JPH066912B2 - 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 in addition to the air-fuel ratio feedback control related to the air-fuel ratio control apparatus for an internal combustion engine which performs air-fuel ratio feedback back control by the O ₂ sensor downstream by _two sensors.

[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,
The basic injection amount is corrected according to the air-fuel ratio correction coefficient FAF calculated based on the detection signal of the O ₂ sensor that detects the concentration of a specific component in the exhaust gas of the engine, for example, the oxygen component, and the corrected injection amount The amount of fuel actually supplied is controlled according to 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, the air-fuel ratio can be controlled within a very narrow range near the stoichiometric air-fuel ratio, so that a three-way catalytic converter provided in the exhaust system, that is, C contained in the exhaust gas, is included.
The catalytic converter purifying ability to purify three harmful components of O, HC and NO _x 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) Individual difference of the O ₂ sensor itself, (2) Non-uniform mixing of exhaust gas at the O ₂ sensor location due to tolerance of assembly position of parts such as fuel injection valve and exhaust gas recirculation valve to the engine, (3) Time-dependent or time-dependent relationship of the output characteristics of the O ₂ sensor.

In addition to the O ₂ sensor, the combustion injection valve, the exhaust gas recirculation flow rate, the tappet clearance, and other changes in the engine state over time or over time, and the non-uniformity of exhaust gas mixing due to manufacturing variations change and expand. 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) Downstream of the catalytic converter, the exhaust temperature is low, so there is little thermal effect.

(2) Downstream of the catalytic converter, various poisons are trapped in the catalyst, so the amount of poisoning of the downstream O ₂ sensor is small.

(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 the double O ₂ sensor system described above, the downstream O ₂
Generally the sensor, so that the temperature characteristic of the oxygen concentration cell type O ₂ sensor 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) Is stable at rising high levels, while
When the air-fuel ratio A / F is lean, it stabilizes at a certain low level as the element temperature rises. In addition, FIG.
The case where the outflow type is used as the O ₂ sensor output processing circuit is shown. When the inflow type is used as the O ₂ sensor output processing circuit, the result becomes as shown in FIG. 3B, and in the inactive state, it is rich. , The lean signal becomes high level.

[Problems to be solved by the invention]

However, an outflow type is used as the O ₂ sensor output processing circuit, and as shown in FIG. 4 (B), the air-fuel ratio of the entire engine is lean due to variations in the injection valve, aging of the downstream O ₂ sensor, and the like. In this case, as shown in FIG. 4 (A), the output V ₂ of the downstream O ₂ sensor is the O ₂ sensor activity,
Feedback start voltage V _fr as a criterion of inactivity
As a result, the feedback control by the downstream O ₂ sensor cannot be started, and the air-fuel ratio correction amount FAF2 by the downstream O ₂ sensor is fixed to, for example, the rich side as shown in FIG. 4 (C). Deterioration of drivability, NOx
There is a problem that it leads to deterioration of emission. Similarly, a flow type is used as the O ₂ sensor output processing circuit,
In addition, as shown in FIG. 5 (B), when the air-fuel ratio of the entire engine is rich due to variations in the injection valve, aging of the downstream O ₂ sensor, etc., as shown in FIG. 5 (A), the downstream side O ₂ sensor output V ₂ is O ₂ sensor active, can not reach the feedback start voltage V _fr as a criterion for deactivation, this result can not start the feedback control by the downstream O ₂ sensor, 5 ( As shown in C), there is a problem in that the air-fuel ratio correction amount FAF2 by the downstream O ₂ sensor is fixed to, for example, the lean side, which causes deterioration of fuel consumption and deterioration of HC and CO emissions.

