JP4277374B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device that purifies exhaust gas discharged from an internal combustion engine, and more particularly to an exhaust gas purification device that purifies exhaust gas using an oxidizing action or a reducing action of a catalyst.
[0002]
[Prior art]
As a means for reducing the amount of harmful components in the exhaust gas discharged from the internal combustion engine to the atmosphere, there is a system for purifying the harmful components using the oxidizing or reducing action of a catalyst.
[0003]
Recent improvements in catalyst performance have led to remarkable improvements in catalyst performance, and it has become possible to realize a catalytic device with high purification performance despite its small size. As a result, in recent years, exhaust gas purification devices incorporating a catalyst have been widely used as an exhaust gas purification system for purifying exhaust gas of a vehicle internal combustion engine.
[0004]
Currently, exhaust gas purification catalysts in practical use include oxidation catalysts, three-way catalysts, NOx catalysts, etc., and these catalysts are used as combustion forms and air-fuel ratios of internal combustion engines, or harmful substances to be purified. It is properly used according to the type.
[0005]
Among these catalysts, the NOx catalyst includes a selective reduction type NOx catalyst and an occlusion reduction type NOx catalyst. A selective reduction type NOx catalyst is a catalyst that reduces or decomposes NOx in the presence of hydrocarbons (HC) in an oxygen-excess atmosphere. On the other hand, an occlusion reduction type NOx catalyst is an air-fuel ratio of inflowing exhaust gas that is lean. In this case, NOx is absorbed, and when the oxygen concentration in the inflowing exhaust gas decreases, the absorbed NOx is released and N₂Refers to a catalyst that reduces to These NOx catalysts have an oxidizing action for oxidizing and purifying HC in the exhaust gas, and a reducing action for reducing and purifying NOx in the exhaust gas.
[0006]
In general, when a catalyst is used for a long period of time, there is a phenomenon in which the oxidation action or reduction action of the catalyst declines. If the NOx catalyst is used for a long period of time, the HC purification ability is reduced due to the deterioration of the oxidizing action, or the NOx purification ability is reduced due to the reduction of the reducing action. If the NOx catalyst that causes a decrease in the HC purification capacity (hereinafter also referred to as HC degradation) or a decrease in the NOx purification capacity (hereinafter also referred to as NOx degradation) is used, There is a risk that exhaust gas containing harmful substances may be exhausted to the atmosphere because the harmful substances in the gas cannot be completely purified. Therefore, measures such as replacement are necessary for such a NOx catalyst having a reduced purification capability, and for that purpose, management of the purification capability of the catalyst (in other words, determination of catalyst deterioration) is extremely important.
[0007]
[Problems to be solved by the invention]
As a catalyst deterioration determination technique, for example, there is one disclosed in Japanese Patent Laid-Open No. 9-144431. In the technique described in this publication, a catalyst (such as a NOx catalyst or a three-way catalyst) that purifies by oxidizing or reducing harmful components in the exhaust gas is provided in the exhaust passage of the internal combustion engine, and the exhaust gas is disposed downstream of the catalyst. A NOx sensor that measures the concentration of NOx in the gas and a gas sensor (HC sensor or CO sensor) that measures the concentration of harmful substances (HC and CO) other than NOx in the exhaust gas are installed. When the value is exceeded, it is determined that the reduction action of the catalyst has deteriorated, and when the output value of the gas sensor exceeds a predetermined value, it is determined that the oxidation action of the catalyst has deteriorated.
[0008]
Thus, in order to determine the deterioration of a catalyst having both an oxidation action and a reduction action, conventionally, there are two types of sensors, that is, a sensor for obtaining data necessary for judging the deterioration of the oxidation action, A sensor was needed to obtain the data needed to determine the degradation of action. The reason is that the deterioration of the oxidation action and the reduction action of the catalyst do not always proceed at the same rate.
[0009]
Thus, when the number of sensors increases, there is a problem that not only the cost increases but also the number of maintenance targets increases.
The present invention has been made in view of the problems of the prior art as described above, and the problem to be solved by the present invention is that the purification ability of the catalyst can be known while having a simple structure. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can be known to a degree.
[0010]
Another problem to be solved by the present invention is to provide an HC concentration detection function to the NOx concentration detection means by using the output characteristics of the oxygen pump type NOx concentration detection means, thereby simplifying the exhaust purification device. Is to plan.
[0011]
[Means for Solving the Problems]
  In order to solve the above problems, the invention according to the present application employs the following means.
(1) An exhaust gas purification apparatus for an internal combustion engine according to a first aspect of the present application includes an HC concentration increasing means for increasing the HC concentration of exhaust gas of the internal combustion engine, and an oxygen pump using an oxygen ion conductor. NOx concentration detecting means installed in the exhaust passage of the engine for detecting the NOx concentration of the exhaust gas, and the HC concentration increasing meansIs exhaustedHC concentration of gas, Compared to before the increase of the HC concentration, the NO x The detection value of the concentration detection means decreases temporarilyWhen rapidly increasingThe NDetection value of Ox concentration detection meansDecrease amountHC concentration increase amount estimation means for estimating the HC concentration increase amount of the exhaust gas based on the above.
[0012]
The NOx concentration detection means having an oxygen pump using an oxygen ion conductor is affected by interference caused by the increased amount of HC concentration when the HC concentration (hydrocarbon concentration) of the exhaust gas flowing in rapidly increases. Even though the NOx concentration of the exhaust gas to be changed has not changed, the detected value of the NOx concentration detecting means decreases momentarily. All inventions according to the present application, including the first invention, utilize this output characteristic of the NOx concentration detecting means.
[0013]
In an exhaust gas purification apparatus for an internal combustion engine, for example, to act as a reducing agent for NOx or to oxidize on a catalyst to raise the exhaust gas temperature, the HC concentration of the exhaust gas is temporarily or continuously used for various purposes. Increase operation may be performed. In this case, management of the HC concentration is very important.
[0014]
In the exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention, when the HC concentration of the exhaust gas is rapidly increased by the HC concentration increasing means, the HC concentration increase estimating means is the detection value of the NOx concentration detecting means. The amount of increase in the HC concentration of the exhaust gas is estimated based on the amount of decrease in the exhaust gas.
[0015]
In the first invention, it is preferable that the HC concentration of the exhaust gas before the HC concentration is increased by the HC concentration increasing means is low. When the HC concentration of the exhaust gas before the HC concentration increase is extremely lower than the HC concentration of the exhaust gas after the HC concentration increase, the HC concentration increase amount estimated by the HC concentration increase amount estimating means is Therefore, the estimated increase amount of HC concentration can be regarded as the HC concentration of exhaust gas after the increase in HC concentration.
[0016]
Since the HC supply amount is obtained by multiplying the HC concentration by the exhaust gas flow rate and the circulation time, in the first aspect of the invention, the exhaust gas flow rate and the circulation time are known in advance or can be detected. Thus, it can be said that the HC concentration increase amount estimated by the HC concentration increase amount estimation means is equivalent to the HC supply amount.
[0017]
Accordingly, the first aspect of the invention includes (a) an HC supply means for intermittently supplying HC to the exhaust passage of the internal combustion engine, and (b) an exhaust passage of the internal combustion engine having an oxygen pump using an oxygen ion conductor. And (c) an HC supply amount for estimating an HC supply amount based on a detected value of the NOx concentration detection means at the time of HC supply by the HC supply unit. It can be said that it is equivalent to an exhaust emission control device for an internal combustion engine comprising an estimation means.
[0018]
(2) An exhaust gas purification apparatus for an internal combustion engine according to a second aspect of the present application is based on the first aspect, and further includes an estimated HC concentration increase amount estimated by the HC concentration increase amount estimating means and the HC concentration And a failure determining means for determining that the HC concentration increasing means is in failure when the comparison value with the target HC concentration increasing amount to be increased by the concentration increasing means is out of a predetermined allowable range.
