RING 5291111 - Caterpillar

Propel System in REVERSE, HIGH SPEED
Illustration 3 g01124422
This slide shows the propel system under the following condition: the propel lever is in the REVERSE position. The parking brake switch is in the OFF position. The shift switch is in the HIGH SPEED position.Charge oil flows to the brake and shift valve and to the charge filter. With the parking brake switch OFF, the brake solenoid is energized. The brake solenoid directs charge oil into the piston cavities of the parking brakes. The charge pressure in the 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 shift solenoid directs charge oil into the piston cavities in the right and left propel motors. The propel motors move to the minimum displacement angle.When the propel lever is moved into the REVERSE range, the direction control spool sends charge oil into the reverse cavity for the pump servo and to the interlock solenoid. The interlock solenoid is energized when the brake solenoid is energized. When the interlock solenoid is energized, the passage between the forward and reverse chambers of the propel pump is closed. Under these conditions, the swashplate in the pump can move.Charge pressure in the cavity for the pump servo overcomes the force of the springs, and the servo piston moves. Movement of the servo piston causes the angle of the swashplate to change. This action causes the pump to produce flow. If the engine speed decreases, charge pressure upstream of the 6.8 mm (0.27 inch) orifice in the DA valve decreases. This decrease causes the DA valve to shift. Shifting of the DA valve opens a passage between the servo piston and the case drain. Under these conditions, the swashplate in the pump moves back toward the minimum angle. The DA valve maintains the output from the pump in proportion to the engine speed.Supply oil flows to the following components:
reverse combination valve
pressure override relief valve
flushing spool
reverse side of the propel motorsThe pressure differential between the forward and reverse sides of the propel motors causes the motors to turn. After turning the propel motors, oil at a reduced pressure flows back to the forward side of the pump.If the pressure in the circuit is greater than charge pressure and less than relief pressure, the makeup valve in the reverse combination valve remains seated. In this case, the high pressure relief valve remains closed.Supply oil which flows into