JP4071696B2 - Hydraulic system for excavator - Google Patents

Description

  The present invention relates to a hydraulic system for a hydraulic excavator, and more particularly to improvement in operability and effective use of hydraulic power.

  As shown in FIG. 1 of Japanese Patent Laid-Open No. 4-146336 (Patent Document 1), a conventional hydraulic system for a hydraulic excavator is provided with one traveling switching valve, a boom switching valve, and the like in the first pump. A first control valve group connected, the other travel switching valve, an arm switching valve, and the like, and a second control valve group connected to the second pump, a waste earth switch valve, and the like. And a third control valve group connected to the pump.

  As another conventional example, as shown in FIG. 1 of Japanese Patent Laid-Open No. 5-302603 (Patent Document 2), a single variable displacement pump is provided, and a single operation of a low load side actuator is changed from a single operation. The present invention relates to a regenerative hydraulic circuit that improves workability and energy saving by preventing a rapid decrease in speed of a low load side actuator and maintaining it as fast as possible when a load side actuator is operated in combination.

  In Patent Document 1, three pumps are used as hydraulic pressure sources, and both are connected to an open center type switching valve. In this hydraulic system, three pumps are used for the purpose of improving the turning operability, etc., but when the switching valve is in the neutral position, the total amount of oil discharged from each pump is discharged through the switching valve to the tank, resulting in energy loss. And the hydraulic circuit for merging is complicated.

Further, in Patent Document 2, since one variable displacement pump is used as a hydraulic source, a merging pipe or the like is unnecessary, and the hydraulic system is simplified. However, in a hydraulic excavator, it is very inertial. In the case of simultaneously operating other actuators having a large swivel and a small inertia with a common hydraulic pressure source, many technical difficulties are involved in obtaining a good combined operability.
JP-A-4-146336 (FIG. 1) Japanese Patent Laid-Open No. 5-302603 (FIG. 1)

  An object of the present invention is to provide a hydraulic system for a hydraulic excavator that can greatly improve energy saving and combined operability, which have been problems in conventional hydraulic systems, in a very simple manner.

To achieve the above object, a hydraulic system for a hydraulic excavator according to the present invention includes a variable displacement first pump that supplies pressure oil to a hydraulic actuator mounted on the hydraulic excavator, and a plurality of hydraulic pumps corresponding to each of the hydraulic actuators. A first control valve formed by connecting a closed center type switching valve in parallel to the pressure oil supply line of the first pump; and a switching valve operating means for operating the switching valves. To supply pressure oil from the first pump to the actuator and discharge the return oil to the tank so that the amount of oil supplied to the actuator becomes constant at the meter-in differential pressure of the switching valve. A first system configured to adjust a discharge flow rate of the first pump, and a hydraulic actuator for a turning operation mounted on the hydraulic excavator. Oil variable or a second pump of the fixed displacement and supplies, the second confluence switching valve of the hydraulic fluid supply line of the pump is connected to the pressure oil supply line of the first pump and the turning operation selector valve And each switching valve is formed as an open center type, and the switching valve for merging includes a second control valve configured to be operated by a switching valve operation signal connected to the first pump. 2 systems.

  In that case, the switching valve for turning operation can be configured to have a priority function with respect to the pressure oil supply line of the second pump with respect to the switching valve for merging.

  In this case, the priority function can be configured such that the switching valve connection order to the second pump is tandemly connected to the merging switching valve by disposing the switching valve for turning operation upstream.

  Further, in that case, the priority function arranges the switching valve connection order to the second pump, and arranges the switching valve for turning operation on the upstream side with respect to the switching valve for merging, connects them in tandem in parallel, and A parallel line can be provided with a diaphragm.

  In that case, the control valve 1 and the control valve 2 can be integrally formed.

  In this case, an engine that drives the first pump and the second pump, a hydraulic motor that drives a cooling fan of the engine, and a switching valve that switches supply and discharge of pressure oil to and from the hydraulic motor are provided. The switching valve can be configured to be formed in the second control valve.

  And a bypass line connected from the pressure oil supply line of the first pump to the tank line, a pressure compensation flow rate adjusting valve and a pressure generating means provided in order from the upstream side on the bypass line, The discharge flow rate of the first pump can be adjusted by the upstream pressure of the generating means.

