JP3142170B2 - Pressure relief device in hydraulic circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure relief device in a load pressure introduction path in a hydraulic circuit for supplying discharge pressure oil of a hydraulic pump to an actuator by an operation valve.

[0002]

2. Description of the Related Art As shown in FIG. 1, a discharge path 1a of a first hydraulic pump 1 and a discharge path 2a of a second pump 2 are connected, and a plurality of closed center type operation valves 3 are connected to the discharge paths 1a and 1b. Is arranged. A pressure compensating valve 5 is provided in each of the operation valve 3 and the connection circuit 4 of the actuator. The check valve 6 detects the highest load pressure among the load pressures of the actuators. There is known a hydraulic circuit in which the detected load pressure is supplied to a spring chamber 5a of each pressure compensating valve 5, and each pressure compensating valve 5 is set to a set pressure corresponding to the load pressure.

In this hydraulic circuit, when a plurality of operation valves 3 are simultaneously operated, a pressure compensating valve 5 is set according to the highest load pressure among the load pressures acting on a plurality of actuators. Thereby, the flow rate can be distributed to the plurality of actuators by the opening area ratio of the operation valve 3 regardless of the load pressure of the plurality of actuators. The pressure compensating valve 5 operates so that the differential pressure across the operating valves 3 becomes equal.

[0004] With this hydraulic circuit, when a plurality of actuators are operated simultaneously, the pressure compensating valve is set according to the highest load pressure. The pump discharge pressure is set to be slightly higher than the highest load pressure. For this reason, when the difference between the load pressures of the actuators is large, the pressure loss in the pressure compensating valve on the actuator side with a small load pressure becomes large. The loss horsepower of the prime mover that drives the first and second hydraulic pumps 1 and 2 increases. Since the lost horsepower changes into heat, the temperature of the hydraulic oil increases and the deterioration of the hydraulic oil is accelerated. For example, when hydraulic pressure is supplied to the boom cylinder and the swing motor of a hydraulic excavator to lower the boom and swing the upper body, the load pressure is low because the boom drops by its own weight, but the swing motor starts and accelerates the upper body. Therefore, the load pressure becomes high. Since the pump discharge pressure at that time is slightly higher than the high load pressure, the pressure compensating valve on the boom cylinder side causes a pressure loss corresponding to the high pressure-low pressure. As described above, since the difference between the load pressures is large, the pressure loss becomes large. This is the same because the load pressure of the arm cylinder is high and the load pressure of the bucket cylinder is low when the arm is raised by the arm cylinder and the bucket is dumped by the bucket cylinder to discharge earth and sand.

FIG. 2 shows a known hydraulic circuit for solving this problem. That is, as shown in FIG. 2, the discharge path 1a of the first hydraulic pump 1 and the discharge path 2a of the second hydraulic pump 2 are connected by the first junction valve 7. The first load pressure introduction passage 8 is connected to the pressure compensating valve 5 of the operation valve 3 connected to the discharge passage 1a of the first hydraulic pump 1. The second load pressure introducing passage 9 is connected to the pressure compensating valve 5 of the operation valve 3 connected to the discharge passage 2a of the second hydraulic pump 2. This is a hydraulic circuit in which the second load pressure introduction path 9 and the first load pressure introduction path 8 are connected by a second merge / branch valve 10. As a result, the first and second diverting valves 7, 10
Discharge passages 1a, 1b and load pressure introduction passages 8, 9
When the actuator 11 connected to one discharge path 1a and the actuator 12 connected to the other discharge path 2a are operated simultaneously, each pressure compensating valve is set with the load pressure of each actuator, Loss can be reduced.

[0006]

In this hydraulic circuit, the swash plate 13 of the first hydraulic pump 1 and the swash plate 13 of the second hydraulic pump 2 are driven by a large-diameter piston operated by pressure oil supplied from an LS valve 14. The discharge amount is controlled by tilting in the small discharge direction at 15 and tilting in the maximum discharge direction by the small diameter piston 16 operated by the pump discharge pressure. The LS valve 14 is switched to the supply position on the left side in FIG. 2 by the pump discharge pressure and to the drain position on the right side in FIG. 2 by the load pressure and the spring. This ensures that the pump discharge pressure is always slightly higher than the load pressure by the set pressure.

By doing so, the pump discharge pressure when the operation valve 3 is at the neutral position becomes low. That is, when the operation valve 3 is in the neutral position, the discharge passages 1a and 1b are stopped at the operation valve 3, and the pump discharge pressures of the first and second hydraulic pumps 1 and 2 increase. At this time, since the load pressure in the load pressure introduction paths 8 and 9 is zero, the pump discharge pressure rises only to the set pressure, and the pump discharge pressure becomes low.

