Abstract:
A method of evaluating intake air temperature (IAT) sensor rationality may include measuring a first intake air temperature associated with an engine using an IAT sensor when the engine is in a non-operating condition, determining a second intake air temperature associated with the engine using a hot wire air flow meter when the engine is in the non-operating condition, and indicating an IAT sensor fault when a difference between the first and second intake air temperatures exceeds a predetermined temperature limit.

Description:
FIELD 
       [0001]    The present disclosure relates to engine diagnostic systems, and more specifically to intake air temperature sensor diagnostic systems. 
       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 air and fuel mixture is compressed within a cylinder using a piston. The air and fuel mixture is combusted within the cylinder to reciprocally drive the piston within the cylinder, which in turn rotationally drives a crankshaft of the engine. 
         [0004]    Engine operation is regulated based on several parameters including, but not limited to, intake air temperature (IAT), manifold absolute pressure (MAP), throttle position (TPS), engine RPM and barometric pressure (P BARO ). With specific reference to the throttle, the state parameters (e.g., air temperature and pressure) before the throttle may be used for engine control and diagnostic systems. Traditional internal combustion engines include an IAT sensor that directly measures the IAT. In some instances, however, the IAT sensor can become inaccurate as a result of damage, wear and/or a number of other factors. Accordingly, the IAT sensor should be monitored to determine whether the IAT that is determined based on the IAT sensor reading is accurate. 
         [0005]    Traditional internal combustion engine systems may additionally include a second IAT sensor, the reading from which is compared to that of the first IAT sensor in order to determine whether the first IAT sensor is accurate. This additional IAT sensor increases cost and complexity and itself must be monitored for accuracy. 
       SUMMARY 
       [0006]    A method of evaluating intake air temperature (IAT) sensor rationality may include measuring a first intake air temperature associated with an engine using an IAT sensor when the engine is in a non-operating condition, determining a second intake air temperature associated with the engine using a hot wire air flow meter when the engine is in the non-operating condition, and indicating an IAT sensor fault when a difference between the first and second intake air temperatures exceeds a predetermined temperature limit. 
         [0007]    The method may further include determining a mass air flow (MAF) rate into an engine during operation thereof using the hot wire air flow meter. 
         [0008]    A control module may include an intake air temperature (IAT) sensor temperature determination module, a mass air flow (MAF) sensor temperature determination module, an intake temperature evaluation module, and an IAT sensor fault determination module. The IAT sensor temperature determination module may determine a first intake air temperature measurement associated with an engine using an IAT sensor when the engine is in a non-operating condition. The MAF sensor temperature determination module may determine a second intake air temperature associated with the engine using a hot wire air flow sensor when the engine is in a non-operating condition. The intake temperature evaluation module may be in communication with the IAT sensor temperature determination module and the MAF sensor temperature determination module and may determine a difference between the first and second intake air temperatures. The IAT sensor fault determination module may be in communication with the intake temperature evaluation module and may indicate an IAT sensor fault when the difference exceeds a predetermined temperature 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 . 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  32 , a mass air flow (MAF) sensor  34 , and a manifold absolute pressure (MAP) sensor  36 . IAT sensor  32  may provide a signal to control module  14  indicative of an intake air temperature, MAF sensor  34  may provide a signal to control module  14  indicative of a mass air flow into engine  16 , and MAP sensor  36  may provide a signal to control module  14  indicative of a manifold absolute pressure. The signal provided by MAF sensor  34  may additionally be used to determine an intake air temperature. 
         [0017]    MAF sensor  34  may be a hot wire balanced bridge air flow sensor commonly used for MAF sensor applications. MAF sensor  34  may include a wheatstone thermocouple bridge  38  positioned in the intake air flow path provided to intake manifold  24  and may include a first side having a heated sensing element and calibration resistors and a second side having an air temperature sensitive resistor and calibration resistors. 
         [0018]    The heated element may be in the form of a wire or a film. A voltage may be applied to the heated element to maintain a predetermined temperature and balance the bridge  38 . As air flow across the heated element increases, the electric power required to maintain the predetermined temperature increases. As air flow across the bridge decreases, the electric power required to maintain the predetermined temperature decreases. The voltage across bridge  38 , therefore, provides an indication of the mass flow rate of air across bridge  38 . The temperature sensitive resistor may compensate the air flow determination based on an ambient air temperature. 
         [0019]    The bridge output voltage may be converted to a pulse modulated signal which may be sent to control module  14 . The frequency of the pulse modulated signal may be interpreted by control module  14  as an air flow value. The frequency may additionally be used to determine an air temperature. 
         [0020]    More specifically, when engine  16  is in a non-operating condition, there may be generally zero flow into engine  16  through intake manifold  24 . As such, there is generally no flow across MAF sensor  34 , and therefore bridge  38 . During this no-flow condition, the heat from the heated element is dissipated into the air surrounding the heated element in intake system  18 . In this no-flow condition, bridge  38  outputs a low voltage and is balanced mainly based on the temperature of the surrounding air in intake system  18 . 
         [0021]    During this no-flow condition, a generally linear relationship may exist between the frequency provided by the bridge output voltage and the temperature of the surrounding air in intake system  18 . More specifically, the frequency provided by the bridge output voltage may be inversely proportional to the air temperature in intake system  18 . It is understood that MAF sensor  34  may alternatively provide a frequency that is directly proportional to the air temperature in intake system  18 . 
         [0022]    Referring to  FIG. 2 , control module  14  may include an engine-off evaluation module  40 , an IAT sensor temperature determination module  42 , a MAF sensor temperature determination module  44 , an intake temperature evaluation module  46 , and an IAT sensor fault determination module  48 . Engine-off evaluation module  40  may determine when engine  16  is in a non-operating state and may determine an elapsed time of the non-operating state. Engine-off evaluation module  40  may be in communication with IAT sensor temperature determination module  42  and MAF sensor temperature determination module  44  and may provide the elapsed time of the non-operating state of engine  16  thereto. 
         [0023]    IAT sensor temperature determination module  42  may determine the temperature (T IAT ) of air in intake system  18  provided by IAT sensor  32 . IAT sensor temperature determination module  42  may be in communication with intake temperature evaluation module  46  and may provide T IAT  thereto. MAF sensor temperature determination module  44  may determine the temperature (T MAF ) of air in intake system  18  based on the frequency of the signal provided by MAF sensor  34 . MAF sensor temperature determination module  44  may include a look-up table and/or a function to convert the frequency to a temperature. MAF sensor temperature determination module  44  may be in communication with intake temperature evaluation module  46  and may provide T MAF  thereto. 
         [0024]    Intake temperature evaluation module  46  may determine a temperature difference (ΔT) between T IAT  and T MAF  (ΔT IAT −T MAF |). Intake temperature evaluation module  46  may be in communication with IAT sensor fault determination module  48  and may provide ΔT thereto. IAT sensor fault determination module  48  may determine whether ΔT exceeds a predetermined limit and may indicate an IAT sensor fault when ΔT exceeds the predetermined limit. 
         [0025]    With reference to  FIG. 3 , control logic  100  generally illustrates operation of an IAT sensor diagnostic system. Control logic  100  may begin at block  102  where an engine operating state may be evaluated by engine-off evaluation module  40 . If engine  16  is in an operating state, control logic  100  may return to block  102 . If engine  16  is in a non-operating state, control logic  100  may proceed to block  104 . 
         [0026]    Block  104  may include evaluation of an elapsed time that engine  16  has been in the non-operating state by engine-off evaluation module  40 . If engine  16  has been in the non-operating state for a time less than or equal to a predetermined time limit, control logic  100  may return to block  102 . If engine  16  has been in the non-operating state for a time period greater than the predetermined time limit, control logic  100  may proceed to block  106 . The predetermined time limit may generally correspond to a time after engine shutdown sufficient to provide a steady state condition within intake system  18 . For example, the predetermined time limit may include a time period of greater than 15 minutes after engine shutdown. 
         [0027]    Block  106  may determine T IAT  with IAT sensor temperature determination module  42 . Control logic  100  may then proceed to block  108  where T MAF  is determined using MAF sensor temperature determination module  44 . Control logic  100  may then proceed to block  110  where difference (ΔT) between T IAT  and T MAF  is determined by intake temperature evaluation module  46 . Control logic  100  may then proceed to block  112  where ΔT is evaluated by IAT sensor fault determination module  48 . 
         [0028]    Block  112  may compare ΔT to a predetermined temperature limit. If ΔT is less than or equal to the predetermined temperature limit, control logic  100  may terminate. If ΔT is greater than the predetermined temperature limit, control logic  100  may proceed to block  114  where an IAT sensor fault condition may be indicated. Control logic  100  may then terminate. 
         [0029]    Furthermore, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations may be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.