Degree:Philosophiae Doctor (Mechanical Engineering)This thesis examines the classic ride comfort vs. handling compromise when designing a vehicle suspension system. A controllable suspension system, that can, through the use of suitable control algorithms, eliminate this compromise, is proposed and implemented.It is a well known fact that if a vehicle suspension system is designed for best ride comfort, then handling performance will suffer and vice versa. This is especially true for the class of vehicle that need to perform well both on-and off-road such as Sports Utility Vehicles (SUV's) and wheeled military vehicles. These vehicles form the focus of this investigation.The ride comfort and handling of a Land Rover Defender 110 Sports Utility Vehicle is investigated using mathematical modelling and field tests. The full vehicle, non-linear mathematical model, built in MSC ADAMS software, is verified against test data, with favourable correlation between modelled and measured results. The model is subsequently modified to incorporate hydropneumatic springs and used to obtain optimised spring and damper characteristics for ride comfort and handling respectively. Ride comfort is optimised by minimising vertical acceleration when driving in a straight line over a rough, off-road terrain profile. Handling is optimised by minimising the body roll angle through a double lane change manoeuvre. It is found that these optimised results are at opposite corners of the design space, i.e. ride comfort requires a soft suspension while handling requires a stiff suspension. It is shown that the ride comfort vs. handling compromise can only be eliminated by having an active suspension system, or a controllable suspension system that can switch between a soft and a stiff spring, as well as low and high damping. This switching must occur rapidly and automatically without driver intervention.A prototype 4 State Semi-active Suspension System (4S 4 ) is designed, manufactured, tested and modelled mathematically. This system enables switching between low and high damping, as well as between soft and stiff springs in less than 100 milliseconds.A control strategy to switch the suspension system between the "ride" mode and the "handling" mode is proposed, implemented on a test vehicle and evaluated during vehicle tests over various on-and off-road terrains and for various handling manoeuvres. The control strategy is found to be simple and cost effective to implement and works extremely well. Improvements of the order of 50% can be achieved for both ride comfort and handling. In hierdie proefskrif word die klassieke kompromie wat getref moet word tussen ritgemak en hantering, tydens die ontwerp van 'n voertuig suspensiestelsel ondersoek. 'n Beheerbare suspensiestelsel, wat die kompromie kan elimineer deur gebruik te maak van toepaslike beheeralgoritmes, word voorgestel en geïmplementeer.Dit is 'n bekende feit dat, wanneer die karakteristieke van 'n voertuigsuspensiestelsel ontwerp word vir die beste moontlike ritgemak, die hantering nie n...

This paper reports on an investigation to determine the spring and damper settings that will ensure optimal ride comfort of an off-road vehicle, on different road profiles and at different speeds. These settings are required for the design of a four stage semi-active hydro-pneumatic spring damper suspension system (4S 4 ). Spring and damper settings in the 4S 4 can be set either to the ride mode or the handling mode and therefore a compromise ride-handling suspension is avoided. The extent to which the ride comfort optimal suspension settings vary for roads of different roughness and varying speeds and the levels of ride comfort that can be achieved, are addressed. The issues of the best objective function to be used when optimising and if a single road profile and speed can be used as representative conditions for ride comfort optimisation of semi-active suspensions, are dealt with. Optimisation is performed with the Dynamic-Q algorithm on a Land Rover Defender 110 modelled in MSC.ADAMS software for speeds ranging from 10 to 50 km/h. It is found that optimising for a combined driver plus rear passenger seat weighted root mean square vertical acceleration rather than using driver or passenger values only, returns the best results. Results indicate that optimisation of suspension settings using one road and speed will improve ride comfort on the same road at different speeds. These settings will also improve ride comfort for other roads at the optimisation speed and other speeds, although not as much as when optimisation has been done for the openUP (July 2007) particular road. For improved ride comfort damping generally has to be lower than the standard (compromised) setting, the rear spring as soft as possible and the front spring ranging from as soft as possible to stiffer depending on road and speed conditions. Ride comfort is most sensitive to a change in rear spring stiffness.

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Highlights Estimation of road profiles and classes using neural networks on measured data. Discrete obstacles are reconstructed with higher correlation than Belgian pave. Ride comfort mode has better quality in reconstructed profiles than handling mode. Consistently good approximations of DSDs occur between 0.2 and 1.8 cycles/m. AbstractThis paper reports the performance of an Artificial Neural Network based road condition monitoring methodology on measured data obtained from a Land RoverDefender 110 which was driven over discrete obstacles and Belgian paving. In a previous study it was demonstrated, using data calculated from a numerical model, that the neural network was able to reconstruct road profiles and their associated defects within good levels of fitting accuracy and correlation. A nonlinear autoregressive network with exogenous inputs was trained in a series-parallel framework. When compared to the parallel framework, the series-parallel framework offered the advantage of fast training but had a shortcoming in that it required feed-forward of true road profiles. In this study, the true profiles are not available and the test data are obtained from field measurements. Training data are numerically generated by making minor adjustments to the real measured profiles and applying them to a full vehicle 2 model of the Land Rover. This is done to avoid using the same road profile and acceleration data for training and testing or validating the neural network. A static feedforward neural network is trained and consequently tested on the real measured data.The results show very good correlations over both the discrete obstacles and the Belgian paving. The random nature of the Belgian paving necessitated correlations to be made using their displacement spectral densities as well as evaluations of RMS error percent values of the raw road profiles. The use of displacement spectral densities is considered to be of much more practical value than the road profiles since they can easily be interpreted into road roughness measures by plotting them over an internationally recognized standard roughness scale.

ISTVS embarked on a project in 2016 that aims at updating the current ISTVS standards related to nomenclature, definitions, and measurement techniques for modelling, parameterizing, and, respectively, testing and validation of soft soil parameters and vehicle running gear-terrain interaction. As part of this project, a comprehensive literature review was conducted on the parameterization of fundamental terramechanics models. Soil parameters of the empirical models to assess off-road vehicle mobility, and parameters of the models to characterize the response of the terrain interacting with running gears or plates from the existing terramechanics literature and other researchers' reports were identified. This review documents and summarizes the modelling approaches that may be applicable to real-time applications of terramechanics in simulation, as well as in controller design.

To design a vehicle's suspension system for a specific, well defined road type or manoeuvre is not a challenge any more. As the application profile of the vehicle becomes wider, it becomes more difficult to find spring and damper characteristics to achieve an acceptable compromise between ride comfort and handling. For vehicles that require both good on-and off-road capabilities, suspension design poses a significant challenge. Vehicles with good off-road capabilities usually suffer from poor on-road handling. These vehicles are designed with a high centre of gravity due to the increased ground clearance, soft suspension systems and large wheel travel to increase ride comfort and ensure traction on all the wheels. All of these characteristics contribute to bad handling and increased rollover propensity even on good level roads. It is expect from these vehicles to have the same handling characteristics as a normal on-road vehicle. This paper analyses the use of an active anti-roll bar as a means of improving the handling of an off-road vehicle without sacrificing ride comfort. The proposed solution is simulated, designed, manufactured, implemented and tested to quantify the effect of the active anti-roll bar on both the handling and ride comfort of an off-road vehicle.

This study concentrates on obtaining profiles of rough terrain suitable for vehicle dynamics simulations cost effectively. Commercially available inertial profilometers are unable to profile the terrains of interest due to the severe roughness of these terrains. A mechanical profilometer is developed and evaluated by profiling obstacles with known profiles as well as rough 3-D test track profiles. Good correlation between the profiled and actual terrains is achieved. Realistic three dimensional (3-D) terrain models are generated from the terrain profiles. The Displacement Spectral Densities of the profiled terrains are found to contain discrete peaks and that a straight line fit would not be an accurate estimation for the specific rough terrains. Comparisons between the terrains defined in the International Roughness Index (IRI) and the present study indicate that the roughness index of the terrains profiled with the mechanical profilometer is significantly higher than the terrains normally profiled by inertial profilometers.

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