US20110314796A1 - Particulate matter detection sensor and control device of controlling the same - Google Patents

Particulate matter detection sensor and control device of controlling the same Download PDF

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Publication number
US20110314796A1
US20110314796A1 US13170269 US201113170269A US2011314796A1 US 20110314796 A1 US20110314796 A1 US 20110314796A1 US 13170269 US13170269 US 13170269 US 201113170269 A US201113170269 A US 201113170269A US 2011314796 A1 US2011314796 A1 US 2011314796A1
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Prior art keywords
detection
particulate matter
part
pm
sensor
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Abandoned
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US13170269
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Satoshi Nakamura
Shinya Teranishi
Hirofumi Takeuchi
Takashi Sawada
Hideaki Itoh
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Denso Corp
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Denso Corp
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N9/00Electrical control of exhaust gas treating apparatus
    • F01N9/002Electrical control of exhaust gas treating apparatus of filter regeneration, e.g. detection of clogging
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02DCONTROLLING COMBUSTION ENGINES
    • F02D41/00Electrical control of supply of combustible mixture or its constituents
    • F02D41/02Circuit arrangements for generating control signals
    • F02D41/14Introducing closed-loop corrections
    • F02D41/1438Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1466Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being a soot concentration or content
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
    • G01N15/06Investigating concentration of particle suspensions
    • G01N15/0656Investigating concentration of particle suspensions using electric, e.g. electrostatic methods or magnetic methods
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02TCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00Road transport of goods or passengers
    • Y02T10/10Internal combustion engine [ICE] based vehicles
    • Y02T10/40Engine management systems
    • Y02T10/47Exhaust feedback

Abstract

A particulate matter (PM) detection sensor is placed in an exhaust gas pipe of a diesel engine. The PM sensor element has a detection part composed of a pair of detection electrodes and a heater part. The detection electrodes and the heater part are stacked in the PM sensor element. A control circuit instructs a heater power supply to supply electric power to the heater part when the diesel engine is started to operate. The heater part heats the detection part at a predetermined temperature T1 within a range of 600° C. to 900° C. for a predetermined period S1 of time, for example, 650° C. for 20 seconds, in order to burn and completely eliminate particulate matter accumulated in the detection part. This control process avoids incorrect detection of the PM detection sensor. After this process, the control circuit executes usual control of the PM detection sensor.

Description

    CROSS-REFERENCE TO RELATED APPLICATION
  • This application is related to and claims priority from Japanese Patent Application No. 2010-147862 filed on Jun. 29, 2010, the contents of which are hereby incorporated by reference.
  • BACKGROUND OF THE INVENTION
  • 1. Field of the invention
  • The present invention relates to particulate matter detection sensors and control devices of controlling such a particulate matter detection sensor, and more particularly, particulate matter detection sensors of an electric-resistance type and control devices of detecting a quantity of particulate matter contained in target detection gas such as exhaust gas emitted from an internal combustion engine. Such a particulate matter detection sensor is placed in an exhaust gas pipe of an exhaust gas purifying system of the internal combustion engine and is applied to detecting defect of a diesel particulate filter which traps or traps particulate matters contained in the exhaust gas in order to purify the exhaust gas.
  • 2. Description of the Related Art
  • In general, a diesel engine exhaust gas system of a diesel engine is equipped with a diesel particulate filter (DPF). The DPF is placed in an exhaust gas pipe of the diesel engine exhaust gas system. The DPF can trap and eliminate conductive particulate matter PM from exhaust gas emitted from the diesel engine. The particulate matter PM contains environmental harmful matter, in particulate, soot and soluble organic fraction (SOF), etc. The DPF is made of porous ceramics with a high heat resistance. When exhaust gas passes in the exhaust gas pipe, cell walls having pores in the DPF trap particulate matter contained in the exhaust gas in order to purify the exhaust gas.
  • When a quantity of particulate matter PM trapped in the DPF exceeds a predetermined allowable quantity, clogged cell walls occur in the DPF, and a pressure loss of the DPF is thereby increased. The clogged cell walls in the DPF allow the particulate matter contained in the exhaust gas to pass through the DPF without trapping the particulate matter. This prevents the exhaust gas from being purified. In order to avoid this, it is required to execute the regeneration of the DPF every predetermined period of time in order to recover the trapping function of the DPF.
  • For example, it is possible to detect the time to execute the regeneration of the DPF by using a differential sensor, because the pressure difference of the differential sensor is increased when the quantity of trapped particulate matter in the DPF is increased. In the regeneration of the DPF, combustion exhaust gas at a high temperature is forcedly introduced into the inside of the DPF by using a heater or executing post-injection in order to burn and eliminate the trapped particulate matter from the DPF.
  • On the other hand, there has been proposed a particulate matter detection sensor capable of directly detecting particulate matter contained in exhaust gas emitted from an internal combustion engine. Such a particulate matter detection sensor is placed at a downstream side of the DPF in order to detect the quantity of particulate matter contained in exhaust gas after passing through the DPF. For example, an on-board diagnosis device (OBD) monitors the operation condition of the DPF can use the detection result of a particulate matter detection sensor in order to detect defect and damage to the DPF.
  • When such a particulate matter detection sensor is placed at the upstream side of the DPF, it is possible to detect the quantity of particulate matter contained in the exhaust gas which is introduced into the DPF and to detect the optimum time to execute the regeneration of the DPF, instead of using the differential sensor.
  • For example, Japanese patent publication No. JP H02-44386 discloses a soot concentration sensor of an electric resistance type. In the soot concentration sensor, a pair of conductive detection electrodes is formed on a front surface of an insulation substrate, and a heater is formed on the back surface or in the inside of the insulation substrate. This soot sensor uses conductive characteristics of soot. The soot sensor detects an electric resistance which is changed in accordance with the change of the quantity of soot particles accumulated between the detection electrodes. The detection electrodes form a detection part in the soot sensor. A heater part generates heat energy when receiving electric power in order to heat the detection part at a temperature within the range of 400° C. to 600° C., and detect the resistance between the detection electrodes. After detecting the resistance, the accumulated particulate matter is burned in order to eliminate the particulate matter from the soot sensor and regenerate it.
  • In addition, Japanese patent laid open publication No. 2009-144577 discloses a device equipped with a particulate matter trap sensor in which a plurality of electrodes, which face to each other at a predetermined gap, is formed on an insulation material. The device calculates an index corresponding to the electric resistance value between the detection electrodes, and judges occurrence of faulty in a particulate filter when the detected index becomes smaller than a predetermined reference value. Further, the device resets the PM trap sensor every regular condition (every predetermined driving time, predetermined driving distance, and quantity of used fuel).
  • There are other conventional techniques for detecting particulate matter contained in exhaust gas on the basis of detecting heat energy generated by oxidizing particulate matter by using catalyst and a thermocouple, monitoring temperature and chemical seeds contained in exhaust gas by using wavelength variable diode sensor. In particular, particulate matter detection sensors of an electric resistance type have a simple configuration and can output a relatively stable output signal.
  • By the way, there is a possibility of being particulate matter emitted from a previous combustion of an internal combustion engine and trapped and remained in a detection part of a particulate matter detection sensor when the engine is restarted.
  • The former conventional technique (Japanese patent publication No. JP H02-44386) previously described burns off remained particulate matter which is trapped and accumulated on the particulate matter detection sensor by continuing heating after completion of the detection process. However, when the detection process is executed, the temperature of the particulate matter detection sensor is within a range of 400° C. to 600° C., and this temperature is not always an adequate high temperature capable of completely eliminating remained particulate matter from the particulate matter detection sensor. Still further, it is difficult to regenerate the particulate matter detection sensor unless an adequate period of time is elapsed.
  • Still further, the sensor disclosed in the latter conventional technique Japanese patent laid open publication No. 2009-144577 is burned every predetermined period of time for a predetermined time in order to reset the sensor. However, there is a possibility of generating the engine stop without resetting the sensor completely.
  • This often causes incorrect output of the sensor after the engine restart because the characteristics of particulate matter trapped and remained in the detection part of the particulate matter detection sensor is changed by the environment during the engine stop or when the engine restart. For example, the sensor often outputs an incorrect detection signal during the engine stop and when the engine is restarted by adhering water and oil components remained in the exhaust gas pipe to the particulate matter detection sensor and by evaporating soot organic fraction (SOF) contained in particulate matter remained in the exhaust gas pipe.
  • SUMMARY OF THE INVENTION
  • It is an object of the present invention to provide a particulate matter detection sensor of an electric resistance type and a control device of preventing particulate matter accumulated in a detection part of the particulate matter detection sensor from being remained, and further preventing the detection accuracy of the particulate matter detection sensor from being deteriorated and decreased. The particulate matter detection sensor according to the present invention outputs a stable and correct detection signal with high accuracy.
  • To achieve the above purposes, the present invention provides a control device which controls the operation of a particulate matter detection sensor. The particulate matter detection sensor is placed in an exhaust gas pipe of an internal combustion engine through which exhaust gas emitted from the internal combustion engine flows and is discharged to the outside. The particulate matter detection sensor is equipped with a particulate matter sensor element. The particulate matter sensor element is comprised of an insulation substrate, a detection part and a heater part. The detection part in the particulate matter sensor element is comprised of a pair of detection electrodes formed on a surface of the insulation substrate. The heater part generates heat energy when receiving electric power in order to heat the detection part at a predetermined temperature for a predetermined period of time.
  • The control device has a control part. The control part receives a detection signal transferred from the particulate matter detection sensor and detects an electrical resistance value between the pair of the detection electrodes in the detection part on the basis of the received detection signal, etc. In general, the electrical resistance value between the pair of the detection electrodes is changed in accordance with a quantity of particulate matter accumulated in the detection part. The control part supplies electric power to the heater part. For example, the control part instructs a heater power supply to supply electric power to the heater part.
  • In particular, the control part is comprised of a combustion control means and a usual control means. The combustion control means executes combustion control when the internal combustion engine starts to operate. The combustion control is executed when the engine is started or restarted. In the combustion control, the combustion control means supplies electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at a predetermined temperature T1 for a predetermined period S1 of time in order to burn the accumulated particulate matter and eliminate the accumulated particulate matter from the detection part of the particulate matter detection sensor. On the other hand, the usual control means executes usual control after completion of the combustion control previously described which is executed when the internal combustion engine is started to operate. In the usual control, the usual control means supplies electric power to the heater part in order to maintain the detection part of the particulate matter sensor element in the particulate matter detection sensor at a temperature T2 which is less than the predetermined temperature T1 in order to detect particulate matter adhered to and accumulated in the detection part.
  • The combustion control means in the control circuit according to the present invention executes the combustion control every time when the internal combustion engine is started (or restarted) to operate. In the combustion control, the combustion control means supplies electric power to the heater part in order to execute the combustion of particulate matter accumulated in the detection part of the particulate matter sensor element. This eliminates the accumulated particulate matter from the detection part of the particulate matter sensor element. This can prevent incorrect detection of the particulate matter detection sensor caused by the particulate matter remained in the detection part, and prevent the output of the particulate matter detection sensor from being separated from a correct output value. According to the present invention, it is possible for the particulate matter detection sensor to output a stable and correct detection signal with high accuracy regardless of operation conditions and environmental condition of the internal combustion engine even if it is before or after the start or stop of the internal combustion engine.
  • In the control device as another aspect of the present invention, the control part further comprises an electric power supply timing means which determines a timing to supply electric power to the heater part, counted from a time when the internal combustion engine is started to a time when the electric power is supplied to the heater part on the basis of the operation state of the internal combustion engine.
  • In general, when the internal combustion engine is restarted, there is a possibility of adhering water contained in the inside of the exhaust gas pipe to the particulate matter sensor element of the particulate matter detection sensor and causing incorrect detection of the particulate matter detection sensor. Further, there is a possibility for the particulate matter detection sensor to be broken by adhering water to the particulate matter detection sensor. In order to avoid this problem, the electric power supply timing means in the control device according to the present invention delays the time to supply electric power to the heater part of the particulate matter sensor element. It is therefore possible to prevent the breaking of the particulate matter detection sensor by adhering water. The control device according to the present invention allows the particulate matter detection sensor to output a correct detection signal with high accuracy.
  • 0014
  • In the control device as another aspect of the present invention, the electric power supply timing means calculates an amount (or degree of risk) of condensed water remained in the exhaust gas pipe adhering to the detection part in the particulate matter detection sensor, and delays the timing to supply the electric power to the heater part on the basis of the calculated amount of condensed water.
  • According to the present invention, the electric power supply timing means in the control device calculates the timing when the electric power is supplied to the heater part on the basis of the calculated amount (or the degree of risk) of condensed water adhering to the detection part in the particulate matter detection sensor. This control makes it possible to avoid the problem caused by adhering water contained in the exhaust gas pipe to the particulate matter detection sensor.
  • In the control device as another aspect of the present invention, the combustion control means supplies the electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at the predetermined temperature T1 within a range of not less than 600° C. to not more than 900° C.