[0019]
In the second invention, the comparison value between the estimated HC concentration increase amount and the target HC concentration increase amount may be a difference between the former and the latter, or a ratio (quotient) between the former and the latter. In short, any numerical value based on an error between the estimated HC concentration increase amount and the target HC concentration increase amount can be used as long as it can serve as an index for determining the failure of the HC concentration increasing means.
[0020]
  (3) An exhaust emission control device for an internal combustion engine according to a third aspect of the present invention is provided in an exhaust passage of the internal combustion engine.
An exhaust gas which is installed downstream of the catalyst and has an oxygen pump using an oxygen ion conductor and an HC concentration increasing means for increasing the HC concentration of the exhaust gas of the internal combustion engine flowing into the catalyst. Catalyst downstream NOx concentration detecting means for detecting the NOx concentration of gas, and the HC concentration increasing meansIs HC concentration, The catalyst downstream NO. x The detection value of the concentration detection means decreases temporarilyWhen rapidly increasingThe touchDetection value of medium downstream NOx concentration detection meansDecrease amountHC purification capacity estimation means for estimating the HC purification capacity of the catalyst based on
It is characterized by providing.
[0021]
When the catalyst has an HC purification capability, when the HC concentration of the exhaust gas upstream of the catalyst is the same, the HC concentration of the exhaust gas downstream of the catalyst decreases as the HC purification capability of the catalyst increases.
[0022]
In the third invention, the HC concentration of the exhaust gas upstream of the catalyst is rapidly increased by the HC concentration increasing means, and the HC concentration of the exhaust gas downstream of the catalyst is estimated from the detected value detected by the catalyst downstream NOx concentration detecting means at that time. To do. From this, the HC purification capacity estimation means estimates the HC purification capacity of the catalyst.
[0023]
  (4) An exhaust gas purification apparatus for an internal combustion engine according to a fourth aspect of the present invention is based on the third aspect of the present invention and further includes an oxygen pump using an oxygen ion conductor and is installed upstream of the catalyst. And a catalyst upstream NOx concentration detecting means for detecting the NOx concentration of the exhaust gas, and the HC purification capacity estimating means includes the HC concentration increasing meansIs HC concentration, The catalyst upstream NO. x Concentration detection means and catalyst downstream NO x The detection value of the concentration detection means decreases temporarilyWhen rapidly increasingThe touchDetection value of medium upstream NOx concentration detection meansDecrease amountWhenThe touchDetection value of medium downstream NOx concentration detection meansDecrease amountAnd the HC purification capacity of the catalyst is estimated based on the comparison value.
[0024]
When the HC purification capacity of the catalyst is equivalent, the HC concentration downstream of the catalyst varies depending on the magnitude of the HC concentration upstream of the catalyst. Therefore, in order to more accurately determine the HC purification capability of the catalyst, it is necessary to know the HC concentration upstream of the catalyst.
[0025]
In the fourth aspect of the invention, the HC concentration of the exhaust gas upstream of the catalyst is estimated from the detected value of the catalyst upstream NOx concentration detecting means when the HC concentration is rapidly increased by the HC concentration increasing means. The HC purification capacity estimating means detects the detected value of the catalyst upstream NOx concentration detecting means corresponding to the HC concentration of the exhaust gas upstream of the catalyst and the detection of the catalyst downstream NOx concentration detecting means corresponding to the HC concentration of the exhaust gas downstream of the catalyst. The HC purification capacity of the catalyst is estimated from the magnitude of the comparison value compared with the value.
[0026]
The comparison value may be a difference between a detection value (the former) of the catalyst upstream NOx concentration detection means and a detection value (the latter) of the catalyst downstream NOx concentration detection means, or may be a ratio (quotient) between the two. . When the comparison value is represented by a difference (the former-the latter), the larger the comparison value, the higher the HC purification capacity. When the comparison value is represented by the ratio of the latter to the former (the latter / the former), the comparison value is The smaller the value, the higher the HC purification capacity.
[0027]
(5) The exhaust gas purification apparatus for an internal combustion engine according to a fifth aspect of the present application is based on the third aspect, and further, the HC concentration increase amount increased by the HC concentration increasing means is an operating state of the internal combustion engine. It is characterized in that it is preset according to the above.
[0028]
When the amount of HC concentration increase to be increased by the HC concentration increasing means is set in advance according to the operating state of the internal combustion engine, the HC concentration of the exhaust gas upstream of the catalyst can be provided without providing the NOx concentration detecting means upstream of the catalyst. In addition, the detection value of the catalyst upstream NOx concentration detecting means when the HC concentration is rapidly increased by the HC concentration increasing means can be estimated in advance. It can be omitted.
[0029]
(6) An exhaust emission control device for an internal combustion engine according to a sixth aspect of the present application is based on the third aspect, the fourth aspect, or the fifth aspect, and further includes the HC purification capacity estimating means. HC deterioration determination means for determining that the catalyst has deteriorated HC when the estimated HC purification capacity of the catalyst is equal to or less than a predetermined capacity is provided.
[0030]
(7) An exhaust gas purification apparatus for an internal combustion engine according to a seventh aspect of the present application is based on the third aspect, the fourth aspect, or the fifth aspect, and further includes HC by the HC concentration increasing means. The NOx purification capacity of the catalyst is obtained from the detection value of the catalyst downstream NOx concentration detection means when the concentration is not increased, and NOx is determined that the catalyst has deteriorated in NOx when the NOx purification capacity is below a predetermined capacity. Deterioration determining means is provided.
[0031]
In the first to seventh inventions of the present application, “when the HC concentration is rapidly increased by the HC concentration increasing means” includes the following (1) or (2).
(1) During intermittent supply of HC when HC is intermittently supplied into the exhaust gas
(2) When HC is continuously supplied to the exhaust gas, and the HC supply amount is suddenly increased
[0032]
In the first to seventh inventions of the present application, the HC concentration increasing means can be constituted by an HC supply device that intermittently supplies HC to the exhaust passage. As the HC component that increases the HC concentration of the exhaust gas by the HC concentration increasing means, a fuel of an internal combustion engine such as gasoline or light oil can be employed. When the fuel of the internal combustion engine is the HC component, the HC concentration increasing means can be constituted by a sub-injection device that sub-injects fuel into the combustion chamber of the internal combustion engine during the expansion stroke or exhaust stroke of the internal combustion engine. Examples of the internal combustion engine include diesel engines and gasoline engines (including lean-burnable gasoline engines, so-called lean burn gasoline engines).
[0033]
In the first to seventh inventions of the present application, the “oxygen pump” in the NOx concentration detecting means refers to a function of ionizing oxygen and pumping it through an oxygen ion conductor.
[0034]
In the third to seventh aspects of the present invention, examples of the catalyst include an occlusion reduction type NOx catalyst and a selective reduction type NOx catalyst.
The NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases, and N₂It is a catalyst that reduces to This NOx storage reduction catalyst uses, for example, alumina as a carrier, and an alkali metal such as potassium K, sodium Na, lithium Li and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and lanthanum La. And at least one selected from rare earths such as yttrium Y and a noble metal such as platinum Pt are supported.
[0035]
The selective reduction type NOx catalyst is a catalyst that reduces or decomposes NOx in the presence of hydrocarbons in an oxygen-excess atmosphere. A catalyst in which a transition metal such as Cu is ion-exchanged on zeolite, and a noble metal is supported on zeolite or alumina. Supported catalyst, and the like.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings of FIGS. In addition, embodiment described below is the aspect which applied the exhaust gas purification apparatus which concerns on this invention to the diesel engine for vehicles as an internal combustion engine.
