Abstract
We have examined reliability in the case of applying cables to a steering system which transmit steering torque to front wheel. As a current automobile steering system is constructed by a column shaft, an intermediate shaft and universal joints between a handle and a steering gear box, the shaft's reliability is ensured by ordinal mechanical design method. However, it is difficult to design cables by using the ordinal mechanical design method. After we clarified the subject in the case of applying the cable to front steering, we proposed the new structure of the cables. And we confirmed an ability to ensure the reliability by an ordinal mechanical design method by using the S-N diagram which is delivered from fatigue test of the new cables. As a first step, the reliability of cable was evaluated by FTA method. Then, the main factors controlling the reliability of cable system was made clear to be wear fatigue behavior of cable which contact with pulley. Therefore in this paper, fatigue behavior of cable used in the abovementioned front steering system was investigated, especially in relation to the wear characteristics of cable material. Fatigue tests were conducted under the condition of loading torque of 29.4 Nm using cable made of SWRH62A covered with plastic coating filled oil inside of coating. From these experiments, degradation behavior of cable made of SWRH62A under repeated bending fatigue condition was investigated, and effect of amount of oil supply upon wear behavior of was examined. As a result, acceleration fatigue damage by wear was indicated in the cable especially under insufficient oil supply conditions.
