JP2012087749A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine which is hardly affected by an amount of NOx in an LNT (Lean NOx Trap) and deviation of an A/F sensor and the like and highly accurately detects sulfur poisoning (S poisoning) of the LNT.SOLUTION: The LNT 6 is divided into an LNT 60 and an LNT 61, and A/F sensors 41, 42 and 43 are disposed respectively before, between and after the LNTs 60 and 61. During NOx reduction control of the LNT 6, a ratio of an NOx occlusion amount of the LNT 61 (rear part) to that of the whole LNT 6 is calculated by integration of difference of measurement values of the A/F sensors 41, 42 and 43 and when the ratio is large, it is determined that SOx is accumulated on a front part of the LNT 6 and that the LNT 6 is S-poisoned.

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  In the recent trend of emphasizing environmental protection, technology for purifying exhaust from internal combustion engines mounted on automobiles and the like is essential. For example, in a diesel engine, it is necessary to remove exhausted nitrogen oxides (NOx) from the exhaust. For this purpose, a NOx storage reduction catalyst (LNT: Lean NOx Trap) may be provided in the middle of the exhaust pipe.

  NOx is occluded in the LNT during the basic lean state in a diesel engine, and the NOx occluded in the LNT reacts with the fuel components and is harmless when the rich state is changed over time. It is discharged as fresh nitrogen. For example, barium is supported on the LNT as a storage agent for storing NOx.

  However, in LNT, the storage agent that originally stores NOx is combined with the sulfur component in the fuel, and a phenomenon called sulfur poisoning (S poisoning, S deterioration) that reduces the NOx storage performance of LNT occurs. To do. In order to regenerate LNT from this S degradation, S regeneration to a rich atmosphere and high temperature (for example, 600 degrees Celsius or higher) must be performed every time S degradation progresses.

  In the S regeneration, since the concentration of sulfur contained in the exhaust gas is not constant, it is necessary to detect the amount of sulfur stored in the LNT in order to maintain the NOX purification performance of the LNT with high accuracy. In response to this problem, for example, in Patent Document 1 below, when the air-fuel ratio detected by the A / F sensor on the downstream side of the LNT is switched from lean to rich, it is determined that the NOx releasing action of the LNT is completed, and NOx release is performed. A technique for detecting a decrease in the NOx occlusion amount based on the required reaction time or the difference area between the front and rear A / F sensors is disclosed.

JP 2000-34946 A

  However, the method of Patent Document 1 has the following two problems. First, it is necessary to detect the amount of NOx entering the LNT with high accuracy. If an error occurs in the amount of NOx entering the LNT, the accuracy of deterioration determination is significantly reduced. And it is known that the A / F sensor used for detection is easily affected by exhaust gas components and has a large deviation under a rich atmosphere. In this case, the deterioration detection accuracy is significantly reduced. It is desired to develop an exhaust purification device that solves the above problems.

  Therefore, in view of the above problems, the problem to be solved by the present invention is an exhaust gas purification of an internal combustion engine that is not easily affected by the amount of NOx contained in LNT, the deviation of the A / F sensor, etc., and detects the S deterioration of LNT with high accuracy. To provide an apparatus.

Means for Solving the Problems and Effects of the Invention

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a catalyst unit that is provided in an exhaust passage of the internal combustion engine and stores nitrogen oxides, and an amount of nitrogen oxides stored in the catalyst unit. Sulfur degradation in the catalyst section using a distribution detection means for detecting a spatial distribution in the flow direction of the exhaust gas and a spatial distribution of the storage amount of nitrogen oxides in the catalyst section detected by the distribution detection means And determining means for determining.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the spatial distribution of the storage of nitrogen oxides in the catalyst part is detected, and the sulfur deterioration of the catalyst part is determined using the information. By detecting the spatial distribution of the storage of nitrogen oxides, which has not been performed in the above, the state of storage of nitrogen oxides in the catalyst part is detected more precisely than before. Therefore, it is possible to determine the sulfur deterioration of the catalyst portion with high accuracy by using the information of the spatial distribution of the occlusion that is precisely detected.

  Further, in the spatial distribution of the storage amount of nitrogen oxides in the catalyst unit detected by the distribution detection unit, the determination unit is configured such that the ratio of the total storage amount of the downstream storage amount in the exhaust flow direction is less than the threshold value. When it is high, it may be determined that the catalyst portion is sulfur-degraded.

  Thereby, in the catalyst part, when the ratio of the storage amount of nitrogen oxide on the downstream side in the exhaust flow direction to the total storage amount is higher than the threshold value, it is determined that the catalyst part has deteriorated sulfur. When sulfur deteriorates, sulfur oxide gradually accumulates from the upstream side in the flow direction, and appropriately using the fact that the storage location of nitrogen oxides moves to the downstream side due to the effect, Sulfur degradation can be accurately determined from the spatial distribution of nitrogen oxide storage.

  The catalyst unit further includes a reducing unit that supplies a reducing agent to reduce the stored nitrogen oxides. The distribution detecting unit includes a first position upstream of the catalyst unit in the exhaust flow direction, and a downstream first position. An air-fuel ratio detecting means for detecting at least three air-fuel ratios at a third position, a second position between the first position and the third position, and the air-fuel ratio detecting means during execution of the reduction by the reducing means First calculation means for calculating a spatial distribution of the amount of occluded nitrogen oxide in the catalyst unit based on at least three air-fuel ratios at the first position, the second position, and the third position detected by And may be provided.

