Cylinder Unit

Abstract

To provide a cylinder device capable of reducing its weight and cost.SOLUTION: A cylinder device C1 in the present invention comprises: a cylinder body 1 having a cylinder 2, a piston 3 that divides the inside of the cylinder 2 into a rod-side chamber 5 and a piston-side chamber 6, and a rod 4 connected to the piston 3; a tank 8; a first on-off valve 12; a second on-off valve 14; an attenuation passage 21 through which liquid passes when the cylinder body 1 expands and contracts; a bypass attenuation passage 25 parallel to the attenuation passage 21; an attenuation valve 22 provided in the attenuation passage 21; a bypass attenuation passage attenuation valve 26 provided in the bypass attenuation passage 25; and a direction switching valve 28 that is provided upstream of the attenuation valve 22, opens the attenuation passage 21 and blocks the bypass attenuation passage 25 when a pressure on the upstream side is less than a predetermined pressure, and blocks the attenuation passage 21 and opens the bypass attenuation passage 25 when the pressure on the upstream side is equal to or larger than the predetermined pressure.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a cylinder device. [Background technology]

[0002] Conventionally, this type of cylinder device has been used, for example, as a vibration damping device for railway vehicles that suppresses vibrations in the left-right direction relative to the traveling direction of the car body of a railway vehicle. The vibration damping device for railway vehicles is composed of multiple cylinder devices interposed between the car body and the bogie, and suppresses vibrations of the car body by the thrust or damping force exerted by the cylinder devices.

[0003] A conventional cylinder device is composed of, for example, a cylinder, a piston slidably inserted into the cylinder, a rod inserted into the cylinder and connected to the piston, a rod side chamber and a piston side chamber partitioned by the piston within the cylinder, a tank, and an electromagnetic relief valve provided midway through a damping passage connecting the rod side chamber and the tank (see, for example, Patent Document 1).

[0004] Conventional cylinder devices control the pressure inside the cylinder by means of an electromagnetic relief valve to adjust the thrust or damping force generated by the cylinder device to a high or low level, thereby suppressing vibration of the body of the railway vehicle.

[0005] In addition, the conventional cylinder device is provided with a passageway that passes through the damping valve downstream of the electromagnetic relief valve and a bypass passageway that is parallel to the passageway, and the passageway and the bypass passageway can be selectively switched by a switching valve. In the conventional cylinder device configured in this manner, when large vibrations are input, the switching valve selects the passageway in which the damping valve is provided, and the damping valve exerts a high damping force, so that vibrations of the car body of the railway vehicle can be suppressed even in the case of large vibration inputs. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-043296 A

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in a conventional cylinder device, when a large vibration is input and the pressure in the cylinder becomes extremely high, a high pressure acts on the electromagnetic relief valve. Therefore, an electromagnetic relief valve that can withstand high pressure must be adopted. Then, measures such as increasing the wall thickness of the components of the electromagnetic relief valve are required to ensure the strength of the electromagnetic relief valve. As a result, the weight of the electromagnetic relief valve increases, and the weight of the entire cylinder device also increases, and the cost also increases.

[0008] Therefore, an object of the present invention is to provide a cylinder device capable of reducing weight and cost.

Means for Solving the Problems

[0009] The cylinder device of the present invention includes a cylinder filled with a liquid, a piston that is inserted into the cylinder so as to be movable in the axial direction and divides the inside of the cylinder into a rod side chamber and a piston side chamber, a rod that is inserted into the cylinder so as to be movable in the axial direction and is connected to the piston, a cylinder body having the above, a tank for storing the liquid, a first on-off valve for switching the communication and blocking between the rod side chamber and the piston side chamber, a second on-off valve for switching the communication and blocking between the piston side chamber and the tank, a damping passage through which the liquid passes when the cylinder body expands and contracts, a bypass damping passage arranged in parallel with the damping passage, a damping valve provided in the damping passage, a bypass damping passage damping valve provided in the bypass damping passage, and a direction switching valve provided upstream of the damping valve, which opens the damping passage and blocks the bypass damping passage when the upstream pressure is less than a predetermined pressure, and blocks the damping passage and opens the bypass damping passage when the upstream pressure is greater than or equal to the predetermined pressure.

[0010] Another cylinder device of the present invention includes a cylinder body having a cylinder filled with liquid, a piston inserted into the cylinder so as to be movable in the axial direction and dividing the inside of the cylinder into a rod side chamber and a piston side chamber, a rod inserted into the cylinder so as to be movable in the axial direction and connected to the piston, a tank for storing liquid, a first on-off valve for switching between communication between the rod side chamber and the piston side chamber and between blocking communication, a second on-off valve for switching between communication between the piston side chamber and the tank and between blocking communication, a damping passage through which the liquid passes when the cylinder body is expanded or contracted, and a bypass damping valve arranged in parallel with the damping passage. The damping passage system includes a damping passage, a damping valve provided in the damping passage, a bypass damping passage damping valve provided in the bypass damping passage, a damping passage opening / closing valve provided upstream of the damping valve in the damping passage for opening the damping passage when the pressure on the upstream side is less than a predetermined pressure and for closing the damping passage when the pressure on the upstream side is equal to or greater than the predetermined pressure, and a bypass damping passage opening / closing valve provided upstream of the bypass damping passage damping valve in the bypass damping passage for closing the bypass damping passage when the pressure on the upstream side is less than the predetermined pressure and for opening the bypass damping passage when the pressure on the upstream side is equal to or greater than the predetermined pressure.

[0011] According to the cylinder device configured in this manner, when the pressure on the upstream side becomes equal to or higher than a predetermined pressure during extension and contraction, the directional control valve blocks the damping passage and opens the bypass damping passage, or when the pressure on the upstream side becomes equal to or higher than a predetermined pressure during extension and contraction, the damping passage opening / closing valve blocks the damping passage and the bypass damping passage opening / closing valve opens the bypass damping passage. Therefore, the damping valve is protected by preventing it from being exposed to high pressure, while the damping force can be exerted by the bypass damping passage damping valve.

[0012] Furthermore, according to a cylinder device including a damping passage opening / closing valve provided upstream of the damping valve in the damping passage for opening and closing the damping passage, and a bypass damping passage opening / closing valve provided upstream of the bypass damping passage damping valve in the bypass damping passage for opening and closing the bypass damping passage, switching between the damping passage and the bypass damping passage can be performed by multiple lightweight and small opening / closing valves, and the entire device can be made compact by appropriately arranging the opening / closing valves.

[0013] Furthermore, the cylinder device may include a common passage communicating with the piston side chamber, a first passage having one end communicating with the rod side chamber via a damping passage and communicating with the piston side chamber via the common passage, and provided with a first on-off valve, a second passage having one end communicating with the piston side chamber via the common passage and the other end communicating with the tank, and provided with a second on-off valve, and a common passage on-off valve provided in the common passage.

