RELAY AS 2640454 - Caterpillar

When both of the travel levers/pedals are operated, pilot system oil pressure flows from travel pilot control valve (44) through pilot lines (42) and (43) to left travel control valve (38) and right travel control valve (41). The pilot system oil pressure shifts the spools in both of the travel control valves in a downward direction. The travel control valves allow the oil delivery from the drive pump and the idler pump to flow to swivel (30). The swivel transfers the oil delivery from the rotating upper structure to the lines in the lower structure. The oil delivery flows to left travel motor (1) and right travel motor (15).Note: The right and left travel controls function in the same manner. The explanation for the left travel control will be used to explain both the right and left travel controls.When the left travel lever/pedal is moved to the FORWARD TRAVEL position, pilot system oil pressure from travel pilot control valve (44) flows through pilot line (42) to left travel control valve (38). The spool in the left travel control valve shifts in a downward direction. The oil delivery from the idler pump in center bypass passage (40) flows through left travel control valve (38), passage (35), line (33), swivel (30), and line (29) to left travel motor (1).The oil delivery from the idler pump enters left travel motor (1) and flows through counterbalance valve (8) and passage (5) to motor rotary group (3). At the same time, a portion of the oil delivery from the idler pump flows through passage (7) and to parking brake (10). The parking brake is released and the oil delivery from the idler pump causes the motor to rotate.LOW SPEED
Illustration 7 g06271985
Left travel motor (LOW SPEED)
(1) Left travel motor
(2) Swashplate
(3) Motor rotary group
(4) Swashplate control piston
(5) Passage (supply oil)
(8) Counterbalance valve
(11) Passage (return oil)
(12) Displacement change valve
(13) Passage
(27) Pilot line
(47) Pressure sensor (idler pump)
(48) Travel speed solenoid valve
(49) Idler pump
(51) Pilot pump
(56) Travel speed control switch
(58) Left travel lever/pedal
(B) Indicator for HIGH SPEED
(C) Indicator for LOW SPEED
(D) Machine ECM
(E) Main control valveWhen travel speed control switch (56) is set at the LOW SPEED position, an electrical signal is sent to machine ECM (D). The machine ECM does not energize travel speed solenoid valve (48) and pilot system oil pressure does not flow through pilot line (27) to displacement change valve (12). The spool in the displacement change valve does not shift, blocking the oil from idler pump (49) to reach swashplate control piston (4). As a result, swashplate control piston (4) moves swashplate (2) to the maximum displacement position. At the same time, the oil that acts on swashplate control piston (4) flows into the case drain of the travel motor. One rotation of motor rotary group (3) displaces a larger amount of oil flow. The rotational speed of the left travel motor decreases. The left track moves slowly and better traction is achieved.The return oil from motor rotary group (3) flows through passage (11),