Low idle boom noise reduction on Light Weight Agricultural Cabin Tractor

In Last two decades, Farm customer expectation on Cabin comfort has been increased multifold. To provide the best-in-class customer experience in terms of comfort without adding cost and weight is bigger challenge for all NVH Engineers. It is evident from literature survey that cabin tractors with better comfort is well accepted by customers in US and European Market. Apart from engine excitation, customer has become more sensitive to customer-actuated-accessory noises due to overall reduction in cabin noise in last 2 decades. This paper presents the study conducted on HVAC blower noise in 30HP cabin tractor Tactile vibrations and Cabin Noise is not acceptable when AC is switched on due to low frequency modulating nature in frequency range of ~65Hz and 130Hz. The investigation is carried out systematically considering each component of Source-Path-Receiver model. HVAC blower unit as source is diagnosed in detail to understand root cause. Strong dominance of first order of blower been observed on tactile vibrations and cabin noise. Blower unbalance is identified major cause of excitation. Effect of Blower rpm on tactile vibration and boom noise is studied. Structural transfer paths were investigated in terms of stiffness & damping of radiating panels. Use of isolation strategy for blower is also explored for reduction in OEL noise. The damping of blower housing casing has shown contribution of 2-3 dB (A) at OEL noise. Both improvement in reduction of blower 1st order excitation and isolation strategy has shown to reduce low idle cabin noise by 10-15 dB (A) at 63Hz while operating at blower speed-3. Design NVH contenting in terms of modal frequency criteria for transfer paths, selection of blower speed is discussed to avoid similar issues in future.