## 4 Study on Active Sound Control Method under Constant Speed Condition
### Uniform Driving Conditions Sound Total Value Target Setting  
The target setting of the total sound value of the ASGS under the condition of constant speed driving is carried out according to the 3 rd gear driving condition of the target FV. According to the engine speed of 1000-6000 rpm in the operating condition, the sound inside the vehicle of the FV in the 3 rd gear running at a uniform speed was tested. The engine order sound and the background sound in the vehicle were separated, and the total value of the vehicle sound, the total value of the engine order sound, the total value of the background sound, and the sound pressure level difference between the engine order sound and the background sound were calculated at a constant speed, as shown in Table 8 and Figure 11. The change curve of sound pressure level difference between engine order sound and background sound in the vehicle is shown in Figure 12.  
According to Table 8, Figures 11 and 12, it can be concluded that:  
1. With the increase of engine speed, the amplitude of engine order sound and the amplitude of background sound show a linear increase trend, and the increase of engine order sound amplitude is greater than that of background sound amplitude.
2. With the increase of engine speed, the difference between engine order sound and background sound tends to decrease linearly.  
For an A-class pure electric SUV studied in this paper, the vehicle speed corresponding to each virtual engine speed was calculated, and the amplitude of the sound inside the vehicle at each speed is tested and calculated, as shown in Table 9. It is further compared with the background sound inside the FV, as shown in Figure 13.  
Figure 11: Comparison of sound and noise results in the FV under constant speed driving conditions.  
Figure 12: The variation curve of the difference between the engine order sound and the background sound of the FV driving at a constant speed.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Engine Speed (rpm)** & **1000** & **2000** & **3000** & **4000** & **5000** & **6000** \\ \hline Corresponding speed (km/h) & 13.0 & 36.5 & 57.9 & 78.9 & 99.6 & 121.0 \\ Total sound in vehicle/dB (A) & 49.6 & 57.1 & 59.7 & 64.3 & 68.6 & 70.0 \\ Engine order sound in vehicle/dB (A) & 42.7 & 50.9 & 54.1 & 59.4 & 64.4 & 66.4 \\ Background sound in vehicle/dB (A) & 48.6 & 55.9 & 58.3 & 62.6 & 66.5 & 67.5 \\ Difference between engine order sound and background sound/dB (A) & \(-5.9\) & \(-5.0\) & \(-4.2\) & \(-3.2\) & \(-2.1\) & \(-1.1\) \\ \hline \hline \end{tabular}
\end{table}
Table 8: Test results of in-vehicle sound of the target FV at constant speed.  
According to the amplitude relationship between the engine order sound and the background sound of the FV in Figure 12, on the basis of the original internal sound of the EV, the target setting of the sound amplitude and the total value of the internal sound of the ASGS in the uniform driving condition is carried out, as shown in Table 10 and Figure 14.  
The sound amplitude target line of the ASGS under uniform driving conditions is the blue dashed line in Figure 14. It is required that the sound produced by the system should not exceed the target curve to ensure the low amplitude noise level in the EV under uniform driving condition, so as to meet the requirements of comfort sound quality control.