Abstract

Steering system in vehicle helps a driver to keep vehicle in desired direction. In both front and rear wheels the vehicle’s weight is distributed. But with increasing vertical load on front wheels driver feels hard steering. So power steering system is used to assist driver to reduce steering effort to move vehicles road wheel easily. In conventional power system discharged flow rate of belt driven vane pump is proportional to vehicle engine speed. So at low vehicle speed assist power is minimum and at high vehicle speed assist power is maximum. At parking driver feels hard steering. At high vehicle speed steering is very light and most of the time power steering remain unused. The hydraulic circuit drops power because of using open center rotary valve. As vehicle is run on fuel so it’s a waste of fuel energy. Good steering feel means light steering at parking but less light steering at high speed. So in this paper an energy saving model is proposed which can save power consumption and save fuel and maintain a good steering feel. To reduce energy consumption instead of fuel energy electrical energy can be used and the electrical power consumption can be reduced by controlling the motor efficiently. The proposed model is simulated in Matlab. Toyota Premio car specification is used in calculation. The simplified flow equation for rotary valve is used. The relation between flow rate and rack speed is linear. So the force acting on rack depends on pressure developed in cylinder. And pressure depends on discharged flow rate. To provide good steering feel rack force is controlled according to vehicle speed. And for obstacle avoidance at high speed rack speed is controlled according to steering rate. There is motor speed map. The motor speed is controlled using pid method. Fuzzy method used in motor speed map. Static steering torque to steer the road wheels is calculated from force acting on tie rod and rack and from tire contact patch. Dynamic steering torque is calculated using friction coefficient variation. The steering torque also varies with steering angle which is calculated through Ackerman steering principle. The proposed model shows low energy consumption compared to conventional power steering system.