Manual servo variable mechanism

创建于03.21

Manual servo variable mechanism

② Composition, principle and characteristics of typical variable mechanism

a. Figure o (a) of manual servo variable mechanism shows a typical structure of manual servo variable mechanism, which is composed of servo valve core 1 (connected with pull rod 8), variable piston 4 and shell 5. The effective area of the upper end of the variable piston is larger than that of the lower end. The valve sleeve 7 matched with the servo valve core is integrated with the variable piston 4. The three channels (cavities) e, F and h of the valve sleeve and the variable piston are respectively connected with the lower cavity D, the upper cavity g of the variable piston and the inner cavity of the pump body, and the inner cavity of the pump body is connected with the oil tank through the oil drain Li. When variable piston 4 moves up and down, the inclination angle of swashplate 3 changes through ball hinge 2. The hydraulic oil from the pump enters the lower chamber D of the variable piston 4 through the check valve 6, and the hydraulic pressure acts on the lower end of the variable piston 4. When the pull rod 8 connected with the servo valve core 1 does not move [the state shown in Fig. o (a)], the upper chamber g of the variable piston 4 is in a closed state, the variable piston does not move but is in a balanced state, and the inclination angle of the swash plate 3 remains unchanged.

When the servo spool L is pushed down by the pull rod 8, the upper valve port is opened, and the pressure oil in chamber D enters the upper chamber g through the port E. Because the effective area of the upper end of the variable piston is larger than the effective area of the lower end, and the downward hydraulic pressure is greater than the upward hydraulic pressure, the original equilibrium state of variable piston 4 is destroyed, and it also moves downward with the spool until the upper valve port is closed. When the variable piston moves down, the inclination of swash plate increases and the displacement of pump increases. The displacement of the variable piston is equal to the displacement of the pull rod, which also corresponds to a certain swash plate angle. When the pull rod drives the servo valve core to move upward, the lower valve port opens, the upper chamber g of the variable piston is connected with the H chamber through the channel f, the pressure of the upper chamber drops, and the variable piston moves upward under the action of the pressure oil in the lower chamber until the lower valve port is closed. The displacement of the variable piston is equal to that of the pull rod. When the variable piston moves upward, the inclination of swash plate decreases and the displacement of pump decreases. Figure o (b) shows the hydraulic principle of manual servo variable mechanism.

It can be seen from the above:

i. In the manual servo variable mechanism shown in Figure o, the pressure oil that pushes the variable piston to move comes from the pump itself, so it belongs to the internal control type; it can also be supplied by the control oil source, that is, the external control type. The same principle can also form a manual servo variable motor.

II. Although the manual servo control reduces the manual force through hydraulic amplification and can realize the displacement adjustment in operation, it still can not realize remote control.

III. If the manual servo valve in Figure o is changed into electro-hydraulic control valve (electro-hydraulic servo valve, electro-hydraulic proportional valve or electro-hydraulic digital valve), electro-hydraulic servo (or proportional or digital) control can be formed, and its displacement is proportional to the control current or pulse frequency, then remote control can be realized; if the output parameters (pump flow, pressure or motor torque, speed, etc.) are changed into The output can be fed back to form a closed-loop control, thus greatly improving the automatic control level of variable displacement pump.

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