EP2409010A1

EP2409010A1 - Method for determining the spark advance of a heat engine

Info

Publication number: EP2409010A1
Application number: EP10708337A
Authority: EP
Inventors: Ludovic Nowak; Smaïl MOKHTARI
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2009-03-16
Filing date: 2010-02-11
Publication date: 2012-01-25
Also published as: FR2943100B1; FR2943100A1; WO2010106259A1; CN102428260A; BRPI1006744A8; BRPI1006744B1; BRPI1006744A2; CN102428260B

Abstract

The invention relates to a method for determining the spark advance of a heat engine of a vehicle using a physical model that uses input parameters. The method comprises the following steps: using a test bench, determining different values of calibration parameters associated with several engine-speed/engine-load pairs, said values of the load/speed pair and the values of said calibration parameters defining reference points; determining the values of the input parameters for each operating cycle of the vehicle; storing, in a computer onboard said vehicle, said reference points, said input parameters and said physical model consisting of at least two equations; and calculating said spark advance of said engine from said reference points, said input parameters and said physical model.

Description

METHOD FOR DETERMINING THE ADVANCE AT IGNITION OF A THERMAL MOTOR

The present invention claims the priority of the French application 0951644 filed March 16, 2009 whose content (text, drawings and claims) is here incorporated by reference. The present invention relates to a method for determining the ignition advance of a spark ignition engine.

[0003] A spark ignition internal combustion engine is a machine in which the thermal energy released by combustion is converted into mechanical motive power. In this type of engine, unlike the diesel engine, the fuel mixture does not ignite spontaneously, but under the action of a spark caused by a candle. To maximize the fuel efficiency of combustion the fuel mixture must be ignited so as to match the peak pressure in the combustion chamber with an ideal position of the piston / crankshaft torque. However, there is a delay between the moment when the spark is produced and the moment when the ignition of the mixture propagates, corresponding to the beginning of the sharp combustion phase of the mixture and to obtaining a peak of maximum pressure in the combustion chamber. It is for this reason that the ignition of the candle is triggered with an advance.

The electronically controlled ignition advance by a computer, expressed in degree of rotation angle of the crankshaft, corresponds to the angle between the triggering of the spark and the top dead center of the piston. The advance value makes it possible to synchronize the appearance of the pressure peak in the combustion chamber with the optimum and predetermined position of the piston in the combustion chamber.

At present, the setting and obtaining optimum ignition advance values are determined during the development of the engine for all operating conditions that may be encountered by the engine. These optimal advance values determined on the calibration banks are then stored in the form of several maps and control strategies in the engine computer. This calibration phase currently requires a large number of engine tests. The addition of additional actuators by manufacturers (camshaft phase shifters), in order to comply with increasingly stringent environmental standards and limit consumption, significantly increases the number of engine tests needed to develop them.

The technical solution proposed by the present patent application limits the number of tests and thus reduce the cost and duration of the engine calibration phase.

Instead of tabulating the ignition advances and subsequently making linear or polynomial interpolations between the tabulated points, the invention proposes to use a calculation algorithm based in part on the physics of combustion. . According to the invention, the ignition advances are calculated from equations which retranscribe the thermodynamic evolutions in terms of differences in advance with respect to tabulated reference advances. More specifically, the present invention relates to a method for determining the ignition advance of thermal engines using a physical model using input parameters, the method comprising the steps following:

By using a test bench, to determine different values of calibration parameters associated with several engine speed-engine load torques, said parameters making it possible to estimate the average flame speed from the thermodynamic conditions in a chamber combustion engine, said load-speed torque values and the values of said calibration parameters constituting the fulcrums;

• determining the values of said input parameters for each engine operating cycle;

• register in an on-board computer on said vehicle said support points, said input parameters and said physical model represented by at least two equations; and

From said points of support, said input parameters and said physical model, calculating said ignition advance of said motor. This method is advantageously valid throughout the range and in all operating modes of spark ignition engines.

In a variant, said calibration parameters may comprise the following parameters: the optimum ignition advance of reference AAO _ref , the point FMBx _ref corresponding to a burned fraction of x% of the total mass of the mixture; a reference initialization constant C | _N ι _ref , a combustion constant Cc _MBref βt an estimated global laminar flame speed SL _ref .

In a variant, said input parameters may be chosen from the following parameters:

• the mass of fresh air admitted into the cylinder ( ^mr )

• the mass of gas burned in the cylinder ( ^{mGBR = MlGR + mEGR} ) • the fuel mass in the cylinder ( ^m ≈ ^" *)

• the load (^ ")

T

• the average temperature ( ^{MEL (} ' ^rc) ) of the gases in the cylinder at the time of closing of the intake valves

• the ratio (' ^MEL ') of the heat capacity at constant pressure and the heat capacity at constant volume of the mixture

• the molar mass ^(M MEL) o _f the mixture air + fuel + residual burnt gas and recirculated

• the opening angle of admission (OA)

• the engine speed (N).

T

• the engine water temperature ( ^water ). In a variant, said ignition advance AAO is determined by calculating the combustion time of the point FMBx at the point FMBy respectively corresponding to x% and y% of the fuel burned and the ignition delay for FMBx

In a variant, the evolution of the pressure and the temperature of the air-fuel mixture in the combustion chamber of the engine during the combustion cycle is determined.

In a variant, said physical model can be represented by two equations, one giving the initialization delay to the combustion (D | _N0 depending in particular on a constant (C | _N | ₎ , the other giving the duration of the burning time (D _C MB) in particular according to a constant

In a variant, in order to calculate said ignition advance (AAO): a- an estimated value (AAO _e st _ιm ) of the ignition advance is calculated using a relationship of proportionality with the speed laminar flame; b- the optimum ignition advance (AAO) is determined by iteration, the first iteration comprising: * the calculation of the initialization delay D | _N , from the estimated optimum advance AAO _estιm and said points of support,

^* the determination of FMBx from the values of D | _N , and AAO _estιm

^* calculation of the combustion time D _C MB from FMBx, and

^* the calculation of the ignition advance optimum AAO c- the value of said optimum ignition advance AAO can be corrected by taking into account the engine temperature

In a variant, the initialization delay (D, _N |) can be calculated using an equation of the type: In a variant, the combustion time (DCMB) can be calculated using an equation of the type:

with: H _{ch (FMBy)} length characterizing the distance to be traveled by the flame front of the mixture ignited for an amount of mixture burned at y%, [0018] In a variant, the preceding step b may advantageously comprise two steps of iteration, the second iteration being performed using the value of FMBx obtained with the first iteration.

In a variant, the value of FMBx from the preceding step b can be determined by FMBx = D | _N | - AAO _is . _m, the value of D | _N , being that obtained by the first iteration. In a variant, the ignition advance AAO can be determined by:

AAO = - FMBy _ref + D | _Nht1 + D _CM B m

FMBy _ref being the value of FMB obtained by calibration, D | _N , _lt1 and D _C MB _M being the values obtained using said first iteration. [0021] Said estimated value (AAOestim) can be determined from an equation of the type:

AAO _^ = C _AAO * l ₊ ^ ^"SL - ^] * AAO _ref

The estimated flame speed (SL _estιm ) can be determined using an equation of the type:

gold _ gold χ

[0023] Advantageously x = 5 and y = 50.

Other advantages and features of the invention will become apparent from the following description of an embodiment of the invention, given by way of non-limiting example, with reference to the accompanying drawings and in which:

FIG. 1 schematically illustrates the method according to the invention, and FIG. 2 illustrates the various angular positions taken by the crankshaft, as well as the initialization delay D | _N | and the burning time D _C MB-

The presentation of an embodiment of the invention makes use of numerous abbreviations. We will first give, under the heading Nomenclature, the meaning of these abbreviations.

Nomenclature

AAO: Optimum ignition advance TDC: Top dead center

D | _N | : Initialization delay or delay between ignition (AA) and the 5% FMB point. D _C MB: Burning time or delay between 5% FMB point and 50% FMB point. GBR: residual and recirculated burn rate (which is equal to IGR + EGR, IGR means "Internai Gas

Recirculation "and EGR" External Gas Recirculation ") GBR = ^^ ≤ m _GBR + m _mr + m _carb

H _ch : length characterizing the distance to be traveled by the flame front of the lit mixture. IVC: "Intake Valve Closing" which is the angle of the crankshaft at the moment when the intake valve closes K _Aero : aerodynamic correction coefficient. L: length Ld: "Load": Load or fill

BKM: mass fraction burned

FMBx and FMBy: point corresponding to a burned fraction of respectively x% and y% of the total mass of the mixture. This point can be expressed preferably in degrees of crank angle or time. v + v

R _vo i: volumetric ratio o compression ratio R _{vg [} = dead cyl

Vmort: volume of the combustion chamber when the piston is in the top dead center PMH Vcyl = volume swept by the piston

FRG: Delay Closure Admission o IVC "Intake Valve Closing" (Angle of closure of the intake valves)

