Effect of frame flexibility on the ride vibration of trucks

Abstract

The aim of the paper is to study the ride vibration behaviour of trucks and in particular the effect of including a flexible frame. The work is a theoretical investigation and concentrates on the ride comfort, cargo protection, structural integrity and vehicle safety. The road surface irregularities are represented as stationary Gaussian random excitations. To analyse the vehicle dynamic responses, the spectral analysis technique has been used and the driver acceleration reponses have been weighted according to the ISO ride comfort techniques. To study the effects of the frame flexibility, the truck frame has been modelled using the FEM (finite element method) and its modal properties have been calculated. An explanation of the modal superposition theory is given and the possibility of incorporating this theory with Lagrange's equations for modelling a truck containing flexible subsystems is discussed and applied. Numerical results are presented for the truck, including power spectral densities and root mean square values of the vehicle dynamic response variables. The results show that there is good agreement with the previous experimental published work and that the modelling technique established is very powerful and economical for the analysis of complex vehicle structures. From comparison of the responses of the rigid and flexible body models it has been found that the frame flexibility strongly affects the accelerations of both the driver and the truck body. Therefore, it is critical that frame flexibility effects are taken into account in the design of primary, cab and engine suspension systems.