Abstract:
The invention relates to an SCR exhaust gas aftertreatment device, particularly for diesel motor internal combustion engines having a very large exhaust gas volume and/or divided exhaust gas trains. In order to be able to manufacture this SCR exhaust gas aftertreatment device in a cost-efficient manner, also for a high mixing degree of exhaust gas and AUS, it is proposed that a plurality of metering units (D 1 , D 2 , D n ) is provided, each of which has an atomizing nozzle, which nozzle-injects the aqueous urea solution into the exhaust gas train. In this case, the pressure existing in a common line for all metering units (D 1 , D 2 , D n ) can be determined by means of a pressure sensor.

Description:
[0001]    This application claims the benefit of German Patent Application No. 10 2009 035 940.0 filed on Aug. 3, 2009. 
         [0002]    The present disclosure relates to the subject matter disclosed in German patent application number 10 2009 035 940.0, which is incorporated herein by reference in its entirety and for all purposes. 
       BACKGROUND OF THE INVENTION 
       [0003]    The invention relates to an SCR exhaust gas aftertreatment device which is particularly useful, e.g., for diesel motor internal combustion engines having a very large exhaust gas volume and/or divided exhaust gas trains. 
         [0004]    Already known from DE 198 17 994 A1—first embodiment—is an exhaust gas aftertreatment device in which a pump pumps ammonia from an ammonia reservoir into a line and places it therein under constant pressure. Four metering valves open off the line. Each of these metering valves feeds the ammonia into the partial train of an exhaust gas manifold, which is assigned to a combustion compartment of an internal combustion engine. In this way, nitrogen oxides (NO x ) will be reduced in the exhaust gas. 
         [0005]    In its embodiment of  FIG. 2A , DE 699 10 605 T2 relates to an SCR catalyst in which urea is fed directly in stages to the SCR catalyst by means of three metering valves, at the beginning, in the middle, and at the end. 
         [0006]    DE 41 04 382 A1 relates to a gas turbine in which an aqueous ammonia solution is fed by means of three nozzles to points of various compression. 
         [0007]    The unpublished DE 10 2008 012 780 relates to an SCR exhaust gas aftertreatment device in which a supply unit is employed together with a diaphragm pump and a pressure filter. Further provided is a metering unit, which has a pressure sensor, a valve, and an atomizer. As a reductant, an aqueous urea solution circulates in an open circuit. The open circuit, along with other measures, ensures that aqueous urea solution expanding below the freezing point cannot damage the SCR exhaust gas aftertreatment device. Provided in the metering unit in order to build up sufficient pressure at the valve for the atomizer, in spite of the open circuit, is a backflow restrictor. 
         [0008]    The problem of the invention is to create a low-cost SCR exhaust gas aftertreatment device for internal combustion engines having very large exhaust gas volumes and/or divided exhaust gas trains. 
         [0009]    This problem is solved in accordance with the invention by the features of patent claim  1 . 
       SUMMARY OF THE INVENTION 
       [0010]    The aqueous urea solution will be referred to below abbreviated as AUS. 
         [0011]    The SCR exhaust gas aftertreatment device according to the invention can be employed, in particular, in ship diesel engines, stationary diesel engines, construction machine engines, large emergency electric power systems, and engines having divided cylinder banks, such as V engines and W engines. 
         [0012]    Provided in accordance with the invention are a plurality of metering units, which have a metering valve and an atomizing nozzle, so that the AUS can be nozzle-injected at a plurality of points of the large exhaust gas volume or the divided exhaust gas train. This alone ensures a better distribution or else enables such a distribution at all in a divided exhaust gas train. In addition, the atomization has the advantage over injection—in particular over the injection of a barely distributed AUS jet onto a hot face of the exhaust gas pipe—of an appreciably better distribution with a correspondingly large reactive surface of the AUS. As a result, a very high fraction of the AUS is completely reacted, so that especially good exhaust gas values can be attained with low AUS consumption. This is particularly of advantage for large exhaust gas volumes, which already pose a blending problem. Also, no hot face is required, which would have to be heated additionally during the start-up operation or in the warm-up phase. For example, an atomizing nozzle can be realized by means of a plurality of discs, which have slits and/or perforations such that they divert the AUS repeatedly, so that the AUS is imparted a strong swirl on exiting the atomizing nozzle. This swirl provides for an atomization of the AUS when it enters the exhaust gas flow. Such swirl nozzles are known from the field of heating burners, which is a concept outside the field of the invention. Swirl nozzles are also furnished the English name “pressure swirl atomizer” as a technical term. 
