Methodology for generating off-road tracks for powertrain simulation of off-road passenger vehicles

For off-road driving, particularly on steep grades and over barriers, the engine torque is a key design criterion of off-road vehicles. In conventional powertrains with combustion engines, mechanical all-wheel-drive systems combined with differential locks are used to distribute the torque demand between the front and the rear axle based on wheel-specific traction. With the growing market share of electric powertrains, off-road applications are becoming increasingly relevant for electric passenger cars. In comparison to conventional powertrains, electric all-wheel-drive configurations do not have a mechanical torque transfer between the two axles. If one axle experiences low traction, the second axle can rely on its own torque capability only. Transfer of unused torque of the slipping axle to the other one is not possible. The challenge, therefore, is to specify the right torque requirements for each axle for off-road driving while avoiding an over-dimensioning and high powertrain costs. The torque requirements must be defined in the very early stages of the development, when real-world measurements are not available. As a result, these definitions must be based on simulation. This paper presents a simulation approach to address this engineering challenge. A key aspect is the modeling of the representative off-road track as input for the simulation. A method of track generation was developed by using real vehicle measurement data from off-road tracks, combined with GPS and road information. The virtual track modelling process was designed to match the overall torque behavior observed in both simulation and measurement to confirm a validated and trustful simulation approach. The validation of the approach will be shown. Finally, the method will be applied to the dimensioning of the powertrain of a hypothetical electric off-road vehicle for a proof of concept.