JP2582066Y2 - Relief valve - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relief valve for relieving a high-pressure fluid having a relief pressure to a low-pressure side.

[0002]

2. Description of the Related Art Generally, in a fluid circuit for driving a crawler vehicle or the like, when a switching valve is switched to a flow position when the crawler vehicle stops, a fluid motor and the crawler vehicle continue to stop due to inertia. If the pressure in the circuit rises rapidly and the switching valve is switched to the neutral position during traveling of the crawler vehicle, the fluid motor rotates by a short time due to the inertial traveling of the crawler vehicle, so that the pressure in the fluid circuit rises rapidly. . Therefore, in such a fluid circuit, a relief valve is provided in the middle of the fluid passage connecting the fluid motor and the switching valve, and when any of the fluid passages has a high relief pressure, the relief valve is connected via the relief valve. Thus, the high pressure fluid that has risen to the relief pressure is relieved to the low pressure side. However, in such a fluid motor, since the valve opening pressure (relief pressure) is limited to one high pressure value, the pressure rapidly rises to this relief pressure when the fluid motor is started or when braking is started. However, there is a problem that a large shock is applied to the fluid motor and the reduction gear.

In order to solve such a problem, conventionally,
For example, the one described in Japanese Utility Model Publication No. Sho 62-31681 has been proposed. In this device, an adjustment piston is provided around each spring chamber, and a space defined on one side of the adjustment piston is separated from a supply / discharge passage connecting an inflow side of a relief valve communicating with the spring chamber. While communicating with the supply / discharge passage, the adjustment chamber partitioned on the other side is communicated with the spring chamber, and when the inflow-side supply / discharge passage becomes a set pressure lower than the relief pressure, the fluid of the set pressure is passed through the spring chamber. By guiding the relief piston to the space, a pressure difference is generated before and after the relief valve, and the relief valve is moved in the valve opening direction only until the adjustment piston reaches the stroke end. The shock at the set pressure is relieved to the supply / discharge passage on the low pressure side for a short time to reduce the shock.

[0004]

However, in such a conventional relief valve, since the stop position of the adjusting piston is not fixed, the moving distance (moving time) of the adjusting piston varies for each relief. Thus, there is a problem that the effect of reducing the shock varies. In addition, the relief valve is closed once after opening at the set pressure, immediately after that, the pressure is increased to the relief pressure and then opened again, but since the pressure increase from the set pressure to the relief pressure is performed instantaneously, At this time, there is also a problem that a certain degree of shock occurs and the effect of reducing the shock is not sufficient. Further, since the adjusting piston is provided around each spring chamber, its axial length (moving time of the adjusting piston) is limited, and as a result, the shock is continuously generated and the effect of reducing the shock is small. There is also a problem that it becomes. In addition, since the adjusting piston is provided around each spring chamber, a pair of adjusting pistons is required, and as a result, there is a problem that the structure is complicated.

An object of the present invention is to provide a relief valve which has a simple structure and can effectively reduce a shock generated at the time of starting or braking a fluid motor every time.

[0006]

SUMMARY OF THE INVENTION An object of this invention is to provide a pair of supply and discharge passages which are provided in the middle of a pair of supply and discharge passages connecting a switching valve and a fluid motor, and which constitute a part of the supply and discharge passages inside. A case in which a passage is formed, provided in the case, and when any of the supply / discharge passages is at a relief pressure, by being pushed by the relief pressure and moving in the valve opening direction against a spring, And a pair of poppet valve bodies for relieving a fluid at a relief pressure to a supply / discharge path on the low pressure side, wherein the spring is housed in a case while forming a through hole in each poppet valve body. And a pair of fluid chambers into which fluid from the supply / discharge passage passing through the fine holes flows, and a single cylinder chamber in which a single piston is slidably housed in a case. One side of the series The cylinder chamber is connected to one of the fluid chambers, the cylinder chamber on the other side of the piston is connected to the remaining fluid chambers, and the cylinder chamber is connected between one end of the cylinder chamber and the other end face and the piston. A return spring for biasing the piston toward a neutral position located at the center of the cylinder chamber is arranged, and when any of the supply / discharge paths has a set pressure lower than the relief pressure, the fluid of the set pressure is discharged. By flowing into the fluid chamber through the pores of one of the poppet valve elements, the piston in the cylinder chamber is pressed and moved while compressing the return spring, thereby generating a pressure difference across the poppet valve element. Move the poppet valve in the valve opening direction only until the piston reaches the stroke end,
This can be achieved by causing the fluid in the supply / discharge path, which gradually increases in pressure from the set pressure, to be relieved to the supply / discharge path on the low pressure side.

