JP2012021419A - Control system of electric heating catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove a PM more suitably which adheres on an end face of an insulating member installed between a carrier and a case in an EHC when the EHC is used as a three way catalyst.SOLUTION: An air-fuel ratio of exhaust of an internal combustion engine is repeatedly changed into a lean air-fuel ratio and a rich air-fuel ratio, and thereby its average value is maintained in the vicinity of a theoretical air-fuel ratio. While the PM adhering on the end face of the insulating member of the EHC is removed, when a PM adhesion amount is large, the air-fuel ratio during the rich air-fuel ratio is set lower than the case that the PM adhesion amount is small, and furthermore, a period of the rich air-fuel ratio is set shorter or a period of the lean air-fuel ratio is set longer.

Description

  The present invention relates to a control system for an electrically heated catalyst provided in an exhaust passage of an internal combustion engine.

Conventionally, as an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine, an electrically heated catalyst (hereinafter referred to as EHC) that is heated by energization of a carrier has been developed. Patent Document 1 discloses a technology related to an exhaust purification device for a hybrid vehicle using EHC.

Patent Document 2 discloses a configuration in which an oxidation catalyst, a particulate filter, and a NOx absorbent are arranged in this order from the upstream side in the exhaust passage of an internal combustion engine. According to this, NO ₂ is produced by NO in the exhaust gas is oxidized in the oxidation catalyst. The generated NO ₂ reacts with the soot trapped in the particulate filter, and soot burns. NO produced by the reaction between NO ₂ and soot is absorbed by the NOx absorbent.

  In Patent Document 3, in order to increase the activity of the three-way catalyst provided in the exhaust passage, the exhaust air-fuel ratio is larger than the stoichiometric air-fuel ratio until the three-way catalyst is in a first oxygen storage state in which oxygen is sufficiently stored. A technique for maintaining a lean air-fuel ratio and then maintaining a rich air-fuel ratio smaller than the stoichiometric air-fuel ratio until the three-way catalyst reaches a second oxygen storage state in which oxygen is sufficiently released is disclosed.

JP 2009-281254 A JP 2006-283766 A JP 2004-285948 A JP 2006-112414 A JP 2004-068804 A JP 2000-356155 A

  In the EHC heated by energizing the carrier, it is necessary to insulate the flow of electricity between the case (or the exhaust pipe) housing the carrier (catalyst body) and the carrier. Therefore, an insulating member for insulating electricity is provided between the carrier and the case. However, particulate matter (hereinafter referred to as PM) in exhaust gas may adhere to the upstream or downstream end face of the insulating member. When the adhesion amount of PM on the end face of the insulating member increases, there is a possibility that the carrier and the case are short-circuited by the PM.

  As a method for suppressing the adhesion of PM to the end face of the mat, a method of installing a particulate filter in the exhaust passage upstream of the EHC can be considered. However, if the particulate filter is installed at such a position, it tends to increase the back pressure and deteriorate the warm-up performance of EHC. In addition, the mountability is deteriorated and the cost is increased. Furthermore, even if a particulate filter is installed, it is difficult to collect all the PM in the exhaust gas, and it is difficult to completely prevent the PM from adhering to the end face of the mat.

  Further, when EHC is used as a three-way catalyst, as in the case of a normal three-way catalyst, it is necessary to control the air-fuel ratio of the exhaust to be close to the stoichiometric air-fuel ratio in order to maintain its exhaust purification capacity high.

  The present invention has been made in view of such problems, and when EHC is used as a three-way catalyst, PM adhering to the end face of an insulating member provided between the carrier and the case in the EHC is obtained. It aims at removing more suitably.

  In the present invention, a catalyst having an oxidation function is supported on the end surface of an insulating member of EHC, which is a three-way catalyst, or on a catalyst supporting member provided in the vicinity of the end surface. Further, by repeatedly changing the air-fuel ratio of the exhaust gas of the internal combustion engine to the lean air-fuel ratio and the rich air-fuel ratio, the average value is maintained near the stoichiometric air-fuel ratio. When removing PM adhering to the end face of the insulating member of the EHC, when the amount of PM adhering on the end face of the insulating member is large, the air-fuel ratio at the rich air-fuel ratio is greater than when the amount of PM adhering is small. Lower the rich air / fuel ratio period or make the lean air / fuel period longer.

The control system for the electrically heated catalyst according to the present invention includes:
A three-way catalyst provided in an exhaust passage of an internal combustion engine,
A carrier that generates heat when energized;
A case for storing the carrier;
An insulating member provided between the carrier and the case for insulating electricity;
An electrically heated catalyst having an oxidation function carried on at least one of the upstream or downstream end face of the insulating member, or a catalyst carrying member provided in the vicinity of the end face;
Air-fuel ratio control means for maintaining the average value in the vicinity of the theoretical air-fuel ratio by repeatedly changing the air-fuel ratio of the exhaust gas of the internal combustion engine to a lean air-fuel ratio and a rich air-fuel ratio;
PM adhesion amount estimation means for estimating the amount of particulate matter adhered to the end face of the insulating member,
When the particulate matter adhering to the end face of the insulating member is removed, if the air-fuel ratio control means has a large amount of PM attached to the end face of the insulating member estimated by the PM attached amount estimating means, the PM attachment Compared to when the amount is small, the air-fuel ratio when the exhaust air-fuel ratio is controlled to a rich air-fuel ratio is made lower, and the rich air-fuel ratio period is made shorter or the lean air-fuel ratio period is made longer.

  According to the present invention, when the amount of PM adhering to the end face of the insulating member is large, more unburned fuel components can be supplied to the catalyst having an oxidation function and is necessary for the oxidation of the unburned fuel components. The supply amount of oxygen can be ensured. Thereby, oxidation / removal of PM can be promoted. As a result, it is possible to suppress a short circuit between the carrier and the case in the EHC without installing a particulate filter upstream of the EHC. Moreover, since the average value of the air-fuel ratio of the exhaust can be maintained in the vicinity of the stoichiometric air-fuel ratio, the exhaust purification ability of EHC, which is a three-way catalyst, can be maintained high.

  According to the present invention, when EHC is used as a three-way catalyst, PM adhering to the end face of the insulating member provided between the carrier and the case in the EHC can be more suitably removed.

1 is a diagram illustrating a schematic configuration of an intake / exhaust system of an internal combustion engine according to Embodiment 1. FIG. 1 is a diagram illustrating a schematic configuration of an EHC according to Embodiment 1. FIG. FIG. 3 is a first diagram illustrating a schematic configuration of another EHC according to the first embodiment. FIG. 6 is a second diagram illustrating a schematic configuration of another EHC according to the first embodiment. FIG. 6 is a third diagram illustrating a schematic configuration of another EHC according to the first embodiment. It is a figure which shows the relationship between the rich side A / F and lean side A / F, and PM adhesion amount in stoichiometric A / F control based on Example 1. FIG. 6 is a time chart showing the transition of the air-fuel ratio of exhaust when executing stoichiometric A / F control according to the first embodiment. It is a figure which shows the relationship between the rich side A / F and the temperature rise amount of an oxidation catalyst at the time of execution of stoichiometric A / F control based on Example 1. FIG. 3 is a flowchart illustrating a flow of stoichiometric A / F control according to the first embodiment. It is a figure which shows the relationship between the fuel injection timing from the fuel injection valve in an internal combustion engine, and the discharge amount of the unburned fuel component from an internal combustion engine based on Example 2. FIG. It is a figure which shows the relationship between the fuel injection timing from the fuel injection valve in an internal combustion engine, and PM adhesion amount based on Example 2. FIG. 6 is a flowchart illustrating a flow of fuel injection timing control according to the second embodiment. It is a figure which shows the relationship between the exhaust stroke injection ratio and PM adhesion amount based on Example 3. FIG. 12 is a flowchart showing a flow of exhaust stroke injection control according to the third embodiment. 12 is a flowchart illustrating a flow of air supply stop control according to a fourth embodiment. 12 is a flowchart illustrating a flow of air supply amount reduction control according to a modification of the fourth embodiment. FIG. 18 is a flowchart shown in FIG. 17 showing a flow of overlean fuel injection control according to the fifth embodiment.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
[Schematic configuration of intake and exhaust system of internal combustion engine]
FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a gasoline engine for driving a vehicle. Each cylinder of the internal combustion engine 1 is provided with a fuel injection valve. The fuel injection valve may inject fuel into the intake port, or may inject fuel directly into the cylinder. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1.

  An air flow meter 4 and a throttle valve 5 are provided in the intake passage 2. The air flow meter 4 detects the intake air amount of the internal combustion engine 1. The throttle valve 5 adjusts the flow rate of the intake air flowing through the intake passage 2 by changing the cross-sectional area of the intake passage 2.

  An EHC 6 is provided in the exhaust passage 3. The EHC 6 is supplied with power from the battery 7. The detailed configuration of the EHC 6 will be described later.

An air-fuel ratio sensor 11 and an upstream exhaust temperature sensor 12 are provided upstream of the EHC 6 in the exhaust passage 3. An O ₂ sensor 13 and a downstream exhaust temperature sensor 14 are provided downstream of the EHC 6 in the exhaust passage 3. The air-fuel ratio sensor 11 detects the air-fuel ratio of the exhaust. The upstream and downstream exhaust temperature sensors 12 and 14 detect the temperature of the exhaust. The O ₂ sensor 13 detects the oxygen concentration in the exhaust.

The internal combustion engine 1 is also provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. An air flow meter 4, an air-fuel ratio sensor 11, an upstream side exhaust temperature sensor 12, an O ₂ sensor 13, and a downstream side exhaust temperature sensor 14 are electrically connected to the ECU 10. Further, the ECU 10 is electrically connected to a cooling water temperature sensor 15 that detects the temperature of the cooling water of the internal combustion engine 1 and an accelerator opening sensor 16 that detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. ing. These output signals are input to the ECU 10.

  Further, the ECU 10 is electrically connected to the throttle valve 5, the EHC 6, and a fuel injection valve (not shown) of the internal combustion engine 1. The operation of these devices is controlled by the ECU 10.

[Schematic configuration of EHC]
FIG. 2 is a diagram illustrating a schematic configuration of the EHC 6 according to the present embodiment. FIG. 2 is a cross-sectional view of the EHC 6 cut in the longitudinal direction along the central axis A of the exhaust passage 3. Since the shape of the EHC 6 is line symmetric with respect to the central axis A, only the upper part is shown in FIG.

  The EHC 6 according to this embodiment includes a catalyst carrier 61, a case 62, a mat 63, an inner tube 64, and an electrode 65. The catalyst carrier 61 is formed in a cylindrical shape, and is installed so that its central axis is coaxial with the central axis A of the exhaust passage 3. In this embodiment, the catalyst carrier 61 carries a three-way catalyst 67 as an exhaust purification catalyst.

  The case 62 houses the catalyst carrier 61. A mat 63 is sandwiched between the outer wall surface of the catalyst carrier 61 and the inner wall surface of the case 62. An inner pipe 64 is sandwiched between the mats 63. A pair of electrodes 65 (only one electrode is shown in FIG. 2) is connected to the catalyst carrier 61.

  The catalyst carrier 61 is formed of a material that generates electrical resistance and generates heat when energized. Examples of the material of the catalyst carrier 61 include SiC. The catalyst carrier 61 has a plurality of passages extending in the direction in which the exhaust flows (that is, in the direction of the central axis A) and having a cross section perpendicular to the direction in which the exhaust flows in a honeycomb shape. Exhaust gas flows through this passage. Note that the cross-sectional shape of the catalyst carrier 61 having a cross section orthogonal to the central axis A may be, for example, an ellipse. The central axis A is a central axis common to the exhaust passage 3, the catalyst carrier 61, the inner pipe 64, and the case 62.

  Electric power is supplied to the catalyst carrier 61 by supplying electric power from the battery 7 to the pair of electrodes 65 connected to the catalyst carrier 61. When energized, the catalyst carrier 61 generates heat due to its electrical resistance. As a result, the three-way catalyst supported on the catalyst carrier 61 is heated and its activation is promoted.

  The mat 63 is made of an electrical insulating material. As a material for forming the mat 63, a ceramic fiber mainly composed of alumina can be exemplified. The mat 63 is wound around the outer peripheral surface of the catalyst carrier 61 and the outer peripheral surface of the inner tube 64. By providing the mat 63 between the catalyst carrier 61 and the case 62, electricity is suppressed from flowing to the case 62 when the catalyst carrier 61 is energized.

The inner tube 64 is made of an electrical insulating material. As a material for forming the inner tube 64, alumina can be exemplified. The inner tube 64 is formed in a tubular shape centered on the central axis A. As shown in FIG. 2, the length of the inner tube 64 in the direction of the central axis A is longer than that of the mat 63. Therefore, the upstream and downstream end portions 64 a and 64 b of the inner pipe 64 protrude from the upstream and downstream end surfaces 63 a and 63 b of the mat 63.

The case 62 is made of metal. As a material forming the case 62, a stainless steel material can be exemplified. The case 62 includes an accommodating portion 62a that includes a curved surface parallel to the central axis A, and a tapered portion 62b that connects the accommodating portion 62a and the exhaust passage 3 on the upstream side and the downstream side of the accommodating portion 62a. 62c. The passage sectional area of the accommodating portion 62a is larger than the passage sectional area of the exhaust passage 3, and the catalyst carrier 61, the mat 63, and the inner pipe 64 are accommodated therein. The tapered portions 62b and 62c have a tapered shape in which the passage cross-sectional area decreases as the distance from the accommodating portion 62a increases.

  In the case 62 and the inner tube 64, through holes 62c and 64c are opened to allow the electrode 65 to pass therethrough. Further, no mat 63 is provided around the electrode 65 until the electrode 65 is connected to the catalyst carrier 61 in the case 62. A support member 66 that supports the electrode 65 is provided in the through-hole 62 c opened in the case 62. The support member 66 is formed of an electrical insulating material, and is provided between the case 62 and the electrode 65 without a gap.

  In the EHC 6 configured as described above, water condensed on the upstream side of the catalyst carrier 61 may flow on the exhaust passage 3 or the inner wall of the case 62 and adhere to the mat 63. At this time, since water flows through the inner wall of the accommodating portion 62a, the water adheres to the mat 63 between the inner tube 64 and the accommodating portion 62a. In other words, since the inner pipe 64 protrudes upstream and downstream of the mat 63, water is prevented from entering the direction of the central axis A from the inner pipe 64. As a result, the case 62 and the catalyst carrier 61 are prevented from being short-circuited by water on the upstream and downstream end faces 63a, 63b of the mat 63.

Further, PM in the exhaust gas adheres to the upstream or downstream end faces 63a and 63b of the mat 63. When this amount of PM adhesion increases, the case 62 and the catalyst carrier 61 may be short-circuited by the PM. Therefore, in this embodiment, the oxidation catalyst 68 is supported on the protrusions 64 a and 64 b from the mat 63 on the upstream side and the downstream side of the inner pipe 64. When the unburned fuel component (HC, CO) in the exhaust gas is supplied to the oxidation catalyst 68, the unburned fuel component is oxidized in the oxidation catalyst 68. The PM adhering to the end faces 63a and 63b of the mat 63 can be oxidized and removed by the oxidation heat generated at that time. As a result, it is possible to prevent the case 62 and the catalyst carrier 61 from being short-circuited by PM.

The catalyst supported on the protrusions 64a and 64b of the inner pipe 64 is not necessarily an oxidation catalyst, and may be any catalyst as long as it has an oxidation function.

In this embodiment, EHC6 corresponds to the electrically heated catalyst according to the present invention. The catalyst carrier 61 corresponds to the carrier according to the present invention, the case 62 corresponds to the case according to the present invention, and the mat 63 corresponds to the insulating member according to the present invention. The protrusions 64a and 64b correspond to the catalyst support member according to the present invention, and the oxidation catalyst 68 corresponds to the catalyst having an oxidation function according to the present invention.

[Other configurations of EHC]
The configuration of the EHC 6 according to the present embodiment is not limited to the configuration shown in FIG. 3 to 5 are diagrams showing other configurations of the EHC 6 according to the present embodiment. A description of the same parts as those in the configuration shown in FIG. 2 is omitted.

  In the EHC 6 shown in FIGS. 3 to 5, the inner tube 64 is provided such that the outer peripheral surface thereof is in contact with the inner peripheral surface of the housing portion 62 a of the case 62. The mat 63 is sandwiched between the outer wall surface of the catalyst carrier 61 and the inner wall surface of the inner tube 64.

In the EHC 6 shown in FIG. 3, an oxidation catalyst 68 is supported on the inner wall surfaces of the protrusions 64 a and 64 b from the mat 63 on the upstream side and the downstream side of the inner pipe 64. EHC6 shown in FIG.
, The oxidation catalyst 68 is carried on the upstream and downstream end faces 63a, 63b of the mat 63. In the EHC 6 shown in FIG. 5, the upstream and downstream ends of the catalyst carrier 61 protrude from the mat 63. An oxidation catalyst 68 is supported on the outer peripheral surface of the catalyst carrier 61 in the vicinity of the upstream and downstream protrusions.

  3 to 5, similarly to the configuration shown in FIG. 2, the unburned fuel component in the exhaust is supplied to the oxidation catalyst 68, and the unburned fuel component is oxidized in the oxidation catalyst 68. The The PM adhering to the end faces 63a and 63b of the mat 63 can be oxidized and removed by the oxidation heat generated at that time.

[Exhaust air / fuel ratio control]
In this embodiment, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is set to a rich air-fuel ratio lower than the stoichiometric air-fuel ratio in order to keep the exhaust purification capacity of the three-way catalyst 67 supported on the catalyst carrier 61 high. The air-fuel ratio is repeatedly changed to a lean air-fuel ratio higher than the stoichiometric air-fuel ratio, and the average value is maintained near the stoichiometric air-fuel ratio. Hereinafter, such exhaust air-fuel ratio control is referred to as stoichiometric A / F control. The air-fuel ratio of the exhaust can be controlled by adjusting the fuel injection amount and intake air amount in the internal combustion engine 1.

  Further, as described above, it is necessary to supply unburned fuel components to the oxidation catalyst 68 in order to promote the oxidation of PM adhering to the end faces 63a and 63b of the mat 63 of the EHC 6 and to remove the PM. By executing the stoichiometric A / F control, an unburned fuel component can be supplied to the oxidation catalyst 68 when the air-fuel ratio is rich, and oxygen can be supplied to the oxidation catalyst 68 when the air-fuel ratio is lean. Therefore, the PM adhering to the end faces 63a and 63b of the mat 63 can be oxidized and removed.

  Further, in this embodiment, when removing PM adhering to the end faces 63a and 63b of the mat 63, when the rich air-fuel ratio is controlled according to the adhering amount (hereinafter simply referred to as PM adhering amount). The air-fuel ratio and the rich air-fuel ratio period are changed.

  FIG. 6 shows an air-fuel ratio at the time of rich air-fuel ratio (hereinafter also referred to as a rich side A / F) and an air-fuel ratio at the time of lean air-fuel ratio (hereinafter referred to as lean-side A / F) in stoichiometric A / F control. It is a figure which shows the relationship between PM adhesion amount and a case. In FIG. 6, the horizontal axis represents the PM adhesion amount, and the vertical axis represents the air-fuel ratio of the exhaust. In FIG. 6, the solid line indicates the rich side A / F, and the broken line indicates the lean side A / F. In FIG. 6, kpm0 represents a PM adhesion amount serving as a threshold for executing the removal of PM from the end faces 63a and 63b of the mat 63.

  FIG. 7 is a time chart showing the transition of the air-fuel ratio of the exhaust when the stoichiometric A / F control is executed. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the air-fuel ratio of the exhaust. In FIG. 7, the solid line indicates a case where the PM adhesion amount is relatively large, and the broken line indicates a case where the PM adhesion amount is relatively small. Δtr represents a period during which the rich air-fuel ratio is set (hereinafter also referred to as a rich A / F period).

  FIG. 8 is a diagram showing the relationship between the rich side A / F and the temperature increase amount of the oxidation catalyst 68 when the stoichiometric A / F control is executed. In FIG. 8, the horizontal axis represents the rich side A / F, and the vertical axis represents the temperature increase amount of the oxidation catalyst 68.

As shown in FIGS. 6 and 7, in this embodiment, the richer A / F control in the stoichiometric A / F control is made lower and the rich A / F period is made shorter as the PM adhesion amount is larger. Thereby, when the amount of PM adhesion is large, more unburned fuel components can be supplied to the oxidation catalyst 68, and the supply amount of oxygen necessary for oxidation of the unburned fuel components can be ensured. Therefore, as shown in FIG. 8, the amount of temperature increase due to oxidation of the unburned fuel component can be further increased, thereby further promoting the oxidation / removal of PM adhering to the end faces 63a, 63b of the mat 63. Is possible. As a result, a short circuit between the catalyst carrier 61 and the case 62 in the EHC 6 can be suppressed with a higher probability.

  Further, according to the stoichiometric A / F control as described above, the average value of the air-fuel ratio of the exhaust can be maintained in the vicinity of the theoretical air-fuel ratio even when the rich side A / F is made lower. Therefore, the exhaust purification capacity of the three-way catalyst 67 supported on the catalyst carrier 61 can be maintained high.

  Instead of or simultaneously with shortening the rich A / F period, a period during which the air-fuel ratio of the exhaust is set to be a lean air-fuel ratio (hereinafter sometimes referred to as a lean A / F period) may be lengthened. Good. This also makes it possible to ensure the supply amount of oxygen necessary for oxidizing the unburned fuel component when the rich side A / F is lowered, and to bring the average value of the exhaust air / fuel ratio close to the stoichiometric air / fuel ratio. Can be maintained.

  Even if the lean side A / F is increased when the rich side A / F is lowered without changing the lengths of the rich A / F period and the lean A / F period, oxygen necessary for oxidizing the unburned fuel component Can be ensured, and the average value of the air-fuel ratio of the exhaust gas can be maintained in the vicinity of the theoretical air-fuel ratio. However, as described above, the value of the lean side A / F is not changed, and the rich side A / F is made lower, and at the same time, the lean side A / F is made higher. Can be made lower. As a result, more unburned fuel components can be supplied to the oxidation catalyst 68, and therefore oxidation and removal of PM adhering to the end faces 63a and 63b of the mat 63 can be further promoted.

[Stoichi A / F control flow]
Here, the flow of stoichiometric A / F control according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals.

  In this flow, first, in step S101, the PM adhesion amount kpm on the end faces 63a and 63b of the mat 63 is calculated. The PM adhesion amount kpm can be estimated based on the history of the operating state of the internal combustion engine 1 or the like.

  Next, in step S102, the coolant temperature Thw of the internal combustion engine 1 and the temperature Tcat of the EHC 6 are read. The coolant temperature Thw of the internal combustion engine 1 is detected by a coolant temperature sensor 15. The temperature Tcat of the EHC 6 is calculated based on the detection value of the downstream side exhaust temperature sensor 14.

  Next, in step S103, it is determined whether or not the PM adhesion amount kpm is greater than or equal to the PM removal execution threshold value kpm0. The threshold value kpm0 is determined in advance based on experiments or the like. If a negative determination is made in step S103, the process of step S108 is then executed. In step S108, the rich side A / F and the rich A / F period in the stoichiometric A / F control are respectively set to standard values. The standard values are values of the rich side A / F and the rich A / F period when normal stoichiometric A / F control is executed, and are predetermined values. Next, in step S107, stoichiometric A / F control is performed with the rich side A / F and rich A / F periods as standard values.

If an affirmative determination is made in step S103, then the process of step S104 is executed. In step S104, it is determined whether or not the coolant temperature Thw of the internal combustion engine 1 is equal to or higher than the lower limit temperature Thw0 for PM removal execution. The lower limit temperature Thw0 is determined in advance based on experiments and the like. If an affirmative determination is made in step S104, the process of step S105 is executed next, and if a negative determination is made, the process of step S108 is executed next.

  In step S105, it is determined whether or not the temperature Tcat of the EHC 6 is not less than the lower limit temperature Tcat0 for executing PM removal and not more than the upper limit temperature Tcat1. The lower limit temperature Tcat0 and the upper limit temperature Tcat1 are determined in advance based on experiments and the like. If an affirmative determination is made in step S105, the process of step S106 is executed next. If a negative determination is made, the process of step S108 is executed next.

  In step S106, Rr_pm and Δtr_pm which are the rich side A / F and rich A / F period in the stoichiometric A / F control when removing PM adhering to the end faces 63a and 63b of the mat 63 are set to the PM adhering amount kpm. It is calculated based on each. The value of Rr_pm is smaller than the standard value of the rich A / F, and the value of Δtr_pm is smaller than the standard value of the rich A / F period. Further, the values of Rr_pm and Δtr_pm are both smaller as the PM adhesion amount kpm is larger. The relationship between the PM adhesion amount and Rr_pm and the relationship between the PM adhesion amount and Δtr_pm can be obtained in advance based on experiments or the like, and these relationships are stored in the ECU 10 as a map.

  Next, in step S107, stoichiometric A / F control is performed in which the rich A / F is set to Rr_pm calculated in step S106, and the rich A / F period is set to Δtr_pm calculated in step S106.

  At the time of PM removal execution, instead of shortening the rich A / F period in the stoichiometric A / F control, or at the same time, when the lean A / F period is lengthened, in step S106 in the above flow, A lean A / F period is calculated based on the PM adhesion amount. At this time, the lean A / F period becomes longer as the PM adhesion amount increases. In this case, in step S107, stoichiometric A / F control is executed with the lean A / F period as the value calculated in step S106.

<Example 2>
A second embodiment of the present invention will be described. Here, only differences from the first embodiment will be described.

[Fuel injection timing control]
In this embodiment, in each cylinder of the internal combustion engine 1, a fuel injection valve is provided in the intake port, and fuel is injected into the intake port from the fuel injection valve. In this embodiment, when the PM adhering to the upstream or downstream end faces 63a, 63b of the mat 63 is removed, the fuel injection timing from the fuel injection valve is controlled, so that the oxidation catalyst 68 is not subjected to the control. Supply fuel components. At this time, the fuel injection timing is changed according to the PM adhesion amount.

  FIG. 10 is a diagram showing the relationship between the fuel injection timing from the fuel injection valve in the internal combustion engine 1 and the discharge amount of the unburned fuel component from the internal combustion engine 1. In FIG. 10, the horizontal axis represents the fuel injection timing from the fuel injection valve, and the vertical axis represents the discharge amount of the unburned fuel component. In the horizontal axis of FIG. 10, the intake stroke top dead center is set to 0 CA °.

FIG. 11 is a diagram showing the relationship between the fuel injection timing from the fuel injection valve in the internal combustion engine 1 and the PM adhesion amount. In FIG. 11, the horizontal axis represents the PM adhesion amount, and the vertical axis represents the fuel injection timing from the fuel injection valve. In FIG. 11, kpm0 is an end face 63 of the mat 63.
a represents the amount of PM adhering to be a threshold value for executing the removal of PM from a and 63b.

  As shown in FIG. 10, when fuel injection is performed in the intake stroke, the amount of unburned fuel component increases as the fuel injection timing is delayed until a certain time. That is, the amount of unburned fuel component supplied to the oxidation catalyst 68 increases. Therefore, in the present embodiment, as shown in FIG. 11, the fuel injection timing is delayed within a range until the amount of unburned fuel components discharged from the internal combustion engine 1 reaches the maximum value as the PM adhesion amount increases. .

  Thereby, when the amount of PM attached is large, more unburned fuel components can be supplied to the oxidation catalyst 68. Therefore, it becomes possible to further promote the oxidation / removal of PM adhering to the end faces 63a and 63b of the mat 63. As a result, a short circuit between the catalyst carrier 61 and the case 62 in the EHC 6 can be suppressed with a higher probability.

  Even if the fuel injection timing from the fuel injection valve is different from the standard value, the average value of the exhaust air-fuel ratio can be maintained near the theoretical air-fuel ratio. Therefore, the exhaust purification capacity of the three-way catalyst 67 supported on the catalyst carrier 61 can be maintained high.

[Flow of fuel injection timing control]
Here, the flow of fuel injection timing control according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals. Note that steps S101 to S105 in this flow are the same as those in the flow shown in FIG.

  In this flow, if a negative determination is made in step S103, S104, or S105, the process of step S208 is executed. In step S208, the fuel injection timing from the fuel injection valve is set to a standard value. The standard value is determined in advance and is the value of the fuel injection timing during normal operation. Next, in step S207, fuel injection with the fuel injection timing as a standard value is executed.

  If an affirmative determination is made in step S105, then the process of step S206 is executed. In step S206, tinj_pm, which is the fuel injection timing from the fuel injection valve when removing PM adhering to the end faces 63a, 63b of the mat 63, is calculated based on the PM adhering amount kpm. tinj_pm is a time later than the standard value of the fuel injection time, and becomes a later time as the amount of PM adhesion increases. The relationship between the PM adhesion amount and tinj_pm can be obtained in advance based on experiments or the like, and these relationships are stored in the ECU 10 as a map.

  Next, in step S207, fuel injection is performed with the fuel injection timing as tinj_pm calculated in step S206.

<Example 3>
A third embodiment of the present invention will be described. Here, only differences from the first embodiment will be described.

[Exhaust stroke injection control]
In this embodiment, in each cylinder of the internal combustion engine 1, fuel is directly injected into the cylinder from the fuel injection valve. In this embodiment, when removing the PM adhering to the upstream or downstream end faces 63a, 63b of the mat 63, in addition to the normal main fuel injection performed in the compression stroke, the fuel injection valve in the exhaust stroke The unburned fuel component is supplied to the oxidation catalyst 68 by executing the exhaust stroke injection for injecting the fuel. At this time, the exhaust stroke injection ratio, which is the ratio of the fuel injection amount by the exhaust stroke injection to the total fuel injection amount, is changed according to the PM adhesion amount.

  FIG. 13 is a diagram showing the relationship between the exhaust stroke injection ratio and the PM adhesion amount. In FIG. 13, the horizontal axis represents the PM adhesion amount, and the vertical axis represents the exhaust stroke injection ratio. In FIG. 13, kpm0 represents a PM adhesion amount serving as a threshold for executing the removal of PM from the end faces 63a and 63b of the mat 63.

  The fuel injected into the cylinder of the internal combustion engine 1 by the exhaust stroke injection is discharged from the internal combustion engine 1 as an unburned fuel component. Therefore, the higher the exhaust stroke injection ratio, the greater the amount of unburned fuel component supplied to the oxidation catalyst 68. Therefore, in the present embodiment, as shown in FIG. 13, the exhaust stroke injection ratio is increased as the PM adhesion amount increases.

  Thereby, when the amount of PM attached is large, more unburned fuel components can be supplied to the oxidation catalyst 68. Therefore, it becomes possible to further promote the oxidation / removal of PM adhering to the end faces 63a and 63b of the mat 63. As a result, a short circuit between the catalyst carrier 61 and the case 62 in the EHC 6 can be suppressed with a higher probability.

  Even if a part of the total fuel injection amount injected from the fuel injection valve is injected by the exhaust stroke injection, the average value of the exhaust air / fuel ratio can be maintained in the vicinity of the theoretical air / fuel ratio. Therefore, the exhaust purification capacity of the three-way catalyst 67 supported on the catalyst carrier 61 can be maintained high.

[Flow of exhaust stroke injection control]
Here, the flow of the exhaust stroke injection control according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals. Note that steps S101 to S105 in this flow are the same as those in the flow shown in FIG.

  In this flow, if a negative determination is made in step S103, S104, or S105, the process of step S308 is executed. In step S308, execution of exhaust stroke injection is prohibited. Next, in step S307, only normal main fuel injection is executed by the fuel injection valve.

  If an affirmative determination is made in step S105, then the process of step S306 is executed. In step S306, the exhaust stroke injection ratio when exhaust stroke injection is executed to remove PM adhering to the end faces 63a and 63b of the mat 63 is calculated. The exhaust stroke injection ratio increases as the PM adhesion amount increases. The relationship between the PM adhesion amount and the exhaust stroke injection ratio can be obtained in advance based on experiments or the like, and these relationships are stored in the ECU 10 as a map.

  Next, in step S307, the exhaust stroke injection is executed in addition to the main fuel injection, with the exhaust stroke injection ratio being the value calculated in step S306.

<Example 4>
Embodiment 4 of the present invention will be described. Here, only differences from the first embodiment will be described.

[Fuel cut control]
In the present embodiment, in the internal combustion engine 1, so-called fuel cut control is performed in which fuel injection from the fuel injection valve is stopped during deceleration operation. When the fuel cut control is executed, the opening degree of the throttle valve 5 is also reduced, and the intake air amount of the internal combustion engine 1 is reduced. However, since no combustion is performed in the internal combustion engine 1, fresh air (air) sucked into the internal combustion engine 1 is directly discharged into the exhaust passage 3. Therefore, a large amount of oxygen is supplied to EHC6. As a result, if a sufficient temperature is maintained, oxidation of PM adhering to the end faces 63a and 63b of the mat 63 is promoted.

  However, when the low temperature fresh air is supplied to the EHC 6, the temperature of the upstream end face 63a of the mat 63 may be lowered. In this case, on the contrary, the oxidation reaction of PM is suppressed.

  The three-way catalyst 67 supported on the catalyst carrier 61 of EHC 6 has an oxygen storage capacity. Therefore, even if the execution of the fuel cut control is started and a large amount of oxygen is supplied to the EHC 6, the oxygen concentration on the downstream side of the EHC 6 is reduced while the oxygen is stored in the three-way catalyst 67. As a result, when the amount of oxygen supplied to the downstream side of the EHC 6, that is, the downstream side end surface 63 b of the mat 63 is insufficient, the oxidation reaction of PM adhering to the downstream side end surface 63 b is suppressed.

  Therefore, in this embodiment, after the start of the fuel cut control, it is determined that a sufficient amount of oxygen is supplied to the downstream side of the EHC 6 to oxidize and remove the PM adhering to the downstream end surface 63b of the mat 63. At this point, control for stopping the supply of air to the EHC 6 (hereinafter, this control is referred to as air supply stop control) is executed.

  By executing the air supply stop control at such timing, it is possible to reduce the temperature of the upstream end surface 63a of the mat 63 while supplying a sufficient amount of oxygen to the upstream and downstream end surfaces 63a, 63b of the mat 63. It can be suppressed as much as possible. As a result, it is possible to promote the oxidation / removal of PM on the upstream and downstream end faces 63a and 63b of the mat 63 when the fuel cut control is executed.

  The air supply stop control can be realized by closing control of the throttle valve 5, closing control of the intake valve or exhaust valve in the internal combustion engine 1, and the like.

[Air supply stop control flow]
Here, the flow of the air supply stop control according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals.

In this flow, first, in step S401, it is determined whether or not fuel cut control has been executed. If it is determined in S401 that the fuel cut control has been executed, then in step S402, it is determined whether or not the O ₂ concentration Cd on the downstream side of the EHC 6 is equal to or less than a predetermined concentration Cd0. Here, the predetermined concentration Cd0 is a threshold at which it is possible to determine that the O ₂ concentration Cd on the downstream side of the EHC 6 has decreased due to oxygen being stored in the three-way catalyst 67. Such a predetermined concentration Cd0 can be obtained in advance based on experiments or the like.

If it is determined in step S403 that the O ₂ concentration Cd on the downstream side of EHC6 is equal to or lower than the predetermined concentration Cd0, then in step S404, the O ₂ concentration Cd on the downstream side of EHC6 becomes equal to or lower than the predetermined concentration Cd0. The integrated value (hereinafter referred to as the integrated air amount) Σga of the intake air amount of the internal combustion engine 1 is calculated.

Next, in step S405, it is determined whether or not the integrated air amount Σga is equal to or greater than a predetermined integrated air amount Σga1. Here, the predetermined integrated air amount Σga1 is a threshold at which it can be determined that a sufficient amount of oxygen has been supplied to the downstream side of the EHC 6 to oxidize and remove the PM adhering to the downstream end surface 63b of the mat 63. Such a predetermined integrated air amount Σga1 can be obtained in advance based on experiments or the like.

  If it is determined in step S405 that the integrated air amount Σga has become equal to or greater than the predetermined integrated air amount Σga1, then in step S406, air supply stop control is executed.

[Modification]
A modification of this embodiment will be described. In the above, when the fuel cut control is executed, the air supply stop control is executed so as to suppress the temperature drop of the upstream end surface 63a of the mat 63 of the EHC 6. However, if the excessive temperature drop of the upstream end face 63a of the mat 63 can be suppressed by reducing the air supply amount to the EHC 6 (hereinafter referred to as supply air amount), the supply of air to the EHC 6 is not necessarily stopped. do not have to. If the temperature at which PM can be oxidized can be maintained without stopping the supply of air to the EHC 6, more oxygen can be supplied. Therefore, oxidation / removal of PM can be performed during fuel cut control. It can be promoted more.

  In addition, when control for reducing the supply air amount (hereinafter, this control is referred to as air supply amount reduction control) is performed according to the temperature of the air supplied to the EHC 6 (hereinafter referred to as supply air temperature). The amount of air may be controlled. When the supply air temperature is high because the temperature of the internal combustion engine 1 at the time of executing the fuel cut control is high, the temperature at which PM can be oxidized can be maintained even if the supply air amount is increased. Therefore, the higher the supply air temperature, the more the supply air amount when the air supply amount decrease control is executed (that is, the decrease amount of the supply air amount is decreased). Thereby, more oxygen can be supplied to EHC6, maintaining the temperature which can oxidize PM.

  The supply air amount can be controlled by adjusting the opening degree of the throttle valve 5 and the opening / closing timing of the intake valve or the exhaust valve of the internal combustion engine 1.

[Flow of air supply reduction control]
Here, the flow of the air supply amount reduction control according to this modification will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals. Note that steps S401 to S405 in this flow are the same as those in the flow shown in FIG.

  In this flow, if it is determined in step S405 that the integrated air amount Σga is equal to or greater than the predetermined integrated air amount Σga1, then in step S506, the supply air temperature Tair detected by the upstream side exhaust temperature sensor 12 is read. .

  Next, in step S507, based on the supply air temperature Tair read in step S506, a target value Qairt of the supply air amount when the air supply amount reduction control is executed is calculated. Here, as the supply air temperature Tair is higher, the target value Qairt of the supply air amount becomes larger. The relationship between the supply air temperature Tair and the target value Qairt of the supply air amount can be obtained in advance based on experiments or the like, and is stored in the ECU 10 as a map.

  Next, in step S508, air supply amount reduction control is executed. At this time, the supply air amount is controlled to the target value Qairt calculated in step S507.

<Example 5>
A fifth embodiment of the present invention will be described. Here, only differences from the first embodiment will be described.

[Overlean fuel injection]
In this embodiment, in each cylinder of the internal combustion engine 1, a fuel injection valve is provided in the intake port, and fuel is injected into the intake port from the fuel injection valve. In the internal combustion engine 1, fuel cut control is performed during deceleration operation.

  When removing the PM adhering to the end faces 63a and 63b of the mat 63 during execution of the fuel cut control, a small amount of fuel is injected from the fuel injection valve of the internal combustion engine 1 so as not to burn in the cylinder due to excess oxygen. (Hereinafter, such fuel injection is referred to as overlean fuel injection). The fuel injected by the over lean fuel injection is discharged from the internal combustion engine 1 in an unburned state, and is supplied to the oxidation catalyst 68 together with air. Then, the fuel is oxidized in the oxidation catalyst 68. The oxidation heat generated at this time can promote the oxidation of PM adhering to the end faces 63a and 63b of the mat 63 during the execution of the fuel cut control.

[Overlean fuel injection control flow]
Here, the flow of overlean fuel injection control according to the present embodiment will be described based on the flowchart shown in FIG. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10 at predetermined intervals.

  In this flow, first, in step S601, it is determined whether or not fuel cut control has been executed. If it is determined in S601 that the fuel cut control has been executed, then in step S602, the PM adhesion amount kpm on the end faces 63a and 63b of the mat 63 is calculated.

  Next, in step S603, it is determined whether or not the PM adhesion amount kpm is equal to or greater than a PM removal execution threshold value kpm1 during execution of fuel cut control. The threshold value kpm1 is determined in advance based on experiments or the like.

  If it is determined in step S603 that the PM adhesion amount kpm is equal to or greater than the threshold value kpm1, then in step S604, the supply air temperature Tair detected by the upstream side exhaust temperature sensor 12 is read.

  Next, in step S605, based on the supply air temperature Tair read in step S604, a target fuel injection amount Qft in overlean fuel injection is calculated. In order to promote the oxidation of PM adhering to the end faces 63a and 63b of the mat 63, it is necessary to increase the amount of heat generated by the oxidation of the fuel in the oxidation catalyst 68 as the supply air temperature Tair is lower. Therefore, the lower the supply air temperature Tair, the greater the target fuel injection amount Qft in overlean fuel injection. The target fuel injection amount Qft is an amount that does not burn in the cylinder. The relationship between the supply air temperature Tair and the target fuel injection amount Qft in overlean fuel injection can be obtained in advance based on experiments or the like, and is stored in the ECU 10 as a map.

  Next, overlean fuel injection control is executed in step S606. At this time, the fuel injection amount is controlled to the target fuel injection amount Qft calculated in step S605.

  When the fuel injection valve of the internal combustion engine 1 directly injects fuel into the cylinder, the fuel injection is performed in the exhaust stroke at the time of executing the fuel cut control. The fuel in the state can be supplied to the oxidation catalyst 68 together with air.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 5 ... Throttle valve 6 ... EHC
61..Catalyst carrier 62..Case 63..Mat 64..Inner tube 65..Electrode 67..Three-way catalyst 68..Oxidation catalyst 7 ... Battery 10..ECU
11. Air-fuel ratio sensor

Claims (1)

A three-way catalyst provided in an exhaust passage of an internal combustion engine,
A carrier that generates heat when energized;
A case for storing the carrier;
An insulating member provided between the carrier and the case for insulating electricity;
An electrically heated catalyst having an oxidation function carried on at least one of the upstream or downstream end face of the insulating member, or a catalyst carrying member provided in the vicinity of the end face;
Air-fuel ratio control means for maintaining the average value in the vicinity of the theoretical air-fuel ratio by repeatedly changing the air-fuel ratio of the exhaust gas of the internal combustion engine to a lean air-fuel ratio and a rich air-fuel ratio;
PM adhesion amount estimation means for estimating the amount of particulate matter adhered to the end face of the insulating member,
When the particulate matter adhering to the end face of the insulating member is removed, if the air-fuel ratio control means has a large amount of PM attached to the end face of the insulating member estimated by the PM attached amount estimating means, the PM attachment Electric heating type that lowers the air-fuel ratio when controlling the exhaust air-fuel ratio to a rich air-fuel ratio and shortens the rich air-fuel ratio period or lengthens the lean air-fuel ratio period compared to when the amount is small Catalyst control system.

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