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United States Patent Application 20180087427
Kind Code A1
KORENAGA; Shingo March 29, 2018

EXHAUST GAS PURIFICATION APPARATUS OF INTERNAL COMBUSTION ENGINE

Abstract

An exhaust gas purification apparatus of an internal combustion engine of the invention includes an electrical heating catalyzer. The catalyzer includes a catalyst carrier which produces heat when the catalyst carrier is energized, a pair of electrodes provided on the catalyst carrier, a casing which houses the catalyst carrier and at least one insulation member provided between the catalyst carrier and the casing. The apparatus executes a PM removal control for increasing a temperature of the electrical heating catalyzer by using energy discharged from the engine to an exhaust passage to remove particulate matter from the catalyzer in response to temperature of the particulate matter and an insulation resistance value between the catalyst carrier and the casing satisfying a predetermined removal condition.


Inventors: KORENAGA; Shingo; (Shizuoka-shi, JP)
Applicant:
Name City State Country Type

TOYOTA JIDOSHA KABUSHIKI KAISHA

Toyota-shi

JP
Assignee: TOYOTA JIDOSHA KABUSHIKI KAISHA
Toyota-shi
JP

Family ID: 1000002848562
Appl. No.: 15/689392
Filed: August 29, 2017


Current U.S. Class: 1/1
Current CPC Class: F01N 3/2013 20130101; F01N 9/002 20130101; F01N 2900/16 20130101; F01N 13/14 20130101; F01N 2550/04 20130101; F01N 3/035 20130101
International Class: F01N 3/20 20060101 F01N003/20; F01N 9/00 20060101 F01N009/00; F01N 3/035 20060101 F01N003/035; F01N 13/14 20060101 F01N013/14

Foreign Application Data

DateCodeApplication Number
Sep 28, 2016JP2016-189726

Claims



1. An exhaust gas purification apparatus of an internal combustion engine, the exhaust gas purification apparatus comprising: an electrical heating catalyzer provided in an exhaust passage of the internal combustion engine, the electrical heating catalyzer including: a catalyst carrier which carries catalyst, the catalyst carrier producing heat when the catalyst carrier is energized; a pair of electrodes provided on the catalyst carrier, the electrodes being provided to energize the catalyst carrier; a casing which houses the catalyst carrier provided with the electrodes; and at least one insulation member provided between the catalyst carrier and the casing; and an electronic control unit configured to apply potential difference to the electrodes to energize the catalyst carrier when energization of the catalyst carrier is requested, wherein the electronic control unit is configured: to acquire an insulation resistance value corresponding to an electric resistance value between the catalyst carrier and the casing as a acquired resistance value; to estimate a temperature of accumulating particulate matter which is particulate matter accumulating in the electrical heating catalyzer as an estimated PM temperature; and to execute a PM removal control for increasing a temperature of the electrical heating catalyzer by using energy discharged from the internal combustion engine to the exhaust passage to remove the accumulating particulate matter in response to the estimated PM temperature and the acquired resistance value satisfying a predetermined removal condition which is satisfied when the accumulating particulate matter should be removed in the state that the catalyst carrier is not energized.

2. The exhaust gas purification apparatus of the internal combustion engine according to claim 1, wherein the electronic control unit is configured to execute the PM removal control in response to the electronic control unit estimating that no water adheres to the electrical heating catalyzer and the estimated PM temperature and the acquired resistance value satisfying the predetermined removal condition.

3. The exhaust gas purification apparatus of the internal combustion engine according to claim 1, wherein the electronic control unit is configured: to acquire the estimated PM temperature acquired at a time of acquiring the acquired resistance value as a particular PM temperature; to convert the acquired resistance value on the basis of the particular PM temperature to acquire a converted resistance value corresponding to the acquired resistance value to be acquired when the particular PM temperature corresponds to a predetermined base temperature; to determine that the predetermined removal condition is satisfied and execute the PM removal control when the converted resistance value is smaller than a predetermined first resistance threshold which is a threshold of the insulation resistance value used for determining whether the accumulating particulate matter should be removed when the particular PM temperature corresponds to the predetermined base temperature; to acquire the converted resistance value which increases as the particular PM temperature increases when the particular PM temperature is higher than or equal to the predetermined base temperature; and to acquire the converted resistance value which decreases as the particular PM temperature decreases when the particular PM temperature is lower than the predetermined base temperature.

4. The exhaust gas purification apparatus of the internal combustion engine according to claim 1, wherein the electronic control unit is configured: to acquire the estimated PM temperature acquired at a time of acquiring the acquired resistance value as a particular PM temperature; to convert a base resistance threshold on the basis of the particular PM temperature to acquire a second resistance threshold which corresponds to a threshold of the insulation resistance value used for determining whether the accumulating particulate matter should be removed on the basis of the acquired resistance value, the base resistance threshold being a threshold of the insulation resistance value used for determining whether the accumulating particulate matter should be removed when the particular PM temperature corresponds to a predetermined base temperature; to determine that the predetermined removal condition is satisfied and execute the PM removal control when the acquired resistance value is smaller than the second resistance threshold; and to acquire the second resistance threshold such that the second resistance threshold acquired when the particular PM temperature is relatively high, is smaller than the second resistance threshold acquired when the particular PM temperature is relatively low.

5. The exhaust gas purification apparatus of the internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus further comprises a voltage measuring device for measuring a voltage between the catalyst carrier and the casing and the electronic control unit is further configured to acquire the acquired resistance value on the basis of the voltage.
Description



BACKGROUND

Field

[0001] The invention relates to an exhaust gas purification apparatus of an internal combustion engine including an electrical heating catalyzer.

Description of the Related Art

[0002] A known electrical heating catalyzer includes a catalyst carrier which carries a catalyst, a pair of electrodes provided on the catalyst carrier, and a casing which houses the catalyst carrier provided with the electrodes. The electrodes are provided to energize the catalyst carrier. When the catalyst carrier is energized, the catalyst carrier produces heat. At least one insulation member is provided between the catalyst carrier and the casing. When a temperature of the catalyst of the electrical heating catalyzer is low, the electrical heating catalyzer energizes the catalyst carrier to increase the temperature of the catalyst, thereby activating the catalyst promptly. Hereinafter, the electrical heating catalyzer will be referred simply to as "the catalyzer".

[0003] When the catalyst carrier is energized while an electric resistance value between the catalyst carrier and the casing is small, an excessive electric current may flow from the catalyst carrier and/or the electrodes to the casing. In other words, an electric leak may occur in the catalyzer. Accordingly, when the electric resistance value between the catalyst carrier and the casing is small, the catalyst carrier should not be energized.

[0004] Even when the catalyzer is normal, if condensed water exists between the catalyst carrier and the casing and/or particulate matter such as carbon included in exhaust gas adheres to and/or accumulates on and/or in the insulation member, the electric resistance value between the catalyst carrier and the casing decreases. Electric resistivity of the condensed water and electric resistivity of the particulate matter are generally smaller than electric resistivity of the insulation member, respectively.

[0005] Additionally, as an amount of the condensed water existing between the catalyst carrier and the casing increases, the electric resistance value between the catalyst carrier and the casing decreases. Similarly, as an amount of the particulate matter accumulating on and/or in the insulation member increases, the electric resistance value between the catalyst carrier and the casing decreases.

[0006] In this regard, there is known a technique for removing the condensed water and the particulate matter by increasing a temperature of the catalyzer without energizing the catalyst carrier when the electric resistance value between the catalyst carrier and the casing is smaller than a threshold (for example, see JP 2012-72665 A).

[0007] Further, there is known a process for removing the particulate matter by switching air-fuel ratio of mixture gas supplied to the internal combustion engine between rich air-fuel ratio and lean air-fuel ratio at an interval to increase the temperature of the catalyst and then, performing a fuel-cut process for stopping a supply of fuel from fuel injectors to combustion chambers, thereby supplying oxygen to the catalyst (for example, see JP 2013-181517 A).

[0008] Furthermore, there is known a process for removing the particulate matter existing on the catalyst by changing a timing for injecting the fuel from the fuel injectors and/or a timing for igniting the fuel to increase a temperature of the exhaust gas, thereby burning the particulate matter.

[0009] Hereinafter, the aforementioned processes for removing the particulate matter will be collectively referred to as "the PM removal process".

[0010] When the PM removal process is performed, thermal efficiency of the internal combustion engine decreases and as a result, a fuel consumption rate of the engine increases.

SUMMARY

[0011] The electric resistivity of the particulate matter decreases as a temperature of the particulate matter (hereinafter, the temperature of the particulate matter will be referred to as "the PM temperature") increases. Therefore, when the PM temperature is high, the electric resistance value between the catalyst carrier and the casing may be smaller than the threshold despite the smaller amount of the particulate matter accumulating on and/or in the insulation member than an amount where the PM removal process should be performed. In this case, the PM removal process is performed and as a result, the fuel consumption rate increases.

