Unit injector for staged injection

Claim 1

A unit injector for injecting fuel in an internal combustion engine, said unit injector comprising a fuel pump and a spray nozzle combined in a single unit adapted to be mounted on said engine with said fuel pump being adapted to be driven by a mechanism provided on said engine, the improvement comprising means for producing a plurality of discrete fuel injections during a single stroke of said internal combustion engine, said fuel pump comprising means defining a first relatively large diameter cylinder, a first relatively large diameter plunger positioned at least partially within said first cylinder and adapted to be driven along the longitudinal axis of said cylinder by said mechanism provided on said engine for pumping said fuel, an end of said first plunger within said first cylinder defining an end of a first fuel compression chamber of said pump within said first cylinder, said end of said first plunger having a second relatively small diameter cylinder formed therein, a second plunger extending through said first fuel compression chamber and into said second cylinder for relative movement in said second cylinder as said first plunger is driven by said mechanism, an end of said second plunger within said second cylinder defining an end of a second fuel compression chamber of said pump within said second cylinder, fuel inlet and outlet passage means for conveying fuel to and from said first and second fuel compression chambers, said inlet and outlet passage means being arranged to be opened and closed by the movement of said first plunger in said first cylinder and relative to said second plunger for producing discrete fuel injections from said first and second fuel compression chambers during a single stroke of said first cylinder.