For its 6HP family of six-speed transmissions. Four and now five speed automatic transmissions are a given in the “landscape” of today’s passenger automobiles. Tasked with optimizing delivery of engine torque to drive wheels under varying conditions of load, demand, and terrain, automatic transmissions are meant to operate as seamlessly and transparently as possible, to provide satisfactory performance, comfort, and efficiency.
More recently other criteria have begun to be important, too, or more important than previously. Handling ever-greater amounts of available power or torque, while at the same time reversing the trend that more speeds means more parts, greater size, more weight, and higher costs, are two such demands. Increased efficiency is another, meaning greater fuel economy. Reducing manufacturing cost at the same time is yet another.
ZF’s solution, which at first might seem evolutionary, since six speeds is one more than five, is a totally new architecture for its HP six-speed automatic transmission, and it succeeds in an innovative way in managing all these criteria successfully. Using a new Lepelletier gear set, which needs less space than previous ones, ZF has designed a new gearbox architecture that is totally electronic, requiring no mechanical linkages to control it, and has a capacity of 260 lb-ft., making it more than adequate for today’s generation of high torque diesels, and compatible with any common drivetrain configuration. Simultaneously, production techniques for this new architecture were revolutionized, so that, for example, many machined parts have now become stampings.
The overall result of the innovative design of the new six speed automatic transmission vis-a-vis today’s five speeds is greater torque capacity, 30% fewer parts, 13% reduction in weight, 5-7% less fuel consumption, better acceleration, and a smaller package size, with one extra gear. The transmission made its debut in the new 2002 7 Series BMW