JPH11218180A - Variable damping force damper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase damping force near the stroke end of a piston rod regardless of the damping force selection of damping force adjusting mechanism in a variable damping force damper. SOLUTION: A piston 11 with a piston rod 12 connected thereto is slidably fitted into a cylinder 9 with oil filled inside. Cylinder chambers 9a, 9b and a reservoir 10 are connected to damping force adjusting mechanism 29 through a variable restriction mechanism 27. The flow of oil generated by the movement of the piston 11 associated with the stroke of the piston rod 12 is controlled by the damping force adjusting mechanism 29 to generate damping force and to adjust it. When the piston rod 12 moves close to the stroke end, the variable restriction mechanism 27 is driven by a stroke detecting rod 47 to restrict an oil passage to the damping force adjusting mechanism 29. Damping force is therefore increased regardless of the damping force selection of the damping force adjusting mechanism 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a damping force variable damper used for a vibration damping device for a vehicle such as a railway vehicle.

[0002]

2. Description of the Related Art An example of a lateral vibration damping device for a railway vehicle will be described with reference to FIG. As shown in FIG. 12, a railway vehicle 1 has a bogie 4 on which a wheel 2 is mounted, and a vehicle body 4 is elastically floated and supported in the left-right direction, and a damping force variable damper is provided between the bogie 3 and the vehicle body 4. 5 are provided. In FIG. 12, reference numeral 6 denotes a rail constituting a track.

A controller (not shown) is used for the curvature and deflection of the track based on the lateral acceleration of the vehicle body 4 detected by a lateral acceleration sensor (not shown).
By appropriately controlling the damping force of the damping force variable damper 5 (so-called semi-active control), the lateral sway of the vehicle body 4 is suppressed and the riding comfort is improved.

In the case of performing the semi-active control, the damping force variable damper 5 has a combination of different types of damping force characteristics different in magnitude between the extension side and the contraction side (for example, the extension side and the contraction side are hard and soft or soft and hard respectively ), A proper damping force can be quickly obtained according to the running state of the vehicle, and the vibration damping effect can be enhanced. It has been known.

When the railway vehicle 1 passes on a curved track,
The vehicle body 4 is displaced outward of the curved track due to the excessive centrifugal acceleration a. In a general example, the displacement of the cart 3 and the vehicle body 4 in the left-right direction is determined by a resin stopper or the like (not shown).
Is regulated to about ± 25mm, and the excessive centrifugal acceleration
At about 0.08G, the vehicle body 4 is displaced about 20 mm outside the curved track with respect to the bogie 3. In this state, the lateral vibration damping control is performed within a range of about 5 mm outside the curved track. At this time, if the rail 6 on the curved track is largely deflected inward beyond the control range of about 5 mm (the direction of deflection is indicated by an arrow b), the vehicle body 4 collides with the stopper, and the wheels 2 Large lateral pressure acts on the vehicle body 4, and the reaction may cause a sudden lateral sway of the vehicle body 4.

Therefore, conventionally, near the stroke end of the damping force variable damper 5 in which the vehicle body 4 abuts on the stopper, the damping force of the damping force variable damper 5 is switched to the hard side by the controller to prevent the collision of the vehicle body 4 with the stopper. Prevention and buffering.

An oil liquid passage communicating with the variable damping mechanism is opened near the end of the cylinder side wall of the variable damping damper, and the opening is closed by the piston when the piston rod extends or contracts near the stroke end. By interrupting the oil liquid passage to the damping force variable mechanism, the damping force is increased near the stroke end of the piston rod regardless of the damping force selected by the damping force adjusting mechanism, thereby increasing the damping force of the vehicle body 4. To prevent and buffer collisions.

[0008]

However, the above-mentioned conventional lateral vibration damping device has the following problems.

In the case where the damping force of the variable damping force damper is switched to the hard side by the controller, when the damping force of the variable damping force damper 5 is set to the soft side, the rail 6 is suddenly greatly swung, and If there is a delay in the switching control to the hard side due to the above, or if the damping force adjusting valve of the damping force variable damper 5 is fixed to the soft side by fail, etc., it is sufficient near the stroke end of the damping force variable damper 5 A large damping force cannot be generated, and the collision of the vehicle body 4 with the stopper cannot be sufficiently prevented and cushioned.

