CB44B Vibratory Asphalt Compactor Propel System (Solid Drum) Caterpillar

Illustration 1	g03266965
Propel Hydraulic Schematic NEUTRAL (1) Main hydraulic pump (2) Vibratory control valve (3) Interlock valve (4) Charge filter (5) From fan motor (6) Forward solenoid (7) Propel control valve (8) Reverse solenoid (9) Reverse combination valve (10) Front propel motor (11) Flushing spool (12) Flushing relief valve (13) Parking brake (14) To vibratory system (15) Vibratory combination valve (16) Vibratory combination valve (17) To vibratory system (18) Vibratory rotating group (19) Servo piston (20) Charge relief valve (21) Servo piston (22) Return manifold (23) Propel rotating group (24) Oil cooler (25) Forward combination valve (26) Rear propel motor (27) Flushing spool (28) Flushing relief valve (29) Shuttle valve (30) Shift spool (31) Shift cylinder (32) Parking brake (33) Machine valve (34) Manual brake release pump (35) Shift valve (36) Shuttle valve (37) Shift spool (38) Shift cylinder

The above illustration shows the propel hydraulic system under the following conditions:

• The propel lever is in the NEUTRAL position.

• The parking brake switch is in the ON position.

The propel circuit consists of a hydrostatic drive circuit for the forward drum and the rear drum. The closed loop circuit has propel rotating group (23) in main hydraulic pump (1) and two motors (10) and (26), one for each drum.

Displacement of propel rotating group (23) is electronically controlled. The machine ECM number one calculates the desired speed and energizes the appropriate pump control solenoid in order to move the machine at the desired speed. When the propel lever is in the NEUTRAL position, the swashplate in the rotating group is at zero angle. The swashplate is also at zero angle if the machine ECM number one has disabled the propel system. In either of these cases, the rotating group does not produce flow.

The charge pump provides hydraulic oil to drive the fan system. Oil from fan motor (5) flows through charge filter (4) in order to provide charge oil to the propel system (and the vibratory system) when the engine is running. Charge oil from the charge filter flows to port "E" of main hydraulic pump (1). Charge oil also flows to shift valve (35). Inside the main hydraulic pump, charge oil flows to interlock valve (3).

Charge pressure acts on charge relief valve (20). When charge pressure reaches 3000 ± 300 kPa (435 ± 45 psi), the oil pressure overcomes the spring force and the charge relief valve opens. This action directs charge pump flow into the case drain.

When the parking brake switch is in the ON position or the machine ECM number one has disabled the propel system, solenoid in interlock valve (3) is not energized. This solenoid prevents charge oil from reaching pump control solenoids (6) and (8) and from reaching the parking brake piston cavities. Under these conditions, the brake piston cavities and both sides of servo piston (21) are open to the pump case. The servo piston holds the swashplate in the rotating group at zero angle. The springs that are acting against the brake pistons engage parking brakes (13) and (32).

As long as the solenoid in interlock valve (3) is not energized, the swashplate in rotating group (23) remains in the zero angle position. In this case, charge pressure is blocked at the interlock valve and the servo chambers of the pumps are vented to the pump case. These conditions are maintained, regardless of the position of the propel lever.

Charge pressure acts against the makeup valves in each combination valve. If the pressure in either the forward loop or the reverse loop falls below charge pressure, the makeup valves open. In this case, charge oil flows into the loop.

Since the pressure in the forward circuit is equal to the pressure in the reverse circuit when the machine is not moving, flushing spool (11) and (27) in each propel motor is in the center position. In this case, the spool prevents flushing oil from flowing into the case drains of the motors.

Pressure in the forward circuit can be measured at the pressure tap in port "MB" of the main hydraulic pump. Reverse pressure can be measured at the pressure tap in port "MA" of the main hydraulic pump.

Illustration 2	g03266984
Hydraulic Schematic FORWARD (1) Main hydraulic pump (2) Vibratory control valve (3) Interlock valve (4) Charge filter (5) From fan motor (6) Forward solenoid (7) Propel control valve (8) Reverse solenoid (9) Reverse combination valve (10) Front propel motor (11) Flushing spool (12) Flushing relief valve (13) Parking brake (14) To vibratory system (15) Vibratory combination valve (16) Vibratory combination valve (17) To vibratory system (18) Vibratory rotating group (19) Servo piston (20) Charge relief valve (21) Servo piston (22) Return manifold (23) Propel rotating group (24) Oil cooler (25) Forward combination valve (26) Rear propel motor (27) Flushing spool (28) Flushing relief valve (29) Shuttle valve (30) Shift spool (31) Shift cylinder (32) Parking brake (33) Machine valve (34) Manual brake release pump (35) Shift valve (36) Shuttle valve (37) Shift spool (38) Shift cylinder

The above illustration shows the propel hydraulic system under the following conditions:

• The parking brake switch is in the OFF position.

• The propel mode is set to low.

• The propel lever is in the forward range with the operator station facing the front of the machine or the propel lever is in the reverse range with the operator station facing the rear of the machine.

Charge oil flows to combination valves (9) and (25) and to interlock valve (3). With the parking brake switch in the OFF position, the interlock valve directs charge oil into the piston cavities of parking brakes (13) and (32). The charge pressure in the parking brake piston cavities overcomes the spring force, and the parking brakes release. At the same time, charge oil is also routed to the pump control spool.

When the propel mode is set to low, shift valve (35) is not energized. In this case, shift spools (37) and (30) open the head end of shift cylinders (38) and (31) to the tank. When this situation happens, propel motors (10) and (26) operate at low speed and full torque.

When the machine ECM number one determines that the machine should be moving forward, ECM energizes forward solenoid (6). In this case, the solenoid directs charge oil into the forward side of servo piston (21). The pressure in the forward side of the servo piston causes the pump servo to move. This movement changes the angle of the swashplate in propel rotating group (23). The stronger the signal to the solenoid, the greater the swashplate angle, and therefore, the greater the oil flow from the main hydraulic pump.

As the swashplate moves, the feedback linkage tends to move the pump solenoid spool back to neutral through an internal feedback spring. This action prevents the servo piston from tilting the swashplate too far.

Supply oil from propel rotating group (23) flows to the following locations:

• Forward combination valve (25)

• The forward side of front propel motor (10)

• The forward side of rear propel motor (26)

• Port "MB" on main hydraulic pump (1)

The pressure differential between the forward and reverse sides of propel motors (10) and (26) causes the motors to turn. After turning the motors, oil at a reduced pressure flows to the following locations:

• Flushing spool (11) and (27) in each motor

• The reverse side of propel rotating group (23)

• Port "MA" on main hydraulic pump (1)

Inside main hydraulic pump (1), forward supply oil from the propel rotating group acts against the relief valve in forward combination valve (25). As long as the pressure in the forward circuit is greater than charge pressure, the makeup valve in the combination valve remains seated. As long as the supply pressure is less than relief pressure, the relief valve in the combination valve remains closed.

If pressure in the reverse loop falls below charge pressure, the makeup valve in reverse combination valve (9) opens. In this case, charge oil flows into the low-pressure side of the loop. When pressure in the low-pressure side of the loop rises above charge pressure, the makeup valve closes.

Loop flushing occurs in rear propel motor (26) and front propel motor (10). In each motor, forward circuit oil acts against one side of the flushing spool. Reverse circuit oil acts against the opposite side of each flushing spool. In both motors, the higher pressure oil moves the flushing spool. This movement allows reverse circuit oil to flow across the spool to the flushing relief valve.

Any time the pressure in either reverse circuit is greater than the setting of the flushing relief valve, the corresponding flushing relief valve opens. In this case, oil from the reverse circuit flows into the motor case drain line.

The pressure setting of the flushing relief valve is less than the pressure setting of the charge relief valve. This fact ensures that oil is sent through the motor case drain under normal operating conditions. The flow should be between 5.5 - 12.5 L/min (1.4 - 3.3 US gpm). The flushing relief valve will stop flow if the charge pressure is less than the setting of the flushing relief valve. This fact ensures that flow through the flushing orifice does not cause charge pressure to decrease to the point at which charge pressure becomes less than the brake release requirement.

Illustration 3	g03266989
Hydraulic Schematic REVERSE (1) Main hydraulic pump (2) Vibratory control valve (3) Interlock valve (4) Charge filter (5) From fan motor (6) Forward solenoid (7) Propel control valve (8) Reverse solenoid (9) Reverse combination valve (10) Front propel motor (11) Flushing spool (12) Flushing relief valve (13) Parking brake (14) To vibratory system (15) Vibratory combination valve (16) Vibratory combination valve (17) To vibratory system (18) Vibratory rotating group (19) Servo piston (20) Charge relief valve (21) Servo piston (22) Return manifold (23) Propel rotating group (24) Oil cooler (25) Forward combination valve (26) Rear propel motor (27) Flushing spool (28) Flushing relief valve (29) Shuttle valve (30) Shift spool (31) Shift cylinder (32) Parking brake (33) Machine valve (34) Manual brake release pump (35) Shift valve (36) Shuttle valve (37) Shift spool (38) Shift cylinder

The above illustration shows the propel hydraulic system in the following conditions:

• The parking brake switch is in the OFF. position

• The propel mode is set to high.

• The propel lever is in the reverse range with the operator station facing the front of the machine or the propel lever is in the forward range with the operator station facing the rear of the machine.

During reverse operation, propel rotating group (23) directs oil out port "A" on main hydraulic pump (1). This oil flows to the reverse side of propel motors (10) and (26) and to port "MA" on the main hydraulic pump. The motors rotate, and reduced pressure oil returns to the rotating group through port "B" on the main hydraulic pump. On each propel motor, the flushing spools and flushing relief valves direct oil from the forward side of the circuit to the case drain of the motor. The relief valve in reverse combination valve (9) limits the maximum pressure in the reverse circuit. The makeup valve in forward combination valve (25) allows charge oil to enter the forward circuit to replenish oil lost to loop flushing.

When the propel mode is set to high, shift valve (35) is energized and the valve shifts. The position of the shift valve allows charge oil to act on shift spool (37) in front propel motor (10) and shift spool (30) in rear propel motor (26). When this situation happens, high-pressure oil in each motor is directed through shuttle valves (29) and (36) to act against shift cylinders (31) and (38). In this case, the motors will operate at high speed but with less torque.