JP3182614B2 - Hydraulic device in load sensing system - Google Patents

Description

The present invention relates to a hydraulic device in a load sensing system, in particular, to a discharge circuit of a single variable displacement pump, which is provided with a plurality of compensator valves and a directional switching valve. The present invention relates to a hydraulic device in a load sensing system as an oil drive device of a construction machine in which actuators are connected in parallel and the plurality of actuators can be operated simultaneously or individually.

(Prior Art) Conventionally, a plurality of high pressure actuators and low pressure actuators are connected in parallel to the discharge circuit of a single variable displacement pump, and the plurality of actuators can be operated simultaneously or individually. JP-A-1-
There is one as shown in Japanese Patent No. 176803.

In this device, a plurality of (for example, two) actuators are connected in parallel to a discharge circuit of a single variable displacement pump via a flow control valve with a compensator valve, and a connection circuit to each actuator is provided with a compensator valve. A flow control valve comprising a switching valve is provided, and the highest load pressure of each load pressure of each actuator is selected by a shuttle valve in a pump control device for controlling a variable displacement pump, and introduced via a pilot pipe. The discharge pressure of the pump is introduced, and the pressure and flow according to the load pressure of each actuator are controlled by the operation of the pump control device.

The compensator valve is resiliently pressed by a compensator spring, and a plunger on which a load pressure of an actuator acts is provided in the flow path. Fluid pressure downstream of a throttle provided in the plunger faces the plunger with the spring. The plunger is moved to a position where the force of the spring and the load pressure balances with the force of the fluid pressure downstream of the throttle when the control valve flows from the discharge circuit to the actuator via the connection circuit by operating the switching valve. It moves to adjust the throttle area, and the pressure of the control flow rate is compensated.

Further, the pump control device includes a pressure control valve for controlling the introduction and discharge of the fluid to the tilt cylinder for changing the pump capacity, and a flow control valve. When it increases, the fluid of the discharge circuit is guided to the tilt cylinder so as to perform the operation of reducing the pump capacity, and the flow control valve has the highest load pressure and pump discharge pressure among the actuators introduced through the pilot arrangement. When the difference becomes equal to or larger than the set value, the fluid of the discharge circuit is guided to the tilt cylinder, and the pump discharge amount of the pump is reduced.

(Problems to be Solved by the Invention) However, in this case, in the load sensing system, in order to control the flow rate, the maximum pressure among the load pressures of the actuators is selected by a shuttle valve, and the variable displacement pump is used. Feedback to
When none of the directional control valves is operated, the feedback signal circuit is at tank pressure. When the directional control valve is operated so as to guide the pressure oil to the holding side of the actuator, the holding pressure is transmitted to the feedback circuit.

Naturally, in such a hydraulic device in the conventional load sensing system, the actuator holding pressure in the feedback signal circuit depends on the length of the pipe or hose of the feedback signal circuit, their material, and the like. Immediately after the signal line of each actuator is opened, in other words, immediately before the actuator starts to move, pressure oil on the holding side of each actuator may flow back to the signal line due to the volume change caused by The following inconveniences may occur.
(A) For example, when a target object is hung by the hook in a crane operation or the like, a part of the pressure oil that maintains its operating state at the beginning of its movement despite the operation of raising the boom. Moves to the signal circuit side, the boom cylinder shrinks a little (corresponding amount) and the telescopic boom lowers, and the telescopic boom itself interferes with other buildings, structures, etc. around the same boom, Inadvertent lowering of the suspended luggage and the like may cause interference with buildings, equipment, and the like around the boom.

(B) When working on a slope, for example, when performing a turning operation toward an upper side of a slope, at the beginning of turning of the turntable, there is a possibility that the turntable actually falls slightly below a reverse slope. .

(C) Even in the case of excavator work, if the arms, buckets, and the like are moved in the direction opposite to the direction of the load on them, there is a possibility that the arms, buckets, and the like slightly move in the direction of the load at the beginning of their operation.

The present invention has been made in view of such a problem in the conventional example, and by preventing a backflow of oil in a feedback signal circuit by a switching valve having a check valve,
An object of the present invention is to provide a hydraulic device in a load sensing system that can solve the above-described problems.

