JPH04194403A - Hydraulic driving device for construction machine - Google Patents

Abstract

PURPOSE:To realize a fixed flow rate in a low flow rate region and flow rate increase control proportional to delivery pressure increase in a high flow rate region by providing a throttle means, which opens and closes in accordance with a flow rate of a pressure oil from an oil pressure source, between an inlet side and outlet side of a pressure compensation valve for controlling differential pressure between before and behind of a directional control valve. CONSTITUTION:A spool 13 is housed inside a spool chamber 11 and a pressure chamber 12 in a sleeve 10 provided with an inlet and outlet ports 14, 15 of a pressure compensation valve 9, and a variable throttle 18 is controlled by balance between a spring 20 and pressure inside the pressure chamber 12. Consequently, a fixed flow rate is maintained in a low flow rate region regardless of delivery pressure increase while an increasing flow rate is conducted in proportion to pump delivery pressure increase in a high flow rate region so as to easily realize work by very low speed operation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydraulic drive device for controlling the drive speed of a hydraulic actuator provided in a construction machine such as a hydraulic excavator or a crane.

[Prior Art] FIG. 3 is a hydraulic circuit diagram showing a hydraulic circuit of a conventional hydraulic drive system for construction machinery, and here, for convenience of explanation, a hydraulic circuit equipped with two hydraulic actuators is shown.

A conventional hydraulic drive device is provided with a variable displacement hydraulic pump 2 having a regulator 1 for changing the displacement as a hydraulic power source, and a downstream pump connected in parallel to the hydraulic pump 2 so as to branch out. A directional control valve 3.4, which can be opened and closed by an operator, and a hydraulic actuator 7.8 via a check valve 5.6 are sequentially connected to the side pipe. A pressure compensating valve 9.10, which will be described later, is connected between the upstream pipe line and the downstream pipe line of each of the directional switching valves 3.4. Further, the downstream pipe line of the directional control valve 3.4 is connected to the regulator l via another check valve 1.12. - FIG. 4 is a partially cutaway sectional view showing the internal structure of the pressure compensation valve 9.

This pressure compensating valve 9 has a cylindrical spool chamber 11 in a sleeve 10 forming an outer wall, and a pressure chamber 12 which is connected to the spool chamber 11 and has a larger diameter than the spool chamber 11. A spool 13 is housed in a chamber 11' so as to be freely deflectable.

The above-mentioned spool chamber 11 is formed with an inlet boat 14 to which the discharge pressure of the hydraulic pump 2 is introduced and an outlet boat 15 connected to the upstream side of the directional control valve 3. ; A pipe line 16 communicating with the downstream side of the directional control valve 3 connected to the hydraulic actuator tough via the check valve 5 shown.
is formed. The load pressure is led to the pressure chamber 12 via the downstream side of the directional control valve 3, and further to the regulator 1.

On the other hand, a fixed throttle 17 and a variable throttle 18 are provided on the side surface of the spool 13, and a wide-diameter spring holder that is integrated with the other end of the spool 13 and can freely slide within the pressure chamber 12 is provided at the other end of the spool 13.
9 is formed. This spring receiver has a pressure chamber 1 in the part 19.
A spring 20 supported by the end face of 2 is in contact with the spring 20 .

Note that the pressure compensation valve 1o also has a similar configuration, although the explanation is omitted.

In the hydraulic drive system configured in this way, when the on-off switching valve 3 is opened, the pressure oil from the hydraulic pump 2 is supplied via the pressure compensating valve 9 so that the differential pressure across the directional switching valve 3 is kept constant. The flow flows through the directional switching valve 3 and the check valve 5 in a leaning state, and then flows directly to the hydraulic actuator 7 to drive the hydraulic actuator 7.The load pressure of the load that drives the hydraulic actuator 7 is controlled by the pilot circuit. 21 to the regulator 1. This controls the discharge pressure of the hydraulic pump 2 so that the difference with the self-pressure of the hydraulic pump 2 is kept constant. When multiple operations are performed at the same time, if the operation amount of these directional valves 3.4 is kept constant, the pressure compensation valve 9
．． Due to the action of 10, these hydraulic actuators 7 can be operated without being subjected to fluctuations in the load pressure of other hydraulic actuators.
．． A constant flow rate flows through the hydraulic actuators 8, and each hydraulic actuator 8 is driven at a constant speed.

