JP2012193696A - Particulate-matter processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set the appropriate timing for regeneration of an electrode.SOLUTION: A particulate-matter processing device is configured such that a processing part installed with an electrode is provided in an exhaust passage of an internal combustion engine and PM is aggregated by generating a potential difference between the electrode and the processing part. The device includes: a power supply connected to the electrode in order to apply a voltage thereto; a current detecting device for detecting a current flowing through the electrode; a determination device for determining whether or not to regenerate the electrode on the basis of the current detected when a voltage is applied to the electrode; an air-fuel ratio detecting device for detecting or estimating the air-fuel ratio in exhaust gas; and an inhibition device that inhibits the determination by the determination device when the air-fuel ratio is rich.

Description

  The present invention relates to a particulate matter processing apparatus.

  A technique is known in which a discharge electrode is provided in an exhaust passage of an internal combustion engine, and corona discharge is generated from the discharge electrode to charge particulate matter (hereinafter also referred to as PM) to agglomerate PM (for example, (See Patent Document 1). By aggregating PM, the number of PM particles can be reduced. Moreover, since the particle diameter of PM becomes large, when a filter is provided on the downstream side, PM is easily collected by the filter.

  Further, a technique is known in which when the current passing through the discharge electrode is equal to or greater than a predetermined value, it is determined that PM is attached to the discharge electrode, and the applied voltage is increased in order to remove PM from the discharge electrode ( For example, see Patent Document 2.) The removal of deposits from the electrode is called electrode regeneration.

  In addition, an insulator is provided between the electrode and the housing to which the electrode is attached, so that an electric current does not flow, and an average of a predetermined period when an inspection voltage about a fraction of the voltage for corona discharge is applied to the electrode A technique is known in which when the current is greater than or equal to a predetermined value, it is determined that PM adheres to the insulator and the insulation performance is degraded (see, for example, Patent Document 3).

  However, the electric current detected when electricity flows through the substance contained in the exhaust gas has not been considered. Therefore, if it is determined whether or not to regenerate the electrode based on the current passing through the electrode, there is a risk that the determination accuracy is lowered due to the substance contained in the exhaust gas.

JP 2006-194116 A JP 2006-105081 A JP-A-6-173635

  The present invention has been made in view of the above-described problems, and an object thereof is to optimize the timing of electrode regeneration.

In order to achieve the above object, the particulate matter processing apparatus according to the present invention is:
In the particulate matter processing apparatus which comprises a processing unit in which an electrode is installed in an exhaust passage of an internal combustion engine, and agglomerates PM by causing a potential difference between the electrode and the processing unit,
A power source connected to the electrode for applying a voltage;
A current detection device for detecting a current passing through the electrode;
A determination device for determining whether or not to regenerate the electrode based on a current detected by the current detection device when a voltage is applied to the electrode by the power source;
An air-fuel ratio detection device for detecting or estimating the air-fuel ratio of the exhaust gas flowing through the exhaust passage;
When the air-fuel ratio detected or estimated by the air-fuel ratio detection device is a rich air-fuel ratio, a prohibition device that prohibits determination by the determination device;
Is provided.

  Here, when voltage is applied to the electrodes, PM can be charged. The charged PM moves toward the inner wall of the processing unit due to the Coulomb force or the flow of exhaust. Since PM that has reached the inner wall of the processing unit emits electrons to the processing unit, electricity flows to the ground side from the electrode. And since PM which emitted the electron aggregates with other PM which exists near, the number of particles can be decreased.

  If HC or CO, which is unburned fuel, is contained in the exhaust gas, the unburned fuel becomes a carrier, so that a current flows through the unburned fuel when a voltage is applied to the electrode. This current is detected by a current detection device. When the air-fuel ratio of the exhaust gas is a rich air-fuel ratio, a large amount of unburned fuel is contained in the exhaust gas, so that the current detected by the current detection device becomes very large.

  On the other hand, when electricity flows between the electrode and the exhaust passage through a substance such as PM attached to the electrode, the current detected by the current detection device increases. Therefore, it is possible to determine whether or not to regenerate the electrode by increasing the current.

