JPH04351304A - Hydraulic driving device - Google Patents

Abstract

PURPOSE:To eliminate instability of load sensing control in a hydraulic driving device. CONSTITUTION:Flow rate control valves 5a, 5b are opened on the basis of signals output from operating quantity sensors 7a, 7b. When hydraulic cylinders 4a, 4b are driven, a controller 11 takes in a differential pressure of the flow rate control valves from differential pressure sensors 8a, 8b, to carry out load sensing control with respect to a hydraulic pump 1 on the basis of a minimum differential pressure. Simultaneously, a valve opening degree of the flow rate control valves is reduced in proportion to a value of a square root of a ratio of a set differential pressure to a differential pressure of the flow rate control valves other than the minimum differential pressure. Consequently, a pressure compensating valve becomes unnecessary, and stable control can be achieved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive system for driving a plurality of hydraulic actuators with one variable displacement hydraulic pump.

0002

2. Description of the Related Art There are various types of hydraulic drive devices that simultaneously drive a plurality of hydraulic actuators using pressure oil from a single variable displacement hydraulic pump (hereinafter simply referred to as a hydraulic pump). Among these systems, West German Patent Specification No. 3321483, Japanese Patent Publication No. 11706/1983,
The so-called load sensing type hydraulic drive device proposed in Japanese Patent Application Laid-Open No. 2-261902 and others is equipped with a pressure compensation valve between the hydraulic pump and each flow control valve, and the pressure compensation valve controls the flow rate control valve. In addition to compensating the difference (differential pressure) between inlet pressure and outlet pressure to a predetermined pressure,
The discharge flow rate of the hydraulic pump is controlled so that the discharge pressure of the hydraulic pump is higher than the load pressure by the pressure loss of the pressure compensation valve and the flow rate control valve. With this configuration, during combined operation of each hydraulic actuator, it is possible to perform appropriate branch flow control in which the flow rate of pressure oil supplied to them is proportional to the opening area of the flow control valve, and the hydraulic actuator can be controlled by changes in load pressure. It is possible to demonstrate the excellent feature of being able to perform stable control without being affected by the

0003

[Problems to be Solved by the Invention] The pressure compensation valve used in the load sensing method has the function of keeping the flow rate constant even if the load pressure (or hydraulic pump pressure) fluctuates. It operates to override the damping effect of the valve. Furthermore, the load sensing method itself is a control that maintains the differential pressure constant. For these reasons, the load sensing method has problems with the stability of hydraulic system control and is prone to hunting. To prevent this, conventionally,
Methods have been adopted in which the spool of the pressure compensating valve is machined into a special shape or a suitable damper is provided, but the former method is difficult to process, and the latter method increases costs. SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic drive device that solves the problems in the prior art described above and can perform stable control without using a pressure compensation valve.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a variable displacement hydraulic pump, a plurality of hydraulic actuators driven by pressure oil of the variable displacement hydraulic pump, and a drive system for driving these hydraulic actuators. In a hydraulic drive device, the hydraulic drive device is equipped with a differential pressure detector that detects a differential pressure in each of the flow control valves, and a minimum differential pressure among the differential pressures detected by these differential pressure detectors. a flow rate control means for controlling the discharge flow rate of the variable displacement hydraulic pump based on a difference from a predetermined set differential pressure; and a valve opening degree of a flow control valve other than the flow control valve generating the minimum differential pressure. The present invention is characterized in that it is provided with a valve opening correction control means for reducing the pressure difference in proportion to the square root of the ratio between the set differential pressure and the differential pressure of the flow control valve.