         [0013]    Present in accordance with the invention is a pressure sensor, which, in comparison to a purely mechanical—that is, spring-controlled—pressure regulation, enables a precise regulation of the pressure. This precise regulation of the pressure enables, in turn, an especially high metering accuracy. In a particularly advantageous embodiment of the invention, the function of a temperature sensor can be integrated into this pressure sensor. In another particularly advantageous embodiment of the invention, the pressure sensor is arranged in the metering unit, so that the temperature of the aqueous urea solution can be measured directly in spatial proximity prior to nozzle injection into the exhaust gas flow. This configuration allows a relatively high pressure to be applied, which supports the fine atomization in large exhaust gas volumes. Used in a particularly advantageous embodiment of the invention for application of this high pressure is a diaphragm pump, which, even at this high pressure, protects the pump drive against the aggressive AUS to a special degree on account of the sealing diaphragm. In a particularly advantageous embodiment of the invention, the diaphragm of the diaphragm pump is moved back and forth by a crankshaft drive or by an eccentric gearing. Such a membrane pump drive enables very high pressures to be attained, which makes possible an even finer atomization of the AUS in the exhaust gas flow with the aforementioned advantages. 
         [0014]    Provided in accordance with the invention is a proportional valve, which regulates the through-flow from the metering unit to the AUS tank, from which the AUS is pumped again via the pump and the common line to the metering valves opening off the latter. This circuit ensures that cooled AUS can constantly reach the metering valves and that heat supplied by hot exhaust gas can be dissipated. In addition, the proportional valve allows a passive protection against freezing of the circuit to be realized, when it is ensured that the proportional valve is in the open position in the absence of a supply of electric power. As a result, even after the system is switched off, it is ensured that no pressurized AUS is present any longer in the SCR exhaust gas aftertreatment device. This also secures the common line, from which the metering units are supplied with the AUS, against damage due to freezing. This protection against freezing functions even when a pump after-run is no longer possible, because, for example, the electric power supply to the SCR exhaust gas aftertreatment device is interrupted due to actuation of the “emergency shut-off.” 
         [0015]    In a particularly advantageous embodiment of the invention, all of the metering units have their own pressure sensor. A mean value can then be formed from the pressure values of the pressure sensors for the control of the pump. Particularly when a diaphragm pump having an electric motor crankshaft drive is used, it is possible to regulate the speed of the electric motor of the diaphragm pump. This makes possible a modular system in a cost-efficient manner, in which the same metering units that are also used in motor vehicles having only one metering unit in the SCR exhaust gas aftertreatment device are used. This in itself “superfluous” use of pressure sensors is economically reasonable, because the unit numbers for the special engines mentioned in the beginning—ship diesel engines, stationary diesel engines, W engines, etc.—are relatively small in comparison to those of standard engines. Included in the standard engines are, in particular, in-line engines having three to six cylinders, such as those employed in automobiles and commercial vehicles. 
         [0016]    In a particularly advantageous embodiment of the invention, the metering units are classified with the atomizing nozzles, with only metering units of one class being employed at the SCR exhaust gas aftertreatment device. In this way, the tolerances of the metering units and, in particular, the tolerances of the atomizing units can be compensated. Thus, depending on manufacture, the pressure that has to be applied varies so as to supply a defined quantity of AUS through the respective atomizing nozzle. However, the pressure sensors in the metering units have analyzing electronics with an engine program map in which the output voltage is plotted via the pressure. This engine map can be calculated. As a result, for each metering unit, it is possible to measure the pressure that is required in order to eject a defined quantity of AUS. Correspondingly, the engine map of the pressure sensor is calibrated so that the metering units can be divided into classes. If, for example, it is known that the atomizer varies by +/−6%, it is possible to make a division into the following classes through calibration of the characteristic line of the analyzing electronics of the pressure sensor:
       Class A: 94% nominal pressure to 96% nominal pressure   Class B: &gt;96% nominal pressure to 98% nominal pressure   Class C: &gt;98% nominal pressure to 100% nominal pressure   Class D: &gt;100% nominal pressure to 102% nominal pressure   Class E: &gt;102% nominal pressure to 104% nominal pressure   Class F: &gt;104% nominal pressure to 106% nominal pressure       
 
         [0023]    On a given internal combustion engine, then, only metering units of one of the classes A to F may be used. This results in a simplification of the servicing and the provision of replacement parts, because no setting needs to be changed, but rather attention needs to be paid only to the use of replacement parts of the same class. The mean value of all output voltages of the pump sensors then forms the theoretical value for the control circuit of the pump pressure. 
         [0024]    Particularly in the case of the modular system described above, in which nearly the same metering units are used for the mass market of internal combustion engines as are used for large-volume internal combustion engines having a plurality of AUS nozzle-injection points, it is possible to design the metering units for the mass market with unchangeable backflow restrictors that are adjusted only once, whereas the metering units for the large-volume internal combustion engines are designed without the backflow restrictors and, instead, have the above-described, central, continuously adjustable proportional valve for all metering units. 
         [0025]    Provided in the supply unit according to another advantage of the invention is a fine pressure filter, which protects the atomizing nozzles of the metering units from becoming clogged. In this case, this fine pressure filter is arranged in the AUS flow downstream of the diaphragm pump. As a result, the pressure loss at the fine pressure filter is less noticeable than when this pressure filter is arranged in the suction intake channel upstream of the diaphragm pump. In an advantageous embodiment, the diaphragm can be protected by means of a coarse intake filter against coarse contaminants, with only a small pressure loss occurring at this coarse intake filter. As a result, the diaphragm pump—in particular its check valves—are also protected against contaminant particles. Accordingly, it is possible to ensure the functional reliability of the diaphragm pump to an especially high degree. 
         [0026]    According to another advantageous embodiment, a control unit for controlling the diaphragm pump is integrated into the supply unit. In this case, in a particularly advantageous embodiment, a thermally loaded circuit board of this control unit can be fixed in place within a housing at an outward-facing metal plate in a dust-protected manner, so that the heat of the circuit board can be dissipated out of the housing. In order to enhance this cooling of the circuit board, the metal plate can be furnished with cooling ribs outside of the housing. 
         [0027]    In a particularly advantageous embodiment, the supply unit can be connected to the cooling water circuit of the motor vehicle drive engine. As a result, for example, the AUS and/or the control unit can be thawed by the cooling water circuit of the motor vehicle drive engine. 
         [0028]    In a particularly advantageous embodiment, it is possible to provide an electric heating for the metering unit for fast thawing. 
