JPH0639933B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention provides an air-fuel ratio sensor (an oxygen concentration sensor (O ₂ sensor) in this specification) on the upstream side and the downstream side of a catalytic converter, and O ₂ relates to an air-fuel ratio control apparatus for an internal combustion engine which performs air-fuel ratio feedback control by the O ₂ sensor downstream in addition to the air-fuel ratio feedback control by the sensor.

[Conventional technology]

Generally, the basic injection amount of the fuel injection valve is calculated according to the intake air amount (or intake air pressure) and the rotation speed of the engine,
Correcting the basic injection amount according to an air-fuel ratio correction coefficient FAF calculated based on a detection signal of an O ₂ sensor that detects the concentration of a specific component in the exhaust gas of the engine, for example, an oxygen component,
The amount of fuel actually supplied is controlled according to the corrected injection amount. By repeating this control, the air-fuel ratio of the engine is finally converged within the predetermined range. By such air-fuel ratio feedback control, since the air-fuel ratio can be controlled within a very narrow range near the theoretical air-fuel ratio, a three-way catalytic converter provided in the exhaust system, that is, CO, HC contained in the exhaust gas,
The purification capacity of the catalytic converter that purifies three harmful components of NOx at the same time can be kept high.

In the above-mentioned air-fuel ratio feedback control (single O ₂ sensor system), an O ₂ sensor for detecting the oxygen concentration is provided at a location in the exhaust system that is as close to the combustion chamber as possible, that is, at a collective portion of the exhaust manifold that is upstream from the catalytic converter. However, the variation in the output characteristics of the O ₂ sensor hinders the improvement of the air-fuel ratio control accuracy. The causes of variations in the output characteristics of the O ₂ sensor are listed below.

(1) Solid difference of O ₂ sensor itself, (2) Non-uniform mixing of exhaust gas at the location of O ₂ sensor due to tolerance of assembly position of parts such as fuel injection valve and exhaust gas recirculation valve to the engine, (3) Changes in the output characteristics of the O ₂ sensor over time or over time.

In addition to the O ₂ sensor, the non-uniformity of the exhaust gas mixture changes and expands due to changes in the engine state such as the fuel injection valve, the exhaust gas recirculation flow rate, the tappet clearance, and the like over time, and manufacturing variations. Sometimes.

A second O ₂ sensor is provided downstream of the catalytic converter in order to compensate for such variations in the output characteristics of the O ₂ sensor, variations in parts, and changes over time or over time, and the air-fuel ratio feedback control is performed by the upstream O ₂ sensor. In addition, a double O ₂ sensor system that performs air-fuel ratio feedback control using a downstream O ₂ sensor has already been proposed. In this double O ₂ sensor system, the O ₂ sensor provided on the downstream side of the catalytic converter has a lower response speed than the upstream O ₂ sensor, but the variation in the output characteristics is small for the following reasons. Have advantages.

(1) Since the exhaust temperature is low downstream of the catalytic converter, there is little thermal influence.

(2) Downstream of the catalytic converter, various poisons are trapped in the catalyst, so that the downstream O ₂ sensor is less toxic.

(3) The exhaust gas is sufficiently mixed downstream of the catalytic converter, and the oxygen concentration in the exhaust gas is close to the equilibrium state.

Therefore, as described above, the air-fuel ratio feedback control based on the outputs of the two O ₂ sensors (double O ₂ sensor system), the variations in the output characteristic of the upstream O ₂ sensor can be absorbed by the downstream O ₂ sensor. In fact, as shown in FIG. 2, in a single O ₂ sensor system, O ₂
When the output characteristic of the sensor deteriorates, it directly affects the exhaust emission characteristic, whereas in the double O ₂ sensor system, even if the output characteristic of the upstream O ₂ sensor deteriorates,
Exhaust emission characteristics do not deteriorate. In other words, double O
_{In the two-} sensor system, good exhaust emission is guaranteed as long as the downstream O ₂ sensor maintains stable output characteristics. In general, the temperature characteristics of the oxygen concentration cell type O ₂ sensor, as shown in FIG. 3A, when the air-fuel ratio A / F is rich, the output of the O ₂ sensor as the element temperature rises (rich signal) When the air-fuel ratio A / F is lean, it stabilizes at a low level as the element temperature rises. Note that FIG. 3A shows the case where the outflow type is used as the O ₂ sensor output processing circuit, and when the inflow type is used as the O ₂ sensor output processing circuit, it becomes as shown in FIG. 3B.
In the inactive state, both the rich and lean signals are at high level. In any case, the O ₂ sensor becomes inactive or active depending on the element temperature, and the usable area is limited. Generally, the range of 400 to 700 ° C. is considered suitable. However, it is practically difficult to directly measure the element temperature, and the activation is normally determined by using the engine cooling water temperature or the output of the O ₂ sensor as a substitute value of the element temperature.

As a method for determining the activation of the O ₂ sensor, the activation is determined based on the engine cooling water temperature at the cold start of the engine, and the element temperature of the O ₂ sensor decreases earlier than the cooling water temperature at the hot start. In view of this, a method of determining activation based on the output of the O ₂ sensor instead of the engine cooling water temperature is disclosed in JP-A-58-77150.

According to the activation determination method described above, activation of the O ₂ sensor can be determined without erroneous detection during cold start and hot start of the engine.

[Problems to be solved by the invention]

However, if the above-mentioned conventional activation determination method is simply adopted for the two O ₂ sensors of the above-mentioned double O ₂ sensor system, there is a problem that the emission of exhaust gas deteriorates after the engine is started. This problem will be detailed below.

In the activation determination method disclosed in JP-A-58-77150, activation is determined based only on the output of the O ₂ sensor when the engine is hot started. Therefore, when the air-fuel ratio of the exhaust gas O ₂ sensor after the start of the engine is discharged from the engine for a long time more than the time required to activate is biased to the rich or lean, the O ₂ sensor is even inactive Even if the state changes to the active state, the output value does not cross the activation determination reference value, and as a result, it is determined that the O ₂ sensor is not yet activated. Therefore, in this state, the air-fuel ratio feedback control cannot be started even though the O ₂ sensor is activated, and the emission is deteriorated.

On the other hand, if the activation determination based on the output of the coolant temperature or the O ₂ sensor is conventionally was simply adopted for two O ₂ sensors double O ₂ sensor system, hot start coolant temperature is high at the time of starting Sometimes, it is determined that both O ₂ sensors are activated immediately after the start, and the upstream O ₂ sensor is activated.
_The air-fuel ratio feedback control by the _two sensors and the air-fuel ratio feedback control by the downstream O ₂ sensor for correcting the deviation of the air-fuel ratio from the target air-fuel ratio (theoretical air-fuel ratio, stoichiometry) by this air-fuel ratio feedback control are started. become. In this case, since the element temperature of the upstream O ₂ sensor is relatively strongly affected by the temperature of the engine, the element temperature of the upstream O ₂ sensor is certainly in the activated state in most cases, and therefore the start of the air-fuel ratio feedback control by the upstream O ₂ sensor. There is no problem. However, there are many cases where the downstream O ₂ sensor has not been reliably activated, that is, there are many cases where the air-fuel ratio cannot be accurately detected, and nevertheless the downstream O ₂ sensor starts the air-fuel ratio feedback control. It Therefore, the original intention of the air-fuel ratio feedback control by the downstream O ₂ sensor (the intention of correcting the deviation of the air-fuel ratio feedback control by the upstream O ₂ sensor from the target air-fuel ratio)
On the contrary, the control center of the air-fuel ratio feedback control by the upstream O ₂ sensor is corrected in the direction away from the target air-fuel ratio, and the emission is deteriorated.

[Means for solving problems]

Upstream O ₂ sensor object in the double O ₂ sensor system of the present invention, by setting the appropriate activation determining means, respectively downstream O ₂ sensor, air-starting after-start quick air-fuel ratio feedback control of the engine While suppressing the fuel ratio fluctuation, the output of the downstream side O ₂ sensor which is in a completely active state accurately assures the deviation of the air-fuel ratio feedback control due to the output of the upstream side O ₂ sensor, thereby preventing the deterioration of the emission after the engine start. In particular, the means is shown in FIGS. 1A and 1B.

FIG. 1A shows a double air-fuel ratio sensor system that introduces two air-fuel ratio correction amounts. In FIG. 1A, first and second air-fuel ratio sensors for detecting a specific component concentration in exhaust gas are provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine. Each is provided. The first active / inactive determining means determines whether the first air-fuel ratio sensor is in the active state or the inactive state based on the engine coolant temperature THW. The second active / inactive determining means determines whether the first air-fuel ratio sensor is in the active state or the inactive state based on the output V ₁ of the first air-fuel ratio sensor. When the first or second active / inactive determining means determines that the first air-fuel ratio sensor is in the active state, the first air-fuel ratio correction amount calculating means outputs the output of the first (upstream side) air-fuel ratio sensor. A _first air-fuel ratio correction amount FAF1 is calculated according to V ₁ . Also, cold /
The hot start determination means determines whether the engine is cold start or hot start. As a result, when the engine is cold started, the third activation / deactivation determination means determines whether the second air-fuel ratio sensor is in the activated state or the inactivated state based on the cooling water temperature THW of the engine, while the engine is in the hot start state. At this time, the fourth active / inactive determining means determines whether the second air-fuel ratio sensor is in the active state or the inactive state based on the output V ₂ of the second air-fuel ratio sensor. When the third or third active / inactive determining means determines that the second air-fuel ratio sensor is in the active state, the second air-fuel ratio correction amount calculating means outputs the output of the second (downstream) air-fuel ratio sensor. _Second according to V 2
The air-fuel ratio adjustment amount FAF2 of is calculated. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the first and second air-fuel ratio correction amounts FAF1 and FAF2.

FIG. 1B shows a double air-fuel ratio sensor system that corrects constants involved in air-fuel ratio feedback control. In FIG. 1B, as in the case of FIG. 1A, first and second air-fuel ratio sensors, first and second active / inactive discrimination means, cold / hot start discrimination means, and third and third air-fuel ratio sensors. There are four active / inactive discriminating means. When the third or fourth activation / deactivation determination means determines that the second air-fuel ratio sensor is in the active state, the constant changing means performs the air-fuel ratio feedback control according to the output V ₂ of the second air-fuel ratio sensor. Change the constants involved. Further, when the first or second active / inactive determining means determines that the first air-fuel ratio sensor is in the active state, the air-fuel ratio correction amount calculating means causes the constant and the first air-fuel ratio feedback control to be involved. The air-fuel ratio correction amount FAF is calculated according to the output V _{1 of the} fuel ratio sensor. Then, the air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[Action]

According to the above-mentioned means, the upstream side air-fuel ratio sensor is judged to be in the activated state immediately after the start by the activation judgment by the cooling water temperature THW of the engine at the time of hot start of the engine, and the air conditioner by the upstream side air-fuel ratio sensor is judged. The fuel ratio feedback control is started quickly. Further, the downstream side air-fuel ratio sensor can surely determine that it is in the activated state by separate activation determination means at the time of hot start and cold start of the engine,
Deviation of the air-fuel ratio feedback control by the upstream O ₂ sensor output by accurate output signal in an active state with high accuracy can be guaranteed.

〔Example〕

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

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention. In FIG. 4, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. The air flow meter 3 directly measures the intake air amount, and has a built-in potentiometer to generate an output signal of an analog voltage proportional to the intake air amount. This output signal is supplied to the A / D converter 101 with a built-in multiplexer of the control circuit 10. In Distributor 4,
For example, a crank angle sensor 5 whose axis is converted into a crank angle to generate a reference position detection pulse signal every 720 ° and a crank angle sensor which is converted into a crank angle and generates a reference position detection pulse signal every 30 ° 6 is provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to the input / output interface 102 of the control circuit 10, of which the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from the fuel supply system to the intake port for each cylinder.

The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 is the temperature of the cooling water THW
Generates an electric signal of analog voltage according to. This output is also supplied to the A / D converter 101.

An exhaust system downstream of the exhaust manifold 11 is provided with a catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, CO, and NOx in the exhaust gas.

The exhaust manifold 11 includes the catalytic converter 1
A first O ₂ sensor 13 is provided on the upstream side of 2, and a _second O ₂ sensor 15 is provided on the exhaust pipe 14 on the downstream side of the catalytic converter 12. The O ₂ sensors 13 and 15 generate electric signals according to the concentration of oxygen components in the exhaust gas. That is, the O ₂ sensors 13 and 15 output different output voltages depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio via the O ₂ sensor output processing circuits 111 and 112 of the control circuit 10.
Generated in the / D converter 101. The O ₂ sensor output processing circuits 111 and 112 are roughly classified into an outflow type and an inflow type. When the O ₂ sensor is in an active state, both generate substantially the same level of output, but are in an inactive state. In this case, the former produces a low level output and the latter produces a high level output (see FIGS. 3A and 3B). However, the outflow type is used here.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101 and an input / output interface 1
02, CPU 103, O ₂ sensor output processing circuit 111, 112, R
An OM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, etc. are provided.

Further, in the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110 include the fuel injection valve 7
Is for controlling. That is, when the fuel injection amount TAU is calculated in the routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and finally its carry-out terminal becomes "1" level, the flip-flop 109 is set and the drive circuit 110 is set.
Stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, and accordingly, the amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

It should be noted that the interrupt generation of the CPU 103 is caused by the A / D converter 101 A / D
For example, when the D conversion is completed, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6, or when the interrupt signal from the clock generation circuit 107 is received.

The intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105. That is, the data Q and THW in the RAM 105 are updated every predetermined time. The rotation speed data Ne is calculated by interruption every 30 ° CA of the crank angle sensor 6 and stored in a predetermined area of the RAM 105.

FIG. 5 shows an active / inactive discrimination routine, which is executed every predetermined time, for example, every 0.1 _s .

In step 501, the water temperature data THW is read from the RAM 105.
It is determined whether THW> T ₁ or. Note that T ₁ is, for example, 80 ° C. If THW> T ₁ , the hot start flag FCS is set to "1" in step 502, while if THW≤T ₁ , the hot start flag FCS is set to "0" in step 502 'and the routine proceeds to step 503. That is, steps 501, 502 and 502 'are for determining whether it is cold start or hot start. Once the hot start is determined, the hot start flag FCS is held at "1".

If cold start (FCS = "0"), step 50
The process proceeds from step 3 to step 504, and it is determined whether THW> T ₂ . T
₂ is T ₂ <T ₁ , for example 70 ° C. And an active flag CF / B "1" at step 507, if THW> T _2. If THW ≤ T ₂ , then go directly to step 508. In this way, in the case of cold start, the downstream O ₂ sensor 15 is determined to be active or inactive according to the temperature of the cooling water of the engine.

If it is a hot start (FCS = "1"), step 503
To step 505, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and it is determined in step 506 whether V ₂ exceeds a predetermined value, for example, 0.45V. V ₂
If> 0.45V, the activation flag CF / B is determined in step 507.
If V ₂ ≦ 0.45V in which is set to “1”, the process directly proceeds to step 508. Thus, if hot start, the activity of the downstream O ₂ sensor 15, the determination of inactive performed in accordance with the output V ₂ of the downstream O ₂ sensor 15.

FIG. 6 shows a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF1 based on the output of the upstream O ₂ sensor 13, which is executed every predetermined time, for example, 4 ms.

In step 601, it is determined whether or not the closed loop (feedback) condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied. During engine start, during fuel increase operation after start,
The closed loop condition is not satisfied during the warm-up increase operation, the power increase operation, the lean control, the inactive state of the upstream O ₂ sensor 13, and the closed loop condition is satisfied in other cases. To determine the active / inactive state of the upstream O ₂ sensor 13, the water temperature data THW is read from the RAM 105 and once
This is performed by determining whether or not HW ≧ 70 ° C. or whether or not the output level of the upstream O ₂ sensor 13 has once risen / falled. When the closed loop condition is not satisfied, the routine proceeds to step 617, where the air-fuel ratio correction coefficient FAF1 is set.
Set to 1.0. On the other hand, if the closed loop condition is satisfied, step
Proceed to 602.

In step 602, the output V ₁ of the upstream O ₂ sensor 13 is A / D-converted and taken in, and in step 603 it is determined whether or not V ₁ is the comparison voltage V _R1 or less than 0.45 V, that is,
Determine whether the air-fuel ratio is rich or lean. Lean (V ₁ ≦
If it is V _R1 ), the first delay counter CDLY1 is decremented by 1 in step 604, and the first delay counter CDLY1 is guarded by the minimum value TDR1 in steps 605 and 606. The minimum value TDR1 is a rich delay time for holding the determination of the lean state even when the output of the upstream O ₂ sensor 13 changes from lean to rich,
Defined with a negative value. On the other hand, if rich (V ₁ > V _R1 ), the first delay counter CDLY1 is incremented by 1 in step 607, and the first delay counter CDLY1 is guarded by the maximum value TDL1 in steps 608 and 609. The maximum value TDL
1 is a rich delay time for holding the determination that the output is in the rich state even when the output of the upstream O ₂ sensor 13 changes from rich to lean, and is defined by a positive value.

Here, the reference of the first delay counter CDLY1 is set to 0, the air-fuel ratio after delay processing is considered rich when CDLY1> 0, and the air-fuel ratio after delay processing is considered lean when CDLY1 ≦ 0. To do.

In step 610, it is determined whether or not the sign of the first delay counter CDLY1 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay process is inverted. If the air-fuel ratio has been reversed, it is determined in step 611 whether rich-lean reversal or lean-rich reversal is performed. If it is the reverse from rich to lean, in step 612 FAF1 ← FAF
1 + RS1 and skip-wise increase. On the contrary, if lean-to-rich inversion, in step 613 FAF1 ← FAF1-R
S1 and skip-like reduction. That is, skip processing is performed.

If the sign of the first delay counter CDLY1 is not inverted in step 610, integration processing is performed in steps 614, 615 and 616. That is, in step 614, it is determined whether or not CDLY1 ≦ 0. If CDLY1 ≦ 0 (lean), in step 615
FAF1 ← FAF1 + KI1. On the other hand, if CDLY1> 0 (rich), FAF1 ← FAF1-KI1 is set in step 616. Here, the integration constant KI1 is set sufficiently smaller than the skip constant RS1, that is, KI1 <RS1. Therefore,
Step 615 gradually increases the fuel injection amount in the lean state (CDLY1 ≦ 0), and step 616 is in the rich state (CDLY1>
In 0), the fuel injection amount is gradually reduced.

The air-fuel ratio correction coefficient FAF1 calculated in steps 612, 613, 615, 616 has a minimum value of 0.8 and a maximum value of 1.2.
Therefore, if the air-fuel ratio correction coefficient FAF1 becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled by that value to cause overrich or over lean. prevent.

The FAF1 calculated as described above is stored in the RAM 105, and this routine ends at step 618.

FIG. 7 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. When the rich-lean air-fuel ratio signal A / F1 is obtained from the output of the upstream O ₂ sensor 13 as shown in FIG. 7 (A), the first delay counter CDLY1 is shown in FIG. 7 (B). As usual, it counts up in the rich state, and gowns down in the lean state. As a result, as shown in FIG. 7C, the delayed air-fuel ratio signal A / F1 'is formed. For example, the time after the air-fuel ratio signal A / F1 at time t ₁ is also changed from lean to rich, the air-fuel ratio signal A / F1 delayed processed 'is held lean only the rich delay time (-TDR1) It changes to rich at t ₂ . Be changed from the air-fuel ratio signal A / F1 is rich at time t ₃ to lean, the delayed air-fuel ratio signal A / F1 'is at time t ₄ after being held rich only equivalent lean delay time TDL1 Change to lean. But,
Invert a shorter period of time than the air-fuel ratio signal A / F1 is the time t _5, t ₆ t ₇ rich delay time as the (-TDR1), takes time first delay counter CDLY1 crosses the reference value 0 As a result, at time t ₈ , the air-fuel ratio signal A after the delay processing is
/ F1 'is inverted. That is, the air-fuel ratio signal A / F1 'after the delay processing is more stable than the air-fuel ratio signal A / F1 before the delay processing. In this way, the stable air-fuel ratio signal A after the delay processing is performed.
/ F1 'based on the air-fuel ratio correction coefficient shown in Fig. 7 (D)
FAF1 is obtained.

Next, the second air-fuel ratio feedback control by the downstream O ₂ sensor 15 will be described. As the second air-fuel ratio feedback control, a system that introduces the second air-fuel ratio correction coefficient FAF2 and delay times TDR1, TDL1 and skip amount RS as constants involved in the first air-fuel ratio feedback control are used.
1 (in this case, the rich skip amount from lean to rich)
RS1R and lean skip amount from rich to lean RS1L
, The integration constant KI1 (also in this case, the rich integration constant KI1R and the lean integration constant KI1L are set separately), the integration constant KI1 (also in this case, the rich integration constant KI).
1R and lean integration constant KI1L are set separately), or there is a system in which the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13 is made variable.

