JPH10169495A - Air-fuel ratio feedback control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control an air-fuel ratio to a target air-fuel ratio in a lean area using an inexpensive O2 sensor by setting the target air-fuel ratio according to an engine operating state, and computing an actual air-fuel ratio using an output signal detected by the O2 sensor. SOLUTION: A target air-fuel ratio setting part 82 for setting a target air-fuel ratio according to an engine operating state is connected to a fuel injection quantity computing part 84, an actual air-fuel ratio computing part 85 and a pulse control part 86. In case of the target air-fuel ratio being set to a lean area, the pulse control part 86 changes pulse width so as to be formed from the lean side to the rich side under a specified condition. The air-fuel ratio detecting part 83 for detecting an actual air-fuel ratio is formed of a switching type O2 sensor 52 with a Z-characteristic of detecting on-off signals with a stoichiometric air-fuel ratio as a boundary. A feedback correction factor computing part 87 computes a feedback correction factor for feedback-controlling the air-fuel ratio on the basis of the detected result of the O2 sensor 52.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio feedback control device for an engine, and more particularly to an air-fuel ratio feedback control device for an engine using a switching type O ₂ sensor.

[0002]

2. Description of the Related Art The stoichiometric air-fuel ratio (hereinafter referred to as "the stoichiometric air-fuel ratio")
As a method of controlling to “stoichio”, a switching type O ₂ sensor having a Z characteristic is provided in the exhaust system of the engine, and the fuel injection amount is PI controlled (proportional integral control) according to the detection value of the O ₂ sensor. ), The air-fuel ratio is generally controlled so as to converge to the vicinity of stoichio. Further, in order to further purify harmful components in exhaust gas, Japanese Patent Application Laid-Open No. 2-111347 discloses that exhaust air purification efficiency by a catalyst is maximized by forcibly oscillating an air-fuel ratio in the vicinity of stoichio. An air-fuel ratio control method for reducing emissions is disclosed.

On the other hand, Japanese Patent Application Laid-Open No. 64-56935 discloses a technique in which a wide-range air-fuel ratio sensor capable of obtaining a linear output is used in place of a switching type O ₂ sensor to control the air-fuel ratio near stoichiometry. It has been disclosed. Using this wide-range air-fuel ratio sensor, it is also possible to perform air-fuel ratio feedback control for controlling the air-fuel ratio to a target air-fuel ratio in a lean region.

[0004]

However, in order to further reduce exhaust emissions and improve fuel efficiency, air-fuel ratio feedback control for controlling the air-fuel ratio to a target air-fuel ratio in a lean region other than the stoichiometric condition, which is shown in the former case, is required. It is required to do.

The latter is disclosed in Japanese Patent Application Laid-Open No. 64-56935.
The wide-range air-fuel ratio sensor used in the above publication is more expensive than the O ₂ sensor, which leads to an increase in cost.

The present invention has been made in view of the above-mentioned various problems, and has as its object to control the air-fuel ratio to a target air-fuel ratio in a lean region using an inexpensive O ₂ sensor. An object of the present invention is to provide an air-fuel ratio control device for an engine that can be used.

[0007]

According to a first aspect of the present invention, there is provided an air-fuel ratio feedback control device for an engine, comprising: a target air-fuel ratio setting means for setting a target air-fuel ratio in accordance with an engine operating state; A pulse width of a pulse signal for controlling a fuel injection amount from an injector is controlled based on a detection signal of a switching type O ₂ sensor provided in an exhaust system of an engine so as to inject a target fuel injection amount according to a fuel ratio. And target injection pulse control means. Then, when the target air-fuel ratio is set in the lean region, the pulse width is changed at predetermined intervals at predetermined intervals for a predetermined period of time so that the air-fuel ratio changes stepwise from the lean side to the rich side by a predetermined amount of change. Means and means for calculating an actual air-fuel ratio which is an actual air-fuel ratio using an output signal detected by the O ₂ sensor.

According to a second aspect of the present invention, the pulse control means changes the pulse width such that the actual air-fuel ratio has a rich spike having a constant variation exceeding the stoichiometric air-fuel ratio. .

Therefore, the actual air-fuel ratio calculating means measures the change of the output signal of the O ₂ sensor for a predetermined period, and when the output signal of the O ₂ sensor changes at the same cycle as the interval of the rich spike, the actual air-fuel ratio becomes equal to the target air-fuel ratio. When it is determined that the air-fuel ratio is close to the fuel ratio and the output signal is only in the OFF state, it can be determined that the actual air-fuel ratio is leaner than the target air-fuel ratio by a predetermined change amount of the rich spike.

In the case of only the ON state, it can be determined that the actual air-fuel ratio is on the richer side than the stoichiometric ratio. Therefore, it is determined whether the actual air-fuel ratio is rich or lean with respect to the target air-fuel ratio set in the lean region.
Recognition can be performed using output signals of _two sensors.

According to a third aspect of the present invention, there is provided an air-fuel ratio feedback control apparatus for an engine, wherein the pulse control means includes a large rich spike having a large change amount in which the actual air-fuel ratio exceeds the stoichiometric air-fuel ratio and a small rich spike having a small change amount not exceeding the stoichiometric air-fuel ratio. And the pulse width is changed so as to alternately configure at predetermined intervals.

Here, the actual air-fuel ratio calculating means measures the output signal of the O ₂ sensor for a predetermined period. Therefore, when the output signal of the O ₂ sensor changes at the same cycle as the interval of only the large rich spike, it is determined that the actual air-fuel ratio based on the target fuel injection amount is near the target air-fuel ratio, and the large rich spike and the small rich spike are determined. If the actual air-fuel ratio is in the range between the target air-fuel ratio and the stoichiometric air-fuel ratio, that is, if the actual air-fuel ratio is in the region between the target air-fuel ratio and the target air-fuel ratio, Can be determined.

Further, the output signal of the O ₂ sensor is set for a predetermined period,
In the case of only the OFF state, it can be determined that the actual air-fuel ratio is on the lean side by more than the predetermined change amount of the large rich spike than the target air-fuel ratio, and in the case of only the ON state, the actual air-fuel ratio is on the rich side of the stoichiometric ratio. It can be determined that there is.