For this purpose, the first and second load pressure introducing passages 8 and 9 are connected to the LS valve 14 to apply a load pressure. When the operation valve 3 is returned to the neutral position or the like, pressure may be trapped in the first and second load pressure introduction paths 8 and 9. When the pressure builds up in the first and second load pressure introduction paths 8 and 9, the load pressure acting on the LS valve 14 increases, and the LS valve 14 is brought to the drain position. L
When the S valve 14 is at the drain position, the discharge amount of the first and second hydraulic pumps 1 and 2 is increased by the small-diameter piston 16, and the pump discharge pressure becomes higher than the pressure set for the pressure actually acting on the actuator. Therefore, conventionally, the first and second
The load pressure introduction paths 8, 9 are connected to a tank 18 via a throttle 17, so that the pressure in the first and second load pressure introduction paths 8, 9 is constantly released. If the pressure in the first and second load pressure introducing passages 8 and 9 is released, the load pressure does not act on the LS valve 14. Therefore, even when the operation valve 3 is in the neutral position, the pump discharge pressure is maintained as described above. The set pressure is reached.

However, as described above, the first and second
If the pressure in the load pressure introducing passages 8 and 9 is reduced, the following problem occurs. Since there are two pipes flowing out to the tank 18 via the throttle 17, the load pressure introduction path is connected to the tank when the first and second merging valves 7 and 10 are at the merging position and at the branching position. Therefore, the characteristics of the load pressure introduction path change. In addition, the first and second
A part of the load pressure flowing into the load pressure introduction paths 8 and 9
Through the tank 18. Therefore, the load pressure acting on the LS valve 14 decreases. When the operating valve 3 is suddenly operated from the neutral position, the time until the LS valve 14 is operated to the drain position by the load pressure and the discharge amount of the hydraulic pump 1 changes becomes long, and the acceleration is slow, that is, the responsiveness deteriorates. . In addition, an error occurs in the differential pressure between the pump discharge pressure and the load pressure, resulting in poor control accuracy. Here, if the diameter of the throttle 17 is reduced, it is possible to prevent the change in characteristics due to the difference in the flow rate from having a practical support in the calculation, and to improve the responsiveness and control accuracy to make the support practical. You can not. However, by reducing the diameter, there is a new danger that dust existing in the hydraulic circuit may be clogged. Therefore, there is a limit in reducing the diameter of the diaphragm 17 in an actual design. As shown in FIG. 3, the first load pressure introduction path 8
If only the tank 18 is connected via the throttle 17
-There is no problem when the second merging valves 7 and 10 merge.
However, when the first and second merging valves 7 and 10 are divided into the shut-off positions, the pressure in the second load pressure introducing passage 9 on the second hydraulic pump 2 side cannot be reduced.

It is conceivable to use an unload valve as a means for reducing the pump discharge pressure when the operation valve is in the neutral position. For example, an unload valve is provided in the discharge path of the hydraulic pump. The unload valve is configured to communicate discharge pressure oil to the tank when the pressure difference between the pump discharge pressure and the pressure in the load pressure introduction path is greater than a set value. With this configuration, when the operation valve is at the neutral position, the pressure in the load pressure introduction path becomes zero, so that the pump discharge pressure has the above-described set value.

However, even if an unload valve is provided, if the pressure builds up in the load pressure introduction path, the load pressure acting on the LS valve will increase, and the pump discharge flow will be increased. Also, the load pressure acting on the unload valve increases. As a result, the unloading start pressure becomes high, so that the pump discharge pressure becomes high. Therefore, if the load pressure introduction path is communicated with the tank via the throttle in the same manner as described above and the pressure is released, a part of the load pressure flows out of the tank through the throttle when the operating valve is operated from the neutral position. For this reason, the response becomes poor when the operation valve is suddenly operated from the neutral position for the same reason as described above.

Therefore, the present invention reduces the built-in pressure in the load pressure introduction path while maintaining the responsiveness when the operation valve is suddenly operated, and particularly, the operation valve is suddenly operated even in a hydraulic circuit having a plurality of pumps. It is an object of the present invention to provide a pressure relief device in a hydraulic circuit that reduces the build-up pressure in a load pressure introduction path while maintaining responsiveness at the time.

[0013]

The first invention acts on a hydraulic pump 30, an operating valve 31 provided in a discharge passage 30a of the hydraulic pump 30, and an actuator 32 connected to the operating valve 31, respectively. Among the load pressures, a load pressure introduction path 35 for detecting a pressure corresponding to the maximum load pressure, an unload valve 42 provided in a discharge path 30a of the hydraulic pump 30, and the unload valve 42 is connected to the discharge path 30a. When the pressure difference between the pressure of the hydraulic pressure pump and the pressure of the load pressure introduction path 35 is larger than a set value, the discharge pressure oil of the hydraulic pump 30 is communicated with the tank 71,
An unload valve that does not communicate the discharge pressure oil of the hydraulic pump 30 to the tank 71 when the differential pressure is smaller than the set value. In the hydraulic circuit, wherein the pressure oil of the load pressure introduction path 35 is not communicated to the tank 71 in a state where the pressure oil is communicated to the tank 71 via the throttle 70, and the discharge pressure oil is not communicated to the tank 71. It is a pressure relief device.

