STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 2) Control of discharge amount If the swash plate angle α becomes larger, the dif- ference between volumes E and F becomes larger and discharge amount Q increases. Swash plate angle α is changed by servo piston (12). Servo piston (12) moves in a reciprocal move- ment ( ) according to the signal pressure from the PC and LS valves. This straight line move- ment is transmitted through rod (13) to rocker cam (4), and rocker cam (4), which is supported by the cylindrical surface to cradle (2), slides in a rotating movement in direction of arrow.
With servo piston (12), the area receiving the pressure is different on the left and the right, so main pump discharge pressure (self pressure) PP is always brought to the chamber receiving the pressure at the small diameter piston end. Output pressure Pen of the LS valve is brought to the chamber receiving the pressure at the large diameter end. The relationship in the size of pres- sure PP at the small diameter piston end and pressure Pen at the large diameter end, and the ratio between the area receiving the pressure of the small diameter piston and the large diameter piston controls the movement of servo piston (12). 10-34 PC210/240-7K