JPH10220304A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an air-fuel ratio to accurately accord with a target air-fuel ratio while securing responsiveness of an opening degree of an EGR control valve. SOLUTION: In this controller, an EGR control valve 19 for controlling a quantity of EGR gas is disposed on an EGR passage 18 for connecting an intake duct 13 to an exhaust manifold 17. A target air-fuel ratio is calculated according to an engine operating state. An air excess rate is calculated based on a fuel injection quantity and an intake air quantity. A smoothening coefficient is calculated according to an opening degree of the EGR control valve 19. A smoothening air excess rate is calculated using smoothening coefficient. The opening degree of the EGR control valve 19 controlled in such a manner that the air excess rate becomes the target a excess rate based on the smoothening air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for an internal combustion engine.

[0002]

2. Description of the Related Art An EGR control valve for controlling an EGR gas amount is disposed in an EGR passage connecting an intake passage and an exhaust passage of an engine, and an air-fuel ratio sensor is mounted in the exhaust passage so that the air-fuel ratio is equal to a target air-fuel ratio. An air-fuel ratio control device for an internal combustion engine in which the opening degree or the valve opening ratio of an EGR control valve is feedback-controlled in such a manner is known (JP-A-63-94061).
Reference). When the EGR gas amount is increased or decreased by changing the opening of the EGR control valve in the same engine operating state, the fresh air amount is increased or decreased by an amount corresponding thereto. Therefore, EG
The air-fuel ratio can be changed by changing the R gas amount. Therefore, in the above-described air-fuel ratio control device, the opening degree of the EGR control valve is controlled so that the air-fuel ratio becomes the target air-fuel ratio.

[0003]

By the way, when the air-fuel ratio is feedback-controlled as in the above-described air-fuel ratio control apparatus, the air-fuel ratio fluctuates due to intake pulsation and rotation fluctuation even if the engine operation state is steady. I do. However, if the opening degree of the EGR control valve is controlled based on the fluctuating air-fuel ratio, the opening degree of the EGR control valve fluctuates, so that the EGR gas amount fluctuates. As a result, the air-fuel ratio may diverge from the target air-fuel ratio. There is.

[0004] Therefore, if the opening of the EGR control valve is controlled based on the smoothed air-fuel ratio obtained by smoothing the detected air-fuel ratio, the fluctuation of the opening of the EGR control valve can be reduced. The divergence of the fuel ratio can be prevented. However, if the opening of the EGR control valve is controlled based on the smoothed air-fuel ratio, the responsiveness of the opening of the EGR control valve deteriorates. Therefore, there is a problem that the air-fuel ratio cannot be made to exactly match the target air-fuel ratio simply by controlling the opening of the EGR control valve using the smoothed air-fuel ratio.

[0005]

According to a first aspect of the present invention, there is provided an EG for controlling an EGR gas amount in an EGR passage connecting an intake passage and an exhaust passage of an engine.
In an internal combustion engine provided with an R control valve, the target air-fuel ratio is calculated in accordance with the engine operating state, the air-fuel ratio is detected in accordance with the air-fuel ratio, and the opening of the EGR control valve is determined. Smoothing air-fuel ratio calculating means for calculating a smoothing air-fuel ratio using a smoothing coefficient, and EGR control for controlling an opening of an EGR control valve based on the smoothed air-fuel ratio so that the air-fuel ratio becomes a target air-fuel ratio. Valve opening control means. The effect of the variation in the opening of the EGR control valve on the air-fuel ratio differs depending on the opening of the EGR control valve. Therefore, in the first invention, a smoothed air-fuel ratio is calculated using a smoothing coefficient determined according to the opening of the EGR control valve, and the opening of the EGR control valve is controlled based on the smoothed air-fuel ratio. ing.
As a result, the responsiveness of the opening degree of the EGR control valve is ensured, and the air-fuel ratio is favorably matched with the target air-fuel ratio.

