JP2011094996A - Exhaust oxygen concentration detection apparatus - Google Patents

Abstract

An exhaust oxygen concentration detection device capable of appropriately adjusting the responsiveness required for detecting the oxygen concentration of exhaust gas is provided.
The apparatus includes an air-fuel ratio sensor that is provided upstream of a three-way catalyst in the exhaust flow direction of the collective portion of the exhaust passage of the internal combustion engine and detects the oxygen concentration of the exhaust of the internal combustion engine. The engine system detects both the air-fuel ratio control for adjusting the air-fuel ratio of the air-fuel mixture in each cylinder of the internal combustion engine and the air-fuel ratio variation determination for determining the air-fuel ratio variation of the air-fuel mixture between the cylinders of the internal combustion engine. Run based on the value. Compared to the temperature (S107) of the oxygen sensor when the air-fuel ratio variation determination is not performed (S106: YES), the temperature (S102) of the air-fuel ratio sensor when the air-fuel ratio variation determination is performed (S101: YES) is increased. Adjust.
[Selection] Figure 3

Description

  The present invention relates to an exhaust oxygen concentration detection device having an oxygen sensor for detecting the oxygen concentration of exhaust gas from an internal combustion engine.

  In an engine system, a three-way catalyst is often used in an exhaust passage of an internal combustion engine (see Patent Document 1). In this engine system, combustion gas (exhaust gas) discharged from each cylinder of the internal combustion engine to the exhaust passage is purified by a three-way catalyst. The three-way catalyst exhibits a high purification function when the air-fuel ratio of the air-fuel mixture combusting in each cylinder of the internal combustion engine is within a predetermined range (so-called window). For this reason, in an engine system provided with a three-way catalyst, so-called air-fuel ratio control is performed in which the nature of the exhaust gas is detected and the air-fuel ratio of the air-fuel mixture in each cylinder of the internal combustion engine is feedback controlled based on the same nature.

  Specifically, oxygen for detecting the oxygen concentration of the exhaust at a position upstream of the three-way catalyst in the exhaust flow direction in the collective portion of the exhaust passage of the internal combustion engine (specifically, the portion where the passages extending from the cylinders merge) A sensor is provided. The oxygen concentration detected by the oxygen sensor is supplied to each cylinder of the internal combustion engine so that a predetermined concentration (for example, the oxygen concentration of the exhaust gas when the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio) matches. The amount of fuel to be discharged (fuel supply amount) is feedback-controlled.

  Through such air-fuel ratio control, the air-fuel ratio of the air-fuel mixture is adjusted to the ratio in the window so that the three-way catalyst exhibits a high purification function, and the exhaust gas of the internal combustion engine is appropriately purified. .

  Here, in the air-fuel ratio control, the fuel supply amount to each cylinder is adjusted to be the same amount according to the detection value of the oxygen sensor provided in the collection portion of the exhaust passage. Therefore, although the average value of the air-fuel ratio of each cylinder of the internal combustion engine can be adjusted so as to be the ratio in the window, the air-fuel ratio of each cylinder cannot be adjusted separately, and the intake system of the engine system and It is inevitable that the air-fuel ratio of each cylinder varies due to the influence of individual differences and deterioration of the fuel system.

  In a multi-cylinder internal combustion engine, even if the average value of the air-fuel ratio of each cylinder is a ratio in the window, if the variation in the air-fuel ratio between the cylinders becomes large, the oxygen concentration of the exhaust becomes the concentration corresponding to the window. Since it periodically deviates from the range, the purification function by the three-way catalyst is lowered and the exhaust properties are deteriorated. Therefore, even in an engine system in which air-fuel ratio control is executed, it is possible to determine the degree of air-fuel ratio variation between the cylinders of the internal combustion engine, and appropriately deal with this when the variation is large. desirable.

  For this reason, conventionally, when the variation in the air-fuel ratio between the cylinders of the internal combustion engine increases, the fluctuation range of the detection value of the oxygen sensor also increases. Therefore, the fluctuation range (specifically, the fluctuation range of the detection value at a specific frequency) increases. Therefore, it has been proposed to determine the occurrence of an abnormality in which the variation becomes large (see, for example, Patent Document 2).

JP 2000-179381 A JP 2000-220489 A

  By the way, when performing the above-described air-fuel ratio control, the fuel supply amount to each cylinder is adjusted to the same amount based on the detection value of the common oxygen sensor. Therefore, when performing air-fuel ratio control, a value corresponding to the average value of the air-fuel ratio of each cylinder may be detected by the oxygen sensor, and the detection response required for the oxygen sensor (following of the detected value with respect to the actual exhaust oxygen concentration) ) Is low. If the detection responsiveness of the oxygen sensor is increased at this time, the fluctuation speed and fluctuation range of the detected value are increased, and the difference between the detected value and the value corresponding to the average value is easily caused. The air-fuel ratio of the air-fuel mixture in each cylinder tends to become unstable.

  On the other hand, when determining the degree of variation in the air-fuel ratio as described above, if the detection response of the oxygen sensor is low, fluctuations in the exhaust oxygen concentration due to the difference in the air-fuel ratio of each cylinder are properly detected. Therefore, the oxygen sensor is required to have high detection responsiveness in order to accurately detect such fluctuations in the exhaust oxygen concentration.

  As described above, the detection responsiveness required for the oxygen sensor when detecting the exhaust oxygen concentration differs between the execution of the air-fuel ratio control and the determination of the air-fuel ratio variation, and both the air-fuel ratio control and the determination of the air-fuel ratio variation are accurate. In order to perform well, it is necessary to set the detection response of the oxygen sensor appropriately.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust oxygen concentration detection device capable of appropriately adjusting the responsiveness required for detecting the oxygen concentration of exhaust gas.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
The invention according to claim 1 is provided with an oxygen sensor that is provided upstream of the three-way catalyst in the exhaust passage direction of the collective portion of the exhaust passage of the multi-cylinder internal combustion engine and detects the oxygen concentration of the exhaust of the internal combustion engine, Both the air-fuel ratio control for adjusting the air-fuel ratio of the air-fuel mixture in each cylinder of the internal combustion engine and the air-fuel ratio variation determination for determining the air-fuel ratio variation of the air-fuel mixture between the cylinders of the internal combustion engine are both based on the detected value of the oxygen sensor. In the exhaust oxygen concentration detection device applied to the engine system to be executed, the temperature of the oxygen sensor when the air-fuel ratio variation determination is performed is compared with the temperature of the oxygen sensor when the air-fuel ratio variation determination is not performed. The gist of the invention is to provide temperature adjusting means for adjusting to a high temperature.

