EP1117920B1 - Common rail injector - Google Patents

Abstract

The injector has an injector housing (1) with a fuel feed connected to a central high pressure fuel reservoir and an internal pressure chamber. A reciprocally movable nozzle needle movable axially against a spring force is raised from as eat if the pressure in the pressure chamber exceeds that in a control chamber connected via a feed choke to the fuel feed. The control chamber (30) is bounded by a sleeve (28) that can be moved into contact with the injector housing under the sealing effect of the end of the needle (8) remote from the combustion chamber and with the aid of the nozzle spring (19).

Description

State of the art

The invention relates to a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine according to the Oberbergiff of claim 1.

In common-rail injection systems, a high-pressure pump delivers the fuel into the central high-pressure accumulator, which is referred to as a common rail. From the high pressure accumulator high pressure lines lead to the individual injectors, which are assigned to the engine cylinders. The injectors are individually from the engine electronics driven. The rail pressure is in the pressure chamber and on the control valve. When the control valve opens, high pressure fuel passes past the nozzle needle lifted against the biasing force of the nozzle spring and into the combustion chamber.

In conventional injectors, as are known for example from DE 197 24 637 A1 or DE 197 32 802 A1, relatively long nozzle needles are used. In operation, very large forces act on the nozzle needle as a result of the high pressures and the rapid load changes. These forces cause the nozzle needle to be stretched and compressed in the longitudinal direction. This in turn has the consequence that the nozzle needle stroke varies depending on the forces acting on the nozzle needle forces.

An injector is known from US Pat. No. 4,572,433, in which a combustion chamber distal end of the nozzle needle and a sleeve delimit a control chamber. At the same time the nozzle needle is guided in this sleeve. The sleeve in turn is not centered directly in the housing of the injector, but is centered only over the nozzle needle tip and the nozzle needle seat. A disadvantage of this Kosntruktion are the indirect centering of the guide sleeve and the large axial distance between the nozzle needle seat and the leadership of the nozzle needle at its end remote from the combustion chamber.

The object of the invention is to provide a common rail injector with a small volume, which is simple and inexpensive to produce. In particular, a good closing behavior should be ensured even at a high nozzle needle speed.

The object is achieved with a common rail injector for injecting fuel in a common rail injection system of an internal combustion engine with the features of claim 1.

The sleeve provides the advantage that the control chamber and the nozzle spring chamber can be combined at the combustion chamber remote end of the nozzle needle without the volume of the control chamber depends on the space of the nozzle spring. Therefore, it is possible to install a nozzle spring with a high spring stiffness, which ensures a good closing of the nozzle needle. As a result, the injection time and the injection timing can be set exactly. In addition, the control chamber can be made very small, resulting in a fast response of the injector according to the invention. Furthermore, there is a relationship between the maximum achievable nozzle needle speed and the nozzle needle diameter. In order to get higher nozzle needle speeds, which is especially important when needle closing, the nozzle needle diameter must be reduced. For a closing speed of 1 m / sec, a needle diameter of less than 3.5 mm ^{3 is} necessary with an acceptable control quantity. This is technically very complicated and therefore expensive. According to the present invention, the nozzle needle diameter can be chosen freely and is not dependent on the dimensions of the nozzle spring. Compared to conventional nozzle needles, the inner diameter of the sleeve may be smaller than a guide diameter. As a result, the volume of the control room is reduced. The smaller the control chamber volume can be chosen, the more responsive the injector is. In addition, the length can be significantly reduced, which contributes to a precise stroke stop.

A particular embodiment of the invention is characterized in that a biting edge is formed on the surface of the sleeve, which is in contact with the injector housing. This ensures that the formed inside the sleeve control chamber of the sleeve surrounding nozzle spring chamber remains separated.

Another particular embodiment of the invention is characterized in that the inner diameter of the sleeve is smaller than the guide diameter of the nozzle needle. The smaller the control chamber volume can be chosen, the more responsive the injector is. According to the present invention, the inner diameter of the sleeve and the corresponding outer diameter on the nozzle needle can be made much smaller than in conventional injectors.

Another particular embodiment of the invention is characterized in that the nozzle spring chamber communicates via a bore with the pressure chamber. As a result, the complete circumference of the nozzle needle can be used for guidance purposes.

A further particular embodiment of the invention is characterized in that at least one flat surface is formed on the nozzle needle between the nozzle spring chamber and the pressure chamber, past which fuel can pass from the nozzle spring chamber into the pressure chamber. This embodiment offers particular advantages in terms of high pressure resistance.

Further special embodiments of the invention are characterized in that the inlet throttle is integrated into the nozzle needle, the sleeve or the injector housing. The inlet throttle is used to prevent pressure surges during operation.

Another particular embodiment of the invention is characterized in that the sleeve has a collar at its end remote from the combustion chamber. The collar forms a first abutment for the nozzle spring.

Another particular embodiment of the invention is characterized in that a step is formed on the nozzle needle, which forms a stop for a spring plate. The spring plate forms a second abutment for the nozzle spring.

Another particular embodiment of the invention is characterized in that in the nozzle needle, a circumferential groove is recessed, in which a retaining ring is supported, which forms a stop for a spring plate. In this embodiment, the outer diameter of the nozzle needle in the control chamber and the guide diameter of the nozzle needle between the nozzle spring chamber and the pressure chamber can be the same size. This is in the manufacturing, e.g. by lapping, an advantage.

Another particular embodiment of the invention is characterized in that the retaining ring is in two parts and is fixed in the assembled state by the spring plate. As a result, a release of the spring plate is prevented during operation in a simple manner.

Another particular embodiment of the invention is characterized in that the Düsennadelhub defined by the distance between the sleeve and the spring plate is. This purely mechanical Düselnadelhubendanschlag provides the advantage that the Düsennadelhub is exactly reproducible. As a result, the course of injection can be reliably shaped. So-called hydraulic bonding is avoided.

Another particular embodiment of the invention is characterized in that the Düsennadelhub and the Düsenfedervorspannung by means of spacer elements are adjustable, which are arranged between the spring plate and the stop for the spring plate or between the nozzle spring and the abutments for the nozzle spring. As a result, the closing behavior of the injector can be improved.

Another particular embodiment of the invention is characterized in that the Düsennadelhub is defined by the distance between the combustion chamber remote end face of the nozzle needle and the injector. This embodiment has the advantage that it is particularly easy to implement in terms of manufacturing technology.

Another particular embodiment of the invention is characterized in that in the combustion chamber remote end face of the nozzle needle and / or in the opposite surface of the injector housing recesses are provided whose dimensions are adapted to the volume of the control chamber. In order to achieve the most linear quantity characteristic diagram possible during operation of the injector, it makes sense not to design the nozzle needle stroke stop purely hydraulically. In a purely hydraulic Düsennadelhubanschlag it may happen that the nozzle needle in the open position on a pressure pad "floats". This can lead to vibrations of the nozzle needle. The oscillations in turn result in non-linear quantity maps. Since this is a dynamic movement, results in a greater tolerance dependence. The vibrations of the nozzle needle may depend on the inlet and the outlet throttle, the friction of the nozzle needle guide, the control chamber volume, etc. In a purely mechanical stop a vibration of the nozzle needle is indeed avoided, but a slightly larger amount of control is required. This has an unfavorable effect on the efficiency of the injector. Through the recesses, which may have the shape of Phillips, for example, a "semi-hydraulic" stop is created. The remaining at the stop flow cross-section is just chosen so large that a vibration of the nozzle needle while avoided, the control amount at the end stop, however, is lowered as much as possible. In this case, it is advantageous that the injector according to the invention has no leakage, ie no return quantity is generated without activation of the injector.

Another particular embodiment of the invention is characterized in that in the combustion chamber remote end face of the nozzle needle at least one axial bore is provided which is in communication with at least one radial bore in the nozzle needle. This embodiment has the advantage that it is insensitive to mechanical shrinkage, i. the flow cross section does not change over the service life.

