JP2011112026A - Electric power supply device for exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power supply device for an exhaust emission control device whose purifying amount is improved. <P>SOLUTION: The exhaust emission control device is equipped with the electric power supply device 50 (an electric power supply means) which is applied to an exhaust emission control system 10 for oxidizing and purifying PMs (particulate) within exhaust by executing a corona discharge from a discharging electrode 21 arranged in an exhaust passage 11 of an internal combustion engine, and repeats an instantaneous voltage application to the discharging electrode 21 two or more times to thereby supply electric power employed for the corona discharge. The time required for the instantaneous voltage application by the electric power supply device 50 is made shorter than a given time period (a predetermined time period) required for arc discharge. Accordingly, the arc discharge can be restrained from being generated and therefore an applied voltage can be driven to be higher, eventually enabling an increase in a PM purifying amount. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power supply device for an exhaust gas purification device applied to an exhaust gas purification device that purifies particulates contained in the exhaust gas of an internal combustion engine.

  2. Description of the Related Art Conventionally, an exhaust gas purification device that purifies by oxidizing PM (particulate matters (fine particles)) in exhaust gas by corona discharge from a discharge electrode disposed in an exhaust passage of an internal combustion engine, or collecting and purifying PM by charging PM. It is known (see Patent Document 1).

JP 2009-243419 A

  In purifying PM using the above apparatus, the higher the voltage applied to the discharge electrode, the more the PM oxidation or charging can be promoted, and the PM purification amount can be increased. However, when the voltage is increased in order to increase the amount of PM purification, there is a high possibility that arc discharge will occur between the ground electrode (counter electrode) facing the discharge electrode and the discharge electrode. When such arc discharge occurs, most of the electric energy input to the discharge electrode flows into the arc and the corona discharge disappears. As a result, most of the PM passing through the vicinity of the discharge electrode is not oxidized or charged, resulting in a problem that the amount of PM purification is significantly reduced.

Further, when electrons subjected to corona discharge collide with exhaust molecules such as O ₂ and N ₂ contained in the exhaust, the molecular vibrations of the exhaust molecules are promoted. The more the molecular vibrations are activated, the more the corona discharges from the corona. The discharged electrons have a higher probability of colliding with exhaust molecules that undergo molecular vibration. As a result, the probability that the corona-discharged electrons collide with the PM as a contradiction is low, so that the PM is not sufficiently oxidized or charged, resulting in a problem that the PM purification amount is reduced.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a power supply device for an exhaust purification device that improves the purification amount.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  According to the first aspect of the present invention, there is provided an exhaust gas purification apparatus that oxidizes and purifies particulates in exhaust gas by corona discharge from a discharge electrode disposed in an exhaust passage of an internal combustion engine, or charges and collects and purifies the particulates. It is applied and includes a power supply means for supplying power to be used for the corona discharge by repeating applying an instantaneous voltage to the discharge electrode a plurality of times, and a time for applying a voltage instantaneously by the power supply means, It is characterized by being shorter than a predetermined time.

  According to this, when supplying the electric power used for corona discharge to the discharge electrode, the voltage is not applied continuously all the time, but the voltage is applied instantaneously for a plurality of times. Therefore, the applied voltage is temporarily interrupted before the electric arc reaches the other side after the electric arc is generated on one of the counter electrode (for example, the ground electrode) and the discharge electrode facing the discharge electrode. There is a high possibility that the near electric arc will disappear on the way. As described above, according to the present invention, since the occurrence of arc discharge can be suppressed, it is possible to promote the increase of the applied voltage and to improve the purification amount of the fine particles.

  Contrary to the above-described invention, if the voltage application to the discharge electrode is continuously performed without temporarily interrupting the applied voltage, the aforementioned molecular vibration of the exhaust molecules is promoted. On the other hand, in the above-described invention, since power is supplied by repeating voltage application a plurality of times, molecular vibrations of exhaust molecules can be suppressed, and the probability that corona-discharged electrons collide with fine particles can be increased. Therefore, the oxidation amount or charge amount of the fine particles can be improved, and the purification amount of the fine particles can be improved.

  According to the second aspect of the present invention, the time required for the electric arc to reach the other of the counter electrode and the discharge electrode after the electric arc is generated on the one side of the counter electrode and the discharge electrode facing the discharge electrode. Is the arc discharge required time, and the arc discharge required time is the predetermined time.

  According to this, it is possible to improve the certainty that the applied voltage is cut off after the electric arc is generated on one of the counter electrode (for example, the ground electrode) and the discharge electrode and before the electric arc reaches the other. Therefore, generation | occurrence | production suppression of arc discharge can be accelerated | stimulated and by extension, the purification amount improvement of microparticles | fine-particles can be accelerated | stimulated.

  According to the third aspect of the present invention, the time required for the exhaust molecules to vibrate with a strength of a predetermined value or more after receiving the energy of the corona-discharged electrons after starting the instantaneous voltage application is required for molecular vibration. The time required for the molecular vibration is defined as the predetermined time.

  According to this, it is possible to improve the certainty that the exhaust molecules can avoid the molecular vibration with the intensity of a predetermined value or more. Therefore, improvement in the oxidation amount or charge amount of the fine particles can be promoted, and as a result, improvement in the purification amount of the fine particles can be promoted.

  The invention according to claim 4 is characterized in that the predetermined time is set to 100 nanoseconds or more and 500 nanoseconds or less.

  Contrary to the above invention, if the predetermined time is set to less than 100 nanoseconds, there is a concern that oxidation or charging of the fine particles due to corona discharge may be insufficient as a contradiction that can improve suppression of arc discharge and molecular vibration. Also, contrary to the above invention, if the predetermined time is set to be greater than 500 nanoseconds, there is a concern that arc discharge suppression and molecular vibration suppression may be insufficient. In view of these concerns, according to the above invention set to “100 nanoseconds ≦ predetermined time ≦ 500 nanoseconds”, the effects of arc discharge suppression and molecular vibration suppression and the effects of fine particle oxidation or charging are exhibited in a balanced manner. be able to.

  The invention according to claim 5 is characterized in that a period in which voltage is instantaneously applied by the power supply means is set to 500 Hz or more and 100 kHz or less.

  Contrary to the above invention, if the period is set to less than 500 Hz, the interval time during which no voltage is applied is too long, and as a contradiction to suppress arc discharge suppression and molecular vibration suppression, oxidation or charging of fine particles due to corona discharge is caused. There is concern that it will be insufficient.

  On the other hand, if the period is set to be larger than 100 kHz contrary to the above invention, the interval time will be too short as will be described below. That is, an electric arc that has become an arc discharge is about to disappear in the middle by temporarily interrupting the applied voltage, but if the interval time is too short, the next voltage is applied before the electric arc is completely extinguished. There is a concern that the electric arc generated in one of the counter electrode and the discharge electrode reaches the other and falls into an arc discharge state. There is also a concern that molecular vibrations cannot be sufficiently suppressed.

  In view of these concerns, according to the above invention set to “500 Hz ≦ period of applying voltage instantaneously ≦ 100 kHz”, the effects of arc discharge suppression and molecular vibration suppression and the effects of fine particle oxidation or charging are well balanced. Can be made.

  The invention according to claim 6 is characterized in that the absolute value of the voltage peak value when the voltage is instantaneously applied by the power supply means is set to 5 kV or more and 15 kV or less.

  Contrary to the above invention, if the absolute value of the voltage peak value is set to less than 5 kV, there is a concern that the oxidation or charging of fine particles due to corona discharge may be insufficient as a contradiction that can improve the suppression of arc discharge and molecular vibration. . Further, contrary to the above invention, if the absolute value of the voltage peak value is set to be larger than 15 kV, there is a concern that arc discharge suppression and molecular vibration suppression are insufficient. In view of these concerns, according to the above invention set to “5 kV ≦ absolute value of voltage peak value ≦ 15 kV”, the effects of arc discharge suppression and molecular vibration suppression and the effects of fine particle oxidation or charging are exhibited in a balanced manner. be able to.

  The invention according to claim 7 is characterized in that the discharge electrode has a shape including a plurality of protruding emission portions from which electrons are emitted by corona discharge.

  According to this, since the electric charge supplied to the electrode is easily released to the exhaust passage, the corona discharge can be promoted while suppressing the applied voltage to improve the oxidation amount or the charge amount of the fine particles. Therefore, it is possible to promote fine particle purification by corona discharge while promoting suppression of arc discharge and molecular vibration.

  According to an eighth aspect of the present invention, a counter electrode facing the discharge electrode is disposed on an inner wall surface of the exhaust pipe forming the exhaust passage, and a portion of the exhaust passage where the discharge electrode is disposed. The passage cross-sectional area is greater than or equal to the minimum passage cross-sectional area of the exhaust passage.

  Here, the larger the gap between the discharge electrode and the counter electrode, the greater the resistance (impedance) between the two electrodes, making it difficult for the charge supplied to the discharge electrode to be released, resulting in insufficient corona discharge. Concerned. Therefore, if the passage cross-sectional area of the exhaust pipe is reduced, the gap is reduced and the above-mentioned concern is solved. However, if only the passage cross-sectional area of the exhaust pipe where the counter electrode is disposed is reduced, the exhaust pipe is exhausted at this portion. This causes a problem that the flow resistance of the exhaust gas is restricted and the flow resistance of the exhaust gas increases.

  In the above invention in view of this point, the passage cross-sectional area of the portion of the exhaust passage where the counter electrode is disposed is equal to or larger than the minimum passage cross-sectional area of the exhaust passage, so the portion of the exhaust pipe where the counter electrode is disposed In this way, it is possible to prevent the exhaust flow from being restricted. In addition, if the passage cross-sectional area of the portion where the counter electrode is disposed is set to the minimum passage cross-sectional area, it is possible to promote corona discharge by reducing the gap while suppressing an increase in exhaust flow resistance. This is preferable.