  In this case, the switching valve in the second control valve that is operated in accordance with the operation of the switching valve in the first control valve is the second control valve after the switching valve of the first control valve has moved a predetermined stroke. The pressure oil supply line of the pump can be connected to the pressure oil supply line of the first pump.

According to the present invention, a variable displacement type first pump for supplying pressure oil to a hydraulic actuator mounted on a hydraulic excavator, and a plurality of closed center type switching valves corresponding to each of the hydraulic actuators are provided in the first pump. A first control valve formed in parallel to the pressure oil supply line, and a switching valve operating means for operating each of the switching valves. The switching valve is operated to operate the switching valve from the first pump. The pressure oil is supplied to the actuator and the return oil is discharged to the tank, and the discharge flow rate of the first pump is adjusted so that the amount of oil supplied to the actuator becomes constant at the meter-in side differential pressure of the switching valve. A first system configured as described above, a variable or fixed displacement type second pump for supplying pressure oil to a hydraulic actuator for turning operation mounted on the hydraulic excavator, and , Each selector valve with a built-in confluence switching valve and the switching valve for turning operation for connecting the hydraulic fluid supply line of the second pump to the hydraulic fluid supply line of said first pump is formed by an open-center The merging switching valve is composed of a second system having a second control valve configured to be operated by a switching valve operation signal connected to the first pump. Compared to a hydraulic system, the system has an effect that an extremely excellent system can be configured in terms of operability and effective use of hydraulic energy.

  FIG. 1 is an embodiment illustrating the basic configuration of the present invention, and has two systems SYS1 and SYS2 surrounded by a broken line. One system SYS1 includes a variable displacement pump VPM and a first control valve CVL1 connected to the pressure oil supply line 3 of the variable displacement pump VPM.

  The hydraulic oil supply line 3 is connected in parallel with various hydraulic actuator switching valves mounted on a hydraulic excavator excluding the turning operation switching valve. A valve OPT, a bucket cylinder switching valve BKT, an arm cylinder switching valve AM, a boom cylinder switching valve BM, a left traveling hydraulic motor switching valve TL and a right traveling hydraulic motor switching valve TR, which are switched as shown in the figure. The valve is formed as a closed center type switching valve.

  Further, a bypass line 4 is provided from the pressure oil supply line 3 and is connected in order from the upstream side to a tank 7 via a pressure compensation flow control valve 5 and a throttle 6 as pressure generating means in the present invention. The upstream pressure 6 is applied to the capacity adjusting mechanism 8 of the variable capacity pump VPM. Reference numeral RFV1 is a relief valve. A pressure detection signal indicated by a broken line is joined from each switching valve of the first control valve CVL1 via a check valve, and the joined pressure signal is given to the pressure compensation flow rate adjusting valve 5. In other words, the pressure compensation flow rate adjusting valve 5 is selected and given the highest value among the pressure detection signals of the switching valves.

  A more detailed configuration of the first control valve CVL1 is described in the above-mentioned Patent Document 2, and a configuration example of the arm cylinder switching valve AM is shown in FIG. Then, the explanation is omitted.

  Next, the system SYS2 in FIG. 1 will be described.

  The system SYS2 includes a fixed displacement pump FPM and a second control valve CVL2 connected to the pressure oil supply line of the pump FPM. The second control valve CVL2 is provided with a turning operation switching valve SWVL and a merging switching valve FSVL in order from the upstream side, both of which are formed as an open center type switching valve. Reference numeral HDMTR is a turning drive hydraulic motor, and RFV2 is a relief valve.

  An operation signal from each switching valve on the system SYS1 side is inputted to one side operation input portion of the switching valve for merging operation FSVL, and the merging switching valve FSVL is switched by these signals ( The pressure oil from the right end) and the pump FPM reaches the merge line 10 via the input port 9 and further merges with the pressure oil supply line 3. Further, in the turning operation switching valve SWVL, when a pressure oil signal is given to the left or right operation section, the pressure oil from the pump FPM rotates the hydraulic motor HDMTR. At this time, the open center passage is blocked.

