JP4114355B2 - Exhaust gas purification device for internal combustion engine and method for determining deterioration thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to a method for determining deterioration thereof.
[0002]
[Prior art]
As a catalyst for purifying nitrogen oxides (NOx) in exhaust gas, NOx is occluded in an oxygen concentration excess (lean) state, and a fuel that is a reducing agent is added to the exhaust gas, resulting in a lean oxygen concentration state. There is an NOx storage reduction catalyst that releases NOx stored when it is turned on, reacts with fuel (HC) by an activated catalyst (Pt or the like), is reduced to N ₂ and discharged to the outside air.
[0003]
As described above, this NOx catalyst is activated by the NOx storage agent that is stored when the exhaust gas is lean and released when it is rich and the fuel that is the reducing agent, and causes a redox reaction on the exhausted NOx. The exhaust gas is purified by combining the occlusion / release function and the activation function, respectively.
[0004]
In determining such deterioration, as a conventional example, as disclosed in Japanese Patent Application Laid-Open No. 11-229859, in a NOx catalyst, a temperature sensor provided in the catalyst and a NOx sensor provided downstream of the catalyst are used. As disclosed in Japanese Patent Laid-Open No. 7-208151, there is a method for determining catalyst deterioration based on the NOx purification state of the NOx catalyst at a high temperature and a low temperature according to the time-lapse information of the NOx sensor and temperature sensor as temperature specifying means. When the NOx sensor provided downstream of the NOx catalyst is used and the time until the output value output according to the NOx concentration sensed by the NOx sensor rises to a predetermined value after completion of NOx discharge by the catalyst is less than a predetermined time There is a method for determining the catalyst deterioration.
[0005]
In any of these deterioration determination methods, the deterioration of the catalyst is determined using the NOx concentration in the exhaust gas. In other words, it is necessary to determine the deterioration of the catalyst using a NOx sensor that detects the NOx concentration.
[0006]
[Problems to be solved by the invention]
The NOx sensor used for the deterioration determination has a high NOx concentration measurement accuracy that is not yet at a practical level. Therefore, when the deterioration determination is actually performed using the NOx sensor, it is extremely difficult. The cost is high, or the deterioration determination accuracy is low.
[0007]
In view of the above problems, an object of the present invention is to determine the deterioration of the NOx purification capacity of a catalyst without using a NOx sensor.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, when the catalyst in the exhaust purification device provided in the exhaust system of the internal combustion engine reaches a predetermined judgment temperature equal to or higher than the light-off temperature of the catalyst that has not deteriorated, the catalyst is reduced to the catalyst. An exhaust agent is added, the upstream exhaust temperature and the catalyst bed temperature of the catalyst are measured, and the deterioration state of the exhaust purification device is determined based on the temperature difference between the upstream exhaust temperature and the catalyst bed temperature. Deterioration is determined by a deterioration determination method for the purifier.
[0009]
In order to perform the deterioration determination method, a catalyst provided in an exhaust passage of an internal combustion engine for purifying exhaust gas discharged, catalyst inflow exhaust gas temperature measuring means for measuring an exhaust gas temperature flowing into the catalyst, and a bed of the catalyst A catalyst bed temperature measuring means for measuring temperature, a reducing agent adding means for adding a reducing agent to the catalyst when the catalyst bed temperature reaches a predetermined judgment temperature that is equal to or higher than a light-off temperature of an undegraded catalyst, and the reduction a differential temperature detecting means for detecting a difference between the catalyst bed temperature to the catalyst inlet exhaust gas temperature at the time of the reducing agent was added to the catalyst by agent addition means, the temperature difference detected by the previous SL differential temperature detecting means is higher than a predetermined temperature difference A deterioration determination device for an exhaust gas purification apparatus, which includes deterioration determination means for determining that the catalyst has deteriorated when the catalyst is small is used.
[0011]
On the catalyst, HC, CO, and NOx undergo oxidation-reduction reactions, change into H ₂ O, CO ₂ , N _2, etc., and are discharged to the outside air. When the catalyst is activated, the temperature at which the HC, CO, and NOx start a redox reaction (light-off temperature) on the catalyst increases as the catalyst deteriorates. Similarly, the deteriorated catalyst also decreases the ability to occlude and release NOx, so that the amount of NOx that reacts with the reducing agent per unit time on the catalyst is also reduced. That is, the oxidation-reduction reaction amount also decreases, and the decrease in the oxidation-reduction reaction amount also reduces the increase in the catalyst bed temperature due to the heat of reaction during the oxidation-reduction reaction, that is, the difference between the catalyst bed temperature and the catalyst inflow exhaust temperature. Become.
