JP2010203413A - Air-fuel ratio control device for each of cylinders of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration of the accuracy of the control of an air-fuel ratio for each of cylinders due to the influence of the pulsation of the exhaust gas pressure in a system in which the air-fuel ratio of each cylinder is estimated based on the output of the air-fuel ratio sensor mounted to the exhaust gas collection portion of an engine to control separately the air-fuel ratio of the each cylinder based on the estimated results. <P>SOLUTION: The influence coefficient of the exhaust gas pressure (the influence degree of the exhaust gas pressure on the output of an air-fuel ratio sensor 24) is calculated at each timing of the detections of the air-fuel ratio of the each cylinder (each sampling timing of the output of the air-fuel ratio sensor 24) based on the operational conditions of an engine (for example, an engine rotation speed, a load of an engine and the like) and the length (or volume) of an exhaust gas manifold 39, and then the output of the air-fuel sensor 24 is corrected using the obtained influence coefficient of the exhaust gas pressure, whereby the air-fuel ratio of each cylinder is estimated with high accuracy without being influenced by the pulsation of the exhaust gas pressure by excluding the fraction coming from the influence of the pulsation of the exhaust gas pressure from the output of the air-fuel ratio sensor 24 to estimate the air-fuel ratio of the each cylinder based on the corrected output of the air-fuel ratio sensor 24. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cylinder of an internal combustion engine that estimates the air-fuel ratio of each cylinder based on the output of an air-fuel ratio sensor installed in an exhaust collecting portion of the internal combustion engine and controls the air-fuel ratio of each cylinder for each cylinder based on the estimation result. It is an invention related to another air-fuel ratio control device.

  In recent years, in order to improve the air-fuel ratio control accuracy of an internal combustion engine, as described in, for example, Japanese Patent Application Laid-Open No. 2008-14178, exhaust gases from a plurality of cylinders of an internal combustion engine are gathered. Estimate the air-fuel ratio of each cylinder using a model that associates the detection value of the air-fuel ratio sensor installed in the flowing exhaust gas collection part (the air-fuel ratio of the exhaust gas collection part) with the air-fuel ratio of each cylinder. On the basis of this, there is a type in which cylinder-by-cylinder air-fuel ratio control is performed in which the air-fuel ratio (for example, fuel injection amount) of each cylinder is controlled on a cylinder-by-cylinder basis so that the variation in the air-fuel ratio of each cylinder is reduced.

JP 2008-14178 A

  By the way, in a system including an exhaust turbine supercharger that drives a compressor by an exhaust turbine provided in an exhaust passage of an internal combustion engine to supercharge intake air, when performing air-fuel ratio control by cylinder, When the air-fuel ratio sensor is installed upstream of the exhaust turbine rather than downstream, the air-fuel ratio sensor is more likely to change in the output of the air-fuel ratio sensor depending on the air-fuel ratio of each cylinder. It is preferable to do this.

  However, since the exhaust pressure tends to pulsate (fluctuate) greatly on the upstream side of the exhaust turbine, and the air-fuel ratio sensor has a characteristic that the output changes depending on the exhaust pressure, if the air-fuel ratio sensor is installed upstream of the exhaust turbine, There is a possibility that the error of the output of the air-fuel ratio sensor becomes large due to the influence of the exhaust pressure pulsation. When the error in the output of the air-fuel ratio sensor becomes large due to the influence of exhaust pressure pulsation in this way, the estimation accuracy of the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor is lowered, and the accuracy of cylinder-by-cylinder air-fuel ratio control is lowered. Therefore, the emission reduction effect by the cylinder-by-cylinder air-fuel ratio control is diminished. The problem due to the influence of the exhaust pressure pulsation is not limited to an internal combustion engine with a supercharger, and is also a problem that similarly occurs to some extent even with an internal combustion engine without a supercharger.

  Accordingly, 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 prevent a decrease in accuracy of cylinder-by-cylinder air-fuel ratio control due to the influence of exhaust pressure pulsation.

  In order to solve the above-mentioned problems, an invention according to claim 1 is provided such that an air-fuel ratio sensor is installed in an exhaust gas collecting portion where exhaust gases of a plurality of cylinders of an internal combustion engine flow to flow, and each air-fuel ratio detection timing of each cylinder is detected. In the air-fuel ratio control apparatus for each cylinder of an internal combustion engine that estimates the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor and controls the air-fuel ratio of each cylinder based on the estimation result, the air-fuel ratio of each cylinder Exhaust pressure influence degree determining means for determining the degree of influence of the exhaust pressure of the internal combustion engine on the output of the air fuel ratio sensor at each detection timing, and the exhaust pressure determined by the exhaust pressure influence degree determining means at each air fuel ratio detection timing of each cylinder Sensor output correction means for correcting the output of the air-fuel ratio sensor based on the degree of influence of the air-fuel ratio, and the air-fuel ratio sensor output corrected by the sensor output correction means at each air-fuel ratio detection timing of each cylinder based on the output of the air-fuel ratio sensor. It is obtained by a structure in which a cylinder air-fuel ratio estimating means for estimating a ratio.

  In this configuration, the influence of the exhaust pressure pulsation from the output of the air-fuel ratio sensor is corrected by correcting the output of the air-fuel ratio sensor based on the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor at each air-fuel ratio detection timing of each cylinder. By estimating the air-fuel ratio of each cylinder based on the corrected output of the air-fuel ratio sensor, the air-fuel ratio of each cylinder can be accurately estimated without being affected by the exhaust pressure pulsation. be able to. Thereby, it is possible to prevent the accuracy of the cylinder-by-cylinder air-fuel ratio control from being lowered due to the influence of the exhaust pressure pulsation, and it is possible to avoid the reduction in the emission reduction effect by the cylinder-by-cylinder air-fuel ratio control.

  In this case, as a specific method for determining the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor, for example, an exhaust pressure sensor for detecting the exhaust pressure is provided at the exhaust collecting portion as in claim 2, and this exhaust The influence degree of the exhaust pressure may be determined based on the output of the atmospheric pressure sensor. In this way, it is possible to accurately determine the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor installed in the exhaust collection portion based on the exhaust pressure of the exhaust collection portion detected by the exhaust pressure sensor.

  Alternatively, as in claim 3, an exhaust pressure sensor for detecting the exhaust pressure is provided for each exhaust manifold of each cylinder, and the degree of influence of the exhaust pressure is determined based on the output of the exhaust pressure sensor of each cylinder. May be. Since the exhaust pressure of the exhaust collecting portion changes depending on the exhaust pressure of each cylinder, if the exhaust pressure of each cylinder detected by the exhaust pressure sensor of each cylinder is used, the exhaust effect on the output of the air-fuel ratio sensor installed in the exhaust collecting portion is affected. The degree of influence of atmospheric pressure can be accurately determined.

  Further, as in claim 4, there is provided in-cylinder pressure acquisition means for detecting or estimating the in-cylinder pressure of each cylinder, and the in-cylinder pressure of each cylinder detected or estimated by this in-cylinder pressure acquisition means and the length of the exhaust manifold of each cylinder. Alternatively, the influence degree of the exhaust pressure may be determined based on the volume (= channel cross-sectional area × length). The exhaust pressure of each cylinder varies depending on the in-cylinder pressure of each cylinder (for example, the in-cylinder pressure at the time of combustion or the in-cylinder pressure when the exhaust valve is opened) and the length or volume of the exhaust manifold of each cylinder. Because the air pressure changes, using the in-cylinder pressure of each cylinder and the length or volume of the exhaust manifold of each cylinder accurately determines the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor installed in the exhaust collection section can do.

  Further, as in claim 5, the degree of influence of the exhaust pressure may be determined based on the operating state of the internal combustion engine and the length or volume of the exhaust manifold of each cylinder. The combustion state of each cylinder changes according to the operating state of the internal combustion engine (for example, rotation speed, load, etc.), and the in-cylinder pressure of each cylinder (for example, the in-cylinder pressure during combustion or the in-cylinder pressure when the exhaust valve opens) changes. Since the exhaust pressure of each cylinder changes due to the in-cylinder pressure of each cylinder and the length and volume of the exhaust manifold of each cylinder, and the exhaust pressure of the exhaust collecting portion changes, the operating state of the internal combustion engine and the exhaust manifold of each cylinder If the length or the volume is used, it is possible to accurately determine the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor installed in the exhaust collecting portion.

  According to another aspect of the present invention, an air-fuel ratio sensor is installed in an exhaust gas collecting portion where exhaust gases from a plurality of cylinders of an internal combustion engine flow, and the air-fuel ratio of each cylinder is determined based on the output of the air-fuel ratio sensor. In the cylinder-by-cylinder air-fuel ratio control apparatus for executing the cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio of each cylinder based on the estimation result, the exhaust pressure of the internal combustion engine that affects the output of the air-fuel ratio sensor Exhaust pressure influence degree determining means for determining whether or not the influence degree of the exhaust gas has exceeded the allowable level, and if the exhaust pressure influence degree determining means determines that the influence degree of the exhaust pressure has exceeded the allowable level, the air-fuel ratio for each cylinder It is good also as a structure provided with the cancellation means to cancel or prohibit control.

  In this configuration, when it is determined that the degree of influence of the exhaust pressure of the internal combustion engine on the output of the air-fuel ratio sensor has exceeded the allowable level, the error in the output of the air-fuel ratio sensor increases due to the influence of exhaust pressure pulsation. Therefore, the estimation accuracy of the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor is lowered, and it is determined that the cylinder-by-cylinder air-fuel ratio control cannot be performed accurately, and the cylinder-by-cylinder air-fuel ratio control is stopped or prohibited. Can do. As a result, it is possible to prevent a decrease in the accuracy of cylinder-by-cylinder air-fuel ratio control due to the influence of exhaust pressure pulsation.

  In this case, a specific method for determining whether or not the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor has exceeded an allowable level is, for example, as in claim 7, an exhaust manifold or an exhaust manifold of each cylinder. An exhaust pressure sensor that detects the exhaust pressure is provided every time, and when the fluctuation amount of the output of the exhaust pressure sensor in a predetermined period (for example, between 720 CAs in one cycle) is a predetermined value or more, the influence level of the exhaust pressure reaches an allowable level. You may make it determine with having exceeded. In this way, when the amount of fluctuation of the exhaust pressure in the exhaust collecting portion or the amount of fluctuation in the exhaust pressure of each cylinder exceeds a predetermined value, the exhaust pressure exerted on the output of the air-fuel ratio sensor installed in the exhaust collecting portion. It can be determined that the degree of influence exceeds the allowable level.

  Alternatively, the frequency component (for example, the frequency component related to the combustion interval in the output of the air-fuel ratio sensor is analyzed by frequency analysis of the output of the air-fuel ratio sensor in a predetermined period (for example, between 720 CA which is one cycle). In the case of four cylinders, it may be determined that the degree of influence of the exhaust pressure exceeds the allowable level when the amplitude of the frequency component corresponding to the period of 180 CA intervals is equal to or greater than a predetermined value. In this way, when the amplitude of the frequency component related to the combustion interval out of the output of the air-fuel ratio sensor exceeds a predetermined value due to the influence of the exhaust pressure pulsating at each combustion interval, the output of the air-fuel ratio sensor is increased. It can be determined that the degree of influence of the exhaust pressure exerted exceeds an allowable level.

