JP2000274406A - Hydraulic control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a pressure control characteristic with a reduction in cut-off range, and a dynamic characteristic at the time of switching from flow control to pressure control. SOLUTION: When pressure liquids discharged from variable delivery hydraulic pumps 4 and 5 are joined via a check valve 1 by operating a direction switching valve 6, an operating command input means 30 outputs an operating pressure command value Sp2 identically for control devices 18 and 27. At that time a pressure signal switch 15 switches each control pressure signal of the variable delivery hydraulic pumps 4 and 5 to a pressure signal of a pressure detector 7a. Thereby an increase in cut-off range due to a pressure loss of the check valve 1 and a control oscillation phenomenon due to a rapid shutoff of the same are prevented. And a head differential set switch 16 outputs an operating signal Sh2 to a control valve 9 such that a pressure P2 is controlled much lower than a pressure P1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control system for driving an industrial machine such as an injection molding machine, which comprises a plurality of variable displacement hydraulic pumps. The present invention relates to a hydraulic control system capable of controlling the pressure and flow rate of a joined hydraulic fluid.

[0002]

2. Description of the Related Art Some industrial machines require a large flow rate, and such industrial machines are generally inexpensive. Therefore, a very expensive large-sized variable displacement hydraulic pump cannot be used for an industrial machine requiring such a large flow rate. Therefore, a hydraulic system that can supply a required flow rate by combining a plurality of small or medium-sized variable displacement hydraulic pumps is being studied.

[0003] Today, the pressure and the flow rate are freely controlled by electric control so that the hydraulic circuit on the base machine side does not require a plurality of valves for controlling the pressure and the flow rate. The development of a pump system designed to reduce the cost is also being studied. However, at present, such pump systems are not generally used due to performance problems described below and difficulty in handling due to adjustment of a control system.

That is, the problem will be described with reference to FIG. FIG. 3 is a hydraulic circuit diagram showing a hydraulic control system in which a plurality of conventional variable displacement hydraulic pumps are combined. In this hydraulic control system, two variable displacement hydraulic pumps 4 and 5 are provided in a circuit, and a port 4a on the discharge side of the variable displacement hydraulic pump 4 is connected to an actuator 21.
Connected to A port. Further, the discharge-side port 5a of the variable displacement hydraulic pump 5 can be connected to the port of the actuator 21B via the direction switching valve 6.

A check valve 1 and a directional control valve 6 are connected by a flow path 23 between a discharge port 4 a of the variable displacement hydraulic pump 4 and a discharge port 5 a of the variable displacement hydraulic pump 5. Connected so that they can communicate with each other. Further, a pressure detector 7a for detecting the pressure of the discharge-side port 4a is provided, and a pressure detector 7b for detecting the pressure of the discharge-side port 5a is provided.

The displacement of the variable displacement hydraulic pump 4 is controlled by a control valve 8, and the discharge flow rate corresponding to the displacement of the variable displacement hydraulic pump 4 is detected by a flow detector 10. It is supposed to be. Similarly, the displacement of the variable displacement hydraulic pump 5 is controlled by the control valve 9, and the discharge flow rate corresponding to the displacement of the variable displacement hydraulic pump 5 is determined by the flow detector 1.
1 is detected.

In FIG. 3, reference numeral 18 denotes a control unit which controls the pressure of the discharge side port 4a output from the pressure detector 7a and the variable displacement hydraulic pump 4 detected and output by the flow rate detector 10. A discharge flow rate, a pressure command value Sp1 input from the outside (base unit), and a flow rate command value SQ1 are input,
An operation signal Sh1 is output to the control valve 8.

Similarly, in FIG. 3, reference numeral 17 denotes a control device, which is a variable displacement hydraulic pump 5 which detects the pressure at the discharge port 5a output from the pressure detector 7b and outputs the detected flow rate by the flow detector 11. , The pressure command value Sp2 and the flow command value SQ2 input from the outside, and the control valve 9
And outputs an operation signal Sh2.