[0014] According to the cylinder device configured in this manner, not only can an increase in the weight of the components of the damping passage and the damping valve be avoided, but by providing a common passage opening / closing valve, the first passage, the second passage, the first opening / closing valve and the second opening / closing valve can be prevented from being exposed to high pressure, thereby avoiding an increase in the weight of the components of the first passage, the second passage, the first opening / closing valve and the second opening / closing valve and more effectively reducing the weight and cost of the entire device. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram showing the cylinder device when mounted on a railway vehicle. [Diagram 2] 2 is a hydraulic circuit diagram of the cylinder device according to the first embodiment. FIG. [Diagram 3] FIG. 4 is a hydraulic circuit diagram of a cylinder device in a first modified example of the first embodiment. [Figure 4] FIG. 11 is a hydraulic circuit diagram of a cylinder device in a second modified example of the first embodiment. [Diagram 5] FIG. 11 is a hydraulic circuit diagram of a cylinder device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described below based on the embodiment shown in the drawings. The same reference numerals are used for the configurations common to the cylinder devices C1, C2, C3, and C4 of the embodiments described below, and in order to avoid duplication of explanation, detailed explanations of the configurations described in the description of the first embodiment will be omitted in the descriptions of the other embodiments. In this embodiment, the cylinder devices C1, C2, C3, and C4 are used for vibration damping of the car body B of the railway vehicle V, but the cylinder devices C1, C2, C3, and C4 may be used for purposes other than vibration damping of the railway vehicle V.

[0017] <First embodiment> As shown in Fig. 1, the cylinder device C1 in the first embodiment is interposed between a carbody B and a bogie T of a railway vehicle V, and is used for vibration control of the carbody B. In the case of the railway vehicle V, the cylinder device C1 is connected to a pin P hanging down below the carbody B, and is interposed in parallel in a pair between the carbody B and the bogie T. The bogie T holds the wheels W so that they can rotate freely, and a suspension spring CS is interposed between the carbody B and the bogie T, and the carbody B is elastically supported from below, allowing the carbody B to move lateral to the bogie T.

[0018] As shown in FIG. 2, the cylinder device C1 includes a cylinder body 1, a tank 8 for storing liquid, a first on-off valve 12, a second on-off valve 14, a damping passage 21 through which liquid passes when the cylinder body 1 is extended or retracted, a bypass damping passage 25 arranged in parallel with the damping passage 21, a variable relief valve 22 provided in the damping passage 21 as a damping valve, a bypass damping passage damping valve 26 provided in the bypass damping passage 25 and providing greater resistance to the flow of liquid than the variable relief valve 22, and a directional control valve 28.

[0019] Hereinafter, each part of the cylinder device C1 of the first embodiment will be described in detail. As shown in Fig. 2, the cylinder body 1 includes a cylinder 2 filled with liquid, a piston 3 inserted axially movably into the cylinder 2 to divide the inside of the cylinder 2 into a rod side chamber 5 and a piston side chamber 6, a rod 4 inserted axially movably into the cylinder 2 and connected to the piston 3, and an outer cylinder 7 covering the cylinder 2 and the outer periphery of the cylinder 2. The cylinder device C1 is interposed between the car body B and the bogie T, with the cylinder 2 connected to the car body B of the railway vehicle V and the rod 4 connected to the bogie T.

[0020] 2 of the cylinder 2 and the outer cylinder 7 that covers the cylinder 2 are closed by an annular rod guide 9, and the openings on the right end side of the cylinder 2 and the outer cylinder 7 are closed by a bottom cap 10 that fits over both of them. In this way, the annular gap between the cylinder 2 and the outer cylinder 7 is closed by the rod guide 9 and the bottom cap 10, forming a tank 8 that stores liquid.

[0021] The rod 4, which is movably inserted into the cylinder 2, is slidably inserted into the rod guide 9, and the axial movement of the rod 4 is guided by the rod guide 9. One end of the rod 4 protrudes outside the cylinder 2 through the rod guide 9, and the other end inside the cylinder 2 is connected to a piston 3, which is movably inserted into the cylinder 2.

[0022] The outer periphery of the rod 4, between the rod guide 9 and the cylinder 2, between the rod guide 9 and the outer cylinder 7, between the cylinder 2 and the bottom cap 10, and between the outer cylinder 7 and the bottom cap 10 are each sealed with a sealing member (not shown). This keeps the inside of the cylinder 2 and the tank 8 sealed.

[0023] The rod side chamber 5 and the piston side chamber 6 partitioned by the piston 3 in the cylinder 2 are filled with liquid, and the tank 8 is filled with gas in addition to the liquid stored therein. Note that it is not necessary to compress and fill the tank 8 with gas to create a pressurized state. The liquid is, for example, hydraulic oil, but may be a liquid other than hydraulic oil.

[0024] Although not shown, the cylinder device C1 is interposed between the bogie and the carbody of the railway vehicle V, with the rod 4 connected to one of the bogie and the carbody and the cylinder 2 connected to the other of the bogie and the carbody. Since the cylinder device C1 is set to a single rod type, it is easier to ensure the stroke length compared to a double rod type cylinder device, and the overall length of the cylinder device C1 is shorter, improving the ease of mounting on the railway vehicle V. Note that the left end of the rod 4 in FIG. 2 and the bottom cap 10 closing the right end of the cylinder 2 are provided with mounting parts (not shown), allowing this cylinder device C1 to be interposed between the carbody B and the bogie T of the railway vehicle V.

[0025] 2, the cylinder device C1 of the first embodiment is provided with a flow straightening passage 18 that allows only a flow from the piston side chamber 6 to the rod side chamber 5. The flow straightening passage 18 may be provided in a location other than the piston 3. Furthermore, the cylinder device C1 of this example is provided with a suction passage 19 that allows only a flow from the tank 8 to the piston side chamber 6.

[0026] Next, one end of the damping passage 21 is connected to the rod side chamber 5 and the other end is connected to the tank 8, thereby communicating between the rod side chamber 5 and the tank 8. Also, a damping valve is provided in the damping passage 21. In the cylinder device C1 of the present embodiment, the damping valve is a variable relief valve 22 capable of changing the valve opening pressure. In this example, the variable relief valve 22 is a proportional electromagnetic relief valve equipped with a solenoid, and is capable of adjusting the valve opening pressure according to the amount of current supplied, and is configured to minimize the valve opening pressure when the amount of current is maximized, and maximize the valve opening pressure when no current is supplied. More specifically, although not shown in detail, the variable relief valve 22 has as its main components a valve element 22a that opens and closes the damping passage 21, a housing (not shown) that accommodates the valve element 22a and has a valve hole that is connected to the damping passage 21, a spring 22b that urges the valve element 22a in a valve closing direction, a solenoid 22c that exerts a thrust to urge the valve element 22a in a valve opening direction when current is applied, and a pilot passage 22d that is provided to act on the valve element 22a using pressure upstream of the valve element 22a as a pilot pressure to urge the valve element 22a in the valve opening direction by the pilot pressure.

