Patent Publication Number: US-2017356376-A1

Title: Engine stop position control system and method

Description:
FIELD 
     The present invention relates to stop-start control systems for automobile powertrains, and more particularly to systems and methods for managing the engine stop position during a stop-start sequence to improve the overall efficiency of the powertrain. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Air is drawn into an engine through an intake manifold. A throttle valve controls airflow into the engine. More specifically, the throttle valve adjusts throttle area, which increases or decreases airflow 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 into the engine cylinders to provide a desired air/fuel mixture to the cylinders and/or to achieve a desired torque output. Increasing the amount of air and fuel provided to the cylinders increases the torque output of the engine. 
     The air/fuel mixture is combusted within one or more cylinders of the engine. In spark-ignition engines, spark initiates combustion of the air/fuel mixture provided to the cylinders. In compression-ignition engines, compression of the air/fuel mixture in the cylinders combusts the air/fuel mixture. Spark timing and airflow are the primary mechanisms for adjusting the torque output of spark-ignition engines, while fuel flow is the primary mechanism for adjusting the torque output of compression-ignition engines. Incomplete, or partial combustion of the air/fuel mixture during engine start may cause the engine to vibrate. 
     During engine shutdown, a rotation direction of a crankshaft in the engine may be reversed before the crankshaft stops. In turn, a piston coupled to the crankshaft may stop near top dead center (TDC) before movement of the piston is reversed. This reversal of piston movement during engine shutdown is referred to as rock back. As the piston rocks back, the piston draws exhaust gas into the cylinder in which the piston is disposed. Exhaust gas is also be drawn into an intake manifold of the engine due to a pressure difference between the intake manifold and the cylinders. When the engine is restarted, exhaust gas flows from the intake manifold to the cylinder, and exhaust gas present within the cylinder may cause the cylinder to misfire which in turn may cause the engine and the passenger compartment to vibrate. 
     An engine control module (ECM) controls the torque output of the engine. Under some circumstances, the ECM shuts down the engine between vehicle startup (e.g., key ON) and vehicle shutdown (e.g., key OFF). The ECM selectively shuts down the engine, for example, to increase fuel efficiency (i.e., reduce fuel consumption). The ECM starts the engine at a later time. 
     While traditional stop-start systems for internal combustion engines are effective, there is room in the art for an improved stop-start system and method that ensures the appropriate amount of air and fuel are supplied to the cylinders for low-vibration engine start. Especially desirable, would be a stop-start system that performs under a wide variety of ambient conditions while reducing engine start vibration. 
     SUMMARY 
     In one embodiment of the present invention, an engine control system for controlling the resting position of at least one piston within a cylinder of an engine of an auto-stop/start vehicle includes an auto-stop/start module that selectively generates an auto-stop command for shutting down an engine while an ignition is in an ON state and that selectively generates an auto-start command for re-starting the engine after the generation of the auto-stop command. The engine control system also includes an actuator control module that, in response to the generation of the auto-stop command and before the generation of the auto-start command: disables a load on the engine, parks exhaust cam phasers and intake cam phasers, disables fuel to the engine, sets a throttle valve opening to a first predetermined throttle opening level, monitors a crankshaft rotational position, determines if a position of a piston is entering a predetermined position based on the crankshaft rotational position, monitors an engine speed, determines if the engine speed is less than a first predetermined engine speed, monitors a barometric pressure, sets a throttle valve opening to a second predetermined throttle opening level, sets a throttle valve opening to a third predetermined throttle opening level after a predetermined time has elapsed from the setting of the second predetermined throttle opening level, determines if an engine speed is less than a second predetermined speed, sets a throttle valve opening to a fourth predetermined throttle opening level when the engine speed is less than the second predetermined speed, and the resting position of the piston is in a predefined piston position range. 
     In another embodiment of the present invention, the actuator control module estimates a remaining degrees of engine rotation when the piston is entering the predetermined position, and the remaining degrees of engine rotation estimation is based on the first predetermined engine speed and the barometric pressure. 
     In another embodiment of the present invention, the actuator control module maintains the throttle valve at first predetermined throttle opening level to further reduce pressure in the intake manifold. 
     In yet another embodiment of the present invention, the actuator control module maintains the throttle valve at a second predetermined throttle opening level to rapidly increase the pressure in the intake manifold. 
     In yet another embodiment of the present invention, the actuator control module maintains the throttle valve at a third predetermined throttle opening level to return the opening position to a position at or slightly above the position associated with an unpowered throttle actuator. 
     In yet another embodiment of the present invention, the actuator control module further comprises sets a predetermined fuel rail pressure. 
     In yet another embodiment of the present invention, the actuator control module further comprises monitors a barometric pressure. 
     In yet another embodiment of the present invention, the actuator control module further comprises estimates degrees of engine rotation before the engine stops rotating based on a speed of the engine, an engine deceleration and the barometric pressure. 
     In yet another embodiment of the present invention, the predetermined position is one of a predefined crankshaft rotational position. 
     In yet another embodiment of the present invention, the second predetermined throttle opening level is configured to raise the air pressure in at least one cylinder to approximately ambient barometric pressure. 
     In yet another embodiment of the present invention, the actuator control module further comprises sets a throttle valve opening to a fourth predetermined throttle opening level when the engine speed is about zero. 
     In a further embodiment of the present invention, an engine control method for controlling the resting position of at least one piston within a cylinder of an engine of an auto-stop/start vehicle includes, generating an auto-stop command for shutting down an engine while an ignition is in an ON state. The method also includes generating an auto-start command for re-starting the engine after the generation of the auto-stop command. The method also includes, disabling a load on the engine in response to the generation of the auto-stop command and before the generation of the auto-start command. The method also includes, parking exhaust cam phasers and intake cam phasers in response to the generation of the auto-stop command and before the generation of the auto-start command. The method also includes disabling fuel to the engine in response to the generation of the auto-stop command and before the generation of the auto-start command: setting a throttle valve opening to a first predetermined throttle opening level, monitoring a crankshaft rotational position, determining if a position of a piston is entering a predetermined position, monitoring a barometric pressure, setting a throttle valve opening to a second predetermined throttle opening level, setting a throttle valve opening to a third predetermined throttle opening level after a predetermined time has elapsed from the setting of the second predetermined throttle opening level, determining if an engine speed is less than a second predetermined speed, setting a throttle valve opening to a fourth predetermined throttle opening level when the engine speed is less than the second predetermined speed, and achieving a resting position of the piston that is in a predefined piston position range. 
     In a further embodiment of the present invention, the method includes estimating a remaining degrees of engine rotation when the piston is entering the predetermined position, and the remaining degrees of engine rotation estimation is based on the first predetermined engine speed and the barometric pressure. 
     In a further embodiment of the present invention, the method includes maintaining the throttle valve at the first predetermined throttle opening level further comprises maintaining the throttle valve at an opening level to further reduce pressure in the intake manifold. 
     In a further embodiment of the present invention, the method includes maintaining the throttle valve at the second predetermined throttle opening level further comprises maintaining the throttle valve at an opening level to rapidly increase the pressure in the intake manifold. 
     In a further embodiment of the present invention, the method includes maintaining the throttle valve at the third predetermined throttle opening level further comprises maintaining the throttle valve at an opening level to return the opening position to a position at or slightly above the position associated with an unpowered throttle actuator. 
     In a further embodiment of the present invention, the method includes setting a predetermined fuel rail pressure in response to the generation of the auto-stop command and before the generation of the auto-start command. 
     In a further embodiment of the present invention, the method includes monitoring a barometric pressure in response to the generation of the auto-stop command and before the generation of the auto-start command. 
     In a further embodiment of the present invention, the method includes estimating degrees of engine rotation before the engine stops rotating based on a speed of the engine, an engine deceleration and the barometric pressure. 
     In a further embodiment of the present invention, the method includes wherein the predetermined position is one of a predefined crankshaft rotational position. 
     In a further embodiment of the present invention, the method includes the predetermined position for the piston is entering an intake stroke. 
     In a further embodiment of the present invention, the method includes the second predetermined throttle opening level is configured to raise the air pressure in at least one cylinder to approximately ambient barometric pressure. 
     In a further embodiment of the present invention, the method includes setting a throttle valve opening to a fourth predetermined throttle opening level when the engine speed is approximately zero. 
    
