JP2014047670A - Control method and unit for nox aftertreatment device of engine including ozone generation means - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a NOx aftertreatment device of an engine which can purify NOx immediately after start-up and speedily realizes a necessary and sufficient ozone supply flow rate in accordance with a change in a NOx flow rate without requiring a large-scale device.SOLUTION: A controller 4 of a NOx aftertreatment device 3 of an engine including ozone generation means 6 which supplies ozone to an exhaust pipe 2 of the engine 1: estimates flow rates of NO and NO; decides a target ozone flow rate corresponding to a total flow rate of the estimated flow rates of the NO and the NO; and operates the ozone generation means 6 to achieve the target ozone flow rate. The generated ozone is added to exhaust through an ozone supply passage 31. Then, NOx absorption means 5 removes HNOgenerated by the NO, the NOand moisture in the exhaust.

Description

  The present invention relates to a post-treatment device that absorbs and separates NOx components in exhaust gas, in particular, an ozone generating means, and a control method for an engine post-treatment device that has NOx absorption and separation capability even in a cold state immediately after the engine is cold-started. The present invention relates to a control device.

  In an aftertreatment device for NOx discharged from an engine, in particular, a diesel engine, a system is generally used in which NOx reduction treatment is performed using a catalyst to purify the NOx component. As the catalyst, NOx occlusion reduction type and adsorption reduction type catalysts that store or adsorb NOx when lean and release and purify when rich, and selective reduction type catalysts that add urea water to the exhaust as a reducing agent are known. In this technique, since NOx purification cannot be achieved at a temperature lower than the operating temperature (about 200 ° C. or higher) at which the catalyst operates, a technique for realizing this is required.

  In addition, the NOx occlusion reduction type or adsorption reduction type catalyst needs to use expensive noble metals such as platinum. On the other hand, although the selective reduction catalyst can use base metal, a device for metering and injecting urea water to the exhaust system is required, and further, an ammonia removal catalyst is required in order not to release ammonia gas into the atmosphere. The whole device is expensive. Therefore, there is a need for a new type of NOx aftertreatment device that can be realized at a lower cost.

In Patent Document 1, an ozone-containing gas generated by an ozone generator is supplied to an ozone adsorption device, and a nitrogen oxide-containing gas stream is supplied to a reactor duct, while a slip stream of the nitrogen oxide-containing gas stream is converted into ozone. There has been proposed a method of removing nitrogen oxides from a gas stream by a series of steps of supplying an adsorber to desorb ozone and supplying an ozone-containing slip stream to a reactor duct. In the reactor duct, nitrogen oxides react with ozone and are converted to N ₂ O _5, and nitric acid is also produced when moisture is present in the air. The stream containing N ₂ O ₅ and nitric acid is further fed to an aqueous scrubber where it contacts the aqueous solution and is absorbed and removed.

  In the method of Patent Document 1, in order to supply high-concentration ozone to exhaust gas, an ozone adsorption device including a structural sorbent material such as silica gel is provided, and the ozone adsorption process to the adsorption device and the desorption are performed. The separation process for supplying exhaust gas is alternately performed.

JP 2001-187316 A

  A method such as Patent Document 1 is suitable for removing NOx from the flue gas of a large-scale combustion apparatus that is installed stationary because the apparatus is large-scale, but for vehicles in which the usage load changes frequently. Not suitable for engines. Further, such an apparatus configuration is difficult to apply to a vehicle engine in which the ozone supply flow rate cannot be changed rapidly, the exhaust flow rate changes greatly every moment, and the NOx concentration also changes greatly.

The first object of the present invention is that NOx purification can be performed even at a low temperature immediately after the engine is cold-started, an expensive catalyst such as a precious metal is not used for NOx purification, or a large-scale apparatus. Therefore, the present invention is to provide a new type of NOx aftertreatment device that can reduce the cost of the apparatus and satisfy these requirements and is suitable for a vehicle engine.
The second object of the present invention is an ozone which is suitable for a vehicular engine having a large load fluctuation, can quickly follow the ozone supply flow rate according to the change in the NOx flow rate of exhaust gas, and can generate high-concentration ozone. It is an object of the present invention to provide a control method and a control device for an engine aftertreatment device that realizes a generation means and has high purification performance that can cope with strict exhaust gas regulations in the future.

In order to solve the above-mentioned problem, the invention according to claim 1 is a control method of an NOx aftertreatment device for an engine including an ozone generating means for supplying ozone to exhaust from the engine,
The NO and NO ₂ flow rates in the exhaust gas are estimated, the ozone target flow rate is determined according to the estimated total flow rate of NO and NO ₂ , and generated by operating the ozone generating means so as to be the determined target flow rate Ozone is added to the exhaust gas, and HNO ₃ produced by the ozone, NO, NO ₂ and moisture in the exhaust gas is removed from the exhaust gas.

In order to solve the above-mentioned problem, the invention according to claim 2 is an ozone which has an ozone supply passage connected to the exhaust passage of the engine and an air inflow passage connected to the intake passage, and generates ozone from the inflowing air. A control device for a NOx after-treatment device for an engine that includes a generation unit and causes the NOx absorption unit to absorb a reaction product of NOx and ozone,
NOx flow rate estimating means for estimating NO and NO ₂ flow rates in the exhaust gas flowing through the exhaust passage;
Target flow rate determining means for determining the ozone target flow rate in correspondence with the total flow rate of NO and NO ₂ estimated by the NOx flow rate estimating means;
Drive means for operating the ozone generation means so as to be the ozone target flow rate determined by the target flow rate determination means,
The ozone generated by the ozone generating means is added to the exhaust gas from the ozone supply passage, and HNO ₃ generated by the added ozone, NO, NO ₂ and moisture in the exhaust gas is absorbed by the NOx absorbing means and removed. It is characterized by.

In the apparatus according to claim 3, filter means carrying an oxidation catalyst or an oxidation catalyst is arranged upstream of the exhaust passage where the ozone supply passage joins,
The NOx flow rate estimating means includes the NO and NO ₂ flow rates in the exhaust gas, the NO concentration estimated value in the exhaust gas exhausted from the engine, the engine intake flow rate, the temperature of the filter means carrying the oxidation catalyst or the oxidation catalyst, or The estimated NO flow rate and NO ₂ estimated flow rate estimated using the exhaust gas temperature are obtained.

5. The apparatus according to claim 4, wherein the target flow rate determining means is a flow rate of 1.5 equivalent ratio times NO estimated flow rate and 0 of NO ₂ estimated flow rate estimated by the NOx flow rate estimating means of claim 3. The ozone target flow rate is determined corresponding to a value equal to or greater than the sum of the flow rates multiplied by .5 equivalent ratio, and the ozone generating means is operated based on the ozone target flow rate.

  The apparatus according to claim 5 includes: a gas flow rate estimating unit configured to estimate a gas flow rate passing through the ozone generating unit; and an ozone target unit determined from the estimated gas flow rate and the ozone target flow rate determined by the target flow rate determining unit. Is provided with an ozone generation concentration calculating means for obtaining an ozone concentration to be generated, and the ozone generation means is operated so as to obtain this ozone generation concentration.

7. The apparatus according to claim 6, wherein the target flow rate determining means obtains a ratio at which the ozone generated by the ozone generating means disappears before reacting with NO, NO ₂ , and moisture, and in accordance with the ratio, Correct the target flow rate.

