Abstract:
A method of determining an engine intake air leak may include measuring an air flow rate into an internal combustion engine, comparing the measured air flow rate to a first predetermined air flow limit, calculating an estimated air flow rate into the engine when the measured air flow rate is less than the first predetermined air flow limit, comparing the estimated air flow rate to second and third predetermined air flow limits, and indicating an air leak when the estimated air flow rate is greater than the second predetermined air flow limit and less than the third predetermined air flow limit.

Description:
FIELD 
       [0001]    The present disclosure relates to engine air intake system diagnostics, and more specifically to air leak detection in an engine air intake system. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Internal combustion engines combust a fuel and air mixture to produce drive torque. More specifically, air is drawn into the engine through a throttle. The air is mixed with fuel and the mixture is combusted within a cylinder to reciprocally drive a piston within the cylinder, which in turn rotationally drives a crankshaft of the engine. 
         [0004]    Engine operation may be regulated based on several parameters including the air flow rate provided to the engine. The air flow provided to the engine may be determined by a mass air flow (MAF) sensor. If an air leak is present at a location downstream of the MAF sensor, the air flow into the engine measured by the MAF sensor may not accurately reflect the actual amount of air provided to the engine. 
         [0005]    An inaccurate MAF sensor measurement may result in operation of the engine based on an improper air-fuel ratio. More specifically, when an air leak is present downstream of the MAF sensor, the actual air flow into the engine may be greater than the measured value. As such, an actual air-fuel ratio provided to the engine may be leaner than the commanded air-fuel ratio. The inaccurate MAF sensor measurement may result in poor engine operation including engine stalling. 
       SUMMARY 
       [0006]    A method of determining an engine intake air leak may include measuring an air flow rate into an internal combustion engine, comparing the measured air flow rate to a first predetermined air flow limit, calculating an estimated air flow rate into the engine when the measured air flow rate is less than the first predetermined air flow limit, comparing the estimated air flow rate to second and third predetermined air flow limits, and indicating an air leak when the estimated air flow rate is greater than the second predetermined air flow limit and less than the third predetermined air flow limit. 
         [0007]    The method may additionally include controlling an amount of fuel supplied to the engine based on the estimated air flow rate after the air leak is indicated. 
         [0008]    A control module may include an air flow measurement module, an air flow calculation module, and an air leak determination module. The air flow measurement module may measure an air flow rate into an internal combustion engine. The air flow calculation module may calculate an estimated air flow rate into the engine. The air leak determination module may be in communication with the air flow measurement module and the air flow calculation module and may determine an air leak condition in an intake system of the engine when the measured air flow rate is less than a first predetermined air flow limit and the estimated air flow rate is greater than a second predetermined air flow limit and less than a third predetermined air flow limit. 
         [0009]    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. 
     
    
     
       DRAWINGS 
         [0010]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0011]      FIG. 1  is a schematic illustration of a vehicle according to the present disclosure; 
           [0012]      FIG. 2  is a control block diagram of the control module shown in  FIG. 1 ; and 
           [0013]      FIG. 3  is a flow diagram illustrating steps for control of the vehicle of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, 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 execute one or more software or firmware programs, a combinational logic circuit, or other suitable components that provide the described functionality. 
         [0015]    Referring to  FIG. 1 , a vehicle  10  may include an engine assembly  12  and a control module  14 . Engine assembly  12  may include an engine  16 , an intake system  18 , an exhaust system  20 , and a fuel system  22 . Intake system  18  may be in communication with engine  16  and may include an intake manifold  24 , a throttle  26 , and an electronic throttle control (ETC)  28 . ETC  28  may actuate throttle  26  to control an air flow into engine  16 . Exhaust system  20  may be in communication with engine  16  and may include an exhaust manifold  30  and a catalyst  32 , such as a catalytic converter. Fuel system  22  may provide fuel to engine  16 . Exhaust gas created by combustion of the air-fuel mixture may exit engine  16  through exhaust system  20 . 
