Evaluating the ratcheting performance of park lock mechanism for electric drive unit using Multi body dynamic approach

Electric Drive Unit (EDU) is essential system in electric vehicles and one of the important features in EDU is the Park Lock mechanism. It ensures safety of vehicle in parked condition and prevents vehicle from rolling on grades by locking the transmission. When vehicle is on a grade and park lock is activated, a pawl and ratchet system gradually slows down the vehicle to the critical speed of engagement with a series of acute ratcheting events between rachet gear and pawl teeth before fully locking the axle output shaft. This phenomenon is crucial because high speed engagement damages the mechanism due to sudden loads while low speed engagement causes risk of vehicle roll. Ratcheting phenomenon of park lock mechanism is highly nonlinear, dynamic and depends on different factors like rachet and pawl profiles in contact, friction properties, spring loads, actuation mechanism etc. Due to these uncertainties, critical ratchet engagement speed is not a single value as calculated by analytical formulae, but it varies between a certain speed range. Physical testing of park lock mechanism gives accurate engagement speed measurements, but it has dependencies on prototypes that are expensive, and feedback is not available at design stage. To address this need, MBD simulation approach is proposed to analyze ratcheting in a park lock mechanism at design stage using MSC Adams. The MBD model for ratcheting analysis incorporates contact friction and dynamic loads to ensure model accuracy and DOE of rachet positions to replicate vehicle rolling condition. The ratchet engagement speed is evaluated as output for each experiment. The proposed simulation method is validated with physical testing where a range of ratchet engagement speeds are correlated. It shows the reliability and applicability of proposed approach for ratcheting analyses to reduce development time and cost with improving safety in electric vehicles.