JP2002235702A - Pressure-compensating hydraulic circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable normal pressure compensation by allowing a main pressure to be stably assured even when load sensing is not performed to increase the controllability and responsiveness of a control valve controlled by the main pressure, and providing a function not affecting the main pressure when the load sensing is performed. SOLUTION: A pressure-compensating circuit comprises a bleed-off valve 4 for generating the main pressure based on a pilot pressure PLS for the bleed- off valve and an operating valve 11 capable of taking neutral, first, and second positions and connected to an actuator 19. When the operating valve 11 takes the first position, the actuator 19 is driven based on the main pressure, and the operating valve 11 provides the pilot pressure PLS for the bleed-off valve having a first value corresponding to a load pressure acting on the actuator 19 to the bleed-off valve 4. When the operating valve 11 takes the neutral or second position, the operating valve 11 provides the pilot pressure PLS for the bleed-off valve having a second value so that the main pressure is increased to a specified pressure even if the load pressure is not led into the bleed-off valve 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure compensation hydraulic circuit, and more particularly to a pressure compensation hydraulic circuit used for load sensing.

[0002]

2. Description of the Related Art A load sensing circuit for controlling the hydraulic pressure applied to an actuator based on the hydraulic pressure received by the actuator is used. FIG. 3 shows a known general load sensing circuit. The load sensing circuit 101 includes a hydraulic pressure source 102. The hydraulic pressure source 102 is connected to a bleed-off valve 104 via a pump pressure line 103. The hydraulic pressure source 102 generates hydraulic energy and applies a pump pressure to the load sensing circuit 101. The bleed-off valve 104 is connected to a drain line 105 and is connected to a main pressure line 106. The drain line 105 is connected to the tank 107,
The hydraulic pressure of the drain line 105 is substantially zero.

[0003] The bleed-off valve 104 has a pilot pressure line 108 and a spring 109. The pilot pressure line 108 supplies the bleed-off valve 104 with the pilot pressure _PLS for the bleed-off valve, which is the hydraulic pressure. The bleed-off valve 104 receives a force Fa acting on the bleed-off valve pilot pressure _PLS and the spring 109, and a force Fb acting on the pump pressure. The bleed-off valve 104 is connected to the pump pressure line 103 at all times.
Are connected to the main pressure line 106. For this reason, the oil pressure in the pump pressure line 103 is substantially equal to the oil pressure in the main pressure line 106. The bleed-off valve 104 has a force Fa
If smaller (Fa <Fb), the pump pressure line 103 is connected to the drain line 105 to reduce the oil pressure in the pump pressure line 103 and the oil pressure in the main pressure line 106.

That is, the main pressure P applied to the main pressure line 106 by the bleed-off valve 104 is higher than the bleed-off valve pilot pressure P _LS by a predetermined oil pressure ΔP, and is represented by the following equation: P = P _LS + ΔP. The predetermined oil pressure ΔP is determined by the spring 109.

[0005] The main pressure line 106 is connected to a spool switching valve 111. Spool switching valve 111
Has four ports. The four ports are
They are connected to the main pressure line 106, the drain line 105, the line 112 and the line 113, respectively. Conduit 112
Is connected to the cylinder 119. The spool switching valve 111 can take three positions: a neutral position, a lowered position, and a raised position.

[0006] The pump pressure line 103 further includes a pressure reducing valve 12.
8 is connected. The pressure reducing valve 128 is connected to the pipe 129, and the pipe 129 is connected to the spool switching valve 111. The pressure reducing valve 128 disconnects the connection between the pump pressure line 103 and the line 129 when the oil pressure in the line 129 exceeds a predetermined pressure, and determines the upper limit of the oil pressure in the line 129. The pipe 129 is connected to the spool switching valve 111 via an electromagnetic proportional pressure reducing valve. Electromagnetic proportional pressure reducing valve
Current is supplied by the operation of the operator, it gives the spool switching valve 111 to depressurize the hydraulic and is operated pilot pressure P _p of the conduit 129 to the hydraulic proportional to the current. The spool switching valve 111 switches between three positions according to the hydraulic pressure given from the electromagnetic proportional pressure reducing valve.

[0007] The line 113 is connected to the shuttle valve 121. Shuttle valve 121 is connected to line 122 and to line 123. The line 122 is connected to a switching valve (not shown) for operating another section. The shuttle valve 121 connects the pipe line 123 or the pipe line 122 with the higher hydraulic pressure to the pipe line 123.

[0008] The conduit 123 is connected to a filter 124. The filter 124 is connected to the pipe 125. The filter 124 removes impurities mixed into the passing hydraulic oil. Line 125 is connected to orifice 12
6 is connected to the pilot pressure line 108.

The pilot pressure line 108 is connected to the relief valve 1
27. The relief valve 127 is connected to the drain line 105. The relief valve 127 connects the pilot pressure line 108 to the drain line 105 when the hydraulic pressure of the pilot pressure line 108 becomes a predetermined pressure or more,
The upper limit of the hydraulic pressure of pilot pressure line 108 is determined.

The spool switching valve 111 has a neutral position,
It can take three positions, a descending position and a rising position.
In the neutral position, line 112 is closed and main line 1
06 is closed and the line 113 is connected to the drain line 105. Therefore, the pilot pressure P _LS for the bleed-off valve is P _LS ≒ 0, and the main pressure is only a predetermined oil pressure ΔP. The operating pilot pressure _Pp also does not have a hydraulic pressure required to switch the spool switching valve 111. For this reason, even if the operator operates the spool switching valve 111, it does not immediately switch from the neutral position to another position, resulting in poor responsiveness.

In the raised position, the drain line 105 is closed, the main pressure line 106 is connected to the line 112 via the variable orifice 118, and the line 113 is connected to the line 112. At this time, the load pressure _{P C} of the conduit 112 conduit 1
13 given Puridoofu valve 104 as bleed-off valve for pilot pressure _{P LS} enters, bleed-off valve 10
4, the main pressure is the pilot pressure P for the pre-off valve
_LS (= _{P C)} is from only high boost predetermined hydraulic pressure [Delta] P. Spool switching valve 111 from main pressure line 106
, The flow rate determined by the opening area of the variable orifice 118 and the pressure difference (ＰΔP) before and after the orifice is supplied to the pipeline 112, and the cylinder 119 moves (rises).

In the lowered position, line 112 is connected to drain line 105 via variable orifice 117, main pressure line 106 is closed, and line 113 is connected to drain line 10
5 is connected. Therefore, as in the neutral position,
Even if the required main pressure is not raised and the operator operates the spool switching valve 111, the responsiveness is poor because the operator does not immediately switch from the lowered position to another position.

FIG. 4 shows a bleed-off valve 104 and a spool switching valve 111 in the load sensing circuit 101.
Are shown in detail. The bleed-off valve 104 and the spool switching valve 111 are provided in the main body 150. The main body 150 includes a spool chamber 151 having a cylindrical sliding surface. A spool 152 is provided in the spool chamber 151. The spool 152 is inscribed in the spool chamber 151 so as to be slidable in a direction parallel to the axial direction A. The bleed-off valve 104 includes a spool chamber 151 and a spool 152.

The spool 152 includes a spring-side portion 15.
3, a central portion 154, and a pressure chamber side portion 155. A spring chamber 156 is provided in the spring side portion 153. The spring 109 is provided in the spring chamber 156. Spring 109
Pushes the spool 152 in the axial direction A. The spring chamber 156 is connected to the pilot pressure line 108, and the spring chamber 153 has a pilot pressure P for the bleed-off valve.
_LS has joined. Pilot pressure P for bleed-off valve
_{The LS} pushes the spool 152 in the axial direction A.

The central section 154 includes a pump pressure line 103
And a connection chamber 158 connected to the drain conduit 105 is provided. The connection chamber 157 is further connected to the main pressure line 106. Between the connection room 157 and the connection room 158,
A variable orifice 159 is provided. The orifice area of the variable orifice 159 increases when the spool 152 moves in the direction opposite to the axial direction A, and
Move in the axial direction A and become smaller at the end.
And the connection chamber 158 are closed. The pressure chamber 161 is provided in the pressure chamber side portion 155. Inside the central portion 154 and the pressure chamber side portion 155, a flow passage hole 162 is provided along the axis of the spool 152. Channel hole 162
Connects the connection chamber 157 to the pressure chamber 161. The oil pressure in the pressure chamber 161 pushes the spool 152 in the direction opposite to the axial direction A.

When the combined force Fa of the force of the spring 109 in the spring chamber 156 pressing the spool 152 and the force of the bleed-off valve pilot pressure P _LS pressing the spool 152 is greater than the force Fb of the pressure in the pressure chamber 161 pressing the spool 152. (Fa> Fb), the spool 152 moves in the axial direction A, the variable orifice 159 closes, and the main pressure P increases. When Fa <Fb, the spool 152 moves in the direction opposite to the axial direction A, the variable orifice 159 opens, and the main pressure P decreases.

That is, the main pressure P applied to the main pressure line 106 by the bleed-off valve 104 is higher than the bleed-off valve pilot pressure P _LS by a predetermined oil pressure ΔP, and is expressed by the following equation: P = P _LS + ΔP. The predetermined oil pressure ΔP is determined by the pressure receiving area of the spring 109 and the spool 152. The bleed-off valve 104 shown in FIG. 4 is in a position where the connection chamber 157 is closed with the connection chamber 158 and the spool 152
Moves in the direction opposite to the axial direction A, the orifice area of the variable orifice 159 increases.

The main body 150 is further provided with a main spool chamber 171 having a cylindrical sliding surface. The main spool chamber 171 is provided with a main spool 172. The main spool 172 is inserted into the main spool chamber 171 so as to be slidable in a direction parallel to the axial direction B. The spool switching valve 111 is
It is composed of a main spool chamber 171 and a main spool 172.

Both ends of the main spool chamber 171 are closed by a cap 163 and a cap 166. The cap 163 forms a spring chamber 164.
A spring 165 is provided in the spring chamber 164. The spring 165 presses the main spool 172 in the direction opposite to the axial direction B. Spring chamber 164
Is connected to the line 12 via an electromagnetic proportional pressure reducing valve (not shown).
9 is connected. The electromagnetic proportional pressure reducing valve applies a hydraulic pressure to the spring chamber 164 based on the input current. The oil pressure in the spring chamber 164 pushes the main spool 172 in the direction opposite to the axial direction B.

The cap 166 forms a spring chamber 167. The spring chamber 167 has a spring 1
68 are provided. The spring 168 pushes the main spool 172 in the axial direction B. Spring room 1
67 is connected to the line 129 via an electromagnetic proportional pressure reducing valve (not shown). The electromagnetic proportional pressure reducing valve applies a hydraulic pressure to the spring chamber 167 based on the applied current.
The oil pressure in the spring chamber 167 pushes the main spool 172 in the axial direction B. The spool switching valve 111 shown in FIG. 4 is in the neutral position.

The main spool 172 has a first portion 17.
3, the second portion 174 and the third portion 175. The connection chamber 181 is provided in the first portion 173. The connection chamber 181 is connected to the main pressure line 106. The connection chamber 182 is provided in the second portion 174. The connection chamber 181 is connected to the connection chamber 182 via the variable orifice 118. Variable orifice 1
18 is closed in the neutral position and the main spool 172 is closed.
Moves in the axial direction B, the orifice area increases.

A connection chamber 183 is provided in the second portion 174. The connection chamber 183 is connected to the conduit 112. A connection chamber 184 is further provided in the third portion 175. The connection chamber 184 is connected to the drain line 105. The connection chamber 183 is connected to the connection chamber 184 via the variable orifice 117. Variable orifice 1
The main spool 172 is closed in the neutral position.
Moves in the direction opposite to the axial direction B, thereby increasing the orifice area.

A flow passage hole 188 is provided inside the second portion 174 and the third portion 175. Channel hole 188
Connects the connection chamber 182 to the connection chamber 184.

When the spool switching valve 111 is in the neutral position, the connection chamber 181 and the connection chamber 183 are closed,
The connection room 182 is connected to the connection room 184. Line 113
The pilot pressure P _LS for the bleed-off valve given to
P _LS ≒ 0. Pilot pressure P for bleed-off valve
_LS is line 113, shuttle valve 121, filter 12
4 and the bleed-off valve 10 via the orifice 126
4 is input. The bleed-off valve 104 generates only a predetermined oil pressure ΔP as a main pressure. Therefore, the operation pilot pressure P _p has no hydraulic pressure required in order to stroke the main spool 172, even worker operates the spool switching valves 111, immediately to another position from the neutral position Responsiveness is poor.

When the main spool 172 moves in the axial direction B from the neutral position, the spool switching valve 111 switches to the raised position. When the spool control valve 111 is raised position, the load pressure _{P C} of the connecting chamber 182 is connected to the connecting chamber 183 conduit 112 is being provided to the pipe 113.
The load pressure is the line 113, the shuttle valve 121, the filter 1
Bleed-off valve 1 via an orifice 126 and 24
04 is input as the bleed-off valve pilot pressure _PLS . Bleed-off valve 104 generates a high pressure of the main pressure by a predetermined pressure ΔP than the pilot pressure P _LS for bleed-off valve in response to the pilot pressure P _LS for bleed-off valve provided to the main pressure line 106. At this time, the operating pilot pressure P _p has sufficient hydraulic pressure to cause the main spool 172 to stroke, and switches from the raised position to another position immediately in response to the operator's operation. Can be.

