JPH06323185A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To realize high accurate control of air-fuel ratio in an engine just after starting it or at the time of its transient operation by concurrently using an ion concentration sensor and an oxygen concentration sensor, combining or selectively using detection values of both the sensors, and detecting air-fuel ratio. CONSTITUTION:In an engine for feedback controlling air-fuel ratio of a mixture to a target value by controlling an amount of fuel, injected from an injector 21 provided to appear in an intake pipe 15 of the engine in accordance with concentration of oxygen in exhaust, the engine is provided with an oxygen concentration sensor 29 arranged in the upstream of a catalytic converter 23 and an ion concentration sensor 31 formed to be exposed in a combustion chamber 30, as the sensor for detecting air-fuel ratio. Air-fuel ratio control is executed by using the ion oxygen sensor 31 at non-activation time of the oxygen concentration sensor 29 and by using the oxygen concentration sensor 29 at activation time in a non-transient condition, and air-fuel ratio control is executed by mainly using a detection value of the ion concentration sensor 31 corrected by an output of the oxygen concentration sensor 29 at transient condition time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device,
In particular, the present invention relates to an air-fuel ratio control device that detects an air-fuel ratio of combustion gas and feedback-controls an air-fuel mixture supplied to an internal combustion engine to a predetermined air-fuel ratio based on the air-fuel ratio.

[0002]

2. Description of the Related Art Conventionally, in a vehicle-mounted internal combustion engine,
In order to maintain good emission of exhaust gas discharged into the atmosphere, a configuration in which a catalytic converter having an exhaust gas purification action is arranged in the exhaust passage is widely used.
This catalytic converter is required to be able to effectively remove unburned components such as carbon monoxide CO and hydrocarbons HC contained in exhaust gas, or oxides represented by nitrogen oxides NOx.

In order to meet such requirements, a catalytic converter for a vehicle-mounted internal combustion engine generally includes a three-way catalyst. Here, the three-way catalyst is a member that adsorbs oxygen when the exhaust gas contains excess oxygen, and releases the adsorbed oxygen when the exhaust gas lacks oxygen. is there.

That is, when the air-fuel ratio is lean, oxygen is taken from oxides such as NOx existing in the exhaust gas to exert a reducing action, and when the air-fuel ratio is rich in fuel, the exhaust gas is exhausted. It is a member that purifies exhaust gas by releasing oxygen into gas and exerting an action of oxidizing unburned components such as CO and HC.

Therefore, in order to ensure good exhaust emission after passing through the catalytic converter, it is necessary to continue the transfer of oxygen within the range of the oxygen adsorption capacity of the three-way catalyst. For that purpose, it is necessary to control the air-fuel ratio of the exhaust gas flowing into the catalytic converter from the internal combustion engine so that fuel rich and fuel lean are repeated centering on the theoretical air-fuel ratio. If the air-fuel ratio is greatly deviated to either rich or lean, the excess or insufficient amount of oxygen in the combustion gas may not be absorbed by the oxygen adsorption capacity of the three-way catalyst.

Therefore, in the internal combustion engine equipped with the above-mentioned catalytic converter, the air-fuel ratio feedback control, which is known to be capable of accurately performing the air-fuel ratio control, is widely performed. In this air-fuel ratio feedback control, an air-fuel ratio sensor that detects the air-fuel ratio of combustion gas is arranged in the exhaust system of the internal combustion engine, and the amount of fuel supplied to the internal combustion engine is finely adjusted based on the detected value. .

As an air-fuel ratio sensor for realizing such an air-fuel ratio feedback sensor, an oxygen concentration sensor has been widely used. This oxygen concentration sensor is a sensor that generates a current according to the oxygen concentration in the atmosphere, and can easily and directly detect the air-fuel ratio of the combustion gas.

However, in the structure for performing air-fuel ratio control using this oxygen concentration sensor, in order to ensure stable detection accuracy, it is necessary to measure the air-fuel ratio after the combustion gases are sufficiently mixed until they become uniform. Therefore, an appropriate distance is required between the combustion chamber and the oxygen concentration sensor. Therefore, the detection of the air-fuel ratio by the oxygen concentration sensor is unavoidably accompanied by a time delay.

Such a time delay does not cause any problem when the operating state of the internal combustion engine is in a steady state, but under the situation where the operating state changes in accordance with the acceleration / deceleration request to the vehicle. Then, the control accuracy is greatly deteriorated.

Further, the oxygen concentration sensor that has been generally used conventionally has an output characteristic that varies depending on the ambient temperature and does not emit any output until it reaches a predetermined activation temperature range. Therefore, when the air-fuel ratio control device is configured using such an oxygen concentration sensor, the air-fuel ratio feedback control should be executed until the oxygen concentration sensor is appropriately heated and reaches a predetermined temperature after the internal combustion engine is started. There was a problem that I could not do it.

As described above, the air-fuel ratio control device using the oxygen concentration sensor has various problems, and it is not always possible to realize ideal air-fuel ratio feedback control. On the other hand, Japanese Patent Laid-Open No. 4-194336 discloses
In order to improve the characteristics of the air-fuel ratio control device, an air-fuel ratio control device is disclosed that calculates the air-fuel ratio based on the concentration of ionized ions generated when the air-fuel mixture burns in the combustion chamber.

The apparatus described in the above publication installs a known ion concentration sensor for each cylinder constituting the internal combustion engine and detects the ion concentration generated by combustion in each cylinder. In this case, unlike the oxygen concentration, the ionized ions to be detected by the ion concentration sensor can be stably detected even if the combustion gas is not sufficiently mixed.

Therefore, as described above, it is possible to detect the air-fuel ratio in the combustion chamber of each cylinder, and it is possible to perform accurate detection for each cylinder with almost no time delay after combustion of the air-fuel mixture. Further, unlike the conventional oxygen concentration sensor, such an ion concentration sensor does not require time for activation and can start accurate detection of the air-fuel ratio immediately after starting the internal combustion engine. Therefore, the air-fuel ratio feedback control can be executed immediately after the internal combustion engine is started.

[0014]

However, in the above-mentioned conventional air-fuel ratio control device, it is an essential requirement that the ion concentration sensor be provided in an exposed state in each cylinder combustion chamber of the internal combustion engine. Then, under such an environment, "soot" or the like generated by the combustion of the air-fuel mixture adheres to the ion concentration sensor.

It is known that when such "soot" adheres, the ion concentration sensor changes its output characteristics due to its structure. Therefore, in the configuration in which the ion concentration signal generated by the ion concentration sensor is directly used for the air-fuel ratio control without providing any calibration means like the above-mentioned conventional air-fuel ratio control device, accurate control is performed when the output characteristic changes. There is a problem that you can not continue.

That is, the conventional air-fuel ratio control device for calculating the air-fuel ratio based on the detected value of the ion concentration sensor can start the air-fuel ratio control immediately after the start of the internal combustion engine and has a real-time property without a time delay. Although excellent air-fuel ratio control can be executed, there is a problem that the detected air-fuel ratio is lacking in credibility and highly accurate air-fuel ratio control cannot be realized.

The output value of the ion concentration sensor with respect to the air-fuel ratio has a peak value in the normal air-fuel ratio region. That is, the output value of the ion concentration sensor becomes smaller as the air-fuel ratio of the measurement target becomes leaner than the air-fuel ratio showing the peak value and as the air-fuel ratio of the measurement target becomes richer than the air-fuel ratio showing the peak value.

Therefore, as long as the output value of the ion concentration sensor does not show the peak value, the air-fuel ratios corresponding to the output value are considered to be on the rich side and the lean side, respectively. A situation occurs in which it is not possible to determine whether the fuel ratio is detected. In particular, when the operating state of the internal combustion engine is in a transient state, the amount of fuel adhering to the intake port, the magnitude of the intake pipe negative pressure, etc. interact to cause a large change in the air-fuel ratio. It may be difficult to accurately determine the air-fuel ratio based on only the output value.

As described above, in the above conventional device,
The excellent characteristics that can be realized by detecting the air-fuel ratio using the ion concentration sensor cannot be fully exerted,
After all, there is a problem that the purpose of realizing highly accurate air-fuel ratio control cannot be achieved immediately after the start of the internal combustion engine and during the transient operation of the internal combustion engine.

The present invention has been made in view of the above-mentioned points, and it is possible to use the ion concentration sensor and the oxygen concentration sensor in combination, and to appropriately combine the detection values of both sensors or to selectively use the above values. An object is to provide an air-fuel ratio control device that can solve the problems.

[0021]

FIG. 1 is a block diagram showing the principle of an air-fuel ratio control system for achieving the above object. That is,
As shown in FIG. 1A, an oxygen concentration sensor 1 for detecting the oxygen concentration in the combustion gas of the internal combustion engine is provided, and the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine based on the detection value of the oxygen concentration sensor 1. In an air-fuel ratio control device for feedback control of oxygen concentration sensor activity detecting means 2 for detecting whether or not the oxygen concentration sensor 1 has reached a predetermined activation state,
If the ion concentration detecting means 3 for detecting the concentration of ions generated in the combustion chamber of the internal combustion engine and the oxygen concentration sensor 1 have not reached a predetermined activation state, the ion concentration detecting means 3 detects the ion concentration. According to the air-fuel ratio control device including the air-fuel ratio control means 4 for calculating the air-fuel ratio of the combustion gas based on the ion concentration and performing the air-fuel ratio control of the air-fuel mixture supplied to the internal combustion engine according to the calculated value, Highly accurate air-fuel ratio control is realized immediately after the start of the internal combustion engine.

Further, as shown in FIG. 1 (B), a transient state detecting means 5 for detecting whether or not the operating state of the internal combustion engine exceeds a predetermined level is provided. When a transient state exceeding a predetermined level is detected, the oxygen concentration detected by the oxygen concentration sensor 1 and
An air-fuel ratio control means 6 for calculating an air-fuel ratio of the combustion gas based on the ion concentration detected by the ion concentration detection means 3 and controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine in accordance with the calculated value. According to the air-fuel ratio control device including the above, highly accurate air-fuel ratio feedback control is realized during transient operation.

[0023]

In the air-fuel ratio control apparatus shown in FIG. 1A, the ion concentration detecting means 3 immediately starts detecting the ion concentration in the combustion gas when the internal combustion engine is started. On the other hand, the oxygen concentration sensor 1 cannot detect the oxygen concentration in the combustion gas until the predetermined activation temperature region is reached after the internal combustion engine is started, but after reaching the activation temperature region, The oxygen concentration is detected with high accuracy.

Further, the air-fuel ratio control means 4 judges whether or not the oxygen concentration sensor 1 is activated based on the detection signal of the oxygen sensor activity detection means 2, and is not activated yet. If it is determined that the air-fuel ratio of the combustion gas is calculated based on the detection value of the ion concentration detecting means 3. When it is determined that the oxygen concentration sensor 1 has already been activated, the air-fuel ratio of the combustion gas is calculated based on the detection value of the oxygen concentration sensor 1.

Therefore, in the internal combustion engine equipped with the air-fuel ratio control device of FIG. 1 (A), the air-fuel ratio control based on the detection value of the ion concentration detecting means 3 is started immediately after the engine is started, and the oxygen concentration sensor 1 is operated. After is activated, highly accurate air-fuel ratio control based on the detection value of the oxygen concentration sensor 1 is executed.

Further, in the air-fuel ratio control device shown in FIG. 1B, when the transient state detecting means 5 detects a transient state exceeding a predetermined level, the air-fuel ratio controlling means 6
Takes in the detection value of the ion concentration detecting means 3 as a value representing an actual air-fuel ratio with no time delay. At this time, the air-fuel ratio control means 6 also takes in the detection value of the oxygen concentration sensor 1 and determines whether the combustion gas is on the fuel rich side or the fuel lean side.

As a result, does the detected value of the ion concentration sensor 3 represent the air-fuel ratio on the fuel rich side, even though the air-fuel ratio of the combustion gas fluctuates greatly with the change of the operating state of the internal combustion engine? , Or the air-fuel ratio on the fuel lean side can be determined. Therefore, FIG. 1 (B) above
In an internal combustion engine equipped with the air-fuel ratio control device of No. 1, even if the operating state of the internal combustion engine changes transiently, highly accurate air-fuel ratio control is executed.

[0028]

FIG. 2 is a general view showing the configuration of an embodiment of a fuel injection device for an internal combustion engine according to the present invention. An ignition plug 12 is arranged at the center of a cylinder head 11 of an internal combustion engine 10 including the device of this embodiment. A water temperature sensor 14 that detects the temperature of the cooling water flowing in the water jacket is provided on the outer wall of the cylinder 13 that forms the combustion chamber of the internal combustion engine 10.

An intake pipe 15 communicates with an intake hole of the internal combustion engine 10. The intake pipe 15 has a surge tank 16 for absorbing pulsation of intake air and an accelerator pedal (not shown).
Throttle valve 1 that adjusts the intake air amount in conjunction with
7 and an air flow meter 18 for detecting the amount of intake air. The surge tank 16 has an intake pressure sensor 19 for measuring its internal pressure, and the throttle valve 17 has a throttle sensor 20 for detecting its opening.
Is installed.

Reference numeral 21 indicates an injector for supplying fuel into the intake pipe 15. Fuel is supplied to the injector 21 at a predetermined pressure from a known fuel system (not shown). Then, the supplied fuel passes through the inside of the injector 21 and is guided to the fuel injection hole provided at the tip thereof.

The fuel injection hole has an electronic control unit (E
A fuel injection valve that opens and closes in response to a drive signal supplied from the CU) 40 is provided. Therefore, when the fuel injection valve is appropriately opened, fuel is intermittently injected according to the opening time of the fuel, and if the duty of the valve opening time is appropriately controlled, the fuel injection amount per unit time can be easily increased. Can be changed to

The exhaust pipe 22 communicating with the exhaust hole of the internal combustion engine 10 has a manifold catalytic converter as a catalytic converter for purifying unburned components such as HC and CO and oxides such as NOx contained in the exhaust gas. 23 and the underfloor catalytic converter 24 communicate with each other.

Here, the structure in which the catalytic converters 16 are stacked in two stages is adopted in order to sufficiently secure the oxygen adsorption capacity of the catalyst and obtain better exhaust emission. Therefore, it is not always necessary to stack two layers,
A configuration in which only one of them is provided may be adopted.

The distributor 25 is interlocked with a crankshaft (not shown) and distributes a high voltage ignition signal to each cylinder ignition plug 12 according to an ignition signal supplied from the ECU 40. Also, the distributor 2
3 is provided with crank angle sensors 26 and 27 for detecting the rotation state of the crankshaft.

Here, the crank angle sensor 26 outputs a pulse signal a predetermined number of times, for example 24 times, while the crankshaft makes two revolutions (one cycle of the internal combustion engine). Also,
The crank angle sensor 27 outputs a pulse signal once while the crankshaft makes two revolutions. Then, the electronic control unit 40 combines the output signals of the both crank angle sensors 24 and 25 to detect the number of revolutions of the crankshaft per unit time and the rotational position of the crankshaft.

In the internal combustion engine 10 shown in FIG. 2, the exhaust temperature sensor 2 is provided upstream of the manifold catalytic converter 23.
Both 8 are equipped with an oxygen concentration sensor 29. In this case, the exhaust temperature sensor 28 uses the catalytic converters 23, 24.
Is installed in order to appropriately control the temperature of the exhaust gas discharged from the internal combustion engine 10 so as not to be overheated.

The oxygen concentration sensor 29 is a sensor for detecting the oxygen concentration sensor in the exhaust gas discharged from the internal combustion engine 10. This oxygen concentration is a characteristic value representing the air-fuel ratio of the exhaust gas, and if the fuel supply amount is controlled so that a predetermined oxygen concentration is maintained, the exhaust gas discharged toward the catalytic converters 23, 24 will be It becomes possible to control near the stoichiometric air-fuel ratio.

Further, in this embodiment, as a means for detecting the air-fuel ratio of the combustion gas, in addition to the oxygen concentration sensor 29, the ion concentration sensor is exposed in the combustion chamber 30 of the internal combustion engine 10 with its detecting portion exposed. 31 are provided. The ion concentration sensor 31 is known as a sensor that generates an ion current according to the concentration of ionized ions existing in the atmosphere, and detects the ion concentration generated when the air-fuel mixture burns in the combustion chamber 30. It is provided for.

