JPH01318735A - Control device for air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a fuel cost and drivability by stopping the operation of the air-fuel ratio control quantity based on the output of the air fuel ratio sensor provided at the downstream side of the catalytic converter rhodium in an exhaust passage at the time when an operating range is transitted to a different zone. CONSTITUTION:An air-fuel ratio sensor 15 is provided on the exhaust passage of the downstream side of a catalytic converter rhodium 12 and an air fuel ratio control amt. is operated by an air fuel ratio control amt. arithmetic means A according to the output thereof. Whether the operating range of an engine is belonged to either of plural ranges is decided by an operating range discriminating means B, the center value of the air fuel ratio control amt. is operated by a study means C at the time when the operating range is belonged to the same range, the center value thereof is stored as a study value on each range and the study value of the operating range after transition is migrated as the air fuel ratio control amt. at the transition time of the operating range to a different range. At the time when the transition of the operating range to a different range is detected by a detection means E the operation of the air fuel ratio control amt. is stopped by specified period by a stopping means F.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides an air-fuel ratio sensor (herein, an oxygen concentration sensor (0□ sensor)) at least on the downstream side of a catalytic converter.
This invention relates to improvements in area-specific (block) learning control in an air-fuel ratio sensor system equipped with an air-fuel ratio sensor system.

[Conventional technology]

In simple air-fuel ratio feedback control (single 0□ sensor system), the 02 sensor that detects oxygen concentration is installed in the exhaust system as close to the combustion chamber as possible, that is, in the gathering part of the exhaust manifold upstream of the catalytic converter. Due to variations in the output characteristics of the 0□ sensor, it is difficult to improve the control accuracy of the air-fuel ratio. It takes 0□
In order to compensate for variations in sensor output characteristics, variations in parts such as fuel injection valves, and changes over time or aging, a second 0 sensor is provided downstream of the catalytic converter, and air-fuel ratio feedback control by the upstream 02 sensor is performed. In addition, a double 02 sensor system that performs air-fuel ratio feedback control using a downstream 02 sensor has already been proposed (
Reference: Japanese Unexamined Patent Publication No. 58-72647). This double 0
In the □ sensor system, the 02 sensor installed on the downstream side of the catalytic converter has a lower response speed than the 0□ sensor on the upstream side, but has the advantage of less variation in output characteristics for the following reasons. ing.

(1) Downstream of the catalytic converter, the exhaust gas temperature is low, so there is little thermal influence.

(2) Since various poisons are trapped in the catalyst downstream of the catalytic converter, the amount of poisoning of the downstream 02 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 an equilibrium state.

Therefore, as described above, by using the air-fuel ratio feedback control '4B (double 0□ sensor system) based on the outputs of the two Ot sensors, variations in the output characteristics of the upstream 02 sensor can be absorbed by the downstream 02 sensor. In fact, as shown in Figure 2, in a single 0□ sensor system,
When the output characteristics of the Ot sensor deteriorate, it directly affects the exhaust emission characteristics, whereas in the double 02 sensor system, even if the output characteristics of the upstream 02 sensor deteriorate, the exhaust emission characteristics do not deteriorate. In other words, in the double 0□ sensor system, good exhaust emissions are guaranteed as long as the downstream 02 sensor maintains stable output characteristics.

In the above-mentioned double 0□ sensor system, the required level for air-fuel ratio correction during feedback control (hereinafter referred to as air-fuel ratio required level) may be significantly different from that during non-feedback control. The following problem occurs when feedback control is started using two 0□ sensors. That is, in this case, the air-fuel ratio feedback control speed by the downstream 02 sensor is normally the same as that of the upstream 02 sensor.
Since it is set small compared to the air-fuel ratio feedback control speed by the sensor, the air-fuel ratio control amount, for example, the skip amount R5R, is controlled by the air-fuel ratio feedback control by the downstream 0□ sensor.

It takes time for the RSL to reach the required skip amount level, and in turn, it takes time for the air-fuel ratio to reach the required control level due to air-fuel ratio feedback control, resulting in insufficient correction, This leads to deterioration of fuel efficiency, deterioration of drivability, deterioration of emissions, etc.

Additionally, even during air-fuel ratio feedback control, when the engine state transitions to a different operating range, the air-fuel ratio control level may still deviate from the air-fuel ratio request level, and in this case as well, insufficient correction may occur. , leading to deterioration of fuel efficiency, deterioration of drivability, deterioration of emissions, etc.

For example, due to the 02 storage effect of the catalyst, the amount of gas is smaller in the low load range than in the high load range, and the amount of 02 consumed stored in the catalyst is small (the downstream 02 sensor takes a longer time to indicate lean). , As a result, the air-fuel ratio control amount R5R in the high load range and the low load range.

The RSL value shifts. This is particularly noticeable when a new catalyst with a large 0□ storage effect is used.

Therefore, when the load changes from a low load range to a high load range, the air-fuel ratio feedback period of the downstream Ot sensor is relatively long, resulting in a delay in downstream 02 control, causing the air-fuel ratio to become over-representative, resulting in reduced fuel consumption and emissions. This may lead to deterioration.

