System Overview: Notes

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Fig 1: Identifying Rear Electronic Module (REM)

Courtesy of VOLVO CARS CORPORATION

AW55-51 (and AW50AWD) is a 5-speed electronically controlled automatic transmission with a lock-up function for the three highest gears. The transmission control module (TCM) adapts the gear changes to ensure that the correct gear is selected for the driving mode, engine load, driver requirements, speed etc. This gives good fuel economy combined with increased comfort by ensuring smoother gear changes and lower noise levels.

The transmission control module (TCM) receives information about the desired gear position and driving mode from the driver. In conjunction with the signals from a number of sensors in the transmission and the engine control system, unlike with a purely hydraulically controlled transmission, this allows the control module to calculate the optimal shifting points and engagement of lock-up. The control module allows for small changes in the operating conditions and adapts the various transmission functions to ensure that the correct gear is always selected in relation to the driving mode selected by the driver.

The transmission control module (TCM) has adaptive capability. This is to ensure smooth shifting throughout the service life of the transmission.

In order to precisely determine the gear shift and lock-up engagement points based on the driving mode selected, the control module receives information about the following:

Selected gear position - from the gear-shift position sensor
Selected driving mode economy/sport - reactive function programmed in the control module which is controlled by the speed at which the accelerator pedal (AP) is depressed. Quick "pedal movement" = sport mode. Winter (W) mode is activated using a switch on the gear selector assembly
Transmission input shaft RPM - from the transmission speed sensor
The transmission output shaft RPM - from the transmission output speed sensor
Transmission fluid temperature - from the temperature sensor in the transmission
The engine speed (RPM) and torque as well as throttle opening - from the engine control module (ECM) via the controller area network (CAN)
If the accelerator pedal (AP) is depressed and to what extent - from the engine control module (ECM) via the controller area network (CAN)
The engine coolant temperature - from the engine control module via the controller area network
Vehicle speed - from the brake control module via the controller area network
If the brake pedal is depressed and to what extent - from the brake control module via the controller area network.