[0012] The invention has been made by solving problems described above. An object of the invention is to provide an exhaust gas purification apparatus of an internal combustion engine which performs a process for removing the particulate matter from the catalyzer in consideration of a change of the electric resistivity of the particulate matter, depending on the PM temperature, thereby avoiding unnecessary consumption of the fuel.

[0013] The exhaust gas purification device of the internal combustion engine (11) according to the invention comprises an electrical heating catalyzer (13) and an electronic control unit (20). The electrical heating catalyzer is provided in an exhaust passage (12) of the internal combustion engine.

[0014] The electrical heating catalyzer includes a catalyst carrier (31), a pair of electrodes (33), a casing (32) and at least one insulation member (34). The catalyst carrier carries catalyst and produces heat when the catalyst carrier is energized. The electrodes are provided on the catalyst carrier to energize the catalyst carrier. The casing houses the catalyst carrier provided with the electrodes. The insulation member is provided between the catalyst carrier and the casing.

[0015] The electronic control unit is configured to apply potential difference to the electrodes to energize the catalyst carrier (see a process of a step S106 of FIG. 4) when energization of the catalyst carrier is requested (see a determination "Yes" at a step S105 of FIG. 4).

[0016] The electronic control unit is further configured to acquire an insulation resistance value corresponding to an electric resistance value between the catalyst carrier and the casing as a acquired resistance value (see processes of a step S406 of FIG. 7 and a step S506 of FIG. 9) and to estimate a temperature of accumulating particulate matter which is particulate matter accumulating in the electrical heating catalyzer as an estimated PM temperature (see processes of a step S402 of FIG. 7 and a step S502 of FIG. 9).

[0017] The electronic control unit is further configured to execute a PM removal control for increasing a temperature of the electrical heating catalyzer by using energy discharged from the internal combustion engine to the exhaust passage to remove the accumulating particulate matter (see processes of a step S409 of FIG. 7 and a step S509 of FIG. 9) in response to the estimated PM temperature and the acquired resistance value satisfying a predetermined removal condition which is satisfied when the accumulating particulate matter should be removed in the state that the catalyst carrier is not energized (see determinations "Yes" at a step S408 of FIG. 7 and a step S508 of FIG. 9).

[0018] As the temperature of the accumulating particulate matter increases, the electric resistivity of the accumulating particulate matter decreases and as a result, the insulation resistance value decreases. Thus, the temperature of the accumulating particulate matter is high, it cannot be determined which causes the insulation resistance value to decrease, a decreasing of the electric resistivity of the accumulating particulate matter due to the temperature of the accumulating particulate matter or an increasing of the amount of the accumulating particulate matter.

[0019] According to the invention, the electronic control unit executes the PM removal control only when the estimated PM temperature and the acquired resistance value satisfy the predetermined removal condition. Thereby, it is determined whether the accumulating particulate matter should be removed in consideration of the change of the electric resistivity of the accumulating particulate matter due to the change of the temperature of the accumulating particulate matter. Thus, the accumulating particulate matter can be removed at an appropriate timing to restore the insulation resistance value without consuming the fuel unnecessarily.

[0020] According to one aspect of the invention, the electronic control unit (20) may be configured to execute the PM removal control (see the processes of the step S409 of FIG. 7 and the step S509 of FIG. 9) in response to the electronic control unit estimating that no water adheres to the electrical heating catalyzer (see determinations "Yes" at a step S404 of FIG. 7 and a step S504 of FIG. 9) and the estimated PM temperature and the acquired resistance value satisfying the predetermined removal condition (see the determinations "Yes" at the step S408 of FIG. 7 and the step S508 of FIG. 9).

[0021] When the water adheres to the electrical heating catalyzer, the water causes the insulation resistance value to decrease. Thus, even when the predetermined removal condition is satisfied while the water adheres to the electrical heating catalyzer, the amount of the accumulating particulate matter may be smaller than an amount where the accumulating particulate matter should be removed.

[0022] According to the aspect of the invention, the electronic control unit executes the PM removal control when the electronic control unit estimates that no water adheres to the electrical heating catalyzer and the estimated PM temperature and the acquired resistance value satisfy the predetermined removal condition. Thereby, it is sufficient to consider the decreasing of the insulation resistance value due to the accumulating particulate matter without considering the decreasing of the insulation resistance value due to the water for the determination of whether the PM removal control should be executed. Thus, the electronic control unit can exactly determine whether the amount of the accumulating particulate matter is excessive on the basis of the estimated PM temperature and the acquired resistance value. As a result, the accumulating particulate matter can be removed at the appropriate timing to restore the insulation resistance value without consuming the fuel unnecessarily.

[0023] According to another aspect of the invention, the electronic control unit (20) may be configured to acquire the estimated PM temperature acquired at a time of acquiring the acquired resistance value as a particular PM temperature (see the process of the step S402 of FIG. 7). In this case, the electronic control unit may be configured to convert the acquired resistance value on the basis of the particular PM temperature to acquire a converted resistance value corresponding to the acquired resistance value to be acquired when the particular PM temperature corresponds to a predetermined base temperature (see a process of a step S407 of FIG. 7). In this case, the electronic control unit may be configured to determine that the predetermined removal condition is satisfied and execute the PM removal control (see the process of the step S409 of FIG. 4) when the converted resistance value is smaller than a predetermined first resistance threshold which is a threshold of the insulation resistance value used for determining whether the accumulating particulate matter should be removed when the particular PM temperature corresponds to the predetermined base temperature (see the determination "Yes" at the step S408 of FIG. 7). In this case, the electronic control unit may be configured to acquire the converted resistance value which increases as the particular PM temperature increases when the particular PM temperature is higher than or equal to the predetermined base temperature (see the process of the step S407 of FIG. 7). Further, the electronic control unit may be configured to acquire the converted resistance value which decreases as the particular PM temperature decreases when the particular PM temperature is lower than the predetermined base temperature (see the process of the step S407 of FIG. 7).

[0024] As the temperature of the accumulating particulate matter increases, the insulation resistance value decreases. According to the further aspect of the invention, when the particular PM temperature is higher than or equal to the predetermined base temperature, the electronic control unit acquires the converted resistance value which increases as the particular PM temperature increases. Further, when the particular PM temperature is lower than the predetermined base temperature, the electronic control unit acquires the converted resistance value which decreases as the particular PM temperature decreases, When the thus-acquired converted resistance value is smaller than the base resistance threshold, the amount of the accumulating particulate matter must be larger than a predetermined amount, independently of the particular PM temperature. In this case, the electronic control unit determines that the predetermined removal condition is satisfied and executes the PM removal control. Therefore, the accumulating particulate matter can be removed to restore the insulation resistance value without consuming the fuel unnecessarily when the particular matter should be removed,

[0025] According to further another aspect of the invention, the electronic control unit (20) may be configured to acquire the estimated PM temperature acquired at a time of acquiring the acquired resistance value as a particular PM temperature (see the process of the step S502 of FIG. 9). In this case, the electronic control unit may be configured to convert a base resistance threshold on the basis of the particular PM temperature to acquire a second resistance threshold which corresponds to a threshold of the insulation resistance value used for determining whether the accumulating particulate matter should be removed on the basis of the acquired resistance value (see a process of a step S507 of FIG. 9). The base resistance threshold may be a threshold of the insulation resistance value used for determining whether the accumulating particulate matter should be removed when the particular PM temperature corresponds to a predetermined base temperature. In this case, the electronic control unit may be configured to determine that the predetermined removal condition is satisfied and execute the PM removal control (see the process of the step S509 of FIG. 9) when the acquired resistance value is smaller than the second resistance threshold (see the determination "Yes" at the step S508 of FIG. 9). In this case, the electronic control unit may be configured to acquire the second resistance threshold such that the second resistance threshold acquired when the particular PM temperature is relatively high, is smaller than the second resistance threshold acquired when the particular PM temperature is relatively low (see the process of the step S507 of FIG. 9).

[0026] The insulation resistance value decreases as the temperature of the accumulating particulate matter increases. According to the further aspect of the invention, the electronic control unit changes the threshold of the insulation resistance value (the second resistance threshold) used for determining whether the PM removal control should be executed, depending on the particular PM temperature. When the acquired resistance value is smaller than the second resistance threshold, the amount of the accumulating particulate matter must be larger than a predetermined amount, independently of the particular PM temperature. In this case, the electronic control unit determines that the predetermined removal condition is satisfied and executes the PM removal control. Therefore, the accumulating particulate matter can be removed to restore the insulation resistance value without consuming the fuel unnecessarily when the accumulating particulate matter should be removed.

[0027] According to further another aspect of the invention, the exhaust gas purification apparatus may further comprise a voltage measuring device (25) for measuring a voltage between the catalyst carrier and the casing. In this case, the electronic control unit (20) may be further configured to acquire the acquired resistance value on the basis of the voltage.

