K. Hebbale’s research while affiliated with R&D Systems and other places

Automatic transmissions arc used in more than 85 percent of the automotive applications in North America. In most of these transmissions, a single shift schedule map is used to determine points when the transmission is shifted from one gear to another. The shift schedule is predetermined and is optimised for fuel economy/performance for a certain vehicle load and with acceptable drive-ability. These shift points arc a function of throttle position and vehicle speed. The shift points do not take into consideration the load on the vehicle, be it extra passengers in the vehicle or extra load in cargo or towing a trailer or driving up a grade. In most cases, the shift points arc not adapted based on the load on the vehicle. Some automakers do provide a tow/haul switch, which provides a different shift schedule. Again, this towing schedule is pre-programmed and hence is not a function of the actual load on the vehicle. Some automakers inhibit certain shifts when the engine power is deemed not sufficient in the new gear. In this paper, an adaptive shift schedule system is described in which the deviation of current transmission output acceleration (which is a direct reflection of the actual load on the vehicle) from a nominal value is used to obtain a new shift point. The load on a vehicle can be indirectly estimated without computing the vehicle mass and/or the gradient of the road. The current transmission output (or vehicle) acceleration can be compared with the acceleration of a nominal vehicle to estimate the load on the vehicle. The nominal value of the acceleration is calculated in real time from a mathematical model of the nominal vehicle. The nominal could be defined as a vehicle with two passengers on a flat road. The deviation of the current acceleration from the nominal is used to compute a modification factor for the shift schedule. The adaptation method can be redesigned for fuel economy gains by suitably defining the nominal vehicle and appropriately designing the shift maps used in this method. Vehicle test results arc presented to show that shift points can be adapted to obtain enhanced performance from the powertrain under certain loading conditions.

Automotive transmission is a key element in the powertrain that connects the power source to the wheels of a vehicle. To improve fuel economy, reduce emission and enhance driving performance, many new technologies have been introduced in the transmission area in recent years. This paper first reviews different types of automotive transmissions and explains their unique control characteristics. We then address the challenges facing automotive transmission control from three aspects: calibration, shift scheduling, and sensing, actuation and electronics. Along the way, research opportunities to further improve system performance are discussed.

The split-torque, geared-neutral transmission concept has potential for simplifying transmission design by eliminating the need for launching devices such as torque converters, fluid couplings, or slipping clutches. In addition, it can provide forward and reverse ratios without the need for additional clutches or gearing. Because of the theoretical infinite ratio range of the transmission, it has considerable potential for improving vehicle fuel economy and performance. However, the difficulty associated with the control of such transmissions has prevented the concept from being successfully implemented in automobiles. A dual-cavity, half-toroidal, traction-drive transmission design using the geared-neutral concept was developed. Several transmissions were built for control development and vehicle implementation. This paper describes the control system developed for the geared neutral part of the transmission operation. The control strategies and algorithms were developed based on a detailed dynamic mathematical model and computer simulation of the complete driveline of the vehicle. Both engine and transmission controls were coordinated to ensure smooth and stable operation of the geared neutral point. Specific attention was given to providing characteristics similar to those of a conventional automatic transmission, such as forward and reverse creep. Both simulation and vehicle test results are presented to show that stable geared neutral operation is possible under all conditions.