WO2012107484A1

WO2012107484A1 - Injector for a urea-water solution

Info

Publication number: WO2012107484A1
Application number: PCT/EP2012/052123
Authority: WO
Inventors: Cheikh Diouf
Original assignee: Emitec Gesellschaft Für Emissionstechnologie Mbh
Priority date: 2011-02-09
Filing date: 2012-02-08
Publication date: 2012-08-16
Also published as: KR20130117861A; DE102011010641A1; JP2014506648A; RU2566208C2; KR101521741B1; US20140034170A1; EP2673483A1; RU2013141033A; CN103370507A; JP5934256B2; CN103370507B

Abstract

Injector (1) for a urea-water solution, comprising at least a main body (2) with a fitting (3) for the urea-water solution, a valve (4) with a valve drive (5) and a separate feed pipe (6) for a urea-water solution, said feed pipe extending through the main body (2), at least in part.

Description

Injector for a urea-water solution The present invention relates to an injector for a urea-water solution, with which a urea-water solution can be added in particular to exhaust gas systems of a motor vehicle. In particular, the injector is used to add liquid urea-water solution in a precisely metered manner to the exhaust gas of an internal combustion engine, it then being possible for the proc- ess of selective catalytic reduction (SCR process) to be carried out in the exhaust gas system in such a way that nitrogen oxides contained in the exhaust gas can be considerably reduced.

A large number of different injectors have already been proposed for this purpose. However there is a need for improvement, in particular with regard to cost-effective production of an injector of this type for the automotive industry. A particular problem encountered with previous injectors is that the injectors also have to be able to remain functional in icy conditions. In this regard it should be taken into account in particular that the urea-water solution contained in the injector may also freeze under the normal conditions of use of a motor vehicle, and this leads to an increase in the volume of the urea-water solution. This increase in volume may repeatedly lead to blockages in the pipe system as well as malfunctions or destruction of component parts of the injector as a result of the high ice pressure. A further problem encountered with injectors of this type is that they are normally positioned on a hot exhaust gas pipe. This exposure to heat, which is sometimes considerable, may also cause problems with the conveying or metering of urea-water solution. This is true, in particular, if a gaseous supply of urea is to be avoided where possible, or if a threshold temperature of the urea-water solution is not to be exceeded during the feed process. In this regard it should be noted that urea-water solution already starts to evaporate at approximately 110 °C, so a controlled precisely metered feed of the urea-water solution may possibly be impeded. Undesirable residues which are difficult to remove may also be formed and may hinder the feed of the urea-water solution to the exhaust gas. In this respect the problem of injector cooling also arises repeatedly.

Starting from the foregoing, it is an object of the present invention to solve at least some of the problems mentioned with reference to the prior art. In particular, an injector for a urea-water solution is to be provided which can be produced in a cost-effective manner, is not susceptible to ice pressure of the urea-water solution when frozen, and is adequately protected from the high temperatures of the exhaust gas system.

These objects are achieved with an injector according to the features of claim 1. Further advantageous configurations of the injector are provided in the dependent claims. It should be noted that the features recited individually in the claims may be combined with one another in any techno- logically feasible manner and illustrate further configurations of the invention. The description, in particular in conjunction with the figures, explains the invention and provides additional embodiments.

The injector for a urea-water solution comprises at least a main body with a fitting for a urea-water solution, a valve with a valve drive and a separate feed pipe for urea-water solution, which extends through the main body, at least in part.

The urea-water solution is occasionally also referred to as a reducing agent or reducing agent precursor since the urea-water solution is converted to ammonia after thermolysis or hydrolysis and can then react with the nitrogen oxides in the exhaust gas. In this instance, in particular, a 32 % urea-water solution is used which, for example, is also commercially available under the trade name AdBlue^®.

