How does a Rexroth variable piston pump control variation?

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We know that achieving variable performance in a Kressler piston pump is accomplished by controlling the pump’s speed or adjusting its displacement. By adjusting the flow rate by changing the displacement V (a geometric parameter) of the hydraulic pump, the discharge flow rate of the pump changes when its speed remains constant, thereby enabling the creation of a flow-control pump. 　　Since there is always a resistive load at the pump outlet, changes in the pump outlet flow rate will affect the pump outlet pressure. Sometimes, controlling the pump’s displacement can also control its operating pressure, resulting in a pressure-controlled variable pump. It can be seen that there are a wide variety of variable control methods. In practical engineering applications, axial piston pumps are structurally the most suitable for installing various variable control mechanisms, which is why there are the most variable control methods. Vane pumps can also be equipped with several variable control mechanisms. 　　Some typical methods of variable control include the following: manual variable control, manual servo variable control, hydraulic control with manual flow limitation, hydraulic control with pressure proportional control, hydraulic control with pressure proportional control and power limitation, hydraulic control with electro-hydraulic servovalves, hydraulic control with manual servo, direct-control constant power control, direct-control hydraulic control with pressure limiting devices, pilot-controlled constant power control, pilot-controlled constant power control with pressure limiting devices, directly-mounted constant pressure variable control, separately-mounted constant pressure variable control, constant pressure variable control with relief valves, constant pressure variable control with two-stage pressure regulation, electrical control, stepper motor control, load-sensing control, speed-sensing control, constant flow control, and so on. 　　The control methods and characteristics of Rexroth variable displacement piston pumps essentially boil down to those mentioned above. In summary, regardless of the specific method or characteristic, the control principle remains the same: it involves using different approaches to adjust the speed or displacement of the Rexroth piston pump, with the goal of achieving variable displacement for this pump.