  If the temperature of the oxygen sensor is adjusted within an appropriate temperature range, the detection response of the oxygen sensor increases as the temperature increases. According to the above configuration, when the air-fuel ratio variation determination is executed, the oxygen sensor becomes high temperature and the detection responsiveness thereof becomes high. Therefore, the oxygen sensor causes the difference in exhaust oxygen concentration of each cylinder of the internal combustion engine. Therefore, it is possible to properly detect the fluctuation of the exhaust oxygen concentration, and to perform the air-fuel ratio variation determination with high accuracy. In addition, when the air-fuel ratio variation determination is not performed, the oxygen sensor becomes relatively low temperature and the detection responsiveness is low, so the oxygen sensor appropriately detects a value close to the average value of the exhaust oxygen concentration of each cylinder. The air-fuel ratio control can be executed with high accuracy based on the detected value. As described above, according to the above configuration, the responsiveness for detecting the oxygen concentration of the exhaust gas can be appropriately adjusted in order to execute both the air-fuel ratio control and the air-fuel ratio variation determination with high accuracy.

  The invention according to claim 2 is the exhaust oxygen concentration detection device according to claim 1, wherein the temperature adjusting means adjusts the temperature of the oxygen sensor to a lower temperature as the intake air amount of the internal combustion engine increases. That is the gist.

  As the intake air amount of the internal combustion engine increases, the exhaust amount of the internal combustion engine, that is, the amount of exhaust gas that passes through the portion where the oxygen sensor is disposed, increases the followability of the detected value of the oxygen sensor to the change in the oxygen concentration of the exhaust gas. Can be said to be high. The difference in the change rate of the detection value of the oxygen sensor due to the difference in the intake air amount is a cause of lowering the execution accuracy of the air-fuel ratio control and the determination accuracy of the air-fuel ratio variation determination, similarly to the difference in the detection response of the oxygen sensor. There is a possibility.

  According to the above configuration, it is possible to change the temperature of the oxygen sensor and set its detection responsiveness so as to suppress the difference in the change rate of the detection value of the oxygen sensor due to such a difference in the intake air amount. Therefore, the difference between the change speeds and the error due to the difference can be suppressed, and the air-fuel ratio control and the air-fuel ratio variation determination can be executed with high accuracy.

  In addition, as said temperature control means, what has what has a heater for adjusting the electric power supplied to the heater for heating the said oxygen sensor as Claim 3 is employable.

  According to a fourth aspect of the present invention, in the exhaust gas oxygen concentration detection device according to the third aspect, the oxygen sensor has a detection element whose impedance increases as the temperature rises, and the temperature adjusting means includes the detection element. In addition to detecting the correlation value of the impedance of the element, the supply power to the heater is adjusted based on the correlation value, and the exhaust oxygen concentration detection device is configured to detect the correlation of the heater before and after the execution of the air-fuel ratio variation determination is stopped. The gist of the present invention is that it further comprises a deterioration determining means for determining a deterioration abnormality of the oxygen sensor on condition that the difference in power consumption is equal to or greater than a predetermined determination value.

  In the above configuration, when setting the temperature of the oxygen sensor, the correlation value of the impedance is detected and the correlation value is the target value based on the characteristic that the impedance of the detection element of the oxygen sensor decreases as the temperature of the oxygen sensor increases. The power supplied to the heater is adjusted to a value corresponding to the temperature. Thereby, the element temperature of the oxygen sensor is adjusted to a desired temperature.

  The detection element of the oxygen sensor has a characteristic that the impedance increases with deterioration. Therefore, in a device that adjusts the power supplied to the heater based on the correlation value of the impedance of the detection element, when the impedance of the detection element increases due to deterioration, the power supplied to the heater increases to reduce the increase. The power consumption of the heater is unnecessarily increased by that amount. Therefore, it becomes possible to determine the deterioration abnormality of the oxygen sensor when the power consumption of the heater is increased in this way.

  However, since the exhaust temperature of the internal combustion engine varies depending on its operating state, the power consumption of the heater required to maintain the temperature of the oxygen sensor at the target temperature also varies depending on the engine operating state. Even if the power consumption is monitored, it is difficult to accurately determine the deterioration abnormality of the oxygen sensor.

  When the impedance of the detection element increases due to deterioration, the power consumption of the heater increases from time to time, and the difference in power consumption of the heater before and after the execution of air-fuel ratio variation determination is stopped also increases. Although the difference in power consumption varies depending on the engine operating state, the change width accompanying the change in the engine operation state is compared with the change width accompanying the change in the engine operation state of the heater power consumption at that time. It was confirmed by the inventors that it was very small.

  According to the above configuration, it is possible to accurately determine the deterioration abnormality of the oxygen sensor based on the difference in the heater power consumption before and after the execution stop of the air-fuel ratio variation determination. As the impedance correlation value, admittance can be employed in addition to the impedance itself.

  According to a fifth aspect of the present invention, in the exhaust oxygen concentration detection device according to any one of the first to fourth aspects, the engine system detects the oxygen concentration detected by the oxygen sensor in the air-fuel ratio variation determination. The gist of the present invention is to determine that there is an abnormality in which the variation in the air-fuel ratio of the air-fuel mixture increases between the cylinders of the internal combustion engine when the change speed of the engine is equal to or higher than a predetermined determination speed.

  When the air-fuel ratio varies between the cylinders of the internal combustion engine, the oxygen concentration of the exhaust gas that passes through the aggregate portion of the exhaust passage changes periodically, so that the oxygen concentration detected by the oxygen sensor is also cycled similarly. Will fluctuate. When the variation increases, the fluctuation range of the exhaust oxygen concentration detected by the oxygen sensor also increases, and the change rate of the exhaust oxygen concentration increases.

  In this regard, according to the above configuration, it can be determined that the variation in the air-fuel ratio between the cylinders of the internal combustion engine has increased due to the increase in the change rate of the exhaust oxygen concentration detected by the oxygen sensor. It is possible to accurately determine the occurrence of an abnormality that increases the variation.

  According to a sixth aspect of the present invention, in the exhaust oxygen concentration detection device according to any one of the first to fifth aspects, the engine system executes the air-fuel ratio control when the execution condition is not satisfied, and The gist of the present invention is to execute the air-fuel ratio control and the air-fuel ratio variation determination together when the execution condition is satisfied, without executing the fuel-fuel ratio variation determination.

  According to the above configuration, when both the air-fuel ratio control and the air-fuel ratio variation determination are executed, the detection response of the oxygen sensor is increased so that the determination accuracy of the air-fuel ratio variation determination has priority over the execution accuracy of the air-fuel ratio control. can do. In addition, when the air-fuel ratio control is executed without executing the air-fuel ratio variation determination, the detection response of the oxygen sensor can be lowered so that the air-fuel ratio control can be executed with high accuracy.

  As described above, according to the above configuration, the detection response of the oxygen sensor can be appropriately adjusted as compared with a device in which the detection response of the oxygen sensor is kept constant regardless of whether or not the air-fuel ratio variation determination is performed. Thus, it is possible to achieve both the execution of the air-fuel ratio control with high execution accuracy and the execution of the air-fuel ratio variation determination with high determination accuracy.

1 is a schematic diagram showing a schematic configuration of an engine system to which an oxygen concentration detection device according to an embodiment embodying the present invention is applied. The time chart which shows an example of transition of the oxygen concentration detected by an air fuel ratio sensor. The flowchart which shows the execution procedure of a temperature control process. The flowchart which shows the execution procedure of a temperature control process. The graph which shows an example of the relationship between the temperature of the detection element of an air fuel ratio sensor, response time, and intake air amount.

Hereinafter, an exhaust oxygen concentration detection apparatus according to the present invention will be described.
FIG. 1 shows a schematic configuration of an engine system to which an exhaust oxygen concentration detection device according to an embodiment embodying the present invention is applied.

  As shown in FIG. 1, the internal combustion engine 10 includes a plurality (four in the present embodiment) of cylinders (# 1 to # 4). The intake passage 11 of the internal combustion engine 10 includes a portion extending from each cylinder as a starting point (each intake branch passage 11a) and a collective portion (intake collect passage 11b) in which the intake branch passages 11a are gathered.

  A throttle valve 12 is provided in the intake manifold passage 11 b in the intake passage 11, and a throttle motor 13 is connected to the throttle valve 12. Through the operation control (throttle control) of the throttle motor 13, the opening degree (throttle opening degree TA) of the throttle valve 12 is adjusted. Through this throttle control, the passage cross-sectional area of the intake passage 11 (specifically, the intake manifold passage 11b) of the internal combustion engine 10 is adjusted, and the amount of air taken into each cylinder of the internal combustion engine 10 through the intake passage 11 Is adjusted.

  Each intake branch passage 11a (specifically, intake port) in the intake passage 11 is provided with a fuel injection valve 14 for injecting fuel. In the present embodiment, a total of four fuel injection valves 14 are provided for each intake branch passage 11a. Through the operation control (fuel injection control) of these fuel injection valves 14, the amount of fuel (fuel injection amount) injected into each intake branch passage 11a of the internal combustion engine 10 is adjusted.

  During operation of the internal combustion engine 10, the intake air passing through the intake branch passage 11a and the fuel injected from the fuel injection valve 14 are mixed and sucked into each cylinder of the internal combustion engine 10 to be mixed into each cylinder. Qi is formed.

  Each cylinder of the internal combustion engine 10 is provided with a spark plug 15. Through the operation control (ignition control) of the spark plug 15, the air-fuel mixture in each cylinder of the internal combustion engine 10 is ignited and combusted, and rotational torque is applied to the output shaft 16 of the internal combustion engine 10 by the energy generated by the combustion. .

  Combustion gas (exhaust gas) in each cylinder of the internal combustion engine 10 is discharged to the exhaust passage 17. The exhaust passage 17 includes a portion (each exhaust branch passage 17a) extending from each cylinder of the internal combustion engine 10 as a starting point and a collective portion (exhaust collect passage 17b) in which the exhaust branch passages 17a are gathered. .

  A three-way catalyst 18 is provided in the exhaust collecting passage 17 b in the exhaust passage 17. Exhaust gas from each cylinder of the internal combustion engine 10 is collected in the exhaust collecting passage 17b via the exhaust branch passages 17a, purified by the three-way catalyst 18, and then discharged to the outside of the exhaust passage 17.

  The engine system of the present embodiment includes various sensors for detecting the operating state of the internal combustion engine 10. Examples of various sensors include an accelerator sensor 21 for detecting an operation amount (accelerator operation amount ACC) of an accelerator operation member (not shown) such as an accelerator pedal, an intake passage 11 (specifically, an intake collective passage) of the internal combustion engine 10. An intake air amount sensor 22 for detecting the amount of air passing through 11b) (passage intake air amount GA) is provided. Further, the crank sensor 23 for detecting the rotational speed of the output shaft 16 (engine rotational speed NE) of the internal combustion engine 10, the air-fuel ratio sensor 24 for detecting the oxygen concentration OX of the exhaust, and the throttle opening TA are detected. A throttle sensor 25 for the purpose is also provided.

  Specifically, the air-fuel ratio sensor 24 is attached to a position upstream of the three-way catalyst 18 in the exhaust collecting passage 17b of the exhaust passage 17 in the exhaust flow direction. The air-fuel ratio sensor 24 is a well-known limiting current type oxygen sensor, and includes a detection element 24a sintered using zirconia as a material. The limit current type oxygen sensor is a sensor that obtains an output current according to the oxygen concentration of the exhaust gas, and the air-fuel ratio of the air-fuel mixture that is closely related to the oxygen concentration of the exhaust gas is a predetermined ratio (specifically Specifically, in the case of 14.5), the output current is almost “0”. The output current increases in the negative direction as the air-fuel ratio of the air-fuel mixture becomes rich, and the output current increases in the positive direction as the air-fuel ratio becomes lean. Therefore, based on the output signal of the air-fuel ratio sensor 24, the lean degree or rich degree of the air-fuel ratio of the air-fuel mixture can be detected.

  The air-fuel ratio sensor 24 has a built-in heater 24b. The heater 24b is for heating the detection element 24a, and the temperature of the detection element 24a can be adjusted through adjustment control (heater control) of power supplied to the heater 24b.

  The engine system according to the present embodiment includes an electronic control unit 20 mainly composed of a microcomputer and the like, and output signals of various sensors are taken into the electronic control unit 20. The electronic control unit 20 performs various calculations through calculation processes executed at predetermined intervals based on output signals of various sensors, and based on the calculation results, an internal combustion engine such as throttle control, fuel injection control, ignition control, heater control, etc. Various controls related to the operation of the engine 10 are executed.

  The throttle control according to the present embodiment is executed as follows. That is, first, a control target value (target throttle opening Tta) for the throttle opening TA is calculated based on the operating state of the internal combustion engine 10 (specifically, the accelerator operation amount ACC and the engine speed NE). Then, the operation of the throttle motor 13 is controlled so that the target throttle opening degree Tta and the actual throttle opening degree TA coincide with each other. As a result, the amount of air taken into each cylinder of the internal combustion engine 10 (intake air amount) is adjusted in accordance with the operating state of the internal combustion engine 10.

  Further, the fuel injection control of the present embodiment is executed as follows. That is, first, a control target value (target fuel injection amount TQ) for the fuel injection amount is calculated based on the passage intake air amount GA and the engine rotational speed NE. Then, each fuel injection valve 14 is driven to open so that the same amount of fuel as the target fuel injection amount TQ is injected. In the present embodiment, the operating state of the internal combustion engine 10 determined by the passage intake air amount GA and the engine rotational speed NE and the air-fuel ratio of the air-fuel mixture in each cylinder of the internal combustion engine 10 are set to a predetermined ratio (for example, 14.5). The relationship with the fuel injection amount that can be made is obtained in advance from the results of experiments and simulations and stored in the electronic control unit 20, and the target fuel injection amount TQ is calculated based on the relationship.

Further, in the present embodiment, so-called air-fuel ratio control is performed in which the fuel injection amount is feedback-controlled based on the detected value (oxygen concentration OX) of the air-fuel ratio sensor 24. This air-fuel ratio control is executed by the electronic control unit 20 as a calculation process for every predetermined period executed on condition that the execution condition is satisfied. The fact that the execution condition of the air-fuel ratio control is satisfied is determined by satisfying both of the following conditions.
The air-fuel ratio sensor 24 is activated (specifically, the temperature of the detection element 24a is equal to or higher than a predetermined temperature [for example, 300 ° C.]).
The warm-up of the internal combustion engine 10 is completed (specifically, the temperature of the engine cooling water is equal to or higher than a predetermined temperature [for example, 70 ° C.]).

  In the process related to the air-fuel ratio control, first, a deviation between the oxygen concentration OX of the exhaust detected by the air-fuel ratio sensor 24 and a predetermined concentration (oxygen concentration when the air-fuel ratio of the air-fuel mixture is the predetermined ratio) is calculated. And a correction term K is calculated based on the deviation. Then, a new target fuel injection amount TQ is calculated by correcting the target fuel injection amount TQ with the correction term K. In the present embodiment, the relationship between the deviation and the correction term K that can quickly reduce the deviation is obtained in advance from the results of experiments and simulations and stored in the electronic control unit 20. Based on the above, the correction term K is calculated. As the correction term K, a value for correcting the target fuel injection amount TQ to be larger as the deviation is larger is basically calculated. Through such air-fuel ratio control, the amount of fuel supplied to each cylinder of the internal combustion engine 10 is adjusted so that the air-fuel ratio of the air-fuel mixture of each cylinder of the internal combustion engine 10 matches the predetermined ratio. In the present embodiment, as the target fuel injection amount TQ and the correction term K, a value common to each cylinder of the internal combustion engine 10, that is, only one value is set.

In addition, the heater control of the present embodiment is executed as follows.
If the temperature of the detection element 24a is adjusted within an appropriate temperature range, the air-fuel ratio sensor 24 has a higher responsiveness for detecting the oxygen concentration of the exhaust gas as the temperature of the detection element 24a is higher. It has the characteristics. Therefore, if the detection responsiveness of the air-fuel ratio sensor 24 changes unnecessarily due to the temperature change of the detection element 24a, the fluctuation speed and fluctuation width of the detection value (oxygen concentration OX) of the air-fuel ratio sensor 24 also change unnecessarily. End up. Therefore, when the temperature of the detection element 24a changes during the execution of the air-fuel ratio control, the deviation and the correction term K calculated in the air-fuel ratio control also change accordingly, which is an unstable air-fuel ratio control. It will be a cause of inducing. Therefore, it can be said that it is important to maintain the temperature of the detection element 24a of the air-fuel ratio sensor 24 at an appropriate temperature in order to execute the air-fuel ratio control with high accuracy. In view of this point, in the present embodiment, the temperature of the detection element 24a of the air-fuel ratio sensor 24 is adjusted to an appropriate temperature through the execution of heater control.

  The detection element 24a of the air-fuel ratio sensor 24 has a characteristic that the impedance decreases as the temperature rises. In the heater control of the present embodiment, based on this point, the correlation value (specifically, admittance) of the impedance of the detection element 24a is detected based on the applied voltage, output current, etc. of the detection element 24a. The power supplied to the heater 24b is adjusted so that the detected admittance becomes a value corresponding to the target temperature. Specifically, this adjustment is performed by executing a control (so-called duty control) that alternately repeats supply and stop of power supply to the heater 24b and a ratio (duty ratio) between the time when the power is supplied and the time when the power is not supplied. ) Is adjusted. As a result, the temperature of the detection element 24a of the air-fuel ratio sensor 24 is adjusted to the target temperature. As the target temperature, a predetermined temperature TH1 (for example, 650 ° C.) is set when the air-fuel ratio control is executed.

  Here, in the fuel injection control and the air-fuel ratio control, the fuel supply amount to each cylinder of the internal combustion engine 10 is adjusted to be the same amount based on the common target fuel injection amount TQ and the correction term K. Therefore, although the average value of the air-fuel ratio of the air-fuel mixture in each cylinder of the internal combustion engine 10 can be adjusted to a ratio within a predetermined range (so-called window), the air-fuel ratio of the air-fuel mixture in each cylinder is adjusted individually. I can't do it. Therefore, the air-fuel ratio of the air-fuel mixture of each cylinder of the internal combustion engine 10 varies due to the influence of individual differences and deterioration of the intake system (intake port, intake valve, etc.) and fuel supply system (fuel injection valve 14, etc.) of the engine system. Inevitable.

  When such variation in the air-fuel ratio between the cylinders of the internal combustion engine 10 occurs, the oxygen concentration of the exhaust passing through the exhaust collecting passage 17b of the exhaust passage 17, that is, the exhaust flowing into the three-way catalyst 18, periodically varies. . When this variation becomes large, the oxygen concentration of the exhaust gas flowing into the three-way catalyst 18 periodically deviates from the concentration range corresponding to the window, so that the exhaust purification function of the three-way catalyst 18 is reduced. Exhaust properties will be deteriorated. Therefore, in the present embodiment, air-fuel ratio variation determination is performed to determine whether or not an abnormality (an abnormality in variation) that increases the degree of variation in the air-fuel ratio between the cylinders of the internal combustion engine 10 occurs.

  FIG. 2 shows an example of the transition of the oxygen concentration OX detected by the air / fuel ratio sensor 24. In FIG. 2, line L1 shows the transition of oxygen concentration OX when the degree of variation is very small, and line L2 in FIG. 2 shows the transition of oxygen concentration OX when the degree of variation is large. Yes.

  As shown by the line L1 in FIG. 2, when the variation in the air-fuel ratio between the cylinders of the internal combustion engine 10 is very small, the oxygen concentration of the exhaust gas passing through the exhaust collecting passage 17b hardly fluctuates. do not do. On the other hand, as shown by the line L2 in FIG. 2, when the variation in the air-fuel ratio between the cylinders of the internal combustion engine 10 is large, the fluctuation range of the oxygen concentration of the exhaust gas passing through the exhaust collecting passage 17b becomes large, and the oxygen The change rate of the concentration OX increases.

  Based on this point, in the air-fuel ratio variation determination according to the present embodiment, it is determined that a variation abnormality has occurred based on the change rate of the oxygen concentration OX being equal to or higher than a predetermined determination rate. . If it is determined that a variation abnormality has occurred, a warning lamp (not shown) provided in the vehicle interior is turned on, or a history of occurrence of the variation abnormality is stored in the electronic control unit 20. I am doing so. Thereby, when a variation abnormality occurs, it is possible to appropriately cope with this.

Specifically, the processing for air-fuel ratio variation determination is executed as follows.
This process is executed by the electronic control unit 20 as an interruption process for each predetermined period on condition that an execution condition for air-fuel ratio variation determination is satisfied during execution of the air-fuel ratio control. The fact that the air-fuel ratio variation determination execution condition is satisfied is determined by satisfying the condition that the engine speed NE is stable within a predetermined range (2000 to 3000 rpm). The

  In the present embodiment, when the execution condition of the air-fuel ratio control is not established, neither the air-fuel ratio control nor the air-fuel ratio variation determination is executed. In addition, when the execution condition of the air-fuel ratio control is satisfied, if the execution condition of the air-fuel ratio variation determination is not satisfied, the air-fuel ratio control is performed and the air-fuel ratio variation determination is not performed, and the execution condition of the air-fuel ratio variation determination is satisfied. Sometimes air-fuel ratio control and air-fuel ratio variation determination are both executed.

  In the process related to the air-fuel ratio variation determination, first, the first-order differential value of the oxygen concentration OX after the execution condition of the air-fuel ratio variation determination is satisfied is calculated and all the same-order differential values are stored. Specifically, as the first-order differential value, the difference between the oxygen concentration OX [i−1] at the previous execution of this process and the oxygen concentration OX [i] at the current execution (= OX [i−1]). -OX [i]) is calculated. Then, based on the stored first-order differential value, the timing T1 (see FIG. 2) at which the oxygen concentration OX, which is periodically changing, is minimized for the first time after the execution condition of the air-fuel ratio variation determination is satisfied. Thereafter, a timing T2 that once becomes maximum and a timing T3 that once becomes minimum after that are specified. As timings T1 and T3, the timing at which the same-order differential value is closest to “0” in the process of increasing the first-order differential value is adopted. As timing T2, the same-order differential value is used in the process of decreasing the first-order differential value. The timing closest to “0” is adopted.

  Thereafter, an average value of first-order differential values in a period from timing T1 to timing T2 is calculated, and the calculated value is stored as an increase rate Va of the oxygen concentration OX. In addition, an average value of first-order differential values in a period from timing T2 to timing T3 is calculated, and the calculated value is stored as a decrease rate Vb of the oxygen concentration OX.

After the change rate of oxygen concentration OX (specifically, increase rate Va and decrease rate Vb) is calculated in this manner, it is determined whether or not a variation abnormality has occurred based on the change rate. Specifically, when at least one of the following (determination condition a) and (determination condition b) is satisfied, it is determined that a variation abnormality has occurred, while those (determination condition a) and (determination condition b) ) Are not satisfied, it is determined that no variation abnormality has occurred.
(Determination condition a) The increase speed Va is equal to or higher than a predetermined determination speed J1.
(Determination condition b) The sum of the absolute value of the increase speed Va and the decrease speed Vb is not less than a predetermined determination speed J2.

  Note that both the determination speed J1 (determination condition A) and the determination speed J2 (determination condition B) are values that can accurately determine the occurrence of variation abnormality based on the results of experiments and simulations. It is obtained and stored in the electronic control unit 20.

  By the way, in the present embodiment, the fuel supply amount to each cylinder # 1 to # 4 of the internal combustion engine 10 is based on the correction term K calculated based on the detected value (oxygen concentration OX) of the air-fuel ratio sensor 24. It is adjusted to be the same amount.

  Therefore, when the air-fuel ratio control is executed, a value corresponding to the average value of the air-fuel ratio of each cylinder of the internal combustion engine 10 may be detected by the air-fuel ratio sensor 24, and the detection response required for the air-fuel ratio sensor 24 is low. At this time, if the detection responsiveness of the air-fuel ratio sensor 24 becomes excessively high, the fluctuation rate of the oxygen concentration OX increases or the fluctuation range increases, and the difference between the oxygen concentration OX and the concentration corresponding to the average value is increased. The air-fuel ratio control (specifically, the air-fuel ratio of the air-fuel mixture in each cylinder) tends to become unstable.

  On the other hand, when the air-fuel ratio variation determination is executed, if the detection responsiveness of the air-fuel ratio sensor 24 is low, the actual exhaust oxygen concentration fluctuation caused by the difference in the air-fuel ratio between the cylinders # 1 to # 4 of the internal combustion engine 10 is reduced. The air-fuel ratio sensor 24 may not be able to properly detect the air-fuel ratio sensor 24, and the air-fuel ratio sensor 24 is required to have high detection responsiveness in order to accurately detect the fluctuation of the exhaust oxygen concentration.

  Thus, the detection responsiveness required when the oxygen concentration is detected by the air-fuel ratio sensor 24 differs between the execution of the air-fuel ratio control and the execution of the air-fuel ratio variation determination, and both the air-fuel ratio control and the air-fuel ratio variation determination are accurate. In order to perform well, it is necessary to set the detection response of the air-fuel ratio sensor 24 appropriately.

  In view of this point, in the present embodiment, the temperature of the air-fuel ratio sensor 24 is adjusted to be higher than the temperature when the air-fuel ratio variation determination is not performed, compared to the temperature when the air-fuel ratio variation determination is not performed. Like to do.

