Microscopic investigations into lubricated friction pairs in synchronizers

Abstract

An essential component of manually operated vehicle transmissions is the synchronising device. Synchronizers have the task of minimizing the speed difference between the shifted gearwheel and the shaft by means of frictional torque before engaging the gear. Proper operation requires a sufficiently high coefficient of friction. An optimized design of the system with regard to appropriate function and durability on the one hand as well as low cost, low mass, and compact over-all dimensions on the other hand today requires time-consuming and expensive component testing. As it is easier to coat plane surfaces with a friction material than to coat the inner or outer cones of synchronizer rings, this paper investigates if the component tests can be substituted by simpler pin-on-disc type model tests. For this purpose, such model tests and tests with original synchronizers are compared, in particular, regarding the friction characteristics of different materials. Furthermore, a fluorescence-based method is successfully applied to observe the lubricant distribution and the contact conditions during shifts. The investigations reveal that there are limitations to the applicability of tests with plane model pins to real conical component behaviour, which can partly be attributed to differences in drainage efficiency. © IMechE 2008.