JP3307436B2 - Hydraulic control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control apparatus used for construction machines such as power shovels and for operating 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 or the like, there is a conventional hydraulic control device as shown in FIG. This figure 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 communicated via a neutral passage 1. On the neutral passage 1, two switching valves 2, 3 of a center open type, which are always in communication with the neutral passage 1 in a switching process, are provided in series, and a throttle 4 is provided upstream of the tank T. Provided.

A pilot passage 5 branches from the upstream of the throttle 4, and the pilot passage 5 is connected to a variable discharge pump P.
Is connected to a regulator 6 for controlling the discharge amount of the liquid. With this connection, 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 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. Operate to increase volume.

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 thereof, and at the downstream thereof, the operating load pressure is reduced. Are connected to actuators of a cylinder 8 and a turning hydraulic motor 9, respectively. The switching valves 2 and 3 have switching positions 2a to 2c and 3a to 3c. When the switching valves 2 and 3 are in the neutral positions 2b and 3b, respectively, the total flow rate of the variable discharge pump P is stored in the tank via the neutral passage 1. It is a center-open type that returns to T, and is always connected to the neutral passage 1 in the switching process. These switching valves 2 are switched by an operation lever such as a hydraulic joystick (not shown). Symbols 10, 11, and 20 are relief valves, respectively.
Check valve. Reference numeral 12 denotes a tank passage for guiding return oil from the switching valve to the tank T.

In the hydraulic control apparatus having such a configuration, when the switching valves 2 and 3 are set to the neutral positions 2b and 3b, the entire flow returns to the tank T through the neutral passage 1. Thus, the total discharge amount of the variable discharge pump P is
, The pressure upstream thereof increases. 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 above neutral state, the operating levers connected to the respective actuators are switched, and the switching valves 2 and 3 are switched.

For example, the switching valve 2 downstream of the variable discharge pump P
Is switched, the communication opening degree to the neutral passage 1 is reduced 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 increases, and the check valve 11 is pushed open by this pressure. When the check valve 11 is opened, communication with the hydraulic motor 9 connected to the switching valve 2 becomes possible, and the discharge flow rate from the variable discharge pump P is supplied to the hydraulic motor 9.

As described above, as the position is switched from the neutral position 2b to the switching position 2a, the supply flow rate to the hydraulic motor 9 increases, and the flow rate flowing through 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 supply flow rate 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 in this way, when the flow rate passing through the neutral flow path 1 decreases, the pressure upstream of the throttle 4 decreases, and the reduced pressure is supplied to the regulator via the pilot passage 5. Acts on 6. The regulator 6 controls the variable discharge pump P according to the low pressure.
, The variable discharge pump P operates in a direction 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 smaller than the pressure set by the regulator 6, the variable discharge pump P discharges the maximum discharge amount. Become. 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 simultaneously. In this 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, the flow rate passing through the neutral passage 1 changes in accordance with the switching amount of the switching valves 2 and 3, and the pressure upstream of the throttle 4 increases in accordance with the flow rate. When 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. It is called a negative control system or a 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, in accordance with 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 a negative control signal pressure.

[0011]

The conventional hydraulic control circuit as described above has the following problems. That is,
For example, when excavating work using the cylinder 8 as an actuator for extending and retracting the arm of a power shovel, the cylinder 8 is extended. When the cylinder 8 is extended, the cylinder 8 extends in the extension direction of the cylinder 8 due to its own weight. Counter load occurs. Because of this counter load, the cylinder 8 runs away in the extension direction, so that the flow rate on the bottom side 8a decreases and the pressure decreases. 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 is increased due to the escape of the cylinder 8 in the extending direction. SUMMARY OF THE INVENTION It is an object of the present invention to provide a hydraulic control device capable of keeping the operation speed of an actuator constant irrespective of a change in load pressure and preventing cavitation.

[0012]

According to the present invention, there is provided a hydraulic control system comprising a switching valve connected to a pump and an actuator which operates in accordance with a switching amount of the switching valve. the switching valve, set the throttle meter aperture and meter-out in one switching position
A pressure compensating valve is provided upstream or downstream of the meter-out restrictor , and this pressure compensating valve is
And a throttle chamber that maximizes the opening
Consists, the pressure downstream throttle the meter-out first
Working on the direct chamber side of the pressure compensation valve via the pilot passage
To apply the pressure upstream of the meter-out throttle to the throttle chamber side of the pressure compensating valve via the second pilot passage, and further apply the pressure downstream of the meter-in throttle to the direct chamber of the pressure compensating valve via the third pilot passage. It is configured to act on the side .

[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 amount of movement of the actuator, but the pressure upstream and downstream of the meter-out throttle is reduced by the first and second pilot passages. Acts on the pressure compensating valve via. Thereby, the pressure compensating valve controls the flow rate by changing its opening degree in accordance with the pressure from the upstream and downstream of the meter-out restrictor, and reduces the pressure difference between the upstream and downstream of the meter-out restrictor downstream of the pressure-compensating valve. Keep it constant and control the flow through the meter-out restrictor constant.

The pressure downstream of the meter-in throttle acts on the pressure compensating valve via a third pilot passage. Therefore, the pressure compensating valve changes its opening degree according to the pressure from the meter-in throttle downstream, 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 those in the conventional example, and the detailed description is omitted. Figure 1,
Reference numeral 2 denotes the first embodiment, which uses the same center open type switching valves 2 and 13 as the conventional example.
Here, in the switching valve 13 provided downstream of the neutral passage 1, a meter-in throttle 14 and a meter-out throttle 15 are provided on the switching position 13a side where the cylinder 8 is extended. FIG. 2 is an enlarged view of the switching position 2a. A meter-in throttle 14 is provided in a supply path 16 to the bottom 8a of the cylinder 8, and a meter-out throttle 15 is provided in a return path 17 of the rod 8b.

A pressure compensating valve 18 is provided upstream of the meter-out restrictor 15. This pressure compensating valve 18
In the normal state shown in the drawing, the air conditioner includes a direct chamber 18a having the maximum opening degree and a throttle chamber 18b having the maximum opening degree. The opening degree is narrowed according to the switching amount to control the flow rate. The metering-out throttle 1 is connected to the pressure compensating valve 18 via first and second pilot passages 19 and 20.
(5) The upstream and downstream pressures are applied. In other words, the pressure downstream of the meter-out restrictor 15 acts on the side of the direct-flow chamber 18a having the maximum opening through the first pilot passage 19, and the pressure upstream of the meter-out restrictor 15 is controlled via the second pilot passage 20. 18b.

Therefore, when the pressure upstream of the meter-out restrictor 15 acts, the opening of the pressure compensating valve 18 is reduced by restricting the opening thereof, and when the pressure downstream of the meter-out restrictor 15 acts, the opening thereof is widened. To increase the flow rate. As described above, the opening of the pressure compensating valve 18 is changed so as to keep the pressure at the upstream and downstream of the meter-out restrictor 15 constant, and the flow rate passing through the meter-out restrictor 15 is controlled to be constant. The meter-in throttle 1 is connected via a third pilot passage 21 to the direct communication chamber 18a side of the pressure compensating valve 18.
4 Connected to downstream. As shown in FIG. 1, the downstream side of the meter-in throttle 14 is located at the bottom side 8 of the cylinder 8.
a, this pressure is equal to the load on the cylinder 8. Thus, the meter-in aperture 14
Since the downstream pressure acts on the side of the direct chamber 18a of the pressure compensating valve 18, if the load on the cylinder 8 rises, the opening of the pressure compensating valve 18 widens, and the return oil corresponding to the load on the cylinder 8 is measured It passes through the out-aperture 15.

Further, a communication passage 22 is provided between the downstream of the third pilot passage 21 and the upstream of the pressure compensating valve 18. The communication path 22 is provided with a check valve 23 that allows only the flow from the return path 17 to the supply path 16. A throttle 24 is provided between the check valve 23 and the return path 17. The communication path 22, the check valve 23 and the throttle 24 constitute a regeneration circuit. This regeneration circuit functions to supply the return oil on the rod side 8b to the bottom side 8a. Other configurations are the same as those of the above-described conventional example.

In such a configuration, when the switching valve 13 is switched to the switching position 13a to extend the cylinder 8, the operating oil flowing from the parallel passage 7 into the supply passage 16 passes through the meter-in throttle 14 and is supplied to the cylinder 8 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 compensating valve 18 and the meter-out throttle 15 in the return path 17 and returns to the tank T via the tank passage 12. At this time,
The pressure at the upstream and downstream of the meter-out restrictor 15 acts on the pressure compensating valve 18 through the first and second pilot passages 19 and 20, and the pressure compensating valve 18 determines that the pressure at the upstream and downstream of the meter-out restrictor 15 is constant. So that the flow rate is limited.

As described above, if the flow rate passing through the meter-out restrictor 15 is controlled to be constant, for example, the cylinder 8
Even if a counter load is applied during the extension of the cylinder, the cylinder 8 does not suddenly operate, and the operation speed can be kept constant. Also, even if a counter load etc. act,
Since the cylinder 8 does not operate at a speed higher than the supplied flow rate, the flow supplied to the bottom side 8a does not decrease. Therefore, there is no pressure drop in the bottom side 8a,
No cavitation occurs. Further, when the load pressure of the cylinder 8 rises, the pressure downstream of the meter-in throttle 14 acts on the pressure compensating valve 18 and expands the opening in accordance with the load, so that the cylinder 8 has a speed corresponding to the magnitude of the load pressure. Can be activated. The above meter
The pressure downstream of the in-throttle 14 is directly applied to the pressure compensating valve 18.
And the pressure compensating valve 18 is switched by this pressure.
So that the pressure downstream of the meter-in throttle 14
And can respond sensitively. In addition, 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 set to the switching valve 1
The third embodiment is different from the first embodiment in that the third embodiment is provided in the tank passage 12 downstream and that the regeneration circuit is not provided, but the rest is the same as the first embodiment. FIG. 4 shows the third embodiment. The third embodiment is the same as the first embodiment except for the reproduction circuit in the first embodiment. FIG. 5 shows a fourth embodiment. This embodiment is a circuit using a closed center type switching valve 13. The configuration of a switching position 13a indicated by reference numeral A is the same as that of FIG.

Further, in the above-described 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 simultaneously operated, such as a hydraulic motor 9 for turning, an extra flow rate is not taken by the cylinder 8 having a lower load pressure, and the optimum operation can be performed. .

[0023]

The pressure compensating valve constantly controls the flow rate of the return oil while keeping the differential pressure between the upstream and downstream of the meter-out throttle constant, so that the actuator can always be operated at a constant speed. Thereby, for example, even when a counter load occurs when the cylinder as the actuator is extended,
The cylinder does not move suddenly, and the occurrence of cavitation can be prevented. Further, the pressure compensating valve changes its opening in accordance with the pressure from the meter-in throttle downstream, and controls the flow rate passing through the meter-out throttle, so that, for example, the operating speed corresponding to the load of the actuator Obtainable. Furthermore, the meter-in throttle downstream
The pressure directly acts on the pressure compensating valve, and this pressure
Since the force compensation valve is switched, the meter-in
Responsive to pressure downstream of the throttle.

[Brief description of the 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 an enlarged view of a switching position 13a of a switching valve 13 according to a second embodiment of the present invention.

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

FIG. 5 is a view 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 compensating valve 19 first pilot passage 20 second pilot passage 21 third pilot passage

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Haruhiko Kawasaki 1-12-1 Asamidai, Sagamihara-shi, Kanagawa Kayaba Industry Co., Ltd. Sagami Factory (72) Inventor Haruki Ikigata 1-12-1 Asamidai, Sagamihara-shi, Kanagawa No. Kayaba Industry Co., Ltd. Sagami Plant (56) References WO 89/9343 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F15B 11/05 E02F 9/22

Claims (1)

(57) [Claims] 1. 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, wherein the switching valve has a meter-in throttle and a meter-out throttle at one switching position. the door is provided, provided the pressure compensating valve upstream or downstream of the throttle meter-out
And the pressure compensating valve has its opening in the normal position.
The room consists of a direct room that maximizes
And the pressure downstream of the meter-out restrictor is
The pressure compensating valve acts on the direct chamber side through the
The pressure upstream of the meter-out throttle acts on the throttle chamber side of the pressure compensating valve via the second pilot passage, and the pressure downstream of the meter-in throttle acts on the direct chamber side of the pressure compensating valve via the third pilot passage. Hydraulic control device configured to act on