JP6982517B2 - Fluid pressure controller - Google Patents

Description

The present invention relates to a fluid pressure control device.

In a high-altitude work vehicle, crane vehicle, etc., a hydraulic cylinder that raises and lowers the boom, a switching valve that controls the flow of hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder, and a hydraulic cylinder to prevent the boom from falling. A hydraulic circuit including a holding valve provided in a load-side pipeline connected to a bottom-side chamber is known (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2003-29409

However, in the hydraulic circuit described in Patent Document 1, for example, when the boom is lowered, the hose between the holding valve (load holding mechanism) and the switching valve (control valve) bursts, causing an oil leak. In some cases, the boom may drop sharply.

The present invention has been made in view of the above problems, and an object of the present invention is to prevent the actuator from suddenly operating when an oil leak occurs due to a hose bursting or the like.

The first invention is a fluid pressure control device, which is a control valve that controls the flow of working fluid from a fluid pressure supply source to an actuator, and a load on which a load pressure due to a load acts when the control valve is in a neutral position. When the side flow path and the control valve are in the neutral position, the pressures of the non-load side flow path and the load side flow path on which the load pressure does not act are detected, and the detected pressure drops below a predetermined pressure. In some cases, a flow path limiting device that reduces the opening area of the load side flow path is provided , and the flow path limiting device is provided in the load side flow path to allow the flow of working fluid from the control valve to the actuator. An operating check valve that allows or blocks the flow of working fluid from the actuator to the control valve according to the pressure of the non-load side flow path, the first pilot chamber on which the pressure of the non-load side flow path acts, and the load side flow path. It has a second pilot chamber on which pressure acts and a switching valve having a spool that operates based on the pressure in the first and second pilot chambers, the switching valve being the pressure acting on the second pilot chamber. When is above the specified pressure, the pressure in the non-load side flow path is guided to the operating check valve, and by opening the operating check valve, it is switched to the open position that allows the flow of working fluid from the actuator to the control valve. When the pressure acting on the second pilot chamber is less than the predetermined pressure, the flow path between the non-load side flow path and the operation check valve is cut off, and the operation check valve is closed to transfer from the actuator to the control valve. It is characterized by being switched to a closed position that blocks the flow of working fluid.

In the first invention, when the pressure acting on the load-side flow path drops below a predetermined pressure, the opening area of the load-side flow path is reduced and the flow of the working fluid toward the control valve is restricted. Further, when the pressure acting on the load-side flow path drops below a predetermined pressure, the operated check valve is closed, so that the operation of the actuator can be quickly restricted.

In the second invention, the spool has a first pressure receiving surface on which the pressure of the first pilot chamber acts, and a second pressure receiving surface on which the pressure of the second pilot chamber acts, and the pressure receiving area of the second pressure receiving surface. However, it is characterized in that it is larger than the pressure receiving area of the first pressure receiving surface.

In the second invention, the control valve is switched to operate the actuator, and it is possible to prevent the switching valve from being switched to the closed position when the pressure in the non-load side flow path rises.

A third invention is a fluid pressure control device, which is a control valve that controls the flow of working fluid from a fluid pressure supply source to an actuator, and a load on which a load pressure due to a load acts when the control valve is in a neutral position. When the side flow path, the non-load side flow path that communicates with the tank and the load pressure does not act when the control valve is in the neutral position, and the load side flow path are detected, the detected pressure is predetermined. The flow path limiting device includes a flow path limiting device that reduces the opening area of the load side flow path when the pressure drops below the pressure, and the flow path limiting device includes a load holding mechanism that holds the load pressure acting on the actuator and a load holding mechanism. It has a pressure sensor that detects the pressure in the load side flow path between the control valve and the control valve, and a valve control device that controls the control valve. A load holding mechanism is provided in the load side flow path to provide a non-load side flow. A counter balance valve and a counter that shut off the load side flow path when the road pressure is less than the predetermined set pressure and open the load side flow path when the pressure of the non-load side flow path exceeds the set pressure. It has a check valve, which is provided in parallel with the balance valve and allows only the flow of working fluid from the control valve to the load side pressure chamber of the actuator, and the valve control device is the load side flow path detected by the pressure sensor. It is characterized in that the control valve is controlled to return to the neutral position when the pressure drops below a predetermined pressure.

In the third invention, when the control valve is switched and the actuator is operating, when the pressure acting on the load side flow path between the load holding mechanism and the control valve drops below a predetermined pressure, the control valve is operated. Since the pressure in the non-load side flow path drops after returning to the neutral position, the flow of the working fluid toward the control valve can be restricted by closing the load side flow path with the counterbalance valve.

According to the present invention, it is possible to prevent the actuator from suddenly operating when an oil leak occurs due to a hose bursting or the like.

It is a figure which shows the structure of the fluid pressure control apparatus which concerns on 1st Embodiment of this invention. It is a partially broken sectional view of a valve unit. FIG. 3 is an enlarged view of Part III of FIG. It is a figure which shows the structure of the fluid pressure control apparatus which concerns on 2nd Embodiment of this invention.

<First Embodiment>
The fluid pressure control device according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 3. The fluid pressure control device controls the operation of hydraulic work machines such as cranes and aerial work platforms. In the first embodiment, the cylinder 2 that drives the boom (load) 1 of the crane shown in FIG. 1 A hydraulic control device that controls expansion and contraction operation will be described.

The crane includes a boom 1 undulatingly attached to a swivel body (not shown), and a cylinder 2 which is a hydraulic actuator for undulating the boom 1.

The cylinder 2 is connected to a cylindrical cylinder tube 2c, a piston 2d that is slidably inserted into the cylinder tube 2c and divides the inside of the cylinder tube 2c into a rod side chamber 2a and an anti-rod side chamber 2b, and one end thereof is connected to the piston 2d. The other end side is provided with a rod 2e extending to the outside of the cylinder tube 2c and connected to the boom 1.

An engine (not shown) is mounted on the crane, and the power of the engine drives a pump 4 as a fluid pressure supply source and a pilot pump 5 as a pilot pressure supply source.

The hydraulic control device has a control valve 160 that controls the flow of hydraulic oil from the pump 4 to the cylinder 2, a pilot control valve 9 that controls the pilot pressure guided from the pilot pump 5 to the control valve 160, and a plurality of valves. The valve unit 150 is provided.

The control valve 160 and the rod side chamber 2a of the cylinder 2 are connected by a first main passage 7, and the control valve 160 and the anti-rod side chamber 2b of the cylinder 2 are connected by a second main passage 8. The valve unit 150 is interposed in the first main passage 7 and the second main passage 8.

The control valve 160 operates by the pilot pressure guided from the pilot pump 5 to the pilot chambers 161, 162 via the pilot control valve 9 as the crane operator manually operates the operating lever 10.

