JP3703300B2 - Hydraulic control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control device used for a forklift or the like.
[0002]
[Prior art]
An example of a hydraulic control device used for a forklift is shown in FIG.
In the conventional hydraulic control apparatus shown in FIG. 3, electromagnetic pilot switching valves 1 and 2 for controlling the lift cylinder are connected in parallel to the control flow path 3. The control flow path 3 is connected to the pump P via the compensator valve 4. The compensator valve 4 is provided with first and second pilot chambers 4a and 4b at both ends of the spool, and a spring 4c is interposed in the first pilot chamber 4a.
In addition, an extra flow path 5 is connected to the compensator valve 4, and an electromagnetic pilot switching valve 6 that controls an actuator for attachment is connected to the surplus flow path 5. The surplus flow path 5 also communicates with the pump P via the compensator valve 4.
[0003]
However, according to the switching position of the compensator valve 4, the flow rate distributed to the control flow path 3 side and the flow flow allocated to the surplus flow path 5 side in the discharge amount of the pump P are determined.
The switching position of the compensator valve 4 is determined by the pressure action between the first and second pilot chambers 4a and 4b. The pilot pressure guided to the pilot chambers 4a and 4b will be described in detail later.
[0004]
A first pilot flow path 7 is connected to the upstream side of the compensator valve 4, and the first pilot flow path 7 is connected to the first pilot chamber 4 a of the compensator valve 4 via a flow control valve 8. are doing.
The flow control valve 8 includes first and second pilot chambers 8a and 8b, and a spring 8c on the first pilot chamber 8a side. A throttle 9 is provided on the downstream side of the flow control valve 8 as described above, the pressure on the downstream side of the throttle 9 is guided to the first pilot chamber 8a, and the pressure on the upstream side is guided to the second pilot chamber 8b. Yes.
Therefore, the flow control valve 8 exhibits a control function of keeping the differential pressure before and after the throttle 9 at a pressure corresponding to the spring force of the spring 8c and keeping the flow rate passing therethrough constant.
In the figure, reference numeral 10 denotes a damper orifice provided in a flow path leading to the second pilot chamber 8b.
[0005]
The downstream side of the flow control valve 8 is connected to the first pilot chamber 4 a of the compensator valve 4 via the first shuttle valve 11. Moreover, a relief valve 12 for setting pilot pressure is connected to the upstream side of the first shuttle valve 11.
The first shuttle valve 11 is connected to the second shuttle valve 13. The second shuttle valve 13 is connected to the actuator port side of the electromagnetic pilot switching valves 1 and 2. Therefore, the higher load pressure of the two switching valves 1 and 2 is selected by the second shuttle valve 13 and is set by the pressure selected by the second shuttle valve 13 and the relief valve 12. The higher pressure is selected by the first shuttle valve 11 and guided to the first pilot chamber 4 a of the compensator valve 4.
[0006]
On the other hand, the pressure on the upstream side of the electromagnetic pilot switching valves 1 and 2 is guided to the second pilot chamber 4 b of the compensator valve 4.
Therefore, the compensator valve 4 operates in a balance between the pressure upstream of the electromagnetic pilot switching valves 1 and 2 and the pilot pressure set by the relief valve 12, and the upstream of the switching valves 1 and 2. In some cases, the operation is performed with a balance between the pressure and the pressure on the downstream side.
[0007]
The pilot pressure generated as the set pressure of the relief valve 12 is supplied from the second pilot flow path 14 branched from between the flow control valve 8 and the first shuttle valve 11 to the pilot chambers of the switching valves 1, 2, 6. Led to. The electromagnetic pilot switching valves 1, 2, 6 further control the pilot pressure from the second pilot flow path 14 using the electromagnetic valve, and switch the pilot pressure proportional to the excitation current to the switching valves 1, 2, 6. It is made to act on the pilot room.
In the figure, reference numeral 15 is a main relief valve, 16 is a relief valve for an actuator connected to the excess flow path 5 side, and 17 is a damper orifice of a compensator valve.
[0008]
Next, the operation of this conventional hydraulic control device will be described.
When the electromagnetic pilot switching valves 1 and 2 are kept in the neutral position shown in the drawing, that is, when the pump P is driven, the pump discharge oil tends to flow to the control flow path 3 side. Therefore, no flow occurs in the control flow path 3. However, the pressure generated in the control flow path 3 acts on the second pilot chamber 4 b of the compensator valve 4.