(Means for Solving the Problems) In order to solve the problems of the conventional example as described above, the present invention provides a plurality of actuators in parallel in a discharge circuit of a single variable displacement pump via a compensator valve and a direction switching valve. A load sensing system for controlling the discharge amount of the variable displacement pump by selecting the maximum load pressure of the plurality of actuators by a shuttle valve and applying the selected maximum pressure as a feedback signal to the control unit of the variable displacement pump. In a feedback signal circuit between the pressure oil supply / discharge direction switching valve to each of the actuators and the variable displacement pump, a switching valve for switching the signal pressure of the feedback circuit is provided, and the holding pressure of each of the actuators is adjusted. To prevent the backflow of the pressure oil in the feedback signal circuit, A spring is used to urge the spool open side for releasing the flow from the supply / discharge direction switching valve provided in the path to the variable displacement pump control device, and the feedback circuit pressure is applied as a pilot pressure of the switching valve. The discharge pressure of the variable displacement pump is simultaneously applied as a pilot pressure to a spool closing side for blocking the flow from the supply / discharge direction switching valve to the variable displacement pump control device.

(Operation) Since the present invention has the above-described configuration, a plurality of actuators are connected in parallel to a discharge circuit of a single variable displacement pump via a compensator valve and a direction switching valve, and the variable displacement pump is connected. In controlling the discharge flow rate or the like by selecting the maximum load pressure of the plurality of actuators by a shuttle valve and applying the maximum discharge pressure as a feedback signal to the control unit of the variable displacement pump, the feedback circuit The spring opening side (the state of FIG. 2 in which the spring 62 extends) for releasing the flow from the supply / discharge direction switching valve provided to the variable displacement pump control device is biased by a spring, and the feedback circuit pressure is also switched. While applying the pilot pressure of the valve, the flow from the supply / discharge direction switching valve to the variable displacement pump control device is shut off. The discharge pressure of the variable displacement pump is simultaneously applied as the pilot pressure to the spool closed side (the compressed state of the spring 62 for pressing the spool 61 in FIG. 2), and the switching valve provided in the feedback circuit is operated by the operation of each actuator. The switching operation is performed before the start to prevent the backflow of the pressure oil in the feedback signal circuit due to the holding pressure of each of the actuators, thereby preventing the inadvertent movement of each of the actuators such as the boom.

(Embodiment) Hereinafter, a main part of an example in which a switching valve can be automatically switched by a branch pressure between a feedback signal circuit and a discharge circuit according to an embodiment of a hydraulic device in a load sensing system according to the present invention will be described. This will be described with reference to FIGS. 1 and 2.

Figure 1 is a branch circuit 64 pressure p ₂ of the feedback signal circuit 7 a switching valve 60 of the present invention, description of the control circuit of the example of switching operation by the branch circuit 65 pressure p ₁ of the discharge circuit 3 of the variable displacement pump 1 FIG. 2 is an enlarged explanatory view of the main part.

1 and 2, 1 is a variable displacement pump, 2
Is a control section of the variable displacement pump 1, 3 is a discharge circuit of the variable displacement pump 1, 4 is a discharge circuit, 5 is a main relief valve, 6 is an unload valve, 7, 7b are feedback signal circuits, 7bb
Is a branch path from the feedback signal circuit 7b, 10 is a direction switching valve block, 11 to 17 are direction switching valves, and each of the direction switching valves 11 to 17 is a pressure oil discharged from a single variable displacement pump 1, respectively. Are supplied to and discharged from a plurality of actuators such as a bucket cylinder 21, a boom cylinder 23, left and right traveling motors 24 and 25, a swing motor 26, and an arm cylinder 27 via the drive circuits 11E to 17E.

21A, 21B, 23A, 23B, 27A, 27B are bucket cylinders
21, port relief valves of the hydraulic oil supply / discharge circuits 11E, 13E, 17E to the boom cylinder 23, the arm cylinder 27, 31 to 37 are compensator valves, and the compensator valves 31 to 37 are in front of the direction switching valves 11 to 17. (Variable displacement pump 1
The pressure oil supplied from the discharge circuit 3 of the variable displacement pump 1 is adjusted and supplied to the actuators 21 to 27 via the directional switching valves 11 to 17. 42 or 4
6 and 48 are shuttle valves for selecting the maximum load pressure of the adjacent actuators 21 to 27.

A switching valve 60 having a branch 7bb is provided in the feedback signal circuit 7 connecting the shuttle valve 48 and the control unit 2 of the variable displacement pump 1, and a spool 61 of the switching valve 60 has one side (first, second, The switching valve 60 is constantly pressed to the right by a spring 62 provided on the left side (in the figure, on the left side), and the switching valve 60 sends the signal pressure of the feedback signal circuit 7 to the control unit 2 of the variable displacement pump 1 via the check valve 63. The feedback signal circuit 7 is timely shut off by applying the voltage via the oil path 7b with 7bb and moving the spool 61 to the left against the spring 62.