  The invention according to claim 9 includes a catalyst that oxidizes or reduces a specific substance in the exhaust, and a case that is connected to an exhaust pipe that forms the exhaust passage and holds the catalyst inside. In addition to having an inflow port through which exhaust flows from the exhaust pipe, an inlet taper part that gradually increases the cross-sectional area of the passage from the inflow port toward the exhaust flow downstream side, and an outflow port through which the exhaust flows out to the exhaust pipe And an outlet taper portion that gradually increases a passage sectional area from the outlet toward the upstream side of the exhaust flow, and a holding portion that connects the inlet taper portion and the outlet taper portion and holds the catalyst therein. The discharge electrode is disposed in the exhaust passage in the vicinity of the downstream side of the outlet taper portion and at the center of the cross section of the exhaust passage. Wherein (see Fig. 11).

  Generally, the case holding portion is formed to have a passage cross-sectional area larger than that of the exhaust pipe in order to reduce pressure loss when the exhaust passes through the catalyst. Therefore, the case has an outlet tapered portion that connects the downstream end of the holding portion and the exhaust pipe. In the above invention, the amount of purification by corona discharge is increased by using the outlet taper portion.

  That is, the exhaust gas positioned at the outlet taper portion is guided by the inner wall surface of the outlet taper portion and flows toward the center of the exhaust passage (see arrow Y in FIG. 11). Therefore, the PM concentration in the central portion of the passage section of the exhaust passage is higher than the PM concentration in the outer peripheral portion of the passage section. Therefore, according to the above-described invention in which the discharge electrode is disposed in the vicinity of the downstream side of the outlet taper portion and in the central portion of the passage cross section of the exhaust passage, the discharge electrode is disposed in a portion having a high PM concentration. The amount of purification can be increased.

In 1st Embodiment, (a) is a figure which shows the engine mounting position of an exhaust gas purification apparatus, (b) is a figure which shows the structure of an exhaust gas purification apparatus, (c) is A arrow view of (b). The figure explaining the mechanism in which PM is purified by the exhaust gas purification apparatus of FIG. The figure which shows the structure of the electric power supply apparatus which supplies electric power to the discharge plug of FIG. The figure which shows the time change of the voltage applied to a discharge plug by the electric power supply apparatus of FIG. The figure which shows the test result at the time of applying a voltage continuously contrary to 1st Embodiment. The figure explaining one of the effects by 1st Embodiment. The figure which shows the structure of the exhaust gas purification apparatus concerning 2nd Embodiment. The figure which shows the example of arrangement | positioning of the discharge | release part concerning 3rd Embodiment. The figure which shows the example of arrangement | positioning of the discharge | release part concerning 3rd Embodiment. The figure which shows the example of a shape of the discharge | release part concerning 3rd Embodiment. The figure which shows the example of arrangement | positioning of the discharge | release part concerning 4th Embodiment.

  Hereinafter, embodiments embodying the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals in the drawings, and the description of the same reference numerals is used.

(First embodiment)
Hereinafter, a first embodiment in which the present invention is applied to an exhaust emission control device for a diesel engine (internal combustion engine) will be described with reference to the drawings. 1A shows the mounting position of the exhaust purification device 10 with respect to the engine 41, FIG. 1B shows the overall configuration of the exhaust purification device 10, and FIG. 1C shows the A arrow in FIG. 1B. FIG.

  In the figure, the exhaust emission control device 10 includes a discharge plug 20 having a discharge portion 21b for discharging electrons, and a ground electrode 30 (counter electrode) disposed so as to face the discharge portion 21b. The ground electrode 30 has a cylindrical shape disposed along the inner wall surface of the cylindrical housing H connected to the exhaust pipe 42 of the engine 41. The housing H is a cylindrical tube having a diameter larger than that of the exhaust pipe 42, and the inside thereof becomes the exhaust passage 11 having a circular cross section, and is connected to the straight portion of the exhaust pipe 42 at the small diameter portions at both ends.

  In FIG. 1B, the discharge plug 20 has an upper half protruding from the cylindrical wall of the housing H to the outside (upward in the figure), and a lower half positioned in the exhaust passage 11 in the housing H. The discharge plug 20 includes a discharge electrode 21 that performs corona discharge so that electrons are supplied to discharge electrons into the exhaust passage 11, and an insulator portion 22 that holds the discharge electrode 21. The discharge electrode 21 includes a rod-shaped conductive portion 21a whose outer periphery is held by the insulator portion 22, and a discharge portion 21b provided at the tip thereof. Direct current high voltage power is supplied from the power supply device 50 (power supply means) to the base end of the conductive portion 21a located outside the housing H and protruding from the insulator portion 22.

  A portion of the conductive portion 21a exposed in the exhaust passage 11 is bent in an L shape, extends along the axis of the exhaust passage 11 (exhaust flow direction), and supplies a high voltage current to the discharge portion 21b connected to the tip. Lead.

