JPH06229295A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To carry out a control with excellent follow-up performance, and enable stable control in spite of a noise of an oxygen sensor by carrying out feedback control on an air-fuel ratio according to deviation between a controlling air-fuel ratio increased and decreased according to output of the oxygen sensor and a target air-fuel ratio. CONSTITUTION:Output voltage of an oxygen sensor 11 is inputted to a linearizer 50, and a standard air excessive rate is calculated. This calculated result is inputted to respective correcting linearizers 51 and 53 for non-idle time and for idle time, and a controlling air excessive rate is calculated. These respective calculated results are inputted to respective deviation operation circuits 55 and 57, and operation is carried out on deviation between the controlling air excessive rate and a target air excessive rate. The non-idle time deviation is inputted to respective PID controllers 59 and 61 for stationary time and for rapid acceleration time, and air-fuel ratio correction factors outputted from these are inputted successively to the first and the second respective selecting circuits 63 and 67. An operation result of a multiplier 69 is outputted to an injector 5 as a target fuel injection quantity.

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, which executes air-fuel ratio feedback control in accordance with an output signal of an oxygen sensor whose output changes rapidly near the stoichiometric air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, there is an air-fuel ratio control device for performing air-fuel ratio control by making a lean or rich determination by comparing an output signal of an oxygen sensor with a reference value representing a theoretical air-fuel ratio. In this air-fuel ratio control device, the feedback correction coefficient is greatly skipped in a stepwise manner according to the determination result of lean or rich, and then the feedback correction coefficient is gradually changed by integration, and the actual air-fuel ratio is changed to the theoretical air-fuel ratio. Converge to. However, this air-fuel ratio control device cannot directly calculate the deviation between the actual air-fuel ratio and the theoretical air-fuel ratio. Further, since it takes time for the deviation to be reflected in the integration result, there is a problem that control followability is poor. In the vicinity of the stoichiometric air-fuel ratio, even if the oxygen sensor output increases or decreases, the corresponding air-fuel ratio hardly changes. Therefore, the correspondence between the oxygen sensor output and the air-fuel ratio could not be directly applied to the air-fuel ratio control.

Therefore, as an air-fuel ratio control device for eliminating the poor control followability, there is a conventional air-fuel ratio control device, for example, Japanese Patent Laid-Open No. 1-12.
The device described in Japanese Patent No. 1541 has been proposed. This conventional air-fuel ratio control device executes the air-fuel ratio control using the relationship correction characteristic in which the correspondence relationship between the oxygen sensor output and the control air-fuel ratio is defined by a substantially linear function. In the relation correction characteristic defined by the linear function, the control air-fuel ratio uniformly increases or decreases according to the increase or decrease in the oxygen sensor output, either near or at the theoretical air-fuel ratio. Therefore, as the value of the oxygen sensor output deviates from the value corresponding to the stoichiometric air-fuel ratio, the value of the control air-fuel ratio becomes sufficiently deviated from the stoichiometric air-fuel ratio. In this conventional device, the magnitude of the output signal of the oxygen sensor is compared with the correction characteristic to calculate the control air-fuel ratio, and the air-fuel ratio feedback control is executed based on the deviation between the control air-fuel ratio and the target air-fuel ratio. The control followability is improved.

[0004]

However, when the control followability is improved in this way, the following problems newly occur. Noise may be superimposed on the output signal of the oxygen sensor due to the influence of electromagnetic waves. This type of noise usually has a short-width waveform that has a sharp peak and changes abruptly.

Therefore, the influence of this kind of noise on the integrated value of the oxygen sensor output is extremely small. Therefore, in the air-fuel ratio control based on the above-mentioned integral value, the superposition of noise could be almost ignored. However, in the air-fuel ratio control using the relation correction characteristic, the noise of this kind is immediately reflected in the air-fuel ratio control as a change in the control air-fuel ratio due to the improvement of the control followability. Therefore, when noise is superimposed on the output of the oxygen sensor, the feedback control amount of the air-fuel ratio does not correspond to the actual air-fuel ratio, which may result in deterioration of fuel consumption and emission.

