JP5561262B2 - Detection system - Google Patents

Description

  The present invention relates to a detection system.

  Today, excellent exhaust gas purification performance is required for internal combustion engines. Particularly in diesel engines, it is important to remove so-called exhaust particulates (particulate matter, PM) such as black smoke discharged from the engine. In order to remove PM, a diesel particulate filter (DPF: Diesel Particulate Filter) is often provided in the middle of the exhaust pipe.

  There is a PM sensor as means for detecting the amount of PM in the exhaust. For example, when a PM sensor is arranged downstream of the DPF, it can be determined whether or not the DPF is out of order using the detection value of the PM sensor. In the future, it is expected that vehicle post-processing failure detection will become more severe, and it is necessary to equip a PM sensor to detect failure of the DPF. For this purpose, the PM sensor itself must be normal, and PM sensor failure detection (determination of PM sensor rationality) is also important. For example, Patent Document 1 below discloses a PM sensor failure detection apparatus.

JP 2010-275977 A

  When the DPF is normal, the amount of PM that passes through the DPF is very small, so the output value of the PM sensor mounted downstream of the DPF is small. Therefore, PM sensor failure detection involves a problem of determining whether or not the PM sensor has failed using a small output value. In the apparatus of Patent Document 1, a PM sensor failure is determined within the same period by utilizing the relatively large amount of PM that passes through the DPF for a predetermined period from the end of regeneration of the DPF.

  However, generally, a period in which the amount of PM passing through the DPF after the regeneration of the DPF is relatively large is very short, and it is difficult to accurately detect a failure of the PM sensor within the short period. Therefore, it is required to develop a mechanism for detecting a failure of the PM sensor with high accuracy regardless of the method described in Document 1.

  Therefore, in view of the above problems, the problem to be solved by the present invention is to provide a detection system that detects a failure of a PM sensor arranged downstream of a DPF with high accuracy.

In order to achieve the above object, a detection system according to the present invention is equipped with a filter that is provided in an exhaust passage of an internal combustion engine and collects particulate matter discharged from the internal combustion engine; Is also provided downstream, and during the interval period between the detection means for detecting the particulate matter and the filter regeneration process for burning the particulate matter deposited on the filter, the output from the detection means is the detection means. And a first determination unit that determines that the detection unit is malfunctioning at the end of the interval period when the output is not a predetermined output indicating that it is functioning normally.

  Thus, the detection system according to the present invention detects when the output of the detection means arranged downstream of the filter is not a predetermined output during the regeneration interval of the filter arranged in the exhaust passage and collecting particulate matter. It is determined that the means is malfunctioning. Therefore, it is possible to determine the failure of the detection means with high accuracy using the information on whether or not the output of the detection means is a predetermined output indicating that the output is normal during the filter regeneration interval.

  In addition, the determination means has a predetermined output indicating that the detection means is functioning normally during an interval period between filter regeneration processes for burning particulate matter deposited on the filter. If the output from the detection means is not the predetermined output even during the predetermined period after the start of the filter regeneration process is delayed for a predetermined period of time, it is determined that the detection means is out of order. It is good.

  According to the present invention, when the amount of particulate matter passing through the filter is small, for example, when the collection rate of the filter is high, the detection means is normal only by the determination during the normal filter regeneration interval period. However, since there is a possibility of erroneous determination as a failure, if the filter regeneration start is delayed for a predetermined period and a predetermined output is not obtained during that period, the detection means determines that there is a failure. This can reduce the possibility of erroneous determination by the detection means.

  The first determination means determines that the output is not the predetermined output when the output of the detection means does not exceed the first threshold, and the output of the detection means exceeds the second threshold greater than the first threshold. Second filter means for determining that the filter is faulty may be provided.

  According to this invention, in addition to the means for determining the failure of the detecting means, the means for determining the failure of the filter is provided, and the threshold value is provided for both determinations, and the second threshold value for determining the filter failure is determined as the failure means for detecting the filter. Greater than the first threshold. Therefore, it is possible to appropriately determine the failure of the detection means in a situation where the amount of the particulate matter passing through the filter is small, and it is possible to accurately determine the filter failure with a relatively high threshold.