[0012]
Therefore, the deterioration determination method is performed using this characteristic, and a temperature equal to or higher than the light-off temperature of an undegraded catalyst is set as a predetermined determination temperature, and the reducing agent is used as a catalyst for determining deterioration at this determination temperature. Addition is performed, and the deterioration state of the catalyst is determined by the degree of the temperature rising reaction at this time. The determination temperature may be equal to or higher than the light-off temperature of the non-degraded catalyst and in the vicinity of the light-off temperature. The determination temperature may be a temperature that is equal to or higher than the light-off temperature of the non-degraded catalyst and lower than the light-off temperature of the degrading catalyst.
[0013]
If the catalyst is below the activation temperature at which the oxidation-reduction reaction starts when fuel is added to the exhaust passage of the internal combustion engine, and the temperature rise reaction does not occur, the exhaust emission control device having the catalyst is part of the exhaust passage. It becomes. In this state, the exhaust gas temperature upstream of the catalyst and the catalyst bed temperature are equal. Therefore, if the fuel is added below the activation temperature, the added fuel is attached to the catalyst or is directly discharged to the outside air. Therefore, it is possible to determine the deterioration of the catalyst by adding the fuel when the bed temperature of the catalyst to be determined rises above the temperature at which the oxidation-reduction reaction starts with the catalyst that has not deteriorated.
[0014]
As for the catalyst inflow exhaust gas temperature measuring means and the catalyst bed temperature measuring means, a method for measuring the exhaust gas temperature and the catalyst bed temperature directly by a thermocouple, etc. A measurement method in which the temperature is used as the catalyst bed temperature can be exemplified. Regarding the differential temperature detection means, a signal detected based on the temperature measured by the catalyst inflow exhaust gas temperature measurement means and the catalyst bed temperature measurement means is processed by an ECU (electronic control unit), and the temperature difference (Δt) is calculated. There is a method of detecting the generated exhaust gas temperature.
[0015]
The exhaust purifier stores nitrogen oxides present in the exhaust when the inflowing exhaust is in an oxygen concentration excess state, and the nitrogen oxidation stored in the precursor when the inflowing exhaust is in a lean oxygen concentration state. And a storage amount estimating means for estimating the storage amount of the nitrogen oxides, and the storage amount estimation means estimates that the storage amount of nitrogen oxides is less than or equal to a predetermined amount. In this case, the reducing agent is not added by the reducing agent addition means .
[0016]
The NOx catalyst is configured such that a NOx occlusion agent that occludes and releases NOx by an ambient atmosphere and a noble metal that reacts the released NOx and a reducing agent are supported on a carrier. Therefore, the temperature of the added fuel is raised by the reaction heat generated when an oxidation-reduction reaction is caused on the NOx released from the NOx storage agent and the noble metal, and the deterioration of the NOx catalyst is judged using this temperature rising reaction. is there. In order to perform the deterioration determination of the NOx catalyst by the above method, the NOx amount necessary for performing the deterioration determination is previously stored in the NOx catalyst, and this is stored when reacting with the reducing agent to perform the deterioration determination. It is necessary to release NOx. Therefore, the NOx occlusion amount of the NOx catalyst to be determined is estimated, and if the estimated NOx occlusion amount is not more than a predetermined amount necessary for performing the deterioration determination, the reducing agent is added to the NOx catalyst included in the exhaust purification device. It was decided not to perform the deterioration determination, that is, the deterioration determination.
[0017]
In each of the above determination methods, the most NOx occlusion amount is required for the determination, that is, the temperature rising reaction by the oxidation-reduction reaction of NOx and the reducing agent is required in the determination method of catalyst deterioration due to the difference in the maximum value of Δt. . Therefore, another determination method can be performed by using the NOx storage amount necessary for this determination method as the estimated storage amount. Further, as the storage amount estimation means, the maximum value of Δt is similarly determined in the new catalyst in a state where the load state of the internal combustion engine, the amount of fuel added to the combustion chamber, the exhaust temperature, the time required for NOx storage, etc. are grasped. The NOx occlusion amount necessary until the occurrence of NO is calculated in advance and stored in the ECU as a NOx occlusion amount map. There is a method of estimating the minimum NOx occlusion amount stored in the catalyst for determining deterioration from this map and using this value as the NOx occlusion amount.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment in which a deterioration determination device and method for an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine system will be described.
[0019]
In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 is an in-line four-cylinder diesel engine system that includes a fuel supply system 10, a combustion chamber 20, an intake system 30, an exhaust system 40, and the like as main parts. Hereinafter, the configuration of the diesel engine system will be described.
[0020]
The fuel supply system 10 includes a supply pump 11, a pressure accumulating chamber (common rail) 12, a fuel injection valve 13, a shutoff valve 14, a fuel addition nozzle 17, an engine fuel passage P1, an addition fuel passage P2, and the like.
[0021]
The supply pump 11 increases the pressure of the fuel pumped up from the fuel tank (not shown) and supplies it to the common rail 12 through the engine fuel passage P1. The common rail 12 has a function of holding (accumulating) high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and is appropriately opened to supply and inject fuel into the combustion chamber 20.
[0022]
On the other hand, the supply pump 11 supplies a part of the fuel pumped up from the fuel tank to the fuel addition nozzle 17 via the added fuel passage P2. A shutoff valve 14 is disposed from the supply pump 11 toward the fuel addition nozzle 17 in the addition fuel passage P2 . In an emergency, the shutoff valve 14 shuts off the added fuel passage P2 and stops the fuel supply. The fuel addition nozzle 17 is an electromagnetic valve similar to the fuel injection valve 13 and injects and adds fuel as a reducing agent into the exhaust system 40.
[0023]
The intake system 30 forms a passage (intake passage) for intake air supplied into each combustion chamber 20. On the other hand, the exhaust system 40 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.
[0024]
The engine 1 is provided with a known supercharger (turbocharger) 50. The turbocharger 50 includes a turbine wheel 52 and a compressor 53 that are connected via a shaft 51. One compressor 53 is exposed to intake air in the intake system 30, and the other turbine wheel 52 is exposed to exhaust gas in the exhaust system 40. The turbocharger 50 having such a configuration has an effect of increasing the intake pressure (supercharging effect) by rotating the compressor 53 using the exhaust flow (exhaust pressure) received by the turbine wheel 52.
[0025]
In the intake system 30, an intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been raised by supercharging. The throttle valve 32 provided further downstream than the intercooler 31 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and restricts the flow passage area of the intake passage under predetermined conditions. The function of adjusting (reducing) the supply amount of the intake air is provided.
[0026]
Further, an exhaust gas circulation passage (EGR passage) 60 that bypasses the upstream (intake system 30) and the downstream (exhaust system 40) of the combustion chamber 20 is formed in the engine 1. Specifically, the EGR passage 60 communicates the exhaust collecting pipe 40 a upstream of the turbocharger 50 in the exhaust system 40 and the downstream side of the throttle valve 32 in the intake system 30. The EGR passage 60 has a function of returning a part of the exhaust gas to the intake system 30 as appropriate. The EGR passage 60 is opened and closed steplessly by electronic control, and the exhaust gas flowing through the EGR passage 60 can be freely adjusted, and the exhaust gas passing through (circulating) the EGR passage 60 is cooled. EGR cooler 62 is provided.
[0027]
Further, in the exhaust system 40, an exhaust passage 40b along the exhaust gas flow path is provided downstream of the exhaust collecting pipe 40a connected from the combustion chamber and a portion where the turbine wheel 52 is provided, and a NOx catalyst casing 42 is provided downstream thereof. Further, the exhaust passage 40c is sequentially connected further downstream. The NOx catalyst casing 42 houses a NOx storage reduction catalyst 42b that purifies harmful components such as NOx contained in the exhaust gas, as will be described later.
[0028]
Further, various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of the part and the operating state of the engine 1 are output.
[0029]
That is, the rail pressure sensor 70 outputs a detection signal corresponding to the fuel pressure stored in the common rail 12. The fuel pressure sensor 71 outputs a detection signal corresponding to the pressure (fuel pressure) of the fuel introduced into the fuel addition nozzle 17 among the fuel flowing through the added fuel passage P2. The air flow meter 72 outputs a detection signal corresponding to the flow rate (intake amount) of intake air upstream of the throttle valve 32 in the intake system 30. The air-fuel ratio (A / F) sensor 73 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas upstream of the catalyst casing 42 of the exhaust system 40. Similarly, the catalyst outflow exhaust temperature sensor 74 outputs a detection signal corresponding to the temperature of exhaust gas (exhaust temperature) downstream of the catalyst casing 42 of the exhaust system 40. The catalyst inflow exhaust gas temperature sensor 78 outputs a detection signal corresponding to the temperature of the exhaust gas flowing in at the catalyst casing 42 inlet.
[0030]
Further, the accelerator opening sensor 76 is attached to an accelerator pedal (not shown), and outputs a detection signal that is a basis of a work amount required in the engine 1 according to the depression amount of the pedal. The crank angle sensor 77 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. Each of these sensors 70 to 79 is electrically connected to an electronic control unit (ECU) 80.
[0031]
As shown in FIG. 2, the ECU 80 includes a central processing unit (CPU) 81, a read only memory (ROM) 82, a random access memory (RAM) 83, a backup RAM 84 in which stored information is not erased even after the operation is stopped, and a timer counter 85. , An input port 86 including an A / D converter, and an output port 87 are connected to each other by a bidirectional bus 88.
[0032]
The ECU 80 inputs the detection signals of the various sensors through the input port 86, and based on these signals, the CPU 81 included in the ECU 80 performs basic control on the fuel injection of the engine 1 from the program stored in the ROM 82. In addition to the control, various controls related to the operating state of the engine 1 such as determination of the supply amount of the fuel injection related to the addition of the reducing agent (fuel that functions as the reducing agent) and the reducing agent (fuel) addition control related to the addition timing and the like are performed.
[0033]
The fuel supply system 10 that supplies fuel to each cylinder through the fuel injection valve 13, the NOx catalyst provided in the exhaust system 40, the ECU 80 that controls the functions of the fuel supply system 10 and the NOx catalyst, etc. The exhaust emission control device of the engine 1 according to the embodiment is configured. The fuel addition control and the like are performed through the operation of various members constituting the exhaust gas purification apparatus, including the ECU 80 that outputs a command signal related to the control.
[0034]
Next, among the components of the engine 1 described above, the configuration and functions of the catalyst casing 42 provided in the exhaust system 40 will be described in detail.
[0035]
FIG. 3 is an enlarged sectional view of the catalyst casing 42 shown in FIG. 1 together with a part of its internal structure. The catalyst casing 42 accommodates the NOx storage reduction catalyst 42b therein.
[0036]
The NOx catalyst 42b is, for example, a carrier mainly composed of alumina (Al ₂ O ₃ ) , and functions as a NOx occlusion agent on the surface of the carrier, for example, potassium (K), sodium (Na), lithium (Li), cesium. An alkali metal such as (Cs), an alkaline earth metal such as barium (Ba), calcium (Ca), or a rare earth such as yttrium (Y) and an oxidation catalyst (noble metal catalyst), for example, platinum It is configured by supporting a noble metal such as (Pt).
[0037]
The NOx storage agent has a characteristic of retaining NOx when the oxygen concentration in the exhaust gas is high and releasing NOx when the oxygen concentration in the exhaust gas is low. In addition, when NOx is released into the exhaust gas, if HC, CO, or the like is present in the exhaust gas, the noble metal catalyst promotes an oxidation reaction of these HC and CO, thereby converting NOx into an oxidizing component, HC, A redox reaction using CO as a reducing component occurs between the two. That is, HC and CO are oxidized to CO ₂ and H ₂ O, and NOx is reduced to N ₂ .
[0038]
Further, the noble metal catalyst constituting the NOx catalyst 42b promotes the oxidation of HC and raises the bed temperature by the heat of oxidation reaction of HC.
[0039]
Further, even when the NOx storage agent has a high oxygen concentration in the exhaust gas, if it retains a predetermined limit amount of NOx, it will no longer retain NOx. In the engine 1, before the NOx retention amount of the NOx catalyst 42b accommodated in the catalyst casing 42 reaches a limit, the NOx catalyst 42b is activated by adding and supplying a reducing agent upstream of the catalyst casing 42 in the exhaust passage. The control of reducing and purifying the held NOx and restoring the NOx holding ability of the NOx catalyst 42b is repeated at a predetermined interval.
[0040]
The NOx purification will be specifically described below.
[0041]
In general, in a diesel engine, the oxygen concentration of a mixture of fuel and air used for combustion in a combustion chamber is in a high concentration state in most operating regions. The oxygen concentration of the mixture used for combustion is usually reflected in the oxygen concentration in the exhaust gas as it is after subtracting the oxygen used for combustion, and the oxygen concentration (air-fuel ratio) in the mixture is high. For example, the oxygen concentration (air-fuel ratio) in the exhaust gas basically increases similarly.
[0042]
On the other hand, as described above, the NOx catalyst 42b has a characteristic of holding NOx if the oxygen concentration in the exhaust gas is high, and reducing NOx to NO ₂ or NO if the oxygen concentration is low, so that the oxygen in the exhaust gas has a high concentration. Keep NOx as long as possible. However, there is a limit in the NOx retention amount of the NOx catalyst 42b, and in the state where the NOx catalyst 42b retains the limit amount of NOx, NOx in the exhaust gas is not retained by the NOx catalyst 42b and the catalyst casing 42 is Go through.
[0043]
In order to restore the NOx retention action of the NOx catalyst 42b, it is necessary to add a reducing agent to the NOx storage agent in the NOx catalyst 42b. However, due to the configuration of the engine, the oxygen concentration is low when normal fuel injection is performed. That is, the exhaust gas containing a large amount of fuel as a reducing agent is difficult to be discharged.
[0044]
Therefore, in addition to the main fuel injection for power conversion performed in the combustion chamber of the internal combustion engine, a method of performing secondary fuel injection that mainly injects fuel as unburned fuel, or provided in the exhaust passage, The fuel is added to the exhaust gas by, for example, a method of injecting the fuel into the exhaust gas to increase the amount of the reducing agent component in the exhaust gas, and the NOx holding action is restored and regenerated by this reducing component (NOx catalyst regeneration control).
[0045]
When this NOx catalyst regeneration control is performed, the amount of fuel added as the reducing agent, the timing of addition, and the like differ depending on the bed temperature (exhaust temperature) of the NOx catalyst 42b to be regenerated, the NOx occlusion amount, and the like. In addition, when determining the addition amount and the addition timing, values are set based on the purification ability of the NOx catalyst 42b when the vehicle is mounted. However, if the NOx catalyst 42b is used for a long period of time, the exhaust purification ability of the NOx catalyst 42b changes due to its aging and the like. Therefore, it is necessary to determine the degree of deterioration of the NOx catalyst 42b and change each control value of the NOx catalyst regeneration control in accordance with the degree of deterioration.
[0046]
Hereinafter, the catalyst deterioration determination for the NOx catalyst 42b will be described. As shown in FIG. 4, the problem that occurs when the exhaust gas purification performance of the catalyst declines is due to a reduction in oxidation-reduction capability, resulting in an oxidation-reduction reaction between the reducing agent added to the exhaust gas and NOx discharged from the NOx catalyst 42 b. Examples include an increase in starting temperature (light-off temperature), a decrease in the amount of NOx stored in the NOx catalyst 42b, and a decrease in NOx storage reaction performance such as the amount of NOx released. Thus, if NOx purification control is performed with a catalyst that has deteriorated with the light-off temperature or the like of the catalyst in a new state (new catalyst) as a predetermined temperature, sufficient NOx purification cannot be performed due to the difference in the light-off temperature. In other words, if fuel is added to a catalyst that has deteriorated near the light-off temperature of the new catalyst, the oxidation-reduction reaction does not proceed, so the fuel adheres to the catalyst or is directly released into the atmosphere as unburned gas. .
[0047]
Further, even when the oxidation-reduction reaction is performed, in the deteriorated catalyst, the maximum temperature reached by the oxidation-reduction reaction is lowered and the reaction rate is also lowered. When the catalyst regeneration control based on the new catalyst is performed based on the above matters, the catalyst based on the new catalyst is used even if the catalyst bed temperature of the deteriorated catalyst reaches the highest temperature generated in the oxidation-reduction reaction. In the regeneration control, it is determined that the temperature rise does not proceed because the fuel that reacts with the catalyst is insufficient. This determination may add a larger amount of fuel to the catalyst than is necessary to purify NOx. Therefore, in this case, after regeneration of the catalyst, the fuel remains attached to the catalyst as it is, or the attached fuel is released into the atmosphere as unburned gas.
[0048]
As a means for measuring the light-off temperature, a catalyst inflow exhaust gas temperature sensor 78 and a catalyst outflow exhaust gas temperature sensor 74 are used. If the reducing agent is not included in the exhaust gas or the NOx catalyst 42b is below the activation temperature even if the reducing agent is included, the NOx catalyst 42b does not perform the redox reaction with fuel and NOx. . Therefore, in this state, the inflow side exhaust temperature: Tin and the exhaust side exhaust temperature: Tex of the NOx catalyst 42b show substantially the same temperature.
