Damping force-adjustable shock absorber

Abstract

In this damping force-adjustable shock absorber, a control device is provided to a vehicle and can set a solenoid valve to a closed condition or an openable / closable condition, by changing the output current value to an actuator according to a first travel mode and a second travel mode that a driver of the vehicle can select at will, and in an extremely low-speed range of the movement speed of a piston, when the current value that is inputted to the actuator is a current value that closes the solenoid valve, a first damping force valve opens, and when the current value that is inputted to the actuator is a current value that opens the solenoid valve, the first damping force valve produces a damping force while in a closed condition.

Description

Damping force adjustable shock absorber

[0001] The present disclosure relates to a damping force adjustable shock absorber.

[0002] Patent Document 1 discloses a damping force adjustable shock absorber having a piston that divides a cylinder into two chambers and is attached to a piston rod, and a damping force adjustment mechanism including a solenoid. In this damping force adjustable shock absorber, a very low speed valve that opens in a very low speed range of the moving speed of the piston is provided in the piston and the damping force adjustment mechanism.

[0003] International Publication No. 2020 / 246316

[0004] By the way, in a damping force adjustable shock absorber, there is a demand for optimizing the damping force characteristics.

[0005] Therefore, an object of the present disclosure is to provide a damping force adjustable shock absorber capable of optimizing the damping force characteristics.

[0006] To achieve the above objective, a first embodiment of the damping force adjustable shock absorber of this disclosure is a damping force adjustable shock absorber installed between the vehicle body and the wheel side of a vehicle, and capable of adjusting the damping force by operating an actuator with an electrical signal from a control device. The damping force adjustable shock absorber comprises: a cylinder filled with working fluid; a reservoir filled with working fluid and gas; a piston slidably fitted into the cylinder and dividing the inside of the cylinder into a first chamber and a second chamber; a piston rod with one end connected to the piston and the other end extending to the outside through the first chamber; a base valve dividing the second chamber and the reservoir; a first passage connecting the first chamber and the second chamber; a first damping force valve provided in the first passage for controlling the flow of the working fluid; a second passage provided in parallel with the first passage and connecting the first chamber and the second chamber; a second damping force valve provided in the second passage for controlling the flow of the working fluid; a third passage connecting the first chamber and the reservoir; and a solenoid valve provided in the third passage and operated by the actuator capable of arbitrarily adjusting the flow of the working fluid. The control device comprises a fourth passage provided in parallel with the third passage and connecting the first chamber and the reservoir, and a third damping force valve provided in the fourth passage for controlling the flow of the working fluid. The control device can close or open the solenoid valve by changing the output current value to the actuator according to a first driving mode and a second driving mode, which are provided in the vehicle and can be arbitrarily selected by the driver of the vehicle. In the very low speed range of the piston's movement speed, if the current value input to the actuator is a current value that closes the solenoid valve, the first damping force valve opens, and if the current value input to the actuator is a current value that opens the solenoid valve, the first damping force valve is closed and damping force is generated.

[0007] A second aspect of the damping force adjustable shock absorber of the present disclosure is a damping force adjustable shock absorber installed between the vehicle body and the wheel side of a vehicle, and capable of adjusting the damping force by operating an actuator with an electrical signal from a control device. The damping force adjustable shock absorber comprises: a cylinder filled with working fluid; a reservoir filled with working fluid and gas; a piston slidably fitted into the cylinder and dividing the inside of the cylinder into a first chamber and a second chamber; a piston rod with one end connected to the piston and the other end extending to the outside through the first chamber; a base valve dividing the second chamber and the reservoir; a first passage connecting the first chamber and the second chamber; an orifice passage provided in the first passage to control the flow of the working fluid; a second passage provided so as to branch off from the first passage and arranged in parallel with the orifice passage; a first damping force valve provided in the second passage to control the flow of the working fluid; a second damping force valve provided in the first passage and arranged in series with the orifice passage or the second passage to control the flow of the working fluid; and a third passage connecting the first chamber and the reservoir. The device comprises: a solenoid valve operated by an actuator provided in the third passage and capable of arbitrarily adjusting the flow of the working fluid; a fourth passage provided in parallel with the third passage and connecting the first chamber and the reservoir; and a third damping force valve provided in the fourth passage for controlling the flow of the working fluid. The control device can close or open the solenoid valve by changing the output current value to the actuator according to a first driving mode and a second driving mode provided in the vehicle and arbitrarily selectable by the driver of the vehicle. In the very low speed range of the piston's movement speed, if the current value input to the actuator is a current value that closes the solenoid valve, the first damping force valve opens, and if the current value input to the actuator is a current value that opens the solenoid valve, the first damping force valve is closed and a damping force is generated.

[0008] A third aspect of the damping force adjustable shock absorber of the present disclosure is a damping force adjustable shock absorber in which the damping force can be adjusted by operating an actuator with an electrical signal from a control device. The damping force adjustable shock absorber includes a cylinder, a piston slidably provided in the cylinder, a piston rod with one end fixed to the piston and the other end protruding from the cylinder, an electromagnetic valve that can be opened and closed arbitrarily by a solenoid, a first damping force valve that opens by a predetermined first pressure generated in the cylinder, and a second damping force valve that opens by a second pressure different from the first pressure generated in the cylinder. The control device is provided in a vehicle and can change the output current value to the actuator according to a first driving mode and a second driving mode that can be arbitrarily selected by the driver of the vehicle, thereby making the electromagnetic valve closed or open. In the very low speed range of the piston's movement speed, if the current value input to the actuator is such that it closes the solenoid valve, the first pressure is generated and the first damping force valve opens. If the current value input to the actuator is such that it opens the solenoid valve, the generation of the first pressure is suppressed and damping force is generated with the first damping force valve closed.

[0009] According to this disclosure, it becomes possible to optimize the damping force characteristics.

[0010] This is a cross-sectional view showing a damping force adjustable shock absorber according to the first embodiment of the present disclosure. This is a partial cross-sectional view showing the main part of the damping force adjustable shock absorber. This is another partial cross-sectional view showing the main part of the damping force adjustable shock absorber. This is a hydraulic circuit diagram of the damping force adjustable shock absorber. This is a diagram showing the damping force with respect to the current value to the actuator in the very low speed range of the damping force adjustable shock absorber. This is a hydraulic circuit diagram showing a damping force adjustable shock absorber according to the second embodiment of the present disclosure. This is a hydraulic circuit diagram showing a damping force adjustable shock absorber according to the third embodiment of the present disclosure.

[0011] [First Embodiment] The damping force adjustable shock absorber of the first embodiment according to the present disclosure will be described with reference to Figures 1 to 5. For the sake of convenience in the following description, the upper side in Figure 1 will be referred to as "upper" and the lower side in Figure 1 will be referred to as "lower".

[0012] As shown in Figure 1, in the damping force adjustable shock absorber 1 of the first embodiment, the damping force adjustment mechanism 121 is mounted laterally to the cylinder 2. Therefore, the damping force adjustable shock absorber 1 is a so-called control valve-mounted type damping force adjustable shock absorber.

[0013] The cylinder 2 has a cylindrical inner cylinder 3 and a bottomed cylindrical outer cylinder 4 that is positioned coaxially with the inner cylinder 3, with the inner cylinder 3 positioned inside it. A reservoir 6 is formed between the inner cylinder 3 and the outer cylinder 4. The inner cylinder 3 is sealed with oil liquid L (working fluid), and the reservoir 6 is sealed with oil liquid L and gas G.

[0014] A disc-shaped piston 18 is slidably fitted inside the inner cylinder 3 of the cylinder 2. The piston 18 divides the inner cylinder 3 into two chambers: the upper cylinder upper chamber 2A (first chamber) and the lower cylinder lower chamber 2B (second chamber). The lower end, which is one end in the axial direction of the piston rod 21, is connected to the piston 18. The upper end, which is the other end in the axial direction of the piston rod 21, extends to the outside of the cylinder 2 through the cylinder upper chamber 2A. At this time, the upper end of the piston rod 21 is inserted through a rod guide 22 and a seal member 23 attached to the upper end of the cylinder 2. The piston rod 21 has a cylindrical main shaft portion 27 that slides against the seal member 23 and is guided by the rod guide 22 so as to be axially movable, and a cylindrical mounting shaft portion 28 at the lower end which is positioned inside the inner cylinder 3 and to which the piston 18 is attached. The piston rod 21 has a stepped portion 29 that extends perpendicular to the axis at the end of the main shaft portion 27 on the mounting shaft portion 28 side. A threaded portion 31 is formed at the lower end of the mounting shaft portion 28. The main shaft portion 27 is formed with a larger outer diameter than the mounting shaft portion 28, but a threaded hole may be provided in the main shaft portion 27 and the mounting shaft portion 28 may be formed with a bolt member.

[0015] As shown in Figure 2, the piston 18 is provided with passages 37 and 39 that can connect the upper cylinder chamber 2A and the lower cylinder chamber 2B. Passage 37 opens to the inner circumference of the piston 18 on the side of the lower cylinder chamber 2B and to the outer circumference of the piston 18 on the side of the upper cylinder chamber 2A. Passage 37 is the extension-side passage through which the oil liquid L flows during the extension stroke when the piston rod 21 extends out of the cylinder 2. Passage 39 opens to the outer circumference of the piston 18 on the side of the lower cylinder chamber 2B and to the inner circumference of the piston 18 on the side of the upper cylinder chamber 2A. Passage 39 is the compression-side passage through which the oil liquid L flows during the compression stroke when the piston rod 21 enters the cylinder 2.

