International Journal of Scientific Engineering and Technology (ISSN : 2277-1581) Volume No.3 Issue No.7, pp : 994-997 1 July 2014 IJSET@2014 Page 994 Control Strategy and Simulation In Steer By Wire System Jack J. Kenned Professor V.R. Patil jackbrilly@yahoo.com Abstract-- The stability and manoeuvrability of vehicles have been gradually focused on and improved by the automotive industry. Therefore, the SBW system becomes a wonderful choice to improve the performance of the vehicle, because there are some advantages, such as stability and manoeuvrability for the vehicles, and safety can be guaranteed for the operators. However, disadvantages also exist: the feedback from the front wheel may not be as perfect as the traditional vehicles, which means the drivers can not feel the road condition as easily as without SBW. Therefore, how to improve the feedback on the hand wheel and enhance the driving feeling to the drivers is the focus of this paper. Keywords—steer by wire, Gear ratio, steering angle, PID controller. I Introduction 1.1 Control Strategy The SBW system controller is divided into the steering wheel motor control and the front wheel motor control. The purpose of the steering wheel control is to improve the driver's steering feel by generating reactive torque. The purpose of the front wheel motor control is to steer the front wheel angle appropriately for improving the vehicle's maneuverability and stability. The proposed SBW control system is shown in Fig. 1.1 where the driver torque applied to the steering wheel is considered as the input, and the front wheel angle is defined as the output. The system is composed of two loops: upper loop, which mainly consists of steering wheel and torque feedback motor, and lower loop, which mainly consists of front wheel and a driving motor. To achieve the bilateral control performance, these two loops are controlled by two PID controllers, respectively[1]. The PID controller in lower loop is designed to control the actual front wheel angle to track the steering wheel angle. Its input is the error between the desired front wheel angle and the actual front wheel angle. tis output is the control voltage sent to the steering motor. [3] The desired front wheel angle is calculated based on the variable gear-ratio and the defined steering wheel angle. The actual front wheel angle is measured by an encoder installed with the driving motor. In the upper loop, there is another PID controller, which is used to provide the feedback torque to steering wheel so that driver can have a feeling about different steering situation. This feedback torque reflects the tyre-road contact and is generated reactive torque map in the system. When the front wheel turns to a certain angle, the torque will be generated in terms of this angle and vehicle velocity. This torque is regarded as a reference torque. The error between this reference torque and the measured torque from the torque feedback motor is defined as the input to the PID controller. The output of the PID controller is the control voltage, which is sent to the feedback torque motor so that the output torque of the motor can follow the reference torque. As this motor is connected to the steering wheel, the driver can feel this torque when steering the wheel. The output torque of the motor will be measured by a current sensor as the current of a DC motor is proportional to its torque[5]. In addition, the actual constraints on the steering wheel and the front wheel are also included in the too loops. The PID controllers will be designed to reduce the tracking errors. The controller gains are adjusted according to the simulation results referring to the Ziegler-Nicholas rules. As for different velocities the gear-ratio will be different. To account for this variation, several PID controllers will designed for several typical velocities such as 20km/h, 5km/h, 60km/h, 70km/h, 80km/h, and for other velocities, the PID controllers will be scheduled by interpolating the relevant controller gains. [9] Fig 1.1 Control System Model Design II Material and Methodology 2.1 Steering Wheel Motor Control The basic purpose of the steering wheel motor control is to generate reactive torque like a real commercial vehicle when the driver steers[6]. Furthermore, it makes the steering wheel easy to steer at low speed or when parking the vehicle and to make steering wheel tight at high speed for improving the driver's steering feel by adjusting reactive torque. It is relied on the variable steering ratio. PID control method is used to control the steering wheel reactive torque motor in this thesis, as the fig.1.1 shown above. 2.2 Front Wheel Motor Control For control of the front wheel, the signal from the HILINK board is very important because there is no mechanical linkage between the steering wheel and the front wheel like there is in a conventional steering system. [2] To control the