Electric Power Steering Assist Mechanism Noise Issue Study Based On 6 Sigma Methodology

In recent years, China is actively developing new energy vehicles, one of the most representative for related product is electric car. Followed, the electric power steering system has become the state encouraged product, also complied with the trend of the automobile electronic. Thanks to electric control, steering tends to be more perfect, more precise. Current drive-by-wire technology cost is relatively high, mechanical transmission mechanism is still the subject of assist mechanism, so the requirement of mechanical transmission mechanism is quite high. At present there are two kinds of main steering assist mechanism. One kind is worm gear and worm, the other one is ball screw and belt transmission. From two aspects of the production practice and after-market service performance, noise is one of the major problems affecting the quality of the steering assist mechanism. The improvement of the noise performance becomes one of the important tasks of most suppliers.The content of research on the noise also belongs to harshness(NVH). The current research mainly adopts the harshness(NVH) technology, the research needs professional theory knowledge.Six sigma method is used in the paper, to identify the key process factors, optimize and control them by experiment design and some tools. The first thing is to describe the problem, statistic and main failure modes, analyze the relationship between them and the capability index level. After problem description, the process need to be analyzed, including the repeatability and reproduceability, meanwhile the primary process factors is identified. Next stage is detailed factor analysis, at this stage some typical tools are used, for example Turkey test, Histogram, scat plot, mulitivary diagram, one way Anova, mixture design, response surface design and so on. Next step will be factor optimization and verification, the final step is to standardize the process factors.