JPH06123303A - Oil pressure controller - Google Patents

Abstract

PURPOSE:To stabilize working speed of an actuator regardless of variation of load pressure and also prevent cavitation. CONSTITUTION:A meter-out throttle 15 and a meter-in throttle 14 are provided in one side changeover position 13a of a changeover valve 13. In an oil pressure controller formed of the changeover valve 13 connected to a pump, and an actuator connected to the changeover valve 13, and a pressure compensation valve 18 is provided upstream or downstream from the meter-out throttle 15, and pressure upstream or downstream from the meter-out throttle 15 is exerted on the pressure compensation valve 18 via first and second pilot passages 19, 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control device which is used for construction machines such as power shovels and operates a plurality of actuators with one variable discharge pump.

[0002]

2. Description of the Related Art As a hydraulic control device for controlling an actuator of a construction machine, there is a conventional hydraulic control device as shown in FIG. This drawing shows a device for controlling an actuator of a power shovel, in which a variable discharge pump P connected to an engine E as a drive source and a tank T are connected via a neutral passage 1. On the neutral passage 1, two switching valves 2 and 3 of a center open type which are always in communication with the neutral passage 1 in the switching process are provided in series, and a throttle 4 is provided upstream of the tank T. It is provided.

A pilot passage 5 branches off from the upstream side of the throttle 4, and the pilot passage 5 is connected to the variable discharge pump P.
It is connected to the regulator 6 that controls the discharge amount of. By connecting in this way, the pressure generated upstream of the throttle 4 acts on the regulator 6 via the pilot passage 5, and the regulator 6 operates according to the acting pressure. Then, the discharge amount of the variable discharge pump P changes according to the operation amount of the regulator 6. In this case, when a high pressure is generated upstream of the throttle 4, the regulator 6 operates so as to reduce the discharge amount of the variable discharge pump P. Conversely, when the pressure upstream of the throttle 4 is low, the discharge of the variable discharge pump P is reduced. It works to increase the amount.

Further, the switching valves 2 and 3 are connected in parallel to the variable discharge pump P by a parallel passage 7 branched from the neutral passage 1 at the upstream of each of them, and at the downstream thereof, a working load pressure is used. Are connected to actuators of different cylinders 8 and hydraulic motors 9 for turning. When the switching positions of these switching valves 2 and 3 are 2a to 2c and 3a to 3c and they are respectively in the neutral positions 2b and 3b, the total flow rate of the variable discharge pump P is passed through the neutral passage 1 to the tank. It is a center open type that returns to T, and is always connected to the neutral passage 1 during the switching process. These switching valves 2 are switched by an operating lever such as a hydraulic joystick (not shown). Reference numerals 10, 11, and 20 are relief valves,
It is a check valve. Reference numeral 12 is a tank passage for guiding the return oil from the switching valve to the tank T.

In the hydraulic control device having such a configuration, when the respective switching valves 2 and 3 are set to the neutral positions 2b and 3b, the total flow rate returns to the tank T through the neutral passage 1. In this way, the total discharge amount of the variable discharge pump P is reduced by
When passing through, the pressure rises upstream. And
Since this pressure acts on the regulator 6 via the pilot passage 5, the discharge amount of the variable discharge pump P is minimized. In order to operate the cylinder 8 and the hydraulic motor 9 from the neutral state as described above, the operation levers connected to the respective actuators are switched to switch the switching valves 2 and 3.

For example, the switching valve 2 downstream of the variable discharge pump P
If only is switched, the communication opening degree to the neutral passage 1 is narrowed according to the switching amount to the switching position 2a. As a result, the pressure in the parallel passage 7 branched from the neutral passage 1 rises, and the check valve 11 is pushed open by this pressure. By opening the check valve 11, communication with the hydraulic motor 9 connected to the switching valve 2 is possible, and the discharge flow rate from the variable discharge pump P is supplied to the hydraulic motor 9.

Thus, as the neutral position 2b is switched to the switching position 2a, the supply flow rate to the hydraulic motor 9 increases and the flow rate flowing to the neutral passage 1 decreases. That is, when the operation amount of the operation lever is small, the switching amount is also small, so the flow rate supplied to the hydraulic motor 9 is small and the flow rate returning from the neutral passage 1 to the tank T is large, but as the switching amount increases, The supply flow rate to the hydraulic motor 9 increases, and the return flow rate to the tank T decreases.

As the switching amount of the switching valve 2 increases, the flow rate passing through the neutral flow passage 1 decreases, and the pressure upstream of the throttle 4 decreases, and the reduced pressure is supplied to the regulator via the pilot passage 5. Act on 6. The regulator 6 controls the variable discharge pump P according to the low pressure.
The variable discharge pump P operates to increase the discharge amount.

Finally, when the flow rate to the neutral passage 1 decreases and the pressure upstream of the throttle 4 becomes lower than the set pressure of the regulator 6, the variable discharge pump P discharges the maximum discharge amount. Become. Further, this series of operations is the same when only the cylinder 8 is driven, and hydraulic oil is supplied to the bottom side 8a and the rod side 8b by the switching positions 3a and 3c of the switching valve 3. further,
In this device, since the switching valves 2 and 3 are connected in parallel to the variable discharge pump P, the cylinder 8 and the hydraulic motor 9 can be operated at the same time, but in that case, the most downstream switching of the neutral passage 1 is performed. The discharge amount of the variable discharge pump P is controlled according to the flow rate flowing from the valve 3 to the neutral passage 1.

As described above, when the flow rate passing through the neutral passage 1 changes according to the switching amount of the switching valves 2 and 3, and the pressure upstream of the throttle 4 increases according to the flow rate, the variable discharge pump P of the variable discharge pump P increases. If the discharge flow rate decreases and the pressure upstream of the throttle 4 decreases, the discharge flow rate of the variable discharge pump P increases, such that a circuit in which the pressure upstream of the throttle 4 and the discharge amount of the variable discharge pump P have a negative relationship is We call it the negative control system or the negative control system.
In other words, this negative control system is also called surplus flow control for controlling the discharge signal pressure of the variable discharge pump P, that is, the pressure upstream of the throttle 4, according to the switching amount of the switching valves 2 and 3. . And it acts on the regulator 6,
The pressure upstream of the throttle 4 is called the negative control signal pressure.

[0011]

The conventional hydraulic control circuit as described above has the following problems. That is,
For example, when the cylinder 8 as an actuator is used for expanding and contracting the arm of a power shovel for excavation work, the cylinder 8 is extended, but when the cylinder 8 extends, the cylinder 8 extends in the extension direction of the cylinder 8 due to the weight of the arm. Counter load occurs. The counter load causes the cylinder 8 to escape in the extending direction, so that the flow rate on the bottom side 8a decreases and the pressure becomes low. For this reason, there is a problem that cavitation may occur on the bottom side 8a of the cylinder 8. There is also a problem that the operating speed becomes high due to the escape of the cylinder 8 in the extension direction. An object of the present invention is to provide a hydraulic control device that can keep the operating speed of an actuator constant regardless of changes in load pressure and can prevent cavitation.

[0012]

In order to solve the above-mentioned problems, the present invention provides a hydraulic control device comprising a switching valve connected to a pump and an actuator which operates according to the switching amount of the switching valve. The switching valve is provided with a meter-in throttle and a meter-out throttle at one switching position, and a pressure compensating valve is provided upstream or downstream of the meter-out throttle so that the pressures upstream and downstream of the meter-out throttle are respectively controlled by The pressure compensating valve is made to act via the second pilot passage, and the pressure downstream of the meter-in throttle is made to act on the pressure compensating valve via the third pilot passage.

[0013]

When the switching valve is switched, the actuator operates according to the switching amount. In this case, the return oil passes through the pressure compensating valve provided at one of the switching positions and the meter-out throttle according to the movement amount of the actuator, but the pressures upstream and downstream of the meter-out throttle have the first and second pilot passages. Through the pressure compensating valve. As a result, the pressure compensation valve controls the flow rate by changing the opening degree according to the pressure from the upstream and downstream of the meter-out throttle, and controls the differential pressure between the upstream and downstream of the meter-out throttle downstream of the pressure compensation valve. Keep it constant and control the flow rate through the meter-out throttle to be constant.

The pressure downstream of the meter-in throttle acts on the pressure compensation valve via the third pilot passage. Therefore, the pressure compensating valve changes its opening degree according to the pressure from the downstream of the meter-in throttle and controls the flow rate passing through the meter-out throttle.

[0015]

1 to 5 show an embodiment of the present invention. The same reference numerals are used for the same components as in the conventional example, and detailed description thereof is omitted. Figure 1,
Reference numeral 2 shows the first embodiment, which uses the same center open type switching valves 2 and 13 as in the conventional example.
Here, in the switching valve 13 provided on the downstream side of the neutral passage 1, a meter-in throttle 14 and a meter-out throttle 15 are provided on the side of the switching position 13a for extending the cylinder 8. FIG. 2 is an enlarged view of the switching position 2a, but a meter-in throttle 14 is provided in the supply passage 16 to the bottom side 8a of the cylinder 8 and a meter-out throttle 15 is provided in the return passage 17 on the rod side 8b.

A pressure compensating valve 18 is provided upstream of the meter-out throttle 15. This pressure compensation valve 18
In the normal state shown in the figure, it is composed of a direct passage chamber 18a whose opening is maximized and a throttle chamber 18b which narrows the opening, and the flow is controlled by narrowing the opening according to the switching amount. The pressure compensating valve 18 is connected to the meter-out throttle 1 via the first and second pilot passages 19 and 20.
5 The pressures of upstream and downstream are applied. That is, the pressure downstream of the meter-out throttle 15 is made to act on the direct passage chamber 18 a side having the maximum opening degree through the first pilot passage 19, and the pressure upstream of the meter-out throttle 15 is passed through the second pilot passage 20. It acts on the 18b side.

Therefore, when the pressure upstream of the meter-out throttle 15 acts, the pressure compensating valve 18 throttles the opening to limit the flow rate, and when the pressure downstream of the meter-out throttle 15 acts, the opening is widened. Increase the flow rate. In this way, the pressure compensating valve 18 changes its opening so as to keep the pressures upstream and downstream of the meter-out throttle 15 constant, and controls the flow rate passing through the meter-out throttle 15 to be constant. The direct chamber 18 a side of the pressure compensating valve 18 is connected to the meter-in throttle 1 via the third pilot passage 21.
4 is connected to the downstream. As seen from FIG. 1, the downstream side of the meter-in throttle 14 is located on the bottom side 8 of the cylinder 8.
Since it is connected to a, this pressure is equal to the load on the cylinder 8. In this way, the meter-in diaphragm 14
Since the downstream pressure is applied to the direct passage chamber 18a side of the pressure compensating valve 18, if the load of the cylinder 8 increases, the opening degree of the pressure compensating valve 18 expands and the return oil corresponding to the load of the cylinder 8 is metered. It passes through the aperture stop 15.

Further, a communication passage 22 is provided between the downstream side of the third pilot passage 21 and the upstream side of the pressure compensation valve 18. The communication passage 22 is provided with a check valve 23 that allows only the flow from the return passage 17 in the direction of the supply passage 16, and a throttle 24 is provided between the check valve 23 and the return passage 17. The communication passage 22, the check valve 23 and the throttle 24 constitute a regeneration circuit. This regeneration circuit serves to supply the return oil from the rod side 8b to the bottom side 8a. The rest of the configuration is the same as the above-mentioned conventional example.

In such a structure, when the switching valve 13 is switched to the switching position 13a and the cylinder 8 is extended, the hydraulic oil flowing from the parallel passage 7 into the supply passage 16 passes through the meter-in throttle 14 and the cylinder 8 extends. Is supplied to the bottom side 8a, and the cylinder 8 is extended. At the same time, the flow rate of the return oil on the rod side 8b is controlled by the pressure compensation valve 18 and the meter-out throttle 15 in the return passage 17, and returns to the tank T via the tank passage 12. At this time,
The pressures upstream and downstream of the meter-out throttle 15 act on the pressure compensating valve 18 through the first and second pilot passages 19 and 20, and the pressure compensating valve 18 maintains a constant pressure upstream and downstream of the meter-out throttle 15. The flow rate is limited so that

In this way, if the flow rate passing through the meter-out throttle 15 is controlled to be constant, for example, the cylinder 8
Even if a counter load is applied during extension, the cylinder 8 does not suddenly operate and the operation speed can be kept constant. Also, even if counter load etc. acts,
Since the cylinder 8 does not operate at a speed higher than the supplied flow rate, the flow rate supplied to the bottom side 8a does not decrease. Therefore, there is no pressure drop in the bottom side 8a,
No cavitation will occur. Further, when the load pressure of the cylinder 8 rises, the pressure downstream of the meter-in throttle 14 acts on the pressure control valve 18 to widen the opening according to the load, so that the cylinder 8 is moved at a speed corresponding to the magnitude of the load pressure. Can be activated. Further, since the return oil is supplied to the bottom side 8a by the regeneration circuit, it is more effective in preventing cavitation.

FIG. 3 shows a second embodiment of the present invention. Here, at the switching position 13a of the switching valve 13, the pressure compensating valve 18 shown in the first embodiment is replaced by the switching valve 1
3 is different from the first embodiment in that it is provided in the tank passage 12 on the downstream side and in that the regeneration circuit is not provided, but the other points are the same as in the first embodiment. Further, FIG. 4 shows a third embodiment, but this third embodiment is the same as the first embodiment except that the reproducing circuit in the first embodiment is omitted. And FIG. 5 shows a fourth embodiment. Although this embodiment is a circuit using a closed center type switching valve 13, the structure of the switching position 13a indicated by the symbol A is the same as in FIG.

Further, in the above-mentioned first to fourth embodiments, the return oil is controlled by the meter-out throttle 15 to keep the moving speed of the cylinder constant. This is the same as controlling the supply flow rate to the cylinder 8. Therefore,
Even when an actuator having a higher load pressure than the cylinder 8 is actuated at the same time as the turning hydraulic motor 9, the cylinder 8 having a lower load pressure does not have an extra flow rate and can perform an optimum operation. .

[0023]

[Effect] Since the pressure compensating valve controls the flow rate of return oil by keeping the differential pressure between the upstream and downstream of the meter-out throttle constant, the actuator can always be operated at a constant speed. As a result, for example, even when a counter load is generated when the cylinder as the actuator is extended,
The cylinder does not move suddenly and cavitation can be prevented from occurring. Further, the pressure compensating valve controls the flow rate passing through the meter-out throttle by changing the opening degree according to the pressure from the meter-in throttle downstream, so that, for example, the operating speed corresponding to the load of the actuator is adjusted. Obtainable.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is an enlarged view of a switching position 13a of the switching valve 13 of FIG.

FIG. 3 is a second embodiment of the present invention and is an enlarged view of a switching position 13a of a switching valve 13.

FIG. 4 is a third embodiment of the present invention and is an enlarged view of a switching position 13a of the switching valve 13.

FIG. 5 is a diagram showing a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional device.

[Explanation of symbols]

 13 Switching valve 14 Meter-in throttle 15 Meter-out throttle 18 Pressure compensation valve 19 First pilot passage 20 Second pilot passage 21 Third pilot passage

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Fujii 8-7-24 Tsuji, Urawa-shi, Saitama Kayaba Industrial Co., Ltd. Urawa factory (72) Inventor Haruhiko Kawasaki 1-12-1, Asamizodai, Sagamihara-shi, Kanagawa Kayaba Industry Co., Ltd. Sagami Plant (72) Inventor Haruki Igata 1-12-1, Asamizodai, Sagamihara City, Kanagawa Prefecture Kayaba Industry Co., Ltd. Sagami Plant

Claims (1)

[Claims] 1. A hydraulic control device comprising a switching valve connected to a pump and an actuator that operates according to the switching amount of the switching valve, wherein the switching valve has a meter-in throttle and a meter-out throttle at one switching position. And a pressure compensating valve is provided upstream or downstream of the meter-out throttle so that the pressures upstream and downstream of the meter-out throttle act on the pressure compensating valve via the first and second pilot passages, respectively. A hydraulic control device configured such that the pressure downstream of the meter-in throttle is made to act on the pressure compensation valve via a third pilot passage.