COVER 3904866 - Caterpillar

Illustration 1 g01232154
Travel pilot control valve
(1) Travel lever/pedal
(2) Pedal
(3) Rod
(4) Seat
(5) Spring
(6) Spring
(7) Spool
(8) Passage
(9) Passage
(10) Spring
(11) Spool
(12) Return port
(13) Return chamber
(14) Passage
(15) Passage
(16) Pilot port
(17) Passage
(18) Port
(19) Passage
(20) Passage
(21) Passage
(22) Port
(23) Piston chamber
(24) Orifice
(25) Piston
(26) Spring
(27) Spring
(28) Spring chamber
(29) Ball
(30) Rod
(31) Spring
(32) Spring
(33) Spring chamber
(34) Ball When travel lever/pedal (1) is moved to the FORWARD TRAVEL position, rod (3) moves downward. As rod (3) moves downward, seat (4) moves downward against the force of springs (5) and (6). Passage (19) opens.As passage (19) opens, the pilot oil from pilot port (16) flows through passages (21), (19), (20), and (9) to port (18). The pilot oil flows through port (18) to the travel control valve. The pilot oil pressure shifts the spool of travel control valve. The oil delivery from the pump now flows through the travel control valve to the travel motor. The travel motor rotates. The machine travels forward.The return pilot oil at the opposite end of the spool in the travel control valve returns to the travel pilot control valve through port (22). Since spool (11) is pushed upward by the force of spring (10), the return pilot oil flows through passage (17), passage (15), passage (14), return chamber (13) and port (12) to the hydraulic tank.When travel lever/pedal (1) is moved slightly from the NEUTRAL position for fine travel, rod (3) moves downward and seat (4) moves downward. Spring (6) forces spool (7) downward. Passage (19) opens slightly and the pilot oil pressure increases in port (18). When this pilot oil pressure becomes higher than the force of spring (6), spool (7) moves upward opening passage (8). The pilot pressure oil from port (18) flows through passages (9), (20) and (8) into return chamber (13). The pilot oil pressure decreases slightly. Spool (7) is held in a pressure modulating position. Spool (7) establishes a balance between the pressure in port (18) and the force of spring (6).When travel lever/pedal (1) is released, spring (5) forces seat (4) and rod (3) in an upward direction. The force of spring (6) decreases. Spool (7) moves upward. The pilot oil pressure at port (18) flows through passage (9), passage (20), passage (8) and return chamber (13) to the hydraulic tank.A dampening function is built into the travel pilot control valve which allows the operational speed of the travel lever/pedal to correspond to the movement of the operator's foot. The dampening function also prevents the vibration that occurs when the travel lever/pedal is released.When travel lever/pedal (1) is moved suddenly from the NEUTRAL position, rod (3) is pushed downward. Rod (3) moves piston (25), spring (26) and spring (27) downward. The hydraulic oil in spring chamber (28) is pressurized. Ball (29) closes the opening. Orifice (24) allows the confined hydraulic oil in spring chamber (28) to gradually flow into piston chamber (23). The gradual flow of oil through orifice (24) causes the dampening function.Rod (30) is forced upward by springs (31) and (32). The oil pressure in spring chamber