STRUCTURE, FUNCTION, & MAINTENANCE STANDARD HYDRAULIC PUMP 12 Port C of the PC valve is connected to port E of the LS valve (see (1) LS valve). Self pressure PP1 enters port B and the small diameter end of servo piston (9), and other pump pressure PP2 enters port A . When pump pressures PP1 and PP2 are small, spool (3) is on the right. At this point, port C and D are con- nected, and the pressure entering the LS valve becomes drain pressure PT . If port E and port G of the LS valve are connected (see (1) LS valve), the pressure entering the large diameter end of the piston from port J becomes drain pressure PT , and servo pis- ton (9) moves to the right.
In this way, the pump dis- charge amount moves in the direction of increase. As servo piston (9) moves further, springs (4) and (6) expand and the spring force becomes weaker. When the spring force becomes weaker, spool (3) moves to the left, so the connection between port C and port D is cut, and the pump discharge pressure ports B and C are connected. As a result, the pressure at port C rises, and the pressure at the large diameter end of the pis- ton also rises, so the movement of piston (9) to the right is stopped.
In other words, the stop position for piston (9) (= pump discharge amount) is decided at the point where the force of springs (4) and (6) and the pushing force from the PC-EPC valve solenoid and the pushing force created by the pressures PP1 and PP2 acting on the spool (3) are in balance. PC210/240-7K 10-43