[0016] A damping force generating mechanism 41 for extension is provided on the cylinder lower chamber 2B side of passage 37. The damping force generating mechanism 41 for extension generates damping force by controlling the flow of oil L from the cylinder upper chamber 2A to the cylinder lower chamber 2B through passage 37. A damping force generating mechanism 42 for compression is provided on the cylinder upper chamber 2A side of passage 39. The damping force generating mechanism 42 for compression generates damping force by controlling the flow of oil L from the cylinder lower chamber 2B to the cylinder upper chamber 2A through passage 39.

[0017] The compression-side damping force generating mechanism 42 has an annular seat portion 50 formed on the outer circumference of the end face of the piston 18 on the cylinder upper chamber 2A side. Between the clamp portion 47, which is the radially inner portion of the piston 18, and the stepped portion 29 of the piston rod 21, a retainer 62, a valve disc 63 consisting of multiple discs, multiple retainers 64, a spacer 65, a retainer 66, and an annular member 67 are provided in order from the piston 18 side. The retainer 62, valve disc 63, retainer 64, spacer 65, retainer 66, and annular member 67 constitute the compression-side damping force generating mechanism 42.

[0018] The compression-side damping force generating mechanism 42 has an intake valve 71 (second damping force valve) that allows the flow of oil L through a passage 39 from the lower cylinder chamber 2B to the upper cylinder chamber 2A. The intake valve 71 generates a damping force when the oil L flows from the lower cylinder chamber 2B to the upper cylinder chamber 2A. The intake valve 71 consists of an annular seat portion 50 of the piston 18 and a valve disc 63 that can seat on and off the seat portion 50. When the intake valve 71 opens and the valve disc 63 separates from the seat portion 50 of the piston 18, the upper cylinder chamber 2A side of the passage 39 on the inner circumference side of the seat portion 50 opens to the upper cylinder chamber 2A. Note that the intake valve 71 of the compression-side damping force generating mechanism 41 is not provided with a fixed orifice that keeps the passage 39 and the upper cylinder chamber 2A in constant communication.

[0019] The extension-side damping force generating mechanism 41 has an annular seat portion 48 formed on the outer circumference of the end face of the piston 18 on the cylinder lower chamber 2B side. Between the clamp portion 47, which is the radially inner portion of the piston 18, and the cap 101 (described later), a retainer 82, a valve disc 83 consisting of multiple discs, a spacer 84, and a retainer 85 are provided in order from the piston 18 side. The retainer 82, valve disc 83, spacer 84, and retainer 85 constitute the extension-side damping force generating mechanism 41.

[0020] The extension damping force generating mechanism 41 has a relief valve 91 (second damping force valve) that allows the flow of oil liquid L through a passage 37 from the cylinder upper chamber 2A to the cylinder lower chamber 2B. The relief valve 91 generates a damping force when the oil liquid L flows from the cylinder upper chamber 2A to the cylinder lower chamber 2B. The relief valve 91 consists of an annular seat portion 48 and a valve disc 83 that can seat on and off the seat portion 48. The retainer 82 is provided with an orifice 88, which is a notch. The orifice 88 keeps the passage 37 in constant communication with a passage 30 formed in the mounting shaft portion 28 of the piston rod 21, via an annular passage 46 formed between the large diameter portion of the insertion hole 44, which is the axial hole of the piston 18, and the mounting shaft portion 28. The passage 30 is provided in the mounting shaft portion 28, for example, by forming a two-sided width. Furthermore, the relief valve 91 of the extension damping force generating mechanism 41 is not provided with a fixed orifice that constantly connects the passage 37 and the lower cylinder chamber 2B.

[0021] On the side of the retainer 85 of the extension-side damping force generating mechanism 41 that is opposite the piston 18, the following components are provided in order from the retainer 85 side: the aforementioned cap 101, passage member 102, retainer 103, spacer 104, valve disc 100 consisting of multiple discs, and valve body 106. The valve disc 100, consisting of multiple discs, constitutes the compression-side damping force valve 105 (first damping force valve). The cap 101 is formed in a substantially bottomed cylindrical shape with the side opposite the piston 18 open. The space between the inner circumferential surface of the cylindrical portion of the cap 101 and the outer circumferential surface of the valve body 106 is sealed by an annular sealing member 107.

[0022] On the side of the valve body 106 opposite to the valve disc 100, a valve disc 120 consisting of multiple discs, multiple spacers 109, a retainer 110, and an annular member 111 are provided in order from the valve body 106 side. The valve disc 120 consisting of multiple discs constitutes the extension damping force valve 108 (first damping force valve). The component through which the mounting shaft portion 28 between the annular members 67 and 111 passes, including the piston 18, is fixed to the mounting shaft portion 28 at least on its inner circumference by a nut 112 fastened to the threaded portion 31 of the mounting shaft portion 28.

[0023] The valve body 106 has a clamp portion 134 with an axial hole 131 formed therein on its radially inward side. An annular seat portion 136 is formed on the outer circumference of the end face of the valve body 106 on the piston 18 side, on which the outer peripheral edge of the valve disc 100 can seat and detach.

[0024] On the end face of the valve body 106 on the piston 18 side, an annular seat portion 135 is formed between the clamp portion 134 and the seat portion 136, allowing the valve disc 100 to seat at an intermediate radial position. The valve disc 100, the seat portion 136, and the seat portion 135 constitute the compression damping force valve 105.

[0025] An annular seat portion 139 is formed on the end face of the valve body 106 opposite to the piston 18 side, allowing the outer peripheral edge of the valve disc 120 to seat and release. The valve disc 120 and the seat portion 139 constitute the extension damping force valve 108.

[0026] The valve body 106 is provided with passages 141 and 143 that penetrate the valve body 106 axially, i.e., vertically. The multiple passages 141 provided on the inner circumference side of the valve body 106 have their extension-side damping valve 108-side end (lower end) opening to the inner circumference side of the seat portion 139, and their compression-side damping valve 105-side end (upper end) opening to the inner circumference side of the seat portion 135. On the other hand, the multiple passages 143 provided on the outer circumference side of the valve body 106 have their extension-side damping valve 108-side end opening to the cylinder lower chamber 2B, and their compression-side damping valve 105-side end opening between the seat portion 135 and the seat portion 136.

[0027] A cap chamber 146 is formed between the cap 101 and the valve body 106. The cap chamber 146 is in constant communication with the cylinder upper chamber 2A via a passage 153 formed in the passage member 102, a passage 30 formed in the piston rod 21, an annular passage 46 formed on the inner circumference of the piston 18, an orifice 88 formed in the retainer 82, and an extension-side passage 37 formed in the piston 18. The cap chamber 146 is also in constant communication with the passage 141 of the valve body 106 via a passage 161 formed in the valve disc 100 of the compression-side damping force valve 105.

[0028] The damping force valve 105 functions as a check valve that allows the flow of oil L from the lower cylinder chamber 2B to the cap chamber 146. The damping force valve 105 generates a damping force when it opens and allows the oil L to flow from the lower cylinder chamber 2B to the cap chamber 146. The damping force valve 108 functions as a check valve that allows the flow of oil L from the cap chamber 146 to the lower cylinder chamber 2B. The damping force valve 108 generates a damping force when it opens and allows the oil L to flow from the cap chamber 146 to the lower cylinder chamber 2B.

[0029] As shown in Figure 1, a base valve 25 is provided at the bottom of the outer cylinder 4 of the cylinder 2. The base valve 25 has a valve body 191 that defines the lower cylinder chamber 2B and the reservoir 6, a valve disc 188 provided on the reservoir 6 side, i.e., the lower end side, of the valve body 191, a valve disc 189 provided on the lower cylinder chamber 2B side, i.e., the upper end side, of the valve body 191, and mounting pins 194 that attach the valve disc 188 and the valve disc 189 to the valve body 191. The valve disc 188 and the seat portion of the valve body 191 on which the valve disc 188 sits constitute a relief valve 192. The valve disc 189 and the seat portion of the valve body 191 on which the valve disc 189 sits constitute a suction valve 193.

[0030] The valve body 191 has passages 195 and 196 that penetrate it axially, i.e., vertically. The relief valve 192 functions as a check valve that allows the flow of oil L from the lower cylinder chamber 2B to the reservoir 6 via a plurality of passages 195 provided on the inner circumference side of the valve body 191. The relief valve 192 generates a damping force when it opens and allows oil L to flow from the lower cylinder chamber 2B to the reservoir 6. The relief valve 192 is provided with an orifice 198 that maintains constant communication between the lower cylinder chamber 2B and the reservoir 6. The suction valve 193 functions as a check valve that allows the flow of oil L from the reservoir 6 to the lower cylinder chamber 2B via a plurality of passages 196 provided on the outer circumference side of the valve body 191. The suction valve 193 does not generate a substantial damping force when allowing oil L to flow from the reservoir 6 to the lower cylinder chamber 2B. The suction valve 193 reduces the pressure in the reservoir 6 to the pressure in the lower cylinder chamber 2B when the pressure in the reservoir 6 becomes higher than the pressure in the lower cylinder chamber 2B. The valve body 191 is provided with a notch 197 that keeps the space at the lower end of the valve body 191 in constant communication with the reservoir 6.

[0031] A separator tube 10 is attached to the outer circumference of the inner cylinder 3 via a pair of sealing members 9, 9. An annular oil passage 11 is formed between the separator tube 10 and the inner cylinder 3. The annular oil passage 11 communicates with the upper cylinder chamber 2A through a plurality of passages 12 provided in the side wall of the inner cylinder 3. A cylindrical connection port 13 is provided on the side wall at the lower end of the separator tube 10, with its tip protruding laterally and opening. A mounting hole 14 is provided on the side wall of the outer cylinder 4 at a position opposite to the connection port 13.

