Longitudinal Vehicle Dynamics Modeling for AWD/4WD Vehicles to Study Torque Split between Front and Rear Axles

All-wheel Drive (AWD) is a mature technology and most automobile manufacturers offer this feature on their vehicles. Improved traction, enhanced vehicle stability, and better handling are some of the key characteristics of AWD vehicles which are achieved by distributing the appropriate level of torque to the front and rear axles. Accurately capturing the torque split between the two axles is essential for sizing of driveline components like gears, bearings, and shafts. Traditionally, the torque split is considered to be either 50-50%, or solely proportional to the static weight distribution between the two axles. Design decisions are made based on historical test data. In this paper a longitudinal vehicle dynamics model for AWD systems is proposed to understand the influence of various key factors such as dynamic weight transfer, compliance of driveline components, and changing tire radius on the torque split. Comparison with the test data is performed to understand the significance and limitations of the model. While more detailed models have been built and used for various purposes, to the authors’ knowledge, this is the first time a model with this level of fidelity is being used to evaluate driveline component durability.