JPH09287510A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve air-fuel ratio controlling performance during a transient period that uses lean air-fuel ratio control and EGR control at the same time. SOLUTION: The detected value Q1 of an intake air amount from an airflow meter is read in, a cylinder intake air amount Q1 ' is calculated by applying phase delay compensation, differential pressure between intake pressure and exhaust pressure in an EGR gas introducing part is estimated, an EGR gas amount QE is estimated on the basis of the differential pressure and an EGR valve opening control rate, and an air amount Q2 in EGR gas is calculated on the basis of the EGR gas amount QE and an air-fuel ratio of EGR gas ($11-S15), then an air amount Q2 ' in EGR gas sucked into a cylinder is calculated by applying phase delay compensation. The air amount Q1 ' and the air amount Q2 ' are summed up, and a total air amount Q' sucked into the cylinder is calculated, then a fuel amount T1 is calculated (S16-S18) so as to obtain a target air-fuel ratio for the total air amount Q'.

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, and more particularly to a control technique for bringing the air-fuel ratio close to a target value during the combined use of lean air-fuel ratio combustion and EGR control.

[0002]

2. Description of the Related Art In recent years, even in a spark ignition type engine such as a gasoline engine, direct injection into a combustion chamber is performed to cause stratified combustion,
Therefore, it has been attempted to enable combustion at a significantly leaner air-fuel ratio and greatly improve exhaust gas purification performance and fuel efficiency. Further, even in a normal type engine for injecting fuel into the intake system, there is one in which the air-fuel ratio is made as lean as possible for combustion.

On the other hand, in a normal vehicle engine, as is well known as a NOx purification measure, NOx is reduced by recirculating a part of the exhaust gas to the intake system to reduce the combustion temperature.
It is equipped with a GR device.

[0004]

In the engine that burns at the lean air-fuel ratio, if the EGR control is also used during the lean air-fuel ratio combustion, a large amount of air is contained in the EGR gas. If the fuel amount is controlled so that the target air-fuel ratio is obtained only based on the detected value of the amount of air taken in from the engine, the actual air-fuel ratio will be significantly leaner than the target air-fuel ratio, and the engine will run due to misfiring. May cause upset.

In this case, if an air-fuel ratio sensor capable of linearly detecting the air-fuel ratio by detecting the concentration of a specific component in the exhaust gas, for example, oxygen, is provided and the fuel amount is feedback-controlled based on the detected air-fuel ratio. Since the combustion air-fuel ratio of the air-fuel mixture including air in the EGR gas is detected, it is possible to control to the target air-fuel ratio during steady operation. However, it is necessary to detect the intake air amount including the auxiliary air flow rate that bypasses the throttle valve, etc., so the air flow meter is installed upstream of the intake system, for example, immediately after the air cleaner. During the transient operation, the detected air amount causes a phase delay with respect to the air amount sucked into the cylinder. Therefore, in the feedback control based on the air-fuel ratio detection value by the air-fuel ratio sensor, the deviation from the target air-fuel ratio is caused. Is getting too big.

Therefore, the amount of air in the EGR gas is changed to EGR.
Calculated based on the gas amount and the target air-fuel ratio, with respect to the total air amount summed with the intake air amount, phase delay compensation is performed,
It is conceivable to control the fuel amount so that the target air-fuel ratio becomes the target air-fuel ratio with respect to the compensated air amount and suppress the deviation of the air-fuel ratio. However, regarding the EGR gas, since the phase delay of the EGR gas amount from the EGR valve portion where the EGR gas amount is detected to the cylinder is different from the phase delay of the intake air amount, the intake air amount and the EGR gas amount are Even if the fuel amount is set by performing the phase delay correction according to the phase delay of the intake air amount on the total air amount, the fuel amount corresponding to the correct cylinder intake air amount will not be set.

The present invention has been made from various viewpoints as described above, and in a state where lean air-fuel ratio combustion and EGR control are used together, it is possible to suppress deviation from the target air-fuel ratio even during a transient state. The purpose is to enable various air-fuel ratio control.

[0008]

Therefore, as shown in FIG. 1, the invention according to claim 1 is an EGR control in which a part of exhaust gas is recirculated to an intake system via an EGR valve under a predetermined engine operating condition. Is performed, in the air-fuel ratio control device of the internal combustion engine in which the air-fuel mixture leaner than the stoichiometric air-fuel ratio is burned, the amount of air sucked from the atmosphere is detected at a predetermined position of the intake system,
Intake air amount calculating means for calculating the amount of air taken into the cylinder by compensating the detected value for the phase delay from the detected portion to the cylinder; and EGR during the EGR control.
An EGR gas in-air amount calculating means for calculating an air amount in the EGR gas sucked into the cylinder by compensating a phase delay from the EGR valve to the cylinder to the air amount in the EGR gas from the valve; Intake air amount and EGR
And a fuel amount calculation means for calculating the fuel amount supplied to the engine so that the total air amount obtained by summing the air amount in the gas becomes the target air-fuel ratio.

[0009] The amount of air supplied to the cylinder is sucked from the operation and effect air is asked subjected to phase lag compensation to the cylinder from the detection position to the detection value of the intake air amount, is contained in the EGR gas into the cylinder The amount of air supplied is obtained by performing phase delay compensation from the EGR valve to the cylinder on the amount of air in the EGR gas of the EGR valve section.

As described above, the intake air amount from the atmosphere or the air amount in the EGR gas is independently compensated for the phase delay from the detection location or the EGR valve portion to the cylinder, so that the detection can be performed during the transition. Even when the amount of air at the location or the EGR valve portion and the amount of air actually supplied to the cylinder are different, the amount of each air supplied to the cylinder can be obtained as a value close to the actual value.

Therefore, by calculating the fuel amount so that the target air-fuel ratio can be obtained with respect to the total air amount supplied to the cylinder, which is the sum of the air amounts, the air-fuel ratio is sufficiently set to the target value even in the transient state. It is possible to perform good air-fuel ratio control that approaches the exhaust gas, and it is possible to improve exhaust gas purification performance and fuel efficiency performance as much as possible. The invention according to claim 2 is the E
The amount of air in the EGR gas from the GR valve is characterized by being calculated based on the amount of EGR gas and the air-fuel ratio at the time of combustion of the EGR gas.

Action / Effect Since the air amount in EGR gas when theoretically burning at the air-fuel ratio is theoretically 0, the ratio of the air amount in EGR gas when burning at the actual air-fuel ratio is determined, Therefore, the amount of air in the EGR gas can be obtained based on the amount of EGR gas and the air-fuel ratio at the time of combustion of EGR gas.

Further, the invention according to claim 3 is the EGR.
The EGR amount from the valve is characterized in that it is obtained based on the differential pressure between the intake pressure and the exhaust pressure of the EGR gas introducing portion and the opening control amount of the EGR valve. Action / effect Without directly detecting the EGR gas amount from the EGR valve,
The cost can be obtained based on the differential pressure between the intake and exhaust pressures and the opening control amount of the EGR valve, and the cost is low.

The invention according to claim 4 is the EGR.
The air-fuel ratio at the time of gas combustion is characterized by being detected by an air-fuel ratio sensor which is provided in the exhaust and detects the air-fuel ratio from a specific component in the exhaust. Action / Effect By using the air-fuel ratio sensor provided in the exhaust gas and used for the air-fuel ratio control, the air-fuel ratio at the time of combustion of the EGR gas can be detected with high accuracy.

The invention according to claim 5 is characterized in that the target torque is set based on the engine operating state, and the amount of air and the amount of fuel supplied to the engine are controlled simultaneously in accordance with the target torque. To do. By setting the action / effect target torque and applying it to the one for controlling the air amount and the fuel amount at the same time, when the desired target torque is set during the transient operation, the air-fuel ratio that makes the target air-fuel ratio follow well. While ensuring the fuel ratio control, it is possible to follow the target torque with good responsiveness, thereby ensuring good transient operation performance.

Further, in the invention according to claim 6, the phase delay compensation performed for the intake air amount from the atmosphere or the air amount in the EGR gas is a weighted average of the air amounts at the detection points or the EGR valve portion, respectively. It is characterized in that it is a process of calculating a value. Air that is close to the actual amount of air supplied to the cylinder with well-compensated phase delay by weighted averaging the latest value and the past value of the amount of air at the action / effect detection location or EGR valve section with appropriate weighting. You can get the quantity.

Further, in the invention according to claim 7, the phase delay compensation performed for the intake air amount from the atmosphere or the air amount in the EGR gas is the primary delay of the air amount at the detection location or the EGR valve portion, respectively. It is characterized in that it is a process of calculating a value. By calculating the primary delay value of the air amount at the action / effect detection location or the EGR valve portion as the phase delay compensation value, it is possible to obtain the air amount supplied to the cylinder that is closer to the actual value.

The invention according to claim 8 is characterized in that the fuel is directly supplied into the cylinder of the engine. By directly injecting the action fuel into the cylinder, stratified combustion is performed and combustion with a significantly lean air-fuel ratio is performed, so the air in the EGR gas has a large effect, so phase lag compensation is especially required. The effect of performing each air amount independently is great.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a system configuration (common to each control embodiment to be described later) of an embodiment of the present invention. The accelerator opening sensor 1 detects the amount of depression of an accelerator pedal depressed by a driver.

The crank angle sensor 2 generates a position signal for each unit crank angle and a reference signal for each cylinder stroke phase difference, and measures the number of generated position signals per unit time, or the reference signal generation. The engine speed can be detected by measuring the cycle. The air flow meter 3 detects the amount of intake air to the engine 4 (intake air amount per unit time = intake air flow rate).

The water temperature sensor 5 detects the cooling water temperature of the engine. The engine 4 is provided with a fuel injection valve 6 that is driven by a fuel injection signal and directly injects fuel into the combustion chamber, and a spark plug 7 that is mounted in the combustion chamber and ignites. By the direct injection method into the combustion chamber, leaning by stratified combustion becomes possible, and the air-fuel ratio can be variably controlled over a wide range. A throttle valve 9 is provided in the intake passage 8 of the engine 4, and a throttle valve control device 10 capable of electronically controlling the opening of the throttle valve 9 is provided.

A vehicle speed sensor 11 for detecting the vehicle speed is also provided. Detection signals from the various sensors are input to the control unit 12 and the control unit 12
Controls the opening degree of the throttle valve 9 via the throttle valve control device 10 according to the operating state detected based on the signals from the sensors and drives the fuel injection valve 6 to drive the fuel injection amount. (Fuel supply amount) is controlled, ignition timing is set, and control is performed to ignite the spark plug 7 at the ignition timing.

An EGR passage 22 connecting the exhaust passage 21 and the intake passage 8 of the engine 1 and an EGR valve 23 composed of a step motor or the like installed in the EGR passage 22 are provided, and the control is performed. The unit 12 performs EGR in a predetermined region represented by the engine speed Ne and the engine load (represented by the fuel injection amount, etc.) to obtain the target EGR rate (EGR
The opening degree of the EGR valve 23 is controlled so as to obtain (amount / intake air flow rate).

The exhaust passage 21 is provided with an air-fuel ratio sensor 24 which detects the concentration of a specific component in the exhaust gas such as oxygen to detect the air-fuel ratio of the air-fuel mixture. First, the throttle valve control will be described according to the flowchart of FIG. In step 1, the accelerator operation amount (accelerator pedal depression amount) Acc detected by the accelerator opening sensor 1 and
The target torque tT of the engine required to obtain the target driving force of the vehicle based on the vehicle speed VSP by the vehicle speed sensor 2
Calculate e.

In step 2, the target torque t of the engine is set.
Based on Te and the engine rotation speed Ne calculated based on the detection signal from the crank angle sensor 2, the target fuel amount tQf is calculated by searching a map as shown in the figure or the like. In step 3, the target air-fuel ratio tA / F is calculated based on the target torque tTe and the engine rotation speed Ne by searching a map as shown in the figure.

In step 4, the target fuel amount tQf
And the target air-fuel ratio tA / F are multiplied to calculate the target air amount tQa taken into the cylinder. In step 5, based on the engine rotation speed Ne and the target air amount tQa, by a search from a map as shown, or the like,
The target opening area tAa of the throttle valve is calculated.

In step 6, the target opening area tAa is set.
The opening control amount tTVO of the throttle valve that obtains is calculated by searching a map as shown in the figure or the like. In step 7, the opening control amount tTVO thus obtained is obtained.
Is output to the throttle valve control device 10. As a result, the throttle valve 9 is controlled to the set opening degree tTVO and the target air amount is obtained.

Next, the air-fuel ratio control according to the present invention will be described with reference to the flowchart of FIG. In step 11, the intake air amount Q ₁ detected by the air flow meter 3 is read. In step 12, the detected value Q _{1 of the} intake air amount
On the other hand, the phase lag compensation from the position detected by the air flow meter 3 to the cylinder is performed to calculate the air amount Q ₁ ′ sucked into the cylinder.

