JP2010190339A - Relief valve for travel unit brake valve - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a relief valve for a travel unit brake valve reducing shock in transition from a low pressure relief pressure to a high pressure relief pressure and preventing generation of shock and vibration due to quick movement and stop of a free piston without fluidic and mechanical shock in relief valves for brake valves equipped with free pistons. <P>SOLUTION: The relief valve for the travel unit brake valve includes the free piston 178, and includes a first space formed at a rear side of the free piston in a casing communicating with a through hole through a restriction part, and an oil discharge hole and an oil discharge hole communication path formed to make a second space between the free piston and a poppet in the casing communicate with a channel on a downstream side when overload pressure is released. In this case, the restriction part reduces opening while the free piston is moving to a front end position from a rear end position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a brake valve relief valve used in a traveling unit such as a hydraulic crawler vehicle, and more particularly to a brake valve relief valve having a free piston.

  In the brake valve of a hydraulic vehicle traveling unit, if the control valve is set to the neutral position when the vehicle decelerates or stops, the check valve stops the oil flow path to the hydraulic motor. The pressure of the oil on the side becomes negative, and the pressure of the oil on the return side instantaneously rises above the set pressure of the relief valve, which causes a shock to the vehicle when braking or stopping There was a problem like that.

Therefore, in order to reduce or eliminate a shock generated in the vehicle when the vehicle is braked or stopped, a relief valve for a brake valve having a free piston as disclosed in, for example, Japanese Patent Laid-Open No. 8-296604 (Patent Document 1) has been proposed. Yes.
Hereinafter, a conventional example of a relief valve for a brake valve provided with the above-described free piston will be described as background art of the present invention. In the embodiment of the present invention to be described later, the present invention is the same as the following conventional example except for matters that are different from the conventional example.

  FIG. 11 shows a relief valve for a brake valve having a conventional free piston. As shown in FIGS. 12 and 13, this relief valve 70 is used by incorporating two sets of relief valves 70 </ b> R and 70 </ b> L together with one set of counter balance valve 60 in the brake valve 50. The brake valve 50 is provided between the control valve 40 for switching the hydraulic pressure from the hydraulic power source 30 and the hydraulic motor 20, and adjusts the operation such as braking and stopping. FIG. 10 shows a main part of a hydraulically driven crawler type vehicle travel drive device incorporating a travel unit in which the brake valve 50 is used.

  First, the hydraulic drive crawler type vehicle travel drive apparatus shown in FIG. 10 will be described. In FIG. 10, reference numeral 11 denotes a crawler shoe, and a number of crawler shoes 11 are endlessly connected in an endless manner to be bent. The crawler shoe 11 meshes with the teeth of the sprocket 12 fixed to the rotary casing 13 with bolts 12a, and the rotary casing 13 is connected to be driven by a hydraulic motor 20 via a speed reducer 14. The fixed casing 17 of the hydraulic motor 20 is fixed to the vehicle fixing frame 19 with bolts 17a. 50 is a brake valve. The traveling unit includes 14 parts of a speed reducer housed in the rotary casing 13, 20 parts of a hydraulic motor housed in the fixed casing 17, and 50 parts of a brake valve attached to the fixed casing.

  Next, the operation of the hydraulic drive crawler type vehicle travel drive apparatus shown in FIG. 10 will be described. Although not shown in FIG. 10, when hydraulic pressure is supplied from the hydraulic source 30 (see FIG. 12 or 13) provided in the vehicle body to the hydraulic motor 20 via the control valve 40 and the brake valve 50. The hydraulic motor 20 rotates. The rotation is decelerated and increased by the speed reducer 14 to rotate the rotating casing 13 and the sprocket 12, and the endless crawler shoe 11 meshing with the teeth of the sprocket 12 is driven to advance or reverse the vehicle.

  Next, the hydraulic device shown in FIGS. 12 and 13 will be described. 12 and 13, reference numeral 30 denotes a hydraulic pressure source. For example, a hydraulic pump 31 that is driven by an internal combustion engine to send out high-pressure hydraulic oil, a hydraulic pressure relief valve 32 that relieves hydraulic pressure from the hydraulic pump 31, and a reservoir (Oil tank) 33 and the like. A control valve 40 is connected to the flow paths K and M of the brake valve 50 by switching the reciprocating flow path from the hydraulic power source 30 to normal rotation, neutral and reverse rotation according to a command from a control device (not shown). In the brake valve body 52 of the brake valve 50, one set of counter balance valves 60 and two sets of relief valves 70R and 70L are provided. The counter balance valve 60 is provided with a spool 64, check valves 65R and 65L, springs 66R and 66L, and the like.

  Next, the operation of the hydraulic apparatus shown in FIGS. 12 and 13 will be described. As shown in FIG. 12, when the control valve 40 is set to the neutral position, the flow path K and the flow path M are both communicated with the return pipe 34 and no pressure is applied. The spool 64 of the counter balance valve 60 is in a neutral position by both springs 66R and 66L, and the flow paths R and L are blocked by check valves 65R and 65L, respectively, so that oil does not flow freely from the hydraulic motor 20. This is to prevent such a situation because if the oil freely enters and exits the hydraulic motor 20, the vehicle may move freely due to external force, ground inclination, or the like.

  In the right position of the control valve 40 shown in FIG. 13, the hydraulic pressure enters the flow path K, the spool 64 is pushed from right to left, the pressure oil flows from the flow path K to the flow path R, and from the right of the hydraulic motor 20. It flows to the left and rotates, flows from the flow path L to the flow path M, and returns to the reservoir 33. Although not shown, at the left position of the control valve 40, oil flows in the opposite direction to that shown in FIG. 13, and the hydraulic motor 20 is driven to rotate in the direction opposite to the direction in FIG. When the overload pressure is generated in the flow path L, the relief valve 70R releases the overload pressure from the branch flow path Ld to the flow path R. The relief valve 70L releases the overload pressure from the branch channel Rd to the channel L when an overload pressure is generated in the channel R.

  Next, a relief valve for a brake valve provided with this conventional free piston shown in FIG. 11 will be described. As shown in FIGS. 12 and 13, relief valves 70 </ b> R and 70 </ b> L are incorporated in the brake valve body 52 of the brake valve 50. FIG. 11 shows the relief valve 70R, but the relief valve 70L has exactly the same structure except that the flow path R and the flow path L are opposite to each other. In FIG. 1, reference numeral 71 denotes a cartridge which is a cylindrical housing of the relief valve 70. As shown in FIGS. 12 and 13, the brake valve body 52 in which the flow path R and the flow path L of the brake valve 50 are formed. It is oil-tightly screwed in and incorporated. The flow path L and the flow path R are separated by bringing the tip of the relief valve 70 into close contact with each of the flow paths R and L where the branch flow paths Ld and Rd of the other flow path are connected. Is formed. As shown in the figure, the relief valve 70R is assembled so that the branch flow path Ld of the flow path L hits the tip of the relief valve 70R and the flow path R is in contact with the outer periphery of the tip of the relief valve 70R. The relief valve 70L has the same structure with the flow paths R and L reversed.

  As shown in FIG. 11, the opening of the relief valve 70 </ b> R in the cartridge 71 </ b> R is opened so that the opening to the branch flow path Ld and the opening in contact with the flow path R are communicated with each other at the tip surface. A poppet seat 71b, which is a valve seat, is formed inside the opening with respect to the branch flow path Ld, and a poppet 73, which is a valve body that closes the flow path so as to be openable and closable with the poppet sheet 71b, is provided. . The poppet 73 is formed in a cylindrical shape, and the outer peripheral surface is in contact with the inner peripheral surface of the cartridge 71 so as to be slidable in the axial direction. A small hole (orifice 1) 73o penetrating from the front surface (tip surface) to the back surface of the poppet 73 is formed. Further, a rod 76 that is oil-tight and slidable in the axial direction is provided on the inner peripheral surface on the back side of the poppet 73. A rod through hole 76h that penetrates from the front end to the rear end is also formed in the center of the rod 76. A flange 76f is formed at an intermediate portion of the rod 76, and the poppet 73 is pushed between the rear end surface of the poppet 73 and the front end surface of the collar 76f so as to abut against the poppet sheet 71b with a predetermined force. A spring 72 is provided. The poppet spring 72 is given a predetermined elastic force as one element for setting an overload pressure to be released. In the illustrated example, the rear end surface of the rod 76 is formed into a spherical surface. A stopper 77 is provided at the rear end of the inner surface of the cartridge 71 of the relief valve 70 so as to receive the rear end of the rod 76. The stopper 77 can be adjusted in the axial direction by an adjusting screw 75a and an adjusting nut 75b, the axial position of the rod 76 received by the stopper 77 can be adjusted, and the poppet spring 72 pushed by the flange 76f of the rod 76 can be adjusted. The power can be adjusted. Assuming that the area due to the diameter of the poppet sheet 71b is A1, and the area due to the inner diameter of the poppet 73 or the outer diameter of the rod 76 that slides on the poppet 73 is A2, A1 is formed larger than A2 by a predetermined value.

  As shown in FIG. 11, a free piston 78 is provided in the free piston chamber 79 formed at the rear of the cartridge 71 so as to be freely movable in the axial direction. The outer peripheral surface of the free piston 78 is fitted into the inner peripheral surface of the cartridge 71 so as to be oil-tight and slidable, and is externally fitted to the outer peripheral surface of the rod 76 so as to be oil-tight and slidable. In a space equipped with a poppet spring 72 that communicates with the front chamber 79 b of the free piston chamber 79, an oil drain hole 71 d and a drain oil hole communication path 71 e are formed so as to communicate with the flow path R. The rod through hole 76h opens to the rear chamber 79a of the free piston chamber 79 on the rear (right side of the figure) side of the free piston 78 through a small hole (orifice 2) 76a provided on the rear end side of the rod 76. . The diameter of the rod 76 where the free piston 78 is externally fitted is smaller than the diameter of the rod 76 where the free piston 78 is internally fitted.

  Next, the operation of the brake valve relief valve shown in FIG. 11 will be described. Since the poppet 73 is closed by being pressed against the poppet seat 71b by the force of the poppet spring 72, the branch passage Ld is caused by the poppet 73R of the relief valve 70R unless the pressure exceeds a predetermined overload pressure in a normal operation state. Is closed and does not communicate with the flow path R. Similarly, the branch flow path Rd does not communicate with the flow path L by the poppet 73L of the relief valve 70L. For example, as shown in FIG. 13, when the control valve 40 is in the right position, high pressure oil enters the flow path K, the spool 64 of the counter balance valve 60 is pushed from right to left, and the high pressure from the hydraulic pump 31 enters the flow path R. When the oil flows to drive the hydraulic motor 20 and the flow path L is in communication with the return pipe 34 and the non-pressure return oil flows, the relief valve 70R has a flow as shown in FIG. The high-pressure oil in the path R flows into the front chamber 79b on the front side of the free piston 78 through the drain hole communicating passage 71e and the drain hole 71d, and presses the free piston 78 to the rear end. Although not shown as the relief valve 70L, as shown in FIG. 13, in the relief valve 70L, the high-pressure oil in the branch flow path Rd is free through the small holes 73o and the rod through holes 76h and 76a of the relief valve 70L. The piston 78L enters the rear chamber 79a on the rear side, and the free piston 78 is pressed to the front end.

  In the state shown in FIG. 13, when an overloaded high pressure occurs in the flow path R, the pressure entering the branch flow path Rd is applied to the front of the poppet 73L of the relief valve 70L (not shown), and the free piston 78L is shown in FIG. Since it exists in the position shown to b), the pressure which entered from the small hole 73o is applied also to the poppet back surface chamber 73p. Therefore, when the force obtained by multiplying the pressure by the area (A1-A2) exceeds the force of the poppet spring 72, the poppet 73L is pushed open, and the overload pressure escapes from the branch channel Rd to the channel L. That is, in this case, the operation is performed to release the overload pressure at the same high pressure as in the prior art. The above is the operation of the relief valve 70L (not shown), and the relief valve 70R does not operate.

  However, when the control valve 40 is moved from the state shown in FIG. 13 to the neutral position shown in FIG. 12, both the flow paths K and M are connected to the return pipe 34 and no pressure is applied. The spool 64 is in the center position due to the balance between the spring 66R and the spring 66L, and the check valves 65R and 65L close the flow paths R and L so as to stop the flow of oil from the outlet side of the hydraulic motor 20. The oil that has been flowing from the flow path R to the flow path L through the hydraulic motor 20 until now is suddenly stopped. However, since the oil tends to flow as before due to the inertial force of the mass movement of the vehicle body and the like, a high pressure is instantaneously generated in the flow path L and a negative pressure is generated in the flow path R. At that time, the free piston 78R of the relief valve 70R is at the rear end position of the free piston chamber 79, as shown in FIG. However, the flow path R has no pressure or negative pressure, and the front chamber 79b of the free piston 78 communicating with the flow path R through the oil drain hole communication passage 71e and the oil drain hole 71d is also no pressure or negative pressure. Therefore, when the high pressure instantaneously generated in the flow path L due to the sudden stop is applied to the front surface of the poppet 73R of the relief valve 70R from the branch flow path Ld, the pressure that has entered the poppet back chamber 73p through the small hole 73o is: The free piston 78R enters the rear chamber 79a through the rod through hole 76h and the small hole 76a. The free piston 78R easily moves to the left because the front surface 79b has no pressure, and enters the poppet back surface chamber 73p. There is no pressure. Therefore, the pressure from the branch channel Ld is applied to the area A1 and pushes the poppet 73. If this force exceeds the force of the poppet spring 72, the poppet 73 is pushed open and the pressure in the branch flow path Ld escapes to the flow path R. Since the pressure applied to the area A1, that is, the low pressure applied to the area A1 larger than the area (A1-A2) is released, the instantaneous high pressure is released sufficiently to prevent the occurrence of impact and vibration.

  However, due to the pressure entering through the small hole 73o, the rod through hole 76h, and the small hole 76a, the free piston 78 is immediately at the position shown in FIGS. After the free piston 78 reaches the position shown in FIG. 11B, the same pressure as the front surface is applied to the poppet back chamber 73p, and the force pushing the poppet 73 is a force obtained by multiplying the pressure by the area (A1-A2). If the pressure is not high, the poppet 73 cannot be pushed open, and desired braking and stopping capabilities can be exhibited.

  The operation when the control valve 40 shown in FIG. 13 is changed from the right position to the neutral position shown in FIG. 12 has been described. The operation when the control valve 40 is changed from the left position to the neutral position shown in FIG. Since it is easily understood that the flow path R and the flow path L are changed, and that the relief valve 70R and the relief valve 70L are changed and perform the same operation, the drawings and description are omitted.

  Since the diameter of the portion of the rod 76 fitted into the poppet 73 is equal to or larger than the diameter of the portion fitted into the free piston 78, the position of the rod 76 is stabilized. Further, when the rear end of the rod 76 is a spherical surface, an extra twisting force is not applied.

  According to the conventional relief valve for a brake valve equipped with a free piston, shock and vibration are generated by releasing the instantaneous overload pressure generated immediately after the control valve is switched by the free piston at a low pressure. After that, since the relief pressure is set to a high setting, the braking force and the stopping force can be exhibited.

  However, the brake valve relief valve 70 having the above-described conventional free piston 78 allows the brake valve relief valve 70 to release an overload pressure with a low relief pressure initially when the vehicle is decelerated or stopped. However, if the free piston 78 moves from the rear end position before movement (right end position in FIG. 11) to the front end position after movement (left end position in FIG. 11), that is, the stroke end, the steady braking force and stopping force are reduced. Therefore, there is a problem that a shock at the time of transition from the low pressure relief pressure to the high pressure relief pressure is large, and the occurrence of the impact or vibration may not be sufficiently prevented. In addition, the shockless time due to the low pressure relief pressure obtained during the movement of the free piston is short, and there is a problem that an impact is generated by shifting to the high pressure relief pressure without sufficiently releasing the overload pressure.

  Regarding this, as shown in FIG. 14 in Japanese Patent Application Laid-Open No. 6-137307 (Patent Document 2), the front end position from the rear end position (the right end position in FIG. 14) before the movement of the free piston 2 of the relief valve 1. During the shockless time up to (stroke end: left end position in FIG. 14), the pressure on the poppet 3 in the same direction as the pressing force of the poppet spring 4 is increased stepwise in accordance with the movement of the free piston 2 to reduce the pressure. One that generates a stepwise intermediate relief pressure between the relief pressure and the high pressure relief pressure has been proposed.

  However, the structure shown in Patent Document 2 is different from the relief valve 70 shown in Patent Document 1 in that the poppet 3 itself has a rod-shaped rear member 3a, and the throttle portion extends from the axial through hole 5 thereof. The pressure of the oil in the rear chamber 6 of the free piston 2 that has been reduced in pressure via the pressure is applied to the poppet 3 as a pressure in the same direction as the pressing force of the poppet spring 4. (The thing of the said patent document 1 differs in the point which the pressure of the poppet back surface chamber 73p acts before it is pressure-reduced by the small hole 76a which is an aperture | diaphragm | restriction part, and enters into the rear chamber 29a.)

14 is a free piston that is externally fitted to the rear member 3a of the poppet 3 so as to be slidable in the axial direction, in addition to the throttle portion 7 that always opens to the rear chamber 6 at the rear end portion of the axial through hole 5. When the free piston 2 moves forward (leftward in FIG. 14), it is closed when the rear end 2 is in the rear end position. , 9 are sequentially opened to gradually increase the pressure in the rear chamber 6 by gradually reducing the flow resistance of the entire throttle portion, thereby generating an intermediate relief pressure that is gradually increased. It is.
Therefore, when the vehicle is decelerated or stopped, the relief pressure can be reached from the initial low pressure relief pressure to the final high pressure relief pressure through the intermediate relief pressure. However, there are the following problems. .

That is, in the thing of patent document 2, since the some throttle parts 8 and 9 open sequentially, the passage oil amount of the whole throttle part increases sequentially, and the moving speed of the free piston 2 increases gradually, Finally, it stops suddenly at the front end position of the stroke end (left end position in FIG. 14).
Therefore, since the oil flow rate to the free piston 2 gradually increases and then suddenly becomes zero at the end, the shock at the final stage of the shockless operation due to this becomes large, and this problem has to be solved. .

JP-A-8-296604 (pages 3-5, FIGS. 1-4) JP-A-6-137307 (pages 3 to 4, FIG. 1)

  The present invention relates to a relief valve for a traveling unit brake valve equipped with a free piston, from the initial low pressure relief pressure that releases the instantaneous overload pressure that occurs immediately after the control valve is switched by the free piston. Reduce the shock at the time of transition to the high pressure relief pressure set for steady braking force and stopping force at the front end position, and prevent the occurrence of shock and vibration. Provides a relief valve for the traveling unit brake valve that can be performed without any problems, and further increases the shockless time obtained during the movement of the free piston, so that the overload pressure cannot be sufficiently released and the high pressure relief pressure is obtained. It is an object of the present invention to provide a relief valve for a traveling unit brake valve that can prevent occurrence of an impact due to transition.

