JP2006037875A - Engine air-fuel ratio control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set proper limit values of a feedback correction amount and allow maintaining satisfactory air-fuel control for a period from when an engine is operated at a rich air-fuel ratio immediately after start and then air-fuel ratio feedback control is started to when the air-fuel ratio is made converge to a stoichiometry point. <P>SOLUTION: A rich part of a target air-fuel ratio correction factor TFBYA is gradually reduced after start and activity of an O2 sensor is judged. The rich part is then substituted for an increment in an air-fuel feedback correction factor ALPHA and the air-fuel ratio feedback control is started. The upper and lower limit values αmax, αmin of the air-fuel feedback correction factor ALPHA are simultaneously set by setting a correction factor ALPHA0 at the time of starting the air-fuel ratio feedback control as the basis and setting initial values at a value smaller by a predetermined amount than the basis and at a value larger by a predetermined mount than the basis and by reducing them by the same amount with an integral value of the air-fuel feedback control one by one until the limit values ALPMAX, ALPMIN corresponding to the stoichiometry air-fuel ratio are gotten. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control device for an engine, and more particularly, to perform control without trouble after operating at a rich air-fuel ratio immediately after starting, and thereafter starting air-fuel ratio feedback control until it converges to a stoichiometric point. It relates to the technology that made it possible.

Patent Document 1 discloses that an air-fuel ratio sensor is set with a target air-fuel ratio correction coefficient TFBYA that is set so as to enrich the air-fuel ratio immediately after startup and gradually converge the air-fuel ratio to stoichiometric with time, and an air-fuel ratio feedback control condition. In the engine air-fuel ratio control apparatus for calculating and controlling the fuel injection amount using the air-fuel ratio feedback correction coefficient ALPHA set so as to converge the air-fuel ratio to stoichiometric based on the signal from It is disclosed that after the detection, the amount of increase by the target air-fuel ratio correction coefficient TFBYA is set to 0, and the increase is added to the air-fuel ratio feedback correction coefficient ALPHA, and then the control proceeds to air-fuel ratio feedback control.
JP 2001-23479A

  In the air-fuel ratio feedback control, if the air-fuel ratio feedback correction coefficient becomes too large or too small for some reason, it becomes excessively rich or lean, and the drivability and exhaust purification performance are impaired. Therefore, in order to prevent this, the upper and lower limit values of the air-fuel ratio feedback correction coefficient (feedback correction amount) are set so as not to become excessive.

  However, when performing the air-fuel ratio control at the start as shown in Patent Document 1, the upper and lower limit values are corrected with respect to the feedforward control amount corresponding to the target air-fuel ratio (generally the theoretical air-fuel ratio). Since it is set as a fixed value based on a feedback correction amount that is not made (for example, 1.0 when set as a correction coefficient multiplied by the feedforward control amount), the following problems occur.

  In other words, if the air-fuel ratio feedback control is started in a state where the air-fuel ratio sensor is active and the rich amount by the target air-fuel ratio correction coefficient TFBYA is large, the increase amount by the target air-fuel ratio correction coefficient TFBYA is empty. The value converted to the fuel ratio feedback correction coefficient ALPHA may exceed the upper limit value. In this case, the initial value of the converted air / fuel ratio feedback correction coefficient ALPHA is limited by the upper limit value. As a result, the torque level difference is generated and the drivability and the exhaust purification performance are deteriorated (see the comparative example in FIG. 6).

Further, if the air-fuel ratio feedback correction coefficient ALPHA is reduced to the lower limit value for some reason, there is a concern that the engine may be excessively leaned and misfired.
In view of such a conventional problem, the present invention appropriately sets the limit value of the feedback correction amount immediately after the start of the air-fuel ratio feedback control, thereby appropriately limiting the feedback correction amount, thereby improving the drivability, exhaust The purpose is to maintain good purification performance.

  For this reason, the present invention provides the air-fuel ratio feedback control after the start-up and after the air-fuel ratio sensor is activated and after the air-fuel ratio feedback control based on the output of the air-fuel ratio sensor is started until the air-fuel ratio converges to the stoichiometry. Based on the feedback correction amount corresponding to the air-fuel ratio state at the start, the limit value of the feedback correction amount until the air-fuel ratio converges to the stoichiometric is set.

  According to the present invention, even when the amount of rich increase when the air-fuel ratio feedback control is started in the air-fuel ratio rich state is large, the upper limit value is set based on the feedback correction amount at the start of the air-fuel ratio feedback control. Therefore, without being limited by the upper limit value, it is possible to smoothly converge to stoichiometry by air-fuel ratio feedback control without causing a torque step due to insufficient increase, and maintain good operability and exhaust purification performance. be able to.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine (internal combustion engine) showing an embodiment of the present invention.
Air is sucked into the combustion chamber of each cylinder of the engine 1 from the air cleaner 2 through the intake duct 3, the throttle valve 4, and the intake manifold 5. Each branch portion of the intake manifold 5 is provided with a fuel injection valve 6 for each cylinder. However, the fuel injection valve 6 may be disposed directly in the combustion chamber.

  The fuel injection valve 6 is an electromagnetic fuel injection valve (injector) that opens when the solenoid is energized and closes when the energization is stopped, and a drive pulse signal from an engine control unit (hereinafter referred to as ECU) 12 described later. The fuel is energized to open the valve, and the fuel is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator. Therefore, the fuel injection amount is controlled by the pulse width of the drive pulse signal.

Each combustion chamber of the engine 1 is provided with a spark plug 7, which sparks and ignites and burns the air-fuel mixture.
Exhaust gas from each combustion chamber of the engine 1 is discharged through an exhaust manifold 8. Further, an EGR passage 9 is led out from the exhaust manifold 8, whereby a part of the exhaust is recirculated to the intake manifold 5 via the EGR valve 10.

On the other hand, an exhaust purification catalyst 11 is provided in the exhaust passage so as to be positioned immediately below the exhaust manifold 8.
The ECU 12 includes a microcomputer that includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, receives input signals from various sensors, performs arithmetic processing as described later, and performs fuel injection. 6 is controlled.

  The various sensors include a crank angle sensor 13 that can detect the engine rotational speed Ne together with the crank angle based on the crankshaft or camshaft rotation of the engine 1, an air flow meter 14 that detects the intake air amount Qa in the intake duct 3, and a throttle valve. 4 includes a throttle sensor 15 (including an idle switch that is turned on when the throttle valve 4 is fully closed), a water temperature sensor 16 that detects the cooling water temperature Tw of the engine 1, and an exhaust manifold 8. An O2 sensor 17 is provided as an air-fuel ratio sensor that outputs a signal corresponding to the rich / lean exhaust air-fuel ratio. The O2 sensor 17 has a built-in heater, and early activation can be achieved by energizing the heater from the start and increasing the element temperature. A signal is also input to the ECU 12 from the start switch 18 and the like.

FIG. 2 is a flowchart of a fuel injection amount calculation routine executed by the ECU 12 in time synchronization or rotation synchronization after the engine is started (after the start switch is turned ON → OFF). The starting fuel injection amount is calculated by another method.
In S1, the intake air amount Qa detected by the air flow meter and the engine rotational speed Ne detected by the crank angle sensor are read. The intake air amount Qa is smoothed based on the detection signal, but is omitted in the flow.

In S2, a basic fuel injection amount (basic injection pulse width) Tp is calculated from the intake air amount Qa and the engine rotational speed Ne by the following equation.
Tp = K × Qa / N where K is a constant.
In S3, the target air-fuel ratio correction coefficient (post-startup air-fuel ratio enrichment correction coefficient) TFBYA and air-fuel ratio feedback correction coefficient ALPHA set as described later are read, and the final fuel injection amount (injection pulse width) is calculated by the following equation. Calculate Ti.

Ti = Tp × TFBYA × ALPHA
Both the target air-fuel ratio correction coefficient TFBYA and the air-fuel ratio feedback correction coefficient ALPHA have a reference value (a stoichiometric equivalent value) of 1.
In addition, the calculation of the fuel injection amount (injection pulse width) Ti includes a transient correction based on the change in the throttle opening TVO and the addition of the invalid injection pulse width based on the battery voltage. did.

When the fuel injection amount Ti is calculated, a drive pulse signal having a pulse width corresponding to Ti is output to the fuel injection valve 6 at a predetermined timing for each cylinder in synchronism with engine rotation, and fuel injection is performed. .
Next, setting of the target air-fuel ratio correction coefficient (post-startup air-fuel ratio enrichment correction coefficient) TFBYA and air-fuel ratio feedback correction coefficient ALPHA will be described.

FIG. 3 is a flowchart showing the flow of the air-fuel ratio control after the start executed by the ECU 12, whereby the target air-fuel ratio correction coefficient TFBYA and the air-fuel ratio feedback correction coefficient ALPHA after the start are set.
In S11, the water temperature Tw at the time of starting is detected, and the initial value KAS of the post-starting increase rate and the subsequent unit decrease rate ΔK are set accordingly (see the following equation).

KAS = f1 (Tw)
ΔK = f2 (Tw)
Specifically, the initial value KAS of the post-starting increase rate is set to be larger as the starting water temperature Tw is lower, and the unit decreasing rate ΔK is set to be smaller so that the amount of water decreases over time as the starting water temperature Tw is lower. .

In S12, the target air-fuel ratio correction coefficient TFBYA is set based on the post-startup increase rate KAS, and the air-fuel ratio feedback correction coefficient ALPHA is fixed to 1 (see the following equation).
TFBYA = 1 + KAS
ALPHA = 1
The set value here is used to calculate the first fuel injection amount Ti after start-up, and the air-fuel ratio is enriched by the target air-fuel ratio correction coefficient TFBYA.

Thereafter, in S13, the post-startup increase rate KAS is decreased by the unit decrease rate ΔK by time synchronization (KAS = KAS−ΔK), and the target air-fuel ratio correction coefficient TFBYA is set based on the decreased post-startup increase rate KAS. By calculating (TFBYA = 1 + KAS), the target air-fuel ratio correction coefficient TFBYA is decreased. However, KAS ≧ 0 and TFBYA ≧ 1.
In S14, it is determined whether the O2 sensor is activated. As a specific activation determination method, it is determined that a predetermined time has elapsed after the output voltage VO2 of the O2 sensor exceeds a predetermined rich-side activation determination slice level RSL. If NO, the process proceeds to S13. Returning, the target air-fuel ratio correction coefficient TFBYA is decreased.

Therefore, by setting the target air-fuel ratio correction coefficient TFBYA, it is possible to enrich the air-fuel ratio immediately after startup and gradually converge the air-fuel ratio to stoichiometric with the passage of time thereafter.
If it is determined that the O2 sensor is activated, the process proceeds from S14 to S15 in order to start air-fuel ratio feedback control based on the output of the O2 sensor.

In S15, the amount of increase (KAS) by the target air-fuel ratio correction coefficient TFBYA is cut, here, 0, and the amount of increase (KAS) is added to the air-fuel ratio feedback correction coefficient ALPHA.
In particular,
TFBYA = 1
ALPHA = 1 + KAS
And operate.

With the air-fuel ratio feedback correction coefficient ALPHA as an initial value, air-fuel ratio feedback control by PI control using a proportional component P and an integral component I is started as described later.
FIG. 4 is a flowchart of a routine for setting a limit value of the feedback correction amount (air-fuel ratio feedback correction coefficient ALPHA) in the air-fuel ratio feedback control according to the present invention.

In S21, whether the initial value ALPHA0 of the air-fuel ratio feedback correction coefficient ALPHA0 set when it is determined that the O2 sensor is activated is larger than the normal upper limit value ALPMAX set with the stoichiometric air-fuel ratio as a reference. Determine.
If it is determined in S21 that ALPHA0 ≦ ALPMAX, there is no torque step because the torque limit is not limited by the upper limit value ALPMAX, so the routine proceeds to S22, where the upper limit value αmax and the lower limit value αmin are set to the stoichiometric air-fuel ratio. It is set equal to the upper limit value ALPMAX and the lower limit value ALPMIN set as the reference.

When it is determined in S21 that ALPHA0> ALPMAX, the process proceeds to S23, and the initial value ALPHA0, that is, the initial value αmax (0) of the upper limit value and the lower limit value with reference to the feedback correction amount at the start of the air-fuel ratio feedback control, αmin (0) is set as follows.
αmax (0) = ALPHA0 + K
αmin (0) = ALPHA0-K
Here, K is set to the value (= 1, 100%) of the air-fuel ratio feedback correction coefficient ALPHA corresponding to the feedback correction amount 0 at the stoichiometric air-fuel ratio with reference to the initial value ALPHA0 of the air-fuel ratio feedback correction coefficient ALPHA. On the other hand, it is set as a value for a predetermined ratio (for example, 0.25, 25%), αmax (0) (= 1.25, 125%), αmin (0) (= 0.75, 75%) To do.

After the initial values αmax (0) and αmin (0) of the upper limit value and the lower limit value are set as described above, the process proceeds to S24 and air-fuel ratio feedback control is started.
In S25, at the same cycle as the execution cycle of the air-fuel ratio feedback control, the upper limit value and the lower limit value are subtracted from the previous value (the initial value is the initial value) by a predetermined value as shown in the following equation. Update.

αmax (n) = αmax (n−1) −IID
αmin (n) = αmin (n−1) −IID
Here, the predetermined value IID is set to the same value as the integral I in the air-fuel ratio feedback control.
In S26, it is determined whether the upper limit value αmax (n) is smaller than the upper limit value ALPMAX set with reference to the stoichiometric air-fuel ratio. If αmax (n) ≧ ALPMAX, the process returns to S25 to return to the upper limit value. The limit values αmax (n) and αmin (n) are decreased, and when it is determined that αmax (n) <ALPMAX, the process proceeds to S27.

In S27, αmax (n) = ALPMAX and αmin (n) = ALPMIN are set.
Here, since the predetermined value IID for decreasing the limit value is set to the same value as the integral I in the air-fuel ratio feedback control, while the air-fuel ratio is in the rich state, the air-fuel ratio during the air-fuel ratio feedback control is set. The limit value decreases by the same amount as the feedback correction coefficient ALPHA, and reaches ALPMAX, αmin (n) = ALPMIN during normal air-fuel ratio feedback control. That is, an upper limit value and a lower limit value that are larger by an equal amount up and down around the ALPHA when controlled along the target rich increase amount gradually decreasing characteristic are appropriately set.

In addition, it is good also as a structure which sets the upper / lower limit limit value on the basis of the feedback correction amount at the time of the start of air-fuel ratio feedback control, without performing determination by S21.
FIG. 5 is a flowchart of a routine executed in time synchronization in the air-fuel ratio feedback control.
In S31, lean / rich is determined based on the O2 sensor output.

  In the case of lean, the process proceeds to S32, and it is determined whether or not the inversion from rich to lean (previous rich). In the case of reversal from rich to lean, the process proceeds to S33, where the air-fuel ratio feedback correction coefficient ALPHA is increased by a proportionally proportional proportion (proportional constant) P and updated (ALPHA = ALPHA + P). When the lean state is continuing, the routine proceeds to S34, where the air-fuel ratio feedback correction coefficient ALPHA is increased by a minute integral (integral constant) I and updated (ALPHA = ALPHA + I).

In S35, the air-fuel ratio feedback correction coefficient ALPHA updated in S33 or S34 is compared with the upper limit value αmax, and when ALPHA ≦ αmax is determined, the updated ALPHA is output as it is in S42, but ALPHA> When αmax is determined, ALPHA is limited to αmax at S36, and then the ALPHA limited at S42 is output. When rich is determined at S31, the process proceeds to S37, and when lean to rich is reversed (previous time). Lean). In the case of reversal from lean to rich, the process proceeds to S38, and the air-fuel ratio feedback correction coefficient ALPHA is reduced by a proportionally set amount P and updated (ALPHA = ALPHA-P). When the rich state is continuing, the process proceeds to S39, and the air-fuel ratio feedback correction coefficient ALPHA is decreased by a minute integral I and updated (ALPHA = ALPHA-I).

In S40, the air-fuel ratio feedback correction coefficient ALPHA updated in S38 or S39 is compared with the lower limit value αmin, and when ALPHA ≧ αmin is determined, the updated ALPHA is output as it is in S42, but ALPHA < When it is determined that αmin, in S41, ALPHA is limited to αmin, and then the ALPHA limited in S42 is output. Here, as described above, the air-fuel ratio feedback control is started in the air-fuel ratio rich state, and ALPHA Normal air-fuel ratio feedback control that increases / decreases the ALPHA while the O2 sensor output periodically repeats rich / lean inversion after the O2 sensor output is inverted to lean determination after decreasing by the integral I, and converges to stoichiometric. Transition.

FIG. 6 shows a state in which the air-fuel ratio control after the start is performed using the upper and lower limit values as described above, and the control is performed according to the target rich increase amount gradually decreasing characteristic.
By setting the target air-fuel ratio correction coefficient TFBYA, control is performed so that the air-fuel ratio is enriched immediately after start-up and the air-fuel ratio is gradually converged to stoichiometric with the passage of time thereafter.
When the predetermined time has elapsed after the output of the O2 sensor exceeds the rich-side activity determination slice level RSL and the activity of the O2 sensor is detected, the increase amount (KAS = KAS1) by the target air-fuel ratio correction coefficient TFBYA is set to zero. At the same time, the increased amount (KAS = KAS1) is added to the air-fuel ratio feedback correction coefficient ALPHA to start the air-fuel ratio feedback control.

Prior to the start of air-fuel ratio feedback control, the initial values αmax (0) and αmin (0) of the upper and lower limit values are set as described above with reference to the initial value ALPHA0 of the air-fuel ratio feedback correction coefficient at the start. Therefore, the air-fuel ratio feedback control is started without being limited to the upper and lower limit values.
Thereafter, while the detected air-fuel ratio is in a rich state, the air-fuel ratio feedback correction coefficient ALPHA decreases by an integral amount I, but the upper and lower limit values αmax and αmin also decrease by the same amount IID. Control is performed without being limited to the limit values αmax and αmin, and when the limit values αmax and αmin decrease to ALPMAX and ALPMIN, the values are thereafter fixed at ALPMAX and ALPMIN.

  Here, when the limit values αmax and αmin decrease to ALPMAX and ALPMIN, if the detected air-fuel ratio continues to be rich, ALPHA decreases to a stoichiometric value (= 1), and the fuel injection amount decreases. It is controlled to an equivalent value. When ALPHA further decreases and the actual air-fuel ratio is made leaner than stoichiometric, the O2 sensor output is judged to be lean, a proportional amount P is added to ALPHA, and thereafter, the O2 sensor output is periodically rich / lean inverted. The routine proceeds to normal air-fuel ratio feedback control to increase or decrease ALPHA while repeating the above. Note that, even if the fuel injection amount is controlled to a stoichiometric equivalent value due to variations in the fuel injection amount characteristic by the fuel injection valve and the intake air flow rate detection characteristic of the air flow, the actual air-fuel ratio causes an error with respect to the stoichiometry, so the O2 sensor There is a difference in the timing at which the output is first determined to be lean, that is, the normal air-fuel ratio feedback control start timing. Therefore, air-fuel ratio learning for correcting the air-fuel ratio error is generally performed at the time of air-fuel ratio feedback control. Therefore, if ALPMAX and ALPMIN are corrected and set by the air-fuel ratio learning value, normal air-fuel ratio feedback is performed. Deviation deviation between ALPHA and limit values αmax and αmin at the control start time can be suppressed.

  FIG. 7 shows a state where the actual air-fuel ratio has a fuel injection amount characteristic that is excessively leaner than the target air-fuel ratio when the above-described start-up air-fuel ratio feedback control is performed. In such a case, after the start of the air-fuel ratio feedback control, the time when the O2 sensor output makes a lean determination is advanced by the decrease of the air-fuel ratio feedback correction coefficient ALPHA, and the proportional component P and the integral component I after the lean determination are added. The air-fuel ratio feedback correction coefficient ALPHA that increases by the value is limited by the decreasing upper limit value αmax, decreases along the upper limit value αmax, and after αmax decreases to ALPMAX, until the O2 sensor output is judged to be lean After maintaining ALPHA = ALPMAX, the routine proceeds to normal air-fuel ratio feedback control. For example, the above phenomenon occurs when the amount of volatile fuel causes a delay in reaching an equilibrium state at the stoichiometric air-fuel ratio due to a shortage of the rich increase at low temperatures. Note that the normal air-fuel ratio feedback control may start earlier than the above, and may be started before αmax decreases to ALPMAX.

  As described above, the upper limit value αmax is set to an appropriate value that is larger by a predetermined amount than the ALPHA when the target value is reduced as desired, so that the torque step at the start of the air-fuel ratio feedback control can be eliminated, while the stoichiometric value is increased. Until it converges, the normal air-fuel ratio feedback control can be started as quickly as possible while preventing ALPHA from being set excessively and preventing deterioration of combustibility and exhaust emission.

FIG. 8 shows a state where a load (air conditioner or the like) due to disturbance or the like is applied when the start-up air-fuel ratio feedback control is performed.
When the load is applied, the air amount is increased, and the fuel increase is delayed due to the detection delay of the air amount increase. Therefore, the air-fuel ratio is temporarily leaned, and the air-fuel ratio feedback correction coefficient ALPHA is temporarily proportional to P and Although the integral I is added and increases, the normal air-fuel ratio feedback control is started with a delay by the load without being limited to the upper limit value αmax set to an appropriate value as described above.

  On the other hand, as for the lower limit value, as long as normal air-fuel ratio feedback control is performed, the air-fuel ratio feedback correction coefficient ALPHA decreases by an integral amount I until it converges to stoichiometry. However, if the ALPHA is abnormally small due to a bug, the lower limit value ALPMIN corresponding to the stoichiometric air-fuel ratio continues to be excessively leaned during the period in which rich control should be performed. Although the starting performance may be greatly impaired, in the present embodiment, the lower limit value αmin is set to an appropriate value that is smaller by a predetermined amount than the ALPHA when the target value is reduced as desired. Can be prevented from being excessively leaned, and as good start-up performance as possible can be maintained.

Next, a second embodiment in which the same problem is solved with a simple configuration will be described with reference to the flowchart of FIG.
In S51, it is determined whether or not the engine water temperature Tw at the time of start detected by the water temperature sensor 16 is the first set temperature Twc (for example, 30 ° C.) or less.
When it is determined that the engine is cold with Tw ≦ Twc, the upper limit value αmax of the air-fuel ratio feedback correction coefficient ALPHA is set to SMALMAX that is corrected to increase from the normal value ALPMAX corresponding to the stoichiometric air-fuel ratio after warm-up in S52. .

In S53, it is determined whether or not the water temperature Tw has risen to the second set temperature (for example, 60 ° C.) Twh. Until the water temperature Tw rises, the process returns to S52 and the control with the upper limit value αmax being set to LMALMAX is continued.
After completion of warming up to Tw ≧ Twh, the process proceeds to S53, and the upper limit value αmax is returned to the normal value ALPMAX corresponding to the stoichiometric air-fuel ratio after warming up.

Further, at the time of warm-up starting when Tw ≧ Twh is determined from the start at S51, the upper limit value αmax is set to the normal value ALPMAX at S53.
In this way, at the time of cooling down below the first set temperature Twc, the air-fuel ratio feedback correction coefficient ALPHA0 at the start of air-fuel ratio feedback is larger than the normal upper limit value αmax (= ALPMAX), and the upper limit value αmax The upper limit value αmax, which is limited by (= ALPMAX) and causes a torque step, is corrected to increase to LMALMAX, so that the air / fuel ratio feedback control is not limited to the upper limit value αmax (= LMALMAX). And the generation of a torque step can be avoided.

In addition, after the warm-up is completed, an appropriate limiting function can be obtained by returning to the normal upper limit value αmax (= ALPMAX).
Although the limit value can be set more finely in the first embodiment, the configuration in the second embodiment is simpler.

Engine system diagram showing one embodiment of the present invention Flow chart of fuel injection amount calculation routine Flow chart showing the flow of air-fuel ratio control after startup Flow chart for setting limit values in air-fuel ratio feedback control Air-fuel ratio feedback control routine flowchart Time chart showing basic form of air-fuel ratio control after startup Time chart showing the form in which the feedback correction amount sticks to the upper limit value in air-fuel ratio control after startup Time chart showing the form when a load is temporarily applied due to disturbance or the like in air-fuel ratio control after starting Flowchart for setting limit value in air-fuel ratio feedback control of another embodiment

Explanation of symbols

1 engine
6 Fuel injection valve
12 ECU
16 Water temperature sensor
17 O2 sensor
18 Start switch

Claims (7)

An engine control device that enriches the air-fuel ratio immediately after startup and starts air-fuel ratio feedback control based on the output of the air-fuel ratio sensor after activation of the air-fuel ratio sensor,
A limit value of the feedback correction amount until the air-fuel ratio is converged to stoichiometric is set with reference to the feedback correction amount according to the air-fuel ratio state at the start of the air-fuel ratio feedback control. Fuel ratio control device.   The limit value of the feedback correction amount is set to a feedback correction amount corresponding to the stoichiometric air-fuel ratio from an initial value of upper and lower limit values set with reference to the feedback correction amount at the start of the air-fuel ratio feedback control. An air-fuel ratio control device for an engine, wherein the air-fuel ratio control device is set so as to gradually decrease to a lower limit value.   The engine air-fuel ratio control apparatus according to claim 2, wherein the upper and lower limit values are reduced at a rate equivalent to an integral part of the feedback correction amount.   The air-fuel ratio is enriched by the target air-fuel ratio correction coefficient from immediately after the start until the air-fuel ratio sensor activity is detected, and when the air-fuel ratio sensor activity is detected, the air-fuel ratio rich coefficient by the target air-fuel ratio correction coefficient is detected. The engine air-fuel ratio control device according to any one of claims 1 to 3, wherein the minute portion is cut and the rich portion is converted into a feedback correction amount in the air-fuel ratio feedback control and added. An engine control device that enriches the air-fuel ratio immediately after startup and starts air-fuel ratio feedback control based on the output of the air-fuel ratio sensor after activation of the air-fuel ratio sensor,
An air-fuel ratio control apparatus for an engine, wherein an upper limit value of a feedback correction amount at the time of air-fuel ratio feedback control is increased and corrected when the engine is cold.   When the engine water temperature is lower than the first set temperature, the upper limit value is increased and corrected, and when the engine temperature is higher than the second set temperature, the increase correction is stopped and returned to the normal upper limit value. The engine air-fuel ratio control apparatus according to claim 5.   The engine air-fuel ratio control apparatus according to any one of claims 1 to 6, wherein the air-fuel ratio sensor is an oxygen sensor sensitive to an oxygen concentration in exhaust gas.

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