According to a second aspect, in the first aspect, the opening of the EGR control valve is controlled based on the detected air-fuel ratio which is not smoothed during the transient operation of the engine. If the target air-fuel ratio is suddenly changed due to engine transient operation, the opening of the EGR control valve must be suddenly changed. Therefore, in the second invention, the EGR is performed based on the detected air-fuel ratio that is not smoothed during the transient operation of the engine.
The opening of the control valve is controlled so that the EGR
A good response of the opening of the control valve is ensured.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where the present invention is applied to a diesel engine will be described below. However, the present invention can also be applied to a spark ignition type engine. Referring to FIG. 1, 1 is a cylinder block, 2 is a piston, 3
Represents a cylinder head, 4 represents a combustion chamber, 5 represents an intake port, 6 represents an intake valve, 7 represents an exhaust port, 8 represents an exhaust valve, 9 represents a fuel injection valve for directly injecting fuel into the combustion chamber 4, and 10 represents a fuel injection valve. 9
1 shows an engine-driven fuel pump for pumping fuel. The intake port 5 of each cylinder is connected to a common surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air flow meter 14 and an air cleaner 15 via an intake duct 13. In the intake duct 13, an intake throttle valve 16 driven by a negative pressure type or electromagnetic actuator or a wire directly connected to an accelerator pedal 39 is arranged. On the other hand, the exhaust port 7 of each cylinder is connected to a common exhaust manifold 17. The fuel pump 10 is controlled based on an output signal from the electronic control unit 30.

An EGR passage 18 connects the exhaust manifold 17 and the intake duct 13 downstream of the intake throttle valve 16 to each other.
Inside, an EGR control valve 19 for controlling the amount of EGR gas flowing through the EGR passage 18 is arranged. The valve element of the EGR control valve 19 is fixed to the diaphragm 20,
The opening of the EGR control valve 19 is controlled in accordance with the pressure in a negative pressure chamber 21 formed on one side of the diaphragm 20. A negative pressure formed by an engine driven vacuum pump 23 or the atmosphere is selectively introduced into the negative pressure chamber 21 via an electromagnetic three-way valve 22. The three-way valve 22 is controlled based on an output signal from the electronic control unit 30. Further, the three-way valve 22 is connected to the negative pressure chamber 21 with respect to the cycle time.
Is controlled by a duty ratio DUTY which is a ratio of a time during which the vacuum pump 23 should be connected to the vacuum pump 23. Therefore, the opening degree of the EGR control valve 19 increases as the duty ratio DUTY increases.

An electronic control unit (ECU) 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, R
An AM (random access memory) 33, a CPU (microprocessor) 34, an input port 35, and an output port 36 are provided. The air flow meter 14 has an intake air amount G
An output voltage proportional to a is generated, and the output voltage of the air flow meter 14 is input to the input port 35 via the AD converter 37. The input port 35 is connected to a crank angle sensor 38 that generates an output pulse each time the crankshaft rotates, for example, 30 degrees. The CPU 34 calculates the engine speed N based on the output pulse. Further, the output voltage of the depression amount sensor 40 that generates an output voltage proportional to the depression amount DEP of the accelerator pedal 39 is input to the input port 35 via the AD converter 41.
On the other hand, the output port 36 is connected to the corresponding drive circuit 42
Are connected to the fuel pump 10 and the three-way valve 22, respectively.

In the internal combustion engine shown in FIG. 1, the excess air ratio is controlled by controlling the opening of the EGR control valve 19, that is, the duty ratio DUTY. in this case,
If the duty ratio DUTY is controlled based on the detected excess air ratio LACT, the duty ratio DUTY fluctuates due to the fluctuation of the excess air ratio, and thus the excess air ratio may diverge. Therefore, in the internal combustion engine of FIG. 1, the duty ratio DUTY is controlled based on the smoothed excess air ratio LSM obtained by smoothing the detected excess air ratio LACT. This excess air ratio LSM
Is calculated based on the following equation.

