Abstract:
A method of controlling a torque output of an internal combustion engine includes determining a pressure ratio, determining a reference torque based on the pressure ratio and a torque request, calculating a desired throttle area based on the reference torque and regulating operation of the engine based on the desired throttle area to achieve the desired torque.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/860,010, filed on Nov. 17, 2006. The disclosure of the above application is incorporated herein by reference. 
     FIELD 
     The present invention relates to engines, and more particularly to engine torque control while the engine is operating at a high pressure ratio. 
     BACKGROUND 
     Internal combustion engines combust an air and fuel mixture within cylinders to drive pistons, which produces drive torque. Air flow into the engine is regulated via a throttle. More specifically, the throttle adjusts throttle area, which increases or decreases air flow into the engine. As the throttle area increases, the air flow into the engine increases. A fuel control system adjusts the rate that fuel is injected to provide a desired air/fuel mixture to the cylinders. As can be appreciated, increasing the air and fuel to the cylinders increases the torque output of the engine. 
     Engine control systems have been developed to accurately control engine torque output to achieve a desired engine speed, particularly when operating under high pressure ratios. Traditional engine control systems, however, do not control the engine speed as accurately as desired. Further, traditional engine control systems do not provide as rapid of a response to control signals as is desired or coordinate engine torque control among various devices that affect engine torque output. Such traditional control systems are often more complex than desired and require time and cost intensive calibration processes. 
     SUMMARY 
     Accordingly, the present disclosure provides a method of controlling a torque output of an internal combustion engine. The method includes determining a pressure ratio, determining a reference torque based on the pressure ratio and a torque request, calculating a desired throttle area based on the reference torque and regulating operation of the engine based on the desired throttle area to achieve the desired torque. 
     In other features, the method further includes calculating a desired manifold absolute pressure (MAP) of the engine based on the reference torque and calculating a desired air-per-cylinder (APC) of the engine based on the reference torque. The desired throttle area is calculated based on the desired MAP and the desired APC. The desired MAP is determined using an inverted MAP-based torque model and the desired APC is determined using an inverted APC-based torque model. The method further includes filtering the desired MAP based on the pressure ratio and on whether the engine is operating in a steady-state. The method further includes determining a desired mass air flow (MAF) based on the desired APC. The desired throttle area is calculated based on the desired MAF. 
     In other features, the method further includes determining an estimated torque of the engine and correcting the reference torque based on the estimated torque, the pressure ratio and on whether the engine is operating in a steady-state. The method further includes calculating a torque error based on the reference torque and the estimated torque. The reference torque is corrected based on the torque error. 
     In another feature, the method further includes determining whether the engine is operating in a steady-state based on the pressure ratio and an engine RPM. The desired throttle area is calculated based on whether the engine is operating in the steady-state. 
     In still another feature, the method further includes rate limiting the reference torque. 
     In yet another feature, the method further includes calculating the pressure ratio as a ratio between a MAP and a barometric pressure. 
     Further advantages and areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating an embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of an exemplary engine system according to the present disclosure; 
         FIG. 2  is a flowchart illustrating steps executed by the engine torque control of the present disclosure; and 
         FIG. 3  is a block diagram illustrating exemplary modules that execute the engine torque control of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, 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 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 . Air within the intake manifold  14  is distributed into cylinders  18 . Although a single cylinder  18  is illustrated, it can be appreciated that the coordinated torque 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 that 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 cam shaft  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, which drives the piston in the cylinder  18 . The piston, in turn, 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 cam shaft  30 . The exhaust is treated in an exhaust system and is released to atmosphere. 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 cam shafts  24 ,  30 . More specifically, the timing or phase angle of the respective intake and exhaust cam shafts  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. 
     The engine system  10  can also include an exhaust gas recirculation (EGR) system  36 . The EGR system  36  includes an EGR valve  38  that regulates exhaust flow back into the intake manifold  14 . The EGR system is generally implemented to regulate emissions. However, the mass of exhaust air that is circulated back into the intake manifold  14  also affects engine torque output. 
     A control module  40  operates the engine based on the torque-based engine control of the present disclosure. More specifically, the control module  40  generates a throttle control signal and a spark advance control signal based on a desired engine speed (RPM DES ). A throttle position signal generated by a throttle position sensor (TPS)  42 . An operator input  43 , such as an accelerator pedal, generates an operator input signal. The control module  40  commands the throttle  16  to a steady-state position to achieve a desired throttle area (A THRDES ) and commands the spark timing to achieve a desired spark timing (S DES ). A throttle actuator (not shown) adjusts the throttle position based on the throttle control signal. 
     An intake air temperature (IAT) sensor  44  is responsive to a temperature of the intake air flow and generates an intake air temperature (IAT) signal. A mass airflow (MAF) sensor  46  is responsive to the mass of the intake air flow and generates a MAF signal. A manifold absolute pressure (MAP) sensor  48  is responsive to the pressure within the intake manifold  14  and generates a MAP signal. An engine coolant temperature sensor  50  is responsive to a coolant temperature and generates an engine temperature signal. An engine speed sensor  52  is responsive to a rotational speed (i.e., RPM) of the engine  12  and generates in an engine speed signal. Each of the signals generated by the sensors is received by the control module  40 . 
     The engine system  10  can also include a turbo or supercharger  54  that is driven by the engine  12  or engine exhaust. The turbo  54  compresses air drawn in from the intake manifold  14 . More particularly, air is drawn into an intermediate chamber of the turbo  54 . The air in the intermediate chamber is drawn into a compressor (not shown) and is compressed therein. The compressed air flows back to the intake manifold  14  through a conduit  56  for combustion in the cylinders  18 . A bypass valve  58  is disposed within the conduit  56  and regulates the flow of compressed air back into the intake manifold  14 . 
     The engine torque control of the present disclosure determines a desired throttle area (A THRDES ) based on a pressure ratio (P R ), a requested engine torque (T REQ ) and an estimated engine torque (T EST ). T REQ  is determined based on an operator input including, but not limited to, an accelerator pedal position. P R  is determined as the ratio between MAP and a barometric pressure (P BARO ). P BARO  can be directly measured using a sensor (not shown) or can be calculated using other known parameters. A reference torque (T REF ) is initially provided by an arbitration ring and is subsequently rate limited based on P R  and T REQ  to provide a rate limited T REF  (T REFRL ) By rate limiting T REF , undesired, abrupt changes in engine operation are avoided. 
     T REFRL  is summed with a corrected torque error (T ERRCOR ). More specifically, a torque error (T ERR ) is determined as the difference between T REFRL  and T EST . T EST  is determined by an engine control module (ECM), as explained in further detail below. T ERRCOR  is determined using a proportional-integral function based on the following relationship:
 
 T   ERRCOR   =k   P ( P   R )* T   ERR   +k   1 ( P   R )*∫ T   ERR   (1)
 
where:
         k P  is a pre-determined proportional constant; and   k I  is a pre-determined integral constant.
 
T REFRL  is summed with T ERRCOR  to provide a corrected reference torque (T REFCOR ). It should be noted that T ERR  is only corrected when the engine is operating in steady-state. If the engine is not operating in steady-state, T ERRCOR  is equal to T ERR .
       

     Whether the engine is operating in steady-state is determined based on RPM and T REFRL . For example, current and previous values are monitored for both RPM and T REFRL . These values are filtered and a comparison is made between the respective current and previous values. For example, a current RPM is compared to a previous RPM and a current T REFRL  is compared to a previous T REFRL . If the differences between the respective values are both less than corresponding threshold differences, the engine is deemed to be operating in steady-state and a steady-state flag (FLAG SS ) is set equal to 1. If either one of the respective differences is greater than its corresponding threshold difference, the engine is deemed to be operating in a transient state and FLAG SS  is set equal to 0. 
     A desired MAP (MAP DES ) and a desired air per cylinder (APC DES ) are determined based on T REFCOR . More specifically, MAP DES  is determined using an inverse MAP-based torque model in accordance with the following relationship:
 
 MAP   DES   =T   MAP   −1 (( T   REFCOR   +f (Δ T )),  S, I, E, AF, OT, N )  (2)
 
where:
         ΔT is a filtered difference between MAP and APC based torque estimators;   S is an ignition timing;   I is an intake valve timing;   E is an exhaust valve timing;   AF is an air-to-fuel ratio;   OT is the engine oil temperature; and   N is the number of cylinders.
 
The calculation of ΔT is described in further detail in commonly assigned U.S. Pat. No. 7,069,905, the disclosure of which is expressly incorporated herein by reference. Similarly, APC DES  is determined using an inverse APC-based torque model in accordance with the following relationship:
 
 APC   DES   =T   APC   −1 ( T   REFCOR   , S, I, E, AF, OT, N )  (3)
       

     MAP DES  can be filtered to provide a filtered MAP DES  (MAP DESF ). More specifically, MAP DESF  is determined based on P R  and SS in accordance with the following relationship: 
                     MAP   FILTD     =     [           LPF   (       MAP   DES     ,       K   1     ⁡     (     P   R     )       ,               If   →   SS     =   1               LPF   (       MAP   DES     ,       K   2     ⁡     (     P   R     )       ,               If   →   SS     =   0           ]             (   4   )               
where:
         K 1  is a pre-determined filter constant;   K 2  is a pre-determined filter constant; and   LPF indicates that a low-pass filter is implemented.
 
A desired MAF (MAF DES ) is determined based on APC DES  in accordance with the following relationship:
       
                     MAF   DES     =         APC   DES     *   R       k   cyl               (   5   )               
where:
         R is the universal gas constant; and   k cyl  is a constant that is determined based on the number of cylinders (e.g., 15 for an 8-cylinder engine, 20 for a 6-cylinder engine and 30 for a 4-cylinder engine).
 
A THRDES  is subsequently determined based on MAF DES  and MAP DESF  in accordance with the following relationship:
       
                     A   THRDES     =         MAF   DES     *       R   *   IAT             P   BARO     *     Φ   (       MAP   DESF       P   BARO       )                 (   6   )               
Φ is based on P R  in accordance with the following relationships:
 
                   Φ   =     {                 2   ⁢   γ       γ   -   1       ⁢     (     1   -     P   R       γ   -   1     γ         )                   if   ⁢           ⁢     P   R       &gt;     P   critical       =         (     2     γ   +   1       )       γ     γ   +   1         =   0.528                   γ   ⁢             2     γ   +   1       ⁢             γ   +   1       (     γ   -   1     )                         if   ⁢           ⁢     P   R       ≤     P   critical                       (   7   )               
P CRITICAL  is defined as the pressure ratio at which the velocity of the air flowing past the throttle equals the velocity of sound. This condition is called choked or critical flow. The critical pressure ratio is determined by:
 
                     P   CRITICAL     =       (     2     γ   +   1       )       γ     γ   -   1                 (   8   )               
where γ is equal to the ratio of specific heats for air and range from about 1.3 to about 1.4.
 
     Referring now to  FIG. 2 , exemplary steps executed by the engine torque control will be described in detail. In step  200 , control determines whether the engine is on. If the engine is not on, control ends. If the engine is one, control monitors the engine operating parameters (e.g., RPM, MAP, MAF, I, E, S, P BARO , IAT, etc.) in step  202 . In step  204 , control determines P R  as the ratio of MAP to P BARO . In step  206 , control determines T REF  based on the above-described rate limiting function using T REQ  and P R  as inputs Control determines T EST  in step  208 . In step  210 , control determines T ERR  based on T EST  and T REFRL . 
     In step  212 , control determines whether the engine is operating in steady-state. If the engine is operating in steady-state, control continues in step  214 . If the engine is not operating in steady-state, control continues in step  216 . In step  214 , control sets FLAG SS  equal to 1. In step  216 , control sets FLAG SS  equal to 0. In step  217 , control corrects T ERR  based on FLAG SS , as described above. In step  218 , control corrects T REF  based on the corrected T ERR . 
     Control determines MAP DES  and APC DES  based on the corrected T REF  in step  219 . Control filters MAP DES  based on FLAG SS , as described in detail above, in step  220 . In step  222 , control determines MAF DES  based on APC DES . Control determines A THRDES  based on MAP DES  and MAF DES  in step  224 . In step  226 , control regulates engine operation based A THRDES  and control ends. 
     Referring now to  FIG. 3 , exemplary modules that execute the engine torque control will be described in detail. The exemplary modules include a P R  module  300 , a T REF  module  302 , a MAP DES  module  304 , an APC DES  module  306 , a corrector module  308 , a FLAG SS  module  310 , a filter module  312 , a MAF DES  module, an A THRDES  module  316  and an ECM  318 . Although various modules are described herein, it is anticipated that the individual modules can be combined as sub-modules into a single module or a plurality of modules using various combinations of the modules. 
     The P R  module  300  determines P R  based on MAP and P BARO . P R  is output to the T REF  module  302 , the corrector module  308  and the filter module  312 . The T REF  module determines and rate limits T REF  (i.e., to provide T REFRL ) based on T REQ  and P R . T REFRL  is output to a summer  320 , a summer  322  and the FLAG SS  module  310 . The FLAG SS  module  310  determines whether the engine is operating in steady-state and sets FLAG SS  accordingly. FLAG SS  is output to the corrector module  308  and the filter module  312 . The summer  322  inverts T EST , which is output from the ECM  318 , and sums T REFRL  and the inverted T EST  to determine T ERR . TERR is output to the corrector module  308 . 
     The corrector module  308  selectively corrects T ERR  based on P R  and FLAG SS , and outputs T ERRCOR . More specifically, if FLAG SS  indicates that the engine is operating in steady-state, T ERR  is corrected, whereby T ERR  is not equal to the output T ERRCOR . If FLAG SS  does not indicate that the engine is operating in steady-state, T ERR  is not corrected, whereby T ERR  is equal to the output T ERRCOR . The summer  320  sums T REFRL  and T ERRCOR  to provide T REFCOR , which is output to the MAP DES  module  304  and the APC DES  module  306 . 
     The MAP DES  module  304  determines MAP DES  based on RPM and T REFCOR  and outputs MAP DES  to the filter module  312 . The APC DES  module  306  determines APC DES  based on T REFCOR  and outputs APC DES  to the MAF DES  module  314 . The filter module  312  filters MAP DES  based on FLAG SS  and P R  to provide MAP DESF . The MAF DES  module  314  determines MAF DES  based on APC DES . Both MAP DESF  and MAF DES  are output to the A THRDES  module  316 , which determines A THRDES  based thereon. A THRDES  is output to the ECM  318 , which regulates engine operation based thereon. 
     The engine torque control of the present disclosure provides accurate transient or steady-state torque control under varying environmental conditions by considering the pressure ratio. Traditional systems that don&#39;t consider the pressure ratio implement a linear relationship for all pressures. As a result, a high gain is provided for all pressures, which can lead to instability and overshooting in such traditional systems. This accurate engine torque control is achieved under all combinations of engine load, RPM, ignition timing, intake and exhaust timing and the like. Furthermore, the engine torque control enables an automated calibration process to be implemented, which significantly reduces the time and effort required to calibrate an engine. More specifically, the engine torque control is based on a torque model, which unifies all of the inputs and outputs. As a result, the torque model automates the calibration process, wherein an input or inputs can be changed and the effect on the outputs is readily provided. 
     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.