BUCKET AR 5662008 - Caterpillar

STANDBY Position
All of the joysticks and the travel levers/pedals are in the NEUTRAL position. The main pump regulators are controlled by the negative flow control pressure (PN) in piston chamber (29) .When all of the joysticks and the travel levers/pedals are in the NEUTRAL position, all of the control valves for the implements, swing and travel are in the NEUTRAL position. The oil flow rate through the center bypass passage in the main control valve is maximum. The oil flow through the center bypass passage is restricted at the negative flow control orifice. High negative flow control pressure (PN) flows from the main control valve through line (30) to piston chamber (29) of the idler pump regulator. When the negative flow control pressure is maximum, the output flow of the pump is maintained at a minimum (STANDBY).Negative flow control pressure (PN) enters the idler pump regulator through line (30). The negative flow control pressure (PN) flows to piston chamber (29). When the negative flow control pressure (PN) increases, control piston (27) is pushed to the left against the force of spring (28). As the negative flow control pressure increases further, control piston (27) pushes pilot piston (26) and spool (22) to the left. The movement of the control piston, the pilot piston and the spool will stop when the force of the negative flow control pressure becomes equal to the force of springs (20), (21) and (28). Oil pressure from the idler pump (P2) is now blocked at passage (17) .The negative flow control pressure in piston chamber (6) flows through passage (12), passage (17), past spool (22) and through passage (24) to the case drain of the pump.The oil pressure from the idler pump (P2) in piston chamber (9) pushes piston (11) to the right. Piston (11) moves to the right until the piston contacts stopper (7). Control linkage (5) causes swashplate (18) to rotate toward the minimum angle position. As a result, the output flow of the pump decreases.During STANDBY, power shift pressure is present in passage (16). This pressure acts on the right end of pilot piston (26). The average delivery pressure of the drive pump and the idler pump is present in passage (13). This pressure acts on shoulder (25) in the center of pilot piston (26). NFC pressure forces the pilot piston against shoulder (25). Therefore, the effects of PS and PM are very slight.UPSTROKE Position
Illustration 4 g00786706
(4) Oil passage for idler pump pressure (P2) (5) Linkage (6) Piston chamber (7) Stopper (8) Passage (9) Piston chamber (10) Pin (11) Piston (12) Passage (13) Passage for the average delivery pressure (PM = (P1 + P2)/2) of the idler pump (P2) and the drive pump (P1) (14) Guide (15) Passage (16) Passage for power shift pressure (PS) (17) Passage (18) Swashplate (19) Pin (20) Spring (21) Spring (22) Spool (23) Sleeve (24) Passage (25) Shoulder (26) Pilot piston (27) Control piston (28) Spring (29) Piston chamber (30) Line for negative control pressure (PN) (31) Dowel