A Real-time Capable, Three-dimensional, and Nonlinear Multibody Model of the Mercedes-Benz G-Class for an Efficient Assessment of Off-road Performance in Early Stages of Vehicle Development

This article deals with the development of a real-time capable, three-dimensional model of the Mercedes-Benz G-Class with flexible ladder frame that considers nonlinear suspension kinematics and force elements. The shift to new drivetrain technologies often results in a significant increase in vehicle weight and requires corresponding design modifications - also applying to off-road vehicles. These modifications result in changed stiffness of elements such as the ladder frame or anti-roll bar, which significantly affect vehicle dynamics and off-road performance. Therefore, strategic, efficient assessments must be made in early development stages, where no detailed information about individual systems and components is available yet, to detect and avoid potential massive, costly changes in later stages. This requires a “handmade” vehicle simulation model specifically tailored to this particular application, since the use of commercial multi-purpose simulation packages is not effective or suitable in this highly problem-oriented case. Based on a rigid multibody system approach and principles of analytical mechanics, the equations of motion of this novel model are derived in their mathematically most efficient form and implemented in MATLAB/Simulink. The complete system is separated into a modular structure of subsystems to enable efficient numerical solving of the complex overall system as well as easy modifications of certain characteristics or whole subsystems such as frame, body, wheel suspensions, and tires. All couplings are modelled by appropriate force elements or kinematic constraints. The parameter identification process is described and an experimental validation of the vehicle model based on measurements of the Ramp Travel Index (RTI) is presented. The results show that the model enables numerically efficient and physically plausible assessments with sufficient accuracy. Finally, an outlook and recommendations regarding further investigations are given.