JP2008002440A - Abnormality determination device for exhaust gas concentration sensor of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect an abnormality of a NOx sensor irrespective of whether a NOx catalyst deteriorates or not. <P>SOLUTION: An abnormality of the NOx sensor is determined from an output of the NOx sensor when an NOx concentration of exhaust gas is varied before the activation of the NOx catalyst. The activation of the NOx catalyst is estimated from a temperature of cooling water, and a concentration of NOx in exhaust gas is varied by controlling EGR. An abnormality of the NOx sensor is determined based on whether a difference between a controlled NOx concentration and the NOx concentration detected by the NOx sensor is in a predetermined range, or whether an output of the NOx sensor corresponding to the controlled NOx concentration is in a fixed period of time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an abnormality determination device for an exhaust gas concentration sensor of an internal combustion engine.

  Conventionally, an exhaust gas concentration sensor for detecting an exhaust gas concentration is provided in an exhaust passage of the internal combustion engine, and a fuel injection amount of the internal combustion engine is controlled based on an output value of the exhaust gas concentration sensor. If the exhaust gas concentration sensor is abnormal, optimal engine control is not performed, so it is necessary to determine whether or not the exhaust gas concentration sensor is abnormal. Generally, in an exhaust gas concentration sensor such as a NOx sensor or an air-fuel ratio sensor, when the output value is smaller than a value that can be taken when it is normally normal, the exhaust gas concentration sensor is determined to be abnormal. .

  However, when the catalyst is disposed upstream of the exhaust gas concentration sensor, the exhaust gas concentration reaching the exhaust gas concentration sensor is reduced by the purification action of the catalyst, and the difference from the reference concentration that determines that the exhaust gas concentration sensor is abnormal is reduced. There was a problem that the accuracy of determination of abnormality of the exhaust gas concentration sensor was low.

In order to solve this problem, in the known document shown in Patent Document 1, the exhaust gas concentration exhausted from the engine is forcibly greatly vibrated to improve the determination accuracy of the abnormality determination of the exhaust gas concentration sensor.
JP 2003-120399 A

  The abnormality detection device for a NOx sensor, which is a kind of exhaust gas concentration sensor, disclosed in Patent Document 1 described above detects abnormality in the NOx sensor regardless of whether or not the NOx catalyst arranged upstream of the NOx sensor is activated. Judgment. However, if the sensor deterioration determination is performed while the NOx catalyst is activated, there is a problem that the NOx sensor abnormality determination is erroneously determined. Hereinafter, the reason for causing the problem will be described in detail with reference to FIGS.

    FIG. 5 is a diagram schematically showing changes in the NOx concentration before and after the NOx catalyst when exhaust gas containing NOx flows into the NOx catalyst. In FIG. 5, the solid line indicates the NOx concentration in the exhaust gas flowing into the NOx catalyst, and the broken line indicates the NOx concentration in the exhaust gas downstream of the NOx catalyst when the NOx catalyst is normal. The alternate long and short dash line indicates the NOx concentration in the exhaust gas downstream of the NOx catalyst when the NOx catalyst is deteriorated. FIG. 6 is a diagram schematically showing values output from the NOx sensor when exhaust gas containing NOx passes through the NOx sensor. In FIG. 6, the solid line indicates the output when the NOx sensor 21 is normal, and the broken line indicates the output when the NOx sensor 21 is abnormal.

  When the NOx concentration in the exhaust gas flowing into the NOx catalyst is changed as shown by the solid line in FIG. 5, the NOx catalyst is normal before the NOx catalyst is activated, for example, during a cold start of the engine. In both cases, the concentration downstream of the NOx catalyst is almost the same as the fluctuation of the NOx concentration before the NOx catalyst. This is because before the NOx catalyst is activated, the NOx purification ability is low regardless of whether the NOx catalyst is normal or deteriorated, so that the NOx in the exhaust gas flowing into the NOx catalyst passes through without being purified. Because.

