Abstract:
The invention relates to a device for cooling a metering module ( 10 ), in particular a module for metering an operating agent/auxiliary agent such as a reducing agent into the exhaust gas system of an internal combustion engine. A cooling device comprising a cooling member ( 17, 20, 24, 28, 29 ) through which a cooling liquid flows is associated with the metering module ( 10 ). The cooling member ( 17, 20, 24, 28, 29 ) acts as a housing ( 12 ) for the metering module ( 10 ). A first group of parts ( 17, 20, 28 ) forms an air gap insulation ( 38; 54, 56, 58 ) on an electric contact ( 16, 36 ), while cooling fluid flows through a second group of parts ( 28, 29, 40 ).

Description:
BACKGROUND OF THE INVENTION 
     DE 44 36 397 B4 relates to a device for the aftertreatment of exhaust gases. The device comprises an exhaust gas collecting system, in which a reduction catalytic converter for reducing the levels of NO x  constituents in the exhaust gas of the internal combustion engine is arranged. The device furthermore comprises a metering device, comprising an electrically controlled metering valve for the metered introduction of a reducing agent into the flow of exhaust gas supplied to the catalytic converter, depending on a value, which is stored in the map, for the NO x  content in the exhaust gas at various operating parameters of the internal combustion engine and of the catalytic converter. The valve for controlling the supply of air is an electrically controlled control valve which is arranged downstream of the outlet opening of the metering valve and the outlet opening thereof leads directly into the exhaust gas flow of the internal combustion engine. The control valve is accommodated by a body through which a cooling medium can flow such that the control valve is cooled. 
     US 2008 0236147 A1 discloses an injection system which is used within the scope of selective catalytic reduction in a motor vehicle in order to reduce the levels of NO x  portions in the exhaust gas. According to this solution, the injection system comprises an injector which is supplied with current via an electric terminal. The electric terminal contains an electric contact which is configured for receiving a plug of a connecting line. 
     US 2010 0108020 A1 relates to a connecting system for electric lines which are laid in hazardous areas, for example, an area in which there is a risk of explosion, such as, for example, the environment of an internal combustion engine. The disclosed connecting system is suitable for the electric connection of lines of various sensors and components. The connecting system comprises a rubber bush and a cap provided with an internal thread. The rubber bush here serves as an electric and thermal insulator and is compressed in the fitted state of the connecting system. 
     DE 10 2009 060 065 A1 discloses a fluid line for urea-water solutions in NO x  reduction devices which operate in accordance with selective catalytic reduction (SCR). The fluid line is produced from a thermoplastic vulcanizate (TPV). The thermoplastic vulcanizate has rubber-like properties and is also known under the designation “thermoplastic elastomer”. The thermoplastic vulcanizate is distinguished in particular by high resistance to aggressive liquids and has a very high degree of flexibility and excellent pliability. According to DE 10 2009 060 065 A1, a fluid line manufactured from thermoplastic vulcanizate is used for connecting tanks, pumps, injection nozzles or for receiving couplings. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of providing a metering module for an exhaust gas aftertreatment system, said metering module withstanding high thermal loadings which occur during the operation of an internal combustion engine. 
     According to the invention, it is proposed, in a metering module, in order to protect the latter from overheating, to surround a wall of said component with an insulation shell and/or to implement water cooling. When an insulation shell is used, it is possible, for example to realize an air gap insulation which provides protection from overheating damage in particular in the plug region or in the region of the valve coil. 
     Following the solution proposed according to the invention, the metering element is enclosed by a heat sink which, comprising a plurality of parts, completely encloses the metering valve for introducing a fuel/additive, in particular a reducing agent, into the exhaust section of an internal combustion engine. According thereto, the heat sink constitutes a housing of the metering element. In a preferred variant embodiment of the solution proposed according to the invention, the heat sink constituting the housing of the metering valve is of multi-part design and comprises, for example, an upper shell, a central shell and a plug-in contact cover which is manufactured from a material having elastic properties, and is designed, for example, as a plastics bush or rubber bush. Furthermore, the housing of the metering module comprises a lower shell which is located below the central shell, wherein a cup-shaped insert is embedded in the lower shell of the heat sink constituting the housing of the metering module. 
     Whereas the upper shell of the heat sink, which is in particular of multi-part design, comprises a reducing agent inlet and also cavities through which a cooling fluid does not flow, but which constitute air gap insulation means, the central shell arranged below the upper shell comprises cavities through which the cooling fluid flows and cavities which are merely filled with air and therefore constitute air gap portions of an air gap insulation of an electric plug-in contact. 
     The lower shell, which accommodates the cup-shaped insert, is provided with a cavity through which cooling fluid flows. The circulation of the cooling fluid in the cup-shaped insert of the lower shell or through those parts of the central shell through which cooling liquid flows takes place through a cooling fluid inlet, which is accommodated on the lower shell, and via a cooling fluid return located on the circumferential surface of the central shell. Passage openings which permit cooling fluid to flow from the cavity of the lower shell into the cavity of the upper shell are located between the cup-shaped insert, which is accommodated in the lower shell, and the base of the central shell arranged above said lower shell. 
     Following the solution proposed according to the invention, the central shell constitutes to a certain extent a “hybrid component” which firstly permits air gap insulation with respect to the electric plug-in contact connection running through said central shell, but secondly has regions through which the cooling fluid flows. In the manner proposed according to the invention, the regions which conduct the cooling fluid are separated from the regions which constitute the air gap insulation of the electric content, wherein the number of required sealing points is reduced to a minimum. In order to separate the air gap portions constituting the air gap insulation in the central shell from the cavities which are formed in the central shell and conduct the cooling fluid, mention should advantageously be made of a separating rib which runs at an inclination through the central shell and separates the air gap portions of the air gap insulation from that cavity of the central shell which conducts the cooling fluid. 
     Following the solution proposed according to the invention, not only can the region of the metering module that lies in the region of an outlet opening of the fuel/additive, in particular of the reducing agent, be cooled with a cooling fluid, but further regions of the metering module can be cooled, this being achieved with the aid of the air gap insulation. In a particularly advantageous manner, the air gap insulation of the electric contact for activating the metering module can take place in the region, in particular in the central shell of the multi-part heat sink constituting a housing of the metering valve, since the electric contact connection is enclosed by a plastics cover which is manufactured from a material which has elastic properties. Owing to the elastic properties of the plastics cover, different coefficients of expansion of regions of the heat sink manufactured from metallic material and of parts of the heat sink manufactured from plastics material can be compensated for. The plug-in contact cover, which is designed, for example, as a plastics bush or rubber bush, can be fastened releasably to the upper shell by means of a latching closure and to the central shell in a latching means formed opposite on said component. By means of the plastics cover which can be fastened releasably to the upper shell and to the central shell of the multi-part heat sink constituting the housing, the air gap insulation can be effectively closed, but, at the same time, by omission of a welded joint, relative movements can be permitted without losses of sealing effect. 
     The solution proposed according to the invention takes simplifications in terms of assembly into consideration by virtue of the fact that the cooling is brought about in the upper region by convection, i.e. in the path of the air gap insulation, whereas liquid cooling can be implemented in the lower region of the metering module such that, following the solution proposed according to the invention, the entire cooling of the metering module can be achieved. 
     In addition, by the use of the water-cooled central shell, the thermal mass, this means the heat storage capacity, in the upper region of the metering module is increased. As a result, retarded heating of the valve can be achieved even if the cooling fluid circulation is interrupted. Therefore, even without active cooling fluid circulation, temporary temperature peaks do not result in damage of the metering module. 
     Furthermore, the metering module housing proposed according to the invention constitutes a means of protecting the metering valve from thermal shock in the event of abrupt cooling. Such cooling may occur, for example, when cleaning an engine when the engine is hot or when passing through water. A thermal shock is avoided since the heat sink with the large thermal mass thereof is cooled first. The metering valve enclosed by the heat sink is cooled more slowly as a result, and therefore stresses in the component due to different coefficients of thermal expansion are avoided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described in more detail below with reference to the drawing, in which: 
         FIG. 1  shows a perspective reproduction of the metering module, the metering valve of which is enclosed by a multi-part heat sink constituting a housing, 
         FIG. 2  shows a cross section through the metering module illustrated in  FIG. 1  and through the multi-part heat sink thereof, and 
         FIGS. 3.1 and 3.2  show perspective views of the plug-in contact cover. 
     
    
    
     DETAILED DESCRIPTION 
     The metering module described below with reference to  FIGS. 1 to 3.2  is a metering module for introducing a fuel/additive, in particular a reducing agent, such as, for example, urea or a urea-water solution, into the exhaust section of an internal combustion engine. Temperatures in the range between 100° C. and 160° C. prevail in the environment in which the metering module  10  proposed according to the invention is installed. Higher or lower temperature levels may also be present depending on the intended purpose and installation location. By means of the fuel/additive, in particular a reducing agent, such as, for example, urea or a urea-water solution, the NO x  constituents which are present in the exhaust gas of internal combustion engines are reduced to H 2 O and N 2 . The apparatus proposed according to the invention for cooling a metering module  10  can also be used in other metering apparatuses, which are to be operated within a certain temperature range, as a cooling means therefor. 