Specifically, when the pilot pressure is guided to the pilot chamber 161, the control valve 160 switches to the lowered position (L), and hydraulic oil is supplied from the pump 4 to the rod side chamber 2a through the first main passage 7. At the same time, the hydraulic oil in the anti-rod side chamber 2b is discharged to the tank T through the second main passage 8. As a result, the cylinder 2 contracts and the boom 1 rotates in the direction of lying down (boom lowering direction).

On the other hand, when the pilot pressure is guided to the pilot chamber 162, the control valve 160 switches to the raised position (U), and hydraulic oil is supplied from the pump 4 to the anti-rod side chamber 2b through the second main passage 8. , The hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7. As a result, the cylinder 2 is extended and rotated in the direction in which the boom 1 stands up (boom raising direction).

When the pilot pressure is not guided to the pilot chambers 161, 162, the control valve 160 is in the neutral position (N), and the supply and discharge of hydraulic oil to the cylinder 2 is cut off. At this time, the load of the cylinder 2 is held by the load holding mechanism 120 described later, so that the suspended load 3 and the boom 1 are prevented from descending due to their own weight, and the boom 1 is kept in a stopped state.

In this way, the control valve 160 has three positions: a lowering position (L) for contracting the cylinder 2, an raising position (U) for extending the cylinder 2, and a neutral position (N) for holding the load of the cylinder 2. It has, switches the supply and discharge of hydraulic oil to the cylinder 2, and controls the expansion and contraction operation of the cylinder 2.

When the control valve 160 is switched to the neutral position (N) with the suspended load 3 lifted and the movement of the boom 1 is stopped, the cylinder 2 contracts due to the weight of the suspended load 3 and the boom 1 and the like. The force of the action. As described above, in the cylinder 2 that drives the boom 1, the anti-rod side chamber 2b is a load side pressure chamber on which the load pressure acts when the control valve 160 is in the neutral position (N). That is, when the control valve 160 is in the neutral position (N), the second main passage 8 is the load side flow path on which the load pressure due to the load acts, and the first main passage 7 is the non-load on which the load pressure due to the load does not act. It becomes a side passage.

The valve unit 150 has a load holding mechanism 120 and a flow path limiting device 130. The load holding mechanism 120 is provided in the second main passage 8. The load holding mechanism 120 holds the load pressure acting on the anti-rod side chamber 2b when the control valve 160 is in the neutral position (N), and is fixed to the cylinder 2.

The load holding mechanism 120 has a counter balance valve 121 provided in the second main passage 8 and a check valve 122 provided in parallel with the counter balance valve 121.

The counter balance valve 121 is a valve that operates using the pressure in the first main passage 7, that is, the pressure in the rod side chamber 2a of the cylinder 2 as the pilot pressure, and has a pilot chamber 121b communicating with the first main passage 7. The counter balance valve 121 closes when the pressure in the rod side chamber 2a of the cylinder 2 is less than the set pressure Ps, and shuts off the second main passage 8. This prevents the hydraulic oil from being discharged from the anti-rod side chamber 2b of the cylinder 2. That is, the counter balance valve 121 holds the load pressure acting on the cylinder 2 and stops the operation of the boom 1 in the lodging direction.

The counter balance valve 121 opens when the pressure in the rod side chamber 2a of the cylinder 2 becomes equal to or higher than the set pressure Ps, and opens the second main passage 8. The counter balance valve 121 operates so that the opening degree increases as the pressure in the rod side chamber 2a of the cylinder 2 increases.

The set pressure Ps is predetermined by the return spring 121a. When the boom 1 is operated in the lodging direction, the set pressure Ps causes the boom 1 to operate in the lodging direction faster than the speed corresponding to the flow rate of the hydraulic oil supplied to the cylinder 2 due to the own weight of the boom 1. Is set to prevent.

The check valve 122 allows only the flow of hydraulic oil in the direction from the control valve 160 toward the counter rod side chamber 2b of the cylinder 2. That is, the check valve 122 blocks the flow of hydraulic oil in the direction from the counter-rod side chamber 2b of the cylinder 2 toward the control valve 160.

The flow path limiting device 130 includes an operating check valve 140 and a switching valve 110. The operation check valve 140 is provided between the load holding mechanism 120 and the control valve 160 in the second main passage 8. The operating check valve 140 allows the flow of hydraulic oil from the control valve 160 to the cylinder 2, and allows or shuts off the flow of hydraulic oil from the cylinder 2 to the control valve 160 according to the pressure in the first main passage 7.

The structure of the valve unit 150 will be described mainly with reference to FIGS. 2 and 3. As shown in FIGS. 1 and 2, the valve unit 150 includes a counter balance valve 121, a check valve 122, an operated check valve 140, a switching valve 110, and a valve body 151 for accommodating these valves. ..

As shown in FIGS. 1 and 3, the valve body 151 includes A port 150A and C port 150C connected to the control valve 160, B port 150B connected to the anti-rod side chamber 2b of the cylinder 2, and cylinder 2. It is provided with a D port 150D connected to the rod side chamber 2a. An in-valve passage 7a forming a part of the first main passage 7 is provided between the C port 150C and the D port 150D. An in-valve passage 8a forming a part of the second main passage 8 is provided between the A port 150A and the B port 150B.

Hereinafter, the structure of the flow path limiting device 130 according to the first embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3. In FIG. 2, the counter balance valve 121 and the check valve 122 constituting the load holding mechanism 120 are not shown.

The structure of the operation check valve 140 constituting the flow path limiting device 130 will be described. As shown in FIG. 2, the operated check valve 140 has a valve body 143 that opens and closes the valve inner passage 8a, a seat forming portion 144 that forms a seat portion 144a on which the valve body 143 sits, and a picture on the back surface of the valve body 143. It includes a formed back pressure chamber 145 and a push spring 147 arranged in the back pressure chamber 145. The valve body 143 is provided with a passage 143a that guides the hydraulic oil in the counter-rod side chamber 2b of the cylinder 2 to the back pressure chamber 145. The pressure of the back pressure chamber 145 and the elastic force of the push spring 147 act in the direction in which the valve body 143 is seated on the seat portion 144a.

The operated check valve 140 includes a piston 142 that separates the valve body 143 from the seat portion 144a against the urging force due to the pressure of the back pressure chamber 145 and the urging force due to the elastic force of the push spring 147, and the seat forming portion 144 and the piston. The communication chamber 148 defined between the communication chamber 148, the return spring 146 arranged in the communication chamber 148 and urging the piston 142 in the direction away from the valve body 143, and the piston 142 against the urging force of the return spring 146. Is further provided with a control pressure chamber 141, which urges the valve body 143 toward the valve body 143.

When the valve body 143 is seated on the seat portion 144a, the operated check valve 140 shuts off the flow of hydraulic oil from the counter rod side chamber 2b of the cylinder 2 to the control valve 160. When the valve body 143 is seated away from the seat portion 144a, the operated check valve 140 allows the flow of hydraulic oil from the counter-rod side chamber 2b of the cylinder 2 to the control valve 160.

The piston 142 is slidably inserted into the circular opening provided in the valve body 151 of the valve unit 150. The piston 142 has a small piston 142a that abuts on the valve body 143 and a large piston 142b that houses the base of the small piston 142a. The hydraulic oil from the first main passage 7 is supplied to the control pressure chamber 141 through the switching valve 110. When the urging force due to the pressure of the first main passage 7 acting on the control pressure chamber 141 becomes larger than the urging force due to the elastic force of the return spring 146, the piston 142 moves toward the valve body 143.

When the pressure of the first main passage 7 acting on the control pressure chamber 141 becomes larger than the predetermined pressure, the piston 142 presses the valve body 143, and the valve body 143 separates from the seat portion 144a. Here, the predetermined pressure at which the valve body 143 is seated is referred to as a seating pressure. The release pressure is set by the pressure of the back pressure chamber 145, the elastic force of the push spring 147, and the elastic force of the return spring 146.

The structure of the switching valve 110 constituting the flow path limiting device 130 will be described. The switching valve 110 is a pilot type switching valve that controls the opening and closing of the operating check valve 140 by controlling the pressure led to the control pressure chamber 141 of the operating check valve 140.

As shown in FIG. 3, the switching valve 110 has a spool 113 slidably accommodated in a sliding hole 159 formed in the valve body 151, and the pressure of the first main passage 7 closes the spool 113 in the valve closing direction. A first pilot chamber 111 acting as a pilot pressure urging the spool 113, a second pilot chamber 112 acting as a pilot pressure in which the pressure of the second main passage 8 urges the spool 113 in the valve opening direction, and a first pilot chamber. It has a spring 114 as an urging member that urges the spool 113 in the valve opening direction against the pressure of 111.

The spool 113 is a valve body that operates based on the pressure of the first pilot chamber 111 and the second pilot chamber 112. The spool 113 allows the flow of hydraulic oil from the first main passage 7 to the control pressure chamber 141 of the operating check valve 140 when the valve is opened, and allows the hydraulic oil to flow from the first main passage 7 to the operating check valve 140 when the valve is closed. The flow of hydraulic oil to the control pressure chamber 141 is blocked.

The spool 113 has a through hole 139a extending in the axial direction and a plurality of through holes 139b extending in the radial direction. One end of the through hole 139a is closed by the plug 113p, and the other end of the through hole 139a faces the first pilot chamber 111. One end of the through hole 139b faces the through hole 139a, and the other end of the through hole 139b faces the pilot passage 154, which is a flow path communicating with the control pressure chamber 141 of the operation check valve 140. That is, the through hole 139a and the through hole 139b function as a spool communication passage 139 that communicates the first pilot chamber 111 and the pilot passage 154.

The spool 113 includes a first land portion 131 that slides in the sliding hole 159, a second land portion 132, a third land portion 133, and a protruding portion 134 that projects axially from the first land portion 131. Has. The protrusion 134 is slidably accommodated in a small diameter opening between the first pilot chamber 111 and the sliding hole 159. Further, the spool 113 includes an annular groove 137 provided between the first land portion 131 and the second land portion 132, and an annular groove 138 provided between the second land portion 132 and the third land portion 133. Has. The through hole 139b is formed so as to open into the annular groove 138.

The outer diameter of the protruding portion 134 is smaller than that of the first land portion 131, and a stepped surface 135 is formed between the protruding portion 134 and the first land portion 131. When the spool 113 moves in the valve opening direction (to the right in the drawing) due to the pressure of the second pilot chamber 112 and the elastic force of the spring 114, the stepped surface 135 of the spool 113 extends from the first pilot chamber 111 to a small diameter opening. The movement is restricted by abutting on the stepped surface 156 formed between the portion and the sliding hole 159.

When the spool 113 moves in the valve closing direction (left direction in the drawing), the stepped surface 135 separates from the stepped surface 156. A drain chamber 158 is formed between the step surface 135 and the step surface 156. A drain passage 157 connected to the tank T is formed in the drain chamber 158. The drain passage 157 is connected to the tank T via the drain port 150DR (see FIG. 1) of the valve body 151. When the spool 113 moves in the valve opening direction (right direction in the drawing), the hydraulic oil is discharged to the tank T through the drain passage 157.

If the drain passage 157 is not provided in the pressure chamber formed between the step surface 135 and the step surface 156, the pressure in this pressure chamber acts to urge the spool 113 in the valve closing direction. Therefore, if the drain passage 157 is not provided, smooth movement of the spool 113 in the valve opening direction may be hindered. On the other hand, in the first embodiment, since the drain passage 157 is provided in the drain chamber 158, the spool 113 can smoothly move in the valve opening direction.

The first land portion 131 always cuts off the communication between the drain chamber 158 and the discharge passage 155 communicating with the second pilot chamber 112. The second land portion 132 and the annular groove 137 communicate or block the adjacent pilot passage 154 and the discharge passage 155.

When the pressure of the second pilot chamber 112 rises above a predetermined pressure and the spool 113 moves to the right in the figure and is located at the open position (O), the through hole 139b communicates with the pilot passage 154 and discharges from the pilot passage 154. Communication with the passage 155 is cut off by the second land portion 132. That is, when the spool 113 is in the open position (O), the control pressure chamber 141 and the first main passage 7 communicate with each other via the pilot passage 154 and the spool inner communication passage 139.

When the pressure of the second pilot chamber 112 drops below a predetermined pressure and the spool 113 moves to the left in the figure and is located at the closed position (C), the annular groove 138 formed at the open end of the through hole 139b becomes a valve. It is closed by the inner peripheral surface of the sliding hole 159 of the body 151. As a result, the communication between the pilot passage 154 and the in-spool communication passage 139 is cut off. At this time, the pilot passage 154 and the discharge passage 155 communicate with each other via the annular groove 137. That is, when the spool 113 is in the closed position (C), the control pressure chamber 141 and the second main passage 8 communicate with each other via the pilot passage 154 and the discharge passage 155, and the control pressure chamber 141 and the first main passage 7 are communicated with each other. Communication with is cut off.

