Rapid transient electroinjector

Claim 1

An electroinjector for delivering intermittent feeds of fuel at low pressure to an internal combustion engine of the Otto cycle, the electroinjector comprising an outer casing, a feed duct for the low pressure fuel, at least one injection nozzle, a valve member for said nozzle, and an operating coil provided with a core in the form of a ferromagnetic hollow cylinder, said coil being arranged to cylically control the opening of said valve member by the effect of suitable control signals, said feed duct for the pressurised fuel being disposed inside said core, said valve member forming the coil armature and being in the form of a cup having a lateral wall of ferromagnetic material and a base wall of a material suitable for sealing the low pressure fuel, resilient means within said cup and urging said base wall into contact with the injection nozzle, a guide sleeve within said core and projecting into said cup, said cup being slidably supported by said guide sleeve, said coil being wound on a spool inside which said coil core and said cup are partly received and aligned in an axial direction, between the core and cup there being present a first annular air gap which corresponds to the cup stroke and is therefore variable, between the lateral wall of the cup and an outer casing there being present a second annular air gap of fixed thickness, wherein in the electroinjector said first air gap and said second air gap have a reluctance of substantially equal value when the first air gap corresponds to the maximum stroke of said cup.