Electronic control system
The transmission control module (TCM) exactly determines gear shift and lock-up engagement points based on the driving mode selected. To do this it receives information about the following:
- Selected gear - from the gear-shift position sensor (8).
- Selected driving mode - from the mode selector (11).
- Vehicle speed - from the ABS system (17).
- Transmission input shaft RPM - from transmission speed sensor (5).
- Engine speed and load - from the engine control module (ECM) (18).
- Throttle opening - from the engine control module (ECM) (18).
- Brake pedal position - from the stop (brake) light switch (19).
- Whether the accelerator pedal (AP) is fully depressed - from the kickdown switch (20) on the floor under the accelerator pedal (AP).
- Transmission fluid temperature - from a temperature sensor (6) in the transmission.
All of this information is processed by the transmission control module (TCM) (21). The control module calculates which gear will provide the best driving performance for the driving mode selected. The transmission control module (TCM) orders gear shifting by transmitting gear shifting signals to two shift solenoids (S1, S2) in the transmission. Depending on the input signals, the control module determines if and when torque converter lock- up should be activated. Lock- up is engaged with the help of a special solenoid (SL).
During gear shifting the transmission control module (TCM) modulates the transmission oil pressure via a line pressure solenoid (STH), while simultaneously sending a torque limiting signal to the engine control module (ECM) (18).
The transmission control module (TCM) is also connected to the data link connector (DLC) (22). Faults occurring in the electronic system are recorded in the control module memory for subsequent display as diagnostic trouble codes (DTCs). If a fault is serious enough to require immediate attention, the warning lamp (23) in the combined instrument panel flashes.
The gear-shift position sensor (8) provides the transmission control module (TCM) with information about the selected gear.
Engine torque is reduced during some gear shifts to provide smoother gear shifting and to minimize transmission wear. To control these functions a torque limiting request is transmitted to the engine control module (ECM) via a cable. This cable is also used to inform the engine control module (ECM) which position the gear selector is in. This is so the engine control module (ECM) can adjust the engine speed (RPM) when a gear is engaged.
The speed signal comes from the vehicle speed sensor (VSS) (17) which receives pulses from a pulse wheel, the locking wheel for the shift-lock on the output shaft. Transmission speed information is transmitted by the transmission speed sensor (5).
Information about engine speed and load comes from the engine control module (ECM). The engine control module (ECM) also provides information about the throttle opening.
If the brake pedal is depressed, the brake light switch closes and transmits a signal to the control module.
When the accelerator pedal (AP) is fully depressed, the kickdown switch (20) closes.
The transmission control module (TCM) uses the above signals to calculate the following:
- The control module determines the engine power output by comparing information about the throttle opening with the values for engine load and speed. This forms the basis for calculating gear shift engagement pressure.
- Signals from the stop (brake) light switch are used to disengage lock- up during braking in order to avoid slap in the transmission.