JPH03217634A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE:To keep the best emission by utilizing catalytic action fully, even if the catalytic performance has been lowered due to deterioration, through decreasing an air fuel ratio feedback control constant when a reversing interval of an output of a down stream air-fuel ratio sensor becomes smaller than a preset reference value. CONSTITUTION:When deterioration of catalytic performance has been detected by means of a judging means 41 on the basis of, e.g. the output OSR2 of an O2 sensor 40, which is arranged in an exhaust passage in a downstream of a catalytic converter and outputs a signal according to the air-fuel ratio of exhaust gas, the control constant necessary for calculating an air-fuel ratio feedback correction amount is decreased by means of a changing means 42. When the control constant has been decreased, at least one of a proportional part and an integral part is decreased, e.g. in the case of a proportional-plus- integral control, and amplitude of the air-fuel ratio feedback correction amount alphais decreased. Consequently, the amplitude corresponds to the degree of deterioration of the catalytic performance and the best emission can be kept.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention provides a device for performing feedback control of an air-fuel ratio;
In particular, the present invention relates to purifying exhaust gas by making the most of the capabilities of a catalytic converter.

(Jumei's technique? In) Oxygen sensors (0
There is a so-called Guburu 02 sensor system device (Japanese Patent Application Laid-open No. 1-113552, Japanese Patent Application Laid-Open No. 1979-5), which is equipped with
8-72647).

To explain this with younger brother diagram 10, the diagram shows that the air-fuel ratio is 7 i.d. γ9'MI based on the upstream gao2 sensor output OSRI.
This is a routine for calculating the positive coefficient α, which is calculated every predetermined time (
For example, every Ams).

S I F++ μ Tower side Convex 1F ・7 赫 1- Re 1 Torou U- ＾ - Check whether the feedback control condition (feedback control condition is abbreviated as rF/BJ in the figure. The same applies hereinafter) is satisfied. Check it, and if it is, proceed to S2. Even if 1! , when the cooling water temperature Tw is below a predetermined value, at the time of starting, immediately after starting, during fuel increase for warming up, when the output signal of the upstream 02 sensor has never been reversed, when fuel is cut, etc., feedback control is performed. This is a case where the condition is not satisfied, and the air-fuel ratio feedback control condition is satisfied in other cases.

In S2, the upstream side 02 sensor output OSRI is A/D converted and taken in, and in S3, OSRI is compared with a slice level SLF (for example, 0.45V) corresponding to the buried air-fuel ratio,
If OSRI≦SLF, it is determined that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the 7-lag F1 is lowered (F1=0) in S4.

If OSRI>SLF, a 7-lag F1 is set in S5 (F=1).

7 lag F1 is a flag indicating whether the air-fuel ratio is on the rich or lean side, F1=0 indicates that it is on the lean side, and F1=1 indicates that it is on the rich side.

86 to S8 are parts where four cases are divided by comparing the previous F1 value and the current F1 value, S9 to S1
2 is a part that calculates the air-fuel ratio feedback correction coefficient α based on the results of the case classification, and is summarized as follows.

(i) At 86→S7→S9, it is determined that the richness is immediately after a sudden reversal, and the proportional amount PL is added to α (α
=a+PL). In addition, the temperature and air-fuel ratio are returned to the rich side in steps.

(ii) In S6→S7→SIO, it is determined that the state has just changed from lean to rich, and the proportional amount PR is subtracted from a (a=α−PR). With this, the air-fuel ratio is returned to the lean side in steps.

(iii) In S6→S8→S11, it is determined that lean is in effect this time as well, and the integral IL is added to a (α=α10×L).

With this, the air-fuel ratio is gradually returned to the rich side.

(iv) In S6→S8→S12, it is determined that it is rich this time as well, and the integral IR is subtracted from a (α=aIR).

As a result, the void ratio is gradually returned to the lean side.

Figure 11 shows the downstream side 02 sensor output OSR2 and the upstream side 0.
This is a routine for correcting a determined by two sensors.
It is executed at predetermined time intervals (for example, every 512+os). The reason why the execution cycle (512ass) in this case is longer than that of the routine shown in Fig. 10 is that air-fuel ratio feedback control is mainly performed by the upstream 02 sensor output, which has good responsiveness, and is controlled by the downstream 02 sensor, which has poor responsiveness. This is to make the control subordinate.