[0007]

When the fluid motor is started or when the braking of the fluid motor is started, the pressure of any of the supply / discharge passages and the supply / discharge passage increases due to the inertia of the fluid motor or the like. Since the fluid flows into the fluid chamber and the cylinder chamber one after another through the pores of the valve body, the piston is pressed and starts moving. At this time, a pressure difference is generated due to the pressure drop caused by the passage of the fluid through the pores before and after the poppet valve body, whereby a fluid force in the valve opening direction acts on the poppet valve body. Further, at this time, the force acting on the poppet valve body in the valve closing direction is substantially only the urging force of the spring. Then, when the pressure in the supply / discharge passage rises to a set pressure, the fluid force acting on the poppet valve body exceeds the biasing force of the spring, and the poppet valve body faces the spring in the valve opening direction. Moving. As a result,
The two supply / discharge paths communicate with each other, and the pressurized fluid is relieved from the high pressure side supply / discharge path to the low pressure side supply / discharge path. Here, when the piston moves as described above, the return spring is gradually compressed by the movement of the piston, so that the pressure in the fluid chamber gradually increases according to the compression amount of the return spring, and as a result, the poppet valve The force for closing the body is a value obtained by adding a gradually increasing fluid force based on the pressure in the fluid chamber to the biasing force of the spring. For this reason, the fluid in the supply / discharge path follows the pressure and is relieved while the pressure gradually increases. When the piston moves to the stroke end in the cylinder chamber, the movement of the piston stops, so that the fluid does not flow through the pores of the poppet valve body, and the pressure difference before and after the poppet valve body disappears. As a result, the poppet valve element is urged by the spring to move in the valve closing direction and stop the relief. In this way, the fluid in the supply / discharge path is relieved while gradually increasing the pressure only from when the set pressure is reached to when the piston reaches the stroke end. Next, when the pressure in the supply / discharge passage on the high pressure side becomes the relief pressure, the fluid force acting on the remaining poppet valve exceeds the urging force of the spring, and the poppet valve opens against the spring. Move in valve direction. As a result, the two supply / discharge paths communicate with each other, and the pressurized fluid is relieved from the high pressure side supply / discharge path to the low pressure side supply / discharge path. When the pressure in the supply / discharge passage reaches the set pressure, relief starts,
Thereafter, the relief is performed while gradually increasing the pressure from the set pressure, and then when the pressure is increased to a high relief pressure, the relief is performed again, so that the shock given to the fluid motor and the reduction gear is reduced. Thereafter, when the internal pressure of the supply / discharge path decreases to a normal operating pressure, the piston is returned to the neutral position by the elastic force of the compressed return spring. As a result, the piston always returns to the neutral position and stops, and as a result, the movement distance (movement time) of the piston at the time of relief becomes constant, and the shock can always be reduced at a constant rate. Also, since the valve opening pressure of the poppet valve body gradually increases from the set pressure, the valve opening pressure when the piston reaches the stroke end becomes a pressure close to the relief pressure, and as a result, the pressure from the pressure to the relief pressure Even if the climb occurs in an instant, the shock is small, which effectively reduces the shock. Further, since the adjusting piston can be provided at a distance from the fluid chamber, its axial length (moving time of the piston) can be increased, and as a result, a situation in which a shock is continuously generated can be prevented. , Can effectively reduce the shock. Moreover, only one cylinder chamber and one piston are required, and the structure is simplified.

