Abstract:
The present disclosure relates to a method or apparatus for controlling reductant dosing level introduced to a selective catalytic reduction device. The method or apparatus may determine available reductant and determine a distance to a source of reductant. This may be followed by adjusting a reductant dosing level based upon the available reductant and the distance to the reductant source. The apparatus may be installed in a vehicle and may also regulate in-cylinder emission control variables to reduce NOx emissions.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to an apparatus and method for improving the performance of an exhaust treatment device such as a selective catalytic reduction (SCR) system. More particularly, the disclosure relates to adaptive reductant dosing and emission control strategies which may be used in diesel engines. The process may therefore rely upon monitoring of in-tank reductant levels and consideration of variables that may include distance to a reductant refill station, monitoring of reductant consumption level and adjusting reductant dosing to control tailpipe (NOx) emissions which may be combined with in-cylinder emission control methods to satisfy emission standards. 
       BACKGROUND 
       [0002]    Internal combustion engines such as those found in cars and trucks may produce combustion byproducts and/or products of incomplete combustion which may be in the engine exhaust and emitted into the environment. Pursuant to emissions regulations, the exhaust may be treated to reduce the concentration of such products and, therefore, reduce pollution. Although spark ignition (i.e., gasoline) engines may use three-way catalytic converters to satisfy emissions regulations, compression ignition (i.e., diesel) engines typically employ two-way catalytic converters which may not efficiently reduce nitrogen oxides (NO x ). Accordingly, diesel engines may include a reductant-based selective catalytic reduction (SCR) device in order to seek reduction in nitrogen oxide concentrations. In addition, diesel engines may also include diesel particulate filters (DPF) for particulate matter (PM) control. Improving the performance of such systems remains an ongoing area of research and development. 
       SUMMARY 
       [0003]    An aspect of the present disclosure relates to a controller amounting to a control unit capable of controlling a reductant dosing level introduced to a selective catalytic reduction catalyst wherein the control unit is capable of determining available reductant and a distance to a source of reductant. The control unit may then adjust a reductant dosing level based upon the available reductant and the distance to a source of reductant. The control unit may be installed in a vehicle and may also regulate in-cylinder emission control variables to reduce NOx emissions. 
         [0004]    Another aspect of the disclosure relates to a method of controlling the reductant dosing level introduced to a SCR device. The method may include determining available reductant and determining a distance to a source of reductant. This may then be followed by adjusting a reductant dosing level based upon the available reductant and the distance to a source of reductant. 
         [0005]    Another aspect of the present disclosure relates to an article comprising a storage medium having stored thereon instruction that when executed by a machine result in the following operations: determining available reductant and determining a distance to a source of reductant. This may then be followed by adjusting a reductant dosing level based upon the available reductant and the distance to a source of reductant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Features and advantages of the claimed subject matter will be apparent from the following detailed description of embodiments consistent therewith, which description should be considered with reference to the accompanying drawings, wherein: 
           [0007]      FIG. 1  illustrates the relationship between reductant consumption and vehicle fuel consumption, performance and emissions. 
           [0008]      FIG. 2  illustrates an exemplary wireless communication network as between relatively light and heavy-duty vehicles and a reductant service station which system may monitor distance to reductant fill-up and availability of reductant for a given vehicle. 
           [0009]      FIGS. 3A and 3B  provides a flow-chart illustrating the determination of a reductant dosing mode. 
           [0010]      FIG. 4  illustrates selection of a corresponding engine control mode according to the reductant dosage mode as illustrated in  FIG. 3 . 
           [0011]      FIG. 5  illustrates selection of an engine control mode ( FIG. 4 ) and a reductant dosing mode ( FIGS. 3A and 3B ). 
           [0012]      FIG. 6  illustrates an exemplary overview of the exemplary vehicle control system disclosed herein. 
           [0013]      FIG. 7  illustrates the engine combustion controller herein as including a processor, machine readable media and a user interface. 
       
    
    
       [0014]    Although the following detailed description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art. 