Therefore, whether the actual air-fuel ratio is adjusted to the target air-fuel ratio set in the lean region or whether the actual air-fuel ratio is on the rich side or on the lean side is determined more precisely by using the output signal of the O ₂ sensor. Can be recognized.

According to a fourth aspect of the present invention, there is provided an air-fuel ratio feedback control device for an engine, wherein the pulse control means generates a large rich spike whose actual air-fuel ratio exceeds the stoichiometric air-fuel ratio and a change amount which exceeds the stoichiometric air-fuel ratio but smaller than the large rich spike. The injection pulse width is controlled so that the medium rich spikes and the small rich spikes that do not exceed the stoichiometric air-fuel ratio are sequentially formed at predetermined intervals.

Therefore, when the output signal of the O ₂ sensor changes in the same cycle as the interval of only the large rich spike, it is determined that the actual air-fuel ratio is leaner than the target air-fuel ratio, and the large rich spike and the middle rich spike are determined. If it changes at the same cycle as both of the intervals, it can be determined that the actual air-fuel ratio is near the target air-fuel ratio.

If the output signal changes in the same cycle as the intervals of the large, medium, and small rich spikes, the actual air-fuel ratio is in the range between the target air-fuel ratio and the stoichiometric air-fuel ratio, that is, the target air-fuel ratio is smaller than the target air-fuel ratio. Can be determined to be within the range of the change amount of the small rich spike.

In addition, the output signal of the O ₂ sensor is
In the case of only the OFF state, it can be determined that the actual air-fuel ratio is on the lean side by more than the predetermined change amount of the large rich spike than the target air-fuel ratio, and in the case of only the ON state, the actual air-fuel ratio is on the rich side of the stoichiometric ratio. It can be determined that there is.

Therefore, the state of the actual air-fuel ratio with respect to the target air-fuel ratio set in the lean region can be more precisely and accurately recognized using the output signal of the O ₂ sensor.

The air-fuel ratio feedback control device for an engine according to the present invention increases the target fuel injection amount when the actual air-fuel ratio is leaner than the target air-fuel ratio, and increases the target fuel injection amount when the actual air-fuel ratio is richer. There is provided a pulse shift value calculating means for calculating a pulse shift value for changing the pulse width so as to reduce the injection amount.

According to a sixth aspect of the present invention, in the air-fuel ratio feedback control apparatus for an engine, the pulse shift value calculating means performs integral control using a deviation assuming a difference between the target air-fuel ratio and the actual air-fuel ratio. Calculate the shift value.

Therefore, lean feedback control for adjusting the actual air-fuel ratio to the target air-fuel ratio set in the lean region by feeding back the pulse shift value can be executed.

According to a seventh aspect of the present invention, when the measured output signal of the O ₂ sensor is ON only or OFF for a predetermined period, the pulse shift value calculating means increases the deviation. Then, the pulse shift value is calculated, and the pulse control means changes the pulse width so as to reduce the amount of change of the rich spike to the rich side.

Therefore, when the actual air-fuel ratio deviates greatly from the target air-fuel ratio, the convergence of the actual air-fuel ratio to the target air-fuel ratio can be improved. Further, it is possible to prevent a surge that occurs when the actual air-fuel ratio is varied between the rich side and the lean side in a state where the air-fuel ratio deviates from the target air-fuel ratio, thereby improving drivability.

According to an eighth aspect of the present invention, the pulse control means changes the pulse width so that the amount of change of the rich spike is variably set in accordance with the operation state of the engine. Further, in the air-fuel ratio feedback control device for an engine according to the ninth aspect, the pulse control means changes the pulse width so that the predetermined interval of the rich spike is variably set according to the operation state of the engine.

Therefore, the target air-fuel ratio can be freely set within the lean range in accordance with the operating state of the engine, and the lean feedback control can be performed. Further, by adjusting the period of the air-fuel ratio feedback control and the detection accuracy of the O ₂ sensor, the accuracy of the air-fuel ratio feedback control can be improved, and drivability can be maintained.

According to a tenth aspect of the present invention, there is provided an air-fuel ratio feedback control device for an engine, comprising ignition correction means for delay-correcting the ignition timing of the engine simultaneously with the rich spike. Therefore, the output torque can be made uniform regardless of the presence or absence of the rich spike, and the drivability can be improved.

The air-fuel ratio feedback control device for an engine according to the present invention has a pulse shift value learning control means for learning a pulse shift value for each engine operation region. In the air-fuel ratio feedback control device for an engine according to claim 12, the pulse shift value learning control means includes:
The pulse shift value is learned when the output signal of the O ₂ sensor shows a predetermined change for a predetermined time or more.

Therefore, it is possible to perform air-fuel ratio feedback control corresponding to the individual variations of each engine and the variations in the operating range, and to the aging of the engine, thereby improving the convergence to the target air-fuel ratio. .

According to a thirteenth aspect of the present invention, the air-fuel ratio feedback control means of the engine is arranged such that, when the engine is a four-cycle multi-cylinder engine, the pulse control means forms a rich spike in only one cycle of one cylinder. Control the injection pulse width. Therefore, a change in engine output due to a change in air-fuel ratio due to a rich spike can be suppressed as much as possible, and a torque shock due to a change in output can be reduced, and drivability can be improved.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

First, FIG. 1 is a schematic overall configuration diagram of an automobile engine device to which an air-fuel ratio feedback control device for an engine according to an embodiment of the present invention is applied. An intake passage 12 and an exhaust passage 14 communicate with the horizontally opposed engine 10.

The intake chamber 1 is located upstream of the intake passage 12.
6 is opened in front of the vehicle body (not shown), and a surge tank 2 is provided downstream of the intake passage 12 so as to correspond to each cylinder.
The intake pipes 22 branched from the intake pipes 2 communicate with each other.
The downstream end of 2 communicates with each combustion chamber 26 via an intake port 24. On the other hand, a downstream side of the exhaust passage 14 is connected to a muffler 28 attached to a rear portion of the vehicle body, and an exhaust pipe 32 communicates with each combustion chamber 26 via each exhaust port 30 on an upstream side of the exhaust passage 14.

