A Study of Transmission fluid Performance on Fuel Economy 2007-01-1980
To apply a fuel economy performance to AT&CVT fluid for common use (hereinafter AT/CVT fluid) and manual transmission fluid, by optimizing fluid viscosity, a fundamental study was investigated. Generally, it is well known that the viscosity of polymer-added transmission fluids is gradually reduced, due to deterioration of the viscosity index improver caused by shear stress. An excessive viscosity reduction causes an operation failure or damage to the transmission.
Considering above factor, the authors focused attention on the potential of a low viscosity formulation to improve fuel efficiency by reducing an internal stirring-resistance of the transmission. Also from the viewpoint of friction characteristics, the performance of a base oil was studied. Utilizing the EHL (Elast-Hydrodynamic Lubrication) tester  and vehicle tests, the performance of base oils was evaluated for the fluid development. Considering fluid viscosity and friction characteristics, transmission fluid formulations were studied.
In the case of AT/CVT fluid, considering the stability of a hydraulic pressure system, a low viscosity fluid was developed. It was clarified that the developed AT/CVT fluid showed an excellent performance on the property of torque transmittance. Torque transmittance loss is extremely reduced at low fluid temperature and low speed driving conditions, which contributes to improving the performance of the practical driving condition of vehicles. On the other hand, manual transmission fluid was also studied by applying a low viscosity fluid, using the same concept as the developed AT/CVT fluid. The developed manual transmission fluid showed a better fuel efficiency, while providing the improved shift feeling.
This paper describes the study of transmission fluids with a low viscosity property, by applying several rig tests and actual transmission tests. The developed low viscosity fluid shows excellent performance on fuel efficiency, while ensuring practical performance. This fluid formulation technology has further potential for fuel efficiency improvement.