PANEL AS 4616278 - Caterpillar

Illustration 3 g03610679
Attachment pump cross section (19) EDC (20) Servo piston (21) Feedback link (22) Servo springs (23) Swashplate (24) Slipper pad (25) Input shaft (26) Rotating group (27) Piston (28) Charge pumpEngine rotation turns the pump input shaft, which then rotates the rotating group (26). The rotating group contains a piston (28) and barrel assembly. The pistons in the group rotate with the barrel assembly. The piston slipper pads (24) allow the pistons to follow the angle of swashplate (23). The rotating group only generates flow when the swashplate is not at zero angle.When the XA2 module in the cab sends an output signal to one of the solenoids, the solenoid moves a spool. Spool movement directs oil into the chamber at one end of servo piston (20) (the high side) and opens the chamber at the other end of the servo piston (the low side) to the case drain. Under these conditions, the servo piston moves.As servo piston (20) moves, the action of the control linkage causes the angle of swashplate (23) to change. As the swashplate moves, feedback link (21) tends to move the spool of the active solenoid back to neutral through an internal feedback spring. This action prevents the servo piston from tilting the swashplate too far by blocking the charge oil supply, once the tilt angle is equal to the input signal from the XA2 module in the cab.Slipper pads (24) in each rotating group (26) follow the angle of swashplate (23). This action causes the pistons to move in and out of the barrel assembly as input shaft (25) rotates. As a piston moves out of the barrel assembly, oil in the low-pressure circuit is drawn into the piston chamber. As a piston moves into the barrel assembly, oil is forced out of the piston chamber and into the high-pressure circuit.
Illustration 4 g03610684
Attachment pump pressure limiter valve: Top= Closed, Bottom= Open (29) To servo piston chamber (low side) (30) High-pressure oil (31) Poppet (32) Spring High-pressure oil acts against one side of the poppet (31) in the pressure limiter valve. A spring acts against the other side of the poppet. When the pressure in the high-pressure circuit reaches 37,370 345 kPa (5420 50 psi), the force from the pressure moves the poppet against the force of spring (32). As the poppet moves, a passage opens. This opening purges high-pressure oil (30) into the low side of the servo piston.The low side of the servo piston (29) is open to the pump case drain across the spool in the EDC. However, the passage across the spool in the EDC cannot purge all the oil entering the servo piston through the pressure limiter. Therefore, the pressure in the low side of the servo piston increases. Eventually the pressure in the low side of the servo piston becomes greater than the pressure in the high side of the servo piston. In this case, the servo piston moves the swashplate (23) to a lesser angle,