Abstract:
A method of determining a barometric pressure of atmosphere, in which an internal combustion engine of a vehicle is located includes monitoring operating parameters of the internal combustion engine and the vehicle, determining a healthy status of an air filter of the internal combustion engine, and calculating the barometric pressure based on the operating parameters and the healthy status of the air filter.

Description:
FIELD 
     The present disclosure relates to internal combustion engines, and more particularly to adaptively estimating a barometric pressure of an environment, within which an internal combustion is present. 
     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. 
     Engine operation is regulated based on several parameters including, but not limited to, intake air temperature (T PRE ), 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 are good references that can be used for engine control and diagnostic. For example, proper functioning of the throttle can be monitored by calculating the flow through the throttle for a given throttle position and then comparing the calculated air flow to a measured or actual air flow. As a result, the total or stagnation air pressure before the throttle (i.e., the pre-throttle air pressure) is critical to accurately calculate the flow through the throttle. Alternatively, the total pressure and/or static pressure can be used to monitor air filter restriction. 
     Traditional internal combustion engines include a barometric pressure sensor that directly measures the P BARO . However, such additional hardware increases cost and manufacturing time, and is also a maintenance concern because proper operation of each sensor must be monitored and the sensor must be replaced if not functioning properly. 
     SUMMARY 
     Accordingly, the present invention provides a method of determining a barometric pressure of atmosphere, in which an internal combustion engine of a vehicle is located. The method includes monitoring operating parameters of the internal combustion engine and the vehicle, determining a healthy status of an air filter of the internal combustion engine, and calculating the barometric pressure based on the operating parameters and the healthy status of the air filter. 
     In one feature, the method further includes determining a drag coefficient based on at least one of the operating parameters and the healthy status. The barometric pressure is calculated based on the drag coefficient. 
     In other features, the method further includes determining whether at least one of the operating parameters is less than a corresponding threshold. The healthy status of the air filter is determined based on a known barometric pressure if the at least one of the operating parameters is not less than the corresponding threshold. The at least one operating parameter includes a time difference between update times of the barometric pressure. The at least one operating parameter includes a travel distance of the vehicle. 
     In still other features, the healthy status is determined based on a pre-throttle inlet pressure. The pre-throttle inlet pressure is determined based on an intake air temperature. Alternatively, the pre-throttle inlet pressure is monitored using a sensor. 
     In yet another feature, the operating parameters comprise a mass air flow, an intake cross-sectional area, an air density and a pre-throttle inlet pressure. 
     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 functional block diagram of an internal combustion engine system that is regulated in accordance with the adaptive barometric pressure estimation control of the present disclosure; 
         FIG. 2  is a flowchart illustrating exemplary steps that are executed by the adaptive barometric pressure estimation control of the present disclosure; and 
         FIG. 3  is a functional block diagram illustrating exemplary modules that execute the adaptive barometric pressure estimation control. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, 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 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. 
     Referring now to  FIG. 1 , an exemplary internal combustion engine system  10  is illustrated. The engine system  10  includes an engine  12 , an intake manifold  14  and an exhaust manifold  16 . Air is drawn into the intake manifold  14  through an air filter  17  and a throttle  18 . The air is mixed with fuel, and the fuel and air mixture is combusted within a cylinder  20  of the engine  12 . More specifically, the fuel and air mixture is compressed within the cylinder  20  by a piston (not shown) and combustion is initiated. The combustion process releases energy that is used to reciprocally drive the piston within the cylinder  20 . Exhaust that is generated by the combustion process is exhausted through the exhaust manifold  16  and is treated in an exhaust after-treatment system (not shown) before being released to atmosphere. Although a single cylinder  20  is illustrated, it is anticipated that the pre-throttle estimation control of the present invention can be implemented with engines having more than one cylinder. 
     A control module  30  regulates engine operation based on a plurality of engine operating parameters including, but not limited to, a pre-throttle static pressure (P PRE ), a pre-throttle stagnation pressure (P PRE0 ) (i.e., the air pressures upstream of the throttle), an intake air temperature (T PRE ), a mass air flow (MAF), a manifold absolute pressure (MAP), an effective throttle area (A EFF ), an engine RPM and a barometric pressure (P BARO ). P PRE0  and P PRE  are determined based on a pre-throttle estimation control, which is disclosed in commonly assigned, co-pending U.S. patent application Ser. No. 11/464,340, filed Aug. 14, 2006. 
     T PRE , MAF, MAP and engine RPM are determined based on signals generated by a T PRE  sensor  32 , a MAF sensor  34 , a MAP sensor  36  and an engine RPM sensor  38 , respectively, which are all standard sensors of an engine system. A EFF  is determined based on a throttle position signal that is generated by a throttle position sensor, which is also a standard sensor. A throttle position sensor  42  generates a throttle position signal (TPS). The relationship between A EFF  to TPS is pre-determined using engine dynamometer testing with a temporary stagnation pressure sensor  50  (shown in phantom in  FIG. 1 ) installed. Production vehicles include the relationship pre-programmed therein and therefore do not require the presence of the stagnation pressure sensor. 
     The P BARO  estimation control of the present disclosure estimates P BARO  without the use of a barometric pressure sensor. More specifically, in the air intake system, the mass air flow (MAF) or {dot over (m)} can be treated as an incompressible flow before the throttle. Accordingly, {dot over (m)} can be determined based on the following relationship:
 
 {dot over (m)}=C   d   ·A   INLET ·√{square root over (2·ρ·( P   BARO   −P   PRE ))}  (1)
 
where:
         {dot over (m)} is the rate of mass air flow (MAF);   C d  is a drag or loss coefficient;   A INLET  is the effective cross-sectional area of pre-throttle inlet system including air filter;   P PRE  is the inlet or pre-throttle absolute pressure; and   ρ is the air density (i.e., a function of P INLET , IAT, R).
 
Equation 1 can be transformed to provide the following relationship:
       

     
       
         
           
             
               
                 
                   
                     P 
                     BARO 
                   
                   = 
                   
                     
                       P 
                       PRE 
                     
                     + 
                     
                       
                         
                           ( 
                           
                             
                               m 
                               . 
                             
                             
                               
                                 C 
                                 d 
                               
                               · 
                               
                                 A 
                                 INLET 
                               
                             
                           
                           ) 
                         
                         2 
                       
                       
                         2 
                         ⁢ 
                         ρ 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     C d  can be determined as a function of {dot over (m)} and an air filter healthy status (AFHS). The AFHS is a variable that indicates the degree to which the air filter is dirty. A clean air filter enables a minimally restricted air flow therethrough, while a dirty air filter more significantly restricts the air flow therethrough. The learning of AFHS can be independent of barometric conditions and can be updated within the control module  30 . The AFHS can be determined based on one of the following relationships: 
                   AFHS   =       f   1     ⁡     [           (       P   BARO     -     P   PRE       )     t     -       (       P   BARO     -     P   PRE       )       t   -   1               m   .     t     -       m   .       t   -   1           ]               (   3   )               
where t is a current time of a measured flow rate and t−1 is a previous time of another measured flow rate. P PRE  can be either physically measured or calculated from throttle flow dynamics. AFHS is learned using minimum resources. More specifically, AFHS is event-based calculated using a known P BARO , but is a more slowly updated variable than a time-based calculation of P BARO . For example, the values of (P BARO −P PRE ) t  and (P BARO −P PRE ) t-1  can be determined over a long time period provided that the value ({dot over (m)} t −{dot over (m)} t-1 ) (Δ{dot over (m)}) is greater than a threshold value (Δ{dot over (m)} THR ). Further, P BAROt  and P BAROt-1  can be different in this case.
 
     Under limited operating conditions, the AFHS can be determined based on the following relationship: 
                   AFHS   =       f   2     ⁡     [           (     P   PRE     )     t     -       (     P   PRE     )       t   -   1               m   .     t     -       m   .       t   -   1           ]               (   4   )               
For example, if the difference between time steps (Δt) is less than a threshold difference (Δt THR ) and the vehicle travel distance (Δd) is less than a threshold difference (Δd THR ) (i.e., the vehicle does not move too far), it can be assumed that any change in P BARO  is negligible.
 
     Referring now to  FIG. 2 , exemplary steps that are executed by the P BARO  estimation control will be described in detail. In step  200 , control initializes C d  and monitors the vehicle operating parameters. In step  201 , control event-based determines whether Δ{dot over (m)} is greater than Δ{dot over (m)} THR . If Δ{dot over (m)} is greater than Δ{dot over (m)} THR , control continues in step  202 . If Δ{dot over (m)} is not greater than Δ{dot over (m)} THR , control continues in step  212 . In step  202 , control determines whether the time difference (Δt) between the sufficiently high airflow rate change is less than Δt THR . If Δt is less than Δt THR , control continues in step  204 . If Δt is not less than Δt THR , control continues in step  206 . In step  204 , control determines whether Δd is less than Δd THR . If Δd is less than Δd THR , control continues in step  208 . If Δd is not less than Δd THR , control continues in step  206 . In step  206 , control determines AFHS based on MAF ({dot over (m)}), P PRE  and a known P BARO , and control continues in step  210 . In step  208 , control determines AFHS based on MAF and P PRE  and control continues in step  210 . In step  210 , control determines C d  based on MAF and AFHS. In step  212 , control updates P BARO  based on MAF, C d  and P PRE  and control ends. The engine can be subsequently operated based on the updated P BARO . 
     Referring now to  FIG. 3 , exemplary modules that execute the P BARO  estimation control will be described in detail. The exemplary modules include a first comparator module  300 , a second comparator module  302 , a third comparator module  303 , an AND module  304 , an AFHS module  306 , a C d  module  308  and a P BARO  update module  310 . The first comparator module  300  determines whether Δt is less than Δt THR  and outputs a corresponding signal to the AND module  304 . Similarly, the second comparator module  302  determines whether Δd is less than Δd THR  and outputs a corresponding signal to the AND module  304 . 
     The AND module  304  generates a signal indicating the manner in which AFHS is to be calculated based on the outputs of the first, second and third comparator modules  300 ,  302 ,  303 . For example, if the first comparator module  300  indicates that Δt is less than Δt THR  and the second comparator module  302  indicates that Δd is less than Δd THR , the signal generated by the AND module  304  indicates that AFHS is to be determined based on P PRE  and MAF. If, however, the first comparator module  300  indicates that Δt is not less than Δt THR  or the second comparator module  302  indicates that Δd is not less than Δd THR , the signal generated by the AND module  304  indicates that AFHS is to be determined based on P PRE , MAF and a known P BARO . The third comparator module  303  determines whether Δ{dot over (m)} is greater than Δ{dot over (m)} THR  and outputs a corresponding signal to the AFHS module  306 . 
     The AFHS module  306  determined AFHS based on MAF, P PRE  and a known P BARO , depending upon the output of the AND module  304 . The C d  module  308  determines C d  based on AFHS and MAF. The P BARO  update module  310  updates P BARO  based on C d , MAF and P PRE . The engine can be subsequently operated based on the updated P BARO . 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention 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.