JP2002286002A - Hydraulic controlling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate a cylinder operated by means of load in regular speed irrespective of a scale of load. SOLUTION: A load retaining mechanism A is arranged in a main oil passage 15 connecting a control unit 1 controlling a cylinder C and an oil chamber 4 of the cylinder where loaded pressure is generated. The load retaining mechanism A is comprised of a pilot check valve 16 arranged in the main oil passage controlling an oil flow from the oil chamber of the cylinder to the control unit by means of a checking mechanism, a pilot line 19 connecting both of a pressure chamber 18 and a back pressure chamber 17 of the pilot check valve 16, a first switching means 21 in which the back pressure chamber 17 is connected to the pressure chamber 18 or a tank T in proportion to switching positions, a bypass oil passage 20 connecting both in front and in the rear of the pilot check valve, a second switching means 21 throttling the bypass oil passage or the connection of the bypass oil passage in proportion to switching positions, and a flow controlling valve 24 controlling its openness in proportion to differential pressure generated between in front and in the rear of throttling of the second switching means.

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 having a load holding mechanism for holding a cylinder in a stopped state, for use in a hydraulic working machine such as a hydraulic shovel.

[0002]

2. Description of the Related Art A conventional hydraulic control device shown in FIG. 2 is used, for example, for a hydraulic excavator. A control unit 1 is connected via a main oil passage 2 to a bottom chamber 4 of a cylinder C for moving a boom (not shown).
The control unit 1 supplies pressure oil to the bottom chamber 4 of the cylinder C and discharges return oil from the bottom chamber 4 to a tank (not shown). The control unit 1 controls the movement of the cylinder C.

A load holding mechanism 3 is connected to the main oil passage 2. The load holding mechanism 3 is provided on a pilot check valve 5 connected to the main oil passage 2, a pilot line 8 connecting the back pressure chamber 6 and the pressure chamber 7 of the pilot check valve 5, and the pilot line 8. And a pilot switching valve 9. The pilot switching valve 9 normally keeps the position shown in the figure due to the elastic force of the spring 10, and the back pressure chamber 6 of the pilot check valve.
And the pressure chamber 7. When a predetermined pilot pressure is supplied to the pilot chamber 11, the pilot switching valve 9 switches to a position on the left side in the drawing, and connects the back pressure chamber 6 and the tank T. The load holding mechanism 3 thus configured is
When the operation of the cylinder C is stopped, the pressure oil is prevented from leaking from the bottom side chamber 4.

That is, as shown in the figure, when the movement of the cylinder C is stopped and the state is maintained, the load pressure of the cylinder C is applied to the pressure chamber 7 of the pilot check valve 5 via the main oil passage 2. You are being led. Also, this pressure chamber 7
The load pressure led to the pressure is also led to the back pressure chamber 6 via the pilot switching valve 9. That is, the pressure chamber 7 of the valve body 12
In both the pressure receiving surface at
The same pressure is acting. Further, since both pressure receiving areas of the valve element 12 are equalized, the valve element 12 is
The thrust acting on is canceled. Then, only the elastic force of the spring 13 acts on the valve element 12, and the valve element 12 is firmly pressed against the seat surface by the elastic force. Therefore, when the operation of the cylinder C is stopped, the pressure oil does not leak from the bottom side chamber 4.

Next, the operation of the conventional example will be described. First, the case where the boom cylinder C is extended will be described. When pressure oil is supplied from the control unit 1 to the pressure chamber 7 of the pilot check valve 5, an upward thrust acts on the valve body 12 in the drawing. When the thrust acting on the valve body 12 exceeds the elastic force of the spring 13, the valve body 12 is pushed upward in the drawing against the spring 13. When the valve body 12 is pushed up in this way, the control unit 1 and the cylinder C communicate with each other. Therefore, pressure oil is supplied to the bottom chamber 4 of the cylinder C, and the cylinder C is extended. When the cylinder C is extended in this way, a boom (not shown) provided on the rod 14 is raised.

When the boom raised as described above is held at a predetermined position, the supply of pressure oil from the control unit 1 to the cylinder C is stopped, and the pilot switching valve 9 is switched to the right position in the drawing. . When the supply of the pressure oil is stopped, the load pressure due to the load on the boom side acts on the bottom chamber 4 of the cylinder C. Then, the load pressure is guided to the pressure chamber 7 of the pilot check valve 5 via the main oil passage 2.

When the pilot switching valve 9 is switched to the right position in the drawing as described above, the pressure chamber 7 and the back pressure chamber 6 communicate with each other. Therefore, the back pressure chamber 6 and the pressure chamber 7 have the same pressure, and the valve body 12 is pressed against the seat surface by the elastic force of the spring 13. If the valve body 12 is firmly pressed against the seat surface and the pilot check valve 5 is kept closed, the pressure oil in the bottom chamber 4 of the cylinder C does not leak to the control unit 1 side. Therefore, the position of the boom linked to the rod 14 of the cylinder C is maintained.

When lowering the boom from the above state,
The main passage 2 communicates with the tank via the control unit 1. At the same time, the pilot switching valve 9 is switched to the left side position in the drawing to make the back pressure chamber 6 of the pilot check valve 5 communicate with the tank T. When the back pressure chamber 6 of the pilot check valve 5 is communicated with the tank T in this manner, the back pressure chamber 6 becomes the tank pressure, and the valve body 12 is pushed up by the load pressure of the pressure chamber 7. Therefore, the bottom chamber 4 of the cylinder C communicates with the control unit 1, and the pressure oil in the bottom chamber 4 is supplied from the main oil passage 2 to the pilot check valve 5.
→ It is discharged to a tank (not shown) via the control unit 1. When the pressure oil in the bottom chamber 4 of the cylinder C is discharged in this manner, the cylinder C contracts and the boom descends. In other words, when lowering the boom,
The boom-side load acting on the cylinder C is used.

[0009]

In the above-mentioned conventional apparatus,
Since the cylinder C is contracted using the load acting on the boom, if the magnitude of the load acting on the boom changes, the lowering speed of the boom also changes. That is,
When the load acting on the boom is large, the load pressure acting on the cylinder C is also large, so the descent speed of the boom is fast. However, when the load acting on the boom is small,
Since the load pressure also decreases, the lowering speed of the boom decreases. As described above, since the descending speed changes according to the magnitude of the load of the boom, there is a problem that the descending speed cannot be controlled.

[0010] In addition, since the lowering speed of the boom cannot be controlled, there is the following problem. For example, if a large load is expected to act on the boom,
The maximum opening of the pilot check valve 5 is set to a small value so that the boom does not drop suddenly. However, if the setting is performed based on such a large load, when the load is small, the lowering speed of the boom becomes extremely slow, which causes a problem that the working efficiency is deteriorated. Further, if the load is too small, there is a problem that the boom cannot be lowered. The purpose of this invention is
An object of the present invention is to provide a hydraulic control device that can operate a cylinder that operates using a load at a constant speed regardless of the magnitude of the load.

[0011]

According to a first aspect of the present invention, there is provided a cylinder, a control unit for controlling the cylinder,
A main oil passage connecting the control unit and an oil chamber of the cylinder where a load pressure is generated; and a load holding mechanism provided in the main oil passage.
A pilot check valve that is provided in the main oil passage and regulates the flow from the oil chamber of the cylinder to the control unit side by a check function, a pilot line that communicates the pressure chamber and the back pressure chamber of the pilot check valve, A first switching means provided in the pilot line and communicating the back pressure chamber of the pilot check valve to the pressure chamber or the tank according to the switching position; a bypass oil passage communicating the pilot check valve before and after the main oil passage; A second switching unit that is provided between the second switching unit of the bypass oil passage and the cylinder, and is provided between the cylinder and the second switching unit that narrows the bypass oil passage according to the switching position and cuts off the communication with the bypass oil passage. And a flow control valve for controlling an opening degree according to a differential pressure generated before and after the throttle of the second switching means. Thus in a state that focus bypass oil passage, when discharging the pressurized oil from the oil chamber of the cylinder, characterized in that the arrangement for controlling the flow rate constant by the flow control valve.

According to a second aspect of the present invention, the first switching means, the second switching means, and one switching valve in the first aspect of the present invention are provided, and the switching valve is located behind the pilot check valve in the first switching position. At the same time that the pressure chamber communicates with the pressure chamber, the bypass oil passage is shut off, and in the second switching position,
The back pressure chamber of the pilot check valve is communicated with the pressure chamber, the bypass oil passage is throttled, and at the third switching position, the back pressure chamber of the pilot check valve is communicated with the tank and the bypass passage is communicated. Features.

[0013]

FIG. 1 shows an embodiment of the present invention. This embodiment is a circuit used for a hydraulic excavator, and since the configurations of a cylinder C and a control unit 1 are the same as those of the related art, the same components are denoted by the same reference numerals and detailed description thereof will be omitted. As shown in the figure, a load holding mechanism A is provided in a main passage 15 connecting the control unit 1 and the bottom chamber 4 of the cylinder C. The load holding mechanism A includes a main oil passage 1
5, a pilot check valve 16 is connected to the back pressure chamber 17 and the pressure chamber 18 of the pilot check valve 16.
And are connected by a pilot line 19.

A bypass oil passage 20 connects the front and rear of the pilot check valve 16 in the main oil passage 15, and a pilot switching valve 21 is connected to the bypass oil passage 20. This pilot switching valve 21
Are switched by the pilot pressure, and the pilot line 19 is also connected. The communication state of the pilot oil passage 19 and the bypass oil passage 20 can be controlled according to the switching position of the pilot switching valve 21. For example, when the pilot switching valve 21 is at the illustrated first switching position (a), the pilot line 19 connects the back pressure chamber 17 and the pressure chamber 18 to shut off the bypass passage 20. Also, the second switching position (b)
Then, the bypass passage 22 is communicated via the throttle 22 while maintaining the communication between the back pressure chamber 17 and the pressure chamber 18. Further, when switching to the third switching position (c), the back pressure chamber 17 is communicated with the tank T by the pilot line 19, and the bypass passage 20 is communicated without the throttle. At this time, the back pressure chamber 17 and the tank T communicate with each other via the throttle 23.

A flow control valve 24 is connected to the bypass oil passage 20 between the pilot switching valve 21 and the cylinder C. The flow control valve 24 includes one pilot chamber 24 a and the pilot switching valve 21 and the flow control valve 2.
4 and a spring 25
The pilot chamber 24b provided with
The main oil passage 15 is connected to a bypass passage 20.

Next, the operation of this embodiment will be described. First, the case where the boom cylinder C is extended will be described. When pressure oil is supplied from the control unit 1 to the pressure chamber 18 of the pilot check valve 16, an upward thrust acts on the valve body 26 in the drawing. When the thrust acting on the valve element 26 exceeds the elastic force of the spring 27, the valve element 2
6 is pushed upward in the drawing against the spring 27. When the valve body 26 is pushed up, the control unit 1
And the cylinder C communicate with each other, and the discharge oil of the pump P is directly supplied to the bottom chamber 4 of the cylinder C via the main oil passage 15. When the pressurized oil is supplied to the bottom chamber 4 of the cylinder C in this manner, the cylinder C expands and its rod 1
The boom (not shown) provided at 4 rises.

On the other hand, when holding the raised boom at a predetermined position, the supply of the pressure oil from the control unit 1 to the cylinder C is stopped. At this time, the pilot switching valve 21 is normally held at the first switching position (a). The switching operation of the pilot switching valve 21 is linked with the control unit 1. When the supply of the pressure oil is stopped as described above, the load pressure due to the load on the boom side acts on the bottom chamber 4 of the cylinder C. Then, the load pressure is guided to the pressure chamber 18 of the pilot check valve 16 via the main oil passage 15.

The pressure chamber 18 communicates with the back pressure chamber 17 via a pilot line 19. for that reason,
The load pressure led to the pressure chamber 18 is also led to the back pressure chamber 17,
The thrust acting on the valve body 26 is canceled by the load pressure. The valve 26 is firmly pressed against the seat surface by the elastic force of the spring 27. That is, the pilot check valve 16 maintains the illustrated closed state. Accordingly, communication between the bottom chamber 4 of the cylinder C and the control unit 1 is completely cut off, and the boom can maintain its raised position.

When lowering the boom from the above state, the main oil passage 15 is connected to the tank via the control unit 1. At the same time, the pilot switching valve 21 is switched to the second switching position (b), and the bypass passage 20 is communicated via the throttle 22. At this time, the back pressure chamber 17 of the pilot check valve 16 and the pressure chamber 18
And maintain a state of communication. When the bypass passage 20 is communicated as described above, the pressure oil in the bottom chamber 4 of the cylinder C is discharged to the tank T via the bypass passage 20. At this time, a differential pressure is generated before and after the throttle 22, and the upstream pressure is guided to the pilot chamber 24 a of the flow control valve 24, and the downstream pressure is guided to the pilot chamber 24 b of the flow control valve 24.

Therefore, the opening of the flow control valve 24 is adjusted so that the differential pressure generated before and after the throttle 22 is equivalent to the spring force of the spring 25, and the flow passing through the throttle 22 is kept constant. If the flow rate discharged from the bottom chamber 4 of the cylinder C is kept constant in this way, the contraction speed of the cylinder C is also controlled to be constant. Therefore, the lowering speed of the boom linked to the rod 14 of the cylinder C can be controlled to be constant regardless of the load fluctuation on the boom side. The flow rate passing through the throttle 22 is determined by the opening degree of the throttle 22 and the elastic force of the spring 25 provided on the flow control valve 24.
By adjusting the opening of the cylinder C and the elastic force of the spring 25, the lowering speed of the cylinder C can be freely set.

Further, when the pilot switching valve 21 is switched from the above state to the third switching position (c), the back pressure chamber 17 of the pilot check valve 16 becomes the tank pressure. The valve body 26 is pushed up, and the bottom chamber 4 of the cylinder C communicates with the control unit 1. Therefore, the pressure oil in the bottom chamber 4 of the cylinder C is discharged to the tank T via the main oil passage 15 → the pilot check valve 16 → the control unit 1. When the pressure oil in the bottom chamber 4 of the cylinder C is discharged through the pilot check valve 16 in this manner, the contraction speed of the cylinder C, that is, the descent speed of the boom can be increased because the throttle 22 is not provided.

On the other hand, in the conventional example, when the boom is lowered, the flow rate discharged from the bottom chamber 4 of the cylinder C is guided to the valve in the control unit 1 without any control. Therefore, when a large load acts on the boom and a large load pressure acts on the bottom side chamber 4 of the cylinder C, the valve pressure in the control unit 1 is deformed by the load pressure, or a large flow rate flows, so that the fluid force is reduced. Or increase. Due to these factors, there is a problem that a large hysteresis occurs in the relationship between the pilot pressure and the control flow rate. However, according to this embodiment, the flow control valve 2
Since the pressure compensation is performed by the control valve 4, even if the load pressure acting on the bottom chamber 4 of the cylinder C increases, a large flow rate can be prevented from flowing into the control valve 1. Therefore, adverse effects such as fluid force can be prevented.

In this embodiment, the first switching means of the present invention is constituted by the positions (a) and (c) of the pilot switching valve 21, and the (a),
(B) Although the second switching means is constituted by the position, a switching valve constituting the first switching means is provided in the pilot line 19, and a switching valve constituting the second switching means is separately provided in the bypass oil passage 20. You may. However, as in this embodiment, the first pilot switching valve 21 allows the
If the two switching means are configured, the entire apparatus can be made compact.

Further, in this embodiment, the excavator has been described as an example, but the present invention is not limited to the excavator. For example, it can be used for controlling a lift cylinder of a forklift. That is, the present invention can be used for a hydraulic working device having a structure that operates a cylinder using a load.

[0025]

According to the first aspect of the present invention, when the cylinder is operated by the load, the flow rate passing through the pilot switching valve can be kept constant by the flow control valve. The cylinder can be operated at the speed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

A load holding mechanism C cylinder 1 control unit 4 cylinder bottom oil chamber 15 main oil passage 16 pilot check valve 17 back pressure chamber 18 pressure chamber 19 pilot line 20 bypass oil passage 21 first switching means and second switching of the present invention Pilot switching valve constituting means 24 Flow control valve a First switching position b Second switching position c Third switching position

Claims (2)

[Claims] 1. A cylinder, a control unit for controlling the cylinder, a main oil passage connecting the control unit and an oil chamber of the cylinder for generating a load pressure, and a load holding mechanism provided in the main oil passage. The load holding mechanism is provided in the main oil passage, and a pilot check valve that regulates the flow from the oil chamber of the cylinder to the control unit side by a check function, and a pressure chamber and a back pressure of the pilot check valve. A pilot line communicating with the chamber, first switching means provided in the pilot line, and communicating a back pressure chamber of the pilot check valve to the pressure chamber or the tank according to a switching position; and a pilot check valve for the main oil passage. A bypass oil passage that connects the front and rear, and provided in this bypass oil passage, A second switching means for narrowing or interrupting the communication of the bypass oil passage, and a second pressure switch provided between the second switching means of the bypass oil passage and the cylinder, and a differential pressure generated before and after the second switching means is throttled. When the pressurized oil is discharged from the cylinder oil chamber with the bypass oil passage narrowed by the second switching means, the flow rate is controlled by the flow control valve. A hydraulic control device characterized in that the hydraulic control device is configured to control the hydraulic pressure. 2. A switch valve comprising: a first switching means, a second switching means, and a switching valve, which switches a back pressure chamber of a pilot check valve to a pressure chamber at a first switching position. At the second switching position, the back pressure chamber of the pilot check valve is communicated with the pressure chamber, the bypass oil passage is throttled, and the back pressure of the pilot check valve is reduced at the third switching position. The hydraulic control device according to claim 1, wherein the chamber communicates with the tank and the bypass passage communicates with the tank.