  Thus, during the nitrogen oxide reduction control, the air-fuel ratio is detected at at least three positions upstream, intermediate, and downstream of the catalyst unit, and the spatial distribution of the storage amount of nitrogen oxides is calculated from the numerical values. Therefore, during the reduction control of nitrogen oxides, fuel is consumed in the catalyst unit for the reduction of nitrogen oxides, so that the amount of nitrogen oxides stored in the catalyst unit can be detected by detecting the air-fuel ratio. By effectively using this and arranging a plurality of air-fuel ratio detection means, it is possible to accurately calculate the spatial distribution of the storage amount of nitrogen oxides inside the catalyst portion.

  In addition, the first calculation means calculates the difference between the two positions by integrating the difference values of the air-fuel ratios at any two of the at least three air-fuel ratio calculation positions detected by the air-fuel ratio detection means. There may be provided a second calculation means for calculating the consumption of the reducing agent having a correlation with the amount of occlusion of nitrogen oxides.

  As a result, the consumption of reducing agent (fuel) between the positions is calculated by integrating the difference values of the air-fuel ratios at any two positions among at least three positions upstream, intermediate, and downstream of the catalyst section. Therefore, it is possible to effectively use the fact that the amount of nitrogen oxides occluded between the two positions can be calculated by integrating the difference values of the air-fuel ratios at the two positions during the reduction control. By arranging, the spatial distribution of the storage amount of nitrogen oxides inside the catalyst part can be calculated with high accuracy.

  Further, the first calculating means may be configured such that, in any two positions among at least three or more air-fuel ratio detection positions detected by the air-fuel ratio detection means, the upstream position of the two positions has a rich atmosphere. The consumption time of the reducing agent having a correlation with the amount of occlusion of nitrogen oxides between the two positions due to the difference between the time when the two positions become the downstream atmosphere of the two positions and the rich atmosphere. There may be provided third calculation means for calculating.

  Thereby, in two positions during the reduction control of nitrogen oxides, the difference between the time when the upstream position becomes rich atmosphere and the time when the downstream position becomes rich atmosphere is the reducing agent between the two positions. By effectively utilizing the property that the consumption time has a correlation with the storage amount of nitrogen oxide between both positions, the storage amount of nitrogen oxide can be calculated with high accuracy.

  The distribution detecting means includes at least three or more at a first position upstream of the catalyst portion in the exhaust flow direction, a third position downstream, and a second position between the first position and the third position. Nitrogen oxide detection means for detecting a nitrogen oxide concentration, and at least three or more nitrogen oxide concentrations at the first position, the second position, and the third position detected by the nitrogen oxide detection means, And fourth calculating means for calculating a spatial distribution of the amount of occluded nitrogen oxides in the catalyst unit.

  Thereby, the nitrogen oxide concentration is detected at at least three positions upstream, intermediate, and downstream of the catalyst portion, and the spatial distribution of the storage amount of nitrogen oxide is calculated from the numerical values. Therefore, by arranging a plurality of nitrogen oxide detecting means, the spatial distribution of the storage amount of nitrogen oxide inside the catalyst portion can be calculated with high accuracy.

  In addition, the fourth calculation means calculates the difference between the two positions by integrating the difference value of the nitrogen oxide concentration at any two positions among at least three detection positions detected by the nitrogen oxide detection means. There may be provided fifth calculation means for calculating the amount of occlusion of nitrogen oxides.

  As a result, the amount of occluded nitrogen oxide between the positions is calculated by integrating the difference value of the nitrogen oxide concentration at any two positions among at least three positions upstream, intermediate and downstream of the catalyst section. Therefore, a plurality of nitrogen oxide detecting means are arranged by effectively utilizing the fact that the amount of nitrogen oxide stored between the positions can be calculated by integrating the difference value of the nitrogen oxide concentration at the two positions. Thus, the spatial distribution of the storage amount of nitrogen oxides inside the catalyst part can be calculated with high accuracy.

  In addition, the second calculation means, consumption of the reducing agent between the first position and the third position, consumption of the reducing agent between the second position and the third position, The determination means calculates the second position and the third position with respect to the amount of consumption of the reducing agent between the first position and the third position calculated by the second calculation means. When the ratio of consumption of the reducing agent during the period is larger than a threshold value, it may be determined that the catalyst unit is sulfur-degraded.

  As a result, when the ratio of the reducing agent consumption at the rear of the catalyst part to the reducing agent consumption of the entire catalyst part during the reduction control exceeds the threshold value, it is determined that the sulfur deterioration has occurred. Therefore, it is possible to accurately determine the sulfur deterioration by effectively utilizing the property that the nitrogen oxides are occluded and the consumption of the reducing agent (fuel) in the rear part during the reduction control is increased.

  Further, the fifth calculation means includes a storage amount of nitrogen oxides between the first position and the third position, a storage amount of nitrogen oxides between the second position and the third position, The determination means calculates the second position and the third position with respect to the storage amount of nitrogen oxides between the first position and the third position calculated by the fifth calculation means. When the ratio of the amount of occluded nitrogen oxide is larger than the threshold value, it may be determined that the catalyst unit has deteriorated sulfur.