[0027] In addition, the damping valve may be any damping valve that is equipped with a driving source such as a solenoid that drives the valve body and is capable of adjusting the damping force (thrust) exerted by the cylinder device C1. In addition to the variable relief valve 22, it may be a variable throttle valve that can change the flow path area by driving a spool with a driving source such as a solenoid, or a valve unit as disclosed in JP 2017-82874 A that has a passage in which an opening / closing valve and a passive valve are provided and a passage in which a variable relief valve is provided in parallel, and that opens and closes the opening / closing valve and controls the opening pressure of the variable relief valve with a single driving source such as a solenoid.

[0028] Moreover, the bypass damping passage 25 has one end connected to the rod side chamber 5 and the other end connected to the tank 8, and communicates between the rod side chamber 5 and the tank 8 in parallel with the damping passage 21. And, a bypass damping passage damping valve 26 is provided in the bypass damping passage 25. In the illustrated example, the bypass damping passage damping valve 26 is a variable orifice whose opening area can be adjusted by manual operation, but it may be a fixed orifice or a relief valve.

[0029] In the cylinder device C1 of the present embodiment, the direction switching valve 28 is a two-position three-port directional control valve that includes a valve element 28a provided in the damping passage 21 on the rod side chamber side upstream of the connection point of the variable relief valve 22 as a damping valve and the first passage 11, a pilot passage 28d that applies pressure on the rod side chamber side upstream of the direction switching valve 28 as pilot pressure to the valve element 28a, and a spring 28e that biases the valve element 28a against the pilot pressure.

[0030] The valve body 28a has a damping passage communicating position 28b where the damping passage 21 is connected and the bypass damping passage 25 is blocked, and a bypass damping passage communicating position 28c where the damping passage 21 is blocked and the bypass damping passage 25 is connected.

[0031] The pilot passage 28d guides the pressure upstream of the directional control valve 28 of the damping passage 21 to act on the valve element 28a. The valve element 28a is always biased by the force of the pressure to take the bypass damping passage communicating position 28c. In contrast, the spring 28e biases the valve element 28a to take the damping passage communicating position 28b. Thus, the valve element 28a takes the damping passage communicating position 28b until the force of the pressure applied to the valve element 28a exceeds the biasing force of the spring 28e, and when the pressure increases and the force pressing the valve element 28a exceeds the biasing force of the spring 28e, the valve element 28a takes the bypass damping passage communicating position 28c. When the pressure upstream reaches or exceeds a predetermined pressure, the directional control valve 28 switches from the damping passage communicating position 28b to the bypass damping passage communicating position 28c.

[0032] As described above, when the pressure in the rod side chamber 5, which is upstream, is less than a predetermined pressure, the directional control valve 28 opens the damping passage 21 to allow the liquid to flow to the tank 8 through the variable relief valve 22. On the other hand, when the pressure in the rod side chamber 5, which is upstream, is equal to or greater than the predetermined pressure, the directional control valve 28 selects the bypass damping passage 25 to allow the liquid to flow to the tank 8 through the bypass damping passage damping valve 26. Therefore, when the pressure in the rod side chamber 5 reaches or exceeds the predetermined pressure, no liquid flows through the variable relief valve 22, which serves as a damping valve. The predetermined pressure, which is the upstream pressure at which the directional control valve 28 closes the damping passage 21, is set to be at least less than a pressure that the variable relief valve 22 can withstand.

[0033] Furthermore, in the cylinder device C1 of the first embodiment, in order to protect the hydraulic circuit, a protective passage 29 that communicates between the rod side chamber 5 and the tank 8 in parallel with the damping passage 21 and the bypass damping passage 25, and a relief valve 30 provided in the protective passage 29 are provided. When the pressure in the rod side chamber 5 reaches a preset upper limit pressure, the relief valve 30 opens to discharge the liquid from within the cylinder body 1 to the tank 8, thereby preventing the pressure in the cylinder body 1 from becoming excessive, and protecting the cylinder device C1.

[0034] Furthermore, the cylinder device C1 of the first embodiment includes a first passage 11 that is located in the middle of the damping passage 21, one end of which is connected to the rod side chamber 5, between the direction switching valve 28 and the variable relief valve 22 serving as a damping valve, and that is connected to a common passage 27, the other end of which is connected to the piston side chamber 6. The first passage 11 is connected to the rod side chamber 5 via the damping passage 21 and the direction switching valve 28, and is connected to the piston side chamber 6 via the common passage 27. Thus, the first passage 11 communicates between the rod side chamber 5 and the piston side chamber 6. In addition, a first on-off valve 12 is provided in the first passage 11. The first on-off valve 12 is an electromagnetic on-off valve, and has a communication position that connects the rod side chamber 5 and the piston side chamber 6 and a blocking position that blocks communication between the rod side chamber 5 and the piston side chamber 6. When energized, the first passage 11 is opened to connect the rod side chamber 5 and the piston side chamber 6, and when deenergized, the first passage 11 is blocked to block the rod side chamber 5 and the piston side chamber 6. In this way, the first on-off valve 12 switches between communication and blocking between the rod side chamber 5 and the piston side chamber 6.

[0035] The cylinder device C1 of this embodiment is also provided with a second passage 13, one end of which is connected to the common passage 27 connected to the piston side chamber 6, and the other end of which is connected to the tank 8. The second passage 13 communicates the piston side chamber 6 and the tank 8 via the common passage 27, and a second on-off valve 14 is provided in the second passage 13. The second on-off valve 14 is an electromagnetic on-off valve, and has a communication position that communicates the piston side chamber 6 and the tank 8, and a blocking position that blocks communication between the piston side chamber 6 and the tank 8. When energized, the second passage 13 is opened to communicate the piston side chamber 6 and the tank 8, and when deenergized, the second passage 13 is blocked to block the piston side chamber 6 and the tank 8. In this way, the second on-off valve 14 switches between communication and blocking between the piston side chamber 6 and the tank 8.

[0036] In this way, the first passage 11 branches off from the damping passage 21 upstream of the variable relief valve 22 and downstream of the directional control valve 28 and is connected to the common passage 27, and the second passage 13 branches off from the common passage 27 and is connected to the tank 8.

[0037] The cylinder device C1 configured in this manner operates as follows. When the first on-off valve 12 and the second on-off valve 14 are in the shutoff position, and the cylinder body 1 is extended by receiving an external force, liquid is pushed out from the compressed rod side chamber 5. Then, liquid is supplied to the expanding piston side chamber 6 from the tank 8 through the suction passage 19. When the pressure in the rod side chamber 5 upstream of the directional control valve 28 of the damping passage 21 during this extension operation is less than a predetermined pressure, the directional control valve 28 closes the bypass damping passage 25 to communicate the damping passage 21, so that the cylinder device C1 exerts a damping force that suppresses the extension of the cylinder body 1 by providing resistance to the flow of liquid pushed out from inside the cylinder 2 with the variable relief valve 22. Then, the valve opening pressure of the variable relief valve 22 can be changed by adjusting the amount of current supplied to the variable relief valve 22, so that the cylinder device C1 of this embodiment allows adjustment of the damping force on the extension side.

[0038] In addition, when the pressure in the rod side chamber 5 becomes equal to or higher than a predetermined pressure during extension operation, the directional control valve 28 blocks the damping passage 21 and opens the bypass damping passage 25, so that the cylinder device C1 provides resistance to the flow of liquid pushed out from inside the cylinder 2 with the bypass damping passage damping valve 26, thereby exerting a damping force that suppresses extension.

[0039] On the other hand, when the first on-off valve 12 and the second on-off valve 14 are in the shutoff position, if the cylinder body 1 contracts under the influence of an external force, the liquid moves from the compressed piston side chamber 6 to the expanding rod side chamber 5 via the rectifying passage 18. Also, when the cylinder device C1 contracts, the rod 4 enters the cylinder 2, so that the liquid in the cylinder 2 is excessive in the volume corresponding to the volume of the rod 4 entering the cylinder 2, and is pushed out of the cylinder 2. During this contraction operation, if the pressure in the rod side chamber 5 upstream of the directional control valve 28 of the damping passage 21 is less than a predetermined pressure, the directional control valve 28 closes the bypass damping passage 25 to communicate the damping passage 21, so that the cylinder device C1 exerts a damping force that suppresses the contraction of the cylinder body 1 by providing resistance to the flow of the liquid pushed out from the cylinder 2 with the variable relief valve 22. The valve opening pressure of the variable relief valve 22 can be changed by adjusting the amount of current supplied to the variable relief valve 22, so that the cylinder device C1 of this embodiment allows adjustment of the damping force on the contraction side.

[0040] In addition, when the pressure in the rod side chamber 5 becomes equal to or higher than a predetermined pressure during contraction operation, the directional control valve 28 blocks the damping passage 21 and opens the bypass damping passage 25, so that the cylinder device C1 provides resistance to the flow of liquid pushed out from inside the cylinder 2 with the bypass damping passage damping valve 26, thereby exerting a damping force that suppresses the contraction of the cylinder body 1.

[0041] In the case of this cylinder device C1, the cross-sectional area of ​​the rod 4 is half that of the piston 3, and the pressure-receiving area on the rod side chamber 5 side of the piston 3 is half that on the piston side chamber 6 side. Therefore, the flow rate of the liquid discharged from inside the cylinder 2 to the tank 8 through the damping passage 21 or the bypass damping passage 25 becomes equal when the cylinder device C1 is extended and when it is contracted. Therefore, the cylinder device C1 can exert an equal damping force if the moving speed of the piston 3 is the same on both sides of the extension and contraction.

[0042] In addition, both the first opening / closing valve 12 and the second opening / closing valve 14 take the cut-off position when not energized, and in the event of a failure in which power cannot be supplied, the cylinder device C1 of this example always exerts a damping force against expansion and contraction as described above, and therefore functions as a passive damper.

[0043] In the cylinder device C1 of this example, when the first on-off valve 12 is in the communicating position and the second on-off valve 14 is in the blocking position, the rod side chamber 5 and the piston side chamber 6 are communicated through the first passage 11, but the communication between the piston side chamber 6 and the tank 8 through the second passage 13 is cut off. When the cylinder body 1 is contracted under an external force in this state, the liquid corresponding to the volume of the rod 4 entering the cylinder 2 is pushed out from the rod side chamber 5 toward the damping passage 21, and a damping force that suppresses the contraction of the cylinder body 1 is exerted by the variable relief valve 22 or the bypass damping passage damping valve 26 selected by the directional control valve 28 according to the pressure of the rod side chamber 5. On the other hand, when the cylinder body 1 is extended in this state, the liquid moves from the contracting rod side chamber 5 to the expanding piston side chamber 6 through the first passage 11, and the liquid corresponding to the volume of the rod 4 withdrawing from the cylinder 2 is supplied from the tank 8 to the cylinder 2 through the suction passage 19. Therefore, in this case, the liquid does not flow to the damping passage 21 or the bypass damping passage 25, and the pressure inside the cylinder 2 becomes the tank pressure, so that the cylinder device C1 does not exert a damping force.

[0044] Furthermore, in the cylinder device C1 of this example, when the first on-off valve 12 is in the shutoff position and the second on-off valve 14 is in the communicating position, the communication between the rod side chamber 5 and the piston side chamber 6 via the first passage 11 is cut off, but the piston side chamber 6 and the tank 8 are communicated via the second passage 13. When the cylinder body 1 is extended by an external force in this state, the liquid is pushed out from the rod side chamber 5 toward the damping passage 21 as the rod side chamber 5 contracts, and a damping force that suppresses the extension of the cylinder body 1 is exerted by the variable relief valve 22 or the bypass damping passage damping valve 26 selected by the directional control valve 28 according to the pressure of the rod side chamber 5. On the other hand, when the cylinder body 1 contracts in this state, the liquid moves from the contracting piston side chamber 6 to the expanding rod side chamber 5 via the straightening passage 18, and the liquid of the volume of the rod 4 entering the cylinder 2 is discharged from the piston side chamber 6 to the tank 8 via the second passage 13. Therefore, in this case, the liquid does not flow to the damping passage 21 or the bypass damping passage 25, and the inside of the cylinder 2 becomes the tank pressure, so that the cylinder device C1 does not exert a damping force. In this way, the cylinder device C1 can function as a one-sided damper that exerts a damping force by selecting either extension or contraction.

[0045] In this way, when the first on-off valve 12 is in the communicating position and the second on-off valve 14 is in the shutoff position, and when the first on-off valve 12 is in the shutoff position and the second on-off valve 14 is in the communicating position, the cylinder device C1 exerts a damping force only in either extension or contraction, as described above. Therefore, if this mode is selected, for example, when the damping force is exerted in a direction in which the vibration of the bogie T of the railway vehicle V causes the car body B to vibrate, the cylinder device C1 can be made a one-sided damper so as not to exert a damping force in such a direction. Therefore, with this cylinder device C1, semi-active control based on Karnop's skyhook theory can be easily realized, so that the cylinder device C1 can function as a skyhook semi-active damper.

[0046] In addition, when the first opening / closing valve 12 and the second opening / closing valve 14 are open, the rod side chamber 5 and the piston side chamber 6 are connected to the tank 8, the pressure in the rod side chamber 5 and the pressure in the piston side chamber 6 become the tank pressure, and the cylinder device C1 is in an unloaded state in which no damping force is generated whether the cylinder body 1 extends or contracts.

[0047] The opening pressure of the relief valve 30 provided in the protective passage 29 is higher than the aforementioned predetermined pressure. In the cylinder device C1 of the first embodiment, when the pressure inside the cylinder 2 reaches the opening pressure of the relief valve 30, the liquid moves to the tank 8 not only through the bypass damping passage damping valve 26 but also through the relief valve 30, so that the pressure inside the cylinder 2 is prevented from becoming excessive and the cylinder device C1 is protected.

[0048] As described above, the cylinder device C1 of the first embodiment is configured to include the cylinder 2 filled with liquid, the piston 3 inserted into the cylinder 2 so as to be axially movable and dividing the inside of the cylinder 2 into a rod side chamber 5 and a piston side chamber 6, the cylinder body 1 having the rod 4 inserted into the cylinder 2 so as to be axially movable and connected to the piston 3, the damping passage 21 through which liquid passes when the cylinder body 1 expands and contracts, the bypass damping passage 25 arranged in parallel with the damping passage 21, the variable relief valve (damping valve) 22 provided in the damping passage 21, the bypass damping passage damping valve 26 provided in the bypass damping passage 25, and the directional control valve 28 provided upstream of the variable relief valve (damping valve) 22, which opens the damping passage 21 and closes the bypass damping passage 25 when the pressure on the upstream side is less than a predetermined pressure, and closes the damping passage 21 and opens the bypass damping passage 25 when the pressure on the upstream side is equal to or greater than the predetermined pressure.

[0049] In the cylinder device C1 configured as described above, when the pressure in the rod side chamber 5 becomes equal to or higher than a predetermined pressure during extension and contraction, the directional control valve 28 blocks the damping passage 21 and communicates with the bypass damping passage 25. In this manner, in the cylinder device C1, when the pressure in the cylinder 2 becomes equal to or higher than a predetermined pressure when the cylinder body 1 expands and contracts due to input of a large vibration, the directional control valve 28 blocks the damping passage 21, preventing the variable relief valve 22 as a damping valve from being exposed to high pressure, thereby protecting the variable relief valve 22, while allowing the bypass damping passage damping valve 26 to exert a damping force. Therefore, since it is not necessary to employ a variable relief valve 22 that can withstand high pressure, it is possible to avoid an increase in the weight of the components of the variable relief valve 22 and the damping passage 21 in order to ensure the strength of the variable relief valve 22 and the damping passage 21. As described above, according to the cylinder device C1 of this embodiment, the weight and cost of the entire device can be reduced.

[0050] Incidentally, the damping passage 21 communicates between the inside of the cylinder 2 and the tank 8, and the downstream side of the variable relief valve 22 is always at tank pressure, and no high pressure acts from the downstream side. Therefore, if the damping passage 21 upstream of the variable relief valve 22 is blocked by the directional control valve 28, the variable relief valve 22 will not be exposed to high pressure.

[0051] The predetermined pressure, which is the upstream pressure at which the directional control valve 28 blocks the damping passage 21, is set to a pressure lower than the pressure that the variable relief valve 22 can withstand, so that high pressure that would deteriorate the variable relief valve 22 does not act on the variable relief valve 22, and the variable relief valve 22 can be used safely.

[0052] The pressure flow rate characteristics of the bypass damping passage damping valve 26 can be set independently of the pressure flow rate characteristics of the variable relief valve 22, but a situation in which the pressure inside the cylinder 2 becomes extremely high is considered to be a situation in which large vibrations are input to the cylinder body 1. For this reason, it is advisable to set the pressure flow rate characteristics of the bypass damping passage damping valve 26 so that, under a situation in which the directional control valve 28 blocks the damping passage 21, the bypass damping passage damping valve 26 can exert a damping force higher than the damping force that can be exerted by the variable relief valve 22, thereby sufficiently damping the vibrations of the vehicle body B.

[0053] 3, in addition to the directional control valve 28, the common passage 27 may be provided with a common passage on-off valve 31 that opens and closes the common passage 27. The common passage on-off valve 31 includes a valve body 31a provided in the common passage 27, a pilot passage 31d that applies the pressure of the common passage 27 on the piston side chamber side relative to the common passage on-off valve 31 as a pilot pressure to the valve body 31a, and a spring 31e that biases the valve body 31a against the pilot pressure.

[0054] The valve body 31a has a communication position 31b for communicating the common passage 27 and a blocking position 31c for blocking the common passage 27. The pilot passage 31d guides the pressure of the piston side chamber 6 to act on the valve body 31a. The valve body 31a is always biased to take the blocking position 31c by the force of the pressure. In contrast, the spring 31e biases the valve body 31a to take the communication position 31b. Therefore, the valve body 31a takes the communication position 31b until the force of the pressure applied to the valve body 31a exceeds the biasing force of the spring 31e, and when the pressure increases and the force pressing the valve body 31a exceeds the biasing force of the spring 31e, the valve body 31a takes the blocking position 31c. When the pressure of the piston side chamber 6 becomes equal to or higher than a second predetermined pressure, the common passage opening / closing valve 31 switches from the communication position 31b to the blocking position 31c.

[0055] As described above, when the pressure in the piston side chamber 6 is less than the second predetermined pressure, the common passage on-off valve 31 opens the common passage 27 to enable the first on-off valve 12 in the first passage 11 and the second on-off valve 14 in the second passage 13, and when the pressure in the piston side chamber 6 is equal to or greater than the second predetermined pressure, it closes the common passage 27 to prevent the first on-off valve 12 in the first passage 11 and the second on-off valve 14 in the second passage 13 from being exposed to high pressure. The second predetermined pressure, which is the pressure in the piston side chamber 6 at which the common passage on-off valve 31 closes the common passage 27, is set to be at least less than the pressure that the first on-off valve 12 and the second on-off valve 14 can withstand. Incidentally, like the directional control valve 28, the common passage on-off valve 31 may utilize the pressure in the rod side chamber 5 as the pilot pressure. In that case, the common passage on-off valve 31 opens the common passage 27 when the pressure in the rod side chamber 5 is less than a second predetermined pressure, and blocks the common passage 27 when the pressure in the rod side chamber 5 is equal to or greater than the second predetermined pressure, thereby preventing the first on-off valve 12 and the second on-off valve 14 from being exposed to high pressure.

[0056] When the common passage 27 is blocked by the common passage opening / closing valve 31 and the damping passage 21 is blocked by the directional control valve 28, the cylinder device C2 functions as a passive damper and exerts a damping force against the expansion and contraction of the cylinder body 1 by the bypass damping passage damping valve 26 or the bypass damping passage damping valve 26 and the relief valve 30.

[0057] According to the cylinder device C2 of the first modified example of the first embodiment configured in this manner, not only can an increase in weight of the components of the variable relief valve 22 and the damping passage 21 for ensuring the strength of the variable relief valve 22 as a damping valve and the damping passage 21 be avoided, but also, since the provision of the common passage on-off valve 31 can suppress exposure of the first passage 11, the second passage 13, the first on-off valve 12 and the second on-off valve 14 to high pressure, an increase in weight of the components of the first passage 11, the second passage 13, the first on-off valve 12 and the second on-off valve 14 can be avoided. Thus, according to the cylinder device C2 of the present embodiment, the weight and cost of the entire device can be reduced more effectively.

[0058] Even if the common passage on-off valve 31 is provided in the common passage 27, when the first on-off valve 12 and the second on-off valve 14 are opened, the rod side chamber 5 and the piston side chamber 6 in the cylinder 2 are connected to the tank 8, and therefore the pressure in the rod side chamber 5 and the pressure in the piston side chamber 6 become the tank pressure. Therefore, the common passage on-off valve 31 does not block the common passage 27, and the cylinder device C2 can be unloaded.

