“Tough Gear”and “High Quality”for New X-TRAIL - 3. Engine Evolution of e-POWER 2.2 Working principle of variable compression ratio Fig. 3. Configuration of Multilink mechanismFig. 4 Torque curve of the new engine3. Achieved performanceengine3.1 Fixed-point operation, best fuel efficiency, and 18Fig. 5 Compression ratio mapFig. 6 EGR rate mapquietnessFig. 3 shows the configuration of the multilink system in the VCR mechanism. When the rotational posture of the control shaft changes clockwise with respect to the engine block and the eccentric axis, i.e., when the swing point of the C-link moves downward, the L-link rotates clockwise around the crankpin to enlarge the angle between the U link and L link at the top dead center; further, the U-link and piston move upward, which increases the mechanical compression ratio of the engine(1). Conversely, changing the rotational attitude of the control shaft to counterclockwise can reduce the mechanical compression ratio. For an in-line multicylinder engine, the control shaft is shared by each cylinder, and thus, by changing the rotational posture of one control shaft relative to the cylinder block, the mechanical compression ratios of all cylinders can be switched simultaneously.The adoption of the VC-TURBO engine greatly improved the engine torque compared to that with HR12DE engine (Fig. 4). This increases the flexibility of the engine operating point required for power generation and energy management, which in turn improves both the fixed-point operating points and quietness. Further, the generated engine noise is greatly reduced by lowering the engine speed at the maximum output point, even when the engine is under heavy load.Compared to the previous e-POWER HR12DE engine, the EGR rate and compression ratio (C/R) for the new e-POWER system are controlled throughout the low-load and high-load fuel consumption ranges, respectively, to improve both fuel efficiency and quietness. A transition from the quick engine start to a fixed-point operation was implemented, and performance-based design was conducted with the best thermal efficiency point at 2000 rpm (minimum brake specific fuel consumption: 217 g/kWh) as the steady-state operation point (Figs. 5 and 6).a) A negative-pressure-control butterfly valve was added to the EGR inlet to expand the EGR range and improve thermal efficiency by suppressing knocking under supercharging and high compression ratios.b) A flat piston and high tumble-intake port strengthen the gas flow in the cylinder and ensure combustion stability in the high EGR range.c) The multilink mechanism reduces piston thrust force, which leads to low friction.
元のページ ../index.html#23