JP2008138757A - Damping force adjustable hydraulic shock absorber - Google Patents

Abstract

In a damping force adjusting hydraulic shock absorber, the damping force at low current is set to the soft side to reduce power consumption, and the damping force is fixed to the hard side at the time of failure such as disconnection.
A piston rod 7 is connected to a cylinder 2 in which oil is sealed, and the piston 3 is slidably fitted. A solenoid actuator 35 controls a valve opening of a seat valve 32 to adjust a damping force. To do. When the coil 38 is not energized, the plunger 36 and the seat valve 32 are urged in the valve closing direction by the resultant force of the first and second valve springs 45 and 47, and the damping force becomes the hard side. When the coil 38 is energized, the movable member 42 moves against the urging force of the second valve spring 47 to reduce the valve opening pressure of the seat valve 32 (damping force soft). When the energizing current increases, the movable member 42 moves away from the plunger 36, and the valve opening pressure of the seat valve 32 increases due to the thrust of the plunger 32 in the valve closing direction of the seat valve 32 (hardening force).
[Selection] Figure 1

Description

  The present invention relates to a damping force adjusting hydraulic shock absorber mounted on a suspension device of a vehicle such as an automobile.

  The hydraulic shock absorber mounted on the suspension system of a vehicle such as an automobile has a damping force adjustment type that allows the damping force to be adjusted appropriately in order to improve ride comfort and handling stability according to road surface conditions, driving conditions, etc. There is a hydraulic shock absorber.

  A damping force adjusting hydraulic shock absorber generally has a piston in which a piston rod is connected in a cylinder filled with oil so as to be slidable, and the oil is circulated by sliding of the piston in the cylinder. The oil passage is provided with a damping force adjusting mechanism. The damping force adjustment mechanism generates a damping force by controlling the flow of the oil liquid using an orifice and a disk valve, and further changes the flow area of the oil liquid using a valve means such as a spool or a shutter. adjust.

  Some damping force adjustment type hydraulic shock absorbers adjust the damping force by driving a valve body of a valve means such as a spool or shutter of a damping force adjusting mechanism by an actuator such as a proportional solenoid. As a result, the damping force adjusting mechanism can be remotely operated, so that the damping force can be adjusted even while the vehicle is running.

When a damping force adjusting type hydraulic shock absorber provided with this type of solenoid actuator is mounted on a suspension device of a vehicle, for example, as described in Patent Document 1, a valve body of a damping force adjusting mechanism is provided by a spring means. By energizing in the valve closing direction (damping force hard side) and energizing the coil against the spring force of the spring means, the valve body is biased in the valve opening direction (damping force soft side), thereby reducing the damping force. I try to adjust it. As a result, as shown in FIG. 5, the damping force becomes maximum when the energization current to the coil is 0, and becomes smaller as the energization current increases. As a result, when the coil cannot be energized due to the occurrence of a failure such as disconnection, the damping force is fixed to the hard side, and vehicle handling stability can be ensured.
JP 2002-292092 A

  However, the damping force adjusting hydraulic shock absorber in which the damping force when the coil is not energized has a hard side has the following problems. In order to adjust the damping force to the soft side, it is necessary to energize the coil. However, in the damping force adjustment type hydraulic shock absorber mounted on the vehicle suspension system, the damping force is generally adjusted to the hard side. Power consumption is increased because it is adjusted to the soft side in most situations.

  The present invention has been made in view of the above points, and adjusts the damping force from the soft side to the hard side by increasing the energization current to the coil, and also has a predetermined value larger than the soft side even during non-energization. An object of the present invention is to provide a damping force adjustable hydraulic shock absorber capable of generating a damping force.