[Means for solving problems]

The object of the present invention is to start the feedback control by the downstream O ₂ sensor by changing the feedback start voltage when the output of the downstream O ₂ sensor is on the lean side or the rich side for a predetermined period or longer, and ,
It is to prevent deterioration of fuel efficiency, deterioration of drivability, deterioration of emissions, etc. Of course, if the downstream O ₂ sensor is actually inactive, feedback control by the downstream O ₂ sensor is not performed even if the feedback start voltage is changed as described above. That is, in the present invention, in order to confirm whether the downstream O ₂ sensor holds the lean signal (flow-out type) or the rich signal (flow-in type) even if activated, the feedback start voltage is set. It is changing.

The means of the present invention is shown in FIGS. 1A and 1B. 1A
The figure 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 the concentration of a specific component 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, respectively. Each is provided. The first air-fuel ratio correction amount calculation means determines the first air-fuel ratio correction amount FAF1 according to the output V ₁ of the upstream (first) air-fuel ratio sensor.
Is calculated. The feedback start determination means determines whether or not the output V ₂ of the downstream (second) air-fuel ratio sensor has reached the feedback start voltage V _fr . When the output V ₂ of the air-fuel ratio sensor does not reach the feedback start voltage V _fr for a predetermined time, the feedback start voltage varying means changes the feedback start voltage to the output level side of the second air-fuel ratio sensor. After the output V ₂ of the air-fuel ratio sensor reaches the feedback start voltage V _fr , the second air-fuel ratio correction amount calculation means sets the second air-fuel ratio correction amount FAF2 according to the output V ₂ of the downstream side air-fuel ratio sensor. Calculate 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, 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, feedback start determination means, and feedback start voltage varying means are provided. When the feedback start determination means determines that the output V ₂ of the downstream side air-fuel ratio sensor has reached the feedback start voltage V _fr , the control constant calculation means participates in the air-fuel ratio feedback control according to the output of the downstream side air-fuel ratio sensor. Calculate the constant. The air-fuel ratio correction amount calculation means calculates the air-fuel ratio correction amount FAF according to the constant relating to the air-fuel ratio feedback control and the output V ₁ of the upstream side air-fuel ratio sensor. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the air-fuel ratio correction amount FAF.

[Work]

According to the above-mentioned means, even if the downstream side air-fuel ratio sensor is activated, if the output holds the lean signal (outflow type) or the rich signal (inflow type), the downstream side air-fuel ratio sensor is used. It is possible to reliably start the air-fuel ratio feedback control.

〔Example〕

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

FIG. 6 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. 3, 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 that generates a reference position detection pulse signal every 720 ° converted into a crank angle and a crank angle sensor that generates a reference position detection pulse signal every 30 ° converted into a crank angle 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 TH of the cooling water.
An electric signal having an analog voltage corresponding to W is generated. 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, outside the O ₂ sensor output processing circuit 111, 112,
ROM 104, RAM 105, backup RAM 106, 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 are for controlling the fuel injection valve 7. 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 the "1" level, the flip-flop 109 is set and the driving circuit 1
10 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is biased by the above-mentioned fuel injection amount TAU, and therefore,
An 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. Also, the rotation speed data N
e is calculated by interruption of the crank angle sensor 6 every 30 ° CA and is stored in a predetermined area of the RAM 105.

The operation of the control circuit 10 shown in FIG. 6 will be described below. 7th A
The figure shows a feedback start voltage setting routine, which is executed every predetermined time, for example, every 4 ms. The counter C is reset by an initial routine (not shown). At step 701, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and at step 70
At 2, the feedback start voltage V _fr is read from the backup RAM 106, and the output V ₂ is the feedback start voltage V _fr.
Determine whether it exceeds _fr . If V ₂ > V _fr, it is considered that the downstream O ₂ sensor 15 has been activated, and the feedback control execution flag C by the downstream O ₂ sensor 15 is considered.
Set F / B to "1". The flag CF / B
Is reset in the initial routine.

