WO2015116145A1

WO2015116145A1 - On-board diagnostic monitoring of selective catalytic reduction catalysts

Info

Publication number: WO2015116145A1
Application number: PCT/US2014/014052
Authority: WO
Inventors: Richard J. Ancimer; Suo GUOTAO
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2014-01-31
Filing date: 2014-01-31
Publication date: 2015-08-06
Anticipated expiration: 2016-07-31

Abstract

Systems, methods and apparatus are disclosed for enabling an on-board diagnostic of a selective catalytic reduction catalyst under operating conditions that reduce or prevent false positive indications of a faulty catalyst. The catalyst can be in an exhaust system that receives exhaust gas produced by operation of an internal combustion engine connected to the exhaust system.

Description

ON-BOARD DIAGNOSTIC MONITORING OF SELECTIVE CATALYTIC

REDUCTION CATALYSTS

Field of the Invention:

[0001] The present invention relates generally to selective catalytic reduction (SCR) in exhaust systems, and in particular to in-board diagnostic monitoring of SCR catalysts.

BACKGROUND

[0002] NOx emission requirements and particulate standards are becoming more stringent in many markets. To meet the lower NOx emission requirements, selective catalyst reduction (SCR) aftertreatment systems are often used. The high sulfur content of the fuel used in certain markets, such as in emerging markets where fuel sulfur levels may vary widely, can temporarily deteriorate SCR catalyst performance, especially under low temperature operating conditions. The SCR performance deterioration caused by the temporary accumulation of sulfur may eventually trigger an engine derate, fault code or other indication of a faulty SCR catalyst when an OBD is performed under these conditions. However, since these sulfur accumulation conditions are temporary, the OBD indication of a faulty SCR catalyst performance may be incorrect, resulting in unnecessary derate conditions or service events. Therefore, a need remains for further improvements in systems, apparatus, and methods for OBD of SCR catalysts. SUMMARY

[0003] Systems, methods and apparatus are disclosed for performing an OBD of an SCR catalyst under conditions which reduce or prevent false positives of faulty SCR performance. In one embodiment, a system, method and/or apparatus is configured to enable an OBD of an SCR catalyst in an exhaust system when the engine is operating at a temperature above an OBD temperature threshold. In another embodiment, a system, method and/or apparatus is configured to enable the performance of an OBD of an SCR catalyst in an exhaust system when the engine connected to the exhaust system is operating in an OBD fuelling range. In a further embodiment, the OBD fuelling range is located within a fuelling range that corresponds to high exhaust temperatures. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. Further embodiments, forms, objects, features, advantages, aspects, and benefits shall become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Fig. 1 is a schematic illustration of a system including an exemplary engine and exhaust aftertreatment system.

[0005] Fig. 2 is a flow diagram of one embodiment of a procedure that can be performed to enable an OBD of an SCR catalyst.

[0006] Fig. 3 is a flow diagram of another embodiment of a procedure that can be performed to enable an OBD of an SCR catalyst.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0007] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, any alterations and further modifications in the illustrated embodiments, and any further applications of the principles of the invention as illustrated therein as would normally occur to one skilled in the art to which the invention relates are contemplated herein.

[0008] With reference to FIG. 1, there is illustrated a system 100 that includes an exhaust aftertreatment system 110. System 100 may be provided on a vehicle powered by an engine 102 such as a diesel engine, or on an engine 102 utilized in other applications such as power generation or pumping systems. Engine 102 includes an intake system 104 through which charge air enters and an exhaust system 106 through which exhaust gas resulting from combustion in engine 102 exits, it being understood that not all details of these systems that are typically present are shown. Before entering the atmosphere, however, the exhaust gas is treated by one or more aftertreatment devices in the exhaust aftertreatment system 110.

[0009] The exhaust system 106 includes the exhaust aftertreatment system 110 having a selective catalytic reduction (SCR) catalyst 116, and a location for receiving a reductant from a reductant dosing system 120. The exhaust aftertreatment system 110 may also include a diesel oxidation catalyst (DOC) 112, and a diesel particulate filter (DPF) 114 upstream of SCR catalyst 116. In certain embodiments, the DOC 112 and DPF 114 may not be present, may be located in different locations than what is shown in Fig. 1, and/or may be provided at multiple locations.

