EP2129903B1 - Fuel injector having an additional outlet restrictor or having an improved arrangement of the same in the control valve - Google Patents

Abstract

The present invention relates to a fuel injector (1) for injecting fuel into a combustion chamber of an internal combustion engine, comprising a valve piston (3) that is displaceably guided in an injector body (2) in terms of lifting motions, wherein the lifting motion of the valve piston (3) can be controlled by a control valve, which has a valve needle (5) with a guide bore (6), the needle being displaceably guided in the direction of a lifting axis (4) in terms of lifting motions. A guide section (7) integrally formed on an end of a valve piece (8) extends into the guide bore for the displaceable guidance of the valve needle (5) in terms of lifting motions, wherein along the lifting axis (4) a vertical bore (9) extends through the valve piece (8) into the guide section (7), with fuel being able to flow through said bore from a control chamber (10) into an annular chamber (11) introduced between the guide bore (6) and the guide section (7) for controlling the lifting motion of the valve piston (3), wherein the fuel volume conducted through the vertical bore (9) furthermore flows through at least one outlet restrictor (12), wherein the outlet restrictor (12) is disposed in the region of the transition from the vertical bore (9) into the annular chamber (11).

Description

The present invention relates to a fuel injector for injecting fuel into a combustion chamber of an internal combustion engine according to the closer defined in the preamble of claim 1, such as in the EP 1731752 ,

State of the art

From the publication EP 1 612 404 A1 a fuel injector is known which comprises a liftable guided in an injector body valve piston which cooperates in its lifting movement with the nozzle needle. According to another also generic type of fuel injectors, the nozzle needle projects directly into the area of the control valve. The valve piston or the nozzle needle adjoin a control chamber, which can be acted upon by high fuel pressure. If the control chamber is subjected to high-pressure fuel, the valve piston or the nozzle needle is moved along the lifting axis in the direction of the injection openings in the lower region of the fuel injector, so that the injection openings are closed. If the control chamber is relieved, then the valve piston or the nozzle needle lifts off from the injection openings, in which it performs a movement along the lifting axis. Thus, the movement of the valve piston or the nozzle needle can be controlled via the pressure in the control chamber. The fuel injector further includes a valve piece which merges into a guide portion which is cylindrically shaped and extends into the guide bore of a valve needle. Thus, the valve needle is guided on the guide portion and can take an opening position and a closed position by a movement along the lifting axis.

For venting the control chamber, a channel system is provided, which consists of at least one riser hole. These vent the control chamber into an annular space, which is introduced through a constriction in the jacket area of the guide section. If the valve needle is arranged in a lower vertical position along the lifting axis, then the annular space is closed, so that the pressure in the control chamber remains at high fuel pressure level. If the valve needle is raised, the compressed fuel can flow out of the annular space into a discharge chamber, so that the pressure in the control chamber decreases. Adjacent to the annulus is in the obliquely arranged riser or one with the centric riser cooperating transverse bore an outlet throttle provided to limit the pressure reduction rate and thus the lifting speed of the valve needle.

In such an arrangement of an outlet throttle the problem arises that in the area of the riser, the transverse bores and in the region of the annulus a large dead or Schadvolumen prevails. Since, due to the large opening cross-section of the control valve, an opening stroke of the valve needle with large armature strokes (> 20 μm) quickly leads to cavitation of the flow in the area or downstream of the outlet throttle, this volume is filled with steam. After closing the control valve, the volume must be refilled with fuel against the gas pressure, raising the pressure to the high fuel pressure (rail pressure). Only then does the valve piston close the nozzle needle again against the injection openings. The greater the vapor content within the harmful volume, the longer the process of closing the nozzle needle, which is subjected to correspondingly large variations. As a result, the stability of the injections deteriorates and the stroke-to-stroke spread from injection to injection increases. Also increases the possible distance to a subsequent injection, so that the ability of the multiple injection decreases.

