Pneumatic tyres of fabricless construction
The aim of the research described in this thesis is to assess the technical feasibility of pneumatic tyres for passenger cars which have no directional reinforcement in their carcasses. Conventional tyres are constructed from composites of twisted textile or steel cords in a rubber matrix, a process which is both labour intensive and costly. If it were possible to injection mould or cast tyre carcasses in a single operation, and if the performance of the resulting tyres matched that of modern radial ply tyres, then the implications for the tyre industry would be of major proportions. After reviewing the history of pneumatic tyres and summarising their principal attributes, the design of unreinforced or fabricless tyres is investigated and methods developed for defining their meridional profiles. Materials suitable for their carcasses and treads are then considered, prior to describing the manufacture of two series of tyres designed to have section height to width ratios, or aspect ratios, of 0.9 and 0.7 respectively. To facilitate experimental work, two sizes of tyres were employed: half scale models for which testing procQdures had been developed previously; and a size suitable for small saloon cars. The results obtained on a range of tyre properties are presented and analysed to give a number of empirical relationships between the properties and the design variables: carcass material Young's modulus, carcass wall thickness and the inflation pressure. For the important property of radial stiffness which affects other tyre characteristics, an improved method of analysis is developed to allow the structural and pneumatic components to be quantified. Using the relationships established experimentally, consideration is given to optimising the design of a fabricless tyre. It is concluded that to approach the performance of a conventional tyre, a design with a low aspect ratio is preferred but, to restrict growth with inflation'pressure, limited directional reinforcement must be included as a circumferential-belt beneath the tread. Nevertheless, the discussion concludes that there are fundamental reasons why even the optimised tyre would be unacceptable for use on modern passenger cars, although less demanding applications may be identified.