NVH Challenges for Low Cost and Light Weight Small Cars

摘要

In worldwide automotive markets, the migration of customers towards smaller cars having compact, fuel-efficient design is well established and accepted as an engineering challenge by global automotive OEMs. Tata Motors of India has established a precedent by developing an ultra low cost and light weight car (the Nano), and has thereby created a new market segment for such cars that are more affordable to most of the population. This is now becoming established as a brand of low cost, safe transport in both rural and urban market segments. Despite the market moving towards such compact, fuel-efficient designs, customers are unwilling to lose many of the vehicle attributes to which they have been accustomed in previous types of entry-level cars. Addressing this marketing requirement places some significant challenges before the designers of this type of car. This paper considers some of the fundamental technical challenges faced in delivering acceptable NVH performance in a light weight, low cost car. One of the most significant issues is the use of engines with lower cylinder counts than conventional cars, leading to strong impulsiveness and lower firing frequencies. These can become problematic when mounted in vehicle structures that have a high interior volume in proportion to their mass and are often not able to meet established norms for benchmark vibro-acoustic performance. Other matters considered include the high ratio of power train mass to total vehicle mass and the higher ratio of laden to un-laden mass. Such vehicles are also generally intended for manufacture by lower skilled workers in regions with little or no automotive assembly heritage, so they must be designed for ease of "right first time" assembly. Using the example of this product, some of the possible solutions to these challenges faced by the NVH team are examined. The paper will show that it is feasible to deliver market-acceptable NVH behavior despite the strong constraints inherent in such types of vehicle, by means of lean and innovative design.