KR0145367B1 - Apparatus for controlling air fuel ratio of an engine - Google Patents

Abstract

In the present invention, in order to reduce HC emissions in a range that does not increase NOx emissions immediately after start-up, the calculation means 38 sets the initial value and the reduction rate at the time of reversal to the lean side to PSLO and ΔP _SL , PSLO, PSRO, and ΔP _SL and ΔP _SR at the start-up temperature to set PSLO and ΔP _SR as PSLOPSRO, ΔP _SL ΔP _SR, and ΔP _SL / ΔP _SR PSLO / PSRO respectively. The amount of correction at the time of reversal to the lean side and to the dense side is a value that is set according to the equivalent value and decreases with time elapsed after starting from PSLO and ΔP _SL or PSRO and ΔP _SR. The calculation means 39 of (PSL, PSR) calculates. The amount of correction (PSL, PSR) at the time of turbulence is added to the step values matched in the active state of the catalyst, and the calculation means 40 for calculating the step values PL, PR for the reversal to the lean side and the reversal to the dense side is performed. Calculate.

Description

Engine air-fuel ratio control device

1 is a flow diagram generally illustrating the contents of the present invention.

2 illustrates a system of one embodiment of the present invention.

3 is a flowchart for explaining the calculation of the feedback correction coefficient α of the air-fuel ratio.

4 is a characteristic diagram showing a map value of the step value PR in the hot state of the three-way catalyst used at the time of inversion to the rich side.

5 is a characteristic diagram showing a map value of the step value PL in the active state of the three-way catalyst used at the time of inversion to the lean side.

Fig. 6 shows the change waveforms of the normal air-fuel ratio after completion of the three-way catalyst and the feedback correction coefficient α of the output and air-fuel ratio of the O ₂ detector.

7 is a flowchart for explaining the calculation of the fuel injection pulse width Ti.

8 is a flowchart for explaining the calculation of the correction amounts PSL and PSR in turbulence.

9 is a characteristic diagram of initial values (PSLO, PSRO) of the correction amount at the time of turbulence.

10 is a characteristic diagram of the reduction rates DELTA P _SL and DELTA P _SR .

11 is a characteristic diagram of the correction amount (PSL, PSR) at the time of warming with respect to the time after starting.

12 shows the exhaust temperature when the air-fuel ratio feedback correction is performed using an O ₂ detector having a detection responsiveness in which the degree of reversal to the lean side is slower than the reversal to the dense side in a lack of turbulence. Figure of characteristic of mean of air-fuel ratio.

13 is a characteristic diagram of the air-fuel ratio with respect to the level of activation of the catalyst before the completion of turbulence of the three-way catalyst.

14 is a waveform diagram for explaining the operation during cold start of the embodiment.

15 is a characteristic diagram of HC emissions and NOx emissions of the embodiment.

* Explanation of symbols for main parts of the drawings

4: Fuel supply device 6: 3-element catalyst

7: Air flow meter 10: Crank angle detector

12: O ₂ detector 21: control device

31: O ₂ detector 32: Initiation means for feedback correction

33: concentration determination means 34: inversion determination means

35: means for calculating active state step values

36: calculation means of the integral value 37: measurement means of the time after starting

38: setting means of initial value and reduction rate

39: calculation means of the amount of correction at the time of turbulence

40: calculation means of step value at the time of turbulence

41: Calculation means of feedback correction amount of performance ratio

42: means for calculating fuel injection amount 43: fuel supply device

[Industrial use]

The present invention relates to an apparatus for feedback correction so that the air-fuel ratio of a mixer supplied to an engine becomes a theoretical performance ratio based on a signal from an O ₂ detector provided in the exhaust pipe.

[Prior art]

In the so-called three-way catalytic method, the air-fuel ratio feedback correction is performed so that the air-fuel ratio of the mixer converges within a narrow range (called “catalyst window”) centered on the theoretical performance ratio in order to purify exhaust three components (CO, HC, NOx) at once. (See Japanese Patent Application Laid-Open No. 61-241434).

In this case, the feedback correction is to make the air-fuel ratio oscillate in the catalyst window by using the step value and the integral value as the renewal amount of the feedback correction coefficient (α) of the air-fuel ratio, so as soon as the air-fuel ratio is reversed from the lean side to the rich side. By adding a step value (even when reversed in the reverse direction), the air-fuel ratio responds to the lean side (inverted and reverse direction) in response, and then controls by adding a small integral value until the air-fuel ratio reverses to the dense side. It is to stabilize.

