Abstract
Keywords - Steer-By-Wire, steering torque, steering gain, drivers feeling, steering system characteristics
Abstract - An experimental vehicle equipped with Steer-By-Wire (SBW) system is fabricated, which is capable of changing freely the vehicle steering gear ratio, by changing the steering angle gain, and steering reactive torque (or steering torque), Tq characteristics. Drivers feeling about the steering angle gain and steering torque is experimentally investigated, for various steering angle gain, steering torque magnitude, and steering torque delay (Mode 1 to Mode 6). A single lane change test with vehicle velocity at constant 60km/h is executed.
According to the drivers comments, the author founds that drivers good feeling in this lane change greatly depends on two factors, which are the Tq delay, and Tq magnitude. The magnitude of Tq here is related to the drivers physical effort, while Tq delay (Tt) is related to the drivers mental workload. When Tq delay is small or within the good feeling range, subjective assessment by both drivers, Driver 1 & 2 for the SBW system are: easy-to handle, easy to stabilize the vehicle after lane-change, and a quick feeling about the vehicle response. Moreover, among the two important factors that influences the drivers good feeling, Driver 1 is more sensitive to the Tq delay, while Driver 2 is more sensitive to the magnitude of Tq.
Steering torques proportional to vehicle yaw rate and lateral acceleration as response-feedback information to the driver about the vehicle state of motion through the steering wheel are investigated too. However, it is found that due to the delay of yaw rate and lateral acceleration to steering input, drivers found these types of steering torque to be unsuitable for medium-speed lane change.
Besides this, both drivers rating for steering angle gain of 2 (steering gear ratio of 8) is better than steering angle gain of 1 (steering gear ratio of 16) in this lane change, due to the reduction of drivers steer input that is required, and thus, the drivers physical effort. However, this is under the condition that the Tq proportional gain is doubled in accordance to the decrement of steering gear ratio from 16 to 8. This is because although the steering wheel angle needed becomes half of the conventional vehicle, it is found that the amount of Tq needed by the driver to complete the lane change task remains same amount as for the conventional vehicle. In other words, the steering torque should correspond to the vehicle motion, rather than merely the drivers steer input.
The current study could be extended to different categories of drivers also, to investigate on the optimum range of Tq magnitude, Tq delay and ideal steering angle gain, in accordance to vehicle velocity, for good feeling and minimum physical or mental effort.