JPH04285303A - Hydraulic circuit for improving operability in load sensing system - Google Patents

Abstract

PURPOSE:To improve the operability of a hydraulic drive vehicle by preventing the effect that when, during the running of the hydraulic driven vehicle with a load sensing system, for instance a hydraulic excavating machine, its work machine is driven, a pressure compensating valve acts to distribute a flow rate according to the opening area ratio of the valve and the flow rate to a running motor decreases to greatly reduce the vehicle speed. CONSTITUTION:When the operating lever 17B of a work machine is operated during its running, pressure switches 20L, 20R, 20B severally send a detection signals to a controller 22, and an electromagnetic valve 26 is actuated by a command current issued from the controller 22 to change over a switching valve 23. A signal pressure PLS' acting on the pressure compensating valves 8L, 8R of directional control valves 3L, 3R to control running motors 2L, 2R is made smaller than a signal pressure PLS acting on a LS valve 5 by variable throttles 14a, 14b to increase a difference in a pressure before and behind the valves 3L, 3R. Thus a larger quantity of oil flows into the running motors 2L, 2R to prevent the lowering of a vehicle speed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic circuit for improving operability in a load sensing system.

0002

2. Description of the Related Art A hydraulic circuit shown in FIG. 4 is used in a vehicle equipped with a hydraulic drive device equipped with a load sensing system, such as a hydraulic excavator. This figure shows the schematic configuration of the hydraulic circuit related to the boom cylinder of the travel hydraulic motor (hereinafter referred to as the travel motor) and the hydraulic actuator that drives work equipment such as the boom, arm, and bucket. one variable displacement hydraulic pump (hereinafter referred to as pump) 1 driven by a power source; a left drive wheel drive motor 2L driven by the pressure oil discharged by this pump 1; and a right drive wheel drive motor 2.
R, boom cylinder 2B, closed center directional control valves 3L, 3R, 3B that switch the direction of the pressure oil sent from the pump 1 to the travel motors 2L, 2R and the boom cylinder 2B, and It is equipped with a regulator 4 and an LS valve 5 that control the flow rate.

One end of the LS valve 5 is connected to the discharge pressure PP of the pump 1 by a pilot circuit 16 branching from the circuit 6.
is guided to the other end, and the highest pressure PLS among the load pressures of each actuator including the travel motors 2L and 2R is guided to the other end.
is guided through shuttle valves 10, 11, a pilot circuit 12, and the like. In addition, the directional control valves 3L and 3R
, 3B, the pressure PLS is also guided to pressure compensating valves 8L, 8R, 8B provided at the outlet ports of the valves 8L, 3B, respectively, via pilot circuits 15L, 15R, 15B.

[0004] 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 stroke of the operating lever.

[0005]

Problems to be Solved by the Invention A hydraulic excavator sometimes drives working equipment such as a boom, an arm, and a bucket while traveling within a work site. When such a complex operation is performed, the deceleration rate of traveling is large due to the following reasons. Now, the discharge pressure of pump 1 is PP, the discharge amount is QP, and the flow rates to left travel motor 2L and right travel motor 2R are respectively Q1,
Q2, the flow rate to the boom cylinder 2B that drives the work equipment, for example, the boom, is Q3, the opening areas of the directional control valves 3L, 3R, and 3B that control each actuator are A1, A2, and A3, respectively, and the directional control valves 3L, 3R are , 3B are respectively P1, P2, P3, the load pressure of each actuator is PLS1, PLS2, PLS3, respectively, and the flow coefficient is c, then the boom cylinder load pressure PLS3
is larger than the load pressure PLS1, PLS2 of the traveling motor, so each pressure compensation valve 8L, 8R, 8B has the above-mentioned PLS3.
acts. Therefore, the pressure compensating valves 8L and 8R are throttled more than when only traveling, and the traveling motor 2L
, 2R decreases, resulting in deceleration. The flow rate to each actuator at this time can be expressed by the following formula. Q1 =c×A1×(PP-P1)1/2≒c
×A1×(PP-PLS3)1/2 Q2 =c
×A2×(PP-P2)1/2≒c×A2×(PP-P
LS3)1/2 Q3 =c×A3×(PP-P
3) 1/2≒c×A3×(PP-PLS3)1/2 The flow rate distribution to each actuator is QP = Q1+Q2+Q
3, so Q1=A1/(A1+A2+A3)×QPQ2=A2/
(A1+A2+A3)×QPQ3=A3/(A1+A2
+A3)×QP.

