Control system for variable displacement pumps

Claim 1

In a control system which includes a prime mover, a plurality of independently adjustable variable displacement pumps driven thereby and an independent control for selectively varying the displacement of each pump, the improvement comprising a load sensing means connected to the prime mover, the load sensing means having an output signal proportional to the load on the prime mover, means connecting the output signal to each independent control, each independent control including input means for selectively setting the displacement of the pump, the input means includes means responsive to said output signal for proportionally changing the displacement of each pump when said output signal reaches a predetermined value which indicates the prime mover is overloaded, the input means further includes a servo valve which operates a fluid motor to set the displacement of the pump and manually operable means for setting the position of the servo valve to thereby set the displacement of the pump, the servo valve further includes a movable valve member and movement of the valve member operates the servo valve between a first position of maximum pump displacement and a second position of minimum pump displacement, and the manually operable means includes movable setting means which operates the valve member and a ratio changing device which changes the ratio between the amount of movement of the setting means and the amount of corresponding movement of the valve member.