阅读说明：本技术 流体回路 (Fluid circuit ) 是由 岛田佳幸 于 2019-09-25 设计创作，主要内容包括：本发明提供一种利用了负载监控系统的能量效率高的流体回路。流体回路具备：压力流体源(2),其供给压力流体；多个致动器(8,9),其与压力流体源(2)连接；方向切换阀(6,7),其对从压力流体源(2)供给的压力流体的供给方进行切换；以及排出量控制机构(41,42),其以相对于多个致动器的负载压力内最大的最高负载压力,差压(ΔP)成为目标值(ΔPt)的方式,来控制压力流体源(2)的输出,具备对来自致动器(8,9)的回流流体的一部分进行蓄压的蓄压器(60),蓄压器(60)能够将蓄压的压力流体排出到方向切换阀(6,7)的压力流体源侧流路(22),具备基于蓄压器(60)的压力来调整压力流体源(2)的控制量的调整单元(50)。(The invention provides a fluid circuit with high energy efficiency by using a load monitoring system. The fluid circuit includes: a pressure fluid source (2) for supplying a pressure fluid; a plurality of actuators (8, 9) connected to a source of pressurized fluid (2); direction switching valves (6, 7) for switching the supply direction of the pressure fluid supplied from the pressure fluid source (2); and a discharge amount control mechanism (41, 42) that controls the output of the pressure fluid source (2) so that the differential pressure (Δ P) becomes a target value (Δ Pt) with respect to the highest load pressure among the load pressures of the plurality of actuators, wherein the control mechanism is provided with an accumulator (60) that accumulates a part of the return fluid from the actuators (8, 9), wherein the accumulator (60) is capable of discharging the accumulated pressure fluid to the pressure fluid source side flow path (22) of the directional control valves (6, 7), and the control mechanism is provided with an adjustment means (50) that adjusts the control amount of the pressure fluid source (2) on the basis of the pressure of the accumulator (60).)

1. A fluid circuit is provided with: a pressure fluid source that supplies pressure fluid; a plurality of actuators connected to the source of pressurized fluid; a direction switching valve that switches a supply direction of the pressure fluid supplied from the pressure fluid source; and a discharge amount control means for controlling an output of the pressure fluid source so that a highest load pressure differential pressure with respect to a maximum load pressure among the plurality of actuators becomes a target value,

the fluid circuit includes an accumulator that accumulates a part of return fluid from the actuator,

the accumulator is capable of discharging pressure fluid accumulated in the accumulator to a pressure fluid source side flow passage of the direction switching valve,

the fluid circuit is provided with an adjusting unit that adjusts a control amount of the pressure fluid source based on the pressure of the accumulator.

2. The fluid circuit of claim 1,

the control amount is adjusted by the adjusting means when pressure fluid is discharged from the accumulator to a pressure fluid source side flow passage of the direction switching valve.

3. The fluid circuit of claim 1 or 2,

comprises a pressure detection unit for detecting the pressure of the accumulator and a control part with an arithmetic circuit,

the adjusting means is operated based on the pressure detected by the pressure detecting means in accordance with an electric signal output from the control unit.

4. The fluid circuit of any one of claims 1 to 3,

the discharge amount control mechanism includes a load monitoring valve that adjusts an opening degree in accordance with a differential pressure between a pressure source side pressure and an actuator side pressure of the directional control valve introduced from a pilot line,

a pressure reducing valve as the adjusting means is provided in the pilot line from which the actuator-side pressure of the direction switching valve is derived.

5. The fluid circuit of claim 4,

the amount of pressure reduction in the pressure reducing valve can be adjusted based on at least the pressure source side pressure and the actuator side pressure of the direction switching valve and the pressure of the accumulator.

Technical Field

The present invention relates to a fluid circuit for flowing a pressure fluid from a pressure fluid source into an actuator to drive a load.

Background

Conventionally, in order to drive a vehicle, a construction machine, an industrial machine, or the like, a fluid circuit is used in which a pressure fluid such as oil is caused to flow from a pressure fluid source into an actuator to drive a load. For example, hydraulic excavators have been variously improved in view of improvement in operability, energy saving, speed increase, and safety by supplying pressure fluid from a hydraulic pump to a plurality of actuators such as a loading cylinder and a boom cylinder that are fluidly connected in parallel to a hydraulic circuit as a fluid circuit to simultaneously drive a plurality of load operations.