LSM = LSM + K · (LACT−LSM) where K is a smoothing coefficient. When the duty ratio DUTY is controlled using the smoothed excess air ratio LSM in this manner, the influence of the fluctuation of the excess air ratio can be reduced, and therefore, the divergence of the excess air ratio can be prevented.
However, if the duty ratio DUTY is controlled using the smoothed excess air ratio LSM, the responsiveness of the duty ratio DUTY deteriorates. On the other hand, duty ratio D to excess air ratio
The influence of the UTY fluctuation is, for example, the engine load and the duty ratio D.
It depends on UTY. That is, when the engine load is high, the influence of the fluctuation of the excess air ratio is smaller than when it is low, and when the duty ratio DUTY is large, the influence of the fluctuation of the excess air ratio is smaller than when it is small. As described above, when the influence of the fluctuation of the excess air ratio is small, it is preferable to secure the response of the duty ratio DUTY rather than to reduce the influence of the fluctuation. Therefore, in this embodiment,
When the fuel injection amount Q representing the engine load is large, the degree of smoothing is reduced as compared with when the fuel injection amount Q is small, and the duty ratio DUTY
Is large, the degree of smoothing is lower than when it is small. As a result, good responsiveness of the duty ratio DUTY can be ensured while reliably preventing the excess air ratio from diverging.

In this embodiment, the smoothing coefficient K representing the degree of smoothing is defined as the product (K = KQ.KEGR) of the smoothing coefficient KQ based on the fuel injection amount Q and the smoothing coefficient KEGR based on the duty ratio DUTY. Is calculated. As shown in FIG. 2, when the fuel injection amount Q is small, the smoothing coefficient KQ is smaller than when the fuel injection amount Q is large, that is, when the fuel injection amount Q is small, as can be seen from the above-described equation for calculating the smoothed air excess ratio LSM. The degree of smoothing is increased compared to when the number is large. This smoothing coefficient KQ is stored in advance in the ROM 32 in the form of a map as shown in FIG. On the other hand, as shown in FIG. 3, when the duty ratio DUTY is small, the smoothing coefficient KEGR is made smaller than when it is large, that is, when the duty ratio DUTY is small, the degree of smoothing is made larger than when it is large. The smoothing coefficient KEGR is stored in the ROM 32 in advance in the form of a map as shown in FIG. Note that these smoothing coefficients KQ and KEGR are determined between 0 and 1, respectively. Further, the fuel injection amount Q can be represented by a pump command value, injector energizing time, pump pumping value, and the like.

However, if the target excess air ratio is suddenly changed due to the engine transient operation, the duty ratio DUTY needs to be suddenly changed. That is, the duty ratio D
It is necessary to ensure the responsiveness of UTY. Therefore, in the present embodiment, the duty ratio DUT is determined based on the detected excess air ratio LACT that is not smoothed during the transient operation of the engine.
And calculate the duty ratio DUTY based on the smoothed excess air ratio LSM when the engine is not in transient operation.
Is calculated. This makes it possible to maintain good responsiveness of the duty ratio DUTY during the transient operation.

FIG. 4 shows a routine for executing the above-described excess air ratio control method. The excess air ratio control routine shown in FIG. 4 is executed by interruption every predetermined time. Referring to FIG. 4, first, at step 40, the fuel injection amount Q is read. The fuel injection amount Q is calculated as a product of a basic fuel injection amount QB and a correction coefficient in a routine not shown. Basic fuel injection amount QB
Is an injection amount necessary for setting the engine output torque to the required torque, and is stored in the ROM 32 in advance as a function of the depression amount DEP of the accelerator pedal 39 and the engine speed N. In the following step 41, the target excess air ratio LTGT
Is calculated. The target excess air ratio LTGT is a best excess air ratio to reduce the NO _x exhausted from the engine while preventing the smoke discharged from the engine, it is determined by experiment. This target excess air ratio LT
The GT is stored in the ROM 32 in advance in the form of a map shown in FIG. 5 as a function of the engine operating state, for example, the fuel injection amount Q and the engine speed N. Next step 4
In step 2, the actual excess air ratio LACT is calculated. In the internal combustion engine of FIG. 1, the actual excess air ratio LACT is calculated using the intake air amount Ga detected by the air flow meter 14 and the fuel injection amount Q. In the engine exhaust passage,
An excess air ratio sensor or an air-fuel ratio sensor that generates an output voltage corresponding to the excess air ratio or the air-fuel ratio may be provided, and the excess air ratio LACT may be detected by this sensor.

In the following step 43, it is determined whether or not the engine is currently in a transient operation. Although it may be determined in any way whether or not the engine is in the transient operation, in the internal combustion engine of FIG. 1, the depression amount DEP of the accelerator pedal 39 and the intake air amount G
a, when the change rate of the fuel injection amount Q, the engine speed N, or the like is larger than a predetermined set change rate, it is determined that the engine is in the transient operation. When the change rate is smaller than the set change rate, the transient operation is performed. It is determined that the vehicle is not driving. When it is determined that the vehicle is not in the transient operation, the process proceeds to step 44.

In steps 44 to 46, the smoothing coefficient K
Is a part for calculating. First, at step 44, a smoothing coefficient KQ based on the fuel injection amount is calculated from the map of FIG. In the following step 45, the smoothing coefficient KEGR based on the opening degree of the EGR control valve 19, that is, the duty ratio DUTY
Is calculated from the map of FIG. In the following step 46, the product of the smoothing coefficient KQ and the smoothing coefficient KEGR (KQ
A smoothing coefficient K is calculated as (KEGR). In the following step 47, a smoothed excess air ratio LSM obtained by smoothing the detected excess air ratio LACT is calculated based on the following equation.

LSM = LSM + K · (LACT−LSM) In the following step 48, the LSM is set to L, and then the process jumps to step 50. On the other hand, if it is determined in step 43 that the vehicle is in the transient operation, then step 4 is executed.
9, the detected excess air ratio L that has not been smoothed
ACT is set to L. Next, the routine proceeds to step 50.

The following steps 50 to 53 are for calculating the duty ratio DUTY. First, in step 50, a proportional term P is calculated based on the following equation. P = KP · (LTGT−L) where KP is a proportional gain constant. Next step 51
Then, the integral term I is calculated based on the following equation.

I = I + KI. (LTGT-L) Here, KI is an integral gain constant. Subsequent step 52
Then, the differential term D is calculated based on the following equation. D = KD · (L−HOLD) Here, KD is a differential gain constant, and OLD is L in the previous processing routine. In the following step 53, the sum (P + I +) of these proportional term P, integral term I, and differential term D
The duty ratio DUTY is calculated as D). The three-way valve 22 is driven with this duty ratio DUTY. In the following step 54, L is set to LOLD.

As described above, in this embodiment, the influence of the fluctuation of the excess air ratio can be reduced, and the excess air ratio can be stabilized. As a result, each gain constant KP, KI,
KD can be set relatively large, so that the initial response during transient operation can be further enhanced. In this embodiment, each gain constant KP, K
Although I and KD are constant values, the gain constants KP and KP are smaller when the duty ratio DUTY is smaller than when they are large.
I and KD are reduced, and the duty ratio DUTY
Is small, the proportional term P, the integral term I, and the derivative term D may each be smaller than when it is large.

[0021]

The air-fuel ratio can be made to exactly match the target air-fuel ratio while ensuring the responsiveness of the opening of the EGR control valve.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a smoothing coefficient based on a fuel injection amount.

FIG. 3 is a diagram illustrating a smoothing coefficient based on a duty ratio.

FIG. 4 is a flowchart for executing an excess air ratio control.

FIG. 5 is a diagram showing a target excess air ratio.

[Explanation of symbols]

 4 Combustion chamber 9 Fuel injection valve 13 Intake duct 14 Air flow meter 17 Exhaust manifold 18 EGR passage 19 EGR control valve

Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/14 310 F02D 41/14 310L

Claims (2)

[Claims] In an internal combustion engine in which an EGR control valve for controlling an EGR gas amount is disposed in an EGR passage connecting an intake passage and an exhaust passage of the engine, a target air-fuel ratio is calculated according to an engine operating state. Fuel-ratio calculating means, air-fuel-ratio detecting means for detecting an air-fuel ratio, smoothed air-fuel-ratio calculating means for calculating a smoothed air-fuel ratio using a smoothing coefficient determined according to an opening of an EGR control valve, An air-fuel ratio control device comprising: an EGR control valve opening control means for controlling the opening of the EGR control valve so that the air-fuel ratio becomes a target air-fuel ratio based on the air-fuel ratio. 2. The EGR control valve according to claim 1, wherein the opening degree of the EGR control valve is controlled so that the air-fuel ratio becomes the target air-fuel ratio based on the detected air-fuel ratio that has not been smoothed during the transient operation of the engine. Air-fuel ratio control device.