If V ₂ ≦ V _fr in step 702, step 7
The counter C is incremented at 04, then step 7
Proceed to 05 to compare the duration C of V ₂ ≦ V _fr with C ₀ . If the duration C ≦ C ₀ , the process proceeds directly to step 708, and if the duration C> C ₀ , the process proceeds to step 706. In step 706, the current air-fuel ratio feedback correction coefficient FAF2 by the downstream O ₂ sensor 15 (when a double O ₂ sensor system with _two air-fuel ratio feedback correction coefficients is adopted) is read out from the RAM 105 and based on FAF2. New feedback start voltage V by dimensional map
Interpolate _fr and V _fr backup RAM in step 707
Store in 707 and proceed to step 708.

That is, if FAF2> R, the feedback start voltage V _fr
Is smaller than when FAF2 = 1.0.

The parameters in step 706 are the cooling water temperature THW,
The rotation speed Ne and the intake air pressure PM may be used. Further, in the double O ₂ sensor system in which the constants involved in the upstream air-fuel ratio feedback control are variable, the constants involved in the control such as the delay time are used as parameters.

Further, as an O ₂ sensor output processing circuit, a flow type (3rd
7B), the routine of FIG. 7A becomes the routine of FIG. 7B. That is, steps 702,706
Becomes steps 702 ′ and 706 ′.

As described above, by storing the feedback start voltage V _fr backup RAM 105, the activity of the downstream O ₂ sensor 15 with always new feedback start voltage at the time of restart, determined i.e. the downstream O ₂ sensor 15 inactive The start of air-fuel ratio feedback control is determined by. However, when the engine performs learning control, in step 707, V is returned in order to return the original feedback start voltage.
Store _fr in RAM 105.

FIG. 8 is 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 and is executed every predetermined time, for example, 4 ms.

In step 801, 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 THW ≧ 70 ° C. or whether the output level of the upstream O ₂ sensor 13 has once risen / fallen. If the closed loop condition is not satisfied, the routine proceeds to step 817, where the air-fuel ratio correction coefficient FAF1
Is set to 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 802.

In step 802, the output V ₁ of the upstream O ₂ sensor 13 is A / D converted and captured, and in step 803, 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 V _R1 ), the first delay counter CDLY1 is decremented by 1 in step 804, and the first delay counter CDLY1 is guarded by the minimum value TDR1 in steps 805 and 806. In addition,
The minimum value TDR1 is a rich delay time for holding the determination that the output is the lean state even when the output of the upstream O ₂ sensor 13 changes from lean to rich, and is defined as a negative value. On the other hand, if rich (V ₁ > V _R1 ),
In step 807, the first delay counter CDLY1 is incremented by 1, and in steps 808 and 809, the first delay counter CDL1 is added.
Guard Y1 with maximum value TDL1. It should be noted that the maximum value TDL1 is a lean delay time for holding the determination that the output is the rich state even if the output of the upstream O ₂ sensor 13 changes from rich to lean, and is defined as a positive value. It

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 810, 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 processing is inverted. If the air-fuel ratio is reversed, it is determined in step 811 whether rich-to-lean reversal or lean-to-rich reversal is performed. If it is the reverse from rich to lean, in step 812 FAF1 ← FAF
1 + RS1 and skip-wise increase. On the contrary, if lean to rich inversion, in step 813 FAF1 ← FAF1-RS
Decrease to 1 and skip. That is, skip processing is performed.

If the sign of the first delay counter CDLY1 is not inverted in step 810, integration processing is performed in steps 814, 815 and 816. That is, in step 814, it is determined whether or not CDLY <0. If CDLY1 ≦ 0 (lean), in step 815, FAF1 ← FAF1 + KI1 is set, while on the other hand, CDLY1> 0 (rich).
If so, in step 816, FAF1 ← FAF1-KI1.

Here, the integration constant KI1 is set sufficiently smaller than the skip constant RS1, that is, KI1 << RS1. Therefore, step 815 gradually increases the fuel injection amount in the lean state (CDLY1 ≦ 0), and step 816 is in the rich state (CDLY1 ≦ 0).
> 0), the fuel injection amount is gradually reduced.

