# Patent

## Title
Adaptive barometric pressure estimation in which an internal combustion engine is located

## 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.

## Background
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 (TPRE), manifold absolute pressure (MAP), throttle position (TPS), engine RPM and barometric pressure (PBARO). 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 PBARO. 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 (PPRE), a pre-throttle stagnation pressure (PPRE0) (i.e., the air pressures upstream of the throttle), an intake air temperature (TPRE), a mass air flow (MAF), a manifold absolute pressure (MAP), an effective throttle area (AEFF), an engine RPM and a barometric pressure (PBARO). PPRE0 and PPRE 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.
TPRE, MAF, MAP and engine RPM are determined based on signals generated by a TPRE 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. AEFF 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 AEFF 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 PBARO estimation control of the present disclosure estimates PBARO 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)}=Cd·AINLET·√{square root over (2·ρ·(PBARO−PPRE))}  (1)

where:

    
    
        {dot over (m)} is the rate of mass air flow (MAF);
        Cd is a drag or loss coefficient;
        AINLET is the effective cross-sectional area of pre-throttle inlet system including air filter;
        PPRE is the inlet or pre-throttle absolute pressure; and
        ρ is the air density (i.e., a function of PINLET, 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
        )
      
    
  




Cd 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. PPRE 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 PBARO, but is a more slowly updated variable than a time-based calculation of PBARO. For example, the values of (PBARO−PPRE)t and (PBARO−PPRE)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, PBAROt and PBAROt-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 (ΔtTHR) and the vehicle travel distance (Δd) is less than a threshold difference (ΔdTHR) (i.e., the vehicle does not move too far), it can be assumed that any change in PBARO is negligible.

Referring now to FIG. 2, exemplary steps that are executed by the PBARO estimation control will be described in detail. In step 200, control initializes Cd 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 ΔtTHR. If Δt is less than ΔtTHR, control continues in step 204. If Δt is not less than ΔtTHR, control continues in step 206. In step 204, control determines whether Δd is less than ΔdTHR. If Δd is less than ΔdTHR, control continues in step 208. If Δd is not less than ΔdTHR, control continues in step 206. In step 206, control determines AFHS based on MAF ({dot over (m)}), PPRE and a known PBARO, and control continues in step 210. In step 208, control determines AFHS based on MAF and PPRE and control continues in step 210. In step 210, control determines Cd based on MAF and AFHS. In step 212, control updates PBARO based on MAF, Cd and PPRE and control ends. The engine can be subsequently operated based on the updated PBARO.
Referring now to FIG. 3, exemplary modules that execute the PBARO 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 Cd module 308 and a PBARO update module 310. The first comparator module 300 determines whether Δt is less than ΔtTHR and outputs a corresponding signal to the AND module 304. Similarly, the second comparator module 302 determines whether Δd is less than ΔdTHR 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 ΔtTHR and the second comparator module 302 indicates that Δd is less than ΔdTHR, the signal generated by the AND module 304 indicates that AFHS is to be determined based on PPRE and MAF. If, however, the first comparator module 300 indicates that Δt is not less than ΔtTHR or the second comparator module 302 indicates that Δd is not less than ΔdTHR, the signal generated by the AND module 304 indicates that AFHS is to be determined based on PPRE, MAF and a known PBARO. 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, PPRE and a known PBARO, depending upon the output of the AND module 304. The Cd module 308 determines Cd based on AFHS and MAF. The PBARO update module 310 updates PBARO based on Cd, MAF and PPRE. The engine can be subsequently operated based on the updated PBARO.
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.

## Claims

1. A method of determining a barometric pressure of atmosphere, in which an internal combustion engine of a vehicle is located, comprising:
monitoring operating parameters of the internal combustion engine and the vehicle;
determining a healthy status of an air filter of the internal combustion engine;
determining a drag coefficient of an air intake system of the internal combustion engine based on at least one of said operating parameters and said healthy status; and
calculating the barometric pressure based on said operating parameters, said drag coefficient and said healthy status of said air filter.

2. The method of claim 1 further comprising determining whether at least one of said operating parameters is less than a corresponding threshold, wherein said healthy status of said air filter is determined based on a known barometric pressure if said at least one of said operating parameters is not less than said corresponding threshold.

3. The method of claim 2 wherein said at least one operating parameter includes a time difference between update times of the barometric pressure.

4. The method of claim 2 wherein said at least one operating parameter includes a travel distance of the vehicle.

5. The method of claim 1 wherein said healthy status is determined based on a pre-throttle inlet pressure.

6. The method of claim 5 wherein said pre-throttle inlet pressure is determined based on an intake air temperature.

7. The method of claim 5 wherein said pre-throttle inlet pressure is monitored using a sensor.

8. The method of claim 1 wherein said operating parameters comprise a mass air flow, an effective intake cross-sectional area, an air density and a pre-throttle inlet pressure.

9. A system for determining a barometric pressure of atmosphere, in which an internal combustion engine of a vehicle is located, comprising:
a first module that monitors operating parameters of the internal combustion engine and the vehicle,
wherein the operating parameters comprise one of a travel distance of the vehicle and a time difference between update times of the barometric pressure;
a second module that determines a healthy status of an air filter of the internal combustion engine; and
a third module that calculates the barometric pressure based on said operating parameters and said healthy status of said air filter,
wherein the barometric pressure is calculated based on at least one of the time difference and the travel distance exceeding a threshold.

10. The system of claim 9 further comprising a fourth module that determines a drag coefficient of an intake system of the internal combustion engine based on at least one of said operating parameters and said healthy status, wherein said barometric pressure is calculated based on said drag coefficient.

11. The system of claim 9 further comprising a fourth module that determines whether at least one of said operating parameters is less than a corresponding threshold, wherein said healthy status of said air filter is determined based on a known barometric pressure if said at least one of said operating parameters is not less than said corresponding threshold.

12. The system of claim 9 wherein said healthy status is determined based on a pre-throttle inlet pressure.

13. The system of claim 12 wherein said pre-throttle inlet pressure is determined based on an intake air temperature.

14. The system of claim 12 further comprising a sensor that monitors said pre-throttle inlet pressure.

15. The system of claim 9 wherein said operating parameters comprise a mass air flow, an effective intake cross-sectional area, an air density and a pre-throttle inlet pressure.

16. A method of regulating operation of an internal combustion engine of a vehicle, comprising:
monitoring operating parameters of the internal combustion engine and the vehicle, wherein the operating parameters comprise an effective intake cross-sectional area of a pre-throttle inlet system;
determining a healthy status of an air filter of the internal combustion engine;
calculating a barometric pressure of atmosphere, in which the internal combustion engine is located, based on said operating parameters and said healthy status of said air filter; and
regulating operation of the vehicle based on said barometric pressure.

17. The method of claim 16 further comprising determining a drag coefficient of an intake system of the internal combustion engine based on at least one of said operating parameters and said healthy status, wherein said barometric pressure is calculated based on said drag coefficient.

18. The method of claim 16 further comprising determining whether at least one of said operating parameters is less than a corresponding threshold, wherein said healthy status of said air filter is determined based on a known barometric pressure if said at least one of said operating parameters is not less than said corresponding threshold.

19. The method of claim 18 wherein said at least one operating parameter includes a time difference between update times of the barometric pressure.

20. The method of claim 18 wherein said at least one operating parameter includes a travel distance of the vehicle.

21. The method of claim 16 wherein said healthy status is determined based on a pre-throttle inlet pressure.

22. The method of claim 21 wherein said pre-throttle inlet pressure is determined based on an intake air temperature.

23. The method of claim 21 wherein said pre-throttle inlet pressure is monitored using a sensor.