Improvement of Steering Performance using Steering Rack Force Control 2019-01-1234
In recent years, steering performance has been improved considerably. Yet there are still complaints about steering feel, especially feedback performance on the road. The existing logic is not focused on steering performance. Therefore, it has a limitation in improving the steering performance. In addition, the steering system has friction and inertia due to the operating structure. this is felt to the driver by friction feeling and inertia feeling. As a result, the steering feedback performance deteriorates.
In this study, the following steps are developed to develop new logic.
First, The analysis of the steering system determines the key factors that affect the steering fell of the driver and defines the ideal steering system. To implement this ideal steering system, a rack-based feedback control is proposed.
Secondly, The observer of rack force was designed to estimate the rack force. In general, the rack force estimator is estimated using the driver's torque, assist torque, etc. However, the friction of the steering system is difficult to estimate, which causes an error compared to the actual rack force.
Especially, at high speed, which is important for the steering feeling, the higher the vehicle speed, the greater the friction on the rack force and the greater the error.
In order to solve this problem, we design two estimators deduced from vehicle model and steering system model. The observer that uses two estimators can reflects various operating conditions by using characteristics of each estimator performance. Therefore, it reflects the driving situation more precisely. Therefore, it can be estimated more accurately than existing estimators.
We evaluated vehicle performance under various operating conditions to compare the actual rack force and the rack force of the estimator and verify the accuracy of the rack force estimator.
Finally, Simulation evaluation confirmed that the proposed logic improves the steering feedback performance and is robust to component dispersion.
Chanjung Kim, Dayul SON, Zachary Sabato, Byoungyun Lee
Hyundai Motor Company, Univ of California-Davis, Hyundai Mobis