Abstract:
A method for compensating for thermal transient conditions of an engine that can cause valve growth or contraction is disclosed. In one example, the method provides cylinder air amount compensation during non-blow-through and blow-through conditions. The approach may improve cylinder air amount estimates, thereby improving engine emissions.

Description:
BACKGROUND/SUMMARY 
       [0001]    Direct acting mechanical bucket (DAMB) valve actuators may be produced with no valve lash adjustment. As such, DAMB operated valves may respond quickly, however, temperature changes occurring within the engine having DAMB operated valves may cause expansion or contraction of valves resulting in changes to valve event timing. For example, a change in engine load can cause engine temperatures and pressures to increase. The increased cylinder temperature can cause exhaust valve expansion. Further, the cylinder head may also expand, and the exhaust valve expansion rate may be different from the cylinder head expansion rate because the exhaust valve and the cylinder head may be formed from different materials or because the exhaust valves are cooled differently from the cylinder head. The temperature changes in the cylinder may cause changes in valve stem length and valve diameter. As a result, valve timing changes may occur by way of a valve opening and/or closing at different times as valve temperature and cylinder head temperature change. Consequently, volumetric efficiency of the engine may change during transient engine operating conditions where valve and/or cylinder head temperatures change due to changes in engine operating conditions. 
         [0002]    The inventors herein have recognized the above-mentioned disadvantages and have developed a method of compensating for thermal conditions during transient engine conditions, comprising: adjusting an engine air amount parameter and a cylinder residual gas amount via an engine MAP and cylinder air amount volumetric efficiency relationship in response to a rate of change of cylinder air amount; and adjusting output of an engine actuator in response to the engine air amount parameter. 
         [0003]    By adjusting cylinder air amount and a cylinder residual gas amount via an engine manifold absolute pressure (MAP) and cylinder air amount volumetric efficiency relationship in response to a rate of change of cylinder air amount, it may be possible to account for valve temperatures that can affect engine volumetric efficiency. The change of cylinder air amount may be indicative of a valve temperature change so that cylinder air amount and cylinder residual gas may be compensated until the engine reaches an equilibrium temperature where the MAP and cylinder air amount relationship may be used without compensation. 
         [0004]    The present description may provide several advantages. In particular, the approach can reduce vehicle emissions by providing improved engine air-fuel control. Further, the approach may also reduce engine misfires and/or slow combustion events which also may increase engine emissions. Further still, the approach provides a simple way to compensate cylinder air amount and cylinder exhaust residuals during transient engine operating conditions. 
         [0005]    The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
         [0006]    It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0007]      FIG. 1  shows a schematic depiction of an engine; 
           [0008]      FIG. 2  shows a plot of simulated error on cylinder air amount, residual gas, and blow-through air caused by valve temperature related to transient engine operating conditions; 
           [0009]      FIG. 3  shows a high level block diagram of a method for compensating valve temperature; 
           [0010]      FIG. 4  shows a plot illustrating compensation for cylinder volumetric efficiency impacting cylinder air amount and cylinder exhaust gas dilution as determine from MAP; 
           [0011]      FIG. 5  shows a plot illustrating compensation for cylinder volumetric efficiency impacting inferred manifold pressure as determined from MAF; and 
           [0012]      FIG. 6  shows a flowchart of an example method compensating for exhaust valve timing changes during transient conditions. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The present description is directed to adjusting cylinder air amount and cylinder residual gas amount of a cylinder of an engine.  FIG. 1  shows one example system for adjusting cylinder air amount of a cylinder. In some examples, the system may include a turbocharger with a spark ignited mixture of air and gasoline, alcohol, or a mixture of gasoline and alcohol. However, in other examples, the engine may be a compression ignition engine, such as a diesel engine.  FIG. 2  shows a simulated example plot of curves that are the basis for compensating cylinder air amount and cylinder residual amount. 
         [0014]      FIG. 3  shows an example method for adjusting cylinder air amount. Visual examples of how cylinder air amount, MAP, and cylinder residual amount are adjusting according to the method disclosed herein are shown in  FIGS. 4-5 . A flowchart of a method for adjusting cylinder air amount and cylinder residual gas amount is shown in  FIG. 6 . 
         [0015]    Referring to  FIG. 1 , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , is controlled by electronic engine controller  12 . Engine  10  includes combustion chamber  30  and cylinder walls  32  with piston  36  positioned therein and connected to crankshaft  40 . Combustion chamber  30  is shown communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  and exhaust valve  54 . Each intake and exhaust valve may be operated by an intake cam  51  and an exhaust cam  53 . Alternatively, one or more of the intake and exhaust valves may be operated by an electromechanically controlled valve coil and armature assembly. The position of intake cam  51  may be determined by intake cam sensor  55 . The position of exhaust cam  53  may be determined by exhaust cam sensor  57 . 
         [0016]    Fuel injector  66  is shown positioned to inject fuel directly into combustion chamber  30 , which is known to those skilled in the art as direct injection. Alternatively, fuel may be injected to an intake port, which is known to those skilled in the art as port injection. Fuel injector  66  delivers liquid fuel in proportion to the pulse width of signal FPW from controller  12 . Fuel is delivered to fuel injector  66  by a fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Fuel injector  66  is supplied operating current from driver  68  which responds to controller  12 . In addition, intake manifold  44  is shown communicating with optional electronic throttle  62  which adjusts a position of throttle plate  64  to control air flow from intake boost chamber  46 . 
         [0017]    Exhaust gases spin turbocharger turbine  164  which is coupled to turbocharger compressor  162  via shaft  161 . Compressor  162  draws air from air intake  42  to supply boost chamber  46 . Thus, air pressure in intake manifold  44  may be elevated to a pressure greater than atmospheric pressure. Consequently, engine  10  may output more power than a normally aspirated engine. 
         [0018]    Distributorless ignition system  88  provides an ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Ignition system  88  may provide a single or multiple sparks to each cylinder during each cylinder cycle. Further, the timing of spark provided via ignition system  88  may be advanced or retarded relative to crankshaft timing in response to engine operating conditions. 
         [0019]    Universal Exhaust Gas Oxygen (UEGO) sensor  126  is shown coupled to exhaust manifold  48  upstream of exhaust gas after treatment device  70 . Alternatively, a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor  126 . In some examples, exhaust gas after treatment device  70  is a particulate filter and/or a three-way catalyst. In other examples, exhaust gas after treatment device  70  is solely a three-way catalyst. 