[0028] In the above description, for facilitating understanding of the present invention, elements of the present invention corresponding to elements of an embodiment described later are denoted by reference symbols used in the description of the embodiment accompanied with parentheses. However, the elements of the present invention are not limited to the elements of the embodiment defined by the reference symbols. The other objects, features and accompanied advantages of the present invention can be easily understood from the description of the embodiment of the present invention along with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a general view for showing an exhaust gas purification apparatus of an internal combustion engine according to a first embodiment of the invention and the internal combustion engine including an exhaust system, to which the exhaust gas purification apparatus is applied.

[0030] FIG. 2 is a general view for showing an electrical heating catalyzer shown in FIG.

[0031] FIG. 3 is a graph for showing a relationship between a temperature of the electrical heating catalyzer and an insulation resistance value between a catalyst carrier and a casing.

[0032] FIG. 4 is a view for showing a flowchart of a routine executed by an ECU (i.e., an electronic control unit) shown in FIG. 1.

[0033] FIG. 5 is a view for showing a flowchart of a routine executed by the ECU.

[0034] FIG. 6 is a view for showing a flowchart of a routine executed by the ECU.

[0035] FIG. 7 is a view for showing a flowchart of a routine executed by the ECU.

[0036] FIG. 8 is a view for showing a time chart of an operation of the ECU.

[0037] FIG. 9 is a view for showing a flowchart of a routine executed by an ECU according to a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

[0038] (Configuration)

[0039] As shown in FIG. 1, an exhaust gas purification apparatus 10 of an internal combustion engine according to a first embodiment of the invention is applied to an internal combustion engine 11. Hereinafter, the exhaust gas purification apparatus 10 will be referred to as "the first apparatus 10".

[0040] The engine 11 is installed on a vehicle (not shown) as a driving source. The engine 11 is a multi-cylinder (in this embodiment, in-line four-cylinder) four-cycle piston-reciprocation spark-ignition gasoline-fuel engine. The engine 11 may be a four-cycle piston-reciprocation compression-ignition diesel-fuel engine. An exhaust pipe 12 for discharging exhaust gas discharged from the engine 11, to an outside air, is connected to the engine 11. The exhaust pipe 12 defines an exhaust passage of the engine 11.

[0041] The first apparatus includes an electrical heating catalyzer 13. The catalyzer 13 is provided in the exhaust pipe 12. The catalyzer 13 is an exhaust gas purification catalyst apparatus which produces heat to increase a temperature thereof by the catalyzer 13 being supplied with electricity from a battery 14 (see FIG. 2) installed on the vehicle (not shown), i.e., by the catalyzer 13 being energized. A configuration of the catalyzer 13 will be described later in detail.

[0042] The first apparatus includes an ECU (electronic control unit) 20, an air-fuel ratio sensor 21, an upstream temperature sensor 22, an oxygen concentration sensor (or an O.sub.2 sensor) 23, a downstream temperature sensor 24, an insulation resistance detection device (or a voltage measurement device) 25, an ignition switch 26, an air-flow meter 27 and a water temperature sensor 28,

[0043] The ECU 20 is electrically connected to the sensors 21 to 24 and 28, the insulation resistance detection device 25, the ignition switch 26 and the air-flow meter 27 and is configured to receive signals from the sensors 21 to 24 and 28, the device 25, the switch 26 and the air-flow meter 27, respectively. The ECU 20 is configured to send command signals to fuel injectors (not shown) of the engine 11 to control an air-fuel ratio of a mixture gas supplied to the engine 11, i.e., an engine air-fuel ratio,

[0044] The ECU 20 is an electronic control circuit including as a main component, a micro-computer including a CPU, a ROM, a RAM, a back-up RAM, an interface and the like. The CPU executes instructions or routines or programs stored in a memory such as the ROM to realize various functions described later.

[0045] The air-fuel ratio sensor 21 measures an air-fuel ratio AFS of the exhaust gas flowing through the exhaust pipe 12 into the catalyzer 13 and outputs a signal indicating the air-fuel ratio (i.e., a catalyzer upstream air-fuel ratio) AFS to the ECU 20,

[0046] The upstream temperature sensor 22 measures a temperature Tup of the exhaust gas flowing through the exhaust pipe 12 into the catalyzer 13, i.e., the exhaust gas existing upstream of the catalyzer 13 and outputs a signal indicating the temperature Tup to the ECU 20. Hereinafter, the temperature Tup will be referred to as "the upstream exhaust gas temperature Tup".

[0047] The oxygen concentration sensor 23 measures an oxygen concentration Cox of the exhaust gas flowing out from the catalyzer 13 to the exhaust pipe 12 and outputs a signal indicating the oxygen concentration Cox to the ECU 20.

[0048] The downstream temperature sensor 24 measures a temperature Tdn of the exhaust gas flowing out from the catalyzer 13 to the exhaust pipe 12, i.e., the exhaust gas existing downstream of the catalyzer 13 and outputs a signal indicating the temperature Tdn to the ECU 20.

[0049] The insulation resistance detection device (i.e., the voltage measurement device) 25 will be described later in detail.

[0050] The ignition switch 26 is a switch operated by a driver of the vehicle for starting and stopping an operation of the engine 11 and outputs a signal indicating an ON state or an OFF state of the ignition switch 26 to the ECU 20.

[0051] The air flow meter 27 measures a mass flow rate Ga of air flowing through an intake pipe (not shown) of the engine 11 into the engine 11 and outputs a signal indicating the mass flow rate Ga to the ECU 20. Hereinafter, the rate Ga will be referred to as "the intake air amount Ga".

[0052] The water temperature sensor 28 measures a temperature THW of cooling water for cooling the engine 11 and outputs a signal indicating the temperature THW, i.e., a cooling water temperature THW to the ECU 20.

[0053] Below, the configuration of the catalyzer 13 will be described in detail with reference to FIG. 2. The catalyzer 13 includes a catalyst carrier 31, a casing 32 and a mat member 34.

[0054] The catalyst carrier 31 has a cylindrical honeycomb body. The honeycomb body is made of porous ceramic such as SiC. Three-way catalyst is carried on the catalyst carrier 31. Catalyst carried on the catalyst carrier 31 may be catalyst other than the three-way catalyst. The catalyzer 13 may be a NOx storage reduction catalyst converter carrying oxidation catalyst having oxidative function and catalyst having NOx storage reduction function or a selective catalytic reduction NOx catalyst converter or the like.

[0055] A pair of electrodes 33 are provided on an outer circumferential surface or peripheral portion adjacent thereto of the catalyst carrier 31. The electrodes 33 are located opposite to each other across the catalyst carrier 31. The catalyst carrier 31 produces heat by an electric difference being applied to the electrodes 33. Therefore, the catalyst carrier 31 is a heat production body which produces the heat when an electricity is supplied to the catalyst carrier 31. Hereinafter, an application of the electric difference to the electrodes 33 will be referred to as "energization of the catalyst carrier 31 or the catalyzer 13".

[0056] The casing 32 is a housing for housing the catalyst carrier 31. The casing 32 is made from metal such as stainless steel. The casing 32 has an electric conductivity. The casing 32 has a cylindrical shape having an inner radius larger than an outer radius of the catalyst carrier 31. The casing 32 houses the catalyst carrier 31 such that a center axis of the catalyst carrier 31 is aligned with a center axis of the casing 32. An upstream end portion of the casing 32 is tapered such that a radius of the upstream end portion decreases at greater distance from the catalyst carrier 31. A downstream end portion of the casing 32 is tapered such that a radius of the downstream end portion decreases at greater distance from the catalyst carrier 31.

[0057] The mat member 34 is an annular member. The mat member 34 is pressed between the outer peripheral surface of the catalyst carrier 31 and an inner peripheral surface of the casing 32. The mat member 34 is made from material (for example, inorganic fiber such as alumina fiber) having a low electric conductivity. The mat member 34 supports or holds the catalyst carrier 31 in the casing 32 while the insulation member 34 insulates the catalyst carrier 31 and the electrodes 33 from the casing 32. Therefore, the mat member 34 is an insulation member. The mat member 34 may be made of any material having the low electric conductivity, high heat-resistance property and cushioning function.

[0058] A pair of cylindrical through holes 35 are formed in the mat member 34 at areas adjacent to a center of the mat member 34 in an axial direction of the mat member 34, respectively such that an axis of each through hole 36 extends perpendicular to an axis of the mat member 34 and extends through center areas of the electrodes 33. A pair of cylindrical through holes are formed in the casing 32 at areas adjacent to a center of the casing 32 in an axial direction of the casing 32, respectively such that an axis of each through hole extends perpendicular to an axis of the casing 32 and extends through the center areas of the electrodes 33. A cylindrical conductive member or electrode terminal 37 is inserted in one of the through hole 35 of the mat member 34 and the corresponding through hole of the casing 32. Another cylindrical conductive member or electrode terminal 37 is inserted in the other through hole 35 of the mat member 34 and the corresponding through hole of the casing 32. One end of each conductive member 37 is electrically connected to the corresponding electrode 33. The other end of each conductive member 37 extends through the casing 32 to outside of the casing 32. A voltage potential difference is applied between the conductive members 37, thereby applying the voltage potential difference to the electrodes 33. Hereinafter, the mat member 34 will be referred to as "the insulation member 34".