The second invention comprises a plurality of hydraulic pumps 30,
An operation valve 31 provided in each of the discharge passages 30a of the plurality of hydraulic pumps 30 and an actuator 32 connected to each of the operation valves 31 to form an independent hydraulic circuit. A load pressure introduction path 35 for detecting a pressure corresponding to a maximum load pressure among load pressures to be performed, a first junction valve 55 for joining and separating respective discharge paths 30a of the plurality of hydraulic pumps 30, Second merging valve 5 for merging and separating the load pressure introduction paths 35, 35
6 and the respective discharge paths 30 of the plurality of hydraulic pumps 30
a, the unload valves 42, 42 are connected to the hydraulic pump 30 when the pressure difference between the pressure of the discharge passage 30a and the pressure of the load pressure introduction passage 35 is larger than a set value. Is an unload valve that does not communicate the discharge pressure oil of the hydraulic pump 30 to the tank 71 when the differential pressure is smaller than a set value, and discharges the discharge pressure oil to the tank 71. In the communication state, the pressure oil of the load pressure introduction path 35 is communicated to the tank 71 through the throttle 70,
A pressure relief device in a hydraulic circuit, wherein the pressure oil in the load pressure introduction path 35 is not communicated with the tank 71 in a state where the discharge pressure oil is not communicated with the tank 71.

A third aspect of the present invention relates to the plurality of hydraulic pumps 3
A first short-circuit path 65 for detecting the maximum pressure among the pressures of the discharge paths 30a, 30a of 0, 30 and a second short-circuit path for detecting the maximum pressure among the pressures of the plurality of load pressure introduction paths 35, 35. And the second short-circuit path 62 communicates with the tank via the throttle 67, and the pressure of the first short-circuit path 65 and the second short-circuit path 62
An unload valve 66 is provided for unloading the pressure in the first short circuit 65 to the tank by a pressure difference between the pressure in the short circuit 62 and the pressure in the first short circuit 65. This is a pressure relief device in a hydraulic circuit smaller than the set differential pressure.

According to a fourth aspect of the present invention, in the first to third aspects, the hydraulic pump 30 is of a variable displacement type, and the pressure difference between the discharge pressure of the hydraulic pump 30 and the load pressure introducing passage 35 is kept constant. A pressure relief device in a hydraulic circuit, comprising: a discharge amount control unit that controls a discharge amount so as to maintain the pressure.

According to a fifth aspect, in the first to fourth aspects, each of the plurality of operation valves includes a pressure compensating valve, and each of the pressure compensating valves is set according to the pressure of the load pressure introducing passage. This is a pressure relief device in a hydraulic circuit, characterized in that a flow rate corresponding to the degree of opening of the operation valve 34 is supplied to each actuator when the pressure is determined.

[0018]

According to the first aspect of the present invention, even if the pump discharge pressure rises due to the build-up pressure in the load pressure introduction passage 35, the unload valve 42 operates and the unload state is established. At this time, the pressure in the load pressure introduction path 35 flows out to the tank 71 via the throttle 70, so that the stagnation pressure in the load pressure introduction path 35 can be released. As a result, the pump discharge pressure becomes a discharge pressure corresponding to the actual load pressure of the actuator. Even if a stuck pressure is generated in the load pressure introducing passage 35, the stuck pressure is immediately released by the operation of the unload valve 42 in accordance with an increase in the pump discharge pressure. When the operation valve 31 is operated from the neutral position, a pressure corresponding to the load pressure of the actuator is first applied to the load pressure introduction path 3.
5 is introduced. Due to the introduced load pressure, the unload valve 42 enters the on-load state, and the load pressure introduction passage 35 is not communicated with the tank 71, and the load pressure in the load pressure introduction passage 35 immediately increases. Therefore, the pump discharge pressure when the operation valve 31 is at the neutral position can be reduced. Further, when the operation valve 31 is operated from the neutral position, the load pressure in the load pressure introduction path 35 immediately rises, and the responsiveness is improved.

According to the second invention, a plurality of hydraulic pumps 3
0 can be merged and divided by the first merging valve. The load pressure introduction paths 35, 35 can be joined and split by the second joining valve 56. The unload valve 42 is connected to each hydraulic pump 30
Are provided in the discharge paths 30a, respectively, so that pressure can be released both at the time of merging and at the time of branching. Accordingly, even when the independent hydraulic circuits are merged and divided, the pump discharge pressure when the operation valve 31 is at the neutral position can be reduced as in the first invention. Further, the responsiveness when the operation valve 31 is operated from the neutral position can be improved.