  In addition, a second determination unit that determines that the filter is faulty based on an output of the detection unit is provided. The first determination unit and the second determination unit include an electric circuit, and the first determination unit includes the first determination unit. One circuit may be a circuit having higher sensitivity than the second circuit included in the second determination unit.

  According to the present invention, the detection circuit and the electric circuit for determining the failure of the filter are provided, and in the case of detecting the failure of the detection unit, an electric circuit having higher sensitivity than that in the case of detecting the filter failure is used. Therefore, normally, in the case of failure determination of the detection means, it is determined whether or not it is a failure with a smaller amount of particulate matter attached than in the case of filter failure determination, but by using a circuit with higher sensitivity, Even with a small amount of particulate matter, the failure of the detection means can be determined with high accuracy.

  Further, the first determination means indicates that the output from the detection means is functioning normally during the interval period between filter regeneration processes for burning particulate matter deposited on the filter. If the predetermined output is not shown, the temperature of the detection means is increased, and if the output from the detection means whose temperature has been raised is not the predetermined output, it may be determined that the detection means has failed. .

  According to the present invention, when the predetermined output is not output during the normal filter regeneration interval, the temperature of the detection means is increased, and when the predetermined output is still not output, it is determined that the detection means has failed. Therefore, when the electrical resistance value of the particulate matter adhering to the detection means is high and the adhesion amount does not appear as an output to the detection means, the temperature characteristic of the particulate matter is effectively used to raise the temperature of the detection means. This reduces the electrical resistance of the particulate matter and facilitates the output of the detection means. Therefore, it is possible to prevent the detection means from erroneously determining that the particulate matter has a failure due to a high electrical resistance value.

  Further, the first determination means indicates that the output from the detection means is functioning normally during the interval period between filter regeneration processes for burning particulate matter deposited on the filter. When the output is not the predetermined output, the voltage applied to the detection means is increased, and the output from the detection means to which a higher voltage is applied is not the predetermined output, the detection means has failed. May be determined.

  According to the present invention, when the predetermined output is not output during the normal filter regeneration interval, the voltage applied to the detection means is increased, and the detection means fails when the predetermined output is still not output. judge. Therefore, when the electrical resistance value of the particulate matter adhering to the detection means is high and the adhesion amount does not appear as an output to the detection means, the voltage applied to the detection means is increased so that the electrical resistance of the particulate matter is high. Make the output of the detection means easier. Therefore, it is possible to prevent the detection unit from erroneously determining that the particulate matter is faulty due to the high electrical resistance.

The block diagram in the Example of the detection system in this invention. The figure which shows the example of the structure of PM sensor. The figure which shows the example of the output of PM sensor. 3 is a flowchart of failure detection processing in the first embodiment. FIG. 3 is a diagram illustrating an example of a time chart in the first embodiment. 10 is a flowchart of failure detection processing in the second embodiment. FIG. 10 is a diagram illustrating an example of a time chart in the second embodiment. The figure which shows the example of the threshold value of DPF sensor failure determination and DPF failure determination. 10 is a flowchart of detection processing according to the third embodiment. FIG. 10 is a diagram illustrating an example of a time chart in the third embodiment. 10 is a flowchart of detection processing according to the fourth embodiment. FIG. 10 is a diagram illustrating an example of a time chart in the fourth embodiment. 1 is a schematic diagram of a system configuration example of a PM sensor.

  Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic diagram of an apparatus configuration in an embodiment of a detection system 1 (hereinafter, system) according to the present invention. The configuration of FIG. 1 may be used in all the following embodiments.

  The system 1 is a system for detecting the amount of PM in an exhaust pipe (exhaust passage) of a diesel engine 2 (engine) of an automobile. A DPF 3 and a PM sensor 4 are disposed on the exhaust pipe of the engine 2 from the upstream side.

  For example, the DPF 3 may have a structure in which the inlet side and the outlet side are alternately clogged in a so-called honeycomb structure. The exhaust discharged during operation of the engine 2 contains PM (particulate matter), and this PM is collected inside or on the surface of the DPF wall when the exhaust gas passes through the DPF wall having the above structure of the DPF 3. The exhaust discharged outside the vehicle is purified. For example, the DPF 3 may be a DPF with an oxidation catalyst on which an oxidation catalyst is supported.

