Abstract:
A liquid fuel detection system for a fuel vapor system of a vehicle providing fuel vapor to an engine operating in closed loop includes an oxygen sensor that generates an oxygen signal based on an oxygen level in engine exhaust. An engine speed sensor generates a speed signal based on a speed of the engine. And a control module receives the oxygen signal and the speed signal, determines a fuel control factor based on the oxygen signal, determines a long term modifier based on long term changes of the fuel control factor, and detects the presence of liquid fuel in the fuel vapor system based on the fuel control factor, the speed signal, and the long term modifier.

Description:
FIELD 
     The present invention relates to detection systems, and more particularly to liquid fuel detection systems. 
     BACKGROUND 
     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 and an intake manifold via a throttle. A fuel injection system supplies fuel from a fuel tank to provide fuel from a desired A/F mixture to the cylinders. To prevent release of fuel vapor, vehicles also typically include an evaporative emissions system, which includes a canister that absorbs fuel vapor from a 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. 
     Closed-loop control systems adjust inputs of a system based on feedback from outputs of the system. By monitoring the amount of oxygen in the exhaust, closed-loop fuel control systems manage fuel delivery to an engine. Based on the output of oxygen sensors, the engine control module adjusts the fuel delivery to match the ideal A/F ratio (14.7 to 1). By monitoring the engine speed variation at idle, closed-loop speed control systems manage engine intake airflows and spark advance. 
     Under some circumstances, liquid fuel rather than fuel vapor can be present in the canister. Controlling the fuel system when liquid fuel is present in the canister can be a difficult task. Liquid fuel in the canister can produce high engine emissions, undesirable idle surge, steady throttle surge, or engine stall. If this problem occurs, a vehicle may also fail evaporative emissions requirements. 
     SUMMARY 
     Accordingly, a liquid fuel detection system for a fuel vapor system of a vehicle providing fuel vapor to an engine operating in closed loop includes an oxygen sensor that generates an oxygen signal based on an oxygen level in engine exhaust. An engine speed sensor generates a speed signal based on a speed of the engine. And a control module receives the oxygen signal and the speed signal, determines a fuel control factor based on the oxygen signal, determines a long term modifier based on long term changes of the fuel control factor, and detects the presence of liquid fuel in the fuel vapor system based on the fuel control factor, the speed signal, and the long term modifier. 
     In another feature, the control module detects the presence of liquid fuel when the fuel control modifier drops below a minimum for a selectable period of time. 
     In another feature, the control module detects the presence of liquid fuel in the fuel vapor system when the speed signal and the fuel control factor indicate engine instability. 
     In other features, the control module detects the presence of liquid fuel in the fuel vapor system when engine idle conditions are met. Engine idle conditions are met if throttle position is less than a minimum throttle position value and vehicle speed is less than a minimum vehicle speed value. 
     In still other features, the control module sets a liquid fuel notification code when the presence of liquid fuel is detected a selectable number of times and the control module sends an off-board communication signal when the presence of liquid fuel is detected a selectable number of times. 
     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 engine control system and a fuel system according to the present invention; 
         FIG. 2  is a flowchart illustrating a method of detecting the presence of liquid fuel in the fuel vapor system; 
         FIG. 3  is a flowchart illustrating a method of checking engine idle conditions; 
         FIG. 4  is a flowchart illustrating a method of checking engine stability conditions; and 
         FIG. 5  is a flowchart illustrating a method of checking long term modifier low conditions. 
     
    
    
     DETAILED DESCRIPTION 
     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 will be used in the drawings to identify similar elements. 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 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 more or fewer 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 into the cylinders  28 . 
     Exhaust flows through the exhaust manifold  24  and is treated in a catalytic converter  30 . First and second exhaust oxygen sensors  32  and  34  (e.g., wide-range A/F ratio sensors) communicate exhaust A/F ratio signals to the control module  16 . A mass air flow (MAF) sensor  36  is located within an air inlet and communicates to the control module  16  a MAF signal based on the mass of air flowing into the engine system  12 . An engine speed sensor  38  senses the speed of the engine and communicates an engine speed signal to the control module  16 . A throttle position sensor  40  senses the position of the throttle  26  and communicates a throttle position signal to the control module  16 . 
     The control module  16  controls the fuel and air provided to the engine based on oxygen sensor signals and throttle valve position. This form of fuel control is also referred to as closed loop fuel control. Closed loop fuel control is used to maintain the air/fuel mixture at or close to an ideal stoichiometric air/fuel ratio by commanding a desired fuel delivery to match the airflow. Stoichiometry is defined as an ideal air/fuel ratio, which is 14.7 to 1 for gasoline. The engine control may command different airflow to compensate the engine speed changes during engine idle operation. 
     The engine system  12  operates in a lean condition (i.e. reduced fuel) when the A/F ratio is higher than a stoichiometric A/F ratio. The engine system  12  operates in a rich condition when the A/F ratio is less than the stoichiometric A/F ratio. A fuel control factor helps determine whether the A/F ratio is within an ideal range, i.e., greater than a minimum value and less than a maximum value. An exemplary fuel control factor includes a short term integrator (STI) that provides a rapid indication of fuel enrichment based on input from the oxygen sensor signals. For example, if the signals indicate an air/fuel ratio greater than a specified reference, STI is increased a step and if the signals indicate an air/fuel ratio less than the specified reference, STI is decreased a step. A fuel control modifier monitors changes in the fuel control factor over a long term. An exemplary fuel control modifier includes a long term modifier (LTM). LTM monitors STI and uses integration to produce its output. 
     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  and a fuel vapor line  54 . 
     The fuel pump  50  pumps liquid fuel through the liquid fuel line  52  to the fuel injection system  20  of the engine  18 . A fuel vapor system includes the 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  60  to the canister  56 . The control module  16  modulates the purge valve  60  to selectively enable fuel vapor flow to the intake system of the engine  18 . The control module  16  modulates a canister vent valve  62  to selectively enable air flow from atmosphere into the canister  56 . 
     Referring to  FIGS. 1 and 2 , the steps performed by the control module to detect liquid fuel in the fuel vapor system will be described in more detail. The following method is performed continually when the engine system  12  is operating under closed loop fuel control. Control checks idle conditions to determine if the vehicle  10  is operating at idle at  100 . Control checks engine operating characteristics to determine instability at  110 . If idle conditions are met and the engine operating conditions indicate instability at  120 , control checks LTM low conditions at  130 . LTM low conditions occur when LTM value remains low for a selectable period of time. If idle conditions are not met or engine operating conditions indicate stability at  120 , control returns to checking idle conditions at  100 . If LTM low conditions are met at  140 , liquid fuel is deemed present in the fuel vapor system at  150 . If the LTM low conditions are not met, control returns to check idle conditions at  100 . 
     Once control detects liquid fuel in the fuel vapor system, control may set a notification code at  160  and a notification signal is sent at  170 . The signal can be in the form of a diagnostic code that can be retrieved by a service tool connected to the vehicle, in the form of a signal that illuminates an indicator light viewable by an operator and/or in the form of a diagnostic code that is broadcast to a remote service technician. Alternatively (flow not shown), control may wait until fuel has been detected in the vapor system a consecutive number of times or a selected number of times within a specified time period before setting a notification signal or sending the notification signal. 
     Referring now to  FIG. 3 , a method of checking idle operating conditions referred to at process box  100  in  FIG. 2  will be discussed in more detail. Control evaluates whether the throttle position signal is less than a minimum value at  200 . The minimum value can be selectable. If the throttle position is less than the minimum at  200 , control evaluates the vehicle speed at  210 . If the vehicle speed is less than a minimum speed value at  210 , idle conditions are deemed met at  220  and an idle conditions met flag is set to TRUE. If the throttle position is greater than or equal to the minimum at  200  or the vehicle speed is greater than or equal to the maximum at  210 , idle conditions are deemed not met and the idle conditions met flag is set to FALSE at  230 . 
     Referring now to  FIG. 4 , a method of checking engine stability referred to at process box  110  of  FIG. 2  will be discussed in more detail. Control evaluates engine speed at  300 . If engine speed deviates from a desired engine speed a selectable number of times at  300 , control evaluates STI in step  310 . If STI deviates from a selected value (i.e. 100 percent) by a selectable amount and for a selectable number of times, engine is deemed unstable and an engine unstable flag is set to TRUE at  320 . If the engine is stable at  300  and the STI is stable at  310 , the engine unstable flag is set to FALSE at  330 . 
     Referring now to  FIG. 5 , a method of checking LTM low conditions referred to at process box  130  of  FIG. 2  will be discussed in more detail. A counter is initialized to zero at  390 . If the LTM is less than or equal to a selectable minimum at  400 , a counter is incremented at  410 . If the counter is greater than a threshold at  420 , a LTM low condition is set to TRUE at  430 . If the counter is less than or equal to the threshold at  420 , control returns to evaluate LTM at  400 . If the LTM is greater than the selectable minimum at  400 , the LTM low condition flag is set to FALSE at  440 . 
     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, specification, and the following claims.