Exhaust System For An Internal Combustion Engine, and Method For Operating Such An Exhaust System

Abstract

An exhaust system of an internal combustion engine includes a first filter device and a second filter device located downstream of the first. Both filter devices filter soot particles out of the exhaust gas. At least the first filter device has a catalytic material, which promotes an exothermic soot burnoff in such a way that as a result of the corresponding heating up of the exhaust gas, the soot burnoff in the second filter device is set in motion. The materials of the two filter devices are selected such that the soot burnoff in the first filter device ensues at a lower temperature and/or at a similar temperature is stronger than in the second filter device.

1 - 11 . (canceled)  
   
   
       12 . In an exhaust system for an internal combustion engine, in particular in a motor vehicle, having a first filter device and a second filter device, located downstream of the first, each of which filters soot particles out of the exhaust gas, and at least the first filter device has a catalytic material which promotes an exothermic soot burnoff, in such a manner that as a result of the corresponding heating up of the exhaust gas, the soot burnoff in the second filter device is set in motion, the improvement wherein the materials of first and second filter devices are selected such that the soot burnoff in the first filter device ensues at a lower temperature and/or at a similar temperature is stronger than in the second filter device.  
   
   
       13 . The exhaust system as defined by  claim 12 , wherein essentially no catalytic material that promotes the soot burnoff is present in the second filter device.  
   
   
       14 . The exhaust system as defined by  claim 12 , wherein the first filter device comprises a depth filter, preferably comprising an open-pore ceramic foam, and the second filter device comprises a surface filter, preferably of metal and even more preferably of special steel.  
   
   
       15 . The exhaust system as defined by  claim 13 , wherein the first filter device comprises a depth filter, preferably comprising an open-pore ceramic foam, and the second filter device comprises a surface filter, preferably of metal and even more preferably of special steel.  
   
   
       16 . The exhaust system as defined by  claim 12 , wherein the second filter device comprises a catalytic material which promotes the oxidation of CO to CO 2  and/or the oxidation of NO to NO 2 .  
   
   
       17 . The exhaust system as defined by  claim 13 , wherein the second filter device comprises a catalytic material which promotes the oxidation of CO to CO 2  and or the oxidation of NO to NO 2 .  
   
   
       18 . The exhaust system as defined by  claim 14 , wherein the second filter device comprises a catalytic material which promotes the oxidation of CO to CO, and/or the oxidation of NO to NO 2 .  
   
   
       19 . The exhaust system as defined by  claim 16 , wherein the second filter device comprises a catalytic material, which includes platinum and/or palladium.  
   
   
       20 . The exhaust system as defined by  claim 17 , wherein the second filter device comprises a catalytic material, which includes platinum and/or palladium.  
   
   
       21 . The exhaust system as defined by  claim 18 , wherein the second filter device comprises a catalytic material, which includes platinum and/or palladium.  
   
   
       22 . The exhaust system as defined by  claim 19 , wherein the catalytic material is coated on a large-surface-area oxide or directly on a filter body.  
   
   
       23 . The exhaust system as defined by  claim 20 , wherein the catalytic material is coated on a large-surface-area oxide or directly on a filter body.  
   
   
       24 . The exhaust system as defined by  claim 21 , wherein the catalytic material is coated on a large-surface-area oxide or directly on a filter body.  
   
   
       25 . The exhaust system as defined by  claim 12 , wherein the first filter device and the second filter device are located immediately adjacent one another.  
   
   
       26 . The exhaust system as defined by  claim 14 , wherein the first filter device and the second filter device are located immediately adjacent one another.  
   
   
       27 . The exhaust system as defined by  claim 16 , wherein the first filter device and the second filter device are located immediately adjacent one another.  
   
   
       28 . The exhaust system as defined by  claim 12 , wherein the first filter device and the second filter device are integrated into a filter unit.  
   
   
       29 . The exhaust system as defined by  claim 12 , wherein the first filter device comprises at least one catalytic material, which is a member of the following group: 1 to 50 weight % Ag on an oxidic substrate, and/or V and/or Mo and/or W and/or Mn and/or Cu on an oxidic substrate, the substrate including: Al 2 O 3 , TiO 2 , CeO 2 , ZrO 2 , and/or SiO 2 ; Ag in chemical combination with oxides of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Al, and/or Zr, in particular Ag 2 CrO 4  or AgMn 2 O 5 ; metal vanadate; molybdate; tungstenates; metal-V mixed oxide, in particular Cs 2 V 2 O 4 ; Cr mixed oxide; Mo mixed oxide; manganese oxide; rhenium oxide; metal manganate; metal rhenate.  
   
   
       30 . A method for operating an exhaust system for an internal combustion engine, in particular in a motor vehicle, having a first filter device and a second filter device, located downstream of the first, each of which filter soot particles out of the exhaust gas, and at least the first filter device has a catalytic material which promotes an exothermic soot burnoff in such a manner that as a result of the corresponding heating up of the exhaust gas, the soot burnoff in the second filter device is set in motion, the method comprising selecting the materials of the two filter devices are selected such that the soot burnoff in the first filter device ensues at a lower temperature and/or at a similar temperature is stronger than in the second filter device.  
   
   
       31 . The method as defined by  claim 30 , wherein, for regenerating the filter devices, the exhaust gas temperature upstream of the first filter device is elevated to a first level, at which in the first filter device a soot burnoff ensues to such an extent that as a result the exhaust gas temperature is additionally elevated to a second level, at which in the second filter device a soot burnoff is likewise set into motion.