JP2001046910A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the electric power controlling method for a discharge type exhaust emission control device. SOLUTION: In this exhaust emission control device, the exhaust gas of an internal combustion engine is purified by passing to a flow passage formed between at least a pair of discharge electrodes and applying AC high voltage between the discharge electrodes. In the device, all of pulse of the AC high voltage are applied between the discharge electrodes in high loading where an exhaust gas flow rate is maximum. In middle/low loading where the exhaust gas flow rate is lower than that of high loading, the pulse of the AC high voltage is intermittently thinned out in accordance with the exhaust gas flow rate. In such a way, power supply is lowered in accordance with the exhaust gas flow rate without lowering the applied voltage (discharge capacity) between the discharge electrodes. In the case when the exhaust gas flow rate is low, not only the probability that the exhaust gas meets with the discharge but also the exhaust gas purifying efficiency are not changed so much even if the generating ratio of the discharge is lowered by thinning out the pulse of the AC high voltage since the flow velocity of the exhaust gas passing between the discharge electrodes is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, which purifies exhaust gas with discharge energy.

[0002]

2. Description of the Related Art In recent years, a new exhaust gas purifying technique for purifying exhaust gas using discharge energy has been studied.
According to this technique, as described in, for example, JP-A-5-59934 and JP-A-6-10652, exhaust gas of an internal combustion engine is caused to flow through a flow path formed between at least one pair of discharge electrodes. The exhaust gas is purified by applying an AC high voltage from an AC high voltage power supply between the discharge electrodes to generate a discharge. Incidentally, Japanese Patent Application Laid-Open No. 5-5993
Japanese Patent Application Laid-Open No. 6-10652 discloses a rectangular high-voltage power supply and a sine-wave high-voltage power supply.

[0003]

In order to efficiently purify the exhaust gas by using the exhaust gas purifying apparatus having such a structure, it is necessary to apply an AC high voltage pulse applied between the discharge electrodes to a voltage higher than a voltage at which discharge is likely to occur. (For example, 10 kV or more). Even if the frequency of the rectangular high-voltage AC power supply is low, the voltage waveform rises instantaneously, so that the applied voltage between the discharge electrodes can be quickly raised to a voltage higher than the voltage at which discharge is likely to occur. Efficiency can be increased. However, with a square wave AC high voltage power supply,
For example, in order to generate a high-voltage rectangular wave pulse of 10 kV or more, an extremely expensive high-voltage / high-speed switch is required, and the product price becomes extremely high, and it is difficult to put it into practical use.

On the other hand, a sine-wave AC high-voltage power supply has the advantage of being relatively inexpensive and light-weight using a high-voltage transformer. Can be. However, the conventional sine-wave AC high-voltage power supply has a problem in controlling the supplied power. In other words, the rated power of the AC high-voltage power supply is set so that the entire exhaust gas can be purified even at a high load and a high speed where the exhaust gas flow rate is maximized. At medium load and low load when the gas flow rate is low, power is excessively supplied, and power is wasted. Therefore, it is preferable to change the supplied power according to the operating state of the internal combustion engine (exhaust gas flow rate).

In general, when controlling the supply power with a sine-wave AC high-voltage power supply, a method of adjusting the supply power by changing the applied voltage, or adjusting the supply power by changing the frequency of the sine wave. Is adopted. However, when the applied voltage is reduced, it becomes difficult to generate a discharge between the discharge electrodes, and the purification performance of the exhaust gas itself is reduced. Therefore,
From the viewpoint of ensuring purification performance (securing applied voltage), power control by voltage adjustment cannot be adopted. On the other hand, when the supply power is adjusted by changing the frequency of the sine wave, there is a disadvantage that the efficiency of the high-voltage transformer decreases. In addition, when the frequency of the sine wave is reduced, the rise of the voltage waveform is delayed, so that the applied voltage cannot be quickly raised to a voltage higher than the voltage at which discharge is likely to occur, and the exhaust gas purification efficiency is reduced.

The present invention has been made in view of such circumstances, and accordingly, an object of the present invention is to control the supply power without lowering the exhaust purification efficiency, and to improve the exhaust purification efficiency and reduce the power consumption. An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that can achieve both.

[0007]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, comprising: intermittently thinning out alternating high voltage pulses applied between discharge electrodes; All pulses can be applied without thinning, and the pulse thinning rate of the AC high voltage is changed by the power control means according to the operating state of the internal combustion engine. As described above, when the AC high voltage pulse applied between the discharge electrodes is intermittently thinned out, the supplied power can be reduced without lowering the applied voltage (discharge capability) between the discharge electrodes. Moreover, even if the AC high voltage pulse is intermittently thinned out, the pulse waveform applied between the discharge electrodes is the same as when all the pulses are applied, so that the rising of the voltage waveform does not become slow and the applied voltage is applied to all the pulses. It is possible to quickly start up to the same voltage as at the time, and to obtain the same exhaust gas purification efficiency as at the time of applying all the pulses. Therefore, if the pulse thinning rate of the AC high voltage is changed according to the operation state of the internal combustion engine, the supply power can be controlled according to the operation state of the internal combustion engine without lowering the exhaust purification efficiency, and the exhaust purification efficiency can be improved. Power consumption can be reduced at the same time.

In this case, it is preferable to control the pulse thinning rate of the AC high voltage to increase as the exhaust gas flow rate decreases. Increasing the AC high voltage pulse thinning rate decreases the discharge occurrence rate, but when the exhaust gas flow rate is low, the flow rate of the exhaust gas flowing between the discharge electrodes decreases, so the AC high voltage pulse is thinned out. Even if the rate of occurrence of discharge decreases, the probability that exhaust gas encounters discharge, and thus the exhaust gas purification efficiency, does not change much.
In consideration of this point, if the pulse thinning rate of the AC high voltage is increased as the flow rate of the exhaust gas decreases, the supply power according to the flow rate of the exhaust gas is maintained while the probability that the exhaust gas encounters the discharge is kept almost constant. Can be controlled to the minimum necessary.

The present invention can be applied to an exhaust gas purifying apparatus for applying a rectangular wave voltage pulse between discharge electrodes. However, as in claim 3, a sine wave pulse is applied between discharge electrodes. It is better to do. A sine wave AC high-voltage power supply has the advantage of being relatively inexpensive and lightweight using a high-voltage transformer.
Can meet light weight requirements.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a gasoline engine will be described below with reference to the drawings. FIG.
As shown in FIG. 1, an exhaust purification device 12 is provided in the exhaust pipe 11 of an internal combustion engine (engine). In the exhaust gas purification apparatus 12, a plurality of discharge electrodes 13 and 14 are arranged in parallel along the flow of exhaust gas, and a large number of dielectric particles 15 are accommodated between the discharge electrodes 13 and 14. Grain 15
Exhaust gas passes through the gap. The surface of the dielectric particles 15 is coated with a catalyst that promotes a purification reaction of exhaust gas. The discharge electrodes 13, 1
The space may be formed without accommodating the dielectric particles 15 between the four.

A high frequency AC high voltage generated by an AC high voltage generator 16 is applied between the opposed discharge electrodes 13 and 14, and a discharge occurs between the dielectric particles 15. As a result, the exhaust gas flowing through the gap between the dielectric particles 15 is exposed to the discharge field, and the discharge energy and the catalyst on the surface of the dielectric particles 15 accelerate the purification reaction of NOx, CO, HC, etc. in the exhaust gas. Is done. If the dielectric particles 15 are not accommodated between the discharge electrodes 13 and 14, the discharge electrodes 13 and
NOx, C in the exhaust gas by the discharge generated between
The purification reaction of O, HC, etc. is promoted.

Next, the configuration of the AC high voltage generator 16 will be described with reference to FIG. This AC high voltage generator 16
The inverter circuit 18 converts a 12 V DC voltage supplied from a power supply 17 mounted on a vehicle to a high frequency (for example, 10 to 20 kHz) AC high voltage (for example, 10 kV).
And applied between the discharge electrodes 13 and 14. The inverter circuit 18 of the present embodiment is, for example, of a center tap transformer type, in which a power line on the positive terminal side of the power supply 17 is connected to a center tap on the primary side of the high voltage transformer 19,
Both ends of the primary winding are respectively connected to the ground via semiconductor switching elements A and B such as MOSFETs. ON / OFF of each of the switching elements A and B is controlled by the control unit 20 (power control unit).

The control unit 20 determines the exhaust gas flow rate from the intake air amount, the engine speed, and the like. When the exhaust gas flow rate is maximized and the load is high, as shown in FIG. Output pulse. At the time of outputting all the pulses, the two switching elements A and B are alternately turned on in synchronization with the frequency of the AC high voltage, so that the high-voltage transformer 19 is turned on.
AC high voltage is continuously output from the secondary side of.

The controller 20 controls the AC high voltage applied between the discharge electrodes 13 and 14 at medium and low loads when the exhaust gas flow rate is lower than at high loads, as shown in FIGS. 3 (b) and 3 (c). Pulse is intermittently thinned out. When thinning out pulses, 2
By keeping both of the switching elements A and B in the off state, the primary current of the high-voltage transformer 19 is cut off, and no pulse is generated on the secondary side of the high-voltage transformer 19.

In this case, the control unit 20 controls the pulse thinning rate of the AC high voltage to increase (that is, to reduce the number of output pulses) as the exhaust gas flow rate decreases. Since the exhaust gas flow rate is lower at low load than at medium load, the pulse thinning rate is higher at low load than at medium load, and the number of output pulses is higher than at medium load. Less at low load. In the case of thinning out the pulses, the pulses may be evenly thinned out as shown in FIG. 3A, but as shown in FIG. 3A, the output pulses and the thinned out pulses may be continued by a predetermined number, respectively. . This is because the pulse frequency (discharge generation frequency) is much higher than the flow rate of the exhaust gas, so that the probability of the exhaust gas encountering the discharge is not affected by the pulse thinning method.

When the pulse thinning rate of the AC high voltage is increased, the rate of occurrence of discharge is reduced. However, when the flow rate of exhaust gas is small, the flow rate of exhaust gas flowing between the discharge electrodes 13 and 14 is reduced. Even if the generation rate of discharge is reduced by thinning out the pulses of the AC high voltage, the probability that the exhaust gas encounters the discharge, and consequently the exhaust purification efficiency does not change so much. In consideration of this point, if the pulse thinning rate of the AC high voltage is increased as the flow rate of the exhaust gas decreases, the supply power according to the flow rate of the exhaust gas is maintained while the probability that the exhaust gas encounters the discharge is kept almost constant. Can be controlled to the minimum necessary.

In the above-described embodiment, the pulse of the AC high voltage applied between the discharge electrodes 13 and 14 is intermittently thinned when the exhaust gas flow rate is lower or medium load than when the load is high. Therefore, the supply power can be reduced according to the exhaust gas flow rate without lowering the applied voltage (discharge capability) between the discharge electrodes 13 and 14. Moreover, even if the AC high voltage pulse is intermittently thinned out, the pulse waveform applied between the discharge electrodes 13 and 14 is the same as when all the pulses are applied. It is possible to quickly start up to the same voltage as when all pulses are applied, and to obtain the same exhaust gas purification efficiency as when all pulses are applied.
Therefore, if the pulse thinning rate of the AC high voltage is changed according to the exhaust gas flow rate as in the present embodiment, the supply power can be controlled to a necessary minimum according to the exhaust gas flow rate without lowering the exhaust gas purification efficiency. As a result, both improvement in exhaust gas purification efficiency and reduction in power consumption can be achieved.

Moreover, since the AC high voltage generator 16 of the present embodiment is configured to generate a sine wave AC high voltage, it can be made relatively inexpensive and lightweight by using the high voltage transformer 19. Therefore, the low-priced and lightweight conditions required for mounting on an automobile can be satisfied. The AC high voltage generator 16 is not limited to the center tap transformer type as shown in FIG. 1, and it goes without saying that another type of inverter circuit may be used.

Further, the present invention may use an AC high voltage generator for generating a square wave AC high voltage. Even in this case, the intended purpose of the present invention (to improve exhaust gas purification efficiency and reduce power consumption). Can be achieved).

In this embodiment, the pulse thinning rate of the AC high voltage is changed in accordance with the flow rate of the exhaust gas. However, the intake air amount detected by various sensors, the engine speed, the throttle opening, the intake The pulse thinning rate of the AC high voltage may be controlled using at least one of the engine operating state parameters such as the pipe pressure. Since all of these engine operating state parameters are parameters that affect the exhaust gas flow rate, controlling the pulse thinning rate using these parameters means controlling the pulse thinning rate using the exhaust gas flow rate. Almost the same effects can be obtained.

In addition, the present invention can be implemented with various changes, such as changing the number and arrangement of the discharge electrodes 13 and 14, the structure of the flow path, and the like, and applying the present invention to an exhaust gas purification device for a diesel engine. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of an AC high voltage generator according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a mechanical configuration of the exhaust gas purification device.

3A is a time chart showing an output voltage waveform of the AC high voltage generator under a high load, and FIG. 3B shows a different example of an output voltage waveform of the AC high voltage generator under a medium load. FIG. 3C is a time chart showing an output voltage waveform of the AC high voltage generator at a low load.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Exhaust pipe, 13, 14 ... Discharge electrode, 15 ... Dielectric particles, 16 ... AC high voltage generator, 17 ... Power supply, 18 ... Inverter circuit, 19 ... High voltage transformer, 20 ... Control part (voltage control means) , A, B ... switching elements.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B03C 3/38 B01D 53/34 ZABZ F01N 3/08 B03C 3/14 C (72) Inventor Nobuhiko Sugie Aichi 1-1-1 Showa-cho, Kariya F-term in Denso Corporation (reference) 3G091 AA02 AA17 AA18 AB14 BA14 BA15 BA19 DA01 DA02 DA03 DA04 DB10 EA01 EA05 EA06 EA07 FA12 FA13 FA14 4D002 AA08 AA12 AA34 AC10 BA05 BA07 CA07 GA03 GB01 GB20 4D054 AA03 BA01 BB05 BC02 BC13 BC14 BC25 CA03 CA20 CB10

Claims (3)

[Claims] An exhaust gas of an internal combustion engine is caused to flow through a flow path formed between at least one pair of discharge electrodes, and a discharge is generated by applying an AC high voltage between the discharge electrodes, so that the exhaust gas is discharged. In the exhaust gas purification apparatus for purifying, it is possible to intermittently thin out pulses of the AC high voltage applied between the discharge electrodes, or to apply all the pulses without thinning out, and to thin out the pulses of the AC high voltage. An exhaust gas purification device for an internal combustion engine, comprising: power control means for changing a rate according to an operation state of the internal combustion engine. 2. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said power control means controls the pulse thinning rate of said AC high voltage to increase as the exhaust gas flow rate decreases. . 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the AC high voltage pulse applied between the discharge electrodes is a sine wave pulse.