JP5783099B2 - Sensor failure determination device - Google Patents

Description

  The present invention relates to a sensor failure determination apparatus.

  In Patent Document 1, a failure of the NOx sensor is diagnosed by comparing the NOx concentration in the gas discharged from the internal combustion engine estimated based on the operating state of the internal combustion engine and the detected value of the NOx sensor. It is described to do.

  Patent Document 2 describes that NOx sensors are provided upstream and downstream of the catalyst, and the deterioration of the catalyst is determined based on the detected value of the NOx sensor.

Patent Document 3 describes that the NO ₂ ratio is estimated based on the temperature of the oxidation catalyst and the sensor value is corrected.

  Further, Patent Document 4 discloses that when the internal combustion engine reaches a preset reference operating condition, NOx is based on the difference between the output value of the NOx sensor and the reference output value preset according to the reference operating condition. It is described that the output of the sensor is corrected.

Here, when a catalyst is provided upstream of the NOx sensor, the NOx concentration in the exhaust is affected by the passage of NOx through the catalyst. For example, when an oxidation catalyst is provided upstream of the NOx sensor, the oxidation catalyst adsorbs NOx in the process in which NO is oxidized to NO ₂ in the oxidation catalyst. NO and NO ₂ are detected by the NOx sensor, but by being adsorbed by the oxidation catalyst, there is a difference between the NOx concentration in the gas discharged from the internal combustion engine and the NOx concentration detected by the NOx sensor. . This deviation also changes depending on the degree of deterioration of the oxidation catalyst. That is, when the degree of deterioration of the oxidation catalyst is low (for example, in a new state or a state close to a new state), the shift becomes large in order to adsorb more NOx. On the other hand, when the degree of deterioration of the oxidation catalyst is high, NOx is not adsorbed by the oxidation catalyst and easily passes through, so the deviation is small.

  However, since the detection value of the NOx sensor is required to detect the degree of deterioration of the oxidation catalyst, it is difficult to detect the degree of deterioration of the oxidation catalyst before the failure diagnosis of the NOx sensor. It is also conceivable to estimate the degree of deterioration of the oxidation catalyst based on the past operating state of the internal combustion engine, or to estimate the degree of deterioration of the oxidation catalyst based on the state of heat generation in the oxidation catalyst. Since these estimation accuracy is low, there is a possibility that an erroneous determination is made.

JP 2009-128237 A JP 2011-058415 A JP 2010-031761 A JP 2009-127552 A

  The present invention has been made in view of the above-described problems, and an object thereof is to determine a sensor failure with higher accuracy.

In order to achieve the above object, a failure determination device for a sensor according to the present invention comprises:
In a failure determination device for a NOx sensor, which is provided downstream of a catalyst having oxidation ability in an exhaust passage of an internal combustion engine and detects a NOx concentration in exhaust gas,
Estimating means for estimating or detecting the concentration of NOx in the exhaust gas upstream of the catalyst;
The length of the locus of the detected value of the NOx sensor in a predetermined period is equal to or greater than the threshold, and the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means is the threshold. In the above case, determination means for determining that the NOx sensor has failed,
Is provided.

  The estimation means may estimate or detect the NOx concentration in the gas discharged from the internal combustion engine, may estimate or detect the NOx concentration in the exhaust passage between the internal combustion engine and the catalyst, and flows into the catalyst. The NOx concentration in the gas may be estimated or detected.

  The length of the detected value locus of the NOx sensor is, for example, the length of a line indicating the transition of the detected value when the horizontal axis is time and the vertical axis is the detected value, and the transition of the detected value is illustrated in the figure. It is. When the NOx sensor detects NOx over time, a value obtained by integrating the length of the line connecting the previous detection value and the current detection value every time becomes the length of the locus of the detection value.

  Even if the NOx concentration is the same, the length of the locus of the detected value (hereinafter also referred to as the locus length) varies depending on the state of deterioration of the catalyst. That is, as the degree of deterioration of the catalyst increases, the amount of NOx adsorbed by the catalyst decreases, so that NOx easily passes through the catalyst. For this reason, the detected value of the NOx sensor is close to the NOx concentration upstream of the catalyst. On the other hand, the closer the catalyst is to a new one, the more NOx is adsorbed and desorbed by the catalyst, so it takes time until NOx reaches the NOx sensor. Thereby, since the fluctuation | variation of NOx concentration is absorbed by the catalyst, the fluctuation | variation of NOx concentration downstream from a catalyst becomes small.

  From the above, the higher the degree of catalyst deterioration, the longer the locus of the detected value of the NOx sensor. Therefore, it is possible to determine whether or not the catalyst has deteriorated by comparing the locus length of the detected value of the NOx sensor for a predetermined period with the threshold value. That is, if the length of the locus of the detected value of the NOx sensor in the predetermined period is equal to or greater than the threshold value, it can be determined that the catalyst has deteriorated. Here, the predetermined period can be a period required until the length of the locus of the detected value of the NOx sensor becomes a size necessary for determining the deterioration of the catalyst. The threshold value also changes depending on the predetermined period. The threshold here is a lower limit value of the length of the locus of the detected value of the NOx sensor when the catalyst is deteriorated. Note that “degraded” means that the catalyst function is inferior to that of a new product, and the detected value of the NOx sensor is different from that of a new catalyst. Further, even if the catalyst is deteriorated, it does not mean only the state in which the catalyst does not perform its function. Further, the catalyst may be deteriorated when the degree of deterioration of the catalyst is a predetermined value or more. This can include cases where the degree of degradation is high but within an acceptable range. For example, it may be determined that the catalyst has deteriorated before the degree of deterioration exceeds the allowable range. In addition, the new article can include not only a state where it is not deteriorated at all, but also a case where there is almost no influence on the purification performance even if it is deteriorated.

When the catalyst is deteriorated, the difference between the NOx concentration in the exhaust upstream of the catalyst and the NOx concentration in the exhaust downstream of the catalyst is small. That is, if the NOx sensor is normal, the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means becomes small. Therefore, for example, if the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means is greater than or equal to the threshold value, it can be determined that the NOx sensor is malfunctioning. This threshold value is a lower limit value of the absolute value of the difference when the NOx sensor is malfunctioning.

  The detected value of the NOx sensor based on the value obtained by dividing the length of the locus of the detected value of the NOx sensor in the predetermined period by the integrated value of the detected value of the NOx sensor and the NOx concentration estimated by the estimating means. The absolute value of the difference between the estimated value obtained by dividing the length of the trajectory by the integrated value of the detected value of the NOx sensor, and the detected value of the NOx sensor, When the absolute value of the difference between the NOx concentration estimated or detected by the estimating means is greater than or equal to a threshold value, it can also be determined that the NOx sensor has failed.

  Further, the length of the locus of the detected value of the NOx sensor in a predetermined period and the estimated value when the length of the locus of the detected value of the NOx sensor is estimated based on the NOx concentration estimated by the estimating means, When the absolute value of the difference is less than the threshold and the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means is equal to or greater than the threshold, the NOx sensor It can also be determined that a failure has occurred.

  In the present invention, the determination means is estimated or detected by the detection value of the NOx sensor and the estimation means when the length of the locus of the detection value of the NOx sensor in a predetermined period is less than a threshold value. The failure determination of the NOx sensor by comparing the absolute value of the difference with the NOx concentration and the threshold value can be stopped.

  Here, when the length of the locus of the detected value of the NOx sensor in the predetermined period is less than the threshold value, the catalyst is in a new state or close to a new state. There is a large difference between the NOx concentration and the NOx concentration in the exhaust downstream of the catalyst. Therefore, it becomes difficult to determine the failure of the NOx sensor using the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means. In such a case, the NOx sensor failure determination based on the comparison between the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means and the threshold value is stopped. It can suppress that the precision of failure determination of falls.

  In the present invention, when the length of the locus of the detected value of the NOx sensor in a predetermined period is less than the threshold value, the determining means estimates the integrated value of the detected value of the NOx sensor and the estimating means. Alternatively, a failure of the NOx sensor can be determined by comparing the detected integrated value of the NOx concentration.

Here, since the amount of NOx adsorbed by the catalyst is very small, even if the catalyst is new, there is not much difference between the total amount of NOx flowing into the catalyst and the total amount of NOx flowing out from the catalyst. Note that NO is oxidized to NO ₂ in the catalyst, but both NO and NO ₂ are detected as NOx.

  As described above, if there is no difference between the integrated value of the detected values of the NOx sensor and the integrated value of the NOx concentration estimated or detected by the estimating means, if any, it is determined that the NOx sensor is normal. be able to. The integrated value may be an integrated value for a predetermined period. This predetermined period can be set to a period required until the integrated value of the detected values of the NOx sensor reaches a size necessary for determining deterioration of the catalyst.

  In addition, when the absolute value of the difference between the integrated value of the detected value of the NOx sensor and the integrated value of the NOx concentration estimated or detected by the estimating means is equal to or greater than the threshold value, it is determined that the NOx sensor has failed. Also good. The threshold here is the absolute value of the difference when the NOx sensor is malfunctioning.

In the present invention, when the length of the locus of the detected value of the NOx sensor in a predetermined period is less than a threshold value, the determining unit estimates the estimating unit based on the amount of NOx adsorbed on the catalyst. Alternatively, it is possible to determine a failure of the NOx sensor by correcting the detected NOx concentration and comparing the corrected NOx concentration with the detected value of the NOx sensor.

  Here, when the length of the locus of the detected value of the NOx sensor in the predetermined period is less than the threshold value, the catalyst is not deteriorated. In this case, since the function of the catalyst is functioning normally, the amount of NOx adsorbed can be estimated, and furthermore, the change in the NOx concentration when exhaust passes through the catalyst can be estimated. By correcting the NOx concentration estimated or detected by the estimating means based on the change in the NOx concentration, the NOx concentration in the exhaust gas downstream of the catalyst can be obtained. If the NOx sensor is normal, the corrected NOx concentration is detected by the NOx sensor. Therefore, the failure of the NOx sensor is determined by comparing the corrected NOx concentration with the detected value of the NOx sensor. Can do.

  Note that when the absolute value of the difference between the corrected NOx concentration and the detected value of the NOx sensor is equal to or greater than a threshold value, it may be determined that the NOx sensor is malfunctioning. The threshold here is the absolute value of the difference when the NOx sensor is malfunctioning. Further, instead of correcting the NOx concentration estimated or detected by the estimating means, the detected value of the NOx sensor may be corrected.

  According to the present invention, sensor failure can be determined with higher accuracy.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is a time chart which showed transition of the detected value of a NOx sensor. It is the time chart which showed transition of the locus length of the detected value of the NOx sensor. It is a time chart which showed transition of the integrated value of the detected value of a NOx sensor. It is the figure which showed the relationship between the locus | trajectory length of the detected value of a NOx sensor in a deterioration catalyst and a new catalyst, and the integrated value of the detected value of a NOx sensor. 3 is a flowchart illustrating a flow of a NOx sensor failure determination according to the first embodiment. 6 is a flowchart illustrating a flow of a NOx sensor failure determination according to Embodiment 2. 10 is a flowchart illustrating a flow of a NOx sensor failure determination according to a third embodiment.

  Hereinafter, specific embodiments of a sensor failure determination apparatus according to the present invention will be described with reference to the drawings.

<Example 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 may be a diesel engine or a gasoline engine.

  An exhaust passage 2 is connected to the internal combustion engine 1. An oxidation catalyst 3 is provided in the exhaust passage 2. In addition, it may replace with the oxidation catalyst 3 and the other catalyst (for example, three-way catalyst) provided with the oxidation capability may be provided.

A NOx sensor 4 for detecting the NOx concentration in the exhaust gas is provided in the exhaust passage 2 downstream of the oxidation catalyst 3.

  The internal combustion engine 1 is provided with an ECU 5 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 5 controls the internal combustion engine 1 in accordance with the operating conditions of the internal combustion engine 1 and the driver's request.

  In addition to the NOx sensor 4, the ECU 5 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 6 by the driver, and an accelerator opening sensor 7 that detects the engine load, and a crank position that detects the engine speed. Sensors 8 are connected via electric wiring, and output signals from these various sensors are input to the ECU 5.

  Then, the ECU 5 determines a failure of the NOx sensor 4. Here, the detected value of the NOx sensor 4 is affected by the degree of deterioration of the oxidation catalyst 3. For this reason, the failure determination method of the NOx sensor 4 is changed according to the degree of deterioration of the oxidation catalyst 3.

  FIG. 2 is a time chart showing the transition of the detected value of the NOx sensor 4. A new catalyst is the oxidation catalyst 3 in a new state or a state close to a new state, and is a catalyst that has not deteriorated. Moreover, the deterioration catalyst is the oxidation catalyst 3 having a relatively high degree of deterioration. The deterioration catalyst may be the oxidation catalyst 3 when the degree of deterioration is equal to or greater than a threshold value. Further, the deteriorated catalyst may be a catalyst within a range that can be said to be normal, although the oxidation ability is inferior to that of a new catalyst. The vehicle speed is the speed of the vehicle on which the internal combustion engine 1 is mounted. The detected value of the NOx sensor 4 in the deteriorated catalyst and the new catalyst is a detected value at the same vehicle speed.

  When the oxidation catalyst 3 is a new catalyst, more NOx is adsorbed on the oxidation catalyst 3 and then desorbed. For this reason, the maximum value of the detected value of the NOx sensor 4 becomes relatively small. That is, the time from when NOx is discharged from the internal combustion engine 1 until it reaches the NOx sensor 4 becomes longer (the responsiveness becomes lower), and the NOx concentration in the exhaust downstream of the oxidation catalyst 3 approaches the average. . Thereby, when the oxidation catalyst 3 is a new catalyst, the fluctuation range of the detected value of the NOx sensor 4 is small. For this reason, the NOx concentration is likely to change when passing through the oxidation catalyst 3.

  On the other hand, when the oxidation catalyst 3 is a deteriorated catalyst, the amount of NOx adsorbed on the oxidation catalyst 3 decreases, so the time from when NOx is discharged from the internal combustion engine 1 until it reaches the NOx sensor 4 is shortened ( Responsiveness increases). For this reason, the NOx concentration in the exhaust gas downstream of the oxidation catalyst 3 becomes close to the NOx concentration in the gas discharged from the internal combustion engine 1, and the maximum value of the detected value also increases. For this reason, the fluctuation range of the detected value of the NOx sensor 4 is large. Thus, when the oxidation catalyst 3 is a deterioration catalyst, the NOx concentration hardly changes when the exhaust gas passes through the oxidation catalyst 3.

  Here, FIG. 3 is a time chart showing the transition of the locus length of the detection value of the NOx sensor 4. FIG. 4 is a time chart showing the transition of the integrated value of the detected value of the NOx sensor 4. The locus length of the detected value of the NOx sensor 4 is the length of a line indicating the transition of the detected value of the NOx sensor 4 as shown in FIG. Further, the integrated value of the detected value of the NOx sensor 4 is a value obtained by integrating the detected value of the NOx sensor 4 for every predetermined time, for example, and shows the transition of the detected value of the NOx sensor 4 as shown in FIG. The area below the line.

  In the case of a new catalyst, the fluctuation range of the detected value of the NOx sensor 4 is smaller than in the case of a deteriorated catalyst. For this reason, the trajectory length of the new catalyst is shorter than the trajectory length of the deteriorated catalyst. The ratio of the trajectory length of the new catalyst to the trajectory length of the deteriorated catalyst is, for example, about 40%.

On the other hand, in the integrated value of the detected value of the NOx sensor 4 shown in FIG. 4, the difference between the new catalyst and the deteriorated catalyst is small. Here, since the amount of NOx adsorbed by the oxidation catalyst 3 is very small, the amount of NOx reaching the NOx sensor 4 is not so different between the new catalyst and the deteriorated catalyst. The ratio of the integrated value of the new catalyst to the integrated value of the deteriorated catalyst is, for example, about 90%.

  As described above, the difference between the locus length of the NOx concentration in the gas discharged from the internal combustion engine 1 and the locus length of the detected value of the NOx sensor 4 is large, and the integration of the NOx concentration in the gas discharged from the internal combustion engine 1 is performed. When the difference between the value and the integrated value of the detected value of the NOx sensor 4 is small, it is considered that the oxidation catalyst 3 is a new catalyst and the NOx sensor 4 is normal. Further, it is also possible to determine whether or not the oxidation catalyst 3 is a new catalyst by comparing the trajectory length of the detected value of the NOx sensor 4 in a predetermined period with the threshold value.

  Here, as the failure of the NOx sensor 4, a gain deviation or an offset deviation can be considered. When the gain deviation occurs, the ratio (slope) of the sensor output to the NOx concentration is different from that of the normal NOx sensor 4. When only a gain deviation occurs, if the actual NOx concentration becomes zero, the detection value of the NOx sensor 4 also becomes zero.

  On the other hand, when an offset deviation occurs, the ratio (inclination) of the sensor detection value to the NOx concentration is the same as that of the normal NOx sensor 4, but a certain amount of deviation from the detection value of the normal NOx sensor 4 occurs. Occurs. When only the offset deviation occurs, the detected value of the NOx sensor 4 does not become 0 even if the actual NOx concentration becomes 0.

  FIG. 5 is a diagram showing the relationship between the locus length of the detected value of the NOx sensor 4 and the integrated value of the detected value of the NOx sensor 4 in the deteriorated catalyst and the new catalyst. “Normal sensor” is when the NOx sensor 4 is normal. “Gain−50%” is a case where a gain deviation has occurred in the NOx sensor 4 and the detected value of the NOx sensor 4 is 50% of the actual NOx concentration. “Offset−30 ppm” is a case where an offset deviation has occurred in the NOx sensor 4 and the detected value of the NOx sensor 4 is 30 ppm lower than the actual NOx concentration. Further, “offset + 30 ppm” is a case where an offset deviation has occurred in the NOx sensor 4 and the detected value of the NOx sensor 4 is 30 ppm higher than the actual NOx concentration.

  The “trajectory length” is the trajectory length of the detected value of the NOx sensor 4. “Integrated value” is an integrated value of the detected value of the NOx sensor 4. The “trajectory length / estimated trajectory length” is a value obtained by dividing “trajectory length” by an estimated trajectory length (estimated trajectory length). The estimated trajectory length is the trajectory length of the NOx concentration in the gas upstream of the oxidation catalyst 3 estimated from the operating state of the internal combustion engine 1. This estimated trajectory length is a case where it is assumed that the oxidation catalyst 3 is not provided, and may be a trajectory length of a detected value of the NOx sensor 4 when the NOx sensor 4 is normal, and is discharged from the internal combustion engine 1. Alternatively, the NOx concentration locus length when the NOx concentration in the detected gas is detected or estimated may be used. The “integrated value / estimated integrated value” is a value obtained by dividing the “integrated value” by the estimated integrated value (estimated integrated value). The estimated integrated value is an integrated value of the NOx concentration in the gas upstream of the oxidation catalyst 3 estimated from the operating state of the internal combustion engine 1. This estimated integrated value is a case where it is assumed that the oxidation catalyst 3 is not provided, and may be an integrated value of the detected value of the NOx sensor 4 when the NOx sensor 4 is normal, and is discharged from the internal combustion engine 1. The integrated value of the NOx concentration when the NOx concentration in the detected gas is detected or estimated may be used. “A / B” is a value obtained by dividing “trajectory length / estimated trajectory length” by “integrated value / estimated integrated value”. That is, “A / B” is a value obtained by dividing “trajectory length / integrated value” by “estimated trajectory length / estimated integrated value”. The trajectory length and the integrated value are values in a predetermined period. Hereinafter, unless otherwise specified, the trajectory length, integrated value, estimated trajectory length, and estimated integrated value are values in a predetermined period.

