Abstract:
A vehicle includes an engine, a sealed fuel system having a fuel tank, a canister for storing fuel vapor, a vapor circuit external to the fuel tank, and a control valve. The vapor circuit includes an absolute pressure sensor and a switching valve connecting the fuel tank to the control valve. A controller evaluates or diagnoses a vapor purge function of the sealed fuel system using vacuum measurements from the absolute pressure sensor, executing or diagnosing only when the engine is running, purge is enabled, and the pump is off. The controller diagnoses the vapor purge function by comparing the vacuum measurements to a threshold vacuum. An apparatus includes the vapor circuit and controller. A method for diagnosing the vapor purge function includes actuating the switching valve, measuring a vacuum in the system using the absolute pressure sensor, and comparing the measured vacuum to a threshold vacuum.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method and apparatus for detecting or diagnosing fuel vapor purge functionality in a sealed fuel system aboard a vehicle. 
       BACKGROUND 
       [0002]    Vehicle fuel systems store and supply fuel used by an internal combustion engine. A typical vehicle fuel system includes a fuel tank, a pump operable for drawing fuel from the tank, and fuel lines interconnecting various fuel handling components. A filter may also be included within the fuel system to remove suspended particulate matter and other entrained contaminants prior to combustion of the fuel within the engine&#39;s cylinder chambers. A fuel regulator maintains sufficient pressure in the fuel lines, and also cycles excess fuel to the fuel tank. 
         [0003]    In order to prevent fuel vapor from escaping into the surrounding atmosphere, vehicles may include equipment that isolates and stores vapor from the fuel tank, and that ultimately purges the stored vapor to the engine intakes. Certain vehicles, such as extended-range electric vehicles (EREV) or plug-in hybrid electric vehicles (PHEV), use sealed fuel systems to substantially prevent atmospheric discharge of hydrocarbon vapors, thus helping to minimize the vehicle&#39;s environmental impact. 
       SUMMARY 
       [0004]    Accordingly, an algorithm and apparatus are provided herein for use aboard a vehicle having a sealed fuel system. Execution of the algorithm diagnoses vapor purge functionality in the sealed fuel system. Such systems may be used aboard vehicles having relatively short engine run cycles. For example, an extended-range electric vehicle (EREV) has an engine that, when it runs at all, typically does so at wide-open throttle over a short operating duration. Plug-in hybrid electric vehicles (PHEV) and other emerging vehicle designs having sealed fuel systems may also be used with the diagnostic algorithm and apparatus as set forth herein. 
         [0005]    In particular, a vehicle as disclosed herein includes an internal combustion engine, a sealed fuel system having a fuel tank, a canister for storing fuel vapor from the fuel tank, a vapor circuit positioned external to the fuel tank and in fluid communication with the fuel tank, and a control valve. The control valve is operable for controlling a flow of fuel vapor from the vapor circuit into the canister, wherein the vapor circuit includes an absolute pressure sensor, a pump, and a switching valve selectively connecting the fuel tank to the absolute pressure sensor when the control valve is open. The vehicle further includes a controller having an algorithm for evaluating or diagnosing a vapor purge function of the sealed fuel system using vacuum measurements from the absolute pressure sensor. The controller executes the algorithm only when the engine is running, vapor purge is enabled, and the pump is off, and diagnoses the vapor purge function by comparing the vacuum measurements to a calibrated vacuum. 
         [0006]    The controller may actuate the switching valve to thereby place the pump in fluid communication with the rest of the sealed fluid system, and thereafter measure the vacuum in the sealed fuel system using the absolute pressure sensor to thereby determine the vacuum measurements. A purge valve selectively connects the canister to the engine, and a fuel tank pressure sensor measures a gauge pressure level in the fuel tank. The controller opens the purge valve and control valve simultaneously when the fuel tank pressure sensor measures a vacuum in the fuel tank, and opens the purge valve a calibrated amount of time before the control valve when the fuel tank pressure sensor measures a pressure in the fuel tank. 