[0005]

[Operation] The differential pressure of each flow control valve of the hydraulic actuator that is being driven in combination is taken, and the minimum differential pressure among those differential pressures is used to perform load sensing control on the variable displacement hydraulic pump. That is, the flow rate control means controls the discharge flow rate of the hydraulic pump based on the difference between the minimum differential pressure and the set differential pressure. At the same time, the valve opening correction control means performs control to correct the valve opening of the flow control valve corresponding to each differential pressure, based on the differential pressure other than the minimum differential pressure. This correction is performed by reducing the valve opening in proportion to the square root of the ratio between the set differential pressure and each differential pressure.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on the illustrated embodiments. FIG. 1 is a system diagram of a hydraulic drive device according to an embodiment of the present invention. In the figure, 1 is a hydraulic pump, 1a is a hydraulic pump 1
variable displacement mechanism (hereinafter represented by the swash plate);
2 is a hydraulic cylinder that drives the swash plate 1a, and 3a and 3b are electromagnetic valves that control the drive of the hydraulic cylinder 2. A regulator of the hydraulic pump 1 is configured by the hydraulic cylinder 2 and the electromagnetic valves 3a and 3b. 4a and 4b are hydraulic cylinders driven by the hydraulic pump 1; 5a and 5b are flow control valves that control the flow rate of pressure oil supplied to the hydraulic cylinders 4a and 4b; and 6a and 6b are the flow control valves 5a and 5b and the machine. This is a directional valve connected to the Reference numerals 7a and 7b are operating amount sensors for operating levers that operate the hydraulic cylinders 4a and 4b, and output electrical signals proportional to the operating amounts of the operating levers. Note that each operating lever directly controls the flow rate control valves 5a and 5b.
Controls the valve opening degree. 8a and 8b are differential pressure sensors;
The pressure on the inlet side and the pressure on the outlet side of each flow control valve 5a, 5b are inputted, and an electric signal proportional to the pressure difference between the two is outputted. 9 is a pressure sensor that detects the discharge pressure of the hydraulic pump 1 and outputs an electric signal proportional to the value; 10 is a bleed valve; and 11 is a controller that performs various controls.

Next, the operation of this embodiment will be explained with reference to FIGS. 2, 3, and 4. 2 is a block diagram explaining part of the contents of the controller 11 shown in FIG. 1, FIG. 3 is a diagram showing calculations in the valve opening correction control section shown in FIG. 2, and FIG. 4 is a diagram showing the calculation of the valve opening command value and flow rate. It is a characteristic diagram showing a relationship. When each operating lever is operated, signals from the operating amount sensors 7a, 7b are input to the controller 11, and the controller 11 opens the flow control valves 5a, 5b in response to these signals. As a result, the hydraulic cylinders 4a and 4b are driven at a speed corresponding to the supplied flow rate. In this state, the differential pressure sensor 8
a and 8b detect the differential pressure between each flow control valve 5a and 5b, and input these to the controller 11. Controller 11
The minimum differential pressure selection section 110 shown in FIG. The load sensing control unit 111 outputs a required signal to the solenoid valves 3a and 3b based on the differential pressure ΔPimin and a preset differential pressure (set differential pressure), and controls the load flow rate of the hydraulic pump 1. Perform sensing control. Furthermore, in this embodiment, valve opening degree correction control is performed on the other flow control valve. That is, in FIG. 2, when the minimum differential pressure ΔPimin is selected by the minimum differential pressure selection section 110, other differential pressure signals are input to the valve opening correction control section 112. Although differential pressure sensors 8a to 8n are shown in FIG. 2, in the configuration shown in FIG. 1, there are two differential pressure sensors 8a and 8b. Therefore, when one differential pressure is selected by the minimum differential pressure selection section 110, the other differential pressure is input to the valve opening correction control section 112. Here, the calculations executed by the valve opening correction control section 112 will be explained with reference to the formula shown in FIG. 3.

