Abstract:
A fault system for flexible fuel systems is provided. The system includes: a fault monitor module that monitors fuel estimation inputs and detects fuel estimation faults; and a fuel estimation module that selectively estimates a concentration level based on whether a fuel estimation fault is detected.

Description:
FIELD 
     The present disclosure relates to methods and systems for flexible fuel systems. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Ethanol, also know as ethyl alcohol, is a flammable, colorless chemical compound that can be mixed with gasoline to fuel an internal combustion engine. Flexible fuel vehicles include adaptations that allow the vehicle to run on various blends of gasoline and ethanol. For example, E85 fuel contains a mixture of 85% ethanol and 15% gasoline. A virtual flex fuel sensor along with a fuel estimation method determines a concentration of ethanol in the fuel. Based on the concentration level, the air/fuel ratio is adjusted and the engine operation is controlled accordingly. 
     If a fault were to occur on any one of the inputs to the fuel estimation system, the estimation method typically is disabled. Therefore, the estimate of the concentration level is not updated. If a refuel event were to occur after disabling the estimation method, the actual ethanol concentration level could diverge from the estimated concentration level. For example, if the vehicle contained E85 fuel prior to the fault and the driver added gasoline after the fault, the estimate will be very different from the actual concentration level. An incorrect estimation can impact vehicle startability and vehicle drivability. 
     SUMMARY 
     Accordingly, a fault system for flexible fuel systems is provided. The system includes: a fault monitor module that monitors fuel estimation inputs and detects fuel estimation faults; and a fuel estimation module that selectively estimates a concentration level based on whether a fuel estimation fault is detected. 
     In other features, a flexible fuel fault warning system for a vehicle is provided. The system includes: a warning lamp that illuminates based on a flexible fuel fault indicator signal. The warning lamp includes a flexible fuel fault warning message. 
     Still in other features, a monitoring method for a flexible fuel system is provided. The method includes: monitoring the flexible fuel system for faults; generating a fault indicator signal when a fault is detected; and selectively estimating a concentration level of the fuel system based on whether a fault is detected. 
     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 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 of a vehicle including a flexible fuel system. 
         FIG. 2  is a dataflow diagram illustrating a flexible fuel fault system. 
         FIG. 3  is a flowchart illustrating a flexible fuel fault method. 
     
    
    
     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 now to  FIG. 1 , a vehicle  10  includes an engine  12 , an exhaust system  14 , and a control module  16 . The engine  12  includes an intake manifold  17 , a throttle position sensor (TPS)  18 , and a mass air flow (MAF) sensor  20 . The throttle position sensor  18  and the MAF sensor  20  communicate with the control module  16 . The exhaust system  14  includes a catalytic converter  22 , a pre-catalyst or inlet oxygen sensor  24 , and a post-catalyst or outlet oxygen sensor  26 . The inlet and outlet oxygen sensors  24 ,  26  communicate with the control module  16  to provide inlet and outlet F/A ratio signals, respectfully. The control module  16  communicates with a fuel system  28  to regulate fuel flow to the engine  12 . 
     The control module  16  includes a fuel estimation system that estimates a composition of fuel in the fuel system  28 . In various embodiments, the fuel system  28  may include a flex fuel sensor  29 . The flex fuel sensor  29  generates a fuel signal to the control module  16 . The fuel estimation system interprets a composition of the fuel based on the fuel signal. In various other embodiments, the fuel estimation system estimates a composition of the fuel in the fuel system based on engine operating parameters. For example, the fuel estimation system may estimate a concentration of ethanol in the fuel system based on fuel trim values. This method is described in commonly assigned U.S. patent application Ser. No. 11/232,704, and incorporated herein by reference. 
     Based on the fuel composition, the control module  16  regulates the F/A ratio of the engine  12 . In addition, the control module  16  monitors the engine  12  and fuel system  28  for faults. Faulty sensor readings may occur that affect the estimate of the composition. When related faults are detected, the control module  16  controls the engine  12  and fuel system  28  and communicates with a warning system based on the flexible fuel fault method of the present disclosure. The warning system may include at least one of a warning lamp  30 , an audio system  32 , and a telematics system  34  (i.e., Onstar®). The warning system notifies one or more persons of the fault. 
     Referring now to  FIG. 2 , a dataflow diagram illustrates various embodiments of a flexible fuel fault system that may be embedded within the control module  16 . Various embodiments of flexible fuel fault systems according to the present disclosure may include any number of sub-modules embedded within the control module  16 . The sub-modules shown may be combined and/or further partitioned to similarly provide control when a fault occurs. Inputs to the system may be received from sensors within the vehicle  10 , received from other control modules (not shown) within the vehicle  10 , 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 fault monitor module  40 , a fuel estimation module  42 , and a message module  44 . 
     The fault monitor module  40  receives as input fault data  48  corresponding to faults relating to fuel estimation (e.g. flex fuel sensor faults, vehicle speed faults, MAF faults, purge solenoid faults, fuel trim faults, and oxygen sensor faults). If the fault data  48  indicates that one or more of the inputs to the fuel estimation system are faulty, a fault flag  50  is set accordingly. The message module  44  receives the fault flag  50  and issues a fault indicator signal  52  accordingly. In various embodiments, the fault indicator signal  52  illuminates the warning lamp  30  of  FIG. 1 . Wherein the warning lamp  30  may illuminate a message including, but not limited to, “Service Engine Soon” or “Use Unleaded Gasoline Only.” In various embodiments, the fault indicator signal  52  initiates an audible warning signal to the audio system  32  located within the vehicle  10  of  FIG. 1 . In various embodiments, the fault indicator signal  52  contains a diagnostic code. Wherein the diagnostic code can be transmitted via the telematics system  34  of  FIG. 1  to a remote location or retrieved via a service tool (not shown) in communication with the vehicle  10 . 
     The fuel estimation module  42  receives as input the fault flag  50 , fuel event data  56 , and fuel estimation data  58  and/or the flex fuel sensor signal  60 . The fuel estimation module  42  generates an estimate  62  of a concentration level of ethanol in the fuel system  28  of  FIG. 1  after each refuel event according to one of at least two estimation methods. If the fault flag  50  indicates no faults were detected, the estimate  62  level is determined according to conventional estimation methods such as according to fuel trim values as described above. 
     If the fault flag  50  indicates a fault was detected, the fuel estimation module  42  computes estimate  62  based on a weighted volume average method. The weighted volume average method computes the estimate  62  of the ethanol concentration level based on a current and a previous fuel volume, a previous ethanol percent, and assuming that gasoline was added during the refuel event. After a number of refuel events, by using the weighted volume average method, the estimated concentration level will converge with the actual concentration level and hence improve startability and drivability. 
     Referring now to  FIG. 3 , a flowchart illustrates a flexible fuel fault method as performed by the control module  16 . The method may be run periodically during engine operation. Control monitors fault conditions at  100 . If fault data indicates that one or more inputs to the fuel estimation system are faulty at  102 , a fault indicator signal is initiated at  102 . Otherwise control proceeds to monitor for a refuel event at  104 . If a refuel event occurs at  104  and a fault is detected at  106 , a concentration level is estimated based on the weighted volume average method as discussed above at  108 . Otherwise, if a refuel event occurs at  104  and no faults have been detected at  106 , a concentration level is estimated based on a conventional method such as according to a flex fuel sensor signal at  110  as discussed above. Otherwise, if a refuel event has not been detected, control loops back and continues to monitor for a refuel event at  104 . 
     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.