WO2015043913A1

WO2015043913A1 - Fuel injection valve and a process for production thereof

Info

Publication number: WO2015043913A1
Application number: PCT/EP2014/068891
Authority: WO
Inventors: Katja Grothe; Christian Berg
Original assignee: Robert Bosch Gmbh
Priority date: 2013-09-27
Filing date: 2014-09-05
Publication date: 2015-04-02
Also published as: DE102013219568A1

Abstract

Fuel injection valve (100) for internal combustion engines for injecting fuel under high pressure with a pressure chamber (20) which is formed in a nozzle body (10) and in which a nozzle needle (30) is arranged such that it can be displaced longitudinally. A nozzle needle tip (31) is formed on the nozzle needle (30), which nozzle needle tip (31) interacts with a nozzle needle seat (11) which is formed on the nozzle body (10) and opens and closes at least one injection opening (19) as a result, wherein a first throttle point (12) is formed between the nozzle needle tip (31) and the nozzle needle seat (11) when the nozzle needle tip (31) is raised up from the nozzle needle seat (11). A middle region (34) which is formed on the nozzle needle (30) forms a second throttle point (50) on the inner surface (15) of said middle region (34) with a shank region (14) which is formed on the nozzle body (10). The second throttle point (50) has a constant throughflow cross section over a first part stroke (s₁) of the nozzle needle (30). Furthermore, a process for production of the fuel injection valve (100) according to the invention is presented.

Description

Description title

Fuel injection valve and a method for its production

The invention relates to a fuel injection valve for internal combustion engines and a, as it is used for fuel injection into the combustion chamber of an internal combustion engine.

State of the art

From the patent application DE 10 2010 044 088 AI a fuel injection valve for injecting fuel into the combustion chamber of an internal combustion engine is known, comprising a nozzle body in which a high pressure bore or a pressure chamber is formed with a longitudinally displaceably arranged nozzle needle, which with a nozzle needle seat of Nozzle body cooperates. Due to the interaction of the nozzle needle with the nozzle needle seat, a fuel flow is opened or interrupted at least one injection port. The known valve has a first gap throttle between the nozzle body and the nozzle needle and a second gap throttle between nozzle body and nozzle needle, the formation of at least one gap choke is dependent on the stroke of the nozzle needle.

The two gap throttles are used in the known fuel injection valve to allow a good injection characteristic both in the smallest quantity operation as well as in full load operation: fast needle closing in pre- and post-injection and maximum injection pressure in the full load range. That is, with small nozzle needle strokes, a reduction of the system pressure below the gap throttles and thus an increase of the hydraulically resulting closing force on the nozzle needle is desired, while in full load operation below the gap throttles the maximum injection pressure is to rest in order to achieve a very favorable combustion in the internal combustion engine. Furthermore, high pressure overshoots on the nozzle needle seat, such as may occur during nozzle needle closing, are minimized by the known fuel injector. The object of the present invention is to achieve a good injection characteristic both in the smallest quantity operation and in full load operation with minimized high-pressure overshoots on the nozzle needle seat during the nozzle needle closing, and at the same time to reduce the production cost of the fuel injection valve, especially for the nozzle needle.

Disclosure of the invention

To solve the problem, the stroke-dependent throttle point between the nozzle needle tip and nozzle body, which arises when lifting the nozzle needle from the nozzle needle seat, to be used advantageously as a gap throttle or throttle point, so that upstream only between the nozzle body and nozzle needle, a further gap throttle or throttle must be located to achieve the above injection characteristics. As a result, the production cost for the nozzle needle is reduced. High pressure overshoot on the nozzle needle seat are minimized as well as the known fuel injector.

For this purpose, the fuel injection valve has a pressure chamber formed in a nozzle body, in which a nozzle needle is arranged to be longitudinally displaceable. A nozzle needle tip formed on the nozzle needle cooperates with a nozzle needle seat formed on the nozzle body and thereby opens and closes at least one injection opening, wherein a first throttle point is formed when lifting the nozzle needle tip from the nozzle needle tip between the nozzle needle tip and the nozzle needle seat. A central region formed on the nozzle needle forms, with a shaft region formed on the nozzle body, on its inner surface a second throttle point which has a constant flow cross-section over a first partial stroke of the nozzle needle. Thus, the first throttle point is used as a stroke-dependent throttle and the second throttle point as at least until the first partial stroke of the nozzle needle hubunabhängige throttle.

