JPH04191502A - Cut-off cancelling mechanism in load sensing system - Google Patents

Abstract

PURPOSE:To obtain a heavy drilling mode with a sense of powerfulness of a machine by providing a cut-off cancelling means such that an unloaded valve arranged on a circuit branched from a circuit leading from a pump to a directional changeover valve is operated at a value smaller than a set differential pressure of a regulator valve. CONSTITUTION:When an operator sets a cut-off cancelling switch 28 ON, a discharge pressure PP of a pump 1 is detected by a pressure sensor 26 and input to a controller 27. In case that a load to be applied to an operation machine is increased and the discharge pressure PP exceeds a value a little lower than a relief set pressure of a relief valve 21, a solenoid of a solenoid valve 24 is excited by the controller 27 to switch the solenoid valve 24. Pressure oil in a hydraulic pump 25 is applied to one end of an unloading valve 23 through the solenoid valve 24. The unloading valve 23 is operated under a condition that its differential pressure is smaller than a set differential pressure of a regulator valve 17.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hydraulic drive device installed in a construction machine such as a hydraulic excavator, and particularly relates to a hydraulic drive device that is installed on a construction machine such as a hydraulic excavator, and particularly relates to a hydraulic drive device that is attached to a construction machine such as a hydraulic excavator, and particularly relates to a hydraulic drive device that is attached to a construction machine such as a hydraulic excavator. The present invention relates to a cutoff canceling mechanism in a load sensing system that controls the discharge amount of a hydraulic pump so that the discharge amount is maintained at a set value.

[Prior Art] In a hydraulic machine equipped with a load sensing system, such as a hydraulic excavator, as shown in FIG. 4, a variable displacement hydraulic pump (
(hereinafter referred to as a pump) 1, actuators 2 and 3 for working machines such as booms, arms, packets, and swing devices driven by the pressure oil discharged by the pump 1, and the pump 1.
Closed center directional control valves 4, 5 that switch the direction of pressure oil sent from the to the actuators 2, 3, etc.
etc., and a regulator 16 and a regulator valve 17 that control the flow rate of pressure oil discharged by the pump 1.

The directional control valves 4, 5, etc. are combined into one and connected to the pump 1 through a circuit 6, and to the oil tank 7 through a circuit 8. Further, one end of the regulator valve 17 is connected to a pilot circuit 19 branched from the circuit 6 to receive the discharge pressure Pρ of the pump 1, and the other end receives the highest pressure among the load pressures of each actuator 2, 3, etc. through an orifice 20. Pressure PL
The discharge amount Qρ of the pump 1 is controlled via the regulator 16.

Circuits 6a, 6b, etc. are connected to the directional control valves 4, 5, etc. in parallel with the circuit 6 from the pump 1, and the actuator 2 is connected to circuits 2a, 2b, and the actuator 3 is connected to circuits 3a, 3b, respectively. It is connected. The directional control valves 4, 5, etc. have three positions, and are connected to the shuttle valves 10, 11, etc. via the boat R at each position. These shuttle valves 10, 11, etc. are equipped with pilot circuits 12a, 12b.
etc. are connected to the circuits 2a, 2b, 3a of each actuator 2, 3, etc. via the pilot circuit 13.
, 3b, etc. are inserted into the pressure reducing valves 14a, 14b.

15a, 15b, etc. An unload valve 23 is provided in a branch circuit of the circuit 6, and an orifice 20 and an LS relief valve 21 are provided in the pilot circuit 12b. A pump 1 is connected to one end of the unload valve 23.
The discharge pressure PP is guided by a pilot circuit 6C, and the actuator load pressure PLS that has passed through the orifice 20 is guided to the other end by a pilot circuit 12c.

When the load applied to the actuator is small, the pump discharge amount is O, p, the pump discharge pressure is PP, and the flow coefficient is C.
If the opening area of the one-way switching valve is A, and the hydraulic pressure of the pilot circuit 12c is PLS, it can be expressed by the following equation.

Qp: CXAX PP-Pts Since the differential pressure between PP and Pts is controlled to be constant, for example, the differential pressure is 20 Rg/c +n2
Then, Q p = CX A X v'woki.

When a heavy load is applied to a working machine, such as a bucket, and the load pressure on the packet drive actuator increases, the LS relief valve 21 is activated. Then pilot circuit 1
The pump discharge pressure P is controlled by the orifice 20 located in 2b.
The differential pressure between P and the hydraulic pressure PLS of pilot circuit-〇-12c is 20 kg/cm
2, the regulator valve 17 is switched to drive the regulator 16, the swash plate angle of the hydraulic pump 1 decreases, and the amount of oil sent to the actuator is cut off. Normally, during relief, the unload valve 23
Due to the operation, PP PLS≧30kg/cm2.

