Abstract:
A method and control system for a selective catalytic reduction (SCR) catalytic converter and a diesel particulate filter (DPF) includes a DPF control module that determines a particulate matter (PM) load progress of the DPF and generates a DPF regeneration request based on the PM load progress. The control system also includes an SCR control module that selectively adjusts an ammonia load of the SCR catalytic converter prior to regeneration of the DPF based on a storage capacity of the SCR catalytic converter and the PM load progress.

Description:
FIELD 
     The present disclosure relates to vehicle exhaust systems and, more particularly, to controlling ammonia prior to regenerating an exhaust treatment system. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Diesel engine operation involves combustion that generates exhaust gas. During combustion, an air/fuel mixture is delivered through an intake valve to cylinders and is combusted therein. After combustion, the piston forces the exhaust gas in the cylinders into an exhaust system. The exhaust gas may contain emissions such as oxides of nitrogen (NO x ) and carbon monoxide (CO). 
     More and more exhaust hardware technology is being added to meet emissions on diesel applications. After treatment of exhaust gases includes the installation of multiple bricks, mixers and injectors for the exhaust stream. A diesel particulate filter is regenerated periodically to reduce the amount of soot therein. During the process, ammonia is deposited on the selective catalyst-reducing catalysts. During regeneration, if ammonia loading on the selective catalyst-reducing catalyst is too high, the regeneration process will release ammonia into the exhaust stream. To prevent this occurrence, a delay is typically initiated so that when a regeneration of the diesel particulate filter is triggered, an amount of time is waited and dosing fluid injection is terminated. Typically, the process may take 30-60 minutes. Soot-loading rates may cause the diesel particulate filter to become overloaded or the filter being plugged. 
     SUMMARY 
     Accordingly, the present disclosure provides for a system and method for reducing the amount of time between a regeneration trigger and starting the actual regeneration process. 
     In one aspect of the disclosure, a control module for a selective catalytic reduction (SCR) catalytic converter includes a storage adjustment module that determines a storage scalar based on a particulate matter (PM) load progress of a diesel particulate filter (DPF). The control module also includes a dose module that determines an ammonia dose based on a storage capacity of the SCR catalyst and the storage scalar. 
     In a-another aspect of the disclosure, a control system for a selective catalytic reduction (SCR) catalytic converter and a diesel particulate filter (DPF) includes a DPF control module that determines a particulate matter (PM) load progress of the DPF and generates a DPF regeneration request based on the PM load progress. The control system also includes an SCR control module that selectively adjusts an ammonia load of the SCR catalytic converter prior to regeneration of the DPF based on a storage capacity of the SCR catalytic converter and the PM load progress. 
     In yet another aspect of the disclosure, a method includes generating a particulate matter (PM) load progress signal corresponding to a load progress the DPF, generating a DPF regeneration request based on the PM load progress and selectively adjusting an ammonia load of the SCR catalytic converter prior to generating the DPF regeneration request based on a storage capacity of the SCR catalytic converter and the PM load progress. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an engine system including an exhaust treatment system with temperature sensors integrated within a catalyst according to the present disclosure; 
         FIG. 2  is a functional block diagram of the controller of  FIG. 1 ; 
         FIG. 3  is a functional block diagram of the SCR control module of  FIG. 2 ; 
         FIG. 4  is a functional block diagram of the dosing management module of  FIG. 3 ; 
         FIG. 5  is a flowchart of a method for controlling the dosing system; and 
         FIG. 6  is a plot of a diesel particulate filter load progress signal, an SCR temperature signal, an ammonia capacity signal and an ammonia stored signal. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     While the following disclosure is set forth for diesel engines, other types of engines such as gasoline engines, including direct injection engines, may benefit from the teachings herein. 
     Referring now to  FIG. 1 , a diesel engine system  10  is schematically illustrated. The diesel engine system  10  includes a diesel engine  12  and an exhaust treatment system  13 . The exhaust treatment system  13  further includes an exhaust system  14  and a dosing system  16 . The diesel engine  12  includes a cylinder  18 , an intake manifold  20 , a mass air flow (MAF) sensor  22  and an engine speed sensor  24 . Air flows into the engine  12  through the intake manifold  20  and is monitored by the MAF sensor  22 . The air is directed into the cylinder  18  and is combusted with fuel to drive pistons (not shown). Although a single cylinder  18  is illustrated, it can be appreciated that the diesel engine  12  may include additional cylinders  18 . For example, diesel engines having 2, 3, 4, 5, 6, 8, 10, 12 and 16 cylinders are anticipated. 
