Centre Differential Units 4x4 front/rear power-splitters

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Front/Rear (Centre) Differential Unit NVH

The helical gear based centre-differential units commonplace in today's all-wheel (4x4) drive vehicles, raise their own specific NVH issues. Most of the time time these units operates with very small (sometimes zero) amounts of speed differential, so the relative speed between loaded gears can be very small.

The NVH issues from such units therefore tend to be low-frequency "growls" and "groans", particularly during higher-speed cornering manoeuvres (where the front and rear wheels are forced to rotate at slightly different speeds). NVH testing for such issues can easily be carried out using a sequence of speed differential values (typically up to +/-150 rpm front/rear), with representative drive & coast side loadings.

It is also important to ensure that the dynamic sensors used are capable of delivering good results down to below 10Hz, and ABD has achieved particular success with strain-gauged based dynamic torque sensors for this application.