The main body is, in particular, a metal component which may be constructed, on the one hand, with passages, surface recesses, contact surfaces for the valve and a cooling system and with ducts for conveyance of the urea-water solution. The main body is, in particular, a solid compo- nent which simultaneously serves as a base or a mount for the valve. Al- though in principle it is possible for the main body to comprise a plurality of valves and/or a plurality of fittings for the urea-water solution, the configuration with a single valve and a single fitting is still preferred. The fitting is generally constructed as a passage in the main body. Since in this respect the main body is also in contact, at least in part, with the urea-water solution, the material for the main body and/or a coating on the contact surfaces exposed to the urea-water solution is/are constructed so as to be resistant to the urea-water solution. The fitting is, in particular, also configured in such a way that conventional connecting joints to the pipes may optionally be integrated therein or fastened thereto.

The valve generally comprises a valve element in which the intake pipes and the metered-flow pipes are formed. In addition, a controllably ac- tuatable piston may be provided which may be actuated by the valve drive as necessary, in such a way that the fitting in particular from the intake pipes to the metered-flow pipe can be opened and closed as necessary (for example as a function of time). For this purpose the valve may additionally comprise a plug connector for connecting the valve or valve drive to a control unit (electric or signal-conducting) which initiates operation of the valve and thus of the injector as necessary. It is particularly preferred for the valve and the valve drive to be constructed as far away as possible from the urea-water solution feed point, i.e. in particular on the side of the main body remote from the exhaust gas pipe. This pro- duces, in particular, the position of the fitting for the urea-water solution which is therefore positioned between the exhaust gas pipe and the valve.

It is also provided for the injector to have a separate feed pipe for urea- water solution, which extends through the main body, at least in part. The separate feed pipe is therefore configured, in particular, in such a way that it is a separate component which is accommodated, preferably completely, inside the main body. The feed pipe is constructed, in particular, in the form of a small tube, in particular as a small tube extending in a straight line. A metal feed pipe is preferably used which consists, in particular, of a material different from that of the main body. Further- more, it is preferred for the separate feed pipe to be positioned predominantly at a distance from the main body in such a way that, in particular, heat conduction between the separate feed pipe and the main body is minimised. Most preferably, at most 10 % of the surface of the separate feed pipe is therefore in contact with the main body. The term feed pipe refers, in particular, to the portion of the pipe system for the urea-water solution, which is arranged downstream of the valve, in particular right to the delivery point into the exhaust gas system. Since, in accordance with the above-described variant, the valve is preferably arranged on the side of the main body remote from the exhaust gas pipe, the feed pipe thus extends, for example centrally, through the entire main body.

Such a configuration of the injector alone leads to a considerable improvement with regard to the problems detailed above. On the one hand, the valve can thus be protected against the high temperatures of the exhaust gas system, but at the same time boiling of the urea-water solution in the separate feed pipe is also reduced as a result of the low level of heat conduction to the main body. In accordance with a development of the injector, it is also proposed for the separate feed pipe to end in a nozzle plate. This nozzle plate is preferably fastened opposite the valve to the end face of the separate feed pipe. In particular, the separate feed pipe and the nozzle plate form a separately detachable unit. The nozzle plate is characterised, in particu- lar, in that it is perforated by nozzle orifices which now spray the urea- water solution from the feed pipe into the exhaust gas pipe at a predetermined jet angle. The jet angle maybe adjusted, in particular, to allow for the configuration of the nozzle or the spray cone produced therewith. The nozzle plate is preferably constructed in the form of a disc, in par- ticular the space surrounding the separate feed pipe being limited when arranged in the injector, in particular, by the spaced main body. In addition, the nozzle plate may be used to construct a connection or fixing to the injector, positioned at a distance from the separate feed pipe, in such a way that precise orientation of the feed direction is possible. The noz- zle plate may also be provided with a material which exhibits low thermal conductivity (for example compared to the main body), is resistant to high temperatures (since it may be in contact with the exhaust gas) and is optionally constructed with a surface which repels urea-water solution. The nozzle plate is thus constructed, in particular towards the exhaust gas system in such a way that any remaining droplets of the urea-water solution thereon can only remain there in the short term. This repellent coating prevents, in particular, (merely) partial evaporation of the urea- water solution and thus the formation of undesirable by-products or deposits. The external face of the nozzle plate preferably exhibits a rough- ness of less than 0.2 mm and/or a titanium oxide coating.

