Unit injector with hard stop timing plunger

Abstract

An improved cam operated, open nozzle, unit injector is disclosed including an injector body formed by a barrel, spring housing, and nozzle and containing a central bore for receiving a variable length plunger assembly mounted for reciprocal movement within the injector body wherein the variable length plunger is formed by an outer plunger and inner plunger combined with a timing plunger, mounted between the inner and outer plungers to form a collapsible timing chamber into which a variable quantity of fuel may be metered and expelled on a cycle by cycle basis to provide a variable effective length to the plunger assembly to cause controlled variation in injection timing based on variation in the timing fluid supplied to the injector and wherein the timing plunger is provided with a radial flange for engaging a stop formed in the injector barrel to hold the timing plunger in a predetermined precise location during metering of timing fluid into the collapsible timing chamber and to render the injector timing insensitive to unpredictable pressure variations. The disclosed injector may include a damping chamber for receiving the radial flange of the plunger to eliminate damaging engagement between the timing plunger and the injector barrel. Improved fuel flow passages, check valves and an improved coupling between the outer plunger and the injector's outer return spring are provided along with means for easily changing the rated injection quantity of the disclosed injector.