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Transmission General Description

Transmission General Description


The AF 40-6 automatic transmission is an electronic 6-speed automatic transmission with lock-up. The transmission is mounted directly against the engine and has a final drive with integrated differential. The power unit is transverse mounted with all-wheel drive. Gear positions P-R-N-D are selected with the selector lever mounted in the centre console. Manual up/downshifting is possible.


A special automatic transmission fluid must be used. The transmission does not have an oil dipstick. The plug has an extra center plug to check the level. It is connected to a rising tube that leads to the right level in the gearbox. Fill the oil through the conventional oil filler plug until the level is correct and oil runs out of the check plug hole in the rising tube. Measure the temperature when checking the level. The temperature is read using a scan tool.


The AF 40-6 transmission has planetary gears, disc clutches, brakes and torque converter with lock-up. The clutches and brakes are applied hydraulically. The hydraulic system is controlled by the Transmission Control Module (TCM) with the help of 8 solenoids, 2 shaft speed sensors and one oil temperature sensor. TCM communicates on the high speed bus.


The TCM is mounted directly on top of the transmission and has one connector to the car's electrical system and one directly to the transmission. The gear position sensor is a Hall sensor and is integrated in the control module. The TCM is mounted so that the selector lever shaft goes through the control module. The selector lever position can be calibrated with the scan tool, there is no mechanical adjustment.


The TCM controls the transmission according to its programming, the information from its own sensors and from other control modules. The control module adapts its control of the solenoids to compensate for normal wear in the transmission. The TCM is SPS programmable.

Shifting

The TCM can determine whether to leave a gear engaged or to change up or down. What it does is determined mainly by the gear that is currently engaged, the speed of the output shaft and the position of the accelerator pedal. The TCM changes gear by applying or releasing a friction element in the transmission. The application is regulated with PWM from the respective solenoid.

The gear can also be changed manually with the selector lever in D position if using the Tap Up/Tap Down switch. The switch is hardwired to the BCM which converts the information into a HSCAN message that is used by the TCM.

The maximum shift speed is at 7000 rpm.

Lock Up

The torque converter clutch is activated at a steady speed when there is no need of torque amplification. If the brakes are applied or acceleration increases, the function will be deactivated.

Safety Features

To protect the transmission there are temperature programs to prevent overheating. The TCM can choose to raise the shift points and activate lock up more often if the oil temperature is too high.

The reverse gear will not be activated if the car is travelling faster than 7 km/h (4 mph). If the power supply to the solenoids fails, it is still possible to drive the car. The gear position D/M gives 2nd gear and P-R-N will work as usual. In case of a major fault in the transmission, mechanical or electrical, the TCM will cut the supply to the solenoids in a controlled manner (limp home).

In case the TCM detects a failure it will go into emergency mode.

Special Gear Change Program

If an uphill gradient is detected, the gears will change at higher engine speeds and each gear will remain engaged for longer periods.

The Sport Mode can be engaged by a switch. Upon detecting the sport mode request TCM adapts the shift lines in order to enable a more progressive driving.