Shock absorbers with damping force control

Abstract

Shock absorber (1) with damping force control comprising: a cylinder (2) which has a fluid sealed inside it; a piston (5) which is slidably fitted in the cylinder (2); a piston rod (6) which is connected at one end to the piston (5), the other end of the piston rod (6) extending outwards with respect to the cylinder (2); a main valve (27) that generates a damping force by controlling a fluid flow induced by a displacement of the piston (5) in the cylinder (2); a pilot chamber (51) which applies pressure therein to the main valve (27) in a direction to close the main valve (27); an inlet passage (49, 50, 53) that introduces the fluid into the pre-control chamber (51); a pilot control passage (52, 55, 56, 57) which puts the pilot control chamber (51) and a downstream side of the main valve (27) into communication; a control valve (28) provided in the pilot passage (52, 55, 56, 57), wherein the control valve (28) has a valve body (58) which is pushed by a thrust element (67) in a direction to open the control valve (28), and an actuator (S) which moves the valve body (58) in a direction to close the control valve (28) by means of a thrust from a solenoid; and a fail-safe valve (29) which is provided in the pilot passage (52, 55, 56, 57) on a downstream side of the control valve (28), wherein the valve body (58) of the control valve (28) is provided in a valve chamber (55), the valve chamber (55) opening at one end into the pilot chamber (51), and another end of the valve chamber (55) opening downstream of the fail-safe valve (29), wherein one end of the valve chamber (55) is selectively opened and closed by one end of the valve body (58), wherein another end of the valve chamber (55) is opened and closed by both the fail-safe valve (29) and another end of the valve body (58), wherein the fail-safe valve (29) is adjacent to the valve body (58) to close the pilot passage (52, 55, 56, 57) when the valve body (58) is pushed by the thrust element (67) and moves in the direction to open the control valve (28), wherein the fail-safe valve (29) separates from the valve body (58) to open the pilot passage (52, 55, 56, 57) when the pressure in the pilot chamber (51) reaches a certain pressure.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a damping force control type shock absorber capable of controlling the damping force.

[0002] Shock absorbers mounted on suspension systems of automobiles or other vehicles include a damping force control shock absorber designed to appropriately adjust the damping force according to road conditions, vehicle running conditions, etc. to improve ride quality and steering stability.

[0003] Generally, the damping force control shock absorber includes a cylinder sealingly containing a fluid. A piston connected to a piston rod is slidably fitted into the cylinder. A damping force control mechanism is provided in a passage through which the fluid flows in response to displacement of the piston in the cylinder. Japanese Patent Application Publication No. JP 2001-12534 A discloses a damping force control mechanism that generates a damping force by controlling the fluid flow through a damping control valve and further adjusts the damping force by controlling an actuator-operated control valve provided in a passage through which the control pressure is discharged.

[0004] However, the damping force control mechanism disclosed in Japanese Patent Application Publication No. JP 2001-12534 A suffers from the problem that the control valve is undesirably closed when the actuator is not driven due to a failure or the like, resulting in the damping force becoming excessively large.

[0005] JP H07-269 627 A, US 2009 / 0 242 339 A1 and US 6 182 805 B1 describe further shock absorbers. SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a damping force control type shock absorber which has a simple structure and is capable of obtaining an appropriate damping force even when no electric current is supplied to an actuator.

[0007] The present invention is described in claim 1 and provides a damping force control shock absorber comprising a cylinder sealed with a fluid therein, a piston slidably fitted in the cylinder, and a piston rod connected to the piston at one end. The other end of the piston rod extends outwardly of the cylinder.The damping force control shock absorber further includes a main valve that generates a damping force by controlling the fluid flow induced by displacement of the piston in the cylinder, a pilot chamber that applies the pressure therein to the main valve in a direction to close the main valve, an inlet passage that introduces the fluid into the pilot chamber, a pilot passage that communicates between the pilot chamber and the downstream side of the main valve, and a control valve provided in the pilot passage. The control valve includes a valve body that is urged by an urging member in a direction to open the control valve, and an actuator that moves the valve body in a direction to close the control valve by means of a push from a solenoid.A fail-safe valve abuts the valve body to close the pilot passage when the valve body, urged by the urging element, moves in the direction to open the control valve. The fail-safe valve separates from the valve body to open the pilot passage when the pressure in the pilot chamber reaches a certain value. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an enlarged longitudinal sectional view of a damping force generating mechanism which is a main part of the damping force control type shock absorber according to a first embodiment of the present invention. Fig. 2 is a longitudinal sectional view of the damping force control type shock absorber according to the first embodiment of the present invention. Fig. 3 is an enlarged longitudinal sectional view of a damping force generating mechanism which is a main part of a damping force control type shock absorber according to a second embodiment of the present invention. Fig. 4 is a longitudinal sectional view of a damping force generating mechanism which is a main part of a damping force control type shock absorber according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0009] A first embodiment of the present invention will be described with reference to the Fig. 1 and Fig. 2 described.

[0010] As it is in Fig. 2, a damping force control shock absorber 1 according to this embodiment has a dual-tube structure including a cylinder 2 and an outer tube 3 provided outside the cylinder 2. A reservoir 4 is formed between the cylinder 2 and the outer tube 3. A piston 5 is slidably fitted into the cylinder 2. The piston 5 divides the interior of the cylinder 2 into two chambers, that is, an upper cylinder chamber 2A and a lower cylinder chamber 2B. The piston 5 is connected to one end of the piston rod 6 by means of a nut 7. The other end portion of the piston rod 6 extends through the upper cylinder chamber 2A and further through a rod guide 8 and an oil seal 9 fitted to the upper end portion of the dual-tube structure including the cylinder 2 and the outer tube 3, and protrudes outwardly beyond the cylinder 2.A base valve 10 is provided in the lower end portion of the cylinder 2 to separate the lower cylinder chamber 2B and the reservoir from each other.

[0011] Piston 5 is provided with passages 11 and 12 for communication between the upper and lower cylinder chambers 2A and 2B. Passage 12 is provided with a check valve 13 that only allows fluid flow from the lower cylinder chamber 2B to the upper cylinder chamber 2A. Passage 11 is provided with a disc valve 14 that opens when the fluid pressure in the upper cylinder chamber 2A reaches a certain pressure to relieve the fluid pressure to the lower cylinder chamber 2B.

[0012] The base valve 10 is provided with passages 15 and 16 for communication between the lower cylinder chamber 2B and the reservoir 4. The passage 15 is provided with a check valve 17 that only allows fluid flow from the reservoir 4 to the lower cylinder chamber 2B. The passage 16 is provided with a disc valve 18 that opens when the fluid pressure in the lower cylinder chamber 2B reaches a certain pressure to relieve the fluid pressure to the reservoir 4. As the hydraulic fluid, hydraulic oil is sealed in the cylinder 2, and the hydraulic oil and a gas are sealed in the reservoir 4.

[0013] The cylinder 2 has a separator tube 20 fitted thereover with sealing members 19 provided therebetween at the upper and lower ends of the cylinder 2. Thus, an annular passage 21 is formed between the cylinder 2 and the separator tube 20. The annular passage 21 communicates with the upper cylinder chamber 2A via a passage 22 provided in a side wall of the cylinder 2 near the upper end thereof. The separator tube 20 has a small-diameter opening 23 protruding from a lower part of the side wall thereof. The side wall of the outer tube 3 is provided with a large-diameter opening 24 in substantially concentric relationship with the opening 23. A damping force generating mechanism 25 is attached to the opening 24 of the side wall of the outer tube 3.

[0014] Next, the damping force generating mechanism 25 will be described with reference mainly to Fig. 1 explained.

[0015] As it is in Fig. As shown in Figure 1, the damping force generating mechanism 25 includes a circular cylindrical housing 26 attached to the opening 24 of the outer tube 3. The housing 26 is provided with a pilot main valve (back pressure type) 27 and a pilot valve 28, which is a solenoid-operated pressure control valve that controls the valve opening pressure of the main valve 27. The damping force generating mechanism 25 further includes a fail-safe valve 29 provided downstream of the pilot valve 28. The fail-safe valve 29 operates when a failure occurs.

[0016] The housing 26 includes, in order from the orifice 24 side, an annular passage plate 30, a convex passage member 31, an annular main valve member 32, a convex orifice passage member 33, a circular cylindrical pilot valve member 34 having a bottom in the center thereof, an annular retainer member 35, and a circular cylindrical solenoid housing 36. These members are arranged to abut against each other and are secured by connecting the solenoid housing 36 to the housing 26 by means of a nut 37.

