JPH0988676A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately keep the engine air-fuel ratio at the target air-fuel ratio even at the time of the transient operation. SOLUTION: An electronic control unit(ECU) 10 estimates the air quantity sucked into each cylinder of an engine based on the engine operation parameters detected by a throttle opening sensor 17, a suction pipe pressure sensor 3, and revolving speed sensors 5, 6 and calculates the fuel injection quantity from a fuel injection valve 7 based on the air quantity. The ECU calculates the fuel quantity actually fed into the cylinder based on the output of an exhaust air-fuel ratio sensor 13 and the estimated value of the air quantity sucked into the cylinder and corrects the fuel injection quantity from the fuel injection valve 7 based on the fuel quantity. The air quantity used for the calculation of the actual feed fuel quantity is calculated based on the operating parameters when the suction valve of each cylinder is closed. The accurate feed fuel quantity containing no error is calculated, and the air-fuel ratio is accurately controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine.

[0002]

2. Description of the Related Art An air-fuel ratio control device for an internal combustion engine, which detects an engine exhaust air-fuel ratio by an air-fuel ratio sensor provided in an exhaust passage of the internal combustion engine and feedback-controls a fuel supply amount to the engine based on the exhaust air-fuel ratio. Are known. For example, as this type of air-fuel ratio control device, there is one described in Japanese Patent Laid-Open No. 6-280648.

The apparatus disclosed in the above publication estimates the intake air amount sucked into the cylinder based on the output of the air flow meter, the engine crank rotation angle, and the engine rotation speed, and uses this intake air amount estimation value as a target air-fuel ratio. By dividing, the fuel supply amount (target fuel supply amount) required to bring the in-cylinder combustion air-fuel ratio to the target air-fuel ratio is estimated. In addition, the estimated intake air amount is
The amount of fuel actually supplied to the cylinder is estimated by dividing by the exhaust air-fuel ratio detected by the air-fuel ratio sensor arranged in the exhaust system.

In the device of the above publication, the target fuel supply amount and the fuel amount actually supplied to the cylinder are made to coincide with each other.
That is, the target fuel supply amount is corrected so that the integrated value of the deviation between the target fuel supply amount and the actual fuel amount becomes zero. By correcting the target fuel supply amount as described above, it becomes possible to quickly make the engine air-fuel ratio converge to the target air-fuel ratio even during transient operation.

[0005]

However, in the air-fuel ratio control device of the above-mentioned Japanese Patent Laid-Open No. 6-280648, the amount of fuel actually supplied to the cylinder cannot be estimated with high accuracy, and as a result, There may be a case where the engine air-fuel ratio cannot be swiftly converged to the target air-fuel ratio during transient operation or the like.

The total amount of air drawn into a cylinder is
It is determined when the intake stroke of the cylinder ends and the intake valve closes. Therefore, in order to accurately calculate the target fuel supply amount of each cylinder, the intake air is taken into the cylinder by using the engine operating parameters (for example, air flow meter output, engine speed, etc.) when the intake valve of each cylinder is closed. It is necessary to calculate the amount of air taken. However, for example, when fuel is injected into the intake port of each cylinder using a fuel injection valve, fuel injection can be performed only while the intake valve is open.
Therefore, it is necessary to calculate the target fuel supply amount in time with the fuel injection timing during the intake valve opening, that is, before the intake valve is closed and the intake air amount of the cylinder is determined.

Therefore, the intake air amount is calculated based on the engine operating parameters while the intake valve is open, and the target fuel supply amount is calculated when the engine operating state changes greatly, such as during transient operation. In some cases, the amount of intake air used for the cylinder does not exactly match the amount of air actually sucked into the cylinder. In the device of the above publication, the amount of fuel actually supplied to the cylinder is estimated, and the target fuel supply amount is corrected so that this fuel amount and the target fuel supply amount match. If the supplied fuel amount is accurately estimated, even if there is some error in the intake air amount used to calculate the target fuel supply amount, this error is corrected and the in-cylinder air-fuel ratio is accurately adjusted to the target air-fuel ratio. Should be maintained at.

However, in the apparatus of the above publication, the intake air amount used for calculating the target fuel supply amount is used as it is to calculate the fuel amount actually supplied to the cylinder, and therefore the calculated fuel amount also has an error. In some cases, it will include. For this reason, the device of the above publication cannot correct the target fuel supply amount accurately, and it may be impossible to quickly converge the air-fuel ratio to the target air-fuel ratio during transient operation or the like. .

In view of the above problems, the present invention improves the accuracy of the air-fuel ratio control by accurately estimating the amount of fuel actually supplied to the cylinder, and accurately sets the air-fuel ratio to the target air-fuel ratio even during transient operation. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that enables convergence.