  • The combustion control means in the control device according to the present invention executes the combustion control executed when the internal combustion engine is started so that the detection part in the particulate matter sensor element is maintained at the temperature T1 which is within the range of not less than 600° C. to not more than 900° C. This combustion control makes it possible to maintain the durability of the particulate matter sensor element and completely eliminate accumulated particulate matter from the particulate matter sensor element in the particulate matter detection sensor. Further, this combustion control can suppress energy cost.
  • In the control device as another aspect of the present invention, the combustion control means supplies the electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at the predetermined temperature T1 of not less than 650° C. for the predetermined period S1 of time of not less than 20 seconds.
  • The combustion control means in the control device according to the present invention executes the combustion control executed when the internal combustion engine is started so that the detection part in the particulate matter sensor element is maintained at the temperature T1 of not less than 650° C. for the period S1 of time of not less than 20 seconds. This combustion control makes it possible to completely eliminate accumulated particulate matter from the particulate matter sensor element with high efficiency.
  • In the control device as another aspect of the present invention, the usual control means supplies the electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at a predetermined temperature within a range of not less than 50° C. to not more than 600° C.
  • The usual control means in the control device according to the present invention executes the usual control in order to maintain the detection part at a temperature within a range of not less than 50° C. to not more than 600° C. The usual control makes it possible to allow a stable output, namely, a correct detection signal output from the particulate matter detection sensor.
  • In the control device as another aspect of the present invention, the detection part is comprised of the pair of the detection electrodes having a comb shape and detection lead parts formed on a front surface of the insulation substrate. The heater part is comprised of heater electrodes and heater lead parts formed at the front end in a back surface of the insulation substrate.
  • According to the present invention, it is possible to easily produce the particulate matter sensor element in the particulate matter detection sensor because the detection part is comprised of the pair of the detection electrodes and detection lead parts formed on a front surface of the insulation substrate. On the other hand, the heater part is comprised of heater electrodes and heater lead parts formed at the front end in the back surface of the insulation substrate.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:
  • FIG. 1A is a perspective view showing a schematic structure of a particulate matter (PM) sensor element in a PM detection sensor and a control circuit according to an embodiment of the present invention;
  • FIG. 1B is a schematic view showing an entire configuration of an exhaust gas purifying system of a diesel engine for an motor vehicle to which the PM detection sensor and the control circuit according to the embodiment of the present invention are applied;
  • FIG. 2 is an enlarged view showing a cross section of a part of the PM detection sensor according to the embodiment of the present invention which is mounted to an exhaust gas pipe in the exhaust gas purifying system shown in FIG. 1B;
  • FIG. 3 is a flow chart showing the process for the control circuit to supply electric power to a heater part in the PM sensor element in the PM detection sensor according to the embodiment of the present invention;
  • FIG. 4 is a flow chart showing a detailed process of a combustion control executed when an internal combustion engine is started;
  • FIG. 5 is a view showing an experimental result of a relationship between the temperature T1 (C) of the PM sensor element and the period S1 (seconds) of time to maintain the temperature of the PM sensor element in the PM detection sensor according to the embodiment of the present invention;
  • FIG. 6A is a timing chart showing the output change of the PM detection sensor when the usual control is continuously executed;
  • FIG. 6B is a timing chart showing the output change of the PM detection sensor when the diesel engine is restarted after the engine stop without executing the PM detection sensor regeneration control after the detection process is executed by the PM detection sensor during the usual control; and
  • FIG. 6C is a timing chart showing the output change of the PM detection sensor when the combustion control is executed at the engine start, but a PM detection sensor regeneration control is not executed before the engine stop.
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the various embodiments, like reference characters or numerals designate like or equivalent component parts throughout the several diagrams.
  • Embodiment
  • A description will be given of a particulate matter detection sensor 1 and a control circuit 2 as a control device according to an embodiment of the present invention with reference to FIG. 1 to FIG. 6A, FIG. 6B and FIG. 6C.
  • The embodiment applies the particulate matter detection sensor 1 (hereinafter, referred to the “PM detection sensor 1”) to an exhaust gas purifying system of an internal combustion engine.
  • FIG. 1A is a perspective view showing a schematic structure of a particulate matter sensor element 10 (hereinafter, referred to the “PM sensor element 10”) in the PM detection sensor 1 and the control device 2 according to the embodiment of the present invention. FIG. 1B is a schematic view showing an entire configuration of the exhaust gas purifying system of an on-vehicle diesel engine of an motor vehicle to which the PM detection sensor 1 and the control device 2 according to the embodiment of the present invention are applied. FIG. 2 is an enlarged view showing a cross section of a part of the PM detection sensor 1 according to the embodiment of the present invention. In particular, the PM detection sensor 1 is mounted to an exhaust gas pipe EX in the exhaust gas purifying system of an on-vehicle diesel engine as an internal combustion engine shown in FIG. 1B.
  • The diesel engine E/G shown in FIG. 1B is equipped with a common rail fuel injection system. The common rail fuel injection system increases the pressure of fuel by a high-pressure pump PMP. The common rail R stores the fuel at a constant high pressure and supplies the high pressure fuel to each of the cylinders by an injector INJ.
  • The PM detection sensor 1 is placed at the downstream side of the diesel particulate filter DPF in the exhaust gas pipe EX of the diesel engine E/G. The control circuit 2 as the control device and each of parts of the diesel engine E/G control the operation of the PM detection sensor 1. The control circuit 2 and the control method will be explained in detail later.
  • A description will now be given of the structure of the exhaust gas purifying system of the on-vehicle diesel engine of an motor vehicle with reference to FIG. 1B.
  • As shown in FIG. 1B, a turbine TRB is mounted to an exhaust gas manifold of the diesel engine E/G. When a turbo charger TRBCGR in accordance with the rotation of the turbine TRB, compressed air is supplied to the intake manifold MHIN through an intercooler CLRINT.
  • A part of the exhaust gas discharged from an outlet manifold MHEX is re-circulated to the intake manifold MHIN through an EGR valve VEGR and an EGR cooler CLREGR. Forced induction increases the quantity of intake air in order to increase combustion efficiency and EGR (Exhaust Gas Recirculation) suppresses the combustion of the diesel engine in order to suppress nitrogen oxide (NOx) from being discharged to the ambient atmosphere of the motor vehicle.
  • A unit having diesel oxidation catalyst DOC and a diesel particulate filter DPF are mounted to the exhaust gas pipe EX connected to the outlet manifold MHEX in order to purify the exhaust gas emitted from the diesel engine. That is, un-burned components such as hydro carbon HC, carbon monoxide and nitric oxide NO are oxidized when the exhaust gas passes through the exhaust gas pipe EX after emitted from the diesel engine, and the diesel particulate filter DPF traps soot (Soot), soluble organic fraction (SOF) and particulate matter (PM) composed of inorganic components contained in the exhaust gas. The diesel particulate filter DPF is placed at the downstream side of the unit having the diesel oxidation catalyst (DOC), as shown in FIG. 1B.
  • In general, such a diesel oxidation catalyst DOC is supported on a surface of a known monolith support, for example, a ceramic honeycomb structure body made of cordierite. When the diesel particulate filter DPF is forcedly regenerated, fuel is supplied and burned in oxidation. This increases the temperature of the exhaust gas and the diesel oxidation catalyst DOC oxides and eliminates soot of fraction (SOF) components contains in particulate matter PM. Nitrogen dioxide NO2 generated by oxidizing nitric oxide NO is used as oxidizing agent of particulate matter PM accumulated in the DPF which is placed at the downstream side of the unit having the diesel oxidation catalyst DOC. This makes it possible to execute continuous oxidizing.
  • The diesel particulate filter DPF has a filter structure of a wall flow type which is well known. For example, a porous ceramic honeycomb structure body is extruded and molded. The porous ceramic honeycomb structure body is made of heat resistance ceramics such as cordierite. On the inlet surface of the diesel particulate filter DPF, cells are alternately plugged by plug members so that the surface of the inlet surface has a checkered pattern in which one of adjacent cells is plugged and the other cell is open, and the outlet surface has the checkered pattern in which one of adjacent cells is plugged and the other cell is open. That is, the diesel particulate filter DPF is composed of a plurality of cells formed by cell walls. One end part of each of the cells is open and the other end part thereof is plugged so that the plugged parts are alternately formed on each of the inlet surface and the outlet surface of the diesel particulate filter DPF.
  • Each of the cells is formed in parallel along the longitudinal direction of the diesel particulate filter DPF. In particular, the cell walls in the adjacent cells have porous structure through which the exhaust gas passes. The porous structure of the cell walls (porous cell walls) traps particulate matter PM contained in the exhaust gas when the exhaust gas passes through the porous cell walls.
  • It is possible to form a continuous type diesel particulate filter composed of the diesel oxidation catalyst DOC and the diesel particulate filter DPF.
  • A differential pressure sensor SP is placed in the exhaust gas pipe EX in order to monitor the quantity of particulate matter PM accumulated in the diesel particulate filter DPF.
  • The differential pressure sensor SP is connected to the exhaust gas pipe EX at the upstream side and the downstream side of the diesel particulate filter DPF through pressure introduction pipes. The differential pressure sensor SP detects the pressure of the exhaust gas at the upstream side and the downstream side of the diesel particulate filter DPF, respectively, and outputs a detection signal corresponding to the pressure difference detected at the upstream side and the downstream side of the diesel particulate filter DPF.
  • Further, temperature sensors S1, S2 and S3 are placed at the upstream side of the unit having the diesel oxidation catalyst DOC, the upstream side and the downstream side of the diesel particulate filter DPF in order to detect the temperature of the exhaust gas.
  • The control circuit 2 receives the detection signals transferred from these sensors and monitors the activation state of the diesel oxidation catalyst DOC and the quantity of particulate matter PM accumulated in the diesel particulate filter DPF on the basis of the detection signals. When the quantity of particulate matter PM accumulated in the diesel particulate filter DPF exceeds a predetermined allowable value, the control circuit 2 forcedly executes the process of burning the particulate matter PM accumulated in the diesel particulate filter DPF in order to regenerate the diesel particulate filter DPF and eliminate the particulate matter PM from the diesel particulate filter DPF.
  • Further, the particulate matter detection sensor (PM detection sensor) 1 detects particulate matter PM which passes through the diesel particulate filter DPF and travels to the downstream side of the diesel particulate filter DPF.
  • As shown in FIG. 1A, the PM detection sensor 1 is composed of a particulate matter sensor element (PM sensor element) 10. The PM sensor element 10 is composed of an insulation substrate 13, a pair of detection electrodes 11 and 12, a pair of electrode leads 111 and 121, and a heater part 300. The insulation substrate 13 is made of electrical insulation material. The pair of the detection electrodes 11 and 12 and the pair of the electrode leads 111 and 121 are formed on one surface of the insulation substrate 13. The detection electrodes 11 and 12 make the detection part 100. The heater part 300 is formed or laminated on the other surface of the insulation substrate 13. The heater part 300 generates heat energy in order to heat the detection part 100 when receiving electric power.
  • The detection part 100 is connected to the control circuit 2 through the electrode leads 111 and 121. The detection part 100 detects a resistance value between the detection electrodes 11 and 12 and outputs a detection signal corresponding to the detected resistance value. The heater part 300 is composed of a heater electrode 31 and heater leads 311 and 321. The heater electrode 31 and the heater leads 311 and 321 are formed on the surface of the insulation substrate 32. The heater part 300 is connected to the heater power source 21 through the heater leads 311 and 321. The control circuit 2 instructs the heater power source 21 to supply electric power to the heater part 300.
  • The detection part 100 is produced by the following method. For example, ceramic material having alumina of a superior electric insulation and a superior heat resistance is formed on the insulation substrate 13 of a plate shape by using doctor blade, and press mold method. The detection electrodes 11 and 12 are formed at the front end of the insulation substrate 13 so that the detection electrodes 11 and 12 have a comb structure in which the detection electrodes 11 and 12 alternately face to each other at a predetermined gap. The detection electrodes 11 and 12 are formed by printing conductive paste containing noble metal such as platinum Pt in a predetermined pattern on a surface (or a front surface) of the insulation substrate 13. The detection electrodes 11 and 12 are connected to one end terminal of each of the electrode leads 111 and 121 formed on the surface of the insulation substrate 13.
  • On the other hand, the heater part 300 is produced by printing the heater electrodes 30 and the heater leads 311 and 312 in a predetermined pattern on the surface (the detection part 100 side) of the insulation substrate 32 by using the same method. The heater electrodes 31 of the heater part 300 are formed directly below the detection electrodes 11 and 12 in order to heat the detection part 100 at a predetermined temperature with good efficiency. In other words, the detection electrodes 11 and 12 are formed on the front surface of the entire insulation substrate composed of the insulation substrate 12 and the insulation substrate 32. The insulation substrate 12 and the insulation substrate 32 are stacked. The heater part 300 is formed on the back surface of the entire insulation substrate composed of the insulation substrate 12 and the insulation substrate 32.
