JPH07279732A - Combustion control method and device for internal combustion engine - Google Patents

Abstract

PURPOSE:To combustion-control each cylinder in its ideal condition by detecting dispersion of an inter-cylinder air-fuel ratio when an internal combustion engine is operated near lean combustion limit on the basis of the detected result of rotational fluctuation, correcting the injector driving time at the time of theovetical air-fuel ratio operation on the basis of the detected result. CONSTITUTION:A rotational fluctuation detecting means 207 for detecting rotational fluctuation which is generated when a multiple cylinder internal combustion engine is operated by the air-fuel ratio on a side leaner than a theovetical air-fuel ratio is provided, and the internal combustion engine is operated near the lean combustion limit by a lean combustion limit operating means 208 on the basis of a detected result. A fuel injection amount is changed by a fuel injection amount changing means 210 at the time of lean combustion operation so as to maintain combustion fluctuation found out from rotational fluctuation in an allowable range, and also dispersion of an inter-cylinder air-fuel ratio is detected from the changing amount by a dispersion detecting means 209, and an injector driving time at the time of a theovetical air-fuel ratio operation is corrected by an injector driving correcting means 211 on the basis of dispersion detected result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to combustion of an internal combustion engine suitable for use in a lean-burn internal combustion engine (engine) that performs lean-burn operation at a leaner air-fuel ratio than the theoretical air-fuel ratio under required operating conditions. The present invention relates to a control method and a combustion control device.

[0002]

2. Description of the Related Art In recent years, a lean burn internal combustion engine (so-called lean burn engine) has been provided which performs a lean burn operation at a leaner air-fuel ratio (lean) than a stoichiometric air-fuel ratio (stoichio) under required operating conditions. There is. In such a lean burn engine, during lean burn operation (lean burn operation), the air-fuel ratio is set as large as possible (that is, the air-fuel mixture becomes lean as much as possible) in order to reduce the NOx emission amount. The value of the fuel ratio is set near a limit (lean limit) at which the air-fuel mixture can perform stable combustion.

By performing such lean burn operation, NOx emission can be suppressed and fuel consumption can be greatly improved. Here, a three-way catalyst or the like is used to reduce NOx emissions, and the fuel injection amount is controlled so that the catalyst is used at maximum efficiency. In this fuel injection amount control, a method of detecting the composition of combustion gas by an air-fuel ratio sensor (A / F sensor) and correcting the fuel injection amount is used.

[0004]

By the way, the air-fuel ratio sensor is generally arranged in the exhaust pipe collecting portion and can detect only the average air-fuel ratio of each cylinder. It is controlled by the fuel ratio. Here, the characteristics of the ejector flow rate in the multi-cylinder internal combustion engine have variations as shown in FIG. That is, FIG. 15 shows the fuel injection pulse width on the horizontal axis and the flow rate error on the vertical axis, and shows the injection characteristics of the arbitrarily extracted injectors, in particular, the injection amount of each injector, for comparison. As shown, there is an error of 2-3%.

The error in the injection characteristic tends to be amplified by the shape error in the vicinity of the valve seat in addition to the variation in the injector valve drive. In addition to this, due to variations in intake air amount between cylinders due to arrangement of intake pipes, variations in intake air amount between banks due to variations in intake valve opening / closing timing, etc., the air-fuel ratio of each cylinder is within a certain range around the theoretical air-fuel ratio. It is distributed (see FIG. 14).

Therefore, it is difficult for the conventional control means to operate all the cylinders at the maximum efficiency point of the catalyst.
Here, it is conceivable that air-fuel ratio feedback control is performed for each cylinder, and as a means that can be adopted as such control means, for example, JP-A-2-227534.
It is conceivable to control the injection amount by using the rotation fluctuation for each cylinder as disclosed in Japanese Patent Publication No.

However, with such means, it is difficult to detect the variation for each cylinder during stoichiometric operation. That is, in order to detect the variation between the cylinders during stoichiometric operation, it is necessary to make the internal combustion engine idle operation at an extremely low speed, and it is difficult to detect the variation during normal operation.

The present invention was devised in view of the above problems, and by utilizing the rotation fluctuation during lean burn operation, reliable combustion control for each cylinder can be performed even during operation at the stoichiometric air-fuel ratio. An object of the present invention is to provide a combustion control method and a combustion control device for an internal combustion engine.

[0009]

Therefore, the combustion control method for an internal combustion engine of the present invention detects, for each cylinder, the rotational fluctuation that occurs when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the theoretical air-fuel ratio. However, in the case where the internal combustion engine can be operated in the vicinity of the lean combustion limit based on the detection result, the fuel injection amount is changed to keep the combustion fluctuation obtained from the rotation fluctuation within the allowable range during the lean combustion operation. Step, a second step of detecting the variation in the air-fuel ratio between the cylinders from the change amount of the fuel injection amount, and a third step of correcting the injector drive time during the stoichiometric air-fuel ratio operation based on the detection result. It is characterized by having.

Further, the combustion control apparatus for an internal combustion engine according to the present invention includes a rotation fluctuation detecting means for detecting a rotation fluctuation for each cylinder when a multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the theoretical air-fuel ratio. A lean combustion limit operating means for operating the internal combustion engine in the vicinity of the lean combustion limit based on the detection result of the rotation variation detecting means, and a combustion variation obtained from the rotation variation during the lean combustion operation by the lean combustion limiting operating means. Fuel injection amount changing means for changing the fuel injection amount so as to keep it within an allowable range, inter-cylinder air-fuel ratio variation detecting means for detecting variation in inter-cylinder air-fuel ratio from the variation amount in the fuel injection amount changing means, and the cylinder Injector drive correction means for correcting the injector drive time during stoichiometric air-fuel ratio operation based on the detection result by the inter-air-fuel ratio variation detection means is provided. It is a symptom.

[0011]

In the combustion control method for an internal combustion engine according to the present invention as set forth in claim 1, the rotational fluctuation that occurs when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the theoretical air-fuel ratio is detected for each cylinder. The internal combustion engine is operated in the vicinity of the lean burn limit based on the detection result. However, when the lean burn operation of the internal combustion engine is performed, the fuel injection amount is set to the first amount in order to keep the combustion variation obtained from the rotation variation within the allowable range. The change is made in the step, and the variation of the air-fuel ratio between the cylinders is detected from the change amount in the second step. Then, based on the detection result, the injector drive time during the stoichiometric air-fuel ratio operation is corrected in the third step.

Further, in the combustion control device for an internal combustion engine according to the present invention as set forth in claim 2, the rotational fluctuation generated when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the theoretical air-fuel ratio is rotational fluctuation detecting means. Is detected for each cylinder, and the internal combustion engine is operated by the lean burn limit operating means near the lean burn limit based on the detection result. Then, the fuel injection amount changing means changes the fuel injection amount in order to keep the combustion fluctuation obtained from the rotation fluctuation within the allowable range during the lean combustion operation by the lean combustion limit operating means. The variation of the air-fuel ratio between the cylinders is detected from the change amount by the air-fuel ratio variation detection means between the cylinders, and the injector drive time during the stoichiometric air-fuel ratio operation is corrected by the injector drive correction means based on the detection result.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A combustion control method and a combustion control apparatus for an internal combustion engine as an embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 are control block diagrams of an apparatus for carrying out the method. 3 is an overall configuration diagram of an engine system having this device, FIG. 4 is a hardware block diagram showing a control system of an engine system having this device, FIGS. 5 to 7 are flow charts for explaining the operation of this device, and FIG. FIG. 9 is a waveform diagram for explaining the operation of the apparatus, FIG. 9 is a correction characteristic map for explaining the operation of the apparatus, FIG. 10 is a schematic graph for explaining the operation of the apparatus, and FIG. 11 is the apparatus. Is a schematic graph for explaining the operation of FIG. 12, FIG. 12 is a normalization characteristic map for explaining the operation of the present apparatus, and FIG. 13 is a schematic perspective view showing a rotation fluctuation detection unit in the present apparatus.