[0010] The system 100 further includes a reductant injector 122 operationally coupled to the exhaust conduit at a position upstream of the SCR catalyst 116 with its outlet, or nozzle, arranged to spray reductant into the exhaust system 106 where it mixes with engine exhaust gas produced by engine 102. SCR catalyst 116 promotes a chemical reaction between the reductant and NO_x in the exhaust gas that converts substantial amounts of NO_x to reduce NO_x emissions before the exhaust gas passes into the atmosphere. The reductant injector 122 is fluidly coupled to a reductant source 124, such as a storage tank for storing a liquid reductant or a housing for storing a dry reductant in a solid storage media that is released in gaseous form when heated. The reductant is any type of reductant utilized in an SCR aftertreatment system that results in ammonia being utilized as the final reductant - including at least ammonia (gaseous or aqueous) and urea.

[0011] The aftertreatment system 110 may include one or more other

aftertreatment components not shown, such as an ammonia oxidation (AMOX) catalyst, an ammonia slip catalyst, and various temperature, pressure and exhaust gas constituent sensors. Exhaust system 106 may also include various components not shown, such an exhaust gas recirculation system, a turbocharger system, coolers, and other components connecting exhaust system 106 to intake system 104.

[0012] The system 100 further includes a controller 130. In certain embodiments, the controller 130 forms a portion of a processing subsystem including one or more computing devices having memory, processing, and communication hardware. The controller 130 may be a single device or a distributed device, and the functions of the controller may be performed by hardware or software.

[0013] Controller 130 is in communication with any component of the system 100 to receive inputs and provide commands to, for example, interpret operating parameters, control various actuators, switches and other components, and perform diagnostics.

Controller 130 is operatively coupled with and configured to store instructions in a memory which are readable and executable by controller 130 to perform on-board diagnostic (OBD) tests in response to signals received and interpreted by controller 130 from sensors connected to components of the system 100.

[0014] In FIG. 1, controller 130 is further operatively coupled with and may receive signals from SCR catalyst temperature sensor 132, engine exhaust temperature sensor 134, and reductant storage tank level sensor 136. Other aftertreatment system sensors not shown can also be connected to controller 130 to provide operating condition signals, such as exhaust flow rates, reductant concentrations and/or amounts, oxygen amounts or concentrations, pressure conditions, and NOx amounts or concentrations at one or more locations in SCR catalyst 116 and exhaust system 106. SCR catalyst temperature sensor 132 is operable to provide a signal indicating the temperature of a bed of SCR catalyst 116. Engine exhaust temperature sensor 134 is operable to provide a signal indicating the temperature of the exhaust gas from the engine 102. Reductant storage tank level sensor 136 is operable to provide a signal indicating the level of the reductant in reductant storage tank 124. SCR catalyst temperature sensor 132 and engine exhaust temperature sensor 134 need not be in direct communication with the exhaust system 106, and can be located at any position within system 100 that provides a suitable actual or virtual indication of an exhaust system temperature and/or a temperature of one or more aftertreatment system components in the system 100.

[0015] System 100 may further include a fuelling system 150 that includes a fuel line 152 connected to engine 102 to deliver a fuelling amount to one or more cylinders 158 of engine 102 according to a fuelling command from controller 130 that satisfies a torque request. Controller 130 may also be connected to one or more engine sensors 154 that provide outputs of engine speed and engine output torque, which are used to determine the fuelling command and the associated fuelling amount from a speed versus torque fuel map stored in controller 130.

[0016] The system 100 further includes an output device 140 responsive to commands from the controller 130. It should be appreciated that the output device 140 can be any suitable device for displaying a result of the OBD tests to a user, operator, service technician, or other party, and can include an indicator lamp, a gauge, a printer, a memory device, an audible alarm, a display device, and/or other suitable output device.

