773E Off-Highway Truck ASK00001-UP (MACHINE) POWERED BY 3412E Engin...

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Product:  TRUCK 
Model:  773E TRUCK ASK 
Configuration: 773E Off-Highway Truck ASK00001-UP (MACHINE) POWERED BY 3412E Engine 

Systems Operation
773E Off-Highway Truck Power Train
Media Number -KENR8331-01 Publication Date -01/12/2011 Date Updated -12/12/2011

i03485725

General Information
SMCS - 4000-PWT

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Illustration 1 g00516606

Basic diagram for the power train systems

The power train is made up of four basic systems. The following systems are the four systems:

• Power Train Electronic Control Module

• Torque Converter

• Transfer Gears and Transmission

• Differential and Final Drives

The four basic systems have a hydraulic connection, an electrical connection, a magnetic connection,
or a mechanical connection.

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The operation of the power train begins at the Power Train Electronic Control Module (Power Train
ECM). The Power Train ECM receives information of the selected speed of operation through the
shift lever switch in the electrical system. The Power Train ECM uses the information from several
switches and sensors in the electrical system to control the power train hydraulic system. This is done
by energizing the appropriate solenoids.

The torque converter has a lockup clutch for direct drive and a one-way clutch for torque converter
drive mode. During the torque converter drive mode, the torque converter hydraulically drives the
transmission. The torque converter is fastened directly to the flywheel of the engine.

The Power Train ECM will activate the lockup clutch solenoid when direct drive is necessary. When
the lockup clutch solenoid is activated, the lockup clutch is hydraulically engaged. The rotating
housing of the torque converter becomes mechanically connected to the output shaft of the torque
converter through the lockup clutch. The drive shaft mechanically connects the torque converter to
the transfer gears. The transfer gears are fastened directly to the transmission. When the lockup clutch
is not activated, the torque converter drives the transmission hydraulically.

The upshift solenoid and the downshift solenoid hydraulically activate the rotary actuator of the
transmission. Movement of the rotary actuator mechanically selects the position of the rotary selector
spool. The flow through the rotary selector spool hydraulically activates the correct valves in the
pressure control valve. These valves engage the correct transmission clutches. This mechanically
connects the transmission input shaft to the output shaft and to the differential. The transmission will
not drive the output shaft unless power is flowing through the torque converter. The power that is
flowing through the torque converter can be hydraulic or mechanical.

The transmission has forward speeds and one reverse speed. The selection of reverse, neutral, or first
speed is done manually. The selection of second speed through the highest speed is done
automatically.

Reverse uses only the torque converter drive mode. First speed has both a torque converter drive and
a direct drive. All speeds above first speed use the direct drive. The torque converter will be in torque
converter drive for a short time during transmission shifts. This provides smoother engagement of the
transmission clutch. The transmission output shaft is fastened directly to the differential and the bevel
gear. The differential and the bevel gear are fastened directly to the rear axle housing.

Power is supplied from the engine to the torque converter. Power goes from the torque converter to
the transfer gears. The power then goes to the transmission. If the transmission is in gear, power
flows from the transmission to the differential. The rear axles mechanically connect the differential to
the final drives. The final drives are connected to the rear wheels. Power is then sent to the tires.

When the transmission is in the correct speed position, the mechanical movement of the rotary
selector spool causes the transmission gear switch to electronically signal the Power Train ECM that
the shift is complete. When the output shaft of the transmission is rotating the transmission speed
sensor electrically signals the Power Train ECM that the machine has moved.

The lower section of the torque converter housing is the torque converter sump. The torque converter
sump is the oil sump for the power train system.

The power train gear pump is located at the rear of the torque converter. This is a two-section gear
pump. The rear section is the scavenge pump for the power train and the front section is the charge
pump for the power train.

The power train scavenge pump section will pull oil through the magnetic screen. The magnetic
screen is located at the bottom of the transmission case. The oil from the bottom of the transmission
case is transferred into the torque converter sump.

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The power train charging pump section pulls oil from the torque converter sump through a suction
screen. Oil flows from the power train charging pump section to the power train oil filter. The flow of
oil is split after going through the power train oil filter. Some of the oil is sent to the torque converter
lockup clutch and solenoid valve. The rest of the oil is sent to the transmission hydraulic control.

The oil that is sent to the torque converter lockup clutch and solenoid valve is used to engage the
torque converter lockup clutch. When the lockup clutch solenoid is energized by the Power Train
ECM, the lockup clutch valve will send oil to the lockup clutch. The lockup clutch is engaged. The
machine will be in direct drive. When the lockup clutch solenoid is de-energized the lockup clutch
valve will allow the oil in the lockup clutch to drain to the torque converter housing. The lockup
clutch will disengage and the machine will be in torque converter drive.

The oil that is sent to the transmission hydraulic control also is sent to the upshift solenoid and the
downshift solenoid. The basic components of the transmission hydraulic control are the rotary
actuator, the selector and pressure control valve, and the pressure control valve.

When the upshift solenoid or the downshift solenoid is activated, oil is sent to the rotary actuator. The
rotary actuator turns the rotary selector spool in the selector and pressure control valve. This sends oil
to the pressure control valve. The pressure control valve sends oil at the correct rate so that the
correct clutches in the transmission are engaged smoothly.

The rotary selector spool can be manually moved through all the positions when the engine is
stopped. This is done by removing a plug on the side of the transmission case. The rotary selector
spool is in the NEUTRAL position when the spool is turned manually in a clockwise direction to the
farthest point. The counterclockwise order of each detent position after the NEUTRAL position is
REVERSE, FIRST, SECOND, THIRD, FOURTH, FIFTH, SIXTH, SEVENTH, and EIGHTH speed.
SEVENTH and EIGHTH speed may not be used.

The relief valve in the selector and pressure control valve will control the maximum pressure in the
transmission charging system. When the relief valve opens oil is sent past the torque converter inlet
relief valve and to the torque converter. If the torque converter inlet oil pressure gets too high, the
torque converter inlet relief valve will open. This oil will flow into the transmission case.

The oil that is sent to the torque converter is used as the hydraulic coupling inside the torque
converter. The oil exits the torque converter through the torque converter outlet relief valve. The
torque converter outlet relief valve will control the pressure of the oil inside the torque converter in
order to keep the torque converter full of oil at all times.

The oil flows from the torque converter outlet relief valve to the power train oil cooler. The oil is sent
from the power train oil cooler to the transmission for lubrication. The transmission lubrication oil
flows through the transfer gears and the transmission. This oil is used for cooling and for lubrication.
This oil is then deposited in the transmission case.

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