Analysis of the possibility of using the phase angle in the Eusama method as an additional diagnostic parameter in the assessment of the technical condition of the vehicle suspension system

Summary Vehicle suspension system diagnostics is essential to both operation and maintenance of automotive vehicles. Diagnostic methods should provide signals that in-service defects have occurred as early as possible and make it possible to identify such defects in an unambiguous manner. Among the most popular oscillatory methods used to examine the technical condition of suspension systems, the EUSAMA method, developed by the European Shock Absorbers Manufacturers Association, has enjoyed particularly wide application, and it consists in establishing the ratio between the minimum value of the wheel adhesion force within the band of resonance of unsprung masses and the static wheel load value, expressed in per cent. Technical condition classification is based on comparing the values of what is commonly referred to as the EUSAMA coefficient (percentage ratio of a minimum wheel load force to a tangential vehicle wheel load on a test stand plate) for two wheels of a single axle. Such a test stand typically features only a load force sensor integrated with the test plate. The modification proposed by the authors involves installing an additional test plate displacement sensor at the test stand. When performed simultaneously, measurements of the load force affecting the plate and of its displacement make it possible to determine the phase angle between the relevant signals and to analyse the possibility of using the phase angle as an additional source of information about the technical condition of the vehicle suspension system.