Case Study: NVH: Interior Noise Reduction

Case description

Approach and Solution

Initially, a combination of subjective appraisals and objective measurements were used to identify the major areas in which the vehicle failed to meet the NVH targets( The NVH targets, which were set during an earlier exercise, were based on the class-leading vehicle in the local market.  The target lines shown in the graphs have an upper and lower tolerance band. ).

The dominant issues identified were powertrain ‘booming’ noise, wind noise and idle refinement.  Figure 1 shows the overall interior noise level against engine speed recorded during a 3rd gear wide-open throttle acceleration test in relation to the NVH targets already established.

Prototype solutions for each of these issues were designed, manufactured and assessed on the prototype vehicle to validate the findings of the investigations. Noise and vibration testing on the modified ‘simulator’ vehicle showed that significant improvements in subjective and objective refinement were achieved for each of the NVH attributes under consideration.  Figure 2 shows the performance of the simulator vehicle against the NVH targets for a 3rd gear wide open throttle test.

Figure shows the NVH performance of the modified ‘simulator’ vehicle.  The sound level is now within the target band for much of the engine speed range.  The peaks in interior noise are much less prominent, leading to a ‘smoother’ sound.

 

Conclusions