In this embodiment, the side on which the force (F) of the spring 62 of the spool 61 of the switching valve 60 acts (the left side in FIGS. 1 and 2).
At the same time, the hydraulic pressure of the feedback signal circuit 7 (P ₂ )
Is applied via the branch path 64, and the hydraulic pressure (P ₁ ) of the discharge circuit 3 of the variable displacement pump 1 is simultaneously applied to the other side of the spool 61 via the branch circuit 65 from the discharge circuit 3. .

This relationship will be described in more detail with reference to FIG. In FIG. 2, P ₁ : hydraulic pressure of the pump discharge circuit 3 P ₂ : hydraulic pressure of the feedback signal circuit 7 F: force of the spring 62 A: area of the spool 61. (F + P ₂ × A) acts on the left side of (61), and (P ₁ + A) acts on the right side.

 As a result, the spool 61 moves in the following relationship.

Movement _{F + P 2 × A> P} 1 × mobile A ··· spool 61 to the right _{F + P 2 × A <P} 1 × A ··· spool 61 to the left also, the force F of the spring 62 under the following relationship Set with.

ΔP ₀ × A <F <Pa × A where ΔP _{0 is} the control pressure of the control unit 2 of the variable displacement pump 1 (P ₁ , P ₂
Pa: relief pressure (cracking pressure) of the unload valve 6 A: area of the spool 61 (operation of the embodiment) (D) In the embodiment of the present invention, when the engine is stopped, the variable displacement pump 1 Both the discharge pressure P ₁ and the circuit pressure P ₂ of the feedback signal circuit 7 are the tank T pressure (= 0 Kg / c
m ² ), the relationship on both sides of the spool 61 of the switching valve 60 is as follows.

_{Left: F + P 2 × A =} F right: P ₁ × A = 0 Therefore, the _{F + P 2 × A> P} 1 × A or more, the spool 61 is moved to the right as in FIG. 1, the signal of the feedback signal circuit 7 The pressure acts on the controller 2 of the variable displacement pump 1.

(E) Before the engine is started and before the operation of the operation lever of each actuator is started, when the spool of each of the directional control valves 11 to 17 is in a neutral state, the discharge pressure P ₁ of the variable displacement pump ₁ is Since the relief pressure Pa is reached and the circuit pressure P ₂ of the feedback signal circuit 7 communicates with the tank T in any of the directional control valves 11 to 17, the tank pressure (= 0 kg)
/ cm ² ), the relationship between the two sides of the spool 61 of the switching valve 60 is as follows.

_{Left: F + P 2 × A =} F right: the settings in the force F P ₁ × A = Pa × A spring 62, since the F <Pa × A, by _{F + P 2 × A <P} 1 × A or more, the spool 61 Moves to the left and the check valve 63
Works.

(F) When the operation of the operation lever of each actuator is started, the spool of each of the directional control valves 11 to 17 moves, the feedback signal circuit 7 and the drive circuits 11E to 17E communicate in the spool, and immediately before each actuator starts to move, and When the required flow rate of the actuator determined by the opening degree of the direction switching valve is smaller than the minimum discharge rate of the variable displacement pump 1 at the time of inching operation or the like after the movement starts, an excess flow rate is generated. Is discharged to the tank.

The pressure of the surplus flow rate, that is, the discharge pressure P ₁ of the variable displacement pump 1 becomes the set pressure of the unload valve 6 (cracking pressure Pa of the unload valve 6 + feedback pressure P ₂ ). Is as follows.

Left: F + P ₂ × A _{right: P 1 × A = (P} 2 + Pa) × A = the setting of the force F P ₂ × A + Pa × A spring 62, since the F <Pa × A, F + P 2 × A < P ₁ × A With the above, the spool 61 remains moved to the left,
Since the check valve 63 operates, backflow of the pressure oil is prevented.

(G) When the required amount of the actuator is equal to or more than the minimum discharge flow rate of the variable displacement pump 1, the unload valve 6 is closed and the total discharge flow rate of the variable displacement pump 1 is reduced
Flow to 27. Since the variable displacement pump 1 controls the flow rate, the discharge pressure P ₁ of the variable displacement pump 1 becomes feedback circuit pressure P ₂ + control pressure ΔP ₀ , and the relationship between the two sides of the spool 61 of the switching valve 60 is as follows.

Left: F + P ₂ × A right: P ₁ × A = a _{(P 2 + ΔP 0) ×} A = P 2 × A + ΔP 0 × force F of A spring 62 set, since the _{F> ΔP 0 × A, F} + P 2 × A> P ₁ × A With the above, the spool 61 moves to the right and the check valve 63
Function is lost.

