JPH0533705A - Control apparatus for internal combustion engine - Google Patents

Abstract

PURPOSE:To provide a control apparatus for internal combustion engine, of which the air-fuel ratio can be quickly made a theoretical air-fuel ratio upon commencement and completion of the injection dither. CONSTITUTION:ECU2, during the time period in which the warming-up of a catalyst 19 is not completed, performs its catalyst warming-up operation through adjustment of the fuel injection quantity so that the air-fuel ratio may be compulsively inclined toward the rich and lean side, alternately, from the theoretical air-fuel ratio for each specified time period. Further, when starting the catalyst warming-up operation, the ECU2 sets a first air-fuel ratio feedback control constant (initial value of the skip quantity) for making the central air-fuel ratio the theoretical air-fuel ratio. When completing the catalyst warming-up operation, the ECU2 sets a second air-fuel feedback control constant (initial value of the skip quantity) for making the central air-fuel ratio the theoretical air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine, and more particularly to an engine control device for early warming up a catalyst for purifying exhaust gas.

[0002]

2. Description of the Related Art Conventionally, oxygen concentration detectors are installed upstream and downstream of a three-way catalyst, and depending on the output signal of the upstream oxygen concentration detector, the delay time for rich / lean determination by the upstream oxygen concentration detector. Has been proposed or a constant of air-fuel ratio feedback has been changed to control the center air-fuel ratio to the theoretical air-fuel ratio (λ = 1).
234241).

On the other hand, the applicant of the present invention previously filed Japanese Patent Application No. 3-18.
In No. 695, by forcibly increasing / decreasing the supply amount and making the final injection, the exothermic reaction is forcibly performed and the catalyst is warmed up early. This is defined as jet dither.

By combining these two techniques, it is conceivable to construct a system that enables early warm-up of the catalyst and controls the center air-fuel ratio to the stoichiometric air-fuel ratio (λ = 1). That is, as shown in FIG. 14, when feedback control is performed using the oxygen concentration detector on the upstream side of the three-way catalyst, the air-fuel ratio fluctuates due to the injection dither, and only the increase / decrease of the fuel is fed back by the air-fuel ratio feedback. There is a delay in rich / lean determination, and the feedback cycle becomes long (T1 <T2 in FIG. 14).
The central air-fuel ratio deviates as this cycle becomes longer. However, the central air-fuel ratio can be converged to the stoichiometric air-fuel ratio by gradually correcting the rich skip amount RSR and the lean skip amount RSL by the oxygen concentration detector on the downstream side of the three-way catalyst.

[0005]

However, in this system, although the correction is made by using the output of the oxygen concentration detector on the downstream side, as shown in FIG. It is not possible to quickly respond to sudden changes in the air-fuel ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for an internal combustion engine which can quickly bring the stoichiometric air-fuel ratio to the start / end of injection dither.

[0007]

A first aspect of the present invention, as shown in FIG. 15, is a fuel injection valve M1 for injecting fuel into an internal combustion engine.
A catalyst M2 arranged in an exhaust pipe of the internal combustion engine for purifying exhaust gas; a warm-up state detecting means M3 for detecting a warm-up state of the catalyst M2; and an operation for detecting an operating state of the internal combustion engine. A state detection means M4, a first air-fuel ratio sensor M5 provided on the upstream side of the catalyst M2 for detecting the concentration of a specific component in the exhaust gas, and a downstream side of the catalyst M2,
A second air-fuel ratio sensor M6 that detects the concentration of a specific component in the exhaust gas, and the fuel injection valve M1 that controls the operation state detection means M4 to inject a quantity of fuel according to the operation state of the internal combustion engine. According to the outputs of the fuel injection control means M7 and the first air-fuel ratio sensor M5, the fuel injection amount by the fuel injection control means M7 is adjusted so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio. Air-fuel ratio feedback means M8 for feedback-correcting the air-fuel ratio, and air-fuel ratio feedback so that the central air-fuel ratio by the air-fuel ratio feedback means M8 approaches the stoichiometric air-fuel ratio according to the outputs of the second air-fuel ratio sensor M6. Control constant changing means M9 for changing the control constant and the warm-up state detecting means M3
Thus, in a state where the catalyst M2 has not been warmed up, the fuel injection amount by the fuel injection control means M7 is forcibly set so that the air-fuel ratio becomes the rich side and the lean side with respect to the stoichiometric air-fuel ratio every predetermined period. To warm the catalyst to warm up the catalyst, and to start the catalyst warm-up processing by the catalyst warm-up means M10, the center air-fuel ratio by the air-fuel ratio feedback means M8 is set to the stoichiometric air-fuel ratio. A second air-fuel ratio feedback control constant is set, and a second air-fuel ratio is set to the theoretical air-fuel ratio by the air-fuel ratio feedback means M8 when ending the catalyst warm-up process.
The gist of the control device for an internal combustion engine is provided with a control constant setting means M11 for setting the air-fuel ratio feedback control constant.