According to the second aspect of the invention, when the piston starts moving from the neutral position, the relief is not affected by the spring force of the spring, so that the relief can be accurately started at the set pressure. it can. Further, according to the third aspect, when the piston moves to the stroke end, the pressure of the fluid acting on the poppet valve body rises to the relief pressure, and as a result, the pressure rises sharply. And the shock is reduced more effectively.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. 1, 2 and 3, reference numeral 11 denotes a fluid motor for driving a crawler vehicle, for example. The fluid motor 11 and the switching valve 12 are connected by a pair of supply / discharge passages 13 and 14. Further, the switching valve 12 and the fluid pump 15 are connected to a supply passage.
By 16, the switching valve 12 and the tank 17 are connected by a discharge passage 18. A counterbalance valve 19 is provided in the middle of the supply / discharge passages 13 and 14, and the counterbalance valve 19 is provided.
A relief valve 24 is provided in the supply / discharge passages 13 and 14 between the motor 19 and the fluid motor 11.

The relief valve 24 has a main body block 25 in which a pair of main passages 26 and 27 are formed. Reference numerals 28 and 29 denote a pair of holders inserted and fixed in the main body block 25.
Inside the insides of the insides 8 and 29, chambers 30 and 31 are formed at the front end (inner end), respectively, and these chambers 30 and 31 and the main passages 26 and 27 are formed.
Are connected to each other by a plurality of holes 32, 33. The main passages 26, 27, the chambers 30, 31, and the holes 32, 33 constitute a pair of supply / discharge passages 34, 35 as a whole, and these supply / discharge passages 34, 35 are one of the supply / discharge passages 13, 14. Make up the part. The chambers 30, 31 and the main passages 27, 26 are provided in the holders 28, 29 on the tip side of the chambers 30, 31,
That is, a pair of communication passages 36 and 37 that connect the supply / discharge passages 34 and 35 to each other are formed. And these communication paths 36 and 37
And the chambers 30 and 31, that is, the supply / discharge passages 34 and 35, are valve seats 38 and 39 with which a poppet valve body described later contacts in a liquid-tight state.
Further, a pair of fluid chambers 42 and 43 are formed in the holders 28 and 29 behind the chambers 30 and 31, and the pair of fluid chambers 42 and 43 and the chambers 30 and 31, that is, the supply and discharge paths 34 and 35 They are connected by a pair of connection holes 44 and 45. Stoppers 48, 49 for closing the fluid chambers 42, 43 are screwed and fixed to the rear ends of the fluid chambers 42, 43. Main body block 25 and holder 2 described above
8, 29 and the stoppers 48, 49 constitute the case 50 as a whole.

Reference numerals 54 and 55 denote a pair of poppet valve bodies. These poppet valve bodies 54 and 55 have tapered portions 56 and 57 tapering toward the front end, and the tapered portions 56 and 57 at the rear end side. Are provided, respectively. These poppet valve bodies 54 and 55 are housed in holders 28 and 29, respectively.
8, 39 can be contacted, and cylindrical parts 58, 59
Are slidably inserted in the connection holes 44 and 45 in a liquid-tight state. And in both poppet valve bodies 54 and 55,
The pressure receiving areas A1, A2 located on the tip side from the contact positions of the valve seats 38, 39 and the tapered portions 56, 57 are smaller than the pressure receiving areas B1, B2 located on the rear end side from the contact position, The outer diameter of the cylindrical portions 58, 59 is larger than the diameter of the valve seats 38, 39. Further, pores 60, 61 for connecting the supply / discharge passages 34, 35 and the fluid chambers 42, 43 are formed in the poppet valve bodies 54, 55, and a throttle 62 is provided in the middle of the pores 60, 61. , 63 are formed. 67 and 68 are a pair of springs housed in the fluid chambers 42 and 43, respectively.
Are the rear end faces of the poppet valve bodies 54 and 55 and the stoppers 48 and 49
The poppet valve bodies 54, 55 are urged toward the distal ends to press the tapered portions 56, 57 against the valve seats 38, 39, respectively, to close the relief valve 24.

A single through-hole 71 is formed in the case 50, specifically, the main body block 25, in parallel with the holders 28 and 29, and both ends of the through-hole 71 are screwed and fixed to both ends of the through-hole 71, respectively. It is closed by stoppers 72, 73 having small diameter portions 72a, 73a at the inner ends. As a result, the through hole 71 between the stoppers 72 and 73 becomes one cylinder chamber 74, and one piston 75 is slidably housed in the cylinder chamber 74. The cylinder chamber 74 on one side of the piston 75 and the fluid chamber 42 are connected to a hole 76 formed in the holder 28 and a passage 77 formed in the main body block 25.
On the other hand, the cylinder chamber 74 on the other side of the piston 75 and the fluid chamber 43 are connected to a hole 78 formed in the holder 29.
And are connected via a passage 79 formed in the main body block 25. A return spring 81 is disposed between one end face 80 of the cylinder chamber 74, that is, between the inner end face of the stopper 73 and the piston 75, and another end face of the cylinder chamber 74.
82, that is, a return spring 83 is disposed between the inner end surface of the stopper 72 and the piston 75.
1 and 83 urge the piston 75 toward the neutral position C located in the center of the cylinder chamber 74. Here, the free length (length at no load) of each return spring 81, 83 is determined by the cylinder chamber.
74 is set to be slightly smaller than 1/2 of the value obtained by subtracting the axial length of the piston 75 from the distance between the end surfaces 80 and 82 on the other side, and as a result, the piston 75 is set to the neutral position C. At some point, gaps 84 and 85 having a small distance L are formed between the inner ends of the return springs 81 and 83 and the end face of the piston 75, and the urging forces from the return springs 81 and 83 to the piston 75 are both zero. . The minute distance L between the gaps 85 and 84 is equal to the distance pieces 86 interposed between the head 72b of the stopper 72 and the main body block 25 and between the head 73b of the stopper 73 and the main body block 25, respectively. It is adjusted by changing the thickness of 87. In order to make the urging force from the return springs 81 and 83 to the piston 75 both zero as described above, the free length of each of the return springs 81 and 83 is set to one side of the cylinder chamber 74 and the other end surfaces 80 and 82. Piston from distance between
75 may be made equal to 1/2 of the value obtained by subtracting the axial length, and the minute distance L may be set to zero. However, in such a case, since a high-precision part is required, molding processing is somewhat difficult.

A check passage 89 connecting the main passage 27 and the cylinder chamber 74 on the other side of the piston 75 is provided in the case 50, and a check passage 89 connecting the main passage 26 and the cylinder chamber 74 on one side of the piston 75. A check passage 90 to be connected is formed, and check valves 91 and 92 are provided in the middle of the check passages 89 and 90, respectively. And these check valves 91, 92
Prevents the flow of the fluid from the main passages 27 and 26 toward the cylinder chamber 74, and allows the fluid pushed out of the cylinder chamber 74 by the movement of the piston 75 to flow out to the low-pressure supply / discharge passages 35 and 34. . And such a check valve 9
When the pistons 75 are moved, the cylinder chamber 74
Since the fluid pushed out from the valve pushes the check valves 91 and 92 open and quickly flows out to the low pressure side supply / discharge passages 35 and 34, the movement of the poppet valve bodies 54 and 55 is inhibited by the pushed fluid. This allows the poppet valves 54, 55 to open and relieve at exactly the desired pressure.

Next, the operation of the first embodiment of the present invention will be described. Now, the switching valve 12 is switched from the neutral position to the flow position, and the high-pressure fluid from the fluid pump 15 is supplied to the fluid motor 11 through one of the supply / discharge passages, for example, the supply / discharge passage 13, and the fluid motor 11 is started. To start. At this time, since the fluid motor 11 and the crawler vehicle continue to stop due to inertia, the pressure in one of the supply / discharge passages, here, the supply / discharge passage 13 increases, and at this time, the supply / discharge passage 34 and the supply The pressure in the communication path 37 which is always in communication with the discharge path 34 also increases.

At this time, since the pressure fluid in the supply / discharge passage 34 flows into the fluid chamber 42 through the fine holes 60 of the poppet valve body 54, the piston communicates with the fluid chamber 42 through the hole 76 and the passage 77. The pressure fluid also flows into the cylinder chamber 74 on one side of the cylinder chamber 75, whereby the piston 75 in the cylinder chamber 74 starts moving toward the stroke end on the other side. At this time, the fluid in the cylinder chamber 74 on the other side of the piston 75 is quickly discharged through the check passage 89 to the supply / discharge passage 35 on the low pressure side while pushing the check valve 91 open. Here, in the initial stage of the movement of the piston 75, a pressure difference occurs due to a pressure drop before and after the poppet valve element 54 when the fluid passes through the fine hole 60, so that the poppet valve element 54 The fluid gives a fluid force in the valve opening direction. At this time, the force acting on the poppet valve body 54 in the valve closing direction is substantially only the biasing force of the spring 67.

When the pressure in the supply / discharge passage 34 rises to a set pressure lower than the relief pressure, the poppet valve 54
The fluid force acting on the large pressure receiving area B1 exceeds the urging force of the spring 67, and the poppet valve element 54 moves in the valve opening direction against the spring 67. As a result, the tapered portion 56 of the poppet valve element 54 is separated from the valve seat 38, the two supply / discharge passages 34 and 35 communicate with each other, and the pressure fluid flows from the high-pressure supply / discharge passage 34 to the low-pressure supply / discharge passage 35. Is relieved through the communication passage 36. Here, when the piston 75 is located at the neutral position C as described above, the urging force applied to the piston 75 from the return spring 83 is zero, so that the initial period when the piston 75 starts moving from the neutral position C In the meantime, the piston 75 is not affected by the spring force of the spring 83, and as a result, the poppet valve element 54 can start the relief at the exactly set pressure. When the piston 75 moves by the minute distance L, the piston 75 comes into contact with the inner end of the return spring 83.
Moves to the other end, the return spring 83 is gradually compressed by the movement of the piston 75, and the cylinder chamber on one side is returned.
The pressure in 74 and the fluid chamber 42 gradually increases according to the compression amount of the return spring 83. As a result, the force for closing the poppet valve element 54 has a value obtained by adding a gradually increasing fluid force based on the pressure in the fluid chamber 42 to the urging force of the spring 67. From this, the fluid in the supply / discharge path 34 follows this and the pressure is gradually increased, and the fluid is relieved. As described above, the relief in the supply / discharge path 34 starts when the fluid reaches the set pressure, and thereafter, while the pressure gradually increases from the set pressure until the piston 75 reaches the stroke end on the other side. It is relieved. At this time, the pressure receiving area A2 of the other poppet valve element 55 is also provided with the fluid force in the valve opening direction that gradually increases from the set pressure. However, as described above, the pressure receiving area A2 is small, At pressure, the fluid force is less than the biasing force of the spring 68,
The other poppet valve element 55 cannot be opened.

When the piston 75 moves to the other stroke end in the cylinder chamber 74 and comes into contact with the stopper 72, the movement of the piston 75 is stopped. And the pressure difference before and after the poppet valve element 54 disappears. As a result, the poppet valve element 54 is urged by the spring 67 to move in the valve closing direction, and the tapered portion 56 is pressed against the valve seat 38. This stops the relief from the poppet valve 54 side.

When the relief stops, the pressure in the supply / discharge passage 13 further increases. When the pressure in the supply / discharge path 34 rises to the relief pressure, the remaining poppet valve element
The fluid force acting on the narrow pressure receiving area A2 of 55 exceeds the biasing force of the spring 68, the poppet valve body 55 moves in the valve opening direction against the spring 68, and the tapered portion 57
Separated from 39. As a result, the two supply / discharge paths 34 and 35 communicate with each other, and the pressure fluid at the relief pressure is relieved from the high-pressure supply / discharge path 34 to the low-pressure supply / discharge path 35 through the communication path 37. As described above, the relief starts when the pressure in the supply / discharge passage 34 reaches the set pressure, and thereafter, while gradually increasing the pressure from the set pressure, the relief is performed. Therefore, the shock applied to the fluid motor 11 and the reduction gear is reduced. Further, since the valve opening pressure of the poppet valve element 54 gradually increases from the set pressure as described above due to the compression of the return spring 83, the valve opening pressure when the piston 75 reaches the stroke end becomes a pressure close to the relief pressure. As a result, even if the pressure rises from the pressure to the relief pressure in an instant, the shock is small, and the shock is effectively reduced. Here, in order to eliminate the above-mentioned pressure rise and almost eliminate the shock, the return spring 83 compressed when the piston 75 moves to the stroke end is moved by the piston.
The urging force applied to the piston 75 and the fluid force applied to the piston 75 by the relief pressure fluid (the internal pressure of the supply / discharge passage 34 and the internal pressure of the one-side cylinder chamber 74 are the same because the piston 75 has moved to the stroke end). It is sufficient to set the spring force of the return spring 83 so that? By doing so, when the piston 75 moves to the stroke end, the pressure of the fluid acting on the poppet valve element 54 increases to the relief pressure, and as a result, the sudden pressure as described above The rise disappears and the shock almost disappears.

Thereafter, when the internal pressure of the supply / discharge passage 34 decreases to a normal operating pressure, the piston 75 is moved to the compressed return spring.
It is pushed back by the elastic force of 83 and returned to the neutral position C. As a result, the piston 75 always returns to the neutral position C and stops, and as a result, the movement distance (movement time) of the piston 75 at the time of relief becomes constant, and the shock is always reduced at a constant rate. it can. In addition,
Such an operation is similarly performed at the start of braking the fluid motor 11 or when the supply / discharge passage 14 is on the high pressure side. In this embodiment, the piston 75 is connected to the fluid chambers 42 and 43.
, The axial length (movement time of the piston 75) can be lengthened, and as a result, it is possible to prevent a situation in which a shock is continuously generated, and to effectively reduce the shock. Can be reduced. Further, only one cylinder chamber 74 and one piston 75 are required, and the structure is simplified.

FIG. 4 shows a second embodiment of the present invention. In this embodiment, the free length of each of the return springs 81 and 83 is slightly less than 1/2 of the value obtained by subtracting the axial length of the piston 75 from the distance between one end surface 80 and 82 of one side of the cylinder chamber 74. As a result, when the piston 75 is at the neutral position C, the return springs 81 and 83 are slightly compressed, and a biasing force corresponding to the compression elastic force is applied to the piston 75 from both sides. Other configurations and operations are almost the same as those of the first embodiment.

[0021]

As described above, according to the present invention, the shock generated at the start of the fluid motor or the start of braking can be effectively reduced each time while the structure is simple.

[Brief description of the drawings]

FIG. 1 is a plan sectional view showing the vicinity of a poppet valve body, a part of which is shown by a symbol, showing a first embodiment of the present invention;

FIG. 2 is a plan sectional view showing the vicinity of a piston according to the first embodiment.

