JP2011080439A - Device for detecting abnormality of particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new method using an electric resistance type emitted particulate sensor for determining existence of abnormality of a particulate filter. <P>SOLUTION: The particulate filter DPF is disposed in an exhaust pipe 2 of a diesel engine and particulate matter PM passing through the filter in abnormal time is detected by an electric resistance type PM sensor 1. An electronic control unit ECU compares output values of a detection part 100 under a first temperature condition where exhaust gas temperature T1 and temperature T2 of a pair of detection electrodes 11, 12 of the PM sensor 1 are same and under second temperature condition of T2>T1, and determines abnormality when difference value exceeds a prescribed value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a particulate filter abnormality detection device that collects particulate matter present in exhaust gas from an internal combustion engine for a vehicle, and more particularly, particulates that pass through a particulate filter using an electrical resistance type exhaust particulate sensor. The present invention relates to an apparatus for detecting an abnormality such as breakage by detecting the amount of a particulate material.

  In automobile diesel engines, etc., environmental pollutants contained in exhaust gas, especially particulate matter (Particulate Matter; hereinafter referred to as PM as appropriate), mainly composed of particulate carbon (Soot) and soluble organic components (SOF), are captured. In order to collect, a diesel particulate filter (hereinafter referred to as DPF as appropriate) is installed in the exhaust passage. The DPF is generally made of porous ceramics having excellent heat resistance, and traps PM by passing exhaust gas through a partition wall having a large number of pores. Further, when the amount of collected PM exceeds a specified amount, high-temperature combustion exhaust gas is introduced into the DPF by heater heating or post injection, and PM is burned and removed to regenerate the DPF. For example, the regeneration time can be determined by using the fact that the differential pressure increases due to an increase in the amount of collected PM, and the amount of collected PM is detected based on the detection result of the differential pressure sensor.

  On the other hand, Patent Documents 1 and 2 propose a sensor for directly detecting PM in exhaust gas. Patent Documents 1 and 2 are electrical resistance type sensors that utilize the conductivity of particulate carbon, and have a basic configuration in which a pair of conductive electrodes are formed on the surface of an insulating substrate. Yes. When this sensor is disposed in the exhaust gas passage containing PM, PM can be detected from a change in resistance value caused by the adhesion of particulate carbon between the electrodes serving as the detection units. Further, in Patent Document 1, when a heating element is formed on the back surface or inside of a substrate and the temperature of the detection unit is heated to 400 ° C. to 600 ° C., the resistance change amount is large, the recovery time is shortened, and the detection accuracy is improved. It is disclosed to improve.

  Therefore, it has been studied to install an electrical resistance type sensor upstream of the DPF and measure the amount of PM flowing into the DPF, or install it downstream of the DPF and measure the amount of PM passing through the DPF. The former is used for determining the regeneration time instead of the differential pressure sensor, and the latter is used for monitoring the operating state of the DPF and determining deterioration, breakage, and the like. In recent years, in order to prevent environmental pollution, the installation of an onboard diagnosis (OBD) is obligatory, and the importance of the latter is increasing. In addition, as a technique for detecting PM, there are a sensor for detecting heat generated by oxidation reaction of PM using a catalyst and a thermocouple, and a method for monitoring chemical species and temperature of exhaust gas using a wavelength tunable diode laser. As is known, the electric resistance type sensor has an advantage that a relatively stable output can be obtained with a simple configuration.

  Regarding failure diagnosis, Patent Document 2 discloses a configuration in which a detection electrode made of a porous conductive material is inserted between a pair of electrodes of an electric resistance type sensor so that a small amount of current always flows. It is disclosed that PM can be detected. Patent Documents 3 and 4 propose a failure determination system including an electric resistance type sensor that measures the amount of PM leaking from the DPF. The failure sensor of Patent Document 3 includes an upstream sensor that determines the amount of PM introduced into the DPF and a downstream sensor that measures the amount of PM leaking from the DPF, and is estimated to leak from the DPF by integrating the PM amount from the upstream sensor. The amount of PM to be determined is determined, and a failure is detected from comparison with the measured value by the downstream sensor. In Patent Document 4, a sensor having a plurality of electrodes provided on an electrical insulating layer to which PM adheres is disposed downstream of the DPF, and an index correlating with an electrical resistance value between the plurality of electrodes is measured. Thus, a failure determination device including an ECU that determines that a DPF failure occurs when a measured value becomes smaller than a predetermined reference is disclosed.

Japanese Examined Patent Publication No. 2-44386 JP 2006-266961 A JP 2008-298071 A JP 2009-1444577 A

  However, as shown in Patent Document 1, the electrical resistance type sensor has temperature dependence, and the resistance value changes according to the temperature of the detection unit. For this reason, in Patent Document 2, the relationship between the ambient temperature change and the electrical resistance value is obtained in advance, and the electrical resistance value detected by the temperature obtained by the temperature measurement unit is corrected. . In addition, in order to calculate the PM amount from the difference between the corrected electrical resistance value and the initial value, it is necessary to investigate the relationship between the PM deposition amount and the electrical resistance value (or change amount) by conducting an experiment or the like in advance. Furthermore, the detection amount in the normal state is examined and specified in advance, and it is determined whether or not the collection by the DPF is normally performed by comparing with the calculated PM amount.

  However, the amount of PM contained in the exhaust gas from the engine also varies greatly depending on the operating state (load and rotation speed). The tendency for the PM to increase is that, as the load becomes higher, for example, the amount of PM increases in the entire region from a low rotation speed to a high rotation speed as when the engine is started. Further, the PM amount tends to increase as the rotational speed increases to the output region. Furthermore, when the properties and particle distribution of the discharged PM vary depending on the operating state, the amount of PM that passes through the DPF also varies. Therefore, in order to determine the presence or absence of performance degradation or damage of the DPF, the current PM amount is compared with the PM amount map obtained in advance with respect to the operating state. Is not easy. Further, since the amount of passing PM varies depending on the PM accumulation state on the DPF, it is necessary to map the relationship with the PM accumulation amount, and the map amount to be stored is increased, and the failure determination process is complicated. There is a problem to become.

  Patent Document 3 does not describe a specific method for determining a failure. In the failure determination of Patent Document 4, as in Patent Document 2, a failure determination threshold value is obtained from the relationship between the PM accumulation amount and the electrical resistance value obtained in advance. And, if the monitored interelectrode resistance value becomes smaller than the threshold value, it is considered as a minor failure. Although this threshold value is based on the OBD reference value, there is no specific description of the operating state and the like. There are concerns about problems.

  Therefore, the present invention provides a novel method using an electric resistance type exhaust particle sensor for determining the presence or absence of an abnormality in a DPF that processes exhaust gas of an internal combustion engine, and has a simple configuration and a large number of maps and It is an object of the present invention to realize an abnormality detection device with high responsiveness and accuracy without requiring complicated correction processing.

The invention according to claim 1 of the present invention provides
A particulate filter disposed in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust gas;
An exhaust particulate sensor installed downstream of the particulate filter to detect the amount of particulate matter in the exhaust gas;
An abnormality detection unit that detects an abnormality of the particulate filter based on a detection result of the discharged particulate sensor,
The discharged particulate sensor has a detection part in which a pair of detection electrodes are formed on the surface of an insulating substrate, and a heater part for heating the detection part to a predetermined temperature, and the particulate matter adhered between the pair of detection electrodes The electrical resistance value changes according to the amount of
When the temperature of the exhaust gas is T1, and the temperature of the pair of detection electrodes of the detection unit is T2, the abnormality detection unit has a first temperature T1 of the pair of detection electrodes equal to a temperature T1 of the exhaust gas. The output value of the detection unit under the temperature condition is compared with the output value of the detection unit under the second temperature condition in which the temperature T2 of the pair of detection electrodes is higher than the temperature T1 of the exhaust gas. A determination unit is provided that determines that the particulate filter is abnormal when the ratio value exceeds a predetermined value.

  In the invention according to claim 2 of the present invention, the abnormality detection unit has a difference between the temperature T2 of the pair of detection electrodes and the temperature T1 of the exhaust gas in the second temperature condition of 50 ° C. to 200 ° C. The temperature T2 of the pair of detection electrodes is set so as to be in the range.

  In the invention according to claim 3 of the present invention, the abnormality detection unit calculates the difference between the temperature T2 of the pair of detection electrodes and the temperature T1 of the exhaust gas under the second temperature condition, as the temperature of the internal combustion engine or Set based on operating conditions including load.

  In the invention according to claim 4 of the present invention, the exhaust particulate sensor is formed by forming the pair of comb-like detection electrodes and the lead portion on the surface of the distal end portion of the insulating base located in the exhaust passage. A heater electrode and a lead part are formed on the back surface of the front end of the insulating substrate to form the heater part.

  The invention according to claim 1 of the present invention detects an abnormality of a particulate filter by a novel method using an electric resistance type discharged particulate sensor. When an abnormality such as breakage occurs in the particulate filter, the particulate matter in the exhaust gas passes through the particulate filter and flows into the exhaust particulate sensor downstream. The abnormality detection unit heats the detection unit of the exhaust particulate sensor by the heater unit, and the first temperature condition in which the exhaust gas temperature T1 and the detection electrode temperature T2 are equal, and the detection electrode temperature T2 is higher than this. The sensor output value is obtained for each of the second temperature conditions. Here, since the particulate matter that passes through the particulate filter at the time of abnormality is relatively coarse particles and is easily affected by thermophoresis, the particulate matter is not suitable for the second temperature condition higher than the first temperature condition. It becomes difficult to adhere.

  For this reason, the sensor output value detected at these two levels of temperatures is larger when the particulate filter is abnormal than when the difference value is normal. Therefore, by comparing these output values, it is possible to easily determine whether the particulate filter is functioning normally. Therefore, a simple configuration and a large amount of maps and complicated correction processing are unnecessary, and a highly responsive and accurate abnormality detection apparatus can be realized.

  Specifically, as in the second aspect of the present invention, specifically, the difference between the temperature T2 of the pair of detection electrodes and the temperature T1 of the exhaust gas is set to 50 ° C. or more under the second temperature condition. For example, abnormality determination based on the difference value of the sensor output value is possible. Further, even if the temperature exceeds 200 ° C., the output value does not change greatly, and the energy required for the temperature rise increases, so that an abnormality can be detected effectively by setting an appropriate temperature difference.

  As in the third aspect of the present invention, the difference between the temperature T2 of the pair of detection electrodes and the temperature T1 of the exhaust gas is preferably set according to the temperature or load of the internal combustion engine. For example, under low-temperature or low-load operation conditions, unburned HC is likely to be discharged and particulate matter is likely to adhere, so the difference between the temperature T2 of the pair of detection electrodes and the temperature T1 of the exhaust gas can be reduced. And efficient detection is possible. Conversely, it is better to increase the temperature difference under high-load operation conditions, and accurate determination can be made.

  As in the invention according to claim 4 of the present invention, the exhaust particulate sensor is configured such that the detection part is formed at the tip of the insulating substrate and installed in the exhaust passage, and the heater part is arranged on the back surface thereof. The detection part can be efficiently heated and the abnormality can be determined with high accuracy.

In 1st Embodiment of this invention, it is a flowchart which shows the content of the determination means with which the electronic control unit used as an abnormality detection part is provided. 1 is an overall system diagram of a diesel engine to which an abnormality detection device of the present invention is applied. It is a figure which shows PM detection element structure which is the principal part of PM sensor. It is a figure which shows the state which attached PM sensor to the exhaust pipe of the diesel engine. It is a figure which shows the relationship between PM deposition amount and inter-electrode resistance value. It is a figure which shows the relationship between the temperature rise of the detection part of PM sensor, and resistance change rate by the time of normal time and the time of abnormality. It is a figure which shows the relationship between the temperature increase of the detection part of PM sensor, and resistance change rate, when the exhaust temperature is high and when it is low.

  A first embodiment in which the particulate filter abnormality detection device of the present invention is applied to an exhaust gas purification system for an automobile diesel engine, which is an internal combustion engine, will be described with reference to the drawings. FIG. 2 is a schematic diagram of the entire system of the diesel engine E / G. A common rail fuel injection system for accumulating high pressure fuel boosted by a high pressure pump PMP to a common rail R common to each cylinder so as to become a predetermined injection pressure. Adopted as a direct injection engine that is directly injected into the combustion chamber by an injector INJ. The exhaust pipe 2 having the inside as an exhaust passage is provided with a diesel particulate filter DPF that is a particulate filter and a PM sensor 1 that is an exhaust particulate sensor, and together with an electronic control unit ECU serving as an abnormality detection unit, This constitutes an abnormality detection device for the particulate filter. FIG. 1 is a flowchart of abnormality detection processing by the electronic control unit ECU, which will be described in detail later.

In FIG. 2, the exhaust manifold MH _EX of the diesel engine E / G is provided with a turbine TRB. When the turbocharger TRB _CGR rotates in conjunction with the turbine TRB, the compressed air passes through the intercooler CLR _INT. Sent to the intake manifold MH _IN . A part of the combustion exhaust discharged from the exhaust manifold MH _EX returns to the intake manifold MH _IN via the EGR valve V _EGR and the EGR cooler CLR _EGR . The intake amount is increased by supercharging to increase combustion efficiency, and the combustion is moderated by EGR to suppress the emission of NOx and the like.

The exhaust pipe 2 connected to the exhaust manifold MH _EX is provided with a diesel oxidation catalyst DOC and a diesel particulate filter DPF, and processes combustion exhaust gas. That is, while the combustion exhaust gas discharged to the exhaust pipe 2 passes through the upstream diesel oxidation catalyst DOC, unburned hydrocarbons HC, carbon monoxide CO, and nitrogen monoxide NO are oxidized, and the downstream side While passing through the diesel particulate filter DPF, the particulate matter PM is collected. For NOx removal, for example, a selective catalyst reduction SCR (not shown) or the like is provided after the diesel particulate filter DPF, and NOx is reduced to N ₂ and H ₂ O and removed.

The diesel oxidation catalyst DOC is formed by supporting an oxidation catalyst on a known monolithic carrier, for example, a carrier surface made of a ceramic honeycomb structure such as cordierite. The diesel oxidation catalyst DOC raises the exhaust temperature by oxidative combustion of the supplied fuel or oxidizes and removes the SOF component in the particulate matter PM during forced regeneration of the diesel particulate filter DPF. Further, NO ₂ generated by oxidation of NO is used as an oxidant for the particulate matter PM deposited on the diesel particulate filter DPF at the subsequent stage, and enables continuous oxidation.

  The diesel particulate filter DPF has a known wall flow type filter structure. For example, a porous ceramic honeycomb structure made of heat-resistant ceramics such as cordierite is formed, and either the inlet side or the outlet side of a large number of cells serving as gas flow paths are staggered in adjacent cells. Seal the filter to make a filter. At this time, a large number of pores are formed through the cell walls defining the gas flow path, and the particulate matter PM in the exhaust gas introduced into the diesel particulate filter DPF is captured. Here, although the diesel oxidation catalyst DOC and the diesel particulate filter DPF are provided separately, they can be configured as a continuous regenerative diesel particulate filter in which these are integrated.

  In the present embodiment, a differential pressure sensor SP is provided in order to know the amount of particulate matter PM deposited on the diesel particulate filter DPF (PM trapping amount). The differential pressure sensor SP is connected to the upstream side and the downstream side of the diesel particulate filter DPF via a pressure introduction pipe, and outputs a signal corresponding to the differential pressure before and after to the electronic control unit ECU. Further, temperature sensors ST1, ST2, and ST3 are disposed upstream of the diesel oxidation catalyst DOC and upstream and downstream of the diesel particulate filter DPF to monitor the exhaust temperature of each part. The electronic control unit ECU monitors the catalytic activation state of the diesel oxidation catalyst DOC and the PM collection state of the diesel particulate filter DPF based on these outputs, and performs forced regeneration when the PM collection amount exceeds the allowable amount. Regeneration control for burning and removing the particulate matter PM is performed.

  In the regeneration control by the electronic control unit ECU, for example, post injection is performed to increase the amount of HC in the exhaust, the temperature of the diesel particulate filter DPF is changed by the heat of HC reaction in the diesel oxidation catalyst DOC, and the combustion temperature of the particulate matter PM. Raise more. At this time, the inlet gas temperature and the outlet gas temperature of the diesel particulate filter DPF are monitored, and the diesel particulate filter DPF is controlled to be in a predetermined temperature range. Under the operating conditions in which the particulate matter PM can spontaneously burn, the fuel consumption can be suppressed by setting the regeneration control not to be performed. The electronic control unit ECU further receives detection signals from various sensors (not shown), calculates the optimum fuel injection amount, injection timing, injection pressure, and the like based on these signals, and controls fuel injection.

  A PM sensor 1 is disposed in the exhaust pipe 2 downstream of the diesel particulate filter DPF to detect particulate matter PM that passes through the diesel particulate filter DPF. FIG. 3 is a diagram showing the PM detection element 10 which is a main part of the PM sensor 1, and FIG. 4 is a diagram showing a state where the PM sensor 1 including the PM detection element unit 10 is attached to the exhaust pipe 2. In FIG. 3, the PM detection element 10 includes a detection unit 100 in which a pair of detection electrodes 11 and 12 are formed on the surface of an insulating substrate 13 that is an insulating base, a pair of detection electrodes 11 and 12, and an external resistance measurement unit. Lead portions 111 and 121 to be conducted and a heater portion 300 that is stacked on the back side of the detection portion 100 and heats the lead portions to a predetermined temperature.