Advantageously, the first partial stroke is less than 20% of a maximum stroke of the nozzle needle. The first and the second throttle point are particularly effective for nozzle needle strokes up to the first partial stroke; In this area, above all, they determine the injection characteristics during the pilot injections or during the

Kleinstmengenbetriebs and not the at least one injection port.

In an advantageous embodiment of the fuel injection valve according to the invention, the central region has at least one, but preferably three in the longitudinal direction of the nozzle needle Axial throttle thrust of depth h, which form the second throttle point with the inner surface. As a result, the second throttle point is not formed over the entire circumference of the central region of the nozzle needle, but via the Drosselanschliffe. On the one hand, the manufacturing tolerances between the middle region of the nozzle needle and the shaft region of the nozzle body need not be made too narrow; on the other hand, the throttling function of the second orifice during operation (eg at extreme temperatures or temperature differences) can be kept more robust.

Advantageously, the at least one throttling ground on a slot end face with the radius R is rounded to form a cylindrical outer surface of the central area. As a result, on the one hand, a favorable flow of fuel into the throttle grind can be achieved, on the other hand an undesirable formation of burrs is avoided.

In a further advantageous embodiment, a plurality of injection openings are present, and during the first part of the stroke, the flow cross section of the first throttle point is less than the summed flow area of all injection ports, preferably by more than 50% less. As a result, the throttle effect of the injection openings compared to the throttling effect of the first throttle point is low, and thus the injection characteristic in the smallest quantity operation or in the partial load range to the first partial stroke is hardly influenced by the flow area of the injection openings.

Advantageously, the flow cross section of the second throttle point when reaching the first partial stroke of the nozzle needle is at least approximately as large as the flow cross section of the first throttle point. Depending on the application and nozzle needle stroke, either the first or the second throttle point can be used as an essential throttle function for the first partial stroke. However, until the first partial stroke, both throttle points advantageously have a smaller flow cross section than the summed flow cross section of all injection ports. This reduces the nozzle pressure in the system pressure in the pressure chamber between the first throttle point and the injection openings, so that the hydraulically resulting closing force increases on the nozzle needle and it comes to a faster closing of the nozzle needle and thus to a better injection characteristics with small injection quantities.

In a further advantageous embodiment of the fuel injection valve according to the invention, the second throttle point between the first partial stroke and a second partial stroke of the nozzle needle, which is greater than the first partial stroke and smaller than the maximum stroke, a steadily expanding flow area on. As a result, in the partial load range at strokes that are greater than the first partial stroke, the pressure difference in the pressure chamber upstream to the downstream of the second throttle point less pronounced; during the opening stroke, the hydraulically resulting opening force on the nozzle needle in this area is thus greater and the nozzle needle opens faster.

In a further advantageous embodiment, the flow cross section of the second throttle point is greater than the flow cross section of the first throttle point from the second partial stroke. As a result, the pressure in the entire pressure chamber is approximately the same; the hydraulically resulting opening force on the nozzle needle is maximum. From the second partial stroke of the nozzle needle, the influence of the second throttle point on the injection characteristic of the fuel injection valve decreases; the injection characteristic is determined in this stroke range mainly from the first throttle point and / or the injection openings.

In an advantageous embodiment, the middle region of the nozzle needle in the region of the second throttle point has a tapering towards the nozzle needle tip transition region, wherein the transition region is designed either as a chamfer, preferably at an angle α of 35 ° to 80 ° to the cylindrical lateral surface of the central region, or has at least one concave circular arc shape with radius R. As a result, the flow cross section is increased by the second throttle point, when the tapered transition region of the nozzle needle forms the second throttle point with the shaft region of the nozzle body, so at nozzle needle strokes greater than the first partial stroke until reaching the second partial stroke. Between the first and the second partial lift of the nozzle needle, the gap width of the second throttle point thereby increases while at the same time being easier to manufacture. Depending on the requirement, the execution of the transition region as a chamfer or as a concave circular arc shape may be more advantageous. Depending on the angle between the transition region and the central region, in the case of the concave arc shape of the angle between lateral surface and imaginary tangential extension of the circular arc shape, and depending on the chamfer length or circular arc length so the injection characteristics of the fuels insp - valve in the partial load range can be designed depending on the application.

In a further advantageous embodiment, the nozzle needle tip between the transition region and nozzle needle seat on longitudinal cuts, which extend in the direction of the nozzle needle axis. As a nozzle needle tip, the entire region of the nozzle needle is designated from the transition region in the direction of the combustion chamber of the internal combustion engine. This will be a sufficient fuel flow between the first and second throttle point achieved by the longitudinal grinding with good management of the nozzle needle tip in the shaft region of the nozzle body. The leadership of the nozzle needle tip in the shaft region takes place on the surfaces of the nozzle needle tip on which no longitudinal cuts are formed.

