“Tough Gear”and “High Quality”for New X-TRAIL2.1 Aim of engine developmentFig. 1 New KR15DDT engine1. IntroductionFig. 2 Engine operating range for e-POWER system*Powertrain and EV Engineering Division Powertrain and EV Project Management Department**Powertrain and EV Engineering Division Powertrain and EV Mechanical system Technology Department***Powertrain and EV Engineering Division Powertrain and EV Performance Calibration Engineering DepartmentA 1.5 L turbo engine is developed for the new X-TRAIL to further enhance the powerful acceleration, quietness, and fuel efficiency performance features of the e-POWER system. This engine combines the world's first variable compression ratio (VCR) mechanism adopted in a mass-in 2018 and a new produced engine by Nissan low-pressure-cooled EGR (LP-EGR). The outline and features of the new KR15DDT engine installed in the new X-TRAIL are described in this chapter.The 1.2-L 3-cylinder naturally aspirated engine installed in the previous e-POWER system was improved to considerably increase the power output, quietness, and efficiency for improving the power generation energy to realize the concept of the new X-TRAIL (“Tough Gear” and “High Quality”). A 100% motor drive is attractive to achieve the high levels of quietness and smooth acceleration performance (EV-ness). To further upgrade these features, the engine was developed with the following aims.[1] High thermal efficiency at a fixed-point operation[2] High power at the maximum output point[3] High level of quietness[4] Compact engineFig. 2 shows the engine operating range and key performance concepts in the e-POWER system. Nissan has already succeeded in mass-producing the VCR system, and thus, it is possible to switch to a high compression ratio at [1] and to a low compression ratio at [2] using that mechanism. Moreover, it is possible to achieve both high efficiency and high output if the VCR mechanism is combined with LP-EGR.(1)The multilink system that comprises the VCR mechanism can reduce the friction of the piston in the thrust direction. Therefore, the engine speed at the optimum fuel efficiency point can be lowered if it is combined with the improved thermal efficiency achieved by setting a high compression ratio. Further, it is possible to lower the rpm at the maximum output point by setting a low compression ratio, which helps satisfy the quietness requirement [3].For compactness [4], the variable timing control system(VTC) is simplified for further downsizing and a 3-cylinder engine is selected. In conventional hybrid electric vehicle (HEV) engines, the compression reaction force of the engine is reduced as a vibration damping measure at engine startup. However, it is now possible to reduce the compression reaction force without the intake VTC and satisfy the relevant performance by utilizing the VCR mechanism. In addition to narrowing down the engine operating range specific to the e-POWER system, the performance-based design of variable compression and LP-EGR can achieve high efficiency, high output, and excellent exhaust performance without relying on the VTC.17Kazuhiro Ogino* Yorihisa Tsuchiya* Hideaki Mizuno**3. Engine Evolution of e-POWER Yuuki Sakai** Yasuhide Abe***
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