ABSTRACT Advanced Controls for Heavy Duty Transmission Applications J.G. Bender and K.D. Struthers Allison Transmission Div. General Motors Corp. Allison Transmission Division of General Motors Cor- poration is currently developing an electronically con- trolled automatic transmission system utilizing advanced technologies in microprocessors, application specific inte- grated circuits (ASICs), sensors, actuators, displays, and direct electronic clutch pressure control. The transmission system has been designated the World Transmission (WT). Included is a complete family of heavy duty automatic transmissions which will become part of the Allison Trans- mission product line starting in 1991. The WT design provides expanded capabilities over present transmission technology and results in improved performance with ben- efits in life cycle cost. A key advancement in the state-of-art of transmission shift quality has been achieved with the WT transmission through use of a fully automatic self calibration feature. Implementation of this feature is achieved through use of an adaptive closed-loop clutch pressure control system. The microprocessor based con- troller is a second generation Allison Transmission Elec- tronic Control system (ATEC 11). The system utilizes the Motorola MC 68HCll microcomputer which provides in- creased computational speed for enhanced transmission control, on-chip functions for expanded diagnostics and communication, and inputloutput capability to meet cur- rent and future customer needs. In the following sections, the WT transmission system concept is presented together with a description of the ATEC I1 system. Included is an overview of the electronic hardware components, the system operating features, and the adaptive clutch control system. The electronic control unit interfaces associated with the operator, transmission, and vehicle systems are also addressed as a part of this description. Standardized serial data links provide digital communication with a remote shift selector, vehicle dis- plays, diagnostic equipment, and other vehicle systems. Various adaptive shift control test results are also provided to illustrate the transmission system operating benefits. BACKGROUND Allison has been the world's largest producer of truck and bus automatic transmissions since the first heavy duty automatic transmissions were introduced in 1946. The transmissions are available worldwide in the products of every major truck and bus manufacturer. Allison is also the primary supplier to the military market for medium and heavy duty wheeled and tracked vehicles. User needs are the major force stimulating the devel- opment of the new WT transmission product line. Lower unit, operating, and maintenance costs coupled with out- standing shift quality are the primary demands of the end users and the primary goals of Allison. Also, fuel economy continues to be an important concern. In most applications, fuel represents the largest or second largest direct operat- ing expense. As the trend toward lower engine operating speed continues, automatic transmission systems must change to work in partnership with the engine and other vehicle systems and displays to produce the most efficient overall integrated system, while continuing to provide the same or improved speed and grade climbing capabilities. Beyond the requirements of lower costs, improved quality, and increased fuel economy, today's industry also demands ease of installation, both for the vehicle builder at assembly and for the end user at repair time. The WT transmission is a direct response to the changing needs in the world marketplace. The WT transmission series consists of a full line of heavy duty automatic transmissions for truck and bus models. The transmission series, along with the tools for fabrication and service, are a part of a simultaneous en- gineering design effort that allows prod