  The operation signal to the merging switching valve FSVL may correspond to all the switching valves of the first control valve CVL1, or may not necessarily correspond to all the switching valves, and is required. Depending on the maximum flow rate, only the operation signal of a specific switching valve, for example, a boom switching switch or an arm switching valve may be selected.

  FIG. 3 shows a state of the merging switching valve FSVL in the case where, for example, the arm switching valve AM in FIG. In FIG. 3, the discharge oil of the variable displacement pump VPM reaches the arm switching valve AM via the pressure oil supply line 3 and is uniquely determined according to the operation amount of the switching valve. Then, the oil flows into the oil chamber 20 of the arm cylinder 19 which is an actuator and drives the arm cylinder 19, and at the same time, the return oil from the oil chamber 21 of the cylinder is a passage 46, a switching valve passage 47, a passage 43, and a shunt compensation valve. It is discharged to the tank 7 through the passage 45 of 31. Reference numeral 22A denotes a control stick for another actuator, and the high pressure side pressure of the high pressure selection means 35C is input to the right side of the high pressure selection means 35B.

On the other hand, in the case of this embodiment, when one operation end bAM of the arm switching valve AM is operated , the pressure oil signal on the line 33 reaches the line 25 via the high pressure selection means 35A, 35B, and the merging switching valve FSVL. The variable displacement pump acts on the discharge end 37 of the fixed displacement pump FPM via the check valve 48, the input port 9 of the merging switching valve FS, the passage 41 in the switching valve, and the merging passage 10. It is made to merge with the pressure oil supply line 3 of VPM.

  Therefore, in such a state, the total discharge amount of the fixed displacement pump FPM and the differential pressure at the meter-in side variable throttle 11 of the arm switching valve AM are supplied to the arm cylinder 19 from the discharge amount of the constant displacement pump FPM. The amount of oil discharged from the variable displacement pump VPM that is constant is supplied.

  In this case, the discharge flow rate of the variable displacement pump VPM is small compared to the case where the oil amount of the variable displacement pump VPM is not merged, but the variable minimum flow rate of the variable displacement pump VPM is set to be relatively small. Therefore, the total flow rate of the variable displacement pump VPM and the fixed displacement pump FPM does not become excessive with respect to the opening degree of the variable throttle 11.

  Therefore, when operating the swing actuator of the hydraulic excavator, the switching valve SWVL is an open center type switching valve. Therefore, when the switching valve is operated, there is no sense of abnormal popping out despite large inertia. As a result, good operability as an open system can be obtained.

  On the other hand, when the swing actuator is not operated, the pressure oil of the fixed displacement pump FPM can be effectively used for actuators other than the swing via the merging switching valve FSVL, and connected to the variable displacement pump VPM as described above. The discharge oil amount of the variable displacement pump VPM is adjusted according to the meter-in side opening of the switching valve so that the meter-in side differential pressure at the total oil amount of the fixed displacement pump FPM and the variable displacement pump VPM becomes a predetermined value. Therefore, the pressure in the pressure oil supply line 3 is appropriately maintained without abnormally increasing. Accordingly, a hydraulic system that is excellent in energy saving and that can effectively utilize the discharge oil of each pump VPM and FPM is configured.

  Furthermore, in a conventional system using only the variable displacement pump VPM as a hydraulic source, when a plurality of actuators such as arms and booms are simultaneously operated, the meter-in side variable throttles of the plurality of switching valves are naturally pressure oil. Since it opens with respect to the supply line 3, even if it has the single discharge amount of the variable displacement pump VPM, the differential pressure on the meter-in side does not reach a predetermined value, and the variable displacement pump VPM may be saturated. In the example of the present invention, in addition to the variable displacement pump VPM, the discharge oil of the fixed displacement pump FPM also joins, so that the pump discharge oil amount can be ensured with respect to the total required amount of the actuator. As a result, a hydraulic system excellent in combined operability and productivity can be formed.

  Further, in the case of only the system SYS1, for example, in FIG. 3, the discharge flow rate of the variable displacement pump VPM is changed to the pressure compensation flow rate adjusting valve 5 on the bypass line 4 through the signal lines 30 and 14 and the pressure on the meter-in side of the switching valve. And this causes a flow rate change of the bypass line 4 and a pressure change upstream of the throttle 6 which is a pressure generating means, and the discharge flow rate of the variable displacement pump VPM is adjusted by this signal pressure. Therefore, in a cold environment, there is a problem such as a delay in adjusting the pump discharge flow rate with respect to the operation of the switching valve. However, in this embodiment, the discharge oil of the fixed displacement pump FPM is merged at the same time. There is no delay in starting the actuator.