For this reason, the applicant has already divided engine load conditions such as intake air amount, intake air pressure, throttle valve opening, rotational speed, vehicle speed, or reversal period of the output of the upstream 0□ sensor into multiple categories. If the engine load state belongs to the same operating range and the engine satisfies the learning conditions, calculate the center value of the air-fuel ratio control amount, and The central value of the fuel ratio control amount is stored for each operating region, and when the engine does not satisfy the air-fuel ratio feedback condition or when the engine state changes to a different operating region thereafter, the air-fuel ratio control amount l is stored. proposed a block learning control in which the central value of the air-fuel ratio control amount stored in the current operating region is used (reference: Japanese Patent Application Laid-open No. 1982-1999).
60941, Japanese Patent Application No. 61-241484, Japanese Patent Application No. 63-14614). According to this, when starting the air-fuel ratio feedback control by the downstream side 02 sensor, it starts from the center value of the stored air-fuel ratio control amount B, and further,
Even when the state of the engine changes to a different operating range thereafter, the process starts from the center value of the air-fuel ratio control amount stored for each operating range.

[Problem to be solved by the invention]

However, in the above-described block learning control based on the operating range, the learned value of the operating range is used as the air-fuel ratio control amount immediately after the engine state changes to a different operating range. As a result, when the output of the downstream 02 sensor indicates lean, the learned value RSRG (n) after the operating range transition, for example, the learned value RSRG (n) of the R3R amount, is the learned value R5RG before the operating range transition. (n o), the controlled air-fuel ratio does not immediately reach the stoichiometric air-fuel ratio because the catalyst shifts to a lean state, and therefore the fuel consumption, IIc
, leading to worsening of CO emissions. On the other hand, downstream 0
If the output of the two sensors indicates lean and the learned value RSRG (n) after the operating range transition is smaller than the learned value RSRG (no) before the operating range transition, the catalyst will shift to a lean state. The controlled air-fuel ratio does not immediately reach the stoichiometric air-fuel ratio, resulting in deterioration of drivability and NOx emissions.

For example, as shown in Fig. 3, the learned value R3RGA of the rich skip amount R3R in the A 5p area is 4%, and the learned value R3RGB of the rich skip amount R3R in the B area is 8%.
%, in the period T after the operating region transitions from the A region to the B region, the lean state in the A region continues due to the gas transport delay, the 02 storage effect of the catalyst, etc. As a result, the air-fuel ratio becomes overlifted during the period T immediately after entering the B region. Also, when transitioning from area A to area B SN, for example, if the boundary (vehicle speed classification learning) is 49 km/h, the difference between 39 km/h and 41 km/h is originally that much (that is, 4% and 8 km/h). %) There is no difference in the required rich skip amount. Therefore, if the rich skip amount R3R is adjusted to the learned value RSRG after the transition immediately after the region transition,
This causes deterioration of emissions.

In this way, when the learning region of the catalyst downstream air-fuel ratio sensor changes, the control results before the region transition may erroneously affect the control after the transition.
This leads to worsening of emissions, combustion, and drivability.

The above-mentioned problem is the same in a single O2 sensor system in which an O□ sensor is provided only downstream of or inside the catalyst.

Therefore, the object of the present invention is to
The object of the present invention is to provide a block learning control system that sufficiently prevents deterioration of emissions, fuel consumption, drivability, etc.

[Means to solve the problem]

Means for solving the above problems are shown in FIGS. 1A to 1D.

In FIG. 1A, an air-fuel ratio sensor for detecting the air-fuel ratio of the engine is provided in the exhaust passage downstream of the three-way catalyst CC1o provided in the exhaust passage of the internal combustion engine. The air-fuel ratio control amount calculation means calculates the air-fuel ratio control amount according to the output (2) of the air-fuel ratio sensor. Further, the operating region determining means determines whether the operating region of the engine, for example, the vehicle speed SPD, belongs to one of the regions divided into a plurality of regions. As a result, the learning means calculates the center value of the air-fuel ratio control amount when the operating regions belong to the same region, stores the center value of the air-fuel ratio control amount as a learned value for each region, and When transitioning to a different region, the learned value of the operating region after the transition is transferred as the air-fuel ratio control amount. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine according to the air-fuel ratio control amount. On the other hand, the region transition detection means detects whether or not the operating region has transitioned to a different region, and as a result, when the operating region has transitioned to a different region, the stopping means detects the output V2 of the air-fuel ratio sensor for a predetermined period M. This is to stop the calculation of the air-fuel ratio control amount according to.

In the means shown in FIG. 1B, instead of the stopping means shown in FIG. 1A, there is provided update speed reduction means for reducing the update speed of the air-fuel ratio control amount for a predetermined period when the operating region transitions to a different region. .

In the means shown in FIG. 1C, instead of the stopping means shown in FIG. 1A, when the operating region changes to a different region, the air-fuel ratio control amount before the region transition and the operating region after the bB region transition are used for a predetermined period T. The intermediate level between the learned value and the air fuel pressure '431
! An intermediate value transfer means is provided to transfer the value as ffl.

In the means shown in FIG. 1D, instead of the stop means shown in FIG. 1A, when the operating region changes to a different region, the difference between the air-fuel ratio control amount before the region transition and the learned value of the operating region after the region transition is determined. A gradual transition means is provided for transitioning the gradually changed level as the air-fuel pressure control amount.

[For production]

The operation of the above-described means is illustrated in FIGS. 4A, 4B, 5A, 5B, 6A, 6B and 7.