In an advantageous embodiment, the longitudinal sections to the transition region are each rounded with the radius R. As a result, the fillets of the longitudinal cuts simultaneously represent the transition region of the nozzle needle, and the second throttle point can be manufactured on the nozzle needle side with the same tool as the longitudinal cuts.

In a further advantageous embodiment, the summed flow cross section of all injection openings is less than the flow cross section of the first throttle point and less than the flow cross section of the second throttle point at the maximum stroke of the nozzle needle. As a result, determine the maximum lift, so for large injection quantities in full load operation, especially the injection ports, the injection characteristics of the fuel injection valve. Thus, the gap widths of the first and second throttle body need not be made robust over the entire stroke of the nozzle needle, which would mean an extremely high production accuracy.

A manufacturing method of the fuel injection valve according to the invention having the following features: formed in a nozzle body pressure chamber in which a nozzle needle is arranged longitudinally displaceable, wherein a formed on the nozzle needle nozzle needle cooperates with a formed on the nozzle body nozzle needle seat and thereby at least one injection opening opens and closes, wherein the Lifting the nozzle needle tip from the nozzle needle seat between the nozzle needle tip and the nozzle needle seat, a first throttle point is formed, wherein a formed on the nozzle needle central region form on its outer surface with a formed on the nozzle body shaft portion on the inner surface of a second throttle point, wherein on the nozzle needle, a central region is formed and the nozzle needle tip between the central region and nozzle needle seat has longitudinal sections which extend in the direction of the nozzle needle axis, wherein the longitudinal sections are rounded to the central region in a concave transition region having a first rounding and a second rounding, wherein the second throttle point over a first partial stroke of the nozzle needle has a constant flow cross-section and wherein the second throttle point between the first partial stroke and a second partial stroke of the nozzle needle, which is greater than the first partial stroke, has a steadily widening flow cross-section comprises the following steps, which with a Grinding tool: grinding the planar surface of a longitudinal grinding,

Grinding the second rounding, which is made by a convex radius R of the grinding tool together with the planar surface,

Grinding the first rounding by the radius R of the grinding tool while the grinding tool is lifted off the planar surface of the longitudinal grinding,

Repeat the previous steps for all longitudinal cuts.

As a result, the fillets in the transition region and the longitudinal cuts are made with a tool, which significantly reduces the production costs. Advantageously, steps 1) and 2) are carried out together in one production step.

An advantageous development of the production method, wherein the central region in the longitudinal direction of the nozzle needle axis extending Drosselanschliffe the depth h has, which expire in each case in the first rounding of the longitudinal cuts, comprises the following additional or modified process steps, which are performed with a grinding tool:

3b) grinding the Drosselanschliffs (40) together with a at the Drosselanschliff (40) formed Nutstirnseite (42), which also has the radius R.

Repeating the previous steps for all longitudinal cuts (38) and all throttle cuts (40). In an advantageous development of the production method, the first rounding at a first angle α and the second rounding be ground at a second angle ß to the cylindrical surface, where α <ß, and the first rounding and the second rounding have the same radius R, where the second fillet is ground in a tangential manner to the longitudinal cuts and the grinding tool has a corresponding negative mold. Due to the angular relationship α <β, the flow cross-section through the second throttle point from the second partial stroke is increased more than between the first and the second partial stroke. Since the first and second fillets have the same radius R, the same radius of the grinding tool can be used for the grinding processes. Due to the tangential discharge from the second rounding to the longitudinal cuts, a sharp edge or burr formation is avoided at the transition of the longitudinal cuts to the transition region; subsequent deburring production steps can be omitted at this transition.

drawings

Fig.l shows a longitudinal section through a fuel injection valve according to the invention in a schematic representation, wherein only the essential areas are shown.

2 shows a longitudinal section of a further embodiment of the fuel injection valve according to the invention in a schematic representation, wherein only the essential areas are shown.

3 shows the designated III section of Fig.2

FIG. 4 shows the detail of FIG. 3 designated IV

Fig.5 shows a step of a manufacturing process of the embodiment of Fig.2.

description

Fig.l schematically shows a detail of a fuel injection valve 100 according to the invention in longitudinal section. The fuel insp scrib valve 100 has a formed in a nozzle body 10 pressure chamber 20 in which a nozzle needle 30 is arranged longitudinally displaceable. Due to the longitudinal movement of the nozzle needle 30, a nozzle needle 30 acts on the nozzle needle 30. formed nozzle needle tip 31 with a formed on the nozzle body 10 nozzle needle seat 11 and thereby opens and closes at least one formed in the nozzle body 10 injection port 19 for injection of fuel under high pressure in a combustion chamber 110 of an internal combustion engine.

When lifted from Düsennadelsitz 11 nozzle needle tip 31 is formed between Düsennadelsitz 11 and nozzle needle tip 31, a first throttle point 12th

At the nozzle needle tip 31, a transition region 37 and a central region 34 adjoin one another as further components of the nozzle needle 30 away from the combustion chamber. The central region 34 has a cylindrical lateral surface 35 with a diameter d ₃₅ , the transition region 37 is conical in the illustrated embodiment with an angle α to the cylindrical lateral surface 35.

The nozzle body 10 has a shank region 14 with a cylindrical inner surface 15 of diameter d _i5 and, facing away from the combustion chamber, thereupon a nozzle body shoulder 17, the inner diameter of which widens in the direction away from the combustion chamber. In the closed position of the nozzle needle 30, ie upon contact of the nozzle needle tip 31 with the nozzle needle seat 11, is on the nozzle body shoulder 17 combustion chamber side then between the inner surface 15 and lateral surface 35, a second throttle gap 50 with the width (di ₅ -d ₃₅ ) / 2 and with formed the length Si, wherein the length Si corresponds to a first partial stroke Si. The second throttle gap 50 divides the pressure chamber 20 into a upper pressure chamber 21 facing away from the combustion chamber and a lower pressure chamber 22 facing the combustion chamber.

A second partial stroke s ₂ is defined by the sum of the first partial stroke Si and the axial length IÜ of the transitional region 37. The maximum stroke v of the nozzle needle 30 is greater than the second partial stroke s ₂ , it applies to this embodiment: v> s ₂ > 5 _j , with s ₂ = S _j + 1 ₀

2 shows a further exemplary embodiment of the fuel injection valve 100 according to the invention. Differences from the embodiment of FIG. 1 are essentially the arrangement of longitudinal cuts 38 on the nozzle needle tip 31 and the formation of the second throttle restriction 50 not over the entire circumference of the middle region 34 of the nozzle needle 30 , but only in the range of arranged in the central region 34 Drosselanschliffe 40th In the central region 34 of the nozzle needle 30 Drosselanschliffe 40 are arranged with the depth h in the longitudinal direction of the nozzle needle 30, which lead into the transition region 37 of the nozzle needle 30. Preferably, the depth h is 25 μηη to 40 μηη. The illustrated embodiment has three Drosselanschliffe 40, which are arranged uniformly distributed over the circumference. Further embodiments with two or four throttle slits 40 are also possible.

A throttle grind 40 consists of a usually planar groove base 41, which terminates in the transition region 37 and a Nutstirnseite 42, which is designed as a rounding with the radius R to the lateral surface 35 of the central region 34.

The second throttle restriction 50 is essentially formed between the throttle snares 40 and the cylindrical inner surface 15 of the shaft region 14 of the nozzle body 10. The diameter d _{35 of} the lateral surface 35 of the central region 34 is in this embodiment only slightly smaller than the diameter d _{i5 of} the inner surface 15 of the shaft portion 14, so that outside the Drosselanschliffe 40 between the central region 34 and shaft portion 14 no throttle gap is formed; In these areas, the nozzle needle 30 to the nozzle body 10 is almost dense.

On the nozzle needle tip 31 longitudinal slits 38 are arranged in this embodiment, the downstream of the second throttle body 50 form a substantial part of the flow cross-section between the nozzle needle tip 31 and shaft portion 14. The longitudinal cuts 38 are made almost over the entire length of the nozzle needle tip 31, ie from the transition region 37 to near the first throttle point 12, and have largely a planar base. In the transition region 37 to the central region 34, the longitudinal cuts 38 are rounded, viewed in cross section, first with the second rounding 37b, which preferably terminates tangentially into the planar base of the longitudinal cut 38, and subsequently with the first fillet 37a, both fillets 37a, 37b the same Radius R have.

In another embodiment, the transition region 37 may be instead of two

Rounding 37a, 37b as a chamfer and paragraph - similar to Fig.l - be executed, but which are arranged only in the region of the longitudinal cuts 38.