  8. The apparatus according to claim 7, wherein the target flow rate determining means determines the ratio at which ozone disappears in correspondence with exhaust gas temperature.

  The apparatus according to claim 8 is the apparatus according to claim 7, wherein the target flow rate determining means determines the ratio at which the ozone disappears from the lower unsaturated hydrocarbon in the exhaust gas at the junction of the ozone supply passage. It is determined according to the concentration.

  The apparatus according to claim 9, further comprising a correcting unit that corrects the ozone target flow rate determined by the target flow rate determining unit based on information on humidity in the atmosphere.

  The apparatus according to claim 10 is the apparatus according to claims 5 to 8, wherein a humidity removing means and an oxygen enriching means are installed in the air inflow passage upstream of the ozone generating means and flows into the ozone generating means. Correction means for correcting the ozone generation concentration based on a change in the oxygen concentration in the gas is provided.

According to the control method of claim 1, the NOx aftertreatment device that generates and adds ozone to the exhaust system of the engine is arranged, and the ozone target flow rate is set in advance in accordance with the NO and NO ₂ flow rates that vary depending on the operation state. Once determined, the ozone generating means is activated. The ozone generating means can generate ozone according to the supplied power with good controllability using, for example, discharge plasma, and can maintain the ozone target flow rate by following changes in the NO and NO ₂ flow rates. Ozone reacts with NO and NO ₂ in the exhaust to generate the _{N 2 O 5, N 2 O} 5 is converted to HNO ₃ readily reacts with moisture in the exhaust gas. This HNO ₃ can be removed from the exhaust by contacting with the absorbent.

  According to this method, it is possible to efficiently purify NOx immediately after starting the engine without requiring a large-scale device or an expensive catalyst. Therefore, it is suitably used for a vehicle engine having a large NOx fluctuation, and even when the engine load is high, necessary and sufficient ozone can be supplied to the exhaust gas to achieve high purification performance.

In order to realize the control method of the first aspect, the control device of the second aspect introduces air in the intake passage into the ozone generation means to generate ozone, and supplies the ozone from the ozone supply passage to the exhaust. At this time, the NOx flow rate estimating unit estimates the total flow rate of NO and NO ₂ discharged from the engine, and the drive unit operates the ozone generating unit so that the ozone target flow rate determined by the target flow rate determining unit is reached. Necessary and sufficient ozone can be supplied. The exhaust gas is mixed with ozone and reacts at the merging portion of the ozone supply passage, and the generated HNO ₃ is removed while passing through the NOx absorbing means disposed downstream of the merging portion. Therefore, ozone can be efficiently generated according to the operating state of the engine, and NOx discharged from the engine can be purified.

It is a whole block diagram of the control apparatus of the NOx aftertreatment device for engines in a 1st embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the ozone production | generation means of the NOx aftertreatment apparatus for engines in 1st Embodiment. It is a schematic diagram which shows a waveform when the frequency of the high voltage pulse which a high voltage generator produces | generates is low, and a waveform when it is high. It is a flowchart which shows the principal part of the control program incorporated in the controller in 1st Embodiment. It is a figure which shows the relationship between engine rotation speed, injection amount, and NO density | concentration of exhaust_gas | exhaustion. It is a diagram showing the relationship between NO ₂ conversion ratio from the intake air flow exhaust temperature and NO. It is a figure which shows the relationship between exhaust temperature and an ozone extinction coefficient. It is a figure which shows the relationship between an intake air flow rate, exhaust temperature, and exhaust pressure. It is a figure which shows the relationship between the humidity in air, the high voltage frequency applied to a discharge device, and ozone generation density | concentration. It is a figure which shows the relationship between the humidity coefficient corresponding to the humidity in air, and the ozone concentration to produce | generate. It is a figure which shows the flow volume characteristic of the frequency corresponding to correction ozone production | generation density | concentration. It is a whole block diagram of the control apparatus of the NOx aftertreatment device for engines in a 2nd embodiment of the present invention. It is a schematic sectional drawing which shows the structure of the oxygen enrichment means in 2nd Embodiment. It is a figure which shows the relationship between the upstream / downstream pressure ratio and the oxygen concentration of downstream oxygen-enriched air in an oxygen-enriched membrane having a predetermined separation coefficient. It is a flowchart which shows the principal part of the control program incorporated in the controller in 2nd Embodiment. It is a flowchart following the flowchart shown in FIG. 14A. It is a figure which shows the relationship between oxygen concentration and an oxygen enrichment coefficient.

(First embodiment)
1 and 2 show a first embodiment of an engine NOx aftertreatment device (hereinafter abbreviated as NOx aftertreatment device) including an ozone generating means to which the present invention is applied. In FIG. 1, the engine 1 is a diesel engine provided with a turbocharger (supercharger) 15, and the control device of the NOx aftertreatment device 3 of the present embodiment processes NOx in the exhaust discharged from the engine 1. A DPF (diesel particulate filter) 21 serving as a filter means is disposed in the middle of the exhaust pipe 2 serving as an exhaust passage, and an exhaust cooling means 22 and a NOx absorption means 5 constituting the NOx aftertreatment device 3 are disposed downstream thereof. Be placed. A passage that joins the exhaust pipe 2 a between the exhaust cooling means 22 and the NOx absorption means 5 is provided, and is connected to the ozone generation means 6 of the NOx aftertreatment device 3 to become an ozone supply passage 61.

  The engine 1 takes in air from the intake inlet 16. The air is pressurized by the compressor 14 of the turbocharger 15, and the air that has become hot due to the pressurization is cooled by an intercooler 19 installed in an intake pipe 18 as an intake passage, and then sent to the intake manifold 10. It is sucked into the combustion chamber of the engine 1 from the port. In the combustion chamber of the engine 1, air and fuel are mixed and burned. The piston of the engine 1 is pushed down by the combustion, and power is generated as the rotational force of the engine output shaft 11.

  The exhaust after the combustion is exhausted from the combustion chamber of the engine 1 to the exhaust manifold 12. After that, the exhaust gas is discharged to the exhaust pipe 2 after rotating the turbine 13 directly connected to the compressor 14 of the turbocharger 15 to pressurize the air. The exhaust passes through the DPF 21 here, and particulate matter (PM) in the exhaust is filtered and collected by the DPF 21. At the same time, the HC component and the CO component are also purified by the oxidation catalyst coated on the surface of the DPF 21 through which the exhaust passes. Thereafter, the exhaust passes through the exhaust cooling means 22 and is cooled, so that the exhaust temperature usually falls between 100 ° C. and 180 ° C.

  The DPF 21 used here is a known wall flow type exhaust filter in which a porous wall formed of ceramic works as a filter. The exhaust cooling means 22 is a known Rankine cycle exhaust heat recovery system. For example, the heat energy obtained by cooling the exhaust gas evaporates the refrigerant to become a high-pressure gas, rotates the gas turbine, and is directly connected to the gas turbine. It is like being converted into electrical energy by a machine and stored in a battery.

  The cooled exhaust gas is introduced into the NOx aftertreatment device 3, passes through the exhaust pipe 2 a where the ozone supply passage 61 joins, and further passes through the NOx absorption means 5. Here, the NOx contained in the exhaust gas reacts with ozone in the ozone-containing air supplied from the ozone generating means 6 and is absorbed in contact with the NOx absorbing liquid in the NOx absorbing means 5. Up to this point, PM, HC, CO, and NOx are removed, and the exhaust becomes clean and exhausted from the exhaust pipe outlet 23 into the atmosphere.