[0037]
FIG. 1 is a diagram showing an overall configuration of an embodiment of an exhaust gas purification apparatus for an internal combustion engine. The engine 1 is a 6-cylinder diesel engine, and an intake pipe 2 and an intake manifold are provided in the combustion chambers of the cylinders 11, 12, 13, 14, 15, 16 of the first cylinder (# 1) to the sixth cylinder (# 6). New air is introduced through 3. In the middle of the intake pipe 2, an air flow meter 7, a compressor 4 a of the turbocharger 4, an intercooler 5, and an intake throttle valve 6 are provided. The intake throttle valve 6 is controlled by an engine control electronic control unit (ECU) 100 according to the operating state of the engine 1.
[0038]
Further, the engine 1 is provided with fuel injection valves 21, 22, 23, 24, 25, and 26 for injecting fuel into the cylinders 11 to 16, respectively. The valve opening timing and valve opening time of the fuel injection valves 21 to 26 are controlled by the ECU 100 according to the operating state of the engine 1.
[0039]
Exhaust gas generated in the combustion chambers of the cylinders 11 to 16 is discharged to the exhaust pipe 31 via the exhaust manifold 30 and discharged to the atmosphere via a muffler (not shown). A part of the exhaust gas flowing into the exhaust manifold 30 can be recirculated to the intake manifold 3 through the exhaust gas recirculation pipe 32. An EGR cooler 33 and an EGR valve 34 are provided in the middle of the exhaust gas recirculation pipe 32. The opening degree of the EGR valve 34 is controlled by the ECU 100 according to the operating state of the engine 1 to control the exhaust gas recirculation amount.
[0040]
In the middle of the exhaust pipe 31, a casing 37 containing a turbine 4 b of the turbocharger 4, an exhaust throttle valve 35, and an NOx storage reduction catalyst 36 is provided. The NOx storage reduction catalyst 36 will be described in detail later.
[0041]
The exhaust gas drives the turbine 4b, drives the compressor 4a connected to the turbine 4b, and supercharges the intake air. The exhaust throttle valve 35 is controlled by an engine control electronic control unit (ECU) 100 in accordance with the operating state of the engine 1.
[0042]
In the exhaust pipe 31, an HC supply device (HC concentration increasing means) 40 is installed between the exhaust throttle valve 35 and the casing 37 to supply light oil as fuel for the engine 1 into the exhaust pipe 31. The HC supply device 40 includes a supply pump 41 that pressurizes and pumps light oil in a fuel tank (not shown), an introduction pipe 42 that introduces light oil pressurized by the supply pump 41 into the exhaust pipe 31, and an intermediate part of the introduction pipe 42. A control valve 43 is provided.
[0043]
In the exhaust pipe 31, downstream of the HC supply device 40 and upstream of the casing 37, an input gas that outputs to the ECU 100 an output signal corresponding to the temperature of exhaust gas flowing into the casing 37 (hereinafter referred to as input gas). A temperature sensor 51 and an input gas NOx sensor (catalyst upstream NOx concentration detection means) 52 for outputting an output signal corresponding to the NOx concentration of the input gas to the ECU 100 are attached.
[0044]
Further, in the exhaust pipe 31, downstream of the casing 37, an output gas temperature sensor 53 that outputs an output signal corresponding to the temperature of exhaust gas (hereinafter referred to as output gas) flowing out from the casing 37 to the ECU 100, An output gas NOx sensor (catalyst downstream NOx concentration detection means) 54 for outputting an output signal corresponding to the NOx concentration to the ECU 100 is attached.
[0045]
Based on the output signals of the inlet gas temperature sensor 51 and the outlet gas temperature sensor 53, the ECU 100 calculates the catalyst temperature of the NOx storage reduction catalyst 36. The input gas NOx sensor 52 and the output gas NOx sensor 54 will be described in detail later.
[0046]
The ECU 100 is a digital computer, and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, and an output port that are connected to each other via a bidirectional bus. In addition to performing basic control such as injection amount control, in this embodiment, HC supply control of the HC supply device 40 is performed.
[0047]
For these controls, an input signal from the accelerator opening sensor 61 and an input signal from the crank angle sensor 62 are input to the input port of the ECU 100. The accelerator opening sensor 61 outputs an output voltage proportional to the accelerator opening to the ECU 100, and the ECU 100 calculates the engine load based on the output signal of the accelerator opening sensor 61. The crank angle sensor 62 outputs an output pulse to the ECU 100 every time the crankshaft rotates by a certain angle, and the ECU 100 calculates the engine speed based on the output pulse. The engine operating state is determined based on the engine load and the engine speed.
[0048]
Next, the NOx storage reduction catalyst (hereinafter sometimes simply referred to as NOx catalyst) 36 built in the casing 37 will be described.
The NOx storage reduction catalyst 36 is, for example, alumina (Al₂O_Three) On the support, and selected from alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y. At least one of these and a noble metal such as platinum Pt are supported.
[0049]
The NOx catalyst 36 absorbs NOx when the air-fuel ratio of the inflowing exhaust gas (hereinafter referred to as exhaust air-fuel ratio) is lean, and absorbs NOx that releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases. Perform release action. Here, the exhaust air-fuel ratio means the ratio of the total amount of air supplied to the exhaust passage, engine combustion chamber, intake passage, etc. upstream of the NOx catalyst 36 and the total fuel (hydrocarbon). And Therefore, when fuel, reducing agent, or air is not supplied into the exhaust passage upstream of the NOx catalyst 36, the exhaust air-fuel ratio matches the air-fuel ratio of the air-fuel mixture supplied into the engine combustion chamber.
[0050]
The absorption / release action of the NOx catalyst 36 is considered to be performed by the mechanism shown in FIG. Hereinafter, this mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported on the support, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0051]
First, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG.₂Is O₂ ^-Or O^2-It adheres to the surface of platinum Pt. On the other hand, NO contained in the inflowing exhaust gas is O on the surface of platinum Pt.₂ ^-Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂).
[0052]
Then the generated NO₂As shown in FIG. 2A, nitrate ions NO are absorbed into the NOx catalyst 36 while being oxidized on the platinum Pt and combined with the barium oxide BaO._Three ^-In the form of NOx catalyst 36. In this way, NOx is absorbed into the NOx catalyst 36.
[0053]
As long as the oxygen concentration in the inflowing exhaust gas is high, NO on the surface of platinum Pt₂As long as NOx is not saturated and the NOx absorption capacity of the NOx catalyst 36 is saturated.₂Is absorbed in the NOx catalyst 36 and nitrate ions NO._Three ^-Is generated.
[0054]
In contrast, when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the oxygen concentration in the inflowing exhaust gas decreases.₂Production amount decreases and the reaction proceeds in the reverse direction (NO_Three ^-→ NO₂), And nitrate ion NO in the NOx catalyst 36_Three ^-Is NO₂Alternatively, it is released from the NOx catalyst 36 in the form of NO. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the NOx catalyst 36.
[0055]
On the other hand, at this time, HC and CO in the exhaust gas are oxygen O on platinum Pt.₂ ^-Or O^2-It reacts with and is oxidized. Further, the NOx released from the NOx catalyst 36 due to the decrease in the oxygen concentration in the inflowing exhaust gas.₂Alternatively, NO is reduced by reacting with unburned HC and CO as shown in FIG.₂It becomes.
[0056]
That is, HC and CO in the inflowing exhaust gas are first oxygen O on platinum Pt.₂ ^-Or O^2-Immediately reacts with and oxidizes, then oxygen O on platinum Pt.₂ ^-Or O^2-If HC and CO still remain after the consumption of NOx, NOx released from the NOx catalyst and NOx discharged from the engine by the HC and CO are N₂To be reduced.
