F2008-06-098
A New Approach for Variable Displacement : The OVaLiD Concept
Compared to Diesel engines, gasoline engines have suffered for a long time from poor efficiency. As far as after treatment and cost are concerned, gasoline engines still present some advantages. Nowadays downsizing is a reality for medium displacement engine but difficult to apply on large displacement engines because of drivers' acceptance. To downsize small displacement engines is also problematic because of the increase in thermal losses that have negative effect on turbo lag and engine maximum efficiency. Stratified combustion could be a more attractive way of improvement but has great effect on engine cost. Consequently, IFP has been engaged in a new development based on variable displacement using cylinder deactivation. As a matter of fact, deactivation is very attractive : o no effect on engine driveability and fun to drive, o no effect on engine maximum efficiency, o no effect on after treatment complexity and consequently cost o low cost technology when using mechanical process The main disadvantage is engine vibrations but also engine blow-by and oil consumption in case of valve deactivation. The OVaLiD concept is based on the development of valve event that allows not only further consumption gain but also to run the engine continuously in deactivation mode without any drawbacks. It only requires mechanical variable valve actuation, reliable technology already used by most of car manufacturers. This concept has been compared to "conventional" deactivation approach and has shown great interest. During the development we had to face some problems especially due to the specific valve event and the interaction between activated and deactivated cylinders. Applied on a 2L engine using the HONDA VTEC technology, the concept has shown consumption gain equivalent to stratified combustion process but this approach is still compatible with three way catalyst. Nevertheless, high vibration levels occur with deactivation process, investigations are currently in progress in order to reduce this drawback.
To conclude, the fuel consumption benefit thanks to the OVaLiD concept is estimated between 12 and 15 % in case of naturally aspirated engines. This concept can be combined with downsizing that could allow further gain on the NEDC cycle. The great challenge of this approach is engine vibrations, especially in case of four cylinder engines that IFP is currently considering. Some consider deactivation can only be applied on large displacement engines other believe that drivers acceptance depend on vehicle cost and consumption what is IFP point of view.
Session: Engine Mechanics