As shown in FIG. 16, a second aspect of the present invention is a fuel injection valve 21 for injecting fuel into an internal combustion engine, and a catalyst 22 disposed in an exhaust pipe of the internal combustion engine for purifying exhaust gas.
A warming-up state detecting means M23 for detecting a warming-up state of the catalyst 22, an operating state detecting means M24 for detecting an operating state of the internal combustion engine, and an upstream side of the catalyst M22,
A first air-fuel ratio sensor M25 for detecting a specific component concentration in the exhaust gas, and a second air-fuel ratio sensor M provided downstream of the catalyst M22 for detecting a specific component concentration in the exhaust gas.
26, a fuel injection control means M27 for controlling the fuel injection valve M21 to inject an amount of fuel according to the operating state of the internal combustion engine by the operating state detecting means M24, M27, and the first air-fuel ratio sensor M25. Air-fuel ratio feedback means M2 that adjusts the fuel injection amount by the fuel injection control means M27 and feedback-corrects the air-fuel ratio so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio according to the output.
8 and the output of the second air-fuel ratio sensor M26,
Delay time changing means M29 for changing the delay time of the output determination of the first air-fuel ratio sensor M25 in the air-fuel ratio feedback means M28 so that the central air-fuel ratio by the air-fuel ratio feedback means M28 approaches the stoichiometric air-fuel ratio. In a state in which the warm-up state detecting means M23 has not finished warming up the catalyst M22, the fuel injection is forcibly made so that the air-fuel ratio becomes richer or leaner than the stoichiometric air-fuel ratio every predetermined period. The catalyst warm-up means M30 for adjusting the fuel injection amount by the control means M27 to perform the catalyst warm-up processing, and the center air-fuel ratio by the air-fuel ratio feedback means M28 for starting the catalyst warm-up processing by the catalyst warm-up means M30. The first air-fuel ratio sensor M2 for achieving the stoichiometric air-fuel ratio
The first air-fuel ratio sensor M25 is used to set the first air-fuel ratio by the air-fuel ratio feedback means M28 to the theoretical air-fuel ratio when the first time delay is set as the time delay for the output determination of No. Delay setting means M for setting a second delay time as a delay time for the output determination of
The gist of the invention is a control device for an internal combustion engine, which is provided with 31.

[0009]

In the first aspect of the present invention, the fuel injection control means M7 controls the fuel injection valve M1 so that the operation state detection means M4 injects a quantity of fuel according to the operating state of the internal combustion engine.
Further, the air-fuel ratio feedback means M8 adjusts the fuel injection amount by the fuel injection control means M7 according to the output of the first air-fuel ratio sensor M5 so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio. Correct the air-fuel ratio by feedback. Further, the control constant changing means M9 is the second air-fuel ratio sensor M6.
The air-fuel ratio feedback control constant is changed so that the central air-fuel ratio by the air-fuel ratio feedback means M8 approaches the stoichiometric air-fuel ratio.

Then, the catalyst warm-up means M10 is forced to make the air-fuel ratio rich and lean with respect to the theoretical air-fuel ratio at every predetermined period in a state where the warm-up state detection means M3 has not finished warming up the catalyst M2. The fuel injection control means M7 adjusts the fuel injection amount so that the catalyst warm-up process is performed. That is, by repeating rich combustion and lean combustion in the internal combustion engine, heat is generated by the oxidation reaction of carbon monoxide generated during rich combustion and oxygen generated during lean combustion, and the heat is used to heat the catalyst, Warm up early.

Further, the control constant setting means M11 is a first air-fuel ratio feedback control constant for making the center air-fuel ratio by the air-fuel ratio feedback means M8 the stoichiometric air-fuel ratio when starting the catalyst warm-up processing by the catalyst warm-up means M10. When the catalyst warm-up process is completed, the second air-fuel ratio feedback control constant for setting the central air-fuel ratio by the air-fuel ratio feedback means M8 to the stoichiometric air-fuel ratio is set.
That is, the first air-fuel ratio feedback control constant when the catalyst warm-up process is performed from the state where the catalyst warm-up process is not performed, and the first air-fuel ratio feedback control constant when the catalyst warm-up process is not performed from the state where the catalyst warm-up process is not performed. By preparing the air-fuel ratio feedback control constant of 2 as different values and selecting the air-fuel ratio feedback control constant when switching is performed,
The center air-fuel ratio can be brought closer to the theoretical air-fuel ratio more quickly.

In the second aspect of the invention, the fuel injection control means M27 controls the fuel injection valve M21 so that the operation state detection means M24 injects a quantity of fuel according to the operating state of the internal combustion engine. Further, the air-fuel ratio feedback means M28 responds to the output of the first air-fuel ratio sensor M25 so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio.
The fuel injection amount by 27 is adjusted to feedback-correct the air-fuel ratio. Further, the delay time changing means M29 responds to the output of the second air-fuel ratio sensor M26 so that the center air-fuel ratio by the air-fuel ratio feedback means M28 approaches the stoichiometric air-fuel ratio and the first air-fuel ratio feedback means M28 is operated. The delay time for the output determination of the fuel ratio sensor M25 is changed.

Then, the catalyst warm-up means M30 is compulsorily forced to have the air-fuel ratio rich and lean with respect to the theoretical air-fuel ratio every predetermined period in a state where the warm-up state detecting means M23 has not completed warming up the catalyst M22. The fuel injection control unit M27 adjusts the fuel injection amount so that the catalyst warm-up process is performed. That is, by repeating rich combustion and lean combustion in the internal combustion engine, heat is generated by the oxidation reaction of carbon monoxide generated during rich combustion and oxygen generated during lean combustion, and the heat is used to heat the catalyst, Warm up early.

Further, the delay time setting means M31 of the first air-fuel ratio sensor M25 sets the center air-fuel ratio by the air-fuel ratio feedback means M28 to the theoretical air-fuel ratio when starting the catalyst warm-up processing by the catalyst warm-up means M30. A first delay time is set as a delay time for the output determination, and when the catalyst warm-up process is finished, the output determination of the first air-fuel ratio sensor M25 is performed so that the center air-fuel ratio by the air-fuel ratio feedback means M28 becomes the theoretical air-fuel ratio. The second delay time is set as the delay time. That is, the first delay time when the catalyst warm-up processing is performed from the state where the catalyst warm-up processing is not performed, and the second delay time when the catalyst warm-up processing is not performed from the state where the catalyst warm-up processing is performed. The central air-fuel ratio can be brought closer to the stoichiometric air-fuel ratio more quickly by preparing time and different values and selecting the delay time when switching is performed.

[0015]

【Example】

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an engine 1 and its peripheral devices in which fuel injection control and ignition timing control are performed. As shown in the figure, in the present embodiment, each of the ignition timing AESA of the engine 1 and the fuel injection amount TAU is controlled by an electronic control unit (hereinafter referred to as ECU) 2.

The engine 1 is of a 4-cylinder 4-cycle spark ignition type, and its intake air is supplied from the upstream through an air cleaner 3, an intake pipe 4, a throttle valve 5, a surge tank 6, and an intake branch pipe 7. Inhaled into each cylinder.

On the other hand, fuel is pressure-fed from a fuel tank (not shown) and fuel injection valves 8a, 8a provided in the intake branch pipe 7 are provided.
It is configured to be injected and supplied from b, 8c, and 8d. Further, the engine 1 is provided with a distributor 9 for distributing the high-voltage electric signal provided from the ignition circuit 10 to the ignition plugs 11a, 11b, 11c, 11d of the respective cylinders.

Further, a rotation speed sensor 12 and a cylinder discrimination sensor 13 are mounted in the distributor 9,
The rotation speed sensor 12 detects the rotation speed Ne of the engine 1. That is, the rotation speed sensor 12 is provided so as to face a ring gear that rotates in synchronization with the crankshaft of the engine 1, and 24 rotations are generated every two rotations of the engine 1 (that is, 720 ° C.A) in proportion to the rotation speed Ne. The pulse signal of is output. The cylinder discrimination sensor 13 discriminates the cylinder of the engine 1. That is, the cylinder discrimination sensor 13 is also provided so as to face the link gear that rotates in synchronization with the crankshaft of the engine 1, and the engine 1 makes two revolutions at the compression top dead center of a predetermined cylinder (that is, 720 ° C. A). Then, one pulse signal G is output.

The throttle sensor 14 outputs an analog signal corresponding to the opening TH of the throttle valve 5 and an idle signal indicating that the throttle valve 5 is almost fully closed. The intake pressure sensor 15 detects the intake pressure PM downstream of the throttle valve 5. Warm-up sensor 1
6 detects the cooling water temperature Thw of the engine 1, and the intake air temperature sensor 17 detects the intake air temperature Tam.

Further, in the exhaust pipe 18 of the engine 1, harmful components (CP,
A three-way catalyst 19 for reducing HC, NO _x, etc. is provided.

Further, on the upstream side of the three-way catalyst 19, an air-fuel ratio sensor 2 which is an oxygen concentration sensor for outputting a linear detection signal corresponding to the air-fuel ratio λ of the air-fuel mixture supplied to the engine 1.
0 is provided. Further, an air-fuel ratio sensor 21, which is an oxygen concentration sensor that outputs a linear detection signal according to the air-fuel ratio λ of the air-fuel mixture supplied to the engine 1, is provided downstream of the three-way catalyst 19.

The ECU 2 is a well-known CPU 22 and ROM 2
3, an RAM 24, a backup RAM 25, etc., as an arithmetic and logic operation circuit, and an input port 26 for inputting from each sensor, an output port 27 for outputting a control signal to each actuator, and a bus 28. Are connected to each other.

The ECU 2 inputs the intake pressure PM, the intake temperature Tam, the throttle opening TH, the cooling water temperature Thw, the air-fuel ratio λ, the rotational speed Ne, etc. via the input port 26, and based on these inputs, the fuel injection amount TAU. , The ignition timing AESA is calculated, and the fuel injection valves 8a to 8d are output through the output port 27.
A control signal is output to each of the ignition circuits 10.

Next, the operation of the control device for the internal combustion engine having the above-described structure will be described. In explaining this action, the timing chart of FIG. 8 is used. In addition, in FIG.
The injection dither is not performed before the timing of t6 ', and the injection dither control is performed after t6'.

Further, as shown in FIG. 8, the upstream air-fuel ratio sensor (O ₂ sensor) 20 with respect to the actual air-fuel ratio has a delay τ 1 when reversing from lean to rich,
Also, there is a delay τ 2 when reversing from rich to lean.

FIG. 2 shows a fuel injection dither control determination process, which is executed every 40 msec. This fuel injection dither control is a process for early warm-up of the three-way catalyst 19. In other words, the fuel injection amount is increased / decreased for each combustion, and the air-fuel ratio is swung to the rich side and the lean side with respect to the stoichiometric air-fuel ratio, whereby rich combustion and lean combustion are repeated, and carbon monoxide (CO) and lean are burned by rich combustion. Oxygen (O ₂ ) is generated by combustion. Then, the carbon monoxide and oxygen thus generated carry out an oxidation reaction represented by the following formula to generate heat (Q).

[0028]

## EQU1 ## 2CO + O ₂ = 2CO ₂ + Q The exhaust gas temperature rises due to the heat (Q) generated by this oxidation reaction, and the warm-up of the three-way catalyst 19 is promoted.

More specifically, in step 100 of FIG. 2, after the engine 1 has been started (for example, Ne> 500 rp).
m) Determine whether a predetermined time has passed. This predetermined time is the time until the temperature at which the three-way catalyst 19 performs the emission purification action is reached, and is set to 100 seconds, for example.

If it is within the predetermined time in step 100, the cooling water temperature Thw is read in step 101 and the cooling water temperature Tw is read.
Whether hw is in the range of 20 to 60 ° C is determined, and if it is in the range, the dither determination flag FDit indicating whether or not the injection dither execution condition is satisfied is set (= 1) and this routine is ended. To do.

If it is determined in step 100 that the predetermined time has elapsed after the completion of startup, and if the cooling water temperature Thw is out of the range of 20 to 60 ° C. in step 101, the dither determination flag FDit is cleared in step 102. (= 0)
Then, this routine is finished.

