Technical Committee Lubricants
Investigation on the Influence of the Lubricant on the Synchronizer Losses in Transmissions
This paper aims to investigate the influences of the lubricant on the drag torque of
transmission synchronizers. Thereto, twelve lubricants, consisting of different base oils
(mineral oil group 1, group 2, group 3 and ester oil) and additives (extreme-pressure and
viscosity-index-improver), with different viscosity grades are used. It can be shown that the
synchronizer drag torque depends significantly on the oil viscosity at operating conditions.
Variation in base oil, additives and viscosity grade do not affect the drag torque. Thus, in
order to minimize the synchronizer drag torque of transmissions, it is favorable to reduce the
viscosity of the transmission fluid at operating conditions. Thereby, it is not relevant how the
viscosity-reduction is achieved. For example, low viscosity base oils and viscosity reducing
additives will show the same effect on the drag torque, as long as they equally reduce the
viscosity at operating conditions. A regression analysis of the synchronizer drag torque
shows a good match of measured and calculated synchronizer drag torques and confirms
the significant impact of the oil viscosity at operating conditions.
The IGF project (16458 N) of the research association DGMK was funded by the Federal Ministry of Economics and Technology via the AiF within the framework of the programme for the promotion of joint industrial research and development (IGF) on the basis of a resolution of the German Bundestag.