Electromagnetic fuel injector for an internal combustion engine with a monolithic tubular member

An electromagnetic fuel injector for an internal combustion engine, comprising a main body having a central cylindrical cavity adapted to act as a duct for the fuel, a valve which is disposed to close an end of the central cylindrical cavity and is provided with a moving shutter, an electromagnetic actuator which is provided with a coil, a fixed armature, and a moving armature mechanically connected to the shutter and adapted to be magnetically attracted by the fixed armature against the action of a spring, and a monolithic tubular member which is disposed coaxially within the central cylindrical cavity and houses the fixed armature and the moving armature.

The present invention relates to an electromagnetic fuel injector for an internal combustion engine.

BACKGROUND OF THE INVENTION

An electromagnetic fuel injector comprises a main body having a central cylindrical cavity which acts as a duct for the fuel and ends in a valve adapted to regulate the flow of fuel and provided with a moving shutter controlled by an electromagnetic actuator. The main body is made from ferromagnetic material and houses a coil of the electromagnetic actuator. A fixed armature and a moving armature of the ferromagnetic actuator are disposed in the central cavity and are made from ferromagnetic material. In operation, the fixed armature is adapted magnetically to attract the moving armature against the action of a spring in order to cause a displacement of the shutter which is mechanically rigid with this moving armature. It will be appreciated that, because a force of magnetic attraction is generated between the fixed armature and the moving armature, it is necessary for the fixed armature and the moving armature to be traversed by the magnetic flux generated by the coil.

In order to try to reduce the magnetic flux dispersed, i.e. to try to reduce the magnetic flux generated by the coil which does not impinge on the fixed armature or the moving armature, at least one insert of non-ferromagnetic material (metal or plastic) is provided in the main body and is adapted to create a barrier to the passage of the magnetic flux so as to force this magnetic flux to pass through the fixed armature and the moving armature. However, the production of the insert from non-ferromagnetic material requires special processing which substantially increases the cost of the injector; moreover, at the junctions between the insert of non-ferromagnetic material and the main body there may be leakages of fuel.

As an alternative to the above-described use of an insert of non-ferromagnetic material, it is possible appropriately to shape the main body in order to create air gap zones adapted to perform the same function of creating a barrier to the passage of the magnetic flux in order to force this magnetic flux to pass through the fixed armature and the moving armature. However, the production of these air gap zones in the main body is laborious and complex.

US2002130206 discloses a fuel injector including a tubular casing having an axial fuel passage; disposed within the fuel passage are a valve seat element, a core cylinder, and a valve element axially moveably disposed therebetween and opposed to the core cylinder with an axial air gap. An electromagnetic actuator cooperates with the casing, the valve element and the core cylinder to form a magnetic field forcing the valve element to the open position against a spring between the valve element and the core cylinder upon being energized. The casing includes a reluctance portion producing an increased magnetic reluctance and allowing the magnetic field to extend to the valve element and the core cylinder through the air gap; the reluctance portion has a reduced radial thickness and an axial length extending over the air gap.

JP2002206468 discloses an injection port, which is opened and closed by a valve element, and an armature connected to the rear end of a movable body, to which the valve element is fixed; a fixed core is arranged inside the magnetic pipe, at a position opposite to a rear end surface of the armature. The valve element is energized in the closing direction by a coil spring, and a solenoid coil is arranged outside the magnetic pipe; the magnetic pipe as a whole is formed of a magnetic material.

WO9419599 discloses a fuel injector having combination valve-armature fabricated by laser welding relatively more magnetically permeable armature element to relatively less magnetically permeable valve element. Valve element contains sealing ring and landing ring, the latter being circumferentially discontinuous because of fuel passage holes through valve element, the former being non-symmetrical so that magnetic opening force causes valve-armature to open by tilting about consistent circumferential location on valve element.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an electromagnetic fuel injector for an internal combustion engine which is free from the drawbacks described above and, in particular, is simple and economic to produce.

The present invention therefore relates to an electromagnetic fuel injector for an internal combustion engine in accordance with claim1.

DETAILED DESCRIPTION OF THE INVENTION

InFIG. 1, a fuel injector is shown overall by1, and is substantially cylindrically symmetrical about a longitudinal axis2and is adapted to be controlled to inject fuel from its injection nozzle3. The injector1comprises a main body4, made substantially from ferromagnetic material, which comprises, along its entire length, a central cylindrical cavity5which is adapted to act as a duct for the fuel and ends in the injection nozzle3; the terminal end of the cylindrical cavity5is closed by a valve6which comprises a valve seat7having a central injection hole8which defines the injection nozzle3and a shutter9which can move between a position opening and closing the central hole8in order to regulate the flow of fuel through the injection nozzle3. The shutter9comprises a moving plate10which has at least one peripheral supply hole11and a sealing member12which is circular in shape, projects from the plate10and is adapted to isolate the supply hole11from the injection hole8when the shutter9is disposed in the closed position bearing on the valve seat7.

The main body1further houses an electromagnetic actuator13which is supplied by a control unit (not shown) via an electrical cable14in order to displace the shutter9of the valve6between the positions opening and closing this valve6. The electromagnetic actuator13comprises a coil15disposed coaxially about the central cylindrical cavity5and enclosed in a toroidal housing16of plastic material, a fixed armature17which is magnetically coupled to the coil15and is made from a ferromagnetic material, and a moving armature18which is made from a ferromagnetic material, is mechanically connected to the shutter9and is adapted to be magnetically attracted by the fixed armature against the action of a spring19; the spring19is, in particular, compressed between an abutment body20rigid with the fixed armature17and the plate10of the shutter9and tends to urge the plate10of the shutter9against the valve seat7in order to keep the valve6in the closed position.

The fixed armature17and the moving armature18of the electromagnetic actuator have respective central holes21and22, which are coaxial with one another, have the same dimension, and are adapted both to house the spring19with the relative abutment body20, and to allow fuel to flow to the valve6; for this purpose, the abutment body20has a central through hole23. The plate10of the shutter9is welded to a wall of the moving armature18, so as to dispose its own supply hole11in communication with the central hole22of this moving armature18.

Lastly, the injector1comprises a monolithic tubular member24which is made from a ferromagnetic material, has an axial length substantially equal to the axial length of the central cylindrical cavity5, and is disposed coaxially within this central cylindrical cavity5in order internally to house the fixed armature17, the moving armature18, the spring19and the valve6.

According to an embodiment which is not shown, the injector1is provided with a non-return device interposed between the fixed armature17and the moving armature18of the electromagnetic actuator13and an atomiser coupled to the valve6.

In operation, when the coil15of the electromagnetic actuator13is not excited, the fixed armature17and the moving armature18are not substantially impinged upon by a magnetic field and, therefore, the fixed armature17does not exert a force of attraction on the moving armature18, which is urged by the spring19against the valve6; in this situation, the plate10of the shutter9is urged into contact against the valve seat7and the fuel cannot therefore flow though the injection hole8(closed position of the valve6). When the coil15of the electromagnetic actuator13is excited, a magnetic field is generated and impinges upon the fixed armature17and the moving armature18, which is magnetically attracted by the fixed armature17together with the shutter9thus enabling fuel to flow through the injection hole8(open position of the valve6).

InFIG. 2, letter A shows a field line relative to a dispersed magnetic flux, i.e. a magnetic flux generated by the coil16, which does not impinge upon the fixed armature17or the moving armature18, and letter B shows a field line relative to a working magnetic flux, i.e. to a magnetic flux generated by the coil16which impinges upon the fixed armature17and the moving armature18. By appropriately dimensioning both the section of the tubular member24with respect to the section of the fixed armature17and the moving armature18, and the position of the fixed armature17and the moving armature18with respect to the coil15, it is possible to reduce the quantity of magnetic flux dispersed to a very low value to the benefit of the quantity of working magnetic flux. Experimental tests have shown, in particular, that by using a ratio of 1:4 between the section of the tubular member24and the section of the fixed armature17and the moving armature18, the quantity of magnetic flux dispersed does not exceed 20% of the total quantity of flux generated by the coil15.

In order further to reduce the quantity of magnetic flux dispersed, it is possible to produce the fixed armature17and the moving armature18from a first ferromagnetic material and to produce the tubular member24from a second ferromagnetic material having a magnetic permeability lower than the first ferromagnetic material.

As a result of the presence of the tubular body24, the injector1is simple and economic to produce and, at the same time, fuel leakages are cancelled out while keeping the quantity of magnetic flux dispersed at a low level.