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Improving Fuel Economy by Increasing Gear Steps of Automatic Transmissions
Technical Paper
912483
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English
Abstract
A method for the determination of the optimum number of gear ratio steps is discussed in consideration of transmission efficiency, vehicle weight, and engine performance, with a view to improving the fuel economy of passenger cars.
Shifting mechanisms which had gear ratios in the practical 5-8 step range with common planetary gear trains were selected. The efficiency of each type was estimated based on the measurement of spin losses on 4-speed automatic transmission units, with considerations of the number of gear trains, clutches etc. The effect of the increase in gear ratio steps on fuel economy was simulated for different combinations of vehicles of various weights and engines of different performance.
The 5-speed unit was found to be the most practical among the transmissions studied in effectively improving fuel economy. It was also found that improvement in fuel economy is greater on cars having higher engine torque per vehicle weight.
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Citation
Ueda, K., Sakurai, S., and Sado, O., "Improving Fuel Economy by Increasing Gear Steps of Automatic Transmissions," SAE Technical Paper 912483, 1991.Also In
References
- Chana, H. E. et al “An Analytical Study of Transmission Modifications as Related to Vehicle Performance and Economy” SAE Paper 770418 1977
- Hattori, N. “A New Five-Speed Nissan Automatic Transmission for Passenger Cars” SAE Paper 900551 ( 1990
- Tsai, L. W. et al “The Categorization of Planetary Gear Trains for Automatic Transmissions According to Kinematic Topology” SAE Paper 885062 1988