Automatic Transmission/Transaxle: Description and Operation

ELECTRONIC SHIFT CONTROL SYSTEM





TRANSMISSION CONTROL MODULE (TCM)
The TCM is an electronic circuit component that controls gear shift and idle-up according to the signal from each sensor. It is microcomputer consisting of an IC, transistor, diode, etc. It is installed to the underside of the instrument panel at the driver's seat side.





Throttle Position Sensor
This sensor is installed to the throttle valve shaft. Throttle valve opening signal are transmitted from TP sensor to ECM as voltage signal. The signal is converted to duty signal in ECM and it is sent to transmission control module.





Vehicle Speed Sensor
This sensor is a pulse generator type that detects revolution of the output shaft (vehicle speed) in the transmission case.
The pulse generator is a noncontact sensor consisting of a permanent magnet, coil and gears.
As the gear of the output shaft turns, the magneflux from the permanent magnet varies and a voltage of the frequency corresponding to the rotor revolution occurs in the coil. This voltage is inputted to the TOM where TOM judges the output shaft revolution or the vehicle speed. The vehicle speed is also detected from the speed meter.








Transmission Range Switch
A transmission range switch is provided so that the engine can be started only when the shift lever is in the "P" or "N" position.





Brake Switch
The same switch is used as the brake lamp switch. It disengages the lock-up clutch when the brake is depressed while the lock-up clutch is operating.





Engine Coolant Temperature Sensor (ECT Sensor)
The coolant temperature sensor of the electronic fuel injection system is used and it prevents gear change to the O/D gear and lock-up when the engine coolant temperature is 3O°C (86°F) or lower.





Cruise Control Unit (if equipped)
Cruise control unit is also can be control the gear shift up or shift down to and from the O/D gear and lock-up when cruise control system is operating.








O/D Cut Switch
The gear shift up or shift down to and from the O/D gear can be selected with this switch.





Transfer 4L Switch (4WD Model)
This switch detects that the 4-wheel drive low gear is engaged and prevents the gear change into O/D and lock-up.





P/N Change Switch
The gear shift timing, normal or power, can be selected by using this switch.





Noise Suppressor (Engine Speed Signal)
Engine speed signal is from the noise suppressor. By using this signal TCM knows the engine speed and detect the actual transmission gear ratio (input/output ratio).





Fail Safe Function
This function is provided by the safe mechanism that assures safe driveability even when the shift solenoid valve or speed sensor fails.
The table below shows the gear position in each shift under a normal/abnormal condition.





Change Mechanism
The same select pattern shift lever is used as the floor type and frequently used "N" and "D" ranges are made selectable freely.