  The detection unit 100 is formed on a flat insulating substrate 13 using a known method such as a doctor blade method or a press molding method with a ceramic material excellent in electrical insulation and heat resistance, such as alumina, and is formed on the surface of the tip portion. A pair of comb-shaped detection electrodes 11 and 12 are arranged to face each other at a predetermined inter-electrode distance. The detection electrodes 11 and 12 are formed by printing a conductive paste containing a noble metal such as platinum in a predetermined pattern. The heater unit 300 includes a flat insulating substrate 33 formed in the same manner and a heater electrode 30 formed in a predetermined pattern on the surface of the front end portion, and is connected to external energizing means by lead portions 31 and 32.

  In FIG. 4, the PM sensor 1 has a cylindrical housing 50 that is screwed to the tube wall 20 of the exhaust pipe 2, and the upper half of the PM detection element 10 that is inserted into and fixed to the cylindrical insulator 60 is disposed therein. keeping. The lower half of the PM detection element 10 is positioned in a hollow cover body 40 that is fixed to the lower end of the cylindrical housing 50 and protrudes into the exhaust pipe 2. Holes 410 and 411 through which exhaust gas containing particulate matter PM that has passed through the diesel particulate filter DPF flows are formed in the bottom and side portions of the cover body 40.

  At this time, in order to surely capture the particulate matter PM, it is preferable to arrange the PM detection element 10 so that the detection unit 100 faces the upstream side of the exhaust pipe 2 as illustrated. Further, when the insulating protective layer 14 is formed on the surface of the insulating substrate 13 excluding the detection unit 100 so as to cover the lead units 111 and 112, erroneous detection due to accumulation of particulate matter PM between the lead units 111 and 112 is detected. Can be prevented.

Next, the basic operation of the PM sensor 1 will be described. In FIG. 4, the exhaust gas to be measured gas is introduced into the inside from the holes 410 and 411 of the cover body 40 of the PM sensor 1 and reaches the detection unit 100 of the PM detection element 10. In FIG. 3, comb-shaped detection electrodes 11 and 12 are formed on the surface of the detection unit 100 with a predetermined gap, so that conductive fine carbon particles are formed by contact with exhaust gas. When the contained particulate matter PM adheres and gradually accumulates, the detection electrodes 11 and 12 become conductive at a certain point. FIG. 5 shows changes in the electrical resistance value between the detection electrodes 11 and 12 when the PM deposition amount is increased at a constant rate. In the initial state, which is a substantially insulated state, the interelectrode resistance is 1 ×. When it is 10 ⁷ Ω or more and the detection electrodes 11 and 12 are conductive, the resistance between the electrodes rapidly decreases with the increase in the PM deposition amount, and becomes about 1 × 10 ³ Ω.

  Here, if any problem such as breakage or melting of the cell wall occurs in the diesel particulate filter DPF and normal collection becomes difficult, the particulate matter PM released together with the exhaust gas increases. Therefore, conventionally, the current flowing between the detection electrodes 11 and 12 of the PM sensor 1 is measured, and failure determination is performed based on the relationship between the PM deposition amount and the electrical resistance value. For example, if the particulate matter PM that passes through the diesel particulate filter DPF during a predetermined period is clearly more than normal, it can be determined as abnormal.

  However, as described above, the interelectrode resistance or the resistance change rate varies depending on the temperature of the detection unit 100. For this reason, in the conventional method, it is assumed that the temperature of the detection unit 100 is kept constant by the heater unit 300. However, since the surrounding exhaust temperature varies greatly depending on the operating state, it is not easy to maintain the detection unit 100 at a constant temperature, and temperature correction is essential. Further, since the amount and properties of the particulate matter PM discharged from the engine E / G vary depending on the operating state, the amount of the particulate matter PM that passes through the diesel particulate filter DPF is also increased and decreased, and the determination threshold is set to a constant value. There is a risk of misjudgment. Alternatively, it is possible to perform correction or change the determination threshold based on a map corresponding to the driving state, but the map amount increases.

  In order to eliminate such a conventional problem, the particulate filter abnormality detection device of the present invention is configured such that the exhaust temperature is T1, the detection electrodes 11 and 12 are T2, and T2-T1 is the elevated temperature ΔT. The particulate matter PM is detected by the PM sensor 1 under the first temperature condition of T2 = T1 (increased temperature ΔT = 0 ° C.) and the second temperature condition of T2−T1> 0 ° C. That is, the first temperature condition is such that the exhaust temperature T1 is equal to the temperature T2 of the detection unit 100, and the second temperature condition is such that the temperature T2 of the detection unit 100 is higher than the exhaust temperature T1. In addition, the heater unit 300 is controlled, and the presence or absence of an abnormality is determined by comparing the sensor output values under these two types of temperature conditions.

  FIG. 6 shows the relationship between the temperature increase ΔT of the detection unit 100 of the PM sensor 1 and the resistance change rate ΔR between the detection electrodes 11 and 12 of the PM sensor 1 after a predetermined time has elapsed from the initial state. Here, a normal diesel particulate filter DPF (when normal) that is not damaged and a diesel particulate filter DPF (when the DPF is damaged) in which the internal cell wall is damaged are prepared. The resistance change rate ΔR of the detection unit 100 was measured while changing the temperature from 0 ° C. to 200 ° C. As apparent from the figure, the resistance change rate ΔR gradually decreases as the temperature rise ΔT increases at normal times, but the rate of change is small and almost constant, and the temperature rise ΔT is 0 ° C. The difference in resistance change rate ΔR at 200 ° C. is slight.

  On the other hand, when the diesel particulate filter DPF is damaged, the particulate matter PM increases as a whole from the normal time. Furthermore, as the temperature increase ΔT is smaller, the resistance change rate ΔR is larger and changes more rapidly. It is presumed that the tendency different from the normal time is due to the difference in particulate matter PM that passes through the diesel particulate filter DPF and accumulates on the PM sensor 1. That is, fine particles (eg, about 0.1 μm to 0.01 μm) that are difficult to be trapped in the pores of the diesel particulate filter DPF under normal conditions. On the other hand, if damage such as cracks occurs, the particulate matter PM The amount of slipping increases, and in particular, coarse particles (for example, about 1 μm to 10 μm) increase. Since coarse particles of 1 μm or more are easily affected by thermophoresis, it is considered that the adhesion rate to the PM sensor 1 varies depending on the temperature rise ΔT.

  Thermophoresis is a phenomenon in which fine particles existing in a temperature gradient field move from a high temperature side to a low temperature side due to the interaction between the particles and gas molecules. If the temperature of the detection unit 100 of the PM sensor 1 is equal to the exhaust gas temperature to be introduced and there is no temperature difference, the particulate matter PM in the exhaust gas reaches the detection unit 100 and accumulates. However, when the temperature of the detection unit 100 of the PM sensor 1 is increased, the momentum of the nearby gas molecules becomes larger, resulting in a force toward the low temperature side. Since collisions with gas molecules become more frequent as the particles become larger, the particulate matter PM, especially coarse particles of 1 μm or more, receives a thermophoretic force and decreases the adhesion rate (resistance change rate) to the detection unit 100. However, the difference in adhesion rate (resistance change rate) from the case where there is no temperature difference becomes large. On the other hand, it is presumed that during normal times, it is difficult to receive thermophoretic force because it is mainly composed of fine particles.

  FIG. 7 also shows the results of examining whether the relationship between the temperature increase ΔT and the resistance change rate ΔR changes between when the exhaust temperature is low and when the exhaust temperature is high. As shown in the figure, when the exhaust gas temperature is lower than when the exhaust gas temperature is high, the overall resistance shift rate is shifted to the higher side. This is because when the exhaust gas temperature is low, the amount of HC discharged without being burned increases, and the amount of SOF in the particulate matter PM also increases, so these are the PM sensor elements 1 of the particulate matter PM. It is considered that the adhesion to the detection unit 100 is promoted and the adhesion rate (resistance change rate) is increased. The condition where the exhaust temperature is low is, for example, a low temperature start or a low load operating condition.

  Next, an example of determination means provided in the electronic control unit ECU serving as the abnormality detection unit will be described based on the flowchart of FIG. In step S100 of FIG. 1, data is first captured, and the output of the temperature sensor ST3 downstream of the diesel particulate filter DPF is captured as the exhaust temperature T1 introduced into the PM sensor 1. Further, the cooling water temperature Tw of the diesel engine E / G is taken from a water temperature sensor (not shown), the rotational speed NE of the diesel engine E / G is taken from the engine speed sensor, and the fuel injection amount Q is obtained based on the output of the accelerator opening sensor or the like. .

  In step S110, the detection unit 100 of the PM sensor 1 is set to the first temperature condition. Here, the energization control of the heater unit 300 is performed so that the exhaust temperature T1 taken in step S100 and the detection electrodes 11 and 12 temperatures T2 of the detection unit 100 become equal. Since the heater unit 300 is disposed in close contact with the back surface of the detection unit 100, the detection unit 100 including the detection electrodes 11 and 12 is controlled by controlling the temperature of the heater unit 300 to be equal to the exhaust temperature T1. The predetermined temperature can be set. The temperature of the heater unit 300 can be easily controlled by detecting the resistance value of the heater electrode 30.

