Air supply and exhaust device

Abstract

To provide an air supply / discharge device capable of adjusting the initial state with a simple configuration. [Solution] An air supply and discharge device A is used in an air suspension equipped with multiple air springs S, including a first air spring S1 and a second air spring S2, and comprises a piston P cantilevered on a rod R, a cylinder C that houses the piston P so that it can move back and forth and whose interior is divided by the piston P into a first chamber r1 through which the rod R passes and a second chamber r2 in which the rod R is not present, and a drive mechanism M that drives the piston P back and forth via the rod R, wherein the first air spring S1 is in a state that tends to become higher in pressure than the second air spring S2, and the first chamber r1 is provided with a first port p1 connected to the first air spring S1, and the second chamber r2 is provided with a second port p2 connected to the second air spring S2.

Description

[Technical Field]

[0001] The present invention relates to an air supply / discharge device that is used, for example, in an air suspension equipped with a plurality of air springs, and that includes a piston that is reciprocally movable inside a cylinder, and a drive mechanism that drives the piston via a rod. [Background technology]

[0002] Conventionally, an air suspension device related to such an air supply / discharge device is disclosed in, for example, Patent Document 1 (see paragraphs

[0007] to

[0012] and FIG. 1).

[0003] In this device, a pair of air springs interposed between the vehicle body and the axle are connected by a passage, with a cylinder provided midway along the passage. A slidable piston is provided inside the cylinder, and the interior of the cylinder is divided into one chamber connected to one air spring and another chamber connected to the other air spring. The piston is driven to reciprocate by a drive means, which alternately changes the volume of the one chamber and the other chamber, supplying and discharging air to and from the one air spring and the other air spring.

[0004] According to this air suspension system, when controlling the vehicle's posture, instead of adjusting the vehicle height by supplying or discharging compressed air from an external source, a cylinder and piston are individually connected to each air spring. As a result, the vehicle's posture can be controlled simply by displacing the piston, which is inserted so that it can slide freely, relative to the cylinder, making it less susceptible to the effects of air compressibility based on acceleration acting on the vehicle.

[0005] In other words, with systems that supply and exhaust external compressed air, air is highly compressible, making it difficult to control the vehicle's posture while the vehicle is moving. Furthermore, a fast response is required for vehicle height adjustment, which increases the air volume, making the adverse effects of compressibility more pronounced. Furthermore, a large-capacity air pressure source requires larger pipes connecting the air pressure source to the air springs, which increases the size of the air suspension system. This conventional technology is said to solve these problems. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-298170 Summary of the Invention [Problem to be solved by the invention]

[0007] In the conventional air suspension system described above, the air supply capacity to both air springs is set to be equal. For example, one of the pistons is equipped with a drive shaft, and the other is equipped with a shaft of the same diameter. This makes the effective area of ​​the piston in one chamber and the other chamber equal, and the absolute amount of change in air volume in both chambers is equal.

[0008] However, this configuration requires a certain area for both shafts to stroke, which increases the size of the cylinder, etc. Also, because the shafts pass through the bottoms of both the first and second chambers, sealing members are required between each shaft and the bottom, which increases the number of parts.

[0009] In such a device, if the shaft of the other chamber, which is not involved in the transmission of driving force, is omitted, there is a concern that a difference in the sensitivity of air compression will occur between the one chamber and the other chamber, causing the piston to move to one side from its initial position. To prevent this problem, it has been necessary to use a control to temporarily fix the position of the piston using an actuator or the like, or a piston fixing mechanism that intervenes in part of the piston's linear motion mechanism.

[0010] As described above, conventional air suspension systems have various problems to be solved, and there has been a demand for an air supply / discharge system that is simple in construction yet allows the initial state to be adjusted. [Means for solving the problem]

[0011] (Features and configuration) The characteristic configuration of the air supply and discharge device according to the present invention is as follows: An air supply / discharge device used in an air suspension equipped with a plurality of air springs including a first air spring and a second air spring, a piston cantilevered on a rod; a cylinder that houses the piston so that the piston can reciprocate, and whose interior is divided by the piston into a first chamber through which the rod passes and a second chamber in which the rod does not exist; a drive mechanism that reciprocates the piston via the rod, The first air spring is in a state where it is likely to become relatively high pressure relative to the second air spring, The first chamber is provided with a first port connected to the first air spring, and the second chamber is provided with a second port connected to the second air spring.

