Shock absorber

Abstract

A shock absorber (D) comprises: an outer shell (1); a piston rod (2); a piston (3) that is inserted into the outer shell (1) to be movable in an axial direction; and a solenoid valve (V) accommodated in the outer shell (1). The solenoid valve (V) has: a coil (4); a first fixed iron core (5) having a recess portion (51c); a second fixed iron core (6) that is disposed below the coil (4) and spaced apart from the first fixed iron core (5); a first movable iron core (7) that is attracted to the first fixed iron core (5) by energization of the coil (4); a second movable iron core (8) that is attracted to the second fixed iron core (6) by energization of the coil (4); a spring (9) that is accommodated in the recess portion (51c) and biases the first movable iron core (7) toward the second fixed iron core (6) side; a valve member (12) that receives thrust from the second movable iron core (8); and an air release passage (P) that communicates with the recess portion (51c).

Description

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[0001] The present invention relates to a shock absorber.

[0002] A shock absorber generally comprises a cylinder, a piston rod inserted into the cylinder so as to be movable in the axial direction, a piston connected to the piston rod and inserted into the cylinder so as to be movable in the axial direction, and a damping valve provided in the piston and in a passage connecting the extension-side chamber and the compression-side chamber.The shock absorber is interposed between the body and wheels of a vehicle and damps vibrations of the body with the damping force generated when the shock absorber extends or contracts.

[0003] In order to more effectively damp vibrations in the vehicle body and improve ride comfort, some such shock absorbers use solenoid valves as damping valves, and the damping force generated during expansion and contraction can be adjusted by the current supplied to the solenoid valve (see, for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2023-157938

[0005] In conventional shock absorbers, the piston and piston rod are cylindrical, the solenoid of the solenoid valve is housed in the piston, and wiring that conducts electricity to the coil in the solenoid is housed in the piston rod, with the solenoid valve housed in the cylinder.

[0006] More specifically, the solenoid is disposed at an upper portion inside the topped cylindrical piston, and the valve portion is disposed below the solenoid. The solenoid includes a cylindrical coil, a first fixed core disposed above the coil, a second fixed core disposed below the coil, a first movable core and a second movable core disposed within the coil between the first fixed core and the second fixed core, and a coil spring interposed between the first fixed core and the first movable core to bias the first movable core toward the second movable core, and is housed inside the piston with the first fixed core facing up.

[0007] Furthermore, in a shock absorber configured in this manner, if the first movable iron core and the second movable iron core move too quickly, the damping force will change suddenly. Therefore, in order to apply a damping force to the movement of the first movable iron core and the second movable iron core and slow down the movement, a passage is provided that applies throttling resistance to the first movable iron core and the second movable iron core.

[0008] However, if air bubbles are left behind in the solenoid when the shock absorber is assembled, or if air bubbles generated in the cylinder infiltrate the inside of the coil, the upper end of the coil is blocked by the first fixed iron core, so the air bubbles remain inside the coil, and when the solenoid is driven, the air bubbles expand and contract, resulting in insufficient damping force on the first movable iron core and the second movable iron core, causing hunting and vibration of the first movable iron core and the second movable iron core, resulting in the problem of abnormal noise.

[0009] Therefore, an object of the present invention is to provide a shock absorber that can suppress the generation of abnormal noise.

[0010] In order to solve the above problems, the shock absorber of the present invention includes an outer shell, a piston rod inserted into the outer shell so as to be axially movable, a piston connected to the piston rod and inserted into the outer shell so as to be axially movable, and a solenoid valve housed in the outer shell and arranged between two working chambers provided in the outer shell, and the solenoid valve includes a coil, a case containing the coil, a first fixed iron core arranged above the coil in the axial direction, a second fixed iron core arranged below the coil in the axial direction with a gap from the first fixed iron core, and a coil arranged between the first fixed iron core and the second fixed iron core a first movable core that is attracted to the first fixed core when current is passed through the coil; a second movable core that is arranged between the first fixed core and the second fixed core and is attracted to the second fixed core when current is passed through the coil; a spring that urges the first movable core toward the second fixed core; and a valve member that receives thrust from the second movable core; the case has a cylindrical body that contains the coil, and a bridge that has a girder that spans two points on the upper end of the cylinder and contains wiring that is connected to the coil; an imaginary line passing through the center of the cross section of the girder when viewed from the axial direction of the cylinder is positioned at a position offset from the central axis of the cylinder; and an air vent passage that leads to a space between the first fixed core and the first movable core is provided.

[0011] With a shock absorber configured in this manner, even if gas enters the solenoid during assembly or operation of the shock absorber, the gas can be discharged to the outside of the solenoid through the air vent passage.

[0012] Furthermore, with a shock absorber configured in this manner, the imaginary line passing through the center of the girder in the bridge located above the cylinder is offset from the axial line of the cylinder, and the girder is positioned at a radially offset position relative to the cylinder. This makes it possible to secure a wide space on the opposite side to the offset direction of the girder to install the air vent passage that should extend upward from the recess in the first fixed iron core, and makes it possible to easily install the air vent passage while avoiding the bridge that gets in the way when installing the air vent passage.

[0013] Fig. 1 is a longitudinal sectional view of a shock absorber according to an embodiment of the present invention. Fig. 2 is an enlarged longitudinal sectional view of a solenoid of the shock absorber according to an embodiment of the present invention. Fig. 3 is a plan view of a case of the shock absorber according to an embodiment of the present invention. Fig. 4 is a perspective view of the case of the shock absorber according to an embodiment of the present invention. Fig. 5 is a characteristic diagram showing the relationship between the amount of current in the coil of the solenoid according to an embodiment of the present invention and the thrust of the solenoid.

[0014] An embodiment of the present invention will be described below with reference to the drawings. As shown in Fig. 1, a shock absorber D in one embodiment of the present invention includes a cylinder 1 as an outer shell, a piston rod 2 inserted into the cylinder 1 so as to be axially movable, a piston 3 connected to the piston rod 2 and inserted into the cylinder 1 so as to be axially movable, a solenoid valve V housed in the cylinder 1 and disposed between two working chambers, an extension-side chamber R1 and a compression-side chamber R2, provided in the cylinder 1, and an air vent passage P. This shock absorber D is installed between the body and wheels of a vehicle (not shown) to suppress vibrations of the vehicle body and wheels.

