JPH06280810A - Hydraulic driving device for hydraulic operation machine - Google Patents

Abstract

PURPOSE:To provide a good metering characteristic by controlling the opening area of a center bypass passage in accordance with the detected results of dislodging amount of a direction changeover valve, rate of flow through the center bypass passage and delivery rate of flow of a variable displacement hydraulic pump. CONSTITUTION:A dislodging amount of a direction changeover valve 1, or in other words, the target rate of flow of an actuator 3 being controlled, the delivery rate of flow of a pump 2 and the rate of flow passing through a center bypass 1a are detected, and when the rate of flow supplied to the actuator 3 is less than the target rate of flow, the difference between the delivery pressure and the actuator load pressure is small because of the low pump delivery pressure and causes more delivery flow to flow into a tank through the center bypass passage 1a. If the opening area of the center bypass passage 1a is made small so that the difference may come up to the specified pressure, the delivery pressure rises up to the specified difference of the delivery pressure and the load pressure and flowing into the tank is regulated. When the flow supplied is more than the target flow, flowing into the tank may increase. Thus a target rate of flow can be supplied to the actuator 3 and a good metering characteristic can be maintained at the time of a heavy load.

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 equipped with a hydraulic working machine such as a hydraulic excavator and equipped with a directional control valve having a center bypass passage.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing a hydraulic drive system for a hydraulic working machine of this type. This conventional technique is provided, for example, in a hydraulic excavator, and includes a variable displacement hydraulic pump 2
And an actuator driven by pressure oil discharged from the variable displacement hydraulic pump 2, for example, an arm cylinder 3
And a directional control valve having a center bypass passage 1a for controlling the flow of pressure oil supplied from the hydraulic pump 2 to the arm cylinder 3, that is, the directional control valve 1 for the arm, and the directional control valve 1 for the arm downstream. A pressure generator provided, for example, a throttle valve 4, a regulator 6 that controls the displacement of the hydraulic pump 2, and a conduit 5 that guides the pressure generated by the throttle valve 4 to the regulator 6 are provided.

For example, as shown in FIG. 6, the regulator 6 described above has a piston 6a, a small diameter chamber 6b and a large diameter chamber 6c in which the respective ends of the piston 6a are housed, and a pressure introduced by a passage 5. It is composed of a flow rate control spool 6d which operates according to the size. The small-diameter chamber 6b described above is connected to the discharge pipe line of the hydraulic pump 2, and the large-diameter chamber 6c is the small-diameter chamber 6 according to the operation of the flow control spool 6d.
It can be selectively connected to b or to the tank.

The characteristics of this regulator are as follows. That is, when the arm directional control valve 1 is kept neutral and the pressure generated by the throttle valve 4 and guided to the passage 5 is large, the flow rate control spool 6d shown in FIG.
To the left, and the small diameter chamber 6b and the large diameter chamber 6c communicate with each other. At this time, the pump pressure is supplied to both the small diameter chamber 6b and the large diameter chamber 6c, and the piston 6a moves leftward in FIG. 6 due to the area difference between the small diameter chamber 6b and the large diameter chamber 6c. As a result, as shown in FIG. 7, the hydraulic pump 2 is controlled so as to have a relatively small predetermined capacity 10a.

When the arm directional control valve 1 is operated to start closing the center bypass passage 1a and the pressure generated by the throttle valve 4 is reduced to a value smaller than P _C1 shown in FIG. 7, The flow rate control spool 6d shown in FIG. 6 moves to the right in FIG. 6, and the large diameter chamber 6c communicates with the tank. At this time, the piston 6a moves to the right in FIG. 6 by the pump pressure applied to the small diameter chamber 6b. As a result, as shown in FIG. 7, the hydraulic pump 2 is controlled so that the capacity 10b becomes gradually larger than the capacity 10a.

Further, the arm directional control valve 1 is switched to the maximum stroke to completely close the center bypass passage 1a, or the center bypass passage 1a has the minimum opening area, and the pressure generated by the throttle valve 4 is smaller. When the pressure becomes P _C2 or less, the hydraulic pump 2 is controlled so as to have the predetermined maximum capacity 10c shown in FIG.