As an example of a conventional fluid circuit, a hydraulic circuit applied to an open center (open center) system of a hydraulic excavator or the like discharges a pressure fluid from a hydraulic pump as a pressure fluid source to a tank through a bypass passage at a neutral position of a direction switching valve connected to an actuator and an operation lever, strokes a spool of the direction switching valve by a pilot pressure based on an operation amount of the operation lever, and obtains an operation speed of the actuator corresponding to the operation amount of the operation lever. However, in this system, if a large load pressure is applied to the actuator, the operation lever must be operated to the high output side.

As a fluid circuit that solves such a problem, a fluid circuit of a load monitoring system is known that performs control so that the supply pressure of a hydraulic pump is always higher than a target differential pressure with respect to the highest load pressure in a plurality of actuators (see patent document 1). As an example of the fluid circuit of such a load monitoring system, the fluid circuit shown in fig. 7 mainly includes: a swash plate type variable displacement hydraulic pump 102 driven by a drive mechanism such as an engine or an electric motor; two actuators 108, 109 fluidly connected in parallel with the hydraulic pump 102; two directional control valves 106 and 107 connected to the actuators 108 and 109 and the control levers 110 and 111, respectively, and switching a supply direction of the pressure fluid supplied from the hydraulic pump 120; pressure compensation valves 104 and 105 provided in pressure fluid source side flow passages of the directional control valves 106 and 107, respectively; and a load monitoring valve 141 and a swash plate controller 142 as a discharge amount control means for controlling the discharge amount (output) of the pressure fluid in the hydraulic pump 102, wherein the load monitoring valve 141 is adjusted in the degree of opening of the load monitoring valve 141 such that the highest load pressure of the actuators (i.e., the higher one of the load pressures of the two actuators 108 and 109 selected by the shuttle valve 116 via the pilot line 120 with respect to the load monitoring valve 141) and the supply pressure of the hydraulic pump 102 from the pressure fluid source side flow path of the directional switching valves 106 and 107 are derived to the load monitoring valve 141, that is, the difference between the supply pressure of the hydraulic pump 102 and the highest load pressure of the actuators, that is, the pressure difference between the pressure fluid source side of the directional switching valves 106 and 107 and the side of the actuators 108 and 109 (the differential pressure of the directional switching valves) becomes a target value (fixed value), and the inclination of the swash plate 143 is increased and, thereby controlling the output of the hydraulic pump 102. Therefore, in the fluid circuit of the load monitoring system, when a large load pressure is applied to the actuators 108 and 109, the control of the discharge amount control mechanism can be made to correspond to the variation in the load pressure of the actuators 108 and 109.

Documents of the prior art

Patent document

Patent document 1, Japanese patent application laid-open No. 3-74605 (page 28, FIG. 1).

However, in the fluid circuit of the load monitoring system of fig. 7, when a large load is applied to the two actuators, a hydraulic pump corresponding to the load may be used, but there is a problem that a large hydraulic pump is required, and energy efficiency is deteriorated.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a highly energy-efficient fluid circuit using a load monitoring system.

In order to solve the above problem, a fluid circuit according to the present invention includes: a pressure fluid source that supplies pressure fluid; a plurality of actuators connected to the source of pressurized fluid; a direction switching valve that switches a supply direction of the pressure fluid supplied from the pressure fluid source; and a discharge amount control mechanism that controls an output of the pressure fluid source so that a maximum load pressure differential pressure with respect to a maximum load pressure among load pressures of the plurality of actuators becomes a target value, wherein the fluid circuit includes an accumulator that accumulates a part of return fluid from the actuators, the accumulator is capable of discharging the accumulated pressure fluid to a pressure fluid source side flow passage of the directional control valve, and the fluid circuit includes an adjustment unit that adjusts a control amount of the pressure fluid source based on a pressure of the accumulator.

Thus, the fluid circuit that performs control so that the supply pressure of the pressure fluid source is always higher than the target differential pressure with respect to the highest load pressure in the plurality of actuators can supplement the output of the pressure fluid source with the pressure of the accumulator discharged to the pressure fluid source side flow passage of the directional control valve, and therefore a fluid circuit with high energy efficiency can be obtained.

Preferably, the control amount is adjusted by the adjusting means when discharging the pressure fluid from the accumulator to the pressure fluid source side flow path of the direction switching valve.

This makes it possible to adjust the output of the pressure fluid source at an appropriate timing, and therefore, energy efficiency is high.

Preferably, the pressure control device includes a pressure detection unit that detects a pressure of the accumulator, and a control unit having an arithmetic circuit, and the adjustment unit is operated based on the pressure detected by the pressure detection unit and an electric signal output from the control unit.

This improves the response of the adjustment means.