[0015] Hereinafter, each part of the shock absorber D will be described in detail. As shown in Fig. 1 , the shock absorber D includes a cylindrical cylinder 1 with a bottom as an outer tube, a piston rod 2 movably inserted into the cylinder 1, and a piston 3 connected to the piston rod 2 and movably inserted into the cylinder 1, which divides the interior of the cylinder 1 into an extension-side chamber R1 and a compression-side chamber R2 as working chambers.

[0016] A bracket (not shown) is provided at the base end of the piston rod 2, which is the upper end in Fig. 1, and the piston rod 2 is connected to a vehicle body (not shown) of a vehicle via the bracket (not shown). A bracket (not shown) is also provided at the bottom 1a of the cylinder 1, and the cylinder 1 is connected to a wheel (not shown) of the vehicle via the bracket (not shown).

[0017] In this way, shock absorber D is interposed between the vehicle body and the wheels of the vehicle. When the vehicle travels on an uneven road surface and the wheels vibrate up and down relative to the vehicle body, piston rod 2 moves in and out of cylinder 1, expanding and contracting shock absorber D, and piston 3 moves up and down (axially) within cylinder 1.

[0018] The shock absorber D also includes an annular rod guide 10 that closes the upper end of the cylinder 1 and through which the piston rod 2 is slidably inserted, forming an enclosed space inside the cylinder 1. A free piston 11 is slidably inserted into the cylinder 1 on the opposite side of the piston 3 from the piston rod 2.

[0019] A liquid chamber L is formed above the free piston 11 in the cylinder 1, and an air chamber G is formed below it. The liquid chamber L is further divided by the piston 3 into an extension-side chamber R1 on the piston rod 2 side and a compression-side chamber R2 on the piston 3 side, and the extension-side chamber R1 and the compression-side chamber R2 are each filled with a liquid. The liquid filled in the shock absorber D may be hydraulic oil, water, an aqueous solution, or other liquid. On the other hand, compressed air or a gas such as nitrogen gas is sealed in the air chamber G.

[0020] When the shock absorber D is extended, the piston rod 2 retracts from the cylinder 1, and the internal volume of the cylinder increases by the volume of the retracted piston rod 2, so the free piston 11 moves upward within the cylinder 1, expanding the air chamber G. Conversely, when the shock absorber D is retracted, the piston rod 2 advances into the cylinder 1, and the internal volume of the cylinder decreases by the volume of the advanced piston rod 2, so the free piston 11 moves downward within the cylinder 1, reducing the air chamber G.

[0021] Instead of the free piston 11, a bladder or bellows or the like may be used to separate the liquid chamber L and the air chamber G, and the configuration of the movable partition that separates the liquid chamber L and the air chamber G may be changed as appropriate.

[0022] Furthermore, in this embodiment, the shock absorber D is a single-rod, single-cylinder shock absorber, and when the shock absorber D expands or contracts, the air chamber G is expanded or contracted by the free piston 11 to compensate for the volume of the piston rod 2 moving in and out of the cylinder 1. However, the configuration for this volume compensation can also be changed as appropriate.

[0023] For example, in the case where the free piston 11 and the air chamber G are eliminated and an outer tube is provided around the cylinder 1, and a reservoir for storing liquid is formed between the cylinder 1 and the outer tube, making the shock absorber a twin-cylinder shock absorber, the reservoir may be used to compensate for the volume of the piston rod 2 moving in and out of the cylinder 1. The reservoir may be formed in a tank that is separate from the cylinder 1. The shock absorber D may also be configured as a double-rod shock absorber in which the piston 3 is attached to the center of the piston rod 2 and the ends of the piston rod 2 protrude outside the cylinder 1 from both ends of the cylinder 1.

[0024] The piston rod 2 is cylindrical and includes a rod main body 2a whose upper end protrudes outward from the cylinder 1 via the rod guide 10, and a topped cylindrical housing 2b connected to the lower end of the rod main body 2a and accommodating a solenoid S of the solenoid valve V. The housing 2b is made of a soft magnetic material and, as shown in Fig. 2, includes an annular top portion 2b1 whose inner periphery is connected to the lower end of the rod main body 2a, and a cylindrical portion 2b2 hanging down from the outer periphery of the top portion 2b1. The top portion 2b1 of the housing 2b is provided with an oblique passage 2b3 that connects the interior of the housing 2b with the expansion-side chamber R1.

[0025] As described above, the piston 3 is connected to the piston rod 2 and divides the fluid chamber L in the cylinder 1 into an extension-side chamber R1 on the piston rod 2 side and a compression-side chamber R2 on the opposite side (opposite the piston rod side). More specifically, the piston 3 includes a piston body 3a that is threadably connected to the inner periphery of the cylindrical portion 2b2 of the housing 2b of the piston rod 2 and that holds, at its lower end, a piston ring 3b that slides against the inner periphery of the cylinder 1, and a damping passage 3c that is provided in the piston body 3a and that communicates between the extension-side chamber R1 and the compression-side chamber R2. The damping passage 3c is connected to the extension-side chamber R1 via a through-hole 2b5 provided in the cylindrical portion 2b2 of the housing 2b of the piston rod 2. However, if the damping passage 3c is connected directly to the extension-side chamber R1 without passing through the through-hole 2b5, the through-hole 2b5 can be eliminated.

[0026] The solenoid valve V includes a solenoid S and a valve member 12 that is driven by the solenoid S. The solenoid S is accommodated in a housing 2b of the piston rod 2, and the valve member 12 adjusts the flow path area of ​​a damping passage 3c in the piston 3 in accordance with the magnitude of the thrust applied by the solenoid S.

[0027] The valve member 12 includes a valve element 12a provided in the damping passage 3c, an expansion-side pilot passage 12b through which the pressure of the expansion-side chamber R1 acts in a direction to open the valve element 12a, and a compression-side pilot passage 12c through which the pressure of the compression-side chamber R2 acts in the valve opening direction. The solenoid S applies a thrust to the valve element 12a in a direction to close the valve.

[0028] The solenoid valve V increases the valve opening pressure of the valve member 12 when the thrust applied to the valve body 12a by the solenoid S increases, and decreases the valve opening pressure of the valve member 12 when the thrust applied to the valve body 12a by the solenoid S decreases. Thus, the solenoid valve V can change the valve opening pressure by adjusting the thrust of the solenoid S.

