777F Off-Highway Truck Power Train. Relief Valve (Pilot Control Pressure), Torque Converter Inlet and Outlet Relief Valves & Modulating Valve (Torque Converter Lockup Clutch)

1.-Relief Valve (Pilot Control Pressure)

(1) Relief valve for the pilot pressure control

The gear pump for the torque converter lockup clutch supplies oil to the modulating valve for the torque converter lockup clutch. A portion of the supply oil is used as pilot oil for the hoist control valve. If equipped, the Rockford fan clutch and the Traction Control System (TCS) also use this supply oil.

The relief valve (1) for the pilot pressure control is located between the filter for the lockup clutch and the modulating valve for the torque converter lockup. The relief valve (1) is also located between the filter for the lockup clutch and the pilot circuits of the hoist control valve.

Relief valve (1) reduces the pump pressure from the gear pump for the lockup clutch to 2760 ± 350 kPa (400 ± 50 psi). The pressure is set for the pilot system requirements for the hoist control valve and used as supply oil to the modulating valve for the torque converter lockup clutch.

This valve is set at the factory and may not to be adjusted.

2.-Torque Converter Inlet and Outlet Relief Valves

Location of torque converter relief valves (1) Torque converter inlet relief valve(2) Torque converter outlet relief valve

Torque converter inlet relief valve (1) Torque converter inlet relief valve (3) Passage to the hydraulic tank (4) Spool (5) Inlet passage(6) Shims

Torque converter outlet relief valve (2) Torque converter outlet relief valve (7) Shims (8) Inlet passage (9) Spool(10) Outlet passage to the torque converter and front brake cooling screen

Torque converter inlet relief valve (1) and torque converter outlet relief valve (2) are installed on the outside of the torque converter housing. The operation of both valves is identical.

Inlet relief valve (1) controls the maximum pressure of the oil that is flowing to the torque converter. The oil supply comes from the torque converter charging section of the oil pump and the relief valve for the pilot control valve. The oil comes through the torque converter hydraulic filter. The inlet relief valve ensures that the maximum oil pressure to the torque converter does not exceed approximately 930 ± 35 kPa (135 ± 5 psi).

NOTICE
The inlet pressure going to the torque converter must not exceed 930 kPa (135 psi). Pressure that is greater than the maximum setting will damage the torque converter.

Torque converter outlet relief valve (2) controls the minimum pressure of the oil that is inside the torque converter. Oil comes from the torque converter through passage (8) . The oil then flows past spool (9) . The oil then exits through passage (10) . The outlet oil goes through the screen for the torque converter and the front brake. The oil then goes to the diverter valve for the torque converter and the front brake. The diverter valve sends the oil through the oil cooler or around the oil cooler for the torque converter and the front brake. The oil will flow through the front brakes. The oil then returns to the hydraulic tank.

Note: Some machines may have dry front brakes. On machines with dry front brakes, the oil flows from the screen for the torque converter or from the diverter valve to the tank.

The outlet relief valve ensures that the pressure of the oil that is inside the torque converter does not exceed 552 kPa (80 psi) for trucks with dry front brakes.

The outlet relief valve ensures that the pressure of the oil that is inside the torque converter does not exceed 758 kPa (110 psi) for trucks with wet front brakes.

3.-Modulating Valve (Torque Converter Lockup Clutch)

(1) Modulating valve (torque converter lockup clutch)

Modulating valve (torque converter lockup clutch)

The modulating valve for the torque converter lockup clutch (1) is mounted to the rear of the torque converter housing.

The modulating valve is an output of the chassis electronic control module (ECM). The modulating valve for the torque converter lockup clutch is a proportional solenoid valve. The modulating valve is used by the chassis ECM to directly modulate the oil pressure that is sent to the torque converter lockup clutch. When the operator selects a direction or when the operator selects a speed the chassis ECM sends a pulse width modulated signal (PWM) in order to vary the current to the clutch solenoid. The distance that is travelled by the solenoid plunger (valve) is proportional to the electrical current of the solenoid. The position of the solenoid plunger (valve) controls the oil pressure of the selected clutch. The amount of current that is sent to the modulating valve regulates the amount of oil pressure that is supplied to the selected clutch. When the chassis ECM sends the maximum current to the modulating valve, the oil pressure in the clutch is at the maximum. When no current is sent to the modulating valve, the oil pressure in the clutch is at the minimum.

The modulating valve has a connector with two contacts. One contact receives power from the corresponding connector contact of the chassis ECM (J1-48). The other contact of all the modulating valves join together. The contacts return power to connector contact J1-50 of the chassis ECM.

Note: The solenoid coil is not designed to be operated at 24 DCV directly. The chassis ECM sends a 24 volt PWM signal at a duty cycle which provides an average voltage of about 12 volts to the solenoid coil. Do not energize the solenoid coil with 24 DCV (+battery). The life of the solenoid coil will be drastically reduced if the solenoid coil is energized with 24 DCV (+battery). If the solenoid coil must be energized by a source that is different from the chassis ECM, use 12 DCV to energize the solenoid coil.

ReferenceFor information on troubleshooting the transmission, refer to the Service Manual module for Testing and Adjusting, "Chassis Troubleshooting" for the machine that is being serviced.

ReferenceFor information on calibrating the modulating valves, refer to the Service Manual module for Testing and Adjusting, "Calibration and Programming" for the machine that is being serviced.

ReferenceFor information on calibrating the modulating valves, refer to the Service Manual module for Testing and Adjusting, "Fill Time for the Transmission Clutch - Calibrate" for the machine that is being serviced.

ReferenceFor more information on the chassis electronic control module (ECM), refer to the Service Manual module for Systems Operation, "Electronic Control Module (chassis)" for the machine that is being serviced.

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777F Off-Highway Truck Power Train. Relief Valve (Pilot Control Pressure), Torque Converter Inlet and Outlet Relief Valves & Modulating Valve (Torque Converter Lockup Clutch) 2013-01-04T15:39:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown