HUB 1P8190 - Caterpillar

Illustration 3 g01416517
Hydraulic Schematic
(1) Direction control valve
(2) Drum pump
(3) From front charge filter
(4) Direction control valve
(5) Neutral start switch
(6) Loop balance orifice
(7) Axle pump
(8) From rear charge filter
(9) Servo piston
(10) Drum pump
(11) Reverse combination valve
(12) Drum interlock valve
(13) Passage plugged
(14) Servo piston
(15) Axle pump
(16) Reverse combination valve
(17) Axle interlock valve
(18) Passage plugged
(19) Forward combination valve
(20) Charge relief valve
(21) POR valve
(22) Forward combination valve
(23) Charge relief valve
(24) POR valve
(25) Drum brake
(26) Drum motor
(27) Servo piston
(28) Shift spool
(29) Flushing spool
(30) Flushing relief valve
(31) Tank
(32) Oil cooler
(33) Relief valve
(34) Thermal bypass valve
(35) Return manifold
(36) Loop balance orifice
(37) Shift spool
(38) Axle motor
(39) Shift valve
(40) Axle motor
(41) Flushing spool
(42) Flushing relief valve
(43) Axle brakes This Illustration shows the propulsion system with the propulsion lever in the REVERSE position, the parking brake switch in the OFF position, and the shift switch in the HIGH SPEED position.Charge oil flows through the charge filters to the charge relief valve, to the relief valve cartridges, and to the interlock solenoid of the drum propulsion pump and the axle propulsion pump. With the parking brake switch in the OFF position, the drum interlock solenoid directs charge oil into the piston cavities of the parking brakes. The charge pressure in the parking brake piston cavities overcomes the spring force, and the parking brakes release.When the shift switch is in the HIGH SPEED position, the shift solenoid is energized. The position of the shift valve allows charge oil to act on the shift spools in the axle and drum motors. The shift valves in the motors move, and oil is directed from the reverse circuit into the high side of the servo piston chambers.The shift mechanism that is for the axle motor is different than the shift mechanism that is for the drum motor. In the axle motor, oil from the high pressure side of the loop acts against both sides of the servo piston. However, the effective area on the high side of the servo piston is greater than the effective area on the low side of the piston. The difference in the effective area allows the servo piston to shift. This causes the rotating group in the axle motor to move against the minimum displacement adjustment screw and this causes the motor to operate at high speed.In the drum motor, the shift valve directs high pressure oil into the piston chamber on one side of the servo piston. Also, this oil opens the chamber on the opposite side of the servo piston to the thermal bypass manifold. The oil pressure causes the servo piston to shift. This shift causes the rotating group in the drum motor to move against the minimum displacement adjustment screw.When the