JP2016035222A - Inter-cylinder air-fuel ratio variation detector of multiple cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the occurrence of variation (imbalance) of air-fuel ratios among cylinders in a multiple cylinder internal combustion engine, without providing a temperature sensor in an exhaust gas purification catalyst.SOLUTION: In a multiple cylinder internal combustion engine including a plurality of cylinders; an exhaust gas purification catalyst provided in an exhaust passage; an oxygen concentration sensor provided downstream of the exhaust gas purification catalyst in the exhaust passage; and a control unit controlling electric power supplied to an electric heater heating the oxygen concentration sensor, thereby controlling a temperature of the oxygen concentration sensor to match a predetermined target temperature, it is determined imbalance occurs if a difference between standard electric power supplied to the electric heater determined to correspond to an intake amount of the internal combustion engine and actual electric power supplied to the electric heater is greater than a predetermined threshold.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an apparatus for detecting variation in air-fuel ratio between cylinders of a multi-cylinder internal combustion engine.

  In general, in an internal combustion engine, for example, for the purpose of improving fuel efficiency (fuel consumption rate) and exhaust gas purification efficiency using a catalyst, the ratio of the mixture of air and fuel (that is, the air-fuel ratio) in the air-fuel mixture combusted in the internal combustion engine. Control is essential. Such control of the air-fuel ratio is performed by, for example, feedback control in which an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine, and the air-fuel ratio detected thereby coincides with a predetermined target air-fuel ratio.

  However, in an internal combustion engine having a plurality of cylinders (multi-cylinder internal combustion engine), since air-fuel ratio feedback control is performed using the same control amount for all cylinders, variation in air-fuel ratio among cylinders (imbalance). : Imbalance) may occur. When this imbalance occurs, there is a possibility that it may lead to problems such as deterioration of fuel consumption and / or exhaust emission. Therefore, it is desirable to detect the occurrence of imbalance as an abnormality.

  Therefore, it is known in the technical field that the temperature of the exhaust purification catalyst (catalyst temperature) rises due to the occurrence of imbalance in a multi-cylinder internal combustion engine. Therefore, it has been proposed to provide a temperature sensor for detecting the catalyst temperature and detect the occurrence of imbalance in the multi-cylinder internal combustion engine based on the catalyst temperature detected by the temperature sensor (for example, Patent Document 1). See).

JP 2011-179492 A

  As described above, in this technical field, a temperature sensor for detecting the temperature of the exhaust purification catalyst (catalyst temperature) is provided, and imbalance occurs in the multi-cylinder internal combustion engine based on the catalyst temperature detected by the temperature sensor. It has been proposed to detect. However, in this case, in order to detect the catalyst temperature, it is necessary to provide a temperature sensor in the exhaust purification catalyst, which increases the manufacturing cost.

  The present invention has been made to address the above-described problems. That is, one object of the present invention is to provide an “inter-cylinder air-fuel ratio variation detecting device” (hereinafter referred to as “the present invention”) that can detect the occurrence of imbalance in a multi-cylinder internal combustion engine without providing a temperature sensor in the exhaust purification catalyst. It may be referred to as a “device”. In order to achieve this object, the present inventor, as a result of earnest research, the power supplied to the heater for heating the oxygen concentration sensor disposed on the downstream side of the exhaust purification catalyst in the exhaust passage is It was found that it changes depending on the presence or absence.

  More specifically, as shown in FIG. 1, when the temperature of the oxygen concentration sensor changes, its impedance also changes. Therefore, in order to obtain a detection signal that accurately reflects the oxygen concentration, it is necessary to keep the temperature of the oxygen concentration sensor constant. Therefore, the power supplied to the electric heater that heats the oxygen concentration sensor is controlled so as to keep the temperature of the oxygen concentration sensor constant.

