Analysis And Improvement Of Brake Pull For A Certain Light Truck Based On Six-σ

Brake pull is a serious issue that affect driving safety. Driver is relatively nervous when braking, at the same time he handle the steering wheel to control unexpected brake pull, which burden the driver and make him in potential unsafety. Electrical brake system has contribution in brake stability, but more attention must be paid for mechanical brake system, because many vehicles'brake system is mechanical and excellent performance of EBS depends on good foundation brake and chassis system. In this paper, the study has been done for a light truck's brake bull from enterprise exist issue based on research results at home and abroad with six sigma method and Minitab software. The paper did the following jobs:The first chapter introduced the current research status of brake stability and production development of internal enterprises. Foreign engineers study the steering compliance during brake by K&C rig test and A'rope potentiometer'method was selected to measure deflections of the wheels and suspension. Different compliance of rubbers in the suspension system cause different deflection wheel alignment, which cause braking pull.The second chapter introduced P-diagram of brake pull based on variation factors , design factors and noise factors and exclude obvious non-associated items according to detailed trouble and product history. Conclude two points causing brake pull: unbalanced brake force and different yaw moment. It is assumed as main factor which are pressure difference of master cylinder, disc process, friction variation and wheel alignment. Analyse process capability of important parts and screen significant elements by 2-level fractional factors design.The three chapter focused on the issue that brake force is not equal. Study pressure difference by changing the stiffness of return spring of master cylinder through rig test. And process of disc has an effect on brake balance by front brake rig test. Compare 20 vehicle test data from end of line between before process and after process. It proves out solution is effective.The fourth chapter focused on wheel alignment how to affect on brake pull. Analysis the effect of critical dimensions of important parts on kingpin inclination angle balance according to Doe result of second chapter. Front crossmember and front beam are important parts. Describle measure data by boxplot and distinguish major factor from cross member. Compare Cpk after improvement with Cpk before improvement and verify improvement by hypothesis testing F-test and T-test. P-value is more than 0.5, it indicates significant improvement. The fifth chapter inputs improvement to PFMEA, Control plan and QPS card.According to above research: select 10 vehicles at random, brake with initial speed of 60km/h, brake displacement meet requirement, so it proved that methods were effective to resolve brake pulling.