[0059] In addition, the second predetermined pressure, which is the pressure in the piston side chamber 6 or the rod side chamber 5 at which the common passage on-off valve 31 blocks the common passage 27, and the predetermined pressure, which is the pressure in the rod side chamber 5 at which the directional control valve 28 blocks the damping passage 21, may be set to the same value or may be set independently.

[0060] Furthermore, like a cylinder device C3 of a second modified example of the first embodiment shown in FIG. 4, in addition to the configuration of the cylinder device C1 of the first embodiment, a supply passage 16 communicating between the tank 8 and the rod side chamber 5, a pump 15 provided in this supply passage 16 for sucking up liquid from the tank 8 and discharging it to the rod side chamber 5, and a check valve 17 provided on the discharge side of the pump 15 of the supply passage 16 for blocking the flow of liquid from the rod side chamber 5 toward the tank 8 may be provided.

[0061] The pump 15 is driven by a motor 20 controlled by a controller (not shown) and is a pump that discharges liquid in only one direction. The pump 15 is installed in the supply passage 16 with its suction port facing the tank 8 and its discharge port facing the rod side chamber 5. When driven by the motor 20, the pump 15 sucks liquid from the tank 8 and supplies the liquid to the rod side chamber 5.

[0062] As described above, the pump 15 discharges liquid in only one direction and does not switch the rotation direction, so there is no problem of the discharge amount changing when the rotation direction is switched, and an inexpensive gear pump or the like can be used.

[0063] Furthermore, since the rotation direction of the pump 15 is always the same, the motor 20, which is the drive source for driving the pump 15, does not require high responsiveness to rotation switching, and therefore a less expensive motor can be used for the motor 20. The check valve 17 is provided to prevent the liquid from flowing back toward the pump 15 when the cylinder device C3 is forcibly expanded or contracted by an external force.

[0064] Next, when the cylinder device C3 configured as described above is caused to exert a desired thrust in the extension direction, the motor 20 is rotated to supply liquid from the pump 15 into the cylinder 2, while the first on-off valve 12 is set to the communicating position and the second on-off valve 14 is set to the blocking position. Then, the rod side chamber 5 and the piston side chamber 6 are placed in a communicating state, liquid is supplied to both from the pump 15, the piston 3 is pushed to the left in FIG. 4, and the cylinder device C3 exerts a thrust in the extension direction. When the pressure in the rod side chamber 5 and the piston side chamber 6 exceeds the valve opening pressure of the adjustable relief valve 22, the adjustable relief valve 22 opens and the liquid is discharged to the tank 8 through the damping passage 21. Therefore, the pressure in the rod side chamber 5 and the piston side chamber 6 is adjusted to be equal to the valve opening pressure of the adjustable relief valve 22, which is determined by the amount of current applied to the adjustable relief valve 22. The cylinder device C3 exerts a thrust in the extension direction equal to the pressure difference between the pressure-receiving areas of the piston side chamber 6 side and the rod side chamber 5 side of the piston 3 multiplied by the pressures in the rod side chamber 5 and the piston side chamber 6.

[0065] On the other hand, when the cylinder device C3 is caused to exert a desired thrust in the contraction direction, the motor 20 is rotated to supply liquid from the pump 15 into the rod side chamber 5, while the first on-off valve 12 is set to the shutoff position and the second on-off valve 14 is set to the communication position. Then, the piston side chamber 6 and the tank 8 are placed in a communication state, and liquid is supplied from the pump 15 to the rod side chamber 5, so that the piston 3 is pushed to the right in FIG. 4, and the cylinder device C3 exerts a thrust in the contraction direction. Then, as described above, by adjusting the amount of current given to the adjustable relief valve 22, the cylinder device C3 exerts a thrust in the contraction direction obtained by multiplying the pressure-receiving area on the rod side chamber 5 side of the piston 3 by the pressure in the rod side chamber 5. In this way, the cylinder device C3 can function as an actuator.

[0066] In addition, when the rod 4 moves to the left in FIG. 4 by an external force with the first on-off valve 12 open and the second on-off valve 14 closed, the cylinder device C3 does not exert a force in a direction that hinders the movement of the rod 4, that is, in a contracting direction, regardless of whether the pump 15 is driven or not. In this case, when the pump 15 is driven, the discharge flow rate of the pump 15 cannot keep up with the volume change in the cylinder 2 that decreases when the rod 4 retreats from the cylinder 2, but liquid is supplied from the tank 8 to the cylinder 2 through the suction passage 19. In addition, in this case, when the pump 15 is not driven, liquid equivalent to the volume of the rod 4 retreating from the cylinder 2 is supplied from the tank 8 to the cylinder 2 through the suction passage 19. In any case, in this case, the pressure in the cylinder 2 becomes the tank pressure, so the cylinder device C3 does not exert a damping force in a direction that hinders the movement of the rod 4, that is, in a contracting direction.

[0067] 4 due to an external force with the first on-off valve 12 open and the second on-off valve 14 closed, the liquid pushed out of the cylinder 2 by the entry of the rod 4 into the cylinder 2 is returned to the tank 8 through the damping passage 21, regardless of whether the pump 15 is driven or not. In this case, the pressure inside the cylinder 2 is controlled to the desired pressure by the variable relief valve 22, so the cylinder device C3 can exert a force in a direction that hinders the movement of the rod 4, that is, in the extension direction.

[0068] On the other hand, when the rod 4 moves to the right in FIG. 4 due to an external force with the first on-off valve 12 closed and the second on-off valve 14 open, the cylinder device C3 does not exert a force in a direction that hinders the movement of the rod 4, that is, in the extension direction, regardless of whether the pump 15 is driven or not. In this case, while the pump 15 is driven, the discharge flow rate of the pump 15 cannot keep up with the volume change in the rod side chamber 5 that increases when the rod 4 advances into the cylinder 2, but liquid is supplied from the piston side chamber 6 to the rod side chamber 5 through the flow straightening passage 18. In addition, as the rod 4 advances into the cylinder 2, the liquid in the cylinder 2 is excessive by the volume of the rod 4 entering the cylinder 2, but the piston side chamber 6 on the compression side passes through the second passage 13, and this excess liquid is discharged to the tank 8. In this case, even when the pump 15 is not driven, the liquid in the rod side chamber 5 that increases when the rod 4 advances into the cylinder 2 is supplied from the piston side chamber 6 through the flow straightening passage 18, as in the case of being driven. Then, the excess liquid in the volume of the rod 4 entering the cylinder 2 is discharged from the compressed piston side chamber 6 to the tank 8 via the second passage 13. In either case, in this case, the pressure in the cylinder 2 becomes the tank pressure, so the cylinder device C3 does not exert a damping force in the direction that hinders the movement of the rod 4, that is, in the extension direction.

[0069] 4 by an external force with the first on-off valve 12 closed and the second on-off valve 14 open, the liquid pushed out from the rod side chamber 5 is returned to the tank 8 through the damping passage 21 regardless of whether the pump 15 is driven or not. In this case, since the pressure in the rod side chamber 5 is controlled to a desired pressure by the variable relief valve 22, the cylinder device C3 can exert a force in a direction that hinders the movement of the rod 4, that is, in the contracting direction.

[0070] In other words, when the first opening / closing valve 12 is opened and the second opening / closing valve 14 is closed, or when the first opening / closing valve 12 is closed and the second opening / closing valve 14 is opened, the cylinder device C3 is in a state in which it exerts a damping force in only one of the directions of extension or contraction in response to vibration input from an external force, regardless of the driving status of the pump 15.

[0071] Therefore, for example, when the direction in which the force is exerted is a direction in which the vehicle body B is vibrated due to the vibration of the bogie T of the railway vehicle V, the cylinder device C3 of this example can function as a one-sided damper so as not to exert force in such a direction. Therefore, this cylinder device C3 can easily realize semi-active control based on Karnop's Skyhook theory, and can also function as a semi-active damper.

[0072] As can be understood from the description of the cylinder device C1 of the first embodiment, this cylinder device C3 can also function as a damper by only opening and closing the first on-off valve 12 and the second on-off valve 14. In other words, even in a situation where the pump 15 is driven by the motor 20, when the cylinder device C3 is forcibly expanded and contracted by an external force, it can function as a skyhook semi-active damper or a passive damper, and the damping force can be adjusted by adjusting the valve opening pressure of the variable relief valve 22. In this way, the cylinder device C3 not only functions as an actuator, but can also function as a damper by only opening and closing the first on-off valve 12 and the second on-off valve 14, regardless of the driving state of the motor 20. The direction in which the cylinder device C3 should exert a thrust or a damping force is controlled only by opening and closing the first on-off valve 12 and the second on-off valve 14, and when the directions in which the thrust and the damping force should be exerted are the same, the opening and closing states of the first on-off valve 12 and the second on-off valve 14 are the same. Therefore, in the cylinder device C3, the states of the actuator and the skyhook semi-active damper can be switched without switching between stopping and driving the pump 15 or without the troublesome and steep switching operation of the first on-off valve 12 and the second on-off valve 14. Therefore, the cylinder device C3 is a system with high responsiveness and reliability.

[0073] The cylinder device C3 configured as described above includes the directional control valve 28, so that, similarly to the cylinder device C1, when a large vibration is input to the cylinder body 1 and the pressure in the rod side chamber 5 becomes high above a predetermined pressure, the directional control valve 28 shuts off the damping passage 21 to protect the variable relief valve 22 as a damping valve, while the bypass damping passage damping valve 26 exerts a damping force that prevents the cylinder body 1 from expanding and contracting. Therefore, even in the cylinder device C3 in the second modified example of the first embodiment, it is possible to avoid an increase in the weight of the components of the variable relief valve 22 and the damping passage 21 for ensuring the strength of the variable relief valve 22 and the damping passage 21, and the weight and cost of the entire device can be reduced. In addition, the cylinder device C3 may include a common passage opening / closing valve 31 in the common passage 27. In that case, the first opening / closing valve 12 and the second opening / closing valve 14 can also be protected, so that the weight and cost of the entire device can be further reduced.

[0074] <Second embodiment> As shown in FIG. 5, the cylinder device C4 in the second embodiment differs from the cylinder device C1 in that, instead of the directional control valve 28 in the configuration of the cylinder device C1 in the first embodiment, a damping passage opening / closing valve 33 is provided upstream of the variable relief valve 22 serving as a damping valve in the damping passage 21 and opens and closes the damping passage 21, and a bypass damping passage opening / closing valve 34 is provided upstream of the bypass damping passage damping valve 26 in the bypass damping passage 25 and opens and closes the bypass damping passage 25.

[0075] As described above, the cylinder device C4 is provided with the damping passage opening / closing valve 33 that opens and closes the damping passage 21 and the bypass damping passage opening / closing valve 34 that opens and closes the bypass damping passage 25, instead of the directional control valve 28.

[0076] The damping passage opening / closing valve 33 includes a valve element 33a provided in the damping passage 21 on the rod side chamber side upstream of a connection point between the variable relief valve 22 as a damping valve and the first passage 11, a pilot passage 33d that applies pressure on the rod side chamber side of the damping passage 21 relative to the damping passage opening / closing valve 33 as a pilot pressure to the valve element 33a, and a spring 33e that urges the valve element 33a against the pilot pressure. In the cylinder device C4, one end of the first passage 11 is communicated with the rod side chamber 5 via the damping passage 21 and the damping passage opening / closing valve 34, and the other end is communicated with the piston side chamber 6 via the common passage 27.

[0077] The valve body 33a has a communication position 33b for communicating with the damping passage 21 and a blocking position 33c for blocking the damping passage 21. The pilot passage 33d guides the pressure of the rod side chamber 5 to act on the valve body 33a. The valve body 33a is always biased to take the blocking position 33c by the force of the pressure. In contrast, the spring 33e biases the valve body 33a to take the communication position 33b. Therefore, the valve body 33a takes the communication position 33b until the force of the pressure applied to the valve body 33a exceeds the biasing force of the spring 33e, and when the pressure increases and the force pressing the valve body 33a exceeds the biasing force of the spring 33e, the valve body 33a takes the blocking position 33c. When the pressure of the rod side chamber 5 becomes equal to or higher than the predetermined pressure, the damping passage opening / closing valve 33 switches from the communication position 33b to the blocking position 33c.

[0078] The bypass damping passage opening / closing valve 34 is provided with a valve body 34a located midway through the bypass damping passage 25 on the rod side chamber side upstream of the bypass damping passage damping valve 26, a pilot passage 34d that applies pressure on the rod side chamber side of the bypass damping passage 25 relative to the bypass damping passage opening / closing valve 34 as pilot pressure to the valve body 34a, and a spring 34e that biases the valve body 34a against the pilot pressure.

[0079] The valve body 34a has a blocking position 34b for blocking the bypass damping passage 25 and a communicating position 34c for communicating with the bypass damping passage 25. The pilot passage 34d guides the pressure of the rod side chamber 5 to act on the valve body 34a. The valve body 34a is always biased to take the communicating position 34c by the force of the pressure. In contrast, the spring 34e biases the valve body 34a to take the blocking position 34b. Therefore, the valve body 34a takes the blocking position 34b until the force of the pressure applied to the valve body 34a exceeds the biasing force of the spring 34e, and when the pressure increases and the force pressing the valve body 34a exceeds the biasing force of the spring 34e, the valve body 34a takes the communicating position 34c. When the pressure of the rod side chamber 5 becomes equal to or higher than the predetermined pressure, the bypass damping passage opening / closing valve 34 switches from the blocking position 34b to the communicating position 34c.

