Patent Abstract:
An SCR exhaust gas aftertreatment device in which a urea-water solution is injected into an exhaust gas line is provided. At least one component of the device (e.g., a filter element) lies in an area of an internal space, and is bounded by an elastomer membrane that is embedded in a frost equalization foam. This prevents freezing damage even over a very long period of time and a large number of freezing cycles.

Full Description:
The present application claims priority of German application number 10 2010 061 222.7 filed on Dec. 14, 2010, which is incorporated herein by reference in its entirety for all purposes. 
     BACKGROUND OF THE INVENTION 
     The invention concerns an SCR exhaust gas aftertreatment device designed to protect against freezing damage. 
     An SCR exhaust gas aftertreatment device is already known from DE 10 2008 012 780 A1. In it, a urea-water solution is injected into an exhaust gas line. A pump unit with a pressure filter is provided to produce the pressure needed for injecting the urea-water solution. This pressure filter lies in the area of an internal space of the pump unit. A compressible equalization element is also arranged on the pump unit. However, this equalization element does not lie in the area of the pressure filter. 
     The urea-water solution is abbreviated UWS hereafter. 
     Furthermore, filters for a UWS are known from DE 102 20 662 B4 and DE 102 20 672. These filters are structurally designed for expansion upon freezing of the UWS. 
     DE 103 62 140 B4 concerns an extension part made from an elastomer material, which yields when freezing UWS expands. 
     SUMMARY OF THE INVENTION 
     The problem to be solved by the present invention is to protect components with UWS arranged in internal spaces of a SCR exhaust gas aftertreatment device against freezing damage over a very long period of time with a large number of freezing cycles. 
     For this, a frost equalization foam is provided, whose surface is protected against penetration of UWS by an elastomer membrane. It has been found that UWS over a lengthy time can destroy even closed-pore foams, since the sharp-edged urea crystals after several freezing cycles can tear the thin foam walls. UWS then gets into the internal space of such a foam bubble and expands upon freezing, so that gradually the foam is destroyed after a multitude of freezing cycles. But the elastomer membrane of the invention is designed to be sufficiently thick that the frozen urea crystals cannot tear it. Thus, the UWS cannot penetrate into the foam bubble. 
     The invention encompasses a greater range of structural configurations of the frost equalization foam. As an example, even an open-pore foam can be utilized in accordance with the present invention, which can be designed according to other structural, cost, or manufacturing requirements. For example, workability is one such requirement. In particular, however, one can also choose a material that maintains its elasticity over a long lifetime. In addition, with the present invention, the foam does not have to be resistant to the very corrosive and creep-prone UWS. 
     In one example embodiment of the invention, the elastomer membrane together with the frost equalization foam is designed to be so rigid that it prevents a volume decrease greater than 10% at a pressure of 10 bars. 
     In a further example embodiment, a ventilation element can be provided. With this ventilation element, an air loss occurring over a lengthy term of operation can be equalized. This ventilation element may be connected to the surrounding atmospheric pressure in air and vapor permeable fashion. On the other hand, it may not be liquid-permeable. 
     The component being protected may be a filter element, whose inner dead space is filled up by a plug, so that the volume of the freezing UWS and thus also its volume increase upon freezing is kept small. 
     Further benefits and advantages of the invention will emerge from the claims, the specification, and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the appended drawing figures, wherein like reference numerals denote like elements, and: 
         FIG. 1  shows, schematically, an exhaust gas aftertreatment device with a pressure filter protected against freezing, and 
         FIG. 2  shows the pressure filter of  FIG. 1  in detail. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows schematically an exhaust gas aftertreatment device, by which a UWS is injected into an exhaust gas flow  1  of a Diesel motor  2 . The exhaust gas aftertreatment device has a pump unit  3 , which aspirates the UWS and pressurizes the UWS and delivers it under pressure to a dispensing unit  4 , which injects a portion of the UWS into the hot exhaust gas flow  1 . Furthermore, the dispensing unit  4  is cooled by the UWS flowing in the circuit between the pump unit  3  and the dispensing unit  4 . 