         [0016]    Control module  14  may be in communication with fuel system  22 , ETC  28 , an intake air temperature (IAT) sensor  33 , a mass air flow (MAF) sensor  34 , a barometric pressure (P BARO ) sensor  35 , a manifold absolute pressure (MAP) sensor  36 , an engine speed sensor  38 , and an oxygen sensor  40 . IAT sensor  33  may provide a signal to control module  14  indicative of an air temperature within intake system  18 . MAF sensor  34  may be located upstream of intake manifold  24  and throttle  26  and may provide a signal to control module  14  indicative of an engine air flow rate (EFR MAF ) past MAF sensor  34  and into engine  16 . MAP sensor  36  may be located downstream of MAF sensor  34 , generally between throttle  26  and engine  16  and may provide a signal to control module  14  indicative of MAP within intake manifold  24 . Engine speed sensor  38  may provide a signal to control module  14  indicative of the operating speed of engine  16 . P BARO  sensor  35  may provide a signal to control module  14  indicative of barometric pressure. Oxygen sensor  40  may be located between exhaust manifold  30  and catalyst  32 , generally at an inlet of catalyst  32 , and may provide a signal to control module  14  indicative of an oxygen level of exhaust gas exiting engine  16 . 
         [0017]    Referring to  FIG. 2 , control module  14  may include an air flow measurement module  42 , an air flow calculation module  44 , a fuel control module  46 , an exhaust gas evaluation module  48 , an air leak determination module  50 , and an air leak control module  52 . Air flow measurement module  42  may receive the air flow measurement signal from MAF sensor  34 . Air flow measurement module  42  may be in communication with fuel control module  46  and air leak determination module  50  may provide the engine air flow rate (EFR MAF ) based on the measurement from MAF sensor  34  thereto. 
         [0018]    Air flow calculation module  44  may receive the MAP measurement signal from MAP sensor  36 . Air flow calculation module  44  may additionally be in communication with engine speed sensor  38  and may receive the engine speed signal. Air flow calculation module  44  may determine a calculated engine air flow rate (EFR MAP ) into engine  16  based on the MAP measurement provided by MAP sensor  36  and the engine speed provided by engine speed sensor  38 . 
         [0019]    More specifically, EFR MAP  may be determined by the function shown below: 
         [0000]        EFR   MAP   =RPM*MAP*NoCyl*Disp*VE*Bcorr/( 120 *R*T   m ) 
         [0000]    where RPM is engine speed, MAP is manifold absolute pressure, NoCyl is number of cylinders, Disp is engine displacement, VE is volumetric efficiency (which is a function of RPM and MAP), Bcorr is a barometric correction for VE (which is a function of P BARO  and RPM), R is the gas constant for Air (287 m 2 /(s 2 *° K)), and Tm is manifold air charge temperature. Air flow calculation module  44  may be in communication with fuel control module  46  and air leak determination module  50  and may provide EFR MAP  thereto. 
         [0020]    Fuel control module  46  may be in communication with fuel system  22  and may determine an amount of fuel needed to meet a desired air-fuel ratio. Fuel control module  46  may receive EFR MAF  from air flow measurement module  42  and EFR MAP  from air flow calculation module  44 . Fuel control module  46  may additionally be in communication with air leak determination module  50  and air leak control module  52 . 
         [0021]    Exhaust gas evaluation module  48  may be in communication with oxygen sensor  40  and may determine a concentration of oxygen in exhaust gas from engine  16 . Exhaust gas evaluation module  48  may be in communication with air leak determination module  50  and may provide the determined oxygen concentration thereto. 
         [0022]    Air leak determination module  50  may determine whether an air leak is present in intake system  18  based on inputs from air flow measurement module  42 , air flow calculation module  44 , fuel control module  46 , and exhaust gas evaluation module  48 . Air leak determination module  50  may compare EFR MAF  and EFR MAP  to predetermined limits LIMIT LOW  and LIMIT HIGH . LIMIT LOW  and LIMIT HIGH  may be lower and upper calibrated limits for air flow into engine  16 , and may be defined as the functions shown below: 
         [0000]      LIMIT LOW   =f 1( RPM,IAT,P   BARO   ,EngDes ); and 
         [0000]      LIMIT HIGH   =f 2( RPM,IAT,P   BARO   ,EngDes ); 
         [0000]    where EngDes includes engine stroke, displacement, and valve timing/cam phase. 
         [0023]    Air leak control module  52  may be in communication with air leak determination module  50  and may determine remedial actions when an air leak is detected at air leak determination module  50 . Air leak control module  52  may additionally be in communication with fuel control module  46  and may adjust fuel supplied to engine  16  when an air leak is detected, as discussed below. 
         [0024]    With reference to  FIG. 3 , control logic  100  generally illustrates an air leak detection and management system for an air leak in intake system  18 . Control logic  100  may begin at block  102  where applicable active diagnostic faults are evaluated. If an active diagnostic fault is present, control logic  100  returns to block  102 . Applicable active faults may include faults that will prevent diagnostic systems from making a correct or robust detection. Applicable active faults may include a MAF sensor fault and a MAP sensor fault. It is understood that other fault signals may additionally be considered. If no applicable active faults are detected, control logic  100  may proceed to block  104  where engine idle conditions are evaluated. Vehicle speed and throttle position may be used to make sure that engine  16  is operating at idle. More specifically, a vehicle speed of approximately 0 miles per hour and a closed throttle position may correspond to the idle condition. If idle conditions are met, control logic  100  may proceed to block  106 . Otherwise, control logic  100  may return to block  102 . 
         [0025]    Block  106  may evaluate EFR MAF  from MAF sensor  34 . If EFR MAF  is less than a first predetermined air flow limit, control logic  100  may proceed to block  108 . In the present example the first predetermined air flow limit may include LIMIT LOW . Otherwise, control logic  100  may return to block  102 . Block  108  may determine EFR MAP , as discussed above. Control logic  100  may then proceed to block  110  where EFR MAP  is evaluated relative to second and third air flow limits. 
         [0026]    In the present example, the second air flow limit may include LIMIT LOW  and the third air flow limit may include LIMIT HIGH . Therefore, the second air flow limit may be equal to the first air flow limit. If EFR MAP  is between LIMIT LOW  and LIMIT HIGH , control logic  100  may proceed to block  112 . Otherwise, control logic  100  may return to block  102 . Block  112  may evaluate an exhaust oxygen level. If the exhaust oxygen level is greater than a predetermined upper limit (LIMIT O2 ), control logic  100  may proceed to block  114 . LIMIT O2  may generally correspond to an oxygen level associated with EFR MAF  for a generally stoichiometric air-fuel ratio. 
         [0027]    When an air leak is present downstream of MAF sensor  34 , the amount of fuel provided to engine  16  to maintain a commanded air-fuel ratio may be less than the amount actually needed for the commanded air-fuel ratio due to a greater amount of air entering engine  16  than measured by MAF sensor  34 . More specifically, the greater amount of air may result in a lean air-fuel ratio (greater than 14.7-to-1) when the commanded air fuel ratio is stoichiometric, resulting in a greater exhaust oxygen level than would be present from a generally stoichiometric air-fuel ratio. 
         [0028]    Block  114  may evaluate exhaust oxygen levels relative to the commanded air-fuel ratio from fuel control module  46 . The commanded air-fuel ratio may include a stoichiometric air-fuel ratio (14.7-to-1) or a rich air-fuel ratio (less than 14.7-to-1). More specifically, block  114  may generally determine whether the high oxygen level in the exhaust gas is due to the commanded air-fuel ratio. The evaluation at block  114  may include a comparison between an expected exhaust gas oxygen level associated with the commanded air-fuel ratio and the measured exhaust oxygen level. If the oxygen level corresponds to the commanded air-fuel ratio, control logic  100  may return to block  102 . Otherwise, control logic  100  may proceed to block  116 . 
         [0029]    For example, if the commanded air-fuel ratio is rich (less than 14.7-to-1), a relatively low oxygen level would be expected in the exhaust gas. Therefore, the high oxygen level would generally indicate an air leak. However, if the commanded air-fuel ratio is lean, the high exhaust oxygen level may be due to the commanded air-fuel ratio and not an air leak. 
         [0030]    Block  116  may generally indicate an air leak in intake system  18 . Control logic  100  may then proceed to block  118  where remedial actions may be initiated. Remedial actions may include controlling fuel supplied to engine  16  based on EFR MAP  rather than EFR MAF . Control logic  100  may then terminate.