As described above, the switching valve 60 is switched just before the actuator starts to move and during the inching range after the actuator starts to move, and the check signal 63 is transmitted to the feedback signal circuit 7 by the feedback signal circuit 7 and the drive circuit. Is inserted, and backflow of the pressure oil on the holding side of the actuator to the feedback signal circuit 7 is prevented.

In addition, when the operation levers of the directional control valves 11 to 17 are fully operated (when the directional control valves 11 to 17 are fully opened), the check function of the check valve 63 is lost, and the state becomes the same as the conventional state. Does not wake up.

(Effects of the Invention) Since the present invention has the above-described configuration and operates, the following effects can be obtained.

(1) A switching valve having a branch circuit with a check valve is provided in a feedback circuit of a load sensing system in which a plurality of actuators can be operated simultaneously or individually by a single variable displacement pump. There is no danger that the pressure oil in the signal circuit will inadvertently flow backward, and therefore, there will be no danger of inadvertent movement of the boom or the like.

(2) A spring is applied to one side of a spool of a switching valve provided in a feedback circuit, a circuit pressure of the feedback signal circuit is applied as a pilot pressure of the valve, and the variable capacity is applied to the other side of the spool. Since the discharge pressure of the pump is configured to be applied, the spool of the switching valve is automatically switched by operating the operation lever of the direction switching valve of each actuator, and the occurrence of inadvertent movement of each actuator can be prevented. .

(3) At the start of operation of the operation lever of each actuator, the spool of each directional control valve moves, and the feedback signal circuit and the drive circuit pass through the spool of each directional control valve, immediately before each actuator starts to move, and the inching operation at the start of movement. When, for example, the required flow rate of the actuator determined by the degree of opening of each directional control valve is less than the minimum discharge rate of the variable displacement pump, the excess flow generated is discharged from the unload valve to the tank. The pressure (discharge circuit pressure of the variable displacement pump) is determined by the set pressure of the unload valve, and the relationship between the two sides of the spool of the switching valve is determined by the setting of the spring pressure. Normally, the spool is left moved. The check valve acts to prevent the backflow of pressure oil in the discharge circuit of the variable displacement pump, preventing inadvertent movement of each actuator. It is.

(4) In the feedback circuit of the operation circuit for the drive circuit of the multiple actuators by the existing single variable displacement pump,
The present invention can be easily implemented by a simple structural change simply by providing a switching valve with a check valve.

[Brief description of the drawings]

The drawings schematically show an embodiment of a hydraulic device in a load sensing system according to the present invention. FIG. 1 is an explanatory diagram of a control circuit of the first embodiment, and FIG. 2 is an enlarged view of a main part of the control circuit. FIG. (Explanation of symbols) 1... Variable displacement pump 2... Control unit 3... Discharge circuit 4... Discharge circuit 5... Main relief valve 6... Unload valve 7... Feedback signal circuit 7 b. Road 7bb Branch road 11-17 Direction switching valve 11E-17E Drive circuit 21-27 Actuator 21A, B Port relief valve 23A, B Port relief valve 27A, B Port relief Valves 31 to 37 Compensator valves 42 to 46, 48 Shuttle valve 60 Switching valve 61 Spool 62 Spring 63 Check valve 64 Branch circuit (of pilot signal circuit 7) 65 branch circuit (discharge circuit 3) F ...... force p ₁ ...... branching circuit 65 pressure p ₂ ...... branching circuit 64 pressure spring 62

Claims (1)

(57) [Claims] A plurality of actuators are connected in parallel to a discharge circuit of a single variable displacement pump via a compensator valve and a direction switching valve, and a discharge amount of the variable displacement pump is controlled by a maximum load pressure of the plurality of actuators. Is selected by the shuttle valve and controlled by applying the feedback signal to the control unit of the variable displacement pump,
In a load sensing system, a switching valve for switching a signal pressure of the feedback circuit is provided in a feedback signal circuit between a direction switching valve for supplying and discharging pressure oil to each of the actuators and the variable displacement pump; The spool opening side for preventing the backflow of the pressure oil of the feedback signal circuit due to the holding pressure and releasing the flow from the supply / discharge direction switching valve provided in the feedback circuit to the variable displacement pump control device is spring-loaded. And applies the feedback circuit pressure as the pilot pressure of the switching valve, and discharges the variable displacement pump to the spool closed side to shut off the flow from the supply / discharge direction switching valve to the variable displacement pump control device. Load sensing characterized by simultaneously applying pressure as its pilot pressure Hydraulic device in the system.