In this hydraulic control system, when the pressure of the variable displacement hydraulic pump 4 or 5 is controlled, the pressure of one variable displacement hydraulic pump is controlled by the pressure of the other variable displacement hydraulic pump. When the control fluid oscillates interfering with the control or the pressure fluid discharged from the variable displacement hydraulic pump 4 flows back to the other variable displacement hydraulic pump 5 due to a difference in pressure set value or the like, the variable displacement hydraulic pump 5 In order to prevent the pressure pump 5 from being damaged, the check valve 1 is provided in the flow path 23 in the direction shown in FIG. Then, the difference between the pressure command values Sp1 and Sp2 is set such that the left side (upstream side) of the check valve 1 in FIG. 3 is controlled to be lower than the right side (downstream side) in FIG. I try to put it on.

[0010]

However, in such a conventional hydraulic control system, the individual pressure control of the variable displacement hydraulic pumps 4 and 5 is performed based on the pressures detected by the pressure detectors 7a and 7b. As described above, the pressure of the variable displacement hydraulic pump 5 on the side where the pressure is controlled to be low as described above is increased when the flow control is switched from the flow control to the pressure control as shown in FIG. Due to the pressure loss b, the check valve 1 in the flow path 23 actually acting on the load may be higher than the pressure e on the right side in FIG.

For this reason, the pressure control state is entered at a pressure c lower than the pressure command value. Therefore, the control pressure difference a provided in the variable displacement hydraulic pumps 4 and 5 is combined with the actual load at the merging. However, there is a problem that the flow rate range that acts on the surface becomes narrow (the cutoff width d becomes wide).

Further, since the variable displacement hydraulic pump 5 performs pressure control using the pressure detector 7b located downstream in the free flow direction of the check valve 1, the pressure control is switched from flow control to pressure control. When the check valve 1 is closed at the time of switching, the load volume to be controlled changes abruptly, and the control is liable to oscillate, which makes it difficult to adjust the control constant. Further, in the case where the directional switching valve 6 provided in the system is operated to supply the hydraulic pressure by using the variable displacement hydraulic pump 5 alone, the pressure at which the above-mentioned pressure difference is provided at the time of merging is obtained. Since it is necessary to change and input the command value Sp2, there is also a disadvantage that the adjustment of the base unit becomes complicated.

The present invention has been made in view of the above problems, and has been made by improving pressure control characteristics by reducing the cutoff width and improving dynamic characteristics when switching from flow control to pressure control. An object of the present invention is to make it possible to easily adjust a control constant.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention comprises a plurality of variable displacement hydraulic pumps and a plurality of control valves for respectively changing the capacity of the plurality of variable displacement hydraulic pumps. A plurality of flow rate detecting means for detecting a discharge flow rate corresponding to the capacity of each of the variable displacement hydraulic pumps; a plurality of pressure detecting means for detecting a discharge pressure of each of the variable displacement hydraulic pumps; A plurality of control devices for inputting a command value, a flow rate value detected by the flow rate detection means, and a pressure value detected by the pressure detection means and outputting an operation signal to each of the control valves; The discharge-side ports of the variable displacement hydraulic pump are connected to each other via a check valve or a check valve and a direction switching valve so that they can be joined, and the respective discharge-side ports are loaded. The hydraulic control system connected respectively, which are configured as follows.

That is, when the hydraulic pressure control system is connected to the respective ports on the respective discharge sides of the plurality of variable displacement hydraulic pumps to join the hydraulic fluids, the plurality of control devices are operated by the same control device. Operating command input means for respectively outputting the pressure command values of the above, the variable displacement hydraulic pump having a discharge-side port connected to the upstream side in the free flow direction of the check valve among the plurality of control devices. When a control device on the side that outputs an operation signal to the control valve to be controlled receives a merge operation command signal for connecting the respective ports on the respective discharge sides of the plurality of variable displacement hydraulic pumps to merge the hydraulic fluid with each other, The control pressure signals of the plurality of variable displacement hydraulic pumps are respectively detected by detecting the discharge pressure of the variable displacement hydraulic pump positioned downstream of the check valve in the free flow direction among the plurality of pressure detecting means. Do Pressure signal switching means for switching to a pressure signal of a force detection means, and such that when the merging operation command signal is inputted, the pressure on the upstream side in the free flow direction of the check valve is controlled to be slightly lower than the pressure on the downstream side. The value of the pressure signal according to the merge operation command signal is added or the pressure command value input from the operation command input means is subtracted, and the operation signal is changed to a variable displacement type liquid positioned upstream of the check valve in the free flow direction. Pressure difference setting switching means for outputting to a control valve for controlling the pressure pump.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a hydraulic circuit diagram showing one embodiment of a hydraulic control system according to the present invention.
The portions corresponding to are denoted by the same reference numerals.

This hydraulic pressure control system comprises two variable displacement hydraulic pumps 4 and 5 and the variable displacement hydraulic pumps 4 and 5.
5, two control valves 8, 9 for changing the capacity of
Flow rate detectors 10 and 11 which are two flow rate detecting means for detecting the discharge flow rate corresponding to the respective capacities of the variable displacement type hydraulic pumps 4 and 5 are provided.

The hydraulic control system comprises two pressure detecting means 7a and 7b for detecting the discharge pressures of the variable displacement hydraulic pumps 4 and 5, respectively.
There is also provided a control device 18 which inputs a pressure command value Sp2 given from the mother machine, a flow value detected by the flow detector 10 and a pressure value detected by the pressure detector 7a, and outputs an operation signal to the control valve 8. I have.

Further, a pressure command value S given from the mother machine
There is also provided a control device 27 that inputs p2, the flow value detected by the flow detector 11 and the pressure value detected by the pressure detector 7b, and outputs an operation signal to the control valve 9. This hydraulic pressure control system includes a variable displacement hydraulic pump 4.
The discharge side port 4a and the discharge side port 5a of the variable displacement hydraulic pump 5 are connected to each other via a check valve 1 and a direction switching valve 6 so that they can be joined.

Then, the port 4a on the discharge side of the variable displacement hydraulic pump 4 is connected to the actuator 21A serving as a load.
Connected to the port. Further, the port 5a on the discharge side of the variable displacement hydraulic pump 5 can be connected to the port of the actuator 21B via the direction switching valve 6.

The hydraulic pressure control system also includes a control device 1 for connecting the ports 4a, 5a on the respective discharge sides of the variable displacement hydraulic pumps 4, 5 to join the hydraulic fluids.
Operation command input means 30 for outputting the same pressure command value Sp2 for operation is provided at 8, 27 respectively.

Further, this hydraulic pressure control system includes a control device 2 which outputs an operation signal to a control valve 9 for controlling the variable displacement hydraulic pump 5 among the two control devices 18 and 27.
7, when the merging operation command signal Sco for connecting the ports 4a, 5a on the respective discharge sides of the variable displacement hydraulic pumps 4, 5 to each other and joining the pressure fluids is inputted, the variable displacement hydraulic pumps 4, 5 Each control pressure signal is used as a pressure for detecting the discharge pressure of the variable displacement hydraulic pump 4 located downstream (to the right in FIG. 1) of the pressure detectors 7a and 7b in the free flow direction of the check valve 1. A pressure signal switch 15 functioning as pressure signal switching means for switching to the pressure signal of the detector 7a is provided.

When the merging operation command signal Sco is input to the control device 27, the pressure P2 on the upstream side in the free flow direction of the check valve 1 is controlled to be slightly lower than the pressure P1 on the downstream side. The value of the pressure signal is added by the adder 16a or the pressure command value Sp2 is subtracted by the subtractor 16b to reduce the operation signal Sh2 to the variable displacement hydraulic pump 5 located upstream of the check valve 1 in the free flow direction. There is also provided a pressure difference setting switch 16 as pressure difference setting switching means for outputting to the control valve 9 to be controlled.