Next, based on FIG. 3, the final fuel injection amount TA
A method of calculating U will be described. This routine is started at each injection timing. First, steps 200 and 20
The engine speed Ne and the intake pressure PM are read in 1 and the dither discrimination flag FDit is set (= 1) in step 202.
It is determined whether or not it has been done.

If the dither determination flag FDit is set, it is determined in step 203 whether or not the air-fuel ratio feedback condition is satisfied. Here, the air-fuel ratio feedback condition means that the engine speed Ne is equal to or lower than a predetermined value Neo (Ne <Neo) and the intake pressure PM is a predetermined value PM.
o or less (PM <PMo) and the water temperature Thw is 20 ° C.
The above (Thw> 20 ° C.) is referred to.

If the air-fuel ratio feedback condition is satisfied, the dither confirmation flag F indicating whether the air-fuel ratio was swung to the rich side or the lean side in the previous step 205.
It is determined whether or not ri is set (= 1).

If the dither confirmation flag Fri is set, it is assumed that the air-fuel ratio was swung to the lean side last time, and this time, the processing for setting the air-fuel ratio to the rich side is performed in step 206. That is, the final dither coefficient CDit = 1.1. Further, in step 207, the dither confirmation flag Fri is reset (= 0).

In step 205, the dither confirmation flag F
If ri is reset (= 0), it is assumed that the air-fuel ratio was swung to the rich side last time, and this time, the process of setting the air-fuel ratio to the lean side is performed in step 208. That is, the final dither coefficient CDit = 0.9. Further, in step 209, the dither confirmation flag Fri is set (= 1).

If the dither determination flag FDit = 0 in step 202 and if the air-fuel ratio feedback condition is not satisfied in step 203, step 20
In 4, the final dither coefficient CDit = 1.0.

Further, steps 204, 207 and 209
After the above process, in step 210, the basic injection amount TP stored in the two-dimensional map is calculated from the engine speed Ne and the intake pressure PM.

Then, in step 211, the final fuel injection amount TAU is calculated from the basic injection amount TP, the air-fuel ratio correction coefficient FAF, the final dither coefficient CDit, the coefficient α, and the invalid injection time Tv by the following arithmetic expression. However, the coefficient α is determined by the water temperature Thw, the engine speed Ne, and the rate of change ΔPM of intake pressure with time.

[0040]

## EQU00002 ## TAU = TP.FAF.CDit.multidot. (1 + .alpha.) + Tv Then, in step 212, the final fuel injection amount TAU is set and this routine is ended.

In this way, the air-fuel ratio is swung to the rich side and the lean side for each combustion. As a result, the catalyst is warmed up early and the emission of harmful components in the exhaust gas to the atmosphere is reduced.

4 and 5 show a first air-fuel ratio feedback control routine for calculating the air-fuel ratio correction coefficient FAF based on the output of the upstream air-fuel ratio sensor 20, which is executed every predetermined time (for example, 10 msec). To be done.

In step 300, it is determined whether or not the air-fuel ratio feedback control condition (same as in step 203) is satisfied. Then, when the feedback control condition is not satisfied, the routine proceeds to step 301, where the air-fuel ratio correction coefficient FAF is set to 1.0. On the other hand, if the feedback control condition is satisfied, the process proceeds to step 302.

In step 302, the output V1 of the upstream air-fuel ratio sensor 20 is A / D converted and taken in, and in step 303 V1 is compared voltage VR1 (for example, 0.45V).
It is determined whether or not the following. That is, it is determined whether the air-fuel ratio is rich or lean. If lean (V1 ≤ VR1), the delay counter CDLY is decremented by "1" in step 304, and the delay counter CDLY is guarded by the minimum value TDR in steps 305 and 306. The minimum value T
DR is a rich delay time for holding the determination that the output is the lean state even if the output of the air-fuel ratio sensor 20 on the upstream side changes from lean to rich, and is defined by a negative value.

On the other hand, in step 303, the rich (V
If 1> VR1), the delay counter CDLY is incremented by "1" in step 307, and step 30
The maximum value TD of the delay counter CDLY at 8,309
Guard with L. It should be noted that the maximum value TDL is a lean delay time for holding the determination that it is in the rich state even if there is a change from rich to lean in the output of the upstream air-fuel ratio sensor 20, and is defined as a positive value. To be done.

Here, the reference of the delay counter CDLY is set to "0", the air-fuel ratio after delay processing is considered rich when CDLY≥0, and the air-fuel ratio after delay processing is considered lean when CDLY <0. It is a thing.

In step 310 of FIG. 5, it is determined whether or not the sign of the delay counter CDLY is inverted. That is, it is determined whether or not the air-fuel ratio after the delay process has been reversed.
If the air-fuel ratio is reversed, it is determined in step 311 whether the dither determination flag FDit is "1". If FDit = 0, a predetermined value RSR1 is set as the skip amount RSR in step 312, and the skip amount is set. A predetermined value RSL1 is set as RSL. Also, step 31
If it is 1 and the dither discrimination flag FDit = 1, step 31
In step 3, a predetermined value RSR2 is set as the skip amount RSR and a predetermined value R is set as the skip amount RSL.
Set SL2.

Then, in step 314, it is determined whether the inversion from rich to lean or the inversion from lean to rich. If it is a reversal from rich to lean, step 31
At step 5, FAF = FAF + RSR is increased in a skip manner, and conversely, when lean is reversed to rich, at step 516, FAF = FAF-RSL is reduced in a skip manner. That is, skip processing is performed (t2 in FIG. 8,
Timing of t3, t4, t5, t6).

