End of injection rate shaping

Abstract

Fuel injectors equipped with direct control needle valves can add new capabilities to a fuel injection system, but can sometimes have difficulty in achieving low hydrocarbon emissions at levels comparable to ancestor fuel injectors that utilize a simple spring biased needle. The present invention seeks lower hydrocarbon emissions by reducing fuel pressure before the direct control needle valve member has reached its closed position toward the end of an injection event. Reducing fuel pressure can be accomplished in a number of ways depending upon the particular fuel injection system, including spilling fuel pressure in a cam system or possibly relieving pressure on an intensifier piston. By employing this strategy, fuel spray from the fuel injector can effectively end before the direct control needle valve member reaches its closed position, thus avoiding hydrocarbon production that could be caused by a small amount of fuel pushed into the combustion space as the needle moves over the last portion of its movement toward its closed position.

Dependencies are inferred from the claim text.