DAMPER CONTROL DEVICE AND SUSPENSION DEVICE

Abstract

A damper control device and a suspension device of the present invention controls a damping force of the damper based on a bank angle. Since a degree of the bank angle is a measure of easiness of occurrence of highside, and the damping force of dampers is controlled based on the bank angle in the damper control device and the suspension device, the damping force of the dampers can be appropriately controlled in accordance with a situation in which the highside is easy to occur.

Claims

1. A damper control device, comprising a bank angle detector that detects a bank angle being an inclination angle in a lateral direction of a body of a straddle-type vehicle, and controlling a damping force in an extension side of the damper interposed between the body and a wheel of the straddle-type vehicle, to be larger as the bank angle is larger.

2. (canceled)

3. The damper control device according to claim 1, wherein the damper control device sets the damping force in an extension side of the damper to be larger when the bank angle exceeds an angle threshold.

4. The damper control device according to claim 1, wherein the damper control device sets the damping force in a compression side of the damper to be smaller when the bank angle exceeds an angle threshold.

5. A suspension device comprising: a damper that can adjust damping force and is interposed between the body and the wheel of the straddle-type vehicle; and the damper control device according to claim 1.

6. The suspension device according to claim 5, wherein the damper has a damping force adjustment valve having an extension side hard mode in which a damping characteristic in an extension side is made hard and a damping characteristic in a compression side is made soft.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a system configuration diagram of a suspension device according to an embodiment.

[0011] FIG. 2 is a schematic diagram of a damper.

[0012] FIG. 3 is a control block diagram of a damper control device according to an embodiment.

[0013] FIG. 4 is a diagram for explaining a relationship between acceleration in a vertical direction and a lateral direction of a body, and a bank angle.

[0014] FIG. 5 is a diagram for explaining a relationship between angular velocities in a pitch direction and a yaw direction of the body and a bank angle.

[0015] FIG. 6 is a diagram illustrating a dead band area of a bank angle obtained by a second bank angle calculation unit.

[0016] FIG. 7 is a flowchart illustrating an example of a calculation processing procedure of a damping force command value in the damper control device of an embodiment.

DESCRIPTION OF EMBODIMENTS

[0017] The present invention will be described below based on the embodiment illustrated in the drawings. As illustrated in FIGS. 1 to 3, a suspension device S according to an embodiment is configured to include a front wheel side damper DF interposed between a body B and a front wheel WF of a vehicle V that is a straddle-type vehicle, a rear wheel side damper DR that is a rear wheel side damper interposed between the body B and a rear wheel WR, and a damper control device C.

[0018] Each part will be described in detail, and the vehicle V is assumed to be a motorcycle that is the straddle-type vehicle in this example. The front wheel side damper DF is built in a front fork SF interposed between the body B and the front wheel WF being a wheel, together with a front wheel side suspension spring not illustrated, so as to exert damping force at the time of extension and contraction. The rear wheel side damper DR is interposed between the body B and a swing arm SA that rotatably holds the rear wheel WR being a wheel, together with a rear wheel side suspension spring not illustrated, and exerts damping force at the time of extension and contraction.

[0019] In this example, as illustrated in FIG. 2, both the front wheel side damper DF and the rear wheel side damper DR, are configured to include: a cylinder 20; a piston 21 that is slidably inserted into the cylinder 20 and partitions the cylinder 20 into an extension side chamber R1 and a compression side chamber R2; a piston rod 22 that is movably inserted to the cylinder 20, and is connected to the piston 21; a damping valve 23 that is provided in the piston 21, and makes the extension side chamber R1 and the compression side chamber R2 communicate with each other; a bypass passage 24 that makes the extension side chamber R1 and the compression side chamber R2 communicate with each other by bypassing the damping valve 23; a damping force adjustment valve 25 provided in the middle of the bypass passage 24; a reservoir 26 that supplies and discharges hydraulic fluid that is excessive or insufficient in the cylinder 20 by the piston rod 22 that enters and exits the cylinder 20; a suction passage 28 that allows only a flow of the hydraulic fluid from the reservoir 26 to the compression side chamber R2; and a pressure side valve 29 that applies resistance to the flow of the hydraulic fluid from the compression side chamber R2 to the reservoir 26.

