Simulation
Bearing Creep in Electric Vehicle Drivetrains
A reduced-order bearing contact model predicts slow rotational creep of bearing outer rings in EV drivetrains, reducing simulation time from days to minutes while capturing the counterintuitive torque-creep relationship driven by nonlinear stick-slip mechanics.
The Failure Mechanism
Bearing creep is a subtle drivetrain failure mode. A rolling element bearing's outer ring is mounted in a housing with an interference fit designed to prevent relative motion. In practice, the rotating load distribution of the rolling elements induces a travelling deformation wave on the outer ring surface. Under the right conditions, microscopic stick-slip at the ring-housing interface accumulates over millions of revolutions into macroscopic rotation of the ring inside its housing.
The consequences — fretting corrosion, housing bore wear, heat generation, loss of interference fit — develop slowly, which is what makes bearing creep particularly difficult to detect before it becomes a structural problem.
The work was carried out at KU Leuven LMSD in collaboration with Toyota Motor Europe.
The Model
The simulation framework assembles five components. An analytical 5-DOF ball bearing model based on Hertzian contact theory predicts individual rolling element forces on the outer raceway. A finite element model of the outer ring captures the deformation field at the ring's outer surface. A frictional contact model with stick-slip transition governs the ring-housing interface. A Floating Frame of Reference formulation allows the outer ring to undergo macroscopic rigid-body creep while its elastic deformation is described by a linear FE model. Reduced-order modelling based on contact shapes then reduces the full-order model to a manageable size.
The contact shape approach is the key ingredient. Classical modal reduction is efficient when response is dominated by smooth global modes, but bearing creep is driven by a localized travelling deformation wave under moving rolling-element loads. Precomputed contact shapes capture this wave for each angular position of the cage, and these are interpolated during the simulation as the cage rotates. The full-order model with approximately 20,000 degrees of freedom reduces to a few dozen generalized coordinates.
Results
Simulation time drops from the order of days to the order of minutes, making parameter studies and design exploration feasible. A notable result from the analysis is that creep velocity does not increase monotonically with transmitted torque. At low torque, increasing load asymmetry can amplify the travelling-wave effect and accelerate creep. Beyond a certain point, higher contact pressure expands the stick zones at the housing interface and suppresses further ring rotation.
This nonlinear behavior illustrates why physical intuition alone is insufficient for predicting bearing creep — and why a model that correctly represents the coupled rolling-element, elastic-ring, friction, and rigid-body dynamics is necessary for design guidance.