In particular, when the above-described damping force reversing type variable damper is used, the damping force on either the extension side or the contraction side is on the soft side. The problem is that a damping force cannot be obtained.

On the other hand, in the case of using a variable damping force damper in which an oil liquid passage opened in a cylinder side wall is closed by a piston, the variable damping force damper has an opening in a sliding surface of the piston. Therefore, when the piston closes the opening, the seal portion of the piston is likely to be worn and damaged, and the durability may be reduced. Further, since the opening of the oil liquid passage is rapidly closed by the movement of the piston, shock and noise may be generated due to a sudden increase in the damping force.

The present invention has been made in view of the above points, and provides a sufficient damping force in the vicinity of a stroke end and a damping force for preventing deterioration of a seal portion of a piston. It is an object to provide a variable damper.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an invention according to claim 1 includes a cylinder filled with an oil liquid and a cylinder slidably fitted in the cylinder. A piston defining two cylinder chambers, a piston rod having one end connected to the piston and the other end extending outside the cylinder, and an oil provided outside the cylinder and connected to the cylinder chamber A damping force variable damper having a path and a damping force variable mechanism capable of controlling the flow of the oil liquid in the oil path to generate a damping force and adjusting the damping force. A variable throttle mechanism that adjusts the flow path area of the oil passage according to the stroke of the piston rod is provided.When the piston rod moves to near the stroke end, the variable throttle mechanism reduces the flow passage area of the oil passage. squeeze And it said that there was Unishi.

With this configuration, a desired damping force is generated by controlling the flow of the oil liquid generated in the oil passage by the movement of the piston in accordance with the stroke of the piston rod by the damping force variable mechanism. When the piston rod moves to near the stroke end, the flow path area of the oil passage is reduced by the variable throttle mechanism according to the stroke, and the damping force increases regardless of the selection of the damping force by the damping force variable mechanism.

According to a second aspect of the present invention, in the variable damping force damper of the first aspect, the variable throttle mechanism is driven by a stroke detection rod connected to the piston rod.

With this configuration, when the piston rod moves to near the stroke end, the variable throttle mechanism is driven by the stroke detection rod, and the flow passage area of the oil passage is reduced.

According to a third aspect of the present invention, in the damping force variable damper according to the first aspect, the variable throttle mechanism is controlled by a controller based on a stroke of the piston rod detected by a stroke detecting means. It is characterized by being driven by.

With this configuration, when the stroke detecting means detects that the piston rod has moved to near the stroke end, the controller operates the actuator to drive the variable throttle mechanism to reduce the flow passage area of the oil passage. squeeze.

[0019]

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

A first embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the damping force variable damper 7 has a double cylinder structure in which a cylinder 9 is inserted into a bottomed cylindrical outer cylinder 8.
Is formed between them. A piston 11 is slidably fitted in the cylinder 9, and the piston 11 defines the inside of the cylinder 9 as two chambers 9a and 9b. The piston 11 has a piston rod 12
Is connected, and the other end of the piston rod 12 is
It is inserted through a guide seal 13 attached to the ends of the cylinder 9 and the outer cylinder 8 and extends to the outside. An oil liquid is sealed in the cylinder 9, and an oil liquid and a gas are sealed in the reservoir 10.

The piston 11 is provided with a communication passage 14 for communicating between the cylinder chambers 9a and 9b and a check valve 15 for allowing only the flow of the oil from the cylinder chamber 9b side of the communication passage 14 to the cylinder chamber 9a side. Is provided. Also, at the bottom of the cylinder 9,
An oil passage 16 for communicating between the cylinder chamber 9b and the reservoir 10 and a check valve 17 for allowing only the flow of the oil liquid from the reservoir 10 side of the oil passage 16 to the cylinder chamber 9b are provided.

A substantially cylindrical passage member 18 is fitted to the outer peripheral portion on the bottom side of the cylinder 9, and an annular oil passage 19 is formed between the cylinder 9 and the passage member 18. Annular oil passage 19
Is connected to the cylinder chamber 9b by an oil passage 20 provided on a side wall near the bottom of the cylinder 9. A substantially cylindrical passage member 21 is fitted on the outer peripheral portion of the cylinder 9 on the guide seal 13 side, and an annular oil passage 22 is formed between the cylinder 9 and the passage member 21. The annular oil passage 22 is communicated with the cylinder chamber 9a by an oil passage 23 provided on a side wall near the guide seal 13 of the cylinder.

The annular oil passages 22 and 19 formed by the passage members 21 and 18 are connected to one ends of connection pipes 24 and 25, respectively. Further, a connection hole communicating with the reservoir 10 is provided on a side wall of the outer cylinder 8. The other end of the connection pipes 24 and 25 and the connection hole 26 are connected to a variable damping force attached to a side surface of the outer cylinder 8 via a variable throttle mechanism 27 and a connection member 28 (see FIG. 6). It is connected to the mechanism 29.

As shown in FIG. 6 and FIG.
One end is connected to the connection pipes 24, 25 and the connection hole 26, respectively, and three oil passages 30, 31, 32 bent at right angles are provided substantially in parallel to the connection pipes 24, 25 and the connection pipe. The direction of the opening communicating with the hole 26 is changed to a right angle.

As shown in FIGS. 2 to 4 and FIG.
The oil passage 3 of the connecting member 28 is provided in the case 27A of the variable throttle mechanism 27.
Guide holes 33 and 34 communicating with 0 and 31 respectively penetrate, and one end thereof communicates with the guide holes 33 and 34, respectively, and extends from the guide holes 33 and 34 vertically toward the damping force variable mechanism 29. Roads 35 and 36 are provided.

A substantially cylindrical shutter member 37, 38 is rotatably inserted into each of the guide holes 33, 34, and an internal space 39, 38 of a cylindrical portion formed at one end of the shutter member 37, 38 is provided. 40 communicates with the oil passages 30 and 31 of the connecting member 28. Notches 41, 42 are formed in the side walls of the cylindrical portions of the shutter members 37, 38 so as to face oil passages 35, 36 orthogonal to the guide holes 33, 34.
By opening and closing the notches 41 and 42 by rotating the shutter members 37 and 38, the internal spaces 39 and 40 and the oil passages are provided.
The flow path area between 35 and 36 can be adjusted.

Gears 43 and 44 (spur gears) are integrally attached to ends of the shutter members 37 and 38 protruding from the guide holes 33 and 34, respectively. Are meshed with each other via an idler gear 45 attached to the motor. Further, a large-diameter gear 46 is further attached to an end of one shutter member 37.

One end of a stroke detection rod 47 extending in the axial direction along the outer surface of the outer cylinder 8 is connected to the distal end of the piston rod 12 via a bracket 48. A rack 49 is formed at the other end of the stroke detection rod 47, and the rack 49 is engaged with the large-diameter gear 46 of the shutter member 37. A guide member 50 is provided at an end of the outer cylinder 8 on the guide seal 13 side, through which a stroke detection rod 47 is slidably inserted and guided.

When the piston rod 12 strokes, the stroke detection rod 47 moves forward and backward, and the rack 49 moves.
The large-diameter gear 46 meshed with is rotated, and the one shutter member 37 is rotated, and the rotation of the gear 43 of the shutter member 37 causes the other shutter 38 to rotate via the idler gear 45 and the gear 44. I have. At this time, when the piston rod 12 strokes to near the stroke end on the extension side or the contraction side, the shutter member 37,
The notches 41 and 42 of 38 are closed, and the internal spaces 39 and 49 and the oil passages 35 and 36 are closed.
The area of the flow path between them is reduced in accordance with the stroke.

The case 27A of the variable throttle mechanism 27 is provided with an oil path 51 having one end connected to the oil path 32 of the connecting member 28, bent at a right angle, and the other end extending to the damping force variable mechanism.

The variable damping force mechanism 29 includes oil paths 52, 53, 54 communicating with the oil paths 35, 36, and 51 of the variable throttle mechanism 27, respectively.
Is provided. Between the oil passages 52 and 53, the extension side damping valve 55
(Pilot type pressure control valve), extension side fixed orifice 56
And an expansion side variable orifice 57. The oil passages 53 and 54 are communicated with each other via a compression-side damping valve 58 (pilot-type pressure control valve), a compression-side fixed orifice 59, and a compression-side variable orifice 60.

Then, by changing the flow passage area of the expansion-side variable orifice 57, the flow passage area between the oil passages 52 and 53 is directly adjusted, and the pilot pressure is changed to open the expansion-side damping valve 55. The pressure can be adjusted. Also, by changing the flow passage area of the contraction side variable orifice 60, the flow passage area between the oil passages 53 and 54 is directly adjusted, and the pilot pressure is changed to change the contraction side damping valve.
The valve opening pressure of 58 can be adjusted.

The seal guide 13 mounted on the outer cylinder 8 and the end of the cylinder 9 is provided with a relief valve 61 for releasing the oil liquid into the reservoir 10 when the oil liquid in the cylinder chamber 9a reaches a predetermined pressure. Have been. FIG. 8 is a schematic diagram showing a hydraulic circuit of the damping force variable damper 7.

The operation of the present embodiment having the above-described configuration will now be described.

During the extension stroke of the piston rod 12, as the piston 11 moves, the check valve 15 of the piston 11 closes to pressurize the oil liquid in the cylinder chamber 9a, and the oil passage 23, the annular oil passage
22, connection pipe 24, oil passage 30 of connection member 28, internal space 39 of variable throttle mechanism 27, notch 41, oil passage 35, oil passage of damping force variable mechanism 29
52, extension fixed orifice 56, extension variable orifice 5
7, the oil passage 53, the oil passage 36 of the variable throttle mechanism 27, the notch 42, the internal space 40, the oil passage 31, the connection pipe 25 of the connecting member 28, the annular oil passage 19, and the oil passage 20 to the cylinder chamber 9b. . At this time, when the pressure on the cylinder chamber 9a side reaches the opening pressure of the extension side damping valve 55, the extension side damping valve 55 is opened, and the oil liquid flows from the oil passage 52 to the oil passage 53.
Flows through the extension side damping valve 55. On the other hand, the oil liquid corresponding to the withdrawal of the piston rod 12 from the inside of the cylinder 9 opens the check valve 17 and flows from the reservoir 10 to the cylinder chamber 9b.

Therefore, during the extension stroke, the piston speed is low and before opening the extension-side damping valve 55, the orifice characteristics (damping force is approximately equal to the square of the piston speed) according to the flow path area of the extension-side variable orifice 57. When the piston speed increases, the piston speed increases, the pressure in the cylinder chamber 9a rises, and the extension-side damping valve 55 opens, the valve characteristics (damping force decreases with piston speed) according to the degree of opening. Approximately) damping force is generated. By changing the flow path area of the expansion-side variable orifice 57, the orifice characteristics can be directly adjusted, and the pilot pressure of the expansion-side damping valve 55 can be changed to adjust the valve characteristics.

During the contraction stroke of the piston rod 12, the check valve of the piston 11 is moved with the movement of the piston 11.
15 opens and the cylinder chambers 9a and 9b have almost the same pressure.
No oil liquid flows between the oil passages 52 and 53 of the damping force variable mechanism 29. On the other hand, the check valve 17 is closed by the penetration of the piston rod 12 into the cylinder 9, and the inside of the cylinder 9 is pressurized by the penetration of the piston rod 12, and the oil passage
20, annular oil passage 19, connection pipe 25, oil passage 31 of connection member 28, internal space 40 of variable throttle mechanism 27, notch 42, oil passage 36, oil passage 53 of damping force variable mechanism 29, contraction side fixed orifice 59 The fluid flows to the reservoir 10 through the contraction-side variable orifice 60, the oil passage 54, the oil passage 51 of the variable throttle mechanism 27, the oil passage 32 of the connection member 27, and the connection hole 26. At this time, the pressure on the cylinder 9 side is reduced.
When the pressure reaches the valve opening pressure, the contraction-side damping valve 58 opens, and the oil liquid flows from the oil passage 53 to the oil passage 54 via the contraction-side damping valve 58.

Therefore, during the contraction stroke, the piston speed is low, and before the contraction-side damping valve 58 is opened, a damping force having an orifice characteristic is generated according to the flow path area of the contraction-side variable orifice 60, and the piston speed is increased. When the pressure on the cylinder 9 rises and the contraction-side damping valve 58 opens, a damping force having valve characteristics is generated in accordance with the degree of opening. By changing the flow path area of the contraction side variable orifice 60, the orifice characteristics can be directly adjusted, and the pilot pressure of the contraction side damping valve 58 can be changed to adjust the valve characteristics.

At this time, the shutter members 37 and 38 of the variable throttle mechanism 27 rotate in conjunction with the advance / retreat of the stroke detection rod 47 accompanying the stroke of the piston rod 12, and the piston rod 12 moves its stroke on the extension side or contraction side. When the stroke approaches the end, the notches 4 in the shutter members 37 and 38
1 and 42 begin to close, and the flow passage area between the internal spaces 39 and 40 and the oil passages 35 and 36 is reduced according to the stroke of the piston rod 12. Thereby, the flow resistance of the oil liquid to the damping force variable mechanism 27 increases, and the damping force acting on the piston rod 12 increases regardless of the selection of the damping force by the damping force variable mechanism 29.

Then, the notches 41 and 42 are closed and the internal spaces 39 and
When the flow between the oil passages 40 and the oil passages 35 and 36 is interrupted, the flow of the oil liquid in the cylinder chambers 9a and 9b to the damping force variable mechanism 29 is interrupted, the pressure is increased, and the relief valve 61 Open reservoir
Flow to 10. In this manner, a sufficiently large damping force can be generated near the stroke end of the piston rod 12. FIG. 9 shows the damping force with respect to the stroke of the piston rod 12 (constant piston speed).

When the damping force variable damper 7 of the present embodiment is applied to a railcar lateral vibration damping device as shown in FIG.
Regardless of the state of the damping force variable mechanism 29, the piston rod
Since a sufficiently large damping force can be generated near the stroke end on the extension side and the contraction side of 12, the rail suddenly swings greatly when the damping force characteristic of the damping force variable mechanism 29 is set to the soft side. Therefore, even when the controller causes a delay in the switching control to the hard side, or when the extension-side and contraction-side variable orifices 57, 60 are fixed to the soft side by failing, etc. It is possible to reliably generate a sufficiently large damping force, and it is possible to reliably prevent and cushion the collision of the vehicle body with the stopper. As a result, the wheels exert a large lateral pressure on the rails, and the reaction of the wheels can prevent the vehicle body from suddenly swaying, so that rail damage can be reduced, and Comfort can be improved.

The gear ratios of the gears 43 and 44, the idler gear 45 and the large diameter gear 46, and the notches of the shutter members 37 and 38
Depending on the shapes of 41 and 42, the damping force characteristics of the variable throttle mechanism 27 can be variously set. In the damping force variable damper 7 of the present embodiment, since no opening is provided in the sliding surface of the piston, durability does not decrease due to wear and damage of the seal portion of the piston. Further, since the stroke end of the piston rod is detected by a mechanical structure, an electric sensor or the like is not required.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. 10 and FIG. The second embodiment has the same structure as that of the first embodiment except that the variable aperture mechanism is different. Therefore, the same reference numerals are given to the same parts as those of the first embodiment. Only different parts will be described in detail.

As shown in FIGS. 10 and 11, in the variable throttle mechanism 63 of the variable damping force damper 62 of the second embodiment, the large-diameter gear 46 of the shutter member 37 and the stroke detection rod 47 are omitted. Further, a stepping motor 64 (actuator) is connected to the idler gear 45, and a stroke sensor 65 (stroke detecting means) is attached to the piston rod 12. In the present embodiment, a non-contact type, for example, an ultrasonic sensor is used as the stroke sensor 65, and the ultrasonic wave is transmitted to the end surface (the left side in the figure) of the outer cylinder 8 and the reflected ultrasonic wave is received. By measuring the time, the stroke of the piston rod 12 can be detected.

Then, the controller 66 controls the rotation of the stepping motor 64 based on the detection of the stroke sensor 65, and the damping force variable mechanism near the stroke end of the piston rod 12 as in the first embodiment. 29
The flow path to the port is restricted. The stroke detecting means is not limited to the non-contact type, but may be a lever type (contact type) stroke sensor using a photo interrupter.

As a result, the same operation and effect as those of the first embodiment can be obtained. Further, in the damping force variable damper 62 of the second embodiment, the gear ratio of the gears 43 and 44 and the idler gear 45 and the cutouts of the shutter members 37 and 38 are provided.
In addition to the shapes of 41 and 42, the controller 66 can set various damping force characteristics by the variable throttle mechanism 63. In this case as well, since no opening is provided in the sliding surface of the piston, durability does not decrease due to wear and damage of the seal portion of the piston.

[0047]

As described above in detail, according to the damping force variable damper of the first aspect, when the piston rod moves to near the stroke end, the flow path area of the oil passage is increased by the variable throttle mechanism according to the stroke. The damping force is increased regardless of the damping force selected by the damping force variable mechanism, so it is possible to reliably prevent and cushion the collision of the vehicle body with the stopper when it is mounted on the vehicle lateral vibration damping device. it can. Further, since no opening is provided in the sliding surface of the piston, durability is not reduced due to wear and damage of the seal portion of the piston.

According to the damping force variable damper of the second aspect, when the piston rod moves to the vicinity of the stroke end, the variable throttle mechanism is driven by the stroke detecting rod, the flow passage area of the oil passage is reduced, and the damping force variable. Regardless of the damping force selected by the mechanism, the damping force can be increased.

Further, according to the damping force variable damper of the third aspect, when the stroke detecting means detects that the piston rod has moved to near the stroke end, the controller operates the actuator to drive the variable throttle mechanism, and The damping force can be increased by reducing the flow passage area of the road, regardless of the selection of the damping force by the damping force variable mechanism.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing a damping force variable damper according to a first embodiment of the present invention.

FIG. 2 is an enlarged front view showing a variable aperture mechanism of the apparatus shown in FIG. 1;

FIG. 3 is a bottom view of the variable aperture mechanism shown in FIG. 2;

FIG. 4 is a rear view of the variable aperture mechanism shown in FIG. 2;

FIG. 5 is an enlarged perspective view showing a shutter member of the variable aperture mechanism of FIG. 2;

FIG. 6 is an enlarged longitudinal sectional view showing a side surface of a variable aperture mechanism and a connecting member of the apparatus of FIG. 1;

FIG. 7 is a perspective view of the connecting member of FIG. 6;

FIG. 8 is a schematic diagram showing a hydraulic circuit of the apparatus of FIG.

9 is a graph showing a relationship between a stroke and a damping force when a piston rod is stroked at a constant speed in the damping force variable damper of FIG. 1. FIG.

FIG. 10 is a bottom view of a variable throttle mechanism of a variable damping force damper according to a second embodiment of the present invention.

FIG. 11 is a schematic diagram of a damping force variable damper according to a second embodiment of the present invention.

FIG. 12 is an explanatory diagram showing a state in which a railway vehicle equipped with a lateral vibration damping device equipped with a variable damping force damper is traveling on a right curve track.

[Explanation of symbols]

 7 damping force variable damper 9 cylinder 9a, 9b cylinder chamber 11 piston 12 piston rod 27 variable throttle mechanism 29 variable damping force mechanism 47 stroke detection rod 62 variable damping force damper 64 stepping motor (actuator) 65 stroke sensor (stroke detecting means) 66 controller

Claims (3)

[Claims] 1. A cylinder filled with an oil liquid, a piston slidably fitted in the cylinder to define two cylinder chambers in the cylinder, and one end connected to the piston and the other end A piston rod extending outside the cylinder, an oil passage provided outside the cylinder and connected to the cylinder chamber, and generating a damping force by controlling a flow of an oil liquid in the oil passage. And a damping force variable mechanism capable of adjusting the damping force, wherein the variable damping force adjusts a flow passage area of the oil passage according to a stroke of the piston rod in the oil passage. A damping force variable damper having a throttle mechanism, wherein the variable throttle mechanism narrows the flow passage area of the oil passage when the piston rod moves to near a stroke end. 2. The damping force variable damper according to claim 1, wherein the variable throttle mechanism is driven by a stroke detection rod connected to the piston rod. 3. The variable damping force according to claim 1, wherein the variable throttle mechanism is driven by an actuator controlled by a controller based on a stroke of the piston rod detected by a stroke detecting unit. damper.