As described above, in the conventional air-fuel ratio control system for an internal combustion engine, it is extremely difficult to satisfy both good control followability and stability against noise at the same time. Therefore, the present invention has been made for the purpose of providing an air-fuel ratio control device for an internal combustion engine which has good control followability and can continue stable control even if noise is superimposed on the oxygen sensor output.

[0007]

DISCLOSURE OF THE INVENTION The present invention, which has been made in order to achieve the above object, has an oxygen sensor whose output suddenly changes in the vicinity of the stoichiometric air-fuel ratio, as shown in FIG. Corresponding to the oxygen sensor output according to the relationship correction characteristic storage means that stores the relationship correction characteristic storing the relationship correction characteristic that defines the corresponding relationship with the control air-fuel ratio that increases or decreases according to the increase or decrease in the oxygen sensor output. Control air-fuel ratio calculating means for calculating the control air-fuel ratio, air-fuel ratio deviation calculating means for calculating a deviation between the calculated control air-fuel ratio and the target air-fuel ratio, and the calculated control air-fuel ratio and target A controller that executes air-fuel ratio feedback control of the internal combustion engine based on a deviation from the air-fuel ratio, and in an air-fuel ratio control device for an internal combustion engine, the change amount of the oxygen sensor output per predetermined time is a predetermined amount. A sensor abnormality determining means for determining an abnormality in the oxygen sensor output when it is larger, and a sensor output correcting means for correcting the oxygen sensor output when the abnormality in the oxygen sensor output is determined by the sensor abnormality determining means. Provided, when it is determined that the oxygen sensor output is abnormal, the control air-fuel ratio calculation means calculates the control air-fuel ratio corresponding to the corrected oxygen sensor output, the air-fuel ratio of the internal combustion engine The main point is the control device.

[0008]

According to the present invention thus constructed, the control air-fuel ratio calculating means detects the control air-fuel ratio corresponding to the output of the oxygen sensor in accordance with the relation correction characteristic stored in the relation correction characteristic storage means. Here, the control air-fuel ratio increases / decreases according to the increase / decrease in the oxygen sensor output. The deviation calculating means calculates the deviation between the control air-fuel ratio and the target air-fuel ratio, and the controller executes the air-fuel ratio feedback control based on the calculated deviation. Therefore, according to the present invention, it is possible to realize control with good followability, which reflects the deviation amount between the control air-fuel ratio and the target air-fuel ratio.

When noise is superposed on the oxygen sensor output, the oxygen sensor output changes abruptly, and the amount of change per predetermined time becomes larger than the predetermined amount. At this time, the sensor abnormality determining means determines an abnormality in the oxygen sensor output, and the sensor output correcting means corrects the oxygen sensor output. Since the controller executes the air-fuel ratio feedback control using the corrected oxygen sensor output, stable control can be continued even if noise is superimposed on the oxygen sensor output.

There are various methods of correcting the oxygen sensor output, such as a method of substituting the oxygen sensor output with an output before the abnormality is determined, a method of interpolating the output before and after the abnormality is determined, and the like. The method of can be considered.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An air-fuel ratio control system for a vehicle internal combustion engine (hereinafter referred to as an engine) will be described below as an embodiment of the present invention.
FIG. 1 is a block diagram showing the configuration of the air-fuel ratio control system of this embodiment.

