Ride and handling assessment of vehicles using four-post rig testing and simulation
The tuning of production road car suspension parameters in the development stage of a vehicle can be a lengthy and expensive procedure and commonly relies on the subjective judgements of test drivers to assess various aspects of ride and handling. The work in this thesis aims to create a testing and tuning technique using four-post rig testing and vehicle simulation to significantly reduce the amount of physical and subjective testing required within the development stage. A four-post rig testing technique is developed using modal sine sweep inputs to acquire the response of the vehicle in the heave, pitch, roll and warp modes of excitation. An analysis and parameter estimation method is developed based on four-post data and a 7 degree-of-freedom model, with four-post test data used to validate the parameter estimation and vehicle model simultaneously, obtaining satisfactory results in all but the roll mode of excitation. The BS 6841 [1] discomfort acceleration weightings are applied to the modal responses, with road input PSDs representative of standardised roads and driving cycles used to produce a comfort index value for a tested vehicle or setup. A novel performance index is created to estimate grip loss due to static and dynamic tyre properties for each axle, which allows the prediction of road input effects on the total grip and balance of the vehicle, as well as a driver requirement of steering input. MATLAB code is constructed for the parameter estimation procedure and for three general user interfaces to assist with the testing, tuning and benchmarking procedure. An objective-subjective validation exercise is carried out using a single vehicle with four different component setups which are tested on the four-post rig to determine comfort and performance index values, as well as recording the subjective assessments of three test drivers on two drive routes in the UK and Germany. The results show fair to good correlation for comfort measures but generally poor correlation to the performance index, mostly because of large variations between the drivers’ subjective assessment criteria.
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