KR960016819B1 - Flow control hydraulic circuit for a pump - Google Patents

Abstract

No summary

Description

Load pressure compensation pump discharge flow rate control circuit

1 is a hydraulic circuit diagram showing one embodiment of a load pressure compensation pump discharge flow rate control circuit according to the present invention.

FIG. 2 is a graph for explaining the relationship between the bypass opening area and the flow rate in the control circuit shown in FIG.

3 to 6 are hydraulic circuit diagrams showing different embodiments of the load pressure compensation pump discharge flow rate control circuit according to the present invention.

7 is a hydraulic circuit diagram showing a conventional negative pressure compensation pump discharge control circuit.

* Explanation of symbols for main parts of the drawings

20: variable displacement pump 22: supply flow path

24: cylinder 26: center bypass type directional valve

28: Center bypass passage 30: Center bypass passage

32: flow control valve (opening and closing valve) 34: compression spring

36: pilot signal generating means (pressure generating device)

38: main relief valve 40: tank

42: pilot signal pressure pump 44: pilot valve

46: shuttle valve 48: low pressure relief valve

50: flow control valve (variable choke flow control valve)

52: pressure compensation valve 54: variable choke valve

56: Choke opening operation device 58: Directional switching valve operation device

60: operating pressure oil supply pump 62: relief valve

64: Shuttle Valve

70: flow control valve (variable spring load flow control valve)

72: variable spring load means 74: piston

76a, 76b: spring 78: pressure compensation valve

80: fixed choke

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator driving hydraulic circuit of a construction machine, particularly in a variable displacement hydraulic circuit in which the pump discharge flow rate is controlled, wherein the discharge flow rate of the pump is independent of the load pressure of the actuator. The present invention relates to a load pressure compensation pump discharge flow rate control circuit that can be set to correspond to a stroke position.

In the variable displacement hydraulic circuit of a construction machine, the discharge flow rate of the pump can be set constant corresponding to the spool stroke position of the directional valve regardless of the load pressure in order to accurately and smoothly operate various work equipments. Recommended control circuits with load pressure compensation are recommended.

As such a control circuit, what was comprised as shown in FIG. 7, for example is known. In FIG. 7, the control circuit basically supplies the variable displacement pump 10 and the discharge oil of the pump 10 to supply an actuator (cylinder) 12 and an actuator (motor) 14. Direction switching valves (16) and (16) for switching the driving direction of the gears. Here, the direction switching valve 16 is configured in the form of a closed center having no bypass passage, and a variable choke is provided in the passage between the discharge oil supply passage and the actuator port. . In such a configuration, when the spool of the direction switching valve 16 moves, the variable choke in the switching valve changes, and the differential pressure between the upstream pressure and the downstream pressure of the variable choke changes, and the changed differential pressure It acts on the pump via the shuttle valve 18 as pilot pressure. As a result, the pump 10 sets the flow rate at which the discharge flow rate corresponds to the spool stroke position.

In this manner, in this kind of load pressure compensation pump discharge flow rate control circuit, the discharge flow rate of the variable displacement pump is set constant corresponding to the spool stroke position of the direction switching valve, regardless of the load pressure of the actuator. In addition, at the neutral position of the spool, since the direction switching valve is configured as a center closed type, the pump discharge flow rate is set to almost zero.

However, in the conventional load pressure compensation pump discharge flow rate control circuit of this kind, there is a problem as described below.

First, at the time of neutralizing the spool, as described above, since the pump discharge flow rate is set to almost zero, the increase and response of the pump discharge flow rate is delayed. As a result, the response characteristics of the actuator deteriorate, and a king cavitation occurs in an actuator (for example, a turning cylinder or the like) having a large inertial load that requires a makeup effect in a spool neutral state. Further, in such a case, the pump discharge flow rate is configured to be controlled by the pressure difference between the upper and lower oil pressures of the variable choke, that is, the pressure difference between the discharge flow path pressure and the pressure in the cylinder port. If this occurs in the cylinder port, the cavitation increases the differential pressure, and the pump discharge flow rate is controlled in a decreasing direction. In this way, the cavitation is further promoted. In this case, if oil flows out from the cylinder port to the tank port at the pump discharge flow rate or more (considering the area difference), the cavitation is promoted. Therefore, the opening area from the cylinder to the tank and the cylinder from the discharge oil passage are increased. Special care must be taken in setting the opening area of the furnace.

Next, in order to control the pump discharge flow rate, the pressure in the discharge oil flow path and the pressure in the actuator port must be detected. Therefore, the configuration becomes complicated and the cost increases. Especially in the case of multiple valves, since the shuttle valve which detects the maximum load pressure is needed more, cost increases again.

