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Dynamical Simulation of the Urban Lightweight Car Lisa
Published July 02, 1997 by Associazione Tecnica Dell'Automobile in Italy
A team from the Polytechnic Munich develops the lightweight urban car LISA (Leichtes Individuelles Stadtauto). The main goal of the LISA project is to create an ecologically beneficial vehicle by compromising on comfort and performance, but not on safety.
In cooperation with the DLR (German Aerospace Research Establishment) and INTEC, LISA's suspension comfort and handling qualities have been optimized using the Multibody Simulation Software Package SIMPACK. The dynamical model consists of 29 rigid and one elastic body with altogether 36 degrees of freedom modelling frame, suspension and steering elements, wheels and engine.
The model has been validated in the lower frequency range by a number of driving experiments, where the movements of the suspensions due to geometrically defined road imperfections have been recorded with a high speed camera.
Variations of the stiffness and damping coefficients of the shock absorbers, the suspension geometry and the position of the vehicles center of gravity, showed that LISA had too much weight (65%) at the rear of the car. Increasing spring and damping coefficients had no influence without changing the balance. The frame structure is stiff enough to neglect its influence on the handling.
As a result of the simulations, the natural frequencies of the car body are in a range, which is under the given constraints optimal for human frequency sensitivity.
Dynamic loads on the flexible frame structure have been calculated to allow its optimization within the FEM-analysis