Dynamic Analysis of Alternative Suspension Systems for Sport Motorcycles

In this thesis, VehicleSim multi-body software is used to extend and modify an existing motorcycle model by including different non-conventional suspension systems. Girder and Hossack double wishbones front suspension systems are designed, implemented and tested. Using a synthesis of mechanism methodology, they are designed with different kinematic configurations that allow different behaviours of the motorcycle front end. By means of CAD tools and finite element analysis, realistic three dimensional models of the suspension systems designs are developed. The dynamical properties of the mechanical assemblies are obtained from the CAD models and used to build a realistic mathematical model of a sport motorcycle fitted with theses alternative suspension systems. Dynamical and stability analyses of the alternative front suspension systems are performed. For the different kinematic configurations, anti-dive properties and variation of the motorcycle's handling geometric parameters are studied by non-linear dynamical simulations. Stability analyses are performed by means of the motorcycle linear models eigenvalues. Passive interconnection of front and rear suspension systems of a sport motorcycle is also investigated. The effects of an interconnected suspensions system on the motorcycle in-plane motions are studied by means of reduced order linear models. The baseline model is modified to include passive interconnection forces between the front and rear suspension systems. The possible improvement introduced by an interconnected suspensions system in terms of suspension accuracy is investigated through non-linear simulations with delayed step tyres inputs. Appropriate values of the interconnection passive components for different possible mechanical implementation are found by means of optimization processes. Linear stability analyses are performed for each of the different optimal interconnected configurations. Nonlinear frequency analyses of the motorcycle wheels and chassis responses are also performed considering the delay between the front and rear tyre inputs. Non-linear simulations with variable frequency sinusoidal road inputs are run for this purpose. Finally, modal analyses of the motorcycle model are carried out for variable interconnection parameters in order to understand the effect of the interconnected suspensions system on the motorcycle's motion