Abstract:
A sensor diagnostic system comprises first, second, and third dosing agent sensors and a control module. The first, second, and third dosing agent sensors indicate whether a dosing agent is present at first, second, and third volumetric levels of a dosing agent tank, respectively. The second volumetric level is greater than the first volumetric level and the third volumetric level is greater than the second volumetric level. The control module selectively diagnoses a sensor fault in at least one of the first, second, and third dosing agent sensors based on the indications of the first, second, and third dosing agent sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/027,250, filed on Feb. 8, 2008. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to systems and method for monitoring urea levels. 
       BACKGROUND 
       [0003]    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. 
         [0004]    To meet nitrogen oxide (NOx) emission requirements for a vehicle with a diesel engine, urea may be injected into an exhaust stream. The urea is stored in a tank that may be similar to a conventional fuel tank. Since the emissions impact of running out of urea is severe, correct urea level indication is required to inform the driver. For example, the vehicle may be required to operate in a limp home mode when the urea runs out. 
         [0005]    Several unique characteristics of urea delivery systems make urea level sensing systems and on board diagnostic (OBD) monitoring different than fuel level monitoring systems. For example, urea freezes at low temperatures. In addition, the volume of urea consumed per mile may be as low as 5 gallons for 4000 miles. Level sensing systems may be required to independently verify range readings from the sensor. 
       SUMMARY 
       [0006]    A sensor diagnostic system comprises first, second, and third dosing agent sensors and a control module. The first, second, and third dosing agent sensors indicate whether a dosing agent is present at first, second, and third volumetric levels of a dosing agent tank, respectively. The second volumetric level is greater than the first volumetric level and the third volumetric level is greater than the second volumetric level. The control module selectively diagnoses a sensor fault in at least one of the first, second, and third dosing agent sensors based on the indications of the first, second, and third dosing agent sensors. 
         [0007]    In other features, the control module diagnoses the sensor fault when the third dosing agent sensor indicates that the dosing agent is present and at least one of the first and second dosing agent sensors indicates that the dosing agent is absent. 
         [0008]    In still other features, the control module diagnoses the sensor fault when the second dosing agent sensor indicates that the dosing agent is present and the first dosing agent sensor indicates that the dosing agent is absent. 
         [0009]    In further features, the control module diagnoses the sensor fault when the first dosing agent sensor transitions to indicating that the dosing agent is absent while the second dosing agent sensor indicates that the dosing agent is present. 
         [0010]    In still further features, the control module diagnoses the sensor fault when the second dosing agent sensor transitions to indicating that the dosing agent is absent while the third dosing agent sensor indicates that the dosing agent is present. 
         [0011]    In other features, the control module diagnoses the sensor fault when the first dosing agent sensor transitions to indicating that the dosing agent is absent while a pump pressure is greater than a predetermined pressure. 
         [0012]    In still other features, the control module diagnoses the sensor fault when a quantity of the dosing agent injected into an exhaust stream between a first time and a second time is less than a predetermined quantity. The first time corresponds to when the third dosing agent sensor transitions to indicating that the dosing agent is absent while the second dosing agent sensor indicates that the dosing agent is present. The second time is after the first time when the second dosing agent sensor transitions to indicating that the dosing agent is absent. 
         [0013]    In further features, the control module diagnoses the sensor fault when a quantity of the dosing agent injected into an exhaust stream between a first time and a second time is less than a predetermined quantity. The first time corresponds to when the second dosing agent sensor transitions to indicating that the dosing agent is absent while the first dosing agent sensor indicates that the dosing agent is present. The second time is after the first time when the first dosing agent sensor transitions to indicating that the dosing agent is absent. 
         [0014]    A method comprises indicating whether a dosing agent is present at first, second, and third volumetric levels of a dosing agent tank using first, second, and third dosing agent sensors, respectively, and selectively diagnosing a sensor fault in at least one of the first, second, and third dosing agent sensors based on the indications. The second volumetric level is greater than the first volumetric level, and the third volumetric level is greater than the second volumetric level. 
         [0015]    In other features, the selectively diagnosing comprises diagnosing the sensor fault when the indicating comprises indicating that the dosing agent is present at the third volumetric level and that the dosing agent is absent at at least one of the first and second volumetric levels. 
