JP2000136745A - Air-fuel ratio control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the control precision of an air-fuel ratio control device for an engine. SOLUTION: This device includes a mixture amount calculating means 51 for calculating a mixture amount Gm in response to an engine rotating speed Ne, a manifold pressure Pb and a manifold temperature Tb, a target air-fuel ratio calculating means 52 for calculating a target air-fuel ratio OBJ in response to an operated condition and a basic fuel injection amount calculating means 55 for calculating a basic fuel injection amount Gf-FF in response to the mixture amount Gm and the target air-fuel ratio OBJ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an air-fuel ratio control device for an engine.

[0002]

2. Description of the Related Art In an engine using CNG (compressed natural gas) or the like as fuel, gaseous fuel is supplied to an intake passage upstream of a throttle valve to mix fuel and intake air. (For example, 7-1413
No. 5).

Conventionally, this type of CNG engine air-fuel ratio control device detects an intake air amount Ga via an air flow meter, as in a gasoline engine, and calculates a basic fuel injection amount from the intake air amount Ga and the engine speed Ne. Is calculated.

However, in the case of a large engine, since it is difficult to directly detect a large amount of intake air Ga via an air flow meter, there is an engine which calculates the intake air amount Ga from the throttle valve opening, the engine speed Ne, the intake manifold pressure, and the like. .

[0005]

However, in such a conventional air-fuel ratio control device for a CNG engine, since the gaseous fuel is supplied to the upstream side of the throttle valve, the state of the air-fuel mixture containing the gaseous fuel is increased. It is difficult to accurately calculate the intake air amount from the engine, and the control accuracy of the air-fuel ratio cannot be improved.

The present invention has been made in view of the above problems, and has as its object to enhance control accuracy in an air-fuel ratio control device for an engine.

[0007]

The first invention is applied to an air-fuel ratio control device for an engine that adjusts the amount of gaseous fuel injected upstream of a throttle valve in an intake passage in accordance with an operation state.

An engine speed detecting means for detecting the engine speed Ne, a manifold pressure detecting means for detecting a manifold pressure Pb downstream of the throttle valve, and a manifold for detecting a manifold temperature Tb downstream of the throttle valve. Temperature detection means, air-fuel mixture calculation means for calculating an air-fuel mixture Gm according to the engine speed Ne, the manifold pressure Pb and the manifold temperature Tb, and a target air-fuel ratio λ according to the operating state.
A target air-fuel ratio calculating means for calculating the OBJ and a fuel injection amount calculating means for calculating the fuel injection amount in accordance with the air-fuel mixture Gm and the target air-fuel ratio λOBJ are provided.

[0009] The second invention is the first invention, comprising a mixture amount correction coefficient calculating means for calculating the air-fuel mixture amount correction coefficient K ₁ depending on the intake manifold pressure Pb and the engine speed Ne, the fuel injection the amount calculating means is assumed to calculate the intake mixture weight Gm in accordance with the intake manifold pressure Pb intake manifold temperature Tb and mixture amount correction coefficient K _1.

[0010] In a third aspect based on the first or second aspect, the air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture and the fuel injection amount such that the air-fuel ratio of the air-fuel mixture approaches the target air-fuel ratio λOBJ. Air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount Δλ to be corrected; air-fuel ratio learning means for calculating an air-fuel ratio learning value Gm_LN according to the air-fuel ratio correction amount Δλ; It is provided with an air-fuel mixture correction means for correcting according to the air-flow learning value Gm_LN.

The fourth invention is applied to an air-fuel ratio control device for an engine that adjusts the amount of gaseous fuel injected upstream of a throttle valve in an intake passage in accordance with an operation state.

An engine speed detecting means for detecting an engine speed Ne, a manifold pressure detecting means for detecting a manifold pressure Pb downstream of the throttle valve, and a manifold for detecting a manifold temperature Tb downstream of the throttle valve. Temperature detection means, intake air amount calculation means for calculating an intake air amount Ga containing no fuel according to the engine speed Ne, the manifold pressure Pb and the manifold temperature Tb, and a target air-fuel ratio λOBJ according to the operating state. A target air-fuel ratio calculating means and a fuel injection amount calculating means for calculating a fuel injection amount according to the intake air amount Ga and the target air-fuel ratio λOBJ are provided.

[0013] The fifth invention is the first invention, comprises an intake air amount correction coefficient calculating means for calculating the intake air amount correction coefficient K ₁ depending on the intake manifold pressure Pb and the engine speed Ne, the fuel injection the amount calculating means is assumed to calculate the intake air amount Ga in accordance with the intake manifold pressure Pb intake manifold temperature Tb and the intake air amount correction coefficient K _1.

In a sixth aspect based on the first or second aspect, the air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture and the fuel injection amount are adjusted so that the air-fuel ratio of the air-fuel mixture approaches the target air-fuel ratio λOBJ. An air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount Δλ to be corrected, an intake air amount learning means for calculating an intake air amount learning value Ga_LN according to the air-fuel ratio correction amount Δλ, and an intake air amount Ga Intake air amount correction means for correcting according to the learning value Ga_LN is provided.

[0015]

According to the first aspect of the present invention, the air-fuel ratio control accuracy can be improved by accurately calculating the mixture amount Gm containing gaseous fuel in accordance with the engine speed Ne, the manifold pressure Pb and the manifold temperature Tb. . As a result, the exhaust gas can be purified, the output of the engine can be improved, and the fuel consumption can be reduced.

In the second invention, the air-fuel mixture correction coefficient K
_The accuracy of calculating the mixed gas amount Gm by using ₁ can be improved.

In the third aspect, by learning the mixture amount Gm according to the air-fuel ratio correction amount Δλ, it is possible to prevent the calculation accuracy of the mixture amount Gm from deteriorating due to variations in sensors and the like. In addition, the responsiveness of the air-fuel ratio feedback control can be maintained.

In the fourth invention, the engine speed Ne
, Manifold pressure Pb and manifold temperature Tb
Thus, the intake air amount Ga not including the gaseous fuel can be accurately calculated, and the control accuracy of the air-fuel ratio can be improved. As a result, the exhaust gas can be purified, the output of the engine can be improved, and the fuel consumption can be reduced.

[0019] In the fifth invention, it enhances the accuracy of calculating the intake air amount Ga with the intake air amount correction coefficient K _1.

In the sixth aspect, learning of the intake air amount Ga in accordance with the air-fuel ratio correction amount Δλ prevents the calculation accuracy of the intake air amount Ga from being deteriorated due to variations in sensors and the like. In addition, the responsiveness of the air-fuel ratio feedback control can be maintained.

[0021]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in FIG. 1, the engine 1 draws an air-fuel mixture into each cylinder from an intake passage 2 as an intake valve of each cylinder is opened, compresses the air-fuel mixture with a piston, and generates a spark plug. And the exhaust gas is discharged to the exhaust passage 3 as the exhaust valve is opened, and these steps are repeated continuously. In the middle of the exhaust passage 3, a catalyst 31 is provided.
Is installed to purify the exhaust.

In FIG. 1, reference numeral 21 denotes an air cleaner for taking intake air into the intake passage 2. The intake air taken into the intake passage 2 from the air cleaner 21 passes through the compressor 22, the intercooler 23, the throttle valve 24, etc. of the turbocharger and is distributed to each cylinder. A fuel injection nozzle 4 for injecting fuel is provided on the upstream side of the throttle valve 24 in the intake passage 2, and the intake path and the fuel are sufficiently mixed by extending the fuel transport path.