  As a result, when the air-fuel ratio variation determination is performed, the detection element 24a of the air-fuel ratio sensor 24 becomes high temperature and the detection responsiveness is increased, and the cylinders # 1 to ## of the internal combustion engine 10 are increased by the air-fuel ratio sensor 24. Thus, the variation in the exhaust gas oxygen concentration due to the difference in the exhaust gas oxygen concentration 4 is properly detected, and the air-fuel ratio variation determination is performed with high accuracy. At this time, the air-fuel ratio control is also executed, but the detection responsiveness of the air-fuel ratio sensor 24 is set higher so that the determination accuracy of the air-fuel ratio variation determination is given priority over the execution accuracy of the air-fuel ratio control.

  On the other hand, when the air-fuel ratio variation determination is not executed, the detection element 24a of the air-fuel ratio sensor 24 becomes relatively low temperature and the detection response becomes low. A value close to the average value of the oxygen concentration is appropriately detected, and the air-fuel ratio control is accurately executed based on the detected value.

  As described above, in the engine system according to the present embodiment, the detection of the air-fuel ratio sensor 24 is performed in comparison with the device in which the detection response of the air-fuel ratio sensor 24 is kept constant regardless of whether the air-fuel ratio variation determination is performed. The responsiveness can be adjusted appropriately, and both the execution of the air-fuel ratio control with high execution accuracy and the execution of the air-fuel ratio variation determination with high determination accuracy can be achieved. In the present embodiment, the electronic control unit 20 functions as a unit that adjusts the power supplied to the heater 24b.

  Further, in the present embodiment, along with such a change in the temperature of the detection element 24a of the air-fuel ratio sensor 24, a deterioration abnormality of the air-fuel ratio sensor 24 is determined. The process related to the determination of the deterioration abnormality (deterioration abnormality determination process) is executed based on the following idea.

  As described above, the impedance of the detection element 24a of the air-fuel ratio sensor 24 decreases as the temperature of the detection element 24a increases. In the heater control of the present embodiment, the power supplied to the heater 24b is adjusted so that the correlation value (admittance) of the impedance of the detection element 24a matches the value corresponding to the target temperature. Therefore, when the impedance of the detection element 24a increases due to deterioration, the power supplied to the heater 24b becomes unnecessarily large by the amount for reducing the increase, and the power consumption of the heater 24b increases. Therefore, it can be said that the deterioration abnormality of the air-fuel ratio sensor 24 can be determined when the power consumption of the heater 24b is increased in this way.

  However, the exhaust gas temperature of the internal combustion engine 10 varies greatly depending on its operating state, and the power consumption of the heater 24b necessary to maintain the temperature of the detection element 24a of the air-fuel ratio sensor 24 at the target temperature is also the engine from time to time. Since it varies greatly depending on the operating state, it is difficult to accurately determine the deterioration abnormality of the air-fuel ratio sensor 24 even by simply monitoring the power consumption of the heater 24b.

  Here, when the impedance of the detection element 24a increases due to deterioration, the power consumption of the heater 24b increases, and the difference in power consumption of the heater 24b before and after the execution of the air-fuel ratio variation determination is stopped. Also grows. Although the difference in power consumption also varies depending on the operating state of the internal combustion engine 10, the range of change accompanying the change in the engine operating state is accompanied by the change in the engine operating state of the power consumption of the heater 24b at that time. It has been confirmed by the inventor that it is much smaller than the change width.

  Based on this point, in the present embodiment, the difference ΔW in power consumption of the heater 24b before and after the execution of the air-fuel ratio variation determination is stopped is calculated, and on the condition that the difference ΔW is equal to or greater than a predetermined determination value J3. An abnormality in the deterioration of the air-fuel ratio sensor 24 is determined. As a result, when the difference ΔW in the power consumption of the heater 24b before and after the stop of the execution of the air-fuel ratio variation determination is large, it is assumed that this is caused by the deterioration of the air-fuel ratio sensor 24. Abnormalities can be accurately determined.

Hereinafter, processing related to the temperature adjustment of the air-fuel ratio sensor 24 including the deterioration abnormality determination processing (temperature adjustment processing) will be described with reference to the flowcharts shown in FIGS. 3 and 4.
The series of processes shown in this flowchart conceptually shows a specific execution procedure of the temperature adjustment process, and the actual process is executed by the electronic control unit 20 as an interrupt process for each predetermined period. The The temperature adjustment process is executed on condition that the execution condition of the air-fuel ratio control is satisfied. In the present embodiment, this temperature adjustment process functions as a temperature adjustment means and a deterioration determination means.

  As shown in FIG. 3, in this process, first, it is determined whether or not an execution condition for the air-fuel ratio variation determination is satisfied (step S101). When the air-fuel ratio variation determination execution condition is not satisfied (step S101: NO), this processing is terminated without executing the following processing.

  After that, when this process is repeatedly executed and it is determined that the air-fuel ratio variation determination execution condition is satisfied (step S101: YES), the predetermined temperature TH2 is set as the target temperature of the detection element 24a of the air-fuel ratio sensor 24. Is set (step S102). As the predetermined temperature TH2, a temperature (for example, 850 ° C.) higher than the target temperature (the predetermined temperature TH1) when the execution condition of the air-fuel ratio variation determination is not satisfied, that is, when the air-fuel ratio variation determination is not executed is set. Thereby, the power supplied to the heater 24b is adjusted so that the temperature of the detection element 24a of the air-fuel ratio sensor 24 becomes the predetermined temperature TH2 through the heater control thereafter.

  When the temperature of the detection element 24a of the air-fuel ratio sensor 24 reaches the predetermined temperature TH2 through such heater control (step S103: YES), based on the admittance of the heater 24b, the energization time (specifically, the duty ratio), and the applied voltage. The power consumption amount Wst per unit time of the heater 24b is calculated and stored (step S104).

  In addition, execution of the air-fuel ratio variation determination described above is started (step S105). As a result, the temperature of the detection element 24a of the air-fuel ratio sensor 24 is substantially the predetermined temperature TH2, that is, the detection responsiveness of the air-fuel ratio sensor 24 is a value suitable for executing the air-fuel ratio variation determination. The air-fuel ratio variation determination is executed below, and the air-fuel ratio variation determination can be performed with high accuracy.

  Thereafter, when the execution of the air-fuel ratio variation determination is completed (step S106: YES), the predetermined temperature TH1 is set as the target temperature of the detection element 24a of the air-fuel ratio sensor 24 (step S107). As a result, the temperature of the detection element 24a of the air-fuel ratio sensor 24 decreases to a predetermined temperature TH1, that is, a temperature at which the detection responsiveness of the air-fuel ratio sensor 24 becomes a value suitable for execution of the air-fuel ratio control. When the temperature of the detection element 24a of the air-fuel ratio sensor 24 reaches the predetermined temperature TH1, the air-fuel ratio control is performed under a situation where the detection responsiveness of the air-fuel ratio sensor 24 is a value suitable for execution of the air-fuel ratio control. As a result, the air-fuel ratio control can be executed with high accuracy.