In steps 321 to 25, it is determined whether the conditions for feedback control of the air-fuel ratio by the downstream O2 sensor are satisfied. For example, in addition to failure of the feedback control condition by the upstream 02 sensor (S 2 1 ), when the cooling water temperature Tw is below a predetermined value (70° C. in this case) (S 2
2), when the throttle valve is fully closed (LL=1) (82
3), when the load is small (Qa/Ne<X +) (S
2 4 ), when the downstream side 02 sensor is not activated (S 2 5 ), etc. are cases where the feedback control condition is not satisfied, and other cases are cases where the feedback control condition is satisfied.

If the feedback control conditions are satisfied, the process proceeds to 826, where the downstream side 02 sensor output OSR2 is A/D converted and fetched, and in S27, OSR2 is compared with the slice level SLR (for example, 0.55v) corresponding to the stoichiometric air-fuel ratio. , OS
Judging that R2≦SLR is on the iirl7-on side, 3
The process proceeds to steps 28 to 31, and conversely, if OSR2>SLR, it is determined that the rich side is present, and the process proceeds to steps 832 to 35. In addition,
The SLR is set slightly higher than the SLF, taking into account that the output characteristics differ due to the influence of energy upstream and downstream of the catalytic converter, and that the deterioration rate differs.

In S28, a constant value ΔP. (Pt.=
PL + ΔPL), and in S29, the constant value ΔP is calculated from the proportional amount PR.
Subtract R < (P R = P R - ΔPR). As a result, the air-fuel ratio as a whole shifts to the rich side.

However, in order to reduce the increase in the amplitude of a due to the increase in PL at 828, at S30, the integral ■, is kept at a constant value ΔIL
Subtract <(IL = IL - ΔIL). In addition, in S31, a constant value Δ■R is added to the integral IR in order to reduce the delay in the reversal of the upstream 02 sensor output from lean to rich due to the decrease in PR in S29 (IR=IR
+ΔIR).

By such correction control of a in S28 to S31, the waveform of the air-fuel ratio feedback correction coefficient a changes from the waveform shown in the upper part of FIG. 13 to the lower part.

In other words, when it is determined that the air-fuel ratio is on the lean side from the downstream side 02 sensor output, as shown in the upper part of Fig. 13, due to the asymmetry of α (for example, PL = 8%, PR = 2%), This is a state in which the reversal period of the engine control is long, and in this state, the amplitude of fluctuation around the buried air-fuel ratio becomes large, and the purification performance deteriorates.

From this state, I. By decreasing the amplitude of a,
Moreover, by increasing I, the time point at which the upstream 02 sensor output changes from rich to lean is shortened (that is, the reversal cycle of feedback control is shortened).

Similarly, according to 332 to S35, the waveform of a is the first
Changed from the upper row to the lower row in Figure 4.

FIG. 12 shows a routine for calculating the fuel injection pulse width Ti [ms] at every predetermined crank angle (for example, 36
Executed every 0°CA).

In S41, the basic injection pulse width T p("K-Q a/N
e, where K is a constant) [mS].

In S42, the sum CO of 1 and various correction coefficients (for example, water temperature increase correction coefficient KTW) is calculated.

In S43, the fuel injection hull width Ti to be output to the injector is determined by Ti=Tp-CO·a+TS. Note that Ts [ms] is the invalid pulse width.

In S44, Ti is set.

(Problem H to be solved by the invention) By the way, in such a device, the air-fuel ratio in the downstream 02 sensor, where performance deterioration is less likely to occur in the upstream 02 sensor, is determined when performance deterioration occurs in the upstream 02 sensor. ν1 is set so as to compensate for control accuracy.

However, since it is assumed that the catalytic converter is normal, if performance deterioration occurs in the catalytic converter, emissions will deteriorate due to this.

This is because the amplitude of a that provides the best emission depends on the degree of performance deterioration of the catalyst, as shown in FIG. For example, assume that the amplitude W1 of a is set with a margin greater than the line shown (indicating the limit value) for a catalyst with no performance deterioration.

In this case, if the degree of performance deterioration of the catalyst progresses beyond A shown in the figure, it will be located above the line with the same amplitude W1 of α, and it will no longer be possible to optimize emissions.

This invention was made with attention to such conventional problems, and it is an object of the present invention to provide a device that maximizes the use of the catalytic ability even when the performance of the catalytic converter progresses. target

(Means for Solving the Problems) As shown in FIG. 1, the present invention includes sensors 31 and 32 that respectively detect the engine load (for example, intake air amount Qa) and the rotational speed Ne, and means 33 for calculating the basic injection amount Tp accordingly, a sensor (for example, 02 sensor) 34 that is installed in the exhaust passage upstream of the catalytic converter and outputs an output according to the exhaust air-fuel ratio, and this sensor output OS
means 35 for determining whether or not the air-fuel ratio has reversed past the target value by comparing RI with a predetermined target value (for example, stoichiometric air-fuel ratio); means 36 for calculating a feedback correction amount α of the air-fuel ratio so as to control the air-fuel ratio; and means 37 for correcting the basic injection amount Tp using the air-fuel ratio feedback correction amount a to determine the fuel injection amount T1; In an engine air-fuel ratio control device comprising a means 38 for outputting this injection amount Ti to a fuel injection device 39, a second sensor ( 02 sensor) 40, means 41 for determining whether performance deterioration has occurred in the catalytic converter based on the sensor output OSR2, and the air-fuel ratio feedback correction amount when it is determined that performance deterioration has occurred. Means 42 for reducing the control constant required for calculation of is provided.

(Function) In the second invention, the degree of performance deterioration of the catalytic converter is detected by the downstream air-fuel ratio sensor output OSR2 (for example, the reversal period of this output OSR2), and it is determined that the performance deterioration has occurred in the catalytic converter. , the control constant of air-fuel ratio feedback control is reduced.

When the control constant becomes smaller, for example, according to proportional-integral control, at least one of the proportional component and the integral component becomes smaller, so that the amplitude of the air-fuel ratio feedback correction amount α is reduced.

On the other hand, the amplitude of α that provides the best emission becomes smaller as the degree of catalyst performance deterioration progresses.

The reason why the amplitude of α is made small as described above is to match the characteristics of the catalyst ability, and as a result, the amplitude of a controlled by this invention corresponds to the degree of performance deterioration of the catalyst. .

(Embodiment) FIG. 2 is a system diagram of one embodiment. In the figure, intake air passes from the air cleaner through the intake pipe 3 to the engine 1.
The fuel is drawn into the control unit 2 cylinder.
The fuel is injected from an injector (fuel injection device) 4 toward the intake boat of the engine 1 based on an injection signal from the engine 1 .

The gas combusted in the cylinder is introduced into the catalytic converter 6 located downstream of the exhaust pipe 5, where the harmful components (CO=HC, NOx) of combustion are purified by a three-way catalyst and discharged. .

The intake air amount Qa is detected by the air 7 low meter 7,
The flow rate is controlled by a throttle valve 8 that is interlocked with an accelerator valve. The engine speed Ne is detected by a crank angle sensor 10, and the water jacket cooling water temperature Tw is detected by a water temperature sensor 11.

02 sensors (air-fuel ratio sensors) 12A and 12B provided in the exhaust pipes upstream and downstream of the catalytic converter 6, respectively, are as follows:
It has a characteristic that changes suddenly at the latent air-fuel ratio, and outputs a so-called binary value indicating whether the mixture is richer or leaner than the mixture at the latent air-fuel ratio. Note that the sensor is not limited to the 02 sensor, but may be a wide range air-fuel ratio sensor, a lean sensor, or the like.

9 is a sensor for detecting the opening degree of the throttle valve 8, 13 is a knock sensor, and 14 is a high speed sensor.

Outputs from the air 7 low meter 7, crank angle sensor 10, water temperature sensor 11, two 02 sensors 1 2A, 1 2B, etc. are input to the control unit 21, and the control unit 21 sends fuel injection signals to the injector 4. However, monitor display signals are output to the diagnostic monitor 28, respectively.

FIG. 3 shows a block diagram of the control unit 21, and the CPU 23 performs feedback control of the air-fuel ratio and also performs performance deterioration diagnosis of the catalytic converter 6 in accordance with the steps shown in FIGS. 4 to 6.

The I/O boat 22 functions as the output means 38 in FIG.

The younger brother figure 4 is an air-fuel ratio feedback control routine using the upstream side 02 sensor, and the control contents are the younger brother figures 10 and 12, which are unprecedented.
It is almost the same as the figure.

In 652-S54, it is determined whether the air-fuel ratio has reversed with this SLF as a boundary by comparing the upstream side 02 sensor output OSRI and the slice level SLF equivalent to the buried air-fuel ratio, and in 355-S62, this determination result is determined. Accordingly, the air-fuel ratio correction amount α is calculated so that the air-fuel ratio is controlled to be close to the theoretical air-fuel ratio. In other words, 852~S
54, the function of the reversal determining means 35 in FIG.
At S62, the function of the air-fuel ratio feedback correction amount calculation means 36 shown in FIG. 1 is performed.

The fuel injection pulse width Ti is determined from the value α obtained in this way according to FIG. 1st at 841 in younger brother 12 figure
The Isono of the basic injection amount calculation means 33 shown in the figure is determined in S42 and S43.
In this step, the function of the fuel injection amount determining means 37 shown in FIG. 1 is performed.

FIG. 5 shows a routine for measuring the reversal period of the downstream 02 sensor output OSR2, which is executed at regular intervals.

In S71, it is checked whether the air-fuel ratio is in the 7/db/c control range, and if it is in the feedback control range, the process proceeds to S72.

872 to S74 are parts that function as a reversal determining means. For S72 and 373, downstream 02 sensor output OSR2
By comparing the slice level SLR corresponding to the theoretical air-fuel ratio, it is determined whether the air-fuel ratio has reversed from lean to rich. If this is determined, the process proceeds to 875. Similarly, in S72 and S74, it is checked whether the air-fuel ratio has changed from rich to lean, and if so, the process proceeds to 876.

S75, S76 and S79 are portions that function as a reversal period measuring means. The process proceeds to S75 and S76 immediately after the air-fuel ratio is reversed. Here, the timer value at that time is read into a memory called TL or TR, and then the timer is reset in S79. Since S79 is a step that is passed only immediately after the reversal, the timer is reset every time the reversal occurs and measures the time since then (the time since the reversal).

Therefore, the time read in S75 and S76 is the reversal period (time from the previous reversal to the current reversal). However, since we distinguish between the reversal from lean to rich and the reverse, the value of TL is the time during which lean continues, T
The value simply means the amount of time the rich continues.

Here, the reason for measuring the reversal period is as follows. Downstream side 0 when there is no performance deterioration in the catalytic converter
The response speed of the two-sensor output OSR2 is low, as shown by A in the lower part of FIG. 7 (it is hardly inverted in the diagram). However, if the performance of the catalytic converter deteriorates, the catalyst will
Since the ability to store 02 (02 storage capacity) decreases, the downstream 02 sensor output OSR2 becomes B in the lower part of Figure 7.
As shown, the response waveform approaches the response waveform of the upstream 02 sensor output OSRI (the inversion period becomes shorter). In other words, the degree of performance deterioration of the catalytic converter can be determined by the inversion period TLtTR of OSR2. In addition,
It is also possible to use the number of inversions, which is the reciprocal of the inversion period.

In S77 and 378, average values 〒L and 〒R of a predetermined number of times (for example, 5 times) of TL and TR are calculated, respectively.

This is to avoid variations in TL and TR, which may result in unstable air-fuel ratio control if judged based on the values in the case of large variations.

FIG. 6 shows a routine for diagnosing whether performance deterioration has occurred in the catalytic converter and correcting a in accordance with the diagnosis result, and this routine is also executed at regular intervals.

In S81, it is checked whether the predetermined operating conditions are met, and if the predetermined operating conditions are met, the process advances to S82. The predetermined operating conditions are steady operating conditions (for example, when 10 seconds have passed since the vehicle reached a constant speed of 80 km/I+). The reason for proceeding to S82 only in this case is to improve the accuracy of the performance deterioration determination performed in S82.

S82 is a part that performs the function of the performance deterioration determining means 41 in FIG. 1, together with the reversal determining means (872 to S74) and the reversing period measuring means (S75, S76, S79). In S82, the average values 〒R and 〒L are set to a predetermined reference value T1.
If 〒R<Tl or 〒L〉TI, it is determined that performance has deteriorated in the catalytic converter, and S83
Proceed to.

S83 is a part that performs the function of the control constant changing means 42 in FIG. A constant value (PR*PL, I Rt
ΔPRyΔPL, ΔIRtΔ for r L, respectively
IL).

PR=PR-ΔPR...■ PL=PL-ΔPL...■ Engineering R=IR-ΔIR...■ r. = IL - ΔIL...■ Proportional components PR, PL and integral components I R, IL are determined according to the control constants of feedback control (proportional constant for proportional components, integral constant for integral components), so
Reducing the proportional and integral components corresponds to decreasing the control constant.

The reason why the proportional and integral components are made smaller when the performance of the catalyst converter is degraded is as follows. FIG. 8 shows a plot of the amplitude of a, which gives the best emissitan, against the degree of performance deterioration of the catalyst. It can be seen from the figure that as the catalyst performance deteriorates, the amplitude of a must be reduced accordingly. On the other hand, the amplitude of a can be freely changed depending on the magnitude of the proportional and integral components, so if the proportional and integral components are reduced, the amplitude of α is decreased.

Therefore, it is necessary to determine the above reference value T and the proportional and integral decreases (ΔPR, ΔP1, ΔIR?ΔIL) according to the characteristics shown in FIG.

Note that it is not necessarily necessary to reduce all of the proportional and integral components, and it is also possible to reduce only the proportional component or only the integral component.

In S84, the proportional and integral components obtained using the above formulas ``■'' to ``■'' are compared with each lower limit value, and if any is smaller than the lower limit value, the process is performed in S8.
5 fixes the value to the lower limit.

This is to stabilize the air-fuel ratio control by limiting the range that can be controlled by the proportional and integral components.

Proportional part PRyPL and integral part IRtI thus obtained
L is used in steps 359 to S62 of FIG. 4 to calculate a.

In S86 of FIG. 6, a signal indicating that the performance of the catalytic converter has deteriorated is output to the diagnostic monitor 28. If the diagnostic monitor 31 is a warning lamp installed in the driver's seat, this output lights the lamp.

On the other hand, if it is not 〒R>T1 or 〒L<Tl in S82, the process advances to S87, and this time 〒R〒,〒L are compared with another predetermined reference value T2, and 〒R>T2 and〒L> If T2, proceed to 688. In S88, the proportional portion PR, P. and each map value of the integral I Rt I L are calculated by the following formula S8
Contrary to 3, increase it by a certain value.

P R = P R + ΔPR...■ PL = PL + ΔP. ...■ rR=IR+ΔIR...■ I. =IL+Δ■L...■ The above T2 is a criterion for determining whether the ability of the catalyst is higher than normal. In other words, if the catalyst has a higher capacity than normal, increasing the amplitude of a will not worsen emissions, and increasing the amplitude of α will improve the responsiveness of air-fuel ratio control. This has the advantage of increasing

Note that if R>T2 and L>T2 are not determined in S87, it is assumed that the capacity of the catalyst converter is at a normal level, and the proportional and integral map values are used as they are.

In S89 and S90, the proportional and integral components obtained in S88 are limited to an upper limit value.

Here, the operation of this embodiment will be explained.

In this example, the degree of performance deterioration of the catalytic converter is determined by the average values 〒R and 〒L of the reversal period of the downstream side 02 sensor power OSR2, and when 〒R and 〒L become smaller than the reference value T1, the catalytic converter Assuming that performance deterioration occurs in , the proportional components pR, pL and the integral component I R? IL is made smaller. By changing the proportional component and the integral component, for example, the amplitude of a decreases from W1 to W2, as shown in the younger diagram 9.

This means that in Fig. 8, the amplitude that was initially W1 will decrease to W2 and be located below the line again if the degree of deterioration of catalyst performance has progressed beyond A. means. As a result, even if the catalytic ability is reduced due to performance deterioration, it is possible to make the emissive a the best even though the catalytic ability is reduced.

On the other hand, in the US example, no performance deterioration is expected to occur in the catalytic converter, so air-fuel ratio control is performed even though the amplitude of α is so large that it exceeds the line in Figure 8. There were times when the Emissicon became defective.

On the other hand, when the catalyst capacity level is better than normal, the amplitude of a is actively increased by increasing the proportional component and M component, so air-fuel ratio control is performed while making emission 3 the best. can improve responsiveness.

Additionally, if a warning lamp lights up due to performance deterioration, this lamp will let you know that performance has deteriorated in the catalytic converter, so you can take appropriate measures such as sending it in for repair. can.

In the embodiment, performance deterioration was determined from the inversion period of the downstream @02 sensor output OSR2, but it can also be determined that performance deterioration has occurred when the output OSR2 or the amplitude of the output OSR2 is larger than a predetermined value.

(Effects of the Invention) This invention reduces the control constant of air-fuel ratio feedback control when the reversal period of the output of the downstream air-fuel ratio sensor becomes smaller than a predetermined reference value. However, as the catalyst capacity decreases, it is possible to make the most of the catalytic capacity, and in this way, even after the performance of the catalytic converter has deteriorated, it is possible to maintain the best possible emissions.

[Brief explanation of drawings]

Fig. 1 is a diagram corresponding to the claims of this invention, Fig. 2 is a control system diagram of one embodiment, younger Fig. 3 is a block diagram of a control unit of this embodiment, and Figs. 4 to 6 are respective diagrams of this embodiment. A flowchart for explaining the control operation, and Fig. 7 is a characteristic diagram of the downstream side 02 sensor output OSR2 when there is no performance deterioration in the catalytic converter and when it has occurred.
The figure is a characteristic diagram of the amplitude of a that gives the best emission, younger brother 9
The figure is a waveform chart for explaining the operation of the embodiment. 10 to 12 are flowcharts for explaining the control operations of the conventional and unconventional examples, and FIGS. 13 and 14 are waveform diagrams for explaining the effects of the conventional example. 4... Injector (fuel injection device), 5... Exhaust pipe, 6... Catalyst converter, 7... Air 7 low meter (engine load sensor), 10... Crank angle sensor (engine speed sensor) ), 11... water temperature sensor,
12A...Upstream O2 sensor (upstream air-fuel ratio sensor)
, 12B...Downstream 02 sensor (downstream air-fuel ratio sensor), 21...Control unit, 28...Diagnostic monitor 31...Engine load sensor, 32...Engine speed sensor, 33...・Basic injection amount setting means, 3
4... Upstream air-fuel ratio sensor, 35... Reversal determination means, 36.1. Air-fuel ratio feedback correction amount calculation means, 3
7...Fuel injection amount determining means, 38...Output means, 3
9...Fuel injection device, 40...Downstream air-fuel ratio sensor, 41...Performance deterioration determining means, 42...Control constant changing means. 7th Prisoner Figure 9 Figure 12 Figure 13 Figure I [

Claims (1)

[Claims] A sensor that detects the engine load and rotation speed,
means for calculating a basic injection amount according to these detected values;
A sensor installed in the exhaust passage upstream of the catalytic converter outputs an output according to the exhaust air-fuel ratio, and by comparing this sensor output with a predetermined target value, it is determined whether the air-fuel ratio has reversed past this target value. means for determining, means for calculating a feedback correction amount of the air-fuel ratio so that the air-fuel ratio is controlled to be close to the target value according to the determination result, and correcting the basic injection amount using the air-fuel ratio feedback correction amount. In the air-fuel ratio control device for an engine, the engine air-fuel ratio control device includes a means for determining a fuel injection amount by determining a fuel injection amount, and a means for outputting the injection amount to a fuel injection device. a second sensor that outputs an output; a means for determining whether performance deterioration has occurred in the catalytic converter based on the sensor output; and a means for determining the air-fuel ratio feedback correction amount when it is determined that performance deterioration has occurred. 1. An air-fuel ratio control device for an engine, comprising: means for reducing a control constant necessary for calculation of .