Abstract:
A control module and method for operating the same includes a diurnal control valve module that opens a diurnal control valve (DCV) and an evaporative leak check module (ELCM) diverter valve control module that switches on an ELCM diverter valve. The control module includes a correlation module performs a correlation of a ELCM pressure signal and a fuel tank pressure signal and that generates a fault signal in response to the correlation when the DCV valve is open and the ELCM diverter valve is on.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/225,331, filed on Jul. 14, 2009. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a fuel system for a vehicle and more particularly to determining an error in a pressure sensor of a fuel system. 
       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]    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. 
         [0005]    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 an output of oxygen sensors, an engine control module adjusts the fuel delivery to match an ideal A/F ratio (14.7 to 1). By monitoring engine speed variation at idle, closed-loop speed control systems manage engine intake airflows and spark advance. 
         [0006]    Typically, the fuel tank stores liquid fuel such as gasoline, diesel, methanol, or other fuels. The liquid fuel may evaporate into fuel vapor which increases pressure within the fuel tank. Evaporation of fuel is caused by energy transferred to the fuel tank via radiation, convection, and/or conduction. An evaporative emissions control (EVAP) system is designed to store and dispose of fuel vapor to prevent release. More specifically, the EVAP system returns the fuel vapor from the fuel tank to an engine for combustion therein. The EVAP system is a sealed system to meet zero emission requirements. More specifically, the EVAP system may be implemented in a plug-in hybrid vehicle with minimum engine operation that stores fuel vapor prior to being purged to the engine. 
         [0007]    The EVAP system includes an evaporative emissions canister (EEC), a purge valve, and a diurnal control valve. When the fuel vapor increases within the fuel tank, the fuel vapor flows into the EEC. The purge valve controls the flow of the fuel vapor from the EEC to the intake manifold. The purge valve may be modulated between open and closed positions to adjust the flow of fuel vapor to the intake manifold. 
         [0008]    Determining whether a fuel leak occurs is important in a closed system. However, adding additional pressure sensors increases the cost of the system. 
       SUMMARY 
       [0009]    The present disclosure provides a method and system for determining the accuracy of a fuel tank pressure sensor using components found in a vehicle fuel system. 
         [0010]    In one aspect of the disclosure, a method includes opening a diurnal control valve, switching on an ELCM diverter valve, generating a fuel tank pressure signal, generating an ELCM pressure signal, correlating the ELCM pressure signal and the fuel tank pressure signal and generating a fault signal in response to correlating. 
         [0011]    In another aspect of the disclosure, a control module includes a diurnal control valve module that opens a diurnal control valve and an ELCM diverter valve control module that switches on an ELCM diverter valve. The control module includes a correlation module performs a correlation of a ELCM pressure signal and a fuel tank pressure signal and that generates a fault signal in response to the correlation when the DCV valve is open and the ELCM diverter valve is on. 
         [0012]    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 
         [0013]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a functional block diagram of an engine system of a vehicle according to the present disclosure; 
           [0015]      FIG. 2  is a functional block diagram of an engine control module according to the principles of the present disclosure; and 
           [0016]      FIG. 3  is a flowchart depicting exemplary steps performed by the engine control module according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    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. 
         [0018]    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. 
         [0019]    Referring now to  FIG. 1 , a functional block diagram of an exemplary engine system  100  of a vehicle is shown. The engine system may be for a conventional Spark-ignited (SI) engine, a Homogeneous Charge Compression Ignited (HCCI) engine or an extended range electric vehicle engine which is used as a generator for generating electric power for charging a battery pack. The engine system  100  includes a fuel system  102 , an EVAP system  104 , and an engine control module  106 . The fuel system  102  includes a fuel tank  108 , a fuel inlet  110 , a fuel cap  112 , and a modular reservoir assembly (MRA)  114 . The MRA  114  is disposed within the fuel tank  108  and pumps liquid fuel to a fuel injection system (not shown) of the engine system  100  to be combusted. A fuel tank pressure sensor  164  generates a fuel tank pressure signal corresponding to the pressure within the fuel tank. 
         [0020]    The EVAP system  104  includes a fuel vapor line  116 , a canister  118 , a fuel vapor line  120 , a purge valve (PV)  122 , a fuel vapor line  124 , an air line  126 , a diurnal control valve (DCV)  128 , and an air line  130 . 
         [0021]    The fuel tank  108  contains liquid fuel and fuel vapor. The fuel inlet  110  extends from the fuel tank  108  to enable fuel filling. The fuel cap  112  closes the fuel inlet  110 . 
         [0022]    Fuel vapor flows through the fuel vapor line  116  into the canister  118 , which stores the fuel vapor. The fuel vapor line  120  connects the canister  118  to the PV  122 , which is initially closed in position. The engine control module  106  controls the PV  122  to selectively enable fuel vapor to flow through the fuel vapor line  124  into the intake system (not shown) of the engine system  100  to be combusted. Air flows through the air line  126  to the DCV  128 , which is initially closed in position. The engine control module  106  controls the DCV  128  to selectively enable air to flow through the air line  130  into the canister  118 . 
         [0023]    The air line  126  may include an evaporative leak check module (ELCM)  140 . An ELCM filter  141  may filter the air flow to the ELCM  140 . The evaporative leak check module  140  may include an ELCM diverter valve  142 , a vacuum pump  144  and an ELCM pressure sensor  146 . A reference orifice  148  may also be included within the evaporative leak check module  140 . The diverter valve  142  includes a first path  150  and a second path  152  therethrough. In the first position  150 , as illustrated, air is directed through the diverter valve directly from the input to the DCV  128 . In the second position  152 , the diverter valve  142  is controlled upward so that the vacuum pump  144  is in use and air travels through the vacuum pump  144  to the diurnal control  128 . In either case, the pressure sensor  146  generates a pressure signal corresponding to the pressure within the ELCM  140 . 
         [0024]    The engine control module  106  regulates operation of the engine system  100  based on various system operating parameters. The engine control module  106  controls and is in communication with the MRA  114 , the fuel tank pressure sensor  164 , the PV  122 , the DCV  128  and the ELCM  140 . 
         [0025]    Referring now to  FIG. 2 , a functional block diagram of the engine control module  106  is shown. The engine control module  106  includes a correlation module  200 , a fuel tank pressure module  202 , a PV control module  204 , an evaporative leak check module (ELCM) pressure module  206 , a DCV control module  208  and an ELCM control module  210 . 
         [0026]    The fuel tank pressure module  202  receives the fuel tank pressure signal and determines a fuel tank pressure based on the fuel tank pressure signal. 
         [0027]    The ELCM pressure module  206  generates a pressure corresponding to the evaporative leak check module pressure sensor  146  of  FIG. 1 . The ELCM pressure signal and the fuel tank pressure are provided to the correlation module  200 . The correlation module  200  provides control signals to the purge valve control module  204  that controls purge valve  122 . The correlation module  200  also provides control signals to the diurnal control valve control module  208 . The purge valve control module  204  controls the purge valve  122  as will be described below during a correlation of the pressure sensors. Likewise, the DCV control module  208  controls the DCV  128  during correlation of the pressure sensors. 
         [0028]    The ELCM control module  210  includes an ELCM vacuum pump control module  220  and an ELCM diverter valve control module  222 . The ELCM vacuum pump control module  222  controls the ELCM vacuum pump  144  and the ELCM diverter valve control module controls the ELCM diverter valve  142 . 
         [0029]    The correlation module  200  controls the operation of the purge valve  122 , the diurnal control valve  128 , the ELCM diverter valve  142  and the vacuum pump  144  in a predetermined manner to provide a sensor correlation between the fuel tank pressure and the pressure measured at the ELCM pressure sensor  146  of  FIG. 1 . The correlation module  200  may, for example, determine a plurality of differences between the fuel tank pressure and the ELCM pressure and generates an average difference signal. The average difference signal may be compared to a correlation value or threshold. When the difference between the fuel tank and ELCM pressure is outside of a correlation range, an error indicator  230  may be activated. The error indicator  230  may provide an error signal through an on-board diagnostic system, or the like. The error indicator  230  may also be used to provide an audible or visual indicator as to an error to the vehicle operator. 
         [0030]    Referring now to  FIG. 3 , a method for operating the present disclosure is set forth. In step  310 , the initial positions of the various valves are initiated. It should be noted that the present disclosure may be performed both in engine-running and engine-off states. In step  310 , the initial positions correspond to the purge valve being closed, the diurnal control valve being closed, the diverter valve being off and the ELCM vacuum pump being off. At this point, no sensor correlation is taking place. 
         [0031]    In step  312 , the ELCM diverter valve is turned on which places the ELCM diverter valve in the upper-most position  152  illustrated in  FIG. 1 . In step  314 , the DCV valve is opened. In step  316 , the system waits for a stabilization time. The stabilizing time allows the system to equalize prior to pressure measurement. In step  318 , the pressure sensor signals are correlated. 
         [0032]    The correlation of the pressure sensors in step  318  includes many steps including step  320  that measures the fuel tank pressure from the fuel tank pressure sensor. In step  322 , the pressure at the ELCM pressure sensor is determined. In step  324 , a difference of the measured fuel tank pressure and the measured ELCM pressure is determined. The difference may be obtained several times over a range of times and an average difference may be determined. When the average difference is greater than a calibration threshold (CAL) in step  324 , step  326  generates an error signal. In step  324 , when the difference is not greater than a calibration, a correlation signal is generated in step  328 . After step  328 , the DCV valve is closed in step  330  and the ELCM diverter valve is closed in step  332 . 
         [0033]    As will be evident to those skilled in the art, an additional pressure sensor for verifying the proper operation of the fuel tank pressure sensor is not provided. By providing the same pressure to the fuel tank pressure sensor and the ELCM pressure sensor, both of the sensors are exposed to the same pressure/vacuum environment and therefore a correlation of the two sensors may be performed. 
         [0034]    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.