[Problems to Solve Invention]

However, the air-fuel ratio oscillated to a certain width has high conversion efficiency of the three-way catalyst. The above step values are set in the active state of the three-way catalyst (hot state: the three-way catalyst is sufficiently warm-warming).

However, there is a desire to slightly expand the operating region in which the three-way catalyst works effectively and to improve the exhaust performance by performing feedback correction of the air-fuel ratio even before the three-way catalyst becomes active. In this case, the exhaust gas performance immediately after starting the feedback correction of the air-fuel ratio is deteriorated because the demand value for the step value is different from the active state due to the response delay of the fuel when the water temperature is low. When the water temperature is low, the supply of fuel in the port becomes large, so that the step value having the same value as the step value used in the active state becomes smaller in amplitude of the air-fuel ratio and lowers the conversion efficiency of the three-way catalyst.

In addition, as the three-way catalyst warms up after starting, the demand for the step value also changes. In addition, a step value different from the active state is also required at the time of hot restarting (the temperature of the three-way catalyst is lowered even if the cooling water temperature is sufficiently high).

For this treatment, the warm-up correction amount determined by the cooling water temperature at start-up and the time elapsed from the start-up period from the timing of starting the feedback correction of the air-fuel ratio to the completion of the warming-up of the three-way catalyst is determined. It was proposed to add to the step value matched in the state (see Japanese Patent Application Laid-Open No. 4-265064). The initial value of the cooling water decreases with time after starting from the initial value according to the cooling water temperature, and the value which becomes 0 at the time of completion of the three-way catalyst turbulence is calculated as the temperature compensation amount.

Feedback correction of the air-fuel ratio in such a case, but it goes in the step of activation of the warm-up completion O ₂ detector prior to the O ₂ sensor, such warming-up is output response than the reverse turn toward the thickening of the reverse turn of the lean side in the O ₂ detector prior to completion Because of this delay, it is known that the average air-fuel ratio shifts to the lean side to increase the NOx emissions, and the average value of the air-fuel ratio is returned to the theoretical air-fuel ratio by making the initial value of the reversal on the lean side larger than the initial value of the reversal on the dense side. In doing so, it lowers NOx emissions.

However, as for the three-way catalyst itself, as shown in FIG. 13, it is preferable that the required air fuel ratio is on the lean side before the three-way catalyst is warmed up in order to reduce the HC emission. However, since the above-described preliminary device does not take into account the characteristics of the three-way catalyst of FIG. 13, even though the NOx emission can be lowered, the HC emission cannot be lowered.

Therefore, the present invention adds a correction value at the time of warm-up determined by the equivalent value of the temperature of the exhaust system at start-up and the time after start-up to the step value set in the active state of the three-way catalyst, and from the start of the feedback correction of the air-fuel ratio. O until the warm-up completion of the _second detector to control the average value of the air-fuel ratio to move to the side of the dense offset the movement lean due to warm-up the lack of the O ₂ sensor, and the warm-up completion of the three-way catalyst from the warm-up completion of the O ₂ sensor lean average air-fuel ratio by By controlling by the side, it aims at reducing HC emissions in the range which does not increase NOx emissions very much.

[Means for solving the problem]

The present invention provides an O ₂ detector 31 located in an exhaust pipe upstream of a three-way catalyst and means 32 for initiating feedback correction of the air-fuel ratio at the timing of activation of such O ₂ detector, as shown in FIG. Means (33) for determining whether the air-fuel ratio is on the dense side and the lean side based on the output of the O ₂ detector at the start of feedback correction, and means for determining whether to invert the lean side or the dense side from the determination result. (34), and means 35 for calculating the step value matched to the active state of the three-way catalyst at the time of inversion from these two determination results in accordance with the operating conditions, and at the time of inversion from the two determination results. The means 36 for calculating the integral value I, the means 37 for measuring the elapsed time Ta from the start-up time, and the initial value PSLO of the amount of correction at the time of warming up during inversion to the lean side are concentrated on the dense side. Of The exhibition I is greater than the initial value (PSRO) of the correction amount of the origin and the lean reduction of reverse Application of the side (△ P _SL) is to be greater than the reduction rate (△ P _SR) of the inverting Application of the side of the dense reverse Application of the side of the lean Lean so that the ratio (ΔP _SL / ΔP _SR ) of the reduction rate of the reversal to the dense side is greater than the ratio of the initial value of the reversal to the lean side and the initial value of the reversal to the dense side (PSLO / PSRO). The initial value (PSLO) and the reduction rate (ΔP _SL ) at the time of reversal to the side and the initial value (PSRO) and the reduction rate (ΔP _SR ) at the time of reversal to the dense side are respectively equivalent values of the exhaust temperature at start-up (for example, cooling water temperature). Means 38 for setting according to Tw), the initial value PSLO and the reduction rate ΔP _SL at the time of inversion to the lean side thus set, and the elapsed time Ta from the start-up after starting from the initial value PSLO. Decrease value with time The inverting Application of lean side I from the correction amount (PSL) to samgo initial value (PSRO) of the inverting trial toward the thickening of the origin and the reduction rate (△ P _SR) and the elapsed time initial value (PSRO) in (Tas) from the time of the start-up The means 39 for calculating the value of decreasing with the passage of time after starting as the correction amount PSR at the time of inversion to the dense side, respectively, and the correction amount values PSL and PSR at the time of the warming up of the three-way catalyst Means 40 for discriminating and calculating the step value PL for inversion to the lean side and the step value PR for inversion to the dense side by adding to the step value set in the active state, and the step calculated in this manner Using the values PL and PR, the phase value PL for reversing to the lean side is used as the renewal amount, and the phase value PR for reversal to the dense side is renewed for the reversal to the dense side. Quantity, except for this reversal Means 41 for calculating the feedback correction amount α of the air-fuel ratio by using the integral value I as a renewal amount, and correcting the basic injection amount Tp according to the operating conditions in the feedback correction amount α of the air-fuel ratio. Means 42 for calculating the injection amount and an apparatus 43 for supplying fuel of this injection amount to the intake pipe were provided.

[Action]

When the clamp condition is cleared and the air-fuel ratio feedback control starts at the time when the O ₂ detector 31 is activated after the cooling start, the value according to the considerable value of the temperature of the exhaust system is set as an initial value and decreases with time elapsed from the initial value. This value is used as the correction amount at the time of warming up and is added to the step value set in the active state of the exhaust system.

As the step value increases at low water temperature, the amplitude of the air-fuel ratio is increased according to the amount of correction at the time of warming, thereby reducing the reduction of the conversion efficiency of the catalyst due to the supply delay of the fuel in the intake port.

In addition, the exhaust system is in an active state because the temperature rises with the time elapsed from the start time, but when the amount of correction at the time of turbulence decreases gradually in accordance with the temperature rise of the exhaust system, the correction according to the turbulence state of the exhaust system is insufficient. Is done.

In addition, if the correction amount at the time of warming up is also applied at the time of hot restarting, the exhaust performance will be better than when the correction amount at the time of warming up is not applied. Since hot water temperature is high enough during hot restart, there is no supply delay of fuel in the port, but the conversion efficiency of the catalyst decreases due to the decrease in temperature of the exhaust system. Will be.

The initial value of the amount of correction at the time of inversion at the time of inversion to the lean side, with respect to the initial value and the reduction rate which respectively set the amount of correction (PSL) at the time of inversion to the lean side and the amount of correction (PSR) at the time of inversion to the dense side. (PSLO) is larger than the initial value (PSRO) of the correction amount at the time of reversal at the dense side, and the reduction rate (ΔP _SL ) at the time of inversion to the lean side is greater than the reduction rate (ΔP _SR ) at the time of reversal to the dense side, and toward the lean side. So that the ratio of the decrease rate at the time of reversal to the reverse side to the dense side (ΔP _SL / ΔP _SR ) is greater than the ratio of the initial value at the time of reversal to the lean side and the initial value at the time of reversal to the dense side (PSLO / PSRO). When it is set according to the equivalent value of the exhaust temperature at the start-up, the degree of the correction amount (PSL) at the time of reversal to the first lean side for the time after the start-up is the correction amount at the time of reversal at the time of reversal to the dense side (PSR). After the go is large, the PSR to the relationship of the two reversal is larger than PSL.

Accordingly, the average value of the air-fuel ratio is controlled in the dense direction to offset the lean movement due to the lack of turbulence of the O ₂ detector from the start of feedback correction of the air-fuel ratio to the completion of the turbulence of the O ₂ detector, and the three-way catalyst from the incomplete turbulence of the O ₂ detector. Up to the completion of the conversely, the lean side is controlled. If the average value is shifted in accordance with the required performance ratio of the three-way catalyst as well as the O ₂ detector, the NOx emission is not increased so much and the HC emission is drastically reduced.

