JPS6235522B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic control device mainly used for agricultural machinery.
The first hydraulic control circuit includes a first hydraulic control circuit that controls the operation of a hydraulic actuator, and a second hydraulic control circuit that controls the operation of a second hydraulic actuator that operates at a lower operating pressure than the first hydraulic actuator. Connect the position control valve to
The position control valve is automatically switched based on the detection result that the first hydraulic actuator has been operated by an amount corresponding to the operation amount of the human operating tool that operates the position control valve, and the operation of the first hydraulic actuator is stopped. A pressure oil supply path to this position control circuit is connected to a neutral oil drain path of a control valve that operates the second hydraulic actuator, so that the second hydraulic actuator is connected to the first hydraulic actuator. The present invention relates to a hydraulic control device configured to operate preferentially.

According to the above-mentioned hydraulic control device, by simply operating the manual operating tool by an arbitrary amount, the first
It is possible to operate the hydraulic actuator only by an amount corresponding to its operation amount and maintain it in that state. For example, in the agricultural tractor shown in FIG. 1, the lift arm 5 for raising and lowering the work equipment is driven by the hydraulic cylinder 4 The frame 6 for attaching an auxiliary work device installed on the rotary tilling device 3 connected and supported by the lift arm 5 is configured to be movable up and down by a hydraulic cylinder 8, and the two hydraulic There is one in which the lift arm 5 and the auxiliary working device mounting frame 6 can be freely adjusted using operating levers 9 and 10. In this case, the operating pressure of the lift arm hydraulic cylinder 4 is high and the operating pressure of the frame hydraulic cylinder 8 is low, and therefore two types of relief valves with different operating pressures are required in the hydraulic control circuit.

Therefore, in order to simplify the circuit configuration by reducing the number of relief valves to one, a variable relief valve that can switch the relief operating pressure between high and low levels is used. Possible configurations include a configuration in which the lift arm is switched to high and low levels in conjunction with the operation of a control lever for the lift arm, or a configuration in which the lift arm is switched to high and low levels in conjunction with the operation of a control lever for a position control valve that controls the position of the hydraulic cylinder for the lift arm.

However, according to the former configuration, when the frame elevation control valve is in the neutral position, the relief operating pressure is always set to high pressure regardless of whether the lift arm hydraulic cylinder is operated. The drawbacks are that the pump driving load is large and the pressure loss is also large. According to the latter configuration, the operating lever for the position control valve is operated by an arbitrary amount and held at that position, so that the hydraulic cylinder for the lift arm is The position control valve is automatically switched based on the detection result that the lift arm has been operated by an amount corresponding to the amount of operation, and the operation of the lift arm hydraulic cylinder is stopped without the need to return the operating lever to its original position. Therefore, the relief operating pressure of the variable relief valve remains switched to a high pressure, and if the frame elevation control valve is operated in this state, there is a risk that high-pressure hydraulic oil will be supplied to the frame elevation hydraulic cylinder.

The present invention has been made in view of the above circumstances, and allows the relief operating pressure to be changed to high pressure only when high-pressure hydraulic oil is required, while minimizing the drive load and pressure loss of the pump. In order to simplify the circuit structure, we introduced a pilot-type variable relief valve that switches the relief operating pressure between high and low levels by changing the relief spring load, and also ensured that the automatic switching of the operating pressure of this relief valve was carried out appropriately. , it is possible to obtain relief operating pressures suitable for each of the first and second hydraulic actuators.

Embodiments of the present invention will be described below based on the drawings.

Figure 1 shows the state of rice plowing work, with tractor 1
A rotary tiller 3 connected to the rear part of the tiller 3 by a two-point linkage mechanism 2 is supported by a lift arm 5 driven by a single-acting hydraulic cylinder 4 so as to be raised and lowered by its own weight. A pair of left and right ground tail wheels 7 are attached to a frame 6 for attaching an auxiliary working device which is attached to the frame 6 so as to be vertically swingable, and the frame 6 is configured to be vertically driven by a double-acting hydraulic cylinder 8.

The lift arm hydraulic cylinder 4 is position-controlled so as to automatically stop when the lift arm 5 is moved up and down to a height corresponding to the operating position of a lever 9, which is an example of a human operating tool provided beside the driver's seat of the tractor 1. , and a hydraulic cylinder 8 for the tail wheel.
is telescopically driven and hydraulically locked by switching between three positions of another lever 10 provided on the side of the driver's seat, and these hydraulic cylinders 4 and 8 are connected to one control valve unit 11.

FIG. 2 shows a hydraulic control circuit for both hydraulic cylinders 4 and 8. The control valve unit 11 includes a frame lifting valve 12 which can be switched to three positions by the lever 10, and a position control link mechanism 13.
a position control valve 14 operated via;
A drench exhaust valve 15 that operates integrally with this valve 14, an unload valve 16 that operates in conjunction with switching of the position control valve 14, and a main relief valve 17 are incorporated. The frame lifting/lowering valve 12 is connected in series to the position control circuit so that frame lifting/lowering operation takes priority.

The lift arm 5 and the position control link mechanism 13 are connected by a feedback link 18, and the lever 9 is raised by operating it in the U direction, and lowered by operating it in the D direction. Further, numeral 19 in the figure is a check valve for preventing backflow provided in the pressure oil supply path to the lift arm hydraulic cylinder 4.

The spring 20 for setting the operating pressure of the main relief valve 17 is supported by a piston 21 that is displaced by pilot pressure, and is configured to switch to a high relief operating pressure when the pilot pressure is applied.
The cylinder 2 that supported this piston 21
A pilot oil passage 23 led out from 2 is connected to a pilot oil passage 24 for closing and operating the unload valve 16.

In addition, FIG. 3 shows the specific structure of the control unit 11 having the above configuration, and in the figure, P indicates a pump port, a indicates a connection port to the hydraulic cylinder 4 for lift arm, and b and c indicate hydraulic cylinders for lifting and lowering the frame. 8
It is a connection port to.

According to the above configuration, when the unload valve 16 is not closed, that is, when the lift arm hydraulic cylinder is not being driven to supply pressure oil, the operating pressure of the relief valve 17 is set low; It is set to a value suitable for the frame lifting/lowering hydraulic cylinder 8 (for example, 55 kg/cm ² ). Then, when the position control valve 14 is switched to the raised position, pressure is built up in the pilot oil passage 24, the unload valve 16 is closed, and pressure oil is supplied to the hydraulic cylinder 4, the spring receiver 21 is displaced by the pilot pressure. and is switched to a high relief operating pressure, and this operating pressure is set at a value suitable for the hydraulic cylinder 4 (for example, 135 kg/cm ² ).

Furthermore, when the position control valve 14 is switched from the hydraulic cylinder extension drive position (lift arm raised position) to the neutral position (lift arm stop position), the pressure oil in the pilot oil passage 24 leading to the unload valve 16 is increased. An underlap portion 25 is formed in the spool land 14a so that the discharge can be carried out to the tank side while applying resistance, so that the opening/closing operation of the unload valve 16 in response to the operation of the position control valve 14 is not delayed, that is, position control valve 14 without impairing the responsiveness of the entire position control circuit.
When the hydraulic cylinder is about to return from the extended drive position to the neutral position, the pressure in the pilot oil passages 23, 24 is quickly reduced, and the pilot oil passages 24,
23 is maintained at a high pressure to prevent the piston 21 from returning poorly.

That is, in order to quickly open and close the unload valve 16 in response to the operation of the position control valve 14 without the pilot oil passages 23 and 24 communicating with the tank side passage and the pump side passage at the same time, the position control valve The size of the spool land 14a for the 14 pilot oil passages 23 and 24 is formed to the minimum necessary size, and the tank side passage is closed at the same time as the pilot oil passages 23 and 24 communicate with the pump side passage, and the tank side passage is closed. It is desirable to configure the pump side flow path so that it is closed at the same time as it communicates with the side flow path, but even in this case, the pressure in the pilot oil paths 23 and 24 can be reliably lowered to quickly open the unload valve 14. In order to operate, it is necessary to operate the spool by a certain amount so that the pilot oil passages 23 and 24 are reliably communicated with the tank side passage even after the pump side passage is closed.

In contrast, according to the present invention, an underlap portion 25 is formed in the spool land 14a so that when the position control valve 14 is switched from the cylinder extension drive position to the neutral position, that is, the pilot oil passages 23 and 24 are Since the pressure oil in the pilot oil passages 23 and 24 is discharged into the tank side passage while applying a large resistance while the side passage is almost blocked, the flow continues after the pump side passage is closed. To suppress the delay in the opening/closing operation of the unload valve 16 with respect to the operation of the position control valve 14 caused by the constant amount operation on the spool, thereby impairing the responsiveness of the entire position control circuit. Therefore, the relief operating pressure of the variable relief valve 17 can be quickly changed to the low pressure side.

Note that the present invention is applicable not only to agricultural tractors but also to hydraulic control devices for other agricultural machinery. ), it can also be used for control devices such as Further, as the hydraulic actuator, one with an appropriate function such as a hydraulic cylinder or a hydraulic motor may be selected and used.

As explained above, the present invention introduces a variable relief valve 17 whose relief operating pressure is switched high or low depending on the pilot pressure, so that the first hydraulic actuator 4 operates at high pressure and the second hydraulic actuator 4 operates at low pressure.
The relief operating pressure suitable for each hydraulic actuator 8 can be automatically switched and set using one relief valve 17, and the relief operating pressure is switched to the high pressure side only when the first hydraulic actuator 8 is operated. , the structure could be simplified while minimizing the drive load and pressure loss of the pump, but especially when the position control valve 14 that controls the first hydraulic actuator 4 returns from the actuator drive position to the neutral position. The position control valve eliminates the disadvantage that the pilot pressure for switching the relief operating pressure is maintained high due to the surge pressure generated, and the switching of the relief operating pressure to the low pressure side is delayed, without impairing the responsiveness of the entire position control circuit. This problem can be solved with a simple configuration of just forming an underlap part 25 for absorbing surge pressure in the spool land 14a of 14, and automatic switching between high and low relief operating pressures can be performed accurately and quickly in conjunction with the operation of the position control valve 14. It became like that.

[Brief explanation of the drawing]

The drawings show an embodiment of the hydraulic control device according to the present invention, in which Fig. 1 is an overall side view of an agricultural tractor in a wet plowing state, Fig. 2 is a hydraulic circuit diagram, and Fig. 3 is a longitudinal developed view of the hydraulic unit. FIG. 4 is an enlarged view of section A in FIG. 3. 4...First hydraulic actuator, 5...Lift arm, 6...Auxiliary work device mounting frame, 8...
...second hydraulic actuator, 9...human operating tool,
12... Control valve, 14... Position control valve, 14a... Spool land, 16... Unload valve, 17... Relief valve, 23, 24
...Pilot oil passage, 25...Underlap section.

Claims (1)

[Claims] 1. First hydraulic actuator 4 that operates at high operating pressure.
a first hydraulic control circuit that controls the operation of the first hydraulic control circuit;
a second hydraulic control circuit that controls the operation of a second hydraulic actuator 8 that operates at a lower operating pressure than the hydraulic actuator 4; a position control valve 14 is connected to the first hydraulic control circuit; The position control valve 14 is automatically switched to stop the operation of the first hydraulic actuator 4 based on the detection result that the first hydraulic actuator 4 has been operated by an amount corresponding to the operation amount of the human operating tool 9 for operating the The pressure oil supply path to this position control circuit is connected to the neutral oil drain path of the control valve 12 that operates the second hydraulic actuator 8, and the second
The hydraulic control device is configured to operate the hydraulic actuator 8 with priority over the first hydraulic actuator 4, and includes a relief valve 17 in the pressure oil supply path to the control valve 12 in the second hydraulic control circuit.
The relief valve 17 is configured as a variable relief valve that switches the spring load to high pressure by applying pilot pressure, and the pilot oil passage 23 of the relief valve 17 is connected to the position control circuit of the first hydraulic actuator 4. The unload valve 16 is connected to the pilot oil passage 24 for closing the unload valve 16 in the position control circuit, and the position control valve 14 of the position control circuit is switched to the actuator drive position and the unload valve 16 is closed by the pilot pressure. The operating pressure of the relief valve 17 is automatically and reversibly switched to the high pressure side, and when the position control valve 14 is switched from the actuator drive position to the neutral position, the pilot to the unload valve 16 is The spool land 1 of the position control valve 14 is designed so that the pressure oil can be drained with a large throttling resistance.
A hydraulic control device characterized in that an underlap portion 25 is formed at 4a to communicate the pilot oil passage 24 for valve closing operation with a tank side flow passage. 2 The first hydraulic actuator 4 is a hydraulic cylinder that drives the lift arm 5 of the agricultural tractor to move up and down, and the second hydraulic actuator 8 is a hydraulic cylinder that drives the lift arm 5 of the agricultural tractor to move up and down.
2. The hydraulic control device according to claim 1, wherein the hydraulic control device is a hydraulic cylinder that drives up and down a frame 6 for attaching an auxiliary working device installed in the auxiliary work device.