Electronic controls cannot always compensate for the destabilization of a poorly designed vehicle caused by tire delamination. Axle tramp caused from rubber strips on the track showed axle skate. Further research, reported at ESV 2007 demonstrated that lumps on a single rear tire caused 15+ degrees/g of oversteer. The Engineering Institute has shown that the process of tire delamination causes some vehicles to become unstable at highway speeds. This was accomplished by actually preparing tires to partially delaminate while at 95 to 115 kph on a remotely controlled vehicle. This testing demonstrated a severe loss of control as the tire was delaminating. The testing also showed that the predominate mechanism of control loss arises from the imbalance created during the delamination process. A discussion of the testing illustrating accelerations on the rear axle as well as displacements of the shock absorbers will be used to illustrate the imbalance excitation and the tramping motion of the axle. Previous research indicated that the oversteer gradient during such an event to be between 15 and 20degrees per g. This would then yield a critical speed of about 45 kph. The testing illustrates how a vehicle loses control when the vehicle transitions from understeer to oversteer at highway speeds significantly above the critical speed from tire failure induced forces. Alternative suspensions were tested using the same simulated tire failure and illustrated how the vehicle stability is increased. Using these results, a design criteria based upon a percentage of the critical rotational damping is proposed to control axle tramp from excitations at the harmonic frequency. The full text of this paper may be found at: http://www-nrd.nhtsa.dot.gov/pdf/esv/esv21/09-0209.pdf For the covering abstract see ITRD E145407.
Abstract