  Thus, when the ratio of the nitrogen oxide storage amount at the rear of the catalyst portion to the nitrogen oxide storage amount of the entire catalyst portion exceeds the threshold value, it is determined that the sulfur is deteriorated. Therefore, when the sulfur deterioration of the catalyst portion proceeds, the sulfur deterioration can be accurately determined by effectively utilizing the property that the nitrogen oxide is stored in the rear portion.

  In addition, the regeneration unit for removing sulfur accumulated in the catalyst unit and the distribution of the nitrogen oxide storage amount in the catalyst unit before and after the execution of the sulfur removal process by the regeneration unit are compared to determine whether the catalyst unit has failed. Failure determination means for determining.

  Thus, in addition to determining the sulfur deterioration using the spatial distribution of the nitrogen oxide storage amount in the catalyst portion as described above, the spatial storage of the nitrogen oxide storage amount before and after the sulfur removal treatment is further performed. And a failure of the catalyst part is determined with high accuracy from the comparison. Therefore, it is possible to realize an exhaust emission control device that can determine a failure of the catalyst portion with high accuracy using a spatial distribution.

1 is a schematic diagram of an exhaust emission control device for an internal combustion engine in an embodiment of the present invention. 5 is a flowchart of S poison determination processing in Embodiment 1. The figure which shows the example of the spatial distribution of the flow direction of NOx and SOx which accumulated in LNT. The figure which shows the example of the relationship between the amount of NOx which flows into LNT, and the ratio of rear part NOx accumulation amount. The figure which shows the example of the time transition of the air fuel ratio of the upstream of LNT in the NOx reduction | restoration control, an intermediate | middle, and downstream. 10 is a flowchart of S poison determination processing in the second embodiment. The figure which shows the example of the time transition of the NOx density | concentration value of the upstream of LNT in the lean period, an intermediate | middle, and downstream.

  Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic diagram of Embodiment 1 of an exhaust purification device 1 according to the present invention. It is assumed that the exhaust emission control device 1 is configured for a diesel engine 2 (hereinafter simply referred to as an engine).

  The engine 2 and the exhaust purification system 1 include an intake pipe 3, an exhaust pipe 4, and an EGR pipe 5. The exhaust pipe 4 is equipped with LNT6 (Lean NOx Trap, catalyst part) for NOx purification. An electronic control unit 9 (ECU: Electronic Control Unit) for controlling these is provided. The engine 2 and the exhaust purification system 1 may be installed in an automobile.

  Air is supplied to the engine 2 through the intake pipe 3. An air flow meter 31 is disposed in the intake pipe 3. The intake air amount is measured by the air flow meter 31. The intake air amount here may be a mass flow rate per unit time, for example. The engine 2 is equipped with an injector 21. Fuel is supplied into the cylinder by injection from the injector 21. The EGR pipe 5 recirculates exhaust gas from the exhaust pipe 4 to the intake pipe 3 to suppress combustion in the engine cylinder and suppress NOx emission from the engine 2.

  Exhaust gas from the engine 2 is discharged to the exhaust pipe 4. The LNT 6 equipped in the exhaust pipe 4 is divided into two parts, an upstream LNT 60 and a downstream LNT 61. An A / F sensor 41 is provided upstream of the LNT 60, an A / F sensor 42 is provided between the LNT 60 and the LNT 61, and an A / F sensor 43 is provided downstream of the LNT 61. (Air-fuel ratio) is detected. An addition valve 40 for adding fuel to the exhaust pipe 4 is provided upstream of the LNT 6 in the exhaust pipe 4. An exhaust temperature sensor 47 is also provided upstream of the LNT 6 in the exhaust pipe 4 to detect the temperature of the exhaust gas flowing into the LNT 6. The addition valve 40 may not be arranged.

  LNT6 (60, 61) may have a structure in which a carrier layer is formed on a ceramic substrate, for example, and a storage agent and a catalyst are supported on the carrier. As the carrier, for example, gamma alumina is suitable because it can carry a large amount of storage agent and catalyst due to its large surface area due to surface irregularities. Further, for example, barium, lithium, potassium or the like may be used as the occlusion agent, and platinum or the like may be used as the catalyst.

  In LNT6 (60, 61), the fuel is leaner than the stoichiometric air-fuel ratio (usually the A / F value (air-fuel ratio value) is 17 or more), and NOx in the exhaust is occluded in the occlusion agent in a lean atmosphere. When the air-fuel ratio is adjusted to a rich atmosphere where the fuel is more than the stoichiometric air-fuel ratio (usually, the A / F value is 14.5 or less), and the predetermined temperature condition is satisfied, the NOx stored in the storage agent is reduced. It is reduced by the reducing agent generated from the components in the fuel and discharged as harmless nitrogen. In order to form a rich atmosphere and satisfy the temperature rising condition, for example, the fuel is injected from the injector 21 into the cylinder after the main injection (post injection), or the fuel is added from the addition valve 45, and the LNT6 (60 61), the temperature is raised by the action of an (oxidation) catalyst supported by the catalyst. When post injection is used, the addition valve 40 may not be provided.