In accordance with a development of this injector, it is also proposed for the nozzle plate to have at least a plurality of nozzle orifices or to form a protruding end of the feed pipe. It is most preferred for both of these features to be embodied. With regard to the number of nozzle orifices, it is preferred for at least two nozzle orifices to be provided, but for the number of nozzle orifices not to exceed, for example, 5. It is most preferred for the nozzle orifices to be orientated or positioned in such a way that the jets of urea-water solution emerging therefrom intersect or col- lide with one another. A particularly advantageous spray cone can thus be generated. For example, the nozzle orifices are drilled through the nozzle plate in the manner of microducts, preferably by laser drilling.

It is further preferred during use of the injector for exhaust gas to flow where possible in parallel past the nozzle plate (and the nozzle orifices). In order to remove, where possible, all urea-water solution droplets still attached at the end of the metering process, this region should protrude, i.e. in particular it should project at most into exhaust gas pipe. It is sufficient for the protrusion to be very short, for example up to a maximum of 1 mm (millimetre), in particular, even only up to 0.5 mm or up to 0,2 mm. This short protrusion affords the advantage that the heat exposure of the injector in the region of the nozzle plate is simultaneously reduced, in particular, also for the separate feed pipe connected thereto. In addition, it is deemed to be particularly advantageous if the main body also comprises a cooling system which has an inlet and an outlet as well as at least one cooling duct which extends through the main body and is penetrated, in part, by the feed pipe. In other words, this means in par- ticular that the main body comprises passages which form an inlet for coolant and an outlet for coolant. It is particularly preferred for the cooling duct to be constructed concentrically about the feed pipe, i.e. in the form of an annular duct, in particular along a predominant portion of the separate feed pipe. Consequently the cooling duct preferably extends in such a way that, starting from the inlet it extends into an inner region of the main body, extends downwards in a region between the feed pipe and the outer wall or else towards the side opposite the valve, is led there in the region of the feed point or nozzle plate centrally inwards again towards the feed axis and then extends at least in part parallel to the feed axis and concentrically around the feed pipe before the cooling duct finally extends towards the outlet again shortly before it reaches the side with the valve. In this respect the cooling system is designed, in particular, in such a way that a counterflow heat exchanger is formed in the region of the feed pipe, the coolant flowing towards the valve and the added urea-water solution flowing away from the valve. It is most preferred for the cooling duct to also extend to the nozzle plate where, in particular, it is possible for fresh, cool coolant to flow around the entire region surrounding the separate feed pipe. In addition is also deemed to be advantageous for the main body to form a reservoir for a urea-water solution adjacent to the valve, the valve being arranged movably relative to this reservoir. In particular, the reservoir provides urea-water solution for the valve. The reservoir is thus formed, in particular, between the valve and the main body. It is most preferred for the valve to be arranged in the reservoir, at least in part, in such a way that the reservoir is limited by the main body, the valve and sealing means, in particular ring seals. The reservoir in which urea-water solution is ultimately stored for the valve during operation is preferably annular. In particular the central circular segment conveys the added portion of urea-water solution towards the separate feed pipe. Since urea-water so- lution is now generally present in said reservoir and may freeze at low temperatures, the urea-water solution expands in said reservoir. To avoid damaging the injector, the valve is arranged movably relative to said reservoir. This means, in particular, that the (entire) valve can be moved away from the main body, in particular along the feed axis. This movement, in particular a stroke movement (for example up to 2 mm, in particular greater than 1 mm) is reversible, i.e. when the urea-water solution thaws again the valve moves back into the normal position. It is thus also ensured that the reservoir always stores the same amount of urea-water solution during operation.

