JPH07119703A - Hydraulic driver for construction machine - Google Patents

Abstract

PURPOSE:To control the capacity of an oil pressure pump by finding out the discharge flow of the oil pressure pump from pressure of a throttle detected by a pressure detection means and selected characteristics, thereof and indicating the found out discharge flow to a regulator. CONSTITUTION:An output signal Sp from a pressure detector 21, an output signal Pn from a differential pressure detector 15, an output signal Pp from a pump discharge pressure detector 16, and an output signal Ss from a setting device 22 are input into a controller 23. The controller 23 in which these signals are inputted judges types of works and pump loading and selects negative control characteristics according to the kind of work. A signal Qp corresponding to a pump flow according to differential pressure Pn based on the characteristics is output to a pump regulator 3. The pump regulator 3 changes displacement volume of an oil pressure pump 2 so as to provide pump discharge flow in response to the output signal Qp of the controller 23. As a result, discharge flow of the oil pressure pump 2 can be controlled so as to reduce power loss at the time of light loading works.

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 a construction machine of a system (negative control system) for controlling the discharge flow rate of a hydraulic pump according to the downstream pressure of a center bypass line of a directional control valve.

[0002]

2. Description of the Related Art A conventional negative control type hydraulic drive system includes a variable displacement hydraulic pump, a plurality of actuators driven by pressure oil discharged from the hydraulic pump, and a hydraulic pump to a plurality of hydraulic actuators. A plurality of center bypass type directional control valves for controlling the flow of the supplied pressure oil, the center bypass passages of the plurality of directional control valves are connected in series, and the hydraulic pump and these center bypass passages are connected in series to the tank. Center bypass line, a throttle arranged at a position downstream of each direction switching valve in the center bypass line, and a pressure generated by this throttle (negative control pressure)
And a pump flow rate control device for controlling the discharge flow rate of the hydraulic pump in accordance with the above.

A bleed-off variable throttle is provided in the center bypass passage of each direction switching valve, and the opening area of the variable throttle gradually changes from maximum to fully closed depending on the stroke amount of the direction switching valve. In this process, the flow rate flowing through the center bypass line decreases, so the pressure generated by the throttle gradually decreases, and the pump flow rate control device increases the displacement of the hydraulic pump so that the pump discharge flow rate increases when this pressure decreases. Control. That is, the discharge flow rate of the hydraulic pump is controlled according to the stroke amount (required flow rate) of the directional control valve. Such a negative control type hydraulic drive system is disclosed, for example, in Japanese Patent Laid-Open No. 61-24.
No. 802, Japanese Patent Laid-Open No. 1-275902, Japanese Patent Publication No. 1-252121 and the like.

[0004]

In the above negative control type hydraulic drive device, the metering characteristic of the pressure oil supplied to the hydraulic actuator is the characteristic of the pump discharge flow rate with respect to the stroke amount of the directional control valve, that is, the negative control. It is uniquely determined by the characteristics and the aperture characteristics of the bleed-off variable stop. That is, when one of the plurality of directional control valves is operated, the discharge flow rate of the hydraulic pump increases as the stroke amount of the directional control valve increases as described above, but at the same time, as the stroke amount increases, As the opening areas of the meter-in variable throttle and meter-out variable throttle of the directional control valve increase, and the opening area of the bleed-off variable throttle decreases, the flow rate from the hydraulic pump to the center bypass passage decreases. It decreases, which causes the discharge pressure of the hydraulic pump to increase. Then, the pump port of the directional control valve
Pressure from the hydraulic pump begins to flow into the actuator when the pressure of the actuator becomes higher than the load pressure of the actuator, and thereafter the flow rate from the pump through the center bypass passage further decreases. The flow rate flowing into the side increases.

In such a negative control control, considering the operability during light load work, it is necessary to set the aperture characteristic so that the aperture area of the bleed-off variable diaphragm is relatively large in the small stroke region. However, if set in this way, the load pressure will increase during heavy load work, and pressure oil will not start to flow out to the actuator until the stroke amount of the directional control valve becomes relatively large, and the width of the stroke amount in the metering region will be small. As a result, there is a problem that good metering characteristics cannot be obtained during heavy load work, and fine operation becomes difficult.
On the contrary, if the opening area of the bleed-off variable diaphragm is determined in consideration of heavy load work, there arises a problem that operability at light load deteriorates.

