JPH04285301A - Hydraulic circuit for improving work accuracy in load sensing system - Google Patents

Abstract

PURPOSE:To make highly accurate work executable by, when a working machine lever is quickly operated in a construction machine such as a hydraulic excavating machine, actuating a working machine according to a lever operation made by an operator regardless of the quality of the responsiveness of a hydraulic pump. CONSTITUTION:An electromagnetic valve 11 is provided to change an actuator load pressure acting on the left end of LS5 controlling the discharge of a variable delivery hydraulic pump 1 into a pump delivery pressure. When a pressure switch 20 detects the motion of an operation lever 17, a controller 21 sends a command current to the valve 11 to excite it for the above changeover of the pressure. The delivery of the pump 1 therefore attains the maximum regardless of the value of the load pressure of the actuator 2, and an excess flow quantity is drained through an unloading pressure control valve 16. In addition to that, an ordinary load sensing system can be maintained by operating a mode changeover switch 23.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a hydraulic drive device mounted on a construction machine such as a hydraulic excavator, and in particular, the differential pressure between the discharge pressure of a hydraulic pump and the load pressure of an actuator is maintained at a set value. This invention relates to a hydraulic circuit for improving work accuracy in a load sensing system that controls the discharge amount of a hydraulic pump.

0002

[Prior Art] In a hydraulic machine equipped with a hydraulic drive device equipped with a load sensing system, such as a hydraulic excavator, as shown in FIG. 6, a variable displacement hydraulic pump (hereinafter referred to as (referred to as a pump) 1, and a hydraulic actuator (hereinafter referred to as an actuator) 2 driven by the pressure oil discharged by this pump 1.
, a closed center directional control valve 3 that switches the direction of pressure oil sent from the pump 1 to the actuator 2, and a regulator 4 that controls the flow rate of the pressure oil discharged by the pump 1.
and LS valve 5.

The directional control valve 3 has three positions, and is connected to a shuttle valve 10 through a port R at each position. Pilot circuits 12a, 12b, etc. are connected to the shuttle valve 10, and a pressure compensation valve 14 inserted into the circuits 2a, 2b of the actuator 2 via the pilot circuit 13.
a, 14b. In addition, an unload valve 16 is connected to a branch circuit 15 of the circuit 6 leading from the pump 1 to the directional control valve 3.
A pump discharge pressure PP is introduced to one end of the unload valve 16, and a load pressure PLS is introduced to the other end.

The discharge pressure PP of the pump 1 is guided to one end of the LS valve 5 by a pilot circuit 9, and the highest pressure among the load pressures of each actuator is guided to the other end of the shuttle valve 1.
0 as pressure PLS. Note that a coil spring 5a for setting a differential pressure is disposed at the other end of the LS valve 5.

[0005] Pressure oil flow rate QA supplied to the actuator
can be expressed by the following equation, where PP is the pump discharge pressure, c is the flow coefficient, A is the opening area of the directional valve, and PLS is the actuator load pressure. QA = c x A x (PP-PLS) 1/2 differential pressure PP-P
Since LS is controlled to be constant, the actuator flow rate QA is controlled according to the opening area A of the directional control valve, that is, the operating amount of the operating lever. Also, if the differential pressure is 20 kg/cm2, QA =
c×A×201/2.

[0006]

[Problem to be Solved by the Invention] In the load sensing system, since the differential pressure PP-PLS is controlled to be constant, the pump discharge amount QP is determined by the opening area A of the directional valve, that is, the operating amount of the operating lever. This means that there is no loss in flow rate. If the operating lever 17 is held in the neutral position while the pump 1 is being driven, the directional control valve 3 will also be in the neutral position, and the pressure PLS in the pilot line 12b will be the same as the tank pressure. Therefore,
Since the differential pressure PP-PLS becomes larger than the set value, the LS valve 5 is switched, the regulator 4 operates so that the swash plate angle of the pump 1 becomes smaller, and the pump discharge amount QP decreases.

When the work equipment control lever is suddenly operated from a neutral state, the increase in pump discharge amount depends on the responsiveness of the pump. A delay occurs as shown by the solid line. As a result, for example, during straight finishing excavation, there is a time lag in the operation of the working machine relative to the lever operation by the operator, making it impossible to perform work with extremely high precision.

[0008] The present invention has focused on the above-mentioned problems of the conventional art, and is capable of supplying a sufficient flow rate to an actuator in response to a sudden operation of a control lever as needed, regardless of whether the responsiveness of the pump is good or not. The purpose of this invention is to provide a hydraulic circuit for improving work accuracy in a load sensing system that enables high-precision work.

