Automobile hydraulic shock absorber

An automobile hydraulic shock absorber includes a cylinder body, a piston, an upper support, a piston rod, a volume adjustment mechanism, first and second communicating passages, and a pressure-applying mechanism. The piston rod is attached to the upper support via a rubber cushion. The volume adjustment mechanism includes a free piston. The first and second communicating passages communicate the first oil chamber and second oil chamber with each other in the cylinder body via a diaphragm. The pressure-applying mechanism is disposed outside the cylinder body, movement thereof is restricted by the upper support, and the pressure-applying mechanism pushes the piston rod downward.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automobile hydraulic shock absorber provided between the vehicle body and the wheels of an automobile.

2. Description of the Related Art

A conventional automobile hydraulic shock absorber is composed of a hydraulic cylinder, and a diaphragm or the like provided to the hydraulic cylinder to generate a damping force (see WO 2004/065817, for example). The hydraulic cylinder of the hydraulic shock absorber described in WO 2004/065817 is provided with a cylinder body, a piston, and a piston rod. The piston divided inside of the cylinder body into a first oil chamber at the bottom-end side, and second oil chamber at the top-end side. The piston is attached to the piston rod.

The bottom end portion of the cylinder body is attached to a vehicle wheel via a rubber cushion. The piston rod passes through the top end portion of the cylinder body to protrude above the cylinder body. The top end portion of the piston rod is attached via a rubber cushion to a shock absorber connecting portion attached to the vehicle body.

A communicating passage for communicating the first oil chamber and second oil chamber with each other is formed in the piston. A diaphragm is provided to the communicating passage so that a damping force is generated when operating oil flows in the communicating passage. In other words, a damping force is generated when the hydraulic shock absorber extends or retracts and operating oil flows through the communicating passage from one oil chamber to the other oil chamber.

In order for the hydraulic shock absorber to extend or retract, the change in volume of the first oil chamber must match the change in volume of the second oil chamber. However, since the piston rod is inserted into the second oil chamber, the change in volume of the second oil chamber is less than the change in volume of the first oil chamber. In the hydraulic shock absorber disclosed in WO 2004/065817, such a problem is overcome by providing a volume adjustment mechanism inside the cylinder body.

The volume adjustment mechanism has a structure whereby a free piston which forms a part of the wall of the first oil chamber is pushed by the pressure of a high-pressure gas. The free piston is inserted so as to be able to move inside the cylinder body. The first oil chamber is formed between the free piston and the piston attached to the piston rod. High-pressure gas is charged into the space between the free piston and the bottom end of the inside of the cylinder body. In other words, as the hydraulic shock absorber extends and retracts, the free piston moves so that the change in volume of the first oil chamber matches the change in volume of the second oil chamber.

In the hydraulic shock absorber thus provided with a volume adjustment mechanism, the pressure of high-pressure gas is continuously applied from the first oil chamber to the piston for dividing the first oil chamber from the second oil chamber. The pressure of the high-pressure gas is exerted on the entire area of a pressure-receiving surface composed of the bottom surface (surface facing the free piston) of the piston via the operating oil inside the first oil chamber. The pressure of the high-pressure gas is also transmitted from the first oil chamber to the operating oil inside the second oil chamber via the operating oil in the communicating passage of the piston. In other words, the pressure of the high-pressure gas acts on the pressure-receiving surface composed of the bottom surface of the piston, and the pressure-receiving surface composed of the top surface of the piston.

The pressure-receiving surface composed of the top surface of the piston has a surface area smaller than that of the pressure receiving surface composed of the bottom surface of the piston, by an amount equal to the cross-sectional area of the piston rod. The piston is therefore pushed by an oil pressure (pressure of the high-pressure gas) corresponding in size to the difference in surface area between the pressure-receiving surfaces, and the piston rod moves toward the top end portion of the cylinder body so as to push the piston rod out from the cylinder body. In the present specification, the force with which the piston rod is pushed due to the difference in surface area of the pressure-receiving surfaces is referred to as the gas reactive force.

When the piston rod is pushed out from the cylinder body in this manner, the hydraulic shock absorber extends, and the rubber cushion provided between the hydraulic shock absorber and the vehicle body, or between the hydraulic shock absorber and the vehicle wheel, undergoes elastic deformation and hardens. Small bumps on the road over which the vehicle wheel rolls during travel are insufficient to cause the piston of the hydraulic shock absorber to move in relation to the cylinder body, and shocks that occur in such cases cannot be dampened. Small shocks that occur when the vehicle wheel rolls over small bumps during travel must be dampened by the rubber cushion. However, when the rubber cushion hardens as described above, such small shocks are not dampened by the rubber cushion, and are transmitted to the vehicle body.

In order to overcome such problems, a compression coil spring is provided inside the cylinder body in the hydraulic shock absorber disclosed in WO 2004/065817. This compression coil spring is provided inside the cylinder body such that the piston rod passes through the compression coil spring, so that the piston is pushed toward the free piston. The length of the compression coil spring is such that the compression coil spring extends from the piston to the other end portion of the cylinder body when the piston is positioned in a normal zone.

In other words, the piston is pushed toward the free piston by the spring force of the compression coil spring, and the gas reactive force described above is thereby cancelled out.

Besides the conventional hydraulic shock absorber described in WO 2004/065817, a conventional hydraulic shock absorber in which a compression coil spring is provided inside the cylinder body is also described in Japanese Laid-open Patent Publication No. 2001-193782, for example.

The compression coil spring in the cylinder body as described in Japanese Laid-open Patent Publication No. 2001-193782 is provided in order to prevent the piston in the fully extended hydraulic cylinder from colliding with the top end portion of the cylinder body. The compression coil spring does not normally push on the piston, and pushes on the piston only when the hydraulic cylinder is markedly extended.

A space for accommodating the compression coil spring for cancelling out the gas reactive force is necessary inside the cylinder body disclosed in WO 2004/065817. The hydraulic shock absorber disclosed in WO 2004/065817 therefore has drawbacks in that the overall length thereof is increased by an amount commensurate with the required space.

The weight of the compression coil spring in the cylinder body also increases, since the compression coil spring must be formed so as to have a length greater than the gap between the piston positioned within the normal zone and the top end portion of the cylinder body.

Furthermore, the spring force of the compression coil spring and the gas reactive force for raising the piston vary depending on the stroke position of the piston. In other words, in the hydraulic shock absorber disclosed in WO 2004/065817, when the piston is extended from the normal zone, the spring force is increased and the gas reactive force is reduced by the increased stroke amount. The spring force is greater than the gas reactive force in this case.

