Abstract:
A centrifuge ( 10 ) suitable for separating soot from an exhaust gas stream of an internal combustion engine; the centrifuge being disposed between, and arranged coaxially in relation to, a raw gas inlet pipe ( 11 ) and a clean gas outlet pipe ( 12 ); the centrifuge including a rotating body ( 20 ) which is open on both axial end faces, drive vanes ( 26 ) arranged adjacent the inlet for driving the centrifuge, and at least one device ( 29 ) provided inside said rotating body for reversing or deflecting the exhaust gas flow direction.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of international patent application No. PCT/EP03/006781, filed Jun. 26, 2003, designating the United States of America, and published in German as WO 2004/003354 A1 on Jan. 8, 2004, the entire disclosure of which is incorporated herein by reference. Priority is claimed based on Federal Republic of Germany patent application no. DE 102 28 682.5, filed Jun. 27, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a centrifuge, especially for the separation of soot from an exhaust gas stream of an internal combustion engine.  
         [0003]     U.S. Pat. No. 5,016,437 (=DE 38 30 761) discloses a centrifugal separator for soot particles in which the soot particles are deposited against an outer circumferential surface of a housing. Heating elements are arranged adjacent the wall for combusting the soot particles. The turbine rotor of an exhaust gas turbine is utilized as a drive, i.e., as a centrifugal force drive.  
         [0004]     Furthermore, German patent application no. DE 10 39 997 discloses a centrifuge with propellers in which carrier guide ribs are arranged in the interior of the centrifuge and slots are provided through which contaminants, i.e., the separated particles, can be forceably discharged.  
         [0005]     U.S. Pat. 1,434,562 describes a centrifugal separator for the intake air of an internal combustion engine having a plate separator which diverts the gas flow and thereby separates particles from the gas stream. The plate separator is driven by an air rotor constructed as an individual drive, which is arranged at the separator outlet.  
         [0006]     A soot filter is likewise known having a ceramic body which takes up the soot particles. For regeneration an additive is utilized which decreases the soot ignition temperature and facilitates burning off the soot from the ceramic body.  
         [0007]     Another system is known in which the exhaust gas is diverted and the particles are retained in a metal mat. This filter system cannot plug up, and the system can be regenerated at high temperatures because of the resistance or durability of the medium. However, there is a danger that a portion of the particles can pass unhindered through this system and flow out into the environment.  
         [0008]     The known and described devices for separation of particles are expensive to construct and in part require additional devices, such as, for example, heating devices, for burning off the separated particles.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the invention to provide an improved centrifuge for separating soot from exhaust of an internal combustion engine.  
         [0010]     Another object of the invention is to provide a centrifuge for separating particles from a gas stream which has a simple construction.  
         [0011]     A further object of the invention is to provide a centrifuge which does not require supplementary devices for burning off separated soot.  
         [0012]     It is also an object of the invention to provide a centrifuge for separating particulate material from a gas stream which exhibits a high separation efficiency.  
         [0013]     These and other objects are achieved in accordance with the present invention by providing a centrifuge for separating soot from an exhaust gas stream of an internal combustion engine, the centrifuge being disposed between a raw gas inlet pipe and a clean gas outlet pipe and arranged substantially coaxially to the inlet and outlet pipes; the centrifuge comprising a rotatable body open at both axial ends, which has drive vanes arranged on the inlet side for driving the centrifuge and has at least one device for reversing or diverting the flow direction of the exhaust gas stream inside the rotating body.  
         [0014]     The substantial advantage of the centrifuge of the present invention lies in the fact that it is directly installed in the exhaust pipe of an exhaust gas stream, has its own drive, e.g., in the form of drive vanes which are arranged on the inlet side, by which the separation is achieved due to the effects of centrifugal force and the flow is directed to the outlet side.  
         [0015]     One embodiment of the invention envisions that a plurality of flow reversing devices in the form of conical rings is provided. In this way the centrifuge can be constructed in the manner of a plate separator, which achieves a high separation efficiency at a high air throughput.  
