An Advanced Electronic Control and Diagnostic System for Automatic Transmission

The functions, design and mode of operation of a new electronic control system for automatic transmissions for city buses are described. Apart from the dual-channel computer structure for safety functions used here for the first time for electronic transmission control, the principal features of the control unit are its capability of communication, its high level of self-diagnosis, and its modular structure. Furthermore, a new type of actuator has been developed in the form of pressure control solenoid valves. Gearshift programs depending on driving resistance reduce fuel consumption while ensuring optimum drivability. The control pressure required for maintaining a given target slip time is computed in advance with the aid of a simulation model of the transmission memorized in the electronic control unit. Deviations due to tolerances or aging are compensated by adaptive correction of the control pressure. The automatic adaptation to changing conditions leads to a constantly high level of comfort in respect of gearshifts over the entire lifetime.