In addition, since the pump discharge flow rate is set to almost zero when the spool is neutral, the response of the pump is generally poor, and in particular, surge pressure is generated in the operation of rapidly returning the spool from the stroke position to the center position. This impairs the operability, and the surge pressure is generated within the range up to the leaf pressure even if a leaf valve is provided in the circuit.

Accordingly, an object of the present invention is to provide a load pressure compensation pump discharge flow rate control circuit which has a good response and operability of an actuator, can effectively suppress the occurrence of cavitation under various conditions, and has a simple structure. Shall be.

In order to achieve the above object, the load pressure compensation pump discharge flow rate control circuit according to the present invention includes a variable displacement pump, a center bypass type direction switching valve for switching the actuator driving direction by the discharge oil of the variable displacement pump; A flow rate adjustment valve installed on the downstream side of the center bypass passage of the center bypass type directional control valve and controlling the center bypass flow rate, and a downstream flow rate of the flow rate adjustment valve, A pilot signal generating means for controlling the flow rate regulating valve is set so as to be controlled to correspond to the opening / closing opening area of the center bypass passage of the center bypass type directional switching valve and is output from the pilot signal generating means. When the discharge flow rate of the variable displacement pump is neutral at the spool neutral of the center bypass type direction switching valve, It characterized in that the setting to be.

In this case, the flow regulating valve is formed as an on / off valve, and the opening degree of the on / off valve is determined by the differential pressure between the upstream side pressure and the downstream side pressure of the center bypass passage of the center bypass type direction switching valve and the compression spring. It is formed by a flow regulating valve controlled by a spring force or with pressure compensation means having a variable choke or variable spring load means for generating differential pressure, and the opening of the variable choke or the spring load of the load means is controlled by an external signal, in particular a center. It is very good to be configured to control by a switch valve operation signal of a bypass type direction switching valve.

Further, the pilot signal generating means is formed of a pressure generating device, and the variable capacity pump is configured to control negative flow rate by drawing a pilot signal from an upstream side of the pressure generating device, or a pilot signal pressure pumping device. By operating the pilot bypass direction switching valve by the pilot signal drawn from the pump device, the pilot pump signal for the maximum pump discharge flow rate control of the pilot signal is derived to control the positive flow rate of the variable displacement pump. Can be configured.

In the control circuit of the present invention, the direction switching valve is configured of a center bypass type, and the bypass flow rate passing through the center bypass passage corresponds to this stroke position at the time of spool stroke of the direction switching valve. Controlled via a flow regulating valve to be set at a constant flow rate. Therefore, the pump discharge flow rate and the actuator supply flow rate (pump discharge flow rate-bypass flow rate) are set to a constant flow rate corresponding to the spool stroke position regardless of the load pressure of the actuator. That is, load pressure compensation is achieved.

On the other hand, in the spool neutral of the directional switching valve, the bypass flow rate, that is, the pump discharge flow rate in this case is set to a predetermined minimum flow rate via the pilot signal generating means. As described above, in the control circuit of the present invention, even when the spool is neutral, the pump discharge flow rate is set to a predetermined value, and since the minimum flow rate passes through the bypass passage, the response delay of the pump is suppressed and the surge pressure in the circuit is suppressed. Even if this occurs, this surge pressure is absorbed in the barrier passage.

In addition, in the control circuit of the present invention, even if cavitation occurs in a swing cylinder having a large inertia load or the like, at this time, the bypass flow rate decreases and the pilot signal pressure decreases, which causes the pump discharge flow rate to increase and the supply flow rate to the cylinder. This is sufficiently secured, and the cavitation phenomenon is effectively suppressed.

Next, an embodiment of the load pressure compensation pump discharge flow rate control circuit according to the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, the control circuit which concerns on this invention is the actuator (cylinder) connected to the load W by supplying the variable displacement pump 20 and the discharge oil of this pump 20 via the supply flow path 22 ( The center bypass flow direction switching valve 26 for switching the driving direction of the 24 and the flow path 30 through the center bypass passage 28 of the direction switching valve 26 are provided in the center bypass flow rate Q2. Pilot signal generating means 36 for controlling the flow rate regulating valve (referred to as an on / off valve 32 in this embodiment) and the discharge flow rate Q1 (see FIG. 2) of the pump 20 for controlling (see FIG. 2). It is composed of The on-off valve 32 also has a control compression spring 34. In this figure, reference numeral 38 denotes a main relief valve for preventing abnormal rise in circuit pressure, and reference numeral 40 denotes a tank.

