A STUDY OF EFFECT OF STEERING GAIN AND STEERINGTORQUE ON DRIVER’S FEELING FOR SBW VEHICLE

摘要

An experimental vehicle equipped with Steer-By-Wire (SBW) system isfabricated, which is capable of changing freely the vehicle steering gear ratio, by changing thesteering angle gain, and steering reactive torque (or steering torque), TTq characteristics.Driver’s feeling about the steering angle gain and steering torque is experimentallyinvestigated, for various steering angle gain, steering torque magnitude, and steering torquedelay (Mode 1 to Mode 6). A single lane change test with vehicle velocity at constant 60km/his executed.According to the driver’s comments, the author founds that driver’s good feeling in this lanechange greatly depends on two factors, which are the TTq delay, and T Tq magnitude. Themagnitude of TTq here is related to the driver’s physical effort, while T Tq delay (Tt) is related tothe driver’s mental workload. When TTq 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 driver’s good feeling, Driver 1is more sensitive to the TTq delay, while Driver 2 is more sensitive to the magnitude of T Tq.Steering torques proportional to vehicle yaw rate and lateral acceleration asresponse-feedback information to the driver about the vehicle state of motion through thesteering wheel are investigated too. However, it is found that due to the delay of yaw rate andlateral acceleration to steering input, drivers found these types of steering torque to beunsuitable for medium-speed lane change..Besides this, both drivers rating for steering angle gain of 2 (steering gear ratio of 8) is betterthan steering angle gain of 1 (steering gear ratio of 16) in this lane change, due to thereduction of driver’s steer input that is required, and thus, the driver’s physical effort.However, this is under the condition that the TTq proportional gain is doubled in accordance tothe decrement of steering gear ratio from 16 to 8. This is because although the steering wheelangle needed becomes half of the conventional vehicle, it is found that the amount of TTqneeded by the driver to complete the lane change task remains same amount as for theconventional vehicle. In other words, the steering torque should correspond to the vehiclemotion, rather than merely the driver’s steer input.The current study could be extended to different categories of drivers also, to investigate onthe optimum range of TTq magnitude, T Tq delay and ideal steering angle gain, in accordance tovehicle velocity, for good feeling and minimum physical or mental effort.