“Tough Gear”and “High Quality” for New X-TRAIL - 5. NV Technology to Achieve EV-Level QuietnessFig. 9 Peripheral component layoutFig. 10 Noise reduction concept of the muffler specially designed for e- POWERFig. 12 Internal structure of muffler to realize long flow pathFig. 11 Long flow exhaust system6.3 Active noise controlthe e-POWER is equipped with a large Battery, DC-DC converter, Fuel Tank, Rear Suspension, and Rear Bumper. So, it is difficult to install a high-capacity muffler that achieves a high level of vehicle quietness due to packaging restrictions (Fig. 9).Therefore, we focused on the fact that the e-POWER does not use the idle engine speed range which is used by the ICE. The concept was to move the exhaust system full-length resonance to the idle engine speed range of the ICE. This reduces exhaust noise in the speed range which is used by the e-POWER (Fig. 10).On the other hand, to realize a long flow system in a rear muffler, it is necessary to avoid the influence on exhaust noise caused by new resonance of the long tube. 286.2.2 Noise reduction by long flow exhaust systemTo lower the frequency of full-length resonance, the exhaust gas flow path of the exhaust system was lengthened by 1.3 m compared to the conventional design of the ICE. It is most effective to lengthen the tail tube to bring the rear muffler closer to the antinode of the sound pressure in case of ensuring high silencing efficiency by extending the flow path. However, it is difficult to extend the flow path behind the rear muffler due to packaging restrictions. As a way to achieve both silencing efficiency and packaging, a long-flow exhaust system was created by reciprocating the tubes inside the rear muffler. In addition, low exhaust pressure is required to realize high torque engine. Therefore, the optimum bypass path for the e-POWER was designed to control the long tube resonance and gas flow in a rear muffler.To this end, a long-flow exhaust system specially designed for the e-POWER that can be installed in a C-segment package that simultaneously satisfies low exhaust noise and low exhaust pressure was developed (Figs. 11 and 12).In low-load and low-vehicle speed scenes, noise reduction is achieved using the long flow exhaust path to lower the engine speed and ensure quietness. However, the necessary power generation amount needs to be secured through high-torque operation. Therefore, it is necessary to respond to the low-frequency excitation force of a 3-cylinder engine. To this end, active noise control (ANC), which is optimally suited for the VC-TURBO engine and e-POWER system, is also adopted to muffle the sound inside the car in addition to the newly developed engine mount and exhaust system.
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