In the prior art thus constructed, for example, with the intention of extending the arm cylinder 3, the arm directional control valve 1 is gradually stroked to the right position (to the left) in FIG. The relationship between the opening area of the center bypass passage 1a of the arm directional control valve 1 and the opening area of the meter-in passage 1b1 of the arm directional control valve 1 connected to the arm cylinder 3 is shown in FIG. 9 (a). It becomes the characteristic shown. That is, the opening area of the center bypass passage 1a gradually decreases as indicated by the characteristic line 20a, and conversely, the opening area of the meter-in passage 1b1 gradually increases as indicated by the characteristic line 20b. At the start of the stroke of the arm directional control valve 1, that is, at the beginning of closing the center bypass passage 1a, the hydraulic pump 2 is maintained at the predetermined small capacity 10a shown in FIG. 7 and corresponds to the capacity 10a. The standby flow rate, which is a small flow rate, is discharged. As the center bypass passage 1a is gradually throttled, the pressure of the pressure oil discharged from the hydraulic pump 2, that is, the pump discharge pressure increases. Assuming that the load pressure of the arm cylinder 3 is the pressure P2 shown in FIG. 9B, the arm cylinder 3 starts to move when the pump discharge pressure rises above the pressure P2. In this way the arm cylinder 3
Starts to move and the flow rate of the hydraulic pump 2 starts to be supplied to the arm cylinder 3, the flow rate of passage through the center bypass passage 1a decreases. When the passing flow rate decreases in this way, the pressure generated in the throttle valve 4 decreases. Along with this, the pressure value applied to the regulator 6 via the passage 5 also decreases, and the regulator 6 drives so as to increase the capacity of the hydraulic pump 2 as described above. As a result, the flow rate of the hydraulic pump 2 is gradually increased, and a predetermined flow rate characteristic, that is, a metering characteristic is obtained.

Conventionally, a relief valve or the like may be provided in place of the above-mentioned throttle valve 4 as a pressure generator arranged downstream of the center bypass passage 1a.

Further, in the configuration in which the electric signal corresponding to the pressure generated by the pressure generating device is output to the regulator 6 as a control pressure signal, the regulator 6 shown in FIG. 6 is replaced. , As shown in FIG.
A first passage arranged to connect the small diameter chamber 6b and the large diameter chamber 6c with each other to open and close the first passage in response to a control pressure signal.
Second electromagnetic switching valve 6f which is arranged in the large diameter chamber 6c and the second passage connecting the first passage and the tank, and which opens and closes the second passage in response to the control pressure signal. May be provided with.

In the regulator 6 shown in FIG. 8, the second electromagnetic switching valve 6f is maintained in the closed state and the first electromagnetic switching valve 6e is operated in the open state so that the pump discharge pressure is small. The hydraulic pump 2 is supplied to both the large diameter chamber 6b and the large diameter chamber 6c, and the capacity of the hydraulic pump 2 is controlled to be small due to the area difference between the small diameter chamber 6b and the large diameter chamber 6c. Further, the first electromagnetic switching valve 6e is kept closed and the second electromagnetic switching valve 6f is held.
By operating the small diameter chamber 6a and the large diameter chamber 6c, the large diameter chamber 6c communicates with the tank.
The piston 6a is moved to the right by the pump pressure applied to a, and the displacement of the hydraulic pump 2 is controlled to increase.

[0011]

However, the above-mentioned conventional technique has the following problems. That is,
When the load pressure of the arm cylinder 3 is the relatively small pressure P2 shown in (b) of FIG. 9 as described above, the pump flow rate is as shown in the characteristic line 20d of (c) of FIG. As the spool stroke of the switching valve 1 increases relatively slowly, the flow rate supplied to the arm cylinder 3 accordingly increases with the characteristic line 20f in FIG. 9D.
As shown in, the characteristic curve 20d is approximated, and the spool stroke is increased relatively gently, and a good metering characteristic is obtained.

However, when the load pressure of the arm cylinder 3 is the large pressure P1 shown in FIG. 9B,
When the hydraulic pump 2 is in the standby flow rate, the pump discharge pressure is P
The arm cylinder 3 does not start to move unless the center bypass passage 1a is throttled so as to rise to 1 or more. Therefore, when the pump discharge pressure is P1 or less, the center bypass flow rate does not decrease, so the pump flow rate does not increase. When the center bypass passage 1a is throttled until the pump discharge pressure exceeds P1, the center bypass flow rate decreases, and
The pump flow rate sharply increases as indicated by the characteristic line 20e. Along with this, the flow rate supplied to the arm cylinder 3 is approximated to the above-mentioned characteristic line 20e as shown by the characteristic line 20g in FIG. 9D, with respect to the spool stroke of the arm directional control valve 1. As a result, the metering characteristics are significantly deteriorated.

In the case of a hydraulic excavator, this is particularly noticeable when operating an arm or boom. For example, if there is no load in the bucket and the load is light, the operability of these arms and booms can be fully satisfied, but when the work of hanging a heavy load is performed, the directional control valve for the arm is used. Alternatively, the arm or boom will not move if the lever that operates the directional control valve for the boom is moved slightly, and the lever or the boom will start moving only near the end of the stroke. Start to move. Therefore, the operator must be very careful when working,
The work efficiency cannot be expected to be improved, and a great amount of fatigue will be felt.

The present invention has been made in view of the above-mentioned circumstances in the prior art, and an object thereof is to provide a hydraulic drive system for a hydraulic working machine capable of ensuring good metering characteristics even under heavy load. To do.

[0015]

To achieve this object, the present invention provides a variable displacement hydraulic pump, an actuator driven by pressure oil discharged from the variable displacement hydraulic pump, and the variable displacement hydraulic pump. A hydraulic drive system for a hydraulic working machine, comprising: a directional control valve that controls a flow of pressure oil supplied to the actuator and has a center bypass passage; and a regulator that controls a displacement volume of the variable displacement hydraulic pump. A moving amount detecting means for detecting the moving amount of the directional control valve, a first flow rate detecting means for detecting a flow rate passing through the center bypass passage, and a second flow rate detecting means for detecting a flow rate discharged from the variable displacement hydraulic pump.
Of the flow rate detecting means and the downstream of the direction switching valve,
A control means for variably controlling the size of the opening area of the center bypass passage is provided, and the control means is provided according to the detection results of the movement amount detection means, the first flow rate detection means, and the second flow rate detection means. The drive of the control means is controlled.

[0016]

Since the present invention is constructed as described above, the movement amount detecting means detects the movement amount of the directional control valve, that is, the target flow rate of the actuator whose drive is controlled by the directional control valve. Since the difference between the pump discharge flow rate detected by the flow rate detection means and the center bypass passage flow rate detected by the first flow rate detection means is the supply flow rate actually supplied to the actuator,
When the supply flow rate is smaller than the target flow rate described above, the difference between the pump discharge pressure and the actuator load pressure is small due to the small pump discharge pressure, and most of the discharge flow rate of the hydraulic pump passes through the center bypass passage. The control means is driven so that the opening area of the center bypass passage is made smaller so that the difference between the pump discharge pressure and the actuator load pressure becomes a predetermined pressure. Causes the pump discharge pressure to rise until the difference between the pump discharge pressure and the actuator load pressure reaches a predetermined pressure, and the flow rate to the tank via the center bypass passage is suppressed, so that a relatively large flow rate that almost matches the target flow rate is achieved. Can be supplied to the actuator.

Further, when the above-mentioned supply flow rate obtained through the first flow rate detecting means and the second flow rate detecting means is larger than the above-mentioned target flow rate obtained through the moving amount detecting means, pump discharge Due to the large pressure, the difference between the pump discharge pressure and the actuator load pressure is large, and the flow rate from the hydraulic pump to the tank via the center bypass passage is suppressed. The control means may be driven so that the opening area of the center bypass passage is made larger so that the difference between the pump discharge pressure and the actuator load pressure becomes a predetermined pressure. The discharge pressure decreases, the flow rate to the tank via the center bypass passage increases, and a relatively low flow rate that almost matches the target flow rate is actuated. It can be supplied to the over data. In this way, a flow rate that matches the target flow rate of the actuator can be supplied to the actuator according to the operation amount of the operation means that switches the directional control valve, and good metering characteristics under heavy load can be secured. You can

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a hydraulic drive system for a hydraulic working machine according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a first embodiment of the present invention, which is applied to, for example, a hydraulic excavator. This FIG. 1 is drawn corresponding to FIG. 5 described above. That is, also in the first embodiment shown in FIG. 1, a variable displacement hydraulic pump 2 equivalent to that shown in FIG.
And an actuator driven by pressure oil discharged from the variable displacement hydraulic pump 2, for example, an arm cylinder 3
And a flow direction of the pressure oil supplied from the hydraulic pump 2 to the arm cylinder 3 to control the flow direction of the arm directional control valve 1 having the center bypass passage 1a, and the pressure generation disposed downstream of the arm directional control valve 1. A device, for example, a throttle valve 4, a conduit 5 for guiding the pressure on the upstream side of the throttle valve 4, and a hydraulic pump 2
And a regulator 6 for controlling the displacement of the.

In the first embodiment, an operating means for generating a pilot pressure for switching the arm directional control valve 1, for example, an operating lever 8 and a hydraulic pressure source 26 for the pilot pressure generated by the operating lever 8. , A pressure sensor 11 for detecting a pilot pressure applied to the drive portion of the arm directional control valve 1, a pump tilt angle sensor 15 for detecting a tilt angle of a swash plate of the hydraulic pump 2, and a rotational speed of the hydraulic pump 2. , A pressure sensor 10 for detecting the upstream pressure of the throttle valve 4 introduced via the pipe 5, and a pressure downstream of the throttle valve 4 introduced via the pipe 5b. Of the pressure sensor 9 and the arm directional control valve 1 and control means for variably controlling the size of the opening area of the center bypass passage 1a, such as an electromagnetic proportional valve 13, a throttle valve 4 and a tank. Disposed, the filter 46 to the pressure oil flowing through the circuit to clean, pressure sensors 11, 10, 9,
The pump tilt angle sensor 15 and the arithmetic unit 12 that performs a predetermined arithmetic operation according to the detection signal output from the pump revolution counter 16 and outputs a drive signal to the electromagnetic proportional valve 13 are provided.

The above-mentioned pressure sensor 11 constitutes a movement amount detecting means for detecting the movement amount of the arm directional control valve 1. Further, the throttle valve 4 is provided by the pressure sensor 10 described above.
Of the upstream side of the throttle valve 4 is detected, and the pressure of the downstream side is detected by the pressure sensor 9 described above, whereby the differential pressure across the throttle valve 4 can be obtained, and the flow rate can be obtained from that differential pressure in a known manner. it can. From this, the pressure sensors 10 and 9 described above constitute a first flow rate detecting means for detecting the flow rate passing through the center bypass passage 1a.
Further, the discharge flow rate of the hydraulic pump 2 can be obtained by multiplying the number of revolutions detected by the pump revolution counter 16 and the tilt angle of the swash plate detected by the pump tilt angle sensor 15. From this, the pump speed meter 16 described above
The pump tilt angle sensor 15 constitutes second flow rate detecting means for detecting the flow rate discharged from the hydraulic pump 2.

In the arithmetic unit 12 described above, an arithmetic operation for obtaining the movement amount of the arm directional control valve 1 is performed according to the detection signal of the pressure sensor 11, and the arithmetic unit 12 is preliminarily calculated.
2 is set, that is, the relationship between the movement amount of the arm directional control valve 1 that changes with a change in the engine (pump) rotational speed and the target flow rate of the actuator, that is, the arm cylinder 3, Calculation for obtaining the target flow rate of 3 is performed. Also, the pressure sensors 9 and 1
A calculation is performed to obtain the differential pressure across the throttle valve 4 from the detection signal of 0, and a flow rate is calculated from the differential pressure across the throttle valve 4, that is, the flow rate passing through the center bypass passage 1a. Further, a calculation for obtaining the pump discharge flow rate is performed from the pump revolution counter 16 and the pump tilt angle sensor 15. Further, the difference between the pump discharge flow rate and the center bypass flow rate is considered to be the supply flow rate actually supplied to the arm cylinder 3,
A calculation for obtaining the difference between this supply flow rate and the above-mentioned target flow rate of the arm cylinder 3 is performed. The difference flow rate is an error flow rate with respect to the flow rate originally to be supplied to the arm cylinder 3, that is, a shortage flow rate or an excess flow rate. The difference flow rate and the discharge pressure of the hydraulic pump 2 which are set in advance in the arithmetic unit 12 are set. That is, the opening area corresponding to the corresponding differential flow rate is selected from the relationship with the opening area of the center bypass passage 1a, and a drive signal having a value corresponding to the opening area is output to the solenoid proportional valve 13.

The upstream side pressure of the throttle valve 4 guided through the passage 5 is applied to one of the drive portions located on both sides of the regulator 6, and the passage 5 is provided to the other of the drive portions.
The downstream side pressure of the throttle valve 4 introduced via b is applied, and the reguulator 6 determines the displacement volume (capacity) of the hydraulic pump 2 according to the magnitude of the differential pressure across the throttle valve 4, that is, It controls the discharge flow rate.

In the embodiment thus constructed, when the operating lever 8 is operated from the neutral state with the intention of extending the arm cylinder 3, for example, the pressure oil supplied from the hydraulic power source 26 is used as the pilot pressure in the arm direction. It is provided to a drive unit located on the left side of the switching valve 1 in the figure. As a result, the arm directional control valve 1 moves to the right in the figure. Along with this, the opening area of the center bypass passage 1a is gradually reduced, the flow rate of the electromagnetic proportional valve 13 and the throttle valve 4 in the open state is reduced as compared with that before, and the hydraulic pump 2 and the arm cylinder are also reduced. 3 communicates with the bottom side,
The rod side of the arm cylinder 3 communicates with the tank, the discharge flow rate of the hydraulic pump 2 is supplied to the bottom side of the arm cylinder 3, and the oil on the rod side tends to be returned to the tank.
The arm cylinder 3 gradually extends.

During this operation, the pressure sensor 11 detects the pressure applied to the drive portion of the arm directional control valve 1, the pressure sensor 10 detects the upstream pressure of the throttle valve 4, and the pressure sensor 9 detects the throttle. The pressure on the downstream side of the valve 4 is detected, the tilt angle of the swash plate of the hydraulic pump 2 is detected by the pump tilt angle sensor 15, and the pump tachometer 16
The number of rotations of the hydraulic pump 2 is detected by and the detection signals are input to the arithmetic unit 12. In the arithmetic unit 12, as described above, the pressure sensor 11 and the pump revolution counter 16
The target flow rate of the arm cylinder 3 is calculated from the detection signal of the above, the pump discharge flow rate is calculated from the pump tilt angle sensor 15 and the pump tachometer 16, and the center bypass passage is performed from the pressure sensor 10 and the pressure sensor 9. A calculation for calculating the flow rate is performed, and a calculation is performed for calculating the supply flow rate actually supplied to the bottom side of the arm cylinder 3 from the pump discharge flow rate and the center bypass passing flow rate calculated by the calculation. Perform the calculation to find the difference in flow rate. Then, a drive signal corresponding to the difference flow rate is output to the solenoid proportional valve 13.

At this time, when the supply flow rate actually supplied to the arm cylinder 3 is smaller than the target flow rate for the arm cylinder 3, the pump discharge pressure and the arm cylinder 3 are reduced due to the small pump discharge pressure. The difference from the load pressure is small, and most of the discharge flow rate of the hydraulic pump 2 is flowing into the tank via the center bypass passage 1a, and the difference between the pump discharge pressure and the load pressure of the arm cylinder 3 is the predetermined pressure. From the arithmetic unit 12, a drive signal for driving the pump so that the pump discharge pressure is increased according to the magnitude of the difference between the supply flow rate and the target flow rate, that is, the opening area of the center bypass passage 1a is further reduced. It is output to the solenoid proportional valve 13. As a result, the pump discharge pressure rises until the difference between the pump discharge pressure and the actuator load pressure reaches a predetermined pressure, the flow rate flowing into the tank via the center bypass passage 1a is suppressed, and a relatively large amount that substantially matches the target flow rate is obtained. The flow rate can be supplied to the arm cylinder 3.

When the actual flow rate supplied to the actuator 3 is larger than the target flow rate, the difference between the pump discharge pressure and the load pressure of the arm cylinder 3 is large due to the large pump discharge pressure. The arithmetic unit 1 is configured so that the flow rate from the hydraulic pump 2 to the tank via the center bypass passage 1a is suppressed and the difference between the pump discharge pressure and the load pressure of the arm cylinder 3 becomes a predetermined pressure.
A drive signal for increasing the opening area of the center bypass passage 1a is output from 2 to the solenoid proportional valve 13. As a result, the pump discharge pressure decreases until the difference between the pump discharge pressure and the load pressure of the arm cylinder 3 reaches a predetermined pressure, the flow rate of the tank flowing through the center bypass passage 1a increases, and the target flow rate is almost matched. A relatively low flow rate can be supplied to the arm cylinder 3.

In the first embodiment constructed as described above, it is possible to automatically supply the arm cylinder 3 with a flow rate that substantially matches the target flow rate of the arm cylinder 3 in accordance with the operation amount of the operation lever 8. At this time, the required flow rate can be supplied to the arm cylinder 3 regardless of the load pressure of the arm cylinder 3. Therefore, it is possible to secure good metering characteristics not only under light load but also under heavy load, and improve work efficiency under this heavy load, and reduce operator fatigue during this heavy load. it can.

Although the arm cylinder 3 is used as the actuator in the above embodiment, it may be a boom cylinder or the like.

In the above embodiment, since the throttle valve 4 is connected to the tank via the filter 46, the pressure sensor 9 for detecting the pressure on the downstream side of the throttle valve 4 is provided. When directly connecting the downstream side of the tank to the tank, the pressure sensor 9 may be omitted.

In the above embodiment, the second flow rate detecting means for detecting the flow rate discharged from the hydraulic pump 2 is composed of the pump tachometer 16 and the pump tilt angle sensor 15. The invention is not limited to this, and may be constituted by a turbine type flow meter disposed between the hydraulic pump 2 and the arm directional control valve 1, and may be provided between the hydraulic pump 2 and the arm directional control valve 1. It is also possible to configure the throttle valve provided and a pressure sensor for detecting the upstream side pressure and the downstream side pressure of the throttle valve, and obtain the flow rate by calculation from the differential pressure across the throttle valve.

Similarly, in the above embodiment, the first flow rate detecting means for detecting the flow rate passing through the center bypass passage 1a is constituted by the pressure sensors 10 and 9, but the turbine type arranged in the center bypass passage is used. It may be configured by the flow meter of.

Further, in the above embodiment, the pressure sensor 11 for detecting the pressure applied to the drive portion of the arm directional control valve 1 is provided as the moving amount detection means for detecting the amount of movement of the arm directional control valve 1. However, the present invention is not limited to this, and may be a stroke sensor or the like that detects the operation amount of the operation lever 8 that operates the arm direction switching valve 1.

Further, in the above-mentioned embodiment, although the structure of the regulator 6 is not particularly described, the regulator shown in FIG. 6 can be applied. When the regulator shown in FIG. 8 is provided, the throttle valve 4
Of the drive signal corresponding to the pressure difference between the upstream side pressure and the downstream side pressure from the arithmetic unit 12 to the electromagnetic switching valves (high speed electromagnetic valves) 6e, 6
It may be configured to output to f as appropriate.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention. In the second embodiment shown in FIG. 3, a pump discharge pressure sensor 35 for detecting the discharge pressure of the hydraulic pump 2 is provided in addition to the structure of the first embodiment shown in FIG.
Further, in the arithmetic unit 12, a relationship between the correction value K of the volumetric efficiency of the hydraulic pump 2 and the pump discharge pressure P, that is, K = ηP (η is a proportional constant) (1) is set in advance, and The calculated value of the pump discharge flow rate obtained from the pump speed detected by the pump speed meter 16 and the tilt angle of the swash plate detected by the pump tilt angle sensor 15 is obtained by the above formula (1). It includes a calculation means for multiplying the correction value K obtained. This arithmetic unit 12
The arithmetic means included in the above constitutes a control means for variably controlling the size of the opening area of the center bypass passage 1a according to the discharge pressure P of the hydraulic pump 2, that is, a correction means for correcting the drive of the solenoid proportional valve 13. ing.

Generally, the relationship between the pump discharge pressure P and the volumetric efficiency of the pump 2 is as shown in FIG.
Has a relationship in which the volumetric efficiency decreases as becomes larger.
In the second embodiment, the arithmetic unit 12 inputs the detection signal of the pump discharge pressure sensor 35, and the correction value obtained from the relation of the equation (1) is used to calculate the pump revolution counter 16 and the pump tilt angle sensor 15. Therefore, when the pump discharge pressure P is large, a larger pump discharge flow rate is required, and the actual supply flow rate of the arm cylinder 3 is calculated based on the large pump discharge flow rate. Is calculated, and the drive of the solenoid proportional valve 13 is controlled according to the difference between the supply flow rate thus obtained and the target flow rate for the arm cylinder 3. Therefore, the above-mentioned differential flow rate is a flow rate in which the decrease in pump volumetric efficiency due to the increase in pump discharge pressure is corrected, and the influence of the decrease in volumetric efficiency of the hydraulic pump 2 can be eliminated by the control by this differential flow rate. It is possible to realize the flow rate control for the arm cylinder 3 with higher accuracy than in the first embodiment.

[0036]

Since the present invention has the above-mentioned structure, it is possible to secure good metering characteristics not only when the load is light but also when the load is heavy, and the work efficiency is improved as compared with the conventional case. It is possible to reduce the operator's feeling of fatigue.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of a hydraulic drive system for a hydraulic working machine according to the present invention.

FIG. 2 is a diagram showing a relationship between a directional control valve movement amount and an actuator target flow rate set by an arithmetic unit provided in the first embodiment.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between generally known pump discharge pressure and pump volumetric efficiency.

FIG. 5 is a circuit diagram showing a conventional hydraulic drive system for a hydraulic working machine.

6 is a diagram showing an example of a configuration of a regulator provided in the hydraulic drive system shown in FIG.

FIG. 7 is a diagram showing characteristics of the regulator shown in FIG.

FIG. 8 is a diagram showing another configuration of the regulator.

9 is a diagram showing characteristics of the hydraulic drive system shown in FIG.

[Explanation of symbols]

 1 Arm Direction Switching Valve 1a Center Bypass Passage 2 Variable Capacity Hydraulic Pump 3 Arm Cylinder (Actuator) 4 Throttle Valve 5 Passage 5b Passage 6 Regulator 8 Operating Lever 9 Pressure Sensor (First Flow Rate Detection Means) 10 Pressure Sensor (First) Flow rate detection means) 11 pressure sensor (movement amount detection means) 12 arithmetic unit 13 electromagnetic proportional valve (control means) 15 pump tilt angle sensor (second flow rate detection means) 16 pump revolution counter (second flow rate detection) Means) 26 hydraulic power source 35 pump discharge pressure sensor 46 filter

Claims (2)

[Claims] 1. A center bypass for controlling a variable displacement hydraulic pump, an actuator driven by pressure oil discharged from the variable displacement hydraulic pump, and a flow of pressure oil supplied from the variable displacement hydraulic pump to the actuator. In a hydraulic drive system for a hydraulic working machine equipped with a directional control valve having a passage and a regulator controlling the displacement of the variable displacement hydraulic pump, a moving amount detecting means for detecting a moving amount of the directional control valve, A first flow rate detecting means for detecting a flow rate passing through the center bypass passage, and a second flow rate detecting means for detecting a flow rate discharged from the variable displacement hydraulic pump.
Of the flow rate detecting means and the downstream of the direction switching valve,
A control means for variably controlling the size of the opening area of the center bypass passage is provided, and the control means is provided according to the detection results of the movement amount detection means, the first flow rate detection means, and the second flow rate detection means. A hydraulic drive device for a hydraulic working machine, which controls driving of a control means. 2. The hydraulic drive system for a hydraulic working machine according to claim 1, further comprising a correction means for correcting the drive of the control means according to the discharge pressure of the variable displacement hydraulic pump.