## 5 Roll Camber
### Impulse Steering Tests  
The transient-state cornering handling performance of the target vehicle was evaluated by means of a simulated impulse steering test performed at a speed of 70 km/h with a steering wheel angle change of 65\({}^{\circ}\) (corresponding to a lateral acceleration of approximately 0.4 G) within 0.4 s. As described in Section 3.3, the validity of the simulation results was confirmed by comparing the calculated values of the phase lag, natural frequency, yaw rate gain, and damping ratio with the experimental values (see Table 4). For ease of visualization and comparison, the two sets of data were also presented as four-parameter radar charts, as shown in Figure 8, in which the vehicle transient handling performance is represented by the area and position of the enclosed diamond region of the chart.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & **Experimental Data** & & \\ \hline Speed (km/h) & Phase lag (\(\phi\)) (deg) & Natural frequency (fn) (Hz) & Yaw rate gain (a1) (l/s) & Damping ratio (\(\zeta\)) \\
70 & \(-\)36.81 & 1.9567 & 0.24618 & 0.5581 \\ \hline  & & **CAE model Data** & & \\ \hline Speed (km/h) & Phase lag (\(\phi\)) (deg) & Natural frequency (fn) (Hz) & Yaw rate gain (a1) (l/s) & Damping ratio (\(\zeta\)) \\
70 & \(-\)26 & 1.8825 & 0.18099 & 0.94961 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Experimental and simulation results for the impulse steering tests.  
Observation of Figure 8 shows a good quantitative agreement between the experimental and simulation results for the natural frequency (fn) and steady-state yaw rate gain (a1). However, an obvious difference exists between the two sets of results for the damping ratio (\(\zeta\)) and phase lag (\(\phi\)). As described earlier in Section 4.1 for the constant radius cornering test, this discrepancy arises since the CAE model is based on a rigid-body assumption, whereas the linkages, bushes, bearings, racks, and tires in the actual vehicle system are compliant. Nonetheless, a good qualitative agreement was observed between the two radar plots, and, hence, the basic validity of the simulation model was confirmed.  
To further evaluate the transient handling response of the vehicle, additional simulated impulse steering tests were performed at speeds ranging from 40-120 km/h. The corresponding results for the phase lag, natural frequency, steady-state yaw rate gain, and damping ratio are shown in Table 5. In addition, the four-parameter radar plots are presented in Figure 9. In general, the size of the enclosed diamond area of the  
presented in Table 5, the damping ratio decreased with an increasing speed. In other words, the nose convergence worsened as the speed increased, indicating a higher risk of vehicle instability.  
Phase lag (\(\phi\)): \(\phi\) represents the phase lag angle at a 1 Hz lateral acceleration. A smaller value of \(\phi\) represents a better handling performance in emergency cornering. For a low speed of 40 km/h, the phase lag had a low value of \(-\)1.849. However, as the vehicle speed increased, the phase lag increased significantly. In other words, as expected, the handling performance and stability were degraded as the vehicle speed increased.