The study reported here addresses influences of physical objects close to the tyres on tyre/road noise measured with a close-proximity method, i.e. a microphone 0.2-1 m from the tyre. The purposes were to: (1) determine whether it is necessary to use an enclosure around the measuring wheel and microphone(s) in trailers, and possibly in other vehicles where a close-proximity microphone is used when testing tyre/road noise; (2) determine whether the selection of the test vehicle for measuring tyre/road noise emission is an important factor, mainly with respect to a possible influence of wheel housing on the noise; and (3) determine whether the selection of rim used for mounting the test tyre, for the purpose of measuring tyre/road noise emission, is an important factor; mainly with respect to a possible influence of rim width and material. Experiments were designed to address all three of these problems. In addition, the effect of small variations in microphone position was studied. The microphone was then displaced 20 mm in 6 different directions. In order to test the enclosure influence, the trailer at the Technical University of Gdansk (TUG) was tested in the field on a road surface when driving first with and then without its normal enclosure fitted. Tests were run for a number of speed and tyre combinations. Differences in measured A-weighted noise levels and frequency spectra with-without enclosure were calculated and an attempt was made to estimate the frequency spectrum of the "disturbing" noise, i.e. the noise which is eliminated when the enclosure is fitted. The experiments to test whether vehicle selection is important when measuring tyre/road noise were conducted in the TUG laboratory under closely controlled environmental and physical conditions, using a drum facility on which several tyres were run at a number of speeds. This study mainly addresses the problem of different wheel housings in different vehicles. During these tests, the tyres were mounted on five cars as well as on the TUG trailer, which made it possible to study any noise differences for a particular tyre occuring when it was mounted on different vehicles. The third of the problems investigated was that ofa possible influence of the rim on which the tyre is mounted during noise testing. Experiments with regard to this were conducted on the same facility as the vehicle selection study. They were designed in a similar way, except that instead of varying the test vehicle, the test rim was changed. Rims of three different widths (4, 5 and 6 inches) and of three different materials and weights were used. It was believed that the chosen test equipment and parameters would emphasize any potential problems arising when using well-designed, conventional equipment. (A)
Abstract