A Novel Technique to Establish Various Important Characteristic to Analyze Complete Hydraulic Power Steering System using Model Based Design Approach

Steering system deliver a precise directional control to the vehicle chassis and ensure the safe driving at all maneuvers. Hydraulic power assisted system (HPAS) helps drivers to steer by boosting steering assistance of the steering wheel while retaining the road feel. HPAS performance is associated with the design characteristics of rotary valve, steering, suspension, kinematics, brake, tire, vehicle speed and load transfer. Thus a detailed power steering system model is absolutely necessary to evaluate and optimize the performance characteristics. However, many components of HPAS system are proprietary in nature so it is very challenging to get component characteristic of each sub-system for the complete power steering system model. Hence, it is very important to establish a technique to extract all such influencing characteristics with available test facility. The present study shows a detailed vehicle level HPAS system dynamic model to predict various power steering system performance characteristics. A polynomial function of area opening of rotary valve and torsion bar twist angle is used to map the boost characteristic. NLPQL optimization algorithm has been used to find the polynomial coefficient in order to co-relate with known boost characteristics. Similarly, a novel technique has been established to find the parking torque characteristic of tire from the measured test results. A detailed steering system model has been developed and effect of other vehicle sub-systems is studied on steering performance. This model can be used to predict the static and dynamic steering effort as per IS 11948:2010. The Simulation results from the model provide a very good co-relation with the measured test data for different vehicles.