In the deteriorated catalyst, the trajectory length and the estimated trajectory length are substantially the same when the NOx sensor 4 is normal and when the offset deviation occurs in the NOx sensor 4. That is, “trajectory length / estimated trajectory length” is approximately 100%. Therefore, it can be seen that even if an offset deviation occurs in the NOx sensor 4, the trajectory length is not affected. On the other hand, in the deteriorated catalyst, when a gain deviation occurs in the NOx sensor 4, “A / B” is approximately 100%. That is, the value obtained by dividing the trajectory length by the integrated value is substantially the same as the value obtained by dividing the estimated trajectory length by the estimated integrated value. Therefore, it can be seen that even if a gain deviation occurs in the NOx sensor 4, the value obtained by dividing the locus length by the integrated value is not affected.

  Further, when the NOx sensor 4 is normal in a new catalyst, the integrated value is substantially the same as the estimated integrated value. That is, “integrated value / estimated integrated value” is close to 100%. On the other hand, in the case of a new catalyst, when an offset deviation or gain deviation occurs in the NOx sensor 4, there is no correlation between the trajectory length and the integrated value.

  From the above, when the locus length of the detected value of the NOx sensor 4 is substantially equal to the estimated locus length, or the value obtained by dividing the locus length of the detected value of the NOx sensor 4 by the integrated value of the detected value of the NOx sensor 4 is estimated. When the locus length is substantially equal to the value obtained by dividing the locus length by the estimated integrated value, the oxidation catalyst 3 is considered to be a deteriorated catalyst. If the oxidation catalyst 3 is a deteriorated catalyst, the NOx adsorption ability is low, so the influence on the detection value of the NOx sensor 4 is small. For this reason, the failure determination of the NOx sensor 4 can be performed by comparing the detected value of the NOx sensor 4 with the estimated value of the NOx concentration. Thus, by comparing the NOx concentration, the failure determination of the NOx sensor 4 can be performed with high accuracy.

  On the other hand, when the oxidation catalyst 3 does not correspond to the deterioration catalyst, the oxidation catalyst 3 is considered to be a new catalyst. In this case, the failure determination of the NOx sensor 4 is performed by comparing the integrated value of the detected values of the NOx sensor 4 with the estimated integrated value.

  FIG. 6 is a flowchart showing a flow of failure determination of the NOx sensor 4 according to the present embodiment. This routine is repeatedly executed by the ECU 5 every predetermined time. In this embodiment, the ECU 5 that processes the routine shown in FIG. 6 corresponds to the determination means in the present invention.

  In step S101, it is determined whether a precondition for failure determination is satisfied. For example, it is determined that the precondition is satisfied when the coolant temperature of the internal combustion engine 1 is a temperature suitable for determining the failure of the NOx sensor 4 and the NOx sensor 4 is in the active state. Furthermore, it may be determined that the precondition is satisfied when the estimated trajectory length is equal to or greater than a predetermined value required for failure determination. Further, since the failure determination is performed using the detected value of the NOx sensor 4, it is determined that the precondition is satisfied when a certain amount of NOx is discharged from the internal combustion engine 1 (for example, in a predetermined operating state). May be.

  If an affirmative determination is made in step S101, the process proceeds to step S102. On the other hand, if a negative determination is made, failure determination cannot be performed, and thus this routine is terminated.

  In step S102, the trajectory length of the detected value of the NOx sensor 4 is substantially equal to the estimated trajectory length, or a value obtained by dividing the trajectory length of the detected value of the NOx sensor 4 by the integrated value of the detected value of the NOx sensor 4, It is determined whether or not the estimated trajectory length is substantially equal to a value obtained by dividing the estimated trajectory length by the estimated integrated value.

In this step, it is determined whether or not the oxidation catalyst 3 is a deteriorated catalyst. Note that the estimated trajectory length may be the length of a line indicating the transition of the actual NOx concentration upstream of the oxidation catalyst 3. The estimated trajectory length may be the trajectory length of the detected value of the NOx sensor by attaching a NOx sensor upstream of the oxidation catalyst 3. Further, since there is a correlation between the operating state (engine speed and engine load) of the internal combustion engine 1 and the NOx concentration, the relationship between the operating state of the internal combustion engine 1 and the NOx concentration is obtained by experimentation and mapped. You may keep it. Then, the NOx concentration may be calculated from this map and the detected operating state of the internal combustion engine 1, and the length of the line indicating the transition of this value may be used as the estimated trajectory length. In this embodiment, the ECU 5 that estimates the NOx concentration corresponds to the estimation means in the present invention.

  The estimated integrated value may be an integrated value of the actual NOx concentration upstream of the oxidation catalyst 3. The estimated integrated value may be an integrated value of a value detected by a NOx sensor attached to the upstream side of the oxidation catalyst 3. Further, the relationship between the operating state of the internal combustion engine 1 and the NOx concentration is obtained by experimentation or the like and mapped, and the NOx concentration is calculated from this map and the detected operating state of the internal combustion engine 1, and this value is calculated. You may accumulate.

  Here, the locus length of the detected value of the NOx sensor 4 is substantially equal to the estimated locus length, even if there is a difference between the locus length of the detected value of the NOx sensor 4 and the estimated locus length. Or within the range that can be equal. Note that if the absolute value of the difference between the trajectory length and the estimated trajectory length is less than the threshold, the trajectory length and the estimated trajectory length may be substantially equal. This threshold value is a value when the range that can be assumed to be equal is exceeded, and is a lower limit value of the absolute value of the difference when the oxidation catalyst 3 is a new catalyst. Further, in this step, it may be determined whether the trajectory length of the detected value of the NOx sensor 4 is equal to or greater than a threshold value. This threshold value is the lower limit value of the locus length of the detected value of the NOx sensor 4 when the oxidation catalyst 3 is a deteriorated catalyst.

  Even if there is a difference between the value obtained by dividing the locus length of the detected value of the NOx sensor 4 by the integrated value of the detected value of the NOx sensor 4 and the value obtained by dividing the estimated locus length by the estimated integrated value. In this case, it is within a range of errors or within a range that can be equal. If the absolute value of the difference between the value obtained by dividing the trajectory length by the integrated value and the value obtained by dividing the estimated trajectory length by the estimated integrated value is less than the threshold, the value obtained by dividing the trajectory length by the integrated value and the estimated The value obtained by dividing the trajectory length by the estimated integrated value may be substantially equal. This threshold value is a value when the range that can be assumed to be equal is exceeded, and is a lower limit value of the absolute value of the difference when the oxidation catalyst 3 is a new catalyst.

  If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, the process proceeds to step S106.

  In step S103, it is determined whether the detected value of the NOx sensor 4 and the estimated value or detected value of the NOx concentration discharged from the internal combustion engine 1 are substantially equal. The estimated value or detected value of the NOx concentration discharged from the internal combustion engine 1 is hereinafter referred to as “estimated detected value”. The estimated detection value may be an actual NOx concentration upstream of the oxidation catalyst 3. The estimated detection value may be a value detected by attaching a NOx sensor upstream of the oxidation catalyst 3 and detecting the NOx sensor. Further, since there is a correlation between the operating state (engine speed and engine load) of the internal combustion engine 1 and the NOx concentration, the relationship between the operating state of the internal combustion engine 1 and the NOx concentration is obtained by experimentation and mapped. You may keep it. Then, the NOx concentration may be calculated from this map and the detected operating state of the internal combustion engine 1.

  In step S103, “substantially equal” means that even if there is a difference between the detected value of the NOx sensor 4 and the estimated detected value, it is within an error range or within a range that can be made equal. Say. In addition, if the absolute value of the difference between the detected value of the NOx sensor 4 and the estimated detected value is less than the threshold value, the detected value of the NOx sensor 4 and the estimated detected value can be substantially equal. This threshold value is a lower limit value of the absolute value of the difference when the NOx sensor is malfunctioning.

Here, if an affirmative determination is made in step S102, the oxidation catalyst 3 is considered to be a deterioration catalyst. In this case, even if the exhaust gas passes through the oxidation catalyst 3, the NOx concentration hardly changes. For this reason, if the NOx sensor 4 is normal, the detected value of the NOx sensor 4 and the estimated detected value should be substantially equal. Therefore, the failure determination of the NOx sensor 4 can be performed by comparing the detected value of the NOx sensor 4 with the estimated detected value.

  If an affirmative determination is made in step S103, the process proceeds to step S104, where it is determined that the NOx sensor 4 is normal. On the other hand, if a negative determination is made in step S103, the process proceeds to step S105, where it is determined that the NOx sensor 4 is out of order.

  Next, in step S106, it is determined whether or not the integrated value of the detected value of the NOx sensor 4 is approximately equal to the estimated integrated value.

  In step S <b> 106, “substantially equal” means that the difference between the integrated value and the estimated integrated value is within an error range or within a range that can be equal. For example, as shown in FIG. 4 or FIG. 5, a difference of about 10% may occur. Note that if the absolute value of the difference between the integrated value and the estimated integrated value is less than the threshold value, the integrated value and the estimated integrated value may be substantially equal. This threshold value is a lower limit value of the absolute value of the difference when the NOx sensor is malfunctioning.

  Here, when a negative determination is made in step S102, it is considered that the oxidation catalyst 3 is a new catalyst. In this case, the detection value of the NOx sensor 4 changes under the influence of NOx adsorbed by the oxidation catalyst 3. However, if the NOx sensor 4 is normal, the integrated value of the detected value of the NOx sensor 4 and the estimated integrated value should be approximately equal. Therefore, the failure determination of the NOx sensor 4 can be performed by comparing the integrated value of the detected values of the NOx sensor 4 with the estimated integrated value.

  If an affirmative determination is made in step S106, the process proceeds to step S107, and it is determined that the NOx sensor 4 is normal. On the other hand, when a negative determination is made in step S103, the process proceeds to step S108, and it is determined that the NOx sensor 4 is out of order.

  As described above, according to the present embodiment, the failure determination method of the NOx sensor 4 is changed in accordance with the deterioration state of the oxidation catalyst 3, so that failure determination with higher accuracy can be performed.

<Example 2>
In this embodiment, the method for determining the failure of the NOx sensor 4 when the oxidation catalyst 3 is a new catalyst is different from that in the first embodiment. Since other devices are the same as those in the first embodiment, the description thereof is omitted.

  In this embodiment, the estimated detection value is corrected based on the amount of NOx adsorbed by the oxidation catalyst 3 when the oxidation catalyst 3 is a new catalyst. Instead of correcting the estimated detection value, the detection value of the NOx sensor 4 may be corrected. Then, the failure detection of the NOx sensor 4 is performed by comparing the estimated detection value after correction and the detection value.

  Here, when the oxidation catalyst 3 is a new catalyst, NOx is adsorbed at a constant rate when NOx passes through the oxidation catalyst 3. There is a correlation between the amount of NOx adsorbed on the oxidation catalyst 3 and the amount of change in the detected value of the NOx sensor 4 due to NOx adsorbed on the oxidation catalyst 3. By correcting the estimated detection value based on this relationship, the influence of NOx adsorbed on the oxidation catalyst 3 can be canceled.

Since the amount of NOx adsorbed on the oxidation catalyst 3 changes in accordance with the operating state (engine speed and engine load) of the internal combustion engine 1, a correction value of the estimated detection value is associated with the operating state of the internal combustion engine 1 in advance for experiments. Etc. can be obtained.

  FIG. 7 is a flowchart showing a flow of failure determination of the NOx sensor 4 according to the present embodiment. This routine is repeatedly executed by the ECU 5 every predetermined time. In addition, about the step in which the same process as the flow shown in FIG. 6 is made, the same code | symbol is attached | subjected and description is abbreviate | omitted. In this embodiment, the ECU 5 that processes the routine shown in FIG. 7 corresponds to the determination means in the present invention.

  If a negative determination is made in step S102, the process proceeds to step S201, and the detection value of the NOx sensor 4 is corrected. That is, when the oxidation catalyst 3 is a new catalyst, the process proceeds to step S201 to correct the estimated detection value. The correction value of the estimated detection value is obtained in advance through experiments or the like and stored in the ECU 5. Then, after correcting the estimated detection value, the process proceeds to step S103.

  As described above, according to this embodiment, when the oxidation catalyst 3 is a new catalyst, the amount of NOx concentration in the exhaust gas that reaches the NOx sensor 4 changes due to the effect of NOx adsorption on the oxidation catalyst 3. By correcting this, it is possible to cancel this influence, so that it is possible to improve the accuracy of the NOx sensor 4 failure determination.

<Example 3>
In this embodiment, when the oxidation catalyst 3 is a deteriorated catalyst and the NOx sensor 4 is out of order, whether the offset deviation occurs in the NOx sensor 4 or the gain deviation occurs. judge. Since other devices are the same as those in the first embodiment, the description thereof is omitted.

  Here, when the detected value of the NOx sensor 4 and the estimated detected value are substantially the same, the NOx sensor 4 is considered to be normal. On the other hand, even if there is a difference between the detected value of the NOx sensor 4 and the estimated detected value, the NOx sensor 4 may be normal if the oxidation catalyst 3 is a new catalyst.

  When the oxidation catalyst 3 is a deteriorated catalyst and an offset deviation occurs in the NOx sensor 4, the trajectory length and the estimated trajectory length are substantially the same. That is, even if an offset deviation occurs, the trajectory length is not affected. For this reason, when the detected value of the NOx sensor 4 is different from the estimated detected value, and the trajectory length and the estimated trajectory length are approximately the same, the oxidation catalyst 3 is a deteriorated catalyst and an offset deviation occurs in the NOx sensor 4. Can be determined.

  On the other hand, when the oxidation catalyst 3 is a deteriorated catalyst and a gain deviation occurs in the NOx sensor 4, the value obtained by dividing the trajectory length by the integrated value is substantially the same as the value obtained by dividing the estimated trajectory length by the estimated integrated value. become. Further, when the oxidation catalyst 3 is a deteriorated catalyst and a gain shift occurs in the NOx sensor 4, the trajectory length and the estimated trajectory length are different. That is, the detected value of the NOx sensor 4 is different from the estimated detected value, the trajectory length is different from the estimated trajectory length, and the value obtained by dividing the trajectory length by the integrated value is the value obtained by dividing the estimated trajectory length by the estimated integrated value. When the oxidation catalyst 3 is a deteriorated catalyst and the NOx sensor 4 has a gain shift, it can be determined that the gain deviation is generated.

  Further, the detected value of the NOx sensor 4 is different from the estimated detected value, the trajectory length is different from the estimated trajectory length, and the value obtained by dividing the trajectory length by the integrated value and the value obtained by dividing the estimated trajectory length by the estimated integrated value are If they are different, it can be determined that the oxidation catalyst 3 is a new catalyst.

  And when the oxidation catalyst 3 is a new catalyst, if the NOx sensor 4 is normal, the integrated value becomes substantially the same as the estimated integrated value. That is, when the oxidation catalyst 3 is a new catalyst, if the integrated value becomes substantially the same as the estimated integrated value, it can be determined that the NOx sensor 4 is normal.

  On the other hand, when the oxidation catalyst 3 is a new catalyst, if the integrated value is different from the estimated integrated value, it can be determined that the NOx sensor 4 has failed. In this case, it is impossible to determine what kind of failure has occurred in the NOx sensor 4.

  FIG. 8 is a flowchart showing a flow of failure determination of the NOx sensor 4 according to the present embodiment. This routine is repeatedly executed by the ECU 5 every predetermined time. In addition, about the step in which the same process as the flow shown in FIG. 6 is made, the same code | symbol is attached | subjected and description is abbreviate | omitted. In this embodiment, the ECU 5 that processes the routine shown in FIG. 8 corresponds to the determination means in the present invention.

  If a negative determination is made in step S103, the process proceeds to step S301. In step S301, similarly to step S102, it is determined whether the trajectory length of the detected value of the NOx sensor 4 is substantially equal to the estimated trajectory length. If an affirmative determination is made in step S301, the process proceeds to step S302. On the other hand, if a negative determination is made, the process proceeds to step S303.

  In step S <b> 302, it is determined that the oxidation catalyst 3 is a deteriorated catalyst and an offset deviation has occurred in the NOx sensor 4.

  In step S303, as in step S102, the value obtained by dividing the locus length of the detected value of the NOx sensor 4 by the integrated value of the detected value of the NOx sensor 4 is the value obtained by dividing the estimated locus length by the estimated integrated value. It is determined whether or not they are substantially equal. If an affirmative determination is made in step S303, the process proceeds to step S304, where it is determined that the oxidation catalyst 3 is a deteriorated catalyst and that a gain deviation has occurred in the NOx sensor 4.

  On the other hand, if a negative determination is made in step S303, the oxidation catalyst 3 is a new catalyst, and the process proceeds to step S106.

  When it is determined in step S106 that the integrated value and the estimated integrated value are substantially equal (when an affirmative determination is made), the process proceeds to step S305, where the oxidation catalyst 3 is a new catalyst and the NOx sensor. 4 is determined to be normal. On the other hand, if a negative determination is made in step S106, the process proceeds to step S306, where it is determined that the oxidation catalyst 3 is a new catalyst and that the NOx sensor 4 has failed.

  As described above, according to this embodiment, it can be determined whether or not the oxidation catalyst 3 is normal, and whether or not the NOx sensor 4 is normal. If the oxidation catalyst 3 is a deteriorated catalyst, it can be determined whether a gain deviation or an offset deviation has occurred in the NOx sensor 4. Based on this determination, the detection value of the NOx sensor 4 can be corrected.

1 Internal combustion engine 2 Exhaust passage 3 Oxidation catalyst 4 NOx sensor 5 ECU
6 Accelerator pedal 7 Accelerator opening sensor 8 Crank position sensor

Claims (2)

In a failure determination device for a NOx sensor, which is provided downstream of a catalyst having oxidation ability in an exhaust passage of an internal combustion engine and detects a NOx concentration in exhaust gas,
Estimating means for estimating or detecting the concentration of NOx in the exhaust gas upstream of the catalyst;
The length of the locus of the detected value of the NOx sensor in a predetermined period is equal to or greater than the threshold, and the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means is the threshold. In the above case, it is determined that the NOx sensor has failed, and when the length of the locus of the detected value of the NOx sensor in the predetermined period is less than a threshold value, the integrated value of the detected value of the NOx sensor If, by comparing the integrated value of NOx concentration estimated or detected by said estimating means, a determining means for determining a failure of the NOx sensor,
A failure determination device for a sensor comprising:   In a failure determination device for a NOx sensor, which is provided downstream of a catalyst having oxidation ability in an exhaust passage of an internal combustion engine and detects a NOx concentration in exhaust gas,
  Estimating means for estimating or detecting the concentration of NOx in the exhaust gas upstream of the catalyst;
  The length of the locus of the detected value of the NOx sensor in a predetermined period is equal to or greater than the threshold, and the absolute value of the difference between the detected value of the NOx sensor and the NOx concentration estimated or detected by the estimating means is the threshold. In the above case, it is determined that the NOx sensor is out of order, and when the length of the locus of the detected value of the NOx sensor in the predetermined period is less than a threshold value, the amount of NOx adsorbed on the catalyst is reduced. A determination unit that corrects the NOx concentration estimated or detected by the estimation unit and compares the corrected NOx concentration with a detected value of the NOx sensor, thereby determining a failure of the NOx sensor;
  A failure determination device for a sensor comprising:

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