In the current era, vehicle manufacturers focus has increased towards passenger comfort and one of the key areas is NVH. Vehicle level NVH targets are cascaded to component level for obtaining better refinement in cabin. One such performance attribute is sloshing noise of urea in diesel vehicles. Migration from BS4 to BS6.2 norms demand complex technological changes to automobile manufacturers to add extra components to the vehicles which is a big challenge in identifying the locations at critical stage of the project phase. In one of the developments of mid SUV category vehicle, sloshing noise from urea tank is perceived as objectionable during low-speed braking and while passing over speed breakers.
This paper addresses the measurement conditions of sloshing noise and its evaluation procedure to quantify the sloshing noise at vehicle level. The sloshing noise is perceived in the frequency band of 50 to 1000 Hz. This paper also shows road map to reduce sloshing noise at source level by various methods. Fluid flow pattern studies are carried out to identify appropriate location to place baffles inside the tank. Different profiles like straight, inclined, and curved baffles performance contribution is assessed to reduce the level of sloshing noise.
This paper also cites about different design of experiments conducted to reduce structure borne as well as air borne-noise contributions originating from urea tank. The structure borne noise till 350 Hz is reduced by increasing structural stiffness at tank attachment locations and through bush stiffness reduction which reduced the dynamic forces entering the tank. Damping pads are applied over the tank to reduce the noise radiation. Air borne noise contribution to sloshing noise in the band 400 to 1000Hz is reduced by using acoustic package cover over the tank. With all above modifications, the sloshing noise level is reduced by ~5 dB(A) and is acceptable.