JP2856986B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to (an oxygen concentration sensor (O ₂ sensor) in this specification) air-fuel ratio sensor on the upstream side and downstream side of the catalytic converter is provided, the upstream and downstream air The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio control based on the output of a fuel ratio sensor.

[0002]

2. Description of the Related Art Conventionally, in an ordinary simple air-fuel ratio feedback control (single O ₂ sensor system), an air-fuel ratio sensor for detecting an oxygen concentration is provided upstream of a catalytic converter. Of the air-fuel ratio control accuracy.

For this reason, a second air-fuel ratio sensor is provided downstream of the catalytic converter in order to compensate for variations in output characteristics of the air-fuel ratio sensor, variations in components such as fuel injection valves, and changes over time or over time. Dual O ₂ that performs air-fuel ratio feedback control by a downstream air-fuel ratio sensor in addition to air-fuel ratio feedback control by an upstream air-fuel ratio sensor
A sensor system has already been proposed (see US Pat. No. 3,939,654).

FIG. 3 relates to a dual O ₂ sensor system, and is a block diagram showing an example of an air-fuel ratio control device using air-fuel ratio sensors on the upstream and downstream sides of a catalytic converter, respectively. In the figure, 1 is an engine, 2 is an air cleaner, 3 is an intake pipe, 4 is an intake manifold,
5 is an injector, 6 is a pressure sensor, 7 is a throttle valve, 8 is a throttle opening sensor, 9 is an idle switch, 10 is a first air-fuel ratio sensor, 11 is a second air-fuel ratio sensor, 12 is a catalytic converter, 13 Is the ignition coil, 14
Is an igniter, 15 is an exhaust pipe, 16 is a water temperature sensor, 20
Is a battery, 21 is an ignition key switch, 22
Denotes an electronic control unit, and 23 denotes a warning lamp.

[0005] A catalyst converter 12 is provided in the exhaust pipe 15. A first air-fuel ratio sensor 10 and a second air-fuel ratio sensor 11 are provided upstream and downstream of the catalyst converter 12. Each is provided to detect an air-fuel ratio of exhaust gas.

The pressure sensor 6 is for measuring the amount of air taken into the engine 1 from the intake pipe 3 through the intake manifold 4, and is a semiconductor type pressure sensor. The injector 5 is arranged upstream of the throttle valve 7 and injects fuel. The throttle valve 7 is provided with a throttle opening sensor 8 for detecting the opening of the throttle valve.

Further, the water temperature sensor 16 is a thermistor-type sensor for detecting a cooling water temperature of the internal combustion engine. Also,
The ignition coil 13 ignites with a signal from the igniter 14 and sends out the generated ignition signal to the electronic control unit 22.

Next, the electronic control unit 22 includes a pressure sensor 6, a water temperature sensor 16, a throttle opening sensor 8, an ignition coil 13, and an air-fuel ratio sensor 10 for detecting an air-fuel ratio.
The air-fuel ratio control is performed by inputting each signal from 11.

FIG. 4 is a detailed block diagram of the electronic control unit 22. In the figure, reference numeral 100 denotes a microcomputer, which is a CPU 200 for calculating an air-fuel ratio control amount or the like according to the outputs of the air-fuel ratio sensors 10 and 11 according to a predetermined program, and a free running for measuring a rotation cycle of the engine 1. A counter 201, a timer 202 for measuring time for various controls, an A / D converter 203 for converting an analog input signal into a digital signal,
It comprises a RAM 205 used as a work memory, a ROM 206 storing a program, an output port 207 for outputting a drive signal, a common bus 208, and the like.

Reference numeral 101 denotes a first input interface circuit which shapes the waveform of the primary side ignition signal of the ignition coil 13 and outputs it to the microcomputer 100 as an interrupt signal. When this interrupt signal is generated, the CPU
200 reads the value of the counter 201, calculates the cycle of the rotational speed of the internal combustion engine from the difference between the read value and the previous read value, and stores the cycle in the RAM 205.

Reference numeral 102 denotes a second input interface circuit, which inputs signals from the air-fuel ratio sensors 10 and 11, the pressure sensor 6, the throttle opening sensor 8 and the water temperature sensor 16 to the A / D converter 203. Output. Reference numeral 103 denotes an input / output port of the ON / OFF signal of the adder switch 99.
A third input interface circuit 104 for outputting the output signal to the output port 207 amplifies the drive output from the output port 207 and outputs the amplified drive output to the injector 5 and the warning lamp 23.

Next, the operation of the CPU 200 of the air-fuel ratio control device configured as described above will be described with reference to a time chart showing the behavior of the air-fuel ratio control of FIG. 6 based on the control block diagram of FIG. I will explain it.

First, a block 501 compares the output V ₂ of the second air-fuel ratio sensor 11 with a second predetermined signal (target value of air-fuel ratio control) which is set in advance by a comparator, and the output deviation V _S2. In the second PI controller which is a block 502 based on the above, the output deviation is _subjected to PI control, and a predetermined correction output V _2SH is output.

Next, a block 503 is a first predetermined signal which is set in advance and added to the output of the block 502 to be used as a judgment value V _TH of the first air-fuel ratio sensor 10. Then, the output V _{1 of} the first air-fuel ratio sensor 10 and the added value V _TH are compared by a comparator, and based on the output comparison value, the first PI controller which is the block 504 performs the feedback of the air-fuel ratio feedback. The correction amount C _FB is calculated.

Next, the correction amount C _{FB is applied} to block 5.
At 05, the basic fuel amount calculated from the intake air amount detected by the pressure sensor 6 is multiplied. In response to the multiplication result, in block 506, the acceleration / deceleration state is detected from the correction amount corresponding to the warm-up state of the internal combustion engine calculated based on the signal from the water temperature sensor 10 and the signal from the throttle opening sensor 8, A final fuel discharge amount is calculated by multiplying a fuel correction amount such as a correction amount corresponding to the acceleration / deceleration state. Then, in order to calculate the driving time of the injector 5 from this fuel amount, respective calculations are performed in blocks 507 and 508.

As described above, the air-fuel ratio control is performed by correcting the determination value of the first air-fuel ratio sensor 10 using the output of the second air-fuel ratio sensor 11. In the above control operation, if the output of the second air-fuel ratio sensor 11 provided downstream of the catalytic converter 12 is lean, the air-fuel ratio control is controlled to the rich side. On the other hand, the second air-fuel ratio sensor 1
If the output of No. 1 is rich, it is understood that the air-fuel ratio control is controlled to the lean side.

During the transient control, the catalytic converter 1
When the air-fuel ratio control is performed by the output of the second air-fuel ratio sensor 11 provided downstream of the second air-fuel ratio sensor 11, the second air-fuel ratio sensor 11 provided downstream of the catalytic converter 12 as shown in FIG.
There is a time delay until the output V2 of the _second air-fuel ratio changes, so the air-fuel ratio control leans under a rich atmosphere after the transient control due to the time delay, that is, the air-fuel ratio feedback control by the second air-fuel ratio sensor 11 becomes lean. It can be seen that overshoot occurs. This excessive leaning sometimes caused emission deterioration.

On the other hand, the catalyst of the catalytic converter 12 is designed so that its function is not significantly reduced as long as the vehicle is used within the range of operating conditions that can be normally considered. However, in the event of any cause during use, such as misfire, the function of the catalyst may be significantly reduced.

As a result, the catalytic converter 12 may run without sufficiently purifying the exhaust gas. Then, the behavior of the output V ₂ of the downstream second air-fuel ratio sensor 11 changes due to the influence of unburned gases such as HC, CO, and H ₂ . That is, the change degree of the output V ₂ of the second air-fuel ratio sensor 11 on the downstream side increases.

Here, when the above-described air-fuel ratio control is performed for the normal state and the deteriorated state of the catalyst, the catalytic converter 12
8 and 9 show the behavior of the first and second air-fuel ratio sensors 10 and 11 mounted on the upstream and downstream sides of FIG.

First, FIGS. 8A and 8B show the outputs of the first and second air-fuel ratio sensors 10 and 11 when the catalyst is normal. FIG. 8A shows the output V ₁ of the first air-fuel ratio sensor 10 and the first air-fuel ratio sensor 10.
The output V ₁ of the first air-fuel ratio sensor 10 is changed at an appropriate cycle by the air-fuel ratio feedback control. Further, FIG. 8 (b), the output V ₂ of the second air-fuel ratio sensor 11 indicates a relationship between the second predetermined value, the output V ₂ of the second air-fuel ratio sensor 11, since the catalyst is normal A substantially constant output A is obtained by the purifying action of the catalyst.

Next, FIGS. 9A and 9B show the outputs V ₁ and V ₂ of the first and second air-fuel ratio sensors 10 and 11 when the catalyst is deteriorated. FIG. 9A is similar to FIG.
(B) shows the relationship between the output V ₂ of the second air-fuel ratio sensor 11 and a second predetermined value, and the output V ₂ of the second air-fuel ratio sensor 11
_In No. 2, since the catalyst has deteriorated, the purifying action of the catalyst has decreased, and the change in the output V ₂ of the second air-fuel ratio sensor 11 has increased. As a result, there is a problem that the emission is reduced. For this reason, it is important to implement control that is less susceptible to deterioration of the catalytic converter 12.

[0023]

[Problems that the Invention is to Solve In the air-fuel ratio control system of a conventional internal combustion engine, the transient control, catalyst downstream the time delay output V ₂ of the second air-fuel ratio sensor 11 provided downstream of the catalytic converter 12 The feedback control based on the output V ₂ of the second air-fuel ratio sensor 11 on the side becomes temporarily excessive (excessive), and the output V ₂ of the second air-fuel ratio sensor 11 on the downstream side of the catalyst accompanying the deterioration of the catalyst. Changes greatly. For this reason, the air-fuel ratio control becomes over-controlled, and as a result, there is a problem that the emission is reduced.

The present invention has been made in order to solve the above-mentioned problems of the conventional example, and the air-fuel ratio control based on the signals of the air-fuel ratio sensors on the upstream and downstream sides of the catalyst is appropriately performed even during the transient operation and the deterioration of the catalyst. It is an object to obtain an air-fuel ratio control device for an internal combustion engine to be performed.

[0025]

An air-fuel ratio control apparatus for an internal combustion engine according to the present invention is provided on an upstream side and a downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of the internal combustion engine, respectively. A first and second air-fuel ratio sensor for detecting a concentration of a specific component in exhaust gas ;
It is longer than the time constant for eliminating noise, and the air-fuel ratio control is appropriate.
Filter processing time constant is 100 to 300 msec.
And filtering means have been set to filter in order to suppress the output deviation of the second air-fuel ratio sensor, the air-fuel ratio control quantity calculating means for calculating an air-fuel ratio control amount according to the output of the filtering means Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine according to the output of the first air-fuel ratio sensor and the air-fuel ratio control amount.

[0026]

In the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, the time is longer than a time constant for removing noise to the air-fuel ratio sensor.
Filter time constant so that air-fuel ratio control is appropriate.
The filter processing means set to 100 to 300 msec filters the output of the second air-fuel ratio sensor to suppress the output deviation of the second air-fuel ratio sensor, and the air-fuel ratio control amount calculating means includes a filter processing means. The air-fuel ratio control amount is calculated in accordance with the output of. The air-fuel ratio control means controls the air-fuel ratio of the internal combustion engine according to the output of the first air-fuel ratio sensor and the air-fuel ratio control amount. The air-fuel ratio fluctuation at the time of deterioration is reduced, and appropriate air-fuel ratio control is performed.

[0027]

【Example】

Embodiment 1 FIG. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram in which the output V2 of the _second air-fuel ratio sensor 11 is subjected to a filtering process by a smoothing output unit in the filtering process, and then the air-fuel ratio control is performed using the filtered sensor output. This is performed by the CPU 200 in the electronic control unit 22.

In FIG. 1, reference numeral 101 denotes a smooth output means for filtering the output V ₂ of the second air-fuel ratio sensor 11;
102 is an air-fuel ratio control unit based on the output of the filtered sensor, 103 is an air-fuel ratio control unit based on the output V1 of the _first air-fuel ratio sensor 10, and 104 is an injector that adds an output obtained by adding a basic fuel amount and other correction coefficients. 5 is output means for controlling the air-fuel ratio by sending it to the control unit 5.

That is, first, the second air-fuel ratio sensor 11
Output means 10 for filtering the output V ₂ from
1 to perform a filtering process. At this time, the filter processing time constant is set to about 100 to 300 mSec, not to the extent of removing extraneous noise (several mSec).

Using the filtered sensor output, the air-fuel ratio control means 102 controls the air-fuel ratio by the second air-fuel ratio sensor 11 on the downstream side of the catalyst, for example, similar to the above-described conventional example. Further, the air-fuel ratio control by the first air-fuel ratio sensor 10 on the upstream side of the catalyst by the air-fuel ratio control means 103 is performed in the same manner as described above.

As described above, based on the calculated result, the output means 104 adds the basic control amount and other correction items, and drives the injector 5 to perform the air-fuel ratio control. That is, in this embodiment, a smoothing operation means for filtering the output V2 of the _second air-fuel ratio sensor 11 is provided in the conventional air-fuel ratio control device.

As described above, the filtering of the output V ₂ of the second air-fuel ratio sensor 11 suppresses (reduces) the movement of the second air-fuel ratio sensor 11. For this reason, as shown by the dotted line in FIG. 7, the air-fuel ratio fluctuation after the transient operation is suppressed. Also, regarding the deterioration of the catalyst, the degree of change in the output of the second air-fuel ratio sensor 11 is suppressed, so that the air-fuel ratio control is suppressed. For this reason, the air-fuel ratio control is not over-controlled, and the deterioration of the emission is suppressed. Therefore, more appropriate air-fuel ratio control can be performed than before.

FIG. 2 shows the second air-fuel ratio sensor 11 described above.
In the flowchart showing the operation of the smoothing output means 101, this calculation is executed every predetermined time, for example, every 10 ms. In step S201, the second air-fuel ratio sensor 11
Read of the output V _2. Next, in step S202,
It is determined whether or not the sensor output is read for the first time after the power is turned on. If it is the first read, the smoothed output (filter value) is initialized in step S303, and the smoothing process ends.

In step S202, if it is not the first reading, the process proceeds to step S304, where the filter value (current) = filter value (previous) × (1−K _f ) + sensor output (current) × K _f K _f Performs a first-order filter operation on coefficients. Here, the time constant is set longer than the time constant for removing noise to the air-fuel ratio sensor, and is set to about 100 to 300 mSec so that the air-fuel ratio control is appropriate. By the above processing, the second air-fuel ratio sensor 1
Annealing for processing the first output V _2.

As a result, as shown in FIG. 5, the air-fuel ratio control which has conventionally been performed based on the deviation between the second predetermined signal (catalyst downstream target value) and the output V2 of the _second air-fuel ratio sensor is performed. Is to perform the air-fuel ratio control with the second predetermined signal (target value downstream of the catalyst) and the output deviation V _S2 of the smoothed output of the air-fuel ratio sensor. For this reason, the output deviation during the transient operation is reduced, and as a result, the air-fuel ratio control amount is suppressed, and the air-fuel ratio fluctuation during the transient operation is suppressed. When the catalyst deteriorates,
By using the smoothed output, the output deviation from the second predetermined signal is reduced, and as a result, the fluctuation of the air-fuel ratio is suppressed.
Note that the same effect can be obtained even when the second air-fuel ratio sensor 11 is a linear O ₂ sensor.

Embodiment 2 FIG. In the above embodiment has been described how to change the determination of the air-fuel ratio sensor 10 outputs at V ₂ first of the second air-fuel ratio sensor 11, the output V ₂ of the second air-fuel ratio sensor 11 Output V ₁ of 1 air-fuel ratio sensor 10
The same applies to the method of changing the air-fuel ratio control amount (P value, I value, delay time of feedback correction) using.

[0037]

As described above, according to the present invention, the air-fuel
Air-fuel ratio longer than the time constant for removing noise to the ratio sensor
Filter processing time constant is 100 to 3 so that control is appropriate
Since implementing the air-fuel ratio control based on the configured filtering means output which is obtained by filtering in order to suppress the output deviation of the second air-fuel ratio sensor of the 00Msec, touch
Accurate dual O ₂ control regardless of medium deterioration
Thus, the air-fuel ratio control correction amount can be suppressed, and the effect of reducing the air-fuel ratio fluctuation during transient operation and catalyst deterioration and performing appropriate air-fuel ratio control can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of a calculation process performed by a smoothing output unit in FIG. 1;

FIG. 3 is a system configuration diagram showing the entire air-fuel ratio control device.

FIG. 4 is a configuration diagram of an electronic control device.

FIG. 5 is a block diagram of a conventional air-fuel ratio control.

FIG. 6 is a waveform chart showing an example of an air-fuel ratio sensor behavior during conventional air-fuel ratio control.

FIG. 7 is a waveform diagram showing the behavior of the air-fuel ratio upstream and downstream of the catalyst during the transient operation according to the related art and the present invention.

FIG. 8 is a waveform chart showing the behavior of the conventional air-fuel ratio sensor when the catalyst is normal.

FIG. 9 is a waveform chart showing the behavior of the conventional air-fuel ratio sensor when the catalyst is deteriorated.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 1st air-fuel ratio sensor 11 2nd air-fuel ratio sensor 12 Catalytic converter 15 Exhaust pipe 101 Smooth output means (filter processing means)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/00-45/00

Claims (1)

(57) [Claims] 1. A first and a second air space provided upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, respectively, for detecting a concentration of a specific component in the exhaust gas. Noise to fuel ratio sensor and air-fuel ratio sensor
Is longer than the time constant for removing
Filter processing time constant is set to 100 to 300 msec.
And filtering means for filtering in order to suppress the output deviation of the second air-fuel ratio sensor have been, and air-fuel ratio control quantity calculating means for calculating an air-fuel ratio control amount according to the output of the filtering means, the An air-fuel ratio control device for an internal combustion engine, comprising: air-fuel ratio control means for controlling an air-fuel ratio of the internal combustion engine according to an output of a first air-fuel ratio sensor and the air-fuel ratio control amount.