The present invention has been made to solve such problems, and the object of the present invention is to reduce engine noise caused by a collision of a retaining ring when the upper piston returns from the low compression position to the high compression position. An object of the present invention is to provide a piston capable of preventing an increase and a decrease in piston durability reliability.

  In order to achieve the above object, the invention of claim 1 includes a piston base portion having a pin boss, a piston head, a piston moving portion reciprocally movable with respect to the piston base, and either the piston base portion or the piston moving portion. Are arranged on the other side of the piston base and the piston moving part, and with the reciprocating movement of the piston moving part with respect to the piston base. A fitting portion that is slidably fitted to the convex portion, a damper chamber that is formed between the convex portion and the fitting portion, and whose volume changes with the reciprocation of the piston moving portion, and the damper chamber And a passage communicating with the space outside the damper chamber.

According to a second aspect of the present invention, there is provided a separation preventing unit that prevents separation of the piston base and the piston moving unit, and a blocking unit that blocks at least a part of the passage when the piston moving unit moves in a direction away from the piston base. It is what has.
According to the invention of claim 3, the blocking means is a check valve that causes the air in the damper chamber to flow out to the outside when the piston moving portion moves in a direction approaching the piston base.
According to a fourth aspect of the present invention, the convex portion is disposed on the piston base portion, and the fitting portion is formed by a side wall portion protruding from the piston moving portion along the side surface of the convex portion parallel to the reciprocating direction of the piston moving portion. Is.

As described above, according to the piston of the first aspect of the present invention, the piston moving portion can be reciprocated with respect to the piston base, and the convex portion is disposed on either the piston base or the piston moving portion. A fitting portion is arranged on the other side to be slidably fitted to the convex portion, and the volume of the damper chamber formed between the convex portion and the fitting portion is changed with the reciprocating motion of the piston moving portion. On the other hand, the damper chamber communicated with the space outside the damper chamber via the passage. Therefore, since the damper chamber communicates with the outside, it is possible to reduce the impact when the piston moving portion and the piston base collide with each other as compared with the case where the damper chamber is sealed.
According to the piston of the invention of claim 2, the separation of the piston base and the piston moving part is prevented by the separation preventing part, and at least a part of the passage is shut off when the piston moving part moves away from the piston base. Blocked by means. Therefore, since it becomes difficult for air to flow into the damper chamber when the piston moving part moves away from the piston base part, the piston moving part becomes difficult to move away from the piston base part, and the load on the separation preventing part can be reduced.

According to the piston of the third aspect of the present invention, the blocking means is a check valve that causes the air to flow out into the damper chamber when the piston moving portion moves away from the piston base. Therefore, by installing the check valve in the passage, the piston moving part can be quickly displaced from the high compression ratio to the low compression ratio, and at the same time, the load on the separation preventing part can be more reliably reduced.
According to the piston of the invention of claim 4, the convex portion is disposed on the piston base portion, and the fitting portion protrudes from the piston moving portion along the side surface of the convex portion parallel to the reciprocating direction of the piston moving portion. Formed by. Therefore, the piston moving part can be reduced in weight compared to the case where the convex part is arranged on the piston moving part, so that the natural frequency of the piston moving part is increased, and the resonance rotation range is shifted to the high rotation side, resulting in damage caused by resonance. It becomes easy to avoid.

It is sectional drawing which shows the piston of 1st Embodiment. It is sectional drawing which shows the piston of 2nd Embodiment. It is sectional drawing which shows the piston of 3rd Embodiment. It is a perspective view which shows the relationship between a convex part and a fitting part. It is explanatory drawing which shows a process when an upper piston carries out position displacement according to increase / decrease in a cylinder pressure. It is sectional drawing which shows the piston in the high compression position of 4th Embodiment. It is sectional drawing which similarly shows the piston in a low compression position. It is sectional drawing which shows the piston in the high compression position of 5th Embodiment. It is sectional drawing which similarly shows the piston in a low compression position.

[First Embodiment]
Hereinafter, a first embodiment of a piston embodying the present invention will be described.
FIG. 1 is a cross-sectional view showing the piston of the first embodiment, and hatching showing cross-sectional portions is omitted so as to make it easy to grasp the mutual relationship between the members. Since the piston is incorporated in the cylinder of the engine in the illustrated posture, in the following description, the vertical direction is expressed following the piston posture in the drawing.
The piston is divided into a lower piston 1 (piston base) and an upper piston 2 (piston moving part), and these pistons 1 and 2 are slidably inserted in a cylinder (not shown) in the vertical direction. As a whole, the lower piston 1 has a bottomed cylindrical shape that opens downward, and a pair of pin bosses 1a formed opposite to each other in the lower piston 1 are respectively provided with pin holes 1b. Although not shown, the lower piston 1 is connected to the small end portion of the connecting rod through the piston pin inserted into the pin hole 1b, and the large end portion of the connecting rod is connected to the crankshaft. Accordingly, when the engine is in operation, the vertical movement of the lower piston 1 in the cylinder is transmitted as a rotational motion to the crankshaft via the connecting rod, and is output from the crankshaft as engine driving force.

A large-diameter portion 4 is integrally formed on the top of the lower piston 1 via a small-diameter portion 3, and the small-diameter portion 3 and the large-diameter portion 4 have a circular shape centered on the piston axis L in plan view. . The outer periphery of the lower surface of the large-diameter portion 4 faces downward, and an annular region facing downward is used as a contact surface 4a on which a retaining ring 10 described later contacts. A fitting portion 5 is recessed on the large-diameter portion 4, and the fitting portion 5 has a circular shape that coincides with the piston axis L in a plan view and has the same diameter in the vertical direction.
The upper piston 2 has a bottomed cylindrical shape that opens downward as a whole, and is disposed on the upper side (combustion chamber side) of the lower piston 1 so that the large-diameter portion 4 is fitted thereon, and the upper surface thereof is disposed on the piston head 2a. It is said. A convex portion 6 is formed on the lower surface of the upper piston 2 so as to protrude downward. The convex portion 6 has a circular shape corresponding to the fitting portion 5 of the lower piston 1 and has the same diameter in the vertical direction. There is no. A lower portion of the convex portion 6 is fitted in the fitting portion 5 so as to be slidable in the vertical direction, and a damper chamber 7 is formed between the convex portion 6 and the fitting portion 5. The upper piston 2 is displaced in the vertical direction with respect to the lower piston 1 while sliding the convex portion 6 within the fitting portion 5, and the volume of the damper chamber 7 changes accordingly.

An annular space 8 is formed between the lower piston 1 and the upper piston 2 so as to surround the periphery of the convex portion 6, and a disc spring 9 is accommodated in the annular space 8. The inner periphery of the disc spring 9 contacts the lower surface of the upper piston 2, the outer periphery of the disc spring 9 contacts the upper surface of the large-diameter portion 4 of the lower piston 1, and the biasing force of the disc spring 9 burns against the upper piston 2. It acts in the direction of reducing the chamber volume (in the direction of increasing the compression ratio).
The lower inner peripheral surface of the upper piston 2 is positioned on the outer peripheral side so as to surround the large diameter portion 4 of the lower piston 1, and a retaining ring 10 (separation preventing portion) is fitted and fixed to the lower inner peripheral surface. The upper surface of the retaining ring 10 abuts against the abutment surface 4 a of the lower piston 1, thereby preventing the upper piston 2 from being separated from the lower piston 1 by the biasing force of the disc spring 9. Hereinafter, the position of the upper piston 2 when the retaining ring 10 contacts the contact surface 4a in this way is referred to as a high compression position.