According to the third aspect of the present invention, the unload valve 66 operates regardless of whether the first and second merge valves merge or split. That is, the maximum pressure of the pump discharge pressure of the pump acts as a pilot pressure to open (unload) the unload valve 66. Also, the load pressure introduction path 35
Of the pressures acts as a pilot pressure to close the unload valve 66 (on-load). First
When the second merging valve merges, the pump discharge pressures are the same, and the pressure in the load pressure introducing passage 35 is also the same. The set differential pressure of the unload valve 66 is smaller than the set differential pressure of the unload valve 44 provided for each circuit. Therefore, the unload valve 66 functions as an unload valve common to all circuits. When the first and second merging valves diverge, in a steady state, both the pump discharge pressure and the pressure in the load pressure introduction path are introduced from the same circuit. Therefore, the unload valve 66 performs the unload function for the circuit having the highest pump discharge pressure. In other circuits, the unload valve 44 provided in each circuit operates. By using the unload valve 66 in common, it is possible to eliminate the difference in the operation characteristics due to the individual difference of the unload valve 44 provided in each circuit. At the same time, the pressure in the load pressure introducing passage 35 can be reduced as in the second invention.

According to the fourth aspect of the present invention, the capacity (discharge amount) of the hydraulic pump 30 is controlled so as to keep the pressure difference between the pump discharge pressure and the pressure of the load pressure introducing passage 35 constant. Therefore, when the pressure in the load pressure introduction path 35 is at the minimum value, that is, when the operation valve 31 is operated from the neutral position,
As the pressure in the load pressure introduction path 35 increases, the discharge amount increases, and the responsiveness improves. Further, similarly to the first to third aspects, even if the pump discharge pressure increases due to the build-up pressure in the load pressure introduction passage 35, the pump pressure does not remain high. Specifically, the squeeze pressure communicates with the tank via a throttle 67 provided in the second short-circuit path 62. Alternatively, it communicates with the tank through a throttle 70 that is opened by the operation of the unload valve 42. As a result, the pressure in the load pressure introduction path 35 decreases, and the pump discharge pressure decreases.

According to the fifth aspect, when the plurality of operation valves 31 are simultaneously operated, the discharge pressure oil of the hydraulic pump is supplied to the plurality of actuators at a flow rate corresponding to the opening degree of each operation valve regardless of each load. Can only supply.

[0023]

[Embodiment] As shown in FIG. 4, an operation valve 31 is provided in a discharge passage 30a of a hydraulic pump 30. This operating valve 3
A pressure compensating valve 34 is provided in a circuit 33 connecting the actuator 1 and the actuator 32. The load pressure of the actuator 32 is introduced into the load pressure introduction passage 35 through a throttle in the operation valve 31. The load pressure introduction path 35 has an inflow path 35a and an outflow path 35b.

The swash plate 36 of the hydraulic pump 30 is tilted in the large capacity direction by the small diameter piston 37 and tilted in the small capacity direction by the large diameter piston 38. The small-diameter pressure receiving chamber 37a of the small-diameter piston 37 is connected to the discharge path 30a to supply a pump discharge pressure. The large-diameter pressure receiving chamber 38a of the large-diameter piston 38 is controlled to communicate with the discharge path 30a and the tank 40 by the LS valve 39. The LS valve 39 is pushed to the drain position A by the load pressure and the spring 41, and is pushed to the supply position B by the pump discharge pressure. As a result, the swash plate 36 is tilted so that the pump discharge pressure is slightly higher than the load pressure, for example, 20 kg / cm ² higher.

An unload valve 42 is provided in the discharge passage 30a of the hydraulic pump 30. The unload valve 42 is pushed to the on-load position C by the spring and the load pressure of the load pressure introduction path 35 supplied to the first pressure receiving portion 43. The on-load position C is a state in which the discharge pressure oil of the hydraulic pump 30 is not communicated with the tank. The unload valve 42 is pushed to the unload position D by the pump discharge pressure supplied to the second pressure receiving section 44. The unload position D is a state where the discharge pressure oil of the hydraulic pump 30 is communicated with the tank. The unload valve 42 has a set pressure difference between the pump discharge pressure and the load pressure, for example, 30 kg /
When it becomes cm ² or more, it becomes the unload position D. At the time of the unload position D, the load pressure introduction path 35 communicates with the tank 71 via the throttle 70. The unload valve 42 operates only by the pump discharge pressure of the individual hydraulic pump 30 and the pressure of the load pressure introducing passage 35.

The specific structure of the unload valve 42 will be described with reference to FIG. As shown in FIG.
A tank port 74 and a load pressure port 75 are formed in the hole 73. The pressure of the load pressure introduction passage 35 is introduced into the load pressure port 75. A sleeve 76 is fitted in the hole 73, and a large-diameter port 77, a small-diameter port 78, and a load pressure port 75 that open to a tank port 74 are fitted in the sleeve 76.
A small hole 79 is formed to open at the bottom. The sleeve 76
A spool 80 is inserted therein, and a shaft hole 81 and a fine hole 82 are formed in the spool 80. The spool 80 is pushed to the left in the figure by the pressure of the spring 83 and the spring chamber 84 to close the large-diameter port 77, and is held at a position where the small-diameter port 78 and the small hole 82 are shut off, and enters an on-load state. Hole 73
The spool 80 is pushed rightward in the figure by the discharge pressure of the hydraulic pump 30 introduced into the
Is moved to a position communicating with the small-diameter port 78 to be in an unloaded state.