     The pump unit  3  comprises a pump  5 , a pressure filter  6  and a control unit  7 . 
     The pump  5  is designed as a membrane pump and comprises a brushless electric motor  8  with an eccentric gearing  9  working similar to a crank mechanism. This eccentric gearing  9  moves the central region of a membrane  10  back and forth, the membrane  10  being clamped at its periphery in a housing  11 . Two check valves  12 ,  13  are installed in the housing  11 . One check valve  12  opens in one direction, so that a pressure space  14  which can be pressurized by the membrane  10  can deliver pressurized UWS. The other check valve  13  opens in the opposite direction, so that the pressure space  14  can draw in UWS. From each check valve  12 ,  13  there proceeds a dedicated channel worked into the housing  11 . The check valve  13  taking in UWS draws in the UWS by an intake channel  15  from a UWS intake port  16 . 
     From the pressure space  14 , the UWS is conveyed by the membrane  10  across the other check valve  12  and via a pressure channel  18  to the pressure filter  6 . 
     A borehole (not shown in the drawings) emerges from the pressure channel  18  in the housing  11 , with a pressure limiting valve being press-fitted in the boring. This pressure limiting valve opens at a limit pressure and conveys the UWS to a drain channel, which feeds the UWS once again to the intake channel  15 . In order to safely keep the easily percolating UWS out of the environment, there is provided on the one hand a gasket ring at the pressure limiting valve. On the other hand, an additional cover closes the borehole for the pressure limiting valve, which has an additional sealing feature relative to the housing  11 . 
     From the pressure filter  6 , the UWS is taken to a UWS pressure port  17 . The dispensing unit  4  is protected against dirt particles and, thus, clogging up by the pressure filter  6 . The UWS pressure port  17  after the pressure filter  6  is connected to a UWS line  37 . By this external UWS line  37 , the UWS pressure port  17  is connected to the dispensing unit  4 . By a UWS line  19 , the UWS intake port  16  of the pump unit  3  is connected to a tank  21  of UWS. 
     By another UWS line  22 , the dispensing unit  4  is connected to the tank  21 , so that a circulation is formed with the flow across a return diaphragm  23  in the dispensing unit  4 . 
     The pump unit  3  has two cooling water ports  24 ,  25 . These two cooling water ports  24 ,  25  lead to the two ends of a cooling channel, which is worked into the housing  11 . Since the two cooling water ports  24 ,  25  on the other hand are switched into a cooling water circuit  26  of the Diesel motor  2 , the pump unit  3  can thus be thawed by the hot cooling water from the cooling water circuit  26  or held at an operational warm temperature. 
     The dispensing unit  4  comprises the electromagnetic dispensing valve  27 . This electromagnetic dispensing valve  27  has an electromagnet  28  with an armature  29 , which can compress a helical compression spring  30  against its spring force, so that the UWS pressure can push a needle  31  into an opened position. If the electromagnet  28  is not energized by its connections  32 , the helical compression spring  30  again pushes the needle  31  against a valve seat  33  into a closed position. The needle  31  is arranged relatively long in a cooling channel  34 , which closes the circulation between two dispensing unit ports  35 ,  36 . The dispensing unit ports  35 ,  36  are connected to the UWS lines  22 ,  37 . If the UWS is admitted through a central opening in the valve seat  33  when the electromagnet  28  is in the energized condition, the UWS will be taken through an atomizing nozzle. This atomizing nozzle is designed as a swirl nozzle with nozzle disks. Thanks to its configuration, the outflowing UWS is given a swirl, which atomizes the UWS upon its emergence from the atomizing nozzle. 
     The UWS is injected into a region of the exhaust gas line  1  situated upstream from a catalyst  38 . 
