EP2206912B1 - Fuel injector - Google Patents

Abstract

The fuel injector has a multi-part injection valve element (18) adjustable between a closed and an open position. A part (19) is guided in another part (24), and the coupling volume (50) is connected with an injector volume (12) by a choke arrangement (52), which is formed such that the discharge volume flow increases only marginally with increasing pressure difference between the coupling volume and injector volume.

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.

Hub-controlled common rail injectors whose injection valve element is servo-operated are known. Piezo and solenoid valves are used as pressure actuators, with which the servo circuit is controlled. For rapid needle closure, a permanent low pressure stage is often provided which exerts a permanent, closing hydraulic force on the needle. The disadvantage is the high leakage, which occurs between the high pressure and the low pressure stage. Leakage inevitably leads to the requirement for higher pump performance and thus to sacrifice in the efficiency of the system. This situation is problematic especially at high pressures. For this reason, the latest injectors are designed leak-free for highest injection pressures.

In contrast to conventional designs, these so-called leak-free fuel injectors do not have a permanent low-pressure stage acting in the closing direction, which eliminates the leaks caused thereby. Due to the elimination of the low pressure stage, two-piece injection valve elements of the type that are used in practice for use fuel injectors used with low-pressure stage, no longer be used.

While the two injection valve element parts (control rod and nozzle needle) are pressed in today's series injectors with low pressure stage by the resulting pressure forces on each other, a separate positive or non-positive connection must be made at leak-free fuel injectors. For the coupling of two injection valve elements, it has become known to provide a hydraulic coupler volume axially between them. In this case, the coupler volume is usually realized in a coupler sleeve in which one of the injection valve element parts is guided. In this case, the coupler volume is reduced by pushing out of fuel through the guide gap between the guided in the sleeve injection valve member part and the sleeve.

Injectors of this kind are made DE 102007 001 363 A known.

Disclosure of the invention

The invention has for its object to provide a simply constructed fuel injector, in which the coupling of the at least two injection valve element parts is realized with the lowest possible number of components.

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

The invention is based on the idea to introduce two relatively adjustable parts of the injection valve element into one another, so as to be able to dispense with a separate guide sleeve, as used in the prior art, as well as a spring-loaded spring the spring sleeve. In contrast to the provision of a one-piece, long injection valve element, the at least, preferably exclusively two-part, construction has the advantage that the production of the individual injection valve element parts in total is less complicated and thus less expensive than the production of a one-piece long injection valve element. In addition, existing production lines can be maintained and the existing logistics, which is aligned with a multi-part injection valve element. The invention has also recognized that it would result in a solution with in-run injector element parts to a constant increase in the Kopplervolumens in operation of the fuel injector, if the coupler volume would be connected exclusively via a guide gap between the two parts with a Injektorvolumen, since the flow resistance of the guide gap is proportional to the applied pressure difference , The fact that the flow resistance of such a guide gap is linearly related to the magnitude of the pressure difference between the coupler volume and injector volume would cause much fuel to be drawn from the injector volume upon opening of the fuel injector due to the very low pressure in the coupler volume and emptying the Kopplervolumens during the closing process due to the available (short) time would no longer be possible. In extreme cases, this would lead to an axial caulking of the injection valve element in the fuel injector and thus to an adjustment of the fuel injector. In order to avoid such an effect, the coupler volume is additionally or alternatively connected to a guide gap via at least one throttle arrangement with the injector volume in a fuel injector designed according to the concept of the invention, wherein the throttle arrangement is designed such that the fuel volume flow flowing through it ( Flow volume flow) is not proportional to the pressure difference between the coupler volume and injector volume as a guide gap behaves, but disproportionately. In other words, the flow volume flow passing through the throttle assembly does not increase to the same extent as a pressure difference between the volume of the coupler and the injector volume, ie, the flow volume flow and the pressure difference are not linearly related. In other words, it is preferred if the flow volume flow increase becomes smaller and smaller with increasing pressure difference. Ideally, the flow volume flow is proportional to the root of the pressure difference between injector volume and coupler volume. In a trained according to the concept of the invention fuel injector is achieved that even at an extremely large pressure difference between the coupler volume and injector volume at the beginning of an opening process, only a moderate amount of fuel is sucked through the throttle assembly in the coupler volume, the time during the closing process, in the the injection valve element, preferably by means of a closing spring, is moved in the direction of injection valve element seat, sufficient to the previously sucked volume of fuel through the throttle assembly be able to deliver in the injector volume, so as to restore the original state.

One possibility for the design of the throttle arrangement is to provide at least one, preferably only one, realized in particular in the first or second part, throttle bore, the throttle bore very particularly preferably in the manner of a drain throttle from a control chamber as in known servo-circuit fuel injectors is. Thus, the throttle bore is preferably a stepped bore with a diameter step, which preferably leads to the formation of a turbulent, cavitating flow within the throttle bore.

The above-mentioned diameter stage is a possibility for realizing a degressive ratio between flow volume flow and pressure difference between the coupler volume and injector volume. In principle, any throttle stages, in particular hydraulically sharp-edged throttle stages, can be realized for this purpose, preferably with a small longitudinal extension in the flow direction. Preferably, the longitudinal extension of the at least one throttle stage is designed such that a turbulent flow is formed. Under a hydraulically sharp-edged throttle stage while a length to hydraulic diameter ratio is less than or equal to 10 to understand. The following applies to the hydraulic diameter of an annular gap reactor $${\mathrm{D}}_{\mathrm{Hyd}}\mathrm{=}\mathrm{4}\mathrm{\cdot }\frac{\mathrm{durchsttr}\ddot{\mathrm{O}}\mathrm{cross\; section}}{\mathrm{throughflow}\ddot{\mathrm{O}}\mathrm{m.\; Berandungsl}\ddot{\mathrm{a}}\mathrm{nge}}\mathrm{,}$$

The boundary length in this equation is the sum of the inner and the outer boundary length.

It is particularly preferred if the throttle arrangement comprises a plurality of hydraulically connected in series (arranged) throttles. Preferably, the throttles are formed radially between the two injection valve element parts, preferably in the guide region, with which the two parts are guided into one another. As already indicated above, it is particularly preferred if the throttles are designed in such a way, ie have such a small extent in the flow direction, that the guide length is so small that forms a turbulent flow. For a laminar flow, the flow volume flow would be by the throttle arrangement proportional to the pressure difference between the coupler volume and injector volume, which should be avoided.

One possibility for forming the throttle arrangement is to provide a plurality of axially juxtaposed (parallel) grooves on one of the injection valve element parts, wherein the throttles are formed radially between the webs delimiting the grooves and the other injection valve element part. Preferably, the webs, at least approximately, sharp-edged to realize a minimum guide length and thus to force the formation of a turbulent flow. In an embodiment with a plurality of throttles arranged axially behind one another in the flow direction, it is very particularly preferred to dispense with a throttle bore in the injection valve element parts.

Particularly useful is an embodiment of the fuel injector in which the hydraulic coupler is designed as a joint, which allows a certain pivotability of the two hydraulically coupled injection valve element parts to compensate in this way tolerance-related angular errors and inclinations.

A particularly preferred possibility for forming such a pivot joint is to contour the guided injection valve element part in the region of the guide in order to allow a relative pivoting.

In a development of the invention, it is advantageously provided that the fuel injector is leak-free except for leaks which may have been realized in the region of the control valve element. For this purpose, a low-pressure stage acting on the injection valve element in the closing direction on the injection valve element is dispensed with.

Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings.

Fig. 1

ein erstes Ausführungsbeispiel eines Kraftstoff-Injektors, bei dem zwei Teile eines Einspritzventilelementes ineinander geführt und hydraulisch gekoppelt sind, wobei das Kopplervolumen über eine Drosselbohrung mit einem Injektorvolumen verbunden ist, und

Fig. 2

ein weiteres Ausführungsbeispiel eines Kraftstoff-Injektors, bei dem zwei Teile eines Einspritzventilelementes hydraulisch mit- einander gekoppelt sind, derart, dass auf eine Drosselbohrung verzichtet werden kann.

These show in:

Fig. 1

a first embodiment of a fuel injector, in which two parts of an injection valve element are guided into one another and hydraulically coupled, wherein the coupler volume is connected via a throttle bore with an injector volume, and

Fig. 2

a further embodiment of a fuel injector, in which two parts of an injection valve element are hydraulically coupled to each other, such that can be dispensed with a throttle bore.

In the figures, like elements and elements having the same function are denoted by the same reference numerals.

In Fig. 1 is a trained as a common rail injector fuel injector 1 for injecting fuel into a combustion chamber, not shown, also shown an internal combustion engine of a motor vehicle. A high pressure pump 2 delivers fuel from a reservoir 3 in a high-pressure fuel storage 4 (Rail). In this fuel, especially diesel or gasoline, under high pressure, stored in this embodiment about 2000bar. To the high-pressure fuel accumulator 4, the fuel injector 1 is connected via other, not shown, fuel injectors via a supply line 5. The supply line 5 opens into an annular space 6 radially between a valve body 7 and an injector body 8 (housing part). Via axial grooves 10 formed by bevels 9 on the outer circumference of the valve body 7, the high-pressure fuel can flow essentially unthrottled in the axial direction in the plane of the drawing down into a pressure space 11 acting as a mini-rail for pressure oscillation minimization. In an injection process, the fuel flows directly through axial passages 13 into a nozzle chamber 14 (annular space) also belonging to the injector volume 12 and out of this through at least one injection hole 15 into the combustion chamber of the internal combustion engine. The fuel injector 1 is connected via an injector return port 16 to a return line 17. About the return line 17 can be explained later on a control amount of fuel from the fuel injector 1 to the reservoir 3 drain and be fed from there from the high pressure circuit again.

Within the injector body 8, a two-part injection valve element 18 in this exemplary embodiment is arranged to be adjustable in the axial direction. The injection valve element 18 projects with its lower, designed as a nozzle needle first part 19 in a stepped bore 20 of a nozzle body 21 into it. In this, the first part 19 is guided axially displaceably with a guide portion 22. The axial channels 13 are formed by bevels 9 in the guide section 22 radially between the first part 19 and the nozzle body 21. The nozzle body 21 is screwed by means of a union nut, not shown, with the injector body 8.

The first part 19 (nozzle needle) of the injection valve element 18 is guided in an end blind bore 23 of a second part 24 (control rod) of the injection valve element 18.

As it turned out Fig. 1 furthermore, the injection valve element 18 has a closing surface 26 (sealing surface) on a (lower) tip 25 formed on the first part 19, with which the injection valve element 18 can be brought into tight contact with an injection valve element seat 27 formed inside the nozzle body 21. When the injection valve element 18 abuts against its injection valve element seat 27, ie is in a closed position, the fuel outlet from the at least one injection hole 15 is blocked. If, on the other hand, it is lifted off its injection valve element seat 27, fuel can flow from the pressure chamber 11 via the axial channels 13 and the annular chamber 14 to the injection valve element seat 27 to the injection hole 15 where it is injected substantially under high pressure (rail pressure) into the combustion chamber become.

From an upper end face 28 of the second part 24 of the injection valve element 18 and a lower in the drawing plane sleeve-shaped portion of the valve body 7, a control chamber 29 is limited, which extends over a radially extending in the sleeve-shaped portion of the valve body 7 inlet throttle 30 with high-pressure fuel from the Annulus 6 is supplied. The sleeve-shaped portion with control chamber 29 enclosed therein is enclosed radially on the outside with high-pressure fuel, so that an annular Guide gap 31 radially between the sleeve-shaped portion of the valve body 7 and the injection valve element 18, here the second part 24, is comparatively fuel-tight.

The control chamber 29 is connected via a, extending perpendicularly in the valve body 7 axial channel 32 with outlet throttle 33 with a valve chamber 34 which radially outwardly of an axially adjustable, sleeve-shaped control valve element 35 of a pressure-balanced in the axial direction in the closed state control valve 36 (servo valve) is limited. From the valve chamber 34, fuel can flow into a low-pressure region 37 of the fuel injector 1 and thence to the injector return port 16 when the sleeve-shaped control valve element 35 is lifted from its control valve element seat 38 formed on the valve body 7, i. when the control valve 36 is open. To adjust the sleeve-shaped control valve element 35 in the plane above an electromagnetic actuator 39 is provided with an electromagnet 40 which cooperates with an integrally formed with the control valve element 35 anchor plate 41 and subsequently with the sleeve-shaped control valve element 35. When energized the electromagnetic actuator 39 raises the control valve element 35 from its formed on the valve body 7, designed in this embodiment as a flat seat control valve element seat 38 from. The flow cross-sections of the inlet throttle 30 and the outlet throttle 33 are matched to one another such that when open control valve 36, a net outflow of fuel (control amount) from the control chamber 29 in the low pressure region 37 of the fuel injector 1 and from there via the Injektorrücklaufanschluss 16 and Return line 17 results in the reservoir 3. As a result, the pressure in the control chamber 29 decreases rapidly, whereby the injection valve element 18, more precisely the first part 19, lifts off from its injection valve element seat 27 so that fuel can flow out of the injector volume 12 through the injection hole 15 into the combustion chamber.

To stop the injection process, the energization of the electromagnetic actuator 39 is interrupted, whereby the sleeve-shaped control valve element 35 is adjusted by means of a control spring 42 which is supported on the armature plate 41 in the drawing plane down on its control valve element seat 38. The fuel flowing in through the inlet throttle 30 into the control chamber 29 provides for a rapid pressure increase in the control chamber 29 and thus for a force acting on the injection valve element 18 closing force. The resulting closing movement of the injection valve element 18 is assisted by a closing spring 43, which is supported at one end on a circumferential collar 44 of the second part 24 and at the other end on a lower, annular end side 45 of the valve body 7.

Out Fig. 1 It can also be seen that within a bore 46 introduced into the control valve element 35, a loose pressure pin 47 is accommodated, which is designed as a separate component from the valve body 7. The purpose of the cylindrical pressure pin 47 is to seal the valve chamber 34 in the axial direction in order to prevent fuel from the control chamber 29 being able to flow into the low-pressure region 37 when the control valve element 35 is closed, except for an unavoidable amount of leakage. The pressure pin 47 also serves to guide the control valve element 35 at its inner periphery formed by the bore 46.

As further out Fig. 1 results, it is in the fuel injector 1 to a so-called leak-free injector, which has no leakage except for a leak in the region of the control valve 36, since no permanent, acting on the injection valve element 18 in the closing direction low pressure stage is provided.

As already explained, the first part 19 is guided into the second part 24 of the injection valve element 18 and guided on the inner circumference of the blind hole 23. Axially between an upper surface 48 in the plane of the drawing and the upper surface 49 of the blind bore 23 in the plane of the drawing, a hydraulic coupler volume 50 is formed, which couples the movement of the parts 19, 24. How to get out Fig. 1 results, the coupler volume 50 is hydraulically connected to the Injektorvolumen 12 via a consisting of a single throttle bore 51 throttle assembly 52. When the electromagnetic actuator 39 is energized and the upper part of the injection valve element 18, which is in the drawing plane, moves rapidly upwards, the pressure in the coupler volume 50 drops rapidly and the opening force is transmitted to the first part 19 due to the suction effect in the sequence of its injection valve element seat 27 lifts. Due to the aforementioned negative pressure in the coupler volume 50, this increases because fuel from the injector 12 via the throttle assembly 52 in a range between axially the end face 48 of the first part 19 and the bottom 49 of the blind hole 23 flows. The throttle arrangement 52 is designed such that the filling or the increase of the coupler volume 50 does not lead to any functionally relevant change in the maximum stroke of the injection valve element 18. This can also be realized in the case of a multiple injection. The fit between the first part 19 and the inner circumference of the blind hole 23 is dimensioned so that the volume flow occurring here compared to the flow volume flow through the throttle assembly 52 is negligible - so the guide gap 53 is to be described as substantially hydraulic tight.

If the energization of the actuator 39 is interrupted, as explained above, the pressure in the control chamber 29 increases rapidly, whereby initially moves the second part 24 of the injection valve element 18 in the axial direction in the drawing plane down. Once the first part 19 is applied to the injection valve element seat 27, the injection is completed and the coupler volume 50 is depressed by means of the closing spring 43 until the original state is reached again. The emptying of the coupler volume 50 is only possible because the throttle assembly 52 is designed such that the flow rate is less than proportional, i. does not behave linearly to the pressure difference increase between coupler volume 50 and injector volume 12. There is no linear relationship as given in a conventional guide (lubrication cracking theory).

In the embodiment according to Fig. 1 is the first part 19 formed in the region of the guide gap 53 and thus formed as a pivot joint, so as to be able to compensate for angular errors and inclinations between the nozzle-side guide and the guide of the injection valve element 18 in the valve body 7.

This in Fig. 2 shown embodiment of a fuel injector 1 substantially corresponds to the embodiment according to Fig. 1 , so as to avoid repetition in terms of similarities to the preceding description of the figures as well as on Fig. 1 is referenced. In the following, only differences to the preceding embodiment are explained essentially.

Out Fig. 2 It can be seen that a throttle bore for connecting the coupler volume 50 to the injector volume 12 has been dispensed with. The coupler volume 50 is also formed between the bottom 49 of the blind bore 23 and the upper side 48 in the plane of the drawing of the first part 19 of the injection valve element 18. In the exemplary embodiment shown, the throttle arrangement 52 is realized in the region of a guide 54 between the outer circumference of the first part 19 and the inner circumference of the blind bore 23. The throttle arrangement 52 comprises in the exemplary embodiment shown a number of throttles 55 arranged one behind the other in the axial direction. The throttles 55 are each formed between an annular web 56 with a radially tapered outer edge and the inner circumference of the blind bore 23. The axial extent of the webs 56 in a voltage applied to the inner circumference of the blind hole 23 area is so short that can form a turbulent flow, with the result that the flow rate through the throttle assembly 52 only disproportionately increases with increasing pressure difference between the coupler volume 50 and 12 injector. The two adjacent in the axial direction, annular webs 56 define between them a groove 57 (circumferential groove) on the outer periphery of the first part 19. As in the embodiment according to Fig. 1 is the first part 19 in the region of the guide 54 formed somewhat spherical, so that the first part 19 is pivotable relative to the second part 24 within certain limits, so that angle errors can be compensated.

Claims (10)

1. Fuel injector, in particular common rail injector, for injecting fuel into a combustion chamber of an internal combustion engine, having a multi-part injection valve element (18) which can be adjusted between a closed position and an open position and which comprises a first part and at least one second part (24) adjustable relative to the first part (19), said first and second parts being coupled to one another via a hydraulic coupler volume (50),
   characterized
   in that the first part (19) is guided in the second part (24) or the second part (24) is guided in the first part (19), and in that the coupler volume (50) is connected to an injector volume (12) via at least one throttle arrangement (52) designed such that the throughflow volume flow increases only underproportionately with increasing pressure difference between the coupler volume (50) and injector volume (12).
2. Fuel injector according to Claim 1,
   characterized in that
   the throttle arrangement (52) comprises at least one, preferably only one, throttle bore (51) formed in particular in the first or second part (19, 24).
3. Fuel injector according to either of Claims 1 and 2,
   characterized
   in that the throttle arrangement (52) has at least one in particular hydraulically sharp-edged throttle stage with a small longitudinal extent in the flow direction, which longitudinal extent is preferably dimensioned such that a turbulent flow is generated.
4. Fuel injector according to one of the preceding claims,
   characterized
   in that the throttle arrangement (52) comprises a plurality of throttles (55) arranged hydraulically in series.
5. Fuel injector according to Claim 4,
   characterized
   in that the throttles (55) are formed radially between the first and the second part (19, 24).
6. Fuel injector according to Claim 5,
   characterized
   in that the throttle arrangement (52) comprises a plurality of grooves (57) which are arranged axially one behind the other and which are formed in the first or the second part (19, 24).
7. Fuel injector according to one of the preceding claims,
   characterized
   in that the second part (24) is a control piston which delimits a control chamber (29) and the first part (19) is a nozzle needle which interacts with a nozzle needle seat.
8. Fuel injector according to Claim 7,
   characterized
   in that the guide (54) is designed as a pivot joint which permits a relative adjustability of the first and the second part (19, 24) relative to the longitudinal central axis of the injection valve element (18).
9. Fuel injector according to Claim 8,
   characterized
   in that the first or the second part (19, 24) is of spherical design in the region of the guide (54).
10. Fuel injector according to one of the preceding claims,
    characterized
    in that the fuel injector (1) does not have a permanent low-pressure stage.

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