STRUCTURE AND FUNCTION HYDRAULIC PUMP 2) Control of discharge amount If swash plate angle α becomes larger, the dif- ference in volumes E and F becomes larger and discharge volume Q increases. Swash plate angle α is changed by servo piston (11). Servo piston (11) moves in a reciprocal move- ment ( ) under the signal pressure of the PC and LS valves. This straight line movement is transmitted through rod (12) to rocker cam (4), and rocker cam (4), which is supported by the cylindrical surface to cradle (2), slides in a rotat- ing movement in direction ( ).
With servo piston (11), the area receiving the pressure is different on the left and right, so main pump discharge pressure (self pressure) PP is always brought to the pressure chamber on the small diameter piston side (front). Output pressure Pen of the LS valve is brought to the pressure chamber at the large diameter piston end (rear). The relationship in the size of pressure PP at the small diameter piston end and pressure Pen at the large diameter piston end, and the ratio between the area receiving the pressure of the small diameter piston and the large diameter piston controls the move- ment of servo piston (11). 10-41