We have studied the vibrations of a quarter-car model with a softening stiffness of the Duffing type, focusing
on the potential for chaotic behaviour. The model and parameters used were taken from the paper by Li
et al. [6], with the addition of the gravity force. The addition of this gravity force breaks the symmetry of the
potential, so that V ðxÞ 6¼ V ðxÞ. The hysteretic nature of the damper caused a range of interesting system
behaviour, such as quasi-periodic, synchronized and chaotic motion. This had a substantial effect on the heteroclinic
orbits, which transformed into homoclinic orbits.