JPH04249601A - Load sensing circuit - Google Patents

Abstract

PURPOSE:To permit the speedy disposal for the variation of the load pressure by installing a bleed-off circuit which is continuous to a tank from the front of a pressure reducing valve in a discharge circuit leading to an actuator, in branched form, and installing a compensator valve midway in the bleed-off circuit. CONSTITUTION:A pressure reducing valves 5 and a flow rate control valves 6 are installed in succession in a discharge circuit 3 connected with a variable pump 1 having a discharge quantity controller 2. Further, a feedback circuit 8 which extracts the pressure of each actuator 4 from the flow rate control valves 6, and introduces the pressure into each pressure reducing valve 5, and at the same time, introduces the highest pressure to the discharge quantity controller 2 through a shuttle valves 7 is installed. Accordingly, in the load sensing device, a bleed-off circuit 14 which is continuous to a tank 13 from the front of the pressure reducing valves 5 in the discharge circuit 3 is installed in branched form, and a compensator valve 17 which closes the bleed-off circuit 14 by the pressure of the pressure feedback circuit 8 and the force of a spring 15 and opens the bleed-off circuit 14 by the pressure of the discharge circuit 3 is installed in this bleed-off circuit 14.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a load sensing system for rapidly controlling the pressure and flow rate of a hydraulic circuit system by controlling the discharge amount of a variable pump in response to the load pressure of an actuator driven by a variable pump. Regarding equipment.

0002

2. Description of the Related Art Conventionally, as a load sensing device, as shown in FIG. A valve f and a flow rate control valve e having a direction control function are sequentially provided, and the pressure of the actuator c is extracted from the flow rate control valve e and guided to the pressure reducing valve f, and at the same time is transferred to the discharge amount control device a via the shuttle valve g. A configuration is known in which a pressure feedback circuit h is provided to guide the pressure.

While the actuator c is being driven, the highest load pressure of each discharge circuit d is extracted via the shuttle valve g, and this pressure acts on the discharge amount control device a via the pressure feedback circuit h. The discharge amount control device a is
It is connected to a swash plate etc. that changes the pump capacity of the variable pump b, and in the case shown, two control valves k and l are connected to one of two control cylinders i and j that tilt the swash plate. A pilot circuit m is connected to guide the pressure of the discharge circuit d through the control valve k, and one control valve k is controlled and operated so that the pressure of the discharge circuit d is balanced with the force of the spring and the pressure of the pressure feedback circuit h. One of the control valves 1 is configured to operate in a controlled manner so that the pressure in the discharge circuit d and the force of the spring are balanced. In this case, when the pressure in the discharge circuit d becomes higher than the set pressure of the control valve l, the pressure in the discharge circuit d is guided to the control cylinder j via the pilot circuit m, thereby reducing the discharge amount of the variable pump b. In addition, when the differential pressure between the load pressure of any actuator c and the pressure of the discharge circuit d becomes higher than the set pressure of the control valve k, the control valve l and the pilot circuit m are connected to the control cylinder j. The pressure of the discharge circuit d is guided through the pump, and a control operation is performed to reduce the discharge amount of the variable pump b.

By providing such a load sensing device, fluctuations in load pressure are quickly transmitted to the discharge amount control device a, and there is an advantage that the discharge amount and discharge pressure of the variable pump b can be quickly changed in response to the fluctuations. .

[0005]

[Problem to be Solved by the Invention] The load sensing device is characterized by supplying pressure and flow rate according to the load pressure, but when all the flow rate control valves e are in the neutral position, the pressure feedback circuit h is All are connected to the tank, and the control valve k of the variable pump b is switched at relatively low pressure (spring force and tank pressure), the pressure of the discharge circuit d is guided to the control cylinder j, and the pump discharge capacity is close to zero. situation(
The discharge amount is sufficient to maintain the pressure necessary to switch the control valve k.

When the flow rate control valve e is switched from this state,
Although the load pressure is guided to the pressure feedback circuit h, the load pressure is not always high, and the pressure of the control valve k is affected by the compressibility of the fluid existing in the piping of the discharge circuit d and the pressure feedback circuit h. There was a drawback that the switching was delayed, and as a result, the variable pump b could not discharge, resulting in delayed response. SUMMARY OF THE INVENTION An object of the present invention is to provide a load sensing device that can quickly operate a discharge amount control device according to the load pressure of the actuator at the time of starting driving of the actuator.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a pressure reducing valve and a flow rate control valve in a discharge circuit that guides the discharge volume of a variable pump equipped with a discharge volume control device to an actuator. In a load sensing device equipped with a pressure feedback circuit that extracts the pressure of the discharge circuit from a point close to the actuator and guides it to the discharge amount control device, the bleed-off is connected from the front of the pressure reducing valve of the discharge circuit to the tank. A branched circuit is provided, and the bleed-off circuit is moved to close the bleed-off circuit by the pressure of the pressure feedback circuit and the spring force, and moved to open the bleed-off circuit by the pressure of the discharge circuit. A compensator valve is provided with a plunger to ensure a minimum discharge of the variable pump of at least 10% of the maximum discharge of the variable pump.

[0008]

[Operation] When the flow rate control valve is in the neutral position, the discharge amount of the variable pump is in the minimum state, and the discharged flow rate is returned to the full volume tank from the compensator valve equipped with a bleed-off circuit. When the flow rate control valve is switched, the load pressure acts on the compensator valve via the pressure feedback circuit, so the compensator valve closes and the pressure in the discharge circuit increases due to the minimum discharge amount of fluid discharged from the variable pump. The actuator begins to operate. Note that since the compensator valve is provided on the flow control valve side, the influence of the piping of the pressure feedback circuit is reduced.

[0009] In this way, the actuator operates simply by closing the compensator valve, and as a result, the operating pressure of the load acts instantaneously on the pressure feedback circuit, so that the subsequent increase in the discharge amount of the variable pump becomes quick and responsive. Good sexual control.

0010

[Example] An example of the present invention will be explained based on FIG.
In the figure, reference numeral 1 indicates a variable pump equipped with a discharge amount control device 2, and 3 indicates a discharge circuit that guides the discharge amount of the variable pump to a plurality of actuators 4 such as hydraulic cylinders. A valve 5 and a flow control valve 6 having a direction control function are provided in sequence. Further, a pressure feedback circuit 8 extracts the pressure of each actuator 4 from the flow control valve 6 and guides it to the respective pressure reducing valve 5, and at the same time guides the highest pressure among them to the discharge amount control device 2 via the shuttle valve 7. will be provided. This configuration is similar to that of a conventional load sensing device, and the discharge amount control device 2 includes two control cylinders 9 and 10 and two control valves that control the supply and removal of fluid to one of the control cylinders 10. 11 and 12 is also similar to the conventional device. The control valve 11 is operated by the control cylinder 10 by the pressure of the pressure feedback circuit 8, the force of the spring, and the pressure of the discharge circuit 3.
Control operation for supplying fluid to or the control cylinder 10
When the fluid is supplied to the control cylinder 10, the variable pump 1 reduces the pump capacity to the minimum discharge amount, and the control cylinder 10
When the fluid is removed, the pump capacity is increased, and the flow rate to the discharge circuit 3 is increased to maintain a constant differential pressure between the load pressure of the actuator 4 and the discharge pressure of the variable pump 1 discharged to the discharge circuit 3. It is controlled so that it is discharged at 1. Further, the control valve 12 is activated by the control cylinder 1 when the discharge pressure of the discharge circuit 3 becomes higher than the set spring pressure of the control valve 12.
The variable pump 1 is controlled to supply fluid to the variable pump 1, thereby reducing the pump capacity of the variable pump 1 and the discharge amount to the discharge circuit 3. By providing these control valves 11 and 12, the pressure and flow rate of the discharge circuit 3 can be maintained constant when the actuator 4 is driven, and the pressure feedback circuit 8
Since the load pressure is introduced from the actuator 4, the control operation can be performed quickly while the actuator 4 is being driven.

However, if the flow rate control valve 6 is suddenly operated to drive the actuator 4 from a state where the full flow rate control valve 6 is located at the neutral position and the drive of the actuator 4 is stopped, the variable pump 1 to flow control valve 6
Due to the compressibility of the fluid in the discharge circuit 3 and the pressure feedback circuit 8, there is a disadvantage that the transmission of pressure to the discharge amount control device 2 is delayed. A bleed-off circuit 14 is branched and connected from the front of the pressure reducing valve 5 to the tank 13, and the bleed-off circuit 14 is moved to close the bleed-off circuit 14 by the pressure of the pressure feedback circuit 8 and the force of the spring 15. A compensator valve 17 is provided with a plunger 16 that moves to open the bleed-off circuit 14 with the pressure of the discharge circuit 3, and the minimum discharge volume of the variable pump 1 is at least 10% of the maximum discharge volume of the variable pump 1. % was secured. In the case shown, the pressure of the pressure feedback circuit 8 is directed to the plunger 16 via the restriction 18;
The plunger 16 is made to be able to move stably even if there are pressure fluctuations.

With this configuration, when the full flow rate control valve 6 is closed and the actuator 4 is stopped, the compensator valve 17 has a relatively low pressure because the pressure feedback circuit 8 is connected to the tank line by the flow rate control valve 6. The bleed-off circuit 14 is opened by the discharge pressure (force by the spring 15 and tank pressure), and the fluid in the discharge circuit 3 flows to the tank 13 via the bleed-off circuit 14 and the compensator valve 17, so that the discharge rate control device 2 The variable pump 1 is controlled to discharge 10% of its maximum discharge amount, and the discharge circuit 3 is operated even when the actuator 4 is stopped.
is maintained filled with pressure fluid. When the flow control valve 6 is suddenly opened to drive the actuator 4, the compensator valve 17 closes and the actuator 4 starts moving with a small amount of fluid discharged from the variable pump 1. Since the discharge circuit 3 is filled with pressure fluid at the same time that the load pressure is introduced, the time delay in pressure rise is extremely small due to the compressibility of the fluid in the discharge circuit 3, and the discharge amount control device 2 The pump displacement of the variable pump 1 can be controlled immediately, and even when the actuator 4 is started, the operation according to the load pressure, that is, the load sensing operation can be performed quickly.

[0013]

As described above, in the present invention, in the load sensing device, the bleed-off circuit connected from the front of the pressure reducing valve of the discharge circuit to the tank, and the pressure of the pressure feedback circuit and the spring force are used to prevent the bleed-off. a compensator valve having a plunger moved to close the circuit and open the bleed-off circuit at the pressure of the discharge circuit; Even when the machine is stopped, a certain amount of flow is allowed to flow through the discharge circuit, so
Even when the actuator is started, the load sensing operation can be performed instantaneously, and the controllability of the actuator is improved.

[Brief explanation of the drawing]

[Figure 1] Diagram of conventional example

[Figure 2] Diagram of the embodiment of the present invention

[Explanation of symbols]

1 Variable pump 2
Discharge amount control device 3 Discharge circuit 4 Actuator 5 Pressure reducing valve 6 Flow rate control valve 8 Pressure feedback circuit 13 Tank 14 Bleed-off circuit 16
Plunger 17 Compensator valve

Claims (2)

[Claims] Claim 1: A pressure reducing valve and a flow rate control valve are sequentially provided in a discharge circuit that guides the discharge volume of a variable pump equipped with a discharge volume control device to an actuator, and the pressure of the discharge circuit is extracted from a location close to the actuator. In a load sensing device equipped with a pressure feedback circuit leading to a discharge amount control device, a bleed-off circuit is branched from the front of the pressure reducing valve of the discharge circuit to the tank, and a pressure feedback circuit is connected to the bleed-off circuit. A compensator valve having a plunger that is moved by pressure and a spring force to close the bleed-off circuit leaving a small opening area, and moved by the pressure of the discharge circuit to enlarge the opening area of the bleed-off circuit. A load sensing device characterized in that the variable pump is provided with a minimum discharge amount of at least 10% of the maximum discharge amount of the variable pump. 2. The load sensing device according to claim 1, wherein the pressure of the pressure feedback circuit is guided to a compensator valve via a throttle.