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Control Design for Cancellation of Unnatural Reaction Torque and Vibrations in Variable-Gear-Ratio Steering System

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Variable-gear-ratio steering is an advanced feature in automotive vehicles. As the name suggest, it changes the steering gear ratio depending on the speed of the vehicle. This feature can simplify steering for the driver, which leads to various advantages, such as improved vehicle comfort, stability, and safety. One serious problem, however, is that the variable gear-ratio system generates unnatural torque to the driver whenever the variable-gear-ratio control is activated. Such unnatural torque includes both low-frequency and steering speed-dependent components. This paper proposes a control method to cancel this unnatural torque. We address the problem by using a tire sensor and a set of feedback and feedforward algorithms. Effectiveness of the proposed method is experimentally verified using a hardware-in-the-loop experimental setup. Stability and robustness under model uncertainties are evaluated.
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... Therefore, a promising and potential solution to reducing driver workload is to develop an advanced driver assistance steering systems [17] that can lead to smaller steering angle needed and less meticulous steering operation required. For example, reasonable changes of steering ratio and assisted torque of VRSSs based on vehicle states and driver conditions can assist drivers in operating more easily and improve the comfort, stability and maneuverability of vehicles [14], [18], [19]. ...
... To design a more intelligent steering system and reduce driver workload, the shared control systems between driver and controller are also proposed, in which driver characteristics, such as driving mood [23] and steering feeling [18], are considered. For instance, taking driver factors into consideration, Hayakawa et al. [24] proposed a steering smoothness method to overcome the compatibility issue between drivers and steering ratio by using variable multiple look-ahead distances in the steering control. ...
... However, in [23], the influences on steering system gain from vehicle speed and steering angle were set as a constant. Oshima et al. [18] considered one element of driver steering feeling-natural torque-to compensate for the steering torque. ...
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... Shimizu et al. [12] developed a variable steering gain based on vehicle speed and steering angle to improve the performance of a vehicle. Furthermore, one of the elements of the driver's steering feeling (natural torque) was considered to compensate for the steering (steering torque) by Oshima et al [13]. Taking the driver factor into consideration, Hayakawa et al. [14] proposed a method to overcome the compatibility issue between the driver and the variable steering ratio by using variable multiple look-ahead distances in the steering control based on the vehicle speed. ...
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