JPH04191503A - Cut-off cancelling mechanism of load sensing system - Google Patents

Abstract

PURPOSE:To obtain a heavy drilling mode with a sense of powerfulness of a machine by providing means for increasing relief set pressure respectively on an LS relief valve and a main relief valve arranged on a pump discharge circuit, and operating the main relief valve when a negative load pressure to be applied to an actuator is increased. CONSTITUTION:When an operator sets a switch 26 ON, a solenoid of a solenoid valve 23 is excited and pressure oil sent from a hydraulic pump 24 is applied to an LS relief valve 21 through a pilot circuit 25. A relief set pressure of the LS relief valve 21 gets higher than that of a main relief valve 22. In case that a negative load pressure to be applied to an actuator is increased and a discharge pressure of a pump 1 exceeds a specified value, the main relief valve 22 is operated, while the LS relief valve 21 is not operated. A differential pressure between a pump discharge pressure Pp and a pilot pressure PLS, therefore, todes not exceed a set pressure of a regulator valve 17. The pump 1 is thus driven with a maximum tilting plate angle, and cut-off, is not carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a hydraulic drive system installed in 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 differential pressure is maintained at a set value.

[Prior Art] A hydraulic machine equipped with a load sensing system, for example a hydraulic excavator, uses a variable displacement expansion hydraulic pump (
(hereinafter referred to as a pump) 1, actuators 2 and 3 for working machines such as hooms, arms, packets, and swing devices driven by the pressure oil discharged by the pump 1, and the pump 1.
4. A closed center directional control valve that switches the direction of pressure oil sent to the actuators 2, 3, etc. 5th prize and
The pump 1 includes 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 Pp 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. is received as pressure PLS, and the pump 1 receives it as pressure PLS via the regulator 16.
The discharge fit Q p has been controlled.

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 each position is connected to the shuttle valves 10, 11, etc. via the bow 1-R. These shuttle valves 10, 11, etc. have pilot circuits 12a,
12 b etc. are connected, and the pilot circuit 13
The circuits 2a, 2 of each actuator 2, 3 etc. via
Pressure reducing valves 14a, 14 inserted in b, 3a, 31), etc.
1).

15a, I5b, etc. An unload valve 28 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. The discharge pressure PP of the pump 1 is guided to one end of the unload valve 28 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 Qρ, the pump discharge pressure is Pp, the flow coefficient is the opening area of the C1 directional control valve is A, and the hydraulic pressure of the pilot circuit 12c is PLS, it can be expressed by the following formula. can.

o, p = c X A 'T 100.

When a heavy load is applied to a working machine, such as a bucket, and the load pressure on the bucket drive actuator increases, the LS relief valve 21 is activated. Then, due to the orifice 20 in the pilot circuit 121), the differential pressure between the pump discharge pressure PP and the hydraulic pressure PLS of the pilot circuit 12c becomes greater than 20 L (g/cm2), and the regulator valve 17 is switched to drive the regulator 16. However, the swash plate angle of the hydraulic pump 1 decreases, cutting off the amount of oil sent to the actuator.Usually, during relief, the unload valve 23 operates, and Pp-pH≧30 kg/am2.

[Problems to be Solved by the Invention] However, as described above, when the load pressure applied to the actuator increases, if the cutoff mechanism operates to minimize the pump discharge amount, the energy loss caused by relief will be reduced. However, to the operator, there are cases where the machine feels like a weak machine. When the load applied to the working machine (for example, a packet) increases during excavation using a hydraulic excavator, the load pressure on the actuator increases, so as shown in FIG. 4(a), the pump discharge pressure PP increases. Relief pressure is not 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. 4(b). At the same time, the actuator speed also decreases, as shown by the solid line in FIG. 4(C), and reaches 0 at cutoff. The operator senses that the load is excessive and operates the boom lever in the upward direction to slightly raise the packet and relieve the load on the bucket. By this operation, the load applied to the packet is lightened, and the pump discharge pressure Pp decreases (not shown in FIG. 4(a)), and the cut-off action is canceled and the pump discharge pressure increases again (FIG. 4(b)). 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 bucket begins to move, but the bucket movement is relieved after the boom lever is raised to reduce the load on the bucket, as shown by the solid line in Figure 4 (C). It takes time t1 to return to the previous state, giving the impression of a machine with weak digging 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 funnel sensing system that allows selection between an energy saving mode and a heavy excavation mode that gives a sense of 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 (lfFj), and the discharge amount control means a regulator that drives a capacity variable means; and a regulator that controls driving of the regulator according to a differential pressure between a pump discharge pressure PP and a load pressure PLS of the hydraulic actuator, and maintains the differential pressure PP-PLS at a set value. In the hydraulic drive device, the relief set pressure of the LS relief valve is transferred from the hydraulic pump to the LS relief valve provided in a circuit that transmits the actuator load pressure to the regulator valve via the orifice. A relief set pressure variable means for raising the relief set pressure higher than that of the main relief valve provided in the circuit leading to the valve is provided, and in such a structure, the relief set pressure variable means of the LS relief valve and the relief set pressure of the main relief valve are provided. It is also possible to provide a set pressure variable means.

The relief set pressure variable means includes a solenoid valve operated by a switch, a hydraulic pump, and a pilot circuit that guides the pressure oil discharged by the hydraulic pump to the LS relief valve or the main relief valve via the solenoid valve. And so.

[Operation] According to the above configuration, the relief set pressure of the LS relief valve provided in the circuit that transmits the actuator load pressure to the regulator valve is higher than the relief set pressure of the main relief valve provided in the circuit from the pump to the directional control valve. Since a relief set pressure variable means is provided to increase the relief set pressure, when the relief set pressure variable means is activated to make the relief set pressure of the LS relief valve higher than the relief set pressure of the main relief valve, the load pressure applied to the actuator increases. At this time, the main relief valve operates, and the difference between the pump discharge pressure Pp and the actuator load pressure PLS becomes smaller than the set differential pressure of the regulator valve.

Therefore, the pump swash plate angle becomes maximum, and 1-[does not cut off as before.

In addition, as described above, if a relief set pressure variable means for the main relief valve is provided in addition to the relief set pressure variable means for the S relief valve, the relief set pressures of both the I and S relief valves and the main relief valve can be increased. is possible, and LS is lower than the relief set pressure of the main relief valve.
If the relief valve's relief set pressure is high, when the load pressure applied to the actuator increases, the main relief valve will operate and the pump swash plate angle will reach its maximum, making the machine more powerful during heavy excavation or when traveling. I can do something.

Furthermore, when the relief set pressure variable means is not used, it can be operated in the energy saving mode as before.

[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 claims (1) and (3). A pump is installed between a pump 1 driven by a power source such as an engine, and actuators 2 and 3 for working machines such as booms, arms, and packets, or swing devices, which are driven by the pressure oil discharged by this pump 1. Directional switching valves 4, 5, etc. are provided to switch the direction of pressure oil sent from the pump 1 to the actuators 2, 3, etc., and each of the directional switching valves 4, 5, etc. has a circuit 6a connected in parallel to the circuit 6 from the pump 1. , 6b, etc. are connected, and the circuit 8 is connected to the oil tank 7.
connected with.

The directional control valves 4, 5, etc. are combined into one piece, each with 7 valves.
The pump boat is comprised of three positions. In the neutral position N, the pump boat is closed, and up to the switching position, M, the pump boat is marked with a variable ridge 9. At the switching position, M, the orifice 9 has a constant area. In addition, 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 passed through the pilot circuit 13. Each actuator 2゜3
The pressure reducing valve 14 inserted into the circuit 2a, 2b, 3a, 3b, etc. a, 14b, 15a, 151), 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 by a circuit 18. The regulator valve 17 is a 3-bot, 2-position switching valve, and one end of this 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, and a main relief valve 22 is provided in a branch circuit of the circuit 6.

In addition to a normal spring 21a that sets the relief set pressure, pressure oil sent from a hydraulic pump 24 via a solenoid valve 23 is guided to the LS relief valve 21 through a pilot circuit 25, which is installed near the driver's seat. The output wiring of the switch 26 is connected to the solenoid of the electromagnetic valve 23.

Further, a circuit 27 branching from the circuit 6 and reaching the oil tank 7 is provided with an unload valve 1 and a valve 28.
One end is connected to the hydraulic pressure of the circuit 6, that is, the discharge pressure PP of the pump 1.
is guided to the other end, and the pilot pressure PLS that has passed through the pilot circuit 12c is guided to the other end.

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

When the switch 26 is turned OFF, it is exactly the same as the conventional load sensing system, and when 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 reaches the set value, the cutoff mechanism is activated. remains in energy-saving mode, which operates to reduce pump output.

When the operator turns on the switch 26, the solenoid valve 23
The solenoid is energized, and the pressure oil sent from the hydraulic pump 24 passes through the pilot circuit 25 to the LS relief valve 21.
The relief set pressure of the LS relief valve 21 becomes higher than the relief set pressure of the main relief valve 22.

For example, the relief set pressure of the main relief valve 22 remains at 350 kg/cm2, and the relief set pressure of the LS relief valve 21 changes from 320 kg/crn2 to 400 kg/cm2.
g/c rn2 rises.

Therefore, when the load pressure applied to the actuator increases and the discharge pressure of the pump 1 exceeds 350 kg/cm'', the main relief valve 22 operates and the LS relief valve 21 does not operate, so the difference between Pp and Ps The pressure does not exceed the set pressure of the regulator valve 17. Therefore, the pump 1 is driven at the maximum swash plate angle and does not cut off. Then, when the load on the working machine is reduced, the pressure is reduced as shown by the dotted line in No. 41"m (c). As shown in the figure, the work equipment is immediately moved with a sufficient amount of oil, making digging more intuitive and powerful.

FIG. 2 is a hydraulic circuit diagram showing a schematic configuration of a hydraulic drive device equipped with a cut-off canceling mechanism according to claims (2) and (3). In this figure, not only the LS relief valve 21 but also the main relief valve 22 has a solenoid valve 29.
, a hydraulic pump 30, and a switch 31 are provided, and both the LS relief valve 21 and the main relief valve 22 have variable relief set pressures.

As in the case of claim (1) characterized by the switch 26, the solenoid of the electromagnetic valve 23 is energized, and the hydraulic pump 24 is energized.
The pressure oil sent from the LS acts on the LS relief valve 21,
The relief set pressure of the relief valve 21 becomes higher than the relief set pressure of the main relief valve 22.

When both switches 26 and 31 are turned on, the solenoid valve 23
．． Both solenoids 29 are energized, and the hydraulic pump 24
The pressure oil sent from the hydraulic pump 30 acts on the LS relief valve 21, and the pressure oil sent from the hydraulic pump 30 acts on the main relief valve 22. As a result, the relief set pressure of the LS relief valve 21 is 320Rg/crn2 to 400kg
/cm2, and the relief set pressure of the main relief valve 22 is 350kg/crn2 to 3801< g/c
rn2 respectively. For this reason, the load pressure applied to the actuator increases and the discharge pressure of pump 1 increases to 380 kph.
When g/Crr exceeds 12, the main relief valve 22 operates and the LS relief valve 21 does not operate, so Pp and P
The differential pressure with US does not exceed the set pressure of the regulator valve 17. Pump 1 is therefore driven at maximum swash plate angle and does not cut off. That is, in the embodiment according to claim (2), the relief set pressure is increased compared to the embodiment according to claim (1), so that the heavy excavation motor becomes even louder.

[Effects of the Invention] As explained above, according to the present invention, the LS provided in the circuit for transmitting the actuator load pressure to the regulator valve
A means for increasing the relief set pressure of the relief valve, or a means for increasing the relief set pressure in both the LS relief valve and the main relief valve provided in the pump discharge circuit is provided, so that when the load pressure applied to the actuator increases. Since it was decided to operate the main relief valve, the differential pressure between the pump discharge pressure and the actuator load pressure does not exceed the set pressure of the regulator valve. Therefore, even if the load pressure on the actuator increases, the cutoff mechanism does not operate, and the pressure oil continues to be in a relief state, and as soon as the actuator load pressure is reduced, the actuator resumes driving, thereby increasing the strength of the machine.

In addition, 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 the set value, as in the conventional case. . The operator can freely and easily select between the heavy excavation mode and the energy saving mode depending on 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 low 1z sensing system according to an embodiment of claims (1) and (3), and FIG. A schematic hydraulic circuit diagram of a hydraulic drive device equipped with a cut-off canceling mechanism according to the embodiments of claims (2) and (3), FIG. 3 is a schematic hydraulic circuit diagram of a hydraulic drive device equipped with a load sensing system according to the conventional technology Figure 4 is a schematic hydraulic circuit diagram showing changes in major items when the load pressure applied to the actuator increases. (a) is pump discharge pressure, (b) is pump discharge amount, (c) is Actuator operating speed, (d) shows relief flow rate. 1... Variable displacement hydraulic pump 2.3... Actuator = 18-4.5... Directional switching valve 6c, 12a, 12b, 13° 19.25... ...Pilot circuit 16...φ...
φ regulator 17...φ conflict/Regulator valve 20...Orifice 21...LS relief valve 22...Main relief valve 23.29...Solenoid valve 24.30... Hydraulic pump 26.31... Switch Applicant Komatsu Ltd.

Claims (3)

[Claims] (1) A variable displacement hydraulic pump, a hydraulic actuator driven by the pressure oil discharged by the variable displacement hydraulic pump, and a directional control valve that controls the flow of the pressure oil supplied from the hydraulic pump to the hydraulic actuator. , a discharge amount control means for controlling the flow rate of pressure oil discharged from the hydraulic pump, and the discharge amount control means includes a regulator for driving the displacement variable means of the variable displacement hydraulic pump, and a discharge pressure P_P of the hydraulic pump. and the load pressure P of the hydraulic actuator
A hydraulic drive device comprising: a regulator valve that controls driving of the regulator according to a differential pressure between P_P and P_L_S, and maintains the differential pressure P_P−P_L_S at a set value;
A main relief valve provided in a circuit extending from the hydraulic pump to the directional control valve applies the relief set pressure of the LS relief valve to an LS relief valve provided in a circuit that transmits the actuator load pressure to the regulator valve via an orifice. A cut-off canceling mechanism in a load sensing system, characterized in that a relief set pressure variable means is provided to make the relief set pressure higher than the relief set pressure of the load sensing system. (2) LS relief valve relief set pressure variable means;
2. The cut-off canceling mechanism in a load sensing system according to claim 1, further comprising a relief set pressure variable means for the main relief valve. (3) The relief set pressure variable means includes a solenoid valve operated by a switch, a hydraulic pump, and a pilot circuit that guides the pressure oil discharged by the hydraulic pump to the LS relief valve or the main relief valve via the solenoid valve. A cut-off canceling mechanism in a load sensing system according to claim 1 or claim 2, characterized in that the cut-off canceling mechanism comprises: