JPH0311143A - Variable compression ratio piston - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention relates to a variable compression ratio piston for an internal combustion engine,
Specifically, the present invention relates to a piston whose compression hide can be changed according to load conditions of an internal combustion engine.

(Prior art) When an internal combustion engine is under partial load, the amount of intake air is restricted by the throttle valve, leading to a decrease in thermal efficiency.If the compression ratio is increased in an attempt to increase this thermal efficiency, knocking may occur during high loads. There is a risk of it happening. Therefore, a variable compression ratio piston is designed to change the compression ratio according to load conditions in order to obtain high thermal efficiency over the entire load range.

As a variable compression ratio piston, there is conventionally a variable compression ratio piston such as that disclosed in West German Patent Publication No. 3346969, which will be described below with reference to FIG.

In the following description, the top side of the piston will be referred to as upper and the bottom side will be referred to as lower, regardless of the mounting posture of the piston.

The piston 101 is a connecting rod (not shown)
An inch piston 105 is connected to the small end of the inch piston 105 via a piston pin 103, and an outer piston 115 is fitted onto the upper part of the inch piston 105 so as to be able to slide vertically. A stop ring 121 is screwed onto the inner surface. As shown on the right side of the figure (a sectional view shifted by 90 degrees from the left side in a high compression ratio state), the stop ring 121 is brought into contact with the lower surface of the periphery of the upper wall 107 of the inch piston 105, so that the outer piston 115 The upper limit of movement is regulated, and in this state, a disc-shaped upper oil chamber 1 is partitioned by a seal 108 between the upper wall 107 and the upper wall 117 of the outer piston 115.
23 is formed. Further, as shown on the left side of the figure (cross-sectional view in a low compression ratio state), a protrusion 117a formed on the lower surface of the upper wall 117 is connected to the upper wall 10 of the inner piston 105.
7, the lower limit of movement of the outer piston 115 is restricted, and in this state, an annular lower oil chamber 125 partitioned by the seal 104 is formed above the stop ring 121.

On the other hand, the upper wall 107 of the inner piston 105 includes an oil supply valve 129 with a check function for supplying pressure hydraulic oil to the upper oil chamber 123, and a pressure-sensitive drain valve 129 for draining oil from the oil chamber 123. An oil valve 131 is attached. Further, this upper wall 107 is equipped with an orifice 135 that communicates the upper oil chamber 123 and the lower oil chamber 125, and a one-way valve 137 that allows flow only to the lower oil chamber 125 side. This constitutes a control means.

To explain the operation, when the hydraulic oil is now being forced into the piston pin 103 through the connecting rod, it is transferred to the piston pin fitting part 109 of the inner piston 105.
The oil is supplied into the upper oil chamber 123 from the oil supply passage 111 formed in the upper oil chamber 123 via the oil supply valve 129. At this time, pressure sensitive oil drain valve】3
1 is closed, and the pressure receiving area of the lower oil chamber 125 is smaller than that of the upper oil chamber 123, so the outer piston 115 is pushed up to the upper limit of movement (right side in the figure), and this position is the oil supply valve. It is held by the check action of 129. In this state, the piston 101 moves to the compression stroke, and when the air-fuel mixture in the combustion chamber is being compressed, for example under conditions of a high compression ratio, and the end of this stroke approaches, the air-fuel mixture is ignited and its combustion pressure rises rapidly. do. This pressure is the outer piston 11
5 to the hydraulic oil in the upper oil chamber 123. At this time, if the combustion pressure or the corresponding hydraulic pressure is about to rise above a predetermined value, the pressure-sensitive oil drain valve 131
opens to appropriately release the upper oil chamber 123 to the outside of the piston 101. As a result, the outer piston 115
It is rapidly propelled downward while discharging hydraulic oil from 31,
At the same time, hydraulic oil is rapidly sent into the lower oil chamber 125 from both the orifice 135 and the one-way valve 137 via the communication path 113. In other words, when the combustion pressure exceeds a predetermined value,
In response to this, the outer piston 115 moves downward, so
The compression ratio is reduced and the occurrence of knocking is avoided.

Then, when the combustion pressure (working oil pressure) decreases to a predetermined value during the downward movement of the outer piston 115 or at the limit of its downward movement, the oil drain valve 131 closes, and as this expansion stroke progresses, the combustion gas pressure further increases by f'P. When the pressure is lowered, hydraulic oil supply from the oil supply valve 129 is restarted. As a result, the outer piston] -
15 is propelled upward, and at the same time, hydraulic oil is pushed out from the lower oil chamber 125 to the upper oil chamber 123 only through the orifice 135. That is, the upward movement at this time becomes slow due to the throttling action of the orifice 135. This is to avoid the need for the outer piston 115 to make large vertical movements in each cycle by allowing the piston 101 to maintain its low compression ratio configuration as much as possible during high-load operation.

(Problem to be Solved by the Invention) However, in such a conventional example, since the upper oil chamber 123 is configured in a disk shape, the volume is large, and therefore the lower oil chamber 125 is configured in an annular shape. It has a structure with a large volume difference, and an inner piston 105 is attached to the small end of the connecting rod via a piston pin 103, and an outer piston 115 is fitted onto the upper part of the inner piston 105 so as to be able to slide vertically. Because the structure did not restrict the relative rotation in the circumferential direction in a plane perpendicular to the sliding direction, it took a long time to switch to the low compression ratio state by discharging the pressure oil in the upper oil chamber 123. In addition, it takes time to switch to the high compression ratio state by supplying the pressure oil in the lower oil chamber 125, the connecting rod, and the pressure oil supplied through the piston pin 103 to the upper oil chamber 123. That is, there is a problem that the response is poor, and since there is no rotation stopper for the outer piston, there is a problem that the degree of freedom in design is low in terms of compatibility with the shape of the combustion chamber, etc.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a variable compression ratio piston that does not require time to change the compression ratio state, that is, has good responsiveness and has a high degree of freedom in design.

[Structure of the invention] (Means for solving the problem) An inner piston connected to a connecting rod,
The inner piston has an outer piston fitted to the inner piston so as to be able to move relative up and down within a predetermined range, and an upper oil chamber and a lower oil chamber are provided between the inch and outer pistons, respectively, in accordance with the upward and downward movements. It is configured such that a "two-part oil chamber and a lower oil chamber are connected to each other, and a first oil chamber is formed."
．． In a variable compression ratio piston equipped with a flow rate control means configured to restrict the flow of hydraulic oil to the L-port chamber side,
The upper oil chamber is formed in an annular shape, and the inner piston and outer piston are fitted together on the annular inner peripheral surface so that relative rotation in the circumferential direction is restricted.

(Function) Since the upper oil chamber is formed into an annular shape, the inner circumference is missing compared to the conventional disc-shaped one, resulting in a smaller volume.
Therefore, the time for discharging the pressure oil from the upper oil chamber is shortened, and the switching to the low compression ratio state is quick. Similarly, switching to a high compression ratio state is also faster. Additionally, since both the inch and outer pistons are prevented from rotating on the inner circumference, the outer piston does not rotate in the circumferential direction, allowing for design without consideration of interference with valves, crankshafts, etc.

(Example) Embodiments of the present invention will be described below based on the drawings.

1 to 3 are diagrams showing one embodiment of the present invention. FIG. 1 shows a high compression ratio state, and FIG. 2 shows a low compression ratio state.

First, to explain the configuration, a connecting rod 1 having a check valve 5 and an oil passage 3 has a hollow part 15a sealed at both ends with members 15d, and a pressure oil inlet 15b and an outlet 15c.
A piston pin 15 having a diameter is fitted therein. The inner piston 13 is fitted into the piston pin 15 by a fitting part 19, and is prevented from being removed by a sealing plate 23. An outer piston 35 having an outer diameter surface 35a and capable of relative vertical movement within a predetermined range is fitted onto the inner piston 13 at an outer circumferential surface 35b and an inner circumferential surface 35c. Due to the above-mentioned upward and downward movement, an annular lower oil chamber 45 and an annular lower oil chamber 47 are formed between the inch piston 13 and the outer piston 35, respectively, and are partitioned by an outer circumferential surface 35b and an inner circumferential surface 35c. In addition, the inner piston 13 is provided with a communication passage 59a that connects the upper oil chamber 45 and the lower oil chamber 47 via a check valve 61, and a communication passage 59b having an orifice 62. An oil supply valve 51 is provided for supplying pressure oil through the oil passage 53 and the hollow portion of the piston pin 15]-5a.

Seal rings 22 and 25 made of metal or synthetic resin are provided on the inner circumferential surface 35c and outer circumferential surface 35b of the upper oil chamber 45, respectively, and seal rings 22 and 25 are provided on the inner circumferential surface 21 and outer circumferential surface 47a of the lower oil chamber, respectively. Rings 29,27 are provided to seal off the pressure oil.

A stop ring 41 is screwed inside the lower end of the outer piston 35, and the upper surface of the stop ring 41 and the lower stepped lower surface 21a of the inner piston 13 form the upper and lower surfaces of the lower oil chamber 47.

Further, the upper and lower surfaces of the upper oil chamber 45 are formed into a stepped annular shape by the upper wall 37 of the outer piston 35 and the upper wall 31 of the inner piston 13.
In Figure), they are formed so that they almost match, that is, the entire surface serves as a stopper during downward movement.

In this way, the outer piston 35 is attached to the boss 7 (third
(Fig.) is provided with an eccentricity e, which increases the weight accordingly, but this increase can be reduced by providing a hollowed out portion 9 inside.

In the figure, 11 indicates the entire variable compression ratio piston, and 57
indicates the lower end of the inch piston 13. This lower end 57 is formed so as to substantially coincide with the lower surface of the outer piston 35 in the high compression ratio state shown in FIG.

Next, the operation of the above embodiment will be explained.

When an internal combustion engine (not shown) is started, the lubricating oil is pumped through the oil gear gallery, the oil passage 3 of the connecting rod 1, the piston pin 15, and the hollow part 15g sealed at both ends by members 15d. It is sent as oil. The pressure oil is irreversibly introduced into the upper oil chamber 45 from the outlet 15c through the oil supply valve 51 provided in the passage 53 of the inner piston 13, but is then introduced into the upper oil chamber 45, which has a larger area than the lower oil chamber 47. Pressurized oil remains, resulting in a high compression ratio configuration as shown in FIG. When the internal combustion engine is operated under high load and the internal pressure in the upper oil chamber 45 exceeds a predetermined value due to an increase in the gas pressure applied to the upper surface of the outer piston 35, the adjustment load of the backup spring of the oil drain valve 55 and the valve body including the spring are Against the sum of inertial forces acting at the square of the rotational speed, the pressure oil pushes the oil drain valve 55 open and starts draining the hydraulic oil to the outside.At the same time, as the outer piston 35 descends, the lower oil chamber 47 is formed. At the same time, the hydraulic oil (pressure oil) in the upper oil chamber 45
from the lower oil chamber 4 via the orifice 62 to the communication path 59b.
7 to form a low compression ratio configuration as shown in FIG.

Note that when there is no change in the load of the internal combustion engine, when an upward inertial force acts, hydraulic oil flows from the lower oil chamber 47 into the upper oil chamber 45 through the orifice 62 provided in the communication passage 59b.
When the volume of the lower oil chamber 47 becomes zero, the stop ring 41 forming the lower oil chamber 47 collides with the stepped lower surface 21a of the inductor piston 13, but in this case, the diameter of the orifice 62 is appropriately selected. This prevents the collision and thereby restricts the fear of the outer piston.

Next, the internal combustion engine shifts to a low load state or the rotational speed increases, and the spring adjustment load of the oil drain valve 55 and the value of the inertia force applied thereto are the forces that are applied to the oil drain valve action area of the internal pressure of the upper oil chamber 45. When the oil pressure exceeds 100, the oil drain valve 55 is closed. During a stroke where such inertial force acts, hydraulic oil flows from the lower oil chamber 47 to the upper oil chamber 45 via the orifice 62, and the communication passage 5
The upper oil chamber 4 is irreversibly removed by the oil supply valve 51 provided in the upper oil chamber 4.
5, the upper oil chamber 45 expands and returns to the high compression ratio configuration shown in FIG. Among the series of movements described above, quick switching from a high compression ratio state to a low compression ratio state is especially important for avoiding knocking. Therefore, in order to improve responsiveness from high compression ratio to low compression ratio, it is necessary to increase the flow rate passing through the oil drain valve 55 within the restricted space, and to increase the flow rate passing through the check valve 61 from the upper oil chamber 45. At the same time, it is necessary to make the volume of the lower oil chamber 45 smaller so that it approaches the volume of the lower oil chamber 47. Furthermore, from the viewpoint of improving thermal efficiency by designing the combustion chamber shape, it is necessary to design the piston crown surface shape, for example, by creating a recess in the crown of the outer piston 31 to avoid interference with the intake and exhaust valves. Even when provided on the surface (upper surface), it is necessary to restrict rotation of the outer piston in the circumferential direction in order to control the piston posture and to avoid interference between the crankshaft and the outer piston 31.

In such a case, in the above-mentioned embodiment, the upper oil chamber 45 is formed in an annular shape, so that the volume is smaller than that of a conventional disc-shaped one, with the same outer diameter and the same vertical stroke amount. This can satisfy the above-mentioned needs. In other words, switching from the high compression ratio state fl (FIG. 1) to the low compression ratio state (FIG. 2) is achieved by reducing the volume of the upper oil chamber 45, and knocking can be avoided.

In addition, the reverse switching from a low compression ratio state to a high compression ratio state is also faster than in the past, which can help reduce fuel consumption.

Further, the outer circumferential surface 35b of the upper oil chamber 45 is the piston outer diameter surface 3.
5a, the inner circumferential surface 35C is fitted into the inner piston 31 with an eccentric amount e, so that the movement of the outer piston 35 in the circumferential direction with respect to the inner piston 31 is completely restrained. This allows for the setting of a valve recess on the upper surface of the piston and the setting of a part for preventing interference with the crankshaft, providing a degree of freedom in design.

Further, since the mounting groove of the large-diameter seal ring 25 is a circle concentric with the center of the piston, machining is easy and good sealing performance can be achieved. Furthermore, although the small-diameter seal ring 22 is eccentrically provided, since it is also circular, machining is easy and good sealing performance can be achieved.

It should be noted that eccentric setting of the rotation stopper, as in this embodiment, is more effective in maintaining good sealing performance if it is provided in the small diameter part rather than in the large diameter part.

FIG. 4 shows a structure in which the inner periphery 35c of the upper oil chamber 45 is formed into an oval shape with a straight section and is fitted into the inch piston 31. The inner peripheral shape of the upper oil chamber may be oval or polygonal. However, in this case, although the groove machining for the large diameter seal ring 25 is easy as in the previous example, the groove machining for the small diameter seal ring 22 must be machined so as to follow the shape of the inner circumferential surface 35C. It's something you can't get.

Next, an example using the improved seal ring will be described with reference to FIGS. 5 to 13.

In the following example, the variable compression ratio piston 11 will be described with an improved seal ring applied to a conventional structure, but other structures, that is, those with the improved seal ring applied to the structure of the previous example will be explained. Of course, it is also possible to apply.

FIG. 5 shows a high compression ratio version of the variable compression ratio piston 11 according to this embodiment, and FIG. 6 shows a low compression ratio version of the same piston. The inch piston 13 of the variable compression ratio piston 11 is connected to the small end of the connecting rod 1 via a hollow piston pin 15 fitted therein. Show part. This inner piston 1
A small diameter portion 21 is formed at the lower end of the skirt No. 3 via a stepped portion 21a.

On the other hand, both sides of the hollow portion 15a of the piston pin 15 are sealed by a sealing plate 23 which is engaged with the inch piston 13 and also serves as a stopper. The connecting rod 1 also has an oil passage 3 extending from the small end to the big end on the crankbin side.
It is formed. The lubricating oil discharged from the lubricating oil pump of the internal combustion engine to the main gear is forced into the oil passage 3 via the crankshaft, and after passing through the check valve 5 interposed in the oil passage 3, the lubricating oil is sent to the piston pin 15. Pressure hydraulic oil is fed into the hollow portion 15a through the oil passage hole 15b.

The outer piston 35 of the piston 11 has a skirt portion extending below the small diameter portion 21 of the inch piston 13, and is externally fitted onto the skirt portion of the inner piston 13 so as to be able to slide vertically. This prevents the outer piston 35 from swinging and allows smooth vertical movement. A stop ring 41 is screwed onto the lower part of the skirt of the outer piston 35, and the inner peripheral surface of the stop ring 41 is slidably fitted into the small diameter portion 21. Then, fit each of the above-mentioned sliding parts into the inch piston 13. It is sealed by vertical seal rings 25a, 27a, 29a and seal ring seats 25b, 27b, 29b, etc.

In the above configuration, when the outer piston 35 is moved upward, the stop ring 41 comes into contact with the stepped portion 21a to restrict the upper limit of movement, and the upper walls 37 and 31 of the outer piston 35 and the inner piston 13 The dimensional relationship of each part is determined so that an upper oil chamber 45 (FIG. 5) of a predetermined height is formed between them. Therefore, when the outer piston 35 is moved downward, the upper wall 37 comes into contact with the outer piston 31 and the lower limit of movement is restricted, and this downward movement causes the annular lower oil chamber 47 (
FIG. 6) is formed.

An oil supply valve 51 and an oil drain valve 55 are attached to the top of the inner piston 13 to constitute a hydraulic oil supply/discharge means. The oil supply valve 51 and the oil drain valve 55 are ordinary check valves constructed using a spherical valve body and its backup spring, so a description of their basic structure will be omitted.

The oil supply valve 51 is disposed above the piston pin fitting part 19 on one side, and the pressure hydraulic oil fed into the hollow part 15a of the piston pin 15 flows through the oil passage hole 15c of the piston pin 15. The oil reaches the oil supply valve 51 through the oil supply passage 53 formed in the fitting part 19, flows irreversibly through the oil supply valve 51, and is introduced into the upper oil chamber 45. Further, the oil drain valve 55 is arranged above the piston pin fitting portion 17 on the other side. In this oil drain valve 55, as described above, when the combustion pressure rises above a predetermined value and the pressure of the hydraulic oil introduced into the upper oil chamber 45 accordingly exceeds a predetermined value, the spherical valve body 55a opens. The set load of the backup spring 55b is set so that the backup spring 55b contracts and opens the valve. When the oil drain valve 55 is opened in this manner, the hydraulic oil in the upper oil chamber 45 is discharged below the inner piston 13 via the oil drain passage 55C formed in the piston pin fitting portion 17.

Furthermore, a control valve is provided in the piston pin fitting portion 17, in which a series of communication passages 59 are formed that communicate the upper oil chamber 45 and the lower oil chamber 47, and a plate-shaped valve body 81 having an orifice hole 83 is disposed above the communication passage 59. 61 are arranged, and these constitute a flow rate control means (see FIG. 7).

In the drawing, the control valve 61 and the communication path 59, and the oil drain valve 55 and the oil drain path 55c are shown on the same cross section for convenience, but these can be arranged at appropriate locations such as on both sides of the piston pin 15. It is something.

As shown enlarged in FIGS. 7 and 8, the control valve 61 includes a valve chamber 63 that opens on the upper surface of the upper wall 31 of the inch piston 13, and a seal that is screwed and fixed to the opening side of the valve chamber 63. The member 65 and the valve receiver fitted into the bottom of the valve chamber 63 include a member 71 and a valve body 81 disposed between these members 65 and 71. The seal member 65 has a valve hole 67 vertically penetrating through the center thereof, and a valve seat 69 surrounding the lower edge of the valve hole 67. In addition, the valve receiver member 71 has a seat 73 facing the valve seat 69, a through hole 75 formed in the center of the seat 73, and a valve seat 73 that faces the valve seat 69. As shown in FIG. It has a plurality of protruding and downwardly bent legs 77, for example four legs, and these legs 77 form a wide channel 79 leading from the periphery of the seat 73 to the communication channel 59. The valve body 81 has a disc shape, and the valve seat 69 and the receiver are loosely inserted between the valve seat 69 and the seat 73 so as to be movable up and down.
An orifice 8 is formed in the center of the valve body 81 and extends vertically through the valve body 81.
3 is formed.

The embodiment is configured as described above. Therefore, when the internal combustion engine is started, the hydraulic oil is introduced into the upper oil chamber 45 and confined there, so that the piston 11 assumes the high compression ratio configuration shown in FIG. 5 and is ready for operation in a low load region.

Here, when the internal pressure of the upper oil chamber 45 rises beyond a predetermined value due to a transition to a high load operating range, the backup spring 55b of the oil drain valve 55 contracts and the oil drain valve 55 opens. As a result, the outer piston 35 passes through the oil drain path 55 through the oil drain valve 55.
It rapidly moves downward while discharging the hydraulic oil to c, and at the same time forms the lower oil chamber 47 and sends the hydraulic oil from the control valve 61 to the lower oil chamber 47 via the communication path 59. At this time, the control valve 61
As shown in FIG. 7, the valve body 81 is pushed by the flow of hydraulic oil and sits on the seat 73, so the hydraulic oil sent from the valve hole 67 flows through the orifice 83 and the through hole 75. In addition to flowing through the valve chamber 63, the hydraulic oil also flows into the five communication passages through the wide passage 79, so that this hydraulic oil is rapidly introduced into the lower oil chamber 47.

As a result, the piston 11 immediately responds to an excessive rise in combustion pressure and assumes the configuration for a low compression ratio shown in FIG. 6. In this way, when the internal pressure of the upper oil chamber 45 decreases to a predetermined value while the rise in combustion pressure is suppressed, the oil drain valve 55 is closed, and then, when this internal pressure decreases to the working oil pressure, the oil is released via the oil supply valve 51. The supply of hydraulic oil is restarted, and the upward movement of the outer piston 35 is started again. In this process, the outer piston 35 continues to gradually move downward due to its inertia even after the oil drain valve 55 is closed, so that the volume of the lower oil chamber 47 continues to expand and sufficient hydraulic oil is stored there. Ru. In this case, in the embodiment, as described above, the swinging of the outer piston 35 is restrained and the outer piston 35 does not come into contact with the inner piston 13, so that the above-mentioned continuous downward movement is performed smoothly. As a result, the outer piston 35 can be lowered easily and reproducibly, for example, at the lower limit of movement, so that a sufficient amount of hydraulic oil can be stored.

When the upward movement of the outer piston 35 is restarted as described above, the volume of the lower oil chamber 47 is reduced and the hydraulic oil stored there is transferred from the communication path 59 to the upper oil chamber 4 via the control valve 61.
Pushed back to the 5th side. At this time, the valve body 81 of the control valve 61 is pushed up and comes into contact with the valve seat 69 as shown in FIG. 8, so that the hydraulic oil flows only through the orifice 83. As a result, a braking force is applied to the outer piston 35, slowing the upward movement, and combined with the fact that sufficient hydraulic oil for this braking is stored in the lower oil chamber 47, the piston 11 has a low compression rate. The form of comparative approximation can be well maintained.

The function of the seal ring is important in order for each control valve system to perform the operations described above with high precision over a long period of time. Next, the function of the seal ring will be explained.

FIG. 10 shows a state in which the resin seal ring 25a seals within the seal ring groove after a predetermined operating time without the seal ring seat 25b. It can be seen that 25a-1 is beginning to be generated due to the action of the hydraulic pressure P. This protruding portion 25a-1 basically progresses over time and eventually loses its sealing ability.

FIG. 11 shows an improved embodiment in which a conventional seal ring 25a made of synthetic resin and a seal ring sheet 25b made of metal or high hardness resin are used.

In this figure, the hydraulic pressure P acts on the seal ring seat 25b, which can move relative to the seal ring 25a at right angles to the sliding direction and is placed on the low pressure side, and the seal ring seat 25b comes into contact with the sliding member, causing a gap. This shows a state in which the seal ring 25H is buried and the occurrence of protruding parts of the seal ring 25H is suppressed.

The cross section of the seal ring sheet may have an L-shaped cross section with a large pressure receiving area as shown in Fig. 12, and the abutment may have an obtuse angle A as shown in Fig. 13 instead of a straight cut. A bias cut (diagonal cut) may also be applied.

[Effects of the Invention] As explained above, according to the present invention, the structure includes an inner piston connected to a connecting rod, and an outer piston fitted to the inch piston so as to be able to move relative up and down within a predetermined range. The piston is configured such that an upper oil chamber and a lower oil chamber are respectively formed between the inch and outer pistons as the piston moves upward and downward, and further communicates the upper oil chamber and the lower oil chamber. At the same time,
In the variable compression ratio piston, the upper oil chamber is formed in an annular shape, and the inner piston and the outer piston are arranged in the annular shape. Since they are fitted in such a manner that relative rotation in the circumferential direction is restricted on the inner circumferential surface, compression ratio switching responsiveness can be improved. or,
The effect is that the rotational movement of the outer piston in the circumferential direction relative to the inner piston can be completely restricted and the degree of freedom in design can be increased.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 and 2 are sectional views of a piston according to an embodiment of the present invention, and FIG. 1 shows a form for high compression ratio.
In addition, Fig. 2 is a diagram showing the form for low compression ratio, Fig. 3 is a sectional view taken along the line ■-■ of Fig. 1, and Fig. 4 is a sectional view similar to Fig. 3 of another embodiment. Figures 5 to 13 are explanatory diagrams of how to use the improved seal ring, and Figure 5 shows the form for high compression ratios.
The figure shows a configuration for a low compression ratio, and FIGS. 7 and 8 are enlarged cross-sectional views of the control valve in the above-mentioned embodiment. FIG. 7 shows the operation mode when the outer piston moves downward. In addition, Fig. 8 is a diagram showing the operation mode during the same upward movement, Fig. 9 is an enlarged perspective view of the main parts of Figs. 7 and 8, and Fig. 10 is a diagram showing the operation mode when the resin seal ring is used alone. 11 is a cross-sectional view of the seal ring groove in a seal ring structure combining a seal ring and a seal ring sheet according to an improved proposal, and FIG. 12 is a cross-sectional view of a seal ring groove according to another embodiment. A cross-sectional view, FIG. 13 is a view showing the abutment shape of a seal ring seat according to another embodiment, and FIG. 14 is a cross-sectional view of a piston according to a conventional example. 1... Connecting rod 11... Variable compression ratio piston 13... Inner piston 35... Outer piston

Claims (1)

[Claims] an inner piston connected to a connecting rod;
The inner piston has an outer piston fitted to the inner piston so as to be able to move up and down relative to each other within a predetermined range, and an upper oil chamber and a lower oil chamber are provided between the inner and outer pistons, respectively, in accordance with the upward and downward movements. In a variable compression ratio piston, the variable compression ratio piston is configured to form an upper oil chamber and a lower oil chamber, and is further equipped with a flow rate control means configured to connect the upper oil chamber and the lower oil chamber and restrict the flow of hydraulic oil to the upper oil chamber side. A variable compression ratio piston, characterized in that the upper oil chamber is formed in an annular shape, and the inner piston and outer piston are fitted together on the annular inner peripheral surface so that relative rotation in the circumferential direction is restricted. .