Electromagnetic unit fuel injector

Claim 2

An electromagnetic unit fuel injector in which a housing means (1,2) has a pump cylinder means (10) therein, an externally actuated plunger (11) is reciprocable in the cylinder means (10) to define therewith a pump chamber (16) open at one end for the discharge of fuel during a pump stroke and for fuel intake during a suction stroke of the plunger (11), an inlet passage means (31 to 36) with a one-way valve (18) therein is in flow communication at one end with the pump chamber (16) and is connectible at its other end to a source of fuel at a suitable supply pressure, the housing means (1,2) includes a valve body (20) having a spray outlet (53) at one end thereof for the discharge of fuel, an injection valve means (51) is movable in the valve body (20) to control flow through the spray outlet (53), a pressure-modulated servo chamber (56) is arranged in the housing means (1,2), a spring means (65) and a servo piston means (51a) are operatively connected to the injection valve means (51), with the servo piston means (51a) being positioned so as to be acted on by the pressure of fuel in the pressure-modulated servo chamber (56), a discharge passage means (41 to 50) in the housing means (1,2) connects the pump chamber (16) to the spray outlet (53) and to the pressure-modulated servo chamber (56) and has a throttle orifice (43) of predetermined flow area controlling fuel flow into the pressure-modulated servo chamber (56), a drain passage means (66) in the housing means (1,2) is connectible at one end to a source of fuel at a suitable supply pressure, and a solenoid (67)-actuated control valve (68)-controlled orifice passage means (75) is arranged for effecting flow communication between the pressure-modulated servo chamber (56) and the drain passage means (66), characterised in that the control valve (68) is in the form of an unbalanced pressure poppet valve normally biased to a closed position by a valve return spring (84) of preselected force, whereby the control valve (68) is also operative as a pressure relief valve to effect drainage of fuel at a predetermined maximum peak pressure.

Claim 3

An electromagnetic unit fuel injector according to claim 1, characterised in that a discharge passage means (38) connects the pump chamber (16) to the spray outlet (53) as controlled by the injection valve (51), the drain passage means (66) is in flow communication at one end with the servo chamber (56) and at its opposite end with a source of fuel at a predetermined pressure, the drain passage means (66) includes drain chamber means (103) and a pressure equalizing chamber means (88) in axially spaced-apart relationship to each other with a stepped bore (105) extending therebetween and with a conical valve seat (80) encircling the guide bore at the drain chamber end thereof, the control valve (68) comprises a pressure- sensitive control valve which is operatively positioned in the housing means (1,2) and includes a stem (68d) slidably received in the bore (78) and a head (68a) loosely received in the drain chamber (103), together with a valve-seating surface (68b) for movement relative to the valve seat (80) and defining therewith when unseated therefrom a drain orifice, the stem (68d) includes a reduced-diameter stem portion (68c) next adjacent to the valve-seating surface (68b) of the head (68a), whereby to define with the bore (78) an annulus chamber (83) as part of the drain passage means (66), the solenoid (67) comprises a pull-type solenoid means that is operatively supported in the housing means (1,2) and includes an armature means (90) operatively associated with the control valve (68), a valve return spring (84) is operatively associated with the control valve (68) to normally bias the valve-seating surface (68b) of the head (68a) thereof into seating engagement with the valve seat (80), a fuel passage means (6) is connectible at one end to a source of fuel at a suitable supply pressure and is in operative flow communication at its other end with the pump chamber (16), and the stepped bore (105) includes an enlarged internal diameter portion (76) next adjacent to the valve seat (80), whereby the pressure of fuel in the annulus cavity (83) can act against the head (68a) in a valve-opening direction.

Claim 4

An electromagnetic unit fuel injector according to claim 1 or 2, characterised in that the housing means (1,2) additionally includes a secondary pressure relief valve means (133) in flow communication at one end with the discharge passage means (41-50) and in flow communication at its other end with the drain passage means (66) downstream of the drain chamber means (32) in terms of the direction of flow through the drain passage means (66) from the servo chamber (56).