When it is desired to drive the hydraulic actuator 7.8 faster, for example, by adjusting the size of the fixed throttle 17 of the spool 13 of the pressure compensation valve 9, the hydraulic actuator tough can be adjusted with the flow characteristics shown in FIG. 2I. The speed can be increased. Note that ■ in FIG. 2 is the flow rate characteristic obtained when the fixed throttle 17 is not provided.

[Problems to be Solved by the Invention] When using the conventional hydraulic drive device equipped with the above-mentioned pressure compensation valve 9.10 in a low flow rate region, the fixed throttle 17 is not provided as shown in Fig. 2m. Fixed orifice 1 compared to the flow characteristics of ■
Since the flow rate characteristics are greatly influenced by the factor 7, the speed of the hydraulic actuator 7.8 changes when the differential pressure ΔP across the directional control valve 3.4 changes due to changes in load.
Therefore, there is a problem in that the hydraulic actuator 7.8 cannot be driven at a constant speed in a low flow rate region, making it difficult to perform work at very low speed.

The present invention has been made in view of the above circumstances, and its purpose is to be able to flow a constant flow rate in a low flow range regardless of an increase in the discharge pressure of the hydraulic pump.
The object of the present invention is to provide a hydraulic drive device that can increase the flow rate in proportion to an increase in the discharge pressure of a hydraulic pump in a true flow region.

[Means for Solving the Problem] In order to solve the above object, the present invention provides a directional control valve that controls the flow of pressure oil supplied from a hydraulic source to a hydraulic actuator, and a directional control valve that controls the flow of pressure oil supplied from a hydraulic source to a hydraulic actuator. A hydraulic drive device for construction machinery, comprising a pressure compensation valve that controls a pressure difference between the front and rear sides, which is a pressure difference between the front and rear sides, and which controls the driving speed of the hydraulic actuator by operating the direction switching valve. The present invention is characterized in that a throttle means is provided between the inflow side and the outflow side of the hydraulic pressure source, which opens and closes depending on the magnitude of the flow rate of the pressure oil discharged from the hydraulic pressure source. .

[Function] Since the present invention has the above-described configuration, when the flow rate of pressure oil from the hydraulic pump increases and becomes a true flow region and the throttle means is in the open state, the flow rate of the pressure oil before and after the directional control valve is The differential pressure increases, and control can be performed to increase the flow rate to the corresponding actuator. On the other hand, when the flow rate of pressure oil from the hydraulic valve decreases and becomes a low flow area, and the throttling means is closed, the differential pressure across the directional control valve becomes constant, and the pressure to the corresponding hydraulic actuator decreases. It is possible to control the flow rate to be constant.

[Example code] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a partially cutaway cross-sectional view of the pressure compensating valve of this embodiment.
The same parts as those in FIG. 4 already explained are given the same reference numerals.

In addition, the hydraulic pump 2, the directional switching valves 3, 4, and the check valves 5.
6, hydraulic actuator 7.8, and check valve 11,1
2, not shown, are similar to the conventional hydraulic drive device shown in FIG. It can be considered that this is the same as the case of FIG. 3 described above.

As shown in FIG. 1, the pressure compensating valve provided in this embodiment is provided in a spool chamber 11 and a pressure chamber 12 formed in a sleeve 10 having an inlet boat 14 and an outlet boat 15. The spring receiver accommodates the spool 13 with a portion 19 integrally formed therein, and the spring receiver is similar to the conventional structure in that a spring 20 is disposed between the portion 19 and the end face of the pressure chamber 12. However, it differs from the conventional one in that only a variable aperture 18 is provided without providing a fixed aperture.

Further, in the vicinity of the pressure compensation valve of this embodiment, a conduit 22 is provided between the inlet boat 14 and the outlet boat 15, and a throttle 24 that is opened and closed by an on-off valve 23 is provided in this conduit 22. The on-off valve 23 receives detection signals from a flow rate detector of the hydraulic pump 2 (not shown) and a differential pressure detector across the directional control valve 3.4 (not shown), and is driven to open and close by a controller (not shown) that makes logical decisions. It has become.

The above-mentioned controller is stored in advance with a reference flow rate corresponding to the low flow rate region. Note that the above-mentioned pipe line 22, on-off valve 23, and throttle 24 constitute a throttle means that opens and closes depending on the magnitude of the flow rate of pressure oil discharged from the hydraulic pump 2.

In this embodiment configured as described above, when the hydraulic actuator 8 drives the working machine member on the high load side, and the hydraulic actuator 8 drives the working machine member on the low load side, each of the above-mentioned detections is performed. The device detects the pump discharge flow rate and the differential pressure across the directional control valve 3.4.
The on-off valve 23 is driven to open and close by a drive signal output from the controller in response to each detection signal. That is, when the controller determines that the pump discharge flow rate detected by the flow rate detector is larger than the reference flow rate and in the high flow range, the controller outputs a drive signal to open the on-off valve 23. The pressure oil is merged upstream of the directional control valve 3.4 through the pipe 22, the on-off valve 23, and the throttle 24, and the flow rate increases as the differential pressure across the directional control valve 3.4 increases. The flow rate characteristics shown in FIG. 2I, that is, the flow rate characteristics similar to those of the conventional pressure compensation valve 3.4 provided with a fixed throttle can be obtained.

For this reason, the load pressure increases, and along with this, the hydraulic pump 2
When the discharge pressure increases, the flow rate flowing through the directional control valve 3.4 increases in proportion to the discharge pressure, so that the driving speed of the work implement member can be made as fast as possible.

In addition, when it is desired to drive the work equipment member at low speed, the signal output from the flow rate detector is determined by the controller to be a signal corresponding to the reference flow rate, and the controller issues a drive signal to close the on-off valve 23. This on-off valve 23
Control is performed so that the throttle 24 is closed and no pressure oil flows from the throttle 24. As a result, only the variable throttle 18 of the spool 13 works, and the differential pressure across the directional control valve 3.4 becomes constant, and the second
A constant flow rate characteristic as shown in Figure ■ can be obtained.

Thereby, work by slow-speed operation can be easily realized.

[Effects of the Invention] According to the present invention, a throttle means is provided between the inflow side and the outflow side of the spool of the pressure compensating valve, which opens and closes in accordance with the magnitude of the flow rate of the pressure oil discharged from the hydraulic source. In the high flow range, it is possible to flow a flow rate that increases in proportion to the increase in the discharge pressure of the hydraulic pump, and in the low flow range, it is possible to flow a constant flow rate regardless of the increase in the discharge pressure of the hydraulic pump, which was previously difficult. It is possible to easily perform work using slow-speed operation.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sectional view showing the configuration of a pressure compensating valve provided in an embodiment of the hydraulic drive device for construction machinery of the present invention, and FIG.
The figure is a characteristic diagram showing flow characteristics of a pressure compensating valve provided in an embodiment of the present invention and a conventional hydraulic drive device, FIG. 3 is a hydraulic circuit diagram showing the configuration of a conventional hydraulic drive device, and FIG. FIG. 4 is a partially cutaway sectional view showing the configuration of a pressure compensation valve provided in the hydraulic drive device shown in FIG. 3; 2... Hydraulic pump, 3.4... Directional switching valve, 7.8
... Hydraulic actuator, 9.10 ... Pressure compensation valve, 22 ... Pipe line, 23 ... Opening/closing valve, 24 ... Throttle. 1st! ! l Figure 2P Figure 3

Claims (1)

[Claims] A directional switching valve that controls the flow of pressure oil supplied from a hydraulic source to a hydraulic actuator, and a pressure compensation valve that controls a differential pressure between the upstream and downstream sides of the directional switching valve, In the hydraulic drive system for construction machinery, which controls the driving speed of the hydraulic actuator by operating the directional switching valve, pressure oil discharged from the hydraulic source between the inflow side and the outflow side of the pressure compensation valve is provided. A hydraulic drive device for construction machinery, characterized in that it is provided with a throttle means that opens and closes depending on the magnitude of the flow rate.