Further, on the upstream side of the compensator valve 4, the discharge oil of the pump P passes through the flow rate control valve 8, so that a pilot pressure corresponding to the set pressure of the relief valve 12 is generated in the first pilot flow path 7. The pilot pressure generated in the first pilot flow path 7 is selected by the first shuttle valve 11 and guided to the first pilot chamber 4 a of the compensator valve 4.
[0009]
Therefore, the compensator valve 4 maintains a position where the acting force of the pilot pressure in the first pilot chamber 4a, the spring force of the spring 4c, and the acting force of the pilot pressure in the second pilot chamber 4b are balanced. However, in this case, the pilot pressure in the first pilot chamber 4 a is kept at a constant pressure set by the relief valve 12.
If the discharge pressure of the pump P rises from the above balance state, the acting force of the second pilot chamber 4b of the compensator valve 4 is overcome, so that the pump discharge oil is neutralized by the excess flow path 5 and the electromagnetic pilot switching valve 6. It is guided to the tank T through the flow path.
[0010]
Further, if any one of the electromagnetic switching valves 1 and 2, for example, the switching valve 1 is switched, the electromagnetic pilot switching valve 1 maintains a throttle opening corresponding to the switching amount. The upstream pressure of the throttle opening is led to the second pilot chamber 4 b of the compensator valve 4, and the downstream pressure is led to the first shuttle valve 11 via the second shuttle valve 13. When the load pressure of the actuator connected to the switching valve 1 becomes equal to or higher than the set pressure of the relief valve 12, the compensator valve 4 exhibits a load sensing function for this actuator. That is, the differential pressure before and after the throttle determined by the opening degree of the electromagnetic pilot switching valve 1 is controlled to be constant. Therefore, a constant flow rate is supplied to the actuator regardless of its load fluctuation.
[0011]
When both switching valves 1 and 2 are switched simultaneously, the compensator valve 4 is controlled by the higher load pressure among the actuators connected to the switching valves. However, at this time, only the flow rate supplied to the control flow path 3 is controlled, and the compensator valve 4 does not exhibit the load sensing function with respect to the actuator connected to each switching valve 1 or 2. If an actuator connected to both switching valves 1 and 2 is to exhibit the load sensing function, a compensator valve must be provided for each of both switching valves 1 and 2.
[0012]
Further, the surplus flow rate equal to or higher than the control flow rate supplied to the control flow path 3 is supplied from the surplus flow path 5 to the electromagnetic pilot switching valve 6 that controls the actuator for attachment. Therefore, the actuator for attachment can be operated with this excess flow rate.
The characteristic of the conventional hydraulic control apparatus as described above is that the pilot pressure for switching the electromagnetic pilot switching valves 1, 2, 6 can be stabilized. That is, the reason why the pilot pressure is stabilized is that the relief valve 12 functions based on the flow rate controlled to be constant by the flow rate control valve 8.
[0013]
[Problems to be solved by the invention]
The biggest drawback of the conventional apparatus as described above is that when the actuator connected to the control flow path 3 side and the actuator connected to the surplus flow path 5 side are simultaneously operated, the control flow path 3 side When the actuator reaches the stroke end, the pressure oil is not supplied to the excess flow path 5 side, and the reason is as follows.
When the actuator connected to the electromagnetic pilot switching valves 1 and 2 reaches the stroke end, the differential pressures before and after the switching valves 1 and 2 become equal. This equalized pressure acts on both pilot chambers 4a, 4b of the compensator valve 4. Therefore, the compensator valve 4 is completely switched to the left position in the drawing by the spring force of the spring 4c on the first pilot chamber 4a side.
[0014]
When the compensator valve 4 is switched to the left position as described above, the discharge oil of the pump P does not flow to the surplus flow path 5 side, so that the attachment for the attachment connected to the electromagnetic pilot switching valve 6 at that moment The actuator of this attachment suddenly stops, and thereafter, this actuator for attachment cannot be operated.
In this conventional apparatus, since the main relief valve 15 is directly connected to the pump on the upstream side of the compensator valve 4, the capacity of the main relief valve must be set to a large capacity according to the pump discharge amount.
An object of the present invention is to provide a hydraulic control device that can operate an actuator on an excess flow path side even when an actuator connected to the control flow path side reaches a stroke end.
[0015]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a pump, a compensator valve connected to the pump, a control flow path and an excess flow path connected to the compensator valve, a flow control valve connected in parallel to the compensator valve, and the flow control valve A relief valve for setting a pilot pressure provided on the downstream side, and a selection valve for selecting a set pressure of the relief valve and a load pressure of an actuator connected to the control flow path, and the pressure selected by the selection valve In a hydraulic control apparatus configured to guide the pressure upstream of the pilot switching valve to the first pilot chamber of the compensator valve, and to the load side of the pilot switching valve connected to the control flow path, It is characterized in that a main relief valve is provided between the shuttle valve.
The pilot switching valve may be a valve that directly leads the pilot pressure to the pilot chamber, or an electromagnetic pilot switching valve that is used by further controlling the pilot pressure guided to the pilot line.
[0016]
The second invention is characterized in that an orifice is provided on the upstream side of the main relief valve.
In the third invention, a pump port and a tank port are formed in the valve body. A compensator spool is incorporated into the valve body, and one end of the compensator spool faces the first pilot chamber with a spring interposed, and the other end of the compensator spool communicates with the pump port. The first pilot chamber is connected to the load side of the pilot switching valve connected to the control flow path via an orifice. In addition, a main relief valve is connected to the first pilot chamber. In addition, a flow control spool is incorporated in the compensator spool, and one end of the flow control spool is exposed to the first pilot chamber with the spring interposed therebetween, and the other end is exposed to the second pilot chamber connected to the pump port. The first pilot chamber of the flow control valve is connected to a relief valve that sets the pilot pressure.
The fourth invention is characterized in that a main relief valve is provided on the shaft extension line of the compensator spool.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
The circuit diagram shown in FIG. 1 is characterized in that a main relief valve 18 is connected between the first and second shuttle valves 11 and 13 and an orifice 19 is provided on the upstream side of the main relief valve 18. Have. Others are the same as the conventional example shown in FIG. In addition, the said 1st shuttle valve 11 comprises the selection valve of this invention.
[0018]
In the circuit diagram shown in FIG. 1, the main relief valve 18 is provided between the first and second shuttle valves 11 and 13 as described above, and the orifice 19 is provided upstream of the main relief valve 18. When the actuator connected to the pilot switching valve 1 or 2 reaches the stroke end, the pressure on the actuator side rises above the set pressure of the main relief valve 18. For this reason, the main relief valve 18 is opened, but the relief amount at this time is equal to or less than the flow rate controlled by the compensator valve 4 and is determined by the opening degree of the orifice 19.
[0019]
When the main relief valve 18 is opened as described above, a flow is generated in the orifice 19 and a differential pressure is generated before and after the orifice 19. Since this differential pressure appears in the first and second pilot chambers 4 a and 4 b of the compensator valve 4, the compensator valve 4 is switched according to the differential pressure and supplies the flow rate to the surplus flow path 5 side. On the other hand, in the conventional apparatus, when the actuator reaches the stroke end, the pressure oil is not supplied to the excess flow path 5 side. However, in this embodiment, such a situation does not occur.
[0020]
FIG. 2 shows a specific structure of the compensator valve 4, the flow control valve 8, the relief valves 12, 16 and the main relief valve 18 in the circuit shown in FIG.
In FIG. 2, the pump port 21 and the tank port 22 are formed in the valve body 20, and the control flow path 3 and the surplus flow path 5 are also formed.
The valve body 20 thus constructed incorporates the compensator spool 23 of the compensator valve 4. One end of the compensator spool 23 faces the first pilot chamber 4 a and the other end faces the second pilot chamber 4 b. ing. A spring 4c is interposed in the first pilot chamber 4a. The first pilot chamber 4 a is connected to the first shuttle valve 11 via a passage 24. In addition, although the orifice 25 is provided in the channel | path 24, this orifice 25 is equivalent to the orifice 19 in the circuit diagram of FIG.
[0021]
The main relief valve 18 is connected to the first pilot chamber 4a as described above. The configuration of the main relief valve 18 is as follows. That is, the relief body 26 is inserted on the axis extension line of the compensator spool 23. The relief body 26 has a plug 26b fitted into the main body 26a, and a sheet member 27 is crimped to the tip of the plug 26b.