  On the other hand, as described above, the temperature of the exhaust purification catalyst (catalyst temperature) rises due to the occurrence of imbalance in the multi-cylinder internal combustion engine. Due to the increase in the catalyst temperature, the temperature of the exhaust gas discharged from the exhaust purification catalyst to the exhaust passage also rises, and the amount of heat received by the oxygen concentration sensor disposed on the downstream side of the exhaust purification catalyst in the exhaust passage increases (i.e., The oxygen concentration sensor is heated). Therefore, when the electric power supplied to the electric heater that heats the oxygen concentration sensor is constant, the temperature of the oxygen concentration sensor (sensor temperature) increases due to the occurrence of imbalance, and the impedance decreases.

  That is, as shown in FIG. 2, the catalyst temperature rises as the vehicle equipped with the multi-cylinder internal combustion engine travels (see graph (a)), and the catalyst temperature increases as the degree of imbalance increases. (See graph (b)). Therefore, when the power supplied to the electric heater for heating the oxygen concentration sensor is constant, the sensor temperature becomes higher as the degree of imbalance increases, and as a result, the impedance of the oxygen concentration sensor becomes lower (graph (c)). And (d), where the graph (d) is an enlarged view of the portion surrounded by the alternate long and short dash line in the graph (c)).

  However, actually, as described above, the power supplied to the electric heater that heats the oxygen concentration sensor is controlled so as to maintain the temperature of the oxygen concentration sensor constant. Therefore, as the degree of imbalance increases, the power supplied to the electric heater that heats the oxygen concentration sensor is reduced, and the temperature of the oxygen concentration sensor is kept constant. As described above, the power supplied to the electric heater that heats the oxygen concentration sensor changes according to the degree of imbalance.

  In view of this, the present inventor, in a multi-cylinder internal combustion engine that controls the power supplied to the electric heater that heats the oxygen concentration sensor and maintains the sensor temperature constant, applies the electric heater to the electric heater at normal time when no imbalance occurs. Based on the difference between the supplied power (standard supplied power) and the actual supplied power to the electric heater (actual supplied power), it has been thought that the occurrence of imbalance can be detected.

  However, there are other factors that increase the sensor temperature besides imbalance. Specifically, if the air-fuel mixture burned per unit time in a multi-cylinder internal combustion engine increases, the exhaust gas temperature increases, and as a result, the sensor temperature also increases. Therefore, in a multi-cylinder internal combustion engine that controls the power supplied to the electric heater that heats the oxygen concentration sensor and maintains the sensor temperature constant, if the intake air amount increases even when the imbalance does not occur, As indicated by the solid line 3, the power supplied to the electric heater is reduced. That is, the standard supply power is not a constant value but decreases as the intake air amount increases.

  In addition to the above, as the degree of imbalance is larger as described above, the power supplied to the electric heater that heats the oxygen concentration sensor is reduced. Therefore, as shown by the broken lines and dotted lines in FIG. The correspondence relationship between the supplied power and the intake air amount shifts to the low power side as the imbalance increases. The inventor of the present invention is based on whether or not the shift amount (that is, the difference between the standard supply power and the actual supply power at a specific intake air amount) is larger than a predetermined threshold value (a white double arrow in FIG. 3). This led to the idea that it was possible to determine whether imbalance occurred.

  Accordingly, the device of the present invention comprises a plurality of cylinders, an exhaust purification catalyst disposed in the exhaust passage, an oxygen concentration sensor disposed on the exhaust passage downstream of the exhaust purification catalyst, and the oxygen concentration sensor. The present invention is applied to a multi-cylinder internal combustion engine that includes a control unit that controls power supplied to an electric heater to be heated so that the temperature of the oxygen concentration sensor matches a predetermined target temperature.

  In addition, the device of the present invention includes a detection unit that detects the occurrence of imbalance, which is a variation in the air-fuel ratio among the plurality of cylinders.

The detector is
Obtaining an intake air amount correlation value that is an operating state parameter correlated with the intake air amount of the multi-cylinder internal combustion engine, and an actual supply power that is an actual supply power to the electric heater;
Based on the correspondence relationship between the intake air amount and the supply power at normal time when the imbalance has not occurred, the standard supply power that is the supply power corresponding to the intake air amount correlation value is specified,
When the difference obtained by subtracting the actual supply power from the standard supply power is greater than a predetermined threshold, it is determined that the imbalance has occurred.

  According to the device of the present invention, it is possible to detect the occurrence of imbalance in a multi-cylinder internal combustion engine without providing a temperature sensor in the exhaust purification catalyst.

FIG. 1 is a schematic graph showing the correspondence between the temperature of the oxygen concentration sensor and its impedance. FIG. 2 shows (a) the oxygen concentration when the vehicle mounted with the multi-cylinder internal combustion engine travels, (b) the catalyst temperature, and (c) the electric power supplied to the electric heater that heats the oxygen concentration sensor is constant. It is a typical graph which shows the change of the impedance of a sensor. The graph (d) is an enlarged view of a portion surrounded by a dashed line in the graph (c). FIG. 3 is a schematic graph showing the correspondence relationship between the power supplied to the electric heater that heats the oxygen concentration sensor and the intake air amount of the multi-cylinder internal combustion engine. FIG. 4 is a schematic configuration diagram of an inter-cylinder air-fuel ratio variation detecting device of a multi-cylinder internal combustion engine according to an embodiment of the present invention and an internal combustion engine to which the detecting device is applied. FIG. 5 is a flowchart for explaining an “imbalance detection routine” executed by the detection unit provided in the inter-cylinder air-fuel ratio variation detection device of the multi-cylinder internal combustion engine according to one embodiment of the present invention. FIG. 5 is a flowchart for explaining an “imbalance detection routine” executed by a detection unit provided in the inter-cylinder air-fuel ratio variation detection device of a multi-cylinder internal combustion engine according to another embodiment of the present invention.

  Hereinafter, an inter-cylinder air-fuel ratio variation detecting device (hereinafter also referred to as “the present detecting device”) according to an embodiment of the present invention will be described with reference to the drawings.

(Constitution)
This detection apparatus is applied to the internal combustion engine 1 shown in FIG. The internal combustion engine 1 generates power by burning a mixture of fuel and air in a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston in the cylinder. The internal combustion engine 1 is a multi-cylinder internal combustion engine mounted on a vehicle, more specifically, an in-line 4-cylinder, spark ignition type, internal combustion engine. However, the internal combustion engine to which the present detection apparatus can be applied is not limited to the one having such a configuration, and a plurality of cylinders, an exhaust purification catalyst disposed in the exhaust passage, and the exhaust purification catalyst in the exhaust passage. An oxygen concentration sensor disposed on the downstream side, and a control unit that controls the power supplied to an electric heater that heats the oxygen concentration sensor so as to match the temperature of the oxygen concentration sensor with a predetermined target temperature. If it is the multicylinder internal combustion engine which comprises these, it will not specifically limit.

  Although not shown, the cylinder head of the internal combustion engine 1 is provided with an intake valve that opens and closes an intake port and an exhaust valve that opens and closes an exhaust port for each cylinder. Is opened and closed by a camshaft. A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to a surge tank 8 which is an intake air collecting chamber via a branch pipe 4 for each cylinder. An intake pipe 13 is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. The intake port, the branch pipe 4, the surge tank 8, and the intake pipe 13 form an intake passage. An air flow meter 5 for detecting an intake air amount (intake air amount) and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side.

  In the intake port, an injector (fuel injection valve) 12 for injecting fuel is disposed for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture, which is sucked into the combustion chamber 3 when the intake valve is opened, compressed by the piston, and ignited and burned by the spark plug 7. .

  On the other hand, the exhaust port of each cylinder is connected to the exhaust manifold 14. The exhaust manifold 14 includes a branch pipe 14a for each cylinder forming an upstream portion thereof and an exhaust collecting portion 14b forming a downstream portion thereof. An exhaust pipe 6 is connected to the downstream side of the exhaust collecting portion 14b. The exhaust port, the exhaust manifold 14 and the exhaust pipe 6 form an exhaust passage.

  A three-way catalyst 11 is disposed in the exhaust pipe 6. An air-fuel ratio sensor 17 and an oxygen concentration sensor 18 are installed upstream and downstream of the three-way catalyst 11. The air-fuel ratio sensor 17 and the oxygen concentration sensor 18 are installed in the exhaust passage at positions immediately before and after the three-way catalyst 11, and output a detection signal corresponding to the oxygen concentration in the exhaust. As described above, the oxygen concentration sensor 18 includes the electric heater 19 and the temperature sensor 21.

  Various actuators such as the spark plug 7, the throttle valve 10, the injector 12, and the electric heater 19 are electrically connected to an electronic control unit (ECU) 20 as control means. The ECU 20 is an electronic circuit including a known microcomputer, and includes a CPU, a ROM, a RAM, a backup RAM, an interface, and the like. The ECU 20 is connected to sensors described below, and receives (inputs) signals from these sensors.

  The air flow meter 5 measures the mass flow rate (intake amount) of intake air passing through the intake passage and outputs a signal representing the intake amount Ga. The throttle valve opening sensor 41 detects the throttle valve opening and outputs a signal representing the throttle valve opening TA. The crank angle sensor 16 outputs a signal corresponding to a rotational position (that is, crank angle) of a crankshaft (not shown) of the internal combustion engine 1. The ECU 20 acquires a crank angle (absolute crank angle) θ of the internal combustion engine 1 with reference to the compression top dead center of a predetermined cylinder based on signals from the crank angle sensor 16 and a cam position sensor (not shown). Further, the ECU 20 acquires the engine rotational speed Ne based on the signal from the crank angle sensor 16.

  The ECU 20 sends instruction (drive) signals to various actuators such as the spark plug 7, the throttle valve 10, and the injector 12 so that a desired control result can be obtained based on detection values by various sensors, etc. The fuel injection amount, fuel injection timing, throttle valve opening, and the like are controlled. Further, the throttle valve opening is normally controlled to be an opening corresponding to the accelerator opening. Further, the ECU 20 controls the power supplied to the electric heater 19 provided in the oxygen concentration sensor 18 to keep the temperature of the oxygen concentration sensor 18 measured by the temperature sensor 21 provided in the oxygen concentration sensor 18 constant. That is, ECU20 functions also as a control part mentioned above.

(Imbalance detection)
As described above, the detection device determines whether imbalance has occurred based on whether the difference between the standard supply power corresponding to the intake air amount at the time of detection and the actual supply power is greater than a predetermined threshold. . The operation of the detection apparatus in this imbalance detection will be described in detail below.

  Here, it is assumed that the injectors 12 of some cylinders out of all the cylinders have failed and air-fuel ratio variation (imbalance) occurs between the cylinders. For example, the fuel injection amount in the # 1 cylinder is larger than the fuel injection amounts in the other # 2, # 3, and # 4 cylinders, and only the air-fuel ratio in the # 1 cylinder is greatly rich. The case where it shifted to is mentioned. Even in such a case, the air-fuel ratio of the internal combustion engine 1 as a whole may be matched with the stoichiometric air-fuel ratio (stoichiometric) by the above-described feedback control of the air-fuel ratio.

  However, when viewed by cylinder, the air-fuel ratio in the # 1 cylinder is rich (smaller than stoichiometric), and the air-fuel ratio in the # 2, # 3, and # 4 cylinders is lean (larger than stoichiometric). That is, in this case, imbalance has occurred. As described above, since such a situation may lead to problems such as deterioration of fuel consumption and / or exhaust emission, it is desirable to detect the occurrence of imbalance as an abnormality. Therefore, the present detection apparatus includes a detection unit that detects the occurrence of imbalance, which is a variation in the air-fuel ratio among the plurality of cylinders.