It is therefore the object of the present invention to provide a fuel injector in which the harmful volume is reduced after the outlet throttle and thus the dispersion from injection to injection can be reduced. Furthermore, it is the object of the present invention to reduce the time required to build up the high fuel pressure within the control room.

Disclosure of the invention

This object is achieved on the basis of a fuel injector for injecting fuel into a combustion chamber of an internal combustion engine according to the preamble of claim 1 in conjunction with its characterizing features. Advantageous developments of the invention are specified in the dependent claims.

The invention includes the technical teaching that between the end of the riser and the annulus at least one throttle bore with a throttle cross-section which is smaller than the riser hole portion to form the drainage throttle. In this case, the cross section of the throttle bore is expanded before exiting into the annular space to form a diffuser section of larger diameter. The diffuser portion may be formed either cylindrical or conical, wherein the opening of the cone points in the direction of the annulus. The throttle bore has a cross-section which is made so small that the desired throttle effect is achieved. In the diffuser section adjoining the section of the throttle bore, the flow of the fuel can be homogenized over the flow cross section so that it flows into the annular space in a calmer state.

By means of the arrangement of the outlet throttle according to the invention, the advantage is achieved that between the Absteuerraum, in which the fuel prevails at a low pressure, and the outlet throttle remains a small volume, so that is reduced by the small remaining volume and the harmful volume. Only the volume of the annular space and parts of the channels for fuel passage between the riser hole and the annular space form a potential harmful volume so that according to a further advantageous embodiment of the annulus itself can be made relatively small. Thus, a further reduction of the damage volume can be caused in order to further improve the advantages of the present invention.

It is according to the invention that the throttle bores and the diffuser section extend along a bore axis, and this extends at an angle to the stroke axis, wherein the angle has a value of 45 ° Thus, an optimization of the flow behavior is achieved, so that the fuel is not - as in Trap of a transverse bore - a flow deflection of 90 ° is subjected. Therefore, a calmer fuel flow is achieved, which makes a better control of the throttle effect achievable. Both the portion formed by the throttle bore and the adjoining portion of the diffuser bore extend concentrically with the bore axis. Thus, it is possible to first apply the diffuser section in the form of a blind hole along the bore axis in order to produce the throttle bore in the second step. The orifice can either be mechanically drilled conventionally, and an erosion process or a laser drilling process is an advantageous application in which very small and accurate bore geometries can be created. In particular, can be provided to provide after application of the holes edge rounding, so that edge effects in the fuel flow exert no negative influence.

It is further according to the invention that at least two throttle bores extend between the end of the riser bore and the annular space, which are arranged opposite one another at an angle of 180 °. Furthermore, there is the possibility of creating a plurality of throttle bores with adjoining diffuser sections, so that the respective bore axes extend radially evenly distributed on the circumference of the guide section out of this into the annular space.

Further, measures improving the invention will be described in more detail below together with the description of a preferred embodiment of the invention with reference to FIGS.

embodiments

Figur 1

eine quergeschnittene Seitenansicht eines Kraftstoffinjektors gemäß eines ersten Beispiels ;

Figur 2

einen vergrößerten Ausschnitt der nicht erfindungsgemäßen Ausführung der Ablaufdrossel mit einer Drosselgeometrie zwischen der Steigbohrung und der Querbohrung;

Figur 3

eine quergeschnittene Seitenansicht eines Kraftstoffinjektors mit einer nicht erfindungsgemäßen Anordnung der Ablaufdrossel gemäß eines zweiten Beispiels ;

Figur 4

eine vergrößerte Ansicht des zweiten Beispiels der nicht erfindungsgemäßen Ablaufdrossel mit einer entsprechenden Querschnittsgeometrie der Querbohrung;

Figur 5

eine quergeschnittene Seitenansicht eines Kraftstoffinjektors mit einem Ausführungsbeispiel einer Ablaufdrossel gemäß der vorliegenden Erfindung; und

Figur 6

eine vergrößerte Ansicht der Ablaufdrossel gemäß des Ausführungsbeispiels.