[0057]
In this way, NO on the surface of platinum Pt.₂Or, when NO is no longer present, NOx catalyst 36 continues to NO₂Or NO is released and N₂To be reduced. Therefore, when the exhaust air-fuel ratio is made the stoichiometric air-fuel ratio or rich air-fuel ratio, NOx is released from the NOx catalyst 36 in a short time, and N₂Reduced to
[0058]
Thus, when the exhaust air-fuel ratio becomes lean, NOx is absorbed by the NOx catalyst 36, and when the exhaust air-fuel ratio is made the stoichiometric or rich air-fuel ratio, NOx is released from the NOx catalyst 36 in a short time, and N₂Reduced to Accordingly, NOx emission into the atmosphere can be prevented.
[0059]
By the way, in the case of a diesel engine, combustion is performed in a much leaner region than stoichiometric (theoretical air-fuel ratio, A / F = 13 to 14), so that the exhaust gas flowing into the NOx catalyst 36 in a normal engine operation state The air-fuel ratio is very lean, NOx in the exhaust gas is absorbed by the NOx catalyst 36, and the amount of NOx released from the NOx catalyst 36 is extremely small.
[0060]
In the case of a gasoline engine, the air-fuel ratio supplied to the combustion chamber is stoichiometric or a rich air-fuel ratio, so that the air-fuel ratio of the exhaust gas is made the stoichiometric or rich air-fuel ratio, and the oxygen concentration in the exhaust gas is reduced. Thus, NOx absorbed by the NOx catalyst 36 can be released. However, in the case of a diesel engine, if the air-fuel mixture supplied to the combustion chamber is stoichiometric or rich air-fuel ratio, soot is generated during combustion, etc. Because of this problem, it cannot be adopted.
[0061]
Therefore, in the diesel engine, at a predetermined timing before the NOx absorption capacity of the NOx catalyst 36 is saturated, the reducing agent is supplied into the exhaust gas to reduce the oxygen concentration in the exhaust gas and absorbed by the NOx catalyst 36. NOx must be released and reduced. In addition, as the reducing agent, in general, light oil that is a fuel of a diesel engine is often used.
[0062]
Therefore, in this embodiment, the NOx amount absorbed by the NOx catalyst 36 is estimated by the ECU 100 from the history of the operating state of the engine 1, and only when the estimated NOx amount reaches a predetermined value set in advance, only for a predetermined time. The control valve 43 is opened to supply a predetermined amount of fuel into the exhaust pipe 31, the oxygen concentration in the exhaust gas flowing into the NOx catalyst 36 is reduced, the NOx absorbed by the NOx catalyst 36 is released, and N₂I'm trying to reduce it. That is, in this embodiment, hydrocarbon (light oil) is intermittently supplied to the exhaust pipe 31 by the HC supply device 40. The supply pump 41 is basically operated at all times.
[0063]
Therefore, in this embodiment, when the control valve 43 is closed and no fuel is supplied to the exhaust pipe 31, NOx in the exhaust gas is absorbed by the NOx catalyst 36, and the control valve 43 is opened. When fuel is supplied to the exhaust pipe 31, NOx absorbed by the NOx catalyst 36 is released, and N₂Will be reduced.
[0064]
Next, the inlet gas NOx sensor 52 and the outlet gas NOx sensor 54 will be described. The NOx sensors used for the input gas NOx sensor 52 and the output gas NOx sensor 54 are oxygen pumps (O₂As is also disclosed in SAE (Society of Aoutomotive Engineers) 980170 and the like, it is already known. The principle of NOx concentration measurement of this NOx sensor will be described with reference to FIG.
[0065]
First, the basic structure of the NOx sensor will be described. The NOx sensor has a gas passage 203 formed between a pair of partition walls 201 and 202 made of an oxygen ion conductor such as zirconia. In the gas passage 203, both side surfaces parallel to the paper surface of FIG. 3 are closed by side walls (not shown) made of an insulating material, and the gas flows through the gas passage 203 from the left side to the right side in FIG. . The partition walls 201 and 202 are electrically insulated from each other.
[0066]
The gas passage 203 is provided with throttle members 204, 205, and 206 made of a porous material at both ends and the center thereof, and the first reaction chamber 211 and the second reaction chamber are interposed between the throttle members 204, 205, and 206. 212 is formed. The throttle members 204, 205, and 206 function as throttles that limit the flow rate of gas flowing through the gas passage 203 to a flow rate suitable for measuring the NOx concentration.
[0067]
When this NOx sensor is disposed in the gas flow with the side on which the throttle member 204 is provided positioned upstream of the gas flow, the gas is in the throttle member 204, the first reaction chamber 211, the throttle member 205, and the second reaction. It passes through the chamber 212 and the throttle member 206 in this order and flows downstream.
[0068]
A part of the partition wall 201 corresponding to the first reaction chamber 211 is provided with a first closed circuit 220 that applies a predetermined voltage with the first reaction chamber 211 side as a cathode and the outer surface side of the partition wall 201 as an anode. Yes.
[0069]
In addition, a second closed circuit 230 for applying a voltage of a predetermined magnitude is provided at a portion corresponding to the second reaction chamber 212 in the partition wall 202 with the second reaction chamber 212 side as a cathode and the outer surface side of the partition wall 202 as an anode. It has been.
[0070]
Next, the principle of NOx concentration measurement of this NOx sensor will be described. This NOx sensor does not directly measure NOx concentration,₂And O₂O, obtained by decomposing NOx₂The NOx concentration is determined stoichiometrically from this, but when measuring the NOx concentration of exhaust gas based on this principle, oxygen is originally present in the exhaust gas, so NOx in the exhaust gas N₂And O₂If the oxygen in the exhaust gas is not removed before decomposition, the NOx concentration cannot be determined.
[0071]
Therefore, in this NOx sensor, first, oxygen in the exhaust gas is removed in the first reaction chamber 211, and then NOx in the exhaust gas is removed in the second reaction chamber 212 by N.₂And O₂And the NOx concentration is measured.
[0072]
That is, since a voltage is applied to the partition wall 201 by the first closed circuit 220, only oxygen in the exhaust gas in the first reaction chamber 211 is selectively ionized to become oxygen ions. At this stage, NOx is N₂And O₂It will not be broken down. Since the partition wall 201 is composed of an oxygen ion conductor, the oxygen ions flow through the partition wall 201 from the cathode side to the anode side of the first closed circuit 220, and as a result, a current flows through the first closed circuit 220. . In this way, a series of functions for ionizing oxygen in the space and taking it out through the oxygen ion conductor is generally called an “oxygen pump”.
[0073]
Here, if the flow restriction performance by the throttle member 204 is set to a predetermined value and the voltage applied to the first closed circuit 220 is set to a predetermined value, oxygen in the first reaction chamber 211 is pumped to the outside by an oxygen pump. It is possible to make the discharge speed larger than the inflow speed of oxygen newly flowing into the first reaction chamber 211 through the throttle member 204, and if so set, the oxygen in the first reaction chamber 211 is set. Therefore, the oxygen concentration of the exhaust gas in the first reaction chamber 211 can be made almost zero.
[0074]
The exhaust gas whose oxygen concentration has been reduced to zero in the first reaction chamber 211 flows into the second reaction chamber 212 through the throttle member 205. The second reaction chamber 212 is provided with a catalyst (not shown) for promoting the reduction of NOx. Due to this catalytic action, NOx in the exhaust gas in the second reaction chamber 212 is N.₂And O₂Can be disassembled.
[0075]
Here, since the voltage is applied to the partition wall 202 by the second closed circuit 230, the oxygen generated by the decomposition of NOx is ionized into oxygen ions, and the oxygen ions are formed of an oxygen ion conductor. 202 flows from the cathode side to the anode side of the second closed circuit 230, and as a result, a current flows through the second closed circuit 230. The current flowing through the second closed circuit 230 is measured by an ammeter 231, the oxygen concentration is obtained from this current value, and the NOx concentration is obtained stoichiometrically based on this oxygen concentration.
[0076]
The above is the basic principle of the NOx sensor. The present applicant paid attention to the fact that the output of the NOx sensor exhibits a unique behavior when the NOx sensor is used under certain conditions.
First, the case of a NOx sensor that detects the NOx concentration of exhaust gas that is installed upstream of the NOx storage reduction catalyst and flows into the NOx catalyst, such as the input gas NOx sensor 52, will be described with reference to FIG.
[0077]
In order to simplify the explanation, it is assumed that the NOx sensor is installed in a steady exhaust gas flow in which both the NOx concentration and the HC concentration are constant. The output of the NOx sensor at this time is naturally a substantially constant value n1 (in this example, about 100 ppm).
[0078]
Next, when only the HC concentration of the exhaust gas having a constant NOx concentration is increased temporarily (intermittently), the output of the NOx sensor (ie, the NOx concentration of the exhaust gas is constant, that is, The NOx concentration detection value) is affected by interference according to the HC concentration, and as shown in FIG. 4, once it decreases, it returns to the steady value (n1) before the HC concentration increase.
[0079]
The reason why the output of the NOx sensor exhibits such behavior is presumed as follows. When the HC concentration of the exhaust gas is rapidly increased, a part of the increased HC and NOx react in the first reaction chamber 211 of the NOx sensor, NOx is reduced, and N₂As a result, the NOx concentration of the exhaust gas in the first reaction chamber 211 decreases. Since the exhaust gas whose NOx concentration is reduced flows into the second reaction chamber 212, it is presumed that the output of the NOx sensor decreases momentarily when the HC concentration of the exhaust gas is increased.
[0080]
The applicant has confirmed through experiments that this phenomenon is reproducible. FIG. 5 shows an example of this experimental result. As an experimental condition in this case, a NOx sensor is arranged in an exhaust pipe through which a steady exhaust gas having a constant NOx concentration and HC concentration flows, and upstream of this NOx sensor. The HC concentration of the exhaust gas was rapidly increased by instantaneously supplying HC into the exhaust pipe. From this experimental result, as the HC concentration increase amount (HC supply amount) increases, the output decrease of the NOx sensor increases, and when the HC concentration increase amount (HC supply amount) is the same, the NOx concentration of the exhaust gas It can be seen that the larger the value, the greater the decrease in the output of the NOx sensor.
[0081]
Therefore, the NOx sensor detects the NOx concentration of the exhaust gas before the HC supply and the amount of decrease in the NOx sensor output after the HC supply (hereinafter referred to as the “drop amount”), thereby obtaining the HC supply amount. be able to. Therefore, in this embodiment, an experiment is performed in advance so that the supply amount of HC actually supplied from the HC supply device 40 to the exhaust pipe 31 can be estimated and calculated based on the output of the input gas NOx sensor 52. The relationship between the NOx concentration of exhaust gas, the amount of HC supplied, and the amount of decrease in the NOx sensor output after HC supply (that is, the relationship corresponding to FIG. 5) is obtained and stored in the ROM of the ECU 100 as an HC supply amount map. Let me.
[0082]
Next, FIG. 6 shows the case of an NOx sensor that detects the NOx concentration of the exhaust gas that is installed downstream of the NOx storage reduction catalyst and purified by the NOx catalyst, such as the exhaust gas NOx sensor 54. To explain.
[0083]
In order to simplify the explanation, it is assumed that a steady exhaust gas in which both the NOx concentration and the HC concentration are constant flows into the NOx catalyst. In this case, if the NOx purification rate of the NOx catalyst does not change, the NOx concentration of the exhaust gas purified by the NOx catalyst should be almost constant, so the output of the NOx sensor downstream of the NOx catalyst is natural. However, it becomes a substantially constant value n2 (about 100 ppm in this example).
[0084]
Here, when only the HC concentration of the exhaust gas having a constant NOx concentration flowing into the NOx catalyst is increased temporarily (intermittently) rapidly, the output of the NOx sensor (that is, the detected NOx concentration value) is shown in FIG. Thus, after decreasing once, this time, it turns around and becomes larger than before the increase in HC concentration, and then returns to the steady value (n2) before the increase in HC concentration.
[0085]
The reason why the output of the NOx sensor exhibits such behavior is presumed as follows. First, the reason why the output of the NOx sensor decreases momentarily will be inferred. When exhaust gas with a high HC concentration flows into the NOx catalyst, some HC in the exhaust gas reacts with oxygen attached to the NOx catalyst and oxidizes, and other HC is released from the NOx catalyst. It is consumed as a reducing agent for reducing the NOx produced. The remaining HC that could not react with oxygen or NOx in the NOx catalyst passes through the NOx catalyst and flows downstream of the NOx catalyst. Here, when the exhaust gas whose NOx concentration has been rapidly increased is supplied to the NOx catalyst, the HC concentration of the exhaust gas downstream of the NOx catalyst also increases rapidly, so this exhaust gas is supplied to the NOx sensor downstream of the NOx catalyst. When it flows in, it is presumed that the output of the NOx sensor downstream of the NOx catalyst is momentarily reduced due to the influence of interference according to the HC concentration as in the case of the NOx sensor installed upstream of the NOx catalyst.
[0086]
By the way, when the HC purification capacity (oxidation action) of the NOx catalyst decreases (that is, when the HC deterioration progresses), the amount of HC passing through the NOx catalyst increases, so the HC concentration of the exhaust gas flowing into the NOx catalyst is rapidly increased. In this case, the increase in the HC concentration downstream of the NOx catalyst is greater after HC deterioration than before HC deterioration. Therefore, even if the conditions for increasing the HC concentration upstream of the NOx catalyst are the same, the amount of decrease (the amount of drop) in the NOx sensor output downstream of the NOx catalyst is greater after HC deterioration of the NOx catalyst than before HC deterioration. Become.
[0087]
From this, when the HC concentration of the exhaust gas upstream of the NOx catalyst is suddenly increased, the degree of deterioration of the NOx catalyst with respect to the HC purification ability (that is, HC deterioration) from the state of the output reduction of the NOx sensor downstream of the NOx catalyst is determined. Can be determined.
[0088]
Therefore, in this embodiment, when the HC concentration of the exhaust gas upstream of the NOx catalyst is suddenly increased, the amount of NOx sensor output falling upstream of the NOx catalyst and the amount of NOx sensor output falling downstream of the NOx catalyst are calculated. A comparison value of the amount of sagging was obtained, and based on this comparison value, it was decided whether or not the NOx catalyst was deteriorated by HC.
[0089]
The reason why the output of the NOx sensor increases is assumed as follows. When the NOx storage reduction catalyst releases the absorbed NOx by increasing the HC concentration of the exhaust gas, the NOx release immediately stops even if the HC concentration of the exhaust gas is returned to the concentration before the increase. However, it has a characteristic that the release of NOx continues for a while (hereinafter referred to as “NOx exudation”). That is, even though the supply of HC acting as a reducing agent for NOx is lost, NOx exudates from the NOx catalyst, so the NOx concentration downstream of the NOx catalyst increases. Therefore, while NOx exudates from the NOx catalyst, the output of the NOx sensor downstream of the NOx catalyst is assumed to be larger than the output before the HC concentration increase.