  • As shown in FIG. 2, the PM detection sensor 1 has a cylindrical housing case 50 which is screwed into the wall of the exhaust gas pipe EX. The PM detection sensor 1 accommodates the upper half of the PM sensor element 10 which is inserted into and fixed to a cylindrical insulator 60. The bottom half of the PM sensor element 10 is fixed to the base part of the cylindrical housing case 50 and placed in a hollow cover body 40. The hollow cover body 40 with the bottom half of the PM sensor element 10 projects in the inside of the exhaust gas pipe EX. inlet holes 410 and 411 are formed in the base part and the side part of the hollow cover body 40 in order to introduce the exhaust gas in the exhaust gas pipe EX. The exhaust gas flows from the diesel particulate filter DPF and contains particulate matter PM.
  • In order to trap particulate matter PM contained in the exhaust gas, as shown in FIG. 2, it is preferable to place the PM detection sensor 1 in the exhaust gas pipe EX so that the detection part 100 in the PM sensor element 10 faces the upstream side of the exhaust gas pipe EX. Further, it is possible to avoid incorrect detection caused by accumulating particulate matter PM between the electrode leads 111 and 121 when the PM sensor element 10 has a structure in which an insulation protection layer 14 is formed on the surface of the insulation substrate 13 excepting the detection part 100 so that the electrode leads 111 and 121 are covered with the insulation protection layer 14.
  • Next, a description will now be given of the basic operation of the PM detection sensor 1 according to the present invention.
  • As shown in FIG. 2, the exhaust gas of the diesel engine E/G is introduced into the inside of the PM detection sensor 1 through the intake hole 411 which is formed in the cover body 40 of the PM detection sensor 1. The intake hole 411 faces to the upper stream side of the exhaust gas in the exhaust gas pipe EX. After being in contact with the PM sensor element 10, the exhaust gas is discharged into the exhaust gas pipe EX as the outside of the PM detection sensor 1 through the hole 410 formed in the base surface or the hole 411 faced to the downstream side of the exhaust gas.
  • As shown in FIG. 1A, the detection electrodes 11 and 12 having a comb structure at a predetermined gap formed on the surface of the detection part 100. When the PM detection sensor 1 is in its initial condition, no current flows between the detection electrodes 11 and 12 because no particulate matter PM is accumulated between the detection electrodes 11 and 12. When the exhaust gas is introduced into the PM detection sensor 1, particulate matter PM of conductive characteristics is gradually accumulated between the detection electrodes 11 and 12. When the quantity of particulate matter PM accumulated between the detection electrodes 11 and 12 exceeds a predetermined value, a current flows between the detection electrodes 11 and 12. The more the quantity of particulate matter PM is increased, the more the resistance value between the detection electrodes 11 and 12 is decreased. It is therefore possible to detect the resistance value between the detection electrodes 11 and 12 on the basis of this phenomenon. That is, it is possible to execute the diagnosis of detecting defect or failure of the diesel particulate filter DPF on the above relationship.
  • For example, when a defect such as cell-wall defect occurs in the diesel particulate filter DPF, the diesel particulate filter DPF cannot execute a correct operation of trapping particulate matter PM contained in the exhaust gas. This increases the quantity of particulate matter PM contained in the exhaust gas discharged from the diesel particulate filter DPF.
  • The control circuit 2 monitors the quantity of particulate matter PM passing through the diesel particulate filter DPF during a predetermined period of time by using the PM detection sensor 1. When the monitored quantity of particulate matter PM is clearly larger than usual quantity, the control circuit 2 judges an occurrence of failure in the diesel particulate filter DPF. Even if the diesel particulate filter DPF is in the usual condition, when the quantity of particulate matter PM accumulated between the detection electrodes 11 and 12 in the PM sensor element 10 exceeds the predetermined value, the change rate of the resistance value between the detection electrodes 11 and 12 becomes low, that is, the detection accuracy of the PM detection sensor 1 is decreased. In order to avoid this drawback, it is preferable to execute the regeneration of the PM detection sensor 1 at a predetermined period of time.
  • By the way, if the diesel engine E/G is stopped and restarted without executing the regeneration of the PM detection sensor 1, particulate matter PM previously adhered to the detection electrodes 11 and 12 in the PM detection sensor 1 is remained. In this case, the characteristics of particulate matter PM are changed according to the environmental condition when the diesel engine E/G is stopped and restarted. This influences the output of the PM detection sensor 1. For example, when the diesel engine E/G is stopped under the high temperature of the exhaust gas pipe EX, there is a possibility of evaporating soluble organic fraction (SOF) only contained in the particulate matter PM between the detection electrodes. This changes the conductivity of particulate matter PM, the output of the PM detection sensor 1 is also changed when the diesel engine E/G is restarted. Further, when the diesel engine E/G is started in cold environment, there is a possibility of adhering water or dew condensation onto the detection part of the detection electrodes 11 and 12. This changes the conductivity of particulate matter PM, the output of the PM detection sensor 1 is also changed when the diesel engine E/G is restarted. This causes incorrect output of the PM detection sensor 1 because the accumulation of particulate matter PM between the detection electrodes 11 and 12 is changed or the water is evaporated. The above conditions when the diesel engine E/G is started are different every time. Because soluble organic fraction (SOF) is not evaporated, but hardened or burnt according to the change of the temperature and conditions (for example, concentration of oxygen) of the exhaust gas, it is difficult to predict the magnitude of incorrect output of the PM detection sensor 1.
  • In order to solve the above problems causing incorrect output of the PM detection sensor 1, the control circuit 2 adjusts the supply of electric power to the heater part 300 at the engine start and the execution of the usual control. That is, the control circuit 2 firstly executes the process of burning and eliminating particulate matter PM accumulated (or remained) in the PM detection sensor 1 when the diesel engine E/G is started. The control circuit 2 then executes the usual control process which detects the presence and quantity of particulate matter contained in the exhaust gas. Thereby, the control circuit 2 suppresses the fluctuation of the output of the PM detection sensor 1 and avoids causing incorrect detection of the PM detection sensor 1 by burning the accumulated particulate matter PM and eliminating the accumulated particulate matter PM from the PM detection sensor 1 when the diesel engine E/G is started.
  • Specifically, the control circuit 2 instructs the heater power source 21 to supply electric power to the heater part 300 when the diesel engine E/G is started. The detection part 100 of the PM detection sensor 1 is thereby heated at the temperature T1 during the period S1 of time. The temperature T1 allows the detection part 100 to burn and eliminate the accumulated particulate matter PM. That is, the control circuit 2 executes the combustion control at the engine start. In the combustion control executed at the engine start particulate matter PM accumulated on the surface of the detection part 100 is burned and eliminated completely. This combustion control at the engine start corresponds to the function executed by the combustion control means used in the claims.
  • After the combustion control at the engine start, the control circuit 2 adjusts the electric power supply to the detection part 100 in order to maintain the detection part 300 at a temperature T2 which is within a temperature range of less than the temperature T1. This control allows the PM detection sensor 1 to detect particulate matter PM adhered on the detection electrodes 11 and 12 (as the usual control means used in the claims).
  • In the combustion control at the engine start, when the diesel engine start and the electric power supply to the heater part 300 are simultaneously executed, condensed water is scattered in the exhaust gas pipe EX, and the scattered water is adhered to the detection part 100 in the PM detection sensor 1 of a high temperature. When the scattered water is adhered to the PM detection sensor 1 of a high temperature, the PM detection sensor 1 is broken. In order to avoid this, it is necessary to delay the time to start the electric power supply to the PM sensor element 10 until the condensed water in the exhaust gas pipe EX is dried or no condensed water is adhered to the PM sensor element 10.
  • In order to ensure the above problem, it is necessary for the control circuit 2 to calculates an amount (or degree of risk) of condensed water remained in the exhaust gas pipe adhering to the detection part 100 in the particulate matter detection sensor 1 on the basis of the operation condition of the diesel engine E/G, and to delay the execution of the electric power supply to the heater part 300 on the basis of the calculated amount (or degree of risk) of condensed water. That is, it is preferable for the control circuit 2 to delay the execution of the electric power supply to the heater part 300 until the amount (or degree of risk) of condensed water adhering to the detection part 100 in the PM detection sensor 1 is entered into its allowable range. It is also possible to use the relationship between the timing when the electric power supply to the detection part 100 and a coefficient corresponding to the calculated amount (or degree of risk) of condensed water adhering to the detection part 100 which is calculated on the basis of the operation condition of the diesel engine E/G. In the latter case, the control circuit 2 starts the electric power supply to the detection part 100 in the PM sensor element 10 at the timing which is determined on the basis of the coefficient corresponding to the amount (or degree of risk) of condensed water adhering to the detection part 100. This control makes it possible to detect the quantity of particulate matter PM adhered to the PM detection sensor 1 with high accuracy while suppressing the detection part 100 from being broken by adhering condensed water to the detection part 100.
  • A description will be given of the control operation of the control circuit 2 with reference to FIG. 3 and FIG. 4.
  • FIG. 3 is a flow chart showing the process for the control circuit 2 to supply electric power to the heater part 100 in the PM detection sensor 1 according to the embodiment of the present invention.
  • As shown in FIG. 3, when the diesel engine E/G is started, the control circuit 2 receives detection signals transferred from various sensors (step S100). At this time, in order to detect the operation condition of the diesel engine E/G and the temperature condition in the exhaust gas pipe EX, the control circuit 2 receives detection signals transferred from a water temperature sensor (not shown) and an oil temperature sensor (not shown). The water temperature sensor detects the temperature of engine cooling water. The oil temperature sensor detects the temperature of lubricating oil.
  • The control circuit 2 further receives a detection signal transferred from an intake air temperature sensor. The intake air temperature sensor is embedded in an air flow meter AFM capable of detecting the temperature of ambient air. Still further, the control circuit 2 receives a detection signal transferred from a temperature sensor S3 which is placed at the downstream side of the diesel particulate filter DPF in order to detect the temperature of the exhaust gas around the PM detection sensor 1. Still further, the control circuit 2 receives the detection signal transferred from the rotation sensor capable of detecting the rotation of the diesel engine E/G, the detection signal transferred from a sensor capable of detecting the quantity of fuel injection, and the detection signal transferred from a sensor capable of detecting the operation time length of the diesel engine E/G.
  • In step S101, the control circuit 2 calculates an amount (or degree of risk) of condensed water adhering to the detection part 100 in the PM sensor element 10 in the PM detection sensor 1 on the basis of the information obtained from the received detection signals transferred from the various sensors. Specifically, the control circuit 2 predicts the quantity of condensed water which is generated and stayed in the inside of the exhaust gas pipe EX at the upstream of the PM detection sensor 1 on the basis of the elapsed period of time, the operation condition and temperature condition of the diesel engine E/G after the engine start, where, the elapsed period of time is the time length counted form the time when the diesel engine E/G is previously started to the current time.
  • The control circuit 2 then calculates the amount (or degree of risk) of condensed water adhering to the detection part 100 in the PM detection sensor 1 by using the relationship obtained in advance on the basis of the shape of the exhaust gas pipe EX. For example, the ambient temperature is low, water is condensed in the exhaust gas pipe EX when the temperature of the exhaust gas pipe EX is decreased after the engine stop or when exhaust gas is introduced into the inside of the exhaust gas pipe EX at a low temperature immediately after the engine start. Further, when the temperature of the exhaust gas pipe EX is relatively high in a short elapsed period of time after the engine stop, the quantity of condensed water is low, and the condensed water can be evaporated within a short period of time. Still further, even if having the same quantity of condensed water, it is possible to easily generate condensed water in the exhaust gas pipe EX when the exhaust gas pipe EX has a curved shape. It is often difficult to scatter the condensed water in the exhaust gas pipe EX having such a curved shape. Accordingly, it is necessary to make an additional map in advance on the basis of experimental results obtained by considering the above conditions. It is also possible to calculate the amount (or degree of risk) of condensed water adhering to the detection part 100 in the PM detection sensor 1 by using the equation which considers the above conditions.
  • In step S102, the control circuit 2 detects whether or not the calculated amount (or degree of risk) of condensed water, which indicates a probability that condensed water is sc adhered to the PM detection sensor 1, is less than a predetermined value. The predetermined value is the minimum value of causing the PM sensor element 10 in the PM detection sensor 1 breaking when the electric power is supplied to the PM detection sensor 1. When the detection result in step S102 indicates affirmative (“YES” in step S102), there is no possibility of breaking the PM detection sensor 1. The operation flow goes to step S103. In step S103, the control circuit 2 executes the combustion control in order to start the operation of the diesel engine E/G.
  • On the other hand, when the detection result in step S102 indicates negative (“NO” in step S102), there is a possibility of breaking the PM detection sensor 1. The operation flow is returned to step S100. The control circuit 2 continues the routine of steps S100, S101 and S102 until there is no more possibility of breaking the PM sensor 1 in order to delay the start of supplying electric power to the heater part 300.
  • In step S103, the control circuit 2 executes the combustion control at the engine start. Specifically, the control circuit 2 instructs the heater power source 21 to supply electric power to the heater part 300 in the PM detection sensor 1 in order to burn and eliminate particulate matter PM accumulated in the detection part 100.
  • A description will now be given of the combustion control which is executed when the diesel engine E/G is started or restarted with reference to FIG. 4.
  • FIG. 4 is a flow chart showing a detailed process of the combustion control at the engine start.
  • In step S200, the control circuit 2 receives various data items in order to obtain the information regarding the quantity of particulate matter PM accumulated in the detection part 100 in the PM sensor element 10 in the PM detection sensor 1. The information is:
  • (a1) Period of time counted from the time when the PM combustion was executed in the previous usual control to the time when the diesel engine E/G was stopped;
  • (a2) Period of time counted from the time when diesel engine E/G was last stopped to the current time; and
  • (a3) Period of time counted from the time at the current engine start to the time when the combustion control at the engine start is started.
  • The control circuit 2 receives the operation state of the diesel engine E/G and the temperature and time conditions of the operation of the diesel engine E/G, for example, receives the following data items in order to detect the quantity of particulate matter PM adhered to and accumulated in the detection part 100 in the PM sensor element 10 of the PM detection sensor 1 and the change of the quantity of particulate matter PM in each of the periods (a1), (a2) and (a3):
  • (b1) Temperature of cooling water of the diesel engine E/G;
  • (b2) Temperature of lubricating oil;
  • (b3) Temperature of ambient atmosphere;
  • (b4) Temperature of exhaust gas;
  • (b5) Rotation number or speed of the diesel engine E/G; and
  • (b6) Quantity Q of injection fuel.
  • In step S201, the control circuit 2 detects and calculates following values:
  • (c1) Quantity of particulate matter PM accumulated in the detection part 100 in the PM sensor element 10 of the PM detection sensor 1 at the previous engine stop;
  • (c2) Quantity of water and hydro carbon (HC) which are adhered to the PM detection sensor 1 or evaporated in the exhaust gas pipe EX during the engine stop; and
  • (c3) Quantity of particulate matter PM to be adhered and accumulated in the detection part 100 in the PM sensor element 10 of the PM detection sensor 1 during the period of time counted from the current engine start to the time when the combustion control at the engine start is started.
  • Because the change of each of the quantity of accumulated particulate matter PM during the operation of the diesel engine E/G, the quantity of water and hydro carbon (HC) during the engine stop is fluctuated by the operation state of the diesel engine E/G and the environment of the inside of the exhaust gas pipe EX. Accordingly, the control circuit 2 calculates these changes by using the experimental map which is obtained in advance or a theoretical arithmetic equation.
  • The operation flow goes to step S202. In step S202, the control circuit 2 calculates the combustion condition (Temperature and Period of time) of burning particulate matter PM accumulated in the detection part 100 in the PM sensor element 10 of the PM detection sensor 1 on the basis of the adhesion condition (quantity and composition of particulate matter PM) of particulate matter PM calculated in step S201.
  • In general, it is preferable to burn accumulated particulate matter PM at the temperature T1 during the combustion control at the engine start. This temperature T1 is not less than the allowable temperature at which particulate matter PM can be completely burned. In the view of heat resistance of the heater part 300 in the PM sensor element 10, it is preferable for the temperature T1 to be not more than 900° C.
  • Because the period S1 of time depends on the temperature T1, the more the temperature T1 is increased, the more the period S1 of time is decreased. It is preferable for the period S1 of time to be not more than 5 minutes.
  • FIG. 5 is a view showing an experimental result of a relationship between the temperature of the PM sensor element 10 and the period of time to maintain the temperature of the PM sensor element 10 in the PM detection sensor 1 according to the embodiment of the present invention.
  • The experimental condition with which the experimental result shown in FIG. 5 is obtained is as follows.
  • As shown in FIG. 1B and previously described, the PM detection sensor 1 is mounted to the exhaust gas pipe EX. The control circuit 2 instructed the heater power source 21 to supply electric power to the heater part 300 in the Pm sensor element 10 of the PM detection sensor 1 after the engine start in order to maintain the PM sensor 1 at the predetermined temperature T1 for the predetermined period S1 of time. The quantity of particulate matter PM accumulated in the PM sensor element 10 of the PM detection sensor 1 was detected. During this detection, the PM sensor element 10 was maintained at the temperature within a range of 550° C. to 750° C., and the period S1 of time was changed.
  • As shown in FIG. 5, it is possible to eliminate the particulate matter PM from the detection part 100 of the PM sensor element 10 of the PM detection sensor 1 when the predetermined temperature T1 was 600° C. and the period S2 of time was not less than 20 minutes, and when the predetermined temperature T1 was 700° C. and the period S2 of time was not less than 10 minutes.
  • However, it is difficult to completely eliminate the accumulated particulate matter PM from the detection part 100 of the PM sensor element 10 when the predetermined temperature T1 was not more than 550° C. and the period S2 of time was 80 minutes. The above experimental results shown in FIG. 5 indicates that it is necessary to maintain the PM detection sensor 1 at the temperature T1 of not less than 600° C., preferably, at the temperature T1 of not less than 650° C. for the period S1 of time of not less than 20 seconds.
  • In step S203, the control circuit 2 executes the combustion control at the engine start in order to burn the accumulated particulate matter PM and eliminate them from the PM sensor element 10. That is, in step S203, the control circuit 2 instructs the heater power source 21 to supply electric power to the heater part 300 of the PM sensor element 10 in the PM detection sensor 1 under the conditions (temperature T1 and period S1 of time) which are determined in step S202. This control makes it possible to heat the detection part 10 at the temperature T1 for the period S2 of time. The operation flow goes to step S2104. In step S204, the control circuit 2 completes the combustion control at the engine start.
  • Return to the flow chart shown in FIG. 3, the operation flow progresses to step S104. In step S104, the control circuit 2 executes the usual control. In the usual control in step S104, the electric power is supplied to the heater part 300 of the PM sensor element 10 of the PM sensor 1 in order to maintain the detection part 100 at the temperature T2 which is lower than the temperature T1. The execution of the usual control makes it possible to detect the quantity of particulate matter PM accumulated in the detection part 100 of the PM sensor element 10. As previously described, the temperature T1 is used during the combustion control executed when the engine is started (or restarted). Specifically, during the usual control after completion of the combustion control executed during the engine start, the control circuit 2 maintains the detection part 100 in the PM sensor element 10 at the temperature T2 within a range of 50° C. to 600° C. This control makes it possible for the PM detection sensor 1 to output a stable detection signal.
  • FIG. 6A is a timing chart showing the output change of the PM detection sensor 1 when the usual control is continuously executed. FIG. 6A shows the characteristics of the output of the PM detection sensor. The output of the PM detection sensor is increased when the pair of the detection electrodes in the detection part is conducted after a period of time counted from the PM sensor detection is executed, and the output of the PM detection sensor is rapidly increased according to the elapsed of time and saturated.
  • This means that the resistance value between the detection electrodes is decreased according to increasing the quantity of particulate matter PM accumulated in the detection part of the PM sensor element. When the quantity of particulate matter PM accumulated in the detection part exceeds a predetermined value, the resistance value between them is not changed. Accordingly, it is necessary to execute the sensor regeneration control periodically in order to eliminate the particulate matter PM from the detection part of the PM sensor element of the PM detection sensor. The sensor regeneration control in this case can be executed in parallel to the execution of the combustion control at the engine start. That is, it is sufficient to maintain the PM sensor at the predetermined temperature for the predetermined period of time which allows the accumulated particulate matter from being burned. For example, it is preferable to maintain the PM sensor at a temperature within a range of 600° C. to 900° C. for not less than 20 seconds, in more preferable, at a temperature within a range of 650° C. for not less than 20 seconds, or maintain it at the temperature of 700° C. for 10 seconds. After this, the same steps are continuously executed, as previously described.
  • FIG. 6B is a timing chart showing the output change of the PM detection sensor when the diesel engine is restarted (without executing the combustion control at the engine start according to the embodiment of the present invention) after the engine stop without executing the PM detection sensor regeneration control after the detection process is executed by the PM detection sensor during the usual control.
  • The left side in FIG. 6B shows the case when the diesel engine E/G is stopped after the detection electrodes and in the pair in the detection part of the PM sensor element are electrically conducted and the PM detection sensor starts to output the detection signal. In this case, the combustion control at the engine start is not executed when the diesel engine E/G is started (or restarted). At this time, the sensitivity of the PM detection sensor is changed when compared with the normal output curve (designated by dotted line in FIG. 6B), and this has a high possibility of executing incorrect detection of detecting the quantity of particulate matter PM accumulated in the detection part because the characteristics of accumulated particulate matter PM is changed and water is adhered to the detection part when the diesel engine E/G is stopped (at engine stop soaking).
  • The right side in FIG. 6B shows the case in which the diesel engine E/G is stopped during no output of the PM detection sensor after the detection electrodes in the pair in the detection part of the PM sensor element are electrically conducted and the PM detection sensor starts to output the detection signal. In this case shown in the right side in FIG. 6B, there is a high possibility of executing incorrect detection of the quantity of particulate matter PM accumulated in the detection part because particulate matter PM is accumulated between the detection electrodes after the PM detection sensor regeneration control is still remained in the detection part of the PM sensor element. It is difficult to detect the quantity of particulate matter accumulated in the detection part of the PM sensor element of the PM detection sensor with high accuracy.
  • FIG. 6C is a timing chart showing the output change of the PM detection sensor 1 when the control circuit 2 executes the combustion control at the engine start. That is, the combustion control is executed when the diesel engine E/G is started (or restarted). In the case shown in FIG. 6C, the control circuit 2 does not execute the control of regenerating the PM detection sensor 1 before the diesel engine E/G is stopped.
  • FIG. 6C shows the case in which the control circuit 2 executes the combustion control when the diesel engine E/G is started without executing the regeneration control of regenerating the PM detection sensor before the engine stop. As shown in FIG. 6C, it is possible for the present invention to execute the correct detection of detecting the quantity of particulate matter PM accumulated in the detection part 100 between the detection electrodes 11 and 12 with high accuracy without causing the fluctuation of the detection sensitivity of the PM detection sensor and the change of the period of time in which the PM detection sensor outputs no detection signal.
  • INDUSTRIAL APPLICABILITY
  • It is possible to place the PM detection sensor 1 according to the present invention at the downstream side of the diesel particulate filter DPF and detect the failure of the diesel particulate filter DPF under the control of the control circuit 2 according to the present invention. It is also possible to place the PM detection sensor 1 according to the present invention at the upstream side of the diesel particulate filter DPF and directly detect particulate matter PM which is introduced into the diesel particulate filter DPF under the control of the control circuit 2 according to the present invention.
  • While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limited to the scope of the present invention which is to be given the full breadth of the following claims and all equivalents thereof.

Claims (7)

  1. 1. A control device of controlling a particulate matter detection sensor placed in an exhaust gas pipe of an internal combustion engine through which exhaust gas emitted from the internal combustion engine flows and discharged to the outside, the particulate matter detection sensor having a particulate matter sensor element comprised of an insulation substrate, a detection part composed of a pair of detection electrodes formed on a surface of the insulation substrate, and a heater part of generating heat energy when receiving electric power in order to heat the detection part at a predetermined temperature,
    the control device comprising a control part which detects an electrical resistance value between the pair of the detection electrodes in the detection part, the electrical resistance value between the pair of the detection electrodes in the detection part changing in accordance with a change of quantity of particulate matter accumulated in the detection part, and the control part adjusting electric power supply to the heater part,
    the control part comprising:
    combustion control means which executes combustion control when the internal combustion engine is started to operate, and in the combustion control, the combustion control means supplies electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at a predetermined temperature T1 for a predetermined period S1 of time in order to burn the accumulated particulate matter in order to eliminate the accumulated particulate matter from the detection part of the particulate matter detection sensor; and
    usual control means which executes usual control after completion of the combustion control which is executed when the internal combustion engine is started to operate, wherein in the usual control, the usual control means supplies electric power to the heater part in order to maintain the detection part of the particulate matter sensor element at a temperature T2 which is less than the predetermined temperature T1 in order to detect particulate matter accumulated in the detection part.
  2. 2. The control device according to claim 1, wherein the control part further comprises electric power supply timing means which determines a time to supply electric power to the heater part, counted from a time when the internal combustion engine is started to a time when the electric power is supplied to the heater part on the basis of the operation state of the internal combustion engine.
  3. 3. The control device according to claim 2, wherein the electric power supply timing means calculates an amount of condensed water remained in the exhaust gas pipe adhering to the detection part in the particulate matter detection sensor, and delays the timing to supply the electric power to the heater part on the basis of the calculated amount of condensed water.
  4. 4. The control device according to claim 1, wherein the combustion control means supplies the electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at the predetermined temperature T1 within a range of not less than 600° C. to not more than 900° C.
  5. 5. The control device according to claim 4, wherein the combustion control means supplies the electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at the predetermined temperature T1 of not less than 650° C. for the predetermined period S1 of time of not less than 20 seconds.
  6. 6. The control device according to claim 1, wherein the usual control means supplies the electric power to the heater part in order to maintain the detection part of the particulate matter detection sensor at a predetermined temperature within a range of not less than 50° C. to not more than 600° C.
  7. 7. The control device according to claim 1, wherein
    the detection part is comprised of the pair of the detection electrodes having a comb shape and detection lead parts formed on a front surface of the insulation substrate, and
    the heater part is comprised of heater electrodes and heater lead parts formed at the front end in a back surface of the insulation substrate.
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