NVH Measurement

The NVH testing setup is depicted in Figure 6. A Dytran 3055D1T accelerometer (Dytran Inc., USA) was affixed to the bearing housing adjacent to the drive gear to capture vibrational data, while a PCB Piezoelectronics 378B02 free-field microphone (PCB Piezoelectronics Inc., USA) was positioned 50 mm in front of the meshing gear pair to record airborne noise emissions. Data acquisition was carried out using the SIRIUSm data acquisition module from Dewesoft (Dewesoft d.o.o., Slovenia). NVH measurements for polymer gear pairs were conducted after 105 load cycles, a point at which the system was presumed to have reached thermal and mechanical steady-state conditions, with wear effects considered negligible in terms of influencing NVH characteristics. Acoustic and vibrational signals were recorded over a 10-second interval, employing a sampling frequency of 20 kHz. Representative signal traces are shown in Figure 7. For steel gear pairs, measurement was performed following a brief stabilization period, sufficient for torque and rotational speed to reach steady state, given the shorter operational duration of these tests. Three principal quantitative metrics are typically extracted from the acquired vibration and acoustic signals: the peak value (maximum instantaneous amplitude), the peak-to-peak value (the range between maximum and minimum amplitudes), and the root mean square (RMS) value. These parameters are illustrated in Figure 7. The peak and peak-to-peak values reflect singular extrema within the signal and are particularly sensitive to transient phenomena or high-amplitude anomalies. As such, these metrics may be disproportionately influenced by isolated impact events or momentary disturbances, which do not necessarily reflect the sustained dynamic behavior of the system. In contrast, the RMS (Root Mean Square) value provides a robust representation of the signal’s effective energy content over the entire sampling period.

From an applicable standpoint, the RMS value serves as a quantitative measure of the system’s vibratory energy. In contrast to the peak and peak-to-peak metrics—which capture instantaneous amplitude extremes and are susceptible to transient events—the RMS value offers a time-averaged representation of the total energy contained within the signal, thereby providing a more comprehensive and stable indicator of vibrational intensity. The measured sound pressure was converted to sound pressure level (SPL), expressed in decibels (dB), which represents a logarithmic scale of the sound pressure relative to a standardized reference pressure of 20 μPa—commonly recognized as the threshold of human hearing. This threshold corresponds to the quietest sound perceptible to the average young, healthy individual under ideal conditions.