Abstract:
An apparatus for posttreatment of exhaust gases of an internal combustion engine, using a reducing agent to be introduced into the exhaust gases, in particular a urea or a urea-and-water solution, having an improved mixing chamber into which stored reducing agent, via a reducing agent line, and compressed air via a compressed air line can be introduced to create a reducing agent-air mixture, and means for preventing a reverse flow of reducing agent or reducing agent-air mixture from the mixing chamber into the compressed air line are provided which have a spring-loaded sealing hose. This arrangement assures secure sealing off of an attachable compressed air system from the corrosive reducing agent.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/01112 filed on Mar. 27, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for posttreatment of exhaust gases of an internal combustion engine, using a reducing agent to be introduced into the exhaust gases, in particular a urea or a urea-and-water solution, having a mixing chamber, and to a mixing chamber. 
   2. Description of the Prior Art 
   Because of the ever-lower pollutant limits set in recent years, numerous apparatuses and methods for posttreatment of exhaust gases in internal combustion engines have been developed. For instance by means of catalytic converters systems that use urea and/or ammonia as a reducing agent for NO x  conversion, efficient exhaust gas posttreatment systems have been made available. 
   To achieve a reduction in NO x  components in exhaust gases, reduction catalytic converters have been developed, especially for Diesel engines, and these are typically divided into so-called SCR catalytic converters (for Selective Catalytic Reduction), with a urea metering system, and storage-type catalytic converters. The co-called SCR catalytic converters are regenerated by means of supplying a urea and/or ammonia reducing agent, while the so-called storage-type catalytic converters are regenerated, in so-called rich exhaust gas phases, with hydrocarbons from the engine fuel carried along with the exhaust gases. 
   From international patent disclosure WO 96/36797, a urea metering system with a compressed air delivery device for atomizing the urea is known, in which a check valve is provided in the compressed air path. 
   The object of the present invention is to improve an apparatus for posttreatment of exhaust gases in such a way that contamination of the air supply line, or of an on-board compressed air network communicating with it, can be reliably averted. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   By the provision according to the invention of a check valve with a spring-loaded sealing hose, contamination of the compressed air line, or of the on-board compressed air network, can be prevented extremely effectively. As a result, it is for instance possible to subject the air in the compressed air line to a relatively slight pressure, compared to conventional versions. The spring-loaded sealing hose assures a space-saving, compact, economical design and proves in practice to be sturdy and reliable. The spring loading advantageously enhances safety in sealing off the compressed air system from the corrosive reducing agent; moreover, it assures that a defined volumetric flow of air will be furnished over the entire extended service life of the apparatus and of the mixing chamber, since it helps the system to have a sealing point disposed in a defined place. 
   If the spring means has a bracing sleeve, then the assembly of an integrated metering valve and mixing chamber arrangement with an integrated check valve for supplying the compressed air can advantageously be simplified considerably. Particularly when the sealing hose is slipped onto the metering valve body, this makes it possible to prevent damage to the sealing hose, which is made for instance of an elastomer. Moreover, the end of the metering valve body toward the elastomer component can be manufactured more simply, because there is no longer any need to prevent sharp edges or the like under all circumstances. 
   The sealing hose can furthermore be shaped such that it assures not only sealing of the compressed air system and the distribution of compressed air supplied, but also sealing of other points and in particular of the interface between the mixing space and the integrated metering valve. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the apparatus and mixing chamber of the invention will now be described in further detail in conjunction with the accompanying drawing. Shown in the drawings are: 
       FIG. 1 , a view, on the order of a block circuit diagram, of an apparatus for posttreatment of exhaust gases; 
       FIG. 2 , a sectional view of the mixing chamber; 
       FIG. 3 , a check valve; and 
       FIG. 4 , a mixing chamber with an integrated, metal-spring-loaded check valve. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a urea tank  1  is shown, from which a urea-and-water solution is aspirated, via a line  1   a  having a check valve  2  and a filter  3 , embodied as a filter screen, by a feed pump  4  and pumped via a further check valve  6  to a metering valve  7  of a mixing chamber  8 . The metering valve  7  meters the requisite quantity of urea-and-water solution into a mixing space shown at  9  in FIG.  2 . Any overflow quantity of the urea-and-water solution that may occur can be returned to the urea tank  1  through a return line  12 , via a pressure regulator  5  and a further check valve  11 . If ventilation of the line  1   a  may be required, it can be done via a ventilation system having a ventilation valve  10 . 
   A compressed air container is also shown at  20 , from which compressed air can be introduced into the mixing chamber via a pressure limiter  21 , a 2/2-port directional-control valve  22  and a check valve  23 . The provision of the check valve  23 , which may for instance be embodied as a ball valve or as a flat seat valve, makes it possible to prevent a reverse flow of a reducing agent-air mixture from the mixing chamber into the compressed air line  24 . This sharply reduces the danger of contamination of an on-board compressed air network that communicates with the compressed air line  24 , compared to conventional systems. 
   In the mixing chamber  8 , by subjecting the urea-and-water solution to the compressed air, an aerosol is created, which is introduced via an aerosol line  25  into a catalytic converter  30 . A control unit  40  picks up signals, received from a higher-order engine control unit via a CAN data line  41 , along with the signals of pressure, temperature and fill level sensors 50-55, whose mode of operation is known per se and will not be explained here. From this information, the control unit  40  calculates a urea metering quantity that is to be metered to an exhaust gas flowing through the catalytic converter  30 . 
   The control unit  40 , with the aid of the magnet valves  10 ,  22 , regulates the pressure in the compressed airline  24  and also monitors the urea-and-water solution pressure. The control unit  40  detects deviations and errors and stores them in memory, and causes them to be displayed by means of a diagnostic device (not shown), for instance on a PC. 
   Turning now to  FIG. 2 , a mixing chamber of the kind that can be used in the context of the apparatus described above will be described. What is essential in this mixing chamber  8  is that the check valve comprises a silicone hose  14 , or a hose of some similar elastic material, which is slipped onto a valve body  15  and rests tightly against the inner wall  16  of the mixing chamber  8 . If compressed air is flowing out of the compressed air line  24  into the nozzle bore  17  (a plurality of such nozzle bores may also be distributed over the circumference), then the silicone hose  14  is pressed away from the inner wall  16  of the mixing chamber, and the air can flow into a diffusor  18  and onward, via an annular gap  19 , to reach the mixing space  9 . In the mixing space  9 , the air mixes with the aqueous urea solution flowing out of the urea line  1   a.    
   If in non-steady-state operation or in response to turbulence a reverse flow of the mixture out of the mixing space  9  into the diffusor  18  occurs, then the silicone hose  14  is pressed tightly against the inner wall  16  of the mixing chamber and prevents the further reverse flow of the mixture into the compressed air line  24 . 
   A further variant of a check valve that can be used in the apparatus or the mixing chamber of  FIG. 1  will now be described, in conjunction with FIG.  3 .  FIG. 3   a ) shows a sectional view of the check valve, and  FIG. 3   b ) shows a perspective exploded view of it. The key element of the check valve shown in  FIG. 3  is an elastomer valve body  34 , which rests with a sealing lip  35  against the inner wall  36  of a valve housing  46  in airtight fashion. It is equally possible for the sealing lip  35  to rest directly against the inner wall of the compressed air line, as has been described in conjunction with FIG.  1 . When air is flowing In from the air line  24 , the valve opens, while if the air tends to flow in reverse, the valve closes. 
   For the sake of universal use, the valve is preferably embodied as a valve cartridge  70 , which comprises the valve body  34 , the valve housing  46 , and a valve cap  60 . 
     FIG. 4  shows the mixing chamber  8  of an apparatus according to the invention as shown in FIG.  1 . The metering valve  7  for metering the urea-and-water solution forms the end of the urea line  1   a  and protrudes into the base body  200  of the mixing chamber  8 ; an O-ring seal  91  assures sealing of the space between the base body and the metering valve. Fastening means, not identified by reference numeral or described further, fix the metering valve relative to the mixing chamber. The central bore in the base body  200  has a shoulder  210  on which a sealing hose  110  is seated; on its end opposite the metering valve, this sealing hose has a profile that meshes with sealing edges  120  of the central bore. In the smaller-diameter region of the sealing hose, a metal spring cylinder  112  is introduced; it is seated on the sealing hose  110  via a bracing sleeve  115  that is integrated with the spring cylinder. The metering valve  7 , for its part, once the apparatus is put together, can at most be introduced into the larger-diameter region of the sealing hose only as far as the face, remote from the sealing hose, of the bracing sleeve. The spring cylinder  112  has spring tabs  114 , which press the profile of the sealing hose against the sealing edges  120 . Between the region of the sealing edges and the shoulder  210 , an annular groove  100  is provided, which forms a free area between the sealing hose and the base body  200 . The nozzle bore  17 , already shown in  FIG. 2 , discharges into this annular groove  100  and can be connected to the compressed air line  24 , similarly to the arrangement shown in FIG.  2 . The end of the spring cylinder  112 ,  114  remote from the metering valve is adjoined by the mixing space  9 , which as shown in  FIG. 1  can be connected to the aerosol line  25 . 
   The compressed air flows through the nozzle bore  17  into the annular groove  100 , which distributes the air uniformly over the circumference of the hose. The sealing hose  110  is kept in shape by the spring cylinder  112 ,  114 , because the spring cylinder furnishes a contact pressure and improves the sealing action at the sealing edges  120 . The contact pressure at the sealing edges can be selected appropriately, by means of a suitable choice of the spring constant of the spring cylinder. At the same time, the sealing hose assures sealing off of the mixing space from the outside, especially from the region where the metering valve protrudes into the base body. The sealing hose  100  is embodied as a molded part. 
   The foregoing relates to preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.