Modelling and Design of an Air-cushioned Hitch for Passenger Cars

Abstract

Comfort and road handling are two mains areas in which car engineers put a lot of efforts. Suspensions are designed to offer the best compromise between well-being and safety. However, leisure market is appreciably increasing those years and more and more people use their car to carry features as boats, motorbikes or caravans. Extra weight is brought on the rear axle of the towing vehicle, the front one tending to lift. Thus, suspensions efficiency decreases leading to nuisances in comfort or handling. The two major motions that have to be controlled are pitch and bounce. The first represents the rotation of the car around its transversal axis, the second deals with the vertical displacement of the vehicle. The purpose of the thesis consists in modelling and designing an air-cushioned hitch that will reduce vibrations on both car and trailer. This kind of product already exists, especially in the truck field. Indeed, many trucks use a system called fifth wheel that absorbs energy due to the motion of the trailer. Then, the challenge of this project is to design a system applicable on common passenger cars and determining adequate structural parameters values for suspension features. MSC.ADAMS/View and MSC.ADAMS/Insight are the softwares used in this purpose. A simplified model based on mass-spring-damper system is implemented and allows obtaining suboptimal stiffness/damping for the air hitch. This simulation is also a way to get insight into the performance of the product. Design development has been established using Solidworks. All parts are created respecting space constraints and regulations and assembled to give the final product. FEM analysis is performed to check if strength requirements are fulfilled. One of the results from this work is a document with dimensions and characteristics of the final product that can reduce about 30% of vibrations. The air hitch is aimed to be industrialized. However, rig tests and manufacturing cost analysis have to be achieved in order to validate design choices.