  The present invention has been made to solve the above-described problems, and provides the following means (1) to (8), and will be described below in the order of the claims.

  (1) As the first means, a casing in which a fluid flow path and a valve seat are formed, and a small hole penetrating from the front surface to the back surface is provided, and provided in the casing so as to be slidable in the axial direction. It has a poppet, a poppet spring that presses the poppet against the valve seat, and a through hole that penetrates from the front end to the rear end, and the outer peripheral surface of the front end slides in an oil-tight and axial direction inside the cylindrical part on the back of the poppet The rear end of the rod is formed so as to be received by a stopper at the rear of the casing, and the rear end position of the rod is fitted to the inner peripheral surface of the casing. And a free piston that is oil-tight and axially slidable between the front end position and a first piston that is formed on the rear side of the free piston inside the housing and communicates with the through hole via a throttle portion. Space, the poppet in the housing and the Relief for traveling unit brake valve, comprising: oil drainage hole and oil drainage hole communication passage formed so as to communicate the second space between the piston and the downstream flow path when overload pressure is released In the valve, the throttle portion provides a relief valve for a traveling unit brake valve, wherein the opening is reduced while the free piston moves from the rear end position to the front end position.

  (2) As a second means, in the travel unit brake valve relief valve of the first means, the throttle portion is located at a position where the free piston is not blocked by the free piston even when the free piston is at the rear end position. A first hole provided at a rear end portion of the rod and communicating with the through hole and the first space; an annular space provided inside the free piston and surrounding the rod; and provided in the free piston A communication path that always communicates with the annular space and the first space, and the free piston is opened to the annular space while moving in the front end direction by a predetermined distance from the rear end position of the free piston. An annular space is communicated with the through hole, and the rod is moved to the front end position after the free piston moves by the predetermined distance at a position closed by the inner peripheral surface of the free piston. To have a second hole kicked provide a travel unit brake valve relief valve according to claim.

  (3) As a third means, in the travel unit brake valve relief valve of the second means, the second hole is a plurality of holes having different predetermined distances. Relief valve is provided.

  (4) As a fourth means, in the relief valve for a traveling unit brake valve of the first means, the throttle portion is located at a position that is not blocked by the free piston even when the free piston is at the rear end position. A hole provided at a rear end portion of the rod that communicates with the through-hole and the first space; a communication hole that extends in the axial direction of the rod and has a deep rear end portion that communicates with the through-hole; A wedge-shaped notch provided so as to reduce the notch cross-section toward the shallow, an annular space provided inside the free piston and surrounding the rod, the annular space provided in the free piston and the first space The wedge-shaped notch has a full axial length opening in the annular space when the free piston is in the rear end position, and the free piston moves in the front end direction. The free piston is gradually covered from the rear end side by the inner peripheral surface of the free piston, and when the free piston is at the front end position, the entire surface is closed by the inner peripheral surface of the free piston. A relief valve for a traveling unit brake valve is provided.

  (5) As a fifth means, in the relief valve for a brake valve of the traveling unit of the fourth means, when the free piston is in its front end position without providing the hole, the wedge-shaped notch is located within the free piston. A travel unit brake valve relief valve is provided in which the front end portion of the wedge-shaped notch is opened to the annular space instead of being entirely closed by a peripheral surface.

  (6) As a sixth means, in the relief valve for a brake valve of the traveling unit of the first means, the throttle portion is at a position not blocked by the free piston even when the free piston is at the rear end position. A hole provided at a rear end portion of the rod and communicating with the through hole and the first space; a small diameter portion extending in the axial direction of the rod and having a communication hole communicating with the through hole at the rear end portion; An annular space formed inside the free piston and surrounding the rod; and a communication path provided in the free piston and always communicating with the annular space and the first space; When the free piston is at the rear end position, the entire axial length opens in the annular space, and the free piston is gradually covered from the rear end side by the inner peripheral surface of the free piston as it moves in the front end direction. ,same Lee piston provides a driving unit brake valve relief valve, characterized in that provided in the rod such entire surface is closed by the inner circumferential surface of the free piston when the front end position.

  (7) As a seventh means, in the relief valve for a brake valve of the traveling unit of the sixth means, when the free piston is at its front end position without providing the hole, the small-diameter portion is within the free piston. Provided is a relief valve for a traveling unit brake valve, wherein the front end portion of the small diameter portion is opened to the annular space instead of being entirely closed by a peripheral surface.

  (8) As an eighth means, in the relief valve for a brake valve of the traveling unit of any one of the first to seventh means, there is provided a return channel that communicates the first space and the second space. The escape flow path is configured to be closed when the free piston is at the front end position and at the rear end position, and provides a relief valve for a traveling unit brake valve.

(1) According to the first aspect of the present invention, since the relief valve for the traveling unit brake valve is configured as the first means, the throttle portion reduces the opening degree, so that An intermediate relief pressure can be set between the low pressure relief pressure and the high pressure relief pressure, and impact and vibration are greatly reduced as compared with a case where the low pressure relief pressure is directly transferred to the high pressure relief pressure.
Therefore, from the time when the free piston is at the rear end position until it reaches the front end position, the overload pressure can be released at a low pressure initially, and then after the intermediate relief pressure is raised, the pressure is increased. The relief pressure set for steady braking force and stopping force is used, so that the overload pressure can be sufficiently released in the traveling unit, and the occurrence of impact and vibration can be sufficiently prevented thereafter. .
Moreover, since the opening of the throttle portion decreases as the free piston moves, the amount of hydraulic oil flowing into the first space decreases, and the speed of the free piston decreases toward the front end position (stroke end). In the relief valve, hammering of hydraulic oil and impact of free piston collision are prevented.
Therefore, the problem of impact and vibration of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state is solved, and the fluid and mechanical impacts in the relief valve are also eliminated.

  (2) According to the second aspect of the present invention, since the relief valve for the traveling unit brake valve is configured as the second means, in addition to the effect of the first aspect, In addition, the intermediate relief pressure can be set and the free piston and the rod can be partially changed. The structure of the entire relief valve is the same as the conventional one, and the structure is simple and maintenance is easy.

  (3) According to the third aspect of the present invention, since the relief valve for the traveling unit brake valve is configured as the third means, in addition to the effects of the second aspect, The intermediate relief pressure can be set step by step, and the problems of impact and vibration of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state are more preferably solved.

  (4) According to the invention of claim 4 of the claims, since the relief valve for the traveling unit brake valve is configured as the fourth means, in addition to the effect of the invention of claim 1, continuous The intermediate relief pressure that can be boosted can be set, and the impact and vibration problems of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state are more preferably solved, and the fluid and mechanical shocks in the relief valve are also reduced It will be resolved. Moreover, it can be implemented by changing a part of the free piston and the rod, and the overall structure of the relief valve is the same as the conventional one. The structure is simple and maintenance is easy.

  (5) According to the invention of claim 5 of the claims, since the relief valve for the traveling unit brake valve is configured as the fifth means, in addition to the effect of the invention of claim 4, an intermediate The transition from relief pressure to high relief pressure is smoother.

  (6) According to the sixth aspect of the present invention, since the relief valve for the traveling unit brake valve is configured as the sixth means, in addition to the effects of the first aspect, The intermediate relief pressure that can be boosted can be set, and the impact and vibration problems of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state are more preferably solved, and the fluid and mechanical shocks in the relief valve are also reduced It will be resolved. In addition, it can be implemented by changing the free piston and part of the rod. The overall structure of the relief valve is the same as the conventional one. The structure is simple and easy to maintain, and the gap formed by the small diameter part is used as a variable orifice. Since it is used, it is possible to prevent malfunction due to clogging of contaminants rather than orifices due to small holes.

  (7) According to the seventh aspect of the present invention, since the travel unit brake valve relief valve is configured as the seventh means, in addition to the effect of the sixth aspect, The transition from relief pressure to high relief pressure is smoother.

(8) According to the invention of claim 8 of the claims, since the relief valve for the traveling unit brake valve is configured as the eighth means, the invention of any one of claims 1 to 7 In addition to the effects, the travel time from when the free piston was at the rear end position until it reached the front end position, i.e., with a relatively low low pressure relief pressure and intermediate relief pressure before the relief valve reached the high pressure relief pressure. The shockless time during which the load pressure can be released can be extended, the overload pressure can be released sufficiently, and then the high pressure relief pressure set for steady braking and stopping force is used. It is possible to further prevent the occurrence of shock and vibration during the transition to the relief pressure.
In addition, since the escape passage by the communication hole is closed at the front end position of the free piston, the setting and operation of the high pressure relief is not impaired.
In addition, since the escape passage by the communication hole is closed even at the rear end position of the free piston, the second space side can be maintained at a higher pressure than the first space side during normal operation, and the free piston is maintained at the rear end position. There is no loss in doing.
Therefore, there is no oil leakage, and the locking performance for preventing drift on a slope when the vehicle is stopped is not impaired.

