Towards model-based development of heavy truck synchronizers

Gear shifts are becoming more and more important as engines are adapted to low speed and high torque working conditions. Synchronizers are key components for successful gear shifts. To adapt the synchronizers to future engines and thus new working conditions, improved development tools are needed. This thesis includes a comprehensive gear shift and synchronizer frame of reference section with detailed explanations of how a synchronizer works. The thesis also presents two types of numerical models that enable design analyses of the synchronization process. Fluid-structure interaction models were used to simulate oil evacuation between the synchronizer cones to assess the synchronizer performance during the pre-synchronization phase. For the main synchronization phase, thermomechanical finite element models were used to simulate the transient temperature in the synchronizer contact surfaces. To verify and validate the thermomechanical simulations, both bulk and surface temperature measurements were used, as well as a qualitative comparison of the position of initial wear marks relative to the position of high surface temperature areas in the simulation. The validated thermomechanical model was used to predict failure in molybdenum coated synchronizers. It was shown that the simulated temperature is a better predictor of synchronizer failure than the commonly used parameters “synchronization energy” and “synchronization power”. A methodology to develop friction models based on sliding speed, contact pressure and surface temperature was developed, and applied for a molybdenum coated synchronizer. To allow for improved accuracy of carbon fiber reinforced polymer (CFRP) lined synchronizer simulations, material data for a CFRP friction lining was estimated with different test methods. A contact surface temperature threshold where a reduction in coefficient of friction, accelerated wear and formation of hot spots starts was identified. To reduce the maximum surface temperature, a relative angle between the cone contact surfaces can be introduced. The optimum relative cone angle was determined based on measured geometric deviations for a population of manufactured synchronizers. It was shown that there is an optimum relative cone angle that significantly can reduce the maximum surface temperature during synchronization.