[0006] As a countermeasure to the above-mentioned problem, the spring tension of the pressure compensation valve installed in the traveling hydraulic circuit is reduced to loosen the pressure compensation characteristic, and when the vehicle makes a gentle turn from straight traveling,
The running speed of the drive wheel on the outside of the turn decreases, making it impossible for the operator to operate the vehicle as intended.

[0007] The present invention focuses on the above-mentioned conventional problems, and when traveling and driving the work equipment are performed at the same time, the traveling deceleration rate is made as small as possible, and the vehicle can be operated according to the operator's will. The present invention aims to provide a hydraulic circuit that improves operability in a load sensing system.

[0008]

[Means for Solving the Problems] In order to achieve the above object, a hydraulic circuit for improving operability in a load sensing system according to the present invention uses a variable displacement hydraulic pump and pressure oil discharged by the variable displacement hydraulic pump. A hydraulic actuator to be driven, a directional switching 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 by the variable displacement hydraulic pump. and a regulator for driving the variable displacement means of the variable displacement hydraulic pump, and a discharge pressure PP of the variable displacement hydraulic pump.
The drive of the regulator is controlled according to the differential pressure between the load pressure PLS of the hydraulic actuator and the load pressure PLS of the hydraulic actuator, and the differential pressure PP-PL is
In a hydraulic drive device comprising an LS valve that maintains S at a set value, a throttle is provided in a load sensing circuit that transmits a signal pressure to a pressure compensation valve provided between a directional control valve and an actuator, and the load sensing circuit A restrictor and a switching valve are provided in the circuit extending from the oil tank to the oil tank, and means is provided for switching the switching valve based on the operating conditions of the actuator operating lever or the pressure conditions generated by operating the operating lever. , the means for switching the switching valve includes means for detecting operation of an actuator operating lever, a controller for outputting a command current to the electromagnetic valve based on a detection signal outputted by the detection means, and transmitting a switching pilot pressure to the switching valve. The controller outputs a command current to the solenoid valve when at least one of the left and right traveling levers that control the hydraulic motor and at least one of the work equipment operating levers are operated. It was decided that

[0009]

[Operation] According to the above structure, the load sensing circuit that transmits signal pressure to the pressure compensating valve of the directional switching valve that controls the traveling motor is provided with a throttle and a switching valve, and at least one of the left and right traveling levers and the working machine Since means is provided for switching the switching valve by operating at least one of the operating levers, when the working machine is operated while traveling, the switching valve is switched and oil flows into the load sensing circuit. Due to the throttle provided in this circuit, a signal pressure PLS' lower than the maximum pressure PLS of the load acts on the pressure compensation valve of the directional control valve that controls the travel motor. On the other hand, L.S.
Since a signal pressure PLS equal to the maximum pressure of the load acts on the valve, the differential pressure across the directional control valve on the travel side becomes larger than before, and more pressure oil flows to the travel side. Therefore, the deceleration rate of travel can be kept low.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the hydraulic circuit for improving operability in a load sensing system according to the present invention will be described below with reference to the drawings. Figure 1 shows the schematic configuration of the hydraulic circuit related to the travel motor and the boom cylinder of the actuators for each work equipment in the load sensing system used in a hydraulic excavator. Patent application No. 1-82961 previously filed by the inventor
It is as follows. In FIG. 1, the load sensing system includes one pump 1, a travel motor 2L for the left drive wheel driven by the pressure oil discharged by the pump 1, a travel motor 2R for the right drive wheel, a boom cylinder 2B, and the pump 1. Closed center directional control valves 3L, 3R, 3B that switch the direction of pressure oil sent to the travel motors 2L, 2R and boom cylinder 2B, and regulators 4 and L that control the flow rate of the pressure oil discharged by the pump 1.
It is equipped with an S valve 5.

The directional control valves 3L, 3R, 3B are connected to circuits 6L, 6R, 6B branched from the discharge circuit 6 of the pump 1.
are connected to the directional control valves 3L, 3R, and 3B, respectively.
From travel motors 2L, 2R and boom cylinder 2B
Pressure compensation valves 8 are installed in circuits 7L, 7R, and 7B leading to
L, 8R, and 8B are provided. The load pressure of the hydraulic actuators including each travel motor is controlled by the pilot circuits 9L, 9R, 9B and the shuttle valve 10, respectively.
, 11 etc., the maximum value PLS is the pilot circuit 1
2 to one end of the LS valve 5. Further, a variable throttle 14a is provided in the branch circuit 13 of the pilot circuit 12, and the maximum value PLS of the actuator load pressure is applied to each pilot circuit 1 after passing through the variable throttle 14a.
Pressure compensation valves 8L, 8R, through 5L, 15R, 15B
Guided by 8B. The other end of the LS valve 5 is connected to a pilot circuit 16 branched from the circuit 6 and receives the discharge pressure PP of the pump 1.

