Predicting friction in synchronizer systems

• Molybdenum/steel conformal sliding contact under boundary lubrication.
• A new, simplified, description of coefficient of friction during synchronization.
• Integration of physical testing and FE simulation, results in empiric expression.
• Virtual representation of test rig cycles.

The coefficient of friction in synchronizers is important from both a performance and a functional point of view. The synchronization process is highly transient, and the parameters affecting the coefficient of friction have strong mutual dependences, making analysis highly complex. A new friction model for a lubricated molybdenum-steel contact has been developed based on integrating results from physical rig tests and FEM simulations. A simplified thermal model has also been developed, with the purpose to quickly assess the coefficient of friction based on transient force and synchronizer dimensions. The results show good correlation with measured data except at very low sliding speed.