         [0016]     A further embodiment envisions providing the cylindrical inner wall of the housing of the rotating body with a coating or with a roughened surface, which favors adhesion of soot particles and improves the collection of the soot.  
         [0017]     In accordance with a further embodiment, it is proposed to provide the inner wall of the housing with a catalytic coating, which decreases the ignition temperature of the soot. This catalytic coating can be composed either of a silver vanadate or of a copper vanadate, which contains alkali metal. In this way the ignition temperature of the soot or the soot particles can be significantly reduced, e.g. down to about 365° C.  
         [0018]     In accordance with a further embodiment it is proposed in order to achieve a simple mounting of the centrifuge to arrange a first bearing in the raw gas inlet pipe and a second bearing in the clean gas outlet pipe and to attach the centrifuge via these two bearings in the exhaust channel. As a result of this construction, an in-line centrifuge is formed, which is provided in the area of a junction in the exhaust gas channel or which has an openable housing which is integrated in the exhaust gas channel.  
         [0019]     In order to burn off the soot, i.e. for the purpose of regeneration, it is also possible to enrich the exhaust gas with NO x , in order to thereby achieve a rapid and reliable cleaning of the exhaust gas in conjunction with the further measures.  
         [0020]     These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either alone or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The invention will be described in further detail hereinafter with reference to illustrative preferred embodiments shown in the accompanying drawing figures, in which:  
         [0022]      FIG. 1   a  shows a sectional view through a first centrifuge embodiment according to the invention;  
         [0023]      FIG. 1   b  shows a three-dimensional view of the centrifuge shown in  FIG. 1   a;    
         [0024]      FIG. 2   a  shows a sectional view through an alternatively constructed centrifuge according to the invention;  
         [0025]      FIG. 2   b  shows a three-dimensional view of the centrifuge shown in  FIG. 2   a.    
         [0026]      FIG. 3  shows a further sectional view of the centrifuge shown in  FIG. 2   a.    
         [0027]      FIG. 4   a  shows a sectional view of a centrifuge embodiment with a drive turbine; and  
         [0028]      FIG. 4   b  shows a three dimensional view of the centrifuge shown in  FIG. 4   a.   
     
    
       [0029]     In the drawings, like parts are identified by like reference numerals.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]      FIG. 1   a  shows a soot centrifuge  10  which is constructed as an in-line centrifuge and is arranged between a raw gas inlet pipe  11  and a clean gas outlet pipe  12 . The centrifuge is located in a housing  13 , which is directly connected to the raw gas inlet pipe and the clean gas outlet pipe and has a flange joint or connection  14 , which is provided with a suitable closure system  15 . Coaxial bearings  18  and  19  are provided adjacent both the raw gas inlet and also the clean gas outlet, which support the centrifuge rotor  20 . The bearings  18  and  19  are advantageously a slide bearing with ceramic bushings  21 ,  22 , which are resistant to high temperatures. The bearing  18  is attached to struts  23 ,  24 . The bearing  19  is arranged on a housing cover  25 , which joins outlet pipe  12 .  
         [0031]     The centrifuge has drive vanes  26  on the gas inlet side which cause the centrifuge rotor to rotate when exhaust gases flow in. The centrifuge itself is substantially a rotatable body having an inner housing wall  27  on which the separated soot  28  can be deposited. The centrifuge further comprises a plurality of flow reversing devices in the form of plate disks  29 , which achieve a diversion or flow reversal of the exhaust gas stream. On the outlet side, the centrifuge is open to the clean gas outlet pipe  12  and optionally can be provided there with drive vanes under appropriate circumstances. The number of the plate disks  29  depends upon the desired degree of separation or the separation efficiency, and can be varied. In some circumstances a small number of plate disks is sufficient to achieve the desired effect.  
         [0032]     The contaminated exhaust gas flows through the raw gas inlet pipe  11  into the radially outer region of the centrifuge rotor. There it is caused to rotate so that due to the centrifugal force the soot particles  28  are deposited against the housing inner wall  27 . The exhaust gas thereafter flows in accordance with the arrows  30 ,  31  into the radially inner region of the centrifuge rotor and is subjected to a flow diversion or reversal and conducted to the clean gas outlet pipe  12  in accordance with arrow  32 .  
         [0033]     To support the adhesion of soot particles to the housing inner wall  27 , the wall can be roughened. To improve the burn-off characteristics, the inner wall  27  can be coated with a catalyst. By opening the flange connection  14 , it is possible to exchange the entire centrifuge rotor without particular difficulty.  
         [0034]     The three-dimensional depiction in  FIG. 1   b  clearly shows once again the drive vanes  26 , which drive the rotor, as well as the mounting of the bearing or the ceramic bushing  21  via the four struts  23 ,  24 ,  33 ,  34 .  
         [0035]      FIG. 2   a  shows a supplemented variant of a soot centrifuge  10  according to the invention. In order to avoid unnecessary repetition, reference is made to the description of  FIG. 1   b.  The difference with respect to the centrifuge shown in  FIG. 1   b  is in the clean gas line or passage, which is formed by the openings of the individual plate disks  29  together with a pipe nipple  35  which leads to the clean gas outlet pipe  12 . In this clean gas passage  35  there is a stationarily arranged fixed filter cartridge  37 . This filter cartridge  37  may be comprised, for example, of a non-woven metal mesh which is arranged around a supporting body. The fixed filter cartridge  37  is attached to the clean gas outlet pipe  12  via a flange connection  38 . The filter cartridge  37  serves to filter out the soot in the exhaust gas under certain operating conditions, e.g. before start-up of the centrifuge. This soot is deposited on the surface of the filter cartridge.  
         [0036]     In order to avoid accumulation of soot on the filter cartridge  37 , a cleaning device also is provided. The cleaning is effected by a swirl of air which lifts the soot from the surface of the filter  37  and deposits the soot particles on the rotating plate disks  29  during the operation of the centrifuge, which, in turn, convey the soot radially outwardly against the housing inner wall  27 .  
         [0037]     To achieve this cleaning, three vanes  39 ,  40  and  41  are provided distributed around the circumference of the filter cartridge, as shown in  FIG. 3 . These vanes  39 ,  40  and  41  turn with the centrifuge, i.e. they are arranged on the inner openings of the plate disks  29 , and have only a slight spacing from the filter cartridge  37 . The vanes  39 ,  40  and  41  generate a swirling gas flow which lifts the soot particles from the filter cartridge  37  and carries them outwardly onto the spinning plate disks  29 .  
         [0038]     As shown in  FIG. 3 , the spacing of the plate disks  29  relative to the housing inner wall  27  is rather small. The relatively large diameter of the plate disks  29  improves the degree of separation achieved by the soot centrifuge.  
         [0039]      FIG. 2   b  shows once again a three-dimensional representation of the soot centrifuge shown in a sectional view in  FIG. 2   a.  The filter cartridge  37  and its position in the clean gas line  35  can be clearly seen. Likewise the turbulence generating vane  39  can be seen, which is affixed to the plate disks and is spaced only a small distance from the fixed filter cartridge  37 .  
         [0040]      FIG. 4   a  shows a soot centrifuge in which the drive is effected via a turbine  41 . The turbine  41  is comprised of a turbine housing  42  and a turbine rotor  43 . The turbine rotor  43  is mounted in a slide bearing bushing  44  and connected to the centrifuge rotor.  
         [0041]     When the soot-laden exhaust gases flow through the tangentially arranged raw gas inlet  45  shown in  FIG. 4   b,  the turbine  41  causes the soot separator to rotate, the raw gas flows through the turbine in accordance with arrow  46  past the struts  47 ,  48  into the interior space of the centrifuge rotor. This centrifuge is also equipped with a supplemental filter cartridge  37  for cleaning the gas under certain operating conditions of the centrifuge.  
         [0042]     The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.