JPH06213031A - Internal combustion engine controller - Google Patents

Abstract

PURPOSE:To make stable lean burning conformable with a ordinary engine speed sensor as well as to reduce the cost of manufacturing by detecting a variation in intake air flow rate interrelated to an engine speed variation, and compensating a lean-burn factor so as to get an air-fuel ratio thickened. CONSTITUTION:An internal combustion engine is provided with a thermal type air flowmeter 102, measuring an intake air mass flow, and a crank angle sensor 107 detecting the extent of engine speed thereabout. An engine speed variation and an intake air quantity variation are interrelated with each other, so if this intake air quantity variation is grasped, a lean-burn limit, where the engine speed variation grows larger, is also grasped. When a variable state in the intake air flow rate turns to the preset one, it is provided with a lean-burn limit detecting part 307, calculating a correction coefficient of a lean-burn factor according to this variable state, and a lean-burn factor compensating part 30 compensating this lean-burn factor. In addition, it is provided with a fuel injection quantity setting part 310 or the like compensating a basic fuel injection quantity and setting a fuel injection quantity. With this constitution, if it is reached to the lean-burn limit, a target lean air-fuel ratio can be compensated so as to be thickened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an internal combustion engine which burns at an air-fuel ratio leaner than the stoichiometric air-fuel ratio.

[0002]

2. Description of the Related Art As a conventional lean burn control system, for example, there is one described in Japanese Patent Laid-Open No. 176636/1988. This lean burn control device is a basic injection charge setting means for setting a basic injection amount according to the engine operating state, and a feedforward correction coefficient so that the actual air-fuel ratio becomes a target lean air-fuel ratio leaner than the theoretical air-fuel ratio. Feedforward correction coefficient setting means for setting, rotational speed fluctuation detecting means for detecting rotational fluctuation of the engine during lean air-fuel ratio control, and the feedforward correction coefficient set when the detected rotational fluctuation is a predetermined value or more. And an air-fuel ratio correction means for correcting the actual air-fuel ratio to be richer than the target lean air-fuel ratio in a lean air-fuel ratio region leaner than the theoretical air-fuel ratio. That is, this lean burn control device senses the lean burn limit (limit at which the air-fuel ratio can be thinned) based on the rotational speed fluctuation, and temporarily determines the rich air-fuel ratio when it determines that the lean burn limit is exceeded. do it,
This enables stable operation even during lean combustion.

[0003]

However, in such a conventional technique, in addition to a normal crank angle sensor (for example, one incorporated in a distributor) for detecting the rotation speed of the internal combustion engine, a delicate combustion due to lean combustion is performed. It is necessary to install a sensor for accurately detecting the rotation speed fluctuation. As such a sensor, for example, a magnetic pickup type sensor can be considered. However, not only the sensor itself is expensive, but also a magnetic drive circuit and the like are required in addition to the sensor body. Therefore, in the prior art,
There are problems that the manufacturing cost increases and the device becomes large.

The present invention has been made by paying attention to the problems of the prior art, and it is possible to realize stable lean combustion, control the internal combustion engine without increasing the manufacturing cost and increasing the size of the apparatus. The purpose is to provide a device.

[0005]

An internal combustion engine control apparatus for achieving the above object comprises an engine speed detecting means for detecting an engine speed of an internal combustion engine, and an intake air detecting means for detecting a flow rate of intake air drawn into the internal combustion engine. An air flow rate detecting means, a target lean air-fuel ratio setting means for setting a target lean air-fuel ratio which is an air-fuel ratio leaner than the theoretical air-fuel ratio, and a variation state of the intake air flow rate due to a change in the detected rotational speed in advance. When the specified state is reached, it is judged that the actual air-fuel ratio is the lean burn limit,
Lean combustion limit detection means for calculating a target lean air-fuel ratio correction coefficient for correcting the target lean air-fuel ratio in accordance with the fluctuation state of the intake air flow rate, and the target lean air-fuel ratio correction coefficient based on the calculated target lean air-fuel ratio correction coefficient. Target lean air-fuel ratio correction means for correcting the air-fuel ratio, and the actual lean air-fuel ratio to the target lean air-fuel ratio set by the target lean air-fuel ratio setting means, or the target corrected by the target lean air-fuel ratio correction means And a lean fuel injection amount setting means for setting a fuel injection amount so as to obtain a lean air-fuel ratio.

Further, another internal combustion engine control apparatus for achieving the above object is a rotational speed detecting means for detecting the rotational speed of the internal combustion engine, and an intake air flow rate for detecting an intake air flow rate taken into the internal combustion engine. Depending on the detection means, the oxygen concentration detection means for detecting the concentration of oxygen contained in the exhaust gas from the internal combustion engine, the detected intake air flow rate and the detected rotational speed, the actual air-fuel ratio To the stoichiometric air-fuel ratio, a basic fuel injection amount calculation means for setting a basic fuel injection amount, a feedback correction coefficient calculation means for calculating a feedback correction coefficient according to the detected oxygen concentration, and an actual air-fuel ratio A lean combustion coefficient setting means for setting a lean combustion coefficient for correcting the basic fuel injection amount so that the target lean air-fuel ratio is an air-fuel ratio leaner than the theoretical air-fuel ratio, When the fluctuation state of the intake air flow rate due to the change of the rotational speed reaches a predetermined state, it is determined that the actual air-fuel ratio is the lean combustion limit, and the lean combustion is determined according to the fluctuation state of the intake air flow rate. Lean-burn limit detection means for calculating a lean-burn correction coefficient for correcting the coefficient, lean-burn coefficient correction means for correcting the lean-burn coefficient based on the lean-burn correction coefficient calculated, and a combustion state of the internal combustion engine. Accordingly, it is determined whether to perform lean combustion or normal combustion, and when it is determined to perform normal combustion, the set basic fuel injection amount is corrected according to the feedback correction coefficient to obtain the fuel injection amount. When it is determined that the lean combustion is to be performed, the lean combustion coefficient is corrected according to the lean combustion coefficient set by the lean coefficient setting means or the lean burn coefficient corrected by the lean combustion coefficient correction means. Flip and, is characterized in that it comprises a fuel injection quantity setting means for setting a fuel injection amount by correcting the reference fuel injection amount that is set, the.

[0007]

In the internal combustion engine, as the air-fuel ratio becomes leaner, the fluctuation of the rotational speed gradually becomes larger and stable lean burn cannot be performed. For this reason, when performing lean combustion, when the rotational speed fluctuation becomes large to some extent, the lean combustion limit is set as
It is necessary to operate at an air-fuel ratio that is higher than the air-fuel ratio at this lean burn limit (thinner than the stoichiometric air-fuel ratio). By the way, there is a correlation between the rotation speed fluctuation and the intake air amount fluctuation.
That is, when the rotation speed changes, the intake air amount also changes. Therefore, if the fluctuation of the intake air amount is grasped, it is possible to grasp the lean combustion limit where the revolution speed fluctuation becomes large.

Therefore, in the present invention, first, when the intake air amount fluctuation state reaches a predetermined state, the lean combustion detection means determines that the lean combustion limit is reached, and a target corresponding to this variation state is set. A lean air-fuel ratio correction coefficient is calculated. The target lean air-fuel ratio correction means multiplies the target lean air-fuel ratio correction coefficient by the target lean air-fuel ratio and corrects the target lean air-fuel ratio. This target lean air-fuel ratio is richer than the target air-fuel ratio initially set by the target lean air-fuel ratio setting means and leaner than the theoretical air-fuel ratio. Then, the lean fuel injection amount setting means sets the fuel injection amount based on the corrected target lean air-fuel ratio.

As described above, according to the present invention, when the lean combustion limit is reached, the target lean air-fuel ratio is corrected to become rich, so that stable lean combustion can be realized. Further, in the present invention, in order to grasp the fluctuation of the intake air amount, the rotation speed detecting means and the intake air amount detecting means are required.
The intake air amount detection means is absolutely necessary for internal combustion engine control, and is not added by the present invention.
Further, the accuracy of rotation speed detection is not required, and expensive rotation speed detection means such as a magnetic pickup type rotation speed meter is not required, so that the manufacturing cost does not increase. The reason why the accuracy of rotation speed detection is not required is that the rotation speed fluctuation is not directly observed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of the system of the present embodiment.

Around the internal combustion engine 101, a thermal air flow meter 102 for measuring the mass flow rate of intake air, a throttle valve 112 for adjusting the intake air amount, and this throttle valve 11 are provided.
A throttle opening sensor 105 for detecting the valve opening of No. 2,
Air that flows into the internal combustion engine 101 through a crank angle sensor 107 that detects the rotational speed of the internal combustion engine 101, an intake pipe pressure sensor 104 that detects pressure fluctuations in the intake pipe 111, and a bypass pipe 113 that is a bypass of the intake pipe 111. The bypass air flow rate control valve 103 for adjusting the amount, and the internal combustion engine 1
01, a fuel injection valve 106 for supplying fuel, an oxidation-reduction catalyst 110 for purifying the exhaust gas by redox, and an oxygen concentration sensor 108 installed upstream of the oxidation-reduction catalyst 110 for detecting the oxygen concentration in the exhaust gas. An internal combustion engine control unit that drives the actuators such as the fuel injection valve 106 by grasping the operating state of the internal combustion engine based on the signals from the respective sensors, calculating the fuel amount and the like required by the internal combustion engine 101 in a predetermined procedure. And 109 are provided. In this embodiment, the oxygen concentration sensor 108 has a binary output with respect to the threshold value of the air-fuel ratio. In addition, the crank angle sensor 107 in this embodiment is incorporated in a distributor generally called a distributor,
It has a gear that engages with the camshaft of the internal combustion engine 101, and determines the crank angle from the rotation of this gear.