[Problem to be solved by the invention] However, as mentioned above, when the load pressure applied to the actuator increases, if the cutoff mechanism operates and minimizes the pump discharge amount, the energy loss caused by relief will be reduced. However, it may feel like a weak machine to the operator. When the load applied to a working machine, such as a bucket, increases during excavation using a hydraulic bending machine, the load pressure on the actuator increases, and the pump discharge pressure PP increases, as shown in Figure 5 (a). , the relief pressure is reached. The pump discharge amount decreases as PP increases, and when the cutoff mechanism is activated, the pump discharge amount becomes the minimum discharge amount as shown by the solid line in FIG. 5(b). At the same time, the actuator speed also decreases, as shown by the solid line in FIG. 5(C), and reaches O at cutoff. The operator senses that the load is too high and operates the boom lever in the upward direction to slightly raise the hatch to relieve the load on the packet. This operation reduces the load applied to the bucket, lowers the pump discharge pressure PP shown in FIG. 5(a), releases the cut-off action, and increases the pump discharge amount again (FIG. 5b). The discharge rate increase curve at this time is determined by the responsiveness of the pump. As a result, the actuator resumes driving and the packet begins to move, but the movement of the packet is relieved after the boom lever is raised to reduce the load on the bucket, as shown by the solid line in Figure 5 (C). It takes time t to return to the previous state.
1, giving the impression of a machine with weak cutting power.

The present invention focuses on the above-mentioned conventional problems, and includes means for canceling the cut-off effect as necessary.
The purpose of the present invention is to provide a cut-off canceling mechanism in a load sensing system that allows selection between an energy-saving key mode and a heavy excavation mode that makes you feel the strength of the machine.

[Means for Solving the Problems] In order to achieve the above object, a cutoff canceling mechanism in a load sensing system according to the present invention includes a pump, a hydraulic actuator driven by pressure oil discharged by the pump, and the pump. a directional switching valve that controls the flow of pressure oil supplied from the pump to the hydraulic actuator, and a discharge amount control means that controls the flow rate of the pressure oil discharged from the pump, the discharge amount control means being a variable displacement valve of the pump. The regulator that drives the means and the pump discharge pressure Pρ
and the load pressure pH of the hydraulic actuator.
'In a hydraulic drive system equipped with a regulator valve that maintains PLS at a set value and an unload valve that operates above a certain set pressure relative to the load pressure PLS, the pump discharge flow rate is prevented from being minimized during actuator relief. Specifically, in such a configuration, as a means for preventing the discharge flow rate of the pump from being minimized at the time of actuator relief, a cut-off cancel switch that outputs a command signal to the controller, and a means for a pressure sensor that detects the discharge pressure PP of the pump and inputs it to the controller, and an unload valve that is installed in a branch circuit of the circuit from the pump to the directional control valve and that is activated by a change in the differential pressure PP-PLS. It shall be equipped with a solenoid valve that sends pressure oil and a controller that sends a command current to this solenoid valve, or output a command signal to the controller as a means to prevent the pump discharge flow rate from being minimized during actuator relief. A cut-off cancel switch, a pressure sensor that detects the discharge pressure Pρ of the pump and inputs it to the controller, a solenoid valve that sends pressure oil to one end of the regulator valve, and a controller that sends a command current to the solenoid valve. Alternatively, as a means to prevent the pump discharge flow rate from being minimized at the time of actuator relief, a cut-off cancel switch and a restrictor are provided in the pilot circuit that transmits the actuator load pressure PLS to one end of the regulator valve. The switching valve may include a switching valve having a 1" open circuit and a non-restricted circuit, and a solenoid valve for supplying pressure oil to one end of the switching valve.

[Function] In the case of claim (2), as means for preventing the discharge flow rate of the pump from being minimized at the time of actuator relief, there is provided a cut-off cancel switch that outputs a command signal to the controller and detects the pump discharge pressure PP. A pressure sensor inputs to the controller and a branch circuit of the circuit from the pump to the directional control valve.
The configuration includes a solenoid valve that sends pressure oil to one end of the unload valve that is activated by a change in S, and a controller and roller that sends a command current to this solenoid valve. When the discharge pressure PP increases and the solenoid valve operates, the set differential pressure of the unload valve becomes smaller than the set differential pressure of the regulator valve. As a result, even if the unload valve operates, the pump will be driven at the maximum swash plate angle, the cutoff mechanism will not operate, and the pressure oil will continue to be in a relief state. Therefore, as soon as the actuator load is reduced, the actuator resumes driving, making it possible to perform an operation that gives a sense of the strength of the machine.

