## 3 The Method of the Driver's Intention Identification  
_Driver's Characteristic Steering Parameter under Different Conditions_  
In order to accurately describe the steering characteristics of the driver under each steering condition, it is ensured that there will be no loss or distortion of the driver's intention information. According to GB/T 6323-1994 \"Vehicle Handling Stability Test Method\", this paper selects the typical steering conditions of the driver's characteristic parameters, as shown in Table 2. In order to identify the driver's steering intention under different steering conditions, this paper chooses the driver steering parameters and vehicle dynamics parameters for the first two seconds under different operating conditions. The purpose of this is to use the initial operation of the driver to identify the driver's steering intention in the next period. It is helpful to lay the foundation for dynamic control for further advanced driver assistant systems. Furthermore, this can improve the accuracy of the intelligent vehicle active safety control system. However, various uncertainties exist due to the large amount of interference signal in the test data, as shown in Figure 3. Especially, torque, angular velocity, yaw rate and lateral acceleration need to be filtered. \begin{table}
\begin{tabular}{c c c} \hline
**Symbol** & **Meaning** & **Units** \\ \hline \(\delta_{m}\) & Average steering angle & deg \\ \(\delta_{\text{max}}\) & Maximum steering angle & deg \\ \(\hat{\delta}_{\text{m}}\) & Average angular velocity & deg/s \\ \(\hat{\delta}_{\text{max}}\) & Maximum angular velocity & deg/s \\ \(T_{m}\) & Average torque & Nm \\ \(T_{\text{max}}\) & Maximum torque & Nm \\ \(\gamma_{\text{max}}\) & Maximum yaw rate & deg/s \\ \(\phi_{\text{max}}\) & Maximum roll angle & deg \\ \(a_{y_{\text{max}}}\) & Maximum lateral acceleration & m/s\({}^{2}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Driver’s characteristic steering parameters. Figure 2: Experimental vehicles (**1**) GM GL8, (**2**) Skoda Octavia, (**3**) Honda Accord, (**4**) SAIC MG.  
Figure 3: _Cont._  
The Butterworth filter is a kind of electronic filter whose frequency response curve is the smoothest. The filter was first proposed by a British engineer, [PERSON], in a paper published in the British journal Radio Engineering in 1930. The attenuation rate of the first-order Butterworth filter is 6 dB per octave. The second-order Butterworth filter has a decay rate of 12 dB per octave, and the third-order Butterworth filter has an attenuation rate of 18 dB per octave, and so on. The amplitude of the Butterworth filter is monotonically decreasing, and it is also the only filter that maintains the same shape regardless of the order of the amplitude of the diagonal frequency curve. The higher the order of the filter is, the faster the amplitude attenuation in the resistive band is. The difference with the Chebyshev, Bessel and elliptical filters is that the attenuation of the Butterworth filter is slower than the other filters, but is very flat and does not vary. The Butterworth low-pass filter can be expressed by the square of the amplitude:  
\[|H(\omega)|^{2}=\frac{1}{1+\left(\frac{\omega}{\omega_{c}}\right)^{2n}} \tag{1}\]  
where \(n\) is the order of the filter and \(\omega_{c}\) is the cut-off frequency. Therefore, we choose the Butterworth filter with different orders to process the test data. Filter results can be seen in Figure 3. In Figure 3a, the first-order Butterworth filter obtains the closest data to the raw data; simultaneously, the value of torque is also very smooth. Therefore, the first-order Butterworth filter is the most suitable to handle the torque signal. In Figure 3b, we can reach the same conclusion about the angular velocity signal. In Figure 3c,d, although the first-order Butterworth filter obtains the closest data to the raw data, the first-order Butterworth filter is less smooth than the second-order Butterworth filter.