Method for the operation of an exhaust gas aftertreatment system

Abstract

The invention relates to a method for the operation of an exhaust gas aftertreatment system in an exhaust tract of an internal combustion engine. The exhaust gas aftertreatment system includes an SCR particle filter, a first reducing agent feed device for introducing the reducing agent into the exhaust tract upstream of the SCR particle filter, continuous regeneration of the SCR particle filter being possible using nitrogen dioxide as oxidizing agent, an SCR catalytic converter element arranged downstream of the SCR particle filter, and a second reducing agent feed device for introducing the reducing agent into the exhaust tract downstream of the SCR particle filter and upstream of the SCR catalytic converter element. A control unit regulates a quantity of reducing agent introduced into the exhaust tract by the first reducing agent feed device and/or by the second reducing agent feed device as a function of the temperature (T.sub.SCR-PF) of the SCR particle filter.

Claims

1. A method for operating an exhaust gas aftertreatment system in an exhaust tract of an internal combustion engine, the exhaust gas aftertreatment system including: an SCR particle filter configured to filter out and store particles contained in an exhaust gas generated by the internal combustion engine and to reduce nitrogen oxides contained in the exhaust gas using ammonia as a reducing agent, the SCR particle filter being configured to be continuously regenerated using nitrogen dioxide as another oxidizing agent, a first reducing agent feed device configured to introduce the reducing agent into a first area of the exhaust tract upstream of the SCR particle filter with respect to a direction of a flow of the exhaust gas, an SCR catalytic converter element arranged downstream of the SCR particle filter configured to reduce nitrogen oxides contained in the exhaust gas using the reducing agent, and a second reducing agent feed device configured to introduce the reducing agent into a second area of the exhaust tract downstream of the SCR particle filter and upstream of the SCR catalytic converter element, the method comprising: measuring an actual temperature of the SCR particle filter using a first temperature sensor; and regulating a quantity of the reducing agent introduced into the exhaust tract by at least one of the first reducing agent feed device and the second reducing agent feed device as a function of the actual temperature of the SCR particle filter, wherein the step of regulating includes introducing by the first reducing agent feed device no reducing agent into the exhaust tract when the actual temperature of the SCR particle filter is lower than a defined particle filter temperature value, and introducing by the first reducing agent feed device a defined quantity of reducing agent into the exhaust tract when the actual temperature of the SCR particle filter exceeds the defined particle filter temperature value, and the defined particle filter temperature value is lower than an SCR response temperature of the SCR particle filter at which nitrogen oxides contained in the exhaust gas are reduced by the SCR particle filter.

2. The method according to claim 1, wherein the SCR response temperature of the SCR particle filter is in a temperature range from 220 C. to 250 C.

3. The method according to claim 1, further comprising the step of measuring an actual temperature of the SCR catalytic converter element, wherein the step of regulating further comprises regulating the quantity of the reducing agent introduced into the exhaust tract by at least one of the first reducing agent feed device and the second reducing agent feed device as a function of the actual temperature of the SCR catalytic converter element.

4. The method according to claim 3, wherein the step of regulating includes introducing by the second reducing agent feed device no reducing agent into the exhaust tract when the measured temperature of the SCR catalytic converter element is lower than a defined catalytic converter element temperature value, and introducing by the second reducing agent feed device a defined quantity of the reducing agent into the exhaust tract when the measured temperature of the SCR particle filter exceeds the defined catalytic converter element temperature value.

5. The method of claim 4, wherein the defined catalytic converter element temperature value is lower than an SCR response temperature of the SCR catalytic converter element at which nitrogen oxides contained in the exhaust gas are reduced by the SCR particle filter.

6. The method of claim 5, wherein the SCR response temperature of the SCR particle filter is in a temperature range from 220 C. to 250 C.

7. The method of claim 4, wherein the defined catalytic converter element temperature value is in a temperature range from 150 C. to 190 C.

8. The method of claim 1, wherein the defined particle filter temperature value is in a temperature range from 150 C. to 190 C.

9. The method of claim 1, further comprising the step of measuring an actual temperature of the SCR catalytic converter element, wherein when the actual temperature of the SCR particle filter exceeds the defined particle filter temperature value and the actual temperature of the SCR catalytic converter element is lower than the defined catalytic converter element temperature value, the step of regulating includes introducing into the exhaust tract by the first reducing agent feed device a first quantity of reducing agent such that a substantially stoichiometric reducing agent-nitrogen oxide ratio prevails in the first area of the exhaust tract.

10. The method of claim 1, further comprising the step of measuring an actual temperature of the SCR catalytic converter element, wherein when the actual temperature of the SCR particle filter exceeds the defined particle filter temperature value and the actual temperature of the SCR catalytic converter element exceeds the defined catalytic converter element temperature value, the step of regulating includes introducing into the exhaust tract by the first reducing agent feed device a second quantity of reducing agent such that a quantity of reducing agent smaller than is required for a stoichiometric reducing agent-nitrogen oxide ratio is present in the first area of the exhaust tract.

