A fuel injector is described, particularly for fuel injector systems of internal combustion engines, including an actuator, a valve needle actuatable by the actuator for actuation of a valve-closure member, which together with a valve-seat surface forms a sealing seat, and a swirl device, having at least one swirl channel through which fuel flows having a tangential component regarding a longitudinal axis of the fuel injector. The axial position of a bypass disk, which is mechanically linked to a valve needle, determines a cross section of at least one bypass channel, which bypasses the at least one swirl channel without a tangential component.

FIELD OF THE INVENTION

The present invention relates to a fuel injector.

BACKGROUND INFORMATION

A fuel injector for direct injection of fuel into the combustion chamber of a mixture-compressing, spark-ignited internal combustion engine which on the downstream end of the fuel injector has a guide and seat area which is formed from three disk-shaped elements is known from German Published Patent Application No. 197 36 682. A swirl element is embedded between a guide element and a valve seat element. The guide element guides an axially movable valve needle penetrating through it, while a valve closing section of the valve needle cooperates with a valve-seat surface of the valve seat element. The swirl element has an inner opening area containing a plurality of swirl channels which are not connected to the outer periphery of the swirl element. The entire opening area extends fully over the axial thickness of the swirl element.

A particular disadvantage of the fuel injector known from the aforementioned document is the fixedly set swirl angle which cannot be adjusted to the different operating conditions of an internal combustion engine, such as partial load and full load operation. As a result, cone opening angle a of the injected mixture cloud also cannot be adjusted to the different operating conditions, which in turn results in inhomogeneities during combustion, increased fuel consumption, as well as increased exhaust gas emission.

SUMMARY OF THE INVENTION

The fuel injector according to the present invention has the advantage over the related art that the swirl is adjustable as a function of the operating state of the fuel injector, whereby a jet pattern may be produced which is adapted to the operating state of the fuel injector, resulting in an optimization of the mixture formation and the combustion process.

The simple design of the swirl producing components is particularly advantageous over the conventional swirl preparation, because they are extended by an easily manufacturable bypass disk which is connectable to the valve needle.

The possibility of combining the measures according to the present invention with fuel injectors having multi-stage lifts and of allocating different swirl intensities to the different lift positions is particularly advantageous.

The implementation of the measures according to the present invention is also advantageous in a fuel injector having continuous lift, because the desired modeling of the mixture cloud may be achieved in a simple manner using suitable geometry of the swirl channels.

It is also advantageous to design a swirl chamber in which the fuel components streaming through the swirl channels may be mixed with those coming from the bypass channel, thereby influencing the mixture cloud according to the requirements of the instantaneous operating condition.

The design of a catch, as well as the separation of the bypass disk from the valve needle, represent a particular advantage, since the opening operation of the fuel injector is not influenced by the bypass disk being raised while the valve needle initially performs a partial lift until the catch strikes the bypass disk.

DETAILED DESCRIPTION

A first exemplary embodiment of a fuel injector1designed according to the present invention illustrated inFIG. 1is used in particular for direct injection of fuel into the combustion chamber of a spark-ignited, mixture-compressing internal combustion engine.

Fuel injector1includes a solenoid8used as actuator27and is encapsulated in a coil housing9, a tubular internal pole11and an external pole14in the form of a sleeve, which is welded to nozzle body2. An armature12is mechanically linked to valve needle3which is configured as valve-closure member4in the spray-discharge direction. Valve-closure member4cooperates with valve-seat surface6, which is formed on a valve seat body5, to form a sealing seat. This exemplary embodiment is an inwardly opening fuel injector1. At least one spray-discharge orifice7is introduced in valve seat body5.

A swirl device15, which includes a guide disk16, a bypass disk17and swirl channels18, is provided on the upstream side of the scaling seat. Swirl device15is explained in greater detail in the description ofFIGS. 2A and 2B.

In the idle state of fuel injector1, armature12is acted upon by restoring spring10against a lift direction in such a way that valve-closure member4is held on valve-seat surface6in a sealing position. When solenoid8is energized, it generates a magnetic field, which moves armature12against the elastic force of restoring spring I0in the lift direction. Armature12also entrains valve needle3in the lift direction. Valve needle3and valve-closure member4, which have a one-piece design in the exemplary embodiment, are lifted from valve-seat surface6, whereby bypass disk17, friction-locked to valve needle3via weld21, also moves in the lift direction, so that bypass channel19is opened. Fuel is routed to the at least one spray-discharge orifice7through flow-through orifices20in guide disk16, as well as through bypass channel19and swirl channels18bypassing the sealing seat. A detailed illustration of the procedure is provided byFIGS. 2A and 2B.