Therefore, the pressure of the load pressure introducing passage 35 acting on the load pressure port 75 during the unload state is reduced to the small hole 7.
9, spring chamber 84, shaft hole 81, small hole 82, small diameter port 78
The water flows out of the tank port 74 into the tank. In the on-load state, the pressure of the load pressure port 75 does not flow out to the tank.

Next, control of the pump discharge pressure by the unload valve 42 will be described. The unload valve 42 is in an on-load state when the differential pressure between the pump discharge pressure and the load pressure of the load pressure introduction path 35 is equal to or less than a set differential pressure (30 kg / cm ² ).
When the differential pressure is equal to or higher than the set differential pressure, the motor enters the unload state. When the operation valve 31 is set to the neutral position, pressure may remain in the load pressure introduction path 35. At this time, the unload valve 42 enters the unload state when the pump discharge pressure-the retentive pressure becomes equal to or higher than the set differential pressure. As a result, the pump discharge pressure rises to the set differential pressure + the retentive pressure. Unload valve 42
Is in the unload state, the built-in pressure in the load pressure introduction path 35 flows out to the tank through the throttle 70, and the load pressure introduction path 35
Pressure becomes zero. Accordingly, the pump discharge pressure decreases until the above-described set differential pressure with respect to the pressure of the load pressure introduction path 35 that has become zero is reached. By operating the operation valve 31 from the neutral position, the discharge pressure oil of the hydraulic pump 30 is supplied to the actuator 3
2, the pressure corresponding to the load pressure flows into the load pressure introduction path 35. The pressure in the load pressure introducing passage 35 acts on the first pressure receiving portion 43 of the unload valve 42, and the unload valve 42
Is the on-road position. At this time, the load pressure introduction path 35 stops communicating with the tank 71.

Therefore, it is possible to release the built-in pressure in the load pressure introducing passage 35. Further, when the operation valve 31 is operated from the neutral position, the pressure in the load pressure introduction passage 35 immediately increases, so that the responsiveness is improved.

Next, the structure of another part will be described with reference to FIG. The pilot hydraulic valve 45 outputs the pressure oil discharged from the auxiliary pump 47 to one of the first and second pilot lines 48 and 49 by operating the lever 46. The pressure oil in the first and second pilot lines 48 and 49 is supplied to the first and second pressure receiving portions 50 and 51 of the operation valve 31 to move the operation valve 31 from the neutral position E to the first position F and the second position G. Switch. The first and second pressure switches 5 are connected to the first and second pilot lines 48 and 49, respectively.
2 and 53 are provided, and when pressure is generated, an electric signal is output to the controller 54. The above description shows only the left hydraulic pump 30 in FIG. Right hydraulic pump 30
The same applies to the drawings, and the same reference numerals are used in the drawings to omit description.

The discharge path 30a of the left hydraulic pump 30
The discharge path 30a of the hydraulic pump 30 on the right side and the right side can be merged and divided by the first merge / divide valve 55. The left load pressure introduction path 35 and the right load pressure introduction path 35 can be joined and divided by a second junction valve 56. The first and second diverging valves 55 and 5
6 are held at the merging positions H and H by spring force, and the pressure receiving portions 57 and
The flow is switched to the diversion positions I, I by the pilot pressure oil supplied to 58. The discharge pressure oil of the auxiliary pump 47 is supplied to the solenoid valve 5
9, the pressure receiving portions 57, 58 of the first and second branching valves 55, 56
Is controlled. The solenoid valve 59 is held at the drain position J by a spring force, and switches to the supply position K when the solenoid 60 is energized. The energization of the solenoid 60 is controlled by the controller 54.

The left load pressure introducing passage 35 and the right load pressure introducing passage 35 communicate with each other through a first short circuit 62 having a pair of check valves 61, 61.
Is selected and introduced into the first short-circuit path 62. A relief valve 63 is provided in the first short-circuit path 62. The discharge path 30a of the left hydraulic pump 30 and the discharge path 30a of the right hydraulic pump 30
The pump discharge pressures of the left and right hydraulic pumps 30 which are higher in pump discharge pressure are selected and introduced into the second short-circuit path 65. An unload valve 66 is connected to the second short-circuit path 65. The unload valve 66 is held at the on-load position L by a spring force and the pressure of the first short circuit 62 acting on the first pressure receiving portion 66a. The unload position M is set by the pump discharge pressure of the second short circuit 65 acting on the second pressure receiving portion 66b. The set differential pressure of the unload valve 66 (the differential pressure between the pump discharge pressure at the unload position and the pressure of the first short-circuit path 62) is smaller than the set differential pressure of the individual unload valve 42.

Next, the operation will be described. Left operating lever 4
At 6, the pilot hydraulic valve 45 is operated to supply pilot pressure oil to the first pilot line 48. The pilot pressure oil is supplied to the first pressure receiving portion 50 of the operation valve 31, and the operation valve 31
Position F is reached. The pressure oil discharged from the left hydraulic pump 30 is supplied to the left actuator 32. The load pressure of the actuator 32 is introduced into the load pressure introduction path 35 via a throttle provided at the first position F of the operation valve 31. At this time, the unload valve 42 is set to the on-load position C and the load pressure introduction path 35
Does not communicate with the tank 71.

Thus, the first pressure switch 52 inputs an electric signal to the controller 54. Controller 54
Determines that the left operating valve 31 has reached the first position F, and calculates whether or not to merge based on a predetermined pattern. When they merge, the solenoid 60 of the solenoid valve 59 is set to the drain position J without energizing. First
The merging valve 55 is brought to the merging position H by spring force, merges the discharge pressures of the left and right hydraulic pumps 30 and supplies them to the left actuator 32. The second merging valve 56 is brought to the merging position H by spring force, and the left inflow path 35a and the right inflow path 35b
The left outflow channel 35b and the right outflow channel 35b communicate with each other. Load pressure of left inflow channel 35a and right inflow channel 35b
The load pressure having the higher load pressure flows into the outflow passage 35b on the right side by the shuttle valve 35c. That is, the load pressure introduction path 35 detects the highest load pressure.

When the flow is divided, the solenoid 60 of the solenoid valve 59 is energized to the supply position K. Auxiliary hydraulic pump 47
Is discharged to the pressure receiving section 5 of the first / second junction valve 55, 56.
7 and 58, and are set as branch positions I and I. The discharge pressure oil of the left hydraulic pump 30 is supplied only to the left actuator 32. Left inflow channel 35a and right outflow channel 3
5b communicate with the right inflow channel 35a and the right outflow channel 35.
b communicates. The pressure in the load pressure introducing passage 35 acts on the LS valve 39 and tilts the swash plate 36 of the hydraulic pump 30 to set the pressure difference between the pump discharge pressure and the pressure in the load pressure introducing passage 35 as the set pressure. The pressure in the introduction path 35 acts on the pressure compensating valve 34 to compensate the pressure. The same applies to the case where the left operating lever 46 is operated in the opposite direction to supply pilot pressure oil to the second pilot pipeline 49 and the case where the right operating lever 46 is operated.

Next, the unloading operation of the unloading valve 66 at the time of merging (operation of limiting the maximum pump discharge pressure of the hydraulic pump) will be described. When the stroke of the left actuator 32 becomes the end of the stroke in the state described above, or when the actuator 32
Is very large, and the pressure in the load pressure introducing passage 35 is very high. The pressure in the load pressure introduction passage 35 flows from the check valve 61 into the first short circuit passage 62 and is relieved by the relief valve 63. Since the maximum pressure acting on the first pressure receiving portion 66a of the unload valve 66 is the relief set pressure of the relief valve 63, the maximum pressure is equal to the load pressure introduction path 35.
Pressure is lower than the pressure. Left and right hydraulic pumps 30,
The pump discharge pressure oil 30 flows into the second short-circuit path 65 from the check valve 64 and flows into the inlet side of the unload valve 66, and at the same time acts on the second pressure receiving portion 66b of the unload valve 66. The set differential pressure of the unload valve 66 is determined by each hydraulic pump 3
It is smaller than the set differential pressure of the unload valve 42 provided in each of the 0 discharge paths 30a. As a result, the unload valve 6
6 is the unload position M. The discharge pressure oil of the left and right hydraulic pumps 30 introduced into the second short-circuit path 65 is unloaded.

Next, the unloading operation of the unloading valve 66 at the time of branching (the operation of limiting the maximum pump discharge pressure of the hydraulic pump) will be described. The discharge path 30a of the left hydraulic pump 30 and the discharge path 30a of the right hydraulic pump 30 are separated from each other, and at the same time, the left load pressure introduction path 35 and the right load pressure introduction path 35 are separated. When the load pressure of the left actuator 32 becomes extremely high, the load pressure flows from the left check valve 61 to the first short-circuit path 62 through the load pressure introduction path 35, and the right check valve 61 causes the right check valve 61 to move to the right. Flow to the load pressure introduction path 35 is prevented. The pressure in the first short circuit 62 is relieved by the relief valve 63 in the same manner as described above. The discharge pressure of the left hydraulic pump 30 flows into the second short-circuit path 65 from the left check valve 64, and is prevented from flowing to the discharge path 30 a of the right hydraulic pump 30 by the right check valve 64. The pump discharge pressure acts on the inlet side of the unload valve 66. As a result, the unload valve 66 becomes the unload position M and unloads the pump discharge pressure oil as in the case of the merge.

In the above operation, when the right operation valve 31 is at the neutral position E, the right load pressure introduction path 35 is finally connected to the tank, and the pressure of the load pressure introduction path 35 is almost 0 kg / cm ^2. Becomes That is, the unload valve 42 is in the unload position D by the pressure of the load pressure introducing passage 35 acting on the first pressure receiving portion 43 of the right unload valve 42 and the pump discharge pressure of the right hydraulic pump 30. As a result, the pump discharge pressure of the right hydraulic pump 30 becomes low.

As described above, since the load pressure is relieved from one relief valve 63 at the time of merging or branching, the relief flow rate at which the unload valve 66 unloads is determined by the override characteristics of the relief valve 63. You.
At this time, the pressure of the first short-circuit path 62 becomes the same as shown in FIG. 6, and the maximum pump discharge pressure can be made the same at the time of merging and the time of branching. In FIG. 4, the inflow side of the relief valve 63 and the tank communicate with each other through a small-diameter orifice 67. When the operation valve 31 is set to the neutral position E, a pair of check valves 6 are disposed.
This is because the pressure in the first short-circuit path 62, which is cut off from the load pressure introducing path 35 at 1 and 61, immediately flows out to the tank.

[0040]

According to the first aspect of the present invention, even if the pump discharge pressure rises due to the stuck pressure in the load pressure introducing passage 35, the unload valve 42 is operated and the unload state is established. At this time, the pressure in the load pressure introduction path 35 flows out to the tank 71 via the throttle 70, so that the stagnation pressure in the load pressure introduction path 35 can be released. As a result, the pump discharge pressure becomes a discharge pressure corresponding to the actual load pressure of the actuator. Even if a stuck pressure is generated in the load pressure introducing passage 35, the stuck pressure is immediately released by the operation of the unload valve 42 in accordance with an increase in the pump discharge pressure. When the operation valve 31 is operated from the neutral position, first, a pressure corresponding to the load pressure of the actuator is introduced into the load pressure introduction path 35. Due to the introduced load pressure, the unload valve 42 enters the on-load state, and the load pressure introduction passage 35 is not communicated with the tank 71, and the load pressure in the load pressure introduction passage 35 immediately increases. Therefore, the operating valve 3
The pump discharge pressure when 1 is at the neutral position can be reduced. Further, when the operation valve 31 is operated from the neutral position, the load pressure in the load pressure introduction path 35 immediately rises, and the responsiveness is improved.

According to the second aspect of the present invention, the discharge passages 30a of the plurality of hydraulic pumps 30 can be joined and divided by the first joining valve. The load pressure introduction paths 35, 35 can be joined and split by the second joining valve 56. Since the unload valves 42 are provided in the discharge passages 30a of the respective hydraulic pumps 30, the pressure can be released at the time of merging or at the time of branching. Therefore, even when independent hydraulic circuits are merged and separated, claim 1
As in the invention according to the first aspect, the pump discharge pressure when the operation valve 31 is at the neutral position can be reduced. Further, the responsiveness when the operation valve 31 is operated from the neutral position can be improved.

According to the third aspect of the present invention, the first and the second
Unload valve 6 regardless of whether the junction valve
6 acts. That is, the maximum pressure of the pump discharge pressure of the pump acts as a pilot pressure to open (unload) the unload valve 66. In addition, the maximum pressure among the pressures in the load pressure introduction passage 35 acts as a pilot pressure to close (on-load) the unload valve 66. When the first and second merging valves merge, the pump discharge pressures are the same, and the pressure in the load pressure introducing passage 35 is also the same. The set differential pressure of the unload valve 66 is smaller than the set differential pressure of the unload valve 44 provided for each circuit.
Therefore, the unload valve 66 functions as an unload valve common to all circuits. When the first and second merging valves diverge, in a steady state, both the pump discharge pressure and the pressure in the load pressure introduction path are introduced from the same circuit. Therefore,
The unload valve 66 performs an unload function for the circuit with the highest pump discharge pressure. In other circuits, the unload valve 44 provided in each circuit operates. Unload valve 66
Can be used in common to eliminate differences in operating characteristics due to individual differences in the unload valve 44 provided in each circuit. At the same time, the pressure in the load pressure introducing passage 35 can be released in the same manner as in the second aspect of the invention.

According to the fourth aspect of the present invention, the capacity (discharge amount) of the hydraulic pump 30 is determined by the pump discharge pressure and the load pressure introduction path 3.
Control is performed so as to keep the differential pressure from the pressure of No. 5 constant.
Therefore, when the pressure in the load pressure introduction path 35 is at the minimum value, that is, when the operation valve 31 is operated from the neutral position, the discharge amount increases in accordance with the increase in the pressure in the load pressure introduction path 35, and the responsiveness increases. Is improved. Further, similarly to the first to third aspects of the present invention, even if the pump discharge pressure increases due to the stuck pressure in the load pressure introduction passage 35, the pump pressure does not remain high. Specifically, the squeeze pressure communicates with the tank via a throttle 67 provided in the second short-circuit path 62. Alternatively, it communicates with the tank through a throttle 70 that is opened by the operation of the unload valve 42. As a result, the pressure in the load pressure introduction path 35 decreases, and the pump discharge pressure decreases.

According to the fifth aspect of the present invention, when a plurality of operation valves 31 are simultaneously operated, the discharge pressure oil of the hydraulic pump is applied to the plurality of actuators in accordance with the opening degree of each operation valve regardless of each load. It can supply only the flow rate.

