0 ]m[noitaiveD ecarT eniLTechnical Awards：2022 JSAE Award The Outstanding Technical Paper Award - A Study on Pitch Characteristic to Reduce Line Trace Deviation in Small Steering AngleFig.6 Line Trace Deviation by a DriverFig.7 Average of Line Trace Deviation by 25 DriversNISSAN TECHNICAL REVIEW No.88 (2022)3. Causes of variation in line trace deviations and reduction measures3.1 Steering mechanism for minute steering angles and variation in line trace deviationsFig.8 Driver’s Steering Process in Small Steering AngleThe variations in the line trace deviations of 25 drivers based on their respective standard deviations under the same specifi cations are depicted in Fig. 7, with the average value of 0.047 m. This average is not suffi ciently small, even compared with the fl uctuation in the line trace deviations under the different specifi cations defi ned for the average value of all the trials by all the drivers, as shown in Fig. 5.Following our previous work, which clarifi ed the vehicle characteristics that enable drivers to drive accurately, on average, along a target driving line, this research focused on the vehicle characteristics that enable accurate driving with little variations between trials.Various factors can be considered as the causes of the variation in the line trace deviations for each trial of a driver, such as differences in the line of sight, how the steering wheel is held, or the degree of concentration when driving. This work focused on the steering mechanisms of the drivers with minute steering angles, as hypothesized in the previous work, and conducted a detailed analysis. As shown in Fig. 8, when steering from straight running toward the target line, the driver fi rst recognizes that the steering input to the vehicle is commenced at a steering angle of approximately 1° based on the steering reaction force information. Therefore, by setting a dead band in the yaw rate such that the vehicle can initiate the yaw movement simultaneously, the vehicle movement that matches the feeling of the driver can be realized. As a result, on an average, the line trace deviations are reduced. However, the driver can only sense the movement due to this yaw rate as visual information when the value exceeds 0.21°/s and the steering angle reaches approximately 2°. In other words, in the section where the steering angle is 1°–2°, it can be considered that the driver is performing blind steering without obtaining feedback regarding vehicle movement in the visual sense and relying solely on the information from the steering reaction force.It is clear that visual feedback is one of the most important types of information for stable and accurate driving, and it is conceivable that even a small steering angle range, such as 1°–2°, has an unexpectedly large infl uence on stable and accurate driving. In particular, with regard to the line traceability at minute steering angles of less than 5°, as in this case, the effect is considerably large and likely one of the major factors in the variation of the line trace deviations.Therefore, visual information is fed back to the driver, indicating that the vehicle begins to move in the yaw direction at a steering angle of approximately 1°, which the driver can recognize as a steering input. When movement increases with the steering angle, the driver will be able to steer in a more accurate and stable manner; consequently, variations in the line trace deviations will be reduced.As mentioned earlier, the yaw movement itself does not enable the driver to sense that the vehicle responds to the steering and begins to move in the yaw direction; this is because a yaw rate of 0.21°/s or higher is required for the driver to detect movement in the yaw direction. By contrast, if a higher yaw rate threshold for the driver to sense vehicle start movement is set, the yaw-direction movement of the vehicle may become excessive and the vehicle will not travel accurately along the originally 0.080.060.040.020.00Y[m]1.510.50-0.5Target LineVehicle Trace Line3012345678910111213141516171819202122232425Driver No.X[m]9060Driver recognize the InputDeadBand3.2 Vehicle behaviors for providing visual 901031deg2deg0.21deg/s↓ Undetectable Motion ↓information to driversDriver detect the MotionSteering AngleAverage: 0.047mBlind Steerwith only Force Information
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