An engine for an automobile equipped with this device has a stoichiometric air-fuel ratio under required operating conditions.
It is configured as a lean burn engine that performs lean burn operation (lean burn operation) at a leaner air-fuel ratio (lean) than this, and this engine system is as shown in FIG. That is, in FIG. 3, an engine (internal combustion engine) 1 has an intake passage 3 and an exhaust passage 4 communicating with a combustion chamber 2 thereof, and the intake passage 3 and the combustion chamber 2 are controlled to communicate with each other by an intake valve 5. In addition, the exhaust passage 4 and the combustion chamber 2 are controlled to communicate with each other by an exhaust valve 6.

Further, the intake passage 3 is provided with an air cleaner 7, a throttle valve 8 and an electromagnetic fuel injection valve (injector) 9 in this order from the upstream side, and the exhaust passage 4 is provided in order from the upstream side. A three-way catalyst 10 and a muffler (silencer) not shown are provided. The injector 9 is provided for each cylinder of the engine 1. Further, the intake passage 3 is provided with a surge tank 3a.

The three-way catalyst 10 purifies CO, HC and NOx under stoichiometric operation and is a known one. Further, the throttle valve 8 is connected to an accelerator pedal (not shown) via a wire cable, and its opening degree is adjusted according to the depression amount of the accelerator pedal.

A first bypass passage 11A for bypassing the throttle valve 8 is provided in the intake passage 3, and a stepper motor valve (hereinafter referred to as an STM valve) which functions as an ISC valve is provided in the first bypass passage 11A. 12 are installed. In addition, in the first bypass passage 11A,
A wax-type fast idle air valve 13 whose opening is adjusted according to the engine cooling water temperature is also provided, and is attached to the STM valve 12.

Here, the STM valve 12 is a valve body 12a which can abut against a valve seat portion formed in the first bypass passage 11A.
And a stepper motor (I
(SC actuator) 12b, and a spring 12c that urges the valve body in a direction that presses the valve body against the valve seat portion (a direction that closes the first bypass passage 11A). The stepper motor 12b performs stepwise adjustment of the position of the valve body 12a with respect to the valve seat portion (adjustment by the number of steps) to open the valve seat portion and the valve body 12a, that is, the STM valve 12
The opening degree of is adjusted.

Therefore, the opening degree of the STM valve 12 is an electronic control unit (ECU) 2 as a controller which will be described later.
By controlling with 5, the intake air can be supplied to the engine 1 through the first bypass passage 11A regardless of the driver's operation of the accelerator pedal, and the throttle bypass intake amount is adjusted by changing the opening degree. You can do it.

As the actuator for ISC,
A DC motor may be used instead of the stepper motor 12b. Further, the intake passage 3 is provided with a second bypass passage 11B that bypasses the throttle valve 8, and an air bypass valve 14 is interposed in the second bypass passage 11B.

Here, the air bypass valve 14 has a second
It is composed of a valve body 14a capable of contacting a valve seat portion formed in the bypass passage 11B, and a diaphragm type actuator 14b for adjusting the position of the valve body, and a diaphragm chamber of the diaphragm type actuator 14b is provided with: A pilot passage 141 communicating with the intake passage on the downstream side of the throttle valve is provided.
An air bypass valve control solenoid valve 142 is provided at 41.

Therefore, by controlling the opening of the solenoid valve 142 for controlling the air bypass valve by the ECU 25, which will be described later, in this case also, regardless of the operation of the accelerator pedal by the driver, the second bypass passage 11B is used. The intake air can be supplied to the engine 1, and the throttle bypass intake air amount can be adjusted by changing the opening thereof. The air bypass valve controlling solenoid valve 142 is opened during lean burn operation,
Other than that, the basic operation is to be closed.

An exhaust gas recirculation passage (EGR passage) for returning exhaust gas to the intake system is provided between the exhaust passage 4 and the intake passage 3.
The EGR passage 80 is provided with an EG
The R valve 81 is interposed. Here, this EGR valve 81
Is composed of a valve body 81a capable of contacting a valve seat portion formed in the EGR passage 80, and a diaphragm type actuator 81b for adjusting the position of the valve body, and is provided in a diaphragm chamber of the diaphragm type actuator 81b. Is provided with a pilot passage 82 communicating with the intake passage downstream of the throttle valve.
An ERG valve control solenoid valve 83 is interposed in the.

Therefore, by controlling the opening degree of the EGR valve controlling solenoid valve 83 by the ECU 25 described later, the E
The exhaust gas can be returned to the intake system through the GR passage 80. In FIG. 3, reference numeral 15 denotes a fuel pressure regulator, which operates by receiving a negative pressure in the intake passage 3 and regulates the amount of fuel returned from a fuel pump (not shown) to the fuel tank. Thus, the pressure of fuel injected from the injector 9 is adjusted.

Various sensors are provided to control the engine system. First, as shown in FIG. 3, the intake air that has passed through the air cleaner 7 is introduced into the intake passage 3
An air flow sensor (intake air amount sensor) 17 that detects the intake air amount from the Karman vortex information and an intake air temperature sensor 1 that detects the temperature of the intake air of the engine 1
8. An atmospheric pressure sensor 19 for detecting atmospheric pressure is provided.

Further, the throttle valve 8 in the intake passage 3
In addition to the potentiometer-type throttle position sensor 20 that detects the opening of the throttle valve 8, an idle switch 21 is provided in the portion where is arranged. Further, on the exhaust passage 4 side, an oxygen concentration sensor (hereinafter, simply referred to as “O ₂ sensor”) 22 for detecting the oxygen concentration (O ₂ concentration) in the exhaust gas is provided, and other sensors are used as the engine 1 Water temperature sensor 23 for detecting the temperature of the cooling water for cooling, and crank angle sensor 24 for detecting the crank angle shown in FIG. 4 (this crank angle sensor 24 also functions as a rotation speed sensor for detecting the engine rotation speed Ne). The vehicle speed sensor 30 and the like.

The detection signals from these sensors and switches are input to the ECU 25 as shown in FIG. Here, the hardware configuration of the ECU 25 is as shown in FIG.
Is configured as a computer having a CPU (arithmetic unit) 26 as its main part. The CPU 26 includes an intake air temperature sensor 18, an atmospheric pressure sensor 19, a throttle position sensor 20, an O ₂ sensor 22, and a water temperature sensor 2.
The detection signals from 3 and the like are input through the input interface 28 and the analog / digital converter 29.

The CPU 26 also includes an air flow sensor 17, an idle switch 21, a crank angle sensor 24,
A detection signal from the vehicle speed sensor 30 or the like is directly input through the input interface 35. Further, the CPU 26 is a ROM that stores various data in addition to program data and fixed value data via a bus line.
(Memory unit) 36 or RAM that can be updated and sequentially rewritten
Data is exchanged with 37.

Further, as a result of calculation by the CPU 26, EC
From U25, a signal for controlling the operating state of the engine 1, such as a fuel injection control signal, an ignition timing control signal,
Various control signals such as an ISC control signal, a bypass air control signal and an EGR control signal are output. Here, the fuel injection control (air-fuel ratio control) signal is sent to the CPU 26.
Is output to the injector solenoid 9a for driving the injector 9 (accurately, the transistor for the injector solenoid 9a) via the injection driver 39, and the ignition timing control signal is output from the CPU 2
6 is output to a power transistor 41 via an ignition driver 40, and a spark is sequentially generated from the power transistor 41 to an ignition plug 42 by a distributor 43 via an ignition coil 42.

The ISC control signal is output from the CPU 26 to the stepper motor 12b via the ISC driver 44, and the bypass air control signal is output from the CPU 26 via the bypass air driver 45 to the air bypass valve controlling solenoid valve. It is adapted to be output to the solenoid 142a of 142. Further, the EGR control signal is sent to the CPU2.
6 to the solenoid 83a of the EGR valve control solenoid valve 83 via the EGR driver 46.

Now, paying attention to the fuel injection control (air-fuel ratio control), the ECU 25, as shown in FIG. Combustion limit operation means 2
08, inter-cylinder air-fuel ratio variation detecting means 209, fuel injection amount changing means 210, and injector drive correction means 21.
It has one function.

Here, the fuel injection amount changing means 210 sets a desired fuel injection pulse width Tinj in accordance with the control signal output from the lean burn limit operating means 208 in response to the rotation fluctuation detected by the rotation fluctuation detecting means 207. The injector 9 functions as the fuel injection amount changing means 210 by adjusting the state to perform the lean burn operation of the air-fuel ratio to be realized.

The fuel injection pulse width Tinj is expressed by the following equation. Tinj = TB × KAFL × (1 + KC + KAC
(J)) × KAP × KAT × KWUP × (1 + KAS)
× KFI ± acceleration / deceleration correction value + Td TB in this equation is the basic drive time of the injector 9, and the intake air amount A information from the air flow sensor 17 and the engine speed N from the crank angle sensor (engine speed sensor) 24. The intake air amount A / N information per engine revolution is obtained from the information and the basic drive time TB is determined based on this information.

KAFL is a leaning correction coefficient (excess air ratio), which is determined from the characteristics stored in the map in accordance with the operating state of the engine, and the air-fuel ratio is made lean or stoichiometric in accordance with the operating state. You can do it. Further, KC is a correction coefficient for performing combustion state control with respect to rotation fluctuation corresponding to combustion fluctuation, as described later.

As will be described later, KAC (j) is a correction coefficient for the injector drive correction means 211 to perform injector drive correction corresponding to the air-fuel ratio variation among the cylinders. Furthermore, correction factors KAP, KAT, KWU according to atmospheric pressure, intake air temperature, engine cooling water temperature, etc.
P, KAS, and KFI are set, and the drive time is corrected according to the battery voltage by the dead time (ineffective time) Td.

Further, the lean burn operation is performed when the lean operation condition determining means determines that a predetermined condition is satisfied. As a result, the ECU 25 has a function of air-fuel ratio control means for controlling the air-fuel ratio so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio under the required operating conditions, and the air-fuel ratio between the cylinders is increased during the theoretical air-fuel ratio operation. It has a function of performing injector drive correction corresponding to the fuel ratio variation.

By the way, the combustion state control system of the present embodiment is provided with an angular acceleration detecting means 107 for detecting the angular acceleration of the rotating shaft (crankshaft) driven by the engine. Is configured. That is, as shown in FIG. 13, the angular acceleration detecting means 107 includes a crank angle sensor 24 and a cylinder discrimination sensor 23.
0 and an ECU 25 as a controller are provided as main elements, and the crank angle sensor 24 is provided with a rotating member 221 that rotates integrally with the crankshaft 201 of the engine.

Around the periphery of the rotating member 221, first, second and third vanes 221A, 221 projecting in the radial direction are formed.
B, 221C are formed, and the vanes 221A,
221B and 221C are provided so as to face each other on both sides, and a detection unit 222 optically or electromagnetically detects passage of the vanes 221A, 221B and 221C accompanying rotation of the rotating member 221, and a corresponding pulse is detected. It is configured to output.

The vanes 221A, 221B, 22
Each of 1C has a circumferential length corresponding to a crankshaft rotation angle of a constant angle, and is spaced apart at a predetermined angular interval in the circumferential direction. That is, the opposite edges of the adjacent vanes are arranged at an angular interval of 120 degrees from each other.

By the way, the cylinder discrimination sensor 230 is fixed to a cam shaft (not shown), and is connected to the crank shaft 20.
While 1 rotates twice and the camshaft rotates once, a pulse output is generated every time the camshaft takes a specific rotational position corresponding to one cylinder. The device of this embodiment mounted on a 6-cylinder engine in which the ignition operation is performed in the order of the cylinder numbers is, for example, the third vane 2
The edge of 21C (front end 221C 'or rear end) is the detection unit 2
When passing 22, the first crankshaft rotation angle region corresponding to either one of the first cylinder and the fourth cylinder (preferably, mainly the expansion stroke in the one cylinder) of the first cylinder group is passed. When the crankshaft rushes in and the edge of the first vane 221A passes the detection portion 222,
The crankshaft is adapted to be disengaged from the first rotation angle range.

Similarly, when passing through the edge of the first vane 221A, it rushes into the second crankshaft rotation angle region corresponding to one of the second and fifth cylinders forming the second cylinder group, and then, When passing through the edge of the second vane 221B, the second vane 221B is detached from the same area. Further, when passing through the edge of the second vane 221B, it rushes into the third crankshaft rotation angle region corresponding to one of the third and sixth cylinders forming the third cylinder group, and then the third vane 221C. At the time of passing the edge of the, the departure from the same area is performed.

The discrimination between the first cylinder and the fourth cylinder, the discrimination between the second cylinder and the fifth cylinder, and the discrimination between the third cylinder and the sixth cylinder are performed based on the output of cylinder discrimination sensor 230. Is configured. With this configuration,
The detection of angular acceleration is performed as follows. That is, during engine operation, the ECU 25 sequentially receives the pulse output from the crank angle sensor 24 and the detection signal of the cylinder discrimination sensor 230, and periodically repeats the calculation.

Further, the ECU 25 uses the crank angle sensor 2
It is determined whether the pulse output from No. 4 is the one that is sequentially input after the pulse output from the cylinder determination sensor 230 is input. This makes it possible to identify which cylinder the input pulse output from the crank angle sensor 24 corresponds to, and preferably,
A cylinder that is currently executing the expansion stroke (output stroke: BTDC75 °) is identified as an identification cylinder.

Then, the ECU 25 responds to the pulse input from the crank angle sensor 24 in accordance with the identified cylinder group m.
When the entry into the crankshaft rotation angle region corresponding to (m is 1, 2 or 3) is determined, a cycle measuring timer (not shown) is started. Next, the crank angle sensor 22
When the next pulse output is input from 0, the ECU 25 determines the departure from the crankshaft rotation angle region corresponding to the identified cylinder group m, stops the time counting operation of the cycle measuring timer, and reads the time counting result.

This time measurement result is the time interval TN (n) from the time of entry into the crankshaft rotation angle region corresponding to the identified cylinder group m to the time of departure from the region, that is, two time intervals corresponding to the identified cylinder group. A cycle TN (n) determined by a predetermined crank angle is shown. here,
The subscript n in the cycle TN (n) indicates that the cycle corresponds to the n-th (current) ignition operation in the identified cylinder.

Further, the cycle TN (n) is a cycle between 120-degree crank angles of the discriminating cylinder group in the 6-cylinder engine (time interval between operating states BTDC75 ° in adjacent cylinders), and more generally, N cylinders. In the engine (720 /
N) degree crank angle cycle. The pulse output indicating the departure from the crankshaft rotation angle region corresponding to the presently identified cylinder also represents the entry into the crankshaft rotation angle region corresponding to the next identified cylinder.

Therefore, the cylinder identifying step for the next identified cylinder is executed in accordance with the pulse output, and the period measuring timer is restarted to start the period measurement for the next identified cylinder. . By such an operation, the ECU 25 causes the 120 degree crank cycle TN
Although (n) is detected, a series of states from the # 1 cylinder to the # 6 cylinder is shown in FIG. 8, and the 120-degree crank cycle is from TN (n-5) to TN (n). It is represented by. By using these detected values, the angular acceleration ACC (n) of the crankshaft in the period is calculated by the following equation.

ACC (n) = 1 / TN (n). {KL (m) / TN (n)-
KL (m-1) / TN (n-1)} where KL (m) is a segment correction value, which is related to the identified cylinder this time, due to variations in vane angular intervals during vane manufacturing and mounting. The ECU 25 calculates the segment correction value KL (m) by the following equation in order to perform the correction for removing the cycle measurement error.

KL (m) = {KL (m-3) * (1-XMFDKFG) + KR (n) * (XMFDKFD)} where XMFDKFG represents the segment correction value gain. Further, m in KL (m) is set for each corresponding cylinder group, and m = 1 for cylinder groups # 1 and # 4, m = 2 for cylinder groups # 2 and # 5, cylinder group # In FIG. 8, m = 3 corresponds to 3 and # 6, respectively.
KL (1) to KL (3) are repeated as shown in.

Since m-1 in KL (m-1) means the one immediately before the corresponding m, KL (m) = KL
When (1) KL (m-1) = KL (3), KL (m) = KL (2) KL (m-
1) = KL (1), KL (m) = KL (3), KL (m-1) = KL (2). Further, KL (m-3) in the above equation indicates KL (m) of the previous cycle in the same cylinder group, and # 4
KL (m-3) at the time of calculation of cylinder is in the previous # 1 cylinder
KL (1) is used, and KL (m-3) when calculating # 1 cylinder
Uses KL (1) in the previous # 4 cylinder. KL (m-3) when calculating # 5 cylinder is KL in previous # 2 cylinder
(2) is used, and KL (m-3) at the time of calculation for the # 2 cylinder is KL (2) for the previous # 5 cylinder. KL (m-3) when calculating # 6 cylinder is KL (3) in the previous # 3 cylinder
Is used, and the KL (m-3) in the calculation of the # 3 cylinder is the KL (3) of the previous # 6 cylinder.

On the other hand, KR (n) in the above equation is obtained by the following equation. KR (n) = 3 ・ TN (n) / {TN (n) + TN (n-1) + TN (n-2)} This is the measured time from the previous measured time TN (n-2) to the current measured time.
It is a measurement value corresponding to the average measurement time up to TN (n). When calculating the segment correction value KL (m), the first-order filter processing by the segment correction value gain XMFDKFG is applied to KR (n) using the above equation. Performed using.

By the way, as described above, the combustion control system for the internal combustion engine of the present embodiment causes the rotational fluctuation VA that occurs when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio.
Rotational fluctuation detecting means 207 for detecting C for each cylinder (j)
And a lean burn limit operating means 208 for operating the internal combustion engine in the vicinity of the lean burn limit based on the detection result VAC (j) of the rotation variation detecting means 207. In addition to this, each of the following means is provided. It has

That is, during the lean burn operation by the lean burn limit operating means 208, the fuel injection amount changing means 210 for changing the fuel injection amount Tinj so as to keep the combustion variation obtained from the rotation variation VAC (j) within the allowable range. Is provided. Further, inter-cylinder air-fuel ratio variation detecting means 209 is provided for detecting variation in the inter-cylinder air-fuel ratio from the amount of change in the fuel injection amount changing means 210.

Further, the inter-cylinder air-fuel ratio variation detecting means 2
The injector drive time Tinj during stoichiometric air-fuel ratio operation is corrected based on the detection result KAC (j) by
An injector drive correction unit 211 (j) is provided. Here, KCL (j) = (KAC (j) -KACA
V) × KST KST is a gain correction coefficient between the lean air-fuel ratio and the stoichiometric air-fuel ratio, and KACAV is an average value of the detection result KAC (j) by the inter-cylinder air-fuel ratio variation detection means 209, which is calculated from the average. The deviation is used for correction.

KACAV = (1 / n) ΣKAC (j) where ΣKAC (j) means the sum of j = 1 to n. The rotation fluctuation detecting means 207 has the hardware configuration shown in FIG. 13, and uses the detection signal of the angular acceleration detecting means 107 (see FIG. 2) detected by the operation shown in FIG. 8 to change the angular acceleration as described above. The rotation variation is detected by detecting the value.

In addition, the rotation fluctuation detecting means 207 is shown in FIG.
As shown in FIG.
1, a normalized fluctuation value detection means 102, a combustion deterioration determination value calculation means 104, and a threshold value updating means 110,
The computing means that should realize the function of each such means is an ECU
It is equipped with 25. That is, the fluctuation detecting means 101
Is calculated by finding the difference between the smoothed value obtained by smoothing the detected angular velocity by the smoothing means 108 and the angular acceleration output from the angular acceleration detecting means 107.

That is, in the fluctuation detecting means 101, the acceleration fluctuation value ΔACC (n) is calculated by the following equation. ΔACC (n) = ACC (n) -ACCAV (n) Here, ACCAV (n) is a smoothed value obtained by smoothing the detected angular velocity by the smoothing means 108, and a primary filter process according to the following equation should be performed. Is calculated by

ACCAV (n) = αACCAV (n-
1) + (1−α) · ACC (n) Here, α is an update gain in the primary filter processing, and takes a value of about 0.85. Further, the fluctuation value ΔACC (n) output from the fluctuation detecting means 101 is normalized according to the operating state of the engine, and the normalized fluctuation value IAC is obtained.
Normalized variation value detection means 102 for obtaining (n) is provided.

That is, the normalized variation value IAC (n) is calculated by the normalized variation value detecting means 102 according to the following equation. IAC (n) = ΔACC (n) · Kte (Ev, Ne) where Kte (Ev, Ne) is an output correction coefficient,
It is set by the characteristics shown in FIG.

In the characteristic of FIG. 12, the horizontal axis represents the volumetric efficiency Ev, and the output correction coefficient Kte (E
(v, Ne) is shown on the vertical axis, and the characteristic of the upper right line is adopted as the engine speed Ne increases. Therefore, the characteristics of FIG. 12 are stored as a map, and the engine speed Ne and the volumetric efficiency E calculated from the detection signals of the crank angle sensor 24 and the like are stored.
From v, the output correction coefficient Kte (Ev, Ne) is
25, and normalization by correction corresponding to the engine output is performed.

Then, the normalized variation value IAC (n) is compared with a predetermined threshold value IACTH to determine the combustion deterioration determination value VAC.
A combustion deterioration determination value calculation means 104 for determining (j) is provided, and the combustion deterioration determination value VAC (j) is configured to accumulate and calculate deterioration amounts in which the normalized fluctuation value IAC (n) is less than the threshold value IACTH. Has been done. That is, the combustion deterioration determination value VAC (j) is calculated by the following equation.

VAC (j) = Σ {IAC (J) <IACTH}
* {IACTH-IAC (J)} where {IAC (J) <IACTH} in the above equation is IAC (J) <
It is a function that takes "1" when IACTH is established and takes "0" when IACTH is not established.
When (n) is below a predetermined threshold value IACTH, the amount of decrease is accumulated as a deterioration amount.

Therefore, the combustion deterioration determination value VAC (j)
Is obtained by accumulating the deterioration amount with the difference between the threshold IACTH and the normalized fluctuation value IAC (j) as the weight, and the influence of the numerical value near the threshold can be reduced to accurately reflect the deterioration state. Is configured. Then, the combustion deterioration determination value calculation means 1
The predetermined threshold value IACTH in 04 is the threshold value updating means 110.
Is configured to be updated according to the operating state of the engine.

The above subscript j indicates the cylinder number. Further, the combustion deterioration determination value VAC (j) may be obtained by accumulating the number of times the normalized fluctuation value IAC (n) falls below the threshold value IACTH using a simpler program (that is, VAC (j) = Σ {. IAC (j) <IACTH}). The calculation result from the combustion deterioration determination value calculation means 104 as described above is configured to be used by the combustion state control means 105.

That is, the combustion state control means 105 refers to the combustion deterioration determination value VAC (j) calculated by the combustion deterioration determination value calculation means 104 and refers to the combustion of the engine for the predetermined reference value from the reference value setting means 112. It is configured to control the variation adjustment element 106. The combustion variation adjusting element 106 is configured to operate as the fuel injection amount changing means 210 based on the detection signal from the inter-cylinder air-fuel ratio variation detecting means 209 during the theoretical air-fuel ratio operation of the internal combustion engine.

By the way, as the reference values for the control of the combustion fluctuation adjusting element 106 by the combustion state control means 105, the upper limit reference value (VACTH1) set by the upper limit reference value setting means 112U and the upper limit reference value setting means 112L are set. Lower limit reference value (VACTH2) is provided. Then, the control by the combustion fluctuation adjusting element 106 is performed by the lean combustion limit operating means 208 so that the combustion deterioration determination value VAC (j) is set between the upper limit reference value (VACTH1) and the lower limit reference value (VACTH2). Is configured.

That is, the control by the combustion fluctuation adjusting element 106 is configured to be performed by correcting the basic injection pulse width at the time of fuel injection, as described above.
The injection pulse width Tinj (j) is configured to be calculated by the following equation. Tinj (j) = TB × KAFL × (1 + KC + KAC
(J)) × KAP × KAT × KWUP × (1 + KAS)
× KFI ± acceleration / deceleration correction value + Td Then, the correction coefficient KAC (j) in the above equation is adjusted as follows.

First, when the combustion deterioration determination value VAC (j) exceeds the upper limit reference value VACTH1, it is determined that the combustion fluctuation value has deteriorated more than a predetermined value, and the fuel injection amount is increased. Is corrected by calculating the correction coefficient KAC (j) by the following equation. KAC (j) = KAC (j) + KAR · {VAC (j) − VACTH1} This is to calculate the correction value of the rich side upper right characteristic of the correction characteristics shown in FIG. Is a coefficient. Then, KAC (j) on the right side shows the correction coefficient calculated in the previous calculation cycle (n-1) for the number j cylinder, and is updated by the above equation.

In FIG. 9, the abscissa indicates the combustion deterioration determination value VAC.
And the vertical axis represents the correction coefficient KAC to show the correction characteristic. On the other hand, if the combustion deterioration determination value VAC (j) is lower than the lower limit reference value VACTH2, it is considered that there is a margin for further leaning, and the lean leaning correction for reducing the fuel injection amount is performed next. Correction coefficient KAC by formula
This is done by calculating (j).

KAC (j) = KAC (j) −KAL · {VAC (j) −VACTH2} This is to calculate the correction value of the lean side lower left characteristic shown in FIG. 9, and KAL indicates the inclination of the characteristic. It is a coefficient. Further, the combustion deterioration determination value VAC (j) is lower than the lower limit reference value VACTH2.
As described above, when it is equal to or lower than the upper limit reference value VACTH1, the correction coefficient KAC (j) is not changed in order to maintain the fuel injection amount in the previous state as the proper operating state.

This corresponds to the flat characteristic between the lean side lower left characteristic and the rich side upper right characteristic shown in FIG.
It forms a dead zone for correction. Here, the lower limit reference value VACTH2 and the upper limit reference value VACTH1 are combustion fluctuation target values VA
Centering around C0, the lower limit reference value VACTH2 is set to a value of (VAC0-ΔVAC), and the upper limit reference value VACTH1 is set to a value of (VAC0 + ΔVAC).

The combustion fluctuation target value VAC0 is the COV (Coefficie
It is a value corresponding to the target value of nt of variance (about 10%), and the rotation fluctuation is limited for a finite period (128 cycles) by not correcting the fuel in the range of ΔVAC on both sides of the combustion fluctuation target value VAC0. The limit cycle due to an error caused by the evaluation by or calculated by a value less than the threshold is prevented.

The above-mentioned correction coefficient KAC (j) is configured to be clipped by the upper and lower limit values.
It is set so that it falls within the range of 0.85 <KAC (j) <1.1, and the shock is prevented from occurring and stable control is performed by performing the correction gradually without performing the rapid correction. It is configured to Further, the combustion deterioration determination value VAC (j) is updated every set number of combustions, for example, every 128 (or 256) cycles, and the control is performed by grasping the combustion state for a relatively long period. Is performed, stable and reliable control that reflects statistical characteristics is performed.

Then, the misfire determination reference value is set on the combustion deterioration side with respect to the reference value set by the reference value setting means 112, and the normalized fluctuation value IAC (n) exceeds the misfire determination reference value on the combustion deterioration side. Misfire is determined based on that,
Misfiring information is stored in the misfiring information address (j) of the current cylinder, and misfiring is controlled.

Thus, the lean burn limit operation means 208 is constructed so that the lean burn limit operation is performed in the required state. However, the correction coefficient KAC (j) detected by this lean burn limit operation is With reference to this, the inter-cylinder air-fuel ratio variation detecting means 209 is configured to detect the inter-cylinder air-fuel ratio variation as described above.

Then, the correction coefficient KCL (j) is calculated in accordance with this variation as described above, and this correction coefficient KCL (j) is adopted in the following equation, Tinj (j ) = TB × KAFL × (1 + KCL
(J)) × KAP × KAT × KWUP × (1 + KAS)
× KFI ± acceleration / deceleration correction value + Td By the fuel injection with this injector drive pulse width Tinj (j), the injector drive correction means 211 is configured to correct the operation at the stoichiometric air-fuel ratio.

That is, the fuel injection is performed during the stoichiometric operation in consideration of the air-fuel ratio variation among the cylinders. Since the combustion control method and the combustion control device for the internal combustion engine as one embodiment of the present invention are configured as described above, the operations by the respective means shown in FIGS. 1 and 2 are sequentially performed according to the flowcharts of FIGS. Done.

That is, the operation of the flow charts shown in FIGS. 5 and 6 is executed in synchronization with the stroke of the internal combustion engine. First, in step S1 of FIG. 5, the rotation fluctuation detecting means 207 of FIG. The angular acceleration detecting means 107 detects the angular acceleration ACC (n). Here, the calculation used for detection is according to the following equation.

ACC (n) = 1 / TN (n)-{KL (m) / TN (n)-
KL (m-1) / TN (n-1)} Note that KL (m) is a segment correction value, and is related to the identified cylinder this time. To correct the measurement error, use the following formula to correct the segment correction value KL
(M) is calculated.

KL (m) = {KL (m-3) * (1-XMFDKFG) + KR (n) * (XMFDKFD)} However, XMFDKFG represents the segment correction value gain. On the other hand, KR (n) in the above equation is calculated by the following equation. KR (n) = 3 ・ TN (n) / {TN (n) + TN (n-1) + TN (n-2)} This is the measured time from the previous measured time TN (n-2) to the current measured time.
This is a measurement value corresponding to the average measurement time up to TN (n), and when the segment correction value KL (m) is calculated, the first-order filter processing by the segment correction value gain XMFDKFG is performed using the above-mentioned formula.

Then, in step S2, the average acceleration ACCAV (n) is calculated. Where ACCAV
(N) is a smoothed value obtained by smoothing the detected angular velocity ACC (n) by the smoothing means 108, and is calculated by performing a primary filter process according to the following equation. ACCAV (n) = α.ACCAV (n-1) + (1-
α) · ACC (n) Here, α is an update gain in the primary filter processing, and takes a value of about 0.95.

Then, in step S3, the fluctuation detecting means 101 detects the acceleration fluctuation value ΔACC (n). That is, the angular velocity ACC (n) detected by the angular acceleration detection means 107 and the average acceleration ACCAV (n) as a smoothed value smoothed by the smoothing means 108.
Acceleration fluctuation value ΔACC
(N) is calculated by the following equation.

ΔACC (n) = ACC (n) −ACCAV (n) Further, in step S 4, the normalized variation value detecting means 1
02, the normalized variation value IAC (n) obtained by normalizing the variation value ΔACC (n) output from the variation detecting means 101 according to the operating state of the engine is calculated by the following equation. IAC (n) = ΔACC (n) · Kte (Ev, Ne) where Kte (Ev, Ne) is an output correction coefficient,
It is set according to the characteristics shown in FIG.

In the characteristic of FIG. 12, the horizontal axis represents the volumetric efficiency Ev, and the output correction coefficient Kte (E
(v, Ne) is shown on the vertical axis, and the characteristic of the upper right line is adopted as the engine speed Ne increases. That is, in the characteristic of FIG. 12 stored as a map, the output correction coefficient Kte (Ev, Ne) is set in the ECU 25 from the engine speed Ne and the volumetric efficiency Ev calculated from the detection signals of the crank angle sensor 220 and the like. , Normalization by correction corresponding to the engine output is performed.

Here, the control characteristics in the case where the normalization corresponding to the engine output as described above is performed will be described. That is, the angular acceleration ω'is represented by the following equation. ω ′ = 1 / Ie · (Te−Tl) ... Here, Te: engine torque Tl: load torque Ie: moment of inertia while ω ′ = ω ₀ ′ + Δω ′ .... - here, omega ₀ ': the average angular acceleration, the _{equation, ω 0' + Δω '=} 1 / Ie · (Te-Tl) = 1 / Ie · (Te 0 -Tl) + ΔTe / Ie Thus, [Delta] [omega' = .DELTA.Te / Ie ..... By the way, the angular acceleration AC in step S1 described above.
With the C (n) detection method, engine torque information is stored relatively well when there is no load disturbance. Then, as shown in the equation, the variation Δω ′ from the average angular acceleration ω ₀ ′
By using [acceleration fluctuation value ΔACC (n)] and controlling as a normalized output [normalized fluctuation value IAC (n)] considering the average output Te ₀ and the moment of inertia Ie, statistical characteristics of combustion fluctuation are obtained. In consideration of the above, the control that reliably reflects the combustion fluctuation is performed.

When the operation of step S4 is performed, then in step S5, misfire determination is performed. That is, the misfire determination reference value set by the misfire determination reference value setting means 111 is set on the combustion deterioration side with respect to the reference value set by the reference value setting means 112 used in the combustion deterioration determination value calculation means 104. Normalized variation value IAC
It is determined whether or not (n) exceeds the misfire determination reference value on the worsening side of combustion, and if it exceeds, it is determined that a misfire has occurred.

If this determination is made,
Step S6 is executed, misfire information is stored in the misfire information address (j) of the current cylinder, and misfire control is performed. On the other hand, if the misfire is not judged,
Alternatively, after the misfire is determined and step S6 is executed, the operation of the combustion deterioration determination value calculation means 104 in steps S7 to S10 is executed, and the normalized variation value IAC (n) and the predetermined threshold value IACTH are set. And the combustion deterioration determination value VAC (j) is calculated by the following equation.

VAC (j) = Σ {IAC (J) <IACTH}
* {IACTH-IAC (J)} First, in step S7, the normalized fluctuation value IAC
The difference ΔIAC (n) between (n) and the predetermined threshold value IACTH is calculated, and then, in step S8, the difference ΔIAC is calculated.
It is determined whether (n) is negative. This decision is
It corresponds to the function {IAC (J) <IACTH} in the above formula, and takes "1" when IAC (J) <IACTH is satisfied, and takes "0" when it is not satisfied.

That is, when IAC (J) <IACTH is satisfied, ΔIAC (n) is positive, so the combustion deterioration determination value VA in step S10 is obtained through the “NO” route.
Accumulation of C (j) is performed, and the above function is in a state of taking "1". On the other hand, when IAC (J) <IACTH is not established, ΔIAC (n) is negative, so ΔIAC (n) = 0 is executed in step S9 through the “YES” route. As a result, in step S10, the combustion deterioration determination value VAC (j) is not accumulated,
The above function is in the state of taking "0".

As a result, the normalized fluctuation value IAC (n) as shown by points A to D in FIG.
When it is below, the amount below this will be accumulated as a worsening amount. Therefore, the combustion deterioration determination value VA
C (j) is obtained by accumulating the deterioration amount with the difference between the threshold value IACTH and the normalized fluctuation value IAC (j) as the weight, and the influence of the numerical value in the vicinity of the threshold value is reduced so that the deterioration state is combustion deterioration. It is accurately reflected in the judgment value VAC (j).

Then, the predetermined threshold value IACTH in the combustion deterioration determination value calculation means 104 is configured to be updated by the threshold value update means 110 in correspondence with the operating state of the engine, and the operating state closer to the lean limit. Can be realized. The above subscript j indicates the cylinder number, and the combustion deterioration determination value VAC is determined for each cylinder j.
(J) is accumulated.

Then, step S11 is executed to judge whether or not n indicating the number of times of sampling has exceeded 128. That is, it is determined whether or not the integrated section shown in FIG. 10 has elapsed, and if it has not elapsed, the “NO” route is taken, step S13 is executed, and the number of times n is increased by “1” to perform fuel correction. Step S without
20 is executed. As a result, the correction regarding the correction coefficient KAC (j) in the injection pulse width Tinj is not performed within the integration section of 128 cycles, and the combustion deterioration determination value VAC (j) is exclusively accumulated.

Therefore, the deterioration determination value VAC (j) is
It is updated every set number of combustions, for example, 128 cycles. By controlling by grasping the combustion state for a relatively long period, stable and reliable reflection of statistical characteristics can be achieved. Control is performed. Then, when the integration section elapses, “YE
Through the “S” route, steps S12 to S18 are executed.

First, at step S12, the number of times n is reset to "1", and then at steps S14 and S15, the reference value setting means 112 sets the combustion deterioration determination value VAC (j) with reference to it. And a predetermined reference value is compared. First, the combustion deterioration determination value VA
When C (j) is compared with the upper limit reference value (VACTH1) and the combustion deterioration determination value VAC (j) exceeds the upper limit reference value VACTH1, that is, as shown in FIG. If the amount exceeds the upper limit reference value VACTH1, which is the limit, in step S15, the correction coefficient KAC according to the following equation
Calculation of (j) is performed.

KAC (j) = KAC (j) + KAR · {VAC (j) −VACTH1} This is for calculating the correction value of the rich side upper right characteristic shown in FIG. Assuming that the fuel injection amount has deteriorated, the enrichment correction for increasing the fuel injection amount is performed by calculating the correction coefficient KAC (j). Here, KAR is a coefficient indicating the slope of the characteristic, and KAC (j) on the right side is the previous calculation cycle (n
The correction coefficient calculated in -1) is shown, and is updated by the above formula.

If the combustion deterioration determination value VAC (j) is below the lower limit reference value VACTH2, step S16 is performed.
Assuming that the “YES” route is taken and there is room for further leaning, the correction of leaning to reduce the fuel injection amount is performed by the correction coefficient KAC
It is performed by calculating (j). KAC (j) = KAC (j) -KAL- {VAC (j) -VACTH2} This is to calculate the correction value for the lean side lower left characteristic shown in Fig. 9, and KAL is a coefficient indicating the slope of the characteristic. .

Further, the combustion deterioration determination value VAC (j) is
When the lower limit reference value VACTH2 or more and the upper limit reference value VACTH1 or less, the “NO” route is taken in both step S14 and step S15, and the fuel injection amount is maintained in the previous state as the proper operating state. Therefore, the correction coefficient
Do not change KAC (j). This corresponds to the flat characteristic between the lean-side lower left characteristic and the rich-side upper right characteristic shown in FIG. 9, and constitutes a dead zone for correction.

Here, the lower limit reference value VACTH2 and the upper limit reference value VA
CTH1 is centered around the combustion fluctuation target value VAC0, and is the lower limit reference value.
VACTH2 to the value of (VAC0-ΔVAC), and the upper reference value VACTH1 to (VAC
The value is set to 0 + ΔVAC). Combustion fluctuation target value VAC0
Is the target value of COV (Coefficient of variance) (10%
This is a value corresponding to the combustion fluctuation target value VAC0.By not correcting the fuel in the range of ΔVAC on both sides of the combustion fluctuation target value VAC0, the rotation fluctuation can be evaluated for a finite period (128 cycles), A limit cycle due to an error caused by the calculation is prevented.

Then, step S18 is executed and the combustion deterioration determination value VAC (j) is reset to "0". Furthermore, in step S19, when the correction coefficient KAC (j) exceeds the upper and lower limit values, it is clipped to the limit value on the exceeded side. For example, when the value is set to fall within the range of 0.85 <KAC (j) <1.1, the calculated value in step S15 is set to 1.1 when the calculated value exceeds 1.1, and the calculated value in step S16 is set. Is below 0.85, 0.8
Set to 5.

As a result, a shock or the like is prevented and stable control is performed by making a gradual correction without making a rapid correction. In this way, the correction coefficient KAC (j) is calculated, and the operation of the combustion variation adjusting element 106 as the fuel injection amount changing means 210 by the lean combustion limit operating means 208 corrects the fuel injection amount corresponding to the rotation variation. Be done.

By the way, the combustion control of the lean operation and the stoichiometric operation by the fuel injection amount changing means 210 is shown in FIG.
Follow the flow chart of. First, assuming that the vehicle running state and the combustion state of the internal combustion engine are in a state where lean feedback control should be performed, it is determined in step SS1 whether or not the ECU 25 is set to the lean feedback mode.

When the setting is the lean feedback mode, step SS3 is executed through the "YES" route in step SS1. In step SS3, the correction coefficient KAC (j) corresponding to the combustion limit fluctuation control is calculated, and then in step SS4, the fuel injection pulse width Tinj is calculated by the following equation. Tinj (j) = TB × KAFL × (1 + KC + KAC
(J)) × KAP × KAT × KWUP × (1 + KAS)
× KFI ± acceleration / deceleration correction value + Td As a result, the basic injection pulse width at the time of fuel injection is corrected by the correction coefficient KAC (j).

Here, in the lean feedback mode, the lean correction coefficient KAFL is set to a value corresponding to the lean operation, and the lean operation corresponding to the operating state of the engine is performed.
L is set uniformly for all cylinders, and uniform lean burn operation is performed. Then, the correction coefficient KA
The correction of the fuel injection pulse width Tinj by C (j) is performed with a different value for each cylinder j, and the fuel injection control corresponding to the individuality of each cylinder is performed.

Further, the fuel injection pulse width Tin is calculated by using the correction coefficient KAC (j) in such a control situation and the correction coefficient KCL (j) calculated as described later.
j is corrected for each cylinder in response to variations in the air-fuel ratio during the stoichiometric operation, and the stoichiometric operation is performed in a state in which the variations in the air-fuel ratio due to the shape of the intake pipe, the mounting angle of the injector, etc. are corrected.

The combustion state control means 10 is operated by the operation with the fuel injection pulse width Tinj corrected as described above.
5, the combustion fluctuation adjusting element 106 is controlled,
The engine is allowed to reach the desired lean limit operating conditions.
Note that control of the ERG amount can also be considered as a combustion adjustment element. On the other hand, if it is determined in step SS1 that the lean feedback mode is not in effect, step SS2 is executed through the "NO" route.

When the lean mode is determined in step SS2, the fuel injection amount is calculated and corrected as described above in step SS4, and a predetermined lean operation is performed. If it is determined in step SS2 that the lean mode is not set, steps SS5 and SS6 are executed.

That is, in this case, stoichiometric operation is performed by the stoichiometric air-fuel ratio instead of lean operation, and in this case, the correction of the fuel injection pulse width Tinj by the correction coefficient KC (j) is performed. First, in step SS5, the average value KAC of the correction coefficient KAC (j)
AV is calculated by the following equation.

KACAV = (1 / n) Σ KAC (j) Here, ΣKAC (j) means the sum of j = 1 to n. Then, the deviation of the correction coefficient KAC (j) from the average value KACAV is calculated by the following equation. KCL (j) = (KAC (j) −KACAV) × KST This deviation KCL (j) is adopted as the inter-cylinder air-fuel ratio variation detecting means 209, and this deviation KCL (j) is set to “0”. Is corrected by the injector drive correction means 211.

That is, in step SS6, the fuel injection pulse width Tinj is calculated by the following equation. Tinj (j) = TB × KAFL × (1 + KCL
(J)) × KAP × KAT × KWUP × (1 + KAS)
× KFI ± acceleration / deceleration correction value + Td Therefore, for cylinders with large air-fuel ratio variations,
The fuel injection pulse width Tinj is increased by the deviation.

On the other hand, for the cylinder having a small variation in the air-fuel ratio, the fuel injection pulse width Tinj corresponding to the deviation is reduced. Further, for the average cylinder, the fuel injection pulse width Tinj is not changed, and the conventional fuel injection pulse width Tinj is set. In this mode, the lean correction coefficient KAFL is set to "1",
Leaning correction coefficient KAFL of fuel injection pulse width Tinj
Is not performed, and the stoichiometric operation based on the basic fuel injection pulse width TB set corresponding to the theoretical air-fuel ratio is performed corresponding to the operating state of the engine.

Here, this basic fuel injection pulse width TB
Is set uniformly for all cylinders, and operation is performed at a uniform stoichiometric air-fuel ratio. Then, the correction of the fuel injection pulse width Tinj by the correction coefficient KCL (j) is performed with a different value for each cylinder j, and the fuel injection control corresponding to the individuality of each cylinder is performed.

That is, the correction coefficient KCL (j) in the above equation is used to correct the fuel injection pulse width Tinj for each cylinder in accordance with the variation in the air-fuel ratio, and the variation in the air-fuel ratio due to the intake pipe shape, the injector mounting angle, etc. The operation is performed in a state in which is corrected. Then, by the operation with the fuel injection pulse width Tinj corrected as described above, the combustion fluctuation adjusting element 1 by the combustion state control means 105.
By performing the control of 06, the engine is brought into the desired stoichiometric air-fuel ratio operation state for each cylinder.

Although the operation is performed as described above, the present embodiment has the following effects and advantages. (1) It becomes possible to perform combustion fluctuation estimation in consideration of stochastic characteristics and air-fuel ratio control using this estimation. (2) The combustion state control of the engine in consideration of the statistical property of the combustion fluctuation can be performed in real time and on the vehicle-mounted computer.

(3) It becomes possible to reliably correct the inter-cylinder difference of the combustion fluctuation limit due to the variation of the air-fuel ratio due to the variation of the injector flow rate, the shape of the intake pipe, the deviation of the valve timing, etc. You can set the limit. (4) It becomes possible to reliably correct the inter-cylinder difference due to the air-fuel ratio variation due to the injector flow rate variation, intake pipe shape, valve timing deviation, etc., and to ideally correct each of the cylinders. Combustion can be controlled in this condition.

(5) The three-way catalyst can be used with the highest efficiency, and exhaust gas can be purified efficiently. (6) According to the preceding 2 terms, NOx emission can be minimized. (7) Rotational fluctuation detection for each cylinder, air-fuel ratio variation correction and control can now be performed with a single crank angle sensor, and more reliable lean burn control and stoichiometric operation can be performed at low cost. Become.

[0116]

As described in detail above, according to the combustion control method for an internal combustion engine of the present invention as set forth in claim 1, it occurs when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio. In order to maintain the combustion fluctuation obtained from the rotation fluctuation during the lean combustion operation within an allowable range, in which the internal combustion engine can be operated near the lean combustion limit based on the detection result of the rotation fluctuation for each cylinder. A first step of changing the injection amount, a second step of detecting the variation of the air-fuel ratio between cylinders from the change amount of the fuel injection amount, and a correction of the injector drive time during the stoichiometric air-fuel ratio operation based on the detection result. With a simple configuration including the third step of performing the following, the following effects or advantages can be obtained.

(1) It becomes possible to reliably correct the inter-cylinder difference of the combustion fluctuation limit due to the variation of the air-fuel ratio due to the variation of the injector flow rate, the shape of the intake pipe, the deviation of the valve timing, etc. You can set the limit. (2) It is possible to reliably correct the inter-cylinder difference caused by the variation in the injector flow rate, the intake pipe shape, the variation in the air-fuel ratio due to the valve timing deviation, etc. even in the theoretical air-fuel ratio operation. Combustion can be controlled in a normal state.

(3) The three-way catalyst can be used with the highest efficiency, and exhaust gas can be purified efficiently. (4) According to the above items (1) to (3), NOx emission can be minimized. (5) Rotational fluctuation detection for each cylinder, air-fuel ratio variation correction, and control can now be performed with a single crank angle sensor, and more reliable lean burn control and stoichiometric operation can be performed at low cost. Become.

Further, according to the combustion control device for an internal combustion engine of the present invention as defined in claim 2, the rotational fluctuation occurring when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the stoichiometric air-fuel ratio is detected for each cylinder. And a lean combustion limit operating means for operating the internal combustion engine in the vicinity of the lean combustion limit based on the detection result of the rotation variation detecting means, and rotating during lean burn operation by the lean burn limit operating means. Fuel injection amount changing means for changing the fuel injection amount so as to keep the combustion fluctuation obtained from the fluctuation within the allowable range, and the inter-cylinder air-fuel ratio for detecting the variation in the inter-cylinder air-fuel ratio from the change amount in the fuel injection amount changing means. Variation detecting means, and injector drive correction means for correcting the injector drive time during stoichiometric air-fuel ratio operation based on the detection result by the inter-cylinder air-fuel ratio variation detecting means. A simple configuration that is provided,
The following effects or advantages can be obtained.

(6) It is possible to reliably correct the inter-cylinder difference of the combustion fluctuation limit due to the variation of the air-fuel ratio due to the variation of the injector flow rate, the shape of the intake pipe, the deviation of the valve timing, etc. You can set the limit. (7) It is possible to reliably correct the inter-cylinder difference caused by the air-fuel ratio variation due to injector flow rate variation, intake pipe shape, valve timing deviation, etc., even in stoichiometric air-fuel ratio operation. Combustion can be controlled in a normal state.

(8) The three-way catalyst can be used with the highest efficiency, and the exhaust gas can be purified efficiently. (9) From the above items (6) to (8), NOx emissions can be minimized. (10) Rotational fluctuation detection for each cylinder, air-fuel ratio variation correction and control can be performed with a single crank angle sensor, and more reliable lean burn control and stoichiometric operation can be performed at low cost. Become.

[Brief description of drawings]

FIG. 1 is a control block diagram of a combustion control device for an internal combustion engine as an embodiment of the present invention.

FIG. 2 is a control block diagram of a combustion control device for an internal combustion engine as an embodiment of the present invention.

FIG. 3 is an overall configuration diagram of an engine system having a combustion control device as an embodiment of the present invention.

FIG. 4 is a hardware block diagram showing a control system of an engine system having a combustion control device as one embodiment of the present invention.

FIG. 5 is a flow chart for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 6 is a flow chart for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 7 is a flow chart for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 8 is a waveform diagram for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 9 is a correction characteristic map for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 10 is a schematic graph for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 11 is a schematic graph for explaining the operation of the engine combustion control device as one embodiment of the present invention.

FIG. 12 is a normalized characteristic map for explaining the operation of the engine combustion control apparatus as one embodiment of the present invention.

FIG. 13 is a schematic perspective view showing a rotation fluctuation detection unit in the engine combustion control device as one embodiment of the present invention.

FIG. 14 is a graph showing combustion fluctuation characteristics in a lean burn engine.

FIG. 15 is a graph showing variations in ejector flow rate characteristics.

[Explanation of symbols]

1 engine (internal combustion engine) 2 combustion chamber 3 intake passage 3a surge tank 4 exhaust passage 5 intake valve 6 exhaust valve 7 air cleaner 8 throttle valve 9 electromagnetic fuel injection valve (injector) 9a injector solenoid 10 three-way catalyst 11A first bypass passage 11B 2nd bypass passage 12 Stepper motor valve (STM valve) 12a Valve body 12b Stepper motor (ISC actuator) 12c Spring 13 First idle air valve 14 Air bypass valve 14a Valve body 14b Diaphragm type actuator 15 Fuel pressure regulator 16 Spark plug 17 an air flow sensor (intake air amount sensor) 18 intake air temperature sensor 19 atmospheric pressure sensor 20 throttle position sensor 21 the idle switch 22 O ₂ sensor 23 water temperature sensor 24 crank angle sensor (engine Number of revolutions sensor) 25 ECU as air-fuel ratio control means 26 CPU (arithmetic unit) 28 Input interface 29 Analog / digital converter 30 Vehicle speed sensor 35 Input interface 36 ROM (storage means) 37 RAM 39 Injection driver 40 Ignition driver 41 Power transistor 42 Ignition coil 43 Distributor 44 ISC driver 45 Bypass air driver 46 EGR driver 80 Exhaust gas recirculation passage (EGR passage) 81 EGR valve 81a Valve body 81b Diaphragm actuator 82 Pilot passage 83 ERG valve control solenoid valve 83a Solenoid 101 Variation detection means 102 Normalized fluctuation value detection means 103 Accumulation means 104 Combustion deterioration determination value calculation means 105 Combustion state control means 106 Combustion fluctuation adjustment element 107 Corner Acceleration detecting means 108 Smoothing means 109 Burning frequency 110 Threshold updating means 111 Misfire determination reference value setting means 112 Reference value setting means 112U Upper limit reference value setting means 112L Lower limit reference value setting means 141 Pilot passage 142 Air bypass valve controlling solenoid valve 142a Solenoid 207 Rotational fluctuation detecting means 208 Lean combustion limit operating means 209 Inter-cylinder air-fuel ratio variation detecting means 210 Fuel injection amount changing means 211 Injector drive correction means 221 Rotating member 221A First vane 221B Second vane 221C Third vane 222 Detection unit

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Claims (2)

[Claims] 1. A rotation fluctuation that occurs when operating a multi-cylinder internal combustion engine at an air-fuel ratio leaner than the theoretical air-fuel ratio is detected for each cylinder, and the internal combustion engine is operated near the lean-burn limit based on the detection result. The first is to change the fuel injection amount to keep the combustion fluctuation obtained from the rotation fluctuation within the allowable range during lean burn operation.
And a second step of detecting the variation in the air-fuel ratio between cylinders from the change amount of the fuel injection amount, and a third step of correcting the injector drive time during the stoichiometric air-fuel ratio operation based on the detection result. A combustion control method for an internal combustion engine, comprising: 2. A rotation fluctuation detecting means for detecting, for each cylinder, a rotation fluctuation occurring when the multi-cylinder internal combustion engine is operated at an air-fuel ratio leaner than the theoretical air-fuel ratio, and based on a detection result of the rotation fluctuation detecting means. The lean combustion limit operating means for operating the internal combustion engine in the vicinity of the lean combustion limit is provided, and the fuel injection amount is set so as to keep the combustion fluctuation obtained from the rotation fluctuation during the lean combustion operation by the lean combustion limit operating means within the allowable range. Based on the fuel injection amount changing means for changing, the inter-cylinder air-fuel ratio variation detecting means for detecting the variation of the inter-cylinder air-fuel ratio from the variation amount in the fuel injection amount changing means, and the detection result by the inter-cylinder air-fuel ratio variation detecting means. A combustion control device for an internal combustion engine, comprising: injector drive correction means for correcting an injector drive time during stoichiometric air-fuel ratio operation.