BOLT 1397908 - Caterpillar

Illustration 2 g06098764
Propulsion Hydraulic System in Forward Travel
(1) Flushing relief valve
(2) Flushing spool
(3) Servo piston
(4) Right propulsion motor
(5) Parking brake
(6) Passage to oil cooler manifold port "D"
(7) Brake release manifold
(8) Brake pressure switch
(9) Parking brake valve
(10) Shift valve
(11) Flushing relief valve
(12) Flushing spool
(13) Shift spool
(14) Servo piston
(15) Left propulsion motor
(16) Parking brake
(17) POR valve
(18) Shift spool
(19) Right propulsion pump
(20) Reverse combination valve
(21) Direction control valve
(22) Servo piston
(23) Direction control valve
(24) Forward combination valve
(25) Left propulsion pump
(26) POR valve
(27) Passage to oil cooler manifold port "F"
(28) Charge orifice
(29) Forward combination valve
(30) Servo piston
(31) Reverse combination valve
(32) Charge relief valve
(33) Charge pump
(34) Passage from suction and return filter port "B1"When the machine is traveling forward, the forward solenoids in direction control valves (21) and (23) are energized. The transmission ECM analyzes the input signals to determine the magnitude of the output signals that are sent to each forward solenoid.Charge oil flows across direction control valves (21) and (23) and acts against servo pistons (22) and (30). This pressure causes the servo pistons to shift. This action changes the angle of the swashplates in the corresponding pump. Under these conditions, propulsion pumps (19) and (25) generate flow in the corresponding forward hydraulic circuits.Forward circuit oil flows to combination valves (24) and (29). Inside the combination valve, the oil closes the makeup valves and acts against the relief valves. If the pressure in the forward circuit reaches 45000 1500 kPa (6530 200 psi), the relief valve opens. Under these conditions, the valve directs oil from the forward circuit into the charge circuit.Oil in the forward circuit causes propulsion motors (1) and (14) to turn. After the motor turns, the pressure of the forward circuit oil is reduced. Oil at a reduced pressure then enters the reverse circuit. Reverse circuit oil flows to back to the propulsion pump.Inside the motors, forward circuit oil acts against flushing spools (2) and (12), causing the spools to shift. This shift allows oil from the reverse circuit to act against flushing relief valves (1) and (11). The flushing relief valve opens and directs a controlled amount of oil to the motor case drain line. As the flushing valves remove oil from the reverse circuits, the pressure in the reverse circuits decreases. When the reverse circuit pressure decreases below charge pressure, the makeup valve in the reverse circuit opens. This action allows cool, filtered oil from the charge circuits to flush the propulsion circuits.Inside the propulsion pumps, return oil is directed to the following locations:
Reverse combination valves (20) and (31)
The reverse side of the rotating group in propulsion pumps (19) and (25)The drive circuit is then complete.When the parking brake status is set to "off", the electronic control system energizes the brake solenoid in parking brake valve (9). The brake valve shifts and directs charge oil from left propulsion pump (25) to left parking brake (16) and right parking brake (5). The pressure in the brake cylinders overcomes the spring forces and releases the parking brakes.When the