         [0020]    Exhaust gases may be routed from downstream of turbine  164  to upstream of compressor  162  via exhaust gas recirculation (EGR) valve  80 . In another example, exhaust gases may be routed from upstream of turbine  164  to downstream of compressor  162 . Further, engine combustion chamber  30  may contain residual exhaust from a prior combustion event that remains in combustion chamber during a subsequent cylinder cycle. Thus, combustion chamber  30  may include internal (e.g., exhaust gases that remain in the cylinder from one combustion event to the next) EGR and external EGR via EGR valve  80 . 
         [0021]    Controller  12  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , read-only memory  106 , random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; a position sensor  134  coupled to an accelerator pedal  130  for sensing accelerator position adjusted by foot  132 ; a knock sensor for determining ignition of end gases (not shown); a measurement of engine manifold pressure (MAP) from pressure sensor  121  coupled to intake manifold  44 ; a measurement of boost pressure from pressure sensor  122  coupled to boost chamber  46 ; an engine position sensor from a Hall effect sensor  118  sensing crankshaft  40  position; a measurement of air mass entering the engine from sensor  120  (e.g., a hot wire air flow meter); and a measurement of throttle position from sensor  58 . Barometric pressure may also be sensed (sensor not shown) for processing by controller  12 . In a preferred aspect of the present description, engine position sensor  118  produces a predetermined number of equally spaced pulses every revolution of the crankshaft from which engine speed (RPM) can be determined. 
         [0022]    In some embodiments, the engine may be coupled to an electric motor/battery system in a hybrid vehicle. The hybrid vehicle may have a parallel configuration, series configuration, or variation or combinations thereof. Further, in some embodiments, other engine configurations may be employed, for example a diesel engine. 
         [0023]    During operation, each cylinder within engine  10  typically undergoes a four stroke cycle: the cycle includes the intake stroke, compression stroke, expansion stroke, and exhaust stroke. During the intake stroke, generally, the exhaust valve  54  closes and intake valve  52  opens. Air is introduced into combustion chamber  30  via intake manifold  44 , and piston  36  moves to the bottom of the cylinder so as to increase the volume within combustion chamber  30 . The position at which piston  36  is near the bottom of the cylinder and at the end of its stroke (e.g. when combustion chamber  30  is at its largest volume) is typically referred to by those of skill in the art as bottom dead center (BDC). During the compression stroke, intake valve  52  and exhaust valve  54  are closed. Piston  36  moves toward the cylinder head so as to compress the air within combustion chamber  30 . The point at which piston  36  is at the end of its stroke and closest to the cylinder head (e.g. when combustion chamber  30  is at its smallest volume) is typically referred to by those of skill in the art as top dead center (TDC). In a process hereinafter referred to as injection, fuel is introduced into the combustion chamber. In a process hereinafter referred to as ignition, the injected fuel is ignited by known ignition means such as spark plug  92 , resulting in combustion. During the expansion stroke, the expanding gases push piston  36  back to BDC. Crankshaft  40  converts piston movement into a rotational torque of the rotary shaft. Finally, during the exhaust stroke, the exhaust valve  54  opens to release the combusted air-fuel mixture to exhaust manifold  48  and the piston returns to TDC. Note that the above is described merely as an example, and that intake and exhaust valve opening and/or closing timings may vary, such as to provide positive or negative valve overlap, late intake valve closing, or various other examples. 
         [0024]    Turbocharged and supercharged engines pressurize air entering an engine so that engine power may be increased. The pressurized air provides for an increased cylinder air charge during a cycle of the engine as compared to a naturally aspirated engine. Further, the cylinder fuel charge can be increased as the cylinder air charge is increased to increase the amount of energy produced when the fuel is combusted with the air during a cycle of the cylinder. However, during periods of valve overlap where both intake and exhaust valves of a cylinder are simultaneously open, it is possible for air to pass directly from the engine intake manifold to the engine exhaust manifold without participating in combustion within a cylinder. Air passing directly from the intake manifold to the exhaust manifold without participating in combustion may be referred to as blow-through. 
         [0025]    Thus, the system of  FIG. 1  provides for an engine system, comprising: an engine; a turbocharger coupled to the engine; and a controller including instructions for adjusting an engine air amount parameter and a cylinder residual gas amount in response to a rate of change of cylinder air amount flow during blow-through and non-blow-through engine operating conditions, the controller including further instructions for adjusting an actuator in response to the engine air amount parameter. Thus, the system provides compensation for both blow-through and non-blow-through conditions. 
         [0026]    The engine system further comprises adjusting a residual gas amount based on the adjusted engine air amount parameter. The engine system also includes where the rate of change of cylinder air amount flow is determined from a difference between engine air flow and filtered engine air flow. The engine system further comprises additional instructions for adjusting the engine air amount parameter in response to cam timing. The engine system further comprises additional instructions for adjusting the engine air amount parameter in response to engine speed and engine load. In another example, the engine system further comprises additional instructions to determine blow-through during cylinder air flow conditions where cylinder air flow is greater than a cylinder air flow at an intersection of a maximum volumetric efficiency curve and a non-blow-through curve. 
         [0027]    Referring now to  FIG. 2 , a plot of simulated error on cylinder air amount, residual gas, and blow-through air caused by transient thermal engine operating conditions is shown. The X axis of plot  200  represents air mass amount of a cylinder per cylinder intake event or cylinder cycle. Air mass amount increases from the left side of the plot to the right side of the plot. The Y axis of plot  200  represents engine intake manifold absolute pressure (MAP) and MAP increase from the bottom of the origin of the plot in a direction of the Y axis. Vertical marker  250  represents a cylinder air amount where air blow-through occurs if cylinder air amount increases to the right of vertical marker  250 , and where air blow-through does not occur to the left of vertical marker  250 . Vertical marker  250  passes through the intersection of curves  202  and  206  which may be used to identify blow-through conditions via comparing cylinder air flow to the air flow at the intersection of curves  202  and  206   
         [0028]    Curve  202  represents the theoretical maximum air amount (e.g., 100% volumetric efficiency) that the cylinder can hold at a given pressure at intake valve closing (IVC). Thus, the cylinder mass amount increases linearly as the cylinder pressure increases. In one example, the maximum air amount that the cylinder can hold may be characterized as a slope of a line where the slope is described as: 
         [0000]    
       
