Browse Publications Technical Papers 2007-01-0994
2007-04-16

The Study of the Parameter of Roof Rack & Cross Bar for the Reduction of Wind Noise 2007-01-0994

An increasing number of cars which are being used to foster leisure and a convenient life for consumers are being outfitted with roof racks and/or cross bars. This trend of installing roof racks is partly for the function of carrying objects on the roof of the vehicle and partly as a way to affect the style and exterior look of the vehicle. Therefore, the application of roof racks and cross bars is becoming increasingly important in the automotive industry.
Because of the expanding application of roof racks on vehicles, the challenge of reducing wind noise caused by exposed cross bars becomes the main issue in this field. For solving this problem, the cross bar shape is designed and evaluated in the development stage, and if there is a problem, it is re-designed and re-evaluated many times. This repetitive corrective action is called “trial and error”. However, by using DFSS tools such as improving the existing development system and optimizing the cross bar section, this study presents the best way of shortening the development time, explaining the design features, and achieving optimal costs and weight.
Based upon the research of wind noise influence considering roof rack and cross bar design parameters, this report presents the following results:
  1. 1
    Applying the same cross bar design on various vehicles, the wind noise level is different depending on the unique roof shape of each vehicle. Therefore a firm and suitable cross bar design is needed for each roof shape.
  2. 2
    The absolute value between the vehicle evaluation and the air flow and noise analysis is different. However, we can check the optimized value of the cross bar section by comparing the cycle of sound pressure level with the advantage value.
  3. 3
    The most important factor for determining wind noise is the length of cross bar section and the ratio of length to width. The optimal condition is length: 55mm with a ratio of length to width of - 2.8:1.
  4. 4
    Through strength analysis, such as optimizing the thickness of the cross bar, the effects of cutting down costs and weight can be determined.
The results shown above are reached by analyzing and evaluating vehicles and are presented as the design guide for the development of a new model roof rack and cross bar hereafter. By using this guide, the effects of shortening cross bar development time and reducing the wind noise phenomenon can be achieved.

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