The on-off valve 32 is opened and closed by the differential pressure ΔP between the upstream side pressure and the downstream side pressure of the center bypass passage 28 and the spring force of the compression spring 34, and the opening and closing portion of the center bypass passage 28 is opened. Set to be controlled by area. That is, the opening / closing valve 32 is opened large enough by the compression spring 34 when the opening / closing opening area of the center bypass passage 28 is large (when the differential pressure? P is small). When it becomes small (when the differential pressure (DELTA) P becomes large), it is comprised so that opening area may be reduced in opposition to the spring force of the compression spring 34. FIG. Therefore, the bypass flow rate Q2 passing through the center bypass passage 28 is set to a constant flow rate corresponding to the opening / closing opening area of the passage 28 regardless of the pressure of the supply passage 22. The on-off valve 32 may be provided upstream of the center bypass passage 28 in the flow passage 30. In addition, the opening / closing opening area of the center bypass passage 28 becomes maximum at the spool neutral of the directional switching valve 26, becomes maximum at the spool stroke end, and is determined from the relationship with the opening / closing valve 32 during the stroke. Is set to the optimal size. Therefore, the bypass flow rate Q2 becomes maximum at spool neutral.

The pilot signal generating means 36 is composed of a pressure generating device composed of, for example, an orifice and a low pressure leaf valve, and is provided downstream of the center bypass passage 28 and the on-off valve 32. Thus, the negative flow rate control is performed so that the pilot signal drawn out from the upstream side of the generating means 36 causes the discharge flow rate Q1 of the variable displacement pump 20 to be small when the pilot pressure is high and, conversely, to be large when the pilot pressure is low. However, at this time, the pilot signal is set such that the pump discharge amount Q1 is a predetermined minimum flow rate when the spool neutral of the direction switching valve 26 is neutralized.

Therefore, in the control circuit of the present invention, as shown in FIG. 2, the pump discharge flow rate Q1, the bypass flow rate Q2, and the cylinder flow rate Q3 = Q1-Q2 are the stroke positions of the directional valve 26, and thus the bypass passage. It is controlled by a constant flow rate corresponding to the opening / closing opening area of (28), and has no relation to the load pressure of the cylinder 24. In addition, the pump discharge flow rate of the minimum amount is secured even when the spool is neutral, and the entire amount passes through the center bypass passage. In addition, the bypass flow rate Q2 passes through the pressure generating device 36 and is discharged to the tank 40.

Next, the operation of the control circuit of the present invention having such a configuration will be described. The description of this operation partially overlaps with the description in the above configuration.

At the time of spooling of the center bypass type direction switching valve 26, the discharge flow rate Q1 of the variable displacement pump 20 is supplied to the cylinder 24 via the supply passage 22 (cylinder flow rate Q3) and At the same time, a part of the gas is bypassed through the center bypass passage 30 to the center bypass passage 28, the on-off valve 32, and the pressure generating device 36 (bypass flow rate Q2) and discharged to the tank 40. do. By the way, during this spool stroke, the valve opening area of the on-off valve 32 is reduced to a size corresponding to the opening / opening area of the center bypass passage 28 determined by the spool stroke position, so that the bypass flow rate Q2 Is reduced to the corresponding flow rate, so that the pump discharge flow rate Q1 controlled by the pilot pressure drawn from the pressure generating device 36 is increased to the flow rate corresponding to the decrease. Further, at this time, the bypass flow rate Q2 through the center bypass passage 28 is controlled via the open / close valve 32 so that the constant flow rate corresponds to the opening / closing opening area of the passage 28. As a result, the pilot pressure and the pump discharge flow rate Q1 become constant, and therefore the cylinder flow rate Q3 is also set constant. That is, the cylinder flow rate Q3 is set at a constant flow rate corresponding to the spool stroke position regardless of the load pressure, and load pressure compensation is achieved.

In this case, if the inertia force of the load W is large, in the drawing, cavitation may occur in the cylinder port when the direction switching valve 26 is operated in the left direction. In this case, the pump discharge oil flows into the cylinder port on the side with the small load, and the bypass flow rate Q2 flowing through the center bypass passage 28 decreases, so that the prick pressure decreases and the pump discharge amount Q1 increases. As a result, the cylinder flow rate Q3 is increased, and the cavitation is effectively suppressed.

Next, when the center bypass type directional valve 26 is spooled in neutral, the pump discharge flow rate Q1 is the total flow rate of the bypass flow Q2, and the center bypass passage 28, the on-off valve 32 and the pressure generating device 36 ) Is discharged to the tank 40. At this time, since the open / close opening area of the center bypass passage 28 is set to the maximum (thus the valve opening area of the open / close valve 32 is also set to the maximum), the bypass flow rate Q2 also becomes maximum, and the variable displacement pump The discharge flow rate Q1 at 20 is set to the minimum flow rate. This minimum flow rate corresponds to the maximum bypass flow rate as described above.

As described above, in the control circuit of the present invention, the minimum pump discharge flow rate is set even when the spool is in neutral, so that the flow rate flows into the bypass passage as the bypass flow rate, so that the pump response delay is suppressed and in the circuit. Even when a surge pressure is generated, the surge pressure is absorbed in the bypass passage. Moreover, also regarding generation | occurrence | production of said cavitation, generation | occurrence | production of the said cavitation is suppressed more effectively especially when the makeup circuit is provided in the upstream of a pressure generating apparatus.

In addition, since the pump discharge flow rate is directly controlled corresponding to the spool stroke position, the control circuit of the present invention has a relatively simple structure.

3 shows another embodiment of a control circuit according to the present invention. This embodiment is configured to positively control the flow rate control of the variable displacement pump in the above embodiment.

That is, in FIG. 3, a pilot signal pressure pump 42 is used as a pilot signal generating means, and the pilot valve 44 is operated by operating the center bypass type direction switching valve 26 by this pilot signal. And a pilot signal for controlling the maximum pump discharge flow rate control of the pilot signal through the shuttle valve 46, thereby controlling the positive displacement control of the variable displacement pump 20. In this figure, reference numeral 48 denotes a low pressure relief valve. Also in this embodiment, the basic configuration and operation of the control circuit are the same as in the above-described embodiment, and the same effect is achieved. However, it is possible to avoid disadvantages such as requiring an external pilot signal (pump for pilot signal pressure) compared to the negative control in order to control the pump discharge flow rate.

4 shows another embodiment of a control circuit according to the present invention. In this embodiment, in the first embodiment shown in FIG. 1, the center bypass type direction switching valve is composed of multiple valves (two in the figure) 26, 26. As shown in FIG.

Also in this embodiment, the same effect as that of the first embodiment is achieved, but it is also combined with the advantage of improving the metering characteristic of the direction switching valve made of multiple valves. That is, in the conventional conventional multiple valve configuration, since the opening / closing valve 32 is not provided, the opening / closing opening area for bypass flow control at the time of metering the center bypass 28 of the directional valve 26 is Since a relatively low bypass flow rate needs to be controlled at a relatively high load pressure, a relatively small opening area is set. As a result, in the conventional multiple valve, when the directional valves 26 and 26 are operated at the same time, a sudden change in pressure and flow rate occurs in the circuit and the metering characteristics of the directional valves 26 and 26 are damaged. The flaw was basically there. However, in the control circuit of the present invention, since the bypass flow rate is controlled by the on / off valve, the opening / closing opening area at the time of metering can be set relatively large. Therefore, even when the directional control valve is operated at the same time, the above-mentioned fluctuations in pressure and flow rate do not occur, and the metering characteristic is not impaired.

5 shows another embodiment of a control circuit according to the present invention. In the embodiment shown in Figs. 1 to 4, the flow control valve is replaced with an on-off valve, and the flow control valve is provided with a pressure compensating means having a variable choke for generating a differential pressure. The opening of the choke is controlled by an external signal.

That is, in FIG. 5, the flow regulating valve 50 is formed of the variable choke valve 54 provided with the pressure compensation valve 52 in the downstream side, and the choke opening control device ( 56) or an operation signal from the direction switching valve operating device 58 is applied. In this figure, reference numeral 60 denotes an operating pressure oil supply pump for driving an operation signal 56 or 58, reference numeral 62 denotes a relief valve for preventing an abnormal increase in the internal pressure of the circuit, and reference numeral 64 denotes a shuttle valve, respectively. Display.

Also in this embodiment, it is obvious that the same effects and effects as in the above embodiment are achieved, but will be briefly described next.

For example, when the variable choke valve 54 is operated via the direction switching valve operation device 58, the variable choke portion of the variable choke valve 54 is operated via the direction switching valve operation device 58 in the same manner. Control and adjustment are made corresponding to the opening / closing opening area of the direction switching valve 26. Therefore, the pressure flow rate supplied to the cylinder (actuator) is set to a constant flow rate corresponding to the spool stroke position of the direction switching valve regardless of the load pressure of the actuator. In addition, although the direction switching valve 26 of this embodiment consists of two valves, the said direction switching valve 26 is comprised by the center bypass type, and the flow regulating valve 50 is provided in the circuit. Since the directional control valves 26 and 26 are operated at the same time, sudden changes in pressure and flow rate do not occur in the circuit, and thus the metering characteristics are not impaired.

6 shows another embodiment of a control circuit according to the present invention. In the embodiment shown in Fig. 5, the flow regulating valve is constituted by a flow regulating valve having a pressure compensating means having a variable spring load means.

That is, in FIG. 6, the flow regulating valve 70 is comprised from the pressure compensation valve 78 provided with the variable spring load means 72. As shown in FIG. In the present embodiment, the variable spring load means 72 is constituted by interposing a piston 74 between both springs 76a and 76b, and a fixed choke in the center bypass flow path 30. 80 is inserted. In such a configuration, the pressure compensation valve 78 of the flow regulating valve 70 is operated in correspondence with the direction switching valve 26 via the direction switching valve operating device 58, and in this way, the pressure compensation valve Reference numeral 78 is controlled so as to correspond to the opening and closing opening area of the center bypass passage 28 of the directional control valve 26 via the variable spring load means 72. Therefore, also in this embodiment, it is obvious that the same operation and effect as in the case of the embodiment shown in FIG. 5 are achieved, and thus the detailed description thereof will be omitted.

As mentioned above, although this invention was demonstrated about the suitable Example, this invention is not limited to these Examples, A various design change is possible in the range which does not deviate from the mind of this invention.

As described above, the load pressure compensation pump discharge flow rate control circuit according to the present invention comprises a direction switching valve having a center bypass type, and at the time of spool stroke, a bypass flow rate passing through the center bypass passage is provided. It is configured to control the constant flow rate corresponding to the spool stroke position through the flow regulating valve and to set the predetermined minimum flow rate even when the spool is neutral. It can be set to a constant flow rate corresponding to the stroke position. That is, load pressure compensation can be reliably achieved.

In addition, the generation of cavitation and surge pressure can be suppressed, the response delay of the pump can be suppressed, and the apparatus can be constructed with a relatively simple structure.

Claims (8)

A center bypass valve for switching the drive direction of the actuator by the variable displacement pump, the discharge oil of the variable displacement pump, and a center bypass valve installed downstream of the center bypass passage of the center bypass valve. A flow rate adjustment valve for controlling the pass flow rate, and a pilot signal generating means for controlling the discharge flow rate of the variable displacement pump provided on the lower oil side of the flow rate adjustment valve, the flow rate adjustment valve being in the center bypass type direction. The pilot signal drawn from the pilot signal generating means is set so as to be controlled to correspond to the opening / closing opening area of the center bypass passage of the switching valve, and the discharge flow rate of the variable capacity pump is the center bypass type directional switching valve. Pressure compensating pump discharge flow rate control circuit, characterized in that the pump is set to a minimum value when the spool is neutral. 2. The flow rate adjustment valve of claim 1, wherein the opening degree of the on-off valve is set so that the differential pressure between the upstream side pressure and the downstream side pressure of the center bypass passage of the center bypass type direction switching valve and the spring of the compression spring are formed. Load pressure compensation pump discharge flow rate control circuit controlled by force. 2. The load pressure compensation pump discharge flow rate control circuit according to claim 1, wherein the flow rate adjustment valve is made of a flow rate adjustment valve having a pressure compensation means having a variable choke for generating a differential pressure, and which controls the opening degree of the variable choke by an external signal. . The load pressure compensation pump discharge flow control circuit according to claim 3, wherein the external signal for controlling the opening degree of the variable choke is a switching valve operation signal of the center bypass type direction switching valve. The flow regulating valve according to claim 1, wherein the flow regulating valve comprises a flow regulating valve having a pressure compensating means having a variable spring load means for generating a differential pressure, and a load pressure compensation for controlling the spring load of the variable spring load means by an external signal. Pump discharge flow control circuit. The load pressure compensation pump discharge flow control circuit according to claim 5, wherein the external signal for adjusting the spring load of the variable spring load means is a switching valve operation signal of a center bypass type direction switching valve. The load pressure compensation pump discharge flow rate control circuit according to claim 1, wherein the pilot signal generating means comprises a pressure generating device and draws a pilot signal from an upstream side of the pressure generating device to control the variable displacement pump negatively. 2. The pilot signal generating means according to claim 1, wherein the pilot signal generating means comprises a pilot signal pressure pumping device, and while operating a center bypass type direction switching valve by a pilot signal drawn from the pumping device, the maximum pump of the pilot signal is generated. A load pressure compensation pump discharge flow rate control circuit that draws out a pilot signal for discharge flow rate control to positively control a variable displacement pump.