When the directional control valve 6 is at the switching position shown in FIG.
Since the port (not shown) of 1B is cut off from the port 5a on the discharge side of the variable displacement hydraulic pump 5, its driving is stopped. The actuator 21A is driven at a speed according to the pressure of the discharge port 4a of the variable displacement hydraulic pump 4 and the discharge flow rate. When the directional control valve 6 is moved leftward from the position shown in FIG.
1 communicates with the tank 24, and a port (not shown) of the actuator 21B communicates with the discharge-side port 5a of the variable displacement hydraulic pump 5.

Therefore, the actuator 21A is driven at a speed corresponding to the pressure of the discharge port 4a of the variable displacement hydraulic pump 4 and the discharge flow rate. The actuator 21B is also driven at a speed corresponding to the pressure of the discharge port 5a of the variable displacement hydraulic pump 5 and the discharge flow rate. That is, the pressure liquids respectively discharged from the discharge-side port 4a of the variable displacement hydraulic pump 4 and the discharge port 5a of the variable displacement hydraulic pump 5 do not merge, but are independently applied to the actuators 21A and 21B, respectively. Works.

Further, when the directional control valve 6 is moved rightward from the position shown in FIG. 1 in the same figure, a port (not shown) of the actuator 21B communicates with the tank 24 and a port on the discharge side of the variable displacement hydraulic pump 5 5a communicates with the check valve 1 of the flow path 23 to the flow path portion on the left side in FIG.

Therefore, in the flow control state in which the check valve 1 is open, the discharge side port 4a of the variable displacement hydraulic pump 4 and the discharge side port 5a of the variable displacement hydraulic pump 5 The discharged pressure liquid joins through the check valve 1 in the flow path 23, and the combined pressure liquid acts on the actuator 21A, whereby the actuator 21A
Are driven by the combined pressure liquid.

The pressurized liquids are joined to form an actuator 21
When driving A, a joint operation command signal Sco is input from a mother machine (not shown) to the control system of the hydraulic control system. Then, the operation command input means 30 controls the control device 18,
27, the same pressure command value Sp2 for operation is output.

Then, the pressure signal switch 15 transmits each control pressure signal of the variable displacement hydraulic pumps 4 and 5 to the pressure detector 7.
a, 7b on the downstream side in the free flow direction of the check valve 1 (FIG. 1).
Is switched to the pressure signal of the pressure detector 7a for detecting the discharge pressure of the variable displacement hydraulic pump 4 located on the right side (the switching position shown in FIG. 1). Therefore, the cutoff width increases due to the pressure loss of the check valve 1 and the control oscillation phenomenon caused by the rapid shutoff of the check valve 1 is eliminated.

When the merged operation command signal Sco is input to the pressure difference setting switch 16, the pressure difference setting switch 16
Is such that the value of the pressure signal is added by the adder 16a so that the pressure P2 on the upstream side in the free flow direction of the check valve 1 is slightly lower than the pressure P1 on the downstream side, or the pressure command value Sp2
Is subtracted by the subtractor 16b to obtain the operation signal Sh2 on the upstream side of the check valve 1 in the free flow direction.
Is output to the control valve 9 for controlling.

Thus, the control device 18 and the control device 2
7 can input the same pressure operation command value and the same flow rate operation command value to the controller 27a. Can be simplified.

As described above, there is no difference between the command values on the base unit side, and the pressure control at the time of merging is performed by the pressure signal of one pressure detector 7a as described above. Therefore, the pressure setting difference f for backflow prevention shown in FIG. 2 is smaller than the pressure difference a (shown by a broken line in FIG. 2) in the conventional hydraulic control system described in FIG. can do. Check valve 1
It is possible to eliminate an increase in the cutoff width due to a pressure loss such as described above.

[0033]

As described above, according to the present invention, even if the cutoff width is extremely small, it is possible to prevent the pump from being damaged by the backflow of the hydraulic fluid, and the cutoff characteristics are improved. Further, since the dynamic characteristics at the time of switching from the flow control to the pressure control can be stably performed, the control constant can be easily adjusted.

And, although a large variable displacement hydraulic pump is generally expensive, this hydraulic control system can be used without using such a large variable displacement hydraulic pump.
By using a plurality of small or medium-sized variable displacement hydraulic pumps, the hydraulic fluids discharged from the pumps are combined to drive an industrial machine or the like that requires a large flow rate, so that both the pressure and the flow rate can be controlled. .

Therefore, the hydraulic control system does not require any other control valve for controlling the pressure and the flow rate, so that the cost of the mother machine to which the hydraulic control system is connected can be reduced. In addition, since a small or medium-sized variable displacement hydraulic pump with good responsiveness is used, a hydraulic control system having better controllability than a hydraulic control system using a large variable displacement hydraulic pump is obtained. . Further, since it is not necessary to change the control command value in both the merging operation and the single operation, it is possible to easily adjust the control device on the mother device side.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of a hydraulic control system according to the present invention.

FIG. 2 is a diagram illustrating a pressure setting difference f for backflow prevention in the hydraulic control system of FIG. 1;

FIG. 3 is a hydraulic circuit diagram showing a hydraulic control system in which a plurality of conventional variable displacement hydraulic pumps are combined.

FIG. 4 is a diagram for explaining a pressure setting difference a for backflow prevention in the hydraulic control system of FIG. 3;

[Explanation of symbols]

 1: Check valve 4, 5: Variable displacement hydraulic pump 4a, 5a: Discharge port 6: Direction switching valve 7a, 7b: Pressure detector (pressure detecting means) 8, 9: Control valve 10, 11: Flow rate detector (flow rate detecting means) 15: Pressure signal switch (pressure signal switching means) 16: Pressure difference setting switch (pressure difference setting switching means) 16a: Adder 16b: Subtractor 18, 27: Control device 30: Operation command input means

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroyuki Ishikawa 2-16-46 Minami Kamata, Ota-ku, Tokyo Inside Tokimec Co., Ltd. (72) Inventor Kiyotaka Kawashima 2-16-46 Minami-Kamata, Ota-ku, Tokyo Stock F-term within the company Tokimec (reference) GG15

Claims (1)

[Claims] A plurality of variable displacement hydraulic pumps, a plurality of control valves for respectively changing the capacity of the plurality of variable displacement hydraulic pumps, and a discharge corresponding to the capacity of each of the variable displacement hydraulic pumps A plurality of flow rate detecting means for detecting a flow rate, a plurality of pressure detecting means for detecting a discharge pressure of each of the variable displacement hydraulic pumps, a given pressure command value and a flow rate value detected by the flow rate detecting means; A plurality of control devices for inputting a pressure value detected by a pressure detecting means and outputting an operation signal to each of the control valves, and connecting the discharge-side ports of the plurality of variable displacement hydraulic pumps to each other. In a hydraulic control system in which a check valve or a check valve and a direction switching valve are connected via a directional control valve so as to be able to join together and each discharge-side port is connected to a load, When connecting the respective ports on the respective discharge sides of the variable displacement hydraulic pump to join the pressure liquids, the operation command input means for outputting the same pressure command value for operation to the plurality of control devices is provided. And a control valve that outputs an operation signal to the control valve that controls the variable displacement hydraulic pump having a discharge-side port connected to an upstream side of the check valve in a free flow direction of the plurality of control devices. When the controller inputs a merging operation command signal for connecting the respective ports on the respective discharge sides of the plurality of variable displacement hydraulic pumps to join the hydraulic fluid, the control pressure of the plurality of variable displacement hydraulic pumps is controlled. A pressure signal switching means for switching a signal to a pressure signal of a pressure detecting means for detecting a discharge pressure of a variable displacement hydraulic pump located downstream of a free flow direction of the check valve among the plurality of pressure detecting means. When the merging operation command signal is input, the value of the pressure signal by the merging operation command signal is added such that the pressure on the upstream side in the free flow direction of the check valve is controlled to be slightly lower than the pressure on the downstream side. Alternatively, the pressure for outputting the operation signal to the control valve for controlling the variable displacement hydraulic pump located on the upstream side in the free flow direction of the check valve by subtracting the pressure command value input from the operation command input means. A hydraulic control system comprising a difference setting switching means.