JP2013036592A - Shock absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shock absorber capable of generating damping force as intended by reducing hysteresis of damping force characteristics.SOLUTION: In this shock absorber D comprising: a cylinder 1; a piston 2 slidably inserted into the cylinder 1; a pair of actuation chambers R1, R2 provided with the pistons 2 at both sides; a piston rod 3 movably inserted into the cylinder 1 and having one end connected to the piston 2; a movable partition wall member 4 and moved to change a volume of one actuation chamber R1, R2; and a biasing element 5 biasing the partition wall member 4 to pressurize the one actuation chamber R2, since the partition wall member 4 is provided with an actuator 6 for applying thrust in a direction for pressurizing/depressurizing one actuation chamber R2, the pressure of the actuation chamber R2 can be controlled, and the hysteresis in the damping force characteristics is reduced.

Description

  The present invention relates to an improved shock absorber.

  Conventionally, for example, taking a single-cylinder shock absorber as an example, a cylinder, a piston that is slidably inserted into the cylinder and that divides two working chambers in the cylinder, and a movably inserted into the cylinder And a piston rod whose one end is connected to the piston, and a free piston that is slidably inserted into the cylinder and divides the air chamber in the cylinder, and is configured as a single rod type shock absorber ( For example, Patent Document 1) is generally known.

  In this single cylinder type shock absorber, a gas spring is formed by the free piston and the air chamber, and the volume of the piston rod that enters and exits the cylinder during expansion and contraction is compensated by the volume change of the gas in the air chamber. The pressure in the air chamber acts on the piston-side working chamber.

  In addition to the configuration of the shock absorber, a cylinder, a piston that is slidably inserted into the cylinder and that defines two working chambers in the cylinder, and a movably inserted into the cylinder and one end A shock absorber comprising: a piston rod connected to the piston; a gas spring that applies pressure to each working chamber; a pressure regulating piston that is slidably inserted into the cylinder; and an actuator that drives the pressure regulating piston. For example, see Patent Document 2).

  In the shock absorber disclosed in Patent Document 2, the pressure in the working chamber is controlled by changing the volume of the working chamber by driving the pressure regulating piston and displacing the piston with respect to the cylinder. Adjustments can be made.

  In other words, in this shock absorber, when the pressure-regulating piston is driven to reduce the volume of the working chamber, the pressure of the gas spring increases, and the rod reaction force (force acting in the direction of moving the piston rod out of the cylinder) ) Increases to increase the vehicle height, and conversely, if the pressure adjustment piston is driven to increase the volume of the working chamber, the pressure of the gas spring decreases and the rod reaction force decreases to decrease the vehicle height. Can be lowered.

JP 2009-74561 A JP 2009-228724 A

  Here, working oil is filled in the working chamber of each shock absorber. This hydraulic oil has elasticity and is compressed and acts as a spring when pressure is applied.

  Therefore, when the shock absorber is expanded and contracted, the characteristic (damping force characteristic) of the damping force of the shock absorber with respect to the piston speed is a characteristic having hysteresis due to the elasticity of the hydraulic oil.

  In addition, when a solenoid valve that makes the damping force of the shock absorber variable is provided in a passage that communicates between the working chambers, for example, the shock absorber is expanded and contracted, and the expansion side damping starts when the piston speed becomes zero. When the force characteristic (damping force characteristic with respect to the expansion / contraction speed of the shock absorber) is changed to hard, the damping force characteristic on the contraction side is changed to soft, and in addition to the compressibility of the hydraulic oil, the current flowing through the solenoid valve coil is delayed. In addition, as shown in FIG. 6, the damping force characteristic that is actually output has hysteresis as shown by the broken line in the figure as compared with the aimed damping force characteristic (solid line in the figure). In particular, when air is dissolved in the hydraulic oil, the spring rigidity is lower than that of hydraulic oil in which no air is dissolved, so that hysteresis appears significantly.

  The shock absorber disclosed in Patent Document 1 has a damping force characteristic having hysteresis, so that it is difficult to exert a damping force as intended. In particular, when used for a vehicle suspension, The effect cannot be sufficiently obtained, and further improvement in riding comfort is desired.

  Further, since the volume elastic modulus of the hydraulic oil in the working chamber is about 100 times the volume elastic modulus of the gas in the air chamber and the volume change of the hydraulic oil is much smaller than the volume change of the gas, it is disclosed in Patent Document 2. In the shock absorber, when the pressure adjusting piston is displaced, the free piston is displaced accordingly, and it is difficult to efficiently adjust the pressure in the working chamber. Further, in the shock absorber disclosed in Patent Document 2, when the pressure in the working chamber is increased, it is necessary to displace the pressure regulating piston against the pressure in the working chamber. It is necessary to increase the speed reduction ratio, but if the output of the actuator is increased, there will be a problem that the actuator becomes large and the shock absorber cannot be mounted on the vehicle. Since the displacement speed becomes slow and it takes a long time to adjust the pressure in the working chamber, the pressure adjustment cannot be made in time, and the hysteresis cannot be eliminated. As a result, even the shock absorber disclosed in Patent Document 2 eliminates the hysteresis. Is difficult.

  In view of this, the present invention has been devised in order to improve the above-described problems, and a purpose thereof is to provide a shock absorber capable of reducing the hysteresis of the damping force characteristic and generating a damping force as intended. Is to provide.

  The shock absorber in the problem solving means of the present invention is inserted into a cylinder, a piston slidably inserted into the cylinder, a pair of working chambers provided on both sides of the piston, and movably inserted into the cylinder. A piston rod having one end coupled to the piston, a partition member capable of changing the volume of one working chamber, a biasing element that biases the partition member and pressurizes the one working chamber, and the partition And an actuator capable of applying a thrust force to the member in a direction to pressurize or depressurize the one working chamber.

  In the shock absorber of the present invention, the actuator can superimpose the urging force by the urging element to give a thrust to the partition member, and the pressure in one working chamber can be adjusted. It is possible to obtain a damping force characteristic close to the aimed damping force characteristic by reducing the hysteresis.

It is a longitudinal cross-sectional view of the shock absorber in one embodiment of the present invention. It is a longitudinal cross-sectional view of the buffer in the modification of one embodiment of this invention. It is a longitudinal cross-sectional view of the buffer in the other modification of one embodiment of this invention. It is a figure which shows the damping force characteristic of the shock absorber in one embodiment of this invention. It is a longitudinal cross-sectional view of the shock absorber in another modification of one embodiment of the present invention. It is a figure which shows the damping force characteristic in the conventional shock absorber.

  The present invention will be described below based on the embodiments shown in the drawings. As shown in FIG. 1, the shock absorber D in one embodiment includes a cylinder 1, a piston 2 slidably inserted into the cylinder 1, and a pair of working chambers R1, R2 provided with the piston 2 on both sides. A piston rod 3 which is movably inserted into the cylinder 1 and has one end connected to the piston 2, a free piston 4 as a partition member capable of changing the volume of one working chamber R2, and a free piston 4 The urging element 5 that pressurizes and pressurizes one working chamber R2 and the actuator 6 that can apply thrust to the free piston 4 in the direction of increasing and decreasing the pressure of the working chamber R2 are configured.

  The shock absorber D connects the piston rod 3 to one of a sprung member and an unsprung member of a vehicle (not shown), and connects the cylinder 1 to the other of the sprung member and the unsprung member. It can be interposed between the axles.

  Hereinafter, each part of the shock absorber D will be described in detail. The cylinder 1 has a bottomed cylindrical shape, and a piston 2 and a free piston 4 are slidably inserted into the cylinder 1 so as to be axially movable.

  The piston 2 defines working chambers R1 and R2 in the cylinder 1, and the free piston 4 is slidably inserted into the cylinder 1 and faces one working chamber R2 on the side opposite to the rod. An annular seal ring S slidably in contact with the inner periphery of the cylinder 1 is provided on the outer periphery, and an air chamber G filled with gas is formed in the cylinder 1.

  When the free piston 4 is displaced in the vertical direction in FIG. 1, which is the axial direction with respect to the cylinder 1, the volume of the air chamber G changes, and the gas in the air chamber G moves the free piston 4 upward in FIG. 1. The power of power to change is changing. That is, in this case, the urging element 5 that urges the free piston 4 is a gas spring including an air chamber G filled with gas. Accordingly, the free piston 4 can be pressurized by the biasing element 5 to pressurize one working chamber R2. In this case, the urging element 5 is a gas spring. However, a spring may be interposed between the bottom portion of the cylinder 1 and the free piston 4, and this may be used as the urging element 5. You may make it use a gas spring together.

  The piston 2 is slidably inserted into the cylinder 1, and the rod-side working chamber R <b> 1 disposed in the upper part of FIG. A working chamber R2 on the side opposite to the rod disposed in the middle and lower side is defined. The working chambers R1 and R2 are communicated with each other by a passage 7 provided in the piston 2, and the liquid filled in the working chambers R1 and R2 passes through the working chambers R1 and R2 through the passage 7. Can be done. As the liquid filled in the working chamber, various liquids such as a magnetorheological fluid (magnetic fluid), an electrorheological fluid, water, and an aqueous solution can be used in addition to the working oil. In order to reduce the hysteresis in the damping force characteristic, it is preferable to use a liquid having a high volume modulus of elasticity in which gas is difficult to dissolve.

  The piston rod 3 is connected to the piston 2 at the lower end in FIG. 1 as one end, and is pivotally supported by an annular rod guide 10 provided at the upper end in FIG. Projecting out of the cylinder 1. Further, the space between the outer periphery of the piston rod 3 and the cylinder 1 is tightly sealed by an annular seal member 11 so that the inside of the cylinder 1 is sealed.

  The passage 7 includes a damping valve 8 as a damping force adjusting means and a fixed throttle 9 such as an orifice or a choke arranged in parallel with the damping valve 8 on the way. Since the working chambers R1 and R2 communicate with each other via the fixed throttle 9, the pressure in the air chamber G propagates not only to the working chamber R2 but also to the working chamber R1 with a first order delay. However, the effect of the present invention is not lost even without the fixed aperture 9.

  The passage 7 provides resistance to the flow of liquid passing through the damping valve 8 and the fixed throttle 9, so that in the shock absorber D, the shock absorber D is extended or contracted. Further, the damping valve 8 and the fixed valve are fixed to the flow of the liquid moving from one working chamber R1 (R2) whose volume is reduced by the movement of the piston 2 in the vertical direction in FIG. A resistance is given by the throttle 9, and a differential pressure is generated between the working chambers R1 and R2, thereby exerting a damping force. In the present embodiment, since the shock absorber D is a single rod type shock absorber, the volume of liquid of the piston rod 3 that enters and exits the cylinder 1 when the shock absorber D expands or contracts is excessive in the cylinder 1. Although it becomes insufficient, this volume is compensated by a change in the volume of the gas in the air chamber G.

  Further, in this case, the damping valve 8 is a solenoid valve capable of changing the resistance applied to the flow of the liquid passing therethrough, and the damping force generated by the shock absorber D can be adjusted. ing. The damping valve 8 may adjust the damping force in a plurality of stages, or may adjust the damping force in a stepless manner. When a magnetorheological fluid is used for the liquid, a coil for applying a magnetic field to the magnetorheological fluid passing through the passage 7 may be provided as a damping force adjusting means instead of the damping valve. Alternatively, an electric field generator that applies an electric field to the passage 7 by eliminating the damping valve may be used as the damping force adjusting means.

  In the above description, only one passage 7 is provided, but a plurality of passages 7 may be provided. In this case, a part of the passage 7 is allowed to flow only from the working chamber R1 to the working chamber R2, and the remaining passage is provided. May be set so as to allow only the flow of liquid from the working chamber R2 to the working chamber R1, and the damping valve 8 may be provided in the middle of each. In this case, if the fixed throttle 9 is provided, it may be provided only in a part of the plurality of passages 7. Further, the passage 7 only needs to realize communication between the working chambers R1 and R2, so that the passage 7 may be installed outside the cylinder 1 without being provided in the piston 2, and the damping force adjusting means is also the same.

  An actuator 6 is accommodated in the air chamber G. The actuator 6 includes a motor M and a motion conversion mechanism T that reversibly converts the rotational motion of the rotor 12 of the motor M into a linear motion. The linear motion of the motion conversion mechanism T is free piston 4. It is possible to apply thrust to the free piston 4 in the direction of increasing or decreasing the pressure of the working chamber R2. In the case of this embodiment, the free piston 4 as the partition member can pressurize and depressurize the working chamber R2 by moving up and down in the cylinder 1 in FIG. A thrust can be applied to the piston 4 in the vertical direction in FIG.

  In the case of this embodiment, the motion conversion mechanism T specifically includes a ball nut 13 held by the rotor 12 of the motor M, and a screw shaft fixed to the free piston 4 and screwed with the ball nut 13. When the ball nut 13 is rotationally driven by the motor M, the screw shaft 14 exhibits a linear motion in the vertical direction in FIG. When an axial force is applied to 14, the ball nut 13 rotates and the rotor 12 of the motor M can be rotated. In other words, reversibly converting the rotational motion of the rotor 12 into a linear motion indicates not only that the rotational motion can be converted into a linear motion, but conversely, the linear motion can also be converted into a rotational motion. In the above description, the screw shaft 14 is connected to the free piston 4, but the screw shaft 14 may be connected to the rotor 12 and the ball nut 13 may be connected to the free piston 4.

  The free piston 4 may be prevented from coming off as appropriate. The displacement of the free piston 4 when the shock absorber D makes a full stroke, the displacement due to the thrust of the motor M, the upper and lower operating temperatures of the shock absorber D The total displacement amount of the free piston 4 may be obtained by taking into account the displacement amount of the free piston 4 due to the volume difference of the liquid, and a stopper may be provided so as to ensure the total displacement amount. Specifically, for example, a flange may be provided at the lower end of the screw shaft 14 so that the flange and the ball nut 13 are brought into contact with each other. May be provided. Although not shown in detail, the motor M includes a cylindrical stator 15 and a rotor 12 that is rotatably inserted into the stator 15 and has one end projecting outwardly. It has a well-known structure. The rotor 12 allows the screw shaft 14 to be inserted and allows the free piston 4 to approach the motor. In the illustrated example, the motor M is a brushless motor in which the stator 15 is an armature and a magnet is provided on the outer periphery of the rotor 12. However, the motor M is not limited to this and may be a motor with a brush. A motor that can give a thrust to the free piston 4 may be used.

  As a result, the total length of the actuator 6 including the free piston 4 at the time of the most contraction can be set short, and it becomes easy to secure the stroke length of the shock absorber D even when housed in the cylinder 1 and the shock absorber D is shortened. can do. As the motor M, various types can be adopted regardless of direct current or alternating current.

  Moreover, in the said motion change mechanism T, if the screw shaft 14 also rotates with the frictional force around the axis | shaft produced between the screw shaft 14 and the ball nut 13, it will become impossible to move the free piston 4 to an axial direction. Therefore, it is preferable to provide a detent for the screw shaft 14, but the circumferential frictional force generated between the seal ring S mounted on the outer periphery of the free piston 4 and the cylinder 1 causes the screw shaft 14 and the ball nut 13 to When the frictional force around the shaft generated between them is larger, the rotation of the screw shaft 14 is prevented by the seal ring S, so that the rotation prevention can be omitted.

  In this way, the motion conversion mechanism T reversibly converts the rotational motion of the rotor 12 of the motor M into a linear motion, and the actuator 6 does not support the free piston 4 in a fixed manner. A force obtained by superimposing the thrust of the actuator 6 on the urging force can be applied to the free piston 4.

  The actuator 6 is not limited to the structure described above, and may be a solenoid including a movable iron core 16 connected to the free piston 4 and a coil 17 for driving the movable iron core 16 as shown in FIG. Since the free piston 4 is not fixedly supported even by the actuator 6 configured as described above, a force obtained by superimposing the thrust of the actuator 6 on the biasing force of the biasing element 5 acts on the free piston 4 as a partition member. Can be made. The movable iron core 16 is connected to the free piston 4, and is positioned at a position where the gas spring as the biasing means 5 and the force pressing the free piston 4 by the pressure of the working chamber R2 are balanced. Since the means 5 also functions as a spring for energizing the movable core normally provided in the solenoid, it is not necessary to provide a spring only for the purpose of energizing the movable core 16 of the solenoid.

  Furthermore, as shown in FIG. 3, the actuator 6 may be a linear motor including a magnet 19 provided at the lower end of the free piston 4 and a coil 20 provided in the cylinder 1. Also in this case, since the free piston 4 is not fixedly supported, a force obtained by superimposing the thrust of the actuator 6 on the biasing force of the biasing element 5 can be applied to the free piston 4. The linear motor may be configured by providing the magnet 19 in the cylinder 1 and the coil 20 in the free piston 4. That is, it is only necessary that the magnet 19 and the coil 20 can face each other and can function as a linear motor, and so long as the mounting position of the magnet 19 and the coil 20 is not limited to the above. Therefore, the coil 20 may be provided on the outer peripheral side of the cylinder 1, and in this case, the magnet 19 may be provided on the outer periphery of the free piston 4 or inside the free piston 4.

  Next, the operation of the shock absorber D configured as described above will be described. As described above, when the shock absorber D is extended or contracted, the other working chamber R2 whose volume is increased from one working chamber R1 (R2) whose volume is reduced by the movement of the piston 2 in the vertical direction in FIG. A resistance is given to the flow of the liquid moving to (R1) by the damping valve 8 and the fixed throttle 9, and a differential pressure is generated between the working chambers R1 and R2 to exert a damping force.

  For example, the shock absorber D is expanded and contracted, and when the piston speed becomes 0, the damping force is changed from hard to soft, or conversely, the shock absorber D is contracted and extended. If the damping force is changed from soft to hard when the speed reaches zero, if the thrust is not applied to the free piston 4 by the actuator 6, in addition to the compressibility of the liquid, the damping is reduced. In addition to the delay of the current flowing through the coil of the valve 8, as shown in FIG. 6, the actually output damping force characteristic is shown by the broken line in the figure, as shown in FIG. Will have hysteresis. Therefore, in the shock absorber D of the present invention, the hysteresis can be canceled by driving the actuator 6 to apply thrust to the free piston 4 and adjusting the pressure in the working chamber R2. If the damping force is changed from soft to hard when the piston speed reaches zero when the shock absorber D is extended, the shock absorber D is contracted and then extended, and the piston speed becomes zero. Even when the damping force is changed from hardware to software at that time, the hysteresis is obtained by driving the actuator 6 to apply thrust to the free piston 4 and adjusting the pressure in the working chamber R2, as described above. Can be countered.

  Here, the shock absorber D exhibits a damping force due to the differential pressure between the working chamber R1 and the working chamber R2, but an ideal damping force characteristic without hysteresis is, for example, when the expansion / contraction speed is α, the working chamber R1. However, in reality, the expansion and contraction speed is α due to the compressibility of the liquid and the delay of the current flowing through the coil of the damping valve 8. On the other hand, since the differential pressure between the working chamber R1 and the working chamber R2 is not P as intended but P ± ΔP, hysteresis occurs in the damping force characteristic. Therefore, by compensating the pressure corresponding to ΔP with the thrust applied by the actuator 6 to the free piston 4, the differential pressure can be brought close to the target P, and a damping force characteristic close to the target damping force characteristic can be obtained.

  In other words, in the shock absorber D, the actuator 6 can superimpose the urging force by the urging element 5 to give a thrust to the free piston 4 as the partition member, and adjust the pressure in one working chamber R2. Therefore, by controlling the pressure of one working chamber R2, in addition to the compressibility of the liquid, the hysteresis in the damping force characteristic caused by the delay of the current flowing in the coil of the damping valve 8 was reduced and aimed. A damping force characteristic close to the damping force characteristic can be obtained.

  Since the free piston 4 is urged by the urging element 5 to pressurize the working chamber R2, the urging force of the urging element 5 against the force that presses the free piston 4 by the pressure of the working chamber R2. Therefore, the actuator 6 only needs to apply to the free piston 4 a thrust opposite to the pressure corresponding to ΔP that cancels the hysteresis in the damping force characteristic. Therefore, the hysteresis is reduced by the buffer disclosed in Japanese Patent Application Laid-Open No. 2009-228724. Compared to the case, the thrust of the actuator 6 may be small, and the hysteresis in the damping force characteristic can be reduced while avoiding the enlargement of the actuator 6. In other words, according to the shock absorber D of the present invention, the hysteresis in the damping force characteristic can be reduced without sacrificing the mountability of the shock absorber D.

  In addition, in the structure in which a pressure adjusting piston is provided in addition to the free piston, and the pressure adjusting piston is driven by an actuator, when the pressure adjusting piston is driven, the free piston is displaced and a loss occurs, resulting in poor pressure adjustment efficiency in the working chamber. However, the shock absorber D of the present invention employs a structure in which thrust is directly applied to the free piston 4 as the partition member by the actuator 6, so that the pressure in the working chamber R2 is adjusted without loss. Therefore, the pressure can be adjusted efficiently. Therefore, the pressure control response is high, and the hysteresis in the damping force characteristic, which has been difficult with the conventional shock absorber, can be reduced with high response.

  In addition, the hysteresis in the damping force characteristic is caused by a delay in the current flowing through the solenoid of the damping valve 8 that can adjust the damping force in addition to the compressibility of the liquid as described above. In the shock absorber D provided with the adjustable damping valve 8, hysteresis occurs due to a current delay when adjusting the damping force. Therefore, the present invention is effective for the shock absorber D provided with the damping valve 8 capable of adjusting such a damping force. Is.

  For example, when the shock absorber D is expanded and contracted and the damping force characteristic on the expansion side is changed to hard and the damping force characteristic on the contraction side is changed to soft when the piston speed becomes zero, the free piston 4 By applying thrust to the actuator 6 as shown in FIG. 4, the actually output damping force characteristic has hysteresis as shown by the broken line in the figure as shown in FIG. As a result, the damping force characteristic close to the aimed damping force characteristic can be realized. In addition, when the piston speed, which is a point at which the damping force characteristic is switched between hardware and software, becomes zero, the damping force can be smoothly changed to alleviate a sudden change in the damping force characteristic. Hysteresis in the damping force characteristic is also caused by the compressibility of the liquid as described above. Naturally, hysteresis occurs even in a shock absorber without a damping valve that can adjust the damping force. Even if the present invention is applied to a shock absorber that does not include the above, it is possible to exhibit a hysteresis reduction effect. Therefore, for example, the effect of the present invention is not lost even in a shock absorber in which the damping valve 8 in the shock absorber D of FIG. That is, the present invention is also effective for a shock absorber that does not include damping force adjusting means.

  In the above description, the actuator 6 and the free piston 4 control the pressure in the working chamber R2 on the piston side, but the displacement of the free piston 4 changes the volume of the working chamber R1 on the rod side. It may be.

  Further, in this embodiment, the shock absorber D is a single rod type shock absorber in which the piston rod 3 is inserted only into the working chamber R1, but not only in the working chamber R1 but also in the working chamber R2. 1 may also be set to a double rod type shock absorber that protrudes out of the cylinder 1 from the lower end in FIG. In the case of the double rod type shock absorber, unlike the single rod type shock absorber, there is no change in the volume of the piston rod in the cylinder, so the volume compensation is not performed by the movement of the free piston 4, but the partition member By applying a thrust to the free piston 4 by the actuator 6, the pressure in one of the working chamber R1 or the working chamber R2 can be controlled, and the hysteresis in the damping force characteristic can be reduced.

  In addition, since the pressure of one of the working chamber R1 or the working chamber R2 can be controlled by applying a thrust to the free piston 4 as the partition member by the actuator 6, if within the thrust that the motor M can output, The vehicle height can be adjusted, and the shock absorber D can positively exert thrust to suppress vehicle vibration.

  Furthermore, in the present invention, the free piston 4 which is a partition member is slidably inserted into the cylinder 1, but it is sufficient that the pressure in the working chamber R1 or the working chamber R2 can be controlled. A container for accommodating the free piston 4 is provided, and an actuator 6 and an urging element 5 are provided in the container, and the inside of the container is communicated with one of the working chambers R1 and R2 of the cylinder 1 so that each working chamber R1, You may make it control one pressure among R2. In addition, like the shock absorber D of the above embodiment, the free piston 4 is slidably inserted into the cylinder 1 so as to directly face the working chamber R2, and the actuator 6 is accommodated, that is, By accommodating the partition member and the actuator 6 in the cylinder 1, it is possible to minimize the number of parts without providing a separate container for accommodating these.

  As shown in FIG. 5, the partition member is the free piston 4 in this embodiment, but may be a metal bellows 21 provided in the cylinder 1. In this case, the lower end of the metal bellows 21 is fixed to the bottom of the cylinder 1, and the actuator 6 is accommodated in the metal bellows 21. Even in the shock absorber of this embodiment, the working chamber R2 can be pressurized or depressurized by applying a thrust to the apex 21a of the metal bellows 21 in the direction in which the metal bellows 21 is expanded and contracted by the actuator 6. Therefore, the effects of the present invention can be achieved. The metal bellows 21 may be provided in a container that is provided separately from the cylinder 1 and communicated with one of the working chambers R1 and R2, in addition to being housed in the cylinder 1. A guide for guiding the expansion and contraction of the metal bellows 21 to the cylinder 1 may be provided. In this case, the metal bellows 21 expands and contracts along the axial direction of the cylinder 1 so that it does not easily interfere with the cylinder 1 when extended, but the expansion / contraction direction is not limited to this.

  As shown in FIG. 2, when the actuator 6 is a solenoid including a movable iron core 16 connected to the free piston 4 and a coil 17 for driving the movable iron core 16, the urging element 5 is necessary for the solenoid. Therefore, it is not necessary to provide a separate spring for energizing the movable core, and the shock absorber D can be reduced in weight.

  Further, as shown in FIG. 3, the actuator 6 may be a linear motor including a magnet 19 provided at the lower end of the free piston 4 and a coil 20 provided in the cylinder 1. The coil 20 may be provided outside the cylinder 1. In this case, since the coil 20 does not interfere with the free piston 4, the movable range in the axial direction of the free piston 4 can be expanded to the lower end of the cylinder 1. Therefore, it is easy to secure the stroke length of the shock absorber D, and the mountability of the shock absorber D on the vehicle is improved.

  This is the end of the description of the embodiment of the present invention, but the scope of the present invention is of course not limited to the details shown or described.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Piston rod 4 Free piston 5 Energizing element 6 Actuator 7 Flow path 8 Damping valve 16 Movable iron core 17 Coil 18 Spring 19 Magnet 20 Coil D Buffer M Motor R1, R2 Working chamber T Motion conversion mechanism

Claims (9)

A cylinder, a piston slidably inserted into the cylinder, a pair of working chambers provided on both sides of the piston, and a piston rod movably inserted into the cylinder and connected at one end to the piston A partition member capable of changing the volume of one working chamber, a biasing element that biases the partition member to pressurize the one working chamber, and pressurizes and depressurizes the one working chamber to the partition member. A shock absorber comprising an actuator capable of applying a thrust in a direction. The shock absorber according to claim 1, wherein the volume of the piston rod entering and exiting the cylinder is compensated by the movement of the partition member. The shock absorber according to claim 1 or 2, further comprising: a flow path communicating with the working chambers, and provided with an attenuation adjusting means capable of adjusting a damping force in the middle of the flow path. The shock absorber according to any one of claims 1 to 3, wherein the partition member is accommodated in the cylinder and faces one of the working chambers, and the actuator is accommodated in the cylinder. . 5. The actuator according to claim 1, further comprising: a motor; and a motion conversion mechanism that reversibly converts the rotational motion of the rotor of the motor into a linear motion and transmits the linear motion to the partition member. The shock absorber described in the paragraph. The shock absorber according to any one of claims 1 to 4, wherein the actuator is a solenoid including a movable iron core connected to the partition wall member and a coil for driving the movable iron core. 5. The actuator according to claim 1, wherein the actuator is a linear motor including a magnet provided on one of the free piston and the cylinder, a partition member, and a coil provided on the other side of the cylinder. A shock absorber according to claim 1. The shock absorber according to claim 7, wherein the coil is provided on an outer periphery of the cylinder. The shock absorber according to any one of claims 1 to 7, wherein the biasing means includes a gas spring.

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