JPH066919B2 - 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]

In general, the air-fuel ratio feedback control based on a single O ₂ sensor (single O ₂ sensor system), O ₂ portion of the exhaust system close to the combustion chamber as possible sensors, that is, the set portion of the exhaust manifold is upstream of the catalytic converter However, due to the variation in the output characteristics of the O ₂ sensor, the improvement of the air-fuel ratio control accuracy is hindered.
The causes of variations in the output characteristics of the O ₂ sensor are listed below.
It is as follows.

(1) Individual difference of the O ₂ sensor itself, (2) Non-uniform mixing of exhaust gas at the location of the 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) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the poisoning amount 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 original Nuisance air-fuel ratio feedback control to the output 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 ₂ sensor system, as long as the downstream O ₂ sensor has maintained a stable output particular, good exhaust emission is ensured.

[Problems to be solved by the invention]

However, the control air-fuel ratio may remain on the rich side or lean side of the stoichiometric air-fuel ratio due to various manufacturing tolerances of fuel control system parts, changes over time in the use process, or the like. For example, if a fuel injection valve that injects more fuel than the other cylinders is attached to the first cylinder, and the upstream O ₂ sensor is strongly affected by the gas of the first cylinder, the upstream O ₂ sensor By the air-fuel ratio feedback control based on the output of the catalyst and the downstream O ₂
The gas to the sensor is lean. As a result, downstream O ₂
The output of the sensor is kept as a lean signal (low level).

On the other hand, there is a method of determining whether the O ₂ sensor is active or inactive depending on whether the output of the O ₂ sensor has reached a predetermined value or more, or whether it has once risen or falled. In this case, as described above, When the air-fuel ratio becomes lean and the output of the downstream O ₂ sensor is held at the lean signal (low level), it cannot be determined whether it is the inactive lean signal or the active lean signal, that is, even if the downstream O ₂ sensor is Even if activated, the activity of the downstream O ₂ sensor cannot be determined.

[Means for solving problems]

An object of the present invention is to perform air-fuel ratio feedback control by an upstream air-fuel ratio sensor (O ₂ sensor) and a downstream air-fuel ratio sensor, but when the output of the downstream air-fuel ratio sensor holds an active lean signal. Another object of the present invention is to provide a double air-fuel ratio sensor (O ₂ sensor) system that enables air-fuel ratio feedback control by a downstream side air-fuel ratio sensor, and its means is shown in FIG.

In FIG. 1, first and second air-fuel ratio sensor means for detecting a concentration of a specific component in exhaust gas are provided upstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine,
Each is provided downstream. In this case, it is assumed that the first and second air-fuel ratio sensor means generate a lean signal when inactive. The first air-fuel ratio control means are respectively
The air-fuel ratio of the engine is controlled according to the outputs V ₁ and V ₂ of the second air-fuel ratio sensor output, and the second air-fuel ratio control means forcibly enriches the air-fuel ratio of the engine. The active / inactive discriminating means discriminates the active / inactive state of the second air-fuel ratio sensor means by whether or not the output V ₂ of the second air-fuel ratio sensor means becomes equal to or higher than a predetermined value or once rises or falls. . Then, the air-fuel ratio adjusting means normally selects the first air-fuel ratio control means, and selects the second air-fuel ratio control means when the second air-fuel ratio sensor means is inactive during acceleration of the engine. The air-fuel ratio of the engine is adjusted.

[Action]

According to the above-mentioned means, when the air-fuel ratio is lean and it is unknown whether the output of the downstream side air-fuel ratio sensor means is the active lean signal or the inactive lean signal, the air-fuel ratio is forced to the theoretical air-fuel ratio. It is on the rich side of the fuel ratio. Therefore, when the output of the downstream side air-fuel ratio sensor means is the lean signal during activation, it is switched to the rich signal, and as a result, the downstream side air-fuel ratio sensor means is judged to be activated. On the other hand, when the output of the downstream side air-fuel ratio sensor means is the lean signal when inactive, it remains the lean signal, and as a result, the downstream side air-fuel ratio sensor means is still determined to be inactive.

In particular, when the engine is accelerated, the intake air amount and the fuel amount increase and the exhaust gas temperature rises, and the air-fuel ratio sensor tends to be activated from inactive to active.
Make a judgment of inactivity.

〔Example〕

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

FIG. 3 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 the A / D converter 1 with built-in multiplexer of the control circuit 10.
Supplied to 01. The throttle valve 16 in the intake passage 2 is provided with a throttle sensor 17 that generates an analog voltage according to the opening degree TA. The output signal of the throttle sensor 17 is also supplied to the A / D converter 101 of the control circuit 10. The distributor 4 has, for example, a crank angle sensor 5 that generates a reference position detection pulse signal every 720 ° when its axis is converted into a crank angle, and a reference position detection pulse signal every 30 ° when converted into a crank angle. A crank angle sensor 6 for generating 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.

The 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 oxygen component concentration in the exhaust gas.
That is, the O ₂ sensors 13 and 15 output different output voltages to A / A via the O ₂ sensor output processing circuits 111 and 112 of the control circuit 10 depending on whether the air-fuel ratio is leaner or richer than the stoichiometric air-fuel ratio. It is generated in the D converter 101.

In addition, the O ₂ sensor output processing circuits 111 and 112 are usually the fourth
As shown in FIG. 5, when the air-fuel ratio A / F is rich, the output characteristic of the outflow type circuit configuration is that of the O ₂ sensor as the element temperature rises. The output (rich signal) stabilizes at the rising high level,
On the other hand, when the air-fuel ratio A / F is lean, it stabilizes at a certain low level as the element temperature rises.

Reference numeral 18 denotes an alarm, which is displayed when the downstream O ₂ sensor 15 has failed.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101 and an input / output interface 10
2, CPU 103, O ₂ sensor output processing circuit 111, 112 outside,
A ROM 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 the "1" level, the flip-flop 109 is set and the drive circuit 110 causes the fuel injection valve 7 to operate. Stop energizing. 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 of the air flow meter 3, the opening degree data TA of the throttle valve 16 and the cooling water temperature data THW are fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105. . That is, RAM 1
The data Q and THW in 05 are updated every predetermined time. Further, 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.

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 increasing operation, the power increasing operation, the lean control, the inactive state of the upstream O ₂ sensor 13, and the like, and the closed loop condition is satisfied in other cases. To determine whether the upstream O ₂ sensor 13 is active or inactive, read the water temperature data THW from the RAM 105 and temporarily
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. When the closed loop condition is not satisfied, the routine proceeds to step 617, 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 602.

As described above, step 601 is a means for determining whether the upstream O ₂ sensor 13 is active or inactive.

In step 602, the output V ₁ of the upstream O ₂ sensor 13 is set to A
/ D converted and uptake, V ₁ is compared in step 603 the voltage V
_R1 For example, it is determined whether 0.45 V or less, that is, it is determined 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 that the output of the upstream O ₂ sensor 13 is in the lean state even if there is a change from lean to rich, and is defined as a negative value. To be done. On the other hand, rich (V ₁ >
If it is 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.
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 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 ← FA
F1 + RS1 is skipped and increases. Conversely, if lean-to-rich reversal, then in step 613 FAF1 ← FAF
1-RS1 and decrease in a skip manner. 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, CDLY1 ≦ 0
If CDLY1 ≦ 0 (lean), it is determined in step 615 that FAF1 ← FAF1 + KI1 and CDLY1> 0.
If it is (rich), in step 616 FAF1 ← FAF1-KI
Set to 1. Here, the integration constant KI1 is set sufficiently smaller than the skip constant RS1, that is, KI1 <RS1. Therefore, step 615 is in the lean state (CDLY1 ≦
0), the fuel injection amount is gradually increased, and step 616 gradually decreases the fuel injection amount in the rich state (CDLY1> 0).

The air-fuel ratio correction coefficient FAF1 calculated in steps 612, 613, 615 and 616 has a minimum value of 0.8 and a maximum value of 1.
2 is used as a guard, and if the air-fuel ratio correction coefficient FAF1 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 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 by the flow chart of FIG. When the rich / lean discrimination 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 CD
LY1 is counted up in the rich state and counted down in the lean state as shown in FIG. 7 (B). As a result, as shown in FIG. 7 (C), the delayed air-fuel ratio signal A / F1 'is formed. For example, the air-fuel ratio signal A / F1 is changed from lean to rich at time t _1, the air-fuel ratio signal A / F1 delayed processed 'is rich delay time (-TdR
After being held lean for 1), it changes to rich at time 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. However, the air-fuel ratio signal A /
F1 is the rich delay time (−5) at times t ₅ , t ₆ , and t _7.
When inverted in a period shorter than TDR1), it takes time for the first delay counter CDLY1 to cross the reference value 0, and as a result, the delayed air-fuel ratio signal A / F1 ′ is inverted at time t ₈ . To be done. 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. 7D 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 a second air-fuel ratio correction coefficient FAF2, delay times TDR1 and TDL1 as the first air-fuel ratio feedback control constants, and skip amount RS1 (in this case, from lean to rich) Rich skip amount RS1R
And the lean skip amount RS1L from rich to lean are set separately), the integration constant KI1 (again, the rich integration constant KI1R and the lean integration constant KI1L are set separately), or the output of the upstream O ₂ sensor 13 There is a system that makes the comparison voltage V _R1 of V ₁ variable.

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. Further, if the rich skip amount RS1R 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 reach skip amount RS1L is increased. Then, the control air-fuel ratio can be shifted to the lean side, and the control air-fuel ratio can be shifted to the lean side even if the rich skip amount RS1R is reduced. 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.
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 FAF
A double O ₂ sensor system incorporating ₂ 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 of
It is executed every time. In step 801, 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 601 in FIG. Therefore,
Step 801 is a means for determining whether the downstream O ₂ sensor 15 is active or inactive. If it is not a closed loop condition, proceed to step 817 and set FAF2 = 1.0.
Proceed to 802.

In step 802, the output V ₂ of the downstream O ₂ sensor 15 is A / D converted and taken in, and in step 803 it is determined whether or not V ₂ is the comparison voltage V _R2, for example, 0.55 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 rate on the upstream side and the downstream side of the catalytic converter 14. Set high. If lean (V ₂ ≦ V _R2 ), the second delay counter CDLY2 is decremented by 1 in step 804, and the second delay counter CDLY2 is guarded by the minimum value TDR2 in steps 805 and 806. The minimum value TDR
2 is a rich delay time for maintaining a 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 807, and the second delay counter CDLY is added in steps 808 and 809.
Guard 2 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.

In this case as well, 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 810, 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 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 FAF2 ← FA
F2 + RS2 is increased in a skip manner, and conversely, if lean to rich inversion, in step 813 FAF2 ← FAF2
-Reduce RS2 and skip. That is, skip processing is performed.

If the sign of the second delay counter CDLY2 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 CDLY2 <0. If CDLY2 <0 (lean), step
Set FAF2 ← FAF2 + KI2 at 815, while CDLY2> 0
If it is (rich), in step 816 FAF2 ← FAF2-KI
Set to 2. Here, the integration constant KI2 is set sufficiently smaller than the skip constant RS2, that is, KI2 <RS2. Therefore, step 815 is in the lean state (CDLY2 ≦
0), the fuel injection amount is gradually increased, and step 816 gradually decreases the fuel injection amount in the rich state (CDLY2> 0).

The air-fuel ratio correction coefficient FAF2 calculated in steps 812, 813, 815, 816 has a minimum value of 0.8 and a maximum value of 1.2, for example.
Therefore, when 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 818.

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

As described above, FA calculated during air-fuel ratio feedback
F1 and FAF2 can be temporarily 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.

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 rotational speed data N _e to calculate the basic injection amount TAUP. Eg TA
UP ← KQ / N _e (K is a constant). R at step 902
The cooling water temperature data THW is read from the AM105 and the warm-up increase value FWL is interpolated by the one-dimensional map stored in the ROM104. 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 calculated by TAU ← TAUP · FAF1 · FAF2 · (FWL + α) + β. Note that α and β are correction amounts that are determined by other operating state parameters, for example, correction signals that are determined by a signal from a throttle sensor (not shown), a signal from an intake air temperature sensor, a battery voltage, or the like.
It is stored in RAM105.

Steps 904 to 911 determine whether the downstream O ₂ sensor 15 is active or inactive. In step 904, similarly to step 601 in FIG. 6, it is determined whether or not the closed loop condition of the air-fuel ratio by the upstream O ₂ sensor 13 is satisfied,
In step 905, it is determined whether or not the state of the water temperature data THW ≧ 70 ° C. has continued for 60 seconds or longer. That is, steps 904 and 905
Determines whether the activation condition of the downstream O ₂ sensor 15 is satisfied. Only when these conditions are satisfied, step 906 for determining the activity or inactivity of the downstream O ₂ sensor 15 is executed.

In step 906, it is determined whether or not the downstream O ₂ sensor 15 has been activated. For example, activation is determined by whether V ₂ > 0.45 V is satisfied at least once or whether V ₂ once rises or falls. If it is determined that the downstream O ₂ sensor 15 is still inactive, the process proceeds to step 907.

In step 907, the change Δ in the throttle opening data TA
It is determined whether or not TA is a predetermined value, for example, 2 ° / 16 ms or more. That is, it is determined whether or not the vehicle is in an accelerated state. In the acceleration state, in steps 908 to 910, the fuel injection amount TAU is increased by 10% to confirm the activity of the downstream O ₂ sensor 15.
This increase operation is performed up to 5 times, but before that step 90
If it is determined that the downstream O ₂ sensor 15 is activated at 6,
This increase is discontinued. On the other hand, even if this increase operation is performed 5 times, if it is not determined to be activated in step 906, it is considered that the downstream O ₂ sensor 15 has failed, and an alarm is displayed in step 911.

The upstream O ₂ sensor 13 and the downstream O ₂ sensor 1
If the air-fuel ratio feedback control by 5 is the first air-fuel ratio control, the fuel increase in step 910 can be said to be the second air-fuel ratio control.

Next, at step 912, the injection amount TAU is down-counted.
Set to 108 and flip-flop 109 to start fuel injection. Then, in step 913, this routine ends. As described above, the injection amount TA
When the time corresponding to U has elapsed, 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. When the output voltage V ₁ of the upstream O ₂ sensor 13 changes as shown in FIG. 10 (A), the comparison result in step 603 of FIG. 6 is shown in FIG. 10 (B).
It becomes like When the comparison result of FIG. 10 (B) is delayed, it becomes as shown in FIG. 10 (C). As a result, Fig. 10
As shown in (D), FAF1 skips only RS1 at the time of switching between the delayed rich and lean sides. On the other hand, when the output voltage V ₂ of the downstream O ₂ sensor 15 changes as shown in FIG. 10 (E), the comparison result in step 803 of FIG. 8 becomes as shown in FIG. 10 (F), and further, When the delay processing is performed, it becomes as shown in FIG. Second air-fuel ratio correction coefficient When calculated based on the delayed comparison result of FIG. 10 (G), the result is as shown in FIG. 10 (H).

Next, a double O ₂ sensor system in which the delay time as the air-fuel ratio feedback control constant 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. In step 1101, step 801 in FIG. 8 is executed.
Similarly, 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 proceeds to steps 1123 and 1124 to set the rich delay time TDR1 and the lean delay time TDL1 to constant values. For example, TDR1 ← -12 (equivalent to 48ms) TDL1 ← 6 (equivalent to 24ms). Here, the rich delay time (-TDR1) is set larger than the lean delay time TDL1 because the comparison voltage V _R1 is set to a low value, for example, 0.45 V on the lean side.

If the closed loop condition is satisfied, the process proceeds to step 1102.

Steps 1102-1109 correspond to steps 802-809 in FIG. In other words, the rich / lean discrimination is step 1103.
However, the result of this determination is steps 1104-1109.
Will be delayed. And the rich that has been delayed,
Lean determination is performed in step 1110.

At step 1110, the second delay counter CDLY2 is set to CDLY.
It is determined whether or not 2 ≦ 0. As a result, if CDLY2 ≦ 0, it is determined that the air-fuel ratio is lean, and the routine proceeds to steps 1111-1116. On the other hand, if CDLY2> 0, the air-fuel ratio is determined to be rich. Proceed to steps 1117 to 1122.

In step 1111, 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 step 1112 and 1113, the minimum value TDR1 T _R1
To guard. Here, T _{R1 is} also a negative value, so (−T _R1 ) means the maximum rich delay time. Further, in step 1114, TDL1 ← TDL1-1, that is,
The lean delay time TDL1 is reduced to reduce the delay of the change from lean to rich and shift the air-fuel ratio to the rich side. In steps 1115 and 1115, 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 1117, TDR1 ← TDR1 + 1 is set, that is, the 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. In step 1118 to 1119 the TDR1 is guarded by a maximum value T _R2. Here, T _{R2 is} also a negative value, so (−
T _R2 ) means the minimum rich delay time. Further, in step 1120, 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. In steps 1121 and 1122, 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 1125.

FAF1, TDR calculated during air-fuel ratio feedback
1, 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.

FIG. 12 shows an injection amount calculation routine, which is almost the same as that shown in FIG. In other words, step 903 ′ is different from step 903 in FIG. 9 and the final injection amount TAU is set to TAU ← TAUP.
It is calculated by FAF1 ・ (FWL + α) + β.

FIG. 13 is a timing chart of the delay times TDR1 and TDL1 obtained by the flow charts of FIGS. 6 and 11.
When the output voltage V _{2 of the} downstream O ₂ sensor 15 changes as shown in FIG. 13 (A), as shown in FIG. 13 (B),
If the lean state (V ₂ ≦ V _R2 ), the delay time TDR1, TDL
1 is increased together. On the other hand, if rich, delay time
Both TDR1 and TDL1 are reduced. At this time, TDR1 is T
Varies from _R1 through T _R2, TDL1 varies from T _L1 through T _L2. 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-55-37).
The present invention can also be applied to a double O ₂ sensor system that corrects the output of the downstream O ₂ sensor.

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, in the above-described embodiment, the internal combustion engine in which the fuel injection amount to the intake system is controlled by the fuel injection valve has been shown, but the present invention can also be applied to the caplet 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 corresponding to the basic injection amount TAUP in step 901 is determined by the carburetor itself, that is, the intake pipe negative pressure according to the intake air amount and the engine speed, and step 903 At (903 '), 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〕

As described above, according to the present invention, when the output of the downstream side air-fuel ratio sensor of the outflow type process is a lean signal, the air-fuel ratio is forcibly made rich to determine whether it is active or inactive. If the timing for determining active / inactive is advanced and the downstream air-fuel ratio sensor is activated, the air-fuel ratio feedback control by this sensor can be started earlier. Moreover,
Since the determination is made when the engine is accelerated, the air-fuel ratio sensor is likely to be activated from inactive to active, and the determination becomes more effective.

Furthermore, for those that read the resistance value of the air-fuel ratio sensor to determine whether it is active or inactive, no special hardware configuration is required, and for those that only activate or deactivate by water temperature,
There is also an effect that there are few erroneous determinations.

[Brief description of drawings]

FIG. 1 is an overall block diagram 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. 3 is an exhaust emission characteristic diagram illustrating a sensor system, FIG. 3 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention, and FIG. 4 is an O ₂ sensor output processing circuit in FIG. Circuit diagram, FIG. 5 is an output characteristic diagram of the O ₂ sensor output processing circuit of FIG. 3, and FIGS. 6, 8, 9, 11, and 12 are operations of the control circuit of FIG. 7 is a timing chart for supplementary explanation of the flow chart of FIG. 6, FIG. 10 is a timing chart for supplementary explanation of the flow chart of FIG. 6 and FIG. FIG. 11 is a timing chart for supplementary explanation of the flowcharts of FIGS. 6 and 11. 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 ( Second) O ₂ sensor, 17 ... Throttle sensor, 18 ... Alarm.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyasu Katsuno 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (56) Reference JP-A-58-72647 (JP, A) JP-A-52- 135924 (JP, A) JP 52-97030 (JP, A) JP 55-161935 (JP, A)

Claims (1)

[Claims] 1. A specific component in exhaust gas, which is provided upstream and downstream of a catalytic converter for purifying exhaust gas provided in an exhaust system of an internal combustion engine, generates a lean signal when inactive, and when active. First and second air-fuel ratio sensor means for detecting the concentration; first air-fuel ratio control means for controlling the air-fuel ratio of the engine according to the outputs of the first and second air-fuel ratio sensor means; Second air-fuel ratio control means for forcibly making the air-fuel ratio of the engine rich, and activation / deactivation of the second air-fuel ratio sensor means for the second
The active / inactive discriminating means for discriminating whether or not the output of the air-fuel ratio sensor has become equal to or more than a predetermined value at least once, and the first air-fuel ratio control means is normally selected, and when the engine is accelerated, the An air-fuel ratio control device for an internal combustion engine, comprising: air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine by selecting the second air-fuel ratio control means when the second air-fuel ratio sensor means is inactive.