FIG. 3 is a front view showing the first embodiment.

FIG. 4 is a plan sectional view showing the vicinity of a piston according to a second embodiment of the present invention.

[Explanation of symbols]

 11 ... Fluid motor 12 ... Switching valve 13, 14 ... Supply / discharge passage 24 ... Relief valve 34, 35 ... Supply / discharge passage 42, 43 ... Fluid chamber 50 ... Case 54, 55 ... Poppet valve body 60, 61 ... Micropore 67, 68 ... Spring 74 ... Cylinder chamber 75 ... Piston 81,83 ... Return spring

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-106201 (JP, A) JP-A-59-43201 (JP, A) JP-A-4-4303 (JP, A) JP-A-60-1985 172786 (JP, A) Japanese Utility Model 63-123801 (JP, U) Japanese Utility Model 5-94504 (JP, U) Japanese Utility Model 5-81508 (JP, U) Japanese Utility Model 2-21303 (JP, U) Japanese Utility Model Showa 55-1811072 (JP, U) Japanese Utility Model Hei 5-45202 (JP, U) Japanese Utility Model Hei 2-56901 (JP, U) Japanese Utility Model Sho 62-31681 (JP, Y2) Japanese Patent Publication No. 47-9964 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) F15B 11/00-11/22 F16K 17/22

Claims (3)

(57) [Scope of request for utility model registration] A part of a supply / discharge passage (13, 14) is provided in the middle of a pair of supply / discharge passages (13, 14) connecting a switching valve (12) and a fluid motor (11). A case (50) in which a pair of supply / discharge paths (34, 35) is formed, and provided in the case (50), when one of the supply / discharge paths (34, 35) has a relief pressure, A pair of poppet valves which are pressed by the relief pressure and move in the valve opening direction while opposing the springs (67, 68), thereby relieving the fluid of the relief pressure to the supply / discharge passages (34, 35) on the low pressure side. Body (54, 55), and a relief valve (24) having a pore (60, 61) penetrating into each poppet valve body (54, 55).
And a fluid chamber (42) into which a fluid flows from a supply / discharge path (34, 35) that has received the springs (67, 68) in the case (50) and has passed through the fine holes (60, 61). , 43), and a single cylinder chamber (74) in which a single piston (75) is slidably housed in a case (50). Side cylinder chamber (74) and one of the fluid chambers (42, 43), and the piston (75)
The cylinder chamber (74) on the other side is connected to the remaining fluid chambers (42, 43), and the piston (75) is provided between one end of the cylinder chamber (74) and the other end face and the piston (75). Return springs (81, 83) for urging the center position of the cylinder chamber (74) toward the neutral position (C) located in the center of the cylinder chamber (74), and one of the supply / discharge paths (34, 35) is When the set pressure becomes lower than the relief pressure, the fluid of the set pressure is supplied to one of the poppet valve bodies (54, 55).
Flow into the fluid chambers (42, 43) through the small holes (60, 61) of the piston (75) in the cylinder chamber (74) and return the return springs (83, 8).
By pressing and moving while compressing 1), a pressure difference is generated before and after the poppet valve element (54, 55), and the piston (75) reaches the stroke end of the poppet valve element (54, 55). Until the fluid in the supply / discharge path (34, 35), which gradually increases in pressure from the set pressure, is relieved to the supply / discharge path (34, 35) on the low pressure side. Features a relief valve. 2. When the piston (75) is in the neutral position (C), both return springs (81, 83) are set so that the urging force from the return springs (81, 83) to the piston (75) is both zero. The relief valve according to claim 1, wherein a free length of the relief valve is set. 3. A biasing force applied to the piston (75) by the compressed return spring (81, 83) when the piston (75) moves to the stroke end, and a fluid of relief pressure applied to the piston (75). The relief valve according to claim 1, wherein the spring force of the return spring (81, 83) is set so that the fluid force is equal.