The presentation is about steering control of cars by drivers, concentrating on following the roadway which is visible ahead. It builds on a previous presentation to a combined mechanics and control meeting at CUED in which it was shown how problems in automotive suspension control with road preview could be manipulated to deal with vehicle driving. In the formulation used, infinite-horizon discrete-time linear optimal regulator theory is employed. The driver’s preview of the roadway is combined with the linear dynamics of a simple car (or other mathematically linear vehicle) to yield a solution to a “least path error/least control effort” problem. In the prior work, it was shown how an optimal “driver” of a linear car can convert the path preview sample values, modelled as deriving from a Gaussian white noise process, into steering wheel displacement commands to cause the car to follow the previewed path with an attractive compromise between ease and precision.
Recognising that real roadway excitation is not so rich in high frequencies as white noise, a low-pass filter is added to the system. The white noise sample values are filtered before being seen by the driver. It is shown that the optimal control is independent of the filter properties. Then, using the established theoretical basis, new results are generated to show time-invariant optimal preview controls for cars and drivers with different layouts and priorities. Tight and loose controls, representing different balances between tracking accuracy and control effort, are calculated and illustrated through simulation. A new performance criterion with handling qualities implications is set up, involving the minimisation of the preview distance required. The sensitivities of this distance to variations in the car design parameters are calculated. The oscillatory steering of a rally car well in advance of a monotonic bend in the road will be shown to arise naturally from the theory and the motions will be compared qualitatively with those of a Subaru in action. The influence of additional rear wheel steering is studied from the viewpoint of the preview distance required and the form of the optimal preview gain sequence.
The results yield new insights into driver steering control behaviour and vehicle design optimisation. The presentation will conclude with a discussion of research in progress aimed at an improved understanding of how drivers control their vehicles.
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