[0029] Specifically, either calculated as the following equation (1) the cylinder intake air quantity Q ₁ a weighted average of the latest detection value and past values of the intake air quantity Q ₁ as' ( 2) The first-order lag value of the detected value Q ₁ is calculated by the formula 2) and the cylinder intake air amount Q ₁ '
Is calculated as Q ₁ '= Q ₁ x x Q ₁ ' _(-1)・ (1-x) ・ ・ ・ (1) Q ₁ '= Q _{1 (-1)} + (Q ₁ −Q _{1 (-1)} ) × ( 1-e- ^{t / T} ) (2) where x is a positive number less than 1, subscript (-1) is the previous value, T
Indicates a time constant.

In step 13, the differential pressure between the intake pressure and the exhaust pressure in the intake passage where EGR gas is introduced is estimated according to the engine operating state (engine speed Ne, engine load such as basic fuel injection amount T _P ). To do. Alternatively, a sensor for detecting these pressures may be provided to obtain the differential pressure from the detected value,
The estimation does not require a sensor, so that the cost is low.

In step 14, the EGR gas amount Q _E from the EGR valve is calculated based on the differential pressure and the EGR valve opening control amount.
Is estimated. In step 15, based on the estimated EGR gas amount Q _E from the EGR valve and the air-fuel ratio at the time of combustion of the EGR gas, the air amount Q ₂ in the EGR gas is increased.
Is calculated. Here, the current control air-fuel ratio (target air-fuel ratio) may be simply used as the air-fuel ratio at the time of combustion of the EGR gas, and the exhaust from the cylinder to the EGR valve (EGR valve)
If the control air-fuel ratio before the delay time is used in consideration of the transmission delay time of (gas), the air amount can be detected with higher accuracy.

An arithmetic expression of the air amount Q ₂ in the EGR gas using the control air-fuel ratio is shown below. _{Q 2 = Q E × (λ} -1) / λ λ is the excess air ratio = Q _E × - In (control air stoichiometric air-fuel ratio) / control the air-fuel ratio (3) Step 16, from the EGR valve The air amount Q ₂ in the EGR gas is compensated for the phase delay from the EGR valve to the cylinder, and the air amount Q ₂ ′ in the EGR gas sucked into the cylinder is calculated.

Specifically, as in the case of the intake air amount, the weighted average value of the latest estimated value and the past value of the air amount Q ₂ of the EGR valve is stored in the cylinder as shown in the following equation (4). E supplied
Calculate as air volume Q ₂ 'in GR gas, or
(5) the first-order lag value Q _{2 'is} calculated as Q _2' as equation. Q ₂ '= Q ₂・ y + Q ₂ ' _(-1)・ (1-y) ・ ・ ・ (4) Q ₂ '= Q _{2 (-1)} + (Q ₂ -Q _{2 (-1)} ) × ( 1-e- ^{t / T1} ) (5) where y is a positive number less than 1, subscript (-1) is the previous value, T
1 indicates a time constant.

Here, the weight y in the weighted average value calculation
And the time constant T in the first-order lag value calculation are the EGR valve 6
Since it is determined from the volume (fixed value) to the cylinder and the EGR gas amount (variable) from the cylinder to the cylinder, the value obtained by calculation or search from the map is used according to the EGR gas amount (EGR rate). In step 17, the amount of air Q ₁ 'inhaled from the atmosphere and supplied to the cylinder and the EGR supplied to the cylinder.
The air amount Q ₂ 'in the gas is summed up to calculate the total air amount Q'supplied to the cylinder.

In step 18, the fuel injection amount T from the fuel injection valve 6 is set so that the target air-fuel ratio can be obtained with respect to the total air amount Q '(flow rate per unit time) supplied to the cylinder.
_I is calculated by the following formula. T _I = kQ ′ · COEF + T _S (6) where k is a constant, COEF is various correction factors based on water temperature, etc., and T _S is an invalid injection pulse amount set by the battery voltage.

In this way, the air amount Q ₁ 'intaken into the cylinder from the atmosphere and the air amount Q ₂ ' in the EGR gas are set as the air amount Q ₁ or Q ₂ at the detection point or the EGR valve, respectively. On the other hand, the configuration is such that the phase delay up to the cylinder is compensated for, so that each cylinder supply air amount Q ₁ ′, Q ₂ ′ can be obtained with high accuracy, and thus lean air-fuel ratio control and EGR control are performed. The air-fuel ratio can be made to follow the target air-fuel ratio with high accuracy even during transient operation when used together, and exhaust purification performance and fuel consumption can be improved as much as possible.

FIG. 5 shows the air-fuel ratio control according to the second embodiment.
It is shown in the flowchart. The difference from FIG. 4 is that the EG
The value detected by the air-fuel ratio sensor 24 is used when calculating the amount of air in the EGR gas from the R valve. That is, after estimating the EGR gas amount Q _E from the EGR valve in step 14,
In step 21, the air-fuel ratio in the exhaust gas detected by the air-fuel ratio sensor 24 is read, and in step 15, E
When calculating the air amount Q ₂ 'in the GR gas, the air-fuel ratio detection value is substituted for the term of the control air-fuel ratio and used. With this configuration, since the highly accurate value that is actually detected is used as the air-fuel ratio of the EGR gas, the air amount Q ₂ in the EGR gas is increased.
The calculation accuracy of is improved. Actually, since there is a transmission delay of the exhaust gas between the exhaust gas detected by the air-fuel ratio sensor and the EGR gas from the EGR valve 6, the air-fuel ratio detected by the air-fuel ratio sensor before the transmission delay is If used, the accuracy is further improved.

It should be noted that although the one in which the target torque is set as in this embodiment can further improve the transient operation performance, the present invention is sufficiently effective even when applied to the one in which the target torque is not set. . Further, in the case where the target air-fuel ratio is variably controlled, particularly in the case where the air-fuel ratio is variably controlled by a direct fuel injection system, the actual air-fuel ratio can follow the variable target air-fuel ratio with high accuracy. Although it is particularly advantageous, it is sufficiently effective when applied to a device having a limited air-fuel ratio control range.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing a system configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing a throttle valve control routine of the above embodiment.

FIG. 4 is a flowchart showing an air-fuel ratio control routine according to the first embodiment.

FIG. 5 is a flowchart showing an air-fuel ratio control routine according to a second embodiment.

[Explanation of symbols]

 2 Crank angle sensor 3 Air flow meter 4 Engine 6 Fuel injection valve 9 Throttle valve 10 Throttle valve control device 11 Vehicle speed sensor 12 Control unit 21 Exhaust passage 22 EGR passage 23 EGR valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shisei Kai Kai 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (8)

[Claims] 1. A portion of exhaust gas is EG under predetermined engine operating conditions.
In an air-fuel ratio control device for an internal combustion engine in which EGR control is performed to recirculate to the intake system via an R valve, and an air-fuel mixture leaner than the stoichiometric air-fuel ratio is burned, the amount of air taken in from the atmosphere Intake air amount calculation means for detecting at a predetermined position and calculating the amount of air taken into the cylinder by compensating the detected value for the phase delay from the detected position to the cylinder; and during the EGR control, from the EGR valve EGR gas air amount calculating means for calculating the air amount in the EGR gas sucked into the cylinder by compensating the phase delay from the EGR valve to the cylinder to the air amount in the EGR gas, The total amount of intake air and the amount of air in EGR gas is the total amount of fuel supplied to the engine,
An air-fuel ratio control device for an internal combustion engine, comprising: a fuel amount calculation means that calculates a target air-fuel ratio. 2. The internal combustion engine according to claim 1, wherein the air amount in the EGR gas from the EGR valve is calculated based on the EGR gas amount and an air-fuel ratio at the time of combustion of the EGR gas. Air-fuel ratio control system for engines. 3. The EGR amount from the EGR valve is obtained based on a differential pressure between an intake pressure and an exhaust pressure in an EGR gas introduction section and an EGR valve opening control amount. 2. The air-fuel ratio control device for an internal combustion engine according to item 2. 4. The air-fuel ratio at the time of the EGR gas combustion is detected by an air-fuel ratio sensor which is provided in the exhaust gas and detects the air-fuel ratio from a specific component in the exhaust gas. 3. An air-fuel ratio control device for an internal combustion engine according to item 3. 5. A target torque is set based on an engine operating state, and the amount of air and the amount of fuel supplied to the engine are controlled simultaneously according to the target torque. 5. An air-fuel ratio control device for an internal combustion engine according to any one of 1. 6. The phase delay compensation performed on the intake air amount from the atmosphere or the air amount in the EGR gas is a process of calculating a weighted average value of the air amount at a detection point or an EGR valve portion, respectively. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 5. 7. The phase delay compensation for the intake air amount from the atmosphere or the air amount in the EGR gas is a process of calculating a primary delay value of the air amount at a detection point or an EGR valve portion, respectively. Claim 1-Claim 5 characterized by
5. An air-fuel ratio control device for an internal combustion engine according to any one of 1. 8. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the fuel is directly supplied into the cylinder of the engine.