Created on:2021-06-03 10:14

Variable mechanism of axial piston pump

Variable mechanism of axial piston pump

The type and characteristics of variable mechanism axial piston pump is easy to adjust the output flow under the condition of constant pump speed by adjusting the displacement, so as to adapt to the different flow requirements of the hydraulic system, and achieve significant energy saving effect, which is one of the advantages of piston pump compared with gear pump and vane pump.

The mechanism to adjust the parameters is called variable mechanism. When the hydraulic pump works under a certain pressure, there should be force to push the variable mechanism. This force is called external control when it is supplied by external energy, and internal control when it is generated by the hydraulic pressure of pump or motor itself. The external control variable displacement pump usually uses a set of control oil source to provide the hydraulic pressure of the variable displacement mechanism. The control oil source is not affected by the load and pressure fluctuation of the pump itself, so it is relatively stable and can realize two-way variable displacement. Internal control variable displacement pump does not need any additional pump source, but because the pump is in the zero displacement condition, there is no flow output, so the variable mechanism can not continue to move, so that the pump displacement is reversed, so that the pump will stay in the zero displacement position, that is, it can not achieve two-way variable displacement.

No matter external control or internal control, the variable mechanism of axial piston pump has many kinds of classification: according to the way of control force, it can be divided into manual control, mobile control, electric control, hydraulic control and electro-hydraulic control; according to the purpose of control regulation, it can be divided into pressure control, flow control and power control; according to the control information, it can be divided into load sensing, speed sensing and pressure sensing. In this paper, the characteristics and application fields of manual, mobile, electric, hydraulic and electro-hydraulic control variable mechanisms are briefly introduced from the angle of control force.

a. Manual variable mechanism, which is the simplest variable mechanism, usually uses the hand wheel to adjust the swash plate angle through the screw mechanism. For example, A4VSO series Ma controlled plunger pump. When adjusting, manpower must overcome all kinds of resistance of variable mechanism, and the adjusting speed is low. Because the hand control force is not big enough, it is mostly used for the load adjustment of small displacement light series pumps and the no-load adjustment of large displacement pumps. In addition, manual variable mechanism can not realize remote control. In order to adjust the displacement in operation, manual servo control can be used. The servo valve is operated by hand. Through hydraulic amplification, the variable piston drives the variable mechanism to act. A certain position of the control handle corresponds to a certain displacement of the pump. Manual servo control reduces the manual control force, but it still can not achieve remote control.

b. Motorized or electronically controlled variable mechanism variable mechanism can also be driven by other mechanisms (i.e. motorized control) or controlled by servo motor, stepping motor and other control motors (i.e. electronically controlled). For example, A4VSO series EO controlled piston pump. For the electric control form, if the output parameters of the pump (flow, pressure or motor torque, speed, etc.) are changed into electricity by sensors, the output can be fed back to form a closed-loop control. Electronic control can also realize remote control. Motorized or electronically controlled variable mechanism is suitable for fixed equipment.

c. Hydraulic control variable mechanism if the variable mechanism is driven by the controlled oil pressure through the hydraulic cylinder, it is the hydraulic control variable, which is a variable mechanism used by most straight axis swash plate pumps. For example, A4VSO series HD controlled plunger pump. There are several common arrangements of hydraulic control variable displacement mechanism: single double acting variable displacement cylinder parallel to or slightly inclined to the transmission shaft of the pump in longitudinal centralized arrangement (for medium and light series pumps); two or four smaller single acting variable displacement cylinders parallel to or slightly inclined to the transmission shaft of the pump in longitudinal decentralized arrangement (for heavy series pumps) to make full use of the space in the pump shell; transverse arrangement In the end cover (mostly used for non through shaft pump) or side cover, etc. 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.

d. The movement of the piston of the variable displacement mechanism is controlled by the electro-hydraulic servo valve or the electro-hydraulic proportional valve, which becomes the electro-hydraulic variable displacement pump. A4VSO series DFE controlled plunger pump. The variable mechanism of electro-hydraulic control has good controllability and can form different forms of feedback, but its structure is complex. The electro-hydraulic servo control can achieve a higher working frequency, but the variable mechanism of the hydraulic pump has large inertia and low structure frequency, so the electro-hydraulic servo valve can not fully play its role, the anti pollution ability is poor, and the price is expensive. The frequency response of variable mechanism controlled by electro-hydraulic proportional valve is enough. Because the proportional valve is cheap and not as sensitive to oil pollution as servo valve, its application is gradually increasing.

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