Also in the confluence switching valve FSVL, in moving process of the switching valve, so assume an intermediate position between the neutral position A and the stroke end position C as shown in FIG. 2, the center bypass b -1, converging passage 10 The pressure oil supply line 3 is adjusted by adjusting the opening degree of the connecting passage b-2 to the stroke of the switching valve for merging or appropriately adjusting the amount of change of the throttle passage 11 with respect to the stroke of the switching valve AM for arm, for example. The combined timing of the fixed displacement pump FPM with respect to can be set satisfactorily, and the hydraulic system as a whole can constitute an extremely excellent system in terms of operability and effective use of hydraulic energy compared to the prior art. it can.

  FIG. 4 shows that the upstream-side turning operation switching valve SWVL and the downstream-side merging switching valve FSVL built in the second control valve CVL2 are connected by a parallel line passage PAL, and the throttle THR is set on the passage PAL. This is an example of providing.

  As shown in the figure, the parallel line passage PAL is formed between the input port of the merging switching valve FSVL and the pressure oil supply line 3A, and the throttle THR is disposed on the parallel line passage PAL as shown. Yes. In the second control valve CVL2 of FIG. 1, as described above, when the swing operation switching valve SWVL selects a position other than the neutral position, the pressure oil on the pressure oil supply line 3A of the fixed displacement pump FPM is changed to the swing operation switching valve SWVL. And is not supplied to the confluence switching valve FSVL.

  However, in FIG. 4, a part is given to the input port of the merging switching valve FSVL via the parallel line passage PAL. At this time, by providing the throttle THR, the priority function of the turning operation switching valve SWVL with respect to the merging switching valve FSVL is ensured. Here, the priority function of the switching valve for swing operation SWVL is realized by arranging an open center type switching valve for swing operation SWVL on the upstream side of the merging switching valve FSVL and being connected in tandem, In the case of FIG. 1, when the turning operation switching valve SWVL is operated during the operation of the merging switching valve FSVL, the pressure oil of the fixed displacement pump FPM is not supplied to the merging switching valve FSVL and is used for the turning operation. The priority function is absolute in that it is supplied only to the switching valve SWVL.

  On the other hand, in the case of FIG. 4, by providing the parallel line passage PAL and the throttle THR, the function of the merging switching valve FSVL is not lost even when the turning operation switching valve SWVL is operated. In a sense, priority functions are relative.

  FIG. 5 illustrates a case where an engine fan drive hydraulic motor switching valve is provided in the second control valve CVL2. In FIG. 5, an engine ENG drives the variable displacement pump VPM and the fixed displacement pump FPM. In the second control valve CVL2, an open center type engine fan driving hydraulic motor switching valve FNVL is provided on the most downstream side, and the switching motor FNVL is a hydraulic motor HDMTR that rotationally drives an engine cooling fan FN. Is connected.

  Accordingly, when the upstream side switching valves FSVL and SWVL are stopped, that is, when all the actuators are stopped, the engine fan can be hydraulically driven with priority to cool the engine ENG. Thus, the engine fan drive hydraulic motor switching valve FNVL can be operated, and unnecessary engine cooling in a cold environment can be avoided. At the same time, noise can be reduced.

  In the above description of the embodiment, the hydraulic pump in the second system SYS2 has been described as the fixed displacement pump FPM, but is not limited thereto, and may be a variable displacement pump VPM. Although the first control valve CVL1 and the second control valve CVL2 have been described as separate bodies, they may be integrally formed.

  Further, in FIG. 1, in order to accurately control the merging timing of the pressure oil from the fixed displacement pump FPM supplied from the merging switching valve FSVL to the pressure oil supply line 3 via the merging line 10, An electro-conversion means and an electro-oil conversion means may be provided, and the electro-hydraulic conversion pressure oil signal may be electrically delayed to regenerate the pressure oil signal by the electro-oil conversion means.

