Abstract:
A method for monitoring an exhaust after-treatment system that doses an exhaust treatment fluid held from a tank into an exhaust stream. The method includes determining a first temperature of the exhaust treatment fluid in the tank using a temperature sensor. If the first temperature of the exhaust treatment fluid is less than a predetermined temperature, a heater is activated to increase the first temperature of the exhaust treatment fluid. The increasing first temperature is then monitored relative to the predetermined temperature. Then, a second temperature when a phase change of the exhaust treatment fluid occurs is detected. The detected second temperature is then compared to the predetermined temperature to determine whether the exhaust treatment fluid is of sufficient quality, or to determine whether the temperature sensor is rational.

Description:
FIELD 
     The present disclosure relates to an exhaust treatment system with a urea temperature rationality diagnostic. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Systems for treating exhaust gas produced by an internal combustion engine to reduce exhaust gas emissions in the form of particulates and/or NO X  are generally known. Such exhaust gas “after-treatment” systems may include a selective catalytic reduction (SCR) system for the purpose of reducing the NO X  level of the exhaust gas below a specified level. 
     An SCR system generally includes a catalytic reducing agent, or reagent, in the form of an exhaust treatment fluid that is dosed into the exhaust gas stream produced by the engine before entering an SCR catalyst. The SCR catalyst reacts with the combination of engine exhaust gas and reagent solution in a known manner to reduce the NO X  content of the exhaust gas stream. 
     The reagent is generally held in a storage tank. The tank may include fluid level sensors, temperature sensors, and other components that assist in communicating the reagent to a dosing module that doses the reagent into the exhaust gas stream and returning any unused reagent to the tank. Each of these components should be monitored by an on-board diagnostic (OBD) system so that, if a problem with one of the components occurs, an error may be communicated by the OBD system. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure provides an exhaust after-treatment system for treating an exhaust produced by an engine. The system includes an exhaust treatment component, a dosing module positioned upstream from the exhaust treatment component for dosing an exhaust treatment fluid into the exhaust, an exhaust treatment fluid tank that stores and provides the dosing module with the exhaust treatment fluid, a temperature sensor positioned in the tank for detecting a temperature of the exhaust treatment fluid, a fluid heater positioned in the tank for increasing a temperature of the exhaust treatment fluid, and a controller for controlling each of the dosing module, temperature sensor, and fluid heater. 
     The temperature sensor determines a first temperature of the exhaust treatment fluid in the tank and communicates the first temperature to the controller. If the first temperature of the exhaust treatment fluid is less than a predetermined temperature, the controller activates the heater to increase the first temperature of the exhaust treatment fluid. The controller then monitors the increasing first temperature of exhaust treatment fluid detected by the temperature sensor relative to the predetermined temperature, and detects a second temperature where a phase change of the exhaust treatment fluid occurs. The controller then compares the detected second temperature to the predetermined temperature. If the detected second temperature is deviated from the predetermined temperature, the temperature sensor may be irrational, or the exhaust treatment fluid may not be of sufficient quality. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  schematically illustrates an exhaust system according to a principle of the present disclosure; 
         FIG. 2  is a cross-sectional illustration of an exemplary reagent tank that may be used according to a principle of the present disclosure; 
         FIG. 3  is a flow chart illustrating a temperature sensor rationality diagnostic method in accordance with a principle of the present disclosure; 
         FIG. 4  is a graph illustrating temperature curves that assist in determining whether a temperature sensor is rational; 
         FIG. 5  is a flow chart illustrating a reagent quality diagnostic method in accordance with a principle of the present disclosure; and 
         FIG. 6  is a graph illustrating temperature curves that assist in determining whether a reagent is of sufficient quality. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
       FIG. 1  schematically illustrates an exhaust system  10  according to the present disclosure. Exhaust system  10  can include at least an engine  12  in communication with a fuel source (not shown) that, once consumed, will produce exhaust gases that are discharged into an exhaust passage  14  having an exhaust after-treatment system  16 . Downstream from engine  12  can be disposed an exhaust treatment component  18 , which can be a DOC, a DPF component or, as illustrated, a SCR component  20 . Although not required by the present disclosure, exhaust after-treatment system  16  can further include components such as a thermal enhancement device or burner  17  to increase a temperature of the exhaust gases passing through exhaust passage  14 . Increasing the temperature of the exhaust gas is favorable to achieve light-off of the catalyst in the exhaust treatment component  18  in cold-weather conditions and upon start-up of engine  12 , as well as initiate regeneration of the exhaust treatment component  18  when the exhaust treatment component  18  is a DPF. 
     To assist in reduction of the emissions produced by engine  12 , exhaust after-treatment system  16  can include a dosing module  22  for periodically dosing an exhaust treatment fluid into the exhaust stream. As illustrated in  FIG. 1 , dosing module  22  can be located upstream of exhaust treatment component  18 , and is operable to inject an exhaust treatment fluid into the exhaust stream. In this regard, dosing module  22  is in fluid communication with a reagent tank  24  and a pump  26  by way of inlet line  28  to dose an exhaust treatment fluid such as diesel fuel or urea into the exhaust passage  24  upstream of exhaust treatment component  20 . Dosing module  22  can also be in communication with reagent tank  24  via return line  30 . Return line  30  allows for any exhaust treatment fluid not dosed into the exhaust stream to be returned to reagent tank  24 . Flow of the exhaust treatment fluid through inlet line  28 , dosing module  22 , and return line  30  also assists in cooling dosing module  22  so that dosing module  22  does not overheat. As will be described later, dosing modules  22  can be configured to include a cooling jacket ( FIG. 6 ) that passes a coolant around dosing module  22  to cool it. 
     The amount of exhaust treatment fluid required to effectively treat the exhaust stream can also be dependent on the size of the engine  12 . In this regard, large-scale diesel engines used in locomotives, marine applications, and stationary applications can have exhaust flow rates that exceed the capacity of a single dosing module  22 . Accordingly, although only a single dosing module  22  is illustrated for urea dosing, it should be understood that multiple dosing modules  22  for urea injection are contemplated by the present disclosure. 
     The amount of exhaust treatment fluid required to effectively treat the exhaust stream may also vary with load, engine speed, exhaust gas temperature, exhaust gas flow, engine fuel injection timing, desired NO X  reduction, barometric pressure, relative humidity, EGR rate and engine coolant temperature. A NO X  sensor or meter  32  may be positioned downstream from SCR  20 . NO X  sensor  32  is operable to output a signal indicative of the exhaust NO X  content to an engine control unit  34 . All or some of the engine operating parameters may be supplied from engine control unit  34  via the engine/vehicle databus to an exhaust after-treatment system controller  36 . The controller  36  could also be included as part of the engine control unit  34 . Exhaust gas temperature, exhaust gas flow and exhaust back pressure and other vehicle operating parameters may be measured by respective sensors, as indicated in  FIG. 1 . 
     A temperature of the exhaust treatment fluid may also be a parameter monitored by exhaust after-treatment system controller  36 . To monitor a temperature of the exhaust treatment fluid, reagent tank  24  may include a temperature sensor  40  located therein. As best shown in  FIG. 2 , reagent tank  24  can include a tank housing  42 . Tank housing  42  may be formed of materials such as polyethylene, polystyrene, aluminum, steel, or any other type of material suitable for storing a reagent exhaust treatment fluid  44  such as urea. To re-fill tank  24  with an exhaust treatment fluid, tank  24  may include an inlet  46  defined by a threaded neck  48  that may receive a removable cap  50  having a threading that corresponds to that of neck  48 , as is known in the art. 
     Within tank housing  42  can be a pair of suction and discharge tubes  52  and  54 , respectively. Suction tube  52  communicates with pump  26  downstream such that when pump  26  is activated, the urea exhaust treatment fluid  44  is drawn from tank  24  into inlet line  28 . As noted above, inlet line  28  communicates with dosing module  22  to provide exhaust treatment fluid to the exhaust stream. If the urea exhaust treatment fluid  44  is not dosed into the exhaust stream, the urea exhaust treatment fluid  44  may travel back to tank  24  through return line  30 . Return line  30  communicates with discharge tube  54 . 
     To monitor an amount of urea exhaust treatment fluid  44  in tank  24 , a fluid level indicating device  56  may be coupled to inlet tube  52 . In the illustrated embodiment, fluid level indicating device  56  may comprise a float member  58  having a density less than that of the urea exhaust treatment fluid  44 . To communicate a level of the urea exhaust treatment fluid  44  to controller  36 , float member  58  may include a permanent magnet (not shown) embedded or adhered to float member  58 . Suction tube  52  may, in turn, include a plurality of magneto-resistive sensors (not shown) along a length thereof that communicate with controller  36 . 
     When float member  58  aligns with a particular magneto-resistive sensor, the sensor can communicate a level of the urea exhaust treatment fluid  44  to controller  36 . One skilled in the art will readily acknowledge and appreciate that the above-described fluid level sensing is merely exemplary in nature, and that various other methods and devices may be employed to determine the fluid level. The present disclosure, therefore, should not be limited to the above-described configuration. For example, it should be understood that float member  58  may be coupled to discharge tube  54  and that discharge tube  54  can include magneto-resistive sensors (not shown) without departing from the scope of the present disclosure. 
     An exhaust treatment fluid heater  60  may also be positioned in tank  24 . Fluid heater  60  is designed to raise a temperature of the exhaust treatment fluid  44 , particularly in cold-weather conditions where the exhaust treatment fluid  44  can freeze. Fluid heater  60  may be a resistive heater, or may be configured to allow flow of an engine coolant therethrough, without limitation. Fluid heater  60  does not necessarily continuously operate during operation of engine  12 . Rather, fluid heater  60  communicates with controller  36  such that fluid heater  60  can be activated as needed. In this regard, a temperature of the exhaust treatment fluid  44  can be transmitted to controller  36  from temperature sensor  40 . If the sensed temperature is too low, controller  36  can instruct fluid heater  60  to activate to heat or thaw the exhaust treatment fluid  44 . 
     Temperature sensor  40  may be attached to discharge tube  54 . Temperature sensor  40 , however, may be positioned anywhere within tank  24  satisfactory to properly determine a temperature of the exhaust treatment fluid  44 . For example, temperature sensor  40  can be attached to an interior wall  62  of housing  42 , or may be attached to suction tube  52 . Regardless, it is preferable that temperature sensor  40  be positioned proximate a center of tank  24  to more accurately determine a temperature of the exhaust treatment fluid  44 . 
     Urea exhaust treatment fluid may be a mixture of urea and water. A solution containing 32.5% urea provides the lowest freezing point for the urea exhaust treatment fluid, which is −11 degrees C. Such a urea exhaust treatment fluid is commonly used in exhaust after-treatment systems to ensure that the exhaust treatment fluid remains in a liquid state in most weather conditions, which enables dosing of the exhaust treatment fluid even during extremely cold temperatures. 
     The present disclosure provides a diagnostic method for determining whether temperature sensor  40  is rational.  FIG. 3  illustrates an exemplary control algorithm for determining the rationality of temperature sensor  40 . In step  100 , temperature sensor  40  is instructed by controller  36  to determine the temperature of the urea exhaust treatment fluid  44 . If the temperature detected by temperature sensor  40  is determined by controller  36  to be greater than a predetermined temperature, fluid heater  60  is not activated (step  200 ). If fluid heater  60  is already activated, controller  36  deactivates fluid heater  60  (step  200 ). The predetermined temperature preferably is a temperature at which a phase change (e.g., from solid to liquid, or liquid to gas) occurs. 
     If the temperature detected by temperature sensor  40  is determined by controller  36  to be less than the predetermined temperature, fluid heater  60  is activated by controller  36  (step  300 ). Once fluid heater  60  is activated, controller  36  instructs temperature sensor  40  to continually monitor a temperature of the urea exhaust treatment fluid  44  to observe the rate of temperature change (step  400 ). During heating of the urea exhaust treatment fluid, the urea exhaust treatment fluid  44  will eventually reach a temperature at which a phase change can occur. As the phase change occurs, the temperature of the urea exhaust treatment fluid should plateau for a period of time (e.g., 5-10 minutes). The temperature at which this plateau occurs can be used by controller  36  to determine whether temperature sensor  40  is rational. 
     More specifically, if the temperature at which the phase change occurs has deviated from the predetermined temperature, it can be inferred that temperature sensor  40  is not rational or malfunctioning (step  500 ). If temperature sensor  40  properly detects a phase change at the predetermined temperature, temperature sensor  40  will pass the rationality diagnostic (step  600 ). For example, if the initial temperature detected by temperature sensor (step  100 ) is −15 degrees C., the urea exhaust treatment fluid should undergo a phase change at −11 degrees C. where the solid urea exhaust treatment fluid begins to melt and turn to liquid. If, however, the temperature sensor  40  detects a plateau in temperature at −5 degrees C. or −15 degrees C. ( FIG. 4 ), it can be inferred by controller  36  that temperature sensor  40  is either un-calibrated or malfunctioning. The temperature sensor  40 , therefore, would not pass the rationality diagnostic (step  700 ) and controller  36  can send an error flag to ECU  34  of engine  12  that exhaust treatment system  18  requires servicing, or can signal ECU  34  to cease operation of engine  12 . Alternatively, if no plateau is detected during heating of the exhaust treatment fluid  44 , controller  36  can infer that temperature sensor  40  is defective. Temperature sensor  40 , therefore, would not pass the rationality diagnostic (step  700 ) and controller  36  can send an error flag to ECU  34  of engine  12 . 
     It should be understood that the above-described diagnostic algorithm can also be used as a diagnostic tool for reagent quality. As noted above, the aqueous urea exhaust treatment fluid preferably has a urea concentration of 32.5% to ensure the lowest freezing point (i.e., −11 degrees C.) for the solution. If a fluid other than urea exhaust treatment fluid is added to tank  24 , or if a urea exhaust treatment fluid with a lower urea concentration is added to tank  24 , the temperature at which a phase change occurs can be used to determine whether the correct fluid has been added to tank  24 . 
     Now referring to  FIG. 5 , a reagent quality diagnostic algorithm is illustrated. In step  1000 , controller  36  instructs temperature sensor  40  to determine the temperature of the urea exhaust treatment fluid  44 . If the detected temperature is determined to be greater than a predetermined temperature, fluid heater  60  is not activated (step  1100 ). If fluid heater  60  is already activated, controller  36  deactivates fluid heater  60  (step  1100 ). The predetermined temperature preferably is a temperature at which a phase change (e.g., from solid to liquid, or liquid to gas) occurs. 
     If the detected temperature is determined to be less than the predetermined temperature, controller  36  activates fluid heater  60  (step  1200 ). Once fluid heater  60  is activated, controller  36  instructs temperature sensor  40  to continually monitor a temperature of the urea exhaust treatment fluid  44  to observe the rate of temperature change (step  1300 ). During heating of the urea exhaust treatment fluid, the urea exhaust treatment fluid  44  will eventually reach a temperature at which a phase change can occur. As the phase change occurs, the temperature of the urea exhaust treatment fluid should plateau for a period of time. The temperature at which this plateau occurs can be used to determine whether temperature sensor  40  is rational. 
     More specifically, if the temperature at which the phase change occurs has deviated from the predetermined temperature (step  1400 ), it can be inferred that the quality of the reagent is not satisfactory (step  1500 ). If controller  36  detects a phase change at the predetermined temperature, the reagent quality will pass the diagnostic (step  1600 ). For example, if the initial temperature detected by temperature sensor (step  1000 ) is −15 degrees C., the urea exhaust treatment fluid should undergo a phase change at −11 degrees C. where the solid urea exhaust treatment fluid begins to melt and turn to liquid. If, however, controller  36  detects a plateau in temperature at −5 degrees C. ( FIG. 6 ), controller  36  can infer that the incorrect exhaust treatment fluid is being used, or that a fluid that may not be suitable for exhaust treatment (e.g., water) has been added to the tank. The urea exhaust treatment fluid  44 , therefore, would not pass the reagent quality diagnostic (step  1600 ) and controller  36  can send an error flag to ECU  34  of engine  12  that exhaust treatment system  18  requires servicing, or can signal ECU  34  to cease operation of engine  12 . Alternatively, if no plateau is detected during heating of the exhaust treatment fluid  44 , controller  36  can infer that the incorrect exhaust treatment fluid (e.g., a hydrocarbon) has been added to the tank. The urea exhaust treatment fluid  44 , therefore, would not pass the reagent quality diagnostic (step  1600 ) and controller  36  can send an error flag to ECU  34  of engine  12  that exhaust treatment system  18  requires servicing, or can signal ECU  34  to cease operation of engine  12 . 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.