Static analysis and dynamic simulation of linked multi-axle truck suspension units

Abstract

The work undertaken in this study was instigated in response to a desire to gain a better understanding of the behaviour of linked, multi-axle truck suspension units. This desire arose from a need to investigate the dynamic interaction between bridges and vehicles, after high impact values were observed in previous studies. The objectives of the study were: 1) To explore the feasibility of obtaining data on truck suspensions by measuring the dimensions and properties of the suspension in the laboratory without disassembling the suspension; 2) To develop a general computer program which can use the specifications of a truck's suspension, obtained in the laboratory, to study the dynamic behaviour of a variety of linked, multi-axle truck suspension units; and 3) To carry out some exploratory studies using assumed truck suspension data.A generalised approach to modelling linked, multi-axle truck suspension units has been developed. The model assumes large displacements and incorporates realistic spring and tyre models. The static analysis of the model is not trivial due to the presence of geometrical and material nonlinearities. The method of analysis which was developed and implemented successfully, is described. An unusual method was developed to determine the dynamic response of the model in the time domain. The governing incremental equations of equilibrium are reduced to a set of equations involving member-nodal forces only. The member nodal accelerations are found by substitution into the original equations of equilibrium, and displacements and velocities are found subsequently by numerical integration. The Newmark Beta method is used to solve the dynamic equations and the modified Newton-Raphson method is used to ensure equilibrium at each time step. Based on the experience obtained in developing the analytical model, a method for obtaining suspension data from a truck in a laboratory has been postulated. The method requires the removal of shock absorbers and wheels only and by using minimal instrumentation, and software similar to that developed for this project, all the required data can be obtained. The programs based on the developed methods were used to analyse the dynamic response of a McGrath Tandem Axle MF2B trailer suspension. Results of parametric studies confirmed findings of some previous researchers. Based on comparisons with results obtained by other researchers, it is concluded that the model and associated method of analysis constitutes a realistic model of linked multi-axle truck suspension units.