JPH02300100A - Hydraulic control method for forklift - Google Patents

Abstract

PURPOSE:To make descending speed constant from the time of descending start by controlling a lift electromagnetic proportional valve for making change over from a lift cylinder to a tank, by means of a lift lowering current signal from a controller which receives a lift voltage signal and a load pressure signal. CONSTITUTION:A lift electromagnetic proportional valve 4 for making change over from a lift cylinder 5 to a hydraulic tank 12 is provided. A lift voltage signal from control lever 1 for generating a voltage signal having a size corresponding to an operational quantity and a load pressure signal from a hydraulic sensor 3 for detecting a load pressure of a cargo applied to the lift cylinder are inputted in a controller 2. A lift lowering current signal, for making a lift lowering speed constant independent of the load pressure at an optional operation position of a control lever 1 based on the information, is produced from the controller 2. By controlling the lift electromagnetic proportional valve 4 the lift lowering current signal, a lift lowering flow rate can be made constant regardless of the intensity of the load pressure, and inching work can be easily made.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydraulic control method applied to a working machine system of a forklift vehicle.

(Prior art) As shown in Fig. 3, in the conventional method of this kind, a control valve α9 for switching from a lift cylinder (5) to a tank (1) is operated by a control lever α.
e, and the means for keeping the descending speed constant regardless of the magnitude of the load is generally a pressure compensated light amount control valve (14).

In the diagram (6) is the relief valve, (8) is the pump, (9)
indicates the power source, α[ indicates the suction strainer, and αυ indicates the return filter.

(Problem to be Solved by the Invention) However, in the current pressure-compensated light quantity control valve I, the spool operates so that the thrust force due to the differential pressure before and after the fixed throttle valve therein and the spring force are always equal to 72 lances. The lift cylinder (5) is designed to adjust the flow rate by
In the stopped state, the differential pressure before and after the throttle is almost zero, but when the control valve (1!9) is switched to the lowering side of the lift cylinder (5), a differential pressure is generated and the spool returns to the balanced state. When the pressure changes, the pressure changes rapidly and it takes time to reach a balanced state, resulting in a response delay.

Therefore, when the lift starts descending, the instantaneous flow rate braking function of the current pressure compensated flow control valve α does not work, and the lift cylinder (5) once causes a sudden drop phenomenon, and then returns to the predetermined descending speed. There was a problem that the delicate inch leg work when lowering the lift was difficult because the lift was controlled.

The present invention has been proposed in view of the problems of the prior art, and its purpose is to provide a method in which the lift descending flow rate at the start of lift descending is constant.

(Means for Solving the Problems) In order to achieve the above object, the configuration of the present invention will be explained using FIG. 1 corresponding to an embodiment. The lift electromagnetic proportional valve (4) is switched to the lift voltage signal from the lift control lever (1), which generates a voltage signal of a magnitude corresponding to the amount of operation, and the load applied to the lift cylinder (5). It receives the load pressure signal from the hydraulic sensor (3) that detects the load pressure, and based on that information, the lift descending speed becomes constant regardless of the load pressure at any operating position of the lift control lever (1). It is characterized in that it is controlled by a lift descending current signal from a controller (2) that generates a lift descending current signal.

(Function) According to the above-described means, the lift electromagnetic proportional valve (4) is a controller that receives a lift voltage signal from the lift control lever (1) and a load pressure signal from the oil pressure sensor (3). Since it is controlled by the lift descending current signal from (2), the lift descending speed is constant.

(Example) An example of the present invention will be described below with reference to FIG.
) indicates lift control leno 2-, and the lever (1
) generates a lift lowering voltage signal according to the operation amount by the operator's operation toward the lift lowering side, and this signal is sent to the controller (2). On the other hand, the lift cylinder (
5) is provided with an oil pressure sensor (3) that detects the load pressure of the cargo on the cylinder (5), and the sensor (
The load pressure signal from 3) is also sent to said controller (2). Note that this load pressure has a correlation with the weight of the cargo loaded on the forklift, and the weight of the cargo and the load pressure can be considered to be proportional to y.

The controller (2) uses this load pressure signal and the lift lowering voltage signal as input signals, and sends a lift lowering current to the lift electromagnetic proportional valve (4) as an output signal depending on the magnitude thereof.

The output characteristic of this lift descending current is as shown in FIG. 2. The larger the Q, that is, the lift descending voltage signal, or the lower the load pressure, the larger the lift descending current of the output signal.

This lift descending current signal is generated by the lift electromagnetic proportional valve (4
) is used to control the size of the opening area of the lift spool in ), and the dog or y opening area of this current signal is proportional to y.

Here, the lift descending speed, that is, the lift descending flow rate Q, is determined by the opening area A of the spool and the orifice flow rate adjustment equation (1) in which the load pressure rπ is the parameter.

However, C: flow coefficient g; gravitational acceleration γ; unit volume weight lift descending flow rate Q is proportional to the opening area A and the square root 411- of the load pressure, and increases as the opening area A increases and as the load pressure P increases.

Conversely, if you want to keep the lift descending speed, that is, the lift descending flow rate Q, constant even if the load pressure P changes, you can change the size of the opening area A according to the magnitude of the load pressure P.
When the load pressure P becomes large, the opening area A is made small, and when the load pressure P becomes small, the opening area A is made large. Therefore, by setting the input/output characteristics of the controller (2) as shown in Figure 2 and selecting an appropriate input-output diagram according to the magnitude of the load pressure, the lift can be lowered regardless of the magnitude of the load pressure. The flow rate can be kept constant.

In addition, in the figure (aim) is the lower position solenoid 9, (4b
) is the raised position solenoid, (6) is the main circuit relief valve, (power is the pilot hydraulic pump, (8) is the main hydraulic pump, (9) is the power source, (11 is the suction strainer, 1αυ is the return filter, α side is tank, α1
indicates a pilot relief valve.

(Effect of the invention) According to the present invention, the lift electromagnetic proportional nozzle that switches from the lift cylinder to the hydraulic tank is connected to the I of the lift control lever collar, which generates a voltage signal of a magnitude corresponding to the amount of operation. ) Receives the load pressure signal from the hydraulic sensor that detects the load pressure of the load on the lift cylinder and the load pressure signal from the hydraulic sensor that detects the load pressure of the load on the lift cylinder, and based on that information, operates the lift control lever at any position regardless of the load pressure. Because it is controlled by a lift descending current signal from a controller that generates a lift descending current signal that maintains a constant lift descending speed, it is possible to maintain a constant lift descending flow rate regardless of the magnitude of load pressure, unlike conventional methods. This has the effect of eliminating the response delay of the flow rate control function and making delicate inch leg work easier when lowering the lift.

[Brief explanation of drawings]

FIG. 1 is a hydraulic circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the turnout characteristics of the controller of the present invention, and FIG. 3 is a hydraulic control circuit diagram of a conventional example. (1) Lift control lever (2) Controller (3) Oil pressure sensor (4)
... Lift electromagnetic proportional valve (5) ... Lift cylinder (L snoring ... Tank representative Patent attorney Shige Okamoto 1 person outside the kiln 1st cause)

Claims (1)

[Claims] The lift electromagnetic proportional valve that switches from the lift cylinder to the tank is controlled by the lift voltage signal from the lift control lever, which generates a voltage signal corresponding to the amount of operation, and the hydraulic sensor which detects the load pressure of the load on the lift cylinder. The lift controller receives the load pressure signal from the controller, and based on that information, generates a lift descending current signal that makes the lift descending speed constant regardless of the load pressure at any lift control lever operating position. A hydraulic control method for a forklift, characterized by controlling it using a descending current signal.