Abstract
Research and/or Engineering Questions/Objective
Cylinder deactivation by cutting fuelling and disabling valve movement is commonly used on larger displacement spark ignition engines to improve part-load fuel economy. Recently, applications to smaller SI engines have been implemented. This significantly improves the fuel economy of an ‘A’ sector vehicle under NEDC test cycle conditions. However under real world driving conditions, the time spent with cylinders deactivated depends on traffic and terrain conditions, driving style, gear selection, engine speed and load, and the relationship between fuel economy benefit and time spent with cylinders deactivated is complex. The aim of the investigation has been to determine what limits the benefits of cylinder deactivation and establish the relative importance of the factors which influence this.
Methodology
An ‘A’ class vehicle with a 1.4l, 4 cylinder direct injection spark ignition engine has been used in the study. The cylinder deactivation system allows two cylinders to be deactivated. Base line behaviour and performance were established through NEDC tests and results recorded under steady state operating conditions. Real world driving tests were carried out covering a range of urban, extra urban, rural and motorway driving, light and heavy driving conditions and different driving styles. Tests were carried out with and without the cylinder deactivation system enabled. The data logged includes the switching events, average and instantaneous fuel consumption, and other ECU parameters. The data were processed to examine how system operation and benefits were affected by the differences between standard test cycle and real world driving conditions.
Results
Constraints on the operation of cylinder deactivation have been determined for real world driving conditions and compared to NEDC test cycle results. Typically, the time spent with cylinders deactivated was halved under real world driving conditions, from ~50% of the time over the NEDC to ~25%. Low engine speed was the most common constraint on deactivation, but the higher frequency of accelerations and decelerations and higher transient engine loads had increased impact under real world driving conditions. During higher vehicle speed routes, the time spent in 2 cylinders increased to 30% or more. For the city route, gear selection affected 2 cylinder residence times more than driving style. Traffic volume was also found to have a strong influence.
Limitations of the study
Comparisons of results have been limited to cases with cylinder deactivation enabled and switching between 2 and 4 cylinder firing, and cylinder deactivation disabled with continuous 4 cylinder operation.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The study examines the effectiveness of cylinder deactivation on a small capacity engine/ small vehicle engine and how operating strategy affects this. The study shows what limits the use of cylinder deactivation under various real world driving conditions, how the limits affect the improvement in fuel economy.
Conclusions
Cylinder deactivation gave an ~8% fuel economy benefit for a cold start NEDC cycle, but ~3% for a real world city driving route. The difference is due to reduced operation in 2-cylinder mode, associated with engine speed and load limits and the shift towards higher loads under real world driving. Gear selection entails a trade-off between penalties and the benefits of deactivation. Higher gear selection is usually beneficial. Traffic density and driver style influence the number of transient events; accelerations raise engine load. These depress the time spent with cylinders deactivated.
Key Words : Cylinder Deactivation; Spark Ignition; Real World Driving