JPH0617651Y2 - Break hydraulic pressure controller for forklift - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a brake fluid pressure control device used in a forklift truck for cargo handling.

[Prior art]

Conventionally, for example, as disclosed in Japanese Utility Model Laid-Open No. 62-29395, as this type, an inlet pressure on the master cylinder side is added to a piping system from a driver-operated brake master cylinder to a wheel cylinder of a brake device. By comparison, a hydraulic pressure control valve for controlling the outlet pressure on the wheel cylinder side at a pressure equal to or higher than a predetermined pressure is provided, and this hydraulic pressure control valve is provided between the inlet and the outlet and a valve device for opening and closing this valve device. It has a movable plunger and a preload spring for urging the plunger in the direction in which the valve device opens, and the plunger opposes the pressure on the outlet side in the urging direction of the preload spring. It is proposed that the pressure is received and the pressure from the lift cylinder device is supplied to change the biasing force of the preload spring with respect to the plunger.

According to this, since the braking force proportional to the load of the load placed on the lift fork can be obtained, there is an advantage that the cargo handling work in the forklift truck can be performed safely.

[Problems to be solved by the invention]

In the above proposed method, when a lift cylinder failure or a pump drive section failure occurs, the pressure from the lift cylinder device supplied to the hydraulic control valve becomes low, and the hydraulic control valve is not loaded. It will be controlled as the brake pressure at that time, and the braking force will be greatly insufficient.

The present invention has been made in view of these problems, and an object thereof is to provide a brake hydraulic pressure control device for a forklift that can obtain a sufficient braking force even in the case of a failure.

[Means of device]

In the present invention, a bypass passage that connects the inlet and the outlet of the hydraulic pressure control valve is provided, and a switching valve that is normally closed and opens when the pressure source falls below a predetermined pressure is provided in this bypass passage. It is provided.

[Action]

When the pressure of the pressure source of the lift cylinder device is not lower than or equal to the predetermined pressure, the switching valve is closed to shut off the bypass passage, and the pressure is supplied from the lift cylinder device to the hydraulic control valve. The hydraulic pressure control valve can perform control according to the load capacity, and conversely, when the pressure of the pressure source falls below a predetermined pressure, the switching valve is opened and the bypass passage connects the inlet and outlet of the hydraulic pressure control valve. Therefore, the pressure is directly supplied from the master cylinder to the wheel cylinder.

〔Example〕

 FIG. 1 is a diagram showing an embodiment of the present invention.

In the figure, a master cylinder 2 that can generate a pressure by depressing a brake pedal 1 is indicated by an inlet 3 of a hydraulic control valve 3.
A and the inlet 4A of the switching valve 4 communicate with each other, and the outlet 3 of the control valve 3
B and the outlet 4B of the switching valve 4 communicate with a wheel cylinder 5A of a front wheel (only one of the left and right is shown) brake device 5.

In this way, a brake piping system from the master cylinder 2 to the wheel cylinder 5A is formed.

The pump 7, which is driven by appropriate power, pressurizes the hydraulic fluid in the reservoir 8 and supplies it to the accumulator 9 and also supplies the pressurized fluid to the inlet 10A of the driver-operated control valve 10. The control valve 10 connects the drain port 10C to the reservoir 8 and outputs the output port 1
0B is connected to the inlet 11A of the lift cylinder device 11 and the control port 3C of the hydraulic control valve 3. And pump 7
The lift pipe system from the lift cylinder device 11 to the lift cylinder device 11 is formed independently of the brake pipe system described above. In addition, the accumulator 9 and the control valve 10
The control port 4C of the switching valve 4 is connected to the inlet 10A of the control valve 4A.

The hydraulic pressure control valve 3 includes a plunger for receiving the inlet 3A side pressure in a small area and an outlet 3B side pressure in a large area.
The plunger 3 is moved to open and close the entrance 3A and the exit 3
A valve device provided in a passage communicating with B and a spring for applying an urging force to the plunger in a direction of opening and closing the valve device, and the pressure for receiving the small area and the urging force of the spring are provided. It is generally well known that the plunger pushes the valve device in the opening direction and the pressure received in the large area pushes the plunger in the closing direction of the valve device. It can be compressed by the pressure of the control port 3C via the piston so as to increase the force.

The switching valve 4 is an on-off switching type in which the pressure of the accumulator 9 is a pilot pressure, and when the pressure of the accumulator 9 is equal to or higher than a predetermined pressure, a bypass that directly connects the inlet 3A and the outlet 3B of the hydraulic control valve 3 with each other. When the shut-off position A for shutting off the passage 12 is taken and when the pressure falls below a predetermined pressure, the bypass passage 12 takes the communicating position A for directly communicating the inlet 3A and the outlet 3B of the hydraulic pressure control valve 3.

The control valve 10 supplies pressure from the accumulator 9 or the pump 7 to the lift cylinder device 11 in response to the driver's operation to raise the fork, or from the drain port 10C to the reservoir 8 from the cylinder device 11 to the hydraulic fluid. Is discharged to lower the forks.

The operation of the above embodiment will be described below.

〔Normal〕

When a load is placed on a fork (not shown) and the control valve 10 is operated to supply a pressure to the cylinder device 11, this pressure rises to a pressure opposite to the weight of the fork itself and the load of the load placed on the fork. Then raise the fork. The pressure at this time is supplied to the control port 3C of the hydraulic control valve 3, and the decompression start pressure of the hydraulic control valve 3 is determined according to the load placed on the fork. Therefore, after that, when the brake pedal 1 is stepped on and the brake is applied while the luggage is traveling on the forks, the wheel cylinder 5A is supplied with the pressure through the hydraulic control valve 3,
Proper braking can be applied.

At this time, since a sufficiently high pressure is also accumulated in the accumulator 9 by the pump 7, the switching valve 4 is closed at the shut-off position A.
Is taking.

[At the time of failure]

When the pressure of the pressure source disappears during traveling, the pressure in the cylinder device 11 is maintained by the control valve 10, or if the mechanical lock device prevents the fork from descending, the fork itself will be lowered. Although the dangerous phenomenon is prevented, if the pressure of the cylinder device 11 is not maintained, the control port 3C of the hydraulic control valve 3 will be described.
No pressure is supplied to the control port 3C, and in particular, if the pressure of the pressure source is abnormally decreased while the fork is moved up and down while traveling, the pressure is not supplied to the control port 3C of the hydraulic control valve 3.

If no pressure is supplied to the control port 3C of the hydraulic pressure control valve 3 and the pressure in the accumulator 9 is abnormally reduced, the pressure reduction start pressure of the hydraulic pressure control valve 3 becomes the minimum value, but the switching valve 4
Is switched to the communication position B, so that when the brake is applied, the pressure of the master cylinder 2 remains as it is.
Since it can be supplied to the wheel cylinder 5A through 2, the braking force does not become insufficient even when luggage is loaded on the forks.

[Effect of device]

According to the present invention, when the pressure of the pressure source falls below a predetermined pressure due to a failure of the pressure source or the like, the switching valve is opened, and the pressure of the master cylinder is passed through a bypass passage that connects the inlet and the outlet of the hydraulic control valve. Is supplied to the wheel cylinder as it is, so that insufficient braking force will not occur.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention. 3 ... Liquid pressure control valve, 3A ... inlet, 3B ... outlet, 4 ...
... Switching valve, 7 ... Pump, 9 ... Akylumulator, 11
...... Cylinder device, 12 ...... Bypass passage.

Claims (1)

[Scope of utility model registration request] 1. A forklift having a lift piping system extending from a pressure source for generating hydraulic pressure to a lift cylinder device, the master cylinder operated by a driver and a wheel cylinder of a brake device independently of the lift piping system. In the brake piping system up to, a hydraulic pressure control valve that reduces the outlet pressure on the wheel cylinder side at a pressure higher than the inlet pressure on the master cylinder side is provided, and this hydraulic pressure control valve connects the inlet and outlet. A valve device provided between them, a movable plunger that opens and closes the valve device, a preload spring that urges the plunger in a direction in which the valve device closes, and a preload spring that is provided on the plunger. A pressure receiving surface facing the biasing direction for receiving the outlet pressure, and supplying pressure from the lift cylinder device to the plunger of the preload spring. In a forklift brake hydraulic pressure control device configured to change the urging force, a bypass passage that connects the inlet and the outlet of the hydraulic pressure control valve is provided, and the bypass passage is normally closed to close the pressure source. A brake fluid pressure control device for a forklift, which is provided with a switching valve that opens when the pressure falls below a predetermined pressure.