  In the use of LNT6, it is necessary to take measures against poisoning problems caused by sulfur components (sulfur poisoning, S poisoning, sulfur degradation, S degradation). Sulfur poisoning is a phenomenon in which a catalyst (or occluding agent) binds to sulfur in the fuel, and as a result, the catalyst can no longer function for exhaust purification under certain conditions. It is possible to return to the state before S poisoning.

  In order to regenerate the catalyst from sulfur poisoning (S poisoning, S degradation) (S poisoning regeneration or S regeneration), it is necessary to have a rich atmosphere and satisfy a predetermined temperature condition (for example, 600 degrees or more). For this purpose, for example, measures such as post-injection in the cylinder of the engine 2 or addition of fuel from the addition valve 45 to the exhaust pipe 4 are taken. Each time it is considered that S poisoning has progressed in LNT6 (60, 61), such S regeneration is usually performed to keep the function of the catalyst.

  A dotted line shown in FIG. 1 indicates transmission of information. The measured values of the air flow meter 31, the A / F sensors 41, 42, 43 and the exhaust temperature sensor 47 described above are sent to the ECU 9. Further, the ECU 9 adjusts and controls the timing and amount of fuel injection to the engine 2 by the injector 21 and the timing and amount of fuel injection to the exhaust pipe 4 by the addition valve 40. The ECU 9 may have a structure similar to that of a normal computer, and may include a CPU that performs various calculations and a memory 90 that stores various types of information.

  In the present embodiment based on the above configuration, it is determined whether or not the LNT 6 is S-deteriorated. The processing procedure is shown in FIG. The procedure of FIG. 2 (and FIG. 6 described later) may be programmed and stored in the memory 90, for example, and the ECU 9 may automatically execute it.

  In the process of FIG. 2, first, in S10, the ECU 9 determines whether or not a condition for executing the NOx reduction control is satisfied. The condition for executing the NOx reduction control may be, for example, that NOx is sufficiently occluded in the LNT6. At this time, the NOx occlusion amount estimation method in the LNT 6 stores, for example, a map indicating the relationship between the engine operating conditions (engine load, engine speed) and the NOx emission amount from the engine in advance in the memory 90. The amount of NOx emitted from the engine every moment from the engine is calculated using the above, multiplied by the ratio occluded by the LNT 6, and then accumulated. The ratio stored in the LNT 6 is calculated, for example, by storing in the memory 90 in advance a two-dimensional map showing the relationship between the stored ratio, the temperature of the LNT 6 and the instantaneous NOx storage amount.

  If it is determined that the conditions for executing the NOx reduction control are satisfied, that is, if the NOx reduction control should be executed (S10: Yes), the process proceeds to S20, and the conditions for executing the NOx reduction control If it is determined that NOx is not satisfied and NOx reduction control should not be executed (S10: No), the process of FIG. 2 ends.

  Next, in S20, the ECU 9 executes NOx reduction control. Specifically, as described above, the NOx reduction control may be performed by post injection after main injection in the engine cylinder, fuel addition from the addition valve 40, or the like.

  Next, in S30, the ECU 9 determines whether or not the temperature of the LNT 6 is within an appropriate range (for example, 250 to 400 degrees Celsius) for obtaining the NOx storage amount distribution. When the temperature of the LNT 6 is too low, sufficient NOx reduction does not occur, and the NOx occlusion amount (distribution) cannot be accurately calculated from the reducing agent consumption. Further, when the temperature of the LNT 6 is too high, the NOx occluded from the LNT 6 is released, so that the distribution of the NOx occlusion amount is broken and the distribution of the NOx occlusion amount cannot be calculated correctly.

  Therefore, the NOx occlusion amount distribution of LNT6 is calculated by the process of S30 only when the temperature is within an appropriate temperature range. The temperature of the LNT 6 may be the temperature detected by the exhaust temperature sensor 47, for example. When the temperature of the LNT 6 is within an appropriate range (S30: Yes), the process proceeds to S40, and when it is not within the range (S30: No), the process of FIG.

After proceeding to S40, the ECU 9 integrates the amount of consumption of the reducing agent (fuel) for NOx reduction. Specifically, it is calculated by any two of the following formulas (E1), (E2), and (E3). Here, AFf, AFm, and AFr are measured values of the A / F sensors 41, 42, and 43, respectively. Ga is a measured value of the air flow meter 31. Δt indicates the period of integration. Note that the flowchart of FIG. 2 may be repeatedly executed every Δt. Σ is a symbol indicating the integration from the start of NOx reduction control to the current time (• is a product).
A1 = Σ (1 / AFf−1 / AFm) · Ga · Δt (E1)
A2 = Σ (1 / AFm−1 / AFr) · Ga · Δt (E2)
B = Σ (1 / AFf−1 / AFr) · Ga · Δt (E3)

  The meaning of the formula (E1) will be described. Ga is the fresh air amount per unit time measured by the air flow meter, but this numerical value is considered to be equal to the exhaust amount per unit time. Therefore, for example, in the formula (E1), Ga / AFf indicates the flow rate of fuel per unit time in the upstream portion of the LNT6. Similarly, Ga / AFm indicates the flow rate of fuel per unit time in the intermediate portion of the LNT6.

  Therefore, (1 / AFf−1 / AFm) · Ga indicates the amount of fuel consumed per unit time in the front portion of the LNT 6, that is, the LNT 60. Therefore, Σ (1 / AFf−1 / AFm) Ga · Δt is an integrated value of the fuel consumption in the front portion of the LNT 6, that is, the LNT 60 from the start of execution of the NOx reduction control to the current time point.

  Similarly, the equation (E2) is an integrated value of fuel consumption in the rear portion of the LNT 6, that is, the LNT 61 from the start of execution of the NOx reduction control to the current time point. Similarly, the equation (E3) is an integrated value of the fuel consumption in the entire LNT 6 including the LNT 60 and the LNT 61 from the start of execution of the NOx reduction control to the current time point.

  The amount of fuel (reducing agent) consumed by the LNT6 (60, 61) during NOx reduction control is considered to be equal to the amount of NOx stored in the LNT6 (60, 61). Therefore, the equations (E1), (E2), and (E3) indicate the NOx occlusion amounts in the front part (LNT60), rear part (LNT61), and the whole (LNT60, 61) of LNT6, respectively. Clearly, the sum of A1 and A2 is equal to B.

  Subsequently, in S50, the ECU 9 determines whether or not to end the NOx reduction control. When the NOx reduction control is finished (S50: Yes), the process proceeds to S60. When the NOx reduction control is not finished (S50: No), the process returns to S40, and the consumption of the reducing agent (fuel) is increased until the NOx reduction control is finished. Repeat integration.

  FIG. 5 shows an example of transition of measured values of the sensors 41, 42, and 43 during NOx reduction control. In FIG. 5, the horizontal axis represents time, and the vertical axis represents the air-fuel ratio. In FIG. 5, the plots indicated before, during, and after LNT indicate the measured values of the sensors 41, 42, and 43, respectively. With the start of the NOx reduction control in S20, the air-fuel ratio of the exhaust gas flowing into the LNT 6 (before the LNT, the measured value of the sensor 41) becomes lower than the stoichiometric air-fuel ratio, resulting in a rich atmosphere.

  However, as fuel is consumed by the reduction of NOx in the LNT 6, the measured values of the sensors 42 and 43 remain at the stoichiometric air-fuel ratio for a while. When all the NOx occluded in the front part (LNT60) of the LNT6 is reduced after a while, the fuel is not consumed for NOx reduction in the front part (LNT60) of the LNT6. ) Falls to the measured value of the sensor 41.

  FIG. 3 shows an example of the NOx occlusion amount and the SOx occlusion amount in the LNT 6 in which the horizontal axis is a spatial position in the exhaust flow direction. As shown in FIG. 3, when LNT 6 undergoes S degradation, SOx (sulfur oxide) has a property of being deposited from the front (upstream side) of LNT 6. Therefore, NOx stored in the LNT 6 is stored in the rear part (downstream side) as the S deterioration progresses. Therefore, in FIG. 5, the NOx occlusion amount at the front portion (LNT60) of LNT6 decreases as the S deterioration progresses, so the time for the measured value of sensor 42 (during LNT) to drop to the measured value of sensor 41 is accelerated.

  When the time further elapses, fuel is no longer consumed for NOx reduction even at the rear portion of the LNT 6 (LNT 61), and the measured value of the sensor 43 (after LNT) falls to the measured value of the sensor 41. The fact that the measured value of the sensor 43 (after LNT) matches the measured value of the sensor 41 indicates that all NOx occluded in the LNT 6 has been reduced. Therefore, if the measured value of the sensor 43 (after LNT) matches the measured value of the sensor 41, the NOx reduction control may be terminated in S50.

Returning to FIG. 2 and proceeding to S60, the ECU 9 calculates the ratio C of the rear NOx occlusion amount. Specifically, it is calculated by any of the following formulas (E4), (E5), and (E6).
C = (B−A1) / B (E4)
C = A2 / B (E5)
C = A2 / (A1 + A2) (E6)

  Equation (E4) may be used when (E1) and (E3) are calculated in step S40. Equation (E5) may be used when (E2) and (E3) are calculated in step S40. Expression (E6) may be used when (E1) and (E2) are calculated in step S40. Obviously, in each of the formulas (E4), (E5), and (E6), the NOx occlusion amount (A2 = B) of the rear portion of the LNT6 (LNT61) with respect to the NOx occlusion amount (B = A1 + A2) of the entire LNT6 (LNT60, 61). The ratio of -A1) is shown. C is a numerical value indicating the spatial distribution of the NOx occlusion amount in the LNT 6 and further the spatial distribution of the SOx deposition amount.

  As described above, since the NOx occlusion amount at the front portion (LNT60) of the LNT6 decreases as the S deterioration progresses, the time during which the measured value of the sensor 42 (during the LNT) falls to the measured value of the sensor 41 is accelerated. Therefore, as S deterioration progresses, the numerical value of C increases.

  FIG. 4 shows the relationship between the numerical values of C, where the vertical axis is the vertical axis and the horizontal axis is the amount of NOx flowing into the LNT 6 (incoming NOx amount). As this figure shows, the numerical value of C is It becomes almost constant with respect to fluctuations in the amount of entering NOx. Therefore, if the S deterioration determination is performed using C, the determination can be made robustly with respect to fluctuations in the amount of incoming NOx. Also, since C is a ratio, even when the detection value of the A / F sensor is shifted due to the presence of residual oxygen in the exhaust, the shift in the denominator and the numerator is offset between the denominator and the shift to C. The effect of is less likely to appear. Therefore, it is possible to perform the S deterioration determination which is not easily affected by the deviation of the A / F measurement value.