[0017] FIG. 2 illustrates a flow diagram of an exemplary procedure 200 for enabling an OBD for determining a fault condition of SCR catalyst 116 that is put in operation by programming into controller 130 for use in, for example, system 100. A fault condition can be any indication or measurement that the NOx conversion capability of SCR catalyst 116 is degraded below a predetermined performance threshold. Procedure 200 begins at operation 202 which may correspond to an engine start-up request, for example.

[0018] Procedure 200 continues to operation 204 to establish an OBD fuelling range corresponding to high exhaust temperature conditions. In one embodiment, a high temperature exhaust condition exists at temperatures above about 300 °C. In another embodiment, a high temperature exhaust condition exists at temperatures above about 320 °C. In still another embodiment, a high temperature exhaust condition exists above a temperature effective to remove sulfur constituents, such as ammonia sulphate, deposited on SCR catalyst 116 such that the OBD of SCR catalyst 116 is not significantly negatively impacted by the use of sulfur containing fuels, reducing the occurrence of false positive indications of a faulty SCR catalyst condition. In a further embodiment, the OBD fuelling range is further selected so that the OBD fuelling range lies within a standard test cycle established for performance of an SCR catalyst OBD. Accordingly, in this embodiment, the OBD fuelling range corresponds to high exhaust temperature conditions that are also covered by standard OBD test cycles so that the OBD is enabled under test cycle conditions.

[0019] Procedure 200 continues at operation 206 to determine a fuelling amount to the engine. Procedure 200 proceeds from operation 206 to conditional 208 to determine whether the fuelling amount to the engine is within the OBD fuelling range. If conditional 208 is negative, procedure 200 continues at operation 210 where the OBD of SCR catalyst 116 is disabled and the procedure continues at procedure 206. If conditional 208 is positive, procedure 200 continues at operation 212 where the OBD test for SCR catalyst is enabled. After completion of the OBD, the procedure ends at 214.

[0020] FIG. 3 illustrates a flow diagram of an exemplary procedure 300 for enabling an OBD diagnostic that is put in operation by programming into controller 130 for use in, for example, system 100. Procedure 300 begins at operation 302 which may correspond to an engine start-up request, for example. Procedure 300 continues at operation 304 where exhaust system operating conditions are determined.

[0021] The determination of exhaust system operating conditions can the evaluation of various inputs from actual and/or virtual sensors associated with the engine and exhaust system. For example a first input 306 can include a time of operation of the exhaust system at a low temperature operating condition. A second input 308 can include an amount of reductant dosed or injected during the low temperature operating condition of input 306. A third input 310 includes a time of operating of the exhaust system at a high temperature operating condition.

[0022] Procedure 300 continues at operation 312 to select one of a first, high OBD temperature threshold and a second, low OBD temperature threshold in response to the first, second and third inputs 306, 308, 310 that provide an indication of current operating conditions of the exhaust system and the ammonia sulphate accumulation on SCR catalyst 116. The first and second OBD temperature thresholds may be determined based on, for example, ambient conditions, engine operating conditions, or other exhaust system conditions. The first, high OBD temperature threshold is selected when the SCR catalyst 116 is operated in a low temperature condition and a threshold amount of reductant is dosed in the low temperature condition, as indicated by inputs 306, 308, indicating ammonium sulphate accumulation on SCR catalyst 116 that could affect the OBD. The selection of the high OBD temperature threshold ensures that the OBD diagnostic does not run when such conditions are likely to exist. The second, low OBD temperature threshold is selected when the SCR catalyst 116 has been operating in a high temperature condition for a sufficient time that ammonium sulphates are removed, allowing the OBD of SCR catalyst 116 to be performed at lower exhaust temperatures without being adversely affected by ammonium sulphate deposits.

[0023] Procedure 300 continues at operation 314 to enable an OBD of SCR catalyst 116 when the exhaust temperature is greater than the selected one of the first or second OBD temperature thresholds. The exhaust temperature can correspond to a temperature of the exhaust gas at one or more locations, a temperature of SCR catalyst 116, a temperature of a component of the exhaust system, or a combination of these. The exhaust temperature can be determined from a single input from a temperature sensor or combination of sensors, an average or other determination based on a number of inputs from one or more temperature sensors, an input from a virtual temperature sensor, or a derived or calculated value from operating conditions. Procedure 300 returns to operation 304 to continue to determine exhaust system operating conditions during engine operation or ends at 316 in response to, for example, a key-off event.

