JP2009144577A - Failure determination device for particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a failure determination device for a particulate filter capable of accurately detecting even minor failure. <P>SOLUTION: The failure determination device for the particulate filter is provided with DPF 3 provided on an exhaust passage 4 of an engine 1 and capturing a particulate matter in an exhaust gas; an insulation layer 10 comprising an electric insulation material provided on the exhaust passage 4 so as to be positioned on a downstream side of DPF 3 and deposited with the particulate matter passed through DPF 3; a plurality of electrodes provided on the insulation layer 10 so as to be separated from one another; and ECU 7 for measuring an index correlated to an electric resistance value between the plurality of electrodes 11 and determining the failure of DPF 3 when it is detected that the measured index becomes smaller than a predetermined reference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a failure determination device for a particulate filter that purifies exhaust gas from an internal combustion engine.

Particulate matter (PM) emission is a problem in diesel engines and the like that extract their output mainly by diffusion combustion of liquid fuel. As a means for suppressing this PM emission, there is one that installs a diesel particulate filter (DPF; Diesel Particulate Filter) in the exhaust system. Examples of the failure of the DPF include melting damage accompanying overdeposition PM combustion (overheated combustion) during forced regeneration. When a large opening is formed due to DPF breakage, such as melting damage, it is possible to determine a failure by measuring the pressure loss and temperature of the DPF before and after, and such a failure monitoring system Is already known.
As an example, Patent Document 1 discloses a method for determining a failure of a particulate filter based on a temporal change in a deposited PM amount calculated based on a differential pressure across the particulate filter and a volume flow rate of exhaust gas. ing.

JP-A-8-284644

  However, since the above-described conventional failure monitoring system is a method of measuring the pressure loss across the filter by differential pressure measurement, it is difficult to accurately determine minor failures in the DPF such as the occurrence of cracks, for example. .

  In addition, the performance required for a failure monitoring system tends to be required to be accurately detected even for minor failures against the background of increasing social interest in global environmental problems. There is a problem that cannot fully meet social demands.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a particulate filter failure determination device that can accurately detect even a minor failure.

A particulate filter failure determination apparatus according to a first invention for solving the above-described problems is provided.
A particulate filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust gas;
An electrical insulating material that is provided in the exhaust passage located downstream of the particulate filter, and to which the particulate matter that has passed through the particulate filter adheres;
A plurality of electrodes provided at a distance from each other in the electrical insulating material;
Control means for measuring an index correlating with an electrical resistance value between the plurality of electrodes and detecting a failure of the particulate filter when detecting that the measured index is smaller than a predetermined reference. And

A particulate filter failure determination apparatus according to a second invention for solving the above-mentioned problems is as follows.
In the particulate filter failure determination device according to the first invention,
The electrical insulating material has a smaller capacity than the particulate filter.

A particulate filter failure determination device according to a third aspect of the present invention for solving the above-described problem is provided.
In the particulate filter failure determination device according to the first or second invention,
A heater provided on the electrical insulator;
The control means energizes the heater to periodically remove particulate matter adhering to the electrical insulating material.

A particulate filter failure determination device according to a fourth aspect of the present invention for solving the above-described problem is provided.
In the particulate filter failure determination device according to any one of the first to third aspects of the invention,
The control means evaluates the measured index when the exhaust gas temperature is equal to or higher than the vaporization temperature of the condensed water and equal to or lower than the combustion temperature of the particulate matter.

  According to the first invention, an electrical insulating material is provided downstream of the particulate filter, an index that correlates with an electrical resistance value that varies depending on the particulate matter adhering to the electrical insulating material is measured, and a failure is determined based on the index. Therefore, it is possible to make a determination according to the accumulation amount of the particulate matter that has passed through the particulate filter, and it is possible to determine with a high degree of accuracy the performance of the particulate filter. Therefore, even a failure (such as a microcrack) that cannot be detected by the differential pressure across the particulate filter can be detected with high accuracy, and a minor failure monitoring of the particulate filter can be performed.