In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a cylinder in which oil is sealed, a piston slidably fitted in the cylinder, one end connected to the piston, and the like. A piston rod whose end extends to the outside of the cylinder, an oil passage through which oil is circulated by sliding of the piston in the cylinder, and a damping force is adjusted by controlling the flow of the oil in the oil passage A damping force adjusting type hydraulic shock absorber comprising: a damping force adjusting valve that performs a damping force adjusting valve; and a solenoid actuator that drives a valve body of the damping force adjusting valve.
The solenoid actuator includes a plunger coupled to the valve body, first spring means for biasing the plunger in a valve opening direction of the valve body, and a first spring biasing the plunger in a valve closing direction of the valve body. Two spring means, a movable member interposed between the plunger and the second spring means, a first magnetic circuit for biasing the plunger in a valve closing direction of the valve body by energizing a coil, and And a second magnetic circuit for biasing the movable member in the valve opening direction of the valve body.
A damping force adjusting type hydraulic shock absorber according to a second aspect of the present invention is the configuration according to the first aspect, wherein the first magnetic circuit faces the one end side of the plunger and energizes the coil by energizing the coil. The second magnetic circuit includes a first fixed iron core that attracts the valve body in a valve closing direction, and the second magnetic circuit opposes the other end side of the plunger and the movable member to energize the movable member by energizing the coil. Including a second fixed iron core for suction in the valve opening direction.
A damping force adjusting type hydraulic shock absorber according to a third aspect of the invention is characterized in that, in the configuration of the first or second aspect, the damping force adjusting valve is a pressure control valve.
A damping force adjusting type hydraulic shock absorber according to a fourth aspect of the present invention is characterized in that, in the structure according to any one of the first to third aspects, a nonmagnetic member is interposed between the plunger and the movable member. And

According to the damping force adjusting hydraulic shock absorber according to the first aspect of the invention, when the coil is not energized, the valve body of the damping force adjusting valve is biased in the valve closing direction by the first and second spring means. When the damping force increases and the coil is energized, the movable member is biased in the valve opening direction by the second magnetic circuit and resists the spring force of the second spring means. When the energizing current is further increased, the urging force for urging the plunger in the valve closing direction by the first magnetic circuit increases after the movable member moves against the spring force of the second spring means and moves away from the plunger. Damping force increases. As a result, the damping force can be adjusted from the soft side to the hard side by increasing the energization current to the coil, and a predetermined damping force larger than that on the soft side can be generated even during non-energization.
According to the damping force adjusting type hydraulic shock absorber according to the invention of claim 2, when energizing the coil, the first magnetic circuit urges the plunger in the valve closing direction by the suction of the first fixed iron core, The second magnetic circuit biases the movable member in the valve opening direction of the valve body by the suction of the second fixed iron core.
According to the damping force adjusting hydraulic shock absorber according to the invention of claim 3, the damping force is adjusted by controlling the pressure of the oil liquid in the oil passage by the damping force adjusting valve.
According to the damping force adjusting type hydraulic shock absorber according to the fourth aspect of the present invention, adsorption between the plunger and the movable member can be prevented.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
As shown in FIGS. 1 and 2, the hydraulic shock absorber 1 according to the present embodiment is a single cylinder type hydraulic shock absorber, and has a rod guide (not shown) and oil in an opening of a bottomed cylindrical cylinder 2. A seal (not shown) is attached, and a free piston (not shown) is slidably fitted on the bottom side in the cylinder 2. The cylinder 2 is defined by a free piston in a gas chamber on the bottom side and an oil chamber on the other end side. The gas chamber is filled with high-pressure gas, and the oil chamber is filled with oil. Instead of forming the gas chamber by the free piston, a reservoir filled with oil and gas may be connected to the bottom of the cylinder 2.

  A piston 3 is slidably fitted in the oil chamber of the cylinder 2, and the piston 3 defines an oil chamber into two chambers, a cylinder upper chamber 2A and a cylinder lower chamber 2B. The piston 3 has a tip end of a piston bolt 4 inserted therein and fixed by a nut 5. A substantially bottomed cylindrical case 6 is attached to the base end portion (upper part in the drawing) of the piston bolt 4. One end (lower side in the figure) of the piston rod 7 is connected to the bottom of the case 6, and the other end of the piston rod 7 is slidably and liquid-tightly inserted into the rod guide and the oil seal. And extended outside the cylinder 2.

  The piston 3 is provided with an extension side oil passage 8 that opens to the cylinder upper chamber 2A side and a contraction side oil passage 9 that opens to the cylinder lower chamber 2B side. The lower end portion of the piston 3 is provided with an extension side damping valve 10 that controls the flow of the oil liquid in the extension side oil passage 8, and the upper end portion controls the flow of the oil solution in the contraction side oil passage 9. A compression side damping valve 11 is provided.

