JPH05302603A - Regenerative oil pressure circuit - Google Patents

Abstract

PURPOSE:To obtain a regenerative oil pressure circuit which prevents sudden slow-down of a low load side actuator in the course of compound operation and occurrence of shock caused by such slow-down. CONSTITUTION:A return line 28, which is located between a direction switching valve 34 of a specific (low load side) actuator 12 out of actuators 12 and 14 and an auxiliary valve 46, and an oil pressure supply line 20 are connected to each other through a regenerative check valve 82 by means of a by-pass line 80. This regenerative check valve is so arranged as to make the return oil from the return line to flow back to the oil pressure supply line. Further, a variable throttle 84 is provided on the upper course of the regenerative check valve connection point on the oil pressure supply line of the specific actuator 12. The opening of this variable throttle is adjusted by means of the pressure on the return line through a signal line 86.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit of a construction machine such as a hydraulic excavator, and more particularly, to prevent a rapid decrease in speed of a low load side actuator during complex operation to improve work efficiency and energy saving. Regenerative hydraulic circuit capable of

[0002]

2. Description of the Related Art Generally, construction machines such as hydraulic excavators are
For example, various actuators such as a bucket, a boom, and an arm are provided, and these actuators are configured to be driven by pressure oil from a hydraulic pump (preferably a variable displacement pump) supplied through a directional valve. ing. By the way, in such a hydraulic circuit, when the actuators are operated in combination, if the sum of the required pressure oil flow rates of the individual actuators exceeds the discharge flow rate of the hydraulic pump, the flow rate distribution to each actuator is not performed well, Oil flows preferentially to the low load side actuator, which often makes it impossible to drive the high load side actuator. Therefore, the present applicant previously developed a technique for solving such a drawback and filed a patent application (Japanese Patent Application No. 2-89134).

The above-mentioned technique (hereinafter referred to as "conventional technique") will be described with reference to FIG. 3. This hydraulic circuit is driven by a variable displacement pump 10 having a displacement control means 10a and pressure oil of the pump 10. A plurality of (two in the figure) actuators 12, 14 and a tank 16;
Each pressure oil supply line 20, 22 branched from the pump line 18 of the pump 10 and the actuator 1
2, 14 actuator lines 24a, 2 respectively
4b, 26a, 26b are provided between the actuators 12 and 14 to supply the pressure oil of the pump 10 to the respective actuators 12 and 14, and return oil from the actuators 12 and 14 to the tank 16 via the respective return lines 28 and 30. Direction switching valves 34, 36 for discharging to the connected tank line 32
Composed of and. In addition, each of the directional control valves 34, 36
Detecting means (load pressure detection lines) 38 and 40 for detecting the load pressures of the actuator lines 24 and 26 as the unit signal pressures, and the highest pressure among the detected unit signal pressures 38 and 40 is the highest signal. Means for selecting as pressure (check valve 42 and maximum pressure detection line 44), direction switching valves 34, 36 and tank line 16
Auxiliary valves 46, 48 are provided between the return lines 28, 30 and the tank line 32 for adjusting the opening degree between the return lines 28, 30 and the tank line 32. The unit signal pressures 38, 40 and the springs 50, 52 force the auxiliary valves 4 and 4 on one end side of the auxiliary valves 4 and 48.
6 and 48 are actuated in the opening direction and the other end is actuated so that the maximum signal pressure 44 is actuated in the closing direction, and the pump line 18 to the tank line 3 are controlled.
2 is provided with a bypass line 54, and this bypass line 5
4, a flow control valve 56 with pressure compensation and a pressure generating means 58 are provided, and the pressure on the upstream side of the pressure generating means 58 is signal line 6
0 to the capacity control means 10a of the pump 10 to apply the maximum signal pressure 44 and the spring 62 force to the pressure compensating flow rate control valve 56 in the closing direction thereof, and the pressure compensating flow rate control in the opening direction thereof. The upstream pressure of valve 56 is configured to act via signal line 64. In addition, reference numerals 66 and 68 in the drawing denote pressure oil supply lines 20 and 22, respectively.
Shows a load check valve provided in, and reference numeral 7
Reference numerals 0 and 72 denote throttles provided on the directional control valves 34 and 36, respectively.

Next, the operation of the hydraulic circuit having such a configuration will be described. In addition, here, the actuator 12
Is on the low load side, and the actuator 14 is on the high load side. First, when the direction switching valve 34 is operated to the left to drive the actuator 12 on the low load side, the variable displacement pump 1
The pressure oil discharged from No. 8 is supplied to the actuator 12 via the pump line 18, the pressure oil supply line 20, the load check valve 66, the throttle 70 of the direction switching valve 34, and the actuator line 24a. At this time, when the direction switching valve 34 is fully operated, the pressure loss at the throttle 70 is relatively small, and therefore the flow control valve 56 with pressure compensation on the bypass line 54.
If the force due to the pressure difference between the two detection lines 64, 44 acting on the pressure is set to be smaller than or substantially equal to the force of the spring 62 for setting the differential pressure, the flow control valve with pressure compensation 56 is fully opened. Therefore, the entire amount of pressure oil discharged from the pump 10 flows to the actuator 12. Further, in this state, the forces of both detection lines 38 and 44 acting on the auxiliary valve 46 are equal, and the auxiliary valve 46 is held in the fully opened position by the force of the spring 50, so the pressure in the return line 28 is low. Therefore, the pressure oil is returned to the tank 16 from the tank line 32 without pressure loss. That is, the low load side actuator 12 is driven at high speed by the total discharge flow rate of the pump 10.

Further, when the other direction switching valve 36 is operated in the state where the direction switching valve 34 is fully operated, the actuator 14 has a heavier load than the actuator 12, and the pressure oil instantaneously flows to the actuator 14. In the high-pressure side directional control valve 36, the pressure in the pressure oil supply line 22 is directly detected and transmitted to the detection line 40 without causing pressure loss in the throttle 70. On the other hand, since the pressure oil is flowing to the actuator 12, in the directional control valve 34 on the low load side, the pressure in the pressure oil supply line 20 is lower than the pressure loss in the throttle 70, and the detection line 3 is low.
8 is detected and transmitted. Thus, the auxiliary valve 4 on the high load side
8 has the same signal pressure acting on both ends thereof via the detection lines 40 and 44, and therefore is kept in a fully opened state by the force of the spring 52, while the auxiliary valve 46 on the low load side is maintained.
Has a signal pressure corresponding to the pressure difference between the detection lines 44 and 38 at its end in the closing direction, and therefore overcomes the relatively weak force of the spring 50 and moves in the closing direction. In this case, since the flow rate control valve with pressure compensation 56 acts on the high pressure signal pressure in the closing direction via the detection line 44, the pump 10 is in the full discharge state via the signal line 60 and the capacity control means 10a. Has been maintained. As a result, the pressure in the return line 28 of the low load side actuator 12 rises, and resistance to the flow of the pressure oil to the actuator 12 side occurs, the pressure in the pressure oil supply line 20 rises, and the high load side actuator 14 To drive. That is, the high and low load actuators 12 and 14 are simultaneously driven by the total discharge flow rate of the pump 10. In this case, the pump discharge pressure oil is distributed to both actuators 12 and 14 in proportion to the operation amounts of the respective auxiliary valves 46 and 48.

As described above, according to the above-mentioned conventional technique, a low load actuator can be driven independently at high speed, and a plurality of actuators having different load pressures can be simultaneously and reliably driven.

[0007]

However, the above-mentioned prior art still has the following drawbacks, especially in complex operations.

That is, in the above-mentioned prior art, when the actuator on the high load side is fully operated, especially when the actuator on the low load side is fully operated by itself, the pump supplied to the actuator on the low load side. Since the discharge pressure oil is divided into both actuators as described above, as a result, the pressure oil flow rate to the low load side actuator is halved, the driving speed is rapidly reduced, and further due to this rapid deceleration. Often there was a shock with cavitation.

Therefore, in the construction machine such as a hydraulic excavator, an object of the present invention is to rapidly reduce the speed of the low load side actuator when a single operation of the low load side actuator is combined with another operation of the high load side actuator. It is an object of the present invention to provide a regenerative hydraulic circuit capable of improving workability and energy saving by preventing it and maintaining it as fast as possible.

[0010]

In order to achieve the above object, a regenerative hydraulic circuit according to the present invention includes a variable displacement pump having displacement control means, and a plurality of actuators driven by pressure oil of the pump. A tank, a pump line of the pump and an actuator line of each of the plurality of actuators, and supplies pressure oil of the pump to each actuator and returns oil from the actuator via each return line. And a plurality of directional switching valves for discharging to a tank line connected to the tank, and detecting means for detecting the load pressure of the actuator line of each of the directional switching valves as respective unit signal pressure, and each of the detected units. Means for selecting the highest pressure among the signal pressures as the highest signal pressure,
An auxiliary valve that is arranged between the directional switching valve and the tank line and that adjusts the opening degree between the return line and the tank line is provided, and the unit signal pressure and the spring force are provided on one end side of the auxiliary valve. The auxiliary valve is actuated in the opening direction and the other end is actuated so as to control the maximum signal pressure in the closing direction, and a bypass line is provided from the pump line to the tank line. A pressure compensating flow control valve and a pressure generating means, and the upstream pressure of the pressure generating means is applied to the capacity control means of the pump, and the pressure compensating flow control valve has the maximum pressure in its closing direction. In a hydraulic circuit configured to act on the signal pressure and the spring force and act on the upstream side pressure of the flow control valve with pressure compensation in the opening direction, a specific actuation of the plurality of actuators is performed. A return line between the direction switching valve and the auxiliary valve of the user and a pressure oil supply line from the pump line are connected via a regeneration check valve, and the regeneration check valve connects the return oil from the return line to Arranged in such a direction as to flow back to the pressure oil supply line and block the flow in the opposite direction, and to provide a variable throttle upstream of the connection point of the regeneration check valve on the pressure oil supply line of the specific actuator. By adjusting the opening degree of the variable throttle by the pressure on the return line, the maximum opening degree of the variable throttle is decreased as the pressure on the return line increases.

In this case, the variable throttle provided on the pressure oil supply line of the specific actuator is formed by a load check valve on the pressure oil supply line, and this load check valve is auxiliary to the direction switching valve of the specific actuator. The stroke is adjusted by the pressure on the return line between the valve and the valve.

[0012]

[Function] When the high load side actuator is operated in combination with the single load on the low load side actuator, as described above, the pressure oil does not instantaneously flow to the high load side actuator.
As a result, the pressure in the return line of the low load side actuator increases. However, in the present invention, at this time, due to the pressure increase in the return line, the opening of the variable throttle provided on the pressure oil supply line is reduced, and at the same time, between the return line and the pressure oil supply line. Since the provided regeneration check valve is opened, the return oil in the return line is returned to the low load side actuator via the pressure oil supply line. However, since the actuator has inertia and especially the descending arm descends by its own weight, such an actuator on the low load side can continue driving at a relatively high speed without causing cavitation.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a regenerative hydraulic circuit according to the present invention will be described in detail below with reference to the accompanying drawings. For convenience of explanation, the same components as those of the conventional structure shown in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a regeneration hydraulic circuit according to the present invention, and its basic construction is the same as that of the conventional one shown in FIG. It should be noted that although overlapping, it will be described again for the sake of convenience. That is, the hydraulic circuit includes the variable displacement pump 10 having the displacement control means 10a.
A plurality of (two in the figure) actuators 12 and 14 driven by pressure oil of the pump 10, a tank 16, and respective pressure oil supply lines 20 branched from a pump line 18 of the pump 10. 22 and each actuator line 24 of the actuators 12 and 14
pump 10 provided between a, 24b, 26a, 26b
Of the directional control valves for supplying the pressure oil of No. 1 to the respective actuators 12, 14 and discharging the return oil from the actuators 12, 14 to the tank line 32 connected to the tank 16 via the respective return lines 28, 30. 34 and 36. Further, detection means (load pressure detection lines) 38, 40 for detecting the load pressures of the actuator lines 24, 26 of the respective directional control valves 34, 36 as respective unit signal pressures, and these detected unit signal pressures 38. , 40 for selecting the highest signal pressure as the highest signal pressure (check valve 42 and highest pressure detection line 44) and each return line 28 arranged between each directional control valve 34, 36 and the tank line 16. Three
Auxiliary valve 4 for adjusting the opening between 0 and the tank line 32
6, 48 are provided. The auxiliary valves 46 and 48 are actuated in the opening direction on one end side of the auxiliary valves 46 and 48 by the unit signal pressures 38 and 40 and the spring 50 and 52 forces, and the other end of the detection line 44 is connected. The bypass line 54 is provided from the pump line 18 to the tank line 32 so that the maximum signal pressure is controlled so as to be controlled in the closing direction, and the flow control valve 56 with pressure compensation and the pressure generating means 58 are provided on the bypass line 54. And pressure generating means 58
Is applied to the displacement control means 10a of the pump 10 through the signal line 60, and the maximum signal pressure of the detection line 44 and the elasticity of the spring 62 are applied to the pressure compensating flow control valve 56 in its closing direction. The pressure on the upstream side of the flow control valve 56 with pressure compensation is applied to the signal line 64 in the opening direction.
Is configured to act through. In addition, reference numerals 66 and 68 in the drawing denote pressure oil supply lines 20 and 2, respectively.
2 shows the load check valve provided in FIG.
Reference numerals 0 and 72 denote throttles provided on the directional control valves 34 and 36, respectively.

