Modelling and design of a novel air-spring for a suspension seat
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2008.
Suspension seats are commonly used for earth moving machinery to isolate vehicle operators from vibrations transmitted to the vehicle body. To provide the required stiffness and damping for these seats, air-springs are typically used in conjunction with dampers. However, to eliminate the need for additional dampers, air-springs can be used in conjunction with auxiliary air volumes to provide both spring stiffness and damping. The damping is introduced through the flow restriction connecting the two air volumes. In this study, simplified models of an air-spring were derived followed by a model including the addition of an auxiliary volume. Subsequent to simulations, tests were performed on an experimental apparatus to validate the models. The air-spring models were shown to predict the behaviour of the experimental apparatus. The air-spring and auxiliary volume model followed the trend predicted by literature but showed approximately 27 % lower transmissibility amplitude and 21 % lower system natural frequency than obtained by tests when using large flow restriction diameters. This inaccuracy was assumed to be introduced by the simplified mass transfer equations defining the flow restriction between air-spring and auxiliary volume. The models however showed correlation when the auxiliary volume size was decreased by two thirds of the volume actually used for the experiment. This design of a prototype air-spring and auxiliary volume is presented for a suspension seat used in articulated or rigid frame dump trucks. The goal of this study was to design a suspension seat for this application and to obtain a SEAT value below 1,1. The design was optimised by varying auxiliary volume size, flow diameter and load. A SEAT value of less than 0,9 was achieved.