Travel lever 17L provided near the driver's seat
, 17R, and an operating lever 17B for driving the boom are connected to PPC valves 18L, 18R, and 18B, respectively.
Pilot circuits 19L, 19 coming out of these PPC valves
R and 19B are connected to directional control valves 3L, 3R, and 3B, respectively. Also, the output wiring 21L of the pressure switches 20L, 20R, 20B that detect the pilot pressure
, 21R, and 21B are all connected to the controller 22.

A circuit 15c leading to the oil tank 15a is provided on the extension of the pilot circuit 15L, and this circuit 1
A variable throttle 14b and a switching valve 23 are installed at 5c. Further, a solenoid valve 26 is provided in a pilot circuit 25 connecting the hydraulic pump 24 and an end of the switching valve 23, and an output wiring 27 of the controller 22 is connected to a solenoid of the solenoid valve 26.

The controller 22 controls the PPC valve 18L, 1
Pressure switch 20L, 2 that detects pilot pressure of 8R
One or more of 0R is ON, and PPC valve 1
When the pressure switch 20B that detects the pilot pressure of 8B is turned on, a command current is output to the solenoid valve 26 via the output wiring 27.

With respect to the load pressure PLS acting on the LS valve 5, the signal pressure acting on the pressure compensation valves 8L, 8R, 8B is lower than PLS by passing through the variable throttle 14a.
'. The variable throttle 14b is operated by switching the switching valve 23 so that the pressure oil in the pilot circuits 15L and 15R is switched to the circuit 1.
When draining through 5c, pressure compensation valves 8L, 8R,
It is provided to maintain the signal pressure acting on 8B above a certain value.

As shown in FIG. 2, the pressure compensating valves 8L, 8R, and 8B are comprised of a check valve 8a that is slidable inside the valve body, a compensating piston 8c, and a spring 8d, and the signal pressure PLS is applied to the compensating piston 8c. It is guided into the spring chamber 8f from the provided hole 8e. The pressure oil that has passed through the directional control valve enters the check valve 8a from the passage 8g, pushes the compensating piston 8c and the spring 8d to the right in FIG. 2 to open the seat surface, and flows to the actuator port 8h. Now, if the signal pressure is PLS, the pressure in the compensation piston chamber 8f is also PLS, and the compensation piston 8c
Since the diameter of the check valve 8a is equal to the diameter of the check valve 8a, the pressure P1 in the inlet chamber 8g of the check valve 8a is higher than PLS by the spring force of the return spring 8d, but since the spring force is sufficiently weaker than the pressure PLS, P1 It can be considered as ≒PLS. In other words, the inlet pressure of the pressure compensation valve (the outlet pressure of the switching valve) is equal to the signal pressure PLS.
is approximately equal to .

Next, the operation of the above-mentioned operability improving hydraulic circuit will be explained. When the boom is driven while the hydraulic excavator is running, the pressure switches 20L, 20R,
20B are respectively turned ON, the solenoid valve 26 is excited by the command current of the controller 22, and the switching valve 23 is switched. Since the maximum value PLS of the actuator load pressure is the boom cylinder load pressure PLS3, if ΔP=PLS3-PLS'=PLS-PLS', then the flow rate to each actuator can be expressed by the following formula. Q1 =c×A1×(PP-P1)1/2≒c×A1×
(PP-PLS')1/2 (Reason: Depends on the characteristics of the pressure compensation valve) =c×A1×(PP-PLS3+△P)1/2Q2=
c×A2×(PP-P2)1/2≒c×A2×(PP-
PLS')1/2=c×A2×(PP-PLS3+△P
)1/2Q3 =c×A3×(PP-P3)1/2≒c
× A3 × (PP-PLS3) 1/2 (Reason; As can be seen from Fig.
) is high, the compensating piston 8c is pressed to the right end in the figure and the pressure compensating valve acts as a check valve, so the boom circuit with the highest pressure is expressed by this equation. ) Therefore, the differential pressure between Q1 and Q2 becomes larger by ΔP, and the flow rate to the travel motors 2L and 2R becomes larger than before. In the pressure compensation valve 8B, the relationship between the signal pressure PLS' guided to the spring chamber 8f and acting on the compensation piston 8c and the outlet pressure P3 of the directional control valve 3B becomes P3≒PLS3, and the pressure compensation function is lost. Only the check valve 8a functions.

By adjusting the variable throttles 14a and 14b, the magnitude of the signal pressure PLS' of the pressure compensating valves 8L and 8R can be changed, so that the optimum flow rate suitable for the purpose of use of the hydraulic excavator is supplied to the traveling side. can do. Further, the variable apertures 14a and 14b may be fixed apertures.

