US 2009.0024.300A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2009/0024300 A1 Turin et al. (43) Pub. Date: Jan. 22, 2009

(54) AIRFLOWESTIMATION METHOD AND (22) Filed: Jul. 20, 2007 APPARATUS FOR INTERNAL COMBUSTION ENGINE Publication Classification (75) Inventors: Raymond Claude Turin, Grosse (51) Int. Cl. Pointe Park, MI (US); Rong Zhang, F02D 28/00 (2006.01) Troy, MI (US); Man-Feng Chang, (52) U.S. Cl...... 701/103 Troy, MI (US) (57) ABSTRACT Correspondence Address: GENERAL MOTORS CORPORATION A method of estimating an air charge in at least one combus LEGAL STAFF tion cylinder of an internal combustion engine includes cal MAIL CODE 482-C23-B21, PO BOX300 culating cylinder mass air flow based upon a modified Volu DETROIT, MI 48265-3000 (US) metric efficiency parameter, and calculating the intake throttle mass air flow based upon a throttle airflow discharge (73) Assignee: GM GLOBAL TECHNOLOGY parameter and a fuel enrichment factor. Three models includ OPERATIONS, INC., DETROIT, ing a mean-value cylinder flow model, a manifold dynamics MI (US) model, and a throttle flow model are provided to estimate the air charge in the at least one combustion cylinder and to (21) Appl. No.: 11/780,508 control delivery of fuel to the fuel delivery system.

Patent Application Publication Jan. 22, 2009 Sheet 1 of 4 US 2009/0024.300 A1

S s Patent Application Publication Jan. 22, 2009 Sheet 2 of 4 US 2009/0024.300 A1

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Josuºs Patent Application Publication Jan. 22, 2009 Sheet 3 of 4 US 2009/0024.300 A1

|38 Patent Application Publication Jan. 22, 2009 Sheet 4 of 4 US 2009/0024.300 A1

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US 2009/0024300 A1 Jan. 22, 2009

ARFLOWESTIMATION METHOD AND 0007 FIG. 1 is a schematic model of a spark ignited inter APPARATUS FOR INTERNAL COMBUSTION nal combustion engine system; ENGINE 0008 FIG. 2 illustrates a method of estimating cylinder air charge without a mass air flow sensor; TECHNICAL FIELD 0009 FIG. 3 is an illustration of the flow of air from atmosphere to a cylinder within the combustion engine sys 0001. The present invention is related to the field of engine tem shown in FIG. 1; controls for internal combustion engines and more particu 0010 FIG. 4 is a block diagram showing the flow of the larly is directed toward estimation of throttle mass airflow as signals produced in the spark ignited internal combustion used in Such controls. engine system shown in FIG. 1; and 0011 FIG. 5 is a correction look-up table used to deter BACKGROUND OF THE INVENTION mine the correction of the throttle discharge coefficient. 0002 The basic objective for fuel metering in most gaso line engine applications is to track the amount of air in the DESCRIPTION OF THE PREFERRED cylinder with a predefined stoichiometric ratio. Therefore, EMBODIMENT precise air charge assessment is a critical precondition for any 0012 Turning now to FIG. 1, a schematic model of a spark viable open loop fuel control policy in Such engine applica ignited internal combustion engine system (System) 20 is tions. As the air charge cannot be measured directly its assess illustrated. The System 20, in the most general sense, com ment, in one way or another, depends on sensing information prises all engine associated apparatus affecting or affected by involving a pressure sensor for the intake manifold, a mass air gas mass flow and includes the operating environment or flow sensor upstream of the throttle plate, or both. The choice atmosphere from which and to which gas mass flows. The of a particular sensor configuration reflects a compromise internal combustion engine includes a naturally aspirated or a between ultimate system cost and minimum performance boosted internal combustion engine. The atmosphere 66 is requirements. Currently, high cost Solutions involving both shown entering the system at the fresh air inlet 22. sensors are found in markets with Stringent emission stan 0013 The System includes a variety of pneumatic ele dards while low cost solutions, mostly involving just a pres ments, each generally characterized by at least a pair of ports Sure sensor, are targeting less demanding developing markets. through which gas mass flows. For example, air induction 0003 Speed-density methods of computing the mass air including fresh air inlet 22, air cleaner 24, and intake duct 26 flow at the engine intake are known in the art. However, is a first general pneumatic element having ports generally employing the speed-density methods in conjunction with corresponding to the air inlet 22 at one end and another port more complex engine applications such as cam-phasing and/ generally corresponding to the intake duct 26 at the other end. or variable valve lift capability has not been practical or Another example of a pneumatic element is intake manifold economically feasible. 36 having ports interfacing with intake duct 34 and intake 0004. Therefore, what is needed is a method for providing runner 38. Other general examples of pneumatic elements in a low cost air charge estimator without the use of a mass air the System include: intake air throttle orifice 86 including flow sensor that provides cylinder air estimation to satisfy throttle body 28 and throttle plate 32; crankcase 50: combus developing market needs. tion cylinder 46 including combustion chamber 48 and intake valve 40 and cam 72: exhaust including exhaust duct 52, and SUMMARY OF THE INVENTION exhaust outlet 54. 0005. An internal combustion engine system includes a 0014. The various elements shown in FIG. 1 are exem controller in signal communication with the engine and with plary and the present invention is by no means restricted only a fuel delivery system, a combustion cylinder and piston to those specifically called out. Generally, an element in reciprocating therein, an intake manifold directing flow of air accordance with the present invention may take the form of a into the at least one combustion cylinder, and an air throttle simple conduit or orifice (e.g. exhaust), variable geometry having a throttle orifice directing flow of air mass into the valve (e.g. throttle orifice) 86, pressure regulator valve (e.g. intake manifold. A method of estimating an air charge in at PCV valve), major Volumes (e.g. intake and exhaust mani least one combustion cylinder of the engine includes: calcu folds) 36.44, or pneumatic pump (e.g. combustion cylinder) lating cylinder mass airflow based upon a modified Volumet 46. ric efficiency parameter, calculating the intake throttle mass 0015. In illustration of the interrelatedness of the various airflow based upona throttle airflow discharge parameter and elements and flow paths in the internal combustion engine a fuel enrichment factor; and using the cylinder mass airflow system 20, a gas mass (gas) at atmospheric pressure enters and throttle mass airflow to estimate the air charge within the through fresh air inlet 22, passing an intake air temperature at least one combustion cylinder. Three models including a sensor 58, and then passing through air cleaner 24. Gas flows mean-value cylinder flow model, a manifold dynamics from intake duct 26 through throttle body 28. For a given model, and a throttle flow model are provided to estimate the engine speed, the position of throttle plate 32, as detected by air charge in the at least one combustion cylinder and to a throttle position sensor 30, is one parameter determining the control delivery of fuel to the fuel delivery system. amount of gas ingested through the throttle body and into the intake duct 34. From intake duct 34, gas enters an intake BRIEF DESCRIPTION OF THE DRAWINGS manifold 36, whereat individual intake runners 38 route gas into individual combustion cylinders 46. Gas is drawn 0006. The invention may take physical form in certain through cam actuated intake valve 40 into combustion cylin parts and arrangement of parts, the preferred embodiment of der 46 during piston downstroke and exhausted therefrom which will be described in detail and illustrated in the draw through exhaust runner 42 during piston upstroke. These ings incorporated hereinafter, wherein: intake and exhaust events are of course separated by com US 2009/0024300 A1 Jan. 22, 2009

pression and combustion events in full four-cycle operation, 0025. The update of the volumetric efficiency correction is causing rotation of a crankshaft 60, creating an engine speed performed through methods known in the art. In one embodi that is detected by an engine speed sensor 62. Gas continues ment of the invention, a Kalman filter which uses the differ through exhaust manifold 44, past the exhaust temperature ence between the measured and modeled manifold pressure sensor 64, and finally through exhaust outlet 54 to atmosphere as an error metric may be used. 66. 0026 Correction of the throttle discharge coefficient is 0016. In one embodiment of the invention, fuel 68 is mixed with the gas by a fuel injector 56 as the gas passes made using a correction look-up table 100, illustrated in FIG. through individual intake runners 38. In other embodiments 5. The correction look-up table 100 evolves as a function of of the invention, fuel 68 may be mixed with the gas at other the operating condition and is based on an airflow estimation points. error metric that is derived from the stoichiometric offset of a closed-loop fuel factor. 0017. In accordance with an embodiment of the invention, various relatively substantial volumetric regions of the inter 0027 FIG. 2 is a flow diagram of cylinder air estimation nal combustion engine system are designated as pneumatic without a mass air flow sensor. FIG. 2 shows a block flow Volume nodes at which respective pneumatic states are desir diagram representing three physical models, including a ably estimated. The pneumatic states are utilized in determi mean-value cylinder flow model 76, a manifold dynamics nation of gas mass flows that are of particular interest in the model 78, and a throttle flow model 80. By measuring com control functions of an internal combustion engine. For mon engine signals except the mass air flow, the system uses example, mass airflow through the intake system is desirably the three physical models, two adaptation loops 90.92 modi known for development of appropriate fueling commands by fying volumetric efficiency and throttle air flow efficiency, well known fueling controls. and information from a known production closed-loop air to 0.018. In accordance with an embodiment of the invention, fuel ratio control algorithm, to calculate the cylinder mass air the system may include a coolant temperature sensor 70 for flow and the throttle mass air flow. sensing the temperature of the coolant. 0028. The invention requires common engine measure 0019. In accordance with an embodiment of the invention ment inputs that include: throttle position sensor 30, manifold including variable camphasing, the angular positioning of the air pressure sensor (MAP) 84, engine speed sensor (RPM) 62. cam 72 providing the actuation of the cam actuated intake barometric sensor or key-on barometric reading of MAPsen valve 40 may be determined by a cam position sensor 85. Sor 84, variable cam phaser position (intake and exhaust) if 0020. In another embodiment of the invention including applicable 85, variable cam lift position 82 (intake and variable cam lifting, the amount of lift provided by the cam 72 exhaust) if applicable, intake air temperature sensor (IAT) 58, providing the actuation of the cam actuated intake valve 40 coolant temperature sensor 70, and exhaust temperature sen may be determined by a variable cam lift position sensor 82. sor 64. 0021 Turning now to FIG. 2, a method of estimating cyl (0029 FIG. 3 illustrates the flow of air 102 through the inder air charge without a mass air flow sensor 96 in accor throttle orifice 86 and the intake manifold 36 as the air moves dance with an embodiment of the invention is illustrated. FIG. from atmosphere to the cylinder 46. 2 shows a block diagram of a mean-value cylinder flow model 0030 FIG. 4 generally illustrates the flow of the signals 98 76, a manifold dynamics model 78, and a throttle flow model produced by the preceding elements and shows the interre 80. latedness of the various components by depicting the infor 0022. A method of cylinder air charge estimation for inter mation exchanged between them. nal combustion engines without using a mass airflow (MAF) 0031. The manifold dynamics model 78 uses both the sensor 96, which satisfies the need of low cost engine control mean-value cylinder airflow and the throttle airflow to deter systems for markets with moderate emission standards is mine manifold pressure error. The throttle air flow is deter provided. The method estimates the cylinder air charge using mined by the throttle flow model 80. The accuracy of the a speed-density approach. The approach includes physics throttle flow model 80 is improved by correcting the throttle based models for the intake manifold dynamics and the air discharge coefficient through use of fuel correction informa mass flow through the throttle orifice 86, and involves adap tion derived from air to fuel ratio close-loop fuel control tive schemes to adjust the throttle air flow discharge param algorithms known in the art. The correction of the throttle eter and the volumetric efficiency parameter. The method is discharge coefficient defines the second adaptation loop 92. applicable to engines with variable valve timing and/or vari 0032 Transient effects of gas mass stored in a substantial able valve lift. The method also adjusts for variations of fuel Volume in a pneumatic capacitance element, such as an intake properties. manifold 36, are generally modeled in the present invention in 0023 The method does not require a mass air flow sensor accordance with the net gas mass in the fixed Volume of Such (MAF) and does not directly use the measurement of an pneumatic capacitance element. At any given instant, the oxygen sensor (O2) or a wide-range air-fuel ratio sensor finite gas mass M contained in the pneumatic capacitance (WAFR). However, a closed-loop fuel control algorithm element of interest may be expressed in terms of the well known in the art that corrects the fuel injection amount based known ideal gas law: on O2 or WAFR measurements is used. 0024. A mean-value model that models the manifold pres PV=MRT (1) sure dynamics and the gas flow through the throttle orifice 86 0033 where P is the average pressure in the volume, V is is shown in FIG. 2. Nominal static models for the volumetric the Volume of the pneumatic capacitance element, R is the efficiency coefficient of the engine (m) and for the throttle universal gas constant for air, and T is the average temperature discharge coefficient (C) are corrected with correction fac of the gas in the volume. The manifold pressure is related to tors that are adjusted by a controller 94, as shown in FIG. 4. the manifold mass (m) through the gas equation (1): US 2009/0024300 A1 Jan. 22, 2009

0041. The mean-value cylinder flow is the average mass airflow rate out of the intake manifold 36 into all the cylinders Pin Vn (2) 46 and is derived from the cylinder air charge. The accumu iii. RT lated cylinder air charge per cycle (m) is a function of the pressure and the temperature conditions across the intake 0034. Differentiation of equation (2) with respect to time valve 40 during the time between intake valve opening (IVO) yields mean-value mass conservation defining a difference and intake valve closing (IVC). More specifically, accumu between the air mass flow through the throttle and into the lated cylinder air charge per cycle (m) may be expressed as manifold (iii) the airmass flow out of the manifold and into follows: C3 the cylinder (rin) for the manifold volume V: m = n : (8) d (3) aire - lett RI. mm = maira - mair. 0042 wherein p is the intake manifold pressure, T is the 0035 Hence substituting equation (2) into equation (3) manifold air temperature, R is the gas constant of the gas yields the relationship between the manifold mass flow (m) mixture at the manifold intake, V is the total cylinder volume and pressure rate of change p. displacement, m is a volumetric efficiency coefficient that relates the actual fresh air charge mass to the fresh air mass that could occupy the cylinder 46 if the entire displaced |Pin Vinyl-ni. Pm in (4) volume (V) were completely replaced with fresh air under l, RT ) = pn if- " RT2 manifold conditions. The value of the volumetric efficiency coefficient (m) depends on the thermodynamic conditions Vin mm Tin during the ingestion process and on the valve timing and the - PRI. - T. lift profile. = ritair - itair 0043. The volumetric efficiency coefficient (m) may be determined from a look-up table or from an analytical func tion based on physics. 0036. The principle of energy balance applied to the intake 0044) A speed density equation that provides a basis for manifold volume yields: fuel metering calculations defines a mean-value cylinder flow (rin)air. that may be derived from equation (9) as follows: (mney Tn) imney Tin + m,ncy Tin (5)

= finair, CpTih - ritair CpTin mair = n.leff Pnet.RT 2. (9)

I0037 wherein C, and C are the isochoric and isobaric 0045 wherein n is the engine speed and in is the mass heat capacities for air, and T is the gas temperature at the flow out of the manifold 36 and into the cylinder 46. The throttle orifice. Combining (2) and (5) yields equation (6): symbols p and T are the ambient and manifold pressures Tin-th and temperatures, respectively, R is the specific gas constant airti, and the isentropic exponent of air, V, the cylinder displace 0038. Substituting equation (6) into equation (4) defines ment volume, in the engine speed, and m is the volumetric the manifold pressure rate of change p. efficiency of the engine. Pumping effects of a flow source on intake air mass flow, for example due to the engine and effecting the air mass flow at the intake manifold, may be RK (7) approximated by the well known speed-density equation. p = i (mair, Tin -mair. Tn) 0046. The engine and manifold pressure parameters are split into a known nominal part (SuperScript 0) and into an 0039. The mean-value cylinderflow model 76 includes the unknown correction part (prescript A). The nominal parts of calculation of a nominal volumetric efficiency musing the the volumetric efficiency and of the throttle discharge coeffi measured inputs. The mean-value cylinder flow model also cient are either calculated from static engine mapping data includes a volumetric efficiency correction based on the dif (look-up table approach) or via regression functions. ference between the estimated manifold pressure (as obtained 0047. The dynamics of the manifold pressure are from the manifold dynamics model) 78 and the measured described according to methods known in the art using a manifold pressure, obtained from measurements made by the non-minimum order model representation as follows: MAP sensor 84. The volumetric efficiency correction is made using a first adaptation loop. O V in V in (10) 0040 Volumetric efficiency is corrected through the use of (i) = -(nit +k)K. sco - Kv3 pm a manifold pressure error metric determined from a difference in actual measured manifold pressure and estimated manifold V in Rk pressure and is input into the mean-value cylinder flow model W. 2 Whair, Th 76. US 2009/0024300 A1 Jan. 22, 2009

wherein A, is the throttle orifice area, C is the throttle dis -continued charge coefficient, p, and T are the ambient pressure and temperature, respectively, and up is the dimensionless com p = (ks - Aneff)co1 + Co.2 pressible flow coefficient expressed as follows:

0048. The parameter k is an arbitrary design parameter which is used to obtain desirable transient properties for the (17) non-minimum order model 0049. The non-minimum representation model for the manifold pressure dynamics is used to design a state estima tor according to the principles of an extended Kalman-filter for the unknown state 6-k-Am based on the known inputs and outputs rh, and p, respectively, where mair, is the mass airflow through the throttle 28 into the manifold 36. The 0056 wherein K is the isentropic coefficient for air. Kalman-filter state estimator equations are given below: 0057 Similar to the representation of the volumetric effi ciency parameter, the throttle discharge coefficient (C) is 0050 Estimator extrapolation step: represented in terms of a known nominal (CA) and unknown portion (AC) as defined in equation (18): C=C+AC, (18) XI-X-1+9. (11) 0.058 Substituting equation (18) into equation (16), the 0051 Estimator update step: throttle air mass flow in may be expressed as specified in equation (19): (iii,

-l KX-R-101012-i-101F.S.) na, = A (C + AC4) ?eek ) (19) X-1-K-01-XI-1 (12) VRT, Pa 0052. The symbol X denotes the state covariance matrix, K the Kalman gain and Q and S are filter design parameters, 10059) With AC, as the estimate of AC, a throttle mass flow respectively. While the filter design parameters Q and S sig estimate rh, is derived from (19) as follows: nify in principle the state and the output noise covariance (and are hence determined by the statistical properties of the underlying process signals) they are typically chosen arbi - a y Pa Pn (20) trarily in such a way that desired filter performance is estab finair, = Ash (C + AC) fee :) lished. The Kalman filter provides an accurate estimate of the parameter 0 provided that the throttle flow input is accurate. 0060 Assuming that the nominal value of the throttle dis The volumetric efficiency correction Amis calculated from charge coefficient is erroneous, an accurate estimate of the the estimate 0 as follows: throttle mass flow may be obtained if the correction term AC may be determined. To determine the correction term AC. An-k-6 (13) initially, the normalized air-fuel (A/F) ratio w is defined as 0053 An estimate of the volumetric efficiency can be cal follows: culated from a nominal Volumetric efficiency parameterm of and the volumetric efficiency correction parameter Am k 0 as follows: maire (21) = Filmf in ne?t Any (14) 0054 An estimate of the cylinder air charge (8) and of the 0061 The normalized A/F-ratio v is given as the ratio cylinder air flow (9) can be calculated using the estimate for between the amount of cylinder air (m) and the amount of the volumetric efficiency as follows, respectively: fuel (m) in the cylinder scaled by the fuel's stoichiometry factor (f). 0062. The normalized A/F-ratio (W) assumes a value of one , - a Pm a (15) under stoichiometric mixture conditions. The fuel is typically metered as a function of an estimate for the air charge (m) and a fuel enrichment factor (f) and may be expressed as follows:

1 22 mf = fair. (22) 0055. The air mass flow into the intake manifold 36 through the throttle orifice 86 (rin) may be expressed in 0063 Substituting (22) into (21) yields the normalized terms of the compressible flow equation (16) as follows: A/F-ratio (0):

filair,. -F Ath Cd V"Pa PnE} (16) fair (23) finair. US 2009/0024300 A1 Jan. 22, 2009

0064. Assuming that the fuel enrichment factor (f) is estimate of the discharge correction parameter AC equals the adjusted by existing closed-loop A/F ratio control algorithms actual value AC. A discrete-time adaptation scheme for the Such that the engine is running at a stoichiometric mixture unknown throttle air flow discharge parameter AC is readily ratio at all times, expression (23) may be expressed as: derived from equation (29) as follows:

f = lair. lair.. (24)24 dACdk = kodem = kod (f(t)-liair, (t) (30) airc iii. ACdk = AC4-1 + dACas

0065. Thus, the fuel enrichment factor (f) describes the 0071. A more sophisticated adaptation policy involving an ratio between the actual amount of air in the cylinder 46 (or adjustable gain is not favored for two reasons: 1) With the the airflow into the cylinder 46) and an estimate of amount of assumptions and modeling errors associated with equation air in the cylinder 46 (or the air flow into the cylinder 46). (30) together with a need to separate the adaptation rates of Hence, deviations of the enrichment factor (f) from a value the Volumetric efficiency correction and the discharge correc of one precisely characterizes the air flow (or air charge) tion, only a very low adaptation bandwidth would function estimation errors (e) defined by equation (25): well, and 2) since the discharge error AC is probably not constant but a function of both the throttleposition C, and the throttle pressure drop r, the adaptation is implemented in the en = fair - finai - (f - 1)tiair (25) form of a block learn scheme. 0072 A block learn table for throttle discharge correction 100 is defined according to FIG. 5. Per the nomenclature 0066 Under steady state conditions, the mass flow introduced in FIG. 5 and the adaptation scheme incorporated through the throttle orifice 86 in equation (30), the update of the block-learntable evolves as follows: 0073. 1) Calculate the incremental correction for the cur (iair) rent operating point according to equation (31): and the mass flow through the engine dACdk = kcd(f(t)-liair, (t) (31)

(fair.) 0074 2) Identify the four grid points that surround the current operating point and calculate weighting factors for are equivalent: each grid point as follows:

ii Oth (th 32 hair, = fair (26) f = 1, = , (32) hair, = fair gii = (1-fi) (1 - fi), gi+1} = f(1 - fi), 0067 Hence, Substituting equation (26) into equation (25) gi. 1 = (1 - fi) fi, yields: gi+1.j+1 = fif

en = fair, fair,s (f - 1)nair,s (27)27 (0075) wherein C, is the angle of the throttle plate 32, r is the ratio of manifold pressure to ambient pressure. (0076. 3) Update the table value in each of the four current 0068 Subtracting (20) from (19) leads to equation (28): grid-points according to

air - finair...s = (ACd - ACdr At Pa , Pm (28) hair, hair, ( d a) Vief) 0077. In the absence of a mass flow sensor, accuracy of this signal is established gradually by using an adaptive scheme 0069 so that (27) finally becomes for the unknown discharge correction as follows:

s r Pa Pn 29 ACdk = AC4, +ked (f - liair. (34) en = (f - 1)iai = (AC4 - ACa)Ath fief) (29) 0078 Here the symbol f, stands for the closed-loop fuel (0070 Thus, the air flow estimation error (e) is elimi correction factor and k is the adaptation gain. This gain is a nated for arbitrary throttle and pressure conditions if the discretionary parameter and is selected to be small enough to US 2009/0024300 A1 Jan. 22, 2009 establish stable adaptation and yet large enough to achieve a sensible adaptation response time. Because the adaptation -continued bandwidth is rather small, the update law described in equa tion (3) is used along with a look-up table 100 for the dis hairne, (1 -- AC4)n: f charge correction. The use of look-up tables accounts for the hairm, if Ps Prf fact that the discharge erroris typically not constant across the fair = Pit entire engine operating envelope but rather a function of the throttle position and of the pressure conditions across the " in hit (1-km) no if its pe. throttle orifice 86. The look-up table is updated in the four neighboring grid-points of the actual operating point (in I0085 More particularly, when the pressure ratio exceeds a terms of throttle position C, and pressure ratio It, across the certain threshold p, the throttle mass flow is calculated as the throttle plate 32). Hence, weighted average of a mass flow value in which is based on a compressible flow equation approach and a mass flow value rh. The mass flow value in is based on a speed Acan = AC-1 mint gmin -ka (fix - liair, v in ei, i + 1, (35) density equation approach. The arbitration factor ke01 is a calibration parameter and is implemented in terms of a in ei, i + 1 lookup table with respect to pressure ratio. The calculation of the discharge correction estimate AC is independent of the 007.9 The indices i and denote the ith grid point on the load case and remains as described in equation (36). Simi throttle position axis and the jth grid point on the pressure larly, the update of the discharge error lookup table is inde ratio axis, respectively. The parameterg, is a weighting pendent of the load case and remains as described in equation factor associated with the update of the grid point with indices (35). (m, n) that accounts for the distance of the actual operating I0086. The invention has been described with specific ref point from that particular grid point (the weighting factors of erence to the exemplary embodiments and modifications all four grid points add up to a Sum of one). thereto. Further modifications and alterations may occur to 0080. The continuously updated look-up table is then used others upon reading and understanding the specification. It is to calculate the discharge correction term AC applied in (19). intended to include all Such modifications and alterations With the notation introduced above, the mathematical formal insofar as they come within the scope of the invention. ism to describe this step is given as follows: 1. Method of estimating an air charge in at least one com bustion cylinder of an internal combustion engine including a controller in signal communication with the engine and with ACdk = X.i+1 X.i+1 gm.nacan, (36) a fuel delivery system, a combustion cylinder and piston reciprocating therein, an intake manifold directing flow of air into the at least one combustion cylinder, and an air throttle having a throttle orifice directing flow of air mass into the I0081 For the slow adaptation loop 92 of throttle flow intake manifold, the method comprising: model 80, active closed-loop fuel control, precise knowledge calculating cylinder mass airflow based upon a Volumetric of the Stoichiometric factor F, and accurate fuel metering are efficiency parameter; assumed. In cases when these assumptions are not true, the calculating the intake throttle mass air flow based upon a throttle flow adaptation loop 92 needs to be disabled by turn throttle air flow discharge parameter and a fuel enrich ing off switch SW, 88 in FIG.2. Examples of these circum ment factor; and stances include, but are not limited to, a fuel property change using the cylinder mass air flow and throttle mass air flow as detected by a refuel event, a fuel injector fault as detected to estimate the air charge within the at least one com by fuel injector diagnostics, and an oxygen sensor fault as bustion cylinder. detected by emission diagnostics. 2. The method of claim 1, further comprising: 0082. During the time when the throttle model adaptation using a set of engine measurement parameters input into a is disabled, the F value is based on existing fuel type detec mean-value cylinder flow model to calculate a nominal tion algorithms. Meanwhile, the throttle flow model 80 uses Volumetric efficiency parameter. the nominal value of the discharge coefficient C. 3. The method of claim 2, further comprising: 0083. The correction of the discharge coefficient consti using a manifold dynamic model to estimate a manifold tutes the second adaptation loop 92. pressure; 0084 Under high load conditions when the pressure ratio comparing a measured manifold pressure with the esti across the throttle plate approaches a value of one the com mated manifold pressure to determine a manifold pres pressible flow equation becomes increasingly inappropriate Sure error metric; and to characterize the mass flow through the throttle orifice. For updating the nominal Volumetric efficiency parameter with this purpose the calculation of the throttle flow equation (20) a corrected Volumetric efficiency parameter using the is modified for high load conditions as follows: manifold pressure error metric. 4. The method of claim 3, further comprising: correcting the Volumetric efficiency parameter using the iairs = Ah (C + Aca)a y VRT,Pa { E}Pm (37)37 manifold pressure error metric; and inputting the corrected Volumetric efficiency parameter into the mean-value cylinder flow model. US 2009/0024300 A1 Jan. 22, 2009

5. The method of claim 4, further comprising: 13. The method of claim 12, further comprising: determining a mean-value cylinder flow, wherein the determining a fuel enrichment factor, wherein the fuel mean-value cylinderflow is an average mass airflow rate enrichment factor is a ratio of an actual amount of air in out of the intake manifold into each combustion cylinder the combustion cylinder and an estimate of an amount of within the internal combustion engine. air in the combustion cylinder. 6. The method of claim 5, further comprising: 14. The method of claim 13, further comprising: determining the air flow estimation error metric of the fuel using a speed density calculation to determine the mean enrichment factor when the fuel enrichment factor does value cylinder flow. not equal a value of 1. 7. The method of claim 5, further comprising: 15. The method of claim 14, further comprising: using the mean-value cylinder air flow and the intake eliminating the airflow estimation error when an estimated throttle mass airflow to determine the manifold pressure throttle air flow discharge parameter equals an actual error metric. value of the throttle air flow discharge parameter. 8. The method of claim 1, further comprising: 16. The method of claim 10, further comprising: using a first adaptation loop to correct the Volumetric effi using a block look-up table to determine the corrected ciency parameter, and throttle air flow discharge correction parameter. using a second adaptation loop to correct the throttle air 17. The method of claim 16, wherein the corrected throttle flow discharge parameter. air flow discharge parameter is a function of the air intake 9. The method of claim 8, further comprising: throttle position and of pressure across the throttle orifice. disabling the second adaptation loop whena Stoichiometric 18. The method of claim 1, wherein the internal combus fuel enrichment factor and accuratefuel metering are not tion engine comprises a naturally aspirated or a boosted inter known. nal combustion engine. 19. Method of estimating an air charge in at least one 10. The method of claim 1, further comprising: combustion cylinder of an internal combustion engine includ inputting throttle position measurements into a throttle ing a controller in signal communication with the engine and flow model; with a fuel delivery system, a combustion cylinder and piston calculating a nominal throttle airflow discharge parameter reciprocating therein, an intake manifold directing flow of air associated with the throttle flow model; into the at least one combustion cylinder, and an air throttle deriving an airflow estimation error metric from a stoichio having a throttle orifice directing flow of air mass into the metric offset of a closed-loop fuel enrichment factor; intake manifold, wherein the engine has cam-phasing and and variable valve lift capability, the method comprising: updating the nominal throttle airflow discharge parameter calculating cylinder mass airflow based upon a Volumetric with a corrected throttle air flow discharge parameter efficiency parameter; based on the air flow estimation error metric. calculating the intake throttle mass air flow based upon a 11. The method of claim 10, further comprising: throttle air flow discharge parameter and a fuel enrich estimating air flow through the throttle orifice; and ment factor; adjusting the air flow through the throttle orifice in accor using a first cylinder air mass flow adaptation loop to dance with the corrected throttle air flow discharge update the Volumetric efficiency parameter, parameter. using a second throttle mass flow adaptation loop to update 12. The method of claim 11, further comprising: the throttle air flow discharge parameter; and correcting the throttle airflow discharge parameter using a using each of the first cylinder air mass flow adaptation normalized air-fuel ratio, wherein the normalized air loops and the second throttle mass flow adaptation loop fuel ratio is the ratio of an amount of combustion cylin to estimate the air charge within the at least one com der air and an amount of fuel in the at least one combus bustion cylinder. tion cylinder scaled by a stoichiometric fuel enrichment factor associated with the fuel.