  Every time the amount of PM deposited on the DPF 3 becomes sufficiently large, the deposited PM is removed by burning, and the DPF 3 is regenerated. For example, the PM accumulation amount is estimated by, for example, obtaining a functional relationship (map) between the differential pressure before and after the DPF 3 and the PM accumulation amount in advance and storing it in the memory 50, disposing the differential pressure sensor, and detecting it. The PM deposition amount may be estimated from the value and the map. In this map, as a typical characteristic, the relationship between the longitudinal pressure difference and the PM deposition amount on the vertical axis represents the shape of a substantially parallelogram, and the PM is accumulated and burned to form the parallelogram. Take one round.

  The PM sensor 4 detects the amount of PM in the exhaust downstream from the DPF 3. Since the PM sensor 4 is provided downstream of the DPF 3, the PM amount that has passed through the DPF 3 can be detected by the PM sensor 4. Thereby, the presence or absence of a failure of the DPF 3 can be detected.

  An electronic control unit 5 (ECU: Electronic Control Unit) is equipped to control the above system. The ECU 5 may have a structure similar to that of a normal computer and may include a CPU that performs various calculations and a memory 50 that stores various types of information.

  An example of the structure of the PM sensor 4 is shown in FIG. The sensor element 40 (element) of the PM sensor 4 has a structure in which a pair of detection electrodes 42 (electrodes) are formed on a plate-like insulator 44. The whole is covered with, for example, a metal cover 41. Several holes are formed in the cover 41, and PM in the exhaust pipe flows into the cover 41. PM adheres to and accumulates on the element 42 due to its own adhesiveness. Since PM has conductivity, when the pair of electrodes 42 are connected by the PM deposited on the element 40, the electrodes are in a conductive state.

  A voltage is applied between the electrodes from a power source (not shown), and when PM is deposited on the element 40 and the electrodes 42 become conductive, a current flows between the electrodes. The PM sensor 4 may be, for example, a measured value such as a current value (in addition, a voltage value of a certain part on the circuit, and further an impedance value (resistance value or capacitance value) calculated from the voltage value or current value). ) To the ECU 5 as a sensor output.

  FIG. 3 shows an example of such a situation. As described above, even if the amount of PM deposited on the element surface gradually increases, the output value of the PM sensor 4 remains zero until the electrodes are electrically connected, and the electrodes are electrically connected. Thereafter, the output value of the PM sensor 4 increases from zero. When it is considered that a large amount of PM has accumulated (attached) to the PM sensor, the element 40 is heated by the heater 43, and the accumulated PM is burned and removed to regenerate the PM sensor 4.

  A more detailed system configuration example of the PM sensor 4 is shown in FIG. As shown in the figure, the PM sensor 4 includes a temperature adjustment unit 45, a voltage adjustment unit 46, circuits 47a and 47b, a switch 48, and a control unit 49 in addition to the pair of detection electrodes 42 and 42 (electrodes) and the heater 43 described above. Prepare.

  The temperature adjustment unit 45 adjusts the temperature of the element 40 by the power supplied to the heater 43. The voltage adjusting unit 46 adjusts the voltage applied to the electrodes 42 and 42. The circuits 47 a and 47 b are arranged as shown in FIG. 13, for example, and one of the circuits 47 a and 47 b is electrically connected to the detection electrode 42 of the element 40 under the control of the switch 48. The circuits 47a and 47b are equipped to detect information on the amount of PM attached to the element 40 as electrical characteristics (details will be described later). The control unit 49 has a configuration similar to that of a normal computer such as a microprocessor and controls all of the PM sensor 4.

  The circuits 47a and 47b will be described. The PM sensor 4 performs two detections, that is, a failure detection of the DPF 3 and a failure detection of the PM sensor 4 itself, and includes two circuits 47a and 47b for the two detections. The PM sensor 4 performs these two detections using a mechanism in which information on the amount of PM attached to the element 40 becomes an electrical characteristic between the electrodes 42 and 42.

  In the case of the failure determination of the PM sensor 4, a situation where the normal PM amount is smaller than that in the case of the DPF failure determination is assumed. Therefore, as will be described later, the failure determination threshold of the PM sensor 4 is set smaller than the DPF failure determination threshold. In the case of detecting a failure of the PM sensor 4 itself, it is desirable that the PM sensor 4 has higher sensitivity than in the case of detecting a failure of the DPF 3. For this purpose, in the PM sensor 4, for example, the circuit 47a is a circuit for detecting the resistance component (R), and the circuit 47b is a circuit for detecting the capacitance component (C).

  In the detection of the resistance component by the circuit 47a, the resistance component is detected from the current value flowing in a state where the electrodes 42 and 42 are connected by the adhered PM. On the other hand, in the detection of the capacitive component by the circuit 47b, even if the electrodes 42 and 42 are not connected by PM, the separated PM has a capacitive component, so the capacitive component is detected from the current value flowing through the capacitance. .

  Accordingly, the detection result starts to increase from zero when the detection of the capacitive component is clearly earlier than the detection of the resistance component. In this sense, the detection of the capacitive component is more sensitive than the detection of the resistance component. Further, according to the knowledge of the inventor, the detection of the resistance component is more stable than the detection of the capacitance component (such as less error and blurring). Therefore, the circuit 47b has higher sensitivity than the circuit 47a, and the circuit 47a has better output stability than the circuit 47b.

  In the case of detecting the failure of the DPF 3, the circuit 47a is connected by the switch 48, the attached PM amount (a resistance value indicating it) is stably detected, and the failure is determined with a relatively high threshold. In the case of failure detection of the PM sensor 4, the circuit 47 b is connected by the switch 48, the attached PM amount (capacitance value indicating it) is detected with high sensitivity, and failure determination is performed with a relatively low threshold.

  The configuration of FIG. 13 is an example and is a conceptual diagram. For example, although the circuits 47a and 47b are simply arranged in parallel in FIG. 13, the actual circuit configuration may be more complicated. Further, as described above, the circuit 47a is not limited to the resistance component detection and the circuit 47b is not limited to the capacitance component detection, and may be configured to be switched between a circuit with higher sensitivity and a circuit with lower sensitivity. A known method may be used for measuring and calculating the resistance value and the capacitance value.

  Based on the above configuration, the system 1 determines the presence or absence of a failure of the PM sensor 4 from the output of the PM sensor 4. The failure of the PM sensor 4 may include all failures such as clogging of the hole of the cover 41 and failure of the electric system. The processing procedure in the first embodiment is shown in FIG. The flowchart of FIG. 4 (and all that will be described later) may be programmed in advance, and stored in the memory 50, for example, and automatically called by the ECU 5 and executed.

  In the process of FIG. 4, first in step S10, the ECU 5 commands the start of DPF regeneration, and commands the end of DPF regeneration in S20. Therefore, the period after S20 is a period (interval period) between the DPF regeneration and the next DPF regeneration. In the process of FIG. 4 (the same applies to other flowcharts), the PM sensor is not regenerated within the DPF regeneration interval.

  Next, in S25, the ECU 5 selects which of the circuits 47a and 47b is used in the PM sensor 4. As described above, for example, when the circuit 47a is a circuit for detecting the resistance value (R) and the circuit 47b is a circuit for detecting the capacitance value (C), the low-sensitivity circuit 47a detects the failure of the DPF 3. The high-sensitivity circuit 47b is suitable for detecting a failure of the PM sensor 4. Therefore, since the presence or absence of a failure of the PM sensor 4 is determined after S25, the circuit 47b is selected in S25 and the circuit 47b is connected by the switch 48.

  Next, in S30, the ECU 5 detects (acquires) the output of the PM sensor 4. In S40, the ECU 5 determines whether regeneration of the DPF 3 is requested. The regeneration of the DPF 3 is requested when the ECU 5 determines that the estimated value of the PM accumulation amount in the DPF 3 exceeds a predetermined value for starting the DPF regeneration. If regeneration of the DPF 3 is requested (S40: Yes), the process proceeds to S50, and if regeneration is not requested (S40: No), S30 is repeated. Thus, until the next DPF regeneration after the DPF regeneration completed in S20 is requested, S30 is repeated to continuously monitor the PM sensor output value. The acquired PM sensor output value (series) may be stored in the memory 50, for example.

