Redesign of steering knuckle for a sports utility vehicle (SUV) for improved fatigue life

A steering knuckle is a structural component that houses the suspension, brake calipers, wheel, lower control arm and the upper control arm. The main function of the steering knuckle is to drive the wheel, have straight motion and transfer the load to the suspension. Various types of load act on the steering knuckle. The design of the steering knuckle is to be robust to withstand the forces. Steering knuckle is subjected to fatigue loading during its service. This project deals with a steering knuckle of an SUV that failed due to fatigue. Attempt is made to improve its fatigue life by changing the design. Steering knuckle identified for a SUV is reverse engineered and using cloud of points data, the 3D model was created using CATIA software. The 3D model was later used for structural analysis. The virtual prototype of SUV was built in ADAMS car software and torture test track was built. The vehicle was run at different constant speeds of 20 kmph, 40 kmph and 60 kmph respectively on the torture track. The dynamic loads at hard points like upper control arm, steering arm, lower control arm and wheel hub were exported. These loads were given as input to structural analysis using ANSYS Workbench and the stresses were determined using inertia relief method. Fatigue life was calculated for the existing steering knuckle. Design changes were made for the existing steering knuckle for improved fatigue life. With the existing steering knuckle and vehicle running at constant speed of 60 kmph the maximum principal stress was found to be 314 MPa and estimated fatigue life was 3767 cycles. Five design iterations were carried out by changing the existing design of the steering knuckle to improve the fatigue life. Among five design iterations, iteration five with added features like ribs and drafts resulted in 52% reduction in principal stress and improved fatigue life of 1000000 cycles.