Unloaded Synchronizer Wear in Manual Transmission Gearbox

Synchronizers are the most critical parts of a manual transmission. There are classical calculations available for the synchronizer design and studies are available for the normal functioning of synchronizer rings which describes how the synchronizer behaves in the event of gear shifting. The objective of this study is to describe the synchronizer behavior when synchronizers are not functional, i.e., in other gear engaged condition and the rings are free. This study describes the failure mechanism of the unused synchronizer rings which are moving freely in the packaging space. The findings of this synchronizer design cannot be limited only for synchronizer performance and standard durability calculations. To ensure proper function of synchronizer rings and to achieve the required life the external parameters like clearances, lubrication, clutch design for dampening torsional vibration from the engine are to be considered. From the tests, it's observed that the high-speed difference and the vibrations cause the burning of the synchronizer ring and the wear of the threads. This burning increase exponentially with the increase in the testing time. This technical paper covers the failure mechanism and the methodology to avoid unloaded synchronizer wear. The study presented in this paper describes the synchronizer behavior when synchronizers are not functional either gear is engaged, or other gear is engaged in transmission.