Multi-Body analysis of the elasto-kinematic behaviour of a front double wishbone suspension for Front-Wheel-Drive light-duty commercial vehicles

This Thesis is part of a wider feasibility study concerning the transition from the actual internal combustion engine to an electric motor for a Rear-Wheel-Drive light-duty commercial vehicle. Among the available solutions to implement the transition, the possibility of converting the present Rear-Wheel-Drive to Front-Wheel-Drive is investigated. This Thesis is focused on the current double wishbone suspension of the front axle, to assess how the drivetrain affects its elasto-kinematic behaviour and provide some guidelines to the manufacturer. Considering that traditionally Rear-Wheel-Drive is the predominant architecture implemented on light-duty commercial vehicles, understanding whether Front-Wheel-Drive allows to take advantage of the design and knowledge of the actual suspension is crucial. This Thesis is a multi-body analysis performed on Hexagon MSC Software Adams/Car, whose results are processed in MathWorks MatLab. The approach adopted to perform the task is resumed in the workflow below. Firstly, the present Rear-Wheel-Drive model is arranged to obtain two loading conditions, which are maintained throughout the study, because this kind of vehicles belongs to the same category of passenger cars, but it is subject to a load variability that is one order of magnitude greater. Secondly, a Front-Wheel-Drive model is derived from the initial vehicle, according to the approach of maintaining as many elements as possible. The model obtained is still powered by the initial powertrain and driveline, the latter being reverted, so that the torque flows to the front wheels. This model is not representative of a real vehicle, because the longitudinal engine layout is uncommon for Front-Wheel-Drive, but it fits the task, that is to isolate the effect of the drivetrain. Thirdly, a set of suspension tests is performed on both front and rear axles, to validate their behaviours taking as reference the available experimental data. Subsequently, a Ramp Steer test on the initial model provides a comparison with the real vehicle handling. Then, a set of cornering events called Power-Off Cornering and Throttle-On In-Turn is defined, according to the ISO standards. These are transient maneuvers which involve both longitudinal and lateral dynamics and allow a comparison between Front and Rear-Wheel-Drive vehicles. At last, the double wishbone suspension of the Front-Wheel-Drive vehicle is optimized according to two different approaches and tested again, to assess the influence of both caster angle and caster moment arm over the steering system response. A short Appendix is attached at the end of this Thesis. The first document reports the precise parameters and criteria to implement the Power-Off Cornering and Throttle-On In-Turn tests. The second document reports the problems encountered during the development of the Front-Wheel-Drive model and explains the solutions to make it work correctly and consistently.