1 illustrates a basic configuration of the present invention, and includes two systems SYS1 and SYS2 surrounded by a broken line. It is a figure which shows the movement process of the switching valve in the switching valve for merge. It is a figure which shows the state of the switching valve for merge in the case of operating the switching valve for arms in FIG. It is a figure which shows the example which connected the switching valve for upstream turning operation and the switching valve for merging downstream which were built in the 2nd control valve by the parallel line channel | path, and provided the throttle | throttle THR on the channel | path. . It is a figure which illustrates the case where the switching valve for engine fan drive hydraulic motors is provided in the 2nd control valve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 Pressure oil supply line 4 Bypass line 5 Pressure compensation flow control valve 6 Restriction 7 Tank 8 Capacity adjustment mechanism 9 Input port 10 Merge line 11 Pressure generating means 19 Arm cylinder 20, 21 Oil chamber 22, 22A Control rod 35A, 35B, 35C High pressure selection means CVL1 First control valve CVL2 Second control valve FN Cooling fan FNVL Engine fan drive hydraulic motor switching valve FSVL Merge switching valve HDMTR Hydraulic motor OPT Option switching valve BKT Bucket switching valve AM Arm switching valve BM Boom switching valve TL Left traveling switching valve TR Right traveling switching valve FPM Fixed displacement pump VPM Variable displacement pump SYS1 System 1
SYS2 system 2

Claims (8)

A variable displacement type first pump for supplying pressure oil to a hydraulic actuator mounted on a hydraulic excavator, and a plurality of closed center type switching valves corresponding to each of the hydraulic actuators are provided in the pressure oil supply line of the first pump. And a switching valve operating means for operating each of the switching valves, and operating the switching valve to supply pressure oil from the first pump to the actuator. First, the return oil is supplied to the tank, and the amount of oil supplied to the actuator is adjusted to adjust the discharge flow rate of the first pump so that the meter-in side differential pressure of the switching valve becomes constant. System,
A variable or fixed displacement type second pump for supplying pressure oil to a hydraulic actuator for turning operation mounted on the hydraulic excavator, and a pressure oil supply line for the second pump are connected to the pressure oil for the first pump. A switching valve for merging and a switching valve for turning operation connected to the supply line are built in, and each switching valve is formed in an open center type, and the switching valve for merging is connected to the first pump. A hydraulic system for a hydraulic excavator comprising a second system provided with a second control valve configured to be operated at   2. The hydraulic system for a hydraulic excavator according to claim 1, wherein the switching valve for turning operation has a priority function with respect to the pressure oil supply line of the second pump with respect to the switching valve for merging.   3. The hydraulic pressure according to claim 2, wherein the priority function is such that the switching valve connection order to the second pump is tandemly connected to the switching valve for merging and the switching valve for turning operation is arranged upstream. Excavator hydraulic system.   In claim 2, the priority function is arranged such that the switching valve connection order to the second pump is arranged on the upstream side with respect to the merging switching valve, the slewing operation switching valve is connected in tandem parallel, and A hydraulic system for a hydraulic excavator, characterized in that a throttle is provided in the parallel line.   5. The hydraulic system for a hydraulic excavator according to claim 1, wherein the control valve 1 and the control valve 2 are integrally formed.   6. The switching valve according to claim 1, wherein an engine that drives the first pump and the second pump, a hydraulic motor that drives a cooling fan of the engine, and pressure oil supply / discharge to the hydraulic motor are switched. A hydraulic system for a hydraulic excavator, wherein the switching valve is formed in the second control valve.   7. A bypass line connected to the tank line from the pressure oil supply line of the first pump according to claim 1, a pressure compensation flow rate adjusting valve and a pressure generating means provided in order from the upstream side on the bypass line. The hydraulic system for a hydraulic excavator is characterized in that the discharge flow rate of the first pump is adjusted by the upstream pressure of the pressure generating means.   8. The switching valve in the second control valve operated according to the operation of the switching valve in the first control valve according to claim 1, wherein the switching valve in the first control valve is moved by a predetermined stroke. A hydraulic system for a hydraulic excavator, wherein the hydraulic oil supply line of the second pump is connected to the hydraulic oil supply line of the first pump later.

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