JP2866539B2 - Air-fuel ratio 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 control device for an internal combustion engine that performs air-fuel ratio feedback control based on air-fuel ratio signals from two air-fuel ratio sensors provided before and after a catalyst in an exhaust pipe. The present invention relates to an air-fuel ratio control device for an internal combustion engine that suppresses a control error due to a variation in output characteristics and response time of an air-fuel ratio sensor upstream of a catalyst.

[0002]

2. Description of the Related Art Generally, the fuel injection amount of an internal combustion engine is controlled by an air-fuel ratio sensor (O) provided in an exhaust pipe such that the air-fuel ratio of the air-fuel mixture becomes an optimum value (for example, about 14.7) according to the operating state.
Feedback control based on signals from _two sensors).

Usually, the oxygen concentration in the exhaust gas air-fuel ratio of the mixture is reduced in the case of lower richer than 14.7, so increases in the case of lean, the output signal of the O ₂ sensor, air-fuel ratio In response to an oxygen concentration corresponding to 14.7, the voltage level varies between 0 and 1. For example, when the air-fuel ratio is rich, the voltage value of the output signal (air-fuel ratio signal) of the air-fuel ratio sensor increases as the oxygen concentration decreases.

[0004] However, if a single air-fuel ratio sensor is provided only on the upstream side of the catalyst in the exhaust pipe, variations in the output characteristics (operating points) of the air-fuel ratio sensor hinder control accuracy, so that the control accuracy is hindered. There is also proposed a device in which another air-fuel ratio sensor is provided on the side and performs feedback control based on the air-fuel ratio signal on the downstream side in addition to feedback control based on the air-fuel ratio signal on the upstream side of the catalyst.

In this case, the air-fuel ratio sensor on the downstream side of the catalyst detects the exhaust gas having the oxygen concentration averaged after the catalytic reaction, and the deterioration due to the exhaust gas is reduced.
Enables high-precision air-fuel ratio feedback control. That is, it is possible to compensate for variations in the air-fuel ratio sensor, injectors (fuel injection valves), and the like and changes over time in output characteristics.
Such a dual air-fuel ratio sensor system is described, for example, in US Pat. No. 3,939,654.

FIG. 5 is a block diagram showing an example of a general air-fuel ratio control device for an internal combustion engine provided with air-fuel ratio sensors before and after the catalyst (upstream and downstream). In the figure, 1 is an internal combustion engine, that is, an engine, 2 is an intake pipe for supplying an air-fuel mixture to the engine 1, 3 is an air cleaner provided at an intake port on the upstream side of the intake pipe 2, 4 is a downstream side of the intake pipe 2 and the engine An intake manifold 5 formed at a connection with the fuel injection valve 1 is an injector for fuel injection provided upstream of the intake pipe 2.

Reference numeral 6 denotes a pressure P in the intake manifold 4.
, Which measures the amount of air taken into the engine 1 from the intake pipe 2 via the intake manifold 4 as a pressure P. Reference numeral 7 denotes a throttle valve provided on the downstream side of the injector 5 in the intake pipe 2.

Reference numeral 8 denotes a throttle sensor for detecting the throttle opening φ of the throttle valve 7, reference numeral 9 denotes an exhaust pipe for taking out exhaust gas after combustion from the engine 1, and reference numeral 10 denotes a three-way exhaust gas inserted into the exhaust pipe 9 for three-way processing. The reference numeral 11 denotes a first air-fuel ratio sensor provided on the upstream side of the catalyst 10, and 12 denotes a second air-fuel ratio sensor provided on the downstream side of the catalyst 10.

Reference numeral 13 denotes an ignition coil comprising a step-up transformer, 14
Is an igniter composed of a power transistor for interrupting the primary winding of the ignition coil 13. Reference numeral 15 denotes an idle switch integrated with the throttle sensor 8, which detects an idling operation state and turns on when the throttle valve 7 is fully closed. Reference numeral 16 denotes a thermistor-type water temperature sensor for detecting the cooling water temperature T of the engine 1, reference numeral 17 denotes a battery serving as a power supply, reference numeral 18 denotes a key switch for starting power supply from the battery 17 and starting ignition, and reference numeral 19 denotes various abnormality detections. It is an alarm lamp that is sometimes driven.

