Abstract
Steering wheel release stability is one of the important key performance parameter for vehicle design. This paper highlights the approach and methodology followed to meet the steering wheel release stability performance target. According to ISO 17288-Part 2, Steering wheel release stability is also known as “Free Steer”. It is a test carried out to evaluate the ability of the vehicle to return to straight path in response to the steering pulse input during straight-ahead driving. This test is conducted while hands are released off from the steering wheel. The evaluation for Steering wheel release stability is indicated by the time, under the criterion of yaw rate to damp from its peak to 1/10 of its peak. In traditional vehicle engineering phase, the steering wheel release stability is confirmed, iterated and evaluated using prototype vehicles which attracts huge cost and lead time resulting significant impact on the project. Approach is to confirm all performance parameters of Steering wheel release stability by digital engineering methodology and transform the results to physical phase for building prototype vehicles. Digital engineering helps to correlate the simulation result on physical vehicle. Digital engineering also supports to ensure Steerability parameters such as roll steer, tire cornering power, caster trail, mass, yaw inertia, steering gear ratio, lateral compliance steer and roll angle represent accurately to the level of 99%, of actual vehicle dynamic condition. Based on Design of Experiment conducted in-line using Routh Stability Criteria [1], Tire cornering power and Roll steer were identified as most influencing performance parameters. When vehicle development time is challenged, the scope is limited for change in tire cornering power, since it has impact on NVH, Brake, Ride and Handling. CAE analysis was done to improve roll steer by modifying hard point of Steering outer ball joint as a narrow-down approach to improve roll steer. Over-all, doing a minimal change, front roll steer improved, which resulted in reduction of yaw rate 1/10 damping time by 23% on vehicle. With this improvement, driver can quickly regain control of vehicle after a sudden maneuver. Current study has proved to be a satisfactory proactive design tool to minimize time and cost at up-front design stage for steering wheel release stability test.