[0059] A supporting member 36 is provided between each conductive member 37 and the casing 32 at an area where each conductive member 37 extends through the casing 32. The supporting members 36 are made from insulation material having a low electric conductivity. Thus, the supporting members 36 insulate the conductive members 37 from the casing 32, respectively. The supporting members 36 are air-tightly connected to the conductive members 37, respectively. In addition, the supporting members 36 are air-tightly connected to the casing 32.

[0060] When the battery 14 applies a voltage (i.e., a battery voltage) or the electric potential difference to the electrodes 33, the catalyst carrier 31 produces heat. Thereby, a temperature of the catalyst carried on the catalyst carrier 31, i.e., a catalyst bed temperature, increases.

[0061] For example, the battery voltage is applied to the electrodes 33 when the operation of the engine 11 starts while a temperature of the engine 11 is low, i.e., at a cold-start of the engine 11. Thereby, the catalyst carried on the catalyst carrier 31 can be promptly activated.

[0062] Further, the battery voltage is applied to the electrodes 33 when the engine 11 is decelerated by stopping injection of fuel from the fuel injectors, i.e., when the engine 11 is under a deceleration fuel-cut operation state. Thereby, the temperature of the catalyst carried on the catalyst carrier 31 increases. As a result, degree of activation of the catalyst can be prevented from decreasing.

[0063] Below, an acquisition of an insulation resistance value R0 of the catalyzer 13 will be described. The insulation resistance detection device 25 includes a base electric source 251 having a grounded negative terminal, a base resistance 252, a voltmeter 253 and an insulation resistance circuit switch 254. A conduction state of the insulation resistance circuit switch 254 is switched by the ECU 20. The casing 32 is grounded. Therefore, the base resistance 252 and the insulation member 34 are electrically connected in series to the base electric source 251 via the conductive members 37 and the electrodes 33.

[0064] The base electric source 251 applies a constant base voltage to a circuit part electrically connected in series to the base resistance 252 and the insulation member 34 when the insulation resistance circuit switch 254 is set at the conduction state. The voltmeter 253 measures a voltage or an electric potential V between the base resistance 252 and the insulation member 34 and outputs a signal indicating the voltage V to the ECU 20. A circuit for measuring the voltage V is provided, independently of an energization circuit for energizing the catalyzer 13 to cause the catalyzer 13 to produce the heat. The energization circuit includes the battery 14 and a switch 141. A conduction state of the switch 141 is switched by the ECU 20. When the switch 141 is set to the conduction state, the battery 14 applies the battery voltage to the electrodes 33.

[0065] An electric resistance value Rehc of the insulation member 34 is expressed by expressions (1) and (2) described below. In the expressions (1) and (2), "Vref" is a base voltage of the base electric source 251, "Rref" is an electric resistance value of the base resistance 252, i.e., a base resistance value, "I" is an electric current flowing through the base resistance 252 and the insulation member 34 and "Vehc" is a voltage measured by the voltmeter 253.

I=(Vref-Vehc)/Rref (1)

Rehc=Vehc/I=Rref-Vehc/(Vref-Vehc) (2)

[0066] When the insulation resistance value R0 between the catalyst carrier 31 and the casing 32 deceases to below a certain threshold (for example, 1 M.OMEGA.), an electricity may leak to the casing 32 due to the energization of the catalyzer 13 by the energization circuit. Accordingly, when the insulation resistance value R0 is smaller than the threshold, the energization of the catalyzer 13 should be inhibited. This is, for example, provided by North American Regulation (FMVSS305). Hereinafter, a control for performing the energization of the catalyzer 13, using the energization circuit will be referred to as "the energization control".

[0067] There is known an apparatus for performing a process for oxidizing and removing the particulate matter at a sufficiently high temperature by delaying an ignition timing for igniting the fuel in the engine 11 by a predetermined ignition delaying amount relative to an optimal ignition timing (i.e., a base ignition timing) defined by a load and a speed of the engine 11 to increase the temperature of the exhaust gas and temporarily setting the engine air-fuel ratio at a lean air-fuel ratio (i.e., an air-fuel ratio larger than a stoichiometric air-fuel ratio) when the insulation resistance value R0 becomes smaller than the threshold. Hereinafter, the above-mentioned process may be referred to as "the PM removal process" or "the PM removal control".

[0068] An electric resistivity of the particulate matter decreases as a PM temperature Tpm which is a temperature of the particulate matter, increases. Thus, when the PM temperature Tpm is high, the insulation resistance value R0 may be smaller than the threshold with the PM temperature Tpm despite a smaller amount of the particulate matter accumulating on and/or in the insulation member 34 (hereinafter, the amount will be referred to as "the accumulating PM amount Aim") than an amount where the particulate matter should be removed from the insulation member 34. As a result, the PM removal process is performed despite the smaller accumulating PM amount Aim than the amount where the particulate matter should be removed from the insulation member 34. In this case, a fuel consumption rate of the engine 11 may increase due to a decreasing of a thermal efficiency derived from the delay of the ignition timing in the engine 11.

[0069] With reference to a graph shown in FIG. 3, a relationship between the PM temperature Tpm and the electric resistivity of the particulate matter will be described. In the graph shown in FIG. 3, a horizontal axis indicates a catalyzer temperature Tehc which is a temperature of the catalyzer 13 and a vertical axis indicates the insulation resistance value R0 between the catalyst carrier 31 and the casing 32. This graph indicates a result of the insulation resistance values R0 measured in different catalyzer temperatures Tehc when a predetermined amount of the particulate matter accumulates in the catalyzer 13. The catalyzer temperature Tehc can be considered as the PM temperature Tpm.

[0070] As the catalyzer temperature Tehc increases, the PM temperature Tpm or a temperature of the insulation member 34 increases. As the PM temperature Tpm or a temperature of the insulation member 34 increases, the electric resistivity of the particulate matter accumulating on and/or in the insulation member 34 or an electric resistivity of the insulation member 34 decreases. Thus, as shown in FIG. 3, the insulation resistance value R0 decreases as the catalyzer temperature Tehc increases.

[0071] In this regard, for following reasons, even when the catalyzer temperature Tehc increases, there is little change in the electric resistivity of the insulation member 34.

[0072] When the catalyzer temperature Tehc changes within a range lower than a considerably high temperature Ta (hereinafter, will be referred to as "the predetermined temperature Ta"), there is little change in the electric resistivity of the insulation member 34.

[0073] When the operation of the engine 11 is stopped, the catalyzer temperature Tehc may decrease to a certain temperature Tehc_low. When the PM removal control and a control for energizing the catalyzer 13 are executed, the catalyzer temperature Tehc may increase to a certain temperature Tehc_high.

[0074] Normally, the temperatures Tehc_low and Tehc_high are lower than the predetermined temperature Ta. Therefore, the catalyzer temperature Tehc normally changes within a range lower than the predetermined temperature Ta. Thus, even when the catalyzer temperature Tehc changes, there is little change in the electric resistivity of the insulation member 34. Accordingly, as the catalyzer temperature Tehc increases, the insulation resistance value R0 decreases mainly due to the decreasing of the electric resistivity of the particulate matter accumulating on and/or in the insulation member 34.

[0075] Accordingly, the ECU 20 determines whether the PM removal process should be performed on the basis of the PM temperature Tpm (or an estimated PM temperature or a particular PM temperature) of the particulate matter accumulating in the catalyzer 13 and the insulation resistance value R0 (or an acquired resistance) between the catalyst carrier 31 and the casing 32. In other words, the ECU 20 determines whether the particulate matter accumulating in the catalyzer 13 should be removed on the basis of the insulation resistance value R0 in consideration of the PM temperature Tpm.

[0076] In particular, the first apparatus calculates a base insulation resistance value Rpm (or a converted resistance value) which is the insulation resistance value R0 (i.e., the acquired resistance) to be acquired when the PM temperature Tpm (i.e., the estimated PM temperature) corresponds to a base temperature Tpm0, on the basis of the PM temperature Tpm and the insulation resistance value R0.

[0077] Then, the first apparatus performs the PM removal process when the base insulation resistance value Rpm (i.e., the converted resistance value) is smaller than a predetermined resistance value Rpm_th. The predetermined resistance value Rpm_th is the base insulation resistance value Rpm to be acquired when an amount of the particulate matter accumulating in the catalyzer 13 corresponds to an amount where the particulate matter should be removed from the catalyzer 13.