As shown in the figure, an injector 5 for injecting fuel is arranged in the intake system passage upstream of the intake manifold 3 for supplying the air-fuel mixture to the engine 1. Further, an exhaust manifold 7 for exhausting exhaust gas after combustion from the engine 1
An oxygen sensor 11 whose output suddenly changes in the vicinity of the stoichiometric air-fuel ratio of the engine 1 is provided in the exhaust system passage extending from to the catalytic converter 9 filled with the three-way catalyst. Oxygen sensor 11
Output of the injector 5 is input to the electronic control unit 30, and the injector 5
Injects fuel based on a drive signal input from the electronic control unit 30 via a drive circuit (not shown). In the air-fuel ratio control device of the present embodiment configured as described above, the electronic control device 30 is a well-known microcomputer having CPU, ROM, and RAM as main parts, and the oxygen sensor 1
The fuel injection amount by the injector 5 is adjusted based on the output voltage Vox of 1 and the air-fuel ratio feedback control is executed to control the air-fuel ratio so that the air-fuel mixture supplied to the engine 1 has the target excess air ratio λ0. Here, the excess air ratio refers to the ratio of the amount of air supplied for the air-fuel mixture with the amount of air at the stoichiometric air-fuel ratio as a reference (= 1). Next, regarding this air-fuel ratio feedback processing, FIGS.
Will be described together.

FIG. 2 is a flowchart of an air-fuel ratio feedback control processing routine executed in the electronic control unit 30. In addition, a block diagram equivalent to the feedback control realized by executing the routine of FIG. 2 is also shown in the block representing the electronic control unit 30 of FIG.
First, the processing routine of FIG. 2 will be described, and then the main air-fuel ratio feedback control will be described in detail according to the block diagram of FIG.

The air-fuel ratio feedback control routine shown in FIG. 2 is executed as a timer interrupt process every 5 msec. In the execution, first, it is determined whether or not the air-fuel ratio feedback execution condition is satisfied (S100). As the air-fuel ratio feedback execution condition, there are known conditions such as the water temperature level, the presence or absence of fuel cut, and whether or not the acceleration increase is being performed. If it is determined that the air-fuel ratio feedback execution condition is not satisfied (S100: NO), this routine is once ended.

When it is determined that the air-fuel ratio feedback execution condition is satisfied (S100: YES), the output voltage Vox of the oxygen sensor 11 is input (S110). Then, the standard excess air ratio λ1 is calculated from the output voltage Vox by the standard excess air ratio calculation routine shown in FIG. 3 (S12).
0).

Here, in the standard excess air ratio calculation routine, the standard excess air ratio λ1 is calculated from the oxygen concentration in the exhaust path based on the output voltage Vox of the oxygen sensor 11 as follows. As shown in FIG. 3, when the process is started, first, the output voltage Vox input in step S110 this time is displayed.
The output voltage Voxn-1 input in the previous processing is subtracted from n, and the value is set as the change amount ΔVox (S12).
1). Then, it is determined whether or not the absolute value of the change amount ΔVox is less than or equal to a predetermined value (S123).

When | ΔVox | is less than a predetermined value (S
123: YES) calculates the standard excess air ratio λ1 corresponding to the current output voltage Voxn based on the characteristic graph shown in FIG. 4 (S125). If | ΔVox | is larger than the predetermined value (S123: NO), the current output voltage Voxn is replaced with the value of the previous output voltage Voxn-1 (S127), and then the standard excess air ratio λ1 is calculated in step S125. To calculate.

That is, the output voltage Vo of the oxygen sensor 11
When noise is superimposed on x, the output voltage Vox changes sharply. Therefore, when the change amount | ΔVox | of the output voltage Vox for 5 msec is larger than a predetermined value, the output voltage Vox
It is determined that noise is superimposed on x. Then, the output voltage Voxn is corrected to the value of the previous output voltage Voxn-1,
The standard excess air ratio λ1 is calculated based on the corrected output voltage Voxn (that is, the previous output voltage Voxn-1).

In step S125, the standard excess air ratio λ1
After calculating, output voltage Voxn- for the next processing
1 is replaced with the value of the output voltage Voxn after this correction (S129), and the routine returns to FIG. Returning to FIG. 2, after calculating the standard excess air ratio λ1 in step S120, it is determined whether or not an idle switch (not shown) is on (S130). When it is determined that the idle switch is not on (S130: NO), it is determined that the idle state is not established, and the control excess air ratio λ2 corresponding to the standard excess air ratio λ1 obtained in step S120 is determined based on the characteristic graph for non-idle time. Calculate (S140). Then, the control excess air ratio λ2 calculated in step S140 is subtracted from the target excess air ratio λ0, and the subtracted value is set to the deviation Δλ (S150). Here, the target excess air ratio λ0 means an excess air ratio when the target air-fuel ratio is determined according to the running state of the vehicle, and for example, when the target air-fuel ratio is the theoretical air-fuel ratio, λ0 = 1.0. .

Next, it is determined whether or not the current operating condition is rapid acceleration (S160). When it is determined that the acceleration is not sudden (S
160: NO), and search the calculation parameter for PID control described later (S170). On the other hand, when it is determined that the operating state is rapid acceleration (S160: YES), a calculation parameter for PI control described later is searched (S180).

When the idle switch is judged to be on in step S130, the process proceeds as described above when not in idle, but it is determined that the idle state is in the idle state, the characteristic graph for idle is referred to, and the standard obtained in step S120 is determined. A control air excess ratio λ2 corresponding to the air excess ratio λ1 is calculated (S190). Subsequently, the control excess air ratio λ2 calculated in step S190 is subtracted from the target excess air ratio λ0, and the subtracted value is set to the deviation Δλ (S200). Then, the PI control calculation parameter is retrieved (S21).
0).

As described above, the calculation parameters (S170, 180, 210) retrieved according to the operating state of the idle state or the non-idle state, and the non-idle state of the rapid acceleration state or the steady state. Then, the air-fuel ratio correction coefficient FAF is calculated (S220). After this, the process returns to the top step S100.

The calculation result of the air-fuel ratio correction coefficient FAF is used to correct the basic injection amount, and the injector 5 is driven based on the corrected injection amount. Next, the air-fuel ratio feedback control realized by executing the processing routine shown in FIG. 2 will be described with reference to the block diagram shown in FIG.

The output voltage Vox of the oxygen sensor 11 is input to the linearizer 50. The linearizer 50 is realized by the steps S110 and 120, and has the characteristic graph shown in FIG. This characteristic graph shows the oxygen sensor 1
The relationship between the output voltage Vox of No. 1 and the standard excess air ratio λ1 is shown. Referring to this characteristic graph, the linearizer 50
Standard excess air ratio λ corresponding to the input output voltage Vox
Calculate 1. Further, the linearizer 50 outputs the output voltage V
When the amount of change in ox exceeds a predetermined amount, the standard excess air ratio λ1 corresponding to the output voltage Vox input in the previous process
To calculate.

The calculated standard excess air ratio λ1 is input to the non-idle correction linearizer 51 and the idle correction linearizer 53. The correction linearizer 51 is realized by the step S140, and the correction linearizer 53 is realized by the step S190. The correction linearizer 51 is shown in FIG.
The characteristic graph for the non-idle state shown in (B) is provided, and the correction linearizer 53 has the characteristic graph for the idle state shown in FIG. The graphs of FIGS. 4, 5A, 5B and 6 correspond to the relationship correction characteristic storing means, and the linearizer 50 and the correction linearizers 51 and 53 correspond to the control air-fuel ratio calculating means. .

Both the non-idle characteristic graphs of FIGS. 5A and 5B and the idle characteristic graph of FIG. 6 define the relationship between the standard excess air ratio λ1 and the control excess air ratio λ2. However, the characteristic graphs have some common basic relationships. That is, the basic relationship is to increase or decrease the control air excess ratio λ2 in accordance with the increase or decrease of the standard air excess ratio λ1 in the predetermined air-fuel ratio range including the theoretical air-fuel ratio (that is, the excess air ratio = 1.0, the same applies hereinafter). However, outside the predetermined air-fuel ratio range, the control excess air ratio λ2 stops increasing or decreasing regardless of the increase or decrease in the standard excess air ratio λ1.
The predetermined air-fuel ratio range is a range of a total 1% in which the excess air ratio deviates by 0.5% before and after the stoichiometric air-fuel ratio. In this range, the degree of variation in the output due to the difference between the oxygen sensors 11 and the difference in the measured temperature is so small that it can be ignored.

Next, a characteristic graph when not idle (FIG. 5)
The difference between the characteristic graph at idle and the characteristic graph at idle (FIG. 6) will be described. As shown in FIGS. 5A and 5B, in the characteristic graph at the time of non-idling, the control is biased vertically or horizontally within the above predetermined air-fuel ratio range, and increases or decreases according to the increase or decrease of the standard excess air ratio λ1. The relationship is defined in which the value of the excess air ratio λ2 for the air is biased to the rich side or the lean side as a whole. Here, rich or lean means whether the air-fuel ratio is rich or lean, and is shown by the symbols R and L in the figure (the same applies hereinafter).

On the other hand, in the characteristic graph during idling, as shown in FIG. 6, the control air which increases or decreases in accordance with the increase or decrease of the standard air excess ratio λ1 in the predetermined air-fuel ratio range extending before and after the stoichiometric air-fuel ratio. The relationship is defined in which the increase / decrease rate of the excess rate λ2 is made lower than the basic increase / decrease rate (the increase / decrease rate of the chain line in the figure) centering on the theoretical air-fuel ratio.

With reference to the characteristic graphs (FIGS. 5 and 6) described above, the correction linearizer 51 and the correction linearizer 53 output the control excess air ratio λ2 corresponding to the standard excess air ratio λ1 input from the linearizer 50. Is output. The control excess air ratio λ2 output from the non-idle correction linearizer 51 is input to the deviation calculation circuit 55, while the control excess air ratio λ2 output from the idle correction linearizer 53 is the deviation calculation circuit. 57 is input.

The deviations .DELTA..lamda. Between the control excess air ratio .lamda.2 and the target excess air ratio .lamda.0 are output from the respective deviation calculation circuits 55 and 57. After that, based on the deviation Δλ, the air-fuel ratio control described later is performed. In the air-fuel ratio control, the following control characteristics are basically obtained due to the difference in characteristics of the characteristic graph between the non-idle time and the idle time described above.

In both the non-idle state and the idle state, the control air excess ratio λ2 (λR on the rich side, λL on the lean side) is a constant value with respect to the input of the standard air excess ratio λ1 outside the predetermined air-fuel ratio range. Is output). Therefore, when the standard air excess ratio λ1 is within the predetermined air-fuel ratio range, the control air excess ratio λ2 increases or decreases according to the increase or decrease of the standard air excess ratio λ1, but the standard air excess ratio λ1 does not exceed the predetermined air-fuel ratio range. If it deviates, the control air excess ratio λ2 stops increasing or decreasing. Even if the increase / decrease is stopped, the control air excess ratio λ2 has already been increased / decreased to a sufficiently large value or a sufficiently small value.

Here, the control excess air ratio λ2 is 1, λR
, ΛL, the output voltage Vox is V1
, VR, VL, the change in the control air-fuel ratio with respect to the change in the output voltage Vox is illustrated in FIG. 7 (A). That is, when the output voltage Vox exceeds VR, the control excess air ratio λ2 is fixed to λR, and the output voltage Vox is V
Below L, the control air excess ratio λ2 is fixed at λL. In the range of VL ≤ Vox ≤ VR, the output voltage V
As the ox increases and decreases, the control air excess ratio λ2 also increases and decreases.

The control excess air ratio λ2 that increases and decreases in this way
The air-fuel ratio feedback control executed based on the deviation Δλ between the target excess air ratio λ0 and the target excess air ratio λ0 is
And the target excess air ratio λ0 are reflected, and the followability is good. As described above, the followability is excellent, but when the standard air excess ratio λ1 is outside the predetermined air-fuel ratio range, the control air excess ratio λ1 is maintained regardless of the increase or decrease of the standard air excess ratio λ1.
Since the increase / decrease of 2 is stopped, the variation in the output of the oxygen sensor 11, which becomes noticeable outside the predetermined air-fuel ratio range, does not enter the air-fuel ratio feedback control. Therefore, there is no variation in control performance and no influence on emissions.

When noise is superimposed on the output voltage Vox, a sharp peak P is obtained as illustrated in FIGS. 7 (B) and 7 (C).
1, P2 are formed. If the output voltage Vox on which this noise is superimposed is converted as it is, similar peaks P3 and P4 are formed also in the control excess air ratio λ2 as shown in (B). On the other hand, in the present embodiment, when the amount of change in the output voltage Vox exceeds the predetermined value, the control air excess ratio is calculated using the output voltage Vox input in the previous process, so (C ), The influence of noise can be removed.

When the standard excess air ratio is within the predetermined air-fuel ratio range during non-idle, the following control characteristics are basically realized. That is, the center of the air-fuel ratio control can be finely adjusted by changing the setting of the deviation amount that biases the value of the control air excess ratio λ2 in the characteristic graph (FIG. 5) to the lean side or the rich side. Therefore, even if the optimum air-fuel ratio at which the emission falls within the regulation value differs due to the individuality of the engine, the control to set the air-fuel ratio control center at this optimum air-fuel ratio can be easily realized by changing the setting of the deviation amount. Will be.

When the standard excess air ratio is within the predetermined air-fuel ratio range during idling, the following air-fuel ratio feedback control is basically realized. As shown in the characteristic graph of FIG. 6, the control air excess ratio λ2 that increases or decreases in accordance with the increase or decrease of the standard air excess ratio λ1 centering on the theoretical air-fuel ratio.
The rate of increase / decrease is lower than that of the standard characteristic indicated by the chain line. As a result, the change in the control excess air ratio λ2 is set smaller than the actual change in the excess air ratio. As a result, the control amplitude can be reduced during idle,
High stability is obtained. Further, if the standard excess air ratio λ1 tries to deviate from the predetermined air-fuel ratio range, the excess air ratio λ for control
Since 2 rapidly increases or decreases, the control followability also increases.

As described above, the air-fuel ratio control based on the deviation Δλ is basically realized. The air-fuel ratio control will be described in detail below. First, the non-idle time will be described. Deviation Δλ output from deviation calculation circuit 55 for non-idle time
Is output to the PID controller 59 for steady state and the PI controller 61 for rapid acceleration. The PID controller 59 performs feedback control of the transfer function Gc (S) represented by the following Expression 1.

[0038]

[Equation 1]

The differential element (1 + Kd ·
S) / (1 + k · Kd · S) is an approximate derivative. The air-fuel ratio correction coefficient FAF is obtained in step S220 of the above-described processing routine (FIG. 2) according to the equation 1 and the arithmetic expression equivalent to the equation 2.

[0040]

[Equation 2]

Also, the coefficients a, b, and
c, d, and e are as shown in the following Expression 3. In step S170 of the processing routine (FIG. 2), the coefficients a, b, c, d and e are acquired based on the equation 3.

[0042]

[Equation 3]

On the other hand, PI controller 61 for sudden acceleration
Performs feedback control of the transfer function Gc (S) represented by the following Expression 4.

[0044]

[Equation 4]

This equation 4 is a differential element (1 + K
d * S) / (1 + k * Kd * S) is not included. This number 4
In accordance with the arithmetic expression represented by the equation 5 equivalent to, in step S220 of the above-described processing routine (FIG. 2), the air-fuel ratio correction coefficient F
AF is required.

[0046]

[Equation 5]

Further, the coefficients a, b, c, d, of each term of the equation 5 are
e is as shown in Equation 6 below. In step S180 of the processing routine (FIG. 2), the coefficient a,
Get b, c, d, e.

[0048]

[Equation 6]

The reason why PI control is performed during sudden acceleration is as follows. In the above-described steady-state PID control, the output waveform of the oxygen sensor 11 is smoothed by the differential element to eliminate the influence of the dynamic characteristics of the oxygen sensor, but the differential element has a function of impairing the control followability. Therefore, during a transition such as during rapid acceleration, the air-fuel ratio control is performed by PI control without the differential element. As a result, at the time of sudden acceleration, control in which the followability of the control in which the air-fuel ratio control center quickly follows the target air-fuel ratio is realized is realized.

As described above, the PID controller 59
The air-fuel ratio correction coefficient FAF output from the PI controller 61 is input to the first selection circuit 63. Further, the pressure change ΔPm calculated based on the detection signal of the intake pressure sensor (not shown) is input to the first selection circuit 63. The first selection circuit 63 is realized by step S160 of the processing routine (FIG. 2). The first selection circuit 63 determines whether the engine is in the steady state or the rapid acceleration based on the pressure change ΔPm, and outputs the air-fuel ratio correction coefficient FAF from the PID controller 59 to the downstream second selection circuit 67 in the steady state. During rapid acceleration, the air-fuel ratio correction coefficient FA from the PI controller 61
F is output to the second selection circuit 67.

Next, the idle time will be described. The deviation Δλ output from the deviation calculation circuit 57 for idle time is
It is output to the PI controller 65. The PI controller 65 performs feedback control of the transfer function Gc (S) represented by the following Expression 7.

[0052]

[Equation 7]

This equation 7 is a differential element (1 + K
d * S) / (1 + k * Kd * S) is not included. This number 7
According to the arithmetic expression equivalent to Equation 8, the air-fuel ratio correction coefficient FAF is calculated in step S220 of the processing routine (FIG. 2).
Is required.

[0054]

[Equation 8]

Also, the coefficients a, b, and
c, d, and e are as shown in the following Expression 9. In step S210 of the processing routine (FIG. 2), the coefficients a, b, c, d and e are acquired based on the equation 9.

[0056]

[Equation 9]

It should be noted that Kp in Equation 9; proportional constant, K
i; integration constant is P for sudden acceleration during non-idle
The values of Kp and Ki of the I controller 61 are different. In this way, the PI controller 61 realizes PI control. P
Air-fuel ratio correction coefficient FA output from the I controller 65
F is input to the second selection circuit 67. Second selection circuit 67
Further, the signal from the idle switch is input to. The second selection circuit 67 is realized by the above step S130.

The second selection circuit 67 determines whether the engine is idle or not idle depending on the contact state of the idle switch, and if not idle, the air-fuel ratio correction coefficient FAF output from the PID controller 59 or the PI controller 61. Is output to the multiplier 69, and when idle, PI
Air-fuel ratio correction coefficient FAF output from controller 65
Is output to the multiplier 69. The multiplier 69 multiplies the preset basic injection amount by the air-fuel ratio correction coefficient FAF, and outputs the drive signal of the injector 5 with the calculation result as the target fuel injection amount. As a result, the air-fuel ratio feedback control is executed.

According to the air-fuel ratio control apparatus of the present embodiment described above, when noise is superimposed on the output voltage Vox of the oxygen sensor 11, the noise is superimposed on the output voltage Vox at the time of the previous processing, and then the air-fuel ratio is corrected. Since it is used for feedback control, stable control can be continued even if noise is superimposed on the output voltage Vox.

If the standard excess air ratio λ1 obtained from the output signal of the oxygen sensor 11 is within the predetermined air-fuel ratio range,
Control air excess ratio λ according to increase / decrease of standard air excess ratio λ1
Since 2 is increased / decreased, control with good followability can be realized. Further, if the standard excess air ratio λ1 is out of the predetermined air-fuel ratio range, the control excess air ratio λ2 is set to a constant value, so that the variation in the output of the oxygen sensor can be eliminated from the air-fuel ratio feedback control.

As described above, the air-fuel ratio control system of the present embodiment has good control followability and the oxygen sensor 1
Even if noise is superimposed on the output voltage Vox of 1, stable control can be continued. Therefore, if the present embodiment is applied, fuel efficiency and emission can be improved satisfactorily.

In the above embodiment, when noise is superimposed on the output voltage Vox, it is corrected to the output voltage Vox of the previous processing, but the output voltage Vox of the previous processing is corrected.
The output voltage Vox may be corrected by an interpolation method using x or the like. In this case, the air-fuel ratio can be controlled more accurately.

Further, in the above embodiment, the output voltage Vox is converted into the standard excess air ratio λ1, and the control excess air ratio λ.
However, the output voltage Vox may be directly converted into the control excess air ratio λ2. In this case as well, the output voltage V of the oxygen sensor 11 has good followability.
Even if noise is superimposed on ox, stable control can be continued.

[0064]

As described above in detail, in the air-fuel ratio control system for an internal combustion engine according to the present invention, the air-fuel ratio feedback based on the deviation between the target air-fuel ratio and the control air-fuel ratio which increases or decreases according to the oxygen sensor output. Since the control is executed, it is possible to execute the control with good followability. Further, when noise is superimposed on the oxygen sensor output, it is used for air-fuel ratio feedback control after being corrected, so that stable control can be continued even if noise is superimposed on the oxygen sensor output.

Therefore, the present invention has good control followability and can continue stable control even if noise is superimposed on the oxygen sensor output. Therefore, if the present invention is applied, fuel efficiency and emission can be improved satisfactorily.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an air-fuel ratio control device of an embodiment.

FIG. 2 is a flowchart showing an air-fuel ratio control process of an embodiment.

FIG. 3 is a flowchart showing a standard excess air ratio calculation routine of the embodiment.

FIG. 4 is a characteristic graph that defines the relationship between the oxygen sensor output voltage and the standard excess air ratio.

FIG. 5 is a characteristic graph that defines the relationship between the standard excess air ratio and the control excess air ratio when not idle.

FIG. 6 is a characteristic graph that defines the relationship between the standard excess air ratio and the control excess air ratio during idling.

FIG. 7 is a time chart showing changes in the control excess air ratio corresponding to the oxygen sensor output voltage.

FIG. 8 is a diagram illustrating the configuration of the present invention.

[Explanation of symbols]

1 ... Engine 5 ... Injector 11 ...
Oxygen sensor 30 ... Electronic control unit 50 ... Linearizer 51,
53 ... Correction linearizer 59 ... PID controller 61,
65 ... PI controller

Claims (1)

[Claims] 1. An oxygen sensor whose output suddenly changes in the vicinity of the stoichiometric air-fuel ratio, and a relationship correction characteristic which defines a correspondence relationship between the oxygen sensor output and a control air-fuel ratio which increases or decreases in accordance with an increase or decrease in the oxygen sensor output. The stored relationship correction characteristic storage means, the control air-fuel ratio calculation means for calculating the control air-fuel ratio corresponding to the oxygen sensor output in accordance with the stored relationship correction characteristics, the calculated control air-fuel ratio and the target. An air-fuel ratio deviation calculating means for calculating a deviation from the air-fuel ratio; and a controller for executing air-fuel ratio feedback control of the internal combustion engine based on the calculated deviation between the control air-fuel ratio and the target air-fuel ratio. In an air-fuel ratio control device for an internal combustion engine, a sensor abnormality determining means for determining an abnormality in the oxygen sensor output when a change amount of the oxygen sensor output per predetermined time is larger than a predetermined amount; When an abnormality in the oxygen sensor output is determined by the abnormality determination means, a sensor output correction means for correcting the oxygen sensor output is provided, and when the abnormality in the oxygen sensor output is determined, the control air-fuel ratio is set. An air-fuel ratio control device for an internal combustion engine, wherein the calculating means calculates a control air-fuel ratio corresponding to the corrected oxygen sensor output.