JP2006152846A - Air-fuel ratio estimating device and air-fuel ratio controller for each cylinder of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately estimate the air-fuel ratio of each cylinder of an engine even if combustion intervals are unequal to each other or the exhaust pipe length of each cylinder is not equal to each other in the exhaust system of the engine. <P>SOLUTION: In the engine in which the combustion intervals of each cylinder of each bank are not equal to each other or the exhaust pipe length of each cylinder is not equal to each other as in a V-type 8-cylinder engine 11, a relation between the air-fuel ratio of each cylinder and the detected values of air-fuel ratio sensors 16 is modeled for each cylinder by using model parameters different from each other for each cylinder to prepare a plurality of air-fuel ratio estimating models for each cylinder in order to estimate the air-fuel ratio of each cylinder by using the different air-fuel ratio estimating models for each cylinder. The air-fuel ratio estimating models for each cylinder is formed to use, a model input, the combination of the air-fuel ratio of a prescribed cylinder for which the air-fuel ratio is estimated with a disturbance element, and to express the disturbance element by the averaged value of the air-fuel ratios of those cylinders other than the prescribed cylinder for which the air-fuel ratio is estimated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio for each cylinder of an internal combustion engine that estimates the air-fuel ratio of each cylinder based on the air-fuel ratio of a gas detected by an air-fuel ratio sensor installed in a collective exhaust pipe connected to an exhaust manifold of a plurality of cylinders of the internal combustion engine. The invention relates to an estimation device and a cylinder-by-cylinder air-fuel ratio control device.

In recent years, as described in Patent Document 1 (Japanese Patent No. 2717744), the behavior of the exhaust system of an internal combustion engine has been described in order to reduce air-fuel ratio variation between cylinders of the internal combustion engine and improve air-fuel ratio control accuracy. Is set, a detection value of one air-fuel ratio sensor installed in the collective exhaust pipe (the air-fuel ratio of the gas flowing through the collective exhaust pipe) is input to the model, and each observer observes its internal state. There are some which estimate the air-fuel ratio of each cylinder (air-fuel ratio for each cylinder) and feedback control the air-fuel ratio of each cylinder to a target value based on the estimated value.
Japanese Patent No. 2717744 (first page to second page, etc.)

  For example, in an internal combustion engine composed of a plurality of banks (cylinder groups) such as a V-type engine, there is one in which a collective exhaust pipe is provided for each bank, and an air-fuel ratio sensor is installed in each collective exhaust pipe. In this configuration, the air-fuel ratio for each cylinder is estimated for each bank based on the detected value of the air-fuel ratio sensor, but the combustion intervals (exhaust stroke intervals) of a plurality of cylinders provided in one bank are equal. It is not an interval. The reason for this will be described using a V-type 8-cylinder engine as an example. The V-type 8-cylinder engine is composed of two banks, each having four cylinders. The combustion interval is equal (90 ° C. A interval) when viewed from the entire engine (8 cylinders as a whole), but as shown in FIG. 2, the four cylinders # 1, # 3, # 5, # in one bank are shown. If only 7 is seen, since the combustion interval (exhaust stroke interval) changes in three ways of 90 ° C. A, 180 ° C. A, and 270 ° C., the combustion interval becomes unequal. When the combustion interval is long (270 ° C. A), the gas that reaches the position of the air-fuel ratio sensor is not mixed with the gas discharged from the other combustion cylinders, but the combustion interval is short (90 ° C.). In the case of A), it is considered that the gas reaching the position of the air-fuel ratio sensor is mixed with the gas discharged from the other combustion cylinders and the air-fuel ratio is changed.

  However, since the conventional cylinder-by-cylinder air-fuel ratio estimation model models the behavior of the exhaust system of an engine in which the combustion intervals are equal, like an engine with one exhaust system, this model is used as the combustion interval. Even when applied to a V-type 8-cylinder engine or the like having unequal intervals, there is a problem in that the cylinder-by-cylinder air-fuel ratio cannot be accurately estimated.

  Further, as shown in FIG. 3, in the case of an exhaust system in which the length of the exhaust manifold 12 of each cylinder (hereinafter referred to as “exhaust pipe length”) is an unequal length, the exhaust gas of each cylinder reaches the air-fuel ratio sensor 16. Therefore, the exhaust gas from each cylinder may not reach the air-fuel ratio sensor 16 in the order of combustion. However, since the conventional cylinder-by-cylinder air-fuel ratio estimation model is modeled for an exhaust system in which the exhaust pipe length of each cylinder is the same, in the case of an exhaust system in which the exhaust pipe length of each cylinder is unequal, There was a problem that the fuel ratio could not be accurately estimated.

  Accordingly, a first object of the present invention is an internal combustion engine that can accurately estimate the air-fuel ratio of each cylinder even in the case of an exhaust system in which the combustion interval is unequal or the exhaust pipe length of each cylinder is unequal. A cylinder-by-cylinder air-fuel ratio estimation device is provided, and a second object of the present invention is to provide an exhaust system in which the combustion intervals are unequal and the exhaust pipe length of each cylinder is unequal. An object of the present invention is to provide a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine that can accurately perform cylinder-by-cylinder air-fuel ratio control.

  In order to achieve the first object, according to a first aspect of the present invention, an air-fuel ratio for detecting an air-fuel ratio of gas discharged from each cylinder is connected to a collective exhaust pipe connected to an exhaust manifold of a plurality of cylinders of an internal combustion engine. In the cylinder-by-cylinder air-fuel ratio estimation apparatus for an internal combustion engine, the cylinder-by-cylinder air-fuel ratio estimation unit includes a cylinder-by-cylinder air-fuel ratio estimation unit that installs a fuel ratio sensor and estimates the air-fuel ratio of each cylinder based on the air-fuel ratio detected by the air-fuel ratio sensor. The relationship between the air-fuel ratio of the engine and the detected value of the air-fuel ratio sensor is modeled separately for each cylinder to create a plurality of cylinder-by-cylinder air-fuel ratio estimation models. The air-fuel ratio is estimated. In this way, the combustion intervals are unequal (hereinafter referred to as “unequal interval combustion”), or the exhaust pipe length of each cylinder is unequal (hereinafter referred to as “unequal length exhaust system”). Even in this case, the cylinder-by-cylinder air-fuel ratio estimation model for estimating the air-fuel ratio of each cylinder can be modeled separately for each cylinder in consideration of the effects of unequal-interval combustion and unequal-length exhaust systems. Even in the case of an unequal length exhaust system, the air-fuel ratio of each cylinder can be accurately estimated.

  The cylinder-by-cylinder air-fuel ratio estimation model used in the present invention is such that a combination of an air-fuel ratio and a disturbance element of a predetermined cylinder which is an object of air-fuel ratio estimation is input to the model as in claim 2. It is good to configure. In this way, the effects of unequal interval combustion and unequal length exhaust systems can be included in the disturbance element for modeling, and a cylinder-by-cylinder air-fuel ratio estimation model that differs for each cylinder can be created relatively easily. be able to.

  In this case, as in claim 3, the disturbance element is expressed by an average value of the air-fuel ratios of all the cylinders, or as in claim 4, the disturbance element is other than a predetermined cylinder which is an object of air-fuel ratio estimation. It may be expressed by the average value of the air-fuel ratio of the cylinders. In either case, there is an advantage that disturbance elements (influence of unequal interval combustion and unequal length exhaust system) can be easily calculated.

  The cylinder-by-cylinder air-fuel ratio estimation model is preferably modeled separately for each cylinder by using different model parameters for each cylinder. In this way, a cylinder-by-cylinder air-fuel ratio estimation model that differs for each cylinder can be easily created.

  According to a sixth aspect of the present invention, there is provided an internal combustion engine comprising a plurality of cylinder groups, wherein a collective exhaust pipe connected to a plurality of cylinders having unequal combustion intervals is provided for each cylinder group. In addition, in a system in which an air-fuel ratio sensor is installed in each collective exhaust pipe, the air-fuel ratio of each cylinder may be estimated using a cylinder-specific air-fuel ratio estimation model that is different for each cylinder in each cylinder group. . In an internal combustion engine composed of a plurality of cylinder groups, the combustion interval becomes unequal when viewed from only one cylinder group. Therefore, the conventional air-fuel ratio estimation method for each cylinder cannot accurately estimate the air-fuel ratio of each cylinder. By applying the present invention, it is possible to accurately estimate the air-fuel ratio of each cylinder in a cylinder group with unequal combustion intervals, and of course, even in the case of an unequal length exhaust system, the air-fuel ratio of each cylinder is accurately estimated. it can.

  In order to achieve the second object, as in claim 7, according to any one of claims 1 to 6, the cylinder-by-cylinder air-fuel ratio estimation apparatus and the cylinder-by-cylinder air-fuel ratio estimation apparatus A configuration may be provided with cylinder-by-cylinder air-fuel ratio control means for controlling the air-fuel ratio of each cylinder in a direction to reduce the estimated cylinder-by-cylinder variation of the air-fuel ratio. In this way, the cylinder-by-cylinder air-fuel ratio control can be performed with high precision even in the case of unequal interval combustion and unequal length exhaust systems.

Hereinafter, an embodiment in which the present invention is applied to, for example, a V-type 8-cylinder engine will be described.
First, the configuration of the exhaust system of the V-type 8-cylinder engine will be described with reference to FIG. In the V-type 8-cylinder engine 11, two banks (A bank and B bank) constituting two cylinder groups are arranged in a V shape, and four cylinders # 1, # 3, # 5 are arranged in the A bank. # 7 is arranged in series, and the remaining four cylinders # 2, # 4, # 6, and # 8 are arranged in series in the B bank. Separate exhaust systems are configured in the A bank and the B bank, and the four exhaust manifolds 12 in each bank are connected to separate collective exhaust pipes 14 respectively. An air-fuel ratio sensor 16 for detecting the air-fuel ratio of the exhaust gas is installed in the collective exhaust pipe 14 of each bank, and an exhaust gas purification catalyst 18 is installed on the downstream side of each air-fuel ratio sensor 16.

  Outputs of various sensors such as the air-fuel ratio sensor 16 are input to an engine control circuit (ECU) 20. The ECU 20 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel injection amount and ignition timing of each cylinder according to the engine operating state. To control.

  In the present embodiment, the ECU 20 executes each routine for cylinder-by-cylinder air-fuel ratio control, which will be described later, so that the detected value of the air-fuel ratio sensor 16 in each bank using a cylinder-by-cylinder air-fuel ratio estimation model that differs for each cylinder to be described later. The air-fuel ratio of each cylinder (hereinafter referred to as “cylinder-by-cylinder air-fuel ratio”) is estimated for each bank based on (the actual air-fuel ratio of the exhaust gas flowing through the collective exhaust pipe 14 of each bank). An average value of the estimated fuel ratio is calculated, and the average value is set as a reference air-fuel ratio (target air-fuel ratio of each bank). Then, for each bank, a deviation between the estimated value of the air-fuel ratio for each cylinder and the reference air-fuel ratio is calculated for each cylinder, and the correction amount for each cylinder (each cylinder) so that the deviation (air-fuel ratio variation between cylinders) is reduced. And the fuel injection amount for each cylinder is corrected based on the calculation result, thereby correcting the air-fuel ratio of the air-fuel mixture supplied to each cylinder for each cylinder, thereby varying the air-fuel ratio among the cylinders. (Hereinafter, this control is referred to as “cylinder-by-cylinder air-fuel ratio control”).

  Here, a method of estimating the air-fuel ratio of each bank in each bank based on the detected value of the air-fuel ratio sensor 16 in each bank (actual air-fuel ratio of exhaust gas flowing through the collective exhaust pipe 14 in each bank) will be described.

  When the V-type 8-cylinder engine 11 is viewed as a whole engine (8 cylinders as a whole), the interval between adjacent combustion cylinders (hereinafter referred to as “combustion interval”) is equal (90 ° C. A interval). As shown, when only the four cylinders # 1, # 3, # 5, and # 7 in one bank (A bank) are viewed, the combustion intervals (intervals of the exhaust stroke) are 90 ° C. A, 180 ° C. A, 270 ° C. Since A changes in three ways, the combustion interval becomes unequal. When the combustion interval is long (270 ° C. A), the gas reaching the position of the air-fuel ratio sensor 16 is not mixed with the gas discharged from the other combustion cylinders, but the combustion interval is short (90 In the case of the temperature A), it is considered that the gas that reaches the position of the air-fuel ratio sensor 16 is mixed with the gas discharged from the other combustion cylinders and the air-fuel ratio is changed.

  Further, as shown in FIG. 3, in the case of an exhaust system in which the length of the exhaust manifold 12 of each cylinder (hereinafter referred to as “exhaust pipe length”) is an unequal length, the exhaust gas of each cylinder reaches the air-fuel ratio sensor 16. Therefore, the exhaust gas from each cylinder may not reach the air-fuel ratio sensor 16 in the order of combustion.

  Therefore, in the present embodiment, the relationship between the air-fuel ratio of each cylinder and the detected value of the air-fuel ratio sensor 16 is modeled for each cylinder using different model parameters (weighting coefficients) for each cylinder, and a plurality of air-fuel ratios for each cylinder are modeled. An estimation model is being created. Therefore, in the V-type 8-cylinder engine 11, four types of cylinder-by-cylinder air-fuel ratio estimation models are created per bank (four cylinders), and the cylinder-by-cylinder air-fuel ratio estimation models are used to determine the air-fuel ratio of each cylinder. I try to estimate.

  The cylinder-by-cylinder air-fuel ratio estimation model for each cylinder is a model that represents the relationship between the air-fuel ratio of each cylinder and the detected value of the air-fuel ratio sensor 16, and is modeled separately for each cylinder by using different model parameters for each cylinder. It has become. For example, the cylinder-by-cylinder air-fuel ratio estimation models of the four cylinders # 1, # 3, # 5, and # 7 of the A bank are respectively given by the following equations.

Here, y _s is the detected value of the air-fuel ratio sensor 16, u is the input air-fuel ratio (u ₁ is input air-fuel ratio of the cylinders # 1 of each cylinder, u ₃ is the input air-fuel ratio of the cylinder # 3, u ₅ is cylinder # 5 is an input air-fuel ratio, and u ₇ is an input air-fuel ratio of cylinder # 7). a _{1j to} a _7j and b _{1j to} b _7j are model parameters (weighting coefficients) e _{1 to} e ₇ are disturbance elements. i represents the current calculation timing, and j represents the number of calculation timings before the current calculation timing i. In this embodiment, since the calculation interval is set to a half interval (90 ° C. A) of the combustion interval (180 ° C. A), j changes from 1 to 8 per cycle (720 ° C. A).
Maximum value of j = 720 ° C. A / 90 ° C. A = 8

  As described above, the cylinder-by-cylinder air-fuel ratio estimation model of each cylinder is configured so that a combination of the air-fuel ratio and the disturbance element of a predetermined cylinder that is an object of air-fuel ratio estimation is input to the model. It is represented by an average value of air-fuel ratios of cylinders other than the cylinder.

Specifically, the disturbance element e ₁ of the cylinder-by-cylinder air-fuel ratio estimation model of cylinder # 1 is represented by the average value of the air-fuel ratios of the three cylinders # 3, # 5, and # 7 excluding cylinder # 1.
e ₁ = (u ₃ + u ₅ + u ₇ ) / 3

Disturbance element e ₃ of the cylinder-by-cylinder air-fuel ratio estimation model of cylinder # 3 is represented by the average value of the air-fuel ratios of the three cylinders # 1, # 5, and # 7 excluding cylinder # 3.
e ₃ = (u ₁ + u ₅ + u ₇ ) / 3

The disturbance element e ₅ of the cylinder-by-cylinder air-fuel ratio estimation model of cylinder # 5 is represented by the average value of the air-fuel ratios of the three cylinders # 1, # 3, and # 7 excluding cylinder # 5.
e ₅ = (u ₁ + u ₃ + u ₇ ) / 3

The disturbance element e ₇ of the cylinder-by-cylinder air-fuel ratio estimation model of the cylinder # 7 is represented by the average value of the air-fuel ratios of the three cylinders # 1, # 3, and # 5 excluding the cylinder # 7.
u ₇ = (u ₁ + u ₃ + u ₅ ) / 3

Alternatively, the air-fuel ratio # 1 for all the cylinders of each disturbance factor e ₁ to e ₇ Bank A, # 3, # 5, it may be represented by an average value of # 7.
e ₁ = e ₃ = e ₅ = u ₇ = (u ₁ + u ₃ + u ₅ + u ₇ ) / 4
In this way, all the disturbance elements e _{1 to} e ₇ of the cylinder-by-cylinder air-fuel ratio estimation model of each cylinder are the same, and there is an advantage that the arithmetic processing becomes easy.

For the other bank B, the cylinder-by-cylinder air-fuel ratio estimation model for each cylinder # 2, # 4, # 6, and # 8 may be created by the same method.
When the formula of the cylinder-by-cylinder air-fuel ratio estimation model for each cylinder #n (n = 1 to 8) is converted into a state space model, the following formulas (1) and (2) are derived.
X (i + 1) = A n · X (i) + B n · u (i) + W n (i) ...... (1)
_{Y (i) = C n ·} X (i) + D n · u (i) ...... (2)
Here, A _n , B _n , C _n , and D _n are parameters (weighting coefficients) of the cylinder-by-cylinder air-fuel ratio estimation model of each cylinder #n, Y is a detected value of the air-fuel ratio sensor 16, and X is a state variable. The sum of the effects of the cylinder-by-cylinder air-fuel ratio, W is noise.

Furthermore, when the Kalman filter is designed by the above formulas (1) and (2), the following formula is obtained.
X ^ (k + 1 | k ) = A n · X ^ (k | k-1) + K n {Y (k) -C n · A n · X ^ (k | k-1)}
...... (3)
Here, X ^ (X hat) is the estimate of the sum of the effects of the cylinder-by-cylinder air-fuel ratio, K _n is a Kalman gain. The meaning of X ^ (k + 1 | k) represents that the estimated value of time (k + 1) is obtained from the estimated value of time (k).

  As described above, by configuring the cylinder-by-cylinder air-fuel ratio estimation model of each cylinder by the Kalman filter type observer, it is possible to sequentially estimate the sum of the effects of the cylinder-by-cylinder air-fuel ratio as the combustion cycle progresses. When the air-fuel ratio deviation is input, the output Y is replaced with the air-fuel ratio deviation in the above equation (3).

  The ECU 20 executes the routines for cylinder-by-cylinder air-fuel ratio control shown in FIGS. 4 to 6, and uses the cylinder-by-cylinder air-fuel ratio estimation model that is different for each cylinder, based on the detection value of the air-fuel ratio sensor 16 in each bank. Then, the cylinder-by-cylinder air-fuel ratio of each bank is estimated, and the cylinder-by-cylinder air-fuel ratio control is executed to correct the fuel injection amount of each cylinder so as to reduce the air-fuel ratio variation between the cylinders for each bank. The processing contents of each routine will be described below.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control main routine of FIG. 4 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with an output pulse of a crank angle sensor (not shown). When this routine is started, first, in step 101, an execution condition determination routine of FIG. 5 described later is executed to determine whether or not an execution condition for cylinder-by-cylinder air-fuel ratio control is satisfied. Thereafter, the process proceeds to step 102, where it is determined whether or not the execution condition for the cylinder-by-cylinder air-fuel ratio control is satisfied depending on whether or not the execution flag set in the execution condition determination routine of FIG. As a result, when it is determined that the execution flag is OFF (execution condition is not satisfied), this routine is terminated without performing the subsequent processing.

  On the other hand, if it is determined that the execution flag is ON (execution condition is established), the process proceeds to step 103, and whether or not the current crank angle is the air-fuel ratio detection timing of each cylinder (sample timing of the output of the air-fuel ratio sensor 16). If it is not the air-fuel ratio detection timing, this routine is terminated without performing the subsequent processing.

  On the other hand, if the current crank angle is the air-fuel ratio detection timing, the routine proceeds to step 104, where a cylinder-by-cylinder air-fuel ratio control execution routine of FIG.

[Execution condition judgment routine]
The execution condition determination routine of FIG. 5 is a subroutine executed in step 101 of the cylinder-by-cylinder air-fuel ratio control main routine of FIG. When this routine is started, first, at step 201, it is determined whether or not the air-fuel ratio sensor 16 is in a usable state. Here, the usable state is, for example, a state in which the air-fuel ratio sensor 16 is in an active state and has not failed. If the air-fuel ratio sensor 16 is not usable, this routine is terminated without performing the subsequent processing.

  On the other hand, if the air-fuel ratio sensor 16 is in a usable state, the process proceeds to step 202, where it is determined whether or not the coolant temperature is equal to or higher than a predetermined temperature (the engine 11 is warmed up). This routine is terminated without performing the subsequent processing. If the cooling water temperature is equal to or higher than the predetermined temperature, the process proceeds to step 203, and the current engine operation region is controlled by cylinder-by-cylinder air-fuel ratio control with reference to the operation region map using the engine speed and load (for example, intake pipe pressure) as parameters. It is determined whether or not it is an execution region. In the high speed range and the low load range, the estimation accuracy of the cylinder-by-cylinder air-fuel ratio is deteriorated, so that the cylinder-by-cylinder air-fuel ratio control is prohibited.

  If the current engine operating region is the execution region of the cylinder-by-cylinder air-fuel ratio control, the process proceeds to step 204, the execution flag is set to ON, and if it is not the execution region of the cylinder-by-cylinder air-fuel ratio control, the process proceeds to step 205 Set to OFF.

[Cylinder-specific air-fuel ratio control execution routine]
The cylinder-by-cylinder air-fuel ratio control execution routine of FIG. 6 is a subroutine executed in step 104 of the cylinder-by-cylinder air-fuel ratio control main routine of FIG. When this routine is started, first, in step 301, the output of the air-fuel ratio sensor 16 (air-fuel ratio detection value) is read. In the next step 302, the current air-fuel ratio estimation model that differs for each cylinder is used. The air-fuel ratio of the cylinder to be estimated for the fuel ratio is estimated based on the detection value of the air-fuel ratio sensor 16. The processing of step 302 serves as cylinder-by-cylinder air-fuel ratio estimating means in the claims. Thereafter, the process proceeds to step 303, where an average value of estimated air-fuel ratios of all cylinders is calculated, and the average value is set as a reference air-fuel ratio (target air-fuel ratio of all cylinders).

  Thereafter, the routine proceeds to step 304, where the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio is calculated, and the cylinder-specific correction amount is calculated so that the deviation becomes small, and then the routine proceeds to step 305, where the cylinder-specific correction is performed. By correcting the fuel injection amount for each cylinder based on the amount, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder so as to reduce the variation in air-fuel ratio among the cylinders. The processes in steps 303 to 305 serve as cylinder-by-cylinder air-fuel ratio control means.

  In the present embodiment described above, the relationship between the air-fuel ratio of each cylinder and the detected value of the air-fuel ratio sensor 16 is modeled for each cylinder using different model parameters for each cylinder, and a plurality of cylinder-specific air-fuel ratio estimation models are obtained. Because the air-fuel ratio of each cylinder is estimated using a cylinder-by-cylinder air-fuel ratio estimation model that is created for each cylinder, even in the case of unequal interval combustion and unequal length exhaust systems, unequal interval combustion and unequal The air-fuel ratio of each cylinder can be accurately estimated using a cylinder-by-cylinder air-fuel ratio estimation model that takes into account the influence of the long exhaust system.

  In addition, in this embodiment, the cylinder-by-cylinder air-fuel ratio estimation model of each cylinder is configured so that the combination of the air-fuel ratio of the predetermined cylinder, which is the target of air-fuel ratio estimation, and the disturbance element are input to the model. The effects of equal-interval combustion and unequal-length exhaust systems can be included in the disturbance element for modeling, and there is an advantage that a cylinder-by-cylinder air-fuel ratio estimation model that differs for each cylinder can be created relatively easily.

  In addition, in this embodiment, the disturbance element is expressed by the average value of the air-fuel ratios of cylinders other than the predetermined cylinder that is the target of air-fuel ratio estimation, or the disturbance element is expressed by the average value of the air-fuel ratios of all cylinders. Since it did in this way, there exists an advantage which can calculate easily a disturbance element (the influence of non-uniform combustion or an unequal length exhaust system).

  The present invention is not limited to a V-type 8-cylinder engine, but can be applied to an engine having a number of cylinders other than this, and also to other types of engines such as an inline engine and a horizontally opposed engine. Can be applied.

It is a schematic block diagram of the engine exhaust system in one Example of this invention. It is a figure explaining the overlap of the exhaust gas of an adjacent combustion cylinder. It is a figure which shows an example of an unequal length exhaust system. It is a flowchart which shows the flow of a process of the cylinder-by-cylinder air-fuel ratio control main routine. It is a flowchart which shows the flow of a process of an execution condition determination routine. It is a flowchart which shows the flow of a process of the air-fuel ratio control execution routine classified by cylinder.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Exhaust manifold, 14 ... Collective exhaust pipe, 16 ... Air-fuel ratio sensor, 18 ... Catalyst, 20 ... ECU (Air-fuel ratio estimation means according to cylinder, Air-fuel ratio control means according to cylinder), 22 ... Junction

Claims (7)

An air-fuel ratio sensor for detecting the air-fuel ratio of the gas discharged from each cylinder is installed in a collective exhaust pipe to which an exhaust manifold of a plurality of cylinders of the internal combustion engine is connected. Based on the air-fuel ratio of the gas detected by this air-fuel ratio sensor In the cylinder-by-cylinder air-fuel ratio estimation device of the internal combustion engine provided with the cylinder-by-cylinder air-fuel ratio estimation means for estimating the air-fuel ratio of each cylinder,
The relationship between the air-fuel ratio of each cylinder and the detected value of the air-fuel ratio sensor is modeled separately for each cylinder to create a plurality of cylinder-specific air-fuel ratio estimation models,
The cylinder-by-cylinder air-fuel ratio estimation means estimates the air-fuel ratio of each cylinder using a cylinder-by-cylinder air-fuel ratio estimation model that differs for each cylinder.   2. The cylinder-by-cylinder air-fuel ratio estimation model is configured so that a combination of an air-fuel ratio and a disturbance element of a predetermined cylinder that is an object of air-fuel ratio estimation is input to the model. The cylinder-by-cylinder air-fuel ratio estimation apparatus of the internal combustion engine.   3. The cylinder-by-cylinder air-fuel ratio estimation apparatus for an internal combustion engine according to claim 2, wherein the disturbance element is represented by an average value of air-fuel ratios of all cylinders.   3. The cylinder-by-cylinder air-fuel ratio estimation apparatus for an internal combustion engine according to claim 2, wherein the disturbance element is represented by an average value of air-fuel ratios of cylinders other than the predetermined cylinder to be subjected to the air-fuel ratio estimation.   The cylinder of the internal combustion engine according to any one of claims 1 to 4, wherein the cylinder-by-cylinder air-fuel ratio estimation model is modeled separately for each cylinder by using different model parameters for each cylinder. Another air-fuel ratio estimation device. The internal combustion engine is composed of a plurality of cylinder groups, and each cylinder group is provided with a collective exhaust pipe to which an exhaust manifold of a plurality of cylinders having unequal combustion intervals is connected. The air-fuel ratio sensor is installed;
6. The cylinder-by-cylinder air-fuel ratio estimation means estimates the air-fuel ratio of each cylinder using a cylinder-by-cylinder air-fuel ratio estimation model that is different for each cylinder in each cylinder group. A cylinder-by-cylinder air-fuel ratio estimation apparatus for an internal combustion engine.   7. The air-fuel ratio estimation apparatus for each cylinder of an internal combustion engine according to claim 1 and the air-fuel ratio estimation of each cylinder in a direction to reduce the inter-cylinder variation in the air-fuel ratio of each cylinder estimated by the cylinder-by-cylinder air-fuel ratio estimation apparatus. A cylinder-by-cylinder air-fuel ratio control device for an internal combustion engine, comprising: a cylinder-by-cylinder air-fuel ratio control means for controlling the fuel ratio.

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