In the case of claim (3), instead of the unload valve in claim (2), pressure oil is sent to one end of the regulator valve, so when the pump discharge pressure PP rises and the solenoid valve is activated, the regulator The set differential pressure of the valve is greater than the set differential pressure of the unload valve. As a result, even if the unload valve operates, the cutoff mechanism does not operate, as in the case of claim (2) above.

In the case of claim (4), the pilot circuit for transmitting the actuator load pressure PLS to one end of the regulator valve is provided with a switching valve having a circuit with a throttle and a circuit without a throttle, and one end of the switching valve is provided with a pressure oil Since the configuration includes a solenoid valve that sends the pump oil and a cut-off cancel switch, when the solenoid valve is activated and the switching valve is switched to a circuit without restriction, the pump oil is drained through the L-S relief valve. The differential pressure PP PLS becomes less than the set differential pressure of the regulator valve, and the unload valve does not operate, and the above claim (
As in cases 2) and (3), the cutoff mechanism does not operate.

Also, if you turn off the cutoff cancel switch,
It is also possible to select an energy saving mode in which a cutoff mechanism operates to reduce the pump discharge amount when the differential pressure between the pump discharge pressure and the maximum load pressure of each actuator reaches a set value.

[Example] Hereinafter, an example of a cut-off canceling mechanism in a load sensing system according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a schematic configuration of a hydraulic drive device equipped with a cut-off canceling mechanism according to claim (2). A pump is installed between a pump 1 driven by a power source such as an engine and an actuator 2.3 for a working machine or swing device such as a boom, arm, or bucket that is driven by the pressure oil discharged by this pump 1. Directional switching valves 4, 5, etc. for switching the direction of pressure oil sent from pump 1 to actuators 2, 3, etc. are provided, and the directional switching valves 4, 5, etc. are provided with circuits 6a, 6a, etc. in parallel with circuit 6 from pump 1, respectively. 6b etc. are connected, and the circuit 8 is connected to the oil tank 7.

The directional control valves 4, 5, etc. are combined into one piece, each with 7 valves.
The pump port has three positions, and at the neutral position N, the pump port is closed, and up to the switching position M, the pump port is throttled by a variable throttle 9, and at the switching position M, the throttle 9 has a constant area. Also, at each position, the shuttle valve 10.
Pilot circuits 12a, 12b, etc. are connected to these shuttle valves 10, 11, etc., respectively, and the highest pressure that has passed through each shuttle valve 10, 11, etc. is sent to each actuator via a pilot circuit 13. It is led to pressure reducing valves 14a, 14b, i5a, 15b, etc. inserted in circuits 2a, 2b, 3a, 3b, etc. to 2°3, etc. The directional control valves 4, 5, etc. are switched in response to a pressure command from a pilot pressure control valve operated by a lever provided near a driver's seat (not shown).

A regulator 16 that controls the flow rate of pressure oil discharged by the pump 1 and a regulator valve 17 are connected through a circuit 18. The regulator valve 17 is a 3-bot, 2-position switching valve, and one end of the valve 17 is connected to the circuit 6. The branched pilot circuit 19 is connected to receive the discharge pressure PP of the pump 1, and the other end is connected to the pilot circuit 12c to receive the highest pressure among the load pressures of each actuator 2.3 etc. through the orifice 20 to receive the pressure PLS. It is received as such. Further, an LS relief valve 21 is provided downstream of the orifice 20.

An unload valve 23 is provided in a circuit 22 branching from the circuit 6 and leading to the oil tank 7, and one end of the unload valve 23 is connected to the hydraulic pressure of the circuit 6, that is, the discharge pressure Pρ of the pump 1, and the solenoid valve 24. The hydraulic pressure from the hydraulic pump 25 is introduced to the other end, and the actuator load pressure PLS that has passed through the pilot circuit 12c is introduced to the other end. Further, the output wiring of the pressure sensor 26 that detects the oil pressure PP of the circuit 6 is connected to the controller 27, and the output wiring of the cut-off cancel switch 28 installed near the driver's seat is also connected to the controller 27. The output wiring 27 is connected to the solenoid of the electromagnetic valve 24.

Next, the operation of the cutoff canceling mechanism will be explained.