  The extension-side damping valve 10 is formed by an extension-side main valve 13 (disc valve) seated on a seat portion 12 formed on the lower end surface of the piston 3 and a valve member 14 attached to the piston bolt 4 by a nut 5. An extension-side back pressure chamber 15 formed at the back of the valve 13 is provided. The extension-side back pressure chamber 15 causes its internal pressure to act on the extension-side main valve 13 in the valve closing direction. The extension-side back pressure chamber 15 is connected to the cylinder lower chamber 2 </ b> B via a disk valve 16 having an orifice 16 </ b> A (notch) provided in the valve member 14. The orifice 16A allows the extension-side back pressure chamber 15 and the cylinder lower chamber 2B to always communicate with each other, and the disk valve 16 opens when the pressure in the extension-side back pressure chamber 15 reaches a predetermined pressure. Relief to 2B.

  The extension-side back pressure chamber 15 is connected to a radial oil passage 18 of the piston bolt 4 via a back pressure introduction valve 17 provided in the valve member 14, and the radial oil passage 18 is further connected to the piston bolt 4. Are communicated with an axial oil passage 19 extending along the axial center of the shaft. The back pressure introduction valve 17 is a check valve that allows the fluid to flow from the radial oil passage 18 side to the extension side back pressure chamber 15 side. The back pressure introduction valve 17 has an orifice 17 </ b> A that allows the radial oil passage 18 and the extension side back pressure chamber 15 to always communicate with each other. Further, the axial oil passage 19 communicates with the radial oil passage 20, and the radial oil passage 20 extends through a compression check valve 21 having an expansion orifice 21 </ b> A provided in the piston 3. It is connected to the oil passage 8. The extension-side orifice 21A always communicates the radial oil passage 20 and the extension-side oil passage 8, and the contraction-side check valve 21 only allows the flow of oil from the radial oil passage 20 side to the extension-side oil passage 8 side. Allow.

  The contraction side damping valve 11 is contracted by a contraction side main valve 23 (disc valve) seated on a seat portion 22 formed on the upper end surface of the piston 3 and a valve member 24 attached to the piston bolt 4 by a nut 5. A contraction-side back pressure chamber 25 formed at the back of the main valve 23 is provided. The compression side back pressure chamber 25 causes the internal pressure to act on the compression side main valve 23 in the valve closing direction. The compression-side back pressure chamber 25 is connected to the cylinder upper chamber 2 </ b> A via a disk valve 26 having an orifice 26 </ b> A (notch) provided in the valve member 24. The orifice 26A allows the contraction side back pressure chamber 25 and the cylinder upper chamber 2A to always communicate with each other, and the disk valve 26 opens when the pressure in the contraction side back pressure chamber 25 reaches a predetermined pressure, and the pressure is supplied to the cylinder upper chamber. Relief to 2A.

  A valve chamber 27 extending along the axial direction is formed on the base end side of the piston bolt 4. The valve chamber 27 has a larger diameter than the axial oil passage 19, and a distal end portion thereof is the axial oil passage 19. It is communicated to. The contraction-side back pressure chamber 25 is connected to a radial oil passage 29 of the piston bolt 4 via a back pressure introduction valve 28 provided in the valve member 24, and the radial oil passage 29 is formed on the side wall of the valve chamber 27. It is open. The back pressure introduction valve 28 is a check valve that allows the fluid to flow from the radial oil passage 29 side to the contraction side back pressure chamber 25 side. The back pressure introduction valve 28 has an orifice 28 </ b> A that allows the radial oil passage 29 and the contraction side back pressure chamber 25 to always communicate with each other. Further, a radial oil passage 30 is opened on the side wall of the valve chamber 27, and the radial oil passage 30 is contracted via an expansion check valve 31 having a contraction orifice 31 </ b> A provided in the piston 3. It is connected to the side oil passage 9. The contraction-side orifice 31A allows the radial oil passage 30 and the contraction-side oil passage 9 to communicate with each other at all times, and the expansion-side check valve 31 allows the fluid to flow from the radial oil passage 30 side to the contraction-side oil passage 9 side. To do.

