JPH10212979A - Engine control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve controllability of an engine by estimating at least one of quantity of air flowing in a cylinder, exhaust gas recycling rate and oxygen over rate from a detection value of an intake air quantity according to the mathematical model of intake and exhaust system and a combustion reaction formula, and controlling the fuel injection quantity according to the results of estimation. SOLUTION: This engine control method includes an intake system state estimating part 21 for estimating the state related to an intake system such as an air flow, a recycling gas flow and so on, and a combustion system state estimating part 22 for estimating the state related to a combustion system of CO2 component in exhaust or the like. Further, it includes a state estimating part 24 for an exhaust system for estimating the state relates to the exhaust system such as oxygen content in an exhaust pipe or the like and a recycling system state estimating parat 23 for estimating a recycling flow or the like. The quantity of air flowing in a cylinder is estimated from a detection value of an intake air quantity according to the mathematical model of intake and exhaust system and a combustion reaction formula.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating the operating state of an automobile engine, and more particularly, to an engine for estimating an exhaust gas recirculation rate and a cylinder excess oxygen rate when there is exhaust gas recirculation. The present invention relates to an engine control method for controlling.
In addition, the present invention relates to a method for determining a combustion state of an automobile engine, and particularly to a lean burn engine (lean burn engine) to determine whether or not the engine is in an operation range where stable combustion is performed (an operation state in which a misfire does not occur) and control the engine. It relates to an engine control method.

[0002]

2. Description of the Related Art As a technique related to EGR control (exhaust gas recirculation control), electronic control gasoline injection (Sankaido Publishing)
As described from page 159 to page 161,
A mechanical control device for performing a small amount of EGR and an electronic control type for performing a large amount of EGR are known. In the electronic system, a valve provided in a passage for recirculating exhaust gas is controlled to have a pre-programmed valve opening area according to the engine speed and the engine load. This achieves the target exhaust gas recirculation rate.

[0003] As a technique related to the oxygen excess rate in a cylinder, a technique described in Japanese Patent Application Laid-Open No. S61-155561 is known. In this method, a technique for estimating the amount of air flowing into a cylinder is disclosed. If the combustion injection amount is determined based on the estimated air amount, a predetermined air-fuel ratio, that is, a predetermined excess air ratio (equivalent to an excess oxygen ratio when there is no exhaust gas recirculation) is realized.

Further, the relationship between the engine operating state and the torque fluctuation is described in pages 44 to 47 of a new automobile gasoline engine (Sankaido Shuppan). In a lean burn engine that operates the engine at a lean air-fuel ratio, the engine torque fluctuation increases when the air-fuel ratio exceeds a predetermined value, and a misfire occurs at a higher air-fuel ratio.

[0005]

In the above prior art, the exhaust gas recirculation rate in steady operation of the engine is achieved based on information on the number of revolutions and the engine load. Therefore, there is a problem that the exhaust gas recirculation rate in the transient state cannot be accurately grasped (estimated) even though the exhaust gas recirculation rate in the steady state can be grasped (estimated).

Further, it is possible to grasp (estimate) the excess oxygen ratio in the cylinder when there is no exhaust gas recirculation by the conventional cylinder inflow air amount estimation technique. However, if there is exhaust gas recirculation in a lean burn state, the recirculated gas will contain a considerable amount of oxygen. Therefore, there is a problem that the oxygen excess rate estimated by the conventional technique includes an error by the amount of oxygen in the recirculated gas.

Furthermore, in the prior art, it is mainly determined whether or not the engine performs stable combustion (whether or not the engine is in a misfire-free region) based on the air-fuel ratio. However, if there is exhaust gas recirculation, combustion is affected not only by the air-fuel ratio but also by the amount of recirculated gas, so that the determination of stable combustion cannot be made accurately with only the air-fuel ratio. There is. At the time of lean burn, oxygen is contained in the recirculated gas. Therefore, when there is exhaust gas recirculation, combustion determination is made based on the ratio of the sum of oxygen entering the cylinder through the throttle and oxygen in the recirculated gas and the fuel injection amount, that is, the excess oxygen ratio, rather than the air-fuel ratio. Is considered appropriate. However, in the related art, there is a problem that highly accurate determination cannot be performed because the fuel determination is performed based on the amount of the air-fuel ratio that does not necessarily correspond to the oxygen excess ratio.

