A measurement method for damping of drive shaft
Examensarbete för masterexamen
Sound in our society is beginning to be a health hazard in many places. This leads to legislation and recommendations by public authorities and governments. For a truck the sound pressure level should not exceed 80 dB(A) during a drive-by test set by international standards. This leads to development of the noise for the truck, and different parts get their own allowed component noise level. This thesis will look at one of these parts, i.e. the drive shaft. The goal is to find a test method for controlling the damping in the drive shaft for quality purposes. An additional goal is to see if the method also could secure the target value for the sound pressure level in a drive-by test. Using cardboard tubes inside the drive shafts damps them. In the cases where the drive shafts do not fulfil their target value in a drive-by test, an idea is that the insertion of the cardboard tubes has not worked properly. This calls for a test method for quality purposes and the suggested one is measuring the reverberation time. The manufacturer of the drive shaft wants to make the measurements on the steel tube after the cardboard tubes are mounted, but before the universal joints are welded to the steel tube. To determine the measuring method a lot of measurements are made.The purposes are to decide the excitation tool,the attachment of the detection tool and the measurement position. The measurements on the steel tube should be related to the drive-by measurements. Comparisons have been made between measurements on the steel tube, the drive shaft and the drive shaft mounted in the truck. Simple Finite Element Method models are made to see the mode shapes between a steel tube and a drive shaft,since it is difficult to see this result in the measurements. The result shows that the bending modes change much in frequency while the ringing modes are rather stable. Evaluations are made for the drive-by measurements with differently damped drive shafts. The result showed no clear difference between the tested shafts and the method cannot be used to secure the radiated sound pressure level during a drive-by test. Drive shaft losses have been measured using two methods, the backward integration on the Impulse Response and the half power bandwidth method on the Frequency Response Function. Both these methods can be used to obtain the reverberation time to control the steel tubes to secure the damping for them, if the disadvantages in the methods is known and taken into account. However I recommend the half power bandwidth method since it gives more information of the drive shafts.
Samhällsbyggnadsteknik , Civil Engineering