[0029] Next, the solenoid S in this embodiment is configured to include a coil 4 accommodated axially within the housing 2b of the piston rod 2, a first fixed iron core 5 arranged above the coil 4, a second fixed iron core 6 arranged below the coil 4 with a gap between it and the first fixed iron core 5, a first movable iron core 7 arranged between the first fixed iron core 5 and the second fixed iron core 6 and attracted to the first fixed iron core 5 when current is passed through the coil 4, a second movable iron core 8 arranged between the first fixed iron core 5 and the second fixed iron core 6 and attracted to the second fixed iron core 6 when current is passed through the coil 4, and a spring 9 that biases the first movable iron core 7 toward the second fixed iron core 6.

[0030] Each component of the solenoid S according to this embodiment will be described in detail below. As shown in FIGS. 3 and 4 , the coil 4 is housed in a case 20 made of resin. The case 20 includes a cylindrical body 20a containing the coil 4 and a bridge 20b that spans two locations on the upper end of the cylindrical body 20a and contains wiring 21 connected to the coil 4. The case 20 is formed by housing the coil 4 in a mold and then injecting molding resin into the mold. The bridge 20b contains the coil 4 and wiring 21 connected to both ends of the coil 4. As shown in FIG. 4 , the bridge 20b includes legs 20b1 and 20b2 that rise from two locations on the upper end of the cylindrical body 20a and a beam 20b3 that connects the upper ends of the legs 20b1 and 20b2 and extends above the cylindrical body 20a. When viewed axially of the cylindrical body 20a, an imaginary line A passing through the center of the cross section of the beam 20b3 is positioned offset from the central axis B of the cylindrical body 20a. The case 20 can also be made of a non-magnetic material other than resin.

[0031] The wiring 21 extends upward from the center of the girder portion 20b3 of the bridge 20b, and although not shown, passes through the rod body 2a of the piston rod 2 and is pulled out from the upper end of the rod body 2a to the outside of the shock absorber D, and is connected to an external power source (not shown) via an externally installed drive circuit (not shown).

[0032] The first fixed core 5 is composed of two parts: a stopper 51 made of a soft magnetic material that is fitted onto the inner circumference of the upper end side of the cylindrical body 20a in the case 20, and a disk-shaped base 52 made of a soft magnetic material that is stacked on the upper end of the cylindrical body 20a and abuts against the stopper 51.

[0033] The stopper 51 is disk-shaped and includes a flange 51 a provided at the upper end of its outer periphery, an annular groove 51 b provided on the outer periphery, a recess 51 c provided in the center of its lower end, and a hole 51 d that opens from the deepest part of the recess 51 c, extends obliquely with respect to the axis, and leads to the upper end. The outer periphery of the flange 51 a of the stopper 51 is fitted into the inner periphery of the cylindrical body 20 a of the case 20, and the stopper 51 is positioned radially by the case 20 so as to be concentric with the coil 4.

[0034] The stopper 51 is inserted into the cylindrical body 20a together with a guide pipe 53 made of a non-magnetic material that fits into the inner periphery of the cylindrical body 20a on the inner periphery side of the coil 4, and the lower side of the flange 51a fits into the inner periphery of the upper end of the guide pipe 53 in Figure 2. A seal ring 54 is housed in the annular groove 51b of the stopper 51, and the seal ring 54 fits tightly against the inner periphery of the guide pipe 53, thereby sealing the gap between the stopper 51 and the guide pipe 53.

[0035] The base 52 is disk-shaped and has notches 52e that open from the side and accommodate the bridges 20b of the case 20, and holes 52f that open from the top and communicate with the notches 52e. The base 52 is attached to the case 20 by inserting the bridges 20b into the notches 52e and holes 52f from above the case 20 and then stacking it on the top end of the cylindrical body 20a. When the base 52 is stacked on the top end of the cylindrical body 20a, it abuts against the top end surface of a stopper 51 housed in the cylindrical body 20a and cooperates with the stopper 51 to form the first stationary core 5. When attached to the case 20, the first stationary core 5 is positioned above the coil 4 in the axial direction.

[0036] When the base 52 is accommodated in the housing 2b, the upper end of the base 52 abuts against the top 2b1 of the housing 2b. The base 52 has recesses 52a and 52b at its upper and lower ends, respectively, a passage 52c communicating with the recess 52a, and an orifice 52d connecting the passage 52c and the recess 52b. When the base 52 is stacked on the stopper 51, the recess 52b provided at the lower end of the base 52 is connected to the recess 51d formed in the stopper 51. The recess 52a provided at the upper end of the base 52 is located closer to the outer periphery than the recess 52b at the lower end, the passage 52c is formed at an angle, and the orifice 52d opens from the recess 52b and communicates with the lower end of the passage 52c.

[0037] Furthermore, when the base 52 is accommodated in the housing 2b, the upper end of the base 52 abuts against the top 2b1 of the housing 2b, and a recess 52a at the upper end of the base 52 communicates with the diagonal passage 2b3 provided in the top 2b1. An annular seal ring 55 is accommodated in the recess 52a, and the seal ring 55 is in close contact with the base 52 and the housing 2b, allowing communication between the diagonal passage 2b3 and the passage 52c communicating with the recess 52a, while preventing communication between the diagonal passage 2b3 and the passage 52c into the rod main body 2a through the gap between the base 52 and the top 2b1.

[0038] Furthermore, when the base 52 is stacked on the stopper 51, the lower end of the base 52 abuts against the upper end of the stopper 51, and a recess 52b at the lower end of the base 52 communicates with a hole 51d provided in the stopper 51. An annular seal ring 56 is housed in the recess 52b, and the seal ring 56 is in close contact with the base 52 and the stopper 51, allowing communication between the orifice 52d communicating with the recess 52b and the hole 51d, while preventing communication between the orifice 52d and the hole 51d and the inside of the rod main body 2a through the gap between the base 52 and the stopper 51.

[0039] In this way, the recess 51c of the stopper 51 of the first fixed core 5 is in communication with the expansion-side chamber R1 via the hole 51d provided in the stopper 51, the orifice 52d and the passage 52c provided in the base 52 of the first movable core 7, and the diagonal passage 2b3 provided in the top 2b1 of the housing 2b. In this way, in the shock absorber D of the present embodiment, the hole 51d of the stopper 51, the orifice 52d and the passage 52c provided in the base 52, and the diagonal passage 2b3 provided in the top 2b1 of the housing 2b form an air vent passage P. The air vent passage P is in communication with the space between the lower side of the first fixed core 5 and the first movable core 7.

[0040] Returning to the above, the second fixed iron core 6 is formed of a soft magnetic material and is annular as a whole, and includes a fitting portion 6a that is inserted into the inner circumference of a cylindrical body 20a that contains the coil 4 of the case 20 and fits into the guide pipe 53, a flange portion 6b that is connected to the fitting portion 6a and abuts the lower end of the cylindrical body 20a, an annular groove 6c formed on the outer circumference of the fitting portion 6a, an annular groove 6d formed on the outer circumference of the flange portion 6b, and an annular socket 6e that protrudes from the inner circumference side of the fitting portion 6a toward the first fixed iron core side.

[0041] The fitting portion 6a is fitted onto the inner periphery of the lower end of a guide pipe 53 which is fitted onto the inner periphery of the cylindrical body 20a. In this way, the second stationary core 6 is positioned radially by the case 20 via the guide pipe 53 so as to be concentric with the coil 4. A seal ring 61 is housed in the annular groove 6c of the fitting portion 6a, and the seal ring 61 is in close contact with the inner periphery of the guide pipe 53, thereby sealing the gap between the second stationary core 6 and the guide pipe 53.

[0042] The flange portion 6b is fitted into the tubular portion 2b2 of the housing 2b while abutting against the lower end of the cylindrical body 20a of the case 20. A seal ring 62 is housed in an annular groove 6d of the flange portion 6b and is in close contact with the inner periphery of the tubular portion 2b2, thereby sealing the gap between the second stationary core 6 and the housing 2b. A push rod 30, which abuts against the valve element 12a of the valve member 12, is inserted into the inner periphery of the second stationary core 6 so as to be axially movable.

[0043] As shown in Figure 2, the first movable iron core 7 has an outer tube 71 made of a soft magnetic material and including a cylindrical guide portion 71a that slides against the inner circumference of the guide pipe 53 and an annular bottom portion 71b that extends radially inward from the inner circumference of the guide portion 71a, and also has a cup-shaped inner tube 72 made of a non-magnetic material that is fitted onto the inner circumference of the bottom portion 71b of the outer tube 71.

[0044] The inner cylinder 72 has a flange 72a on the outer periphery of its upper end and a hole 72b at its bottom that connects the inside and outside of the inner cylinder 72, and is fitted onto the inner periphery of the bottom 71b of the outer cylinder 71. An annular recess 71c into which the flange 72a fits is provided on the inner periphery of the upper end of the bottom 71b of the outer cylinder 71, and when the inner cylinder 72 is attached to the outer cylinder 71, the upper end of the flange 72a and the upper end of the bottom 71b are flush with each other.

[0045] Furthermore, when the first movable core 7 is inserted into the guide pipe 53, the interior of the inner tube 72 of the first movable core 7 and the recess 51c of the stopper 51 of the first fixed core 5 face each other in the axial direction. A spring 9 is housed between the bottom of the inner tube 72 and the bottom surface of the recess 51c of the stopper 51. The spring 9 is interposed between the first movable core 7 and the first fixed core 5 in a compressed state, and constantly biases the first movable core 7 toward the second fixed core 6.

[0046] Although the first movable core 7 is in sliding contact with the guide pipe 53, the hole 72b of the inner cylinder 72 connects the space between the first fixed core 5 and the first movable core 7 to the space below the first movable core 7. Therefore, when the first movable core 7 moves axially inside the guide pipe 53, the liquid filled in the cylinder 1 passes through the hole 72b and flows in and out of the space between the first fixed core 5 and the first movable core 7. As a result, the space between the first fixed core 5 and the first movable core 7 is not sealed, and the first movable core 7 can move smoothly inside the coil 4. The cross-sectional area of ​​the hole 72b is set so as to provide resistance to the flow of liquid passing through it. Since the hole 72b provides resistance to the flow of liquid passing through it when the first movable core 7 moves up and down in the axial direction, sudden movement of the first movable core 7 is suppressed.

[0047] 2, the second movable core 8 is formed of a soft magnetic material and has a cylindrical shape with a bottom, and includes a sliding contact cylinder 8a that makes sliding contact with the inner periphery of the guide portion 71a of the first movable core 7, and a lid portion 8b that closes the lower end of the sliding contact cylinder 8a, with the outer periphery of the lower end being slidably inserted into the inner periphery of the socket 6e of the second stationary core 6, and is able to move in the axial direction between the first stationary core 5 and the second stationary core 6 within the coil 4. The lower end of the lid portion 8b of the second movable core 8 is in contact with the upper end of a push rod 30 that is axially movably inserted into the inner periphery of the second stationary core 6, and when current is passed through the coil 4 to apply thrust to the second movable core 8, the thrust acts on the valve body 12a of the valve member 12 via the push rod 30.

[0048] The second movable iron core 8 is radially aligned by the guide portion 71a of the first movable iron core 7, and the first movable iron core 7 is radially aligned by the guide pipe 53, and the guide pipe 53 is fitted into the cylindrical body 20a that contains the coil 4, so that the second movable iron core 8 and the first movable iron core 7 can move axially while maintaining coaxiality with the coil 4.

[0049] The second movable core 8 has a communication hole 8c in the cover 8b that communicates the inside and outside of the second movable core 8, and the space between the second movable core 8 and the first movable core 7 is connected to the space below the second movable core 8. Therefore, when the second movable core 8 moves axially relative to the first fixed core 5, the liquid filled in the cylinder 1 passes through the communication hole 8c and flows in and out of the space between the first movable core 7 and the second movable core 8. As a result, the space between the first movable core 7 and the second movable core 8 is not sealed, and the second movable core 8 can move smoothly within the coil 4. The cross-sectional area of ​​the communication hole 8c is set so as to provide resistance to the flow of liquid passing through it. Since the communication hole 8c provides resistance to the flow of liquid passing through it when the second movable core 8 moves up and down in the axial direction, sudden movement of the second movable core 8 is suppressed.

[0050] Furthermore, in shock absorber D of this embodiment, the inner periphery of second fixed core 6 is expanded in diameter on the upper side in Fig. 2 to form a step 6f on the inner periphery of second fixed core 6, and a coil spring 15 is provided between step 6f and cover 8b of second movable core 8. Coil spring 15 constantly biases second movable core 8 toward first fixed core 5, and when current is not applied to coil 4, second movable core 8 and first movable core 7 are compressed by the biasing force of spring 9. When current is not applied to coil 4, second movable core 8 and first movable core 7 are sandwiched between spring 9 and coil spring 15 and are brought into the closest position to each other.

[0051] An annular regulating member 16 is provided between the bottom 71b of the first movable core 7 and the sliding contact cylinder 8a of the second movable core 8 to prevent them from sticking to each other. Even when the second movable core 8 and the first movable core 7 are closest to each other, the regulating member 16 prevents direct surface contact between the bottom 71b and the sliding contact cylinder 8a. The regulating member 16 may be attached to the first movable core 7 or the second movable core 8. An annular regulating member 17 is provided on the inner periphery of the upper end of the fitting portion 6a of the second fixed core 6, and the regulating member 17 prevents the second fixed core 6 and the second movable core 8 from sticking to each other. The regulating member 17 may be attached to the second movable core 8. The regulating members 16, 17 may be made of any non-magnetic material, such as rubber, to function as a cushion.

[0052] The coil 4, first fixed iron core 5, second fixed iron core 6, first movable iron core 7, second movable iron core 8 and spring 9 that constitute the solenoid S configured as described above are housed within the housing 2b of the piston rod 2, and when the piston 3 is screwed to the threaded portion 2b4 provided on the inner circumference of the lower end of the cylindrical portion 2b2 of the housing 2b, it is sandwiched between the top portion 2b1 and the piston 3 and fixed within the housing 2b.

[0053] When no current is applied to the coil 4, the coil spring 15 is compressed by the force of the spring 9, and the first movable iron core 7 and the second movable iron core 8 are positioned at the lowest position closest to each other and closest to the second fixed iron core 6.

[0054] On the other hand, when current is passed through the coil 4, magnetic flux passes through the magnetic path formed by the first fixed core 5, the first movable core 7, the second movable core 8, the second fixed core 6, and the housing 2b, generating a magnetic force that attracts the first movable core 7 and the first fixed core 5 together, providing a thrust that moves the first movable core 7 upward, and also generating a magnetic force that attracts the second movable core 8 and the second fixed core 6 together, providing a thrust that moves the second movable core 8 downward. The magnitude of the thrust that moves the first movable core 7 upward and the magnitude of the thrust that moves the second movable core 8 downward can be adjusted depending on the amount of current passed through the coil 4. Furthermore, since the lower end of the outer periphery of the second movable iron core 8 is in sliding contact with the inside of the annular socket 6e provided on the second fixed iron core 6, when current is applied to the coil 4, the second movable iron core 8 is attracted to the second fixed iron core 6 without moving toward the first fixed iron core 5 together with the first movable iron core 7.

[0055] The restricting member 16 prevents the bottom 71b of the first movable core 7 from coming into direct contact with the sliding contact cylinder 8a of the second movable core 8, preventing the first movable core 7 and the second movable core 8 from being attracted to each other when current begins to flow through the coil 4. Therefore, when current is passed through the coil 4, the first movable core 7 and the second movable core 8 can quickly move in a direction separating them from each other. The restricting member 17 prevents the upper end of the fitting portion 6a of the second fixed core 6 from coming into direct contact with the lower end of the second movable core 8 when current is passed through the coil 4 and the second movable core 8 is attracted to the second fixed core 6, preventing the second fixed core 6 and the second movable core 8 from being attracted to each other. Therefore, when the amount of current flowing through the coil 4 is reduced, the second movable core 8 can quickly move in a direction separating it from the second fixed core 6. The contact length of the coil spring 15 is shorter than the axial length from the upper end of the regulating member 17 to the step 6f, and so even when the coil 4 is energized and the second movable core 8 is attracted to the second fixed core 6, sandwiching the regulating member 17 between them, the coil spring 15 does not fully contract and does not prevent the second movable core 8 from abutting against the regulating member 17. Although the coil spring 15 can be eliminated, providing the coil spring 15 can prevent the second movable core 8 from suddenly displacing toward the second fixed core 6 when the coil 4 is energized and the first movable core 7 is attracted to the first fixed core 5, thereby preventing the opening and closing of the solenoid valve V from becoming oscillatory due to the sudden movement of the second movable core 8.

[0056] Next, the operation of the solenoid S will be described. Fig. 5 shows the relationship between the amount of current supplied to the solenoid S and the force that the solenoid S applies to the valve body 12a. In Fig. 5, Ia is the minimum amount of current required to attract the first movable core 7 to the first fixed core 5 by energizing the coil 4 from a state in which the first movable core 7 and the second movable core 8 are closest to each other and are at the furthest position from the first fixed core 5 without energizing the coil 4, and Ib is the minimum amount of current required to maintain the attracted state between the first fixed core 5 and the first movable core 7 after energizing the coil 4 and attracting the first movable core 7 to the first fixed core 5. Ic will be described later.

[0057] First, when the amount of current supplied to the coil 4 is zero, that is, when the solenoid S is not energized, the first armature 7 is pushed down by the biasing force of the spring 9 and hits the second armature 8 via the regulating member 16, and the second armature 8 is pushed down together with the push rod 30, so that the solenoid S applies a thrust in the valve closing direction to the valve element 12a. In this way, when the solenoid S is not energized, a downward thrust is applied to the valve element 12a of the valve member 12 by the biasing force of the spring 9 via the push rod 30, the second armature 8, the regulating member 16, and the first armature 7. In the shock absorber D of this embodiment, the force pushing the valve element 12a downward is in a direction to close the valve element 12a, so when the solenoid S is not energized, the biasing force of the spring 9 applies a thrust to the valve element 12a in a direction to close the valve element 12a.

[0058] Next, when the amount of current supplied to the coil 4 is increased, the upward force attracting the first movable core 7 toward the first fixed core 5 increases, and the downward force attracting the second movable core 8 toward the second fixed core 6 also increases. In such a case, in the region where the amount of current supplied to the solenoid S is less than Ia, the biasing force of the spring 9 is transmitted to the valve body 12a, but part of the biasing force of the spring 9 that biases the first movable core 7 downward is offset by the force that attracts the first movable core 7 upward (toward the first fixed core 5). For this reason, in the region where the amount of current is less than Ia, the downward thrust that the solenoid S applies to the valve body 12a decreases as the amount of current supplied to the solenoid S increases.

[0059] On the other hand, when the amount of current supplied to the coil 4 is increased and the amount of current is equal to or greater than Ia, the first movable core 7 is attracted to and attracted to the first fixed core 5 against the biasing force of the spring 9. In this state, the biasing force of the spring 9 is not transmitted to the second movable core 8, and only the force attracting the second movable core 8 to the second fixed core 6 acts as a thrust to press the valve body 12a downward. This downward force attracting the second movable core 8 increases in proportion to the amount of current supplied to the coil 4, so in the range where the amount of current supplied to the coil 4 is equal to or greater than Ia, the more the amount of current supplied to the coil 4 is increased, the greater the downward thrust applied by the solenoid S to the valve body 12a in proportion to the amount of current.

[0060] Conversely, when the amount of current supplied to the coil 4 is reduced, the upward force attracting the first movable core 7 to the first fixed core 5 decreases, and the downward force attracting the second movable core 8 to the second fixed core 6 also decreases. Even in such a case, in the region where the amount of current supplied to the coil 4 is Ib or more, the first movable core 7 is attracted to the first fixed core 5, and a state is maintained in which the biasing force of the spring 9 is not transmitted to the second movable core 8. Therefore, in the region where the amount of current supplied to the coil 4 is Ib or more, the more the amount of current supplied to the coil 4 is reduced, the smaller the downward thrust applied to the valve body 12a by the solenoid S becomes in proportion to the amount of current.

[0061] On the other hand, when the amount of current supplied to the coil 4 is reduced and the amount of current is less than Ib, the attracting state between the first movable core 7 and the first fixed core 5 is released by the biasing force of the spring 9, and the biasing force of the spring 9 is transmitted to the second movable core 8. Therefore, in the area where the amount of current is less than Ib, the more the amount of current supplied to the coil 4 is reduced, the greater the downward thrust that the solenoid S applies to the valve body 12a.

[0062] As can be seen from Fig. 5, Ib, which is the minimum amount of current required to maintain attraction between the first movable core 7 and the first fixed core 5, is smaller than Ia, which is the minimum amount of current required to attract the separated first movable core 7 to the first fixed core 5 (Ia > Ib). For this reason, the characteristic of the force applied to the valve body 12a by the solenoid S relative to the amount of current supplied to the coil 4 exhibits hysteresis. Note that in Fig. 5, the region where the amount of current supplied to the solenoid S is small is exaggerated for ease of understanding.

[0063] In this embodiment, when controlling the thrust applied by the solenoid S to the valve disc 12a by controlling the amount of current supplied to the coil 4, a current of Ia or more is first supplied to attract the first movable core 7 to the first fixed core 5, and then the amount of current supplied to the coil 4 is controlled within a range of Ic or more, which is larger than Ib. As a result, during normal operation when the amount of current supplied to the solenoid S is controlled, the state in which the first movable core 7 is attracted to the first fixed core 5 is maintained, so that the amount of current supplied to the solenoid S and the downward thrust applied by the solenoid S to the valve disc 12a are proportional to each other, and the thrust increases as the amount of current supplied to the coil 4 increases.

[0064] In this way, in the shock absorber D of this embodiment, the amount of current supplied to the coil 4 and the thrust applied by the solenoid S to the valve body 12a are proportional to each other, and the thrust increases as the amount of current supplied increases, and decreases as the amount of current supplied decreases.

[0065] On the other hand, in the event of a failure where the solenoid S is de-energized, the valve element 12a is urged downward by the spring 9 of the solenoid S, and the urging force is determined in advance according to the specifications of the spring 9, such as the spring constant. Furthermore, the direction of the urging force of the spring 9 that urges the valve element 12a in the event of a failure (when not energized) is the same as the direction of the thrust that the solenoid S exerts on the valve element 12a in the normal state.

[0066] Next, the operation of the shock absorber D of this embodiment will be described. When the shock absorber D extends and the piston 3 moves upward in FIG. 1 relative to the cylinder 1, the liquid in the expansion-side chamber R1, which is compressed by the movement of the piston 3 relative to the cylinder 1, tries to move through the damping passage 3c to the expanded compression-side chamber R2. The pressure in the expansion-side chamber R1 increases due to the compression of the expansion-side chamber R1, and when the pressure of the expansion-side chamber R1 acting on the valve body 12a via the expansion-side pilot passage 12b reaches the valve opening pressure of the solenoid valve V, the valve body 12a opens to open the damping passage 3c, allowing the liquid in the expansion-side chamber R1 to move to the compression-side chamber R2 via the damping passage 3c, and the solenoid valve V provides resistance to the flow of the liquid.

[0067] In this way, when the shock absorber D is in an extending operation, the pressure in the expansion-side chamber R1 rises and becomes higher than the pressure in the contraction-side chamber R2, so that the force pushing down the piston 3 increases, and the shock absorber D generates a damping force that hinders the extending operation. The solenoid valve V can adjust the valve opening pressure depending on the amount of current supplied to the coil 4 in the solenoid S, so that the damping force generated when the shock absorber D is in an extending operation can be adjusted by the amount of current supplied to the coil 4.

[0068] When the shock absorber D is extended, the piston rod 2 retreats from the cylinder 1, reducing the volume displaced by the piston rod 2 within the cylinder 1. However, the free piston 11 moves upward within the cylinder 1, expanding the air chamber G, thereby compensating for this reduction in volume.

[0069] 1 relative to the cylinder 1, the liquid in the compression-side chamber R2, which is compressed by the movement of the piston 3 relative to the cylinder 1, tries to move through the damping passage 3c to the expanded expansion-side chamber R1. The pressure in the compression-side chamber R2 increases due to the compression of the compression-side chamber R2, and when the pressure in the compression-side chamber R2 acting on the valve body 12a via the compression-side pilot passage 12c reaches the valve opening pressure of the solenoid valve V, the valve body 12a opens to open the damping passage 3c, allowing the liquid in the compression-side chamber R2 to move to the expansion-side chamber R1 via the damping passage 3c, and the solenoid valve V provides resistance to the flow of the liquid.

[0070] In this way, when the shock absorber D is contracting, the pressure in the compression-side chamber R2 rises and becomes higher than the pressure in the extension-side chamber R1, so that the force pushing up the piston 3 increases, and the shock absorber D generates a damping force that hinders the contraction. The solenoid valve V can adjust the valve opening pressure depending on the amount of current supplied to the coil 4 in the solenoid S, so the damping force generated when the shock absorber D is contracting can be adjusted by the amount of current supplied to the coil 4.

[0071] When the shock absorber D is contracting, the piston rod 2 enters the cylinder 1, increasing the volume displaced by the piston rod 2 within the cylinder 1, but the free piston 11 moves downward within the cylinder 1, thereby reducing the air chamber G, thereby compensating for this increase in volume.

[0072] Here, there are cases where air bubbles are left behind in the guide pipe 53 of the solenoid S when the shock absorber D is assembled, or where air bubbles are generated in the liquid in the cylinder 1 when the shock absorber D is activated and enter the solenoid S. Because gas is lighter than liquid, as the first movable iron core 7 and second movable iron core 8 of the solenoid S continue to operate, the gas will eventually enter the space between the first fixed iron core 5 and the first movable iron core 7 via the communication hole 8c and the hole 72b, and will eventually be taken up into the recess 51c in the first movable iron core 7, which is located at the topmost position inside the solenoid S.

[0073] If gas remains in the recess 51c for a long time, as in conventional shock absorbers, the gas behaves as an elastic body, making it difficult for liquid to pass through the communicating hole 8c and the hole 72b when the first movable core 7 and the second movable core 8 are displaced, reducing the resistance to the movement of the first movable core 7 and the second movable core 8, causing the first movable core 7 and the second movable core 8 to move suddenly. However, in the shock absorber D of the present embodiment, the recess 51c is connected to the expansion-side chamber R1 via the air vent passage P extending upward from the recess 51c, so that even if gas enters the solenoid S, the gas can be discharged from the recess 51c to the expansion-side chamber R1. Therefore, in the shock absorber D of this embodiment, unlike conventional shock absorbers, appropriate resistance is provided to the movement of the first movable iron core 7 and the second movable iron core 8 when the solenoid S is driven, so that the first movable iron core 7 and the second movable iron core 8 do not move suddenly, and vibration of the first movable iron core 7 and the second movable iron core 8 due to hunting and the generation of abnormal noise are suppressed.

[0074] In addition, the gap between the guide pipe 53 and the first fixed iron core 5 in the solenoid S is sealed by a seal ring 54, the gap between the guide pipe 53 and the second fixed iron core 6 is sealed by a seal ring 61, and the gap between the second fixed iron core 6 and the housing 2b is also sealed by a seal ring 61, so that gas does not leak into the rod main body 2a of the piston rod 2 by passing between the outer periphery of the solenoid S and the housing 2b.

[0075] As described above, the shock absorber D of this embodiment includes the cylinder (outer shell) 1, the piston rod 2 inserted into the cylinder (outer shell) 1 so as to be movable in the axial direction, the piston 3 connected to the piston rod 2 and inserted into the cylinder (outer shell) 1 so as to be movable in the axial direction, and the solenoid valve V accommodated in the cylinder (outer shell) 1 and arranged between the expansion-side chamber (operating chamber) R1 and the compression-side chamber (operating chamber) R2 provided in the cylinder (outer shell) 1, and the solenoid valve V includes the coil 4 and a first fixed iron core arranged above the coil 4 in the axial direction. 5, a second fixed core 6 arranged axially below the coil 4 with a gap therebetween, a first movable core 7 arranged between the first fixed core 5 and the second fixed core 6 and attracted to the first fixed core 5 when current is passed through the coil 4, a second movable core 8 arranged between the first fixed core 5 and the second fixed core 6 and attracted to the second fixed core 6 when current is passed through the coil 4, a spring 9 that urges the first movable core 7 toward the second fixed core 6, and a valve member 12 that receives thrust from the second movable core 8, and is provided with an air vent passage P that leads to the space between the first fixed core 5 and the first movable core 7.

[0076] According to the shock absorber D configured in this manner, even if gas enters the solenoid S during assembly or operation of the shock absorber D, the gas can be discharged to the outside of the solenoid S through the air vent passage P.

[0077] Therefore, according to the shock absorber D of this embodiment, even if gas enters the solenoid S, the gas can be discharged outside the solenoid S, so that vibration of the first movable iron core 7 and the second movable iron core 8 can be suppressed when the solenoid S is driven, and the generation of abnormal noise can also be suppressed.

[0078] Furthermore, in the shock absorber D of this embodiment, the first fixed core 5 has a recess 51c at the coil side end, the upper end of the spring 9 is housed in the recess 51c, and the air vent passage P may be connected to the recess 51c of the first fixed core 5. With the shock absorber D configured in this manner, gas can be taken into the recess 51c of the first fixed core 5 and discharged to outside the solenoid S via the air vent passage P.

[0079] Furthermore, it is preferable that the air vent passage P opens at the upper end of the recess 51c (the bottom that forms the recess 51c) so that gas within the recess 51c can be discharged without leakage, but it may also open at the side wall that forms the recess 51c. Even in this case, when the first movable iron core 7 moves in a direction approaching the first fixed iron core 5, liquid can flow from the recess 51c to the outside of the solenoid S via the air vent passage P, and gas can be discharged to the outside of the solenoid S together with the liquid.

[0080] Furthermore, in the shock absorber D of this embodiment, the solenoid valve V is a cylindrical member having a top 2b1 at its upper end, and includes a housing 2b that houses therein the coil 4, the first fixed core 5, the second fixed core 6, the first movable core 7, the second movable core 8, and the spring 9, and the air vent passage P opens from the recess 51c, passes through the top 2b1 of the housing 2b, and leads to the upper end of the top 2b1, and is provided with an orifice 52d midway. According to the shock absorber D configured in this manner, the air vent passage P opens from the recess 51c, passes through the top 2b1 of the housing 2b that covers the solenoid S, and leads to the upper end of the top 2b1, and is positioned above the recess 51c, so that gas that has been taken in the recess 51c can be efficiently discharged to the outside of the housing 2b. Furthermore, since the orifice 52d is provided in the air vent passage P, it is possible to prevent liquid from easily moving back and forth between the expansion-side chamber R1 and the recess 51c via the air vent passage P when the first movable iron core 7 moves relative to the first fixed iron core 5. Even if the air vent passage P is provided, the movement of the first movable iron core 7 can be slowed down, and vibration and abnormal noise of the first movable iron core 7 and the second movable iron core 8 can be effectively suppressed when the solenoid S is driven.

[0081] The first fixed core 5 includes a stopper 51 housed within the coil 4 and a base 52 stacked on the upper end of the coil 4 and abutting against the stopper 51, and the hole 51d provided in the stopper 51 and the passage 52c and orifice 52d provided in the base 52 form part of the air vent passage P. With the shock absorber D configured in this manner, in order to ensure that the biasing force of the spring 9 of the first movable core 7 acts evenly in the radial direction, it is necessary to provide the air vent passage P in the recess 51c that houses the spring 9 and must be provided in the center of the stopper 51, while avoiding the wiring 21 of the coil 4. However, because the air vent passage P can be formed by drilling holes in each of the two components, the stopper 51 and the base 52, it is also easy to change the extension direction of the air vent passage P midway, and the air vent passage P can be easily provided in the first fixed core 5. Furthermore, when installing the orifice 52d, the orifice 52d can be installed perpendicular to the lower surface of the base 52, which facilitates the process of installing the orifice 52d formed as a thin hole. Although the orifice 52d is provided in the base 52, it may also be provided in the stopper 51, or it may be provided in the housing 2b instead of being installed in the first fixed core 5. Furthermore, although the first fixed core 5 is made up of two parts, the stopper 51 and the base 52, it may also be made up of a single part.

[0082] In addition, in the shock absorber D of this embodiment, the solenoid valve V has a case 20 that contains the coil 4, and the case 20 comprises a cylindrical body 20a that contains the coil 4 and a bridge 20b that has a girder 20b3 that spans two points on the upper end of the cylindrical body 20a and contains wiring 21 that is connected to the coil 4, and an imaginary line A that passes through the center of the cross section of the girder 20b3 when viewed from the axial direction of the cylindrical body 20a is positioned at a position offset from the central axis B of the cylindrical body 20a.

[0083] In the shock absorber D configured in this manner, an imaginary line A passing through the center of the girder 20b3 of the bridge 20b arranged above the cylindrical body 20a is offset from the central axis B of the cylindrical body 20a, and the girder 20b3 is arranged at a radially offset position relative to the cylindrical body 20a. This makes it possible to secure a wide space on the opposite side to the offset direction of the girder 20b3 for installing the air vent passage P that should extend upward from the recess 51c in the first fixed core 5, and makes it possible to easily install the air vent passage P while avoiding the bridge 20b, which gets in the way of installing the air vent passage P.

[0084] Furthermore, the bridge 20b in the shock absorber D of this embodiment has two legs 20b1 and 20b2 that rise from two positions on the upper end of the cylindrical body 20a and have the girder 20b3 connected to the upper end. According to the shock absorber D configured in this manner, the bridge 20b has the legs 20b1 and 20b2, so that the girder 20b3 can be positioned at a distance from the cylindrical body 20a. This makes it easier to confirm that the first fixed core 5 inserted into the cylindrical body 20a is positioned in the correct position, thereby reducing assembly defects.

[0085] As described above, the first movable iron core 7 and the second movable iron core 8 are cylindrical with a bottom, but the shape and structure of the first movable iron core 7 and the second movable iron core 8 are not limited to those described above and can be modified in design.

[0086] The valve member 12 in the solenoid valve V is not limited to the configuration shown in the figure, and may be a valve that can adjust the valve opening pressure and flow path area by applying thrust from the solenoid S, or may be a control valve that controls the upstream pressure. Furthermore, in the shock absorber D of this embodiment, the valve member 12 includes a valve body 12a provided in the damping passage 3c to provide resistance to the flow of liquid passing through the damping passage 3c, but may also be configured to include a damping valve provided in the passage and a control valve that adjusts the back pressure applied to the damping valve in accordance with the thrust from the solenoid S.

[0087] Furthermore, in the illustrated embodiment, the shock absorber D is a single-cylinder shock absorber with the cylinder 1 as the outer shell, but it may also be a double-cylinder shock absorber that has an outer shell that covers the outer periphery of the cylinder 1 and a reservoir between the cylinder 1 and the outer shell, and the solenoid valve V may be installed between the compression side chamber R2 and the reservoir as working chambers, as long as it is housed within the outer shell.

[0088] Although the preferred embodiment of the present invention has been described in detail, modifications, variations and changes can be made thereto without departing from the scope of the appended claims.

[0089] DESCRIPTION OF SYMBOLS 1: Cylinder (outer shell), 2: Piston rod, 2b: Housing, 2b1: Top, 3: Piston, 4: Coil, 5: First fixed core, 6: Second fixed core, 7: First movable core, 8: Second movable core, 9: Spring, 12: Valve member, 20: Case, 20a: Cylinder, 20b: Bridge, 20b3: Beam, 21: Wiring, 51c: Recess, 52d: Orifice, A: Virtual line, B: Central axis, D: Shock absorber, P: Air vent passage, R1: Expansion side chamber (operating chamber), R2: Compression side chamber (operating chamber), S: Solenoid, V: Solenoid valve

Claims

1. A shock absorber comprising: an outer shell; a piston rod inserted into the outer shell so as to be axially movable; a piston connected to the piston rod and inserted into the outer shell so as to be axially movable; and a solenoid valve housed in the outer shell and arranged between two operating chambers provided in the outer shell, wherein the solenoid valve has: a coil; a case containing the coil; a first fixed iron core arranged axially above the coil; a second fixed iron core arranged axially below the coil with a gap from the first fixed iron core; a first movable iron core arranged between the first fixed iron core and the second fixed iron core and attracted to the first fixed iron core when current is passed through the coil; a second movable iron core arranged between the first fixed iron core and the second fixed iron core and attracted to the second fixed iron core when current is passed through the coil; a spring that urges the first movable iron core towards the second fixed iron core; and a valve member that receives thrust from the second movable iron core, wherein the case a shock absorber comprising: a cylinder containing the coil; and a bridge having a girder spanning two points on the upper end of the cylinder and containing wiring connected to the coil, wherein an imaginary line passing through the center of the cross section of the girder as viewed from the axial direction of the cylinder is positioned at a position offset from the central axis of the cylinder; and an air vent passage leading to a space between the first fixed iron core and the first movable iron core is provided.

2. A shock absorber according to claim 1, wherein the first fixed core has a recess at the coil side end, the upper end of the spring is housed in the recess, and the air vent passage is in communication with the recess.

3. A shock absorber as claimed in claim 1, wherein the solenoid valve is a cylindrical shape with a top at its upper end and has a housing that houses the coil, the first fixed iron core, the second fixed iron core, the first movable iron core, the second movable iron core and the spring inside, and the air vent passage opens from the recess, passes through the top of the housing and leads to the upper end of the top, with an orifice located midway.

4. A shock absorber according to claim 1, wherein the air vent passage is connected to the upper end of the recess.

5. A shock absorber as claimed in claim 1, wherein the first fixed core has a stopper housed within the coil and provided with the recess, and a base stacked on the upper end of the coil and abutting against the stopper, and a part of the air vent passage is formed by a hole provided in the stopper, a passage provided in the base, and an orifice provided in the stopper or the base.

6. A shock absorber according to claim 1, wherein the bridge has two legs that rise from two points on the upper end of the cylindrical body and whose upper ends are connected to the girder.

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