SL: Laminar flame speed

SL ₀ : Laminar flame velocity measured under standard conditions of pressure and temperature. χ ₀ = - ^air - ^stoch : Stoichiometric coefficient: this is the ratio of the air mass and the fuel to the

"Icarb stock stoichiometry m: mass flow

PCI: Lower Calorific Value

Cp: Heat capacity at constant pressure

Index

Air: fresh air

Air swept: air that passes directly from the intake manifold to the exhaust manifold through the combustion chamber when the intake valves open and the exhaust valves close CMB: combustion in point FMB50 comb: with combustion

INI: initiation i.e. between ignition and point FMB5 it1: first iteration it2: second iteration MAP: debugging

MEL: mixture. The mixture consists of air, EGR, IGR and fuel. ref: reference point calibrated in focus wcomb: without combustion

The energy released by the combustion is optimally recovered in the form of mechanical energy by the piston when the FMB50 is wedged to a specific position after the Top Dead Center (TDC) this corresponds to a given operating point ( Speed / load) to adjust the ignition timing to obtain the optimum torque output crankshaft. Indeed, it is when the maximum torque of the engine operating point is reached, the engine consumption is minimal. To do this, the combustion of the mixture must be initiated earlier by taking into account the initialization and combustion time of the fuel mixture. The principle of the model consists of estimating these delays according to the thermodynamic conditions of the fuel mixture and the engine control to calculate the optimum ignition advance (AAO). By calculating the burning time from FMB5 to FMB50 and the timing of ignition at FMB5 according to the physical equations proposed at reference [1] below (equations hereinafter referred to as Hires et al. Equations), it is possible to determine the crankshaft angle at which the ignition of the mixture must be carried out.

The following description relates to a mode of implementation referring to 5% of the burned fuel mass (FM B5) and 50% (FM B50). These percentages could be different and, in general, these percentages are x% and y%.

Initialization and combustion times can be determined from physical models based on knowledge of the thermodynamic conditions in the cylinder. The following two articles [1] and [2] give useful models and equations:> - [1] Hires S. D., Tabaczynski RJ. and Novak J. M., The Prediction of Ignition Delay and Intervals Combustion for a Homogenous Charge, Spark Ignition Engine. SAE 780232

> - [2] Metgalchi M. and J.C. Keck, Burning velocities of mixtures with Methanol Isooctane and Indolene at high pressure and temperature, Combustion and Flame, 48, pp. 191-210, 1982.

FIG. 2 illustrates the various angular positions taken by the crankshaft, as well as the delays D | _N , (initialization delay) and D _C MB (burn time).

The initialization delay and the burning time can not be calculated directly. In order to calculate them, it is necessary to know the pressure and the temperature of the mixture at the moment of ignition and in particular at the FMB5. The evolution of the pressure and temperature of the mixture enclosed in the combustion chamber during the combustion cycle can be estimated via adiabatic compression calculations and simple calculations of the temperature increase due to combustion, but to feed correctly the equations of Hires et al. With the correct pressure and temperature levels, the ignition angle and the angle at which 5% of the fuel has burned (FMB5) must be estimated as accurately as possible. These will be obtained by iteration.

At first the ignition angle is estimated by a simple relationship of proportionality with the laminar flame speed FMB50.

ΛAO _{m m} = [l ₊ ^{SL- L _L ^S ^ ^J AAO _ref eq.1

Indeed, the speed of propagation of the flame front is the physical parameter which has an influence of order 1 on the ignition advance. The flame speed changes with pressure and temperature. For this first calculation of proportionality, the thermodynamic conditions obtained at FMB50 are used. SL _estimated * (1 - C _GBR * GBR) eq.2

The AAO _ref and SL _ref are taken from maps, functions of the speed and the load, predetermined during the calibration of the engine. We take the values of AAO _ref and SL _ref located at the same level of load and speed as the operating point for which we want to determine the advance.

From this first estimate of the AAO, begins the calculation of the advance ignition optimum with the equations of Hires et al. The initialization time is calculated with the pressure and the average temperature of the cylinder between the previously estimated AAO and the angle at which 5% of the fuel fraction burned. At this point, the angle at which 5% of the fuel burned (FMB5) is not precisely known. To remedy this, a mapping of FMB5 optimal combustion was predetermined during the calibration phase of the engine.

Ci _N i _ref is a value derived from a two-dimensional cartography regime and predetermined load during the calibration phase. K _aero is a coefficient which transcribes the internal aerodynamic level prevailing in the combustion chamber. It is a function of the speed and the angular phase shift of the cam shaft relative to the crankshaft. The average speed of the piston function of the regime present in the equation of Hires et al. was replaced by _K _umber -

The determination of NU and H is given in the description of the detailed embodiment given below.

From the estimated AAO and the initialization time previously calculated, a new value of FMB5 of the operating point is approximated:

FMB5 _estimate = D _INIU1 - AAO _estimate eq.4

This new value of the angle where 5% of the burned fuel fraction makes it possible to calculate the combustion time, in particular the representative height H in equation 5 of the scale of turbulence present in the chamber at this moment. of combustion.

^D CMB ₁₁₁ = ^C COMB _r4 °

The values of SL _C MBJ _H , NU _C MB m are calculated at the conditions of pressure and temperature estimated at FMB50 (see detailed description). After calculating the initialization delay and the combustion time, a new estimate of the optimum ignition advance can be calculated according to the following equation: AAO _ιΛ = -FMB50 _ref + D _INhΛ + D _CMBA eq.6

Then, a second iteration is performed. At this new AAO _lt1 are associated new thermodynamic conditions different from those at the time of the determination of the AAO _es u _m - A new calculation of the initiation time is thus carried out (idem eq.3). A new value of FMB5 is then deduced (same as 4). The calculation of a burn time is performed. Compared to the first iteration, only the value of H _CM B changes. Again by Equation 6 a new AAO is determined. This iterative calculation could thus be continued several times in order to obtain a better level of precision on the estimation of the optimal advance, but for questions of time of use of the processor of the onboard computer the iterations are preferably limited to two. To summarize, the calculation of the AAO is iterative. The first step is the initialization stage of the calculation with the estimation of the AAO by a simple relation of proportionality with the laminar flame speed. The second step is the first calculation using the equations of Hires et al. At this stage, not yet knowing the value of the FMB5, we rely on the value of FMB5 _ref determined during the calibration phase. During this phase, a significant number (for example a hundred) so-called "reference" or "support" operating points distributed in the plan-load plan were determined at the test bench with a feedrate adjusted optimal. For this multitude of points, the values of C | _N ι _ref , C _CMBref , FMB5 _ref , FMB50 _ref , SL _ref , AAO _ref have been calculated and tabulated in two-dimensional maps of speed and load. Between this hundred points linear interpolations are made to have access to all the values in the regime-load plan. At the end of this second step an AAO is obtained. From this AAO, the same iterative calculation is done but with the new value of FMB5 that has been obtained.

The advantage of this model is to be able to predict the optimum ignition advances from a few determined support points to the engine bench (which are derived constants necessary for iterative calculation: C | _N ι _ref , C _CMBref , FMB5 _ref , FMB50 _ref , _ref SL, AAO _ref ). The model recalculates the advances taking into account the evolutions of the thermodynamic conditions and the phase displacements of the camshafts with respect to the points of support.

The pressure and the temperature of the mixture in the combustion chamber are not measured directly, these quantities are approximated and then used to calculate the propagation time of the flame in the cylinder. The main steps of the method are shown schematically in FIG. 1.

Synoptically, the first step is to estimate the advance ignition optimum AAO _es u _m , "coarse" taking into account only the speed of propagation of the laminar flame. For this we use the engine parameters which are indicated in Appendix 1 below and the calibrations (or support points) predetermined, indicated in Appendix 2, during the development of the engine on test bench. .

Then, the optimum ignition advance AAO is determined by two calculation iterations. This determination is based on the calculation of the pressure and the temperature for each combustion phase (initialization phase and combustion phase), as well as on the calculation of the viscosity NU kinematics and laminar flame velocity SL from the thermodynamic conditions in the combustion chamber. The first iteration consists of the following steps:

- calculation of the initialization delay D | _Nht1 from the estimated optimal advance AAO _estιm and calibrations, including FMB5. - determination of the point FMB5 _is tιm from D | _N , _lt1 and AAO _are tιm, with FMB5 = D | _N , _lt1 - AAO _is tem. calculation of the combustion time D _C MB _M from FMB5, and

- calculation of the optimal advance AAO _lt1

The second iteration comprises the following steps: calculation of the initialization delay of the combustion D | _N , _lt2 , and calculation of the combustion time D _CM B _ι e which leads to an uncorrected ignition advance value AAO _w∞rr

The value AAOwcorr is then corrected by considering aspects not taken into account by the model (engine water temperature). This advance correction is mapped and added to the optimal advance to provide the value of AAOcorr.

Detailed description of an embodiment:

In order not to burden this description, certain calculations are described below in an "Appendix of the calculation method", composed of annexes 1 to 7.

1. Optimal ignition advance (AAO) estimation [0050] The first step in the calculation is to make an estimate of the AAO:

ΛAO _ism = C _AA A l ₊ ^K - ^f _sL ^ ^J \ * AAO _ref eq. 1 ^'

To do this, the engine parameters (see Appendix 1) and the predetermined calibrations during the development (see Appendix 2) are used. These parameters make it possible to estimate the average flame speed from the thermodynamic conditions in the combustion chamber.

(T Y (P Ϋ eq 2 '

SL _^ = SL, * (-C _-CBR * GBR) τ _n P _n

The temperature at the point FMB50 _ref (eq.3 ') is estimated from the increase in temperature due to the compression of the mixture (it is considered that the compression of the gases enclosed in the cylinder is adiabatic). It is determined from the temperature of the gases locked at the time of the closing of the intake valves (IVC) on the one hand, and of a temperature increase related to the combustion of 50% of the mixture (law of release of simplified heat, eq 5 '), on the other hand, such as:

T _M EL (FMB5Q _mf ) ⁼ ^ MEL _wcomb + ^ MEL _{comh (50} _%) ^β q.3 ' with

J ¹ - T * _r mmma-l

^MEL ^ _o ^ ( ^FMB50 _re f) ¹ MEL (IVC) ^ eff (FMB50 _ref ) eq.4 'and

0.5 * m _carb * PCI

AT M _λ EL _comb (50%) eq.5 'm, "Cp _M [0053] The pressure at the point FMB50 _ref is then deduced from the relation of the perfect gases

TM ₁ EL (FMBSO _n ,) - ^ - ^m MEL

'MEL (FMBSO _n ,)

It will be noted that the molar mass of the mixture (M _MEL ) is calculated from the composition of the gases and the heat capacities of the species (H2O, CO2, CO, NO, O2, N2).

The value of SL _ref is taken from a calibration mapping regime-load. The values of SL _ref will have been calculated in the same way as above for the points of support referred to as "reference", that is to say engine operating points whose advance has been determined with optimum ignition in advance. on the engine bench (when tuning the engine, the engine calibration phase).

2. Determination of the optimal advance in two calculation iterations

The proposed method is based on the calculation of the pressure and the temperature for each of the phases of the combustion, i.e. during the initialization phase and during the combustion phase. From the thermodynamic conditions in the combustion chamber, the kinematic viscosity and the laminar flame velocity are calculated in order to estimate the delays associated with each of the phases.

a) First iteration

> - Calculation of the DINI initialisation delay (1st iteration)

From the estimated optimum advance (AAOestim) and tests, including the FMB5ref, the initialization time of the first iteration (Appendix 3) can be calculated. The FMB5ref is determined on the points of support from the analysis of the cylinder pressure measured with a sensor during the debug phase.

H _^ eq.6 '

D _1N , = C, NU _IN ,) ⁿ -

SL _m ,

To do this, the kinematic viscosity (see Appendix 5), the chamber height and the laminar flame speed must be calculated. Calculations of the chamber volume and the volumetric ratio can be made from, respectively, the equations given on page 44 and page

43 from Heywood JB (1988) Internal Combustion Engine Fundamentals, Mc Graw-Hill International Editions. Average conditions relating to the initialization phase are used for the calculation of NUINNtI, SL INIiti and Hch INIiti: MEL _mb (FMB5 _ref )

¹ ¹ P MMEELL ((AAAAOO _eeΛstl JJ + ^~ ' ^{1 L} PM MEL _mb (FMB5 _ref )

_{HΛ m Hm /} , with β _m = ^AΛO - ^{+ FUB} ^ '

The calculations of the pressures and temperatures at ignition and at the point FMB5 are presented below: ψ - ψ * _τ gamma-l

¹ MEL (AAO ^ ₁ J ^{~ 1} MEL (WC) '^' eff (AAO _eΛm ) ^ P - ^{MEL (} - ^AAO 'ΛJ ^• - ¹⁷¹ MEL rMEL (AAO ^) ^~ - -

¹ MEL- 'ch (AAO _eΛm ) 1MEL (FMBS ^) ^~ - * MEL _mlnb (FMB5 _ref ) ^~ * ^~ ^ ¹ MEL _comb (5%) o _{vpr ψ} _ _ψ *. _τ gamma-1 _f . _ 0.05 * m _∞rb * PCI has ^{CU 1} MEL _wcomb (FMB5 _ref ) ¹ MEL (LVC) 'efj (FMBi',) MEL _cσmb (β%) m _MEL * Cp _h

¹ MEL (FMBS Λ - "- M MEL

* P M> EL (FMB5 _{^ f} )

MM _M e _m Ly- ' _r Ch (FMBS Λ

The combination of the initialization delay and the estimated optimum advance then makes it possible to determine the estimated FMB5 point.

FMB5 _estimated = D _{! Mn} -AAO _estimated

> - Calculation of the combustion time (1st iteration) [0061] From the point FMB5 _estιm , the combustion time of the first iteration can be calculated:

To do this, the kinematic viscosity, the chamber height and the laminar flame speed must be calculated for average conditions relating to the combustion phase. The pressure and temperature corresponding to the point FMB50 _ref are significant for the combustion phase and it can be assumed that:

¹ TMEL _CMB =

P MEL _CMB = ¹ PMEL (FMBSO _n /) It will be noted that the calculations of T _{MEL (FMB50)} and P _{MEL (FMB50)} are similar to those made for the estimation of AAO.

The optimum advance can be calculated from the point FMB50 _ref and the combination with the initialization and combustion delays from the first iteration:

AAO _iΛ = -FMB50 _ref + D _INIiΛ + D _t CMBUl

b) Second iteration

The method is again applied to refine the calculation using the parameters estimated during the first iteration. > - Calculation of the initialization delay of the combustion (2nd iteration)

From the AAOm and the FMB5 _are calculated by the first iteration, the initialization delay can be determined for the second iteration of calculation:

To do this, the kinematic viscosity, the chamber height and the laminar flame speed must be recalculated for the average thermodynamic conditions relating to the initialization phase.

rp _ ¹ TMELjAAO ₁₁₁ ) + T ^L T MEL (FMB5 _βstιm )

¹ MEL ₀₁₁₁₁₂ ^~ ^

P + P rMEL _MIιi2 ^{~ "}

_{HΛ = Hch (θ} with θ _{INI =} ^ O ^ FMB5 _estimated

The calculations of the pressures and temperatures at ignition and at the point FMB5 are detailed below:

_# rp _ rp φ gamma -1 1 MEL (AAO ₁₁₁ ) ¹ MEL (LVC) ^L eff (AAO ₁₁₁ )

^ - ^ - ^m MEL

• ¹ T MEL (FMBi ^ _111n ) = ^λ T MEL _WCnnb (FMBi ^ _111n ) + ~ A ¹ ^ ¹ T MEL _Cnnb (5%) SVPΓ T = T * _T ^gamma - ¹ 0 ^ ¹ MEL _m , _oml , ( FMBi _eaim ) ¹ MEL (LVC) ^ eff (FMBi _eaim ) and Ar 0.05 * m _carb * PCI θ ^{t AT} MEL _mb (i _% ) -

" ¹ MEL

¹ MEL (FMBi ^ _111n ) ^{• 1} ^ - ^m MEL

^P MEL (FMBi _csllm ) _{M v}

MEL - ^r ch {FMB 5 _E3tιm ) The combination of the initialization delay and the advance calculated by the first iteration then makes it possible to refine the position of the point FMB5:

FMB5 _ιtl = D _INIltl - AAO ₁₁₁

* - Calculation of the combustion time (2nd iteration)

From point FMB5 _lt i, the combustion time of the second iteration can be calculated:

7 "

The conditions at point FMB50 _ref remain significant for the combustion phase of this second iteration. Thus, the kinematic viscosity, the chamber height and the laminar flame speed remain unchanged.

The optimum advance can be calculated from the point FMB50 _ref and the combination with the initialization and combustion delays:

AAO ₁₁₂ = -FMB50 _ref + D _INhtl + D _CMBitl

3. Correction applicable to the calculated optimal advance

A correction, in the form of an offset to be applied to the calculated optimal advance, makes it possible to take into account the engine temperature (water) not taken into account by the model. This fix in advance is mapped and is added to the optimal advance.

AAO _cor = AAO ₁₁₁ + AAAO

It will be noted that - AAAO is a mapping function of the charge and the water temperature

Appendices of the calculation method

Appendix 1: Model input parameters

These parameters are not constant and must be determined by calculation [indicated by (shim)] or by measurement (mes) or by modeling (mod), preferably at each combustion cycle. m _αιr : mass of fresh air admitted into the cylinder (for example in kg) (mod) m _GBR : mass of residual burned gas and recirculated in the cylinder (eg in kg) (mod) ^m _carb ^' - mass of fuel in the cylinder (eg in kg) (mes) Recall that: m _MEL = m _air + m _carb + m _GBR and that: GBR = ^ ≤ m _GBR + m _aιr + m _carb

T _{MEL (IVC)} : average temperature of the gases in the cylinder at the time of closing of the intake valves (IVCo Intake Valve Closing) (for example in ⁰ K) (mod) γ _MEL : ratio of the heat capacity at constant pressure (Cp) and the constant volume (Cv) heat capacity of the mixture (shim) M _MEL : molar mass of the air + fuel + burnt gas (g / mol) mixture (shim)

OA: intake opening angle taken with respect to the intake TDC (° Vclear) (mes) N: engine speed (rpm) (mes) T _water ^' - engine water temperature (for example in ⁰ C) ( my)

Annex 2: MAP Calibration

Calibrations are based on the speed and load.

^* AAO _ref is the optimum ignition advance and is determined during calibrations by direct reading on the test bench;

^* FMB5 _ref is the point corresponding to a burned fraction of 5% of the total mass of the mixture and is determined during calibrations by direct reading on the bench (determined from the analysis of the derivative of the cylinder pressure);

^* FMB50 _ref is the point corresponding to a burned fraction of 50% of the total mass of the mixture and is determined during calibrations by direct reading on the bench (determined from the analysis of the derivative of the cylinder pressure);

^* Ci _N i _ref is the initialization constant determined during calibrations.

D _IMref = FMB5 _ref + AA0 _ref

^NU ∞ref ^{= NU} (T _MaiNW ^ ar _rcf >" _{→ ef} " OBR ^ ^ BS ^) AVeC ^M '- _f ^{= ch (AAO} _Yef ^FMBi _Yef ⁾

^SL 'NI _ref ^{= SL} (T _MEIlMr4 P _UEkMγef K ₄ GBIi ₄ )

T MEh _NIrcf = T ^Λ MEL (IVQ ₄ AAO _rcf FMB5 _rcf T _MElRF ^ _f m _a ^ m _{→ ef} M ₀ ^ ₄ y _rcf M _MEIref )

^MEL INI P _ref = P ^MEL ^(T MEI _INIyef ^m is _{fc /} "W ^" ^ ¹ G ₁ / ^M MEI _r4)

^* Cc _MBref is the combustion constant determined during calibrations. C _n CMB _ref with

^NU CMB _ref = ^NU (T _MEICMBr4 , m ^ _ef , m _{→ ef} , m _βB ^ _f , FMBSO _ref )

^H ^ _f = ^H -

^SL CMB _ref ^SL (T _Ml ΛφGBHe _f )

T ^MEL _CM ^ _cf = T ^ME ^^ ^-φFMB50 _rcf , T _MEIχp4 ^, m _a , _wf , m _car ^ _f , mg _B ^ _f , γ _r M M _MEIrtf )

P MEIatfy = P MEL (T _UEIaιv m _aWref , m _caγbref , m _GBBref , M _UEIτef )

^* SL _ref is the estimated overall laminar flame speed.

SL _ref

SL ₀ = SL _(A) a = a _{λ) T = T

¹ MEL (FMBSO 3) ¹ MEL (IVC _ref , FMB50 _ref , T _MELRFAref , m _a , _rref , m _{→ ef} , m _GBRref , _γref , M _M EL _ref )

¹ P MEL (FMBSO ,,,) = ¹ P, m _∞γτ4 , m _caΛer m _GBRτef M _MELτef )

Annex 3: Initialization and combustion time

The calculation is based on the teaching of the reference [1] Hires et al.

2/3

.1 / 3 ^H ch _m λ D _INI = C _m JSP.NU _INI ) ^l!

The term MS (mean piston speed, see Appendix 4) depending on the system was removed from the equations 6 'and 7' and replaced with the _K _umber also dependent on the speed and phase of the intake camshaft ( in fact, the internal aerodynamics are modified by the phase shift of the intake valve lift law).

It should be noted that the delays can be measured on a test bench and correspond to: D _m = FMB5 _ref + AAO _ref D _CMB = FMB50 _ref - FMB5 _ref and to take into account the aerodynamics in the combustion chamber, the relations proposed by Hires et al. (reference [1]) have been adapted (see eq 6 'and eq 7'). The values of the K _Aero coefficient depend on the phase shift of the intake camshaft and the speed. Annex 4: average piston speed

SP = L * - c 30

Appendix 5: Kinematic viscosity

NU is the ratio of the dynamic viscosity (MU) and the density of the mixture (RHO):

NU = ≡- RHO

The density of the mixture is determined from the mass of the mixture in the cylinder (ie the sum of the air masses, IGR, EGR and fuel) and the volume of the chamber: m, _r

RHO = -

K ₁ Dynamic viscosity is determined from Sutherland's law S)

Appendix 6: Effective compression ratio τ _eff represents the ratio of the volumes of the combustion chamber between the angular position (θ) and the closing angle of the inlet valvesiv.

Annex 7: definition of the different angular positions.

The different angular positions of the crankshaft are illustrated in FIG.

The present invention saves time and reduces calibration costs by reducing the number of calibration tests. In addition, the physical model of the invention applies to all modes of operation of the engine and whatever the engine model, while previously it was necessary to make a complete map for each new engine model.

Other embodiments than those described and shown may be designed by those skilled in the art without departing from the scope of the present invention. For example, the rates of 5% and 50% of the mass of fuel burned may be different: in general, they are respectively x% and y%. Likewise, certain equations can be modified without departing from the scope of the invention.

Claims

A method for determining the ignition advance of a heat engine using a physical model using input parameters, characterized in that it comprises the following steps: using a test bench, determine different values of calibration parameters associated with several engine speed-engine load couples, said parameters making it possible to estimate the average flame speed from the thermodynamic conditions in a combustion chamber of the engine. motor, said values of the load-speed torque and the values of said calibration parameters constituting bearing points; - determining the values of said input parameters for each engine operating cycle;

recording, in an on-board computer on board said vehicle, said support points, said input parameters and said physical model represented by at least two equations; and

from said support points, said input parameters and said physical model, calculating said ignition advance of said motor.

2. Method according to claim 1 characterized in that said calibration parameters comprise the following parameters: the optimum ignition advance reference AAO _ref , the point FMBx _ref corresponding to a burned fraction of x% of the total mass of the mixed ; a reference initialization constant C | _N ι _ref , a combustion constant Cc _MBref βt an estimated global laminar flame speed SL _ref .

3. Method according to one of the preceding claims characterized in that said input parameters are chosen from the following parameters:

- the mass of fresh air admitted into the cylinder (m _mr )

- the mass of residual burned gas and recirculated in the cylinder (m _GBR ) - the mass of fuel in the cylinder (m _carb )

- the load (Ld) -

- the average temperature {T _{MEL {IVC)} ) of the gases in the cylinder at the time of closing of the intake valves

the ratio (γ _MEL ) of the heat capacity at constant pressure and the heat capacity at constant volume of the mixture

- the molar mass (M _MEL ) of the mixture air + fuel + residual burned gas and recirculated

- the opening angle of admission (OA)

- the engine speed (N).

- the engine water temperature (T ^water ).

4. Method according to one of the preceding claims characterized in that said ignition advance AAO is determined by calculating the combustion time of the point FMBx in point

FMBy corresponding respectively to x% and y% of the fuel burned and the ignition delay for FMBx.

5. Method according to claim 4 characterized in that it determines the evolution of the pressure and the temperature of the air-fuel mixture in the combustion chamber of the engine during the combustion cycle.

6. Method according to one of the preceding claims characterized in that said physical model is represented by two equations, one giving the initialization time to the combustion (D, _N |) as a function in particular of a constant (C | _N |), the other giving the delay of the burning time (D _C MB) as a function in particular of a constant (C _C MB)

7. Method according to one of the preceding claims characterized in that to calculate said ignition advance (AAO): a- an estimated value (AAO _estιm ) of the ignition advance is calculated using a relationship of proportionality with laminar flame speed; b- the optimum ignition advance (AAO) is determined by iteration, the first iteration comprising:

^* the calculation of the initialization delay D | _N | from the estimated optimum advance AAO _estιm and said points of support, * the determination of FMBx from the values of D | _N | and _{OAA is}

^* calculation of the combustion time D _CM β from FMBx, and

^* the calculation of the ignition advance optimum AAO; c- the value of said advance ignition advance AAO is corrected taking into account the engine temperature.

8. The method as claimed in claim 7, characterized in that said step b comprises two iteration steps, the second iteration being performed using the value of FMBx obtained with the first iteration.

9. Method according to claim 7 characterized in that the FMBx value of step b is determined by FMBx = D | _N , - AAO _estιm ; the value of D | _N , being that obtained by the first iteration.

10. Method according to one of claims 7 to 9 characterized in that the ignition advance AAO is determined by:

AAO = - FMBy _rθf + D, _N ι, ti + D _CM B iti

FMBy being the value of FMB obtained by calibration, DINI iti and DCMB iti being the values obtained using said first iteration.