Test cycle 1 evaluates the controllers during an acceleration from 0 to 20 km/h.
Figure 7.2 shows the result of the PI controller. The left graph shows the friction
coefficient μ as a function of the wheel slip s and the right graph shows the wheel
velocity (solid) compared to the vehicle velocity (dashed). In the right graph it is
very clear that the wheel spins off, since the wheel velocity is much larger than the
vehicle velocity in the beginning. In the left graph it is seen that the slip increases
to more than 4 before the controller reduces the engine torque. This means that
the peak of μ-slip curve has been orderly passed and that the wheels spin off.