Inward-opening variable fuel injection nozzle

A fuel injection nozzle is proposed, in which an inner nozzle needle and an outer nozzle needle can be actuated independently of one another. Upon opening of the outer nozzle needle, a stream of fuel is injected into the combustion chamber in the direction of the longitudinal axis of the fuel injection nozzle, while upon opening of the inner nozzle needle, the fuel is injected laterally into the combustion chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an improved fuel injection nozzle for an internal combustion engine and more particularly to such a nozzle having two coaxial nozzle needles.

2. Description of the Prior Art

From German Patent Disclosure DE 40 23 223 A1, a fuel injection nozzle with two nozzle needles disposed coaxially to one another is known. One common nozzle needle seat for both nozzle needles is provided in the valve body surrounding the nozzle needles. Consequently, both when the first nozzle needle is opened and when the second nozzle needle is opened, fuel is injected into the combustion chamber at an angle of 60°, for instance, to the longitudinal axis of the fuel injection nozzle. These injection angles are necessary, in the so-called heterogeneous operating mode of the engine.

In some load states of the engine, however, it is advantageous if the fuel is injected into the combustion chamber in the direction of the longitudinal axis of the fuel injection nozzle (homogeneous mode).

In International Patent Disclosure WO 02/18775, the distinction between the aforementioned homogeneous mode and the heterogeneous mode of an internal combustion engine is explained in detail. This explanation is hereby incorporated by reference.

OBJECT AND SUMMARY OF THE INVENTION

In a fuel injection nozzle for an internal combustion engine, having a nozzle body protruding into the combustion chamber, having two coaxial spring-loaded nozzle needles, the outer nozzle needle being guided in the nozzle body, having a first nozzle needle seat in the nozzle body for the outer nozzle needle and having a second nozzle needle seat for the inner nozzle needle, the inner nozzle needle is guided in the outer nozzle needle, and the first nozzle needle seat is disposed in the outer nozzle needle, it can be attained that injections can be accomplished both in the direction of the longitudinal axis of the fuel injection nozzle and at a virtually arbitrary angle to this longitudinal axis into the combustion chamber. As a result, the operating performance of the engine can be further optimized, which is advantageous especially in terms of noise and emissions from the engine.

In a variant of the fuel injection nozzle of the invention, it is provided that a first pressure chamber, cooperating with a pressure shoulder of the inner nozzle needle, is embodied in the outer nozzle needle, and that the first pressure chamber is acted upon, at least indirectly, with the pressure of a common rail via a supply bore in the outer nozzle needle.

It can furthermore be provided that the inner nozzle needle, with its end remote from the combustion chamber, defines a first control chamber, present in the outer nozzle needle, and that a closure element cooperating with the outer nozzle needle defines the first control chamber on the other end. In these embodiments, a structure of the fuel injection nozzle of the invention that is simpler in terms of production is made possible.

Alternatively, the diameter of the inner nozzle needle, on its end remote from the combustion chamber, can be greater than the diameter of the first pressure shoulder of the inner nozzle needle, or a closing spring which is braced on one end on the inner nozzle needle and on the other on the closure element can be present in the first control chamber. By means of these alternatives, which can also be combined with one another, the closure of the inner nozzle needle is assured hydraulically in one case and in the other by the prestressing of the closing spring.

Other variants of the fuel injection nozzle of the invention provide that the first control chamber is supplied with fuel from the common rail via a first inlet throttle, that the first control chamber communicates hydraulically with a fuel return via a first outlet throttle and via a first multi-way valve, in particular a 2/2-way valve, and the first inlet throttle can be disposed in the closure element or in the outer nozzle needle, and the first outlet throttle is disposed in the closure element. A common feature of all these variant embodiments is their ease of production, and because of the resultant high precision of production, a favorable operating performance of the fuel injection nozzle.

In a further feature of the invention, it is provided that the outer nozzle needle, with its end remote from the combustion chamber, defines a second control chamber, present in the nozzle body, on one end, and that the closure element defines the second control chamber on the other end. As a result, the number of components required is kept small, and simple production of the fuel injection nozzle of the invention is made possible.

In a further feature of this variant embodiment of the invention, it is provided that the second control chamber is supplied with fuel from the common rail via a second inlet throttle, and that the second control chamber communicates hydraulically with the fuel return via a second outlet throttle and via a second multi-way valve, in particular a 2/2-way valve.

Alternatively, the second control chamber can be supplied with fuel from the common rail via the supply bore, the first control chamber, and the second inlet throttle; in that case the second control chamber communicates hydraulically with the fuel return via a second outlet throttle and a second multi-way valve, in particular a 2/2-way valve, and the first pressure chamber can be acted upon by a pressure which is greater than the pressure in the common rail. This design of the fuel injection nozzle of the invention assures that the pressure required in the common rail need not be as high as the desired maximum injection pressure, and moreover the injection pressure is not applied permanently but instead only during the injection in the fuel injection nozzle.