  As shown in FIG.1 (c), the discharge | release part 21b is a shape which has many processus | protrusions which protrude radially on the outer peripheral surface of the board while it is plate shape. The electrons supplied to the emitting portion 21b are emitted from the tip of the protrusion into the exhaust passage 11 and corona discharge occurs. As described above, the discharge rate can be increased by providing a large number of protrusions on the discharge portion 21b, and the corona discharge can be generated uniformly in the exhaust passage 11 to improve the purification performance.

  Next, the mechanism by which PM (particulate matters (fine particles)) contained in the exhaust gas is purified by the exhaust gas purification device 10 will be described with reference to FIG.

  As shown in FIG. 2 (a), the PM generated in the engine 41 and discharged to the exhaust pipe 42 has a particle size of about 0.01 μm to several μm, and is captured by a normal particulate filter (DPF). Nanoparticles (nano PM) that can not be included. The exhaust emission control device 10 mainly functions to oxidize and purify the nano PM.

As shown in FIG. 2B, when a negative DC high voltage is applied from the power supply device 50 to the conductive portion 21a of the discharge plug 20, a corona discharge is generated in the vicinity of the protrusion at the tip of the emission portion 21b ((1 in the figure)). )reference). At this time, electrons emitted by corona discharge have high energy, and when the electrons collide with oxygen molecules (O ₂ ) in the exhaust, the oxygen molecules are dissociated and oxygen ions (O radicals: O ^{2). -} ) Will be generated (see (2) in the figure). The O radical is in an unstable state, and when the O radical collides with a carbon atom (C) that is a component of nano PM, carbon dioxide (CO ₂ ) is generated ((3 in the figure)). (See (4)).

  In short, as shown in FIG. 2 (c), carbon and oxygen molecules are oxidized to change to carbon dioxide by the energy (activation energy) of electrons emitted by corona discharge. As described above, since nano-PM is oxidized and directly changed to carbon dioxide, which is a gas molecule, by corona discharge, nano-PM can be purified by effectively using the energy generated by corona discharge.

  Next, the configuration of the power supply device 50 will be described with reference to FIG.

  The power supply device 50 uses a battery 51 mounted on the vehicle as a power source, boosts the voltage (12 V) of the battery 51 and supplies the boosted voltage to the discharge plug 20. In addition, the voltage boosted in this way is not continuously applied to the discharge plug 20, but is controlled so as to apply a pulsed voltage so that the voltage application is instantaneously repeated a plurality of times.

  The circuit shown in FIG. 3 is an example of a circuit that performs such boosting and pulse control. The power supply device 50 includes a battery 51, a capacitor 52, a transformer 53, a thyristor 54 (switch means), and a microcomputer (microcomputer 55). It is configured with.

  In a state where the thyristor 54 is turned off and is de-energized, the power supplied from the battery 51 is stored in the capacitor 52. When the thyristor 54 is turned on by a command signal output from the microcomputer 55, the power stored in the capacitor 52 flows to the primary coil of the transformer 53, and accordingly, a high voltage is generated in the secondary coil of the transformer 53. High voltage power is supplied to the discharge plug 20 connected to the next coil.

  In short, when a voltage (pulse voltage) is instantaneously applied to the discharge plug 20, voltage application is started at the timing when the microcomputer 55 outputs a turn-on command. Therefore, the period for applying voltage instantaneously is controlled by the microcomputer 55. In the example of FIG. 3, the signal output from the microcomputer 55 to the thyristor 54 is a clock pulse signal that commands turn-on at a predetermined cycle, and commands turn-on at a cycle of 500 Hz to 100 kHz.

  On the other hand, when the electric charge of the capacitor 52 becomes a predetermined amount or less due to the discharge to the primary coil, the thyristor 54 is turned off and the energization to the primary coil is cut off. Thereby, the power supply to the discharge plug 20 is stopped. Therefore, the timing for ending the instantaneous voltage application and the time for applying the voltage instantaneously are determined by circuit components such as the capacitance of the capacitor 52. In the example of FIG. 3, the capacity of the capacitor 52 and the like are set so that the time for instantaneous voltage application is 100 nanoseconds to 500 nanoseconds.

  The voltage of power supplied to the discharge plug 20 is determined by the specifications of the battery 51 and the transformer 53. The transformer 53 is selected so that when the remaining capacity of the battery 51 is 100%, the voltage applied to the discharge plug 20 is −5 kV to −15 kV.

  As described above, the voltage applied to the discharge part 21b of the discharge plug 20 becomes a voltage of −5 kV to −15 kV at a cycle of 500 Hz to 100 kHz as shown in FIG. 4 and is an extremely short time such as 100 nanoseconds to 500 nanoseconds. Applied instantaneously.

  By the way, as the corona discharge is performed at a higher voltage, the amount of generated O radicals can be increased and the amount of purification of PM can be increased. Further, if the gap G (see FIG. 1B) between the emission portion 21b and the ground electrode 30 is small, electrons are easily emitted from the discharge electrode 21, so that the amount of generated O radicals increases and PM The amount of purification can be increased. However, the higher the applied voltage and the smaller the gap G, the higher the risk that arc discharge will occur between the discharge portion 21b of the discharge electrode 21 and the ground electrode 30. When such arc discharge occurs, all of the electric energy input to the discharge electrode 21 flows into the arc and the corona discharge disappears. As a result, there is a problem that the oxidation of the nano PM becomes insufficient and the PM purification amount is significantly reduced.

  And contrary to the present embodiment in which a DC voltage is applied in a pulsed manner to the emission part 21b, the above problem becomes significant when a DC voltage is continuously applied to the emission part 21b without being temporarily interrupted. It became clear by the test which the present inventors conducted.

  FIG. 5A shows the test results when voltage is continuously applied. In the figure, the horizontal axis indicates the magnitude of the applied voltage, and the vertical axis indicates during exhaust after passing through the exhaust purification device 10. The number of contained PMs, that is, the number of PMs that could not be purified is shown. Moreover, (1) in the figure shows the test results when the gap G = 40 mm, (2) is 30 mm, and (3) is 20 mm. The dotted lines in (2) and (3) indicate estimated values.

  The test result of FIG. 5A shows that the PM purification amount increases as the voltage increases, and the purification amount increases as the gap G is reduced. FIG. 5B is a graph showing the change in PM number when the voltage is gradually increased to a high voltage when the gap G = 20 mm. Arc discharge does not occur when the voltage is −5 kV. When the pressure is increased to -6 kV, the PM number varies greatly (see the dotted line in the figure). This means that the corona discharge disappears and the PM cannot be purified at the moment when the arc discharge occurs. It was also found that the PM purification amount could not be increased even if the pressure was increased by -6 kV or more.

  Incidentally, arc discharge is more likely to occur as the engine speed increases. Further, arc discharge is more likely to occur as the engine load (output torque) increases. FIG. 5 shows test results when the engine speed is 3000 rpm and the output torque is 110 N-m.

  In response to this test result, according to the embodiment described in detail above, a direct current voltage is applied in a pulsed manner to the emitting portion 21b, so that the applied voltage before the electric arc generated in the emitting portion 21b reaches the ground electrode 30 is applied. Is temporarily interrupted, and the electric arc that has become arc discharge is extinguished on the way. Therefore, since generation | occurrence | production of arc discharge can be suppressed, the increase in applied voltage can be accelerated | stimulated, and the gap G can be made small, As a result, improvement of PM purification amount can be aimed at.

  Moreover, in this embodiment, it becomes a voltage of -5 kV to -15 kV with a period of 500 Hz to 100 kHz, and a voltage is instantaneously applied to the emitting part 21b for an extremely short time of 100 nanoseconds to 500 nanoseconds. These numerical values are set so as to cut off the applied voltage before the electric arc generated in the emitting portion 21b reaches the ground electrode 30, and are values obtained by tests.

  That is, when the voltage application time (predetermined time) is set to be greater than 500 nanoseconds, the electric arc reaches the ground electrode 30 and arc discharge is likely to occur. In addition, if the period for applying voltage (pulse-on period) is set larger than 100 kHz, the interval time Ti (see FIG. 4) during which no power is supplied is too short, and the applied voltage is temporarily interrupted to cause arc discharge. However, since the next voltage is applied before the electric arc is completely extinguished, the electric arc generated at the discharge portion 21b reaches the ground electrode 30 and causes arc discharge. There is concern about falling into a state. Further, even if the voltage peak value Vp (see FIG. 4) is lower than −15 kV (excessive pressure increase), arc discharge is likely to occur.

  On the other hand, if the voltage application time (predetermined time) is set smaller than 100 nanoseconds, the voltage application period is set smaller than 500 Hz, or the voltage peak value Vp is set higher than −5 kV, PM oxidation due to corona discharge is not caused. It becomes sufficient, and the amount of PM purification decreases. In view of these points, according to the present embodiment set to the various numerical values described above, the degree of suppression of arc discharge and the degree of increase in the purification amount due to PM oxidation can be balanced.

  When a voltage of −5 kV to −15 kV is applied, the time required to reach the ground electrode 30 after the electric arc is generated in the emitting portion 21b (arc discharge required time) is longer than 500 nanoseconds.

  In the present embodiment, the passage sectional area of the portion of the exhaust passage 11 where the discharge electrode 21 is disposed is equal to or larger than the minimum passage sectional area of the exhaust passage 11. In other words, the portion of the exhaust passage 11 where the discharge electrode 21 is disposed prevents the passage cross-sectional area of the exhaust passage 11 from being reduced.

  Furthermore, it has been found that when a DC voltage is applied in a pulsed manner to the emitting portion 21b as in the present embodiment, molecular vibration described below can be suppressed, and a significant reduction in the amount of PM purification due to molecular vibration can be avoided.

