Unit fuel injector

Claim 1

A unit fuel injector comprising: (a) a body; (b) pump means mounted on said body and including a cylinder hole formed in said body, and a plunger received in said cylinder hole so as to be reciprocally movable along said cylinder hole to achieve a pump stroke and a suction stroke, a pump chamber being defined by said cylinder hole and said plunger; (c) injection nozzle means mounted on said body and including an injection port connected to said pump chamber, and an injection valve for controlling the communication between said injection part and said pump chamber, said injection valve being opened upon increase of the pressure within said pump chamber to a predetermined level, thereby injecting fuel from said injection port; (d) electromagnetic valve means mounted on said body and including a guide hole formed in said body, and a spill chamber formed in said body and connected to said guide hole, a valve seat being provided between said guide hole and said spill chamber, said electromagnetic valve means further including a valve member received in said guide hole for sliding movement there along, and a solenoid drive means for controlling the movement of said valve member, said valve member having a stem portion and an abutment portion formed on said stem portion and disposed in said spill chamber, said stem portion having a reduced diameter portion adjacent to said abutment portion, an annular space being defined by said reduced diameter portion and an inner peripheral surface of said guide hole, said spill chamber being connected to said pump chamber via said annular space, said valve member being movable between a first position where said abutment portion is held away from said valve seat and a second position where said abutment portion is held against said valve seat, the communication between said spill chamber and said pump chamber being interrupted when said valve member is moved from said first position to said second position during said pump stroke, thereby increasing the pressure within said pump chamber to start the injection of the fuel from said injection port, and said spill chamber and said pump chamber being communicated with each other via said annular space when said valve member is moved from said second position to said first position during said pump stroke, so that the fuel of high pressure within said pump chamber is spilled to said spill chamber to thereby terminate the fuel injection; and (e) means for propelling said valve in such a direction that said abutment portion is moved away from said valve seat, said propelling means including a bore formed in said body, and a flange provided on an outer periphery of said stem portion of said valve member, said flange being slidably fitted in said bore to divide said bore into a pressure introduction chamber and a low pressure chamber along the axis of said valve member, said pressure introduction chamber being connected to said spill chamber so as to receive said spill fuel pressure in said spill chamber, said low pressure chamber being connected to a low pressure source disposed exteriorly of said body, the pressure of said low pressure source being lower than said spill fuel pressure, whereby said valve member is propelled in a direction away from said valve seat due to a pressure differential across said flange when said pressure introduction chamber receives said spill fuel pressure.