When the main spool 172 moves from the neutral position in the direction opposite to the axial direction B, the spool switching valve 11
1 switches to the lowered position. Spool switching valve 111
Is in the lowered position, the hydraulic oil input from the conduit 112 to the connection chamber 183 is drained to the connection chamber 184 via the variable orifice 117, and the connection chamber 182 is connected to the connection chamber 184. The orifice area of the variable orifice 117 increases as the main spool 172 moves in the direction opposite to the axial direction B.

The pilot pressure P _LS for the bleed-off valve applied to the line 113 is P _LS ≒ 0. Pilot pressure for the bleed-off valve _{P LS} is conduit 113, shuttle valve 1
21, input to the bleed-off valve 104 via the filter 124 and the orifice 126. The bleed-off valve 104 supplies only a predetermined oil pressure ΔP to the main pressure line 106. Therefore, the operation pilot pressure P _p, as in the case of the neutral position, may not have the hydraulic pressure required in order to stroke the main spool 172, the solenoid proportional pressure reducing valves that provide pressure to the pressure chamber 164 However, there are problems such as poor response and insufficient opening of the variable orifice 117 even if a current is applied to the orifice.

There is known a dynamic signal type load sensing circuit in which the response of the load sensing circuit is improved. FIG. 5 shows a known dynamic signal type load sensing circuit. The dynamic signal type load sensing circuit 201 includes a hydraulic power source 202. The hydraulic pressure source 202 is connected to a bleed-off valve 204 via a pump pressure line 203. The hydraulic pressure source 202 generates hydraulic energy and applies a pump pressure to the pump pressure line 203. Bleed-off valve 204 is connected to drain line 205 and to main pressure line 206. The drain line 205 is connected to the tank 207, and the hydraulic pressure of the drain line 205 is substantially zero.

The bleed-off valve 204 has a pilot pressure line 208 and a spring 209. The pilot pressure line 208 supplies the bleed-off valve 204 with the pilot pressure _PLS for the bleed-off valve, which is the hydraulic pressure. The pump pressure line 203 is connected to the pilot pressure line 208 via an orifice 214. A pilot pressure line 208 is always operating oil through the orifice 214 is supplied To trickles, the pilot pressure P _LS for bleed-off valve is boosted. Bleed-off valve 20
4, a force Fa acting on the pilot pressure _PLS for the bleed-off valve and the spring 209 and a force Fb acting on the pump pressure are applied. Bleed-off valve 20
Numeral 4 always connects the pump pressure line 203 to the main pressure line 206. Therefore, the oil pressure in the pump pressure line 203 is substantially equal to the oil pressure in the main pressure line 206. When the force Fa is smaller than the force Fb (Fa
<Fb) The pump pressure line 203 is connected to the drain line 205 to reduce the oil pressure in the pump pressure line 203 and the main pressure line 206.

That is, the main pressure P applied to the main pressure line 206 by the bleed-off valve 204 is higher than the pilot pressure _PLS for the bleed-off valve by a predetermined oil pressure ΔP, and is expressed by the following equation: P = P _LS + ΔP. The predetermined oil pressure ΔP is determined by the spring 209.

The main pressure line 206 is connected to a spool switching valve 211. Spool switching valve 211
Has four ports, and the four ports are connected to the main pressure line 206, the drain line 205, the line 212, and the line 213, respectively. Line 212
It is connected to a cylinder 219. The spool switching valve 211 can take three positions: a neutral position, a lowered position, and a raised position.

The pump pressure line 203 further includes a pressure reducing valve 22.
8 is connected. The pressure reducing valve 228 is connected to the spool switching valve 211 via a pipe 229. The pressure reducing valve 228 cuts off the connection between the pump pressure line 203 and the line 229 when the oil pressure of the line 229 exceeds a predetermined pressure, and determines the upper limit of the oil pressure of the line 229. Pipe 229 is
It is connected to a spool switching valve 211 via an electromagnetic proportional pressure reducing valve. The electromagnetic proportional pressure reducing valve is supplied with a current by an operation of an operator, and supplies a hydraulic pressure proportional to the current to the line 229.
Was generated from the operation pilot pressure P _p is a hydraulic give the spool switching valve 211. Spool switching valve 2
11 is 3 based on the hydraulic pressure given from the electromagnetic proportional pressure reducing valve.
Switch positions.

The line 213 is connected to the shuttle valve 221. The shuttle valve 221 is connected to the pipe 222 and is connected to the pipe 223. The line 222 is connected to a switching valve (not shown) for operating another section. The shuttle valve 221 connects the pipe 213 or the pipe 222 with a higher hydraulic pressure to the pipe 223.

The pipe 223 is connected to the filter 224. Filter 224 is connected to conduit 225. The filter 224 removes impurities mixed into the passing hydraulic oil. The conduit 225 is connected to the orifice 22
6 to the pilot pressure line 208.

The pilot pressure line 208 is connected to the relief valve 2
27. The relief valve 227 is connected to the drain line 205. The relief valve 227 connects the pilot pressure line 208 to the drain line 205 when the oil pressure of the pilot pressure line 208 becomes a predetermined pressure or more,
The upper limit of the hydraulic pressure of pilot pressure line 208 is determined.

The spool switching valve 211 is in the neutral position,
It can take three positions, a descending position and a rising position.
In the neutral position, line 212 is closed and main line 2
06 is closed and line 213 is connected to drain line 205. At this time, the hydraulic pressure applied by the spool switching valve 211 to the bleed-off valve 204 is substantially zero. The pilot pressure P _LS for the bleed-off valve is
, The operating pilot pressure P _p has a sufficient oil pressure to switch the spool switching valve 211.
Therefore, the responsiveness is better than that of the conventional load sensing circuit.

In the lowered position, line 212 is connected to drain line 205 via variable orifice 217, main pressure line 206 is closed, and line 213 is connected to drain line 20.
5 is connected. At this time, the spool switching valve 211
There is hydraulic pressure applied to the bleed-off valve 204, but generally is 0, the pilot pressure P _LS for bleed-off valve is provided from the pump pressure line 203, the operation pilot pressure P _p is sufficient to switch the spool switching valve 211 With high hydraulic pressure. Therefore, the responsiveness is better than that of the conventional load sensing circuit.

In the raised position, the drain line 205 is closed, the main pressure line 206 is connected to the line 212 via the variable orifice 218, and the line 213 is connected to the line 212. At this time, the load pressure _{P C} of the conduit 212 conduit 2
13 given Puridoofu valve 204 as bleed-off valve for pilot pressure _{P LS} enters, bleed-off valve 20
4, the main pressure is the pilot pressure P for the pre-off valve
The pressure is increased by a predetermined oil pressure ΔP higher than _LS (= P _C ). From the main pressure line 206 to the spool switching valve 211
The main pressure input to the pipe line 21 is a flow rate determined by the opening area of the variable orifice 218 and the pressure difference before and after the orifice.
2 to move the cylinder 219.

The bleed-off valve 204 has a spool switching valve 21 as a pilot pressure _PLS for the bleed-off valve.
1 and a pump pressure line 203 are supplied with hydraulic pressure. Since the oil pressure supplied from the pump pressure line 203 is easily affected by the variation in the orifice diameter of the orifice 214, it is difficult to obtain a predetermined oil pressure.
Even if 14 is processed with high accuracy, it is difficult to stabilize due to a change in the temperature of the hydraulic oil.

As a result, the main pressure becomes unstable, and the controllability decreases. In the worst case, there is a possibility that the pilot pressure P _LS for the bleed-off valve rises at once to the relief pressure of the relief valve 227.

[0041]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pressure compensating hydraulic circuit having good operability and good controllability. Another object of the present invention is to provide a pressure-compensating hydraulic circuit that reliably executes load sensing and has good responsiveness. Still another object of the present invention is to provide a pressure compensation hydraulic circuit that stably secures the main pressure even when load sensing is not being performed.

[0042]

Means for solving the problem are described as follows. The technical items appearing in the expression are appended with numbers, symbols, etc. in parentheses (). The numbers, symbols, and the like are technical items that constitute at least one embodiment or a plurality of the embodiments of the present invention, in particular, the embodiments or the examples. Corresponds to the reference numerals, reference symbols, and the like assigned to the technical matters expressed in the drawings corresponding to the above. Such reference numbers and reference symbols clarify the correspondence and bridging between the technical matters described in the claims and the technical matters of the embodiments or examples. Such correspondence / bridge does not mean that the technical matters described in the claims are interpreted as being limited to the technical matters of the embodiments or the examples.

The pressure compensating hydraulic circuit according to the present invention has a bleed-off valve (4) for increasing the main pressure based on the bleed-off valve pilot pressure (P _LS ), and has a neutral position, a first position, and a second position. And an operating valve (11) connected to the actuator (19). When the operation valve (11) assumes the first position, the actuator (19) is driven based on the main pressure, and the load pressure (P _C ) acting on the actuator (19).
Is supplied to the bleed-off valve (4) as a first value bleed-off valve pilot pressure (P _LS ) by the operating valve (11). When the operation valve (11) assumes the neutral position or the second position, the load pressure (P _C ) is not applied to the bleed-off valve (4) as the pilot pressure (P _LS ) for the bleed-off valve by the operation valve (11). However, the operating valve (11) changes the pilot pressure (P _LS ) for the bleed-off valve of the second value to the bleed-off valve (4) so that the main pressure required to stroke the operating valve (11) is generated. Give to).

The bleed-off valve (4) gives a main pressure, which is higher than the bleed-off valve pilot pressure (P _LS ) by a predetermined pressure, to the operating valve (11). The pressure difference is controlled to be constant. The operation valve (11) is an actuator (19)
The actuator (19) is moved by supplying a working fluid to the actuator or by draining the working fluid in the actuator (19).

The operating valve (11) has an electromagnetic proportional pressure reducing valve. The bleed-off valve (4) supplies the main pressure as an operating pilot pressure to the electromagnetic proportional pressure reducing valve. The electromagnetic proportional pressure-reducing valve applies a hydraulic pressure that is substantially proportional to the input current to the operating valve (11) based on the operating pilot pressure supplied from the bleed-off valve (4). The position is switched to any of the first position, the second position, and the neutral position based on the oil pressure given from the pressure reducing valve. At this time, the operating pilot pressure is set so that the operating valve (11)
Has sufficient pressure to switch to either the position, the second position or the neutral position.

Based on the main pressure, an operating pilot pressure (P _p ) used to switch the operating valve (11) from the neutral position to either the first position or the second position is further generated. The maximum value of the operating pilot pressure (P _p ) is determined by the pressure reducing valve (28), and is substantially equal to the main pressure when the main pressure is lower than the maximum value. Therefore, it is preferable that the main pressure has a sufficient pressure to switch the operation valve (11) from the neutral position to either the first position or the second position. Such an operating pilot pressure (P _p ) improves the responsiveness of the hydraulic circuit.

The first value of the pilot pressure for the bleed-off valve is substantially equal to the load pressure. The operating valve (11) applies a bleed-off valve pilot pressure having a first value substantially equal to the load pressure to the bleed-off valve (4) when in the first position, and when in the neutral position or the second position. A second independent of the load pressure applied to the actuator to the bleed-off valve (4)
To give the pilot pressure for the bleed-off valve.

The operation valve (11) is a main spool (72)
And a main spool chamber (71). The main spool (72) has a first connection chamber (81) to which main pressure is applied together with the main spool chamber (71), and a second connection connected to the actuator (19). Chamber (83) and a third connection chamber (82) for providing pilot pressure for the bleed-off valve.
And a first orifice (18) and a second orifice (1
4). When the operation valve (11) assumes the first position, the second connection chamber (83) and the third connection chamber (82) are connected, and the load pressure acting on the actuator (19) is reduced to a first value. To the bleed-off valve (4) as pilot pressure for the bleed-off valve. Further, the first connection chamber (81) is connected to the second connection chamber (83) via the first orifice (18), and the pressure difference between the main pressure and the load pressure raised by the bleed-off valve (4). A working fluid having a flow rate determined by the opening area of the first orifice is supplied to the actuator (19).

When the operating valve (11) is in the neutral position or the second position, the first connection chamber (81) is in the second orifice (1).
The operation valve (11) is connected to the third connection chamber (82) via 4), and provides the bleed-off valve (4) with the second value of the pilot pressure for the bleed-off valve.

The relief valve (16) further includes a relief valve (16) in which the operation valve (11) is in the neutral position or the second position and the pilot pressure for the bleed-off valve of the second value is lower than a predetermined pressure. When the pressure is high, the working fluid transmitting the pilot pressure for the bleed-off valve is drained. The second value bleed-off valve pilot pressure has an upper limit.

The main spool (72), together with the main spool chamber (71), further forms a fourth connection chamber (84) connected to a drain pipe (5) connected to the tank (7) for draining a working fluid. The relief valve (16) is connected to the third connection chamber (82) and the fourth connection chamber (84) when the operation valve (11) assumes the neutral position or the second position,
Drain the working fluid when the pressure in the third connection chamber (82) is higher than a predetermined pressure, and do not drain the working fluid in the third connection chamber (82) when the operation valve (11) is in the first position. Is preferred.

The second connection chamber (83) is connected to the fourth connection chamber (84) when the operation valve (11) assumes the second position,
Preferably, the working fluid is drained from the actuator (19).

The working fluid transmitting the bleed-off valve pilot pressure is not drained when a current is input to the electromagnetic proportional pressure reducing valve, and the bleed-off valve pilot pressure is reduced when no current is input to the electromagnetic proportional pressure reducing valve. Solenoid valve for unloading (3
It is preferable that the method further includes 1).

The main pressure is provided between the bleed-off valve (4) and the operation valve (11) as an operation pilot pressure to the electromagnetic proportional pressure reducing valve when the main pressure is lower than another predetermined pressure. It is preferable to further include a pressure reducing valve (28) which reduces the main pressure to another predetermined pressure when the pressure is higher than another predetermined pressure, and supplies the main pressure to the electromagnetic proportional pressure reducing valve as an operating pilot pressure.

[0055]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pressure compensating hydraulic circuit according to the present invention will be described with reference to the drawings. The pressure compensating hydraulic circuit 1 includes a hydraulic pressure source 2 as shown in FIG. The hydraulic pressure source 2 is connected to a bleed-off valve 4 via a pump pressure line 3. The hydraulic pressure source 2 generates hydraulic energy and applies pump pressure to the pump pressure line 3. The bleed-off valve 4 is connected to a drain line 5 and to a main pressure line 6. The drain line 5 is connected to the tank 7, and the hydraulic pressure of the drain line 5 is substantially zero.

The bleed-off valve 4 is connected to the pilot pressure line 8
And a spring 9. Pilot pressure line 8
Is the pilot pressure P for the bleed-off valve
_LS is supplied to the bleed-off valve 4. A force Fa acting on the bleed-off valve pilot pressure _PLS and the spring 9 and a force Fb acting on the pump pressure are applied to the bleed-off valve 4. The bleed-off valve 4 always connects the pump pressure line 3 to the main pressure line 6. Therefore, the oil pressure in the pump pressure line 3 is substantially equal to the oil pressure in the main pressure line 6. The bleed-off valve 4 has a force Fa
When it is smaller (Fa <Fb), the pump pressure line 3 is connected to the drain line 5 to reduce the oil pressure in the pump pressure line 3 and the main pressure line 6.

That is, the bleed-off valve 4 is connected to the main pressure line 6
Is higher than the bleed-off valve pilot pressure P _LS by a predetermined oil pressure ΔP, and is expressed by the following equation: P = P _LS + ΔP. The predetermined oil pressure ΔP is determined by the spring 9.

The main pressure line 6 is provided with the spool switching valve 1
1 The spool switching valve 11 has four ports, and the four ports are connected to the main pressure line 6, the drain line 5, the line 12, and the line 13, respectively. The pipe 12 is connected to a cylinder 19. The spool switching valve 11 can take three positions: a neutral position, a lowered position, and a raised position.

The pump pressure line 3 is further connected to a pressure reducing valve 28. The pressure reducing valve 28 is connected to a pipe line 29. The pressure reducing valve 28 disconnects the pump pressure line 3 from the line 29 when the oil pressure in the line 29 becomes equal to or higher than a predetermined pressure, and determines the upper limit of the oil pressure in the line 29. This pressure reducing valve 2
8 does not have to be installed. The line 29 is connected to the spool switching valve 1 via an electromagnetic proportional pressure reducing valve (not shown).
1 An electric current is input to the electromagnetic proportional pressure reducing valve by an operation of an operator. The electromagnetic proportional pressure reducing valve is connected to line 29
Providing hydraulic pressure to the spool control valve 11 based on the operation pilot pressure P _p and the current is given hydraulic from. Hydraulic pressure applied to the spool control valve 11 is roughly proportional to the current, lower than the operation pilot pressure P _p. The spool switching valve 11 switches between three positions according to the hydraulic pressure applied from the electromagnetic proportional pressure reducing valve.

The line 13 is connected to a shuttle valve 21. Shuttle valve 21 is connected to line 22 and
3 is connected. The line 22 is connected to a switching valve (not shown) for operating another section.
The shuttle valve 21 connects the pipe line 23 or the pipe line 22 with the higher hydraulic pressure to the pipe line 23.

The pipe 23 is connected to a filter 24. The filter 24 is connected to the conduit 25.
The filter 24 removes impurities mixed into the passing hydraulic oil. The line 25 is connected to the pilot pressure line 8 via an orifice 26.

The pilot pressure line 8 is connected to a relief valve 27. The relief valve 27 is connected to the drain line 5. The relief valve 27 is connected to the pilot pressure line 8.
When the hydraulic pressure becomes equal to or higher than a predetermined pressure, the pilot pressure line 8 is connected to the drain line 5 to determine the upper limit of the hydraulic pressure of the pilot pressure line 8.

The pilot pressure line 8 is further connected to a solenoid valve 31 for unloading. The unloading solenoid valve 31 disconnects the connection between the pilot pressure line 8 and the drain line 5 as soon as a current is input to the electromagnetic proportional pressure reducing valve. By such a disconnection, at the moment when the spool switching valve 11 is switched from the neutral position to another position, the bleed-off valve pilot pressure P _LS is applied to the bleed-off valve 4 and the position of the spool switching valve 11 is changed to the electromagnetic proportional pressure reducing valve. Operating pilot pressure required to switch the pressure.

The solenoid valve 31 for unloading connects the pilot pressure line 8 and the drain line 5 without inputting the current when the current is not input to the proportional pressure reducing valve, and connects the pilot pressure for the bleed-off valve. P _LS is approximately 0
To reduce the main pressure to a predetermined oil pressure ΔP. This pressure reduction reduces the load on the hydraulic power source 2 and improves the fuel efficiency required for driving the pump. The unloading solenoid valve 31 does not have to be installed. When the unloading solenoid valve 31 is not installed, the spool switching valve 1 is connected to the electromagnetic proportional pressure reducing valve.
An operating pilot pressure necessary for switching the position of No. 1 is always given.

The spool switching valve 11 can take three positions: a neutral position, a raised position, and a lowered position. In the neutral position, the line 12 is closed, the main pressure line 6 is connected to the line 13 via an orifice 14 and the line 13 is connected to the drain line 5 via an orifice 15 and a relief valve 16. . The relief valve 16 is connected to the pipe 13
When the hydraulic pressure becomes equal to or higher than a predetermined pressure, the pipeline 13 is connected to the drain pipeline 5. The relief valve 16 prevents the pipeline 13 from becoming higher than a predetermined oil pressure.

At this time, the main pressure input from the main pressure line 6 to the spool switching valve 11
Bleed-off valve pilot pressure P
Given as _LS . Pilot pressure for the bleed-off valve _{P LS} shuttle valve 21 from the pipe 13, filter 24
And an orifice 26 to the bleed-off valve 4. Bleed-off valve 4 generates a high pressure of the main pressure by a predetermined pressure ΔP than the pilot pressure P _LS for bleed-off valve in response to the pilot pressure P _LS for bleed-off valve provided to the main pressure line 6. Further, the relief valve 16
Restricts the upper limit of the pressure increase of the pilot pressure _PLS for the bleed-off valve when the load pressure of the cylinder 19 is not guided to the pipeline 13. For this reason, the main pressure is prevented from increasing more than necessary.

As a result, even when the spool switching valve 11 is at the neutral position, the main pressure is increased and the operating pilot pressure _Pp is also increased. Therefore, the spool switching valve 11 can be operated with good responsiveness. Further, the pilot pressure P _LS for the bleed-off valve is
Because of the upper limit, the main pressure is prevented from being increased more than necessary.

In the lowered position, the line 12 is connected to the drain line 5 through a variable orifice 17 and the main pressure line 6
Is connected to the line 13 via the orifice 14 and the line 1
Reference numeral 3 is connected to the drain line 5 via an orifice 15 and a relief valve 16. The relief valve 16 connects the line 13 to the drain line 5 when the oil pressure in the line 13 becomes equal to or higher than a predetermined pressure.

At this time, the spool switching valve 11 drains the hydraulic oil from the pipe 12 through the variable orifice 17 to the drain pipe 5. The spool switching valve 11 further applies the main pressure input to the spool switching valve 11 from the main pressure line 6 to the line 13 via the orifice 14 in the same manner as in the neutral position. Given as _LS . The bleed-off valve pilot pressure P _LS is input to the bleed-off valve 4 from the pipe 13 via the shuttle valve 21, the filter 24, and the orifice 26. Bleed-off valve 4 generates a high pressure of the main pressure by a predetermined pressure ΔP than the pilot pressure P _LS for bleed-off valve in response to the pilot pressure P _LS for bleed-off valve provided to the main pressure line 6. Relief valve 16
Restricts the upper limit of the pressure increase of the bleed-off valve pilot pressure _PLS .

As a result, even when the spool switching valve 11 is at the lowered position, the main pressure is increased, and the operating pilot pressure _Pp is also increased. Therefore, the spool switching valve 11 can be operated with good responsiveness. Further, the pilot pressure P _LS for the bleed-off valve is
Because of the upper limit, the main pressure is prevented from being increased more than necessary.

In the raised position, the drain line 5 is closed,
The main pressure line 6 is connected to the line 12 via a variable orifice 18.
, And the pipe 12 is connected to the pipe 13. At this time, the load pressure in the pipe 12 is transferred from the pipe 13 to the shuttle valve 2.
1, a pilot pressure _PLS for the bleed-off valve is input to the bleed-off valve 4 via the filter 24 and the orifice 26. Bleed-off valve 4, it is boosted by a predetermined hydraulic ΔP than the pilot pressure P _LS for bleed-off valve main pressure in response to the pilot pressure P _LS for bleed-off valve.

The pilot pressure P _LS for the bleed-off valve applied to the bleed-off valve 4 is not increased from a pressure other than the load pressure of the cylinder 19. Therefore, the load sensing functions normally and the controllability is good.

FIG. 2 shows the bleed-off valve 4 and the spool switching valve 11 in detail. Bleed-off valve 4
The spool switching valve 11 is provided on the main body 50. The main body 50 includes a spool chamber 51 having a cylindrical sliding surface. The spool 5 is provided in the spool chamber 51.
2 are provided. The spool 52 is provided in the spool chamber 51.
Is inserted so as to slide in a direction parallel to the axial direction A. The bleed-off valve 4 includes a spool chamber 51 and a spool 52.

The spool 52 has a spring-side portion 53,
A central portion 54 and a pressure chamber side portion 55 are formed. A spring chamber 56 is provided in the spring side portion 53. The spring chamber 56 is provided with a spring 9. The spring 9 pushes the spool 52 in the axial direction A. The spring chamber 56 is connected to the pilot pressure line 8, and the bleed-off valve pilot pressure P _LS is applied to the spring chamber 56. The bleed-off valve pilot pressure P _LS is pushing the spool 52 in the axial direction A.

In the central portion 54, a connection chamber 57 connected to the pump pressure line 3 is provided, and a connection chamber 58 connected to the drain line 5 is provided. Connection room 57
Are further connected to the main pressure line 6. Connection room 5
A variable orifice 59 is interposed between 7 and the connection chamber 58. The orifice area of the variable orifice 59 is
When the spool 52 moves in the direction opposite to the axial direction A, the size increases, and when the spool 52 moves in the axial direction A, the size decreases. Finally, the connection chamber 57 and the connection chamber 58 are closed. The pressure chamber 61 is provided in the pressure chamber side portion 55. A spool 52 is provided inside the central portion 54 and the pressure chamber side portion 55.
The flow path hole 62 is provided along the axis of. Channel hole 62
Connects the connection chamber 57 to the pressure chamber 61. Pressure chamber 6
The first hydraulic pressure pushes the spool 52 in the direction opposite to the axial direction A.

The force by which the spring 9 in the spring chamber 56 presses the spool 52 and the pilot pressure P _LS for the bleed-off valve
Is greater than the force Fb for pushing the spool 52 when the hydraulic pressure in the pressure chamber 61 is greater than the force Fa for pushing the spool 52 (Fa>
Fb), the spool 52 moves in the axial direction A, the variable orifice 59 closes, and the main pressure P increases. When Fa <Fb, the spool 52 moves in the direction opposite to the axial direction A, the variable orifice 59 opens, and the main pressure P decreases.

That is, the bleed-off valve 4 is connected to the main pressure line 6
Is higher than the bleed-off valve pilot pressure P _LS by a predetermined oil pressure ΔP, and is expressed by the following equation: P = P _LS + ΔP. The predetermined oil pressure ΔP is determined by the pressure receiving area of the spring 9 and the spool 52. The bleed-off valve 4 shown in FIG. 2 is a position where the connection chamber 57 is closed with the connection chamber 58, and the orifice area of the variable orifice 59 is increased by the movement of the spool 52 in the direction opposite to the axial direction A. ,growing.

The main body 50 is further provided with a main spool chamber 71 having a cylindrical sliding surface. A main spool 72 is provided in the main spool chamber 71. The main spool 72 is inserted in the main spool chamber 71 so as to be slidable in a direction parallel to the axial direction B. The spool switching valve 11 includes a main spool chamber 71 and a main spool 72.

Both ends of the main spool chamber 71 are closed by a cap 63 and a cap 66. The cap 63 forms a spring chamber 64. A spring 65 is provided in the spring chamber 64. The spring 65 presses the main spool 72 in the direction opposite to the axial direction B. The spring chamber 64 is connected to the pipe line 29 via an electromagnetic proportional pressure reducing valve (not shown). The electromagnetic proportional pressure reducing valve applies a hydraulic pressure to the spring chamber 64 based on the applied current. The oil pressure in the spring chamber 64 pushes the main spool 72 in the direction opposite to the axial direction B.

The cap 66 forms a spring chamber 67. A spring 68 is provided in the spring chamber 67. The spring 68 includes a main spool 72
Is pushed in the axial direction B. The spring chamber 67 is connected to the pipe line 29 via an electromagnetic proportional pressure reducing valve (not shown). The electromagnetic proportional pressure reducing valve applies a hydraulic pressure to the spring chamber 67 based on the applied current. The hydraulic pressure in the spring chamber 67 pushes the main spool 72 in the axial direction B.
The spool switching valve 11 shown in FIG. 2 is in the neutral position.

The main spool 72 includes a first portion 73, a second portion 74, and a third portion 75.
A connection chamber 81 is provided in the first portion 73. The connection chamber 81 is connected to the main pressure line 6. Second part 7
4, a connection chamber 82 is provided. The connection room 81
The orifice 14 is connected to the connection chamber 82.
The orifice 14 is formed of a shallow and narrow groove formed in the main spool 72. The orifice 14 is closed when the main spool 72 moves in the axial direction B.

The connection chamber 81 is further connected to the connection chamber 82 via the variable orifice 18. The variable orifice 18 is closed at the neutral position, and the main spool 72 moves in the axial direction B to increase the orifice area.

The second section 74 is provided with a connection chamber 83. The connection chamber 83 is connected to the pipe 12. The third portion 75 is further provided with a connection chamber 84.
The connection chamber 84 is connected to the drain pipe 5. The connection chamber 83 is connected to the connection chamber 84 via the variable orifice 17. The variable orifice 17 is closed at the neutral position, and the main spool 72 moves in the direction opposite to the axial direction B, so that the orifice area increases.

Inside the third portion 75, a spool chamber 85 is provided.
Is provided. A flow path hole 91 is provided between the spool chamber 85 and the connection chamber 84. A valve body 86 is provided inside the spool chamber 85 so as to be slidable. A pressure chamber 88 is provided inside the second portion 74 of the main spool 72. The pressure chamber 88 is connected to the connection chamber 82 via the orifice 15. Spool room 8
A valve seat 87 is interposed and connected between the pressure chamber 5 and the pressure chamber 88. The spool chamber 85 is provided with a spring 89. The spring 89 presses the valve body 86 against the main spool 72 in the axial direction C.

The valve element 86 is pushed in the axial direction C to push the valve seat 87.
, The flow path between the pressure chamber 88 and the connection chamber 84 is closed. The passage hole 91 is connected to the connection chamber 84 in the neutral position.
And the main spool 72 is closed by moving in the axial direction B. When the passage hole 91 is connected to the connection chamber 84 and the oil pressure in the pressure chamber 88 exceeds a predetermined pressure, the valve element 86 moves in the opposite direction to the axial direction C, and the pressure chamber 8
8 is determined.

The spool switching valve 11 is in the neutral position
When the main pressure input from the main pressure line 6 to the connection chamber 81
Pressure through the orifice 14 and into the connection chamber 82
Pilot pressure P for dooff valve_LSConveyed as Yellowtail
Pilot pressure P for load-off valve _LSReplaces the orifice 15
The pressure is transmitted to the pressure chamber 88 through the pressure chamber 88. Transmitted to the pressure chamber 88
If the hydraulic pressure is higher than a predetermined pressure, the relief valve 16
Is opened and the hydraulic oil is drained to the connection chamber 84 and bleeds.
Pilot pressure P for off valve_LSIs decompressed. Breedo
Pilot pressure P for valve_LSIs the shuttle valve 2 from line 13
1, through filter 24 and orifice 26
Is input to the feed-off valve 4. Bleed-off valve 4
Pilot pressure P for load-off valve_LSIn response to
Pilot pressure P for valve_LSHigher pressure than predetermined oil pressure ΔP
Is generated and applied to the main pressure line 6.

As a result, even when the spool switching valve 11 is at the neutral position, the main pressure is increased, and the operating pilot pressure _Pp is also increased. Therefore, the spool switching valve 11 can be operated with good responsiveness. Further, the pilot pressure P _LS for the bleed-off valve is
Because of the upper limit, the main pressure is prevented from being increased more than necessary.

When the main spool 72 moves from the neutral position in the direction opposite to the axial direction B, the spool switching valve 11 switches to the lowered position. When the spool switching valve 11 is at the lowered position, as in the neutral position, the main pressure input from the main pressure line 6 to the connection chamber 81 passes through the orifice 14 and enters the connection chamber 82 for the bleed-off valve. It is transmitted as pilot pressure _PLS . The bleed-off valve pilot pressure P _LS is transmitted to the pressure chamber 88 via the orifice 15. If hydraulic pressure is pressure chamber 88 transmitted more than a predetermined pressure, hydraulic oil relief valve 16 is open is drained to the connection chamber 84, the pilot pressure P _LS for bleed-off valve is depressurized. The bleed-off valve pilot pressure P _LS is input to the bleed-off valve 4 from the pipe 13 via the shuttle valve 21, the filter 24 and the orifice 26. Bleed-off valve 4 generates a high pressure of the main pressure by a predetermined pressure ΔP than the pilot pressure P _LS for bleed-off valve in response to the pilot pressure P _LS for bleed-off valve provided to the main pressure line 6. From the pipe 12 to the connection chamber 83
Is drained to the connection chamber 84 via the variable orifice 17.

[0089] Consequently, even spool switching valve 11 is in the lowered position, the main pressure is boosted, the operation pilot pressure P _p is also boosted. Therefore, the spool switching valve 11 can be operated with good responsiveness. Further, the pilot pressure P _LS for the bleed-off valve is
Since the upper limit is provided, the main pressure is prevented from being increased more than necessary.

When the main spool 72 moves in the axial direction B from the neutral position, the spool switching valve 11 switches to the raised position. When the spool control valve 11 is raised position, the load pressure P _C enters the connecting chamber 82 from the connection chamber 83.
The load pressure that has entered the connection chamber 82 is supplied to the bleed-off valve 4 from the pipe 13 via the shuttle valve 21, the filter 24, and the orifice 26, and the bleed-off valve pilot pressure P _LS.
Is entered as Bleed-off valve 4 generates a high pressure of the main pressure by a predetermined pressure ΔP than the pilot pressure P _LS for bleed-off valve in response to the pilot pressure P _LS for bleed-off valve provided to the main pressure line 6. The flow rate determined by the opening area of the variable orifice 18 and the pressure difference before and after the orifice (predetermined oil pressure ΔP) is supplied to the pipe 12 by the main pressure input from the main pressure pipe 6 to the connection chamber 81 to move the cylinder 19. (To rise.

The pilot pressure P _LS for the bleed-off valve applied to the bleed-off valve 4 is not increased from a load other than the load pressure applied to the cylinder 19. For this reason, pressure compensation functions normally and controllability is good.

[0092]

The pressure-compensating hydraulic circuit according to the present invention can reliably execute pressure compensation by load sensing, and can stably maintain the main pressure even when load sensing is not being executed. it can. as a result,
Operability and responsiveness of the pressure compensation hydraulic circuit are further improved.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a pressure compensation hydraulic circuit according to the present invention.

FIG. 2 is a sectional view showing a bleed-off valve and a spool switching valve.

FIG. 3 is a hydraulic circuit diagram showing an embodiment of a known load sensing circuit.

FIG. 4 is a cross-sectional view showing a known bleed-off valve and a spool switching valve.

FIG. 5 is a hydraulic circuit diagram showing an embodiment of a known dynamic signal type load sensing circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Pressure compensation hydraulic circuit 2 ... Hydraulic source 3 ... Pump pressure line 4 ... Bleed-off valve 5 ... Drain line 6 ... Main pressure line 7 ... Tank 8 ... Pilot pressure line 9 ... Spring 11 ... Spool switching valve 12, 13, 22, 23, 25, 29 ... conduit 14, 15 ... orifice 16 ... relief valve 17, 18 ... variable orifice 19 ... cylinder 21 ... shuttle valve 24 ... filter 26 ... orifice 27 ... relief valve 28 ... pressure reducing valve 31 ... unloading Solenoid valve 50 ... Main body 51 ... Spool chamber 52 ... Spool 53 ... Spring side part 54 ... Central part 55 ... Pressure chamber side part 56 ... Spring chamber 57,58 ... Connection chamber 59 ... Variable orifice 61 ... Pressure chamber 62 ... Flow path Holes 63, 66 Cap 64, 67 Spring chamber 65, 68 Spring 71 In-spool chamber 72 ... Main spool 73 ... First part 74 ... Second part 75 ... Third part 81,82,83,84 ... Connection chamber 85 ... Spool chamber 86 ... Valve body 87 ... Valve seat 88 ... Pressure chamber 89 ... Spring 91: Channel hole

Claims (8)

[Claims] A bleed-off valve for increasing a main pressure based on a pilot pressure for a bleed-off valve, a neutral position, a first position and a second position,
An operating valve connected to an actuator, wherein when the operating valve assumes the first position, the load pressure acting on the actuator is a first value of the bleed-off valve pilot pressure as the pilot pressure. Guided to a bleed-off valve, the bleed-off valve increases the main pressure based on the bleed-off valve pilot pressure of the first value, and when the operating valve assumes the neutral position or the second position The operating valve applies a second value of the pilot pressure for the bleed-off valve to the bleed-off valve so that the main pressure is increased even if the load pressure is not guided to the bleed-off valve. Compensating hydraulic circuit. 2. The electromagnetic proportional pressure reducing valve according to claim 1, wherein the operation valve includes an electromagnetic proportional pressure reducing valve, and the bleed-off valve supplies the main pressure as the operating pilot pressure to the electromagnetic proportional pressure reducing valve. Based on the pilot pressure for operation given from the bleed-off valve, gives a hydraulic pressure proportional to the input current to the operating valve, the operating valve, the hydraulic pressure given from the electromagnetic proportional pressure reducing valve Is switched to any one of the first position, the second position, and the neutral position based on the operating pilot pressure, and the operating pilot pressure moves the operating valve to any one of the first position, the second position, and the neutral position. Pressure compensating hydraulic circuit with sufficient pressure to switch. 3. The control valve according to claim 2, wherein the operation valve has a main spool and a main spool chamber, and the main spool, together with the main spool chamber, a first connection chamber to which the main pressure is applied; A second connection chamber connected to an actuator, a third connection chamber for applying the bleed-off valve pilot pressure to the bleed-off valve, a first orifice, and a second orifice; In the first position, the second connection chamber and the third connection chamber are connected, and the load pressure acting on the actuator is set to the first value as the pilot pressure for the bleed-off valve, and A flow rate determined by a pressure difference between the main pressure and the load pressure, which is applied to an off valve and increased by the bleed off valve, and an opening area of the first orifice. When a fluid is supplied to the actuator, and the operation valve is in the neutral position or the second position, the first connection chamber is connected to the third connection chamber via the second orifice, A pressure compensating hydraulic circuit in which an operating valve applies the second value of the pilot pressure for the bleed-off valve to the bleed-off valve. 4. The relief valve according to claim 3, further comprising a relief valve, wherein the relief valve has the neutral position or the second position and the pilot pressure for the bleed-off valve having the second value is increased. A pressure compensating hydraulic circuit for draining a working fluid transmitting the bleed-off valve pilot pressure when the pressure is higher than a predetermined pressure. 5. The system according to claim 4, wherein the main spool, together with the main spool chamber, further forms a fourth connection chamber connected to a drain pipe connected to a tank. Is connected to the third connection chamber and the fourth connection chamber when the third position is in the neutral position or the second position.
A pressure compensating hydraulic circuit that drains the working fluid when the pressure in the connection chamber is higher than the predetermined pressure, and does not drain the working fluid in the third connection chamber when the operation valve assumes the first position. 6. The pressure according to claim 5, wherein the second connection chamber is connected to the fourth connection chamber when the operation valve takes the second position, and the second connection chamber drains a working fluid transmitting the load pressure. Compensating hydraulic circuit. 7. The electromagnetic pressure reducing valve according to claim 2, wherein the working fluid for transmitting the pilot pressure for the bleed-off valve is not drained when the current is input to the electromagnetic proportional pressure reducing valve. A pressure compensating hydraulic circuit further comprising an unloading solenoid valve that drains a working fluid that transmits the pilot pressure for the bleed-off valve when the current is not input to the proportional pressure reducing valve. 8. The method according to claim 2, wherein the main pressure is interposed between the bleed-off valve and the operation valve, and the main pressure is reduced when the main pressure is lower than another predetermined pressure. When the main pressure is higher than another predetermined pressure, the main pressure is reduced to the other predetermined pressure, and the electromagnetic proportional pressure reducing valve is provided as the operation pilot pressure. Pressure compensating hydraulic circuit further comprising a pressure reducing valve for supplying pressure to the hydraulic circuit.