Sliding mode observers for vehicle mode detection

Abstract

This paper explores the use of sliding mode observers to detect the onset of potentially dangerous vehicle modes such as oversteer, understeer or split-μ braking. Provided these modes can be detected quickly enough, existing stability controllers can be engaged to ensure safe performance of the vehicle. It is shown that the equivalent output error injection signals associated with the sliding mode observer have distinctive signatures depending on the particular mode encountered. Appropriate thresholds on these signals can be set so the scheme ignores variations which arise during normal driving, but can detect and isolate different undesirable vehicle modes within 0.3 seconds of their onset.

Keywords:

• Sliding mode
• Nonlinear observers
• Bicycle model
• Oversteer
• Understeer
• Split-μ
• braking

Acknowledgements

The authors would like to thank Dr Jim Farrelly from TRW Automotive for his considerable help with the development of this work. The second author would also like to acknowledge the financial support of TRW and EPSRC through the provision of an Industrial Case award.

Notes

^†This is not unprecedented—the bicycle model in 11 is given in terms of r and v.

^†In developing (13) is has been assumed u˙ = 0. However providing a good estimate of forward speed is available so that u˙ can also be estimated, this assumption can be dropped at the expense of obtaining a more complicated expression for a˙ _y than that given in (13).