Abstract:
An air dynamic steady state detection system for movement of a cam phaser of an internal combustion engine includes a cam position sensing device and a control module. The cam position sensing device generates a position signal based on a position of the cam phaser of the engine. The control module receives the position signal and applies first and second filters to the position signal to select either a transient or steady state condition. The control module also calculates an estimated air value based on the selection of the transient or steady state condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/702,091, filed on Jul. 22, 2005. The disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to control systems for internal combustion engines, and more particularly to systems and methods for detecting steady state and transient conditions of a cam phaser that are used for estimating air. 
     BACKGROUND OF THE INVENTION 
     Various methods exist for estimating the air in an internal combustion engine. One conventional method uses measurements from a mass airflow sensor to estimate an air value. Another conventional method uses speed density calculations to estimate the value. 
     The first method is shown to be inaccurate during movement of cam phasers coupled to intake and exhaust camshafts of the engine. The second method provides more accurate estimation during transient operating conditions of the cam phasers. Conventional methods of estimating air lack the ability to detect a transient operating condition or a steady state operating condition of the cam phasers and lack the ability to apply the proper air estimation method during the transient operating condition. 
     SUMMARY OF THE INVENTION 
     An air dynamic steady state detection system for movement of a cam phaser of an internal combustion engine according to the present invention includes a cam position sensing device and a control module. The cam position sensing device generates a position signal based on a position of the cam phaser of the engine. The control module receives the position signal and applies first and second filters to the position signal to select either a transient or steady state condition. The control module also calculates an estimated air value based on the selection of the transient or steady state condition. 
     In other features, the air dynamic steady state detection system includes a second cam position sensing device. The second cam position sensing device generates a second position signal of a second cam phaser of the engine. The cam phaser is coupled to an intake cam shaft of the engine and the second cam phaser coupled to an exhaust camshaft of the engine. The control module applies third and fourth filters to the second position signal and selects either a steady state or transient condition based on a difference between the first and second filters and a difference between the third and fourth filters. 
     In still other features, the control module calculates an estimated air value based on a speed density calculation when the control module determines the transient condition. When the control module determines the steady state condition, the control module calculates an estimated air value based on a mass airflow sensor signal and an engine speed. The control module controls a fuel injector of the engine based on the estimated air value. 
     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 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a functional block diagram illustrating a vehicle engine system including a control module that controls engine operation according to the air dynamic steady state detection system and method of the present invention; 
         FIG. 2  is a data flow diagram illustrating a control module including an air dynamic steady state detection system according to the present invention; 
         FIG. 3  is a flowchart illustrating the steps performed by the state determination module; and 
         FIG. 4  is a flowchart illustrating the steps performed by the air estimation module. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) 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 the same 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. 
     Referring to  FIG. 1 , an engine system  10  includes an engine  12  that combusts an air and fuel mixture to produce drive torque. Air is drawn into an intake manifold  14  through a throttle  16 . The throttle  16  regulates mass air flow into the intake manifold  14 . A mass airflow sensor  15  senses the mass of air flowing into the engine. A manifold absolute pressure sensor  17  senses the air pressure in the intake manifold  14 . Air within the intake manifold  14  is distributed into cylinders  18 . Although a single cylinder  18  is illustrated, it is appreciated that the engine control system of the present invention can be implemented in engines having a plurality of cylinders including, but not limited to, 2, 3, 4, 5, 6, 8, 10 and 12 cylinders. 
     A fuel injector (not shown) injects fuel which is combined with the air as it is drawn into the cylinder  18  through an intake port. The fuel injector may be an injector associated with an electronic or mechanical fuel injection system  20 , a jet or port of a carburetor or another system for mixing fuel with intake air. The fuel injector is controlled to provide a desired air-to-fuel (A/F) ratio within each cylinder  18 . 
     An intake valve  22  selectively opens and closes to enable the air/fuel mixture to enter the cylinder  18 . The intake valve position is regulated by an intake camshaft  24 . A piston (not shown) compresses the air/fuel mixture within the cylinder  18 . A spark plug  26  initiates combustion of the air/fuel mixture, driving the piston in the cylinder  18 . The piston drives a crankshaft (not shown) to produce drive torque. Combustion exhaust within the cylinder  18  is forced out an exhaust port when an exhaust valve  28  is in an open position. The exhaust valve position is regulated by an exhaust camshaft  30 . The exhaust is treated in an exhaust system. Although single intake and exhaust valves  22 , 28  are illustrated, it can be appreciated that the engine  12  can include multiple intake and exhaust valves  22 , 28  per cylinder  18 . 
     The engine system  10  can include an intake cam phaser  32  and an exhaust cam phaser  34  that respectively regulate the rotational timing of the intake and exhaust camshafts  24 , 30 . More specifically, the timing or phase angle of the respective intake and exhaust camshafts  24 , 30  can be retarded or advanced with respect to each other or with respect to a location of the piston within the cylinder  18  or crankshaft position. In this manner, the position of the intake and exhaust valves  22 , 28  can be regulated with respect to each other or with respect to a location of the piston within the cylinder  18 . By regulating the position of the intake valve  22  and the exhaust valve  28 , the quantity of air/fuel mixture ingested into the cylinder  18  and therefore the engine torque is regulated. 
     A control module  40  detects transient and steady state operating conditions of the cam phasers  32 ,  34  and calculates an estimated air value  62  according to the present invention. Referring now to  FIG. 2 , the control module  40  is shown in more detail. The control module  40  receives an intake cam phaser position  52  and an exhaust phaser position  54 . The positions can be either sensed from the cam phasers  32 , 34  ( FIG. 1 ) or determined from other engine operating conditions. A state determination module  56  determines either a steady state operating condition or transient operating condition of each cam phaser. A cam phaser is operating in a transient condition when the cam phaser is moving. A cam phaser is operating in a steady state condition when the cam phaser is at rest. An air estimation module  60  calculates the estimated air value  62  based on a condition flag  58  received from the state determination module  56 . 
     Referring to  FIG. 3 , the flowchart illustrates the steps performed by the state determination module according to the method of the present invention. In steps  100  and  110 , a pair of lowpass filters are applied to the intake phaser position and/or the exhaust phaser position. In step  100  a fast lowpass filter is applied. In step  110 , a slower lowpass filter is applied. When the cam phasers are not moving, the output of both filters will be the same. However, when either cam phaser moves the filters will produce different outputs. In step  120 , a difference between the filter outputs is calculated for the exhaust cam phaser position and/or the intake cam phaser position. 
     In step  130 , if the absolute value of the intake position difference is greater than or equal to a first selectable threshold or the absolute value of the exhaust position difference is greater than or equal to a second selectable threshold, transient operating conditions are determined and a transient flag is set to TRUE. In step  130 , if the absolute value of the intake position difference is less than the first selectable threshold or the absolute value of the exhaust position difference is less than the second selectable threshold, a steady state operating condition is determined and a steady state flag is set to TRUE. In an alternative embodiment, a variable size offset (truncation) can be applied to the differences to allow for the fact that the cam phasers can move some distance from the park position without providing a significant effect. 
     Referring now to  FIG. 4 , the steps performed by the air estimation module  60  is shown in more detail. While the transient flag is set to TRUE, the estimator uses the speed density calculation method for the estimated air value. A transient estimated air value is calculated in step  220 , based on a pressure of the intake manifold, an engine speed, the intake cam phaser position, the exhaust cam phaser position, and an estimated air temperature per cylinder. Otherwise, the steady state condition flag is TRUE in step  230  and a steady state estimated air value is calculated based on a signal from the mass airflow sensor and an engine speed in step  240 . 
     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.