[0010]

According to the present invention, an in-cylinder air amount estimating means for calculating an estimated value of an intake air amount taken into a cylinder based on an operating state parameter of an internal combustion engine, and a predetermined Fuel supply for calculating a target fuel supply amount necessary for setting the combustion air-fuel ratio of the cylinder to the target air-fuel ratio based on the intake air amount estimated value calculated by the in-cylinder air amount estimating means at the fuel supply amount calculation timing Quantity calculation means,
Based on an air-fuel ratio detecting means for detecting an exhaust air-fuel ratio from the cylinder, an exhaust air-fuel ratio of the cylinder detected by the air-fuel ratio detecting means, and an intake air amount estimated value calculated by the in-cylinder air amount estimating means. Then, the in-cylinder fuel amount calculating means for calculating the amount of fuel actually supplied to the cylinder, the fuel amount calculated by the in-cylinder fuel amount calculating means, and the fuel supply amount calculating means are calculated. Air-fuel ratio correction means for correcting the target fuel supply quantity so that the target fuel supply quantity matches, and fuel supply means for supplying the fuel of the target fuel supply quantity corrected by the air-fuel ratio correction means to the cylinder. In the air-fuel ratio control device for an internal combustion engine, the in-cylinder fuel amount calculation means estimates the exhaust air-fuel ratio and the intake air amount estimated by the in-cylinder air amount estimation means when the intake valve of the cylinder is closed. Based on and Air-fuel ratio control apparatus for an internal combustion engine and calculates the fuel quantity which is actually supplied into the cylinder is provided.

That is, according to the present invention, the in-cylinder fuel amount calculating means actually uses the air amount calculated by the in-cylinder air amount estimating means based on the engine operating parameter when the cylinder intake valve is closed, to determine whether the cylinder is actually in the cylinder. Calculate the amount of fuel supplied. Since the amount of air taken into the cylinder is determined when the intake valve is closed, the amount of air estimated based on the engine operating parameters when the intake valve is closed has a small error and is extremely close to the actual air amount. Therefore, the in-cylinder fuel amount calculating means can accurately estimate the amount of fuel actually supplied into the cylinder.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing the entire configuration when the present invention is applied to an internal combustion engine for a vehicle. In FIG. 1, reference numeral 1 denotes an internal combustion engine body. In this embodiment, a multi-cylinder engine is used as the internal combustion engine 1, and although FIG. 1 shows only one of the cylinders, the other cylinders have the same configuration.

In FIG. 1, 2 is an intake pipe of the engine 1, and 16
Is a throttle valve which is arranged in the intake pipe 2 and has an opening degree according to the operation amount of the accelerator pedal 21 by the driver.
2 is an intake manifold that connects the intake port of each cylinder and the surge tank 2a, and 7 is a fuel injection valve that injects pressurized fuel to the intake port of each cylinder of the engine 1.

In this embodiment, the throttle valve 16 has
A throttle opening sensor 17 for generating a voltage signal according to the throttle valve opening is arranged, and an intake pipe pressure sensor 3 for generating a voltage signal according to the absolute pressure in the surge tank 2a is provided in the surge tank 2a. It is connected. On the other hand, in FIG. 1, reference numeral 11 denotes an exhaust manifold for connecting the exhaust port of each cylinder to a common exhaust pipe 14.
Although not shown, the collective exhaust pipe 14 has HC, CO, NO _x in the exhaust gas when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio.
A three-way catalyst capable of simultaneously purifying the three components is disposed. An air-fuel ratio sensor 13 is provided at the exhaust merging portion where the exhaust gas from each cylinder of the exhaust manifold 11 merges. In this embodiment, the air-fuel ratio sensor 13 is a linear output type air-fuel ratio sensor that detects the oxygen concentration in the exhaust gas and generates a linear output voltage proportional to the air-fuel ratio.

In FIG. 1, a water jacket 8 of a cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of cooling water. The water temperature sensor 9 generates an electric signal of analog voltage according to the temperature of the cooling water. The air-fuel ratio sensor 13, the throttle valve opening sensor 17, the intake pipe pressure sensor 3 and the water temperature sensor 9 described above.
Output signal is input to an A / D converter 101 with a built-in multiplexer of the ECU 10, which will be described later.

Reference numerals 5 and 6 in FIG.
Is a crank angle sensor that detects the crank rotation angle of the.
The crank angle sensor 5 is provided in the vicinity of a camshaft (not shown) of the engine 1, and generates a reference position detection pulse signal every 720 ° in terms of the camshaft rotation angle, for example, converted into the crankshaft rotation angle. The crank angle sensor 6 is provided in the vicinity of the crank shaft and generates a crank angle detection pulse signal at every 30 ° rotation of the crank shaft. The pulse signals of the crank angle sensors 5 and 6 are supplied to the input / output interface 102 of the ECU 10, and the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

The ECU (Electronic Control Unit) 10 is configured as, for example, a microcomputer, and includes an A / D converter 101, an input / output interface 102, a CPU 10
3, a ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, etc. are provided. In the present embodiment, the ECU 10 controls the fuel injection valve 7 of the engine 1 and performs fuel injection control for injecting the amount of fuel calculated in a fuel injection amount calculation routine described later into the intake port of the cylinder.

The down counter 108, flip-flop 109, and drive circuit 110 of the ECU 10 are for controlling the fuel injection valve 7. That is, in the routine described later, when the fuel injection amount (injection time) TAU is calculated, the injection time TAU is preset in the down counter 108 and the flip-flop 109 is set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and the output terminal finally becomes the “1” level, the flip-flop 109
Is reset and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized for the above-described fuel injection time TAU, and the amount of fuel corresponding to the time TAU is supplied to the combustion chamber of the engine 1.

The engine rotational speed (rotational speed) data is calculated based on the pulse interval of the crank angle sensor 6 by interruption at every predetermined crank angle (for example, every 30 °), and is stored in the RAM.
It is stored in a predetermined area 105. That is, the RAM 105
The latest rotation speed data is always stored in. Next, calculation of the fuel injection amount of the engine of this embodiment will be described.

In this embodiment, the fuel injection amount (injection time of each fuel injection valve) TAU is calculated from the following equation based on the intake air amount of each cylinder and the engine speed. TAU = PMGA × KINJ × α + ΔTAU (1) Here, PMGA is an intake air amount parameter that represents the amount of air flowing into each cylinder during intake valve opening, and as described later, It is calculated using the intake pipe pressure calculated based on the engine speed and the output of the intake pipe pressure sensor 3 and the engine speed.

In the equation (1), KINJ is the intake air amount parameter (PMGA) and is the basic fuel injection amount (PM).
It is a conversion constant for conversion into GA × KINJ). The basic fuel injection amount (PMGA × KINJ) is a fuel amount required to set the in-cylinder combustion air-fuel ratio to the target air-fuel ratio (theoretical air-fuel ratio). Further, α is a correction coefficient determined from the engine warm-up state and other operating states, and ΔTAU is the air-fuel ratio correction amount. The air-fuel ratio correction amount ΔTAU is calculated based on the deviation between the fuel amount ATAU actually supplied to the cylinder and the fuel injection amount TAU from the fuel injection valve 7.
The integrated value of the deviation between U and TAU is set to 0.

As can be seen from the above equation (1), in this embodiment, the fuel injection amount TAU of the engine is the intake air amount (PMG) of each cylinder calculated from the intake pipe pressure and the engine speed.
First, based on A), the basic fuel injection amount (PMGA x KI
NJ) is calculated, and this basic fuel injection amount is obtained by correcting the basic fuel injection amount according to the engine operating state (α) such as warm-up operation and the fuel amount ATAU actually supplied into the cylinder.

Next, a method of calculating the intake air amount parameter PMGA of this embodiment will be described. In a normal engine, when the engine is operating in steady state (ie,
When the engine speed NE and the throttle valve opening TA are maintained constant), the intake pipe pressure becomes a function of TA and NE, and if TA and NE are determined, the intake pipe pressure PM is uniquely determined. It is determined. The intake air amount PMGA of each cylinder is calculated as the product of the intake pipe pressure PM and the charging efficiency KTP (that is, PMGA = PM × KTP). Further, the charging efficiency KTP is uniquely determined from the throttle valve opening TA and the engine speed NE. That is, the intake air amount PMG
A can be calculated using the throttle valve opening TA and the engine speed NE.

In the present embodiment, the intake pipe pressure PM under each condition of the engine speed NE and the throttle valve opening TA is measured in advance during steady engine operation using an actual engine, and the intake pipe pressure PM Value E in the form of a map using TA and NE
It is stored in the ROM 104 of the CU 10. During engine operation,
The ECU 10 uses the throttle valve opening TA detected by the throttle opening sensor 17 and the engine speed NE to calculate the intake pipe pressure in the engine steady operation from this map.
The intake pipe pressure given as a map of TA and NE is a value at the time of steady operation in the standard state, and may differ from the value actually detected by the intake pipe pressure sensor 3. Therefore, in the following description, the measured value of the intake pipe pressure (the value detected by the intake pipe pressure sensor 3) is referred to as PM, and the intake pipe pressure value stored as a function of TA and NE in the above map is referred to as PMTA. We will distinguish between the two.

By the way, as described above, the amount of air actually taken into the cylinder is determined when the intake valve of the cylinder is closed. Further, in actual operation, the intake pipe pressure when the intake valve of each cylinder is closed corresponds to the amount of air taken into the cylinder most accurately. However, in order to supply fuel into the cylinder, it is necessary to inject fuel from the fuel injection valve 7 while the intake valve is open, and it is necessary to calculate the intake air amount PMGA before the intake valve is closed. For this reason,
In the present embodiment, the intake pipe pressure when the intake valve is closed is predicted using PMTA and the value of PM at the fuel injection timing (while the intake valve is open) (hereinafter, the intake pipe pressure predicted value when the intake valve is closed is The intake air amount PMGA is calculated based on this predicted value PMFWD.