That is, in the internal combustion engine, the combustion chamber
When the air-fuel mixture burns at₃H₃ ⁺, COH ⁺, H₃O⁺， H
_FiveO₂ ⁺， C₂HO⁺Ionized ions such as
It is known to show a value corresponding to the air-fuel ratio of the burned mixture.
ing. Therefore, this ion concentration can be detected.
If so, it is possible to detect the air-fuel ratio of the air-fuel mixture. Book
The ion concentration sensor 31 in the embodiment meets such a requirement.
It is provided as a means for filling.

Then, the ECU 40 determines the air-fuel ratio of the air-fuel mixture to be supplied to the internal combustion engine 10 based on the detected values of the water temperature sensor 14, the air flow meter 18, the intake pressure sensor 19, the throttle sensor 20, the exhaust temperature sensor 28, etc. The calculated reference value is corrected based on the detection values of the oxygen concentration sensor 29 and the ion concentration sensor 31, and in the intake stroke of each cylinder, the injector 2 is supplied so that a desired injection amount is supplied.
2 is supplied with a drive signal.

Next, the output characteristics of the ion concentration sensor 31 and the detection circuit for processing the output signal to obtain an appropriate air-fuel ratio signal will be described in detail with reference to FIGS.

FIG. 3 shows a block diagram of a circuit provided in the ECU 40 for processing the output signal of the ion concentration sensor 31. As shown in the figure, the ion concentration sensor 31
Is driven by direct current from a power supply 41, and a power supply voltage E is supplied to one terminal thereof.

The other terminal of the ion concentration sensor 31 is grounded so that the potential of the ground level is maintained, and the input of the resistor 42 having the predetermined resistance value Rc and the detection circuit 43 having the input impedance Rin. Connected to the terminal. The other end of the resistor 42 and the other input terminal of the detection circuit 43 are both connected to the negative terminal of the power supply 41.

When the ion concentration sensor 31 exposed in the combustion chamber 30 of the internal combustion engine 10 is connected, the combustion chamber 3
When ionized ions are generated in 0, the ion concentration sensor 31
A current Ig corresponding to the ion concentration flows through the. When the current Ig flows through the ion sensor 31, the current is shunted to the resistor 42 and the detection circuit 43 and flows through a closed loop that leads to the negative terminal of the power supply 41.

Therefore, the resistor 42 (or the detection circuit 4)
If the voltage across both ends of 3) is Vc, the ion concentration sensor 31
The current Ig flowing through can be expressed as follows.

Ig = Vc · (1 / Rc + 1 / Rin) (1) As described above, since Rc and Rin are set values of predetermined values and are constants, if Vc can be detected after all. Therefore, the current Ig flowing through the ion concentration sensor 31 can be calculated. That is, the detection circuit 43 of this embodiment
Is a circuit for outputting the potential difference generated between the input terminals, and when the air-fuel mixture burns in the combustion chamber 30 in which the ion concentration sensor 31 is installed, outputs a signal having a waveform as shown in FIG. 4, for example.

The waveform shown in FIG. 4 is a signal when ignition in the explosion process is executed at the time t ₁ in the combustion chamber 30, and the hatched portion in FIG. 4 is generated with combustion. It is a voltage signal caused by the generated ionized ions.

The signal processing circuit 44 is a circuit for processing such a voltage signal supplied from the detection circuit 43 so that the air-fuel ratio can be easily calculated. FIG. 5 shows a signal waveform when a process of holding the peak value of the voltage signal supplied from the detection circuit 43 is performed as an example of the process.

In this case, in the signal processing circuit 43, first, as shown in FIG. 5A, from the voltage signal supplied from the detection circuit 43, the signal portion generated due to the generation of ionized ions (in FIG. 4, above). Only the shaded area) is taken out. Due to the influence of the grounding property of the ion concentration sensor 31,
This is because there is a case where bias voltages are superimposed as shown in FIG.

Then, the voltage waveform after the processing is performed
An arithmetic circuit that holds the peak value and calculates the air-fuel ratio
45 has enough time to get the signal
It In this case, in this embodiment, as shown in FIG.
Time t₁(Or t ₁₁) Is the ignition timing,
Crank angle supplied from crank angle sensors 26, 27
Predetermined time t before and after the signal₂(T₁₂)as well as
t₃(T₁₃) Is set and the interval between
is doing.

This is because the voltage signal generated during a period other than the period in which the explosion process is performed in the combustion chamber 30 in which the ion concentration sensor 31 is disposed is ignored. As a result, the signal output from the signal processing circuit 44 is, as shown in FIG.
Until t ₄ (t ₁₄ ) set as the reset time, the voltage value representing the ionized ion concentration is reliably maintained until reset.

Therefore, in the arithmetic circuit 45, the voltage signal supplied from the signal processing circuit 44 can be read as it is in correspondence with the air-fuel ratio. That is, when performing the peak hold process in the signal processing circuit 44 as described above, there is a graph between the peak voltage value and the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 30 when the voltage value is generated. The relationship shown in 6 is established. Therefore, if such a relationship is stored in advance as a map, the air-fuel ratio of the burned air-fuel mixture can be calculated based on the processing signal peak value supplied from the signal processing circuit 44.

FIG. 7 shows a signal waveform when the signal processing circuit 44 integrates the voltage signal supplied from the detection circuit 43 to secure a time sufficient for the arithmetic circuit 45 to read it.

That is, when this processing example is performed, the signal processing circuit 44 first removes the offset voltage from the voltage signal supplied from the detection circuit 43, as in the case of the peak hold described above (FIG. 7A). . Then, the signals input at the predetermined fetch timing set based on the detection signals of the crank angle sensors 26 and 27 are integrated,
The waveform is as shown in (B).