  After proceeding to S50, the ECU 5 determines whether or not it is during the DPF regeneration interval. When it is during the DPF regeneration interval period (S50: Yes), the process proceeds to S60, and when it is not the DPF regeneration interval period (S50: No), the process of FIG.

  After proceeding to S60, the ECU 5 determines whether or not at least one numerical value among the outputs of the PM sensor 4 detected (acquired) at S30 is smaller than a threshold value. Here, the threshold value is a numerical value that allows the PM sensor 4 to be considered normal if the output of the PM sensor 4 exceeds the numerical value. When the output (sequence) of the PM sensor 4 is smaller than the threshold value (S60: Yes), the process proceeds to S90, and when it is equal to or greater than the threshold value (S60: No), the process proceeds to S100.

  The process proceeds to S90 when the output of the PM sensor 4 has never exceeded the threshold value. Accordingly, in S90, the ECU 5 determines that the PM sensor 4 has failed. On the other hand, when the process proceeds to S100, the output of the PM sensor 4 exceeds the threshold value once. Accordingly, in S100, the ECU 5 determines that the PM sensor 4 is normal. The above is the processing procedure of FIG. In FIG. 4 (or FIG. 4 is changed), S60 to S100 may be executed in a predetermined cycle, for example, during the DPF regeneration interval. In this case, the PM sensor 4 is determined to be normal if there is even one output that exceeds the threshold value during the DPF regeneration interval.

  An example of a temporal transition (time chart) when the process of FIG. 4 is executed is shown in FIG. In the configuration of FIG. 1, a small amount of PM discharged from the engine 2 during the DPF regeneration interval period usually passes through even if the DPF 3 is normal. Therefore, as shown in the figure, the accumulated amount of PM (or soot) that has passed through the DPF 3 gradually increases with time. Depending on the setting of the degree of PM emission from the engine 2 and the performance of collecting the base material of the DPF 3, the travel distance of the vehicle on which the engine 2 is mounted during the DPF regeneration interval period is about 200 km to about 800 km.

  For a certain period after the start of the DPF regeneration interval period, the amount of PM adhering to the element 40 is small and the electrodes are not connected, so the output value of the PM sensor 4 remains zero. Thereafter, when the amount of PM attached to the element 40 increases, the electrodes are electrically connected from a certain point, and the output value of the PM sensor 4 starts increasing from zero. In the process of FIG. 4, when the output value of the PM sensor 4 exceeds the PM sensor failure determination threshold value (even once) within the DPF regeneration interval period, it is determined that the PM sensor 4 is normal. If the output value of the PM sensor 4 does not exceed the PM sensor failure determination threshold value (at least once) during the DPF regeneration interval, the PM sensor 4 is determined not to have a normal output value and is defective.

  In S60, the failure determination is made based on whether or not the PM sensor output during the DPF regeneration interval exceeds the threshold. However, the present invention is not limited to this, and the predetermined output when the PM sensor output is normal is used. It may be determined whether there is a failure or not. In this case, as a method for determining whether or not the output is normal, for example, if the rise time of the PM sensor output is faster than a predetermined time, it is normal (failure if it is late), and the rising speed (slope) of the PM sensor output is If it is larger than a predetermined value, it is normal (if it is smaller, it is a failure).

  As described above, in the first embodiment, when the PM sensor output is not normal during the DPF regeneration interval, it is determined that the PM sensor 4 is out of order. At that time, PM sensor regeneration was not performed during the interval, and a highly sensitive circuit was used as a circuit for detecting the amount of PM adhering to the element 40. Thereby, the failure of the PM sensor 4 can be detected with high accuracy.

  Next, Example 2 will be described. In the second embodiment, if the PM sensor output does not exceed the threshold during the normal DPF regeneration interval, the start of DPF regeneration is delayed for a predetermined period, and the failure determination is continued for the predetermined period. The processing procedure in the second embodiment is shown in FIG. In the processing procedure of FIG. 6, S65 to S85 are added to the processing procedure of FIG. Since the processes with the same reference numerals as those in FIG. 4 are the same processes, the overlapping description will be omitted below.

  In the process of FIG. 6, when an affirmative determination is made in S60 (S60: Yes), the process proceeds to S65. In S65, the ECU 5 suspends (delays) the start of regeneration of the DPF 3 although it is confirmed in S40 that a DPF regeneration request has been issued. In subsequent S70, the ECU 5 continues to detect (acquire) the PM sensor output.

  The ECU 5 determines whether or not the elapsed time from the DPF regeneration request in S80 (that is, the elapsed time since the DPF regeneration start suspension is started in S65 (DPF regeneration start suspension time)) exceeds a predetermined threshold value. To do. When the DPF regeneration start holding time exceeds the threshold (S80: Yes), the process proceeds to S85, and when the threshold is not exceeded (S80: No), the detection (acquisition) of the PM sensor output in S65 is repeated. By repeatedly executing S65, the PM sensor output value is continuously monitored even during the DPF regeneration start suspension period.

  After proceeding to S85, the ECU 5 determines whether or not at least one of the outputs of the PM sensor 4 during the DPF regeneration start suspension period detected (acquired) in S70 is greater than a threshold value. The threshold value in S85 may be the same as the threshold value in S60. When all the outputs of the PM sensor 4 during the DPF regeneration start suspension period are smaller than the threshold (S85: Yes), the process proceeds to S90, and at least one of the outputs of the PM sensor 4 during the DPF regeneration start suspension period is equal to or more than the threshold. In (S85: No), it progresses to S100.

  When the process proceeds to S90, the output value of the PM sensor 4 never reaches the threshold value within the normal DPF regeneration interval period (S60: Yes), and the output value of the PM sensor 4 remains within the DPF regeneration start suspension period. This is a case where the threshold has never been reached (S85: Yes). Accordingly, in S90, the ECU 5 determines that the PM sensor 4 has failed.

  On the other hand, when the process proceeds to S100, the output value of the PM sensor 4 once exceeded the threshold value within the normal DPF regeneration interval period (S60: No), or the output value of the PM sensor 4 within the DPF regeneration start suspension period. Is once the threshold value is exceeded (S85: No). Accordingly, in S100, the ECU 5 determines that the PM sensor 4 is normal. The above is the processing procedure of FIG.

  FIG. 7 shows an example of a time chart when the processing of FIG. 6 is executed. As in the case of FIG. 5, during the DPF regeneration interval, a small amount of PM discharged from the engine 2 passes through even if the DPF 3 is normal, and the PM accumulated amount that has passed through the DPF 3 as shown is gradually increased with time. Will increase. When the amount of PM attached to the element 40 increases, the electrodes are electrically connected from a certain point, and the output value of the PM sensor 4 starts increasing from zero. Similarly to FIG. 5, in the case of FIG. 7 as well, if the output value of the PM sensor 4 exceeds the PM sensor failure determination threshold even once within the DPF regeneration interval period, it is determined that the PM sensor 4 is normal.

  On the other hand, if the output value of the PM sensor 4 has never exceeded the PM sensor failure determination threshold value during the DPF regeneration interval, the PM sensor failure determination is not performed at that time, and the DPF regeneration start is suspended for a predetermined period. To do. If the output value of the PM sensor 4 exceeds the PM sensor failure determination threshold during the DPF regeneration start suspension period, the PM sensor 4 is determined to be normal. Conversely, even during the DPF regeneration start suspension period, if the output value of the PM sensor 4 has never exceeded the PM sensor failure determination threshold value during the period, the PM sensor 4 has failed at the end of the suspension period. Is determined. As a result, the start of DPF regeneration is suspended, and a PM sensor failure can be determined more reliably.

  As described above, in the second embodiment, when the output value of the PM sensor 4 does not reach the threshold value within the normal DPF regeneration interval period, the regeneration of the DPF 3 is suspended without determining that the PM sensor 4 has failed immediately. Thus, when the output value of the PM sensor 4 does not reach the threshold even during the holding period, it is determined that the PM sensor 4 has failed. Therefore, the failure determination of the PM sensor 4 becomes more reliable.

