Patent Publication Number: US-8983753-B2

Title: Combustion setpoint control systems and methods

Description:
FIELD 
     The present disclosure relates to internal combustion engines and more particularly to engine actuator control systems and methods. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Air is drawn into an engine through an intake manifold. A throttle valve controls airflow into the engine. The air mixes with fuel from one or more fuel injectors to form an air/fuel mixture. The air/fuel mixture is combusted within one or more cylinders of the engine. Combustion of the air/fuel mixture may be initiated by, for example, injection of the fuel or spark provided by a spark plug. 
     Combustion of the air/fuel mixture produces torque and exhaust gas. Torque is generated via heat release and expansion during combustion of the air/fuel mixture. The engine transfers torque to a transmission via a crankshaft, and the transmission transfers torque to one or more wheels via a driveline. The exhaust gas is expelled from the cylinders to an exhaust system. 
     An engine control module (ECM) controls the torque output of the engine. The ECM may control the torque output of the engine based on driver inputs and/or other inputs. The driver inputs may include, for example, accelerator pedal position, brake pedal position, and/or one or more other suitable driver inputs. The other inputs may include, for example, cylinder pressure measured using a cylinder pressure sensor, one or more variables determined based on the measured cylinder pressure, and/or one or more other suitable values. 
     SUMMARY 
     A system for a vehicle, includes first, second, and third setpoint generation modules, a scaling module, and an actuator control module. The first setpoint generation module generates a first target value for an combustion parameter of an engine based on a predetermined value of a combustion stability of the engine. The second setpoint generation module generates a second target value for the combustion parameter based on a predetermined fuel efficiency. The scaling module generates a scaled value for the combustion parameter based on the first and second target values and a scalar value. The third setpoint generation module generates a third target value for the combustion parameter based on the first target value and the scaled value. The actuator control module controls at least one engine actuator associated with the combustion parameter based on the third target value. 
     A method for a vehicle, includes: generating a first target value for an combustion parameter of an engine based on a predetermined value of a combustion stability of the engine; generating a second target value for the combustion parameter based on a predetermined fuel efficiency; generating a scaled value for the combustion parameter based on the first and second target values and a scalar value; generating a third target value for the combustion parameter based on the first target value and the scaled value; and controlling at least one engine actuator associated with the combustion parameter based on the third target value. 
     Further 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 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 functional block diagram of an example engine system according to the present disclosure; 
         FIG. 2  is a functional block diagram of an example setpoint set generation module according to the present disclosure; and 
         FIG. 3  is a functional block diagram of an example method of controlling engine actuators according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely illustrative 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 phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     As used herein, the term module may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC); an electronic circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor (shared, dedicated, or group) that executes code; other suitable components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip. The term module may include memory (shared, dedicated, or group) that stores code executed by the processor. 
     The term code, as used above, may include software, firmware, and/or microcode, and may refer to programs, routines, functions, classes, and/or objects. The term shared, as used above, means that some or all code from multiple modules may be executed using a single (shared) processor. In addition, some or all code from multiple modules may be stored by a single (shared) memory. The term group, as used above, means that some or all code from a single module may be executed using a group of processors. In addition, some or all code from a single module may be stored using a group of memories. 
     The apparatuses and methods described herein may be implemented by one or more computer programs executed by one or more processors. The computer programs include processor-executable instructions that are stored on a non-transitory tangible computer readable medium. The computer programs may also include stored data. Non-limiting examples of the non-transitory tangible computer readable medium are nonvolatile memory, magnetic storage, and optical storage. 
     An engine control module (ECM) controls engine actuators based on a set of combustion setpoints or target values. Example combustion setpoints include, but are not limited to, amount and timing of fuel injection for a combustion event, spark timing for the combustion event, air to fuel ratio for the combustion event, amounts of oxygen and exhaust gas within an intake manifold, intake manifold pressure, cam phaser position(s), and throttle opening. 
     The ECM may generate the set of setpoints at a given time using a first predetermined relationship or a second predetermined relationship. The first predetermined relationship (e.g., function or mapping) is calibrated based a desired level of combustion stability. The second predetermined relationship (e.g., function or mapping) is calibrated based on a desired level of fuel efficiency. The ECM may select which one of the predetermined relationships to use, for example, based on input from a user. 
     The ECM of the present disclosure generates two sets of setpoints at a given time: a first set of setpoints generated using the first predetermined relationship and a second set of setpoints generated using the second predetermined relationship. The ECM generates a set with differences between the setpoints of the first and second sets, respectively, and scales the differences. The ECM selectively adjusts one or more of the setpoints of the first set based on the scaled differences, respectively, to produce a final set of setpoints. 
     The final set of setpoints provides a balance between the desired level of combustion stability and the desired level of fuel efficiency. More specifically, the final set may provide combustion that is less stable relative to the first set but more stable relative to the second set. Additionally, the final set will provide an increase in fuel efficiency relative to the first set and a decrease in fuel efficiency relative to the second set. The ECM controls the engine actuators based on the setpoints of the final set. 
     Referring now to  FIG. 1 , a functional block diagram of an example engine system  100  is presented. The engine system  100  includes an engine  102  that combusts an air/fuel mixture to produce drive torque for a vehicle. While the engine  102  will be discussed as a spark ignition direct injection (SIDI) engine, the engine  102  may include another suitable type of engine, such as a homogenous charge compression ignition (HCCI) engine. One or more electric motors and/or motor generator units (MGUs) may be used with the engine  102 . 
     Air is drawn into an intake manifold  106  through a throttle valve  108 . The throttle valve  108  varies airflow into the intake manifold  106 . For example only, the throttle valve  108  may include a butterfly valve having a rotatable blade. An engine control module (ECM)  110  controls a throttle actuator module  112  (e.g., an electronic throttle controller or ETC), and the throttle actuator module  112  controls opening of the throttle valve  108 . 
     Air from the intake manifold  106  is drawn into cylinders of the engine  102 . While the engine  102  may include more than one cylinder, only a single representative cylinder  114  is shown. Air from the intake manifold  106  is drawn into the cylinder  114  through one or more intake valves, such as intake valve  118 . 
     The ECM  110  controls a fuel actuator module  120 , and the fuel actuator module  120  controls opening of a fuel injector  121 . The fuel injector  121  injects fuel into the cylinder  114 . Fuel is provided to the fuel injector  121  by a low pressure fuel pump and a high pressure fuel pump (not shown). The low pressure fuel pump draws fuel from a fuel tank and provides fuel at low pressures to the high pressure fuel pump. The high pressure fuel pump selectively further pressurizes the fuel, for example, for direct injection into the cylinders of the engine  102 . 
     The injected fuel mixes with air and creates an air/fuel mixture in the cylinder  114 . A piston (not shown) within the cylinder  114  compresses the air/fuel mixture. Based upon a signal from the ECM  110 , a spark actuator module  122  energizes a spark plug  124  in the cylinder  114 . Spark generated by the spark plug  124  ignites the air/fuel mixture. The timing of the spark may be specified relative to the time when the piston is at its topmost position, referred to as top dead center (TDC). In various types of engines, such as diesel engines, the spark plug  124  and the spark actuator module  122  may be omitted. 
     The combustion of the air/fuel mixture drives the piston down, and the piston drives rotation of a crankshaft (not shown). After reaching a bottom most position, referred to as bottom dead center (BDC), the piston begins moving up again and expels the byproducts of combustion through one or more exhaust valves, such as exhaust valve  126 . The byproducts of combustion are exhausted from the vehicle via an exhaust system  127 . 
     One combustion cycle, from the standpoint of the cylinder  114 , may include two revolutions of the crankshaft (i.e., 720° of crankshaft rotation) in various implementations. One combustion cycle for the cylinder  114  may include four phases: an intake phase; a compression phase; an expansion phase; and an exhaust phase. For example only, the piston lowers toward the BDC position and air is drawn into the cylinder  114  during the intake phase. The piston rises toward the TDC position and compresses the contents of the cylinder  114  during the compression phase. Fuel may be injected into the cylinder  114  during the compression phase. Fuel injection may also occur during the expansion phase. Combustion drives the piston toward the BDC position during the expansion phase. The piston rises toward the TDC position to expel the resulting exhaust gas from the cylinder  114  during the exhaust phase. One engine cycle may refer to the period associated with each of the cylinders undergoing one complete combustion cycle. 
     The intake valve  118  may be controlled by an intake camshaft  128 , while the exhaust valve  126  may be controlled by an exhaust camshaft  130 . In various implementations, multiple intake camshafts may control multiple intake valves per cylinder and/or may control the intake valves of multiple banks of cylinders. Similarly, multiple exhaust camshafts may control multiple exhaust valves per cylinder and/or may control exhaust valves for multiple banks of cylinders. The time at which the intake valve  118  is opened may be varied with respect to the TDC position by an intake cam phaser  132 . The time at which the exhaust valve  126  is opened may be varied with respect to the TDC position by an exhaust cam phaser  134 . A phaser actuator module  136  may control the intake and exhaust cam phasers  132  and  134  based on signals from the ECM  110 . Fuel injection timing may also be specified relative to the position of the piston. 
     A crankshaft position sensor  142  monitors rotation of the crankshaft and generates a crankshaft position signal  146  based on the rotation of the crankshaft. For example only, the crankshaft position sensor  142  may include a variable reluctance (VR) sensor or another suitable type of crankshaft position sensor. The crankshaft position signal  146  may include a pulse train. An N-toothed wheel (not shown) rotates with the crankshaft. A pulse may be generated in the crankshaft position signal  146  as a tooth of the N-toothed wheel passes the crankshaft position sensor  142 . Accordingly, each pulse corresponds to an angular rotation of the crankshaft by an amount approximately equal to 360° divided by N teeth. The N-toothed wheel may also include a gap of one or more missing teeth, and the gap may be used as an indicator of one complete revolution of the crankshaft (i.e., 360° of crankshaft rotation). 
     One or more other sensors  158  may also be provided. For example, the other sensors  158  may include a mass air flowrate (MAF) sensor, a manifold absolute pressure (MAP) sensor, an intake air temperature (IAT) sensor, a coolant temperature sensor, an oil temperature sensor, one or more camshaft position sensors, one or more cylinder pressure sensors, and/or one or more other suitable sensors. 
     The ECM  110  includes a setpoint generation module  180  that generates a first set of setpoints for controlling engine actuators to achieve a desired combustion stability under the operating conditions. The setpoint generation module  180  also generates a second set of setpoints for controlling the engine actuators to achieve a desired fuel efficiency under the operating conditions. Controlling the engine actuators based on the first set of setpoints may provide more stable combustion relative to the second set of setpoints. Controlling the engine actuators based on the second set of setpoints may provide an increase in fuel efficiency relative to the first set of setpoints. 
     The setpoint generation module  180  determines a set of differences between setpoints of the first and second sets, respectively. The setpoint generation module  180  selectively scales the differences and selectively adjusts one or more of the setpoints of the first set of setpoints based on the scaled differences, respectively. The selectively adjusted set of setpoints will be referred to as a final setpoint set, and the final setpoint set may provide a balance between the desired combustion stability and the desired fuel efficiency. 
     An actuator control module  190  may control the engine actuators based on the final set of setpoints. For example only, the actuator control module  190  may control fuel injection (e.g., timing, amount, number of injections, amount of each injection, etc.), throttle opening, spark timing, intake and/or exhaust valve lift and/or duration, boost of a boost device (e.g., a turbocharger), exhaust gas recirculation (EGR) opening, and/or one or more other suitable engine actuators based on the fourth set of setpoints. 
     Referring now to  FIG. 2 , a functional block diagram of an example implementation of the setpoint generation module  180  is presented. A first setpoint set generation module  204  generates a first set of setpoints (first setpoint set)  208  based on an engine speed  212 , an engine temperature  216 , and an engine load  220  to achieve a desired (e.g., best) value of a combustion stability  224  under the operating conditions. For example only, the first setpoint set generation module  204  may generate the first setpoint set  208  using a function or a mapping that relates the engine speed  212 , the engine temperature  216 , and the engine load  220  to the setpoints of the first setpoint set  208 . 
     Each set of setpoints, such as the first setpoint set  208 , includes one or more target (or setpoint) values for one or more combustion parameters, respectively, for a next combustion event of the cylinder  114 . For example only, a set of setpoints may include a first mass of fuel to inject, a first time (e.g., crankshaft angle) to begin injecting the first mass of fuel, a second mass of fuel to inject, a second time to begin injecting the second mass of fuel, and a ratio for splitting an amount of fuel into multiple pulses. The set of setpoints may additionally or alternatively include third and fourth times at which the spark plug  124  should be energized, an air fuel ratio, a ratio of oxygen to recirculated exhaust gas within the intake manifold  106 , and/or intake and/or exhaust camshaft phaser angles. The set of setpoints may additionally or alternatively include intake manifold pressure or intake manifold vacuum, a crankshaft angle (CA) at which 50 percent of injected fuel should be burned within the cylinder  114  (referred to as CA50), and/or one or more other target values for one or more other combustion parameters, respectively. 
     The engine speed  212  may be generated, for example, based on the crankshaft position signal  146  generated by the crankshaft position sensor  142 . For example only, the engine speed  212  may be generated based on a period between the rising edges of two pulses in the crankshaft position signal  146  and a rotational distance between the rising edges of the two pulses where the rising edges are separated by at least 90 degrees (of crankshaft rotation). The engine temperature  216  may be generated, for example, based on engine coolant temperature, engine oil temperature, an air temperature (e.g., ambient or IAT), and/or one or more other suitable temperatures. The engine load  220  may be generated, for example, based on one or more engine airflow parameters, such as a ratio of the MAF to a maximum MAF. Additionally or alternatively, the engine load  220  may be generated, for example, based on one or more engine torque parameters, such as a brake torque, a net torque, and/or an indicated torque. Additionally or alternatively, the engine load  220  may be generated, for example, based on one or more engine effective pressure parameters, such as a brake mean effective pressure (BMEP), a net mean effective pressure (NMEP), and/or an indicated mean effective pressure (IMEP). The combustion stability  224  may be generated, for example, based on an IMEP parameter, such as a coefficient of variation (COV) of IMEP, a change in IMEP, or another suitable value indicative of combustion stability. 
     A second setpoint set generation module  228  generates a second set of setpoints (second setpoint set)  232  based on the engine speed  212 , the engine temperature  216 , and the engine load  220  to achieve a desired (e.g., best) fuel efficiency for the operating conditions. For example only, the second setpoint set generation module  228  may generate the second setpoint set  232  using a function or a mapping that relates the engine speed  212 , the engine temperature  216 , and the engine load  220  to the setpoints of the second setpoint set  232 . The second setpoint set  232  includes one or more target values for the one or more combustion parameters, respectively, for which target values are also included in the first setpoint set  208 . In this manner, the first and second setpoint sets  208  and  232  each include a target value for each of the given combustion parameters. One or more of the target values in the second setpoint set  232  may be different than the corresponding target values in the first setpoint set  208 . 
     Each set of setpoints (e.g., the first setpoint set  208  and the second setpoint set  232 ) may be embodied as a vector matrix (i.e., a matrix with only 1 row or column) in various implementations. An example vector matrix illustrating a set of setpoints, such as the first setpoint set  208  or the second setpoint set  232 , is provided below 
                   Parameter   ⁢           ⁢   1   ⁢           ⁢   Setpoint               Parameter   ⁢           ⁢   2   ⁢           ⁢   Setpoint             …             Parameter   ⁢           ⁢   N   ⁢           ⁢   Setpoint               
where Parameter N Setpoint is the target value for the N-th combustion parameter in the vector matrix and N is an integer greater than zero.
 
     A difference determination module  236  generates a set of differences (difference set)  240  based on the first and second setpoint sets  208  and  232 . More specifically, the difference determination module  236  generates the difference set  240  based on differences between the corresponding target values of the first and second setpoint sets  208  and  232 , respectively. For example only, the difference determination module  236  may set the difference set  240  equal to the first setpoint set  208  (in matrix form) minus the second setpoint set  232  (in matrix form). An example vector matrix illustrating the entries of the difference set  240  and how the entries of difference set  240  may be calculated is provided below. 
     
       
         
           
             
               
                 
                   
                     Parameter 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Setpoint 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     from 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     First 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Setpoint 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Set 
                   
                   - 
                 
               
             
             
               
                 
                   Parameter 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   Setpoint 
                   ⁢ 
                   
                       
                   
                   ⁢ 
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                   ⁢ 
                   
                       
                   
                   ⁢ 
                   Second 
                   ⁢ 
                   
                       
                   
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                   Setpoint 
                   ⁢ 
                   
                       
                   
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                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                     ⁢ 
                     
                         
                     
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                     Setpoint 
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                     ⁢ 
                     
                         
                     
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                     First 
                     ⁢ 
                     
                         
                     
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                     Set 
                   
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                   Parameter 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                   ⁢ 
                   
                       
                   
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                   Setpoint 
                   ⁢ 
                   
                       
                   
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                   ⁢ 
                   
                       
                   
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                     Parameter 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     N 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Setpoint 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     from 
                     ⁢ 
                     
                         
                     
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                     First 
                     ⁢ 
                     
                         
                     
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                     Setpoint 
                     ⁢ 
                     
                         
                     
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                     Set 
                   
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                   Parameter 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   N 
                   ⁢ 
                   
                       
                   
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                   Setpoint 
                   ⁢ 
                   
                       
                   
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                   ⁢ 
                   
                       
                   
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                   Second 
                   ⁢ 
                   
                       
                   
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                   Setpoint 
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     A scaling module  244  generates a scaled set of differences (scaled difference set)  248  based on the difference set  240  and a setpoint scalar  252 . For example only, the scaling module  244  may set the scaled setpoint set  248  equal to the product of the difference set  240  (in matrix form) and the setpoint scalar  252  (e.g., a 1×1 matrix). An example vector matrix illustrating the entries of the scaled difference set  248  and how the entries of the scaled difference set  248  may be calculated is provided below. 
                   Scalar   *     (       Parameter   ⁢           ⁢   1   ⁢           ⁢   Setpoint   ⁢           ⁢   from   ⁢           ⁢   First   ⁢           ⁢   Setpoint   ⁢           ⁢   Set     -     Parameter   ⁢           ⁢   1                       Setpoint   ⁢           ⁢   from   ⁢           ⁢   Second   ⁢           ⁢   Setpoint   ⁢           ⁢   Set     )               Scalar   *     (       Parameter   ⁢           ⁢   2   ⁢           ⁢   Setpoint   ⁢           ⁢   from   ⁢           ⁢   First   ⁢           ⁢   Setpoint   ⁢           ⁢   Set     -     Parameter   ⁢           ⁢   2                       Setpoint   ⁢           ⁢   from   ⁢           ⁢   Second   ⁢           ⁢   Setpoint   ⁢           ⁢   Set     )             …             Scalar   *     (       Parameter   ⁢           ⁢   N   ⁢           ⁢   Setpoint   ⁢           ⁢   from   ⁢           ⁢   First   ⁢           ⁢   Setpoint   ⁢           ⁢   Set     -   Parameter                     N   ⁢           ⁢   Setpoint   ⁢           ⁢   from   ⁢           ⁢   Second   ⁢           ⁢   Setpoint   ⁢           ⁢   Set     )               
where Scalar is the setpoint scalar  252 . The setpoint scalar  252  is discussed in further detail below.
 
     A final setpoint set generation module  256  generates a final setpoint set  260  based on the first setpoint set  208  and the scaled difference set  248 . More specifically, the final setpoint set generation module  256  generates the final setpoint set  260  based on differences between the corresponding target values of the first setpoint set  208  and the scaled difference set  248 , respectively. For example only, the final setpoint set generation module  256  may set the final setpoint set  260  equal to the first setpoint set  208  (in matrix form) minus the scaled difference set  248  (in matrix form). An example vector matrix illustrating the entries of the final setpoint set  260  and how the entries of the final setpoint set  260  may be calculated is provided below. 
     
       
         
           
             
               
                 
                   
                     Parameter 
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                     1 
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                     First 
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                     Scalar 
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                         Parameter 
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                         Setpoint 
                       
                     
                   
                 
               
             
             
               
                 
                   
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     The actuator control module  190  controls the engine actuators based on the final setpoint set  260 . For example only, the actuator control module  190  may control the fuel actuator module  120  based on one or more setpoints of the final setpoint set  260 . For another example only, the actuator control module  190  may control the spark actuator module  122  and/or the throttle actuator module  112  based on one or more setpoints of the final setpoint set  260 . In various implementations, one or more offsets, scalars, and/or other adjustments may be applied to one or more of the setpoints of the final setpoint set  260  before use by the actuator control module  190 . 
     A setpoint scalar generation module  264  generates the setpoint scalar  252  based on the engine speed  212 , the engine load  220 , and the combustion stability  224 . The scaling module  244  generates the setpoint scalar  252  further based on a learned scalar  268 . For example only, the setpoint scalar generation module  264  may generate the setpoint scalar  252  using a function or a mapping that relates the engine speed  212 , the engine load  220 , the combustion stability  224 , and the learned scalar  268 . 
     A scalar learning module  272  generates the learned scalar  268 . The scalar learning module  272  may set the learned scalar  268  to a predetermined value when an ignition system is turned on. The predetermined value may be set based on the desired value of the combustion stability  224  or another suitable value of the combustion stability  224 . 
     When a learn signal  276  is in an active state, the scalar learning module  272  may selectively adjust (i.e., increase and/or decrease) the learned scalar  268  based on the engine speed  212 , the engine temperature  216 , the engine load  220 , and/or the combustion stability  224 . For example only, the scalar learning module  272  may adjust the learned scalar  268  based on the engine speed  212 , the engine temperature  216 , the engine load  220 , and/or the combustion stability  224  to increase the fuel efficiency. The scalar learning module  272  may begin adjusting the learned scalar  268  from the predetermined value when the learn signal  276  is transitioned from an inactive state to the active state. The scalar learning module  272  may limit the learned scalar  268  to a scalar limit value  280 . 
     A limit generation module  282  may generate the scalar limit value  280  based on the engine speed  212 , the engine temperature  216 , and/or the engine load  220 . For example only, the limit generation module  282  may generate the scalar limit value  280  using a function or a mapping that relates the engine speed  212 , the engine temperature  216 , and the engine load  220  to the scalar limit value  280 . The scalar limit value  280  may be based on the desired value of the combustion stability  224  or another suitable value of the combustion stability  224 . 
     When an unlearn signal  284  is in an active state, the scalar learning module  272  may adjust the learned scalar  268  toward the predetermined value. The scalar learning module  272  may adjust the learned scalar  268  toward the predetermined value at a predetermined rate when the unlearn signal  284  is in the active state. After reaching the predetermined value, the scalar learning module  272  may maintain the learned scalar  268  at the predetermined value until the unlearn signal  284  is in the inactive state and the learn signal  276  is in the active state. 
     A triggering module  288  may generate the learn signal  276  and the unlearn signal  284 . The triggering module  288  may generate the learn signal  276  and the unlearn signal  284  based on an engine runtime period  292 , an engine run condition  294 , and an engine run condition period  296 . The engine runtime period  292  may indicate how long (i.e., the period) the engine  102  has been running since a last engine startup event or when the ignition system was last turned on. The engine run condition  294  may include, for example, a changing running condition, a wide open throttle (WOT) running condition, a steady-state (SS) cruising running condition, an idle running condition, and/or one or more other suitable engine running conditions. The engine run condition period  296  may indicate how long (i.e., the period) the engine run condition  294  has been the same. 
     For example only, the triggering module  288  may selectively set the unlearn signal  284  to the active state when the engine run condition  294  is a predetermined engine run condition and the engine runtime period  292  is greater than a predetermined period. The predetermined engine run condition may be, for example, the WOT running condition. The engine  102  running at the WOT running condition for the predetermined period may clear deposits from the engine  102 . Thus, the scalar learning module  272  may return the learned scalar  268  to the predetermined value for relearning. For another example only, the triggering module  288  may selectively set the learn signal  276  to the active state when the engine run condition  294  is the SS cruising running condition or the idle condition for a predetermined period. 
     Referring now to  FIG. 3 , a flowchart  300  depicting an example method of controlling engine actuators is presented. Control may begin with  304  where control generates the first and second setpoint sets  208  and  232 . The first and second setpoint sets  208  and  232  include corresponding target values for the combustion parameters, respectively. Control generates the first and second setpoint sets  208  and  232  based on the engine speed  212 , the engine temperature  216 , and the engine load  220 . For example only, control may generate the first setpoint set  208  using a first function or mapping that relates the engine speed  212 , the engine temperature  216 , and the engine load  220  to the first setpoint set  208 . Control may generate the second setpoint set  232  using a second, different, function or mapping that relates the engine speed  212 , the engine temperature  216 , and the engine load  220  to the second setpoint set  232 . The first function or mapping may be calibrated based on the desired value of the combustion stability  224 , while the second function or mapping may be calibrated based on the desired value of the fuel efficiency. 
     At  308 , control generates the difference set  240  based on differences between the corresponding target values of the first and second setpoint sets  208  and  232 , respectively. For example only, control may set the difference set  240  (in matrix form) equal to the first setpoint set  208  (in matrix form) minus the second setpoint set  232  (in matrix form). Control generates the scalar limit value  280  at  312 . Control may generate the scalar limit value  280  using a function or a mapping that relates the engine speed  212 , the engine temperature  216 , and the engine load  220  to the scalar limit value  280 . 
     At  316 , control generates the learned scalar  268 . Control may selectively initialize the learned scalar  268  to the predetermined value, which may be set based on the desired level of the combustion stability  224 . Control may selectively adjust the learned scalar  268  during engine operation based on the combustion stability  224 , the engine speed  212 , the engine temperature  216 , and/or the engine load  220 . Control limits the learned scalar  268  to the scalar limit value  280 . 
     Control generates the setpoint scalar  252  at  320  based on the combustion stability  224 , the engine speed  212 , the engine load  220 , and the learned scalar  268 . Control generates the scaled difference set  248  at  324  based on the setpoint scalar  252  and the difference set  240 . For example only, control may set the scaled difference set  248  (in matrix form) to the product of the difference set  240  (in matrix form) and the setpoint scalar  252 . 
     At  328 , control generates the final setpoint set  260 . Control generates the final setpoint set  260  based on the first setpoint set  208  and the scaled difference set  248 . For example only, control may set the final setpoint set  260  (in matrix form) based on the first setpoint set  208  (in matrix form) minus the scaled difference set  248  (in matrix form). Control may set one or more of the target values of the final setpoint set  260  equal to the corresponding target values of the first setpoint set  208  such that the target values of the first setpoint set  208  are not adjusted by the corresponding value of the scaled difference set  248 . Control selectively controls the engine actuators based on the final setpoint set  260  at  332 . 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, 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.