With the above-described configuration, the in-cylinder pressure in the combustion stroke of the engine always acts on the disc spring 9 via the upper piston 2. The biasing force (so-called set load) of the disc spring 9 at the high compression position is set corresponding to the in-cylinder pressure immediately before knocking occurs in the cylinder, and the in-cylinder pressure exceeds the biasing force of the disc spring 9. At this point, the upper piston 2 starts to move downward from the high compression position. Since the urging force of the disc spring 9 increases with the amount of deflection, the downward displacement of the upper piston 2 is stopped at a certain point, and the position of the upper piston 2 at this time is referred to as a low compression position. However, the setting of the biasing force of the disc spring 9 is not limited to the above, and can be arbitrarily changed.
When the in-cylinder pressure decreases as the expansion stroke proceeds, the upper piston 2 is displaced from the low compression position toward the high compression position by the biasing force of the disc spring 9, and the retaining ring 10 is brought into contact with the lower piston 1. 4a is returned to the high compression position. Along with the upward displacement of the upper piston 2, the convex portion 6 changes the volume of the damper chamber 7 in the expansion direction while sliding upward in the fitting portion 5 of the lower piston 1. The volume change of the damper chamber 7 is performed while allowing the air in the annular space 8 to flow into the damper chamber 7 through the clearance (passage) between the convex portion 6 and the fitting portion 5. It is set so as to appropriately limit the inflow of air into the damper chamber 7. For this reason, the displacement of the upper piston 2 when receiving the urging force of the disc spring 9 and returning to the high compression position becomes gentler than when the damper chamber 7 is not provided. In this embodiment, the clearance between the convex portion 6 and the fitting portion 5 is set to about 100 to 200 μm. However, the present invention is not limited to this, and the in-cylinder pressure of the engine and the biasing force of the disc spring 9 are not limited thereto. It can be arbitrarily changed according to the above.

The piston of the present embodiment is configured as described above, and has the following effects during engine operation.
When the combustion of the engine is normal without causing knocking, the in-cylinder pressure in the combustion stroke is always lower than the urging force of the disc spring 9. For this reason, the upper piston 2 continues to be held at the high compression position by the urging force of the disc spring 9, and in this state, the piston receives the in-cylinder pressure and transmits to the crankshaft side while sliding downward in the cylinder.
In the combustion stroke, immediately before the occurrence of knocking due to an increase in the in-cylinder pressure, the upper piston 2 moves from the high compression position to the low compression position while bending the disc spring 9, that is, in the direction of expansion of the combustion chamber volume (compression ratio of the compression ratio). Displacement (downward direction). For this reason, an increase in in-cylinder pressure is prevented and knocking is suppressed. Accordingly, the retaining ring 10 of the upper piston 2 is separated downward from the contact surface 4a of the lower piston 1.

When the in-cylinder pressure thereafter decreases, the upper piston 2 is displaced upward and returns to the high compression position. The convex portion 6 of the upper piston 2 expands the volume of the damper chamber 7 while sliding upward in the fitting portion 5 of the lower piston 1, and accordingly, the air in the annular space 8 is brought into contact with the convex portion 6. 5 flows into the damper chamber 7 through the clearance with respect to 5. The rapid displacement of the upper piston 2 is suppressed by the restriction of the air flowing into the damper chamber 7 through the clearance, and the retaining ring 10 is brought into contact with the abutting surface 4a of the lower piston 1 when the upper piston 2 reaches the high compression position. Gently contact
As a result, it is possible to reduce the noise during engine operation by preventing the occurrence of hitting sound due to the collision of the retaining ring 10 as in the technique of Patent Document 1, and also due to the collision of the retaining ring 10 with the contact surface 4a. It is possible to avoid a decrease in the durability reliability of the piston.
By the way, in this embodiment, while letting air flow into the damper chamber 7 through the clearance between the convex portion 6 and the fitting portion 5, the inflow air is limited by setting this clearance appropriately. The invention is not limited to this. For example, air may be introduced into the damper chamber 7 via the orifice 11 and the inflowing air may be limited by appropriately setting the diameter of the orifice. This example will be described below as a second embodiment.

[Second Embodiment]
FIG. 2 is a cross-sectional view showing the piston of the second embodiment. The basic configuration of the piston of the second embodiment is the same as that of the first embodiment, and the difference is in the configuration related to the orifice 11. Therefore, common parts are denoted by the same member numbers, description thereof is omitted, and differences are mainly described.
In the lower piston 1 of the present embodiment, an orifice 11 (passage) is provided in a vertical direction along the piston axis L, and the inside of the fitting portion 5 and the lower side of the piston (on the pin boss 1a side) are connected through the orifice 11. ). The orifice 11 is set to have an opening area corresponding to the clearance between the convex portion 6 and the fitting portion 5 described in the first embodiment. In this embodiment, the clearance between the convex portion 6 and the fitting portion 5 is as follows. The air pressure is set to be much narrower than that of the first embodiment so that almost no air flows into and out of the damper chamber 7.

Since the operation of the piston of the present embodiment configured as described above is the same as that of the first embodiment, only the outline will be described.
As the in-cylinder pressure rises, the upper piston 2 is displaced from the high compression position to the low compression position to suppress knocking, and thereafter, as the in-cylinder pressure decreases, the upper piston 2 is displaced upward to the high compression position. Return. At this time, the air below the lower piston 1 flows into the damper chamber 7 through the orifice 11, and the inflow air is restricted when flowing through the orifice 11, thereby suppressing rapid displacement of the upper piston 2. The retaining ring 10 of the upper piston 2 gently contacts the contact surface 4a of the lower piston 1. Therefore, although not redundantly described, the effects of reducing engine noise and improving durability reliability can be obtained as in the first embodiment.
In addition, since the adjustment of the opening area of the orifice 11 is easier and more reliable than the clearance adjustment of the first embodiment, there is also an advantage that a stable function can be obtained at a lower manufacturing cost than the first embodiment.

  In addition, in the second embodiment, air flows into the damper chamber 7 when the upper piston 2 returns to the high compression position via the clearance between the convex portion 6 and the fitting portion 5 in the first embodiment. Although it was performed through the orifice 11, these may be combined so that air flows into the damper chamber 7 through both the clearance and the orifice 11.

[Third Embodiment]
Next, a third embodiment embodying the present invention will be described.
FIG. 3 is a cross-sectional view showing the piston of the third embodiment, and FIG. 4 is a perspective view showing the relationship between the convex portion 6 and the fitting portion 5. The basic configuration of the piston of the third embodiment is the same as that of the second embodiment. The differences are the check valve 21 (blocking means) provided in place of the orifice 11 of the second embodiment, and the convex portion 6. And the configuration of the fitting portion 5. Therefore, common parts are denoted by the same member numbers, description thereof is omitted, and differences are mainly described.
The lower piston 1 of the present embodiment is provided with a check valve 21 so as to be in series with the passage 22 instead of the orifice 11 of the second embodiment, and the fitting portion is interposed through the passage 22 and the check valve 21. 5 and the lower side of the piston communicate with each other. The check valve 21 is set so as to allow air to flow from the inside of the damper chamber 7 to the lower side of the piston (forward direction) and to prevent air from flowing from the lower side of the piston to the damper chamber 7 (reverse direction). Has been.

On the other hand, the convex portion 6 of the upper piston 2 is integrally formed by a lower sliding contact portion 23 and an upper reduced diameter portion 24, and the sliding contact portion 23 is set to have the same diameter as the convex portion 6 of the first embodiment. The reduced diameter portion 24 is formed to have a smaller diameter through the step. Further, the fitting portion 5 of the lower piston 1 is integrally formed by an upper sliding contact portion 25 and a lower enlarged diameter portion 26, and the sliding contact portion 25 has the same diameter as the fitting portion 5 of the first embodiment. The enlarged diameter portion 26 is formed to have a larger diameter through the step. The clearance between the sliding contact portion 23 on the upper piston 2 side and the sliding contact portion 25 on the lower piston 1 side is set so narrow that air hardly flows into or out of the damper chamber 7 as in the second embodiment. ing.
A pair of guide grooves 27 are formed on the outer periphery of the sliding contact portion 23 on the side of the upper piston 2 at positions opposed to each other by 180 degrees, and each guide groove 27 has a triangular cross section and extends over the entire vertical direction of the sliding contact portion 23. It is extended. In order to correspond to these guide grooves 27, a pair of guide protrusions 28 having a triangular cross section are provided on the inner periphery of the sliding contact portion 25 and the enlarged diameter portion 26 on the lower piston 1 side so as to extend over the entire vertical direction. Each guide protrusion 28 is slidably fitted in the corresponding guide groove 27. While the guide groove 27 is slid on each guide protrusion 28, the convex portion 6 is guided in the vertical direction in the fitting portion 5, and accordingly, the upper piston 2 with respect to the lower piston 1 is in a high compression position and a low compression position. The position is displaced between.

In the vicinity of the high compression position, the sliding contact portion 23 of the upper piston 2 corresponds to the sliding contact portion 25 of the lower piston 1, so that the flow of air into the damper chamber 7 is restricted. On the other hand, on the lower compression position side, the sliding contact portion 23 of the upper piston 2 corresponds to the enlarged diameter portion 26 on the lower piston 1 side, so that the inside of the damper chamber 7 communicates with the inside of the annular space 8 to the inside. The air inflow and outflow is no longer restricted.
The piston of the present embodiment is configured as described above, and has the following effects during engine operation.

FIG. 5 is an explanatory diagram showing a process when the position of the upper piston 2 is displaced in accordance with the increase or decrease of the in-cylinder pressure.
When the combustion of the engine is normal, the in-cylinder pressure in the combustion stroke is lower than the biasing force of the disc spring 9, so that the upper piston 2 continues to be held at the high compression position as shown in FIG. In the combustion stroke, when the in-cylinder pressure increases immediately before the occurrence of knocking, the upper piston 2 starts to be displaced from the high compression position to the low compression position while bending the disc spring 9 as shown in FIG. At this time, the sliding contact portions 23 and 25 on the upper piston 2 side and the lower piston 1 side correspond to each other to restrict the outflow of air from the damper chamber 7, but the check valve 21 prevents the air in the forward direction. Since the circulation is permitted, the air in the damper chamber 7 flows out to the lower side of the piston through the check valve 21. For this reason, as shown in FIG. 5 (c), the upper piston 2 is quickly displaced toward the low compression position, preventing an increase in in-cylinder pressure and suppressing knocking.

Thereafter, when the in-cylinder pressure decreases, the upper piston 2 is displaced upward while receiving the urging force of the disc spring 9 and returns to the high compression position as shown in FIG. At this time, the check valve 21 prevents the flow of air in the reverse direction. Therefore, the check valve 21 prevents the inflow of air from the lower side of the piston into the damper chamber 7. However, when the displacement starts from the low compression position, the sliding contact portion 23 of the upper piston 2 corresponds to the enlarged diameter portion 26 of the lower piston 1, so that the air in the damper chamber 7 flows into the sliding contact portion 23 and the enlarged diameter portion 27. Flows out into the annular space 8 through a gap between the upper piston 2 and the upper piston 2 is quickly displaced toward the high compression position.
When the upper piston 2 is displaced to the vicinity of the high compression position, the sliding contact portion 23 corresponds to the sliding contact portion 25 of the lower piston 1 and restricts the outflow of air from the damper chamber 7. Since the displacement of the upper piston 2 at this time is performed while increasing the volume in the damper chamber 7, the sudden displacement of the upper piston 2 is suppressed, and the retaining ring 10 is gently applied to the contact surface 4a in the high compression position. The effect of reducing engine noise and improving durability reliability can be obtained.

In this embodiment, when the upper piston 2 is displaced from the high compression position to the low compression position, the check valve 21 is operated in the forward direction so that the air in the damper chamber 7 flows out to the lower side of the piston. Accordingly, it is possible to prevent the problem that the displacement of the upper piston 2 to the low compression position becomes slow due to the action of the clearance and the orifice 11 as in the first and second embodiments, and the upper piston 2 is quickly moved to the low compression position side. The effect that knocking can be more reliably suppressed by displacing is obtained.
Moreover, the sliding contact portion 23 of the upper piston 2 restricts the flow of air into and out of the damper chamber 7 corresponding to the sliding contact portion 25 of the lower piston 1 only in the vicinity of the high compression position, and the compression position is lower than that. On the side, the inflow / outflow of air is not restricted by corresponding to the enlarged diameter portion 26 of the lower piston 1. For this reason, when the upper piston 2 is displaced from the low compression position to the high compression position, the upper piston 2 is initially displaced quickly, and thereafter, abrupt displacement is suppressed near the high compression position. As a result, after preventing the retaining ring 10 from colliding with the contact surface 4a, the upper piston 2 can be quickly returned to the high compression position when there is no possibility of knocking, and the operation frequency at the high compression position is increased. As a result, the thermal efficiency of the engine can be further improved.

[Fourth Embodiment]
Next, a fourth embodiment embodying the present invention will be described.
FIG. 6 is a cross-sectional view showing the piston in the high compression position according to the fourth embodiment, and FIG. 7 is a cross-sectional view showing the piston in the low compression position. The difference from the third embodiment is that the check valve 21 is omitted and the shape of the convex portion 6 of the upper piston 2 and the fitting portion 5 of the lower piston 1 is changed. Therefore, common parts are denoted by the same member numbers, description thereof is omitted, and differences are mainly described.
The convex part 6 of the upper piston 2 and the fitting part 5 of the lower piston 1 do not have a stepped shape as in the third embodiment, but have the same shape as that of the first embodiment, for example. A valve hole 31 having a circular cross section is provided vertically in the center of the bottom surface of the fitting portion 5 of the lower piston 1, and the damper chamber 7 communicates with the lower side of the piston through the valve hole 31. A spool portion 32 having the same diameter as the valve hole 31 protrudes from the lower surface of the convex portion 6 of the upper piston 2, and the spool portion 32 is fitted in the valve hole 31 so as to be slidable in the vertical direction.
The clearance between the convex portion 6 of the upper piston 2 and the fitting portion 5 of the lower piston 1 and the clearance between the spool portion 32 and the valve hole 31 are in the damper chamber 7 as in the third embodiment. It is set so narrow that air hardly flows in and out.

A communication passage 33 bent at a right angle is formed in the lower piston 1, one end of the communication passage 33 is opened on one inner peripheral side of the valve hole 31, and the other end of the communication passage 33 is opened in the damper chamber 7. Further, a communication passage 34 bent at a right angle is formed in the spool portion 32 of the upper piston 2, one end of the communication passage 34 opens to one side of the outer periphery of the spool portion 32, and the other end of the communication passage 34 is connected to the spool portion 32. An opening is made so as to face the lower side of the piston from the lower surface. Although not shown in the drawings, in this embodiment, the upper piston 2 is restricted from rotating about the axis L with respect to the lower piston 1, whereby one end of the communication passage 33 that opens to the inner periphery of the valve hole 31 and the spool portion. The one end of the communication path 34 opened to the outer periphery of 32 always corresponds in the piston circumferential direction.
Accordingly, as the upper piston 2 is displaced, the convex portion 6 slides in the vertical direction within the fitting portion 5 of the lower piston 1, and the spool portion 32 slides in the valve hole 31 in the vertical direction.