Preferably, the discharge amount control mechanism includes a load monitoring valve whose opening degree is adjusted based on a differential pressure between a pressure source side pressure of the direction switching valve and an actuator side pressure introduced from a pilot conduit, and a pressure reducing valve as the adjusting means is provided in the pilot conduit that guides the actuator side pressure of the direction switching valve.

Thus, the opening degree of the load monitoring valve can be adjusted based on the value based on the maximum load pressure of the actuator and the pressure of the accumulator, and the control amount of the discharge amount control mechanism can be adjusted by a simple circuit.

Preferably, the amount of pressure reduction in the pressure reducing valve can be adjusted based on at least the pressure source side pressure and the actuator side pressure of the direction switching valve and the pressure of the accumulator.

Thus, the amount of pressure reduction in the pressure reducing valve can be adjusted based on the pressure of the pressure source side of the directional control valve, the pressure of the actuator side, and the pressure of the accumulator, and the differential pressure of the directional control valve can be quickly controlled to a target value.

Drawings

FIG. 1 is a side view of a loader of an embodiment of the present invention.

Fig. 2 is a diagram illustrating a hydraulic circuit of the load monitoring system of the embodiment.

Fig. 3 is a diagram illustrating a relationship between an electric signal to a solenoid and a secondary pressure in the electromagnetic proportional pressure reducing valve according to the embodiment.

Fig. 4 is a diagram illustrating a relationship between the lever operation amount and the pilot secondary pressure in the hydraulic remote control valve according to the embodiment.

Fig. 5 is a diagram illustrating a relationship between a lever operation amount and an operation speed (cylinder speed) in the actuator (cylinder) according to the embodiment.

Fig. 6 is a diagram illustrating a relationship between a spool stroke and a spool opening area of the directional control valve according to the embodiment.

Fig. 7 is a diagram illustrating a hydraulic circuit of a conventional load monitoring system.

Detailed Description

Hereinafter, a mode for implementing the fluid circuit according to the present invention will be described based on examples.

Examples

A fluid circuit according to an embodiment will be described with reference to fig. 1 to 6, taking a hydraulic circuit of a loader as an example.

As shown in fig. 1, the loader 100 includes a loading bucket 108(W2, see fig. 2) that stores earth and sand or the like, a lift arm 109(W1, see fig. 2) that is linked to the loading bucket 108, and a loading cylinder 8 and a boom cylinder 9 that are actuators that are driven by hydraulic pressure. Hereinafter, a hydraulic circuit as a fluid circuit of the load monitoring system for the loading cylinder 8 and the boom cylinder 9 will be described.

As shown in fig. 2, the hydraulic circuit mainly includes: a main hydraulic pump 2 and a pilot hydraulic pump 3 that are driven by a drive mechanism 1 called an engine or an electric motor as a variable displacement type pressure fluid source; a load direction switching valve 6 as a direction switching valve and an arm direction switching valve 7 as a direction switching valve that switches the supply direction of pressurized oil as a pressure fluid supplied from the main hydraulic pump 2; pressure compensation valves 4 and 5 connected to the pressure fluid source sides of the load direction switching valve 6 and the arm direction switching valve 7; a loading cylinder 8 and a boom cylinder 9 connected to actuator sides of the loading direction switching valve 6 and the arm direction switching valve 7; a loading hydraulic remote control valve 10 and an arm hydraulic remote control valve 11 that switch the supply direction of the pressure oil supplied from the pilot hydraulic pump 3; a load monitoring valve 41 and a swash plate control device 42 as a discharge amount control means for controlling the output of the main hydraulic pump 2; an adjusting unit provided in the secondary pressure pilot line 20 as a pilot line and an electromagnetic proportional pressure reducing valve 50 as a pressure reducing valve; and an accumulator 60 that accumulates a part of the return oil from the boom cylinder 9. Since the hydraulic circuit on the loading cylinder 8 side and the hydraulic circuit on the boom cylinder 9 side, which are fluidly connected in parallel to the main hydraulic pump 2 and the pilot hydraulic pump 3, have substantially the same configuration, the hydraulic circuit on the boom cylinder 9 side will be described, and the description of the hydraulic circuit on the loading cylinder 8 side will be omitted.

The main hydraulic pump 2 and the pilot hydraulic pump 3 are coupled to the drive mechanism 1, rotate according to power from the drive mechanism 1, and are supplied with pressurized oil through oil passages connected thereto.

