JP2841001B2 - Air-fuel ratio feedback control device for internal combustion engine - Google Patents

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 feedback control device for an internal combustion engine, and more particularly to a technique for correcting a response delay of a control system to improve the response of the air-fuel ratio feedback control.

[0002]

2. Description of the Related Art As an air-fuel ratio feedback control device for an internal combustion engine, a rich air-fuel ratio of an actual air-fuel ratio to a stoichiometric air-fuel ratio is determined based on the oxygen concentration in exhaust gas detected by an oxygen sensor.
It is known to determine lean, and to feedback-control the amount of fuel supplied to the engine based on the result of the determination so that the actual air-fuel ratio approaches the stoichiometric air-fuel ratio (target air-fuel ratio). No. 240840).

[0003]

In the above-described air-fuel ratio feedback control, when a large deviation of the air-fuel ratio occurs due to transient operation or the like, a large control operation amount is given to quickly converge to the target air-fuel ratio. Is required. However, until the result of the air-fuel ratio feedback control for correcting the fuel supply amount is actually detected by the oxygen sensor (air-fuel ratio sensor), the intake transport time, the gas remaining time in the cylinder, the exhaust transport time, the oxygen sensor alone Since there is a response delay time of the feedback control system including the response delay time of the control system, conventionally, the control time constant is set to be substantially equal to the response delay so as to prevent the divergence of the control. I was

As described above, due to the presence of the response delay time, the control response cannot be accelerated even if a large air-fuel ratio deviation occurs, and when a large air-fuel ratio deviation occurs due to transient operation or the like, the target air-fuel ratio is reduced. Until the convergence, there is a problem that the exhaust properties deteriorate. The present invention has been made in view of the above-described problems, and enables the air-fuel ratio feedback control in consideration of the response delay time to enhance the responsiveness of the air-fuel ratio feedback control.
The purpose is to improve exhaust properties during transient operation.

[0005]

Accordingly, an air-fuel ratio feedback control device for an internal combustion engine according to the present invention is configured as shown in FIG. In FIG. 1, the air-fuel ratio sensor is
This is a sensor whose output value changes in response to the concentration of a specific gas component in exhaust gas that changes according to the air-fuel ratio of the engine intake air-fuel mixture.

The air-fuel ratio feedback control means includes:
On the basis of the output value of the air-fuel ratio sensor, an air-fuel ratio feedback correction value for correcting the fuel supply amount by the fuel supply means so as to bring the actual air-fuel ratio close to the target air-fuel ratio is controlled. On the other hand, the response delay time calculating means calculates a response delay time in the feedback control system by the air-fuel ratio feedback control means based on operating conditions of the engine .

The air-fuel ratio deviation calculating means calculates a value indicating a difference between an actual air-fuel ratio and a target air-fuel ratio with the output value of the air-fuel ratio sensor or the air-fuel ratio feedback correction value and the target value.
It is calculated as a deviation from a value corresponding to the target air-fuel ratio . Also correct
The value and correction time setting means is configured to output the calculated response delay.
The air-fuel ratio feedback based on the
The correction value and the correction time of the lock correction value are set. Then, the response delay correcting means determines that the time is within the set correction time.
In this case, the air-fuel ratio feedback correction value is supplemented by the correction value.
Set correctly .

[0008] Here, the response delay time calculating means, the machine
Calculates the gas residence time in the cylinder according to the rotation speed
Together with the exhaust transport delay time according to the intake air flow rate of the engine
And the gas residence time in the cylinder and the exhaust gas transport
Delay time and response delay of the air-fuel ratio sensor alone stored in advance
It is preferable to calculate the sum of time and the response delay time .

[0009]

According to this configuration, in a system for performing feedback control of a fuel supply amount so that an actual air-fuel ratio detected by an air-fuel ratio sensor becomes a target air-fuel ratio, a response delay time of the air-fuel ratio feedback control system is calculated. ,
Based on the response delay time and the air-fuel ratio deviation at that time (the deviation between the target air-fuel ratio and the actual air-fuel ratio) , the air-fuel ratio
The correction value and the correction time of the debug correction value are set, and
Within the correction time, the air-fuel ratio feedback correction value
It is corrected by the correction value.

That is, based on the response delay time and the air-fuel ratio deviation, the necessary correction amount can be set to avoid overshoot and reduce the response.
So that it can be added within a time that balances
By setting a correction time and a correction value and correcting the air-fuel ratio feedback correction value based on the correction time and the correction value, the control response delay due to the presence of the response delay time can be eliminated.

[0011]

Embodiments of the present invention will be described below. In FIG. 2 showing one embodiment, air is sucked into an internal combustion engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4 and an intake manifold 5. The intake manifold 5
Each of the branch portions is provided with a fuel injection valve 6 as a fuel supply means for each cylinder.

The fuel injection valve 6 is an electromagnetic fuel injection valve which is energized by a solenoid to open, and is deenergized and closed by being energized by an injection pulse signal from a control unit 12 which will be described later. Then, the fuel which is pressure-fed from a fuel pump (not shown) and adjusted to a predetermined pressure by the pressure regulator is injected and supplied to the engine 1. Institution 1
Each of the combustion chambers is provided with an ignition plug 7 for igniting and sparking the mixture by spark ignition. And institution 1
From the exhaust manifold 8, exhaust duct 9, three-way catalyst
Exhaust gas is exhausted through 10 and muffler 11.

The control unit 12 includes a CPU, an RO,
A microcomputer including an M, a RAM, an A / D converter, an input / output interface, and the like is provided. The microcomputer receives input signals from various sensors, performs arithmetic processing as described later, and operates the fuel injection valve 6. Control. As the various sensors, an air flow meter 13 is provided in the intake duct 3, and outputs a signal corresponding to the intake air flow rate Q of the engine 1.

A crank angle sensor 14 is provided to output a reference angle signal REF for each reference piston position and a unit angle signal POS for each crank angle of 1 ° or 2 °. Here, the engine rotation speed Ne can be calculated by measuring the cycle of the reference angle signal REF or the number of occurrences of the unit angle signal POS within a predetermined time. Further, a water temperature sensor 15 for detecting a cooling water temperature Tw of the water jacket of the engine 1 is provided.

In addition, an oxygen sensor 16 as an air-fuel ratio sensor is provided at a collecting portion of the exhaust manifold 8. The oxygen sensor 16 is an oxygen concentration cell that generates an electromotive force according to the ratio of the oxygen concentration in the exhaust to the oxygen concentration in the atmosphere (reference oxygen concentration). Using the sudden change around the target air-fuel ratio in the example, the output changes suddenly near the stoichiometric air-fuel ratio, and only the stoichiometric air-fuel ratio (rich / lean relative to the stoichiometric air-fuel ratio)
Is a known sensor that can detect the

Here, the CPU of the microcomputer built in the control unit 12 determines the basic fuel injection amount corresponding to the target air-fuel ratio (the stoichiometric air-fuel ratio in this embodiment) based on the intake air flow rate Q and the engine speed Ne. While calculating Tp (basic injection pulse width), the cooling water temperature Tw is calculated.
Various correction coefficients COEF including a basic correction coefficient and an acceleration / deceleration correction coefficient are set based on the above, and further, the actual air-fuel ratio is feedback-controlled to the target air-fuel ratio (the stoichiometric air-fuel ratio) based on the detection result by the oxygen sensor 16. -Fuel ratio feedback correction coefficient (air-fuel ratio feedback correction value) α
Is calculated. Then, the basic fuel injection amount Tp is multiplied by the various correction coefficients COEF and the air-fuel ratio feedback correction coefficient α to obtain an effective injection amount Te (← Tp × COEF × α).
Is calculated, and a correction amount Ts for correcting a change in the effective valve opening time of the fuel injection valve 6 due to a change in the battery voltage is added to the effective injection amount Te. The quantity (injection pulse width) is set as Ti (← Te + Ts).

Further, the control unit 12 outputs an injection pulse signal having a pulse width corresponding to the calculated fuel injection amount Ti to the fuel injection valve 6 at a predetermined timing, so that the fuel supply amount to the engine is electronically controlled. Control. here,
The manner in which the control unit 12 calculates the air-fuel ratio feedback correction coefficient α will be described in detail with reference to the flowchart of FIG.

In this embodiment, the functions of the air-fuel ratio feedback control means, the response delay time calculation means, the air-fuel ratio deviation calculation means, the correction value and correction time setting means, and the response delay correction means are shown in the flowchart of FIG. As shown in (1), the control unit 12 is provided as software. In the flowchart of FIG.
In step S1 in the figure, the output voltage Vs of the oxygen sensor 16 is read.

In the next step 2, the read output voltage Vs is compared with a reference voltage corresponding to the stoichiometric air-fuel ratio to determine whether the actual air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio as the target air-fuel ratio. Is determined. Here, when it is determined that the output voltage Vs is higher than the reference voltage and the actual air-fuel ratio is richer than the stoichiometric air-fuel ratio, the process proceeds to step 3, and the rich determination is performed for the first time (inversion from lean to rich). ) Is determined.

If it is the first time of the rich determination, the process proceeds to step 4, where a predetermined proportional component P is subtracted from the air-fuel ratio feedback correction coefficient α up to the previous time. ΔI is subtracted from the previous air-fuel ratio feedback correction coefficient α.
Here, the decreasing change of the air-fuel ratio feedback correction coefficient α causes the fuel injection amount Ti to be reduced, and the integration control in step 5 is repeated until the reduction state eliminates the rich state with respect to the stoichiometric air-fuel ratio. And gradually make the air-fuel ratio lean.

The proportional component P and the integral component I may be changed on the basis of information such as the engine load.
Similarly, when it is determined in step 2 that the output voltage Vs is lower than the reference voltage and leaner than the stoichiometric air-fuel ratio, it is determined in step 6 whether or not the lean determination is the first time. In step 7, the correction coefficient α is increased by the proportional control, and when it is not the first time, the correction coefficient α is increased in the step 8 by the integral control.

Thus, steps 1 to 8 are
By performing proportional / integral control on the air-fuel ratio feedback correction coefficient α, the fuel injection amount is controlled so that the actual air-fuel ratio approaches the target air-fuel ratio (see FIG. 4). When the air-fuel ratio feedback correction coefficient α is set by the proportional integral control as described above, in the next step 9, the control result of the air-fuel ratio feedback correction coefficient α is
A response delay time (a response delay time of the air-fuel ratio feedback control system) until the air-fuel ratio change is detected is calculated by 16.

That is, even if the air-fuel ratio feedback correction coefficient α is controlled, there is a delay time until the fuel injection using the correction coefficient α is actually performed. Intake transport time before being sucked into the cylinder, gas residence time in the cylinder,
There is an exhaust transportation time until the exhaust gas discharged from the cylinder reaches the oxygen sensor 16, and a response delay time of the sensor itself until the output of the oxygen sensor 16 actually changes in response to a change in the oxygen concentration in the exhaust gas. However, if the response delay time obtained by the sum of these times does not elapse, the result of the air-fuel ratio feedback control cannot actually be regarded as the change in the oxygen concentration in the exhaust gas, which is the response of the air-fuel ratio feedback control system in the present embodiment. It will be a delay time.

Incidentally, since the response delay time exists,
The control constants (proportional amount P and integral amount ΔI) in the proportional integral control are set to be time constants substantially equal to the response delay time. Here, the response delay time until the fuel injection is performed can be calculated based on the difference between the current crank angle and the crank angle at the injection timing, and the gas residual time in the cylinder depends on the engine rotation speed Ne. Therefore, a map in which the residual time is stored according to the engine speed Ne is provided, the residual time is obtained by referring to the map, and the sum of the response time until the injection and the residual time is determined as the response delay time. A.

In this embodiment, the intake air transport time which constitutes the response delay time in the intake system is not included in the time A. However, this is necessary during transient operation in which low responsiveness due to the intake air transport time becomes a problem. This is because it is premised that the transient correction (wall flow correction) of the fuel injection amount Ti in consideration of the intake transport delay is performed by the acceleration / deceleration correction coefficient included in the various correction coefficients COEF. Therefore, the time A
Alternatively, an intake air transport delay time depending on the intake air flow rate Q may be added.

On the other hand, although the exhaust gas transport delay depends on the exhaust gas flow rate, an intake air flow rate Q is used instead of this exhaust gas flow rate, and a map in which the exhaust gas transport delay time is stored in advance according to the intake air flow rate Q is referred to. Then, the current exhaust transportation delay time B is obtained. Further, a delay time of a change in the output of the oxygen sensor 16 with respect to a change in the oxygen concentration in the atmosphere is stored as a fixed time t _O2 , and is set as the delay time C.

In the next step 10, the sum of the response delay times A, B, and C individually set as described above is set to Tφ as the response delay time of the air-fuel ratio feedback control system. Further, in the next step 11, a deviation between the value α _ST of the correction coefficient α corresponding to the target air-fuel ratio and the current correction coefficient α is obtained, and this is calculated as a value corresponding to the deviation between the target air-fuel ratio and the actual air-fuel ratio. Is set to Δα.

The correction coefficient α _ST corresponding to the target air-fuel ratio is obtained as the average (a + b) / 2 of the latest maximum value a and minimum value b of the correction coefficient α obtained for each rich / lean inversion of the air-fuel ratio. That is, the engine is transiently operated from a stable state in which the correction coefficient α is controlled around a certain level to cause a deviation in the air-fuel ratio, and the correction coefficient α is increased in proportion to the air-fuel ratio by proportional integral control in order to compensate for the air-fuel ratio deviation. When the control is largely performed in the decreasing direction, the correction coefficient α has a relatively large deviation from the average value. Therefore, the deviation is regarded as a deviation between the actual air-fuel ratio and the target air-fuel ratio. Things.

Here, when a known full-range air-fuel ratio sensor capable of measuring the entire region from rich to lean is used in place of the oxygen sensor 16 capable of detecting only the stoichiometric air-fuel ratio, Δα is calculated as follows: The air-fuel ratio sensor may be a deviation between a predetermined output level corresponding to the target air-fuel ratio and the current sensor output, and the air-fuel ratio sensor is not limited to the stoichiometric air-fuel ratio sensor (oxygen sensor 16). With the configuration using the full-range air-fuel ratio sensor, the air-fuel ratio deviation can be quantitatively detected, so that the effect of increasing the response by the later-described response delay correction is greater than when the oxygen sensor 16 is used.

When the full-range air-fuel ratio sensor is used, in the proportional-integral control in steps 1 to 8,
The proportional component may be set according to the deviation between the actual air-fuel ratio and the target air-fuel ratio, and the integral component may be set based on the integral value of the deviation. When the response delay time Tφ and Δα indicating the air-fuel ratio deviation are obtained as described above, in the next step 12, the correction value of the correction coefficient α is calculated based on the response delay time Tφ and the air-fuel ratio step Δα. β and the correction time Tx are set.

That is, as shown in FIG. 5, the product of the response delay time Tφ and the air-fuel ratio deviation Δα corresponds to the necessary correction amount when there is no response delay. If added immediately, the effect of the response delay can be apparently eliminated. However, if the required correction amount is added in a short period of time, an overshoot may occur. Therefore, the required correction amount (Tφ × Δα) within a time Tx that balances the avoidance of overshoot and the improvement of responsiveness.
Is converted into a correction addition time Tx and a correction value β so that is added.

In the next step 13, it is determined whether or not the correction additional time Tx set in the latest step 12 has elapsed. When the correction additional time Tx is within the correction additional time Tx, the process proceeds to step 14, where the correction additional time Tx is determined. At the same time, the correction value β that has been set is added to the correction coefficient α that has been subjected to the proportional-integral control, and the basic fuel injection amount Tp is corrected with the added value to obtain the fuel injection amount Ti (← Tp × C
OEF × (α + β) + Ts) is calculated.

When the latest correction addition time Tx has elapsed, the routine proceeds to step 15, where the addition of the correction value β is stopped, and the basic fuel injection amount Tp is corrected only by the correction coefficient α controlled by the proportional-integral control. And the fuel injection amount Ti (← T
p × COEF × α + Ts). Therefore, when the target air-fuel ratio is stable near the target air-fuel ratio, the fuel injection amount is corrected only by the correction coefficient α that is normally controlled by proportional integral control.

As described above, if the correction value β for the response delay is added to the correction coefficient α, the response of the air-fuel ratio feedback control system is increased, and for example, as shown in FIG. Thus, when an air-fuel ratio deviation occurs, the correction coefficient α can be promptly converged to a value corresponding to the target air-fuel ratio (the stoichiometric air-fuel ratio), thereby improving the exhaust properties during the transient operation.

In this embodiment, the oxygen sensor 16 for detecting only the stoichiometric air-fuel ratio is used. However, as described above, an air-fuel ratio sensor for the entire region can be used, and is generally more expensive than the oxygen sensor 16. Although the cost is increased by providing the full-range air-fuel ratio sensor, the deviation from the target air-fuel ratio can be directly obtained, so that the air-fuel ratio can be feedback-controlled with higher responsiveness.

Further, in the present embodiment has been controlled by a proportional integral air-fuel ratio feedback correction coefficient alpha, it has name limited to proportional integral control.

Further, in the present embodiment, the target air-fuel ratio is set to the stoichiometric air-fuel ratio. However, it is obvious that a configuration may be adopted in which the target air-fuel ratio is set to a value other than the stoichiometric air-fuel ratio by using a full-range air-fuel ratio sensor. .

[0038]

As described above, according to the present invention, the actual air-fuel ratio is detected based on the detection of the concentration of the specific gas component in the exhaust gas, and the fuel supply amount is feedback-controlled based on the detection result. In the fuel ratio feedback control, the response delay of the control system can be corrected, and the response of the air-fuel ratio feedback control can be increased, so that the target air-fuel ratio can be quickly changed during the transient operation of the engine in which a deviation from the target air-fuel ratio occurs. This has the effect of converging on the fuel ratio and improving the exhaust properties during transient operation.

[Brief description of the drawings]

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

FIG. 2 is a system schematic diagram showing one embodiment of the present invention.

FIG. 3 is a flowchart illustrating setting of an air-fuel ratio feedback correction coefficient.

FIG. 4 is a time chart showing a state of proportional integral control of an air-fuel ratio feedback correction coefficient.

FIG. 5 is a diagram for explaining setting characteristics of a correction value β in the embodiment.

FIG. 6 is a time chart showing how a response delay is corrected in the embodiment.

[Explanation of symbols]

 1 engine 6 fuel injection valve 12 control unit 13 air flow meter 14 crank angle sensor 15 water temperature sensor 16 oxygen sensor

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/14 310 F02D 41/34

Claims (2)

(57) [Claims] An air-fuel ratio sensor whose output value changes in response to the concentration of a specific gas component in exhaust gas that changes according to the air-fuel ratio of an engine intake air-fuel mixture; and an actual air-fuel ratio sensor based on the output value of the air-fuel ratio sensor. Air-fuel ratio feedback control means for controlling an air-fuel ratio feedback correction value for correcting the fuel supply amount by the fuel supply means so as to bring the air-fuel ratio closer to the target air-fuel ratio; and a response delay time in a feedback control system by the air-fuel ratio feedback control means. Based on engine operating conditions
A response delay time computing means for computing Te, the actual value that indicates the deviation between the air-fuel ratio and the target air-fuel ratio, the output value or the air-fuel ratio feedback correction of the air-fuel ratio sensor
Air-fuel ratio deviation calculating means for calculating a deviation between the air-fuel ratio deviation value and the value corresponding to the target air-fuel ratio; and a correction value for the air-fuel ratio feedback correction value based on the calculated response delay time and air-fuel ratio deviation.
A correction value and correction time setting means for setting the air-fuel ratio value when the air-fuel ratio is within the set correction time.
An air-fuel ratio feedback control device for an internal combustion engine, comprising: response delay correction means for correcting and setting a feedback correction value with the correction value . 2. The method according to claim 1, wherein said response delay time calculating means includes an engine speed.
Calculate the gas residence time in the cylinder according to the degree,
Calculate exhaust transport delay time according to engine intake air flow rate
When the gas residence time in the cylinder and the exhaust transportation delay
And the response delay time of the air-fuel ratio sensor alone stored in advance and
2. The air-fuel ratio feedback control device for an internal combustion engine according to claim 1 , wherein the sum of the above is calculated as the response delay time .