Controlling Engine Load by Means of Early Intake-Valve Closing 820408
Early closing of the intake valve was examined as a means for controlling the load of a homogeneous-charge, spark-ignition engine. The engine was operated unthrottled, with load controlled by closing the intake valve during the intake stroke of the engine after the required amount of charge had been inducted into the cylinder. The concept was examined both experimentally, using intake cams giving reduced intake-valve lift and opening duration, and analytically, using an engine simulation.
Comparisons to a conventional throttled engine operating at part load show the early intake-valve-closing engine to have lower pumping loss, lower specific fuel consumption, lower cylinder-gas temperatures, lower heat transfer, lower NOx emissions, similar combustion duration and cyclic variability, and somewhat higher HC emissions. However, the fuel economy benefit offered by this load-control concept would be diminished by the frictional losses of a control mechanism and by the current trends toward lower vehicular power/weight ratios and broader-range transmissions.