  Further, as in claim 9, when the difference between the peak value and the bottom value of the output of the air-fuel ratio sensor in a predetermined period (for example, between 720 CA which is one cycle) is a predetermined value or more, the influence degree of the exhaust pressure is allowed. It may be determined that the level has been exceeded. In this way, when the difference between the peak value and the bottom value of the output of the air-fuel ratio sensor exceeds a predetermined value due to the pulsation of the exhaust pressure, the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor is at an allowable level. Can be determined to have exceeded

  According to a tenth aspect of the present invention, there is provided an exhaust turbine type supercharger that drives a compressor by an exhaust turbine provided in an exhaust passage of an internal combustion engine to supercharge intake air, and is provided upstream of the exhaust turbine. You may apply to the system in which the air fuel ratio sensor was installed. When performing cylinder-by-cylinder air-fuel ratio control in a system equipped with an exhaust turbine supercharger, it is more effective to install an air-fuel ratio sensor upstream of the exhaust turbine than downstream of the exhaust turbine. Therefore, it is preferable to install an air-fuel ratio sensor upstream of the exhaust turbine. However, if an air-fuel ratio sensor is installed upstream of the exhaust turbine, an error in the output of the air-fuel ratio sensor increases due to the influence of exhaust pressure pulsation, and the accuracy of air-fuel ratio control for each cylinder may be reduced. Therefore, if the present invention is applied, an air-fuel ratio sensor is installed on the upstream side of the exhaust turbine in which the output corresponding to the air-fuel ratio of each cylinder easily appears in the output of the air-fuel ratio sensor, and the cylinder-by-cylinder air due to the effect of exhaust pressure pulsation is installed. A decrease in the accuracy of the fuel ratio control can be prevented.

FIG. 1 is a schematic configuration diagram of the entire engine control system in Embodiment 1 of the present invention. FIG. 2A is a time chart showing the behavior of the exhaust pressure, and FIG. 2B is a time chart showing the behavior of the air-fuel ratio sensor output. FIG. 3 is a block diagram illustrating a method for determining the degree of influence of the exhaust pressure on the air-fuel ratio sensor output and a method for correcting the air-fuel ratio sensor output based on the degree of influence of the exhaust pressure. FIG. 4 is a diagram for explaining the influence of the exhaust pressure pulsation on the air-fuel ratio sensor output. FIG. 5 is a flowchart for explaining the flow of processing of the cylinder-by-cylinder air-fuel ratio control main routine according to the first embodiment. FIG. 6 is a flowchart for explaining the flow of processing of the exhaust pressure influence degree determination and sensor output correction routine of the first embodiment. FIG. 7 is a flowchart for explaining the processing flow of the exhaust pressure influence degree determination routine of the second embodiment.

  Hereinafter, some embodiments in which the mode for carrying out the present invention is applied to an internal combustion engine with an exhaust turbine supercharger will be described.

A first embodiment of the present invention will be described with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A downstream side of the air flow meter 14 is provided with a compressor 27 of an exhaust turbine supercharger 25 described later and an intercooler 31 that cools intake air pressurized by the compressor 27. A throttle valve 15 whose opening is adjusted by a motor or the like and a throttle opening sensor 16 for detecting the opening (throttle opening) of the throttle valve 15 are provided on the downstream side of the intercooler 31.

  Further, a surge tank 17 is provided on the downstream side of the throttle valve 15, and an intake pressure sensor 18 that detects a downstream pressure (intake pressure) of the throttle valve 15 is provided in the surge tank 17. The surge tank 17 is provided with an intake manifold 19 that introduces air into each cylinder of the engine 11, and a fuel injection valve that injects fuel toward the intake port in the vicinity of the intake port of the intake manifold 19 of each cylinder. 20 is attached. A spark plug 21 is attached to the cylinder head of the engine 11 for each cylinder, and an air-fuel mixture in each cylinder is ignited by spark discharge of each spark plug 21.

  On the other hand, in the exhaust pipe 22 (exhaust passage) of the engine 11, the exhaust gas collection portion 40 (the portion where the exhaust gas from each cylinder joins and flows) where the exhaust manifold 39 of each cylinder gathers has an air-fuel ratio of the exhaust gas. An air-fuel ratio sensor 24 for detection is provided, and a catalyst 23 such as a three-way catalyst for purifying exhaust gas is provided downstream of the air-fuel ratio sensor 24.

  An exhaust turbine supercharger 25 is mounted on the engine 11. In the exhaust turbine supercharger 25, an exhaust turbine 26 is disposed between the air-fuel ratio sensor 24 and the catalyst 23 in the exhaust pipe 22, and between the air flow meter 14 and the throttle valve 15 in the intake pipe 12. A compressor 27 is arranged in the front. In the supercharger 25, an exhaust turbine 26 and a compressor 27 are connected, and the exhaust turbine 26 is rotationally driven by the kinetic energy of exhaust gas, whereby the compressor 27 is rotationally driven to supercharge intake air. .

  Further, the intake pipe 12 is provided with an intake bypass passage 28 that bypasses the upstream side and the downstream side of the compressor 27 on the upstream side of the throttle valve 15. An air bypass valve (hereinafter referred to as “ABV”) 29 is provided. The ABV 29 is configured such that the opening / closing operation of the ABV 29 is controlled by controlling the ABV vacuum switching valve 30.

  On the other hand, the exhaust pipe 22 is provided with an exhaust bypass passage 32 that bypasses the upstream side and the downstream side of the exhaust turbine 26, and a waste gate valve (hereinafter referred to as a waste gate valve) that opens and closes the exhaust bypass passage 32 in the middle of the exhaust bypass passage 32. 33 (denoted as “WGV”). The WGV 33 is configured such that the opening degree of the WGV 33 is controlled by controlling the WGV vacuum switching valve 34 and the diaphragm actuator 35.

