Abstract:
A method of torque-based control for an internal combustion engine may include determining a desired airflow rate into an intake manifold of the internal combustion engine during an engine start condition, determining a torque limit for a torque-based engine control module based on the desired airflow rate, and regulating engine torque based on the determined torque limit.

Description:
FIELD 
     The present disclosure relates to engine control systems, and more particularly to torque-based engine control systems. 
     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 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. 
     Torque-based engine control systems may regulate engine torque output levels during engine operation. Engine starting may be controlled based on a desired torque level. A desired throttle area for engine starting may be calibrated in terms of the desired torque level. Alternately, a throttle area may be directly calibrated for engine starting conditions. Control of throttle position ultimately controls airflow into the engine. 
     SUMMARY 
     Accordingly, a method of torque-based control for an internal combustion engine may include determining a desired airflow rate into an intake manifold of the internal combustion engine during an engine start condition, determining a torque limit for a torque-based engine control module based on the desired airflow rate, and regulating engine torque based on the determined torque limit. 
     The method may further include calculating the torque limit. The torque limit may be used as a minimum torque value for regulation of the engine torque. 
     An engine control module may include an engine start module, an airflow-to-torque determination module, and a system torque control module. The engine start module may determine a first desired airflow rate into an intake manifold of an internal combustion engine during an engine start condition. The airflow-to-torque determination module may be in communication with the engine start module to determine a torque limit based on the first desired airflow rate. The system torque control module may be in communication with the airflow-to-torque determination module to regulate engine torque based on the determined torque limit. 
     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 schematic illustration of a vehicle according to the present disclosure; 
         FIG. 2  is a control block diagram of the control module shown in  FIG. 1 ; and 
         FIG. 3  is a flow diagram illustrating steps for determining torque-based engine control according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, 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 vehicle  10  is schematically illustrated. Vehicle  10  may include an engine  12  in communication with an intake system  14 , a fuel system  16 , and an ignition system  18 . Intake system  14  may include an intake manifold  20  and a throttle  22 . Throttle  22  may control an airflow into engine  12 . Fuel system  16  may control a fuel flow into engine  12  and ignition system  18  may ignite the air/fuel mixture provided to engine  12  by intake system  14  and fuel system  16 . 
     Vehicle  10  may further include an accelerator pedal  24 , a control module  26 , and an electronic throttle control (ETC)  28 . Accelerator pedal  24  may be in communication with an accelerator pedal sensor  30 . Accelerator pedal sensor  30  may be in communication with control module  26  and may provide a signal indicative of accelerator pedal position. 
     Control module  26  may be in communication with ETC  28  and may provide a signal indicative of the position of accelerator pedal  24  to ETC  28 . ETC  28  may be in communication with throttle  22  and may control operation thereof based on the accelerator pedal position. An intake air temperature (IAT) sensor  32 , an engine coolant temperature sensor  33 , a manifold absolute pressure sensor  35  and a barometric pressure sensor  37 , may be in communication with control module  26  and may provide signals thereto indicative of an intake air temperature, a coolant temperature, a manifold absolute pressure (MAP), and a barometric pressure (P BARO ), respectively. 
     Control module  26  may provide a torque-based control of engine  12 . With reference to  FIG. 2 , control module  26  may include an engine start module  34 , an airflow-to-torque determination module  36 , a system torque control module  38 , a torque-to-airflow determination module  40  (which may generally include the inverse solution of airflow-to-torque determination module  36 ), and a throttle position determination module  42 . Engine start module  34  may be in communication with airflow-to-torque determination module  36  and may provide a signal thereto indicative of an initial desired airflow value (MAF DES     —     i ) for an engine start condition. Engine start module  34  may determine MAF DES     —     i  based on a series of parameters including engine coolant temperature, engine run time, and barometric pressure, as discussed below. Engine start module  34  may determine MAF DES     —     i  at predetermined time steps throughout engine cranking at startup. When engine  12  transitions from cranking to idle, engine start module  34  may provide a signal to airflow-to-torque determination module  36  indicative of a current MAF DES     —     i . 
     Airflow-to-torque determination module  36  may be in communication with system torque control module  38  and may provide a signal thereto indicative of a minimum torque level (T MIN ) for engine  12  based on MAF DES     —     i  from engine start module  34 . Airflow-to-torque determination module  36  may determine the T MIN  value corresponding to MAF DES     —     i  through a calculation. MAF DES     —     i  may be converted to an air-per-cylinder (APC) value and passed to the calculation. The calculation may include a torque model, such as an APC torque model as disclosed in U.S. Provisional Patent Application Ser. No. 60/861,494, the disclosure of which is expressly incorporated herein by reference. 
     T MIN  provided to system torque control module  38  may be used as a minimum torque level for operation of engine  12  during vehicle operation. More specifically, T MIN  may be used for torque regulation of engine  12 . System torque control module  38  may set a minimum torque level for engine idle control. System torque control module  38  may further include a torque arbitration system, such as the system disclosed in U.S. patent application Ser. No. 11/712,597, the disclosure of which is expressly incorporated herein by reference. System torque control module  38  may generally control vehicle torque requests based on the minimum torque level needed to prevent undesirable conditions such as engine stall. 
     An adjusted torque level (T ADJ ) from system torque control module  38  may then be passed to torque-to-airflow determination module  40 . T ADJ  provided by system torque control module  38  may be generally similar to T MIN  provided by airflow-to-torque determination module  36 . However, system torque control module  38  may additionally account for driver torque requests. For example, the position of accelerator pedal  24  may be provided to system torque control module  38  by accelerator pedal sensor  30 . 
     During the determination of MAF DES     —     i  from engine start module  34 , accelerator pedal position may be initialized to a zero position corresponding to a non-actuated accelerator pedal  24 . Initialization of accelerator pedal position may generally provide for elimination of a “dead pedal” condition. A “dead pedal” condition may generally be characterized as a displacement of accelerator pedal  24  without a corresponding increase in throttle opening. As such, the zero pedal position may correspond to a position of throttle  22  corresponding to T ADJ  with accelerator pedal  24  in a non-actuated position. Therefore, if a user steps into accelerator pedal  24 , a torque request is generated at system torque control module  38 . This request is passed on to torque-to-airflow determination module  40  where a final desired engine airflow (MAF DES     —     f ) is determined. 
     MAF DES     —     f  may be determined in a manner similar to that described above regarding the T MIN  determination at airflow-to-torque determination module  36 . The calculation may include a torque model, such as an inverse APC torque model as disclosed in U.S. Provisional Patent Application Ser. No. 60/861,494. As indicated above, the MAF DES     —     f  determined by torque-to-airflow determination module  40  may generally be equal to MAF DES     —     j  from engine start module  34  adjusted by any further torque requests from system torque control module  38 . MAF DES     —     f  may then be used to adjust a throttle area for engine starting. 
     More specifically, torque-to-airflow determination module  40  may provide a signal to throttle position determination module  42  indicative of MAF DES     —     f . Throttle position determination module  42  may determine the desired throttle area (A THRDES ) associated with MAF DES     —     f . A THRDES  may be determined based on a flow density associated with atmospheric conditions and MAF DES     —     f . As such, varying atmospheric conditions are automatically accounted for. A THRDES  may be determined as follows: 
               A   THRDES     =         MAF     DES   ⁢   _   ⁢   f       *       R   *   IAT             P   BARO     *     Φ   ⁡     (     MAP     P   BARO       )                 
where R is the universal gas constant and 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                     
P R  is generally determined as the ratio between MAP and P BARO . P BARO  can be directly measured with barometric pressure sensor  37  or may be calculated using other known parameters. 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             
where γ is equal to the ratio of specific heat for air and range from about 1.3 to about 1.4. As such, the present disclosure provides for accurate torque control under varying environmental conditions by consideration the pressure ratio P R .
 
       FIG. 3  depicts the airflow-based crank throttle control system control logic generally at  100 . Control logic  100  may generally determine an airflow rate needed to provide a stable start-up and idle condition for engine  12 . Control logic  100  may use the determined airflow value to set minimum torque levels for engine operation, as well as a throttle area for engine start. Control logic  100  may begin at determination block  102  where engine operating parameters are determined. Engine operating parameters may include engine coolant temperature, engine run time, and barometric pressure. Control logic  100  may then proceed to determination block  104  where MAF DES     —     i  is determined. 
     MAF DES     —     i  may be determined based on a predetermined lookup table as a function of the determined engine operating parameters. MAF DES     —     i  may generally be associated with an airflow that is desirable for an engine cranking/start condition. Once MAF DES     —     i  is determined, control logic  100  proceeds to determination block  106 , where a torque value is determined. The torque value may be determined based on MAF DES     —     i . The torque value may be determined as indicated above regarding airflow-to-torque determination module  36 . Control logic  100  may then proceed to control block  108  where system torque minimums (T MIN ) may be set. T MIN  may be set as indicated above regarding system torque control module  38 . 
     Control block  108  may additionally account for additional torque requests from a user, such as accelerator pedal actuation. Control block  108  may modify the torque value provided by determination block  106  based on these additional user torque requests to an adjusted torque (T ADJ ). The T ADJ  request may be provided to determination block  110  where a final desired airflow (MAF DES     —     f ) is determined. 
     Determination block  110  may determine MAF DES     —     f  based on the T ADJ  provided by control block  108  using an inverse torque calculation, as indicated above regarding torque-to-airflow determination module  40 . Control logic  100  may then proceed to determination block  112  where a desired throttle area (A THRDES ) is determined. 
     MAF DES     —     f  may be used to determine A THRDES , as indicated above regarding throttle position determination module  42 . As indicated above, A THRDES  may account for intake air temperature, barometric pressure relative to MAP, as well as MAF DES     —     f . 
     Control logic  100  may then proceed to decision block  114  where engine operation is evaluated. If engine  12  is still in a starting mode, control logic  100  returns to determination block  102  and continues as indicated above. Engine  12  may transition to an idle condition after completion of the starting mode. If engine  12  is no longer in the starting mode (i.e., engine  12  has transitioned to the idle condition), control logic  100  may terminate. The last values generated for system torque minimums, desired airflow, and desired throttle area by determination blocks  106 ,  110 , and  112 , respectively may be used for transition from engine starting mode to engine idle. 
     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 and the specification.