FIG. 2 shows an internal circuit block of the internal combustion engine control unit 109. Internal combustion engine control unit 1
Reference numeral 09 denotes a driver circuit 201 for inputting signals from various sensors and converting a small signal into a large signal for driving an actuator.
And an input / output circuit 202 for converting an input / output signal into an analog-digital signal so as to perform digital arithmetic processing, a microcomputer for performing digital arithmetic processing, or an arithmetic circuit 203 corresponding thereto, and constants and variables used for arithmetic processing of the arithmetic circuit 203. , And a memory 2 for storing a program
05 and 206. The memory includes a non-volatile ROM 205 and a volatile RAM 206. The internal combustion engine control device 109 further includes a volatile R
A backup circuit 204 that holds the contents of the AM 206 is also provided. Here, as an input signal to this unit 109, a signal from the oxygen concentration sensor 108, a signal from the throttle opening sensor 105, the crank angle sensor 1
There is a signal from 07 and a signal from the thermal type air flow meter 102. The output signals from the unit 109 include an ignition signal to the spark plug 114, a valve control signal to the bypass air flow rate control valve 103, and an injection valve drive signal to the fuel injection valve 106. In this embodiment, the unit 109 is composed of a digital arithmetic unit,
It goes without saying that an analog type arithmetic unit can also be used.

By the way, the configuration of the hard surface of the internal combustion engine control unit 109 has been described above. However, as shown in FIG. 3, the internal combustion engine control unit 109 is detected by software. A basic fuel amount vehicle calculation unit 301 that calculates the basic fuel injection amount from the fuel amount correction coefficient storage unit 302 that stores a correction coefficient for correcting the variation of the fuel injection amount due to the machine difference of the fuel injection valve and the like. And a lean combustion coefficient for correcting the fuel injection amount so that the fuel injection amount becomes the fuel amount corresponding to the target lean air-fuel ratio, and is stored in accordance with the detected intake air amount Q and rotational speed N. A lean burn coefficient setting unit 304 that sets a lean burn coefficient, and a lean burn correction coefficient that is used to correct the lean burn coefficient by detecting the lean burn limit from the detected intake air amount Q and the rotational speed N. And baked limit detection unit 307, a lean-burn coefficient for correcting the lean burn coefficient based on the lean combustion correction coefficient output from the lean combustion limit detection unit 307 correction unit 306
And a lean-burn coefficient learning unit 305 that stores the lean-burn coefficient corrected by the lean-burn coefficient correction unit 306 in the lean-burn coefficient setting unit 304, and a feedback correction that calculates a feedback correction coefficient based on the output from the oxygen concentration sensor 108. A coefficient calculation unit 308 and a fuel injection amount setting unit 310 that corrects the basic fuel injection amount with a fuel amount correction coefficient, a lean combustion coefficient, and a feedback correction coefficient and outputs the corrected fuel injection amount to the fuel injection valve 106 are provided. is doing.

The fuel amount correction coefficient storage unit 302 stores a fuel amount correction coefficient corresponding to the intake air amount Q and the rotation speed N. That is, the fuel amount correction coefficient storage unit 302 maps the fuel amount correction coefficient with the intake air amount Q and the rotation speed N as parameters. Further, the lean combustion coefficient setting unit 304 also maps the lean combustion coefficient with the intake air amount Q and the rotational speed N as parameters. Also,
After correcting the basic fuel injection amount with the fuel amount correction coefficient, the fuel injection amount setting unit 310 corrects the fuel amount with one of the lean combustion coefficient and the feedback correction coefficient according to the state of the internal combustion engine 101. To do. The specific configuration of the lean burn limit detector 307 will be described later.

FIG. 4 shows an example of measuring the intake air amount from the output from the thermal air flow meter 102. The block 401 is a voltage value filter for the voltage signal from the thermal air flow meter 102. The filter 401 is classified into a continuous band configured by a circuit and a discrete band configured by software. A block 402 is a block that converts a voltage into a flow rate. This conversion is performed by table search or linear calculation. Although the blocks 401 and 402 are provided in the internal combustion engine control unit 109, they are not shown in FIG. 3 to simplify the drawing.

Incidentally, the intake air amount can be measured by directly converting the voltage signal from the thermal air flow meter 102 into a flow rate as described in the present embodiment (the one described with reference to FIG. 4). However, as shown in FIG. 5 and FIG. 6, it can be obtained from the output of the intake pipe pressure sensor and the output of the intake temperature sensor, or can be obtained from the output of the throttle opening sensor and the output of the intake temperature sensor. Is.

FIG. 5 shows an example of calculating the air flow rate from the output of the intake pipe pressure sensor and the output of the intake air temperature sensor. Similar to the example of FIG. 4, the captured voltage signal from the intake pipe pressure sensor is filtered at block 501. In block 503, the voltage signal from the intake air temperature sensor is converted into intake air temperature. In block 502, the output voltage of the pressure sensor is converted into pressure, and in block 504, the intake air amount is calculated from the intake air temperature and the pressure.

FIG. 6 shows an example of calculating the air flow rate from the output of the throttle opening sensor and the output of the intake air temperature sensor. In block 601, the voltage signal from the throttle opening sensor is converted into the throttle opening. Block 60
In step 2, the intake air amount table is searched to find the volumetric air flow rate. Block 603 converts the voltage signal from the intake air temperature sensor into intake air temperature. In block 604, the volumetric air flow rate obtained in block 602 is converted into a mass air flow rate using the intake air temperature described above. In addition, also in the examples shown in FIGS. 4 and 5, the mass air flow rate is finally obtained.

FIG. 7 shows the relationship between the air-fuel ratio of the internal combustion engine 101 and the rotation fluctuation.

In the theoretical air-fuel ratio region shown in the figure, the rotational fluctuation in units of several seconds is small and there is no problem. However, when the air-fuel ratio becomes leaner than the air-fuel ratio in the stoichiometric air-fuel ratio region, the rotational fluctuation in units of several seconds gradually increases, exceeds the rotational fluctuation allowable limit, and the internal combustion engine 101 cannot operate stably.
The lean combustion limit of the air-fuel ratio shown in the same figure is the value of the air-fuel ratio that reaches the rotation fluctuation allowable limit.

FIG. 9 shows an example of fluctuations in the intake air amount. It should be noted that FIG. 11A shows the intake air amount variation at the stoichiometric air-fuel ratio, and FIG. 9B shows the intake air amount variation at the lean combustion limit air-fuel ratio. As shown in the figure,
The fluctuation of the intake air amount at the stoichiometric air-fuel ratio is smaller than the fluctuation of the intake air amount at the lean-burn limit air-fuel ratio. Therefore, a variation pattern of the intake air amount at the stoichiometric air-fuel ratio is prepared in advance, and if the difference between the intake air amount on this pattern and the intake air amount at the time of lean combustion becomes larger than a predetermined value, the lean air amount becomes lean. It can be judged that the combustion limit has been reached.

Therefore, the deviation d between the intake air amount at a certain crank angle on the intake air amount fluctuation pattern at the stoichiometric air-fuel ratio and the intake air amount at the time of lean combustion at the same crank angle as this crank angle is obtained. Further, the deviation d is similarly obtained for other crank angles. And (Equation 1)
As shown in, the average deviation S of these is calculated, and this value S
Is the lean burn limit, and further, how much the lean burn coefficient should be corrected if it is the lean burn limit,
As an index.

[0023]

[Equation 1]

As described above, the rotational speed fluctuation in the unit of several seconds is larger than the rotational speed fluctuation in the stoichiometric air-fuel ratio, and the rotational speed fluctuation in the lean combustion limit is larger in the unit of several hundred crank angles. The rotational speed fluctuation is larger at the stoichiometric air-fuel ratio than at the lean burn limit. In other words, when the rotational speed fluctuation is regarded as a large swell, the rotational speed fluctuation at the lean combustion limit is larger than that at the stoichiometric air-fuel ratio, and the rotational speed fluctuation When it is considered as a fine fluctuation, it means that the fluctuation in the rotational speed at the theoretical air-fuel ratio is larger than the fluctuation in the rotational speed at the lean burn limit.

FIG. 11 is a diagram showing the detailed structure of the lean burn limit detector 307. The lean burn limit detector 307
Air flow rate sampling unit 1 for sampling air flow rate
101, a sampling initial position compensation unit 1102 for compensating the initial position sampled by the air flow rate sampling unit 1101, a standard air flow rate storage unit 1103 in which the air flow rate at the stoichiometric air-fuel ratio is stored, and a sampled air flow rate. A subtracter 1106 that obtains a deviation d from the air flow rate stored in the standard air flow rate storage unit 1103, an average deviation calculation unit 1104 that obtains an average deviation S of a plurality of deviations d using (Equation 1), and The lean burn correction coefficient for correcting the lean burn coefficient is output when the lean burn limit is reached, and when the lean burn limit is reached, the lean burn correction coefficient for outputting the lean burn correction coefficient is output. The calculation unit 1105 is included.

Here, the sampling initial position compensation unit 11
In order to explain the operation of No. 02, the relationship between the fluctuation of the intake air amount and the fluctuation of the rotation speed of the internal combustion engine will be described with reference to FIG. As shown in the figure, the intake air amount fluctuates in synchronization with the fluctuation of the rotation speed of the internal combustion engine. However, the intake air enters the internal combustion engine, and the rotation speed of the internal combustion engine is one of the parameters representing the phenomenon that occurs as a result of the air entering the internal combustion engine. Conversely speaking, it exploded in the internal combustion engine,
The crankshaft rotates, and as a result, the internal pressure of the internal combustion engine becomes negative, and air is sucked into the internal combustion engine. Therefore, there is a time lag between the fluctuation of the intake air amount and the fluctuation of the rotation speed.
Therefore, in order to compensate for this time shift, the sampling initial position compensating unit 1102 compensates the initial position of the air flow rate sampling. Note that the air flow rate is sampled for each predetermined constant crank angle after the initial sampling.

The standard air flow rate storage unit 1103 stores the intake air amount at a certain crank angle on the intake air amount variation pattern at the stoichiometric air-fuel ratio described with reference to FIG. This intake air amount is mapped using the intake air amount and the rotation speed as parameters. When the current intake air amount and rotation speed are detected, the air flow rates corresponding to these parameters are output to the subtractor 1106. Will be. The lean burn correction coefficient calculated by the lean burn correction coefficient calculation unit 1105 is output to the lean burn coefficient correction unit 306, where it is multiplied by the lean burn coefficient output from the lean burn coefficient storage unit 304, and the lean burn coefficient is calculated. Is corrected. This corrected lean burn coefficient is used as the lean burn coefficient learning unit 305.
And to the fuel amount correction unit 310.

FIG. 10 shows the fluctuation of the intake air amount. It should be noted that FIG. 11A shows the intake air amount variation at the stoichiometric air-fuel ratio, and FIG. 9B shows the intake air amount variation at the lean combustion limit air-fuel ratio. Since the fluctuation of the intake air amount at the stoichiometric air-fuel ratio is smaller than the fluctuation of the intake air amount at the lean-fuel limit air-fuel ratio, the variance value of the intake air amount is less than that at the theoretical air-fuel ratio. The dispersion value at the fuel ratio is smaller. Therefore, if the dispersion value of the intake air amount becomes smaller than a predetermined value, it can be determined that the lean combustion limit has been reached.

Therefore, the lean burn limit detector 307 can also be constructed as shown in FIG. The lean burn limit detection unit 307 calculates a weighted average Q _ave of a plurality of sampled intake air flow rates by using ( _Equation 2), and a weighted average Q _ave that has been sampled. a subtracter 1202 for obtaining and using the difference s _i of the intake air quantity Q _i (number 3) of the subtractor 12
A dispersion calculation unit 1203 that obtains the variance value σ of the intake air amount from the difference s _i obtained in 02 by using (Equation 4), and it is determined from the obtained variance value σ whether the lean combustion limit has been reached. In addition, it has a lean burn correction coefficient calculation unit 1204 that outputs a lean burn correction coefficient for correcting the lean burn coefficient when it is determined that the lean burn limit has been reached.

[0030]

[Equation 2]

[0031]

[Equation 3]

[0032]

[Equation 4]

FIG. 13 shows the above-mentioned mean deviation S and variance σ.
And the air-fuel ratio. The average deviation S increases as the air-fuel ratio becomes leaner. Therefore, if the average deviation S ₀ that becomes the rotational fluctuation allowable limit, that is, the lean combustion limit, is set in advance, the obtained average deviation S ₀ is the predetermined value S _0.
Whether or not the lean burn limit has been reached can be determined depending on whether or not the lean burn limit has been reached. Further, the dispersion σ decreases in inverse proportion to the dilution of the air-fuel ratio. Therefore, as in the case of using the average deviation S, if the variance σ ₀ that is the lean combustion limit is set in advance, it is possible to determine whether or not the lean combustion limit has been reached.

Since the target lean air-fuel ratio is the theoretical air-fuel ratio multiplied by the lean combustion coefficient, the target lean air-fuel ratio setting means in this embodiment is the basic fuel injection amount calculated from the theoretical air-fuel ratio. The fuel injection amount calculation unit 301 and the lean combustion coefficient setting unit 304 are included. Further, in the present embodiment, since the lean burn limit detection unit 304 obtains the lean burn correction coefficient that corrects the lean burn coefficient, the target lean air-fuel ratio correction coefficient that indirectly corrects the target lean air-fuel ratio is used as the lean burn limit. The lean combustion limit detecting means is configured to include the lean burn limit detecting unit 304 because the detecting unit 304 determines the lean burn limit. Further, since the lean combustion coefficient correction unit 306 indirectly corrects the target lean air-fuel ratio, the target lean air-fuel ratio correction unit includes the lean combustion correction unit 306.

FIG. 14 is a flow chart showing the operation of the internal combustion engine control unit 109.

In step 1501, the amount of air taken in by the internal combustion engine 101 is read. In step 1502, the rotation speed of the internal combustion engine 101 is read. In step 1503, the output of the oxygen concentration sensor 108 is read. Then, in step 1504, the basic fuel calculation unit 301 calculates the basic fuel injection amount. In step 1505, it is determined whether or not the current air-fuel ratio is in the stoichiometric air-fuel ratio region. If it is in the stoichiometric air-fuel ratio region, the process proceeds to step 1506, and if it is not in the stoichiometric air-fuel ratio region, the process proceeds to step 1508.

In step 1506, the feedback correction coefficient calculation unit 308 calculates the feedback correction coefficient based on the output from the oxygen concentration sensor 108. In step 1507, the fuel injection amount setting unit 310 multiplies the feedback correction coefficient and the fuel correction coefficient stored in the fuel correction coefficient storage unit 302 by the basic fuel injection amount to determine the fuel injection amount during normal combustion. Ask. In step 1513, the calculated fuel injection amount is set to the fuel injection valve 106.
Output to.

At the step 1505, step 15
When the routine proceeds to 08, in step 1508, the lean burn coefficient setting unit 304 obtains the lean burn coefficient corresponding to the current rotational speed and the intake air amount. In step 1509, the lean combustion limit detection unit 304 determines whether or not the lean combustion limit has been reached from the fluctuation state of the intake air amount. Here, when it is determined that the lean combustion limit is reached, the routine proceeds to step 1510, and when it is determined that the lean combustion limit is not reached,
Proceed to step 1512. In step 1510, the lean burn limit detection unit 304 obtains a lean burn correction coefficient from the fluctuation state of the intake air amount. In step 1511, the lean burn coefficient correction unit 306 corrects the lean burn coefficient by multiplying the lean burn coefficient by the lean burn correction coefficient. Step 15
In 12, the fuel injection amount setting unit 310 multiplies the basic fuel injection amount by the fuel correction coefficient and the lean combustion coefficient stored in the fuel correction coefficient storage unit 302 to obtain the fuel injection amount during lean combustion. At this time, if the lean burn coefficient has been corrected, the corrected lean burn coefficient is used to
The basic fuel injection amount is corrected, and it is determined that the lean combustion limit is not reached (step 1509). If the lean combustion coefficient is not corrected, the lean combustion coefficient initially determined (step 1508) is used to perform the basic fuel injection. Correct the amount. If the fuel injection amount at the time of lean combustion is obtained, step 15
At 13, the fuel injection amount is output to the fuel injection valve 106.

FIG. 15 is a flow chart showing the operation of the lean burn limit detector 304 shown in FIG. In step 1801, it is determined whether or not the sample initial position compensation is completed. If the sample initial position compensation is completed, the sampling of the intake air amount is started in step 1802. If it is not compensated, the sample initial position compensation is performed in step 1809. Step 1
At 803, the rotational speed of the internal combustion engine is read. Step 18
At 04, the standard air amount stored in the standard air amount storage unit 1103 is searched for the standard air amount according to the state at that time, and at step 1805, the difference between this standard air amount and the sampled intake air amount is searched. Then, the sum of the absolute values of this difference is calculated. In step 1806, it is determined whether or not the crank angle synchronization trigger 2 has just been input. Immediately after the input, in step 1807, the average deviation S that is an index is calculated and output to the lean combustion coefficient correction unit 306,
In step 1808, the integrated value is initialized.

FIG. 16 is a detailed flowchart of the sample initial position compensation processing in step 1809. In step 1701, the minimum value of the sampled air flow rate is searched. If there is a minimum value (step 1702), that position is set as the initial position, the crank angle at the minimum value is stored in the memory, and the air flow rate sampling unit 1101 starts sampling the air flow rate from the crank angle (step 1702). Step 1703).

FIG. 17 is a flow chart showing the operation of the lean burn limit detector 307 shown in FIG. In step 1601, a weighted average of a plurality of sampled intake air amounts is performed. In step 1602, the absolute value of the difference between the weighted average value and one sampled intake air amount is calculated, and in step 1603, the integrated value of the absolute values of the differences is calculated. In step 1604, the crank angle synchronization trigger 2
Immediately after is input, and if it is immediately after input, in step 1605, the average of the differences is calculated. In step 1606, the average of the differences is used to calculate the variance σ that is an index, which is output to the lean burn coefficient correction unit 306, and in step 1607 the index is initialized.

As described above, in the present embodiment, paying attention to the fact that there is a correlation between the rotational speed fluctuation of the internal combustion engine and the fluctuation of the intake air flow rate, the fluctuation status of the intake air flow rate is set to a predetermined state. In this case, the lean combustion coefficient is corrected so that the air-fuel ratio is enriched. Therefore, it is possible to suppress fluctuations in the rotational speed and perform stable lean combustion.

Further, in this embodiment, since the fluctuation of the intake air flow rate due to the change of the rotation speed of the internal combustion engine is observed, the rotation speed sensor is necessary, but the normal sensor incorporated in the distributor or the like is used. Since the rotation speed is detected, like a magnetic pickup type rotation speed sensor,
No expensive sensors are needed. This is because, since the rotation speed fluctuation is not directly observed, the accuracy of rotation speed detection is not required, and the average rotation speed obtained by filtering the output from a normal sensor is sufficient. Furthermore, in this embodiment, an intake air flow meter is used, but this is absolutely necessary for controlling the internal combustion engine, and in this embodiment,
It was not added in particular. Therefore, the manufacturing cost can be reduced.

In this embodiment, the basic fuel injection amount is calculated from the theoretical air-fuel ratio, and the basic fuel injection amount is multiplied by the lean combustion coefficient so that the air-fuel ratio becomes the target lean air-fuel ratio, and the lean combustion is performed. The fuel injection amount at the time of is calculated, but the target lean air-fuel ratio (theoretical air-fuel ratio x lean combustion coefficient = target lean air-fuel ratio) is found instead of the lean combustion coefficient, and the lean lean combustion ratio is calculated from this target lean air-fuel ratio. The fuel injection amount may be obtained directly.

[0045]

According to the present invention, when the fluctuation of the intake air flow rate that is correlated with the fluctuation of the rotational speed of the internal combustion engine is detected and the fluctuation state becomes a predetermined state, the lean combustion coefficient is changed to the air-fuel ratio. Is corrected so as to be enriched, it is possible to suppress fluctuations in the rotational speed and perform stable lean combustion. Also,
Since the rotation speed fluctuation is not directly observed, the accuracy of the rotation speed detection is not required, and a normal rotation speed sensor can be used, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration around an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a block diagram of an internal circuit of an internal combustion engine control unit according to an embodiment of the present invention.

FIG. 3 is a functional block diagram of an internal combustion engine control unit according to an embodiment of the present invention.

FIG. 4 is a circuit block diagram of intake air amount detection according to an embodiment of the present invention.

FIG. 5 is a circuit block diagram for detecting an intake air flow of another embodiment according to the present invention.

FIG. 6 is a circuit block diagram for detecting an intake air amount according to still another embodiment of the present invention.

FIG. 7 is a graph showing changes in the number of revolutions with respect to changes in the air-fuel ratio.

FIG. 8 is a graph showing fluctuations in air flow rate and fluctuations in rotation speed with respect to changes in crank angle of the internal combustion engine.

FIG. 9 is a graph showing a change in intake air amount with respect to a change in crank angle of the internal combustion engine.

FIG. 10 is a graph showing fluctuations in intake air amount with respect to changes in crank angle of the internal combustion engine.

FIG. 11 is a functional block diagram of a lean burn limit detection unit according to an embodiment of the present invention.

FIG. 12 is a functional block diagram of a lean burn limit detector of another embodiment according to the present invention.

FIG. 13 is a graph showing a relationship between a lean burn index and an air-fuel ratio in each example according to the present invention.

FIG. 14 is a flowchart showing the operation of the internal combustion engine control unit of the embodiment according to the present invention.

15 is a flowchart showing the operation of the lean burn limit detection unit shown in FIG.

16 is a detailed flowchart of step 1809 in FIG.

FIG. 17 is a flowchart showing the operation of the lean burn limit detector shown in FIG.

[Explanation of symbols]

101 ... Internal combustion engine, 102 ... Thermal air flow meter, 106 ...
Fuel injection valve, 107 ... Crank angle sensor, 108 ... Oxygen concentration sensor, 109 ... Internal combustion engine control unit, 203
... arithmetic unit, 205 ... ROM, 206 ... RAM, 301
... basic fuel injection amount calculation unit, 302 ... fuel correction coefficient storage unit, 304 ... lean burn coefficient setting unit, 305 ... lean burn coefficient learning unit, 306 ... lean burn coefficient correction unit, 307 ... lean burn limit detection unit, 308 ... Feedback correction coefficient calculation unit 310 ... Fuel injection amount setting unit.

Claims (5)

[Claims] 1. A rotation speed detecting means for detecting a rotation speed of an internal combustion engine, an intake air flow rate detecting means for detecting a flow rate of intake air drawn into the internal combustion engine, and an air-fuel ratio leaner than a theoretical air-fuel ratio. The target lean air-fuel ratio setting means for setting the target lean air-fuel ratio and the actual air-fuel ratio is the lean combustion limit when the fluctuation state of the intake air flow rate due to the change in the detected rotation speed becomes a predetermined state. And a lean combustion limit detecting means for calculating a target lean air-fuel ratio correction coefficient for correcting the target lean air-fuel ratio according to the fluctuation state of the intake air flow rate, and the calculated target lean air-fuel ratio correction coefficient Based on the target lean air-fuel ratio correction means for correcting the target lean air-fuel ratio based on the actual lean air-fuel ratio, the actual lean air-fuel ratio to the target lean air-fuel ratio set by the target lean air-fuel ratio setting means, or the target lean air-fuel ratio correction means So that the target lean air-fuel ratio which Tadashisa, internal combustion engine control apparatus characterized by comprising a lean fuel injection amount setting means for setting a fuel injection amount, the. 2. The lean combustion limit detection means includes standard intake air flow rate storage means for storing a predetermined standard intake air flow rate, and the standard intake air stored with the detected intake air flow rate. A deviation calculating means for obtaining a difference from the air flow rate, and when the difference becomes a predetermined difference, it is judged that the actual air-fuel ratio is the lean combustion limit, and the target lean air-fuel ratio correction is made according to the difference. The internal combustion engine control apparatus according to claim 1, further comprising: a correction coefficient calculation unit that calculates a coefficient. 3. The lean burn limit detection means is a variance calculation means for obtaining a variance of the detected intake air flow rate, and when the variance becomes a predetermined value, the actual air-fuel ratio is the lean burn limit. 2. The internal combustion engine control apparatus according to claim 1, further comprising: a correction coefficient calculation unit that calculates the target lean air-fuel ratio correction coefficient according to the dispersion. 4. An oxygen concentration detecting means for detecting a concentration of oxygen contained in exhaust gas from the internal combustion engine, and a feedback correction coefficient calculating means for calculating a feedback correction coefficient according to the detected oxygen concentration. The normal fuel injection amount setting means for correcting the set reference fuel injection amount according to the feedback correction coefficient to obtain a fuel injection amount, and a normal fuel injection amount setting means. Fuel control device for internal combustion engine. 5. A rotation speed detecting means for detecting a rotation speed of an internal combustion engine, an intake air flow rate detecting means for detecting a flow rate of intake air drawn into the internal combustion engine, and exhaust gas from the internal combustion engine. An oxygen concentration detecting means for detecting the concentration of oxygen, and a basic fuel injection amount for setting an actual air-fuel ratio to a stoichiometric air-fuel ratio are set according to the detected intake air flow rate and the detected rotational speed. Basic fuel injection amount calculation means, feedback correction coefficient calculation means for calculating a feedback correction coefficient according to the detected oxygen concentration, and target lean air-fuel ratio in which the actual air-fuel ratio is leaner than the theoretical air-fuel ratio. A lean combustion coefficient setting means for determining a lean combustion coefficient for correcting the basic fuel injection amount so as to obtain a fuel ratio, and a variation state of the intake air flow rate due to a change in the detected rotational speed is predicted. When the predetermined state is reached, it is judged that the actual air-fuel ratio is at the lean combustion limit, and the lean burn limit detection for calculating the lean burn correction factor for correcting the lean burn factor according to the fluctuation state of the intake air flow rate is detected. Means, a lean combustion coefficient correction means for correcting the lean combustion coefficient based on the calculated lean combustion correction coefficient, and a determination as to whether to perform lean combustion or normal combustion according to the combustion state of the internal combustion engine. However, when it is determined that the normal combustion is performed, the set basic fuel injection amount is corrected according to the feedback correction coefficient to obtain the fuel injection amount, and when it is determined that the lean combustion is performed, the lean coefficient setting means is set. In accordance with the lean combustion coefficient set by the above, or in accordance with the lean combustion coefficient corrected by the lean combustion coefficient correction means, the set reference fuel injection amount is corrected An internal combustion engine control device comprising: a fuel injection amount setting means for setting an injection amount;