[0049]
However, when NOx is purified by the fuel added to the exhaust gas by the NOx catalyst 42b, Tex increases due to the oxidation-reduction reaction accompanying this purification, and Tin <Tex, where a temperature difference between Tin and Tex: Δt is generated. Therefore, the temperature of Tin at the time when this Δt occurs becomes the light-off temperature.
[0050]
Next, after reaching the light-off temperature, attention is paid to the temperature difference Δt between Tin and Tex. With deteriorated catalysts, the NOx storage and release capacity required for oxidation-reduction reactions is reduced, especially when the catalyst atmosphere becomes rich due to a decrease in the release capacity per unit time of NOx released into the exhaust compared to the new catalyst. The amount of release is reduced. Since there is sufficient fuel in the exhaust gas to cause a redox reaction with the released NOx and raise the catalyst bed temperature, the reaction amount per unit time of the redox reaction is determined by the NOx emission amount.
[0051]
Therefore, due to the difference in the amount of oxidation-reduction reaction per unit time, a difference occurs in the catalyst bed temperature increase value during oxidation-reduction. That is, as shown in FIG. 5, Δt (Tex−Tin) between Tin and Tex is not so large in a deteriorated catalyst with a small amount of redox reaction, but Δt is large in a new catalyst with a large amount of redox reaction. Become.
[0052]
Further, since the redox ability of the deteriorated catalyst is also reduced, the deteriorated catalyst is deteriorated due to the synergistic effect of the reduction in the amount of NOx released for the redox reaction and the reduction in the redox ability. As a result, the maximum value of the catalyst bed temperature due to the oxidation-reduction reaction is lower than that of the catalyst without.
[0053]
Based on the above matters, the deterioration of the catalyst is judged based on the difference in temperature difference between the deteriorated catalyst and the undegraded catalyst at the light-off temperature. As a determination method, a light-off determination temperature, which is a determination criterion for deterioration, is set in advance, and fuel is added when the catalyst to be determined reaches the light-off determination temperature. The deterioration of the catalyst is judged depending on the degree.
[0054]
More specifically, a light-off determination temperature that serves as a criterion for determining deterioration is determined in advance, and a temperature rise value at the time of fuel addition in a catalyst at which the light-off determination temperature becomes the light-off temperature is measured. This is determined as a predetermined temperature rise value and stored in the ROM 82 in the ECU 80. On the other hand, exhaust gas is caused to flow into the NOx catalyst 42b for which the deterioration is determined, and Tin and Tex are measured by the catalyst inflow exhaust temperature sensor 78 and the catalyst outflow exhaust temperature sensor 74 before and after the NOx catalyst 42b. When the CPU 81 recognizes that Tin and Tex have reached the light-off determination temperature, a signal is sent to the fuel addition nozzle 17 to add a predetermined amount of fuel during exhaust.
[0055]
In performing this fuel addition, it is confirmed in advance that a predetermined amount of NOx is occluded in the NOx catalyst 42b. The predetermined amount is the NOx occlusion amount required for the oxidation-reduction reaction until the temperature of the NOx catalyst 42b is increased by the oxidation-reduction reaction due to the addition of fuel and the catalyst bed temperature reaches the maximum value due to the temperature increase. Therefore, the predetermined fuel addition amount is also an amount necessary for the oxidation / reduction reaction with the NOx storage amount.
[0056]
As a means for confirming the NOx occlusion amount, a map for calculating the NOx amount discharged from the engine 1 from information such as the fuel injection amount in the engine 1, the accelerator opening sensor 76, the air-fuel ratio sensor 73, etc. is stored in the ROM 82 in advance. Keep it. The amount of NOx that has flowed into the NOx catalyst 42b is calculated from this map and the time during which fuel is added this time from the time when fuel was added last time. When this value reaches a predetermined NOx storage amount, it is estimated that the predetermined NOx amount is stored in the NOx catalyst 42b.
[0057]
If there is no temperature difference Δt between Tin and Tex, which are temperatures detected by the catalyst inflow exhaust temperature sensor 78 and the catalyst outflow exhaust temperature sensor 74 after the fuel addition, the NOx catalyst 42b has deteriorated. Is determined by the CPU 81. Further, if the Δt is equal to or greater than a predetermined value, it is determined that the NOx catalyst 42b has not deteriorated.