         [0029]    Further advantages of the invention ensue from the other patent claims, the description, and the drawing. The invention is described in detail below on the basis of an exemplary embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    Shown here are: 
           [0031]      FIG. 1 , the circuit diagram of an SCR exhaust gas aftertreatment device having a supply unit and a plurality of metering units, 
           [0032]      FIG. 2 , in detail, the supply unit illustrated only schematically in  FIG. 1 , which comprises a diaphragm pump with a diaphragm, 
           [0033]      FIG. 3 , a detail of the diaphragm pump of  FIG. 2  in the region of the diaphragm, 
           [0034]      FIG. 4 , the supply unit of  FIG. 2  in a view from below, with the pump unit being illustrated in an exploded view in the region of the AUS connections and a pressure-limiting valve, and 
           [0035]      FIG. 5 , the supply unit of  FIG. 2 ,  FIG. 4  in a view from above, with the supply unit being illustrated in an exploded view in the region of a compressible compensating element, 
           [0036]      FIG. 6 , the supply unit of  FIG. 2  to  FIG. 5  in a view from above, with the supply unit being illustrated in an exploded view in the region of a cooling water connection, 
           [0037]      FIG. 7 , a stamped circuit board, which is overmolded by plastic of the supply unit, 
           [0038]      FIG. 8 , in a first view, the first metering unit of the metering units illustrated only schematically in  FIG. 1 , 
           [0039]      FIG. 9 , the metering unit of  FIG. 8  in a second view, 
           [0040]      FIG. 10 , a nozzle disc of an atomizing nozzle, which is employed in the metering units, 
           [0041]      FIG. 11 , another nozzle disc, which, together with the nozzle disc according to  FIG. 10 , forms a nozzle disc packet, and 
           [0042]      FIG. 12 , an adapter plate, which is arranged between the nozzle disc packet and a valve seat of the metering units. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]      FIG. 1  shows the circuit diagram of an SCR exhaust gas aftertreatment device. By means of this SCR exhaust gas aftertreatment device, an AUS is injected into an exhaust gas train  177  of a large-displacement internal combustion engine  155 —in particular, a diesel engine. Provided for this purpose is a supply unit  1  with a pump  2 . In this case, this supply unit  1  sucks in the AUS from a tank  200 , pressurizes it, and passes it under pressure via a common line  50  to a plurality of metering units D 1 , D 2 , D n . 
         [0044]    These metering units D 1 , D 2 , D n  nozzle-inject a portion of the AUS into the hot exhaust gas flow via atomizing nozzles  101 . Moreover, the metering units D 1 , D 2 , D n  are cooled by AUS circulating in the circuit between the supply unit  1  and the metering units D 1 , D 2 , D n . 
         [0045]      FIG. 2  shows that the supply unit  1  comprises, besides said pump  2 , also a pressure filter  3  and a control unit  4 . 
         [0046]    The pump  2  is designed as a diaphragm pump and comprises a brushless electric motor  5  having an eccentric gearing  6  operating similarly to a crankshaft drive. This eccentric gearing  6  moves back and forth the central region of a diaphragm  7 , which is clamped at its rim in an intermediate housing  8 . Placed in this intermediate housing  8  are, in addition, two plastic discs  207 ,  208 , which can be seen in more detail in  FIG. 3  and are designed as injected-molded parts. In this case, the upper plastic disc  207  is placed on the lower plastic disc  208  in such a manner that, as a result of the tongue-like moldings in the region of contact between the two plastic discs  207 ,  208 , two check valves  9 ,  10  are formed. These two check valves  9 ,  10  are designed as shutter valves. Provided in the plastic discs  207 ,  208 , furthermore, are the channels required for the AUS through-flow. One of the check valves  10  opens in one direction, so that a pressure chamber  190  that can be pressurized by the diaphragm  7  can deliver pressurized AUS. The other check valve  9  opens in the opposite direction, so that the pressure chamber  190  can suck in AUS. A channel, incorporated independently into the intermediate housing  8 , opens off of each check valve  9 ,  10 . These channels are sealed by means of O-rings  240 ,  241 . Only a partial segment  11  of these channels is seen in  FIG. 2 . The check valve  9  that sucks in AUS, sucks in the AUS via the partial segment  11  and another channel  242 , which opens off it, from an AUS intake connection  12 . This other channel  242  and an intake filter  243 , arranged in front of it, are seen in  FIG. 4 . In this case, the intake filter  243  protects the pump  2  against coarse contaminants. This intake filter  243  is built into the AUS intake connection  12 . 