     Exhaust gas is produced inside the cylinder  18  as a result of the combustion process. The exhaust system  14  treats the exhaust gas before releasing the exhaust gas to the atmosphere. The exhaust system  14  includes an exhaust manifold  26  and a diesel oxidation catalyst (DOC)  28 . The exhaust manifold  26  directs exhaust exiting the cylinder towards the DOC  28 . The exhaust is treated within the DOC  28  to reduce the emissions. The exhaust system  14  further includes a catalyst  30 , preferably a selective catalyst reducing (SCR) catalyst, a temperature sensor  31 , an inlet temperature sensor  32 , an outlet temperature sensor  34  and catalyzed diesel particulate filter (CDPF)  36 . The DOC  28  reacts with the exhaust gas prior to treating the exhaust to reduce emission levels of the exhaust. The catalyst  30  reacts subsequent to treating the exhaust to further reduce emissions. 
     The temperature sensor  31  may be positioned between the engine and the DOC  18 . The inlet temperature sensor  32  is located prior to the catalyst  30  to monitor the temperature change at the inlet of the catalyst  30 , as discussed further below. The outlet temperature sensor  34  is located after the catalyst to monitor the temperature change at the outlet of the catalyst  30 , as discussed further below. Although the exhaust treatment system  13  is illustrated as including the inlet and outlet temperature sensors  32 ,  34  as being outside the catalyst  30 , the inlet and outlet temperature sensors  32 ,  34  can be located internally with the catalyst to monitor the temperature change of the exhaust at the inlet and outlet of the catalyst. The CDPF  36  further reduces emissions by trapping diesel particulates (i.e., soot) within the exhaust. 
     The dosing system  16  includes an injection fluid supply  38  that may be used for injecting urea from a tank and a dosing injector  40 . The dosing system  16  injects injection fluid such as urea into the exhaust. The urea mixes with the exhaust and further reduces the emissions when the exhaust/urea mixture is exposed to the catalyst  30 . A mixer  41  is used to mix the injection fluid such as urea with the exhaust gasses prior to the exhaust gases entering the catalyst. 
     A control module  42  regulates and controls the operation of the engine system  10  and monitors operation of the dosing system  16 . 
     An exhaust gas flow rate sensor  44  may generate a signal corresponding to the flow of exhaust in the exhaust system. Although the sensor is illustrated between the catalyst  30  and the CDPF  36  various locations within the exhaust system may be used for measurement including after the exhaust manifold and before the catalyst  30 . 
     A temperature sensor  46  generates a particulate filter temperature sensor signal that corresponds to a measured particulate filter temperature. The temperature sensor  46  may be disposed on or within the diesel particulate filter  36 . The temperature sensor  46  may also be located just after or just before the diesel particulate filter relative to the exhaust stream. The temperature sensor  46  communicates a measured particulate filter temperature signal to the control module  42 . 
     Other sensors in the exhaust system may include a NOx sensor  50  which generates a signal corresponding to the amount of oxides of nitrogen in the exhaust system. This may be referred to NOx-In since this sensor is upstream of the catalyst. A NOx-Out sensor  52  may be positioned downstream such as after the diesel particulate filter for generating a signal corresponding to the oxides of nitrogen leaving the diesel particulate filter. In addition, an ammonia (NH 3 ) sensor  54  generates a signal corresponding to the amount of ammonia within the exhaust stream. 
     The control module  42  may include an exhaust control module  60  that is used to control the exhaust conditions and regeneration of the diesel particulate filter. Further details of the control module  42  and the exhaust control module  60  is provided below. 
     Referring now to  FIG. 2 , the exhaust control module  60  of  FIG. 1  is illustrated in further detail. The exhaust control module  60  receives inputs from the various sensors including the oxides of nitrogen sensors  50 ,  52 , the temperature sensors  31 ,  32  and  34 , the oxygen sensor  56  and the ammonia sensor  54 . 
     The exhaust control module  60  may include a diesel particulate control module  70 , an SCR control module  72 , an injector actuator module  74 . A diesel oxygen catalyst control module  76  may also be included within the exhaust control module  60 . The diesel particulate filter control module  70  may generate signals including a diesel particulate filter load progress signal, a diesel particulate filter load progress rate signal and a diesel particulate filter regeneration request signal. The diesel particulate filter load progress rate signal may be obtained by taking the derivative or slope of the diesel particulate filter load progress signal. 
     The diesel particulate filter load progress signal, the diesel particulate filter load progress rate signal and the diesel particulate filter regeneration request signal may all be communicated to the SCR control module  72 . The SCR control module  72  may generate an SCR ready signal and a dosing amount input signal (DA in ). The dosing amount input signal may be communicated to the injector actuator module  74 . The injector actuator module  74  controls the dosing fluid injector  40 . Feedback may also be provided from the SCR control module  72  to the DPF control module  70  in the form of the SCR-ready signal. As mentioned above, as the diesel particulate filter increases toward regeneration, the amount of dosing fluid provided through the injector actuator module  74  is reduced to reduce the amount of ammonia build-up within the SCR. 