According to the means shown in FIG. 1A, as shown in FIGS. 4A and 4B, during the predetermined period T after the operating region changes from A to B, the calculation of the air-fuel ratio control amount R3R is stopped, and its value is held at a constant value. As one aspect, the air-fuel ratio control amount R3
R is held at the learned value R5RGB of area B after the transition (Fig. 4A), and as another aspect, the air-fuel ratio control amount R3R is held at the learned value 1-5RGA of area A before the transition (or the value immediately before the transition). (Figure 4B). Therefore, erroneous control is suppressed.

According to the means shown in FIG. 1B, as shown in FIGS. 5A and 5B, during a predetermined period T after the operating region changes from A to B, the update speed of the air-fuel ratio control ff1R3R is reduced. Part 1
As one aspect, the air-fuel ratio control amount R3R is in the region B after the transition.
After shifting to the learned value R5RGB, the air-fuel ratio control amount R8
In another aspect, the air-fuel ratio control amount R3R is changed to the learned value RSR of the region A before the transition.
Air fuel pressure from GA (or value just before transition) '4Ta
The update speed of the amount R3R is reduced, and after a predetermined period T, the area B
Let the learned value R5RGB be. Therefore, erroneous control is suppressed, and the air-fuel ratio control amount R3R reaches the post-transition learning value R5RGB after the predetermined period T, making it possible to follow the output of the air-fuel ratio sensor.

According to the means shown in FIG. 1C, as shown in FIGS. 4A and 4B, during the predetermined period T after the operating region changes from A to B, the calculation of the air-fuel ratio control amount R3R is stopped, and its value is It is held at an intermediate level between the learned value 1-5RGA (or the value immediately before the transition) of area A and the learned value R5RGB of area B (FIG. 6A). In this case, this intermediate level is set to the air-fuel ratio control 11.
It may also be used as a guard value for R3R (Fig. 6B). As a result, the intermediate level of the learned values between the operating regions A and B is close to the required level of the air-fuel ratio control amount R3R at the time of region transition, which helps prevent deterioration of emissions.

According to the means shown in FIG. 1D, as shown in FIG. 7, after the operating region changes from A to B, the air-fuel ratio control amount R3R changes to the learned value RSI? From GA (or the value just before the transition) to B
The learning value of the area gradually changes to R5RGB.

〔Example〕

FIG. 8 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. In FIG. 8, an air flow meter 3 is provided in the intake passage 2 of the engine body 1. As shown in FIG. The air flow meter 3 directly measures the intake air amount, has a built-in potentiometer, and generates an analog voltage output signal proportional to the intake air amount. This output signal is supplied to the MA/D converter 101 in the multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30'' in terms of crank angle. A crank angle sensor 6 is provided to generate pulse signals.The pulse signals of these crank angle sensors 5 and 6 are supplied to the input/output interface 102 of the control circuit IO, and the output of the crank angle sensor 6 is CPt11.
03 interrupt terminal.

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

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body l. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101.

A catalytic converter 12 that accommodates a three-way catalyst that simultaneously purifies three harmful components HC, GO, and NO in exhaust gas is provided in the exhaust system downstream of the exhaust manifold 11.

A first 0□ sensor 13 is provided in the υ air manifold 11, that is, on the upstream side of the catalytic converter 12, and a second 0□ sensor 13 is provided in the exhaust pipe 14 on the downstream side of the catalytic converter 12.
A sensor 15 is provided.

The 0□ sensors 13 and 15 generate electrical signals corresponding to the concentration of oxygen components in the exhaust gas. That is, 02 sensor 13
, 15 is an A/D control circuit 10 which outputs different output voltages depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
occurs in converter 101.

Further, the throttle valve 16 of the intake passage 2 is provided with an idle switch 17 for detecting whether or not the throttle valve 16 is fully closed, and this output signal is supplied to the human output interface 102 of the control circuit 10. be done.

Reference numeral 18 denotes a vehicle speed sensor, which is composed of, for example, a permanent magnet and a reed switch, and its output is sent to a control circuit lO.
It is sent to the vehicle speed formation circuit 111.

The control circuit IO is configured as a microcomputer, for example, and includes an A/D converter 101, a Tough Eight 102, a CPU 103, a vehicle speed forming circuit 111, and a ROM 104, a RAM 105, and a backup RO.
M106 and a clock generation circuit 107 are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection 11 TAU is preset in the down counter 108 and the flip-flop 10
9 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down counter 108
counts a clock signal (not shown) and finally when its carrier terminal reaches the "L" level, the flip-flop 109 is reset and the drive circuit 110 stops energizing the fuel injection valve 7. . In other words, the above fuel injection I
The fuel injection valve 7 is energized by TAU, and therefore, an amount of fuel corresponding to 1 TAU of fuel injection is sent into the combustion chamber of the engine body 1.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 10.
1, the input/output interface 102
When the controller receives a pulse signal from the crank angle sensor 6, when it receives an interrupt signal from the clock generation circuit 107, etc.

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

FIG. 9 shows a first air-fuel ratio feedbank control routine that calculates an air-fuel ratio correction factor FAF based on the output of the upstream 0□ sensor 13, and is executed every predetermined period of time, for example, every 4 ms.

In step 901, it is determined whether a closed loop (feedback) condition for the air-fuel ratio by the upstream 0□ sensor 13 is satisfied. For example, when the cooling water temperature is below a predetermined value, when the engine is starting, when increasing the amount after starting, when increasing the warm-up amount, when increasing the power, when oTPf*+iT is in progress to prevent catalyst overheating, when the upstream side is 0
When the output signal of the second sensor 13 has never been inverted, the closed loop condition is not satisfied during fuel cut, etc.
In other cases, the closed loop condition is met. If the closed-loop condition is not satisfied, the process proceeds to step 927 and the FAF is set to the value immediately before the end of the closed-loop control. Note that it may be set to a constant value, for example, 1.0. On the other hand, if the closed loop condition is satisfied, the process proceeds to step 902.

In step 902, the output vI of the upstream 02 sensor 13 is
is A/D converted and taken in, and in step 903, it is determined whether or not ■ is a comparison voltage ■□, for example, 0.45V or less.
That is, it is determined whether the air-fuel ratio is rich or lean. In other words, if the air-fuel ratio is lean (V, ≦V R1), it is determined in step 904 whether the delay counter CDLY is negative or not, and if CDLY>0. If so, CDL in step 905
Set Y to 0 and proceed to step 906. In step 906, the delay counter CDLY is decremented by 1, and in step 9
07. At 908, the delay counter CD L'/ is guarded at the minimum value TDL. In this case, when the delay counter CDLY reaches the minimum value TDL, the first air-fuel ratio flag Fl is set to "0" (lean) in step 909. Note that the minimum value TDL is the upstream 0□ sensor 13.
This is a lean delay state that maintains the determination that the state is rich even if the output changes from rich to lean, and is defined as a negative value. On the other hand, Rich (V,
>V□), it is determined in step 910 whether the delay counter CDIJ is positive or not, and if CDLY<Q, CDLY is set to 0 in step 911, and step 912
Proceed to. In step 912, the delay counter CDLY
is incremented by 1, and the process proceeds to step 913. At 914, the delay counter CDLY is guarded at the maximum value TDR.

In this case, when the delay counter CDLY reaches the maximum value TDR, the first air-fuel ratio flag F1 is set to 1'' (rich) in step 915.
is a rich delay time for maintaining the determination that the engine is in a lean state even if there is a change from lean to rich in the output of the upstream 02 sensor 13, and is defined as a positive value.

In step 916, it is determined whether the sign of the first air-fuel ratio flag F1 has been inverted, that is, it is determined whether the air-fuel ratio after the delay processing has been inverted. If the air-fuel ratio is reversed, then in step 917, it is determined whether the reversal is from rich to lean or from lean to rich, based on the value of the first air-fuel ratio flag F1. If it is a reversal from rich to lean, it is increased in a skip manner as FAF-FAF+R5R in step 918, and conversely, if it is a reversal from lean to rich, it is increased by step 7'919 and FAF 4-FI.
Decrease in skips with EF-R5L. In other words, skip processing is performed.

If the sign of the first air-fuel ratio flag F1 is not inverted in step 916, steps 920, 921, 922
Integration processing is performed at . That is, in step 920, F
Determine whether l-“0” or not, F1=“0° (lean)
If so, in step 921 FAF −FAF+KIR
On the other hand, if F1="l" (rich), then in step 922 FAF +-FAF-KIL is set. Here, the integral constants KIR, and IL are skipped l RSR, R
It is set sufficiently small compared to 5L, that is, K[l
? (KIL) <RSR (RS. Therefore, step 921 gradually increases the fuel injection amount in the lean state a (Ft="0"), and step 922 gradually increases the fuel injection amount in the rich state (Ft="0").
- "1") gradually reduces the fuel injection amount.

The air-fuel ratio correction coefficient FAF calculated in steps 918, 919, 921, and 922 is guarded at a minimum value, for example, 0.8, in steps 923 and 924, and is guarded at a minimum value of 0.8, for example, in steps 925. At 926, it is guarded at a maximum value of 1.2, for example. As a result, for some reason, the air-fuel ratio correction coefficient F
When AF becomes too large or too small, the engine's air-fuel ratio is controlled using that value to prevent over-rich or over-lean conditions.

The FAF calculated as described above is stored in the RAM 105, and the routine ends in step 927.

FIG. 10 is a timing diagram supplementary explanation of the operation according to the flowchart of FIG. 9. When the air-fuel ratio signal A/F for rich/lean discrimination is obtained from the output of the upstream 0□ sensor 13 as shown in Fig. 1O (A), the delay counter CDLY is set to indicate the rich/lean ratio as shown in Fig. 1O (B). The count is amplified in the state, and the count is counted down in the lean state. As a result, as shown in FIG. 10(C), a delayed air-fuel ratio signal A/F' (corresponding to flag Fl) is formed. For example, at time t1, the air-fuel ratio signal A/F
Even if ' changes from lean to rich, the delayed air-fuel ratio signal A/F' changes to rich at time 1t after being held on for the rich delay time TDR. Even if the air-fuel ratio signal A/F changes from rich to lean at time t, the delayed air-fuel ratio signal A/F' is held rich for an amount equivalent to the lean delay time (-TDL), and then returns to time t4. Changes to lean. However, the air-fuel ratio signal A/F
'is time tSr 6, t? If the rich delay time TDR is reversed in a short period as shown in FIG.
' is reversed. In other words, the air-fuel ratio signal A/ after the delay processing is
F' becomes more stable than the air-fuel ratio signal A/F before the delay process. In this way, after the delay processing, the stable air-fuel ratio signal A/
Based on F', the air-fuel ratio correction coefficient FAF shown in FIG. 10(D) is obtained.

Next, the second air-fuel ratio feedback control by the downstream 02 sensor 5 will be explained. As the second air-fuel ratio feedback control, the skimp amount I? as the first air-fuel ratio feed bank control constant? S+? ,I? SLX integral constants KIR, KIL, delay time TDR.

There is a system in which TDL or the comparison voltage Vllll of the output V1 of the upstream 02 sensor 13 is made variable, and a system in which a second air-fuel ratio correction coefficient FAI'2 is introduced.

For example, if the rich skip amount R3R is increased, the control air-fuel ratio can be shifted to the rich side, and even if the lean skip IR3L is decreased, the control air-fuel ratio can be shifted to the rich side. , the controlled air-fuel ratio can be shifted to the lean side, and the controlled air-fuel ratio can also be shifted to the lean side even if the control air-fuel ratio is made smaller.

Therefore, the air-fuel ratio can be controlled by correcting the rich skip amount R5R and the lean skip amount R3L according to the output of the downstream 02 sensor 15.

In addition, by increasing the rich integral constant KIR, the control air-fuel ratio can be shifted to the rich side, and the lean integral constant KIL
On the other hand, increasing the lean integral constant Kl+- allows the controlled air-fuel ratio to be shifted to the lean side even if the rich integral constant KIR is decreased. can be shifted to the lean side. Therefore, the air-fuel ratio can be controlled by correcting the rich integral constant KTR and the lean integral constant KIL according to the output of the downstream 02 sensor 15. If the rich delay time TDR is set large or the lean delay time (-TDL) is set small, the controlled air-fuel ratio can be shifted to the rich side.Conversely, if the lean delay time (-TDL) is set large or the rich delay time (TDR) is set small If set to a small value, 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 TDR and TDL according to the output of the downstream 02 sensor 15. Furthermore, by increasing the comparison voltage ■□, the controlled air-fuel ratio can be shifted to the rich side, and by decreasing the comparison voltage Vllll, the controlled air-fuel ratio can be shifted to the lean side. Therefore, by correcting the comparison voltage ■□ according to the output of the downstream sensor 15, the air-fuel ratio can be controlled.

Making these skip amount, integral constant, delay time, and comparison voltage variable by the downstream 02 sensor has its own advantages. For example, the delay time allows very delicate adjustment of the air-fuel ratio, and the skip amount can be controlled with good response without lengthening the air-fuel ratio feedbank period unlike the delay time. Therefore, naturally, two or more of these variable amounts can be used in combination.

Next, a double 02 sensor system in which the skip amount as an air-fuel ratio feedback control constant is made variable will be described.

11A is skipped based on the output of the downstream side 02 sensor 15. I? This is a second air-fuel ratio feedback control routine that calculates SR and R5L, and is executed every predetermined period of time, for example, every 512 m5.

In step 1101, vehicle speed data SPD is taken from the vehicle speed forming circuit 111, and n''sPD/ΔSPD is calculated as a constant value. Note that n is an integer and SPD/Δsp.

The decimal places shall be rounded down. In this way, it is determined whether the vehicle speed SPD belongs to any of the following regions: O≦spo<ΔSPD, region ΔSPD≦sp2・ΔSPD (k−1), ΔSPD≦SPD<k・ΔSPD. Note that step 1101
The vehicle speed SPD in may be an annealed value.

In steps 1102 to 1106, downstream side 02 sensor 1
It is determined whether or not the closed loop condition is satisfied by 5. For example, in addition to the failure of the closed loop condition determined by the upstream 0□ sensor 13 (step 1102), the cooling water temperature T HW is set to a predetermined value (
For example, when the temperature is below 70°C (step 1103),
When the throttle valve 16 is fully closed (LL-“1”) (step 1104), when the downstream 0□ sensor 15 is not activated (step 1105), when the load is light (Q
/Ne≦XI) (step 1106), etc., the closed loop condition is not satisfied, and in other cases, the closed loop condition is satisfied. If the condition is not a closed loop condition, the process proceeds to step 1123.

If the closed loop condition is satisfied, the process proceeds to step 1107. In other words, the current operating region ρ and the previous operating region n
0 is the same. As a result, when the region n of the vehicle speed SPD changes, in step 1108, the RAM
The intake air amount data Q is successively obtained from 105, and the difference between the learned values between area n and area n0 is calculated as l R3RG(n) -R5RG(no) 1, and these two parameters are stored in ROM 104. The delay time CNT is calculated using the two-dimensional map obtained.

Note that the intake air amount Q indicates the gas transport delay, and the difference between the two learned values is the delay time CNT based on these two parameters in order to indicate the degree of influence of the control result before the transition on the control after the transition. (-T) is calculated. Then, the process advances to step 1123. Furthermore, if the region n of the vehicle speed SPD is the same (n=n), the learning value counter CNT is calculated by -tS in step 1107, and step 11 is performed until CNT=0.
The process also proceeds to step 1123 via step 10.

In step 1123, the learned value RSRG(n) of the area n after the transition, that is, the current area n, is stored in the bank up RAM1.
Rich skip amount R3R by reading from corresponding area n of 06
to be migrated as That is, until the time after the region transition reaches T, the rich skip IR3R is held at the learned value R3RG(n) of the region n after the transition.

When the time after region transition passes T, step 1110
The flow proceeds to step 1111, where the counter CNT
is guarded to 0 and the process proceeds to steps 1112 to 1122.

In step 1112, the output V of the downstream side 02 sensor 15 is
2 is A/D converted and taken in, and in step 1113 V2
is the comparison voltage ■. For example, it is determined whether the voltage is 0.55V or less. In other words, it determines whether the air-fuel ratio is rich or lean. The comparison voltage Vllll is determined by the upstream side 02 sensor 13 in consideration of the fact that the output characteristics are different due to the influence of raw gas and the deterioration rate is different upstream and downstream of the catalytic converter 12.
is set higher than the comparison voltage V□ of the output. As a result,
If v2≦■1 (lean), the second air-fuel ratio flag F2 is set to “0” in step 1114, and on the other hand, V2>V
, □ (rich), the second air-fuel ratio flag F2 is set to "1" in step 1115. Next, step 111
In step 6, it is determined whether the second air-fuel ratio flag F2 has been inverted. As a result, if it is reversed, step 1117
Are the learning conditions satisfied? (Learning execution flag F, -
If the learning condition is satisfied, learning control is performed in step 1118. Note that the learning execution flag F and the learning step 1118 will be described later.

Steps 1119 to 1121 perform integral control. That is, it is determined whether the output V2 of the steering knob 11 (9) is lean or not. As a result, if it is lean (F2-"0"), step 112
0, the rich skip amount R5R is set to a relatively small value ΔR3
On the other hand, if it is rich (F2-“l”)
In step 1121, the rich skip amount R5R is set to the value ΔR.
Decrease by 3. Note that steps 1120 and 112
The integral amount ΔR3 at 1 may be different or may be variable. Step 1122 includes R
It performs guard processing of SR, for example, the minimum value M
I N = 2.5%, maximum value M A X = 7.
Guard at 5%. Note that the minimum value MIN is a value at a level that does not impair transient followability, and the maximum value MA
X is a level at which drivability does not deteriorate due to air-fuel ratio fluctuations.

In step 1124, the lean skip 1lR3L is
Calculate by R51110%-RSR. That is, RSR+RSL=10%.

In step 1125, the area n is set to 00 in preparation for the next execution.

After the RSR calculated as described above is stored in the RAM 105, this routine ends in step 1126.

In this way, according to the routine shown in FIG. 11A, when the operating region transitions from the Aa region to the B region, for example,
As shown in FIG. 4A, the update of the rich skip IR3R is stopped at the time T set in step 1108.

FIG. 11B is a modification of FIG. 11A, in which steps 1131 to 1133 are added to the routine of FIG. 11A. That is, in step 1131 after the area transition, the flag F is set (F="l"), and after a certain period of time T has passed (CN
'r=0), the process proceeds to step 1123 via steps 1132 and 1133, and as a result, the rich skip amount R3R of the learning value R3RG (n) after region transition is
The transition to is delayed by a certain period of time T. As a result, the 4th B
As shown in the figure, for example, when the operating region transitions from A to B, the rich skip amount R3R is held at the value immediately before the transition, and after a certain period of time T has passed, the learned value R3RGB of region B is skipped to rich lil RS R. Migrate.

Next, the learning execution flag FG and the learning control step 1117 in FIG. 11A will be explained.

FIG. 12 shows a routine for setting the learning execution flag FG, which is executed every predetermined period of time, for example, 512 ms or every predetermined crank angle, for example, 180°.

Steps 1201 to 1205 are step 11 in FIG.
02 to 1106 are the same, but only step 1202 is different. That is, step 1202
In this case, the cooling water temperature THW is within a predetermined range, for example, 70℃<TH
Determine whether W<90°C. That is, a stable cooling water temperature is determined.

The process proceeds to step 1206 only when all the conditions in steps 1201 to 1205 are satisfied.

In step 1206, it is determined whether the amount of change ΔQ of the intake air amount data Q per time or per crank angle is less than a certain value A. As a result, if ΔQ≧A, step 1206 is performed.
The counter CAQ is cleared in step 09, and when ΔQ<A, the counter CAQ is counted up in step 1207. In step 1208, only when CAQ>B (constant value), the learning execution flag F is cleared in step 1210. is set to "1", and in other cases, the learning execution flag FC, is set to O" at step 1211. Note that the counter C
Δ. is guarded at a certain maximum value. The routine then ends at step 1212.

In this way, under the conditions where the air-fuel ratio feedback control by the upstream 02 sensor 13 and the air-fuel ratio feedback control by the downstream Ot sensor 15 are performed, the conditions are limited by the cooling water 'tL T ■■W. , Furthermore, only when a stable state in which the intake air amount change ΔQ is smaller than the constant value A continues for a certain period of time, the learning execution flag Fc is set to "1".
As a result, learning control will be executed.

FIG. 13 is a detailed flowchart of the learning step 1118 of FIG. 11A. As described above, this routine is executed when the output (2) of the downstream side 02 sensor 15 is inverted and the learning condition is satisfied. In addition,
In this learning step, learning values are calculated for each region n and stored in the backup RAM 106 as shown in the table below.

In step 1301, the current rich skip amount R3R
The average value R3R of and the previous rich skip 1R5RO is calculated, that is, R-(R3R+R5RO) /2, and in step 1302, the learned value R5RG (n) of the rich skip amount of the current area n is averaged. The value becomes R3R. In other words, let. Then, in step 1303, the learning value R5R
G (n) is stored in the corresponding area of the bank amplifier RAM 106.

In step 1304, R5R is set to R5 in preparation for the next execution.
RO, and the routine ends at step 1305.

FIG. 14 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA.

In step 1401, the RAM 105 reads out the intake air amount data Q and the rotational speed data Ne to calculate the basic injection amount TAUP. For example, TAUP-α・Q/
Ne (α is a constant). At step 1402, the RAM
Read the cooling water temperature data THW from 105 and store it in ROM10.
The warm-up increase value FWL is calculated by interpolation using the one-dimensional map stored in step 4. As shown in the figure, this warm-up increase value FWL is set to decrease as the current cooling water temperature THW increases. In Ste Knob 1403, the final injection amount TAU is TAtl-TAUP-I'AP ・(FWL+β)
Calculate by +r. Note that β and γ are correction amounts determined by other operating state parameters, such as a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, battery voltage, etc. These are also correction amounts determined by the RAM 105. is stored in. Next, in step 1404, the injection 11 TAU is set in the down counter 108 and the flip-flop 1 is set.
Set 09 to start fuel injection. This routine then ends in step 1405. As mentioned above, when the time corresponding to the injection amount TAU elapses,
The flip-flop 109 is reset by the carrier signal of the down counter 108, and the fuel injection ends.

Note that each vehicle speed region does not need to be divided at equal intervals based on a constant value Δspo, and may be divided at irregular intervals.

In addition, regions are divided based on other parameters such as intake air amount, intake air pressure, throttle valve opening, rotational speed, intake air per revolution ff1 (Q/Ne), and the amount of reversal period of the output of the upstream Oz sensor. You can.

Fig. 15A shows a further modification of Fig. 11A;
2501 and 1502 are added. That is,
If it is within a certain time T after the region transition, in step 1502, the update amount ΔR3 of the rich skip amount R8R is set to the normal value Y.
After that, in step 1501, the update amount ΔR5 of the rich skip amount R3R is set to a value Y2 smaller than 1.
1 Y r .

In this manner, according to the routine of FIG. 15A, when the operating region transitions from, for example, region A to region B,
As shown in FIG. 5A, the update speed of the rich skip amount R8R becomes slow at the time T set in step 110B.

Figure 15B is a modification of Figure 11B, and Figure 15A is a modification of Figure 11B.
This is an example of a modification of the diagram, in which step 1 is added to the routine of Figure 11B.
501 and 1502 are added. That is, after the area transition, in step 1131, the flag F is changed to
"1"), and after a certain period of time T has passed (CNT=O), the process proceeds to step 1123 via steps 1132 and 1133, thereby controlling the learned value R5RG (
The transition to the rich skip amount R8R of n) is delayed by a certain period of time T. As a result, as shown in FIG. 5B, for example, when the operating region changes from A to B, the rich skip amount R8R changes from the value immediately before the transition to the normal rich skip amount R.
It is updated with a value Y2 smaller than the value Y+ of the update amount ΔR3 of 3R, and after - a certain period of time T has elapsed, the learning value RSRGB of the area B is transferred as a rich skip jlR3R.

FIG. 16 is also a modification example of FIG. 11A, and steps 1601, 1602, 1603 are added to the routine of FIG. 11A.
, 1604 are added. That is, after the region transition, in step 1601, the learned value R of the region n0 before the transition is
5RG(no) and the learning value R5RG(n
) is transferred as the rich skip amount R3R, and the flag F is set in step 1602.
l″), step 1 after a certain period of time T (CNT=O)
603° 1604 to proceed to step 1123, whereby the learned value RSRG(n) after region transition
The transition to the rich skip amount R3R is delayed by a certain period of time T. As a result, as shown in FIG. 6A (for example,
When the operating region transitions from A to B, the rich skip amount R3R is the intermediate value (R3RGA + RSRGB) /2
The learning value R3R of area B is maintained after a certain period of time T has elapsed.
Migrate GB as rich skip flR5R.

Note that the intermediate value (RSRG (n) + RSRG (
The control shown in FIG. 6B can also be easily performed by allowing (no) ) / 2 to act as a guard value for a certain period of time T.

FIG. 17 also shows a modification of FIG. 11A, with step 1
701 is added. That is, if the predetermined time T has elapsed after the region transition, rich skip IR3R is calculated in step 1701.

Details of step 1701 are shown in FIG. That is, in step 1801, the learned value R5 of the area n0 before the transition is
RG (no) is compared with the learning value R5RG (n) after the transition, and as a result, RSRG(n) <RSRG(n
o), the flow of steps 1802 to 1804 is executed, and if RSRG (n)≧R5RG(no), the flow of steps 1805 to 1807 is executed.

In step 1802, rich skip 11R5R is decreased by a constant value ΔD, and in steps 1803 and 1804
The rich skip amount R3R is guarded by the learned value RSRG (n) of the region n after the transition.

Similarly, in step 1805, the rich skip amount R3R
is increased by a constant value ΔD, and step 1806°180
In step 7, the rich skip amount R3R is guarded by the learned value R5RG(n) of the region n after the transition.

Then, in step 1808, the process returns to the routine shown in FIG.

In this way, according to the routines shown in FIGS. 17 and 18, when the operating region transitions from the A Rp region to the B region, for example, the rich skip amount R
3R gradually increases (or decreases) toward the learned value R3RGB of the region B after the transition at the time T set in step 1108.

In addition, in the routine of FIG. 17, rich skip 1iR
Although the gradual increase or decrease of 3H is limited to a certain time T, it can also be performed until the learned value n0 of the post-transition area n0 is reached.

Note that in a single Oz sensor system in which an 02 sensor is provided only downstream of the catalyst or in the catalyst to perform air-fuel ratio feedback control, the second air-fuel ratio feedback routine R5R, It is sufficient to calculate RSL as FAF.

Furthermore, the first air-fuel ratio feedback control is 4LIls
Also, the second air-fuel ratio feedback control is 512
The air-fuel ratio feedback control that is performed every 1 trs is mainly performed by the upstream Ot sensor, which has good responsiveness, and the downstream Ot sensor, which has poor responsiveness, controls air-fuel ratio feedback control. This is because control by the sensor is performed in a secondary manner.

In addition, other control constants in the air-fuel ratio feedback control by the upstream 02 sensor, such as delay time, integral constant, and comparison voltage of the upstream 02 sensor (see 2 Japanese Patent Laid-Open No. 55-3
The present invention can also be applied to a double 0□ sensor system that corrects the air-fuel ratio (No. 7562) etc. using the output of a downstream 0□ sensor, or a double 0□ sensor system that introduces a second air-fuel ratio correction coefficient.

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

Furthermore, in the above embodiment, the fuel injection amount is calculated according to the intake air amount and the engine rotation speed, but the fuel injection amount is calculated according to the intake air pressure and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by the amount of fuel injected, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) is used to control the air-fuel ratio by adjusting the intake air amount of the engine, and an electric bleed air control valve is used to adjust the amount of air bleed from the carburetor to control the main system passage and slow air. The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into system passages, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1401 is determined by the carburetor itself, that is, it is determined according to the intake pipe negative pressure depending on the intake air amount and the rotational speed of the engine, and in step 1403 The supplied air amount corresponding to the final fuel injection amount TAU is calculated.

Further, in the above-described embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, a lean mixture sensor, etc. may also be used.

Furthermore, although the embodiments described above are constructed using a microcomputer, that is, a digital circuit, they may also be constructed using an analog circuit.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to reduce the influence of the control before the transition of the driving range after the transition, and therefore, the stoichiometric air-fuel ratio can be quickly obtained. It is possible to prevent deterioration, deterioration of emissions, etc.

[Brief explanation of the drawing]

Figures 1A to 1D are overall block diagrams for explaining the present invention in detail. Figure 2 is a single 02 sensor system and a double 0□
An exhaust emission characteristic diagram explaining the sensor system, FIG. 3 is a timing diagram explaining the problem to be solved by the present invention, FIG. 4A, FIG. 4B, FIG. 5A, FIG. 5B, FIG. 6A,
6B and 7 are timing diagrams explaining the present invention in detail; FIG. 8 is an overall schematic diagram showing an embodiment of the air-fuel ratio side '4B device for an internal combustion engine according to the present invention; FIGS. Figure 11A, Figure 11B, Figure 12, Figure 13, Figure 14, Figure 15A, Figure 15B, Figure 16, Figure 1
7 and 18 are flowcharts for explaining the operation of the control circuit of FIG. 8, and FIG. 1O is a timing diagram for supplementary explanation of the flowchart of FIG. 9. 1... Engine body, 3... Air flow meter, 4... Distributor, 5.6... Crank angle sensor, IO... Control circuit, 12... Catalytic converter, 13... Upstream side 02 sensor, 15...downstream side 0. Sensor, 17... Idle switch.

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
an air-fuel ratio sensor (15) provided in the exhaust passage downstream of the three-way catalyst to detect the air-fuel ratio of the engine; and an air-fuel ratio sensor (15) to calculate an air-fuel ratio control amount according to the output of the air-fuel ratio sensor. a control amount calculating means; an operating region determining means for determining whether the operating region of the engine belongs to one of a plurality of regions divided into a plurality of regions; The center value of the fuel ratio control amount is calculated and the center value of the air-fuel ratio control amount is stored as a learned value for each region, and when the operating region transitions to a different region, the learned value of the operating region after the transition is a learning means for shifting the air-fuel ratio control amount; an air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine according to the air-fuel ratio control amount; and a region transition for detecting whether the operating region has transitioned to a different region. An air-fuel ratio control device for an internal combustion engine, comprising: a detection means; and a stop means for stopping calculation of an air-fuel ratio control amount according to the output of the air-fuel ratio sensor for a predetermined period when the operating region transitions to a different region. 2. An internal combustion engine according to claim 1, further comprising update speed reducing means for reducing the update speed of the air-fuel ratio control amount for a predetermined period when the operating region transitions to a different region, in place of the stopping means. Air-fuel ratio control device. 3. In claim 1, in place of the stopping means, when the operating region transitions to a different region, for a predetermined period, the air-fuel ratio control amount before the region transition and the learned value of the operating region after the region transition are used. An air-fuel ratio control device for an internal combustion engine, comprising an intermediate value transition means for shifting an intermediate level of the air-fuel ratio as the air-fuel ratio control amount. 4. In claim 1, in place of the stopping means, when the operating region changes to a different region, a difference between the air-fuel ratio control amount before the region transition and the learned value of the operating region after the region transition is determined. An air-fuel ratio control device for an internal combustion engine, comprising a gradual transition means for shifting the air-fuel ratio control amount to a gradually changed level.