Valve opening and closing event finalization for cost effective valve train of Gasoline engine
To be published on April 2, 2019 by SAE International in United States
With more stringent emission norm coming in future, add more pressure on IC engine to improve fuel efficiency for survival in next few decades. In gasoline SI engine, valve events have major influence on fuel economy, performance and exhaust emissions. Optimization of valve event demands for extensive simulation and testing to achieve balance between conflicting requirement of low speed torque, power output, part load fuel consumption and emission. Balance between these requirements will become more critical when designing low cost engine without VVT. Higher compression ratio is an important low cost measure to achieve higher thermal efficiency but creates issue of knocking thereby limiting the low speed performance. The effective compression ratio reduction by means of late intake valve closing (LIVC) strategy is one way to achieve higher expansion ratio. But due to backflow at low engine speed it is challenging to implement this strategy. This study is done using 1-D simulation tool and review of testing data using three pressure analyses. Study include four valve timing points (IVO, IVC, EVO, EVC) and assessment of impact on idle stability, idle fuel consumption, part load fuel consumption, WOT performance and exhaust emission. P-V diagram is analyzed to understand the impact of all four timing point on PMEP and valve timing is optimized to minimize the PMEP while improving IMEP area. To achieve the better low speed performance without engine knocking late IVC and valve overlap is optimized to minimize internal EGR and optimize effective compression ratio (with high geometric compression ratio). Challenge was to achieve better low speed torque, power output, part load fuel consumption and emission without using VVT so as to obtain a cost effective solution. This work presents the approach to be used for finalizing the valve timing strategy for achieving best compromise in fuel efficiency and engine performance with minimum incremental cost.