Chrysler PT Cruiser 2001 Service Manual Supplement page 1243

21 - 58 TRANSAXLE
DESCRIPTION AND OPERATION (Continued)
TORQUE CONVERTER
DESCRIPTION
The torque converter is located in the bellhousing
area of the transaxle, between the engine and tran-
saxle. The torque converter is a fluid coupling that
transmits torque from the engine drive plate to the
input shaft of the transaxle. The torque converter
consists of four main components (Fig. 3) :
• Impeller
• Turbine
• Stator
• Converter Clutch assembly
Fig. 3 Torque Converter Assembly
1 – TURBINE
2 – IMPELLER
3 – HUB
4 – STATOR
5 – CONVERTER CLUTCH DISC
6 – DRIVE PLATE
OPERATION
The converter impeller (driving member), which is
integral to the converter housing and bolted to the
engine drive plate, rotates at engine speed. The con-
verter turbine (driven member), which reacts from
fluid pressure generated by the impeller, rotates and
turns the transmission input shaft.
Torque is transmitted by fluid passing through
curved vanes in both the impeller and turbine. Since
the coupling is produced by transmission fluid, the
turbine can slip or turn slower than the impeller.
The stator contains a one-way overrunning clutch,
which free-wheels when the impeller and turbine are
rotating at the same speed. However, the stator stops
when speed reduction or torque increase take place.
When the stator stops, it changes the direction of the
fluid leaving the turbine vanes. This directs fluid
back into the impeller with greater force, resulting in
torque multiplication.
The torque converter clutch is hydraulically oper-
ated and controlled by the TCM. It consists of a pis-
ton and a frictional disc that form a direct
mechanical link between the impeller and turbine
when slippage is inefficient or unnecessary.
The torque converter hub drives the transmission
oil pump.
ELECTRONICALLY MODULATED CONVERTER
CLUTCH
In order to reduce heat build-up in the transmis-
sion and buffer the powertrain against torsional
vibrations, the TCM can duty cycle the LR/CC sole-
noid to achieve a smooth application of the torque
converter clutch. This function, also referred as
"Electronically Modulated Converter Clutch (EMCC),
can occur at various times depending on the follow-
ing variables:
• Shift lever position
• Current gear range
• Transmission fluid temperature
• Engine coolant temperature
• Input speed
• Throttle angle
• Engine speed
The TCM controls the torque converter by way of
internal logic software. The programming of the soft-
ware provides the TCM with fine control over the
LR/CC solenoid. There are four output logic states
that can be applied as follows:
• No EMCC
• Partial EMCC
• Full EMCC
• Gradual-to-no EMCC
NO EMCC
Under No EMCC conditions, the L/R Solenoid is
OFF. There are several conditions that can result in
NO EMCC operations. No EMCC can be initiated
due to a fault in the transaxle or because the TCM
does not see the need for EMCC under current driv-
ing conditions.
PARTIAL EMCC
Partial EMCC operation modulates the L/R Sole-
noid (duty cycle) to obtain partial torque converter
PT