         [0047]    The AUS is conveyed out of the pressure chamber  190  from the diaphragm  7  via the other check valve  10  and the channel that opens off it, which is not seen in more detail, to the pressure filter  3 . From this pressure filter  3 , the AUS is conveyed to an AUS pressure connection  153 , seen in  FIG. 5 . By means of this pressure filter  3 , the metering units D 1 , D 2 , D n  are protected against contaminant particles and thus against clogging. The AUS pressure connection  153  is joined to the metering units D 1 , D 2 , D n  via the common line  50  seen in  FIG. 1 . The AUS intake connection  12  of the supply unit  1  is connected to the AUS tank  200  via the AUS line  151 . Each of the metering units D 1 , D 2 , D n  has two metering unit connections  156   a ,  157   a ,  156   b ,  157   b . The metering unit connections  156   a ,  156   b , conveying the AUS, are joined via parallel lines to another AUS line  201 . This AUS line  201  is connected to the AUS tank  200  via a proportional valve  223 , so that, via the proportional valve  223 , which can be regulated continuously in terms of the degree of opening, a circuit is formed for the circulating AUS cooling the metering units D 1 , D 2 , D n . The degree of opening of the proportional valve  223  is regulated depending on the quantity of AUS that is nozzle-injected via the metering valves  34  and the atomizing nozzles  101  into the exhaust gas train  177 . To this end, the metering valves  34  are connected via control wires to the control unit  4 , which is in signal transmission with the ECU engine control via the CAN bus. 
         [0048]    The pressure filter  3  comprises a filter cartridge  15 , which is placed in a pot  16 . In this case, this pot  16  has an outer thread  17 , which is screwed into an inner thread  14  of a sleeve  13 . In this case, the inner thread  14  is arranged at one end of the sleeve  13 . At its other end, the sleeve  13  is joined in an immovable manner to the intermediate housing  8 . Accordingly, the filter cartridge  15  is pulled tightly against the intermediate housing  8 . 
         [0049]    In order to bend the diaphragm  7  back and forth, the electric motor  5 , which is designed in a space-saving manner as an external rotor, rotates. In accordance therewith, a stationary stator  18  of the electric motor  5  is surrounded radially within a rotor  19  by the latter. The stator  18  has coils with wires  20  that lead to an engine-control circuit board  205  within the control unit  4 . On the side facing away from the eccentric gearing  6 , the rotor  19  is connected to a centrally perforated disc  21 , through the central hole of which a shaft  22  is inserted in such a manner that the rotor  19  and the shaft  22  do not rotate with respect to each other. The shaft  22  is roller-bearing-mounted in two roller bearings  23 ,  24  in the region of the eccentric gearing  6 . These two roller bearings  23 ,  24  are accommodated in a bearing housing  25 , which is joined to the intermediate housing  8  in an immovable manner. Provided for this purpose is a screw joint  26 . In this case, the diaphragm  7  is clamped by means of this screw joint  26  between one support plate  206  of the bearing housing  25  and the upper plastic disc  207 . A cam  27  is pressed onto the shaft  22  in frictional engagement in the region between the two roller bearings  23 ,  24 . The central axis of this cam  27  is displaced parallel to the axis of rotation of the shaft  22 . Arranged coaxially on the cam  27  is a roller bearer  28  of a connecting rod  29 . Its other end is screwed via a threaded bolt  30  with a support bushing  31 , which is joined in an immovable manner to a rounded contact sleeve  32 . The support bushing  31  is vulcanized into the diaphragm  7 . The contact sleeve  32  serves to support the diaphragm  7  during the pressure stroke. The threaded bolt  30  is furnished in the middle with a hex head  33  and has threads at its two ends. 
         [0050]    The roller bearings  23 ,  24 , and  28  have a permanent grease packing for lubrication. 
         [0051]    The control unit  4  is arranged within a control housing  37 , which is designed in one-piece with a pump housing  38 . The control housing  37  is separated from the pump housing  38  in an oil-tight manner by means of a partition  39 , with said wires  20  of the coils being connected to the engine control circuit board  205  by means of strip conductors  40 , which are embedded in the injected-molded plastic material of the pump housing  38 . The metering control, pressure regulation, sensor analysis, and CAN communication functions are located on another circuit board  41 . The other circuit board  41  is screwed onto one side of an aluminum plate  42 , on the other side of which cooling ribs  43  are arranged. This aluminum plate  42  is placed into an opening of the control housing  37  in such a manner that the cooling ribs  43  are directed outward and such that the heat is conveyed from the circuit board  41  with the electronics toward the outside. 
