Validation of the mathematical model of the front drive axle suspension according to frequency response

Background: Power units and drivetrain units including front axle drive are highly vibration active having a sufficient influence on passengers’ comfort during the vehicle motion. Necessary noise and vibration isolation are ensured with proper dynamic behavior of bushings and local dynamic stiffness of a supporting structure where the unit is mounted. Development of target stiffness properties of bushings and supporting structures as well as analysis of the NVH issues are conducted using multibody simulation. Ensuring the adequacy of the mathematical models for solving the given tasks is necessary. Objective: Development and validation of the multibody mathematical models of the front axle drive (FAD) suspension with different content according to criteria of correlation of frequency response at the front axle drive bushings. Formulation of requirements to the multibody mathematical model for solving the NVH tasks for units with a single stage suspension as part of a vehicle. Methods: Mathematical modeling of the front axle drive suspension is made in the MSC Adams multibody simulation software. Different approaches of modeling of dynamic properties of rubber-metal bushings and the local dynamic stiffness of a supporting structure are considered. In simulation, frequency response is determined as a result of a swept sine unit force. Measurements of frequency response at the mounts after the hammer impact at the axle drive body in chosen directions are used as a validation basis. Results: The best correlation of the simulation results and the validation basis was achieved using description of rubber-metal bushings based on the Pfeffer model with scaling of properties as well as considering the front subframe flexibility using the reduced finite element model. Using of more sophisticated models of rubber-metal bushings does not contribute to better model adequacy. Considering the supporting structure flexibility as values of local dynamic stiffness has both positive and negative effects. Conclusions: In order to solve the NVH tasks of units with a single stage suspension as part of a vehicle, like a front axle drive, it is necessary to use proper inertia data, description of dynamic behavior of bushing based in the Pfeffer model and considering supporting structure flexibility in the unit mount points.