FIG. 12 is a longitudinal sectional view schematically showing a portion corresponding to part A in FIG. 11 of the relief valve for the traveling unit brake valve according to the first embodiment of the present invention, where (a) is a position where the free piston moves during braking or stopping. The previous state, (b), shows the state in which the free piston is moving, and shows a state in which a low pressure relief pressure is exhibited. FIG. 12 is a longitudinal sectional view schematically showing a portion corresponding to part A in FIG. 11 of the relief valve for the traveling unit brake valve according to the first embodiment of the present invention, where (a) is a position where the free piston moves during braking or stopping. The state which exhibits intermediate relief pressure in the inside, (b) shows the state which exhibits high pressure relief pressure after the above-mentioned movement of a free piston. It is explanatory drawing of the relief pressure setting in the relief valve concerning this invention, (a) shows typically the principal part of the relief valve of FIG. 11, (b) is explanatory drawing of the relationship between an orifice and pressure. It is. It is explanatory drawing of the change of the relief pressure at the time of braking or a stop by this invention. FIG. 12 is a longitudinal sectional view schematically showing a portion corresponding to part A in FIG. 11 of a relief valve for a traveling unit brake valve according to Embodiment 2 of the present invention, in which (a) is a position where a free piston moves during braking or stopping. A state in which the previous low pressure relief pressure is exhibited, (b) indicates a state in which the intermediate relief pressure during the movement of the free piston is exhibited, and (c) indicates a state in which the high pressure relief pressure after the movement of the free piston is exhibited. It is explanatory drawing which shows typically the modification of Example 2, and shows the state in which a free piston exhibits the high pressure relief pressure after a movement at the time of braking or a stop. FIG. 12 is a longitudinal sectional view schematically showing a portion corresponding to part A in FIG. 11 of a relief valve for a traveling unit brake valve according to Embodiment 3 of the present invention, in which (a) is a position where a free piston moves during braking or stopping. A state in which the previous low pressure relief pressure is exhibited, (b) indicates a state in which the intermediate relief pressure during the movement of the free piston is exhibited, and (c) indicates a state in which the high pressure relief pressure after the movement of the free piston is exhibited. It is explanatory drawing which shows typically the modification of Example 3, and shows the state in which a free piston exhibits the high pressure relief pressure after a movement at the time of braking or a stop. It is a longitudinal cross-sectional view which shows typically the principal part of the part corresponded to A part in FIG. 11 of the relief valve for traveling unit brake valves which concerns on Example 4 of this invention. It is a principal part schematic diagram of the traveling drive apparatus of a hydraulic drive crawler type vehicle. 1 shows a relief valve for a brake valve having a conventional free piston, wherein (a) is a longitudinal sectional view when the flow path R is at a high pressure, and (b) is a longitudinal sectional view when the flow path R is at a low pressure. It is a figure which shows the state at the time of neutral of the hydraulic system which has a relief valve for brake valves provided with the conventional free piston. It is a figure which shows the state at the time of driving | running | working of the hydraulic system which has the relief valve for brake valves provided with the conventional free piston. It is a longitudinal cross-sectional view of the other example of the relief valve for brake valves provided with the conventional free piston.

Based on the relief valve 70R shown in FIG. 11, the relief pressure of the relief valve at the time of braking or stopping will be briefly described with reference to FIG.
FIG. 3A schematically shows a main part of the relief valve of FIG. 11, and the same parts as those in FIG.
As described above, during traveling while sending hydraulic pressure to the flow path R, when decelerating or stopping, a high pressure is instantaneously generated in the flow path L due to the inertial force of the movement of the vehicle body or other mass, and a negative pressure is generated in the flow path R. appear. At that time, the free piston 78 of the relief valve 70R is located at the rear end position of the free piston chamber 79, the flow path R has no pressure or negative pressure, and the oil discharge hole 71d and the oil discharge hole communication path 71e ( The pressure p4 in the front chamber 79b of the free piston chamber 79 communicated via (see FIG. 11) is also no pressure or negative pressure. Therefore, when the high pressure p1 generated instantaneously due to the sudden stop is applied to the front face of the poppet 73R of the relief valve 70R from the branch flow path Ld, it easily passes through the small hole 73o (orifice 1: diameter d1) and the poppet back surface chamber 73p. Oil enters the rear chamber 79a of the free piston 78 (pressure p3) through the small through hole 76a (orifice 2: diameter d2) through the rod through hole 76h (pressure p3). The oil (pressure p4) in the front chamber 79b is discharged into the flow path R as it moves.

At that time, the push-up force F of the poppet 73 is defined as the area by the diameter of the poppet sheet 71b is A1, and the area by the inner diameter of the poppet is A2.
F = A1 * p1-A2 * p2.
Therefore, when F becomes equal to the spring force W of the poppet spring 72 that presses the poppet, the poppet 73 starts to open. (Here, the change in W due to the displacement of the spring is relatively small and will be omitted below.)
F = W
A1 * p1-A2 * p2 = W
p1 = (W + A2 × p2) / A1 (1)
At this time, p1 is the relief pressure. Since W, A1, and A2 are known predetermined values for the valve,
If poppet internal pressure p2 becomes small, p1 as relief pressure also becomes small,
If the poppet internal pressure p2 is increased, the relief pressure p1 is also increased. (2)

In the initial stage of the deceleration or stop operation, the flow path R has no pressure or negative pressure as described above, and the pressure p4 of the front chamber 79b of the free piston chamber 79 communicating with the flow path R is also no pressure or negative pressure (≈0). The free piston 78 is easily moved by the oil (pressure p3) entering the rear chamber 79a of the free piston 78 via the small hole 76a (orifice 2: diameter d2). During the shockless time during the movement of the free piston 78, the following can be said.
p3 ≒ p4 ≒ 0 (3)

On the other hand, as shown in FIG. 3B, the small hole 73o (orifice 1: diameter d1) and the small hole 76a (orifice 2: diameter d2) are arranged in series, and the oil flow rate Q2 passing through the small hole 76a. Is represented below.
^{Q2 = α (πd2 2/4} ) × √ {2g (p2-p3) / γ}
(Α, π, g, and γ are constants)
Therefore, during the shockless time during free piston movement, considering (3),
^{γQ2 2 / {2gα 2 (πd2} 2/4) 2} = p2-p3 ≒ p2 ········ (4)
It becomes.
From (4), under the same Q2,
When d2 is relatively large, p2 is relatively small,
It can be seen that when d2 is relatively small, p2 is relatively large. ... (5)

When the relationship (5) is combined with the relationship (2) between the poppet internal pressure p2 and the relief pressure p1, the following can be said.
When d2 is relatively large, the relief pressure p1 is relatively small (low),
When d2 is relatively small, the relief pressure p1 is relatively large (high).・ (6)
Further, when the small hole 73o (orifice 1: diameter d1) is constant, from the relationship of (6),
When d1-d2 is relatively small, the relief pressure p1 is relatively small (low),
When d1-d2 is relatively large, the relief pressure p1 is relatively large (high), ... (7)
I can say that.

On the other hand, when the free piston 78 reaches the front end portion (left end portion: stroke end), oil cannot flow into the rear chamber 79a, Q1 = Q2 = 0, and the pressure to the rear chamber 29a becomes the same, p1 = p2 = p3.
Therefore, (1) above is
p1 = (W + A2 × p1) / A1
p1 = W / (A1-A2) (8)
The high pressure relief pressure Pr2.

From the above, the low pressure relief pressure Pr1 during the shockless time from the beginning of the operation of the relief valve 70R of FIG. 11 is due to the relatively low pressure p2 over a large area A1, as described in (1) above.
Pr1 = (W + A2 × p2) / A1 (9)
The high pressure relief pressure Pr2 after the shockless time is due to a relatively small area difference as described in (8) above.
Pr2 = W / (A1-A2) (10)
However, the shock at the time of switching the relief pressure in two stages has been a problem.

Therefore, the present invention recalls that the relationship (6) is combined with the relationship (1) above, and the diameter d2 of the small hole 76a (orifice 2) as an index of the “opening” of the “throttle portion”. Is made “variable” in accordance with the movement of the free piston 78 and is changed to a relatively small d2 ′ (decreasing the “opening degree”) following the low pressure relief pressure Pr1 due to d2 at the beginning of operation of the relief valve. An intermediate relief pressure higher than the low pressure relief pressure Pr1,
Pr3 = (W + A2 × p2 ′) / A1 (11)
After that, the high pressure relief pressure Pr2 at the stroke end of the free piston 78 is obtained.
Therefore, in the present invention, from the low pressure relief pressure Pr1 to the high pressure relief pressure Pr2,
Since the switching is performed via the intermediate relief pressure Pr3 that is an intermediate pressure, the problem of shock at the time of switching the relief pressure as in the case of the two-stage relief pressure of the relief valve 70R of the conventional example of FIG. 11 is solved.

In addition, as described later, the problems pointed out in the above-mentioned Patent Document 2 are also solved by the present invention.
Further, according to the present invention, it is possible to extend the moving time of the free piston. By extending the shockless time, the overload pressure is sufficiently released, and then the reset is set for the steady braking force and stopping force. Since it becomes a high relief pressure, it is possible to sufficiently prevent the occurrence of impact and vibration.

In the present invention, the diameter d2 of the small hole 76a (orifice 2) defined as “variable” in the present invention is from the poppet back surface chamber 73p and the rod through hole 76h to the rear chamber 79a of the free piston 78. Assumed orifice diameter when the entire "throttle part" corresponding to the small hole 76a for feeding hydraulic oil is converted into one orifice small hole, it is hereinafter treated as "equivalent orifice diameter d2" and so on. I will do it.
Further, in the embodiment of the present invention, the throttle portion (orifice) corresponding to the “equivalent orifice diameter d2” is formed by a plurality of small holes and various forms of flow paths.