  According to the second invention, since the electrical insulating material is made smaller than the particulate filter, it is possible to determine the performance deterioration of the particulate filter with good responsiveness, and to suppress the enlargement of the apparatus.

  According to the third and fourth inventions, particulate matter adhering to the electrical insulating material is periodically removed, and the exhaust temperature is equal to or higher than the vaporization temperature of the condensed water, and the combustion temperature of the particulate matter. Since the measured index is evaluated when the following is true, it is possible to prevent erroneous determination and achieve highly accurate determination.

  Hereinafter, the particulate filter failure determination device according to the present invention will be described in detail with reference to FIGS.

  FIG. 1A is a schematic diagram showing a particulate filter failure determination apparatus according to the present invention, and FIG. 1B is an enlarged view of a portion A thereof. FIG. 2 is a flowchart for explaining the control in the particulate filter failure determination apparatus according to the present invention, and FIG. 3 is a graph for explaining the failure determination.

The internal combustion engine in the present invention is a diesel engine (hereinafter referred to as an engine) 1 that obtains an output mainly by diffusion combustion of fuel, and is disposed in the exhaust passage 4 as shown in FIG. Diesel Oxidation Catalyst (hereinafter abbreviated as DOC) ₂ that oxidizes NO in NO ₂ , and DPF 3 that is provided downstream of DOC 2 in exhaust passage 4 and collects PM in the exhaust Is provided.

  Furthermore, a PM trap sensor 5 is provided in the exhaust passage 4 that is located downstream of the DPF 3 and measures the accumulated amount of PM that has passed through the DPF 3 without being collected. The sensor head 6 of the PM trap sensor 5 is disposed inside the exhaust passage 4, and the amount of PM detected by the sensor head 6 is abbreviated as an electronic control device (control means; hereinafter referred to as an ECU (Electronics Control Unit)). .) The control described later is performed by 7 monitoring.

The PM trap sensor 5 will be described in more detail with reference to FIG.
The sensor head 6 of the PM trap sensor 5 includes an insulating layer 10 made of an electrical insulating material to which PM 16 that has passed through the DPF 3 without being collected and two or more plural pieces provided on the insulating layer 10 apart from each other. Electrode 11 and a measuring instrument 12 for measuring the electrical resistance value between the plurality of electrodes 11. Instead of the electrical resistance value, an index correlated with the electrical resistance value, for example, a current or a voltage may be measured. As the insulating layer 10, for example, alumina or the like is used.

  Further, the insulating layer 10 is provided with a heater layer 13 for heating the insulating layer 10, and by applying a voltage from the heater control power supply 15 to the heating resistor 14 of the heater layer 13, the insulating layer 10 is heated to the PM combustion temperature. As a result, the PM adhering to the insulating layer 10 is burned.

  Note that the insulating layer 10 has a smaller capacity than the DPF 3. This is to reduce the performance of the DPF 3 with good responsiveness and reduce the size of the device by reducing the capacity of the insulating layer 10.

  Although details will be described with reference to FIG. 3, in the sensor head 6, when PM 16 is deposited on the insulating layer 10, a change appears in the electric resistance value between the electrodes 11. Can be detected.

  Here, with reference to FIG. 2 and FIG. 3, the control in the particulate filter failure determination apparatus according to the present invention will be described.

  In the ECU 7, the elapsed period since the previous PM trap sensor 5 was reset (the reset will be described later) is monitored. If the predetermined period has elapsed, the process proceeds to step S2, and if the predetermined period has not elapsed, the process proceeds to step S3 (step S1). For example, the elapsed period is obtained by integrating the travel distance, travel time, and amount of fuel used.

  If the predetermined period has elapsed, the PM trap sensor 5 is reset (step S2). That is, the PM trap sensor 5 is reset periodically (every predetermined travel time, every predetermined travel distance, every amount of fuel used) in order to improve the measurement accuracy of the electrical resistance value described later.

  Here, reset of the PM trap sensor 5 will be described. As shown in FIG. 1B, in the sensor head 6, the insulating layer 10 is provided with a heater layer 13, and the heater layer 13 can be used to heat the insulating layer 10 to the PM combustion temperature or higher. It has become. When a predetermined period has elapsed, the heating resistor 14 of the heater layer 13 is energized, the insulating layer 10 is heated to a temperature equal to or higher than the PM combustion temperature for a predetermined time, the adhered PM is burned, and the PM adhered to the insulating layer 10 The PM trap sensor 5 itself is reset by removing.

  This is a numerical value less than the OBD regulation value even if the DPF 3 is functioning normally, but there is PM passing through the DPF 3, and even such a minute amount of PM adheres to the insulating layer 10. This is because if the layers are stacked, an error may occur in the measurement of the electric resistance value in the insulating layer 10. Therefore, in the present invention, the PM trap sensor 5 is reset in order to suppress such an error and prevent erroneous determination.

  Next, similarly, in order to improve the measurement accuracy, it is confirmed whether or not a condition for monitoring the electrical resistance value between the electrodes 11 is satisfied. If the monitorable condition is satisfied, the process proceeds to step S4. If the monitorable condition is not satisfied, the present control is terminated (step S3).

  Specifically, the conditions under which the electrical resistance value can be monitored are such that the exhaust temperature is equal to or higher than the vaporization temperature of the condensed water (≈100 ° C.) by monitoring a temperature sensor (not shown) for measuring the exhaust temperature with the ECU 7. And it is confirmed whether it is below the combustion temperature of PM. This is because if the condensed water adheres to the insulating layer 10, an error may occur in the electrical resistance measurement due to the influence of the condensed water (conductor). As the timing for monitoring the resistance value, for example, in order to eliminate the influence of the condensed water in the exhaust passage 4, the temperature becomes a temperature at which the condensed water evaporates, and this temperature is measured after a predetermined time has elapsed, or the condensed water is condensed. The temperature of the heater layer 13 is set to be equal to or higher than the vaporization temperature and equal to or lower than the combustion temperature of PM, and monitoring is performed when the temperature is stabilized.

  If the conditions are such that the electrical resistance value can be monitored, then the electrical resistance value between the electrodes 11 is monitored to check whether there is an abnormality and to evaluate it. If there is an abnormality, the process proceeds to step S5. If there is no abnormality, the present control is terminated (step S4).

  At this time, whether there is an abnormality is determined using the graph shown in FIG. The graph shown in FIG. 3 obtains a relationship between the amount of PM deposited on the PM trap sensor 5 and the resistance value between the electrodes 11 in advance, and obtains a failure determination threshold Rt (predetermined reference) based on this relationship. deep. This is because, since PM (soot) is a conductor, the resistance value between the electrodes that was initially in an insulating state decreases depending on the amount of PM deposited. When it is detected that the monitored electrical resistance value is smaller than the failure determination threshold value Rt, it is determined that there is a minor failure in the DPF 3. The failure determination threshold value Rt may be defined based on, for example, an OBD (On Board Diagnosis) regulation value.

  When PM that is not collected by DPF 3 increases due to failure of DPF 3, even if it is a minor failure such as generation of a microcrack, the amount of PM deposited on PM trap sensor 5 arranged downstream of DPF 3 Will increase. Then, when the predetermined accumulation amount is exceeded, the monitored electric resistance value falls below the failure determination threshold value Rt, and therefore, it can be determined that the DPF 3 has failed.

  Next, when there is an abnormality in the electrical resistance value between the electrodes 11, a warning lamp is turned on and a failure is stored in the memory of the ECU 11 (step S5).

  As described above, in the above control, the PM trap sensor 5 is used to determine a failure based on the electrical resistance value that changes depending on the amount of deposited PM. Therefore, the determination according to the amount of accumulated PM passing through the DPF 3 is performed. Even if a failure (such as a microcrack) that cannot be detected by the differential pressure across the DPF 3 can be performed, it is possible to determine the performance degradation of the DPF 3 with high accuracy, and it is possible to monitor the failure with good responsiveness and accuracy. .

  FIG. 4 is a schematic diagram illustrating another example of the particulate filter failure determination apparatus according to the present invention, and illustrates a modification of the particulate filter failure determination apparatus according to the first embodiment. Accordingly, the same components as those shown in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The particulate filter failure determination apparatus according to the present embodiment includes a PM trap sensor 20 on the downstream side of the DPF 3 itself. Similar to the PM trap sensor 5 shown in FIG. 1B, the PM trap sensor 20 itself includes an insulating layer made of an electrical insulating material and a plurality of electrodes provided on the insulating layer. It is the structure which can measure the resistance value between (or the electric current value and voltage value which correlate with resistance value). The configuration of the PM trap sensor 20 is such that when it is difficult to incorporate the heater layer 13 in the sensor head 6 in the first embodiment, when the DPF 3 is forcedly regenerated, the temperature rises similarly to the DPF 3, specifically, the DPF 3 itself. The PM trap sensor 20 is disposed downstream of the heater, and the heater itself is omitted. In addition, the electrical insulating material in a present Example is also a thing of the magnitude | size used as a small capacity | capacitance compared with DPF3.

  Also in the particulate filter failure determination apparatus of the present embodiment, it is possible to determine the failure of the DPF 3 using the control shown in FIGS. 2 and 3 of the first embodiment. However, since the PM trap sensor 20 of the present embodiment does not include a heater, when the sensor is reset, the heat of the DPF 3 heated to a temperature equal to or higher than the combustion temperature of the PM is used when the DPF 3 is forcibly regenerated. The PM trap sensor 20 itself is reset by burning and removing the PM adhering to the electrical insulating material of the trap sensor 20.

  The present invention performs failure determination of a particulate filter and can determine even a minor failure.

(A) is the schematic which shows the failure determination apparatus of the particulate filter which concerns on this invention, (b) is the enlarged view of the A section. It is a flowchart explaining the control in the failure determination apparatus of the particulate filter concerning the present invention concerning the present invention. It is a graph explaining the failure determination in the failure determination apparatus of the particulate filter concerning the present invention concerning the present invention. It is the schematic which shows another example of the failure determination apparatus of the particulate filter which concerns on this invention.

Explanation of symbols

1 Engine 2 DOC
3 DPF
4 Exhaust passage 5, 20 PM trap sensor 6 Sensor head 10 Insulating layer 11 Electrode 12, 21 Measuring device 13 Heater layer 14 Heating resistance 15 Heater control power supply

Claims (4)

A particulate filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust gas;
An electrical insulating material that is provided in the exhaust passage located downstream of the particulate filter, and to which the particulate matter that has passed through the particulate filter adheres;
A plurality of electrodes provided at a distance from each other in the electrical insulating material;
Control means for measuring an index correlating with an electrical resistance value between the plurality of electrodes and detecting a failure of the particulate filter when detecting that the measured index is smaller than a predetermined reference. Particulate filter failure determination device. In the particulate filter failure determination device according to claim 1,
The particulate filter failure determination device, wherein the electrical insulating material has a smaller capacity than the particulate filter. In the particulate filter failure determination device according to claim 1 or 2,
A heater provided on the electrical insulator;
The particulate filter failure determination device, wherein the control means periodically energizes the heater to remove particulate matter adhering to the electrical insulating material. In the particulate filter failure determination device according to any one of claims 1 to 3,
The particulate filter failure determination device characterized in that the control means evaluates the measured index when the exhaust temperature is equal to or higher than the vaporization temperature of the condensed water and equal to or lower than the combustion temperature of the particulate matter. .

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