THROTTLE MODULATNO REGULATOR AND ENSORSt=GOVERNOR SS PE 1n1' VAL MN AMWE MAIN MUUORVAE fl RELAY ate VALVESHIFT TOWERAWN SUFI811255 Microprocessor Controls for Truck and Bus Transmissions G. W. Schaefer Detroit Diesel Allison Div. of General Motors Corp. ABSTRACT Controls are the key to meeting increasing transmission and diesel engine performance needs. Customer demands for optimum vehicle performance and rapidly increasing number of differing heavy duty transmission applications are pushing present hydraulic controls to their limits, and require the current controls be specifically calibrated for the various appli- cations. A microcomputer-based control system can overcome these limitations and also provide performance improvements. Application of the microcomputer for truck and bus transmissions is of considerable inter- est at this time as it has already been devel- oped for the automobile industry, thus assuring high reliability and a large production base to minimize cost. CONTROLS ARE THE KEY to meeting increasing transmission durability, reliability and per- formance needs. Present truck and bus trans- missions have open loop hydraulic controls very similar to the type used on automobile trans- missions. These controls have provided, and continue to provide, excellent performance; however, rapidly increasing number of different transmission applications, customer demands for optimum vehicle performance, increased dura- bility and reliability, and anticipated govern- ment legislations are pushing these controls to their limits requiring that they be specially calibrated for the various applications. Improvement of performance can be achieved by replacing the hydraulic transmission con- trols with electrohydraulic controls which in- corporate electronics for intelligence but con- tinue to employ hydraulics for the power to apply the clutches in the transmission. For the near term, open loop electronic transmis- sion controls are being developed. To achieve the longer term objectives, closed loop elec- tronic transmission clutch controls are re- quired. Microcomputer technology appears to be ideally suited for these developments. The major challenge is to develop cost effective microcomputer based transmission control sys- tems and associated sensors and transducers. Achievement of a high level of overall system reliability is a key development requirement.TRANSMISSION CONTROLS In the early 1970's Detroit Diesel Allison of General Motors introduced into production automatic, discrete component, open loop, elec- tronic transmission controls for heavy duty off-highway vehicles. Prior to being equipped with the automatic controls, these vehicles utilized manual powershift transmissions. These electronic controls have been very successful in reducing overall vehicle operating costs and in increasing vehicle availability. The micro- computer-based electronic controls under devel- opment build on the successful production elec- tronic controls system by improving and refin- ing it and making it cost effective for on- highway transmission applications. Figure 1 shows a partial mechanization of an automatic hydraulic transmission control presently used in on-highway vehicles. In the AIR PRESSV TRONA VALVEPEDAL Fig. 1 - Automatic hydraulic control present production electronic control system, added computational capabilities are provided by replacing the hydraulic logic with elec- tronic intelligence, as shown in Figure 2. With this system, the operator selects the highest range that he wants the transmission to reach. The electronics, using inputs of engine throttle and transmission output speed, com- pares these conditions to pre-programmed shift conditions and determines when a shift should be made. A signal is then sent to the valve 43Downloaded from SAE International by University of Auckland, Saturday, September 29, 201844 Fig. 2 - Automatic electronic control body to initiate the shift. The rate of applica- tion of the clu