When the cut-off cancel switch 28 is set to OFF or F, the differential pressure between the pump discharge pressure PP and the maximum value PLS of each actuator load pressure that has passed through the orifice 20 becomes the set value, just like the conventional load sensing system. When the pump reaches the limit, the cut-off mechanism is activated and the pump remains in energy-saving mode to reduce the pump discharge amount.

The operator turns the cutoff cancel switch 28 to O.
When set to N, the pressure sensor 26 detects the discharge pressure PP of the pump 1 and inputs it to the controller 27 manually. Then, when the load applied to the work machine increases and the discharge pressure PP of the pump 1 exceeds a value slightly lower than the relief set pressure of the LS relief valve 21, the controller 27 energizes the solenoid of the solenoid valve 24. Switch. As a result, the pressure oil of the hydraulic pump 25 acts on one end of the unload valve 23 via the electromagnetic valve 24, and the unload valve 23 operates with its set differential pressure being smaller than the set differential pressure of the regulator valve 17. For example, when the differential pressure of the regulator valve 170 is 20 kg/crn2 and the differential pressure of the unload valve 23 reaches PP PLS'; 10 kg/am2, the unload valve 23 is switched and a part of the oil discharged from the pump 1 is It is drained into the oil tank 7 via the load valve 23. Therefore, the regulator valve 17 is not switched, the pump 1 is driven at the maximum swash plate angle, and the relief flow rate in the LS relief valve 21 increases as shown by the dotted line in FIG. 5(d). When the load applied to the work machine is reduced, the work machine is immediately moved with a sufficient amount of oil, as shown by the dotted line in Fig. 5(C), and excavation becomes visually powerful.

Figure 2 is a hydraulic circuit diagram of claim (3) and claim (2).
, instead of applying the pump discharge pressure PP and hydraulic pressure due to the operation of the solenoid valve to one end of the unload valve 23, the actuator load pressure PL is applied to one end of the regulator valve 17.
In addition to S, hydraulic pressure is applied by operating a solenoid valve 24.

The operator turns the cutoff cancel switch 28 to O.
When set to N, the pressure sensor 26 detects the discharge pressure Pρ of the pump 1 and inputs it to the controller 27. When the load applied to the work machine increases and exceeds a value slightly lower than the discharge pressure PP of the pump 1 or the relief set pressure of the LS relief valve 21, the controller 27 energizes the solenoid of the solenoid valve 24. Switch. Thereby, the pressure oil of the hydraulic pump 25 acts on one end of the regulator valve 17 through the solenoid valve 24 and the pilot circuit 29 together with the actuator load pressure PLS. Since the regulator valve 17 does not operate unless the differential pressure becomes larger than that of the unload valve 23, the unload valve 23 operates first. As a result, the pump 1 is driven at the maximum swash plate angle and the cut-off mechanism is not activated.

FIG. 3 is a hydraulic circuit diagram of claim (4), in which the shuttle valve 11
A switching valve 30 is provided in the pilot circuit 12c extending from the regulator valve 17 to one end. This switching valve 30
is in position (A) when the cut-off cancel switch 28 is OFF, throttles the pressure oil passing through the pilot circuit 12c, and puts pressure PLS at one end of the regulator valve 17.
is guiding. Therefore, similar to conventional energy saving mode circuits, when the actuator load increases and the LS relief valve 21 is actuated, the regulator valve 17 is switched and drives the regulator 16 to minimize the swash plate angle of the pump 1. In other words, a cutoff is performed.

However, when the cut-off cancel switch 28 is turned ON, the solenoid valve 24 is excited, and the pressure oil discharged from the hydraulic pump 25 acts as pilot pressure on one end of the switching valve 30 via the solenoid valve 24 and the pilot circuit 31. Then, switch the switching valve 30 to the position (B). As a result, the pressure oil passing through the pilot circuit 12c is allowed to flow as it is without being throttled, so the pilot pressure PLS acting on the left end of the regulator valve 17 does not decrease, and the regulator valve 1
7 cannot be switched. Therefore, even if the LS relief valve 21 is relieved, the pump 1 does not reach the minimum swash plate angle, and the heavy excavation mode is realized without cut-off.

In the embodiment of claim (4) above, the solenoid valve 24 is used as a means for switching the switching valve 30 at the time of canceling the cut-off, but the switching valve 30 is provided with a solenoid and used as a solenoid valve.
The cut-off cancel switch 28 may be used to directly switch.

[Effects of the Invention] As explained above, according to the present invention, the unload valve provided in the branch circuit of the circuit from the pump to the directional control valve operates at a value smaller than the set differential pressure of the regulator valve. The cut-off mechanism is equipped with an off-cancelling means, a switching valve in the load sensing circuit, and a cut-off canceling means that increases the load sensing pressure, so even if the load pressure of the actuator increases, the cut-off mechanism does not operate and the will remain in relief mode.

