JP2007205415A - Control circuit for hydraulic actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To save energy by eliminating the need of a pump for a pilot pressure source. <P>SOLUTION: When control valves 7, 8, 9 are kept in neutral positions, a fluid from a pump P is led into a tank T via. a bleed-off passage 11. When the control valves are changed over, the working fluid is supplied into actuators. The control circuit comprises pilot primary pressure passages 17, 18 for leading a pilot primary pressure into the control valves, a high-pressure selection circuit 19 selecting the maximum load pressure of the load pressures of the actuators, and a connection passage 20 connecting the downstream side of a bleed-off valve 10 in the bleed-off passage 11 to the high-pressure selection circuit 19. When the control valves are neutral, a pressure is generated in the bleed-off passage 11, and the pressure is used as the pilot pressure source. When the actuators are controlled and the bleed-off circuit is cut off, the pressure in the high-pressure selection circuit 19 is used as the pilot pressure source. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control circuit that controls hydraulic actuators such as a boom, an arm, and a traveling motor of a power shovel.

As a circuit for controlling a hydraulic actuator of a construction machine such as a hydraulic excavator, there is a circuit as shown in Patent Document 1. In such a circuit, a control valve is provided between the main hydraulic pump and the actuator, and the supply amount and direction of the pressure oil supplied from the main pump to the actuator are controlled by the switching position of the control valve. .
A pilot passage is provided separately from the supply passage for supplying hydraulic oil from the main pump to the actuator, and the pilot pressure generated in the pilot passage is supplied to the pilot chamber according to the amount of operation of the operation lever provided in the pilot passage. The control valve is switched.
The pilot passage is connected with a pilot pump different from the main pump that supplies the working fluid to the actuator as a pilot pressure source that leads to the pilot chamber of the control valve.
JP 2003-49810 A

In the above circuit, a pilot pump, which is different from the main pump for working fluid for supplying the working fluid to the actuator, is used as a pilot pressure source for switching the control valve.
Since two pumps are used in this way, a drive source for driving the two pumps is required, and energy corresponding to that is required.

  An object of the present invention is to provide a hydraulic actuator control circuit that eliminates the need for a dedicated pump for a pilot pressure source in order to realize energy saving.

  A first invention includes a pump, a supply passage connected to the pump, and a control valve connected to the supply passage and controlling the direction and amount of the working fluid supplied to the actuator, and all the control valves are neutral. When the position is maintained, the fluid discharged from the pump is guided to the tank via the bleed-off valve provided in the bleed-off passage branched from the supply passage, and one of the control valves is switched to a position other than the neutral position. In the hydraulic actuator control circuit configured to supply the working fluid to the actuator connected to the switched control valve, the pilots for connecting the control valves in series and leading the pilot primary pressure to the control valves A primary pressure passage, a high pressure selection circuit for selecting the highest load pressure among the load pressures of the actuators connected to each control valve, and a bleed-off passage in the bleed-off passage. A connection path connecting the downstream side of the off valve and the high pressure selection circuit, the pilot primary pressure path being connected between the connection paths, and when the control valves are in a neutral state, the bleed-off A pressure is generated in the passage and used as a pilot pressure source that guides the pressure to the pilot primary pressure passage through the connection passage. On the other hand, the control valve is switched to control the actuator, and the bleed-off valve It is characterized in that it is configured as a pilot pressure source that guides the pressure of the high-pressure selection circuit to the pilot primary pressure passage through the connection path when shut off.

  The second invention is based on the first invention, and a relief valve is provided on the downstream side of the bleed-off valve, and a bypass route that bypasses the relief valve and communicates with the tank, and a second route provided in the bypass route. 1 on-off valve, and a second on-off valve provided between the connection path and the high pressure selection circuit, and when each control valve is in a neutral state, the first on-off valve is kept in a closed position to bypass the valve. A pressure is generated based on the set pressure of the relief valve in the bleed-off passage, and the pressure is used as a pilot pressure source, while the bleed-off passage is shut off in response to switching of the control valve. At the timing, the second on-off valve is opened, the high pressure selection circuit and the pilot primary pressure passage are communicated with each other via the connection path, and the pressure of the high pressure selection circuit is reduced via the pressure reduction valve to reduce the pilot pressure. source It has a feature in that the configuration of.

