I. Introduction
The introduction of actively controlled the wheel dynamics of a vehicle first appeared in antilock braking systems (ABS). The primary function is to prevent the lock-up of the wheel during an emergency brake maneuver [1]–[8]. Ideally, it is desired for ABS to maintain the wheel slip, , at the peak of the curve (see Figure 2). By maintaining the wheel slip, , at the peak, maximum longitudinal tire force , is generated. This allows for shorter stopping distances compared to other operating point on the curve [2], [4]. However, automotive control problems are highly nonlinear and subject to high amount of disturbances and uncertainties, the main difficulty arising in the design of an appropriate wheel slip control, i.e. controlling .