     In the region of the UWS line  37 , the pressure and the temperature of the exhaust gas aftertreatment device can be determined by means of a pressure and temperature sensor (not shown in the drawings). 
     The dispensing unit  4  has the return diaphragm  23  in the region of the dispensing unit port  36 . By this return diaphragm  36 , a constant flow of UWS through the dispensing unit  4  is assured. In this way, on the one hand the temperature of the dispensing unit  4  is kept low. On the other hand, when the power supply is switched off, the pressure in the exhaust gas aftertreatment device is relaxed to the tank pressure, without needing energy for the opening of a valve to do this. 
     All components of the exhaust gas aftertreatment device are designed so that a freezing of the pressureless UWS does not result in damage. 
       FIG. 2  shows the pump unit  3 , also known as a supply unit, in the installation area of the pressure filter  6 . This pressure filter  6  has a pump port housing  39 , a plug designed as a press-fit bolt  40 , a filter element  41 , an elastomer membrane  42 , a frost equalizing foam  43 , a filter housing  44 , and a ventilating membrane  45 . 
     The pump port housing  39  is made of aluminum. It has a receiving part  20  with a sleevelike region  46 . An outer thread  47  is provided on this sleevelike region  46 . The filter housing  44  is screwed onto this outer thread  47 . For this, the filter housing  44  is bell-shaped. At the inside of the screwing region, the filter housing  44  has an internal thread  48  that is screwed into the outer thread  47 . When the filter housing  44  is screwed onto the pump housing  39 , the bell-shaped filter housing  44  presses a ring-shaped sealing element  49  against the pump housing  39 . The sealing element  49  tightly closes off the inner space  50  inside the filter housing  44 , although an air exchange occurs via the ventilating membrane  45 , which is arranged in a ventilation element  51 . The ventilation element  51  is locked in a funnel-shaped opening  52  in a bell bottom of the filter housing  44 . 
     The frost equalizing foam  43  is placed in the filter housing  44 . The frost equalizing foam  43  also has a corresponding bell shape. Inside this frost equalizing foam  43  is inserted the pot-shaped elastomer membrane  42 . The upper edge of this elastomer membrane  42  is provided with a bulge  53 . This bulge  53  is pushed by a ring-shaped peripheral locking lug  54  of the sleeve-shaped region  46  and inserted into an annular groove  55  lying behind it. The bulge  53  is stressed with radial pressure against the filter housing  44  by the sleeve-shaped region  46 . The filter element  41  is inserted in the inner space  56  formed inside the sleeve-shaped region  46  and the elastomer membrane  42 . This filter element  41  has a central recess  57 . The press-fit bolt  40  extends inside this recess  57 , one end of which is press-fitted into the pump port housing  39 . 
     The filter element  41  has a paper filter  58 , which is closed off at the bottom by a cover  59 . Moreover, the filter element  41  has a closure ring  60 , which closes the paper filter  58  at the side lying opposite the cover  59 . The press-fit bolt  40  sticks through a central recess  61  of the closure ring  60  as far as a blind borehole  62  inside the pump port housing  39 , in which the press-fit bolt  40  is fitted. The closure ring  60  comprises a side facing towards the pump port housing  39 . On this side the closure ring  60  comprises a sealing sleeve  63 . This sealing sleeve  63  makes a single piece with a disk-shaped region  64  of the closure ring  60 . The closure ring  60  comprises an end facing towards the pump port housing  39 . This end is provided with a peripheral annular groove  65  in which an O-ring  66  is installed. The sealing sleeve  63  is inserted in a recess  67  of the pump port housing  39 , so that the O-ring  66  is sealed against the inner wall of this recess  67 . 
     The UWS is taken via the pressure channel  18  and the central recess  61  to the inner space  57  inside the paper filter  58 . From there, the UWS is forced under the operating pressure of the pump  5  of up to 10 bar through the paper filter  58 . In this way, the UWS gets into an annular space  69  that is bounded radially on the inside by the paper filter  58  and radially on the outside by the sleeve-shaped region  46  and the elastomer membrane  42 . From this annular space  69 , the UWS is brought out through a channel  70  in the pump port housing  39 , which can be seen symbolically in  FIG. 1 . 