The present applicant has confirmed through experiments that the output characteristics as shown in FIG. 6 of the NOx sensor arranged downstream of the NOx catalyst are also reproducible.
[0090]
Next, the operation of the exhaust gas purification apparatus for an internal combustion engine in this embodiment will be described.
As described above, in this embodiment, when the ECU 100 estimates the NOx amount absorbed by the NOx catalyst 36 from the history of the operating state of the engine 1, and when the estimated NOx amount reaches a preset predetermined value, A predetermined amount of hydrocarbon (light oil) is intermittently supplied to the exhaust pipe 31 upstream of the NOx catalyst 36 by the HC supply device 40, thereby releasing NOx absorbed by the NOx catalyst 36, and N₂To reduce.
[0091]
Since intermittent supply of HC by the HC supply device 40 temporarily increases the HC concentration of the input gas flowing into the NOx catalyst 36, the input gas NOx sensor 52 and the output gas NOx sensor 54 are at this time. The output change mentioned above is shown. Therefore, in this embodiment, the ECU 100 is based on the outputs of these two NOx sensors 52 and 54.
(1) Calculation of NOx purification rate of NOx catalyst 36 and determination of NOx deterioration
(2) Estimation of actual HC supply amount and failure determination of HC supply device
(3) Calculation of HC purification index of NOx catalyst 36 and determination of HC deterioration
I do. Hereinafter, each processing will be described.
[0092]
(1) Calculation of NOx purification rate of NOx catalyst 36 and determination of NOx deterioration
In this exhaust purification device, the ECU 100 determines the NOx catalyst from the output values of the input gas NOx sensor 52 and the output gas NOx sensor 54 when HC is not supplied from the HC supply device 40 to the exhaust pipe 31 (when HC is not supplied). A NOx purification rate representing the magnitude of the NOx purification capacity (reduction action) 36 is calculated, and based on this, it is determined whether or not the NOx catalyst 36 has deteriorated in NOx.
[0093]
That is, the NOx purification rate of the NOx catalyst 36 is obtained by dividing the output value (detection value) of the output gas NOx sensor 54 when HC is not supplied by the output value (detection value) of the input gas NOx sensor 52. Is obtained by subtracting 1 from 1. For example, if the NOx concentration detected by the inlet gas NOx sensor 52 is 100 ppm and the NOx concentration detected by the outlet gas NOx sensor 54 is 30 ppm, the NOx purification rate of the NOx catalyst 36 at this time is 70%. Become.
[0094]
When the NOx catalyst 36 has not deteriorated in NOx, the NOx purification rate of the NOx catalyst 36 can be restored to the initial state by intermittent supply of HC by the HC supply device 40. However, when NOx deterioration of the NOx catalyst 36 proceeds, the NOx purification rate cannot be restored to the initial state even if intermittent supply of HC is performed by the HC supply device 40.
[0095]
Therefore, in this embodiment, the ECU 100 always determines the NOx catalyst 36 based on the output value (detected value) of the outlet gas NOx sensor 54 and the output value (detected value) of the inlet gas NOx sensor 52 when HC is not supplied. When the NOx purification rate is calculated and the degree of NOx deterioration is obtained by comparison with the initial NOx purification rate of the NOx catalyst 36 (hereinafter referred to as the initial NOx purification rate), and the degree of NOx deterioration becomes greater than a predetermined level ( For example, it is determined that the NOx catalyst 36 has deteriorated in NOx when the NOx purification rate becomes 50% or less.
[0096]
In this embodiment, the initial NOx purification rate that is a reference for obtaining the degree of NOx deterioration is obtained as follows (see FIG. 7).
An exhaust gas having a constant NOx concentration (for example, 100 ppm) continues to flow through a new NOx catalyst 36 that has not yet been used for NOx purification, and the NOx catalyst 36 is once saturated with NOx. At this time, the outputs of the input gas NOx sensor 52 and the output gas NOx sensor 54 are the same.
[0097]
Next, HC is supplied upstream of the NOx catalyst 36 under the same conditions as normal HC intermittent supply at predetermined intervals (for example, 6 to 7 seconds). In FIG. 7, point A indicates the HC intermittent supply start point. Then, when the HC is not supplied, the NOx concentration detected by the outgas NOx sensor 54 gradually decreases and converges after a predetermined time has elapsed (for example, after 100 to 120 seconds) after starting the intermittent supply of HC. Shows a substantially constant value (point B in FIG. 7). Immediately after the convergence, the NOx purification rate calculated from the output value of the output gas NOx sensor 54 and the output value of the input gas NOx sensor 52 was used as the initial NOx purification rate of the NOx catalyst 36.
[0098]
Next, the NOx deterioration determination processing routine of the NOx catalyst 36 in this embodiment will be described with reference to FIG. A flowchart including the steps constituting this routine is stored in the ROM of the ECU 100, and all processes in the steps of the flowchart are executed by the CPU of the ECU 100.
[0099]
<Step 101>
First, in step 101, the ECU 100 detects the input gas NOx concentration detected by the input gas NOx sensor 52 and the output gas NOx when HC is not supplied from the HC supply device 40 to the exhaust pipe 31 (when HC is not supplied). The output gas NOx concentration detected by the sensor 54 is read.
[0100]
<Step 102>
Next, the ECU 100 proceeds to step 102, and calculates the NOx purification rate of the NOx catalyst 36 at the present time (hereinafter referred to as the current NOx purification rate) from the input gas NOx concentration and the output gas NOx concentration read in step 101.
[0101]
<Step 103>
Next, the ECU 100 proceeds to step 103, calculates the difference between the initial NOx purification rate obtained in advance and the current NOx purification rate obtained in step 101, and whether or not this difference is larger than a preset determination value α. To determine.
[0102]
<Step 104>
If an affirmative determination is made in step 103, the ECU 100 proceeds to step 104, determines that the NOx catalyst 36 has deteriorated in NOx, and ends this routine.
[0103]
<Step 105>
If a negative determination is made in step 103, the ECU 100 proceeds to step 105, determines that the NOx catalyst 36 has not yet deteriorated, and ends this routine.
[0104]
Since the NOx concentration of the exhaust gas upstream of the NOx catalyst 36 can be estimated from the operating state (operating conditions) of the engine 1, the operating state of the engine 1 and the NOx concentration of the input gas of the NOx catalyst 36 are If the map corresponding to is stored in the ROM of the ECU 100 in advance and the NOx concentration of the input gas is estimated with reference to this map, as far as the above-mentioned “NOx purification rate calculation and NOx deterioration determination” is concerned. The omission gas NOx sensor 52 can be omitted.
[0105]
In this embodiment, when the ECU 100 executes this NOx deterioration determination processing routine, the NOx deterioration determination means according to the present invention is realized.
[0106]
(2) Estimation of actual HC supply amount and failure determination of HC supply device
Next, in this exhaust purification device, the ECU 100 is actually supplied into the exhaust pipe 31 based on the output change of the input gas NOx sensor 52 when HC is intermittently supplied to the exhaust pipe 31 by the HC supply device 40. The HC supply amount (hereinafter referred to as the actual HC supply amount) is calculated and estimated, and it is determined whether or not the HC supply device 40 has failed based on the actual HC supply amount.
[0107]
That is, the ECU 100 reduces the input gas NOx concentration detected by the input gas NOx sensor 52 immediately before the HC supply device 40 supplies HC into the exhaust pipe 31 and the drop in the output change that occurs in the input gas NOx sensor 52 immediately after HC supply. Based on the amount, the actual HC supply amount supplied to the exhaust pipe 31 is calculated with reference to the HC supply amount map (not shown).
[0108]
Next, the ECU 100 determines the target HC supply amount to be supplied to the exhaust pipe 31 by the HC supply device 40 (the HC supply amount that should be supplied from the HC supply device 40 according to a command from the ECU 100), and the actual HC supply amount. And based on the comparison value (difference or quotient between the two), it is determined whether or not the error between the two is within a preset allowable error range. If the error between the two is within the allowable error range, it is determined that the HC supply device 40 is operating normally. If the error is outside the allowable error range, it is determined that the HC supply device 40 is abnormal.
[0109]
Next, the failure determination processing routine of the HC supply device in this embodiment will be described with reference to FIG. A flowchart including the steps constituting this routine is stored in the ROM of the ECU 100, and all processes in the steps of the flowchart are executed by the CPU of the ECU 100.
[0110]
<Step 201>
First, in step 201, the ECU 100 reads the input gas NOx concentration detected by the input gas NOx sensor 52 before supplying HC by the HC supply device 40.
[0111]
<Step 202>
Next, the ECU 100 proceeds to step 202, and calculates the amount of sag based on the output change of the input gas NOx sensor 52 immediately after HC supply.
[0112]
<Step 203>
Next, the ECU 100 proceeds to step 203 and calculates the actual HC supply amount with reference to the HC supply amount map based on the input gas NOx concentration read in step 201 and the drop amount calculated in step 202.
[0113]
<Step 204>
Next, the ECU 100 proceeds to step 204, calculates the difference between the target HC supply amount and the actual HC supply amount calculated in step 203, and whether or not the difference (absolute value) is smaller than a preset allowable range β. To determine.
[0114]
<Step 205>
If the determination in step 204 is affirmative, the ECU 100 proceeds to step 205, determines that the HC supply device 40 is operating normally, and ends this routine.
[0115]
<Step 206>
If a negative determination is made in step 204, the ECU 100 proceeds to step 206, determines that the HC supply device 40 has failed, and ends this routine. Note that if a failure is determined in step 206, the ECU 100 can also perform processing such as turning on a warning light on a meter panel (not shown).
[0116]
In this embodiment, the ECU 100 executes steps 201 to 203 in the failure determination processing routine of the HC supply device, thereby realizing the HC concentration increase amount estimation means according to the present invention. When the ECU 100 executes 206, the failure determination means according to the present invention is realized.
[0117]
(3) Calculation of HC purification index of NOx catalyst 36 and determination of HC deterioration
Next, in this exhaust purification device, the ECU 100 determines the NOx catalyst 36 based on the output changes of the input gas NOx sensor 52 and the output gas NOx sensor 54 when HC is intermittently supplied to the exhaust pipe 31 by the HC supply device 40. An HC purification index (comparison value) representing the magnitude of the HC purification capacity (oxidation action) of the engine is calculated, and based on this, it is determined whether or not the NOx catalyst 36 has deteriorated.
[0118]
The HC purification index is defined as a drop amount (b) in the output change of the output gas NOx sensor 54 that occurs immediately after HC is supplied from the HC supply device 40 into the exhaust pipe 31 (a drop amount in the output change of the input gas NOx sensor 52 ( Obtained as the quotient (b / a) divided by a).
[0119]
FIG. 10 shows an example of changes in the output of the input gas NOx sensor 52 and the output gas NOx sensor 54 at the time of intermittent supply of HC. FIG. 10A shows the output when the NOx catalyst 36 is not deteriorated by HC. FIG. 10B shows an output waveform when the HC deterioration of the NOx catalyst 36 has progressed considerably. As described above, since the HC passing through the NOx catalyst 36 increases as the HC deterioration progresses, the HC purification index (b / a) increases, and when it completely deteriorates and the HC purification capacity is lost, the HC purification index (b / A) becomes “1”.
[0120]
Therefore, in this embodiment, the ECU 100 always calculates the amount of decrease (b) in the output of the output gas NOx sensor 54 immediately after the intermittent supply of HC and the amount of decrease (a) in the output of the input gas NOx sensor 52. From the above, the HC purification index (b / a) of the NOx catalyst 36 is calculated, and when the HC purification index (b / a) becomes larger than a preset judgment value γ, it is judged that the NOx catalyst 36 has deteriorated HC. . Note that the determination value γ is a value determined from the HC concentration allowed for the output gas (allowable output gas HC concentration) in the exhaust purification apparatus, and can be set to γ = 0.5, for example.
[0121]
Next, the HC deterioration determination processing routine in this embodiment will be described with reference to FIG. A flowchart including the steps constituting this routine is stored in the ROM of the ECU 100, and all processes in the steps of the flowchart are executed by the CPU of the ECU 100.
[0122]
<Step 301>
First, in step 301, the ECU 100 calculates a drop amount (a) based on the output change of the input gas NOx sensor 52 immediately after HC supply, and based on the output change of the output gas NOx sensor 54 immediately after HC supply. The amount of depression (b) is calculated.
[0123]
<Step 302>
Next, the ECU 100 proceeds to step 302 where the current HC purification index (b / a) is calculated on the basis of the drop amount (a, b) of the output of both NOx sensors 52, 54 obtained by calculation in step 301. calculate.
[0124]
<Step 303>
Next, the ECU 100 proceeds to step 303 and determines whether or not the current HC purification index (b / a) obtained in step 302 is larger than a predetermined determination value γ.
[0125]
<Step 304>
If an affirmative determination is made in step 303, the ECU 100 proceeds to step 304, determines that the NOx catalyst 36 has deteriorated HC, and ends this routine.
[0126]
<Step 305>
If the determination in step 303 is negative, the ECU 100 proceeds to step 305, determines that the NOx catalyst 36 has not yet deteriorated in HC, and ends this routine.
[0127]
In this embodiment, the ECU 100 executes steps 301 to 302 in the HC deterioration determination processing routine, thereby realizing the HC purification capacity estimating means according to the present invention, and the ECU 100 executes steps 303 to 305. Thus, the HC deterioration determination means according to the present invention is realized.
[0128]
Note that the change in the output of the input gas NOx sensor 52 immediately after the intermittent supply of HC is reproducible and changes substantially constant in accordance with the intermittent supply amount of HC. The drop amount (a) can be estimated if the intermittent supply amount of HC is known.
[0129]
Therefore, when the intermittent supply amount of HC by the HC supply device 40 is set in advance according to the operating state of the engine, the HC intermittent supply amount and the drop amount of the output of the input gas NOx sensor 52 (a ) And stored in the ROM of the ECU 100, and referring to this map to estimate the drop amount (a) of the output of the input gas NOx sensor 52, the above-mentioned “NOx catalyst” is obtained. As long as the calculation of the HC purification index of 36 and the determination of HC deterioration are concerned, the input gas NOx sensor 52 can be omitted.
[0130]
Thus, in the exhaust gas purification apparatus for an internal combustion engine of this embodiment, only the NOx sensors 52 and 54 are provided one upstream and one downstream of the NOx catalyst 36, but the outputs of these NOx sensors 52 and 54 are output. By performing the predetermined processing as described above, the NOx purification capacity (NOx purification rate) of the NOx catalyst 36 can be obtained to determine NOx deterioration, and the actual HC supply amount can be estimated to determine the HC supply device 40. Failure determination can be performed, and the HC purification ability (HC purification index) of the NOx catalyst 36 can be obtained to determine HC deterioration.
[0131]
[Other Embodiments]
In the above-described embodiment, intermittent supply of HC to the exhaust pipe 31 by the HC supply device 40 is employed to rapidly increase the HC concentration of the exhaust gas, but instead, for example, expansion of the engine The HC concentration of the exhaust gas may be rapidly increased by sub-injecting fuel into the combustion chamber during the stroke or the exhaust stroke.