In this case, the peak value of the signal shown in FIG. 7B is the current Ig flowing through the ion concentration sensor 31 due to the ionized ions generated in the combustion chamber 30 in which the ion concentration sensor 31 is arranged. It corresponds to the integral value and serves as a substitute characteristic value of the air-fuel ratio of the air-fuel mixture, like the signal processing peak value shown in FIG.

FIG. 8 shows the relationship between the air-fuel ratio of the burned air-fuel mixture and the processing signal integral value generated for it. As shown in the figure, even when such a configuration is adopted, it is possible to obtain the same characteristics as when the peak hold processing is performed, and it is possible to detect the air-fuel ratio with high accuracy in the arithmetic circuit 45.

By the way, the ion concentration sensor 31 in the present embodiment is installed in the combustion chamber 30 with its detecting portion exposed as described above. That is, the ion concentration detected by the ion concentration sensor 31 can be used to detect the ion concentration of the actually burned mixture, which is extremely excellent in real time as compared with the oxygen concentration sensor 22 arranged in the exhaust pipe 22. Have sex.

Further, the oxygen concentration sensor 29 cannot detect the oxygen concentration unless its temperature has reached the predetermined activation temperature region, whereas the ion concentration sensor 31 has no limitation and the internal combustion period 10 Stable ion concentration detection is possible even immediately after the cold start.

Therefore, if the air-fuel ratio control is executed based on the ion concentration detected by the ion concentration sensor 31, the air-fuel ratio control which cannot be realized by the conventional oxygen concentration sensor 29, that is, immediately after the internal combustion engine is started. It is possible to realize the air-fuel ratio control in a predetermined period and the air-fuel ratio control without a time delay when the operating state of the internal combustion engine is transiently changed.

However, as shown in FIGS. 6 and 8, the detected value of the ion concentration sensor 31, that is, the output value of the signal processing circuit 44 has a characteristic having a peak value in the normal air-fuel ratio region. Therefore, in a situation where the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 fluctuates greatly,
Whether the detection value of the signal processing circuit 44 (I in FIGS. 6 and 8) is the result of detecting the air-fuel ratio on the rich side (A in FIGS. 6 and 8), the air-fuel ratio on the lean side (in FIGS. 6 and 8: There may be a case where it is not possible to determine whether the result is the result of detecting B).

That is, as shown in FIG. 9A, time t ₁
When the opening degree of the throttle valve 17 (hereinafter referred to as the throttle opening degree) becomes large due to the acceleration in the above, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 (FIG.
(C)) usually leans toward the lean side. During acceleration, a larger amount of fuel may be needed at the stage of injecting the fuel calculated as an appropriate amount, and immediately after the fuel injection amount has been increased, the adhesion to the area around the intake port This is because an increase in the amount does not directly lead to an increase in the amount of fuel flowing into the combustion chamber 30.

On the other hand, when the vehicle is suddenly decelerated from such a state, the throttle opening becomes small (see FIG. 9).
In (A), the air-fuel ratio (FIG. 9 (C)) at time t ₂ is biased to the rich side. This is because as the throttle opening becomes smaller and the intake negative pressure becomes larger, the fuel adhering to the vicinity of the intake port is rapidly vaporized.

FIG. 10 shows the results of measurement of the air-fuel ratio (FIG. 10 (A)) and the HC concentration in the exhausted combustion gas (FIG. 10 (B)) in such a situation. From the figure, it can be seen that the air-fuel ratio and the HC acquisition mission vary greatly.

As described above, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 greatly changes according to the operating state when the operating state changes. Further, in FIG. 9, time t
₃ If ~t ₅ sudden acceleration and sudden deceleration, as shown in is repeated, despite the transition to the acceleration at time t _5, the fuel-rich sustained under the influence of fuel adhering to the intake port during deceleration In some cases, it may occur.

In such a case, it cannot be determined from the operating state of the internal combustion engine 10 whether the air-fuel ratio is biased to the rich side or the lean side, and the detected value of the ion concentration sensor 31 becomes rich. Side shows the air-fuel ratio,
Alternatively, it is impossible to specify whether the air-fuel ratio on the lean side is indicated.

Therefore, in the air-fuel ratio control system of this embodiment, the ion concentration sensor 31 and the oxygen concentration sensor 29 are used together, and when the operating state of the internal combustion engine 10 is in the transient state, the ion concentration sensor 31 is used. The air-fuel ratio indicated by the detected value without time delay supplied from the oxygen concentration sensor 2
It was decided to specify based on the detection value supplied from No. 9.

The operation of the apparatus of this embodiment will be described below with reference to the flowchart of the routine processing executed by the arithmetic circuit 45 shown in FIG.

As shown in FIG. 11, when this routine is started, first, at step 100, it is judged if the oxygen sensor 29 is activated. Whether or not it is activated can be determined by measuring the temperature of the oxygen concentration sensor 29 and determining whether or not the temperature has reached the activation temperature region, for example, 200 ° C.

The oxygen concentration sensor 2 is used to make such a determination.
This is because the air-fuel ratio control using both the ion concentration sensor 31 and the oxygen concentration sensor 29 cannot be executed unless 9 has reached the activation temperature region. Therefore, when it is determined in step 100 that the oxygen concentration sensor 29 has not reached the activation temperature range, the air-fuel ratio control by using both sensors together is not executed.

By the way, it is determined that the oxygen concentration sensor 29 has not reached the activation temperature range.
Only for a predetermined period after it has been started. Further, during this period, generally, the fuel amount increase correction for the purpose of early warm-up of the internal combustion engine 10 is performed. Therefore, it is possible to determine that the air-fuel ratio is biased toward the rich side without performing detection by the oxygen concentration sensor 29.