[0032] The mounting hole 14 is positioned coaxially with the connection port 13 and has an inner diameter larger than the outer diameter of the connection port 13. A roughly bottomed cylindrical case 15 is provided on the outer surface of the side wall of the outer cylinder 4, surrounding the mounting hole 14. The damping force adjustment mechanism 121 is housed in the case 15.

[0033] Referring to Figure 3, the damping force adjustment mechanism 121 consists of a valve block 125 that integrates a back pressure type main valve 122 (third damping force valve), a pilot valve 123 which is a control valve that controls the opening pressure of the main valve 122, and a fail-safe valve 124 provided downstream of the pilot valve 123, and an actuator 201 (solenoid) that incorporates a mechanism for operating the pilot valve 123.

[0034] A joint member 127, which is a passage member, is inserted into the case 15. The joint member 127 has a cylindrical tube portion 128 at one end which is inserted into the connection port 13, and a flange portion 129 formed at the other end of the tube portion 128. The joint member 127 is covered with a sealing member, thereby sealing the contact portion with the connection port 13 and the main body 73, which will be described later. The bottom of the case 15 is provided with a plurality of grooves that connect the flow path 74 outside the valve block 125, i.e., the damping force adjustment mechanism 121, and the reservoir 6, thereby forming a plurality of passages 75 that connect the flow path 74 and the reservoir 6.

[0035] The valve block 125 includes an annular main body 73, an annular pilot body 53, and a pilot pin 54 that connects the main body 73 and the pilot body 53. One end face of the main body 73 on the axial side facing the cylinder 2 (the left end face in Figure 3) abuts against the flange portion 129 of the joint member 127. An annular seat portion 76 is formed on the outer peripheral edge of the other end face of the main body 73 opposite to the axial side facing the cylinder 2 (the right end face in Figure 3). The outer peripheral edge of the main valve disc 77, which together with the seat portion 76 constitutes the main valve 122, seats to and from this seat portion 76.

[0036] The inner peripheral edge of the main valve disc 77 is clamped between the pilot pin 54 and the clamp portion 78 of the main body 73. An annular packing 79 is fixed to the outer peripheral edge of the main valve disc 77 on the back side (right side in Figure 3) opposite to the cylinder 2 in the axial direction. An annular clamp portion 78 is formed on the inner peripheral edge of the main body 73. An annular recess is provided on the other end face of the main body 73 opposite to the cylinder 2 in the axial direction, and an annular passage 95 is formed when the main valve disc 77 sits on the seat portion 76. On the other hand, a recess 96 is formed on one end face of the main body 73 on the cylinder side. The main body 73 is also provided with a plurality of passages 97 that connect the recess 96 on the cylinder 2 side in the axial direction and the annular passage 95 on the opposite side of the cylinder.

[0037] The pilot pin 54 is formed in a bottomed cylindrical shape, with an introduction orifice 55 formed at the bottom. A large-diameter portion 56 for clamping the main valve disc 77 is formed at the axial intermediate position of the pilot pin 54. One end of the pilot pin 54 on the cylinder side (the left end in Figure 3) is press-fitted into the axial hole 98 of the main body 73. The other end of the pilot pin 54 (the right end in Figure 3) is press-fitted into the axial hole 58 of the pilot body 53. Multiple grooves extending in the axial direction (left-right direction in Figure 3) are formed on the outer circumferential surface of the end of the pilot pin 54 opposite to the cylinder 2 in the axial direction. By press-fitting the end of the pilot pin 54 opposite to the cylinder 2 in the axial direction into the axial hole 58 of the pilot body 53, multiple passages 57 are formed between the end of the pilot pin 54 opposite to the cylinder 2 and the pilot body 53.

[0038] The pilot body 53 is formed in a substantially bottomed cylindrical shape with an opening on the side opposite to the axial cylinder 2. A flexible disc 59 is provided on the end face of the pilot body 53 on the side of the axial cylinder 2, clamped by the large-diameter portion 56 of the pilot pin 54. A cylindrical portion 60 coaxial with the pilot body 53 is formed on the outer peripheral edge of the pilot body 53 on the side of the axial cylinder 2. A packing 79, fixed to the back side of the main valve disc 77 opposite to the axial cylinder 2, is slidably fitted to the inner circumferential surface of the cylindrical portion 60. As a result, a pilot chamber 115 is formed on the back side of the main valve disc 77.

[0039] The pilot chamber 115 applies internal pressure in the closing direction to the main valve disc 77, i.e., the main valve 122. The main valve 122 opens when the main valve disc 77 separates from the seat portion 76 due to the pressure of the oil liquid L introduced into the annular passage 95 from the annular oil passage 11, through the flow path 116 inside the joint member 127, the recess 96 in the main body 73, and the multiple passages 97. When the main valve 122 opens, it connects the passage 97 in the main body 73 to the flow path 74 outside the valve block 125.

[0040] The pilot body 53 has multiple passages 117 that penetrate its bottom in the axial direction. An annular seat portion is provided on one end face of the bottom of the pilot body 53 on the cylinder 2 side in the axial direction, and a flexible disc 59 is seated on this seat portion. This forms an annular passage between the flexible disc 59 and the end face of the bottom of the pilot body 53 on the cylinder 2 side in the axial direction. The cylinder 2 side (left side in Figure 3) of the passage 117 opens into this annular passage. The flexible disc 59 flexes in response to the internal pressure of the pilot chamber 115, thereby imparting volume elasticity to the pilot chamber 115.

[0041] The flexible disc 59 is centered by its outer peripheral edge contacting the inner circumferential surface of the cylindrical portion 60 of the pilot body 53. The flexible disc 59 is constructed by stacking multiple discs, and among these multiple discs, the disc that contacts the large diameter portion 56 of the pilot pin 54 has a notch 118 that communicates with a passage 57 formed between the pilot body 53 and the pilot pin 54. The oil L from the annular oil passage 11 is introduced into the damping force adjustment mechanism 121 via the connection port 13 and the flow path 116 in the joint member 127, and further introduced into the pilot chamber 115 via the introduction passage, i.e., the introduction orifice 55, the axial hole 119 of the pilot pin 54, the passage 57, and the notch 118.

[0042] A valve chamber 168 is formed inside the pilot body 53. An annular seat portion 169 is provided at the bottom of the pilot body 53, formed on the periphery of the opening of the shaft hole 58 opposite to the cylinder 2 in the axial direction. The valve body 171, provided in the valve chamber 168, seats onto and away from the seat portion 169. The seat portion 169 and the valve body 171 constitute the pilot valve 123. The valve body 171 is formed in a substantially cylindrical shape, and one end on the axial side facing the cylinder 2 that seats onto and away from the seat portion 169 is tapered. An outer flange-shaped spring receiving portion 172 is formed on the other end of the valve body 171 opposite to the cylinder 2 in the axial direction.

[0043] The valve body 171 is elastically supported by a pilot spring 173 and a fail-safe disc 179 so as to be movable in the axial direction (left-right direction in Figure 3) opposite the seat portion 169. A stepped portion 177 is formed on the cylindrical portion 175 of the pilot body 53 opposite the cylinder 2 in the axial direction. The outer peripheral edge of the pilot spring 173 is supported by the stepped portion 177. Inside the cylindrical portion 175, the pilot spring 173, retainer 178, fail-safe disc 179, retainer 180, spacer 181, and washer 182 are inserted in this order.

[0044] The washer 182 has a shaft hole 183 through which an operating rod 207 described later is inserted. Between the washer 182 and a solenoid case 202 described later, a substantially bottomed cylindrical cap 157 is provided. The cylindrical portion of the cap 157 is fitted to the outer peripheral side of the cylindrical portion 175 of the pilot body 53. The cap 157 is provided with a passage (not shown) that constantly connects the passage between the operating rod 207 and the shaft hole 183 of the washer 182 and the flow path 74 outside the valve block 125.

[0045] The actuator 201 is an integrated unit in which a coil 203, a core 204, a core 205, a plunger 206, and a hollow operating rod 207 connected to the plunger 206 are incorporated in a solenoid case 202. A spacer 208 and a cover 209 are inserted into the end of the solenoid case 202 on the opposite side of the cylinder 2 in the axial direction, and the components in the solenoid case 202 are fixed by caulking the end of the solenoid case 202 on the opposite side of the cylinder 2 in the axial direction. When the coil 203 is energized from the control device 300 via the lead wire 301, the plunger 206 generates an axial thrust corresponding to the current value. Therefore, the actuator 201 is a solenoid actuator. The pilot valve 123 and the actuator 201 constitute the solenoid valve 200. The solenoid valve 200 can be arbitrarily opened and closed by the actuator 201 which is a solenoid for the pilot valve 123. The solenoid valve 200 is of the normally open type that is in the open state when not driven. Note that the solenoid valve 200 can also be changed to the normally closed type that is in the closed state when not driven.

[0046] One end side of the solenoid case 202 is inserted into the case 15 from the opening of the case 15, and the gap between them is sealed by a seal member 210. The end of the operating rod 207 on the cylinder 2 side in the axial direction projects into the valve chamber 168, and a valve body 171 is fixed to this end. The solenoid case 202 is fixed to the case 15 by tightening the nut 211 to compress a retaining ring 212 mounted in an annular groove. Thereby, the valve block 125 and the actuator 201 are coupled.

[0047] When the coil 203 is de-energized, the valve body 171 is biased in the separating direction of the valve body 171 (right direction in FIG. 3) by the spring force of the pilot spring 173, and the spring receiving portion 172 abuts (seats) against the fail-safe disk 179. On the other hand, when the coil 203 is energized, the operating rod 207 is biased in the seating direction of the valve body 171 (left direction in FIG. 3), so that the valve body 171 moves against the spring force of the pilot spring 173 and seats on the seat portion 169 of the pilot pin 54. Then, by changing the current value supplied to the coil 203, the opening pressure of the valve body 171 is controlled.

[0048] For the sake of convenience, the flow of the hydraulic fluid L in the damping force adjusting mechanism 121 is roughly classified into a main flow and a pilot flow. The main flow is the flow of the hydraulic fluid L flowing through the main passage 225 (fourth passage (see FIG. 4)) that connects the recess 96 on one end side of the main body 73 and the downstream side (flow path 74 side) of the main valve 122. The main passage 22 is composed of a plurality of passages 97 and an annular passage 95 of the main body 73, and discharges the hydraulic fluid L introduced into the annular passage 95 through the plurality of passages 97 from the connection port 13 side to the flow path 74 communicating with the reservoir 6 through the main valve 122 that opens the valve. The main valve 122 generates a damping force at that time. The main passage 225 is a portion provided in the damping force adjusting mechanism 121 of the passage 221 (see FIG. 4) that connects the upper cylinder chamber 2A and the reservoir 6, and is a passage for flowing the hydraulic fluid L from the upper cylinder chamber 2A to the reservoir 6 through the main valve 122. The main passage 225 includes the passage 97, the annular passage 95, and the main valve 122. The main passage 225 communicates with the upper cylinder chamber 2A through the passage 12 of the inner cylinder 3, the annular oil passage 11, the flow path 116, and the recess 96. The main passage 225 communicates with the reservoir 6 through the flow path 74, the passage 75, and the mounting hole 14.

[0049] On the other hand, the pilot flow is the flow of oil L through the aforementioned introduction passage, namely the pilot passage 226 (third passage (see Figure 4)) which includes the introduction orifice 55, the shaft hole 119 of the pilot pin 54, the passage 57 and the notch 118. The pilot passage 226 discharges the oil L introduced into the valve chamber 168 from the connection port 13 via the introduction orifice 55 when the pilot valve 123 is open to the reservoir 6 via the passage between the shaft hole 183 of the washer 182 communicating with the valve chamber 168 and the operating rod 207, the passage of the cap 157 (not shown), and the flow path 74 on the outside of the valve block 125. The pilot passage 226 is the portion of the passage 221 that connects the cylinder upper chamber 2A and the reservoir 6 that is provided within the damping force adjustment mechanism 121, and is the passage through which oil L flows from the cylinder upper chamber 2A to the reservoir 6 via the pilot valve 123. The pilot passage 226 includes an introduction orifice 55, a shaft hole 119, a pilot valve 123, a valve chamber 168, a shaft hole 183, and a passage (not shown) of the cap 157. The pilot passage 226 communicates with the cylinder upper chamber 2A via the passage 12 of the inner cylinder 3, the annular oil passage 11, the flow path 116, and the recess 96. The pilot passage 226 communicates with the reservoir 6 via the flow path 74, the passage 75, and the mounting hole 14.

[0050] The solenoid valve 200 operates such that the pilot valve 123 can arbitrarily adjust the flow of the oil liquid L depending on the magnitude of the current supplied from the control device 300 to the coil 203 of the actuator 201.

[0051] Referring to Figure 4, the hydraulic circuit of the damping force adjustable shock absorber 1 according to the first embodiment will be described.

[0052] The damping force adjustable shock absorber 1 has passages 220a (second passage) and 220b (second passage) that connect the upper cylinder chamber 2A and the lower cylinder chamber 2B. Passages 220a and 220b are provided in parallel. Passage 220a is provided in the piston 18 and has passage 39. Passage 220a is provided with a compression-side intake valve 71 (second damping force valve) that allows the flow of oil L from the lower cylinder chamber 2B to the upper cylinder chamber 2A and controls its flow.

[0053] The passage 220b is provided in the piston 18 and has a passage 37. The passage 220b is provided with an extension-side relief valve 91 (second damping force valve) that allows the flow of oil L from the upper cylinder chamber 2A to the lower cylinder chamber 2B and controls its flow.

[0054] The damping force adjustable shock absorber 1 has a passage 223 (first passage) that connects the upper cylinder chamber 2A and the lower cylinder chamber 2B. The passage 223 is provided in parallel with passages 220a, 220b and passage 221, which will be described later. The passage 223 includes the passage 37 of the piston 18, the orifice 88 of the retainer 82, the annular passage 46 of the piston 18, the passage 30 of the piston rod 21, the passage 153 of the passage member 102, the cap chamber 146, the passage 161 of the valve disc 100, and the passages 141 and 143 of the valve body 106.

[0055] The passage 223 splits into passage 223a and passage 223b on the side of the cylinder lower chamber 2B that is above the orifice 88.

[0056] The passage 223a includes the passage 143 of the valve body 106. The passage 223a is provided with a compression-side damping force valve 105 (first damping force valve) that allows the flow of oil L from the lower cylinder chamber 2B to the upper cylinder chamber 2A and controls its flow.

[0057] The passage 223b includes the passage 161 of the valve disc 100 and the passage 141 of the valve body 106. The passage 223b is provided with an extension damping force valve 108 (first damping force valve) that allows the flow of oil L from the upper cylinder chamber 2A to the lower cylinder chamber 2B and controls its flow.

[0058] In the passage 223, damping force valves 105 and 108 are provided in parallel, and an orifice 88 is provided in series with damping force valves 105 and 108 on the cylinder upper chamber 2A side of damping force valves 105 and 108.

[0059] The passage 223 has an extension-side path passing through the extension-side passage 37 formed in the piston 18, the orifice 88 formed in the retainer 82, the annular passage 46 formed on the inner circumference of the piston 18, the passage 30 formed in the mounting shaft portion 28, the passage 153 formed in the passage member 102, the cap chamber 146, the passage 161 formed in the valve disc 100, the passage 141 formed in the valve body 106 and the extension-side damping force valve 108, and a compression-side path passing through the passage 143 formed in the valve body 106, the compression-side damping force valve 105, the cap chamber 146, the passage 153, the passage 30, the annular passage 46, the orifice 88 and the passage 37.

[0060] The lower cylinder chamber 2B and the reservoir 6 are connected by a passage 222. The passage 222 includes passages 195, 196 and an orifice 198 formed in the base valve 25. The passage 222 is divided into passage 222a, passage 222b, and passage 222c.

[0061] Passage 222a includes passage 195 of the base valve 25. A relief valve 192 is provided in passage 222a. Passage 222b includes passage 196 of the base valve 25. A suction valve 193 is provided in passage 222b. An orifice 198 is provided in passage 222c. Therefore, the relief valve 192, suction valve 193, and orifice 198 are provided in parallel in passage 222.

[0062] The cylinder upper chamber 2A and the reservoir 6 are connected by a passage 221. The passage 221 includes a main passage 225 formed in the damping force adjustment mechanism 121, a pilot passage 226, and a connecting passage 227 that connects the main valve 122 and the pilot passage 226. The passage 221 includes a passage 12 in the inner cylinder 3, an annular oil passage 11, a flow path 116, a recess 96, a flow path 74, a passage 75, and a mounting hole 14. The connecting passage 227 includes a plurality of passages 117 in the pilot body 53, a notch 118 in the flexible disc 59, and a pilot chamber 115.

[0063] The main passage 225 is provided with the main valve 122 of the damping force adjustment mechanism 121. The main valve 122 controls the flow of oil L in the main passage 225 from the upper cylinder chamber 2A to the reservoir 6 to generate damping force. The pilot passage 226 is provided with an introduction orifice 55. The introduction orifice 55 is positioned on the upper cylinder chamber 2A side with respect to the connection portion 228 between the pilot passage 226 and the connecting passage 227. The pilot passage 226 is also provided with a pilot valve 123 and a solenoid valve 200 including an actuator 201. The solenoid valve 200 is positioned on the reservoir 6 side with respect to the connection portion 228. In passage 221, the main valve 122, the introduction orifice 55, and the solenoid valve 200 are provided in parallel.

[0064] In the damping force adjustment mechanism 121 of the first embodiment, the damping force valve 105 (first damping force valve) opens at a lower pressure than the intake valve 71 (second damping force valve) during the compression stroke. In other words, the damping force valve 105 opens in the compression stroke due to a predetermined first pressure generated in the cylinder 2, and the intake valve 71 opens in the compression stroke due to a second pressure generated in the cylinder 2 that is different from this first pressure. Furthermore, the damping force valve 105 opens in the compression stroke due to a predetermined first pressure generated in the lower cylinder chamber 2B, and the intake valve 71 opens in the compression stroke due to a second pressure generated in the lower cylinder chamber 2B that is higher than this first pressure. The piston speed, which is the axial movement speed of the piston 18, is such that the piston speed at which the compression-side damping force valve 105 opens is lower than the piston speed at which the intake valve 71 opens during the compression stroke.

[0065] The damping valve 105 opens at a lower pressure than the relief valve 192 provided in the base valve 25 during the compression stroke. In other words, the damping valve 105 opens at a predetermined first pressure generated in the cylinder 2 during the compression stroke, and the relief valve 192 opens at a third pressure, different from this first pressure, generated in the cylinder 2 during the compression stroke. To put it another way, the damping valve 105 opens at a predetermined first pressure generated in the lower cylinder chamber 2B during the compression stroke, and the relief valve 192 opens at a third pressure, higher than this first pressure, generated in the lower cylinder chamber 2B during the compression stroke. During the compression stroke, the piston speed at which the compression-side damping valve 105 opens is lower than the piston speed at which the compression-side relief valve 192 opens.

[0066] The damping force valve 108 (first damping force valve) opens at a lower pressure than the relief valve 91 (second damping force valve) during the extension stroke. In other words, the damping force valve 108 opens in the extension stroke due to a predetermined first pressure generated in the cylinder 2, and the relief valve 91 opens in the extension stroke due to a second pressure, which is different from this first pressure, generated in the cylinder 2. Furthermore, the damping force valve 108 opens in the extension stroke due to a predetermined first pressure generated in the lower cylinder chamber 2B, and the relief valve 91 opens in the extension stroke due to a second pressure, which is lower than this first pressure, generated in the lower cylinder chamber 2B. During the extension stroke, the piston speed at which the extension-side damping force valve 108 opens is lower than the piston speed at which the extension-side relief valve 91 opens.

[0067] In the damping force adjustable shock absorber 1, for example, the portion of the main shaft portion 27 of the piston rod 21 that extends outward from the sealing member 23 is connected to the vehicle body side, and the outer cylinder 4 of the cylinder 2 is connected to the wheel side. The damping force adjustable shock absorber 1 is installed between the vehicle body side and the wheel side of the vehicle and generates damping force, and the damping force can be adjusted by operating the actuator 201 with an electrical signal from the control device 300.

[0068] The control device 300 is installed in the vehicle. The vehicle is equipped with a switch (not shown) that can be switched at will by the vehicle's driver. The switch (not shown) allows the vehicle to switch between a first driving mode (Comfort mode) and a second driving mode (Sport mode).

[0069] When the vehicle driver operates a switch and selects either the first or second driving mode, the control device 300 changes the output current value to the actuator 201. This allows the control device 300 to control the opening and closing of the solenoid valve 200, making it possible to keep the solenoid valve 200 closed or open. In other words, the control device 300 is installed in the vehicle and can make the solenoid valve 200 closed or open by changing the output current value to the actuator 201 according to the first and second driving modes, which can be arbitrarily selected by the vehicle's driver. Here, the closed state is a state in which the solenoid valve 200 is closed regardless of the pressure it receives. The open state is a state in which the solenoid valve 200 can be closed and opened depending on the pressure it receives. The control device 300 makes the output current value to the actuator 201 lower when the first driving mode is selected than the output current value to the actuator 201 when the second driving mode is selected.

[0070] In the damping force adjustable shock absorber 1, when the piston speed during the extension stroke is in the very low speed range (for example, 0.002 to 0.008 m / s), the damping force valve 108 opens if the current value input from the control device 300 to the actuator 201 is a current value that closes the solenoid valve 200. When the second travel mode is selected, the control device 300 controls the damping force adjustable shock absorber 1 so that the current value input to the actuator 201 in the very low speed range of the piston speed during the extension stroke is a current value that closes the solenoid valve 200. Therefore, in this case, the damping force valve 108 opens and generates damping force.

[0071] The damping force adjustable shock absorber 1 generates damping force with the damping force valve 108 closed when the current value input from the control device 300 to the actuator 201 is the current value that opens the solenoid valve 200 during the very low speed range of the piston speed in the extension stroke. When the first travel mode is selected, the control device 300 controls the damping force adjustable shock absorber 1 so that the current value input to the actuator 201 is the current value that opens the solenoid valve 200 during the very low speed range of the piston speed in the extension stroke. In this case, the solenoid valve 200 opens and generates damping force.

[0072] In the damping force adjustable shock absorber 1, if the current value input from the control device 300 to the actuator 201 is a current value that closes the solenoid valve 200 in the very low speed range of the piston speed during the extension stroke, the first pressure during the extension stroke is generated in the cylinder lower chamber 2B and the damping force valve 108 opens. When the second travel mode is selected, the control device 300 controls the damping force adjustable shock absorber 1 so that the current value input to the actuator 201 is a current value that closes the solenoid valve 200 in the very low speed range of the piston speed during the extension stroke. In this case, the damping force valve 108 opens and generates damping force.

[0073] The damping force adjustable shock absorber 1, in the very low speed range of the piston speed during the extension stroke, generates damping force with the damping force valve 108 closed when the first travel mode is selected and the current value input from the control device 300 to the actuator 201 is the current value that opens the solenoid valve 200. When the first travel mode is selected, the damping force adjustable shock absorber 1 controls the control device 300 so that the current value input to the actuator 201 in the very low speed range of the piston speed during the extension stroke is the current value that opens the solenoid valve 200. In this case, the solenoid valve 200 opens and generates damping force.

[0074] The damping force adjustable shock absorber 1 opens the damping force valve 105 when the current value input from the control device 300 to the actuator 201 is a current value that closes the solenoid valve 200 in the very low speed range of the piston speed during the compression stroke (for example, 0.002 to 0.008 m / s). When the second travel mode is selected, the control device 300 controls the damping force adjustable shock absorber 1 so that the current value input to the actuator 201 is a current value that closes the solenoid valve 200 in the very low speed range of the piston speed during the compression stroke. In this case, the damping force valve 105 opens and generates damping force.

[0075] The damping force adjustable shock absorber 1 generates damping force with the damping force valve 105 closed when the current value input from the control device 300 to the actuator 201 is the current value that opens the solenoid valve 200 during the very low speed range of the piston speed in the compression stroke. Then, when the first travel mode is selected, the damping force adjustable shock absorber 1 controls the control device 300 so that the current value input to the actuator 201 is the current value that opens the solenoid valve 200 during the very low speed range of the piston speed in the compression stroke. In this case, the solenoid valve 200 opens and generates damping force.

[0076] In the damping force adjustable shock absorber 1, when the second travel mode is selected and the current value input from the control device 300 to the actuator 201 is a current value that closes the solenoid valve 200, the first pressure is generated in the compression stroke and the damping force valve 105 opens. Furthermore, when the second travel mode is selected, the damping force adjustable shock absorber 1 controls the control device 300 so that the current value input to the actuator 201 in the very low speed range of the piston speed during the compression stroke is a current value that closes the solenoid valve 200. In this case, the damping force valve 105 opens and generates damping force.

[0077] In the damping force adjustable shock absorber 1, if the current value input from the control device 300 to the actuator 201 in the very low speed range of the piston speed during the compression stroke is the current value that opens the solenoid valve 200, the generation of the first pressure during the compression stroke is suppressed and damping force is generated with the damping force valve 105 closed. Furthermore, when the first travel mode is selected, the control device 300 controls the damping force adjustable shock absorber 1 so that the current value input to the actuator 201 in the very low speed range of the piston speed during the compression stroke is the current value that opens the solenoid valve 200. In this case, the solenoid valve 200 opens and damping force is generated.

[0078] The damping force adjustable shock absorber 1 operates, for example, as follows: <Extension stroke in hard mode> When the second driving mode is selected, the damping force adjustable shock absorber 1 enters hard mode, which generates a damping force with hard characteristics. In this hard mode, the current value input from the control device 300 to the actuator 201 becomes higher than in the soft mode, which will be described later.

[0079] In the hard mode extension stroke, in the friction region from when the piston speed is 0 until it reaches Ha1 (for example, 0.002 m / s), a damping force Fa1 (axial force) is generated by the frictional force of the sliding parts in the damping force adjustable shock absorber 1. When the piston speed reaches Ha1, the extension-side damping force valve 108, located in the passage 223b of the piston 18, opens, allowing the oil liquid L to flow from the upper cylinder chamber 2A to the lower cylinder chamber 2B via the passage 223b. Then, in the very low-speed range from when the piston speed at which the damping force valve 108 opens is Ha2 (for example, 0.008 m / s), which is greater than Ha1, a damping force is mainly generated by the damping force valve 108. Here, in the very low-speed range of the piston speed during the extension stroke in hard mode, the current value input from the control device 300 to the coil 203 of the actuator 201 is the current value that closes the solenoid valve 200. Therefore, the pilot valve 123 of the solenoid valve 200 provided in the pilot passage 226 is in the closed state. As a result, the first pressure during the extension stroke is generated in the lower cylinder chamber 2B, and as described above, with the pilot valve 123 remaining in the closed state, the damping force valve 108 opens and generates damping force.

[0080] After the piston speed reaches Ha2, the pilot valve 123 opens, allowing the oil L to flow from the upper cylinder chamber 2A to the reservoir 6 via the pilot passage 226. In the low-speed range after the pilot valve 123 opens, from Ha2 until the piston speed increases to Ha3 (which is greater than Ha2), a damping force is generated in proportion to the amount the pilot valve 123 is open. Therefore, in the extension stroke of hard mode, the damping force is higher in the low-speed range of the piston speed compared to the very low-speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0081] When the piston speed reaches Ha3, the flow of the oil L is restricted by the introduction orifice 55 of the damping force adjustment mechanism 121, increasing the differential pressure generated at the main valve 122 in the main passage 225. This causes the main valve 122 to open, allowing the oil L to flow from the upper cylinder chamber 2A to the reservoir 6 via the main passage 225. In the medium speed range from when the piston speed is Ha3 until it reaches Ha4 (which is higher than Ha3), after the main valve 122 has opened, damping force is generated by the main valve 122. Therefore, in the extension stroke of hard mode, the damping force is higher in the medium speed range of piston speed compared to the low speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0082] Furthermore, in the high-speed range after the piston speed reaches Ha4, the relief valve 91 provided in the passage 220b of the piston 18 opens, generating a damping force. Therefore, in the extension stroke of hard mode, the damping force is higher in the high-speed range of piston speed compared to the medium-speed range, but the rate of increase in damping force with increasing piston speed is lower, resulting in a softer characteristic.

[0083] <Soft Mode Extension Stroke> When the first driving mode is selected, the damping force adjustable shock absorber 1 enters soft mode, which generates a damping force with soft characteristics. In this soft mode, the current value input from the control device 300 to the actuator 201 is lower than that of the hard mode described above.

[0084] In this soft mode, in the friction region from when the piston speed is 0 until it reaches a value greater than 0, Sa1 (for example, 0.002 m / s), a damping force Fa1 (axial force) is generated by the frictional force of the sliding parts in the damping force adjustable shock absorber 1. In the very low speed range from when the piston speed is 0 until it reaches Sa2 (for example, 0.008 m / s), which is greater than Sa1 and causes the damping force valve 108 to open, the current value input from the control device 300 to the actuator 201 is the current value that causes the solenoid valve 200 to open. Therefore, the pilot valve 123 of the solenoid valve 200, which is located in the pilot passage 226, opens before the damping force valve 108, which is located in the passage 223b, opens, allowing the oil L from the cylinder upper chamber 2A to flow to the reservoir 6 via the pilot passage 226. Thus, in the very low speed range, the pilot valve 123 of the solenoid valve 200 generates damping force with the damping force valve 108 closed. In the very low speed range, the pilot valve 123 of the solenoid valve 200 suppresses the generation of the first pressure in the lower cylinder chamber 2B during the extension stroke, maintaining the damping force valve 108 in a closed state, and the pilot valve 123 generates damping force.

[0085] After the piston speed reaches Sa2, the damping force valve 108 located in the passage 223b opens, and damping force is generated by the damping force valve 108. In the low-speed range from when the piston speed is Sa2 until it reaches Sa3, which is greater than Sa2, damping force is generated by the damping force valve 108. Therefore, in the extension stroke of the soft mode, the rate of increase in damping force relative to the increase in piston speed is lower in the low-speed range of the piston speed than in the very low-speed range, resulting in a softer ride.

[0086] When the piston speed reaches Sa3, the main valve 122 located in the main passage 225 opens. After the main valve 122 of the damping force adjustment mechanism 121 opens, in the medium speed range from when the piston speed is Sa3 until it reaches Sa4 (which is greater than Sa3), damping force is generated by the main valve 122. Therefore, in the extension stroke of the soft mode, the damping force is higher in the medium speed range of the piston speed compared to the low speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a soft characteristic.

[0087] In the high-speed range after the piston speed reaches Sa4, the relief valve 91 of the piston 18 opens, generating a damping force. Therefore, in the extension stroke of the soft mode, the damping force is higher in the high-speed range of the piston speed compared to the medium-speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0088] During the extension stroke, the suction valve 193 opens to allow oil L to flow from the reservoir 6 into the cylinder lower chamber 2B so that the pressure in the cylinder lower chamber 2B does not fall below the pressure in the reservoir 6.

[0089] In the extension stroke, the damping force of the adjustable shock absorber 1 is lower and softer than the damping force generated when the first travel mode is selected, for the same piston speed across the entire range of piston speeds.

[0090] Furthermore, in the very low-speed range of the extension stroke, even with the same piston speed, the damping force adjustable shock absorber 1 has the damping force valve 108 open and generate damping force in the second travel mode, while in the first travel mode, the damping force valve 108 does not open and does not generate damping force. Therefore, as shown by the solid line above the horizontal axis in Figure 5, in the extension stroke at a very low piston speed (for example, 0.005 m / s), in the first travel mode, where the current value to the actuator 201 is in region A1 and the damping force valve 108 is closed, the solenoid valve 200 that opens while the damping force valve 108 is closed generates a lower and softer damping force than the damping force generated by the damping force valve 108 that opens while the solenoid valve 200 is closed in region A2 and the current value to the actuator 201 is high. In other words, in the extension stroke, in the second travel mode where the current value to the actuator 201 is in region A2, the damping force valve 108, which opens when the solenoid valve 200 is closed, generates a higher and harder damping force than the damping force generated by the solenoid valve 200, which opens when the damping force valve 108 is closed, in the first travel mode where the current value to the actuator 201 is in region A1. Note that the dashed line above the horizontal axis in Figure 5 shows the damping force when the damping force valve 108 is not provided. In this configuration, in the extension stroke at a very low piston speed (for example, 0.005 m / s), the damping force is equally soft in the first travel mode where the current value to the actuator 201 is in region A1, and in the second travel mode where the current value to the actuator 201 is in region A2.

[0091] <Compression Stroke in Hard Mode> When the second driving mode is selected, the damping force adjustable shock absorber 1 enters hard mode, which generates a damping force with hard characteristics. In this hard mode, the current value input from the control device 300 to the actuator 201 becomes higher than in the soft mode, which will be described later.

[0092] In this hard mode compression stroke, in the friction region from when the piston speed is 0 until it reaches Hb1 (for example, 0.002 m / s), a damping force Fb1 (axial force) is generated by the frictional force of the sliding parts in the damping force adjustable shock absorber 1. When the piston speed reaches Hb1, the orifice 198 of the base valve 25 allows oil L to flow from the lower cylinder chamber 2B to the reservoir 6, and the compression-side damping force valve 105 provided in the passage 223a of the piston 18 opens, allowing oil L to flow from the lower cylinder chamber 2B to the upper cylinder chamber 2A via the passage 223a. Then, in the very low speed region from when the piston speed is 0 until it reaches Hb2 (for example, 0.008 m / s), which is greater than Hb1, a damping force is generated by the damping force valve 105.

[0093] Here, during the compression stroke, the volume of the oil L in the upper cylinder chamber 2A attempts to flow to the damping force adjustment mechanism 121 due to the volume of the piston rod 21 entering the cylinder 2. However, in the very low speed range of the compression stroke in hard mode, the current value input from the control device 300 to the actuator 201 is the current value that closes the solenoid valve 200. Therefore, in the very low speed range where the piston speed is up to Hb2, the pilot valve 123 provided in the pilot passage 226 is in a closed state. As a result, the first pressure during the compression stroke is generated in the lower cylinder chamber 2B, and as described above, with the pilot valve 123 in a closed state, the damping force valve 105 opens, and the damping force valve 105 generates damping force.

[0094] After the piston speed reaches Hb2, the pilot valve 123 of the solenoid valve 200 located in the pilot passage 226 opens, allowing the oil fluid L, which is the volume of the piston rod 21 entering, to flow from the upper cylinder chamber 2A to the reservoir 6 via the pilot passage 226. In the low-speed range after the pilot valve 123 opens, from when the piston speed is Hb2 until it reaches Hb3 (which is greater than Hb2), a damping force is generated in proportion to the amount the pilot valve 123 is opened. Therefore, in the compression stroke of hard mode, the damping force is higher in the low-speed range of the piston speed compared to the very low-speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0095] When the piston speed reaches Hb3, the flow of the oil L is restricted by the introduction orifice 55 of the damping force adjustment mechanism 121, which increases the differential pressure generated in the main valve 122 provided in the main passage 225. This causes the main valve 122 to open, allowing the oil L to flow from the cylinder upper chamber 2A to the reservoir 6 via the main passage 225. After the main valve 122 opens, in the medium speed range from Hb3 to before the piston speed increases to Hb4 (which is greater than Hb3), damping force is generated by the main valve 122. Therefore, in the compression stroke of hard mode, the damping force is higher in the medium speed range of the piston speed compared to the low speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0096] Furthermore, in the high-speed range after the piston speed reaches Hb4, the intake valve 71 opens, allowing the oil liquid L to flow through the passage 220a. In the high-speed range, damping force is generated by the intake valve 71. Therefore, in the compression stroke of hard mode, although the damping force is higher in the high-speed range of piston speed compared to the medium-speed range, the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0097] <Compression stroke in soft mode> When the first driving mode is selected, the damping force adjustable shock absorber 1 enters soft mode, which generates a damping force with soft characteristics. In this soft mode, the current value input from the control device 300 to the actuator 201 is lower than that of the hard mode described above.

[0098] In this soft mode compression stroke, in the friction region from when the piston speed is 0 until it reaches Sb1 (for example, 0.002 m / s), a damping force Fb1 (axial force) is generated by the frictional force of the sliding parts in the damping force adjustable shock absorber 1. In the very low speed range from when the piston speed is 0 until it reaches Sb2 (for example, 0.008 m / s), which is greater than Sb1, oil L flows from the lower cylinder chamber 2B to the reservoir 6 via the orifice 198 of the base valve 25. Also in the very low speed range, the current value input from the control device 300 to the actuator 201 is the current value that opens the solenoid valve 200, and the pilot valve 123 of the solenoid valve 200 provided in the pilot passage 226 opens before the damping force valve 105 provided in the passage 223a opens, allowing the increase in oil L in the upper cylinder chamber 2A due to the entry of the piston rod 21 to flow to the reservoir 6 via the pilot passage 226. Therefore, in the very low speed range, the damping force valve 105 is closed, and the pilot valve 123 of the solenoid valve 200 generates damping force. In the very low speed range, the pilot valve 123 of the solenoid valve 200 suppresses the generation of the first pressure in the lower cylinder chamber 2B during the compression stroke, thereby maintaining the damping force valve 105 in a closed state.

[0099] After the piston speed reaches Sb2, the damping force valve 105 provided in the passage 223a opens, and damping force is generated by the damping force valve 105. In the low-speed range from when the piston speed is Sb2 until it is greater than Sb2 and before the main valve 122 of the damping force adjustment mechanism 121 opens at Sb3, damping force is generated by the damping force valve 105. Therefore, in the compression stroke of the soft mode, the damping force is higher in the low-speed range of the piston speed compared to the very low-speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a soft characteristic.

[0100] When the piston speed reaches Sb3, the main valve 122 located in the main passage 225 opens. After the main valve 122 of the damping force adjustment mechanism 121 opens, in the medium speed range from Sb3 to before the piston speed increases to Sb4 (which is greater than Sb3), damping force is generated by the main valve 122. Therefore, in the compression stroke of the soft mode, the damping force is higher in the medium speed range of the piston speed compared to the low speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a soft characteristic.

[0101] In the high-speed range after the piston speed reaches Sb4, the intake valve 71 of the piston 18 opens, generating a damping force from the intake valve 71. Therefore, in the compression stroke in soft mode, the damping force is higher in the high-speed range of piston speed compared to the medium-speed range, but the rate of increase in damping force with increasing piston speed is low, resulting in a softer characteristic.

[0102] In the compression stroke, the damping force of the damping force adjustable shock absorber 1 is lower and softer than the damping force generated when the first travel mode is selected, for the same piston speed across the entire range of piston speeds.

[0103] Furthermore, in the compression stroke, even at the same piston speed, the damping force adjustable shock absorber 1 has the damping force valve 105 open in the second travel mode and generates damping force, whereas in the first travel mode, the damping force valve 105 does not open and does not generate damping force. Therefore, as shown by the solid line below the horizontal axis in Figure 5, in the compression stroke at a very low piston speed (for example, 0.005 m / s), in the first travel mode, where the current value to the actuator 201 is in region A1 and the damping force valve 105 is closed, the solenoid valve 200 that opens while the damping force valve 105 is closed generates a lower and softer damping force than the damping force generated by the damping force valve 105 that opens while the solenoid valve 200 is closed in the second travel mode, where the current value to the actuator 201 is in region A2 and the damping force valve 200 is closed. In other words, in the second travel mode, where the current value to the actuator 201 is in region A2 and the current value to the actuator 201 is high during the compression stroke, the damping force valve 105, which opens when the solenoid valve 200 is closed, generates a higher and harder damping force than the damping force generated by the solenoid valve 200, which opens when the damping force valve 105 is closed, in the first travel mode, where the current value to the actuator 201 is in region A1 and the current value to the actuator 201 is low. Note that the dashed line below the horizontal axis in Figure 5 shows the damping force when the damping force valve 105 is not provided. In this configuration, during the compression stroke at a very low piston speed (for example, 0.005 m / s), the damping force is equally soft in the first travel mode, where the current value to the actuator 201 is in region A1 and the second travel mode, where the current value to the actuator 201 is in region A2.

[0104] Patent Document 1, mentioned above, discloses a damping force adjustable shock absorber having a piston attached to a piston rod and dividing the inside of a cylinder into two chambers, and a damping force adjustment mechanism including a solenoid, wherein a very low-speed valve that opens in the very low-speed range of the piston speed is provided on both the piston and the damping force adjustment mechanism. However, there is a need to optimize the damping force characteristics in a damping force adjustable shock absorber.

[0105] In the damping force adjustable shock absorber 1 of the first embodiment, the control device 300 can change the output current value to the actuator 201 to set the solenoid valve 200 to a closed state or an open / closed state. In the very low speed range of the piston speed during the extension stroke (for example, 0.002 to 0.008 m / s), if the current value input to the actuator 201 is the current value that closes the solenoid valve 200, the damping force valve 108 opens, and if the current value input to the actuator 201 is the current value that opens the solenoid valve 200, the damping force valve 108 is closed and damping force is generated. This makes it possible to generate damping force by opening the damping force valve 108, or to generate damping force by closing the damping force valve 108 and generating damping force with a device other than the damping force valve 108. Therefore, it is possible to optimize the damping force characteristics during the extension stroke.

[0106] Furthermore, in the damping force adjustable shock absorber 1, when the piston speed in the compression stroke is in the very low speed range, if the current value input to the actuator 201 is the current value that closes the solenoid valve 200, the damping force valve 105 opens, and if the current value input to the actuator 201 is the current value that opens the solenoid valve 200, the damping force valve 105 is closed and damping force is generated. This makes it possible to generate damping force by opening the damping force valve 105, or to generate damping force by closing the damping force valve 105 and generating damping force with a valve other than the damping force valve 105. Therefore, it is possible to optimize the damping force characteristics in the compression stroke.

[0107] The damping force adjustable shock absorber 1 is controlled by the control device 300 so that when a first driving mode, which can be arbitrarily selected by the vehicle driver, is selected, the current value input to the actuator 201 is a current value that opens the solenoid valve 200. When the first driving mode is selected according to the vehicle driver's request, damping force can be generated by closing the damping force valve 108 during the extension stroke, and damping force can be generated by closing the damping force valve 105 during the compression stroke. When the first driving mode is selected, during the extension stroke, the solenoid valve 200 is in an open state, allowing the oil liquid L to flow from the cylinder upper chamber 2A to the reservoir 6, and the opening of the damping force valve 108 is suppressed in the very low speed range, resulting in a low damping force. During the compression stroke, the solenoid valve 200 is in an open state, allowing the oil liquid L to flow from the cylinder upper chamber 2A to the reservoir 6, and the opening of the damping force valve 105 is suppressed in the very low speed range, resulting in a low damping force.

[0108] The damping force adjustable shock absorber 1 generates a damping force lower when the first driving mode is selected by the vehicle driver than when the second driving mode is selected. For example, as shown in Figure 5, in region A1 where the current value to the actuator 201 is low due to the selection of the first driving mode, a soft damping force characteristic is achieved in the very low-speed range, and in region A2 where the current value to the actuator 201 is high due to the selection of the second driving mode, a hard damping force characteristic is achieved in the very low-speed range, making it possible to achieve damping force characteristics that meet the vehicle driver's requirements. In the first driving mode, the damping force is lower, prioritizing ride comfort over the second driving mode. In the second driving mode, the damping force is higher, prioritizing handling stability over the first driving mode.

[0109] The damping force adjustable shock absorber 1, in the very low speed range of the piston speed during the extension stroke, if the current value input to the actuator 201 is the current value that closes the solenoid valve 200, the first pressure is generated during the extension stroke and the damping force valve 108 opens. If the current value input to the actuator 201 is the current value that opens the solenoid valve 200, the generation of the first pressure during the extension stroke is suppressed and damping force is generated with the damping force valve 108 closed. This makes it possible to generate damping force by opening the damping force valve 108, or to generate damping force by closing the damping force valve 108 and generating damping force with something other than the damping force valve 108. Therefore, it is possible to optimize the damping force characteristics during the extension stroke.

[0110] Furthermore, in the damping force adjustable shock absorber 1, when the current value input to the actuator 201 is the value that closes the solenoid valve 200 during the compression stroke, the first pressure is generated during the compression stroke and the damping force valve 105 opens. When the current value input to the actuator 201 is the value that opens the solenoid valve 200, the generation of the first pressure during the compression stroke is suppressed and damping force is generated with the damping force valve 105 closed. This makes it possible to generate damping force by opening the damping force valve 105, or to generate damping force by closing the damping force valve 105 and generating damping force with something other than the damping force valve 105. Therefore, it is possible to optimize the damping force characteristics during the compression stroke.

[0111] In the damping force adjustable shock absorber disclosed in Patent Document 1 mentioned above, a damping force valve that opens in the very low piston speed range is provided on both the piston and the damping force adjustment mechanism. As a result, the damping force adjustment mechanism becomes large, which presents challenges such as reduced vehicle mountability and difficulty in vehicle layout. Furthermore, if the damping force valve that opens in the very low piston speed range is provided on the damping force adjustment mechanism, this damping force valve will also generate damping force when the oil liquid L is flowed through the damping force adjustment mechanism, making it unclear the difference in damping force characteristics compared to when the damping force is generated by the damping force valve provided on the piston without flowing the oil liquid L through the damping force adjustment mechanism.

[0112] In the damping force adjustable shock absorber 1 of the first embodiment, the damping force valves 105 and 108 that open in the very low piston speed range are not provided in the damping force adjustment mechanism 121, but only in the piston 18. Therefore, it is possible to suppress the enlargement of the damping force adjustment mechanism 121, suppress the decrease in vehicle mountability of the damping force adjustable shock absorber 1, and suppress the difficulty of vehicle mounting layout.

[0113] Furthermore, in the damping force adjustable shock absorber 1, the damping force valves 105 and 108 that open in the very low piston speed range are not provided in the damping force adjustment mechanism 121, but only on the piston 18. Therefore, in the very low piston speed range when the first driving mode is selected, when the damping force adjustment mechanism 121 flows the oil liquid L, the damping force valves that open in the very low piston speed range do not generate damping force, and the difference in damping force characteristics compared to when the damping force adjustment mechanism 121 does not flow the oil liquid L in the very low piston speed range when the second driving mode is selected and damping force is generated by the damping force valves 105 and 108 provided on the piston 18 becomes clear. By generating damping force with the damping force valves 105 and 108 provided on the piston 18 in the very low piston speed range when the second driving mode is selected, it is possible to improve the handling stability of the vehicle.

[0114] [Second Embodiment] The damping force adjustable shock absorber of the second embodiment according to the present disclosure will be described mainly with reference to Figure 6. Here, the differences from the first embodiment will be described. Note that the same designations and reference numerals will be used for parts common to the first embodiment, and redundant explanations will be omitted.

[0115] In the damping force adjustable shock absorber 1A of the second embodiment, passage 223c is provided in parallel with passages 223a and 223b in passage 223, and an orifice 311 (connecting passage) is provided in passage 223c. Therefore, the orifice 311 is provided in parallel with the damping force valves 105 and 108. The orifice 311 constantly communicates between the cylinder upper chamber 2A and the cylinder lower chamber 2B in passage 223. The orifice 311 can be formed, for example, by a notch provided in at least one of the valve disc 100 and seat portion 136 of the damping force valve 105, or by a notch provided in at least one of the valve disc 120 and seat portion 139 of the damping force valve 108. The orifice 311 can also be formed by notches provided in both the damping force valves 105 and 108.

[0116] Here, the flow path area of ​​the orifice 311 is formed to be such that, when the solenoid valve 200 is closed in the very low piston speed range (for example, 0.002 to 0.008 m / s), a flow path area is generated in the cylinder upper chamber 2A that generates enough pressure to open the damping force valves 105 and 108.

[0117] Therefore, the damping force adjustable shock absorber 1A can achieve the same effects as the damping force adjustable shock absorber 1 of the first embodiment. Furthermore, since the damping force adjustable shock absorber 1A is provided with an orifice 311 that constantly communicates between the upper cylinder chamber 2A and the lower cylinder chamber 2B, for example, air can be bled when inserting the assembly of the piston 18 and piston rod 21 into the cylinder 2, improving ease of assembly. Here, if the flow area of ​​the orifice 311 is large, even if the solenoid valve 200 is closed in the very low piston speed range, the damping force valves 105 and 108 will not open and no damping force will be generated. Therefore, by setting the flow area of ​​the orifice 311 to a flow area that can generate a pressure in the upper cylinder chamber 2A that allows the damping force valves 105 and 108 to open in the very low piston speed range, it is possible to achieve both securing damping force in the very low speed range and improving ease of assembly.

[0118] [Third Embodiment] The damping force adjustable shock absorber of the third embodiment according to this disclosure will be described mainly with reference to Figure 7. Here, the differences from the first embodiment will be described. Note that the same designations and reference numerals will be used for parts common to the second embodiment, and redundant explanations will be omitted.

[0119] The damping force adjustable shock absorber 1B of the third embodiment has a passage 223B (first passage) that connects the upper cylinder chamber 2A and the lower cylinder chamber 2B. The damping force adjustable shock absorber 1B also has an orifice passage 322 provided in the passage 223B that controls the flow of oil liquid L by an orifice 321. The damping force adjustable shock absorber 1B also has a passage 323 (second passage) and a passage 324 (second passage) provided so as to branch off from the passage 223B and arranged in parallel with the orifice passage 322. The damping force adjustable shock absorber 1B also has a damping force valve 105B (first damping force valve) provided in the passage 323 that controls the flow of oil liquid L in the same way as the damping force valve 105, and a damping force valve 108B (first damping force valve) provided in the passage 324 that controls the flow of oil liquid L in the same way as the damping force valve 108. Furthermore, the damping force adjustable shock absorber 1B has passages 331, 332, and orifice passage 333 that branch in three directions toward the cylinder lower chamber 2B side of passage 223B, beyond orifice passages 322, 323, and 324. Passage 331 is provided with an intake valve 71B (second damping force valve) that controls the flow of oil L in the same way as the intake valve 71. Passage 332 is provided with a relief valve 91B (second damping force valve) that controls the flow of oil L in the same way as the relief valve 91. Orifice passage 333 is provided with an orifice 334 that controls the flow of oil L. Therefore, passage 223B has an orifice passage 322, or intake valve 71B, relief valve 91B, and orifice 334 which are all provided in series with passages 323 and 324 and control the flow of oil L.

[0120] Furthermore, in the very low speed range of the piston speed during the extension stroke, the damping force adjustable shock absorber 1B generates damping force with the damping force valve 108B open when the current value input to the actuator 201 is the current value that closes the solenoid valve 200, and with the damping force valve 108B closed when the current value input to the actuator 201 is the current value that opens the solenoid valve 200.

[0121] Furthermore, in the compression stroke, the damping force adjustable shock absorber 1B generates damping force with the damping force valve 105B open when the current value input to the actuator 201 is the value that closes the solenoid valve 200, and with the damping force valve 105B closed when the current value input to the actuator 201 is the value that opens the solenoid valve 200.

[0122] In the damping force adjustable shock absorber 1B, the orifice passage 322 with orifice 321, the passage 323 with damping force valve 105B, and the passage 324 with damping force valve 108B are provided on the cylinder upper chamber 2A side than the passage 331 with intake valve 71B, the passage 332 with relief valve 91B, and the orifice passage 333 with orifice 334. However, the orifice passage 322, passage 323, and passage 324 may be provided on the cylinder lower chamber 2B side than the passage 331, passage 332, and orifice passage 333.

[0123] According to the damping force adjustable shock absorber in the above-described embodiment of this disclosure, it is possible to optimize the damping force characteristics.

[0124] 1, 1A, 1B... Damping force adjustable shock absorber, 2... Cylinder, 2A... Upper cylinder chamber (first chamber), 2B... Lower cylinder chamber (second chamber), 6... Reservoir, 18... Piston, 21... Piston rod, 25... Base valve, 71, 71B... Intake valve (second damping force valve), 91, 91B... Relief valve (second damping force valve), 105, 105B, 108, 108B... Damping force valve (first damping force valve), 122...Main valve (third damping force valve), 200...Solenoid valve, 201...Actuator (solenoid), 220a, 220b, 323, 324...Passage (second passage), 223, 223B...Passage (first passage), 225...Main passage (fourth passage), 226...Pilot passage (third passage), 300...Control device, 311...Orifice (connecting passage), 322, 333...Orifice flow path, L...Oil (working fluid).

Claims

1. A damping force adjustable shock absorber provided between the vehicle body and the wheel side, which is capable of adjusting the damping force by operating an actuator via an electrical signal from a control device, the damping force adjustable shock absorber comprises: a cylinder filled with working fluid; a reservoir filled with working fluid and gas; a piston slidably fitted into the cylinder and dividing the inside of the cylinder into a first chamber and a second chamber; a piston rod, one end of which is connected to the piston and the other end of which extends to the outside through the first chamber; a base valve dividing the second chamber and the reservoir; a first passage connecting the first chamber and the second chamber; a first damping force valve provided in the first passage for controlling the flow of the working fluid; a second passage provided in parallel with the first passage and connecting the first chamber and the second chamber; a second damping force valve provided in the second passage for controlling the flow of the working fluid; and a third passage connecting the first chamber and the reservoir. A damping force adjustable shock absorber comprising: a solenoid valve operated by an actuator provided in the third passage and capable of arbitrarily adjusting the flow of the working fluid; a fourth passage provided in parallel with the third passage and connecting the first chamber and the reservoir; and a third damping force valve provided in the fourth passage for controlling the flow of the working fluid, wherein the control device can change the output current value to the actuator by changing the output current value to the actuator according to a first driving mode and a second driving mode provided in the vehicle and arbitrarily selectable by the driver of the vehicle, and in a very low speed range of the piston's movement speed, the first damping force valve opens when the current value input to the actuator is a current value that closes the solenoid valve, and the first damping force valve closes when the current value input to the actuator is a current value that opens the solenoid valve, thereby generating a damping force.

2. A damping force adjustable shock absorber according to claim 1, wherein the control device controls the current value input to the actuator when the first driving mode is selected to be a current value that causes the solenoid valve to open.

3. A damping force adjustable shock absorber according to claim 1, wherein the damping force generated when the first driving mode is selected is lower than the damping force generated when the second driving mode is selected.

4. A damping force adjustable shock absorber according to claim 1, comprising a communication passage that is always in communication between the first chamber and the second chamber, wherein the flow area of ​​the communication passage is formed such that a flow area is sufficient to generate a pressure in the first chamber that allows the first damping force valve to open when the solenoid valve is closed at a very low speed range of the piston's movement.

5. A damping force adjustable shock absorber provided between the vehicle body and the wheel side, which is capable of adjusting the damping force by operating an actuator with an electrical signal from a control device, the damping force adjustable shock absorber comprises: a cylinder filled with working fluid; a reservoir filled with working fluid and gas; a piston slidably fitted into the cylinder and dividing the inside of the cylinder into a first chamber and a second chamber; a piston rod with one end connected to the piston and the other end extending to the outside through the first chamber; a base valve dividing the second chamber and the reservoir; a first passage connecting the first chamber and the second chamber; an orifice passage provided in the first passage to control the flow of the working fluid; a second passage provided so as to branch off from the first passage and arranged in parallel with the orifice passage; a first damping force valve provided in the second passage to control the flow of the working fluid; and a second damping force valve provided in the first passage and arranged in series with the orifice passage or the second passage to control the flow of the working fluid. A damping force adjustable shock absorber comprising: a third passage connecting the first chamber and the reservoir; a solenoid valve operated by an actuator provided in the third passage and capable of arbitrarily adjusting the flow of the working fluid; a fourth passage provided in parallel with the third passage and connecting the first chamber and the reservoir; and a third damping force valve provided in the fourth passage for controlling the flow of the working fluid, wherein the control device can change the output current value to the actuator by changing the output current value to the actuator according to a first driving mode and a second driving mode provided in the vehicle and arbitrarily selectable by the driver of the vehicle, thereby closing or opening the solenoid valve, and generating damping force in a very low speed range of the piston's movement speed when the current value input to the actuator is a current value that closes the solenoid valve, and when the current value input to the actuator is a current value that opens the solenoid valve, the first damping force valve is closed and damping force is generated.

6. A damping force adjustable shock absorber capable of adjusting damping force by operating an actuator with an electrical signal from a control device, the damping force adjustable shock absorber comprising: a cylinder; a piston slidably mounted within the cylinder; a piston rod with one end fixed to the piston and the other end protruding from the cylinder; an electromagnetic valve that can be opened and closed arbitrarily by a solenoid; a first damping force valve that opens by a predetermined first pressure generated within the cylinder; and a second damping force valve that opens by a second pressure different from the first pressure generated within the cylinder, wherein the control device is provided in the vehicle and can change the output current value to the actuator according to a first driving mode and a second driving mode that can be arbitrarily selected by the driver of the vehicle, thereby enabling the electromagnetic valve to be in a closed state or an open state. A damping force adjustable shock absorber in which, in the very low speed range of the piston's movement speed, if the current value input to the actuator is a current value that closes the solenoid valve, the first pressure is generated and the first damping force valve opens, and if the current value input to the actuator is a current value that opens the solenoid valve, the generation of the first pressure is suppressed and damping force is generated with the first damping force valve closed.

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