  Subsequently, in S70, the ECU 9 determines whether or not the ratio C of the rear NOx occlusion amount calculated in S60 is greater than or equal to a threshold value. When the ratio of the rear NOx occlusion amount is equal to or greater than the threshold (S70: Yes), the process proceeds to S80, and when the ratio of the rear NOx occlusion amount is less than the threshold (S70: No), the process proceeds to S90.

  As described above, the larger the S deposition in the LNT 6, the larger the rear NOx storage amount ratio C. Therefore, for example, as shown by the broken line in FIG. 4, a numerical value that can be used to determine whether or not S degradation has progressed to the extent that S regeneration is necessary is obtained in advance, and this may be used as the threshold value used in S70.

  When it progresses to S80, it is a case where the ratio C of rear NOx occlusion amount is larger than a threshold value. Therefore, in S80, the ECU 9 determines that the LNT 6 is S deteriorated. In S90, the ECU 9 determines that the LNT 6 is not S-degraded (not determined to be S-degraded). The above is the processing of FIG.

  In the processing procedure of FIG. 2, the S deterioration determination of the LNT 6 is performed based on the calculation of the difference area by the equations (E1), (E2), and (E3), but this may be performed based on the calculation of time. Specifically, for example, in FIG. 5, the start time of NOx reduction control is T1, the time when the measured value during LNT (sensor 42) decreases is T2, and the time when the measured value after LNT (sensor 43) decreases is T3. Then, C = (T3−T2) / (T3−T1). As described above, T2 gets earlier as S deterioration progresses, and thus C calculated in this way is also a numerical value indicating the degree of S deterioration. For example, the time measurement may be performed by providing the ECU 9 with a time measuring function.

  Next, a second embodiment of the present invention will be described. Also in the second embodiment, the ratio of the NOx occlusion amount in the rear part of the LNT 6 is calculated as in the first embodiment, but the calculation method is changed. In the second embodiment, the NOx occlusion amount in the rear part and the whole of the LNT 6 is calculated using the NOx sensor during the lean period. For this purpose, the A / F sensors 41, 42, 43 in the first embodiment are replaced with NOx sensors 44, 45, 46. The NOx concentration in the exhaust is detected by the NOx sensors 44, 45, and 46. Other apparatus configurations may be the same as those in the first embodiment.

  A processing procedure for determining S deterioration in the second embodiment is shown in FIG. In the procedure of FIG. 6, first, in S100, the ECU 9 determines whether or not it is within the lean period. When it is within the lean period (S100: Yes), the process proceeds to S110, and when it is not within the lean period (S100: No), the process of FIG. 6 is terminated.

After proceeding to S110, the ECU 9 integrates the NOx occlusion amount. Specifically, it is calculated by any two of the following formulas (E7), (E8), and (E9).
D1 = Σ (NOxf−NOxm) · Ga · Δt (E7)
D2 = Σ (NOxm−NOxr) · Ga · Δt (E8)
F = Σ (NOxf−NOxr) · Ga · Δt (E9)

  Here, NOxf, NOxm, and NOxr are measured values of the NOx sensors 44, 45, and 46, respectively. Ga is a measured value of the air flow meter 31. Δt indicates the period of integration. Note that the flowchart of FIG. 6 may be repeatedly executed every Δt. Σ is a symbol indicating the integration from the start of calculation of NOx occlusion amount (start of lean combustion period) to the present time.

  The meaning of the formula (E7) will be described. Ga is the fresh air amount per unit time measured by the air flow meter, but this numerical value is considered to be equal to the exhaust amount per unit time. Therefore, for example, in the formula (E7), NOxf · Ga indicates the flow rate of NOx per unit time in the upstream portion of the LNT6. Similarly, NOxm · Ga indicates the flow rate of NOx per unit time in the intermediate part of LNT6.

  Therefore, (NOxf−NOxm) · Ga indicates the storage amount of NOx per unit time in the front portion of the LNT 6, that is, the LNT 60. Therefore, Σ (NOxf−NOxm) Ga · Δt is an integrated value of the NOx occlusion amount in the front portion of the LNT 6, that is, the LNT 60 from the start of calculation of the NOx occlusion amount (start of the lean combustion period) to the current time point.

  Similarly, the equation (E8) is an integrated value of the NOx occlusion amount in the rear portion of the LNT 6, that is, the LNT 61 from the start of calculation of the NOx occlusion amount (start of the lean combustion period) to the current time point. Similarly, the equation (E9) is an integrated value of the NOx occlusion amount in the entire LNT6 composed of the LNT60 and the LNT61 from the start of calculation of the NOx occlusion amount (start of the lean combustion period) to the current time point.

  Subsequently, in S120, the ECU 9 determines whether or not the NOx occlusion is saturated in the LNT6. When the NOx occlusion is saturated in the LNT6 (S120: Yes), the process proceeds to S130, and when the NOx occlusion is not yet saturated (S120: No), the process returns to S110, and the NOx occlusion amount is integrated until the NOx occlusion is saturated. Execute.

  FIG. 7 shows an example of transition of measured values of the NOx sensors 44, 45, and 46 during NOx reduction control. In FIG. 7, the horizontal axis represents time and the vertical axis represents NOx concentration. In FIG. 7, the plots indicated before, during, and after LNT indicate the measured values of the sensors 44, 45, and 46, respectively.

  It is assumed that the lean atmosphere is started in a state where NOx is not occluded in the LNT 6 and the NOx concentration of exhaust gas flowing into the LNT 6 (before the LNT, measured value of the sensor 44) is a substantially constant value. At this time, almost all NOx flowing into the LNT 6 is occluded in the LNT 6 at first, so that the measured values of the sensors 42 and 43 are initially zero. However, as the storage amount of NOx increases, NOx passing through the front part of LNT6 (LNT60) and the rear part of LNT6 (LNT61) increases.

  As a result, the measured value of the sensor 45 (during LNT) and the measured value of the sensor 46 (after LNY) begin to rise. The time (t1 in FIG. 7) at which the measured value of the sensor 44 (before LNT) matches the measured value of the sensor 45 (during LNT) is the time when the NOx occlusion at the front part (LNT60) of LNT6 is considered saturated. .

  As described above, as S deterioration progresses, SOx accumulates at the front portion (LNT60) of LNT6, so that the NOx occlusion amount at the front portion (LNT60) of LNT6 decreases. Therefore, the time t1 at which the measured value of the sensor 45 (during LNT) coincides with the measured value of the sensor 44 (before LNT) is advanced as the S deterioration progresses.

  The time when the measured value of the sensor 44 (before LNT) and the measured value of the sensor 46 (after LNT) coincide (t2 in FIG. 7) is regarded as the NOx occlusion in the entire LNT6 (LNT60, 61) is saturated. It is. Therefore, time t2 is the time when NOx occlusion is determined to be saturated in S120.

Returning to FIG. 6, after proceeding to S <b> 130, the ECU 9 calculates the ratio C of the rear NOx occlusion amount. Specifically, it is calculated by any of the following formulas (E10), (E11), and (E12).
C = (F−D1) / F (E10)
C = D2 / F (E11)
C = D2 / (D1 + D2) (E12)

  Equation (E10) may be used when (E7) and (E9) are calculated in step S110. Equation (E11) may be used when (E8) and (E9) are calculated in step S110. Equation (E12) may be used when (E7) and (E8) are calculated in step S110. The expressions (E10), (E11), and (E12) clearly show the NOx occlusion amount (D2 = F2) in the rear part (LNT61) of the LNT6 with respect to the NOx occlusion amount (F = D1 + D2) of the entire LNT6 (LNT60, 61). -D1) ratio.

  Subsequently, in S140, the ECU 9 determines whether or not the ratio of the rear NOx occlusion amount is equal to or greater than a threshold value. When the rear NOx storage amount ratio C is equal to or greater than the threshold (S140: Yes), the process proceeds to S150, and when the rear NOx storage amount ratio is less than the threshold (S140: No), the process proceeds to S160.

  As described above, it is considered that the S deterioration progresses as the ratio C of the rear NOx storage amount increases. Therefore, for example, as shown by the broken line in FIG. 4, a numerical value that can be used to determine whether or not S deterioration has progressed to the extent that S regeneration is necessary is obtained in advance, and this may be used as the threshold value used in S140. In S150, the ECU 9 determines that the LNT 6 is S deteriorated. In S160, the ECU 9 determines that the LNT 6 is not S deteriorated. The above is the processing of FIG.

  The ECU 9 may perform S regeneration control (S regeneration) for regenerating the LNT 6 from the S deteriorated state when it is determined that the S deterioration is caused by the processing of FIG. 2 or FIG. In the S regeneration, the SOx deposited on the LNT 6 is reduced by forming a rich atmosphere and a state of a predetermined temperature (for example, 600 degrees Celsius) or higher. In order to create a rich atmosphere, for example, fuel is added from the addition valve 40, or post-injection that is re-injected after the combustion reaction is completed in the cylinder of the engine 2, or the combustion gas itself is enriched by reducing the intake air. Rich combustion may be performed.

  Furthermore, the ECU 9 may have a failure detection function of the LNT 6. Specifically, for example, the above-described calculation of C is performed even after the S reproduction, and if the difference value of the C value before and after the S reproduction is smaller than a predetermined threshold, even if the S reproduction is executed, the C Since the value is not improved so much, it is determined that the LNT 6 has failed. As described above, since the information on S degradation is accurately reflected in C, a failure of LNT 6 can be detected with high accuracy.

  The above embodiments may be changed as appropriate without departing from the scope of the claims. For example, in the above, LNT6 is divided into two parts LNT60 and 61, but the number of divisions is 3 or more (4 divisions, 5 divisions, etc.), and an A / F sensor (NOx sensor) is arranged between them. Also good. Then, the spatial distribution of the NOx occlusion amount (SOx accumulation amount) in the LNT 6 is calculated more precisely (or the entire NOx occlusion amount of the NOx occlusion amount (SOx accumulation amount) in a part of the divided intervals). The ratio to the amount (SOx accumulation amount) is calculated), and it may be determined that the S deterioration is caused as NOx is occluded in the rear part.

