Instability issues of an agriculturaltire testing convoy

• Main Author: Travers, Vincent
• Format: Others
• Language: English
• Published: KTH, Fordonsdynamik 2013
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-142396

Michelin develops and manufactures tires. To check their tire, different tires tests are used. During the testing process of agricultural tires, some endurance tests are performed on a circular test track where a convoy, made of a truck pulling two single-axle trailers without suspension system, is driven at a constant speed. Depending on the tested tires, it has been observed that the convoy may become severely instable. This instability is a large problem for the test team since the tires undertake too much overload which makes test results unexploitable. This is time consuming and expensive for the company. The aim of this thesis is two-folded. The first aim is to identify the phenomenon causing the instability from experimental data and also the parameters which influence the phenomenon. The second aim is to model the phenomenon from technical data in order to predict instability behaviors in advance. Models have been developed and the behavior have been analyzed and compared with experiments. The main result of this work is that the instable behavior is due to the excitation of natural modes of the convoy by the tires frequencies. Natural modes are identified as the natural bouncing mode of the trailers. The bouncing natural mode of a trailer depends on tires stiffnesses and the load on the trailer. Tires excitation frequencies are related to the test speed, the trailer track width and the rolling circumference of the tires. To get a good prediction tires stiffness and tires rolling circumference under operation require to be better characterized. Thanks to this work the test teams have a better understanding of the phenomenon and a tool which can be used to give a rough indication about problematic configurations. This tool cannot totally predict instable behaviors with the technical data at our disposal since some more parameters, which are not quantified for now, might influence the phenomenon. Nevertheless, these parameters have been highlighted by this study and if explored by the test team, a working predicting tool could be achieved.