JPH0465224B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine.

[Conventional technology]

In recent years, oxygen concentration sensors (hereinafter referred to as "O ₂ sensors") have been developed as shown in Japanese Patent Application Laid-open No. 54-57029.
A number of control devices have been proposed that are equipped with the following and control the air-fuel ratio of an internal combustion engine.

In such an air-fuel ratio control device, an O ₂ sensor installed in the exhaust system outputs an output as shown in Figure 3a according to the residual oxygen concentration in the exhaust gas, and this output determines the stoichiometric air-fuel ratio (air-fuel ratio, that is, A/ F=approximately 15), and based on this detection signal, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is feedback-controlled to the stoichiometric air-fuel ratio.

When this air-fuel ratio control device is combined with a catalyst, particularly a three-way catalyst, it is possible to extremely efficiently purify harmful components such as NO _x and CO in exhaust gas.

[Problem that the invention seeks to solve]

However, in the above-mentioned air-fuel ratio control device, due to deterioration of the O ₂ sensor due to aging etc.
The output characteristics of the O ₂ sensor begin to deviate from the initial characteristics shown by the solid line in Figure 3a, and as a result of this change in characteristics, the control range by feedback to the stoichiometric air-fuel ratio changes from the range shown by the diagonal lines in Figure 3. become. When the control range changes in this way, the purification rate of harmful components (NO _x , CO, etc.) by the catalyst is extremely reduced, and as shown in Figure 3b, the harmful components ( The problem is that the concentration of _NOx , CO, etc. becomes extremely high.

Therefore, an object of the present invention is to suppress the harmful components in the exhaust gas that passes through the catalyst and are discharged into the atmosphere to a sufficiently low value, and to maintain the exhaust state in which the harmful components are suppressed to a sufficiently low value by O ₂ An object of the present invention is to provide an air-fuel ratio control device that can continue to maintain a sensor even when the sensor is in a deteriorated state.

[Means for solving problems]

In order to solve the above problems, in the present invention, as shown in FIG. at least two harmful gas concentration detection means for detecting the concentration and the concentration of at least one of carbon monoxide and hydrocarbons; at least two comparison means for comparing the oxygen concentration with a preset set value; an oxygen concentration detection means for detecting the oxygen concentration contained in the exhaust gas before passing through the catalyst; and an output of the oxygen concentration detection means to detect the internal combustion air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine; and according to the comparison results of the respective comparison means, feedback control of the air-fuel ratio is performed when the concentration of nitrogen oxides is equal to or higher than a set value. If it is determined that the range has shifted to the lean side and a correction is made to the air-fuel ratio control means, and the concentration of at least one of the carbon monoxide and hydrocarbons is equal to or higher than the set value, the air-fuel ratio feedback control range is changed. The air-fuel ratio control apparatus is characterized in that the air-fuel ratio control apparatus further comprises a correction means for determining that the air-fuel ratio has shifted to the rich side and correcting the air-fuel ratio control means.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an internal combustion engine equipped with an air-fuel ratio control device.The intake system of an engine (hereinafter referred to as "engine") 1 includes an air flow meter 2, a throttle valve 3, and a throttle sensor 4. etc. are provided. The air taken in from this intake system is passed through the surge tank 5 to the intake manifold 6.
The mixture is mixed with fuel injected from a fuel injection valve 7 operated in response to an electric pulse signal, and is supplied to the combustion chamber 8 of the engine 1 as a mixture having a predetermined air-fuel ratio.

In this combustion chamber 8, a mixture of fuel and air is mixed with a spark plug 1 provided in a cylinder head 9.
The combustion gas is ignited and burned by the exhaust valve 1.
1 to the exhaust system 12.

This exhaust system 12 includes a solid electrolyte, e.g.
An oxygen concentration sensor (O ₂ sensor) 13 that uses ZrO ₂ to generate a voltage signal according to the residual oxygen concentration in exhaust gas is provided, and as shown in Figure 3a, the output of this O ₂ sensor 13 The air-fuel ratio is detected by the signal. Also, the O ₂ sensor 1 of the exhaust system 12
A three-way catalyst 14 that purifies harmful components contained in the exhaust gas, such as HC, CO, and _NOx , is provided downstream of the position where the exhaust gas is provided. Furthermore, the exhaust system 12 on the downstream side of the three-way catalyst 14 is equipped with an NO _X sensor 15 that uses a semiconductor, for example, S _{O 2} , and whose resistance value changes depending on the NO _X concentration, and also uses, for example, S _O O _2. A CO sensor 16 whose resistance value changes depending on the CO concentration is provided.
It is known that the resistance values of the NO _X sensor 15 and the CO sensor 16 change depending on the NO _X concentration D ( _NO The change in resistance value is detected as voltage signals V _N and V _C , and from these output signals _{V N and} V _C , the NO Ru.

Further, the cylinder block 19 of the engine 1 is provided with a water temperature sensor 20 that detects the engine cooling water temperature, and the distributor 22 that distributes the ignition signal from the igniter 21 to each cylinder includes a cylinder discrimination sensor 23 and a rotation angle sensor. 24 is built-in. The air flow meter 2 and the O ₂ sensor 13 detect each operating condition of the engine 1;
NO _X sensor 15, CO sensor 16, water temperature sensor 2
0, cylinder discrimination sensor 23, and rotation angle sensor 2
The detection signal from 4 is supplied to a control unit 26. The control unit 26 is constructed using, for example, a microcomputer, and FIG. 2 shows its construction. That is, a central processing unit (hereinafter referred to as "CPU") 27 that executes arithmetic processing
Random access, which performs temporary storage etc.
It is equipped with a memory (hereinafter referred to as "RAM") 28, a read-only memory (hereinafter referred to as "ROM") 29 used for program memory, etc., and a CPU 2
7. RAM28, ROM29, etc. are data bus 30
connected by. This data bus 30 includes input/output ports 31, 32, output ports 33,
34 are connected, and the input/output port 31 has an air flow meter 2, an O ₂ sensor 13, and a NO _X sensor 1.
5. Signals from the CO sensor 16 and water temperature sensor 20 are taken out via the multiplexer 36, converted into digital signals by the A/D converter 37, and supplied. Signals from the cylinder discrimination sensor 23 and rotation angle sensor 24 are shaped into waveforms by a waveform shaping circuit 38 and supplied to the input/output port 32, and furthermore, the detection signal from the throttle sensor 4 is A/D converted by an input circuit 40 as appropriate. and is supplied to the input/output port 32. Output signals from the output ports 33 and 34 are supplied to the igniter 21 and the fuel injection valve 7 via drive circuits 41 and 42, and ignition control and fuel injection amount control are performed. 44 is a clock oscillator;
Gives a timing clock signal to the CPU 27, etc.

The operation of the above configuration will be described below.

First, the CPU 27 of the control unit 26 uses the intake air amount obtained from the detection signal of the air flow meter 2 and the engine rotational speed obtained from the detection signal of the rotation angle sensor 24 from a map stored in advance in the ROM 29. Read out the injection time TP.

Furthermore, the fuel injection time TAU is calculated by correcting the basic injection time TP according to the detection signals from each sensor.

TAU=TP*K Here, K is a correction coefficient.

Fuel injection time TAU determined in this way
A fuel injection signal corresponding to the injector 7 is sent to the drive circuit 4.
2, the injection valve 7 is opened for the fuel injection time TAU in synchronization with the engine rotation, and fuel is injected into the intake manifold 6 of the engine 1.

By injecting fuel in this manner, an air-fuel mixture having a predetermined air-fuel ratio is supplied into the combustion chamber 8.

Next, compensation for deviations in the control range due to deterioration of the O ₂ sensor 13 in this embodiment will be described.

FIG. 5 shows a program routine that is executed in the CPU 27 at predetermined time intervals to change a predetermined control value of the air-fuel ratio correction coefficient in consideration of compensation for deterioration of the O ₂ sensor 13. First step 1
At 00, it is determined whether feedback control to the stoichiometric air-fuel ratio by the O ₂ sensor 13 is currently being executed, and if feedback control is not in progress, this routine ends. If feedback control _is in progress, _in step 101 the output signal V _N of the _NO
Find the concentration D( _NOx ). Next, in step 103, the output signal V _C of the CO sensor 16 converted into a digital value by the A/D converter 37 is read, and in step 104
Find the CO concentration D (CO) from the output signal V _C at .

Next, in step 105, a feedback control range for the _{stoichiometric} air-fuel ratio determined by the NO _x concentration D ( _NO A comparison is made with a set value D ₀₁ (see FIG. 3b), which is set in advance to a sufficiently small value. And D ₀₁ > D(NO _x )
If so, proceed to step 106. Also, D ₀₁ <D
( _NOx ), proceed to step 107.

In step 106, the result obtained in step 104 is
The set value D ₀₂ (second value) is set in advance to a sufficiently small value corresponding to the feedback control range for the stoichiometric air-fuel ratio determined by the CO concentration D (CO) and the characteristics of the O ₂ sensor 13 in an undegraded state. (See Figure 3 b)
If D ₀₂ > D(CO), step
Proceed to step 109, and if D ₀₂ < D(CO), step 108
Proceed to.

In accordance with the above comparison result, in step 107, the delay time t (delay time t will be described later), which is the control value of the air-fuel ratio correction coefficient, is set to a predetermined value Δ.
t is added and this delay time t+Δt is stored in the RAM 28 as t. Further, in step 108, the delay time t is subtracted by a predetermined value Δt, and this delay time t−Δt is stored in the RAM 28 as t.

In step 109, the air-fuel ratio correction coefficient is set in accordance with the delay time t set as described above, and the present routine ends.

In other words, according to the above routine, it is determined in step ₁₀₅ that D ₀₁ <D( _NO , the setting of the control value (delay time) of the air-fuel ratio correction coefficient is changed in step 107, and the air-fuel ratio correction coefficient is changed in step 109 according to the control value with this setting changed.
It is set to compensate for the deviation towards the Lean side.
In addition, in step 106, it is determined that D ₀₂ <D(CO), so it is determined that the feed control range has shifted to the Rich side, and the control value setting is changed in step 108. In step 109, the air-fuel ratio correction coefficient is set using the changed control value to compensate for the deviation toward the rich side.

What is shown in FIG. 6 is a time chart showing changes in the air-fuel ratio correction coefficient set according to the output of the O ₂ sensor 13. Figure 6 shows the O ₂ sensor 13.
When the output of the O ₂ sensor 13 shows a value larger than the comparison value, the air-fuel ratio correction coefficient is set so that the air-fuel ratio is on the lean side, and vice versa. In this case, it is set to be on the Rich side.

In the air-fuel ratio correction coefficient setting routine described above,
When _{NO X} concentration _{D ( NO}
3 is considered not to have deteriorated, and as shown in Fig. 6, the air-fuel ratio correction coefficient is changed according to the change in Fig. 6, and the average value a (when the O ₂ sensor 13 is not deteriorated, the theoretical The control variables (corresponding to the air-fuel ratio), that is, the delay time t, the skip amount G, and the integral constant H, are contrasted between the rich side and the lean side.

However, O ₂ sensor 13 deteriorates and O ₂ sensor 1
For example, if the output of the O ₂ sensor 13 shifts to the Lean side, the deterioration is detected by an increase in the NO _X concentration D ( _NO As shown in FIG. 6, the setting is changed by adding a predetermined value △t to the delay time t from the state shown in FIG. 6, and the control value of the air-fuel ratio correction coefficient is changed to The rich side and the lean side are made asymmetrical with respect to the average value a in the state, and the average of the air-fuel ratio correction coefficients is set to the average value b. By doing this,
Even if the control range changes to the Lean side due to deterioration of the O ₂ sensor 13, the difference between the three-way catalyst 14 and the average value a of the air-fuel ratio correction coefficient (Fig _. 6) set only by the output of the O 2 sensor 13 Downstream _NOx concentration D ( _NOx )
The average value b of the air-fuel ratio correction coefficient (Fig. 6) with the delay time t changed according to the predetermined amount C
is switched to the Rich side, and therefore the O ₂ sensor 13
The feedback control range, which had changed to the lean side due to deterioration, is now returned to the rich side as a whole, and the three-way catalyst 14 purifies harmful components by maintaining the control range near the stoichiometric air-fuel ratio where the purification rate is high. By doing so, you can maintain a good condition. In addition, if the output of the O ₂ sensor deviates to the rich side, its deterioration is detected by the CO concentration D (CO),
In contrast to the above, the entire feedback control range is returned to the Lean side.

As mentioned above, once the air-fuel ratio correction coefficient is set,
The basic injection time TP is corrected according to the correction coefficient that compensates for the deterioration of the O ₂ sensor 13, and the fuel injection time TAU is set. Then, the injection valve 7 injects fuel into the intake manifold 6 of the engine 1 according to the fuel injection time TAU, and the air-fuel mixture at the stoichiometric air-fuel ratio is supplied into the combustion chamber 8. Therefore, the harmful components in the exhaust gas can be maintained in a sufficiently reduced state.

In the above embodiment, the shift of the control range toward the rich side due to the shift of the output of the O ₂ sensor 13 toward the rich side is detected by the CO concentration D (CO) obtained from the output of the CO sensor 16. An HC sensor that detects the concentration of HC whose concentration change is similar to that of CO on the downstream side of the main catalyst 14 is used instead of the CO sensor 16.
The shift toward the rich side may be compensated for depending on the HC concentration. In addition, Fig. 4c shows one component of HC.
It shows the resistance value change of HC sensor against CH ₄ .

Furthermore, in the above embodiment, the delay time t among the control values of the air-fuel ratio correction coefficient was changed to provide an air-fuel ratio correction coefficient that compensated for the deterioration of the _O2 sensor 13, but by changing the skip amount G and the integral constant H, the delay time t was changed. ₂ sensor 1
An air-fuel ratio correction coefficient that compensates for the deterioration of 3 may be set.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to maintain the purification of harmful components by the catalyst in a good condition, and the amount of harmful components in the exhaust gas that passes through the catalyst and is emitted to the atmosphere is sufficient. It becomes possible to suppress the In addition, even if a deviation occurs in the air-fuel ratio feedback control range due to deterioration of the oxygen concentration sensor, the nitrogen oxide concentration and carbon monoxide concentration or hydrocarbon concentration will change, and this deterioration will be detected and the purification performance of the catalyst will be improved. Since it is controlled so that the oxygen concentration is maintained, it is possible to compensate for deviations in the control range due to deterioration of the oxygen concentration sensor, and therefore the harmful components in the exhaust gas emitted into the atmosphere can be maintained at a sufficiently reduced level. It has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing the configuration of an internal combustion engine and its peripheral equipment equipped with the configuration of the present invention, and FIG.
Figure 3 is a block diagram showing the configuration of the control unit in the figure, Figure 3 is a graph showing changes in _O2 sensor output and exhaust harmful component concentration with respect to air-fuel ratio, Figure 4 is a graph showing changes in the concentration of harmful components discharged.
A characteristic diagram showing the characteristics of the NO _X sensor, CO sensor, and HC sensor, FIG.
FIG. 7 is a time chart showing changes in the air-fuel ratio correction coefficient with respect to the O ₂ sensor output, and is a block diagram showing the schematic configuration of the present invention. 1...Engine, 2...Air flow meter, 7
...Fuel injection valve, 12...Exhaust system, 13...O ₂
Sensor, 14... Three-way catalyst, 15... NO _X sensor, 16... CO sensor, 26... Control unit,
27...CPU, 28...RAM, 29...ROM.

Claims (1)

[Claims] 1. Among the harmful gas components contained in the exhaust gas that has passed through a catalyst provided in the exhaust system of an internal combustion engine, the concentration of nitrogen oxides and the concentration of at least one of carbon monoxide and hydrocarbons. and at least 2
at least two comparison means for comparing the concentration of each harmful component detected by each of the detection means with a preset value corresponding to each detected component; and the catalyst passing through. an oxygen concentration detection means for detecting the oxygen concentration contained in the preceding exhaust gas; an air-fuel ratio control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the output of the oxygen concentration means; Depending on the comparison result of the comparison means, it is determined that the feedback control range of the air-fuel ratio is shifted to the lean side when the concentration of nitrogen oxides is equal to or higher than a set value, and the air-fuel ratio control means is corrected; and a correction unit that determines that the air-fuel ratio feedback control range has shifted to the rich side when the concentration of at least one of the carbon monoxide and hydrocarbons exceeds a set value, and corrects the air-fuel ratio control unit. An air-fuel ratio control device comprising: