Sub-frame and vehicle body interaction under in-service brake judder loads has a big influence on the final vehicle judder performance. It is found that this interaction can affect general vehicle body vibration or produce an amplification of the vibrations exhibited by target cabin components such as the steering wheel and the brake pedal. Thus, the understanding of this phenomenon allows a more accurate characterisation of brake judder problems in vehicles. In general, sub-frame – vehicle body interaction can be characterised by locating an array of tri-axial accelerometers on relevant vehicle points defining a system containing the brake, the suspension, the chassis and part of the vehicle body. These points are characterised by their 3dimensional movement using tri-axial accelerometers. In our case, an accelerometer layout has been selected in order to determine the operational relative vibration movement (in three dimensions) of the sub-frame with respect to the body under operational judder conditions. A test SUV with two sub-frame boundary conditions has been considered in this work to analyse the differences in judder performance. The results obtained with the approach described above are based on the experimental quantification of the relative vibration displacement of the sub-frame and the vehicle body under judder conditions. This quantification is carried out in the time and frequency domain and along the three space directions. The relative movement is measured as acceleration and then transformed into displacement. This gives a better understanding of the mechanical limitations in the assembly between the sub-frame and the vehicle body.

J.J. García-Bonito, Applus+ IDIADA, Tarragona, Spain; B Ferrer, O Calvo, F Squadrani, A Claverias; D. H. Jeon, Hyundai Motor Group, South Korea