A relief poppet 28 is incorporated in the relief body 26, and the spring force of a spring 29 is applied to the relief poppet 28. The relief poppet 28 is pressed against the seat 27 a of the seat member 27 by the spring force of the spring 29. Accordingly, when the pressure on the load side, which is the pressure on the upstream side of the first shuttle valve 11, becomes equal to or higher than the set pressure determined by the spring 29, the main relief valve 18 is opened.
[0022]
The set pressure of the main relief valve 18 is determined by the spring force of the spring 29 applied to the relief poppet 28. The spring force of the spring 29 is adjusted by an adjusting screw 26c provided on the plug 26b. ing.
When the relief poppet 28 is opened as described above, the hydraulic oil flowing out from the first pilot chamber 4a is returned from the tank port 22 to the tank T via the flow passage 26d formed in the main body 26a.
[0023]
The compensator spool 23 as described above is formed with an annular groove 30 that is always in communication with the pump port 21. When the compensator spool 23 is in the illustrated neutral position, the pump port 21 and the control flow path 3 communicate with each other through the annular groove 30. However, in this neutral position, the annular groove 30 is different from the surplus flow path 5 and the communication between the surplus flow path 5 and the control flow path 3 is blocked.
When the compensator spool 23 moves against the spring 4c, the amount of wrap between the annular groove 30 and the control flow path 3 decreases, and the annular groove 30 and the excess flow path 5 wrap. Since the annular groove 30 wraps in both the control flow path 3 and the surplus flow path 5 in this way, the pressure oil flowing in from the pump port 21 is controlled by the control flow path 3 and the surplus flow path according to the wrap amount. It is divided into five.
[0024]
The control flow path 3 communicates with the second pilot chamber 4 b of the compensator valve 4 via the damper orifice 17. Therefore, the discharge pressure of the pump P is guided to the second pilot chamber 4b, and the pressure selected by the first shuttle valve 11 is guided to the first pilot chamber 4a.
[0025]
The compensator spool 23 incorporates a flow rate control spool 31 of the flow rate control valve 8. The flow control spool 31 has one end facing the first pilot chamber 8a and the other end facing the second pilot chamber 8b. A spring 8c is interposed in the first pilot chamber 8a, and the pilot chamber 8a is connected to both the relief valve 12 for setting the pilot pressure and the first shuttle valve 11.
[0026]
An annular recess 32 is formed in the flow control spool 31 thus configured. The annular recess 32 determines the amount of lap with the control port 33 formed in the annular groove 30 of the compensator spool 23 in accordance with the amount of movement of the flow control spool 31. However, when the compensator spool 23 is in the illustrated normal position, the opening degree of the control port 33 with respect to the annular recess 32 is maximized. When the flow control spool 31 moves against the spring 8c, the amount of wrap between the annular recess 32 and the control port 33 decreases, and the relative opening of the control port 33 decreases.
In the flow rate control spool 31 as described above, a throttle 9 opened in the annular recess 32 is formed, and this throttle 9 is communicated with the first pilot chamber 8a. Therefore, the first pilot chamber 8 a communicates with the pump port 21 via the throttle 9 → the annular recess 32 → the control port 33.
[0027]
Next, the operation of the specific example of FIG. 2 will be described.
Now, when the pressure oil of the pump P flows from the pump port 21, the pressure at this time is guided to the second pilot chamber 4 b of the compensator valve 4 through the annular groove 30 → the control flow path 3 → the damper orifice 17.
Further, the pressure oil from the pump port 21 passes through the control port 33 → the annular recess 32 → the throttle 9 → the first pilot chamber 8 a → the first shuttle valve 11 → the orifice 25 → the passage 24, and the second pressure oil of the compensator valve 4. It is led to 1 pilot room 4a.
[0028]
Thus, in the process in which the pressure oil from the pump P passes through the flow control valve 8, the pressure upstream of the throttle 9 acts on the second pilot chamber 8 b via the damper orifice 10. However, if neither of the electromagnetic pilot switching valves 1 and 2 is switched at this time, the pressure in the first pilot chamber 8a rises to the set pressure of the relief valve 12 for setting the pilot pressure. Therefore, the relief valve 12 is opened, but this causes a flow in the throttle 9, and a differential pressure is generated before and after that. At this time, the pressure on the downstream side of the throttle 9 acts on the first pilot chamber 8a, and the pump pressure on the upstream side acts on the second pilot chamber 8b.
[0029]
When a pressure difference occurs between the pilot chambers 8a and 8b in this way, the flow control spool 31 of the flow control valve 8 balances where the differential pressure before and after the throttle 9 becomes constant. If the differential pressure across the throttle 9 is kept constant, the flow rate flowing therethrough will be constant. Therefore, the relief valve 12 for setting the pilot pressure keeps the pressure in the passage 24, that is, the pressure in the first pilot chamber 4 a of the compensator valve 4, while discharging the constant flow controlled by the flow control valve 8.
[0030]
On the other hand, the pump pressure from the pump port 21 is guided to the second pilot chamber 4 b of the compensator valve 4.
At this time, if the electromagnetic pilot switching valves 1 and 2 are in the neutral position shown in the figure, the control flow path 3 becomes dead end, so that the pump pressure increases. Due to the pressure action of the raised pump, the compensator spool 23 moves against the spring 4 c and balances at a position immediately before the annular groove 30 wraps in the surplus flow path 5. Thus, the state in which the annular groove 30 is balanced at the position immediately before wrapping in the surplus flow path 5 is the standby state of the compensator valve 4.
[0031]
In this standby state, if the discharge pressure of the pump P, that is, the pressure of the second pilot chamber 4b of the compensator valve 4 increases even slightly, the compensator spool 23 moves against the spring 4c. This is because the pressure on the first pilot chamber 4a side is maintained at a constant pressure set by the relief valve 12 regardless of the pump discharge pressure. If the compensator spool 23 moves further in this way, the annular groove 30 and the surplus flow path 5 are wrapped, and the flow rate distributed to the surplus flow path 5 side is determined by the amount of wrap at this time. However, if the pump discharge pressure rises steadily while keeping the electromagnetic pilot switching valves 1 and 2 in the neutral position, most of the discharge amount is supplied to the surplus flow path 5 side.
At this time, if the electromagnetic pilot switching valve 6 connected to the surplus flow path 5 is held in the illustrated neutral position, the pump discharge oil is returned to the tank T via the neutral flow path of the switching valve 6.
[0032]
Further, when the electromagnetic pilot switching valve 6 is switched while the electromagnetic pilot switching valves 1 and 2 are kept at the neutral positions as described above, the pump discharge rises according to the load pressure at this time. This increased pressure acts on the second pilot chamber 4 b of the compensator spool 4. On the other hand, a constant pilot pressure set by the relief valve 12 continues to act on the first pilot chamber 4a of the compensator valve 4.
Therefore, the compensator spool 23 moves against the spring 4c, and the amount of lap between the annular groove 30 and the surplus flow path 5 is maintained almost at the maximum. Since the wrap amount is sufficiently maintained in this way, sufficient pressure oil is supplied to the actuator connected to the electromagnetic pilot switching valve 6.
[0033]
Assume that, for example, only the electromagnetic pilot switching valve 1 is switched from the state where the compensator valve 4 is in the standby state as described above. By switching the switching valve 1 in this way, a load pressure is generated in the actuator connected thereto, but the discharge pressure of the pump P also rises according to the load pressure.
When the load pressure of the actuator becomes higher than the pilot pressure set by the relief valve 12, the load pressure is selected by the first shuttle valve and guided to the first pilot chamber 4a.
[0034]
Therefore, the compensator valve 4 operates as follows. That is, the pressure on the downstream side of the throttle determined by the switching amount of the electromagnetic pilot switching valve 1 acts on the first pilot chamber 4a, and the pressure on the upstream side acts on the second pilot chamber 4b.
At this time, a differential pressure is generated before and after the throttle of the electromagnetic pilot switching valve 1, but the compensator valve 4 controls the differential pressure to be equal to the spring force of the spring 4c. Accordingly, if the switching amount of the switching valve 1 is determined, a constant flow rate is always supplied to the actuator connected to the electromagnetic pilot switching valve 1 regardless of the load pressure. That is, load sensing control is performed. This is exactly the same when only the electromagnetic pilot switching valve 2 is switched.
Next, when the electromagnetic pilot switching valves 1 and 2 are simultaneously switched, the compensator valve 4 is controlled with the higher load pressure of the actuators connected to the switching valves 1 and 2. However, at this time, only the flow rate to the control flow path 3 is controlled by the higher load pressure, and a constant flow rate is not supplied to each actuator regardless of the load pressure. This is exactly the same as the conventional apparatus.
[0035]
When the actuator connected to the control flow path 3 is operating as described above, when it reaches the stroke end, the pressure on the control flow path 3 side increases. If the increased load pressure is equal to or higher than the set pressure of the main relief valve 18, the main relief valve 18 is opened. When the main relief valve 18 is thus opened, a flow is generated in the orifice 25 and a differential pressure is generated before and after the flow. Since the differential pressure acts on both of the pilot chambers 4a and 4b of the compensator valve 4, the pressure oil is also supplied to the surplus flow path 5 as described with reference to FIG.
[0036]
As described above, according to this embodiment, even if the actuator connected to the control flow path 3 reaches the stroke end, the main relief valve 18 is opened and the differential pressure across the orifice 25 is maintained. Accordingly, the annular groove 30 of the compensator spool 23 is kept in a state of being wrapped with the surplus flow path 5, and the flow rate is supplied to the surplus flow path 5.
Since the main relief valve 18 only needs to secure a capacity for discharging the flow rate controlled by the compensator valve 4, the capacity of the main relief valve 18 can be made smaller than that for directly discharging the discharge amount of the pump P. .
[0037]
【The invention's effect】
According to the first invention, the capacity of the main relief valve can be reduced. This is because the main relief valve only needs to have a capacity for discharging only the control flow distributed by the compensator valve.
According to the second aspect of the invention, for example, even when the actuator connected to the control flow path reaches the stroke end, the pump discharge amount can be supplied to the surplus flow path side.
According to the third invention, since the compensator valve, the flow rate control valve, and the like can be incorporated into one valve body, the entire apparatus can be reduced in size.
According to the fourth invention, since the main relief valve is provided on the shaft extension of the compensator spool, the space for providing the main relief valve can be kept to a minimum.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a hydraulic control device.
FIG. 2 is a cross-sectional view specifically showing components except a switching valve in a circuit diagram.
FIG. 3 is a circuit diagram showing a conventional hydraulic control device.
[Explanation of symbols]
P pump
1, 2 Solenoid pilot switching valve
3 Control flow path
4 Compensator valve
4a 1st pilot room
4b Second pilot room
4c spring
8 Flow control valve
8a 1st pilot room
8b Second pilot room
8c spring
11 First shuttle valve
12 Relief valve for pilot pressure setting
18 Main relief valve
20 Valve body
21 Pump port
22 Tank port
23 Compensator spool
25 Orifice
31 Flow control spool

Claims (4)

A pump, a compensator valve connected to the pump, a control flow path and an excess flow path connected to the compensator valve, a flow control valve connected in parallel to the compensator valve, and a pilot provided downstream of the flow control valve A relief valve for setting the pressure, and a selection valve for selecting a high pressure between the set pressure of the relief valve and the load pressure of the actuator connected to the control flow path, and the pressure selected by the selection valve is used as the first pressure of the compensator valve. In the hydraulic control apparatus configured to guide the pilot pilot to the first pilot chamber and to guide the pressure upstream of the pilot switching valve to the second pilot chamber, the load is connected between the pilot switching valve connected to the control flow path and the selection valve. And a main relief valve. The hydraulic control device according to claim 1, wherein an orifice is provided upstream of the main relief valve. While forming a pump port and a tank port in the valve body, a compensator spool is incorporated in the valve body, and one end of the compensator spool faces the first pilot chamber with a spring interposed therebetween, and the other end of the compensator spool The first pilot chamber is connected to the load side of the pilot switching valve connected to the control flow path via an orifice, and the first pilot chamber is connected to the first pilot chamber. The main relief valve is connected, and the flow control spool is incorporated in the compensator spool. One end of the flow control spool faces the first pilot chamber with a spring interposed, and the other end communicates with the pump port. The first pilot chamber of this flow control valve. Chamber of the hydraulic control device according to claim 1 or 2, wherein connected to the relief valve for setting a pilot pressure. 4. The hydraulic control apparatus according to claim 3, wherein a main relief valve is provided on the shaft extension line of the compensator spool.

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