JP2011241697A - Device for control of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable correction considering collision of exhaust gas from the respective cylinders by using a contribution ratio to the second air/fuel ratio sensor, thereby the air/fuel ratio in a catalyzer can be controlled such that the cleaning performance thereof is maximized even when there is fluctuation of the air/fuel ratio among the cylinders.SOLUTION: Ratios where exhaust gas exhausted from the respective cylinders contribute to the output of the second air/fuel ratio sensor arranged in the catalyzer or in the downstream of the catalyzer is estimated in the respective cylinders. The air/fuel ratio of the exhaust gas present near the second air/fuel ratio sensor is estimated as the first air/fuel ration evaluated value from the fuel ratios of the respective cylinders detected by the first air/fuel ratio sensor arranged in the upstream of the catalyzer and the estimated contribution ratio of the respective cylinders. Further, the air/fuel ratio of the exhaust gas present near the second air/fuel ratio sensor is estimated as the second air/fuel ration estimated value based on the average value of the air/fuel ratios of the respective cylinders. The air/fuel ratio output displacement of the second air/fuel ratio sensor is corrected based on the first and second air/fuel ratio estimated values.

Description

  The present invention relates to a control device for an internal combustion engine.

  In an internal combustion engine having a plurality of cylinders, if the air-fuel ratio of the air-fuel mixture varies between the cylinders, the purification rate of the catalyst that purifies the exhaust gas decreases, and the emission may be deteriorated. Therefore, it has been proposed to correct the fuel injection amount for each cylinder in order to eliminate the variation.

  In Patent Document 1 below, the exhaust gas per cylinder of the air-fuel ratio variation inspection target with respect to the main sensor provided upstream of the catalyst is weaker than the exhaust gas per other cylinder, and is based on the main sensor output value. When the sub-sensor output value provided downstream of the catalyst indicates rich when air-fuel ratio feedback control is being performed, the air-fuel ratio of the air-fuel ratio variation inspection target cylinder is on the rich side with respect to the other cylinders. It is described that it is determined that there is variation, and the fuel injection amount for each cylinder is corrected based on this determination.

JP 2002-266682 A

  In the above technique, the gas per the main sensor provided upstream of the catalyst is considered, but the gas per sub sensor provided downstream of the catalyst or the catalyst is not considered. In addition, the fuel injection amount is corrected on the assumption that the output of the sub sensor is correct. However, if the gas contact with the sub sensor is not uniform, such correction may reduce the accuracy of the air-fuel ratio control. There is.

  Accordingly, an object of the present invention is to propose a technique that can realize more appropriate air-fuel ratio control by taking into consideration the gas hit of the sensor for detecting the air-fuel ratio provided downstream of the catalyst or the catalyst.

  According to one aspect of the present invention, an internal combustion engine control device including a plurality of cylinders includes a first air-fuel ratio sensor (16) disposed upstream of a catalyst (15) provided in an exhaust passage of the internal combustion engine. The second air-fuel ratio sensor (17) disposed in the catalyst or downstream of the catalyst, and the rate at which the exhaust gas discharged from the cylinder contributes to the output of the second air-fuel ratio sensor for each cylinder (K (i)) is estimated by the contribution rate estimation means (72), the air-fuel ratio (AF (i)) of each cylinder detected by the first air-fuel ratio sensor, and the contribution rate estimation means. First air-fuel ratio estimating means (73) for estimating the air-fuel ratio of the exhaust gas existing in the vicinity of the second air-fuel ratio sensor as the first air-fuel ratio estimated value from the contribution ratio (K (i)) of each cylinder ) And each gas detected by the first air-fuel ratio sensor. Second air-fuel ratio estimating means for estimating the air-fuel ratio of the exhaust gas existing in the vicinity of the second air-fuel ratio sensor as the second air-fuel ratio estimated value based on the average value of the air-fuel ratio (AF (i)) of (74) and the second air-fuel ratio sensor estimated based on the first air-fuel ratio estimated value estimated by the first air-fuel ratio sensor and the second air-fuel ratio estimated value estimated by the second air-fuel ratio estimating means. Correction means (77) for correcting the air-fuel ratio output deviation.

  According to the present invention, the deviation of the air-fuel ratio output of the catalyst or the second air-fuel ratio sensor provided downstream of the catalyst is based on the ratio of the exhaust gas discharged from each cylinder to the output of the second air-fuel ratio sensor. Therefore, it is possible to perform correction in consideration of the gas hit of the exhaust gas from each cylinder to the second air-fuel ratio sensor. Therefore, by using the output of the second air-fuel ratio sensor corrected in this way, air-fuel ratio control with better accuracy can be performed. Even when the air-fuel ratio varies between the cylinders, the air-fuel ratio in the catalyst can be controlled so that the purification performance is maximized, so that the emission performance and the merchantability can be improved.

  According to an embodiment of the present invention, the contribution rate estimating means is set according to the amount of exhaust gas discharged from each cylinder. Thus, since the contribution rate is estimated according to the amount of exhaust gas from each cylinder, the accuracy of the contribution rate can be improved. Further, by estimating the contribution ratio of the second air-fuel ratio sensor according to the operating state of the internal combustion engine, it becomes possible to perform correction according to the operating condition, and to improve its toughness with respect to emission performance. it can.

 Other features and advantages of the present invention will be apparent from the detailed description that follows.

The figure which shows the whole structure of an engine and its control apparatus according to one Embodiment of this invention. The figure for demonstrating arrangement | positioning of the air fuel ratio sensor according to one Embodiment of this invention. The figure which shows the variable valve mechanism according to one Embodiment of this invention. The figure which shows the operating characteristic of the variable valve mechanism according to one Embodiment of this invention. The figure for demonstrating the per-gas with respect to an exhaust gas sensor and the output characteristic of an exhaust gas sensor according to one Embodiment of this invention. The block diagram of the control apparatus according to one Embodiment of this invention. The table which prescribes | regulates the contribution rate according to the driving | running state according to one Embodiment of this invention. The figure which shows an example of the estimated contribution rate according to one Embodiment of this invention. The figure which shows the example of the output characteristic of the exhaust gas sensor which shifted | deviated to the example of calculation of the 1st air fuel ratio estimated value and the 2nd air fuel ratio estimated value according to one Embodiment of this invention, and the lean side. The figure which shows the map for converting output deviation (DELTA) SVO2 into correction amount (DELTA) SVO2F according to one Embodiment of this invention. The figure which shows an example of the output characteristic of the exhaust gas sensor which shifted | deviated to the rich side according to one Embodiment of this invention. The flowchart of the exhaust gas sensor output correction process according to one Embodiment of this invention. The figure which shows an example of the output characteristic of the exhaust gas sensor according to other embodiment of this invention. The flowchart of the cylinder-by-cylinder air-fuel ratio calculation process according to one embodiment of the present invention. The figure which shows the behavior of the air fuel ratio deviation signal and the reference signal of each cylinder according to one Embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as an engine) and its control device according to an embodiment of the present invention.

  An electronic control unit (hereinafter referred to as “ECU”) 1 is a computer including a central processing unit (CPU) and a memory. The memory can store a computer program for realizing various controls of the vehicle and data (including a map) necessary for executing the program. The ECU 1 receives a signal from each part of the vehicle and performs an operation according to data and a program stored in the memory to generate a control signal for controlling each part of the vehicle.

  The engine 2 is an engine having a plurality of cylinders (four cylinders in this embodiment). The engine 2 is provided with a continuously variable valve mechanism 31 that can change the valve timing of the intake valve, and in this embodiment, includes a variable lift mechanism and a variable phase mechanism. The variable lift mechanism is a mechanism that can continuously change the lift amount of the intake valve of each cylinder in accordance with a control signal from the ECU 1. An example of the variable lift mechanism will be described later. The variable phase mechanism is a mechanism that can continuously change the phase of the intake valve of each cylinder in accordance with a control signal from the ECU 1. The variable phase mechanism can be realized by any known method. For example, a method has been proposed in which the phase of the intake valve is electromagnetically controlled to advance or retard (see, for example, JP 2000-227033 A).

  The continuously variable valve mechanism 31 is provided with a sensor 32 for detecting the lift amount of the intake valve of each cylinder, and the detection result of the sensor 32 is sent to the ECU 1.

  In this embodiment, the lift amount and the phase can be changed continuously. However, the present invention is not limited to this, and the mechanism can change the lift amount and the phase stepwise. In addition, the present invention is applicable.

  An intake passage 3 and an exhaust passage 4 are connected to the engine 2. A throttle valve 5 is provided in the intake passage 3. The opening degree of the throttle valve 5 is controlled in accordance with a control signal from the ECU 1. A throttle valve opening (θTH) sensor 6 for detecting the opening of the throttle valve is connected to the throttle valve 5, and this detected value is sent to the ECU 1.

  In this embodiment, the intake air amount to each cylinder of the engine 2 not only controls the opening degree of the throttle valve 5, but also controls the lift amount of the intake valve of each cylinder via the continuously variable valve mechanism 31. It is realized by doing.

  A fuel injection valve 7 is provided for each cylinder between the engine 2 and the throttle valve 5 and slightly upstream of the intake valve (not shown) of the engine 2. The fuel injection valve 7 is connected to a fuel tank (not shown) and injects fuel from the fuel tank. The fuel injection timing and the fuel injection amount of the fuel injection valve 7 are changed according to a control signal from the ECU 1.

  An air flow meter (AFM) 8 that detects the amount of air flowing through the intake passage 3 is provided upstream of the throttle valve 5.

  An absolute pressure (PB) sensor 9 is provided downstream of the throttle valve 5 and detects the pressure PB in the intake passage 3. An intake air temperature (TA) sensor 10 is provided downstream of the absolute pressure sensor 9 and detects the temperature in the intake passage 3. These detected values are sent to the ECU 1. The engine 2 is provided with an engine water temperature sensor 11 for detecting the engine water temperature TW, and the detected value of the sensor is sent to the ECU 1. Further, an atmospheric pressure sensor 12 for detecting the atmospheric pressure PA is installed at an arbitrary position outside the engine, and the detected value of the sensor is sent to the ECU 1.

  A crank angle sensor 13 for detecting the rotation angle of the crankshaft of the engine 2 is connected to the ECU 1, and the detected value of the sensor is supplied to the ECU 1. The crank angle sensor 13 generates one pulse (CRK pulse) every predetermined crank angle (for example, 30 degrees), and can specify the rotational angle position of the crankshaft by the pulse. The ECU 1 calculates the engine speed NE based on the CRK pulse. The crank angle sensor 13 outputs a TDC signal to the ECU 1 at a crank angle related to the top dead center (TDC) position of the piston.

  As a result of the mixture of fuel from the fuel injection valve 7 and air from the intake passage 3 combusting in each cylinder of the engine 2, exhaust gas from each cylinder flows out into the exhaust passage 4. The exhaust passage 4 is provided with a catalyst device (CAT) 15 that can be realized by various catalysts, for example, and purifies the exhaust gas flowing out into the exhaust passage and releases it to the atmosphere.

  An air-fuel ratio (LAF) sensor 16 for detecting the air-fuel ratio of the exhaust gas is provided upstream of the catalyst device 15. The air-fuel ratio sensor 16 linearly detects the air-fuel ratio in the region ranging from lean to rich of the air-fuel mixture and sends it to the ECU 1. In this embodiment, the detected equivalent ratio KACT is detected from the output of the air-fuel ratio sensor 16. The detected equivalent ratio KACT is a signal indicating the air-fuel ratio, and is calculated by “theoretical air-fuel ratio / air-fuel ratio”. If the value of the detected equivalent ratio KACT is smaller than 1, it indicates that the air-fuel ratio is lean, and if it is larger than 1, it indicates that it is rich.

  An exhaust gas (O 2) sensor 17 is provided in the catalyst device 15. The exhaust gas sensor 17 is a binary exhaust gas concentration sensor. The exhaust gas sensor 17 outputs a high-level signal when the air-fuel ratio of the exhaust gas is richer than the stoichiometric air-fuel ratio, and outputs a low-level signal when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. The output signal is sent to the ECU 1. Alternatively, the exhaust gas sensor 17 may be arranged downstream of the catalyst device 15.

  The ECU 1 detects the operating state of the engine 2 in accordance with programs and data (including a map) stored in the memory in accordance with input signals from the various sensors, and controls the throttle valve 5, the fuel injection valve 7, and the A control signal for controlling the variable valve mechanism 31 and the like is generated.

  FIG. 2 is a schematic diagram for explaining the arrangement of the air-fuel ratio (LAF) sensor 16 and the exhaust gas sensor 17 when the engine 2 of FIG. 1 is an in-line four-cylinder engine. In this engine, four cylinders 2a to 2d are provided, and intake pipes 3a to 3d branched at a collecting portion 35 of the intake passage 3 are connected to each cylinder, and exhaust pipes 4a to 4b of each cylinder are connected to a collecting portion 36. Are connected to the exhaust passage 4. The air-fuel ratio sensor 16 is provided downstream of the collecting portion 36 on the exhaust passage 4, and the exhaust gas sensor 17 is provided in the catalyst device 15 arranged further downstream thereof. As described above, the exhaust gas sensor 17 may be disposed further downstream of the catalyst device 15.

  FIG. 3 is a view for explaining an example of a variable lift mechanism mounted on the variable valve mechanism 31 of FIG. As shown in (a), the variable lift mechanism swings the cam shaft 61 provided with the cam 62, the control arm 65 supported by the cam holder so as to be swingable around the support portion 65a, and the control arm 65. A control shaft (control shaft) 66 provided with a control cam 67 to be driven, a sub cam 63 that is swingably supported by the control arm 65 via a sub cam shaft 63b, and that swings in accordance with the cam 62; A rocker arm 64 that is driven by the sub cam 63 and drives the intake valve 14 is provided. The rocker arm 64 is supported in the control arm 65 so as to be swingable by a rocker shaft 68.

  The sub cam 63 has a roller 63 a that abuts the cam 62, and swings about the sub cam shaft 63 b as the cam shaft 61 rotates. The rocker arm 64 has a roller 64a that contacts the sub cam 63, and the movement of the sub cam 63 is transmitted to the rocker arm 64 via the roller 64a. The control arm 65 has a roller 65b that abuts on the control cam 67, and swings about the support portion 65a as the control shaft 66 rotates.

  (A), (b), and (c) show the high lift state, the middle lift state, and the low lift state of the intake valve 14, respectively, as indicated by arrows. By changing the position of the control arm 65 via the control shaft 66, it is possible to continuously transition between the high lift state as shown in (a) and the low lift state as shown in (c). In the state shown in (a), the movement of the sub cam 63 is transmitted to the intake valve 14 via the rocker arm 64, and the intake valve 14 opens with the maximum lift amount. In the state shown in (b), the amount of transmission of the movement of the sub cam 63 to the intake valve 14 via the rocker arm 64 is less than (a), and therefore the valve is opened with a lift amount smaller than (a). In the state shown in (c), since the movement of the sub cam 63 is hardly transmitted to the rocker arm 64, the intake valve 14 is in a low lift state.

  An actuator motor (not shown) is connected to the control shaft 66. By rotating the control shaft 66 by the motor, the lift amount of the intake valve 14 is continuously changed, and the combustion chamber (cylinder) The intake air amount to the inside can be changed continuously. In this embodiment, the above-described sensor 32 (FIG. 1) for detecting the lift amount is provided so as to detect the rotational angle position of the control shaft 66. The detected rotation angle position CSA of the control shaft 66 is used as a parameter indicating the lift amount.

  Referring to FIG. 4, the operating characteristics of the exhaust valve of each cylinder and the operating characteristics of the intake valve 14 controlled by the continuously variable valve mechanism 31 are shown. The vertical axis represents the lift amount, and the horizontal axis represents the crank angle in one combustion cycle.

  EX indicates the operating characteristic of the exhaust valve. IN indicates the operating characteristic of the intake valve 14, and as indicated by a plurality of solid lines, the operating characteristic IN is continuously changed according to the operating state of the engine, that is, the phase and lift amount of the intake valve are continuously changed. Can be made. Thus, in this embodiment, the lift amount of the intake valve 14 can be continuously changed from a low lift to a high lift according to the operating state of the engine. Note that “lift amount” in the following description represents a peak in each operating characteristic, that is, a maximum lift amount (amount of opening the intake valve (mm)).

  Here, the general outline of the air-fuel ratio control in this embodiment will be described. The target air-fuel ratio is set based on the output of the exhaust gas sensor 17. Specifically, the exhaust gas sensor 17 is configured such that a predetermined value of its output corresponds to a predetermined air-fuel ratio. Therefore, the output of the exhaust gas sensor 17 (represented by a voltage value in this embodiment) is a predetermined value SVO2CMD (corresponding to the theoretical air-fuel ratio value in this embodiment) corresponding to the air-fuel ratio value set in this embodiment (the stoichiometric air-fuel ratio value). The target air-fuel ratio KCMD (expressed by an equivalence ratio) is controlled so that it becomes a reference value. For example, when the output of the exhaust gas sensor 17 is at a high level (indicating that the air-fuel ratio is richer than the stoichiometric air-fuel ratio), the target air-fuel ratio KCMD is gradually decreased to reduce the output of the exhaust gas sensor 17 to the reference value SVO2CMD. Take it. When the output of the exhaust gas sensor 17 is at a low level (indicating that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio), the output of the exhaust gas sensor is brought to the reference value SVO2CMD by gradually increasing the target air-fuel ratio KCMD. .

  Thereafter, the actual air-fuel ratio KACT (representing the average value of the air-fuel ratios of all cylinders) detected by the air-fuel ratio sensor 16 by the air-fuel ratio feedback control is converged to the target air-fuel ratio KCMD thus set. The fuel injection amount is controlled.

  As described above, the output of the exhaust gas sensor 17 is used for air-fuel ratio control. If the exhaust gas hits the detection part of the exhaust gas sensor 17 (referred to as “per gas”) is uneven, the air-fuel ratio control is performed. The accuracy may be reduced. This point will be discussed in more detail with reference to FIG.

  (A1) in FIG. 5 schematically shows a cross section of the catalyst 15 at a portion where the exhaust gas sensor 17 is provided, and shows that the exhaust gas discharged from each cylinder has a uniform per-gas perception to the exhaust gas sensor 17. ing. (A2) shows the output characteristic 101 (in this case, the voltage value with respect to the air-fuel ratio) of the exhaust gas sensor 17 when the gas contact is uniform as in (a1). Since the exhaust gas from each cylinder is uniform, the output characteristic 101 is such that the output value SVO2CMD of the exhaust gas sensor 17 indicates the stoichiometric air-fuel ratio (stoichiometric). Therefore, for example, as described above, the actual air-fuel ratio KACT can be made the stoichiometric air-fuel ratio by controlling the target air-fuel ratio KCMD so that the output of the exhaust gas sensor 17 becomes the reference value SVO2CMD. In this embodiment, the catalyst device 15 is configured to have the maximum purification rate at the stoichiometric air-fuel ratio. Therefore, when the actual air-fuel ratio KACT becomes the stoichiometric air-fuel ratio, the catalyst device 15 performs optimal purification. Emission can be suppressed.

  (B1) conceptually represents a state in which the exhaust gas discharged from each cylinder is not uniformly hit by the exhaust gas sensor 17, and is richer than the stoichiometric air-fuel ratio in the vicinity of the exhaust gas sensor 17 as indicated by reference numeral 111. As shown by reference numeral 113, a lean portion is locally generated. Even if the air-fuel ratio feedback control in which the actual air-fuel ratio KACT converges to the target air-fuel ratio KCMD as described above is performed, for example, due to a slight deviation of the actual lift amount of each cylinder from the target lift amount, etc. This can occur when the air-fuel ratio varies between. In this case, there are cylinders in which the air-fuel ratio is shifted to the rich side with respect to the target air-fuel ratio and cylinders in which the air-fuel ratio is shifted to the lean side, and the exhaust gas from the rich side cylinder and the lean side cylinder May not evenly hit the detection part of the exhaust gas sensor 17.

  (B2) shows an example of the output characteristic 103 of the exhaust gas sensor 17 in the case of non-uniform gas per (b1). The solid line output characteristic 101 is the same as (a2) and is shown for comparison. In this example, the contribution ratio of the exhaust gas from the cylinder having an air-fuel ratio richer than the target air-fuel ratio to the exhaust gas sensor output (the ratio reflected (contributed) to the exhaust gas sensor output) is less than the target air-fuel ratio. The exhaust gas from the cylinder having a lean air-fuel ratio is higher than the contribution rate to the exhaust gas sensor output. Therefore, the output characteristic 103 of the exhaust gas sensor 17 moves parallel to the lean side with respect to the output characteristic 101, and shifts in a direction in which the output value of the exhaust gas sensor 17 for a given air-fuel ratio increases (indicates rich). As a result, the air-fuel ratio corresponding to the reference value SVO2CMD becomes larger than the theoretical air-fuel ratio.

  When the target air-fuel ratio KCMD is controlled so that the output of the exhaust gas sensor 17 becomes the reference value SVO2CMD based on the shifted output characteristics 103, the target air-fuel ratio KCMD is set to an air-fuel ratio that is leaner than the theoretical air-fuel ratio. Will end up. As a result, the actual air-fuel ratio KACT shifts to the lean side, the purification performance of the catalyst device 15 cannot be exhibited, and the emission may be deteriorated. For example, when the catalyst device 15 is a three-way catalyst, the HC, CO, and NOx are all optimally purified at the stoichiometric air-fuel ratio, but the air-fuel ratio is on the lean side as in this example. If shifted to, the NOx purification performance may be reduced.

  The above problem may also occur when the exhaust gas sensor 17 is provided downstream of the catalyst device 15. Therefore, the present invention proposes a method of correcting the air-fuel ratio output deviation of the exhaust gas sensor 17 so that appropriate air-fuel ratio control can be performed even when the gas contact is uneven as described above. This specific method will be described below.

  FIG. 6 shows a block diagram of a control device for an internal combustion engine according to an embodiment of the present invention. Each function shown in the figure can be realized in the ECU 1.

  The cylinder-by-cylinder air-fuel ratio detector 71 detects, for each cylinder, a cylinder-by-cylinder air-fuel ratio AF (i) representing the air-fuel ratio of the cylinder based on the output of the air-fuel ratio (LAF) sensor 16. i shows the number which identifies a cylinder. This specific method will be described later.

