Abstract
Tyre–road friction characteristics are deeply interlaced with all vehicle safety oriented control systems as road conditions strongly affect the controlled system behaviour. Thus, the capability of estimating in real-time the friction conditions may provide a valuable source of information for any active vehicle control system. In particular, friction information can be used to enhance the performance of wheel slip control systems.
In this chapter we address three different problems related with friction estimation. Specifically, Section 8.2 illustrates an approach that is capable of estimating the sign of the slope of the friction curve, thereby allowing one to detect if the system is operating in the stable or in the unstable region of the friction curve. In fact, as largely discussed in this book, the equilibrium points associated with the wheel braking dynamics are stable for values of the wheel slip before the peak and unstable for those beyond the peak.
Hence, an online detection of the slope of the friction curve can be exploited to adapt and to optimise the closed-loop performance of wheel slip control systems. The advantage of this identification method is that it can be implemented also with a very limited set of sensors.
Secondly, in Section 8.3 an approach to the problem of estimating both the slip value corresponding to the peak of the friction curve and the parameters of the Burckhardt friction model (see Section 2.1) is presented. This is done by setting up a curve fitting problem which is then solved by two different identification approaches, namely a least squares and a maximum likelihood approach, arising from different parametrisations of the friction curve. A detailed analysis of the merits and drawbacks of the two approaches is also provided, which considers both the obtained accuracy in the estimated parameters and the convergence issues which have to do with the length of the available data set.
Finally, Section 8.4 presents an approach for estimating the instantaneous vertical and longitudinal forces from in-tyre acceleration measurements. Specifically, an appropriate set of sensors and regressors is illustrated, based on the measurements provided both by standard vehicle sensors (wheel encoders) and an accelerometer mounted directly in the tyre. Such estimates are based on the idea of extracting information from the phase shift between the wheel hub and the tyre, which is due to the transmission of traction and braking forces exerted on the tyre itself.
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© 2010 Springer-Verlag London Limited
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Savaresi, S., Tanelli, M. (2010). Identification of Tyre–road Friction Conditions. In: Active Braking Control Systems Design for Vehicles. Advances in Industrial Control. Springer, London. https://doi.org/10.1007/978-1-84996-350-3_8
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DOI: https://doi.org/10.1007/978-1-84996-350-3_8
Publisher Name: Springer, London
Print ISBN: 978-1-84996-349-7
Online ISBN: 978-1-84996-350-3
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