The air-fuel ratio correction coefficient FAF1 calculated in steps 812, 813, 815, 816 is guarded at the minimum value, for example 0.8 and the maximum value, for example 1.2. In this case, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF1 calculated as described above is stored in the RAM 105, and this routine ends at step 818.

FIG. 9 is a timing chart for supplementarily explaining the operation according to the flowchart of FIG. When the air-fuel ratio signal A / F1 of the rich / lean discrimination is obtained as shown in FIG. 9 (A) by the output of the upstream O ₂ sensor 13, the first delay counter CDLY1 is shown in FIG. 9 (B). As described above, the rich state is counted up, and the lean state is counted down. As a result, as shown in FIG. 9C, the delayed air-fuel ratio signal A / F1 'is formed. For example,
Also at time t ₁ the air-fuel ratio signal A / F1 is changed from lean to rich, the air-fuel signal A / F1 delayed processed 'the time t ₂ after being held lean only the rich delay time (-TDR1) Changes to rich. 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. However, when inverted in a shorter period the air-fuel ratio signal A / F1 is the time t _5, t _6, t ₇ rich delay time as the (-TDR1), time to first delay counter CDLY1 crosses the reference value 0 the required, as a result, the air-fuel ratio signal a / F1 after the delay process at time t ₈ 'is reversed. 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 air-fuel ratio correction coefficient FAF1 shown in FIG. 9D is obtained based on the stable air-fuel ratio signal A / F1 'after the delay processing.

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
Is set separately), the integration constant KI1 (also in this case, the rich integration constant KI1R and the lean integration constant KI1L are set separately), or the comparison voltage V _R1 of the output V ₁ of the upstream O ₂ sensor 13 is made variable. There is a system to do.

For example, if rich delay time (-TDR1)> lean delay time (TDL1) is set, the control air-fuel ratio can shift to the rich side, and conversely, lean delay time (TDL1)> rich delay time (-TDR1) is set. Then, the control air-fuel ratio can shift 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. If the rich skip amount RS1R is increased,
The control air-fuel ratio can be shifted to the rich side, and the control air-fuel ratio can be shifted to the rich side even if the lean skip amount RS1L is reduced, while the control air-fuel ratio can be shifted to the lean side by increasing the lean skip amount RS1L. , Also 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. 10 to 12, the second air-fuel ratio correction coefficient FA
A double O ₂ sensor system incorporating F2 will be described.

FIG. 10 shows a second air-fuel ratio feedback control routine for calculating the second air-fuel ratio correction coefficient FAF2 based on the output of the downstream O ₂ sensor 15, which is for a predetermined time, for example, 1 s.
It is executed every time. At step 1000, it is judged if the feedback control execution flag CF / B is "1". CF
Only when / B = "1", the process proceeds to step 1001. Step
In 1001, it is judged whether or not the closed loop condition by the downstream O ₂ sensor 15 is satisfied. This step is almost the same as step 801 in FIG. If it is not a closed loop condition, step 1017.
Proceed to. If it is a closed loop condition, the process proceeds to step 1002.

In step 1002, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and in step 1003, it is determined 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 higher than the comparison voltage V _R1 of the output of the upstream O ₂ sensor 13 in consideration of the difference in output characteristics due to the influence of raw gas and the deterioration speed on the upstream and downstream sides of the catalytic converter 12. Set high. If lean (V ₂ ≦ V _R2 ), the second delay counter CDLY2 is decremented by 1 in step 1004, and the second delay counter CDLY2 is guarded by the minimum value TDR2 in steps 1005 and 1006. The minimum value TDR
2 is the rich delay time for maintaining the lean state even when there is a change from lean to rich, and is defined by a negative value. On the other hand, if rich (V ₂ > V _R2 ), the second delay counter CDLY2 is incremented by 1 in step 1007, and the second delay counter CDLY2 is added in steps 1008 and 1009.
Is guarded with the maximum value 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 1010, 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 1011 whether rich-to-lean reversal or lean-to-rich reversal is performed. If it is the reverse from rich to lean, in step 1012 FAF2 ← FA
F2 + RS2 is increased in a skip manner, and conversely, if lean to rich inversion, then in step 1013 FAF2 ← FAF2−
Reduce with RS2 in a skip manner. That is, skip processing is performed.

If the sign of the second delay counter CDLY2 is not inverted at step 1010, integration processing is performed at steps 1014, 1015 and 1016. That is, in step 1014, CDLY2 <0
If CDLY2 <0 (lean), it is determined in step 1015 that FAF2 ← FAF2 + KI2, while CDLY2> 0.
If it is (rich), in step 1016 FAF2 ← FAF2-KI2
And Here, the integration constant KI2 is set sufficiently smaller than the step constant RS2, that is, KI2 <RS2. Therefore, step 1015 is in the lean state (CDLY2 ≦ 0).
In step 1016, the fuel injection amount is gradually increased, and in step 1016, the fuel injection amount is gradually decreased in the rich state (CDLY2> 0).

The air-fuel ratio correction coefficient FAF2 calculated in steps 1012, 1013, 1015, 1016 is the minimum value, for example 0.8, and the maximum value, for example,
If the air-fuel ratio correction coefficient FAF2 becomes too large or too small for some reason, the air-fuel ratio of the engine will be 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 1017.

In this way, the second air-fuel ratio correction coefficient FAF2 is calculated based on the output of the downstream O ₂ sensor 15 that has been subjected to the delay processing.

As described above, the calculated FA 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, which is useful for improving drivability at the time of restart or the like.

FIG. 11 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 1101, the RAM 105 reads the intake air amount data Q and the rotational speed data Ne to calculate the basic injection amount TAUP. For example, TAUP ← KQ / Ne (K is a constant). Step 11
The cooling water temperature data THW is read from RAM 105 at 02 and ROM 10
The warm-up increase value FWL is interpolated by the one-dimensional map stored in 4. 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 1103, the final injection amount TAU is set to T
Calculate by AU ← TAUP / FAF1 / FAF2 / (FWL + α) + β. Note that α and β are correction amounts that are determined by other operating state parameters, and are correction amounts that are determined by, for example, a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, a battery voltage, etc.
Stored in 105. Next, at step 1104, the injection amount TAU is set to the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1105, 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. 12 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. 8 and 10. When the output voltage V ₁ of the upstream O ₂ sensor 13 changes as shown in FIG. 12 (A), the comparison result in step 803 of FIG. 8 becomes as shown in FIG. 12 (B). When the comparison result of FIG. 12 (B) is delayed, it becomes as shown in FIG. 12 (C). As a result,
As shown in FIG. 12D, FAF1 skips only RS1 at the time of switching to the delayed rich lean. On the other hand,
The output voltage V ₂ of the downstream O ₂ sensor 15 is shown in FIG.
When it is changed as shown in FIG. 10, the comparison result in step 1003 of FIG. 10 is as shown in FIG. 12 (F), and when it is delayed, it becomes as shown in FIG. 12 (G). When the second air-fuel ratio correction coefficient FAF2 is calculated based on the delayed comparison result of FIG. 12 (G), it becomes as shown in FIG. 12 (H). Further, the closed loop condition of the downstream O ₂ sensor 15 is not satisfied or the feedback control execution flag CF / B =
When it is "0", FAF2 is held at a predetermined value.

Next, a double O ₂ sensor system having a variable delay time as an air-fuel ratio feedback control constant will be described with reference to FIGS. 13 and 14.

FIG. 13 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, 1 s. In step 1300, it is determined whether or not the feedback control execution flag CF / B = "1". CF / B =
Only when it is “1”, the process proceeds to step 1301. In step 1301, similarly to step 1001 in FIG. 10, it is determined whether or not the closed loop condition of the air-fuel ratio is satisfied.

If the closed loop condition is not satisfied, the process directly goes to steps 1323 and 1324.

If the closed loop condition is satisfied, the process proceeds to step 1302.

Steps 1302 to 1309 correspond to steps 1002 to 1009 in FIG. In other words, the rich / lean discrimination is a step
Although it is done in 1303, the result of this determination is step 1304 ~
Delayed at 1309. Then, the rich / lean discrimination subjected to the delay processing is performed in step 1310.

In step 1310, the second delay counter CDLY2 is set to CDLY2.
It is determined whether or not ≤0. As a result, if CDLY2≤0, the air-fuel ratio is determined to be lean, and the process proceeds to steps 1311-1316. On the other hand, if CDLY2> 0, the air-fuel ratio is determined to be rich and step is determined. Continue to 1317-1322.

In step 1311, 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 1312 and 1313, TDR1 is guarded with 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 1314, 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 1315 and 1316, TDL1 is guarded by the minimum value T _L1 . Here, T _L1 is a positive value, so T _L1 means the minimum lean delay time.

In step 1317, TDR1 ← TDR1 + 1 is set, that is, the rich delay time (-TDR1) is reduced, the change from rich to lean is reduced, and the air-fuel ratio is shifted to the lean side. In step 1318,1319 the TDR1 is guarded by a maximum value T _R2.
Here, _{TR2 is} also a negative value, and therefore ( _-TR2 ) means the minimum rich delay time. Further, in step 1320, 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 1321,1322
Then, TDL1 is guarded with the maximum value TL1. Here T _L1
Is a positive value, so T _L2 means maximum lean delay time.

After the TDR1 and TDL1 calculated as described above are stored in the RAM 105, this routine ends in step 1323.

Note that FAF1, TDR1, calculated during air-fuel ratio feedback
TDL1 can be once converted into other values FAF1 ', TDR1', TDL1 'and stored in the backup RAM 106, which is useful for improving drivability at the time of restart or the like.

FIG. 14 shows an injection amount calculation routine, which is executed every predetermined crank angle, for example, every 360 ° CA. In step 1401
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 1402
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 RAM 104. In step 1403, 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 1404, the injection amount TAU is set to the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1405, this routine ends.

FIG. 15 is a timing chart of the delay times TDR1 and TDL1 obtained by the flow charts of FIGS. 8 and 13. As shown in FIG. 15 (A), when the output voltage V _{2 of the} downstream O ₂ sensor 15 changes, as shown in FIG. 15 (B), if 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
Vary from through T _R2, TDL1 varies from T _L1 through 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 condition of FIG.
Control of TDR1 and TDL1 is stopped.

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).
The present invention can also be applied 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 bleed 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 equivalent to the basic injection amount TAUP in steps 1101 and 1401 is determined by the carburetor itself, that is, determined according to the intake pipe negative pressure according to the intake air amount and the rotational speed of the engine, and to steps 1103 and 1403. Then, 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 CO 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.

〔The invention's effect〕

16 and 17 are timing charts for explaining the effect of the present invention. When the outflow type is used as the O ₂ sensor output processing circuit, and as shown in FIG. 16 (B), the air-fuel ratio of the entire engine is lean due to variations in the injection valve, aging of the downstream O ₂ sensor, etc. As shown in FIG. 16 (A), since the feedback start voltage as a criterion for determining whether the O ₂ sensor is active or inactive is lowered to V _fr ′, the feedback control by the downstream O ₂ sensor can be started at the time indicated by the arrow. Therefore, after that, as shown in FIG. 16C, the air-fuel ratio correction amount by the downstream O ₂ sensor, for example, FA
F2 is controlled, and deterioration of drivability and deterioration of NOx emission can be prevented. Similarly, a flow-in type is used as the O ₂ sensor output processing circuit, and as shown in FIG. 17 (B), the air-fuel ratio of the entire engine is rich due to variations in the injection valve, aging of the downstream O ₂ sensor, and the like. In some cases, as shown in FIG. 17 (A), since the feedback start voltage is raised to V _fr ′ as a criterion for determining whether the O ₂ sensor is active or inactive, feedback control by the downstream O ₂ sensor can be started at the time indicated by the arrow. , Therefore, after that, the first
As shown in FIG. 7 (C), the air-fuel ratio correction amount by the downstream O ₂ sensor, for example, FAF2 is controlled, and the deterioration of fuel efficiency is reduced by HC, CO
Emissions can be prevented from worsening.

[Brief description of drawings]

FIGS. 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 dull O ₂
3A and 3B are graphs showing output characteristics of the O ₂ sensor, FIGS. 4 and 5 are timing charts showing conventional air-fuel ratio control, and FIG. An overall schematic view showing an embodiment of an air-fuel ratio control system for an internal combustion engine according to the present invention, FIG. 7A, FIG. 7B, FIG. 8, FIG. 10, FIG. 11, FIG. 13, FIG. 4 is a flow chart for explaining the operation of the control circuit of FIG. 4, FIG. 9 is a timing chart for supplementary explanation of the flow chart of FIG. 8, and FIG. 12 is for supplementary explanation of the flow chart of FIG. 8 and FIG. FIG. 15, FIG. 15 is a timing chart for supplementary explanation of the flowcharts of FIGS. 8 and 13, and FIGS. 16 and 17 are timing charts 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) 2) O ₂ sensor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshinari Nagai 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP 54-69618 (JP, A) JP 54-89116 (JP, A) JP-A-58-72647 (JP, A) JP-B-56-44258 (JP, B2)

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 air-fuel ratio correction calculation unit that calculates a first air-fuel ratio correction amount according to the output of the first air-fuel ratio sensor, and an output of the second air-fuel ratio sensor is a feedback start voltage. Feedback start determination means for determining whether or not the feedback start voltage has changed, and feedback start voltage varying means for changing the feedback start voltage of the output of the second air-fuel ratio sensor to the output level side of the second air-fuel ratio sensor, A second air-fuel ratio correction amount for calculating a second air-fuel ratio correction amount according to the output of the second air-fuel ratio sensor after the output of the second air-fuel ratio sensor reaches the feedback start voltage. An air-fuel ratio control device for an internal combustion engine, comprising: arithmetic means; and air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the first air-fuel ratio correction amount and the second air-fuel ratio correction amount. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the feedback start voltage varying means changes the feedback start voltage according to the second air-fuel ratio correction amount. 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 feedback start determination unit that determines whether the output of the second air-fuel ratio sensor has reached a feedback start voltage, and an output of the second air-fuel ratio sensor uses the feedback start voltage as the second feedback start voltage. Feedback start voltage varying means for changing to the output level side of the air-fuel ratio sensor, and after the output of the second air-fuel ratio sensor reaches the feedback start voltage, the air-fuel ratio is changed according to the output of the second air-fuel ratio sensor. A constant calculating means for calculating a constant involved in fuel ratio feedback control, a constant involved in the air-fuel ratio feedback control, and an output of the first air-fuel ratio sensor An air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount according to the air-fuel ratio, and an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio correction amount. . 4. The feedback start voltage varying means changes the feedback start voltage according to a second air-fuel ratio correction amount calculated according to the output of the second air-fuel ratio sensor. Item 3. An air-fuel ratio control device for an internal combustion engine according to item. 5. 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 delay time for delaying the rich / lean determination of the air-fuel ratio. 6. 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 integration 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 a skip amount. 8. The internal combustion engine according to claim 3, wherein the constant related to the air-fuel ratio feedback control is a comparison voltage for making an air-fuel ratio rich / lean determination from the output of the first air-fuel ratio sensor. Air-fuel ratio controller.