Multibody model of a competition kart accounting for the chassis flexibility

For the purpose of simplicity, competition karts must not be equipped with neither suspension systems nor differential. Consequently, for this particular type of vehicle, the elastic properties of the chassis structure play an important role in the dynamic behaviour of the kart. For instance, the flexibility of the chassis is exploited to compensate the absence of differential, as it allows the driver to uprise the rear interior wheel in cornering. The performances of the kart are then guided not only from mass distribution and tire characteristics but also from the flexibility of the chassis which can be tuned by means of various devices. The paper presents the numerical model of a particular kart, which was recently initiated. The model is based on the multibody system approach, realized under ADAMS. The chassis frame has been considered as a flexible body, whose deformation is expressed according to the well-known component mode synthesis. The mode shapes and all the necessary data of the flexible body are retrieved from a finite element model created with ANSYS. The classical Craig-Bampton reduction has been chosen to specify the retained mode shapes. The work especially focused so far on the accuracy of the finite element model. As we deal with a tubular frame, only beams and some lumped masses were included in the model. The latter was carefully updated from static and modal experimental tests, performed in different configurations (chassis alone, with or without engine, with or without seat, ...) and can be considered as sufficiently representative. The complete model was used to reproduce some typical maneuvers which allowed to figure out the influence of the flexibility. Other measurements are foreseen in a near future, especially to enrich the data relative to the tyres. In fine, the model is expected to help the driver to optimize the kart in function of the race conditions.