“Tough Gear”and “High Quality”for New X-TRAIL - 2. “VC-TURBO”and“e-POWER”SystemFig. 5 Relationship between background noise and engine noiseFig. 6 Comparison of engine startup frequency5.1.2 Lowering engine speedFig. 7 Engine operation timeFig. 8 Engine speed of fixed-point operationthat to for “EV-ness.”The new e-POWER system defines the area where the driver senses the engine noise, and it is designed to prevent the engine from starting in this area to realize a quieter driving experience wherein the driver does not sense the engine starting noise.Fig. 5 presents the above-mentioned engine operating range. The noise level inside the vehicle is evaluated. The engine startup frequency is reduced in the low speed range where the engine noise is greater than the road noise generated outside the vehicle; the frequency is increased in the high speed range where the engine noise is lower than the background noise.Fig. 6 shows the frequency of engine startups at each vehicle speed in a practical driving pattern. Compared to the 2nd-generation compact car, which reduced the number of engine startups for all vehicle speed ranges, startups for the new vehicle is reduced to the 20–40 km/h range, while it is increased in the 40–60 km/h range. Therefore, it is now possible to improve quietness while increasing power generation energy.13The engine is started and stopped depending on various conditions such as vehicle speed, State of Charge (SOC) of battery, and required driving force. The frequency of engine startups during one run is significantly reduced by increasing the amount of charging energy per power generation cycle at the start. Fig. 7 shows the engine operating time in the Worldwide-harmonized Light vehicle Test Cycle (WLTC) mode. The frequency of the engine startups can be considerably reduced, which helps improve quietness and fuel efficiency.Combined with the newly developed e-POWER system, the VC-TURBO engine can generate higher torque at lower revolutions than that with conventional naturally aspirated engines. This characteristic allows generating equal output at a lower engine speed compared to that with naturally aspirated engines and helps reduce the engine speed during fixed-point engine operation. Fig. 8 shows the engine speed during fixed-point operation at each vehicle speed. Compared the 2nd-generation compact car, it is possible to lower the engine speed over a wide range: from low vehicle speeds with low background noise to high vehicle speeds. This facilitates reducing the engine noise level even when the engine is in operation.
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