Abstract:
An engine control system and method according to the invention controls torque in an internal combustion engine. Engine parameters are measured and an engine torque is estimated. A desired air per cylinder of the engine is calculated. A desired manifold absolute pressure of a manifold of the engine is calculated based on a function of engine torque. A desired RPM of the engine is calculated based on a measured engine RPM and a reference torque of the engine. A desired area is calculated based on the desired manifold absolute pressure. The desired area is implemented into the controller to control torque output of the engine.

Description:
FIELD OF THE INVENTION 
     The present invention relates to engine control systems, and more particularly to an engine control system for improving torque control during transient and steady state operation. 
     BACKGROUND OF THE INVENTION 
     Referring now to  FIG. 1 , an exemplary method for controlling torque of an engine is shown generally at  10 . Torque control begins with step  12 . In step  14 , control determines if the engine is operating. If the engine is operating, instantaneous RPM (R), manifold absolute pressure (MAP), mass air flow (MAF) and air/fuel ratio (AF) are measured in step  16 . If the engine is not operating, control ends in step  28 . In step  18 , a desired air per cylinder (APC des ) is estimated based on an inverse function of torque. APC des  is determined based on parameters measured in step  16  and other measured values. APC des  may be characterized by the following equation:
 
 APC   des   =T   apc   −1 ( T   ref   ,R,S,D,AF,OT ,Ω)  (1) 
 
Where T ref  is reference torque, S is spark, D is dilution based on exhaust gas, OT is oil temperature and # is the number of cylinders of the engine. In step  20 , engine torque is estimated by the following equations:
 
 T=η   of *η Ω *( T   w   +T   ot )  (2) 
 
 T   w   =APC   des   +a   R   *R+a   S   *S+a   S   *S   2   (3) 
 
Where η af  is the efficiency of air flow through the engine manifold,η #  is the efficiency of the cylinders of the engine, T w  is the warm up torque of the engine, T ot  is the initial torque of the engine and a i  are coefficients.
 
     In step  22 , the desired MAF is calculated based on the follow:
 
 MAF   des   =APC   des   *R   (4) 
 
In step  24  the desired area is calculated based on the following: 
               A   des     =         APC   des     *   R   *         R   gas     *   T           15   *   B   *   Φ   ⁢           ⁢     (     P   B     )                 (   5   )             
 
where R is the measured RPM, R gas  is the ideal gas constant, B is barometric pressure and P is the measured MAP. Equation (5) is hereinafter referred to as the compressible flow equation. Control then loops back to step  14 .
 
     As shown, desired area (A des ) is a function of RPM (R) and manifold pressure (P). Under transient conditions, the controller does not have lead information enabling fast torque control response. In this regard, an undesirable time delay may occur while correcting MAP and RPM to a desired level. For example, as illustrated in  FIG. 1A , a time delay Δt may occur. In this way, MAP will grow from idle to wide open throttle causing a delay in area opening. As a result, equation (5) will not provide an instantaneous change in area. A similar undesirable time delay may also result during engine torque control for RPM correction. 
     SUMMARY OF THE INVENTION 
     An engine control system according to the invention includes an engine having a manifold. A controller calculates a desired area based on a desired manifold absolute pressure of said manifold. The controller calculates a warm-up torque based on a requested torque and the manifold absolute pressure is based on the warm-up torque. 
     A method according to the invention controls torque in an internal combustion engine. Engine parameters are measured and an engine torque is estimated. A desired air per cylinder of the engine is calculated. A desired manifold absolute pressure of a manifold of the engine is calculated based on a function of engine torque. A desired area is calculated based on the desired manifold absolute pressure. The desired area is implemented into the controller to control torque output of the engine. 
     A method according to the invention controls torque in an internal combustion engine. Engine parameters are measured and an engine torque is estimated. A desired air per cylinder of the engine is calculated. A desired RPM of the engine is calculated based on a measured engine RPM and a reference torque of the engine. A desired area is calculated based on the desired manifold absolute pressure. The desired area is implemented into the controller to control torque output of the engine. 
     A method according to the invention controls torque in an internal combustion engine. Engine parameters are measured and an engine torque is estimated. A desired air per cylinder of the engine is calculated. A desired manifold absolute pressure of a manifold of the engine is calculated based on a function of engine torque. A desired RPM of the engine is calculated based on a measured engine RPM and a reference torque of the engine. A desired area is calculated based on the desired manifold absolute pressure. The desired area is implemented into the controller to control torque output of the engine. 
     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 flowchart illustrating prior art steps of performing torque control; 
         FIG. 1A  is an illustration of manifold absolute pressure as a function of time for engines having torque control according to prior art. 
         FIG. 2  is a functional block diagram of an engine control system that improves torque control accuracy according to the present invention; 
         FIG. 3  is a flowchart illustrating steps for controlling engine torque according to a first method of the present invention; 
         FIG. 4  is a flowchart illustrating steps for controlling engine torque according to a second method of the present invention; and 
         FIG. 5  is a flowchart illustrating steps for controlling engine torque according to a third method of the present invention. 
     
    
    
     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 similar elements. 
     Referring now to  FIG. 2 , an engine control system  110  according to the present invention includes a controller  112  and an engine  116 . The engine  116  includes a plurality of cylinders  118  each with one or more intake valves and/or exhaust valves (not shown). The engine  116  further includes a fuel injection system  120  and an ignition system  124 . An electronic throttle controller (ETC)  26  adjusts a throttle area of an intake manifold  28  based upon a position of an accelerator pedal (not shown) and a throttle control algorithm that is executed by the controller  112 . One or more sensors  134  and  132  such as a manifold pressure sensor and/or a manifold air temperature sensor sense pressure and/or air temperature in the intake manifold  128 . The controller  112  receives pedal position information from brake and accelerator pedal position sensors  130  and  140 . An output of the engine  116  is coupled by a torque converter clutch  154  to a transmission  158 . 
     Referring now to  FIGS. 2 and 3 , steps for controlling engine torque according to a first method are shown generally at  170 . The torque control method  170  includes similar steps as described with respect to the torque control method  10 . In the first method, a desired MAP is calculated in step  180  during torque control. In step  180 , the controller  112  utilizes the following equations.
 
 P   des   =F   P   −1 ( T   ref   ,R,S,D,AF,OT ,Ω)  (6) 
 
 T=η   of *η Ω *( T   w   +T   ot )  (7) 
 
 T   w   =a   P   *P   des   +a   R   *R+a   S   *S+a   S     2     *S   2   (8) 
 
Equation (6) illustrates desired MAP as an inverse torque model. Equation (7) represents an engine torque model where T w  is the warm up portion. T is a requested torque, η of  is an efficiency of air flow of the intake manifold  128 , η Ω  is an efficiency of the cylinders  118  of the engine  116  and T ot  is an initial torque. From equation (7), all variables are known except T w . The controller  112  solves for T w  and implements the result into equation (8). In equation (8), P des  or desired MAP is calculated.
 
     Once the controller  112  has calculated the desired MAP, the compressible flow equation is utilized in step  224  to calculate the desired area using P des  rather than the measured P. Or more specifically, 
               A   des     =         APC   des     *   R   *         R   gas     *   T           15   *   B   *   Φ   ⁢           ⁢     (       P   des     B     )                 (   9   )             
 
Desired MAP control estimation utilizing a calculated MAP (P des ) enables faster transient response as compared to implementing a measured P during torque control. Control then loops to step  14 .
 
     With reference now to  FIG. 4 , steps for controlling engine torque according to a second method are shown generally at  230 . The torque control method  230  uses an open loop multiplier (OLM) and includes similar steps as described with respect to the torque control method  10 . In the second method, a desired RPM is calculated in step  234  during torque control. In step  234 , control utilizes the following equations: 
               APC   des     =     k   *   η   ⁢           ⁢     (       P   des     ,     R   des       )     *     P   des               (   10   )               η   =       a   0     +       a   1     *   R     +       a   2     *     R   2       +       a   3     *   P     +       a   4     *     P   2                 (   11   )               η   =         APC   des       k   *     P   des         =       a   0     +       a   1     *     R   des       +       a   2     *     R   des   2       +       a   3     *     P   des       +       a   4     *     P   des   2                   (   12   )                 R   des     =     f   ⁢           ⁢     (       APC   des     ,     P   des     ,     a   1       )               (   13   )                 R   des     =     R   *   OLM             (   14   )               OLM   =       f   ⁢           ⁢     (       APC   des     ,     P   des     ,     a   1       )       =     f   ⁢           ⁢     (       T   ref     ,   R     )                 (   15   )             
 
Air per cylinder (APC) is proportional to volumetric efficiency (η) and manifold pressure (P). Accordingly, equation (10) represents a desired air per cylinder (APC) as a function of volumetric efficiency (η) and desired manifold pressure (P des ) where k is a constant.
 
     In equation (11), volumetric efficiency (η) is a function of RPM (R) and manifold pressure (P). Therefore, utilizing equations (10) and (11), efficiency (η) may be characterized by equation (12). As a result and as shown in equation (13), desired RPM (R des ) is a function of desired air per cylinder (APC des ), desired manifold pressure (P des ) and coefficients a i . The function as shown in equation (13), however, may be difficult to calculate. Consequently, for some applications, the desired RPM calculation may be replaced by an OLM representing numeric approximation of the desired RPM. The desired RPM and related OLM are characterized by equations (14) and (15). 
     Once the controller  112  has calculated desired RPM, the compressible flow equation is utilized in step  244  to calculate the desired area using the calculated desired RPM R des  rather than the measured R. Or more specifically, 
               A   des     =         APC   des     *     R   des     *         R   gas     *   T           15   *   B   *   Φ   ⁢           ⁢     (     P   B     )                 (   16   )             
 
Desired MAP control estimation utilizing a calculated RPM enables faster transient response as compared to implementing a measured RPM during torque control. It is noted that a measured manifold pressure (P) is used in torque control method  230 . Control then loops back to step  14 .
 
     Referring now to  FIGS. 2 and 5 , steps for controlling engine torque according to a third method are shown generally at  240 . The torque control method  240  includes similar steps as described with respect to the torque control method  10 . In the third method, both a desired MAP (P des ) and a desired RPM (R des ) are calculated in steps  180  and  234 , respectively, during torque control. The values of P des  and R des  are obtained utilizing the equations set forth with respect to torque control method  170  and  230  above. 
     The compressible flow equation is again utilized in step  264 . For this method however, both P des  and R des  are each implemented rather than a measured manifold pressure (P) and measured RPM (R). The compressible flow equation may be represented by the following equation. 
               A   des     =         APC   des     *     R   des     *         R   gas     *   T           15   *   B   *   Φ   ⁢           ⁢     (       P   des     B     )                 (   17   )             
 
Desired MAP and RPM control estimation utilizing a calculated MAP and a calculated RPM enables faster transient response as compared to implementing a measured P and a measured R during torque control. Control then loops to step  14 .
 
     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. In particular, the equations set forth herein with respect to torque control are merely exemplary. Accordingly, variations to these equations may be implemented while reaching similar results and are considered within the scope of this invention. 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.