An object of the present invention is to solve the above-mentioned problems in the prior art and to provide a hydraulic drive system for a construction machine capable of obtaining good operability during light load work and heavy load work.

[0007]

In order to achieve the above object, the present invention provides a variable displacement hydraulic pump, a plurality of hydraulic actuators driven by the hydraulic pump, and the hydraulic pump to the hydraulic actuator. A plurality of center bypass type directional control valves for controlling the flow of pressure oil, throttles arranged downstream of the respective directional control valves of the center bypass line passing through these directional control valves, and pressure generated by these throttles. In a hydraulic drive device for a construction machine, which is provided with a pressure detection unit that detects the pressure and a regulator that controls the discharge flow rate of the hydraulic pump according to the pressure detected by the pressure detection unit, the pressure is detected by the pressure detection unit. A plurality of types of characteristics of the discharge flow rate of the hydraulic pump with respect to pressure are provided, and based on one of these characteristics, Wherein a controller for instructing the delivery rate of the hydraulic pump, characterized in that a selection means for selecting a desired one characteristic of said respective characteristics.

[0008]

During operation of the construction machine, the required characteristics are selected by the selection means. The controller determines the discharge flow rate of the hydraulic pump from the pressure of the throttle detected by the pressure detecting means and the selected characteristic, and instructs the regulator on the calculated discharge flow rate. This instruction drives the regulator to control the displacement of the hydraulic pump. Since the above characteristics are determined with respect to the magnitude of the load, it is possible to obtain good operability independent of the load, particularly good fine operability.

[0009]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a hydraulic circuit diagram of a hydraulic drive system for a hydraulic excavator according to a first embodiment of the present invention. Referring to FIG. 1, a hydraulic drive system according to the present embodiment includes a variable displacement hydraulic pump 2 that is rotationally driven by an engine 1, a pump regulator 3 that controls the displacement of the hydraulic pump 2, and a pressure from the hydraulic pump 2. A plurality of hydraulic actuators 4, 5 driven by oil, a tank 6 constituting a low pressure circuit, and a plurality of directional switching valves 7, 8 located between the hydraulic pump 2, the hydraulic actuators 4, 5 and the tank 6. Is equipped with.

The direction switching valves 7 and 8 are center bypass type switching valves which control the flow of the pressure oil supplied from the hydraulic pump 2 to the hydraulic actuators 4 and 5. The passages are connected in series by a center bypass line 9, the uppermost stream of the center bypass line 9 is connected to the discharge pipe line 10 of the hydraulic pump 2, and the lowermost stream is connected to the tank 6. The direction switching valves 7 and 8 are connected to the discharge pipe line 11 of the hydraulic pump 10 via a line 11 in parallel with each other. A relief valve 12 for controlling the discharge pressure of the hydraulic pump 2 so as not to exceed a specified pressure is connected to the discharge pipe 10 of the hydraulic pump 2. Directional switching valve 8 for center bypass line 9
A throttle 13 for generating a negative control pressure Pn is connected to a downstream side of the throttle valve 13. In parallel with the throttle 13, a relief valve 14 for controlling the negative control pressure generated in the throttle 13 so as not to exceed a specified pressure is connected. ing.

The negative control pressure generated in the throttle 13 is detected by the differential pressure detector 15. The discharge pressure of the pump 2 is detected by the pump discharge pressure detector 16. Further, the directional control valves 7, 8 are pilot operated type directional control valves, and of the pilot pressures acting on the pilot operating portion of the directional control valve 7, a pilot line 20 for guiding the pilot pressure Pi corresponding to the extension direction of the actuator 4. A pressure detector 21 that detects the pilot pressure Pi as an operation signal for the directional control valve 7 is connected to the. A setting device 22 that is operated by an operator and indicates the type of work performed by the actuator 4 is arranged.