  The ozone generating means 6 generates ozone from air using discharge plasma and sends it out as ozone-containing air, and the detailed configuration will be described later. The ozone generating means 6 forms a passage having a discharge space part in which ozone is generated inside, and one end side thereof is an ozone supply passage 61 that joins the exhaust pipe 2a, and the other end side is air that branches from the intake pipe 18. Connected to the inflow passage 62. The air inflow passage 62 is opened immediately upstream of the intake throttle 17 in order to introduce the air supercharged by the compressor 14 and cooled by the intercooler 19. In the middle of the air inflow passage 62, a fixed throttle 38 and a blower 39 are arranged from the upstream and reach the ozone generating means 6. Thereby, even when the operating load of the engine 1 is high and high concentration NOx is discharged from the engine 1, the supercharged air is supplied to the ozone generating means 6 so that necessary and sufficient ozone can be generated and supplied to the exhaust gas. Introduce. The blower 39 is a known configuration that is driven by an electric motor (not shown). The blower 39 operates to guide the generated ozone to the exhaust even when the engine 1 is operated at a low speed and no supercharging pressure is generated. A flow to the tube 2a is formed.

In the exhaust pipe 2a, ozone (O ₃ ) supplied from the ozone supply passage 61 causes a chemical reaction represented by the following reaction formulas (a) to (c) with NOx (NO, NO ₂ ) in the exhaust, It is converted to N ₂ O ₅ which is a precursor of nitric acid. Further, the produced N ₂ O ₅ reacts again with moisture (H ₂ O) in the exhaust gas and is converted to HNO ₃ as shown in the following reaction formula (d).
NO + O ₃ → NO ₂ + O ₂ (a)
NO ₂ + O ₃ → NO ₃ + O ₂ (b)
NO ₂ + NO ₃ → N ₂ O ₅ (c)
N ₂ O ₅ + H ₂ O → 2HNO ₃ (d)

The reaction product HNO ₃ reaches the NOx absorbing means 5 and is absorbed by the NOx absorbing liquid and separated from the exhaust gas. The NOx absorbing liquid is not particularly limited as long as it is a liquid capable of absorbing and separating HNO _3. For example, water or an alkaline water liquid can be used. As another example of the NOx absorbing liquid, it is conceivable to use an ionic liquid that chemically adsorbs HNO ₃ . In this case, the ionic liquid is stored in a storage unit (not shown), and forms a circulation path with the NOx absorption unit 5 (arrow in the figure). And sent from the inlet 51 of the NOx absorbing means 5 into the interior of the gas-liquid contact portion is contacted with the exhaust adsorbs HNO _3. Thereafter, the ionic liquid sent to the liquid recovery means (not shown) is separated and recovered from the outlet 52 of the NOx absorption means 5 and returned to the storage means again.

  In FIG. 1, an intake flow rate sensor 45 is disposed in the intake system immediately downstream of the intake inlet 16. Further, a throttle opening sensor 44 for detecting the throttle opening of the intake throttle 17 is disposed, and an intake pipe pressure sensor 40 is disposed at the junction of the intake manifold 10. In the vicinity of the output shaft 11 of the engine 1, a rotational speed sensor 41 that measures the engine rotational speed is arranged, and in the exhaust system, an exhaust temperature sensor 42 that measures the exhaust temperature is arranged downstream of the DPF 21. In addition, a humidity sensor 43 that directly or indirectly measures the humidity of the outside air is arranged. Each sensor described above converts the measured information into an electric signal and sends it to the controller 4 which is a control device through a connected electric wire.

  The controller 4 has a known configuration in which a microcomputer is incorporated for control. The controller 4 is connected to the blower 64, the ozone generation means 6, the exhaust cooling means 22, and the NOx absorption means 5 so as to be electrically operable. Based on the input electrical signal, the blower 39, the ozone generation means 6, the exhaust cooling means 22, and the NOx absorption means 5 are controlled based on the information processing and operation program previously programmed in the microcomputer.

The NOx aftertreatment device 3 of the present embodiment supplies ozone generated directly by the ozone generating means 6 directly to the exhaust pipe 2a and causes it to react with NOx in the exhaust. Here, since the reaction from NOx to N ₂ O ₅ and the reaction from HNO ₃ occurs easily even at room temperature, NOx in the exhaust gas can be purified without being influenced by the exhaust gas temperature. Since this method has a simple configuration, a known NOx storage reduction catalyst or urea addition selective reduction catalyst does not work, and can be used even when the exhaust gas temperature is low during engine start or light load operation. The first object can be achieved.

<Configuration example of ozone generating means>
This method is also suitable for the second object of the present invention, and can quickly follow the ozone supply flow rate in accordance with the change in the NOx flow rate of the exhaust gas. Next, a specific configuration of the compact ozone generating means 6 that realizes this object will be described.
FIG. 2 shows a cross-sectional view of the ozone generating means 6 of the present embodiment. The ozone generating means 6 has a U-shaped passage 60 inside, and a passage 60a leading to the air inlet 602 on one end side and a passage 60b leading to the air outlet 601 on the other end side through the connection passage 60c. Communicate. The air inlet 602 is connected to the air inflow passage 62 in FIG. 1, and the air outlet 601 is connected to the ozone supply passage 61 in FIG.

  The passage 60 is formed between the passage walls 603 and 604 having a U-shaped cross section constituting the casing of the ozone generating means 6, and the first creeping discharge is formed along the outer passage wall 604 at a vertically symmetrical position in the drawing. A device 3A and a second creeping discharge device 3B are installed. Each of the first creeping discharge device 3 </ b> A and the second creeping discharge device 3 </ b> B has a discharge electrode 32 formed on the surface of the ceramic body 30 and an induction electrode 31 embedded in the ceramic body 30. In the first and second creeping discharge devices 3A and 3B, the discharge electrode 32 on the surface of the ceramic body 30 is configured as a plurality of lines extending from the front of the figure to the back, and the plurality of lines are electrically connected. .

  In the first creeping discharge device 3A, the discharge electrode 32 and the induction electrode 31 are connected to a first high-voltage generator 34 outside the device via lead wires 33a and 33b. Similarly, the second creeping discharge device 3B is connected to a second high voltage generator 36 outside the device via conductors 33a and 33b. These conducting wires 33a and 33b penetrate the passage wall 604 outside the connection passage 60c and are taken out to the outside, and are electrically insulated from the casing of the ozone generating means 6 by the insulating member 35. Based on the control signal from the controller 4, the sub-controller 37 serving as a driving means controls whether the first and second high voltage generators 34 and 36 are activated or deactivated and generates the first and second high-voltage power supplies. The frequency of the high voltage pulse generated by the devices 34 and 36 is controlled.

In the present embodiment, the air flowing in from the air inlet 602 first passes through the passage 60a formed between the passage wall 603 and the first creeping discharge device 3A. And it passes along the channel | path 60b formed between the channel | path wall 603 and the 2nd creeping discharge apparatus 3B through the connection channel | path 60c. Thereafter, the air flows out from the air outlet 601. Here, when a high voltage pulse is applied between the discharge electrode 32 and the induction electrode 31 of the ozone generating means 6, creeping discharge plasma is generated on the surface of the ceramic body 30 around the discharge electrode 32, which is schematically shown in FIG. A creeping discharge zone 63 as a discharge space portion shown in FIG. In FIG. 2, the creeping discharge zone is shown only for one discharge electrode 32, but the creeping discharge zone 63 is generated in all the applied discharge electrodes 32. Oxygen (O ₂ ) in the air is excited in the creeping discharge zone 63 and generates a chemical reaction with surrounding oxygen molecules to generate ozone (O ₃ ).

FIG. 3 schematically shows a waveform 45 when the frequency of the high voltage pulse generated by the first and second high voltage generators 34 and 36 is low and a waveform 46 when the frequency is high. The frequency of the high voltage pulse is continuously controlled. The time width of the high voltage pulse is constant. When the frequency is low, the power consumption is small, and when the frequency is high, the power consumption is large. Changing the frequency is equivalent to changing the power consumption.
Increasing the frequency of the high voltage pulse increases the ozone generation concentration, and decreasing the frequency decreases the ozone generation concentration. Therefore, when the sub-controller 37 controls the first and second high-voltage generators 34 and 36 so that the ozone generation concentration according to the NOx flow rate in the exhaust gas is obtained based on various signals input to the controller 4. Good.

  In addition to the first creeping discharge device 3A and the first high-voltage generator 34, the ozone generating means 6 of the present embodiment includes a second creeping discharge device in order to efficiently generate a higher concentration of ozone. 3B and a second high voltage power generator 36 are provided. The first and second high voltage generators 34 and 36 can be controlled independently, and when generating a relatively low concentration of ozone, the first creeping discharge device 3A and the first high voltage power source are generated. The device 34 is activated to perform ozone generation. Further, when a large amount of NOx is temporarily discharged due to acceleration operation or high-load operation of the engine, and high-concentration ozone generation is necessary to process it, in addition to the second creeping discharge device 3B, The second high voltage power generator 36 is activated simultaneously.

  In the present embodiment, along the U-shaped passage 60 of the ozone generating means 6, the first creeping discharge device 3A is disposed on the upstream side, and the second creeping discharge device 3B is disposed on the downstream side. Since the inflowing air passes through the first creeping discharge device 3A and then passes through the second creeping discharge device 3B, two chances of generating ozone are given, and high-concentration ozone can be generated. Therefore, it is possible to efficiently generate a necessary amount of ozone by changing the electrode area and power to be operated according to the operating state of the engine 1 with a compact device configuration.

  The ozone generating means 6 of the present embodiment has a configuration in which two creeping discharge devices 3A and 3B having the same configuration are symmetrically arranged. However, the present invention is not limited to this, and there are three or more creeping discharge devices, or individual It is also possible to change the electrode area of the creeping discharge device. The total electrode area of the creeping discharge device is appropriately set according to the target engine 1 so as to obtain a necessary ozone supply flow rate.

<Control of Ozone Flow Rate of First Embodiment>
A method for controlling the ozone supply flow rate using the NOx post-treatment device of the present embodiment shown in FIGS.
FIG. 4 shows a main part of the control program built in the controller 4. When the operation of the control program is started, first, in step 101, the current engine speed measured by the speed sensor 41 and the injection amount indicating the load state of the engine 1 are captured. Next, at step 102, the NO concentration of the exhaust gas discharged from the engine 1 is obtained from the pre-programmed map shown in FIG. 5 based on the engine speed and the injection amount. As shown in FIG. 5, generally, the NO concentration is low at low load and low rotation, and the NO concentration increases as the operation state is high load and high rotation.

In step 103, the current intake flow rate measured by the intake flow rate sensor 45 and the exhaust temperature downstream of the DPF 21 measured by the exhaust temperature sensor 42 are captured. In step 104, based on the intake air flow rate and the exhaust gas temperature, a ratio in which NO in the exhaust gas that has passed through the DPF 21 is converted to NO ₂ by the catalytic reaction is retrieved from a pre-programmed map shown in FIG. 6A. As shown in FIG. 6A, generally, the smaller the intake flow rate and the higher the exhaust gas temperature, the higher the NO ₂ conversion ratio.

In step 105, based on the information obtained so far, the NO flow rate and NO ₂ flow rate flowing into the NOx aftertreatment device 3 are obtained by calculation using the following equations (NOx flow rate estimating means). Here, when the engine intake flow rate >> the fuel flow rate, the intake flow rate is used using the relationship that the exhaust flow rate is substantially equal to the intake flow rate.
(NO flow rate) = (intake flow rate) × (100− (NO ₂ conversion ratio)) × (engine exhaust NO concentration) / 10 ⁸
(NO ₂ flow rate) = (intake flow rate) × (NO ₂ conversion ratio) × (engine exhaust NO concentration) / 10 ⁸

Next, the routine proceeds to step 106, where the ozone target flow rate is obtained by calculation (target flow rate determining means). The reaction for producing HNO ₃ from ozone (O ₃ ) and NO, NO ₂ , H ₂ O is represented by the following chemical reaction formulas (a) to (d).
NO + O ₃ → NO ₂ + O ₂ (a)
NO ₂ + O ₃ → NO ₃ + O ₂ (b)
NO ₂ + NO ₃ → N ₂ O ₅ (c)
N ₂ O ₅ + H ₂ O → 2HNO ₃ (d)
From the above chemical reaction formula, it can be seen that 1.5 mol of O ₃ is required to generate 1 mol of HNO ₃ from 1 mol of NO. It can also be seen that 0.5 mol of O ₃ is required to produce 1 mol of HNO ₃ from 1 mol of NO ₂ .

Since O ₃ (ozone) is a harmful substance, in order to prevent it from being released into the atmosphere when mixed with exhaust gas, it generates and supplies an equivalent amount of O ₃ required for the reaction of NO and NO _{2 in} the exhaust gas. It is desirable. Therefore, the target flow rate of O ₃ is calculated using the following relational expression.
(O ₃ target flow rate) ′ = κ × {1.5 × (O ₃ molecular weight / NO molecular weight) × (NO flow rate) + 0.5 × (O ₃ molecular weight / NO ₂ molecular weight) × (NO ₂ flow rate)}
Here, κ is a coefficient value, and if the reaction proceeds ideally, κ = 1 may be used. However, the reaction of NO, NO ₂ , moisture, and ozone may be completely reacted in a given time depending on conditions. Does not always advance. Therefore, a numerical value between κ = 1 to 2.5 may be selected to determine the ozone target flow rate.

More preferably, when a correction process described below is added, ozone can be stably supplied with respect to a change in exhaust gas temperature. That is, when the exhaust gas temperature is relatively high, some ozone supplied to the exhaust gas disappears over time before reacting with NO, NO ₂ , and moisture. FIG. 6B shows the ratio at which ozone added to the exhaust gas disappears after 2 seconds. Normally, the exhaust is cooled by the cooling means 22 and the exhaust temperature is controlled to be 100 to 180 ° C. Even in this case, it can be seen that when the temperature is 140 ° C. or higher, ozone disappears at a ratio that cannot be ignored. Therefore, based on the relationship shown in FIG. 6B, the ozone extinction coefficient is obtained based on the exhaust temperature, and the following correction is made.
_{(O 3} target flow rate) = _{(O 3} target flow rate) '/ {1- (ozone extinction coefficient)}

Further, according to the study by the present inventors, when lower unsaturated hydrocarbons exist in the exhaust gas supplied with ozone, the lower unsaturated hydrocarbons and ozone react preferentially to eliminate ozone. To find out. Lower unsaturated hydrocarbons are purified by passing the oxidation catalyst in an active state or DPF 21 supporting the oxidation catalyst, but the lower unsaturated hydrocarbons are sufficiently purified in the warm-up operation after the engine is started at a low temperature. There is a risk that it will not be. In this case, the lower unsaturated hydrocarbon is brought to the ozone supply position where the ozone supply passage 61 joins, and the ozone to be used for the reaction with the target NO and NO ₂ is deprived.
Therefore, depending on the operating state of the engine, the lower unsaturated hydrocarbon after passing through the oxidation catalyst or the DPF 21 supporting the oxidation catalyst causes the disappearance of ozone. Based on this relationship, for example, the concentration of the lower unsaturated hydrocarbon It is also possible to provide means for estimating the ozone extinction coefficient based on the estimated value. Then, the total ozone extinction coefficient may be obtained together with the ozone extinction coefficient that occurs when the exhaust gas temperature becomes high, and the O ₃ target flow rate may be obtained.

Next, it progresses to step 107 and calculates | requires the air flow rate Goz which flows in into the ozone production | generation means 6 (gas flow rate estimation means). When the ozone generating means 6 is regarded as a simple fixed throttle, the air flow rate Goz is expressed by the following equation (1).
[(1): Flow rate formula assuming ozone generation means 6 as a fixed throttle]
Goz = Coz × Aoz × {2 gγ (Poz-Pe)} ^1/2
Here, Coz: equivalent throttle flow coefficient of ozone generating means 6
Aoz: Equivalent diaphragm cross section of ozone generating means 6
g: Acceleration of gravity
γ: Specific weight of air
Poz: upstream pressure of ozone generating means 6
Pe: Exhaust pressure Coz, Aoz, g are given in advance.
γ is obtained from γ = γo × (Poz / Po) × (Ta / To).
Where γo: specific weight in standard state
Po: Standard state pressure
Ta: Air temperature
To: Standard state temperatures γo, Po, To are given in advance. Ta is obtained from an air temperature sensor (not shown).
Since the exhaust pressure Pe is given as a function of the intake flow rate Ga and the exhaust temperature Te, the relationship is stored in advance in the form of a map shown in FIG. 7 and retrieved from the map. As shown in FIG. 7, in general, the exhaust pressure Pe increases as the intake flow rate Ga increases or the exhaust temperature Te increases.

The upstream pressure Poz and the air flow rate Goz of the ozone generating means 6 can be solved by combining the equation (1) and the following equations (2), (3), and (4).
[(2): Flow rate of fixed throttle 38]
Gor = Cor * Aor * {2g [gamma] '(Pi-Poz)} ^1/2
γ ′ = γo × (Pi / Po) × (Ta / To)
Where Gor: flow rate through the fixed throttle 38
Cor: Flow coefficient of fixed throttle 38
Aor: cross-sectional area of the fixed throttle 38
Pi: upstream pressure of intake throttle 17

[(3): Pressure change equation between fixed throttle 38 and ozone generating means 6]
The blower 39 in the middle of the air inflow passage 62 overcomes the exhaust pressure and exhausts air containing ozone from the ozone generating means 6 when the turbocharger 14 is not supercharged during idle operation. The blower 39 is stopped when there is a supercharging pressure. Therefore, if you stand as a single volume,
(dPoz / dt) × (Voz / R / Ta) = Gor−Goz
Here, Voz: volume between the fixed throttle 38 and the ozone generating means 6
R: Gas constant

[(4): Formula for changing pressure Pi between compressor 14 and intake throttle 17]
If the flow rate Gor flowing out from the fixed throttle 38 is sufficiently smaller than the intake flow rate Ga and the flow rate passing through the intake throttle 17, the following relational expression can be derived.
(DPi / dt) * (Vi / R / Ta) = Ga-Cth * Ath * {2 g [gamma] "(Pi-Ps)} ^1/2
γ ″ = γo × (Pi / Po) × (Ta / To)
Where Pi: upstream pressure of the intake throttle 17
Ps: Intake pressure
Vi: Volume between the compressor 14 and the intake throttle 17
Cth: Flow rate coefficient of intake throttle 17
Ath: Cross-sectional area of the intake throttle 17 Cth × Ath can be obtained as a function of the throttle opening detected by the throttle opening sensor 44. The intake flow rate Ga and the intake pressure Ps are detected by the intake flow rate sensor 45 and the intake pressure sensor 40. Therefore, Pi can be obtained from the equation (4), and if the obtained Pi is introduced into the equations (1) to (3), the upstream pressure Poz of the ozone generating means 6 and the air flow rate Goz flowing into the ozone generating means 6 Can be requested.

As described above, using the equations (1) to (4) as basic equations, the intake air flow rate Ga, the intake pressure Ps, the throttle opening degree, and the exhaust gas temperature Te are input, and the air flow rate Goz finally flowing into the ozone generating means 6 is obtained. By constructing a transfer function model and simulating air transfer delay, the air flow rate Goz can be estimated correctly even during transient operation.
When the air is sent by operating the blower 39 without applying supercharging pressure as in the idling operation, the process for obtaining the complicated air flow rate Goz as described above is not necessary. Assuming that a constant flow rate of air is being sent to the ozone generator 6 by the blower 39, the air flow rate Goz flowing into the ozone generator 6 may be obtained. As described above, the air flow rate Goz flowing into the ozone generating means 6 is obtained, and the process proceeds to the next step 108.

In step 108, the ozone (O ₃ ) target flow rate obtained in step 106 is divided by the air flow rate Goz flowing into the ozone generation unit 6 obtained in step 107, so that the ozone (O ₃ ) Calculate the production concentration (ozone production concentration calculation means).
Next, the routine proceeds to step 109. The information measured by the humidity sensor 43 is taken in as the current atmospheric humidity, and the ozone generation concentration obtained in step 108 is corrected according to the humidity level (ozone generation concentration correction means).
FIG. 8 shows the relationship between humidity, frequency, and ozone concentration when ozone is generated by the first creeping discharge device 3A. As shown in the drawing, the ozone generation concentration tends to decrease as the humidity increases. In order to correctly generate the target ozone concentration at any humidity, the three-dimensional map of humidity coefficient-humidity-ozone concentration shown in FIG. 9 based on the characteristics shown in FIG. A humidity coefficient for correction is obtained from the humidity, and the corrected ozone generation density is obtained by multiplying the ozone concentration by the humidity coefficient.

  Next, the process proceeds to a determination step 110, where it is determined whether or not the corrected ozone generation concentration obtained in step 109 is greater than or equal to a predetermined determination value. If the corrected ozone generation concentration is equal to or higher than the determination value (YES), the process proceeds to step 111. The determination value is a value used as a reference for determining whether or not the first and second creeping discharge devices 3A and 3B are operated simultaneously, and the ozone of the first creeping discharge device 3A shown in the map B of FIG. It is set as appropriate within the production concentration range. When the corrected ozone generation concentration is equal to or higher than the determination value, the corresponding frequency is selected based on the map A in FIG. The map A is programmed with the relationship between the frequency and the generated ozone concentration at 0% humidity when the first and second creeping discharge devices 3A and 3B are operated simultaneously. As shown in FIG. 10, since this relationship changes depending on the flow rates passing through the first and second creeping discharge devices 3A and 3B, the map A is a three-dimensional map showing the relationship between the corrected ozone generation concentration, the flow rate, and the frequency. It is desirable to give. Next, proceeding to step 112, the first and second high-voltage power supplies 34 and 36 are operated at the determined frequency, and a predetermined high-voltage pulse is applied to the first and second creeping discharge devices 3A and 3B. , Generate ozone.

  In step 110, if the corrected ozone generation concentration obtained in step 109 is less than the determination value (NO), the process proceeds to step 113. In step 111, the corresponding frequency is selected from the corrected ozone generation concentration based on the map B in FIG. Map B is programmed with the relationship between the frequency and the generated ozone concentration at 0% humidity when the first creeping discharge device 3A is operated. Since the relationship varies depending on the flow rate passing through the creeping discharge device 3A, it is desirable that the map B provides a relationship between the corrected ozone generation concentration, the flow rate, and the frequency as a three-dimensional map. Next, it progresses to step 114, the 1st high voltage power supply 34 is operated with the calculated | required frequency, and ozone is produced | generated by applying a predetermined high voltage pulse to the 1st creeping discharge apparatus 3A. Thereafter, this series of programs is temporarily terminated. This program is repeated according to a predetermined repetition rule, and the ozone generation concentration is controlled over time.

  The ozone generation means 6 of this embodiment applies ozone to the first and second creeping discharge devices 3A and 3B to generate ozone by discharge, and generates ozone after the discharge starts. The response delay until it is done is extremely short. Using this characteristic, for the air flow rate with a large response delay, a transfer function model is created to accurately grasp the delay, and the ozone generation concentration is obtained by dividing the ozone target flow rate by the delayed air flow rate. be able to. By operating the ozone generation means 6 so as to realize the ozone generation concentration, an excellent effect that the ozone target flow rate can be supplied without being affected by the delay of the air flow rate is obtained. As another method, a method of obtaining a frequency by using a relationship between the ozone target flow rate, the air flow rate, and the frequency as a three-dimensional map may be used.

  Moreover, the ozone generation means 6 of this embodiment can arrange | position the 1st, 2nd surface discharge apparatus 3A, 3B in series along the channel | path 60, and can control it independently. Accordingly, by changing the frequency of the high voltage pulse having a certain time width, the presence or absence of discharge by the first and second creeping discharge devices 3A and 3B is further selected, and ozone generation is performed by arbitrarily combining these. Thus, it is possible to provide the ozone generating means 6 that realizes the ozone concentration required over a wide range from the low concentration to the high concentration.

Further, by providing the air inflow passage 32 for taking in the air flowing into the ozone generating means 6 from the upstream side of the intake throttle 17, it is possible to introduce the supercharged air having a higher O ₂ partial pressure, so that the concentration is higher. Ozone generation becomes possible. Therefore, the NOx aftertreatment device 3 provided with the ozone generating means 6 of the present embodiment corresponds to the NOx emission amount that varies depending on the operating state, quickly generates necessary ozone, and supplies it to the exhaust from the ozone supply passage 31. An excellent effect that NOx can be purified can be obtained.

  In this embodiment, the ozone concentration to be generated is changed by changing the frequency of the high voltage pulse applied to the first and second creeping discharge devices 3A and 3B of the ozone generating means 6, but other methods are also used. May be adopted. Here, frequency control is shown as an example of implementing the broad concept of controlling the power consumption and controlling the ozone concentration, but it is not limited to only the frequency. For example, there is a method of realizing a change in ozone concentration by changing the voltage value of the high voltage pulse in addition to the frequency.

(Second Embodiment)
FIG. 11 shows a second embodiment of the present invention. The basic configurations of the engine 1 and the NOx aftertreatment device 3 of the present embodiment are the same as those of the first embodiment of FIG. 1, and different portions will be mainly described. In FIG. 11, the NOx aftertreatment device 3 has an ozone supply passage 61 that joins the exhaust pipe 2a between the exhaust cooling means 22 and the NOx absorption means 5 and blows in ozone-containing air, and is supercharged upstream of the intake throttle 17. In the middle of the air inflow passage 62 for taking in the air into the ozone generating means 6, a moisture removing means 9 and an oxygen enriched air generating means (oxygen enriching means) 8 are provided. The moisture separation filter 91 of the moisture removing means 9 located upstream is connected to the passage 92 for returning the separated moisture to the intake pipe 18 downstream of the intake flow sensor 45, and the oxygen-enriched air generating means 8 located downstream is oxygen-poor. Each is connected to a passage 65 for returning air to the intake manifold 10.

  A vacuum pump 66 is disposed immediately upstream of the ozone generating means 6, and the vacuum pump inlet pressure is measured at the passage end of the passage 64 branched from the passage 83 between the oxygen-enriched air generating means 8 and the vacuum pump 66. A pressure sensor 67 is arranged. The measurement information of the pressure sensor 67 is converted into an electrical signal and sent to the controller 4, and the operation of the vacuum pump 66 is controlled by the controller 4. The configuration other than the air inflow passage 62 described above is the same as that of the first embodiment shown in FIG.

  The moisture removing unit 9 suppresses a decrease in ozone generation efficiency due to moisture flowing into the ozone generating unit 6. The moisture separation filter 91 is a filter using a known moisture (water vapor) permeable membrane that easily transmits moisture and does not easily transmit air. The moisture separation filter 91 is a moisture component in the air flowing into the ozone generating means 6 from the air inflow passage 62. Isolate. The moisture component separated by the moisture permeable membrane is returned to the downstream side of the intake flow rate sensor 45 from the passage 92 using the supercharging pressure pressurized by the compressor 14.

FIG. 12 shows a cross-sectional view of the oxygen-enriched air generating means 8. The cover casing 81 and the base casing 80 of the oxygen-enriched air generating means 8 are cylindrical bodies with one end opening, and an internal space is formed by abutting the opening end faces. A sealing material 82 is disposed on the outer peripheral flange portion of the abutting portion, and seals between the cover housing 81 and the base housing 80 from the outside. In the internal space of the oxygen-enriched air generating means 8, three oxygen-enriched membrane elements 70 are stacked in the vertical direction in the figure. Here, only one in the center is shown for easy understanding, and the other two are drawn with imaginary lines.
The oxygen-enriched membrane element 70 includes an element base casing 71, a cover element casing 72, and an oxygen-enriched film 73 that is sandwiched and fixed therebetween. The oxygen-enriched film 73 partitions the upper space in the cover element housing 72 and the lower space in the element base housing 71. The base element casing 71 is provided with a cylindrical protruding portion 76 on the right side of the figure, and this protruding portion 76 is inserted into a through hole 75 formed in a wall portion that partitions the inside of the base casing 80 to the left and right. It is mated. The fitting portion is sealed by a seal member 77 attached to the outer periphery of the protruding portion 76.

A space serving as an air passage is formed between the closed end surface (the left end surface in the figure) of the cover housing 81 and the oxygen-enriched membrane element 70, and an air inlet 78 is opened at the upper end surface of the cover housing 81. . Similarly, the base housing 80 has a space serving as an air passage between the wall portion provided with the through hole 75 and the closed end surface, and an air outlet 79 is opened at the lower end surface of the base housing 80.
The dry air from which the water vapor component has been separated by the water vapor separation filter 91 enters the inside of the casing of the oxygen-enriched air generating means 8 from the air inlet 78 and reaches the left end side of each oxygen-enriched membrane element 70. This dry air enters the element casing through a hole provided on the left side surface of the cover element casing 72, and moves in the upper space from the left to the right in the figure. During the movement, it comes into contact with the oxygen-enriched film 73, and a part of oxygen contained in the air permeates and escapes into the lower space.

The lower space across the oxygen-enriched film 73 is under a negative pressure generated by the operation of the vacuum pump 66 shown in FIG. The air that has moved to the right in the figure in the upper space of the oxygen-enriched film 73 is oxygen-poor air because part of the oxygen has been removed. This oxygen-depleted air passes through a hole provided on the right side surface of the cover element casing 72 and is collected at an oxygen-depleted air outlet 85 opened at the upper end surface of the base casing 80, and is shown in FIG. It is routed through the air passage 65 to the intake manifold 10 of the engine.
The oxygen-enriched air generated through the oxygen-enriched film 73 moves in the lower space to the right in the figure, and passes through the passage 74 in the projecting portion 76 from the right side of the base element casing 71. Collected at oxygen enriched air outlet 79. Then, it is sucked and discharged by the vacuum pump 66 through the oxygen-enriched air passage 83 shown in FIG.

  FIG. 13 is a characteristic diagram showing how much the oxygen concentration can be increased by passing the oxygen-enriched film 73. The separation factor in the figure represents the ratio of the mass velocity at which oxygen and other components (nitrogen in the case of air) permeate the membrane. Here, a separation factor of 5 indicates that the membrane has the characteristics of a permeable membrane in which the oxygen transmission rate is five times the nitrogen transmission rate. The horizontal axis of the figure represents the upstream / downstream pressure ratio of the oxygen-enriched film 73, that is, the pressure ratio when the downstream oxygen partial pressure is placed in the numerator and the upstream oxygen partial pressure is placed in the denominator on the logarithmic axis. . The vertical axis in the figure represents the oxygen concentration of oxygen-enriched air generated downstream of the oxygen-enriched film 73. This result indicates that when the pressure ratio is 0.1, the oxygen concentration of the oxygen-enriched air can be increased to 53% with respect to the oxygen concentration of the upstream air of 21%. Such an oxygen-enriched film 73 is preferably made of a polymer resin film material.

<Control of Ozone Flow Rate of Second Embodiment>
Next, a method of controlling the ozone supply flow rate using the NOx aftertreatment device of the present embodiment shown in FIGS. 11 and 12 will be described.
14A and 14B show a main part of a control program built in the controller 4 applied to the second embodiment. Parts that are the same as those described in the first embodiment of FIG. 4 are not described, and different parts are described. Steps 201 to 206 in FIG. 14A are the same as steps 101 to 105 in FIG. 4. Similarly, the NOx flow rate in the exhaust gas flowing into the NOx aftertreatment device 3 by knowing the operating state of the engine 1 from various sensor information. And the ozone target flow rate to be supplied is calculated.

In step 207 of FIG. 14A, the inlet pressure Pi of the oxygen-enriched air generating means 8 is obtained from the intake pressure Ps, the intake flow rate Ga, and the throttle opening detected by the throttle opening sensor 44. As a formula for obtaining the inlet pressure Pi of the oxygen-enriched air generating means 8, the same formula as the formula (4) in the first embodiment described above can be used.
Next, at step 208, the oxygen concentration of the oxygen-enriched air is determined from the inlet pressure Pi and the outlet pressure Pv of the oxygen-enriched air generating means.
In general, in the case of a two-component gas of A gas and B gas, A gas mol% y _{A in} the gas after permeation is given by the following formula (Reference: “Patent Assistance Flow Chart Gas Membrane Separator”. Outline of the separation device Page 4: Issued by the Industrial Property General Information Center.
y _A = 50 [C- {C ² -4 (x _A / 100) α _AB / γ / (α _AB −1)} ^0.5 ]
C = [1 + {(x _A / 100) + γ} (α _AB −1)] / γ / (α _AB −1)
Where x _A : mol% of A gas before permeation
α _AB : Separation factor
γ: membrane upstream / downstream pressure ratio Since the oxygen concentration before permeation is 21%, the separation factor α _AB and the membrane upstream / downstream pressure ratio γ are input into the above equation to obtain the oxygen mol% y _A after permeation, and the oxygen concentration If converted, the oxygen concentration of the oxygen-enriched air can be obtained.

Next, the routine proceeds to step 209, where the flow rate Goz of the oxygen-enriched air flowing into the ozone generating means 6 is obtained (gas flow rate estimating means). When the ozone generating means 6 is regarded as a simple fixed throttle, the oxygen-enriched air flow rate Goz is expressed by the following equation (5).
[(5): Flow rate formula considering ozone generation means as fixed throttle]
Goz = Coz × Aoz × {2 gγe (Poz-Pe)} ^1/2
Here, Coz: equivalent throttle flow coefficient of ozone generating means 6
Aoz: Equivalent diaphragm cross section of ozone generating means 6
g: Acceleration of gravity
γe: Specific weight of air
Poz: upstream pressure of ozone generating means 6
Pe: Exhaust pressure Coz, Aoz, g are given in advance.
γe is obtained from γe = γeo × (Poz / Po) × (Ta / To).
Where γeo: specific weight in standard state
Po: Standard state pressure
Ta: Air temperature
To: Standard state temperature γeo, Po, To are given in advance. Ta is obtained from an air temperature sensor (not shown).
The exhaust pressure Pe is given as a function of the intake flow rate Ga and the exhaust temperature Te. The relationship can be stored in advance in the form of the map shown in FIG. 7 and retrieved from the map.

The upstream pressure Poz and the oxygen-enriched air flow rate Goz of the ozone generating means 6 can be solved by combining the equation (5) with the following equations (6) and (7).
[(6): Discharge flow rate Gp of vacuum pump 66]
Gp = γe × (Pv / Po) × (Ta / To) × Vp × {1 + Cp−Cp (Poz / Pv) ^{1 / κ} } × Np
Where Pv: downstream pressure of the oxygen-enriched air generating means 8
Vp: Pump suction volume per rotation
Cp: Pump cutoff ratio
Poz: Ozone generating means upstream pressure
κ: Specific heat ratio
Np: Pump speed Vp, Cp, and κ are given in advance, and the pump speed Np is given to be constant.
[(7): Pressure change equation between vacuum pump 66 and ozone generating means 6]
(DPoz / dt) × (Voz / R / Ta) = Gp−Goz
Here, Voz: volume between the vacuum pump 66 and the ozone generating means 6
R: Gas constant

Next, proceeding to step 210, the ozone generation concentration is determined by dividing the ozone target flow rate determined in step 206 by the oxygen-enriched air flow rate Goz determined in step 209 (ozone generation concentration calculation means).
In step 211, the oxygen enrichment coefficient is obtained from the oxygen concentration of the oxygen-enriched air obtained in step 208, and the ozone generation concentration is corrected (ozone generation concentration correction means). FIG. 15 shows the relationship between the oxygen concentration and the oxygen enrichment coefficient. When the oxygen concentration of the inflowing air is increased by the oxygen-enriched air generation means 8, even if the same high voltage pulse frequency is given in the ozone generation means 6, the generated ozone concentration gives the atmosphere (oxygen concentration 21%). More than the case. Therefore, as shown in FIG. 15, the enrichment factor is 1 when operated at an oxygen concentration of 21% in the atmosphere, and the oxygen enrichment factor smaller than 1 when operated at a concentration higher than 21%. It is necessary to correct by multiplying. When the oxygen concentration is 80% or more, ozone-containing air having an ozone concentration twice that of the oxygen concentration of 21% can be generated, and therefore an oxygen enrichment coefficient of 0.5 is given. The corrected ozone generation concentration is determined by correcting the ozone generation concentration determined in step 210 using the oxygen enrichment coefficient.

  Next, the process proceeds to a determination step 212 in FIG. 14B to determine whether or not the corrected ozone generation concentration is equal to or higher than a predetermined value. Subsequent steps 213 to 216 correspond to steps 110 to 114 in FIG. 4 and are the same as those in the first embodiment described above, and thus the description thereof is omitted.

  As described above, in the second embodiment, the moisture component in the air is reduced by the moisture separation filter 91 of the moisture removing means 9, and the dry air is introduced into the ozone generating means 6, thereby stabilizing high concentration ozone. The advantage that can be generated is obtained. Further, by sending high-oxygen-concentrated air to the ozone-generating means 6 using the oxygen-enriched air generating means 8, it is possible to generate ozone with a higher concentration. The post-processing device 3 can be designed.

  Also in the present embodiment, the required ozone generation concentration can be realized with good responsiveness following the change in the operating state by utilizing the characteristics of the discharge plasma that has a very short response delay from the start of discharge to the generation of ozone. For an air flow rate with a large response delay, the ozone generation concentration can be obtained by accurately grasping the delay by the transfer function model, and the ozone generation concentration can be corrected by the oxygen concentration of the oxygen-enriched air. By operating the ozone generation means 6 so as to realize the corrected ozone generation concentration, the ozone target flow rate is supplied without being affected by the delay of the air flow rate, and the excellent effect of purifying NOx is obtained. Can be obtained.

  The control device for the NOx aftertreatment device for an engine according to the present invention is small and low cost, and has high purification performance even in an engine having a large change in environmental temperature and operating condition. However, the present invention can be applied to any engine, not limited to a vehicle or a diesel engine.

1 Engine 18 Intake pipe (intake passage)
2, 2a Exhaust pipe (exhaust passage)
21 DPF (filter means)
3 NOx aftertreatment device 31 Ozone supply passage 32 Air inflow passage 37 Sub controller (drive means)
4 Controller (control device)
5 NOx absorption means 6 Ozone generation means 8 Oxygen-enriched air generation means (oxygen enrichment means)
9 Moisture removal means 91 Moisture separation filter

Claims (10)

A control method for an engine NOx aftertreatment device (3) including ozone generating means (6) for supplying ozone to exhaust from the engine (1),
The NO and NO ₂ flow rates in the exhaust gas are estimated, the ozone target flow rate is determined according to the estimated total flow rate of NO and NO ₂ , and generated by operating the ozone generating means so as to be the determined target flow rate A control method for a NOx aftertreatment device for an engine including an ozone generating means, wherein ozone is added to exhaust gas, and HNO ₃ generated by the ozone, NO, NO ₂ and moisture in the exhaust gas is removed from the exhaust gas. An ozone supply passage (31) connected to the exhaust passage (2) of the engine and an air inflow passage (32) connected to the intake passage (18), including ozone generating means for generating ozone from the inflowing air; A control device (4) for a NOx aftertreatment device for an engine that causes the NOx absorption means (5) to absorb a reaction product of NOx and ozone,
NOx flow rate estimating means (steps 105 and 205) for estimating NO and NO ₂ flow rates in the exhaust gas flowing through the exhaust passage;
Target flow rate determination means (steps 106 and 206) for determining the ozone target flow rate in correspondence with the total flow rate of NO and NO ₂ estimated by the NOx flow rate estimation means;
Drive means (37) for operating the ozone generation means so as to be the ozone target flow rate determined by the target flow rate determination means,
The ozone generated by the ozone generating means is added to the exhaust gas from the ozone supply passage, and HNO ₃ generated by the added ozone, NO, NO ₂ and moisture in the exhaust gas is absorbed by the NOx absorbing means and removed. A control device for an NOx aftertreatment device for an engine including ozone generating means. Filter means (21) carrying an oxidation catalyst or an oxidation catalyst is arranged upstream of the exhaust passage where the ozone supply passage joins,
The NOx flow rate estimating means includes the NO and NO ₂ flow rates in the exhaust gas, the NO concentration estimated value in the exhaust gas exhausted from the engine, the engine intake flow rate, the temperature of the filter means carrying the oxidation catalyst or the oxidation catalyst, or The control device for the NOx aftertreatment device for an engine including the ozone generation means according to claim 2, which is obtained as an estimated NO flow rate and an estimated NO ₂ flow rate estimated using the exhaust gas temperature. The target flow rate determining means, estimated by the NOx flow rate estimation means, NO estimated flow rate of 1.5 equivalent ratio times the flow rate and the NO ₂ estimated flow rate of 0.5 equivalent ratio times the flow rate sum over values of The control device for the engine NOx aftertreatment device including the ozone generation means according to claim 2, wherein the ozone target flow rate is determined corresponding to the ozone target flow rate, and the ozone generation means is operated based on the ozone target flow rate.   The ozone generation unit generates the gas flow rate estimation unit (steps 107 and 209) for estimating the gas flow rate passing through the ozone generation unit, and the estimated gas flow rate and the ozone target flow rate determined by the target flow rate determination unit. 5. Ozone generation according to any one of claims 2 to 4, further comprising ozone generation concentration calculation means (steps 108 and 210) for determining a power ozone concentration, wherein the ozone generation means is operated so as to obtain the ozone generation concentration. A control device for an engine NOx aftertreatment device including means. The target flow rate determining means obtains a ratio at which ozone generated by the ozone generating means disappears before reacting with NO, NO ₂ , and moisture, and corrects the ozone target flow rate according to the ratio. 6. A control device for a NOx aftertreatment device for an engine comprising the ozone generation means according to any one of 5 above.   7. The control device for an engine NOx aftertreatment device including the ozone generation means according to claim 6, wherein the target flow rate determination means determines the ratio at which ozone disappears in accordance with exhaust gas temperature.   The ozone generating means according to claim 7, wherein the target flow rate determining means determines the ratio at which ozone disappears in accordance with the concentration of lower unsaturated hydrocarbons in the exhaust gas at the junction (2a) of the ozone supply passage. A control device for a NOx aftertreatment device for an engine including:   The ozone generating means according to any one of claims 2 to 8, further comprising correcting means (step 109) for correcting the ozone target flow rate determined by the target flow rate determining means based on information on humidity in the atmosphere. Including a control device for an NOx aftertreatment device for an engine.   Humidity removal means (9) and oxygen enrichment means (8) are installed in the air inflow passage upstream of the ozone generation means, and ozone is generated based on a change in oxygen concentration in the gas flowing into the ozone generation means. The control device for the engine NOx aftertreatment device including the ozone generation unit according to any one of claims 5 to 8, further comprising a correction unit (step 211) for correcting the concentration.

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