The requirement to develop lighter vehicle structures arose as a result of the rapidly rising price of oil. The weight of a vehicle makes a considerable contribution to the power required to propel it and therefore the quantity of fuel used. The work presented here is an investigation into the analysis of the components of a vehicle structure, with the aim of obtaining a greater understanding of their behaviour. This knowledge is then applicable to the design of lighter structures made from an assembly of the components studied.

The problem o f disc brake squeal has been examined by developing a finite element model of the coupled pad-disc system , conducting complex eigenvalue analysis and associating unstable modes with potential squeal problem areas. A key issue in this process is the representation of the contact pressure distribution at the frictional interface between the disc and the pad. Non-linear contact analysis using the finite element model of the pad revealed that contact is only partial at the pad-disc interface and that the contact pressure distribution depends on the friction coefficient, Young’s modulus of the friction material and the way the applied pressure is distributed on the pad backplate. A new method is proposed in which interface contact stiffness is related to brake line pressure using a statistical approach based on the measured surface properties of the interface. Complex eigenvalue analysis of the coupled pad-disc system has shown that unstable modes exist within different ranges of contact stiffness thereby providing an explanation of the effect of varying line pressure on squeal. The two most unstable modes from the analysis show good correlation with experimental squeal results. The coupled model is then used for parametric studies the results of which indicate that high coefficient of friction and uniform contact pressure distribution increase instability whilst a trailing edge biased pressure distribution and a high support stiffness at the pad backplate reduce it. Limiting the disc symmetry by introducing equispaced slots was shown to be effective in reducing instabilities involving diametral modes of the disc with the same order of symmetry only Other modes were stabilised by increasing the rigidity of the pad. The overall results suggest that either the pad or the disc can be mainly responsible for the instability depending on the mode thus unifying the different approaches to disc brake squeal and enabling the most appropriate component to be targeted for squeal abatement purposes.

First, techniques for modelling the vehicle and road surface are discussed, and the standard linear and nonlinear analysis methods are reviewed. Then, using the quarter car model and a single idealised road surface, a brief analysis of the passive and active suspensions, including full and limited state feedback schemes, is presented. The performance in terms of ride comfort, road holding ability and suspension travel for both systems is established, providing a yardstick against which the controllable damper systems can be compared. Three suspensions fitted with controllable dampers are then analysed. In order of increasing complexity these are; a three-state adaptive system, a two-state switcliable system, and a continuously variable system. After a performance comparison of the ideal system, the practical limitations present in real hardware are included in the damper model. Their effect on performance is quantified and realistic response targets are set. The model is then extended to a two dimensional “bicycle” model, which enables control laws to be generated which take into account the correlation between front and rear wheel inputs. Using these laws to drive the active and continuously variable damper system, the advantages of a correlated law are identified. The accelerations and suspension displacements of a passively suspended production vehicle are measured during actual runs over three roads of varying roughness. These are used to estimate the surface roughness properties of the roads. Using this range of typical conditions, the idea of system adaptation is then considered. The performance of each controllable damper system lies between that of the active and conventional passive systems. The continuously variable system generally offers the best ride comfort, but worthwhile improvements are also possible with the two-state switchable system. The adaptive system offers only marginal improvements for the conditions considered.

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There has been an impetus in recent years to increase railway train speeds and reduce journey times. As train speeds have increased, other problems have manifested themselves, in particular the consequent deterioration in ride quality at these higher operating speeds. Improvement in suspension design is one option which can circumvent this problem. Suspension design for a modem high-speed train has hitherto been a heuristic procedure directed towards optimising the passive components of the suspension. Performance limits are now being reached with passive suspensions due to the inherent trade-offs which need to be made in the design process. Active suspension, which eases this inherent trade-off, has received a great deal of interest in both academia and industry over recent years. A number of theoretical and experimental studies have highlighted the potential benefits of active suspension technology. Theoretical studies have concentrated on using simple vehicle models and although providing the initial impetus to active suspension they have not given the industry full confidence in them. In contrast, experimental studies have highlighted a number of problems, most notably the significant effect actuators can have on the overall performance.