Reference numeral 20 denotes an electronic control unit (ECU) for driving and controlling the injector 5 and the alarm lamp 19 in accordance with various operating states. The operating state includes a throttle opening φ from the throttle sensor 8 and a pressure sensor 6. From the intake manifold 4, the cooling water temperature T from the water temperature sensor 16, the idle signal D from the idle switch 15, the rotation signal R based on the interruption of the energization of the ignition coil 13, and the output from the air-fuel ratio sensors 11 and 12. Air-fuel ratio signals V1 and V2 are input.

The ECU 20 functions by being supplied with power from the battery 17 when the key switch 18 is closed, generates a fuel injection signal J for the injector 5 in response to the air-fuel ratio signals V1 and V2 and the operating state, and feeds back the air-fuel ratio. In addition to the control, when an abnormality occurs, an abnormality signal E for the alarm lamp 19 is generated. Further, the ignition signal to the igniter 14 may be generated from the ECU 20.

FIG. 6 is a block diagram showing a specific functional configuration of the ECU 20, wherein 21 is an input interface for shaping the waveform of the rotation signal R to be an interrupt signal INT, and 22 is an air-fuel ratio signal.
V1, V2, pressure P, water temperature T and throttle opening φ input interface, input interface 23 for capturing idle signal D, output interface 24 for outputting abnormal signal E, fuel injection signal J, etc., 25 key switch
A power supply circuit connected to the battery 17 via 18, and a microcomputer 30 connected to the input interfaces 21 to 23, the output interface 24 and the power supply circuit 25.

The microcomputer 30 has an air-fuel ratio signal V
A CPU 31 that calculates an air-fuel ratio feedback control amount (hereinafter, simply referred to as an air-fuel ratio control amount) according to 1 and V2 and the like;
A free-running counter 32 that measures the rotation cycle of the engine 1 based on the rotation signal R, that is, the interrupt signal INT, via the input interface 21, a timer 33 that performs timekeeping for various controls, and an input interface 22. AD converter 34 that converts the analog signals (the air-fuel ratio signals V1, V2, the pressure P, the water temperature T, and the throttle opening φ) into digital signals.
An input port 35 for taking in an idle signal D via the input interface 23, a RAM 36 used as a work memory of the CPU 31, a ROM 37 storing an operation program of the CPU 31, and various control signals via the output interface 24. Output port 38 for outputting E and J
And a common bus 39 that couples each of the elements 32-38 to the CPU 31.

When an interrupt signal INT is input via the input interface 21, the CPU 31 reads the value of the counter 32 and calculates the rotation cycle of the engine 1 from the difference between the present value and the previous value of the counter 32. Stored in the RAM 36.
The output interface 24 amplifies the control signal from the output port 38 and outputs it as an abnormal signal E and a fuel injection signal J.

FIG. 7 is a functional block diagram schematically showing the operation of the air-fuel ratio feedback control performed by the conventional microcomputer 30. Reference numeral 41 denotes a PI (proportional to the air-fuel ratio signal V1 from the first air-fuel ratio sensor 11). A first PI controller for performing (integral) control 42 is a second PI controller for performing PI control on the air-fuel ratio signal V2 from the air-fuel ratio sensor 12.

Each of the PI controllers 41 and 42 constitutes computing means for computing each of the air-fuel ratio control amounts C1 and C2 based on each of the air-fuel ratio signals V1 and V2, and comprises a second air-fuel ratio control amount C2. Acts as a correction amount for the first air-fuel ratio control amount C1. Further, the first air-fuel ratio control amount C1 corresponds to the air-fuel ratio correction amount, whereby the final fuel injection signal J to the injector 5 is feedback-controlled, and the second air-fuel ratio signal
V2 is made to coincide with the second target value VR2.

VR1 and VR2 are air-fuel ratio signals V1 and V2, respectively.
The first and second target values for air-fuel ratio control are set in advance, and both are set to voltage values substantially corresponding to the optimal air-fuel ratio 14.7, but the second target value VR2 is First
May be set to a voltage value slightly higher than the target value VR1 (corresponding to the rich side, that is, an air-fuel ratio smaller than 14.7).

