NVH Improvement of a Bus Through AC Compressor Drive-Ratio Change

This paper is an outcome of development work done in improving Noise Vibration Harshness (NVH) performance of a bus. A concern from built-up prototypes was high floor vibration levels at higher speeds when Air-Conditioner (AC) was switched on. Running mode analysis of bus-vibrations was performed to visualize exact behavior of its frame. It was revealed that a 4^th order vibrations of the AC compressor was matching with a structural resonance of the bus frame on which the AC compressor was mounted. The frame suffered from high amplitudes of torsional vibrations especially near a power-train mount. And these excitations were transferred to the bus-floor. With a change in drive-ratio of the AC compressor, decoupling of its vibrations from the Bus-frame mode was made. This led to a significant reduction of the floor vibrations and increased comfort to the passengers at higher speeds.