    
     
       BRIEF DESCRIPTION OF THE 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. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the views. In the drawings: 
         FIG. 1  is a functional block diagram of an exemplary engine system according to the principles of the present disclosure; 
         FIG. 2  is a functional block diagram of an exemplary engine control system according to the principles of the present disclosure; 
         FIG. 3  is a graph of a plurality of engine data traces plotted as functions of time according to the principles of the present disclosure; 
         FIG. 4  is an exemplary crankshaft rotation diagram according to the principles of the present disclosure; and 
         FIG. 5  is a flowchart depicting an exemplary method of controlling the MAP according to the principles of 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. As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Referring now to  FIG. 1 , a functional block diagram of an exemplary engine system  100  is presented. Engine system  100  includes an engine  102  and an engine control system  101 . The engine  102  generates drive torque for the vehicle. While the engine  102  is shown and will be discussed as a spark-combustion internal combustion engine (ICE), the engine  102  may include another suitable type of engine  102 , such as a compression-combustion ICE. One or more electric motors (or motor-generators) may additionally generate drive torque. The engine control system  101  includes an engine control module (ECM)  118  that automatically shuts down the engine  102  when the engine  102  is idling to reduce fuel consumption and emissions and automatically shuts down the engine  102  when a driver depresses a brake pedal and the vehicle speed is zero. The engine control system  101  automatically restarts the engine  102  when the driver releases the brake pedal after the engine  102  is automatically shut down. 
     The engine  102  includes a throttle valve  104 , an intake manifold  106 , a cylinder  108 , a fuel injector  110 , a crankshaft  112 , a spark plug  114 , and a flywheel. Air, designated by arrow “A”, is drawn into the engine  102  through the throttle valve  104  to the intake manifold  106 . Airflow into the engine  102  is varied using the throttle valve  104 . One or more fuel injectors, such as fuel injector  110 , mix fuel with the air to form an air/fuel mixture. The air/fuel mixture is combusted within cylinders of the engine  102 , such as cylinder  108 . Although the engine  102  is depicted as including one cylinder  108 , the engine  102  may include more than one cylinder  108 . 
     The cylinder  108  includes a piston (not shown) that is mechanically linked to the crankshaft  112 . One combustion cycle within the cylinder  108  includes four phases: an intake phase, a compression phase, a combustion (or expansion) phase, and an exhaust phase. During the intake phase, the piston moves toward a bottommost position and draws air into the cylinder  108 . During the compression phase, the piston moves toward a topmost position and compresses the air or air/fuel mixture within the cylinder  108 . 
     During the combustion phase, spark from the spark plug  114  ignites the air/fuel mixture. The combustion of the air/fuel mixture drives the piston toward the bottommost position, and the piston drives rotation of the crankshaft  112 . Resulting exhaust gas is expelled from the cylinder  108  to complete the exhaust phase and the combustion event. The flywheel  116  is attached to and rotates with the crankshaft  112 , and the engine  102  outputs torque to a transmission (not shown) via the crankshaft  112 . 
     The ECM  118  receives data from and controls a plurality of components of engine system  101 . The plurality of components of engine system  101  includes the throttle valve  104 , the fuel injector  110 , the spark plug  114 , a throttle actuator module  120 , a fuel actuator module  122 , a spark actuator module  124 , a crankshaft position sensor  126 , a manifold absolute pressure (MAP)  132  sensor, an accelerator pedal position (APP) sensor  136 , a brake pedal position (BPP) sensor  140 , a transmission control module (TCM)  146 , and an ignition system  148 . 
     The ECM  118  controls the throttle valve  104  via the throttle actuator module  120 , the ECM  118  controls the fuel injector  110  via a fuel actuator module  122 , and the ECM controls the spark plug  114  via a spark actuator module  124 . More specifically, the ECM  118  controls an opening area and opening duration of the throttle valve  104 , a fuel injection amount and timing, and spark timing. While not shown, the ECM  118  may also control other engine actuators, such as one or more camshaft phasers, an exhaust gas recirculation (EGR) valve, a boost device (e.g., a turbocharger or a supercharger), and/or other suitable engine actuators. 
