Automatic Transmission Optimization for Better Fuel Economy 785100

In order to reduce the fuel consumption of vehicle, it is required, as a supplemental effort, to adapt the specification of powertrain to the engine characteristics. For the manual transmission, it has been well known that the specification of powertrain should be chosen so as to operate the engine under its condition of minimum brake specific fuel consumption for required power. For the automatic transmission with torque converter, however, the criteria on the selection of specification of powertrain to reduce the fuel consumption have not yet been clarified.

In this paper, such criteria are analytically examined by considering the torque converter characteristics. It is shown that the optimum condition of engine operation for automatic transmission is different from that for manual transmission, particularly at lower engine speeds. In practice, the total gear ratio of each step of auxiliary gear including the final gear and the gear shift points of automatic transmission should be carefully chosen by the obtained criteria.

By using the computer simulation based on the above analytical consideration, effects of optimum specification of automatic transmission to engine on the fuel consumption are investigated. As an example of the results, the fuel consumption of refined vehicle on the EPA City Driving Cycle is improved by 13% in case of optimum selection of total gear ratio, compared with the vehicle with current automatic transmission.