However, in the present invention, the return line 28 between the directional control valve 34 and the auxiliary valve 46 of a specific (low load side) actuator 12 of the plurality (two in the drawing) of the actuators 12, 14 is provided. And the pressure oil supply line 20 from the pump line 18 are connected by a bypass line 80 via a regeneration check valve 82. The regeneration check valve 82 connects the return oil from the return line 28 to the pressure oil supply line. 20 and the flow in the opposite direction is blocked so that a variable throttle 84 is provided upstream of the connection point of the regeneration check valve 82 on the pressure oil supply line 20 of the specific actuator 12. This variable diaphragm 8
By adjusting the opening degree of No. 4 by the pressure on the return line 28 via the signal line 86, the maximum opening degree of the variable throttle 84 is reduced as the pressure on the return line 28 increases.

The operation of the regenerative hydraulic circuit of the present invention having such a structure will be described. Here, as for the actuator, the actuator 12 is on the low load side and the actuator 14 is on the high load side as in FIG.
First, when the direction switching valve 34 is operated to the left to drive the low load side actuator 12, the pressure oil discharged from the variable displacement pump 18 is pumped by the pump line 18 and the pressure oil supply line 2.
0, the variable throttle 84, the load check valve 66, the throttle 70 of the direction switching valve 34, and the actuator line 24a, and the actuator 12 is supplied. At this time, the directional control valve 3
When 4 is fully operated, the pressure loss at the throttle 70 is relatively small, and therefore the force due to the pressure difference between the two detection lines 64 and 44 acting on the flow control valve 56 with pressure compensation on the bypass line 54 is reduced. If it is set to be smaller than or substantially equal to the force of the pressure setting spring 62, the flow control valve with pressure compensation 56 will be fully opened, so that the entire amount of pressure oil discharged from the pump 10 will flow to the actuator 12. Further, in this state, both detection lines 38, 4 acting on the auxiliary valve 46 are
4 is equal and the auxiliary valve 46 is held in the fully open position by the force of the spring 50 so that the pressure in the return line 28 is kept low and the variable throttle 84 is therefore connected via the signal line 86. Since the regeneration check valve 82 keeps the valve fully open while preventing the reverse flow in the bypass line 80, the pressure oil from the tank line 32 is not lost in the tank 1.
Returned to 6. That is, the low load side actuator 12
However, as in the prior art shown in FIG. 3, the pump 10 is driven at high speed by the total discharge flow rate. Even if the opening degree of the direction switching valve 34 is not fully opened, the same signal pressure is constantly applied to both ends of the auxiliary valve 46 to keep the auxiliary valve 46 in a fully opened state. As a result, the variable throttle 84 is also always opened. It is kept fully open.

Next, when the other direction switching valve 36 is operated in the state where the direction switching valve 34 is fully operated, since the actuator 14 has a higher load than the actuator 12, pressure oil is applied to the actuator 14. Since there is no instantaneous flow, in the high-pressure side directional control valve 36, the pressure in the pressure oil supply line 22 is directly detected and transmitted to the detection line 40 without causing pressure loss in the throttle 70. on the other hand,
Since the pressure oil is flowing to the actuator 12, in the directional control valve 34 on the low load side, the pressure of the pressure oil supply line 20 is detected and transmitted to the detection line 38 at a pressure lower than the pressure loss in the throttle 70. It As described above, since the equal signal pressure acts on both ends of the auxiliary valve 48 on the high load side through the detection lines 40 and 44, the auxiliary valve 48 is maintained in the fully open state by the force of the spring 52, while the low signal is low. Since the signal pressure corresponding to the pressure difference between the detection lines 44 and 38 acts on the end of the auxiliary valve 46 on the load side in the closing direction, the auxiliary valve 46 overcomes the force of the relatively weak spring 50 and moves in the closing direction. To do. In this case, since the high-pressure signal pressure acts on the flow control valve 56 with pressure compensation in the closing direction via the detection line 44, the pump 10 uses the signal line 60 and the capacity control means 10a.
The entire amount is maintained to be discharged through the. As a result, the pressure in the return line 28 of the low-load side actuator 12 rises, resistance is generated in the flow of pressure oil to the actuator 12 side, and the pressure in the pressure oil supply line 20 rises. Since the opening degree of the variable throttle 84 is throttled through the signal line 86 due to the pressure increase, the pressure of the pressure oil supply line 20 (pump discharge pressure) further rises, and the actuator 14 on the high load side is driven. .. That is,
The high and low load actuators 12 and 14 are simultaneously driven by the total discharge flow rate of the pump 10.

However, in the present invention, assuming that the lower load side actuator 12 lowers the arm and the high load side actuator 14 pivots during the combined operation, the pressure to which the bypass line 80 is connected is assumed. The pressure of the downstream side portion 20a of the oil supply line 20 becomes lower than the pressure of the return line 28 due to the throttling effect of the variable throttle 84 and the self-weight falling action of the arm. As a result, the regeneration check valve 82 is opened and the return line 28 is opened. The pressure oil inside returns to the actuator 12 via the line 20a, the direction switching valve 34, and the actuator line 24a. Therefore, the arm (actuator 12) drives (falls by its own weight) at a relatively high speed without causing cavitation. Further, the pressure oil discharged from the pump 10 is unlikely to flow to the arm side due to the throttling effect of the variable throttle 84, so most of it flows to the turning side (actuator 14), and therefore turning is also driven at a relatively high speed. ..

As described above, according to the present invention, by providing the regeneration check valve and the variable throttle at a predetermined position for the specific (low load side) actuator, the low load side actuator can be operated independently from the high load side. When the actuators are operated in combination, the low-load side actuator is configured to be driven mainly by the regenerated pressure oil, which is a drawback of the conventional hydraulic circuit of this type. It is possible to prevent the sudden decrease in speed of the vehicle and the occurrence of a shock associated therewith. Therefore, workability and energy saving can be significantly improved.

Next, FIG. 2 shows another embodiment of the regeneration hydraulic circuit according to the present invention. This embodiment is configured by combining the variable throttle with the load check valve originally provided in the hydraulic circuit in the embodiment shown in FIG. 1, without separately configuring the variable throttle. That is, the variable throttle / load check valve 90 is configured so that the stroke of the load check valve 66 is adjusted by the piston 92 on which the pressure in the return line 28 acts via the signal line 86. It should be noted that, even in such a configuration, it is clear that the same operation as in the case of the embodiment shown in FIG.
Detailed description is omitted.

[0021]

