Optimisation of Steering System Geometry of Longer FOH Commercial Vehicles

Commercial vehicle industry is presently striving towards development of buses with enhanced passenger safety and comfort. This calls for additional components and aggregates that eventually lead to increase in the overall length and gross vehicle weight (GVW) of the bus for the same passenger capacity. Usually, steering system of longer front overhang (FOH) vehicles have multiple linkages such as bevel box arrangement or intermediate pivot arm arrangement instead of single direct draglink because of packaging and design constraints. In this work, an attempt has been made to design the steering system for one of the longer FOH bus with single direct draglink arrangement. Here, single draglink was packaged and designed with commercially available higher strength tube material. Design optimisation of steering geometry was carried such that the steering performance was atleast on par with existing performance. The MBD analysis has been carried out to compare the performance of existing and new steering system. Steering system performance parameters that were studied are steering gear demand torque, bump steer and on-center steering response. Analysis results showed that steering demand torque at the steering gear in the new design got reduced by 22% compared to existing design. Vehicles were tested for steering wheel effort and self-centering efficiency with existing and new steering system. Since, the number of steering system parts was less in the new design, there was also reduction in the cost and weight of the system.