Comparison of pass-by noise from real track and simulated measurement at the roller test bench

The type approval of motor vehicles according to ECE R51 is performed on standardized road surfaces and under defined conditions. The type test takes place in the open air and is highly dependent on the local weather conditions. The Fraunhofer Institute for Building Physics IBP operates a four-wheel drive dynamometer where this measurement can be simulated in a semi-free field acoustic environment. Influences, such as the modified foot print of the tires, the surface of the roller and the floor, cause divergences to the pass-by measurements performed on the test track. Today the standard ISO/FDIS 362-3 for measurement of pass-by noise levels in test halls is emerging. There, the method A describes a procedure combinig simulated pass-by (drive train noise component) and real pass-by (tire rolling noise component). With a validation procedure the precision of such a simulated pass-by in the test rig may be compared with a real dynamometer at Fraunhofer-IBP. The procedure, the essential factors and the results of the measurements are presented and evaluated.