“Tough Gear”and “High Quality” for New X-TRAIL - 5. NV Technology to Achieve EV-Level QuietnessFig. 2 Frequency of engine start for previous e-POWER system to generate negative pressure when driving in urban areas 4. Quieting engine noise5. Matching the engine sound to the driver's request for acceleration6. Vehicle technology that supports Fig. 3 Sensitivity of engine speed to engine noiseFig. 4 Sensitivity of engine torque to engine noiseFig. 5 Difference in engine noise at 0.2G acceleration between the new X-TRAIL e-POWER and competing carsquietnessthe SOC; therefore, some measures have been added to avoid engine startup requirements. There are scenarios in which the engine starts to supply negative pressure to the conventional brake system (Fig. 2); however, new brake system, electric control brake unit*, can avoid engine operation to create negative pressure for braking.* Mainly adopted for Advanced driver-assistance system (ADAS) and collision safety performance, but it is also used for quietness improvement.If the engine starts because of a decrease in SOC in a low-load and low-vehicle-speed scenario, the engine speed is lowered compared to that of the previous e-POWER system to ensure quietness. 1.5 L VC-TURBO engine, that was already adopted with CVT, was optimized for e-POWER system. It enables operation with higher torque and efficiency at a lower speed than the 1.2 L NA engine conventionally installed in compact cars. This allowed low-noise operation while securing sufficient power generation, which helped achieve both engine noise reduction and improved fuel efficiency.High power must be supplied by the engine when strong acceleration is requested by the driver. However, the engine sound level needs to match the driver's request for acceleration to avoid discomfort during acceleration.The engine sound level is highly sensitive to the rotational speed relative to the torque sensitivity (Figs. 3 and 4), and therefore, the engine speed increases linearly with the accelerator opening (acceleration G) and vehicle speed (Fig. 5).In addition, the electric power required for driving* can be obtained through the characteristics of the variable compression (VC) engine by suppressing engine rotation and prioritizing torque so that the increase in rotation is considerably suppressed to provide a comfortable engine sound. For more details on 3, 4, and 5 in this chapter, refer to article 1-2. “VC-TURBO” and “e-POWER” System.*Power generated by the engine = torque × RPM The use of a high-torque 3-cylinder engine is advantageous for reducing engine noise caused by low rotation; however, it is disadvantageous for low-frequency phenomena such as booming noise and vehicle body vibration. Therefore, the engine mount, exhaust, active noise control, and body are improved to reduce the low-frequency sensitivity. 26
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