In today's volatile market environment, and with the change of user priorities, NVH refinement results in silent, vibration-free vehicle. The commercial vehicle industry is also starting to embrace this development in NVH vehicle refinement. There are health concerns associated with the discomfort experienced by occupants. This calls for cabins with no boom noise and less tactile vibrations.
Noise within the vehicle is contributed by excitation from the Powertrain, Intake, Exhaust system, driveline, road excitations, suspension (structure borne noise) and its radiation into the air (air borne noise).
This paper discusses the approach used to reduce “In-cab boom” noise in the operating speed sweep condition and seat track vibration during engine IDLE condition to improve driver comfort. In this paper NVH refinement was carried out on small commercial vehicles.
Higher Seat track vibrations during IDLE and cabin boom noise during wide open throttle condition were observed during development of the product viz. small commercial vehicles.
One of the rigid body power train modes was coupled with IDLE excitation firing frequency in the vehicle. The use of optimized PT mounts stiffness, resulted into separation of PT rigid body mode from IDLE frequency excitation and thus reducing the seat track vibrations to acceptable level.
Another challenge was of In-cab noise with boom perception in speed sweep condition in customer driving pattern in another small commercial vehicle which was contributed by Exhaust and Intake noise. The exhaust engine firing orders were attributed to higher In-cab noise. Boom noise perception was reduced with silencer design optimization without affecting back pressure. The silencer design optimization was carried out through TL prediction.
Intake noise is mostly attenuated by passive control techniques. One of the technique is Helmholtz resonator. Helmholtz resonator was designed and evaluated on vehicle to address resonance at Intake system for the vehicle.
The journey involves various tasks including noise, vibration measurement and analysis, PT mounting stiffness tuning, virtual simulation and evaluation on the vehicle.
It was observed that the engine mounts with correct stiffness’s, seat track vibrations decreased by more than 50% during IDLE, optimised design of exhaust silencer & with Helmholtz resonator at Intake system, the cabin boom noise was reduced by 6 to 8 dB(A) resulted into the targeted NVH performance.