An object of the present invention is to accurately estimate an exhaust gas recirculation rate regardless of whether it is stationary or transient. Another object of the present invention is to estimate an oxygen excess ratio, which is a ratio of oxygen and fuel in a cylinder. Still another object of the present invention is to determine a region where the engine performs stable combustion even when there is exhaust gas recirculation.

[0009]

To achieve the above-mentioned object, the following arrangement is provided. An engine control method for detecting an amount of air taken into an engine and controlling a fuel injection amount and an opening degree of a valve provided in a passage for recirculating combustion gas in an exhaust pipe to an intake pipe. From, sucking,
Based on the mathematical model of the exhaust system and the combustion reaction formula, at least one of the amount of air flowing into the cylinder and the oxygen excess ratio corresponding to the ratio of the exhaust gas recirculation rate and the fuel injection amount, which is the ratio of the recirculated gas amount, An engine control method characterized by estimating and controlling the fuel injection amount and the opening degree of the valve based on a result of the estimation.

With this configuration, based on the chemical reaction equations corresponding to the intake / exhaust system model and the combustion system model, the amount of air flowing into the cylinder and also the amount of recirculated gas flowing into the cylinder can be determined regardless of steady-state transient. Can be estimated. This makes it possible to accurately calculate and estimate the transient exhaust gas recirculation rate.

[0011]

1 to 12 show an embodiment of the present invention.
It will be described based on. FIG. 1 is an overall configuration diagram of a control system when an engine operating state estimating method and a combustion state determining control method of the present invention are realized by an electronic control unit, and shows a case of a four-cylinder engine. This engine is a direct injection engine that supplies fuel directly to a cylinder. The control unit includes a CPU, a RAM, a ROM, a timer, and an I / OLSI.

The I / OLSI receives signals from an air amount sensor, a throttle sensor, a water temperature sensor, an oxygen sensor, a crank angle sensor, an accelerator angle sensor (accelerator depression amount detection), an intake temperature sensor, and exhaust temperature sensors 1 and 2. Is output. In addition, the I / OLSI provides a fuel injector installed in each cylinder, a target opening signal to a throttle control device that controls the throttle to match its target value, and an exhaust gas recirculation passage. Valve (EGR valve)
A pulse signal is output to a step motor for driving. The timer generates an interrupt signal to the CPU at a predetermined cycle, and the CPU executes a control program stored in the ROM in response to the interrupt signal.

FIG. 2 is a block diagram showing a method for estimating the operating state of an engine according to the present invention. Intake system state estimator that estimates the state of the intake system such as air flow rate and recirculated gas flow rate, combustion system state estimator that estimates the state of the combustion system such as CO2 component generated by combustion, and exhaust pressure and exhaust pipe oxygen concentration. The system is composed of four systems: an exhaust system state estimating unit for estimating the state of the system, and a recirculation system state estimating unit for estimating the recirculation flow rate.

The main input signals to these estimators are shown in FIG.
As described above, the throttle passing air amount Qat (kg / s) measured by the above-described air amount sensor and the engine speed N (rp) detected by the crank angle sensor.
m), the fuel injection amount Gf sequentially calculated by the control program stored in the ROM in the engine control unit.
(G / s) and the actual number of steps of the step motor that drives the EGR valve.

The output of the system for estimating the operation state is an EGR rate (rEr) which is a ratio of the amount of air entering the cylinder to the recirculation flow rate.
GR) and the excess oxygen ratio λo2 in the cylinder.

First, the details of the processing of the intake system state estimating unit will be described. The intake system state estimating unit estimates various states related to the intake system by combining the following mathematical models.

Volume Efficiency Calculation Using the estimated intake pipe internal pressure value Pman and the number of revolutions N as parameters, the table shown in FIG. 10 is searched to calculate the volume efficiency VOLN.

Calculation of Cylinder Inflow Amount of the air Qaout entering the cylinder and amount of recirculated gas Qegout are estimated using Equations 1 to 5. In these equations, variables that are not detected by the configuration of FIG. 1 are state variables estimated by the intake system estimating unit or other estimating units, and can be used without being measured. The same applies to all other mathematical expressions shown below.

[0019]

(Equation 1)

[0020]

(Equation 2)

[0021]

(Equation 3)

[0022]

(Equation 4)

[0023]

(Equation 5)

[0024]

(Equation 6)

Here, Mavg: average molecular weight of gas in the intake pipe, aint: mole number of air in the intake pipe, xin
t: the number of moles of CO2 in the intake pipe, yint: the number of moles of O2 in the intake pipe, zint: the number of moles of N2 in the intake pipe, Meg
r: average molecular weight of recirculated gas in the intake pipe, Mair: average molecular weight of air, Qallout: total mass flow rate into the cylinder (kg / s), Qaout: airflow into the cylinder (k)
g / s), Qegout: inflow of recirculated gas into cylinder (kg / s), N: engine speed (rpm), Vd
d: engine displacement (m3), Pman: intake pipe internal pressure (Pa), Pair: partial pressure of air in the intake pipe (Pa),
Pegr: partial pressure (Pa) of the recirculated gas in the intake pipe, R:
Gas constant (8.31 J / mol · K), Tm: gas temperature in intake pipe (K), Ta: intake temperature (K), Texh1:
EGR valve position exhaust temperature (K), rEGR: target EG
The R rate (%).

Calculation of Molar Movement per Unit Time Using Equations 6 to 8, the components CO2, O2, and N2 in the recirculated gas moving per unit time from the intake pipe to the combustion chamber are calculated.

[0027]

(Equation 7)

[0028]

(Equation 8)

[0029]

(Equation 9)

Here, ICCO2: the number of moles of CO2 (mol / s) moving from the intake pipe to the combustion chamber per unit time, IC
O2: Number of moles of O2 (mol / s) moving from the intake pipe to the combustion chamber per unit time, ICN2: Number of moles of N2 (mol / s) moving from the intake pipe to the combustion chamber per unit time, xint:
CO2 mole number (mol) in the recirculated gas in the intake pipe, y
int: O2 mole number (mo) in the recirculated gas in the intake pipe
1), zint: N2 mole number (mol) in the recirculated gas in the intake pipe.

The air partial pressure Pair in the intake pipe is updated based on the following equation.

[0032]

(Equation 10)

Here, dt: time step of pressure update, V
m: Intake pipe volume (m3).

Air mole number aint The air mole number is calculated based on the following equation.

[0035]

[Equation 11]

Here, Vm: intake pipe volume (m3).

CO2 and O2 in the recirculated gas in the intake pipe
The N2 mole number is updated based on the following equation.

[0038]

(Equation 12)

[0039]

(Equation 13)

[0040]

[Equation 14]

Recirculated gas partial pressure Pegr The recirculated gas partial pressure is calculated based on the following equation.

[0042]

(Equation 15)

Intake pipe pressure is calculated based on the following equation.

[0044]

(Equation 16)

The above is the mathematical model used in the intake system state estimating unit. Each state can be estimated by periodically repeating the operations of Equations 1 to 10.

Next, details of the processing of the combustion system state estimating unit will be described. Each state related to the combustion system is estimated by the following mathematical model.

The number of moles of fuel flowing into the cylinder per unit time mα
(Mol / s) It is calculated from the fuel injection amount GF (g / s) based on the following equation.

[0048]

[Equation 17]

Here, m and n are constants relating to the fuel composition, where m = 7 and n = 13.

Number of moles of oxygen flowing into the cylinder per unit time AI
(Mol / s) The mole number of oxygen AI is calculated based on the following equation.

[0051]

(Equation 18)

Here, gamma: the ratio of nitrogen to oxygen in the air is 3.76.

The number of moles of fuel mα flowing into the cylinder for each stroke
s, number of moles of oxygen AIs, number of moles of each component of recirculated gas (IC
CO2s, ICO2s, ICN2s), Air amount Qau
ts, fuel amount Gfs Since a four-cylinder engine is assumed, the mole and the mass flow rate are integrated in the half-rotation time from the top dead center to the bottom dead center including the intake stroke, and flow into the cylinder for each stroke. Calculate the number of moles and mass of each component. The value obtained by the integration is managed for each cylinder in association with which cylinder is in the intake stroke.

[0054]

[Equation 19]

[0055]

(Equation 20)

[0056]

(Equation 21)

[0057]

(Equation 22)

[0058]

(Equation 23)

[0059]

(Equation 24)

[0060]

(Equation 25)

[0061]

(Equation 26)

Here, mαm: the amount of fuel injected into the cylinder (mol / stroke), AIm: the amount of oxygen in the air flowing into the cylinder (mol / stroke), ICCO2m: the amount of CO2 in the recirculated gas flowing into the cylinder, ICO2m: the amount of CO2 in the recirculated gas flowing into the cylinder, ICN2m: the amount of CO2 in the recirculated gas flowing into the cylinder, Qaoutm: the amount of air flowing into the cylinder (kg)
/ Stroke), Gfm: fuel amount in cylinder (kg / stroke), Qe
grout: The amount of recirculated gas flowing into the cylinder (kg / stroke).

EGR Rate The EGR rate (%) is calculated based on the following equation.

[0064]

[Equation 27]

Excess oxygen ratio λo2 The excess oxygen ratio in the cylinder is defined as the amount of oxygen in the cylinder / the amount of oxygen in the cylinder in a stoichiometric state without recirculation of exhaust gas, and the excess oxygen ratio is calculated based on the following equation.

[0066]

[Equation 28]

CO2, O2, N generated by combustion
2, mole number of H2O Here, lean combustion is assumed. It is also assumed that a part of the gas generated by the combustion (a reciprocal value of the compression ratio 11) remains in the cylinder. Under the above assumptions, the gas component generated by combustion in each cylinder is calculated as follows using Equations 29 to 32.

[0068]

(Equation 29)

[0069]

[Equation 30]

[0070]

(Equation 31)

[0071]

(Equation 32)

Here, xoi: generated CO2 mole number (mo
l), yoi: generated O2 mole number (mol), zoi: generated N2 mole number (mol), uoi: generated H2O mole number (mol), RCO2i: residual CO in previous combustion
Two components (mol), RO2i: residual CO2 component (mol) in previous combustion, RN2i: residual CO2 component (mol) in previous combustion, RH2Oi: residual CO2 component (mol) in previous combustion. Note that i (1
= 1, 2, 3, 4) represent cylinder numbers.

Combustion Gas Residual It is assumed that a part of the produced gas (a compression ratio of 1: 1/11) remains in the cylinder. Therefore, a new cylinder residual gas component is calculated by the following equation.

[0074]

[Equation 33]

[0075]

(Equation 34)

[0076]

(Equation 35)

[0077]

[Equation 36]

Combustion gas emission (mol / stroke) Since 10/11 of the produced gas is exhausted to the exhaust pipe, the emission of each gas component in the exhaust stroke is as follows.

[0079]

(37)

[0080]

(38)

[0081]

[Equation 39]

[0082]

(Equation 40)

Here, CO2i: CO2 component emission amount, O2
2i: O2 component emission, N2i: N2 component emission, i:
The cylinder number (i = 1, 2, 3, 4).

Movement amount of combustion gas mole number (mol / s) In each cylinder, it is considered that the combustion gas during the half rotation from the bottom dead center to the top dead center including the exhaust stroke is uniformly discharged. The amount of moles discharged per unit time (moving amount) is as follows.

[0085]

[Equation 41]

[0086]

(Equation 42)

[0087]

[Equation 43]

Here, CECO2: CO2 mole number (mol / s) moving from the combustion chamber to the exhaust pipe per unit time, CE
O2: number of moles of O2 (mol / s) moving from the combustion chamber to the exhaust pipe per unit time, CEN2: number of moles of N2 (mol / s) moving from the combustion chamber to the exhaust pipe per unit time, N: engine speed ( rpm).

The above is the mathematical model used in the combustion system state estimator. As in the case of the intake system, it is possible to estimate each state by periodically repeating the calculations of Formulas 17 to 43.

Next, the processing of the recirculation system state estimating section will be described in detail. Here, the following mathematical model is used for state estimation.

The current EGR valve opening area The current step motor step number information step possessed by the EGR control system in the control unit is used as a parameter in FIG.
To find the current EGR valve opening area Ae
Calculate gr.

Oxygen Concentration The oxygen concentration in the exhaust pipe collecting section is calculated based on the following equation.

