Besides optimal engine systems, high-efficiency vehicle transmissions are generally also required to improve fuel economy in automotive applications. For the energy loss analysis in transmissions, most research focused on the major mechanical components, such as gears, bearings and seals, while the other mechanical losses, like synchronizer losses, were usually not considered. With increasing number of synchronizers in modern transmissions, a recent study indicates that the power loss analysis of synchronizers should also be developed and appended for a more accurate investigation on overall power losses in transmissions. The function of synchronizer is to equalize the different rotational speeds of shafts and gear wheels by frictional torques, for which the synchronizer must be cooled and lubricated in order to enhance the service life. With the supplement of lubricants, fluid friction is generated due to the differential speed, when the synchronizer is in neutral position. This fluid friction can be principally regarded as load-independent synchronizer power loss. In this paper, fluid states and fluid dynamics in synchronizers with spray lubrication are analyzed analogously to multiple-plate clutches. Based on that, synchronizer power losses are modelled physically. With the physical model, possible influential factors on synchronizer power losses are determined. Together with consideration of the current test bench, an experimental design is developed regarding individual power loss testing on the system test bench. Through investigating the test results, the synchronizer power loss behavior is comprehensively analyzed and the physical model is optimized by means of parameter sensitivity analysis and optimization methods. The model is validated by the experimental data from literature.
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