JPH03229941A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve the convergence of a controlled air fuel ratio without lack of correction and minimize torque fluctuation by introducing a specific O2 storage term, and decreasing the integral O2 storage term stepwise in a theoretical air-fuel ratio region. CONSTITUTION:On the basis of the detection output of an air-fuel ratio sensor (b) disposed on the downstream side of a catalytic converter rhodium (a) in the exhaust passage of an internal combustion engine, a coarse control term changed gradually to the opposite side between the rich side and lean side of the detection output is computed by a means (c). A means (d) judges which region among a rich region, a theoretical air-fuel ratio region and a lean region the detection output is placed in. An O2 storage term reset being decreased stepwise from the time the detection output is shifted into the theoretical air-fuel ratio region is computed by a means (f). The air-fuel ratio of the internal combustion engine is then adjusted by a means (g) according to the coarse control term and O2 storage term.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides an air-fuel ratio sensor (in this specification, an oxygen concentration sensor (0□ sensor)) on the downstream side of a catalytic converter, and an O2 sensor downstream of the catalyst. The present invention relates to an air-fuel ratio control device for an internal combustion engine that performs air-fuel ratio feedback control.

(2) [Prior art] Air-fuel ratio feedback control using an 02 sensor includes a single 02 sensor system based on a single 02 sensor and a double 02 sensor system based on two O2 sensors installed upstream and downstream of the catalyst. There is a sensor system, and furthermore,
There are two types of single 02 sensor systems: one in which the 02 sensor is provided upstream of the catalyst, and the other in which the 02 sensor is provided downstream of the catalyst.

In a single 02 sensor system in which the 02 sensor is installed upstream of the catalyst, the 02 sensor is installed at a location in the exhaust system as close to the combustion chamber as possible, that is, at the collection point of the exhaust manifold upstream from the catalytic converter. Equilibrium level (unevenness) For example, the presence of 02 even though the air-fuel ratio is rich may cause the inversion timing of the O2 sensor to shift, and in a multi-cylinder engine, the air-fuel ratio is affected by variations in the air-fuel ratio between cylinders. Therefore, the 0□ sensor cannot detect the average air-fuel ratio, and as a result, there is a problem in that the control accuracy of the air-fuel ratio is low.

(3) On the other hand, in the case of a single 02 sensor system in which the 02 sensor is installed downstream of the catalyst, although the exhaust gas unbalance and non-detection of the average air-fuel ratio are resolved, the position of the 02 sensor is closer to the exhaust valve. 02 due to distance, catalyst capacity increase, and purification performance (size of 02 storage effect, etc.)
The responsiveness of the sensor is low, and therefore the responsiveness of the air-fuel ratio feedback control system is deteriorated, and as a result, the performance of the catalyst cannot be fully demonstrated, leading to a problem of deterioration of emissions.

In addition, double 02 sensors are installed upstream and downstream of the catalyst.
In the sensor system, in addition to air-fuel ratio feedback control by the upstream 02 sensor, air-fuel ratio feedback control is performed by the downstream 02 sensor. For example, the downstream side 02 sensor detects the average air-fuel ratio, and the result is reflected in the value of the skip control constant etc. of the air-fuel ratio feedback control by the upstream side 02 sensor to perform overall air-fuel ratio control.

Therefore, as long as the downstream 02 sensor maintains stable output characteristics, good exhaust emissions are guaranteed (4). However, in the double 02 sensor system, the cost is high because it requires two 02 sensors, and if the air-fuel ratio feedback control period by the upstream 02 sensor decreases due to changes over time, the catalyst performance cannot be fully demonstrated. There is a problem.

For this reason, the applicant has already developed a forced self-excitation control waveform (forced start waveform) with a predetermined amplitude and a predetermined frequency in a single 02 sensor system in which an 02 sensor is provided downstream of the catalyst.
has proposed a method in which the center value of is changed according to the output of the downstream 02 sensor (see Japanese Patent Laid-Open No. 1-66441). That is, as shown in Fig. 2, when the output VOX of the downstream 02 sensor changes, the center value (rough adjustment term) AFo of the forced self-excitation control waveform AFs is changed according to the output Voχ of the downstream 02 sensor. change. In this case, downstream 0
2 sensor output V. If X is lean, the coarse adjustment term A
Fc is gradually increased while the output V of the downstream 02 sensor. If X is rich, the coarse adjustment term A F c is gradually reduced. In other words, the coarse adjustment term (5) AF is integrally controlled. This is shown in Figure 3,
When the forced self-excitation control waveform swings near the stoichiometric air-fuel ratio (λ = 1) (AFC = APS), the catalyst can maximize its purification performance, but when the air-fuel ratio on the rich side (λ = 1) or Even if the forced self-excitation control waveform swings (AFs+, AFS2) at a lean air-fuel ratio (λ>1), the purification performance of the catalyst cannot be demonstrated. For this reason, the forced self-excitation control waveform AFs+ or AFS2 is changed to AFs so that the purification performance of the catalyst can be demonstrated.