[0017] The passage plate 30 is secured by abutting against an inner flange 26A formed at the end portion of the housing 26. The passage plate 30 has a plurality of passages 38 extending axially therethrough to communicate between the reservoir 4 and a chamber 26B in the housing 26. The passage member 31 is secured to a distal end portion of a small diameter thereof extending through the passage plate 30 and to a shoulder of a large diameter thereof abutting against the passage plate 30. The distal end portion of the passage member 31 is fluid-tightly fitted into the opening 23 of the separation tube 20 via a sealing member 39, whereby a passage 40 extending axially through the passage member 31 is in communication with the annular passage 21.The passage member 31 has an annular groove 41 formed at the end of the large-diameter portion thereof. The annular groove 41 communicates with the passage 40 via a radially cutout portion 42.

[0018] The main valve element 32 is secured with an end portion thereof abutting against the large diameter portion of the passage member 31. The area of ​​abutment contact between the main valve element 32 and the passage member 31 is sealed with a sealing member 43 provided in the annular groove 41. The main valve element 32 is provided with a plurality of circumferentially spaced passages 44 extending axially therethrough. The passages 44 communicate with the annular groove 41 of the passage member 31. The other end of the main valve element 32 has an annular seat portion 45 projecting from the outer periphery of the openings of the passages 44, and further has an annular clamp portion 46 projecting from the inner periphery of the openings of the passages 44.

[0019] The outer peripheral portion of a disc valve 47 constituting the main valve 27 is seated on the seat portion 45 of the main valve element 32. The inner peripheral portion of the disc valve 47 is clamped between the clamping portion 46 and a shoulder of a large-diameter portion of the orifice passage member 33. An annular sliding seal member 48 is secured to the outer peripheral portion of the rear side of the disc valve 47. The convex orifice passage member 33 is secured to a small-diameter portion thereof fitted into an opening in the center of the main valve element 32 and to the shoulder of the large-diameter portion thereof abutting against the disc valve 47. The orifice passage member 33 has a passage 49 extending axially therethrough.The passage 49 is in communication with the passage 40 of the passage member 31 via a fixed opening 50 formed in the distal end portion of the small diameter portion of the opening passage member 33.

[0020] The pilot valve element 34 has a substantially circular cylindrical structure having a bottom 34A at its center, and is secured to one end of the bottom 34A abutting against the orifice passage member 33. The sliding seal member 48 of the disc valve 47 is slidably and fluidly fitted to the inner peripheral surface of a circular cylindrical portion at one end of the pilot valve element 34 to form a pilot chamber 41 on the back side of the disc valve 47. The disc valve 47 opens upon receiving the pressure in the passage 44 to place the passages 44 in communication with the chamber 26B in the housing 26, which is located downstream of the passage 44. The pressure in the pilot chamber 41 acts on the disc valve 47 in the direction of closing the disc valve 47.The pilot valve element 34 has a port 52 extending through the center of the bottom 34A. The port 52 communicates with the passage 49 of the orifice passage member 33. The pilot chamber 51 communicates with the passage 49 via a cutout portion 53. The cutout portion 53 is formed in a part of the orifice passage member 33 adjacent to the bottom 34A of the pilot valve element 34. The cutout portion 53, the passage 49, and the fixed orifice 50 communicate to form an inlet passage for introducing hydraulic oil into the pilot chamber 51.

[0021] The retaining member 35 has an annular protrusion 54 formed on the outer periphery of one end thereof. The annular protrusion 54 is secured by abutting against the end of a circular cylindrical portion of the other end of the pilot valve member 34, thereby forming a valve chamber 55 in the cylindrical portion of the pilot valve member 34. The pilot valve member 34 and the retaining member 35 are radially positioned by fitting a circular cylindrical portion of the solenoid housing 36, which is fitted into the housing 26, to the outer peripheral portion of the retaining member 35.The valve chamber 55 communicates with the chamber 26B in the housing 26 via a cutout portion 56 formed in the annular projection 54 of the retaining member 35, a cutout portion (not shown) partially circumferentially formed in a fail-safe disk 40, and a cutout portion 57 formed in the other periphery of the cylindrical portion of the pilot valve member 34. The port 52, the valve chamber 55, and the cutout portions 56 and 57 communicate to form a pilot passage that puts the pilot chamber 51 into communication with the chamber 26B downstream of the disc valve 47 (main valve 27). The valve chamber 55 is provided with a valve body 58 of the pilot valve 28, which is a pressure control valve for selectively opening and closing the port 52.

[0022] The solenoid housing 36 contains a coil 59, cores 60 and 61 inserted into the coil 59, a plunger 62 guided by the cores 60 and 61, and a hollow actuator rod 63 connected to the plunger 62. These elements, housed in the solenoid housing 36, constitute a solenoid actuator S. The distal end portion of the actuator rod 64 extends through the retaining member 35 and is connected to the valve body 58 in the valve chamber 55. When the coil 59 is supplied with electrical current via a lead wire 64, an axial thrust is generated in the plunger 62 in accordance with the supplied electrical current.

[0023] The valve body 58 has an annular seat portion 65 formed at a tapered distal end portion thereof facing the port 52 of the pilot valve element 34. The seat portion 65 selectively seats and releases from a seat surface 66 around the port 52, thereby opening and closing the port 52. The valve body 58 is urged by the spring force of a valve spring 67 (compression coil spring), which is an urging element provided between the valve body 58 and the bottom 34A of the pilot valve element 34. Thus, the valve body 58 is normally in a retracted position, as shown in Fig. 1, i.e., a valve opening position or an open valve position. Meanwhile, when the coil 59 is energized, a thrust is generated in the piston 62, causing the valve body 58 to advance against the spring force of the valve spring 67. As a result, the seat portion 65 seats on the seat surface 66 to close the port 52. The pressure in the port 52, i.e., in the pilot chamber 51, is controlled by controlling the valve opening pressure of the valve body 58 with respect to the port 52 via the thrust of the piston 52, i.e., the electric current supplied to the coil 59.

[0024] The valve body 58 has a hollow actuator rod 63 extending therethrough. When the valve body 58 is in a closed valve position, i.e., when the seat portion 65 is seated on the seat surface 66, a passage 63A in the actuator rod 63 opens into the port 52 to provide communication between the port 52 and a chamber 61A in the core 61 on the back of the actuator rod 63. As a result, the pressure-receiving surface area of ​​the valve body 58 where the hydraulic oil passing through the port 52 acts on the valve body 58 is reduced to enable an increase in the variable range of the valve opening pressure of the valve body 58 with respect to the thrust of the piston 62.In order to increase the variable range of the damping force while maintaining the solenoid thrust, it is necessary to reduce the pressure receiving surface area of ​​the valve body 58 or enlarge the diameter of the port 52 with a view to reducing a soft damping force. In this embodiment, the port 52 communicates with the chamber 61A in the core 61 on the back of the actuator rod 63 via the passage 63A to significantly reduce the pressure receiving surface area of ​​the valve body 58. On the other hand, the diameter of the port 52 increases, and the surface area over which the valve body 58 faces the port 52 is increased. Consequently, it is also possible to reduce the soft damping force. As a result, the variable range of the damping force while maintaining the solenoid thrust can be increased.

[0025] The following is an explanation of the fail-safe valve 29, ie a combination of an orifice 68A and a fail-safe disk 70.

[0026] The valve body 58 has an annular seat portion 58A protruding from the outer periphery of the rear end surface thereof. At least one annular seat disc 68, i.e., either one seat disc 68 or a plurality of stacked annular seat discs 68, abuts the seat portion 58A. The seat disc 68 is secured to the valve body 58, with an inner peripheral portion thereof abutting a spring washer 69 attached to the actuator rod 63. An annular fail-safe washer 70 is clamped at its outer peripheral portion between the end of the cylindrical portion of the pilot valve member 34 and the annular projection 54 of the retaining member 35.The outer peripheral edge portion of the seat disk 68 secured to the valve body 58 selectively engages and disengages from the inner peripheral edge portion of the fail-safe disk 70, thereby opening and closing the flow path between the port 52 and the cutout portion 56 in the valve chamber 55.

[0027] Either the outer peripheral edge portion of the seat disc 68 or the inner peripheral edge portion of the fail-safe disc 70 is provided with an opening (cut-out portion) 68A, which constantly provides communication between the port 52 and the cut-out portion 56. The retaining member 35 has a stopper 71 protruding therefrom to abut against the seat disc 68 to limit the retracted position of the valve body 58. It should be noted that the stopper for limiting the retracted position of the valve body 58 may be provided at another part. The retracted position of the valve body 58 may be limited by abutment between the piston 62 and the core 61.

