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Current demands for shift comfort and driveability, and the need for interaction between the transmission and other vehicle electronic systems provide the impetus for introducing electronic control systems for transmissions. The standard functions of such systems have proven their worth and contributed towards satisfying these demands. For this reason, despite the additional cost involved, most automatic transmissions will be electronically controlled within five years. The need to optimize fuel consumption leads to wider gear ratio spreads. New systems which satisfy this demand will be 5-speed automatic transmissions and CVT in particular, and perhaps twin-clutch transmissions for special applications. All these new systems will need electronic control to reach competitive performance levels.

In the automatic transmissions sector, the use of microcomputer control units has made it possible to introduce systems with previously unattainable performance characteristics in terms of economy and ease of operation. With the new generation of electronic control units for the ZF Ecomat transmission system further improvements by means of new functions such as closed loop shift control and diagnostic capability are introduced. The increasing complexity will place greater emphasis on support during the commissioning phase and the service of these systems. The new generation of electronic control units therefore comprises a range of devices such as portable diagnosis terminals and laptop-PC for a computer-based application of the system.

The paper describes the electronic control of an automatic 4-speed transmission with lock-up clutch. As compared to purely hydraulically controlled transmissions, this control offers a clearly improved quality of shifting and the possibility of achieving improvements in fuel consumption thanks to a special economy program. The electronic control unit is a Bosch MOTRONIC which has been expanded to include the functions of transmission control. A special feature is the engine torque control which is implemented by way of retarding the ignition when shifting. This opens up an additional degree of freedom for optimizing a transmission in terms of shift comfort, life of the friction elements and the power which can be transmitted.