     It can be gathered from the illustration according to  FIG. 1  that a metering valve of a metering module  10  is enclosed by a complete housing  12  which to a certain extent constitutes a second housing. The complete housing  12  comprises an upper shell  20 , which can be designed, for example, in the form of a cap, and a plastics covering  17  which can be manufactured in particular from a material having elastic properties, such as, for example, a plastics material or a rubber. Furthermore, the housing  12  comprises a central shell  28 , and also a guide sleeve  32  arranged below the latter and a lower shell  29  which lies below said guide sleeve and into which a cup-shaped insert  24 —only partially illustrated in  FIG. 1 —is embedded. 
     As emerges from the perspective illustration according to  FIG. 1 , the metering valve of the metering module  10  is entirely enclosed by the components  17 ,  20 ,  28 ,  29  listed above. Only a lower end of the cup-shaped insert  24  protrudes below the lower shell  29  of the complete housing  12  of the metering module  10 . 
     As furthermore emerges from the perspective illustration according to  FIG. 1 , a cooling fluid inlet  22  is located in the circumferential surface of the lower shell  29 . By contrast, a cooling fluid return  26  is located in the circumferential surface of the central shell  28 . 
     A section through the multi-part embodiment of the heat sink of the metering module according to  FIG. 1  can be gathered from the illustration according to  FIG. 2 . 
     The cross section according to  FIG. 2  shows that the entire metering valve  30  is surrounded by the complete housing  12 . The complete housing  12  here includes the upper shell  20 . The fuel/additive inlet  18 , via which in particular a reducing agent, such as, for example, urea or a urea-water solution, is supplied to the metering module  10 , extends through the upper shell  20 .  FIG. 2  shows that said inlet  18  is of angled design and is encapsulated by the upper shell  20  by a flange covering an upper end side of the metering valve  30 . The upper shell  20 , for its part, comprises a cavity  42  which is separated from the cooling fluid by a separating rib  64 , which is denoted by reference number  64 , in relation to the central shell  28 , the cavity  44  of which has a cooling fluid flowing therethrough. As can furthermore be gathered from the sectional illustration according to  FIG. 2 , the upper shell  20  in the region of a plug  16  or an electric plug-in contact  36  comprises an air gap portion  58  which is part of an air gap insulation  14  of the electric plug-in contact  16  or  36  of the metering module  10 . 
     A central shell which is identified by reference number  28  is located below the upper shell  20 , which is part of the complete housing  12  of the metering module. The central shell  28  comprises a receptacle  40  in which the upper shell  20  including the cavity  42  through which cooling fluid does not flow is embedded. 
     The central shell  28  likewise surrounds the metering valve  30  which is accommodated on the central shell  28  via a holding disk  34 . The central shell  28  sits on a guide sleeve  32 . The guide sleeve  32 , for its part, is accommodated on an insert  24  which is of substantially cup-shaped design. 
     It can be seen from the sectional illustration according to  FIG. 2  that the central shell  28  comprises the cavity  44  through which the cooling fluid flows, and at the same time also contains a first air gap portion  54  and a second air gap portion  56 . The first air gap portion  54  and the second air gap portion  56  are separated from the cavity  44  by a separating rib  64  which is formed in the central shell  28 . In particular, the profile of the separating rib  64  in the central shell  28  is selected in such a manner that the first air gap portion  54  and the adjoining, second air gap portion  56  extend along the electric plug-in contact  36  in the direction of the plug-in contact cover  17 . The separating rib  64  which separates the first air gap portion  54  and the second air gap portion  56  from the cavity  44  through which the cooling fluid flows opens out at a wall end  52  of the central shell  28 . A latching connection  50  is also located there in the same manner as on the opposite side of the upper shell, compare position  48  in  FIG. 2 . The plastics covering is latched releasably at the two latching points  48  and  50  which are formed on the upper shell  20  and on the central shell  28 . As already explained in conjunction with  FIG. 1 , the plastics covering  17  is fastened by a latching means  58  to the upper shell  20  and by a latching means  50  opposite the first latching means to the outer side of the central shell  28 . Owing to the geometry of the plug covering  17 , the latching connections  50  and  52  bounding the opening  62  in the latter extend over the corresponding receiving regions of the upper shell  20  and of the central shell  28  in such a manner that extensions caused by temperature differences can be compensated for on account of the elastic properties of the material of the plug covering  17 . This makes it possible to avoid leakages which arise, for example, whenever materials which have different coefficients of thermal expansion, compensate for different extensions occurring during relative movements of the parts with respect to one another. 
     The solution proposed according to the invention firstly prevents leakage of cooling fluid to the outside and secondly ensures that the cooling fluid is kept away from the electric plug-in contact connection  36  such that no electric short circuit can occur in this region. In the region of the electric contact connection  36 , the cooling is realized in the manner proposed according to the invention by the air gap insulation  14  at the air gap portions  38 ,  54  and  56 , as illustrated in  FIG. 2 . 
     It emerges from the illustration according to  FIG. 2  that the central shell  28  constitutes a “hybrid component” which realizes an air gap insulation in the region of the electric plug-in contact  36  and also has at least one cavity  44  through which cooling fluid flows. 
     As can be gathered from the lower region of the illustration according to  FIG. 2 , the lower shell  29  is located below the guide sleeve  32 . The lower shell  29 , for its part, accommodates the cup-shaped insert denoted by reference number  24 . 
     At the lower end of the metering module  10 , temperatures of the order of magnitude of 120° C. and more can occur. For this reason, the cooling fluid inlet  22  into which the cooling fluid flows into the lower shell  29  and from there into a cavity  66  of the cup-shaped insert  24  is located in the region of the lower shell  29 . The lower region of the metering valve  30  also contains the injection nozzle via which a spray mist of fuel/additive and air is injected into the exhaust section of the internal combustion engine. 
     Since the highest temperatures are operationally induced here, in order to optimize the cooling effect the cooling fluid inlet  22  is located in this part of the metering module  10  proposed according to the invention so as to ensure an optimum removal of heat in the range of the high temperatures occurring there. 
     It furthermore emerges from the sectional illustration according to  FIG. 2  that, after the cooling fluid enters through the cooling fluid inlet  22  after flowing through the cavity  66  of the cup-shaped insert  24 , the cooling fluid flows via passage openings  46  to the cavity  44  above the base of the central shell  28 . As  FIG. 2  shows, passage openings  46  in the guide sleeve  32  and in the base of the central shell  28  are aligned with one another such that the cooling fluid, after flowing through the cup-shaped insert  24 , passes into the cavity  44  of the central shell  28 . After passage through the cavity  44  of the central shell  28 , which cavity is separated in a liquid-tight manner from the air gap portions  54 ,  56  by the separating rib  64 , the cooling fluid heated by the waste heat in the metering module  10  after flowing around the latter leaves the cavity  44  of the central shell  28  at the cooling fluid return  26 , as illustrated in  FIG. 2 . 
     The passage openings  46  ensure that the cooling fluid passes from the cavity  66  of the cup-shaped insert  24  into the at least one cavity  44  of the central shell  28  of the housing  2 . As can be gathered from the fitted state according to  FIG. 2 , the plug cover  17  which is preferably manufactured from material having elastic properties permits the production of air gap insulation, i.e. cooling on account of convection in the region of the electric plug-in contact connection  36  in the upper part of the metering module  10 . There is also the possibility of providing water cooling at further components, in particular at the injection part of the metering valve  30  that is exposed to high thermal loadings, said water cooling making it possible for heat to be very reliably transported away. The solution proposed according to the invention realizes the cooling of all of the components of a metering module  10 . By means of the solution proposed according to the invention, materials optimized in each case with regard to the intended purpose thereof can in particular be used without the possibly different coefficients of thermal expansion thereof resulting in leakages or fatigue cracks. 
     Perspective views of the plug cover as illustrated in cross section in  FIG. 1  and  FIG. 2  can be gathered from  FIGS. 3.1 and 3.2 . 
       FIG. 3.1  shows that the plug cover  17  encloses a cable outlet  60  and has an opening  62 . The opening  62  is bounded by latching means  48 ,  50  which are formed opposite each other and can be formed as depressions or elevations, designed in a complementary manner with respect to the geometry thereof, on the upper shell  20  or in the plug region of the central shell  28 .  FIG. 3.2  shows that the opening  62  in the plastics cover  17  can be, for example, of square or else rectangular design, which is favorable in respect of the formation of the latching connections  48 ,  50 . If the latter are opposite each other, when the plug cover  17  is latched and a prestress is produced, a reliably sealing, but also re-releasable fastening of the plastics cover  17  to the upper shell  20  and central shell  28  of the heat sink which constitutes the housing  12  and is of multi-part design can be achieved.