[0009]

[Means for Solving the Problems] In order to achieve the above object, a work accuracy improvement circuit in a load sensing system according to the present invention is driven by a variable displacement hydraulic pump and pressure oil discharged by the variable displacement hydraulic pump. a hydraulic actuator, a directional control valve that controls the flow of pressure oil supplied from the variable displacement hydraulic pump to the hydraulic actuator, and a discharge amount control that controls the flow rate of the pressure oil discharged from the variable displacement hydraulic pump. and an unload valve that operates at a pressure equal to or higher than a certain set pressure relative to the load pressure PLS of the hydraulic actuator, and the discharge amount control means drives the variable displacement means of the variable displacement hydraulic pump;
A hydraulic drive device comprising an LS valve that controls the drive of the regulator according to the differential pressure between the discharge pressure PP of the variable displacement hydraulic pump and the load pressure PLS of the hydraulic actuator, and maintains the differential pressure PP-PLS at a set value. means for detecting movement of an operating lever for driving a hydraulic actuator; and a means for detecting a movement of a control lever for driving a hydraulic actuator, and a means for adjusting a load pressure PLS of the hydraulic actuator acting on the LS valve to a discharge pressure PP of a variable displacement hydraulic pump based on a detection signal of the detection means. In such a structure, the means for switching the load pressure PLS of the hydraulic actuator acting on the LS valve to the discharge pressure PP of the variable displacement hydraulic pump is a mode changeover switch that outputs a command signal to the controller. , a pressure switch that detects an increase in the pilot oil pressure that drives the directional valve and outputs a detection signal to the controller, a solenoid valve installed in the actuator load pressure transmission circuit from the directional valve to the LS valve, and this solenoid valve. The solenoid valve is connected to a transmission circuit for the discharge pressure PP of a variable displacement hydraulic pump, and the solenoid valve is connected to a mode changeover switch connected to the controller, and The pressure switch is driven by a command current output from the controller when the detection signal of the pressure switch is input to the controller.

0010

[Operation] According to the above configuration, when movement of the operating lever is detected, the actuator load pressure acting on one end of the LS valve is switched to the pump discharge pressure, thereby driving the regulator so that the pump discharge amount is maximized. Therefore, the pump discharge amount is always the maximum regardless of the actuator load. Therefore, even if the control lever is suddenly operated, a sufficient flow rate is ensured regardless of the responsiveness of the pump, and the actuator can be driven in accordance with the operation of the control lever.

The above operation for maximizing the pump discharge amount is executed only when the mode changeover switch is changed, so if it is not necessary, by operating the mode changeover switch, the actuator using the conventional load sensing system can be activated. can be driven.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a hydraulic circuit for improving work accuracy in a load sensing system according to the present invention is applied to a hydraulic excavator will be described below with reference to the drawings. Figure 1
is a hydraulic circuit diagram showing the basic configuration of the present invention, which includes a directional control valve,
Only one hydraulic actuator and the like is shown as a representative. A pump 1 and an actuator 2 for a working machine such as a boom, arm, or bucket of a hydraulic excavator or a swing device that is driven by the pressure oil discharged by the pump 1.
, a closed center directional control valve 3 that switches the direction of pressure oil sent from the pump 1 to the actuator 2, and a regulator 4 that controls the flow rate of the pressure oil discharged by the pump 1.
and LS valve 5.

The directional control valve 3 is connected to the pump 1 through a circuit 6 and to the oil tank 7 through a circuit 8. Also L
One end of the S valve 5 is connected to a pilot circuit 9 branched from the circuit 6 to receive the discharge pressure PP of the pump 1, and the other end receives the highest pressure among the load pressures of each actuator to the shuttle valve 1.
0 and through the solenoid valve 11 as pressure PLS, L
The S valve 5 drives the regulator 4 to control the discharge amount QP of the pump 1.

[0014] Circuits 2a and 2b are connected to the actuator 2, respectively. The directional control valve 3 has three positions and is connected to the shuttle valve 10 via a port R at each position. The shuttle valve 10 includes a pilot circuit 12a,
12b is connected to the pressure compensating valves 14a, 1 inserted into the circuits 2a, 2b via the pilot circuit 13.
The pressure PLS is introduced to 4b.

An unload valve 16 is provided in the branch circuit 15 of the circuit 6 leading from the pump 1 to the directional control valve 3, and the pump discharge pressure PP is introduced to one end of the unload valve 16, and the circuit 12b is introduced to the other end of the unload valve 16. The load pressure PLS is guided by a pilot circuit 12c branching from the pilot circuit 12c.

[0016] A pilot pressure proportional control valve (
A pressure switch 20 is provided in a branch circuit of a pilot circuit 19 from a PPC valve (hereinafter referred to as a PPC valve) 18 to a directional control valve 3, and an output wiring 20a of this pressure switch 20 is connected to a controller 21. Further, the output wiring 21a of the controller 21 is connected to the solenoid of the electromagnetic valve 11. The solenoid valve 11 is a 3-port 2-position switching valve, and the inlet port is connected to the circuit 12b and the circuit 9a connected to the pilot circuit 9, and the outlet port is connected to the pilot circuit 22 that transmits the pressure PLS to the LS valve 5. has been done. The output wiring of the mode changeover switch 23 is connected to the controller 21.

Next, the operation of the work precision improving hydraulic circuit having the above structure will be explained. Mode changeover switch 23
When turned on, the controller 21 is switched to high precision mode. When the operator moves the operating lever 17 from the neutral position in either direction, the PPC valve 18 is activated and the oil pressure in the pilot circuit 19 leading to the directional control valve 3 increases in accordance with the operating stroke of the operating lever 17. The pressure switch 20 detects this oil pressure increase, and the controller 21
Outputs a detection signal to When the solenoid of the solenoid valve 11 is excited by the command current of the controller 21 that receives this detection signal and the solenoid valve 11 is switched to the A position, the pump discharge pressure circuit 9a and the circuit 22 are connected via the solenoid valve 11. , the pressure PLSP acting on the left end of the LS valve 5 is P
LSP=PP. In other words, the differential pressure is PP −
Since PLSP =0, the pump discharge amount is fixed at point A in FIG. 2 and always becomes maximum. When the amount of oil supplied to the actuator 2 is too large, the unload valve 16
operates and returns excess oil to the oil tank. Here, the cracking pressure of the unload valve 16 is set to 30 kg/cm, for example.
2, the differential pressure across the directional control valve 3 when the unload valve 16 operates is PP-PLS = 30k.
g/cm2, and the oil amount QA supplied to the actuator 2 is QA=c×A×301/2. As a result, even if the operating lever 17 is suddenly operated, the flow rate of the above formula is always maintained, so there is no delay in the actual pump flow rate corresponding to the operating lever 17, and the work equipment moves without a time lag, resulting in high accuracy. Be able to work.

FIG. 3 is a diagram showing the relationship between the operating lever stroke and the actuator flow rate in the high precision mode. The pump discharge amount QP is always constant at the maximum flow rate. When the operating lever stroke is S1, the flow rate supplied to the actuator is Q1, and the remainder, QP-Q1, is returned to the oil tank through the unload valve. When the operating lever stroke is suddenly operated from S1 to S2, the flow rate supplied to the actuator immediately increases to Q2, and the remainder, QP-Q2, is returned to the oil tank through the unload valve. Therefore, the actuator flow rate increases or decreases without delay in response to the movement of the operating lever.

The movement of the operating lever is detected by a pressure switch, and the relationship between the ON/OFF of this pressure switch and the energization (ON) and demagnetization (OFF) of the solenoid valve is as shown in the time chart of FIG. . When the pressure switch detects the movement of the operating lever and turns on, the solenoid valve is energized almost at the same time. When the operation lever stops moving, the pressure switch detects this and turns OFF. The solenoid valve is energized for 1 to 2 seconds after the pressure switch is turned off.
It is then demagnetized. This is done by temporarily stopping the control lever and
This is to prevent fluctuations in the pump discharge amount due to repeated demagnetization and excitation and wear and tear on the electromagnetic valve solenoid, since the pump may be moved immediately thereafter.

FIG. 5 is a flowchart showing the control procedure of the controller that controls the above operations. In the figure, 1 to 5 indicate steps in the flowchart. When the mode changeover switch is turned on to set the high precision mode, in step 1 it is determined whether a pilot oil pressure detection signal is input from the pressure switch. If a detection signal is input, a command current is output to the solenoid valve in step 2, and the solenoid of the solenoid valve is energized. If no detection signal is input, return to step 1. Next, in step 3, it is determined whether the detection signal is being continuously inputted, and if the detection signal is being continuously inputted, the process returns to step 2, and the command current output to the electromagnetic valve is continued. When the detection signal is cut off, in step 4, it is determined whether one second (or two seconds) has passed since the detection signal was cut off. If the time has not elapsed, step 4 is repeated, and if it has elapsed, the output of the command current to the solenoid valve is stopped in step 5. After that, the process returns to step 1, and it is determined whether or not the next detection signal is input.

When the mode selector switch 23 is OFF, the mode is in the normal mode, and even if the output signal of the pressure switch 20 is input to the controller 21, no command current is output from the controller 21 to the solenoid valve 11, so the solenoid valve is not switched. do not have. Therefore, the actuator load pressure PLS acts as PLSP on the left end of the LS valve 5, and the pump discharge amount changes as shown in B in FIG. 2, thus functioning as a load sensing system.

[0022]

[Effects of the Invention] As explained above, according to the present invention, the flow rate of pressure oil supplied from the pump to the directional control valve can be switched between two types: high precision mode and normal mode. The system ensures that maximum flow is always supplied to the directional valve when movement of the operating lever is detected.
Even when the operating lever is suddenly operated, the actuator flow rate changes immediately in response to the operating lever stroke. Therefore, there is no time lag in the operation of the actuator, and the work machine can be moved as intended by the operator, making it possible to perform work with extremely high precision.

In the normal mode, the pump discharge amount is equal to the actuator flow rate, so there is no loss in pump discharge amount, and energy-saving work can be performed. In the present invention, these two types of work modes can be arbitrarily selected.

[Brief explanation of the drawing]

FIG. 1 is a hydraulic circuit diagram for improving work accuracy showing the basic configuration of the present invention.

FIG. 2 is a diagram showing the relationship between the magnitude of the differential pressure generated before and after the directional switching valve and the pump discharge amount.

FIG. 3 is a diagram showing the relationship between the operating lever stroke and the actuator flow rate in high precision mode.

[Figure 4] Pressure switch ON/O in high precision mode
It is a time chart showing the relationship between FF and excitation and demagnetization of a solenoid valve.

FIG. 5 is a flowchart showing a control procedure of the controller in high precision mode.

FIG. 6 is a hydraulic circuit diagram showing the basic configuration of a conventional load sensing system.

FIG. 7 is an explanatory diagram showing how the actual flow rate of the pump follows the operation of the operating lever.

[Explanation of symbols]

1 Variable displacement hydraulic pump 2 Hydraulic actuator 3 Directional switching valve 4 Regulator 5 LS valve 11 Solenoid valve 16 Unload valve 17 Operation lever 20 Pressure switch 21 Controller 23 Mode changeover switch

Claims (3)

[Claims] 1. A variable displacement hydraulic pump, a hydraulic actuator driven by pressure oil discharged by the variable displacement hydraulic pump, and controlling the flow of pressure oil supplied from the variable displacement hydraulic pump to the hydraulic actuator. a directional switching valve that controls the hydraulic pressure, a discharge amount control means that controls the flow rate of pressure oil discharged from the variable displacement hydraulic pump, and an unload valve that operates at a pressure equal to or higher than a certain set pressure relative to the load pressure PLS of the hydraulic actuator. , a regulator in which the discharge amount control means drives a variable displacement means of a variable displacement hydraulic pump;
A hydraulic drive device comprising an LS valve that controls the drive of the regulator according to the differential pressure between the discharge pressure PP of the variable displacement hydraulic pump and the load pressure PLS of the hydraulic actuator, and maintains the differential pressure PP-PLS at a set value. means for detecting movement of an operating lever for driving a hydraulic actuator; and a means for detecting a movement of a control lever for driving a hydraulic actuator, and a means for adjusting a load pressure PLS of the hydraulic actuator acting on the LS valve to a discharge pressure PP of a variable displacement hydraulic pump based on a detection signal of the detection means. A hydraulic circuit for improving work accuracy in a load sensing system, characterized in that it is provided with a switching means. [Claim 2] The load pressure PLS of the hydraulic actuator acting on the LS valve is set as the discharge pressure PP of the variable displacement hydraulic pump.
The means for switching is a mode changeover switch that outputs a command signal to the controller, a pressure switch that detects the increase in pilot oil pressure that drives the directional control valve and outputs a detection signal to the controller, and a control signal that extends from the directional control valve to the LS valve. It is characterized by comprising a solenoid valve provided in an actuator load pressure transmission circuit and a controller for controlling the drive of this solenoid valve, and a transmission circuit for the discharge pressure PP of a variable displacement hydraulic pump is connected to the solenoid valve. A hydraulic circuit for improving work accuracy in a load sensing system according to claim 1. 3. The solenoid valve is driven by a command current output from the controller when a detection signal from the pressure switch is input to the controller after switching a mode changeover switch connected to the controller. A hydraulic circuit for improving work accuracy in a load sensing system according to claim 1.