JP2538451B2 - Hydraulic circuit of industrial vehicle - 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 circuit of an industrial vehicle such as a forklift truck.

[0002]

2. Description of the Related Art Conventionally, some industrial vehicles such as forklift trucks are provided with a lift cylinder. A hydraulic circuit as shown in FIG. 3 is connected to the lift cylinder, and the hydraulic pressure discharged from the hydraulic pump a of this hydraulic circuit is supplied to the lift cylinder c via the operation valve b. .

Further, a pressure accumulator e is provided in the middle of a pipe line d connecting the operation valve b and the lift cylinder c, and the accumulator e has a range of operating pressure. It is set near the maximum load.

[0004]

However, since this type of industrial vehicle handles loads of various weights within the allowable load range, the operating pressure range of the pressure accumulator e is set near the maximum load like a conventional hydraulic circuit. However, in the case of handling a relatively light load, the pressure accumulator e does not work, and there is a problem in that the buffering effect at the time of lowering cannot be obtained. The present invention has been made for the purpose of improving the above problems, and an object of the present invention is to provide a hydraulic circuit for an industrial vehicle that can obtain a buffering effect when descending regardless of the magnitude of the load.

[0005]

In order to achieve the above object, the present invention provides a hydraulic circuit of an industrial vehicle in which the discharge pressure of a hydraulic pump is supplied from an operation valve to a lift cylinder through a pipe line. A pressure detector for detecting the pressure in the pipeline is connected in the middle of the pipeline, and a plurality of accumulators with different operating pressure ranges are connected via the switching valve, and the switching valve is operated by the pressure signal detected by the pressure detector. Is to switch.

[0006]

With the above structure, the accumulator operates from a small load to a large load, so that a buffering effect can be obtained when the load is lowered regardless of the size of the load.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described in detail with reference to the drawings shown in FIGS. FIG. 1 shows a hydraulic circuit of an industrial vehicle. In this figure, 1 is a hydraulic pump, 2 is an operating valve, and 3 is a lift cylinder. The hydraulic pressure discharged from the hydraulic pump 1 is supplied from the operation valve 2 to the bottom side of the lift cylinder 3 via the pipe line 4, and the hydraulic pressure causes a load (not shown) to move up and down.

A plurality of, for example, two pressure accumulators 7 and 8 are connected in the middle of the pipeline 4 via a pressure detector 5 for detecting the pressure in the pipeline 4 and a switching valve 6 composed of a solenoid valve. There is.
As shown in FIG. 2, one of the pressure accumulators 7 and 8 has an operating range in which the static pressure P ₂ −α at the time of no load is taken into consideration in consideration of the pressure fluctuation, and the intermediate point between the pressure at the time of no load and the pressure at the time of maximum load. It is set up to P ₁ and the other 8 is set up to the static pressure P ₃ + β at maximum load from the midpoint pressure P ₁ in consideration of pressure fluctuation.

The pressure detector 5 detects that the pressure in the pipe 4 is P ₁
Is detected and the signal is sent to the controller 9,
Based on the signal from the pressure detector 5, the controller 9 determines whether the pressure accumulator 7 to the pressure accumulator 8 connected to the pipeline 4 are connected to the pipeline 4 until now.
The switching valve 6 is controlled so as to be connected to.

The operation will now be described. When the hydraulic pressure discharged from the hydraulic pump 1 is supplied to the lift cylinder 3 via the operation valve 2, a load (not shown) is vertically moved by the lift cylinder 3 to be used for cargo handling. However, at this time, a pressure corresponding to the load is generated in the pipeline 4. When this pressure is approximately equal to or less than the midpoint P ₁ between the no-load pressure and the maximum load pressure, the pressure accumulator 7 is connected to the pipe line 4. Since the accumulator 7 has an operating pressure range set from P ₂ −α to P ₁ shown in FIG. 2, it operates even when a relatively light load is lowered, and thereby a buffering effect at the time of lowering is obtained.

When the pressure in the pipe line 4 exceeds approximately the midpoint P ₁ between the no-load pressure and the maximum load pressure, the pressure detector 5 detects this and the switching valve 6 is switched. As a result, the pressure accumulator 8 whose operating pressure range is set from P ₁ to P ₃ + β in FIG. 2 is connected to the pipe line 4, so that the pressure accumulator 8 operates for a heavy load, The buffering effect when descending can be obtained.

[0012]

As described in detail above, the present invention is provided with a plurality of pressure accumulators having different operating pressure ranges, and these pressure accumulators are switched and used according to the load. The accumulator can be operated up to the load. As a result, the cushioning effect when the load is lowered can be obtained regardless of the size of the load, so that cargo handling work can be performed safely.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a hydraulic circuit of an industrial vehicle according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an operating pressure range of a pressure accumulator.

FIG. 3 is a circuit diagram showing a hydraulic circuit of a conventional industrial vehicle.

[Explanation of symbols]

 1 Hydraulic Pump 2 Operation Valve 3 Pipeline 4 Lift Cylinder 5 Pressure Detector 6 Switching Valve 7 Accumulator 8 Accumulator

Claims (1)

(57) [Claims] 1. A hydraulic circuit of an industrial vehicle, wherein a discharge pressure of a hydraulic pump 1 is supplied from an operation valve 2 to a lift cylinder 4 via a pipe line 3, and a pipe line 3 is provided in the middle of the pipe line 3.
A pressure detector 5 for detecting the internal pressure and a plurality of pressure accumulators 7 and 8 having different operating pressure ranges are connected via a switching valve 6, and the switching valve 6 is operated by a pressure signal detected by the pressure detector 5. The hydraulic circuit of an industrial vehicle that can be switched.