CP56, CS56, CP64, CS64, CP74 and CS74 Vibratory Compactors Propel System Hydraulic Schematic (Propel System) Caterpillar

Illustration 1	g01416390
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 NEUTRAL position, the parking brake switch in the ON position, and the shift switch in the LOW SPEED position.

The propulsion circuit consists of two hydrostatic drive circuits. The axle propulsion circuit and the drum propulsion circuit. Each closed loop circuit has a pump and a motor. The displacement control levers in the axle and drum pumps are connected to each other through a mechanical linkage. When the propulsion lever is moved, the displacement control levers on the pumps move equal amounts. When the propulsion lever is in NEUTRAL, the swashplate in each pump is at zero angle, and neither pump produces flow.

The steering system and the fan system provide charge oil to the propulsion system when the engine is running. Charge oil flows through the charge filters to the axle pump, the drum pump, and the shift valve. In the axle pump, charge oil flows to the cartridges of the main relief valves, to the charge relief valve, and to the axle interlock solenoid. In the drum pump, charge oil flows to the cartridges of the main relief valves, to the charge relief valve, and to the drum interlock solenoid.

When the parking brake switch is ON, the axle interlock solenoid and the drum interlock solenoid are de-energized. When the drum interlock solenoid is de-energized this solenoid prevents charge oil from reaching the displacement control spool. Also, when the drum interlock solenoid is de-energized this solenoid prevents charge oil from reaching the parking brake piston cavities. Under these conditions, both sides of the servo piston in the pump are open to the pump case, and all the brake piston cavities are open to the tank. The centering springs in the servo piston cause the piston to hold the swashplate at zero angle. The springs that are acting against the brake pistons engage the disks of the parking brakes.

When the axle interlock solenoid is de-energized this solenoid is identical to the axle pump as the drum interlock solenoid is to the drum pump. However, the axle interlock solenoid does not affect the parking brakes.

If the parking brake switch remains in the ON position, the axle interlock solenoid and the drum interlock solenoid prevent the pump servos from moving the swashplates out of the zero angle position. This is true regardless of the position of the propulsion lever.

Charge pressure acts on the charge relief valve. When charge pressure reaches 2600 ± 250 kPa (377 ± 36 psi), the oil pressure overcomes the spring force and the charge relief valve opens. This action directs charge pump flow into the case drain.

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

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

Illustration 2	g01416444
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 FORWARD position, the parking brake switch in the OFF position, and the shift switch in the LOW 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.

With the shift switch in the LOW SPEED position, the shift solenoid is de-energized, and the propulsion motors remain at the maximum displacement angle.

When the propulsion lever is moved into the forward range, the displacement control spool directs charge oil into the forward side of the pump servo piston. The pressure in the forward side of the servo piston overcomes the spring force, and the pump servo moves. This movement changes the angle of the swashplate. The farther the propulsion lever is moved, the greater the angle of the swashplate. Therefore, the greater the oil flow from the propulsion pump.

As the swashplate moves, the feedback linkage tends to move the direction control spool back to neutral through an internal feedback spring. This action prevents the servo piston from tilting the swashplate too far by blocking the charge oil supply, once the tilt angle is proportional to the input from the direction control lever.

The axle propulsion pump and the drum propulsion pump operate in an identical fashion. The displacement control levers on the axle and drum pumps are connected to each other through a mechanical linkage.

Supply oil from the axle pump flows to the following components: forward combination valve and the pressure override relief valve in the axle pump, forward side of the axle motor and forward balance line.

The pressure differential between the forward and reverse sides of the axle motor causes the motor to turn. After turning the axle motor, oil at a reduced pressure flows back to the reverse side of the axle pump, to the reverse balance line, and to the axle motor flushing valve.

Supply oil from the drum pump follows a similar flow path and flows to the following components: forward combination valve and the pressure override relief valve in the drum pump, forward side of the drum motor and forward balance line. The drum motor turns, and reduced pressure oil flows back to the reverse side of the drum pump, to the reverse balance line, and to the drum motor flushing valve.

The balance lines modulate large pressure differences by allowing oil to transfer between the axle and the drum drive circuits. Essentially, the balance lines act as a hydraulic differential.

Inside the propulsion pump, supply oil acts against the main relief valve. As long as the pressure that is in the forward circuit is greater than charge pressure, the makeup valve that is in the relief valve cartridge remains seated. As long as the supply pressure is less than relief pressure, the main relief valve remains closed.

If pressure in the reverse loop falls below charge pressure, the makeup valve in the relief valve cartridge 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.

Supply oil which flows into the combination valve in each pump acts against the high pressure relief section of the valve. Supply oil which flows into the pressure override relief valve in each pump moves the shuttle valve. Also, this oil acts on the relief section of the pressure override relief valve.

The relief section of the pressure override relief valve is set at 44000 ± 1000 kPa (6380 ± 145 psi), and the main relief valve is set at 46500 ± 1000 kPa (6750 ± 145 psi). As the pressure increases in the system, the pressure reaches the pressure override relief setting first. When the relief section of the pressure override relief valve is open, the control pressure decreases in the servo piston chamber, and the pump destrokes. This action requires a finite amount of time.

If the pressure in the system reaches a pressure of 46500 ± 1000 kPa (6750 ± 145 psi) before the pump destrokes, the main relief valve opens. The main relief valve is a fast acting valve. When the main relief valve is open, oil from the high pressure circuit is directed into the low pressure circuit through the makeup valve in the low pressure circuit. The main relief valve quickly limits the pressure while the pressure override relief valve has time in order to destroke the pump.

Action of the pressure override relief valve maintains the swashplate at an angle that will maintain 44000 ± 1000 kPa (6380 ± 145 psi) in the high pressure side of the loop. If the motors are not rotating, the pump swashplate angle will be near zero. In this case, little heat is being generated.

Loop flushing occurs in the axle and drum motors. In each motor, forward circuit oil acts against one side of the flushing valve, and reverse circuit oil acts against the other side of the flushing valve. In both motors, the higher pressure oil moves the flushing valve spool. This movement allows reverse circuit oil to flow across the spool to the relief section of the flushing valve.

When the pressure in either reverse circuit is greater than 1800 kPa (261 psi), the corresponding flushing relief valve opens. In this case, oil from the reverse circuit flows through an orifice and 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 flushing relief valve will stop flushing flow if the charge pressure is less than 1800 kPa (261 psi). This fact ensures that flow through the flushing orifice does not cause charge pressure to decrease until charge pressure is less than the brake release requirement.

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 propulsion lever is moved into the reverse range, the displacement control spool directs charge oil into the reverse side of the pump servo piston. The pressure in the reverse side of the servo piston overcomes the spring force, and the pump servo moves. This movement changes the angle of the swashplate. The farther the propulsion lever is moved, the greater the angle of the swashplate. As a result, the greater the oil flow is from the propulsion pump.

The axle propulsion pump and the drum propulsion pump operate in an identical fashion. The displacement control levers on the axle and drum pumps are connected to each other through a mechanical linkage.

Supply oil from the axle pump flows to the following components: reverse combination valve and the pressure override relief valve in the axle pump, reverse side of the axle motor and reverse balance line. The pressure differential between the forward and reverse sides of the axle motor causes the motor to turn. After turning the axle motor, oil at a reduced pressure flows back to the forward side of the axle pump, to the forward balance line, and to the axle motor flushing valve.

Supply oil from the drum pump follows a similar flow path and flows to the following components: reverse combination valve and the pressure override relief valve in the drum pump, reverse side of the drum motor and reverse balance line. The drum motor turns, and reduced pressure oil flows back to the forward side of the drum pump, to the forward balance line, and to the drum motor flushing valve.

The balance lines modulate large pressure differences by allowing oil to transfer between the axle and drum drive circuits. Essentially, the balance lines act as a hydraulic differential.

Inside the propulsion pump, supply oil acts against the main relief valve. As long as the pressure in the reverse circuit is greater than charge pressure, the makeup valve in the relief valve cartridge remains seated. As long as the supply pressure is less than relief pressure, the main relief valve remains closed.

If pressure in the forward loop falls below charge pressure, the makeup valve in the relief valve cartridge 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.

Supply oil which flows into the combination valve in each pump acts against the high pressure relief section of the valve. Supply oil which flows into the pressure override relief valve in each pump moves the shuttle valve. Also, this oil acts on the relief section of the pressure override relief valve.

The relief section of the pressure override relief valve is set at 44000 ± 1000 kPa (6380 ± 145 psi), and the main relief valve is set at 46500 ± 1000 kPa (6750 ± 145 psi). As the pressure increases in the system, the pressure reaches the pressure override relief setting first. When the relief section of the pressure override relief valve is open, the control pressure in the servo piston chamber decreases, and the pump destrokes. This action requires a finite amount of time.

If the pressure in the system reaches a pressure of 46500 ± 1000 kPa (6750 ± 145 psi) before the pump destrokes, the main relief valve opens. The main relief valve is a fast acting valve. When the main relief valve is open, oil from the high pressure circuit is directed into the low pressure circuit through the makeup valve in the low pressure circuit. The main relief valve quickly limits the pressure while the pressure override relief valve has time in order to destroke the pump.

Action of the pressure override relief valve maintains the swashplate at an angle that will maintain 44000 ± 1000 kPa (6380 ± 145 psi) in the high pressure side of the loop. If the motors are not rotating, the pump swashplate angle will be near zero. In this case, little heat is being generated.

Loop flushing occurs in the axle and drum motors. In each motor, forward circuit oil acts against one side of the flushing valve, and reverse circuit oil acts against the other side of the flushing valve. In both motors, the higher pressure oil moves the flushing valve spool. This movement allows forward circuit oil to flow across the spool to the relief section of the flushing valve.

Any time the pressure in either forward circuit is greater than 1800 kPa (261 psi), the corresponding flushing relief valve opens. In this case, oil from the forward circuit flows through an orifice and 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 flushing relief valve will stop flushing flow if the charge pressure is less than 1800 kPa (261 psi). This fact ensures that flow through the flushing orifice does not cause charge pressure to decrease until charge pressure is less than the brake release requirement.