As shown in fig. 2, the pressure oil discharged from the main hydraulic pump 2 flows into the arm direction switching valve 7 through oil passages 21 and 22, the pressure compensating valve 5, the check valve 14, and an oil passage 23. The arm direction switching valve 7 is a normally closed pilot direction switching valve having a similar 5-port 3 position, and at its neutral position, the oil passage 23 and the head-side oil passage 25 and the rod-side oil passage 26 of the boom cylinder 9 are closed, and the secondary pressure pilot line 20 is connected to the oil passage 24 and the oil tank 15. In the arm direction switching valve 7, at the extension position 7E, the oil passage 23 is connected to the head-side oil passage 25 and the secondary pressure pilot line 20, and the rod-side oil passage 26 is connected to the oil passage 24 and the oil tank 15. Further, when the arm direction switching valve 7 is at the contracted position 7C, the head-side oil passage 25 is connected to the oil passage 24 and the oil tank 15, and the oil passage 23 is connected to the rod-side oil passage 26 and the secondary pressure pilot conduit 20.

Further, the arm direction switching valve 7 is configured to introduce the secondary pressure of the arm direction switching valve 7, i.e., the actuator-side pressure, into the unload valve 12 and the electromagnetic proportional pressure reducing valve 50 via the shuttle valve 16 through the secondary-pressure pilot line 20 at the extension position 7E or the contraction position 7C. Further, actuator-side pressures of the loading direction switching valve 6 and the arm direction switching valve 7, that is, load pressures of the loading cylinder 8 and the boom cylinder 9 are introduced into the shuttle valve 16 through the secondary pressure pilot line 20, and the shuttle valve 16 selects the highest load pressure of the actuator, which is the higher one of the load pressures of the loading cylinder 8 and the boom cylinder 9, and introduces the unload valve 12 and the electromagnetic proportional pressure reducing valve 50.

As shown in fig. 3, the electromagnetic proportional pressure reducing valve 50 has a pressure characteristic in which the secondary pressure is proportionally reduced in response to an increase in the electric signal to the solenoid, and a controller 70 as a control unit including an arithmetic circuit is connected to an electric signal line 73, and the secondary pressure can be reduced by adjusting the pressure reduction amount (opening degree) in accordance with the electric signal from the controller 70 and releasing a part of the maximum load pressure of the actuator selected by the shuttle valve 16 to the oil tank 15. Further, an electromagnetic proportional pressure reducing valve 50 is provided on the primary side of the load monitor valve 41 in the secondary pressure pilot conduit 20.

The load monitor valve 41 transmits the actuator side pressure of the direction switching valve, which is the maximum load pressure of the actuator regulated by the electromagnetic proportional pressure reducing valve 50, through the secondary pressure pilot line 20, transmits the supply pressure of the main hydraulic pump 2, which is the pressure source side pressure of the direction switching valve, through the primary pressure pilot line 28, which is a pilot line branched from the line 27 branched from the oil passage 21, adjusts the opening degree based on the difference between the supply pressure of the main hydraulic pump 2 and the maximum load pressure of the actuator regulated by the electromagnetic proportional pressure reducing valve 50, which is the pressure difference between the pressure fluid source side of the direction switching valve and the actuator side of the direction switching valve regulated by the electromagnetic proportional pressure reducing valve 50, and can control the pump flow rate control pressure based on the opening degree. The swash plate control device 42 operates in accordance with the pressure oil supplied from the load monitoring valve 41 (hereinafter referred to as "pump flow rate control pressure"), and controls the output of the main hydraulic pump 2 by increasing or decreasing the inclination angle of the swash plate 43 of the main hydraulic pump 2.

As shown in fig. 2, the pressurized oil of the pilot primary pressure discharged from the pilot hydraulic pump 3 is supplied to the arm hydraulic remote control valve 11 through oil passages 31 and 32. The arm hydraulic remote control valve 11 is a variable pressure reducing valve, and is switched to the extension position 7E or the contraction position 7C by operating the operating lever 11-1 of the loader 100, supplying pilot secondary pressure of the lever, which is reduced in pressure by the lever operation amount as shown in fig. 4, to the signal ports 7-1 and 7-2 of the arm direction switching valve 7 through the signal oil passages 33 and 34, and by the stroke of the internal spool of the arm direction switching valve 7. In addition, the remaining oil in the pressurized oil discharged from the pilot hydraulic pump 3, which is not supplied from the arm hydraulic remote control valve 11 to the signal ports 7-1 and 7-2 of the arm direction switching valve 7, is discharged to the oil tank 15 through the oil passage 35, the relief valve 13, and the oil passage 36.

Specifically, by operating the operating lever 11-1 in the extension direction E, the arm-direction switching valve 7 is switched to the extension position 7E, and pressurized oil supplied from the main hydraulic pump 2 flows into the head chamber 9-1 of the boom cylinder 9 through the head-side oil passage 25 connected to the oil passage 23, while the pressurized oil is discharged from the rod chamber 9-2 to the oil tank 15 through the oil passage 24 connected to the rod-side oil passage 26. This allows the boom cylinder 9 to be extended to lift the lift arm 109 (W1).