In the first and second aspects of the invention, as a pilot pressure source for controlling the control valve for the actuator, the pressure generated using the flow rate flowing through the bleed-off passage is used at the neutral time, and the control valve is switched. When controlling the actuator, the load pressure of the actuator is used. Therefore, it is not necessary to provide a dedicated pump as a pilot pressure source.
Therefore, a driving source for the pilot pump is not required, and energy can be saved as compared with the case where two pumps are used as in the prior art.
Particularly, since the load pressure of the actuator can be effectively used as a pilot pressure source, further energy saving can be achieved.

FIG. 1 is a control circuit for a hydraulic excavator according to an embodiment of the present invention.
As shown in FIG. 1, the control circuit C connects a pump passage 1 to a pump P driven by a motor M, and a traveling motor 2, a bucket cylinder 3, and a boom cylinder 4 are disposed downstream of the pump passage 1. Is provided. The traveling motor 2, the bucket cylinder 3 and the boom cylinder 4 correspond to the hydraulic actuator of the present invention. The pump passage 1 is branched into a communication passage 5a connected to the return passage 5 and a supply passage 6. Yes. The passages 6 a and 6 b that further branch from the supply passage 6 and the supply passage 6 are respectively provided with a motor control valve 7 that controls the traveling motor 2 and a bucket control valve 8 that controls the bucket cylinder 3. A boom control valve 9 for controlling the boom cylinder 4 is connected.

The control valve 7 is connected to the ports 2a and 2b of the motor 2 by passages 12a and 12b, the control valve 8 is connected to the ports 3a and 3b of the bucket cylinder 3 by passages 13a and 13b, and the control valve 9 is The passages 14a and 14b are connected to the ports 4a and 4b of the boom cylinder 4.
When each of the control valves 7, 8 and 9 is switched from the neutral position shown in the drawing to the left and right switching positions, the actuator connected to the control valve to be switched is driven and controlled.

  Further, a bleed-off passage 11 is branched from the supply passage 6, and a bleed-off valve 10 is provided there. A relief valve 15 is connected to the downstream side of the bleed-off valve 10 and a bypass circuit 11a that bypasses the relief valve 15 from the branch point A and communicates with the tank T is provided. Is provided with the first on-off valve 16 of the present invention. The set pressure of the relief valve 15 is Pr.

Therefore, when the bleed-off valve 10 is in the open position shown in the figure and the first on-off valve 16 is also in the open position, the fluid discharged from the pump P is tanked via the bleed-off valve 10 and the first on-off valve 16. Return to T. On the other hand, when the bleed-off valve 10 is in the open position and the first on-off valve 16 is in the closed position, the upstream pressure of the relief valve 15 is controlled to the set pressure Pr of the relief valve 15 and is set to the set pressure Pr. A corresponding flow rate passes through the bleed-off passage 11.
However, in order to secure the required flow rate to be supplied to each actuator, in this embodiment, when any of the control valves 7, 8, 9 is switched, the bleed-off valve 10 is switched to the closed position.

Each of the control valves 7, 8, 9 and the bleed-off valve 10 is an electro-hydraulic pilot switching spool valve, and the primary pressure generated in the pilot primary pressure passage 17 or 18 is supplied to the solenoid valves 7c, 8c, The pilot pressure is controlled by 9c and 10c, and the controlled pilot pressure is guided to the pilot chambers 7a, 7b, 8a, 8b, 9a, 9b and 10a to switch the spool position. However, the bleed-off valve 10 is provided with a spring 10d on the drain chamber 10b side so as to maintain the open position shown in the neutral state.
The operation of generating the primary pressure serving as the pilot pressure source in the pilot primary pressure passages 17 and 18 will be described in detail later.

In order to control the control valves 7, 8, 9 and the bleed-off valve 10, the electromagnetic valves 7c, 8c, 9c, 10c are controlled via an operating means such as an operating lever (not shown).
For example, when pilot pressure is introduced into one pilot chamber 7a of the control valve 7 and this control valve 7 is switched from the illustrated state to the left switching position, the primary pressure generated in the pilot primary pressure passage 17 is The pilot pressure is controlled by the valve 7c to guide the pilot pressure to the pilot chamber 7a. If this pilot pressure overcomes the pressing force from the other pilot chamber 7b side, it switches to the left switching position. On the contrary, if the primary pressure of the pilot primary pressure passage 18 is controlled by the electromagnetic valve 7c and led to the pilot chamber 7b, the control valve 7 can be switched to the switching position on the right side of the figure. In short, each control valve is switched to a position where the spring force acting on both sides of the spool and the pressing force in both directions by the pilot pressure are balanced.

  When the control valve 7 is switched from the neutral position shown in the drawing to the left / right switching position, the discharge fluid of the pump P travels as an actuator via the control valve 7 from the passage 6 a branched from the supply passage 6. Supplied to the motor 2. Then, the return fluid from the motor 2 is returned to the return passage 5 via the control valve 7, and the motor 2 can be driven.

Similarly, the other control valves 8 and 9 can be switched.
When the control valve 8 is switched, the working fluid is supplied from the passage 6b via the control valve 8 to the bucket cylinder 3, and the return fluid from the bucket cylinder 3 is returned via the control valve 8 to the return passage. 5 is returned to the tank T.
Further, if the control valve 9 is controlled, the boom cylinder 4 connected thereto can be controlled.
Similarly, if the bleed-off valve 10 is controlled, the total flow rate of the supply passage 6 can be controlled.

  On the other hand, all the passages 12a, 12b, 13a, 13b, 14a, 14b connected to the motor 2, the bucket cylinder 3 and the boom cylinder 4 are connected to a high pressure selection circuit 19 for selecting the highest pressure in all the passages. is doing. In this high pressure selection circuit 19, the load pressure is selected from a pair of passages connected to each actuator, and as a result, the maximum load pressure of all the actuators is selected.

Further, a connection path 20 that connects the high-pressure selection circuit 19 and the bleed-off path 11 is provided, and the pilot primary pressure paths 17 and 18 are connected to a connection point B in the connection path 20. Further, a second on-off valve 21, a pressure reducing valve 22, and a check valve 23 of the present invention are connected in the order shown in the figure between the connection path 20 and the high pressure selecting circuit 19, and the set pressure of the pressure reducing valve 22 is set to Pd. To do.
The first on-off valve 16 and the second on-off valve 21 are each switched by an external signal.

Specifically, before driving the traveling motor 2, the brake release signal output when the operator releases the brake and the operation of the operation lever for switching the other control valves 8 and 9 are started. A control signal for switching the first on-off valve 16 to the closed position is output from a controller (not shown) in conjunction with the operation signal at that time.
Further, when the controller detects that the bleed-off valve 10 is completely switched to the closed position, the controller outputs a control signal for switching the second on-off valve 21 to the open position in conjunction with the detection. To do.

On the other hand, when the bleed-off valve 10 is switched to the open position and all the control valves 7, 8, 9 are in the neutral position and the brake is applied, the first on-off valve 16 A control signal for switching to the open position is input, and a control signal for switching to the closed position is input to the second on-off valve 21.
In this embodiment, the relationship between the set value Pr of the relief valve 15 and the set pressure Pd of the pressure reducing valve 22 is Pr> Pd.

Further, a lock valve 24 is provided in the passage 14a. The lock valve 24 is a valve for preventing fluid from leaking from the port 4a when it is desired to maintain the boom position. The lock valve 24 allows only the flow from the control valve 9 to the port 4a and restricts the backflow. is there. However, when necessary, such as when the boom is contracted, it is opened by an external signal to allow backflow.
In the figure, reference numeral 25 denotes a filter. Reference numeral 26 denotes a main relief valve which prevents the pump passage 1 from becoming a high pressure that exceeds its set pressure.

The operation of this embodiment will be described below.
When it is not necessary to operate any of the actuators, as shown in FIG. 1, each of the control valves 7, 8, 9 is maintained in a neutral position, and the bleed-off valve 10 and the first on-off valve 16 are opened. The second on-off valve 21 is kept in the closed position. Thus, when all the control valves 7, 8, 9 are in the neutral position, the standby flow rate discharged by the pump P is recirculated from the bleed-off valve 10 to the tank T via the first on-off valve 16. In this state, the branch point A of the bleed-off passage 11, that is, the pressure on the upstream side of the relief valve 15 is substantially the tank pressure.

When it is necessary to switch any one of the control valves 7, 8, 9 from this state, that is, when one or more of the motor 2, the bucket cylinder 3 and the boom cylinder 4 are to be controlled, the control valve 7, A pilot pressure for switching between 8 and 9 is required.
For example, when switching the control valve 7 to drive the traveling motor 2, the operator releases the brake, and the first on-off valve 16 closes from the state shown in the figure in conjunction with the brake release signal. Switch to position. As a result, the connection between the bleed-off passage 11 and the tank T is interrupted at one end.

When fluid is discharged from the pump P in a state where the bleed-off passage 11 is disconnected from the tank T, the pressure in the bleed-off passage 11 increases. When the pressure exceeds the set pressure Pr of the relief valve 15, the relief valve 15 is opened to keep the bleed-off passage 11 at the set pressure Pr.
On the other hand, the pressure in the bleed-off passage 11 acts on the pilot primary pressure passages 17 and 18 via the connection passage 20 and the connection point B. Therefore, the control valves 7, 8, 9 and the bleed-off valve 10 can be switched using the pressure controlled by the relief valve 15 as a pilot primary pressure, that is, a pilot pressure source.

As described above, the speed of the actuator can be controlled by controlling the control valves 7, 8, 9 and the bleed-off valve 10 by using the pressure in the bleed-off passage 11 as a pilot pressure source.
When the bleed-off valve 10 is switched to the closed position, no fluid flows in the bleed-off passage 11, so that the pressure at the branch point A, that is, the bleed-off passage 11, can be maintained at the relief setting pressure Pr. Disappear. Therefore, before or simultaneously with switching the bleed-off valve 10 to the fully closed position, the second on-off valve 21 provided between the high pressure selection circuit 19 and the connection path 20 is switched to the open position.

Thus, when the second on-off valve 21 is switched to the open position, the control valves 7, 8, and 9 are switched to other than the neutral position before that. That is, any one of the traveling motor 2, the bucket cylinder 3, and the boom cylinder 4 is controlled, and a load pressure should be generated.
Therefore, the high pressure selection circuit 19 selects the highest load pressure from the passages 12a, 12b, 13a, 13b, 14a, 14b connected to the motor 2, the bucket cylinder 3, and the boom cylinder 4 as the actuators, and the highest load pressure. Acts on the connection path 20 via the second on-off valve 21.

In the connection path 20, the maximum load pressure is lowered to the relief set pressure Pd by the pressure reducing valve 22, and this set pressure Pd functions as a pilot pressure source for the pilot primary pressure passages 17 and 18 connected to the connection point B. .
In this embodiment, since the relationship between the set pressures Pr and Pd of the relief valve 15 and the pressure reducing valve 22 is Pr> Pd, the pressure of the connection path 20 is changed when the second on-off valve 21 is switched to the open position. Pd does not act on the branch point A upstream of the relief valve 15 to open the relief valve 15. That is, there is no concern that the fluid on the actuator side will flow to the tank T via the high pressure selection circuit 19, the connection path 20, and the relief valve 15.

  However, if a check valve that allows only the flow from the branch point A to the connection point B is provided between the connection point B and the branch point A in the connection path 20, the relief valve 15 and the pressure reducing valve 21 are provided. The fluid does not flow from the actuator to the tank T via the relief valve 15 even if the relationship with the set pressure is not as described above.

As described above, in the circuit of this embodiment, in the standby state, when the pressure generated using the fluid passing through the bleed-off passage 11 is used as the pilot pressure source and the flow of the bleed-off passage 11 is interrupted, The load pressure of the actuator is used as a pilot pressure source.
Therefore, unlike the conventional circuit, it is not necessary to provide a pump as a pilot pressure source for controlling the control valve separately from the fluid supply pump, thereby saving energy. Moreover, since the actuator load pressure can be effectively used as a pilot pressure source, further energy saving can be realized.

  In the above embodiment, the timing for switching the pilot pressure source from the pressure in the bleed-off passage 11 to the load pressure is set when the control of the actuator is started by the control valve, but the switching timing is not limited to this. Even if any one of the control valves 7, 8, 9 is controlled, the bleed-off valve 10 is opened if the maximum load pressure selected by the high pressure selection circuit 19 does not reach a sufficient pressure as a pilot pressure source. In this position, the pressure of the bleed-off passage 11 can be used as a pilot pressure source. Further, the pilot pressure source may be switched to the load pressure side at any timing as long as the load pressure becomes higher than the pressure required as the pilot pressure during the control of the actuator.

Further, in FIG. 1, if the electromagnetic relief valve 27 shown in FIG. 2 is used instead of the relief valve 15 provided in the bleed-off passage 11 and the first opening / closing valve 16 provided in the bypass circuit 11a, the bypass is provided. There is no need to provide the path 11a.
The electromagnetic relief valve 27 is a valve that can adjust the relief set pressure by an electromagnetic solenoid. When the set pressure is set to substantially zero at the neutral time, the electromagnetic relief valve 27 opens at a pressure close to zero, and acts in the same manner as when the first on-off valve 16 in FIG. 1 is in the open position.
In a situation where a pilot pressure source is required, if the set pressure is set to Pr by the electromagnetic solenoid, the pressure Pr can be generated as a pilot pressure source in the bleed-off passage 11. Therefore, it can function in the same manner as the circuit shown in FIG.

1 is a circuit diagram showing an embodiment of the present invention. It is the example of a change of FIG.

Explanation of symbols

P Pump T Tank 1 Pump passage 2 Motor 3 Bucket cylinder 4 Boom cylinder 5 Return passage 6 Supply passage 7 Control valve 7a, 7b Pilot chamber 8 Control valve 8a, 8b Pilot chamber 9 Control valve 9a, 9b Pilot chamber 10 Bleed-off valve 11 Bleed-off passage 11a Detour 15 Relief valve 16 First on-off valve 17, 18 Pilot primary pressure passage 19 High-pressure selection circuit 20 Connection 21 Second on-off valve 22 Pressure-reducing valve 27 Electromagnetic relief valve B Connection point

Claims (2)

  When a pump, a supply passage connected to the pump, and a control valve connected to the supply passage for controlling the direction and amount of the working fluid supplied to the actuator are maintained at the neutral position When the fluid discharged from the pump is guided to the tank via the bleed-off valve provided in the bleed-off passage branched from the supply passage, and the control valve is switched to a position other than the neutral position, the switched control is performed. In a hydraulic actuator control circuit configured to supply a working fluid to an actuator connected to a valve, each control valve is connected in series, and a pilot primary pressure passage for guiding pilot primary pressure to each control valve; A high pressure selection circuit that selects the highest load pressure among the load pressures of the actuator connected to the control valve, and the bleed-off valve downstream of the bleed-off valve. And a connection path connecting the high pressure selection circuit, and the pilot primary pressure path is connected between the connection paths, and when the control valves are in a neutral state, pressure is generated in the bleed-off path. When the pilot pressure source that guides the pressure to the pilot primary pressure passage through the connection path is controlled while the actuator is controlled by switching the control valve and the bleed off passage is blocked by the bleed off valve, A control circuit for a hydraulic actuator configured to be a pilot pressure source that guides the pressure of the high pressure selection circuit to the pilot primary pressure passage through the connection path. A relief valve is provided on the downstream side of the bleed-off valve, a bypass circuit that bypasses the relief valve and communicates with the tank, a first on-off valve provided in the bypass circuit, the connection path, and the high-pressure selection circuit, And when the control valves are in a neutral state, the bypass circuit is closed by keeping the first open / close valve in the closed position, and the relief valve is set in the bleed-off passage. A pressure based on the pressure is generated, and the pressure is used as a pilot pressure source, and at a predetermined timing until the bleed-off passage is shut off in accordance with the switching of the control valve, the second on-off valve is set to the open position to 2. The hydraulic pressure according to claim 1, wherein the high pressure selection circuit and the pilot primary pressure passage are communicated with each other through a connection path, and the pressure of the high pressure selection circuit is reduced through a pressure reducing valve to be a pilot pressure source. Actuator control circuit.

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