[0058]
By the above method, the reducing agent is added at the light-off determination temperature to determine the deterioration of the catalyst. When fuel is added at the light-off determination temperature in the above determination method, a temperature rise reaction is observed, but if Δt is lower than a predetermined value, the NOx occlusion amount or the reducing agent addition amount is insufficient. Since there is a suspicion that the temperature raising reaction has not been performed, in this case, the determination is made without performing the determination, or the determination method is performed again by performing the determination method.
[0059]
Hereinafter, with respect to the “degraded catalyst determination control” performed by the ECU 80 of the engine 1 according to the present embodiment, a specific processing procedure will be described with reference to the flowchart shown in FIG.
[0060]
First, the catalyst bed temperature is set to the light-off determination temperature in S601 to S603. If the catalyst bed temperature at S601 is higher than the light-off determination temperature, repeat this step until the lower, the process proceeds to the next step when it becomes less than the light-off determination temperature. In S602, it is determined whether or not the catalyst bed temperature is equal to or lower than the light-off determination temperature. If a negative determination is made in S601, since the catalyst bed temperature is equal to or lower than the light-off determination temperature, an affirmative determination is made in S602, and the process proceeds to S603.
[0061]
In S603, it is determined the catalyst bed temperature = whether the light-off decision making temperature is, when a catalyst bed temperature = light-off determination temperature, the fuel is added in a predetermined amount proceeds to S604. If the catalyst bed temperature = light-off determination temperature is not confirmed in S603 , the process returns to S602, and the determinations of S602 and S603 are repeated until the catalyst bed temperature = light-off determination temperature. If the catalyst bed temperature is raised to a temperature higher than the light-off determination temperature while repeating the determinations of S602 and S603, a negative determination is made in S602 and the process returns to S601. After the catalyst bed temperature coincides with the light-off determination temperature by the processing of S601 to S603, the process proceeds to S604 and a predetermined amount of fuel is added.
[0062]
After fuel addition in S604, the temperature difference between the inflow exhaust temperature detected by the catalyst inflow exhaust temperature sensor 78 and the outflow exhaust temperature detected by the catalyst outflow exhaust temperature sensor 74 in S605 (outflow exhaust gas temperature-inflow exhaust gas temperature). Is determined whether the temperature is lower than the predetermined temperature . If the determination result is equal to or greater than the predetermined value, the process proceeds to S609, where it is determined that the catalyst has not deteriorated, and this chart ends. If the determination result is below a predetermined value, the process proceeds to the next step.
[0063]
In S606, the temperature difference is determined. If the temperature difference is 0 ° C. or less, the process proceeds to S608, where it is determined that the catalyst has deteriorated, and then this chart is terminated. If the temperature difference is higher than 0 ° C., the process proceeds to S607 and ends without making a clear determination due to insufficient redox reaction, or returns to S601 and the same determination is performed again.
[0064]
In this embodiment, when performing the determination, fuel is added at the light-off determination temperature, and the presence / absence of the temperature rising reaction and the temperature rising reaction amount at this time are determined at the same time. May be. That is, the temperature at which the catalyst starts the temperature rising reaction is detected first, Δt at the detected temperature is obtained, and the deterioration determination may be performed by comparing this value with the light-off determination temperature. At this time, as a method for detecting the temperature at which the catalyst starts a temperature rising reaction, the catalyst for detecting the light-off temperature is added at a low temperature, for example, at the time of the light-off temperature of the new catalyst, and is added to the catalyst bed. Adhere fuel . After that, there is a method of increasing the catalyst bed temperature and detecting the light-off temperature, which is the temperature at which the difference between Tin and Tex is caused by the attached fuel. Then, after detecting the light-off temperature, Δtmax is similarly detected. With this determination method, in addition to the presence or absence of deterioration, it is possible to determine the degree of deterioration of the catalyst for which deterioration is determined based on the degree of increase in light-off temperature.
[0065]
Further, in the present embodiment, the fuel addition nozzle 17 that is a fuel injection device is provided in the exhaust passage as the reducing agent addition means, and thereby the fuel is added to the exhaust gas. However, the addition means is not limited to this. . For example, when adding fuel into the combustion chamber, fuel may be added outside the combustion process, exhausted unburned, and the unburned fuel used as a reducing agent. In short, if the reducing agent can be added to the exhaust gas purification device, there is no particular limitation on the means.
[0066]
【The invention's effect】
By using the catalyst deterioration determination device and method according to the present invention, it is possible to determine the deterioration of the NOx purification ability of the catalyst without using the NOx sensor.