As described above, the detection unit
(1) obtaining an intake air amount correlation value that is an operating state parameter correlated with an intake air amount of the multi-cylinder internal combustion engine, and an actual supply power that is an actual supply power to the electric heater;
(2) Based on the correspondence relationship between the intake air amount and the supplied power at the normal time when the imbalance has not occurred, a standard supply power that is a supply power corresponding to the intake air amount correlation value is specified,
(3) If the difference obtained by subtracting the actual supply power from the standard supply power is greater than a predetermined threshold, it is determined that the imbalance has occurred.

  The detection unit is an electronic circuit including a known microcomputer, and the ECU 20 described above may function as the detection unit, or an ECU separate from the ECU 20 described above may function as the detection unit. Good. The operation of the detection apparatus shown in the above (1) to (3) will be described below with reference to the flowchart shown in FIG.

  The CPU executes an “imbalance detection routine” shown by a flowchart in FIG. 5 every time a predetermined time elapses. Accordingly, when the appropriate timing is reached, the CPU starts the process from step 500 in FIG. 5 and proceeds to the next step 510 to determine whether or not the internal combustion engine 1 has already been started. If the internal combustion engine 1 has not yet been started, the CPU makes a “No” determination at step 510 to proceed to step 595 to end the present routine tentatively.

  On the other hand, if the internal combustion engine 1 has already been started, the CPU makes a “Yes” determination at step 510 and proceeds to step 530 where the electric power is actually supplied to the electric heater 19 provided in the oxygen concentration sensor 18. The actual supply power (P) is acquired from the control unit. Next, the CPU proceeds to step 540 to acquire an intake air amount correlation value (A) that is an operation state parameter having a correlation with the intake air amount of the internal combustion engine 1.

  The intake air amount correlation value A is not particularly limited as long as it is an operating state parameter having a correlation with the intake air amount of the internal combustion engine. Typically, the intake air amount correlation value A is the intake air amount Ga which is the mass flow rate of the intake air passing through the intake passage detected by the air flow meter 5. Alternatively, the intake air amount correlation value A may be a throttle valve opening degree TA detected by the throttle valve opening degree sensor 41, and is an engine rotational speed Ne calculated by the ECU 20 based on a signal from the crank angle sensor 16. There may be.

  Further, for example, from the viewpoint of reducing the influence of detection error or sudden abnormal value of the detection means, the actual supply power P acquired in step 530 and the intake air amount correlation value A acquired in step 540 are predetermined values. It is desirable to set the average value of the measured values over a period (for example, 100 seconds). Further, in FIG. 5, the actual supply power P is acquired in Step 530 and the intake air amount correlation value A is acquired in Step 540, but the order of acquiring these may be reversed. These steps 530 and 540 correspond to the operation of the present detection apparatus shown in (1) above.

  Next, the CPU proceeds to step 550, and based on the correspondence relationship between the power supplied to the electric heater 19 provided in the oxygen concentration sensor 18 and the intake air amount Ga when the internal combustion engine 1 is not imbalanced at normal time, the step A standard supply power (Ps) that is a supply power corresponding to the intake air amount correlation value A acquired at 540 is specified. This step 550 corresponds to the operation of the present detection apparatus shown in (2) above.

  In addition, the correspondence relationship between the power supplied to the electric heater 19 provided in the oxygen concentration sensor 18 and the intake air amount Ga in a normal state where no imbalance has occurred in the internal combustion engine 1 is, for example, based on a preliminary experiment using the internal combustion engine 1. It can be specified in advance by measuring the power supplied to the electric heater 19 provided in the oxygen concentration sensor 18 at various intake air amounts. Further, the correspondence relationship specified in advance in this way is stored in, for example, a data rule device (for example, ROM) provided in the ECU 20 as a map (data table), and is referred to by the CPU when executing step 550. Also good.

  Furthermore, when the intake air amount correlation value A acquired in step 540 is the intake air amount Ga, the intake air amount Ga can be directly applied to the correspondence relationship to identify the corresponding standard supply power Ps. On the other hand, when the intake air amount correlation value A acquired in step 540 is an operating state parameter other than the intake air amount Ga (for example, the throttle valve opening TA or the engine rotational speed Ne), the intake air converted from these operating parameters. The amount Ga may be directly applied to the correspondence relationship to identify the corresponding standard supply power Ps. Alternatively, instead of the correspondence between the power supplied to the electric heater 19 and the intake air amount Ga, the correspondence between the electric power supplied to the electric heater 19 and the throttle valve opening TA, or the electric power supplied to the electric heater 19 and the engine rotation The correspondence relationship with the speed Ne may be specified in advance by a prior experiment.

  Next, the CPU proceeds to step 560 to determine whether or not the difference obtained by subtracting the actual supply power P acquired in step 530 from the standard supply power Ps specified in step 550 is greater than a predetermined threshold (Tp). judge. This threshold value Tp depends on, for example, an imbalance allowable range that does not substantially cause problems such as measurement error of power supplied to the electric heater 19 provided in the oxygen concentration sensor 18, fuel consumption, and / or deterioration of exhaust emission. Can be set as appropriate.

  When the difference obtained by subtracting the actual supply power P from the standard supply power Ps is larger than the threshold value Tp, the CPU determines “Yes” in step 560 and proceeds to the next step 570 to determine that imbalance has occurred. (Abnormality judgment). On the other hand, if the difference obtained by subtracting the actual supply power P from the standard supply power Ps is equal to or less than the threshold value Tp, the CPU makes a “No” determination at step 560 to proceed to the next step 580, where no imbalance has occurred. Judge (normal judgment). These steps 560 to 580 correspond to the operation of the present detection apparatus shown in (3) above. After determining whether or not imbalance has occurred in this way, the CPU proceeds to step 595 to end the present routine tentatively.

  In the above description, whether or not the difference (Ps−P) between the standard supply power Ps and the actual supply power P is larger than the threshold value Tp is used as a determination criterion. However, for example, the lower limit supply power obtained by subtracting the threshold value Tp from the standard supply power Ps corresponding to various intake air amounts Ga is calculated, and the correspondence relationship between the intake air amount Ga and the lower limit supply power is, for example, as shown in Table 1 below. It may be stored in a data regulation device (for example, ROM) provided in the ECU 20 as a simple data table. In this case, in step 550, the CPU compares the lower limit supply power with the actual supply power, and determines that an imbalance has occurred if the actual supply power is smaller than the lower limit supply power.

  As described above, the present detection device can detect the occurrence of imbalance in the multi-cylinder internal combustion engine (internal combustion engine 1) without providing a temperature sensor in the exhaust purification catalyst (three-way catalyst 11).

(Modification)
As described above, the device of the present invention increases the catalyst temperature when imbalance occurs in a multi-cylinder internal combustion engine that controls the power supplied to the electric heater that heats the oxygen concentration sensor and maintains the sensor temperature constant. As a result, the oxygen concentration sensor is heated, and as a result, the occurrence of imbalance is detected by utilizing the phenomenon that the power supplied to the electric heater decreases.

  Therefore, in the period when the temperature of the oxygen concentration sensor has not yet reached the target temperature (corresponding to the desired impedance), for example, immediately after cold start, the power supplied to the electric heater to raise the temperature of the oxygen concentration sensor Is increased. Therefore, in such a period, it may be difficult to accurately detect the occurrence of imbalance based on the difference obtained by subtracting the actual supply power from the standard supply power as described above.

  Therefore, as shown in the flowchart in FIG. 6, the inventor determines whether or not the temperature of the oxygen concentration sensor has reached the target temperature when executing the “imbalance detection routine”. If the temperature of the battery does not reach the target temperature, it is possible to detect the occurrence of imbalance more accurately based on the difference obtained by subtracting the actual supply power from the standard supply power by stopping the detection of the occurrence of imbalance. I came to the idea that I could do it.

  That is, the flowchart of FIG. 6 corresponding to this modification is based on step 510 for determining whether or not the internal combustion engine 1 has already been started, and the electric power actually supplied to the electric heater 19 provided in the oxygen concentration sensor 18. Only in that a step 520 for determining whether or not the temperature of the oxygen concentration sensor 18 has reached the target temperature is newly provided between the step 530 for obtaining a certain actual power supply (P). Different from the flowchart of FIG.

  If the temperature of the oxygen concentration sensor 18 has not yet reached the target temperature, the CPU makes a “No” determination at step 520 to proceed to step 595 to end the present routine tentatively. On the other hand, if the temperature of the oxygen concentration sensor 18 has already reached the target temperature, the CPU makes a “Yes” determination at step 520 to proceed to the next step 530. Note that the processing flow after step 530 is the same as that in the flowchart of FIG. 5 and will not be described again here.

  As described above, in this modified example, when the temperature of the oxygen concentration sensor 18 has not yet reached the target temperature, occurrence of imbalance is not detected. As a result, it is possible to prevent imbalance detection from being performed inaccurately due to the influence of electric power supplied to the electric heater 19 for raising the temperature of the oxygen concentration sensor 18. That is, according to this modification, it is possible to more accurately detect the occurrence of imbalance in the multi-cylinder internal combustion engine (internal combustion engine 1) without providing a temperature sensor in the exhaust purification catalyst (three-way catalyst 11).

  For the purpose of illustrating the present invention, several embodiments having specific configurations have been described above and sometimes with reference to the accompanying drawings. However, the scope of the present invention is limited to these exemplary embodiments. Needless to say, the present invention should not be construed as being limited, and modifications can be made as appropriate within the scope of the claims and the specification.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 3 ... Combustion chamber, 5 ... Air flow meter, 6 ... Exhaust pipe, 11 ... Three-way catalyst, 12 ... Injector, 14 ... Exhaust manifold, 17 ... Air-fuel ratio sensor, 18 ... Oxygen concentration sensor, 19 ... Electric heat 20 ... an electronic control unit (ECU), 21 ... a temperature sensor, 22 ... a water temperature sensor, and 41 ... a throttle valve opening sensor.

Claims (1)

Multiple cylinders,
An exhaust purification catalyst disposed in the exhaust passage;
An oxygen concentration sensor disposed downstream of the exhaust purification catalyst in the exhaust passage;
A control unit for controlling the temperature of the oxygen concentration sensor to coincide with a predetermined target temperature by controlling power supplied to an electric heater that heats the oxygen concentration sensor;
Applied to a multi-cylinder internal combustion engine having
A detector that detects the occurrence of imbalance, which is a variation in air-fuel ratio among the plurality of cylinders;
A cylinder-to-cylinder air-fuel ratio variation detecting device for a multi-cylinder internal combustion engine,
The detector is
Obtaining an intake air amount correlation value that is an operating state parameter correlated with the intake air amount of the multi-cylinder internal combustion engine, and an actual supply power that is an actual supply power to the electric heater;
Based on the correspondence relationship between the intake air amount and the supply power at normal time when the imbalance has not occurred, the standard supply power that is the supply power corresponding to the intake air amount correlation value is specified,
When the difference obtained by subtracting the actual supply power from the standard supply power is greater than a predetermined threshold, it is determined that the imbalance has occurred.
An inter-cylinder air-fuel ratio variation detecting device for a multi-cylinder internal combustion engine.

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