In the intake passage 12, in order from the upstream side,
An air cleaner 34 for removing dust from the air, an air flow meter 36 for detecting the amount of intake air Q, and a throttle valve 38 for controlling the amount of intake air according to the amount of depression of an accelerator pedal (not shown) are provided.

The intake passage 12 is provided with an idle speed control (hereinafter simply referred to as "ISC") passage 40 which bypasses the throttle valve 38. In the middle of the ISC passage 40, the amount of intake air during idling is adjusted. An ISC valve 42 is mounted.

The injector 44 is located downstream of the intake pipe 22.
Are provided to face the intake port 24, and each of these injectors 44 is connected to a fuel pipe 48 from a fuel pump 46.
Is atomized and injected through the fuel pumped through the nozzle.

On the other hand, a catalyst 50 such as a three-way catalyst for purifying exhaust gas is interposed in the exhaust passage 14 near the engine body 10, and an oxygen concentration in the exhaust gas is provided upstream of the catalyst 50. the air-fuel ratio of the mixture detected by detecting, O ₂ sensor 52 outputs the boundary of the stoichiometric air-fuel ratio has a Z characteristic is provided.

The EGR passage 54, which has a smaller passage area than the intake pipe 22 and the exhaust pipe 32,
An EGR valve 56, which is driven by, for example, a stepping motor, is provided in the middle of the EGR passage 54 so as to communicate between the exhaust pipe 32 and a collection portion of the intake pipe 22.

The cylinder head 58 has a combustion chamber 26
A spark plug 60 is provided facing the inside, and the ignition plug 60 is provided with an igniter 62 and an ignition coil 6.
The air-fuel mixture in the combustion chamber 26 is forcibly ignited at a predetermined ignition timing by the high voltage supplied via the power supply 4.

In this figure, reference numeral 66 denotes a crank angle sensor for detecting the crank angle and the engine speed Ne.
8 is a knock sensor for detecting knocking of the engine body 10, 70 is a water temperature sensor for detecting the temperature of cooling water, 72
Denotes a cam angle sensor for detecting the rotation angle of the camshaft 74 to determine the cylinder, and 76 denotes a throttle opening sensor for detecting the throttle opening θ of the throttle valve 38.

As shown in FIG. 2, an electronic control unit (hereinafter, simply referred to as an ECU) 78 for controlling the driving of each member and receiving an output signal from each sensor is provided with an input for receiving a signal from each sensor. Interface 78a, output interface 7 for outputting a drive control signal to each member
8b, a CPU 78c as a main processing unit, a ROM 78 for storing a control program and preset fixed data
d, RAM 78 for storing output signals and the like from each sensor
e, backup RA for storing learning data, etc.
It is configured as a microcomputer system in which an M78f, a timer 78g, and the like are mutually connected by a bus line 78f.

Next, a functional block diagram of the first embodiment of the present invention shown in FIG. 3 will be described. The engine operating state detecting unit 80 is configured by the air flow meter 36, the crank angle sensor 66, and the water temperature sensor 70,
It is connected to a target air-fuel ratio setting unit 82 configured in U78. Here, the intake air amount Q, the engine speed Ne,
And the cooling water temperature Tw is detected, and the engine operation state is determined.

The target air-fuel ratio setting unit 82, which is a target air-fuel ratio setting unit, sets a target air-fuel ratio in accordance with the operating state of the engine. The actual air-fuel ratio calculation unit 85 is a fuel ratio calculation unit, and the pulse control unit 86 is a pulse control unit. When the target air-fuel ratio is set in the lean region, the pulse control unit 86 changes so that the air-fuel ratio suddenly projects from the lean side to the rich side in a stepwise manner by a predetermined change amount for a predetermined time at predetermined intervals. The pulse width is changed so as to form a rich spike, and a pulse control value (FBPULS) is output to the feedback correction coefficient calculation unit 87.

On the other hand, an air-fuel ratio detecting section 83 provided in the exhaust system for detecting an actual air-fuel ratio is provided with an air-fuel ratio O.
It is constituted by a switching type O ₂ sensor 52 having a Z characteristic for detecting an N · OFF signal, and is connected to an actual air-fuel ratio calculation unit 85 provided in the ECU 78. The actual air-fuel ratio calculation unit 85 compares the state of the air-fuel ratio detected by the air-fuel ratio detection unit 83 with the target air-fuel ratio set by the target air-fuel ratio setting unit 82, and compares the actual air-fuel ratio with the target air-fuel ratio. Is also shifted to the rich side or the lean side, and the determination result is output to the shift value calculation unit 88 and the feedback correction coefficient calculation unit 87.

The shift value calculating section 88 includes an actual air-fuel ratio calculating section 8.
Based on the determination result of 5, the pulse shift value (FBSHIFT) for shifting the entire pulse control value (FBPULS) of the pulse control unit 86 to the rich side or the lean side is calculated and output to the feedback correction coefficient calculation unit 87. The feedback correction coefficient calculation section 87 calculates a feedback correction coefficient for performing feedback control of the air-fuel ratio based on the detection result of the O ₂ sensor 52, and outputs the feedback correction coefficient to the fuel injection amount calculation section 84.

The fuel injection amount calculation section 84 calculates a fuel injection effective pulse width (Te), which is the final fuel injection amount, and outputs it to the injector control section 89. Injector control unit 89
Controls the injector 44 connected to the output side using the fuel injection effective pulse width (Te).

Next, the operation of this embodiment will be described with reference to FIGS. FIG. 4 is a flowchart showing the air-fuel ratio feedback control in the present embodiment. This routine is executed by a periodic interrupt every fixed program cycle.

First, at S201, the engine speed N
e, the operating state of the engine is detected based on the intake air amount Q and the cooling water temperature Tw. Here, the engine rotation speed Ne is detected by the crank angle sensor 66, the intake air amount Q by the air flow meter 36, and the cooling water temperature Tw by the water temperature sensor 70, respectively. In S202, a target air-fuel ratio is set based on the engine speed Ne and the intake air amount Q. Here, in the ROM 78d of the ECU 78, a data map using the engine speed Ne and the intake air amount Q as parameters is stored in advance, and the target air-fuel ratio is set by referring to this data map, and S203
Proceed to the following. If the cooling water temperature Tw has not reached the predetermined temperature at which the warm-up is determined to be completed, the target air-fuel ratio is set to stoichiometric.

In S203, it is determined whether or not the target air-fuel ratio set in S202 is stoichiometric.
Here, a selection is made as to whether to perform the conventional stoichiometric feedback control or to perform the lean feedback control. Here, if it is stoichiometric (YES), the process proceeds to S208 to perform the conventional air-fuel ratio control, that is, the stoichiometric air-fuel ratio feedback control by PI control.
If it is not stoichiometric (NO), the process proceeds to S204 to determine whether the target air-fuel efficiency has been set in the lean region.

In S204, it is determined whether the target air-fuel ratio set in S202 is in a lean region. Here, the target air-fuel ratio is not set in the lean region (N
If O), that is, if the target air-fuel ratio is set in the rich region, the routine exits from this routine assuming that the air-fuel ratio feedback control is not performed (return).

If the target air-fuel ratio is set in the lean region (YES), the process proceeds to S205 in order to determine whether or not the operation state of the engine is such that lean feedback control is possible.

In S205, it is determined whether or not the engine operating state is in the middle / low load range, and it is determined whether or not the lean feedback control can be performed. That is, in the present embodiment, the lean feedback control is executed only in the middle / low load region where the amount of NOx emission after activation of the catalyst is small. Thereby, fuel efficiency can be improved without deteriorating drivability and exhaust emission (NOx).

Here, if the engine operating state is in the middle / low load range (YES), the process proceeds to S206 to perform lean feedback control, and if it is not in the middle / low load range (NO), the stoichiometric air-fuel ratio S2 to perform control
08. Note that the stoichiometric air-fuel ratio control performed in S208 is the conventional control, that is, the air-fuel ratio feedback control to the stoichio by the PI control based on the ON / OFF signal of the O ₂ sensor, and thus detailed description thereof is omitted. I do.

In S206, air-fuel ratio control is performed with the target air-fuel ratio set in a lean region. That is, the ECU sets the actual air-fuel ratio to the target air-fuel ratio set in S203.
A target fuel injection amount is injected from the injector 44 based on data stored in advance in the ROM 78d of the CPU 78. As a result, the engine can perform lean combustion, thereby reducing exhaust emissions and improving fuel efficiency.

Here, the pulse width is changed by the pulse control unit 86 so that there are two types of rich spikes in which the actual air-fuel ratio suddenly changes by a predetermined value at predetermined intervals so as to protrude to the rich side. Pulse control is performed.

The change amount of the rich spike having a large change amount on the rich side (hereinafter, simply referred to as “large rich spike”) is set to the lean side when the actual air-fuel ratio is near the target air-fuel ratio. A change amount of a rich spike having a small change amount (hereinafter, simply referred to as “small rich spike”) from the target air-fuel ratio to a change amount slightly exceeding the stoichiometric ratio is determined when the actual air-fuel ratio is near the target air-fuel ratio. Is set so as not to exceed slightly.

Here, the amount of change between the large rich spike and the small rich spike and their intervals are determined by the engine speed Ne and the intake air amount Q previously stored in the ROM 78d.
It is set variably by referring to the dimensional data map. In the present embodiment, the change amount and the interval between the large rich spike and the small rich spike are freely set using a two-dimensional map. However, the change amount and the interval between the rich spikes are fixed values. However, lean feedback control can be performed. FIG. 5 shows a data map of the change amount and the interval setting of the rich spike, and FIGS. 5A and 5B show the change amount setting data map of the large rich spike and the small rich spike, and FIG. Shows an interval setting data map between rich spikes.

Next, the air-fuel ratio feedback control in the lean region using the O ₂ sensor 52, which is performed in S207, will be described with reference to the flowchart of FIG.

FIG. 6 shows a final fuel injection effective pulse width T per unit time representing a final fuel injection amount finally injected from the injector 44 by the air-fuel ratio feedback control.
11 is a flowchart illustrating a calculation routine of e.

First, at S301 in FIG. 6, the air flow meter 36 and the crank angle sensor 66 detect the intake air amount Q and the engine speed Ne to recognize the current engine operating state. In S302, the basic injection pulse width Tp is calculated based on the engine operation state detected in S301.
Is calculated.

Here, the basic injection pulse width Tp is determined by the ECU
78 is set according to the engine operating state by a data map set in advance in the ROM 78d. next,
In S303, the feedback correction coefficient calculation unit 87 calculates an air-fuel ratio feedback correction coefficient (LAMBDA) for lean feedback control. Here, the air-fuel ratio feedback correction coefficient (LAMBDA) is a pulse control value (FB) of the pulse width changed by the pulse control unit 86.
PULS) and the pulse shift value (FBSHIFT) calculated by the shift value calculation unit 88 are calculated (LAMBDA ← FBPULS + FBSHIF).
T).

Then, in S304, the final effective fuel injection pulse width Te per unit time, which indicates the final fuel injection amount finally injected from the injector 44, is calculated. The final fuel injection effective pulse width Te is calculated by the following equation (1).

Te = Tp × COEF × LAMBDA (1) In the above equation (1), COEF is various correction coefficients, for example, an increase coefficient added to increase the fuel at the time of engine acceleration. Then, after calculating the final fuel injection effective pulse width Te, the process exits from this routine (return).

Next, the air-fuel ratio feedback correction coefficient (L
Pulse shift value (FBSHI) used for AMBDA)
The method of calculating FT) will be described with reference to FIGS. FIG. 7 is a flowchart showing a routine for calculating the pulse shift value (FBSHIFT), and FIG. 8 is a time chart showing the state of the air-fuel ratio by the lean feedback control. FIG. 9 is an explanatory diagram showing the relationship between the air-fuel ratio feedback correction coefficient (LAMBDA) calculated by the above routine and the deviation.

First, the output signal of the O ₂ sensor 52 is detected in S401 of FIG. 7, and in S402, the change of the output signal of the O ₂ sensor 52 during a predetermined period is measured. And
In S403, the output signal of the O ₂ sensor 52 is
A determination is made as to whether or not only the F state is present. Where O
Only in the FF state (the stoichiometric air-fuel ratio never reaches the specified period)
(YES), it is determined that the actual air-fuel ratio is deviated from the target air-fuel ratio to the lean side (see FIG. 8B), and
The process moves to S409. Then, in step S409, a deviation 1 is assigned as a deviation that assumes a difference between the target air-fuel ratio and the actual air-fuel ratio, that is, a deviation that adjusts the actual air-fuel ratio deviating leaner than the target air-fuel ratio to the target air-fuel ratio. (See FIG. 9).

[0066] Also, when the output signal of the O ₂ sensor 52 has not only a predetermined period OFF state (NO), in S403, the O ₂ sensor 52 output signal is determined whether only the ON state The process moves to S404 in order to proceed. If it is determined that the air-fuel ratio is ON only for the predetermined period in S404 (YES), it is determined that the actual air-fuel ratio is richer than the stoichiometric ratio (see FIG. 8D), and the process proceeds to S410. Then, in step S410, the actual air-fuel ratio deviating on the rich side from the stoichiometric ratio is used as a deviation for adjusting the actual air-fuel ratio to the target air-fuel ratio.
3 (see FIG. 9).

[0067] When not only the ON state (NO), in S404, the output signal of the O ₂ sensor 52 is ON ·
It is determined that the OFF state is being repeated, and the process shifts to S405 to measure the repetition period. Here, the fact that the O ₂ sensor 52 repeatedly outputs ON / OFF signals means that the O ₂ sensor 52 is detecting a rich spike (FIG. 8A or FIG. 8C).
), It can be determined that the actual air-fuel ratio is between the target air-fuel ratio and stoichiometry.

Therefore, the ON / OF of the O ₂ sensor 52
From the period of the F signal, it can be determined whether the actual air-fuel ratio is near the target air-fuel ratio or on the richer side than the target air-fuel ratio.

In S405, the ON / O of the O ₂ sensor 52
The cycle of the FF signal is measured for a predetermined period, and in order to determine the state of the actual air-fuel ratio with respect to the target air-fuel ratio in accordance with the cycle, S40
Move to 6. In S406, the cycle measured in S405 corresponds to the interval of the large rich spike (hereinafter simply referred to as “cycle”).
It is determined whether or not the actual air-fuel ratio is substantially the same as the target air-fuel ratio (see FIG. 8A). , S40
Move to 7. In S407, the deviation 0 is assigned as the deviation for maintaining the actual air-fuel ratio (see FIG. 9).

If the cycle of the large rich spike is different (NO) in S406, that is, if the O ₂ sensor 52
Has detected both a large rich spike and a small rich spike (hereinafter, simply referred to as “period”), it is determined that the actual air-fuel ratio is on the rich side of the target air-fuel ratio (FIG. 8). (C)), and the process proceeds to S408. S408
In this example, a deviation -1 for adjusting the actual air-fuel ratio on the rich side of the target air-fuel ratio and on the lean side of the stoichiometric ratio to near the target air-fuel ratio is assigned (see FIG. 9).

Then, in S411, a pulse shift value (FBSHIFT) for shifting the entire actual air-fuel ratio to the rich side or the lean side by increasing or decreasing the entire pulse control value (FBPULS) is calculated. Here, the pulse shift value (FBSHIFT) is obtained by performing integral control using the deviations assigned in S407 to S410. That is, it is calculated by adding the value obtained by multiplying the allocated deviation by the coefficient C and the pulse shift value (FBSHIFT _old ) calculated during the previous execution of this routine (FBSHIFT ← FBSHIFT _old + deviation × C). Then, after performing the above control, the process exits from this routine (return).

Accordingly, by substituting the air-fuel ratio feedback correction coefficient (LAMBDA) into the above equation (1), it is possible to obtain the final fuel injection effective pulse width Te which is a pulse signal for controlling the fuel injected from the injector 44. it can. By performing the above routine, it is possible to perform the air-fuel ratio feedback control to the target air-fuel ratio set in the lean region.

Next, a second embodiment will be described. A characteristic of this embodiment is that, in the first embodiment, the output signal of the O ₂ sensor 52 is OFF for a predetermined time.
If only the state or only the ON state, that is, it is determined that the actual air-fuel ratio is leaner than the change amount of the large rich spike with respect to the target air-fuel ratio or is located richer than the stoichiometric ratio Only the deviations (deviation 1, deviation −3) are allocated, but in the present embodiment, the convergence to the target air-fuel ratio is more positively improved.

That is, in this embodiment, the O ₂ sensor 5
If the output signal of No. 2 continues for more than a predetermined time, the pulse shift value is calculated by increasing the number of steps of the deviation, and the pulse control unit 86 changes the large rich spike and the small rich spike. By reducing the amount, convergence to the target air-fuel ratio can be improved.

The operation will be described below with reference to FIG. FIG. 10 is a flowchart showing a routine for calculating the above-described pulse shift value. Note that S601 to S6
Until 08, S4 of FIG. 6 in the above-described first embodiment is performed.
Since these steps are the same as steps 01 to S408, a detailed description thereof will be omitted.

In S603, it is determined whether or not the output signal of the O ₂ sensor 52 is in the OFF state only for a predetermined period. If the output signal is in the OFF state only (YES), S609 is performed.
Then, it is determined whether the OFF state is maintained for a predetermined time.

If it is determined in S609 that the OFF state has not been maintained for a predetermined time (NO), the flow shifts to S610, and S4 is executed.
If the deviation 1 similar to 09 is assigned and maintained for a predetermined time (YES), the process proceeds to S611 in order to assign a deviation toward the rich side more quickly. In S611,
The deviation 3 having a value larger than the deviation 1 of S610 is assigned, and the process proceeds to S612, where the change amount of the rich spike is reduced.

If it is determined in S604 that the ON state is maintained only for the predetermined period (YES), the flow shifts to S613, and it is determined whether the ON state is maintained for the predetermined time.

If it is determined in S613 that the ON state has not been maintained for a predetermined time (NO), the flow shifts to S615, and S41 is executed.
When the deviation -3 similar to 0 is allocated and maintained for a predetermined time (YES), the process proceeds to S615 in order to allocate the deviation toward the lean side faster. In S615,
The deviation -5 having a value larger than the deviation -3 of S614 is assigned, and the process proceeds to S616, where the change amount of the rich spike is reduced.

Thus, when the actual air-fuel ratio deviates greatly from the target air-fuel ratio, the shift value is changed more finely by increasing the number of steps of the deviation and decreasing the amount of change in the rich spike. The convergence of the air-fuel ratio to the target air-fuel ratio can be further improved. Further, it is possible to prevent a surge that occurs when the air-fuel ratio is vibrated in a state where the air-fuel ratio deviates from the target air-fuel ratio, thereby improving drivability.

Next, a third embodiment will be described. The feature of the present embodiment is that the first and second
In this embodiment, the ignition timing correction means for controlling the ignition timing simultaneously with the configuration of the rich spike is provided.

The configuration and operation will be described below. First, although not shown, a correction means for calculating an ignition timing correction amount (ADVSFT) is provided in the ECU 78, and the ROM 78d of the ECU 78 has an ignition timing (ADVL) during lean control as a data map. doing. The ignition timing (ADVR) at the time of rich spike is
It is calculated by the following equation (2).

ADVR = ADVL−ADVSFT (2) Therefore, the calculated ignition timing at the time of the rich spike (A
By using DVR) to retard the ignition timing during a rich spike, the output torque can be made uniform regardless of whether the air-fuel ratio has changed due to the rich spike, and drivability can be improved. .

In the above embodiment, when the engine 10 is a multi-cylinder engine, the pulse control means may configure the rich spike in one cycle and only in one cylinder. As a result, it is possible to minimize a change in output due to a change in the air-fuel ratio during a rich spike, reduce a shock due to the change in the air-fuel ratio, and improve drivability.

In the present embodiment, the exhaust gas is purified by using a three-way catalyst as the catalyst 50. However, the present invention is not limited to this. For example, a three-way catalyst using a NOx storage type three-way catalyst is used. Is also good. The NOx storage three-way catalyst is a catalyst that once adsorbs and accumulates NOx discharged during the lean operation into the catalyst and purifies the accumulated NOx during the rich operation. Therefore, the exhaust emission (NOx) can be further reduced as compared with the case where the lean feedback control is executed alone.

Next, a fourth embodiment of the present invention will be described. The characteristic feature of the present embodiment is that the lean air-fuel ratio control in each of the above-described embodiments is performed immediately after the engine is started and before the catalyst is activated.
(Hereinafter simply referred to as “slight lean”), and the air-fuel ratio feedback control is performed.

The operation of this embodiment will now be described with reference to FIG.
1 will be described. FIG. 11 is a flowchart illustrating a control routine of the air-fuel ratio feedback control device according to the present embodiment. First, in S501, the coolant temperature Tw of the engine 10 is detected by the coolant temperature sensor 70, and the time t when the engine is started is set to E.
The integration is performed by the timer 78g of the CU 78.

In S502, it is determined whether or not the cooling water temperature Tw detected in S501 is within a set range preset in the ROM 78d of the ECU 78. Thereby, it is determined whether or not the current engine operation state can perform the lean feedback control. Here, if it is within the setting range (YES), S5
Shift to 03.

In S503, it is determined whether or not the time t after the start of the engine integrated by the timer 78g is within a set value. This makes it possible to determine whether or not the operation state of the engine 10 is in a state in which lean feedback control can be performed. Here, if the time t is within the set value (YES), S50
Move to 4.

At S504, lean control is performed.
Note that the lean control performed here is the same as the lean control in the first embodiment (see S206 in FIG. 4), and thus a detailed description thereof will be omitted. And S505
Then, the output signal of the O ₂ sensor 52 is detected, and the ECU 7
8 is temporarily stored as data in the RAM 78e.

In S506, it is determined whether or not the catalyst 50 is in the activated state. That is, whether or not the catalyst 50 is activated by the lean control in S504 is determined in S50.
5, the O ₂ sensor 52 temporarily stored in the RAM 78e
Is determined by the output of Here, when the catalyst 50 is activated (YES), the process proceeds to S507 to perform the lean feedback control. Note that the lean feedback control performed in S507 is the same as the lean feedback control in the first embodiment (see S207 in FIG. 4), and a detailed description thereof will be omitted.

If the catalyst 50 has not been activated in S506 (NO), the flow shifts to S508, and in S508, open-loop control of the air-fuel ratio is performed.

[0093] Thus, by performing the immediately lean feedback control after the activation of the catalyst 50, it is possible to effectively perform reduction of exhaust emissions, higher reliability than the uncontrolled condition of the open loop, O ₂ sensor 52
Over time and performance variations.

Next, a fifth embodiment will be described with reference to FIG.
This will be described below with reference to FIG. A characteristic of the present embodiment is that the state of the actual air-fuel ratio with respect to the target air-fuel ratio is determined by one type of rich spike having a constant change amount, and lean feedback control is performed. FIG.
FIG. 5 is an explanatory diagram showing a relationship between an air-fuel ratio feedback correction coefficient (LAMBDA) and a deviation.

As shown, the feedback coefficient is
The rich spikes having a constant change amount are changed so as to constitute at predetermined intervals, and are divided into three deviations (deviation 1, deviation-1, and deviation-3). Therefore, the actual air-fuel ratio calculation unit 85 measures the change of the output signal of the O ₂ sensor 52 for a predetermined period, and when the output signal repeats ON / OFF at a constant cycle (period in FIG. 12), the actual air-fuel ratio is calculated. It can be determined that the air-fuel ratio is between the target air-fuel ratio and stoichiometry, and a deviation of −1 is set to calculate the pulse shift value (FBSHIFT).

When the air-fuel ratio is ON only, it is determined that the actual air-fuel ratio is on the rich side of stoichiometry, and the pulse shift value (FBSH) for adjusting this to the target air-fuel ratio is determined.
A deviation 1 is set to calculate (IFT). Also, OFF
If only the state is present, it is determined that the actual air-fuel ratio is leaner than the target air-fuel ratio, and the deviation -3 is calculated to calculate a pulse shift value (FBSIFT) for adjusting the actual air-fuel ratio to the target air-fuel ratio. Set. Thereby, the shift value calculating unit 8
8 can calculate the pulse shift value (FBSHIFT) by performing integral control using the set deviation, and can calculate the feedback coefficient.

Therefore, the state of the actual air-fuel ratio with respect to the target air-fuel ratio set in the lean region can be recognized even by a rich spike having a constant change amount, and lean feedback control can be performed.

Next, a sixth embodiment will be described below. A characteristic of this embodiment is that lean feedback control is performed by judging the state of the actual air-fuel ratio with respect to the target air-fuel ratio by using three types of rich spikes having large, medium, and small change amounts. .

[0099] Large rich spike, the actual air-fuel ratio is set to change the amount that exceeds the slice level when the O ₂ sensor 52 in the vicinity of the target air-fuel ratio (near stoichiometric), medium rich spike exceeds the slice level and a large rich Is set to a smaller change amount than the change amount. In addition, the small rich spike is set to a change amount that does not exceed the slice level.

FIG. 13 is an explanatory diagram showing the relationship between the air-fuel ratio feedback correction coefficient (LAMBDA) and the deviation.
As shown in the figure, the feedback coefficient changes so that rich spikes having large, medium, and small changes are formed at predetermined intervals, and five differences (difference 2, deviation 1, deviation 0, deviation -1, and deviation -3).

Therefore, the actual air-fuel ratio calculation unit 85 determines that the O ₂
The change of the output signal of the sensor 52 is measured for a predetermined period, and the output signal is turned ON / OFF at the same cycle as the interval of the large rich spike.
Is repeated (period in FIG. 13), it can be determined that the actual air-fuel ratio is leaner than the target air-fuel ratio, and a deviation 2 is set to converge to the target air-fuel ratio.

The output signal of the O ₂ sensor 52 is output at the same cycle as the interval between the large rich spike and the middle rich spike.
When N · OFF is repeated (period in FIG. 13), the actual air-fuel ratio is leaner than the small rich spike change amount and richer than the middle rich spike change amount, that is, the actual air-fuel ratio. Is in the vicinity of the target air-fuel ratio, and a deviation 0 is set to maintain the actual air-fuel ratio.

Further, when the output signal of the O ₂ sensor 52 repeats ON / OFF at the same cycle as the interval of the large / medium / small rich spike (the cycle in FIG. 13), the actual air-fuel ratio becomes small. , Ie, the actual air-fuel ratio is richer than the target air-fuel ratio, and the deviation -1 is set so as to converge to the target air-fuel ratio. The output signal of the O ₂ sensor 52 is O
When only the N state or the OFF state is present, the deviation 2 and the deviation -3 are set so that the actual air-fuel ratio converges to the target air-fuel ratio.
Set.

Therefore, the shift value calculating section 88 can calculate the pulse shift value (FBSHIFT) by performing integral control using the set deviation, and can calculate the feedback coefficient.

Thus, the rich / lean state of the actual air / fuel ratio with respect to the target air / fuel ratio can be determined in more detail by a plurality of rich spikes having a predetermined change amount, and more precise air / fuel ratio feedback control can be performed. Thus, the convergence to the target air-fuel ratio can be further improved.

Next, a seventh embodiment will be described below. A characteristic of the present embodiment is that, in the lean feedback control in each of the above embodiments, the pulse shift value (FB
(SHIFT) is provided. The same components as those in the above-described embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 14 is a functional block diagram of the present embodiment. The shift value learning control unit 81 is a shift value learning control unit for inputting and outputting data of the shift value calculation unit.
Is provided. The same elements as those in the other embodiments described above are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 15 shows a pulse shift value (FBSH) for each operation region based on the intake air amount Q and the engine speed Ne.
3 shows a shift value learning map for learning IFT).

The operation of the present embodiment will be described below. First, the shift value (FBSHIFT) in the shift value calculating means is determined by the learning shift value (FBSHIFT) referred to from the shift value learning map shown in FIG.
g) and the actual shift value (FBSHIFTi) calculated from the output signal of the O ₂ sensor 52 (FBSHIFT ← FBSIFTg + FB)
SHIFTi).

Next, as the learning conditions, the engine operating state determining unit determines that the engine operating state remains in the same operating region for a predetermined time or more, and that the O ₂ sensor 52 is turned on / off at a target cycle for a set time or more. Is detected,
That is, when the state of the deviation 0 continues, the weighted average value of the shift value (FBSHIFTg) at that time and the learned shift value (FBSHIFTg) is calculated and updated as a new learning value.

In this embodiment, the update condition is a condition in which the state of zero deviation continues for a set time or more. However, the condition is set to another embodiment and the sign of the difference is inverted more than a set number of times. It is good also as a case where it is repeated. When the condition for updating the learning value is satisfied, a new learning shift value (FBSHIFTgnew) is calculated and updated by the following equation (3).

New learning shift value (FBSHIFTgnew) = shift value (FBSIFTTi) × (weighting coefficient) + old learning shift value (FBSIFTTold) × (1−weighting coefficient) (3) Therefore, as described above, the engine operation is performed. By learning the pulse shift value for each operation area according to the state and performing lean feedback control, it is possible to respond to variations due to individual differences of the engine and changes over time due to long-term use, and converge to the target air-fuel ratio Can be improved.

The present invention is not limited to the embodiments described above, but can be implemented by arbitrarily combining the embodiments.

[0113]

Thus, the state of the actual air-fuel ratio with respect to the target air-fuel ratio set in the lean region can be determined by using an inexpensive switching type O ₂ sensor. The air-fuel ratio feedback control in the lean region can be performed based on the determination. This makes it possible to reduce costs.

[Brief description of the drawings]

FIG. 1 is a schematic overall configuration diagram of an automobile engine device to which an engine air-fuel ratio feedback control device according to an embodiment of the present invention is applied.

FIG. 2 is a diagram illustrating the configuration of an ECU shown in FIG. 1;

FIG. 3 is a functional block diagram of the first embodiment of the present invention.

FIG. 4 is a flowchart illustrating air-fuel ratio feedback control according to the first embodiment.

FIG. 5 is a data map for setting a change amount and an interval of a rich spike.

FIG. 6 is a flowchart illustrating a routine for calculating a final fuel injection effective pulse width.

FIG. 7 is a flowchart illustrating a routine for calculating a pulse shift value according to the first embodiment.

FIG. 8 is a time chart showing a state of an air-fuel ratio by lean feedback control.

FIG. 9 shows an air-fuel ratio feedback correction coefficient (LAMBD).
It is explanatory drawing which showed the relationship between A) and deviation.

FIG. 10 is a flowchart illustrating a routine for calculating a pulse shift value according to the second embodiment;

FIG. 11 is a flowchart illustrating a control routine of an air-fuel ratio feedback control device according to a fourth embodiment.

FIG. 12 is an explanatory diagram showing a relationship between an air-fuel ratio feedback correction coefficient (LAMBDA) and a deviation in the fifth embodiment.

FIG. 13 is an explanatory diagram showing a relationship between an air-fuel ratio feedback correction coefficient (LAMBDA) and a deviation in a sixth embodiment.

FIG. 14 is a functional block diagram according to a seventh embodiment.

FIG. 15 is a shift value learning map according to the seventh embodiment.

[Explanation of symbols]

Reference Signs List 10 engine 14 exhaust passage 44 injector 52 O ₂ sensor 66 crank angle sensor 70 water temperature sensor 78 ECU 80 engine operating state detecting section 82 target air-fuel ratio setting section (target air-fuel ratio setting means) 83 air-fuel ratio detecting section (O ₂ sensor) 84 Fuel injection amount calculation unit (target injection pulse control unit) 85 Actual air-fuel ratio calculation unit (actual air-fuel ratio calculation unit) 86 Pulse control unit (pulse control unit) 88 Shift value calculation unit (pulse shift value calculation unit)

Claims (13)

[Claims] An air-fuel ratio feedback control device for an engine that controls a fuel injection amount from an injector by a pulse signal based on a detection signal of a switching type O ₂ sensor provided in an exhaust system of the engine to adjust an air-fuel ratio. Target air-fuel ratio setting means for setting a target air-fuel ratio in accordance with an operation state of the engine; a target injection pulse for controlling a pulse width of the pulse signal so as to inject a target fuel injection amount corresponding to the target air-fuel ratio Control means, when the target air-fuel ratio is set in the lean region, at predetermined intervals, for a predetermined time, for a predetermined time, by changing the pulse width so that the air-fuel ratio changes stepwise from the lean side to the rich side by a predetermined change amount. and pulse control means for changing, actual air-fuel ratio der obtained by the target fuel injection amount using an output signal detected by the O ₂ sensor Air-fuel ratio feedback control apparatus for an engine and having an actual air-fuel ratio calculating means for calculating an actual air-fuel ratio, a. 2. The air-fuel ratio of an engine according to claim 1, wherein the pulse control unit changes the pulse width so that the actual air-fuel ratio has a constant variation exceeding a stoichiometric air-fuel ratio. Feedback control device. 3. The pulse control means according to claim 1, wherein a predetermined interval is set between a large rich spike having a large change amount where the actual air-fuel ratio exceeds the stoichiometric air-fuel ratio and a small rich spike having a small change amount not exceeding the stoichiometric air-fuel ratio. The air-fuel ratio feedback control device for an engine according to claim 1, wherein the pulse width is changed so that the pulse width is alternately configured. 4. The pulse control device according to claim 1, wherein the actual air-fuel ratio has a large change amount exceeding the stoichiometric air-fuel ratio, and a large rich spike having the change amount exceeding the stoichiometric air-fuel ratio and smaller than the large rich spike. The pulse width is changed so that a rich spike and a small rich spike having a small change amount not exceeding the stoichiometric air-fuel ratio are sequentially formed at a predetermined interval.
3. The air-fuel ratio feedback control device for an engine according to claim 1. 5. The method according to claim 5, wherein the target fuel injection amount is increased when the actual air-fuel ratio is leaner than the target air-fuel ratio, and the target fuel injection amount is decreased when the actual air-fuel ratio is richer. 5. The air-fuel ratio feedback control device for an engine according to claim 1, further comprising a pulse shift value calculating means for calculating a pulse shift value for changing a pulse width. 6. The pulse shift value calculating means calculates the pulse shift value by performing integral control using a deviation assuming a difference between the target air-fuel ratio and the actual air-fuel ratio. An engine air-fuel ratio feedback control device according to claim 5. 7. When the measured output signal of the O ₂ sensor is ON only or OFF only for a predetermined period, the pulse shift value calculating means calculates the pulse shift value by increasing the deviation. 7. The air-fuel ratio feedback control device for an engine according to claim 6, wherein the pulse control unit changes the pulse width so as to reduce a change amount of the rich spike toward the rich side. 8. The pulse control device according to claim 1, wherein the pulse control unit changes the pulse width so as to variably set a change amount of the rich spike according to an operation state of the engine. Air-fuel ratio feedback control means for the engine. 9. The pulse control device according to claim 1, wherein the pulse control unit changes the pulse width so as to variably set a predetermined interval of the rich spike according to an operation state of the engine. Air-fuel ratio feedback control means for the engine. 10. The air-fuel ratio feedback control means for an engine according to claim 1, further comprising an ignition timing correction means for delay-correcting the ignition timing of the engine simultaneously with the change of the pulse width. 11. The air-fuel ratio feedback control means for an engine according to claim 1, further comprising a pulse shift value learning control means for learning the pulse shift value according to an operation state of the engine. 12. The pulse shift value learning control means learns the pulse shift value when an output signal of an O ₂ sensor shows a predetermined change for a predetermined time or more. Air-fuel ratio feedback control means of the engine. 13. The pulse control means according to claim 1, wherein said rich spike is provided in one of a four-cycle multi-cylinder engine.
The basic injection pulse width is controlled so as to be constituted by only one cycle and one cylinder.
4. The air-fuel ratio feedback control means for an engine according to claim 1.