JPS63223347A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To attain target air-fuel ratio by using an air-fuel ratio sensor of bear output type and Z-characteristic output type, which is to be installed upstream a ternary catalyzer, and by using the sensor selectively either of linear output type or Z-characteristic output type according to the activated condition of the sensor element. CONSTITUTION:A ternary catalyzer CCRO in the exhaust passage is furnished at its upstream with an air-fuel ratio sensor 13, which takes either linear output characteristic with linear sensing of the air-fuel ratio in the No.1 operating condition or the Z-characteristic with sudden change of the output bordering the theoretical air-fuel ratio in No.2 operating condition. An activity judging means A is furnished to judge whether the element temp. of the air-fuel sensor 13 lies within a specific range, for ex. 300-600 deg.C. If yes, No.1 air-fuel ratio adjusting means B allows the air-fuel ratio sensor 13 to work as the one of Z-characteristic output type in No.2 operating condition, and if no, No.2 air-fuel ratio adjusting means C permits the sensor 13 to work as the one of linear output type in No.2 operating condition, and according to the output of the sensor 13 the air-fuel ratio is adjusted.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a linear output type front Z characteristic output type air-fuel ratio sensor (in this specification, an oxygen concentration sensor (02 sensor)) installed on the upstream side of a catalytic converter of an internal combustion engine. ) is installed to perform air-fuel ratio feed bank control using the output of this air-fuel ratio sensor.In addition, a Z-characteristic output type air-fuel ratio sensor is installed downstream of the catalytic converter to control the air-fuel ratio using the upstream air-fuel ratio sensor. The present invention relates to a double air-fuel ratio sensor system that performs air-fuel ratio feedback control using a downstream air-fuel ratio sensor in addition to feedback control.

[Problems to be solved by conventional technology and invention]

In the conventional single 02 sensor system, the 02 sensor that detects oxygen concentration is installed in the exhaust system as close as possible to the combustion chamber, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. Since the type with the Z-characteristic output shown in Figure 2, that is, the type in which the output changes suddenly at the stoichiometric air-fuel ratio (λ-1), is used, only the stoichiometric air-fuel ratio can be detected, and as a result, the air-fuel ratio feedbank During control, the controlled air-fuel ratio is usually the stoichiometric air-fuel ratio. In this case, it is possible to set the controlled air-fuel ratio to the lynch side or lean side by air-fuel ratio feedbank control by using asymmetric skip processing, asymmetric integral processing, asymmetric delay processing, changing the comparison voltage vR, etc. The fuel ratio cannot be accurately set to any rich air-fuel ratio or any lean air-fuel ratio. Therefore, if the control air-fuel ratio is set to the lynch side "slightly" during high load with a lot of +)N Ox emissions, 1i) HC, Co
iii) When setting the control air-fuel ratio to the "slightly" lean side during light loads with high emissions, iii) When setting the control air-fuel ratio to the "slightly" lean side during idling, when catalyst exhaust odor is likely to occur, and iv) When controlling during warm-up. When setting the air-fuel ratio to Lynch side, etc., the target air-fuel ratio cannot be obtained accurately,
As a result, this results in deterioration of emissions, deterioration of fuel efficiency, deterioration of drivability, or generation of abnormal odor from the catalyst exhaust.

Therefore, by switching the voltage applied to the 02 sensor, the 0□ sensor can be used as the Z-characteristic output type shown in Figure 2 and the linear output type (voltage application type) shown in Figure 3, for feedbank control of the stoichiometric air-fuel ratio. In addition, there is a system that enables feedbank control of an arbitrary rich air-fuel ratio or lean air-fuel ratio (see Japanese Patent Laid-Open No. 143108/1983).

The activation of the above-mentioned linear output type lid Z characteristic output type 0□ sensor is normally performed without distinguishing whether it is activated as a Z characteristic output type or whether it is activated as a linear output type.

However, if the 0□ sensor is a Z characteristic output type,
The 0□ sensor acts as a 02 concentration battery, and therefore, if the temperature of the 02 sensor element rises to the extent that an electromotive force can be generated, for example, 300°C or higher, Z is almost independent of the internal resistance of the element. Can generate characteristic output. On the other hand, when the O2 sensor is a linear output type, since the O2 sensor applies the O2 pumping action, the internal resistance of the ZrO□ electrolyte is greatly related to its output characteristics, and therefore the 0□ sensor element temperature is fairly high temperature, for example 600
Requires temperature above ℃.

However, as mentioned above, since the activation of the linear output type lid Z characteristic output type 0□ sensor is performed without distinguishing between the linear output type and the Z characteristic output type, it is not possible to use it as the Z characteristic output type. or not used regardless of the
Even though it is not activated as a linear output type, the air-fuel ratio feed puncture control by the 0□ sensor as a linear output type may be performed based on the inactive 0° sensor, and as a result, the air-fuel ratio correction amount is Over-correction still poses a problem in that it leads to deterioration of emissions, deterioration of fuel efficiency, deterioration of drivability, or generation of abnormal odor from the catalyst exhaust.

On the other hand, 0□ in the single 02 sensor system described above
Improving the accuracy of air-fuel ratio control is hindered by variations in sensor output characteristics. In order to compensate for variations in the output characteristics of the 0□ sensor, variations in parts such as fuel injection valves, and changes over time or aging, a second 02 sensor is provided downstream of the catalytic converter, and the air-fuel ratio is determined by the upstream 0□ sensor. In addition to feedback control, downstream 0. A double 02 sensor system that performs air-fuel ratio feedback control using sensors has already been proposed (reference: Japanese Patent Application Laid-open No. 1983
-48756). In this double 02 sensor system, although the 02 sensor installed downstream of the catalytic converter has a lower response speed than the upstream 02 sensor, it has the advantage of less variation in output characteristics for the following reasons. are doing.

(1) Downstream of the catalytic converter, the exhaust gas temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 02 sensor is small.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to an equilibrium state.

