JP2012012960A - Particulate matter detection sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of detection accuracy, and to obtain a stable sensor output, in a particulate matter detection sensor of an electric resistance type used for detecting PMs in exhaust gas.SOLUTION: A gas sensor element 10 of the PM sensor 1 attached to an exhaust pipe EX of an engine E/G is constituted by laminating a heater 300 on a detection part 100 having detection electrodes 11, 12. A control circuit 2 executes starting combustion control for holding a temperature of the detection part 100 at a temperature T1 at which the particulate matter PM can be burnt for a preset time S1 by carrying electricity to the heater 300 at start-up, after that, performs normal control, and prevents wrong detection caused by the residue of the particulate matter PM.

Description

  The present invention relates to an electrical resistance particulate matter detection sensor for detecting the amount of particulate matter present in exhaust gas in an exhaust gas purification system for an internal combustion engine for a vehicle. This is effective for detecting abnormalities in the particulate filter.

  Collects environmental pollutants contained in exhaust gas, especially particulate matter (Particulate Matter; hereinafter referred to as PM as appropriate) mainly composed of soot particles and soluble organic components (SOF) in automobile diesel engines, etc. In order to do this, a diesel particulate filter (hereinafter referred to as DPF as appropriate) is installed in the exhaust passage. The DPF is 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.

  If the amount of collected PM exceeds the allowable amount, DPF may cause clogging and increase the negative pressure or increase the slipping of PM. It is recovering. 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. In the regeneration process, high-temperature combustion exhaust gas is introduced into the DPF by heater heating or post injection, and PM is burned and removed.

  On the other hand, a sensor for directly detecting PM in exhaust gas has been proposed. This PM sensor is installed downstream of the DPF, for example, and the amount of PM passing through the DPF is measured. In an on-board diagnosis (OBD), monitoring of the operating state of the DPF, for example, abnormalities such as cracks and breakage It can be used for detection. Alternatively, it is also considered to install upstream of the DPF, measure the amount of PM flowing into the DPF, and use it to determine the regeneration time instead of the differential pressure sensor.

  As a conventional technique, Patent Document 1 discloses an electric resistance type smoke density sensor in which a pair of conductive electrodes are formed on the surface of an insulating substrate and a heating element is formed on the back surface or inside of the substrate. ing. This sensor utilizes the conductivity of the soot particles, and detects a change in the electrical resistance value caused by the soot particles being deposited between the electrodes serving as the detection unit. The heating element heats the temperature of the detection unit to 400 ° C. to 600 ° C., measures the interelectrode resistance according to the PM concentration, and then burns off the attached PM to restore the detection capability.

  Patent Document 2 uses a PM trap sensor in which a plurality of electrodes that are spaced apart from each other are formed on an electrical insulating material, measures an index that correlates with the electrical resistance value between the two electrodes, and when it becomes smaller than a predetermined reference, An apparatus for determining a failure of a particulate filter is disclosed. Further, in order to improve the measurement accuracy of the electric resistance value, the PM trap sensor is reset periodically (every predetermined travel time, every predetermined travel distance, and every amount of fuel used).

  In addition, as a technique for detecting PM, there are a sensor for detecting heat generation 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.

Japanese Examined Patent Publication No. 2-44386 JP 2009-1444577 A

  By the way, when starting the engine, there is a possibility that PM discharged by the previous operation remains attached to the sensor detection unit when the engine is stopped. In the sensor of Patent Document 1, the PM is burned out each time by continuing the heating after the measurement, but the heater temperature of 400 ° C. to 600 ° C. at the time of detection is not necessarily a sufficiently high temperature for PM combustion. If there is not enough time to stop the engine, it is difficult to reliably recover. In the sensor of Patent Document 2, every time a predetermined period elapses, the PM combustion temperature is heated for a predetermined time and reset. However, in this case, the engine may stop without being reset depending on the timing.

  In such a case, the property of the PM remaining on the sensor detection unit changes depending on the environment when the engine is stopped or restarted, and the error of the sensor output value after starting tends to increase. For example, if moisture or oil-derived components contained in the exhaust pipe when the engine is stopped adheres or the SOF content contained in the PM evaporates, the output value changes when the engine is stopped.

  Therefore, the present invention prevents the detection accuracy from deteriorating due to the remaining exhaust particulate matter remaining in the detection part in the electric resistance type particulate matter detection sensor used for detecting PM in the exhaust gas of the internal combustion engine. An object of the present invention is to provide a particulate matter detection sensor capable of always obtaining a stable sensor output and realizing high detection accuracy.

The invention according to claim 1 of the present invention is a particulate matter detection sensor which is disposed in an exhaust passage of an internal combustion engine and detects the amount of particulate matter in exhaust gas,
A detection unit having a pair of detection electrodes formed on the surface of the insulating substrate; and a sensor element having a heater unit for heating the detection unit to a predetermined temperature;
A controller that detects an electrical resistance value between the pair of detection electrodes that changes in accordance with the amount of particulate matter introduced into the detector, and that controls the energization of the heater;
In the control unit,
When the internal combustion engine is started, the heater is energized, and the temperature of the detection unit is maintained for a preset time S1 at a temperature T1 at which the particulate matter can burn, and the particulate matter on the surface of the detection unit is removed by combustion. A starting combustion control means,
After the start-up combustion control, the energization to the heater unit is controlled to maintain the temperature of the detection unit in a temperature range lower than the temperature T1, and the particulate matter adhering to the detection unit is detected in a normal time. Control means is provided.

  In the invention according to claim 2 of the present invention, the control unit is provided with energization timing determining means for determining a timing from start to energization of the heater unit based on an operating state of the internal combustion engine.

  In the invention according to claim 3 of the present invention, the energization timing determining means calculates a water exposure risk due to the condensed water present in the exhaust passage of the internal combustion engine, and determines the water exposure risk according to the calculated water exposure risk. Delay energization to the heater.

  In the invention according to claim 4 of the present invention, the starting combustion control means has a temperature T1 of 600 ° C. or higher and 900 ° C. or lower.

  In the invention according to claim 5 of the present invention, the starting combustion control means controls the temperature T1 to 650 ° C. or more and the time S1 to a preset value of 20 seconds or more.

  In the invention according to claim 6 of the present invention, the normal time control means controls the temperature range to a preset value between 50 ° C. and 600 ° C.

  In the invention according to claim 7 of the present invention, the pair of detection electrodes and the lead part having a comb shape are formed as the detection part, and the heater electrode and the lead part are provided on the back surface of the tip part of the insulating substrate. The heater portion is formed.

  The particulate matter detection sensor according to claim 1 of the present invention performs start-up combustion control in which the particulate matter accumulated in the detection unit is burned and removed by energizing the heater unit each time the engine is started when the engine is stopped. Therefore, it is possible to prevent an increase in sensor output error due to the influence of the remaining particulate matter. Therefore, stable and accurate detection is possible regardless of the environment when the engine is stopped or restarted.

According to the invention described in claim 2 of the present invention, when the environment at the time of restart is, for example, when moisture in the atmosphere adheres, an error in sensor output may increase, or water cracking may occur. The timing for energizing the heater can be delayed. Therefore, accurate detection is possible while preventing problems such as water cracking.

  According to the invention described in claim 3 of the present invention, when the energization timing is determined, the water exposure risk level is calculated and determined, so that it is possible to reliably prevent problems due to water exposure.

  According to the invention described in claim 4 of the present invention, the temperature T1 in the start-up combustion control is set to 600 ° C. to 900 ° C. or less, so that the element durability is maintained, and the particulates are surely formed while suppressing the energy cost. Substances can be burned off.

  According to the fifth aspect of the present invention, the particulate matter can be efficiently burned and removed by setting the temperature T1 for starting combustion control to 650 ° C. or more and the time S1 to 20 seconds or more. .

  According to the invention described in claim 6 of the present invention, in the normal control, a stable sensor output can be obtained by maintaining the temperature range of 50 ° C. to 600 ° C. or less.

  According to the invention described in claim 7 of the present invention, preferably, the detection portion is configured by a pair of detection electrodes and a lead portion, and the heater portion including the heater electrode and the lead portion is laminated on the back side thereof. Thus, the sensor element can be easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is 1st Embodiment of this invention, (a) is a schematic perspective view which shows PM sensor element structure which is the principal part of PM sensor, (b) is exhaust gas purification of the diesel engine for motor vehicles to which this invention is applied. It is the schematic which shows the whole structure of a system. It is a principal part enlarged view of FIG.1 (b), and is a schematic sectional drawing which shows the state which attached the PM sensor to the exhaust pipe of the diesel engine for motor vehicles. In 1st Embodiment of this invention, it is a flowchart which shows the electricity supply control content to the heater part of PM sensor by a control circuit. It is a flowchart which shows the detailed content of the combustion control at the time of starting. It is a figure which shows the combination of element temperature and holding time in combustion control at the time of starting. (A) is a time chart showing the time lapse of PM sensor output during normal control, (b) is a time chart showing the lapse of time of PM sensor output when the combustion control at start-up is not performed, and (c) is It is a time chart which shows the time passage of PM sensor output at the time of implementing combustion control at the time of starting.

  Hereinafter, a first embodiment in which a particulate matter detection sensor of the present invention is applied to an exhaust gas purification system of an internal combustion engine will be described with reference to the drawings. FIG. 1B is a system schematic diagram of an automotive diesel engine E / G that is an internal combustion engine, and shows an overall configuration of an exhaust gas purification system including a PM sensor 1 as a particulate matter detection sensor. FIG. 1A is a diagram showing a configuration of a PM sensor element 10 which is a main part of the PM sensor 1, and FIG. 2 is an enlarged view of a main part of FIG. The state which attached PM sensor 1 to exhaust pipe EX of diesel engine E / G is shown.

  The engine E / G in FIG. 1B employs a common rail fuel injection system that accumulates high pressure fuel that has been boosted by a high pressure pump PMP in a common rail R that is common to each cylinder so as to achieve a predetermined injection pressure. The engine is configured as a direct injection engine that directly injects into the combustion chamber by INJ. The PM sensor 1 is provided downstream of the diesel particulate filter DPF in the exhaust pipe EX, which is an exhaust passage of the engine E / G, and is controlled by a control circuit 2 serving as a control unit together with each part of the engine E / G. Details of this control will be described later.

First, referring to FIG. 1B, the system configuration of the engine E / G will be described. The exhaust manifold MH _EX of the 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 and enters the intake manifold MH _IN . Sent. 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 EX 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 into the exhaust pipe E 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 composed of soot particles (Soot), soluble organic components (SOF) and inorganic components is collected.

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. It can also be configured as a continuously regenerating diesel particulate filter in which the diesel oxidation catalyst DOC and the diesel particulate filter DPF are integrated.

  The exhaust pipe EX is provided with a differential pressure sensor SP in order to monitor the amount of particulate matter PM deposited on the diesel particulate filter DPF. The differential pressure sensor SP is connected to the upstream side and the downstream side of the diesel particulate filter DPF via a pressure introducing pipe, and outputs a signal corresponding to the differential pressure before and after that. Further, temperature sensors S1, S2, and S3 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. Based on these outputs, the control circuit 2 monitors the catalyst activation state of the diesel oxidation catalyst DOC and the PM trapping state of the diesel particulate filter DPF. If the PM trapping amount exceeds an allowable amount, the control circuit 2 performs forced regeneration to generate fine particles. The regeneration control for burning and removing the particulate matter PM is performed.

  Further, the control circuit 2 has various sensor signals for knowing the operating state of the engine E / G, for example, intake air amount and intake air temperature from the air flow meter AFM, engine lubricating oil and cooling water temperature, engine speed, throttle opening degree. Etc. are entered. The control circuit 2 calculates the fuel injection amount, the injection timing, and the like based on these signals, and controls the fuel injection.

  The PM sensor 1 of the present embodiment detects the particulate matter PM that passes through the diesel particulate filter DPF and slips downstream. In FIG. 1A, the PM sensor element 10 has a pair of detection electrodes 11 and 12 and electrode lead portions 111 and 121 constituting the detection unit 100 on the surface of an insulating substrate 13 that is an insulating substrate. A heater unit 300 for heating the detection unit 100 is stacked on the back side of the insulating substrate 13. The detection unit 100 is connected to the control circuit 2 via the electrode lead portions 111 and 121, and outputs a value corresponding to the interelectrode resistance between the detection electrodes 11 and 12. The heater unit 300 has a heater electrode 31 and heater lead portions 311 and 312 formed on the surface of the insulating substrate 32, and is connected to the heater power source 21 via the heater lead portions 311 and 312, and is energized by a command from the control circuit 2. Is controlled.

  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. Comb-shaped detection electrodes 11 and 12 that face each other at a predetermined inter-electrode distance are formed. The detection electrodes 11 and 12 are formed by printing a conductive paste containing a noble metal such as platinum in a predetermined pattern, and similarly, one ends of electrode lead portions 111 and 121 printed on the surface of the insulating substrate 13. Are connected to each other. The heater unit 300 is formed by forming a flat insulating substrate 32 by the same method, and printing and forming a predetermined pattern of heater electrodes 30 and heater lead portions 311 and 312 on the surface (surface on the detection unit 100 side). The heater electrode 31 of the heater unit 300 is disposed immediately below the detection electrodes 11 and 12 and efficiently heats the detection unit 100 to a predetermined temperature.

  In FIG. 2, the PM sensor 1 has a cylindrical housing 50 screwed to the tube wall of the exhaust pipe EX, and holds the upper half of the PM sensor element 10 inserted and fixed in the cylindrical insulator 60 therein. is doing. The lower half of the PM sensor 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 EX. Through holes 410 and 411 through which exhaust gas containing particulate matter PM that has passed through the diesel particulate filter DPF flows in and out are formed in the bottom and sides of the cover body 40.

  At this time, in order to surely capture the particulate matter PM, it is preferable to arrange the detection unit 100 of the PM sensor element 100 so as to face the upstream side of the exhaust pipe EX 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 electrode lead units 111 and 121, erroneous detection due to accumulation of particulate matter PM between the lead units 111 and 121. Can be prevented.

  Next, the basic operation of the PM sensor 1 will be described. In FIG. 2, the exhaust gas of the engine E / G, which is the gas to be measured, is introduced into the inside through the through hole 411 on the upstream side of the cover body 40 of the PM sensor 1, contacts the PM sensor element 100, and then passes through the bottom surface. The gas is discharged from the hole 410 or the downstream through hole 411. In FIG. 1A, since comb-shaped detection electrodes 11 and 12 are formed on the surface of the detection unit 100 with a predetermined gap, the initial state is a non-conductive state. When the particulate matter PM containing conductive soot particles adheres and gradually accumulates by contacting with the exhaust gas, the detection electrodes 11 and 12 are electrically connected at a certain point. Since the interelectrode resistance greatly decreases as the PM deposition amount increases, the failure determination of the diesel particulate filter DPF can be performed based on this relationship.

  For example, when a certain problem such as a cell wall breakage occurs in the diesel particulate filter DPF and normal collection becomes difficult, the particulate matter PM released together with the exhaust gas rapidly increases. Therefore, the control circuit 2 monitors the amount of the particulate matter PM that passes through the diesel particulate filter DPF during a predetermined period. If the amount is clearly larger than normal, it can be determined as abnormal. Even if it is normal, if the amount of accumulated PM exceeds a certain amount, the change in inter-electrode resistance becomes small and the detection accuracy decreases, so usually a sensor that burns and removes the deposited PM after a predetermined period of time. It is desirable to perform playback control.

  However, when the engine E / G is stopped and restarted without performing the sensor regeneration control, the particulate matter PM previously adhered to the detection unit 100 of the PM sensor 1 remains. In this case, the property of the particulate matter PM changes depending on the environment at the time of stopping and restarting, and affects the sensor output. For example, when the engine is stopped with the exhaust pipe EX at a high temperature, it is conceivable that only the organic component (SOF) of the attached particulate matter PM evaporates. As a result, the conductivity of the particulate matter PM changes, and the sensor output after startup differs from the initial behavior. In addition, when the environment at the time of start-up is low, the detector is condensed by water vapor in the exhaust, and moisture is attached. Then, the adhesion state of the particulate matter PM at the time of sensor operation is different, or an error occurs in the sensor output due to evaporation of moisture. The environment at the time of stopping and starting is different each time. For example, the organic component (SOF) hardens or burns without evaporating depending on the temperature and exhaust component (oxygen concentration), so the error that occurs is predicted. Is difficult.

Therefore, in the present invention, the control circuit 2 controls the energization to the heater unit 300 at the start time and the normal time, and in particular, after the particulate matter PM is burned and removed at the start time, control for normal PM detection is performed. By doing so, the output error is suppressed. In particular,
When the engine E / G is started, the heater unit 300 is energized, and the temperature of the detection unit 100 is maintained for a preset time S1 at a temperature T1 at which the particulate matter PM can burn, and the particulate matter PM on the surface of the detection unit 100 The combustion control at the start to remove the combustion (combustion control means at the start),
After the start-up combustion control, the energization to the heater unit 300 is controlled to keep the temperature of the detection unit 300 in a temperature range lower than the temperature T1, and the particulate matter PM adhering to the detection unit 100 is detected. Control is performed (normal time control means).

  In the start-up combustion control, when the energization of the heater unit 300 is started simultaneously with the start-up, water condensed in the exhaust pipe EX may scatter and adhere to the high-temperature detection unit 100 and may break. In order to prevent this, it is necessary to delay the start of energization until the condensed water in the exhaust pipe EX is not dried or scattered and does not adhere to the sensor element 10. Therefore, in such a case, the energization for starting combustion control is not performed immediately, the water exposure risk level is determined from the operating state of the engine E / G, and the energization is performed until the water exposure risk level is within an allowable range. It is better to delay the timing. Alternatively, the relationship between the water exposure risk coefficient calculated from the operating state of the engine E / G and the energization timing is experimentally obtained in advance, and energization is started at a timing determined according to the water exposure risk coefficient. You can also. Thereby, it becomes possible to detect with high accuracy while suppressing water cracking.

  Next, an example of the control performed by the control circuit 2 will be specifically described based on the flowcharts of FIGS. In FIG. 3, when starting the engine E / G, first, in step S100, data acquisition from various sensors is performed. At this time, in order to know the operating state of the engine E / G and the temperature condition in the exhaust pipe EX, for example, the engine cooling water temperature and the lubricating oil temperature are taken in from a water temperature sensor and an oil temperature sensor (not shown), and the air flow meter AFM is used as the outside temperature. The temperature sensor S3 output downstream of the diesel particulate filter DPF is taken as the output of the intake air temperature sensor built in the exhaust gas near the PM sensor 1. Further, the engine E / G rotation speed, fuel injection amount Q, operating time, and the like are taken in.

  In step S101, the water exposure risk of the PM sensor 1 is calculated based on these data. Specifically, the amount of condensed water generated and retained in the exhaust pipe EX upstream from the PM sensor 1 is predicted from the time since the previous operation stop, and the operating conditions and temperature conditions after the start, and from the shape of the exhaust pipe EX The flooding risk coefficient can be calculated using the relationship obtained in advance. For example, under conditions where the outside air temperature is low, moisture in the atmosphere is condensed due to the temperature drop of the exhaust pipe EX after the operation is stopped, or moisture in the exhaust is condensed when the exhaust flows into the low temperature exhaust pipe EX immediately after the start. Further, if the time from the stop of operation is relatively short and the temperature in the exhaust pipe EX is relatively high, the amount of condensed water is small, and the time until the condensed water evaporates due to an increase in exhaust gas temperature is also short. Even if the amount of condensed water is the same, for example, when the exhaust pipe EX has a bent portion, the condensed water tends to stay and is not easily scattered by the exhaust. Therefore, a map can be created based on the experimental results obtained by changing these conditions, or can be obtained using an arithmetic expression.

  In step S102, it is determined whether the water exposure risk obtained in step S101 is smaller than a certain value. This constant value is the lowest value that may cause water cracking due to the start of energization of the PM sensor 1, and if an affirmative determination is made, it is determined that there is no possibility of water cracking, that is, the energization start timing. Then, the process proceeds to start-up combustion control in step S103. If a negative determination is made, the process returns to step S100, and steps S100 to S102 are repeated in order to delay the energization until there is no risk of water cracking.

In step S103, the heater part 300 of the PM sensor 1 is energized by the combustion control at start-up to burn and remove the particulate matter PM. Details of this control will be described with reference to FIG. In step S200 of FIG. 4, data acquisition is performed in order to know the deposition state of the particulate matter PM on the PM sensor 1. At this time,
1) Period from the time when PM combustion is performed by normal control to the time when operation is stopped in the previous operation 2) Operation stop period 3) PM for each period of the period from the current start to the start of start-time combustion control In order to know the particulate matter PM adhering to the sensor 1 or its change, the operation state, temperature conditions such as engine cooling water temperature, lubricating oil temperature, outside air temperature, exhaust temperature, engine speed, injection amount Q from various sensors, Capture data such as operation time.

In step S201, based on these data,
1) The amount of particulate matter PM adhering to the PM sensor 1 at the time of the previous operation stop 2) Moisture adhering or evaporating during the operation stop period, HC content 3) From the current start to the start of start-up combustion control The amount of the particulate matter PM adhering to the particle is obtained, and the current adhesion state (attachment amount and component ratio) of the particulate matter PM is predicted. Changes in the amount of particulate matter PM deposited during operation, moisture during stoppage, and HC content vary depending on the operating conditions and the environment in the exhaust pipe EX. It can be calculated using an arithmetic expression based on it.

  Next, the process proceeds to step S202, and combustion control conditions (temperature and time) of the particulate matter PM are calculated from the adhesion state (attachment amount and component ratio) of the particulate matter PM calculated in step S201. In the start-up combustion control, the temperature T1 is preferably set to be equal to or higher than the temperature at which the particulate matter PM can be combusted, usually 600 ° C. or higher. It is good that it is below ℃. The time S1 depends on the temperature T1, and the higher the temperature T1, the shorter the time S1 can be. From the viewpoint of controllability, the time S1 is preferably 5 minutes or less.

  FIG. 5 shows the result of examining the relationship between the element temperature T1 and the holding time S1. As shown in FIG. 1B, the test condition is that the PM sensor 1 is attached to the exhaust pipe EX, the energization control is performed on the heater unit 300 of the PM sensor 1 after the engine E / G is started, and the time is set to a predetermined temperature (T1). (S1) The adhesion state of the particulate matter PM when held was observed. At this time, the element temperature T1 was set to 550 ° C. to 750 ° C., and the holding time S1 was changed to indicate the presence or absence of adhesion. As shown in the figure, when the element temperature T1 is 600 ° C., the holding temperature is 20 seconds or more, and when the element temperature T1 is 700 ° C., the holding temperature is 10 seconds or more. When the element temperature T1 is 550 ° C. or lower, the particulate matter PM is adhered even when the holding time S1 is 80 seconds, and it is necessary to set the temperature to 600 ° C. or higher for combustion removal. Preferably, the element temperature T1650 ° C. or higher and the holding temperature 20 seconds or higher are preferable.

  In step S203, start-up combustion control is started, and energization control is performed on the heater unit 300 of the PM sensor 1 under the conditions determined in step S202 (temperature T1, time S1) to burn and remove the particulate matter PM. After the detection unit 100 is held at the temperature T1 for a time S1 by energization of the heater unit 300 of the PM sensor 1, the start-up combustion control is terminated in step S204.

  Thereafter, the process proceeds to step S104 in FIG. 3, and normal time control is started. In the normal control, the particulate matter adhering to the detection unit 100 in this state is maintained by keeping the temperature of the detection unit 100 in a temperature range lower than the temperature T1 of the start-time combustion control by energizing the heater unit 300 of the PM sensor 1. PM detection is performed. Specifically, a stable output can be obtained by controlling the temperature range to a preset value in the range of 50 ° C. to 600 ° C.

  FIG. 6A is a diagram illustrating the output of the PM sensor 1 when the normal control is continuously performed, and after a certain dead time has elapsed since the start of detection, the pair of detection electrodes 11 of the detection unit 100, The sensor output rises when 12 are connected, and the sensor output rapidly increases with time, and then saturates. This is because the inter-electrode resistance rapidly decreases as the amount of particulate matter PM adhering to the detection unit 100 increases, but the resistance value does not change any more when a predetermined amount is exceeded. To remove the deposited particulate matter PM. The sensor regeneration control in this case can be performed in the same manner as the start-up combustion control, and it may be held for a predetermined time at a temperature at which the particulate matter PM can be combusted or higher. For example, it is maintained at 600 ° C. to 900 ° C., preferably 650 ° C. or higher for 20 seconds or longer, and 700 ° C. for 10 seconds or longer. Thereafter, similar control is repeated.

  FIG. 6B is a diagram showing a change in sensor output at the restart when the engine is stopped without performing the sensor regeneration control after the detection by the normal time control is started. The left figure shows a case where the engine is stopped after the pair of detection electrodes 11 and 12 of the detection unit 100 are conducted and the sensor output rises, and the start-up combustion control is not performed at the time of restart. At this time, the PM sensitivity changes with respect to the original output change (dotted line) due to the change in the properties of the particulate matter PM during soaking, moisture adhesion, and the like, and there is a high possibility of erroneously detecting the PM deposition amount. The right figure shows a case where the engine is stopped in a dead time after the sensor regeneration control, after the pair of detection electrodes 11 and 12 of the detection unit 100 are connected and the sensor output rises. Also in this case, the dead time changes due to the effect that the particulate matter PM deposited after the sensor regeneration control remains, and accurate detection becomes difficult.

  On the other hand, FIG. 6C shows the case where the start-up combustion control of the present invention is performed at the time of restart, and even when the engine is stopped without performing the sensor regeneration control, the PM sensitivity change and dead time are reduced. The particulate matter PM can be normally detected without causing any deviation.

  The fine particle sensor of the present invention formed in this way has high detection accuracy, can be installed downstream of the DPF, and can be used for detecting an abnormality of the DPF. Alternatively, it can be used in a system that is installed upstream of the DPF and directly detects the particulate matter PM flowing into the DPF.

DPF Diesel particulate filter EX Exhaust pipe (exhaust passage)
E / G diesel engine (internal combustion engine)
1 PM sensor (particulate matter detection sensor)
10 PM sensor element (sensor element)
100 Detection part 11, 12 Detection electrode 111, 121 Electrode lead part 13 Insulating substrate (insulating base)
14 Insulating protective layer 2 Control circuit (control unit)
21 Heater power supply 300 Heater part 31 Heater electrode 32 Insulating substrate 311, 312 Heater lead part 40 Cover body 410, 411 Through hole 50 Housing 60 Insulator

Claims (7)

A particulate matter detection sensor that is disposed in an exhaust passage of an internal combustion engine and detects the amount of particulate matter in exhaust gas,
A detection unit having a pair of detection electrodes formed on the surface of the insulating substrate; and a sensor element having a heater unit for heating the detection unit to a predetermined temperature;
A controller that detects an electrical resistance value between the pair of detection electrodes that changes in accordance with the amount of particulate matter introduced into the detector, and that controls the energization of the heater;
In the control unit,
When the internal combustion engine is started, the heater is energized, and the temperature of the detection unit is maintained for a preset time S1 at a temperature T1 at which the particulate matter can burn, and the particulate matter on the surface of the detection unit is removed by combustion. A starting combustion control means,
After the start-up combustion control, the energization to the heater unit is controlled to maintain the temperature of the detection unit in a temperature range lower than the temperature T1, and the particulate matter adhering to the detection unit is detected in a normal time. A particulate matter detection sensor comprising a control means.   The particulate matter detection sensor according to claim 1, wherein the control unit is provided with energization timing determining means for determining a timing from start to energization of the heater unit based on an operating state of the internal combustion engine.   3. The energization timing determining means calculates a water exposure risk due to condensed water existing in an exhaust passage of the internal combustion engine, and delays the power supply to the heater unit according to the calculated water exposure risk. Particulate matter detection sensor.   The particulate matter detection sensor according to any one of claims 1 to 3, wherein the start-up combustion control means has a temperature T1 of 600 ° C or higher and 900 ° C or lower.   5. The particulate matter detection sensor according to claim 4, wherein the start-up combustion control means controls the temperature T1 to 650 ° C. or more and the time S1 to a preset value of 20 seconds or more.   The particulate matter detection sensor according to any one of claims 1 to 5, wherein the normal time control means controls the temperature range to a preset value of 50 ° C or more and 600 ° C or less.   A pair of comb-like detection electrodes and a lead portion are formed as the detection portion, and a heater electrode and a lead portion are formed on the back surface of the distal end portion of the insulating substrate to form the heater portion. 6. The particulate matter detection sensor according to any one of 6 above.

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