Therefore, in the present embodiment, when it is determined that the oxygen concentration sensor is not activated, the routine proceeds to step 110, where the air-fuel ratio control is performed by the ion concentration sensor 31 alone. That is, in step 110, the concentration of ions generated in the combustion chamber 30 is detected.

When the detection is completed, the routine proceeds to step 120, where the air-fuel ratio of the air-fuel mixture burned in each combustion chamber 30 is calculated with reference to the map shown in FIG. 6 or 8. After that, in step 130, known air-fuel ratio feedback control is executed based on the calculated air-fuel ratio, and the current processing is ended.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, the air-fuel ratio control can be reliably performed by the ion concentration sensor 31 even before the oxygen concentration sensor 29 is activated.

In this embodiment, the fuel amount is corrected immediately after the internal combustion engine is started, so that it is determined that the fuel is biased toward the rich side. However, the present invention is not limited to this, and the space between them is not limited. It suffices that the fuel ratio is forcibly biased to the rich side or the lean side.

On the other hand, if it is determined in step 100 that the oxygen concentration sensor 29 is activated,
In step 140, it is determined whether the internal combustion engine 10 is in a transient state. In the transient state, it is necessary to execute the air-fuel ratio control using both the oxygen concentration sensor 29 and the ion concentration sensor 31 as described above, while in the non-transient state, the oxygen concentration sensor 29 alone is used as described later. This is because it is preferable to execute the air-fuel ratio control.

Therefore, if it is determined in step 140 that the state is the transient state, the routine proceeds to step 150, where the detected value of the ion concentration by the ion concentration sensor 31 is fetched, and in the following step 160, the oxygen concentration sensor 29 detects the oxygen concentration. Capture the value.

When the acquisition of these data is completed, at step 170, the mixture as burned in the internal combustion engine 10 in the transient state is referred to by referring to the map as shown in FIG. Specify the air-fuel ratio of. After that, in step 130, known air-fuel ratio feedback control is executed based on the specified air-fuel ratio, and the current processing is ended.

By performing such processing, the internal combustion engine 1
When the operating state of 0 is transiently changed, it becomes possible to detect the air-fuel ratio of the air-fuel mixture burned in each combustion chamber 30 in real time, and the amount of fuel to be supplied to each cylinder fluctuates moment by moment. However, it is possible to supply the required amount with extremely high accuracy.

By the way, when the internal combustion engine 10 is judged not to be in the transient state in the apparatus of this embodiment, the air-fuel ratio control by the oxygen concentration sensor 29 alone is executed as described above. That is, in step 140, the internal combustion engine 1
When it is determined that 0 is not in the transient state, the routine proceeds to step 180, where the oxygen concentration sensor 29 detects the oxygen concentration.

When the detection is completed, the routine proceeds to step 190, where the air-fuel ratio is calculated based on the detected oxygen concentration, and thereafter, the air-fuel ratio feedback control based on the air-fuel ratio calculated at step 130 is executed to execute this time. Ends the process.

The above processing is performed when the internal combustion engine 10 is in a steady state.
This is because calculation of the air-fuel ratio based on the detection value of the oxygen concentration sensor 29 can ensure better accuracy than the detection value of. That is, the problems in the air-fuel ratio control based on the oxygen concentration sensor 29 are that the control cannot be started until the oxygen concentration sensor 29 is activated, and that there is a certain amount of time from the combustion of the air-fuel mixture to the detection of the oxygen concentration. The point is.

Therefore, when the oxygen concentration sensor 29 is activated and the internal combustion engine is operating steadily, that is, when the fuel supply amount is substantially constant, the oxygen concentration sensor 29 is used.
No drawbacks are recognized in the air-fuel ratio control by.

On the other hand, the output characteristics of the ion concentration sensor 31 as shown in FIG.
As is clear from comparison with the aged product characteristics indicated by the broken line, the output value tends to decrease with use. This tendency is caused by the attachment of "soot" generated during the combustion of the fuel to the ion concentration detecting portion of the ion concentration sensor 31, and is avoided when the air-fuel ratio is detected using the ion concentration sensor 31. There is no configuration.

As described above, the ion concentration sensor 31 is superior to the oxygen concentration sensor 29 in terms of responsiveness and handleability, but is superior to the oxygen concentration sensor 29 in terms of stability of the detected value. In the present embodiment, the reason why the air-fuel ratio control by the oxygen concentration sensor 29 alone is executed when the internal combustion engine 10 is in steady operation is to consider the advantages and disadvantages of both sensors.

By the way, as described above, since the output characteristics of the ion concentration sensor 31 change with time,
In order to ensure good accuracy in the air-fuel ratio control based on the detected value of the ion concentration sensor 31, that is, in the air-fuel ratio control immediately after the internal combustion engine 10 is started and during the transient operation of the internal combustion engine 10, It is necessary to take measures.

Therefore, in this embodiment, as shown in FIG. 13, the output characteristic of the ion concentration sensor 31 which has changed with time is corrected to be normalized to the output characteristic of a new product. In this correction, the output characteristic of the ion concentration sensor 31 is monitored with reference to the detection value of the oxygen concentration sensor 29, and the characteristic is learned and corrected at any time. By executing the processing according to the flowchart shown in FIG. Will be realized.

The operation when the learning correction is executed in the arithmetic circuit 45 according to the flowchart shown in the figure will be described below.

When the routine shown in FIG. 14 is started, first, at step 200, a correction coefficient K described later is set to the value KK calculated at the time of the previous processing. When the setting of K is completed, the routine proceeds to step 210, where the signal processing voltage supplied from the signal processing circuit 44 is corrected based on the output signal of the ion concentration sensor 31.

That is, using the correction coefficient K set in step 200, the correction voltage value = K * process voltage (2) is calculated to calculate the correction voltage value representing the proper air-fuel ratio. Then, the result is stored as H ₁ .

Next, at step 220, it is determined whether the air-fuel ratio feedback control by the oxygen concentration sensor 29 is being executed, that is, whether the oxygen concentration sensor 29 has reached the activation temperature region and the internal combustion engine 10 is in the steady state. Determine. This routine corrects the output characteristic of the ion concentration sensor 31 based on the detected value of the oxygen concentration sensor 29 as described above, and the accurate air-fuel ratio is detected based on the oxygen concentration sensor 29. This is a prerequisite.

Therefore, when it is determined in step 220 that the air-fuel ratio feedback control by the oxygen concentration sensor 29 is not being executed, the current processing is ended without performing any processing. On the other hand, when it is determined that the air-fuel ratio feedback control by the oxygen concentration sensor 29 is being executed, the routine proceeds to step 230, where the air-fuel ratio A / F based on the detection value of the oxygen concentration sensor 29 is calculated, and the value is calculated. Store as A.

Next, in step 240, based on H ₁ stored in step 210, that is, based on the output value of the ion concentration sensor 31, a preset map as shown by the solid line in FIG. 15 is referred to. Then, the air-fuel ratio A / F is calculated, and the value is stored as B.

Then, in the following step 250, | A
It is determined whether -B | is smaller than a predetermined determination value ε. Here, assuming that the output characteristics of the ion concentration sensor 31 have not changed and correction is not required, A and B should be substantially equal values. In addition, as shown in FIG. 15, when the output value of the ion concentration sensor 31 is lower than a predetermined level due to aging (curve shown by a broken line in FIG. 15), A> B should hold. is there.

Therefore, if | AB | <ε is satisfied, it means that the correction voltage value calculated in step 210 does not need to be corrected at this moment. In such a case, the current process is terminated. And | AB |
If it is determined that <ε is not satisfied, it is necessary to update the correction coefficient K to a new value, and the process proceeds to step 260.

That is, the processing from step 260 onward is as follows.
The correction voltage value lowered as shown by the broken line in FIG. 15 due to the change in the output characteristic of the ion concentration sensor 31 is corrected to the value that can be corrected to the normal correction voltage value as shown by the solid line in FIG. It tries to update the value. Below, Figure 1
The procedure for updating the correction coefficient K will be described with reference to FIG.

As shown in FIG. 15, if the air-fuel ratio calculated based on the output value of the oxygen concentration sensor 29, that is, the true air-fuel ratio is A, it is calculated based on the output value of the ion concentration sensor 31. The corrected voltage value should originally be H ₂ . However, when the output characteristic of the ion concentration sensor 31 changes with time, the value thereof becomes less than H ₁ as shown by the broken line in FIG.

Therefore, in order to accurately calculate the air-fuel ratio from the output value of the ion concentration sensor 31, the above step 21
It is necessary to correct the corrected voltage value calculated as H _{1 at} 0 to H ₂ . Then, when such correction is performed, the characteristic of the corrected voltage value calculated based on the output value of the ion concentration sensor 31 matches the characteristic shown by the solid line in FIG. 15, and the accurate calculation of the air-fuel ratio is performed. Will be realized.

Therefore, in step 260, first, the normal corrected voltage value for the true air-fuel ratio A is back-calculated from the map shown by the solid line in FIG. 15, and in the following step 270, the correction coefficient K is updated as in the following equation. (In the formula, _n and _n-1 indicate after updating and before updating) K _n = (H ₂ / H ₁ ) * K _n-1 (3) Then, the value after updating is stored as KK. This processing ends.

Therefore, when this routine is started next time, the calculation of (H ₂ / H ₁ ) * K _n-1 * process voltage = (H ₂ / H ₁ ) * H ₁ = H ₂ is performed in step 210. When executed, the processing voltage value will be calculated as H ₂ . As described above, according to the apparatus of the present embodiment, even if the output characteristic of the ion concentration sensor 31 changes, the change can be canceled and an appropriate corrected voltage value can be calculated. An appropriate air-fuel ratio can be calculated based on the value.

Then, the learning correction of the corrected voltage value is
Since the configuration is performed during the air-fuel ratio feedback, when performing the air-fuel ratio feedback control based on the output value of the ion concentration sensor 31 immediately after the internal combustion engine 10 is started and when the internal combustion engine 10 is in the transient state. Always realizes highly accurate calculation of the air-fuel ratio.

That is, according to the present embodiment, after the internal combustion engine 10 is started, until the oxygen concentration sensor 29 is activated, the internal combustion engine 10 is activated based on the output value of the ion concentration sensor 31. After conversion, the ion concentration sensor 31
Based on the output values of both the air-fuel ratio sensor 29 and the air-fuel ratio sensor 29, it is possible to calculate the air-fuel ratio with high accuracy and without time delay.

Therefore, the air-fuel ratio feedback control can be executed in a wider area and with higher responsiveness as compared with the air-fuel ratio control device which takes in only the output value from the oxygen concentration sensor and calculates the air-fuel ratio. Become. Further, as compared with the air-fuel ratio control device that calculates the air-fuel ratio based only on the output value from the ion concentration sensor, the calculation accuracy of the air-fuel ratio is significantly improved, and more appropriate air-fuel ratio feedback control can be executed.

[0103]

As described above, according to the invention described in claim 1, when the oxygen concentration sensor does not reach the activation temperature region, the air-fuel ratio is calculated based on the value detected by the ion concentration detecting means. , The air-fuel ratio control based on that value is executed. Then, after the oxygen concentration sensor 1 is activated, more accurate air-fuel ratio control can be executed based on the output value of the oxygen concentration sensor exhibiting stable output characteristics.

Therefore, according to the air-fuel ratio control device of the present invention, it is possible to execute the air-fuel ratio control in a wider range than the air-fuel ratio control device which employs only the oxygen concentration sensor, and the ion concentration detecting means. Compared with the air-fuel ratio control device that employs only the air-fuel ratio control device, it has the feature that it can execute highly accurate air-fuel ratio control.

According to the second aspect of the invention, when the internal combustion engine is in a transient state and the amount of fuel to be supplied fluctuates at any time, the air-fuel ratio of the burned mixture is determined by the ion concentration detecting means. Can be detected without time delay. Therefore, unlike the case where the oxygen concentration sensor detects the air-fuel ratio, it is possible to execute the air-fuel ratio control without a time lag.

Further, according to the air-fuel ratio control device of the present invention, even if the air-fuel ratio fluctuates greatly in the transient state, it is possible to roughly understand the air-fuel ratio based on the output value of the oxygen concentration sensor. It is possible to calculate an appropriate air-fuel ratio based on the detection value of the ion concentration detection means. Therefore, compared with the conventional air-fuel ratio control device, the accuracy of calculating the air-fuel ratio in the transient state is remarkably improved, and a more appropriate air-fuel ratio control can be realized.

[Brief description of drawings]

FIG. 1 is a principle diagram of an air-fuel ratio control device according to the present invention.

FIG. 2 is a configuration diagram of an embodiment of an air-fuel ratio control device according to the present invention.

FIG. 3 is a block configuration diagram of an example of a processing circuit of an output signal of an ion concentration sensor in the device of this embodiment.

FIG. 4 is a waveform showing an example of an output signal of an ion concentration sensor.

FIG. 5 is an example of a waveform after processing an output signal of an ion concentration sensor.

FIG. 6 is an example of a graph showing the relationship between the output signal and the air-fuel ratio of the exposed combustion gas of the ion concentration sensor.

FIG. 7 is another example of the waveform after processing the output signal of the ion concentration sensor.

FIG. 8 is another example of a graph showing the relationship between the air-fuel ratio of the exposed combustion gas of the ion concentration sensor and its output signal.

FIG. 9 is a diagram for explaining the relationship between the load state of the internal combustion engine and the air-fuel ratio of the air-fuel mixture.

FIG. 10 is an example of a graph showing how the air-fuel ratio and the exhaust gas acquisition mission change when the internal combustion engine decelerates rapidly.

FIG. 11 is a flowchart of an example of a routine process executed by the device of this embodiment.

FIG. 12 is an example of a graph showing changes over time in the output characteristics of the ion concentration sensor.

FIG. 13 is a diagram for explaining the necessity of normalizing the output characteristics of the ion concentration sensor.

FIG. 14 is a flowchart of an example of a routine process for learning and correcting the output characteristic of the ion concentration sensor.

FIG. 15 is a diagram for explaining the principle of learning correction of the output characteristic of the ion concentration sensor.

[Explanation of symbols]

 1, 29 Oxygen concentration sensor 2 Oxygen concentration sensor activity detection means 3 Ion concentration detection means 4 Air-fuel ratio control means 5 Transient state detection means 6 Air-fuel ratio control means 10 Internal combustion engine 23 Manifold catalytic converter 24 Underfloor catalytic converter 26, 27 Cranks Sensor 30 Combustion chamber 31 Ion concentration sensor 40 Electronic control unit (ECU) 41 Power supply 42 Resistor 43 Detection circuit 44 Signal processing circuit 45 Arithmetic circuit

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Makoto Ueno 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Shigeki Miyashita 1, Toyota Town, Aichi Prefecture, Toyota Motor Co., Ltd.

Claims (2)

[Claims] 1. An air-fuel ratio control for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, comprising an oxygen concentration sensor for detecting an oxygen concentration in combustion gas of an internal combustion engine, based on a detection value of the oxygen concentration sensor. In the apparatus, an oxygen concentration sensor activity detecting means for detecting whether or not the oxygen sensor has reached a predetermined activation state, an ion concentration detecting means for detecting the concentration of ions generated in the combustion chamber of the internal combustion engine, When the oxygen concentration sensor has not reached a predetermined active state, the air-fuel ratio of the combustion gas is calculated based on the ion concentration detected by the ion concentration detection means, and the internal combustion engine is responsive to the calculated value. An air-fuel ratio control device, comprising: an air-fuel ratio control means for controlling an air-fuel ratio of an air-fuel mixture to be supplied. 2. An air-fuel ratio control for feedback-controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine, comprising an oxygen concentration sensor for detecting an oxygen concentration in combustion gas of an internal combustion engine, based on a detection value of the oxygen concentration sensor. In the device, a transient state detecting means for detecting whether or not the operating state of the internal combustion engine exceeds a predetermined level, and an ion concentration detecting means for detecting the concentration of ions generated in the combustion chamber of the internal combustion engine. When the transient state exceeding the predetermined level is detected by the transient state detecting means, the combustion gas is generated based on the ion concentration detected by the ion concentration detecting means and the oxygen concentration detected by the oxygen concentration sensor. And an air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine in accordance with the calculated value. apparatus.