| 摘要 |
The invention comprises a strategy and method for phase shifting intake and exhaust valve timing relative to crankshaft position as a function of engine operating variables, whereby valve overlap is delayed to obtain improved fuel economy resulting from a late intake valve closing to reduce pumping work during the intake stroke. The exhaust gases are drawn into the combustion cylinder of the engine during the intake stroke, which reduces oxides of nitrogen in the exhaust gas and reduces unburned hydrocarbons. Improved thermal efficiency and reductions in oxides of nitrogen are achieved as the combustion charge is diluted at higher loads by an external exhaust gas recirculation system, thereby combining the effects of exhaust gas recirculation and dual equal variable camshaft timing to obtain fuel economy benefits that cannot be achieved with either a conventional EGR system acting alone or dual equal variable camshaft timing acting alone. |
