Comprehend Dynamic Behaviour of Vehicle Body for Refined NVH Performance

Modal performance of a vehicle body often influences tactile vibrations felt by passengers as well as their acoustic comfort inside the cabin at low frequencies. This paper focuses on a premium hatchback’s development program where a design-intent initial batch of proto-cars were found to meet their targeted NVH performance. However, tactile vibrations in pre-production pilot batch vehicles were found to be of higher intensity. As a resolution, a method of cascading full vehicle level performance to its Body-In-White (BIW) component level was used to understand dynamic behavior of the vehicle and subsequently, to improve structural weakness of the body to achieve the targeted NVH performance. The cascaded modal performance indicated that global bending stiffness of the pre-production bodies was on the lower side w.r.t. that of the design intent body. To identify the root cause, design sensitivity of number and footprint of weld spots, roof bows’ and headers’ attachment stiffness to BIW, panel gages, body pillars joints’ attachment stiffness etc. was conducted using CAE tools. Identified structural weaknesses were converted into optimum design solutions, which were then validated using Experimental Modal Analysis (EMA). The proposed structural modifications in the body showed good improvement in the idle tactile vibrations and overall NVH of all production vehicles, validating the whole approach.