FR is a basic fuel amount calculated from a pressure P corresponding to an intake air amount, CF is a fuel correction amount corresponding to an acceleration / deceleration state based on a water temperature T and a throttle opening φ, and KF is an injector 5 for a target fuel amount. Injection time correction coefficient,
Q is a dead time correction amount for the driving time of the injector 5.

Reference numeral 43 denotes a subtractor for calculating a deviation ΔV2 between the second target value VR2 and the air-fuel ratio signal V2 and inputting the difference ΔV2 to the second PI controller 42; Quantity C2
Is a subtractor that calculates a deviation ΔV1 between the correction target value VT1 and the air-fuel ratio signal V1 and inputs the deviation ΔV1 to the first PI controller 41. Adder 44
Constitutes a correction means for correcting the air-fuel ratio control amount C1 calculated by the first PI controller 41.

Reference numeral 46 denotes a target fuel amount F1 obtained by multiplying the air-fuel ratio control amount C1 from the first PI controller 41 by the basic fuel amount FR.
, And 47 is a fuel correction amount C for the target fuel amount F1.
F is a multiplier that generates the corrected fuel amount F by multiplying F, 48 is a multiplier that generates the drive time G of the injector 5 by multiplying the corrected fuel amount F by the injection time correction coefficient KF, and 49 is a wasteful drive time G. This is an adder that adds the time correction amount Q to generate a final fuel injection signal J for the injector 5. The multipliers 46 to 48 and the adder 49 constitute control amount conversion means for converting the air-fuel ratio control amount C1 into the fuel injection signal J.

Next, a specific operation of the conventional air-fuel ratio control apparatus for an internal combustion engine will be described with reference to FIGS. First, the subtractor 43
Is compared with the second target value VR2 to generate a deviation ΔV2 (= VR2−V2), and the second PI controller 42 controls the deviation ΔV2 by PI. Air-fuel ratio control amount
Calculate C2.

On the other hand, the adder 44 adds the air-fuel ratio control amount C2, that is, the correction amount, to the first target value VR1, and the first air-fuel ratio sensor
A correction target value VT1 (= VR1 + C2) for 11 is generated.
Further, the subtractor 45 outputs the first air-fuel ratio signal V on the upstream side of the catalyst 10.
1 and the correction target value VT1 to compare the deviation ΔV1 (= VT1−V
1), and the first PI controller 41 performs PI control on the deviation ΔV1 to calculate the air-fuel ratio control amount C1 for feedback.

In this way, the air-fuel ratio control amount C1 based on the first air-fuel ratio signal V1 is corrected by the second air-fuel ratio control amount C2 to become the final air-fuel ratio control amount. From FIG. 8, it can be seen that the air-fuel ratio control amount C1 is substantially equal to the number and cycle of crossing the correction target value VT1.

Next, while detecting the intake air amount based on the pressure P from the pressure sensor 6, the basic fuel amount FR is calculated from the intake air amount, and the basic fuel amount is added to the air-fuel ratio control amount C1 by the multiplier 46. The target fuel amount F1 is obtained by multiplying FR.

Subsequently, a correction amount corresponding to the warm-up state of the engine 1 is calculated based on the water temperature T from the water temperature sensor 16, and acceleration / deceleration is performed based on the correction amount and the throttle opening φ from the throttle sensor 8. The state is detected, and a fuel correction amount CF is calculated from a correction amount or the like corresponding to the acceleration / deceleration state. Then, the multiplier 47 multiplies the target fuel amount F1 by the fuel correction amount CF to obtain a corrected fuel amount F corresponding to the final fuel injection amount.

Further, a multiplier 48 multiplies the correction fuel amount F by an injection time correction coefficient KF to calculate the driving time G of the injector 5.
The adder 49 adds the dead time correction amount Q to the driving time G to obtain a final fuel injection signal J for the injector 5.

As described above, by correcting the target value VR1 for the first air-fuel ratio sensor 11 using the air-fuel ratio signal V2 from the second air-fuel ratio sensor 12, the air-fuel ratio signal on the downstream side of the catalyst 10 is corrected. The air-fuel ratio feedback control is performed so that V2 becomes the second target value VR2.