  A seat valve 32 (valve element) is slidably fitted in the valve chamber 27. The seat valve 32 is a damping force that opens and closes the flow path between the axial oil passage 19 and the valve chamber 27 by detaching and seating an annular seat portion 33 formed at the tip portion on the seat surface 34 of the valve chamber 27. A regulating valve is formed. The seat valve 32 is a pressure control valve, receives pressure on the axial oil passage 19 side by a circular pressure receiving surface on the inner peripheral side of the seat portion 33, and has a diameter by an annular pressure receiving surface on the outer peripheral side of the seat portion 33. These pressures are controlled by receiving pressures on the directional oil passages 29 and 30 side.

  A base end portion of the seat valve 32 is connected to a plunger 36 of a solenoid actuator 35 provided in the case 6 via a nonmagnetic member 32A. The solenoid actuator 35 includes a plunger 36, a piston bolt 4 (first fixed iron core) that faces one end of the plunger 36, a second fixed iron core 37 that opposes the other end of the plunger 36, and a coil that surrounds the plunger 36. 38 and a case 6 for housing them.

  A guide bore 39 for guiding one end of the plunger 36 is formed in the piston bolt 4 forming the first fixed iron core. The plunger 36 is slidably guided along the axial direction by the inner peripheral surface of the bobbin 40 of the coil 38. The plunger 36 has a stepped shape in which a small diameter portion 41 is formed on the other end side, and an annular movable member 42 that is a ferromagnetic body is slidably fitted to the small diameter portion 41. The movable member 42 has an outer diameter substantially equal to the outer diameter of the plunger 36 and is guided together with the plunger 36 by the inner peripheral surface of the bobbin 40 of the coil 38. An annular nonmagnetic member 43 is fitted and fixed to the base of the small diameter portion 41 of the plunger 36, and the nonmagnetic member 43 is interposed between the stepped portion of the plunger 36 and the movable member 42. A guide bore 44 that guides the outer peripheral portion of the movable member 42 is formed in the second fixed iron core 37.

  A first valve spring 45 (first spring means) that is a compression spring is interposed between the plunger 36 and the bottom of the guide bore 39 of the piston bolt 4. Further, a second valve spring 47 (second spring means), which is a compression spring, is interposed between the movable member 42 and a spring receiver 46 provided at the bottom of the guide bore 44 of the second fixed iron core 37. The second fixed iron core 37 is provided with an adjusting screw 48 that presses the spring receiver 45 and adjusts the set load of the first and second valve springs 45 and 47. In the plunger 36, a balance passage 49 for balancing the hydraulic pressure acting at both ends of the plunger 36 is penetrated in the axial direction.

  A magnetic circuit is formed by the piston bolt 4 (first fixed iron core), the case 6 (frame), the second fixed iron core 37, the movable member 42, and the plunger 36 (see the arrow in FIG. 2). The plunger 36 is moved toward the piston bolt 4 (in the valve closing direction of the seat valve 32) by the magnetic flux in the region A (first magnetic circuit) between the piston bolt 4 (first fixed iron core) and the guide bore 39. The movable member 42 is attracted and moved toward the second fixed iron core 37 (in the valve opening direction of the seat valve 32) by the magnetic flux in the region B (second magnetic circuit) between the movable member 42 and the guide bore 44 of the second fixed iron core 37. It comes to be sucked.

  The first valve spring 45 urges the plunger 36 toward the second fixed iron core 37, and the second valve spring 47 urges the plunger 36 toward the piston bolt 4 via the movable member 42. The spring 47 has a larger spring force than the first valve spring 45. Thereby, in the non-energized state of the coil 38, the plunger 36 is urged toward the piston bolt 4, the seat portion 33 of the seat valve 32 is pressed against the seat surface 34, and the valve opening pressure of the seat valve 32 is desired. This is a predetermined pressure for generating a damping force necessary to ensure the steering stability. Further, the thrust generated in the movable member 42 by energizing the coil 38 is larger than the thrust generated in the plunger 36.

The operation of the present embodiment configured as described above will be described next.
During the extension stroke of the piston rod 7, the oil liquid on the cylinder upper chamber 2 </ b> A side is before the extension main valve 13 is opened, the extension side oil passage 8, the extension side orifice 21 </ b> A, the radial oil passage 20, and the axial oil. The expansion check valve 31 is opened through the passage 19, the valve chamber 27, and the radial oil passage 30, and flows to the cylinder lower chamber 2 </ b> B through the contraction-side oil passage 9. When the pressure on the cylinder upper chamber 2A side reaches the valve opening pressure of the extension side main valve 13, this opens and the oil liquid flows directly from the extension side oil passage 8 to the cylinder lower chamber 2B. At this time, the gas in the gas chamber or the reservoir expands to compensate for the volume change in the cylinder 2 as the piston rod 7 is withdrawn from the cylinder 2.

