The influence of bicycle fork bending on brake control

Bicycle forks are prone to bending, introducing a flexible structure between front wheel and vehicle body. This has substantial influence on brake control, not only by altering the system dynamics but also causing serious estimation problems. These consist in considerable measurement errors in the incremental wheel speed and longitudinal tyre velocity signals, both affecting the wheel slip estimation. This paper provides an in-depth analysis of this problem that represents a profound difference to classical vehicle dynamics. For this purpose, measurements are recorded in test manoeuvres using an extensive set of measurement variables. Based on this data, the complex nonlinear couplings of longitudinal and vertical dynamics are included in a full-vehicle multibody model. The measurement errors as well as compensation methods are evaluated using both simulation and experimental data. In order to examine the influence on closed-loop brake control a linear control-oriented model is derived. Finally numerical full-vehicle simulations show the influence of fork bending on discrete anti-lock brake control systems (ABS), distinguishing the sheer dynamic phenomenon and the related estimation problem.