Speaker: David Limebeer,
University of Oxford, UK, USA
Title: Suppression of Burst Oscillations in Racing Motorcycles
Abstract: Burst oscillations occurring at high speed, and under firm
acceleration, can be suppressed with a mechanical steering compensator that
replaces the conventional steering damper. Burst instabilities are the result of
interactions that occur between the wobble and weave modes under high-speed
firm-acceleration conditions. Under some operating conditions the wobble-mode
frequency (of the subject motorcycle) decreases, while the weave mode frequency
increases until destabilizing interactions occur.
The design analysis is based on a timeseparation principle, whereby bursting is
assumed to occur on time scales over which speed variations can be neglected.
Even under braking and acceleration linear time-invariant models corresponding
to constant-speed operation can be utilized in the design process. The
influences of braking and acceleration are studied using d’Alembert-type
inertial forces that are applied at the mass centres of each of the model’s
constituent bodies.
The resulting steering compensator is a simple mechanical network that comprises
a conventional steering damper in series with a spring. In control theoretic
terms, this network is a mechanical lag compensator. Given the inevitable
uncertainties in the motorcycle model, in combination with nonlinearities that
occur over a wide range of operating conditions, a robust control framework was
chosen for the design optimization. The optimization process ensures improved
performance over the machine’s entire operating regime.