  That is, contrary to the present embodiment, when a DC voltage is continuously applied to the emitting portion 21b, immediately after the voltage application is started, as shown in FIG. Further, it can reach and collide with oxygen molecules located in a place away from the emitting portion 21b (near the ground electrode 30), and O radicals can be generated in a wide range. Therefore, the amount of PM flowing through the exhaust passage 11 without reacting with O radicals can be reduced, and the amount of PM purification can be kept above a certain level.

  However, when the voltage application time to the emission part 21b is increased, when electrons subjected to corona discharge from the emission part 21b repeatedly collide with oxygen molecules and nitrogen molecules (exhaust molecules) in the exhaust gas, the electrons of these molecules are changed. The energy is increased and the vibration becomes intense (see FIG. 6B). Then, the probability that the electrons subjected to corona discharge will collide with these vibrating molecules increases, and the probability that the electrons collide with oxygen molecules located away from the emitting portion 21b decreases. As a result, O radicals cannot be generated in a wide range, and as a result, the PM purification amount is significantly reduced.

  In order to solve this problem, in the present embodiment, a direct current voltage is applied in a pulsed manner to the emission portion 21b. Therefore, the exhaust molecules in the vicinity of the emission portion 21b are cut off before being subjected to molecular vibration with an intensity of a predetermined value or more. The gas is discharged from the exhaust passage 11. Therefore, O radicals can be generated in a wide range, and a significant decrease in the amount of PM purification can be avoided.

(Second Embodiment)
In the first embodiment, the power supply device 50 is applied to the exhaust gas purification device 10 that oxidizes and purifies PM by corona discharge. However, in the present embodiment shown in FIG. 7, the PM is charged by corona discharge. The power supply device 50 is applied to the exhaust gas purification device 100 that collects and purifies. The exhaust purification device 100 according to the present embodiment has a configuration in which the exhaust purification device 10 according to the first embodiment includes a collection unit 31 described later. Other hardware configurations of the power supply device 50 and the like are the same as those in the first embodiment, and a pulsed voltage is applied to the emission unit 21b.

  However, in this embodiment, the absolute value of the applied voltage is set lower than that in the first embodiment. Then, although the amount of energy input by corona discharge decreases and PM is not oxidized (or only slightly oxidized), PM is charged and aggregated as described below, so that PM is collected by the collection unit 31. be able to.

  That is, when corona discharge occurs and electrons are emitted (see (1) in FIG. 7), some of them negatively ionize gas molecules (oxygen) with high electron affinity to generate O radicals ( (Refer to (2)), and adhere to the nearby nano PM to negatively charge it (see (3)). The charged nano PM is attracted to the ground electrode 30 that also serves as a dust collecting electrode by the Coulomb force, gradually departs from the gas flow toward the downstream, moves to the outer peripheral side of the exhaust passage 11 while aggregating, and collects 31. Invade inside. (Refer to (4)). Thereafter, when the nano PM that has moved and aggregated to the back of the collection unit 31 reaches the ground electrode 30, it is discharged and aggregated and held (see (5)).

  In addition, the collection part 31 is comprised from the hollow cylindrical conductive cylinder, and is arrange | positioned at the internal peripheral surface of the ground electrode 30. FIG. The hollow mesh conductive cylindrical body constituting the collecting part 31 usually has a size that does not hinder the inflow of coarse particles having a particle size of about 1 μm to 10 μm, and contains aggregated fine particles inside. It is desirable to have sufficient space to hold.

  Also in the present embodiment, since a pulse voltage is applied to the emission part 21b in the same manner as in the first embodiment, the occurrence of arc discharge can be suppressed. Therefore, the applied voltage can be increased and the gap G can be reduced, so that the amount of PM purification can be improved. In addition, since a pulsed voltage is applied to the emission part 21b, the exhaust molecules in the vicinity of the emission part 21b are cut off from the applied voltage before molecular vibrations with an intensity of a predetermined value or more and are discharged from the exhaust passage 11 as they are. . Therefore, since O radicals can be generated in a wide range and PM can be charged in a wide range, a significant reduction in the PM purification amount can be avoided.

(Third embodiment)
By the way, in order to emit corona discharge by emitting electrons from the emission part 21b, it is desirable to reduce the electrical resistance (impedance R) in the exhaust passage 11 between the emission part 21b and the ground electrode 30. Since the impedance R is inversely proportional to the capacitance C formed by the gap G between the emitting portion 21b and the ground electrode 30, the capacitance C may be increased to reduce the impedance R. Since the capacitance C is proportional to the facing area S between the emitting portion 21b and the ground electrode 30, and is inversely proportional to the size of the gap G, the facing area S is increased to increase the capacitance C. At the same time, the gap G may be reduced.

  Therefore, in the present embodiment, in order to increase the facing area S, one discharge plug 20 is provided with a plurality of discharge portions 21b. In the example shown in FIG. 8, a plurality of discharge portions 21 b are arranged radially in the radial direction of the exhaust passage 11. In the example of FIG. 9, in addition to arranging a plurality of discharge portions 21 b in the radial direction of the exhaust passage 11, a plurality of discharge portions 21 b are also arranged in the exhaust flow direction. Further, the number (8) of protrusions of the discharge portion 21b in FIG. 1C may be further increased as shown in FIG. 10 to increase the facing area S.

  Further, if the gap G is reduced to such an extent that arc discharge does not occur, the impedance R can be reduced and the amount of electron emission applied to corona discharge can be increased. However, if an attempt is made to reduce the gap G by reducing the passage cross-sectional area of the portion of the exhaust passage 11 where the discharge portion 21b is disposed, the exhaust is constricted in that portion, leading to an increase in the flow resistance of the exhaust. End up. Therefore, it is desirable to set the passage cross-sectional area of the portion where the discharge portion 21b is arranged to be larger than the smallest passage cross-sectional area of the entire length of the exhaust passage 11.

(Fourth embodiment)
In the present embodiment shown in FIG. 11, the exhaust emission control device 10 of the first embodiment is applied to an internal combustion engine provided with a catalyst device 60 that oxidizes or reduces a specific substance in exhaust gas. The configurations of the discharge plug 20 and the power supply device 50 according to the present embodiment are the same as those in the first embodiment.

  The catalyst device 60 is configured by accommodating a catalyst 60a inside a case connected to the exhaust pipe 42. Specific examples of the catalyst 60a include a reduction catalyst that reduces NOx in exhaust gas, CO and HC in exhaust gas, and the like. An oxidation catalyst that oxidizes NOx, and a three-way catalyst that is used mainly in gasoline engines to oxidize and reduce NOx, CO, and HC.

  The case includes the following inlet taper portion 61, outlet taper portion 62, and holding portion 63. The inlet taper portion 61 has an inflow port 61a through which exhaust gas flows from the exhaust pipe 42, and has a conical shape that gradually increases the cross-sectional area of the passage from the inflow port 61a toward the downstream side of the exhaust flow. The outlet taper portion 62 has a conical shape that has an outflow port 62a through which the exhaust gas flows out to the exhaust pipe 42 and gradually increases the cross-sectional area of the passage from the outflow port 62a toward the upstream side of the exhaust flow. The holding part 63 has a cylindrical shape that connects the inlet taper part 61 and the outlet taper part 62, and holds the catalyst 60a therein.

  The discharge plug 20 is attached to the outlet taper portion 62 of the case. The discharge portion 21 b of the discharge plug 20 is disposed in the exhaust passage 11 formed by the exhaust pipe 42 in the vicinity of the downstream side of the outlet taper portion 62 and in the central portion of the passage cross section of the exhaust passage 11. Therefore, the ground electrode 30 disposed to face the discharge portion 21 b is located in the vicinity of the downstream side of the outlet taper portion 62 on the inner surface of the exhaust pipe 42.

  The arrangement of the discharge part 21b will be described in detail. A virtual line K in FIG. 11 indicates an extension line of the inner wall surface 62b of the outlet taper part 62, and the discharge part 21b is on the virtual line K or the virtual line K. It is desirable to arrange on the upstream side.

  As described above, according to the present embodiment, the exhaust gas positioned at the outlet taper portion 62 is guided by the inner wall surface 62b of the outlet taper portion 62 and flows toward the center of the exhaust passage 11 (in FIG. 11). (See arrow Y). Therefore, the PM concentration in the central portion of the passage section of the exhaust passage is higher than the PM concentration in the outer peripheral portion of the passage section. Therefore, according to the present embodiment in which the discharge electrode 21 is disposed in the vicinity of the downstream side of the outlet taper portion 62 and in the central portion of the passage cross section of the exhaust passage 11, the discharge electrode 21 is disposed in a portion having a high PM concentration. Therefore, the amount of purification by corona discharge can be increased.

  In the present embodiment, the pulsed voltage is controlled to be applied to the discharge plug 20 in the same manner as in the first embodiment, but the voltage applied to the discharge electrode 21 is not temporarily interrupted. You may control to perform an application continuously. That is, from this embodiment, the following invention independent from claim 1 described in the claims is extracted.

That means
“In an exhaust purification device that oxidizes and purifies particulates in exhaust by corona discharge from a discharge electrode disposed in an exhaust passage of an internal combustion engine, or charges and collects and purifies the particulates,
A catalyst that oxidizes or reduces a specific substance in the exhaust, and a case that is connected to an exhaust pipe that forms the exhaust passage and holds the catalyst inside.
The case is
An inlet tapered portion that has an inlet through which exhaust gas flows from the exhaust pipe, and that gradually expands a cross-sectional area of the passage from the inlet toward the downstream side of the exhaust flow;
An outlet taper portion that has an outlet for allowing exhaust to flow into the exhaust pipe, and that gradually increases the cross-sectional area of the passage from the outlet toward the upstream side of the exhaust flow;
A holding part for connecting the inlet taper part and the outlet taper part and holding the catalyst inside;
Is configured with
An exhaust emission control device, wherein the discharge electrode is disposed in the exhaust passage in the vicinity of the downstream side of the outlet taper portion and in the center of the cross section of the exhaust passage. ]
It is such an invention.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows. Moreover, you may make it combine the characteristic structure of each embodiment arbitrarily, respectively.

  In the first embodiment, the voltage application time is set shorter than the arc discharge required time. On the other hand, in response to the energy of the electrons discharged by corona discharge, the molecular vibration required time required until the exhaust molecules vibrate with a strength of a predetermined value or more as shown in FIG. The voltage application time may be set so as to be shorter than the time required for the molecular vibration.

  -The ease of occurrence of arc discharge varies depending on the engine operating conditions such as the exhaust flow rate, exhaust temperature, and PM amount at that time. Therefore, when applying the pulse voltage to the discharge portion 21b, at least one of the voltage application time, the voltage peak value Vp, and the voltage application cycle may be variably set according to the engine operating state. According to this, in accordance with the engine operating state, the input energy to the discharge part 21b can be increased so as not to generate arc discharge, and the amount of PM purification can be increased.

  The method of oxidizing and purifying PM as in the first embodiment may be combined with the method of purifying PM by charging and aggregation as in the second embodiment. For example, when a sufficient amount of electric power is stored in the battery 51 and the battery voltage is equal to or higher than a predetermined value, the PM is oxidized and purified, and when the battery voltage is lower than the predetermined value, PM may be purified by charging and aggregating.

  -The collection part 31 of the said 2nd Embodiment may be abolished, and you may make it hold nanoPM directly on the ground electrode 30 by aggregation.

DESCRIPTION OF SYMBOLS 10,100 ... Exhaust gas purification apparatus, 11 ... Exhaust passage, 21 ... Discharge electrode, 21b ... Release | release part, 30 ... Ground electrode (counter electrode), 50 ... Electric power supply apparatus (electric power supply means), 60a ... Catalyst, 61 ... Inlet Tapered portion, 61a ... inlet, 62 ... outlet tapered portion, 62a ... outlet, 63 ... holding portion.

Claims (9)

Applied to an exhaust purification device that oxidizes and purifies particulates in exhaust by corona discharge from a discharge electrode arranged in an exhaust passage of an internal combustion engine, or charges and collects and purifies the particulates,
Power supply means for supplying power used for the corona discharge by repeatedly applying a voltage to the discharge electrode a plurality of times,
The exhaust gas purifier power supply apparatus characterized in that the time for applying voltage instantaneously by the power supply means is shorter than a predetermined time. The time required for the electric arc to reach the other of the counter electrode and the discharge electrode after the electric arc occurs on one of the counter electrode and the discharge electrode facing the discharge electrode is the arc discharge required time,
2. The exhaust gas purifier power supply apparatus according to claim 1, wherein the arc discharge required time is the predetermined time. The time it takes for the exhaust molecules to vibrate at an intensity of a predetermined value or more after receiving the energy of the corona-discharged electrons after starting the instantaneous voltage application is the molecular vibration required time.
The power supply device for an exhaust gas purification apparatus according to claim 1, wherein the time required for the molecular vibration is the predetermined time.   The power supply device for an exhaust gas purification apparatus according to any one of claims 1 to 3, wherein the predetermined time is set to 100 nanoseconds or more and 500 nanoseconds or less.   The power supply device for an exhaust gas purification apparatus according to any one of claims 1 to 4, wherein a period of instantaneous voltage application by the power supply means is set to 500 Hz or more and 100 kHz or less.   The exhaust gas purification apparatus according to any one of claims 1 to 5, wherein an absolute value of a voltage peak value when voltage is instantaneously applied by the power supply means is set to 5 kV or more and 15 kV or less. Power supply equipment.   The power supply device for an exhaust gas purification apparatus according to any one of claims 1 to 6, wherein the discharge electrode has a shape including a plurality of protruding emission portions from which electrons are emitted by corona discharge. . On the inner wall surface of the exhaust pipe forming the exhaust passage, a counter electrode facing the discharge electrode is disposed,
8. The passage cross-sectional area of a portion of the exhaust passage where the discharge electrode is disposed is equal to or greater than the minimum passage cross-sectional area of the exhaust passage. Power supply device for exhaust gas purification device. A catalyst that oxidizes or reduces a specific substance in the exhaust, and a case that is connected to an exhaust pipe that forms the exhaust passage and holds the catalyst inside.
The case is
An inlet tapered portion that has an inlet through which exhaust gas flows from the exhaust pipe, and that gradually expands a cross-sectional area of the passage from the inlet toward the downstream side of the exhaust flow;
An outlet taper portion that has an outlet for allowing exhaust to flow into the exhaust pipe, and that gradually increases the cross-sectional area of the passage from the outlet toward the upstream side of the exhaust flow;
A holding part for connecting the inlet taper part and the outlet taper part and holding the catalyst inside;
Is configured with
9. The discharge electrode according to claim 1, wherein the discharge electrode is disposed in a vicinity of a downstream side of the outlet taper portion in the exhaust passage and in a central portion of a passage cross section of the exhaust passage. Power supply device for exhaust gas purification device.

Images