  In step S120, the resistance change rate ΔR1 between the detection electrodes 11 and 12 of the PM sensor 1 is measured under the first temperature condition. At this time, the resistance change rate of the detection unit 100 after a lapse of a certain time is proportional to the change rate (attachment area) of the particulate matter PM attached between the detection electrodes 11 and 12, and in the first temperature condition, Since there is no influence of thermophoresis, when there is some abnormality in the diesel particulate filter DPF, the detected resistance change rate ΔR1 becomes larger than that in the normal state as shown in FIG.

  Next, in step S130, a temperature increase ΔT for setting the second temperature condition is determined. The temperature increase ΔT determined here is, for example, a temperature difference at which an obvious change with respect to the first temperature condition can be detected when there is an abnormality such as a DPF breakage in the medium load operating condition. Preferably, a predetermined reference value can be set in advance in the range of 100 ° C. to 200 ° C., for example, from the relationship between the temperature increase ΔT and the resistance change rate ΔR in FIG. Since the exhaust temperature during normal operation is, for example, about 300 ° C. to 350 ° C., by providing a temperature difference of 100 ° C. or more, the resistance change rate ΔR can be accurately detected in a temperature range where stable output can be obtained. . Further, when the temperature difference exceeds 200 ° C., the resistance value hardly changes and approaches the combustion temperature of the particulate matter PM. By setting the temperature to 200 ° C. or less, energy required for temperature rise is suppressed, and detection error is reduced. Can be prevented.

  In step S140, in order to correct the reference temperature increase ΔT set in step S130, it is determined whether the operating condition is a low temperature or low load. Specifically, from the data captured in step S100, it is determined that the temperature is low when the cooling water temperature Tw of the diesel engine E / G is equal to or lower than a predetermined temperature (for example, 80 ° C.), or the rotational speed NE of the diesel engine E / G When the fuel injection amount Q is equal to or less than a predetermined value, it is determined that the operating condition is a low load. For example, at the time of low temperature start, the amount of HC that is discharged increases, so that the particulate matter PM easily adheres. As shown in FIG. 7, the relationship between the temperature increase ΔT and the resistance change rate ΔR is compared with that during normal operation. Change. The same applies to low load operation.

  Therefore, when an affirmative determination is made in step S140, the process proceeds to step S150, and the temperature increase ΔT set in step S130 is corrected. Specifically, since the difference in the adhesion amount (resistance change rate) of the particulate matter PM tends to increase, the temperature increase ΔT is made smaller. For example, when the reference temperature increase ΔT is 100 ° C., the corrected temperature increase ΔT is set to −50 ° C. and the corrected temperature increase ΔT is set to 50 ° C. If a negative determination is made in step S140, step S150 is skipped and the process proceeds to step 160.

  Next, in step 160, the detection unit 100 of the PM sensor 1 is set to the second temperature condition based on the determined temperature increase ΔT. Here, the energization control of the heater unit 300 is performed so that the detection electrodes 11 and 12 of the detection unit 100, temperature T2 = exhaust temperature T1 + temperature increase ΔT. Further, in step S170, the resistance change rate ΔR2 between the detection electrodes 11 and 12 of the PM sensor 1 is measured under the second temperature condition. Under this second temperature condition, the detection unit 100 becomes higher than the ambient temperature, so that the influence of thermophoresis occurs, and even if there is some abnormality in the diesel particulate filter DPF, as shown in FIG. The detected resistance change rate ΔR2 is relatively small.

  Therefore, in the subsequent step 180, the measured resistance change rates ΔR1 and ΔR2 are compared, and abnormality determination is performed. Here, the difference between the resistance change rate ΔR1 and the resistance change rate ΔR2 is calculated, and it is determined whether or not the difference value ΔR1−ΔR2 exceeds a predetermined value set in advance. The predetermined value may be larger than the difference value when the diesel particulate filter DPF is operating normally based on the relationship shown in FIG. A plurality of values corresponding to the types of abnormalities such as minor breakage, performance degradation or melting damage can be set in advance by experiments or the like.

  If the determination in step 180 is affirmative, it is determined that there is some abnormality in the diesel particulate filter DPF, and the process proceeds to step 190, for example, a warning lamp is lit to notify the driver of the abnormality. When a negative determination is made in step 180, it is determined that the diesel particulate filter DPF is normal, and this process is temporarily terminated.

  As described above, in the present embodiment, when the temperature of the detection unit 100 of the PM sensor 1 is set to the first temperature condition based on the exhaust gas temperature T1 and the second temperature condition higher than this by the temperature increase ΔT. The abnormality of the diesel particulate filter DPF can be easily detected on the basis of the resistance change rates ΔR1 and ΔR2. Therefore, with a relatively simple configuration using an electrical resistance PM sensor, a large amount of maps and temperature correction are not required, and accurate determination is possible.

  In the above embodiment, in steps 140 and 150 in FIG. 1, the temperature increase ΔT is corrected under the low temperature or low load operating condition. However, the temperature increase ΔT is corrected under the high load operating condition. It may be. Under such operating conditions, the discharge of unburned HC is reduced and the particulate matter PM is less likely to adhere, so it is preferable to increase the temperature rise ΔT. At this time, the temperature difference between the first temperature condition and the second temperature condition increases, and the difference between the resistance change rates ΔR1 and ΔR2 at these temperatures increases, thereby preventing detection errors. Further, in step S180 of FIG. 1, the difference between the resistance change rates ΔR1 and ΔR2 at these temperatures is compared and determined, but the determination is performed based on the ratio value ΔR1 / ΔR2 of the resistance change rates ΔR1 and ΔR2 at each temperature. It is also possible.

  Further, the PM sensor used in the present invention is not limited to the configuration of the above-described embodiment, and the shape and arrangement of the pair of detection electrodes, the heater unit, the cover body, and other components can be changed as appropriate. Furthermore, the configuration of the particulate filter and the configuration of each part of the exhaust treatment system and the fuel injection system can be arbitrarily changed.

  The particulate filter abnormality detection device of the present invention is used for applications such as an on-board failure diagnosis device (OBD) that is required to be installed in an automobile equipped with a diesel particulate filter, and prevents discharge of environmental pollutants. . In addition to the automobile diesel engine, it can be suitably used for any other engine having a different system configuration or a system having a particulate filter for collecting particulate matter contained in exhaust gas in the exhaust passage. it can.

DPF Diesel particulate filter (particulate filter)
ECU Electronic control unit (abnormality detection unit)
E / G diesel engine (internal combustion engine)
ECU Electronic control unit (abnormality detection unit)
1 PM sensor (exhaust particulate sensor)
DESCRIPTION OF SYMBOLS 10 PM detection element 100 Detection part 11, 12 Detection electrode 111, 121 Lead part 13 Insulating substrate (insulating base | substrate)
14 Insulating protective layer 2 Exhaust pipe (exhaust passage)
20 Tube wall 30 Heater electrode 31, 32 Lead part 300 Heater part 40 Cover body 410, 411 hole 50 housing 60 insulator

Claims (4)

A particulate filter disposed in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust gas;
An exhaust particulate sensor installed downstream of the particulate filter to detect the amount of particulate matter in the exhaust gas;
An abnormality detection unit that detects an abnormality of the particulate filter based on a detection result of the discharged particulate sensor,
The discharged particulate sensor has a detection part in which a pair of detection electrodes are formed on the surface of an insulating substrate, and a heater part for heating the detection part to a predetermined temperature, and the particulate matter adhered between the pair of detection electrodes The electrical resistance value changes according to the amount of
When the temperature of the exhaust gas is T1, and the temperature of the pair of detection electrodes of the detection unit is T2, the abnormality detection unit has a first temperature T1 of the pair of detection electrodes equal to a temperature T1 of the exhaust gas. The output value of the detection unit under the temperature condition is compared with the output value of the detection unit under the second temperature condition in which the temperature T2 of the pair of detection electrodes is higher than the temperature T1 of the exhaust gas. A particulate filter abnormality detection device comprising: a determination unit that determines that the particulate filter is abnormal when the ratio value exceeds a predetermined value.   The abnormality detection unit is configured so that a difference between the temperature T2 of the pair of detection electrodes and the temperature T1 of the exhaust gas in the second temperature condition is in a range of 50 ° C. to 200 ° C. 2. The particulate filter abnormality detection device according to claim 1, wherein the temperature T2 is set.   The abnormality detection unit sets a difference between a temperature T2 of the pair of detection electrodes and a temperature T1 of the exhaust gas in the second temperature condition based on an operating condition including a temperature or a load of the internal combustion engine. The particulate filter abnormality detection device according to claim 1.   The exhaust particulate sensor includes a pair of comb-like detection electrodes and a lead portion formed on a surface of a tip portion of the insulating base located in the exhaust passage to form the detection portion, and the tip of the insulating base The particulate filter abnormality detection device according to claim 1, wherein a heater electrode and a lead portion are formed on the back surface to form the heater portion.

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