[0078] Hereinafter, the predetermined resistance value Rpm_th will be referred to as "the first resistance threshold Rpm_th", the amount of the particulate matter accumulating in the catalyzer 13 will be referred to as "the accumulating PM amount Aehc" and the amount where the particulate matter should be removed from the catalyzer 13 will be referred to as "the PM removal amount Aehc_th.

[0079] On the other hand, when the insulation resistance value R0 decreases mainly due to the decreasing of the electric resistivity of the particulate matter derived from the increasing of the PM temperature Tpm, the base insulation resistance value Rpm becomes larger than the first resistance threshold Rpm_th. In this case, the first apparatus does not perform the PM removal process. Thereby, the fuel consumption rate is avoided from increasing.

[0080] (Concrete Operation)

[0081] Below, a concrete operation of the CPU of the ECU 20 will be described. The CPU is configured or programmed to execute a catalyzer energization start control shown by a flowchart in FIG. 4 each time a predetermined time elapses. At a predetermined timing, the CPU proceeds with the process to a step S101 of FIG. 4 to determine whether following three conditions are satisfied.

[0082] (1) A value of a condensed water removal control execution flag Xw is "0".

[0083] (2) A value of a PM removal control execution flag Xpm is "0".

[0084] (3) A value of a malfunction flag or a catalyzer failure flag Xijo is "0".

[0085] The value of the condensed water removal control execution flag Xw is set to "1" when a condensed water removal control described later is executed. On the other hand, the value of the condensed water removal control execution flag Xw is set to "0" when the condensed water removal control is not executed. The value of the condensed water removal control execution flag Xw is stored in the RAM.

[0086] The value of the PM removal control execution flag Xpm is set to "1" when a PM removal control (or a PM removal process) described later is executed. On the other hand, the value of the PM removal control execution flag Xpm is set to "0" when the PM removal control is not executed. The value of the PM removal control execution flag Xpm is stored in the RAM.

[0087] The values of the condensed water removal control execution flag Xw and the PM removal control execution flag Xpm are set to "0", respectively by an initial routine. The initial routine is executed by the CPU when an operation state of the ignition switch 26 changes from the ON state to the OFF state.

[0088] As described later, the value of the malfunction flag Xijo is set to "1" when it is determined that the catalyzer 13 malfunctions or fails. The value of the malfunction flag Xijo is stored in the back-up RAM.

[0089] When at least one of the values of the condensed water removal control execution flag Xw, the PM removal control execution flag Xpm and the malfunction flag Xijo is "1", the CPU determines "No" at the step S101 and then, terminates this routine once. On the other hand, when all of the values of the condensed water removal control execution flag Xw, the PM removal control execution flag Xpm and the malfunction flag Xijo are "0", respectively, the CPU determines "Yes" at the step S101 and then, proceeds with the process to a step S102.

[0090] At the step S102, the CPU determines whether the catalyzer temperature Tehc is lower than a first temperature Tth, in other words, a request of energizing the catalyzer 13 is generated.

[0091] The CPU acquires or estimates the catalyzer temperature Tehc, for example, using a following expression (3). In the expression (3), a parameter "a" is a predetermined constant larger than zero and smaller than one. The predetermined constant a is set appropriately in consideration of a degree of influence of the upstream exhaust gas temperature Tup with the catalyzer temperature Tehc, a heat radiation rate of the catalyzer 13 and the like. A parameter "Tehc last" is the catalyzer temperature Tehc calculated the predetermined time ago, using the expression (3). A parameter "Tup" is the temperature of the exhaust gas existing upstream of the catalyzer 13, i.e., the upstream exhaust gas temperature measured by the upstream temperature sensor 22. A method for acquiring or estimating the catalyzer temperature Tehc is not limited to a method using the expression (3) and may be a known method.

Tehc=.alpha.Tup+(1-.alpha.)Tehc_last (3)

[0092] When the catalyzer temperature Tehc is higher than or equal to the first temperature Tth, the CPU determines "No" at the step S102 and then, terminates this routine once. On the other hand, when the catalyzer temperature Tehc is lower than the first temperature Tth, the CPU determines "Yes" at the step S102 and then, proceeds with the process to a step S103.

[0093] At the step S103, the CPU determines whether the catalyzer 13 is energized. When the catalyzer 13 is energized, the CPU determines "Yes" at the step S103 and then, terminates this routine once. On the other hand, when the catalyzer 13 is not energized, the CPU determines "No" at the step S103 and then, proceeds with the process to a step S104.

[0094] At the step S104, the CPU acquires the present insulation resistance value R0, using the signal output from the insulation resistance detection device 25 and then, proceeds with the process to a step S105.

[0095] At the step S105, the CPU determines whether the insulation resistance value R0 is larger than a predetermined resistance value Rth. When the insulation resistance value R0 is larger than or equal to the predetermined resistance value Rth, the CPU determines "Yes" and then, proceeds with the process to a step S106 to change a state of the switch 141 from a shut-off state to the conduction state to apply the electric potential difference to the electrodes 33, thereby to energize the catalyzer 13. Then, the CPU terminates this routine once.

[0096] The predetermined resistance value Rth is the insulation resistance value R0 where an excessive current may flow from the catalyst carrier 31 and/or the electrodes 33 to the casing 32 when the energization of the catalyzer 13 is performed. Therefore, when the insulation resistance value R0 is larger than the predetermined resistance value Rth, the excessive current is unlikely to flow from the catalyst carrier 31 and/or the electrodes 33 to the casing 32. On the other hand, when the insulation resistance value R0 is smaller than or equal to the predetermined resistance value Rth, the excessive current is likely to flow from the catalyst carrier 31 and/or the electrodes 33 to the casing 32.

[0097] When the insulation resistance value R0 is smaller than or equal to the predetermined resistance value Rth, the condensed water may exist on and/or in the catalyst carrier 31. In this case, the CPU determines "No" at the step S105 and then, proceeds with the process to a step S107 to set the value of the condensed water removal control execution flag Xw to "1". Then, the CPU terminates this routine once. As a result, as described later, an execution of the condensed water removal control starts.

[0098] The CPU is configured or programmed to execute a catalyzer energization stop control routine shown by a flowchart in FIG. 5 each time a predetermined time elapses in addition to the catalyzer energization start routine shown in FIG. 4. At a predetermined timing, the CPU proceeds with the process to a step S201 of FIG. 5 to determine whether the catalyzer 13 is energized. When the catalyzer 13 is not energized, the CPU determines "No" at the step S201 and then, terminates this routine once. On the other hand, when the catalyzer 13 is energized, the CPU determines "Yes" at the step S201 and then, proceeds with the process to a step S202.

[0099] At the step S202, the CPU determines whether the catalyzer temperature Tehc is higher than or equal to a second temperature Tdanki or a catalyzer catalyst warming-up completion temperature Tdanki. The second temperature Tdanki is the catalyzer temperature Tehc where it is determined that a warming-up of the catalyzer 13 completes. The second temperature Tdanki is higher than the first temperature Tth. When the catalyzer temperature Tehc is lower than the second temperature Tdanki, the CPU determines "No" at the step S202 and then, terminates this routine once.

[0100] On the other hand, when the catalyzer temperature Tehc is higher than or equal to the second temperature Tdanki, the CPU determines "Yes" at the step S202 and then, proceeds with the process to a step S203 to change the state of the switch 141 from the conduction state to the shut-off state to stop the energization of the catalyzer 13. Then, the CPU terminates this routine once.

[0101] The CPU is configured or programmed to execute a condensed water removal control routine shown by a flowchart in FIG. 6 each time a predetermined time elapses in addition to the catalyzer energization start control routine shown in FIG. 4 and the catalyzer energization stop control routine shown in FIG. 5.

[0102] At a predetermined timing, the CPU proceeds with the process to a step S301 to determine whether the present time is immediately after the value of the condensed water removal control execution flag Xw changes from "0" to "1". When the present time is immediately after the value of the condensed water removal control execution flag Xw changes from "0" to "1", the CPU determines "Yes" at the step S301 and then, proceeds with the process to a step S302 to set a catalyzer input energy E to "0". Then, the CPU proceeds with the process to a step S307.

[0103] The catalyzer input energy E is an energy which has been input since the condensed water removal control starts.

[0104] At the step S307, the CPU determines whether the value of the condensed water removal control execution flag Xw is "1", When the value of the condensed water removal control execution flag Xw is "1", the CPU determines "Yes" at the step S307 and then, proceeds with the process to a step S308 to execute a condensed water removal control. Then, the CPU terminates this routine once.

[0105] The condensed water removal control is a control for performing an ignition delay process for delaying the ignition timing of the engine 11 by the predetermined ignition delay amount from the base ignition timing corresponding to the optimum ignition timing defined by the load and the speed of the engine 11. When the ignition delay process is performed, an energy discharged from the engine 11 to the exhaust passage increases and thus, the temperature of the exhaust gas increases. Therefore, the catalyzer temperature Tehc can be increased without energizing the catalyzer 13. Thereby, the condensed water adhering to the catalyzer 13 can be removed.

[0106] The condensed water removal control is not limited to the ignition delay process and may be any processes for increasing the catalyzer temperature Tehc without energizing the catalyzer 13. For example, the condensed water removal control may be a process for advancing a timing of opening exhaust valves (not shown) of the engine 11 to discharge the exhaust gas having a large energy, i.e., a high temperature, thereby increasing the catalyzer temperature Tehc.

[0107] When the value of the condensed water removal control execution flag Xw is "0", the CPU determines "No" at the step S307 and then, proceeds with the process to a step S309 to set the ignition delay amount to zero to stop the condensed water removal control. Then, the CPU terminates this routine once.

[0108] When the present time is not immediately after the value of the condensed water removal control execution flag Xw changes from "0" to "1" , that is, when the value of the condensed water removal control execution flag Xw is maintained at "0" or "1", the CPU determines "No" at the step S301 and then, proceeds with the process to a step S303.

[0109] At the step S303, the CPU determines whether the value of the condensed water removal control execution flag Xw is "1". When the value of the condensed water removal control execution flag Xw is "0", the CPU determines "No" at the step S303 and then, proceeds with the process directly to the step S307. On the other hand, when the value of the condensed water removal control execution flag Xw is "1", the CPU determines "Yes" at the step S303 and then, proceeds with the process to a step S304.

[0110] At the step S304, the CPU sets a value obtained by Tex.gamma.Ga East as the catalyzer input energy E. A parameter "Tex" is equal to the temperature of the exhaust gas existing upstream of the catalyzer 13, i.e., the upstream exhaust gas temperature Tup measured by the upstream temperature sensor 22. A parameter's is a specific heat. A parameter "Ga" is the intake air amount Ga measured by the air flow meter 27. A parameter "Elast" is the catalyzer input energy E calculated by the routine shown in FIG. 6 executed last time. The catalyzer input energy E may be estimated, for example, on the basis of the ignition delay amount and the intake air amount Ga.

[0111] Then, the CPU proceeds with the process to a step S305 to determine whether at least one of following conditions is satisfied.

[0112] (1) The catalyzer input energy E is larger than or equal to a predetermined energy Eth.

[0113] (2) The catalyzer temperature Tehc is higher than or equal to the second temperature (i.e., the catalyzer catalyst warming-up completion temperature) Tdanki.

[0114] When the catalyzer input energy E is smaller than the predetermined energy Eth and the catalyzer temperature Tehc is lower than the second temperature Tdanki, the condensed water may not evaporate or be removed from the catalyst carrier 31. In this case, the CPU determines "No" at the step S305 and then, proceeds with the process directly to the step S307. In this case, the value of the condensed water removal control execution flag Xw is "1". Therefore, the execution of the condensed water removal control continues by the process of the step S308.

[0115] On the other hand, when the catalyzer input energy E is larger than or equal to the predetermined energy Eth or when the catalyzer temperature Tehc is higher than or equal to the second temperature Tdanki, the condensed water may evaporate or be removed from the catalyst carrier 31. In this case, the CPU determines "Yes" at the step S305 and then, proceeds with the process to a step S306 to set the value of the condensed water removal control execution flag Xw to "0". Then, the CPU proceeds with the process to the step S307. In this case, the CPU determines "No" at the step S307 and then, proceeds with the process to the step S309 to stop the condensed water removal control.

[0116] The CPU is configured or programmed to execute a PM removal control routine shown by a flowchart in FIG. 7 each time a predetermined time elapses in addition to the routines shown in FIGS. 4 to 6.

[0117] At a predetermined timing, the CPU proceeds with the process to a step S401 of FIG. 7 to determine whether the catalyzer 13 is energized. When the catalyzer 13 is energized, the CPU determines "Yes" at the step S401 and then, terminates this routine once. On the other hand, when the catalyzer 13 is not energized, the CPU determines "No" at the step S401 and then, proceeds with the process to a step S402.

[0118] At the step S402, the CPU acquires the catalyzer temperature Tehc calculated separately, using the expression (3). Then, the CPU proceeds with the process to a step S403 to determine whether the value of the PM removal control execution flag Xpm is "0".

[0119] When the value of the PM removal control execution flag Xpm is "0", the CPU determines "Yes" at the step S403 and then, proceeds with the process to a step S404 to determine whether the present time is immediately after the value of the condensed water removal control execution flag Xw changes from "1" to "0". In other words, the CPU determines whether the present time is immediately after the condensed water removal control is stopped. When the present time is immediately after the value of the condensed water removal control execution flag Xw changes from "1" to "0", the CPU determines "Yes" at the step S404 and then, proceeds with the process to a step S406.

[0120] At the step S406, the CPU acquires the present insulation resistance value R0 as an insulation resistance value R1 (i.e., the acquired resistance value), using the signal output from the insulation resistance detection device 25 and then, proceeds with the process to a step S407.

[0121] At the step S407, the CPU acquires the base insulation resistance value Rpm (i.e., the converted resistance value) on the basis of the present insulation resistance value R1 and the present catalyzer temperature Tehc, i.e., the catalyzer temperature Tehc (i.e., the particular PM temperature) acquired at a time of acquiring the present insulation resistance value R1 (i.e., the acquired resistance).

[0122] The base insulation resistance value Rpm is the insulation resistance value R0 between the catalyst carrier 31 and the casing 32 to be acquired when no condensed water exists in the catalyzer 13, the catalyzer temperature Tehc (i.e., the temperature of the particulate matter accumulating on and/or in the catalyst carrier 31) corresponds to the base temperature T0 and the same amount of the particulate matter as the amount of the particulate matter now accumulating in the catalyzer 13, accumulates in the catalyzer 13.

[0123] In particular, an experiment is performed to measure the insulation values while changing an amount Acc of the particulate matter accumulating on and/or in the catalyst carrier 31 (hereinafter, the amount Acc will be referred to as "the accumulating PM amount Acc") and the PM temperature (i.e., the catalyzer temperature Tehc). In this experiment, the condensed water is removed from the catalyst carrier 31. Then, the insulation resistance value Rt0 to be acquired when the accumulating PM amount Acc is a certain amount X and the PM temperature Tpm is the base temperature T0, is acquired.

[0124] In addition, the insulation resistance value Rtx to be acquired when the accumulating PM amount Acc is the amount X and the PM temperature Tpm is an optional temperature Tx, is acquired.

[0125] Then, a ratio (=Rt0/Rtx) of the insulation resistance value Rt0 to the insulation resistance value Rtx is acquired as a conversion coefficient k. The acquired conversion coefficients k are stored in the ROM in the form of a look-up table MapA. Therefore, the look-up table MapA can be expressed by following expression (4).

k=MapA(Tx,Rtx) (4)

[0126] The CPU applies the present catalyzer temperature Tehc to a parameter Tx of the look-up table MapA(Tx,Rtx) and the present insulation resistance value R1 (i.e., the acquired resistance value) to a parameter Rtx of the look-up table MapA(Tx, Rtx) to acquire the conversion coefficient k. Then, as described by following expression (5), the CPU multiplies the present insulation resistance value RI by the acquired conversion coefficient k to acquire the base insulation resistance value Rpm (i.e., the converted resistance value).

Rpm=k(Tehc,R1)R1 (5)

[0127] As described above, the base insulation resistance value Rpm is acquired by multiplying the insulation resistance value R1 by the conversion coefficient k acquired on the basis of the catalyzer temperature Tehc and the insulation resistance value R1. Therefore, assuming that "fa" is a predetermined function, the base insulation resistance value Rpm can be expressed by an expression "Rpm=fa(Tehc,R1)". Accordingly, the base insulation resistance value Rpm can be acquired directly on the basis of the insulation resistance value R1 and the catalyzer temperature Tehc corresponding to the PM temperature Tpm acquired at the time of acquiring the insulation resistance value R1, Therefore, the CPU may be configured or programmed to acquire the base insulation resistance value Rpm directly, using a look-up table MapB shown by following expression (6).

Rpm=MapB(Tehc,Rpm)=fa(Tehc,R1) (6)

[0128] Then, the CPU proceeds with the process to a step S408 to determine whether the base insulation resistance value Rpm (i.e., the converted resistance value) acquired at the step S407, is smaller than the first resistance threshold Rpm_th. When the base insulation resistance value Rpm is larger than or equal to the first resistance threshold Rpm_th, it can be determined that the accumulating PM amount Acc is not large enough to remove the particulate matter adhering to or accumulating in the catalyzer 13. In this case, the CPU determines "No" at the step S408 and then, terminates this routine once.

[0129] On the other hand, when the base insulation resistance value Rpm is smaller than the first resistance threshold Rpm_th, it can be determined that the accumulating PM amount Acc is larger than an amount where the particulate matter accumulating in or adhering to the catalyzer 13 should be removed. In this case, the CPU determines "Yes" at the step S408 and then, proceeds with the process to a step S409 to set the value of the PM removal control execution flag Xpm to "1" and start art execution of the PM removal control. Then, the CPU terminates this routine once.

