Applications of VVT and VCR on Fuel Economy Improvement Based Engine Electronic Control

Abstract

Variable valve timing (VVT) and variable compression ratio (VCR) are two technologies to obtain fuel economy benefit. On the other hand, there is a tradeoff among fuel economy, engine performance and emission levels. Advantages of two technologies vary a lot on different engine operating regions. Recently some experiments are conducted on a Port Fuel Injection (PFI) engine in a city drive cycle to investigate the fuel economy impact from VVT, VCR and the technology integration. The testing results show clearly that the synergy of two technologies has further improved the fuel economy, while suitable operating regions need to be determined where the maximal benefit can be achieved. A typical 1.8L four-cylinder gasoline engine is used for experiments using VVT and VCR technologies for fuel economy improvement. The objective is to create a synergy scheme for the optimal fuel economy performance. The supercharged testing engine with VVT and VCR can implement similar performance to that of a larger replacement engine. The fuel economy optimization problem is simply converted into searching for the lowest engine power output region with respect to the same fuel economy improvement level. These optimal points are useful to determine potential best fuel economy operating regions whether VVT and VCR should be implemented individually or combined together.