         [0052]    For connection of
       the engine control circuit board  205 ,   the other circuit board  41 , and   the CAN bus of the motor vehicle,
 
a stamped circuit board  44  is overmolded with the plastic of the control housing  37 . This stamped circuit board  44  is also seen in  FIG. 7  and has four knifelike contact plugs  45 ,  210 ,  211 ,  212  that extend vertically upward from the stamped circuit board  44 . A 20-pin contact plug  45  makes a connection between the stamped circuit board  44  and the other circuit board  41 . This connection is made when the circuit board  41  is plugged into the control housing  37 . A 4-pin contact plug  210  makes the connection to the engine-control circuit board  205 . There are two contact plugs  211 ,  212  for the connection to the outside. The 8-pin contact plug  211  is responsible for the connection to the metering units D 1 , D 2 , D n  for
   the control or electric power supply of its metering valves  34 ,   the control or electric power supply of electric heaters  265 ,   the electric power supply of pressure sensors  221 , which, in addition, have the function of a temperature sensor, and   the signal reception from these pressure sensors  221 .       
 
         [0060]    The 7-pin contact plug  212  makes the connection to the motor vehicle electronics and to the voltage supply. In this case, the communication takes place via CAN bus signals. 
         [0061]    Provided on the side lying opposite the intake connection  12  of the intermediate housing  8  are two cooling water connections  46 ,  154 , which can be seen especially in  FIG. 4  to  FIG. 6 . These two cooling water connections  46 ,  154  lead to the two ends of a cooling channel  47 , which is embedded in the intermediate housing  8 . Because the two cooling water connections  46 ,  154 , on the other hand, are connected to a cooling water circuit of the internal combustion engine  155 , which is not shown in detail, the supply unit  1  can thus be kept thawed or at operating heat temperature by the hot cooling water from the cooling water circuit of the internal combustion engine  155 . 
         [0062]    Illustrated in  FIG. 8  and  FIG. 9  is the first metering unit D 1  of the identically designed metering units D 1 , D 2 , D n  in two cut-away views. This metering unit D 1  comprises the electromagnetic metering valve  34 . This electromagnetic metering valve  34  has an electromagnet  158  with an armature  159 , which can press a helical compression spring  161  against its spring force, so that the AUS pressure can shift a needle  160  into the open position. In this case, the helical compression spring  161  rests on a threaded bolt  191 , by means of which the pretension of the helical compression spring  161  can be adjusted. If the electromagnet  158  is not supplied with electric current via its terminals  162 , the helical compression spring  161  presses the needle  160  once again against the valve seat  102  into a closed position. In this case, the needle  160  is relatively long and is guided, on the one side, in a linear sliding bearing  163 . On the other side, the guiding takes place by means of a sealing membrane  164 , which protects the electromagnet  158  against the aggressive AUS. Provided between these two guides is a cooling channel  165 , which completes the circuit between the two said metering unit connections  156   a ,  157   a . The first metering unit connection  156   a  is connected to the line  201  for this purpose, whereas the second metering unit connection  157   a  is connected to the line  50 . From the one metering unit connection  157   a , which is designed as inlet, the AUS is conveyed via a filter sieve  260  through a plurality of recesses in the front linear sliding bearing  163  to the valve seat  102 . If the AUS is allowed to pass through a central opening in the valve seat  102  in the current-supplied state of the electromagnet  158 , the AUS is passed through an atomizing nozzle  101 . This atomizing nozzle  101  is designed as a pressure swirl nozzle and has the two nozzle discs  167 ,  168  placed over each other, illustrated in  FIG. 10  and  FIG. 11 . In this case, these two nozzle discs  167 ,  168  are tensioned against the valve seat  102  by means of an output nozzle insert  169 , with, additionally, an adapter plate  170 , seen in  FIG. 12 , being tensioned between the nozzle discs  167 ,  168  and the valve seat  102 . Provided for producing the tensioning of the adapter plate  170  and the nozzle discs  167 ,  168  is a crimping at the output nozzle insert  169 , which is not illustrated in more detail. This output nozzle insert  169  has an output with a funnel-shaped enlargement—which is not seen in more detail. Due to the shaping of openings  180 ,  181  of the nozzle disks  167 ,  168 , the out-flowing AUS is imparted a swirl, which atomizes the AUS when it is output. 
         [0063]    The AUS is nozzle-injected, in accordance with  FIG. 1 , into a region of an exhaust gas train  177  that lies in front of a catalyst  178 . 
         [0064]    Via said proportional valve  223  of  FIG. 1 , the constant flow of AUS through the metering units D 1 , D 2 , D n  is ensured. As a result, the temperature of the metering units D 1 , D 2 , D n  is kept low, on the one hand. On the other hand, when the electric power supply is switched off, the pressure builds up to tank pressure in the exhaust gas aftertreatment device, without any energy being required for opening a valve. 
         [0065]    All components of the exhaust gas aftertreatment device are designed so that a freezing of the unpressurized AUS does not lead to damage. This also applies as such to the metering units D 1 , D 2 , D n . In the electromagnetic metering valve  34 , the AUS can expand against the sealing membrane  164 . Incorporated into the pressure and temperature sensor  221  is a bellows  224  made of metal, which can expand against a compression spring  225 . 
         [0066]    However, this also applies to the supply unit  1 . In this supply unit  1 , the AUS can expand against
       the diaphragm  7 ,   a delimiter membrane  244 , seen in  FIG. 4 , and   a compressible compensating element  245 , seen in  FIG. 5 .       
 
         [0070]    The delimiter membrane  244 , seen in  FIG. 4 , belongs to a pressure-limiting valve  246 , also seen in  FIG. 1 . Provided on the side of the delimiter membrane  244  facing away from the pressure-limiting valve  246  is a branch channel  252 , which is linked to the AUS flow in the intermediate housing  8 . The pressure-limiting valve  246  has a delimiter housing  250 , which is screwed rigidly to the intermediate housing  8 . Within the delimiter housing  250 , the delimiter membrane  244  rests via a central supporting and guiding disc  247  and a helical compression spring  248  on an adjusting element  249  in an elastic manner. This adjusting element  249  is screwed from the outside into the delimiter housing  250 . The pretensioning of the helical compression spring  248  can be adjusted by screwing it in and out. 
         [0071]    The compressible compensating element  245 , seen in  FIG. 5 , is held by means of a cover  251  in a recess of the intermediate housing  8 . By means of a branch channel  253 , the compressible compensating element  245  is linked in the AUS flow to the AUS pressure connection  153 . In order to prevent any leakage of the aggressive AUS, an O-ring is arranged as a seal between the cover  251  and the intermediate housing  8 . 
         [0072]    A compressible compensating element similar to the compensating element  245  can also be arranged in or next to the pressure filter  3 . 
         [0073]    The other components of the exhaust gas aftertreatment device, that is, particularly
       the tank  200     the lines  50 ,  151 ,  201 ,   the AUS intake connection  12 ,   the AUS pressure connection  153 , and   the metering unit connections  156   a ,  156   b ,  157   a ,  157   b  
 
are also protected against freezing as a consequence of the choice of material and/or compressible compensating elements.
       
 
         [0079]    If individual or all components in an alternative embodiment are not designed to be protected against freezing, it is also possible to provide a device that enables the AUS to be sucked out or pumped out of the pump unit, so that, at external temperatures below the freezing point, there is no danger of destruction as a result of expanding AUS. 
         [0080]    In particular, instead of the plastic shutter valves, it is also possible to employ ball check valves made of stainless steel. 
         [0081]    The nozzle-injection into the exhaust gas train can take place in such a manner that each of the metering valves introduces AUS into the partial train of the exhaust gas manifold, which is assigned to a combustion compartment of an internal combustion engine. Alternatively, it is also possible to arrange a plurality of metering valves on a rim of a collecting pipe of the exhaust gas train, so that an exhaust gas flow having an especially large cross section is mixed nearly homogeneously with atomized AUS. 
         [0082]    The described embodiments are only exemplary embodiments. A combination of the features described for different embodiments is also possible. Other features, particularly those not described, of the device parts belonging to the invention may be taken from the geometries of the device parts illustrated in the drawings.