On the other hand, if the sign of the delay counter CDLY is not inverted in step 310, integration processing is performed in steps 317, 318 and 319. That is,
In step 317, it is determined whether CDLY <0, and the CDL
If Y <0 (lean), in step 318 FAF =
FAF + K1 is set. On the other hand, if CDLY ≧ 0 (rich), FAF = FAF-K1 is set in step 319.
Here, the integration constant K1 is set sufficiently smaller than the skip constant RS, that is, K1 << RS. Therefore, step 318 gradually increases the fuel injection amount in the lean state (CDLY <0) (t2 to t3, t4 in FIG. 8).
~ T5), step 319 is in a rich state (CDLY ≧ 0)
Gradually decrease the fuel injection amount (from t1 to t2 in FIG. 8,
t3 to t4, t5 to t6).

Incidentally, steps 315, 316, 318, 3
It is assumed that the air-fuel ratio correction coefficient FAF calculated in 19 is guarded by the minimum value (for example, 0.8) and the maximum value (for example, 1.2). When it becomes too large or too small, the air-fuel ratio of the engine is controlled by that value to prevent overrich or over lean.

The FAF calculated as described above is stored in the RAM 2
4 and the routine ends. 6 and 7 show the skip amount RSR based on the output of the downstream air-fuel ratio sensor 21,
It is a second air-fuel ratio feedback control routine for calculating RSL, and is executed every predetermined time (for example, 100 msec).

In step 400, it is determined whether or not the feedback control condition of the air-fuel ratio by the downstream air-fuel ratio sensor 21 (the same as in step 203) is satisfied.
If the air-fuel ratio feedback control condition is not satisfied, the routine ends.

If the air-fuel ratio feedback control condition is satisfied, the routine proceeds to step 401, where the output voltage V2 of the downstream air-fuel ratio sensor 21 is A / D converted and taken in, and at step 402 the dither discrimination flag FDit is set to ". 1 ”is determined.

If FDit = 0, it is determined in step 416 of FIG. 7 whether the output voltage V2 of the downstream air-fuel ratio sensor 21 is equal to or lower than the comparison voltage VR2 (for example, 0.55V). That is, it is determined whether the air-fuel ratio is rich or lean.
Note that the comparison voltage VR2 in step 416 takes into consideration the output characteristics due to the influence of raw gas and the output characteristics due to the difference in the speed of deterioration because the air-fuel ratio sensors 20 and 21 come before and after the catalyst. Is set higher than the comparison voltage VR1.

If lean (V2 ≤ VR2) in step 416, RSR1 = RSR1 + ΔR in step 417
S (constant value), that is, the rich skip amount RSR is increased to shift the air-fuel ratio to the rich side. Step 4
In 18 and 419, RSR is guarded with the maximum value MAX. Further, in step 420, RSL1 = RSL1-
Let ΔRS (constant value). That is, the rich skip amount R
SL is decreased to shift the air-fuel ratio to the rich side. In steps 421 and 423, RSL1 is guarded with the minimum value MIN.

On the other hand, in step 416, the rich (V
2> VR2), RSR1 = in step 423
RSR1-ΔRS (constant value), that is, the rich skip amount RSR is decreased to shift the air-fuel ratio to the lean side. In steps 424 and 425, RSR is set to the minimum value MIN.
To guard. Further, in step 426, RSL1
= RSL1 + ΔRS (constant value), that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. In steps 427 and 428, RSL is set to the maximum value MA.
Guard with X.

On the other hand, if the dither determination flag FDit = 1 in step 402 of FIG. 6, the output voltage V2 of the downstream air-fuel ratio sensor 21 is the comparison voltage VR2 (for example, 0.55).
V) It is determined whether it is less than or equal to. That is, it is determined whether the air-fuel ratio is rich or lean.

In step 403, lean (V2≤V
If R2), RSR2 = RSR2 in step 404
+ ΔRS (constant value), that is, the rich skip amount R
SR2 is increased to shift the air-fuel ratio to the rich side. In steps 405 and 406, RSR2 is guarded with the maximum value MAX. Further, in step 407, RSL2 = R
SL2-ΔRS (constant value). That is, the lean skip amount RSL is decreased to shift the air-fuel ratio to the rich side. In steps 408 and 409, RSL2 is set to the minimum value MI.
Guard with N.

On the other hand, in step 403, the rich (V
2> VR2), RSR2 = at step 410
RSR2-ΔRS (constant value), that is, the rich skip amount RSR is decreased to shift the air-fuel ratio to the lean side. In steps 411 and 412, RSR is set to the minimum value MIN.
To guard. Further, in step 413, RSL2
= RSL2 + ΔRS (constant value), that is, the lean skip amount RSL is increased to shift the air-fuel ratio to the lean side. In steps 414 and 415, RSL is set to the maximum value MA.
Guard with X.

The RSR and RSL calculated as described above are stored in the RAM 24, and this routine ends. still,
The minimum value MIN in FIGS. 6 and 7 is a value equivalent to a level (for example, 3%) at which the transient followability is not impaired, and the maximum value MAX is a level at which the deterioration of drability due to the air-fuel ratio fluctuation does not occur (for example, 10%).

As described above, according to the routines of FIGS. 6 and 7, if the output of the downstream air-fuel ratio sensor 21 is lean, the rich skip amount RSR is gradually increased, and
The lean skip amount RSL is gradually reduced, whereby the air-fuel ratio is shifted to the rich side. If the output of the downstream air-fuel ratio sensor 21 is rich, the rich skip amount RSR is gradually reduced and the lean skip amount R
SL is gradually increased, whereby the air-fuel ratio is shifted to the lean side.

At this time, when there is no injection dither, FIG.
In Steps 417, 420, 423, and 426, the RSR2 and RSL2 are calculated, and when there is an injection dither, Steps 404, 407, and 41 in FIG.
RSR1 and RSL1 were calculated by the process of 0,413. That is, two types of coefficients that determine the skip amount are prepared and selected depending on the presence or absence of dither.

As described above, in this embodiment, the ECU 2 controls the fuel injection valves 8a to 8d so as to inject the fuel in an amount according to the operating state of the engine 1, and in accordance with the output of the air-fuel ratio sensor 20, The fuel injection amount is adjusted so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio, and the air-fuel ratio is feedback-corrected. Further, the ECU 2 is the air-fuel ratio sensor 2
In accordance with the output of 1, the skip amount as the air-fuel ratio feedback control constant is changed so that the central air-fuel ratio approaches the stoichiometric air-fuel ratio, and further, in the state where the warm-up of the catalyst 19 is not completed, it is forced. So that the air-fuel ratio becomes richer and leaner than the theoretical air-fuel ratio every predetermined period.
The fuel injection amount is adjusted and the catalyst warm-up process is performed. In other words, by repeating rich combustion and lean combustion to generate carbon monoxide during rich combustion and oxygen during lean combustion to cause an oxidation reaction with carbon monoxide, the heat at this time completes catalyst warm-up. Let Further, the ECU 2 sets a first air-fuel ratio feedback control constant (initial value of the skip amount) for making the center air-fuel ratio the stoichiometric air-fuel ratio when starting the catalyst warm-up process, and when ending the catalyst warm-up process. A second air-fuel ratio feedback control constant (initial value of skip amount) for setting the central air-fuel ratio to the stoichiometric air-fuel ratio is set.
That is, the first air-fuel ratio feedback control constant (initial value of the skip amount) when the catalyst warm-up process is performed from the state where the catalyst warm-up process is not performed, and the catalyst warm-up process is performed when the catalyst warm-up process is performed. The second air-fuel ratio feedback control constant (the initial value of the skip amount) when the process is not performed is prepared as a different value, and when the switching is performed, the air-fuel ratio feedback control constant is selected, so that the speed can be increased more quickly. Therefore, the center air-fuel ratio can be brought close to the theoretical air-fuel ratio.

As an application of this embodiment, different initial values of the skip amount are set depending on the presence or absence of dither control in the above embodiment, but different integration processing values (integral constants K1 and K2) depending on the presence or absence of dither control. May be set. (Second Embodiment) Next, a second embodiment will be described.

In the first embodiment, the initial value of the skip amount which is different depending on the presence / absence of the dither control is set. However, in this embodiment, even if the output of the air-fuel ratio sensor 20 on the upstream side changes from rich to lean, it takes a certain period of time. It is regarded as rich, and conversely, delay processing is performed in which, even if the output of the air-fuel ratio sensor 20 on the upstream side changes from lean to rich, it is considered lean for a certain period of time,
The above-mentioned delay processing time (delay time TD) is adjusted according to the output of the air-fuel ratio sensor 21 on the downstream side.

The overall configuration is the same as that of FIG. 1, and the processing of FIGS. 2 and 3 is also the same. The operation of this embodiment will be described with reference to the timing chart of FIG. 9 and 10 show the air-fuel ratio correction coefficient FAF based on the output of the upstream air-fuel ratio sensor 20.
Is a first air-fuel ratio feedback control routine that calculates ## EQU1 ## and is executed every predetermined time (for example, 10 msec).

At step 500, it is judged if the feedback control condition of the air-fuel ratio is satisfied. here,
The air-fuel ratio feedback condition is that the engine speed Ne is equal to or lower than a predetermined value Neo (Ne <Neo) and the intake pressure P
M is a predetermined value PMo or less (PM <PMo), and the water temperature Thw is 20 ° C. or higher (Thw> 20 ° C.).

When the feedback control condition is not satisfied, the routine proceeds to step 501, where the air-fuel ratio correction coefficient F
The AF is set to 1.0. On the other hand, if the feedback control condition is satisfied, the process proceeds to step 502.

In step 502, the dither discrimination flag F
It is determined whether or not Dit is "1", and if FDit = 0, a value TD set in advance as the delay time TDR in step 503.
R1 is set and a predetermined value TDL1 is set as the delay time TDL. If the dither determination flag FDit = 1 in step 502, the predetermined value TDR2 is set as the delay time TDR in step 504, and the predetermined value TD is set as the delay time TDL.
Set L2.

Then, in step 505, the output V1 of the upstream side air-fuel ratio sensor 20 is A / D converted and taken in, and in step 506 V1 is compared voltage VR1 (for example, 0.45).
V) It is determined whether it is less than or equal to. That is, it is determined whether the air-fuel ratio is rich or lean. If lean (V1 ≤ VR1),
In step 507, the delay counter CDLY is decremented by "1", and in steps 508 and 509, the delay counter CDLY is guarded by the minimum value TDR.

On the other hand, in step 506, the rich (V
If 1> VR1), the delay counter CDLY is incremented by "1" in step 510, and step 51
The maximum value TD of the delay counter CDLY at 1,512
Guard with L.

In step 513 of FIG. 10, it is determined whether or not the sign of the delay counter CDLY has been inverted. That is, it is determined whether or not the air-fuel ratio after the delay process has been reversed.
If the air-fuel ratio has been reversed, it is determined in step 514 whether the reversal from rich to lean or the reversal from lean to rich. If it is a reversal from rich to lean, step 5
In step 15, FAF = FAF + RSR is increased in a skip manner, and conversely, if lean to rich inversion, in step 516, FAF = FAF-RSL is decreased in a skip manner. That is, skip processing is performed.

On the other hand, if the sign of the delay counter CDLY is not inverted in step 513, integration processing is performed in steps 517, 518 and 519. That is,
In step 517, it is determined whether CDLY <0, and the CDL
If Y <0 (lean), in step 518 FAF =
FAF + K1 is set. On the other hand, if CDLY ≧ 0 (rich), FAF = FAF-K1 is set in step 519.
Therefore, step 518 is in the lean state (CDLY <0).
In step 519, the fuel injection amount is gradually increased, and in step 519, the fuel injection amount is gradually decreased in the rich state (CDLY ≧ 0).

The FAF calculated as described above is stored in the RAM 2
4 and the routine ends. 11 and 12 show the delay time T based on the output of the air-fuel ratio sensor 21 on the downstream side.
A second air-fuel ratio feedback control routine for calculating DR and TDL, which is performed for a predetermined time (for example, 100 mse
It is executed every c).

In step 600, it is determined whether or not the feedback control condition of the air-fuel ratio by the downstream air-fuel ratio sensor 21 is satisfied. If the condition is not satisfied, the same routine is ended.

If the air-fuel ratio feedback control condition is satisfied, the routine proceeds to step 601, where the output voltage V2 of the downstream air-fuel ratio sensor 21 is A / D converted and taken in, and at step 602, the dither determination flag FDit is set to " 1 ”is determined.

If FDit = 0, the output voltage V2 of the downstream air-fuel ratio sensor 21 is determined in step 616 of FIG.
Is below the comparison voltage VR2 (for example, 0.55V). That is, it is determined whether the air-fuel ratio is rich or lean. When lean (V2 ≤ VR2) in step 616, TDR1 = TDR1 + ΔTD (constant value) is set in step 617, that is, the rich delay time TDR is increased to shift the air-fuel ratio to the rich side. Step 618,
At 619, TDR is guarded with the maximum value MAX. Further, in step 620, TDL1 = TDL1-ΔTD
(Constant value). That is, the lean delay time TDL
Is reduced to shift the air-fuel ratio to the rich side. In steps 621 and 622, TDL1 is guarded with the minimum value MIN.

On the other hand, in step 616, the rich (V
2> VR2), TDR1 = at step 623
TDR1-ΔTD (constant value), that is, the rich delay time TDR is reduced to shift the air-fuel ratio to the lean side. In steps 624 and 625, TDR is set to the minimum value MI.
Guard with N. Further, in step 626, TDL
1 = TDL1 + ΔTD (constant value), that is, the lean delay time TDL is increased to shift the air-fuel ratio to the lean side. In steps 627 and 628, TDL is guarded with the maximum value MAX.

On the other hand, if the dither determination flag FDit = 1 in step 602 of FIG. 11, the output voltage V2 of the downstream air-fuel ratio sensor 21 is the comparison voltage VR2 (for example, 0.5).
5 V) or less is determined. That is, it is determined whether the air-fuel ratio is rich or lean.

In step 603, lean (V2 ≤ V
R2), TDR2 = TDR2 in step 604
+ ΔTD (constant value), that is, the rich delay time TDR2 is increased to shift the air-fuel ratio to the rich side.
In steps 605 and 606, TDR2 is guarded with the maximum value MAX. Further, in step 607, TDL2 =
TDL2-ΔTD (constant value). That is, the lean delay time TDL is reduced to shift the air-fuel ratio to the rich side. In steps 608 and 609, TDL2 is guarded with the minimum value MIN.

On the other hand, in step 603, the rich (V
2> VVR2), TDR2 in step 610
= TDR2-ΔTD (constant value), that is, the rich delay time TDR is reduced to shift the air-fuel ratio to the lean side. In steps 611 and 612, TDR is set to the minimum value M.
Guard at IN. Further, in step 613, TD
L2 = TDL2 + ΔTD (constant value), that is, the lean delay time TDL is increased to shift the air-fuel ratio to the lean side. In steps 614 and 615, TDL is guarded with the maximum value MAX.

The TDR and TDL calculated as described above are stored in the RAM 24, and this routine ends. As described above, according to the routines of FIGS. 11 and 12, when the output of the downstream air-fuel ratio sensor 21 is lean, the rich delay time TDR is gradually increased and the lean delay time TDL is gradually decreased. , As a result, the air-fuel ratio is shifted to the rich side. If the output of the downstream air-fuel ratio sensor 21 is rich, the rich delay time TDR is gradually decreased and the lean delay time TDL is gradually increased, whereby the air-fuel ratio is shifted to the lean side. It

At this time, when there is no injection dither, FIG.
In step 2 617, 621, 623, 626, TDR2 and TDL2 are calculated, and if injection dither is present, steps 604, 607, 6 in FIG.
TDR1 and TDL1 were calculated in the processing of 10,613. That is, two types of coefficients that determine the delay time TD are prepared and selected depending on the presence or absence of dither.

As described above, in this embodiment, the ECU 2 changes the delay time of the output determination of the air-fuel ratio sensor 20 according to the output of the air-fuel ratio sensor 21 so that the center air-fuel ratio approaches the stoichiometric air-fuel ratio. Then, when starting the catalyst warm-up process, the ECU 2 sets the first delay time as the delay time of the output determination (rich / lean determination) of the air-fuel ratio sensor 20 in order to make the center air-fuel ratio the stoichiometric air-fuel ratio. When the warm-up process ends, the second delay time is set as the delay time of the output determination (rich / lean determination) of the air-fuel ratio sensor 20 so that the center air-fuel ratio becomes the stoichiometric air-fuel ratio. That is, the first delay time when the catalyst warm-up processing is performed from the state where the catalyst warm-up processing is not performed, and the second delay time when the catalyst warm-up processing is not performed from the state where the catalyst warm-up processing is performed. The central air-fuel ratio can be brought closer to the stoichiometric air-fuel ratio more quickly by preparing time and different values and selecting the delay time when switching is performed.

The present invention is not limited to the above embodiments. For example, although the dither amount is a constant value in each of the above embodiments, when the dither amount is variable, the dither amount is changed according to the dither amount. The correction coefficient may be selected.

[0086]

As described above in detail, according to the present invention,
It exhibits an excellent effect that the stoichiometric air-fuel ratio can be promptly set at the start and end of the injection dither.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an embodiment.

FIG. 2 is a flowchart for explaining the operation.

FIG. 3 is a flowchart for explaining an operation.

FIG. 4 is a flowchart for explaining the operation.

FIG. 5 is a flowchart for explaining the operation.

FIG. 6 is a flowchart for explaining the operation.

FIG. 7 is a flowchart for explaining the operation.

FIG. 8 is a timing chart for explaining the operation.

FIG. 9 is a flowchart for explaining the operation of the second embodiment.

FIG. 10 is a flow chart for explaining the operation of the second embodiment.

FIG. 11 is a flow chart for explaining the operation of the second embodiment.

FIG. 12 is a flow chart for explaining the operation of the second embodiment.

FIG. 13 is a timing chart for explaining the operation of the second embodiment.

FIG. 14 is a diagram for explaining a conventional technique.

FIG. 15 is a diagram corresponding to a complaint.

FIG. 16 is a claim correspondence diagram.

[Explanation of symbols]

1 engine 2 warm-up state detecting means, operating state detecting means, fuel injection control means, air-fuel ratio feedback means, control constant changing means, catalyst warm-up means, control constant setting means, delay time changing means, delay time setting means ECU 8a, 8b, 8c, 8d Fuel injection valve 18 Exhaust pipe 19 Three-way catalyst 20 Air-fuel ratio sensor 21 Air-fuel ratio sensor

Claims (2)

[Claims] 1. A fuel injection valve for injecting fuel into an internal combustion engine, a catalyst arranged in an exhaust pipe of the internal combustion engine for purifying exhaust gas, and a warm-up state detection for detecting a warm-up state of the catalyst. Means, an operating state detecting means for detecting an operating state of the internal combustion engine, a first air-fuel ratio sensor provided on the upstream side of the catalyst for detecting the concentration of a specific component in exhaust gas, and a downstream side of the catalyst. A second air-fuel ratio sensor that is provided and detects the concentration of a specific component in the exhaust gas, and controls the fuel injection valve so as to inject fuel in an amount according to the operating state of the internal combustion engine by the operating state detecting means. According to the outputs of the fuel injection control means and the first air-fuel ratio sensor, the fuel injection amount by the fuel injection control means is adjusted so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio. The feedback to correct the sky Ratio feedback means, and control constant changing means for changing the air-fuel ratio feedback control constant so that the center air-fuel ratio by the air-fuel ratio feedback means approaches the stoichiometric air-fuel ratio in accordance with the output of the second air-fuel ratio sensor, In a state in which the catalyst has not been warmed up by the warm-up state detection means, the fuel injection control means is forcibly set so that the air-fuel ratio becomes richer or leaner than the stoichiometric air-fuel ratio at predetermined intervals. Catalyst warm-up means for adjusting the fuel injection amount by the catalyst warm-up processing, and when starting the catalyst warm-up processing by the catalyst warm-up means, the center air-fuel ratio by the air-fuel ratio feedback means is set to the theoretical air-fuel ratio. The first air-fuel ratio feedback control constant is set, and when the catalyst warm-up process is finished, the central air-fuel ratio by the air-fuel ratio feedback means is theoretically calculated. Control apparatus for an internal combustion engine characterized by comprising a second control constant setting means for setting an air-fuel ratio feedback control constant for the ratio. 2. A fuel injection valve for injecting fuel into an internal combustion engine, a catalyst arranged in an exhaust pipe of the internal combustion engine for purifying exhaust gas, and a warm-up state detection for detecting a warm-up state of the catalyst. Means, an operating state detecting means for detecting an operating state of the internal combustion engine, a first air-fuel ratio sensor provided on the upstream side of the catalyst for detecting the concentration of a specific component in exhaust gas, and a downstream side of the catalyst. A second air-fuel ratio sensor that is provided and detects the concentration of a specific component in the exhaust gas, and controls the fuel injection valve so as to inject fuel in an amount according to the operating state of the internal combustion engine by the operating state detecting means. According to the outputs of the fuel injection control means and the first air-fuel ratio sensor, the fuel injection amount by the fuel injection control means is adjusted so that the air-fuel ratio falls within a narrow range near the stoichiometric air-fuel ratio. The feedback to correct the sky A ratio feedback means and a first air-fuel ratio sensor of the air-fuel ratio feedback means such that the central air-fuel ratio of the air-fuel ratio feedback means approaches the stoichiometric air-fuel ratio according to the outputs of the second air-fuel ratio sensor. Delay time changing means for changing the delay time of the output determination, and in a state in which the catalyst has not been warmed up by the warming-up state detecting means, the air-fuel ratio is forcibly richer than the stoichiometric air-fuel ratio for each predetermined period. Side and lean side, the catalyst warm-up means for adjusting the fuel injection amount by the fuel injection control means to carry out the catalyst warm-up processing, and the catalyst warm-up processing for starting the catalyst warm-up processing by the catalyst warm-up means In order to make the center air-fuel ratio by the fuel ratio feedback means the stoichiometric air-fuel ratio, the first delay time is set as the delay time for the output determination of the first air-fuel ratio sensor, and the catalyst warm-up process is performed. And a delay time setting means for setting a second delay time as a delay time for the output determination of the first air-fuel ratio sensor so that the center air-fuel ratio by the air-fuel ratio feedback means becomes the stoichiometric air-fuel ratio. A control device for an internal combustion engine, characterized by: