JPH03111647A - Exhaust gas purifier - Google Patents

Abstract

PURPOSE:To improve purifying efficiency by comparing an air-fuel ratio sensor output with a basic signal through a waveform processing means whose time limit is controlled, generating an oscillation signal centered on integration value of an air-fuel ratio discriminating signal to add it to the air-fuel ratio discriminating signal for feedback control. CONSTITUTION:Basic injecting time is determined from an intake air amount Qa and engine speed Ne by a CPU 7 used in ECU 70 so as to add compensation of water temperature Tw, intake air temperature TA and acceleration increase. Besides, the output of an air-fuel ratio sensor 12 is compared with a reference signal 21 by a comparator 20 through a waveform processing circuit 26 whose time limit is controlled so as to integrate a rich/lean discrimination signal by means of an integrator 22, and the oscillation signals of amplitude and frequency corresponding to an engine running condition are generated by means of a generating circuit 24 with the output level centered. The discriminating signal is added to a signal proportionally amplified in a circuit 23 according to a driving condition for adding feedback compensation of air-fuel ratio. It is thus possible to make sufficient use of exhaust gas purifying ability of a catalytic converter.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an engine purification device, and more specifically,
The present invention relates to an exhaust gas purification device that performs feedback control to a predetermined air-fuel ratio using an air-fuel ratio sensor provided in an engine exhaust system to maximize the purification function of a three-way catalytic converter provided in an exhaust passage.

(Prior art) In order for the so-called three-way catalytic converter, which functions to remove the three harmful components contained in engine exhaust gas, to work effectively, the air-fuel ratio of the exhaust gas entering the three-way catalytic converter must be adjusted. It is necessary to maintain the air-fuel ratio close to the stoichiometric air-fuel ratio.For this reason, regardless of whether the fuel supply function is a carburetor type or a fuel injection type, an air-fuel ratio sensor (oxygen
An exhaust purification system has been adopted that uses a so-called Ot sensor (based on the action of a main battery) to feedback-control the air-fuel ratio of the air-fuel mixture taken into the engine. For example, JP-A-52-4
An air-fuel ratio control method using a conventional air-fuel ratio sensor disclosed in Japanese Patent Publication No. 8738, Japanese Patent Publication No. 62-12379, etc. will be briefly explained with reference to FIGS. 10 and 11. FIGS. 10 and 11 are signal waveform diagrams each showing the air-fuel ratio feedback control operation of the conventional device. In Figure 10 (
a), (a) of FIG. 11 is the output signal of the 0□ sensor which generates an output voltage according to the 02 concentration in the exhaust gas. Q)) in Figure 10 and (b) in Figure 11 are (Q)) in Figure 10 above.
a), The voltage signal in (a) of Fig. 11 is compared with the reference voltage signal of 0.5■, and the air-fuel ratio signal is waveform-shaped. 10th
As shown in (C) of the figure and (C) of FIG. 11, the air-fuel ratio is subjected to proportional-integral control (PI control).

The air-fuel ratio sensor detects 0□4 degrees in exhaust gas, and indicates that the air-fuel ratio during combustion in the engine combustion chamber is smaller than the stoichiometric air-fuel ratio (usually about 14.7) (hereinafter referred to as rich state). , ) or is large (hereinafter referred to as a lean state). The amount of fuel supplied to the engine, that is, the air-fuel ratio λ, is controlled as follows according to this discrimination signal.

First, the case where the engine speed Ne is low will be considered with reference to FIG. In FIG. 10, when the air-fuel ratio sensor output signal in (b) is reversed from a lean state to a rich state, the feedback control amount signal in (C) is delayed by a delay time D0 to shift the skip amount B0 as a proportional bone to the lean side. Just skip it. From then on, the air-fuel ratio signal in (b) is integrated toward the lean side with an integral constant (slope) C0 until the air-fuel ratio signal inverts from rich to lean. Skip to sideff1ao
, and then integrates toward the rich side with a slope C0 until the transition from lean to rich again occurs. This will be repeated in the following actions.

(g)) and (C) in Fig. 11 are feedback control amount signals ((C) in Fig. 11) for the air-fuel ratio sensor output signal (Φ in Fig. 11) when the engine speed Ne is high. The control method is the same as for low rotation. Note that the delay time D0 is to compensate for the difference in the detection response delay of the air-fuel ratio sensor output signal when the atmosphere around the detection part of the air-fuel ratio sensor changes from lean to rich or from rich to lean. In FIG. 11, the length is exaggerated for the sake of explanation. With this control method, the average air-fuel ratio can be controlled to the stoichiometric air-fuel ratio, and the exhaust purification function of the three-way catalytic converter can be maximized.

[Problem to be solved by the invention]

However, as is clear from FIGS. 10 and 11, the control period T0 and control amplitude angle 〇 are small at high engine speeds and high loads, and T6. AO also becomes larger. This is due to various transmission delays between the time when the controlled air-fuel ratio actually reverses and the time when the air-fuel ratio sensor output reverses. This is because the transmission delay increases at low rotation speeds and low loads. If the transmission delay becomes even larger, as shown in FIG. 10(C), even if the feedback control amount is skipped by 80 when the air-fuel ratio sensor is inverted, a phenomenon occurs in which the air-fuel ratio sensor does not invert and only inverts after a while of integration. Therefore, the control period T0 becomes much larger by the delay time from the reversal of the air-fuel ratio sensor to the reversal of the feedback control amount, and the control amplitude ^ accordingly. also becomes larger. As a result, engine vibration (hunting) especially during idling may cause discomfort to the driver, and the feedback control 'a may become leaner, as shown in Figure 10 (C) and Figure 11 (C). Since the waveform when reversing from rich to lean or from rich to lean differs between low engine speed and high engine speed, the variation (difference) in the detection response delay of the air-fuel ratio sensor itself at the time of reversal may be slightly different. There is a problem in that the delay time D0 that compensates for the detection response delay in the prescribed figure 100 may not be suitable depending on the engine operating conditions, and the control air-fuel ratio deviates from the stoichiometric air-fuel ratio, deteriorating the exhaust purification characteristics of the three-way catalytic converter. Ta.

Furthermore, due to variations in 0□ sensor characteristics and changes over time,
Since it is difficult to always achieve the maximum possible purification characteristics for each three-way catalytic converter, there are issues such as having to use a three-way catalytic converter with an excessively large capacity with some margin. there were.

The present invention has been made to solve the above-mentioned problems, and aims to provide an exhaust gas purification device that can improve the exhaust gas purification efficiency of a catalytic converter and can also reduce the capacity of the catalytic converter. purpose.

[Means to solve the problem]

The exhaust gas purification device according to the present invention includes an air-fuel ratio sensor, a comparing means for comparing an output signal of the air-fuel ratio sensor with a reference signal and outputting a discrimination signal, and an integrating means for integrating the discrimination signal.
a means for detecting the operating state of the engine; a proportional processing means for proportionally processing the discrimination signal; and a signal generating means for generating a vibration signal centered on the output level of the integrating means by changing the amplitude according to the proportional gain; A means for feedback controlling the air-fuel ratio of the engine based on the addition result of the vibration signal and the proportional processing means, and a means for feedback controlling the air-fuel ratio of the engine based on the addition result of the vibration signal and the proportional processing means; The air-fuel ratio sensor is provided with a signal processing means for delaying the response of the output signal of the air-fuel ratio sensor by an amount of time after the discrimination signal is inverted.

An exhaust gas purification device according to another aspect of the present invention includes an air-fuel ratio sensor, a comparing means for comparing an output signal of the air-fuel ratio sensor with a reference signal and outputting a discrimination signal, and an integrating means for integrating the discrimination signal. means for detecting the operating state of the engine; signal generating means for changing the period of vibration according to the operating state and generating a vibration signal centered on the output level of the integrating means; and means for detecting the air-fuel ratio of the engine based on the vibration signal. The system includes means for performing feedback control, and signal processing means for delaying the response of the output signal of the air-fuel ratio sensor by a predetermined time period depending on the operating state after the discrimination signal is inverted.

[For production]

The exhaust gas purification device according to the present invention obtains a lean signal by comparing the output signal of the air-fuel ratio sensor with a reference signal.

A signal that oscillates around a signal level proportional to and integrated with the rich discrimination signal is used as the air-fuel ratio control signal. Add signal processing that slows down the response of the sensor output signal.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the entire system of an embodiment of the present invention, which is a typical internal combustion engine equipped with a fuel injection device using a microcomputer.