The calculation of PMFWD will be described below. The value of the intake pipe pressure PMTA read out from the map using TA and NE changes immediately when the throttle valve opening TA or the engine speed NE changes, but the actual intake pipe pressure PM Does not become the changed PMTA immediately even if TA and NE change, but changes with a certain delay time.

FIG. 2 is a diagram for explaining the actual change in the intake pipe pressure PM when the map value PMTA of the intake pipe pressure changes stepwise due to changes in TA, NE and the like. FIG.
As shown in, when PMTA changes stepwise, P
M changes relatively slowly and reaches the changed PMTA after a certain period of time. This PM behavior can be approximated to a change in PMTA by a first-order lag response system. Therefore, the current intake pipe pressure can be calculated from the values of the past intake pipe pressure and the current PMTA using a temporary delay response model. That is, assuming that the current calculated value of the intake pipe pressure is PMCRT, PMCRT can be expressed using the following temporary delay response equation.

PMCRT = PMCRT _i-1 + (PMTA-PMCRT _i-1 ) × (1 / N) (2) where PMCRT is the current intake pipe pressure (calculated value), PM
CRT _i-1 is the intake pipe pressure before the time Δt from the present, PMT
A is an intake pipe pressure (map value) in a steady state determined by the current throttle valve opening TA and the engine speed NE.

N is a weighting coefficient, which is expressed as N = T / Δt using the time constant T of the first-order lag response and the above Δt. The time constant T is a value determined by the throttle valve opening TA and the engine speed NE, and can be obtained as a function of TA and NE by an experiment using an actual engine in advance. The throttle valve opening TA and the engine speed N
Since the intake pipe pressure PMTA in the steady state is uniquely determined by E and E, the intake pipe pressure PMTA in the steady state is replaced by the throttle valve opening TA and the engine speed NE in the present embodiment.
And the time constant T is obtained as a function of the engine speed NE.

In this embodiment, the PMCRT is used when the engine is started.
= Starting the calculation of the above formula (2) using the initial value of PMTA, and repeating the calculation of the above formula (2) at every engine operating time Δt, the result of the sequential calculation from the engine start The current intake pipe pressure PMCRT is calculated. As is clear from the equation (2), when the engine steady operation (that is, the operation with the PMTA being constant) continues to some extent, the value of PMCRT coincides with PMTA.

By the way, PMCR calculated by the above
T is the current value of the intake pipe pressure, but as described above, the value that most reflects the actual amount of air taken into the cylinder is the value of the intake pipe pressure when the intake valve of each cylinder is closed. Because
In order to accurately calculate the intake air amount PMGA, it is preferable to use the intake pipe pressure when the intake valve is closed.
On the other hand, since the current intake pipe pressure PMCRT is calculated by approximating the response of the intake pipe pressure by the first-order lag response system as shown in FIG. 2, it is the same if PMTA is maintained constant after the change. By repeating the sequential calculation of equation (2) using the first-order lag response model, the current (PM
It is possible to predict the intake pipe pressure before the CRT calculation time). That is, after calculating PMCRT, if the calculation of formula (2) is performed once using the same value of PMTA, the intake pipe pressure after Δt from the present is calculated,
If the calculation of the equation (2) is repeated twice, the intake pipe pressure after 2 × Δt has elapsed can be calculated. That is, assuming that the time from the present (at the time of calculating PMCRT) to the closing of the intake valve of any cylinder next is L, the calculated PMCRT value is used as an initial value and the current PMTA is used to calculate the expression (2). Calculation of L / Δ
By repeating t times, it is possible to calculate the intake pipe pressure when the next cylinder is closed. Here, when the calculated value of the intake pipe pressure when the intake valve of any one of the cylinders is closed next is called PMVLV (see FIG. 3), PMCRT _{i + 1} = PMCRT + (PMTA-PMCRT) × (1 / N) PMCRT _{i + 2} = PMCRT _{i + 1} + (PMTA-PMCRT _{i + 1} ) × (1 / N) ………… (Repeated P times, but P = L / Δt) ………… PMVLV = PMCRT PMVLV is calculated by sequential calculation of _{i + P} = PMCRT _{i + P-1} + (PMTA-PMCRT _{i + P-1} ) * (1 / N).

The value of PMTA used for the above-mentioned sequential calculation is a map value based on the current TA and NE. For example, the values of TA and NE, especially the value of TA, are in transient operation (during rapid acceleration, sudden When decelerating), there may be a large change in a short time. Therefore, when PMVLV is calculated from the current intake pipe pressure PMCRT by the above-described sequential calculation, it is more accurate to find PMTA based on the value of TA when the intake valve is closed. Therefore, in the present embodiment, the throttle valve opening T when the intake valve is closed is calculated by the following equation.
AO is predicted, and the above sequential calculation is performed using the value of PMTA read from the map using this TAO and the current engine speed NE.

That is, TAO = TA + (TA−TA _i−1 ) × L / Δt (3) and PMCRT _{i + 1} = PMCRT + (PMTAO−PMCRT) × (1 / NO) PMCRT _{i + 2} = PMCRT _{i + 1} ＋ (PMTAO −PMCRT _{i + 1} ) × (1 / NO) ………… (Repeated P times, but P = L / Δt) ………… PMVLV = PMCRT _{i + P} ＝ PMCRT _{i + P -1} + (PMTAO-PMCRT _{i + P-1} ) x (1 / NO) (4) where TAO in equation (3) is the predicted value of the throttle valve opening when the intake valve is closed, TA Is the current throttle valve opening, TA
_i-1 is the throttle valve opening at the time Δt before the present, L is the time from the present to the time when the intake valve is closed, and PMT
AO is an intake pipe pressure map value in a steady state obtained by using the throttle valve opening predicted value TAO and the current engine speed NE. Further, NO is a weighting coefficient, and is calculated as NO = TO / Δt using the time constant TO determined from the throttle valve opening predicted value TAO and the engine speed NE.

That is, in this embodiment, the intake pipe pressure calculation value PMCRT calculated at the time point Δt before the present time
_{Using i-1} and the current intake pipe pressure map value PMTA,
Current intake pipe pressure calculated value PMC from first-order lag response model
RT is calculated (Equation (2) above), and after a lapse of time L from the present from the throttle valve opening TA _i-1 at the time point Δt before the present time and the current throttle valve opening TA (that is, the intake valve is closed). The throttle valve opening TAO (when the valve is open) is predicted (Equation (3) above), and the predicted value PMTAO of the intake pipe pressure map value when the intake valve is closed is calculated from this TAO and the current engine speed NE. . Next, the predicted value PMTA
Using the current intake pipe pressure calculation value PMCRT calculated by O and O, the intake pipe pressure calculation value (predicted value) PMVLV at the time of closing the intake valve is calculated by sequential calculation ((4) above).
formula).

FIG. 3 is a diagram for explaining the relationship between the pressures of the intake pipes. As can be seen from FIG. 3, in the present embodiment, the current throttle valve opening TA and the engine speed NE, and the intake pipe pressure calculated value PMCRT at the time point Δt before the present time.
The intake pipe pressure calculated value PMVLV when the intake valve is closed is calculated based only on _i-1 . By the way, it is possible to obtain a temporary cylinder intake air amount by multiplying the intake pipe pressure calculated value PMVLV by the charging efficiency KTP as described above. However, as described above, the value of PMVLV is sequentially calculated from the time of engine start. Since it is based on the current intake pipe pressure calculated value PMCRT, the value of PMVLV may include a steady error associated with the sequential calculation of PMCRT.

Therefore, in the present embodiment, the actual intake pipe pressure measurement value PM is used to correct the steady-state deviation contained in the value of PMVLV to improve the prediction accuracy of PMVLV. FIG.
FIG. 4 is a diagram showing a principle of correcting the steady deviation. In FIG. 4, the horizontal axis represents time and the vertical axis represents intake pipe pressure. Curve A is the intake pipe pressure calculated value PMCR
A curve B shows an example of a change over time of the intake pipe pressure actual measurement value PM actually measured by the intake pipe pressure sensor 3. Since the output of the intake pipe pressure sensor 3 has a response delay (sensor response delay) similar to that shown in FIG. 2 with respect to the actual intake pipe pressure change, it is between the intake pressure calculation value PMCRT and the actual measurement value PM. In addition to the above-mentioned steady deviation, there is a difference including the sensor response delay.

Further, in FIG. 4, a curve C is a curve A.
Shows the curve of the first-order delay response corresponding to the sensor response delay. That is, the difference between the curve A and the curve C (ΔD in FIG. 4) represents the sensor response delay. Therefore, if the calculated intake pipe pressure value PMCRT does not include any steady-state deviation due to successive calculation, the output of the intake pipe pressure sensor 3 changes as shown by the curve C in FIG. The difference between curve C and curve B (actual intake pipe pressure sensor 3 output) (ΔPD in FIG. 4) represents a steady deviation included in the intake pipe pressure calculated value PMCRT.

Further, FIG. 4 curve C (that is, PMCR
Since the calculated intake pipe pressure sensor 3 output corresponding to T, hereinafter, the calculated sensor 3 output value is referred to as PMCRT4) has a first-order lag characteristic with respect to the curve A (PMCRT), Similarly to the equation), it can be calculated as PMCRT4 = PMCRT4i _-1 + (PMCRT-PMCRT4i _-1 ) * (1 / M) (5). Here, PMCRT4 is the output of the sensor 3 in the present calculation, PMCRT4 _i-1 is the value of PMCRT4 before time Δs before the present, and PMCRT is the present intake pipe pressure calculated value, which is calculated from the above equation (2). It is a value. Further, M is a weighting coefficient, which is expressed as M = S / Δs using the time constant S of the response delay of the intake pipe pressure sensor and the time Δs. The time constant S is a constant that is experimentally obtained in advance using an actual sensor.

The steady deviation ΔPD included in PMCRT is expressed as ΔPD = PMCRT4-PM as described above (FIG. 4). Since this steady-state deviation ΔPD is a substantially constant value, the value of PMVLV with the deviation corrected, that is, the intake pipe pressure predicted value PMFWD when the intake valve is closed, which should be used to calculate the intake air amount PMGA, is PMFWD = PMVLV- ΔPD = PMVLV-PMCRT4 + PM (6)

Similarly, the present true intake pipe pressure PMTR in which the steady-state deviation ΔPD is similarly corrected is PMTR = PMCRT-ΔPD = PMCRT-PMCRT4 + PM (7). In this embodiment, the fuel injection amount is calculated (the above (1)
The intake air amount PMGA used in the equation) is calculated by using the intake pipe pressure predicted value PMFWD when the intake valve is closed, and the air-fuel ratio correction amount ΔTAU is calculated when fuel injection is performed in the same cylinder last time. Intake pipe pressure PMT when the actual intake valve is closed
The intake air amount PMGR calculated based on R is used.

The reason why different intake pipe pressures are used for the basic fuel injection amount calculation and the air-fuel ratio correction amount calculation is as follows. That is, fuel injection from the fuel injection valve to the intake port must be performed before the intake valve closes. Therefore, the basic fuel injection amount must be calculated without waiting for the intake valve to close and the amount of air in the cylinder to be determined.
Therefore, in the present embodiment, the basic fuel injection amount is calculated by predicting the intake pipe pressure PMFWD when the intake valve is closed from the engine operating parameter during the intake valve opening. However, the time L between the predicted intake pipe pressure and the actual closing of the intake valve is L (Fig. 4).
Since there is a gap between them, the difference between the intake pipe pressure when the intake valve is actually closed and the predicted value PMFWD may be large, especially when the engine operating state changes greatly. As described above, since the actual fuel injection amount TAU is a value obtained by correcting the basic fuel injection amount by the air-fuel ratio correction amount ΔTAU, ΔTA
If U is set accurately, the prediction error of PMFWD should be corrected. However, if the same PMFWD used for calculating the basic fuel injection amount is used for calculating ΔTAU, the correction amount ΔTAU itself includes a prediction error of PMFWD, and the error of the actual fuel injection amount TAU is corrected. I can't.

On the other hand, the air-fuel ratio correction amount ΔTAU is the fuel amount actually supplied to the cylinder and the target fuel amount (basic fuel amount).
Is calculated on the basis of the deviation between and, but the actual calculation timing of the in-cylinder fuel amount is when the gas burned in the cylinder reaches the air-fuel ratio sensor 13 of the exhaust manifold 11, that is, the intake valve is closed. After the intake air amount is confirmed. Therefore, the calculation of ΔTAU does not have the time constraint as in the calculation of the basic fuel injection amount, and the intake pipe pressure when the intake valve is actually closed can be used. Therefore, in the present embodiment, the intake air amount used to calculate the air-fuel ratio correction amount ΔTAU is not the predicted value PMFWD but the intake pipe pressure at the time when the actual intake valve is closed (that is, the PMT when the intake valve is actually closed).
The calculation is performed based on R (equation (7)). As a result, it is possible to set an accurate air-fuel ratio correction amount ΔTAU that does not include the PMFWD prediction error, so that the fuel injection amount can be accurately calculated according to the operating state, and even during transient operation. It is possible to quickly make the engine air-fuel ratio converge to the theoretical air-fuel ratio.

5 and 6 are flowcharts showing the intake air amount calculation routine in this embodiment. This routine is executed by the ECU 10 at regular intervals (for example, 5 to 10
every ms). In this routine, the calculated value PMCRT4 of the intake pipe pressure sensor output for correcting the deviation ΔPD is calculated each time the routine is executed (step 527 in FIG. 5), and the intake pipe pressure calculated values PMCRT, PMV are calculated every time the routine is executed twice.
The intake pipe pressures of LV, PMFWD, and PMTR are calculated. Set the calculation interval of PMCRT4 to 1 of the other pressure calculation intervals.
The reason for setting / 2 is to improve the correction accuracy of the deviation ΔPD (FIG. 4).

When the routine starts in FIG. 5,
At step 501, the value of the counter C is incremented by 1. Here, C is a counter that is cleared in step 541 (FIG. 6) every time the routine is executed twice, and P
It is used to calculate only the value of MCRT4 every time the routine is executed, and to calculate other intake pipe pressure values every time the routine is executed twice.

In step 503, the measured intake pipe pressure PM detected by the intake pipe pressure sensor 3 is read,
Next, at step 505, it is judged from the value of the counter C whether or not the current routine execution timing is the execution timing of steps 507 to 525 (C = 2). If C = 2 in step 505, steps 507 to 525 are executed, and PMCRT and PMVLV are executed.
Is calculated.

That is, at step 507, the output of the throttle valve opening sensor 17 is AD-converted and taken in as throttle valve opening data TA, and the RAM 1
The latest rotation speed data NE stored in 05 is read. Further, in step 509, the time L from the present until the intake valve of any of the cylinders is closed is calculated based on the current crankshaft rotation phase detected by the crank sensors 6 and the engine speed NE. It

Further, in step 511, based on the time L calculated above and the previous throttle valve opening degree TA _i-1 , the throttle valve opening at the time when the cylinder intake valve is closed next from the equation (3). The predicted degree value TAO is calculated. Here, Δt in the equation (3) is a value twice the execution interval of this routine. Steps 513 to 517 show the calculation of the value of the current intake pipe pressure PMCRT. In step 513,
Using TA and NE read in step 507, the intake pipe pressure (map value) PMTA in the steady state is read out, and in step 515, the weighting coefficient N of the equation (3) is read out from PMTA and NE. Further, in step 517, the current intake pipe pressure PMCRT is calculated from the PMTA, N, and the value of PMCRT (PMCRT _i-1 ) at the time of execution of the previous routine using the equation (2).

Similarly, at steps 519 and 521, the intake pipe pressure map value PMTA is calculated from the throttle valve opening predicted value TAO when the intake valve is closed and the current engine speed NE.
O and the weighting coefficient NO of the equation (4) are calculated respectively, and in step 523 of FIG. 6, the intake pipe pressure predicted value PMVLV at the time of closing the intake valve is calculated by the sequential calculation of the equation (4). In step 525, the values of TA _i-1 and PMCRT _i-1 are updated in preparation for the next routine execution. After calculating the values of PMCRT and PMVLV as described above, in step 527, P calculated in step 517 is calculated.
MCRT and previous PMCRT4 value (PMCRT
4 _{i- 1} ) and the current calculated value PMCRT4 of the output of the intake pipe pressure sensor 3 is calculated based on the equation (5), and in step 528, PMCRT is prepared for the next routine execution.
The value of 4 _i-1 is updated. In step 505, C ≠
If it is 2, step 527 is directly followed by step 527.

Steps 529 to 539 are the calculation of the intake valve closing predicted intake pipe pressure value PMFWD after the deviation correction, the current intake pipe pressure PMTR after the deviation correction, and PMFW.
The calculation of the cylinder intake air amount based on each of D and PMTR is shown. The steps 531 to 539 are executed only every time the routine is executed twice (when C = 2 in step 529).

In steps 531 and 533, the above (6) is executed.
PMFWD and PMTR are calculated from the equation (7),
At step 535, the current charging efficiency KTP is calculated from the current throttle valve opening TA and the engine speed NE, and the predicted charging efficiency when the intake valve is closed is calculated from the throttle valve opening predicted value TAO and the rotational speed NE. Each KTPO is calculated.

Further, the intake air amount PMGA used for the fuel injection amount calculation is calculated by using PMFWD and KTPO.
= PMFWD × KTPO (step 537), the intake air amount PMGR based on the current intake pipe pressure is PMTR and KT
Based on P and P, PMGR = PMTR × KTP (step 539) is calculated and stored in a predetermined area of the RAM.

Next, the actual in-cylinder intake air amount PMGRVCL when the intake valve is closed, which is used to calculate the air-fuel ratio correction amount ΔTAU.
The calculation of will be described. As described above, in the routines of FIGS. 5 and 6, the routine 2 is executed independently of each crank rotation.
The intake air amount PMGR is calculated based on the current intake pipe pressure PMTR for each execution. In the present embodiment, a storage routine (not shown) is executed each time the crank rotation angle reaches an angle corresponding to the intake valve closing timing of each cylinder, so that the current intake pipe pressure is adjusted when the intake valve of each cylinder is closed. The intake air amount PMGR based on this is read and stored in the RAM 105 as the actual cylinder intake air amount PMGRVCL. As will be described later, the actual cylinder intake air amount PM
The value of GRVCL is used to calculate ΔTAU at the time when the exhaust gas after combustion reaches the position of the air-fuel ratio sensor, so a certain time delay occurs. Therefore, by executing the storage routine, the RAM 105 always stores the actual intake air amount PMGRVCL of each cylinder in the past fixed period (for example, about 10 engine revolutions), and is updated every time the routine is executed.

FIG. 7 is a flow chart showing the fuel injection amount calculation routine of this embodiment. This routine is EC
It is executed by U10 at every constant rotation of the crankshaft (at each fuel injection timing of each cylinder). When the routine starts in FIG. 7, the latest intake air amount PMGA value calculated by the routine of FIG. 5 and FIG. 6 executed immediately before is read in step 701. In step 703, the current air-fuel ratio sensor 13 is read. The actual intake air amount PMGR _iK (for example, the value of PMGR read before 10 engine revolutions) when the exhaust gas that has reached the position is burned in the cylinder is R
It is read from AM105.

Next, at step 705, the air-fuel ratio sensor
13 outputs are AD converted and based on this output the current output
The air-fuel ratio A / F is calculated. Furthermore, in step 707
Is PMGR_iKAnd A / F are actually supplied into the cylinder.
Fuel quantity ATAU_iKIs calculated. Also step
In 709, ATAU _iKAnd the fuel injection amount TA at this time
U_iKThe air-fuel ratio correction amount ΔTAU is calculated using and.
In this embodiment, the above-mentioned Japanese Patent Laid-Open No. 6-280648 is used.
ATAU in the same way as_iKAnd TAU_iKBased on
ATAU_iKAnd TAU_iKThe integrated value of the deviation between and becomes 0
As described above, the value of the air-fuel ratio correction amount ΔTAU is determined.
The calculation of TAU is performed by another known method such as TAU._iKAnd A
TAU_iKPID (proportional, derivative, product
Min) processing.

When the air-fuel ratio correction amount ΔTAU is calculated in step 709, the current fuel injection amount TAU is calculated based on the above equation (1) in step 711, and step 713 prepares for the next routine execution. The value of this TAU is stored in the RAM 105. In addition, step 715
Then, the calculated TAU value is preset in the down counter 108 (FIG. 1), and fuel injection is executed.

As described above, according to this embodiment, the in-cylinder intake air amount for calculating the air-fuel ratio correction amount ΔTAU is set as the engine operating parameter (throttle valve opening TA, Engine speed NE, intake pipe pressure measured value PM
And the like), the air-fuel ratio correction amount ΔTAU is determined based on the amount of air actually sucked into the cylinder. Therefore, the calculated Δ
The value of TAU is an accurate value that reflects the actual engine operating state.

[0057]

According to the present invention, the amount of fuel actually supplied to the cylinder is calculated by using the intake air amount in the cylinder estimated based on the engine operating parameter when the intake valve of each cylinder is closed. By doing so, the amount of fuel actually supplied to the cylinder can be accurately estimated, so that the air-fuel ratio can be accurately converged to the target air-fuel ratio even during the transient operation.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an automobile engine.

FIG. 2 is a diagram illustrating a response characteristic of intake pipe pressure.

FIG. 3 is a diagram illustrating an intake pipe pressure prediction method in the embodiment of FIG.

FIG. 4 is a diagram illustrating an intake pipe pressure prediction method in the embodiment of FIG.

5 is a part of a flowchart showing a cylinder intake air amount estimation routine in the embodiment of FIG.

6 is a part of a flowchart showing a routine for estimating the intake air amount in a cylinder in the embodiment of FIG.

7 is a flow chart showing a fuel injection amount calculation routine of the embodiment of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Intake pipe pressure sensor 10 ... Electronic control unit (ECU) 11 ... Exhaust manifold 13 ... Air-fuel ratio sensor 17 ... Throttle opening sensor

Claims (1)

[Claims] 1. An in-cylinder air amount estimating means for calculating an estimated value of an intake air amount taken into a cylinder based on an operating state parameter of an internal combustion engine, and the in-cylinder air at a predetermined fuel supply amount calculation timing. A fuel supply amount calculation means for calculating a target fuel supply amount necessary to bring the combustion air-fuel ratio of the cylinder to a target air-fuel ratio, based on the intake air amount estimated value calculated by the amount estimation means, and an exhaust gas from the cylinder Based on the air-fuel ratio detecting means for detecting the air-fuel ratio, the exhaust air-fuel ratio of the cylinder detected by the air-fuel ratio detecting means, and the intake air amount estimated value calculated by the in-cylinder air amount estimating means, the actual In-cylinder fuel amount calculation means for calculating the amount of fuel supplied to the cylinder, the fuel amount calculated by the in-cylinder fuel amount calculation means, and the target fuel supply amount calculated by the fuel supply amount calculation means When An internal combustion engine including: an air-fuel ratio correction unit that corrects the target fuel supply amount so as to match; and a fuel supply unit that supplies the fuel of the target fuel supply amount corrected by the air-fuel ratio correction unit to the cylinder. In the air-fuel ratio control device, the in-cylinder fuel amount calculation means is a cylinder based on the exhaust air-fuel ratio and an intake air amount estimated value calculated by the in-cylinder air amount estimation means when the intake valve of the cylinder is closed. An air-fuel ratio control device for an internal combustion engine, which calculates the amount of fuel actually supplied to the internal combustion engine.