That is, if the air-fuel ratio signal V2 on the downstream side of the catalyst 10 indicates the lean side (the air-fuel ratio is larger than 14.7), the fuel injection signal J is set long, and the air-fuel ratio is controlled to the rich side.
If the air-fuel ratio signal V2 on the downstream side of the catalyst 10 indicates the rich side (the air-fuel ratio is smaller than 14.7), the fuel injection signal J is set short, and the air-fuel ratio is controlled to the lean side.

However, each of the air-fuel ratio sensors 11 and 12
Has variations in individual output characteristics, and in particular, the characteristics of the first air-fuel ratio sensor 11 on the upstream side change with time due to deterioration of the sensor element and the like. Hereinafter, the problem due to the variation in the output characteristics and the element deterioration will be specifically described.

FIG. 9 is a waveform diagram showing the output response characteristics of a general air-fuel ratio sensor when the air-fuel ratio (A / F) is forcibly changed. Va denotes the air-fuel ratio obtained by the air-fuel ratio sensor at the center of the characteristic. A signal Vb is an air-fuel ratio signal from an air-fuel ratio sensor having characteristic variations, and Vc is an air-fuel ratio signal from an air-fuel ratio sensor whose elements have deteriorated.

As is apparent from FIG. 9, the air-fuel ratio fluctuation on the lean side and the rich side with the target value 14.7 as the boundary is
The air-fuel ratio signal Va from the air-fuel ratio sensor at the characteristic center responds in about 100 msec, the air-fuel ratio signal Vb from the air-fuel ratio sensor having characteristic variation responds in about 200 msec, and the air-fuel ratio The fuel ratio signal Vc responds in a maximum of about 1.0 ms.

FIG. 10 is a waveform diagram showing the air-fuel ratio feedback control operation when the air-fuel ratio sensor having the output characteristics of the air-fuel ratio signals Va to Vc of FIG. 9 is used as the first air-fuel ratio sensor 11.

Here, the first target value VR1 for the first air-fuel ratio signal V1 is α, the correction target value VT1 is β, and the second target value VR1 is β.
Shows a case where the first target value is corrected from α to β by the air-fuel ratio control amount C2 based on the air-fuel ratio signal V2. That is, the second
Indicates the rich side (the voltage value is higher) than the second target value VR2, and adds the negative air-fuel ratio control amount C2 to lower the correction target value VT1, whereby the air-fuel ratio becomes leaner. Shows a case where feedback control is performed.

In FIG. 10, Tα and Tβ are times when the air-fuel ratio signal V1 is compared with the target values α and β to determine the rich side, and Tα is a rich determination time when the target value is α, Tβ Is the rich determination time when the target value is β. For example, the air-fuel ratio control amount C1 of the air-fuel ratio signal Va (characteristic center) based on the air-fuel ratio sensor 11 is reduced on the decreasing side (air-fuel ratio lean) as indicated by a broken line by correcting the rich determination time to Tβ longer than Tα. Side), so that the air-fuel ratio can be made lean as a result.

Similarly, when the air-fuel ratio sensor 11 for the air-fuel ratio signal Vb (characteristic variation) or Vc (element deterioration) is used, the rich determination time is determined by changing the target value of the first air-fuel ratio signal V1 from α to β. The correction changes to Tβ longer than Tα. At this time, the response time differs as shown in FIG. 9 due to the variation in the output characteristics of the air-fuel ratio sensor 11 such as the air-fuel ratio signals Va to Vc. Thus, as shown in FIG. Alternatively, the change amount (Tβ−Tα) of the rich determination time differs between the case of the element deterioration Vc.

As described above, when the output characteristics of the first air-fuel ratio sensor 11 are different, the rich judgment is made with respect to the change amount (β-α) of the first target value VR1 by the second air-fuel ratio control amount C2. Since the change amounts of the times Tα and Tβ are different, the final air-fuel ratio control amount C1 is different. Therefore, the first air-fuel ratio sensor
Due to the difference in the output characteristics and the response time of 11, the amount of change of the air-fuel ratio control amount C1 with respect to the correction amount C2 of the first target value VR1 differs, and it becomes impossible to correct the air-fuel ratio to an appropriate value.

