On the non-linear behaviour of motorcycle shock absorbers

Motorcycle shock absorbers exhibit a non-linear behaviour characterized by hysteresis in the force–velocity diagram. The presence of hysteresis is the main obstacle in the identification of parameters and the development of computationally efficient shock absorber models. Gas compression, oil compressibility, mechanical compliance of chambers, and oil inertia are the most important causes of hysteresis. This paper deals with experimental research carried out on a twin-tube shock absorber equipped with pressure gauges in the chambers. A physical model is developed to explain the behaviour of the shock absorber from the measured pressures. The relevance of the various non-linear phenomena is discussed. The friction, hydraulic, and compliance parameters are identified from the measurements. The mathematical model fitted with the identified parameters is able to predict with accuracy the force generated by the shock absorber.