[0093]

[Equation 44]

Here, DO2 is the oxygen concentration (%) of the exhaust pipe collecting section, xex is the number of moles of CO2 in the exhaust pipe, yex is the number of O2 moles in the exhaust pipe, and zex is the number of N2 moles in the exhaust pipe.
Note that xex, yex, and zex are estimated by the exhaust system state estimation unit.

EGR valve position oxygen concentration DOegr The EGR valve position oxygen concentration is calculated based on the following equation, assuming that there is a dead time + first-order lag relationship with the concentration of the collecting portion.

[0096]

[Equation 45]

Here, DOegr: oxygen concentration (%) of the EGR valve position, Ttr: dead time (s), Tc: time constant (s). Here, Ttr is fixed at 0.15 and Tc is fixed at 0.3. Note that these variables may be functions of the air flow rate, the rotation speed, and the like in order to increase the accuracy.

Based on the oxygen concentration at the EGR valve position calculated by the corrected oxygen mole number yexc (36), the corrected oxygen mole number yexc in the exhaust pipe is calculated based on the following equation.

[0099]

[Equation 46]

The average molecular weight Me of the gas at the position of the EGR valve
xh1 Calculate the average molecular weight of the gas based on the following equation.

[0101]

[Equation 47]

The amount of recirculated gas flowing into the intake pipe Qegrin The amount of recirculated gas flowing is calculated based on the following equation.

[0103]

[Equation 48]

Here, GCDegr: flow path resistance coefficient of the EGR valve, Pexh: exhaust pipe internal pressure (Pa), k: specific heat ratio (approximately 1.4 here), Texh1: recirculated gas at the position of the EGR valve Temperature (K). Where the function f is
It satisfies the following equation.

[0105]

[Equation 49]

[0106]

[Equation 50]

Recirculated gas C moving from the exhaust pipe to the intake pipe
The number of moles of O2, O2, and N2 components The number of moles is calculated based on the following equation.

[0108]

(Equation 51)

[0109]

(Equation 52)

[0110]

(Equation 53)

The above is the mathematical model for the state estimation of the recirculation system state estimation unit.

Finally, the details of the processing of the exhaust system state estimating unit will be described. The state estimating unit estimates a state such as an exhaust pressure based on a mathematical model relating to the exhaust system.

Average Molecular Weight of Exhaust Pipe Assembly The average molecular weight is estimated based on the following equation.

[0114]

(Equation 54)

Here, Mexh: average molecular weight (kg).

Outflow of combustion gas into the atmosphere The outflow is calculated based on the following equation.

[0117]

[Equation 55]

Here, Qout2: the amount of combustion gas flowing out into the atmosphere (kg / s), Pexh: the exhaust pressure (Pa), P
a: Atmospheric pressure (Pa), Mexh: Average molecular weight (kg) of the exhaust pipe assembly, Texh: Gas temperature (K) of the exhaust pipe assembly, Kout: Flow resistance coefficient.

The molar outflow of the combustion gas into the atmosphere The outflow of the CO2, O2, and N2 components of the combustion gas in the exhaust pipe to the atmosphere is calculated based on the following equation.

[0120]

[Equation 56]

[0121]

[Equation 57]

[0122]

[Equation 58]

Here, EACO2: molar outflow of CO2 gas in the exhaust pipe to the atmosphere (mol / s), EAO2: molar outflow of O2 gas in the exhaust pipe to the atmosphere (mol / s)
s), EAN2: molar outflow (mol / s) of N2 gas into the atmosphere in the exhaust pipe.

CO2, O2, N in the combustion gas in the exhaust pipe
The number of moles of each component of 2 The number of moles of CO2, O2, N2 in the exhaust pipe is updated based on the following equation.

[0125]

[Equation 59]

[0126]

[Equation 60]

[0127]

[Equation 61]

Here, xex: CO2 mole number (mol) in the exhaust pipe, yex: O2 mole number (mo) in the exhaust pipe
l), zex: N2 mole number (mol) in exhaust pipe, d
t: Time increment.

Exhaust Pipe Pressure The exhaust pipe pressure is calculated based on the following equation of state of ideal gas.

[0130]

(Equation 62)

Here, Texh: gas temperature (K) of the collecting portion in the exhaust pipe, Vexh: exhaust pipe volume (m3), R: gas constant (J / mol · K).

The above is the mathematical model of the exhaust system state estimating unit. By repeatedly performing the calculations of Equations 54 to 62 at predetermined intervals, each variable in the equation can be estimated. The above is the content of the processing of the engine operating state estimation method represented by the block diagram of FIG.

In the engine control unit shown in FIG. 1, these state estimation processes are executed by a control program stored in the ROM. The processing of this program will be described with reference to FIGS.

FIG. 3 is a flowchart of a main program for estimating a state, which is executed at a predetermined cycle. First, in step 301, the rotation speed,
Initialize variables such as pressures (exhaust pressure, partial pressure of air in the intake pipe, partial pressure of recirculated gas). For example, rotation speed 7
00rpm, exhaust pressure 102MPa, partial pressure of air 10MP
a, the partial pressure of the recirculated gas is set to 0 Pa or the like.

Next, at step 302, a subroutine for performing the intake system state estimation processing (corresponding to the processing of block 21 in FIG. 2) is called, and the processing is executed. Further, also in steps 303 to 305, the combustion system state estimation processing (corresponding to the processing in block 22 in FIG. 2), the recirculation system state estimation processing (corresponding to the processing in block 23 in FIG. 2), and the exhaust system state estimation processing, respectively. A subroutine for performing (corresponding to the processing of #lock 24 in FIG. 2) is called, the respective processings are executed, and the process stands by until there is a next program execution request.

FIG. 4 to FIG. 7 are flowcharts of subroutines for performing state states of the intake system, the combustion system, the recirculation system, and the exhaust system, respectively. In FIG. 4, first, step 40
In step 1, the table of FIG. 10 is searched using the rotation speed and the estimated intake pipe internal pressure as parameters to obtain the volumetric efficiency VOLN. Thereafter, the processing from step 402 to step 412 is for sequentially calculating the state variables according to the above-described equations 1 to 16, and the latest calculated value is the RA in the control unit in FIG.
M. After all the above processes are completed, the process returns to the main program.

FIG. 5 is a flowchart of a subroutine for performing a combustion system state estimation process. Step 501, 50
In step 2, the number of moles of fuel and the number of moles of oxygen flowing into the cylinder are calculated based on equations 17 and 18, respectively. Step 5
In 03, the following addition operation is performed each time this subroutine is called, whereby the number of moles of fuel mα, the number of moles of oxygen AI, and the number of moles of each component in the recirculated gas (ICCO2, ICO2, ICN2), the cylinder inflow air amount Qout, and the fuel injection amount Gf for the half-revolution time integral calculation.

[0138]

[Equation 63]

[0139]

[Equation 64]

[0140]

[Equation 65]

[0141]

[Equation 66]

[0142]

[Equation 67]

[0143]

[Equation 68]

[0144]

[Equation 69]

[0145]

[Equation 70]

In step 504, it is determined whether or not the cylinder having the engine is in a state immediately after passing through the bottom dead center. Once this determination is received, it is not determined that the cylinder is in a state immediately after passing through the bottom dead center until another cylinder passes through the bottom dead center after about half a rotation.

Variables mαm, AIm, I just after passing through bottom dead center
CCO2m, ICO2m, ICN2m, Qaoutm,
GFm and Qegrout are variables mα and A, respectively.
I, ICCO2, ICO2, ICN2, Qaout, G
F, which is a time integral value of a half rotation of Qegrout. That is, the respective variables are the number of moles of fuel and the number of moles of oxygen flowing into the cylinder during the intake stroke, the CO2 and O2 in the recirculated gas.
2, the number of moles of the N2 component, the amount of air flowing into the cylinder, the amount of fuel
Shows the value of the amount of recirculated gas.

In steps 505 and 506, the current EGR rate and oxygen excess rate are calculated based on equations (27) and (28). In step 507, the inhalation ends or
The number of the cylinder immediately before the end is determined. In step 508, the CO generated after the combustion stroke in the determination cylinder
The number of moles of each component of 2, O2, N2, and H2O is calculated based on Equations 29 to 32.

In step 509, based on equations 33 to 40, the number of moles of each component discharged when the determination cylinder enters the exhaust stroke and the number of moles of each component remaining in the cylinder are calculated and stored in advance. I do.

In step 510, the latest cylinder that has entered the exhaust stroke is determined. In step 511, the current CO2, O2 discharged to the exhaust pipe using equations 41 to 43 is used.
2. The unit time molar transfer amount (molar flow rate) of N2 is previously calculated in step 509 for the cylinder determined to have entered the exhaust stroke, and is based on the stored mole number of each component. To calculate.

In step 512, the variables mαm, AI
m, ICCO2m, ICO2m, ICN2m, Qau
Initialize tm, GFm and Qegrotm. (Substituting 0) With the above, the processing of the subroutine for estimating the combustion system state ends, and the processing returns to the main program.

Next, the contents of the recirculation system state estimation subroutine will be described with reference to FIG. In step 601, the table of FIG. 11 is searched to calculate the opening area of the EGR valve. In steps 602 to 606, state variables of the recirculation system are sequentially estimated based on equations 44 to 53, and the latest values are stored in the RAM.

Finally, the contents of the processing of the exhaust system state estimation subroutine will be described with reference to FIG. In steps 701 to 705, the exhaust system state variables are sequentially calculated based on Equations 54 to 62, the calculated values are stored in the RAM, and the processing is returned to the main program.

In the above operating state estimating method, although the estimation accuracy is lowered, the intake air temperature and the exhaust gas temperature are fixed values, or the estimated values are estimated from other amounts (air amount, recirculation flow rate, fuel injection amount, rotation speed). For example, the number of sensors can be reduced. This concludes the description of the overall configuration of the control system and the contents of processing of the program when the method for estimating the operating state of the engine of the present invention is implemented by the digital control unit.

Next, an embodiment of the method for determining the combustion state of an engine according to the present invention will be described with reference to FIGS. 8, 9 and 12. Here, the EGR estimated by the above embodiment is used.
It is to determine whether or not the engine is in an operation state in which stable combustion is performed based on the rate and the oxygen excess rate.

FIG. 8 is a table for determining the combustion state according to the first embodiment. Here, it is assumed that homogeneous combustion, which is a combustion mode similar to that of the current multipoint injection system, is performed. In the homogeneous combustion, the air-fuel ratio (here, the ratio of the amount of air passing through the throttle to the cylinder and the amount of fuel injected is referred to as the air-fuel ratio, and the amount of oxygen contained in the recirculated gas is not included in the amount of air) to a certain degree , Combustion stops and the engine will misfire. Further, even at the same air-fuel ratio, the more the EGR amount is, the more likely it is for a misfire to occur. The table in FIG. 8 gives this combustion characteristic. EGR at the boundary between stable combustion and unstable combustion using the air-fuel ratio as a parameter
The EGR rate is obtained, and is compared with the current estimated EGR rate to determine whether the engine is in the stable combustion area or the unstable combustion area based on the magnitude of the value. By sequentially performing the stable combustion determination, when the vehicle enters or is about to enter the unstable combustion region, the target air-fuel ratio or the target EGR rate can be reduced to avoid unstable combustion.

FIG. 9 is a table for determining the combustion state according to the second embodiment. The horizontal axis uses the oxygen excess ratio instead of the air-fuel ratio. Here, the excess oxygen ratio is used because when the air-fuel ratio is lean and the exhaust gas is recirculated, the recirculated gas contains a considerable amount of oxygen, so that the ratio between the amount of oxygen and the amount of fuel in the cylinder is stable. This is because the accuracy of determination can be improved by using the index as a determination index. In particular, when the engine is in a steady operation state in which the various states are constant, the air-fuel ratio and the oxygen excess ratio correspond one-to-one, so that the first and second embodiments perform exactly the same determination. However, in a transient state in which the air-fuel ratio changes, the air-fuel ratio and the oxygen excess ratio do not always correspond one-to-one, and in this region, the effect of improving the combustion determination accuracy in the second embodiment is better. is there. Although the discrimination accuracy is lower than that of the second embodiment, even if the stable combustion discrimination is performed only by the excess oxygen ratio, the effect is improved in that the discrimination accuracy is improved as compared with the conventional method of performing the stable combustion discrimination using only the air-fuel ratio. is there.

Next, based on the flowchart of FIG. 12, the above-described combustion state determination method will be described with reference to the RO of the control unit of FIG.
A description will be given of the contents of the processing of the program when the processing is realized by the program stored in M. In step 1201,
Using the air-fuel ratio or the oxygen excess rate estimated by the above method as a parameter, the table in FIG. 8 or FIG. 9 is searched to calculate the EGR rate at the boundary between stable combustion and unstable combustion. In step 1202, it is determined whether or not this value is larger than the current EGR rate calculated by another program. If it is larger, it is determined in step 1203 that it is in the stable combustion region, otherwise it is determined in step 1204 that it is in the unstable combustion region. Thus, the process ends. This concludes the description of the engine combustion state determination method of the present invention.

[0159]

【The invention's effect】

(1) In the present invention, based on chemical reaction equations corresponding to an intake / exhaust system model and a combustion system model,
In addition to the amount of air flowing into the cylinder, the amount of recirculated gas flowing into the cylinder can be estimated. This makes it possible to accurately calculate and estimate the transient exhaust gas recirculation rate.

(2) In the present invention, a chemical reaction equation is introduced as a combustion system model in addition to the intake and exhaust system models.
This makes it possible to determine the amount of recirculation based on components such as oxygen and nitrogen. Since the amount of oxygen in the recirculated gas flowing into the cylinder can also be estimated, the in-cylinder excess oxygen ratio can be calculated and estimated with high accuracy.

(3) Stable combustion can be accurately determined by taking into consideration the in-cylinder excess oxygen ratio and the exhaust gas recirculation ratio, which are indicators of whether stable combustion can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an engine control system.

FIG. 2 is a block diagram of a driving state estimation method.

FIG. 3 is a flowchart of an operation state estimation program.

FIG. 4 is a flowchart of an intake system state estimation subroutine.

FIG. 5 is a flowchart of a combustion system state estimation subroutine.

FIG. 6 is a flowchart of a recirculation system state estimation subroutine.

FIG. 7 is a flowchart of an exhaust system state estimation subroutine.

FIG. 8 is a stable combustion determination table according to the first embodiment.

FIG. 9 is a stable combustion determination table according to a second embodiment.

FIG. 10 is a table for storing volumetric efficiency;

FIG. 11 is a characteristic table of a valve opening area with respect to a target number of steps.

FIG. 12 is a flowchart of a program for determining a combustion state.

[Explanation of symbols]

21: intake system state estimating unit, 22: combustion system state estimating unit, 2
3: Recirculation system state estimator, 24: Exhaust system state estimator

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 25/07 550 F02M 25/07 550R 550E

Claims (6)

[Claims] An engine control method for detecting an amount of air taken into an engine and controlling a fuel injection amount and an opening degree of a valve provided in a passage for recirculating combustion gas in an exhaust pipe to an intake pipe. Based on the detected air amount, it is equivalent to the ratio of the amount of air flowing into the cylinder based on the mathematical model of the intake and exhaust systems and the combustion reaction equation, and the ratio of the amount of recirculated gas to the exhaust gas recirculation rate and the amount of fuel injection. An engine control method comprising: estimating at least one of an excess oxygen ratio to be performed, and controlling the fuel injection amount and the valve opening based on a result of the estimation. 2. The engine control method according to claim 1, wherein the mathematical model is created based on a material balance of each gas component in an intake pipe and an exhaust pipe. 3. The engine control method according to claim 1, wherein the mathematical model is created by applying a state equation of an ideal gas to the gas in the intake and exhaust pipes. 4. The engine control method according to claim 1, further comprising: estimating an intake pipe gas temperature in an intake air temperature and an exhaust gas temperature; and based on the estimated result, the exhaust gas recirculation rate and the exhaust gas recirculation rate. An engine control method comprising estimating one of the oxygen excess rates. 5. The engine control method according to claim 1, wherein the engine is operated in a stable operating range based on at least one of the exhaust gas recirculation rate and the in-cylinder excess oxygen rate. An engine control method characterized by determining whether or not there is an engine. 6. The engine control method according to claim 1, wherein, based on the exhaust gas recirculation rate and the in-cylinder excess oxygen rate, whether or not the engine is in an operating range in which stable combustion is performed. An engine control method characterized by determining the following.