[0130] In particular, the PM removal control is a control for delaying the ignition timing of the engine 11 by the predetermined ignition delay amount from the optimum ignition timing (i.e., the base ignition timing) defined by the load and the speed of the engine 11 to increase the temperature of the exhaust gas and sating a fuel injection amount which is an amount of the fuel injected from each fuel injectors, to an amount defined by the intake air amount Ga, the speed of the engine 11 and a target air-fuel ratio.

[0131] While the PM removal control is executed, the target air-fuel ratio is switched between a strong rich air-fuel ratio which is considerably smaller than the stoichiometric air-fuel ratio and a strong lean air-fuel ratio which is larger than the stoichiometric air-fuel ratio. The strong rich air-fuel ratio is an air-fuel ratio smaller than a rich air-fuel ratio which may be normally accomplished when an air-fuel ratio feedback control is executed and the PM removal control is not executed. The strong lean air-fuel ratio is an air-fuel ratio larger than a lean air-fuel ratio which may be normally accomplished when the air-fuel ratio feedback control is executed and the PM removal control is not executed.

[0132] An air-fuel ratio control for switching the air-fuel ratio between the strong rich and lean air-fuel ratios is generally called as an active air-fuel ratio control or an air-fuel ratio perturbation control.

[0133] The temperature of the exhaust gas is increased by the ignition delay process and a large amount of oxygen is supplied to the catalyzer 13 when the target air-fuel ratio is set to the strong lean air-fuel ratio. Thereby, the particulate matter can be oxidized in the catalyzer 13 and thus, the particulate matter accumulating in the catalyzer 13 can be removed. It should be noted that an average of the air-fuel ratio of the exhaust gas supplied to the catalyzer 13 is maintained at around the stoichiometric air-fuel ratio by the active air-fuel ratio control and thus, an exhaust emission property is prevented from decreasing considerably.

[0134] When the time of the CPU performing the process of the step S404 is not immediately after the value of the condensed water removal control execution flag Xw changes from "1" to "0", in other words, when the value of the condensed water removal control execution flag Xw is maintained at "1" or "0" at the time of the CPU performing the process of the step S404, the CPU determines "No" at the step S404 and then, proceeds with the process to a step S405.

[0135] At the step S405, the CPU determines whether the catalyzer temperature Tehc is higher than or equal to the second temperature (i.e., the catalyzer catalyst warming-up completion temperature) Tdanki. When the catalyzer temperature Tehc is lower than the second temperature Tdanki, the CPU determines "No" at the step S405 and then, terminates this routine once.

[0136] On the other hand, when the catalyzer temperature Tehc is higher than or equal to the second temperature Tdanki, the condensed water may completely evaporate or be removed from the catalyst carrier 31. In this case, the CPU determines "Yes" at the step 405 and then, proceeds with the process to the step S406 described above. At this time, the CPU sets the value of the condensed water removal control execution flag Xw to "0".

[0137] When the value of the PM removal control execution flag Xpm is "1" at the time of the CPU performing the process of the step S403, the CPU determines "No" at the step S403 and then, proceeds with the process to a step S410. At the step S410, the CPU determines whether a duration time of the execution of the PM removal control is longer than or equal to a predetermined time Tpm_th.

[0138] When the duration time Tpm is shorter than the predetermined time Tpm_th, the CPU determines "No" at the step S410 and then, terminates this routine once. In this case, the execution of the PM removal control continues.

[0139] On the other hand, when the duration time Tpm is longer than or equal to the predetermined time Tpm, it can be determined that a removal of the particulate matter adhering to or accumulating in the catalyzer 13 is completed. In this case, the CPU determines "Yes" at the step S410 and then, proceeds with the process to a step S411 to set the value of the PM removal control execution flag Xpm to "0" and stop the PM removal control,

[0140] Then, the CPU proceeds with the process to a step S412 to acquire the present insulation resistance value R0 as an insulation resistance value R2 (i.e., the acquired resistance value), using the signal output from the insulation resistance detection device 25. Then, the CPU proceeds with the process to a step S413 to determine whether the insulation resistance value R2 is larger than a predetermined resistance value Rth or a resistance value slightly smaller than the predetermined resistance value Rth.

[0141] Currently, the removal of the particulate matter adhering to or accumulating in the catalyzer 13 is completed. Therefore, if the catalyzer 13 is normal, the insulation resistance value R2 must be sufficiently large. Accordingly, when the insulation resistance value R2 is larger than the predetermined resistance value Rth, the CPU determines "Yes" at the step 413 and then, proceeds with the process to a step S414 to set the value of the malfunction flag Xijo to "0". Then, the CPU terminates this routine once. In this case, the CPU determines that the catalyzer 13 is normal.

[0142] On the other hand, when the insulation resistance value R2 is smaller than or equal to the predetermined resistance value Rth, the catalyzer 13 is likely to malfunction. In this case, the CPU determines "No" et the step S413 and then, proceeds with the process to a step S415 to set the value of the malfunction flag Xijo to "1". Then, the CPU terminates this routine once.

[0143] Below, with reference to FIG. 8, an actual operation of the exhaust gas purification apparatus 10 when the routines shown in FIGS. 4 to 7 are executed, will be described, assuming that the catalyzer 13 is normal and the condensed water and the particulate matter adhere to the catalyzer 13.

[0144] The CPU acquires or measures the catalyzer temperature Tehc at a time t1 and determines whether the catalyzer temperature Tehc is lower than the first temperature Tth. In an example shown in FIG. 8, the catalyzer temperature Tehc is lower than the first temperature Tth. Therefore, an energization request for energizing the catalyzer 13 to increase the catalyzer temperature Tehc is generated,

[0145] Then, the CPU realizes that the catalyzer 13 is not energized and acquires or detects the insulation resistance value R0, using the signal output from the insulation resistance detection device 25. Then, the CPU determines whether the insulation resistance value R0 is larger than or equal to the predetermined resistance value Rth. In the example shown in FIG. 8, the insulation resistance value R0 is smaller than the predetermined resistance value Rth. Therefore, the condensed water may adhere to the catalyzer 13. Thus, the CPU starts the execution of the condensed water removal control and initializes a value of the catalyzer input energy E (i.e., sets the value of the catalyzer input energy E to zero).

[0146] Thereafter, the value of the catalyzer input energy E increases as the time elapses. At a time t2 when the catalyzer input energy E reaches the predetermined energy Eth, the CPU stops the execution of the condensed water removal control.

[0147] Thereafter, at a time t3, the CPU acquires the present insulation resistance value R1 (i.e., the acquired resistance value), using the signal output from the insulation resistance detection device 25. Then, the CPU acquires the base insulation resistance value Rpm (i.e., the converted resistance value) on the basis of the present insulation resistance value R1 and the present catalyzer temperature Tehc (i.e., the estimated PM temperature, in particular, the particulate PM temperature). Then, the CPU determines whether the base insulation resistance value Rpm is smaller than the first resistance threshold Rpm_th. In the example shown in FIG. 8, the base insulation resistance value Rpm is smaller than the first resistance threshold Rpm_th. Therefore, the particulate matter must accumulate in the catalyzer 13. Thus, the CPU starts the execution of the PM removal control.

[0148] Thereafter, at a time t4 when a predetermined time T0 elapses after the time t3, the CPU stops the execution of the PM removal control. Thereby, the PM removal control has been executed for the predetermined time T0. Therefore, the particulate matter accumulating in the catalyzer 13 can be removed.

[0149] Thereafter, at a time t5, the CPU acquires the present insulation resistance value R2, using the signal output from the insulation resistance detection device 25 and determines whether the insulation resistance value R2 is larger than the predetermined resistance value Rth. In the example shown in FIG. 8, the insulation resistance value R2 is larger than the predetermined resistance value Rth. Therefore, the CPU determines that the catalyzer 13 is normal. In addition, the catalyzer temperature Tehc is higher than the first temperature Tth. Thus, the CPU stops this control without energizing the catalyzer 13.

[0150] As described above, in the first apparatus, the insulation resistance values corresponding to the different accumulating PM amounts, respectively while the PM temperature changes, are previously acquired by the experiment. The first apparatus calculates the base insulation resistance value Rpm (i.e., the converted resistance value) which is the insulation resistance value R0 (i.e., the acquired resistance value) to be acquired when the PM temperature Tpm (i.e., the estimated PM temperature, in particular, the particular PM temperature) corresponds to the base temperature T0 on the basis of the insulation resistance value R1 (i.e. the acquired resistance value) and the PM temperature Tpm (i.e., the estimated PM temperature, in particular, the particular PM temperature) acquired at the time of acquiring the insulation resistance value R1.

[0151] When the base insulation resistance value Rpm is smaller than the first resistance threshold Rpm_th, the amount of the particulate matter accumulating in or adhering to the catalyzer 13 must be larger than the amount where the accumulating or adhering particulate matter should be removed. Thus, only when the base insulation resistance value Rpm is smaller than the first resistance threshold Rpm_th, the first apparatus executes the PM removal control for removing the particulate matter. Thereby, the first apparatus can restore the insulation resistance value without consuming the fuel unnecessarily.

Second Embodiment

[0152] Below, the exhaust gas purification apparatus of the internal combustion engine according to a second embodiment of the invention will be described. Hereinafter, the exhaust gas purification apparatus according to the second embodiment will be referred to as "the second apparatus".

[0153] The second apparatus is the same as the first apparatus except that the ECU 20 executes a routine shown by a flowchart in FIG. 9 in place of the routine shown in FIG. 7. Below, the routine shown in FIG. 7 will be mainly described.

[0154] Processes of steps S501 to S515 of the routine shown in FIG. 9 are the same as the processes of the steps S401 to S415 of the routine shown in FIG. 7, respectively except for processes of steps S507 and S508 of the routine shown in FIG. 9. Therefore, the processes of the steps S507 and S508 will be described.

[0155] At the step S507, the CPU calculates a second resistance threshold Rth_ehc (or a converted resistance threshold) which is used as a threshold of the insulation resistance value, on the basis of the present catalyzer temperature Tehc (i.e., the estimated PM temperature, in particular, the particular PM temperature).

[0156] In particular, an experiment is previously performed for acquiring the insulation resistance values corresponding to the different PM temperatures Tpm, i.e., the different catalyzer temperatures Tehc while accumulating an amount Y of the particulate matter in the catalyst carrier 31. The amount Y is the amount of the particulate matter accumulating on and/or in the catalyst carrier 31, used for determining whether the PM removal control should be executed and when the amount of the particulate matter accumulating on and/or in the catalyst carrier 31 is larger than or equal to the amount Y, the PM removal control should be executed. Hereinafter, the amount Y will be referred to as "the accumulating PM removal amount Y". It should be noted that in the experiment, the condensed water is removed from the catalyst carrier 31.

[0157] Further, the insulation resistance value R0 is acquired as an insulation resistance value Rt0 when the accumulating PM amount Acc is the accumulating PM removal amount Y and the PM temperature Tpm is the base temperature T0.

[0158] Furthermore, the insulation resistance value R0 is acquired as an insulation resistance value Rty when the accumulating PM amount Acc is the accumulating PM removal amount Y and the PM temperature Tpm is an optional temperature Ty.

[0159] Then, a ratio m of the insulation resistance value Rty to the insulation resistance value Rt0 is acquired as a conversion coefficient m (m=Rty/Rt0). The conversion coefficients m are stored in the ROM in the form of a look-up table MapC. Therefore, the look-up table MapC can be expressed by following expression (7).

m=MapC(Ty) (7)

[0160] The CPU applies the present catalyzer temperature Tehc (i.e., the estimated PM temperature, in particular, the particular PM temperature) to a parameter Ty of the look-up table MapC to acquire the conversion coefficient m.

[0161] In addition, as shown in following expression (8), the CPU multiplies the insulation resistance value Rt0 which is acquired when the PM temperature Tpm is the base temperature T0, by the acquired conversion coefficient m to acquire the second resistance threshold Rth_ehc (i.e., the converted resistance threshold).

Rth_ehc=mRt0 (8)

[0162] It should be noted that the second resistance threshold Rth_ehc is acquired by converting the insulation resistance value Rt0 which is acquired when the PM temperature Tpm is the base temperature T0, by the conversion coefficient m such that the second resistance threshold Rth_ehc acquired when the present catalyzer temperature Tehc is relatively high, is smaller than the second resistance threshold Rth_ehc acquired when the present catalyzer temperature Tehc is relatively low. This is because the electric resistivity of the particulate matter decreases as the PM temperature Tpm increases and thus, the insulation resistance value R0 decreases.

[0163] It should be noted that the second resistance threshold Rth_ehc has a relationship that Rth_ehc=mRt0=ga(Tehc). In this regard, "ga" is a predetermined function. Accordingly, the second resistance threshold Rth_ehc can be directly acquired on the basis of the catalyzer temperature Tehc which is estimated to be the PM temperature Tpm. Therefore, the CPU may be configured or programmed to acquire the second resistance threshold Rth_ehc directly from look-up table MapD(Tehc) as described by following expression (9).

Rth_ehc=MapD(Tehc)=ga(Tehc) (9)

[0164] Then, the CPU proceeds with the process to the step S508 to determine whether the present insulation resistance value R1 (i.e., the acquired resistance value) acquired at a step S506 is smaller than the second resistance threshold Rth_ehc (i.e., the converted resistance value).

[0165] When the present insulation resistance value R1 is larger than or equal to the second resistance threshold Rth_ehc, the CPU determines "No" at the step S508 and then, terminates this routine once. On the other hand, when the present insulation resistance value R1 is smaller than the second resistance threshold Rth_ehc, the CPU determines "Yes" at the step S508 and then, proceeds with the process to a step S509.

[0166] The second apparatus has previously acquired the second resistance thresholds Rth_ehc which are the insulation resistance values corresponding to the different catalyzer temperatures Tehc, each of which is estimated to be the PM temperature Tpm when the accumulating PM amount Acc is the accumulating PM removal amount Y (i.e., a predetermined accumulating amount).

[0167] When the insulation resistance value acquired, using the signal output from the insulation resistance detection device 25, is smaller than the second resistance threshold (i.e, the converted resistance threshold) Rth_ehc, the second apparatus determines that the amount of the particulate matter accumulating on and/or in an end of the catalyzer 13 is larger than the accumulating PM removal amount Y, independently of the PM temperature and then, executes the PM removal control.

[0168] Therefore, only when the accumulating PM amount Acc is larger than the accumulating PM removal amount Y, the PM removal control is executed. Thus, the insulation resistance value can be restored without consuming the fuel unnecessarily.

[0169] As described above, according to the embodiments, it can be determined whether the particulate matter should be removed in consideration of the change of the electric resistivity of the particulate matter due to the change of the PM temperature Tpm. Thus, the insulation resistance value can be restored without consuming the fuel unnecessarily. It should be noted that the present invention is not limited to the aforementioned embodiments and various modifications can be employed within the scope of the present invention.

[0170] For example, the first and second apparatuses may be configured to execute any routine for determining whether the particulate matter should be removed, i.e., the PM removal control should be executed on the basis of the PM temperature and the insulation resistance value in place of the routines shown in FIGS. 7 and 9.

[0171] In this regard, an area map or a lookup table which has the catalyzer temperature Tehc and the insulation resistance value R1 as parameters and defines an area where the PM removal control should be executed. In this case, the first and second apparatuses may be configured or programmed to directly determine whether the PM removal control should be executed by applying the present catalyzer temperature Tehc acquired at the step S402 (S502) and the present insulation resistance value R1 acquired at the step S406 (S506) to the area map without performing the processes of the steps S407 (S507) and S408 (S508). Thereby, a process for calculating the base insulation resistance value Rpm and the second resistance threshold Rth_ehc can be omitted. Therefore, the insulation resistance value can be restored without consuming the fuel unnecessarily in consideration of the change of the electric resistivity of the particulate matter due to the change of the PM temperature Tpm and the routine of the PM removal control can be simplified.

[0172] Furthermore, when the engine 11 is the diesel-fuel engine, the PM removal control may be a control for delaying a fuel injection timing or performing a post fuel injection after a main fuel injection to cause the fuel to burn in the exhaust pipe, in other words, increase the energy discharged from the engine 11 to the exhaust passage, thereby increasing the catalyzer temperature Tehc by heat produced by the burning of the fuel and supplying excessive oxygen to the catalyzer 13 to bum the particulate matter, thereby removing the particulate matter. In this case, a part of the fuel supplied to the combustion chambers of the engine 11 is used for increasing the temperature of the exhaust gas. However, according to the invention, the PM removal control is not unnecessarily executed and thus, the fuel consumption rate can be prevented from increasing.

[0173] Further, when the engine 11 is the gasoline-fuel engine or the diesel-fuel engine, the first and second apparatuses may be configured or programmed to execute the PM removal control for advancing the timing of opening the exhaust valves to discharge the combustion gas having high temperature to the exhaust passage, in other words, increase the energy discharged from the engine 11 to the exhaust passage, thereby increasing the catalyzer temperature Tehc and thereafter, setting the air-fuel ratio of the mixture gas supplied to the engine 11 to the lean air-fuel ratio to supply a sufficient amount of the oxygen to the catalyzer 13 to burn the particulate matter, thereby removing the particulate matter. Therefore, the exhaust gas purification apparatus according to the invention may be an apparatus for burning and removing the particulate matter by increasing the catalyzer temperature Tehc, i.e., the temperature of the particulate matter accumulating in the catalyzer 13 by the energy discharged from the engine 11 to the exhaust passage without energizing the catalyzer 13.

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