Furthermore, it is advantageous for the main body to form a reservoir for urea-water solution adjacent to the valve, the valve comprising a plurality of intake pipes which open into the reservoir. It is preferred for a plural- ity of intake pipes to be formed, for example with a uniform pitch in the circumferential direction of the valve, i.e. for example one intake pipe every 120°. The configuration with a plurality of intake pipes affords the advantage that the injector can be used in a versatile manner with regard to final positioning relative to the exhaust gas system. Similarly, a supply to the valve from the reservoir is also ensured if the injector is subjected, for example, to vibrations, etc. during operation. Depending on the position or filling level of the reservoir, it is thus basically ensured that at least one of the plurality of intake pipes is arranged in the region of the reservoir which currently provides urea-water solution. This significantly increases versatility and metering precision during operation.

In accordance with a development of the injector, at least one spring element is provided which biases the valve against the main body. In particular, the object of the spring element is to reverse the stroke move- ment or movement of the valve relative to the main body which occurred after ice formation. In addition, taking into account the reservoir or the amount of urea-water solution stored therein, the spring element may be designed in such a way that it actually only allows a movement of the valve relative to the reservoir when there is ice formation. The spring ele- ment may be arranged, in particular, between a cap and the valve drive, but it is also possible for example to fasten a cap to the main body using fixing means, spring elements optionally being provided between the cap and the main body or the fixing means. In particular the spring elements may be constructed as annular springs or spring washers.

Furthermore, it is deemed to be advantageous if a base with a socket for the main body is provided, air-gap insulation being formed between the base and the main body in a region around part of the feed pipe. In particular, the object of the base is to orientate the main body relative to the exhaust gas pipe and to fix it there securely. The base is also metallic in particular. The socket is configured, in particular, in such a way that the position of the main body is orientated in the base. The heat flux towards the main body can be reduced since a large area of the base is generally fixed to the hot exhaust gas system. For this reason it is proposed that, in particular, the lower region of the main body facing the exhaust gas pipe is thermally decoupled. Here, it is preferred to mainly avoid an unwanted heat flux from the exhaust gas pipe to the urea-water solution on the one hand (Avoiding of boiling) and to avoid an unwanted strong cooling of the exhaust gas pipe on the other hand (Reduction of the risk of deposi- tions on the inner side of the exhaust gas pipe). For this purpose an annular or else cup-shaped cavity is formed in particular between the base and the main body and forms air-gap insulation. It is thus preferred, in particular, for contact between the main body and the base to be provided directly only on the side of the base remote from the exhaust gas pipe. In particular it is also preferred for only linear contact or repeated point contacts to be formed between the feed pipe or the nozzle plate and the base in the urea-water solution delivery region. The gap between the base and the nozzle plate may optionally also be sealed by sealing means or spacers arranged in the air gap.

In accordance with a development of the injector, at least one spacer is provided in the at least one air-gap insulation. The spacer serves in particular for exact orientation or simplified assembly of the base and the main body relative to one another. This spacer may be constructed for example as a washer, as a metal seal, as a spring element or the like. The spacer is shaped, in particular, in such a way that heat conduction from the base to the main body is slight. In particular, materials exhibiting low thermal conductivity and/or components having small areas of contact with the base and main body are provided. It is most preferred for merely a single spacer to be provided which forms a guide for the main body in the socket in the base.

In addition, it is also proposed that the fitting for the urea-water solution be constructed with a closable exit. An injector of this type is generally arranged downstream of a conveying device for urea-water solution. This means that urea-water solution is stored at increased pressure, for example at a pressure from 5 to 8 bar, in the connecting pipe from the conveying device (for example a pump) to the injector and therefore also in the region of the fitting in the main body. The object of the closable exit is to allow this pressure to be relieved at a predetermined position, for example when the injector needs to be serviced or replaced. In particular the volume of urea-water solution under pressure in the injector can thus be depressurised and can flow out through the exit, at least in part. The exit is formed, in particular, as a spur passage to the fitting and is closed by a stopper, for example a sealing screw.

