Car Body Influence on the Perceived Driving Dynamics due to Feelable Structure Vibrations

This article focuses on passenger cars whose car structure is separated from the chassis. The elastic properties of the car structure, often measured with static and dynamic stiffness parameters, have significant influence on driving dynamics (which includes handling and riding comfort). However, a design process based on empirically determined target values for those stiffness parameters does not guarantee adequate structural quality in terms of driving dynamics requirements. Vehicle vibration behavior, which is perceived as driving dynamics, has a frequency range up to approximately 20 Hz with acceleration amplitudes sufficiently large to be feelable. Previous research assumes that the vibration behavior of the car structure itself cannot be relevant for driving dynamic perception as the lower limit for its vibrations is given by the first-order bending and torsional modes, which are normally above 20 Hz. In contrast, the analysis in this article yields the following hypothesis: vibrations of the car structure in relation to the chassis (e.g., pitching, rolling, yawing) have frequencies as low as to be sensed as driving dynamics and are influenced by variations in the car structure itself. A method based on a transient calculation to simulate the observed vibration behavior is developed by considering nonlinear effects. It is used to evaluate the influence on driving dynamics of structural variations of a test car. Frequency-weighted accelerations show differences among the structure variants which are perceivable as differences in driving dynamics. A validation based on hardware tests confirms this result. This outcome validates the hypothesis and establishes the calculation method as a basis for subsequent investigations like developing new design criteria with target values for the car structure.