  Examples 1 to 4 will be described below as modes for carrying out the present invention.

A travel unit brake valve relief valve according to a first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a longitudinal sectional view schematically showing a portion corresponding to the portion A in FIG. 11 of the relief valve for the traveling unit brake valve of the present embodiment, and in FIGS. 12 and 13 similarly to the relief valve 70R of FIG. The relief valve 170R arranged on the right side is illustrated, (a) shows the state before the free piston has moved during braking or stop, and (b) shows the state of the free piston being moved, both exhibiting a low pressure relief pressure. Indicates the state.
2A and 2B are schematic longitudinal sectional views of the same part, in which FIG. 2A shows a state in which the free piston is moving during braking or stopping and exhibits an intermediate relief pressure, and FIG. 2B shows a high pressure relief after the free piston has moved. The state which shows a pressure is shown.

  The first embodiment is the same as the relief valve for a brake valve and the travel drive device described in the conventional example except that the configuration of the rod and the free piston is different, and the illustration is omitted. FIG. 1 is a schematic diagram for explaining different parts. Detailed shapes of cartridges, rods, etc., and illustration of members (for example, collar 76f, poppet spring 72, etc.) are omitted. 10 to 13 is the same as that described with reference to FIGS. The parts described in the conventional example are assigned the same reference numerals and the description thereof is omitted, and the parts according to the present embodiment are assigned reference numerals in the 100s with the same last two digits to clarify the relationship.

  As shown in FIG. 1A, the rod 176 of the relief valve 170R of the present embodiment has a position where the free piston 178 is not covered by the free piston 178 when the free piston 178 is at the rear end position (right end position in the figure). A first small hole 176a is provided as an orifice that communicates the rod through hole 76h and the rear chamber 79a of the free piston chamber 79 on the rear (right side) of the free piston 178. The number of the first small holes 176a or the number of the first small holes 176a, the cross-sectional shape dimensions, and the like are appropriately set so as to obtain the required flow rate and the throttling effect.

  The free piston 178 includes an annular space 178a and a communication passage 178b communicating the annular space 178a and the rear chamber 79a so as to surround the rod 176. The communication passage 178b opens to the rear chamber 79a even when the free piston 178 is at the rear end position, and an appropriate notch 178c or the like is provided when necessary to obtain an open state.

As shown in FIG. 1A, the rod 176 faces the annular space 178a from when the free piston 178 is at the rear end position until it moves a predetermined distance as shown in FIG. After moving a predetermined distance as shown in FIG. 2 (a), at the front end position (left end position in the figure) as shown in FIG. 2 (b), it is in a position where it is in contact with and closed by the inner peripheral surface 178d of the free piston 178. A second small hole 176b is provided as an orifice for communicating the rod through hole 76h and the annular space 178a. One or a plurality of the second small holes 176b, their cross-sectional shape dimensions, and the like are appropriately set so as to obtain the required flow rate and throttling effect.
In addition, when the rear end of the rod 176 is formed into a spherical surface, an extra twisting force is not applied.

  The operation of the relief valve 170R of this embodiment will be described. As described in the conventional example, during normal operation by applying hydraulic pressure to the flow path R, the free piston 178 of the relief valve 170R is at the rear end position as shown in FIG. When the control valve 40 is set to the neutral position, the oil that has been flowing from the flow path R to the flow path L through the hydraulic motor 20 until then is suddenly stopped. As a result, the high pressure is instantaneously generated in the flow path L, the negative pressure is generated in the flow path R, and the pressure p4 in the front chamber 79b in front of the free piston 178 communicating with the flow path R is also No pressure or negative pressure.

Therefore, when the high pressure instantaneously generated in the flow path L due to the sudden stop is applied from the branch flow path Ld to the front face of the poppet 73R of the relief valve 170R, the pressure p4 in the front chamber 79b is no pressure or negative pressure. The low pressure relief pressure Pr1 = (W + A2 × p2) / A1 is low without significantly increasing the pressure p3 in the rear chamber 79a and the pressure in the poppet p2, and the hydraulic oil a1 is easily supplied from the orifice 73o and the rod through hole 76h. The hydraulic oil a2 enters the annular space 178a of the free piston 178 from the second small hole 176b through the first small hole 176a and enters the rear chamber 79a behind the free piston 178 and from the rod through hole 76h. Enter the rear chamber 79a through the passage 178b.
Since the left side of the free piston 178 and the front chamber 79b side are under no pressure p4, as shown in FIG. 1B, the free piston 178 easily moves in the direction of the white arrow in the drawing (leftward).
At this time, the “equivalent orifice diameter d2” is the entire “restricted portion” including the first small hole 176a, the second small hole 176b, the annular space 178a, and the communication path 178b.

However, when the free piston 178 further moves and the inner peripheral surface 178d of the free piston 178 covers and closes the second small hole 176b as shown in FIG. 2A, the hydraulic oil a2 from the second small hole 176b is closed. Is stopped, and the hydraulic oil a1 flows only from the first small hole 176a.
Accordingly, since the “equivalent orifice diameter d2 ′” at this time is only due to the first small hole 176a, it is clearly smaller than the “equivalent orifice diameter d2” in the state shown in FIG. Also, the pressure inside the poppet changes to p2 ', and the relief pressure also increases, so that the intermediate relief pressure Pr3 = (W + A2 * p2') / A1.

  If the high pressure is maintained in the branch flow path Ld with respect to the intermediate relief pressure Pr3, the inflow of the hydraulic oil a1 from the first small hole 176a still continues, but as shown in FIG. When 178 reaches the front end position and stops, the hydraulic oil a1 cannot flow in, and is pushed in as shown by the dotted line arrow in the figure, p3 = p2 = p1, and the relief pressure is the high pressure relief pressure Pr2 = W / (A1- A2) After that, the operation proceeds to the high pressure relief pressure setting state.

The change in the relief pressure is shown by a solid line in FIG. As described above, initially, the hydraulic oil a1 from the first small hole 176a and the hydraulic oil a2 from the second small hole 176b are supplied, and then the low pressure relief pressure Pr1, and then the hydraulic oil a1 from the first small hole 176a. After passing through the intermediate relief pressure Pr3 in a state where only the pressure is supplied, the pressure reaches the high pressure relief pressure Pr2. Therefore, the impact is far greater than the case where the low pressure relief pressure Pr1 directly shifts from the low pressure relief pressure Pr1 to the high pressure relief pressure Pr2 as in the conventional example shown by the broken line. And vibration is reduced.
Therefore, from the time when the free piston 178 is at the rear end position until the front end position is reached, the overload pressure can be released at a low pressure initially, and then the intermediate relief pressure is increased. Later, the relief pressure set for steady braking force and stopping force is set, so that the overload pressure can be sufficiently released in the traveling unit, and the occurrence of impact and vibration can be sufficiently prevented thereafter. it can.

  Moreover, as the free piston 178 moves, the “equivalent orifice diameter d2” decreases stepwise, so that the amount of hydraulic fluid flowing into the rear chamber 29a decreases stepwise, and the speed of the free piston 178 increases at the front end position (stroke end). In the relief valve 170R, the hammer phenomenon of hydraulic oil and the impact of the collision of the free piston are prevented, and the problem assumed in the above-mentioned Patent Document 2 is also solved.

  When the free piston 178 is at the rear end position, it opens to the annular space 178a, and when the free piston 178 is at the front end position, the position is covered and closed by the inner peripheral surface 178d of the free piston 178, and the rod axial position It is also possible to provide a plurality of second small holes 176b with different (the predetermined moving distance from the rear end position of the free piston 178 when closing the second small hole from the opening is different), The intermediate relief pressure becomes multistage, and the problem of impact and vibration of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state is more preferably solved.

  As described above, the present embodiment has been exemplified and described as the relief valve 170R disposed on the right side in FIGS. 12 and 13 in the same manner as the relief valve 70R in FIG. 11, but the relief valve disposed on the left side in FIGS. By simply reversing the paths R and L, the relief valve 170R can be constructed in exactly the same manner, and the same effect can be obtained.

  Since the relief valve for the traveling unit brake valve of the first embodiment is configured and operates as described above, the problem of impact and vibration of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state is solved. Fluid and mechanical shocks in the relief valve are also eliminated. Moreover, it can be implemented by changing a part of the free piston and the rod, and the overall structure of the relief valve is the same as the conventional one. The structure is simple and maintenance is easy.

  A travel unit brake valve relief valve according to a second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a longitudinal sectional view schematically showing a portion corresponding to the portion A in FIG. 11 of the relief valve for the traveling unit brake valve of the present embodiment. FIG. (B) shows the state which exhibits the intermediate relief pressure during the said movement of a free piston, (c) shows the state which exhibits the high pressure relief pressure after the said movement of a free piston.

  The second embodiment is the same as the brake valve relief valve and travel drive device described in the conventional example except that the configuration of the rod and the free piston is different, and the illustration is omitted. FIG. 5 is a schematic diagram for explaining different parts, and detailed shapes of cartridges, rods, etc., and illustration of members (for example, collar 76f, poppet spring 72, etc.) are omitted, and there are no particular descriptions. 10 to 13 is the same as that described with reference to FIGS. The parts described in the conventional example are assigned the same reference numerals and the description thereof is omitted, and the parts according to the present embodiment are assigned the reference numerals in the 200s with the same last two digits to clarify the relationship.