  As described above, in the system 1, both the failure of the DPF 3 and the failure of the PM sensor 4 are determined by looking at the output of the PM sensor 4. An example of setting the threshold value in both determinations is shown in FIG. The DPF failure determination threshold is a numerical value that determines that the DPF 3 has failed if the output of the PM sensor 4 exceeds the numerical value. The PM sensor failure determination threshold value is a numerical value that determines that the PM sensor 4 has failed if the output of the PM sensor 4 does not reach the value (threshold value used in S60 and S85 described above).

  The situation in which the PM sensor failure determination is performed is normally assumed to be a situation in which the amount of PM passing through from the downstream side of the DPF is small. Further, even if the threshold value for determining the DPF failure is a relatively large value, the DPF failure determination can be performed with high accuracy. For the above reasons, as shown in FIG. 8, the DPF failure determination threshold value is set to a larger value than the PM sensor failure determination threshold value. As a result, it is possible to avoid the occurrence of a case in which the failure of the DPF 3 is determined by the output of the failed PM sensor 4.

  Next, Example 3 will be described. In the third embodiment, in order to reliably determine the failure of the PM sensor 4, the element temperature of the PM sensor 4 is increased and the electrical resistance of the PM attached to the PM sensor 4 is decreased. The processing procedure in the third embodiment is shown in FIG. In the processing procedure of FIG. 9, the process of S66 is added to the processing procedure of FIG. Since the processes with the same reference numerals as those in FIG. 6 are the same processes, the overlapping description is omitted below.

  In the process of FIG. 9, after S65 is processed, S66 is processed next. In S <b> 66, the ECU 5 controls the temperature of the element 40 of the PM sensor 4 to rise by heating the heater 43 with the temperature adjustment unit 45. The reason for increasing the element temperature is that the electric resistance of the PM adhering to the element 40 is high, so that even if PM is deposited on the PM sensor, the effect may not easily appear as the output of the PM sensor. In general, the electrical resistance value of PM has a specific temperature characteristic. At the temperature assumed in the configuration of FIG. 1 and the like (for example, in the range of room temperature to about 300 degrees Celsius), the electrical resistance value of PM becomes ( Decrease in the graph). Therefore, by raising the temperature of PM adhering to the element 40, the electric resistance of the PM decreases, current flows easily, and the output of the PM sensor is easily output.

  An example of the temperature rise of the element 40 of the PM sensor 4 is shown in FIG. As shown in FIG. 10, the PM sensor element temperature may be raised for a relatively short period (a period shorter than the DPF regeneration start suspension period). If the PM sensor output rises within the DPF regeneration start suspension period and exceeds the threshold even once due to the effect of this temperature rise, the PM sensor 4 is determined to be normal. If the PM sensor output does not increase despite the temperature rise and does not exceed the threshold even once, it is determined that the PM sensor 4 has failed.

  In Example 3, if the output value of the PM sensor 4 does not reach the threshold value within the normal DPF regeneration interval period, the regeneration of the DPF 3 is suspended for a predetermined period without immediately determining that the PM sensor 4 has failed. During the period, the element temperature of the PM sensor 4 is raised, the electric resistance of the PM attached to the element is lowered, and if the output value of the PM sensor 4 still does not reach the threshold value, it is determined that the PM sensor 4 has failed. Therefore, from the failure determination of the PM sensor 4, the influence of the high PM electric resistance value is removed, and the failure determination becomes more reliable.

  Next, Example 4 will be described. In the fourth embodiment, the voltage applied to the PM sensor 4 is increased in order to reliably determine the failure of the PM sensor 4. The processing procedure in the fourth embodiment is shown in FIG. In the processing procedure of FIG. 11, the process of S67 is added to the processing procedure of FIG. Since the processes with the same reference numerals as those in FIG. 6 are the same processes, the overlapping description is omitted below.