A coarse adjustment term AFc (integral term) is introduced in order to approach the equation.

[Problems to be Solved by the Invention] However, the conventional device described above has a problem in that it is not possible to control the air-fuel ratio with high accuracy in vehicles where situations in which the 0□ storage effect cannot be achieved frequently occur.

For example, if the air-fuel ratio of the gas containing the catalyst deviates significantly from the stoichiometric air-fuel ratio, and this deviation continues for a long time, the three-way catalyst will reach zero.
If the amount of 02 storage fluctuates significantly compared to the amount of 02 storage in the normal state and the 02 storage effect cannot be achieved (6), the conventional device described above simply uses integral control to adjust the center value of the forced self-excitation control waveform. Since the control air-fuel ratio is controlled, the convergence of the controlled air-fuel ratio to the stoichiometric air-fuel ratio is poor, and as a result, there is a problem that the purification performance of the catalyst cannot be exhibited, leading to deterioration of emissions.

For this reason, the applicant proposed that when the output of the downstream 02 sensor deviates significantly from the stoichiometric air-fuel ratio equivalent value to the rich side or lean side by a predetermined value or more, the 02 storage term AFCCR
It has already been proposed to shift (skip) the value of the coarse adjustment term AF, which is the control center value, by introducing O (skip term).
85), this 02 storage term AFCCR8 is reset immediately when the output of the downstream 02 sensor changes from the rich region to the stoichiometric air-fuel ratio region or from the lean region to the stoichiometric air-fuel ratio region. result,
Torque fluctuation becomes large and drivability deteriorates.

In particular, when the fluctuation range of the air-fuel ratio upstream of the catalyst increases due to deposits, errors in the fuel injection valve, air flow meter, etc., the fluctuation range of the 02 storage amount increases by (7). As described above, when the range of variation in the 02 storage amount increases, the torque variation further increases, and drivability deteriorates.

However, in the stoichiometric air-fuel ratio region, if the 02 storage term is kept as is, the variation in the 02 storage amount and the
As a result, deviation of the control air-fuel ratio from the stoichiometric air-fuel ratio cannot be prevented, which also leads to deterioration of emissions.

Therefore, an object of the present invention is to take the above-mentioned prior application one step further and improve drivability by reducing torque fluctuations due to fluctuations in the 02 storage term, as well as reduce air-fuel ratio control accuracy due to fluctuations in the 02 storage amount. An object of the present invention is to provide an air-fuel ratio feedback control system that prevents deterioration of emissions.

[Means to solve the problem]

A means for solving the above problem is shown in FIG.

That is, a catalyst downstream air-fuel ratio sensor that detects the air-fuel ratio of the engine is provided in the exhaust passage downstream of a three-way catalyst provided in the exhaust passage of the internal combustion engine. The coarse adjustment term calculation means is the output V of the air-fuel ratio sensor. A rough adjustment term A F c is calculated that gradually changes to the lean side when X is rich, and gradually changes to the rich side when the output of the air-fuel ratio sensor is lean. The region determining means determines whether the output VOX of the air-fuel ratio sensor is in a predetermined rich region R1, stoichiometric air-fuel ratio region S1, or lean region, and the region transition determining means determines whether the output VOX of the air-fuel ratio sensor is in a predetermined rich region R1, stoichiometric air-fuel ratio region S1, or lean region. It is determined whether or not X has transitioned to the stoichiometric air-fuel ratio region. As a result, the 02 storage term calculation means calculates the output V of the air-fuel ratio sensor.
. When X is in the rich region, the value on the lean side (-AFC
CROP ) is set, and the output V of the air-fuel ratio sensor. X
is in the lean region, the rich side value (APCCRO
P) is set, and when the output VOX of the air-fuel ratio sensor is in the stoichiometric air-fuel ratio region, the above set value (±AFC
The absolute value of CROP) is the output V of the air-fuel ratio sensor. The 02 storage term AFCCRO, which is gradually decreased and reset from the time when X transitions to the stoichiometric air-fuel ratio region, is calculated.

The air-fuel ratio adjustment means adjusts the air-fuel ratio of the engine in accordance with the coarse (9)□C adjustment term AFc and the 0□ storage term AFCCRO.

[For production]

According to the above-mentioned means, as shown in FIG. 4, the air-fuel ratio of the internal combustion engine is adjusted by the air-fuel ratio adjusting means according to the coarse adjustment term AFc and the 02 storage term AFCCR8. Here, the coarse adjustment term is the output V of the air-fuel ratio sensor provided in the exhaust passage downstream of the three-way catalyst by the coarse adjustment term calculation means. According to X, when the output of the air-fuel ratio sensor is rich (VOX<
VR) Gradually changes to the lean side, and when the air-fuel ratio sensor output is lean (VOX < VR)! Gradually changes to J Petucci. As a result, the engine air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio. On the other hand, the 0□ storage term is the output V of the air-fuel ratio sensor provided in the exhaust passage downstream of the three-way catalyst by the storage term calculating means of the area discriminating means 02. When it is determined that X is in the rich region (R region), that is, 02 storage amount is insufficient, it is set to a value on the lean side as shown by arrow x1, and the air-fuel ratio (10) sensor output V. When X is in the lean region (L region), that is, when it is determined that the 02 storage amount is excessive, it is set to a value on the rich side as shown by arrow X2, and as a result, even when the 02 storage amount fluctuates. too,
The air-fuel ratio is corrected by the 02 storage term, increasing the convergence of the air-fuel ratio to the stoichiometric air-fuel ratio. In addition, arrow XI,
Although the shaded area indicated by X2 changes gradually, it may be constant. Further, the 02 storage term APCCRO is indicated by arrow Y when it is determined by the area determining means, the area transition determining means, and the 02 storage term calculating means that the output level of the air-fuel ratio sensor has shifted to the stoichiometric air-fuel ratio area (S area).

As shown in Zr, Y2, and Z2, the set values X+ and X2 are gradually decreased and reset from the time of transition to the S region. As a result, the 02 storage term changes as the 02 storage amount changes, and since the change is gradual, the torque fluctuation becomes smaller, and the convergence of the air-fuel ratio to the stoichiometric air-fuel ratio can be improved.

(11) [Embodiment] FIG. 5 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. 5, 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 an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 includes a crank angle sensor 5 that generates a pulse signal for detecting a reference position every 720 degrees in terms of crank angle, and a pulse signal for detecting a reference position every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided which generates a signal. The pulse signals of these crank angle sensors 5.6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is CP[11
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 (12) to the intake port 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 1. 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.

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 toxic components 11C, Co, and NOX in the exhaust gas.

An 02 sensor 14 is provided in the exhaust pipe 13 downstream of the catalytic converter 12. The 02 sensor 14 generates an electrical signal according to the concentration of oxygen components in the exhaust gas. That is, the 02 sensor 14 outputs different output voltages to the control circuit 1 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio.
0 is generated in the A/D converter 101.

The control circuit 10 includes, for example, a microcomputer (13
), and in addition to the A/D converter 101, input/output interface 102, and CPU 103, there is a ROM1RO
M104RA, backup RAM 106, clock generation circuit 107, etc. are provided.

The throttle valve 15 of the intake passage 2 also has an idle switch 1 for detecting whether the throttle valve 15 is fully closed.
6 is provided, and this output signal is supplied to the input/output interface 102 of the control circuit 10.

Reference numeral 17 denotes a secondary air intake valve, which supplies secondary air to the exhaust pipe 11 during predetermined deceleration or idling.
This is to reduce C, Co emissions.

Further, in the control circuit 10, a down counter ICl3
, flip-flop 109, and drive circuit 110 are for controlling the fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, the fuel injection amount TAU is counted down by the down counter 1.
08 and flip-flop 109
is also set. As a result, the drive (14) circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts the clock signal (not shown) and finally its borrow-out terminal reaches the "1" level, the flip-flop 109 is set and the drive circuit 110 controls the fuel injection valve 7. Stop biasing. That is, the fuel injection valve 7 is energized by the above-mentioned fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU 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. In addition, the rotational speed data Ne is calculated by the crank angle (15) sensor 6's interrupt every 30° CA.
It is stored in a predetermined area of AM105.

FIG. 6 shows a routine for calculating the fine adjustment term AF, which is executed every predetermined period of time, for example, every 4 ms. In step 801, it is determined whether the air-fuel ratio feedback condition is satisfied. For example, when the cooling water temperature is below a predetermined value, e.g. 70°C, while the engine is starting, during engine startup, during warm-up, during power increase, during fuel cut, when the rotational speed Ne
, vehicle speed, idle switch 16 signal LL, cooling water temperature T
When secondary air is introduced based on HW etc., 0
When the two sensors 14 are not activated, the air-fuel ratio feedback condition is not satisfied, and in other cases, the air-fuel ratio feedback condition is satisfied. If the air-fuel ratio feedback condition is not satisfied, the process directly proceeds to step 613. If the air-fuel ratio feedback condition is satisfied, the process proceeds to step 602. In step 602, the 02 sensor 14
output V. , is A/D converted and imported, step 603
The voltage is compared with a reference voltage VR, for example, 0.45 V. As a result, if VOX≦VR (lean), the air-fuel ratio flag XOX is set to "o"<lean at step 604, and the previous air-fuel ratio flag XOXO is set to "1" (!) at step 605. It is determined whether or not it is J Petit. As a result, the flag XOX is set to
As shown in FIG. 7, the fine adjustment term AF is set in step 607 only when the value is reversed from "o" (rich) to "o"< v-n).

Let be ΔAFf (constant value). and step 612
Proceed to. On the other hand, in step 603, V. If X>VR (J-ch), the air-fuel ratio flag XOx is set to 'i'< rich in step 608, and in step 609 it is determined whether the previous air-fuel ratio flag X0XO is "O" (!J-n). As a result, the flag XOX becomes “0” (!7-
7th only if it is reversed from “1” (!
As shown in the figure, in step 611, the fine adjustment term AF is set to -ΔAFf (a constant value). And step 6
Proceed to step 13.

In step 612, the output V of the 02 sensor 14 is determined in the routine shown in FIG. 8, which will be described later. A counter CNT for calculating the inversion period of X is cleared.

Then, this routine ends in step 613 (17
) do.

As described above, according to the routine shown in FIG. 6, the fine adjustment term AF of the skipped waveform is calculated every time the output of the 02 sensor 14 is inverted, as shown in FIG.

In other words, a self-excitation control waveform can be obtained from the output of the 02 sensor 14 itself. In other words, the control of the fine adjustment term A F r corresponds to skip control.

FIG. 8 shows a routine for calculating the coarse adjustment term A F t, which is executed every predetermined period of time, for example, every 64 m5.

In step 801, similarly to step 601 in FIG. 6, it is determined whether the air-fuel ratio feedback condition is satisfied. As a result, the flow of steps 802 to 807 is executed only when the air-fuel ratio feedback condition is satisfied. That is, in step 802, the counter CNT is set to a constant value KC.
Determine whether NT has been reached. In addition, counter CN
T is the output V of the 02 sensor 14 as described above. It is cleared every time X is reversed. Therefore, initially, the process proceeds from step 802 to step 803, where the counter CNT is incremented by +1, and the process proceeds to step 808. Counter CN (18) When T reaches KCNT, i.e. time KCNT
After 64 m5 has elapsed, the flow in step 802 proceeds to steps 804-807.

In step 804, the counter CNT is cleared, and in step 805, the air-fuel ratio flag xOx determines whether the current downstream air-fuel ratio of the catalyst is lean ("O") or rich ("1").
). As a result, if the result is lean, the coarse adjustment term A F c is increased by ΔAF, (a constant value) in step 806, and on the other hand, if it is rich, step 807
is decreased by ΔAFc. And step 808
Proceed to.

Note that the value ΔAF is smaller than the skip amount ΔAF used in steps 607 and 611 in FIG.

That is, ΔAFc<ΔAFf. Therefore, as shown in FIG. 9, if the air-fuel ratio is lean (XOX="0"), the coarse adjustment term AF.

is gradually increased by △AFo, and if the air-fuel ratio is rich (XOX-"1"), the rough adjustment term A F c becomes Δ
It is gradually reduced by AFo. In other words, the control of the coarse adjustment (19) integral term AFo corresponds to integral control. Furthermore, the convergence of the air-fuel ratio can be improved by introducing skip control for each reversal of the air-fuel ratio into the rough adjustment term AF.