Now, Cv is the flow coefficient of the flow control valve, A(
x) is the valve opening degree with respect to the stroke x of the flow control valve, ρ is the oil density, and ΔPi is the differential pressure between the other flow control valves, then the flow rate Qi passing through the flow control valve is expressed by equation (1) in Fig. 3. expressed. In this example, the valve opening degree A(x) in the equation (1) is changed to the valve opening degree A(xm) shown in the equation (2) in FIG.
control to correct it. In equation (2), xm is the corrected stroke of the flow control valve, and ΔPLS is the set differential pressure. The value A(x) in equation (1) is added to the value A(xm
) is substituted to determine the flow rate Qim after the valve opening degree is corrected, this flow rate Qim is expressed by equation (3) in FIG. Comparing equations (1) and (3), the differential pressure ΔPi in the former is the set differential pressure ΔPLS in the latter. That is, since the set differential pressure ΔPLS is a fixed value, the corrected flow rate Qim depends only on the stroke xm. In other words, for flow control valves other than the flow control valve producing the minimum differential pressure, the valve openings are corrected so that the differential pressure becomes the set differential pressure ΔPLS, and the pressure compensation valve is It will be in the same condition as it is used. The meaning of the above correction operation will be explained with reference to FIG. In FIG. 4, the horizontal axis shows the valve opening command value (the operating amount of the operating lever or the stroke amount of the flow rate control valve), and the vertical axis shows the flow rate. Each curve is a curve showing the relationship between the valve opening command value and the flow rate at a certain differential pressure of the flow control valve, ΔPi is the curve at a certain differential pressure, Δ
PLS shows the curve at the set differential pressure. The differential pressure of the flow control valve controlled by the valve opening correction control section 112 is ΔPi
, and the valve opening command value for the flow control valve is xi
, the flow rate is (1
), the value Qi corresponding to point a on the curve ΔPi is
However, under the control of the valve opening correction control section 112, the valve opening command value is corrected to the value xm, and the flow rate becomes the value Qim shown in equation (2). That is, the above control is based on the valve opening command value x
This control moves point b on the curve ΔPLS for i to point c on the curve ΔPi, and the flow rate at this time is the value Qi
m, the valve opening command value becomes the value xm. In addition, in the above-mentioned valve opening correction control, the differential pressure ΔPi of the flow control valve is set to the set differential pressure ΔP.
It is performed when the differential pressure is LS or more, and is not performed when the differential pressure is less than the set differential pressure ΔPLS.

As described above, in this embodiment, load sensing control is performed based on the minimum differential pressure of each flow control valve, and at the same time, load sensing control is performed for the flow control valves other than the flow control valve generating the minimum differential pressure. Since the valve opening correction control is performed in the case of a pressure compensation valve, control similar to load sensing control can be performed without using a pressure compensation valve, and the occurrence of hunting etc. can be controlled by using a pressure compensation valve. The instability of can be eliminated. Also, since no pressure compensation valve is used,
The overall structure can be simplified. In addition, in the description of the above embodiment, the configuration in which the flow rate control valve and the directional switching valve are mechanically connected has been described, but the present invention is not limited to this.
A single flow control valve can also be used.

0010

As described above, in the present invention, load sensing control is performed based on the minimum differential pressure among the differential pressures of a plurality of flow control valves, and the Since the control valve is controlled to correct the valve opening degree, the pressure compensation valve can be removed, thereby eliminating control instability. Furthermore, since no pressure compensation valve is used, the overall structure can be simplified.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a hydraulic drive device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating part of the contents of the controller shown in FIG. 1;

FIG. 3 is a diagram showing mathematical formulas used in the valve opening correction control section shown in FIG. 2;

FIG. 4 is a characteristic diagram showing the relationship between the valve opening command value and the flow rate.

[Explanation of symbols] 1 Hydraulic pump 1a Swash plate 4a, 4b Hydraulic cylinder 5a, 5b Flow control valve 6a, 6b Directional switching valve 7a, 7b Operation amount sensor 8a, 8b Differential pressure sensor 9 Pressure sensor 11 Controller

Claims (1)

[Claims] 1. A hydraulic drive device comprising a variable displacement hydraulic pump, a plurality of hydraulic actuators driven by pressure oil of the variable displacement hydraulic pump, and flow control valves for controlling the driving of these hydraulic actuators, A differential pressure detector detects the differential pressure in each of the flow control valves, and the variable capacity is adjusted based on the difference between the minimum differential pressure and a predetermined set differential pressure among the differential pressures detected by these differential pressure detectors. A flow control means for controlling the discharge flow rate of the hydraulic pump, and a ratio of the valve opening degree of the flow control valve other than the flow control valve generating the minimum differential pressure to the set differential pressure and the differential pressure of the flow control valve. A hydraulic drive device comprising a valve opening correction control means that reduces the opening degree in proportion to the square root of.