When the coil current is switched off, armature12, after sufficient decay of the magnetic field, drops away from internal pole11due to the force of restoring spring10, whereby valve needle3, being mechanically linked to armature12, moves against the lift direction, bypass disk17closes bypass channel19, valve-closure member4comes to rest on valve-seat surface6, and fuel injector1is closed.

In a partial, schematic axial sectionFIG. 2Ashows fuel injector1, designed according to the present invention, in its closed state in area II of FIG.1. The enlarged illustration shows only those components which are relevant to the present invention. The design of the remaining components may be identical with a known fuel injector1. Elements already described are provided with the same reference symbols in all figures, so that a repeat description is unnecessary.

A mixture-compressing, spark-ignited engine has different requirements with regard to form, stoichiometry, and the penetration capability of the mixture cloud being injected into the combustion chamber in partial load operation as opposed to full load operation. During partial load operation the mixture cloud should have a relatively small opening angle α, a great penetration capability, a narrow core area due to the small opening angle α, with a richer mixture, and a very lean envelope, while during full load operation a wide opening angle α and with it an almost homogeneous filling of the cylinder with ignitable mixture is present.

The modeling of the parameters of the mixture cloud may be facilitated by influencing the swirl through the above-described measures according to the present invention. If the fuel exits the spray-discharge orifice with little swirl, a mixture cloud having a small opening angle α is injected, while a strong swirl causes the jet to widen more and thus the mixture cloud to have a wide opening angle α. The present invention is particularly advantageously applicable in connection with a fuel injector1having multi-stage lift or piezoelectric actuators27.

Swirl device15having a bypass channel19, as indicated inFIG. 1, allows the fuel flow rate to be configured by swirl device15as a function of the lift of valve needle3of fuel injector1. In the closed state of fuel injector1, as it is apparent inFIG. 2A, bypass channel19is closed, and thus the fuel may only flow through swirl channels18.

FIG. 2Bshows fuel injector1according to the present invention in its opened state in the same detail as in FIG.2A.

If, according to the present exemplary embodiment, actuator27designed as a solenoid is actuated, then valve needle3is raised in a lift direction against the flow direction of the fuel, whereby bypass disk17which is connected to valve needle3by weld21is also moved in the lift direction. This results in the opening of bypass channel19, the amount of fuel that flows through depending on the axial position of valve needle3, i.e., on the distance of bypass disk17from an upstream side22of swirl channels18. The fuel flows via flow-through orifices20in guide disk16to bypass channel19.

While the flow in swirl channels18has a tangential component with regard to a longitudinal axis26of fuel injector1, the flow in bypass channel19has no tangential component but only a radial component.

Since the portion of fuel flowing through bypass channel19and the portion of fuel flowing through swirl channels18are reunited in swirl chamber23, a mixture cloud develops which contains swirled and unswirled components. This makes it possible, by having a suitable geometry of the swirl-generating components, to generate a mixture cloud which has the characteristics suitable for the operating condition of fuel injector1.

FIGS. 3A and 3Billustrate a second exemplary embodiment of fuel injector1according to the present invention using the same view as inFIGS. 2A and 2B.

Bypass disk17in the present second exemplary embodiment, in contrast to the first exemplary embodiment illustrated inFIGS. 2A and 2B, is not connected to valve needle3by weld21or by pressure force, but is instead set on valve needle3in an axially movable manner.

Valve needle3has a catch24which is positively connected to valve needle3by weld25or by pressure force, etc. This design in particular is advantageously applicable in fuel injectors1having two-stage lifts.

If fuel injector1is closed, the same conditions as in the first exemplary embodiment of a fuel injector1according to the present invention, illustrated inFIG. 2A, prevail. As is apparent inFIG. 3A, bypass channel19is closed and fuel flows exclusively through swirl channels18.

If fuel injector1is switched to a first lift position, valve needle3performs a partial lift which, for example, accompanies only a slight lift of bypass disk17via catch24or no lift at all of bypass disk17; therefore the fuel has a strong tangential swirl component downstream from the sealing seat.

If fuel injector1is switched to a second lift position, which corresponds to a greater lift, more fuel flows through wider opened bypass channel19, because catch24has raised bypass disk17further. This results in a displacement of the mass ratio between swirled and unswirled fuel, because more fuel flows through bypass channel19than through swirl channels18. Subsequently opening angle a of the injected mixture cloud decreases, while the penetration increases.

The present invention is not limited to the illustrated exemplary embodiments and it is particularly implementable in fuel injectors1having multi-stage lifts, in fuel injectors1having piezoelectric or magnetostrictive actuators27, and in any design variant of fuel injectors1.