FIG. 3 shows the relationship between the operation state of the work equipment operating lever and the flow rate of pressure oil supplied to the travel motor. When the hydraulic excavator is running and the control lever of the work equipment, for example, the boom, is in the neutral position, the flow rate of pressure oil supplied to the drive motor is a flow rate that corresponds to the amount of operation of the drive lever, and this is 100%. %. When the boom operation lever is operated to full stroke in this state, the switching valve will turn OFF.
At F, that is, in the case of a normal load sensing system, the flow rate of pressure oil supplied to the travel motor is reduced to about 50%. However, when the switching valve is ON, the pressure oil flow rate is maintained at 70 to 80%, and the deceleration shock during operation of the working machine is also small.

In this embodiment, a pressure switch that detects the pilot pressure of the PPC valve is used as a means for detecting the operation of the actuator operating lever, but the present invention is not limited to this. A limit switch or a proximity switch, etc., which is activated when the

[0021]

As explained above, according to the present invention, a switching valve is provided in the load sensing circuit for a specific actuator, and the switching valve is driven based on the operating conditions or pressure conditions of the actuator operating lever. Since the pressure compensation characteristics of the directional switching valve that controls a specific actuator are made variable, when the switching valve is switched, the differential pressure across the directional switching valve increases, and the flow rate distribution is proportional to the opening area of each directional switching valve. It temporarily collapses, allowing more pressure oil to flow to a particular actuator. Therefore, when the present invention is applied to a travel actuator for a hydraulically driven vehicle,
When traveling and driving the work equipment at the same time, the travel deceleration rate is reduced, allowing the operator to operate the vehicle as desired. Furthermore, since the deceleration shock during operation of the work equipment is reduced, operator fatigue is reduced and work efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic partial hydraulic circuit diagram showing the basic configuration of the present invention.

FIG. 2 is a sectional view of the pressure compensation valve.

FIG. 3 is a diagram showing changes in the flow rate of pressurized oil supplied to the travel motor when the work implement lever is operated while the vehicle is traveling.

FIG. 4 is a schematic partial hydraulic circuit diagram showing the basic configuration of a hydraulic drive device equipped with a conventional load sensing system.

[Explanation of symbols]

1 Variable displacement hydraulic pump 2L Left travel hydraulic motor 2R Right travel hydraulic motor 2B Boom cylinder 3L, 3R, 3B Directional switching valve 4 Regulator 5 LS valve 6, 6L, 6R, 6B, 7L, 7R, 7B, 15c
Circuit 8L, 8R, 8B Pressure compensation valve 9L, 9R, 9B, 12, 15L, 15R, 15B, 1
6, 19L, 19R, 19B, 25 Pilot circuit 14a, 14b
Variable throttle 15a Oil tank 17L, 17R Travel lever 17B Boom lever 20L, 20R, 20B Pressure switch 22 Controller 23 Switching valve 26 Solenoid valve

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. and a discharge amount control means for controlling the flow rate of pressure oil discharged by the variable displacement hydraulic pump, the discharge amount control means being a regulator for driving the displacement variable means of the variable displacement hydraulic pump. , discharge pressure PP of variable displacement hydraulic pump
The drive of the regulator is controlled according to the differential pressure between the load pressure PLS of the hydraulic actuator and the load pressure PLS of the hydraulic actuator, and the differential pressure PP-PLS is
In a hydraulic drive device consisting of an LS valve that maintains the directional control valve at a set value, a throttle is provided in a load sensing circuit that transmits signal pressure to a pressure compensation valve provided between the directional control valve and a specific actuator, and the load sensing A load characterized in that a throttle and a switching valve are provided in a circuit leading from the circuit to an oil tank, and means is provided for switching the switching valve based on operating conditions of an actuator operating lever or pressure conditions generated by operating the operating lever. Hydraulic circuit for improved operability in sensing systems. 2. The means for switching the switching valve comprises: means for detecting operation of an actuator operating lever; a controller for outputting a command current to the electromagnetic valve based on a detection signal output by the detection means; and a controller for switching the switching valve. 2. A hydraulic circuit for improving operability in a load sensing system according to claim 1, further comprising a solenoid valve for transmitting pilot pressure. 3. The specific actuator is a left and right travel hydraulic motor, and the controller is configured to operate when at least one of a left and right travel lever that controls the hydraulic motor and at least one of a work equipment operating lever is operated. 2. A hydraulic circuit for improving operability in a load sensing system according to claim 1, wherein the hydraulic circuit outputs a command current to a solenoid valve.