JPH01242801A - Hydraulic pressure drive unit - Google Patents

Abstract

PURPOSE:To perform fine operation well by changing pressure generated on a pressure generator so as to become in higher pressure as flow rate of pressure oil discharged from a pilot pump gets large. CONSTITUTION:A flow metering valve 21 changing pressure generated on pressure generators 19, 20 so as to become in higher pressure as flow rate of pressure oil discharged from a pilot pump 3 gets larger is provided in a pipe lime communicating a pilot relief valve 4 to a tank. Thereby, speed on an actuator can be surely reduced as engine speed lowers therefore it can be done to perform fine operation well.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is a hydraulic system equipped in a hydraulic machine such as a hydraulic excavator, which controls the drive of a directional control valve according to the pressure of pressure oil discharged from a pilot pump. Regarding a drive device.

<Prior Art> FIG. 4 is a circuit diagram showing an example of a conventional hydraulic drive device of this type provided in a hydraulic excavator.

This hydraulic drive system includes a prime mover, that is, an engine 1, a variable displacement hydraulic pump, that is, a main hydraulic pump 2, which is driven by the engine 1, a pilot pump 3, and a pressure of pressure oil discharged from the pilot pump 3 to a predetermined value. A regulator 5 is provided to control the discharge volume of the main hydraulic pump 2.

In addition, actuators driven by pressure oil discharged from the main hydraulic pump 2, such as a recessed rotary motor 6, a left travel motor 7, a right travel motor 8, a boom cylinder 9, an arm cylinder 10, and a packet cylinder 1), and the main hydraulic pump A turning direction control valve 12 and a right travel direction control valve 13 control the flow of pressure oil supplied from 2 to these actuators.
, right travel direction control valve 14, boom direction control valve 15,
A directional control valve block 18 including an arm directional control valve 16 and a packet directional control valve 17 is provided.

Furthermore, corresponding to each of the directional control valves 12 to 17, a pressure generator converts the pressure of the pressure oil discharged from the pilot pump 3 into a predetermined pressure and supplies it to the drive section of the directional control valves 12 to 17. For example, one pressure generator is a pressure generator for rotation, and the pressure generator 20 is a pressure generator for an arm. These pressure generators are constituted by hydraulic pilot valves, for example, as shown by pressure generator 19 in FIG. 5.

In the hydraulic drive device configured in this way, when the engine 1 is driven and, for example, the operating lever of one pressure generator is operated, the pressure oil of the pilot pump 3 is transferred to the pressure generator 19.
Pressure oil is supplied to the driving part of the swing direction control valve 12 via the swing direction control valve 12, and this direction control valve 12 is switched, and the pressure oil discharged from the main hydraulic pump 2 is supplied to the swing motor 6 via the swing direction control valve 12. The rotation motor 6 is driven.

In this hydraulic drive device, the discharge port of the main hydraulic pump 2 and one boat of the directional control valve connected to each actuator are each connected to a regulator 5. The pressure difference ΔP between the pressure and the load pressure of each actuator is always a constant value,
For example, the discharge volume of the main hydraulic pump 2 is controlled to be 20 kg/cm2. Thereby, the operating speed of each actuator is determined by the pressure loss from the discharge port of the main hydraulic pump 2 to the boat of each directional control valve 12 to 17. Therefore, the opening area of each directional control valve 12 to 17 is
If the above-mentioned differential pressure ΔP is set to be 20 kg/cm2 at the flow rate that determines the required speed of the relevant actuator, if each actuator attempts to reach a speed higher than the above-mentioned required speed, the differential pressure ΔP will increase. becomes large and the discharge volume of the main hydraulic pump 2 decreases via the regulator 5, and conversely, when the speed is about to drop below the above-mentioned required speed, the differential pressure ΔP decreases and the main hydraulic pressure decreases via the regulator 5. The displacement of the pump 2 is increased and in this way each actuator speed is kept at the required speed. In addition, as an example of the required speed of the above-mentioned actuator, the required speed of the swing motor 6 that performs the swing operation is 1/1 of the maximum discharge volume.
The speed is preset to correspond to a volume of 2 or less.

<Problems to be Solved by the Invention> In the conventional hydraulic drive device configured as described above, when attempting to lower the engine speed and slow down the actuator speed, there is a need for a margin in the discharge volume of the main hydraulic pump 2. In some cases, the speed of the actuator is determined by the pressure loss from the discharge port of the main hydraulic pump 2 to the boat of the directional control valves 12 to 17, as described above, so that the speed does not slow down. Therefore, when it is necessary to swing slower than normal excavation work, such as when lifting a load by mooring it to a packet and moving the arm up and down, it is possible to lower the engine speed. Unable to realize slow turns.

The present invention has been made in view of the actual situation in the prior art described above, and its purpose is to increase the discharge volume of a variable displacement hydraulic pump so that the differential pressure between the pump discharge pressure and the load pressure of the actuator is constant. An object of the present invention is to provide a hydraulic drive device that can reliably reduce the speed of an actuator as the engine speed decreases.

Means for Solving the Problems To achieve this object, the present invention provides a prime mover, a variable displacement hydraulic pump and a pilot pump driven by the prime mover, and a pressure oil discharged from the variable displacement hydraulic pump. a directional control valve that controls the flow of pressure oil guided from the variable displacement hydraulic pump to the actuator, and a directional control valve that converts the pressure of the pressure oil discharged from the pilot pump into a predetermined pressure to drive the directional control valve. and a pressure generator that supplies the drive unit, and the discharge volume of the variable displacement hydraulic pump is controlled so that the differential pressure between the discharge pressure of the variable displacement hydraulic pump and the load pressure of the actuator is a constant value. This hydraulic drive device is equipped with a pressure changing means that changes the pressure generated by the pressure generator so that the pressure increases as the flow rate of pressure oil discharged from the pilot pump increases.

Since the hydraulic drive device of the present invention is configured as described above, when the engine speed is raised to the maximum, a large flow rate flows from the pilot pump, and the pressure changing means responds accordingly. is activated, high pressure is applied to the pressure generator,
By operating this pressure generator, high pressure is supplied to the drive part of the directional control valve. Therefore, the opening amount of the directional control valve is maximized, and the maximum flow rate of pressure oil is supplied from the variable displacement hydraulic pump to the actuator via the directional control valve, thereby ensuring the speed required by the actuator. In addition, when operating to lower the engine speed from the above state, the flow rate of the pressure oil discharged from the pilot pump decreases, a correspondingly low pressure is applied to the pressure generator, and the directional control valve is driven. supplied to the department. Therefore, the opening amount of the directional control valve is smaller than in the maximum state, and a relatively small flow of pressure oil is supplied to the actuator from the variable displacement hydraulic pump through the directional control valve, ensuring the speed of the actuator. Can be lowered.

<Example> Hereinafter, the hydraulic drive device of the present invention will be explained based on the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the hydraulic drive device of the present invention. In this embodiment as well, as in the conventional hydraulic drive device described above, the prime mover, that is, the engine l,
The discharge volume of the variable displacement hydraulic pump, that is, the main hydraulic pump 2 and the pilot pump 3, the pilot relief valve 4, and the main hydraulic pump 2 driven by the engine 1 is the discharge pressure of the main hydraulic pump 2 and the load pressure of the actuator. A regulator 5 that controls the differential pressure between the
and a swing motor 6, a left travel motor 7, a right travel motor 8,
Actuators such as a boom cylinder 9, an arm cylinder 10, a packet cylinder 1), and a swing direction control valve 12
, left travel direction control valve 13, right travel direction control valve 14,
A directional control valve block 18 including a boom directional control valve 15, an arm directional control valve 16, and a packet directional control valve 17
and one pressure generator 20, which converts the pressure of the pressure oil discharged from the pilot pump 3 and supplies it to the driving parts of the directional control valves 12 to 17.

In this embodiment, the pilot relief valve 4
A pressure changing means, for example, a throttle valve 21, is provided in the pipe line communicating with the tank and the pressure generator to change the pressure generated by the pressure generator so that the pressure increases as the flow rate of the pressure oil discharged from the pilot pump 3 increases. It is.

In the hydraulic drive device configured in this way, when the engine 1 is driven and the operating lever of the pressure generator 19 is operated, for example, the pressure oil of the pilot pump 3 is directed to the turning direction via one pressure generator. The directional control valve 12 is switched by being supplied to the driving part of the control valve 12, and the pressure oil discharged from the main hydraulic pump 2 is supplied to the swing motor 6 via the swing direction control valve 12, and the swing motor 6 is driven.

In this case, when the engine 1 is set to the maximum rotational speed N1, the maximum flow rate flows from the pilot pump 3, and the pressure at this time becomes the maximum pressure P1 as shown in FIG. 2(a). At this time, as shown by the solid line in Fig. 2(b), the pilot pressure whose maximum pressure is P3, which is lower than the pressure P1, controls the direction according to the maximum stroke S of the Heroku S (one operating lever of the pressure generator). It is supplied to the drive part of the valve 12, and the
c>, the maximum stroke L1 of the directional control valve 12
This directional control valve 1
2 is switched, and the pressure oil discharged from the main hydraulic pump 2 is transferred to the swing motor 6 via the swing direction control valve 12 so that the maximum flow rate corresponding to 1/2 or less of the discharge volume of the main hydraulic pump 2 is switched to the swing motor 6.
The swing motor 6 is driven at the speed required for normal swing operations. The relationship between the stroke L of the directional control valve 12 and the operating lever stroke S of one pressure generator is as shown in FIG.
) is the relationship shown by the solid line.

From this state, the engine speed is increased to a second speed with the intention of driving the swing motor 6 at a slower speed.
As shown in Figure (a), when the rotation speed is lowered to N2, which is lower than the maximum rotation speed N1, the flow rate discharged from the pilot pump 3 decreases, and a part of the pressure oil is accordingly reduced by the action of the throttle valve 21. It gradually escapes to the tank, and the pilot pressure P becomes P.
It drops to 2. This pressure P2 is calculated as shown in Figure 2 (
As shown in b), the operating lever stroke S corresponds to a stroke S2 smaller than the maximum stroke S3, and the second
As shown in Figure (c), the direction control valve S I/loaf L corresponds to a stroke L2 smaller than the maximum stroke L1.

From the relationship in Fig. 2(b) and (c), in this case Fig. 2(d)
, ), when the operating lever stroke S of the pressure generator 19 is equal to or greater than the stroke S2, the directional control valve 1
The stroke L of No. 2 is a stroke L2 smaller than the maximum stroke L1, and its opening amount is limited. As a result, a flow rate lower than the maximum flow rate corresponding to 1/2 or less of the discharge volume of the main hydraulic pump 2 is supplied to the swing motor 6, and the swing motor 6 is driven at a speed lower than that required for normal swing operation. Can be driven at slow speeds.

In the embodiment configured in this way, when the engine speed is lowered as described above, the speed of the swing motor 6 is reliably slowed down, and it is possible to realize a very low speed swing during lifting work. .

FIG. 3 is a circuit diagram showing the main parts of another embodiment of the present invention. In this other embodiment, a relief valve 4 for regulating the pressure of the pilot pump 3 is not provided, and only a throttle valve 21 is provided in the pipe line connecting the pilot pump 3 and the tank. In the embodiment configured in this manner, the pilot pressure changes in a curve from approximately 0 to the maximum pressure P1 as the engine speed increases, and the ratio of change in the pressure P to the pressure P with respect to the engine speed increases.

Even with this configuration, when the engine speed is lowered, the pilot pressure P decreases, so it is possible to limit the stroke of the directional control valve to a stroke smaller than the maximum stroke L1. , the speed of the swing motor 6 can be reliably reduced.

In the above embodiment, the pressure generator is configured by a hydraulic pilot valve, but the present invention is not limited to this, and may be configured by an electromagnetic proportional valve.

<Effects of the Invention> Since the hydraulic drive device of the present invention is configured as described above, the discharge volume of the variable displacement cedar hydraulic pump is adjusted so that the differential pressure between the discharge pressure of the pump and the load pressure of the actuator is constant. The speed of the actuator can be reliably lowered as the engine speed decreases, making it possible to perform fine operations that have been difficult in the past.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the hydraulic drive device of the present invention, and Figs. 2 (a), (b), (c), and (d) show the characteristics obtained in the embodiment shown in Fig. 1. Figure 3 shows main parts of another embodiment of the present invention.
Prime mover), 2...Main hydraulic pump (variable capacity cedar hydraulic pump), 3...Pie four 1~ pump, 4...
...Pilot relief valve, 5...Regulator, 6...Swivel motor, 7...
Left travel motor, 8...Right travel motor, 9...
...Boom cylinder, 10...Arm cylinder, 1)...Packet cylinder, 12...
... Direction control valve for turning, 13 ... Direction control valve for left travel, 14 ... Direction control valve for right travel, 15.
... Directional control valve for boom, 16 ... Directional control valve for arm, 17 ... Directional control valve for baguette, 18 ... Directional control valve block, 19 .2o
. . . Pressure generator, 21 . . . Throttle valve (pressure changing means). Figure 2 Figure 3

Claims (2)

[Claims] (1) A prime mover, a variable displacement hydraulic pump and a pilot pump driven by the prime mover, an actuator driven by pressure oil discharged from the variable displacement hydraulic pump, and a variable displacement hydraulic pump driven by the actuator. A directional control valve that controls the flow of the guided pressure oil, and a pressure generator that converts the pressure of the pressure oil discharged from the pilot pump into a predetermined pressure and supplies it to the drive section of the directional control valve, In a hydraulic drive device in which the discharge volume of a variable displacement hydraulic pump is controlled so that the differential pressure between the discharge pressure of the variable displacement hydraulic pump and the load pressure of the actuator is a constant value, the pressure generated by the pressure generator is controlled. A hydraulic drive device, characterized in that it is provided with a pressure changing means that changes the pressure to a higher pressure as the flow rate of the pressure oil discharged from the pilot pump increases. (2) The hydraulic drive device according to claim (1), wherein the pressure changing means includes a throttle valve.