[0020] Although not illustrated in detail, in the present example, the damping force adjustment valve 25 includes: an extension side hard position in which large resistance is applied to the flow of the hydraulic oil from the extension side chamber R1 to the compression side chamber R2 and a small resistance is applied to the flow to the opposite side; and a medium position in which the same degree of resistance is applied to both the flow of hydraulic oil from the extension side chamber R1 to the compression side chamber R2 and the flow of the hydraulic oil from the compression side chamber R2 to the extension side chamber R1. In this example, the damping force adjustment valve 25 is connected to an actuator 27 via a control rod 27a, and is driven by the actuator 27 so as to be switchable to each position. As the damping force adjustment valve 25, for example, a rotary valve disclosed in JP 05-238235 A, or the like may be used, but the damping force adjustment valve 25 is not limited to this rotary valve.

[0021] In these dampers DF, DR, there are two flows as hydraulic oil flows, that is, a flow of hydraulic oil passing through the damping valve 23 and a flow of hydraulic oil passing the damping force adjustment valve 25 and passing through the bypass passage 24.

[0022] When the damping force adjustment valve 25 adopts the extension side hard position, if both the dampers DF, DR extend, large resistance is applied to the flow of the hydraulic oil passing through the bypass passage 24, so that both dampers DF, DR show damping characteristics with a large damping coefficient. On the contrary, when the damping force adjustment valve 25 adopts the extension side hard position, if both the dampers DF, DR contract, only small resistance is applied to the flow of the hydraulic oil passing through the bypass passage 24, so that both dampers DF, DR show damping characteristics with a small damping coefficient. Therefore, when the damping force adjustment valve 25 adopts the extension side hard position, the damper DF on the front wheel side and the damper DR on the rear wheel side are in the extension side hard mode in which the damping coefficient on the extension side is increased, and the damping coefficient on the contraction side is decreased. The damping force adjustment valve 25 can adjust the valve opening degree by adjusting the position of the actuator 27 in the extension side hard mode, so that the magnitude of the extension side damping force can be adjusted while minimizing the compression side damping force.

[0023] When the damping force adjustment valve 25 adopts the medium position, even if both the dampers DF, DR extend or contract, medium resistance is applied to the flow of the hydraulic oil passing through the bypass passage 24, so that both dampers DF, DR show damping characteristics with a medium damping coefficient. Therefore, when the damping force adjustment valve 25 adopts the medium position, the damper DF on the front wheel side and the damper DR on the rear wheel side are in the medium mode in which the damping coefficients on both extension and contraction sides are medium.

[0024] The damping force adjustment valve 25 may be a solenoid valve of which the resistance applied to the flow of the passing hydraulic oil can be changed by adjusting the opening degree. In this case, the damping force adjustment valve 25 may apply resistance to both flow of the hydraulic fluid from the extension side chamber R1 to the compression side chamber R2 and flow of the hydraulic fluid from the compression side chamber R2 to the extension side chamber R1. In this case, both the damping force (extension side damping force) during an extension stroke and the damping force (compression side damping force) during a contraction stroke of the dampers DF, DR can be adjusted by adjusting the opening degree of the damping force adjustment valve 25. The damping force adjustment valve 25 may be an electromagnetic relief valve capable of adjusting the valve opening pressure, and any electromagnetic relief valve may be utilized as the damping force adjustment valve 25 as long as at least the valve can adjust the damping force of the extension side exerted by the dampers DF, DR.

[0025] The faster the speed of turning of the vehicle V becomes, the greater the centrifugal force acting on the vehicle V becomes. Therefore, it is necessary to increase the bank angle of when banking of the body B is performed toward the turning center. In other words, when the bank angle of the body B increases, the speed of the vehicle V increases and the centrifugal force acting on the vehicle V also increases. As the centrifugal force increases, the grip of the tires of the front and rear wheels WF, WR is lower than the centrifugal force, and a state is established where skidding and the highside is easy to occur. Here, as a result of earnest studies on the process of occurrence of the highside, the inventor has found that one of the causes of the highside is that, after the ground loads of the front and rear wheels WF, WR are released by the skidding of the front and rear wheels WF, WR, at the time of the grip recovery, the load exerted by the suspension abruptly changes when the ground load suddenly returns to the original state. In addition, the inventor has found that if the extension side damping force of the dampers DF, DR is increased to suppress the extension of the dampers DF, DR in a situation where the highside occurs, the reduction of the load of the suspension can be suppressed even at the skidding. The highside is easier to occur as the bank angle increases, as described above.

[0026] Therefore, the damper control device C and the suspension device S of the present invention are configured to control the extension side damping force of the dampers DF, DR based on the bank angle so that the highside is prevented from occurring.

[0027] Specifically, as illustrated in FIGS. 1 and 3, the control device C is configured to include: an acceleration sensor 1 that detects acceleration Gz, Gy of the vertical direction and the lateral direction of the body B of the vehicle V; a gyro sensor 2 that detects angular velocities R, R in the pitch direction and the yaw direction of the body B; a bank angle detector 3 that obtains a bank angle e that is an inclination angle of the body B; and a control unit 4 that obtains the damping force command value of the dampers DF, DR based on the bank angle e to drive the actuator 27, and control the damping force exerted by the dampers DF, DR.

[0028] As illustrated in FIG. 1, the acceleration sensor 1 is provided directly below a seat B1 on which a rider is seated, the seat B1 provided in the body B of the vehicle V. The acceleration sensor 1 detects the acceleration Gz, Gy in the vertical direction and the lateral direction of the body B. The acceleration sensor 1 of this example may be a triaxial acceleration sensor that detects not only the acceleration Gz, Gy in the longitudinal direction and the lateral direction of the body B, but also the acceleration of the longitudinal direction of the body B.

[0029] As illustrated in FIG. 1, as similar to the acceleration sensor 1, the gyro sensor 2 is provided directly below the seat B1 in the body B, and detects the angular velocities R, R in the pitch direction and the yaw direction of the body B. The gyro sensor 2 of this example may be a triaxial gyro sensor that detects not only the angular velocities R, R in the pitch direction and the yaw direction of the body B, but also the angular velocity of the bank direction of the body B.

[0030] The bank angle detector 3 includes: a first bank angle calculation unit 31 that obtains a bank angle G that is an inclination angle in the lateral direction of the body B based on the acceleration Gz, Gy; a second bank angle calculation unit 32 that obtains a bank angle J that is an inclination angle of the lateral direction of the body B based on the angular velocities R, R; and a bank angle selection unit 33 that selects a larger bank angle among the bank angle G and the bank angle J as the bank angle e of the body B. As illustrated in FIG. 4, the bank angle is an angle formed by a vertical direction axis BL of the body B with respect to a vertical axis Ver.

[0031] The first bank angle calculation unit 31 obtains the bank angle G based on the acceleration Gz, Gy in the vertical direction and the lateral direction of the body B detected by the acceleration sensor 1. As illustrated in FIG. 4, when the body B banks by the bank angle with respect to the vertical axis Ver, if the centrifugal force is neglected, the resultant force of the acceleration GOz in the vertical direction and the acceleration GOy in the lateral direction of the body B acting on the center of gravity O of the body B coincides with the gravitational acceleration g. Therefore, the bank angle can be obtained by detecting the acceleration Gz, Gy.

[0032] The centrifugal force acting on the vehicle V increases as the speed Vv of the vehicle V increases during turning of the vehicle V, and the value of the acceleration Gy in the lateral direction detected by the acceleration sensor 1 tends to decrease. Therefore, as the speed Vv of the vehicle V increases during turning of the vehicle V, the bank angle G obtained by the first bank angle calculation unit 31 tends to be smaller than the actual bank angle.

[0033] The second bank angle calculation unit 32 obtains the bank angle J based on the angular velocities R, R in the pitch direction and the yaw direction of the body B detected by the gyro sensor 2. As illustrated in FIG. 5, when the pitch angular velocity R and the yaw angular velocity R are obtained, the bank angle of the body B with respect to the vertical axis Ver is unambiguously determined. The second bank angle calculation unit 32 obtains the bank angle J from the pitch angular velocity R and the yaw angular velocity R instead of obtaining the bank angle by integrating the bank angular velocity. Thus, the second bank angle calculation unit 32 can obtain the bank angle J not including an error due to the integral drift with respect to the actual bank angle. Therefore, the second bank angle calculation unit 32 can obtain the bank angle J having a high degree of coincidence with the bank angle of the actual body B.

[0034] The bank angle selection unit 33 selects a larger one of the bank angle G obtained by the first bank angle calculation unit 31 and the bank angle J obtained by the second bank angle calculation unit 32, to determine the one as the conclusive bank angle e.

[0035] As described above, the first bank angle calculation unit 31 obtains the bank angle G from the acceleration Gz, Gy detected by the acceleration sensor 1. However, when the speed Vv of the vehicle V increases, the bank angle G obtained by the centrifugal force during the turning tends to be smaller than the actual bank angle of the body B. On the other hand, in a state where a large centrifugal force does not act on the body B, the degree of coincidence of the bank angle G obtained by the first bank angle calculation unit 31 utilizing the output of the acceleration sensor 1 with respect to the actual bank angle is high. That is, the bank angle G obtained based on the acceleration Gz, Gy in the vertical direction and the lateral direction of the body B has a high degree of coincidence with the bank angle of the body B of when the vehicle V is traveling at a low speed or stopped.

[0036] On the other hand, the second bank angle calculation unit 32 obtains the bank angle J based on the angular velocities R, R in the pitch direction and the yaw direction detected by the gyro sensor 2, so that the bank angle J with which the drift is small and with high coincidence with the actual bank angle can be obtained. On the other hand, the gyro sensor 2 has a characteristic of being difficult to accurately detect the pitch angular velocity R and the yaw angular velocity R with respect to the operation in which the body B slowly tilts. Under such circumstances, the bank angle J obtained by the second bank angle calculation unit 32 tends to be smaller than the actual bank angle.

[0037] Therefore, when a large angle among the bank angle G obtained by the first bank angle calculation unit 31 and the bank angle J obtained by the second bank angle calculation unit 32 is selected as the bank angle e, regardless of the situation of the vehicle V, the bank angle e having a high degree of coincidence with the actual bank angle of the body B can be detected.

[0038] Since the gyro sensor 2 is equipped in the vehicle V and provided on the body B to which the engine vibration is transmitted, a component due to vibration is superimposed on the pitch angular velocity R and the yaw angular velocity R, so that an error tends to occur when the bank angle J has a value around 0 degree. Therefore, as illustrated in FIG. 6, it is preferable that a predetermined range including 0 degree with respect to the bank angle J obtained by the second bank angle calculation unit 32 is set as a dead band area, and the bank angle J with which the obtained bank angle J is within the dead band area is set to 0. Then, in the range in which an error is likely to occur in the bank angle J obtained from the output of the gyro sensor 2, the chance of selecting the bank angle G obtained from the output of the acceleration sensor 1 increases, and the bank angle e with a higher degree of coincidence with the actual bank angle of the body B can be detected. The range of the dead band area can be arbitrarily set. It is sufficient that the bank angle band in which the error easily occurs is set as the dead band area.

[0039] Further, as described above, when the speed Vv of the vehicle V is low, the bank angle G obtained by the first bank angle calculation unit 31 has a high degree of coincidence with the actual bank angle of the body B. As described above, the bank angle J obtained by the second bank angle calculation unit 32 tends to be smaller than the actual bank angle, with respect to the operation in which the body B tilts slowly. Therefore, when a threshold V is provided for the speed Vv, and the speed Vv is equal to or less than the threshold V, the bank angle selection unit 33 may select without fail the bank angle G obtained from the output of the acceleration sensor 1 by the first bank angle calculation unit 31. In this way, the bank angle e with a higher degree of coincidence with the actual bank angle of the body B can be detected. In this case, a technique of setting a dead band area with respect to the bank angle J obtained by the second bank angle calculation unit 32 and setting the bank angle J with which the obtained bank angle J is within the dead band area, to 0, may be adopted at the same time.

[0040] In addition to the technique described above, the bank angle detector 3 may obtain the bank angle e by using another technique such as obtaining the bank angle e by integrating the roll angular velocity.

[0041] Subsequently, the control unit 4 obtains a damping force command value that is a command given to the actuator 27 of dampers DF, DR, based on the bank angle e obtained as described above, and supplies a current to the actuator 27 as instructed by this damping force command value.

[0042] Specifically, as illustrated in FIG. 3, the control unit 4 is configured to include: a damping force command value calculation unit 41 that obtains a damping force command value FF of a front wheel side and a damping force command value FR of a rear wheel side, based on the bank angle e; and a driver 42 that supplies a current to the actuators 27 of the dampers DF, DR in accordance with the amount of current instructed by the damping force command values FF, FR.

[0043] The damping force command value calculation unit 41 obtains the damping force command values FF, FR based on the bank angle e. In this example, the damping force command value calculation unit 41 obtains the damping force command value FF, FR so that the extension side damping force of the dampers DF, DR increase in proportion to the bank angle e. That is, when the bank angle e increases beyond the predetermined angle threshold, the damping force command value calculation unit 41 sets the damping force adjustment valve 25 to the extension side hard mode, and obtains the damping force command value FF, FR instructing the valve opening degree of the damping force adjustment valve 25 according to the degree of the bank angle e.

[0044] When the bank angle e is equal to or smaller than the angle threshold, the damping force command value calculation unit 41 obtains the damping force command values FF, FR so that the damping force adjustment valve 25 of the dampers DF, DR is in the medium mode.

[0045] In this example, since the damping force adjustment valve 25 adjusts the opening degree even in the extension side hard mode, in order to increase the damping force of the dampers DF, DR in proportion to the bank angle e, the damping force command value calculation unit 41 obtains the damping force command value FF, FR so that damping coefficients in the extension side of the dampers DF, DR increase. The damping force command value calculation unit 41 obtains the damping force command value FF, FR so that the opening degree of the damping force adjustment valve 25 becomes smaller as the bank angle e becomes larger.

[0046] As described above, in this example, the damping force command value calculation unit 41 obtains the damping force command value FF, FR so that the extension side damping coefficients of the dampers DF, DR increase in proportion to the obtained bank angle e. Instead of this, the damping force command value FF, FR may be obtained so that the damping coefficients of the dampers DF, DR incrementally increase in accordance with the bank angle e. A map for obtaining the damping force command values FF, FR for determining the damping coefficient on the extension side of the damping force adjustment valve 25 in the extension side hard mode may be prepared with the bank angle e as a parameter, so that the damping force command value calculation unit 41 performs a map operation from the bank angle e to obtain the damping force command values FF, FR.

[0047] When the damping force adjustment valve 25 adjusts the valve opening pressure, the damping force command value calculation unit 41 may obtain the damping force command value FF, FR to increase the extension side damping force so that the valve opening pressure of the damping force adjustment valve 25 is larger as the bank angle e is larger, when the dampers DF, DR are in the extension stroke. Since there is a limit in increasing of the damping force, the damping force command value FF, FR may be limited to the damping force command value that maximizes the damping force or the damping coefficients of the dampers DF, DR.

[0048] The driver 42 has a drive circuit for supplying a current to the actuator 27 and supplies a current to the actuator 27 according to an instruction by the damping force command value FF, FR obtained as described above. When the damping force adjustment valve 25 is a rotary valve enabling both selection of each position and adjustment of the valve opening degree described above, and the actuator 27 is a stepping motor, it is sufficient that the driver 42 supplies a current as described below. Specifically, for example, the driver 42 supplies a pulse current to the actuator 27 that is a stepping motor so that the damping force adjustment valve 25 is rotation driven so as to take a position in which a damping force instructed by the damping force command values FF, FR can be exerted. In this way, the driver 42 supplies the pulse current to the actuator 27, the position and the valve opening degree of the damping force adjustment valve 25 are adjusted according to the instruction of the damping force command value FF, FR as described above, and the damping force of the dampers DF, DR is controlled.

[0049] When the damping force adjustment valve 25 is a spool valve enabling both selection of each position described above and adjustment of the valve opening degree, and the actuator 27 is a solenoid, it is sufficient that the driver 42 supplies a current as described below. Specifically, for example, the driver 42 supplies a current of a current amount according to the damping force command value FF, FR to the actuator 27 that is a solenoid so that the damping force adjustment valve 25 is driven so as to take a position in which a damping force instructed by the damping force command values FF, FR can be exerted. It is sufficient that the driver 42 detects the current flowing through the actuator 27 and controls the current flowing through the actuator 27 by current feedback control. In this way, the driver 42 supplies a current to the actuator 27, the position and the valve opening degree of the damping force adjustment valve 25 are adjusted according to the instruction of the damping force command value FF, FR as described above, and the damping force of the dampers DF, DR is controlled.

[0050] A hardware resource in each part of the control device C described above, specifically, although not illustrated, for example, may be configured as a computer system including: an amplifier for amplifying the signals output by the acceleration sensor 1 and the gyro sensor 2; a converter that converts an analog signal into a digital signal; a storage device such as a central processing unit (CPU) or a read only memory (ROM); a random access memory (RAM); a crystal oscillator; and a bus line connecting these components. A control processing procedure for processing each signal to obtain the bank angle e may be stored in advance in the ROM or another storage device, as a program.

[0051] Since the control device C is a well-known computer system, when the vehicle V includes an electronic control unit (ECU), the control device C can be integrated into the ECU.

[0052] Here, a processing procedure in the damper control device C described above will be described with reference to a flowchart illustrated in FIG. 7.

[0053] First, the control device C reads the acceleration Gz, Gy, the pitch angular velocity R, and the yaw angular velocity R detected by the acceleration sensor 1 and the gyro sensor 2 (step 101). Subsequently, the control device C detects the bank angle e from the acceleration Gz, Gy, the pitch angular velocity R, and the yaw angular velocity R (step 102).

[0054] The control device C obtains the damping force command values FF, FR from the bank angle e (step 103). The control device C supplies a current from the driver 42 to the actuator 27 and drives the damping force adjustment valve 25 to control the damping force of the dampers DF, DR (step 104). The control device C repeatedly processes from steps 101 to 104 described above, and controls the damping force of the dampers DF, DR.

[0055] As described above, the control unit 4 executes the series of processes described above, thereby realizing the processes of each part of the bank angle detector 3 and the control unit 4. Each part described above is realized by reading the program described above and executing each calculation processing described above by the CPU.

[0056] The damper control device C and the suspension device S are configured as described above and control the damping force of the dampers DF, DR based on the bank angle e. As described above, since the degree of the bank angle e is a measure of the easiness of occurrence of the highside and the damping force of the dampers DF, DR is controlled based on the bank angle e in the damper control device C and the suspension device S, the damping force of the dampers DF, DR can be appropriately controlled in accordance with a situation in which the highside is easy to occur. Therefore, in the damper control device C and the suspension device S of the present invention, the extension side damping force of the dampers DF, DR is properly controlled even in the condition where the highside is easy to occur, and the change in the load (the sum of the spring force of the suspension spring and the extension side damping force exhibited by the dampers DF, DR) exhibited by the suspension composed of the suspension spring and the dampers DF, DR decrease, and thereby, occurrence of the highside can be prevented.

[0057] In the damper control device C and the suspension device S of this example, the larger the bank angle e is, the greater the extension side damping force of the dampers DF, DR is made. In other words, as the highside becomes easier to occur, the extension side damping force of the dampers DF, DR that exert an effect to prevent occurrence of the highside is increased, so that occurrence of the highside can be more effectively prevented.

[0058] In the damper control device C and the suspension device S of this example, when the bank angle e is larger than the angle threshold, the extension side damping force of the dampers DF, DR is made larger. When the bank angle e is small and there is no possibility of occurrence of the highside, the extension side damping force of the dampers DF, DR does not become large, so that the damping force does not become excessive and the riding comfort of the vehicle V and the acceleration performance are not deteriorated.

[0059] In the damper control device C and the suspension device S of this example, when the bank angle e exceeds the angle threshold, the damping force in the compression side of the dampers DF, DR is made smaller. Specifically, in the extension side hard mode of the damping force adjustment valve 25, the damping force in the extension side is increased as hard and the damping force on the compression side is decreased as soft, and when the bank angle e exceeds the angle threshold, the damping force on the compression side of the dampers DF, DR is reduced. In this way, in a situation where the highside occurs, the dampers DF, DR are difficult to extend and easy to compress, so that the load exerted by the entire suspension is less likely to be lost and the occurrence of the highside can be suppressed more. It is sufficient that the angle threshold is set to a value of the bank angle e at which no highside occurs.

[0060] The control in the damper control device C may be used in combination with other control. For example, control may be performed by using this control together with posture control of the body B by skyhook control or the like, comparing the damping force command value by the posture control with the damping force command value by the control of the present invention, and adopting the damping force command value that increases the generation damping force of the dampers DF, DR.

[0061] When hydraulic fluid of the dampers DF, DR is electrorheological fluid or magnetorheological fluid, instead of providing the damping force adjustment valve 25 in the bypass passage 24, an electrode or coil for applying an electric or magnetic field may be provided so that the damping force adjustment can be performed. In this case, the bypass passage 24 may also be eliminated, and instead of the damping valve 23, an electrode or a coil may be provided in a passage communicating the extension side chamber R1 and the compression side chamber R2.

[0062] Although the preferred embodiments of the present invention have been described in detail, modifications, variations and changes can be made without departing from the scope of the claims.

[0063] This application claims priority based on JP 2016-053223 filed on Mar. 17, 2016 with the Japanese Patent Office, the entire contents of which are incorporated herein by reference.