The output signal Sp from the pressure detector 21, the output signal Pn from the differential pressure detector 15, the output signal Pp from the pump discharge pressure detector 16, and the output signal Ss from the setting device 22 are input to the controller 23. Then, the controller 23 determines the type of work and the load of the pump from these signals, selects the negative control characteristic according to the type of work, and sets the pump flow rate according to the differential pressure Pn based on this characteristic. The signal Qp is output to the pump regulator 3. The pump regulator 3 controls the discharge flow rate of the hydraulic pump 2 by changing the displacement volume of the hydraulic pump 2 so that the pump discharge flow rate corresponds to the output signal Qp of the controller 23.

FIG. 2 is an explanatory view for explaining each variable throttle of the directional control valve. As shown in this figure, the directional control valves 7, 8
Are meter-in variable diaphragms 24a and 24b (hereinafter represented by 24) and meter-out variable diaphragm 25, respectively.
a and 25b (represented by 25 below),
A bleed-off variable throttle 26 is provided in the center bypass passage. These meter-in variable diaphragms 2
4 and the meter-out variable diaphragm 25 and the bleed-off variable diaphragm 26 show the relationship between the stroke amount S and the opening area A in FIG.

That is, in FIG. 3, curves 27 and 28 show the characteristics of the opening areas of the meter-in variable diaphragm 24 and the meter-out variable diaphragm 25, and the line 29 shows the characteristics of the opening area of the bleed-off variable diaphragm 26. is there. The meter-in variable throttle 24 and the meter-out variable throttle 25 are fully closed when the stroke amount S is 0 (when the directional control valve is in the neutral position), and the opening area A increases as the stroke amount S increases. On the other hand, the bleed-off variable diaphragm 26 is fully opened when the stroke amount is 0, and the opening area A is reduced as the stroke amount S increases.

By setting the opening characteristic of the bleed-off variable throttle 26 in this manner, the flow rate (center bypass flow rate) passing through the center bypass passage becomes maximum when the directional control valve 7 is in the neutral position, for example. 1
The negative control pressure generated by 3 also becomes maximum, and as the stroke amount S of the directional control valve 7 increases, the center bypass flow rate decreases and the negative control pressure decreases. On the other hand, when the directional control valve 7 is operated, the hydraulic actuator 4 is supplied with the remaining flow rate obtained by subtracting the flow rate (center bypass flow rate) passing through the bleed-off variable throttle 26 from the pump discharge flow rate. The control characteristic of the directional control valve regarding the flow rate of the pressure oil supplied to the hydraulic pressure control valve 4 is determined by the opening characteristic of the bleed-off variable throttle 26 and the flow rate of the hydraulic pump 2.

The throttle 13 is a stroke amount S of the directional control valve 7.
A negative control pressure Pn corresponding to the above is generated. Fig. 4 shows the stroke amount S when the load pressure is constant.
And the negative control pressure Pn, and FIG. 5 shows the relationship between the negative control pressure Ps and the pump flow rate Qp. As is clear from FIG. 4, the negative control pressure Pn increases as the stroke amount S increases.
Will fall. In FIG. 5, reference numeral 30 indicates a first negative control characteristic and reference numeral 31 indicates a second negative control characteristic, which are determined by the controller 23.

From the relationship shown in FIGS. 4 and 5, the stroke amount S and the pump discharge flow rate Qp when the load pressure is constant are shown.
The relationship between and is as shown in FIG. In the figure, the solid line 32 is the characteristic when the first negative control characteristic is used, and the broken line 33 is the characteristic when the second negative control characteristic is used. That is, the pump discharge flow rate Qp increases as the stroke amount S increases, and the pump discharge flow rate Qp is larger in the first negative control characteristic. The negative control characteristic can be changed in the controller 23 from the solid line 32 to the broken line 33 and vice versa.

FIG. 7 is a block diagram showing the configuration of the controller shown in FIG. The controller 23 is composed of a microcomputer, and as shown in FIG.
From the differential pressure detector 15, the signal Pn from the differential pressure detector 15, and the signal P from the discharge pressure detector 16.
p, an A / D converter 23a for converting the signal Ss output from the setting device 22 into a digital signal, a central processing unit (CPU) 23b, a control procedure program, and a first negative control characteristic and a second negative Read-only memory (RO
M) 23c, a random access memory (RAM) 23d for temporarily storing a numerical value during calculation, an I / O interface 23e for output, and an amplifier 23g connected to the pump regulator 3 described above.

Next, the operation of this embodiment will be described with reference to the flow chart shown in FIG. 8 which is a program of the control procedure stored in the ROM 23c. In this description, a case where standard work is performed as light load work and hanging work is performed as heavy load work will be described as an example. First, when performing standard work as light load work, the operator selects and sets the standard work by the setting device 22, and operates the direction switching valve 7 in this state. As shown in FIG. 8, the controller 23, in step S1, outputs the output signal Sp of the pressure detector 21,
Output signal Ss of setting device 22 and output signal P of differential pressure detector
n, read the output signal Pp of the discharge pressure detector. Then, in step S2, the operator operates the setting device 22 from the signal Ss.
It is determined whether or not the hanging work, which is a heavy load work, is selected in step S3. In this case, since the standard work is selected, the process proceeds to step S3. In step S3, the first negative control characteristic is selected from the negative control characteristics stored in the ROM 23c.

On the other hand, when performing hanging work as heavy load work, the operator selects and sets the hanging work by the setting device 22, and operates the direction switching valve 7 in this state. At this time, in the controller 23, the signals Ss, Sp, Pn, and Pp are read in the procedure S1 of FIG. 8 in the same manner as described above, and then in step S2, the operator uses the setting device 22 to perform the heavy load work from the signal Ss. Determine whether you have selected a task. This time, since the hanging work is selected, the affirmative result is obtained in step S2, and in step S4, the signal Sp is compared with a predetermined value So for determining that the extending operation of the hydraulic actuator 4 has been performed, and Sp> So (extension It is determined whether or not (operation is performed), and if Sp> So, the process proceeds to step S5, and if not, the process proceeds to step S3. In step S5, it is determined whether the actual pump load is a heavy load (Po). If the load is heavy, the process proceeds to step S6, and if not, the process proceeds to step S3. In step S6, the second negative control characteristic stored in the ROM 23c is selected.

As described above, the first negative control characteristic is selected for light load work, and the second negative control characteristic is selected for heavy load work.
In step S7, as shown in FIG. 5, based on the negative control pressure Pn, which is the detection value of the differential pressure detector 15 read in step S1, and the negative control characteristic selected in step S3 or step S6, as shown in FIG. Qp is calculated and output to the pump regulator 3.

In the present embodiment, as described above, the pump flow rate is controlled by the first negative control characteristic in the standard work which is the light load work and by the second negative control characteristic in the heavy load work. The effect is obtained. As described above, in this embodiment, the negative control characteristic is the solid line 32 and the broken line 3 in FIG.
Two characteristics shown by 3 and 3 can be taken. Since the first negative control characteristic is selected during light load work, the pump flow rate characteristic is as shown by the solid line 32. The negative control characteristic 32 suppresses an increase in the discharge flow rate Qp of the hydraulic pump 2 in a region where the stroke amount S of the directional control valve 7 is relatively small, so that the pressure of the pump port of the directional control valve 7 does not become excessively high. It is a characteristic.

When the negative control characteristic during light load work is set as described above, the metering characteristic of the pressure oil supplied to the hydraulic actuator 4 depends on the negative control characteristic and the opening characteristic of the bleed-off variable throttle 26. As shown in FIG. That is, in FIG. 9, the negative control characteristics during light load work are shown in FIG.
The reference numeral 32 is the same as the reference numeral 32, and the bleed-off flow rate passing through the bleed-off variable throttle 26 under the load pressure during light load work is 29A corresponding to the opening characteristic 29 of FIG.
As shown in. At this time, the metering characteristic of the pressure oil supplied to the actuator 4 is as shown by the solid line 40A obtained by subtracting the bleed-off flow rate of the characteristic 29A from the pump discharge flow rate of the characteristic 32, and satisfactory fine operability can be obtained. it can. Also, power loss can be reduced.

Here, assuming that the first negative control characteristic is selected during heavy load work, the pump flow rate is one point corresponding to the solid line 32 which is the characteristic during light load work as shown in FIG. It changes like a chain line 34. That is, since the load pressure increases during heavy load work, the negative control pressure Pn becomes higher than during light load work, and the increase in pump discharge flow rate decreases. The negative control characteristic is indicated by reference numeral 34 in FIG. on the other hand,
The bleed-off flow rate during heavy load work is greater than during light load work due to the high load pressure, as indicated by 29B in FIG. 9, and the metering characteristic of the pressure oil supplied to the actuator 4 is the pump of characteristic 34. A solid line 40X is obtained by subtracting the bleed-off flow rate of the characteristic 29B from the discharge flow rate. That is, since the pump discharge flow rate is small and the bleed-off flow rate is large in a region where the stroke amount S is relatively small, pressure oil does not start to flow out to the actuator 4 until the stroke amount S of the directional control valve becomes large, and the metering region The stroke width Sx becomes smaller. For this reason, good metering characteristics cannot be obtained during heavy load work, and fine operation becomes difficult.

On the other hand, in the present embodiment, the negative control characteristic changes during heavy load work as shown by the alternate long and two short dashes line 36 corresponding to the broken line 33 during heavy load work in FIG.
The negative control characteristic is shown in FIG.
Indicate. On the other hand, the bleed-off flow rate during heavy load work is larger than that during light load work as indicated by 29B in FIG. 9 as described above, and the metering characteristic of the pressure oil supplied to the actuator 4 is the pump of the characteristic 36. Characteristics from discharge flow rate 29
The solid line 40B is obtained by subtracting the B bleed-off flow rate. That is, comparing the alternate long and short dash line 40X and the solid line 40B, in the characteristic of the solid line 40B, the pump discharge flow rate increases in a region where the stroke amount S is relatively small, so that the stroke position at which pressure oil starts to flow out to the actuator 4 becomes smaller. The width Sb of the stroke amount of the metering region is remarkably expanded as compared with the width Sx in the case of the characteristic of the solid line 40X. Therefore, good metering characteristics can be obtained during heavy load work, and fine operation becomes easy.

From the above, according to the present embodiment, good metering characteristics can be obtained both during light load work and heavy load work, and operability in the fine operation region can be improved. . Also, power loss during light load work can be reduced.

FIG. 10 is a hydraulic circuit diagram of a hydraulic drive system for a hydraulic excavator according to a second embodiment of the present invention, and FIG. 11 is FIG.
4 is a flowchart illustrating an operation of the controller shown in FIG. In this embodiment, the operating direction of the directional control valve is not judged, but the setting device and the type of pump discharge pressure work are instructed. In each figure, members and procedures equivalent to those shown in FIGS. 1 and 8 are designated by the same reference numerals.

In FIG. 10, the hydraulic drive system of this embodiment has a setting device 22 that is operated by an operator and sets the type of work as means for instructing the type of work.
As shown in FIG. 11, the controller 23A selects one of the negative control characteristics from the output signal Ss of the setting device 22 and the output signal Pp of the discharge pressure detector 16. The effect of this embodiment is the same as the effect of the previous embodiment.

FIG. 12 is a hydraulic circuit diagram of a hydraulic drive system for a hydraulic excavator according to a third embodiment of the present invention, and FIG. 13 is FIG.
4 is a flowchart illustrating an operation of the controller shown in FIG. In this embodiment, the negative control characteristic is selected by detecting the operation signal of the directional control valve without using the setting device. In the figure, members and procedures equivalent to those shown in FIGS. 1 and 8 are designated by the same reference numerals.

In FIG. 12, the hydraulic drive system according to the present embodiment is a pilot pressure Pi which is an operation signal for a specific directional switching valve 7 among a plurality of directional switching valves 7 and 8 as means for instructing the type of work. As shown in FIG. 13, the controller 23B determines only the output signal Sp of the pressure detector 21 to determine the type of work and determines the negative control characteristic. That is,
A heavy load and a light load are determined from the hydraulic actuator to be driven and the driving direction.

According to this embodiment, since the negative control characteristic is selectively set by the operation signal of the directional control valve, the type of work can be instructed automatically, and the effect of the first embodiment can be annoyed by the operator. You can get it without letting it go.

In the above description of the embodiment, an example in which the negative control characteristic is set for two works, a light load work and a heavy load work, has been described. In addition to this, a work equivalent to medium load work (excavation work in a hydraulic excavator, etc.) can be set, another intermediate negative control characteristic can be provided, and switching to three levels is possible. May increase. Further, it may be further subdivided according to the type of work and the magnitude of load, and may be continuously changed within the range of the first and second metering characteristics. By doing so, it is possible to obtain good metering characteristics that facilitate fine operation in a wide range of work. Further, in the above embodiment, the differential pressure across the throttle 13 is used as the negative control pressure, but the upstream pressure of the throttle 13 may be used.

[0033]

According to the present invention, good metering characteristics can be obtained during both light load work and heavy load work, and operability in fine operation can be improved.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a transitional position of the directional control valve shown in FIG.

FIG. 3 is a diagram showing an opening characteristic of each aperture shown in FIG.

FIG. 4 is a characteristic diagram of the negative control pressure with respect to the stroke amount of the directional control valve.

FIG. 5 is a characteristic diagram of pump discharge flow rate with respect to negative control pressure.

FIG. 6 is a characteristic diagram of a pump discharge flow rate with respect to a stroke amount.

FIG. 7 is a block diagram showing the configuration of the controller shown in FIG.

FIG. 8 is a flowchart illustrating an operation of the controller shown in FIG.

9 is a metering characteristic diagram of the directional control valve shown in FIG.

FIG. 10 is a hydraulic circuit diagram of a hydraulic drive system for a construction machine according to a second embodiment of the present invention.

11 is a flowchart illustrating an operation of the controller shown in FIG.

FIG. 12 is a hydraulic circuit diagram of a hydraulic drive system for a construction machine according to a third embodiment of the present invention.

13 is a flowchart illustrating the operation of the controller shown in FIG.

[Explanation of symbols]

 2 Hydraulic pump 3 Pump regulator 4, 5 Hydraulic actuator 6 Tank 7, 8 Directional switching valve 9 Center bypass line 13 Throttle 15 Differential pressure detector 16 Pump discharge pressure detector 21 Pressure detector 22 Setting device 23 Controller

Claims (5)

[Claims] 1. A variable displacement hydraulic pump, a plurality of hydraulic actuators driven by the hydraulic pump, and a plurality of center bypass type directional switches for controlling the flow of pressure oil from the hydraulic pump to the hydraulic actuator. A valve, a throttle disposed on the center bypass line passing through these directional control valves at a position downstream of the respective directional control valves, a pressure detecting means for detecting the pressure generated by the throttle, and a pressure detecting means for detecting the pressure. A hydraulic drive device for a construction machine, comprising: a regulator for controlling a discharge flow rate of the hydraulic pump according to a pressure; and a plurality of characteristics of the discharge flow rate of the hydraulic pump with respect to the pressure detected by the pressure detection means. A controller for instructing the regulator on the basis of one of the characteristics of the discharge flow rate of the hydraulic pump; A hydraulic drive system for a construction machine, comprising: a selection unit that selects one of the required characteristics. 2. The hydraulic drive system for a construction machine according to claim 1, wherein the selection means is constituted by setting means for setting the type of work based on the magnitude of the load. 3. The hydraulic drive system for a construction machine according to claim 1, wherein the selecting means is an operation detecting means for detecting an operation of a specific directional switching valve of the directional switching valves. 4. The hydraulic drive system for a construction machine according to claim 1, wherein the selecting means is constituted by setting means for setting a type of work based on a magnitude of a load. 5. The discharge pressure detecting means for detecting the discharge pressure of the hydraulic pump, the pressure detected by the discharge pressure detecting means, and a predetermined pressure. A hydraulic drive system for a construction machine, comprising: comparison means for comparison.