Fig. 1

ein erstes Ausführungsbeispiel im Längsschnitt durch den Injektor mit einer Bohrung zwischen dem Düsenfederraum und dem Druckraum;

Fig. 2

ein zweites Ausführungsbeispiel im Längsschnitt durch den Injektor mit einer Abflachung an der Düsennadel zwischen dem Düsenfederraum und dem Druckraum;

Fig. 3

ein weiteres Ausführungsbeispiel im Längsschnitt durch den Injektor, wobei die Zulaufdrossel in die Düsennadel oder in das Injektorgehäuse integriert ist;

Fig. 4

ein weiteres Ausführungsbeispiel im Längsschnitt durch den Injektor mit einer Umfangsnut in der Düsennadel, in der sich ein Haltering abstützt, der einen Anschlag für einen Federteller bildet;

Fig. 5

eine Variante des in Fig. 4 dargestellten Ausführungsbeispiels mit einem zweiteiligen Haltering;

Fig. 6

die Ansicht eines Schnitts entlang der Linie VI-VI in Fig. 5;

Fig. 7

ein weiteres Ausführungsbeispiel im Längsschnitt durch den Injektor mit Distanzelementen zur Einstellung des Düsennadelhubs und der Düsenfedervorspannkraft;

Fig. 8

ein weiteres Ausführungsbeispiel im Längsschnitt durch den Injektor mit Kreuznuten in der brennraumfernen Stirnfläche der Düsennadel;

Fig. 9

die brennraumferne Stirnfläche der Düsennadel aus Fig. 8 in der Draufsicht;

Fig. 10

ein weiteres Ausführungsbeispiel im Längsschnitt durch den Injektor mit Bohrungen in der brennraumfernen Stirnfläche; und

Fig. 11

ein weiteres Ausführungsbeispiel im Längsschnitt durch den Injektor mit einer Nut in dem Injektorgehäuse.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, various embodiments of the invention are described in detail. The features mentioned in the claims and in the description may each be essential to the invention individually or in any desired combination. In the drawing show:

Fig. 1

a first embodiment in longitudinal section through the injector with a bore between the nozzle spring chamber and the pressure chamber;

Fig. 2

a second embodiment in longitudinal section through the injector with a flattening on the nozzle needle between the nozzle spring chamber and the pressure chamber;

Fig. 3

a further embodiment in longitudinal section through the injector, wherein the inlet throttle is integrated in the nozzle needle or in the injector housing;

Fig. 4

a further embodiment in longitudinal section through the injector with a circumferential groove in the nozzle needle, in which a retaining ring is supported, which forms a stop for a spring plate;

Fig. 5

a variant of the embodiment shown in Figure 4 with a two-part retaining ring.

Fig. 6

the view of a section along the line VI-VI in Fig. 5;

Fig. 7

a further embodiment in longitudinal section through the injector with spacers for adjusting the nozzle needle stroke and the Düsenfedervorspannkraft;

Fig. 8

a further embodiment in longitudinal section through the injector with cross grooves in the combustion chamber remote end face of the nozzle needle;

Fig. 9

the combustion chamber remote end face of the nozzle needle of Figure 8 in plan view.

Fig. 10

a further embodiment in longitudinal section through the injector with holes in the combustion chamber remote end face; and

Fig. 11

a further embodiment in longitudinal section through the injector with a groove in the injector.

The illustrated in Fig. 1 in longitudinal section first embodiment of the injector according to the invention has a generally designated 1 injector. The injector housing 1 comprises a nozzle body 2, which projects with its lower free end into the combustion chamber of the internal combustion engine to be supplied. With its upper, combustion chamber remote end face of the nozzle body 2 is clamped by means of a clamping nut 5 axially against a valve body 3 and an injector 4.

In the nozzle body 2, an axial guide bore 6 is recessed. In the guide bore 6, a nozzle needle 8 is guided axially displaceable. At the tip 9 of the nozzle needle 8, a sealing surface is formed, which cooperates with a sealing seat which is formed on the nozzle body 2. When the tip 9 of the nozzle needle 8 is in contact with the sealing seat with its sealing surface, two spray holes 10 and 11 in the nozzle body 2 are closed. When the nozzle needle tip 9 lifts off its seat, high pressure fuel is injected through the injection holes 10 and 11 into the combustion chamber of the engine.

Starting from the tip 9, the nozzle needle 8 has three regions with different diameters d ₁ , d ₂ and d ₃ . The diameter d ₂ is the largest and serves to guide the nozzle needle 8 in the nozzle body 2. The diameter d ₁ is the smallest. In the section with the Diameter d ₁ , a collar 16 is formed with a flat 17 on its outer peripheral surface. The collar 16 forms a second guide for the nozzle needle 1. The flattening 17 in the collar 16 allows a flow connection in the longitudinal direction of the nozzle needle 1 from one side of the collar 16 to the other side. The diameter d ₃ is greater than the diameter d ₁ , but smaller than the diameter d ₂ . The diameter d ₃ is also referred to as the control diameter.

The nozzle needle 8 is biased by means of a nozzle spring 19 against the nozzle needle seat in the region of the injection holes 10 and 11. The nozzle spring 19 is arranged in a nozzle spring chamber 20, in which a fuel inlet 21 opens. By an arrow 22 is indicated that the fuel inlet 21 is supplied from a (not shown) rail with fuel, which is acted upon by high pressure. Via a bore 23, the high-pressure fuel from the nozzle spring chamber 20 passes into a pressure chamber 24. The pressure chamber 24 is connected via an annular space 25 with the spray holes 10 and 11 in connection, when the nozzle needle 1 against the biasing force of the nozzle spring 19 lifted from its seat is.

As a result of the difference in size between the diameter d ₂ and the diameter d ₃ results in the nozzle needle 8, a step which forms a stop for a spring plate 26. About the spring plate 26, the biasing force of the nozzle spring 19 is transmitted to the nozzle needle 8. The other end of the nozzle spring 19 is supported on a collar 27, which is formed on a sleeve 28. The inner diameter of the sleeve 28 is slightly larger than the control diameter d _{3 of} the nozzle needle 8. The dimensions of the diameters are selected so that the sleeve 28 is displaceable relative to the nozzle needle 8 under sealing action. Due to the biasing force of the nozzle spring 19, the sleeve 28 with a Biting edge 29 pressed against the valve body 3. As a result, a control chamber 30 provided in the interior of the sleeve 28, which is delimited by the end face of the nozzle needle 8 remote from the combustion chamber, is sealed off from the nozzle spring chamber 20.

The control chamber 30 is connected via an inlet throttle 31 with the nozzle spring chamber 20. In addition, the control chamber 30 is connected via an outlet throttle 32 with a (not shown) discharge space in connection. The connection of the control chamber 30 with the discharge chamber depends on the position of a control valve member 33.

The injector shown in Fig. 1 functions as follows:

From the fuel inlet 21 receives high-pressure fuel in the nozzle spring chamber 20. From there passes the high-pressure fuel on the one hand via the inlet throttle 31 into the control chamber 30 and the other via the bore 23 into the pressure chamber 24. The diameter ratios are chosen in a known manner in that, as a result of the high pressure in the control chamber 30, the nozzle needle 8 is in contact with the nozzle needle seat with its tip 9. When the control valve member 33 opens, the control chamber 30 is depressurized and the nozzle needle tip 9 lifts off its seat. Then, as long as high-pressure fuel is injected through the injection holes 10 and 11 in the combustion chamber of the internal combustion engine until the control valve member 33 closes again. This has the consequence that the pressure in the control chamber 30 rises again and the nozzle needle 8 is pressed with its tip 9 again against the associated nozzle needle seat.

The second embodiment shown in FIG. 2 largely corresponds to the first shown in FIG Embodiment of the invention. For simplicity, the same reference numerals will be used to designate like parts. In addition, in order to avoid repetition, reference is made to the above description of the first embodiment. In the following, only the differences between the two embodiments will be discussed. In the detailed description of the embodiments shown in FIGS. 3-11, the procedure is analogous.

In the second exemplary embodiment illustrated in FIG. 2, a connecting bore between the nozzle spring chamber 20 and the pressure chamber 24 is missing. Instead, a flattening 36 is formed in the section of the nozzle needle 8 with the diameter d ₂ . The flattening 36 provides a connection between the nozzle spring chamber 20 and the pressure chamber 24. Otherwise, there are no differences between the two embodiments.

The third embodiment shown in Fig. 3 differs from the second embodiment in that the inlet throttle is not disposed in the sleeve 28. At 38 is indicated in Fig. 3 that the inlet throttle in the form of holes of different orientations and different dimensions can be integrated into the nozzle needle 8. Indicated at 39 is that the inlet throttle can also be integrated in the valve body 3.

In the fourth embodiment shown in Fig. 4, the spring plate 26 is not supported directly on the nozzle needle 8, but only indirectly via a resilient retaining ring 42 having a rectangular cross-section. In order to allow insertion of the retaining ring 42 in a formed in the nozzle needle 8 circumferential groove, the retaining ring 42 is formed slotted.

In FIGS. 5 and 6 it is shown that instead of a one-piece, clip-on retaining ring, a two-part retaining ring 46 can also be used. The retaining ring 46 consists of two ring halves, which are placed in the associated groove in the nozzle needle 8 and fixed by means of the spring plate 26.

In the embodiment shown in Fig. 7, the stroke is not, as in the embodiment shown in FIG. 1, limited by the distance H _{1 of} the combustion chamber remote end face of the nozzle needle 8 and the opposite surface of the valve body 3, but by the distance H ₂ between the sleeve 28 and the spring plate 26. In Fig. 7 it can also be seen that the stroke H ₂ can be adjusted by a spacer 51. The spacer 51 is arranged for this purpose between the shoulder, which results from the difference in diameter between d ₂ and d ₃ , and the spring plate 26. In addition, the spring biasing force of the nozzle spring 19 can be adjusted by means of a spacer 50. For this purpose, the spacer 50 between the nozzle spring 19 and the collar 27 of the sleeve 28 is arranged. These adjustment options can prevent hydraulic sticking or complete pressurization of the nozzle needle 8 in the control chamber 30. This results in a better closing behavior of the injector.

In the exemplary embodiments illustrated in FIGS. 8-11, the nozzle needle stroke, as in the exemplary embodiment illustrated in FIG. 1, results from the distance H ₁ between the nozzle needle 8 and the valve body 3. In order to prevent the nozzle needle 8 in the Flopped open position on a pressure pad, the following solutions are provided:

In the embodiment shown in FIGS. 8 and 9, two grooves 55 and 56 are arranged crosswise in the end face 54 of the nozzle needle 8. As a result, a purely mechanical stop of the needle nozzle is realized. If the dimensions of the grooves 54 and 55 are adapted to the injector, this can become a "semi-hydraulic stop". The breakthrough cross-section remaining at the stop is selected to be just so large that an oscillation of the nozzle needle 8 is indeed avoided, but the control amount at the end stop is lowered as far as possible.

In the exemplary embodiment illustrated in FIG. 10, a throttle bore 58 is arranged parallel to the longitudinal axis of the nozzle needle 8 in the end face 54 of the nozzle needle 8. The throttle bore 58 opens into a bore 59 which extends transversely to the longitudinal axis of the nozzle needle 8. When the bore 59 is a blind bore, which is open to the combustion chamber distant, frustoconical end of the nozzle needle 8 out. This embodiment has the advantage that it is insensitive to mechanical shrinkage.

In the embodiment shown in FIG. 11, a groove 61 is recessed in the opposite face 62 of the valve body 3, instead of in the end face 54 of the nozzle needle 8 remote from the combustion chamber. The groove 61 has the same function as the grooves 54 and 55 in the embodiment shown in Figs. 8 and 9.

Claims (15)

1. Common-rail injector for the injection of fuel in common-rail injection system of an internal combustion engine, which common-rail injector has an injector housing (1) with a fuel inflow (21) which is connected to a central high-pressure fuel accumulator outside the injector housing (1) and, via a nozzle spring space (20), to a pressure space (24) inside the injector housing (1), out of which pressure space fuel acted upon by high pressure is injected as a function of the position of a control valve (33) which ensures that a nozzle needle (8), movable to and fro in a longitudinal bore (6) of the injector axially counter to the prestressing force of a nozzle spring (19) received in the nozzle spring space (20), lifts off from a seat when the pressure in the pressure space (24) is higher than the pressure in a control space (30) which is connected to the fuel inflow via an inflow throttle (31, 38, 39), the control space (30) being delimited by a sleeve (28) which is displaceable under sealing action on that end of the nozzle needle (8) remote from the combustion space and which is held in bearing contact against the injector housing (1) with the aid of the nozzle spring (19), the nozzle needle (8) having three regions with different diameters (d₁, d₂, d₃), characterized in that the nozzle needle (8) is guided, in its region with the largest diameter (d₂) designed as a guide diameter, in a nozzle body (2) between the nozzle spring space (20) and the pressure space (24).
2. Common-rail injector according to Claim 1, characterized in that a biting edge (29) is formed on that face of the sleeve (28) which is in bearing contact against the injector housing (1).
3. Common-rail injector according to one of the preceding claims, characterized in that the inside diameter (d₃) of the sleeve (28) is smaller than the guide diameter (d₂) on the nozzle needle (8).
4. Common-rail injector according to one of the preceding claims, characterized in that the nozzle spring space (20) is connected to the pressure space (24) via a bore (23).
5. Common-rail injector according to one of Claims 1 to 3, characterized in that the nozzle needle (8) has formed on it, between the nozzle spring space (20) and the pressure space (24), at least one plane face (36) past which fuel can pass from the nozzle spring space (20) into the pressure space (24).
6. Common-rail injector according to one of the preceding claims, characterized in that the inflow throttle (31, 38, 39) is integrated into the sleeve (28), the nozzle needle (8) or the injector housing (1).
7. Common-rail injector according to one of the preceding claims, characterized in that the sleeve (28) has a collar (29) at its end remote from the combustion space.
8. Common-rail injector according to one of the preceding claims, characterized in that the nozzle needle (8) has formed on it a step which constitutes a stop for a spring plate (26).
9. Common-rail injector according to one of Claims 1 to 7, characterized in that, in the nozzle needle (8), a circumferential groove is cut out, in which is supported a holding ring (42, 46) which constitutes a stop for a spring plate (26).
10. Common-rail injector according to Claim 9, characterized in that the holding ring (42) is in two parts and is fixed in the assembled state by the spring plate (26).
11. Common-rail injector according to one of Claims 8 to 10, characterized in that the nozzle-needle stroke (H₂) is defined by the distance between the sleeve (28) and the spring plate (26).
12. Common-rail injector according to one of Claims 8 to 11, characterized in that the nozzle-needle stroke (H₂) and the nozzle-spring prestress are adjustable with the aid of spacer elements (50, 51) which are arranged between the spring plate (26) and the stop for the spring plate or between the nozzle spring (19) and the abutments for the nozzle spring (19).
13. Common-rail injector according to one of the preceding claims, characterized in that the nozzle-needle stroke (H₁) is defined by the distance between that end face (54) of the nozzle needle (8) remote from the combustion space and the injector housing (1).
14. Common-rail injector according to Claim 13, characterized in that recesses (55, 56; 61), the dimensions of which are adapted to the volume of the control space (30), are provided in that end face (54) of the nozzle needle (8) remote from the combustion space and/or in the opposite face (62) of the injector housing (1).
15. Common-rail injector according to Claim 13, characterized in that at least one axial bore (58), which is connected to at least one radial bore (59) in the nozzle needle (8), is provided in that end face (54) of the nozzle needle (8) remote from the combustion space.

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