[0028] When the winding 59 is not excited, the valve body 58 is retracted by the spring force of the valve spring 67 and, as shown in Fig. 1, the seat disc 68 abuts against the fail-safe disc 70 to close the flow path between the port 52 and the cutout portion 56 in the valve chamber 55. In this state, when the pressure of the fluid on the port 52 side in the valve chamber 55 increases to a certain pressure, the fail-safe disc 70 is displaced and separates from the seat disc 68 after the retracted position of the valve body 58 is restricted by the stopper 71, thereby opening the flow path between the port 52 and the cutout portion 56. When the valve body 58 abuts against the stopper 71, the seat disc 68 is in abutting contact with the fail-safe disc 70.In this state, when the pressure in the valve chamber 55 increases, the fail-safe disc 70 is displaced to separate from the seat disc 68, thereby allowing the fluid in the valve chamber 55 to flow into the downstream side chamber 26B via the cutout portions 56 and 57.

[0029] On the other hand, when the coil 59 is energized, the seat portion 65 of the valve body 58 seats on the seat surface 66 to perform pressure control by the pilot valve 28, as stated above. In this state, the seat disc 68 separates from the fail-safe disc 70, and the valve chamber 55 and the cutout portion 56 communicate with each other via the opening in the center of the fail-safe disc 70.

[0030] The following is an explanation of the operation of this embodiment described above.

[0031] The damping force control shock absorber 1 is installed between the sprung and unsprung elements of a vehicle's suspension system. The lead wire 64 is connected to an in-vehicle control unit or the like. In a normal operating state, the coil 59 is energized to seat the seat portion 65 of the valve body 58 onto the seat surface 66 to perform pressure control through the pilot valve 28.

[0032] During the extension stroke of the piston rod 6, the movement of the piston 5 in the cylinder 2 closes the check valve 13 of the piston 5. Thus, before the disc valve 14 opens, the fluid in the upper cylinder chamber 2A is pressurized to flow through the passage 22 and the annular passage 21 into the passage 40 of the passage member 31 of the damping force generating mechanism 25 from the opening 23 of the separator pipe 20.

[0033] At that time, an amount of fluid corresponding to the amount of movement of the piston 5 flows from the reservoir 4 into the lower cylinder chamber 2B by opening the check valve 17 of the base valve 10. It should be noted that when the pressure in the upper cylinder chamber 2A reaches the valve opening pressure of the disc valve 14 of the piston 5, the disc valve 14 opens to relieve the pressure in the upper cylinder chamber 2A into the lower cylinder chamber 2B, thereby avoiding an excessive increase in the pressure in the upper cylinder chamber 2A.

[0034] In the damping force generating mechanism 25, the fluid flows from the passage 40 of the passage member 31 as follows. Before the disc valve 47 of the main valve 27 opens (in the low piston speed range), the fluid flows through the fixed orifice 50 and the passage 49 of the orifice passage member 33 and the port 52 of the pilot valve member 34, and pushes the valve body 58 of the pilot valve 28 to flow into the valve chamber 55. At this time, the valve body 58 of the pilot valve 28 does not abut against the stopper 71. The fluid flowing into the valve chamber 55 further passes through the opening of the fail-safe disc 70 (ie,a circular opening formed in the center of the fail-safe disc 70) and flows into the reservoir 4 through the cutout portion 56 of the retainer member 34, the cutout portion (not shown) partially formed circumferentially in the fail-safe disc 70, the cutout portion 57 of the pilot valve member 34, the chamber 26B in the housing 26, and the passages 38 of the passage plate 30 into the reservoir 4. When the piston speed increases and the pressure in the upper cylinder chamber 2A reaches the valve opening pressure of the disc valve 47, the fluid flowing into the passage 40 passes through the cutout portion 42, the annular groove 41, and the passages 44, and pushes the disc valve 47 open to flow directly into the chamber 26B in the housing 26.

[0035] During the compression stroke of the piston rod 6, the movement of the piston 5 in the cylinder 2 opens the check valve 13 of the piston 5 and closes the check valve 17 for the passage 15 of the base valve 10. Thus, before the disc valve 18 opens, the fluid in the lower cylinder chamber 2B flows into the upper cylinder chamber 2A, and an amount of fluid corresponding to the amount by which the piston rod 6 enters the cylinder 2 flows from the upper cylinder chamber 2A into the reservoir 4, via a flow path comparable to that during the expansion stroke described above. It should be noted that when the pressure in the lower cylinder chamber 2B reaches the valve opening pressure of the disc valve 18 of the base valve 10, the disc valve 18 opens to release the pressure in the cylinder chamber 2B into the reservoir 4, thereby preventing an excessive increase in the pressure in the lower cylinder chamber 2B.

[0036] Thus, during both the extension and compression strokes of the piston rod 6, before the disc valve 47 of the main valve 27 opens in the damping force generating mechanism 25 (in the low piston speed range), the damping force is generated by the fixed orifice 50 and the valve opening pressure of the valve body 58 of the pilot valve 28. After the disc valve 47 is opened (in the high piston speed range), the damping force is generated according to the opening degree of the disc valve 47. The damping force can be directly controlled, regardless of the piston speed, by controlling the valve opening pressure of the pilot valve 28 through the electric current supplied to the coil 59.In this connection, a change in the valve opening pressure in the pilot valve 28 causes a change in the pressure in the pilot chamber 51, which communicates with the passage 49 on the upstream side of the pilot valve 28, and the pressure in the pilot chamber 51 acts in the direction of closing the disc valve 47. Consequently, by controlling the valve opening pressure of the pilot valve 28, the valve opening pressure of the disc valve 47 can be controlled at the same time, and thus the control range for the damping force characteristics can be expanded.

[0037] In this context, when the electric current supplied to the coil 59 is reduced to reduce the thrust of the piston 62, the valve-opening pressure of the pilot valve 28 decreases, and a soft damping force is generated. When the electric current supplied to the coil 59 is increased to increase the thrust of the piston 62, the valve-opening pressure of the pilot valve 28 increases, and a hard damping force can be generated. Consequently, a soft damping force, which is generally frequently used, can be generated with a reduced electric current, and energy consumption can be reduced.

[0038] In a case where the thrust of the piston 62 is lost due to a fault such as a power interruption to the coil 59, a problem in the vehicle's internal control device, etc., the valve body 58 is retracted to the position shown in Fig. 1, by means of the spring force of the valve spring 67. As a result, the port 52 opens, and the seat disk 68 of the valve body 58 abuts against the fail-safe disk 70 to close the flow path between the port 52 and the cutout portion 56 in the valve chamber 55. In this state, the fluid flow in the valve chamber 55 from the port 52 to the cutout portion 56 is controlled by the fail-safe valve 29, that is, the orifice 68A and the fail-safe disk 70. Consequently, it is possible to generate a desired damping force and control the pressure in the pilot chamber 51, that is, the valve-opening pressure of the main valve 27, by adjusting the flow path area of ​​the orifice 68A and the valve-opening pressure of the fail-safe disk 70. As a result, an appropriate damping force can be obtained even when a malfunction occurs.

[0039] Consequently, the passage for the fluid when the coil 59 is energized and the passage for the fluid when a failure occurs are brought into agreement (continued). Consequently, the structure can be simplified and space efficiency can be increased. Furthermore, the fail-safe disc 70 is a disc valve, and the passage for the fluid when a failure occurs is selectively opened and closed by the disc valve and the end of the valve body. Consequently, productivity and assemblability can be improved compared with a structure using, for example, a ball valve. Furthermore, a soft damping force, which is generally frequently used, can be generated by supplying a reduced electric current to the coil 59. Consequently, power consumption can be reduced.When the coil 59 is not energized, the fail-safe valve 29 provides an appropriate damping force that is greater than the soft damping force. Consequently, the steering stability of the vehicle can be ensured and the fail-safe function can be realized. Furthermore, it is possible to avoid adverse effects, such as an increase in vibrations transmitted to the vehicle body, due to the fact that the damping force characteristic is fixed to the hard damping force characteristic side.

[0040] Next, a second embodiment of the present invention will be described with reference to the Fig. 3. It should be noted that elements or portions of the second embodiment that are the same as those of the first embodiment are denoted by the same reference numerals as used in the first embodiment, and only points that differ in the second embodiment from the first embodiment will be described in detail.

[0041] In this embodiment, as shown in Fig. 3, the outer peripheral portion of the fail-safe disc 70 of the fail-safe valve 29 is not clamped but fitted into an inner peripheral groove 72 formed by the retainer member 35 and the pilot valve member 34, thereby movably supporting it to be axially movable by a predetermined distance. The annular projection 54 of the valve body 58 and the seat disc 68 are omitted. Instead, the outer peripheral edge portion of the end surface of the valve body 58 directly abuts the inner peripheral edge portion of the fail-safe disc 70. It should be noted that the opening 68A may be provided in the inner peripheral edge portion of the fail-safe disc 70 or in the outer peripheral edge portion of the end surface of the valve body 58.The valve chamber 55 communicates with the chamber 26B in the housing 26 via a passage 77 extending axially through the retaining member 35, a recessed portion 78 formed in the end portion of the retaining member 35, a recessed portion 79 formed in the outer peripheral portion of the retaining member 35, and the recessed portion 57 of the pilot valve element 34. Thus, the second embodiment can provide the same advantageous effects as the first embodiment. Furthermore, the second embodiment can improve durability.

[0042] Next, a third embodiment of the present invention will be described with reference to the Fig. 4. It should be noted that the elements or portions of the third embodiment that are the same as those of the first embodiment are denoted by the same reference numerals as used in the first embodiment, and only points in which the third embodiment differs from the first embodiment will be described in detail.

[0043] In this embodiment, as shown in Fig. 4, the retaining member 35 is omitted. Instead, the solenoid housing 36 abuts against the end of the cylindrical portion of the pilot valve member 34, and the cutout portion 26 communicating with the valve chamber 55 is formed in the end of the cylindrical portion of the pilot valve member 34. A fail-safe disc 73 constituting the fail-safe valve 29 is secured at its inner peripheral portion to a circular cylindrical portion 60A protruding from the core 60, so that the outer peripheral portion of the fail-safe disc 73 is displaceable. The cylindrical portion 60A also serves as a stopper. The valve body 58 of the pilot valve 28 has an enlarged diameter portion 74 formed at the distal end thereof.The outer periphery of the enlarged diameter portion 74 is in slidable contact with the inner peripheral surface of the cylindrical portion of the pilot valve element 34 and is thus guided. The enlarged diameter portion 74 has a plurality of passages 75 extending axially therethrough to face the fail-safe disc 73. An annular seat portion 76 protrudes from the outer periphery of the openings of the passages 75. The fail-safe disc 73 sits on the seat portion 76. The opening 68A may be formed in the outer peripheral portion of the fail-safe disc 73 or in the seat portion 76.

[0044] With the arrangement described above, the fluid in the valve chamber 55 flows into the recessed portion 56 through the passages 75 into the enlarged diameter portion 74 of the valve body 58. If a malfunction occurs, as described in Fig.As shown in Fig. 4, the seat portion 76 of the enlarged diameter portion 74 of the valve body 58 abuts against the fail-safe disc 73 to close the passages 75. The valve body 58 is retracted into the valve chamber 55 by the fluid pressure on the port 52 side to abut against the cylindrical portion 60A as a stopper. Thereafter, the fail-safe disc 73 is displaced to separate from the seat portion 76, thereby opening the passages 75. Thus, the third embodiment can provide the same advantageous effects as the first embodiment described above.

[0045] The processes that occur when a misfire occurs will be described in more detail in order. First, the valve body 58 is retracted to the position shown in the figure by the spring force of the valve spring 67. At this time, the port 52 opens, and the seat disc 68 of the valve body 58 abuts against the fail-safe disc 70 to close the flow path between the port 52 and the cutout portion 56 in the valve chamber 55. Thereafter, when the pressure in the valve chamber 55 increases to reach the valve opening pressure of the fail-safe disc 70, the fail-safe disc 70 is displaced to allow the fluid in the valve chamber 55 to flow downstream via the cutout portion 56. Thus, when a misfire occurs, it is possible to generate an intermediate damping force that is between the soft and hard damping forces.

[0046] Although the aforementioned first to third embodiments use hydraulic oil and gas as hydraulic fluids in consideration of operational stability and manageability, the present invention is not limited thereto, but other fluids may be used alone or in combination. Although the sectional configurations of the components such as the piston, cylinder, and valves are suitably circular in consideration of sealability, manufacturability, etc., the components may have polygonal or other sectional configurations.

[0047] Although in the first embodiment, the damping force generating mechanism 25 is provided on the cylinder side, the damping force generating mechanism 25 may be provided at any location where hydraulic fluid flow is induced by displacement of the piston, for example, in the piston part.

[0048] Although in the first to third embodiments, the pilot valve 28 is a pressure control valve, it may also be a flow control valve that controls the flow rate of the fluid.

[0049] Although in the first to third embodiments, the pilot chamber 51 and the valve chamber 55 are two separate chambers connected to each other by the cutout portion 53, the pilot chamber 51 and the valve chamber 55 may be integrated as a common chamber, and the cutout portion 53 may be omitted.

[0050] In the first to third embodiments, one end of the valve body 58, which is in the shape of a block, serves as the valve portion of a control valve, and the other end of the valve body 58 functions as the valve seat of a fail-safe valve. However, the present invention is not limited to this. The valve portion of the control valve and the valve seat of the fail-safe valve may be formed by two discrete elements that are connected to each other during use, although the structure becomes complicated.

[0051] The damping force control type shock absorber according to the present invention enables an appropriate damping force to be obtained even when the supply of an electric current to the control system is interrupted due to a malfunction or the like.

[0052] Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that various modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.

[0053] This application claims priority under 35 USC Section 119 to Japanese Patent Application No. 2009-228705, filed on September 30, 2009.

[0054] The entire disclosure of Japanese Patent Application No. 2009-228705, filed on September 30, 2009, including the specification, claims, drawings, and abstract, is incorporated herein by reference in its entirety.

Claims

[1] Shock absorber (1) with damping force control, comprising: a cylinder (2) having a fluid sealed therein; a piston (5) slidably fitted in the cylinder (2); a piston rod (6) connected at one end to the piston (5), the other end of the piston rod (6) extending outwardly with respect to the cylinder (2); a main valve (27) that generates a damping force by controlling a fluid flow induced by a displacement of the piston (5) in the cylinder (2); a pilot chamber (51) applying a pressure therein to the main valve (27) in a direction to close the main valve (27); an inlet passage (49, 50, 53) which introduces the fluid into the pilot chamber (51); a pilot passage (52, 55, 56, 57) communicating the pilot chamber (51) and a downstream side of the main valve (27); a control valve (28) provided in the pilot passage (52, 55, 56, 57), the control valve (28) having a valve body (58) urged by an urging member (67) in a direction to open the control valve (28), and an actuator (S) that moves the valve body (58) in a direction to close the control valve (28) by means of a thrust from a solenoid; and a fail-safe valve (29) provided in the pilot passage (52, 55, 56, 57) on a downstream side of the control valve (28), wherein the valve body (58) of the control valve (28) is provided in a valve chamber (55), the valve chamber (55) opens at one end thereof into the pilot chamber (51), another end of the valve chamber (55) opening downstream of the fail-safe valve (29), wherein one end of the valve chamber (55) is selectively opened and closed by one end of the valve body (58), wherein another end of the valve chamber (55) is opened and closed by both the fail-safe valve (29) and another end of the valve body (58), wherein the fail-safe valve (29) abuts against the valve body (58) to close the pilot passage (52, 55, 56, 57) when the valve body (58) is urged by the urging element (67) and moves in the direction of opening the control valve (28), wherein the fail-safe valve (29) separates from the valve body (58) to open the pilot passage (52, 55, 56, 57) when the pressure in the pilot chamber (51) reaches a certain pressure. [2] Damping force control shock absorber (1) according to claim 1, wherein an opening (68A) is formed in the fail-safe valve (29) and / or the valve body (58) which can be brought into abutment against the fail-safe valve (29). [3] Damping force control type shock absorber (1) according to claim 1 or 2, wherein the control valve (28) is a pressure control valve which opens when the pressure in the pilot passage (52, 55, 56, 57) reaches a certain pressure. [4] Damping force control type shock absorber (1) according to claim 1, wherein the other end of the valve body (58) is provided with an annular seat portion (58A) adapted to be abutted against the fail-safe valve (29). [5] Damping force control shock absorber (1) according to claim 1, wherein the fail-safe valve (29) is a disc valve.

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