JP2015017560A - Piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable compression ratio engine having a mechanism for preventing the withdrawal of an outer piston and an inner piston by a simple and high-rigidity structure.SOLUTION: In a variable compression ratio engine, a piston 2 is divided into an upper piston 3 (outer piston) and a lower piston 4 (inner piston) which can move to the upper piston 3 in the slide direction of the piston 2, and a stopper 28 is disposed which is supported to the upper piston 3, abuts on the lower piston 4, and regulates the movement of the lower piston 4 to the upper piston 3 by a prescribed distance or longer. An internal peripheral face screw part 27 is formed at an internal peripheral face of the upper piston 3, the stopper 28 comprises an external peripheral face screw part 29, the external peripheral face screw part 29 is screwed into the internal peripheral face screw part 27, and the stopper 28 is fixed to the upper piston 3.

Description

  The present invention relates to an engine piston structure capable of varying a compression ratio.

Conventionally, a variable compression ratio engine in which a piston has a double structure of an outer piston and an inner piston is known. In the variable compression ratio engine, for example, as disclosed in Patent Document 1, an inner piston connected to a connecting rod is disposed inside an outer piston, and the inner piston and the outer piston can move in the same direction as the sliding direction of the piston. It is configured.
Specifically, in Patent Document 1, a storage chamber is provided in the outer piston, the inner piston is disposed so as to be movable in the storage chamber along the sliding direction of the piston, and a spring is provided between the inner piston and the outer piston. Is provided. As a result, the outer piston moves toward the inner piston against the biasing force of the disc spring due to the pressure in the combustion chamber, so that the volume of the combustion chamber changes according to the pressure in the combustion chamber and the compression ratio is changed. It has a configuration.

JP 2012-137060 A

In Patent Document 1, when the inner piston moves away from the outer piston, a circumferential groove is provided on the inner peripheral surface of the outer piston so that the inner piston is not detached from the outer piston storage chamber. A snap ring that restricts movement of the inner piston in a direction away from a predetermined distance is supported in the circumferential groove.
However, as in Patent Document 1, in a variable compression ratio engine having a structure in which the inner piston and the outer piston are prevented from being separated by a snap ring, the inner piston collides with the snap ring every time the cylinder reciprocates. Further, in order to securely support the snap ring on the outer piston, it is necessary to secure the depth of the circumferential groove of the outer piston, so that the circumference of the circumferential groove of the outer piston is thickened, etc. It is necessary to ensure the strength, which may increase the weight of the piston.

  The present invention has been made to solve such a problem, and the object of the present invention is to provide a variable compression ratio engine having a simple and strong structure for preventing the outer piston and the inner piston from separating. It is providing the piston used for.

  In order to achieve the above object, in the piston of claim 1, the outer piston, the inner piston capable of reciprocating in the direction of the central axis of the piston with respect to the outer piston, and the outer piston are supported and contacted with the inner piston. A piston comprising a stopper for restricting the movement of the inner piston, an inner peripheral surface threaded portion formed on the inner peripheral surface of the outer piston, and an outer peripheral surface threaded portion formed on the outer peripheral surface of the stopper, The inner peripheral surface thread portion and the outer peripheral surface thread portion are screwed together and fastened to the outer piston.

The piston according to claim 2 is characterized in that, in claim 1, the inner peripheral surface screw portion and the outer peripheral surface screw portion are round screws.
According to a third aspect of the present invention, in the first or second aspect of the present invention, the axial line is disposed in parallel with the sliding direction of the piston, and an insertion member for inserting and inserting the inner piston and the stopper is provided.

  According to the first aspect of the present invention, the outer piston and the inner piston move relatively along the sliding direction of the piston, thereby moving the position of the outer piston in the cylinder with respect to the connecting position of the connecting rod. The compression ratio can be changed by changing the volume of the combustion chamber in the cylinder. And since the stopper that contacts the inner piston and regulates the movement of the inner piston away from the outer piston by a predetermined distance or more is screwed and fixed to the inner peripheral surface thread portion formed on the inner peripheral surface of the outer piston, Compared with the conventional structure in which the snap ring is supported as a stopper in the groove provided in the outer piston, the concentration of stress in the support portion of the stopper is suppressed, and the strength of the outer piston can be improved.

According to the second aspect of the present invention, the inner peripheral surface threaded portion of the outer piston and the outer peripheral surface threaded portion of the stopper are round screws. The strength of the piston can be further improved.
According to the invention of claim 3, the axial line is arranged parallel to the sliding direction of the piston, and the inner piston and the stopper are inserted and inserted into the sliding direction of the piston of the inner piston with respect to the outer piston. While allowing, the rotation of the stopper in the radial direction of the piston can be restricted. Thereby, since the rotation of the stopper in the piston radial direction is restricted, it is possible to prevent the stopper from loosening due to the reciprocating motion of the piston with a simple structure.

It is sectional drawing which shows the structure of the piston of the variable compression ratio engine which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the piston provided with the locking function of the stopper. It is sectional drawing which shows the shape of other embodiment of the fastening part of a stopper.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing the structure of a piston of a variable compression ratio engine according to an embodiment of the present invention.
As shown in FIG. 1, a piston 2 is slidably disposed in an axial direction (vertical direction in FIG. 1) in a cylinder 1 of a variable compression ratio engine (hereinafter referred to as an engine) of the present embodiment. .

The piston 2 of this embodiment has a double structure of an upper piston 3 (outer piston) and a lower piston 4 (inner piston).
The upper piston 3 is formed in a cylindrical shape with the upper part closed, forms the outer shape of the piston 2, and is constituted by the upper piston head 5 and the side wall part 6. The piston head 5 is formed in a disc shape, and the upper surface 5 a faces the combustion chamber 7. The side wall portion 6 is formed in a cylindrical shape extending downward (on the opposite side to the combustion chamber) from the lower surface of the peripheral edge portion of the piston head 5, and a plurality of ring grooves 9 for supporting the piston ring 8 are provided in the upper portion. .

Further, a columnar convex portion 10 that protrudes downward is provided at the center of the lower surface of the piston head 5.
The lower piston 4 is housed in the upper piston 3, and is disposed so as to be able to reciprocate in the upper piston 3 in the vertical direction (the central axis direction of the piston 2). The lower piston 4 is provided with a disc-shaped main body portion 21, a pin boss 22 connected to the connecting rod, and a cylindrical guide portion 23.

The diameter of the main body 21 is set so that a slight gap is provided between the outer peripheral end of the main body 21 and the inner peripheral wall 3 a of the upper piston 3.
The pin boss 22 is provided so as to protrude downward from the lower surface of the main body 21, and is pivotally supported via a piston pin 24 at one end of an engine connecting rod (not shown).
The guide portion 23 is provided so as to protrude upward from the central portion of the upper surface of the main body portion 21 and is formed so that the convex portion 10 of the upper piston 3 can be smoothly inserted from above with substantially no gap. The convex portion 10 and the guide portion 23 have a function of guiding so that the upper piston 3 and the lower piston 4 can move in the vertical direction. Further, when the main body 21 of the lower piston 4 and the piston head 5 of the upper piston 3 move in the approaching direction, a space is formed between the piston head 5 and the main body 21 of the lower piston 4. The protrusion length of the guide part 23 is set.

A disc spring 26 is accommodated in a storage chamber 25 that is a space between the piston head 5 and the lower piston 4. The disc spring 26 is arranged so as to be biased in a direction in which the piston head 5 of the upper piston 3 and the main body portion 21 of the lower piston 4 are separated from each other.
An inner peripheral surface screw portion 27 is formed at a substantially central portion in the vertical direction of the inner peripheral surface of the side wall portion 6 of the upper piston 3. A stopper 28 is fastened to the inner peripheral surface screw portion 27. The stopper 28 is formed in an annular plate shape, and an outer peripheral surface screw portion 29 that is screwed into the inner peripheral surface screw portion 27 of the upper piston 3 is formed on the outer peripheral portion.

The stopper 28 is disposed below the main body 21 of the lower piston 4 when the lower piston 4 is housed in the upper piston 3 together with the disc spring 26. The lower piston 4 has a function of restricting the downward movement of the lower piston 4 more than a predetermined value, that is, the predetermined movement of the upper piston 3 in the direction in which the lower piston 4 is separated from the piston head 5.
In the above embodiment, the disc spring 26 is inserted into the storage chamber 25 of the upper piston 3, the storage chamber 25 is covered with the lower piston 4, and the stopper 28 is fastened to the upper piston 3. The lower piston 4 is assembled so as to be integrated.

  With the above-described configuration, the piston 2 of the present embodiment is configured such that the upper piston 3 and the lower piston 4 are integrated, and the upper piston 3 with respect to the lower piston 4 is in the direction of the central axis of the piston 2, that is, It can reciprocate up and down, which is the sliding direction. The piston head 5 of the upper piston 3 and the lower piston 4 are biased in a direction away from each other by a disc spring 26, and the upper piston 3 is moved downward against the biasing force of the disc spring 26 by the pressure in the combustion chamber 7. It is configured to be movable.

Further, when the lower piston 4 moves downward, the lower surface of the outer circumferential portion of the main body 21 of the lower piston 4 comes into contact with the stopper 28, and separation of the upper piston 3 and the lower piston 4 is prevented. In particular, immediately after the cylinder 1 moves downward from the top dead center, the lower piston 4 strongly collides with the stopper 28.
Thus, since the upper piston 3 is movable along the sliding direction of the piston 2 with respect to the lower piston 4 connected to the connecting rod, combustion is caused by relative movement between the upper piston 3 and the lower piston 4. The volume in the chamber 7 can be changed, and the compression ratio can be changed.

  The relative movement between the lower piston 4 and the upper piston 3 is automatically performed by the disc spring 26 according to the pressure in the combustion chamber 7. For example, when the pressure in the combustion chamber 7 rises more than necessary near the top dead center of the piston 2, the upper piston 3 moves downward to increase the volume in the combustion chamber 7, thereby reducing the compression ratio. Knocking can be prevented. Further, when the compression ratio decreases when the engine is under a low load, the volume in the combustion chamber 7 can be decreased to increase the compression ratio, and fuel consumption can be reduced. Therefore, it is possible to provide an engine in which the compression ratio can be appropriately set with a simple configuration using the disc spring 26 without using an actuator or the like for relatively moving the lower piston 4 and the upper piston 3.

  In this embodiment, the inner peripheral surface screw portion 27 is provided on the inner peripheral surface of the side wall portion 6 of the upper piston 3, and the inner peripheral surface screw portion 27 and the outer peripheral surface screw portion 29 of the stopper 28 are screwed together. The upper piston 3 and the stopper 28 are fastened together, the lower piston 4 is brought into contact with the stopper 28 to restrict the movement of the upper piston 3 and the lower piston 4, and the upper piston 3 and the lower piston 4 are separated. To prevent. Therefore, as compared with the structure in which the separation of the upper piston and the lower piston is prevented by the snap ring as in the prior art, in this embodiment, instead of providing the circumferential groove for supporting the snap ring in the piston 2, the inner peripheral surface thread portion By providing 27, the groove provided in the upper piston 3 can be shallowed. Thereby, the strength of the upper piston 3 can be improved at the support portion of the stopper 28, and the weight of the piston 2 can be reduced by suppressing the thickness of the support portion. Therefore, the weight of the entire engine can be suppressed and the acceleration performance of the engine can be improved.

  The material of the stopper 28 is preferably the same member as the upper piston 3, for example, aluminum. In the present embodiment, the stopper 28 has a structure that is fastened by a screw, so that it is not necessary to use an elastic member such as a snap ring. And the stress concentration with respect to the upper piston 3 can be relieved by making the stopper 28 and the upper piston 3 into the same member. The material of the stopper 28 may be a member having a lower strength than that of the upper piston 3, and the stopper 28 is set to be damaged before the upper piston 3 is damaged when an excessive load is applied to the stopper 28. Thus, the engine can be repaired by exchanging the stopper 28, and the cost of replacement parts and the reduction in the number of repair work can be reduced.

Further, since the stopper 28 is structured to rotate and fasten with respect to the upper piston 3, the stopper 28 may be loosened by the reciprocating motion of the piston 2. Therefore, it is desirable to add a function of preventing the stopper 28 from loosening.
As a loosening prevention function, for example, as shown in FIG. 2, a structure that restricts relative rotation between the stopper 28 and the lower piston 4 by a pin 31 (insertion member) may be used. The disc spring 26, the stopper 28, and the lower piston 4 (at least the stopper 28 and the lower piston 4) are each provided with an insertion hole for the pin 31 so that the axis is parallel to the sliding direction of the piston 2. When the pin 31 is fitted and the position of the insertion hole is matched with the upper piston 3 being fastened to the upper piston 3, the relative rotation between the lower piston 4 and the stopper 28 is restricted, and the stopper 28 is prevented from loosening. be able to. In order to prevent the pin 31 from falling off, for example, a structure in which the pin 31 is pivotally supported on the lower surface of the stopper 28 with a split pin or the like may be used.

When the rotation restriction by the pin 31 is performed, for example, a marker for defining the rotation position of the stopper 28 is provided on the stopper 28 and the upper piston 3 so that the pin 31 can be easily inserted at the time of assembly. The holes 28 and the holes of the lower piston 4 may be matched.
This is the end of the description of the embodiment of the invention, but the invention is not limited to this embodiment.

For example, as shown in FIG. 3, the inner peripheral surface screw portion 27 of the upper piston 3 and the outer peripheral surface screw portion 29 of the stopper 28 of the above embodiment may be round screws having a semicircular cross-sectional shape of the thread. Thereby, the concentration of stress at the valley portions of the inner peripheral surface screw portion 27 and the outer peripheral surface screw portion 29 can be relaxed, and the strength of the upper piston 3 can be further improved.
Further, as a function of preventing the stopper 28 from loosening, in addition to the above embodiment, for example, a lock nut having substantially the same shape as the stopper 28 is used. By tightening, the looseness of the stopper 28 can be suppressed.

Further, the stopper 28 may be rotated in the tightening direction by the pressing force of the lower piston 4 by making the contact portion between the stopper 28 and the lower piston 4 an inclined surface. Accordingly, the stopper 28 can be automatically tightened every time the stopper 28 and the lower piston 4 collide.
Further, the material of the stopper 28 and the upper piston 3 are made of materials having different thermal expansion coefficients, and the thermal expansion of the outer peripheral surface screw portion 29 of the stopper 28 and the thermal expansion of the inner peripheral surface screw portion 27 of the upper piston 3 due to the heat of the cylinder 1. Depending on the difference, the friction between the stopper 28 and the upper piston 3 may be increased to prevent the stopper 28 from loosening.

  The present invention can be widely applied to engines in which pistons are used.

2 Piston 3 Upper piston (Outer piston)
4 Lower piston (inner piston)
27 Inner peripheral surface thread part 28 Stopper 29 Outer peripheral surface thread part 31 Pin (insertion member)

Claims (3)

An outer piston,
An inner piston capable of reciprocating in the direction of the center axis of the piston with respect to the outer piston;
A stopper that is supported by the outer piston, abuts against the inner piston, and restricts movement of the inner piston;
An inner peripheral surface thread portion formed on the inner peripheral surface of the outer piston;
An outer peripheral surface threaded portion formed on the outer peripheral surface of the stopper,
The piston, wherein the inner peripheral surface thread portion and the outer peripheral surface thread portion are screwed together and fastened to the outer piston.   The piston according to claim 1, wherein the inner peripheral surface screw portion and the outer peripheral surface screw portion are round screws.   3. The piston according to claim 1, further comprising an insertion member that is arranged in parallel with a sliding direction of the piston and that inserts the inner piston and the stopper. 4. .

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