         [0007]    The controller is operable for executing a time delay equal to a first delay value when the fuel tank pressure sensor detects a vacuum in the fuel tank, and equal to a second delay value when the fuel tank pressure sensor detects a pressure in the fuel tank. The controller may execute the algorithm after the second delay even when pressure remains in the fuel tank. 
         [0008]    An apparatus for use aboard a vehicle having the sealed fuel system includes a vapor circuit positioned external to the fuel tank and in fluid communication with the fuel tank and the control valve, and having an absolute pressure sensor, a pump, and a switching valve selectively connecting the fuel tank to the absolute pressure sensor when the control valve is open. A controller evaluates or diagnoses a vapor purge function of the sealed fuel system using vacuum measurements from the absolute pressure sensor. The controller executes a diagnostic algorithm only when the engine is running, vapor purge is enabled, and the pump is off, and diagnoses the vapor purge function by comparing the vacuum measurements to a calibrated vacuum. 
         [0009]    A method is also disclosed for evaluating or diagnosing a vapor purge function of a sealed fuel system aboard a vehicle having an internal combustion engine and a fuel tank. The method includes actuating a switching valve in a vapor circuit positioned external to the fuel tank when the engine is running and a fuel system purge cycle is enabled, the vapor circuit including an absolute pressure sensor and a pump. The method then includes measuring a vacuum level using the absolute pressure sensor while the pump is off, comparing the vacuum level from the absolute pressure sensor to an initial vacuum level after a control valve is opened and the switching valve is activated to thereby determine a vacuum differential, and executing a control action corresponding to the vacuum differential. 
         [0010]    The method may also include detecting the gauge pressure in the fuel tank using the fuel tank pressure sensor, and simultaneously opening the purge valve and the diurnal control valve only when the gauge pressure corresponds to a vacuum. 
         [0011]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a schematic illustration of a vehicle having a vapor purge diagnostic algorithm and apparatus as set forth herein; 
           [0013]      FIG. 2  is a schematic illustration of a control module usable with the vehicle shown in  FIG. 1 ; and 
           [0014]      FIG. 3  is a flowchart describing a possible embodiment of the present diagnostic algorithm. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring to the drawings, wherein like reference numbers correspond to like or similar components throughout the several figures, and beginning with  FIG. 1 , a vehicle  10  includes a vapor purge diagnostic algorithm  100  as described below. Vehicle  10  includes an internal combustion engine  12  that is selectively connectable to a transmission  14  via a clutch  13 . Engine torque is ultimately transferrable through the clutch  13  to a set of wheels  16  to thereby propel the vehicle  10 . Vehicle  10  may also include at least one electric motor/generator unit (MGU)  18  capable of selectively delivering motor torque to the wheels  16 , either in conjunction with or independently of the transfer of engine torque to the wheels from the engine  12 , depending on the design of the vehicle. 
         [0016]    MGU  18  is adapted for generating electrical energy for onboard storage within an energy storage system (ESS)  20 , e.g., a rechargeable high-voltage direct current battery. ESS  20  may be recharged using an off-board power supply (not shown) when used aboard a plug-in hybrid electric vehicle (PHEV), or directly by the MGU  18 , for example during a regenerative braking event or other regenerative event. Vehicle  10  may be alternatively configured as an extended-range electric vehicle (EREV) as noted above, an emerging design wherein the ESS  20  electrically powers the vehicle over a threshold distance or operating range before starting the engine  12 , and thereafter using engine torque to recharge the ESS and/or MGU  18  to thereby indirectly power the vehicle. 
         [0017]    A controller  24 , e.g., a hybrid engine control module or other suitable host machine, is programmed with or that has access to diagnostic algorithm  100 . Controller  24  may include one or more digital computers each having a microprocessor or central processing unit, read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) and/or digital-to-analog (D/A) circuitry, and input/output circuitry and devices (I/O), as well as appropriate signal conditioning and buffer circuitry. Any algorithms resident in the controller  24  or accessible thereby, including algorithm  100 , can be automatically executed by the controller to provide the required functionality. 
         [0018]    Still referring to  FIG. 1 , the vehicle  10  also includes a sealed fuel system  30 , which is in communication with the controller  24  via signals  11 . As used herein, the term “sealed fuel system” refers to a fuel system configured to seal at all times other than during a refueling event, wherein an insertion of a gas nozzle at a refueling station temporarily breaks the seal. By sealing the sealed fuel system  30  substantially all of the time, atmospheric venting of hydrocarbon vapors is largely prevented during normal vehicle operation. The sealed fuel system  30  includes a vapor circuit  28 , which as used herein is an Evaporative Leak Check Pump (ELCP) circuit having a set of fluid control components or hardware as described in detail below with reference to  FIG. 2 . Certain elements of vapor circuit  28  are used in conjunction with execution of the algorithm  100  to provide a low purge flow diagnostic tool suitable for evaluating the proper vapor purge functionality of the sealed fuel system  30 . 
         [0019]    Referring to  FIG. 2 , in addition to the vapor circuit  28  noted above, the sealed fuel system  30  includes an evaporative emission control (EVAP) system  34 , a fuel tank  36 , a fuel inlet  38 , a fuel cap  40 , and a modular reservoir assembly (MRA)  42 . EVAP system  34  includes a first fuel vapor line  44 , an EVAP canister  46 , a second fuel vapor line  48 , a purge valve  50 , and a first fuel vapor line  52  that feeds the intakes of engine  12  (see  FIG. 1 ). First fuel vapor line  44  connects the fuel tank  36  to canister  46 , and the second fuel vapor line  48  connects the canister to the purge valve  50 . EVAP system  34  further includes a third fuel vapor line  54 , a control valve  56 , a relief valve  57 , and a second fuel vapor line  58  connecting the control valve to the canister  46 . 
         [0020]    In one embodiment, the control valve  56  may be configured as a solenoid-actuated diurnal control valve suitable for controlling a flow of fresh air when purging the canister  36 , or fuel vapor when refueling the canister, and may be normally closed to further minimize vapor emissions. Control valve  56  can be selectively opened to allow fuel vapor residing within canister  46  to be purged to the engine  12  (see  FIG. 1 ) at certain predetermined times when the engine is running, e.g., at least once per trip as explained below with reference to  FIG. 3 . 
         [0021]    Fuel tank  36  contains a mix of liquid fuel  35  and fuel vapor  37 . The fuel inlet  38  extends from the fuel tank  36  to the fuel cap  40 , thus enabling filling of the fuel tank. Fuel cap  40  closes and seals the fuel inlet  38 , and may include a fresh air opening  60  in fluid communication with a filter  62 , e.g., a mesh, screen, sintered element, or other suitable filter media. Cap  40  may include a position sensor  41  and a lock solenoid  43  to optimize sealing functionality. 
         [0022]    A vehicle integration control module (VICM)  64  having a clock  66  communicates with the lock solenoid  43  and with the position sensor  41 , as indicated in  FIG. 2  by arrows  19 . In some vehicle designs, such as certain EREVs, an optional refuel request button or switch  61  may be used. Switch  61  is in communication with the VICM  64 , with an operator actuating the switch to generate signals  21  signaling for a relief of excess pressure or vacuum prior to unlocking of the fuel cap  40  during refueling. 
         [0023]    Still referring to  FIG. 2 , MRA  42  is positioned within the fuel tank  36 , and is adapted for pumping liquid fuel  36  to the engine  12  shown in  FIG. 1 . Fuel vapor  37  flows through the first fuel vapor line  44  into canister  46 , which temporarily stores the fuel vapor. Second fuel vapor line  48  connects canister  46  to the purge valve  50 , which is initially closed. Controller  24  controls the purge valve  50  to selectively enable fuel vapor  37  to flow through the fuel vapor line  52  into the intake system (not shown) of engine  12  (see  FIG. 1 ), where it is ultimately combusted. Vapor also flows from vapor circuit  28 , through the third fuel vapor line  54 , and to the control valve  56 , with the control valve being initially closed. Controller  24 , which communicates with the control valve  56  and the vapor circuit  28  via the signals  11 , ultimately controls operation of the control valve to selectively enable fuel vapor to flow through line  58  into the canister  46  as noted above. 
