## 4 Experimental Results  
### Pump-Level Test Results  
Table 1 provides the main characteristics of the electric oil pump used in the experiment, and Figure 8 shows the experimental environment, including the electric oil pump installed in the anechoic chamber and the location of the installed acoustic noise and vibration sensors. Table 2 provides the control parameters of the electric control unit. Figure 7: Proposed shape of asymmetric pitch control. To measure airborne noise that is transmitted directly into the interior of the vehicle through air gaps, a microphone (1/2-inch free-field type, PCB 377B02 amplifier 426E01, 50 mV/Pa) was installed at a distance of 30 cm from the system under tests. To measure structure-borne noise that is transmitted into the interior of the vehicle through the vibration of the pump, a three-axis vibration acceleration sensor (PCB ICP HT356A33, 1.02 mV/(m/s\({}^{2}\))) was attached to the surface of the electric oil pump as shown in Photo 1. Automatic transmission oil (ATF SP-4M) was used, and the oil temperature was 60 \({}^{\circ}\)C. A strain gauge-type (MNEBEA NS30T) hydraulic pressure sensor was installed at the pump discharge section to measure the hydraulic pressure. The pump driving speed was tested at 1500 rpm (25 Hz), which is mainly required for low-speed vehicle driving and stopped, and 3000 rpm (50 Hz), which is required for high-speed driving. Even though the absolute noise and vibration level at 3000 rpm is greater than at 1500 rpm, the impact of pump noise at 3000 rpm is smaller than at 1500 rpm. This is because the pump noise might be drowned out by the vehicle's driving noise and engine noise when driving at high speeds, which requires 3000 rpm of pump operation. The pump noise at 1500 rpm can be irritating to the driver's ears when driving at low speeds or when the vehicle is stopped, so noise reduction is required even more during low-speed operations in pumps. Figure 9 shows the results of comparing the pump hydraulic performance and current consumption according to the application of general control and asymmetric pitch control. \begin{table}
\begin{tabular}{c c c} \hline
**Specifications** & **Value** & **Unit** \\ \hline Pump Type & External & - \\ Number of Teeth & 11 & EA \\ Max Operating Speed & 3200 & RPM \\ Max Hydraulic Pressure & 4 & Bar \\ Max Hydraulic Flow Rate & 16 & lpm \\ Max Electric Power & 400 & W \\ \hline \end{tabular}
\end{table} 
Table 1: Specification of the tested system. Figure 8: Noise and vibration measurements for the electric oil pump under tests in the anechoic room (The electric oil pump manufacturer: Myunghwa Ind, Co., Ltd., Seoul, Republic of Korea). It can be seen that when the maximum magnitude of the current reference for the asymmetric pitch control is increased to 40% of the rated current, the flow rate performance is reduced by about 10%. The experiment was conducted by setting the maximum size of the asymmetric pitch control command to less than 20% of the rated current, such that the change in both electric and hydraulic performance was maintained within 1%. Figure 10 shows the change in pump hydraulic pulsation according to the control method. The asymmetric pitch control shape factor \(B_{m}\) was determined to be 30, in order to maintain a similar pulsation width to the hydraulic pulsation measurement results. The average value of the hydraulic pulsation is the same in both normal control and asymmetric pitch control, but the peak-to-peak value of pulsation in the asymmetric pitch control is larger than the normal control, as shown in Figure 10.  
Unlike other noise reduction methods, such as mechanical geometric optimization and material optimization of pumps [10], the proposed control method increases the peak value of the pressure pulsations. These increases might affect the durability of pumps and system stability.