  The contribution rate estimation unit 72 estimates, for each cylinder, a ratio that contributes (reflects) to the output of the exhaust gas sensor 17 of exhaust gas discharged from the cylinder, that is, a contribution rate. Since the contribution rate may vary depending on the amount of exhaust gas from each cylinder, it is preferable to estimate the contribution rate according to the amount of exhaust gas. In this embodiment, the engine speed NE (rpm) and the intake air amount GAIRAFM (g / TDC) are used as operating parameters representing the amount of exhaust gas. The engine speed NE can be detected from the output of the crank angle sensor 13, and the intake air amount GAIRAFM can be detected from the output of the AFM 8. Here, the intake air amount GAIRAFM is used as an operation parameter representing a load. Therefore, for example, a gauge pressure (a differential pressure between the intake pipe pressure and the atmospheric pressure, and the intake pipe pressure sensor 9 and the atmospheric pressure are used instead. Other operating parameters such as those that can be detected from sensor 12) may be used.

  In this embodiment, the contribution ratio according to the engine speed NE and the intake air amount GAIRAFM is defined in advance in a table or a map as shown in FIG. 7, for example, as shown in FIG. Stored in the storage device. The contribution rate estimation unit 72 refers to the table and map based on the detected current engine speed NE and the intake air amount GAIRAFM, and obtains the contribution rate K (i) of each cylinder.

  FIG. 8 shows an example of the contribution ratio obtained under a certain driving condition as a graph. The horizontal axis indicates the cylinder number i. In this embodiment, as described above, there are the first to fourth cylinders. The vertical axis indicates the contribution rate (%), and the contribution rate of each cylinder is set so that the sum is 100%. When the exhaust gas per cylinder has a uniform per-gas per exhaust gas sensor 17, the contribution ratio of each cylinder is 25%.

  In this example, the gas per- fluence of the exhaust gas of each cylinder with respect to the exhaust gas sensor 17 is non-uniform, the contribution ratio of the first cylinder is the highest, and the contribution ratio of the second cylinder is the lowest.

The first air-fuel ratio estimation unit 73 is based on the air-fuel ratio AF (i) of each cylinder detected by the cylinder-by-cylinder air-fuel ratio detection unit 71 and the contribution rate K (i) of each cylinder estimated by the contribution rate estimation unit 72. Thus, the air-fuel ratio (referred to as the first air-fuel ratio estimated value) of the exhaust gas existing in the vicinity of the exhaust gas sensor 17 is estimated. Specifically, the first air-fuel ratio estimated value is calculated as follows. Here, N is the number of cylinders, and in this embodiment, N = 4.

  The first air-fuel ratio estimated value represents the air-fuel ratio that the exhaust gas sensor 17 should output when the exhaust gas from each cylinder contributes to the exhaust gas sensor output with the estimated contribution rate.

The second air-fuel ratio estimating unit 74 is based on the average value of the air-fuel ratio AF (i) of each cylinder detected by the cylinder-by-cylinder air-fuel ratio detecting unit 71, and the air-fuel ratio (first fuel gas) of the exhaust gas existing in the vicinity of the exhaust gas sensor 17. (Referred to as 2 air-fuel ratio estimated value). Specifically, the second air-fuel ratio estimated value AFave is calculated as follows.

  The second air-fuel ratio estimated value represents the air-fuel ratio that the exhaust gas sensor 17 should output when the exhaust gas from each cylinder hits the exhaust gas sensor 17 evenly. In other words, when the exhaust gas from each cylinder contributes to the exhaust gas sensor output at a contribution rate of 25%, it represents the air-fuel ratio that the exhaust gas sensor 17 should output.

The output deviation calculator 75 calculates the deviation ΔSVO2 between the first air-fuel ratio estimated value and the second air-fuel ratio estimated value as follows.

  Since the second air-fuel ratio estimated value AFave is a value estimated on the assumption of uniform gas contact, it represents the value of the air-fuel ratio that should be output by the exhaust gas sensor 17, that is, the correct value. On the other hand, the estimated value of the first air-fuel ratio represents a value that the exhaust gas sensor 17 will output, that is, a value to be corrected, when it comes to per gas as represented by a contribution rate. If the contribution ratio indicates a uniform per gas, the first air-fuel ratio estimated value becomes equal to the second air-fuel ratio estimated value. However, if the contribution ratio indicates non-uniform gas perception, a difference occurs between the two, and it is estimated that the exhaust gas sensor output actually outputs the first air-fuel ratio estimated value.

  As a specific example, referring to FIG. 9, (a) shows an example of calculation results of the first air-fuel ratio estimated value and the second air-fuel ratio estimated value when the contribution ratio of each cylinder is uniform at 25%. (B) shows a calculation result example of the first air-fuel ratio estimated value and the second air-fuel ratio estimated value when the contribution ratios of the respective cylinders are not uniform. As shown to (a), when the contribution rate of each cylinder is 25%, since the gas per shot of the exhaust gas from each cylinder with respect to the exhaust gas sensor 17 is uniform, the first and second air-fuel ratio estimated values Are the same values and are the stoichiometric air-fuel ratio values (in this example, 14.5 is the stoichiometric air-fuel ratio). Therefore, the output deviation ΔSVO2 is zero.

  As shown in (b), when the contribution ratios of the cylinders are not uniform, the gas permeation of the exhaust gas from the cylinders with respect to the exhaust gas sensor 17 is not uniform, and therefore the first and second air-fuel ratio estimated values are , Become different values. In this example, the output deviation ΔSVO2 is (14.8-14.5) = 0.3.

  (C) shows the output characteristic 121 of the exhaust gas sensor 17 when the gas contact is uniform, and the air-fuel ratio corresponding to the reference value SVO2CMD of the exhaust gas sensor 17 is 14.5 (this is the second air-fuel ratio). Value, and here, it is assumed that the stoichiometric air-fuel ratio). The first air-fuel ratio value calculated from the contribution rate shown in (b) is 14.8. As shown by the arrow 131, the air-fuel ratio corresponding to the reference value SVO2CMD is 14.5, and the output deviation ΔSVO2 (Here, 0.3) is shifted to the lean side. Therefore, in the situation of the contribution rate shown in (b), the output characteristic of the exhaust gas sensor 17 is shifted (shifted) by the output deviation ΔSVO2 from the output characteristic 121 to the lean side, and is as indicated by the dotted line 123. Conceivable. As a result, the reference value corresponding to the theoretical air-fuel ratio value is also shifted from the reference value SVO2CMD to SVO2CMDF as indicated by an arrow 133.

  The correction amount calculation unit 76 obtains the amount of deviation, that is, the correction amount ΔSVO2F of the output value of the exhaust gas sensor 17 from the output deviation ΔSVO2. Specifically, for example, as shown in FIG. 10, a conversion map between the output deviation ΔSVO2 and the correction amount ΔSVO2F (represented by a voltage value here) can be defined in advance and stored in a memory or the like. As is apparent from the map, when the output deviation ΔSVO2 takes a positive value, the correction amount ΔSVO2F takes a negative value, and when the output deviation ΔSVO2 takes a negative value, the correction amount ΔSVO2F takes a positive value. The correction amount calculation unit 76 refers to the map based on the output deviation ΔSVO2, and obtains a corresponding correction amount ΔSVO2F.

  The correcting unit 77 calculates the target value SVO2CMDF by subtracting the correction amount ΔSVO2F calculated in this way from the reference value SVO2CMD (SVO2CMDF = SVO2CMD−ΔSVO2F). In the above example, since the output deviation ΔSVO2 is 0.3 and is a positive value, a negative correction amount ΔSVO2F is calculated. Therefore, the correction amount of the magnitude of ΔSVO2F is substantially equal to the reference value SVO2CMD. As shown in the figure, a new target value SVO2CMDF is calculated.

  The target value SVO2CMDF indicates an output value corresponding to a predetermined target air-fuel ratio value (here, the theoretical air-fuel ratio value) on the output characteristic 123. In this way, the output value of the exhaust gas sensor 17 corresponding to the target air-fuel ratio value is appropriately corrected, so that appropriate air-fuel ratio control can be performed using the output of the exhaust gas sensor 17. For example, in the target air-fuel ratio control, the target air-fuel ratio KCMD is controlled so that the output (detected value) of the exhaust gas sensor 17 becomes the target value SVO2CMDF. By doing so, the air-fuel ratio can be controlled so as to obtain a desired target air-fuel ratio value even when the gas contact is uneven.

  In this example, the case where the output characteristic of the exhaust gas sensor 17 is shifted to the lean side has been described. However, the output characteristic may be shifted to the rich side. This case is shown in FIG. 11, and the output characteristic 125 is shifted to the rich side by the output deviation ΔSVO2 with respect to the output characteristic 121 as indicated by an arrow 135. Here, the output deviation ΔSVO2 is calculated to take a negative value. As described above, the correction amount ΔSVO2F is obtained with reference to a conversion map as shown in FIG. 10 and takes a positive value. Therefore, target value ΔSVO2CMDF is positioned at a position lower than reference value ΔSVO2CMD by correction amount ΔSVO2F, as indicated by arrow 137.

  FIG. 12 is a flowchart of a process for correcting an air-fuel ratio output deviation of the exhaust gas sensor according to one embodiment of the present invention. The predetermined time interval is determined by the CPU of EUC1, more specifically, by each functional block of FIG. Can be realized in.

  In step S11, a cylinder-by-cylinder air-fuel ratio calculation process is executed. By executing this process, the air-fuel ratio AF (i) of each cylinder is detected. Details of this process will be described later with reference to FIG.

  In step S12, the output of the crank angle sensor 13 is acquired, and the current engine speed NE (rpm) is detected. In step S13, the output of the AFM 8 is acquired, and the current intake air amount GAIRAFM (g / TDC) is detected.

  In step S14, the contribution rate of each cylinder is estimated. Specifically, as described with reference to FIG. 7, the corresponding contribution rate map (table) is selected based on the engine speed NE and the intake air amount GAIRAFM detected in steps S12 and S13, and the selection is performed. The contribution rate K (i) of each cylinder is read from the map. In this way, it is possible to estimate the contribution rate according to the current amount of exhaust gas.

  In step S15, for each cylinder, the first air-fuel ratio is executed by executing equation (1) based on the contribution rate K (i) acquired in step S14 and the air-fuel ratio AF (i) detected in step S11. Calculate an estimate. In step S16, the second air-fuel ratio estimated value is calculated for each cylinder by executing equation (2) based on the air-fuel ratio AF (i) detected in step S11.

  In step S17, the output deviation ΔSVO2 is calculated by subtracting the second air-fuel ratio estimated value from the first air-fuel ratio estimated value. The output deviation ΔSVO2 is expressed in units of air-fuel ratio.

  In step S18, a conversion map as shown in FIG. 10 is referred to based on the calculated output deviation ΔSVO2, and a corresponding correction amount ΔSVO2F is obtained. In this embodiment, the correction amount ΔSVO2F is expressed in units of the exhaust gas sensor output (for example, voltage value (mV)).

  In step S19, correction is made from the reference value SVO2CMD of the output of the exhaust gas sensor 17 (the output value corresponding to a predetermined target air-fuel ratio value (for example, the theoretical air-fuel ratio value) when the gas contact is uniform as described above). The target value SVO2CMDF is calculated by subtracting the amount ΔSVO2. This is newly used as an output value corresponding to the predetermined target air-fuel ratio value. As described above, for example, the target air-fuel ratio KCMD is set so that the exhaust gas sensor output (detected value) becomes the target value SVO2CMDF.

  In this embodiment, the output deviation ΔSVO2 is converted into a correction amount ΔSVO2F with reference to a conversion map as shown in FIG. However, such conversion is not necessarily performed. For example, in the case of an exhaust gas sensor that directly outputs an air-fuel ratio value, it is not necessary to perform such conversion. An example of the output characteristics of the exhaust gas sensor in this case is shown in FIG.

  The output of the exhaust gas sensor is output in units of air-fuel ratio. The output characteristic 201 indicates a case where the per-gas ratio is uniform. When the actual air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric), the exhaust gas sensor also outputs the stoichiometric air-fuel ratio, which becomes the reference value SO2CMD. The output characteristic 203 shows an example when the gas contact is non-uniform, and is shifted to the lean side with respect to the output characteristic 201 as in the case of FIG. 9C. Therefore, the air-fuel ratio corresponding to the reference value SO2CMD is leaner than the stoichiometric air-fuel ratio.

  An arrow 205 indicates the output deviation ΔSO2, and takes a positive value in this example. An arrow 207 indicates the correction amount ΔSO2F. The magnitude of the output deviation ΔSO2 and the magnitude of the correction amount ΔSO2F are the same. Therefore, the target value SO2CMDF can be calculated by adding the output deviation ΔSO2 (that is, the correction amount ΔSO2F having the same sign (positive or negative) as the output deviation) to the reference value SO2CMD. Of course, the same correction can be performed when the output characteristics are shifted to the rich side.

  Next, the cylinder-by-cylinder air-fuel ratio calculation process executed in step S11 of FIG. 12 will be described. A flowchart illustrating an example of the process is shown in FIG.

  In step S41, the reference signal Fcr # i for each cylinder is read. Here, i indicates a cylinder identification number. The reference signal Fcr # i is set in advance for each cylinder.

  In step S42, a signal representing the air-fuel ratio KACT (expressed in equivalent ratio) is acquired from the air-fuel ratio sensor 16.

  In step S43, based on the signal representing the air-fuel ratio KACT, an air-fuel ratio deviation DKCMD signal representing the deviation of the air-fuel ratio KACT from the target air-fuel ratio KCMD (in this embodiment, the stoichiometric air-fuel ratio) is generated. A correlation function Cr # i is calculated for each cylinder by multiplying the signal of the fuel ratio deviation DKCMD by a predetermined reference signal set for each cylinder. Here, the calculation method of the correlation function will be described with reference to FIG.

  FIG. 15 shows the transition of the signal of the air-fuel ratio deviation DKCMD with respect to the target air-fuel ratio KCMD (in this embodiment, the stoichiometric air-fuel ratio) in one combustion cycle (in this embodiment, a crank angle period of 720 degrees). An example is shown. In this embodiment, in one combustion cycle, combustion is performed in the order of the first cylinder, the third cylinder, the fourth cylinder, and the second cylinder every crank angle period of 180 degrees. Therefore, in the first period, the air-fuel ratio of the exhaust gas resulting from the combustion of the first cylinder is detected, and in the example of the figure, it is shown that the air-fuel ratio is richer than the target air-fuel ratio KCMD (DKCMD is a positive value). . In the second period, the air-fuel ratio of the exhaust gas resulting from the combustion of the third cylinder is detected, and in the example shown in the figure, it is shown that the air-fuel ratio is leaner than the target air-fuel ratio KCMD (DKCMD is a negative value). Similarly, in the third period, the air-fuel ratio of the exhaust gas of the fourth cylinder is detected, which is rich, and in the fourth period, the air-fuel ratio of the exhaust gas of the second cylinder is detected, This is lean.

  Further, the drawing shows a reference signal Fcr # 1 for the first cylinder, a reference signal Fcr # 3 for the third cylinder, a reference signal Fcr # 4 for the fourth cylinder, and a reference signal for the second cylinder. The transition of Fcr # 2 is shown. The reference signal is predetermined for each cylinder, and is generated so as to correspond to the exhaust gas emission behavior of each cylinder. In this example, the reference signal is generated so as to have a triangular wave signal having a peak value of 1 only in the crank angle range of the exhaust timing of each cylinder. For example, Fcr # 1 has a triangular wave signal in the first period in which the exhaust gas of the first cylinder is exhausted. The shape of the reference signal is not limited to a triangular wave, and may be a sine wave or a square wave.

The correlation function Cr # i for each cylinder is calculated by multiplying the DKCMD signal and the reference signal Fcr # i for the cylinder, as shown in the following equation. Here, N is the number of pulses of the CRK signal per combustion cycle. If the CRK signal is emitted every 30 degrees, N = 24. K is a time step.

  For example, when the DKCMD signal is multiplied by the reference signal Fcr # 1 for the first cylinder, the first reference signal Fcr # 1 has a value only in the first period, and thus the correlation function Cr # of the first cylinder. 1 is calculated so that only the section corresponding to the first period has a value reflecting the value of the air-fuel ratio deviation DKCMD, that is, a value reflecting the value of the air-fuel ratio KACT. The richer the value of the air-fuel ratio KACT, the larger the correlation function Cr, and the smaller the value, the smaller the value. Thus, a signal indicating the magnitude of the air-fuel ratio of each cylinder is calculated as the correlation function Cr # i.

  The behavior of the exhaust gas in each cylinder, more specifically, the timing at which the exhaust gas from each cylinder reaches the air-fuel ratio sensor 16 may vary depending on the engine speed and the load. When this timing fluctuates, the peak position of the air-fuel ratio KACT signal in each period (in the example shown, the crank angle position is the maximum value in the first and third periods, and the minimum value is in the second and fourth periods. The corresponding crank angle position) may fluctuate and the peak position of the corresponding reference signal may shift. Therefore, in order to increase the accuracy, the peak position can be defined in advance and stored in a map or the like according to the engine speed NE and the load. As a parameter indicating the load, an intake air amount can be used. In step S41, the map is referred to based on the engine speed NE and the intake air amount GAIRAFM detected via the crank angle sensor 13 and the AFM 8, so that the corresponding peak position is obtained, and the peak is obtained at the obtained position. A reference signal having a triangular wave is generated and can be used for the calculation of the correlation function Cr # i performed in step S43.

  Since the correlation function Cr # i represents the magnitude of the air-fuel ratio of each cylinder by the deviation from the target air-fuel ratio KCMD, in step S44, the target air-fuel ratio KCMD is added to the correlation function Cr # i, and the cylinder-specific air-fuel ratio is determined. The fuel ratio KACT (i) is calculated. Here, the cylinder-by-cylinder air-fuel ratio KACT (i) is represented by an equivalent ratio (theoretical air-fuel ratio / air-fuel ratio). In step S45, for each cylinder, the cylinder-by-cylinder air-fuel ratio KACT (i) represented by the equivalence ratio is converted into the cylinder-by-cylinder air-fuel ratio AF (i) represented by the unit of the air-fuel ratio. The conversion can be performed by dividing the theoretical air-fuel ratio by the equivalent ratio.

  In the above embodiment, the reference value SVO2CMD or SO2CMD corresponding to the target air-fuel ratio value (in this embodiment, the theoretical air-fuel ratio value) when the gas hit is uniform is corrected with the correction amount ΔSVO2F or ΔSO2F, It has been described that the target air-fuel ratio KCMD is controlled so that the output (detected value) of the exhaust gas sensor 17 converges on the target value SVO2CMDF or SO2CMDF obtained by the correction. That is, in this case, the reference value SVO2CMD or SO2CMD side corresponding to the predetermined target air-fuel ratio value is corrected to correct the air-fuel ratio output deviation of the exhaust gas sensor. Alternatively, the output (detection value) side of the exhaust gas sensor 17 may be corrected to correct the air-fuel ratio output deviation of the exhaust gas sensor. That is, the output value (detected value) of the exhaust gas sensor 17 is corrected by the correction amount ΔSVO2F or ΔSVO2F, and the target air-fuel ratio KCMD is controlled so that the corrected output value converges to the reference value SVO2CMD or SO2CMD. It may be.

  In this case, the blocks denoted by reference numerals 71 to 76 in the functional block diagram of FIG. 6 perform the same operations as in the above embodiment. The correcting unit 77 acquires an output value (detected value) from the exhaust gas sensor 17, and corrects the acquired output value with a correction amount ΔSVO2F. As shown in FIG. 9C, when the output characteristic of the exhaust gas sensor 17 is shifted to the lean side (that is, when ΔSVO2 takes a positive value), the acquired output value corresponds to the output deviation ΔSVO2. The acquired output value is corrected by adding a correction amount ΔSVO2F (takes a negative value). Further, as shown in FIG. 11, the same applies when the output characteristics of the exhaust gas sensor 17 are shifted to the rich side (that is, when ΔSVO2 takes a negative value), and the output deviation ΔSVO2 is added to the acquired output value. The obtained output value is corrected by adding a correction amount ΔSVO2F (takes a positive value) corresponding to. The air-fuel ratio value at that time is represented by the corrected output value. Therefore, the target air-fuel ratio KCMD may be controlled so that the corrected output value becomes the reference value SVO2CMD.

  In the case of this alternative form, the process of FIG. 12 is the same from step S11 to S18. In step S19, as described above, the output value (detected value) of the exhaust gas sensor 17 is obtained, The output value of the exhaust gas sensor 17 may be corrected with the correction amount ΔSVO2F.

  Such an alternative correction method can be similarly applied to the case of the exhaust gas sensor that outputs the air / fuel ratio in FIG.

  In the above embodiment, the correction of the air-fuel ratio output deviation of the exhaust gas sensor 17 is used for controlling the target air-fuel ratio KCMD. However, the application of the correction method of the present invention is limited to this. It is not a thing. For example, the correction method can also be applied when air-fuel ratio feedback control is performed so that the air-fuel ratio detected by the output of the exhaust gas sensor 17 converges to a predetermined target air-fuel ratio. It should be noted that the correction method of the air-fuel ratio output deviation of the exhaust gas sensor according to the present invention can be applied to any control using the output of the exhaust gas sensor.

  Although the present invention has been described with respect to specific embodiments, the present invention is not limited to such embodiments, and can be used for both gasoline engines and diesel engines.

1 Electronic control unit (ECU)
2 Engine 15 Catalytic device 16 Air-fuel ratio sensor 17 Exhaust gas sensor

Claims (2)

A control device for an internal combustion engine having a plurality of cylinders,
A first air-fuel ratio sensor disposed upstream of a catalyst provided in an exhaust passage of the internal combustion engine;
A second air-fuel ratio sensor disposed in or downstream of the catalyst;
For each cylinder, contribution rate estimating means for estimating the rate at which the exhaust gas discharged from the cylinder contributes to the output of the second air-fuel ratio sensor;
Based on the air-fuel ratio of each cylinder detected by the first air-fuel ratio sensor and the contribution rate of each cylinder estimated by the contribution rate estimating means, the exhaust gas vacancy in the vicinity of the second air-fuel ratio sensor is determined. First air-fuel ratio estimating means for estimating the fuel ratio as a first air-fuel ratio estimated value;
Based on the average value of the air-fuel ratio of each cylinder detected by the first air-fuel ratio sensor, the air-fuel ratio of the exhaust gas existing in the vicinity of the second air-fuel ratio sensor is estimated as the second air-fuel ratio estimated value. Second air-fuel ratio estimating means for
Based on the first air-fuel ratio estimated value estimated by the first air-fuel ratio sensor and the second air-fuel ratio estimated value estimated by the second air-fuel ratio estimating means, the air-fuel ratio output deviation of the second air-fuel ratio sensor Correction means for correcting
An internal combustion engine control device comprising: The contribution rate estimation means is set according to the amount of exhaust gas discharged from each cylinder.
The control apparatus for an internal combustion engine according to claim 1.