         [0024]    Controller  24  controls and is in communication with the MRA  42 , the purge valve  50 , and the control valve  56 . The controller  24  is further in communication with a fuel tank (FT) pressure sensor  63 , which in turn is adapted for measuring gauge pressure in the fuel tank  36 , i.e., a positive pressure or a vacuum. In an EREV and other partial zero-emissions vehicles (PZEV), the FT pressure sensor  63  may be positioned on/within canister  46  as shown in  FIG. 2 , although other designs may place the FT pressure sensor within the fuel tank  36 . 
         [0025]    Regardless of where it is placed, the FT pressure sensor  63  is in communication with the controller  24 , which in turn is in communication with VICM  64  over a serial bus  17 . Clock  66  generates time signals  15  and transmits the same to the VICM  64  based on certain vehicle operating conditions, e.g., an accelerator pedal position and/or length of an engine run cycle. The time signals  15  may be used as an input to controller  24  for determining when to execute different portions of algorithm  100  as explained below with reference to  FIG. 3 . 
         [0026]    Vapor circuit  28  includes various fluid control hardware components, including a switching valve  70 , which is shown in one particular embodiment as a solenoid controlled device. Vapor circuit  28  further includes an absolute pressure sensor  72  adapted for determining whether sealed fuel system  30  has a leak, a pump  74  for creating a vacuum in the sealed fuel system  30 , including within just the vapor circuit or in the entire sealed fuel system as set forth herein, and a control orifice  76  to which the absolute pressure sensor may be calibrated, e.g., for leak detection purposes. 
         [0027]    Controller  24  is in communication with the vapor circuit  28 , and uses portions of the circuit as a diagnostic tool when executing algorithm  100 . That is, controller  24  selectively actuates the switching valve  70  during certain threshold vehicle conditions while the engine  12  is running, and monitors absolute pressure in the vapor circuit  28  using the absolute pressure sensor  72  when the switching valve is actuated. That is, when the pump  74  is off and the switching valve  70  is set to a first position, i.e., a “vent” position, the absolute pressure sensor  72  effectively measures atmospheric pressure. When the switching valve  70  is set to a second position, i.e., a “pump” position, with the pump  74  remaining off so as not to spin when vacuum is delivered through the open control valve  56 , the absolute pressure sensor  72  effectively measures the vacuum in the fuel system  30 . If the measured vacuum exceeds a calibrated vacuum level, i.e., if the measured vacuum is at a sufficiently high level, the controller  24  determines that proper vapor purge functionality is present. The diagnostic test described below with reference to  FIG. 3  may generate a passing result or diagnostic code when a threshold vacuum is measured by the absolute pressure sensor  72  and held for a calibrated duration, conditions which should properly indicate proper purge flow. 
         [0028]    Controller  24  controls the open/closed or on/off status of each of the purge valve  50 , the control valve  56 , and the switching valve  70 , as well as the on/off status of pump  74 . Algorithm  100  may be executed once per trip, always when the engine  12  is running and pump  74  is off. Under such conditions, controller  24  transitions the switching valve  70  from a vent position to a pump position as noted above. Absolute pressure sensor  72  is then closely monitored by the controller  24 , with readings from the absolute pressure sensor of the actual vacuum in the sealed fuel system  30  being compared to a calibrated vacuum level, i.e., if the measured vacuum is at a sufficiently high level, the controller determines that proper vapor purge functionality is present. Controller  24  then records a diagnosis of the sealed fuel system  30  using this information. 
         [0029]    Referring to  FIG. 3  in conjunction with the structure shown in  FIG. 2 , algorithm  100  commences as indicated by the (*) symbol, and begins with step  101 , wherein the controller  24  or other suitable device determines whether engine  12  is running. If so, the algorithm  100  proceeds to step  102 . If the engine  12  is not running, the algorithm  100  is finished. 
         [0030]    At step  102 , readings are taken by FT pressure sensor  63  and processed by the controller  24  to determine if a vacuum is present in the sealed fuel system  30 . If so, the algorithm  100  proceeds to step  104 . If a positive pressure is determined at step  102  instead of a vacuum, the algorithm  100  proceeds to step  106 . 
         [0031]    At step  104 , having determined at step  102  that a vacuum is present in the sealed fuel system  30 , the controller  24  simultaneously opens the purge valve  50  and the control valve  56 . The algorithm  100  then proceeds to step  108 . 
         [0032]    At step  106 , having determined at step  102  that a positive level of pressure is present in the fuel system  30 , the controller  24  first opens the purge valve  50 , and then opens the control valve  56  after a sufficient amount of time has passed to allow the pressure to reach zero or a suitable low non-zero threshold pressure level. The algorithm  100  then proceeds to step  108 . 
         [0033]    At step  108 , controller  24  initiates a calibrated delay before executing the subsequent diagnostic steps of algorithm  100 . The length of the delay may vary depending on whether a vacuum or a pressure was determined at step  102 , and allows the fuel tank  36  to reach a calibrated level. The delay provided by step  108  allows the diagnostic to continue in the presence of a failed purge valve  50 , thus enabling detection of a failed purge valve as set forth below. The algorithm  100  proceeds to step  110  once the calibrated delay is complete. 
         [0034]    At step  110 , the diagnostic continues, doing so even if the FT pressure sensor indicates that pressure remains in the fuel tank  36 , as it is possible that the purge valve  50  has failed in a closed position, i.e., that pressure cannot be purged in the usual manner. Step  110  determines whether a requested purge flow and a level of engine vacuum are above calibrated thresholds. The algorithm  100  proceeds to step  112  when all thresholds are met. If the conditions in step  110  are not met after a calibrated time, the algorithm  100  is finished for that trip without the controller  24  making a decision, as indicated by the (**) symbol in  FIG. 3 . 
         [0035]    At step  112 , controller  24  transitions the switching valve  70  of vapor circuit  28  from a first/vent position to a second/pump position, as shown in  FIG. 3 . The absolute pressure sensor  72  is monitored, and its readings are temporarily recorded in memory. The algorithm  100  then proceeds to step  114 . 
         [0036]    At step  114 , the controller verifies the measurements taken at step  112  against a calibrated or threshold vacuum. As noted above, when the engine  12  is running and the pump  74  is off, switching valve  70  is set to the pump position such that vacuum in the sealed fuel system  30  can be read by the absolute pressure sensor  72 . If absolute pressure sensor  72  shows that the measured vacuum exceeds the calibrated vacuum, i.e., if a predetermined vacuum differential is determined between the measured and calibrated vacuums, the controller  24  may execute a suitable control action. For example, the controller  24  may record or cause the recording of a passing diagnostic code in response to a vacuum measurement exceeding the calibrated vacuum, which may be read by a vehicle maintenance person and/or transmitted to a remote location, e.g., as part of a vehicle telematics unit. Otherwise, the controller  24  records a diagnostic code indicating low purge flow in the sealed fuel system  30 . 
         [0037]    At step  116 , the controller  24  may allow a calibrated amount of time to pass after the diagnostic results are reported at step  114 . This delay can allow vacuum in the fuel tank  36  of  FIG. 1  to bleed down before completing the diagnostic steps, which may help to prevent fuel tank protection logic (not shown) from executing prematurely. The algorithm  100  is then finished, as indicated by the (**) symbol in  FIG. 3 . 
         [0038]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.