Efficient simulation of non-linear kerb impact events in ground vehicle suspensions
thesisposted on 03.06.2013, 15:31 by Hubertus von Chappuis
In the increasing competition which pervades the automobile sector, it is necessary to develop simple methods to enable prediction of suspension loading level envelope in an early development stage. For this purpose, the FORD specified standard driving manoeuvres, based on kerb strike and pothole braking, inducing worst case loading scenarios are employed. The damaging nature of these tests and the relatively expensive physical prototypes make simple simulation models essential. These models should cope with an initial rudimentary assessment, but must suffice to predict the maximum wheel centre loads with a reasonable degree of accuracy. Enhanced model features are required to represent edge-type tyre deformation and impulsive bumper deflection. State of the art approaches are physical tyre models extended to rim clash modelling and rheological bumper models embedded in an multibody system (MBS) environment. These enhancements lead to increased complexity. The thesis proposes a minimal parameter vehicle model, tailored to predict vertical suspension loads caused by the FORD kerb strike manoeuvre. Since the focus is put on model simplicity, an in-plane bicycle model is extended to 7 degrees of freedom. Nonlinear and hysteretic characteristics of the bump-stop elements are included through use of a spatial map concept, based on displacement and velocity dependent hysteresis. Furthermore, a static tyre model is described to predict the radial stiffness against penetration of an edge and flat-type rigid body geometry. The full mathematical model is derived on the basis of the shell theory and represented in terms of few geometrical input parameters. A distinct tyre model, representing the tyre belt as a multi-link chain is also derived to confirm the assumptions made in the simple mathematical model. Model validation is supported through experiments at both component and system levels. It is shown that the bumper map concept provides an accurate, yet simple alternative to a rheological model, if applied to polyurethane foam type bumpers. This approach is also confirmed for the tyre model, substituting a comprehensive physical model approach.
- Mechanical, Electrical and Manufacturing Engineering