  In the process of FIG. 11, after S65 is processed, S67 is processed next. In S <b> 67, the ECU 5 uses the voltage adjustment unit 46 to control the voltage applied to the PM sensor 4 to increase. The reason why the voltage applied to the PM sensor 4 is increased in this way is that, when the electric resistance value of the PM deposited on the PM sensor 4 is high, even if PM is deposited on the PM sensor, the effect is the output of the PM sensor. This is because it may be difficult to appear. By increasing the voltage applied to the PM sensor, the output of the PM sensor can be easily output even when the electrical resistance value of the PM deposited on the PM sensor 4 is high.

  An example of an increase in the voltage applied to the PM sensor 4 is shown in FIG. As shown in FIG. 12, the voltage applied to the PM sensor may be increased stepwise, for example. If the PM sensor output rises within the DPF regeneration start holding engine and exceeds the threshold even once due to the effect of this voltage increase, it is determined that the PM sensor 4 is normal. If the PM sensor output does not increase despite the increase in voltage and the threshold value is never exceeded within the DPF regeneration start suspension engine, it is determined that the PM sensor 4 is in failure.

  In Example 4, when the output value of the PM sensor 4 does not reach the threshold value within the normal DPF regeneration interval period, the regeneration start of the DPF 3 is suspended without determining that the PM sensor 4 has failed immediately, During the holding period, the voltage applied to the PM sensor 4 is increased, and if the output value of the PM sensor 4 still does not reach the threshold value, it is determined that the PM sensor 4 has failed. Therefore, the failure determination of the PM sensor 4 eliminates the effect of the accumulated electrical resistance value of the PM, and the failure determination becomes more reliable.

  In addition, the said Example can be suitably changed in the range which does not deviate from the meaning described in the claim. For example, the engine 2 has the same effect not only as a diesel engine but also as a lean burn gasoline engine. Further, in the case of matters not related to disposing the PM sensor 4 downstream of the DPF 3 (for example, circuit selection), the configuration is not limited to the configuration in which the PM sensor 4 is disposed downstream of the DPF 3.

1 detection system 2 diesel engine (engine, internal combustion engine)
3 Diesel particulate filter (DPF)
4 PM sensor

Claims (6)

A filter that is provided in an exhaust passage of the internal combustion engine and collects particulate matter discharged from the internal combustion engine;
A detection means that is provided downstream of the filter in the exhaust passage and detects particulate matter;
During the interval period between the filter regeneration process for burning the deposited particulate matter in the filter, when the output of said detecting means, said detecting means is not the predetermined output indicating that it is functioning properly, the First determination means for determining that the detection means has failed at the end of the interval period ;
A detection system comprising:   The first determination means indicates that the output from the detection means indicates that the detection means is functioning normally during an interval period between filter regeneration processes for burning particulate matter deposited on the filter. When the output is not a predetermined output, the start of the filter regeneration process is delayed for a predetermined period, and if the output from the detection means is not the predetermined output during the predetermined period, it is determined that the detection means has failed. The detection system according to claim 1. The first determination means is not the predetermined output when the output of the detection means does not exceed a first threshold value,
3. The detection system according to claim 1, further comprising: a second determination unit that determines that the filter is faulty when an output of the detection unit exceeds a second threshold value that is larger than the first threshold value. A second determination unit that determines that the filter is faulty based on an output of the detection unit;
The first determination means and the second determination means include an electric circuit,
The detection system according to claim 1 or 2, wherein the first circuit included in the first determination unit is an electric circuit having higher sensitivity than the second circuit included in the second determination unit.   The first determination means indicates that the output from the detection means indicates that the detection means is functioning normally during an interval period between filter regeneration processes for burning particulate matter deposited on the filter. The detection means according to claim 1, wherein when the output is not a predetermined output, the temperature of the detection means is increased, and when the output from the detection means whose temperature has been raised is not the predetermined output, it is determined that the detection means has failed. The described detection system.   The first determination means indicates that the output from the detection means indicates that the detection means is functioning normally during an interval period between filter regeneration processes for burning particulate matter deposited on the filter. If the voltage applied to the detection means is higher when it is not the predetermined output, and the output from the detection means to which a higher voltage is applied is not the predetermined output, the detection means is faulty. The detection system according to claim 1 for determining.