In the vicinity of the high compression position shown in FIG. 6, the communication hole 34 of the upper piston 2 is displaced in the vertical direction with respect to the communication hole 33 of the lower piston 1, and on the other hand, on the lower compression position side, As shown in FIG. 7, the communication hole 34 communicates with the communication hole 33.
For this reason, when the upper piston 2 is displaced from the low compression position to the high compression position, the communication holes 33 and 34 communicate with each other at the beginning, so that the air in the damper chamber 7 flows out to the lower side of the piston. The piston 2 is quickly displaced. Since the communication holes 33 and 34 do not communicate with each other in the vicinity of the subsequent high compression position, the upper piston 2 is restrained from abrupt displacement by expanding the volume of the damper chamber 7 where the outflow of air is restricted. Therefore, as in the third embodiment, it is possible to quickly return the upper piston 2 to the high compression position when there is no risk of knocking after preventing the retaining ring 10 from colliding with the contact surface 4a.
In addition, as shown in FIG. 6, both the communication holes 33 and 34 do not naturally correspond to each other at the high compression position of the upper piston 2, and the damper chamber 7 and the piston lower side are not in communication. For this reason, the damper chamber 7 can be sealed without providing the check valve 21 as in the third embodiment, and the effect of eliminating the number of parts can be obtained by omitting the check valve 7.
By the way, in 1st Embodiment, although the convex part 6 was formed in the upper piston 2 side and the fitting part 5 which this convex part 6 fits was formed in the lower piston 1 side, you may reverse both. Therefore, another example of the first embodiment will be described below as a fifth embodiment.

[Fifth Embodiment]
FIG. 8 is a cross-sectional view showing the piston in the high compression position according to the fifth embodiment, and FIG. 9 is a cross-sectional view showing the piston in the low compression position. As described above, the difference from the first embodiment lies in the reverse rotation of the convex portion 6 and the fitting portion 5. Therefore, the same components are assigned the same member numbers and the description is omitted, and the difference is emphasized. State it.
On the large-diameter portion 4 of the lower piston 1, a convex portion 6 having a circular shape centered on the piston axis L is formed so as to protrude, and an annular side wall portion is formed on the lower surface of the upper piston 2 so as to correspond to the convex portion 6. 41 (side wall part) protrudes downward, and in this embodiment, the inside of the annular side wall part 41 is used as the fitting part 5. The convex portion 6 of the lower piston 1 is fitted in the fitting portion 5 of the upper piston 2 so as to be slidable in the vertical direction, and a damper chamber 7 is formed between the convex portion 6 and the fitting portion 5. Accordingly, the upper piston 2 is displaced in the vertical direction with respect to the lower piston 1 while sliding the convex portion 6 in the fitting portion 5, and the volume of the damper chamber 7 changes accordingly. In addition, the clearance between the fitting part 5 and the convex part 6 is set so that the inflow and outflow of air into the damper chamber 7 may be appropriately limited as in the first embodiment.

The lower piston 1 is provided with a check valve 42 (blocking means) so as to be in series with the passage 43, and the inside of the damper chamber 7 communicates with the lower side of the piston through the passage 43 and the check valve 42. ing. As in the third embodiment, the check valve 42 allows air to flow from the damper chamber 7 to the lower side of the piston (forward direction), and prevents air from flowing from the lower side of the piston to the damper chamber 7 ( (Reverse direction).
Therefore, when the in-cylinder pressure rises and immediately before knocking, the upper piston 2 starts to be displaced from the high compression position shown in FIG. 8 to the low compression position shown in FIG. 9, and the volume in the damper chamber 7 is reduced accordingly. To do. At this time, the check valve 42 allows the air to flow in the forward direction, and the air in the damper chamber 7 flows out to the lower side of the piston through the check valve. The knocking can be reliably suppressed by being displaced to the position.

When the in-cylinder pressure subsequently decreases, the upper piston 2 is displaced upward and returns to the high compression position. At this time, the check valve 42 prevents air from flowing into the damper chamber 7 from the lower side of the piston. For this reason, the inflow of air into the damper chamber 7 is restricted according to the clearance between the convex portion 6 and the fitting portion 5, so that rapid displacement of the upper piston 2 is suppressed and the retaining ring is held at the high compression position. 10 gently contacts the contact surface 4a. Therefore, although not redundantly explained, the effects of reducing engine noise and improving durability reliability can be obtained.
By the way, in the present embodiment in which the convex portion 6 and the fitting portion 5 are reversed with respect to the first embodiment shown in FIG. 1, the following advantages are also obtained.

First, the upper piston 2 supported on the lower piston 1 via the disc spring 9 resonates in a specific rotation range during engine operation, and the resonance rotation range is a natural vibration associated with the weight reduction of the upper piston 2. The higher the number, the higher the rotation speed, and it becomes easier to avoid breakage due to resonance. Since the solid convex portion 6 causes an increase in weight as compared with the hollow fitting portion 5, the solid convex portion 6 is fitted compared to the first embodiment in which the convex portion 6 is formed on the upper piston 2 side. In the present embodiment in which the portion 5 is formed on the upper piston 2 side, the upper piston 2 can be reduced in weight, and the advantage that the resonance rotation region is inevitably shifted to the high rotation side and damage can be prevented is obtained.
Further, since the check valve 42 employs a basic configuration in which the valve body is urged toward the valve seat side by a valve spring, a certain amount of space is required for arranging the check valve 42 including these members. I need. Since the lower piston 1 of the present embodiment has a sufficient thickness in the vertical direction due to the formation of the convex portion 6, there is also an advantage that the check valve 42 can be easily arranged.

Further, in the annular space 8 that accommodates the disc spring 9, there is not only air but also lubricating oil scattered during engine operation. When such oil enters the damper chamber 7 in a large amount from the annular space 8, The function of the damper chamber 7 that controls the inflow and outflow of air may be impaired. In the first embodiment in which the fitting portion 5 is formed on the large-diameter portion 4 of the lower piston 1, the oil in the annular space 8 easily enters the damper chamber 7, but in this embodiment, the fitting portion 5 is surrounded. The annular side wall portion 41 prevents oil from entering the damper chamber 7. Therefore, there is also an advantage that the intended function and effect can be obtained with certainty by causing the damper chamber 7 to perform its normal function.
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the above embodiment, the upper piston 2 is urged to the high compression position by the disc spring 9 and the upper piston 2 is separated from the lower piston 1 by the urging force by the retaining ring 10, but the present invention is limited to these configurations. There is nothing. For example, another biasing means such as a coil spring may be provided instead of the disc spring 9, or another locking means may be provided instead of the retaining ring 10.
Moreover, in the said embodiment, although the convex part 6 and the fitting part 5 were formed circularly by planar view, it is not restricted to this, For example, the convex part 6 and the fitting part 5 are made into square shape by planar view, An O-ring may be interposed between the convex portion 6 and the fitting portion 5.

DESCRIPTION OF SYMBOLS 1 Lower piston 1a Pin boss 2 Upper piston 2a Piston head 5 Fitting part 6 Convex part 7 Damper chamber 10 Retaining ring (separation prevention part)
11 Orifice (passage)
21, 42 Check valve (blocking means)
41 Annular side wall (side wall)

Claims (4)

A piston base with pin bosses;
A piston moving part comprising a piston head and capable of reciprocating relative to the piston base;
A convex portion that is disposed on one of the piston base and the piston moving portion and protrudes in a direction parallel to the reciprocating direction of the piston moving portion with respect to the piston base;
A fitting portion that is disposed on the other of the piston base and the piston moving portion, and is slidably fitted to the convex portion as the piston moving portion reciprocates with respect to the piston base.
A damper chamber formed between the convex portion and the fitting portion, the volume of which changes with the reciprocation of the piston moving portion;
A piston comprising: a passage communicating the damper chamber and a space outside the damper chamber. A separation preventing portion for preventing separation between the piston base portion and the piston moving portion;
2. The piston according to claim 1, further comprising a blocking unit configured to block at least a part of the passage when the piston moving unit moves in a direction away from the piston base. 3. The piston according to claim 2, wherein the blocking means is a check valve that causes the air in the damper chamber to flow out to the outside when the piston moving portion moves in a direction approaching the piston base. The convex portion is disposed on the piston base,
The said fitting part is formed by the side wall part which protrudes from the said piston moving part along the side surface of the said convex part parallel to the reciprocating direction of the said piston moving part. The piston according to claim 1.

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