[0024] In one embodiment, the high OBD temperature threshold is about 320° C and the low OBD temperature threshold is about 240° C. In another embodiment, the high OBD temperature threshold ranges from about 320° C to about 350° C and the low OBD temperature threshold ranges from about 240° C to about 280° C. Other temperature thresholds are also contemplated and not precluded, and can vary according to catalyst conditions, catalyst formulations, fuels conditions, or other parameters.

[0025] Various aspects of the systems and methods are disclosed herein. For example, one aspect involves a system that includes an internal combustion engine having an exhaust system for receiving an exhaust gas produced from operation of the internal combustion engine. The system also includes an exhaust aftertreatment system having a source of a reductant for injection into the exhaust gas and an SCR catalyst positioned downstream of a reductant injection location into the exhaust gas. The system also includes a plurality of sensors operable to provide signals indicating a temperature condition of the exhaust system and a fuelling amount to the internal combustion engine. The system further includes a controller connected to the plurality of sensors operable to interpret the signals from the plurality of sensors. The controller is configured to enable an OBD of the SCR catalyst in response to at least one of the temperature condition and the fuelling amount indicating a high temperature operating condition of the SCR catalyst.

[0026] In one embodiment, the fuelling amount indicating the high temperature operating condition lies within a fuelling range that generates high exhaust temperature conditions by operation of the internal combustion engine in the fuelling range. In a refinement of this embodiment, the fuelling range lies within a predetermined fuelling range for OBD monitoring. The predetermined fuelling range encompasses high exhaust temperature conditions and low exhaust temperature conditions.

[0027] In another embodiment of the system, the high temperature operating condition is present when the temperature condition of the exhaust system exceeds a high temperature threshold. In a refinement of this embodiment, the controller is further configured to set the high temperature threshold in response to the SCR catalyst receiving exhaust flow in a low temperature operating condition for a time period over which a threshold amount of the reductant is injected into the exhaust gas. In a further refinement, the controller is configured to set a low temperature threshold that is lower than the high temperature threshold in response to the SCR catalyst receiving exhaust flow in the high temperature operating condition for a threshold amount of time. In yet a further refinement, in response to setting the low temperature threshold, the controller is configured to enable the OBD when the temperature condition of the exhaust system exceeds the low temperature threshold.

[0028] In another embodiment, the controller includes an OBD component and the system includes an OBD interface in electrical communication with the controller. The controller alerts the OBD interface when the OBD component indicates a fault condition of the SCR catalyst. In a refinement of this embodiment, the controller is further configured to set an OBD threshold temperature and the OBD component is operable to determine a fault condition of the SCR catalyst when the temperature condition of the exhaust system is above the OBD threshold temperature. In a further refinement, the OBD threshold temperature is set to a low exhaust threshold temperature in response to the exhaust system being in the high temperature operating condition for a threshold amount of time. In another refinement, the OBD threshold temperature is set to a high exhaust temperature threshold in response to the exhaust system being in a low temperature operating condition and SCR catalyst receiving a threshold amount of reductant while the exhaust system is in the low temperature operating condition.

[0029] According to another aspect, a method includes providing an OBD fuelling range for an SCR catalyst and the OBD fuelling range lies within a fuelling range of an internal combustion engine corresponding to a high temperature exhaust condition;

determining a fuelling amount while operating the internal combustion engine to produce an exhaust gas that is provided to the SCR catalyst; and enabling an OBD test of the SCR catalyst only when the fuelling amount is in the OBD fuelling range. [0030] In one embodiment, the high temperature exhaust condition is at least 300° C. In another embodiment the high temperature exhaust condition is at least 350° C. In yet another embodiment, the OBD fuelling range lies within a portion of a standard test cycle of the engine for determining a fault condition of the SCR catalyst. In another embodiment, the fuelling amount is determined by measuring the speed and torque of the internal combustion engine and determining the fuelling amount from a fuelling amp of speed versus torque.

[0031] In another embodiment, a method includes establishing a first temperature threshold and a lower, second temperature threshold of an exhaust system, each of the first and second temperature thresholds being selectable for enabling a performance of an OBD of an SCR catalyst in the exhaust system in response to respective ones of a first operating condition and a second operating condition of the SCR catalyst; determining a presence of one of the first operating condition and the second operating condition in response to a temperature of the exhaust system and a reductant amount dosed upstream of the SCR catalyst during operation of an internal combustion engine that produces exhaust gas into the exhaust system; setting an OBD threshold temperature to one of the first temperature threshold and the second temperature threshold in response to determining the presence of one of the first operating condition and the second operating condition, respectively; and enabling an OBD of the SCR catalyst for performance when the exhaust system

temperature is above the OBD threshold temperature.

[0032] In one embodiment, the method includes setting the OBD threshold temperature to the first temperature threshold in response to the presence of the first operating condition and the first operating condition includes the exhaust system operating in a low temperature operating range during which a threshold amount of the reductant is dosed into the exhaust system. In one refinement of this embodiment, the first temperature threshold is in a range from about 320° C to about 350° C.

[0033] In another embodiment, the method includes setting the OBD threshold temperature to the second temperature threshold in response to the presence of the second operating condition and the second operating condition includes the exhaust system operating in a high temperature operating range for a predetermined amount. In one refinement of this embodiment, the second temperature threshold is in a range from about 240° C to about 280° C.

[0034] In another embodiment, the method includes setting the OBD threshold temperature to the second temperature threshold in response to a cold start of the internal combustion. In a refinement of this embodiment, in response to starting of the internal combustion engine, the method includes maintaining the OBD threshold temperature at the respective one of the first temperature threshold and the second temperature threshold selected during an operating period that ended prior to starting the internal combustion engine.

[0035] While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain exemplary embodiments have been shown and described and that all changes and modifications that come within the spirit of the inventions are desired to be protected.

[0036] It should be understood that while the use of words such as preferable, preferably, preferred or more preferred utilized in the description above indicate that the feature so described may be more desirable, it nonetheless may not be necessary and embodiments lacking the same may be contemplated as within the scope of the invention, the scope being defined by the claims that follow. In reading the claims, it is intended that when words such as "a," "an," "at least one," or "at least one portion" are used there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. When the language "at least a portion" and/or "a portion" is used the item can include a portion and/or the entire item unless specifically stated to the contrary.

Claims

WHAT IS CLAIMED IS:

1. A system, comprising:

an internal combustion engine having an exhaust system for receiving an exhaust gas produced from operation of the internal combustion engine;

an exhaust aftertreatment system that includes a source of a reductant for injection into the exhaust gas, the exhaust aftertreatment system further comprising a selective catalytic reduction (SCR) catalyst positioned downstream of a reductant injection location into the exhaust gas;

a plurality of sensors operable to provide signals indicating a temperature condition of the exhaust system and a fuelling amount to the internal combustion engine; and

a controller connected to the plurality of sensors operable to interpret the signals from the plurality of sensors, wherein the controller is configured to enable an on-board diagnostic (OBD) of the SCR catalyst in response to at least one of the temperature condition and the fuelling amount indicating a high temperature operating condition of the SCR catalyst.

2. The system of claim 1, wherein the fuelling amount indicating the high temperature operating condition lies within a fuelling range that generates high exhaust temperature conditions by operation of the internal combustion engine.

3. The system of claim 2, wherein the fuelling range lies within a predetermined fuelling range for OBD monitoring, the predetermined fuelling range being defined by high exhaust temperature conditions.

4. The system of claim 1, wherein the high temperature operating condition is present when the temperature condition of the exhaust system exceeds a high temperature threshold.

5. The system of claim 4, wherein the controller is further configured to set the high temperature threshold in response to the SCR catalyst receiving exhaust flow in a low temperature operating condition for a time period over which a threshold amount of the reductant is injected into the exhaust gas.

6. The system of claim 5, wherein the controller is configured to set a low temperature threshold for enabling the OBD of the SCR catalyst that is lower than the high temperature threshold in response to the SCR catalyst receiving exhaust flow in the high temperature operating condition for a threshold amount of time.

7. The system of claim 6, wherein, in response to setting the low temperature threshold, the controller is configured to enable the OBD of the SCR catalyst when the temperature condition of the exhaust system exceeds the low temperature threshold.

8. The system of claim 1, wherein the controller includes an OBD component and further comprising an OBD interface in electrical communication with the controller, wherein the controller alerts the OBD interface when the OBD component indicates a fault condition of the SCR catalyst.

9. The system of claim 8, wherein:

the controller is further configured to set an OBD threshold temperature; and the OBD component is operable to determine a fault condition of the SCR catalyst when the temperature condition of the exhaust system is above the OBD threshold temperature.

10. The system of claim 9, wherein the OBD threshold temperature is set to a low exhaust threshold temperature in response to the exhaust system being in the high temperature operating condition for a threshold amount of time.

11. The system of claim 10, wherein the OBD threshold temperature is set to a high exhaust temperature threshold in response to the exhaust system being in a low temperature operating condition and SCR catalyst receiving a threshold amount of reductant while the exhaust system is in the low temperature operating condition.

12. A method, comprising:

determining an on-board diagnostic (OBD) fuelling range for a selective catalytic reduction (SCR) catalyst that lies within a fuelling range of an internal combustion engine corresponding that produces a high temperature exhaust condition;

determining a fuelling amount while operating the internal combustion engine to produce an exhaust gas that is provided to the SCR catalyst; and enabling an OBD test of the SCR catalyst only when the fuelling amount is in the OBD fuelling range.

13. The method of claim 12, wherein the high temperature exhaust condition is 300° C or more.

14. The method of claim 12, wherein the OBD fuelling range lies within a portion of a standard test cycle of the internal combustion engine for determining a fault condition of the SCR catalyst.

15. The method of claim 12, wherein the fuelling amount is determined by measuring a speed and a torque of the internal combustion engine and determining the fuelling amount from a fuelling map of speed versus torque.

16. A method, comprising:

establishing a first temperature threshold and a lower, second temperature threshold of an exhaust system, each of the first and second temperature thresholds being selectable for enabling a performance of an on-board diagnostic (OBD) of a selective catalytic reduction (SCR) catalyst in the exhaust system in response to respective ones of a first operating condition and a second operating condition of the SCR catalyst;

determining a presence of one of the first operating condition and the second operating condition in response to a temperature of the exhaust system and a reductant amount dosed upstream of the SCR catalyst during operation of an internal combustion engine that produces exhaust gas into the exhaust system;

setting an OBD threshold temperature to one of the first temperature threshold and the second temperature threshold in response to determining the presence of one of the first operating condition and the second operating condition, respectively; and

enabling an OBD of the SCR catalyst for performance when the exhaust system temperature is above the OBD threshold temperature.

17. The method of claim 16, further comprising setting the OBD threshold temperature to the first temperature threshold in response to the presence of the first operating condition, wherein the first operating condition includes the exhaust system operating in a low temperature operating range during which a threshold amount of the reductant is dosed into the exhaust system.

18. The method of claim 17, wherein the first temperature threshold is in the range from about 320° C to about 350° C.

19. The method of claim 16, further comprising setting the OBD threshold temperature to the second temperature threshold in response to the presence of the second operating condition, wherein the second operating condition includes the exhaust system operating in a high temperature operating range for a predetermined amount.

20. The method of claim 19, wherein the second temperature threshold is in the range from about 240° C to about 280° C.

21. The method of claim 16, further comprising setting the OBD threshold temperature to the second temperature threshold in response to a cold start of the internal combustion.

22. The method of claim 21, further comprising, in response to starting of the internal combustion engine, maintaining the OBD threshold temperature at the respective one of the first temperature threshold and the second temperature threshold selected during an operating period that ended prior to starting the internal combustion engine.