     Referring now to  FIG. 3 , the SCR control module  72  is illustrated in further detail. The SCR control module  72  may include a dosing-enabling module  110  that enables the dosing system to be enabled upon pre-determined conditions. The dosing-enabling module  110  generates an enable signal that communicates the enable signal to a dosing management module  112 . The dosing management module may also receive a diesel particulate filter load rate signal and a load signal. The output of the dosing management module may be the dosing amount input signal and the SCR-ready signal described above. 
     An SCR analysis module  114  receives inputs from various sensors including the nitric oxide input sensor, the SCR temperature sensor, the oxygen input sensor, the exhaust flow rate sensor, the exhaust pressure sensor, and from a ratio determination module  116 . The ratio determination module  116  may generate a ratio of the nitrogen or nitrogen dioxide to the nitrogen oxide input ratio. The ratio determination module  116  may receive signals from the nitric oxide sensor, a temperature signal from an upstream temperature sensor, an exhaust flow rate sensor and an exhaust pressure sensor. Based upon the various inputs, the amount of ammonia stored and the capacity of ammonia for the SCR is provided to the dosing management module  112 . 
     An SCR temperature module  118  may generate an SCR temperature signal based upon the inputs from various temperature sensors such as an upstream sensor  31 , a midstream temperature sensor  32  and a downstream sensor  34 . Of course, various numbers of temperature sensors as well as various numbers of positions of temperature sensors may be used in the SCR temperature module  118 . 
     The dosing management module  112  may use the ammonia capacity, the ammonia stored as well as the conditions of the diesel particulate filter to determine when to cease providing dosing fluid to the exhaust stream to reduce the amount of ammonia in the system prior to diesel particulate filter regeneration. 
     Referring now to  FIG. 4 , the dosing management module  112  is set forth in further detail. The dosing management module  112  may include a rate adjustment module  210  that generates a load-rate scalar corresponding to the load progress rate of the diesel particulate filter. A load adjustment module  212  generates a load progress signal corresponding to the progress of the diesel particulate filter. A load scalar may be generated from the load adjustment module  212 . A target storage module  214  generates a predicted ammonia signal based upon the ammonia stored and the SCR temperature. The ammonia-predicted signal, the load-scalar signal and the load-rate scalar signal are communicated to the storage control module  216 . The storage control module  216  generates an adjusted ammonia signal and communicates the adjusted ammonia signal to a dose determination module  218  and to a regeneration readiness module  220 . The regeneration readiness module regenerates the SCR ready signal and the dose determination module  218  generates the dose amount input signal. 
     Referring now to  FIG. 5 , a method for operating the system is set forth. In step  310 , the system starts. In step  312 , it is determined whether or not enable conditions are met. Various enable conditions such as the engine running for a predetermined amount of time so that the components are up to a predetermined temperature or the like may be set forth. In step  314 , the ammonia storage capacity of the SCR is determined. In step  316 , the diesel particulate filter load progress may be determined. In step  318 , the load progress rate of the diesel particulate filter may be determined. The load progress rate may be determined from the load progress signal by taking the derivative or slope thereof. In step  320 , the ammonia storage scalars are determined based upon the diesel particulate filter load progress, load rate or load progress and load progress rate. As the DPF reaches a threshold the desired ammonia storage is reduced. This may be referred to as a target load. 
     In step  322 , the desired ammonia storage based upon the ammonia storage capacity and storage scalars is determined. After the amount of ammonia storage based upon the storage capacity, the diesel particulate filter enters regeneration in step  324 . Enough time is preferably allowed so that the amount of storage decreases to a desired amount prior to the regeneration of the diesel particulate filter. After step  324 , step  326  returns the system back to start. 
     Referring now to  FIG. 6 , a plot of various signals including the load progress signal, the SCR temperature signal, the ammonia capacities signal and the stored ammonia signal are provided at various times. The diesel particulate filter load progress rate is indicated by the arrow from the digital or diesel particulate filter load progress signal. At the beginning of time period t 1 , the diesel particulate filter load threshold is reached. The threshold indicates that the diesel particulate filter load is increasing and that regeneration is eminent. At the end of time period t 1 , the diesel particulate filter load is at 100 percent. At the beginning of t 1 , the amount of ammonia injected into the SCR is reduced. As can be seen, during time period t 1  the amount of stored ammonia is reduced from a first level to a second level. During time period t 2  a readiness period is entered in which the system is ready to enter a diesel particulate filter regeneration. During time period t 3  a regeneration of the diesel particulate filter is performed. The ammonia capacity is reduced during the time period. However, the amount of ammonia stored remains constant. This is indicative that no ammonia is lost during the regeneration process. This is a desirable feature of the invention since releasing ammonia may release unwanted oxides of nitrogen into the exhaust stream. 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.