         [0016]    In still other features, the selectively diagnosing comprises diagnosing the sensor fault when the indicating comprises indicating that the dosing agent is present at the second volumetric level and that the dosing agent is absent at the first volumetric level. 
         [0017]    In further features, the selectively diagnosing comprises diagnosing the sensor fault when the indicating transitions to indicating that the dosing agent is absent at the first volumetric level while indicating that the dosing agent is present at the second level. 
         [0018]    In still further features, the selectively diagnosing comprises diagnosing the sensor fault when the indicating transitions to indicating that the dosing agent is absent at the second volumetric level while indicating that the dosing agent is present at the third volumetric level. 
         [0019]    In other features, the selectively diagnosing comprises diagnosing the sensor fault when the indicating transitions to indicating that the dosing agent is absent at the first volumetric level while a pump pressure is greater than a predetermined pressure. 
         [0020]    In still other features, the selectively diagnosing comprises diagnosing the sensor fault when a quantity of the dosing agent injected into an exhaust stream between a first time and a second time is less than a predetermined quantity. The first time corresponds to when the indicating transitions to indicating that the dosing agent is absent at the third volumetric level while indicating that the dosing agent is present at the second volumetric level. The second time is after the first time when the indicating comprises indicating that the dosing agent is absent at the second volumetric level. 
         [0021]    In further features, the selectively diagnosing comprises diagnosing the sensor fault when a quantity of the dosing agent injected into an exhaust stream between a first time and a second time is less than a predetermined quantity. The first time corresponds to when the indicating transitions to indicating that the dosing agent is absent at the second volumetric level while indicating that the dosing agent is present at the first volumetric level. The second time is after the first time when the indicating transitions to indicating that the dosing agent is absent at the first volumetric level. 
         [0022]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0024]      FIG. 1  is a functional block diagram illustrating an exemplary level monitoring system for monitoring urea level in a urea tank; 
           [0025]      FIG. 2  is a functional block diagram of an exemplary control module of  FIG. 1  in further detail; 
           [0026]      FIG. 3  is a functional block diagram of an exemplary invalid level check module; 
           [0027]      FIG. 4  is a functional block diagram of an exemplary sensor stuck high check module; 
           [0028]      FIG. 5  is a functional block diagram of an exemplary first sensor stuck low check module; and 
           [0029]      FIG. 6  is a functional block diagram of an exemplary second sensor stuck low check module and a sensor fault output module. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    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. 
         [0031]    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. 
         [0032]    Referring now to  FIG. 1 , a urea tank  10  stores urea and includes sensors  12 ,  14  and  16 , which may also be referred to herein as sensor  1  (or S 1 ), sensor  2  (or S 2 ), and sensor  3  (or S 3 ), respectively. The urea tank  10  stores urea that is injected into an exhaust system of a diesel engine (not shown). The sensors  12 ,  14 , and  16  sense the presence or absence of urea adjacent thereto and generate first and second signal states based thereon. While the foregoing description describes sensors with a high state in the presence of urea, a low state may also be used to signify the presence of urea. 
         [0033]    The sensor  12  is arranged to sense urea in the urea tank  10  below the sensors  14  and  16 . The sensor  14  is arranged to sense urea in the urea tank  10  between the sensor  12  and  16 . The sensor  16  is arranged to sense urea in the urea tank  10  above the sensors  12  and  14 . A control module  18  receives outputs of the sensors  12 ,  14 , and  16  and performs diagnostics on the sensor outputs to determine sensor faults and verify the sensor outputs. A pump  20  pumps urea and a pressure sensor  22  senses pump pressure. As can be appreciated, the control module  18  may be implemented by an engine control module or other vehicle control module. 
         [0034]    Referring now to  FIG. 2 , an exemplary functional block diagram of the control module  18  of  FIG. 1  is shown in further detail. The control module  18  may include an invalid level check module  24 , a sensor stuck high check module  26 , a first stuck low check module  30  and a second stuck low check module  34 . A sensor fault module  38  generates a sensor fault based on outputs of the modules  24 ,  26 ,  30 , and  34 , as will be described further below. For example only, the sensor fault module  38  may generate a sensor fault signal, set a flag in diagnostic memory, illuminate a light (e.g., a “check engine” light), and/or generate any other indicator of a sensor fault. 
         [0035]    The invalid level check module  24  compares combined sensor states of the sensors  12 ,  14 , and  16  to a table. The table identifies whether the sensor states correspond to a valid combined sensor state for the sensors  12 ,  14 , and  16  or an invalid combined sensor state for the sensors  12 ,  14 , and  16 . In addition, the other modules  26 ,  30 , and  34  perform further diagnostics as will be described further below. 
         [0036]    The stuck high check module  26  determines whether any of the sensors  12 ,  14 , and  16  are stuck in a high state. The sensor stuck high check module  26  selectively asserts first (or S 1 ), second (or S 2 ), and third (or S 3 ) stuck high signals when the sensors  12 ,  14 , and  16  are in a stuck high state, respectively. The sensor stuck high check module  26  may also receive a pump pressure signal from the urea pump and a pump pressure calibration signal. The stuck high state determination may be based on these values. 
         [0037]    The first stuck low check module  30  determines whether the sensors  14  and  16  are in a stuck low state. The first stuck low check module  30  may base the determination on a urea quantity calculation generated by the control module  18  and whether or not urea was injected since a first combined sensor state transition. 
         [0038]    The second stuck low check module  34  determines whether the sensor  12  is in a stuck low state. The second stuck low check module  34  may also base the determination on the urea quantity calculation and whether or not urea was injected since a second combined sensor state transition. 
         [0039]    Referring now to  FIG. 3 , an exemplary invalid level check module  24  is shown. Valid combined sensor states may correspond to combined sensor states 111, 011, 001, and 000. Invalid combined sensor states may correspond to combined sensor states 110, 101, 100, and 010. In each of these combined sensor states, the sensor  16  appears first followed by the sensor  14  and then the sensor  12 . 
         [0040]    Referring now to  FIG. 4 , an exemplary functional block diagram of the sensor stuck high check module  26  is shown. The sensor stuck high check module  26  determines whether there has been a transition from the combined sensor state of 111 to the combined sensor state of 101. If true, then a stuck high signal is generated for the sensor  16 . 
         [0041]    The sensor stuck high check module  26  also determines whether a transition has occurred from the combined sensor state of 011 to the combined sensor state of 010. If true, then the sensor stuck high check module  26  generates a stuck high signal for the sensor  14 . The sensor stuck high check module  26  also determines whether there has been a transition from the combined sensor state of 001 to the combined sensor state of 000. If false, the sensor stuck high check module  26  compares the pump pressure to the pump pressure calibration. If the pump pressure is less than or equal to the pump pressure calibration and the transition from the combined sensor state of 001 to the combined sensor state of 000 has not occurred, the sensor stuck high check module  26  generates a stuck high signal for the sensor  12 . 
         [0042]    Referring now to  FIG. 5 , an exemplary first stuck low check module  30  is shown. The first stuck low check module  30  compares urea injected since transitioning to the state of 011 to a urea quantity calibration. If the urea injected is less than or equal to the urea quantity calibration and the current state is equal to the combined sensor state of 001, then a stuck low signal is generated for the sensor  14 . A stuck low condition for the sensor  16  is undetectable. However, a customer may receive a low urea warning indication even when the urea tank has been filled. 
         [0043]    Referring now to  FIG. 6 , an exemplary functional block diagram of the second stuck low check module  34  and the sensor fault module  38  are shown. The second stuck low check module  34  compares urea injected since transitioning to the combined sensor state of 001 to a urea quantity calibration. If the urea injected is less than or equal to the urea quantity calibration and the current state is equal to the combined sensor state of 000, then a stuck low signal is generated for the sensor  12 . 
         [0044]    Outputs of the invalid combined sensor states generated by the invalid level check module  24 , the stuck high signals, and the stuck low signals are input to the sensor fault module  38 . The sensor fault module  38  may include an OR gate, which outputs a sensor fault when any of these signals are asserted. 
         [0045]    Those skilled in the art can now appreciate from the foregoing description that 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.