[0067]
Further, in the present invention, the configuration and method have been described focusing on the NOx storage reduction catalyst. However, the present invention is not limited to the NOx storage reduction catalyst, but a catalyst that raises the temperature when purifying NOx, for example, an exhaust of a gasoline engine. Even with a three-way catalyst or the like used for purification or the like, the NOx purification ability can be measured without using the NOx sensor with the same configuration.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a diesel engine system according to an embodiment of the present invention.
FIG. 2 is a conceptual diagram of a configuration around an ECU according to the embodiment.
FIG. 3 is a conceptual cross-sectional view of a catalyst casing according to the same embodiment.
FIG. 4 is a graph showing the relationship between the light-off temperature and the catalyst bed temperature according to the embodiment.
FIG. 5 is a graph showing a relationship between Δt and catalyst deterioration according to the embodiment;
FIG. 6 is a flowchart showing catalyst deterioration determination control according to the embodiment;
[Explanation of symbols]
1 engine (internal combustion engine)
10 Fuel supply system 11 Supply pump 12 Common rail (accumulation chamber)
DESCRIPTION OF SYMBOLS 13 Fuel injection valve 14 Control valve 17 Fuel addition nozzle 20 Combustion chamber 30 Intake system 31 Intercooler 32 Throttle valve 40 Exhaust system 40a Exhaust collecting pipe 40b, c Exhaust passage 42 Catalyst casing 42b Occlusion reduction type NOx catalyst (NOx catalyst)
43 Injection fuel pool 50 Turbocharger 51 Shaft 52 Turbine wheel 53 Compressor 60 EGR passage 61 EGR valve 62 EGR cooler 70 Rail pressure sensor 71 Combustion sensor 72 Air flow meter 73 Air-fuel ratio (A / F) sensor 74 Catalyst exhaust temperature sensor 76 Accelerator Opening sensor 77 Crank angle sensor 78 Catalyst inflow exhaust gas temperature sensor 80 Electronic control unit (ECU)
81 Central processing unit (CPU)
82 Read-only memory (ROM)
83 Random access memory (RAM)
84 Backup RAM
85 Timer counter 86 Input port 87 Output port 88 Bidirectional bus P1 Engine fuel passage P2 Addition fuel passage

Claims (4)

A catalyst provided in an exhaust passage of an internal combustion engine for purifying exhaust gas discharged, catalyst inflow exhaust gas temperature measuring means for measuring the exhaust gas temperature flowing into the catalyst, and catalyst bed temperature measuring means for measuring the catalyst bed temperature A reducing agent adding means for adding a reducing agent to the catalyst when the catalyst bed temperature reaches a predetermined judgment temperature that is equal to or higher than a light-off temperature of an undegraded catalyst, and the reducing agent is added to the catalyst by the reducing agent adding means. Difference temperature detection means for detecting the difference in catalyst bed temperature relative to the catalyst inflow exhaust temperature when added to the catalyst, and when the temperature difference detected by the difference temperature detection means is smaller than a predetermined temperature difference, the catalyst deteriorates. Deterioration determining means for determining that the
The deterioration determination unit does not determine whether the catalyst has deteriorated when the temperature difference detected by the difference temperature detection unit is smaller than the predetermined temperature difference and larger than zero, and the difference is not determined. A deterioration determination device for an exhaust gas purification device, wherein when the temperature difference detected by the temperature detection means is less than or equal to zero, it is determined that the catalyst has deteriorated.   2. The deterioration determination device for an exhaust gas purification apparatus according to claim 1, wherein the determination temperature is equal to or higher than a light-off temperature of the catalyst that has not deteriorated and is in the vicinity of the light-off temperature.   2. The deterioration of the exhaust emission control device according to claim 1, wherein the determination temperature is equal to or higher than a light-off temperature of the non-deteriorated catalyst and lower than a light-off temperature of the deteriorating catalyst. Judgment device. The exhaust purifier stores nitrogen oxides present in the exhaust when the inflowing exhaust is in an oxygen concentration excess state, and the nitrogen oxidation stored in the precursor when the inflowing exhaust is in a lean oxygen concentration state. And a storage amount estimating means for estimating the storage amount of the nitrogen oxides, and the storage amount estimation means estimates that the storage amount of nitrogen oxides is less than or equal to a predetermined amount. The deterioration determination device for an exhaust gas purification device according to any one of claims 1 to 3 , wherein the reducing agent is not added by the reducing agent addition means.

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