# Noise Identification for an Automotive Wheel Bearing
## 2 Noise and Vibration of Assembled Wheel Bearing  
In this study, the wheel bearing is a third-generation double-row angular contact ball bearing composed of a hub, inner ring, outer ring, retainer, and balls, as shown in Figure 1a. This third-generation wheel bearing has structural features wherein the hub and inner ring are integrated and the outer ring has a flange. Additionally, the double rows of balls can be divided into an inboard row close to the vehicle body and an outboard row close to the wheel. The bearing specifications of the wheel bearings used in this study are summarized in Table 1, where \(N\) denotes the number of balls, \(B_{d}\) denotes the ball diameter, \(P_{d}\) denotes the pitch diameter, and \(\theta\) denotes the contact angle. To mount the wheel bearing on the vehicle, the wheel bearing and dust shield are bolted to the knuckle connected to the vehicle body, as shown in Figure 1b. Hence, the dust shield prevents brake dust from accumulating in various components, including wheel bearings. The wheel bearing in the vehicle rotates when the outer ring is fixed by the knuckle, and the hub and inner ring rotate together with the drive shaft. Noise is generated when the wheel bearing is mounted on the vehicle and rotated. Thus, we analyzed the noise and vibration of the assembled wheel bearing, which included the knuckle and dust shield. The noise and vibration of the assembled wheel bearings were measured and analyzed experimentally. As shown in Figure 2, the experimental setup for noise/vibration measurement is constructed inside a semi-anechoic room. A motor for rotating the driving shaft was installed outside the semi-anechoic room to minimize the noise generated by the test equipment. The maximum rotation speed of the motor is 2000 rpm. The hub flange of the wheel bearing was bolted to a coupling connected to the driving shaft to fix the assembled wheel bearing to the test device. Then, the knuckle was placed against the edge of the jig to restrict the rotation. In a manner similar to the wheel bearing mounted on the vehicle, the outer ring is fixed by a knuckle whose rotation is restricted, and the hub and inner ring rotate with the driving shaft. The rotational speed of the wheel bearing was confirmed by measuring the rotational speed of the coupling, which rotates with the wheel bearing, via a tachometer (B&K MM-0360). The noise signal was measured by installing a microphone (PCB 378B02) 0.1 m away from the outer ring flange of the wheel bearing, and the vibration signals were measured using the accelerometers (B&K 4383) attached to the dust shield and outer ring. Meanwhile, given that the knuckle is relatively heavy and thick, it only has slight relevance to noise generation; therefore, it was excluded from the vibration measurements. The measured noise and vibration signals were analyzed using a spectrum analyzer (B&K 3050-B-060). \begin{table}
\begin{tabular}{c c c c c} \hline  & \(N\) & \(B_{d}\) (mm) & \(P_{d}\) (mm) & \(\theta\) (rad) \\ \hline Inboard row & 15 & 13.5 & 68.6 & 0.611 \\ \hline Outboard row & 16 & 13.5 & 73.2 & 0.611 \\ \hline \end{tabular}
\end{table} 
Table 1: Design specifications of the wheel bearing. Figure 1: Automotive wheel bearing: (**a**) internal structure and (**b**) assembly with main components. First, the characteristics of the noise and vibration generated on the assembled wheel bearing were investigated. The time responses for the noise and vibration, when the assembled wheel bearing rotates at a constant speed of 200 rpm, are shown in Figure 3. Furthermore, Figure 3a shows the time response for noise while an A-weighting filter is applied. Figure 3b,c show the time responses of the vibration of the dust shield and outer ring, respectively. In Figure 3a, the root-mean-square value for the noise response is 9.34 mPa(A) on a linear scale and 53.4 dB(A) on a logarithmic scale. In Figure 3b,c, the root-mean-square values for the vibration responses are 0.76 m/s\({}^{2}\) and 0.19 m/s\({}^{2}\), respectively.