When the pump turns faster than the turbine, the torque converter is multiplying
torque. When the turbine approaches the speed of the pump, the stator starts to
rotate with the pump and turbine. When this occurs, torque multiplication stops
and the torque converter functions as a fluid coupling.
The lockup clutch is located inside the torque converter and consists of the
following elements:
• Piston and backplate—driven by the engine
• Clutch plate/damper (located between the piston and the
backplate)—splined to the converter turbine
The lockup clutch/torsional damper is engaged and released in response to
electronic signals from the TCM/ECU. Lockup clutch engagement provides a
direct drive from the engine to the transmission gearing. This eliminates converter
slippage and maximizes fuel economy and vehicle speed. The lockup clutch
releases at lower speeds or when the TCM/ECU detects conditions requiring it to
be released.
The torsional damper absorbs engine torsional vibration to prevent transmitting
vibrations through the powertrain.
PLANETARY GEARS AND CLUTCHES
A series of three helical planetary gear sets (four for 4700/4800 EVS) and shafts
provides the mechanical gear ratios and direction of travel for the vehicle. The
planetary gear sets are controlled by five multiplate clutches (six for
4700/4800 EVS) that work in pairs to produce up to six forward speeds (seven for
4700/4800 EVS) and one reverse speed. The clutches are applied and released
hydraulically in response to electronic signals from the TCM/ECU to the
appropriate solenoids.
COOLER CIRCUIT
The transmission fluid is cooled by an integral (transmission-mounted) or
remote-mounted oil cooler. Connections to the cooling circuit are located at the
front or rear of the transmission to facilitate installation of remote cooler lines. On
retarder models, only the rear cooler ports may be used. The integral cooler is
mounted on the lower rear portion of the transmission, replacing the remote cooler
manifold. Integral cooler oil ports are internal requiring coolant to be routed to
and from the cooler.
A new feature has been added on all retarder-equipped transmissions. The retarder
housing now allows addition of either a remote or integral cooler for transmission
sump fluid in addition to retarder out fluid. A by-pass cover is placed over the
sump cooling ports when the provision is not used. The sump cooler ports are
located on the lower right rear face of the retarder housing (refer to Figure 3
through Figure 8).
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