[0012] (effect) The air supply / exhaust device of this configuration uses a drive mechanism to adjust the position of the piston and supply / exhaust compressed air to / from the air chambers that make up the air springs. For example, a first port and a second port are connected to the first and second air springs associated with the left and right wheels of a vehicle, respectively. When the vehicle is stationary, the left and right air springs are in their initial positions, and the piston of the air supply / exhaust device is located in the center of the cylinder. Meanwhile, when the vehicle is moving, the piston is moved to a predetermined position to adjust the pressure of the first and second air springs.

[0013] The piston in this configuration is cantilevered by the rod, and the surface areas of the piston facing the first and second chambers are different. Therefore, when the same pressure acts on the first and second air springs, the pressure in the second chamber is higher than the pressure in the first chamber, and the piston is pressed toward the first chamber. For this reason, to maintain the piston and rod in a predetermined position, such as their initial neutral position, it is necessary to generate a constant driving force in the drive mechanism or to set the components of the drive mechanism in a locked state.

[0014] As a result, when compressed air is supplied to and exhausted from the air chambers of the first and second air springs, the response differs depending on the direction of piston movement. Also, the pressure difference causes the piston's balance position to shift, resulting in different piston strokes in both directions, which could interfere with the intended air supply and exhaust.

[0015] Therefore, in this configuration, a first air spring, which tends to be under high pressure, is connected to the first port, and a second air spring, which tends to be under low pressure, is connected to the second port. For example, in the initial weight distribution of a vehicle, the weight on the driver's side is heavier than the weight on the passenger side. Furthermore, when only the driver is in the vehicle, the driver's side becomes even heavier. In this way, if the weights borne by the first air spring and the second air spring are different from the beginning, connecting the first port to the air spring with a greater weight and higher internal pressure reduces the effect of the difference in area between the two sides of the piston. As a result, the pressing force acting on the piston in the initial state is reduced, resulting in an air supply / exhaust device with good responsiveness, less resistance during operation, and excellent durability.

[0016] The air supply / discharge device according to the present invention may be provided with a biasing portion that biases the piston from the first chamber toward the second chamber or from the second chamber toward the first chamber.

[0017] (effect) The weight distribution borne by each wheel of a vehicle changes depending on the number of passengers and cargo loaded. Therefore, even if the first port and the second port are selectively used depending on the pressure at the connection destination, as described above, it is rare that the pressure difference required to eliminate the imbalance in piston area matches the pressure difference caused by the loading condition at each time. Therefore, by providing a biasing portion that biases the piston toward either the first chamber or the second chamber, as in this configuration, piston deflection can be further reduced.

[0018] In the air supply / discharge device according to the present invention, it is preferable that the biasing portion includes a first spring that contacts the piston in the first chamber, and a second spring that contacts the piston in the second chamber.

[0019] (effect) As in this configuration, by providing a first spring that contacts the piston in the first chamber and a second spring that contacts the piston in the second chamber, the balance position of the piston is determined by the cooperation of the first spring and the second spring. With this configuration, when the normal load condition of luggage is fixed, it is sufficient to install first and second springs with different predetermined spring coefficients. Furthermore, when the load condition of luggage or the like changes frequently, an air supply / exhaust device can be obtained that can always stabilize the state of the air suspension by making the biasing state of the first spring or the second spring adjustable.

[0020] The air supply / exhaust device according to the present invention may include a case that houses the drive mechanism, and the biasing portion may include a swing arm that is supported by a rotation shaft provided on the rod and biased around the rotation shaft, and a step portion formed on the inner surface of the case so as to be pressed by the swing arm.

[0021] (effect) As in this configuration, the biasing portion may rotatably support the biased swing arm on the rod, and the swing arm may press against a step formed on the inner surface of the case. When the swing arm presses against the step, the rod attempts to move in either direction along its longitudinal direction. This biasing force can adjust the piston position. Because a portion of the rod protrudes from the cylinder toward the drive mechanism and the rod itself has length, it is easy to provide the swing arm on a portion of the rod. It is also easy to form a step on the inner surface of the case. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of an air supply / exhaust device according to a first embodiment; [Figure 2] FIG. 10 is an explanatory diagram showing the configuration of an air supply / discharge device according to a second embodiment. [Figure 3] FIG. 10 is an explanatory diagram showing the configuration of an air supply / exhaust device according to a third embodiment. [Figure 4] FIG. 10 is an explanatory diagram showing the operation of the air supply and discharge device according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] [First embodiment] (overview) An air supply and discharge device according to a first embodiment of the present invention is shown in Fig. 1. This air supply and discharge device A is used, for example, in a vehicle B equipped with an air suspension, and adjusts the running posture of the vehicle B by changing the pressure of an air spring S associated with a specific wheel T. In this embodiment, an example is shown in which the air supply and discharge device A is connected to a left front wheel TL and a right front wheel TR of the vehicle B.