     The crankshaft position sensor  126  monitors rotation of the crankshaft  112  and outputs a crankshaft position signal  128  to the ECM  118  based on rotation of the crankshaft  112 . The crankshaft position sensor  126  also measures direction of rotation of the crankshaft  112 , and outputs a direction signal indicating the direction of rotation of the crankshaft  112 , or the crankshaft position sensor  126  indicates the direction of rotation via the crankshaft position signal  128 . The crankshaft position signal  128  is used, for example, to determine rotational speed of the crankshaft  112  (e.g., in revolutions per minute or RPM). The rotational speed of the crankshaft  112  is referred to as engine speed  130 . The MAP  132  sensor measures pressure within the intake manifold  106  and generates a MAP signal  134  based on the pressure within the intake manifold  106 . 
     The ECM  118  controls the torque output of the engine  102  based on one or more driver inputs, such as the accelerator pedal position, brake pedal position, and/or other suitable driver inputs. The APP sensor  136  measures position of an accelerator pedal (not shown) and generates an APP signal  138  based on the position of the accelerator pedal. The BPP sensor  140  measures position of a brake pedal (not shown) and generates a BPP signal  142  based on the position of the brake pedal. 
     The engine system  100  also includes one or more other sensors  144  (collectively illustrated as other sensors), such as a mass air flowrate (MAF) sensor, an intake air temperature (IAT) sensor, an engine coolant temperature sensor, an engine oil temperature sensor, and/or other suitable sensors. The ECM  118  also communicates with one or more other modules, such as the TCM  146 . 
     A user inputs vehicle startup and vehicle shutdown commands to the ECM  118  via the ignition system  148  (collectively illustrated as ignition). In one aspect, the user inputs vehicle startup and vehicle shutdown commands by turning a key, pressing a button, or in another suitable manner. When the user has input a vehicle startup command and before a vehicle shutdown command has been received, the ignition system  148  is in an ON state. The ignition system  148  is in an OFF state when a vehicle shutdown command is input. A key cycle refers to a period between a first time when the user commands vehicle startup and a second time when the user commands vehicle shutdown. The ECM  118  selectively shuts down the engine  102  during a key cycle, (i.e., before a vehicle shutdown command is received) under some circumstances. An auto-stop event refers to shutting down the engine  102  during a key cycle. In one aspect, the ECM  118  selectively performs an auto-stop event during a key cycle when a user applies pressure to the brake pedal and/or when one or more other suitable conditions are satisfied. Shutting down the engine  102  under such conditions may decrease fuel consumption. 
     The ECM  118  selectively terminates the auto-stop event and restarts the engine  102 . An auto-start event refers to starting the engine  102  after an auto-stop event during a key cycle. In one aspect, the ECM  118  performs an auto-start event when the user releases the pressure from the brake pedal, when the user applies pressure to the accelerator pedal, and/or when one or more other suitable conditions are satisfied. 
     Referring now to  FIGS. 2, 3, and 4 , an exemplary engine control system  101  is presented. The engine control system  101  includes an ECM  118  and a plurality of sensors and modules. The ECM  118  includes an engine speed determination module  202 , a target engine speed module  204 , an actuator control module  206 , an engine load estimation module  208 , a throttle controller  210 , and an auto-stop/start module  212 . The ECM  118  also includes a spark timing adjustment module  124  that selectively adjusts spark timing to alter engine  102  torque outputs. 
     The engine speed determination module  202  determines the engine speed  130  based on the crankshaft position signal  128 . In one aspect, the crankshaft position sensor  126  generates a high amplitude reading and a low amplitude reading. The crankshaft position sensor  126  produces a low amplitude reading until a specific condition is met. For example, the low amplitude reading of the crankshaft position sensor  126  is interrupted by the high amplitude reading when a tooth of an N-toothed wheel (e.g., the flywheel  116 ) passes the crankshaft position sensor  126 . For a further example, a target angle crossing pulse  317  is generated as the crankshaft  112  rotates past a predetermined position (for example, TDC 414) for a cylinder  108  of the engine  102 . The engine speed determination module  202  determines the engine speed  130  based on a period between two or more teeth of the N-toothed wheel. The engine speed determination module  202  also determines the engine rate of deceleration based on a time interval between two or more of the target angle crossing pulses  317 . 
     To determine the engine rate of deceleration, the ECM  118  relies upon derivation of angular rotational speed and acceleration of the crankshaft  112  using equations of angular motion for a system undergoing constant angular acceleration. A summary of the relevant equations follows. 
       ω f   2 =ω 0   2 +2·α·Δθ  (600)
 
     In equation (600), ωx=angular speed of the crankshaft  112  in radians/second at a particular point in time x, α is the angular acceleration in radians/second 2  of the crankshaft  112 , and Δθ is angular displacement of the crankshaft  112  in radians during a time interval between a first time t 0  and a second time t f . When crankshaft  112  ceases to rotate and the engine speed  130  drops to zero, ω f =0 radians/second and equation 600 becomes: 
       0=ω 0   2 +2·αΔθ  (602).
 
     Rearranging, equation 602 becomes: 
     
       
         
           
             
               
                 
                   Δθ 
                   = 
                   
                     
                       
                         ω 
                         0 
                         2 
                       
                       
                         ( 
                         
                           2 
                           · 
                           
                              
                             α 
                              
                           
                         
                         ) 
                       
                     
                     . 
                   
                 
               
               
                 
                   ( 
                   604 
                   ) 
                 
               
             
           
         
       
     
     That is, Δθ represents the estimated change in rotational position (angular position) of the crankshaft  112  between the current pulse  317  and when the engine speed  130  becomes zero. The ω represents the angular speed of the crankshaft  112  at a particular point in time, and |α| represents the absolute value of the angular acceleration of the crankshaft  112 . In an exemplary case in which the ECM  118  has initiated an auto-stop, because the engine  102  is decelerating, the angular acceleration of the crankshaft  112  has a negative value. To convert the equation 604 into degrees, rather than radians, a series of substitutions may be made. 
     
       
         
           
             
               
                 
                   
                     ω 
                      
                     
                         
                     
                      
                     
                       ( 
                       
                         rad 
                         sec 
                       
                       ) 
                     
                   
                   = 
                   
                     rpm 
                     · 
                     
                       ( 
                       
                         
                           2 
                            
                           π 
                         
                         60 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   606 
                   ) 
                 
               
             
             
               
                 
                   
                     Δθ 
                      
                     
                       ( 
                       rad 
                       ) 
                     
                   
                   = 
                   
                     Δ 
                      
                     
                         
                     
                      
                     
                       Deg 
                       · 
                       
                         ( 
                         
                           
                             2 
                              
                             π 
                           
                           360 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   608 
                   ) 
                 
               
             
             
               
                 
                   
                     α 
                      
                     
                         
                     
                      
                     
                       ( 
                       
                         rad 
                         
                           sec 
                           2 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       Δrpm 
                       sec 
                     
                     · 
                     
                       ( 
                       
                         
                           2 
                            
                           π 
                         
                         60 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   610 
                   ) 
                 
               
             
           
         
       
     
     In one aspect, the ECM  118  uses the time intervals between pulses  317  to form the foundation of an event-based approach to update the angular displacement estimate. That is, the ECM  118  updates ω on an event basis. For instance, the event may occur at each crossing of a predetermined crankshaft  112  angle θ relative to a predetermined crankshaft  112  rotational position such as TDC  414  for a particular cylinder  108 . 
     The angular acceleration α is calculated as the change in the event-based angular speed of the crankshaft  112  over the time between the prior event sample (n−1) and the current event sample (n), where n represents the current update event value(s) and n−1 represents the prior update event value(s). 
     
       
         
           
             
               
                 
                   
                     α 
                      
                     
                       [ 
                       n 
                       ] 
                     
                   
                   = 
                   
                     
                       { 
                       
                         
                           ω 
                            
                           
                             [ 
                             n 
                             ] 
                           
                         
                         - 
                         
                           ω 
                            
                           
                             [ 
                             
                               n 
                               - 
                               1 
                             
                             ] 
                           
                         
                       
                       } 
                     
                     
                       { 
                       
                         
                           t 
                            
                           
                             [ 
                             n 
                             ] 
                           
                         
                         - 
                         
                           t 
                            
                           
                             [ 
                             
                               n 
                               - 
                               1 
                             
                             ] 
                           
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   612 
                   ) 
                 
               
             
           
         
       
     