       DETAILED DESCRIPTION 
       [0015]    As alluded to above, selective catalytic reduction (SCR) may be understood as a process where a reductant may be added to a combustion engine exhaust stream and interact with a catalyst. A reductant herein may therefore be understood as any compound (e.g. ammonia) or precursor compound (e.g. urea) that may be relied upon to assist a catalyst to reduce output levels of NOx from a combustion process. More specifically, a reductant such as ammonia may therefore react with the NOx in the exhaust gas to form water and nitrogen. In the case of urea (CO(NH 2 ) 2 ), which is one example of a precursor compound, it may react with water (H 2 O) in the presence of a hydrolysis catalyst to yield carbon dioxide (CO 2 ) and ammonia (NH 3 ). The ammonia in turn may act as more fully described below. The selection of urea as an exemplary precursor to provide ammonia and react with NOx in the presence of a catalyst may therefore be illustrated as follows: 
         [0000]      CO(NH 2 ) 2 +H 2 O→CO 2 +2NH 3    
         [0000]      2NH 3 +NO+NO 2 →2N 2 +3H 2 O 
         [0000]      4NH 3 +4NO+O 2 4H 2 +6H 2 O 
         [0016]    Attention is therefore directed to  FIG. 1  which illustrates the relationship between reductant consumption and vehicle fuel consumption, performance and emissions. As may now be appreciated, when the engine is configured for higher fuel economy and relative strong performance, combustion may be optimized and the engine may employ what may be understood as normal engine calibration. However, NOx emissions may then be relatively high which may then require relatively higher reductant consumption in such normal protocol for SCR to convert NOx to NO 2 . Under conservation engine calibration, and although there may be relatively less efficient combustion and lower fuel economy, reductant may be conserved while maintaining emissions below desired target levels. It may therefore be understood herein that normal engine calibration may consume relatively higher dosage levels of reductant than in conservation engine calibration which may use relative lower dosage levels. 
         [0017]    As may also be appreciated, under those circumstances where there may be no precursor such as urea, engine in-cylinder emission control approaches may then be required to maintain emission levels. This may include retarded injection timing (i.e. a delay in the start of fuel injection to reduce combustion temperature), low pressure loop exhaust gas recycling (EGR) and/or high pressure loop EGR (which may lower maximum combustion temperature), lower compression ratios, lower temperature combustion, and/or premixed controlled combustion in order to maintain target emission standards. It may also include control of fuel mass, boost pressure, air flow (amount and temperature) and variable valve actuation timing of the intake/exhaust valves and lift. In addition, with respect to EGR, it may include control of the amount and temperature of such exhaust gas recycling. However, under these circumstances, where the SCR NOx catalyst is not employed, fuel economy and performance may be significantly compromised and may create excess particulate (e.g. soot). It may therefore be appreciated that the availability of reductant may be an important variable in connection with optimizing exhaust treatment. 
         [0018]    Attention is therefore directed to  FIG. 2  which provides an illustration of an exemplary reductant distribution information system now contemplated by the present disclosure. As may be appreciated, relatively light or heavy duty vehicles  202  and  204  may communicate via GPS  206  or by other wireless systems  208  to determine the location of service stations  210  or other fueling stations  212  where reductant may be distributed. The distribution system herein may therefore generate information corresponding to, e.g. the distance between the vehicle and a source for reductant such as an available reductant fill-station. An available reductant fill station may be understood as a fill station confirming the availability of reductant through a communication network (e.g. wireless network) for use by a vehicle. 
         [0019]    Attention is next directed to  FIGS. 3A-3B  which illustrate in scheme  300  how one may intermittently determine a particular reductant dosing mode for engine consumption. Accordingly, at  302  one may start the reductant dosing strategy to initially determine whether a flag should be set indicative of whether or not the reductant in a given vehicle may be above or below some preset limit. At  304  an in-tank monitoring sensor may be triggered for reductant level in a reductant tank  306  and a determination (see below) may be made regarding the reductant level in a given tank. Such determination may be accomplished by, e.g., a fluid level sensor, pressure sensor and/or an optical sensor in communication with the reductant tank. 
         [0020]    Accordingly, at  308 , a determination may be made as to whether or not the reductant is at a given lower limit. Such lower limit may be preprogrammed into the system or be set by the driver. If “yes” at  308  a flag or other indicator may be set at  310  to signify that the reductant is at or below the selected lower limit. At  312  the on-board diagnostics may be informed that the reductant lower limit flag has been set. If “no” at  308  the system may estimate reductant consumption at  314  at normal reductant dosage levels which may depend upon current driving conditions. This may include average speed, average fuel consumption, etc. Again, as noted above, a normal reductant dosage level or consumption may be understood as a dosage level (e.g. grams/unit of time) that may be provided to reduce the relatively high NOx levels during normal engine calibration. Accordingly at  316 , the estimated distance the vehicle may travel employing the normal dosage of reductant may be determined. Furthermore, a determination may then be made at  318  as to whether or not normal dosing of reductant may be continued based upon the normal reductant dosing and the distance to a reductant refill station. 
         [0021]    As noted above, at the time that the above referenced reductant dosing strategy is implemented, the system may initiate at  320  a monitoring protocol to determine reductant refill station availability. The system at  322  may therefore communicate with the reductant distribution information system ( FIG. 2 ) which may then allow the system to determine at  324  the distance to a reductant refill station. For example, GPS or wireless information may be assessed to determine the driving distance to a reductant refill station. 
         [0022]    Accordingly, at  318 , if the system determines that reductant is available under normal dosing conditions through the distance to a reductant refill station, (i.e., that there will be sufficient reductant in the tank to adequately process NOx at some regulatory level over a given distance) the system at  330  may clear any conservation reductant flag (explained below) that may have been previously set. If at  318  the system determines that the normal reductant dosing is not available for the given distance (i.e., that the vehicle will run out of reductant,) the system may set a conservation reductant flag at  340 . Then, the system at  342  may estimate and select a reduced reductant dosing rate. At  344 , the distance for which the reduced dosing rate is available, prior to running out of reductant, may be compared to the distance to a reductant refilling station. If the estimated reduced reductant dosage determined at  342  is too high and the vehicle may run too low or even out of reductant prior to completing the distance to a refilling station at  344 , a new reduced reductant dosing rate may be determined at  342 . It may therefore be appreciated that conservation reductant dosage herein contemplates a reductant dosage that is less than the above described normal reductant dosing. 
         [0023]    If the estimated reduced reductant dosing rate provides a sufficient distance to a refilling station at  344 , then at  346  a determination may be made as to whether the driver has selected or activated an automatic reduced reductant conservation mode. If automatic reductant conservation mode has not been selected at  346 , then at  348  the driver may be advised of possible mandatory action. If automatic reductant conservation mode has been selected at  346  then at  350  the automatic reductant conservation flag may be set. At  352  a driver advisory may be issued warning the driver that the vehicle performance may be reduced or at  354  a driver advisory may be issued warning the driver that the vehicle driving distance may need to be reduced due to reduced fuel economy or performance. A signal may also be sent to the on-board diagnostics at  356  notifying the on-board diagnostics that the automatic conservation flag is set. 
         [0024]    Attention is next directed to  FIG. 4  which illustrates how, after a reductant dosing mode is selected ( FIG. 3 ) a corresponding engine control mode may be implemented. Specifically, at  402  one may start to determine the selection of engine calibration based upon the dosing mode determination and at  404  a determination may be made as to whether or not the reductant low limit flag has been set. If yes, a determination may be made as to whether or not an emergency by-pass of the “reductant-low engine control mode” may have been manually set. If the emergency by-pass was not set at  406  then at  408  the reductant low engine control mode may be implemented. If the emergency by-pass was set at  406  then a counter may be initiated at  410 . Such counter may keep track of the number of times emergency by-pass mode has been entered into. At  412  a determination may be made as to whether or not the number of times emergency by-pass mode has been exceeded. If the counter has been exceeded, the reductant low engine control mode may again be implemented at  408 . If the counter has not been exceeded at  412 , then at  414  the emergency by-pass of the reductant low engine control mode may be set. At  416  the counter may be cleared by an authorized service center. 
         [0025]    If the reductant low limit flag has not been set at  404 , then at  420  a determination may be made as to whether or not the reduction conservation flag has been set. If such flag has not been set then the normal reductant dose and control mode may be implemented at  422 . If such flag has been set a determination may be made at  430  as to whether or not the automatic reductant dosing flag has been set. If yes, at  432 , the reductant dosing conservation engine control mode may be implemented. If not, at  434 , the driver may be advised of possible mandatory action necessary in view of the available reductant. 
         [0026]    It may therefore be appreciated in  FIG. 4  that tailpipe emissions and NOx concentration may be relatively low when the normal reductant dosing control mode is selected. Similarly, the relative level of NOx emissions may be low when the reductant dosing conservation mode is set, or when the reductant low engine control mode is set. However, relatively higher NOx emissions may be observed when the emergency by-pass engine control mode is selected. 
         [0027]      FIG. 5  illustrates selection of an engine control mode ( FIG. 4 ) and a reductant dosing mode ( FIGS. 3A and 3B ). At  502  the system may start consideration of an overall engine control strategy determination. At  506  the system may determine if reductant low-engine control mode has been selected. Such selection may have been made, e.g., at step  408  in  FIG. 4 . The system may then consider at  504  whether the emergency by-pass of reductant low engine control mode has been selected (see e.g., step  414  in  FIG. 4 ). If the mode was selected at  504  and the maximum number of times emergency by-pass mode may be entered has not been exceeded at  511  (as determined by referencing a counter) then at  512  a first timer (t 1 ) may be set for using normal engine calibration without reductant dosing. If t 1  expires a second timer may be set (t 2 ) at  514  for conservation engine calibration without reductant. If t 2  expires the system goes to  520  which is the engine calibration for low-engine out emissions and no reductant dosing  522 . It may be appreciated that during either t 1  or t 2  there may be relatively high tailpipe emissions as shown at  518 . In such a manner, i.e., operating the engine under low engine-out emission calibration at  520 , the engine may then reduce tailpipe emissions, such that relatively low tailpipe emissions may be produced at  524 . Such engine calibrations may include, as noted above, retarded injection timing (i.e. a delay in the start of fuel injection to reduce combustion temperature), low pressure loop exhaust gas recycling (EGR) and or high pressure loop EGR (which may lower maximum combustion temperature), lower compression ratios, lower temperature combustion, and/or premixed controlled combustion. It may also include control of fuel mass, boost pressure, air flow (amount and temperature), variable valve actuation timing and lift, and control of the amount and temperature of recycled exhaust gas. 
         [0028]    If reductant-low engine control mode is not selected at  506  then a determination may be made as to whether reductant dosing conservation engine control mode has been selected at  508 . Such selection may have been made, for example, at step  432  in  FIG. 4 . If reductant doing conservation engine control mode has been selected at  508 , then the engine may be operated under the calibration to provide reductant conservation at  530  and reductant dosing may be set for conservation at  532  which may produce relatively low tailpipe emissions at  524 . 
         [0029]    If reductant dosing conservation engine control mode has not been selected at  508  then at  510  normal reductant dosing mode may be set. Such selection may have been previously made at  422  of  FIG. 4 . Accordingly, in such mode, normal engine calibration may be implemented at  540  and normal reductant dosing may be provided at  542  producing relatively low tailpipe emissions at  524 . 
         [0030]      FIG. 6  illustrates an exemplary overview of the vehicle control system for implementing the above control scheme. A vehicle  600  may include a controller  602  wherein the controller  602  may receive data from wireless communications  620 , GPS  622  as well as driver input  624 . The engine controller may also received data from a sensor  604  in communication with a reductant tank  606 , indicating the level of reductant in the tank. The controller may assess information obtained from the various inputs, such as the driving distance to a reductant refilling station and/or level of reductant in the tank which may be supplied from the GPS  622  and/or wireless tower  620  and/or from manual input. The controller may therefore communicate with the engine  610  and a reductant dosing valve  612 . Exhaust  614  from the engine may be directed to a SCR  616 . Reductant  618  may be added to the exhaust  614 , once the exhaust enters the SCR or just prior to entering the SCR. Once the exhaust is treated with the reductant, as described above, the treated exhaust may be emitted from the tailpipe  618 . The controller may then implement any of the protocols outlined above in  FIGS. 3-5  to control the engine  614  and dosing of the reductant  618  via the reductant dosing valve  612 . The controller  602  may also amount to an after-market controller that may be employed in a given vehicle engine to improve performance of a given SCR system. Accordingly it is contemplated herein that the controller herein may provide the in-cylinder control noted above and/or coordinate with an existing vehicle engine in-cylinder control system. 
         [0031]    It should also be appreciated that the functionality described herein for the embodiments of the present invention may be implemented by using hardware, software, or a combination of hardware and software, either within the engine combustion controller or outside the engine combustion controller, as desired. If implemented by software, a processor and a machine readable medium are required. The processor may be of any type of processor capable of providing the speed and functionality required by the embodiments of the invention. Machine-readable memory includes any media capable of storing instructions adapted to be executed by a processor. Some examples of such memory include, but are not limited to, read-only memory (ROM), random-access memory (RAM), programmable ROM (PROM), erasable programmable ROM (EPROM), electronically erasable programmable ROM (EEPROM), dynamic RAM (DRAM), magnetic disk (e.g., floppy disk and hard drive), optical disk (e.g. CD-ROM), and any other device that can store digital information. The instructions may be stored on medium in either a compressed and/or encrypted format. Accordingly, in the broad context of the present invention, and with attention to  FIG. 7 , the engine combustion controller may contain a processor ( 710 ) and machine readable media ( 720 ) and user interface ( 730 ). Various features, aspects, and embodiments have been described herein. The features, aspects, and embodiments are susceptible to combination with one another as well as to variation and modification, as will be understood by those having skill in the art. The present disclosure should, therefore, be considered to encompass such combinations, variations, and modifications.