     After the Diesel motor  2  is shut off—or possibly also in an emergency or a power outage—UWS remains in the annular space  69 , which freezes at outdoor temperatures below the freezing point of the UWS. The transition from the liquid to the solid state of aggregation is accompanied by an expansion at very high pressure. 
     Since the intake channel  15 , the pressure channel  18  and the channel  70  owing to their small cross section freeze up before the inner space  50  in time, additional pressure may be created in the inner space  50  on occasion. 
     This high pressure presses against the relatively thick elastomer membrane  42 , which consists of HNBR, in order to keep the damage as slight as possible in event of a filling of Diesel fuel instead of UWS by mistake. Thus, this relatively easily elastically deformable elastomer membrane  42  transmits the pressure to the frost equalizing foam  43 . The frost equalizing foam  43  is compressed when the pressure exceeds a limit value of 10 bar. At this pressure, little or no gas escapes from the ventilating element  51 . The frost equalizing foam  43  is in fact a closed-pore foam, so that only the pressure inside the foam bubbles is increased. However, there will basically be a passage of gas through the walls of the foam bubbles over the lifetime of the foam. The ventilating element  51  itself is gas-permeable. But even the elastomer membrane  42  is in a very slight degree gas-permeable, depending on the size of the gas molecule. But thanks to the ventilating element  51 , atmospheric air can get through to the frost equalizing foam  43  and so compensate for a gas loss occurring over the years through the elastomer membrane  42 . 
     The pump port housing need not be made of aluminum. Stainless steel or a plastic resistant to UWS is equally feasible. 
     The filter housing is not in contact with the UWS, so that an especially large choice of material is available for the filter housing. For example, plastics may be used for the filter housing. 
     The filter element need not be made of a paper filter. Other materials are also possible, depending on the sensitivity of the dispensing unit. 
     The embodiments described herein are only example embodiments. A combination of the features described for different embodiments is likewise possible. Other features of the device parts belonging to the invention, especially those not described, can be found in the geometries of the device parts as depicted in the drawings. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  exhaust gas flow 
           2  Diesel motor 
           3  pump unit 
           4  dispensing unit 
           5  pump 
           6  pressure filter 
           7  control unit 
           8  electric motor 
           9  eccentric gearing 
           10  membrane 
           11  housing 
           12  check valve 
           13  check valve 
           14  pressure space 
           15  intake channel 
           16  intake port 
           17  UWS pressure port 
           18  pressure channel 
           19  UWS line 
           20  receiving part 
           21  tank 
           22  UWS line 
           23  return diaphragm 
           24  cooling water port 
           25  cooling water port 
           26  cooling water circuit 
           27  dispensing valve 
           28  electromagnet 
           29  armature 
           30  helical compression spring 
           31  needle 
           32  connections 
           33  valve seat 
           34  refrigerant channel 
           35  dispensing unit port 
           36  dispensing unit port 
           37  UWS line 
           38  catalyst 
           39  pump port housing 
           40  press-fit bolt 
           41  filter element 
           42  elastomer membrane 
           43  frost equalizing foam 
           44  filter housing 
           45  ventilating membrane 
           46  sleevelike region 
           47  outer thread 
           48  internal thread 
           49  sealing element 
           50  inner space 
           51  ventilation element 
           52  opening 
           53  bulge 
           54  locking lug 
           55  annular groove 
           56  inner space 
           57  recess 
           58  paper filter 
           59  cover 
           60  closure ring 
           61  recess 
           62  blind borehole 
           63  sealing sleeve 
           64  disk-shaped region 
           65  annular groove 
           66  O-ring 
           67  recess 
           69  annular space

Technology Classification (CPC): 8