WO1992016754A1

WO1992016754A1 - Hydraulic circuit improved in operability in load sensing system

Info

Publication number: WO1992016754A1
Application number: PCT/JP1992/000268
Authority: WO
Inventors: Hiroshi Imai
Original assignee: Kabushiki Kaisha Komatsu Seisakusho
Priority date: 1991-03-15
Filing date: 1992-03-06
Publication date: 1992-10-01
Also published as: JPH04285303A; JP3006777B2

Abstract

According to the present invention, a running speed reduction rate can be reduced as much as possible and a vehicle can be operated as an operator wishes when running and driving of a working machine are performed simultaneously. For this purpose, a throttle (14a) is provided in a load sensing circuit for transmitting signal pressure to pressure compensating valves (8L, 8R, 8B) provided between direction change-over valves (3L, 3R, 3B) and actuators (2L, 2R, 2B), a throttle (14b) and a change-over valve (23) are provided in a circuit extending from this load sensing circuit to an oil tank, and a means for changing over the change-over valve (23) on the basis of operating conditions and the like of an actuator operating lever is provided. When the working machine is operated during running, the change-over valve (23) is changed over, whereby low signal pressure acts on the pressure compensating valves (8L, 8R, 8B) of a running motor, whereby a signal pressure equal to the maximum pressure of the load acts on an LS valve (5), whereby the pressure difference across the direction change-over valves (3L, 3R) on the running side is increased, so that much more pressure oil is passed to the running side, to thereby decrease a running speed reduction rate.

Description

Improvement of operability in load sensing system Hydraulic surface technology

The present invention relates to a hydraulic circuit for improving operability of a vehicle equipped with a hydraulic drive device including a load sensing system.

Background technology

Vehicles equipped with a hydraulic drive equipped with a load sensing system, such as hydraulic excavators, use the hydraulic circuit shown in FIG. FIG. 1 shows a schematic configuration of a hydraulic motor for traveling (hereinafter referred to as a traveling motor) and a hydraulic circuit for a boom cylinder of a hydraulic actuator for driving a working machine such as a boom, an arm, and a bucket. One variable displacement hydraulic pump (hereinafter referred to as a pump) 1 driven by a power source such as an engine, and a traveling motor 2 for the left drive wheel driven by pressure oil discharged from the pump 1, and a right side Drive wheel travel motor 2R, boom cylinder 2B, and closed center directional control valve 3 that switches the direction of pressure oil sent from pump 1 to left and right travel motors 2L, 2R and boom cylinder 2B. L, 3.3 B and regulator 4 for controlling the flow rate of pressure oil discharged from pump 1 It has a sensing valve (referred to as a lower LS valve) 5.

At one end of the LS valve 5, the discharge pressure PP of the pump 1 is led by a pilot surface 16 branched from the pump discharge circuit 6, and at the other end, the traveling motors 2L and 2R are connected. load pressure P LS caries Chi highest pressure in each Akuchiyue Ichita to the, shuttle valve 1 0, 1 1 and pi Lock preparative circuit 1 2 _e also is led via a direction switching valve 3 The pressure relief valve 8 L. 8 R 8 B provided at the outlet port of L> 3 R and 3 B respectively has the above-mentioned load pressure P LS or the via-lot surface 15 L, 15 R, 1 Guided through 5B ':, ...? The pressure oil flow QA supplied to the tubing is determined by setting the pump discharge pressure to PP When the number is c and the opening area of the directional control valves 3L, 3R, 3β is A. Actuator load pressure is PLS, it can be expressed by the following formula.

Q = c A (PP-PLS) ^1/2

Since the differential pressure (PP-PLS) is controlled to be constant, the actuator flow QA is controlled according to the opening area A of the directional control valve, that is, the operating stroke of the operating lever. .

However, a hydraulic excavator sometimes drives a working machine such as a boom, an arm, and a bucket while traveling in a work site. When such a combined operation is performed, the speed reduction rate of traveling is large for the following reasons.