  A cooling water temperature sensor 36 that detects the cooling water temperature and a crank angle sensor 37 that outputs a pulse signal each time the crankshaft of the engine 11 rotates a predetermined crank angle are attached to the cylinder block of the engine 11. Based on the output signal of the crank angle sensor 37, the crank angle and the engine speed are detected.

  Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 38. The ECU 38 is mainly composed of a microcomputer, and executes various engine control routines stored in a built-in ROM (storage medium), so that the fuel injection amount of the fuel injection valve 20 can be changed according to the engine operating state. The ignition timing of the spark plug 21 is controlled, and the opening of the WGV 33 is controlled to control the amount of exhaust gas supplied to the exhaust turbine 26, thereby controlling the rotation of the exhaust turbine 26 and the compressor 27 to increase the supercharging pressure. Control.

  Further, the ECU 38 executes respective routines for cylinder-by-cylinder air-fuel ratio control shown in FIGS. 5 and 6 to be described later, thereby using the detected values (exhaust gas collection unit) of the air-fuel ratio sensor 24 using a cylinder-by-cylinder air-fuel ratio estimation model to be described later. The air-fuel ratio of each cylinder is estimated based on the actual air-fuel ratio of the exhaust gas flowing through 40, and the deviation between the estimated air-fuel ratio of each cylinder and the reference air-fuel ratio (the average value or control target value of the estimated air-fuel ratio of all cylinders) Is calculated for each cylinder, and the air-fuel ratio correction amount (correction amount of the fuel injection amount of each cylinder) is calculated so that the deviation becomes small, and the fuel injection amount of each cylinder is calculated based on the calculation result By correcting the air-fuel ratio, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder, and the cylinder-by-cylinder air-fuel ratio control is executed to control the variation in the air-fuel ratio among the cylinders.

  Here, a specific example of a model for estimating the air-fuel ratio of each cylinder based on the detected value of the air-fuel ratio sensor 24 (actual air-fuel ratio of exhaust gas flowing through the exhaust collecting portion 40) (hereinafter referred to as "cylinder-specific air-fuel ratio estimation model"). An example will be described.

  Paying attention to the gas exchange in the exhaust collecting section 40, the detected value of the air-fuel ratio sensor 24 is given a predetermined weight to the estimated air-fuel ratio history of each cylinder and the detected value history of the air-fuel ratio sensor 24 in the exhaust collecting section 40, respectively. The model is obtained by multiplying and adding, and the air-fuel ratio of each cylinder is estimated using this model. At this time, a Kalman filter is used as an observer.

More specifically, a gas exchange model in the exhaust collecting portion 40 is approximated by the following equation (1).
ys (t) = k1 * u (t-1) + k2 * u (t-2) -k3 * ys (t-1) -k4 * ys (t-2)
...... (1)
Here, ys is a detected value of the air-fuel ratio sensor 24, u is an air-fuel ratio of the gas flowing into the exhaust collecting section 40, and k1 to k4 are constants.

  In the exhaust system, there are a primary delay element of gas inflow and mixing in the exhaust collecting portion 40 and a primary delay element due to a response delay of the air-fuel ratio sensor 24. Therefore, in the above equation (1), the history for the past two times is referred to in consideration of these first order lag elements.

When the above equation (1) is converted into a state space model, the following equations (2a) and (2b) are derived.
X (t + 1) = A.X (t) + B.u (t) + W (t) (2a)
Y (t) = C · X (t) + D · u (t) (2b)
Here, A, B, C, and D are model parameters, Y is a detected value of the air-fuel ratio sensor 24, X is an estimated air-fuel ratio of each cylinder as a state variable, and W is noise.

Further, when the Kalman filter is designed by the above equations (2a) and (2b), the following equation (3) is obtained.
X ^ (k + 1 | k) = A.X ^ (k | k-1) + K {Y (k) -C.A.X ^ (k | k-1)} (3) where X ^ (X hat) is the estimated air-fuel ratio of each cylinder, and K is the Kalman gain. The meaning of X ^ (k + 1 | k) represents that the estimated value of the next time (k + 1) is obtained from the estimated value of time (k).

  As described above, the cylinder-by-cylinder air-fuel ratio estimation model is configured by the Kalman filter type observer, whereby the air-fuel ratio of each cylinder can be sequentially estimated as the combustion cycle proceeds.

  Next, a method for setting the air-fuel ratio detection timing of each cylinder (sample timing of the output of the air-fuel ratio sensor 24) will be described. In the first embodiment, the delay until the exhaust gas discharged from each cylinder reaches the vicinity of the air-fuel ratio sensor 24 and the air-fuel ratio is detected (hereinafter referred to as “response delay of the exhaust system”) depends on the engine operating state. In consideration of the change, the air-fuel ratio detection timing of each cylinder is set by a map or the like according to the engine operating state (for example, engine load, engine speed, etc.). Generally, as the engine load and the engine speed decrease, the response delay of the exhaust system increases. Therefore, the air-fuel ratio detection timing of each cylinder is shifted to the retard side as the engine load and the engine speed decrease. Is set to

  By the way, in the case of performing the cylinder-by-cylinder air-fuel ratio control in the system including the exhaust turbine supercharger 25, it is preferable to install the air-fuel ratio sensor 24 on the upstream side of the exhaust turbine 26 rather than on the downstream side of the exhaust turbine 26. Since the output corresponding to the air-fuel ratio of each cylinder tends to appear in the output of the air-fuel ratio sensor 24, it is preferable to install the air-fuel ratio sensor 24 upstream of the exhaust turbine 26.

  However, as shown in FIG. 2A, the upstream side of the exhaust turbine 26 has a tendency that the exhaust pressure tends to pulsate (fluctuate), and the air-fuel ratio sensor 24 has a characteristic that the output changes depending on the exhaust pressure. As shown in FIG. 2B, when the air-fuel ratio sensor 24 is installed on the upstream side of the exhaust turbine 26, the output error of the air-fuel ratio sensor 24 may increase due to the influence of the exhaust pressure pulsation. is there. Thus, when the error in the output of the air-fuel ratio sensor 24 due to the influence of the exhaust pressure pulsation increases, the estimation accuracy of the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor 24 decreases, and the cylinder-by-cylinder air-fuel ratio control becomes more accurate. Emissions may be worsened due to poor performance.

  As a countermeasure, in the first embodiment, the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24 is determined for each air-fuel ratio detection timing of each cylinder (each sample timing of the output of the air-fuel ratio sensor 24). The output of the air-fuel ratio sensor 24 is corrected based on the degree of influence of the exhaust pressure, and the air-fuel ratio of each cylinder is estimated based on the corrected output of the air-fuel ratio sensor 24.

Here, a method for determining the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24 and a method for correcting the output of the air-fuel ratio sensor 24 based on the degree of influence of the exhaust pressure will be described. In the following description, the excess air ratio λ, which is the ratio of the actual air-fuel ratio to the stoichiometric air-fuel ratio, is used as “air-fuel ratio” information.
Excess air ratio λ = actual air-fuel ratio / stoichiometric air-fuel ratio

  As shown in FIG. 3, at each air-fuel ratio detection timing of each cylinder, the engine operating state (for example, engine speed and engine load) and the length or volume of the exhaust manifold 39 of each cylinder (= channel cross-sectional area × length). The exhaust pressure of the exhaust collecting portion 40 is calculated (estimated) based on the exhaust pressure of the exhaust collecting portion 40 based on the exhaust pressure of the exhaust collecting portion 40 (the air pressure installed in the exhaust collecting portion 40). Information on the degree of influence of the exhaust pressure on the output of the fuel ratio sensor 24) is calculated from a map or the like. The map of the exhaust pressure influence coefficient base value is set so that the exhaust pressure influence coefficient base value increases as the exhaust pressure of the exhaust collecting portion 40 increases.

  The exhaust pressure of each cylinder is calculated (estimated) based on the engine operating state and the length (or volume) of the exhaust manifold 39 of each cylinder, and the exhaust pressure influence coefficient base value is calculated based on the exhaust pressure of each cylinder. It may be calculated.

  The combustion state of each cylinder changes according to the engine operating state, and the in-cylinder pressure of each cylinder (for example, the in-cylinder pressure at the time of combustion or the in-cylinder pressure at the time of opening of the exhaust valve) changes. Because the exhaust pressure of each cylinder changes depending on the length and volume of the exhaust manifold 39 and the exhaust pressure of the exhaust collecting portion 40 changes, the engine operating state and the length (or volume) of the exhaust manifold 39 of each cylinder can be used. Thus, the exhaust pressure influence coefficient base value can be calculated with high accuracy.

  Furthermore, as the average air-fuel ratio, which is the average value of the output (detected air-fuel ratio) of the air-fuel ratio sensor 24, is more distant from the stoichiometric air-fuel ratio (excess air ratio λ = 1.0), it becomes more susceptible to exhaust pressure pulsation, In consideration of the characteristic that the error in the output of the air-fuel ratio sensor 24 due to the pulsation of the exhaust pressure becomes large (see FIG. 4), the average over one cycle (720 CA) based on the output (detected air-fuel ratio) of the air-fuel ratio sensor 24 By calculating the air-fuel ratio and calculating the difference between this average air-fuel ratio and the stoichiometric air-fuel ratio (excess air ratio λ = 1.0), the deviation of the average air-fuel ratio from the stoichiometric air-fuel ratio is obtained. The final exhaust pressure influence coefficient is obtained by multiplying the deviation by the exhaust pressure influence coefficient base value.

  Then, by calculating the difference between the output of the air-fuel ratio sensor 24 (detected air-fuel ratio) and the stoichiometric air-fuel ratio, the deviation of the output of the air-fuel ratio sensor 24 (detected air-fuel ratio) from the stoichiometric air-fuel ratio is obtained. The output of the air-fuel ratio sensor 24 is corrected by adding the value obtained by dividing the deviation of the output of 24 (detected air-fuel ratio) by the exhaust pressure influence coefficient to the stoichiometric air-fuel ratio. Eliminate the effects of.

  The above-described cylinder-by-cylinder air-fuel ratio control according to the first embodiment is executed by the ECU 38 according to the routines for cylinder-by-cylinder air-fuel ratio control shown in FIGS. Hereinafter, the processing content of each of these routines will be described.

[Air-fuel ratio control routine for each cylinder]
The cylinder-by-cylinder air-fuel ratio control main routine shown in FIG. 5 is started at every predetermined crank angle (for example, every 30 ° C. A) in synchronization with the output pulse of the crank angle sensor 37. When this routine is started, first, in step 101, an exhaust pressure influence degree determination and sensor output correction routine of FIG. 6 described later is executed, so that each air-fuel ratio detection timing (output of the air-fuel ratio sensor 24) of each cylinder is executed. At each sample timing), an exhaust pressure influence coefficient is calculated as information on the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24, and the output of the air-fuel ratio sensor 24 is corrected using this exhaust pressure influence coefficient.

  Thereafter, the routine proceeds to step 102 where the air-fuel ratio of each cylinder is estimated based on the corrected output of the air-fuel ratio sensor 37 using the cylinder-by-cylinder air-fuel ratio estimation model at each air-fuel ratio detection timing of each cylinder. The processing of step 102 serves as cylinder-by-cylinder air-fuel ratio estimation means in the claims.

  Thereafter, the process proceeds to step 103, the average value of the estimated air-fuel ratios of all cylinders is calculated, the average value is set to the reference air-fuel ratio (target air-fuel ratio of all cylinders), and then the process proceeds to step 104, where After calculating the deviation between the estimated air-fuel ratio and the reference air-fuel ratio, and calculating the air-fuel ratio correction amount (correction amount of the fuel injection amount of each cylinder) so that the deviation becomes small, the air-fuel ratio of each cylinder By correcting the fuel injection amount of each cylinder based on the correction amount, the air-fuel ratio of the air-fuel mixture supplied to each cylinder is corrected for each cylinder so as to reduce the air-fuel ratio variation among the cylinders.

[Exhaust pressure influence degree judgment and sensor output correction routine]
The exhaust pressure influence degree determination and sensor output correction routine shown in FIG. 6 is a subroutine executed in step 101 of the cylinder-by-cylinder air-fuel ratio control main routine of FIG. 5, and the exhaust pressure influence degree determination means in the claims. And it plays a role as a sensor output correction means.

  When this routine is started, first, at step 201, it is determined 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 24). Otherwise, this routine is terminated without performing the processing from step 202 onward.

  On the other hand, if it is determined in step 201 that the current crank angle is the air-fuel ratio detection timing of each cylinder, the process proceeds to step 202, and after reading the output of the air-fuel ratio sensor 24, the process proceeds to step 203, where engine operation is performed. The state (for example, engine speed and engine load) is read.

  Thereafter, the routine proceeds to step 204, where the exhaust pressure of the exhaust collecting section 40 is calculated based on the engine operating state (for example, engine rotation speed and engine load) and the length (or volume) of the exhaust manifold 39 of each cylinder. Based on the exhaust pressure of the exhaust collecting portion 40, the exhaust pressure influence coefficient base value is calculated by a map or the like. The exhaust pressure of each cylinder is calculated (estimated) based on the engine operating state and the length (or volume) of the exhaust manifold 39 of each cylinder, and the exhaust pressure influence coefficient base value is calculated based on the exhaust pressure of each cylinder. It may be calculated.

  Thereafter, the routine proceeds to step 205, where the average air-fuel ratio for one cycle (720CA) is calculated based on the output (detected air-fuel ratio) of the air-fuel ratio sensor 24, and this average air-fuel ratio and the stoichiometric air-fuel ratio (excess air ratio λ = 1.0) to obtain the deviation of the average air-fuel ratio with respect to the theoretical air-fuel ratio, and multiply the deviation of the average air-fuel ratio by the exhaust pressure influence coefficient base value to obtain the final exhaust pressure influence coefficient. Ask.

  Thereafter, the process proceeds to step 206, and the difference between the output (detected air-fuel ratio) of the air-fuel ratio sensor 24 and the stoichiometric air-fuel ratio) (excess air ratio λ = 1.0) is calculated, whereby the air-fuel ratio sensor for the stoichiometric air-fuel ratio is calculated. 24 is obtained, and a value obtained by dividing the deviation of the output (detected air-fuel ratio) of the air-fuel ratio sensor 24 by the exhaust pressure influence coefficient is added to the stoichiometric air-fuel ratio 24. And the influence of the exhaust pressure pulsation is excluded from the output of the air-fuel ratio sensor 24.

  In the first embodiment described above, the exhaust pressure influence coefficient is calculated as the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24, and the output of the air-fuel ratio sensor 24 is corrected using this exhaust pressure influence coefficient. Therefore, the influence of the exhaust pressure pulsation can be eliminated from the output of the air-fuel ratio sensor 24, and the exhaust pressure pulsation is estimated by estimating the air-fuel ratio of each cylinder based on the corrected output of the air-fuel ratio sensor 24. It is possible to accurately estimate the air-fuel ratio of each cylinder without being affected by the above. As a result, the air-fuel ratio control for each cylinder due to the influence of the exhaust pressure pulsation is performed while the air-fuel ratio sensor 24 is installed on the upstream side of the exhaust turbine 26 in which the output corresponding to the air-fuel ratio of each cylinder easily appears in the output of the air-fuel ratio sensor 24. A decrease in accuracy can be prevented, and a decrease in emission reduction effect due to cylinder-by-cylinder air-fuel ratio control can be avoided.

  In the first embodiment, the exhaust pressure influence coefficient (the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24) is calculated based on the engine operating state and the length (or volume) of the exhaust manifold 39 of each cylinder. However, the method for calculating the exhaust pressure influence coefficient may be changed as appropriate.

  For example, an in-cylinder pressure sensor (in-cylinder pressure acquisition means) for detecting the in-cylinder pressure is provided for each cylinder, and the in-cylinder pressure of each cylinder detected by the in-cylinder pressure sensor of each cylinder (for example, in-cylinder pressure during combustion or when the exhaust valve is opened) Or the like) and the length (or volume) of the exhaust manifold 39 of each cylinder. Alternatively, the in-cylinder pressure of each cylinder is estimated based on the engine operating state, and the exhaust pressure influence coefficient is obtained based on the estimated in-cylinder pressure of each cylinder and the length (or volume) of the exhaust manifold 39 of each cylinder. Anyway. Since the exhaust pressure of each cylinder changes depending on the in-cylinder pressure of each cylinder and the length and volume of the exhaust manifold 39 of each cylinder, and the exhaust pressure of the exhaust collecting portion 40 changes, the in-cylinder pressure of each cylinder and the exhaust manifold of each cylinder If the length (or volume) of 39 is used, the exhaust pressure influence coefficient can be obtained with high accuracy.

  Further, an exhaust pressure sensor for detecting the exhaust pressure may be provided in the exhaust collecting portion 40, and the exhaust pressure influence coefficient may be obtained based on the output of the exhaust pressure sensor. In this way, the exhaust pressure influence coefficient can be accurately obtained based on the exhaust pressure of the exhaust collecting portion 40 detected by the exhaust pressure sensor.

  Alternatively, an exhaust pressure sensor for detecting the exhaust pressure may be provided for each exhaust manifold 39 of each cylinder, and the exhaust pressure influence coefficient may be obtained based on the output of the exhaust pressure sensor of each cylinder. Since the exhaust pressure of the exhaust collecting portion 40 changes depending on the exhaust pressure of each cylinder, the exhaust pressure influence coefficient can be accurately obtained by using the exhaust pressure of each cylinder detected by the exhaust pressure sensor of each cylinder.

  Next, Embodiment 2 of the present invention will be described with reference to FIG. However, description of substantially the same parts as those in the first embodiment will be omitted or simplified, and different parts from the first embodiment will be mainly described.

  In the second embodiment, the ECU 38 executes an exhaust pressure influence degree determination routine shown in FIG. 7 described later to determine whether or not the influence degree of the exhaust pressure on the output of the air-fuel ratio sensor 24 has exceeded an allowable level. When it is determined that the influence degree of the exhaust pressure exceeds the allowable level, the cylinder-by-cylinder air-fuel ratio control is stopped.

  The exhaust pressure influence degree determination routine shown in FIG. 7 serves as exhaust pressure influence degree determination means and stop means in the claims. When this routine is started, first, at step 301, it is determined 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 24). Otherwise, this routine is terminated without performing the processing from step 302 onward.

  On the other hand, if it is determined in step 301 that the current crank angle is the air-fuel ratio detection timing of each cylinder, the process proceeds to step 302, the output of the air-fuel ratio sensor 24 is read, and then the process proceeds to step 303 for a predetermined period. The frequency of the output of the air-fuel ratio sensor 24 (for example, between 720 CA which is one cycle) is subjected to frequency analysis by FFT (Fast Fourier Transform) or the like, and the amplitude for each frequency component of the output of the air-fuel ratio sensor 24 is obtained.

  Thereafter, the process proceeds to step 304, and the amplitude of the frequency component related to the combustion interval in the output of the air-fuel ratio sensor 24 based on the frequency analysis result (for example, the component of the frequency corresponding to the period of 180 CA intervals in the case of four cylinders). To extract.

  Thereafter, the process proceeds to step 305, in which it is determined whether or not the amplitude of the frequency component related to the combustion interval in the output of the air-fuel ratio sensor 24 is greater than or equal to a predetermined value. As a result, when it is determined that the amplitude of the frequency component related to the combustion interval in the output of the air-fuel ratio sensor 24 has exceeded a predetermined value due to the influence of the exhaust pressure pulsation that pulsates at each combustion interval, the air-fuel ratio sensor It is determined that the degree of influence of the exhaust pressure on the output of 24 exceeds the allowable level. In this case, the error in the output of the air-fuel ratio sensor 24 increases due to the influence of the exhaust pressure pulsation, so that the estimation accuracy of the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor 24 decreases, and the cylinder-by-cylinder air-fuel ratio control Therefore, the process proceeds to step 306, where the cylinder specific air-fuel ratio control execution flag is reset to “OFF” which means that the cylinder specific air-fuel ratio control is stopped, and the cylinder specific air-fuel ratio control is performed. Cancel or ban.

  On the other hand, if it is determined in step 305 that the amplitude of the frequency component related to the combustion interval in the output of the air-fuel ratio sensor 24 is smaller than a predetermined value, the exhaust pressure exerted on the output of the air-fuel ratio sensor 24 is reduced. It is determined that the degree of influence does not exceed the permissible level, the process proceeds to step 307, the cylinder-by-cylinder air-fuel ratio control execution flag is set to “ON” which means execution of the cylinder-by-cylinder air-fuel ratio control, and Execute (continue) control.

  In the second embodiment described above, when it is determined that the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24 exceeds the allowable level, the output of the air-fuel ratio sensor 24 is affected by the exhaust pressure pulsation. Since the error becomes large, the estimation accuracy of the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor 24 is lowered, and it is determined that the cylinder-by-cylinder air-fuel ratio control cannot be performed accurately. Since the air-fuel ratio sensor 24 is installed on the upstream side of the exhaust turbine 26 in which the output corresponding to the air-fuel ratio of each cylinder is likely to appear in the output of the air-fuel ratio sensor 24 because it is stopped or prohibited, The accuracy of the cylinder-by-cylinder air-fuel ratio control can be prevented from being lowered, and the emission reduction effect due to the cylinder-by-cylinder air-fuel ratio control can be avoided.

  In the second embodiment, when the amplitude of the frequency component related to the combustion interval in the output of the air-fuel ratio sensor 24 is greater than or equal to a predetermined value, the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24 is at an allowable level. However, the specific method for determining whether or not the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24 has exceeded the allowable level may be changed as appropriate.

  For example, an exhaust pressure sensor that detects the exhaust pressure is provided for each exhaust manifold 40 or each exhaust manifold 39 of each cylinder, and the fluctuation amount (for example, a predetermined time) of the output of the exhaust pressure sensor in a predetermined period (for example, between one cycle 720CA). It is also possible to determine that the degree of influence of the exhaust pressure has exceeded an allowable level when the amount of change per hit, the difference between the maximum value and the minimum value, etc. is equal to or greater than a predetermined value. In this way, when the fluctuation amount of the exhaust pressure of the exhaust collecting portion 40 or the fluctuation amount of the exhaust pressure of each cylinder exceeds a predetermined value, the output of the air-fuel ratio sensor 24 installed in the exhaust collecting portion 40 is increased. It can be determined that the degree of influence of the exhaust pressure exerted exceeds an allowable level.

  Further, when the difference between the peak value and the bottom value of the output of the air-fuel ratio sensor 24 in a predetermined period (for example, between 720 CAs in one cycle) is a predetermined value or more, it is determined that the influence degree of the exhaust pressure exceeds the allowable level. You may do it. In this way, when the difference between the peak value and the bottom value of the output of the air-fuel ratio sensor 24 exceeds a predetermined value due to the pulsation of the exhaust pressure, the degree of influence of the exhaust pressure on the output of the air-fuel ratio sensor 24 is reduced. It can be determined that the allowable level has been exceeded.

  The present invention is not limited to a system having an exhaust turbine supercharger. The air-fuel ratio of each cylinder is estimated based on the output of the air-fuel ratio sensor, and the air-fuel ratio of each cylinder is calculated based on the estimation result. It can be widely applied to a system that controls by cylinder.

  In addition, the present invention is not limited to the intake port injection type engine as shown in FIG. 1, but includes an in-cylinder injection type engine, and both an intake port injection fuel injection valve and an in-cylinder injection fuel injection valve. It can also be applied to dual-injection engines.

  DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 20 ... Fuel injection valve, 21 ... Spark plug, 22 ... Exhaust pipe, 24 ... Air-fuel ratio sensor, 25 ... Exhaust turbine type supercharger, 26 ... exhaust turbine, 27 ... compressor, 38 ... ECU (exhaust pressure influence degree judging means, sensor output correcting means, cylinder air-fuel ratio estimating means, stopping means), 39 ... exhaust manifold, 40 ... exhaust collecting part

Claims (10)

An air-fuel ratio sensor is installed at an exhaust gas collecting portion where exhaust gases from a plurality of cylinders of an internal combustion engine flow and the air-fuel ratio of each cylinder is determined based on the output of the air-fuel ratio sensor at each air-fuel ratio detection timing of each cylinder. In a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine that estimates and controls the air-fuel ratio of each cylinder for each cylinder based on the estimation result,
Exhaust pressure influence degree determining means for determining the influence degree of the exhaust pressure of the internal combustion engine on the output of the air / fuel ratio sensor at each air / fuel ratio detection timing of each cylinder;
Sensor output correction means for correcting the output of the air-fuel ratio sensor based on the exhaust pressure influence degree determined by the exhaust pressure influence degree determination means at each air-fuel ratio detection timing of each cylinder;
A cylinder-specific air-fuel ratio estimating means for estimating the air-fuel ratio of each cylinder based on the output of the air-fuel ratio sensor corrected by the sensor output correcting means at each air-fuel ratio detection timing of each cylinder. A cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine. An exhaust pressure sensor for detecting an exhaust pressure in the exhaust collecting portion;
2. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the exhaust pressure influence degree determining means includes means for determining the influence degree of the exhaust pressure based on an output of the exhaust pressure sensor. . An exhaust pressure sensor for detecting the exhaust pressure is provided for each exhaust manifold of each cylinder,
2. The cylinder-by-cylinder sky of the internal combustion engine according to claim 1, wherein the exhaust pressure influence degree determining means includes means for determining an influence degree of the exhaust pressure based on an output of an exhaust pressure sensor of each cylinder. Fuel ratio control device. In-cylinder pressure acquisition means for detecting or estimating the in-cylinder pressure of each cylinder,
The exhaust pressure influence degree determining means is means for determining the influence degree of the exhaust pressure based on the in-cylinder pressure of each cylinder detected or estimated by the in-cylinder pressure acquisition means and the length or volume of the exhaust manifold of each cylinder. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1, comprising:   The exhaust pressure influence degree determining means includes means for determining the influence degree of the exhaust pressure based on the operating state of the internal combustion engine and the length or volume of the exhaust manifold of each cylinder. The cylinder-by-cylinder air-fuel ratio control apparatus according to claim. An air-fuel ratio sensor is installed at an exhaust gas collecting portion where exhaust gases from a plurality of cylinders of an internal combustion engine flow, and the air-fuel ratio of each cylinder is estimated based on the output of the air-fuel ratio sensor. In a cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine that executes cylinder-by-cylinder air-fuel ratio control for controlling the air-fuel ratio of each cylinder by cylinder,
An exhaust pressure influence degree determining means for determining whether or not the influence degree of the exhaust pressure of the internal combustion engine on the output of the air-fuel ratio sensor exceeds an allowable level;
An internal combustion engine comprising: a stop unit that stops or prohibits the cylinder-by-cylinder air-fuel ratio control when the exhaust pressure influence level determination unit determines that the exhaust pressure level of influence exceeds a permissible level. Air-fuel ratio control device for each cylinder. An exhaust pressure sensor for detecting an exhaust pressure for each exhaust manifold or each exhaust manifold of each cylinder;
The exhaust pressure influence degree determining means includes means for determining that the influence degree of the exhaust pressure has exceeded an allowable level when the fluctuation amount of the output of the exhaust pressure sensor in a predetermined period is a predetermined value or more. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 6.   The exhaust pressure influence degree determining means performs frequency analysis on the output of the air-fuel ratio sensor during a predetermined period, and when the amplitude of the frequency component related to the combustion interval in the output of the air-fuel ratio sensor is equal to or greater than a predetermined value, 8. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 6, further comprising means for determining that the degree of influence of the exhaust pressure exceeds an allowable level.   The exhaust pressure influence degree determining means is a means for determining that the influence degree of the exhaust pressure exceeds an allowable level when the difference between the peak value and the bottom value of the output of the air-fuel ratio sensor in a predetermined period is equal to or greater than a predetermined value. The air-fuel ratio control apparatus for each cylinder of the internal combustion engine according to any one of claims 6 to 8, characterized by comprising: An exhaust turbine supercharger that supercharges intake air by driving a compressor by an exhaust turbine provided in an exhaust passage of the internal combustion engine;
10. The cylinder-by-cylinder air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio sensor is installed upstream of the exhaust turbine.

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