It shows:

FIG. 1

a cross-sectional side view of a fuel injector according to a first example;

FIG. 2

an enlarged section of the non-inventive embodiment of the outlet throttle with a throttle geometry between the riser and the transverse bore;

FIG. 3

a cross-sectional side view of a fuel injector with a non-inventive arrangement of the outlet throttle according to a second example;

FIG. 4

an enlarged view of the second example of non-inventive discharge throttle with a corresponding cross-sectional geometry of the transverse bore;

FIG. 5

a cross-sectional side view of a fuel injector with an embodiment of an outlet throttle according to the present invention; and

FIG. 6

an enlarged view of the outlet throttle according to the embodiment.

The embodiments of the FIGS. 1 to 4 are not covered by the scope of the patent. In the FIGS. 1 . 3 and 5 each views of a fuel injector 1 are shown, which only show different embodiments of the outlet throttle 12. The fuel injector 1 according to the invention comprises an injector body 2, in which a valve piston 3 is guided in a liftable manner. The lifting movement of the valve piston 3 takes place along a lifting axis 4, wherein the valve piston 3 is adjacent to a control chamber 10 at the end. The control chamber 10 can be acted upon by an inlet throttle with high fuel pressure, so that in a high-pressure state of the control chamber 10 of the valve piston 3 in the direction of - not shown in detail - injectors within the injector body 2 is pressed. If the control chamber 10 is relieved, the valve piston 3 can move vertically upwards in FIG Move the direction of the lifting axis 4, so that the injection openings are released. The outflow of fuel from the control chamber 10 via a riser 9, which extends through a valve member 8 therethrough. Adjacent to the valve piece 8, a guide portion 7 is formed, which merges into the valve piece 8 in one piece and of the same material. The guide section 7 has a cylindrical shape which extends into the guide bore 6 of a valve needle 5. Thus, the valve needle 5 is guided on the guide portion 7 hubbeweglich in the direction of the lifting axis 4, and can be pulled vertically by an electromagnet. When the electromagnet is energized, the valve needle 5 is attracted by an armature section formed on it, so that the valve needle 5 transitions into an open position. When the energization of the electromagnet is stopped, a valve spring pushes the valve needle 5 vertically back down into the sealing seat. The sealing effect is created by a sealing edge at the lower end of the valve needle 5, which comes into sealing engagement with the guide section or against the valve piece in an annular manner. The fuel passes through the riser 9, wherein the outlet throttle according to the invention is formed by a corresponding geometric configuration between the riser 9 and the annular space 11. The different embodiments of the outlet throttle according to the invention are in a detailed view in the Figures 2 . 4 and 6 and are described below.

FIG. 2 shows the outlet throttle 12 according to a first example. The enlarged section according to the FIG. 2 shows the riser 9 within the valve piece 8, which projects at least partially into the guide portion 7. Transverse to the riser 9, a transverse bore 14 is mounted, wherein in the region of the transition of the riser 9 in the transverse bore 14, a throttle geometry 15 is introduced. The fuel therefore exits the control chamber through the riser 9, so that when the valve needle 5 is vertically moved upward in the direction of the lifting axis 4, fuel can escape from the annular space 11 in the outer region of the valve needle 5. Thus, the fuel from the riser 9 passes through the transverse bore 14 into the annular space 11, so that the throttle geometry 15 is flowed through. This has a funnel-shaped contour, wherein the funnel is open in the direction of the transverse bore 14. The transition from the riser bore into the funnel-shaped region of the throttle geometry includes a flow restriction to achieve the required throttle effect. Thus, even with open valve needle 5, the pressure in the riser 9 remains at an elevated level, so that the Schadvolumen does not form within the riser 9, but is either completely suppressed or forms only in the region of the annulus, but this formed correspondingly small is.

FIG. 4 shows a further example of an outlet throttle in the region of the transition from the riser 9 into the annular space 11. The formed within the valve piece 8 riser 9 comprises a riser hole 17, which is formed according to this embodiment considerably larger than the transverse bore cross section 16 of the transverse bore 14. The transverse bore 14 extends transversely to the direction of extension of the lifting axle 4, and forms the connection between the riser 9 and the annular space 11. If the fuel from the riser 9 flows through the transverse bore 14 in the annular space 11, so does the small cross-section of the transverse bore 14 with the transverse bore cross-section 16, the outlet throttle 12. According to the present illustration, the transverse bore 14 is applied over the entire cross section of the guide section 7 in the region of the annular space 11, so that the fuel flows into the annular space 11 at two points of discharge. If the transverse bore cross-section 16 is smaller, the throttling effect of the outlet throttle is increased, whereby the throttle effect decreases with a larger cross-section.

FIGS. 5 and 6 show an embodiment of the discharge throttle 12 according to the invention in the region between the riser 9 and the annular space 11. This is formed by two at an angle of about 45 ° to the lifting axis 4 extending bore axes, so that the fuel through the respective throttle holes 18 from the riser 9th flows into the annular space 11. The throttle bores 18 have a small cross-section in order to achieve the throttling effect, wherein these pass into an enlarged diffuser section 19 before entering the annular space. The diffuser section has an enlarged cross-section so that the amount of fuel exiting the throttle bore can settle to flow into the annulus 11 with less flow turbulence. The cross-section of the riser 9 with the riser 17 can be made arbitrarily large, without the volume forms in the form of a Schadvolumens, as well as in the riser 9 according to this embodiment, the outlet throttle 12 forms a high fuel level, even if the valve needle 5 in the open State is. The arrangement of the throttle bore 18 and the diffuser portion 19 along the bore axis 20 at an angle of approximately 45 ° causes the fuel does not have to be deflected, and the flow channel has a total of a soft contour.

The invention is not limited in its execution to the above-mentioned preferred embodiment. Rather, a number of variants is conceivable.

Claims (2)

1. Fuel injector (1) for injecting fuel into a combustion chamber of an internal combustion engine, comprising a valve piston (3) which is guided, such that it can perform a stroke movement, in an injector body (2), wherein the stroke movement of the valve piston (3) can be controlled by a control valve, said control valve having a valve needle (5) which is guided such that it can perform a stroke movement in the direction of a stroke axis (4) and which has a guide bore (6) into which a guide portion (7) integrally formed at one end on a valve piece (8) extends so as to guide the valve needle (5) such that the latter can perform a stroke movement, wherein a rising bore (9) extends through the valve piece (8) into the guide portion (7) along the stroke axis (4), through which rising bore fuel can flow from a control chamber (10) for controlling the stroke of the valve piston (3) into an annular chamber (11) formed between the guide bore (6) and the guide portion (7), wherein the fuel quantity conducted through the rising bore (9) furthermore flows through at least one outflow throttle (12), wherein the outflow throttle (12) is arranged in the region of the transition from the rising bore (9) to the annular chamber (11), wherein furthermore, at least one throttle bore (18) with a throttle cross section which is smaller than the rising bore cross section (17) extends between the end of the rising bore (9) and the annular chamber (11) in order to form the outflow throttle (12), and wherein the cross section of the throttle bore (18) is widened upstream of the outlet into the annular chamber (11) in order to form a diffuser portion (19) of greater diameter, wherein at least two throttle bores (18) extend between the end of the rising bore (9) and the annular chamber (11), which throttle bores are situated opposite one another by an angle of 180°,
   characterized in that the throttle bore (18) and the diffuser portion extend along a bore axis (20), and said bore axis extends at an angle with respect to the stroke axis (4), said angle having a value of 45°.
2. Fuel injector (1) according to Claim 1,
   characterized in that the diffuser portion (19) is of cylindrical or conical design, wherein the opening of the cone points in the direction of the annular chamber (11).

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