Abstract:
A control system for diagnosing a fuel system of a vehicle is provided. The system generally includes a correction term module that estimates a fuel correction term based on a first fuel correction value and a second fuel correction value, wherein the first fuel correction value is based on a first period and the second fuel correction value is based on a second period, and wherein the first period is longer than the second period. A diagnostic module diagnoses the fuel system of the vehicle based on the fuel correction term.

Description:
FIELD 
     The present disclosure relates to methods and systems for diagnosing a fuel system of a vehicle. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Internal combustion engines combust an air/fuel (A/F) mixture within cylinders to drive pistons and to provide drive torque. Air is delivered to the cylinders via a throttle and an intake manifold. A fuel injection system supplies fuel from a fuel tank to provide fuel to the cylinders based on a desired A/F mixture. To prevent release of fuel vapor, a vehicle may include an evaporative emissions system which includes a canister that absorbs fuel vapor from the fuel tank, a canister vent valve, and a purge valve. The canister vent valve allows air to flow into the canister. The purge valve supplies a combination of air and vaporized fuel from the canister to the intake system. 
     A fuel diagnostic system monitors the fuel delivery to the engine. A fuel correction value can be estimated based on a measured air/fuel ratio and a commanded air/fuel ratio. If the estimated fuel correction value is outside of certain predetermined thresholds, a diagnostic trouble code can be recorded. Multiples instances of the estimated correction value being outside of the certain predetermined thresholds can cause a Service Engine Soon light to illuminate. Thus, properly diagnosing the fuel delivery can affect warranty. 
     In addition, to diagnose the fuel delivery, the purge valve is temporarily controlled such that the air and vaporized fuel is prevented from entering the intake system. Such intrusive interruption to the fueling system can affect fuel economy and/or emissions if the interruptions are frequent and/or are for long periods of time. 
     SUMMARY 
     Accordingly, a control system for diagnosing a fuel system of a vehicle is provided. The system generally includes a correction term module that estimates a fuel correction term based on a first fuel correction value and a second fuel correction value, wherein the first fuel correction value is based on a first period and the second fuel correction value is based on a second period, and wherein the first period is longer than the second period. A diagnostic module diagnoses the fuel system of the vehicle based on the fuel correction term. 
     In other features, a method of diagnosing a fuel system of a vehicle is provided. The method includes: estimating a fuel correction term based on a first fuel correction value and a second fuel correction value, wherein the first fuel correction value is based on a first period and the second fuel correction value is based on a second period, and wherein the first period is longer than the second period; monitoring the fuel correction term for change based on a stability threshold; and diagnosing the fuel system of the vehicle based on the monitoring of the fuel correction term. 
     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. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a functional block diagram illustrating an exemplary vehicle including a fast fuel adjustment diagnostic system according to various aspects of the present disclosure. 
         FIG. 2  is a dataflow diagram illustrating an exemplary fast fuel adjustment diagnostic system according to various aspects of the present disclosure. 
         FIG. 3  is a flowchart illustrating an exemplary fast fuel adjustment diagnostic method that can be performed by the fast fuel adjustment diagnostic system according to various aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 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 executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring to  FIG. 1 , a vehicle  10  includes an engine system  12  and a fuel system  14 . One or more control modules  16  communicate with the engine and fuel systems  12 ,  14 . The fuel system  14  selectively supplies liquid and/or fuel vapor to the engine system  12 , as will be described in further detail below. 
     The engine system  12  includes an engine  18 , a fuel injection system  20 , an intake manifold  22 , and an exhaust manifold  24 . Air is drawn into the intake manifold  22  through a throttle  26 . The throttle  26  regulates mass air flow into the intake manifold  22 . Air within the intake manifold  22  is distributed into cylinders  28 . The air is mixed with fuel and the air/fuel (A/F) mixture is combusted within cylinders  28  of the engine  18 . Although two cylinders  28  are illustrated, it can be appreciated that the engine  18  can include any number of cylinders  28  including, but not limited to 1, 3, 4, 5, 6, 8, 10 and 12 cylinders. The fuel injection system  20  includes liquid injectors that inject liquid fuel into the cylinders  28 . Exhaust from the combustion flows through the exhaust manifold  24  and is treated in a catalytic converter  30 . An exhaust oxygen sensor  32  (e.g., a wide-range A/F ratio sensor) senses a level of oxygen in the exhaust and communicates an exhaust A/F ratio signal to the control module  16 . 
     The fuel system  14  includes a fuel tank  42  that contains liquid fuel and fuel vapor. A fuel inlet  44  extends from the fuel tank  42  to enable fuel filling. A fuel cap  46  closes the fuel inlet  44  and may include a bleed hole (not shown). A modular reservoir assembly (MRA)  48  is disposed within the fuel tank  42  and includes a fuel pump  50 . The MRA  48  includes a liquid fuel line  52 . The fuel pump  50  pumps liquid fuel through the liquid fuel line  52  to the fuel injection system  20  of the engine  18 . 
     In various embodiments, the fuel system  14  can include a fuel vapor system. The fuel vapor system includes a fuel vapor line  54  and a canister  56 . Fuel vapor flows through the fuel vapor line  54  into the canister  56 . A fuel vapor line  58  connects a purge valve  34  to the canister  56 . The control module  16  modulates the purge valve  34  to selectively enable fuel vapor to flow into the intake system of the engine  18 . The control module  16  modulates a canister vent valve  62  to selectively enable air to flow from the atmosphere into the canister  56 . 
     The control module  16  controls the fuel and air provided to the engine  18  based on signals from the oxygen sensor  32  and a position of the throttle valve  26 . This form of fuel control is also referred to as closed loop fuel control. Closed loop fuel control is used to maintain the A/F mixture at or close to a stoichiometric A/F ratio by commanding a desired fuel delivery to match the airflow. Stoichiometry is defined as an ideal A/F ratio (e.g., 14.7 to 1 for gasoline). 
     The control module  16  estimates a fuel control correction term that helps maintain the A/F ratio within an ideal range (i.e., above a minimum value and below a maximum value) of the stoichiometric A/F ratio. An exemplary fuel control correction term includes a short term correction (STC) that provides a rapid indication of fuel correction based on the input signal from the oxygen sensor  32 . For example, if the signal indicates an A/F ratio greater than a specified reference, the STC is increased a step. Conversely, if the signal indicates an A/F ratio less than the specified reference, the STC is decreased a step. A long term correction (LTC) indicates changes in the fuel control factor over a long term. For example, the LTC monitors STC and uses integration to produce an output. 
     According to the fast fuel diagnostic methods and systems of the present disclosure, the control module  16  monitors a combination of the long term correction and the short term correction to enable and disable the diagnosing of the fuel system  14 . The combination correction provides for a faster response, thus, allowing the control module  16  to diagnose the fuel system  14  faster and less often and thus, improving the number of intrusive interruptions to the fuel system  14 . 
     Referring now to  FIG. 2 , a dataflow diagram illustrates various embodiments of a fast fuel adjustment diagnostic system that may be embedded within the control module  16 . Various embodiments of fast fuel adjustment diagnostic systems according to the present disclosure may include any number of sub-modules embedded within the control module  16 . As can be appreciated, the sub-modules shown may be combined and/or further partitioned to similarly diagnose the fuel system  14 . Inputs to the fast fuel adjustment diagnostic system may be sensed from the vehicle  10  ( FIG. 1 ), received from other control modules (not shown) within the vehicle  10  ( FIG. 1 ), and/or determined by other sub-modules (not shown) within the control module  16 . In various embodiments, the control module  16  of  FIG. 2  includes a correction term module  70 , a stabilization evaluation module  72 , and a diagnostic module  74 . 
     The correction term module  70  receives as input a long term correction  76  and a short term correction  78  that can be determined as discussed above. The correction term module  70  combines the long term correction  76  and the short term correction  78  to form a combination correction term  80 . In particular, the correction term module  70  computes a summation of the long term correction  76  and the short term correction  78  and subtracts a predetermined constant (e.g., one) from the summation to form the combination correction term  80 . In various embodiments, the correction term module  70  applies a filter to the combination correction term  80 . Such filter may include, but is not limited to, an exponentially weighted moving average filter. 
     The stabilization evaluation module  72  receives as input the combination correction term  80 . The stabilization evaluation module  72  then monitors the combination correction term  80  for stability or minimal change (i.e., a change less than a stability threshold). In various embodiments, the stabilization evaluation module  72  can compare the current combination term to a previous combination term for a given engine load. Once the combination correction term  80  is stable, the stabilization evaluation module  72  sets a stability status  82  to indicate stability (i.e., stability status=TRUE). Otherwise, the stabilization evaluation module  72  sets the stability status  82  to indicate instability (i.e., stability status=FALSE). 
     The diagnostic module  74  receives as input the stability status  82 . Based on the stability status  82 , the diagnostic module  74  enables the diagnosing of the fuel system  14  ( FIG. 1 ). In various aspects, once the stability status  82  indicates stability, the diagnostic module  74  diagnoses the fuel system  14  ( FIG. 1 ) by comparing the commanded fuel to a desired fuel. Such desired fuel can be determined based on open loop fueling values for particular engine load conditions  81 . Based on the diagnosing, the diagnostic module  74  sets a fault status  84  that indicates whether or not a fault in the fuel system  14  ( FIG. 1 ) exists. 
     As can be appreciated, once the fault status  84  is set to indicate a fault in the fuel system  14  ( FIG. 1 ), additional steps can be performed to notify other systems and users of the failure. In various embodiments, a diagnostic code is set based on the fault status  84 . The diagnostic code can be retrieved by a service tool or transmitted to a remote location via a telematics system. In various other embodiments, an indicator lamp is illuminated based on the fault status  84 . In various other embodiments, an audio warning signal is generated based on the fault status  84 . 
     Referring now to  FIG. 3 , a flowchart illustrates an exemplary fast fuel adjustment diagnostic method that can be performed by the fast fuel adjustment diagnostic system of  FIG. 2  in accordance with various aspects of the present disclosure. As can be appreciated, the order of execution of the steps of the exemplary fast fuel adjustment diagnostic method can vary without altering the spirit of the method. The exemplary method may be performed periodically during control module operation or be scheduled to run based on certain events. 
     In one example, the method may begin at  100 . The combination correction term  80  is computed at  110 . In various aspects, the combination correction term  80  is computed based on the following equation:
 
 CCT=LTC+STC− 1  (1)
 
Where CCT represents the combination correction term  80 , LTC represents the long term correction  76 , and STC represents the short term correction  78 . In various aspects, a filter is applied to the combination correction term  80  at  120 . The filtered combination correction term  80  is then evaluated at  130 . If the combination correction term  80  for a given engine load is stable at  130 , the fuel system  14  ( FIG. 1 ) is diagnosed at  140 . The diagnosing continues at  140  while the combination correction term is stable at  130  and until the diagnostic is complete at  150 . If the combination correction term  80  for a given engine load becomes or remains unstable at  130  or the diagnostic completes at  150 , the diagnostic functions end at  160  thereby terminating any intrusive interruptions to the fuel system  14  ( FIG. 1 ) and the method may end at  170 .
 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, 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, specification, and the following claims.