Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/972,337, filed on Sep. 14, 2007. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to fuel systems, and more particularly to methods and systems for determining the composition of fuel in fuel systems. 
     BACKGROUND OF THE INVENTION 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     An engine may generate power by combusting an air and fuel mixture within cylinders of the engine. The fuel and air may be controlled such that the engine maintains an air-to-fuel ratio at stoichiometry. The engine may operate using fuels with different stoichiometric values, such as a gasoline and ethanol blend. As the percentage of each fuel in the overall fuel mixture changes, the stoichiometric value may change. 
     The stoichiometric value of a fuel mixture may be measured to allow for optimal operation of the engine based on the particular fuel mixture. The engine system may change the relative amounts of air and fuel delivered to the cylinders based on the stoichiometric value for the fuel mixture. In vehicles with a single fuel tank, the fuel mixture may undergo substantial change when the vehicle is refueled, as the new fuel introduced to the fuel tank may have a different fuel mixture than the fuel originally in the fuel tank. The new fuel composition may be measured by direct measurement using a hardware sensor. 
     The fuel mixture may also be calculated from other measured parameters and known relationships in a manner such as that described in commonly-assigned U.S. Pat. No. 7,159,623 (issued Jan. 9, 2007), the disclosure of which is incorporated herein by reference. Exhaust sensors such as oxygen sensors may measure the content of an exhaust flow from an engine. Based on measured values, the fuel and air supplied to the engine may be adjusted, i.e., trimmed, to correct for deviations from a desired air-to-fuel ratio. These fuel trim values may be stored in a memory structure such as a plurality of closed loop correction (“CLC”) cells. The stored CLC values representing fuel trim over time may be used to calculate a fuel composition. 
     Some vehicles have more than one fuel source. Each fuel source may have a different fuel composition. The fuel sources may intermix during vehicle operation such that the fuel mixture supplied to the engine may change multiple times during normal vehicle operation rather than upon refueling. 
     SUMMARY OF THE INVENTION 
     A method comprises detecting a status of a transfer pump for transferring fuel between a first fuel source and a second fuel source; receiving a fuel trim value and a vehicle operating parameter; and calculating a fuel composition of one of the first fuel source and second fuel source based on the fuel trim value, the transfer pump status and the vehicle operating parameter. 
     A control module comprises a secondary pump transfer module detecting a status of a transfer pump for transferring fuel between a first fuel source and a second fuel source; and a fuel composition estimation module in communication with the secondary pump transfer module, receiving a fuel trim value and a vehicle operating parameter, and calculating a fuel composition of one of the first fuel source and second fuel source based on the fuel trim value, the transfer pump status, and the vehicle operating parameter. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram of an exemplary vehicle; 
         FIG. 2  is a functional block diagram of a control module of the exemplary vehicle; 
         FIG. 3  is a flowchart illustrating the operation of a virtual fuel sensor for dual fuel tank applications. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers may be used in the drawings to identify the same elements. As used herein, the term module and/or device 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, or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , an exemplary vehicle  10  is illustrated. The exemplary vehicle  10  includes engine  12 , intake manifold  14 , exhaust manifold  16 , fuel injectors  18 , fuel rail  20 , exhaust sensors  22  and  24 , throttle  26 , catalytic converter  28 , fuel system  30 , control module  40  and ignition system  44 . Fuel system  30  may include primary fuel reservoir  32 , primary fuel pump  34 , secondary fuel reservoir  36 , secondary fuel pump  38 , and balance pipe  42 . 
     Primary fuel reservoir  32  and secondary fuel reservoir  36  may be connected by balance pipe  42 . Balance pipe  42  may prevent primary fuel reservoir  32  from overflowing during refueling, and may balance the amount of fuel between primary fuel reservoir  32  and secondary fuel reservoir  36 . Primary fuel reservoir  32  and secondary fuel reservoir may receive fuels of varied composition, such as fuels with varying percentages of ethanol. For example, “gasohol” may be composed of 90 percent gasoline and 10 percent ethanol and “E85” may be composed of 85 percent ethanol and 15 percent gasoline. Although ethanol and gasoline may be mentioned for example purposes, it should be recognized that other fuels may be used. 