  On the other hand, after the NOx catalyst is activated, there is a difference in the output of the NOx sensor between when the NOx catalyst is deteriorated and when it is normal. That is, when the NOx catalyst is deteriorated, the NOx catalyst can hardly purify NOx, and therefore, the NOx concentration (dashed line) after passing through the NOx catalyst is slightly higher than the NOx concentration (solid line) flowing into the NOx catalyst. Transition at small concentrations. On the other hand, since most NOx can be purified when the NOx catalyst is normal, the NOx concentration (broken line) after passing through the NOx catalyst is very small.

  Next, output when the NOx sensor is normal and abnormal will be described with reference to FIG. When the NOx sensor is normal, the output (solid line) of the NOx sensor increases in proportion to the NOx concentration. On the other hand, when the NOx sensor is abnormal, the output value of the NOx sensor decreases as indicated by a broken line. One reason for this is that the exhaust passage of the NOx sensor is clogged by substances contained in the exhaust gas, and the exhaust passage diameter is reduced, so that the amount of gas that originally reaches the detection portion of the NOx sensor is reduced. It is thought to be a factor. Moreover, it is thought that one factor is that the sensitivity of the NOx sensor becomes dull due to deterioration of the NOx sensor.

  Conventionally, when the NOx sensor abnormality determination is made after the NOx catalyst is activated, there are cases in which an erroneous determination is made as follows. That is, when the NOx catalyst is normal, exhaust gas having a low NOx concentration flows into the NOx sensor as indicated by the broken line in FIG. 5 as described above. If the NOx sensor is normal at this time, the NOx sensor outputs the same low NOx concentration as the broken line. On the other hand, when the NOx catalyst is deteriorated, exhaust gas having a high NOx concentration flows into the NOx sensor as indicated by a one-dot chain line. However, if the NOx sensor is abnormal at this time, the output of the NOx sensor shows a value lower than the actual NOx concentration. Therefore, when the concentration output from the NOx sensor is a low value, it is not possible to identify whether the NOx catalyst is low because the NOx catalyst is normal, or whether it is low because the NOx sensor is abnormal. As a result, there has been a problem that the abnormality of the NOx sensor cannot be detected with high accuracy.

  The present invention has been made in order to solve the above-described problem, and in determining the abnormality of the exhaust gas sensor, the influence of the deterioration of the catalyst provided upstream of the exhaust gas concentration sensor is eliminated, thereby correcting the abnormality of the exhaust gas concentration sensor. An object of the present invention is to provide an abnormality determination device for an exhaust gas concentration sensor that can detect the above with high accuracy.

  An abnormality determination device for an exhaust gas concentration sensor according to claim 1 is a catalyst provided in an exhaust passage of an internal combustion engine, an exhaust gas concentration sensor that is provided downstream of the catalyst and detects a concentration of a specific component of the exhaust gas; An activation detecting means for detecting the presence or absence of activation of the catalyst, and a concentration of a specific component of the exhaust gas detected by the exhaust gas concentration sensor when the activation detecting means determines that the catalyst is not activated. And an abnormality determining means for determining abnormality of the exhaust gas concentration sensor based on the above. Before the catalyst is activated, regardless of whether the catalyst has deteriorated or not, the concentration of a specific component of the exhaust gas downstream of the catalyst does not substantially change, so it is possible to accurately determine the abnormality of the exhaust gas concentration sensor. .

  The abnormality determination device for an exhaust gas concentration sensor according to claim 2 further comprises concentration changing means for changing the concentration of a specific component of the exhaust gas flowing into the catalyst, and the abnormality determining means is provided to the catalyst by the concentration changing means. An abnormality of the exhaust gas concentration sensor is determined based on the concentration of the specific component of the exhaust gas detected by the exhaust gas concentration sensor when the concentration of the specific component of the inflowing exhaust gas is changed. . As a result, a change occurs in the output of the exhaust gas concentration sensor, and the abnormality of the exhaust gas concentration sensor is determined based on the change, so that the abnormality of the exhaust gas concentration sensor can be determined with higher accuracy.

  The abnormality determination device for the exhaust gas concentration sensor according to claim 3, wherein the concentration changing means varies the concentration of a specific component of the exhaust gas flowing into the catalyst, and the abnormality determination means is detected by the exhaust gas concentration sensor. The exhaust gas concentration sensor is determined to be abnormal when the amplitude of the concentration of the specific component of the exhaust gas is equal to or less than the target amplitude. As a result, a change occurs in the output of the exhaust gas concentration sensor a plurality of times, and the number of times the abnormality of the exhaust gas concentration sensor is determined increases, so that the abnormality of the exhaust gas concentration sensor can be determined with higher accuracy.

  The abnormality determination device for the exhaust gas concentration sensor according to claim 4, wherein the abnormality determination means indicates that the exhaust gas concentration sensor is abnormal when the concentration of a specific component of the exhaust gas detected by the exhaust gas concentration sensor is equal to or lower than the target concentration. It is determined that it is.

  The abnormality determination device for an exhaust gas concentration sensor according to claim 5, wherein in the abnormality determination means, when the concentration of the specific component of the exhaust gas flowing into the catalyst is changed by the concentration changing means, the changed exhaust gas is changed. When the response of the output of the exhaust gas concentration sensor corresponding to the concentration of the specific component is not within a predetermined period, it is determined that the exhaust gas concentration sensor is abnormal.

  The abnormality determination device for an exhaust gas concentration sensor according to claim 6 is characterized in that the concentration changing means is an EGR rate control means for controlling the EGR rate in the cylinder.

  The abnormality determination device for an exhaust gas concentration sensor according to claim 7 is characterized in that the exhaust gas concentration sensor is a NOx sensor and the catalyst is a NOx catalyst.

  According to the present invention, the abnormality of the exhaust gas concentration sensor can be accurately determined regardless of whether or not the catalyst has deteriorated by determining the abnormality of the exhaust gas concentration sensor before the catalyst is activated. it can.

  Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, a NOx sensor which is a kind of exhaust gas concentration sensor will be described, but other sensors such as an air-fuel ratio sensor, an oxygen sensor, a hydrogen sensor, and an HC sensor may be used. Further, although an embodiment in which the present invention is applied to a direct injection gasoline engine will be described, the present invention can be applied to an intake port injection engine or a diesel engine.

[Example 1]
FIG. 1 is a diagram for explaining the configuration of an engine 1 (internal combustion engine) used in the first embodiment. The engine 1 includes a plurality of cylinders 2 (only one is shown) and includes a piston 3 that reciprocates within the cylinder 2, and a combustion chamber 4 is formed by the cylinder 2 and the piston 3. An ignition plug 5 that explodes a mixture of intake air and fuel filled in the combustion chamber 4 is attached to the upper portion of the combustion chamber 4, and a fuel injection valve 6 that directly injects fuel into the combustion chamber 4 is attached. ing.

  The combustion chamber 4 is connected to an intake passage 9 through an intake port 8 in which an intake valve 7 is disposed. The intake passage 9 includes an air cleaner 10 that filters intake air, an airflow sensor 11 that detects the intake air amount, a throttle valve 12 that restricts the intake passage 9 and adjusts the intake air amount, and a surge, in that order from the upstream side. A tank 13 is provided.

  The throttle valve 12 is provided with a throttle opening sensor 14 that detects the opening of the throttle valve 12.

  The combustion chamber 4 is connected to an exhaust passage 17 via an exhaust port 16 provided with an exhaust valve 15, and the exhaust passage 17 from each cylinder 2 joins downstream. In the joined exhaust passage 17, in order from the upstream side, a three-way catalyst 18 that purifies HC, CO, and NOx with a theoretical air-fuel ratio, an oxygen sensor 19 that detects the oxygen concentration in the exhaust gas, and NOx in the exhaust gas. And a NOx sensor 21 that detects the NOx concentration of the exhaust gas that has passed through the NOx catalyst 20 is provided.

  The NOx catalyst 20 holds NOx when the exhaust gas oxygen concentration is in a lean state, and the retained NOx is reduced and purified by HC in the exhaust gas when the exhaust gas oxygen concentration is low or in a stoichiometric state. To do. The NOx catalyst 20 has a property that its ability to purify NOx is small when the temperature of the catalyst is equal to or lower than a predetermined temperature, that is, before the NOx catalyst 20 is activated. That is, as shown in FIG. 6, before the NOx catalyst 20 is activated, unlike after it is activated, the NOx in the exhaust gas downstream of the NOx catalyst 20 regardless of whether or not the NOx catalyst 20 is deteriorated. The density is almost the same.

  The NOx sensor 21 is a sensor that generates an output corresponding to the NOx concentration in the exhaust gas, and a schematic diagram thereof is shown in FIG. The NOx sensor 21 has an exhaust gas passage 51 into which exhaust gas flows, and three cells of an oxygen pump cell 52, a monitor cell 53, and a sensor cell 54 are arranged in the exhaust gas passage 51 from the upstream side. One end of each cell is provided in the exhaust gas passage 51, and the other end is provided in the atmospheric spaces 55 and 56 into which the atmosphere flows. In addition, the solid line arrow in FIG. 2 shows the flow of exhaust gas.

  Oxygen in the exhaust gas flowing into the exhaust gas passage of the NOx sensor 21 comes into contact with the oxygen pump cell 52 to which a predetermined voltage is applied from a voltage source (not shown) and is ionized, and passes through the atmospheric spaces 55 and 56 outside the NOx sensor 21. Almost pumped out. At this time, HC, CO, etc. other than NOx are simultaneously combusted on the oxygen pump cell 52, and NOx is reduced to a single gas (NO). The exhaust gas converted into NO and a small amount of oxygen by the oxygen pump cell 52 is then brought into contact with the monitor cell 53, and oxygen in the exhaust gas is ionized by the monitor cell 53 to which a predetermined voltage is applied from a voltage source (not shown). Pumped out of the sensor 21. At this time, the oxygen concentration of the exhaust gas in contact with the monitor cell 53 is detected from the current flowing through the monitor cell 53, and the amount of oxygen pumped out in the oxygen pump cell 52 so that the amount of oxygen in the exhaust gas flowing into the monitor cell 53 becomes a constant value. That is, the voltage value is controlled. The exhaust gas that comes into contact with the monitor cell 53 and is almost NO only finally comes into contact with the sensor cell 54. Then, NO is decomposed into nitrogen and oxygen on the sensor cell 54, and oxygen is pumped out of the NOx sensor 21 in the same manner as the oxygen pump cell 52 and the monitor cell 53. At that time, the current flowing through the sensor cell 54 is measured by the detection unit 57, and the NO amount is detected from the detected current value. The concentration of NOx can be detected based on the NO amount.

  The NOx sensor 21 is warmed by the heater 58. Thereby, the activation of the NOx sensor 21 is accelerated, and the NOx concentration in the exhaust gas can be detected at an early stage.

  Next, as shown in FIG. 1, one end of an EGR passage 22 that recirculates part of the exhaust gas to the intake passage is connected to the exhaust passage 17 upstream of the oxygen sensor. The other end of the EGR passage 22 is connected to the surge tank 13.

  The EGR passage 22 is provided with an EGR valve 23 that can electrically adjust the passage diameter of the EGR passage 22 and an EGR opening degree sensor 24 that detects the opening degree of the EGR valve 23 that changes the passage diameter of the EGR passage 22. These constitute the exhaust gas recirculation means.

  The engine 1 also includes an ECU 25 that issues a control command for the engine 1. The ECU 25 is composed of a digital computer and has a RAM 27, a ROM 28, a CPU 29, an input port 30 and an output port 31 which are connected to each other via a bidirectional bus 26. Further, sensor output values from the air flow sensor 11, the throttle opening sensor 14, the oxygen sensor 19, the NOx sensor 21, the EGR opening sensor 24, and the like are input to the ECU 25. The ECU 25 further receives a response from a water temperature sensor 32 that detects the coolant temperature of the engine 1, a rotation speed sensor 36 that detects the engine speed, and an accelerator opening sensor 37 that detects the accelerator opening. The Input from each sensor is input to the input port 30 via the AD converter 38. The CPU 29 or the like calculates an optimal control command based on the input sensor value, and controls the spark plug 5, the fuel injection valve 6 and the like via the output port 31 and the corresponding drive circuit 39.

  The ECU 25 controls the EGR amount and timing according to the operating state of the engine 1 to change the EGR rate (the ratio between the “EGR amount” and “the intake air amount plus the EGR amount”), ignition, and ignition Ignition timing control for controlling the timing at which the air-fuel mixture in the combustion chamber 4 is ignited by the plug 5, fuel injection pressure control for controlling the injection pressure of fuel injected from the fuel injection valve 6 according to the operating state of the engine 1, exhaust Rich spike control that releases and purifies NOx held in the NOx catalyst 20 by controlling the air-fuel ratio of the gas to be rich, and NOx catalyst deterioration that determines deterioration of the NOx catalyst 20 based on an output value of a NOx sensor 21 described later NOx sensor 21 abnormality in which judgment control, NOx concentration is fluctuated before the NOx catalyst 20 described later is activated, and abnormality of the NOx sensor is judged based on the output of the NOx sensor 21 The constant control and the like.

  Since the NOx concentration in the exhaust gas changes depending on the combustion temperature in the combustion chamber 4, the NOx concentration can be changed by changing the EGR amount, ignition timing, fuel injection pressure, and the like. That is, when the EGR rate is increased by EGR control, the combustion temperature decreases, so that the NOx concentration in the exhaust gas can be decreased. On the other hand, when the EGR rate is lowered, the NOx concentration in the exhaust gas can be increased because the combustion temperature becomes higher. Further, when the ignition timing is advanced from the compression top dead center by the ignition timing control, the combustion temperature becomes high, so that the NOx concentration in the exhaust gas can be increased. On the other hand, when the ignition timing is retarded from the compression top dead center, the combustion temperature becomes lower, so the NOx concentration in the exhaust gas can be lowered. Further, when the fuel injection pressure is increased by the fuel injection pressure control, the combustion temperature increases, so that the NOx concentration in the exhaust gas can be increased. On the other hand, when the fuel injection pressure is lowered, the combustion temperature becomes lower, so the NOx concentration in the exhaust gas can be lowered.

  Next, the abnormality determination method for the NOx sensor 21 of the present invention will be described with reference to the flowchart shown in FIG.

  In step 100, the coolant temperature is detected by the water temperature sensor 27.

  In step 110, it is determined whether or not the cooling water temperature detected in step 100 is less than a predetermined value. If the coolant temperature is less than the predetermined value, it is determined that the NOx catalyst 20 is not active, and the routine proceeds to step 120. On the other hand, when the cooling water temperature is equal to or higher than the predetermined value, the NOx catalyst 20 is sufficiently activated, and the abnormality determination of the NOx sensor 21 cannot be accurately determined. .

  In step 120, the EGR rate, which is the ratio of the EGR amount to the total gas amount flowing into the cylinder, is controlled at a predetermined cycle by controlling the EGR valve 23. When the EGR rate is small, the oxygen concentration of the air-fuel mixture is high, thereby increasing the combustion temperature, so that the NOx concentration of the exhaust gas discharged from the internal combustion engine is high. On the other hand, when the EGR rate is large, the oxygen concentration of the air-fuel mixture becomes low, which increases the combustion temperature, so that the NOx concentration of the exhaust gas can be lowered. In this embodiment, the NOx concentration in the exhaust gas is changed by changing the EGR rate with a predetermined period and amplitude, and the abnormality determination of the NOx sensor 21 is performed based on the output value of the NOx sensor 21 output at this time. .

  In step 130, the amplitude of the NOx concentration in the exhaust gas detected by the NOx sensor 21 is based on a target amplitude (hereinafter referred to as “target amplitude”) determined based on the fluctuation of the NOx concentration controlled in step 120. If larger, the process proceeds to step 150, where it is determined that the NOx sensor 21 is abnormal, and the driver is warned by, for example, an indicator light or a warning sound. If the amplitude of the output value of the NOx sensor 21 is less than or equal to the target amplitude, the process proceeds to step 140.

  In step 140, it is determined whether or not the response of the output of the NOx sensor 21 corresponding to the NOx concentration controlled in step 120 is within a predetermined period. In the NOx sensor 21, for example, when the exhaust gas passage 51 shown in FIG. 2 is clogged and the exhaust gas flow deteriorates, the response of the NOx sensor 21 is delayed compared to the normal exhaust gas passage of the NOx sensor 21. There is. When the response of the NOx sensor 21 is not within the predetermined period, the process proceeds to step 150, where it is determined that the NOx sensor 21 is abnormal in response delay, and the driver is warned. When the response of the NOx sensor 21 is within the predetermined period, the process proceeds to step 160 where it is determined that the NOx sensor 21 is normal and the abnormality determination control of the NOx sensor 21 is terminated.

  As described above, in the first embodiment, since the NOx sensor 21 is determined to be abnormal when the NOx catalyst 20 is not sufficiently activated, the NOx sensor 21 is accurately detected regardless of whether the NOx catalyst 20 is deteriorated. Abnormality can be determined.

  Further, the active state of the NOx catalyst 20 can be accurately determined without requiring a significant system change by determining the active state of the NOx catalyst 20 using the coolant temperature by the water temperature sensor 27.

  Further, the NOx concentration in the exhaust gas can be controlled by changing the EGR rate in the cylinder, and can be controlled using an existing system.

  Furthermore, when it is determined that the NOx sensor 21 is abnormal, a warning is given to the driver or the like, so that the replacement of the NOx sensor 21 or the like can be promoted, and a stable driving state can be established early.

  In the first embodiment, the EGR rate is changed, but the EGR rate may not be changed. That is, before the catalyst is activated, the abnormality of the NOx sensor can be accurately determined without being influenced by the purification action of the NOx catalyst 20.

    In addition, this abnormality determination method is preferably started immediately after the ignition is turned on or immediately after the NOx sensor 21 is energized by activation of the heater of the NOx sensor 21, and it is desirable to detect the abnormality of the NOx sensor 21 at an early stage.

  In the first embodiment, in steps 100 and 110, the presence or absence of activation of the NOx catalyst 20 is detected from the cooling water temperature. Instead of this, for example, the time from ignition on or the NOx catalyst 20 It is also possible to detect whether the NOx catalyst 20 is activated by a temperature sensor that directly detects the temperature.

  Moreover, you may add control before the step 120 whether the EGR valve 23 which controls the EGR rate in a cylinder operate | moves normally. Thereby, since the NOx concentration of the exhaust gas can be changed more reliably by controlling the EGR rate, the reliability of the abnormality determination of the NOx sensor 21 can be improved.

  In the first embodiment, the NOx concentration in the exhaust gas is changed in step 120 by changing the EGR rate in the cylinder. Instead, for example, the ignition timing of the spark plug 5 or the fuel injection is changed. It is also possible to change the NOx concentration of the exhaust gas by changing the pressure.

  Furthermore, in the first embodiment, the abnormality of the NOx sensor 21 is determined from both the output amplitude and the output response of the NOx sensor 21, but it is also possible to determine by either one.

[Example 2]
In the first embodiment, the apparatus that determines the abnormality of the NOx sensor 21 by oscillating the EGR rate in the cylinder with a predetermined amplitude and comparing the amplitude of the NOx concentration detected by the NOx sensor 21 with the predetermined amplitude has been described. In the second embodiment, an apparatus for determining an abnormality of the NOx sensor 21 by simply changing the EGR rate without oscillating it will be described. In addition, about the thing corresponding to FIG.1 and FIG.3, the same code | symbol is attached | subjected and the duplicate description is abbreviate | omitted.

  In the flowchart shown in FIG. 4, steps 100 to 110 and 140 to 160 are controlled in the same manner as in the first embodiment. That is, it is determined whether or not the NOx catalyst 20 is activated.

  In step 200, the EGR rate in the cylinder is changed from the current state by the control of the EGR valve 23. In this embodiment, the EGR rate is changed once. Based on the output value of the NOx sensor 21 at this time, the abnormality determination of the NOx sensor 21 is performed. When the EGR rate is changed, the process proceeds to step 210.

  In step 210, if the NOx concentration in the exhaust gas detected by the NOx sensor 21 is larger than the target concentration determined based on the NOx concentration controlled in step 200 (hereinafter referred to as “target concentration”), step 210. Proceed to 150. On the other hand, if the density is less than the target density, the process proceeds to step 140.

  In step 140, as in the first embodiment, if the response of the output of the NOx sensor 21 corresponding to the NOx concentration controlled in step 200 is not within the predetermined period, the process proceeds to step 150. When this response is within the predetermined period, the process proceeds to step 160, and the abnormality determination control of the NOx sensor 21 is terminated.

  As described above, in the second embodiment, the abnormality of the NOx sensor 21 can be determined only by changing the EGR rate.

  In this embodiment, the EGR rate is changed only once in step 200, but the EGR rate may be changed a plurality of times, and the abnormality of the NOx sensor 21 may be determined from the target concentration based on the EGR rate. .

  Further, in Examples 1 and 2, the EGR rate is controlled to change the NOx concentration in the exhaust gas flowing into the NOx catalyst 20, but the normal control is performed without changing or vibrating the NOx concentration. Alternatively, the abnormality of the NOx sensor 21 may be determined in a state where the NOx concentration is increased. In this case, the abnormality of the NOx sensor 21 can be determined without causing torque fluctuation.

The figure which shows the engine provided with the abnormality determination apparatus of the NOx sensor 21 in embodiment of this invention. The block diagram of the NOx sensor 21 in embodiment of this invention. 3 is a flowchart for explaining an abnormality determination method according to the first embodiment. 7 is a flowchart for explaining an abnormality determination method according to the second embodiment.

Explanation of symbols

1 Engine 23 NOx catalyst 24 NOx sensor 21
26 EGR valve 29 Water temperature sensor

Claims (7)

A catalyst provided in the exhaust passage of the internal combustion engine, an exhaust gas concentration sensor provided downstream of the catalyst and detecting the concentration of a specific component of the exhaust gas, and activation detection detecting whether or not the catalyst is activated And an abnormality of the exhaust gas concentration sensor based on the concentration of a specific component of the exhaust gas detected by the exhaust gas concentration sensor when it is determined by the activation detection means that the catalyst is not activated An abnormality determination device for an exhaust gas sensor of an internal combustion engine, comprising: an abnormality determination means for determining Furthermore, it comprises concentration changing means for changing the concentration of a specific component of the exhaust gas flowing into the catalyst,
The abnormality determining means is based on the concentration of the specific component of the exhaust gas detected by the exhaust gas concentration sensor when the concentration of the specific component of the exhaust gas flowing into the catalyst is changed by the concentration changing means. 2. The exhaust gas sensor abnormality determination device according to claim 1, wherein abnormality of the exhaust gas concentration sensor is determined. The concentration changing means varies the concentration of a specific component of the exhaust gas flowing into the catalyst at a predetermined cycle, and the abnormality determining means is configured to specify a specific exhaust gas detected by the exhaust gas concentration sensor. 3. The exhaust gas sensor abnormality determination device for an internal combustion engine according to claim 2, wherein the exhaust gas concentration sensor is determined to be abnormal when an amplitude of a component concentration is equal to or less than a target amplitude. The abnormality determination unit determines that the exhaust gas concentration sensor is abnormal when a concentration of a specific component of the exhaust gas detected by the exhaust gas concentration sensor is equal to or lower than a target concentration. 3. An abnormality determination device for an exhaust gas sensor of an internal combustion engine according to 1 or 2. In the abnormality determining means, when the concentration of the specific component of the exhaust gas flowing into the catalyst is changed by the concentration changing means, the exhaust gas corresponding to the changed concentration of the specific component of the exhaust gas 3. The exhaust gas sensor abnormality determination device according to claim 2, wherein the exhaust gas concentration sensor determines that the exhaust gas concentration sensor is abnormal when a response of the output of the concentration sensor is not within a predetermined period. The abnormality determination device for an exhaust gas sensor of an internal combustion engine according to claim 2, wherein the concentration changing means is an EGR rate control means for controlling an EGR rate. The abnormality determination device for an exhaust gas sensor of an internal combustion engine according to any one of claims 1 to 6, wherein the exhaust gas concentration sensor is a NOx sensor, and the catalyst is a NOx catalyst.

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