In the embodiment shown in FIG. 2, three longitudinal slits 38 are uniformly distributed over the circumference of the nozzle needle tip 31 and are arranged so that the longitudinal slices 38 in the transition region 37 each lead into a throttle slit 40. Demzufol- ge changed in other embodiments, the number of longitudinal grinding 38 analogous to the number of Drosselanschliffe 40 to two or four longitudinal cuts 38th

In the region of the nozzle needle tip 31 lying in the shaft region 14, which is not provided with longitudinal cuts 38, the nozzle needle tip 31 has a cylindrical shape with the same diameter d ₃₅ as the jacket surface 35 of the middle region 34; As a result, the nozzle needle tip 31 can be guided well in the nozzle body 10 during strokes of the nozzle needle 30.

3 shows for better illustration the detail III of FIG. 2 in the area of the second throttle point 50 with the nozzle needle 30 closed.

The second orifice 50 is formed between the inner surface 15 of the shank portion 14 of diameter d _i5 and the throttle bevels 40 of the central portion 34 over the length Si.

The concave transition region 37 of the nozzle needle 30 between the central region 34 and nozzle needle tip 31 is divided into a first rounding 37 a, which adjoins the central region 34, and a second rounding 37 b, which adjoins the nozzle needle tip 31. The first rounding 37a extends at an angle α to the lateral surface 35 or to the groove bottom 41 and connects directly to this. The second fillet 37b is formed between the first fillet 37a and the nozzle needle tip 31; Their imaginary tangential outlet runs at an angle β to the lateral surface 35 or to the groove base 41. The cylindrical lateral surface 35 is arranged coaxially to a nozzle needle axis 39 of the nozzle needle 30. Both fillets 37a, 37b have the same radius R, with which the Nutstirnseite 42 is rounded. However, the arc length of the first fillet 37a is smaller than the arc length of the second fillet 37b.

In the illustrated closed position of the nozzle needle 30, the first partial stroke Si, the second partial stroke s ₂ and the maximum stroke v of the nozzle needle 30 are outlined. As an axial reference 16 along the nozzle needle axis 39 to the edge between the nozzle body shoulder 17 and the inner surface 15 of the shaft portion 14 of the nozzle body 10 is used, extending from the combustion chamber in the direction away from the diameter of the bore of the nozzle body 10 and thus the volume of the pressure chamber 20 increases : The first partial stroke Si describes the axial distance along the nozzle needle axis 39 from the reference 16 to the transition from the throttle pin 40 to the first rounding 37a.

The second partial stroke s ₂ describes the axial distance along the nozzle needle axis 39 from the reference 16 to the transition from the first rounding 37 a to the second rounding 37 b.

Depending on the application, the maximum stroke v can have a height which leads from the cover 16 either to the second rounding 37b or into the nozzle needle tip 31.

4 shows the detail IV of Figure 3. Shown are the first angle α of the first rounding 37a and the second angle ß of the second rounding 37b to the groove bottom 41 of the Drosselanschliffs 40, which is formed in the central region 34 of the nozzle needle 30. The dashed lines each show the tangential outlet of the two fillets as a reference for the two angles. Ideally, 0 ° <α <β <90 °. In the process, the groove base 41 runs parallel to the longitudinal axis of the nozzle needle 30, and thus also parallel to the lateral surface 35 of the central region 34, within the scope of manufacturing accuracy.

FIG. 5 shows a production step for manufacturing the nozzle needle 30 from the embodiment of FIGS. 2-4: a first rounding 37a is ground. In this case, a grinding tool 200 having a convex radius R is brought into abutment with the first rounding 37a of a longitudinal cut 38. For machining the planar surfaces of the longitudinal cuts 38, the grinding tool 200 likewise has a planar surface which, however, is arranged at a distance from the planar surface of the longitudinal cut 38 in the illustrated production step. In a next step, the throttle section 40 belonging to the longitudinal section 38 can be manufactured by machining the planar surface of the grinding tool 200 the groove base 41 and the convex radius R the groove end side 42.

The operation of the fuel injection valve 100 according to the invention is as follows:

In the closed position of the nozzle needle 30, the nozzle needle tip 31 is in contact with the nozzle needle seat 11, so that the injection openings 19 from the pressure chamber 20 and the lower pressure chamber 22 are separated and therefore no fuel is injected into the combustion chamber 110. The second throttle body 50 is formed between the inner surface 15 of the shaft portion 14 with diameter d _i5 and the lateral surface 35 of the central region 34 with diameter d ₃₅ and the throttle grindings 40 over the length Si corresponding to the first partial stroke Si. At the beginning of the injection process, the nozzle needle 30 via a control device, for example, lowering a pressure on a combustion chamber 110 opposite end face of the nozzle needle 30, lifted from the nozzle needle seat 31, so that the hydraulic connection between the pressure chamber 20 and lower pressure chamber 22 and injection ports 19 is opened and the first throttle 12 is formed. With increasing stroke of the nozzle needle 30, the flow cross-section increases through the first throttle point 12, which is thus dependent on the stroke.