The engine 1 is a known engine installed in a normal car, for example, a 4
This is a four-cylinder, spark-ignition engine that takes in combustion air through an air cleaner 2, an intake pipe 4, and a throttle valve 6. 3 represents a known intake air amount sensor that detects the amount of air taken in. Note that it is also possible to employ the intake pipe pressure sensor 15 instead of the intake air amount sensor 3. As the intake air amount sensor 3, various types such as a potentiometer type, a heat wire type, a Karman vortex type, and an ultrasonic type can be used. 5 is an intake temperature sensor that detects the temperature of intake combustion air and outputs a signal proportional to the detected temperature;
Reference numeral 10 denotes an engine cooling water temperature sensor that outputs a signal proportional to the engine cooling water temperature, and a thermistor type sensor is generally used. On the other hand, fuel is supplied from a fuel system (not shown) through electromagnetic fuel injection valves (hereinafter referred to as injectors) 8 provided corresponding to each cylinder. The injector 8 is of a constant injection pressure type, and the injection amount is proportional to the valve opening time. The exhaust gas after combustion is passed through the exhaust manifold 11. Exhaust pipe 13. It is released into the atmosphere through the catalytic converter 14 and the like. The air-fuel ratio sensor (also referred to as 0 sensor, λ sensor) 12 provided in the exhaust pipe 13 detects the oxygen concentration in the exhaust gas, that is, the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio, as a voltage. When the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich), the output is about 1 IV, and when the air-fuel ratio is larger than the stoichiometric air-fuel ratio (lean), the output is about 06 IV. The catalytic converter 14 is filled with a three-way catalyst that simultaneously purifies the three harmful exhaust gas components (CNOx, Co, and IC), and the zero rotation sensor 9, which exhibits the best purification performance near the stoichiometric air-fuel ratio, is connected to the ignition coil. The signal from the primary side terminal is used as a rotation synchronization signal, and this signal is used to control the injection start timing and calculate the rotation speed. A control circuit (hereinafter referred to as ECU) 7 calculates the optimum fuel injection amount based on the signals from the sensors 3 (or 15), 5, 9, 10.12 and the battery 16, and opens the injector 8. Control time.

Next, the internal structure of the ECU 7 will be explained in detail with reference to FIG. A microcomputer 70 is a main part of the ECU 7, and the inside thereof includes a known ROM, RAM, microprocessor, timer controller, etc., and has digital information input/output, calculation, and storage functions. The microcomputer 70- performs air-fuel ratio feedback control based on the detection signals from the intake air temperature sensor 5, engine cooling water temperature sensor 10, and pantry 16 among the above-mentioned sensors, and the output signal of the air-fuel ratio sensor 12. It is inputted sequentially through the input interface 71 and the A/D converter 72, and if the intake air amount sensor 3 is of the Karman vortex type,
The output pulse signal proportional to the air flow rate is input to the input port of the microcomputer 70 via the input interface 73 together with the output signal of the rotation sensor 9 and the input signal 17 of the key switch. On the other hand, the output signal of the air-fuel ratio sensor 12 is inputted to the inverting input terminal of the comparator 20 via the waveform processing circuit 26, and the output signal f of the reference signal forming circuit 21 is inputted to its non-inverting input terminal. The waveform processing circuit 26 receives the output signal of the comparator 20 from the microcomputer 70, such as a signal corresponding to a time length determined in accordance with the operating state of the engine 1, and receives the output signal of the comparator 20 for a predetermined period of time after the output of the comparator 20 is inverted. For example, a low-pass filter circuit with an electrically variable set-off frequency or a low-pass filter circuit with a predetermined cut-off frequency is used. It consists of a pass filter, a signal path selector switch, etc.

The discrimination signal of the comparator 20 is transmitted to the integrator 22 and the proportional amplifier circuit 23.
is input. The proportional amplification circuit 23 is configured to receive a signal from the microcomputer 70 according to the operating state of the engine 1 and variably set its gain, and proportionally amplify the discrimination signal from the comparator 20 using the gain. and output it. 24 is a vibration signal generation circuit which generates a rectangular wave vibration signal centered on the output signal level of the integrator 22, and the amplitude of the vibration signal is determined by the gain input from the proportional amplifier circuit 23 and the magnitude of the gain signal representing It corresponds to the situation. 25 is an adder which adds the output signal of the proportional amplification circuit 23 and the output (No. 3) of the vibration signal generation circuit 24 and outputs it to the input interface 71.As mentioned above, the addition result is input interface 71,
Microcomputer 7 via A/D converter 72
It is input to 0. 74 is a driver connected between the output port of the microcomputer 70 and the injector 8.

Here, focusing on fuel injection control (air-fuel ratio control), the microcomputer 70 outputs a fuel injection control signal calculated by a method described later via the driver 74, and sequentially drives the four injectors 8.

Next, a functional block diagram for such fuel injection control (injector drive time control) is shown in FIG. That is, ECU 7 operates according to the flow of the program.

The basic driving time determining means 30 determines the intake air flow rate Qa information from the intake air amount sensor 3 (or the pressure information from the intake pipe pressure sensor 15) and the rotation sensor 9. The intake air flow rate Qa/He information per engine rotation is determined from the engine rotational speed Ne, and the basic drive time T is determined based on this information. Next, the correction coefficient KW? according to the engine coolant temperature detected by the engine coolant temperature sensor 10? The cooling water temperature correction means 31 sets the correction coefficient KA? according to the intake air temperature detected by the intake air temperature sensor 5. an acceleration increase correction means 33 that sets a correction coefficient Kac for acceleration increase according to the rate of change of Qa/He (or intake pipe pressure information or throttle opening information); and a battery 1.
dead time correction means 34 for setting a dead time (invalid time) T in order to correct the drive time according to the voltage of step 6;
is provided on the program of the microcomputer 70 to operate. As a result of the feedback operation based on the detection signal of the air-fuel ratio sensor 12, the correction coefficient X
AF is determined by the air-fuel ratio feedback correction means 35 with the same meaning as each correction coefficient described above, and its operation will be explained using FIG. 4 showing a signal waveform diagram.

In FIG. 4, the solid line in (a) is the detection output waveform of the air-fuel ratio sensor] 2 when no vibration signal is applied according to the present embodiment, and the broken line in (a) is the waveform of the detection output of the air-fuel ratio sensor when no vibration signal is applied to the air-fuel ratio control signal. It shows the output waveform seen when a signal is applied. FIG. 4(b) is the input signal waveform to the comparator 20,
The solid line represents the processed signal waveform of the air-fuel ratio sensor signal output from the waveform processing circuit 26, and the two-dot chain line represents the signal VFaf of the reference signal forming circuit 21, which is the other input signal. The comparator 20, which compares the magnitudes of these two input signals, outputs a determination signal indicating whether the air-fuel ratio is rich or lean, as shown in FIG. 4(d). This discrimination signal is transmitted to the waveform processing circuit 26
．． It is input to an integrator 22 and a proportional amplifier circuit 23. The waveform processing circuit 26 uses the “old gh” Loll of this discrimination signal.
It consists of a voltage-controlled low-pass filter circuit whose cutoff frequency decreases only during time T, starting from when the level is inverted, and is shown in Fig. 4.
As can be understood by comparing it with the broken line waveform in a), as shown by the thick solid line in FIG. As will be described later, it is determined through a signal from the microcomputer 70, and is realized, for example, as follows. The waveform processing circuit 26 has a built-in digital timed pulse generator, and this timed pulse generator is triggered at the rising and falling timings of the discrimination signal.
The above-mentioned time is also determined by counting the number of clock pulses sent from the microcomputer 70 and ending the process when a predetermined count value is reached.

FIG. 4C shows the waveform of the timed pulse thus formed. The clock pulses sent out from the microcomputer 70 have a generation cycle that changes depending on the operating state of the engine.
If the period is designed to be short in proportion to Qa, the time T changes to become smaller as the intake air flow rate Oa becomes larger. A more desirable embodiment is a case in which a clock pulse is generated that changes its cycle in relation to both the intake air flow rate Qa and the engine speed Ne. This can be achieved by storing in the form of a two-dimensional table with input variables and sequentially reading out the values, or by determining the period using an algebraic expression including Qa and Ne. As shown in FIG. 4C, the time is preferably set to be slightly shorter than the reversal period of the detection output of the air-fuel ratio sensor 12 when there is no forced vibration. By modifying the air-fuel ratio sensor output signal waveform in this way, stable air-fuel ratio control is possible even when fuel is supplied using an air-fuel ratio control signal to which a vibration signal is added, as described later. By adding this, it is possible to reliably improve the purification efficiency of the three-way catalytic converter. If the output signal of the air-fuel ratio sensor 12 is not subjected to waveform processing as described above,
Regarding the sensor output waveform as shown by the broken line in a), for example, there is a cycle such as the fourth cycle, so as shown in the broken line in FIG. n cycles become unstable. That is, the rich/lean discrimination period is irregularly shortened or lengthened, resulting in an increase in the fluctuation of the average level of the air-fuel ratio, which is improved by adding a vibration signal.

It is known that the effect of improving the purification effect of the catalyst disappears, and the change actually becomes worse. Proportional amplifier circuit 23
Inputs a signal corresponding to the load condition of the engine l from the microcomputer 70, and sets the gain to the signal shown in FIG.
e), and the discrimination signal is processed proportionally to the gain.

For example, the microcomputer 70 determines the intake air amount Qa/Ne information per engine revolution as explained in FIG. If the operating state is larger, it is determined that the operating state is other than that, and a signal corresponding to the result of this determination is output to the proportional amplification circuit 23. As shown in FIG. 4(e), the proportional amplifier circuit 23 sets the gain to a relatively small predetermined value in the no-load operation state, and otherwise sets the gain to a relatively large predetermined value. Set.

On the other hand, the integrator 22 integrates the air-fuel ratio signal ((d) in FIG. 4) inputted from the comparator 20 as shown by the solid line in (f) in FIG. Output. The vibration signal generation circuit 24 generates a rectangular wave vibration signal centered on the output signal of the integrator 22 with an amplitude corresponding to the gain of the proportional amplification circuit 23 in the waveform of the broken line in FIG. 4(f). Output. The amplitude of this vibration signal increases as the gain increases, and it has a period shorter than the inversion period at which the output signal of the comparator 20 is inverted, and in FIG. or approximately 2 within one lean period)
・Exists for 3 cycles. The adder 25 is a proportional amplifier circuit 2
The output signal of the vibration signal generating circuit 24 (the signal indicated by the broken line in (f) of FIG. 4) is added to the output signal of the vibration signal generation circuit 24 (signal obtained by proportionally amplifying the air-fuel ratio signal of (d) in FIG. 4). An air-fuel ratio feedback control signal having a waveform shown by the solid line in the figure is generated. This signal is a voltage signal corresponding to the air-fuel ratio correction coefficient Kay, and is converted into a digital signal via the input interface 71 and the A/D converter 72 The gain is inputted to the microcomputer 70 as follows.The gain is changed in order to improve the air-fuel ratio controllability (mainly responsiveness) when changing from, for example, the state of unpaid pre-operation to other operating states. It was carried out in

Due to the above operation, the injector drive time T! nt can be calculated by the fuel injection time calculation means (program) according to the following formula as shown in FIG. The valve is opened twice per rotation in synchronization with the rotation of 1, and the fuel is supplied to the engine l.
supply to.

Tiaj -T* X Kwt X Kht X KA
I: AF+TD above fuel injection control (air-fuel ratio control <n
) is the air-fuel ratio correction coefficient KAF explained using FIG.
Except for the feedback control circuit for generating a corresponding voltage signal, already known techniques such as Japanese Patent Publication No. 62-123
The program is realized and operated by the method disclosed in Japanese Patent No. 79, etc., and explanation of the program operation using flowcharts and the like will be omitted here.

FIG. 5 is an example of experimental results showing the effect of the above operation.

The three-way catalytic converter used as the catalytic converter 14 is a catalyst currently in practical use with a reduced capacity. Figure 5 (a) - Figure 5 (c) (x
y engine rotation speed 2QOOr, p, m, intake pipe negative pressure 335m
+*Hg, intake air! 13.8P/s), the horizontal axis is the average air-fuel ratio A/F, and the vertical axis is the IIC purification efficiency ηa6. CO purification efficiency η. . , NOx purification efficiency η9°, respectively. As shown by the dashed line for this method and the solid line for the conventional method, the harmful components IIC, CO, and NOx contained in the exhaust gas are
Although the change in purification efficiency characteristics differs depending on the case, in any case, the purification efficiency improves when the average air-fuel ratio A/F is maintained near the stoichiometric air-fuel ratio, and therefore, the purification efficiency improves when the average air-fuel ratio A/F is maintained near the stoichiometric air-fuel ratio. High purification efficiency has been achieved.

As mentioned above, the three-way catalytic converter has a better exhaust gas purifying effect than supplying a mixture with a uniform air-fuel ratio to the engine, as it alternately produces a slightly richer and a slightly leaner mixture around the stoichiometric air-fuel ratio. Experiments have shown that the purification efficiency is higher when the water is supplied by Furthermore, according to the results of measuring the purification efficiency characteristics by changing the amplitude and period of the vibration to various values and using a catalytic converter with a small catalyst capacity, it was found that the air-fuel ratio sensor can obtain a rich or lean reversal output response. It has been found that the purification efficiency is improved by supplying rich and lean exhaust gases to the catalyst at a stoichiometric air-fuel ratio at a shorter cycle of approximately 115 to 1/6 than the regular cycle.

Next, a second embodiment of the present invention will be described.