  As shown in FIG. 5A, the rod 276 of the relief valve 270R of the present embodiment has a position where it is not covered by the free piston 278 when the free piston 278 is at the rear end position (right end position in the figure). A small hole 276a is provided as an orifice that communicates the rod through hole 76h and the rear chamber 79a of the free piston chamber 79 on the rear (right side of the figure) side of the free piston 278. The single or plural small holes 276a, their cross-sectional shape dimensions, and the like are appropriately set so as to obtain the required flow rate and throttling effect.

  The free piston 278 includes an annular space 278a and a communication passage 278b communicating the annular space 278a and the rear chamber 79a so as to surround the rod 276. The communication passage 278b is opened to the rear chamber 79a even when the free piston 278 is at the rear end position, and an appropriate notch 278c and the like are provided when necessary to obtain an open state.

Further, a wedge-shaped notch 280 extending in the axial direction is provided on the surface of the rod 276, and the wedge-shaped notch 280 is deepest on the rod rear end side (right side in the drawing) and communicates with the rod through hole 76h and the annular space 278a. It has a communication hole 280a and is shallower toward the rod front end side (left side in the figure). As shown in FIG. 5 (a), the wedge-shaped notch 280 is fully open to the annular space 278a when the free piston 278 is in the rear end position, and the front end position (left end position in the figure) is shown in FIG. 5 (c). ), The entire surface is in contact with the inner peripheral surface 278d of the free piston 278 so as to be closed. When the free piston 278 moves from the rear end position to the front end position, as shown in FIG. A part is covered with the inner peripheral surface 278d of 278, and the wedge-shaped notch 280 is opened to the annular space 278a at a position where the cross section gradually narrows. That is, the wedge-shaped notch 280 forms a variable orifice including the communication hole 280a, and the wedge-shaped notch 280 is appropriately set so as to obtain a desired flow rate and a throttling effect. .
In addition, when the rear end of the rod 276 is formed into a spherical surface, an excessive twisting force is not applied.

  The operation of the relief valve 270R of this embodiment will be described. As described in the conventional example, during normal operation by applying hydraulic pressure to the flow path R, the free piston 278 of the relief valve 270R is at the rear end position as shown in FIG. When the control valve 40 is set to the neutral position, the oil that has been flowing from the flow path R to the flow path L through the hydraulic motor 20 until then is suddenly stopped. As a result, the high pressure is instantaneously generated in the flow path L, the negative pressure is generated in the flow path R, and the pressure p4 in the front chamber 79b in front of the free piston 278 communicating with the flow path R is also No pressure or negative pressure.

Therefore, when the high pressure instantaneously generated in the flow path L due to the sudden stop is applied to the front face of the poppet 73R of the relief valve 270R from the branch flow path Ld, the pressure p4 in the front chamber 79b is no pressure or negative pressure. The low pressure relief pressure Pr1 = (W + A2 × p2) / A1 is low without significantly increasing the pressure p3 and the poppet internal pressure p2 of the rear chamber 79a, and the hydraulic oil a1 is easily reduced from the orifice 73o and the rod through hole 76h. The hydraulic oil a2 enters the annular space 278a of the free piston 278 through the hole 276a and enters the rear chamber 79a behind the free piston 278 from the rod through hole 76h, and also passes through the communication passage 278b. Enter the rear chamber 79a.
At this time, the “equivalent orifice diameter d2” is a combination of the small hole 276a, the wedge-shaped notch 280, the annular space 278a, and the communication path 278b.
Since the left surface of the free piston 278 and the front chamber 79b side are under no pressure p4, the free piston 278 easily moves to the left in the figure.

However, as shown in FIG. 5B, when the free piston 278 moves in the direction of the white arrow in the drawing (leftward), the inner peripheral surface 278d of the free piston 278 gradually increases from the deep side of the wedge-shaped notch 280. Therefore, the cross section of the wedge-shaped notch 280 opening to the annular space 278a is gradually narrowed, the flow path resistance of the wedge-shaped notch 280 is gradually increased, and the flow rate of the passing hydraulic oil a2 is gradually decreased. Go.
Accordingly, the “equivalent orifice diameter d2 ′” in this state is the entire “restricted portion” including the small hole 276a, the wedge-shaped notch 280 having a gradually narrowing opening cross section, the annular space 278a, and the communication passage 278b. It gradually becomes smaller than the “equivalent orifice diameter d2” at the start of movement.
As a result, the poppet internal pressure changes to the poppet internal pressure p2 ′ that gradually increases, and the intermediate relief pressure Pr3 = (W + A2 × p2 ′) / A1 that also gradually increases the relief pressure.

  Then, when the wedge-shaped notch 280 is closed and only the hydraulic oil a1 flowing in from the small hole 276a is shown in FIG. 5C, when the free piston 278 reaches the front end position and stops, the hydraulic oil a1 cannot flow in. As shown by the middle dotted arrow, the push-in state is established, p3 = p2 = p1, the relief pressure becomes the high-pressure relief pressure Pr2 = W / (A1-A2), and thereafter, the state shifts to the high-pressure relief pressure setting state.

The change in the relief pressure is indicated by a solid line in FIG. As described above, initially, the hydraulic oil a1 from the small hole 276a and the hydraulic oil a2 from the wedge-shaped notch 280 are supplied, and the hydraulic oil a2 from the wedge-shaped notch 280 gradually decreases. Since the intermediate relief pressure Pr3 that gradually increases in the supplied state reaches the high intermediate relief pressure of only the hydraulic oil a1 from the small hole 276a and then reaches the high pressure relief pressure Pr2, the conventional example shown by the broken line The impact and vibration are greatly reduced compared to the case where the low pressure relief pressure Pr1 directly shifts to the high pressure relief pressure Pr2.
Therefore, from the time when the free piston 278 is at the rear end position until it reaches the front end position, the overload pressure can be released at a low pressure initially, and immediately after that, the state of the intermediate relief pressure in which the pressure is gradually increased. The relief pressure set for steady braking force and stopping force is set after the operation is taken, so that the overload pressure is sufficiently released in the traveling unit, and the occurrence of impact and vibration is prevented sufficiently thereafter. can do.

  In addition, since the “equivalent orifice diameter d2 ′” gradually decreases as the free piston 278 moves, the amount of hydraulic oil flowing into the rear chamber 79a gradually decreases, and the speed of the free piston 278 is at the front end position (stroke end). In the relief valve 270R, the hydraulic oil hammer phenomenon and the impact of the free piston collision are prevented, and the problem assumed in the above-mentioned Patent Document 2 is also solved.

  As described above, the present embodiment has been illustrated and described as the relief valve 270R disposed on the right side in FIGS. 12 and 13 in the same manner as the relief valve 70R in FIG. 11, but the relief valve disposed on the left side in FIGS. By simply reversing the paths R and L, the relief valve 270R can be configured in exactly the same manner, and the same effects can be obtained.

  Since the relief valve for the traveling unit brake valve of the second embodiment is configured and operates as described above, the problem of the impact and vibration of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state is described in the above embodiment. It is more preferably eliminated than 1, and the fluid and mechanical shocks in the relief valve are also eliminated. Moreover, it can be implemented by changing a part of the free piston and the rod, and the overall structure of the relief valve is the same as the conventional one. The structure is simple and maintenance is easy.

FIG. 6 shows a modification of the second embodiment. FIG. 6 shows a state in which the free piston exhibits a high-pressure relief pressure after movement when braking or stopping, as in FIG. 5C. .
In this modification, the wedge-shaped notch 280 'is set so as to leave the opening 281 in the annular space 278a even when the free piston 278 is at the front end position.
The opening 281 extends as long as the front end 280b '(left end in the figure) of the wedge-shaped notch 280' does not open to the front chamber 79b of the free piston chamber 79 when the free piston 278 is at the rear end position as shown in the figure. The front end portion 280b ′ may be opened to the annular space 278a when the free piston 278 is at the front end position. For example, the inner surface (for example, the front end of the annular space 278a is formed so that the opening portion 281 is formed). Other means such as a notch 282 may be provided around the rod 276 on the left-hand inner surface in the drawing.
In this modification, the small hole 276a on the rear end side of the rod 276 is omitted.

According to the modification, the wedge-shaped notch 280 is closed immediately before the free piston 278 reaches the front end position as in the second embodiment, and there is no stage in which the hydraulic oil a1 is supplied only from the small hole 276a. As shown in c), the transition from the intermediate relief pressure Pr3 to the high-pressure relief pressure Pr2 becomes smoother.
In addition, since the rod through hole 76h and the rear chamber 79a can be kept in communication with each other through the opening 281 at the front end position of the free piston 278, the free piston 278 can be moved without the small hole 276a on the rear end side of the rod 276. In addition to being able to set the high pressure relief pressure state by pressing to the front end position, there is no hindrance when the free piston 278 moves from the front end position to the rear end position side. In this modification, the small hole 276a may be omitted. Becomes easier.

  A travel unit brake valve relief valve according to a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a longitudinal sectional view schematically showing a portion corresponding to the portion A in FIG. 11 of the relief valve for the traveling unit brake valve of the present embodiment. FIG. (B) shows the state which exhibits the intermediate relief pressure during the said movement of a free piston, (c) shows the state which exhibits the high pressure relief pressure after the said movement of a free piston.

  The third embodiment is the same as the relief valve for a brake valve and the travel drive device described in the conventional example except that the configuration of the rod and the free piston is different, and the illustration is omitted. FIG. 7 is a schematic diagram for explaining different parts, and detailed shapes of cartridges, rods, etc., and illustration of members (for example, collar 76f, poppet spring 72, etc.) are omitted, and there is no particular description. 10 to 13 is the same as that described with reference to FIGS. The parts described in the prior art are given the same reference numerals and the description thereof is omitted, and the parts according to the present embodiment are given the reference numbers in the 300s with the same last two digits to clarify the relationship.

  As shown in FIG. 7A, the rod 376 of the relief valve 370R of the present embodiment has a position where the free piston 378 is not covered by the free piston 378 when the free piston 378 is at the rear end position (right end position in the figure). A small hole 376a is provided as an orifice that communicates the rod through hole 76h and the rear chamber 79a of the free piston chamber 79 on the rear (right side of the drawing) side of the free piston 378. The single or plural small holes 376a, their cross-sectional shape dimensions, and the like are appropriately set so as to obtain the required flow rate and throttling effect.

  The free piston 378 includes an annular space 378a and a communication passage 378b communicating the annular space 378a and the rear chamber 79a so as to surround the rod 376. The communication passage 378b is opened to the rear chamber 79a even when the free piston 378 is at the rear end position, and an appropriate notch 378c or the like is provided when necessary to obtain an open state.

The rod 376 is provided with a small-diameter portion 384 extending in the axial direction. The small-diameter portion 384 has a communicating hole 384a communicating with the rod through hole 76h and the annular space 378a at the axial rear end (right end in the figure). Have. 7A, when the free piston 378 is at the rear end position, the entire surface of the small diameter portion 384 opens into the annular space 378a, and as shown in FIG. 7C, the small diameter portion 384 is at the front end position (the left end position in the figure). ), The entire surface is in contact with the inner peripheral surface 378d of the free piston 378 so as to be closed, and when the free piston 378 moves from the rear end position to the front end position, as shown in FIG. A part of the inner peripheral surface 378d of 378 is covered, and the small-diameter portion 384 is opened to the annular space 378a at an intermediate position in the axial direction. That is, the small-diameter portion 384 has a thin gap portion 385 between the small-diameter portion 384 and the inner peripheral surface 378d of the free piston 378, and becomes a throttle channel with a variable axial length covered by the inner peripheral surface 378d. The variable orifice is formed including the hole 384a, and the small diameter portion 384 is single (entire circumference) or plural (division in the circumferential direction), its cross-sectional shape dimensions (diameter, circumferential length), and the like. Is appropriately set so as to obtain
When the rear end of the rod 376 is formed into a spherical surface, an extra twisting force is not applied.

  The operation of the relief valve 370R of this embodiment will be described. As described in the conventional example, during normal operation by applying hydraulic pressure to the flow path R, the free piston 378 of the relief valve 370R is at the rear end position as shown in FIG. When the control valve 40 is set to the neutral position, the oil that has been flowing from the flow path R to the flow path L through the hydraulic motor 20 until then is suddenly stopped. As a result, the high pressure is instantaneously generated in the flow path L, the negative pressure is generated in the flow path R, and the pressure p4 in the front chamber 79b in front of the free piston 378 communicating with the flow path R is also No pressure or negative pressure.

Therefore, when the high pressure instantaneously generated in the flow path L due to the sudden stop is applied from the branch flow path Ld to the front face of the poppet 73R of the relief valve 370R, the pressure p4 in the front chamber 79b is no pressure or negative pressure. The low pressure relief pressure Pr1 = (W + A2 × p2) / A1 is low without significantly increasing the pressure p3 and the poppet internal pressure p2 of the rear chamber 79a, and the hydraulic oil a1 is easily reduced from the orifice 73o and the rod through hole 76h. The hydraulic oil a2 also enters the annular space 378a of the free piston 378 from the small diameter portion 384 through the hole 376a and enters the rear chamber 79a behind the free piston 378, and further passes through the communication passage 378b. Enter the rear chamber 79a.
At this time, the “equivalent orifice diameter d2” is a combination of the small hole 376a, the communication hole 384a, the following gap 385, the annular space 378a, and the communication path 378b.
And since the left side of the free piston 378 and the front chamber 79b side are under no pressure p4, the free piston 378 easily moves to the left in the figure.

As shown in FIG. 7B, when the free piston 378 moves in the direction of the white arrow in the drawing (leftward), the inner peripheral surface 378d of the free piston 378 is moved to the rear side in the axial direction of the small diameter portion (in the drawing). , The axial length of the gap portion 385 formed by the small diameter portion 384 gradually increases, and the flow path resistance of the gap portion 385 formed by the small diameter portion 384 gradually increases. Then, the flow rate of the hydraulic oil a2 passing therethrough gradually decreases.
Therefore, the “equivalent orifice diameter d2 ′” in this state is that of the entire “restricted portion” including the small hole 376a, the communication hole 384a, the gap portion 385 formed by the gradually increasing small diameter portion 384, the annular space 378a, and the communication passage 378b. Thus, the free piston 378 gradually becomes smaller than the “equivalent orifice diameter d2” at the start of movement.
As a result, the poppet internal pressure changes to the poppet internal pressure p2 ′ that gradually increases, and the intermediate relief pressure Pr3 = (W + A2 × p2 ′) / A1 that also gradually increases the relief pressure.

  Then, the small diameter portion 384 is covered with the inner peripheral surface 378d of the free piston 378, the gap portion 385 is closed, and only the hydraulic oil a1 flowing from the small hole 276a is used as shown in FIG. When the oil reaches the front end position and stops, the hydraulic oil a1 cannot flow in, and is pushed in as shown by the dotted line arrow in the figure, p3 = p2 = p1, and the relief pressure is the high pressure relief pressure Pr2 = W / (A1-A2 After that, it moves to the state of high pressure relief pressure setting.

The change in the relief pressure is indicated by a solid line in FIG. As described above, initially, when the hydraulic oil a1 from the small hole 376a and the hydraulic oil a2 from the communication hole 384a are supplied, the hydraulic oil from the low pressure relief pressure Pr1 and then from the gap 385 formed by the small diameter portion 384 is obtained. After reaching the high intermediate relief pressure of only the hydraulic oil a1 from the small hole 376a through the intermediate relief pressure Pr3 that gradually increases while a2 is gradually reduced and supplied, the high pressure relief pressure Pr2 is reached. The impact and vibration are greatly reduced as compared with the conventional case where the low pressure relief pressure Pr1 directly shifts from the low pressure relief pressure Pr1 to the high pressure relief pressure Pr2 as shown by the broken line.
Therefore, from the time when the free piston 378 is in the rear end position until the front end position is reached, the overload pressure can be released at a low pressure initially, and immediately thereafter, the intermediate relief pressure is gradually increased. The relief pressure set for steady braking force and stopping force is set after the operation is taken, so that the overload pressure is sufficiently released in the traveling unit, and the occurrence of impact and vibration is prevented sufficiently thereafter. can do.

  In addition, since the “equivalent orifice diameter d2 ′” gradually decreases as the free piston 378 moves, the amount of hydraulic oil flowing into the rear chamber 79a gradually decreases, and the speed of the free piston 378 is at the front end position (stroke end). In the relief valve 370R, the hammer phenomenon of hydraulic oil and the impact of the free piston collision are prevented, and the problem assumed in the above-mentioned Patent Document 2 is also solved.

  As described above, the present embodiment has been illustrated and described as the relief valve 370R disposed on the right side in FIGS. 12 and 13 in the same manner as the relief valve 70R in FIG. 11, but the relief valve disposed on the left side in FIGS. By simply reversing the paths R and L, the relief valve 370R can be constructed in exactly the same manner, and the same effects can be obtained.

  Since the relief valve for the traveling unit brake valve of the third embodiment is configured and operates as described above, the problem of the impact and vibration of the traveling unit when shifting from the low pressure relief pressure state to the high pressure relief pressure state is described in the above embodiment. It is more preferably eliminated than 1, and the fluid and mechanical shocks in the relief valve are also eliminated. Moreover, it can be implemented by changing part of the free piston and rod, and the structure of the relief valve as a whole is the same as the conventional one, the structure is simple and maintenance is easy, and the gap 385 formed by the small diameter part 384 is variable. Since it is used as an orifice, it is possible to prevent malfunction due to clogging of contaminants rather than an orifice with a small hole.

FIG. 8 shows a modification of the third embodiment, and FIG. 8 shows a state in which the free piston exhibits a high-pressure relief pressure after movement during braking or stopping, as in FIG. 7C. .
In the relief valve 370R ′ of this modified example, the small diameter portion 384 ′ is set so as to leave the opening 386 in the annular space 378a even when the free piston 378 is in the front end position.
As shown in the figure, the small-diameter portion 384 'is extended so that its front end portion 384b' (left end in the figure) does not open to the front chamber 79b of the free piston chamber 79 when the free piston 378 is in the rear end position. The front end portion 384b ′ may be opened to the annular space 378a when the piston 378 is at the front end position. For example, the inner surface facing the front end of the annular space 378a so as to form the opening 386 (in the drawing, Other means such as a notch 387 may be provided around the rod 376 on the left-facing inner surface.
In this modification, the small hole 376a on the rear end side of the rod 376 is omitted.

According to the above modification, the gap 385 formed by the small diameter portion 384 is closed immediately before the free piston 378 reaches the front end position as in the third embodiment, and the hydraulic oil a1 is supplied only from the small hole 376a. Therefore, as shown in FIG. 4C, the transition from the intermediate relief pressure Pr3 to the high pressure relief pressure Pr2 becomes smoother.
Moreover, since the rod through hole 76h and the rear chamber 79a can be kept in communication with each other through the opening 386 at the front end position of the free piston 378, the free piston 378 can be moved without the small hole 376a on the rear end side of the rod 376. In addition to being able to set the high pressure relief pressure state by pressing to the front end position, there is no hindrance when the free piston 378 moves from the front end position to the rear end position side. In this modification, the small hole 376a may be omitted. Becomes easier.

  A travel unit brake valve relief valve according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a longitudinal sectional view schematically showing an essential part of the relief valve for the traveling unit brake valve of the present embodiment corresponding to the portion A in FIG. 11, and FIG. 12 is similar to the relief valve 70R in FIG. The relief valve 470R arranged on the middle right side is illustrated.

The present embodiment is the same as any one of the first to third embodiments except that a return channel that connects the rear chamber 79a and the front chamber 79b of the free piston chamber 79 is provided, and FIG. 9 is different. It is explanatory drawing which shows only a point.
The free piston 478 of the relief valve 470R of this embodiment has a single free piston chamber communication hole 490 that forms a return channel by communicating the rear chamber 79a and the front chamber 79b of the free piston chamber 79 in the axial direction of the rod 476. Alternatively, a plurality of free piston chamber communication holes 490 have orifice portions 490c.

The free piston chamber communication hole 490 has a rear end opening 490a (right end in FIG. 9) in a position closed by a rear wall 79c of the rear chamber 79a of the free piston chamber 79 when the free piston 478 is in the rear end position. The front end opening 490b (left end in FIG. 9) is in a position closed by the front wall surface 79d of the front chamber 79b of the free piston chamber 79 when the free piston 478 is in the front end position (left end position in FIG. 9).
One or a plurality of free piston chamber communication holes 490, orifice portions 490c, and the like are appropriately set so as to obtain a flow rate and a throttling effect required as the escape flow path. It is also possible to omit providing the special orifice portion 490c by setting the free piston chamber communication hole 490 itself so as to exhibit a predetermined orifice effect.

Since the present embodiment is configured as described above, the following operational effects can be obtained in addition to the operational effects of the first to third embodiments.
That is, since a return channel that connects the rear chamber 79a and the front chamber 79b is formed, when the free piston 478 moves from the rear end position to the front end position, one of the hydraulic oils fed into the rear chamber 79a. The part a3 flows from the rear chamber 79a to the front chamber 79b.

  Therefore, the movement time from when the free piston 478 is at the rear end position until it reaches the front end position, that is, the relatively low low pressure relief pressure Pr1 and intermediate relief pressure Pr3 before the relief valve reaches the high pressure relief pressure Pr2. Since the shockless time during which the overload pressure can be released can be extended, the overload pressure can be sufficiently released, and then the high pressure relief pressure Pr2 set for the steady braking force and stop force Therefore, it is possible to further prevent the occurrence of impact and vibration during the transition to the high-pressure relief pressure Pr2.

Moreover, since the escape passage by the free piston chamber communication hole 490 is closed at the front end position of the free piston 478, the setting and operation of the high pressure relief is not impaired.
Further, since the escape passage by the free piston chamber communication hole 490 is also closed at the rear end position of the free piston 478, the front chamber 79b side of the free piston chamber 79 can be maintained at a higher pressure than the rear chamber 79a side during normal operation. There is no loss of maintaining the free piston 478 at the rear end position.
Accordingly, there is no oil leakage from the free piston chamber 79, and the locking performance for preventing drift on a slope when the vehicle is stopped is not impaired.

  In addition, the return flow path that connects the rear chamber 79a and the front chamber 79b is not limited to the free piston chamber communication hole 490 of the free piston 478 as shown in the figure, and other modes, for example, an axial direction provided on the surface of the rod 467 It may be configured by using a longitudinal notch, a spiral groove, or the like extending in the direction, and may be used as appropriate in combination with the first, second, and third embodiments.

  The present invention has been described with reference to the illustrated embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications may be made to the specific structure and configuration within the scope of the present invention. Nor.

  The travel unit brake valve relief valve of the present invention is effective not only as a travel unit but also as a relief valve for a brake valve of a hydraulic drive unit that is required to prevent the occurrence of shock or vibration during deceleration or stop, as with a travel unit. Available.

20 Hydraulic motor 30 Hydraulic source 40 Control valve 50 Brake valve 60 Counter balance valve 70R, 170R, 270R, 370R, 470R Relief valve 71 Cartridge 76, 176, 276, 376, 476 Rod 76a, 276a, 376a Small hole 76h Rod through hole 77 Stopper 78, 178, 278, 378, 478 Free piston 178a, 278a, 378a Annular space 178b, 278b, 378b Communication passage 178d, 278d, 378d Inner peripheral surface 79 Free piston chamber 79a Rear chamber 79b Front chamber 79c Rear wall 79d Front Wall surface 176a First small hole 176b Second small hole 280 Wedge-shaped notch 280a Communication hole 281 Opening portion 384 Small diameter portion 384a Communication hole 385 Gap portion 386 Opening portion 490 Free piston chamber communication hole 490c Orifice section

Claims (8)

A housing in which a fluid flow path and a valve seat are formed;
A poppet provided with a small hole penetrating from the front surface to the back surface and slidable in the axial direction in the housing;
A poppet spring that presses the poppet against the valve seat;
It has a through-hole penetrating from the front end to the rear end, and the outer peripheral surface of the front end portion is formed in an oil-tight and axially slidable manner in the cylindrical portion on the back of the poppet, and the rear end is a stopper at the rear portion of the casing A rod provided to be received by
A free piston that is externally fitted to the rear outer peripheral surface of the rod, is fitted to the inner peripheral surface of the housing, and is slidable between the rear end position and the front end position in an oil-tight manner in the axial direction;
A first space that is formed on the rear side of the free piston inside the housing and communicates with the through hole via a throttle portion;
An oil drain hole and a drain hole communicating path formed so as to communicate the second space between the poppet in the housing and the free piston to the downstream flow path when the overload pressure is released. ,
In a relief valve for a traveling unit brake valve comprising:
A relief valve for a travel unit brake valve, wherein the throttle portion reduces an opening degree while the free piston moves from a rear end position to a front end position.   The relief valve for a traveling unit brake valve according to claim 1, wherein the throttle portion is provided at a rear end portion of the rod at a position where the free piston is not blocked by the free piston even when the free piston is at a rear end position. A first hole communicating with the through hole and the first space; an annular space provided inside the free piston and surrounding the rod; and the annular space provided in the free piston and the first space A communication path that always communicates with the space, and the free piston opens in the annular space and communicates with the through-hole while the free piston moves in the front end direction by a predetermined distance from the rear end position of the free piston. A second hole provided in the rod at a position closed by the inner peripheral surface of the free piston after the free piston has moved by the predetermined distance until the front end position; Traveling unit brake valve relief valve, characterized in that it comprises.   3. The travel unit brake valve relief valve according to claim 2, wherein the second hole is a plurality of holes having different predetermined distances.   The relief valve for a traveling unit brake valve according to claim 1, wherein the throttle portion is provided at a rear end portion of the rod at a position where the free piston is not blocked by the free piston even when the free piston is at a rear end position. A hole communicating with the through-hole and the first space, and a rod extending in the axial direction to the rod and having a deep rear end communicating with the through-hole, so as to reduce the notch cross section shallower toward the front end. A wedge-shaped notch provided in the free piston, an annular space provided inside the free piston and surrounding the rod, and a communication path provided in the free piston and always communicating with the annular space and the first space. The wedge-shaped notch has a full axial length opening in the annular space when the free piston is at the rear end position, and the free piston is moved as the free piston moves in the front end direction. The rod is gradually covered by the inner peripheral surface from the rear end side, and when the free piston is in the front end position, the rod is provided so that the entire surface is closed by the inner peripheral surface of the free piston. Relief valve for unit brake valve.   5. The relief valve for a traveling unit brake valve according to claim 4, wherein the wedge-shaped notch is entirely blocked by the inner peripheral surface of the free piston when the free piston is at its front end position without providing the hole. Instead, a relief valve for a traveling unit brake valve, characterized in that the front end of the wedge-shaped notch is open to the annular space.   The relief valve for a traveling unit brake valve according to claim 1, wherein the throttle portion is provided at a rear end portion of the rod at a position where the free piston is not blocked by the free piston even when the free piston is at a rear end position. A hole communicating with the through-hole and the first space; a small-diameter portion extending in the axial direction of the rod and having a communication hole communicating with the through-hole at a rear end portion; and provided inside the free piston, An annular space formed around the rod, and a communication path provided in the free piston and always communicating with the annular space and the first space. The small diameter portion has the free piston at a rear end position. In some cases, the entire length in the axial direction is opened in the annular space, and the free piston is gradually covered from the rear end side by the inner peripheral surface of the free piston as the free piston moves in the front end direction. Sometimes the traveling unit brake valve relief valve, characterized in that provided in the rod such entire surface is closed by the inner circumferential surface of the free piston.   The relief valve for a traveling unit brake valve according to claim 6, wherein the small-diameter portion is entirely blocked by the inner peripheral surface of the free piston when the free piston is at its front end position without providing the hole. Instead, a relief valve for a traveling unit brake valve, characterized in that the front end portion of the small diameter portion is open to the annular space.   The relief valve for a traveling unit brake valve according to any one of claims 1 to 7, further comprising a discharge channel that communicates the first space and the second space. A relief valve for a traveling unit brake valve, wherein the relief valve is configured to be closed when in a front end position and in a rear end position.

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