  Then, by adjusting the valve opening pressure of the seat valve 32 by the energizing current to the coil 38 of the solenoid actuator 35, the damping force is adjusted by directly controlling the flow of oil from the axial oil passage 19 to the valve chamber 27. To do. At this time, since the pressure in the axial oil passage 19 is introduced into the extension-side back pressure chamber 15 via the radial oil passage 18 and the back pressure introduction valve 17, the valve opening pressure of the extension-side main valve 13 is simultaneously controlled. be able to.

    During the contraction stroke of the piston rod 7, the oil liquid in the cylinder lower chamber 2 </ b> B side is compressed before the contraction side main valve 23 is opened. Through the axial oil passage 19 and the radial oil passage 20, the contraction-side check valve 21 is opened, and flows through the extension oil passage 8 to the cylinder upper chamber 2A. When the pressure on the cylinder lower chamber 2B side reaches the valve opening pressure of the contraction side main valve 23, this opens and the oil liquid flows directly from the contraction side oil passage 9 to the cylinder upper chamber 2A. At this time, the gas in the gas chamber or the reservoir is compressed as much as the piston rod 7 enters the cylinder 2 to compensate for the volume change in the cylinder 2.

  Then, by adjusting the valve opening pressure of the seat valve 32 by the energization current to the coil 38 of the solenoid actuator 35, the damping force is adjusted by directly controlling the flow of oil from the valve chamber 27 to the axial oil passage 19. To do. At this time, the pressure in the valve chamber 27 is introduced into the contraction side back pressure chamber 25 via the radial oil passage 29 and the back pressure introduction valve 28, so that the valve opening pressure of the contraction side main valve 23 can be controlled simultaneously. it can.

  In this way, the damping force on the expansion side and the contraction side can be adjusted by the common seat valve 32, and at the same time, the expansion side and the contraction side main valve 13 are controlled by the internal pressure of the expansion side and the contraction side back pressure chambers 15 and 25. , 23 can be adjusted, so that the adjustment range of the damping force characteristic can be widened. At this time, the seat valve 32 receives the pressure of the oil on the axial oil passage 19 side by the circular pressure receiving surface on the inner circumferential side during the expansion stroke of the piston rod 7, and the oil on the valve chamber 27 side during the contraction stroke. The fluid pressure is received by the annular pressure receiving surface on the outer peripheral side to control the flow of the oil liquid. By appropriately setting the areas of these pressure receiving surfaces, the damping force on the expansion side and the contraction side can be set to the desired characteristics. Can be set to

  Next, the relationship between the energization current to the coil 38 of the solenoid actuator 35 and the damping force will be described with reference to FIGS. In the non-energized state of the coil 38, the seat portion 33 of the seat valve 32 is pressed against the seat surface 34 by the resultant force of the first and second valve springs 45 and 47, and the valve opening pressure of the seat valve 32 becomes the predetermined pressure. Thus, a damping force necessary to ensure the desired steering stability is generated (see point P1 in FIG. 4).

  When the coil 38 is energized, the plunger 36 is attracted to the piston bolt 4 side and the movable member 42 is attracted to the second fixed iron core 37 side. At this time, since the thrust of the movable member 42 is larger than the thrust of the plunger 36, the valve opening pressure of the seat valve 32 decreases when the energization current increases. When the current becomes a predetermined current (for example, about 0.3 A) and the thrust of the movable member 42 reaches the spring force of the second valve spring 47, the damping force is minimized (see point P2 in FIG. 4). When the energization current further increases, as shown in FIG. 2, the movable member 42 moves toward the second fixed iron core 37 against the spring force of the second valve spring 47 and is fixed to the plunger 36. It is separated from 43. Thereafter, only the thrust generated by energization of the coil 38 and the spring force of the first valve spring 45 are applied to the plunger 36. Therefore, when the energization current increases, the seat valve 32 is increased by the increase in the thrust of the plunger 36. The valve opening pressure increases and the damping force increases, and reaches a predetermined current with a predetermined damping current (for example, about 1.5 A) (see point P3 in FIG. 4). At this time, when the pressure acting on the pressure receiving surface reaches the valve opening pressure, the seat valve 32 opens as shown in FIG.

  Thus, as shown in FIG. 4, when the coil 38 is not energized, a predetermined damping force is generated as shown in FIG. In a region where the energization current is small, the damping force decreases as the current increases, and thereafter, the damping force increases as the current increases. As a result, a soft-side damping force that is frequently used is generated by a small energizing current, and a hardware-side damping force that is not frequently used is generated by a large energizing current, thereby reducing power consumption. Further, when energization to the coil 38 is stopped due to the occurrence of a failure such as disconnection, a predetermined damping force can be generated to ensure the steering stability of the vehicle.

  In the present embodiment, the guide bore 39 has a cylindrical shape with the same diameter, but may have other shapes due to the configuration of the magnetic circuit. For example, as a modified example, as indicated by phantom lines in FIG. 3, the guide bore 39 is composed of a large-diameter portion close to the plunger 36 and a small-diameter portion adjacent to the large-diameter portion. It can comprise as a stepped shape which has the surface to do. According to this configuration, the magnetic flux is more concentrated than in the present embodiment, so that the efficiency of the magnetic circuit is improved.

It is a longitudinal section showing the important section of a damping force adjustment type hydraulic shock absorber concerning one embodiment of the present invention. 2 is an enlarged longitudinal sectional view of a solenoid actuator and a seat valve showing a state in which a movable member is separated from a nonmagnetic member attached to a plunger in the damping force adjusting hydraulic shock absorber shown in FIG. In the damping force adjustment type hydraulic shock absorber shown in FIG. 1, the movable member is separated from the non-magnetic member attached to the plunger, and further, the solenoid actuator and the seat valve showing a state in which the seat valve is opened are enlarged longitudinal sectional views. is there. It is a graph which shows the relationship between the energization current to the coil of the solenoid actuator of the damping force adjustment type hydraulic shock absorber shown in FIG. 1, and damping force. It is a graph which shows the relationship between the energization current to the coil of the solenoid actuator of the conventional damping force adjustment type hydraulic shock absorber, and damping force.

Explanation of symbols

  1 Damping force adjustment type hydraulic shock absorber, 2 cylinders, 3 pistons, 4 piston bolts (first fixed iron core), 7 piston rods, 32 seat valves (valve bodies, damping force adjusting valves), 34 seat surfaces (damping force adjusting valves) ), 35 solenoid actuator, 36 plunger, 37 second fixed iron core, 38 coil, 42 movable member, 45 first valve spring (first spring means), 47 second valve spring (second spring means), A region A ( First magnetic circuit), B region (second magnetic circuit)

Claims (4)

A cylinder filled with oil, a piston slidably fitted in the cylinder, a piston rod having one end connected to the piston and the other end extending outside the cylinder, and the cylinder An oil passage through which oil is circulated by sliding of the piston, a damping force adjusting valve for adjusting the damping force by controlling the flow of the oil in the oil passage, and a valve body of the damping force adjusting valve are driven. In a damping force adjustment type hydraulic shock absorber equipped with a solenoid actuator
The solenoid actuator includes a plunger coupled to the valve body, first spring means for biasing the plunger in a valve opening direction of the valve body, and a first spring biasing the plunger in a valve closing direction of the valve body. Two spring means, a movable member interposed between the plunger and the second spring means, a first magnetic circuit for biasing the plunger in a valve closing direction of the valve body by energizing a coil, and And a second magnetic circuit for biasing the movable member in a valve opening direction of the valve body. The first magnetic circuit includes a first fixed iron core that faces the one end side of the plunger and attracts the plunger in a valve closing direction of the valve body by energizing the coil, and the second magnetic circuit includes the first magnetic circuit, 2. The second fixed iron core according to claim 1, further comprising a second fixed iron core that attracts the movable member in a valve opening direction of the valve body by energizing the coil opposite to the other end side of the plunger and the movable member. Damping force adjustable hydraulic shock absorber. The damping force adjusting hydraulic shock absorber according to claim 1 or 2, wherein the damping force adjusting valve is a pressure control valve. The damping force adjusting type hydraulic shock absorber according to any one of claims 1 to 3, wherein a nonmagnetic member is interposed between the plunger and the movable member.

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