The invention and the technical field will be described in greater detail hereinafter with reference to the figures. It should be noted that the figures illustrate particularly preferred variants of the invention, although the invention is not limited thereto. In the figures,

Fig. 1 is an external partly exploded view of an injector for a urea-water solution, Fig. 2 is a sectional view through an injector for a urea-water solution,

Fig. 3 is a sectional view through a main body and a base in the assembled state, Fig. 4 shows a component formed by a separate feed pipe and nozzle plate,

Fig. 5 shows a detail from Fig. 4,

Fig. 6 shows a detail of air-gap insulation between the base and the main body,

Fig. 7 shows a detail of an injector for a urea-water solution with a clos- able exit, and

Fig. 8 shows a motor vehicle with an exhaust gas after-treatment system comprising an injector for a urea-water solution. Fig. 1 is a perspective partly exploded view of a variant of an injector 1 for a urea-water solution. An adapter for pipe fittings 28 is shown by a dashed line on the right-hand side of Fig. 1, the upwardly directed pipe fittings forming for example the cooling water supply and drain and the central linear pipe fitting representing the connecting pipe for the urea- water solution. These pipe fittings 28 can now be conveniently arranged on the main body 2 of the injector 1, for example by means of screws as shown in this instance. The pipe fittings 28 for the cooling system open into the inlet 11 or outlet 12 provided for this purpose. The fitting 3 is formed in the main body 2 opposite the pipe fitting 28 for the urea-water solution, in particular as a passage. The main body is a cast part. To prevent the introduction of solid constituents into the injector 1, a filter 27 is also provided in the region of the fitting 3 and, in particular, comprises a coarse filter (for example with a mesh size greater than 100 um) and a fine filter (for example with a mesh size of less than 50 μ), i.e. it is made up several layers. The urea-water solution consequently flows into the injector 1 via this fitting 3 and the filter 27.

The valve 4 is also indicated above the main body 2 and, in this instance, is arranged beneath the cap 24. The cap 24 in which the valve 4 is ac- commodated with the associated plug connector 26 is biased against the main body 2 by fixing means 25. It is also optionally possible for spring elements to be provided between the fixing means 25 and the cap 24 in such a way that, in particular when the valve 4 moves, the cap may optionally also effect a compensating movement, in particular in the form of a stroke, relative to the fixing means 25.

This component may now be inserted into a base 17 which is conventionally connected to the exhaust gas pipe. For this purpose the base 17 comprises an inner socket 18 in such a way that the main body 2 is posi- tioned with a precise fit and is circumferentially orientated relative to the base 17.

Fig. 2 shows an embodiment of an injector 1 for a urea-water solution. The fitting 3 for the urea-water solution is again shown to the right of Fig. 2. The direction of flow 30 of the urea-water solution through the injector 1 is also indicated by black arrows. The filter 27 is in turn shown in this fitting 3 and in this instance is curved against the direction of flow 30, which is particularly advantageous since any incoming solid constituents are deposited in the outer edge region and therefore do not impede the flow centrally. The filtered urea-water solution then flows on through a constricted duct portion towards the valve 4. The main body 2 is configured in such a way that a reservoir 14 is formed between the valve 4 penetrating into the main body 2 and the end of the duct portion from the fitting 3 for the urea-water solution. The reservoir 14 is in this in- stance substantially circular and is limited or sealed internally and externally by ring seals 35 (O-rings). The valve 4 comprises a plurality of (namely three) intake pipes 15, with which the urea-water solution can be drawn in. The valve itself (with the valve flap or valve pin) is arranged above them and is actua table by the valve drive 5. The control signals or power supply for the valve drive 5 are fed via the plug connector 26, which protrudes from the cap 24. The plug connector 26 is thus also far removed from the exhaust gas pipe and is therefore exposed to slight heat. If the valve 4 is now actuated, the entrance to the feed pipe 6 is opened in such a way that the predetermined amount of urea-water solu- tion can then flow into the feed pipe 6 until it issues again from the feed pipe 6 at the opposite end, in particular into the exhaust gas flow of an internal combustion engine. The separate feed pipe 6 is arranged flush on the valve 4, and in particular is surrounded by the inner ring seal 35. A welded joint may optionally be formed between the separate feed pipe 6 and the main body 2 in the region of the contact face facing the valve 4.

Since urea-water solution can now collect in the reservoir 14, there is a risk that substantial pressure could build up if the urea-water solution freezes. For this purpose, the valve 4 (together with the valve drive 5) is formed so as to be movable relative to the main body 2 and the cap 24. If the pressure inside the reservoir 14 increases, it is possible that the valve 4 and the valve drive 5 will perform a displacement movement, in particular in the manner of a stroke 22. The outer ring seal 35 thus ensures that the reservoir 14 is still tight. This compensating movement or stroke 22 is made possible or adjusted by a spring element 16, with which the valve (together with the valve drive 5) is biased against the main body 2. If the pressure is too great as a result of ice formation, the valve 4 moves upwards, and if the frozen urea-water solution thaws again and the pressure there is then reduced, the spring element 16 moves the valve 4 back downwards again.

The cooling system 10 is also illustrated in the lower region of the main body 2, the coolant flow direction 29 being indicated by white arrows in this instance. The coolant thus flows via the inlet (not shown here) into the inner regions of the main body 2 until it reaches the illustrated or visible part of the cooling duct 13. Referring to Fig. 2, the coolant flows downwards, at a distance from the feed pipe 6, in the direction of the delivery point or the hottest point for the urea-water solution, where it is diverted (virtually in the opposite direction) and then flows back concen- trically in the direction of the valve 4 over the predominant portion of the separate feed pipe 6 in the manner of a sheathing jet. Shortly before the valve 4 is reached, the cooling duct 13 leaves the region around the separate feed pipe 6 and extends further toward the outlet (not shown). A counterflow heat exchanger is thus formed inside the main body 2, irre- spective of the configuration of the remainder of the injector, and en- sures that the urea-water solution disposed in the feed pipe 6 is reliably cooled and that boiling of the urea-water solution can be prevented. In order to ensure that this also occurs virtually as far as the delivery point for the urea-water solution, the cooling duct 13 extends, in particular, as far as a nozzle plate 7 which forms a protruding end 9 of the injector 1. Therefore even this portion, which is exposed to high temperatures, can be reliably cooled.

Furthermore, the base 17 is also illustrated here, air-gap insulation 20 being formed circumferentially about the main body 2 and also the separate feed pipe 6. On the one hand a coolant jacket and on the other hand an air-gap jacket are consequently provided around the feed pipe 6 in the region 19 close to the delivery point, in such a way that active and passive thermal insulation are provided in the circumferential direction con- centrically to the feed pipe 6.

Fig. 3 is a cross-section through an arrangement in which a main body 2 is inserted into a base 17. In particular, Fig. 3 is an enlarged view of the air-gap insulation 20. It can be seen that the main body 2 is actually only in heat-conducting contact in the region of the end face opposite the exhaust gas pipe. The air-gap insulation 20 and the concentric cooling duct 13 extend about the central feed axis 31, over virtually the entire height of the base 17, but at least over 70 % or even over 80 % of the height of the socket in the base 17. The air-gap insulation 20 is strongest (for ex- ample as a result of a large distance between the base 17 and the main body 2) where the base 17 is solid in the vicinity of the exhaust gas pipe since this is where a high thermal capacity is provided for the waste heat of the exhaust gas system. The air-gap insulation 20 is thus particularly pronounced, precisely in this region 19.

Fig. 4 illustrates a component consisting of a separate feed pipe 6 for urea-water solution and a nozzle plate 7 to be positioned in the vicinity of the delivery point, i.e. opposite the valve (not shown). The separate feed pipe 6 may comprise a widening 38 in the vicinity of the end faces, for example in order to compensate for positional tolerances. The pipe volume 32 inside the feed pipe 6 should be kept low if possible, i.e. a small pipe cross-section 33 should be produced in particular. For example the pipe volume 32 may be less than 100 mm³ or less than 60 mm³. An individual nozzle plate 7 is thus formed on an end face and is rigidly connected (welded) to the feed pipe 6. The nozzle plate 7 comprises a recess 49 around the region of contact with the feed pipe 6, enabling the coolant to flow as close as possible to the end face of the feed pipe 6. In particular it is thus also possible to cool the nozzle orifices 8 formed in the nozzle plate 7 at the end of the feed pipe 6. An enlarged view of this detail is shown in Fig. 5.

Fig. 5 shows the above-mentioned detail from Fig. 4. It can be seen that, at the front, the nozzle plate 7 comprises a welded seam 37 connecting it to the end face of the feed pipe 6. The welded seam 37 may also be con- structed by spot welding. The nozzle plate 7 rests flush against the end face of the feed pipe 6 and also terminates the end of the feed pipe, in the circumferential direction. Two nozzle orifices 8 which extend at an inclination to the feed axis 31 are shown adjacent to the widening 38 shown in this instance. The nozzle orifices 8 are configured, in particular, in such a way that a jet angle 36 is produced between them which is preferably less than 20^°. The nozzle orifices 8 are preferably orientated in such a way that the urea-water solution jets thus formed meet after leaving the nozzle plate 7. A particularly effective spray pattern with very small droplets of urea-water solution can be produced with colliding jets of this type, making it possible to achieve improved distribution of the urea-water solution in the exhaust gas.

Fig. 6 shows a further detail of an injector 1 for a urea-water solution. In this instance a variant of air-gap insulation 20 is again shown in particu- lar. Similarly, in order to now ensure that the main body 2 is securely positioned in the base 17, and with little movement, while heat conduction from the base 17 to the main body 2 is simultaneously reduced, the air- gap insulation 20 is formed with an outlet 12. In this instance the spacer 21 is constructed in the form of a metal profiled part 39 which accom- modates the main body 2 in the manner of a basket. The metal profiled part is, in particular, a type of spring element which is shaped in such a way that it only forms linear contacts 40 with the main body 2 or the nozzle plate 7 on the one hand, and the base 17 on the other. The linear contacts 40 make it possible to orientate the main body 2 or the nozzle plate 7 relative to the base 17, but they do not overcome significant heat conduction via the metal profiled part 39.

Fig. 7 is a further cross-section of an injector for a urea-water solution, in this instance only a lower partial region being shown. The separate feed pipe 6 penetrating the main body 2 is shown centrally with the nozzle plate 7. In this instance the air-gap insulation 20 is also achieved by providing a washer 34 as a spacer. The washer 34 may be formed of by thermal insulator and/or a sealing material toward the exhaust gas pipe. Corresponding air-gap insulation 20 can thus be achieved between the nozzle plate 7 and the base 17 to the delivery point, where the nozzle plate 7 penetrates the base 17. The air-gap insulation 20 can thus also be maintained when the main body 2 and base 17 are assembled via fixing means 25. An exit 23 is also illustrated on the right-hand side of Fig. 7, which allows communication with the fitting 3 in the main body 2 for the urea-water solution. This exit 23 can be closed with a stopper 41, in particular a threaded screw. The stopper 41 may be removed for disassembly or servicing of the injector, in such a way that the volume of urea-water solu- tion disposed in the fitting 3 can be removed via this exit 23.

