Abstract:
A particulate filter regeneration method for an internal combustion engine system is provided. The method includes: receiving an outlet temperature signal corresponding to a temperature at an outlet of a particulate filter; receiving an oxygen signal corresponding to an oxygen level in exhaust flowing from said particulate filter; and controlling at least one of airflow and fuel based on said oxygen level such that said outlet temperature is within a desired range.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to vehicle engine systems, and more particularly to detecting a state of air flow delivered to a cylinder of an engine. 
       BACKGROUND OF THE INVENTION 
       [0002]    Engines combust a mixture of air and fuel (air/fuel) to drive a piston in a cylinder. The downward force of the piston generates torque. A throttle controls air flow delivered to the cylinders. By determining the amount of air ingested by the cylinders, the fuel mass can be calculated and a proper air/fuel mixture can be delivered to the cylinders to obtain the desired air-fuel ratio and torque. 
         [0003]    Air flow delivered to the cylinders can be measured using a mass air flow (MAF) sensor. The MAF sensor measures the air flow across the throttle. During steady-state air flow conditions, the air flow measured across the throttle provides an accurate estimation of the fresh air flow delivered to the cylinders. Because the MAF sensor measures air flow across the throttle and not the air into the cylinders, it is most accurate during steady-state conditions, and is less accurate during transient conditions (e.g., when additional air must flow across the throttle to increase the manifold absolute pressure (MAF), or when the mass of airflow must be reduced to reduce the MAF). 
         [0004]    Air flow can be estimated using a speed density calculation, which is typically based on MAF, engine RPM, as well as intake air temperature and pressure. The speed density calculation is only an approximation that is valid as tong none of the parameters that are not explicitly accounted for in the calculation varies. However, because the not accounted for parameters do vary over a period of time while driving the vehicle, the speed density calculations are only accurate for a short period of time and need to be adjusted over time. In order to maintain the accuracy of the speed density calculations during transient conditions, the MAF sensor is used during stead state conditions to correct speed density calculation. 
         [0005]    In engines without variable cam phasing (VCP) or variable cam timing (VCT), if the mass of fresh air entering the cylinder changes (i.e., is transient) there is a corresponding increase or decrease in MAF. This indicates that the mass of air is either being accumulated or depleted in the intake manifold. During such transient conditions, the speed density calculation is used to determine the mass air flow entering the cylinders. The determination of whether the mass air flow is steady-state or transient can be made by means such as that described in commonly assigned U.S. Pat. No. 5,423,208, the disclosure of which is incorporated herein by reference. The control module uses the appropriate method of estimating the mass air flow into the cylinder based on the air flow state. 
         [0006]    However in engines with VCP or VCT, changes in cam position can occur without changing the MAF while causing the MAF sensor reading to change by a large amount. This occurs because the VCP or VCT system allows varying amounts of residual exhaust gas back into the intake manifold, which replaces the fresh air mass in the manifold. As a result, more or less air flows through the throttle and the air flow is transient. Traditional air flow transient/steady-state detection methods, like that disclosed in U.S. Pat. No. 5,423,208 will see no change in MAF and incorrectly determine that the air flow is steady-state. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, the present invention provides an air flow state determining system that determines a mass air flow into a cylinder of an engine having a cam phaser. The system includes a first module that determines whether an air flow state is one of steady-state and transient based on a cam phaser position. A second module determines the mass air flow using one of a mass air flow sensor signal and a speed density relationship based on whether the mass air flow state is one of steady-state and transient. 
         [0008]    In other features, the system further includes a third module that processes the cam phaser position using a first order linear model and calculates an updated intermediate value based on a cam phaser position. The air flow state corresponding to cam phaser motion is determined based on the updated intermediate value. The air flow state is determined based on a difference between the updated intermediate value and a previous intermediate value. 
         [0009]    In another feature, the system further includes a filter module that filters the cam phaser position. 
         [0010]    In yet other features, the system further includes a dead-band module that adjusts the cam phaser position based on a calibrated offset. The system further includes a minimizing module that minimizes the cam phaser position to zero if the adjustment results in the cam phaser position being less than zero. 
         [0011]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0013]      FIG. 1  is a functional block diagram of an engine system regulating using the air flow state detection control in accordance with the present invention; 
           [0014]      FIG. 2  is a flowchart illustrating exemplary steps executed by the air flow state detection control according to the present invention; and 
           [0015]      FIG. 3  is a functional block diagram of exemplary modules that execute the air flow state detection control of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    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 and/or other suitable components that provide the described functionality. 
         [0017]    Referring now to  FIG. 1 , an engine system  10  is schematically illustrated. The engine system  10  includes an engine  12  that combusts an air and fuel (air/fuel) mixture to produce drive torque. Air is drawn into an intake manifold  14  through a throttle  15 . The throttle  15  regulates mass air flow (MAF) into the intake manifold  14 . The position of the throttle  15  is adjusted based on a signal from a pedal position sensor  16  indicative of a position of an accelerator pedal  17 . Air is drawn into a cylinder  20  of the engine through an intake valve  18 . Although four cylinders  20  are illustrated, it can be appreciated that the engine system  10  can include, but is not limited to, 2, 3, 4, 5, 6, 8, 10 and 12 cylinders. 
         [0018]    The air is mixed with fuel and is combusted within the cylinder  20  to reciprocally drive a piston (not shown) within the cylinder, which rotatably drives a crankshaft  24 . Exhaust is exhausted from the cylinder through an exhaust valve  19  and into an exhaust manifold  25 . A fuel injector (not shown) injects the fuel that is combined with the air. The fuel injector can be an injector that is associated with an electronic or mechanical fueling system, or another system for mixing fuel with intake air. The amount of fuel injected by the fuel injector is regulated based on the mass air flow into the cylinder  20  to deliver a desired air/fuel ratio. 
         [0019]    The opening and closing of the intake and exhaust valves  18 ,  19  are regulated by an intake camshaft  22  and an exhaust camshaft  23 , respectively. The crankshaft  24  rotatably drives intake and exhaust camshafts  22 ,  23  using a chain/belt and pulley system (not shown) to regulate the timing of the opening and closing of the intake and exhaust valves  18 ,  19 , with respect to a piston position within the cylinder  20 . Although a single intake camshaft  22  and a single exhaust camshaft  23  are illustrated, it is anticipated that dual intake camshafts and dual exhaust camshafts may be used. 
         [0020]    An intake cam phaser  26  and an exhaust cam phaser  27  vary an actuation time of the intake and exhaust camshafts  22 ,  23 , respectively, which mechanically actuate the intake and exhaust valves  18 ,  19 . More specifically, the rotational position of the intake and exhaust cam shafts  22 ,  23  can be advanced and/or retarded relative to a position of the piston within the cylinder  20  to vary the actuation time of the opening and/or closing of the inlet and/or exhaust valves  18 ,  19 . In this manner, the timing and/or lift of the intake and the exhaust valves  18 ,  19  can be varied with respect to one another and/or with respect to a location of the piston within the cylinder  20 . 
         [0021]    Adjustment of the intake and exhaust camshafts  22 ,  23  using the intake and/or exhaust cam phasers  26 ,  27  can affect the MAF. For example, when the cam phasers  22 ,  23  are adjusted to increase air delivered to the cylinders  18 , less exhaust residual flows into the intake manifold  14  displacing less fresh air mass. As a result, the mass of combustible air increases. Conversely, the intake and exhaust cam phasers  26 ,  27  can be adjusted to reduce air delivered to the cylinders  20 &gt;while increasing the exhaust gas residual entering the intake manifold  14 . As a result, there is more air mass entering the intake manifold  14  and hence the cylinder  14 . 
         [0022]    When the intake and/or exhaust cam phasers  26 ,  27  remain in a constant position, the actuation timing of the intake and exhaust valves  18 ,  19  remains constant. As a result, steady-state air flow occurs and a constant amount of air is delivered to the cylinders  20 . However, when the intake and/or exhaust cam phasers are adjusted, the actuation timing is correspondingly adjusted and the amount of air delivered into the cylinder  20  either increases or decreases. The resulting sudden change in air flow is typically referred to as an air transient. An air transient that results from a change in the camshaft position typically exists whenever the intake and/or exhaust cam phasers  26 ,  27  are moved from a fixed position. 
         [0023]    The engine system  10  further includes an air flow sensor  30 , an engine speed sensor  31 , cam phaser position sensors  32 ,  33 , an intake manifold air temperature sensor  34  and a MAF sensor  35 . A control module  36  receives the signals generated by the various sensor and regulates operation of the engine system  10  based on the air flow state detection system of the present invention. The air flow sensor  30  measures an amount of air flowing through throttle  15  and the engine speed sensor  31  is responsive to the rotational speed of the engine  12 . The intake manifold temperature sensor  34  measures an air temperature within the intake manifold  14  and the MAF sensor  35  measures the MAF within the intake manifold  14 . 
         [0024]    The cam phaser position sensors  32 ,  33  are coupled to the intake cam phaser  26  and the exhaust cam phaser  27 , respectively, and are responsive their respective rotational positions. When the rotational position of the intake and the exhaust cam phasers  26 ,  27  is adjusted, the cam phaser rotational sensors  32 ,  33  output a position signal to the control module  36 . The position signals can be filtered prior to being received by or within the control module  36  using a first order lag filter to remove any high frequency noise that may exist. 
         [0025]    Airflow transients can occur due to changes that a traditional air flow transient/steady state detector can detect as well as changes in the cam phaser  26 , 27  position, which the traditional transient/steady state detector does not detect. Accordingly, the air flow state detection control of the present invention detects whether the mass air flow is in a steady-state or a transient state based on a signal from a traditional transient/steady state detection control and further based on the rotational velocity of the cam phasers  26 ,  27 . Furthermore, the control module  36  determines the mass air flow into the cylinders  20  based on whether the mass air flow is deemed steady-state or transient. 
         [0026]    Although the air flow state detection control detects steady-state air flow and/or transient air flow based on the intake cam phaser  26  and/or the exhaust cam phaser  27  rotational velocities, the air flow state detection control will be based on the rotational velocity of the intake cam phaser  26  alone being used to detect a steady-state air flow and/or transient air flow. 
         [0027]    At each intake reference pulse, which is based on the engine RPM sensor signal, the air flow state detection control determines the intake cam position (θ ICAM ) based on the intake cam position sensor signal. θ ICAM  can be filtered using a first order lag filter (e.g., y=ay+(1−a)x). Proper selection of the filter coefficient (a) enables successful sampling as slow as every other intake reference pulse. The air flow state detection control subtracts a calibrated offset (θ THR ) from the filtered θ ICAM  to remove a dead-band associated with θ ICAM  (i.e., a cam phaser adjustment value that does not affect MAF). If the difference is less than 0, θ ICAM  is set it to 0). 
         [0028]    The air flow state detection control inputs θ ICAM  into a first order model, which is provided by the following equation: 
         [0000]        X ( k+ 1)=α X ( k )+βθ ICAM    
         [0000]    where X is an intermediate variable, k is the current event and is incremented each intake reference event, and α and β are pre-determined model or filter coefficients. α and β are determined using various optimization techniques, such that the following relationship is minimized: 
         [0000]      |[X(k)−X(k−1)]−MAF(k)−MAF(k−1)] 
         [0000]    where MAF(k)−MAF(k−1) is the change in intake manifold pressure due to only a change in intake cam position. If the following relationship is true: 
         [0000]      | X ( k )− X ( k− 1)|&gt;Δ THR    
         [0000]    the mass air flow is transient and a transient flag is set. Otherwise, the mass air flow is steady-state and a steady-state flag is set. 
         [0029]    If the steady-state flag is set, the control module  36  operates in a steady-state mode and estimates cylinder mass air flow based on the air flow sensor  30 . If the transient flag is set, the control module  36  estimates air flow based on the speed density approach according to the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
                     m 
                     a 
                   
                   = 
                   
                     
                       
                         η 
                         v 
                       
                        
                       
                         V 
                         d 
                       
                        
                       
                         P 
                         m 
                       
                     
                     
                       RT 
                       o 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where m a  is mass air into the cylinder, R is the universal gas constant, V d  is the displacement volume of the engine  12 , η v  is the volumetric efficiency of the engine  12 . T i  is the temperature of the air delivered into the intake manifold  14  and P m  is the intake manifold pressure. Since R and V d  are constants for a given engine, the volume of the engine  12  can be defined according to the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                     d 
                   
                   = 
                   
                     
                       η 
                       v 
                     
                      
                     
                       
                         V 
                         d 
                       
                       R 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    Substituting V e  into equation (1), mass of air into the cylinder  20  can be defined according to the following equation: 
         [0000]    
       
         
           
             
               
                 
                   
                     m 
                     a 
                   
                   = 
                   
                     
                       
                         V 
                         e 
                       
                       
                         T 
                         i 
                       
                     
                      
                     
                       P 
                       m 
                     
                   
                 
               
               
                 
                   ( 
                   3 
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         [0030]    Referring now to  FIG. 2 , a flowchart illustrates exemplary steps executed by the air flow state detection control. In step  200 , control determines θ ICAM . In step  202 , control filters θ ICAM  to provide a filtered θ ICAM . In step  204 , control subtracts θ THR  from θ ICAM  to remove the dead-band around the parked position. Control determines whether θ ICAM  is less than zero in step  206 . If θ ICAM  is less than zero, control continues in step  208 . If θ ICAM  is not less than zero, control continues in step  210 . In step  208 , control sets θ ICAM  to zero. 
         [0031]    Control updates the intermediate variable X(k+1) in step  210 . In step  212 , control determines whether the absolute value of the difference between X(k+1) and X(k) is greater than Δ THR . If the absolute value of the difference between X(k+1) and X(k) is greater than Δ THR , control continues in step  214 . If the absolute value of the difference between X(k+1) and X(k) is not greater than Δ THR , control continues in step  216 . In step  214 , control sets the transient flag and estimates the cylinder mass air flow using the speed density approach in step  218 . In step  216 , sets the steady-state flag. In step  219 , control determines whether the traditional or standard transient/steady state detection control has indicated that the air flow is steady state (SS) by setting a SS flag. If the SS flag is set, control estimates the cylinder mass air flow using the MAF sensor  30  in step  220 . If the SS flag is not set, control continues in step  218 . In step  222  control sets X(k) equal to X(k+1) and control ends. 
         [0032]    Referring now to  FIG. 3 , exemplary modules that execute the air flow state detection control will be described in detail. The exemplary modules include a filter module  300 , a dead-band module  302 , a θ ICAM  minimizing module  304 , an X updating module  306 , a summer  308 , an absolute value module  310 , a comparator module  312  a flag module  314  and a cylinder MAF estimating module  316 . The filter module  300  and the dead-band module  302  respectively filter and remove the dead-band value from θ ICAM . 
         [0033]    The θ ICAM  minimizing module  304  caps the minimum value of θ ICAM  to zero, if θ ICAM  is less than zero after the dead-band removal operation. The X updating module  306  determines X(k+1) based on X(k), θ ICAM  and the first order linear model described in detail above. The summer  308  determines the difference between X(k+1) and X(k) and the absolute value module  310  generates the absolute value of the difference. 
         [0034]    The comparator module  312  compares the absolute value of the difference to Δ THR  and outputs a first signal (e.g., 1) if the difference is greater than Δ THR , and outputs a second signal (e.g., 0) if the difference is less than Δ THR . The flag module  314  sets the steady-state or transient flag based on the output of the comparator module  312 . The cylinder MAF module  316  determines the cylinder MAF based on either the MAF sensor signal or the speed density calculation depending on the output of the comparator module  312  and the condition of the standard SS flag. 
         [0035]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings 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.