That is, when the air-fuel ratio sensor 11 of the air-fuel ratio signal Va (characteristic center) is used, since the response time is relatively fast,
The amount of change of the rich determination time with respect to the correction amount C2 of the first target value VR1 becomes small. As a result, proper air-fuel ratio control cannot be performed unless the correction amount C2 of the first target value VR1 is set large.

When the air-fuel ratio sensor 11 of the air-fuel ratio signal Vc (element deterioration) is used, the amount of change in the rich judgment time becomes larger than when the air-fuel ratio sensor of Vb (characteristic variation) is used. Proper air-fuel ratio control cannot be performed. In particular, the first air-fuel ratio sensor 11 upstream of the catalyst 10
Since the air-fuel ratio is easily deteriorated, such a change in the air-fuel ratio control amount C1 cannot be ignored.

[0039]

As described above, the conventional air-fuel ratio control apparatus for an internal combustion engine has a final value VR1 for the target value VR1 of the first air-fuel ratio signal V1 based on the second air-fuel ratio signal V2. Since the actual change amount of the air-fuel ratio control amount C1 differs due to the difference in the output characteristics and the response time of the first air-fuel ratio sensor 11, there is a problem that the air-fuel ratio control amount cannot be properly corrected. .

The present invention has been made in order to solve the above problems, and is intended for an internal combustion engine in which the difference in the output characteristics and response time of the first air-fuel ratio sensor to the air-fuel ratio control amount is suppressed. An object is to obtain an air-fuel ratio control device.

[0041]

Means for Solving the Problems] air-fuel ratio control system for an internal combustion engine according to claim 1 of the invention, slow the first air-fuel ratio signal
And a time constant of the filter processing means is set to a value that suppresses the influence of the response time of the first air-fuel ratio sensor.

Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 2 of the present invention, the variation of the response time of the first air-fuel ratio sensor is 100 ms to 1 second, and the time constant of the filter processing means is 30 msec. It is set to seconds to 100 ms.

[0043]

According to the first aspect of the present invention, the first air-fuel ratio control amount is obtained by using the filtered signal of the first air-fuel ratio signal, and the second air-fuel ratio control based on the second air-fuel ratio signal. The first air-fuel ratio control amount is corrected by the amount, and the air-fuel ratio control based on the first and second air-fuel ratio signals is appropriately performed. Also,
By appropriately setting the time constant of the filter processing means,
The effect of the response time of the air-fuel ratio sensor is eliminated.

According to a second aspect of the present invention, the response time varies from 100 msec to 1 sec with respect to the air-fuel ratio signal.
The filter processing time constant is set to 30 ms to 100 ms, and variations in output characteristics and response time of the air-fuel ratio sensor are reliably suppressed.

[0045]

【Example】

Embodiment 1 FIG. Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram schematically showing the operation of the air-fuel ratio feedback control according to the first embodiment of the present invention. 30A corresponds to the microcomputer 30,
5, 11, and 12 are the same as described above. The configuration of the entire apparatus (not shown) and the configuration of the ECU are as shown in FIGS.

Reference numeral 50 denotes filter processing means for delay- filtering the first air-fuel ratio signal V1 to generate a filtered signal Vf1, and its filtering time constant is not several milliseconds for removing external noise, but for several milliseconds. In order to suppress the difference in the response time of the air-fuel ratio sensor 11 (100 ms to 1 second),
It is set to about 0 ms.

Reference numeral 51 denotes a first signal based on the filtered signal Vf1.
A first calculating means for calculating the air-fuel ratio control amount Cf1 of
It includes the subtractor 45 and the first PI controller 41 in FIG. In this case, the subtractor 45 in the first calculating means 51
The first air-fuel ratio signal V1 is compared with a first target value VR1 before correction.

Reference numeral 52 denotes a second calculating means for calculating a second air-fuel ratio control amount (correction amount) C2 'based on the second air-fuel ratio signal V2. PI controller 42
Contains. In this case, the second air-fuel ratio control amount C2 ′ is
Since the correction amount is not the correction amount for the first target value VR1, but the correction amount for the first air-fuel ratio control amount Cf1, the PI control amount of the second PI controller 42 is different from that described above.