As described above, the regenerative hydraulic circuit according to the present invention includes a variable displacement pump having displacement control means, and a plurality of actuators driven by the pressure oil of the pump. The pressure oil of the pump is provided between the tank and the pump line of the pump and the actuator lines of the plurality of actuators, and the return oil from the actuator is supplied to the actuators through the return lines. Detecting means comprising a plurality of directional switching valves for discharging to a tank line connected to the tank, detecting the load pressure of the actuator line of each of the directional switching valves as a unit signal pressure for each, and each unit signal pressure thus detected. Means for selecting the highest pressure in the An auxiliary valve that is arranged between the return line and the tank line and that adjusts the opening degree between the return line and the tank line, and opens the auxiliary valve at one end of the auxiliary valve by the unit signal pressure and the spring force. Direction and the other end is configured to operate so as to control the maximum signal pressure in the closing direction, and a bypass line is provided from the pump line to the tank line, and a flow rate with pressure compensation is provided on this bypass line. A control valve and pressure generating means are provided, and the upstream side pressure of the pressure generating means is applied to the capacity control means of the pump, and the maximum flow rate and spring force are applied to the pressure compensating flow control valve in its closing direction. In a hydraulic circuit configured to act on the upstream side pressure of the flow control valve with pressure compensation in the opening direction. A return line between the switching valve and the auxiliary valve and a pressure oil supply line from the pump line are connected via a regeneration check valve, and the regeneration check valve supplies the return oil from the return line to the pressure oil. A variable throttle is provided upstream of the connection point of the regeneration check valve on the pressure oil supply line of the specific actuator, which is circulated to the line and blocks the flow in the opposite direction. By adjusting the opening of the throttle by the pressure on the return line, the maximum opening of the variable throttle is reduced as the pressure on the return line increases, so that the low-load side actuator is operated independently. Therefore, it is possible to drive the low load side actuator mainly by the regenerated pressure oil when the high load side actuator is operated in combination.
It is possible to prevent a sudden decrease in speed of the low load side actuator during the composite operation and a shock associated therewith, which has been a drawback of the conventional hydraulic circuit of this type. Therefore, workability and energy saving can be significantly improved.

[Brief description of drawings]

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

FIG. 2 is a sectional structural view showing another embodiment of a variable throttle applied to the regeneration hydraulic circuit shown in FIG.

FIG. 3 is a circuit diagram showing a configuration of a conventional hydraulic circuit.

[Explanation of symbols]

10 variable capacity pump 10a capacity control means 12, 14 actuator 16 tank 18 pump line 20, 22 pressure oil supply line 24a, 24b, 26a, 26b actuator line 28, 30 return line 32 tank line 34, 36 directional control valve 38, 40 Detection line 42 Check valve 44 Detection line 46, 48 Auxiliary valve 50, 52 Spring 54 Bypass line 56 Flow control valve with pressure compensation 58 Pressure generating means 60 Signal line 62 Spring 64 Signal line 66, 68 Load check valve 70, 72 Throttle 80 Bypass line 82 Regeneration check valve 84 Variable throttle 86 Signal line 90 Variable throttle and load check valve 92 Piston

Claims (2)

[Claims] 1. A variable displacement pump having displacement control means, a plurality of actuators driven by pressure oil of the pump, a tank, a pump line of the pump, and an actuator line of each of the plurality of actuators. A plurality of directional switching valves that are provided between the pumps to supply pressure oil to the respective actuators and discharge return oil from the actuators to the tank lines connected to the tanks via the respective return lines, Detecting means for detecting the load pressure of the actuator line of each direction switching valve as each unit signal pressure, means for selecting the highest pressure among these detected unit signal pressures as the maximum signal pressure, and each direction switching It is placed between the valve and the tank line and controls the opening between each return line and the tank line. An auxiliary valve for adjustment is provided, and the auxiliary signal is actuated in the opening direction by the unit signal pressure and the spring force at one end side of the auxiliary valve, and the maximum signal pressure is controlled in the closing direction at the other end. A bypass line is provided from the pump line to the tank line, and a flow control valve with pressure compensation and a pressure generating means are provided on the bypass line, and the pressure on the upstream side of the pressure generating means is controlled by the pump. The maximum signal pressure and the spring force are applied to the pressure compensating flow control valve in the closing direction and the upstream pressure of the pressure compensating flow control valve is actuated in the opening direction by being applied to the capacity control means. In the hydraulic circuit configured as described above, the pressure oil supply line from the pump line and the return line between the directional control valve and the auxiliary valve of a particular actuator of the plurality of actuators is Is connected via a regeneration check valve, and the regeneration check valve is arranged so as to return the return oil from the return line to the pressure oil supply line and block the flow in the opposite direction. In addition, a variable throttle is provided upstream of the connection point of the regeneration check valve on the pressure oil supply line of the specific actuator, and the opening of the variable throttle is adjusted by the pressure on the return line, so that the return A regeneration hydraulic circuit configured to reduce the maximum opening of the variable throttle as the pressure on the line increases. 2. A variable throttle provided on a pressure oil supply line of a specific actuator comprises a load check valve on the pressure oil supply line, and the load check valve is a combination of a direction switching valve and an auxiliary valve of the specific actuator. The regenerative hydraulic circuit according to claim 1, wherein the stroke can be adjusted by the pressure on the return line between them.