Created on:2021-06-01 09:59

Hydraulic control bidirectional variable and compound control variable

Hydraulic control bidirectional variable and compound control variable

e. The variable is controlled by hydraulic cylinder. Figure u shows the principle of hydraulic control bidirectional variable displacement pump composed of double rod variable displacement cylinder controlled by directional valve. When the three position four-way solenoid directional valve 3 is in the middle position, the two chambers of the variable cylinder are connected with the oil tank. Under the action of the return springs on both sides, the variable cylinder is balanced, and the displacement and oil suction and pressure direction of the main pump 1 remain unchanged. When the valve 3 is switched to the left or right position, the pressure oil from the external control oil source enters the left or right chamber of the variable displacement cylinder through the valves 5 and 3, and the oil returns from the other chamber, and the oil suction and discharge ports of the main pump are replaced with each other to realize bidirectional variable displacement. If the two limit positions of the variable piston are adjusted mechanically, the stroke of the variable piston in the positive and negative directions can be controlled, so the flow of the pump in the positive and negative directions can be adjusted at one time. This kind of pump is mainly used in closed hydraulic system to change direction of hydraulic cylinder or hydraulic motor.

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Simple hydraulic control can only be open-loop control, through a variety of control valves and hydraulic circuits can form a closed-loop control, forming a variety of variable displacement pumps with different functions.

f. The compound control variable diagram V shows the compound control variable pump which is controlled by electro-hydraulic proportional valve (or electro-hydraulic servo valve) and is composed of controlled quantity electric feedback. The control valve is an electro-hydraulic proportional (or servo) control two position three-way pre opening slide valve, which receives the input current from the control amplifier. The input voltage signal of the amplifier is given by the signal processing unit regulator. The regulator can set the input voltage signals UX, UQ, up and upq of variable piston position x, load flow Q, load pressure P and pump output power, and also can accept the feedback voltage signals of X, Q and P, and has the corresponding signal processing function. Usually, PID control unit and coefficient correction and compensation unit are set in the regulator to improve the comprehensive control performance of the pump.

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Using electric feedback can simplify the variable adjustment mechanism of the pump, and its working principle can only be attributed to the control effect of the control slide valve on the speed and displacement of the variable piston.

 

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