In FIG. 1, reference numeral 10 denotes a fuel cylinder filled with high-pressure gas fuel (CNG or the like) as a fuel supply source.
The gas fuel stored in the fuel cylinder 10 is supplied to the fuel injection nozzle 4 through the fuel supply passage 9. In the middle of the fuel supply passage 9, fuel is injected from a manual shutoff valve 11, a fuel pressure sensor 12, an electromagnetic shutoff valve 13, a gas regulator 14 for reducing the fuel pressure to a predetermined value, a fuel temperature sensor 15, and a fuel injection nozzle 4. A gas control valve 17 for adjusting the amount of fuel to be supplied is interposed.

In the figure, reference numeral 5 denotes a control unit for controlling the amount of fuel injected from the fuel injection nozzle 4 by adjusting the opening of the gas control valve 17. The control unit 5 includes a cooling water temperature sensor 41 for detecting an engine cooling water temperature, an engine speed Ne detected by a crank angle sensor 42, an intake pressure sensor 43 for detecting an intake manifold pressure Pb downstream of the throttle valve 24,
Signals are input from an intake air temperature sensor 44 for detecting the intake manifold temperature Tb downstream of the throttle valve 24 and an O ₂ sensor 32 for detecting the oxygen concentration in the exhaust gas, and the gas is supplied so that the mixture becomes the target air-fuel ratio λOBJ. Control valve 17
Is calculated. Gas control valve 1
Numeral 7 changes the opening degree according to the drive pulse width Duty_out to adjust the amount of fuel injected from the fuel injection nozzle 4.

By the way, in the case of a conventional small engine, an air flow meter for directly detecting the intake air amount is provided, but in the case of the large engine 1, it is difficult to directly detect a large amount of intake air via the air flow meter. .

Therefore, in the present embodiment, the intake air-fuel mixture amount Gm is calculated in accordance with the intake manifold pressure Pb, the intake manifold temperature Tb, and the engine speed Ne downstream of the throttle valve 24.

As shown in the block diagram of FIG. 2, the control unit 5 calculates the intake air-fuel mixture amount Gm according to the intake manifold pressure Pb, the intake manifold temperature Tb, and the engine speed Ne. And a target air-fuel ratio calculating means 52 for calculating a target air-fuel ratio λOBJ according to the intake manifold pressure Pb and the engine speed Ne as load signals, and a target air-fuel ratio correction value map according to the engine coolant temperature. Means 49, means 53 for correcting the target air-fuel ratio according to the engine cooling water temperature based on the correction value, and basic fuel injection amount Gf_FF for calculating the basic fuel injection amount Gf_FF according to the intake air-fuel mixture Gm and the target air-fuel ratio λOBJ. The calculating means 55 and the basic fuel injection amount Gf_
A drive pulse width calculating means 56 for converting FF into a drive pulse width Duty_ff of the gas control valve 17 based on a table. In the case of using compressed natural gas (CNG) as fuel, assuming that the stoichiometric air-fuel ratio is 16.8, the basic fuel injection amount Gf
_FF is calculated by the following equation.

Gf_FF = Gm / (16.8 × λOBJ + 1) (1) When liquefied gas (LPG) is used as fuel, if the stoichiometric air-fuel ratio is 15.3, the basic fuel injection amount Gf_FF is
It is calculated by the following equation.

Gf_FF = Gm / (15.3 × λOBJ + 1) (2) Then, a means 54 for converting the signal from the O ₂ sensor 32 into a λ value, and an error between the target air-fuel ratio λOBJ and the detected air-fuel ratio λ , A basic fuel amount correction amount calculating means 58 for obtaining a basic fuel amount correction amount Δλ by PID calculation according to the error, and converting the basic fuel amount correction amount Δλ to the gas control valve 17 based on a table. Drive pulse width correction amount calculating means 59, and the drive pulse width correction amount Duty_F
There is provided a means 60 for correcting the drive pulse width Duty_ff by B_Rate and calculating the output Duty_out to the fuel injector driving means 50 by the following equation.

Duty_out = (1 + Duty_FB_Rate / 100) × Duty_ff (3) FIG. 3 is a block diagram showing a logic for calculating the intake air-fuel mixture Gm. When this is described, the air-fuel mixture amount correction coefficient calculating means 61 for calculating by searching a map for the air-fuel mixture amount correction coefficient K ₁ depending on the intake manifold pressure Pb and the engine speed Ne, the intake manifold pressure Pb
And a intake manifold temperature Tb and mixture weight corrected intake mixture estimated value Gm 'in accordance with the coefficient K ₁ calculated by the following equation intake mixture amount estimation value calculating means 62 and.

Gm ′ = K ₁ × Pb × Ne / (Tb + 273.15) (4) By the way, the estimated intake air-fuel mixture amount Gm calculated in this way.
When the calculation accuracy is deteriorated due to variations in the intake pressure sensor 43 and the intake air temperature sensor 44, the value of the drive pulse width correction amount Duty_FB_Rate increases, and the responsiveness of the air-fuel ratio feedback control deteriorates.

Therefore, in order to learn the air-fuel mixture amount Gm according to the air-fuel ratio correction amount Δλ, the intake air-fuel mixture learning value Gm_LN according to the intake manifold pressure Pb and the engine speed Ne.
Drive pulse width correction amount Duty_F
The intake air-fuel mixture learning value Gm_LN is calculated according to B_Rate, and the intake air-fuel mixture estimated value Gm ′ is corrected according to the intake air-fuel mixture learning value Gm_LN.

More specifically, as shown in FIG. 3, during the air-fuel ratio feedback control, when a predetermined condition for stabilizing the combustion state of the engine 1 is satisfied, a learning determination condition for learning the intake air-fuel mixture Gm is determined. Execution condition determining means 63;
And a correction grid point value learning value calculation means 64 for calculating a correction grid point value of the intake air-fuel mixture learning value Gm_ according to the drive pulse width correction amount Duty_FB_Rate when the learning is permitted. One grid point learning value Gm_LEARN (Ne (I), Pb (J)) is obtained by setting K ₄ to a weighting factor,
Assuming that the stoichiometric air-fuel ratio is 16.8, the drive pulse width correction amount Dut
It is calculated according to the following equation according to y_FB_Rate, basic fuel injection amount Gf_FF, and target air-fuel ratio λOBJ.

Gm_LEARN (Ne (I), Pb (J)) = Gm_LEARN (Ne (I), Pb (J)) × (1−K ₄ ) + Gf_FF × λOBJ × (Duty_FB_Rate / 100) × 16.8 × K ₄ (5) Thus, the other three lattice points are similarly calculated, and the calculated 4
Gm_LEARN (Ne (I), Pb (J)), (Ne (I + 1), Pb (J)), (Ne
(I), Pb (J + 1)) and (Ne (I + 1), Pb (J + 1)) are updated. Here, the weight coefficient K _{4 is set} to, for example, ８, but the weight coefficient K ₄
Is appropriately increased, overshoot can be suppressed and control responsiveness can be improved.

Means 65 for calculating the intake manifold pressure Pb according to the corrected grid point value stored in the map and the intake air-fuel mixture learning value Gm_LN according to the engine speed Ne by surface interpolation; There is provided means 66 for restricting the learning value Gm_LN, and means 67 for calculating the intake air-fuel mixture Gm by adding the intake air-fuel mixture learning value Gm_LN to the estimated intake air-fuel mixture Gm '.

With the above configuration, the engine speed N
by calculating the air-fuel mixture amount Gm containing gaseous fuel in response to e and manifold pressure Pb and the manifold temperature Tb and mixture amount correction coefficient K _1, it enhances the control accuracy of the air-fuel ratio. As a result, while purifying the exhaust,
The engine output is improved and fuel consumption is reduced.

Then, the intake air-fuel mixture learning value Gm_LN is added to the intake air-fuel mixture estimated value Gm ′ to calculate the intake air-fuel mixture Gm, and the air-fuel mixture Gm is learned according to the air-fuel ratio correction amount Δλ. By doing so, it is possible to avoid the calculation accuracy from deteriorating due to variations in the intake pressure sensor 43 and the intake temperature sensor 44, and reduce the value of the drive pulse width correction amount Duty_FB_Rate,
The responsiveness of the air-fuel ratio feedback control can be maintained.

Next, another embodiment will be described. In the present embodiment, the intake manifold pressure Pb and the intake manifold temperature Tb downstream of the throttle valve 24 are provided.
And the intake air amount Ga is calculated in accordance with the engine speed Ne.

As shown in the block diagram of FIG. 4, the control unit 5 calculates the intake air amount Ga according to the intake manifold pressure Pb, the intake manifold temperature Tb, and the engine speed Ne.
And a target air-fuel ratio calculating means 72 for calculating a target air-fuel ratio λOBJ according to the intake manifold pressure Pb and the engine speed Ne as load signals, and a basic fuel injection amount Gf_FF according to the intake air amount Ga and the target air-fuel ratio λOBJ. Based on the table, the basic fuel injection amount calculating means 75 for calculating the basic fuel injection amount calculating means 75 and the driving pulse width Duty of the gas control valve 17 based on the table.
_ff, a driving pulse width calculating means 76 for converting the driving pulse width into _ff.
When using compressed natural gas (CNG) as fuel, assuming a stoichiometric air-fuel ratio of 16.8, the basic fuel injection amount Gf_FF is calculated by the following equation.

Gf_FF = Ga / (16.8 × λOBJ) (6) When liquefied gas (LPG) is used as fuel, if the stoichiometric air-fuel ratio is 15.3, the basic fuel injection amount Gf_FF is
It is calculated by the following equation.

Gf_FF = Ga / (15.3 × λOBJ) (7) Then, a means 74 for converting the signal from the O ₂ sensor 32 into a λ value and an error between the target air-fuel ratio λOBJ and the detected air-fuel ratio λ 77, a basic fuel amount correction amount Δλ for obtaining a basic fuel amount correction amount Δλ by PID calculation in accordance with the error, and a basic fuel amount correction amount Δλ converted to the gas control valve 17 based on a table. Drive pulse width correction amount calculating means 79, and a drive pulse width correction amount Duty_F
There is provided a means 80 for correcting the drive pulse width Duty_ff by B_Rate and calculating the output Duty_out to the fuel injector driving means 70 by the following equation.

Duty_out = (1 + Duty_FB_Rate / 100) × Duty_ff (8) FIG. 5 is a block diagram showing a logic for calculating the intake air amount Ga. When this is described, and the intake air amount correction coefficient calculating means 81 for calculating by searching a map for intake air amount correction coefficient K ₁ depending on the intake manifold pressure Pb and the engine speed Ne, the intake manifold pressure P
b and the intake manifold temperature Tb and the intake air quantity estimation value Ga according to the intake air amount correction coefficient K ₁ 'and a intake air quantity estimation value calculating means 82 for calculating the following equation.

Ga ′ = K ₁ × Pb × Ne / (Tb + 273.15) (9) By the way, the intake air estimated value Ga calculated in this way.
When the calculation accuracy is deteriorated due to variations in the intake pressure sensor 43 and the intake air temperature sensor 44, the value of the drive pulse width correction amount Duty_FB_Rate increases, and the responsiveness of the air-fuel ratio feedback control deteriorates.

Therefore, in order to learn the intake air amount Ga according to the air-fuel ratio correction amount Δλ, the intake manifold pressure Pb
Learning value Ga_LN according to the engine speed Ne and the engine speed Ne.
Drive pulse width correction amount Duty_F
The intake air amount learning value Ga_LN is calculated according to B_Rate, and the intake air amount estimation value Ga is calculated according to the intake air amount learning value Ga_LN.
'Is corrected.

Specifically, as shown in FIG. 5, during the air-fuel ratio feedback control, when a predetermined condition for stabilizing the combustion state of the engine 1 is satisfied, a learning execution condition for determining a learning execution condition for the intake air amount Ga is determined. A condition determining unit 83 and a corrected grid point value learning value calculating unit 84 that calculates a corrected grid point value of the intake air amount learning value Ga_ according to the drive pulse width correction amount Duty_FB_Rate when the learning is permitted. Assuming that K ₄ is a weight coefficient and the stoichiometric air-fuel ratio is 16.8, the drive pulse width correction amount Duty_FB is one lattice point learning value Ga_LEARN (Ne (I), Pb (J)).
_Rate, the basic fuel injection amount Gf_FF, and the target air-fuel ratio λOBJ are calculated by the following equations.

Ga_LEARN (Ne (I), Pb (J)) = Ga_LEARN (Ne (I), Pb (J)) × (1−K ₄ ) + Gf_FF × λOBJ × (Duty_FB_Rate / 100) × 16.8 × K ₄ (10) In this way, the other three lattice points are similarly calculated, and the calculated 4
Ga_LEARN (Ne (I), Pb (J)), (Ne (I + 1), Pb (J)), (Ne
(I), Pb (J + 1)) and (Ne (I + 1), Pb (J + 1)) are updated.

Means 85 for calculating the intake manifold pressure Pb according to the corrected grid point value stored in the map and the intake air amount learning value Ga_LN according to the engine speed Ne by surface interpolation; Means 86 for limiting processing of Ga_LN, and means 8 for calculating intake air amount Ga by adding intake air amount learning value Ga_LN to intake air amount estimation value Ga ′.
7 is provided.

The engine rotation speed N is constructed as described above.
by calculating the intake air amount Ga containing gaseous fuel in response to e and manifold pressure Pb and the manifold temperature Tb and the intake air amount correction coefficient K _1, it enhances the control accuracy of the air-fuel ratio. As a result, the exhaust gas can be purified, the output of the engine can be improved, and the fuel consumption can be reduced.

Then, the intake air amount Ga is calculated by adding the intake air amount learning value Ga_LN to the intake air amount estimated value Ga ′.
By learning the intake air amount Ga according to the air-fuel ratio correction amount Δλ, it is possible to avoid the calculation accuracy from deteriorating due to variations in the intake pressure sensor 43 and the intake temperature sensor 44, and to calculate the drive pulse width correction amount Duty_FB_Rate. , The response of the air-fuel ratio feedback control can be maintained.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram for controlling a fuel injection amount.

FIG. 3 is a block diagram for calculating an intake air-fuel mixture amount;

FIG. 4 is a block diagram for controlling a fuel injection amount in another embodiment.

FIG. 5 is a block diagram for calculating an intake air amount.

[Explanation of symbols]

Reference Signs List 5 control unit 17 gas control valve 32 O ₂ sensor 42 crank angle sensor 43 intake pressure sensor 44 intake temperature sensor 51 intake air-fuel mixture amount calculation means 52 target air-fuel ratio calculation means 55 basic fuel injection amount calculation means 58 basic fuel amount correction amount calculation Means 63 Learning execution condition determination means 64 Corrected lattice point value learning value calculation means 67 Intake air-fuel mixture amount calculation means 71 Intake air amount calculation means 72 Target air-fuel ratio calculation means 75 Basic fuel injection amount calculation means 78 Basic fuel amount correction amount calculation means 83 learning execution condition determination means 84 corrected lattice point value learning value calculation means 87 intake air amount calculation means

Continuing on the front page (72) Inventor Naoya Harayama F-term in Nissan Diesel Industry Co., Ltd., 1st place, Ochome, Saio, Saitama Prefecture 3G092 AA01 AB08 BA04 BB02 BB03 DE01S DF06 DG09 EA06 EB02 EB03 EB06 EB10 EC02 EC05 FA01 FA06 FA24 HA01Z HA04Z HA05Z HA11Z HB01X HB03Z HB04Z HD05X HD05Z HE01Z HE03Z HE08Z 3G301 HA01 HA22 JA01 JA02 JA03 JA20 LB01 LB06 LC02 MA01 MA12 MA13 NA03 NA04 NA05 NA06 NB02 NB05 NC06 ND02 ND22 ND25 ND27 ND41 PA01Z PA07Z PA10Z PA17Z PB01Z PB08Z PD02A PD02Z PE01Z PE03Z PE08Z

Claims (6)

[Claims] 1. An engine air-fuel ratio control device for adjusting an amount of gaseous fuel injected upstream of a throttle valve in an intake passage in accordance with an operation state, comprising: an engine speed detecting means for detecting an engine speed Ne; Manifold pressure Pb downstream of throttle valve
Pressure detection means for detecting the pressure, and a manifold temperature Tb downstream of the throttle valve
, An air-fuel mixture amount calculating means for calculating an air-fuel mixture Gm according to the engine speed Ne, the manifold pressure Pb and the manifold temperature Tb, and a target air-fuel ratio λOBJ according to the operating state. An air-fuel ratio control device for an engine, comprising: a target air-fuel ratio calculating unit; and a fuel injection amount calculating unit that calculates a fuel injection amount according to a mixture amount Gm and a target air-fuel ratio λOBJ. 2. A comprising a mixture amount correction coefficient calculating means for calculating the air-fuel mixture amount correction coefficient K ₁ depending on the intake manifold pressure Pb and the engine speed Ne, is the fuel injection amount calculating means intake manifold pressure Pb
An intake manifold temperature Tb and mixture amount correction coefficient air-fuel ratio control system for an engine according to claim 1, characterized in that to calculate the intake mixture weight Gm according to K _1. 3. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture, and an air-fuel ratio correction for calculating an air-fuel ratio correction amount Δλ for correcting a fuel injection amount such that the air-fuel ratio of the air-fuel mixture approaches a target air-fuel ratio λOBJ. An air-fuel ratio learning means for calculating an intake air-fuel mixture learning value Gm_LN according to the air-fuel ratio correction amount Δλ; and an air-fuel mixture correcting the air-fuel mixture Gm according to the intake air-fuel mixture learning value Gm_LN. The air-fuel ratio control device for an engine according to claim 1 or 2, further comprising: a correction unit. 4. An engine air-fuel ratio control device for adjusting an amount of gaseous fuel injected upstream of a throttle valve in an intake passage in accordance with an operation state, an engine speed detecting means for detecting an engine speed Ne; Manifold pressure Pb downstream of throttle valve
Pressure detection means for detecting the pressure, and a manifold temperature Tb downstream of the throttle valve
Temperature detection means for detecting an intake air amount, an intake air amount calculation means for calculating an intake air amount Ga containing no fuel according to the engine speed Ne, the manifold pressure Pb and the manifold temperature Tb, and a target air-fuel ratio according to the operating state. An air-fuel ratio control device for an engine, comprising: target air-fuel ratio calculating means for calculating λOBJ; and fuel injection amount calculating means for calculating a fuel injection amount according to the intake air amount Ga and the target air-fuel ratio λOBJ. . 5. comprising an intake air amount correction coefficient calculating means for calculating the intake air amount correction coefficient K ₁ depending on the intake manifold pressure Pb and the engine speed Ne, is the fuel injection amount calculating means intake manifold pressure Pb
An intake manifold temperature Tb and the intake air amount correction air-fuel ratio control system for an engine according to claim 4, depending on the coefficients K ₁ and calculates the intake air amount Ga. 6. An air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture, and an air-fuel ratio correction calculating an air-fuel ratio correction amount Δλ for correcting a fuel injection amount so as to bring the air-fuel ratio of the air-fuel mixture closer to a target air-fuel ratio λOBJ. Amount calculation means, intake air amount learning means for calculating intake air amount learning value Ga_LN according to air-fuel ratio correction amount Δλ, and intake air amount correction means for correcting intake air amount Ga according to intake air amount learning value Ga_LN The air-fuel ratio control device for an engine according to claim 4 or 5, further comprising: