Fluid operated pump displacement control system

Claim 1

A fluid operated pump displacement control system comprising: (a) a prime mover having a plurality of output conditions having difference output torque characteristics; (b) at least one variable displacement pump driven by the prime mover for supplying fluid under pressure to actuator means; (c) a fixed displacement pump; (d) a servomechanism comprising: (1) a servoactuator section operatively coupled to the variable displacement pump for varying the per cycle displacement thereof in response to fluid pressure from the fixed displacement pump, said servomechanism further including: (a) a housing; and (b) a servopiston in said servoactuator section slidably mounted in said housing so as to define a pair of opposed fluid chambers and operatively coupled to the variable displacement pump for varying the displacement thereof; (2) a servovalve section for controlling communication between the fixed displacement pump and the servoactuator section of the servomechanism, a servovalve spool slidably mounted in said housing for placing said fixed displacement pump in and out of communication with a selected one of the fluid chambers on the opposite sides of said servopiston; and (3) a control section operated by fluid pressure for controllably actuating the servovalve section, said control section including control piston means mounted in said housing for sliding motion in response to fluid pressure actuation under the control of the torque control valve; and a control lever having a pair of opposite ends operatively engaged with said servopiston and with said servovalve spool and medially pivoted to said control piston means for moving said servovalve spool in response to the movement of said control piston means in order to cause displacement of said servopiston in a manner controlled in accordance with the movement of said control piston means; (4) the servoactuator section, servovalve section and control section of the servomechanism being further structurally and functionally interrelated so that the controlled fluid pressure actuation of the control section results in a controlled change in the displacement of the variable displacement pump; (e) a torque control valve for controllably actuating the control section of the servomechanism by fluid pressure from the fixed displacement pump in order to correspondingly vary the displacement, and therefore the torque requirement, of the variable displacement pump; and (f) control means for sensing the output condition in which the prime mover operates and for actuating the torque control valve so as to cause the same to control the torque requirement of the variable displacement pump in accordance with the sensed output condition of the prime mover, thereby making it possible to make utmost use of the output torque of the prime mover in the entire speed range thereof.