     The ECM  118  uses the target engine speed  216  to determine when to instruct the throttle controller  210  to command specific throttle valve  104  areas during an engine  102  auto-stop. The target engine speed module  204  determines the target engine speed  216  based on barometric pressure. In one aspect, because engine  102  pumping losses decrease with decreased barometric pressure, the target engine speed module  204  will set a target engine speed  216  at ten thousand feet of altitude that is a lower target engine speed  216  than the target engine speed module  204  would set at sea level. In the ten thousand foot example above, because the engine  102  pumping losses are decreased relative to the pumping losses in an engine  102  at sea level, the number of crankshaft  112  revolutions before the engine  102  stops will be greater than the number of crankshaft  112  revolutions before engine stop of the same engine  102  at sea level. Therefore, to reliably predict engine stop position, the target engine speed module  204  alters the target engine speed  216  based in part on barometric pressure. 
     With continued reference to  FIG. 3 , exemplary graphs of alternator load, fuel pressure, intake and exhaust cam phasers, MAP  132 , throttle area, and engine position as functions of time are presented. Exemplary trace  302  tracks auto-stop pre-conditioning and fuel shut-off. Exemplary trace  304  tracks the engine alternator load. Exemplary trace  306  tracks the fuel pressure. Exemplary trace  308  tracks the exhaust cam phaser position. Exemplary trace  310  tracks the intake cam phaser position. Exemplary trace  130  tracks the engine speed. Exemplary trace  312  tracks engine position. Exemplary trace  128  tracks the target angle crossing pulse  317  events. Exemplary trace  132  tracks the MAP. Exemplary trace  316  tracks the actual throttle area. Exemplary trace  314  tracks the desired throttle area. 
     With reference to  FIG. 5 , and with additional reference to  FIGS. 2, 3 and 4 , in one aspect, the engine control system  101  has an exemplary auto-stop sequence  500  that begins at block  502  and proceeds to block  504  where the ECM  118  determines whether an auto-stop event has been commanded during a key cycle. If the auto stop event has not been commanded, the method returns to block  502 . However, if an auto-stop has been commanded, the method proceeds to block  504 , where the method enters a pre-conditioning period P 1  from time T 1  to time T 2 . During the pre-conditioning period P 1 , the ECM  118  first commands the actuator control module  206  to reduce a load on the engine  102  at block  506  by disabling the alternator to reduce an alternator load  304  and disabling the A/C clutch to reduce an A/C load (not shown). Decreasing the load on the engine  102  improves the accuracy of load estimations generated by the engine load estimation module  208 . The method then proceeds to block  508 , where the ECM  118  parks the exhaust cam phaser  308  at a predetermined timing position and the ECM parks the intake cam phaser  310  at a predetermined timing position in preparation for the engine  102  to shut down. At block  510 , the ECM  118  increases a fuel rail pressure  306  to a predetermined target fuel pressure  318 , at which point the ECM  118  disables the engine fuel supply at time T 2  at block  512 . Once the engine fuel supply has been disabled, the auto-stop sequence enters the shut-down period P 2 . 
     During the shut-down period P 2 , from time T 2  to time T 4 , the engine  102  shuts off. In the shut-down period P 2  from T 2  to T 4 , the fuel rail pressure  306  continues to increase to the predetermined target fuel pressure  318 . At block  514 , the ECM  118  sets the desired throttle area  314  of the throttle valve  104  to a first predetermined throttle opening  320 . The first predetermined throttle opening  320  reduces the MAP  132  and thus, reduces the trapped pressure in the cylinder  108  or cylinders  108  entering the intake phase. In one aspect, the first predetermined throttle opening  320  includes a predetermined idle throttle opening or another suitable throttle opening. Setting desired throttle area  314  to the first predetermined throttle opening  320  chokes the engine  102  and minimizes shudder. Shudder refers to vibration experienced within the passenger cabin as the engine speed approaches zero. 
     During the auto-stop sequence, and during the shut-down phase after time T 2  in particular, the ECM  118  monitors a plurality of conditions. The plurality of conditions that the ECM  118  monitors includes crankshaft position  128  data at block  516 , engine speed  130  data at block  518 , barometric pressure at block  520 , engine deceleration data at block  522 , and at block  524  the ECM  118  estimates the remaining degrees of engine rotation prior to a predetermined engine stop position  332 . In one aspect, the predetermined engine stop position  332  for an exemplary piston  400  is within a target auto-stop range  420 . 
     With further reference to  FIG. 4 , a rotational diagram of a combustion cycle for a first cylinder  400  in an exemplary four-stroke four-cylinder engine in terms of crankshaft  112  position is presented. The cylinders  108  of the exemplary four-stroke four-cylinder engine have the firing order 1-3-4-2, repeating. For the purposes of the following explanation, the first cylinder  400  refers to cylinder #1 in the exemplary four-stroke four-cylinder engine. However, the cylinder  400  may be any of the four cylinders in the exemplary four-stroke four-cylinder engine. 
     The crankshaft  112  rotates in a clockwise direction as indicated by reference number  402 . A portion of the combustion cycle of the first cylinder  400  includes an intake valve opening event  404 , an intake valve duration  406 , an exhaust valve closing event  408 , an exhaust valve duration  410 , a valve overlap duration  412 , TDC  414 , a bottom dead center (BDC) position  416 , an intake valve closing event  418 , and a target auto-stop range  420 . 
     For the first cylinder  400  of the exemplary four-stroke four-cylinder engine to complete a full combustion cycle, and return to the same point in the combustion cycle, two full revolutions of the crankshaft  112  are required. An exemplary combustion cycle for the first cylinder  400  begins with the intake phase in which there is an intake valve opening event at  404 . The period during which the intake valve is open is referred to as the intake valve duration  406 . As the intake valve opening event occurs at  404 , an exhaust valve closing event  408  has not yet occurred. The period during which the exhaust valve is open is referred to as the exhaust valve duration  410 . Thus the intake valve duration  406  and the exhaust valve duration  410  may overlap within a portion of the combustion cycle. The portion of the combustion cycle in which both the intake valve and exhaust valve are open is referred to as the valve overlap duration  412  of the first cylinder  400 . The valve overlap duration  412  occurs near TDC  414 . The intake valve overlap duration  406  can vary substantially depending on intake cam phaser  310  timing setting and the exhaust cam phaser  308  timing setting. The valve overlap duration  412  can also vary substantially between engines  102 . Fresh air “A” is drawn into the engine  102  during the intake phase. In one aspect, the intake valve remains open for a duration  406  that extends to an intake valve closing event  418  that is beyond bottom dead center (BDC)  416 . Because of the previously mentioned 1-3-4-2 firing order, when the exemplary first cylinder  400  is in the intake phase and is next in sequence to enter the compression phase, an exemplary third cylinder (cylinder #3, not shown) is in the exhaust phase and is next in sequence to begin the intake phase. Likewise an exemplary second cylinder (cylinder #2, not shown) is in the compression phase and is next in sequence to enter the expansion phase, and an exemplary fourth cylinder (cylinder #4, not shown) is in the expansion phase and is next in sequence to enter the exhaust phase. During the exhaust phase of the first cylinder  400 , the third cylinder is in the expansion phase. Thus, the first cylinder  400  and third cylinder of the exemplary four-stroke four-cylinder engine are always 180° rotationally offset from one another. Likewise, the second cylinder and fourth cylinder of the exemplary four-stroke four-cylinder engine are always 180° rotationally offset from one another. 
     Referring once again to the first cylinder  400 , after completing the intake phase, the first cylinder  400  then enters the compression phase. During the compression phase, the intake valve closing event  418  occurs, and the pressure of the trapped air mixture rises as first cylinder  400  approaches TDC  414 . As the compression phase of the first cylinder  400  is completed, the first cylinder  400  transitions to the expansion phase with both the intake and exhaust valves remaining closed. While the first cylinder  400  is engaged in the compression phase, the third cylinder is engaged in the intake phase. After the first cylinder  400  completes the expansion phase, an exhaust valve opening event  422  occurs, and the exhaust valve remains open for the exhaust valve duration  410 . The first cylinder  400  then re-enters the intake phase in which the intake valve opening event  404  and overlap  412  occur. 
     With continued reference to  FIG. 4 , and with further reference to  FIGS. 2, 3, and 5 , after time T 2 , because the engine fuel supply and spark have been disabled, and because the first predetermined throttle opening  320  reduces the MAP  132  and chokes the engine  102  by reducing the airflow “A” to the intake manifold  104 , the engine speed  130  decreases toward zero as no torque is being produced by the engine  102 . At block  526  the ECM determines whether the engine speed determination module  202  data indicates that the engine speed  130  has decreased to a first predetermined engine speed threshold  322 . Furthermore, at block  526 , the crankshaft position sensor  128  generates the target angle crossing pulse  317  as each cylinder  108  crosses a predetermined engine position (e.g., TDC  414 ) relative to the intake phase. From the pulse  317 , the ECM  118  determines whether the engine  102  has reached a predetermined threshold engine position crossing threshold  326  that indicates the engine  102  will stop with a cylinder  108  within the target engine stop range  420 . If each of the engine speed threshold  322 , remaining rotation threshold (not shown), and engine position crossing threshold  326  have been met, the method proceeds to block  528 . If the predetermined engine speed threshold  322 , remaining rotation threshold (not shown), and engine position crossing threshold  326  have not been met, the method reverts to block  516 , and begins monitoring the crankshaft position, engine speed  130 , barometric pressure, engine rate of deceleration, and the ECM  118  estimates remaining degrees of engine rotation again. 
     At block  528 , if the engine  102  in an auto-stop sequence has reached the shut-down phase, and target angle crossing pulse  317  is generated, the ECM  118  commands the second predetermined throttle opening if the engine speed  130 , and crankshaft position signal  128  allow the ECM  118  to determine that the remaining degrees of rotation will put a cylinder  108  into the target auto-stop position range  420 . 
     To determine the second predetermined throttle opening  328  and predetermined period P 3 , the ECM  118  uses the crankshaft position signal  128 , engine speed  130 , and barometric pressure. In one aspect of the present invention, the ECM  118  also uses an estimate of the number of degrees of rotation remaining before the engine  102  stops to predict the engine stop position  332 . The estimate of degrees of rotation remaining is accomplished by using the engine speed  130  to calculate a rate of angular deceleration (using equation 612 above) at each target angle crossing pulse  317 . Using the unit conversions and simplifying the equations previously discussed, the engine stop position  332  may be predicted by the following remaining degrees of rotation equation 614. 
     
       
         
           
             
               
                 
                   
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     In an aspect of the present invention, the second predetermined throttle position  328  is applied once the engine crankshaft position  128  has crossed a predetermined threshold crankshaft position  330 , and the engine speed  130  is below the engine speed threshold  322  for a particular ambient barometric pressure as determined from a lookup table. The engine speed threshold  322  in the lookup table is a function of barometric pressure, and correlates to a target auto-stop range  420  that reduces the level of auto-stop and auto-start vibration. Therefore, when the ECM  118  uses the barometric pressure at sea-level to calculate the engine speed threshold  322 , the reliability of the engine speed threshold  322  to stop the engine  102  in the target auto-stop range  420  decreases as the difference between the barometric pressure at sea-level and the actual barometric pressure increases. 
     Referring once more to the previous example of a four-stroke four-cylinder engine with the first piston  400 , in  FIG. 3 , as the auto-stop period P 2  progresses past time T 3 , the ECM  118  selects a specific cylinder (in this example, the first cylinder  400 ) for which each of the shutdown threshold criteria: predetermined threshold crankshaft position  330 , engine speed threshold  322 , and/or estimated remaining degrees of rotation threshold have been achieved. The ECM  118  then uses the first cylinder  400  for triggering the second predetermined throttle opening  328  that will control an engine stop position  332 , and more specifically, that will control a stop position of the first cylinder  400 . If at time T 3 , when shutdown threshold criteria have been achieved for the first cylinder  400 , and the ECM  118  instead uses a different cylinder  108 , such as the previously-described second, third, or fourth cylinder, to initiate the second predetermined throttle opening  328 , the target auto-stop range  420  may not be achieved. For a further example, in the case where the ECM  118  targets the second cylinder, which in the exemplary engine precedes the first cylinder  400  in the firing order, the engine speed  130  is higher than the engine speed threshold  322  for the first cylinder  400  for which all of the threshold criteria have been met. In the example, when the engine speed  130  is higher than the engine speed threshold  322  for the first cylinder  400 , the engine  102  will exceed the target auto-stop range  420  and engine position  332 . When the target auto-stop range  420  is not achieved, undesirable noise, vibration, and harshness result during auto-stop and auto-start events. 
     Using equation 614, the ECM  118  commands the second predetermined throttle opening  328 , where the second predetermined throttle opening  328  is greater than the first predetermined throttle opening  320  and includes any single opening or plurality of suitable openings that allow the MAP  132  to rapidly increase toward barometric pressure while also reducing throttle valve  104  audible noise. By rapidly increasing the MAP  132 , pressure in the intake manifold  106  and in one or more cylinders  108  that are in sequence to enter the intake phase is also increased. 
     In the example above, because the exhaust cam phaser and intake cam phaser  308 ,  310  are parked prior to the ECM  118  commanding the second predetermined throttle opening  332 , the intake valve and the exhaust valve of the cylinder in the compression stroke and the cylinder in the expansion stroke (e.g., the first cylinder  400  and the second cylinder respectively) are closed as the engine  102  slows to a momentary stop  334 , and the first cylinder  400  reaches the target auto-stop range  420 . Furthermore, because the second predetermined throttle opening  328  rapidly increases air pressure within the intake manifold  106  and the first cylinder  400  in the intake phase, as the first cylinder  400  completes the intake phase and undergoes the compression phase, the first cylinder  400  stops momentarily at or near TDC  414 . When the first cylinder  108  stops at or near TDC  414 , movement of the crankshaft  112  is momentarily reversed due to trapped pressure in the cylinders. This reversal of crankshaft  112  movement during engine  102  shutdown is referred to as rock back. As the crankshaft  112  rocks back, air pressure within the next cylinder  108  in the firing order (e.g., the third cylinder, relative to the exemplary first cylinder  400 ) tends to approach barometric pressure and comes to rest on the compression stroke in the target auto-stop range  420 . When the MAP  132  and the exemplary third cylinder pressures approach barometric pressure, less exhaust gas is present in the intake manifold  106  and the third cylinder, and the potential for a misfire is reduced when the engine  102  is restarted. Engine vibration may be prevented when the engine  102  is restarted by preventing misfires. 
     Referring once more to  FIG. 5 , and with continuing reference to  FIGS. 1, 2, 3, and 4 , at block  530 , the ECM  118  determines whether the predetermined time period P 3 , has been met. At T 4 , the ECM  118  sets a third predetermined throttle opening  336  at block  532  that is equal to or slightly above or slightly below the first throttle predetermined opening  320 . In part, because there is a lag between the desired throttle area  314  and the actual throttle area  316 , in one aspect, the second predetermined throttle opening  328  holding period P 3  may extend beyond T 4 . Additionally, because the first predetermined throttle opening  320  chokes the engine  102  and because the second predetermined throttle opening  328  pressurizes the intake manifold  106  and at least one cylinder  108 , the desired and actual throttle areas  314 ,  316  further cause the engine speed  130  to decrease and eventually arrest rotation of the engine  102 . 
     The throttle controller  210  also provides throttle valve  104  position commands to the actuator control module  206  under a variety of conditions. In one aspect, during the holding period P 3  of the second predetermined throttle opening  328 , the throttle controller  210  starts a timer in a timer module  218 . The timer in the timer module  218  tracks the duration of the holding period P 3  since the second predetermined throttle opening  328  was set. During the holding period P 3 , the throttle controller  210  selectively varies the desired throttle area  314  to follow a predetermined throttle opening profile, when the timer is less than the predetermined holding period P 3 . In one aspect, the throttle controller  210  transitions the desired throttle area  314  to the third predetermined throttle opening  336  when the auto-stop/start module  212  generates an auto-start command. When the auto-start command is generated, the actuator control module  206  commands a starter actuator module  150  to activate the ignition  148  and thereby start the engine  102 . In this manner, if the engine  102  should be auto-started when the second predetermined throttle opening  328  has been set for less than the full extent of the holding period P 3 , the engine  102  is started without the throttle valve  104  at or near a desired throttle opening. 
     At block  534 , the ECM  118  determines whether the engine  102  has stopped rotating. If the engine speed determination module  202  has determined that the engine speed  130  is approximately zero, the ECM  118  commands a fourth predetermined throttle opening  338  starting at time T 5  at block  536 . The fourth predetermined throttle opening  338  is for example, at a level that is higher than, the same as, or lower than the third throttle opening. At block  538 , the auto-stop method ends. 
     While the principles of the present disclosure are discussed as relating to adjusting spark-ignition engines, the principles of the present disclosure are also applicable to adjusting fuel injection timing in compression-combustion engines. In one aspect, the fuel injection timing is adjusted based on an injection timing correction that is determined based on the difference between the target engine speed  216  and the engine speed in compression-combustion engine systems. 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.