  Further, when the temperature of the detection element 24a of the air-fuel ratio sensor 24 reaches the predetermined temperature TH1 through the heater control (step S108: YES), the unit per unit time of the heater 24b is based on the admittance, energization time, and applied voltage of the heater 24b. The power consumption amount Wsp is calculated and stored (step S109).

  Then, as shown in FIG. 4, a difference ΔW (Wst−Wsp) between the power consumption amount Wst of the heater 24b and the non-execution power consumption amount Wsp when the air-fuel ratio variation determination is performed is calculated. It is determined whether or not the difference ΔW is greater than or equal to a determination value J3 (step S110). As the determination value J3, a value capable of accurately determining that the deterioration of the air-fuel ratio sensor 24 has progressed excessively is obtained in advance based on the results of experiments and simulations and stored in the electronic control unit 20. Has been.

  If the difference ΔW is equal to or greater than the determination value J3 (step S110: YES), it is determined that a deterioration abnormality has occurred (step S111), assuming that the deterioration of the air-fuel ratio sensor 24 has progressed. On the other hand, when the difference ΔW is less than the determination value J3 (step S110: NO), the process of step S111 is jumped on the assumption that the air-fuel ratio sensor 24 has not deteriorated or has not deteriorated so much. As described above, after the presence / absence of the deterioration abnormality of the air-fuel ratio sensor 24 is determined based on the difference ΔW, the present process is terminated.

As described above, according to the present embodiment, the effects described below can be obtained.
(1) The temperature of the detection element 24a of the air-fuel ratio sensor 24 is adjusted to be higher than the temperature when the air-fuel ratio variation determination is not performed, compared to the temperature when the air-fuel ratio variation determination is not performed. . For this reason, when the air-fuel ratio variation determination is performed, the air-fuel ratio sensor 24 becomes high in temperature and the detection response becomes high. Therefore, the exhaust gas of the cylinders # 1 to # 4 of the internal combustion engine 10 is detected by the air-fuel ratio sensor 24. Variations in the exhaust oxygen concentration due to the difference in oxygen concentration can be detected appropriately, and air-fuel ratio variation determination can be performed with high accuracy. In addition, when the air-fuel ratio variation determination is not performed, the air-fuel ratio sensor 24 becomes relatively low in temperature and the detection response becomes low. A value close to the average value of the concentration can be detected appropriately, and the air-fuel ratio control can be accurately executed based on the detected value. Therefore, in order to execute both the air-fuel ratio control and the air-fuel ratio variation determination with high accuracy, it is possible to appropriately adjust the responsiveness for detecting the oxygen concentration of the exhaust gas.

  (2) Deterioration abnormality of the air-fuel ratio sensor 24 is determined on the condition that the difference ΔW in the power consumption of the heater 24b before and after the execution stop of the air-fuel ratio variation determination is equal to or greater than a predetermined determination value J3. Therefore, the deterioration abnormality of the air-fuel ratio sensor 24 can be accurately determined based on the increase in the difference ΔW.

  (3) In the air-fuel ratio variation determination, it is determined that the variation in the air-fuel ratio between the cylinders # 1 to # 4 of the internal combustion engine 10 is increased when the change rate of the oxygen concentration OX is increased. The occurrence of abnormality can be accurately determined.

  (4) When both the air-fuel ratio control and the air-fuel ratio variation determination are executed, the detection response of the air-fuel ratio sensor 24 is increased so that the determination accuracy of the air-fuel ratio variation determination is given priority over the execution accuracy of the air-fuel ratio control. be able to. In addition, when the air-fuel ratio control is executed without executing the air-fuel ratio variation determination, the detection responsiveness of the air-fuel ratio sensor 24 can be lowered to execute the air-fuel ratio control with high accuracy. Therefore, the detection responsiveness of the air-fuel ratio sensor 24 can be appropriately adjusted as compared with a device in which the detection responsiveness of the air-fuel ratio sensor 24 is kept constant regardless of whether the air-fuel ratio variation determination is performed or not. It is possible to achieve both the execution of air-fuel ratio control with execution accuracy and the execution of air-fuel ratio variation determination with high determination accuracy.

The embodiment described above may be modified as follows.
Instead of detecting the admittance of the detection element 24a as a value used for adjusting the temperature of the detection element 24a of the air-fuel ratio sensor 24 or calculating the power consumption of the heater 24b, the impedance of the detection element 24a is detected. Also good.

In the temperature adjustment process (FIGS. 3 and 4), the process (step S104, steps S109 to S111) relating to the deterioration abnormality determination may be omitted.
-When executing the air-fuel ratio variation determination, the execution of the air-fuel ratio control may be stopped without being limited to executing the air-fuel ratio control together. In this case, at the time of executing the air-fuel ratio control, a learning process for learning a steady deviation from the reference value (for example, [0]) of the correction term K as the air-fuel ratio learned value is executed, and the air-fuel ratio control is not executed. It is desirable to stop the calculation of the correction term K and correct the target fuel injection amount TQ with the same air-fuel ratio learning value.

  In the air-fuel ratio variation determination, the determination condition for determining whether or not a variation abnormality has occurred can be arbitrarily changed. Specifically, either (determination condition a) or (determination condition b) can be omitted. In place of (judgment condition a) and (judgment condition b), or in addition, a condition that “the absolute value of the decrease speed Vb is equal to or greater than a predetermined judgment speed”, or “an increase speed Va and a decrease speed” It is also possible to set a condition that the higher speed of the absolute value of Vb is equal to or higher than a predetermined determination speed. In addition, the variation range of the oxygen concentration OX during the execution of the air-fuel ratio variation determination may be calculated, and it may be determined that the variation abnormality has occurred when the variation range is equal to or greater than a predetermined determination value.

  -The calculation method of the change rate of oxygen concentration OX can be changed arbitrarily. For example, when calculating the increase speed Va and the decrease speed Vb, the first-order differential values calculated at the timing immediately before and after the timing T1, T2, T3 may not be used. In addition, a first-order differential value at a predetermined timing (a timing corresponding to the middle between timings T1 and T2 or a timing corresponding to the middle between timings T2 and T3) can also be calculated as a change rate of the oxygen concentration OX.

  Instead of adjusting the temperature of the detection element 24a of the air-fuel ratio sensor 24 so that it becomes a predetermined constant temperature (predetermined temperature TH1 or predetermined temperature TH2) when the air-fuel ratio variation determination is not performed or is performed. Thus, the temperature of the detection element 24a may be adjusted so as to become lower as the intake air amount of the internal combustion engine 10 is larger.

  The larger the intake air amount of the internal combustion engine 10, the greater the exhaust amount of the internal combustion engine 10, that is, the greater the amount of exhaust gas that passes through the portion of the exhaust passage 17 where the air-fuel ratio sensor 24 is disposed (specifically, the exhaust collecting passage 17b). When the amount of oxygen passing through the arrangement portion increases, the rate of change of the detected value (oxygen concentration OX) of the air-fuel ratio sensor 24 increases, for example, the speed at which the exhaust inside the air-fuel ratio sensor 24 is replaced. Becomes higher. Therefore, it can be said that as the intake air amount of the internal combustion engine 10 increases, the followability of the oxygen concentration OX to the actual change in the oxygen concentration of the exhaust gas also increases.

  FIG. 5 shows the time required for the temperature of the detection element 24a of the air-fuel ratio sensor 24 and the oxygen concentration OX to become values corresponding to the actual exhaust oxygen concentration when the air-fuel ratio of the air-fuel mixture is changed in the same manner ( An example of the relationship between the response time) and the intake air amount of the internal combustion engine 10 is shown. As is apparent from FIG. 5, the change rate of the oxygen concentration OX increases as the intake air amount of the internal combustion engine 10 increases.

  The difference in the change rate of the oxygen concentration OX due to the difference in the intake air amount is similar to the difference in detection responsiveness due to the difference in the temperature of the detection element 24a of the air-fuel ratio sensor described above, and the execution accuracy of the air-fuel ratio control and the variation in the air-fuel ratio. There is a possibility that it may cause a decrease in the determination accuracy of the determination.

  In this regard, in the above configuration, the temperature of the detection element 24a is lowered so that the detection response of the air-fuel ratio sensor 24 becomes lower as the intake air amount of the internal combustion engine 10 is larger and the change rate of the oxygen concentration OX is higher. Adjusted. As a result, the temperature of the detection element 24a of the air-fuel ratio sensor 24 is changed and its detection response is set so as to suppress the difference in the change rate of the oxygen concentration OX caused by the difference in the intake air amount of the internal combustion engine 10. Will be able to. Therefore, according to the above configuration, it is possible to suppress the difference in the change rate of the oxygen concentration OX and the occurrence of an error due to the difference, and the air-fuel ratio control and the air-fuel ratio variation determination can be executed with high accuracy. .

  -If the present invention is an engine system in which both air-fuel ratio control and air-fuel ratio variation determination are executed based on the detection value of the oxygen sensor, a limit current type oxygen sensor (so-called air-fuel ratio sensor) The present invention can be applied not only to an engine system provided with a) but also to an engine system provided with a concentration cell type oxygen sensor (so-called O2 sensor). The concentration cell type oxygen sensor has an output voltage of about 1.0 volts when the oxygen concentration of the exhaust gas is a concentration when the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio. When the oxygen concentration is the concentration when the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, this is an oxygen sensor of an output voltage that is about 0 volts.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Intake passage, 11a ... Intake branch passage, 11b ... Intake collecting passage, 12 ... Throttle valve, 13 ... Throttle motor, 14 ... Fuel injection valve, 15 ... Spark plug, 16 ... Output shaft, 17 ... Exhaust passage, 17a ... exhaust branch passage, 17b ... exhaust collecting passage, 18 ... three-way catalyst, 20 ... electronic control unit, 21 ... accelerator sensor, 22 ... intake air amount sensor, 23 ... crank sensor, 24 ... air-fuel ratio sensor, 24a ... detection element, 24b ... heater.

Claims (6)

An oxygen sensor is provided upstream of the three-way catalyst in the exhaust flow direction of the collective portion of the exhaust passage of the multi-cylinder internal combustion engine to detect the oxygen concentration of the exhaust of the internal combustion engine, and the mixture gas in each cylinder of the internal combustion engine Exhaust gas applied to an engine system that executes both air-fuel ratio control for adjusting the air-fuel ratio and air-fuel ratio variation determination for determining variation in the air-fuel ratio of the air-fuel mixture between the cylinders of the internal combustion engine based on the detection value of the oxygen sensor. In the oxygen concentration detection device,
Exhaust gas comprising temperature adjusting means for adjusting the temperature of the oxygen sensor at the time of execution of the air-fuel ratio variation determination to a high temperature as compared to the temperature of the oxygen sensor at the time of non-execution of the air-fuel ratio variation determination. Oxygen concentration detector. The exhaust oxygen concentration detection device according to claim 1,
The exhaust oxygen concentration detection device according to claim 1, wherein the temperature adjusting means adjusts the temperature of the oxygen sensor to a lower temperature as the intake air amount of the internal combustion engine increases. The exhaust oxygen concentration detection device according to claim 1 or 2,
The exhaust gas oxygen concentration detecting device according to claim 1, wherein the temperature adjusting means includes a heater for heating the oxygen sensor and a device for adjusting power supplied to the heater. The exhaust oxygen concentration detection device according to claim 3,
The oxygen sensor has a detection element whose impedance increases with increasing temperature,
The temperature adjusting means detects the correlation value of the impedance of the detection element, and adjusts the power supplied to the heater based on the correlation value.
The exhaust oxygen concentration detection device determines deterioration abnormality of the oxygen sensor on the condition that a difference in power consumption of the heater before and after execution stop of the air-fuel ratio variation determination is equal to or greater than a predetermined determination value. An exhaust oxygen concentration detection device further comprising: In the exhaust gas oxygen concentration detection device according to any one of claims 1 to 4,
In the engine system, in the air-fuel ratio variation determination, the variation in the air-fuel ratio of the air-fuel mixture between the cylinders of the internal combustion engine is large when the change rate of the oxygen concentration detected by the oxygen sensor is equal to or higher than a predetermined determination speed. An exhaust oxygen concentration detection device characterized by determining that an abnormality has occurred. In the exhaust gas oxygen concentration detection device according to any one of claims 1 to 5,
The engine system executes the air-fuel ratio control when the execution condition is not satisfied, makes the air-fuel ratio variation determination non-executed, and executes both the air-fuel ratio control and the air-fuel ratio variation determination when the execution condition is satisfied. An exhaust oxygen concentration detection device characterized by the above.

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