Abstract:
A system for detecting contamination of an air filter for an internal combustion engine includes an air pressure sensor disposed downstream of the air filter, an air flow sensor disposed in an air intake system of the engine, and a control module in communication with the air pressure sensor and the air flow sensor. The control module is configured to estimate an atmospheric pressure based on a signal received from the air pressure sensor. The control module is further configured to determine a contamination level of the air filter based on an air flow rate provided by the air flow sensor and a pressure drop across the air filter based on a pressure difference between the estimated atmospheric pressure and a second pressure measurement from the air pressure sensor that corresponds to the provided air flow rate.

Description:
FIELD 
     The present disclosure relates to internal combustion engine airflow, and more specifically to monitoring a contamination level of an engine air filter. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     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. 
     An air filter is often used in an internal combustion engine to remove contamination from the induction air. Over a period of use the air filter can become plugged and restrict the air flow into the engine. This can reduce performance, reduce fuel economy and increase engine emissions. Therefore, it is important to determine whether air flow is restricted as a result of the air filter. 
     Traditional internal combustion engines include pressure sensors both upstream and downstream of the air filter. Accordingly, a traditional engine system is able to diagnose air flow restriction resulting from an air filter based on a calculated pressure drop across the air filter using the upstream and downstream pressure sensors. However, such additional hardware increases cost and manufacturing time, and is also a maintenance concern because proper operation of the sensors must be monitored and the sensors must be replaced if not functioning properly. 
     SUMMARY 
     Accordingly, a system for detecting contamination of an air filter for an internal combustion engine is provided. The system includes an air pressure sensor disposed downstream of the air filter, an air flow sensor disposed in an air intake system of the engine, and a control module in communication with the air pressure sensor and the air flow sensor. The control module is configured to estimate an atmospheric pressure based on a signal received from the air pressure sensor. The control module is further configured to determine a contamination level of the air filter based on an air flow rate provided by the air flow sensor and a pressure drop across the air filter based on a pressure difference between the estimated atmospheric pressure and a second pressure measurement from the air pressure sensor that corresponds to the provided air flow rate. 
     A method of determining a contamination level of an air filter in an internal combustion engine of a motor vehicle includes taking first and second air pressure measurements at a location downstream of the air filter. The first pressure measurement is taken at a first engine operating condition corresponding to a first engine air flow rate below a first limit. Atmospheric pressure is estimated based on the first air pressure measurement. The second air pressure measurement is taken at a second engine operating condition corresponding to a second engine air flow rate greater than a second limit. The second limit is substantially greater than the first limit. A pressure difference is determined between the first and second air pressure measurements. The pressure difference is compared to a predetermined pressure differential corresponding to the second air flow rate. 
     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 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a schematic illustration of a vehicle according to the present disclosure; 
         FIG. 2  is a functional block diagram of the control module shown in  FIG. 1 ; and 
         FIG. 3  is a flow chart illustrating a method of detecting a contaminated air filter according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     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. 
     As seen in  FIG. 1 , a vehicle  10  is shown including an engine assembly  12 . Engine assembly  12  may include an internal combustion engine  14 , a throttle  16 , an air filter  18 , and a control module  20 . Engine  14  may include intake and exhaust manifolds  22 ,  24 . Intake manifold  22  may provide communication between a fresh air source and engine  14 . Air filter  18  and throttle  16  may be disposed in the path of air entering intake manifold  22 . More specifically, air flow may be metered by throttle  16  and may be required to flow through air filter  18  before entering intake manifold  22 . A throttle inlet absolute pressure (TIAP) sensor  26  and a mass air flow (MAF) sensor  28  may be located downstream of air filter  18 . More specifically, TIAP sensor  26  and MAF sensor  28  may be located between air filter  18  and throttle  16 . A pressure sensor may not be required upstream of air filter  18 , as discussed below. 
     TIAP sensor  26  may be in communication with control module  20  and may provide a signal indicative of an absolute air pressure downstream of air filter  18 . MAF sensor  28  may also be in communication with control module  20  and may provide a signal indicative of a mass air flow rate through air filter  18  and into engine  14 . Control module  20  may also be in communication with engine  14 , providing and receiving signals regarding operation of engine  14 . A vehicle information display  30  may be in communication with control module  20 , providing and receiving signals regarding conditions of vehicle  10 . 
     Referring to  FIG. 2 , control module  20  may include an atmospheric pressure estimation module  110 , an operating pressure determination module  112 , and a contaminated air filter determination module  114 . Atmospheric pressure estimation module  110  may estimate atmospheric pressure based on a pressure measurement from TIAP sensor  26  at a first low air flow rate into engine  14 , and therefore through air filter  18 , as discussed below. Atmospheric pressure estimation module  110  may provide the estimated atmospheric pressure to contaminated air filter determination module  114 . 
     Operating pressure determination module  112  may determine an operating pressure based on a pressure measurement from TIAP sensor  26  at a second air flow rate determined by MAF sensor  28  into engine  14 , and therefore through air filter  18 , as discussed below. Operating pressure determination module  112  may provide the operating pressure and second air flow rate to contaminated air filter determination module  114 . Contaminated air filter determination module  114  may then determine the pressure difference between the estimated atmospheric pressure and the operating pressure and determine if the pressure differential is indicative of a contaminated (or dirty) air filter at the second air flow rate, as discussed below. 
     A flow chart is shown in  FIG. 3  illustrating the control logic  200  for determining air filter contamination. Control logic  200  may run repeatedly during vehicle operation at a predetermined time step (Δt). Each new run of control logic  200  may include resetting a time counter (t). Time counter (t) may be used for vehicle altitude considerations, as discussed below. Control logic  200  may begin by measuring a mass air flow rate through air filter  18  using MAF sensor  28  at control block  210 . Control logic  200  may then proceed to determination block  212  where the measured mass air flow rate is compared to a lower limit. The lower limit may generally correspond to a flow rate providing a minimal pressure drop across air filter  18 . The flow rate lower limit may vary by filter type, but may generally be associated with an engine air flow rate that is less than ten percent of a maximum engine air flow rate. 
     If the mass air flow rate is less than the lower limit, control logic  200  proceeds to control block  214 . Control block  214  determines the absolute air pressure corresponding to the measured mass air flow rate. The air pressure may be measured by TIAP sensor  26  and may be stored in control module  20  as an estimated atmospheric pressure. Control logic  200  may then proceed to control block  216  where time counter (t) is reset. Control logic  200  may wait a predetermined time step (Δt) and then once again proceed to control block  210 . If determination block  212  determines that the measured mass air flow rate is greater than the lower limit, control logic  200  proceeds to determination block  218 . 
     Determination block  218  compares the measured mass air flow rate to an upper limit. The upper limit may generally correspond to a flow rate providing a significant pressure drop across air filter  18 . The flow rate upper limit may vary by filter type, but may generally be associated with an engine air flow rate that is greater than thirty percent of a maximum engine air flow rate. If the mass air flow rate is less than the upper limit, control logic  200  may proceed to control block  220  where time counter (t) is increased by a predetermined time step (Δt). Control logic  200  may wait a predetermined time step (Δt) and then once again proceed to control block  210 . If determination block  218  determines that the measured mass air flow rate is greater than the upper limit, control logic  200  proceeds to control block  222 . 
     Control block  222  determines the absolute air pressure corresponding to the measured mass air flow rate. The air pressure may be measured by TIAP sensor  26  and may be stored in control module  20  as an operating pressure. Control logic  200  then proceeds to control block  224  where a pressure differential is determined. More specifically, control block  224  may calculate the pressure difference between the operating pressure and the estimated atmospheric pressure indicative of a pressure drop across air filter  18 . This calculated pressure drop may generally correspond to the measured mass air flow rate associated with the operating pressure. Control logic  200  then proceeds to control bock  226 . 
     Control block  226  determines a maximum allowable pressure drop across air filter  18 . A predetermined value for a maximum allowable pressure drop indicative of a contaminated (or dirty) air filter is determined for a flow rate corresponding to the measured mass flow rate associated with the operating pressure. The maximum allowable pressure drop may be determined using a look-up table or a predetermined function based on the measured mass flow rate associated with the operating pressure. After the maximum allowable pressure drop is determined, control logic  200  proceeds to determination block  228 . 
     Determination block  228  compares the calculated pressure drop to the maximum allowable pressure drop. If the calculated pressure drop is less than or equal to the maximum allowable pressure drop, control logic  200  ends until the next iteration at a subsequent time step. If calculated pressure drop is greater than the maximum allowable pressure drop, control logic  200  may then proceed to control block  230  where a determination is made regarding whether the calculated pressure drop could be attributable to a change in vehicle altitude. 
     Control block  230  may determine a vehicle altitude parameter. More specifically, control block  230  may determine an elapsed time between the stored atmospheric pressure measurement and the current operating pressure measurement based on time counter (t). The elapsed time may be used by itself or the elapsed time could be used to estimate a distance traveled over the elapsed time. The elapsed time may be indicative of an altitude change in vehicle  10  between measurements, which may contribute to an increased pressure drop across air filter  18 . Control logic  200  may then proceed to determination block  232 . 
     Determination block  232  evaluates the altitude parameter and determines if an altitude criterion is met. More specifically, determination block  232  may compare the elapsed time or distance traveled, as determined above, to a predetermined value. If the elapsed time or distance exceeds the predetermined limit, the calculated pressure drop may be attributable to a change in altitude of vehicle  10 . Therefore, if the altitude parameter exceeds the altitude criterion control logic  200  ends until the next iteration at a subsequent time step so that a false contaminated air filter flag is not set. 
     If the altitude parameter does not exceed the altitude criterion control logic  200  proceeds to control block  234  where a contaminated air filter flag is set. Control block  234  may indicate a contaminated air filter condition on vehicle information display  30 . After control block  234 , control logic  200  may end until the next iteration at a subsequent time step. 
     As indicated in control logic  200  and shown in vehicle  10 , contamination of air filter  18  may be determined based on measuring first and second absolute air pressures downstream of air filter  18  using TIAP sensor  26 . More specifically, the pressure drop across air filter  18  may be determined without the use of an air pressure sensor upstream of air filter  18 . 
     An example of control logic  200  applied to operation of vehicle  10  of the present disclosure may include vehicle  10  being initially in a stopped condition. When in the stopped condition engine  14  may be operating at an idle condition. This vehicle stopped engine idle condition generally corresponds to a low mass air flow rate into engine  14 , and therefore through air filter  18 . A first pressure measurement may be taken by TIAP sensor  26  at this condition. As this condition is associated with a low mass air flow rate, the pressure measurement may be used as an estimated atmospheric pressure. 
     When vehicle  10  accelerates from the stopped condition, the mass air flow into engine  14 , and therefore through air filter  18 , may significantly increase. When accelerating, an air flow measurement may be made using MAF sensor  28 . A second pressure measurement may then be taken using TIAP sensor  26  generally corresponding to the measured mass air flow rate. The difference between the first and second pressures may be calculated and compared to a predetermined value to determine air filter contamination, as indicated above. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present disclosure can be implemented in a variety of forms. Therefore, while this disclosure has been described in connection with particular examples thereof, 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.