[0024] A first air spring S1 is provided on the right front wheel TR, and a second air spring S2 is provided on the left front wheel TL. However, the loads borne by the first air spring S1 and the second air spring S2 are not equal. For example, if the steering mechanism 1 is provided on the right side, this load increases the load borne by the right front wheel TR. Furthermore, when only the driver is on board, the load borne by the right front wheel TR increases even more. As such, the first air spring S1 is likely to be pressurized relatively higher than the second air spring S2. For this reason, in order to maintain the horizontal position of the vehicle B, it is advantageous to set the internal pressure of the first air spring S1 higher than the internal pressure of the second air spring S2, for example.

[0025] In addition, when air springs S are provided on the front and rear wheels, the load borne by the air springs S on the front and rear wheels also changes depending on the longitudinal weight balance of the vehicle. For example, depending on the longitudinal position of the driver's seat and the mounting position of the drive source (engine, transmission, e-Axle, etc.), either the front or rear air springs S are more likely to be under relatively high pressure.

[0026] The air supply and discharge device A of this embodiment has a simple configuration yet allows the initial state to be adjusted so that stable driving characteristics can be achieved in response to internal pressure fluctuations, for example, in the left and right first air springs S1 and second air springs S2 when the vehicle is stationary or in a running state.

[0027] (Configuration of air supply / exhaust device) As shown in FIG. 1, the air supply / exhaust device A of this embodiment includes a piston P and a cylinder C that supply / exhaust air to / from the left front wheel TL and the right front wheel TR, and a drive mechanism M that reciprocates the piston P. The drive mechanism M includes a motor m of any type, and the piston P is reciprocated by forward and reverse rotation of the motor shaft m1. The motor m includes a stator ma provided in a case K and a rotor mb that rotates inside the stator ma. The rotor mb has a hollow structure, and a rod R that supports the piston P is disposed inside the rotor mb and passes through it. A female thread mbs and a male thread Rs that thread into each other are formed on the inner surface of the rotor mb and the outer surface of the rod R, and the rod R, and therefore the piston P, reciprocates as the rotor mb rotates forward and backward.

[0028] A cylinder C is fixed adjacent to the case K of the motor m. A piston P is arranged inside the cylinder C and is cantilevered by a rod R. The inside of the cylinder C is divided by the piston P into a first chamber r1, through which the rod R passes, and a second chamber r2, in which the rod R is not present. A first port p1 is provided in the first chamber r1, and a second port p2 is provided in the second chamber r2. The first port p1 is connected to a first air spring S1, and the second port p2 is connected to a second air spring S2.

[0029] The forward and reverse operation of the drive mechanism M causes the piston P to reciprocate inside the cylinder C, and the first chamber r1 and the second chamber r2 are alternately contracted and expanded. The contraction causes air to be expelled, and the expansion causes air to flow in. The running and stationary states of the vehicle B are calculated by a vehicle height sensor and an acceleration sensor (not shown), and the drive mechanism M is controlled by an ECU or the like to maintain the posture of the vehicle B appropriately.

[0030] For example, if the right side of vehicle B is about to sink while stationary, the first chamber r1 is contracted to supply air from the first port p1 to the first air spring S1, and conversely, the second chamber r2 is expanded to allow air to flow from the second air spring S2 to the second port p2. This maintains the horizontal posture of vehicle B. Also, if the left side of vehicle B is about to sink while traveling around a right curve, the second chamber r2 is contracted to supply air from the second port p2 to the second air spring S2, and the first chamber r1 is expanded to allow air to flow from the first air spring S1 to the first port p1, thereby reducing the tilt of vehicle B.