11. The method of claim 10, wherein when the actual temperature of the SCR particle filter exceeds the defined particle filter temperature value and the actual temperature of the SCR catalytic converter element exceeds the defined catalytic converter element temperature value, the step of regulating includes introducing into the exhaust tract by the second reducing agent feed device a third quantity of reducing agent such that a substantially stoichiometric reducing agent-nitrogen oxide ratio prevails in the second area of the exhaust tract.

12. The method of claim 1, wherein the exhaust gas aftertreatment system includes an oxidation catalytic converter arranged upstream of the SCR particle filter, the method further comprising oxidizing by the oxidation catalytic converter nitrogen monoxide in the exhaust gas to form nitrogen dioxide.

13. The method of claim 1, wherein the exhaust gas aftertreatment system includes a nitrogen oxide storage element, the method further comprising storing and releasing by the nitrogen oxide storage element nitrogen oxides contained in the exhaust gas as a function of the exhaust gas temperature, the nitrogen oxide storage element containing at least one of barium nitrate and cerium oxide as a storage material.

14. The method of claim 1, wherein at least one of the SCR particle filter and the SCR catalytic converter element contains copper, vanadium, or at least one zeolite material as an SCR catalytic material.

15. A device including an internal combustion engine with an exhaust tract and an exhaust gas aftertreatment system incorporated in the exhaust tract, the exhaust gas aftertreatment system comprising: an SCR particle filter configured to filter out and store particles contained in an exhaust gas generated by the internal combustion engine and to reduce nitrogen oxides contained in the exhaust gas using ammonia as a reducing agent, the SCR particle filter being configured to be continuously regenerated using nitrogen dioxide as another oxidizing agent; a first reducing agent feed device configured to introduce the reducing agent into the exhaust tract upstream of the SCR particle filter with respect to a direction of a flow of the exhaust gas; an SCR catalytic converter element arranged downstream of the SCR particle filter and configured to reduce nitrogen oxides contained in the exhaust gas using the reducing agent; a second reducing agent feed device configured to introduce the reducing agent into the exhaust tract downstream of the SCR particle filter and upstream of the SCR catalytic converter element; and a control unit regulating a quantity of the reducing agent introduced into the exhaust tract by at least one of the first reducing agent feed device and the second reducing agent feed device as a function of a temperature of the SCR particle filter, wherein the control unit controls the first reducing agent feed device so that no reducing agent is introduced into the exhaust tract when the actual temperature of the SCR particle filter is lower than a defined particle filter temperature value, and further controls the first reducing agent feed device so that a defined quantity of reducing agent is introduced into the exhaust tract when the actual temperature of the SCR particle filter exceeds the defined particle filter temperature value, the defined particle filter temperature value being lower than an SCR response temperature of the SCR particle filter at which nitrogen oxides contained in the exhaust gas are reduced by the SCR particle filter.

16. A vehicle comprising the device according to claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantageous embodiments and/or developments together with the advantages thereof are explained in more detail below, merely by way of example, referring to drawings, of which:

(2) FIG. 1 is a side view of a truck having the device according to the invention;

(3) FIG. 2 is a schematic block drawing of the device according to the invention;

(4) FIG. 3 is a diagram explaining the method according to the invention; and

(5) FIG. 4 is a flow diagram explaining the sequence of the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(6) FIG. 1 shows a vehicle 1, here embodied as a truck, for example, having the device 3 (FIG. 2) according to the invention.

(7) As FIG. 2 shows, the device 3 comprises an internal combustion engine 5 as drive unit for the vehicle 1 and an exhaust tract 7, which is connected to the internal combustion engine 5 and through which an exhaust gas 9 from the internal combustion engine 5 flows. Viewed in the direction of flow of the exhaust gas, the exhaust tract 7 here comprises an oxidation catalytic converter 11, a first reducing agent introduction area 13, a SCR particle filter 15, a second reducing agent introduction area 17, and a SCR catalytic converter element 19.

(8) Starting from the internal combustion engine 5, the exhaust gas 9 first flows through the oxidation catalytic converter 11, which serves to partially oxidize nitrogen monoxide contained in the exhaust gas 9 to form nitrogen dioxide. Then the exhaust gas 9 flows past the first reducing agent introduction area 13, where a reducing agent for reducing the nitrogen oxides contained in the exhaust gas 9, here in the form of an aqueous urea solution, for example, can be introduced into the exhaust tract 7. The aqueous urea solution here is stored in a urea tank 21 of the device 3 and is introduced into the exhaust tract 7 by a first reducing agent feed device 22. The reducing agent feed device 22 here comprises a pump 23 and a straight-way valve 24, for example. The straight-way valve 24 here is connected and sends signals to a control unit 25, which serves to regulate and control the straight-way valve 24 and therefore the quantity of aqueous urea solution introduced into the exhaust tract 7 at the second reducing agent introduction area 17.

(9) The exhaust gas 9 then flows through the SCR particle filter 15, which serves to filter out from the exhaust gas 9 and to store particles, in particular carbon particles, contained in the exhaust gas 9 from the internal combustion engine 5. The SCR particle filter 15 here is continuously regenerated by the nitrogen dioxide formed by the oxidation catalytic converter 11. As an additional measure for regenerating the SCR particle filter 15, the particles accumulated in the SCR particle filter 15 could also be burned at defined times. Here the times may be fixed at defined time intervals, for example, or determined by calculating the actual storage capacity of the SCR particle filter 15. The particles may be burned, for example, by injecting an increased quantity of fuel, heating the particle filter or causing exhaust gas to back up. In addition, the SCR particle filter 15 also comprises a SCR catalytic material, which serves to reduce nitrogen oxides contained in the exhaust gas 9 from the internal combustion engine 5 using ammonia as reducing agent. The ammonia is introduced into the exhaust tract by the reducing agent feed device 22 in the form of the aqueous urea solution. The SCR particle filter 15 preferably comprises copper and/or vanadium and/or at least zeolite as SCR catalytic material.

(10) From the SCR particle filter 15 the exhaust gas 9 from the internal combustion engine 5 flows past the second reducing agent introduction area 17, where the aqueous urea solution stored in the urea tank 21 can likewise be introduced into the exhaust tract 7. The aqueous urea solution is here introduced into the exhaust tract 7 by a second reducing agent feed device 26. The second reducing agent feed device 26 here likewise comprises a pump 27 and a straight-way valve 28, for example. The straight-way valve 28 here is likewise connected and sends signals to a control unit 25, which serves to regulate and control the straight-way valve 28 and therefore the quantity of aqueous urea solution introduced into the exhaust tract 7 at the second reducing agent introduction area 17. The control device 25 controls the straight-way valves 24 and 28 based on temperatures of the SCR particle filter 15 and the SCR catalytic converter element 19, e.g., using temperature sensors 14, 16, 18.

(11) Finally, the exhaust gas 9 from the internal combustion engine 5 flows through the SCR catalytic converter element 19, which serves to reduce nitrogen oxides likewise contained in the exhaust gas 9 from the internal combustion engine using ammonia as reducing agent. The ammonia needed for this purpose is introduced into the exhaust tract 7 by the reducing agent feed device 22 and/or by the reducing agent feed device 26. The SCR catalytic converter element 19 likewise preferably comprises copper and/or vanadium and/or at least one zeolite as SCR catalytic material.

(12) In an optional embodiment, a nitrogen oxide storage element 24 (shown in dashed lines) that stores and releases nitrogen oxide as a function of the exhaust gas temperature is arranged on the SCR particle filter 15. Alternatively, the nitrogen oxide storage element 24 could be arranged in the exhaust tract 7 upstream of the SCR particle filter 15 and/or upstream of the SCR catalytic converter element 19, and/or on the SCR catalytic converter element 19.

(13) FIG. 3 shows a diagram 29 representing the loading of the SCR particle filter 15 as a function of the quantity of aqueous urea solution introduced into the exhaust tract 7 by the reducing agent feed device 22. From a time to up to a time t.sub.1 such a quantity of aqueous urea solution is introduced into the exhaust tract 7 by the reducing agent feed device 22 that a greater quantity of reducing agent is present on the first reducing agent introduction area 13 than is required for a stoichiometric reducing agent-nitrogen oxide ratio. From the time t.sub.1 to a time t.sub.3 the reducing agent feed device 22 introduces such a quantity of aqueous urea solution into the exhaust tract 7, that a quantity of reducing agent smaller than is required for a stoichiometric reducing agent-nitrogen oxide ratio is present on the first reducing agent introduction area 13. Between the time t.sub.1 and a time t.sub.2 the reducing agent feed device 22 here introduces such a quantity of aqueous urea solution into the exhaust tract 7, that 80% of the quantity of reducing agent which is required for a stoichiometric reducing agent-nitrogen oxide ratio is present on the first reducing agent introduction area 13. Between the time t.sub.2 and the time t.sub.3 the reducing agent feed device 22 introduces such a quantity of aqueous urea solution into the exhaust tract 7 that 50% of the quantity of reducing agent which is required for a stoichiometric reducing agent-nitrogen oxide ratio is present on the first reducing agent introduction area 13.

(14) It can be seen from the diagram 29 that the particle loading of the SCR particle filter 15 increases, when the reducing agent feed device 22 introduces a quantity of aqueous urea solution into the exhaust tract 7 in excess of the stoichiometric quantity. The reason for this is the reduced continuous regeneration of the SCR particle filter 15, due to the competing reaction of the ammonia introduced with nitrogen dioxide. If a quantity of aqueous urea solution less than the stoichiometric quantity is introduced into the exhaust tract 7, the particle loading of the SCR particle filter 15 diminishes again. The diagram 29 therefore clearly shows that the continuous regeneration of the SCR particle filter 15 is disturbed by the introduction of excessive quantities of ammonia into the exhaust tract 7.

(15) In addition, the quantities of reducing agent introduced into the exhaust tract 7 by the reducing agent feed devices 22, 26 are regulated and controlled here by the control unit 25 as a function of the temperature of the SCR particle filter 15 and as a function of the temperature of the SCR catalytic converter element 19. This regulation and control is explained in more detail below with reference to FIG. 4.

(16) In an initial state the internal combustion engine 5 here is switched off, for example. Here no aqueous urea solution is introduced into the exhaust tract 7. After starting the internal combustion engine 5 at step 30, it is examined, in a step 31, whether the temperature of the SCR particle filter T.sub.SCR-PF is greater than or equal to a first release temperature T.sub.release,1. The release temperature T.sub.release,1 here, for example, is lower than a SCR response temperature of the SCR particle filter 15, at which the nitrogen oxides contained in the exhaust gas 9 can be reduced by the SCR particle filter 15 or at which the SCR particle filter 15 reaches its operating temperature for reducing the nitrogen oxides.

(17) If the temperature of the SCR particle filter 15 T.sub.SCR-PF is greater than or equal to the release temperature T.sub.release,1, the first reducing agent feed device 22 introduces a first defined mass flow m.sub.1 of aqueous urea solution into the exhaust tract 7. The first defined mass flow m.sub.1 here is designed in such a way that a substantially stoichiometric reducing agent-nitrogen oxide ratio prevails in the area of the first reducing agent feed device 22. The second reducing agent feed device 26 here still does not introduce any aqueous urea solution into the exhaust tract 7.

(18) In a step 33 it is then examined whether the temperature of the SCR catalytic converter element 19 T.sub.SCR-Kat, is greater than or equal to a second release temperature T.sub.release,2. The release temperature T.sub.release,2 here, for example is likewise lower than a SCR response temperature of the SCR catalytic converter element 19, at which the nitrogen oxides contained in the exhaust gas 9 can be reduced by the SCR catalytic converter element 19 or at which the SCR particle filter 15 reaches its operating temperature for reducing the nitrogen oxides.

(19) If the temperature of the SCR catalytic converter element 19 T.sub.SCR-Kat is greater than or equal to the release temperature T.sub.release,2, the first reducing agent feed device 22 introduces a second defined mass flow m.sub.2 of aqueous urea solution into the exhaust tract 7. The second defined mass flow m.sub.2 here is designed in such away that a quantity of reducing agent smaller than is required for a stoichiometric reducing agent-nitrogen oxide ratio is present in the area of the first reducing agent feed device 22. The second reducing agent feed device 26 then introduces a third defined mass flow m.sub.3 of aqueous urea solution into the exhaust tract 7. The third defined mass flow m.sub.3 is here is designed in such a way that a substantially stoichiometric reducing agent-nitrogen oxide ratio prevails in the area of the second reducing agent feed device 26.

(20) This regulation and control of the reducing agent feed devices 22, 26 serves for particularly efficient cleaning of the exhaust gas 9 from the internal combustion engine 5.

LIST OF REFERENCE NUMERALS

(21) 1 vehicle

(22) 3 device

(23) 5 internal combustion engine

(24) 7 exhaust tract

(25) 9 exhaust gas

(26) 11 oxidation catalytic converter

(27) 13 reducing agent introduction area

(28) 15 SCR particle filter

(29) 17 reducing agent introduction area

(30) 19 SCR catalytic converter element

(31) 21 urea tank

(32) 22 reducing agent feed device

(33) 23 pump

(34) 24 straight-way valve

(35) 25 control unit

(36) 26 reducing agent feed device

(37) 27 pump

(38) 28 straight-way valve

(39) 29 diagram

(40) 31 step

(41) 33 step

(42) m.sub.1 first mass flow

(43) m.sub.2 second mass flow

(44) m.sub.3 third mass flow

(45) t time

(46) t.sub.0 start time

(47) t.sub.1 first time

(48) t.sub.2 second time

(49) t.sub.3 third time

(50) T.sub.release1 first release temperature

(51) T.sub.release2 second release temperature

(52) T.sub.SCR-PF temperature of SCR particle filter

(53) T.sub.SCR-Kat temperature of SCR catalytic converter element