Therefore, as described above, by using air-fuel ratio feedback control (double 0□ sensor system) based on the outputs of the two 02 sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 02 sensor. In fact, as shown in Figure 4, in the single 02 sensor system, 0□
If the output characteristics of the sensor deteriorate, it will directly affect the exhaust emission characteristics, but with the double 02 sensor system, even if the output characteristics of the upstream 02 sensor deteriorate,
Exhaust emission characteristics are not deteriorated. That is, double 0
．． In the sensor system, good exhaust emissions are guaranteed as long as the downstream 02 sensor maintains stable output characteristics.

Even in the double 0□ sensor system described above, the upstream 0
By operating the two sensors as a linear output type lid Z characteristic output type, in addition to feed bank control of the stoichiometric air-fuel ratio, feedback control of an arbitrary rich air-fuel ratio or lean air-fuel ratio is also possible.1. Regarding the activation determination of the upstream 0□ sensor, there are the same problems as in the case of determining the activation of the 02 sensor in a single 02 sensor system.

Therefore, an object of the present invention is to provide a single air-fuel ratio sensor system and a double air-fuel ratio sensor system in which the activation of the air-fuel ratio sensor can be properly determined and a target air-fuel ratio can be accurately obtained.

[Means for solving problems]

A means for solving the above-mentioned problems is shown in FIG. 1A.

As shown in FIG. 1B.

FIG. 1A shows a single air/fuel ratio sensor system. That is, the three-way catalyst CGi installed in the exhaust passage of the internal combustion engine
An air-fuel ratio sensor is provided on the upstream side of o, which has a linear output characteristic that linearly detects the air-fuel ratio of the engine in a first operating state, and a Z-characteristic in which the output suddenly changes around the stoichiometric air-fuel ratio in a second operating state. It is.

The activity determining means determines whether the element temperature of the air-fuel ratio sensor is within a predetermined range, for example, 300 to 600°C. As a result, when the element temperature of the air-fuel ratio sensor is within the predetermined range of 300 to 600°C, the first air-fuel ratio adjustment means adjusts the air-fuel ratio sensor to the second air-fuel ratio sensor.
The air-fuel ratio of the engine is adjusted according to the output (1) of the air-fuel ratio sensor by operating as a two-characteristic output type in the control state of The air-fuel ratio adjusting means causes the air-fuel ratio sensor to act as a linear output type in the second operation state, and adjusts the air-fuel ratio of the engine in accordance with the output (1) of the air-fuel ratio sensor.

FIG. 1B shows a dual air/fuel ratio sensor system.

That is, a Z-characteristic output type downstream air-fuel ratio sensor is added to the components shown in FIG. 1A. As a result, when the element temperature of the upstream air-fuel ratio sensor is, for example, 300 to 600°C, the first air-fuel ratio adjustment means outputs the output (■) of the upstream air-fuel ratio sensor as a Z characteristic output type in the second operating state; The air-fuel ratio of the engine is adjusted according to the output v2 of the downstream air-fuel ratio sensor as a Z-characteristic output type, and when the element temperature of the upstream air-fuel ratio sensor is, for example, 600° C. or higher, the second air-fuel ratio adjusting means In the first operating state, the air-fuel ratio of the engine is adjusted in accordance with the output V of the upstream air-fuel ratio sensor as a linear output type and the output (2) of the downstream air-fuel ratio sensor as a Z-characteristic output type.

[For production]

According to the above means, when the upstream air-fuel ratio sensor is at a relatively low temperature (300 to 600° C.), the upstream air-fuel ratio sensor is determined to be activated for Z characteristic output;
As a result, the first air-fuel ratio adjustment means enables stoichiometric air-fuel ratio feedback control (λ-1), and when the upstream air-fuel ratio sensor is at a relatively high temperature (600°C or higher)
, the upstream air-fuel ratio sensor is determined to be activated for linear output, and as a result, the second air-fuel ratio adjustment means adjusts the stoichiometric air-fuel ratio (λ=1) and the non-stoichiometric air-fuel ratio (λ×1.λ). >1) Feedback control becomes possible.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 5 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. In FIG. 4, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The airflow meter 3 directly measures the amount of intake air, and includes a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided. The pulse signals of these rank angle sensors 5 and 6 are supplied to the human output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is sent to the CPU 1.
．． 03 interrupt terminal.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake port for each cylinder.

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body 1. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101.

The exhaust system downstream of the exhaust manifold 11 is provided with a catalyst converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, Co, and NOX in the exhaust gas.

The exhaust manifold 11 includes a catalytic converter 1.
On the upstream side of the sensor 2, a built-in 0□ sensor 13 is provided which is a linear output type and Z characteristic output type element temperature sensor 13a. That is, when no voltage is applied, the upstream side 0□
The sensor 13 has output characteristics shown in FIG. 3, and the control circuit 10 generates different output voltages to the A/D converter 101 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. On the other hand, when voltage is applied, the upstream 02 sensor 13 has the output characteristics shown in FIG. 6, and the upstream 0□ sensor 13 generates a larger output current ■ as the air-fuel ratio becomes leaner. , this output current I is the current/voltage conversion circuit 1
13 (for example, a resistor), the voltage is converted into a voltage 1, and then supplied to the A/D converter 101. Voltage application to the upstream 0□ sensor 13 is performed by the D/A converter 111 and switch 112 of the control circuit 10. That is, when the upstream side 02 sensor 13 is operated as a Z characteristic output type, the switch 112 is opened and the upstream side 02 sensor 13 is operated as a Z characteristic output type.
The output ■1 (range of 0 to 1■) is the A/D converter 101
The data is A/D converted and captured. On the other hand, the upstream side o
When the 02 sensor 13 is operated as a linear output type, the switch 112 is closed and the output voltage of the D/A converter 111 is applied to the upstream 02 sensor 13. At this time, the output current of the upstream 0□ sensor 13 is the current /voltage conversion circuit 11
Voltage V by 3.