Further, by operating the operating lever 11-1 in the retracting direction C, the arm-direction switching valve 7 is switched to the retracting position 7C, and the pressure oil supplied from the main hydraulic pump 2 flows into the rod chamber 9-2 of the boom cylinder 9 through the rod-side oil passage 26 connected to the oil passage 23, and at the same time, the pressure oil is discharged from the head chamber 9-1 to the oil tank 15 through the oil passage 24 connected to the head-side oil passage 25. Thereby, the boom cylinder 9 is contracted, and the lift arm 109 is lowered (W1).

When the operation lever 11-1 is operated in the extension direction E, the relationship between the lever operation amount and the cylinder speed (operating speed) of the boom cylinder 9 has a characteristic curve as shown in fig. 5. When the operation lever 11-1 is operated in the extension direction E, the relationship between the spool stroke and the spool opening area in the arm direction switching valve 7 has the spool opening characteristic when the lift arm 109 is raised as shown in fig. 6.

As shown in fig. 6, the arm direction switching valve 7 is configured such that the spool opening for controlling the flow rate from the main hydraulic pump 2 into the boom cylinder 9 is changed in accordance with the spool stroke, that is, in accordance with the lever operation amount, and the spool stroke Xm is set in advance such that the flow rate Qm flowing from the main hydraulic pump 2 into the boom cylinder 9 based on the spool opening area Am becomes maximum when the lever operation amount of the operation lever 11-1 becomes maximum Lm (see fig. 5), whereby the pressure loss at the spool opening of the arm direction switching valve 7 can be suppressed when the boom cylinder 9 becomes maximum cylinder speed.

The pressure compensation valves 4 and 5 provided on the pressure fluid source side of the loading direction switching valve 6 and the arm direction switching valve 7 are normally open pressure control valves having 2 ports 2 at similar positions, and when the loading direction switching valve 6 and the arm direction switching valve 7 that drive the loading bucket 108 and the lift arm 109 while deriving the load pressures of the loading cylinder 8 and the lift arm 9 respectively by being connected to the secondary pressure pilot line 20 are simultaneously operated, flow rates corresponding to the spool opening areas of the respective direction switching valves can be made to flow into the loading cylinder 8 and the lift arm cylinder 9 regardless of the magnitudes of the load pressures of the loading cylinder 8 and the lift arm cylinder 9.

In this way, in the load monitoring system, the pump flow rate control pressure is controlled in the load monitoring valve 41 so that the differential pressure Δ P between the front and rear thereof always becomes the target value Δ Pt (fixed value) in accordance with the spool opening area of the directional control valve, and the output of the main hydraulic pump 2 is controlled by increasing or decreasing the inclination angle of the swash plate 43 of the main hydraulic pump 2 by the swash plate control device 42 based on the pump flow rate control pressure. That is, as shown in fig. 6, if the spool opening area is small, the discharge amount discharged from the main hydraulic pump 2 becomes small, and the output of the main hydraulic pump 2 is controlled so that the discharge amount increases as the spool opening area increases.

The unload valve 12 connected to the secondary pressure pilot line 20 is set such that the operating pressure is always higher than the supply pressure of the main hydraulic pump 2 by a target value Δ Pt, and if the pressure of the main hydraulic pump 2 is excessive, the pressurized oil (pressure) is allowed to escape to the oil tank 15. The target value Δ Pt is set in accordance with the biasing force of the spring 12-1 built in the unload valve 12.

Here, the accumulator 60 will be described. As shown in fig. 2, a bypass oil passage 63 branches off from the head-side oil passage 25 of the boom cylinder 9, and the accumulator 60 is connected to the bypass oil passage 63, the electromagnetic switching valve 61, and the bypass oil passages 64 and 65. The accumulator 60 is connected to the oil passage 22, which is a pressure fluid source side passage of the direction switching valve, via bypass oil passages 65 and 66, the electromagnetic switching valve 62, and a bypass oil passage 67.

The electromagnetic switching valves 61 and 62 are normally closed electromagnetic switching valves having 2-port 2 positions, and are connected to the controller 70 via electric signal lines 71 and 72, respectively, and are closed at a neutral position and released by an electric signal from the controller 70. Further, the electromagnetic switching valves 61 and 62 are provided with check valves therein, and allow only one-way flow of the pressure fluid when opened.

The controller 70 receives a signal pressure Pin from a pressure sensor 80 provided in the oil passage 21 and capable of detecting the supply pressure of the main hydraulic pump 2, a signal pressure PLS from a pressure sensor 81 provided in the secondary pressure pilot conduit passage 20 and capable of detecting the maximum load pressure of the actuator selected by the shuttle valve 16, a signal pressure PA from a pressure sensor 82 as pressure detecting means provided in the bypass oil passage 65 and capable of detecting the pressure in the accumulator 60, a signal pressure Px from a pressure sensor 83 provided in the signal oil passage 33 and capable of detecting the pilot secondary pressure of the arm hydraulic remote control valve 11, and a signal pressure Py from a pressure sensor 84 provided in the signal oil passage 34 and capable of detecting the pilot secondary pressure of the arm hydraulic remote control valve 11. The arithmetic circuit of the controller 70 can calculate the differential pressure Δ P of the directional control valve from the signal pressure Pin PLS, the discharge amount of the accumulator 60 from the signal pressure PA, and the lever operation amount of the operation lever 11-1, that is, the spool opening of the directional control valve from the signal pressure Px or the signal pressure Py.

Next, the operation of the accumulator 60 will be described. For example, when the operation lever 11-1 is operated in the contraction direction C, the signal pressure Py is input to the controller 70 from the pressure sensor 84 provided in the signal oil passage 34, an electric signal is input to the electromagnetic switching valve 61 from the controller 70 via the electric signal line 71, and the electromagnetic switching valve 61 is opened. Thus, the discharge oil as the pressure fluid discharged from the head chamber 9-1 of the boom cylinder 9 to the oil tank 15 through the head-side oil passage 25, in other words, a part of the return oil from the boom cylinder 9 is accumulated in the accumulator 60 through the bypass oil passages 63, 64, and 65.

When the operation lever 11-1 is operated in the extension direction E, the signal pressure Px is input to the controller 70 from the pressure sensor 83 provided in the signal oil passage 33, an electric signal is input to the electromagnetic switching valve 62 from the controller 70 via the electric signal line 72, and the electromagnetic switching valve 62 is opened. Thus, the pressure accumulation oil accumulated in the accumulator 60 is discharged from the bypass oil passages 65, 66, 67 to the oil passage 22, and is regenerated in the head chamber 9-1 of the boom cylinder 9 through the head-side oil passage 25. At this time, an electric signal is simultaneously input from the controller 70 to the proportional solenoid pressure reducing valve 50 through the electric signal line 73 based on the pressure in the accumulator 60, and the amount of pressure reduction (opening degree) of the proportional solenoid pressure reducing valve 50 is adjusted, thereby reducing the maximum load pressure of the actuator introduced into the load monitoring valve 41. Thus, in the load monitoring valve 41, the opening degree is adjusted based on the difference between the supply pressure of the main hydraulic pump 2 and the maximum load pressure of the actuator adjusted by the electromagnetic proportional pressure reducing valve 50, that is, based on the pressure difference between the pressure fluid source side of the directional switching valve and the actuator side of the directional switching valve adjusted by the electromagnetic proportional pressure reducing valve 50, the pump flow rate control pressure is controlled according to the opening degree, the swash plate control device 42 operates based on the pump flow rate control pressure, and the output of the main hydraulic pump 2 is reduced by decreasing the inclination angle of the swash plate 43 of the main hydraulic pump 2.

For example, as shown in fig. 5, when the maximum Lm of the lever operation amount of the operation lever 11-1, that is, the maximum flow rate Qm flowing from the main hydraulic pump 2 into the boom cylinder 9, applies a large load pressure to the boom cylinder 9, and the supply flow rate Qx of the pressurized oil required for the boom cylinder 9 becomes Qx > Qm, an electric signal is input from the controller 70 to the electromagnetic switching valve 62 through the electric signal line 72, the electromagnetic switching valve 62 is opened, and the pressurized oil accumulated in the accumulator 60 is regenerated in the head chamber 9-1 of the boom cylinder 9, and the output of the main hydraulic pump 2 is compensated by the regeneration of the accumulator 60. At this time, if the relationship of Qx < Qm + QA is established with respect to the flow rate QA regenerated from the accumulator 60 in the boom cylinder 9 calculated by the controller 70 based on the pressure in the accumulator 60, an electric signal is simultaneously input from the controller 70 to the electromagnetic proportional pressure reducing valve 50 through the electric signal line 73, and the output of the main hydraulic pump 2 is reduced so that the flow rate flowing from the main hydraulic pump 2 into the boom cylinder 9 becomes Qx-QA.

Thus, the hydraulic circuit of the load monitoring system of the present embodiment can discharge the pressure fluid accumulated in the accumulator 60 to the oil passage 22 serving as the pressure fluid source side flow passage of the directional control valve, adjust the control amounts of the load monitoring valve 41 and the swash plate control unit 42 serving as the discharge amount control means based on the pressure in the accumulator 60 by the electromagnetic proportional pressure reducing valve 50 provided in the secondary pressure pilot line 20 that leads the actuator side pressure of the directional control valve to the load monitoring valve 41, and can supplement the output of the main hydraulic pump 2 based on the pressure in the accumulator 60 that can be discharged to the pressure fluid source side flow passage of the directional control valve, and the load monitoring system can provide a hydraulic circuit with high energy efficiency while coping with the fluctuation of the load pressure of the actuator.

Further, when the pressure fluid is discharged from the pressure fluid source side flow path of the direction switching valve with respect to the accumulator 60, the control amounts of the load monitoring valve 41 and the swash plate control device 42 are adjusted by the electromagnetic proportional pressure reducing valve 50, and the output of the main hydraulic pump 2 can be adjusted in accordance with the pressure in the accumulator 60 at an appropriate timing, which is high in energy efficiency.

Further, the controller 70 can adjust the decompression amount (opening degree) of the electromagnetic proportional pressure reducing valve 50 based on the supply pressure of the main hydraulic pump 2, which is the pressure of the source side of the pressure source of the direction switching valve, detected by the pressure sensor 80, the maximum load pressure of the actuator, which is the pressure of the actuator side of the direction switching valve, detected by the pressure sensor 81, and the pressure in the accumulator 60, detected by the pressure sensor 82, and thus can quickly control the differential pressure Δ P between the front and rear of the direction switching valve to the target value Δ Pt. Further, the controller 70 has good responsiveness because the electromagnetic proportional pressure reducing valve 50 is operated by an electric signal.

In addition, by using the electromagnetic proportional pressure reducing valve 50, the pressure reducing valve as the adjusting means can be made to adopt a simple configuration.

Further, as shown in fig. 3, the electromagnetic proportional pressure reducing valve 50 reduces the secondary pressure in proportion to an increase in the electric signal from the controller 70 based on the pressure in the accumulator 60, that is, the electric signal to the solenoid, and therefore can finely control the control amounts of the load monitoring valve 41 and the swash plate control device 42.

Further, the loading-direction switching valve 6 and the loading cylinder 8, the arm-direction switching valve 7, and the boom cylinder 9 are fluidically connected in parallel to the main hydraulic pump 2, the accumulator 60 is connected to bypass oil passages 63, 64, 65, 66, and 67 extending from the head-side oil passage 25 of the boom cylinder 9, and pressurized oil accumulated in the accumulator 60 is supplied from the boom cylinder 9 to both the loading-direction switching valve 6 and the loading cylinder 8, the arm-direction switching valve 7, and the boom cylinder 9, whereby the efficiency of the hydraulic circuit is improved.

Further, by providing the electromagnetic switching valve 62 between the accumulator 60 and the oil passage 22 of the pressure fluid source side flow passage as the direction switching valve, and comparing the differential pressure Δ P before and after the direction switching valve calculated by the arithmetic circuit of the controller 70 with the signal pressure PA based on the pressure in the accumulator 60, the electromagnetic switching valve 62 can be opened and closed as necessary so that the differential pressure Δ P before and after the direction switching valve becomes the target value Δ Pt, and the discharge amount of the stored pressure oil in the accumulator 60 can be controlled.

Further, since the controller 70 can open and close the electromagnetic switching valve 62 by comparing the signal pressure PA, which is the pressure in the accumulator 60 detected by the pressure sensor 82, with the signal pressure Pin, which is the supply pressure of the main hydraulic pump 2 detected by the pressure sensor 80, the electromagnetic switching valve 62 is opened only when the pressure in the accumulator 60 is higher than the supply pressure of the main hydraulic pump 2 (PA > Pin), and the accumulated oil can be reliably discharged from the accumulator 60.

As a modification, the electromagnetic switching valve 62 may be used as a proportional valve, and the opening degree may be finely adjusted based on an input value of an electric signal from the controller 70, thereby controlling the discharge amount from the accumulator 60 to the pressure fluid source side flow passage of the directional switching valve based on the pressure accumulation amount of the accumulator 60. This makes it possible to control the differential pressure Δ P between the direction switching valve and the front and rear sides thereof to the target value Δ Pt while adjusting the balance between the discharge amount from the main hydraulic pump 2 and the discharge amount from the accumulator 60, and the energy efficiency of the entire hydraulic circuit is good.

Although the embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to the embodiments, and modifications and additions, if any, within the scope of the present invention are also included in the present invention.