Until the first partial stroke Si, which is advantageously less than 20% of the maximum stroke v of the nozzle needle 30, the gap width of the second throttle body 50 remains unchanged and thus stroke-independent:

In the case of the embodiment of FIG. 1: (di ₅ -d ₃₅ ) / 2 over the entire circumference of the central region 34

In the case of the embodiment of Figures 2-4: ~ h over the width of Drosselanschliffe 40th

Usually, the first partial stroke Si is less than 20% of the maximum stroke v of the nozzle needle 30, in the case of fuel injection valves for passenger car engines, for example, less than 80 μηη. Furthermore, until the first partial stroke Si, the flow cross section through the first throttle 12 is less than the flow cross section through the injection port 19, or in the case of multiple injection ports 19 less than the summed flow cross section through all injection ports 19, preferably more than 50% lower.

When the first partial stroke Si is reached, the flow cross-section of the first throttle point 12 is at least approximately as large as the flow cross section of the second throttle point 50. The injection characteristic of the fuel injection valve 100 up to the first partial stroke Si therefore primarily determines the first throttle point 12 and the second throttle point 50.

From the first partial stroke Si, the flow cross-section of the second throttle point 50, which thus becomes stroke-dependent, also expands. Depending on the exemplary embodiment, this can be achieved, for example, by means of a transition region 37 designed as a chamfer at the angle α over the entire circumference of the nozzle needle 30, as shown in FIG. 1, or by a rounded transition region 37 with a first rounding 37a, either over the entire circumference the nozzle needle 30 distributed, or arranged in sections in the region of longitudinal cuts 38 - as shown in Figures 2-5 - implemented: the nozzle needle 30 tapers in the transition region 37 - either over the entire circumference or in the region of the longitudinal grind 38 - and thereby increases the width of the second throttle body 50 as soon as the transition region forms the second throttle body 50, ie as soon as the transition region 37 during the stroke movement of the nozzle needle 30th the axial reference 16 passes through.

Even when the second partial stroke s ₂ is reached, the flow cross section of the first throttle point 12 is at least approximately as large as the flow cross section of the second throttle point 50. Thus, for the entire stroke range between the first partial stroke Si and the second partial stroke s ₂ , the flow cross section of the first Throttle 12 is at least approximately as large as the flow area of the second throttle body 50. As a result, during the closing process of the nozzle needle 30, a large part of the momentum of the fuel flowing through the pressure chamber 20 in the direction of the injection openings 19 at the second throttle point 50 is reduced in this stroke region, without being in the

Small quantity operation in the same stroke range downstream of the second throttle point 50, the pressure chamber 20 runs empty.

From the second partial stroke s ₂ , the flow cross-section of the second throttle body 50 increases more than between the first partial stroke Si and the second partial stroke s ₂ . Depending on the application, this can be implemented, for example, via a vertical shoulder on the nozzle needle 30 -as shown in FIG. 1 -or a second rounding 37b in the transition region 37 -as shown in FIGS. 2-5-depending on the embodiment, again over the entire circumference the nozzle needle 30 or only in the region of longitudinal cuts 38:

Practically exists for the fuel flow through the pressure chamber 20 to the injection ports 19, the second throttle body 50 from strokes of the nozzle needle 30, which are larger than the second Partial stroke s ₂ , not in this embodiment. The upper pressure chamber 21 and the lower pressure chamber 22 have the same pressure.

The second rounding 37b of the exemplary embodiments of FIGS. 2-5 leads to a greater increase in the flow cross section of the second throttle point 50 than in the previous stroke phase between the first partial stroke Si and the second partial stroke s ₂ , but not to a sudden increase. For this purpose, the second rounding 37b has a tangential angle β to the lateral surface 35 or to the groove bottom 41, which is greater than the tangential angle α the first rounding 37a to the lateral surface 35 and the groove bottom 41 but less than or equal to 90 °. Advantageously, both fillets 37a and 37b are made with the same radius R, but the second fillet 37b has a longer arc length.

