Studies on Steering Feeling Feedback System Based on Nonlinear Vehicle Model

Paper #:
  • 2017-01-1494

Published:
  • 2017-03-28
Abstract:
Steer-by-wire technology is considered as a next step in steering system evolution. The substitution of electronic systems in place of mechanical components simplifies the car interior design and saves larger space for driver cabin. But the absence of the force coming from the road directly challenges us to model an optimal steering feel. Referring to the structure of the conventional steering systems, the forces transmitted to the driver through handwheel consist of steering system friction and aligning torque. In the paper, the steering system friction is simulated by the Stribeck friction model. The accurate friction model is important for simulating feedback torque during stand-still, low speed and low lateral acceleration conditions. Besides that, the elasticity of steering column should be taken into consideration, which helps to improve the dynamic response performance of the system especially in the condition that the steering angle changes rapidly. The aligning torque is a dominant component influencing driver’s hand feeling. In vehicle model, tire model is especially complicated, which is characterized by 10-20 coefficients for each important force. In the paper, the aligning torque is presented by a modified formula. PMSMs are extensively used in industrial applications due to the high efficiency and high power density. The paper uses a PMSM to provide the desired feedback torque. With handwheel angle sensor, high accuracy of the torque control can be obtained by using a modified direct torque control (DTC) method. Compared with field oriented vector control method, the modified DTC retains all the advantages of the basic DTC, such as no coordinate transformation, robust to machine parameters, no current control loop etc. Instead of hysteresis controllers in basic DTC, the modified DTC method adopt a proportional-integral controller and reference flux vector calculator to determine a reference stator flux linkage, and then a space vector modulator is used to replace the switching table of the basic DTC. The modified DTC method can reduce the torque ripples greatly. Finally, the simulation is carried out to verify the steering feeling feedback system. In the simulation, vehicle model, tire model and PMSM model are established in matlab/Simulink. As a comparison, a corresponding model in CarSim is also established. After using the proposed model generating the desired feedback torque, the steering feel is better than it in CarSim. In addition, the simulation results indicate that the PMSM can track the desired feedback torque with low torque ripples.
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