To raise the pressure in the common rail to the desired injection pressure, between the common rail and the first pressure chamber a hydraulic pressure booster can be provided, whose low-pressure connection communicates hydraulically with the common rail and whose high-pressure connection communicates hydraulically with the first pressure chamber, and whose pressure in a diversion chamber can be made to communicate, via a 3/2-way valve, with either the common rail or the fuel return. By means of this pressure booster, the pressure can be raised in a simple, time-tested way, and the control of both the onset and duration of injection is accomplished by a suitable triggering of the 3/2-way valve.

To supply the high-pressure side of the pressure booster and thus also the fuel injection nozzle of the invention with fuel, between the common rail and the high-pressure chamber of the pressure booster, a hydraulic communication with a check valve can be provided.

A further advantageous feature of the invention provides that the second inlet throttle is disposed in the closure element, so that the adaptation of the inlet throttles and outlet throttles of the fuel injection nozzle of the invention can be done directly in the production of the closure element. Also by this means, the production of the fuel injection nozzle of the invention and its operating performance can be improved in a simple way. The deviations in operating performance of the fuel injection nozzles in large-scale mass production can also be lessened.

According to the invention, the multi-way valves can be actuated by an electromagnet or a piezoelectric actuator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

InFIG. 1, a first exemplary embodiment of a fuel injection nozzle1of the invention is shown in longitudinal section. The fuel injection nozzle1essentially comprises a nozzle body3, in which an outer nozzle needle5is guided sealingly. An inner nozzle needle7is guided, likewise sealingly, in the outer nozzle needle5. With one end9toward a combustion chamber, not shown, of an internal combustion engine, the fuel injection nozzle1protrudes into that combustion chamber. On the end of the nozzle body3remote from the combustion chamber that is not shown, the nozzle body is closed with a closure element11.

The fuel injection nozzle1is supplied with fuel that is at high pressure by a common rail114via a high-pressure fuel line13. The control and leakage quantities are carried away via a fuel return15.

As can be seen fromFIG. 1, the outer nozzle needle5has a stepped center bore17, in which the inner nozzle needle7is guided. The inner nozzle needle7essentially has three different diameters, which inFIG. 1are marked D1, D2and D3. Unless otherwise noted, the following relations apply:

If D3=D2, a closing spring is required.

On its end toward the combustion chamber, the inner nozzle needle7has a first diameter D1, which merges with a pointed tip19. In the closed state, the tip19of the inner nozzle needle7rests on a first nozzle needle seat21, which is present on the end of the stepped center bore17of the outer nozzle needle5.

Between the first diameter D1and the second diameter D2, a pressure shoulder23is embodied on the inner nozzle needle7. This first pressure shoulder23defines a first pressure chamber25, formed by the stepped center bore17of the outer nozzle needle5. The first pressure chamber25is supplied with fuel from the common rail114via a supply bore27in the outer nozzle needle5and the high-pressure line13.

With its second diameter D2, the inner nozzle needle7is guided sealingly in the stepped center bore17of the outer nozzle needle5.

On its end29remote from the combustion chamber, the inner nozzle needle7has a third diameter D3, which is greater than the second diameter D2, and defines a first control chamber31. The inner nozzle needle7is also guided sealingly with its third diameter D3in the stepped center bore17of the outer nozzle needle5.

On the end opposite from the end29of the inner nozzle needle7, the first control chamber31is defined by the closure element11. The closure element11is placed, likewise sealingly, in the stepped center bore17of the outer nozzle needle5. The inner nozzle needle7can move relative to the closure element11and to the outer nozzle needle5.

The first control chamber31communicates hydraulically with the common rail114via the high-pressure line13, in which there is a first inlet throttle33. Via a first outlet throttle35and a first 2/2-way valve37, the first control chamber can be made to communicate hydraulically with the fuel return15.

The actuation of the inner nozzle needle7by triggering of the first 2/2-way valve37is accomplished as follows: If the inner nozzle needle7is to lift from the first nozzle needle seat21in order to trip an injection, the first 2/2-way valve37is opened, causing the pressure in the first control chamber31to drop, and as a result of the hydraulic force acting essentially on the first pressure shoulder23, the inner nozzle needle7lifts from the first nozzle needle seat21. As a consequence, fuel is injected into the combustion chamber through the first injection ports39disposed in the outer nozzle needle5. As soon as the first 2/2-way valve37is closed again, the pressure in the first control chamber31rises again, and the hydraulic force acting on the end29of the inner nozzle needle7remote from the combustion chamber moves the inner nozzle needle7back against the first nozzle needle seat21, counter to the hydraulic force acting on the pressure shoulder23.