[0080] As described above, when the pressure in the rod side chamber 5 is less than a predetermined pressure, the damping passage opening / closing valve 33 opens the damping passage 21 to allow liquid to pass through the variable relief valve 22, and the bypass damping passage opening / closing valve 34 blocks the bypass damping passage 25 to prevent liquid from passing through the bypass damping passage damping valve 26. On the other hand, when the pressure in the rod side chamber 5 is equal to or greater than a predetermined pressure, the damping passage opening / closing valve 33 blocks the damping passage 21 to prevent the variable relief valve 22 from being exposed to high pressure, and the bypass damping passage opening / closing valve 34 communicates with the bypass damping passage 25 to allow liquid to pass through the bypass damping passage damping valve 26. In other words, the damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34 in the cylinder device C4, like the directional control valve 28 in the cylinder device C1, communicate with the damping passage 21 and block the bypass damping passage 25 when the pressure in the rod side chamber 5 is less than a predetermined pressure during extension and contraction of the cylinder body 1, and block the damping passage 21 and communicate with the bypass damping passage 25 when the pressure in the rod side chamber 5 becomes equal to or greater than the predetermined pressure.

[0081] In this way, in the cylinder device C4, when the cylinder body 1 expands or contracts due to the input of large vibration and the pressure inside the cylinder 2 becomes high, equal to or higher than a predetermined pressure, the damping passage opening / closing valve 33 closes the damping passage 21, preventing the variable relief valve 22 serving as a damping valve from being exposed to high pressure and protecting the variable relief valve 22, while the bypass damping passage opening / closing valve 34 opens the bypass damping passage 26, allowing the bypass damping passage damping valve 26 to exert a damping force. Therefore, since it is not necessary to employ a variable relief valve 22 that can withstand high pressure, it is possible to avoid an increase in weight of the components of the variable relief valve 22 and the damping passage 21 in order to ensure the strength of the variable relief valve 22 and the damping passage 21. As described above, according to the cylinder device C4 of this embodiment, the weight and cost of the entire device can be reduced.

[0082] In addition, the cylinder device C4 of the second embodiment is provided with a damping passage opening / closing valve 33 that is provided upstream of the variable relief valve 22 serving as a damping valve in the damping passage 21, and that opens the damping passage 21 when the pressure on the upstream side is less than a predetermined pressure and closes the damping passage 21 when the pressure on the upstream side is equal to or greater than the predetermined pressure, and a bypass damping passage opening / closing valve 34 that is provided upstream of the bypass damping passage damping valve 26 in the bypass damping passage 25, and that closes the bypass damping passage 25 when the pressure on the upstream side is less than the predetermined pressure and opens the bypass damping passage 25 when the pressure on the upstream side is equal to or greater than the predetermined pressure. In this way, when the cylinder device C4 of the second embodiment including the damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34 is compared with the cylinder device C1 of the first embodiment including one 2-position 3-port directional control valve 28, the damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34 are lighter and smaller than the directional control valve 28, and can be arranged separately in the hydraulic circuit constituting the cylinder device C4, so that the damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34 have a high degree of freedom in arrangement. Therefore, by optimizing the arrangement of the damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34, the valve block forming the hydraulic circuit can be made small. As described above, according to the cylinder device C4 of the second embodiment, the damping passage 21 and the bypass damping passage 25 can be switched by the lightweight and small damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34, and the entire device can be made small by appropriately arranging the opening / closing valves.

[0083] In addition, since the cylinder device C4 of the second embodiment is simply changed from the directional control valve 28 to a damping passage opening / closing valve 33 and a bypass damping passage opening / closing valve 34, the damping passage opening / closing valve 33 and the bypass damping passage opening / closing valve 34 can be applied instead of the directional control valve 28 of the cylinder device C2 of the first modified example and the cylinder device C3 of the second modified example of the first embodiment.

[0084] Although the preferred embodiment of the present invention has been described in detail above, modifications, variations and changes can be made without departing from the scope of the appended claims. [Explanation of symbols]

[0085] Description of the Reference Numerals 1...cylinder body, 2...cylinder, 3...piston, 4...rod, 5...rod side chamber, 6...piston side chamber, 8...tank, 11...first passage, 12...first on-off valve, 13...second passage, 14...second on-off valve, 21...damping passage, 22...variable relief valve (damping valve), 25...bypass damping passage, 26...bypass damping passage damping valve, 27...common passage, 28...directional control valve, 31...common passage on-off valve, 33...damping passage on-off valve, 34...bypass damping passage on-off valve, C1, C2, C3, C4...cylinder device

Claims

1. a cylinder body including: a cylinder filled with liquid; a piston inserted into the cylinder so as to be axially movable and dividing the interior of the cylinder into a rod side chamber and a piston side chamber; and a rod inserted into the cylinder so as to be axially movable and connected to the piston; A tank for storing the liquid; a first on-off valve that switches between communication and cut-off between the rod side chamber and the piston side chamber; a second on-off valve that switches between communication and cut-off between the piston side chamber and the tank; a damping passage through which the liquid passes when the cylinder body is extended or retracted; a bypass damping passage arranged in parallel with the damping passage; a damping valve provided in the damping passage; a bypass damping passage damping valve provided in the bypass damping passage; a directional control valve that is provided upstream of the damping valve and opens the damping passage and closes the bypass damping passage when the pressure on the upstream side is lower than a predetermined pressure, and closes the damping passage and opens the bypass damping passage when the pressure on the upstream side is equal to or higher than the predetermined pressure. A cylinder device characterized in that:

2. a cylinder body including: a cylinder filled with liquid; a piston inserted into the cylinder so as to be axially movable and dividing the interior of the cylinder into a rod side chamber and a piston side chamber; and a rod inserted into the cylinder so as to be axially movable and connected to the piston; A tank for storing the liquid; a first on-off valve that switches between communication and cut-off between the rod side chamber and the piston side chamber; a second on-off valve that switches between communication and cut-off between the piston side chamber and the tank; a damping passage through which the liquid passes when the cylinder body is extended or retracted; a bypass damping passage arranged in parallel with the damping passage; a damping valve provided in the damping passage; a bypass damping passage damping valve provided in the bypass damping passage; a damping passage opening / closing valve that is provided in the damping passage upstream of the damping valve and opens the damping passage when the pressure on the upstream side is lower than a predetermined pressure and closes the damping passage when the pressure on the upstream side is equal to or higher than the predetermined pressure; a bypass damping passage opening / closing valve that is provided upstream of the bypass damping passage damping valve in the bypass damping passage and that closes the bypass damping passage when the pressure on the upstream side is lower than a predetermined pressure and opens the bypass damping passage when the pressure on the upstream side is equal to or higher than the predetermined pressure. A cylinder device characterized in that:

3. a common passage communicating with the piston side chamber; a first passage having one end communicating with the rod side chamber via the damping passage and the other end communicating with the piston side chamber via the common passage, the first opening / closing valve being provided therein; a second passage having one end communicating with the piston side chamber via the common passage and the other end communicating with the tank, the second passage including the second on-off valve; a common passage opening / closing valve provided in the common passage; 3. The cylinder device according to claim 1 or 2.

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