[0132]
In the above-described embodiment, the present invention has been described with reference to an example in which the present invention is applied to a diesel engine. However, the present invention can also be applied to a gasoline engine capable of lean combustion. In the case of a gasoline engine, the exhaust gas supplied to the combustion chamber is stoichiometric or rich air-fuel ratio, the exhaust air-fuel ratio is made stoichiometric or rich air-fuel ratio, the oxygen concentration in the exhaust gas is lowered, and the NOx catalyst The NOx absorbed in 36 can be released and reduced.
[0133]
In the above-described embodiment, the catalyst built in the casing 37 is an occlusion reduction type NOx catalyst, but this catalyst may be a selective reduction type NOx catalyst. Even when the catalyst is a selective reduction type NOx catalyst, the same actions and effects as in the case of the storage reduction type NOx catalyst are exhibited.
[0134]
【The invention's effect】
According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, an HC concentration increasing means for increasing the HC concentration of the exhaust gas of the internal combustion engine and an oxygen pump using an oxygen ion conductor are installed in the exhaust passage of the internal combustion engine. The NOx concentration detecting means for detecting the NOx concentration of the exhaust gas, and the HC of the exhaust gas based on the detected value of the NOx concentration detecting means when the HC concentration of the exhaust gas is rapidly increased by the HC concentration increasing means. HC concentration increase amount estimation means for estimating the concentration increase amount, so that the HC concentration increase amount (HC supply amount) of the exhaust gas can be estimated from the detected value of the NOx concentration detection means without the HC concentration detection means. can do.
[0135]
Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the failure determination means is provided, it is possible to determine whether or not the HC concentration increasing means is in failure, and early response at the time of failure becomes possible.
[0136]
According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, a catalyst provided in an exhaust passage of the internal combustion engine, HC concentration increasing means for increasing the HC concentration of the exhaust gas of the internal combustion engine flowing into the catalyst, oxygen A catalyst downstream NOx concentration detecting means which has an oxygen pump using an ionic conductor and is installed downstream of the catalyst to detect the NOx concentration of exhaust gas; and when the HC concentration is rapidly increased by the HC concentration increasing means HC purification capability estimation means for estimating the HC purification capability of the catalyst based on the detection value of the catalyst downstream NOx concentration detection means in the catalyst, in addition to knowing the NOx purification capability of the catalyst, The HC purification capacity can be estimated.
[0137]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the catalyst upstream NOx concentration detecting means is provided upstream of the catalyst, the HC purification capacity of the catalyst can be estimated more accurately.
[0138]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the HC deterioration determination means is provided, it can be determined whether or not the catalyst has deteriorated HC, and early response after deterioration is possible.
[0139]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the NOx deterioration determination means is provided, it can be determined whether or not the catalyst has deteriorated in NOx, and an early response after the deterioration becomes possible.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a diagram for explaining the NOx absorption / release action of the NOx storage reduction catalyst.
FIG. 3 is a diagram showing a schematic configuration of a NOx sensor in the embodiment.
FIG. 4 is a view showing an example of an output change of an input gas NOx sensor at the time of intermittent supply of HC.
FIG. 5 is a diagram showing a relationship between an intermittent supply amount of HC and a drop amount of NOx sensor output.
FIG. 6 is a diagram showing an example of an output change of an outgas NOx sensor at the time of intermittent supply of HC.
FIG. 7 is a diagram for explaining how the output of the output gas NOx sensor converges.
FIG. 8 is a NOx deterioration determination processing routine in the embodiment.
FIG. 9 is an HC supply device failure determination processing routine in the embodiment.
FIG. 10 is a diagram showing an example of output changes of the input gas NOx sensor and the output gas NOx sensor before and after HC deterioration in the embodiment.
FIG. 11 is an HC deterioration determination processing routine in the embodiment.
[Explanation of symbols]
1 Diesel engine
21-26 Fuel injection valve
31 Exhaust pipe (exhaust passage)
36 NOx storage reduction catalyst
40 HC supply device (HC concentration increasing means)
52 Input gas NOx sensor (catalyst upstream NOx concentration detection means)
54 Outgas NOx sensor (catalyst downstream NOx concentration detection means)
100 ECU (HC concentration increase estimation means, failure determination means, HC purification capacity estimation means, HC deterioration determination means, NOx deterioration determination means)

Claims (9)

HC concentration increasing means for increasing the HC concentration of the exhaust gas of the internal combustion engine;
NOx concentration detection means that has an oxygen pump using an oxygen ion conductor and is installed in the exhaust passage of the internal combustion engine and detects the NOx concentration of the exhaust gas;
The N Ox concentrations observed when said HC concentration increasing means is a HC concentration of exhaust gas, the detected value of the concentration of NO x detection means as compared with the previous increase in the HC concentration allowed rapid increases as a temporary drop HC concentration increase amount estimation means for estimating the HC concentration increase amount of the exhaust gas based on the decrease amount of the detection value of the detection means;
An exhaust emission control device for an internal combustion engine, comprising:   The HC concentration increase estimation means is the NO x 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the amount of increase in the HC concentration is estimated as a larger value as the amount of decrease in the detection value of the concentration detection means is larger.   The HC concentration increase estimation means is configured to determine the NO before the increase in HC concentration under the same decrease amount of the detected value. x 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the HC concentration increase amount is estimated as a larger value as the detected value of the concentration detecting means is larger. When the comparison value between the estimated HC concentration increase estimated by the HC concentration increase estimation means and the target HC concentration increase to be increased by the HC concentration increase means is out of a predetermined allowable range, the HC concentration increase means The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3 , further comprising failure determination means for determining that there is a failure. A catalyst provided in the exhaust passage of the internal combustion engine;
HC concentration increasing means for increasing the HC concentration of the exhaust gas of the internal combustion engine flowing into the catalyst;
A catalyst downstream NOx concentration detecting means which has an oxygen pump using an oxygen ion conductor and is installed downstream of the catalyst to detect the NOx concentration of exhaust gas;
The HC concentration increase means H C concentration, the HC concentration the catalyst downstream NO x than before the increase in
HC purification capacity estimation for estimating the HC purifying capability of the catalyst based on the amount of decrease in the detected value of the definitive 該触 medium downstream NOx concentration detection means when the detected value of the concentration detection means is made to increase more rapidly reduced temporarily Means,
An exhaust emission control device for an internal combustion engine, comprising: A catalyst upstream NOx concentration detection means for detecting the NOx concentration of exhaust gas installed upstream of the catalyst having an oxygen pump using an oxygen ion conductor;
The HC purification ability estimation means, the HC concentration increases means H C concentration, the detection value of the catalyst upstream concentration of NO x detection means and the catalyst downstream concentration of NO x detection means as compared with the previous increase in the HC concentration temporary to compare the amount of decrease in the detected value of the reduction amount and 該触 medium downstream NOx concentration detection means of the detection value of 該触 medium upstream NOx concentration detection means definitive when more rapidly made to increase to decrease, with the comparison value 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5 , wherein the HC purification capacity of the catalyst is estimated on the basis of the catalyst. 6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5 , wherein the amount of HC concentration increase that is increased by the HC concentration increasing means is preset according to the operating state of the internal combustion engine. One of claims 5, characterized in that the HC purification ability of the catalyst estimated by the HC purification ability estimation means comprises a HC degradation determination means determines that the catalyst was HC degraded when more than a predetermined capacity 7 An exhaust purification device for an internal combustion engine according to claim 1. The NOx purification capacity of the catalyst is obtained from the detection value of the catalyst downstream NOx concentration detection means when the HC concentration increase is not performed by the HC concentration increase means, and when the NOx purification capacity is less than a predetermined capacity, the catalyst The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 5 to 7 , further comprising NOx deterioration determination means for determining that NOx has deteriorated.

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