Fig. 8 illustrates a particularly preferred field of application of the injector 1 for a urea-water solution. A motor vehicle 50 with an internal combustion engine 42, for example a diesel engine, is illustrated schema ti- cally. The exhaust gas produced in the internal combustion engine is conveyed to an exhaust gas system 43 which comprises at least one exhaust gas pipe 44. In order to carry out the SCR process, a reducing agent (in this instance ammonia) is first added to the exhaust gas and the mixture is then fed via an exhaust gas treatment unit 45, in particular, a SCR cata- lytic converter. The nitrogen oxides contained in the exhaust gas can then undergo catalytic conversion in the exhaust gas treatment unit 45 at an appropriate temperature of the exhaust gas and with selective metering of urea-water solution to the exhaust gas upstream of the exhaust gas treatment unit 45. The ammonia required for this process is produced from the urea-water solution by thermolysis and/or hydrolysis, preferably in the presence of exhaust gas. This solution is in turn fed via the injector 1 as necessary. The urea-water solution may be stored, for example, in a tank 46 and may be conveyed to the injector 1 via a conveying device 47 comprising, in particular, a pump. Operation of the conveying device 47 and/or of the injector 1 may be controlled as necessary by a superordinate control unit. This may take into account test data relating to the exhaust gas composition, exhaust gas temperature and/or the condition of the internal combustion engine. This control unit may also be part of an engine control system.

The invention thus discloses a practical, precisely-metering and freeze- proof injector which can be produced in a cost-effective manner.

List of reference numerals

1 injector

2 main body

3 fitting

4 valve

5 valve drive

6 feed pipe

7 nozzle plate

8 nozzle orifice

9 end

10 cooling system

11 inlet

12 outlet

13 cooling duct

14 reservoir

15 intake pipes

16 spring element

17 base

18 socket

19 region

20 air-gap insulation

21 spacer

22 stroke

23 exit

24 cap

25 fixing means

26 plug connector

27 filter

28 pipe fittings

29 coolant flow direction

30 flow direction

31 feed axis

32 pipe volume pipe cross-section washer

ring seal

jet angle

welded seam

widening

metal profiled part linear contact

stopper

internal combustion engine exhaust gas system exhaust gas pipe exhaust gas treatment unit tank

conveying device connecting pipe

recess

motor vehicle

Claims

Injector (1) according to claim 1, wherein the separate feed pipe (6) ends in a nozzle plate (7).

Injector (1) according to the preceding claim, wherein the nozzle plate (6) has at least a plurality of nozzle orifices (8) or forms a protruding end (9) of the feed pipe (6).

Injector (1) according to any one of the preceding claims, wherein the main body (2) additionally comprises a cooling system (10) comprising an inlet (11) and an outlet (12) as well as at least one cooling duct (13) which extends through the main body (2) and is penetrated, in part, by the feed pipe (6).

Injector (1) according to any one of the preceding claims, wherein the main body (2) forms a reservoir (14) for a urea-water solution adjacent to the valve (4), the valve (4) being arranged movably relative to said reservoir (14).

Injector (1) according to any one of the preceding claims, wherein the main body (2) forms a reservoir (14) for a urea-water solution adjacent to the valve (4), the valve (4) comprising a plurality of in take pipes (15) which open into the reservoir (14).

Injector (1) according to any one of the preceding claims, wherein at least one spring element (16) is provided which biases the valve (4) against the main body (2). Injector (1) according to any one of the preceding claims, wherein a base (17) with a socket (18) for the main body (2) is provided, air- gap insulation (20) being formed between the base (17) and the main body (2) in a region (19) around a part of the feed pipe (6).

Injector (1) according to the preceding claim, wherein at least spacer (21) is provided in the air-gap insulation (20).

Injector (1) according to any one of the preceding claims, wherein the fitting (3) for the urea-water solution is constructed with a closable exit (23).