The outer nozzle needle5is guided sealingly with its diameters D4and D5in a stepped center bore41of the nozzle body3. The stepped center bore41, together with a second pressure shoulder43of the outer nozzle needle5, defines a second pressure chamber45.

With its end47remote from the combustion chamber, the outer nozzle needle5together with the closure element11and the stepped center bore41defines a second control chamber49. Via a second inlet throttle51, the second control chamber49communicates hydraulically with the common rail114.

Via a second outlet throttle53and a second 2/2-way valve55, the second control chamber49can be made to communicate with the fuel return15. The second inlet throttle51and the second outlet throttle53are disposed in the closure element11.

When the outer nozzle needle5is to lift from its seat in the nozzle body3, the second 2/2-way valve55is opened, so that the pressure in the second control chamber49drops, and the hydraulic force acting on the second pressure shoulder43lifts the outer nozzle needle5from its seat, not shown, in the nozzle body3. Once the nozzle needle5has lifted from its seat, not shown, in the nozzle body3, fuel can be injected into the combustion chamber through second injection ports40shown in FIG.4. In a first approximation, the fuel is injected in the direction of the longitudinal axis of the fuel injection nozzle1.

As soon as the second 2/2-way valve55is closed again, a pressure increase occurs in the second control chamber49, so that the outer nozzle needle5is pressed back onto its nozzle needle seat.

In dimensioning the fuel nozzle1of the invention, care must be taken to provide that the annular surface area on the end47of the outer nozzle needle5that is defined by the diameters D5and D3is greater than the area of the second pressure shoulder43, so that for the same pressure in the second pressure chamber45and the second control chamber49, a resultant hydraulic force occurs which presses the outer nozzle needle5against its sealing seat in the nozzle body3.

The second injection ports40, not shown inFIG. 1, of the outer nozzle needle5are disposed such that the fuel is injected (see alsoFIG. 4) in the direction of the longitudinal axis of the fuel injection nozzle1in the combustion chamber, not shown. Slight deviations between the direction of the injected fuel stream and the longitudinal axis of the fuel injection nozzle are also possible and may be wanted. As a result, in some operating states of the engine, improved combustion and emissions performance of the engine can be achieved.

If the fuel is to be injected laterally into the combustion chamber, not shown, the inner nozzle needle7is opened. It is also possible to open the inner nozzle needle7first and, with the inner nozzle needle7open, also to lift the outer nozzle needle5from its nozzle needle seat, so that a large fuel quantity is injected into the combustion chamber within a very brief time.

InFIG. 2, a second exemplary embodiment of a fuel injection nozzle1of the invention is shown, again in longitudinal section. Identical components are identified by the same reference numerals, and their description made in conjunction withFIG. 1applies accordingly.

Between the high-pressure line13and the first pressure chamber25, in this exemplary embodiment, a hydraulic pressure booster57is provided. The pressure booster57essentially comprises a stepped piston59, which on one side defines a low-pressure chamber61and on the other a high-pressure chamber63. The low-pressure chamber61communicates hydraulically with the common rail114via the high-pressure line13. Via a line65, which extends through the closure element11, the nozzle body3, and the outer nozzle needle5, the high-pressure chamber63communicates with the first pressure chamber25. The high-pressure chamber63is filled via a check valve67, which is disposed between the high-pressure line13and the high-pressure chamber63. A diversion chamber69of the pressure booster57communicates hydraulically with either the common rail114or the fuel return15via a 3/2-way valve71. In the diversion chamber69, a closing spring74is provided, which moves the stepped piston59upward in the switching position of the 3/2-way valve71shown inFIG. 2, which causes a reduction in size of the low-pressure chamber61and an increase in size of the high-pressure chamber63. As soon as the 3/2-way valve71is switched over, causing the diversion chamber69to communicate hydraulically with the fuel return15, the stepped piston59is moved downward in terms ofFIG. 2, because the hydraulic forces operative in the low-pressure chamber61are greater than the hydraulic forces operative in the high-pressure chamber63. As a consequence, the pressure in the first pressure chamber25rises, so that the hydraulic force acting on the first pressure shoulder23is greater than the hydraulic force exerted by the first control chamber31and than the force exerted on the inner nozzle needle7by a closing spring73located in the first control chamber31. As a consequence of this, the inner nozzle needle7lifts from its first nozzle needle seat21. When the inner nozzle needle7lifts from its sealing seat, the volume of the first control chamber31decreases. The fuel positively displaced as a result flows back into the high-pressure line13via the supply bore27. Because of the simultaneous volumetric increase of the low-pressure chamber61of the pressure booster57, the high-pressure line13is capable of absorbing the quantity of fuel positively displaced out of the first control chamber31.

In the second exemplary embodiment, shown inFIG. 2, of a fuel injection nozzle1of the invention, the inner nozzle needle7opens under pressure control, so that a first inlet throttle and a first outlet throttle are not necessary.

In this exemplary embodiment, the inner nozzle needle7has only two diameters (D1and D2). The closing force is brought to bear, as already noted, by the closing spring73. This conception can also be employed in the exemplary embodiment of FIG.1.

In this exemplary embodiment, the second control chamber49is supplied with fuel via a second inlet throttle51, and the second inlet throttle51establishes a hydraulic communication between the first control chamber31and the second control chamber49. In this exemplary embodiment, the closure element11is embodied in two parts. This is indicated inFIG. 2by the reference numerals11aand11b. Because of the two-part embodiment of the closure element11, any slight eccentricity of the stepped center bore17relative to the stepped center bore41can be compensated for. Moreover, this simplifies the production of the closure element11.

The outer nozzle needle5is opened by opening the second 2/2-way valve55, causing a pressure reduction in the second control chamber49via the second outlet throttle53. As soon as the hydraulic force acting on the second pressure shoulder43is greater than the hydraulic force exerted on the outer nozzle needle5by the second control chamber49, the outer nozzle needle5lifts from its nozzle needle seat in the nozzle body3and makes an injection possible.

In the high-pressure line13, a combined check valve with a parallel-connected throttle, the latter two elements being identified overall by reference numeral75, is provided in order to reduce pressure fluctuations in the common rail114and in the fuel injection nozzle1.

InFIG. 3, a further exemplary embodiment of a fuel injection nozzle1of the invention with a pressure booster57is shown. Below, only the essential differences will be described, while otherwise reference is made to the description above.

In a distinction from the exemplary embodiment ofFIG. 2, the first control chamber31is supplied with fuel via a first inlet throttle33disposed in the outer nozzle needle5. The first inlet throttle33communicates with the line65that connects the high-pressure chamber63of the pressure booster57with the first pressure chamber25.

The first outlet throttle35communicates with the diversion chamber69of the pressure booster57via a line77. This means that as soon as the 3/2-way valve71establishes a hydraulic communication of the fuel return15and the diversion chamber69, the pressure in the first control chamber31also drops, and the inner nozzle needle7can thus open. In this exemplary embodiment, the second inlet throttle51is disposed in the closure element11, between the high-pressure line13and the second control chamber49. The second outlet throttle53is also disposed in the closure element11a.

InFIG. 4, various embodiments of fuel injection nozzles of the invention are shown in simplified form and on a larger scale. With the enlargements shown inFIGS. 4a-4d, the intent above all is to explain and show various possible dispositions of second injection ports40in the fuel injection nozzle1of the invention. All the embodiments inFIGS. 4a-4dcan be employed in any of the embodiments ofFIGS. 1-3that are explained at length above.

In the exemplary embodiment ofFIG. 4a, a second nozzle needle seat79can be seen. The second nozzle needle seat79indicates the line of contact between the outer nozzle needle5and the nozzle body3, in the closed state of the fuel injection nozzle1. The second injection port40, in this exemplary embodiment, is formed by a cylindrical annular gap between the nozzle body3and the outer nozzle needle5. The second injection port40is not uncovered until the outer nozzle needle5lifts from the nozzle body3and thus uncovers the second nozzle needle seat79.

In the exemplary embodiment ofFIG. 4b, grooves are distributed over the circumference in the outer nozzle needle5and, together with the nozzle body3, these grooves form the second injection ports40.

In the exemplary embodiment ofFIG. 4c, the second injection ports40, like the first injection ports39, are disposed in the outer nozzle needle5.

In the exemplary embodiment ofFIG. 4d, the second injection ports40are disposed in the nozzle body3between the second nozzle needle seat79and the guide81of the outer nozzle needle5.

Referring now toFIG. 5, it will now be explained how the fuel injection nozzle1of the invention is integrated with a fuel injection system102of an internal combustion engine. The fuel injection system102includes a fuel tank104, from which fuel106is pumped by means of an electrical or mechanical fuel pump108. Via a low-pressure fuel line110, the fuel106is pumped to a high-pressure fuel pump111. From the high-pressure fuel pump111, the fuel106reaches a common rail114via a high-pressure fuel line112. A plurality of fuel injection nozzles1according to the invention are connected to the common rail and inject the fuel106directly into combustion chambers118of an internal combustion engine, not shown.