Development and research on electric vehicles in power transmission system are increasing as the demand for ecofriendly and autonomous vehicles increases across the industry. In order to reduce noise, research on high efficiency and low noise due to electrification of the gearbox system is being actively conducted, such as applying design technology to optimize the shape of the gear and increase rigidity. In particular, research on low noise is active because the noise of the electric gearbox could be easily recognized in a vehicle, even with small noise due to its frequency characteristics. Therefore, in this study, effects of main specifications of gears on noise and power loss were studied and analyzed through a Parametric Study. Characteristics of the proportional relationship between noise and power loss according to major specifications were analyzed. Based on study results, NVH analysis in the gear system was performed. After that, actual data were secured through test measurements and a noise reduction effect of 4.4 dB was confirmed.

The gear overlap ratio shows the characteristics of the spur gear and the helical gear and varies according to the torsional angle. The gear ratio, tooth width, and center distance, which are restricted in a space of performance and manufacturing and design in the gearbox, are fixed. A parametric study on modules, the number of teeth, and torsion angles was conducted to analyze the relationship between the overlap ratio and PPTE. Then, contact analysis was performed by correcting the tooth profile to improve the transmission error. Contact analysis was performed through correction of the tooth modification to improve transmission error, and the noise was analyzed according to the overlap ratio by applying a noise prediction equation.

The Effect of Space Velocity(SV) on NOx conversion rate was performed to develop NOx reduction after-treatment system. SV is calculated from engine exhaust gas volume and SCR catalyst volume. Found the Urea injection duty of maximum efficiency for NOx conversion if increase SV, NOx Conversion rate is down. Especially, when SV is more than 110,000h?¹, NOx conversion rate decrease suddenly. Same case, if SV is lower than 40,000h?¹, NOx conversion rate is down.
Also, the characterization of Urea-SCR system was performed. Three candidate injectors for injecting Urea were tested in terms of the injection rate and NOx reduction rate. The performances of SCR catalytic converter on temperature were investigated. The performance of Urea-SCR system was estimated in the NEDC test cycle with and without EGR. It was found that nozzle type injector had high NOx conversion rate. SCR catalytic converter had the highest efficiency at the temperature of 350℃ EGR+Urea-SCR system achieved NOx reduction efficiency of 73% through the NEDC test cycle.