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Brief description of the gearbox

Brief description of the gearbox


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

A new automatic transmission fluid, AW-1, or 93 165 147 Automatic transmission fluid must be used. The gearbox does not have an oil dipstick. The drain plug has an extra, central plug for checking the level that is connected to a pipe that reaches up to the correct level in the box. Fill the oil through the conventional filler plug until the level is correct and oil runs out of the centre plug in the drain plug. Measure the old temperature when checking the level. The temperature is read using Tech 2.

AF 40-6 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 TCM with the help of 8 solenoids.

The TCM is mounted directly on top of the gearbox and has one connector to the car's electrical system and one directly to the gearbox. 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 Tech2, there is no mechanical adjustment.


TCM controls the gearbox 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 gearbox. TCM is SPS programmable using Tech 2.

Shifting

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. TCM changes gear by applying or releasing a friction element in the gearbox. The application is regulated with PWM from the respective solenoid.

The gear can also be changed manually with the selector lever in M position. Changing up and down is then controlled via a resistive multiplexed line from SLM to TCM.

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

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

Special gear change program

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