  Here, when a substance such as PM adheres to the electrode, it becomes difficult to charge the PM floating in the exhaust gas, so that it is difficult to aggregate the PM. For this reason, the process which removes the deposit | attachment of an electrode is performed. The deposits can be removed, for example, by increasing the temperature of the electrode. The removal of deposits from the electrode is called electrode regeneration.

  However, when the air-fuel ratio of the exhaust gas is a rich air-fuel ratio, the current detected by the current detection device becomes large, so it is difficult to distinguish from the case where electricity is flowing through the electrode deposit. Therefore, when the air-fuel ratio of the exhaust is a rich air-fuel ratio, the determination by the determination device is prohibited. The electrode may not be regenerated. Further, it may be determined whether or not to regenerate the electrode by detecting a physical quantity other than the current detected by the current detection device. Thereby, although it is not necessary, it can suppress that the regeneration process of an electrode is performed. For this reason, for example, the temperature of the electrode is not increased when it is not necessary, and the fuel efficiency can be improved.

In the present invention, an insulating portion that insulates electricity between the processing portion and the exhaust passage;
A grounding unit for grounding the processing unit;
With
The current detection device can detect a current at the grounding unit.

  Note that the current detection device detects a current on the potential reference point side of the electrode. Generally, on the power supply side from the electrode, the wiring is longer or thicker than the electrode on the ground side. In addition, charges may be stored on the power supply side of the electrode. Then, if a current is detected on the power supply side with respect to the electrode, even if a strong discharge occurs in the electrode, the current detected by the current detection device rises and falls slowly. On the other hand, on the ground side from the electrode, the wiring can be made relatively short and thin. For this reason, an electric current can be detected more correctly. Moreover, it can suppress that electricity flows other than a grounding part by providing an insulating part. For this reason, an electric current can be detected more correctly.

  In the present invention, the determination device can determine that the electrode is to be regenerated when a current detected by the current detection device is equal to or greater than a threshold value.

This threshold value is the lower limit value of the current detected when electricity flows through the electrode deposit. The current passing through the electrode deposits is greater than the current passing when aggregating PM floating in the exhaust. For this reason, it can be determined that electricity is flowing through the electrode deposit when the detected current becomes larger than the threshold value. At this time, it can be determined that the electrode is to be regenerated. However, when the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio, the current can exceed the threshold due to the influence of unburned fuel. In this case, there is a possibility that it is determined that the electrode is to be regenerated although it is not necessary to regenerate the electrode. On the other hand, in the case of a rich air-fuel ratio, erroneous determination can be suppressed by prohibiting determination by the determination device. Since the current detected by the current detection device also changes depending on the number of PM particles in the exhaust, the threshold value may be changed according to the number of particles in the exhaust.

  According to the present invention, it is possible to optimize the regeneration timing of the electrodes.

It is a figure which shows schematic structure of the particulate matter processing apparatus which concerns on an Example. It is the flowchart which showed the flow for determining the regeneration time of the electrode which concerns on an Example.

  Hereinafter, specific embodiments of the particulate matter processing apparatus according to the present invention will be described with reference to the drawings.

Example 1
FIG. 1 is a diagram illustrating a schematic configuration of a particulate matter processing apparatus 1 according to the present embodiment. The particulate matter processing apparatus 1 is provided in an exhaust passage 2 of a spark ignition type gasoline engine.

  The particulate matter processing apparatus 1 includes a housing 3 whose both ends are connected to an exhaust passage 2. The material of the housing 3 is a stainless steel material. The housing 3 is formed in a hollow cylindrical shape having a diameter larger than that of the exhaust passage 2. Both ends of the housing 3 are formed in a tapered shape in which the cross-sectional area decreases as the distance from the end increases. In FIG. 1, the exhaust flows through the exhaust passage 2 in the direction of the arrow and flows into the housing 3. For this reason, the housing 3 may be a part of the exhaust passage 2.

  The exhaust passage 2 and the housing 3 are connected via an insulating portion 4. The insulating part 4 is made of an electrical insulator. The insulating portion 4 is sandwiched between a flange 21 formed at the end of the exhaust passage 2 and a flange 31 formed at the end of the housing 3. The exhaust passage 2 and the housing 3 are fastened by bolts and nuts, for example. In addition, these bolts and nuts are also insulated so that electricity does not flow through these bolts and nuts. In this way, electricity is prevented from flowing between the exhaust passage 2 and the housing 3.

  An electrode 5 is attached to the housing 3. The electrode 5 penetrates the side surface of the housing 3, extends from the side surface of the housing 3 toward the central axis of the housing 3, bends in the vicinity of the central axis, and upstream of the flow of exhaust gas, and is parallel to the central axis It extends toward the upstream side of the exhaust flow. Further, it bends further to the side surface side of the housing 3 on the upstream side, passes through the side surface of the housing 3 and communicates with the outside.

  In order to prevent electricity from flowing between the electrode 5 and the housing 3, the electrode 5 is provided with insulator portions 51 and 55 made of an electrical insulator. The insulator portions 51 and 55 are located between the electrode 5 and the housing 3, and have a function of insulating electricity and fixing the electrode 5 to the housing 3.

  One end of the electrode 5 is connected to the power supply 6 via the power supply side electric wire 52. The power source 6 can energize the electrode 5 and change the applied voltage. The power source 6 is connected to the control device 7 and the battery 8 through electric wires. The control device 7 controls the voltage that the power source 6 applies to the electrode 5. The power supply 6 is connected to a ground wire 54 for connection to a potential reference point. The power source 6 is grounded by the ground wire 54.

  The other end of the electrode 5 is connected to the ground wire 54 via a short-circuit wire 56. A switch 57 for opening and closing the circuit is provided in the middle of the short-circuit wire 56. When the switch 57 is turned on while a voltage is applied by the power source 6, electricity flows through the short-circuited wire 56. At this time, since the electrode 5 is short-circuited, the temperature of the electrode 5 rises. In the present embodiment, the power supply side electric wire 52 is connected to the downstream side insulator 51 and the short-circuited wire 56 is connected to the upstream side insulator 55, but instead, the downstream side insulator 51 is connected. The short-circuited wire 56 may be connected to the power supply side electric wire 52 and the upstream side insulator portion 55 may be connected.

  A ground side electric wire 53 is connected to the housing 3, and the housing 3 is grounded via the ground side electric wire 53. The ground side electric wire 53 is provided with a detection device 9 that detects a current passing through the ground side electric wire 53. For example, the detection device 9 detects a current by measuring a potential difference between both ends of a resistor provided in the middle of the ground-side electric wire 53. The detection device 9 is connected to the control device 7 via an electric wire. Then, the current detected by the detection device 9 is input to the control device 7. In addition, since the electric capacity of the ground side electric wire 53 is smaller than that of the power source side electric wire 52, the response when detecting the current is higher when the detection device 9 is provided in the ground side electric wire 53. In the present embodiment, the detection device 9 corresponds to the current detection device in the present invention.

  The control device 7 is connected to an accelerator opening sensor 71, a crank position sensor 72, a temperature sensor 73, an air flow meter 74, and an air-fuel ratio sensor 75. The accelerator opening sensor 71 outputs an electrical signal corresponding to the amount of depression of the accelerator pedal by the driver of the vehicle on which the internal combustion engine is mounted, and detects the engine load. The crank position sensor 72 detects the engine speed. The temperature sensor 73 detects the temperature of the internal combustion engine by detecting the temperature of the cooling water of the internal combustion engine or the temperature of the lubricating oil. The air flow meter 74 detects the intake air amount of the internal combustion engine. The air-fuel ratio sensor 75 is attached to the exhaust passage 2 upstream of the housing 3 and detects the air-fuel ratio of the exhaust flowing through the exhaust passage 2. In this embodiment, the air-fuel ratio sensor 75 corresponds to the air-fuel ratio detection device in the present invention. Further, the air-fuel ratio of the exhaust gas may be estimated from the operating state of the internal combustion engine.

  In addition, a switch 57 is connected to the control device 7 via an electric wire, and the control device 7 performs an ON-OFF operation of the switch 57. Here, when the voltage is applied from the power source 6 to the electrode 5, the current passes through the short-circuited wire 56 by turning on the switch. On the other hand, when the switch is turned off, no current flows through the short-circuited wire 56.

  In the particulate matter processing apparatus 1 configured in this way, electrons are emitted from the electrode 5 by applying a negative high DC voltage from the power source 6 to the electrode 5 when the switch 57 is OFF. That is, electrons are emitted from the electrode 5 by making the potential of the electrode 5 lower than that of the housing 3. The electrons in the exhaust gas can be negatively charged by the electrons. Negatively charged PM moves due to Coulomb force and gas flow. When the PM reaches the housing 3, the electrons that have negatively charged the PM are emitted to the housing 3. The PM that has released electrons to the housing 3 aggregates to increase the particle size. Moreover, the number of PM particles is reduced due to aggregation of PM. That is, by applying a voltage to the electrode 5, the particle diameter of PM can be increased and the number of PM particles can be reduced.

  By the way, when a substance such as PM adheres to the electrode 5 including the insulator portion 51, the insulating property of the electrode 5 is lowered. And electricity can flow between the electrode 5 and the housing 3 through these deposits. Then, since electrons emitted from the electrode 5 are reduced, it is difficult to charge the PM floating in the exhaust gas, and it is difficult to aggregate the PM. For this reason, the regeneration process of the electrode 5 is implemented.

  Here, the regeneration process of the electrode 5 is a process for removing deposits such as PM adhering to the electrode 5 including the insulator parts 51 and 55. In this embodiment, the electrode 5 is regenerated by applying a voltage from the power source 6 while turning on the switch 57. That is, by short-circuiting the electrode 5, the temperature of the electrode 5 is raised and the deposits are removed by burning or evaporation.

  In order to oxidize PM quickly, it is better that the oxygen concentration in the exhaust gas is high. Therefore, the oxygen concentration in the exhaust gas may be increased before the electrode 5 is short-circuited or when the electrode 5 is short-circuited. In order to increase the oxygen concentration in the exhaust gas, for example, in a hybrid vehicle including an internal combustion engine and a motor as a vehicle drive source, the crankshaft of the internal combustion engine may be rotated by the motor without supplying fuel to the internal combustion engine. Good. Thereby, since air can be discharged | emitted from an internal combustion engine, the oxygen concentration in exhaust_gas | exhaustion can be raised. Further, by temporarily increasing the engine speed before stopping the internal combustion engine and stopping the fuel supply when the engine speed is high, air can be discharged into the exhaust passage. Then, the electrode 5 may be short-circuited when the internal combustion engine stops thereafter. Further, at the time of fuel cut during the deceleration operation, the oxygen concentration in the exhaust gas becomes high. Therefore, the electrode 5 may be short-circuited at this time.

  Then, the presence of the deposit on the electrode 5 is determined based on the current detected by the detection device 9, and when it is determined that the deposit is present on the electrode 5, the electrode 5 is regenerated. That is, it is determined based on the current detected by the detection device 9 that electricity is flowing between the electrode 5 and the housing 3. Here, when electricity is not flowing between the electrode 5 and the housing 3 via the deposit, the current changes according to the amount of PM floating in the exhaust gas. The current detected at this time is relatively small. On the other hand, the current detected when a current passes through the deposit on the electrode 5 is relatively large. Therefore, a threshold is set for the current detected by the detection device 9, and it is determined that regeneration of the electrode 5 is necessary when the detected current is equal to or greater than the threshold. The threshold value is obtained in advance by experiments or the like as the lower limit value of the detected current when the current passes through the deposit on the electrode 5. The threshold may be changed according to the number of PM particles in the exhaust. The number of PM particles can be detected by a sensor, for example.

  By the way, if unburned fuel such as HC or CO is contained in the exhaust gas, when a voltage is applied to the electrode 5, the unburned fuel becomes an electron carrier and an ionic current flows. When the air-fuel ratio of the exhaust gas becomes a rich air-fuel ratio, the amount of unburned fuel in the exhaust gas increases and the ionic current increases, so that the detection current increases. And the ionic current by unburned fuel is much larger than the electric current which passes through PM when agglomerating PM.

  Then, when it is determined whether or not the regeneration of the electrode 5 is necessary when the air-fuel ratio of the exhaust gas is a rich air-fuel ratio, it may be determined that the regeneration of the electrode 5 is necessary even if it is not actually necessary. is there. In other words, the detection current may increase to a threshold value or more due to an increase in unburned fuel. In this case, regeneration of the electrode 5 is not necessary. However, it is difficult to distinguish whether the detected current is increased due to an increase in unburned fuel or not by simply comparing the detected current with the threshold value. .

  Therefore, in this embodiment, when the air-fuel ratio of the exhaust is a rich air-fuel ratio, it is prohibited to determine whether or not to regenerate the electrode 5. The regeneration of the electrode 5 may be prohibited.

  In addition, since the insulation part 4 is provided in a present Example, it is suppressed that electricity passes to the exhaust passage 2. FIG. Therefore, the current passing through the housing 3 via the deposits on the electrode 5, the PM floating in the exhaust, and the unburned fuel is detected by the detection device 9. Further, by detecting the current in the ground side electric wire 53, the current detection accuracy can be increased. In general, the power supply side electric wire 52 is longer or thicker than the ground side electric wire 53. Then, if a current is detected in the power supply side electric wire 52, the rise and fall of the detected current with respect to the actual current change becomes slow. For this reason, there exists a possibility that the detection accuracy of an electric current may become low.

  On the other hand, in the ground side electric wire 53, wiring can be made relatively short and thin. For this reason, the response to the actual change in current is higher when the current is detected in the ground-side electric wire 53. Therefore, the current can be detected more accurately by detecting the current in the ground side electric wire 53.

  Next, FIG. 2 is a flowchart showing a flow for determining the regeneration time of the electrode 5 according to the present embodiment. This routine is repeatedly executed by the control device 7 every predetermined time.

  In step S101, the operating state of the internal combustion engine is acquired. For example, values necessary for subsequent processing such as engine speed, engine load, and exhaust air-fuel ratio are read. The engine speed is detected by a crank position sensor 72, and the engine load is detected by an accelerator opening sensor 71. Further, the air-fuel ratio of the exhaust is detected by an air-fuel ratio sensor 75. The air-fuel ratio of the exhaust gas can also be estimated from the engine speed, the engine load, the temperature of the internal combustion engine, and the like. Further, the temperature sensor 73 detects the temperature of the internal combustion engine (for example, the temperature of the lubricating oil or the temperature of the cooling water).

In step S102, the voltage applied to the electrode 5 is calculated. The applied voltage is set according to the estimated number of PM particles (number / cm ³ ). The number of PM particles is the number of PM particles discharged from the internal combustion engine, and is the number of PM particles before flowing into the housing 3. Since the number of PM particles is correlated with the engine speed, the engine load, and the temperature of the internal combustion engine (for example, the temperature of the lubricating oil or the temperature of the cooling water), the number of PM particles is calculated based on these values. A plurality of maps for calculating the number of PM particles may be stored according to the temperature of the internal combustion engine from the engine speed and the engine load, and the number of PM particles may be calculated based on the map.

  A sensor for detecting the number of PM particles may be attached to the exhaust passage 2 on the upstream side of the housing 3 and the number of PM particles may be detected by the sensor.

  Then, the applied voltage is calculated based on the number of PM particles and the exhaust gas amount (g / sec) of the internal combustion engine. This relationship may be obtained in advance by experiments or the like and mapped. Since the exhaust gas amount of the internal combustion engine has a correlation with the intake air amount of the internal combustion engine, it can be obtained based on the intake air amount detected by the air flow meter 74.

  Here, since the inertia force of PM becomes smaller as the amount of exhaust gas is smaller, the influence of electrostatic action becomes relatively larger. For this reason, PM tends to aggregate. Therefore, as the amount of exhaust gas decreases, PM aggregates with a smaller applied voltage. For this reason, the applied voltage is reduced as the amount of exhaust gas decreases. Also, the greater the number of PM particles, the shorter the distance between the PM particles, so that the influence of electrostatic action becomes relatively large. Therefore, as the number of PM particles increases, PM aggregates with a smaller applied voltage. For this reason, the applied voltage is decreased as the number of PM particles is increased.

Further, the applied voltage may be a value such that the reduction rate of the number of PM particles becomes a predetermined value (for example, 40%). The applied voltage may be a predetermined value that is determined in advance.

  Then, after the applied voltage is calculated, this voltage is applied, the process proceeds to step S103, and the current is detected. This current is a value detected by the detection device 9.

  In step S104, it is determined whether the air-fuel ratio of the exhaust gas acquired in step S101 is a rich air-fuel ratio. In this step, it is determined whether or not the exhaust gas contains a large amount of unburned fuel.

  If a positive determination is made in step S104, the process proceeds to step S105, and if a negative determination is made, the process proceeds to step S106.

  In step S105, the determination as to whether or not to regenerate the electrode 5 is prohibited. That is, since accurate determination cannot be performed due to the influence of unburned fuel, determination is prohibited. In this embodiment, the control device 7 that processes step S105 corresponds to the prohibition device in the present invention.

  On the other hand, in step S106, it is permitted to determine whether or not to regenerate the electrode 5. Then, it is determined whether or not the electrode 5 is to be regenerated, and the electrode 5 is regenerated as necessary. In this embodiment, the control device 7 that processes step S106 corresponds to the determination device in the present invention.

  In this way, when the air-fuel ratio is rich, the determination as to whether or not to regenerate the electrode 5 is prohibited, so that it is possible to suppress the regeneration of the electrode 5 when it is not necessary. That is, it is possible to optimize the regeneration timing of the electrode 5. Thereby, deterioration of fuel consumption can be suppressed.

DESCRIPTION OF SYMBOLS 1 Particulate matter processing apparatus 2 Exhaust passage 3 Housing 4 Insulation part 5 Electrode 6 Power supply 7 Control apparatus 8 Battery 9 Detection apparatus 21 Flange 31 Flange 51 Insulator part 52 Power supply side electric wire 53 Ground side electric wire 54 Ground electric wire 55 Insulator part 56 Short circuit electric wire 57 Switch 71 Accelerator opening sensor 72 Crank position sensor 73 Temperature sensor 74 Air flow meter 75 Air-fuel ratio sensor

Claims (3)

In the particulate matter processing apparatus which comprises a processing unit in which an electrode is installed in an exhaust passage of an internal combustion engine, and agglomerates PM by causing a potential difference between the electrode and the processing unit,
A power source connected to the electrode for applying a voltage;
A current detection device for detecting a current passing through the electrode;
A determination device for determining whether or not to regenerate the electrode based on a current detected by the current detection device when a voltage is applied to the electrode by the power source;
An air-fuel ratio detection device for detecting or estimating the air-fuel ratio of the exhaust gas flowing through the exhaust passage;
When the air-fuel ratio detected or estimated by the air-fuel ratio detection device is a rich air-fuel ratio, a prohibition device that prohibits determination by the determination device;
A particulate matter processing apparatus comprising: An insulating part for insulating electricity between the processing part and the exhaust passage;
A grounding unit for grounding the processing unit;
With
The particulate matter processing apparatus according to claim 1, wherein the current detection device detects a current at the grounding portion.   The particulate matter processing apparatus according to claim 1, wherein the determination device determines that the electrode is to be regenerated when a current detected by the current detection device is equal to or greater than a threshold value.

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