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LESSON 3: POWERTRAIN
Transmission Shift Strategy
Mechanical throttle versus Electronic Throttle Control (ETC) for transmission operation works in the following
way:
•
With mechanical throttle vehicles, the accelerator pedal is connected by cable to the throttle plate and the driver
controls airflow into the engine directly. The throttle plate position is measured directly and used as a measure
of driver intent. Transmission shift and convertor clutch events are scheduled based on throttle position.
•
With ETC vehicles the accelerator pedal is connected to a pedal position sensor. When in automatic range, the
PCM uses the pedal position and the output shaft speed sensor to determine a desired output shaft torque. Using
a model of the transmissions, this is converted to a commanded throttle angle. Transmission shift and
convertor clutch events are scheduled based on the accelerator pedal position.
•
For either type of throttle system, the pressure control programming used to control shift feel uses an estimate
of the actual torque being made by the engine. This estimate is based on the MAF sensor measurement of
airflow and is not directly related to the commanded engine torque.
3-52
12-AUG-03
2004 Explorer/Mountaineer New Model Technician Training
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