[Brief description of the drawings]

FIG. 1 is a conventional hydraulic circuit diagram.

FIG. 2 is an improved conventional hydraulic circuit diagram.

FIG. 3 is an improved conventional hydraulic circuit diagram with one throttle.

FIG. 4 is a hydraulic circuit diagram showing an embodiment of the present invention.

FIG. 5 is a sectional view of the unload valve.

FIG. 6 is a table showing a relationship between a relief flow rate and a pressure of a first short circuit.

[Explanation of symbols]

Reference numeral 30: hydraulic pump, 30a: discharge path, 31: operating valve, 3
2. Actuator, 34 ... Pressure compensating valve, 35 ... Load pressure introduction path, 42 ... Unload valve, 55 ... Combining / dividing valve, 56 ...
Junction valve, 61 ... check valve, 62 ... first short circuit path, 6
3 Relief valve, 64 Check valve, 65 Second short circuit path, 66 Unload valve, 67 Orifice, 70 Restrictor, 71 Tank.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F15B 11/00-11/22 E02F 9/20-9/22

Claims (5)

(57) [Claims] A hydraulic pump, and an operating valve provided in a discharge passage of the hydraulic pump.
And a load pressure introduction path 35 for detecting a pressure corresponding to a maximum load pressure among load pressures acting on actuators 32 respectively connected to the operation valves 31, and a discharge path 30 a of the hydraulic pump 30. An unload valve 42, which, when the pressure difference between the pressure in the discharge passage 30 a and the pressure in the load pressure introduction passage 35 is larger than a set value, sends the discharge pressure oil of the hydraulic pump 30 to the tank 71. to communicate with each other,
When the differential pressure is smaller than the set value, the hydraulic pump 30
The discharge pressure oil a unloading valve not communicated to the tank 71, communicating said discharge pressure oil in a state of communicating with the tank 71, through a 70 aperture pressure oil of the load pressure introducing passage 35 to the tank 71
In a state where the discharge pressure oil is not communicated with the tank 71,
A pressure relief device in a hydraulic circuit, wherein the pressure oil in the load pressure introduction path 35 is not communicated with the tank 71 . 2. A plurality of hydraulic pumps 30, operating valves 31 provided in respective discharge paths 30a of the plurality of hydraulic pumps 30, and actuators 32 connected to the operating valves 31 to form independent hydraulic circuits. A load pressure introduction path 35 for detecting a pressure corresponding to a maximum load pressure among load pressures acting on the actuators 32 for each hydraulic circuit; and a discharge path 30 a for each of the plurality of hydraulic pumps 30. A first merge valve 55 for merging and separating the hydraulic pressure pumps 35, a second merge valve 56 for merging and separating the load pressure introduction paths 35, 35, and an unload valve 42 provided in a discharge path 30a of each of the plurality of hydraulic pumps 30. , 42, and the unload valves 42, 42, when the pressure difference between the pressure of the discharge passage 30a and the pressure of the load pressure introduction passage 35 is larger than a set value, the discharge pressure oil of the hydraulic pump 30 is removed. Communicated to the click 71, when the differential pressure is smaller than the set value, the hydraulic pump
30 is an unload valve that does not communicate the discharge pressure oil to the tank 71, and communicates the pressure oil of the load pressure introduction path 35 to the tank 71 via the throttle 70 in a state in which the discharge pressure oil communicates to the tank 71.
In a state where the discharge pressure oil is not communicated with the tank 71,
A pressure relief device in a hydraulic circuit, wherein the pressure oil in the load pressure introduction path 35 is not communicated with the tank 71 . 3. A first short-circuit path 65 for detecting a maximum pressure among the pressures of the discharge paths 30a, 30a of the plurality of hydraulic pumps 30, 30, and a pressure of the plurality of load pressure introduction paths 35, 35. And a second short-circuit path 62 for detecting the maximum pressure among the two. The second short-circuit path 62 communicates with the tank via a throttle 67, and the pressure of the first short-circuit path 65 and the second short-circuit path 62 An unload valve 66 is provided for unloading the pressure in the first short-circuit path 65 to the tank by a differential pressure with respect to the pressure.
3. The pressure relief device in a hydraulic circuit according to claim 2, wherein the pressure difference is smaller than a set differential pressure of the hydraulic pressure control circuit. 4. A discharge amount control means for controlling a discharge amount so as to keep a pressure difference between the discharge pressure of the hydraulic pump 30 and the load pressure introduction passage 35 constant. 4. The pressure relief device in a hydraulic circuit according to claim 1, further comprising: 5. Each of the plurality of operation valves 34 includes a pressure compensating valve 34, and each of the pressure compensating valves 34 determines an opening degree of the operation valve 34 by setting a set pressure in accordance with the pressure of the load pressure introducing passage 35. 5. A pressure relief device in a hydraulic circuit according to claim 1, wherein a corresponding flow rate is supplied to each actuator.