Measurement of Transfer Case Imbalance

Different methodologies to test transfer case imbalance were investigated in this study. One method utilized traditional standard single plane and two plane methods to measure the imbalance of the transfer case when running it on a dynamic balance machine at steady RPM, while a second method utilized accelerometers and a laser vibrometer to measure vertical vibration on the transfer case when running it on a dynamic balance machine in 4 Hi open mode during a run up from 1000 to 4000 RPM with a 40 RPM difference between the input and output shaft speeds. A comparison of all of the measurements for repeatability and accuracy was done with the goal of determining an appropriate and efficient method that generates the most consistent results. By using the traditional method, the test results were not repeatable. This may be due to the internal complexity of transfer cases. With the second method, good correlation between the measurements was obtained. Most importantly, the results were consistent and correlated with in-vehicle test results as well. The laser vibrometer, however, is preferable to the contact accelerometers because the set-up was less time-consuming. Based on the test data, a target (threshold) of transfer case vibration has been established, thus making possible a standardized end of line (EOL) test for production before being put into service.