EXAMPLE

In FIG. 2, 7 is an air flow meter which detects the amount of air inhaled from an air cleaner, 9 is an idle switch, and 10 is a reference of a signal and a crank angle, such as a unit crank angle. A crank angle sensor that outputs a signal such as a position (Ref signal), 11 is a water temperature sensor that detects the cooling water temperature (Tw) of the engine, and 12 is an O that rapidly changes the theoretical performance ratio to a threshold corresponding to the oxygen concentration in the exhaust gas. ₂ sensors, 13 are ignition switches, 14 are vehicle speed sensors, and the signals of these sensors are input to the microcomputer control unit 21.

Since the injection of fuel is supplied from one fuel supply device (4: injector) installed at the intake port, when the amount is increased or decreased, the amount adjustment is performed at the injection time by the controller. If the injection time is long, the injection amount is large, and if the injection time is short, the injection amount is small. The concentration of the mixer, that is, the air-fuel ratio, is biased toward the dense side when the fuel injection amount for a predetermined amount of intake air increases, and to the lean side when the fuel injection amount decreases.

Thus, if the basic injection amount of fuel is determined and sent so that the ratio with the intake air amount is constant, a mixer having the same air-fuel ratio is obtained even if the operating conditions are different. When fuel injection is performed once for one revolution of the engine 1, the basic injection pulse width (basic injection quantity equivalent) Tp (= K Qa / Ne, where K is an integer) is applied to the amount of air sucked in one revolution. Is obtained from the intake air amount Qa and the engine speed Ne. Usually, the air-fuel ratio determined by such Tp becomes the vicinity of theoretical performance ratio.

The exhaust pipe 5 is provided with a three-way catalyst 6 for treating three harmful components of CO, HC, and NOx discharged from the engine. Such three-way catalyst 6 can process three components at the same time only when the air-fuel ratio of the mixer supplied to the engine is in a narrow range centering on the theoretical performance ratio. Even if the air-fuel ratio is smaller than this range, the CO and HC emissions increase when the fuel is concentrated on the dense side. On the contrary, when the diesel fuel is lean, the NOx is emitted much.

Thus, the controller 21 feedback-compensates the fuel injection amount based on the output signal from the O ₂ detector so that the average value of the air-fuel ratio is maintained at the theoretical performance ratio capable of fully exhibiting the capability of the three-way catalyst 6.

If the output of the O ₂ detector 12 is higher than the equivalent slice level of the theoretical performance ratio, the air-fuel ratio is on the dense side and is on the lean side.

When the air-fuel ratio is reversed to the dense side than the determination result, the air-fuel ratio must be returned to the lean side. Therefore, as shown in the flowchart of FIG. 3, immediately after the air-fuel ratio is reversed to the dense side, the step value PR is subtracted from the feedback correction coefficient α of the air-fuel ratio, and the integral value IR from α until the air-fuel ratio is immediately reversed to the lean side. Remove (steps 2, 3, 7 and 2, 3, 9).

On the contrary, when the air-fuel ratio is reversed to the lean side, the stage value PL is added to α immediately after the inversion, and the starch value IL is added until the actual performance ratio is immediately reversed to the dense side (steps 2, 4 and 14). , Steps 2,4,12).

The operation of α is also Ref signal synchronous. This is true because fuel injection is Ref signal synchronous and system turbulence is Ref signal synchronous. Also, in the flowchart, “O ₂ ” is the output of the O ₂ detector, and “S / L” is at the slice level.

The values of the step values PR and PL are much larger than those of the integral values IR and IL. This is to give a large step value immediately after the air-fuel ratio is reversed to the dense side or the lean side to change the response to the opposite side. After the step change, the air-fuel ratio is gradually changed to the opposite side with a small integral value, thereby stabilizing the control.

Step values PR and PL are searched for a map using the basic injection pulse width (engine load equivalent weight) Tp and the engine speed Ne as parameters (FIG. 4 is a map of step values PR, and FIG. 5 is a map of step values PL). (Step 5 of FIG. 3, step 10).

In this case, as shown by comparing FIG. 4 and FIG. 5, the map values of PL and PR are different in some driving regions, and the degree of the map values of PL is larger than the map values of PR in the region.

This is because the output response of the O ₂ detector is different at the time of inversion to the dense side and at the inversion to the lean side in this operation region, and the response of the output of the sensor to the lean side as shown in FIG. 6 is delayed. This is because if the size of the map value is increased, the air-fuel ratio moves to the lean side and the average value of the air-fuel ratio cannot be maintained as the theoretical performance ratio. Thus, for in response to the output of hanhaeseoneun O ₂ sensor in some operating range of the response delay in the lean side portion at the time of inversion of the side of the level value map PR (lean (step value to be added at the time of inversion of the lean side) PL Larger than the map value of the step value).

Integral values IR and IL are given in proportion to the fuel injection pulse width (engine load equivalent weight) Ti to be described next (FIG. 3 shows steps 8 and 13).

IR = Ti × KIR ＃, IL = Ti × KIL ＃

However, KIR ＃ is constant and KIL ＃ is constant.

This is to make the amplitude of α almost constant regardless of the control cycle of α because the amplitude of α increases in the operating region in which the control period of α becomes large and exceeds the catalyst window.

The integral IR and IL values may be the same value (KIR '= KIL'). However, KIR 'and KIL' can be different. At this time, since the average value of the air-fuel ratio shifts to either the dense side or the lean side by the difference of the integral values, it is necessary to determine the respective map values of the PR and PL so as not to do so.

In this way, when the mixer becomes thinner than the mixer of theoretical air fuel, the fuel injection amount from the fuel supply device 4 is increased so as to become the theoretical air fuel ratio, and when it is darkened, the fuel injection amount from the fuel supply device 4 is repeated. .

7 is a routine for calculating the fuel injection pulse width Ti, which is executed every 10 ms (milliseconds).

Fuel injection pulse width Ti

Ti = Tp × COEF × α + Ts

Tp: Basic injection pulse width

COEF: Various correction factors

α: Feedback correction coefficient of performance ratio

Ts: Invalid pulse width

Calculate by The COEF includes an increase correction coefficient (Kas) and a temperature increase guarantee coefficient (Ktw) after starting. This is a well-known formula and content.

On the other hand, the controller 21 detects a change in the internal resistance of the detector and a change in the electromotive force since the current flows into the O ₂ detector when the temperature of the O ₂ detector 12 is low before and after the start-up, and the O ₂ detector 12 ), The internal resistance decreases as the temperature increases, and as the voltage of the O ₂ detector decreases as shown in FIG. 14, the slice level is also changed accordingly.

In this case, when the voltage of the O ₂ detector coincides with the slice level 1, it is determined that the O ₂ detector is activated, the clamp condition is canceled and feedback correction of the air-fuel ratio is started. Since the temperature rise of the exhaust system is faster than that of the cooling water temperature, feedback correction of the air-fuel ratio is started even at low water temperature when the clamp condition is released at the time of activation of the O ₂ detector.

However, at low water temperature, since the response delay of the fuel in the intake port becomes large, the step value set in the active state of the three-way catalyst becomes insufficient, and the demand value for the step value also changes as the warming of the three-way catalyst progresses. Also, the step value required for hot restart is different from when the catalyst is in the active state. Therefore, when the feedback correction of the air-fuel ratio uses the stage values (map values of FIG. 4 and FIG. 5) that are set in the active state of the catalyst from the start time, the conversion efficiency of the catalyst is inferior.

In order to cope with this, the controller 21 adds a correction amount at the time of turbulence to the step value which is set in the active state of the exhaust system rather than the timing of activation of the O ₂ detector. In such an example, the amount of correction at the time of reversal of a value that is different at the time of inversion to the dense side and at the time of inversion to the lean side (PSR is the amount of correction at the time of reversal at the time of inversion to the density side and PSL is the amount of correction at the time of reversal at the lean side) Since PSL is introduced to the lean side, the PSL is added to the map value of the PL, and at the time of inversion to the dense side, the PSR is added to the map value of the PR. In FIG. 3, each map value of PR and PL is input to an accumulator A, and the value of the accumulator A and the amount of correction (PSL or PSR) at the time of warming up are added (step 10 in FIG. 11, steps 5,6).

The correction amount (PSL, PSR) at the time of warming up is the initial value of the cooling water temperature at startup (representing the equivalent value of the temperature of the exhaust system at startup) as the initial value, and decreases with time after startup from this initial value. To give a value.

8 is a flowchart for calculating the correction amounts PSL and PSR during turbulence. In the drawing, when the ignition switch 13 is in the starting position, the table of the initial values of the correction amount at the time of warming up is displayed from the cooling water temperature Tw at that time, and the initial values (the initial values at the time of inversion to the lean side and the initial values at the time of inversion to the dense side) And input it into the corresponding PSL and PSR of the register (steps 31 to 33 of FIG. 8). PSL means the amount of correction at the time of inversion at the time of inversion to the lean side, and PSR is the amount of correction at the time of inversion at the time of inversion at the density side.

After the ignition switch is in the starting position, the correction amount (PSL, PSR) for each warm air is

PSL = PSL- △ P _SL * Tas (1)

PSR = PSR- △ P _SR * Tas (2)

Tas: elapsed time since startup

△ P _SL : PSL

ΔP _SR ; PSR

(Step 34,36, step 34,40 in FIG. 8), and when PSL0 or PSR0 is reached, PSL or PSR is set to 0 (step 37, 38, step 41, 42 in FIG. 8). Thereby, it decreases by a fixed amount ((DELTA) P _SL x Tas and (DELTA) P _SR xTas per control period according to the time after starting from the initial values PSLO and PSRO to zero. In addition, the reduction ratios ΔP _SL and ΔP _SR are values that determine the amount of decrease in the amount of correction during warming per one control period (If this value is increased, the amount of correction (PSL, PSR) in the warming decreases quickly. For example,% / s is used as a unit in the correction amount (PSL, PSR) at the time of warming up gradually.

When the characteristics of the initial values PSLO and PSRO are shown in FIG. 9 and the characteristics of the reduction ratios ΔP _SL and ΔP _{SR are} shown in FIG. 10, the initial values and the reduction rate are combined as the cooling water temperature Tw is low. Growing up. This is to prevent the decrease in the air-fuel ratio by increasing the step value as the water temperature becomes low because the supply delay of the fuel in the port becomes larger and the air-fuel ratio becomes smaller as the cooling water temperature Tw decreases.

However, since the rise characteristics from the start of the O ₂ detector 12 and the catalyst 6 vary depending on the system of the exhaust system of the engine, the initial values (PSLO, PSRO) of the correction amount at the time of warming up to a value suitable for each system are different. ) And the reduction rate (ΔP _SL , ΔP _SR ) need to be matched. Here moved toward until the warm-up completion of the O ₂ sensor from the time of the start of the feedback correction to the activation of the O ₂ detector to the average value of the air-fuel ratio dense, and the average value of the air-fuel ratio until the warm-up completion of the subsequent catalyst from the warm-up completion of the O ₂ sensor Conversely, set to move to the lean side.

Specifically, as shown in FIG. 9 and FIG. 10, PSLOPSRO, ΔP _SL ΔP _SR and ΔP _SL / ΔP _SR PSLO / PSRO are used. Where ΔP _SL / ΔP _SR is the rate of reduction and PSLO / PSRO is the rate of initial value, and the degree of reduction rate is greater than the initial value, so that as time is increased after starting, as shown in FIG. The degree of the correction amount PSR at the time of turbulence for trial is made larger than the correction amount PSL at the time of reversal at the time of inversion to the lean side.

First of all, to warm-up to the completion of the O ₂ sensor, the average value of the air-fuel ratio moves toward the thickening is that the response of the O ₂ sensors corresponding to the other with the reverse turn of the lean side. O ₂ sensor is lean, and when the reverse of the side of the dense during the after activation because yet I have output response than when the reverse of the side of the state group did not complete the degree at the time of inversion of the lean side dense delay the warm-up of this O ₂ sensor shortage It is known that the average of the air-fuel ratio shifts to the lean side as shown in FIG. 12 when the feedback correction of the air-fuel ratio is performed using the correction amount at the time of reversal to the side (that is, PSR = PSL). This increases the emissions of NOx. Therefore, in terms of exhaust performance, the average value of the air-fuel ratio must be controlled to move to the dense side before the O ₂ detector is completed in turbulence, and the lean shift described above must be canceled out.

On the other hand, the reason why the average value of the air-fuel ratio is shifted to the lean side from the warming up of the O ₂ detector to the warming up of the three-way catalyst is to match the state of the three-way catalyst before the warming up this time. Since the operation efficiency of HC becomes low with respect to the three-way catalyst before warming-up, as a required air fuel ratio, it is so preferable that it exists in a lean side like FIG.

Here, the lean shift due to the lack of turbulence of the O ₂ detector shown in FIG. 12 appears to match the characteristics of the required air-fuel ratio shown in FIG. 13, but the lean shift shown in FIG. It is much more lean than the required air-fuel ratio shown, and as explained above, it is necessary to offset the lean movement by controlling in the dense direction before the O ₂ detector is completed.

The operation of this example will be described with reference to FIG.

If the clamp condition of air-fuel ratio is canceled and the feedback correction of air-fuel ratio starts after the O ₂ detector is activated after cold start, the value according to the coolant temperature Tw is set as the initial value (PSRO, PSLO), The value which decreases together is added to the map values of PL and PR as correction amounts (PSL, PSR) at the time of turbulence.

If the step value increases at low water temperature by the correction amounts PSL and PSR during turbulence, the amplitude of the air-fuel ratio increases by that amount, thereby preventing a decrease in the conversion efficiency of the catalyst accompanying the supply delay of the fuel in the intake port. In addition, the catalyst and its temperature rise with the time elapsed from the start-up to reach an active state. However, if the correction amount at the time of warming decreases gradually in accordance with the temperature rise of the catalyst, the correction according to the warming state of the catalyst is not sufficient. Is done. For example, if the correction amount at the time of turbulence equal to the initial value (PSRO, PSLO) is continued, the overcorrection becomes close to the active state, but this does not occur.

In this way, the correction amount (PSL, PSR) at the time of warming up is given according to the cooling water temperature Tw at the start-up and the elapsed time Tas after the start-up, taking into account the supply delay caused by the fuel in the port, and controlling the air-fuel ratio according to the temperature rise of the catalyst. It is possible to improve the exhaust performance sufficiently even after starting. In addition, in the case of hot restarting, if the correction amount (PSL, PSR) at the time of warming up is added as in this example, the exhaust performance is better than when the correction amount at the time of warming up is not added. At the time of hot restart, the cooling water temperature is high enough so that there is no supply delay of fuel in the port. It can be improved.

In addition, PSLOPSRO, ΔP _SL ΔP _SR, and ΔP _SL / ΔP _SR PSLO / PSRO are satisfied for the values (initial value and decrease rate) that set the correction amount (PSL, PSR) during warming up. With respect to time, the degree of correction at the time of turbulence at the time of inversion on the lean side becomes larger than the amount of correction at the time of turbulence at the time of inversion on the dense side (PSR), and later, the relationship between the two is reversed, and the degree of PSR is reversed. It will be larger than PSL. As such, and the average value of the air-fuel ratio control as dense to compensate for a lean movement due to warm-up the lack direction of O ₂ sensor until the warm-up completion of the O ₂ sensor from the start of the feedback correction of the air-fuel ratio, the three-from the warm-up completion of the O ₂ sensor Up to the completion of the turbulence of the catalyst is reversely controlled on the lean side. In this way, if the average value of the air-fuel ratio is shifted in accordance with the required performance ratio of the three-way catalyst as well as the O ₂ detector, as shown in the table in Fig. 15, the HC emissions are greatly increased without increasing the NOx emissions in the absence of this control (○ table). Can be reduced. For reference, Fig. 15 shows the case where the average value of the air-fuel ratio was continuously controlled in the dense direction from the start of the feedback correction of the air-fuel ratio to the completion of the catalyst warm up. In this case, the NOx emissions could be reduced. HC emissions do not change.

By the way, the target air fuel ratio is changed to the dense side immediately after starting by the continuation which decreases with time after starting from the initial value according to the cooling water temperature at the time of starting (refer to Unexamined-Japanese-Patent No. 60-209646). This is to stabilize the combustion at low water temperature by moving the target fuel ratio to the dense side rather than the theoretical fuel ratio, and corresponds to the contents of the increase correction coefficient Kas and the temperature increase coefficient Ktw after starting as described above. On the other hand, this invention makes the conversion efficiency of a three-way catalyst to the maximum to the last, and is different from the point of being near the theoretical performance ratio from the average value of air fuel ratio.

In addition, the air-fuel ratio is detected by the wide-area air fuel ratio detector, and the target performance ratio is set from the theoretical performance ratio to a lean (target performance ratio = 17-18) by the engine from the time of activation of the air-fuel ratio detector to the completion of the warming up of the three-way catalyst. In some cases, HC emission is lowered, and after completion of the three-way catalyst turbulence, the target performance ratio is returned to the theoretical performance ratio and feedback correction of the performance ratio is performed (see Japanese Patent Application Laid-Open No. 4-41950). In this case, the HC can be reduced by 50% by setting the target performance ratio to lean between the time of activation of the air-fuel ratio detector and the completion of the three-way catalyst warm-up, and the performance during the cold air immediately after the low-temperature startup (engine cooling). As the ratio is set to lean, engine rotation becomes unstable and poor driving performance. On the contrary the time that O ₂ sensor is activated, the three-way catalyst has already been in part (catalyst center) is enabled, and because the conversion efficiency has reached 60% or more by performing the feedback correction of the air-fuel ratio at the time by the present application and the O ₂ sensor activation 3 By operating the raw catalyst, the overall harmful emissions can be lowered to 40% or less, and since the air-fuel ratio is a theoretical performance ratio even in the cold air immediately after the low temperature startup, the engine rotation is unstable.

[Effects of the Invention]

According to the present invention, the initial value of the amount of correction at the time of reversal at the lean side is greater than the initial value of the amount of correction at the time of reversal at the dense side, and the reduction rate of the reversal at the lean side is greater than the reduction rate of the reversal at the lean side. The initial value and the reduction rate of the reverse application to the lean side and the initial value and the reduction rate of the reversal application to the lean side are respectively increased so that the ratio of the reduction rate of the reverse application to the side and the reduction rate to the dense side is larger than the ratio of the initial value to the lean side. It is set according to the exhaust temperature equivalent value after starting, and the value that decreases with the elapsed time from the initial value from the initial value and the reduction rate and the elapsed time from starting from the initial value at the time of inversion to the lean side thus set is the turbulence at the time of inversion to the lean side. The initial value and the value for reversal to the dense side are calculated with the correction amount of The rate and the time elapsed after starting from the initial value than the elapsed time from starting are calculated as the amount of correction in turbulence for inversion to the dense side, and the amount of correction in turbulence is adjusted in the active state of the three-way catalyst. In addition, the step value for inversion to the lean side and the step value for inversion to the dense side are calculated and added, and the step value for inversion to the lean side is renewed at the time of inversion to the lean side using the calculated step value. When the reversal to the dense side is carried out, the step value for reversal to the dense side is set to the renewal amount. Except for this reversal, the integral correction value is used to calculate the feedback correction amount of the air-fuel ratio. It is possible to control the air-fuel ratio according to the temperature rise of the exhaust system. After that, it is possible to addition to being able to sufficiently improve the exhaust performance at the same time hot retry also can improve the conversion efficiency of the catalyst and reduce the HC emissions drastically without having to much increase the NOx emissions.

Claims (1)

And the O ₂ sensor which is located upstream of an exhaust pipe of a three-way catalyst, an output of the O ₂ sensor from the time of activation of this O ₂ sensor from the time of means for starting the feedback correction of the air-fuel ratio, and the start of the feedback correction of such air-fuel ratio Means for determining whether the air-fuel ratio is on the dense side and the lean side; and means for determining whether the inverted side is inverted to the lean side or the dense side from the determination result, and a three-way catalyst at the time of inversion from these two determination results. Means for calculating the step values set in the active state according to the operating conditions, means for calculating the integral value (I) except for the inversion at the two determination results, and elapsed time (Tas) from the start time. The initial value (PSRO) of the correction amount at the time of reversal at the time of reversal to the lean side, and the initial value (PSRO) of the correction amount at the time of reversal at the time of reversal to the dense side The larger reduction ratio of the reverse Application of the side of the lean (△ P _SL) ratio of the reduction ratio of the reverse Application of the side of the reduction rate of the reverse Application of the side of the dense (△ P _SR) than becomes large rate of decrease of the reverse Application of the side of the lean and dense (ΔP _SL ΔP _SR ) is larger than the ratio (PSLO / PSRO) of the initial value for the reversal to the lean side and the reversal to the dense side, and the initial value (PSLO) and the reduction rate (ΔP _SL ) for the reversal to the lean side. ) And means for setting the initial value (PSRO) and the reduction rate (ΔP _SR ) at the time of reversal to the dense side according to the exhaust temperature equivalence value at the start, respectively, and the initial value (PSLO) and the reduction rate (△ P _SL ) and a value that decreases with the time elapsed after starting from the initial value PSLO than the elapsed time Ta from the start as the correction amount PSL for warming up on the lean side, and is reversed to the dense side. city At the time of reversal at the time of reversal to the dense side, the value which decreases with the initial value PSRO and the reduction rate (ΔP _SR ) of the dragon and the time elapsed after starting from the initial value PSRO than the elapsed time Tas from the start time. A means for calculating each of the correction amounts PSR, and the correction values PSL and PSR during turbulence are added to the step values set in the active state of the three-way catalyst, and the step values PL and dense at the time of inversion to the lean side. Means for distinguishing and calculating the step value PR for inversion to the side) and the step value for inversion to the lean side in the inversion to the lean side using the step values PL and PR calculated in this manner. ) Is used as the renewal amount, and when reversing to the dense side, the step value (PR) for reversal to the dense side is used as the renewal amount, and the integral value (I) is used as the renewal amount except for this reversal. Means for calculating the correction amount α, The air-fuel ratio of an engine characterized by providing a fuel injection amount by correcting the basic injection amount Tp according to the operating conditions by the feedback correction amount α of the air-fuel ratio, and a device for supplying fuel of this injection amount to the intake pipe. Control unit.