Created on:2022-02-25 10:55

Classification and introduction of electro-hydraulic proportional valve

Classification and introduction of electro-hydraulic proportional valve

Electro hydraulic proportional control valve is called proportional valve for short. It is a kind of hydraulic valve that converts the input electrical signal into force or displacement in proportion, so as to continuously control the parameters such as pressure and flow. There are two situations in which it comes into being; One is developed by simplifying the structure and reducing the accuracy of electro-hydraulic servo valve; The other is developed by replacing the manual adjusting device or ordinary electromagnet of ordinary hydraulic valve with proportional electromagnet. The following only introduces the latter case, which is the mainstream of proportional valve and can be interchanged with ordinary hydraulic valve.

The proportional valve is composed of DC proportional electromagnet and hydraulic valve. The hydraulic valve part is not different from the general hydraulic valve, while the DC proportional electromagnet is different from the electromagnet used in the general solenoid valve. The displacement output and suction output proportional to the given current can be obtained by using the proportional electromagnet. The input signal shall be processed and amplified by the electric amplifier before passing through the proportional electromagnet. Electric amplifiers are mostly made into plug-in devices, which are used together with proportional valves. According to its control parameters, proportional valves can be divided into three categories: proportional pressure valve, proportional flow valve and proportional directional valve. The following is a brief introduction to these three types of proportional valves.

1. Electro hydraulic proportional overflow valve

Replace the manual adjusting device of the direct acting overflow valve with the proportional electromagnet to become the direct acting proportional overflow valve, as shown in Figure 155. The push rod of the proportional electromagnet applies thrust to the pressure regulating spring through the spring seat. With the change of the input electric signal strength, the electromagnetic force of the proportional electromagnet will change, so as to change the compression of the pressure regulating spring and make the pressure of the top opening cone valve change with the change of the input signal. If the input signal changes continuously, proportionally or according to a certain program, the system pressure regulated by the proportional relief valve also changes continuously, proportionally or according to a certain program. Therefore, the proportional relief valve is mostly used for multi-stage pressure regulation of the system or continuous pressure control. The direct acting proportional relief valve as a pilot valve can be matched with the main valve of other ordinary pressure valves to form a pilot proportional relief valve, a proportional sequence valve and a proportional pressure reducing valve.

155

2. Electro hydraulic proportional directional valve

A direct acting proportional directional valve is formed by replacing the ordinary electromagnet in the electromagnetic directional valve with a proportional electromagnet, as shown in Figure 156. Due to the use of proportional electromagnet, the valve core can not only be transposed, but also the transposition stroke can be changed continuously or proportionally, so the flow area between the connecting oil ports can also be changed continuously or proportionally. Therefore, the proportional directional valve can not only control the movement direction of the actuator, but also control its speed.

156

3. Electro hydraulic proportional speed regulating valve

Replacing the manual adjusting device of throttle or speed regulating valve with proportional electromagnet and controlling the opening of throttle port with input electric signal can continuously or proportionally remotely control its output flow and realize the speed adjustment of executive parts. Figure 157 shows the structural principle and symbols of the electro-hydraulic proportional speed regulating valve. The throttle valve core in the figure is operated by the push rod of the proportional electromagnet. If the input electrical signal is different, the electromagnetic force is different and the force of the push rod is different. After balancing with the spring force at the left end of the valve core, there will be different throttle opening. Since the constant difference has ensured that the pressure difference before and after the throttle is a constant value, a certain input current corresponds to a certain output flow, and different input signal changes correspond to different output flow changes.

In figures 155 and 156, the front end of the proportional electromagnet is equipped with a displacement sensor (or differential transformer), which is called the stroke control proportional electromagnet. The displacement sensor can accurately measure the stroke of the electromagnet and send an electrical feedback signal to the amplifier. The electric amplifier compares the input signal with the feedback signal, and then sends a correction signal to the electromagnet to compensate the error. In this way, the interference factors such as hydrodynamic force can be eliminated and the accurate valve core position or orifice area can be maintained. This is a sign that the proportional valve has entered the mature stage.

The electro-hydraulic proportional control valve can simply realize remote control and continuous and proportional control of the force and speed of the hydraulic system, simplify the hydraulic system and save hydraulic components. Due to the use of various more perfect feedback devices and optimal design, although the dynamic performance of the proportional valve is still lower than that of the servo valve, the static performance has been roughly the same, and the price is much lower. It is a promising hydraulic control element.

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