NEUTRAL
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| Illustration 1 | g01229759 |
Charge Oil Distribution
When the engine is running, the propel pump and the charge pump rotate. The charge pump draws oil from the tank through a suction screen. Output oil from the charge pump flows to the charge relief valve and flows to the charge filter.
After flowing through the charge filter, charge oil flows to the following locations:
- Port "P2" of the center manifold
- Port "S" of the flow divider manifold
- Port "M3" of the propel pump.
Note: If the pressure differential across the charge filter is greater than 345 kPa (50 psi), oil bypasses the filter and flows directly back to the hydraulic tank. This causes the pressure in the charge system to decrease, and the Caterpillar Monitoring System initiates a "Level 1" warning.
Downstream from port "M3" of the propel pump, charge oil flows to the multifunction control valves and flows to the EDC metering spool.
EDC Metering Spool
When the propel levers are in the NEUTRAL position, or the machine ECM has disengaged the propel levers, the center envelope of the EDC metering spool is active. In this position, the EDC metering spool blocks the charge oil and opens a passage between the propel pump's servo pistons. The pump swashplate then moves to the minimum angle.
Multifunction Valves
Charge oil which enters the multifunction valves seats the check valves and the charge oil acts against the makeup valves. Since the propel pump rotates while the engine is running, normal leakage will occur in the propel circuit. When the pressure in the propel circuit falls below charge pressure, the makeup valves open and the propel circuit fills with charge oil.
When charge pressure increases to 2410 ± 69 kPa (350 ± 10 psi), the charge relief valve opens. Charge oil is then directed into the pump case drain.
FORWARD, LOW SPEED
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| Illustration 2 | g01229766 |
Parking Brake Release
When a parking brake switch is in the OFF position, the brake solenoid is energized. The parking brake valve is located on the rear manifold. The auxiliary hydraulic system provides the oil which releases the parking brakes.
Supply oil from the auxiliary hydraulic pump enters port "P1" of the rear manifold. This oil flows through a check valve and flows to a pressure reducing valve. The pressure reducing valve causes the downstream pressure to decrease. This valve limits the pressure which is available at the brake valve to 6900 kPa (1000 psi).
When the brake solenoid is energized, reduced pressure oil from the auxiliary pump flows to the following components:
- Across the brake valve
- Across the brake check valve
- Into brake release chambers on each parking brake
EDC Metering Spool
When the machine is traveling forward, the machine ECM directs a signal to the forward EDC. The position of the EDC metering spool is determined by the duty cycle of the signal which is sent from the machine ECM. The duty cycle is proportional to the position of the propel lever.
When the EDC metering spool moves, charge oil flows through the orifice and flows to the metering spool. Charge oil is then metered across the EDC metering spool to the forward servo piston. The forward servo piston shifts. The shift changes the angle of the swashplate in the pump. The pump then generates flow in the forward circuit.
FORWARD Circuit Flow
Forward circuit oil acts against the forward multifunction valve and flows out port "A" and out port "M1" of the pump. From port "A" supply oil is directed to port "P" of the flow divider valve. From port "M1" supply oil flows through a check valve. This stream of oil seats the check valve which is at port "M2" of the propel pump and flows to the flow divider solenoid.
Flow Divider
When the flow divider switch is in the OFF position, the flow divider solenoid is de-energized. In this case, the flow divider spool directs supply oil from port "M1" of the propel pump to port "P1" of the flow divider valve.
Inside the flow divider valve, high pressure oil acts against one side of the flow divider control spool, against a spring. The flow divider control spool shifts. This shift creates a relatively unrestricted supply path to the propel motors. In this condition, if one of the tracks were to begin to spin, most of the supply oil would flow through the motor on the spinning track.
Note: Even when the flow divider is off, large orifices in the valve provide some degree of flow control. However, the large orifices do not prevent a track from spinning with very different underfoot conditions.
The line relief and makeup valves in the flow divider valve relieves pressure spikes in the motor supply lines to the charge circuit. Also, if the pressure in any of the supply lines falls below charge pressure, the makeup section of the valve opens, and charge oil is directed into the supply line. This action prevents cavitation.
Note: When the flow divider switch is in the ON position, the flow divider solenoid is energized, and oil from the high pressure circuit is blocked at the solenoid. In this situation, the spring which acts against the flow divider control spool in the flow divider valve shifts. When the machine is operating in FORWARD, an equal amount of flow is directed to each propel motor. When the machine is operating in REVERSE, equal back pressure is created at each propel motor. In either case, action of the flow divider spool results in equal flow being transferred to each track motor.
Shift Solenoid
Forward circuit oil which enters the motors acts against the check valves. The check valves open, allowing forward circuit oil to flow to the shift valves and into the rod ends of the actuator piston chambers. When the speed selector switch is in the L position, the shift solenoid on the center manifold is de-energized. Under this condition, the head end of the actuator piston chambers is open to the motor case drain, across the control spool. The motor control plates are against the maximum stop.
FORWARD Multifunction Valve
Inside the propel pump, forward circuit oil in the forward multifunction valve closes the makeup valve and acts against the pressure limiter and the main relief valves. If pressure in the forward circuit reaches 37700 ± 690 kPa (5470 ± 100 psi), the pressure limiter valve opens. This directs oil from the forward circuit to the reverse servo piston. This action causes the pump to destroke. If the pressure in the reverse servo piston chamber is greater than charge pressure, the check valve in the end housing of the pump opens. The excess oil pressure in the reverse servo piston is relieved into the charge circuit.
The main relief function of the multifunction valve is set approximately 3450 kPa (500 psi) higher than the setting for the pressure limiter. If the pressure in the forward circuit rises to the main relief setting, the main relief valve opens. In this case, oil from the forward circuit is sent into the charge circuit.
REVERSE Circuit Flow
Oil in the forward circuit causes the motors to turn. After the oil flows through the motors, the pressure of the oil is reduced. This reduced pressure oil then enters the reverse circuit. Reverse circuit oil flows to the check valves and flows to the flushing valves inside the motors. Reverse oil also flows out of the motors. Return oil from the motors is combined and sent to port "B" of the propel pump. Inside the propel pump, reverse circuit oil flows to the reverse multifunction valve and flows to the rotating group of the propel pump. This completes the drive circuit.
Loop Flushing
In the propel motors, forward circuit oil causes the flushing spools to shift. This shift allows oil from the reverse circuit to act on the flushing relief valves. When the pressure which is acting against the flushing valves is 345 ± 172 kPa (50 ± 25 psi) less than the charge pressure, the flushing relief valves open. The orifice in each flushing valve allows a maximum of 5 L/min (1.3 US gpm) of oil from the reverse circuit to flow into the motor case drain lines.
Reverse Makeup Valve
In the propel pump, reverse circuit oil acts against the following:
- The makeup valve
- The relief valve
- The pressure limiter valve that is in the reverse multifunction valve
As the flushing valves remove oil from the reverse circuit, the pressure in the reverse circuit decreases. When the pressure in the reverse circuit is less than the pressure in the charge circuit, charge pressure unseats the makeup valve. Flow from the charge pump enters the reverse circuit. This action allows cool, filtered oil from the charge circuit to flush the propel circuit.
REVERSE, HIGH SPEED
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| Illustration 3 | g01229779 |
EDC Metering Spool
When the machine is traveling in reverse, the machine ECM directs a signal to the reverse EDC. The position of the EDC metering spool is determined by the duty cycle of the signal which is sent from the machine ECM. The duty cycle is proportional to the position of the propel lever.
When the EDC metering spool moves, charge oil flows through the orifice and to the metering spool. Charge oil is then metered across the EDC metering spool to the reverse servo piston. The reverse servo piston shifts. The shift changes the angle of the swashplate in the pump, and the pump generates flow in the reverse circuit.
Shift Solenoid
When the shift switch is in the H position, the shift solenoid is energized. The shift valve is located at the center manifold. The shift valve directs charge pressure to the control spools in the propel motors.
The control spools in the motors move, and oil is directed from the reverse circuit into the head end of the actuator piston chambers. Since the effective area of the head end of the piston is greater than the effective area of the rod end of the piston, the piston shifts. This shift moves the control plates in the propel motors against the minimum stops.
REVERSE Circuit Flow
While the machine is traveling in reverse, the following occurs:
- The reverse multifunction valve limits system pressure.
- Oil from the forward circuit flows through the flushing relief valves
- The makeup valve in the forward multifunction valve allows charge oil to flow into the forward circuit.