For example, rich delay time (-TDR1)> lean delay time
If (TDL1) is set, the control air-fuel ratio can shift to the rich side, and conversely, lean delay time (TDL1)> rich delay time (-
If set to TDR1), the control air-fuel ratio can be shifted to the lean side. That is, the air-fuel ratio can be controlled by correcting the delay times TDR1 and TDL1 according to the output of the downstream O ₂ sensor 15. Further, if the rich skip amount RSIR is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip amount RS1L is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean skip amount RS1L is increased. , The control air-fuel ratio can be shifted to the lean side, and the rich skip amount
Even if RS1R is reduced, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount RS1R and the lean skip amount RS1L according to the output of the downstream O ₂ sensor 15. Furthermore, if the rich integration constant KI1R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean integration constant KI1L is decreased, the control air-fuel ratio can be shifted to the rich side, while the lean integration constant is increased.
When KI1L is increased, the control air-fuel ratio can be shifted to the lean side, and even when the rich integration constant KI1R is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integration constant KI1R and the lean integration constant KI1L according to the output of the downstream O ₂ sensor 15.
Furthermore, if the comparison voltage V _R1 is increased, the control air-fuel ratio can be shifted to the rich side, and if the comparison voltage V _R1 is decreased, the control air-fuel ratio can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the comparison voltage V _R1 according to the output of the downstream O ₂ sensor 15.

Referring to FIGS. 8 to 10, the second air-fuel ratio correction coefficient FAF2
A double O ₂ sensor system in which is introduced will be described.

FIG. 8 shows the second based on the output of the downstream O ₂ sensor 15.
Is a second air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF2, and is executed every predetermined time, for example, every 1 s. In step 601, the downstream O ₂ sensor 1
It is determined whether or not the closed loop condition of 5 is satisfied. This step
801 is almost the same as step 601 in FIG. If it is not a closed loop condition, proceed to step 818 and set FAF2 = 1.0,
If it is a closed loop condition, the process proceeds to step 802.

In step 802, it is determined whether or not the activation flag CF / B is "1", and the process proceeds to step 803 only when CF / B = "1".

In step 803, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and in step 804, it is judged whether or not V ₂ is the comparison voltage V _R2, for example, 0.45 V or less, that is,
Determine whether the air-fuel ratio is rich or lean. The comparison voltage V _R2 is the comparison voltage V _R2 of the output of the upstream O ₂ sensor 13 in consideration of the fact that the output characteristics due to the influence of raw gas are different upstream and downstream of the catalytic converter 2 and the activation speed is different.
Set higher than _R1 . If lean (V ₂ ≦ V _R2 ), the second delay counter CDLY 2 is set to 1 in step 805.
Subtract and subtract the second delay counter C in steps 806 and 807.
Guard DLY2 with minimum value TDR2. The minimum value TDR2 is a rich delay time for maintaining a lean state even when there is a change from lean to rich, and is defined as a negative value. On the other hand, if rich (V ₂ > V _R2 ), step 80
In step 8, the second delay counter CDLY2 is incremented by 1, and in steps 809 and 810, the second delay counter CDLY2 is set to the maximum value.
Guard with TDL2. The maximum value TDL2 is a lean delay time for maintaining the rich state even when there is a change from rich to lean, and is defined by a positive value.

Here again, the reference of the second delay counter CDLY2 is set to 0, the air-fuel ratio after delay processing is considered rich when CDLY2> 0, and the air-fuel ratio after delay processing is considered lean when CDLY2 ≦ 0. To do.

In step 811, it is determined whether or not the sign of the second delay counter CDLY2 is inverted, that is, it is determined whether or not the air-fuel ratio after the delay process is inverted. If the air-fuel ratio is reversed, it is determined in step 812 whether rich-to-lean reversal or lean-to-rich reversal is performed. If it is the reverse from rich to lean, in step 813 FAF2 ← FAF
2 + RS2 and increase in a skip manner, and conversely, if lean to rich inversion, in step 814 FAF2 ← FAF2-RS2
And reduce like a skip. That is, skip processing is performed.

If the sign of the second delay counter CDLY2 is not inverted in step 811, integration processing is performed in steps 815, 816 and 817. In other words, in step 815, it is determined whether or not CDLY2 ≦ 0. If CDLY2 ≦ 0 (lean), then in step 816 FAF2 ← FAF2 + KI2, while if CDLY2> 0 (rich), in step 817. FAF2 ← FAF2 + KI2. Here, the integration constant KI2 is set sufficiently smaller than the skip constant RS2, that is, KI2 <RS2. Therefore, step 816 gradually increases the fuel injection amount in the lean state (CDLY2 ≦ 0), and step 817 gradually decreases the fuel injection amount in the rich state (CDLY2> 0).

The air-fuel ratio correction coefficient FAF2 calculated in steps 813, 814, 816, 817 has a minimum value of 0.8 and a maximum value of 1.2, for example.
Therefore, if the air-fuel ratio correction coefficient FAF2 becomes too large or too small for some reason, the air-fuel ratio of the engine is controlled by that value to cause overrich or over lean. prevent.

The FAF2 calculated as described above is stored in the RAM 105, and this routine ends at step 819.

In this way, the second air-fuel ratio correction coefficient FAF2 is calculated based on the output of the downstream O ₂ sensor 15 which is delayed when the closed loop condition is satisfied and the activation flag CF / B = “1”.

As described above, FA calculated during air-fuel ratio feedback
F1 and FAF2 can be once converted into other values FAF1 ′ and FAF2 ′ and stored in the backup RAM RAM 106.
This is useful for improving drivability at the time of restart.

FIG. 9 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 901,
The RAM 105 reads the intake air amount data Q and the rotation speed data Ne to calculate the basic injection amount TAUP. Eg TA
UP ← KQ / Ne (K is a constant). R at step 902
The cooling water temperature data THW is read from the AM 105 and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM 104. This warm-up increase value FWL is set to decrease as the current cooling water temperature THW increases, as shown in the figure.

In step 903, the final injection amount TAU is set to TAU ← TAUP ・ FAF1
・ Calculate by FAF2 ・ (FWL + α) + β. Note that α and β
Is a correction amount determined by other operating state parameters, for example, a signal from a throttle position sensor (not shown) or a signal from an intake air temperature sensor, a correction amount determined by a battery voltage, etc., and these are also stored in the RAM 105. . Next, at step 904, the injection amount TAU is set in the down counter 108 and the flip-flop 1
Set 09 to start fuel injection. Then, in step 905, this routine ends. As described above, when the time corresponding to the injection amount TAU elapses, the flip-flop 109 is reset by the carry-out signal of the down counter 108 and the fuel injection ends.

FIG. 10 is a timing chart for explaining the first and second air-fuel ratio correction coefficients FAF1 and FAF2 obtained by the flow charts of FIGS. 6 and 8. Upstream O ₂ sensor 13
When the output voltage V ₁ of the above changes as shown in FIG. 10 (A), the comparison result in step 603 of FIG. 6 becomes as shown in FIG. 10 (B). The comparison result of FIG. 10 (B) becomes as shown in FIG. 10 (C) when the delay processing is performed. As a result,
As shown in FIG. 10 (D), FAF1 skips only RS1 at the time of the delayed switching between rich and lean. On the other hand, when the output voltage V ₂ of the downstream O ₂ sensor 15 changes as shown in FIG. 10 (E), step 804 in FIG.
The comparison result at is as shown in Fig. 10 (F).
When the delay processing is performed, it becomes as shown in FIG. When the second air-fuel ratio correction coefficient FAF2 is calculated based on the delayed comparison result in FIG. 10 (G), it becomes as shown in FIG. 10 (H).

Next, a double O ₂ sensor system in which the delay time as a constant involved in the air-fuel ratio feedback control is variable will be described with reference to FIGS. 11 and 12.

FIG. 11 is a second air-fuel ratio feedback control routine for calculating the delay times TDR1 and TDL1 based on the output of the downstream O ₂ sensor 15, and is executed every predetermined time, for example, every 1 s. Steps 1101 and 1102 are the same as step 80 in FIG.
Same as 1,802. Therefore, if the closed loop condition is not satisfied or the activation flag CF / B = "0", the steps 1124 and 1
Proceed to 125, rich delay time TDR1, lean delay time TDL1
To a constant value. For example, TDR1 ← -12 (equivalent to 48 ms) TDL1 ← 6 (equivalent to 24 ms). Here, the reason to set the rich delay time (-TDR1) greater than the lean delay time TDL1, the comparison voltage V _R1
Is set to a low value such as 0.45 V on the lean side.

If the closed loop condition is satisfied and the activation flag CF / B = “1”, the process proceeds to step 1103.

Steps 1103 to 1110 correspond to steps 803 to 810 in FIG. In other words, the rich / lean discrimination is made in step 1104.
The result of this determination is steps 1105 to 1110.
Will be delayed. And the rich that has been delayed,
Lean determination is performed in step 1111.

In step 1111, the second delay counter CDLY2 is set to CDLY2.
It is determined whether or not ≤0. As a result, if CDLY2≤0, it is determined that the air-fuel ratio is lean and the routine proceeds to steps 1112 to 1117. On the other hand, if CDLY2> 0, the air-fuel ratio is determined to be rich. Proceed to steps 1118 to 1123.

In step 1112, TDR1 ← TDR1-1 is set, that is, the rich delay time (-TDR1) is increased, the change from rich to lean is further delayed, and the air-fuel ratio is shifted to the rich side. In steps 1113 and 1114, TDR1 is guarded by the minimum value T _R1 . Here, T _R1 is also a negative value, so
(-T _R1 ) means the maximum rich delay time. further,
In step 1115, TDL1 ← TDL1-1 is set, that is, the lean delay time TDL1 is reduced, the delay of the change from lean to rich is reduced, and the air-fuel ratio is shifted to the rich side. In steps 1116 and 1117, TDL1 is guarded with the minimum value T _L1 . Here, T _L1 is a positive value, so T _L1 means the minimum lean delay time.

In step 1118, TDR1 ← TDR1 + 1 is set, that is, the rich delay time (-TDR1) is reduced, the delay of the change from rich to lean is reduced, and the air-fuel ratio is shifted to the lean side. To guard at the maximum value T _R2 the TDR1 in step 1119,1120. Here, T _{R2 is} also a negative value, so (−
T _R2 ) means the minimum rich delay time. Further, in step 1121, TDL1 ← TDL1 + 1 is set, that is, the lean delay time TDL1 is increased, the change from lean to rich is further delayed, and the air-fuel ratio is shifted to the lean side. Step
In 1122 and 1123, TDL1 is guarded with the maximum value T _L1 . Here, T _L1 is a positive value, so T _L2 means the maximum lean delay time.

After the TDR1 and TDL1 calculated as described above are stored in the RAM 105, this routine ends at step 1126.

In this way, the delay times TDR1 and TDL1 are calculated based on the output of the downstream O ₂ sensor 15 that has been delayed when the closed loop condition is satisfied and the activation flag CF / B = “1”.

Note that FAF1, TDR1, calculated during air-fuel ratio feedback
TDL1 can be temporarily converted into other values FAF1 ′ and TDR1′TDL1 ′ and stored in the backup RAM 106. This allows
This is useful for improving drivability when restarting.

FIG. 12 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 1201, the intake air amount data Q and the rotation speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. Eg TA
UP ← KQ / Ne (K is a constant). At step 1202
The cooling water temperature data THW is read from the RAM 105, and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM 104.

In step 1203, the final injection amount TAU is calculated by TAU ← TAUPFAF1 (FWL + α) + β. Note that α and β are correction amounts that are determined by other operating state parameters.

Next, at step 1204, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1205, this routine ends.

FIG. 13 is a timing chart of the delay times TDR1 and TDL1 obtained by the flowcharts of FIGS. 6 and 11. As shown in FIG. 13 (A), when the output voltage V _{2 of the} downstream O ₂ sensor 15 changes, as shown in FIG. 13 (B), in the lean state (V ₂ ≦ V _R2 ), the delay time TDR1 , T
Both DL1 are increased, while the delay times TDR1 and TDL1 are both decreased in the rich state. At this time, TDR1 is T _R1
To T _R2 , and T DL1 changes in the range from T _{L1 to} T _L2 .

If the closed-loop condition of the downstream O ₂ sensor 15 is not satisfied or the activation flag CF / B = “0”, the TDR of FIG.
1, TDL1 control is stopped, eg TDR1 = -12 and
It is held at TDL1 = 6.

The first air-fuel ratio feedback control is performed every 4 ms, and the second air-fuel ratio feedback control is performed every 1 s. The main reason for the air-fuel ratio feedback control is the upstream O ₂ sensor with good responsiveness. This is because the control is performed by the downstream O ₂ sensor, which has poor responsiveness.

Further, other constants related to the air-fuel ratio feedback control by the upstream O ₂ sensor, such as the skip amount, the integration constant, and the comparison voltage of the upstream O ₂ sensor (see JP-A-55-375).
No. 62) and the like are obtained by applying the present invention to a double O ₂ sensor system in which the output of the downstream O ₂ sensor is corrected.

Further, as the intake air amount sensor, a Karman vortex sensor, a heat wire sensor, or the like can be used instead of the air flow meter.

Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed. However, depending on the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may be calculated.

Further, although the internal combustion engine in which the fuel injection amount is controlled by the fuel injection valve is shown in the above-mentioned embodiment, the present invention can be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, an electric free air control valve adjusts the air bleed amount of the carburetor, and the main system passage and The present invention can be applied to those that control the air-fuel ratio by introducing the atmosphere into the slow passage and those that adjust the amount of secondary air sent into the exhaust system of the engine. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in steps 901 and 1201 is determined by the carburetor itself, that is, determined according to the intake pipe negative pressure according to the intake air amount and the rotation speed of the engine, In steps 903 and 1203, the supply air amount corresponding to the final fuel injection amount TAU is calculated.

Further, although the O ₂ sensor is used as the air-fuel ratio sensor in the above-described embodiment, a C0 sensor, a lean mixture sensor, or the like can be used.

Further, although the above-mentioned embodiment is constituted by a microcomputer, that is, a digital circuit, it may be constituted by an analog circuit. FIG. 14 is a timing chart for explaining the effect of the present invention. When the cold start is performed at time t ₁ , the vehicle speed SPD changes as shown in FIG. 14 (A), and in this case, FIG. 14 (B), (C).
As shown in, the cooling water temperature THW and the downstream O ₂ sensor 1
Although the activity of No. 5 is also low, as shown in FIG. 14 (D), the output voltage V ₂ of the downstream O ₂ sensor 15 causes a rich spike due to the influence of unburned gas.

(Note that if the O ₂ sensor output processing circuit is a flow-in type, a lean spike occurs.) Therefore, as in the conventional case, the active / inactive discrimination is made by the output voltage V ₂ of the downstream O ₂ sensor 15 even at cold start. When it is performed, it is considered that the rich spike X ₁ is activated at time t ₂ ′, and as a result, as shown by the dotted line in FIG. 14 (E), the air-fuel ratio feedback by the downstream O ₂ sensor 15 is performed. The control amount, for example, the second air-fuel ratio correction coefficient FAF2 or the delay times TDR1 and TDL1 is corrected to the rich side. (If the flow-in type O ₂ sensor processing circuit is used, it is corrected to the lean side.) As a result, the CO (HC) emission greatly increases as shown by the dotted line in FIG. 14 (F). On the other hand, according to the present invention, since it is determined whether the cooling water temperature THW is active or inactive, it is considered to be activated at time t ₂ . Therefore, the air-fuel ratio feedback control amount by the downstream O ₂ sensor 15 is not rich-corrected as shown by the solid line in FIG.
As shown by the solid line in Fig. 4 (F), CO (HC) emission decreases.

When the hot start is performed at time t ₃ , the output voltage V ₂ of the downstream O ₂ sensor 15 is little affected by unburned gas and is stable as shown in FIG. 14 (D). Therefore, according to the present invention, the output voltage V ₂ of the downstream O ₂ sensor 15 is used to determine whether it is active or inactive. As a result, time t
₄ is considered activated. On the other hand, the upstream O ₂ sensor 1
The active / inactive state of No. 3 is determined by whether the water temperature THW of the engine has once risen to 70 ° C. or higher, or whether the output level of the upstream O ₂ sensor 13 has once risen or falled. The activation state is determined by the activation determination based on the water temperature THW of the engine. Therefore, the air-fuel ratio feedback control according to the output of the upstream O ₂ sensor 13 can be started promptly as soon as the other closed loop (feedback) condition described above is satisfied.

〔The invention's effect〕

According to the present invention described above, the upstream O ₂ sensor in the double O ₂ sensor system, by setting the downstream O ₂ sensor suitable activation determining means, respectively, quick air-fuel ratio feedback after the start of the engine The control is started to suppress the air-fuel ratio fluctuation, and the output of the downstream side O ₂ sensor in the completely active state accurately assures the deviation of the air-fuel ratio feedback control due to the output of the upstream side O ₂ sensor. Emissions can be prevented from deteriorating.

[Brief description of drawings]

1A and 1B are overall block diagrams for explaining the configuration of the present invention, and FIG. 2 is a single O ₂ sensor system and a double O ₂ sensor system.
FIG. 3A and FIG. 3B are graphs showing output characteristics of an O ₂ sensor, and FIG. 4 is an overall view showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention. Schematic diagrams, FIG. 5, FIG. 6, and FIG. 8 to FIG. 12 are flow charts for explaining the operation of the control circuit of FIG. 4, and FIG. 7 is timing for supplementary explanation of the flow chart of FIG. FIG. 10 is a timing chart for supplementary explanation of the flowcharts of FIGS. 6 and 8, and FIG. 13 is a timing chart for supplementary explanation of the flowcharts of FIGS. 6 and 11. FIG. 7 is a timing diagram for explaining the effect of the present invention. DESCRIPTION OF SYMBOLS 1 ... Engine main body, 3 ... Air flow meter, 4 ... Distributor, 5, 6 ... Crank angle sensor, 10 ... Control circuit, 12 ... Catalytic converter, 13 ... Upstream (first) O ₂ sensor, 15 ... Downstream ( First) O ₂ sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyasu Katsuno 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-60-243334 (JP, A) JP-A-60- 36946 (JP, A)

Claims (8)

[Claims] 1. A first and a second detector, which are respectively provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, for detecting a concentration of a specific component in the exhaust gas. An air-fuel ratio sensor, a first active / inactive determination unit that determines whether the first air-fuel ratio sensor is in an active state or an inactive state based on the cooling water temperature of the engine, and an output of the first air-fuel ratio sensor. Second active / inactive discrimination means for discriminating whether the first air-fuel ratio sensor is in an active state or inactive state, and the first air-fuel ratio sensor by the first or second active / inactive discrimination means. A first air-fuel ratio correction amount calculation means for calculating a first air-fuel ratio correction amount according to the output of the first air-fuel ratio sensor, and the engine is cold start or hot start. Cold / hot A start / stop determining means for determining whether the second air-fuel ratio sensor is in an active state or an inactive state based on a cooling water temperature of the engine when the engine is cold started; A fourth active / inactive determining means for determining whether the second air-fuel ratio sensor is in an active state or an inactive state based on the output of the second air-fuel ratio sensor when the engine is hot started; A second air-fuel ratio correction amount is calculated according to the output of the second air-fuel ratio sensor when the fourth active / inactive discrimination means determines that the second air-fuel ratio sensor is in the active state. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio correction amount calculating means; and an air-fuel ratio adjusting means for adjusting an air-fuel ratio of the engine according to the first and second air-fuel ratio correction amounts. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the cold / hot start determination means determines whether it is a cold start or a hot start according to the cooling water temperature of the engine. 3. A first and a second detector, which are respectively provided on the upstream side and the downstream side of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, for detecting a concentration of a specific component in the exhaust gas. An air-fuel ratio sensor, a first active / inactive determination unit that determines whether the first air-fuel ratio sensor is in an active state or an inactive state based on the cooling water temperature of the engine, and an output of the first air-fuel ratio sensor. Second active / inactive determination means for determining whether the first air-fuel ratio sensor is in an active state or inactive state; cold / hot start determination means for determining whether the engine is cold start or hot start; Third active / inactive determining means for determining whether the second air-fuel ratio sensor is in the active state or the inactive state according to the cooling water temperature of the engine when the engine is cold start, and the engine is hot-started. Sometimes, fourth active / inactive determining means for determining whether the second air-fuel ratio sensor is in an active state or an inactive state based on the output of the second air-fuel ratio sensor, and the third or fourth active / inactive state determining means. Constant changing means for changing a constant involved in air-fuel ratio feedback control according to an output of the second air-fuel ratio sensor when the second air-fuel ratio sensor is judged to be in an active state by the inactivity judging means, When the first or second active / inactive determining means determines that the first air-fuel ratio sensor is in the active state, the constant and the first constant that are involved in the air-fuel ratio feedback control.
An internal combustion engine including: an air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount according to the output of the air-fuel ratio sensor; and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount. Air-fuel ratio controller. 4. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein said cold / hot start determination means determines whether it is a cold start or a hot start according to the temperature of the cooling water of said engine. 5. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the constant involved in the air-fuel ratio feedback control is a delay time. 6. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the constant relating to the air-fuel ratio feedback control is a skip control constant. 7. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the constant involved in the air-fuel ratio feedback control is an integral control constant. 8. The air-fuel ratio control device for an internal combustion engine according to claim 3, wherein the constant involved in the air-fuel ratio feedback control is a comparison voltage of the output of the first air-fuel ratio sensor.