EP2314860B1 - Fuel injector - Google Patents

Abstract

The fuel injector, particularly common rail injector has an injection valve element (7) adjustable in axial direction between a closing position and a releasing position opened in the fuel current into the combustion chamber. A squeezing gap (31) is limited on a side of a valve needle (17) opposite to an anchor (19).

Description

State of the art

The invention relates to a fuel injector, in particular a common rail injector, for injecting fuel into a combustion chamber of an internal combustion engine according to the preamble of claim 1.

Compliance with emission limits has the highest priority in the development of internal combustion engines. Especially the common rail injection system has made a decisive contribution to the reduction of pollutants. The advantage of the common-rail systems lies in their independence of the injection pressure of speed and load. For the compliance with future exhaust emission limits, however, a significant increase of the injection pressure is necessary, especially for diesel engines.

The latest fuel injectors for highest injection pressures are leak-free, by dispensing with a permanent low-pressure stage on the injection valve element. Due to the lack of this low-pressure stage only small needle closing forces are available. This leads to steep maps and thus to a poor Kleinstmengenfähigkeit. This disadvantage can be compensated with very fast switching control valves (servo valves).

However, fast-switching control valves often have the problem that due to a Prellers of the control valve element map ripples occur. The control valve element bounce appears in a hard stop (metal to metal) in conjunction with a very fast control valve element (valve needle). Straight bounces have a particularly negative impact on the function of the fuel injector and generally lead to large Hub / Hub scattering. Unlike the upper stroke stop can be on the control valve seat due to its sealing function, no squish gap can be realized to minimize the impact momentum.

In the DE 10 2007 060 396 A1 The Applicant has indicated some mechanical approaches to minimizing closing bounces in fuel injectors. Among other things, it is known from the document, the armature plate relative to the valve needle to arrange adjustable, so that the armature plate can continue their axial movement down after the valve needle is already taken on her valve seat. The movement of the armature plate is braked by a nip, which forms between the armature plate and a separate from the valve needle ring part, which is held on the valve needle.

In the DE 10 2007 060 395 A1 In addition, an injection valve is disclosed which comprises a control valve with a sleeve-shaped valve closing element which is moved by means of a magnetic actuator.

Disclosure of the invention

The invention has for its object to provide a fuel injector, which is characterized on the one hand by a simple structure and on the other hand by a minimized closing bounce. Preferably, the composite anchor and valve needle should be mounted in the simplest way.

This object is achieved in a fuel injector with the features of claim 1. Advantageous developments of the invention are specified in the subclaims.

The invention is based on the idea to minimize the bounce due to the fact that the armature plate designed as an anchor on the side facing away from the electromagnetic actuator a stop or overstroke stop is assigned, which is formed directly from the valve needle, ie the axially closable control valve element. As a result, a nip for braking the armature movement can form directly between the armature and the valve needle, thereby dispensing with a separate ring element used in the prior art and thereby simplifying the structure of the fuel injector. At one after the concept of Invention formed fuel injector acts on the control valve seat only the pulse of the valve needle while the armature swinging in the direction of overstroke. Thus, the impact momentum and the maximum force is reduced, which minimizes both the bounce as well as the wear. The provided in a trained according to the concept of the invention fuel injector overstroke stop, which is formed directly from the valve needle, limits the swinging of the armature, whereby short injection intervals can be realized. It is thus ensured that the resonant anchor is transferred back to its initial position within a very short time. Due to the fact that the overstroke stop is limited directly by the valve needle, the overstroke stop results from the thickness extension of the preferably plate-shaped armature and the armature guide length, which is advantageously ground into a preferably provided, later to be explained anchor guide part. These two dimensions can be very precisely measured, ground or manufactured due to the parallelism of the contact surfaces. The overtravel stop can thus be measured before assembly and, if necessary, adjusted precisely by selection groups. An elaborate setting process, in which the overstroke stop must be determined and corrected in the assembled state, is not required due to the component-independent manufacturing dimensions.

In a further development of the invention is advantageously provided that the valve needle is sleeve-shaped and the nip between the armature and valve needle of a, preferably upper, annular surface of the sleeve-shaped valve needle is limited. The formation of the preferably a stepped bore having valve needle as a sleeve makes it possible in a comparatively simple manner that the control valve is pressure balanced in the closed state in the axial direction, with the aim to be able to use smaller and less powerful electromagnetic actuators.

Very particular preference is given to an alternative embodiment of the fuel injector in which the nip formed between the armature and the valve sleeve for damping the impact of the armature by means of a leakage amount, preferably from a hydraulic coupler to be explained later, since the nip only fulfill its damping function can if it is filled with fuel.

According to the invention, it is provided that for the operative connection of the armature and the valve needle, a hydraulic coupler is provided, which causes the valve needle is adjusted in energizing the electromagnetic actuator together with the preferably plate-shaped armature in the axial direction towards the electromagnetic actuator. It is particularly preferred if a coupler volume of the hydraulic coupler is arranged such that the leaking from this leakage (fuel leakage) is that leakage that flushes the nip, so ensures that the damping function of the nip is maintained. It is particularly expedient that the coupler volume is checked to ensure the coupler function of a high pressure leakage from a limiting of the sleeve-shaped valve needle valve chamber.

Particularly advantageous with regard to the realization of a very simple structure is a variant in which the coupler volume of the hydraulic coupler is axially sealed by a guide gap, said guide gap is preferably arranged radially between the valve needle designed as a sleeve and a bolt projecting axially into the valve needle wherein the bolt preferably has the function of sealing a valve chamber of the control valve in an axial upward direction. For this purpose, the bolt is supported for example on an injector cover or the magnet assembly. It is particularly useful if the coupler volume, in particular in the axial direction is sealed down from a guide gap which is formed between an armature guide member and the sleeve formed as a valve needle. Thus, in addition to the armature and the valve needle, a further component, namely an armature guide part, which is even more preferably inserted into a stepped bore of the valve needle and, on the one hand, has the function of guiding the armature and, on the other hand, a moving component of the hydraulic coupler forms, which sucks the valve needle when energizing the electromagnetic actuator, ie entraining. Advantageously, the armature guide member is relatively adjustable to the valve needle to suck the valve needle in an upward movement and thereby be able to move upward.

As already explained, it is particularly preferred if the armature, the armature guide member and the valve needle can be mounted and axially adjusted by nesting are arranged. Preferably, additional fastening means are dispensed with. The fact that the parts are fixed to each other only by plugging together, easy assembly is given and disassembly is possible at any time.

In order to move the valve needle away from the electromagnetic actuator towards its control valve seat, which is preferably formed on a throttle plate, a closing spring is preferably provided, which is even more preferably supported axially on the armature guide part. It is now particularly useful to provide in addition to the closing spring acting in the opposite direction closing spring, which is supported axially, preferably from below, to the anchor. At the moment of Ankerdurchschwingens the valve needle is thereby pushed back exclusively by the closing spring, while the closing force results from the difference of closing spring and positioning spring. As a result, a greater spring force acts during the rebound than before the valve impact, whereby the locking bounce is further reduced.

In a further development of the invention is advantageously provided that the armature is formed of a material that is different from the valve needle forming material. It is therefore possible due to the multi-part design, the anchor from a special, the magnetic flux optimizing, i. to produce reinforcing magnetic material, for example, a sintered material, in particular having a high ohmic resistance. Overall, can be reduced by a choice of different materials, the total weight and the magnetic force can be increased.

It seems particularly expedient to realize a further (preferably upper) nip for minimizing bouncing burrs in addition to the nip slit minimizing the nip. In this case, this nip can be realized for example between armature and magnet assembly, in particular between the armature and an inner yoke of the magnet assembly.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. This shows in the only one Fig. 1 partially one Fuel injector for injecting fuel in a combustion chamber of an internal combustion engine.

In Fig. 1 is a section of a trained as a common-rail injector fuel injector 1 for injecting fuel in a combustion chamber of an internal combustion engine shown. The fuel injector 1 is a so-called leakage-free injector, ie an injector without a permanent low-pressure stage on the injection valve element - leakage in the servo valve is inevitable in the embodiment shown.

A high pressure pump 2 delivers fuel from a reservoir 3 in a high-pressure fuel storage 4 (Rail). In this fuel, especially diesel, is stored under high pressure of over 2000bar in this embodiment. To the high-pressure accumulator 4, the fuel injector 1 is connected via other, not shown, fuel injectors via a supply line. The supply line 5 opens into a pressure chamber 6, in which a one-piece, only partially illustrated injection valve element 7 is guided axially adjustable. During an injection process, the fuel flows from the pressure chamber 6 in the axial direction past the injection valve element 7 to nozzle bores of a nozzle hole arrangement (not shown) into the combustion chamber of the internal combustion engine. The fuel injector 1 is connected via an injector return port 8 to a return line 9. About this return line 9, a later to be explained control amount of fuel flow from the fuel injector 1 to the reservoir 3 and are fed back from there from the high pressure circuit.

From a plane in the drawing upper side of the injection valve element 7, a control chamber 10 (servo chamber) is limited, which is supplied via an introduced in a lower sleeve-shaped portion 11 of a throttle plate 12 inlet throttle 13 with high-pressure fuel from the pressure chamber 6. The sleeve-shaped portion 11 bounds the control chamber 10 radially outwardly, which is connected via a discharge throttle 14, which is also incorporated in the throttle plate 12, with a valve chamber 15 of a control valve 16 (servo valve). The valve chamber 15 is bounded radially on the outside by a sleeve-shaped valve needle 17 (control valve element), which is equipped with a stepped bore 18. The valve needle 17 is formed with an anchor plate An armature 19 operatively connected via a later to be explained hydraulic coupler 20, so that the valve needle is lifted when energized an electromagnetic actuator 21 from the control valve seat 22 and adjusted in the direction of the actuator 21, which in turn hydraulically the valve chamber 15 with a low pressure region 23 of the fuel injector. 1 is connected. When the control valve is open, the fuel flowing out of the valve chamber 22 flows via radial bores 27 in the annular extension 25 into an armature chamber 28 belonging to the low-pressure region 23. The flow cross-sections of the inlet throttle 13 and the outlet throttle 14 are matched to one another such that when the control valve 16 is open there is a net outflow of fuel resulting in the control chamber 10, whereby the pressure in the control chamber 10 drops rapidly, which in turn causes the injection valve element 7 lifts off from its injector element seat, not shown, and can flow in the sequence of fuel from the pressure chamber 6 into the combustion chamber.

To end the injection process, the energization of the electromagnetic actuator 21 is interrupted, whereby the valve needle 17 is pressed by a closing spring 24 axially downward on the control valve seat 22.

Out Fig. 1 It can be seen that the, a lower biting edge having valve needle 17 is guided in a lower portion on the outer circumference in an annular extension 25 of the throttle plate 12.

Next is out Fig. 1 can be seen that in the valve needle 17, a bolt 26 protrudes in the axial direction from top to bottom and the valve chamber 15 seals in the axial direction upwards. Since act on the valve needle 17 in the closed state, no axial forces, the control valve 16 is referred to as pressure-balanced valve in the axial direction.

As it turned out Fig. 1 results, the plate-shaped armature 19 is formed as a separate component from the valve needle 17. The armature 19 is not arranged stationary to the valve needle 17, but arranged relative to the valve needle 17 adjustable. For this purpose, the plate-shaped armature 19 is not guided on the valve needle 17 but with its inner circumference on the outer circumference of a sleeve-shaped armature guide member 29, which is inserted axially into the stepped bore 18, more precisely in the upper, ie larger diameter portion of the stepped bore 18 of the valve needle 17 is. With a ridge plate 30, the armature guide member 29 projects beyond a central anchor hole in the radial direction, so that the armature 19, the armature guide member 29 and thus, as will be explained later, via the hydraulic coupler 20, the valve needle 17 moves in its upward movement.

Out Fig. 1 It further results that, when the valve needle 17 is hammered on its control valve seat 22 and the armature 19 moves further down in the direction of the valve needle 17, a nip 31 axially between a bottom of the armature 19 and an upper, end face annular surface 32 of the valve needle 17 trains. The nip 31 "destroys" the kinetic energy of the armature 19 and ensures a "soft" impact on the annular surface 32, which forms a stop or overstroke stop for the armature 19.

The hydraulic coupler 20, more precisely a coupler volume of the coupler 20, is bounded axially upwardly from a lower end face of the armature guide member 29 and axially downwardly from a step or annular shoulder of the valve needle 17. The coupler volume is sealed in an upward axial direction by one the first guide gap 33, which is limited in the radial direction of the valve needle 17 and the outer periphery of the armature guide member 29. In the axial direction down the coupler volume is sealed by a second guide gap 34, radially between the pin 26 and the inner circumference of the valve needle 17, more precisely is limited by the bore portion of smaller diameter. The function of the coupler 20 can only be guaranteed if it is always filled with fuel. This is achieved in the exemplary embodiment shown by the fact that the amount of leakage, which flows out of the valve chamber 15 via the second guide gap 34, flows into the volume of the coupler. The leakage quantity then flows further into the first guide gap 33 for the lower overstroke stop, ie into the nip 31. The coupler volume is thus permanently purged with fuel. The coupler volume of the hydraulic coupler 20 is thus arranged such that a leaking from this via the first guide gap 33 leakage directly empties into the nip 31 and flows and rinses in this way, so ensure that the nip 31 filled with fuel is, so that this can exercise its damping function. The first guide gap 33 and a third guide gap 36 radially between the inner circumference of the armature guide part 29 and the bolt 26 are low pressure-sealing guides and are preferably characterized by a The gap between the armature guide part 29 and the valve needle 17 resulting from the upward movement of the armature 19 and thus the armature guide part 29 ensures that the latter is lifted from its control valve seat 22 when the electromagnetic actuator 21 is energized, from which the opening movement of the control valve 16 results.

The armature 19 is associated with a positioning spring 35 which has a larger diameter, but a lower spring constant than the closing spring 24. The positioning spring 35 is supported at one end on the underside of the armature 19 and the other end on an upper side of the throttle plate 12.

To minimize bouncing on an upper stroke stop 37, an upper nip 38 is realized, which is located in the embodiment shown between a chromium layer on the armature and an inner pole 39 of the electromagnetic actuator, more precisely the magnet group.

Claims (9)

1. Fuel injector, in particular common rail injector, for injecting fuel into a combustion chamber of an internal combustion engine, having an injection valve element (7) which can be adjusted in the axial direction between a closed position and an open position which releases the flow of fuel into the combustion chamber, which injection valve element (7) is assigned a control chamber (10) which can be hydraulically connected to a low-pressure region (23) of the injector by means of a control valve (16) which has a valve needle (17) which can be adjusted axially onto a control valve seat (22), wherein an electromagnetic actuator (21) is assigned an armature (19) which can be axially adjusted therewith, is operatively connected to the valve needle (17) and is arranged so as to be adjustable axially in relation to the valve needle (17) in such a way that after the valve needle (17) impacts against the control valve seat (22) the armature (19) continues to move in the direction of the control valve seat (22), wherein the armature (19) is assigned, on a side facing away from the actuator (21), a squeeze gap (31) which is bounded by the armature (19) and has the purpose of damping impacts, wherein the squeeze gap (31) is bounded, on the side opposite the armature (19), by the valve needle (17), characterized in that the armature (19) is operatively connected to the valve needle (17) via a hydraulic coupler (20).
2. Fuel injector according to Claim 1, characterized in that the squeeze gap (31) is bounded by a, preferably upper, annular face of the sleeve-shaped valve needle (17).
3. Fuel injector according to one of Claims 1 or 2, characterized in that the squeeze gap (31) can be rinsed by a fuel leakage.
4. Fuel injector according to Claim 1, characterized in that a coupler volume of the hydraulic coupler (20) is arranged in such a way that the fuel leakage which emerges therefrom rinses the squeeze gap (31).
5. Fuel injector according to one of Claims 1 or 4, characterized in that the coupler volume of the hydraulic coupler (20) is sealed axially by a guide gap (34) radially between the valve needle (17) embodied as a sleeve and a bolt (26) projecting axially into the valve needle (17) and/or a guide gap (33) between an armature guide part (29) and the valve needle (17) which is embodied as a sleeve.
6. Fuel injector according to one of the preceding claims, characterized in that the armature (19), an armature guide part (29), which guides the armature (19) during its axial movement, and the valve needle (17) are mounted by plugging one into the other.
7. Fuel injector according to one of the preceding claims, characterized in that the valve needle (17) is assigned a closing spring (24), and the armature (19) is assigned a positioning spring (35) which spring-loads the armature (19) in the direction of the actuator (21).
8. Fuel injector according to one of the preceding claims, characterized in that the armature (19) is embodied from material other than the valve needle (17), in particular from a material which optimises the magnetic flux.
9. Fuel injector according to one of the preceding claims, characterized in that in order to minimize opening bounce an upper squeeze gap (38) is provided between the armature (19) and the electromagnetic actuator (21).

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