The spool 113 has a first pressure receiving surface 113a on which the pressure of the first pilot chamber 111 acts, and a second pressure receiving surface 113b on which the pressure of the second pilot chamber 112 acts. The pressure receiving area S1 of the first pressure receiving surface 113a is represented by ^{S1 = π × (Da / 2) 2 when the diameter of the protruding portion 134 is Da.} The pressure receiving area S2 of the second pressure receiving surface 113b is represented by ^{S2 = π × (Db / 2) 2 when the diameter of the third land portion 133 is Db.} The pressure receiving area S2 of the second pressure receiving surface 113b is larger than the pressure receiving area S1 of the first pressure receiving surface 113a. In the pressure receiving areas S1 and S2, the switching valve 110 maintains the open position (O) when the control valve 160 is operated to the lowered position (L) and the discharge pressure of the pump 4 acts on the first pilot chamber 111. It is set so that it can be done. In other words, since the pressure receiving area S2 of the second pressure receiving surface 113b is larger than the pressure receiving area S1 of the first pressure receiving surface 113a, the control valve 160 is operated to the lowered position (L), and the discharge pressure of the pump 4 is the rod side chamber. It is possible to prevent the switching valve 110 from being switched to the closed position (C) when it acts on 2a.

As shown in FIG. 1, the switching valve 110 is switched between the open position (O) and the closed position (C). The switching valve 110 is switched to the open position (O) when the pressure acting on the second pilot chamber 112 is equal to or higher than the predetermined pressure P0, and when the pressure acting on the second pilot chamber 112 is less than the predetermined pressure P0. Is switched to the closed position (C). The predetermined pressure P0 is set in advance in order to detect whether or not an oil leak has occurred due to the hydraulic hose constituting the second main passage 8 connecting the valve unit 150 and the control valve 160 bursting or the like. Pressure.

That is, when the pressure acting on the second pilot chamber 112 is a predetermined pressure P0 or more, the switching valve 110 detects that no oil leak has occurred in the second main passage 8 and maintains the open position (O). .. On the other hand, when the pressure acting on the second pilot chamber 112 is less than the predetermined pressure P0, the switching valve 110 detects that an oil leak has occurred in the second main passage 8 and switches to the closed position (C). ..

The open position (O) is a switching position for guiding the pressure of the first main passage 7 to the control pressure chamber 141 of the operation check valve 140 and opening the operation check valve 140, that is, for separating the valve body 143 from the seat portion 144a. Is. Therefore, when the switching valve 110 is switched to the open position (O), the operating check valve 140 allows the flow of hydraulic oil from the cylinder 2 to the control valve 160.

The closed position (C) shuts off the flow path between the first main passage 7 and the control pressure chamber 141 of the operation check valve 140, closes the operation check valve 140, that is, seats the valve body 143 on the seat portion 144a. It is a switching position for. Therefore, when the switching valve 110 is switched to the closed position (C), the operating check valve 140 shuts off the flow of hydraulic oil from the cylinder 2 to the control valve 160.

The operation of the hydraulic control device according to the first embodiment will be described.

As shown in FIG. 1, when the control valve 160 is in the neutral position (N), the hydraulic oil discharged by the pump 4 is not supplied to the cylinder 2. At this time, since the pilot chamber 121b of the counter balance valve 121 has a tank pressure, the counter balance valve 121 is closed. That is, the load pressure acting on the cylinder 2 is held by the counter balance valve 121, and the boom 1 is stopped.

When the operation lever 10 is operated and the pilot pressure corresponding to the operation amount is guided from the pilot control valve 9 to the pilot chamber 161 of the control valve 160, the control valve 160 is lowered by the amount corresponding to the pilot pressure (L). Switch to. When the control valve 160 is switched to the lowered position (L), the discharge pressure of the pump 4 (that is, the pressure acting on the rod side chamber 2a) acts on the pilot chamber 121b of the counterbalance valve 121. When the pressure of the pilot chamber 121b becomes equal to or higher than the set pressure Ps, the counter balance valve 121 opens against the urging force of the return spring 121a.

At this time, the pressure of the first main passage 7 acting on the first pilot chamber 111 of the switching valve 110 is higher than the pressure of the second main passage 8 acting on the second pilot chamber 112. However, the pressure receiving area S1 of the first pressure receiving surface 113a of the spool 113 on which the pressure of the first pilot chamber 111 acts is larger than the pressure receiving area S2 of the second pressure receiving surface 113b of the spool 113 on which the pressure of the second pilot chamber 112 acts. Therefore, the switching valve 110 is maintained in the open position (O).

Therefore, when the control valve 160 is switched to the lowered position (L), the counter balance valve 121 and the operation check valve 140 are opened, and the counter balance valve 121, the operation check valve 140, and the control valve are opened from the counter rod side chamber 2b. The hydraulic oil is discharged to the tank T through 160. The hydraulic oil discharged from the pump 4 is supplied to the rod side chamber 2a, and the cylinder 2 contracts. As a result, the boom 1 rotates in the lodging direction.

When the operation lever 10 is operated and the pilot pressure corresponding to the operation amount is guided from the pilot control valve 9 to the pilot chamber 162 of the control valve 160, the control valve 160 moves to the raising position (U) by the amount corresponding to the pilot pressure. Switch to. When the control valve 160 is switched to the raised position (U), the hydraulic oil discharged from the pump 4 is supplied to the anti-rod side chamber 2b through the operation check valve 140 and the check valve 122, and the rod side chamber 2a The hydraulic oil of the above is discharged to the tank T, and the cylinder 2 is extended. As a result, the boom 1 rotates in the upright direction.

Next, when the control valve 160 is switched to the lowered position (L), the hydraulic hose constituting the second main passage 8 connecting the valve unit 150 and the control valve 160 bursts, and the second The operation when an oil leak occurs in the main passage 8 will be described. When the control valve 160 is switched to the lowered position (L), the hydraulic oil discharged from the anti-rod side chamber 2b is discharged to the tank T through the throttle 160a of the control valve 160. Therefore, the pressure of the second main passage 8 between the control valve 160 and the valve unit 150 is a pressure P1 which is several MPa higher than the tank pressure Pt. The predetermined pressure P0 is set to a value lower than this pressure P1 and higher than the tank pressure Pt (Pt <P0 <P1).

When the control valve 160 is switched to the lowered position (L), the hydraulic hose constituting the second main passage 8 connecting the valve unit 150 and the control valve 160 bursts, and the second main passage 8 is used. When an oil leak occurs in the switch valve 110, the pressure acting on the second pilot chamber 112 of the switching valve 110 decreases. When the pressure acting on the second pilot chamber 112 drops below the predetermined pressure P0, the switching valve 110 switches to the closed position (C). As a result, the control pressure chamber 141 of the operation check valve 140 communicates with the tank T, and the pressure in the control pressure chamber 141 decreases. As a result, the operation check valve 140 is closed, and the operation check valve 140 shuts off the flow path of the second main passage 8.

That is, according to the first embodiment, if an oil leak occurs in the second main passage 8 when the control valve 160 is switched to the lowered position (L), the pressure in the counter-rod side chamber 2b of the cylinder 2 is reached. Is held by the operating check valve 140, so that it is possible to prevent the cylinder 2 from suddenly contracting.

In the first embodiment, the operation check valve 140 is closed to stop the contraction operation of the cylinder 2 due to the oil leak. Therefore, when the pressure acting on the second main passage 8 drops below the predetermined pressure P0, the operation check valve 140 is closed, so that the operation of the cylinder 2 can be quickly restricted and stopped.

According to the first embodiment described above, the following effects are obtained.

The switching valve 110 functions as a pressure detecting device in which the second pilot chamber 112 is connected to the second main passage 8 between the load holding mechanism 120 and the control valve 160 and detects the pressure in the second main passage 8. When the pressure detected by the switching valve 110, that is, the pressure acting on the second pilot chamber 112 drops below a predetermined predetermined pressure P0, the switching valve 110 is switched to the closed position (C). When the switching valve 110 is switched to the closed position (C), the operating check valve 140 reduces the opening area of the second main passage 8, so that the flow of hydraulic oil toward the control valve 160 is restricted. In the first embodiment, the operation check valve 140 blocks the flow of hydraulic oil toward the control valve 160.

Therefore, in the present embodiment, when the control valve 160 is switched to the lowered position (L) and the boom 1 is tilted, the cylinder 2 suddenly moves when an oil leak occurs due to the hydraulic hose bursting or the like. It is possible to prevent the contraction operation.

<Second Embodiment>
The fluid pressure control device according to the second embodiment of the present invention will be described with reference to FIG. The fluid pressure control device controls the operation of hydraulic work machines such as cranes and aerial work platforms. In the second embodiment, the cylinder 2 that drives the boom (load) 1 of the crane shown in FIG. 4 A hydraulic control device that controls expansion and contraction operation will be described.

The crane includes a boom 1 undulatingly attached to a swivel body (not shown), and a cylinder 2 which is a hydraulic actuator for undulating the boom 1.

The cylinder 2 is connected to a cylindrical cylinder tube 2c, a piston 2d that is slidably inserted into the cylinder tube 2c and divides the inside of the cylinder tube 2c into a rod side chamber 2a and an anti-rod side chamber 2b, and one end thereof is connected to the piston 2d. The other end side is provided with a rod 2e extending to the outside of the cylinder tube 2c and connected to the boom 1.

An engine (not shown) is mounted on the crane, and the power of the engine drives the pump 4 as a fluid pressure supply source.

The hydraulic control device includes a control valve 260 for controlling the flow of hydraulic oil from the pump 4 to the cylinder 2, and a valve unit 250 having a plurality of valves.

The control valve 260 and the rod side chamber 2a of the cylinder 2 are connected by a first main passage 7, and the control valve 260 and the anti-rod side chamber 2b of the cylinder 2 are connected by a second main passage 8. The valve unit 250 is interposed in the first main passage 7 and the second main passage 8.

The control valve 260 operates based on an operation signal output from the controller 270 as a valve control device. When the crane operator manually operates the operation lever 10, the operation amount sensor 29 detects the operation direction and the operation amount of the operation lever 10, and the detection signal is output to the controller 270. The controller 270 outputs an operation signal to the control valve 260 based on the operation direction and the operation amount detected by the operation amount sensor 29.

Specifically, when an operation signal (excitation current according to the operation amount) is input to the solenoid 261, the control valve 260 switches to the lowered position (L), and the rod is switched from the pump 4 through the first main passage 7. The hydraulic oil is supplied to the side chamber 2a, and the hydraulic oil in the anti-rod side chamber 2b is discharged to the tank T through the second main passage 8. As a result, the cylinder 2 contracts and the boom 1 rotates in the direction of lying down (boom lowering direction).

On the other hand, when an operation signal (excitation current according to the operation amount) is input to the solenoid 262, the control valve 260 switches to the raised position (U), and the pump 4 passes through the second main passage 8 to the anti-rod side chamber 2b. The hydraulic oil is supplied to the tank T, and the hydraulic oil in the rod side chamber 2a is discharged to the tank T through the first main passage 7. As a result, the cylinder 2 is extended and rotated in the direction in which the boom 1 stands up (boom raising direction).

When the operation signal (excitation current according to the operation amount) is not guided to the solenoids 261,262, the control valve 260 is in the neutral position (N), and the supply and discharge of the hydraulic oil to the cylinder 2 is cut off. At this time, the load of the cylinder 2 is held by the load holding mechanism 120 described later, so that the suspended load 3 and the boom 1 are prevented from descending due to their own weight, and the boom 1 is kept in a stopped state.

As described above, the control valve 260 has three positions: a lowering position (L) for contracting the cylinder 2, an raising position (U) for extending the cylinder 2, and a neutral position (N) for holding the load of the cylinder 2. It has, switches the supply and discharge of hydraulic oil to the cylinder 2, and controls the expansion and contraction operation of the cylinder 2.

When the control valve 260 is switched to the neutral position (N) with the suspended load 3 lifted and the boom 1 stops moving, the cylinder 2 contracts due to the weight of the suspended load 3 and the boom 1 and the like. The force of the action. As described above, in the cylinder 2 that drives the boom 1, the anti-rod side chamber 2b becomes a load side pressure chamber on which the load pressure acts when the control valve 260 is in the neutral position (N). That is, when the control valve 260 is in the neutral position (N), the second main passage 8 is the load side passage on which the load pressure due to the load acts, and the first main passage 7 is the non-load on which the load pressure due to the load does not act. It becomes a side passage.

The valve unit 250 has a load holding mechanism 120. The load holding mechanism 120 is provided in the second main passage 8. The load holding mechanism 120 holds the load pressure acting on the anti-rod side chamber 2b when the control valve 260 is in the neutral position (N), and is fixed to the cylinder 2.

The load holding mechanism 120 has a counter balance valve 121 provided in the second main passage 8 and a check valve 122 provided in parallel with the counter balance valve 121.

The counter balance valve 121 is a valve that operates using the pressure in the first main passage 7, that is, the pressure in the rod side chamber 2a of the cylinder 2 as the pilot pressure, and has a pilot chamber 121b communicating with the first main passage 7. The counter balance valve 121 closes when the pressure in the rod side chamber 2a of the cylinder 2 is less than the set pressure Ps, and shuts off the second main passage 8. This prevents the hydraulic oil from being discharged from the anti-rod side chamber 2b of the cylinder 2. That is, the counter balance valve 121 holds the load pressure acting on the cylinder 2 and stops the operation of the boom 1 in the lodging direction.

The counter balance valve 121 opens when the pressure in the rod side chamber 2a of the cylinder 2 becomes equal to or higher than the set pressure Ps, and opens the second main passage 8. The counter balance valve 121 operates so that the opening degree increases as the pressure in the rod side chamber 2a of the cylinder 2 increases.

The set pressure Ps is predetermined by the return spring 121a. When the boom 1 is operated in the lodging direction, the set pressure Ps causes the boom 1 to operate in the lodging direction faster than the speed corresponding to the flow rate of the hydraulic oil supplied to the cylinder 2 due to the own weight of the boom 1. Is set to prevent.

The check valve 122 allows only the flow of hydraulic oil in the direction from the control valve 260 toward the counter-rod side chamber 2b of the cylinder 2. That is, the check valve 122 blocks the flow of hydraulic oil in the direction from the counter-rod side chamber 2b of the cylinder 2 toward the control valve 260.

The hydraulic control device according to the second embodiment includes a flow path limiting device 230 that controls the opening area of the second main passage 8 based on the pressure of the second main passage 8. In the flow path limiting device 230, the load holding mechanism 120, the pressure sensor 272 that detects the pressure in the second main passage 8 between the load holding mechanism 120 and the control valve 260, and the control valve 260 are in the lowered position (L). Controller 270 that controls the control valve 260 to return to the neutral position (N) when the pressure of the second main passage 8 detected by the pressure sensor 272 drops below the predetermined pressure P0 when the pressure is switched to. And a cutoff switch 271 controlled by the controller 270.

The controller 270 includes a CPU (Central Processing Unit) as an operating circuit, a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output interface (I / O interface), and a microcomputer equipped with other peripheral circuits. Will be done. The controller 270 can also be configured by a plurality of microcomputers.

As the operating circuit, an MPU (Micro Processing Unit), a DSP (Digital Signal Processor), an ASIC (application specific integrated circuit), an FPGA (Field Programmable Gate Array), or the like can be used instead of or together with the CPU. ..

The controller 270 determines whether or not the pressure in the second main passage 8 detected by the pressure sensor 272 is equal to or higher than the predetermined pressure P0. The predetermined pressure P0 is set in advance in order to determine whether or not an oil leak has occurred due to a rupture of the hydraulic hose constituting the second main passage 8 connecting the valve unit 250 and the control valve 260. Pressure is stored in a storage device such as ROM or RAM.

When the pressure of the second main passage 8 detected by the pressure sensor 272 is equal to or higher than the predetermined pressure P0, the controller 270 determines that no oil leakage has occurred, and outputs an ON signal (connection signal) to the cutoff switch 271. Output. When the on signal is input from the controller 270, the cutoff switch 271 switches to the on position (connection state) and connects the controller 270 and the solenoid 261.

When the pressure in the second main passage 8 detected by the pressure sensor 272 is less than the predetermined pressure P0, the controller 270 determines that an oil leak has occurred and outputs an off signal (cutoff signal) to the cutoff switch 271. .. When an off signal is input from the controller 270, the cutoff switch 271 switches to the off position (cutoff position) and cuts off the connection between the controller 270 and the solenoid 261. In the state where the controller 270 and the solenoid 261 are cut off by the cutoff switch 271, an exciting current corresponding to the operation amount is input to the solenoid 261 even when the operation lever 10 is operated in the boom tilting direction (downward direction). Not done.

The operation of the hydraulic control device according to the second embodiment will be described.

When the control valve 260 is in the neutral position (N), the hydraulic oil discharged by the pump 4 is not supplied to the cylinder 2. At this time, since the pilot chamber 121b of the counter balance valve 121 has a tank pressure, the counter balance valve 121 is closed. That is, the load pressure acting on the cylinder 2 is held by the counter balance valve 121, and the boom 1 is stopped.

When the operating lever 10 is operated and the exciting current corresponding to the operating amount is guided from the controller 270 to the solenoid 261 of the control valve 260, the control valve 260 switches to the lowered position (L) by the amount corresponding to the exciting current. .. When the control valve 260 is switched to the lowered position (L), the discharge pressure of the pump 4 (that is, the pressure acting on the rod side chamber 2a) acts on the pilot chamber 121b of the counterbalance valve 121. When the pressure of the pilot chamber 121b becomes equal to or higher than the set pressure Ps, the counter balance valve 121 opens against the urging force of the return spring 121a.

Therefore, when the control valve 260 is switched to the lowered position (L), the counter balance valve 121 opens, and the hydraulic oil is discharged from the counter rod side chamber 2b through the counter balance valve 121 and the control valve 260 to the tank T. Will be done. The hydraulic oil discharged from the pump 4 is supplied to the rod side chamber 2a, and the cylinder 2 contracts. As a result, the boom 1 rotates in the lodging direction.

When the operating lever 10 is operated and the exciting current corresponding to the operating amount is guided from the controller 270 to the solenoid 262 of the control valve 260, the control valve 260 switches to the raised position (U) by the amount corresponding to the exciting current. .. When the control valve 260 is switched to the raised position (U), the hydraulic oil discharged from the pump 4 is supplied to the anti-rod side chamber 2b through the check valve 122, and the hydraulic oil in the rod side chamber 2a is supplied to the tank T. The cylinder 2 is extended. As a result, the boom 1 rotates in the upright direction.

Next, when the control valve 260 is switched to the lowered position (L), the hydraulic hose constituting the second main passage 8 connecting the valve unit 250 and the control valve 260 bursts, and the second The operation when an oil leak occurs in the main passage 8 will be described. When the control valve 260 is switched to the lowered position (L), the hydraulic oil discharged from the anti-rod side chamber 2b is discharged to the tank T through the throttle 260a of the control valve 260. Therefore, the pressure of the second main passage 8 between the control valve 260 and the valve unit 250 is a pressure P1 which is several MPa higher than the tank pressure Pt. The predetermined pressure P0 is set to a value lower than this pressure P1 and higher than the tank pressure Pt (Pt <P0 <P1).

When the control valve 260 is switched to the lowered position (L), the hydraulic hose constituting the second main passage 8 connecting the valve unit 250 and the control valve 260 bursts, and the second main passage 8 is used. When an oil leak occurs in the pressure sensor 272, the pressure detected by the pressure sensor 272 decreases. When the pressure detected by the pressure sensor 272 drops to less than the predetermined pressure P0, an off signal (cutoff signal) is output from the controller 270 to the cutoff switch 271, and the excitation guided from the controller 270 to the solenoid 261 by the cutoff switch 271. The current is cut off. Therefore, the solenoid 261 is degaussed, and the control valve 260 switches from the lowered position (L) to the neutral position (N). As a result, the pressure of the first main passage 7 becomes the tank pressure, the counter balance valve 121 is closed, and the flow path of the second main passage 8 is shut off by the counter balance valve 121.

That is, according to the second embodiment, if an oil leak occurs in the second main passage 8 when the control valve 260 is switched to the lowered position (L), the pressure in the counter-rod side chamber 2b of the cylinder 2 is reached. Is held by the counter balance valve 121, so that it is possible to prevent the cylinder 2 from suddenly contracting.

According to the second embodiment described above, the following effects are obtained.

When the pressure detected by the pressure sensor 272 drops below a predetermined predetermined pressure P0, the control valve 260 is switched to the neutral position (N). When the control valve 260 is switched to the neutral position (N), the counterbalance valve 121 reduces the opening area of the second main passage 8, thus limiting the flow of hydraulic oil toward the control valve 260. In the second embodiment, the counterbalance valve 121 blocks the flow of hydraulic oil toward the control valve 260.

Therefore, in the present embodiment, when the control valve 260 is switched to the lowered position (L) and the boom 1 is tilted down, the cylinder 2 suddenly moves when an oil leak occurs due to the hydraulic hose bursting or the like. It is possible to prevent the contraction operation.

The following modifications are also within the scope of the present invention, and the configurations shown in the modifications may be combined with the configurations described in the above-described embodiments, or the configurations described in the above-mentioned different embodiments may be combined, and the following differences may occur. It is also possible to combine the configurations described in the modified example.

(Modification 1)
In the first embodiment, an example of closing the operation check valve 140 when an oil leak occurs due to a rupture of the hydraulic hose will be described, and in the second embodiment, the hydraulic hose will rupture or the like. An example of closing the counterbalance valve 121 when an oil leak occurs has been described, but the present invention is not limited thereto. For example, when an oil leak occurs, the opening area of the second main passage 8 may be reduced by using an electromagnetic variable throttle valve. At this time, the opening area does not need to be reduced to zero. By making the opening area smaller than the state during normal operation, it is possible to limit the sudden lodging operation of the boom 1.

(Modification 2)
In the above embodiment, an example in which the load holding mechanism 120 is composed of the counter balance valve 121 and the check valve 122 has been described, but the present invention is not limited thereto. For example, instead of the counter balance valve 121 and the check valve 122, the load holding mechanism may be configured by an operated check valve (pilot type check valve). When the load holding mechanism 120 of the second embodiment is configured by the operated check valve, the opening area of the second main passage 8 can be reduced by the operated check valve when an oil leak occurs.

(Modification 3)
In the second embodiment described above, an example in which the exciting current guided from the controller 270 to the solenoid 261 by the cutoff switch 271 is cut off has been described, but the present invention is not limited thereto. When the pressure detected by the pressure sensor 272 drops below the predetermined pressure P0, the exciting current output from the controller 270 to the solenoid 261 is set to a predetermined value (0 or standby current value) regardless of the operation amount of the operating lever 10. May be reduced to. In this case, the cutoff switch 271 can be omitted.

(Modification example 4)
In the second embodiment described above, an electromagnetic control valve 260 that switches based on an operation signal (excitation current) output from the controller 270 has been described as an example, but the present invention is not limited thereto. Instead of the electromagnetic control valve 260, a hydraulic pilot type control valve may be used. In this case, instead of the shutoff switch 271, a shutoff mechanism such as a shutoff valve that connects or shuts off the pilot oil passage connecting the pilot chamber of the hydraulic pilot type control valve and the pilot control valve based on the signal from the controller is provided. It may be provided.

(Modification 5)
In the above embodiment, an example of using the neutral free type control valves 160 and 260 in which both the rod side chamber 2a and the anti-rod side chamber 2b of the cylinder 2 are communicated to the tank T at the neutral position (N) has been described, but the present invention has been described. Not limited to this. At the neutral position (N), a neutral block type control valve that blocks the port connected to the rod side chamber 2a of the cylinder 2 and the port connected to the anti-rod side chamber 2b of the cylinder 2 may be adopted.

(Modification 6)
In the above embodiment, the hydraulic control device for controlling the expansion / contraction operation of the cylinder 2 for driving the boom 1 of the crane has been described as an example, but the present invention is not limited thereto. For example, the present invention may be applied to a hydraulic control device that controls an expansion / contraction operation of a cylinder that drives a boom of an aerial work platform. Further, the present invention may be applied to a hydraulic control device that controls the hoisting / lowering operation of the hydraulic motor of the hoisting device of a crane. That is, the actuator controlled by the hydraulic control device is not limited to the hydraulic cylinder.

(Modification 7)
In the above embodiment, the hydraulic control device that controls the operation of the actuator by the hydraulic oil has been described as an example, but the present invention is not limited thereto. The present invention can be applied to a fluid pressure control device that controls the operation of an actuator by various working fluids such as water.

Although the embodiments of the present invention have been described above, the above embodiments are only a part of the application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiments. No.

Hereinafter, the configurations, actions, and effects of the embodiments of the present invention will be collectively described.

The hydraulic control device is a fluid pressure control device that controls the operation of the cylinder 2 that drives the boom 1, and is a control valve 160, 260 that controls the flow of hydraulic oil from the pump 4 to the cylinder 2, and a control valve 160, The second main passage 8 on which the load pressure by the boom 1 acts when 260 is in the neutral position (N), and the first main where the load pressure does not act when the control valves 160 and 260 are in the neutral position (N). A flow path limiting device 130, which detects the pressure of the passage 7 and the second main passage 8 and reduces the opening area of the second main passage 8 when the detected pressure drops below a predetermined predetermined pressure P0. It is equipped with 230.

In this configuration, when the pressure acting on the second main passage 8 drops below the predetermined pressure P0, the opening area of the second main passage 8 decreases, and the flow of hydraulic oil toward the control valves 160 and 260 is restricted. Therefore, for example, when the control valves 160 and 260 are switched to the lowered position (L) and the boom 1 is tilted down, the cylinder 2 suddenly moves when an oil leak occurs due to the hydraulic hose bursting or the like. It is possible to prevent the contraction operation.

In the hydraulic control device, the flow path limiting device 130 is provided in the second main passage 8 to allow the flow of hydraulic oil from the control valve 160 to the cylinder 2, and from the cylinder 2 according to the pressure of the first main passage 7. The operation check valve 140 that allows or shuts off the flow of hydraulic oil to the control valve 160, the first pilot chamber 111 on which the pressure of the first main passage 7 acts, and the second pilot chamber on which the pressure of the second main passage 8 acts. It has a switching valve 110 having a spool 113 that operates based on the pressure of the first pilot chamber 111 and the second pilot chamber 112, and the pressure that the switching valve 110 acts on the second pilot chamber 112 is When the predetermined pressure is P0 or higher, the pressure of the first main passage 7 is guided to the operating check valve 140, and the operating check valve 140 is opened to allow the flow of hydraulic oil from the cylinder 2 to the control valve 160. When the pressure is switched to (O) and the pressure acting on the second pilot chamber 112 is less than the predetermined pressure P0, the flow path between the first main passage 7 and the operating check valve 140 is cut off, and the operating check valve 140 is blocked. By closing, the position is switched to the closed position (C) that shuts off the flow of hydraulic oil from the cylinder 2 to the control valve 160.

In this configuration, when the pressure acting on the second main passage 8 drops below the predetermined pressure P0, the operated check valve 140 is closed, so that the operation of the cylinder 2 can be quickly restricted.

In the hydraulic control device, the spool 113 has a first pressure receiving surface 113a on which the pressure of the first pilot chamber 111 acts, and a second pressure receiving surface 113b on which the pressure of the second pilot chamber 112 acts. The pressure receiving area S2 of the surface 113b is larger than the pressure receiving area S1 of the first pressure receiving surface 113a.

In this configuration, the control valve 160 is switched to operate the cylinder 2, and it is possible to prevent the switching valve 110 from being switched to the closed position (C) when the pressure in the first main passage 7 rises.

In the hydraulic control device, the flow path limiting device 230 detects the pressure in the second main passage 8 between the load holding mechanism 120 that holds the load pressure acting on the cylinder 2 and the load holding mechanism 120 and the control valve 260. When the pressure sensor 272 and the controller 270 for controlling the control valve 260 are provided, the load holding mechanism 120 is provided in the second main passage 8, and the pressure in the first main passage 7 is less than a predetermined set pressure Ps. , The counterbalance valve 121 that shuts off the second main passage 8 and opens the second main passage 8 when the pressure of the first main passage 7 becomes the set pressure Ps or more, and the counterbalance valve 121 are provided in parallel. It has a check valve 122 that allows only the flow of hydraulic oil from the control valve 260 to the anti-rod side chamber 2b of the cylinder 2, and the controller 270 determines the pressure of the second main passage 8 detected by the pressure sensor 272. When the pressure drops below P0, the control valve 260 is controlled to return to the neutral position (N).

In this configuration, when the control valve 260 is switched to the lowered position (L) and the cylinder 2 is contracted, the pressure acting on the second main passage 8 between the load holding mechanism 120 and the control valve 260 is applied. When the pressure drops below the predetermined pressure P0, the control valve 260 returns to the neutral position (N) and the pressure in the first main passage 7 drops. Therefore, the counterbalance valve 121 closes the second main passage 8 to the control valve 260. The flow of hydraulic fluid to go can be restricted.

1 ... Boom (load), 2 ... Cylinder (actuator), 4 ... Pump (fluid pressure supply source), 7 ... 1st main passage (non-load side flow path), 8 ... 2nd main passage (load side flow path), 110 ... switching valve, 111 ... 1st pilot chamber, 112 ... 2nd pilot chamber, 113 ... spool, 113a ... 1st pressure receiving surface , 113b ... Second pressure receiving surface, 120 ... Load holding mechanism, 121 ... Counter balance valve, 130, 230 ... Flow path limiting device, 140 ... Operated check valve, 154 ... Pilot Passage (flow path), 160, 260 ... Control valve, 270 ... Controller (valve control device), 272 ... Pressure sensor, S1, S2 ... Pressure receiving area

Claims (3)

A fluid pressure control device that controls the operation of the actuator that drives the load.
A control valve that controls the flow of working fluid from the fluid pressure supply source to the actuator,
When the control valve is in the neutral position, the load side flow path on which the load pressure due to the load acts, and
When the control valve is in the neutral position, the non-load side flow path on which the load pressure does not act and the flow path on the non-load side
A flow path limiting device that detects the pressure of the load-side flow path and reduces the opening area of the load-side flow path when the detected pressure drops below a predetermined pressure is provided .
The flow path limiting device is
Provided in the load side flow path, the flow of the working fluid from the control valve to the actuator is allowed, and the flow of the working fluid from the actuator to the control valve is allowed according to the pressure of the non-load side flow path. Or an operating check valve that shuts off,
Operates based on the pressures of the first pilot chamber on which the pressure of the non-load side flow path acts, the second pilot chamber on which the pressure of the load side flow path acts, and the pressures of the first pilot chamber and the second pilot chamber. With a switching valve, which has a spool,
The switching valve is
When the pressure acting on the second pilot chamber is equal to or higher than the predetermined pressure, the pressure in the non-load side flow path is guided to the operating check valve, and the operating check valve is opened to allow the actuator to control the valve. Switched to an open position that allows the flow of working fluid to
When the pressure acting on the second pilot chamber is less than the predetermined pressure, the flow path between the non-load side flow path and the operation check valve is cut off, and the operation check valve is closed. A fluid pressure control device characterized in that it can be switched to a closed position that blocks the flow of working fluid from the actuator to the control valve. In the fluid pressure control device according to claim 1,
The spool has a first pressure receiving surface on which the pressure of the first pilot chamber acts, and a second pressure receiving surface on which the pressure of the second pilot chamber acts.
A fluid pressure control device characterized in that the pressure receiving area of the second pressure receiving surface is larger than the pressure receiving area of the first pressure receiving surface. A fluid pressure control device that controls the operation of the actuator that drives the load.
A control valve that controls the flow of working fluid from the fluid pressure supply source to the actuator,
When the control valve is in the neutral position, the load side flow path on which the load pressure due to the load acts, and
When the control valve is in the neutral position, the non-load side flow path that communicates with the tank and does not act on the load pressure,
A flow path limiting device that detects the pressure of the load-side flow path and reduces the opening area of the load-side flow path when the detected pressure drops below a predetermined pressure is provided.
The flow path limiting device is
A load holding mechanism that holds the load pressure acting on the actuator,
A pressure sensor that detects the pressure in the load-side flow path between the load holding mechanism and the control valve, and
It has a valve control device that controls the control valve, and
The load holding mechanism is
When the pressure of the non-load side flow path provided in the load side flow path is less than a predetermined set pressure, the load side flow path is shut off and the pressure of the non-load side flow path becomes equal to or higher than the set pressure. A counterbalance valve that opens the load-side flow path when
It has a check valve provided in parallel with the counter balance valve and allowing only the flow of the working fluid from the control valve to the load side pressure chamber of the actuator.
The valve control device is characterized in that when the pressure of the load-side flow path detected by the pressure sensor drops below the predetermined pressure, the control valve is controlled to return to the neutral position. Pressure control device.

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