Propel Hydraulic System (NEUTRAL)
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| Illustration 1 | g01166378 |
When the engine is running, the propel pumps and the charge pumps rotate. The charge pumps draw oil from the tank through 150µ suction screens. Output oil from the charge pumps flows to the charge relief valves and to the charge filters.
After flowing through the charge filters, charge oil flows to the following components:
- The electric displacement control valves
- The metering spools for the electric displacement control valves
- The multifunction control valves
Metering Spools (Electric Displacement Control Valves)
When the propel lever is in the NEUTRAL position or the machine ECM has disabled the propel lever, the electric displacement control valves are not energized. Under these conditions, both ends of the metering spools for the electric displacement control valves are open to the case drain. Also, the center envelopes of the metering spools are active. The metering spools for the electric displacement control valves block charge oil. The spools also open a passage between the servo pistons for the propel pump and the pump case drain. The pump swashplate then moves to a minimum angle.
Multifunction Valves
Charge oil that enters the multifunction valves seats the check valves. Charge oil also acts against the makeup valves. Leakage in the propel circuit is normal. The propel pump always rotates when the engine is running. When 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 the relief setting, the charge relief valves open. This directs charge oil into the case drain of each pump.
Parking Brake and Shift Cylinders
The auxiliary hydraulic system controls the oil flow to the parking brake and the shift cylinders and from the parking brake and the shift cylinders. When the parking brake switch is in the ON position, the parking brake solenoid on the auxiliary manifold is not energized. Therefore, supply oil cannot flow to the parking brake cylinders, and the parking brakes are engaged. When the propel mode switch is in the PAVE position or in the MANEUVER position, the shift solenoid on the auxiliary manifold is not energized. As a result, supply oil cannot flow to the shift cylinders.
Note: For additional information about hydraulic control of the parking brake and shift solenoids, refer to Specifications, Systems Operation/Testing and Adjusting, KENR5046.
Propel Hydraulic System (FORWARD)
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| Illustration 2 | g01172467 |
Note: Since the right and left propel circuits operate in the same manner, the following generic circuit description can be used to discuss either circuit.
Electric Displacement Control Valves
When the machine is traveling in the forward direction, the forward electric displacement control valve is energized. The condition of the forward electric displacement control valve is determined by the duty cycle of the signal that is sent from the machine ECM. The machine ECM analyzes the input signals in order to determine the magnitude of the output signal which is sent to the forward electric displacement control valve.
Metering Spool (Electric Displacement Control Valves)
Charge pressure flows across the forward electric displacement control valve. This pressure acts against the top of the metering spool for the electric displacement control valves. The metering spool for the electric displacement control valves moves down. Charge oil is metered across the spool to the forward servo piston. The charge oil causes the forward servo piston to shift. This shift changes the angle of the swashplate in the pump. Then, the pump generates flow in the forward circuit.
Forward Multifunction Valve
Forward circuit oil flows to the forward multifunction valve and flows to the forward side of the propel motor. Forward circuit oil in the forward multifunction valve closes the makeup valve, and then forward oil acts against the pressure limiter and the main relief valves. If the pressure differential between the forward circuit and the charge circuit reaches 41990 ± 1380 kPa (6090 ± 200 psi), the pressure limiter valve opens. This directs oil from the forward circuit into the reverse servo piston in order to destroke the pump. If the pressure in the forward circuit becomes 3450 kPa (500 psi) greater than the pressure limiter setting, the main relief valve opens. This directs oil from the forward circuit into the charge circuit.
Reverse Circuit Oil
Oil in the forward circuit causes the motor to turn. After turning the motor, the pressure of the forward circuit oil is reduced. Oil at a reduced pressure then enters the reverse circuit. Reverse circuit oil flows to the following:
- The flushing valves
- The reverse multifunction valve
- The reverse side of the propel pump
The drive circuit is then complete.
Flushing Valve
Since reverse circuit oil is at a lower pressure than forward circuit oil, forward circuit oil causes the flushing valve to shift. This shift allows oil from the reverse circuit to act on the flushing relief valve. When the pressure (gauge) that acts against the flushing valve is greater than the setting of the flushing relief valve, the flushing relief valve opens. When the flushing relief valve is open, a maximum of 11 L/min (2.9 US gpm) of oil flows from the reverse circuit into the motor case drain line.
Reverse Multifunction Valve
Reverse circuit oil acts against the following:
- The makeup valve
- The relief valve
- The pressure limiter valve in the reverse multifunction valve
As the flushing valve removes 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. As a result, flow from the charge pump enters the reverse circuit. This action allows cool, filtered oil from the charge circuit to flush the propel circuit.
Parking Brake Solenoid
When the propel mode switch is in the PAVE position and the parking brake switch is in the OFF position, the machine ECM energizes the parking brake solenoid. Oil from the auxiliary pump is allowed to flow into the parking brake cylinder, and the shift cylinder is open to the hydraulic tank. The pressure in the parking brake cylinder overcomes the spring forces, and the parking brake releases. Since the shift cylinder is open to the hydraulic tank, the springs disengage the clutch. The machine will operate in the speed range for paving.
Propel Hydraulic System (REVERSE)
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| Illustration 3 | g01172470 |
The following description of the circuit can be used to discuss either the right circuit or the left circuit.
Electric Displacement Control Valves
When the machine is traveling in reverse, the reverse electric displacement control valve is energized. The condition of the reverse electric displacement control valve is determined by the duty cycle of the signal that is sent from the machine ECM. The machine ECM analyzes the input signals in order to determine the magnitude of the output signal. The machine ECM then sends the output signal to the reverse electric displacement control valve.
Metering Spool (Electric Displacement Control Valves)
Charge pressure flows across the reverse electric displacement control valve. The charge pressure acts against the bottom of the metering spool for the electric displacement control valve. The metering spool moves up, and charge oil is metered across the spool to the reverse servo piston. The charge oil causes the reverse servo piston to shift. This shift changes the angle of the swashplate in the pump, and the pump generates flow in the reverse circuit.
Reverse Multifunction Valve
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 valve
- The makeup valve in the forward multifunction valve allows charge oil to flow into the forward circuit.
Shift and Parking Brake Solenoids
When the propel mode switch is in the TRAVEL position and the parking brake switch is in the OFF position, the machine ECM energizes the shift solenoid. The machine ECM also energizes the parking brake solenoid. Oil from the auxiliary pump is directed into the parking brake cylinder and into the shift cylinder. The pressure in these cylinders overcomes the spring forces. This releases the parking brakes and this engages the shift collar. Under these conditions, the machine operates in the travel speed range.