Now, assume that the discharge pressure of pump 1 is PP and the discharge amount is QP, the flow rates to left running motor 2L and right running motor 2β are Ql and Q2, respectively, , The opening areas of the directional control valves 3 L, 3, 3 する that control the actuators are A 1, A 2, A 3, respectively, and the outlet pressures of the directional control valves 3 L, 3 R, 3 B are respectively PI, P2, P 3, the food pressure of each actuator is P LSI, PLS2, PLS3, and the flow coefficient is c,

The load pressure PLS3 acts on each of the pressure supplement valves 8L, 8R, and 8B because the load pressure PLS3 of the bump cylinder is larger than the load pressures PLS1 and PLS2 of the traveling motor. Accordingly, the pressure augmentation valves 8L and 8R are throttled greatly when only traveling, and the flow rate supplied to the traveling motors 2L and 2R is reduced, so that the speed is reduced. At this time, the flow rate to each actuator can be expressed by the following equation.

Ql-c Al X (PP-P 1) ^1/2 ^ c X Al (PP-P LS3) ^1/2 Q2 = c A 2 (PP-P2) ^1/2 ^ cx A2 x (PP-P LS3) ^1/2 Q3 = cx A 3 (PP — P 3) ^lz ^ cx A 3 (PP-P LS3: ^1/2 or .. The flow distribution to each T queue is QP = Q1-Q2-Q3 --AI (A1-A2-A3 :) x QP

Q A 2 / (A 1-A 2 * A 3) Q P

Q ■ = Λ3 '(Al-A2 — A3) QP Which is proportional to the opening areas A l, A 2, and A 3.

Therefore, the pressure compensation characteristic is reduced by reducing the spring tension of the pressure supplement valve 8 L> 8 R installed in the traveling hydraulic circuit so that the flow rate supplied to the traveling motors 2 L and 2 R does not decrease. It can also be done. However, this measure has a problem in that when the vehicle makes a gentle turn from straight traveling, the traveling speed of the drive wheels on the outer side of the turning surface decreases, and the vehicle cannot be operated as intended by the operator. Disclosure of the invention

The present invention focuses on the above-mentioned conventional problems, and makes it possible to minimize the traveling speed ratio as much as possible and to operate the vehicle as the operator intends when traveling and driving of the work machine are performed simultaneously. It is intended to provide a hydraulic circuit for improving operability in a load sensing system.

For this purpose, the present invention provides a variable displacement hydraulic pump, an actuator driven by pressure oil discharged from the variable displacement hydraulic pump, and a flow of pressure oil supplied from the variable displacement hydraulic pump to the actuator. And a discharge amount control means for controlling the flow rate of the pressure oil discharged from the variable displacement hydraulic pump. The discharge amount control means drives the displacement variable means of the variable displacement hydraulic pump. And a LS valve that controls the drive of the regulator according to the differential pressure between the discharge pressure of the variable displacement hydraulic pump and the load pressure of the actuator, and maintains the differential pressure at a set value. In the drive,

A throttle is provided in the load sensing surface for transmitting the signal pressure to the pressure compensating valve provided between the directional switching valve and the actuator, and the throttle extends from this load sensing surface to the oil tank. A circuit is provided with a throttle and a switching valve, and a means for switching the switching valve based on the operating condition of the actuator operating lever or the pressure condition generated by operating the operating lever is provided.

The means for switching the switching valve includes a means for detecting operation of the actuator operating lever, and a command current to the solenoid valve based on a detection signal output from the detecting means. It consists of a controller and a solenoid valve that transmits the pilot pressure to the switching valve.

In addition, the controller outputs a command current to the solenoid valve by operating at least one of the left and right travel levers for controlling the left and right travel motors and at least one of the work implement operation levers. .

Thus, a throttle and a switching valve are provided in the α-sensing surface for transmitting the signal pressure to the pressure compensation valve, and at least one of the left and right traveling levers and at least one of the work implement operation levers are operated. Therefore, a means for switching the switching valve is provided, so that when the work machine is operated during traveling, the switching valve is switched, and oil flows to the load sensing circuit. The throttle provided in this circuit causes a signal pressure lower than the maximum pressure of the load to act on the pressure supplement valve of the directional control valve that controls the traveling motor. On the other hand, since the signal pressure P LS equal to the minimum pressure of the load acts on the LS valve, the pressure difference between the front and rear of the directional control valve on the traveling side becomes larger than before, and more hydraulic oil flows on the traveling side. However, the running deceleration rate can be kept small. BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is a partial hydraulic circuit diagram showing the basic configuration of the present invention, Fig. 2 is an enlarged cross-sectional view of the pressure augmentation valve, and Fig. 3 is the hydraulic oil flow supplied to the traveling motor when the work implement lever is operated during traveling. FIG. 4 is a partial hydraulic circuit diagram showing a basic configuration of a hydraulic drive device provided with a conventional load sensing system. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of a hydraulic circuit for improving operability in a mouth sensing system according to the present invention will be described with reference to the drawings. The figure shows the schematic configuration of the hydraulic surface for the travel motor and the boom cylinder of the work equipment actuator in the code sensing system used for the hydraulic excavator.

In the figure, the load sensing system has one pump 1 and pump 1 The traveling motor 2 for the left driving wheel driven by the pressure oil discharged, the traveling motor 2 R for the right driving wheel, the bump cylinder 2 B, and the left and right traveling motors 2 L, 2 R and the boom cylinder 2 from the pump 1. The closed-center directional control valve 3 L> 3 R, 3 B that switches the direction of the pressure oil sent to B, and the regulator 4 and the LS valve 5 that control the flow rate of the pressure oil discharged from the pump 1 Have.

The directional control valves 3L, 3R, 3B are respectively connected to the surfaces 6L, 6R, 6B branched from the discharge circuit 6 of the pump 1, and the directional control valves 3L, 3R, 3B to the traveling motor 2L. , 2R and circuits 7L, 7R, 7B leading to the boom cylinder 2B are provided with pressure compensating valves 8L, 8R, 8B, respectively. The load pressure of each of the traveling motors 2 and 2R and the like of the cylinder 2B is passed through pilot circuits 9L, 9R and 9B and shuttle valves 10 and 11 respectively. The maximum value PLS is guided to one end of the LS valve 5 via the pilot circuit 12. Further, a variable throttle 14a is provided in the branch surface 13 of the pilot circuit 12 and the maximum value PLS of the actuator load pressure is changed to a signal pressure PLS after passing through the variable throttle 14a. 'Are respectively guided to the pressure recovery valves 8L, 8R, and 8B through the pilot surface paths 15L, 15R, and 15B. The other end of the LS valve 5 is connected to a pilot surface path 16 branched from the circuit 6, and receives the discharge pressure PP of the pump 1.

The traveling levers 17L and 17R provided near the driver's seat and the operating lever 17B for driving the boom are connected to PPC valves 18L, 18R and 18B, respectively. Pilot surfaces 19L, 19R, and 19B from valves 18L, 18R, and 18B are connected to directional valves 3L, 3R, and 3B, respectively. The output wires 21 L, 21 R, 21 B of the pressure switches 20 L, 20 R, 20 B for detecting the pilot pressure are all connected to the controller 22. It is connected to the.

No ,. A circuit 15c leading to the oil tank 15a is provided on the extension of the pilot circuit 15L, and a variable throttle 14b and a switching valve 23 are provided in the circuit 15c. ing. Also, a solenoid valve 26 is provided on a pilot surface 25 connecting the fixed hydraulic pump 24 and a part of the switching valve 23, and a solenoid is provided on the solenoid of the solenoid valve 26. Output wiring of roller 2 2 7 Is connected.

In the controller 22, at least one of the pressure switches 20 L and 20 R for detecting the pilot pressure of the PPC valves 18 L and 18 R is turned on, and the pilot switch of the PPC valve 18 B is turned on. > When the pressure switch 20B for detecting the V-to-pressure is turned ON, the command current is output to the solenoid valve 26 via the output wiring 7.

With respect to the maximum value PLS of the load pressure acting on the LS valve 5, the signal pressure PLS 'acting on the pressure supplementary valves 8L, 8, 8B becomes lower than the PLS by passing through the variable throttle 14a. Note that the variable throttle 14 b is provided with a pressure compensating valve when the switching valve 23 is switched and the pressure oil in the pilot circuits 15 L, 15 R, and 15 B is drained through the surface path 15 c. 8L: Provided to maintain the signal pressure acting on 8E, 8Β above a certain value.

As shown in FIG. 2, each of the pressure supplement valves 8L, 8R, 8Β comprises a check valve 8a slidable in the valve body, a supplement screw 8c, a spring 8d, and a signal pressure PLS. 'Is guided into the spring chamber 8f from the hole 8e provided in the supplementary screw 8c. The hydraulic oil that has passed through the directional control valves 3 L, 3 and 3B enters the check valve 8a from the passage 8g, and pushes the supplementary piston 8c and the spring 8d to the right in FIG. , And flow into Actuate Tappo 8h.

Now, assuming that the signal pressure is PLS ', the pressure in the spring chamber 8 f also becomes PLS'. If the pressure in the inlet chamber 8 g of the check valve 8a is P1, the diameter of the check valve 8a is equal to the diameter of the piston 8c. It increases by the spring force of d. However, the spring force is weak enough against the signal pressure PLS '

P 1 PLS '

Can be considered. That is, the pressure recovery valves 8L, 8R, and 8B have a characteristic that their inlet pressures PLP2 and P3 are almost equal to the signal pressure PLS '.

Next, the operation of the operability improving hydraulic circuit will be described.

When the boom is driven while the hydraulic excavator is traveling, the pressure switches 20 L, 2 OR. 2 OB in FIG. 1 are each 0, and the command current of the controller 22 is reduced to 0. As a result, the solenoid valve 26 is excited, and the switching valve 23 is switched. At this time, since the maximum value PLS of each actuator load pressure is the boost cylinder load pressure PLS3, the differential pressure ΔΡ between this maximum value PLS and the signal pressure PLS 'is

ΔΡ = PLS- PLS '-PLS3-PLS'

Becomes

Therefore, the flow rates Ql, Q2 to the left and right traveling motors 2L, 2R can be expressed by the following equations, respectively.

Ql = c X Al X (PP-P 1) ^1/2

^ c X Al (PP-PLS ') ^1/2

= c Al X (PP — PLS3 + mum P) ^1/2

Q2 = c A2 (PP-P2) ^1/2

-c A2 (PP-P LS ') ^1/2

= c A2 (PP-PLS3 + um P) ^1/2

Therefore, the scenes Ql 'and Q2 for the left and right traveling motors 2L and 2R are larger by the differential pressure △ P than in the past.

The flow rate Q3 to the boom cylinder 2B is

Q3 = c A3 X (PP-P3) ^{1 /}

-c A3 (PP-PLS3) ^1/2

It is represented by

The reason for this is that the boom cylinder food pressure PLS3 is higher than the signal pressure PLS ', so the booster button 8c shown in Fig. 2 is pressed to the right end. Therefore, in the pressure supplement valve 8B, the relationship between the inlet pressure (outlet pressure of the direction switching valve 3B) P3 and the boom cylinder load pressure PLS3 is

P 3 ^ P LS3

As a result, the pressure compensation function is lost, and only the check valve 8a functions. That is, the pressure compensating valve 8B acts as a check valve, and in the boom circuit, the above equation is obtained.

By adjusting the variable throttles 14a and 14b, the signal pressure PLS 'of the pressure compensation valves 8L and 8R Since the size of the excavator can be changed, it is possible to supply an optimal flow rate to the traveling side according to the purpose of use of the hydraulic excavator. Further, the variable diaphragms 14a and 14b may be fixed diaphragms in some cases.

Fig. 3 shows the relationship between the position of the stroke of the boom operation lever and the flow rate of hydraulic oil supplied to the traveling motor. When the hydraulic excavator is traveling and the boom operation lever '-17B is in the neutral position N, the hydraulic oil flow supplied to the left and right traveling motors 2L and 2R is the left and right traveling levers 17L and 17R. Is the flow rate according to the manipulated variable, and this is 100%. When the boom operation lever 17B is operated to the full stroke position gF in this state, when the switching valve 23 is OFF, that is, in the case of a normal load sensing system, the boom operation lever 17B is supplied to the left and right traveling motors 2L and 2B. Pressure oil flow is reduced to about 50%. However, when the switching valve 23 is ON, the flow rate of the hydraulic oil is maintained at 70 to 80%, and the low speed shock when operating the boom operation lever is small.

In this embodiment, as means for detecting the operation of the actuator operation lever, pressure switches 20L, 20B, 20B for detecting the pilot pressures of the PPC valves 18L, 18R, 18B are provided. However, the present invention is not limited to this, and a limit switch or a proximity switch that operates when the stroke of the actuator operation lever exceeds a certain value may be used.

As described above, according to the present invention, the pressure compensation characteristics of the directional control valves 3L, 3R, 3B for controlling the actuators are made variable, so that when the directional control valve 23 is switched, the directional control valves 3L, 3R , 3 B, the pressure difference before and after becomes large, the flow distribution proportional to their opening area is temporarily broken, and more pressure oil flows to a specific actuator. Therefore, if this study is applied to the left and right traveling motors 2L and 2R of the hydraulic excavator, the traveling deceleration rate when traveling and driving of the work equipment are performed at the same time is reduced, and the hydraulic excavator is operated as the operator intends. be able to. In addition, since the speed reduction during operation of the work equipment is reduced, operator fatigue is reduced and work efficiency is improved. Industrial applicability

INDUSTRIAL APPLICABILITY The present invention is useful as a hydraulic circuit for improving the operability of a vehicle equipped with a hydraulic drive device equipped with a load sensing system, particularly a hydraulic excavator.

Claims

The scope of the claims

1. A variable displacement hydraulic pump, an actuator driven by pressure oil discharged from the variable displacement hydraulic pump, and controlling a flow of pressure oil supplied from the variable displacement hydraulic pump to the actuator. Directional switching valve, and discharge amount control means for controlling the flow rate of pressure oil discharged from the variable displacement hydraulic pump, wherein the discharge amount control means drives a displacement variable means of the variable displacement hydraulic pump. And a LS valve that controls the drive of the regulator in accordance with the pressure difference between the discharge pressure of the variable displacement hydraulic pump and the load pressure of the actuator, and maintains the pressure difference at a set value. And

A throttle is provided in a load sensing circuit that transmits a signal pressure to a pressure compensation valve provided between the direction switching valve and the actuator, and the throttle is switched to a surface from the load sensing surface to the oil tank. Operability in a load sensing system, characterized in that a valve is provided, and a means for switching the switching valve is provided based on an operating condition of the operating lever or a pressure condition generated by operating the operating lever. Improved hydraulic surface.

2. 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 solenoid valve based on an output signal output by the detecting means, 2. The hydraulic surface for improving operability in a load sensing system according to claim 1, wherein the hydraulic surface is configured to include a solenoid valve that transmits a switching pressure to a valve.

3. The controller is operated by operating at least one of the left and right travel levers for controlling the left and right travel motors of the actuator and at least one of the work implement operation levers for controlling the work implement. 3. The hydraulic circuit for improving operability in a load sensing system according to claim 2, wherein a command current is output to the solenoid valve.