For example, in the above-described embodiment, the hydraulic circuit of the loader has been described as the fluid circuit of the load monitoring system, but the present invention is not limited to this, and may be applied to fluid circuits of vehicles other than loaders, construction machines, industrial machines, and the like. The pressure fluid used in the fluid circuit may be a liquid gas other than oil.

Further, the above-described embodiment has been described with an example in which a part of the discharge oil discharged from the head chamber 9-1 of the boom cylinder 9 to the oil tank 15 through the head-side oil passage 25 during the contraction operation of the boom cylinder 9 is accumulated in the accumulator 60 through the bypass oil passages 63, 64, 65, and is regenerated in the boom cylinder 9 from the oil passage 22 during the expansion operation of the boom cylinder 9, but the present invention is not limited to this, and it is applicable to a hydraulic circuit of a load monitoring system of the related art if the hydraulic circuit performs accumulation and regeneration by the accumulator 60, and for example, a hydraulic circuit may be configured such that a part of the return oil during driving of the loading cylinder 8 or braking of a traveling hydraulic motor, not shown, by the loader 100 is accumulated in the accumulator 60 and is regenerated during acceleration of the hydraulic motor.

In the above-described embodiment, the description has been given of the mode in which the electromagnetic proportional pressure reducing valve 50 is provided on the primary side of the load monitoring valve 41 in the secondary pressure pilot conduit 20, but the pump flow rate control pressure controlled by the load monitoring valve 41 may be reduced by the electromagnetic proportional pressure reducing valve by providing the electromagnetic proportional pressure reducing valve on the secondary side of the load monitoring valve 41, or the output of the main hydraulic pump 2 may be controlled independently of the secondary pressure pilot conduit 20.

In the above embodiment, the example of the pressure reducing valve using the electromagnetic proportional pressure reducing valve 50 as the adjusting means has been described, but the pressure reducing valve as the adjusting means may be a pilot-operated pressure reducing valve operated by an external hydraulic pressure signal.

In the above-described embodiment, the description has been given of the mode in which the hydraulic remote control valve is used to switch the supply side of the pressurized oil supplied from the pilot hydraulic pump 3, but the same is also applicable to the case in which the electric remote control is used instead of the hydraulic remote control valve, and an electric signal from the electric remote control may be directly input to the controller.

In the above-described embodiment, the swash plate control device 42 operates based on the pump flow rate control pressure controlled by the load monitoring valve 41 to control the output of the main hydraulic pump 2 by increasing or decreasing the inclination angle of the swash plate 43 of the main hydraulic pump 2 in the discharge amount control mechanism, but the discharge amount control mechanism is not limited to this, and may be a mechanism capable of controlling the output of the main hydraulic pump 2 by an electric signal.

In the above embodiment, the description has been given of the configuration in which the pressure reducing valve is provided as the adjusting means in the secondary pressure pilot conduit 20, but a pressure increasing mechanism may be provided as the adjusting means in the primary pressure pilot conduit 28.

The pressure source side pressure and the actuator side pressure of the direction switching valve may be input not through the pilot line but through an electric signal.

In addition, the accumulator 60 may be provided with a bypass oil passage and an electromagnetic switching valve so as to be able to accumulate pressure from the hydraulic circuit on the loading cylinder 8 side.

In addition, the actuator provided in the hydraulic circuit may be one.

Description of the symbols

1 a driving mechanism; 2 main hydraulic pump (pressure fluid source); 3, a pilot hydraulic pump; 4, 5 pressure compensation

A valve; 6 a directional switching valve (directional switching valve); 7 arm direction switching valves (direction switching valves); 8 pack

A carrier cylinder (actuator); 9 lifting arm cylinders (actuators); 10 loading a hydraulic remote control valve; 11 arm hydraulic remote control

A valve; 12 unloading the valve; 13 a safety valve; 15 oil tanks; 16 a shuttle valve; 20 secondary pressure pilot pipeline (pilot pipe)

Way); 22 oil passages (pressure fluid source side passages of the direction switching valve); 25 head-side oil passages; a 26-rod side oil passage;

27 primary pressure pilot line (pilot line); 37 an accumulator; 41 a load monitoring valve (discharge amount control mechanism);

42 swash plate control means (discharge amount control mechanism); 43 a sloping plate; a 50 electromagnetic proportional pressure reducing valve (adjusting unit,

a pressure relief valve); 60 an accumulator; 61. 62 an electromagnetic switching valve; 63-67 bypass oil passages; 70 controller (control)

Section); 80. 81 pressure sensors; 82 pressure sensor (pressure detection unit); 100 a loader; 108

Loading; 109 lift the arms.