Since the actuator resumes driving as soon as the actuator load is reduced, it is possible to realize a heavy excavation mode that makes the machine appear powerful.

When the cut-off canceling means is not used, the cut-off mechanism operates to reduce the pump discharge amount when the differential pressure between the pump discharge pressure and the actuator load pressure reaches a set value, as in the conventional case, resulting in an energy saving mode. The operator can freely and easily select between the heavy excavation mode and the energy saving mode 1 according to the work content.

[Brief explanation of the drawing]

FIG. 1 is a schematic hydraulic circuit diagram of a hydraulic drive device equipped with a cut-off canceling mechanism in a load sensing system according to an embodiment of claim (2), and FIG. 2 is a cut-off diagram according to an embodiment of claim (3). FIG. 3 is a schematic hydraulic circuit diagram of a hydraulic drive device equipped with a canceling mechanism; FIG. 3 is a schematic hydraulic circuit diagram of a hydraulic drive device equipped with a cut-off canceling mechanism according to an embodiment of claim (4); FIG. Figure 5 is a schematic hydraulic circuit diagram of a hydraulic drive device equipped with a technological load sensing system, and is a diagram showing changes in major items when the load applied to the actuator increases, (a) pump discharge pressure, (b) ) shows the pump discharge amount, (C) shows the actuator operating speed, and (d) shows the relief flow rate. 1... Variable displacement hydraulic pump 2.3... Actuator 4.5... Directional switching valves 12 a, 12 b, 12 c, 13.
19°29.31...Pilot circuit 16...
...Regulator 17 ...Regulator valve 23 ...... Unloader 1 Valve 24 ... Solenoid valve 26 ... Pressure sensor 27 ... Controller 28...cutoff cancel switch 30...
...Switching valve applicant Komatsu Ltd.

Claims (4)

[Claims] (1) A variable displacement hydraulic pump, a hydraulic actuator driven by the pressure oil discharged by the variable displacement hydraulic pump, and a direction for controlling the flow of the pressure oil supplied from the variable displacement hydraulic pump to the hydraulic actuator. a switching valve;
a discharge amount control means for controlling the flow rate of pressure oil discharged from the variable displacement hydraulic pump, and the discharge amount control means includes a regulator for driving the variable displacement means of the variable displacement hydraulic pump; The driving of the regulator is controlled according to the differential pressure between the discharge pressure P_P of the pump and the load pressure P_L_S of the hydraulic actuator, and the differential pressure P_P is controlled.
- In a hydraulic drive system equipped with a regulator valve that maintains P_L_S at a set value and an unload valve that operates at a pressure above a certain set pressure relative to the load pressure P_L_S, the discharge flow rate of a variable displacement hydraulic pump is minimized during actuator relief. A cut-off canceling mechanism in a load sensing system, characterized in that the cut-off canceling mechanism is provided with a means for preventing the cut-off from occurring. (2) The means for preventing the discharge flow rate of the variable displacement hydraulic pump from being minimized at the time of actuator relief includes a cut-off cancel switch that outputs a command signal to the controller, and a means for detecting the discharge pressure P_P of the variable displacement pump. and an electromagnetic device that sends pressure oil to one end of an unload valve that is activated by a change in the differential pressure P_P−P_L_S, which is installed in a branch circuit of the circuit from the variable displacement pump to the directional valve. The cutoff canceling mechanism in a load sensing system according to claim 1, comprising a valve and a controller that sends a command current to the electromagnetic valve. (3) The means for preventing the discharge flow rate of the variable displacement hydraulic pump from being minimized at the time of actuator relief includes a cut-off cancel switch that outputs a command signal to the controller, and a means for detecting the discharge pressure P_P of the variable displacement pump. Claim (1) characterized in that the pressure sensor is equipped with a pressure sensor that inputs input to the controller, a solenoid valve that sends pressure oil to one end of the regulator valve, and a controller that sends a command current to the solenoid valve. Cutoff cancellation mechanism in load sensing system. (4) A means for preventing the discharge flow rate of the variable displacement hydraulic pump from being minimized during actuator relief is provided in a cut-off cancel switch and a pilot circuit that transmits the actuator load pressure P_L_S to one end of the regulator valve, A claim characterized in that the switching valve is equipped with a switching valve having a throttled circuit and a non-throttled circuit, and a solenoid valve that sends pressure oil to one end of the switching valve.
1) A cutoff cancellation mechanism in the load sensing system described above.