Reference numeral 53 denotes an adder for adding the second air-fuel ratio control amount C2 'to the first air-fuel ratio control amount Cf1 as a correction amount, and a correction means for correcting the first air-fuel ratio control amount C1. The result of the addition is an air-fuel ratio control amount C1 'corresponding to the final air-fuel ratio correction amount. Numeral 54 denotes control amount conversion means for converting the air-fuel ratio control amount C1 'into a fuel injection signal J for the injector 5, and includes multipliers 46 to 48 and an adder 49 in FIG.

Next, referring to the flowchart of FIG. 2 and the waveform diagram of FIG. 3 together with FIG. 1, the first embodiment of the present invention will be described.
Will be described. Note that the filter processing calculation routine shown in FIG. 2 is executed, for example, every 10 ms. First, the air-fuel ratio signal V1 from the first air-fuel ratio sensor 11 is read (step S1), and it is determined whether or not this is the first reading after the power is turned on (step S2).

If it is determined in step S2 that this is the first reading, the air-fuel ratio signal V1 is initialized as the current filter processing signal Vf1 (n) (step S3), and the filter processing is terminated and the routine returns. . At this time, the current filtered signal Vf1 (n) is the same as the previous filtered signal Vf1 (n).
It is updated and registered as (n-1).

On the other hand, if it is determined in step S2 that the reading is not the first reading, the current filtered signal Vf1 (n)
Is set by a primary filter operation such as the following equation (1) (step S4).

Vf1 (n) = (1−Ks) × Vf1 (n−1) +
Ks × V1 (1)

However, in the equation (1), Ks is a filter operation coefficient, and is set to a value within a range of 0 <Ks <1. The current filtered signal Vf1 calculated by equation (1)
Based on (n), the first air-fuel ratio signal V1 is
The response time is converted to a filtered signal Vf1 whose response time is delayed by a filtering time constant of 0 ms, and the first processing means 51
Is input to

At this time, as shown by a broken line in FIG. 3, the waveform of the filtered signal Vf1 is modified such that the response time is increased by the filtering time constant and the variation of the air-fuel ratio signal V1 is suppressed. FIG. 3 is a waveform diagram showing the air-fuel ratio signal V1 (solid line) having the characteristic center (Va) and the characteristic variation (Vb), and the respective filtered signals Vfa and Vfb (dashed line). The original air-fuel ratio signals Va and Vb It can be seen that even if there is a difference in response time between the filtered signals Vfa and Vfb, there is almost no difference in response time.

As described above, by applying the filtering process to the first air-fuel ratio signal V1, the difference between the output characteristics and the response time of the first air-fuel ratio sensor 11 is absorbed. Therefore, the first air-fuel ratio control amount C1 ′ corrected by the second air-fuel ratio control amount C2 ′ is hardly affected by the difference in the output characteristics and the response time of the first air-fuel ratio sensor 11, and Appropriate air-fuel ratio control can be performed by the final fuel injection signal J.

Since the second air-fuel ratio sensor 12 is provided downstream of the catalyst 10 as described above,
Since there is almost no deterioration due to exhaust gas components and exhaust gas temperature, there is no need to particularly consider variations in output characteristics and response time.

Embodiment 2 FIG. In the first embodiment, the case where the first air-fuel ratio control amount Cf1 is corrected by adding the second air-fuel ratio control amount C2 'has been described as an example.
It may be applied to the case where the first target value VR1 is corrected with the second control amount C2 as described above. Also, the final air-fuel ratio control amount C1 ′
Any method for correcting the P value, the I value, the delay time, or the like of the first PI controller 41 can be applied as long as the method is used to correct.

FIG. 4 is a functional block diagram showing a second embodiment of the present invention in which the first target value VR1 is corrected by the second air-fuel ratio control amount C2, and 5, 11, 12, 44, 50. And 54
Is the same as described above. 51A and 52A correspond to the first and second calculation means 51 and 52, respectively.

In this case, as in the case of FIG.
51A includes a subtractor 45 for comparing the filtered signal Vf1 and the correction target value VT1, and a first PI controller 41,
The second calculation means 52A includes a subtractor 43 and a second PI controller 42.

[0061]

As described above, according to the first aspect of the present invention, filter processing means for delay- filtering the first air-fuel ratio signal is provided, and the time constant of the filter processing means is set to the first air-fuel ratio sensor. To a value that suppresses the effect of response time
A first air-fuel ratio control amount is obtained by using a filter processing signal of the first air-fuel ratio signal, and the first air-fuel ratio control amount is corrected by a second air-fuel ratio control amount based on the second air-fuel ratio signal. Thus, there is an effect that an air-fuel ratio control device for an internal combustion engine can be obtained in which the influence on the air-fuel ratio control amount due to the difference in the output characteristics and response time of the first air-fuel ratio sensor is suppressed.

According to the second aspect of the present invention, the time constant of the filter processing means is set to 30 ms to 100 ms for the first air-fuel ratio signal having a response time variation of 100 ms to 1 second. Therefore, there is an effect that an air-fuel ratio control device for an internal combustion engine in which the influence on the air-fuel ratio control amount due to the difference in the output characteristics and response time of the first air-fuel ratio sensor is reliably suppressed is obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram schematically showing an air-fuel ratio feedback control calculation operation according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a filter processing operation according to the first embodiment of the present invention.

FIG. 3 is a waveform chart showing a filtered signal obtained by the first embodiment of the present invention.

FIG. 4 is a functional block diagram schematically showing an air-fuel ratio feedback control calculation operation according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a general air-fuel ratio control device for an internal combustion engine.

FIG. 6 is a block diagram showing a functional configuration of an ECU in FIG. 5;

FIG. 7 is a functional block diagram schematically showing an air-fuel ratio feedback control operation performed by a conventional air-fuel ratio control device for an internal combustion engine.

FIG. 8 is a waveform diagram for explaining an air-fuel ratio feedback control operation by a general air-fuel ratio control device for an internal combustion engine.

FIG. 9 is a waveform diagram showing output response characteristics of a general air-fuel ratio sensor.

FIG. 10 is a waveform diagram for explaining an air-fuel ratio feedback control operation by a conventional air-fuel ratio control device for an internal combustion engine when air-fuel ratio sensors having different output characteristics are used.

[Explanation of symbols]

 Reference Signs List 1 engine 9 exhaust pipe 10 catalyst 11 first air-fuel ratio sensor 12 second air-fuel ratio sensor 20 ECU 44 adder (correction means) 50 filter processing means 51 first calculation means 52 second calculation means 53 adder ( Correction means) C1 'Air-fuel ratio control amount Cf1 First air-fuel ratio control amount C2, C2' Second air-fuel ratio control amount V1 First air-fuel ratio signal V2 Second air-fuel ratio signal Vf1 Filter processing signal

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Claims (2)

(57) [Claims] An exhaust gas purifying catalyst inserted in an exhaust system of an internal combustion engine, and a first component provided upstream of the catalyst for detecting a specific component concentration of the exhaust gas as a first air-fuel ratio signal. An air-fuel ratio sensor, a second air-fuel ratio sensor provided downstream of the catalyst to detect a specific component concentration of the exhaust gas as a second air-fuel ratio signal, and the first and second air-fuel ratio signals An ECU for calculating an air-fuel ratio control amount based on the first and second air-fuel ratio control amounts, wherein the ECU calculates a first air-fuel ratio control amount based on the first air-fuel ratio signal; A second calculating means for calculating a second air-fuel ratio control amount based on the air-fuel ratio signal; and correcting the first air-fuel ratio control amount by the second air-fuel ratio control amount to obtain the air-fuel ratio control amount. An air-fuel ratio control device for an internal combustion engine, comprising: U, the further comprises a filtering means for filtering delays the first air-fuel ratio signal, the time constant of the filtering means is set to suppress values the influence of the response time of the first air-fuel ratio sensor An air-fuel ratio control device for an internal combustion engine. 2. A method according to claim 1, wherein a variation in response time of said first air-fuel ratio sensor is 100 ms to 1 second, and a time constant of said filter processing means is set to 30 ms to 100 ms. Item 2. An air-fuel ratio control device for an internal combustion engine according to Item 1.