The overall system configuration is the same as in Figure 1, but the ECUT
The internal structure is different from the first embodiment, and FIG. 6 shows the structure. In FIG. 6, the same or equivalent parts as in the first embodiment are given the same reference numerals. 24A is a vibration signal generation circuit that outputs the output signal of the integrator 22 and the D/A (digital/analog) from the microcomputer 70.
In response to the frequency control signal Vfrse sent out via the converter 75, a rectangular wave vibration signal is generated centered around the output signal level of the integrator 22. This is a so-called voltage controlled oscillator configured such that the frequency of the vibration signal is variably set according to the level of the signal Vrr*q. The output signal of the vibration signal generation circuit 24A is input to the input interface 71 as an air-fuel ratio feedback control signal.
, and are input to the microcomputer 70 via an A/D converter 72.

Since the fuel injection control is the same as that explained using FIG. 3 in the first embodiment, the explanation thereof will be omitted.

FIG. 7 is a signal waveform diagram showing the air-fuel ratio feedback control operation in this embodiment.

Next, the operation for determining the air-fuel ratio correction coefficient KAF will be explained with reference to FIGS. 6 and 7. FIG. 7(a) shows the detected output waveform of the air-fuel ratio sensor 12.

The solid line shows the output waveform when the vibration signal according to the second embodiment is not added, and the broken line shows the output waveform generated when the vibration signal is added to the air-fuel ratio control signal. FIG. 7(b) shows the input signal to the comparator 20, the solid line is the signal waveform after processing the air-fuel ratio sensor signal output from the waveform processing circuit 26, and the two-dot chain line is the other input signal. This is the signal νraf of a certain reference signal forming circuit 21. The comparator 20, which compares the magnitudes of these re-input signals, outputs a discrimination signal that is determined to be rich or lean, as shown in FIG. 7(C). This discrimination signal is input to the integrator 22 and the waveform processing circuit 26. The waveform processing circuit 26 starts from the time when the level of this discrimination signal is inverted, and calculates the time T,
Only during this period, the waveform is processed so as to ignore the rapid changes in the output signal of the air-fuel ratio sensor 12, and a signal as shown in FIG. 7(b) is output. The following operation of the waveform processing circuit 26 is the same as that explained using FIG. 4 in the first embodiment, and will therefore be omitted. The air-fuel ratio signal determined to be rich or lean by the comparator 20 ((C) in FIG. 7) is subjected to integration processing by the integrator 22 as shown by the solid line in (e) in FIG. Then, a rectangular wave vibration signal centered around this integrated output signal level is output as a waveform shown by the broken line in FIG. 7(e). (d) in FIG. 7 shows the data from the microcomputer 70 to the D/A converter 75
A frequency control electrical signal Vfr is input to the vibration signal generation circuit 24A via the frequency control signal Vfr. 9, in this case, rotation sensor 9
A voltage proportional to the engine rotational speed Ne obtained from the output of is sent out. The vibration signal generation circuit 24A receives the frequency control electric signal Vtrmq and performs change control to increase the frequency of the vibration signal in accordance with an increase in the engine speed Ne. As can be understood by comparing the signal waveform in Figure 7(d) with the signal waveform in broken line in Figure 7(e), the vibration frequency increases as the engine speed Ne increases. Also, this vibration signal exists for approximately 2 to 3 periods as shown in FIG. 7(e) within one rich or lean period of the signal in FIG. 7(C).

As described above, the vibration signal generation circuit 24A generates the air-fuel ratio feedback control signal shown in the waveform shown in FIG. 7 (same as the waveform indicated by the broken line in FIG. 7(e)). This signal is a voltage signal corresponding to the air-fuel ratio correction coefficient KAF, and is input into the microcomputer 70 as a digital signal via the input interface 71 and the A/D converter 72. Since the subsequent operations are the same as those in the first embodiment, their explanation will be omitted. In the case of this second embodiment as well, characteristics similar to those shown in FIG. 5 can be obtained.

In the case of the second embodiment as well, if no waveform processing is performed, the waveform signal in FIG. 7(a) is input to the comparator as it is, so in the case of the broken line waveform in FIG. 7(a), pulsation As shown by the broken line in Fig. 7 (C), there is a temporary inversion change, and the first
For the same reason as described in the embodiment, subsequent control cycles become unstable.

In the second embodiment, the frequency control electrical signal VfreQ
is made proportional to the engine rotation speed Ne, but it may be made proportional to the intake air flow rate Ωa of the engine, and may be made to correspond to the output of the intake air amount sensor 3 or the intake pipe pressure sensor 15. Better operation can be obtained by slightly changing Vfr□ depending on the output.

Furthermore, the integral characteristic of the integrator 22 may be made different in the direction in which the air-fuel ratio of the air-fuel mixture supplied to the engine is enriched and in the direction in which it is lean.

Next, a third embodiment of the present invention will be described.

The overall system configuration is the same as in Figure 1, but the ECUT
The internal structure is different from the second embodiment, and FIG. 8 shows the structure. In FIG. 8, the sixth embodiment of the second embodiment
The same or corresponding parts as those in the figures are given the same reference numerals, and the explanation thereof will be omitted. The third embodiment differs from the second embodiment in that a proportional amplifier circuit 23A with a constant gain and an adder 25 are added. The adder 25 receives the output signal of the proportional amplifier circuit 23A, which receives the output of the comparator 20, and the vibration signal generation circuit 2.
4A output signal and input the addition result as an air-fuel ratio feedback control signal to the ink face 71, A/D.
The signal is input to the microcomputer 70 via a converter 72.

Since the fuel injection control is the same as that explained using FIG. 3 in the first embodiment, the explanation thereof will be omitted.

FIG. 9 is a signal waveform diagram showing the air-fuel ratio feedbank control operation in the third embodiment.

Next, the operation for determining the air-fuel ratio correction coefficient KAF will be explained with reference to FIGS. 8 and 9. FIG. 9(a) shows the detected output waveform of the air-fuel ratio sensor 12. (a
The solid line in ) is the output waveform when the vibration signal according to this example is not added, and the broken line in (a) is the output waveform when the vibration signal is added to the air-fuel ratio control signal. be. 0) in FIG. 9 is the input signal waveform of the comparator 20,
The solid line indicates the signal waveform after processing the air-fuel ratio sensor output via the waveform processing circuit 26, and the two-dot chain line indicates the other input signal, the signal V of the reference signal forming circuit 21. , is shown. FC) in FIG. 9 is the waveform of the output signal of the comparator 20,
(d) in Figure 9 is the D/A from the microcomputer 7o.
This is the waveform of the frequency control electric signal VfrlIQ input to the vibration signal generation circuit 24A via the converter 75, and is proportional to the engine rotation speed Ne. The solid line in (e) of FIG. 9 is the waveform of the output signal of the integrator 22, and the broken line is the waveform of the output signal of the vibration signal generation circuit 24A.
The operations for obtaining signals with waveforms from ) to (e) have been described in the second embodiment, so their explanation will be omitted.

In addition, a proportional amplifier circuit 2 inputs the output signal of the comparator 20.
3A proportionally amplifies the input signal with a predetermined gain and outputs it to adder 2.
Output to 5. The adder 25 adds the output signal of the proportional amplifier circuit 23A and the output signal of the vibration signal generation circuit 24A (broken line in FIG. 9(e)) to produce a waveform shown in the solid line in FIG. 9(f). generates an air-fuel ratio feedback control signal.

This signal is a voltage signal corresponding to the binary air-fuel ratio correction coefficient KAF, and is input to the microcomputer 70 as a digital signal via the input interface 71 and the A/D converter 72. Since the subsequent operations are the same as those in the first embodiment, their explanation will be omitted. Also in the case of this third embodiment,
Characteristics similar to those shown in FIG. 5 are obtained.

In the case of the third embodiment as well, when the waveform is not processed, it is instantaneously reversed as shown by the broken line in FIG. It becomes stable.

Also in the third embodiment, the frequency control electrical signal vtr*q
Instead of being proportional to the engine rotational speed Ne, it may be made proportional to the intake air amount of the engine. It is also more effective to change Vfr@11 according to the cooling water temperature.

In each of the above embodiments, the feedback operations shown in FIGS. 4, 7, and 9 have been explained in an analog manner, but for example, the output signal of the comparator 20 or the air-fuel ratio sensor A/D conversion is performed in a time sufficiently shorter than the response time of the fuel ratio sensor 12, and in synchronization with the A/D conversion cycle,
If the subsequent operations are executed, it will become somewhat discrete, but
Operations completely similar to those shown in FIGS. 4, 7, and 9 can be realized digitally, and effects similar to those of the above embodiments can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the output of the air-fuel ratio sensor is
Via a time-controlled waveform processing means, an air-fuel ratio discrimination signal for obtaining an air-fuel ratio control signal is generated by comparing it with a reference signal, and a vibration signal centered on the signal level obtained by integrating this air-fuel ratio discrimination signal. is generated, and the imaging width or frequency of this vibration signal is changed according to the operating state of the engine,
The air-fuel ratio of the engine is feedback-controlled based on the vibration signal or a signal obtained by adding a signal obtained by proportionally amplifying the air-fuel ratio signal with a gain according to the operating state, and the waveform processing means further controls the air-fuel ratio After the output level of the discrimination signal is reversed, waveform processing is performed to ignore rapid changes in the output signal of the air-fuel ratio sensor for a predetermined period of time depending on the engine motion state. Air-fuel ratio feedback control is now possible to fully utilize the exhaust gas purification ability of the catalytic converter installed in the exhaust system, making it possible to maintain high exhaust gas purification efficiency over a wider range of air-fuel ratios than before. This has the effect of reducing the capacity.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the entire system of an exhaust gas purification device according to an embodiment of the present invention, Fig. 2 is a block diagram of a control circuit system according to the first embodiment of the present invention, and Fig. 3 is a block diagram of the above-mentioned first embodiment, etc. FIG. 4 is a signal waveform diagram showing the air-fuel ratio feedback control operation in the first embodiment, and FIG. 5 is a comparison between the conventional system and the embodiment of the present invention. A comparison diagram showing an example of experimental data showing the results, FIG. 6 is a configuration diagram of the control circuit system according to the second embodiment, and FIG. 7 is a signal waveform diagram showing the air-fuel ratio feedback control operation in the second embodiment. , FIG. 8 is a configuration diagram of the control circuit system according to the third embodiment, FIG. 9 is a signal waveform diagram showing the air-fuel ratio feedback control operation in the third embodiment, and FIGS. FIG. 6 is a signal waveform diagram showing each fuel ratio feedback control operation. In the diagram, ■...Engine, 3...Intake air amount sensor, 4...
...Intake pipe, 6...Throttle valve, 7...ECU,
8...Injector, 9...Rotation sensor, 1]...
・Exhaust manifold, 12... Air-fuel ratio sensor, 13.
...Exhaust pipe, 14...Catalytic converter, 15...Intake pipe pressure sensor, 20...Comparator, 21...Reference signal formation circuit, 22...Integrator, 23.23A... Proportional amplifier circuit, 24° 24A... Vibration signal generation circuit, 2
5... Adder, 26... Waveform processing circuit, 70...
Microcomputer, 71... Input interface, 72... A/D converter, 73... Input interface, 74... Driver, 75... D/A converter.

Claims (2)

[Claims] (1) An air-fuel ratio sensor that is installed in an engine exhaust system that has a catalytic converter that removes harmful components of engine exhaust gas, and that detects the air-fuel ratio from the engine exhaust gas components, and an output signal of the air-fuel ratio sensor. , a comparison means for outputting a discrimination signal indicating whether the air-fuel ratio is lean or rich; an integrating means having a predetermined integral characteristic for integrating the discrimination signal; a detection means for detecting the operating state of the engine; A vibration signal having an amplitude that changes according to a proportional processing means to be processed and a proportional gain of the proportional processing means and having a period shorter than the inversion period of the discrimination signal is centered around the output signal level of the integrating means. An exhaust gas purification device comprising a signal generating means for generating a signal, and a means for feedback controlling the air-fuel ratio of the engine based on the addition result of the vibration signal and the output signal of the proportional processing means, After the output state of the rich discrimination signal is reversed, receiving a detection signal from the engine operating state detection means, for a predetermined period of time depending on the engine operating state.
An exhaust gas purification device comprising: a signal processing means for slowing down the response of the output signal of the air-fuel ratio sensor input to the comparison means. (2) An air-fuel ratio sensor that is installed in the engine exhaust system and has a catalytic converter that removes harmful components from the engine exhaust gas, and that detects the air-fuel ratio from the engine exhaust gas components, and an output signal of the air-fuel ratio sensor. , a comparing means for outputting a discrimination signal of whether the air-fuel ratio is lean or rich, an integrating means having a predetermined integral characteristic for integrating the discrimination signal, a detection means for detecting the operating state of the engine, and a detection means for detecting the operating state of the engine. signal generating means that receives the signal and generates a vibration signal having a period that is controlled to change according to the operating state of the engine, with the output signal level of the integrating means as the center; and a means for feedback controlling a fuel ratio, the exhaust gas purification device comprising: a means for feedback controlling a fuel ratio, wherein after the output state of the lean/rich discrimination signal is reversed, the comparison is performed for a predetermined time according to the operating state of the engine. An exhaust gas purification device comprising signal processing means for slowing down the response of the output signal of the air-fuel ratio sensor input to the means.