Conversely, in a case in which the hydraulic shock absorber is retracted from the state in which the piston is in the normal zone, the spring force is reduced and the gas reactive force is increased by the increased stroke amount. The gas reactive force is greater than the spring force in this case. In other words, the hydraulic shock absorber disclosed in WO 2004/065817 must generate a predetermined damping force while being subject to the effects both of variation in the spring force and variation in the gas reactive force as described above. It is therefore difficult to set the damping force to the optimum value in this hydraulic shock absorber.

In the hydraulic shock absorber disclosed in Japanese Laid-open Patent Publication No. 2001-193782, the overall length is also increased by the accommodation of a compression coil spring inside the cylinder body, the same as in the hydraulic shock absorber described in WO 2004/065817.

In the hydraulic shock absorber disclosed in Japanese Laid-open Patent Publication No. 2001-193782, when the stroke amount is small, whether during retraction or extension, the gas reactive force cannot be cancelled out. Therefore, when a vehicle provided with this hydraulic shock absorber is traveling on a straight road or a gently curving road, shocks that occur when a vehicle wheel rolls over small bumps on the road surface are transmitted to the vehicle body via the hydraulic shock absorber and the rubber cushion, resulting in poor ride quality.

SUMMARY OF THE INVENTION

In order to overcome such problems, preferred embodiments of the present invention provide an automobile hydraulic shock absorber having a small overall length and light weight despite having a structure whereby the gas reactive force exerted on the piston can be always cancelled out, and whereby the damping force can easily be set to the optimum value.

An automobile hydraulic shock absorber according to a first preferred embodiment of the present invention includes a cylinder body, a piston, a shock absorber connecting portion, a piston rod, a volume adjustment mechanism, a communicating passage, and a pressure-applying mechanism. The cylinder body includes a first end portion as one end portion in an axial direction, and a second end portion as the other end portion in the axial direction. The first end portion of the cylinder body is connected to one of a vehicle body and a vehicle wheel. The piston divides the inside of the cylinder body into a first oil chamber on the first end portion side and a second oil chamber on the second end portion side. The shock absorber connecting portion is connected to the other of the vehicle body and the vehicle wheel. The piston rod passes through the second end portion of the cylinder body from the piston and protrudes to the outside of the cylinder body. The piston rod is attached to the shock absorber connecting portion via a damping member. The volume adjustment mechanism pushes on the operating oil using pressure of a high-pressure gas, thereby canceling out the excess and deficiency of the operating oil corresponding to the increase or decrease in volume of the piston rod during movement of the piston. The communicating passage communicates the first oil chamber and the second oil chamber via a diaphragm. The pressure-applying mechanism is disposed outside the cylinder body. Movement of the pressure-applying mechanism is restricted by the shock absorber connecting portion. The pressure-applying mechanism pushes the piston rod toward the first end portion of the cylinder body. Connection to the vehicle body or a vehicle wheel herein includes direct connection as well as indirect connection via another member.

The automobile hydraulic shock absorber according to a second preferred embodiment of the present invention is the automobile hydraulic shock absorber according to the first preferred embodiment, wherein the size of the pushing force of the pressure-applying mechanism is equal to a gas reactive force for pushing the piston toward the second end portion of the cylinder body with a strength corresponding to a difference in surface area between one pressure-receiving surface of the piston and another pressure-receiving surface thereof.

The automobile hydraulic shock absorber according to a third preferred embodiment of the present invention is the automobile hydraulic shock absorber according to the first preferred embodiment, wherein the size of the pushing force of the pressure-applying mechanism is smaller than a gas reactive force for pushing the piston toward the second end portion of the cylinder body with a strength corresponding to a difference in surface area between one pressure-receiving surface of the piston and another pressure-receiving surface thereof.

The automobile hydraulic shock absorber according to a fourth preferred embodiment of the present invention is the automobile hydraulic shock absorber according to the first preferred embodiment, wherein the size of the pushing force of the pressure-applying mechanism is larger than a gas reactive force for pushing the piston toward the second end portion of the cylinder body with a strength corresponding to the difference in surface area between one pressure-receiving surface of the piston and the other pressure-receiving surface thereof.

The automobile hydraulic shock absorber according to a fifth preferred embodiment of the present invention is the automobile hydraulic shock absorber according to any of the first through fourth preferred embodiments, wherein the first end portion of the cylinder body is connected to the vehicle wheel. The shock absorber connecting portion is connected to the vehicle body. The pressure-applying mechanism is preferably provided between the shock absorber connecting portion and the cylinder body.

The automobile hydraulic shock absorber according to a sixth preferred embodiment of the present invention is the automobile hydraulic shock absorber according to any of the first through fourth preferred embodiments, wherein the first end portion of the cylinder body is connected to the vehicle wheel. The shock absorber connecting portion is connected to the vehicle body. The pressure-applying mechanism is preferably located across from the cylinder body, with the shock absorber connecting portion in between.

The automobile hydraulic shock absorber according to a seventh preferred embodiment of the present invention is the automobile hydraulic shock absorber according to any of the first through sixth preferred embodiments, wherein the pressure-applying mechanism includes a spring member. The spring member is positioned on the same axis as the piston rod, and pushes the piston rod.

The automobile hydraulic shock absorber according to an eighth preferred embodiment of the present invention is the automobile hydraulic shock absorber according to the seventh preferred embodiment, further including a pushing force adjustment mechanism. The pushing force adjustment mechanism has a screw portion extending in a direction parallel or substantially parallel to the piston rod; and a support portion that is caused to move in the axial direction of the piston rod by rotation of the screw portion. One end portion of the spring member is supported by the shock absorber connecting portion via the pushing force adjustment mechanism.

The automobile hydraulic shock absorber according to a ninth preferred embodiment of the present invention is the automobile hydraulic shock absorber according to any of the first through sixth preferred embodiments, wherein the pressure-applying mechanism includes a pushing hydraulic cylinder and a hydraulic passage. The pushing hydraulic cylinder moves the piston rod in relation to the shock absorber connecting portion. The hydraulic passage communicates the inside of the pushing hydraulic cylinder and the first oil chamber inside the cylinder body. The pushing force of the pressure-applying mechanism is the oil pressure transmitted from the first oil chamber in the cylinder body to the pushing hydraulic cylinder via the hydraulic passage.

The automobile hydraulic shock absorber according to a tenth preferred embodiment of the present invention is the automobile hydraulic shock absorber according to the ninth preferred embodiment, wherein the pressure-applying mechanism includes a valve arranged to open and close the hydraulic passage and a non-return valve arranged to direct operating oil from inside the pushing hydraulic cylinder to the hydraulic passage.

According to various preferred embodiments of the present invention, the gas reactive force for pushing the piston toward the second end portion of the cylinder body, the size of the gas reactive force corresponding to the difference in surface area between one pressure-receiving surface of the piston and the other pressure-receiving surface thereof, is reduced by the pushing of the piston rod by the pressure-applying mechanism.

The pressure-applying mechanism is provided outside the cylinder body. The cylinder body can therefore be constructed so as to have the minimum length necessary to enable the movement stroke of the piston to be maintained. Consequently, the hydraulic shock absorber of various preferred embodiments of the present invention can be formed so as to have a shorter overall length than the hydraulic shock absorber described in WO 2004/065817.

The pressure-applying mechanism pushes the piston rod, which does not move significantly in relation to the shock absorber connecting portion. The pressure-applying mechanism can therefore be compactly formed. The hydraulic shock absorber of various preferred embodiments of the present invention can therefore be formed so as to have lighter weight than the hydraulic shock absorber described in WO 2004/065817.

The pressure-applying mechanism pushes the piston rod always with a constant pushing force without being affected by the stroke position of the piston. Therefore, only the gas reactive force varies when the hydraulic shock absorber extends or retracts. The damping force is therefore easier to set in the hydraulic shock absorber of preferred embodiments the present invention than in the hydraulic shock absorber described in WO 2004/065817.

As a result, through various preferred embodiments of the present invention, an automobile hydraulic shock absorber can be provided having a small overall length and light weight despite having a structure whereby the gas reactive force exerted on the piston can be always reduced, and whereby the damping force can easily be set to a suitable value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

A first preferred embodiment of the automobile hydraulic shock absorber of the present invention will be described in detail according toFIG. 1.

The hydraulic shock absorber1shown inFIG. 1is provided between the vehicle body and a wheel of an automobile. The hydraulic shock absorber1preferably includes a hydraulic cylinder2, a diaphragm4provided to a piston3of the hydraulic cylinder2, and other components.

The hydraulic cylinder2preferably includes a cylinder body5, the piston3, a piston rod8, and other components. The bottom end portion of the cylinder body5is connected to the vehicle wheel. The piston3divides the inside of the cylinder body5into a first oil chamber6on the bottom end side and a second oil chamber7on the top end side. The piston rod8is connected to the piston3. The inside of the first oil chamber6and the inside of the second oil chamber7are filed with operating oil. The hydraulic cylinder2according to the present preferred embodiment is inserted into a suspension spring (not shown) to support the weight of the vehicle body.

The suspension spring is provided between the external peripheral portion of the cylinder body5and an upper support9described hereinafter. The piston rod8is therefore not subjected to the weight of the vehicle body. The suspension spring may also be disposed beside and parallel or substantially parallel to the hydraulic cylinder2.

An attachment member5aarranged to attach the cylinder body5to the portion of a suspension device (not shown) that is attached to the vehicle wheel is provided at the bottom end of the cylinder body5.

A volume adjustment mechanism11is provided inside the bottom end portion of the cylinder body5. The volume adjustment mechanism11causes the change in volume of the first oil chamber6to match the change in volume of the second oil chamber7.

The volume adjustment mechanism11according to the present preferred embodiment includes a free piston12and a high-pressure gas chamber13. The free piston12defines a portion of the wall of the first oil chamber inside the cylinder body5. The high-pressure gas chamber13is located below the free piston12. High-pressure nitrogen gas is charged into the high-pressure gas chamber13. In other words, the pressure of the high-pressure nitrogen gas is exerted on the operating oil inside the first and second oil chambers6,7.

The piston3separates the first oil chamber6from the second oil chamber7. The piston3is fitted into the cylinder body5so as to be able to move. The bottom end portion of the piston rod8is fixed to a central axis portion of the piston3. First and second communicating passages14,15arranged to communicate the first oil chamber6and the second oil chamber7with each other via the diaphragm4are provided in the external peripheral portion of the piston3.

The diaphragm4includes a first diaphragm4apositioned on the bottom side of the piston3, and a second diaphragm4bpositioned on the top side of the piston3. The first and second diaphragms4a,4bare each formed preferably by stacking a plurality of leaf springs. The first diaphragm4aopens and closes the opening of the first communicating passage14at the bottom end and generates a damping force when the piston3moves upward in relation to the cylinder body5.

The second diaphragm4bopens and closes the opening of the second communicating passage15at the top end and generates a damping force when the piston3moves downward in relation to the cylinder body5.

The first and second communicating passages14,15and the first and second diaphragms4a,4bare thus provided to the piston3, and minute communicating passages not shown in the drawing are also preferably provided in addition to the communicating passages14,15. The pressure of the high-pressure nitrogen gas thereby passes through these communicating passages and diaphragms to pressurize the operating oil equally in the first and second oil chambers6,7. The surface area of a pressure-receiving surface composed of the bottom surface of the piston3is larger than the surface area of a pressure-receiving surface composed of the top surface of the piston3by an amount commensurate with the cross-sectional area of the piston rod8. A gas reactive force is therefore exerted on the piston3so as to move the piston3toward the top end portion of the cylinder body5.

The piston rod8passes through a lid member5bof the top end portion of the cylinder body5and protrudes above the cylinder body5. The top end portion of the piston rod8is attached to the upper support9via a rubber cushion16. The upper support9is attached to a vehicle body frame member not shown in the drawing.

In the present preferred embodiment, the upper support9constitutes the “shock absorber connecting portion” of a preferred embodiment of the present invention, and the rubber cushion16constitutes the “damping member” of a preferred embodiment of the present invention. The rubber cushion16is fixed to the external peripheral surface of a cylinder17fixed to the top end portion of the piston rod8, and a hole wall surface of a circular hole18of the upper support9.

A pressure-applying mechanism21to cancel out the gas reactive force exerted on the piston3is provided between the upper support9and the cylinder body5. The pressure-applying mechanism21is disposed below the upper support9. In other words, the pressure-applying mechanism21is disposed on the same side of the upper support9as the cylinder body5. The pressure-applying mechanism21preferably includes a support member22, a pressure-receiving member23, a compression coil spring24, and other components. The support member22is fixed to the bottom surface of the upper support9. The pressure-receiving member23is attached to the piston rod8. The compression coil spring24is provided between the support member22and the pressure-receiving member23. The compression coil spring24pushes the pressure-receiving member23downward with a predetermined spring force. In the present preferred embodiment, the compression coil spring24constitutes the “spring member” according to a preferred embodiment of the present invention.

The support member22preferably includes an annular portion22aand a cylindrical portion22b. The annular portion22ais shaped so as to cover the rubber cushion16from below. The cylindrical portion22bextends downward from the central axis portion of the annular portion22a. The annular portion22ais fixed to the bottom surface of the upper support9, and upward movement thereof is thereby restricted.

The piston rod8is passed through the cylindrical portion22b. A clearance25for allowing free movement of the piston rod8is provided between the piston rod8and the internal peripheral surface of the cylindrical portion22b.

The pressure-receiving member23is preferably defined by a ring-shaped plate through which the piston rod8passes. The pressure-receiving member23is attached in a location of the piston rod8between the cylinder body5and the support member22. Downward movement of the pressure-receiving member23is restricted by a circlip26attached to the piston rod8.

The top end portion of the compression coil spring24is in contact with the annular portion22ain a state of being fitted in the cylindrical portion22bof the support member22. The compression coil spring24is therefore positioned on the same axis as the piston rod8. The bottom end of the compression coil spring24is in contact with the top surface of the pressure-receiving member23.

The spring force of the compression coil spring24is equal in size to the gas reactive force which raises the piston3, and is set so that the pressure-receiving member23is pushed downward. In other words, the pressure-applying mechanism21pushes the piston rod8toward the bottom end portion of the cylinder body5with a pushing force equal to the gas reactive force.

In the hydraulic shock absorber1thus configured, the cylinder body5ascends in relation to the piston rod8when the vehicle wheel ascends in relation to the vehicle body. At this time, a damping force is generated by the passage of operating oil through the second diaphragm4bof the piston3. When the cylinder body5descends in relation to the piston rod8, a damping force is generated by the passage of operating oil through the first diaphragm4aof the piston3.

An upward gas reactive force is exerted on the piston3, and the size of the gas reactive force corresponds to the difference in surface area between the pressure-receiving surface composed of the bottom surface and the pressure-receiving surface composed of the top surface. However, this gas reactive force is cancelled out by the pressure-applying mechanism21pushing the piston rod8downward with the spring force of the compression coil spring24.

At this time, since the size of the pushing force of the pressure-applying mechanism21is equal to the size of the gas reactive force, substantially all of the gas reactive force is eliminated by the pushing force of the pressure-applying mechanism21. As a result, the rubber cushion16provided between the piston rod8and the upper support9is maintained in a natural state with almost no elastic deformation thereof, and easily undergoes elastic deformation when the vehicle wheel rolls over small bumps on the road surface.

Consequently, vehicle ride quality is enhanced by attaching the hydraulic shock absorber1according to the present preferred embodiment to a vehicle.

The pressure-applying mechanism21according to the present preferred embodiment is preferably provided on the outside of (above) the cylinder body5. The cylinder body5can therefore be constructed so as to have the minimum length necessary to enable the movement stroke of the piston3to be maintained.

Consequently, the hydraulic shock absorber according to the present preferred embodiment can be constructed so as to have a shorter overall length than the hydraulic shock absorber described in WO 2004/065817. The cylinder body5in the hydraulic shock absorber1according to the present preferred embodiment can also be constructed so as to have a smaller diameter in comparison with the hydraulic shock absorber described in WO 2004/065817, in which the compression coil spring is accommodated inside the cylinder body5.

The pressure-applying mechanism21according to the present preferred embodiment pushes the piston rod8, which does not move significantly in relation to the upper support9. The pressure-applying mechanism21can therefore be compact. The hydraulic shock absorber1according to the present preferred embodiment can therefore be realized using a smaller compression coil spring24and have lighter weight in comparison with the hydraulic shock absorber described in WO 2004/065817.

The pressure-applying mechanism21according to the present preferred embodiment pushes the piston rod8always with a constant pushing force without being affected by the stroke position of the piston3. Therefore, only the gas reactive force varies when the hydraulic shock absorber1extends or retracts. The damping force is therefore easier to set in the hydraulic shock absorber1according to the present preferred embodiment than in the hydraulic shock absorber described in WO 2004/065817.

The pressure-applying mechanism21according to the present preferred embodiment is provided between the upper support9and the cylinder body5. Therefore, according to the present preferred embodiment, since the dead space formed between the upper support9and the cylinder body5can be utilized to accommodate the pressure-applying mechanism21, a compact hydraulic shock absorber can be provided.

The pushing force of the pressure-applying mechanism21according to the present preferred embodiment is the spring force of the compression coil spring24positioned on the same axis as the piston rod8. Therefore, according to the present preferred embodiment, since the pressure-applying mechanism21can be realized using a simple structure, an even more compact hydraulic shock absorber can be provided. A diaphragm spring, air spring, fluid spring, and/or other fluid spring or the like may also be used instead of the compression coil spring24as the source to generate the pushing force of the pressure-applying mechanism21.

The connection between the piston rod8and the pressure-receiving member23of the pressure-applying mechanism21can be formed by a screw extending in the axial direction of the piston rod8. In this case, rotating the pressure-receiving member23causes the pressure-receiving member23to move in the axial direction of the piston rod8. Through this configuration, the pushing force of the pressure-applying mechanism21(spring force of the compression coil spring24) can easily be varied.

Rubber (not shown) may also be placed between the compression coil spring24of the pressure-applying mechanism21and the support member22or pressure-receiving member23. Through this configuration, it is possible to even further reduce transmission of minute shocks from the road surface to the vehicle body.

Second Preferred Embodiment

The automobile hydraulic shock absorber according to a second preferred embodiment of the present invention can be formed as shown inFIG. 2. InFIG. 2, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIG. 1, and no detailed description of such members will be given.

The cylinder body5shown inFIG. 2is inserted into a damping spring31to support the weight of the vehicle body. The damping spring31is provided between the cylinder body5and the upper support9.

In the present preferred embodiment, an attachment flange32aof a rubber cover32is held between the upper support9and the top end portion of the damping spring31. The rubber cover32covers the top portion of the hydraulic cylinder2.

The upper support9according to the present preferred embodiment preferably includes a lower plate9a, and an upper plate9bwhich is placed over the lower plate9a. The upper support9is fixed to a frame member33of the vehicle body by a plurality of fixing bolts34. A cylindrical portion9cwhich protrudes upward is provided on the upper plate9b. The space between the lower plate9aand the inside of the cylindrical portion9cis filled by a ring-shaped rubber cushion16.

A flange35aof a connecting member35is embedded into the center portion of the rubber cushion16. The top portion of the piston rod8is fitted in the connecting member35. The pressure-receiving member23of the pressure-applying mechanism21is fitted on the top portion of the piston rod8. The pressure-receiving member23preferably has a cylindrical shape, and downward movement thereof is restricted by the circlip26. The connecting member35and the pressure-receiving member23are brought into contact with each other and fastened together by a lock nut36, and the piston rod8is thereby fixed to the connecting member35.

A flange23aarranged to support the bottom end portion of the compression coil spring24of the pressure-applying mechanism21is provided to the bottom end portion of the pressure-receiving member23. The top end portion of the compression coil spring24is in contact with a support plate37which is welded to the bottom surface of the upper support9. In other words, in the present preferred embodiment as well, the pressure-applying mechanism21pushes the piston rod8downward in a state in which upward movement of the pressure-applying mechanism21is restricted by the upper support9.

The support plate37preferably has a bottomed cylindrical shape which opens downward. A rubber cylinder body38is fixed on the inside of the support plate37. The cylinder body38prevents the top end portion of the cylinder body5from striking the pressure-applying mechanism21. The cylinder body38surrounds the pressure-applying mechanism21from the outside, and is arranged so as to extend a predetermined length downward from the pressure-receiving member23of the pressure-applying mechanism21.

Even when constructed as shown inFIG. 2, the hydraulic shock absorber1produces the same effects as the hydraulic shock absorber1shown inFIG. 1.

Rubber (not shown) may also be placed between the compression coil spring24of the pressure-applying mechanism21and the support plate37or pressure-receiving member23. Through this configuration, it is possible to even further reduce transmission of minute shocks from the road surface to the vehicle body.

Third Preferred Embodiment

The pressure-applying mechanism can be configured as shown inFIGS. 3A and 3B. InFIGS. 3A and 3B, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIGS. 1 and 2, and no detailed description of such members will be given.

A supporting bracket41shaped so as to cover the top end portion of the piston rod8is attached to the upper support9shown inFIGS. 3A and 3B. The supporting bracket41preferably has a cup shape which opens downward. The supporting bracket41is fixed to the frame member33by a fixing bolt34together with the upper support9so as to cover the upper support9from above.

The pressure-applying mechanism21is attached to the supporting bracket41via a pushing force adjustment mechanism42described hereinafter. In other words, the pressure-applying mechanism21according to the present preferred embodiment is provided above the upper support9(on the opposite side of the shock absorber connecting portion (upper support9) from the cylinder body5).

The pushing force adjustment mechanism42includes an adjusting bolt43and a support member22. The adjusting bolt43extends in a direction parallel or substantially parallel to the piston rod8. The support member22is fixed to the bottom end portion of the adjusting bolt43and is disk-shaped. The adjusting bolt43is screwed into a nut44welded to the highest portion of the supporting bracket41. The adjusting bolt43is attached in a position on the same axis as the piston rod8, and is positioned so that the support member22is separated above the piston rod8by a predetermined interval.

Rotating the adjusting bolt43in relation to the supporting bracket41causes the support member22to move in the axial direction of the piston rod8. In the present preferred embodiment, the adjusting bolt43constitutes the “screw portion” according to a preferred embodiment of the present invention, and the support member22constitutes the “support portion” according to a preferred embodiment of the present invention.

The pressure-applying mechanism21according to the present preferred embodiment has a support member22, a pressure-receiving member23, and a compression coil spring24. The support member22is provided to the bottom end portion of the adjusting bolt43. The pressure-receiving member23is disposed below the support member22, and is connected to the piston rod8. The compression coil spring24is provided between the support member22and the pressure-receiving member23.

The pressure-receiving member23is fixed in between the connecting member35and the lock nut36. The connecting member35is attached to the piston rod8. The connecting member35is supported by a circlip26of the piston rod8via a spacer45so as to be unable to move downward in relation to the piston rod8.

The compression coil spring24has a spring force capable of cancelling out the gas reactive force exerted on the piston3.

In other words, in the present preferred embodiment as well, the pressure-applying mechanism21pushes the piston rod8downward in a state in which upward movement of the pressure-applying mechanism21is restricted by the upper support9.

Even when constructed as shown inFIGS. 3A and 3B, the hydraulic shock absorber1produces the same effects as the hydraulic shock absorbers1shown inFIGS. 1 and 2.

In particular, since the pressure-applying mechanism21according to the present preferred embodiment is preferably provided above the upper support9(on the opposite side from the cylinder body5), installation of the pressure-applying mechanism21on the piston rod8and operation of the adjusting bolt43are facilitated.

Moreover, in the present preferred embodiment, by tightening the adjusting bolt43, the compression coil spring24is compressed, and the pushing force thereof increases. Loosening the adjusting bolt43causes the compression coil spring24to extend, and the pushing force thereof decreases.

Therefore, through the present preferred embodiment, a hydraulic shock absorber can be provided whereby the pushing force of the pressure-applying mechanism21can easily be varied.

Rubber (not shown) may also be placed between the compression coil spring24of the pressure-applying mechanism21and the support member22or pressure-receiving member23. Through this configuration, it is possible to even further reduce transmission of minute shocks from the road surface to the vehicle body.

Fourth Preferred Embodiment

The pressure-applying mechanism can be configured as shown inFIGS. 4 through 6. InFIGS. 4 through 6, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIGS. 1 through 3, and no detailed description of such members will be given.

The pressure-applying mechanism21shown inFIGS. 4 and 5is provided with a pushing hydraulic cylinder51, a hydraulic passage52, a valve53, and a non-return valve54. The pushing hydraulic cylinder51moves the piston rod8in relation to the upper support9. The hydraulic passage52communicates the inside of the pushing hydraulic cylinder51with the first oil chamber6inside the cylinder body5. The valve53opens and closes the hydraulic passage52. The non-return valve54directs operating oil to the hydraulic passage52from within the pushing hydraulic cylinder51.

The pushing hydraulic cylinder51includes a piston portion55and a cylinder body portion56. The piston portion55is attached to the bottom surface of the upper support9. The cylinder body portion56is attached to the piston rod8. The piston portion55has a support body55aand a cylinder55b, as shown inFIG. 5. The support body55aprotrudes downward from the bottom surface of the upper support9, and has a substantially hemispherical shape. The cylinder55bextends downward from the lowest portion of the support body55a. The support body55ais fixed to the upper support9.

The spherical surface of the support body55ais arranged so that the center in the vertical direction in the central axis portion of the cylindrical rubber cushion16is at the center of the support body55a. The support body55ais also not necessarily fixed to the upper support9, and a clearance may be provided between the support body55aand the upper support9.

The top end portion of the cylinder55bis shaped so as to slidably fit on the bottom surface (spherical surface) of the support body55a. The piston rod8is slidably fitted into the cylinder55b. An O-ring57is installed on the internal peripheral portion of the cylinder55bto form a seal against the piston rod8. In other words, when the piston rod8oscillates about the rubber cushion16in conjunction with upward and downward movement of the vehicle wheel, the cylinder55bmoves together with the piston rod8along the spherical surface of the support body55a.

The cylinder body portion56includes a disk-shaped bottom wall56athrough which the piston rod8passes, and a cylindrical peripheral wall56bwhich extends upward from the external peripheral portion of the bottom wall56a. The bottom wall56ais positioned on the same axis as the piston rod8. An O-ring58for forming a seal against the piston rod8is installed in the bottom wall56a. The bottom end portion of the bottom wall56ais in contact with a circlip59attached to the piston rod8. In other words, the cylinder body portion56is attached to the piston rod8so that downward movement of the cylinder body portion56is restricted.

The cylinder55bof the piston portion55is fitted into the peripheral wall56bso as to be able to move. An O-ring60for forming a seal against the peripheral wall56bis installed on the external peripheral portion of the cylinder55b.

The hydraulic passage52communicates the inside of the pushing hydraulic cylinder51with the first oil chamber6. The hydraulic passage52has a through-hole61, an oil hole62of the valve53described hereinafter, and a communicating hole63. The through-hole61is provided in the central axis portion of the piston rod8. The oil hole62of the valve53is provided inside the through-hole61. The communicating hole63extends in the horizontal direction (a direction that is perpendicular or substantially perpendicular to the axial direction of the piston rod8) through the inside of the piston rod8from the through-hole61.

The valve53is provided inside the through-hole61. The valve53includes a valve body64and a handle65. The valve body64is inserted in the through-hole61so as to be able to rotate, and is rod shaped. The handle65is attached to the top end portion of the valve body64. An O-ring66for forming a seal against the hole wall surface of the through-hole61is installed in the valve body64. The oil hole62of the hydraulic passage52is formed in the bottom end portion of the valve body64. The oil hole62extends upward from the bottom surface of the valve body64, and then extends further in the horizontal direction.

A horizontally extending portion62aof the oil hole62is located at the same height as the communicating hole63of the piston rod8. The valve53is opened by connection of the horizontally extending portion62ato the communicating hole63, as shown inFIGS. 4 through 6A.

The handle65connected to the top end portion of the valve body64rotates the valve body64inside the through-hole61. The handle65is screwed into the top end portion of the piston rod8.

A mark is provided to the handle65so that the position of the horizontally extending portion62aof the oil hole62(position at which the valve53is open) can be determined.

The non-return valve54is a so-called ball check valve, and is provided between the inside of the pushing hydraulic cylinder51and the through-hole61of the piston rod8. The ball of the non-return valve54is retained so as to be able to move without dropping into the piston rod8.

In the pressure-applying mechanism21according to the present preferred embodiment, the handle65attached to the top end portion of the piston rod8is operated to open the valve53, and a pushing force is thereby generated. In order to open the valve53, the handle65is rotated, and the horizontally extending portion62aof the oil hole62described above is connected to the communicating hole63of the piston rod8, as shown inFIG. 6A. By connection of the oil hole62to the communicating hole63, the valve53opens, and the oil pressure inside the first oil chamber6is introduced into the pushing hydraulic cylinder51through the hydraulic passage52.

When the oil pressure is introduced into the pushing hydraulic cylinder51, the cylinder body portion56is pushed downward in relation to the piston portion55by the oil pressure. In a case in which the support body55aof the piston portion55is not fixed to the upper support9, the piston portion55is raised at this time by oil pressure and pushed against the upper support9from below.

The cylinder body portion56cannot move downward in relation to the piston rod8. The piston rod8is therefore pushed downward at this time by the oil pressure inside the pushing hydraulic cylinder51. In other words, the pushing force of the pressure-applying mechanism21is the oil pressure transmitted from the first oil chamber6inside the cylinder body5to the pushing hydraulic cylinder51via the hydraulic passage52inside the piston rod8. In other words, in the present preferred embodiment as well, the pressure-applying mechanism21pushes the piston rod8downward in a state in which upward movement of the pressure-applying mechanism21is restricted by the upper support9.

The size of the pushing force according to the present preferred embodiment is set equal to the gas reactive force for pushing the piston3upward. The size of the pushing force can be calculated based on the area of the pressure-receiving surfaces of the piston portion55and the cylinder body portion56.

By returning or further rotating the handle65from the state in which the valve53is open, the oil hole62can no longer be connected to the communicating hole63, and the valve53closes, as shown inFIG. 6B.

When the valve53closes, the supply of oil pressure to the pushing hydraulic cylinder51is stopped. At this time, the piston rod8is pushed upward by the gas reactive force. Therefore, after the valve53is closed, the cylinder body portion56is pushed upward by the gas reactive force, and the operating oil inside the pushing hydraulic cylinder51flows into the through-hole61through the non-return valve54. The cylinder body portion56rises to the position at which the gas reactive force and the repulsive force of deformation of the rubber cushion16due to the gas reactive force are balanced.

The pushing force for cancelling out the gas reactive force is thus eliminated by closing of the valve53. Even in such a state in which the gas reactive force and the repulsive force of the rubber cushion16are balanced, a clearance is maintained between the top end of the peripheral wall56bof the cylinder body portion56and the bottom surface of the support body55aof the piston portion55. Small shocks that occur when the vehicle wheel rolls over small bumps on the road can therefore be at least somewhat dampened by the elasticity of the rubber cushion16.

In the preferred embodiment shown inFIGS. 4 through 6Bas well, since the pressure-applying mechanism21arranged to push the piston rod8downward is provided to the upper support9, equivalent effects to those of the hydraulic shock absorber1shown inFIGS. 1 through 3can be obtained.

As described above, the pushing force of the pressure-applying mechanism21according to the present preferred embodiment is the oil pressure transmitted to the pushing hydraulic cylinder51from the first oil chamber6inside the cylinder body5via the hydraulic passage52inside the piston rod8. In other words, since the source for generating the pushing force is not a spring member, there is no damage due to metal fatigue. Consequently, the present preferred embodiment enables a hydraulic shock absorber to be provided that is highly reliable at cancelling out the gas reactive force.

In the hydraulic shock absorber1according to the present preferred embodiment, operating the handle65makes it possible to easily switch between a state in which pushing force is generated to cancel out the gas reactive force, and a state in which pushing force is not generated. The hydraulic shock absorber1can therefore be used with the valve53closed in a case in which the road surface is smooth, or in a case in which the driver prefers that shocks be transmitted from the vehicle wheel to the vehicle body.

Since the handle65is disposed above the upper support9, the handle65can be easily operated without being blocked by the frame member33, the hydraulic cylinder2, or other components.

Fifth Preferred Embodiment

The pressure-applying mechanism can be configured as shown inFIG. 7. InFIG. 7, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIGS. 1 through 6, and no detailed description of such members will be given.

The pressure-applying mechanism21according to the present preferred embodiment is provided with a pushing hydraulic cylinder71, and is provided on the opposite side (above) of the upper support9from the cylinder body5. The pushing hydraulic cylinder71has a structure that utilizes the oil pressure of the first oil chamber6to move the piston rod8downward in relation to the upper support9.

The pushing hydraulic cylinder71according to the present preferred embodiment includes a cylinder body portion72disposed above the upper support9, and a piston portion73attached to the piston rod8.

The cylinder body portion72includes a support body72aattached on top of the upper support9, and a movable portion72bmounted on top of the support body72a. The top surface of the support body72ais defined by a spherical surface which is upwardly convex. The spherical surface of the support body72ais arranged so that the center in the vertical direction in the central axis portion of the cylindrical rubber cushion16is at the center of the support body72a.

The movable portion72bis provided in a bottomed cylindrical shape which opens downward. The piston rod8passes through the central axis portion of the movable portion72b.

The bottom surface of the movable portion72bis shaped so as to slidably fit on the top surface (spherical surface) of the support body72a. The movable portion72bis configured so as not to separate upward from the support body72aand to always be in contact with the abovementioned top surface even when the movable portion72bis pushed upward by oil pressure. In other words, when the piston rod8oscillates about the rubber cushion16in conjunction with upward and downward movement of the vehicle wheel, the movable portion72bmoves together with the piston rod8along the spherical surface of the support body72a.

The piston portion73is fitted inside a peripheral wall72cof the movable portion72bso as to be able to move. The piston portion73also makes contact with a circlip74from above, the circlip74being attached to the piston rod8. An O-ring75arranged to prevent leakage of operating oil is installed between the cylinder body portion72and the piston portion73.

In the present preferred embodiment as well, since the pressure-applying mechanism21arranged to push the piston rod8downward is provided to the upper support9, equivalent effects to those of the hydraulic shock absorbers1shown inFIGS. 1 through 6can be obtained.

Sixth Preferred Embodiment

The hydraulic shock absorber according to a preferred embodiment of the present invention can be formed as shown inFIGS. 8,9A and9B. InFIGS. 8,9A and9B, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIG. 1, and no detailed description of such members will be given.

The piston rod8of the hydraulic shock absorber1according to the present preferred embodiment is attached to the upper support9via a spherical plain bearing (hereinafter referred to as a spherical joint)81.

The spherical joint81has a ball82through which the piston rod8passes, and a holder83for movably supporting the outer surface of the ball82.

The ball82is fixed to the top end portion of the piston rod8by a fixing nut84. The holder83is fixed in the circular hole18of the upper support9. In the present preferred embodiment, the spherical joint81constitutes the “damping member” according to a preferred embodiment of the present invention.

A clearance C is provided between the ball82and the holder83of the spherical joint81, as shown inFIGS. 9A and 9B.FIG. 9Ashows a state in which the ball82is moved downward from the holder83by an amount commensurate with the clearance C.FIG. 9Bshows a state in which the ball82is moved upward from the holder83by an amount commensurate with the clearance C.

The pushing force of the pressure-applying mechanism21according to the present preferred embodiment is set so as to be larger than the gas reactive force urging the piston3upward. Through this configuration, the clearance C forms a gap between the holder83and the upper half of the ball82as shown in FIG.9A, and the ball82is able to move upward in relation to the holder83.

In the present preferred embodiment, shocks generated by the vehicle wheel rolling over small bumps on the road are dampened by the upward movement of the ball82in relation to the holder83.

The hydraulic shock absorber1configured as described in the present preferred embodiment demonstrates equivalent effects to those of the hydraulic shock absorber1shown inFIG. 1.

Seventh Preferred Embodiment

The pressure-applying mechanism can be configured as shown inFIG. 10. InFIG. 10, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIGS. 1 and 2, and no detailed description of such members will be given.

The pressure-applying mechanism21according to the present preferred embodiment is provided above the upper support9(on the opposite side of the shock absorber connecting portion (upper support9) from the cylinder body5). The pressure-applying mechanism21includes a supporting bracket67, a support member68, and the compression coil spring24. The supporting bracket67has a generally cylindrical shape, and has a flange portion67a. The flange portion67ais welded to the top surface of the cylindrical portion9cof the upper plate9b. The supporting bracket67is thereby fixed to the upper plate9b. A hole67bis also formed in the top surface of the supporting bracket67. The hole67bis disposed so as to face the top end portion of the piston rod8. The support member68has an annular shape. The support member68is fitted in the hole67bof the supporting bracket67and fixed to the supporting bracket67. The support member68is fixed in the hole67bof the supporting bracket67by crimping. The support member68has an annular shape. A hole68ais formed in the support member68. The hole68ais disposed so as to face the top end portion of the piston rod8.

The compression coil spring24is disposed between the connecting member35and the support member68. Specifically, a step portion35bis arranged along the peripheral direction in the top end of the connecting member35. The bottom end portion of the compression coil spring24is in contact with the step portion35b. The top end portion of the compression coil spring24is in contact with the bottom surface of the support member68. The compression coil spring24is positioned on the same axis as the piston rod8. The compression coil spring24has a spring force capable of cancelling out the gas reactive force exerted on the piston3. In other words, in the present preferred embodiment as well, the pressure-applying mechanism21pushes the piston rod8downward in a state in which upward movement of the pressure-applying mechanism21is restricted by the upper support9.

Even when formed as shown inFIG. 10, the hydraulic shock absorber1produces the same effects as the hydraulic shock absorber1shown inFIGS. 1 and 2. Since the pressure-applying mechanism21is provided above the upper support9(on the opposite side from the cylinder body5) in the same manner as in the hydraulic shock absorber1shown inFIGS. 3A and 3B, the pressure-applying mechanism21can easily be installed on the piston rod8.

Eighth Preferred Embodiment

The pressure-applying mechanism can be configured as shown inFIG. 11. InFIG. 11, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIGS. 1 and 2, and no detailed description of such members will be given.

The pressure-applying mechanism21according to the present preferred embodiment is provided above the upper support9(on the opposite side of the shock absorber connecting portion (upper support9) from the cylinder body5). The pressure-applying mechanism21includes a supporting bracket69and the compression coil spring24. The bottom end portion69aof the supporting bracket69has a tapered shape such that the outside diameter of the supporting bracket69decreases toward the bottom. A groove69bis also formed in the supporting bracket69along the peripheral direction thereof. The bottom end portion69aof the supporting bracket69is inserted in a hole9din the top surface of the cylindrical portion9c. The edge of the hole9dof the cylindrical portion9cis fitted into the groove69bof the supporting bracket69. The supporting bracket69is thereby fixed to the upper plate9b. A hole69cis also formed in the top surface portion of the supporting bracket69. The hole69cis disposed so as to face the top end portion of the piston rod8.

The compression coil spring24is disposed between the connecting member35and the supporting bracket69. Specifically, the bottom end portion of the compression coil spring24is in contact with the top surface of the connecting member35. The top end portion of the compression coil spring24is in contact with the inside surface of the top surface portion of the supporting bracket69. The compression coil spring24is positioned on the same axis as the piston rod8. The compression coil spring24has a spring force capable of cancelling out the gas reactive force exerted on the piston3. In other words, in the present preferred embodiment as well, the pressure-applying mechanism21pushes the piston rod8downward in a state in which upward movement of the pressure-applying mechanism21is restricted by the upper support9.

Even when formed as shown inFIG. 11, the hydraulic shock absorber1produces the same effects as the hydraulic shock absorber1shown inFIGS. 1 and 2. Since the pressure-applying mechanism21is provided above the upper support9(on the opposite side from the cylinder body5) in the same manner as in the hydraulic shock absorber1shown inFIGS. 3A and 3B, the pressure-applying mechanism21can easily be installed on the piston rod8.

Ninth Preferred Embodiment

The pressure-applying mechanism can be configured as shown inFIG. 12. InFIG. 12, the same reference numerals are used to refer to members that are the same as or equivalent to those described inFIGS. 1 and 2, and no detailed description of such members will be given.

The pressure-applying mechanism21according to the present preferred embodiment is provided above the upper support9(on the opposite side of the shock absorber connecting portion (upper support9) from the cylinder body5). The pressure-applying mechanism21includes a supporting bracket70and the compression coil spring24. The supporting bracket70has a generally cylindrical shape, and has a flange portion70a. The flange portion70ais fixed to the top surface of the upper plate9bby the fixing bolt34. In other words, the flange portion70ais fixed between the vehicle body and the top surface of the upper plate9b. A hole70bis also formed in the top surface portion of the supporting bracket70. The hole70bis disposed so as to face the top end portion of the piston rod8.

The compression coil spring24is disposed between the connecting member35and the supporting bracket70. Specifically, the bottom end portion of the compression coil spring24is in contact with the top surface of the connecting member35. The top end portion of the compression coil spring24is in contact with the inside surface of the top surface portion of the supporting bracket70. The compression coil spring24is also positioned on the same axis as the piston rod8. The compression coil spring24has a tapered shape such that the outside diameter of the compression coil spring24decreases toward the bottom. The compression coil spring24has a spring force capable of cancelling out the gas reactive force exerted on the piston3. In other words, in the present preferred embodiment as well, the pressure-applying mechanism21pushes the piston rod8downward in a state in which upward movement of the pressure-applying mechanism21is restricted by the upper support9.

Even when formed as shown inFIG. 12, the hydraulic shock absorber1produces the same effects as the hydraulic shock absorber1shown inFIGS. 1 and 2. Since the pressure-applying mechanism21is provided above the upper support9(on the opposite side from the cylinder body5) in the same manner as in the hydraulic shock absorber1shown inFIGS. 3A and 3B, the pressure-applying mechanism21can easily be installed on the piston rod8.

In the first through ninth preferred embodiments described above, examples were described in which the pushing force of the pressure-applying mechanism21is preferably equal in size to the gas reactive force. However, the size of the pushing force of the pressure-applying mechanism21may be smaller than the gas reactive force. In a case in which the compression coil spring24is used as the source for generating the pushing force so as to reduce the pushing force of the pressure-applying mechanism21, a compression coil spring24having a relatively small spring force is preferably used. In a case in which oil pressure is used as the source for generating the pushing force, the surface area of the pressure-receiving surface of the pushing hydraulic cylinder71is reduced.

Even in a case in which the pushing force of the pressure-applying mechanism21is made smaller than the gas reactive force, the gas reactive force exerted on the piston3is reduced, and the rubber cushion16is maintained in a state in which elastic deformation thereof is possible. Consequently, although the effects are reduced in this case in comparison with a case in which the pushing force of the pressure-applying mechanism21is made equal in size to the gas reactive force, the vehicle ride quality can be improved.

In the first through ninth preferred embodiments described above, the pushing force of the pressure-applying mechanism21can be made larger than the gas reactive force described above. To achieve this pushing force in a case in which the compression coil spring24is used as the source for generating the pushing force, a compression coil spring24having a relatively large spring force is used. In a case in which oil pressure is used as the source for generating the pushing force, the surface area of the pressure-receiving surfaces of each of the pushing hydraulic cylinders51,71is increased.

In a case in which the pushing force of the pressure-applying mechanism21is larger than the gas reactive force, not only is the gas reactive force for raising the piston3eliminated, but the piston3is also pushed toward the free piston12. In other words, the piston rod8is pushed downward by the pushing force of the pressure-applying mechanism21. The rubber cushion16between the piston rod8and the upper support9is also elastically deformed so that an external peripheral portion16athereof is higher than an internal peripheral portion16bthereof, as shown inFIG. 13A. The pressure-applying mechanism21is omitted inFIGS. 13A and 13B.

In this case, shocks that occur when the vehicle wheel rolls over small bumps on the road are dampened by the elastic deformation of the rubber cushion16in the opposite direction from that described above, as shown inFIG. 13B.

The bottom end portion of the cylinder body5in the preferred embodiments described above corresponds to the first end portion as one end portion in the axial direction of the cylinder body of the present invention. The top end portion of the cylinder body5in the preferred embodiments described above corresponds to the second end portion as the other end portion in the axial direction of the cylinder body of the present invention. However, as an opposite configuration, the top end portion of the cylinder body5in the preferred embodiments may correspond to the first end portion of the cylinder body of the present invention, and the bottom end portion of the cylinder body5in the preferred embodiments may correspond to the second end portion of the present invention. In other words, the hydraulic shock absorber1of the present invention can be used in the same manner as in the preferred embodiments described above even in a state in which the distal end portion of the piston rod8is connected to the vehicle wheel, and the cylinder body5is connected to the vehicle body.

In each of the preferred embodiments described above, the diaphragm4of the hydraulic cylinder2is provided to the piston3. However, the diaphragm4may be of any configuration in the hydraulic shock absorber according to various preferred embodiments of the present invention. For example, a communicating passage arranged to communicate the first and second oil chambers6,7may be provided outside the cylinder body5, and the diaphragm may be provided to the communicating passage.

In each of the preferred embodiments described above, the volume adjustment mechanism11of the hydraulic cylinder2is preferably configured using the free piston12inside the cylinder body5. However, the volume adjustment mechanism used in the hydraulic shock absorber according to a preferred embodiment of the present invention may be of any configuration. Although not shown in the drawings, a volume adjustment mechanism that uses a reserve tank connected to the first oil chamber6by a communicating passage, or a publicly known twin-tube volume adjustment mechanism may be used.

The inside of the reserved tank described above is partitioned by the free piston into a high-pressure gas chamber and an oil chamber which is filled with operating oil. The oil chamber is communicated with the first oil chamber6or second oil chamber7inside the cylinder body5via a communicating passage. High-pressure gas is charged into the high-pressure gas chamber. In other words, the operating oil inside the cylinder body5is pushed by the pressure of the high-pressure gas in this configuration as well.

In a twin-tube volume adjustment mechanism, the cylinder body5has a double structure including an inner tube and an outer tube. The first oil chamber6and second oil chamber in the inner tube are communicated with a third oil chamber of the outer tube. The inside of the outer tube is also configured so that the operating oil inside the oil chambers is pressurized by high-pressure gas.

Preferred embodiments of the present invention provide an automobile hydraulic shock absorber having a small overall length and light weight despite having a structure whereby the gas reactive force exerted on the piston can be always reduced, and whereby the damping force can easily be set to a suitable value.