Fixed step clutch modeling and simulation for automotive real-time applications

Efficient coordination of actuating elements is an important challenge for modern automotive control units in order to deliver the requested torque for propulsion during all driving conditions. Model-based approaches have large potential to deal with the growing complexity. The need for real-time execution leads to fixed time step solution of the model equations. Solving model equations containing friction elements is a major challenge, since adaptive time step methods involving zero crossing detection are not feasible for real-time execution. This publication focuses on a technique for modeling complex drivetrain layouts that contain several friction elements like clutches and brakes. The main target of this contribution is to loosen requirements on maximum time step size which arise due to discontinuous friction modeling within the model equations. The proposed approach enables model-based calculations at larger time step sizes. This permits online calculation of complex gear transmission models at usual time rasters of common automotive control units.