[0031] In this configuration, the piston P is cantilevered by the rod R. This simplifies the configuration of the piston P. The second chamber r2, where the rod R does not exist, is simply formed by the bottom c1 and side c2 of the cylinder C, which also simplifies the structure of the cylinder C. Furthermore, the rod R enters the case K of the drive mechanism M and penetrates the rotor mb. A female thread mbs is formed on the inner surface of the rotor mb, and a male thread Rs is formed on the outer surface of the rod R. A claw portion Ra for restricting rotation is formed midway along the rod R, and this claw portion Ra is engaged and guided by a groove Ka formed on the inner surface of the case K. As a result, the rod R, i.e., the piston P, reciprocates without rotating based on the rotation of the rotor mb. This configuration reduces the overall size of the air supply / exhaust device A, resulting in an air supply / exhaust device A with excellent mountability.

[0032] However, because the piston P is cantilevered, the initial position of the piston P is prone to fluctuation. The effective area of ​​the piston P that receives air pressure is smaller when the area facing the first chamber r1 is smaller than the area facing the second chamber r2 by the cross-sectional area of ​​the rod R. In this case, if the pressures of the first air spring S1 and the second air spring S2 are the same, the piston P will be pushed from the second chamber r2 toward the first chamber r1. When this initial pushing force is present, it is necessary to generate a constant driving force in the drive mechanism M or to lock the components of the drive mechanism M in order to maintain the positions of the piston P and the rod R in a predetermined position, such as a neutral position, or to equalize the resistance to the start of movement of the piston P in both directions.

[0033] Therefore, in this embodiment, taking into consideration the fact that there is likely to be a difference in internal pressure between the first air spring S1 and the second air spring S2 from the beginning, the first chamber r1 is connected to the first air spring S1, which tends to have a relatively high pressure, and the second chamber r2 is connected to the second air spring S2, which tends to have a relatively low pressure. This balances the pressures acting on both sides of the piston P and improves the position-maintaining function when the piston P is in the reference position, which is approximately the center of the cylinder C, simplifying the structure of the air supply / discharge device A and improving operability.

[0034] In the case where the internal pressure of the first air spring S1 increases, for example, if the air pressure of the air suspension is set so that both the first air spring S1 and the second air spring S2 are at equal pressure and only the driver is in the vehicle, the internal pressure of the first air spring S1 closest to the driver's seat will passively increase. It is also conceivable that in vehicle B equipped with a vehicle height sensor or the like, the internal pressure of the first air spring S1 may be actively increased in response to sinking of the driver's seat side.

[0035] With this configuration, the pressure acting on both sides of the piston P is balanced, improving the piston P's ability to maintain its position. This eliminates the tendency for the piston P to move from its initial position before air is supplied to or discharged from the left and right air springs S. In other words, no external force acts on the components of the drive mechanism M to urge movement in a specific direction. As a result, the responsiveness of the start of operation is improved regardless of the direction in which the drive mechanism M operates from the initial state, resulting in an air supply / discharge device A that provides excellent posture stability for the vehicle B.

[0036] Furthermore, because the piston P in this configuration is supported by a cantilever on the rod R, the overall dimensions are smaller and the number of parts is reduced compared to devices configured with rods R on both sides. Because the rod R is only on one side, the seal 2 between the cylinder C or case K and the rod R is required in only one location, simplifying the configuration of the air supply / discharge device A. This also makes it possible to reduce costs.

[0037] Second Embodiment The weight distribution borne by each wheel T of the vehicle B changes depending on the number of passengers and luggage loaded. Therefore, even if the first port p1 and the second port p2 are selectively used depending on the pressure at the connection destination as described above, the pressure difference due to the weight difference does not necessarily balance with the pressure difference that corrects the imbalance in the area of ​​the piston P. Therefore, in this configuration, a biasing unit F is provided that biases the piston P toward either the first chamber r1 or the second chamber r2. This makes it possible to further reduce the deflection of the piston P.

[0038] An air supply / discharge device A according to a second embodiment of the present invention is shown in Figure 2. Here, an urging portion F is provided that presses a piston P. The urging portion F here is referred to as a first urging portion F1. Specifically, a first spring 11 that presses the piston P from the first chamber r1 toward the second chamber r2 is provided in the first chamber r1, and a second spring 12 that presses the piston P from the second chamber r2 toward the first chamber r1 is provided in the second chamber r2.

[0039] Coil springs are used as the first spring 11 and the second spring 12. The first spring 11 is arranged so as to extend over one surface of the piston P and the bottom c1 of the cylinder C at the boundary with the case K, with the rod R being fitted over it. An annular recess 13 that holds the first spring 11 in place is provided on the surface of the piston P and the surface of the bottom c1.

[0040] The second spring 12 is disposed between the other surface of the piston P and the other bottom c1 of the cylinder C. A spring retainer 14 is attached to the bottom c1 of the cylinder C so that its position can be adjusted, and the second spring 12 abuts against the spring retainer 14. The spring retainer 14 is connected to, for example, an adjustment male screw 16 that is threaded into an adjustment female screw 15 provided on the bottom c1 so as to be relatively rotatable. By changing the threaded position of the adjustment male screw 16, the length of the space in which the first spring 11 and the second spring 12 are disposed is changed, and the balance position of the piston P is adjusted.

[0041] The adjustment male screw 16 may be adjusted by manual rotation, or may be driven by an adjustment motor (not shown), etc. When driven by an adjustment motor, etc., it is advisable to measure the drive torque when the motor m starts to rotate in both forward and reverse directions from a state in which the piston P is in the initial position, and adjust the drive torque so that it is equal.

[0042] The first spring 11 and the second spring 12 may have the same spring constant and length. By changing the position of the spring retainer 14, a neutral position is set by the cooperation of the first spring 11 and the second spring 12, and the direction of pressure on the piston P is changed. For example, when the piston P is located at the center of its stroke in the cylinder C, the closer the spring retainer 14 is to the piston P, the stronger the pressure of the second spring 12, and the piston P is pushed toward the first chamber r1. Conversely, the farther the spring retainer 14 is from the piston P, the longer the second spring 12 is, and the stronger the pressure of the first spring 11 becomes, pushing the piston P toward the second chamber r2.

[0043] The provision of the adjustment male screw 16 of this configuration allows for various settings of the first air spring S1 for the right front wheel TR and the second air spring S2 for the left front wheel TL. By adjusting the position of the spring retainer 14, the balance position due to the biasing forces of the first spring 11 and the second spring 12 is changed, and the initial position of the piston P is determined. The spring constants and lengths of the first spring 11 and the second spring 12 should be set according to the expected load condition, etc.

[0044] In this configuration, the biasing force of the first spring 11 and the second spring 12 acting in concert always acts on the piston P. However, this biasing force increases as the piston P approaches the drive mechanism M, as the first spring 11 and the second spring 12 contract, and decreases as the piston P moves away from the drive mechanism M, as both springs expand. Therefore, it is preferable to select first spring 11 and second spring 12 with a large ratio of overall length to winding diameter so that the change in biasing force during expansion and contraction is small.

[0045] Third Embodiment An air supply / discharge device A according to a third embodiment of the present invention is shown in Figures 3 and 4. In this embodiment, a second biasing portion F2 is provided as the biasing portion F. The second biasing portion F2 includes a swing arm 21 that is supported by a rotation shaft 20 provided on the rod R and is biased around the rotation shaft 20. The swing arm 21 presses against a step portion 22 formed on the inner surface of the case K, thereby determining the initial position of the rod R relative to the cylinder C. The position of the swing arm 21 relative to the rod R is changeable, and the initial position of the piston P is set appropriately.

[0046] The second biasing portion F2 is provided at the end of the rod R, and includes a swing arm 21 that rotates around a rotation shaft 20 provided on the rod R, and a third spring 23 that rotationally biases the swing arm 21 relative to the rod R. In addition, a step 22 against which the tip of the swing arm 21 abuts is formed on the inner surface of the case K. The position of the swing arm 21 is adjustable along the longitudinal direction of the rod R, and the initial position of the piston P can be changed by this adjustment.

[0047] Specifically, a slit 24 is formed in the end of the rod R along the longitudinal direction, and a slide member 25 equipped with a rotation shaft 20 is inserted into the slit 24. A fixed male thread 26 is formed in the end of the rod R so as to encompass the slit 24, and a fixing nut 27 is threadedly engaged with the fixed male thread 26. Conical fastening surfaces 28 are formed on the end of the fixed male thread 26 and on the inner surface of the fixing nut 27, and the width of the slit 24 narrows as the fixing nut 27 is tightened, thereby clamping and fixing the slide member 25. A long gripping portion 29 protrudes from the end of the slide member 25, and with the fixing nut 27 loosened, the gripping portion 29 can be pushed or pulled to adjust the position of the slide member 25. The gripping portion 29 can be grasped with a predetermined tool by opening a lid 30 provided at the end of the case K.

[0048] The swing arm 21 is rotatably biased relative to the rod R by a third spring 23, which is a coil spring. In addition, the swing arm 21 abuts against a stopper 25a formed on the slide member 25, and rotation beyond a predetermined angle is restricted. As a result, when the swing arm 21 is inserted from the right side to the left side in FIG. 3 and set inside the case K, the swing arm 21 is held in a position nearly perpendicular to the rod R, and both ends of the swing arm 21 reliably abut against both step portions 22.

[0049] However, as shown in Figure 3, when the swing arm 21 is in the reference position, both ends simultaneously abut against the upper and lower step portions 22 of the case K, and the swing arm 21 is in a substantially perpendicular position relative to the rod R. Therefore, in normal operation, the swing arm 21 does not abut against the stopper 25a. The swing arm 21 has the same protruding length on both sides about the rotation shaft 20. Both ends are formed, for example, in an arc shape so that the swing arm can easily climb over the step portions 22, which will be described later.

[0050] 3, the position of the swing arm 21 is changed to the tip side of the rod R. Conversely, when the rod R is moved to the right side in FIG. 3, the position of the swing arm 21 is changed to the piston P side of the rod R. As a result, both ends of the swing arm 21, which receives a rotational force, settle in a state of contact with the upper and lower step portions 22, and the initial position of the rod R is determined.

[0051] 4(a) and 4(b) show the operation of the swing arm 21 when the rod R moves left and right. FIG. 4(a) shows a state in which, for example, the motor m is driven and the rod R moves from its initial position toward the second chamber r2. As the rod R moves leftward, the swing arm 21 tilts with its upper end abutting the step 22. As the rod R moves further leftward, the upper end of the swing arm 21 rides up onto the step 22 and then moves along the first guide surface K1. When the swing arm 21 is engaged with the step 22, the more the swing arm 21 tilts, the stronger the biasing force of the third spring 23 becomes, and the greater the driving force of the motor m required to move the rod R. However, after the swing arm 21 rides up onto the first guide surface K1, only frictional force acts between the swing arm 21 and the first guide surface K1, reducing the driving force required of the motor m. This frictional force can be further reduced by providing a roller member at the tip of the swing arm 21. On the other hand, when the rod R moves to the right as shown in Figure 4(b), the lower end of the swing arm 21, the step 22 of the case K, and the second guide surface K2 perform the same function.

[0052] In the air supply / discharge device A of this embodiment, the elasticity of the third spring 23 is used to set the piston P to its initial position, and no special current-carrying circuit is required. This simplifies the configuration and does not consume power to set the initial position of the piston P. Furthermore, because the position of the swing arm 21 can be finely adjusted, the internal pressure difference between the first chamber r1 and the second chamber r2 acting on the piston P in its initial state can be offset. This improves the starting characteristics of the piston P, resulting in an air supply / discharge device A with good responsiveness. [Industrial Applicability]

[0053] The present invention can be widely used in air supply / discharge devices in which a piston for supplying / discharging air has a cantilever structure supported by a rod. [Explanation of symbols]

[0054] 11 First Spring 12 Second spring 20 Rotation axis 21 Swing arm 22 Step section A Air supply and exhaust device C cylinder F biasing part K Case M Drive Mechanism P piston p1 First port p2 Second port R Rod r1 1st room r2 2nd room S Air Spring S1 First Air Spring S2 Secondary Air Spring

Claims

1. An air supply / discharge device used in an air suspension having a plurality of air springs including a first air spring and a second air spring, a piston cantilevered on a rod; a cylinder that houses the piston so that the piston can reciprocate, and whose interior is divided by the piston into a first chamber through which the rod passes and a second chamber in which the rod does not exist; a drive mechanism that reciprocates the piston via the rod, The first air spring is in a state where it is likely to be pressurized relatively more than the second air spring, An air supply / discharge device in which the first chamber is provided with a first port connected to the first air spring, and the second chamber is provided with a second port connected to the second air spring.

2. 2. The air supply / discharge device according to claim 1, further comprising a biasing portion that biases the piston from the first chamber toward the second chamber or from the second chamber toward the first chamber.

3. 3. The air supply / discharge device according to claim 2, wherein the biasing portion includes a first spring that contacts the piston in the first chamber, and a second spring that contacts the piston in the second chamber.

4. 3. The air supply and discharge device according to claim 2, further comprising a case housing the drive mechanism, wherein the biasing portion comprises a swing arm supported by a rotation shaft provided on the rod and biased around the rotation shaft, and a step formed on the inner surface of the case so as to be pressed by the swing arm.

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