         
           
             Slope 
             = 
             
               1 
               
                 
                   ( 
                   
                     1 
                     - 
                     
                       r 
                       pb 
                     
                   
                   ) 
                 
                  
                 
                   c 
                   norm 
                 
               
             
           
         
       
     
         [0000]    where variable c norm  accounts for physical properties of air, intake manifold temperature, and cylinder displacement. Variable r pb  is an effective pushback ratio characterizing a portion of a cylinder mixture that may be pushed into the engine intake manifold from the cylinder as the piston moves in a direction toward the cylinder head while the intake valve is open. The pushback ratio may be determined as the greater of a constant multiplied by the physical ratio of cylinder volume displaced by the piston moving from bottom dead center (BDC) to the intake valve closing (IVC) point, to the total cylinder displacement volume of the cylinder and the pushback ratio computed from engine mapping as: 
         [0000]    
       
         
           
             1 
             - 
             
               1 
               
                 
                   c 
                   norm 
                 
                 * 
                 air_slope 
               
             
           
         
       
     
         [0000]    where air_slope is the least-squares linear fit of the manifold pressure vs. trapped air amount data excluding blow-through data points. 
         [0029]    Curve  204  represents a cylinder air amount vs. MAP volumetric efficiency relationship during cold engine operating conditions where engine and/or cylinder valve temperature are less than at nominal (e.g. steady-state) engine operating conditions. During cool conditions, cylinder valves may expand less than during conditions where the engine is operating at nominal engine temperature (e.g., 90° C.). As a result, exhaust gas residuals held in a cylinder after a compression stroke of the cylinder and into a subsequent compression stroke of the cylinder may decrease as compared to nominal engine operating conditions. 
         [0030]    Curve  206  represents a cylinder air amount vs. MAP volumetric efficiency relationship during nominal mapped engine operating conditions that are stored in controller memory where engine temperature and cylinder valve temperature have time to stabilize. In particular, curve  206  represents steady state engine speed and load conditions. 
         [0031]    Curve  208  represents a cylinder air amount vs MAP volumetric efficiency relationship during warm engine operating conditions where engine and/or cylinder valve temperature are greater than at nominal engine operating conditions. During warm conditions, cylinder valves may expand more than during conditions where the engine is operating at nominal engine temperature. Consequently, exhaust gas residuals held in a cylinder after an intake stroke of the cylinder and into a subsequent compression stroke of the cylinder may increase as compared to nominal engine operating conditions. 
         [0032]    It can be seen that curve  206  exhibits a lower cylinder air amount for an equivalent MAP as compared to curve  202  for cylinder air amounts less than or to the left of vertical marker  250 . The lower cylinder air amount may be attributed to residual exhaust gases remaining in the cylinder from a previous combustion event. 
         [0033]    The engine controller includes a function or table containing values that represent curves  206  and  202 . The engine controller may also contain curves  208  and  204  as well as curves for other engine temperatures; however, storing and retrieving additional curves can complicate, slow down, and increase the cost of the controller. In addition, relationship between the cylinder air amount and MAP represented by the curves  204  and  208  can only be observed during large transients, which makes their characterization more difficult compared to the nominal relationship described by curve  206 . Therefore, it can be beneficial to compensate curve  206  for the conditions that provide curves  204  and  208  according to the methods of  FIGS. 3 and 6 . Thus, cylinder air amount and cylinder residual gas amount can be determined by interpreting curve  206  and adjusting for the engine operating conditions so as to follow curves  204  and  208 . 
         [0034]    Two examples are provided to illustrate how valve and engine temperature affect cylinder air amount and cylinder exhaust gas residual amount. Similar relationships occur to the right of vertical marker  250  between curves  202  and  208 ; however, the distance between curve  202  and curves  204 - 208  represent different amounts of blow-through air (e.g., air that blows through a cylinder when intake manifold pressure is greater than exhaust pressure while intake and exhaust valves of a cylinder are simultaneously open). 
         [0035]    Horizontal marker  260  represents a first constant intake manifold pressure. Horizontal marker  260  intersects curve  202  at  261 . If a vertical line is extended from  261  to the X axis, a cylinder air amount may be determined at the intersection of the vertical line and the X axis. Cylinder air amount at  261  represents a condition of 100% cylinder volumetric efficiency (e.g., the theoretical amount of air a cylinder can hold) when the engine is operated at a MAP of horizontal marker  260  and at the nominal air temperature. Cylinder air amount at  262  represents cylinder air amount at nominal engine operating conditions where the relationship between MAP and cylinder air amount is mapped. If a vertical line is extended from  262  to the X axis, cylinder air amount for nominal mapped conditions may be determined at the intersection of the vertical line and the X axis. Cylinder air amount at  263  represents cylinder air amount at warm engine operating conditions where the relationship between MAP and cylinder air amount is compensated by the methods of  FIGS. 3 and 6 . If a vertical line is extended from  263  to the X axis, cylinder air amount for warm conditions may be determined at the intersection of the vertical line and the X axis. 
         [0036]    The distance between arrows  264  represents a difference in cylinder air amount between nominal engine mapping conditions and warm engine operating conditions at MAP level  260 . In particular, when the engine is operated warm at low load conditions (warmer than steady-state operating temperatures for this condition), cylinder air amount is over estimated because cylinder air amount at nominal engine operating conditions (e.g.,  262 ) is greater cylinder air amount at warm operating conditions (e.g.,  263 ). Thus, cylinder air amount will be overestimated via mapped curve  206  unless compensation is provided to adjust cylinder air amount to  263  during warm engine operating conditions. 
         [0037]    Distance  266  represents an amount of exhaust gas residuals in a cylinder during a cycle of the cylinder for warm engine operating conditions when MAP is at the level of horizontal marker  260 . The amount of exhaust gas residuals in a cylinder for warm engine operating conditions can be determined at the MAP level of  260  via subtracting the cylinder air mass at  263  of warm volumetric efficiency curve  208  of from the cylinder air mass at  261  of maximum volumetric efficiency curve  202 . Distance  268  represents an amount of exhaust gas residuals in a cylinder during a cycle of the cylinder for nominal engine operating conditions. The amount of exhaust gas residuals in a cylinder for nominal operating conditions at MAP level  260  can be determined via subtracting the cylinder air mass at  262  of nominal volumetric efficiency curve  206  from the cylinder air mass at  261  of maximum volumetric efficiency curve  202 . 
         [0038]    Horizontal marker  280  represents a second constant MAP. Horizontal marker  280  intersects maximum volumetric efficiency curve  202  at  281 . If a vertical line is extended from  281  to the X axis, a cylinder air amount may be determined at the intersection of the vertical line and the X axis. Cylinder air amount at  281  represents a condition of 100% cylinder volumetric efficiency when the engine is operated at a MAP of horizontal marker  280 . Cylinder air amount at  282  represents cylinder air amount at cold engine operating conditions where the relationship between MAP and cylinder air amount is compensated by the methods of  FIGS. 3 and 6 . If a vertical line is extended from  282  to the X axis, cylinder air amount for cold conditions may be determined at the intersection of the vertical line and the X axis. Cylinder air amount at  283  represents cylinder air amount at nominal engine operating conditions where the relationship between MAP and cylinder air amount is mapped. If a vertical line is extended from  283  to the X axis, cylinder air amount for nominal mapped conditions may be determined at the intersection of the vertical line and the X axis. 
         [0039]    The distance between arrows  284  represents a difference in cylinder air amount between nominal engine mapping conditions and cold engine operating conditions when MAP is at  280 . In particular, when the engine is operated cold at medium load conditions, cylinder air amount is under estimated because cylinder air amount at nominal engine operating conditions (e.g.,  283 ) is less than cylinder air amount at cold operating conditions (e.g.,  282 ). Thus, cylinder air amount will be underestimated via curve  206  unless compensation is provided to adjust cylinder air amount to  283  during cold engine operating conditions. 
         [0040]    Distance  286  represents an amount of exhaust gas residuals in a cylinder during a cycle of the cylinder for nominal engine operating conditions when MAP is at the level of horizontal marker  280 . The amount of exhaust gas residuals in a cylinder for nominal engine operating conditions can be determined via subtracting the cylinder air mass at  283  of nominal volumetric efficiency curve  206  from the cylinder air mass at  281  of maximum volumetric efficiency curve  202 . Distance  288  represents an amount of exhaust gas residuals in a cylinder during a cycle of the cylinder for cold engine operating conditions. The amount of exhaust gas residuals in a cylinder for cold operating conditions can be determined via subtracting the cylinder air mass at  282  of cold volumetric efficiency curve  204  from the cylinder air mass at  281  of nominal volumetric efficiency curve  202 . 
         [0041]    Thus, it can be observed from  FIG. 2  that when cylinder air amount is estimated according to curve  202 , cylinder air amount will be underestimated when the engine and valves are cold if compensation is not provided. Further, it can be observed that the exhaust gas residual amount estimated in a cylinder will be overestimated when the engine and valves are cold if compensation is not provided. Similarly, cylinder air amount will be overestimated when the engine and valves are warmer than nominal conditions if compensation is not provided. Additionally, the exhaust gas residual amount estimated in a cylinder will be underestimated when the engine and valves are warmer than nominal conditions if compensation is not provided. 
         [0042]    Referring now to  FIG. 3 , a high level block diagram of a method for compensating valve temperature is shown. The method of  FIG. 3  may be implemented via instructions in a controller of a system as shown in  FIG. 1 . 
         [0043]    At  302 , method  300  judges whether or not a condition of blow-through exits. In one example, method  300  may judge that blow-through exists when air flow into a cylinder exceeds a cylinder air amount described by a maximum cylinder volumetric efficiency curve (e.g., to the right of vertical marker  250  of  FIG. 2 ). If a blow-through estimate is determined to be less than or equal to zero (e.g., a non-blow-through condition), a value of one is output at  302 . Otherwise, if the blow-through estimate is determined to be greater than zero, a value of zero is output at  302 . 
         [0044]    At  304 , a base non-blow-through gain is determined. The base gain amount may be empirically determined and stored in a table that is indexed by engine speed, engine load, and engine temperature. The output of  304  and  302  are multiplied at junction  306 . 
         [0045]    At  308 , engine air flow and engine speed are used to determine air flow rate. In one example, air flow rate is determined by integrating engine air flow during a selected engine rotation interval (e.g., one cylinder cycle) and multiplying the result by an engine speed factor (e.g., conversion from engine speed to cylinder strokes) to determine cylinder air amount per cylinder stroke. In other examples, an air flow rate in other units may be provided. An air flow rate is directed from  308  to  310 . 
         [0046]    At  310 , method  300  filters the air flow rate output of  308 . In one example, a low pass filter with a higher cut-off frequency may be applied to the air flow rate. The filtered air flow rate is directed to summing junction  314  and low pass filter  312 . Low pass filter  312  may be a first-order or higher order filter. Low pass filter  312  may include an adjustable time constant that is based on engine operating conditions. For example, low pass filter  312  may have a first time constant at lower engine temperatures and a second time constant for higher engine temperatures. 
         [0047]    At  314 , method  300  subtracts the low pass filtered air flow rate from the non-low pass filtered air flow rate. Subtracting the low pass filtered air flow rate from the air flow rate provides a rate of change of air flow rate. The rate of change in the air flow rate is directed to  316 . 
         [0048]    At  318 , engine speed indexes a function of empirically determined gain that accounts for an engine speed dependency in the air amount adjustment for changes in engine temperature. The output of  318  is directed to  316 . 
         [0049]    At  320 , engine speed indexes a function of empirically determined gain that accounts for engine valve overlap relative to top-dead-center exhaust stroke. The output of  320  is directed to  316 . 
         [0050]    At  322 , engine speed indexes a function of empirically determined gain that accounts for engine valve overlap duration. The output of  322  is directed to  316 . 
         [0051]    At  324 , engine speed indexes a function of empirically determined gain that accounts for an engine load dependency in the air amount adjustment for changes in engine temperature. The output of  324  is directed to  316 . 
         [0052]    At  316 , the outputs of  306 ,  314 ,  318 ,  320 ,  322 , and  324  are multiplied together to provide a non-blow-through volumetric efficiency correction. Thus, if the output of  302  is a value of one, a value other than zero may be output from  316 . If the output of  302  is zero, non-blow-though compensation is not provided. In this way, the non-blow-through volumetric efficiency can be zeroed when blow-through occurs. 
         [0053]    For the blow-through volumetric efficiency correction, the blow-through air estimate is passed directly to  334 . The blow-though air may be determined as described above. 
         [0054]    At  326 , engine air flow and engine speed are used to determine air flow rate as described at  308 . An air flow rate is directed from  326  to  328 . At  328 , method  300  filters the air flow rate output of  326  as described at  310 . However, a different filter and/or filter time constant may be provided at  328 . The filtered air flow rate is directed to summing junction  332  and low pass filter  330 . Low pass filter  330  may be a first-order or higher order filter as described at  312 . However, low pass filter  330  may have a time constant that is different from the time constant of low pass filter  312 . 
         [0055]    At  332 , method  300  subtracts the low pass filtered air flow rate from the non-low pass filtered air flow rate. Subtracting the low pass filtered air flow rate from the air flow rate provides a rate of change of air flow rate. The rate of change in the air flow rate is directed to  334 . 
         [0056]    At  336 , engine speed indexes a function of empirically determined gain that accounts for an engine speed dependency in the air amount adjustment for changes in engine temperature. The values at  336  may be different than the values at  318 . The output of  336  is directed to  334 . 
         [0057]    At  338 , engine speed indexes a function of empirically determined gain that accounts for engine valve overlap. The values at  338  may be different than the values at  320 . The output of  338  is directed to  334 . 
         [0058]    At  340 , engine speed indexes a function of empirically determined gain that accounts for engine valve overlap duration. The values at  340  may be different than the values at  322 . The output of  340  is directed to  334 . 
         [0059]    At  342 , engine load indexes a function of empirically determined gain that accounts for an engine load dependency in the air amount adjustment for changes in engine temperature. The values at  342  may be different than the values at  324 . The output of  342  is directed to  334 . 
         [0060]    At  334 , the blow-through air estimate and the outputs of  332 ,  336 ,  338 ,  340 , and  342  are multiplied together to provide a blow-through volumetric efficiency correction. Thus, if the blow-through amount is non-zero, a value other than zero may be output from  334 . If the blow-through amount is zero, blow-though compensation is not provided. In this way, the blow-through volumetric efficiency correction can be output when blow-through occurs. 
         [0061]    At  350 , the blow-through volumetric efficiency correction and the non-blow-through volumetric efficiency correction amounts are summed. However, because of the way method  300  is structured, either the blow-through compensation or the non-blow-through compensation will be zeroed out so that only blow-through or non-blow-through compensation is provided. The output of  350  is directed to an engine air amount parameter compensation method where an engine air amount parameter (e.g., cylinder air amount or blow-through air amount) and cylinder residual exhaust gases are determined via curves similar to curves  202  and  206  of  FIG. 2 . In particular, if MAP is known, cylinder air amount is determined by indexing a function similar to that of  FIG. 2  with MAP and the cylinder air amount value output is then added with the compensation output of  350 . The exhaust gas residual is determined by subtracting the cylinder air amount from the maximum cylinder air amount at a MAP value as described with regard to  FIG. 2  via curve  202 . In this way, the cylinder air amount and residual exhaust amount may be determined. Further, the cylinder air amount reduction or increase is phased out as time increases from the transient condition. The phase out of cylinder air amount change emulates conditions of a valve thermal transient. 
         [0062]    In other examples, where cylinder air mass is measured, MAP may be determined via indexing a table or function similar to  FIG. 2  which outputs MAP for the determined cylinder air amount. The residual gas amount may be determined as previously described. 
         [0063]    Referring now to  FIG. 4 , a plot illustrating thermal compensation for cylinder volumetric efficiency impacting cylinder air amount and cylinder exhaust gas dilution is shown. The method described herein is executable via instructions of a controller in a system such as in  FIG. 1  and useful for systems that measure mass air flow and is included in the method of  FIG. 6 . 
         [0064]    The X axis represents cylinder air amount and cylinder air amount increases from the left side of the plot to the right side of the plot. The Y axis represents MAP and MAP increases from the X axis in the direction of the Y axis arrow. Vertical marker  450  indicates where air blow-through can occur. Specifically, blow-through can occur when cylinder air flow is greater than or to the right of the level indicated by vertical marker  450 . Blow-thorough is not present during cylinder air flows that are to the left of vertical marker  450 . 
         [0065]    In the example of  FIG. 4 , volumetric efficiency compensation for valve temperature changes during a load change from a lower load to a higher load where valve temperature increases is shown. In this example, the cylinder air amount increases due to compensation for increasing valve temperature. 
         [0066]    Further in this example, cylinder air amount increases from a low level to the level shown by vertical marker  404 . Vertical marker  404  represents a mapped base cylinder air amount that is uncompensated and determined via a MAP sensor, for example. Cylinder air amount may be estimated at a level shown by vertical marker  404  by indexing a table or function via MAP at the level of  402  to output cylinder air amount at the level  404  according to curve  430  (e.g. a mapped non-blow-through curve describing cylinder volumetric efficiency based on MAP and cylinder air amount). The base estimated cylinder exhaust gas dilution is determined as the difference between the value of curve  430  at  404  and the value of curve  431  at  408 , where curve  431  represents the maximum level or theoretical cylinder volumetric efficiency. The base estimated cylinder exhaust gas dilution is indicated by arrow  422 . 
         [0067]    The volumetric efficiency compensation described in  FIGS. 3 and 6  is added to the cylinder air amount represented by vertical marker  404  to provide compensated cylinder air amount as indicated by vertical marker  406 . The amount of cylinder air amount compensation is represented by arrow  420 . The compensated estimated cylinder exhaust gas dilution is determined as the difference between the value of curve  430  at the intersection with vertical marker  406  and the value of curve  431  at the intersection with vertical marker  408 . The compensated estimated cylinder exhaust gas dilution is indicated by arrow  424 . 
         [0068]    The cylinder air amount compensation shown in  FIG. 4  impacts estimated MAP by providing an increased cylinder air amount for a lower MAP. Thus, the compensated cylinder air amount is determined from a base cylinder air amount as determined from MAP added to an amount of cylinder air amount compensation. 
         [0069]    Referring now to  FIG. 5 , a plot illustrating thermal compensation for cylinder volumetric efficiency impacting MAP is shown. The method described herein is executable via instructions of a controller in a system such as in  FIG. 1  and useful for systems that measure MAP and is included in the method of  FIG. 6 . 
         [0070]    The X axis represents cylinder air amount and cylinder air amount increases from the left side of the plot to the right side of the plot. The Y axis represents MAP and MAP increases from the X axis in the direction of the Y axis arrow. Vertical marker  550  indicates where air blow-through can occur. Specifically, blow-through can occur when cylinder air flow is greater than or to the right of the level indicated by vertical marker  550 . Blow-thorough is not present during cylinder air flows that are to the left of vertical marker  550 . 
         [0071]    In the example of  FIG. 5 , volumetric efficiency compensation for valve temperature changes during a load change from a lower load to a higher load where valve temperature increases is shown. In this example, the cylinder air amount increases due to compensation for increasing valve temperature. 
         [0072]    Further in this example, cylinder air amount increases from a low level to the level shown by vertical marker  508 . Vertical marker  508  represents a mapped base cylinder air amount that is uncompensated and determined via a mass air flow meter, for example. MAP may be estimated at a level shown by horizontal marker  502  by indexing a table or function to output MAP at the level of  502  based on cylinder air amount at  508  according to curve  530  (e.g. a mapped non-blow-through curve describing cylinder volumetric efficiency based on MAP and cylinder air amount). The base estimated cylinder exhaust gas dilution is determined as the difference between the value of curve  530  at  508  and the value of curve  531  at  510 , where curve  531  represents the maximum level or theoretical cylinder volumetric efficiency. The base estimated cylinder exhaust gas dilution is indicated by arrow  522 . 
         [0073]    The volumetric efficiency compensation described in  FIGS. 3 and 6  is added to the cylinder air amount represented by vertical marker  508  to compute a temporary cylinder air amount that is the basis for revising MAP. The temporary cylinder air amount is indicated by vertical marker  506  and is not a basis for adjusting the cylinder fuel amount. The amount of cylinder air amount compensation is represented by arrow  520 . MAP at the level of  504  is determined via indexing curve  530  using the temporary cylinder air amount. The compensated estimated cylinder exhaust gas dilution is determined as the difference between the value of curve  530  at the intersection with vertical marker  506  and the value of curve  531  at the intersection with vertical marker  511 . The compensated estimated cylinder exhaust gas dilution is indicated by arrow  524 . 
         [0074]    Referring now to  FIG. 6 , a method for compensating for exhaust valve timing changes during transient conditions due to thermal conditions is shown. The method of  FIG. 6  is executable via instructions of a controller in a system as shown in  FIG. 1 . 
         [0075]    At  602 , method  600  determines engine operating conditions. Engine operating conditions may include but are not limited to engine speed, engine load, engine intake manifold pressure, engine air flow rate, engine temperature, and cam position. Method  600  proceeds to  604  after engine operating conditions are determined. 
         [0076]    At  604 , method  600  judges whether cylinder air amount is based on MAP or MAF sensor inputs. If cylinder air amount is based on MAP YES is answered at  604  and method  600  proceeds to  606 . Otherwise, NO is answered at  604  and method  600  proceeds to  608 . 
         [0077]    At  608 , method  600  determines a base cylinder air amount from a mass air flow (MAF) sensor, and MAP is determined via indexing a table or function that includes a cylinder volumetric efficiency relationship curve according to a MAP cylinder air amount relationship (e.g., curve  530  of  FIG. 5 ) using cylinder air amount as determined from the MAF sensor. The table outputs a base MAP. Further, a base cylinder exhaust gas residual may be determined via subtracting a cylinder air amount determined from the cylinder volumetric efficiency relationship curve (e.g., curve  530  of  FIG. 5 ) from a maximum cylinder air amount determined from a theoretical cylinder air amount curve (e.g.,  531  and residual amount  524  of  FIG. 5 ) at the MAP level determined from cylinder air amount. Method  600  proceeds to  610  after based values of cylinder air amount, MAP, and cylinder exhaust gas residual are determined. 
         [0078]    At  606 , method  600  determines a base cylinder air amount from a MAP sensor via indexing a table or function that includes a cylinder volumetric efficiency relationship curve according to a MAP cylinder air amount relationship (e.g., curve  430  of  FIG. 4 ) using MAP. The table outputs a base cylinder air amount. Further, a base cylinder exhaust gas residual may be determined via subtracting a cylinder air amount determined from the cylinder volumetric efficiency relationship curve from a maximum cylinder air amount determined from a theoretical cylinder air amount curve (e.g., curve  431  of  FIG. 4  and residual amount  422 ) from the MAP determined from the MAP sensor. Method  600  proceeds to  610  after based values of cylinder air amount, MAP, and cylinder exhaust gas residual are determined. 
         [0079]    At  610 , method  600  judges whether or not blow-through is present at the current engine operating conditions. In one example, blow-through may be determined when air flow into a cylinder exceeds a cylinder air amount described by a maximum cylinder volumetric efficiency curve (e.g., to the right of vertical marker  550  of  FIG. 5 ). For example, if the cylinder air amount from curve  530  at a MAP level is subtracted from the maximum cylinder volumetric efficiency curve  531  for cylinder air flow at a level to the right of vertical marker  550  of  FIG. 5  and the result is negative, blow-thorough may be determined. Method  300  proceeds to  614  if blow-through is not determined and the blow-through amount is set to zero. Otherwise, if the answer at  610  is yes, method  600  proceeds to  612 . 
         [0080]    At  612 , method  600  determines the amount of blow-through. A blow-through amount may be determined via subtracting a maximum cylinder air amount at a MAP level from a cylinder air amount at the same MAP level when the cylinder air amount is greater than a cylinder air amount at an intersection of a maximum cylinder air amount curve and a volumetric efficiency curve that represents a cylinder air amount MAP relationship during mapped engine operating conditions where engine temperature and cylinder valve temperature have time to stabilize. For example, at a constant level of MAP greater than MAP at the location where vertical marker  550  intersects curve  531  in  FIG. 5 , subtracting a cylinder air amount as determined from a maximum cylinder air amount curve  531  of  FIG. 5  from cylinder air amount determined from curve  530  of  FIG. 5 . Method  600  proceeds to  616  after the blow-through amount is determined. 
         [0081]    At  614 , method  600  determines a base gain amount for adjusting cylinder air amount. The base gain amount may be empirically determined and stored in memory that is indexed according to engine speed and load, for example. Method  600  proceeds to  616  after the base gain amount is determined. 
         [0082]    At  616 , method  600  determines a rate of change of engine or cylinder air flow rate. In one example, the rate of change of engine or cylinder air flow rate may be determined via subtracting a filtered value of engine or cylinder air flow rate from the engine or cylinder air flow rate. In other example, other approaches such as taking a derivative of cylinder air flow rate may also be used to determine the rate of change of engine or cylinder air flow rate. Method  600  proceeds to  618  after the rate of change of engine or cylinder air flow rate is determined. 
         [0083]    At  618 , method  600  looks up empirically determined gain adjustments for intake and exhaust valve overlap duration, intake and exhaust valve overlap position relative to crankshaft position, engine speed, and engine load. The gain adjustments may be empirically determined and stored in table and/or functions that are indexed via intake and exhaust valve overlap duration, intake and exhaust overlap position relative to crankshaft position, engine speed and engine load. Method  600  proceeds to  620  after gain adjustments are determined at  618 . 
         [0084]    At  620 , method  600  multiplies the base gain, blow-through amount, rate of change of engine or cylinder air flow rate, and gain adjustments from  618  to determine the volumetric efficiency correction that is to be added to the cylinder air amount. During conditions where blow-through is zero, the base gain from  614  is multiplied by the rate of change of engine or cylinder air flow rate and the gain adjustments from  618 . When blow-through is present, the blow-through amount is multiplied by the rate of change of engine or cylinder air flow rate, and the gain adjustments from  618  without using the base gain amount of  614 . Method  600  proceeds to  622  after the volumetric efficiency correction is determined. 
         [0085]    At  622 , method  600  adjusts MAP, cylinder air amount, and cylinder residual gas amount. The cylinder air amount is adjusted via adding the volumetric efficiency correction from  620  to the cylinder air amount as determined at  606  or  608 . 
         [0086]    MAP is adjusted for systems that sense engine air flow rate and infer MAP. In one example, MAP is adjusted as is described in the description of  FIG. 5 . In particular, the cylinder air amount is first measured and then compensation is added to the cylinder air amount to account for thermal conditions. The adjusted cylinder air amount is then used to index a curve in a table or function that represents MAP versus cylinder air amount during mapped engine conditions (e.g., curve  530  of  FIG. 5 ). The table or function outputs the adjusted MAP value. 
         [0087]    Cylinder air amount is adjusted for systems that sense MAP and infer cylinder air amount. In one example, cylinder air amount is adjusted as is described in the description of  FIG. 4 . In particular, MAP is measured and cylinder air amount is determined via index a curve in a table or function that represents MAP versus cylinder air amount during mapped engine conditions (e.g., curve  430  of  FIG. 4 ). The table or function outputs a base cylinder air amount. The cylinder air amount compensation is determined and added to the base cylinder air amount to provide a compensated cylinder air amount. 
         [0088]    Cylinder exhaust residual amounts may be determined as described in the description of  FIGS. 4 and 5 . For example, at a MAP sensed or determined from cylinder air amount, base cylinder exhaust gas residual amount may be determined by taking a difference between a maximum cylinder air amount and a mapped cylinder air amount as determined from taking a difference between a curve representing a theoretical maximum air amount that the cylinder can hold at a given pressure at intake valve closing (IVC) (e.g., curve  431  of  FIG. 4 ) and a curve representing a cylinder air amount MAP relationship during nominal mapped engine operating conditions where engine temperature and cylinder valve temperature have time to stabilize (e.g., curve  430  of  FIG. 4 ). 
         [0089]    Compensated cylinder exhaust residual amounts may be determined as described in the description of  FIGS. 4 and 5 . For example, at an adjusted MAP, compensated cylinder exhaust gas residual amount may be determined by taking a difference between a maximum cylinder air amount (e.g., curve  431  of  FIG. 4 ) and a mapped cylinder air amount (e.g., curve  430  of  FIG. 4 ) plus cylinder air amount compensation as determined from taking a difference between a curve representing a theoretical maximum air amount that the cylinder can hold at a given pressure at intake valve closing (IVC) and a curve representing a cylinder air amount MAP relationship during nominal mapped engine operating conditions where engine temperature and cylinder valve temperature have time to stabilize. Method  600  proceeds to  624  after MAP, cylinder air amount, and cylinder residual gas amount are adjusted via the volumetric efficiency correction. 
         [0090]    During conditions where blow-through is determined at a given MAP level, the amount of blow-through can be revised by adding the volumetric efficiency compensation (e.g,  350  of  FIG. 3 ) to the air flow through the engine at the given MAP level and then subtracting the cylinder air amount described by the maximum cylinder volumetric efficiency curve at the given MAP level. 
         [0091]    At  624 , method  600  adjusts engine actuators in response to MAP, compensated cylinder air amount, and compensated cylinder exhaust residual amount. In one example, where cylinder air amount is increased, the engine throttle position may be reduced so that a desired engine torque may be provided. For example, throttle position can be adjusted based on an empirically determined throttle map that provides a throttle position for a desired air flow rate. If the engine air flow rate increases due to thermal conditions, the throttle may be closed to reduce cylinder air amount and to provide a desired air flow rate based on the compensated cylinder air amount. 
         [0092]    In another example, where the cylinder residual amount increases due to thermal conditions, an opening amount of an EGR valve may be decreased to compensate for the additional amount of cylinder exhaust residual. Specifically, if thermal conditions increase cylinder residuals, the EGR valve opening amount may be decreased according to the pressure across the EGR valve and the amount of increase in cylinder residuals. EGR valve flow is commonly mapped based on pressure drop across the EGR valve and position of the EGR valve so the EGR flow can be reduced proportionally to the increase in EGR flow into the cylinder. Of course, the EGR valve may be opened further when EGR flow into the cylinder decreases so as to better match actual cylinder EGR with desired cylinder EGR. Additionally, position of the EGR valve can be adjusted based on compensated MAP so that EGR flow rate more closely matches desired EGR flow rate. In other words, the flow rate through the EGR valve may be based on adjusted MAP. Additionally, intake and exhaust cam overlap can be adjusted to increase or decrease cylinder exhaust gas residual based on the compensated cylinder exhaust residual amount. 
         [0093]    Spark timing may also be adjusted via an ignition system for compensated cylinder air amount and cylinder exhaust residuals. In particular, the spark is provided at a crankshaft angle that is based on compensated cylinder air amount and engine speed. Further, spark may be further adjusted according to a table that accounts for cylinder exhaust gas residual amount, and the table is indexed via the compensated cylinder exhaust gas residual amount so that spark is adjusted according to compensated cylinder exhaust gas residual amount. 
         [0094]    Fuel injector injection amount may also be adjusted according to the compensated cylinder air amount. For example, if the compensated cylinder air amount increases, fuel injection amount may be increased to provide a desired engine air-fuel ratio Likewise, if the compensated cylinder air amount decreases, fuel injection amount may be decreased to provide a desired engine air-fuel ratio. 
         [0095]    During conditions where the blow-through amount increases or decreases, blow-through may be adjusted. In one example, if a change in engine thermal conditions increases an amount of engine blow-through (e.g., when air flow into a cylinder exceeds a cylinder air amount described by a maximum cylinder volumetric efficiency curve) blow-through may be reduce via partially closing the throttle or reducing boost pressure. Method  600  proceeds to exit after engine actuators are adjusted. 
         [0096]    Thus, the methods of  FIGS. 3 and 6  provide for compensating for thermal conditions during transient engine conditions, comprising: adjusting an engine air amount parameter and a cylinder residual gas amount via an engine MAP and cylinder air amount volumetric efficiency relationship in response to a rate of change of cylinder air amount; and adjusting output of an engine actuator in response to the engine air amount parameter. The method may be particularly useful for providing compensating due to valve timing changes resulting from temperature change. 
         [0097]    The method also includes where the engine actuator is a fuel injector, and where the engine air amount parameter is based on a curve empirically determined from a plurality of engine MAP and cylinder air amount readings. The method further includes where the engine air amount parameter is adjusted in response to a curve representing engine volumetric efficiency in a MAP versus cylinder air amount space, and where the curve accounts for residual exhaust gas. In some examples, the method includes where the engine actuator is an air inlet throttle, and further comprising adjusting a position of an EGR valve in response to the cylinder residual gas amount. The method also includes where the rate of change of cylinder air amount is determined via a difference between an air flow rate and a filtered air flow rate. The method further comprises adjusting the engine air amount parameter in response to engine cam timing. The method also includes where the engine air amount parameter is a cylinder air amount estimate and where the cylinder air amount estimate is reduced when an engine temperature transitions from a higher temperature to a lower temperature, and where the engine temperature is a temperature of a valve of a cylinder. 
         [0098]    In another example, the methods of  FIGS. 3 and 6  provide for a method compensating for thermal conditions during transient engine conditions, comprising: adjusting an engine air amount parameter and a cylinder residual gas amount during a condition of blow-through in response to a rate of change of cylinder air amount; and adjusting an output of an engine actuator in response to the engine air amount parameter. The method also includes where the condition of blow-though is estimated from to a difference between a total cylinder air mass flow curve and a maximum volumetric efficiency curve. The method also includes where the engine air amount parameter is adjusted based on a blow-through air estimate. 
         [0099]    In one example, the method includes where the engine air amount parameter is a cylinder air amount estimate and where the cylinder air amount estimate is increased when an engine temperature transitions from a lower temperature to a higher temperature, and where the engine temperature is a temperature of a valve of a cylinder. In this way, changes due to valve temperature may be compensated. The method also includes where the engine actuator is an ignition coil, and where the output of the ignition coil is a spark timing. The method also includes where the engine actuator is a throttle, and where the output of the throttle is a position of a throttle plate. The method further comprises adjusting a blow-through amount in response to a rate of change of cylinder air amount. 
         [0100]    As will be appreciated by one of ordinary skill in the art, the method described in  FIGS. 3 and 6  may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. 
         [0101]    This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.