When the maximum lift v is reached, the fuel is restricted in its flow from the pressure chamber 20 into the combustion chamber 110 almost exclusively through the injection openings 19. Both at the first throttle point 12 and the second throttle point 50 virtually no pressure drop takes place. The injection characteristic of the fuel injection valve 100 thus determines the injection openings 19 at the maximum stroke v. To this end, the nozzle needle 30 is lifted from the nozzle needle seat 11 so far that in the region of the second throttle body 50 the edge of the nozzle body shoulder 17 faces the inner surface 15 of the nozzle body 10 at the level of the axial reference 16, a region of the nozzle needle 30 is opposite, which has a correspondingly smaller cross-section than the diameter determined by the diameter d ₃₅ , so that a comparatively large gap between the nozzle body 10 and the nozzle needle 30 is formed:

In the exemplary embodiment of FIG. 1, this region is the nozzle needle tip 31 that is tapered due to the vertical shoulder relative to the transition region 37.

In the exemplary embodiments of FIGS. 2-5, this may likewise be the nozzle needle tip 31, or else a region in the transition region 37 which is at the level of the second

Rounding 37b is located.

The following describes production steps with a grinding tool 200 for the nozzle needle 30, as can be used for the embodiment of FIGS. 2-5:

At the beginning, the cylindrical lateral surface 35 of the central region 34 and the nozzle needle tip 31 are made cylindrical to the diameter d ₃₅ . Here, a less high manufacturing accuracy is required to achieve a defined flow cross-section through the second throttle point 50 to the first partial stroke Si, as if the second throttle body 50 would be formed over the entire circumference of the nozzle needle 30, since then still the Drosselanschliffe 40 are made. This manufacturing step can be performed with the grinding tool 200; however, it is advantageously carried out by a turning operation in an upstream production step. In the next production step, the planar surface of a longitudinal grinding 38 on the nozzle needle tip is first ground with the grinding tool 200.

Subsequently or in the same manufacturing step, the second rounding 37b is ground at the outlet of the longitudinal cut 38. For this purpose, the grinding tool 200 has a convex radius R which corresponds to the concave radius R of the second rounding 37b, ie forms a negative mold of the second rounding 37b.

In the following manufacturing step, the first rounding 37a is ground by the radius R of the grinding tool 200, while the grinding tool 200 is lifted off the planar surface of the longitudinal cut 38, as can be seen in FIG. Not all of the radius R of the grinding tool 200 is engaged with the nozzle needle 30, so that the arc length of the first fillet 37a is made shorter than the arc length of the second fillet 37b.

3b) Subsequently, a throttle pin 40 is ground. In this case, the planar groove base 41 is ground with the planar surface of the grinding tool 200 and the Nutstirnseite 42 with the convex radius R of the grinding tool 200, wherein only a small portion of the grinding tool 200 is in engagement with the nozzle needle 30.

The preceding manufacturing steps 1 to 3b are then repeated for the remaining longitudinal cuts 38 and throttle grindings 40. Advantageously, a total of three longitudinal slits 38 and three throttle slits 40 are made, which are arranged uniformly distributed over the circumference of the nozzle needle tip 31, wherein a respective Drosselanschliff 40 terminates in a first rounding 37a of a longitudinal section 38.

Advantageously, steps 1) and 2) are performed together in one manufacturing step, since the grinding tool 200 has the corresponding negative mold of planar surface of the longitudinal cut 38 and second fillet 37b.

It is also conceivable other than the manufacturing sequence described above: for example, the cylindrical surface 35 and the cylindrical portion of the nozzle needle tip 31 can be made only at the end of the production chain to the diameter d ₃₅ , the manufacturing order would then l-2-3-3b -4-0. Or Drosselanschliffe 40, longitudinal grinding 38, fillets 37 and outer surface 35 are made from the outside in, in the order 0-3b-3-2-l-4.

Claims

claims

A fuel injector (100) for internal combustion engines for injecting fuel under high pressure with a nozzle body (10) formed in the pressure chamber (20) in which a nozzle needle (30) is arranged longitudinally displaceable, wherein one of the nozzle needle (30) formed nozzle needle tip (31) cooperates with a nozzle needle seat (11) formed on the nozzle body (10) and thereby opens and closes at least one injection opening (19), wherein when lifting the nozzle needle tip (31) from the nozzle needle seat (11) between the nozzle needle tip (31) and the nozzle needle seat (11) a first throttle point (12) is formed, wherein on the nozzle needle (30) formed central region (34) with a nozzle body (10) formed in the shaft region (14) on the inner surface (15) form a second throttle point (50) , characterized in that the second throttle point (50) over a first partial stroke (si) of the nozzle needle (30) has a constant Durchflußquerschnit t.

2. Fuel injection valve (100) according to claim 1, characterized in that the first partial stroke (sj of the nozzle needle (30) is less than 20% of a maximum stroke (v) of the nozzle needle (30).

3. Fuel injection valve (100) according to claim 1 or 2, characterized in that the central region (34) has at least one, but preferably three extending in the longitudinal direction of the nozzle needle axis Drosselanschliffe (40) of the depth h, with the inner surface (15) the second Form throttle restriction (50).

4. Fuel injection valve (100) according to claim 3, characterized in that the at least one Drosselanschliff (40) on a Nutstirnseite (42) with the radius R to a cylindrical outer surface (35) of the central region (34) is rounded.

5. Fuel injection valve according to one of the preceding claims, characterized in that a plurality of injection openings (19) are present and during the first partial stroke (sj the flow cross-section of the first throttle point (12) is less than the summed flow area of all injection ports (19), preferably by more than 50% lower.

6. Fuel injection valve (100) according to claim 5, characterized in that the

Flow cross section of the second throttle point (50) when reaching the first partial stroke (si) of the nozzle needle (30) is at least approximately as large as the flow cross-section of the first throttle point (12).

7. Fuel injection valve (100) according to claim 6, characterized in that the second throttle point (50) between the first partial stroke (si) and a second partial stroke (s ₂ ) of the nozzle needle (30) which is greater than the first partial stroke (si) and smaller than the maximum stroke

(v) is, has a steadily expanding flow area.

8. Fuel injection valve (100) according to claim 7, characterized in that the

Flow cross-section of the second throttle point (50) from the second partial stroke (s ₂ ) is greater than the flow cross-section of the first throttle point (12).

9. The fuel injection valve (100) according to claim 7 or 8, characterized in that the central region (34) in the region of the second throttle point (50) has a nozzle needle tip (31) towards tapered transition region (37), wherein the transition region (37). is designed either as a chamfer, preferably at an angle α of 35 ° to 80 ° to the cylindrical lateral surface (35) of the central region (34), or in cross-section at least a concave circular arc shape having radius R.

10. Fuel injection valve (100) according to claim 9, characterized in that the nozzle needle tip (31) between transition region (37) and nozzle needle seat (11) has longitudinal cuts (38) which extend in the direction of the nozzle needle axis.

11. Fuel injection valve (100) according to claim 10, characterized in that the longitudinal cuts (38) to the transition region (37) are rounded in each case with the radius R.

12. Fuel injection valve (100) according to one of claims 7 to 11, characterized in that the maximum stroke (v) of the nozzle needle (30) of the summed flow cross-section of all injection ports (19) is less than the flow area of first throttle point (12) and is less than the flow area of the second throttle point (50).

13. A method for producing a fuel injection valve (100) according to claim 1, wherein the nozzle needle tip (31) between the central region (34) and nozzle needle seat (11) has longitudinal cuts (38) which extend in the direction of the nozzle needle axis, wherein the longitudinal cuts (38) for Center region (34) out in a concave transition region (37) are rounded, which has a first rounding (37 a) and a second rounding (37 b), wherein the second throttle point (50) between the first partial stroke (si) and a second partial stroke ( s ₂ ) of the nozzle needle, which is greater than the first partial stroke (si), has a continuously widening flow cross-section, characterized by the following method steps, which are carried out with a grinding tool (200):

Grinding the planar surface of a longitudinal cut (38),

Grinding the second rounding (37b), which is made by a convex radius R of the grinding tool (200) together with the planar surface,

Grinding the first rounding (37a) through the radius R of the grinding tool (200) while the grinding tool (200) is lifted off the planar surface of the longitudinal cut (38),

Repeating the previous steps for all longitudinal cuts (38).

14. A method for producing a fuel injection valve according to claim 13, wherein the middle region has throttle depths (40) running in the longitudinal direction of the nozzle needle axis and each terminating in the first rounding (37a) of the longitudinal cuts (38), characterized by the following method steps, which are carried out with a grinding tool (200):

3b) grinding the Drosselanschliffs (40) together with a at the Drosselanschliff (40) formed Nutstirnseite (42), which also has the radius R. Repeating the previous steps for all longitudinal cuts (38) and all throttle cuts (40).

15. The method according to claim 13 or 14, characterized in that the first

Rounding (37a) at a first angle α and the second rounding (37b) are ground at a second angle β to the cylindrical surface (35), where α <β, and the first rounding (37a) and the second rounding (37b) have the same radius R, wherein the second rounding (37b) is ground expiring tangential to the longitudinal cuts (38) and the grinding tool (200) has a corresponding negative mold.