Automatic transmissions were considered somewhat unusual in motorsport, but ZF one during the 2014 BMW M235i Racing Cup season. The automatic 8-speed transmission eases the workload for competitors, and allows the drivers to stay almost completely focused on their environment and on the track. Mechanical damage as a result of shift mistakes is excluded as are fatal blockages and dynamically unbalancing shocks on the driven axle.
Whereas the previous automatic transmission was based on a standard production line design and modified software, the 8P45R is a pure motorsport planetary transmission. By omitting the converter and other reduction measures, the designers say they saved around 15% on weight while also reducing internal power loss.
The designers retained the fundamental design and assembly - four planetary gear sets and five shift elements - from the previous transmission. One of several new features is the omission of a converter in the transmission. The pulling away or drive-off process is implemented by internal shift elements. A vibration damper upstream from the transmission input prevents damage through engine oscillations. The gear ratio spacing is closer and the rev drops between gears have been reduced.
Throughout the 2015 season, the new gearbox underwent a test and dyno-testing programme and in October it had its first track appearance on the legendary Nürburgring in a specially equipped BMW M235i race car.
Dirk Adorf, chief instructor of the BMW Motorsport junior program, said: “I am truly fascinated by the performance of ZF´s engineers after my first laps with the new gearbox. Being an automotive technician myself, I wouldn´t have thought it possible to build an automatic transmission without a torque converter, that provides such a fast changing of the gears as well as easy and comfortable starting. The clutch elements are extremely fine-tuned. I am sure that this system will be an example for other racing gearboxes and even for the development of series transmissions."
Initially, the 8P45R transmission will be exclusively to BMW M235i Racing. In the future, it is expected to be used in other manufacturers’ sports cars.