(range of 0 to 5V), and further A/D converter 1
The signal is A/D converted and taken in by 01.

Note that the upstream O2 sensor 13 is supplied with a constant voltage, for example, 0.
Although 2 to 0.5 V may be applied, this applied voltage is adjusted to the D/A converter 111 according to the air-fuel ratio range for high-precision control.
By changing the digital value of , the change is made in two stages. That is, when λ≦1, 0.25V is applied, and when λ>1, 0.5V is applied. in this case,
The output characteristics of the upstream 02 sensor 13 are as shown in FIG. Further, in the exhaust pipe 14 on the downstream side of the catalytic converter 12, a Z characteristic output type O2 sensor 15 having the output characteristics shown in FIG.
is provided.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for determining whether the throttle valve 16 is fully closed, and this output signal is sent to the control circuit 100.
It is supplied to the input/output interface 102.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, a D/A converter 111,
In addition to the switch 112 and the current/voltage conversion circuit 113, R
OM 104. RAM 105, bank up l? A
M 106, a clock generation circuit 107, and the like are provided.

Further, in the control circuit IO, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and flip-flop 109
Also cents. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and finally its carrier terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. In other words, the above fuel injection amount TA
The fuel injection valve 7 is energized by U, and therefore the fuel injection amount T
An amount of fuel corresponding to the AU is sent to the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 1.
When the A/D conversion of 01 is completed, the input/output interface 10
2 receives a pulse signal from the crank angle sensor 6, receives an interrupt signal from the clock generation circuit 107, etc.

The intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are taken in by an A/D conversion routine executed at predetermined intervals. It is stored in a predetermined area of AM105. That is, data Q and THW in RAM 105 are updated at predetermined intervals. Also,
The rotational speed data Ne is 30° CA of the crank angle sensor 6.
Is calculated by each interrupt? It is stored in a predetermined area of AM 105.

When the upstream O2 sensor 13 is operated as a linear output type, the comparison reference current II corresponding to the target air-fuel ratio (that is, the comparison voltage VRL in this case also) is set as shown in FIG. control to achieve the target air-fuel ratio.

FIG. 7A shows an air-fuel ratio feed condition determination routine, which is executed every predetermined period of time, for example, every several tens of meters. In the routine of FIG. 7A, two active flags FB1. FB
2 is set. That is, the activation flag FBI: upstream side 0
) (in particular, enables execution of stoichiometric air-fuel ratio feedbank control using the output V of the upstream 02 sensor 13)
; Activation flag FB2: The upstream 02 sensor 13 indicates an active state as a linear output type, and thereby enables execution of stoichiometric air-fuel ratio, non-stoichiometric air-fuel ratio, and stoichiometric air-fuel ratio feedback control (λ≦1 and λ〉■). Enabled, is set.

In step 701, the temperature of the element temperature sensor 13a of the upstream O2 sensor 13 is A/D converted and taken in.
At 02, it is determined based on the element temperature whether the upstream 02 sensor 13 is active as a Z-characteristic output type or whether it is active as a linear output type. As a result, if the element temperature is less than 300°C, the upstream 02 sensor 13 is considered inactive both as a Z-characteristic output type and as a linear output type, and in step 703,
At step 704, the activation flag FB1. Both FB2 are reset (“0”).

Furthermore, if the element temperature is in the range of 300 to 600°C, the upstream 02 sensor 13 is considered to be activated as a Z characteristic output type, and the activation flag FBI is set to 1'' in step 705, and the process proceeds to step 706. The activation flag FB2 is reset (“0”) at step 707.Furthermore, when the element temperature exceeds 600°C, the upstream 0□ sensor 13 is considered to be activated as a linear output type, and the activation flag is reset at step 707. To reset the FBI, set the activation flag FB2 to 1 (“1”) using the steering knob 708.
. In this case, the activation flag FB2 is the activation flag FB2.
Set with priority over I.

This routine then ends in step 709.

In addition, in the routine of FIG. 7A, the upstream 0□ sensor 13
Although the activation of the engine is determined based on the element temperature, it may also be determined based on the engine cooling water temperature THW or oil temperature.

FIG. 7B shows a modification of FIG. 7A, in which the activation of the upstream 02 sensor 13 is determined based on the output 1 of the upstream 02 sensor 13. In this case, the activation as a Z-characteristic output type is determined based on whether the output vl of the upstream O2 sensor 13 once crosses a reference value, for example, 0.35 V when no voltage is applied to the upstream O2 sensor 13. However, activation as a linear output type is determined when a constant voltage, e.g. ), the determination is made based on whether the output of the upstream 02 sensor 13 is a certain voltage or higher, for example 5■ or higher.

First, it is assumed that the upstream 02 sensor 13 is not activated as either a Z-characteristic output type or a linear output type, that is, the activation flag FBLFB2 is both set to O''. In this case, the Z-characteristic output type is activated in steps 713-715. Determine whether it is active as an output type.

That is, in step 713, the switch 112 is opened to turn off the voltage applied to the upstream 0□ sensor 13, and in step 714, the output V of the upstream 02 sensor 13 is changed to A/
D-convert and import, in step 715 V+ > 0.3
It is determined whether the voltage is 5V or not. As a result, if V≦0.35V, it is assumed that the upstream 02 sensor 13 is not activated as a Z-characteristic output type.

In this case, it is assumed that the upstream 02 sensor 13 is not activated even if it is a linear output type. Therefore, flow proceeds directly to step 723 and flags FB1. FB2 remains unchanged and holds "0".

On the other hand, if V is >0.35V in step 715,
It is assumed that the upstream 0□ sensor 13 is activated as a Z-characteristic output type, and the process proceeds to steps 716 to 718, where it is determined whether it is activated as a linear output type.

In step 716, it is determined whether or not the fuel is being cut, and as a result, if the fuel is not being cut, the step 719,
Proceeding to 720, only the flag FBI is set to enable stoichiometric air-fuel ratio feedbank control (λ-1). Conversely, if fuel is being cut, step 717,
In step 718, it is determined whether the output is substantially active as a linear output type. That is, in step 717, the D/A converter 111
While setting the output voltage of the switch 112 to 0.5■
is closed and 0.5 V is applied to the upstream 0□ sensor 13. Next, in step 718, the output ■1 of the upstream 02 sensor 13 is A/D converted and taken in, and in step 719, it is determined whether vl<4■. As a result, if v<4v, it is assumed that the upstream O2 sensor 13 is activated as a Z-characteristic output type but not activated as a linear output type, and the process proceeds to steps 720 and 721 to set the activation flag. Only FBI is set to enable stoichiometric air-fuel ratio feedbank control (λ-1).

On the other hand, if ■1≧4■, it is assumed that the upstream 0□ sensor 13 is activated as a linear output type, and step 7
At 22.723, only the activation flag FB2 is set to enable feedback control of the stoichiometric air-fuel ratio and the non-stoichiometric air-fuel ratio (λ≦1°λ>1). In this case as well, the cent of flag FB2 has priority over the setting of flag FBI.

The routine then ends at step 724.

In FIG. 7B, after it is determined that the upstream 02 sensor 13 has been activated as a Z-characteristic output type, (
When the routine of FIG. 7 is executed again, the activation as a linear output type is determined (steps 716 to 716).
723) is performed.

Moreover, if the routine of FIG. 7 is executed again after the upstream 02 sensor 13 is once activated as a linear output type (FB2-"1"), no activation determination is performed.

In step 801, it is determined whether the closed loop (feedback) condition of the stoichiometric air-fuel ratio by the upstream 0□ sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value (e.g. 60°C), during engine startup, during engine startup,
During warm-up increase, acceleration increase (asynchronous injection), power increase, fuel cut (i.e., idle switch 17 is on (LL-“1”) and rotational speed Ne is above a predetermined value), etc., all are closed loop conditions. is not satisfied, and the closed-loop condition is satisfied in other cases. If the closed loop condition is not satisfied, the process proceeds to step 804, and if the closed loop condition is satisfied, the process proceeds to step 802.

In step 802, it is determined whether or not the activation flag FBI is 1". As a result, when FBI-"0'', the process proceeds to step 805, and it is determined whether or not FB2="1''. As a result, when FB2 is ``1'', the process proceeds to step 806, where the feed hack control of the stoichiometric air-fuel ratio (λ-1) is also performed. and when FB2="0", the process proceeds to step 807 and performs open loop control, that is, RAM 10
5, the intake air amount data Q and rotational speed data Ne are read out, and the fuel injection amount τ is calculated by interpolation using the two-dimensional map τso stored in the backup RAM 106. In this way, in step 801, the closed loop condition by the upstream 02 sensor 13 is satisfied and the activation flags FBI, FB2
If either one of is “1”, the stoichiometric air-fuel ratio (λ-1
) feed bank control is performed.

On the other hand, in step 804, it is controlled whether the control is rich control (λ<1) or lean control (λ>1).

For example, as mentioned above, when enrichment is requested during high load with a lot of NOx emissions, HC.

When a lean request is made during a light load when CO emissions are high, a lean request is made during idling when a catalyst exhaust odor is likely to occur, a rich request is made during warm-up, etc., the process proceeds to step 805, and FB2="1". ” to determine whether or not. As a result, when FB2-“1”, step 8
Feedback control of the non-stoichiometric air-fuel ratio (λ<1.λ>■) is performed in step 06, and when FB2="0", step 8 is performed.
Open loop control is performed at step 07.

The routine then ends at step 808.

FIG. 9 shows a detailed routine of step 803 in FIG.

In step 901, the switch 112 is opened and the upstream side
□The sensor 13 is operated as a Z characteristic output type.

In step 902, the output V1 of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 903 it is determined whether or not V+ is less than the comparison voltage VR+ corresponding to the stoichiometric air-fuel ratio, for example 0.45V. In other words, it determines whether the air-fuel ratio is rich or lean. If lean (■1≦VRI), it is determined in step 904 whether the delay counter CDLY 1 is positive or not, and if CDLY 1 > O, step 90
In step 5, CDLY 1 is set to O, and the process proceeds to step 906.

In steps 907 and 908, delay counter CDL
Y1 is guarded at the minimum value TDL, and in this case, when the delay counter CDLY1 reaches the minimum value TDL, the air-fuel ratio flag F1 is set to "0" (lean) in step 909. In addition, the minimum value TDL is upstream side 0□sensor 1
It is a lean delay time for maintaining the determination that the rich state is present even if there is a change from rich to lean in the output V1 of No. 3, and is defined as a negative value. On the other hand, if it is rich (V+>VRI), it is determined in step 910 whether the delay counter C1)LY1 is negative or not, and CI)
If LY 1 < O, in step 911 CDLY
1 is set to 0, and the process proceeds to step 912. Step 913
, 914, the delay counter CDLY 1 is guarded with the maximum value TDR;
When Y1 reaches the maximum value TDR, step 91
At step 5, the air-fuel ratio flag F1 is set to "1" (rich).

Note that the maximum value TDR is a delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream 02 sensor 13, and is defined as a positive value. .

In step 916, it is determined whether the sign of the air-fuel ratio flag F1 has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, then in step 917, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F1. If it is a reversal from rich to lean, pAps4-p奸S + R2H is increased in a skip manner in step 918, and conversely, if it is a reversal from lean to rich, FAFS 4-PAFS is increased in step 819.
-R3L and decrease in a skip manner. In other words, skip processing is performed. If the sign of the air-fuel ratio flag F1 is not inverted in step 916, step 920.921.9
Integration processing is performed at 22. That is, in step 920, it is determined whether Fl-“0” or not, and if Fl-“0” (lean), PAFS 4-FAF is determined in step 921.
S + KIR, on the other hand, Fl-“l” (rich)
If so, in step 922 FAFS 4-FAFS
-KIL. Here, the integral constant KIR (KIL) is set sufficiently small compared to the skip constants R5II, R3[, that is, KIR (KIL) < R2
H(R3L). Therefore, step 921 gradually increases the fuel injection amount in the lean state (F1="0"),
Step 922 gradually reduces the fuel injection amount in the rich state (Fl-"l"). Step 918°919,9
The air-fuel ratio correction coefficient FAFS calculated at 21.922 is guarded at a maximum value, for example, 1.2, and at a minimum value, for example, 0.8, in a step not shown. As a result, for some reason, the air-fuel ratio correction coefficient FAFS
When becomes too small or too large,
The engine's air-fuel ratio is controlled using this value to prevent over-lean and over-rich conditions.

In step 923, the intake air amount data Q and the rotational speed data Ne are read from the RAM 105, and a two-dimensional map τ5o(Q) is read from the backup RAM 106.

The basic injection amount τ5o is interpolated using τ5o, and in step 824, the fuel injection amount τ is calculated as follows: τ←τ. - Calculate using FAPS and store in 126M 105. Next, in step 925, the smoothed value of the air-fuel ratio correction coefficient PAFS is calculated, and in step 926, the basic injection amount τ, is calculated.

is set as τso←τ5o−FAFS, and in step 927, the backup RAM 106
The two-dimensional map τ,. Rewrite (Q, Ne). In other words,
The basic injection amount τ,0 is learned as a two-dimensional map.

The routine then ends at step 928.

(3I) FIG. 10 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 9. When the air-fuel ratio signal A/F for determining rich and lean is obtained from the output V of the upstream O2 sensor 13 as shown in FIG. 10 (^), the delay counter CDLY 1 is set as shown in FIG. , is counted up in the rich state and counted down in the lean state.As a result, a delayed air-fuel ratio signal A/F' (corresponding to flag F1) is formed as shown in FIG. 10 [C]. For example, even if the air-fuel ratio signal A/F changes from lean to rich at time t1, the delayed air-fuel ratio signal A/F' is held lean for the rich delay time TDR, and then becomes rich at time t2. Changes to Even if the air-fuel ratio signal A/F changes from rich to lean at time t3, the delayed air-fuel ratio signal A/F' remains rich for the lean delay time (-TDL) and then changes to lean at time t4. Changes to lean. However, the air-fuel ratio signal A/F
Is time t5+t6+j? Rich delay time TDR
If it reverses in a shorter period, the delay counter CDLY
It takes time for TDR to reach the maximum value, and as a result,
At time tll, the air-fuel ratio signal A/F' after the delay process is inverted. In other words, the air-fuel ratio signal A/F' after the delay processing
is more stable than the air-fuel ratio signal A/F before the delay processing.

In this way, the stable air-fuel ratio signal A/F' after the delay processing
Based on the air-fuel ratio correction coefficient FA shown in Figure 10 (Dl)
FS is obtained.

Next, the second air-fuel ratio feedbank control by the downstream 0□ sensor I5 will be explained. The second air-fuel ratio feedback control includes skip amounts R3R and R3L as first air-fuel ratio feedback control constants, and an integral constant KI.
There is a system in which R, KIL, delay times TDR, TDL, or a comparison voltage Vll+ of the output V1 of the upstream 0□ sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAF 2 is introduced.

For example, if the rich skip amount R3R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount R3L is decreased, the control air-fuel ratio can be shifted to the rich side.On the other hand, if the lean skip amount R3L is increased, the control air-fuel ratio can be shifted to the rich side. , the control air-fuel ratio can be shifted to the lean side, and even if the rich skip amount R3R is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount R3R and the lean skip amount R3L according to the output of the downstream 02 sensor 15. Also, the Ricci integral constant KI
By increasing R, the control air-fuel ratio can be shifted to the rich side,
In addition, the control air-fuel ratio can be shifted to the rich side even if the lean integral constant KIL is decreased, and on the other hand, the control air-fuel ratio can be shifted to the lean side by increasing the lean integral constant KIL. The controlled air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KIR and the lean integral constant KIL according to the output of the downstream side 02 sensor 15. By setting rich delay time TDR > lean delay time (-TDL), the control air-fuel ratio can shift to the rich side, and conversely, if lean delay time (-TDL) > rich delay time (T D
R), the controlled air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR and TDL according to the output of the downstream 02 sensor 15. Furthermore, if the comparison voltage VRI is increased, the control air-fuel ratio can be shifted to the Lynch side, and the comparison voltage Vll+
By decreasing , the control air-fuel ratio can be shifted to the lean side.

Therefore, by correcting the comparison voltage VRI according to the output of the downstream side 02 sensor 15, the air-fuel ratio can be controlled.

Making the skip amount, integral constant, delay time, and comparison voltage variable by the downstream 0□ sensor has its own advantages. For example, the delay time allows for very delicate air-fuel ratio adjustment, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedback period unlike the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

A double 02 sensor system in which the skip amount as an air-fuel ratio feed bank control constant is made variable will be described with reference to FIG.

FIG. 11 shows a second air-fuel ratio feed bank control routine that calculates skip amounts R3R and R3L based on the output ■2 of the downstream 0□ sensor 15 for a predetermined period of time, for example, 1. executed every time. In steps 1101 to 1103, it is determined whether the downstream O2 sensor 15 is in a closed loop condition. For example, in addition to the failure of the closed loop condition by the upstream 0□ sensor 13 (step 1101) and the activation of the upstream 02 sensor 13 (steps 1102 and 1103), when the cooling water temperature THW is below a predetermined value (for example, 70°C) ( Step 1102), when the throttle valve 16 is fully closed (LL-“1”) (Step 1103), when the output 2 of the downstream side 02 sensor 15 has never crossed the reference value (Step 1104), etc. The closed loop condition is not satisfied, and the closed loop condition is satisfied in other cases.

If the condition is not a closed loop condition, the process directly proceeds to step 1113.

In this case, RSR and R3L are held at the values immediately before the end of the closed loop. Note that RSR and R3L are average values or learned values during closed loop control (values of bank amplifier RAM 106).
But that's fine.

If the closed loop condition is satisfied by the downstream 0□ sensor 15, the process advances to step 1107. In step 1107, the output ■2 of the downstream 0□ sensor 15 is A/D converted and taken in. In step 1108, it is determined whether or not ■2 is equal to the comparison voltage VR corresponding to the stoichiometric air-fuel ratio, for example, 0.55 V or less. In other words, it is determined whether the air-fuel ratio is rich or lean compared to the stoichiometric air-fuel ratio. As a result, in step 1108, ■2≦VR
If 2 (lean), the process proceeds to steps 1109 and 1110, and on the other hand, if V2>V and □ (su, 7chi), the process proceeds to steps 1111 and 1112.

In step 1109, RSR4-R3R+ΔR3 (constant value) is set, that is, the rich skip amount R3R is increased to shift the air-fuel ratio to the rich side, and further, in step 1
At step 110, R3L←R3L-ΔR3 is set, that is, the lean skip amount R3L is decreased and the air-fuel ratio is shifted to the R/R side.

On the other hand, when Vz > VH2 (rich), in step 1111, RSR4-1? SR-ΔR3, that is, the rich skip amount R3R is decreased to increase the air-fuel ratio.
Then, in step 1112, the R3L
4-R5L+ΔR3, that is, the lean skip amount R3L is increased to shift the air-fuel ratio to the lean side.

The RSR and R3L calculated as described above are guarded with a maximum value of 7.5% and a minimum value of 2.5%, and then RA
M105, and the routine ends at step 1113.

In addition, FAPS calculated during air-fuel ratio feedback
, RSR, R3L are once changed to other values FAFS', R
SR'.

R3L' and stored in the back amplifier RAM 106. By using these values during air-fuel ratio open-loop control, for example, drivability dynamics can be determined at restart, immediately after startup, or when the 02 sensor is inactive. It is also useful for improving sex. The minimum value MIN is a value at a level that does not impair transient followability, and the maximum value MAX is a value at a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

FIG. 12 is a detailed routine of step 806 in FIG.

In step 1201, rich control (including the stoichiometric air-fuel ratio) is performed.
λ≦1) or lean control (λ>1) is determined based on predetermined operating parameters such as data Q, Ne, THW, etc. As a result, if it is rich control (λ≦1), the process proceeds to steps 1202 to 1205, and if it is lean control (λ>
1), proceed to steps 1206-1209.

In step 1202, the intake air amount data Q and the rotational speed data Ne are read from the RAM 105, and are stored in the ROM1.
A rich air-fuel ratio correction coefficient KRICI+ (≧1) is calculated by interpolation using the two-dimensional map stored in 04. next,
In step 1203, the rich air-fuel ratio correction coefficient MRIC
The comparison voltage VIIL of the upstream side 02 sensor 13 as a linear output type is calculated using the one-dimensional map stored in the ROM 104 according to H, and further, in step 1204, the output voltage of the D/A converter 111 is calculated. is set to 0.25V and the switch 112 is closed to connect the upstream Ot sensor 13.
acts as a linear output type and outputs 0.25V to 0 on the upstream side.
□Apply to the sensor 13. And step 1205
Let us now refer to them as FAPR and FAF.

On the other hand, in step 1206, intake air amount data Q and rotational speed data Ne are read from the RAM 105.
9) A lean air-fuel ratio correction coefficient KLEAN (<1) is calculated by interpolation using the two-dimensional map stored in the ROM 104.

Next, in step 1207, the lean air-fuel ratio correction coefficient K
The upstream side 0□ sensor 1 as a linear output type uses the one-dimensional map stored in the ROM 104 according to LEAN.
Step 120
At step 8, the output voltage of the D/A converter 111 is set to 0.5■, the switch 112 is closed, and the upstream side 0□ sensor 1
Apply 0.5v to 3. Then, in step 1209, F A F L and FAF are set.

In step 1210, the upstream side 0 as a linear output type
2 sensor 13 is A/D converted and taken in, and in step 1211, ■1 is the comparison voltage V! corresponding to the target air-fuel ratio!
It is determined whether or not it is greater than or equal to I+. In other words, it is determined whether the air-fuel ratio is richer or leaner than the target air-fuel ratio.

If lean (■, ≧VRL), it is determined in step 1212 whether the delay counter CDLY 2 is positive or not;
If CDLY 2 > O, in step 1213
Set DLY 2 to 0 and proceed to step 1214. In steps 1215 and 1216, the delay counter CDL
Y2 is guarded at the minimum value TDL, and in this case, when the delay counter CDLY2 reaches the minimum value TDL, the air-fuel ratio flag F2 is set to "0" in step 7 1217.
(lean).

Note that the minimum value TDL is the output vI of the upstream O2 sensor 13.
It is a lean delay time for maintaining the judgment that the state is rich even if there is a change from rich to lean, and is defined as a negative value.

On the other hand, if it is rich (V+ < V+++), it is determined in step 1218 whether the delay counter CDLY 2 is negative or not, and if CDLY 2 < O, it is determined in step 12
19 near CDLY2 is set to O, and the process proceeds to step 1221. In steps 1221 and 1222, the delay counter CDLY 2 is guarded at the maximum value TDR. In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F2 is set to "1" in step 1223.
(Rich).

The maximum value TDR is a rich delay time for maintaining the determination that the lean state is present even if there is a change from lean to rich in the output of the upstream o2 sensor 13, and is defined as a positive value. Ru.

In step 1224, it is determined whether the sign of the air-fuel ratio flag F2 (old) has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, in step 1225, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the air-fuel ratio flag F2. If it is a reversal from rich to lean, in step 1226 FAF←FAF + R2H
On the contrary, if it is a reversal from lean to rich, FAF 4-FA is increased in step 1227.
Decrease in skips with F-R5L. In other words, skip processing is performed. At step 1224, the air-fuel ratio flag F2
If the sign of is not reversed, step 1228.12
29. Integration processing is performed at 1230. That is, in step 1228, it is determined whether F2="0" or not, and F2-"
0” (lean), FAF in step 1229.
4-FAF+KIR, and on the other hand, if F2="1" (rich), FAF -FAF at step 1230.
-KIL. Here, the integral constant KIR (KIL) is set sufficiently small compared to the skip constants R3R and R5L, that is, KIR (KIL) < R2H (R3L
). Therefore, step 1229 is in the lean state (F
2-“0”), the fuel injection amount is gradually increased, and step 123o is a rich state (F2-“1”), and the fuel injection amount is gradually decreased. Step 1226.1227.12
The air-fuel ratio correction coefficient FAF calculated at 29.1230 is guarded at a maximum value, for example, 1.2, and at a minimum value, for example, 0.8, in a step not shown. As a result, if the air-fuel ratio correction coefficient FAF becomes too small or too large for some reason, the air-fuel ratio of the engine is controlled using that value to prevent overlean or overrich conditions.

In step 1231, it is again determined whether the control is rich control (λ≦1) or lean control (λ>■) including the stoichiometric air-fuel ratio. If rich control (λ≦1), steps 1232 to 123
Proceed to step 4, and if lean control (λ>1), step 12
Proceed to 35-1237.

In step 1232, the FAF is set to FAFR, and in step 1233, the intake air amount data Q and the rotational speed data Ne are read from the RAM 105, and the hackup R is read out.
A two-dimensional map τ, stored in AM 106.

(The basic injection amount τ, 0 is calculated by interpolation using Q, Ne >. Next, in step 1234, the fuel injection amount τ is calculated by τ ← τ, .・FAFR-KRICI and stored in the RAM 105. .

On the other hand, in step 1235, FAF is set to FAFR;
In step 1236, the intake air amount data Q and the rotational speed data Ne are read from the RAM 105, and the two-dimensional map τ stored in the backup RAM 106 is
. The basic injection amount τ3o is calculated by interpolation using (Q, Ne). Next, in step 1237, the fuel injection amount τ is set as ←τ. - Calculate by FAFL -KLEAN and store in RAM 105.

The routine then ends at step 1238.

FIG. 13 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, 360° CA.

In step 1301, step 807 in FIG.
The injection amount τ calculated in step 1234 or 1237 in the figure is input to the down counter 108 and the flip-flop 109 is input to start fuel injection. The routine then ends at step 1302. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carrier load signal of the down counter 10 days, and the fuel injection ends.

Figure 14 is Figure 7B, Figure 8, Figure 9, Figure 11-1.
4 is a timing diagram for supplementary explanation of the flowchart in FIG. 3. FIG. Before time t, the upstream 0□ sensor 13 is inactive both as a Z-characteristic output type and as a linear output type (FBI=FB2="0"), so open-loop control is performed.

Next, time 1. When the output V of the upstream 0□ sensor 13 crosses 0.35V (corresponding to the element temperature of 300°C), the upstream 02 sensor 13 is determined to be active as a Z characteristic output type, and as a result, the activation flag FBI is set to "1". At this time, if the other closed loop conditions also hold true (45), then the upstream O2 sensor 13 as a Z characteristic output type
Air-fuel ratio feed-hack control of the stoichiometric air-fuel ratio (λ=1) is performed in accordance with the output ■. In addition, at this time, the downstream side 0
If the closed loop condition by the □ sensor 15 is also satisfied, the stoichiometric air-fuel ratio feed-hack control is performed also in response to the output signal V2 of the downstream 02 sensor 15, and therefore the function of the double 0□ sensor system is exhibited.

From time t2 to t3, fuel is being cut. Therefore, the output V2 of the downstream side 02 sensor 15 is lean (low level).
becomes. At this time, if the upstream O2 sensor 13 is activated as a linear output type, that is, the output V1 of the upstream O2 sensor 13 exceeds 4■ (equivalent to an element temperature of 600°C),
As a result, the activation flag FBI (-"1") is switched to the activation flag FB2 (-1"), and air-fuel ratio feedback control is performed according to the output v1 of the upstream 02 sensor 13 as a linear output type.

After time t3, flag FB2 is 1'' and λ-1
．． λ〈1. If other closed loop conditions for either λ〉■ are also satisfied, the upstream side 02 sensor 1 of the linear output type
Feed bank control of an arbitrary air-fuel ratio is performed according to the output v1 of No. 3. For example, time t3-t4+jS-t6
Now, λ-1 air-fuel ratio feed hack control, time t4~
At t5, air-fuel ratio feedbank control with λ<1, time t
, ~t, air-fuel ratio feedbank control with λ>1 is performed.

Note that the air-fuel ratio feedback control shown in FIG. 9 is performed every 4 ms, and the air-fuel ratio feedback control shown in FIG. This is because the control by the downstream 02 sensor, which has poor responsiveness, is performed as a secondary control.

It is also applicable to a double 0° sensor system in which other control constants in the air-fuel ratio feedback control by the upstream 02 sensor, such as the integral constant, delay time, and comparison voltage VRI of the upstream 02 sensor, are corrected by the output of the downstream 02 sensor. , and double 02 which also introduces a second air-fuel ratio correction factor.
The present invention can also be applied to sensor systems. Moreover, controllability can be improved by simultaneously controlling two of the skip amount, integral constant, and delay time. Furthermore, one of the skip amounts R3R and R5L can be fixed and only the other variable, one of the integral constants KIR and KIL can be fixed and only the other variable, or the maximum delay time can be It is also possible to fix one of TDR and TDL and make the other variable.

Furthermore, although the embodiments described above have shown a double 0□ sensor system, the present invention may also be applied to a single 02 sensor system.

Further, instead of the air flow meter, a Karman vortex sensor, a heat wire sensor, or the like may be used as the intake air amount sensor.

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a capretor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric link bleed air control pulp adjusts the amount of air bleed from the carburetor to control the air-fuel ratio in the main system passage. The present invention can also be applied to systems that control the air-fuel ratio by introducing atmospheric air into the slow system passage, systems that adjust the amount of secondary air sent to the exhaust system of an engine, and the like.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, since a linear output type is used as the upstream air-fuel ratio sensor, it is possible to accurately obtain any target air-fuel ratio, and moreover, it is possible to accurately determine the activity of the upstream air-fuel ratio sensor. If done properly, it will help reduce exhaust emissions, improve fuel efficiency, improve drivability, and reduce abnormal odors from catalyst exhaust.

[Brief explanation of the drawing]

Fig. 1 is an overall block diagram for explaining the present invention in detail, Fig. 2, Fig. 3, Fig. 6 is an output characteristic diagram of the 02 sensor, and Fig. 4 is a single 02 sensor system and a double 0□.
Fig. 5 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention; Fig. 7A, Fig. 7B, Fig. 8, Fig. 9; , Fig. 11, 1st
2 and 13 are flowcharts for explaining the operation of the control circuit in FIG. 5, FIG. 1O is a timing diagram for supplementary explanation of the flowchart in FIG. 9, and FIG. Fig. 9, Fig. 11, Fig. 1
14 is a timing diagram for supplementary explanation of the flowcharts in FIGS. 2 and 13. FIG. DESCRIPTION OF SYMBOLS 1... Engine body, 3... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 12... Catalytic converter, 13... Upstream side (first) 0□ sensor, 15... downstream (second) 02 sensor, 17... idle switch.

Claims (1)

[Claims] 1. A three-way catalyst provided in an exhaust passage of an internal combustion engine; and a three-way catalyst provided in an upstream exhaust passage of the three-way catalyst, which linearly adjusts the air-fuel ratio of the engine in a first operating state. An air-fuel ratio sensor having a linear output characteristic to be detected and a Z-characteristic in which the output changes suddenly at the stoichiometric air-fuel ratio in a second operating state; and an activation determining means for determining whether the element temperature of the air-fuel ratio sensor is within a predetermined range. and a first adjusting the air-fuel ratio of the engine according to the output of the air-fuel ratio sensor by operating the air-fuel ratio sensor in the second operating state when the element temperature of the air-fuel ratio sensor is within the predetermined range. an air-fuel ratio adjusting means for controlling the air-fuel ratio of the engine according to the output of the air-fuel ratio sensor by operating the air-fuel ratio sensor in the first operating state when the element temperature of the air-fuel ratio sensor is above the predetermined range; An air-fuel ratio control device for an internal combustion engine, comprising: second air-fuel ratio adjusting means for adjusting a fuel ratio. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the activity determining means detects the element temperature of the air-fuel ratio sensor based on the cooling water temperature of the engine. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the activity determining means detects the element temperature of the air-fuel ratio sensor based on the oil temperature of the engine. 4. The activation determining means: a first determining means for determining whether the output of the air-fuel ratio sensor in the second operation state is equal to or higher than a first predetermined value; and the first operation during fuel cut. A second step for determining whether the output of the air-fuel ratio sensor in the state is equal to or less than a second predetermined value.
and determining means for determining that the output of the air-fuel ratio sensor is within the predetermined range when the output of the air-fuel ratio sensor is greater than or equal to the first predetermined value and less than or equal to the second predetermined value. An air-fuel ratio control device for an internal combustion engine according to claim 1. 5. A three-way catalyst provided in the exhaust passage of the internal combustion engine; a linear output characteristic provided in the exhaust passage upstream of the three-way catalyst to linearly detect the air-fuel ratio of the engine in a first operating state; an upstream air-fuel ratio sensor having a Z characteristic in which the output suddenly changes after reaching the stoichiometric air-fuel ratio in a second operating state; and a Z sensor installed in the exhaust passage downstream of the three-way catalyst to detect the air-fuel ratio of the engine. a characteristic output type downstream air-fuel ratio sensor; an activation determination means for determining whether or not an element temperature of the upstream air-fuel ratio sensor is within a predetermined range; a first air-fuel ratio that operates the upstream air-fuel ratio sensor in the second operating state to adjust the air-fuel ratio of the engine according to the output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor; an adjusting means; when an element temperature of the upstream air-fuel ratio sensor is above the predetermined range, the upstream air-fuel ratio sensor is operated in the first operating state to adjust the output of the upstream air-fuel ratio sensor and the downstream side; An air-fuel ratio control device for an internal combustion engine, comprising: second air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the output of an air-fuel ratio sensor. 7. The air-fuel ratio control device for an internal combustion engine according to claim 6, wherein the activity determining means detects the element temperature of the upstream air-fuel ratio sensor based on the cooling water temperature of the engine. 8. Claim 6, wherein the activity determining means detects the element temperature of the upstream air-fuel ratio sensor based on the oil temperature of the engine.
The air-fuel ratio control device for an internal combustion engine as described in 2. 9. The activation determining means includes: a first determining means for determining whether the output of the upstream air-fuel ratio sensor in the second operation state is equal to or higher than a first predetermined value; and the first determining means at the time of fuel cut. and second determining means for determining whether or not the output of the upstream air-fuel ratio sensor in the operating state is equal to or less than the second predetermined value, and the output of the upstream air-fuel ratio sensor is equal to or less than the first predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 6, wherein the output of the upstream air-fuel ratio sensor is determined to be within the predetermined range when the output is above the second predetermined value and below the second predetermined value. .