Substantial execution or non-execution of the coarse adjustment term calculation routine in FIG. 8 means substantial non-execution of the fine adjustment term calculation routine in FIG.
Each depends on the execution. That is, when the air-fuel ratio downstream of the catalyst deviates from the stoichiometric air-fuel ratio, it is maintained at either VOX≦VR (lean) or vox > VR (rich), and therefore, the fine adjustment item by the routine in FIG. AF r is held at either ΔAF or -ΔAF, and as a result, the counter CNT is not cleared in step 612. On the other hand, in this case, the coarse adjustment term A F c according to the routine of FIG.
TX is gradually increased or decreased every 64ms. In other words, rather than controlling the fine adjustment term AF, the coarse adjustment term AFc
control is performed.

Conversely, when the catalyst downstream air-fuel ratio converges to the stoichiometric air-fuel ratio, the output V of the 02 sensor 14. The inversion of The inversion period of X becomes shorter, and the fine adjustment term AFf frequently becomes △AFr,
-△AF, repeat. In this case, the counter CNT is K
It is cleared by step 612 in FIG. 6 before reaching the CNT, so that the flow in step 802 in FIG. 8 always proceeds to step 803. In other words,
There is no increase or decrease in the coarse adjustment term AFc, hence the coarse adjustment term AF.

control is prohibited and its value is held, and the fine adjustment term A
Only F' is controlled.

FIG. 10 shows a routine for calculating the 02 storage term AFCCR8, which is executed at predetermined intervals, for example, every 16 m5. In step 1001, similarly to step 601 in FIG. 6, it is determined whether the air-fuel ratio feedback condition is satisfied. As a result, if the air-fuel ratio feedback condition is not satisfied, the process directly proceeds to step 1011, and only if the air-fuel ratio feedback condition is satisfied, the process proceeds to step 1002.

In step 1002, the output V of the O2 sensor 14 is determined. A/D convert and import X, steps 1003 and 1004
to determine VOX. That is, as shown in FIG. 12 (21), 0 to 1. Divide the OV space into 3 parts,
In other words, 0~Vl (lean (L) region) ■1~V2
(Stoichiometric air-fuel ratio (S) region) ■2-1. OV (Rich (
(R) area) and determine in which of these areas the VOX is located. That is, if 0≦Vox<V+(L area), in step 1005, the integral 02 storage amount AFcci is determined. 1 is gradually increased as AFCCROI ←AFCCROI + ΔAFCCRO (constant value), and in step 1006, 02 storage term AFC
CR8 is defined as FCCRO = AFcciop + AFCCROI, where AFCCROP is a skipped 02 storage term (constant value), and AFCCROP > △AFCCRO. In other words, in the L area, arrow xI in FIG.
As shown in the shaded area, the air-fuel ratio correction coefficient FA (22) F (as described below, depends on AFf + total. +AFCCR8) is shifted by the value AFCCROP, and then ΔAF
Gradually increases at the update rate of CCRO.

If V1≦VOX≦V2 (S region), in step 1007, the integral 02 storage amount AFCCROI is calculated by the routine shown in FIG. 11, which will be described later, and in step 1008, the 0° storage term AFCCRO is F.C.
CRO ←APCCRI.

Furthermore, if VOX≧V2 (R region), step 1
At step 009, the integral 02 storage amount AFCCROI is gradually increased to AFcciot'-AFCCORI-ΔAFCCR8, and at step 1010, the 02 storage term AFCCRO is calculated as follows: FCCRO = A F c CR (l P + A F c C
Set as RO+. In other words, in the R region, the air-fuel ratio correction coefficient (23
) FAF is shifted by the value −AFCCR6, and then Δ
It gradually decreases at the update rate of AFCCRO.

The routine of FIG. 10 then ends at step 1011.

Figure 11A shows the stoichiometric air-fuel ratio region processing step 1 in Figure 10.
This is a detailed routine of 007. That is, step 1
101 is the output V of the 02 sensor 14; It is determined whether the air-fuel ratio downstream of the catalyst is lean or rich depending on whether X is less than or equal to VR, and as a result, an air-fuel ratio flag xOx is set in steps 1102 and 1103. In step 1104, the previous air-fuel ratio flag value X0XO and the current air-fuel ratio flag value
By comparing with x, it is determined whether the air-fuel ratio has been reversed. As a result, only when the air-fuel ratio is reversed, the integral 02 storage term AFcciot is calculated in step 1105.
Clear. Then, in step 1106, xOx is set to X0XO in preparation for the next execution, and in step 1107, this routine ends.

In other words, according to the routine shown in FIG. 11A, as shown in FIG. 11B, the 0□ storage term AFCCRO becomes (2
4) First, the output V of the air-fuel ratio sensor 14 decreases to the integral 02 storage term ±AFCCR8l shown in the shaded area of arrows Yl and Y2. It is only reset when X is reversed.

Therefore, the output V of the 02 sensor 14. Even if X moves from the L region (or R region) to the S region, the control air-fuel ratio will not reach the stoichiometric air-fuel ratio due to the contribution of the 02 storage term AFCCR8 (strictly speaking, the integral 02 storage term...■) In this case, the output V of the 0□ sensor 14. Air-fuel ratio correction coefficient FAF based on
changes in stages, so deterioration of drivability can be prevented.

Note that in FIGS. 11A and 11B, AFCCROI is held until the air-fuel ratio is reversed, but the absolute value of the integral 02 storage term AFcciot may be gradually decreased. That is, as shown in the routine of FIG. 12A, steps 1201 to 1205 are added to the routine of FIG. 11A.
is added, and if the air-fuel ratio is lean (XOX="0"), the integral 02 storage term AP is determined by steps 1201 and 1202. Rot is gradually decreased and this is performed in step 102.
3. Guard at 0 at 1105, and on the other hand, the air-fuel ratio is set (2
5) If it is (XOX="1"), step 1201.1
204, the integral o2 storage term AFCCR81 is gradually increased, and it is guarded with 0 in steps 1205 and 1105. In this way, as shown in FIG. 12B, when transitioning to the S area, first the 02 storage term AF
The absolute value of CCRO is the integral 02 storage term AFCCR
It becomes OI, but then gradually decreases to 0. As a result, the output V of the 02 sensor 14. By inverting X, the air-fuel ratio correction coefficient FAF becomes gentler, and further deterioration of drivability can be prevented.

FIG. 13 is a modification of FIG. 11A. In FIG. 13, the following flags and counters are introduced.

X5 (="1"): Output V of the 02 sensor 14. A flag indicating that X is in the S area, Flag XDLY: Integral 02 storage term AFccu
Flag for delaying the start of ot update, CNTD
: Counter for measuring delay time.

In step 1301, the output V of the 02 sensor 14 is determined by determining whether the flag XS is "0" (outside the S region).
. It is determined whether or not X enters the S area for the first time (26). As a result, the output V of the 02 sensor 14. If X enters the S area after starting from the L area or the R area, the flag XS should be set in step 1302.
, steps 1303 and 13041m are delayed. That is, in step 1303, the delay processing flag X
In step 1304, the delay time CNTDO is set in the counter CNTD, thereby starting the delay process.

Also, the output V of the 02 sensor 14. When X is inverted, that is, the output V of the 02 sensor 14. Delay processing is also performed in steps 1305 to 131 when X crosses reference voltage VR.
Start with 0. That is, in step 1305, 0
□Output V of sensor 14. X is lean (V o x≦VR
) or rich, and as a result, step 13061
At step 307, the air-fuel ratio flag xOx is set and reset. In step 1308, the previous value X0XO and the current value x
By comparing with Ox, the output V of the air-fuel ratio sensor 14
. Determine whether or not X has been reversed. Only when reversed,
In step 1308, the previous value xoxo is replaced with the current value xOx, in step 1309, the integral ○2 (27) storage term AFCCROI is reset, and in steps 1303 and 1304, delay processing is started.

Note that in step 1310, the integral 02 storage term A
Resetting the FCCROI is the same as in the routine of FIG. 11A.

02 sensor 14 output V. Step 1, except when X enters the S region for the first time and crosses the reference voltage VR.
Flows 311 to 1316 are executed.

In steps 1311 and 1312, the counter CNTD
The delay time CTDD is measured, and the process proceeds to steps 1313 and 1315 only when the delay time has elapsed. Note that if the output VOX of the 02 sensor 14 is reversed before the measurement is completed, the delay time CNTD is set again, so the delay time is extended.

After the delay time has elapsed, the arrow Z I + Z in FIG. 14A
At the time indicated by 2+Z3, the counter CNTD is cleared in step 1313, and the delay processing flag XDLY is reset in step 1314 (XDLY "0").
, in step 1315 the integral 02 storage term AFC
Integration processing of CR81, that is, in this case, the absolute value of AFCCROI is gradually increased.

(28) On the other hand, if the delay time has not yet elapsed (CNTD≧0), the process proceeds to steps 1316 to 1318, and the integration process of the integral 02 storage term AFCeROI, that is, in this case, A
The absolute value of FCCROl is gradually decreased.

This routine then ends in step 1319.

Note that the flag xS indicates that the output of the 02 sensor 14 is outside the S area,
That is, it is reset when entering the L area and the R area.

According to the routine of FIG. 13, the output V of the 02 sensor 14 is as shown in FIG. 14A. X is the lean side of the S region (V
+~VR) or the rich side (VR-V2) for a long time, the o2 storage term AF
By introducing CCRO (=AFcciot), the controlled air-fuel ratio is directed toward the stoichiometric air-fuel ratio.

Note that the output V of the 02 sensor 14 after entering the S area from the L area (or R area). Until the inversion of X, the absolute value of the 02 storage term AFCCR8 becomes the integral 02 storage term AFCCROI as in FIG. 11B.

(29) Also in Figures 13 and 14A, AFCCR81 is held until the air-fuel ratio is reversed during the delay process, but as shown in Figure 14B, the integral 02 storage term AFCCR81 is gradually decreased. You may let them. In other words, the first
Similar to FIG. 2B, steps 1201-12 of FIG. 12A
The flow consisting of the steps of clearing 05 and AFCCR8i is shown in step 1312 and step 13 in FIG.
08. As a result, as shown in FIG. 14B, when transitioning to the S region, first, the absolute value of the 02 storage term AFCCR0 becomes the integral 02 storage term A
Fccio+, but then gradually decreases to 0. As a result, the output V of the 02 sensor 14. By inverting X, the air-fuel ratio correction coefficient FAF becomes gentler, and further deterioration of drivability can be prevented.

FIG. 15 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360° CA. Step 1
At step 501, the intake air amount data Q and the rotational speed data Ne are read out from the RAM 105 to calculate the basic injection amount TAUP. For example, TAUP←α・Q/Ne (α is a constant)
shall be. In step 1502, the final injection amount (30) TAU is calculated as TA[I -TA[IP ・(AFf18F
+AFCCRO+β)+γ. In addition, β
, T are correction amounts determined by other operating state parameters. Next, in step 1503, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. The routine then ends in step 1504. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the borrow-out signal of the down counter 108, and the fuel injection ends.

FIG. 16 shows a routine for generating a self-oscillation term (forced oscillation term>AFs), which is executed every predetermined time period, for example, every 4 ms. In step 1601, similar to step 601 in FIG. It is determined whether or not the condition is satisfied.As a result, if the air-fuel ratio feedback condition is not satisfied, the process directly proceeds to step 1610, and only when the air-fuel ratio feedback condition is satisfied, the process proceeds to step 1602.

In step 1602, it is determined whether the counter CNTS has reached T/2 of the period T (31). That is, the counter CNTS is set at step 16.
+1 count was added in 09, and CNTST/
The process proceeds to steps 1603 to 1608 every 2 steps.

That is, in step 1603, the counter CNTS is cleared, and in step 1604, the self-oscillation flag
It is determined whether or not IC is 0", and if X5IC is "0", the self-sustained oscillation term AFS is set to ΔAFs (constant value) in step 1605, and the flag X5IC is set to " in step 1606.
As a result, when the counter CNTS reaches T/2 again, the flow of step 1604 proceeds to steps 1607 and 1608.

In step 1607, the self-oscillation term AFs is set to ΔAFS, and in step 1608, the flag xsrc is inverted to "0".

The routine then ends at step 1610.

In this way, according to the routine of FIG.
A self-oscillating waveform with a constant amplitude (ΔAFS) and period T as shown in the figure can be generated.

Figure 18 shows the injection quantity calculation (32
) This is a calculation routine in which step 1801 is provided in place of step 1702 in FIG. That is, the final injection amount TAU is TAU ←TA[IP ・(AFr+AFs+AFc+AFcc
++o+β) 10r.

That is, the self-oscillation term A F s is also the fine adjustment term A
It takes the place of F. In this case, the amplitude and frequency of the self-oscillation waveform are set so that the purification performance of the three-way catalyst can be fully demonstrated, and disturbances in the air-fuel ratio due to the introduction of the self-oscillation AFS are minimized.

In addition, in the above-mentioned embodiment, in the R region or the L region,
Introducing a skipping 0□ storage term AFCCROP and an increasing integral o2 storage term AFCCROI, S
In the region, 02 storage term AF0°, which gradually decreases. i is introduced, but in the R area or the L area, only the skip-like 02 storage term AFccaop term AFCCR8, is introduced, and in the S area, the initial value is set as the skip-like 02 storage term AFCCROP, and the value is gradually decreased from the 02
A storage term AFCCR81 may also be introduced (33).

In the above embodiment, the fine adjustment term AF and the forced self-excitation term AFs are introduced, but the coarse adjustment term AFc.

Air-fuel ratio control is possible even by introducing only the 0□ storage term AFCCRO.

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 a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) adjusts the intake air amount of the engine to control the air-fuel ratio, and an electric bleed air control valve adjusts the air bleed amount of the engine. The present invention can be applied to things such as those that control the air-fuel ratio by introducing atmospheric air into the main system passage and the slow system passage, and those that adjust the amount of air sent to the exhaust system of an engine. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1501 is determined by the carburetor itself, that is,
It is determined according to the intake pipe negative pressure corresponding to the intake air amount and the rotational speed of the engine, and the supplied air amount corresponding to the final fuel injection amount TAU is calculated in steps 1502 and 1801.

Further, in the above-described embodiment, the 02 sensor was used as the air-fuel ratio sensor, but a CO sensor, lean mix sensor, etc. may also be used. In particular, T as an air-fuel ratio sensor
Using a 10□ sensor improves control responsiveness and prevents overcorrection due to the output of the downstream air-fuel ratio sensor.

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.

(35) [Effects of the Invention] As explained above, according to the present invention, the 02 storage term is introduced, and moreover, in the stoichiometric air-fuel ratio region, the integral 02 storage term is reduced in stages and then reset. As a result, the 02 storage term can respond to fluctuations in the 02 storage amount of the three-way catalyst, and the range of fluctuation of the 02 storage term in the stoichiometric air-fuel ratio region can be reduced, thus improving the convergence of the control air-fuel ratio without undercorrecting. In addition, torque fluctuations can be reduced, and as a result, deterioration of emissions can be prevented.Moreover, the control frequency is maintained high in the stoichiometric air-fuel ratio region, so the purification performance of the catalyst can be maximized, and the driver This can prevent deterioration of performance.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing the basic configuration of the present invention, FIG. 2 is a timing diagram explaining the conventional technology, and FIG. 3 is a graph showing the relationship between forced self-excitation control waveform and catalyst purification performance. ) FIG. 4 is a timing diagram explaining the present invention in detail, FIG. 5 is an overall schematic diagram showing one embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention, FIGS. 6, 8, and 10. Figures, Figure 11A, Figure 12A,
13, 15, 16, and 18 are flowcharts for explaining the operation of the control circuit in FIG. 5; FIG. 7 is a timing diagram supplementary to the flowchart in FIG. 6; Figure 11B is a timing diagram that supplements the flowcharts in Figures 10 and 11A. Figure 12B is a timing diagram that supplements the flowcharts in Figures 10 and 12A. Figure 14A is a timing diagram that supplements the flowchart in Figures 1.3, Figure 14B is a flowchart that shows a modification example of Figure 14A, Figure 17 is a timing diagram that supplements the flowchart in Figure 16. It is a diagram. (37) Figure 15

Claims (1)

[Claims] 1. Three-way catalyst (12) provided in the exhaust passage of an internal combustion engine
and a catalyst downstream air-fuel ratio sensor (14) that is provided in the exhaust passage downstream of the three-way catalyst and detects the air-fuel ratio of the engine; and when the output of the air-fuel ratio sensor is rich, it gradually changes to the lean side. coarse adjustment term calculation means for calculating a coarse adjustment term (AF_C) that gradually changes to the rich side when the output of the air-fuel ratio sensor is lean;
_X) is in a predetermined rich region (R), stoichiometric air-fuel ratio region (S), or lean region (L); region transition determination means for determining whether or not the air-fuel ratio sensor has transitioned to the rich region;
_C_C_R_O_P) is set, and when the output of the air-fuel ratio sensor is in the lean region, the rich side value (AF
_C_C_R_O_P) is set, and when the output of the air-fuel ratio sensor is in the stoichiometric air-fuel ratio region, the absolute value of the set value (±AF_C_C_R_O_P) is set from when the output of the air-fuel ratio sensor transitions to the stoichiometric air-fuel ratio region. O_2 storage term (
AF_C_C_R_O); and an air-fuel ratio adjustment device that adjusts the air-fuel ratio of the engine according to the rough adjustment term and the O_2 storage term.