     Primary fuel pump  34  and secondary fuel pump  38  may be fixed displacement pumps or variable displacement pumps. Secondary fuel pump  38  may provide fuel from secondary fuel reservoir  36  to primary fuel reservoir  32 . For example, secondary fuel pump  38  may provide fuel to primary fuel reservoir  32  when primary fuel reservoir  32  is depleted to a certain level. This depletion may occur because primary fuel pump  34  provides pressurized fuel to fuel rail  20  which is drawn from primary fuel reservoir  32 . As fuel injectors  18  inject fuel into the respective cylinders of engine  12 , primary fuel pump  34  may replenish the pressurized fuel within fuel rail  20 . 
     Fuel may be delivered to cylinders of engine  12  from primary fuel reservoir  32  by primary fuel pump  34  through fuel rail  20  and a plurality of fuel injectors  18 . Air may be drawn into intake manifold  14  through throttle  26  and distributed to cylinders of engine  12 . The air and fuel may mix to form a combustion mixture within cylinders of engine  12  which may be ignited by ignition system  44 . The combustion mixture may be provided at a desired stoichiometric ratio of air and fuel and may combust within the cylinder to reciprocally drive a piston (not shown) of engine  12 , which in turn may drive a crankshaft (not shown) of engine  12 . The fuel and air may be adjusted, or trimmed, to correct for deviations from a desired stoichiometric air-to-fuel ratio. 
     Exhaust gas from combustion within engine  12  may exit engine  12  through exhaust manifold  16 . Exhaust sensors  22  and  24  may be oxygen sensors associated with a cylinder bank of engine  12 . Exhaust sensors  22  and  24  may sense whether the exhaust is lean or rich and may be monitored by control module  40 . The output of exhaust sensors  22  and  24  may be used to control trim values, which in turn may provide information to calculate a fuel composition. 
     Control module  40  may be in communication with engine  12 , fuel injectors  18 , exhaust sensors  22  and  24 , primary fuel reservoir  32 , primary fuel pump  34 , secondary fuel reservoir  36  and secondary fuel pump  38 . Control module  40  may monitor fuel levels of primary fuel reservoir  32  and secondary fuel reservoir  36 . Control module  40  may monitor and control primary fuel pump  34  and secondary fuel pump  38 , including monitoring an ON or OFF status. Control module  40  may monitor exhaust sensors  22  and  24  to receive signals relating to exhaust content. Control module  40  may control engine  12  and fuel injectors  18  at a fuel trim level based on exhaust sensors  22  and  24 . Control module  40  may include memory and algorithms such that changes in fuel trim may be used to estimate relative changes in stoichiometric air-to-fuel or fuel-to-air ratio and, accordingly, to estimate relative changes in fuel composition. 
     Referring now to  FIG. 2 , a functional block diagram of control module  40  is shown. Control module  40  may include fuel composition estimation module  60 , learn limit module  62 , CLC module  64 , secondary transfer pump module  66  and fuel trim control module  68 . 
     Fuel trim control module  68  may be in communication with fuel composition estimation module  60 , CLC module  64 , exhaust sensors  22  and  24 , engine  12  and fuel injectors  18 . Fuel trim control module  68  may monitor exhaust sensors  22  and  24  for an exhaust composition such as oxygen to determine whether engine  12  is being operated with a stoichiometric mixture of air and fuel. Fuel trim control module  68  may trim the fuel supplied to engine  12  by fuel injectors  18  to achieve stoichiometry. 
     Trim values used to make such corrections may be stored in memory locations of fuel trim control module  68  corresponding to a plurality of predefined closed loop air-to-fuel ratio control cells (also referred to as sub-regions) associated with operating regions of vehicle  10 . Cell values may be used to provide closed-loop fuel, air and/or re-circulated exhaust control. For example, long-term multipliers (LTMs) may be used to provide long-term corrections to fuel commands to engine  12  in response to changing engine conditions. LTMs typically are stored in a memory lookup table in non-volatile memory. The fuel trim control module  68  may adjust LTMs periodically in accordance with a long-term time period, e.g., using a period that is longer than 1 second such as ten seconds. Such adjustment may be referred to as “long-term learning”. 
     Additionally or alternatively, short-term integrators (STIs) may be used to provide short-term corrections to fuel commands to the engine  12  in response to engine conditions. The fuel trim control module  68  may adjust STIs periodically in accordance with a short-term time period, e.g., using a period that is less than one second such as every 6.25 milliseconds. Such adjustment may be referred to as “short-term learning”. STIs may be stored in volatile memory and may be adjusted based on an active cell LTM and a signal of exhaust sensors  22  and  24 . Fuel trim control module  68  may communicate fuel trim values (including STI and LTM values) to fuel composition estimation module  60  and CLC module  64 . 
     CLC module  64  may receive fuel trim values from fuel trim control module  68  or fuel composition estimation module  60 . CLC module  64  may include a fuel trim memory structure for use in estimating fuel composition. A plurality of CLC cells may be associated with each cylinder bank of engine  12 . For example, eight cells may be provided for each cylinder bank of engine  12 . CLC cells may be defined based on mass air flow to the engine  12  and may be used to record a total closed-loop fuel trim of the engine  12  at various operating conditions. CLC module  64  may store baseline closed loop correction values for the engine operating regions in the CLC cells. The baseline CLC values may provide a basis for determining new fuel and air ratio estimates. 
     CLC cell values may be stored in non-volatile memory. A CLC value may be obtained by multiplying LTM and STI corrections for an active closed-loop fuel control cell. In other configurations, CLC values may be combined in other ways. For example, a CLC value may be obtained in another configuration by adding LTM and STI corrections for an active closed-loop fuel control cell. CLC module  64  may use separate structures for closed loop fuel control and for fuel composition estimation or may use a single data structure for both operations. CLC module  64  may be in communication with secondary transfer pump module  66 . Based on the input from secondary transfer pump module  66 , CLC module  64  may not calculate or adjust CLC values. 
     Learn limit module  62  may be in communication with secondary transfer pump module  66  and fuel composition estimation module  60 . As will be described below, fuel composition estimation module  60  may utilize a change in fuel trim values over time to estimate fuel composition. Learn limit module  62  may use a change in volume of fuel in a fuel tank to set maximum and minimum boundaries for the fuel trim valves that may be considered by fuel composition estimation module  60 . For example, where a small volume of fuel has been added to a fuel tank, the overall change in fuel composition may be small even if the fuel composition of the added fuel is different from the fuel in the fuel tank. Conversely, when a large volume of fuel has been added, a greater change in overall fuel composition is possible. By setting fuel composition estimation learn limits based on the change in fuel volume, learn limit module  62  serves to filter air, fuel and other faults out of the fuel composition estimation calculations of fuel compensation estimation module  60 . Learn limit module  62  may be disabled based on communication from secondary transfer pump module  66 . 
     Secondary transfer pump module  66  may be in communication with secondary pump  38  to receive a secondary pump status such as OFF or ON. Secondary transfer pump module  66  may monitor the secondary pump status and based on the secondary pump status communicate with fuel composition estimation module  60 , learn limit module  62  and CLC module  64 . 
     Fuel composition estimation module  60  may be in communication with learn limit module  62 , CLC module  64 , secondary transfer pump module  66 , fuel trim control module  68 , primary fuel reservoir  32  and secondary fuel reservoir  36 . Learn limit module  62  and fuel composition estimation module  60  may communicate fuel volumes, fuel composition measurements and fuel composition limits back and forth. Fuel composition estimation module  60  may receive CLC values from CLC module  64  and may provide fuel trim values to be stored in CLC module  64 . Fuel composition estimation module  60  may receive a transfer pump status from secondary transfer pump module  66 , fuel trim values from fuel trim control module  68 , and fuel reservoir measurements from primary fuel reservoir  32  and secondary fuel reservoir  36 . Fuel composition estimation module  60  may utilize these and other parameters to calculate a fuel composition as will be described in more detail below. 
     Referring now to  FIG. 3 , a flowchart illustrating the operation of the control system is shown as control logic  100 . At block  102  fuel composition estimation module  60  may determine whether a conventional refueling event has occurred. A conventional refueling event occurs while the vehicle  10  is turned off and fuel is added to the primary fuel reservoir  32 . Fuel composition estimation module  60  may monitor the vehicle  10  ignition (not shown) or other parameters to determine whether the vehicle  10  was turned off and may monitor the primary fuel reservoir  32  to determine whether fuel was added while vehicle  10  was off. If a conventional refuel has occurred, control logic  102  may continue to block  116 . If a conventional refuel has not occurred, control logic  100  may continue to block  104 . 
     At block  104 , secondary transfer pump module  66  may determine whether secondary fuel pump  38  has transferred from OFF to ON. An OFF to ON transition indicates that secondary fuel pump  38  is transferring fuel from secondary fuel reservoir  36  to primary fuel reservoir  32 . The fuel transferred from secondary fuel reservoir  36  may have a different fuel composition than the fuel already in primary fuel reservoir  32 . If secondary fuel pump  38  indicates an OFF to ON transition, control logic  100  may continue to block  106 . If secondary fuel pump  38  does not indicate an OFF to ON transition, control logic  100  may continue to block  108 . 
     At block  106 , secondary transfer pump module  66  may provide a signal to CLC module  64  indicating that certain CLC functions should be disabled. For example, CLC baseline values may not be updated once secondary fuel pump  38  begins to transfer fuel to primary fuel reservoir  32 , although current CLC values may still be used by fuel trim control module  68  and fuel composition estimation module  60 . It should be recognized that the disabling function described above may be applied to any operating parameters of vehicle  10 , such as stored CLC values, that may operate under the assumption that large changes in fuel composition only occur during a conventional refueling event. Updating these parameters during a fuel transfer may result in skewed calculations and/or operation of vehicle  10 . Control logic  100  may continue to block  108 . 
     At block  108 , secondary transfer pump module  66  may determine whether secondary fuel pump  38  has transferred from ON to OFF. An ON to OFF transition indicates that secondary fuel pump  38  has finished transferring fuel from secondary fuel reservoir  36  to primary fuel reservoir  32 . If secondary fuel pump  38  indicates an ON to OFF transition, control logic  100  may continue to block  112 . If secondary fuel pump  38  does not indicate an ON to OFF transition, control logic  100  may return to block  104 . 
     At block  112 , fuel composition estimation module  60  may receive a signal from secondary transfer pump module  66  indicating that secondary transfer pump  38  has transferred from ON to OFF. Fuel composition estimation module  60  may determine whether a fuel composition estimation is already in progress. If so, control logic  112  may continue to block  118  and loop until the fuel composition estimate is complete as will be described below. If a fuel composition estimation is not already in progress, control logic  100  may continue to block  114 . 
     At block  114 , secondary transfer pump module  66  may provide a signal to fuel composition estimation module  60  and/or learn limit module  62  indicating that the fuel composition learn limits should not be utilized by fuel composition estimation module  60  to determine the fuel composition of primary fuel reservoir  32  after secondary fuel pump  38  has transferred fuel from secondary fuel reservoir  36 . Utilizing fuel composition learn limits during fuel transfer may result in the exclusion of valid fuel trim values from the fuel composition estimation calculations. It should be recognized that the disabling function described above may be applied to any operating parameters of vehicle  10 , such as fuel composition learn limits, that operate under assumptions that are not applicable to an active refueling event during vehicle operation. Control logic  100  may continue to block  116 . 
     At block  116 , fuel composition estimation module  60  may begin estimating the fuel composition of primary fuel reservoir  32 . Fuel trim control module  68  will continue to trim the fuel supplied to engine  12  to maintain stoichiometry even as the fuel composition changes. Fuel trim changes may in turn be represented as CLC values as described above and compared to CLC baseline values during learn stages that occur at predetermined intervals. The predetermined intervals may be based on fuel consumption from primary fuel reservoir  32  as measured by fuel composition estimation module  60 . The ratio of the current CLC value to the CLC baseline provides a percentage change in the fuel-to-air ratio. The fuel composition may be determined from the fuel-to-air ratio based on correlating between fuel composition stoichiometric ratios. 
     At block  118 , fuel composition estimation module  60  may determine if the fuel composition estimation is complete. Fuel composition estimation may be complete when a predetermined number of learn stages are successfully completed or if a predetermined number of learn stages result in the same fuel composition. If fuel composition estimation is not complete, control logic  100  may continue to loop back to block  118 . If fuel composition estimation is complete, control logic  100  may continue to block  120 . 
     At block  120 , fuel compensation estimation module  60  may communicate to learn limit module  62  and CLC module  64  that fuel composition estimation is complete. Learn limit module  62  and CLC module  64  may then re-enable fuel composition estimation learn limits and updating of CLC baseline values, as well as any other parameters that may have been disabled by control logic  100 . Control logic  100  may then end. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention 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.

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