  In the said Example, LNT6 comprises a catalyst part. The procedure of S60 and S130 and the ECU 9 constitute a distribution detecting means. The procedure of S70 and S140 and the ECU 9 constitute a distribution detecting means. The procedure of S20 and the ECU 9 constitute a reducing means. Sensors 41, 42 and 43 constitute air-fuel ratio detection means. The procedure of S60 and the ECU 9 constitute first calculation means and second calculation means. Sensors 44, 45, and 46 constitute nitrogen oxide detecting means. The ECU 9 constitutes third calculation means. The procedure of S130 and the ECU 9 constitute fourth calculation means and fifth calculation means. The injector 21 or the addition valve 40 constitutes a regeneration unit. The ECU 9 constitutes failure determination means. In the above embodiment, a diesel engine is used, but this may be a lean burn gasoline engine.

1 Exhaust gas purification device 2 Diesel engine (internal combustion engine)
3 Intake pipe 5 Exhaust pipe (exhaust passage)
6 NOx storage catalyst (LNT, catalyst part)

Claims (10)

A catalyst portion that is provided in an exhaust passage of the internal combustion engine and stores nitrogen oxides;
A distribution detecting means for detecting a spatial distribution of the amount of nitrogen oxides occluded in the catalyst portion in the flow direction of the exhaust;
Determination means for determining sulfur deterioration in the catalyst unit using a spatial distribution of the storage amount of nitrogen oxides in the catalyst unit detected by the distribution detection unit;
An exhaust emission control device for an internal combustion engine, comprising:   In the spatial distribution of the storage amount of nitrogen oxide in the catalyst unit detected by the distribution detection unit, the determination unit has a ratio of the downstream storage amount in the exhaust flow direction to the total storage amount higher than a threshold value. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the catalyst unit determines that the sulfur has deteriorated. A reducing means for reducing the stored nitrogen oxides by supplying a reducing agent to the catalyst unit;
The distribution detecting means includes
An air-fuel ratio for detecting at least three air-fuel ratios at a first position upstream in the exhaust gas flow direction, a third position downstream, and a second position between the first position and the third position in the catalyst portion. Detection means;
During execution of reduction by the reduction means, nitrogen oxides in the catalyst unit are obtained by at least three or more air-fuel ratios in the first position, the second position, and the third position detected by the air-fuel ratio detection means. First calculating means for calculating the spatial distribution of the occlusion amount of
An exhaust emission control device for an internal combustion engine according to claim 1 or 2, further comprising:   The first calculation means calculates the difference between the two positions by integrating the difference values of the air-fuel ratios at any two positions among at least three or more air-fuel ratio detection positions detected by the air-fuel ratio detection means. The exhaust emission control device for an internal combustion engine according to claim 3, further comprising second calculating means for calculating a consumption amount of the reducing agent having a correlation with a storage amount of nitrogen oxides.   In the first calculation means, at any two of the at least three air-fuel ratio detection positions detected by the air-fuel ratio detection means, the upstream position of the two positions is a rich atmosphere. Of the reducing agent having a correlation with the amount of occlusion of nitrogen oxides between the two positions, based on the difference between the time when the downstream position and the time when the downstream position of the two positions becomes a rich atmosphere. The exhaust emission control device for an internal combustion engine according to claim 3, further comprising third calculation means for calculating. The distribution detecting means includes
In the catalyst unit, the concentration of at least three or more nitrogen oxides at a first position upstream in the exhaust flow direction, a third position downstream, and a second position between the first position and the third position is detected. Nitrogen oxide detection means;
The amount of occlusion of nitrogen oxides in the catalyst unit is spatially determined by the concentration of at least three or more nitrogen oxides at the first position, the second position, and the third position detected by the nitrogen oxide detecting means. A fourth calculation means for calculating the distribution;
An exhaust emission control device for an internal combustion engine according to claim 1 or 2, further comprising:   The fourth calculation means calculates the difference between the two positions by integrating the difference value of the nitrogen oxide concentration at any two positions among at least three detection positions detected by the nitrogen oxide detection means. The exhaust emission control device for an internal combustion engine according to claim 6, further comprising fifth calculation means for calculating the storage amount of nitrogen oxides in the engine. The second calculating means includes: a consumption amount of the reducing agent between the first position and the third position; and a consumption amount of the reducing agent between the second position and the third position. Calculate
The determination means is calculated by the second calculation means and the consumption of the reducing agent between the first position and the third position is between the second position and the third position. The exhaust emission control device for an internal combustion engine according to claim 4, wherein when the ratio of the consumption of the reducing agent is larger than a threshold value, it is determined that the catalyst unit has deteriorated sulfur. The fifth calculation means includes a storage amount of nitrogen oxides between the first position and the third position, and a storage amount of nitrogen oxides between the second position and the third position. Calculate
The determination means is the nitrogen between the second position and the third position with respect to the storage amount of nitrogen oxides between the first position and the third position calculated by the fifth calculation means. The exhaust purification device for an internal combustion engine according to claim 7, wherein when the ratio of the amount of occluded oxide is larger than a threshold value, it is determined that the catalyst unit has deteriorated sulfur. A regeneration means for removing sulfur accumulated in the catalyst part;
A failure determination means for comparing the distribution of the storage amount of nitrogen oxides in the catalyst portion before and after the execution of the sulfur removal process by the regeneration means, and determining failure of the catalyst portion;
An exhaust purification device for an internal combustion engine according to any one of claims 1 to 9, further comprising: