JP2018071482A - Adsorption amount estimation device - Google Patents

Abstract

To provide an adsorption amount estimation device capable of estimating an adsorption amount with high accuracy while eliminating the need to forcibly reduce the adsorption amount of a reducing agent to zero. An adsorption amount estimation apparatus includes a gradual change control unit in step S7, a change index detection unit in step S8, and a change adsorption amount estimation unit in step S9. The gradual change control unit executes gradual change control for controlling the operation of the addition valve so as to gradually change the addition amount of the reducing agent. The change index detection unit uses the purification index when the amount of change in the purification index that occurs each time the addition amount is gradually changed by gradual change control as a change index, and changes based on the detection value by the detection device. Detect time indicators. The change-time adsorption amount estimation unit estimates a change-time adsorption amount, which is an adsorption amount at the time when the change-time index is detected, based on the change-time index detected by the change-time index detection unit. [Selection] Figure 6

Description

  The present invention relates to an adsorption amount estimation device that estimates an adsorption amount of a reducing agent to a purification device.

  A purification device disposed in the exhaust passage of the internal combustion engine, and an addition valve for adding a reducing agent to the upstream side of the purification device in the exhaust passage, and NOx in the exhaust gas on the catalyst of the purification device is reduced with the reducing agent. A purification system for reducing and purifying is conventionally known (see Patent Document 1). Most of the added reducing agent is adsorbed by the catalyst, and then NOx is reduced by a chemical reaction with NOx in the exhaust gas on the catalyst.

  If the reducing agent adsorption amount is too small relative to the NOx inflow amount to the purification device, the amount of NOx (NOx slip amount) that passes through the purification device without being reduced increases. On the other hand, if the adsorption amount of the reducing agent is excessive, the amount of reducing agent flowing out from the purification device (reducing agent slip amount) increases. In order to reduce these slip amounts, it is required to control the supply amount of the reducing agent so that the reducing agent adsorption amount falls within an appropriate range.

  In response to this request, the amount of adsorption may be estimated from the history of the operating state of the internal combustion engine, and the amount of reducing agent added may be controlled so that the estimated amount of adsorption falls within the proper range. As a result, estimation errors are accumulated and sufficient estimation accuracy cannot be secured. In order to solve this problem, the adsorption amount estimation apparatus described in Patent Document 1 forcibly stops the addition of the reducing agent, thereby matching the actual adsorption amount to a known amount (zero) and resetting the estimation error. Calibration control such as is periodically executed.

US Patent Application Publication No. 2005/0282285

  However, during the calibration control execution period described above, the amount of adsorption is too small or zero, so the amount of NOx slip increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an adsorption amount estimation device that can estimate the adsorption amount with high accuracy while eliminating the need to forcibly reduce the adsorption amount of the reducing agent to zero. Is to provide.

  The invention disclosed herein employs the following technical means to achieve the above object. Note that the reference numerals in parentheses described in the claims and in this section indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the invention. .

The disclosed invention
A purification device (30) having a catalyst for reducing and purifying NOx contained in the exhaust gas of the internal combustion engine (10), and an addition for adding a reducing agent to the upstream side of the purification device in the exhaust passage (11a) of the internal combustion engine Applying to a purification system comprising a valve (20) and a detection device (50) that is disposed on the downstream side of the purification device in the exhaust passage and detects at least one of the NOx amount and the reducing agent amount, the reduction to the purification device In the adsorption amount estimation device for estimating the adsorption amount of the agent,
A gradual change control unit (S7) for executing a gradual change control for controlling the operation of the addition valve so as to gradually change the addition amount of the reducing agent;
An index indicating the purification performance of the purification apparatus is used as a purification index, and the purification index when the amount of change (ΔR) in the purification index that occurs each time the addition amount is gradually changed by gradual change control is changed by a predetermined amount or more. R2y, R3y), and a change time index detection unit (S8) that detects a change time index based on the detection value by the detection device;
Based on the change time index detected by the change time index detection unit, the change time adsorption amount estimation unit (S9) for estimating the change amount adsorption amount (M2x, M3x) that is the amount of adsorption at the time when the change time index is detected. When,
Is an adsorption amount estimation device.

  Here, when the solid line illustrated in FIG. 4 representing the relationship between the adsorption amount and the purification index is called a characteristic line, the amount of change in the purification index caused by the change in the addition amount by the gradual change control has changed by a predetermined amount or more. The hour index (change index) is highly correlated with the actual characteristic line. Therefore, if the index at the time of change can be grasped, the amount of adsorption at that time (the amount of adsorption at the time of change) can be grasped with high accuracy. Focusing on this point, in the above invention, the change index is detected to detect the change index, and the change adsorption amount is estimated based on the detected change index, so the change adsorption amount is estimated with high accuracy. become able to. In addition, since the change index used for the above estimation can be calculated by gradually changing the addition amount, the change adsorption amount (without the control of forcing the adsorption amount to zero (known amount) is unnecessary. Estimation of the known amount) can be realized.

1 is a schematic diagram of a purification system to which an adsorption amount estimation device according to a first embodiment of the present invention is applied. The schematic diagram which shows the internal state of a NOx purification apparatus in case NOx slip has arisen. The schematic diagram which shows the internal state of a NOx purification apparatus in case the reducing agent slip has arisen. The figure which shows the characteristic line showing the relationship between adsorption amount and a purification rate. The figure which shows an example of the state change of the characteristic line showing the relationship between adsorption amount and a purification rate. The flowchart which shows the procedure of the process which the processor of the adsorption amount estimation apparatus which concerns on 1st Embodiment performs. The flowchart which shows the process sequence of the gradual change control shown in FIG. It is a figure which shows the characteristic line showing the relationship between adsorption amount and purification rate, Comprising: The figure explaining the outline | summary of the gradual change control which concerns on 2nd Embodiment of this invention. The flowchart which shows the procedure of the process which the processor of the adsorption amount estimation apparatus which concerns on 2nd Embodiment performs.

  Hereinafter, a plurality of modes for carrying out the invention will be described with reference to the drawings. In each embodiment, portions corresponding to the matters described in the preceding embodiment may be denoted by the same reference numerals and redundant description may be omitted. In each embodiment, when only a part of the configuration is described, the other configurations described above can be applied to other portions of the configuration.

(First embodiment)
An internal combustion engine 10 shown in FIG. 1 is mounted on a vehicle, and a purification system for purifying exhaust gas is mounted on the vehicle. The purification system includes an addition valve 20 attached to the exhaust pipe 11 of the internal combustion engine 10, a NOx purification device 30, an oxidation device 40, and a NOx sensor 50.

  The NOx purification device 30 includes a carrier 31 having a selective reduction type reduction catalyst, and a case connected to the exhaust pipe 11 while holding the carrier 31 inside. This reducing catalyst has a reducing function that promotes a reaction in which the reducing agent reduces NOx, and an adsorption function that adsorbs the reducing agent, and a specific example of the reducing catalyst is zeolite.

  The addition valve 20 adds urea water to the upstream side of the NOx purification device 30 in the exhaust passage 11a. The urea water stored in the urea water tank 20t mounted on the vehicle is supplied to the addition valve 20 by the urea water pump 20p. The addition valve 20 includes a valve body 21 that opens and closes the nozzle hole, and an electromagnetic coil 22 that generates an electromagnetic force when energized. The electromagnetic force is applied to the valve body 21 as a valve opening force. Therefore, when energization to the electromagnetic coil 22 is started, the valve element 21 is opened, urea water is injected from the nozzle hole, and urea water is added to the exhaust passage 11a. When energization of the electromagnetic coil 22 is finished, the valve body 21 is closed, and the addition of urea water to the exhaust passage 11a is finished.

  The urea water added to the exhaust passage 11a is heated and hydrolyzed in a route from the addition valve 20 to the reduction catalyst in the exhaust passage 11a. By this hydrolysis, ammonia as a reducing agent is generated and supplied to the NOx purification device 30. Most of the supplied ammonia is adsorbed by the reduction catalyst of the carrier 31 as shown in FIGS. Thereafter, NOx contained in the exhaust gas is chemically reacted with the reduction catalyst to reduce NOx (see FIG. 2). Further, a part of the supplied ammonia reduces NOx on the reduction catalyst without being adsorbed by the reduction catalyst.

  The oxidation apparatus 40 includes a carrier having an oxidation catalyst and a case connected to the exhaust pipe 11 while holding the carrier inside. Of the ammonia supplied to the NOx purification device 30, the ammonia that has flowed out of the NOx purification device 30 without reacting with NOx is oxidized on the oxidation catalyst.

  The NOx sensor 50 is disposed downstream of the NOx purification device 30 in the exhaust passage 11a, and detects the NOx amount and the ammonia amount contained in the exhaust. Specifically, the NOx sensor 50 outputs a signal having a voltage value corresponding to the NOx concentration in the exhaust gas to the electronic control unit (ECU 60). The NOx sensor 50 also outputs a signal in response to ammonia in the exhaust gas, and detects both the ammonia amount (reducing agent amount) and the NOx amount. The NOx sensor 50 corresponds to the detection device described in the claims.

  The ECU 60 includes a microcomputer (microcomputer 61) having a processor 61a and a memory 61b, an input processing circuit and an output processing circuit (not shown), and the like. The processor 61a executes various calculations, estimations, settings, commands, and the like by executing arithmetic processing according to various programs stored in the memory 61b.

  The ECU 60 receives the signal output from the NOx sensor 50, that is, a signal including the detected value of NOx or ammonia detected by the NOx sensor 50 as information. Further, the ECU 60 receives a signal including information representing the operating state of the internal combustion engine 10 such as the rotational speed of the output shaft of the internal combustion engine 10, the load of the internal combustion engine 10, and the exhaust temperature. The ECU 60 controls the opening / closing operation of the valve body 21 by controlling the energization state of the electromagnetic coil 22 based on these signals, thereby controlling the amount of urea water added. Specifically, the mass of urea water added to the exhaust passage 11a per unit time is controlled as the addition amount. Then, by controlling the amount of urea water added, the amount of ammonia adsorbed on the reduction catalyst (hereinafter referred to as the adsorption amount) is controlled.

  The control of the urea water addition amount will be described in more detail below. In the following description, the target value of the addition amount is the target addition amount, the target value of the adsorption amount is the target adsorption amount, the estimated value of the current adsorption amount is the estimated adsorption amount, and the NOx amount flowing into the purifier 30 is the NOx. The amount of inflow is taken as the catalyst temperature. The NOx inflow amount is estimated by the microcomputer 61 based on the above-described rotational speed and load. The catalyst temperature is estimated by the microcomputer 61 based on the exhaust gas temperature described above. A method of calculating the target adsorption amount and the estimated adsorption amount will be described in detail later with reference to FIG.

  The microcomputer 61 sets the target addition amount based on the NOx inflow amount, the catalyst temperature, the target adsorption amount, and the estimated adsorption amount. Further, the microcomputer 61 controls the energization time to the electromagnetic coil 22 based on the set target addition amount and the pressure of the urea water supplied to the addition valve 20 so that the addition amount becomes the target addition amount. The operation of the valve 20 is controlled.

  Here, if the adsorption amount of ammonia (reducing agent) with respect to the NOx inflow amount is too small, the NOx amount that passes through the NOx purification device 30 without being reduced, that is, the NOx slip amount indicated by symbol A in FIG. On the other hand, if the amount of addition of the reducing agent relative to the current adsorption amount is excessive, the amount of the reducing agent that is not adsorbed and passes through the NOx purification device 30, that is, the reducing agent slip amount indicated by symbol B in FIG. Therefore, it is required to control the supply amount of the reducing agent so that the reducing agent adsorption amount falls within the appropriate range W1 (see FIG. 4).

  The horizontal axis in FIG. 4 indicates the amount of adsorption, and the vertical axis indicates the purification rate. The purification rate here is the ratio of the detected value of the NOx sensor 50 to the NOx inflow amount, and corresponds to a purification index representing the purification performance of the NOx purification device 30. As described above, the NOx sensor 50 detects both the NOx amount and the reducing agent amount. Therefore, the greater the NOx slip amount, the lower the purification rate, and the greater the reducing agent slip amount, the lower the purification rate. That is, when both the NOx slip amount and the reducing agent slip amount are reduced, the purification rate shown on the vertical axis in FIG. 4 is increased.

  Compared to estimating the amount of reducing agent adsorbed to the reduction catalyst based on the detected value of the NOx sensor 50, it is possible to estimate the purification rate more accurately based on the detected value of the NOx sensor 50. As shown in FIG. 4, the purification rate and the amount of adsorption have a correlation. Focusing on this point, the ECU 60 stores information representing a characteristic line Ma (see FIG. 4) representing the relationship between the adsorption amount and the purification rate as correlation information. For example, a characteristic map M (see FIG. 4) indicating the value of the adsorption amount with respect to the purification rate and a mathematical expression representing the adsorption amount with the purification rate as a variable are given as specific examples of the correlation information. In the example of FIG. 4, the values of the characteristic line Ma and the characteristic map M are the same.

  As indicated by the characteristic line Ma, for example, when the adsorption amount is changed by a predetermined amount ΔM, the purification rate also changes. However, the change in the purification rate with respect to the change in the adsorption amount is small depending on the region of the adsorption amount. Thus, the range of the adsorption amount in which the change in the purification rate caused by the change in the adsorption amount is less than a predetermined value is referred to as an appropriate range W1. Further, the adsorption amount range on the side smaller than the appropriate range W1 is referred to as an excessive range W2, and the adsorption amount range on the side larger than the appropriate range W1 is referred to as an excessive range W3. In the excessive range W2, the purification rate increases as the adsorption amount increases. In the excessive range W3, the purification rate decreases as the adsorption rate increases. Further, in the appropriate range W1 of the characteristic line Ma illustrated in FIG. 4, the purification rate also increases as the adsorption amount increases.

  The ECU 60 calculates the purification rate based on the detected value of the NOx sensor 50 as described above, and calculates the adsorption amount corresponding to the estimated purification rate from the characteristic map M. Thus, the ECU 60 functions as an adsorption amount estimation device that estimates the adsorption amount. The change point of the characteristic line Ma located at the boundary between the appropriate range W1 and the underrange W2 is called an underside change point R2, and the change point of the characteristic line Ma located at the boundary between the appropriate range W1 and the overrange W3 is defined as This is referred to as an excessive side change point R3. Further, the purification rate at these change points corresponds to a change time index.

  The correlation between the adsorption amount and the purification rate, that is, the characteristic line Ma changes according to the aging deterioration of the NOx purification device 30, the poisoning state of the reduction catalyst, or the like. Therefore, even if the characteristic map M is set according to the characteristic line in the initial state of the reduction catalyst as shown by the one-dot chain line shown in FIG. 5, the actual characteristic line Ma changes as indicated by the solid line, and the characteristic map M And the characteristic line Ma do not coincide with each other, and the estimation accuracy of the adsorption amount is deteriorated. Therefore, in the present embodiment, the characteristic map M stored in the ECU 60 is corrected so as to approach the actual characteristic line Ma by executing the control of FIG. 6 described below.

  The flowchart shown in FIG. 6 is a process repeatedly executed by the processor 61a at a predetermined cycle during the operation period of the internal combustion engine 10. Specific examples of the predetermined cycle include a calculation cycle of the processor 61a and a cycle each time the output shaft of the internal combustion engine 10 rotates by a predetermined angle.

  First, in step S1 of FIG. 6, the amount of reducing agent adsorbed on the reduction catalyst (hereinafter referred to as adsorption amount) is estimated as follows. The processor 61a when executing the process of step S1 corresponds to an adsorption amount estimation unit described in the claims. In this estimation process, first, an adsorption rate, a desorption rate, an oxidation rate, and a reduction rate described below are calculated.

  The adsorption rate is a rate of increase in the amount of adsorption caused by the reducing agent adsorbed on the reduction catalyst, and is calculated using the previous value of the urea water addition amount, the hydrolysis rate, the catalyst temperature, and the exhaust gas flow rate as parameters. As the values of these parameters are larger, the adsorption speed is generally calculated as a larger value. For example, the adsorption speed corresponding to these parameters is mapped and stored in advance, and the adsorption speed is calculated with reference to the map based on these parameters.

  The previous value of the urea water addition amount is calculated based on the energization time to the addition valve 20 and the pressure of the urea water supplied to the addition valve 20. The hydrolysis ratio is a ratio in which ammonia (reducing agent) is generated by hydrolysis in the added urea water, and is calculated based on the exhaust temperature. The exhaust temperature may be detected by an exhaust temperature sensor (not shown) or may be estimated based on the operating state of the internal combustion engine. The catalyst temperature is estimated based on the exhaust temperature. The exhaust flow rate is a value obtained by dividing the exhaust flow rate flowing into the purification device 30 by the catalyst volume, and is the exhaust inflow rate per unit volume. The exhaust gas flow rate thus defined is estimated based on the operating state of the internal combustion engine.

  The desorption rate is a rate of decrease in the amount of adsorption that occurs when the reducing agent adsorbed on the reduction catalyst desorbs from the reduction catalyst, and is calculated using the previous value of the estimated amount of adsorption and the catalyst temperature as parameters. The larger the values of these parameters, the greater the desorption rate is calculated. For example, the desorption rate corresponding to these parameters is mapped and stored in advance, and the desorption rate is calculated with reference to the map based on these parameters.

  The oxidation rate is the rate of decrease in the amount of adsorption that occurs when the reducing agent adsorbed on the reduction catalyst is oxidized by oxygen in the exhaust without reducing NOx. The temperature and the exhaust flow rate are calculated as parameters. As the values of these parameters are larger, the oxidation rate is generally calculated to be larger. For example, the oxidation rate corresponding to these parameters is mapped and stored in advance, and the oxidation rate is calculated with reference to the map based on these parameters.

The reduction rate is a reduction rate of the adsorption amount generated when the reducing agent adsorbed on the reduction catalyst reduces NOx. The previous value of the estimated adsorption amount, the catalyst temperature, the exhaust flow rate, and the purification device 30 The NOx inflow amount and the NO ₂ / NO ratio are calculated as parameters. The NOx inflow amount and the NO ₂ / NO ratio are estimated based on the operating state of the internal combustion engine. As the values of these parameters are larger, the reduction rate is generally calculated as a larger value. For example, the reduction rate corresponding to these parameters is mapped and stored in advance, and the reduction rate is calculated with reference to the map based on these parameters.

  Then, a value obtained by subtracting the desorption rate, the oxidation rate, and the reduction rate from the adsorption rate and the length of a predetermined cycle in which the process of FIG. 6 is performed is calculated as the adsorption amount per unit time. The adsorption amount per unit time is added every time the process of step S1 is executed, and the accumulated value is calculated as the estimated adsorption amount. Therefore, the estimated adsorption amount increases as the adsorption rate increases, and the estimated adsorption amount decreases as the desorption rate, oxidation rate, and reduction rate increase.

  In subsequent step S2, the operation of the addition valve 20 is controlled so that the estimated adsorption amount estimated in step S1 becomes the target adsorption amount. Specifically, by controlling the energization time to the electromagnetic coil 22 according to the deviation of the estimated adsorption amount with respect to the target adsorption amount, the valve opening time of the valve body 21, that is, the addition amount of urea water from the addition valve 20 is controlled. Control. The target adsorption amount is set to the median value A1 of the appropriate range W1. The appropriate range W1 or the median value A1 is set to an initial value of the characteristic map M or a value corrected in step S10 described later.

  In subsequent step S3, it is determined whether or not the estimated adsorption amount estimated in step S1 matches the target adsorption amount. If it is determined that they do not match, the process returns to step S1, and the addition valve control in step S2 is continued until they match. If it is determined that they match, the process proceeds to step S4.

  In the next step S4, the purification rate described in FIG. 4 is calculated based on the detection value of the NOx sensor 50, and it is determined whether or not the detected purification rate is less than the target purification rate. The purification rate is calculated as follows. That is, the NOx purification amount is calculated by subtracting the NOx slip amount detected by the NOx sensor 50 from the NOx inflow amount to the purification device 30. Then, the ratio of the NOx purification amount to the NOx inflow amount is calculated as the purification rate. Even when the NOx sensor 50 detects the reducing agent slip amount, the purification rate is similarly calculated by replacing the NOx slip amount with the reducing agent slip amount.

  Here, since it is difficult to directly detect the actual adsorption amount, it is difficult to directly check the error of the estimated adsorption amount calculated in step S1 with respect to the actual adsorption amount. Therefore, in step S4, an error with respect to the actual adsorption amount of the estimated adsorption amount is checked by the purification rate. That is, as shown by the characteristic line Ma in FIG. 4, if the actual adsorption amount matches the target adsorption amount, there is a high probability that a sufficient purification rate can be obtained. Therefore, when the estimated adsorption amount is equal to the target adsorption amount, but the purification rate is not less than the target purification rate, it can be considered that the estimation error of the estimated adsorption amount is large. Therefore, if the detected purification rate is not less than the target purification rate, it is considered that the estimation error in step S1 exceeds the allowable range. And if it determines with the purification rate detected in step S4 not being less than target purification rate, the process of step S1-S3 will be continued until it will become less than target purification rate, and it is less than target purification rate. If it is determined, the process proceeds to step S5.

  In the next step S5, it is identified whether the current amount of adsorption corresponds to any of the appropriate range W1, the under range W2, and the over range W3. Specifically, the operation of the addition valve 20 is controlled so as to increase the addition amount by a predetermined amount with respect to the target adsorption amount set in step S2 and then decrease the addition amount by a predetermined amount (dither control). To do. These increase and decrease are performed for a predetermined time (for example, several seconds). Then, the identification is performed based on the change in the detected value of the NOx sensor 50 that is caused by changing the amount of adsorption by executing dither control. Note that the processor 61a when executing the process of step S5 corresponds to a range identifying unit described in the claims.

  For example, when the actual adsorption amount matches the median value of the appropriate range W1 of the actual characteristic line Ma at the start of execution of the dither control, the purification rate based on the detected value of the NOx sensor 50 should hardly change. is there. Further, when the actual adsorption amount exists in the underrange W2, the purification rate decreases with the decrease in the dither control, and the purification rate should not change depending on the increase. Further, when the actual adsorption amount exists in the excessive range W3, the purification rate decreases with the increase in dither control, and the purification rate should not change depending on the decrease. Thus, the above identification is performed by detecting how the purification rate has changed with the execution of the dither control.

  In subsequent step S6, it is determined whether or not both the catalyst temperature and the exhaust gas flow rate are in a steady state. Specifically, if the amount of change in the catalyst temperature per unit time is less than a predetermined threshold, the catalyst temperature is considered to be in a steady state. If the amount of change in the exhaust flow rate per unit time is less than a predetermined threshold, the exhaust flow rate is considered to be in a steady state. If it is determined that the state is not a steady state, the process of FIG. 6 is terminated without executing the processes after step S7. If it is determined that it is in a steady state, the process proceeds to step S7.

  In the next step S7, the subroutine processing shown in FIG. 7 is executed to control the operation of the addition valve 20 so as to gradually change the addition amount of the reducing agent (gradual change control). In subsequent step S8, the purification rates R2y and R3y (see FIG. 5) at the time of change, which are the purification rates when the change amount of the purification rate caused by the change in the addition amount due to the gradual change control changes by a predetermined amount or more, are determined as NOx sensor 50 Detect based on the detected value. The processor 61a when executing the process of step S7 corresponds to a gradual change control unit, and the processor 61a when executing the process of step S8 corresponds to a change index detecting unit.

  In the gradual change control process shown in FIG. 7, first, in step S20, the identification result by the dither control in step S5 is acquired. If it is identified as the underrange W2, the operation of the addition valve 20 is controlled to increase the current adsorption amount by a predetermined amount ΔM2 (see FIG. 4) in step S21, and this control is performed for a predetermined time (for example, several seconds). ) Only continue. The predetermined amount ΔM2 to be increased is variably set according to the catalyst temperature and the exhaust gas flow rate acquired in step S6. Specifically, the predetermined amount ΔM2 to be increased is decreased as the catalyst temperature is higher and the exhaust gas flow rate is higher.

  If the excessive range W3 is identified, in step S22, the operation of the addition valve 20 is controlled so as to decrease the current adsorption amount by a predetermined amount ΔM3 (see FIG. 4), and this control is performed for a predetermined time (for example, several seconds). ) Only continue. The predetermined amount ΔM3 to be reduced is variably set according to the catalyst temperature and the exhaust gas flow rate acquired in step S6. Specifically, the predetermined amount ΔM3 to be reduced is reduced as the catalyst temperature is higher and the exhaust gas flow rate is higher.

  In the subsequent step S23, it is determined whether or not the amount of adsorption has exceeded the underside change point R2 or the overside change point R3 toward the appropriate range W1. When the change points R2 and R3 are exceeded, the purification rate change amount ΔR (see FIG. 4) corresponding to the change amount of the detected value should be drastically smaller than the previous purification rate change amount ΔR. Therefore, when the purification rate change amount ΔR changes by a predetermined amount or more with respect to the previous value, it can be considered that the change points R2 and R3 have been exceeded to the appropriate range W1 side.

  In view of this point, in step S23, it is determined whether or not the amount of change in the detected value of the NOx sensor 50 caused by the increase in step S21 or the decrease in step S22 has changed by a predetermined amount or more. Specifically, it is determined whether or not the purification rate change amount ΔR is less than a predetermined value. When the amount of adsorption after the above increase or decrease is the amount in the underrange W2 or the overrange W3, the purification rate change amount ΔR is equal to or greater than a predetermined value, and the amount is changed to the appropriate range W1. The predetermined value is set so that the purification rate change amount ΔR is less than the predetermined value.

  If it is determined in step S23 that the purification rate change amount ΔR is not less than the predetermined value, it is considered that the increased adsorption amount continues to be in the underrange W2, or the decreased adsorption amount continues to be in the excessive range W3. It returns to the process of step S20. Therefore, the current amount of adsorption is further increased or decreased. If it is determined in step S23 that the purification rate change amount ΔR is less than the predetermined value, the gradual change control in FIG. 7 is terminated.

  On the other hand, if it is determined in step S20 that the appropriate range W1 is identified, in step S24, the operation of the addition valve 20 is controlled to increase or decrease the current adsorption amount by a predetermined amount, This control is continued for a predetermined time (for example, several seconds).

  In subsequent step S25, it is determined whether or not the amount of adsorption has exceeded the underside change point R2 or the overside change point R3 from the appropriate range W1 side. When the change points R2 and R3 are exceeded, the purification rate change amount ΔR should increase rapidly compared to the previous purification rate change amount ΔR. Therefore, when the purification rate change amount ΔR changes by a predetermined amount or more with respect to the previous value, it can be considered that the change points R2 and R3 have been exceeded from the appropriate range W1 side.

  In view of this point, in step S25, it is determined whether or not the amount of change in the detected value of the NOx sensor 50 caused by the increase or decrease in step S24 has changed by a predetermined amount or more. Specifically, it is determined whether or not the purification rate change amount ΔR is greater than or equal to a predetermined value. In the case where the amount is decreased in step S24, if the amount of adsorption after the decrease continues to be in the appropriate range W1, the purification rate change amount becomes less than the predetermined value, and the amount changes to the amount in the underrange W2. The predetermined value is set so that the purification rate change amount is not less than the predetermined value. Further, in the case where the amount is increased in step S24, if the amount of adsorption after the increase is continuously in the appropriate range W1, the purification rate change amount is less than a predetermined value and the amount is changed to the excessive range W3. The predetermined value is set so that the amount of change in the purification rate is equal to or greater than the predetermined value. The predetermined value used for the determination in step S23 is set to the same value as the predetermined value used for the determination in step S25.

  If it is determined in step S25 that the purification rate change amount is not equal to or greater than the predetermined value, the adsorption amount after the decrease or increase is regarded as being in the appropriate range W1, or the adsorption amount after the decrease is continuously excessive. It is regarded as W3, and the process returns to step S20. Therefore, the current amount of adsorption is further increased or decreased. And when it determines with the purification rate change amount being more than predetermined value in step S23, the gradual change control of FIG. 7 is complete | finished.

  Returning to the description of FIG. 6, after the gradual change control in step S7 is executed, in step S8, the above-described purification rates R2y and R3y at the time of change are detected. That is, among the change points R2 and R3 where the slope of the characteristic line Ma changes greatly, the change point located at the boundary between the appropriate range W1 and the underrange W2 is called the underside change point R2, and the appropriate range W1 and the overrange W3 are set. The change point located at the boundary is referred to as an excessive change point R3. Then, the purification rate at the underside change point R2 is detected as an underside change purification rate R2y, and the purification rate at the overside change point R3 is detected as an excess side purification rate R3y.

  Specifically, the purification rate at the time when the gradual change control in step S7 is completed, that is, when the affirmative determination is made in steps S23 and S25, is calculated based on the detected value of the NOx sensor 50. In the gradual change control, when the adsorption amount is increased at step S21 or when the adsorption amount is decreased at step S24, the purification rate detected at step S8 is changed at the change at the underside change point R2. The purification rate is R2y. In short, the amount of adsorption in the underrange W2 gradually approaches the underside change point R2 by repeating the increase in step S21, and when the excess side change point R2 is exceeded, the slope of the purification rate is greater than or equal to a predetermined value. It changes to less than a predetermined value. In addition, when the adsorption amount in the appropriate range W1 exceeds the underside change point R2 by repeating the decrease in step S24, the slope of the purification rate changes from less than a predetermined value to more than a predetermined value. The purification rate at this time is detected as the change-time purification rate R2y at the underside change point R2.

  Further, in the gradual change control, when the adsorption amount is decreased in step S22 or when the adsorption amount is increased in step S24, the purification rate detected in step S8 is changed at the excessive change point R3. The purification rate is R3y. In short, when the amount of adsorption in the excessive range W3 exceeds the excessive side change point R3 by repeating the decrease in step S22, the absolute value of the slope of the purification rate changes from a predetermined value to a predetermined value. Further, the adsorption amount in the appropriate range W1 gradually approaches the excess side change point R3 by repeating the increase in step S24, and when the excess amount change point R3 is exceeded, the absolute value of the slope of the purification rate is predetermined. It changes from less than the value to more than the predetermined value. The purification rate at this time point is detected as the change-time purification rate R3y at the excessive side change point R3.

  As described above with reference to FIG. 5, the shape of the characteristic line Ma changes due to deterioration with time of the reduction catalyst. Since this mode of change has a predetermined tendency, the knowledge that the characteristic line Ma can be predicted according to the degree of progress of deterioration if the change purification rates R2y, R3y are known is known. The inventor has gained.

  Specifically, as the deterioration of the reduction catalyst progresses with time, the purification rate at the underside change point R2 decreases, and the amount of adsorption at the underside change point R2 tends to increase. Therefore, if the purification rate at the underside change point R2 (change-time purification rate R2y) is detected, the adsorption amount at the underside change point R2 (adsorption amount during change M2x) can be estimated from the detected value. The coordinates of the change point R2 can be estimated. Further, as the deterioration of the reduction catalyst progresses with time, the purification rate at the excessive change point R3 tends to decrease, and the amount of adsorption at the excessive change point R3 tends to decrease. Therefore, if the purification rate at the excessive change point R3 (change purification rate R3y) is detected, the adsorption amount (adsorption amount M3x at change) at the excessive change point R3 can be estimated from the detected value. The coordinates of the change point R3 can be estimated.

  Furthermore, since the underside change point R2 and the overside change point R3 are highly correlated, the coordinates of the overside change point R3 can be estimated from the coordinates of the underside change point R2 estimated as described above. The underside change point R2 can also be estimated from the overside change point R3. Therefore, if one of the underside change point R2 and the overside change point R3 can be estimated, the shape of the entire characteristic line Ma can also be estimated. That is, based on the detection value of at least one of the purification rate at the underside change point R2 (purification rate during change R2y) and the purification rate at the overside change point R3 (change purification rate R3y), the actual characteristic line Ma shape Can be estimated.

  Based on the above knowledge, in step S9, the estimated adsorption amount estimated in step S1 is corrected as described below. That is, the characteristic map M for the underside corresponding to the purification rate R2y at the time of change at the underside change point R2 and the characteristic map M for the excess side corresponding to the purification rate R3y at the time of change at the excess side change point R3. , Stored in advance in a memory of the ECU 60. The values of these characteristic maps M are set to different values according to the catalyst temperature and the exhaust gas flow rate. More specifically, the higher the catalyst temperature, the smaller the amount of adsorption corresponding to the purification rate. Further, the larger the exhaust gas flow rate, the smaller the adsorption amount corresponding to the purification rate.

  If the purification rate detected in step S8 is the change rate purification rate R2y on the underside, the underside characteristic map M corresponding to the purification rate is acquired from the memory. On the other hand, when the purification rate detected in step S8 is the excessive-side change purification rate R3y, the excessive-side characteristic map M corresponding to the purification rate is acquired from the memory. Then, referring to the acquired characteristic map M, the change-time adsorption amounts M2x and M3x are calculated based on the change-time purification rates R2y and R3y detected in step S8. That is, the adsorption amounts at change M2x and M3x corresponding to the purification rates at change R2y and R3y in the characteristic map M are estimated. Furthermore, the estimated adsorption amounts estimated in step S1 are replaced with the adsorption amounts M2x and M3x at the time of change estimated in this way for correction.

  Accordingly, in the next step S1, the estimated adsorption amount is updated by adding the adsorption amount per unit time to the estimated adsorption amount corrected in step S9. As described above, the amount of adsorption per unit time is calculated by multiplying the value obtained by subtracting the desorption rate, oxidation rate, and reduction rate from the adsorption rate by the length of a predetermined period. In short, by executing the gradual change control and detecting the purification rate R2y, R3y at the time of change, the adsorption amounts M2x, M3x at the time of change based on the characteristic map M can be estimated with high accuracy. Further, by correcting the estimated adsorption amount estimated in step S1 to the change-time adsorption amounts M2x and M3x, the accumulated amount of the estimated adsorption amount estimation error is reset.

  In step S9, the characteristic map M acquired as described above is replaced with the current characteristic map M. The processor 61a when executing the process of step S9 corresponds to the change-time adsorption amount estimation unit described in the claims, and calculates the adsorption amount estimated by step S1 (adsorption amount estimation unit). It also functions as a correction unit for correcting.

  In subsequent step S10, the target adsorption amount used for the addition valve control in step S2 is corrected based on the purification rate detected in step S8. Specifically, the target adsorption amount is decreased as the detected purification rate is smaller. Alternatively, the median value A1 of the appropriate range W1 in the corrected characteristic map M is set as the target adsorption amount. Further, the target adsorption amount is decreased as the catalyst temperature is higher. In subsequent step S11, the target purification rate used for the determination in step S4 is corrected based on the purification rate detected in step S8. Specifically, the target purification rate is decreased as the detected purification rate is smaller.

  In subsequent step S12, the cumulative value of the correction amount with respect to the estimated adsorption amount in step S9 or the cumulative value of the correction amount with respect to the target purification rate in step S11 is calculated as the degree of deterioration. Then, it is determined whether or not the accumulated value is equal to or greater than a predetermined value. If the accumulated value is less than the predetermined value, the process of FIG. 6 is terminated. Set warning flag on. When the warning flag is set to ON, it is considered that the reduction in the purification performance of the reduction catalyst due to sulfur poisoning or the like has progressed beyond the allowable level, and this is notified to the vehicle user by a warning display or warning sound. Inform.

  When the purification device 30 is replaced with a new one or the poisoning component of the existing purification device 30 is removed and the deterioration of the reduction catalyst is recovered, the warning flag is turned off and used for the determination in step S12. Reset the current value of the degradation index purification rate to the initial value. In addition, the processor 61a at the time of performing the process of step S12 is corresponded to the abnormality determination part as described in a claim.

  As described above, according to the present embodiment, the gradual change control unit in step S7, the change index detection unit in step S8, and the change adsorption amount estimation unit in step S9 are provided. The gradual change control unit controls the operation of the addition valve 20 so as to gradually change the addition amount of the reducing agent. The change index detection unit is a change index that is a purification index when the amount of change in the purification index caused by the change in the addition amount due to the gradual change control changes by a predetermined amount or more, that is, the change purification rates R2y and R3y. It detects based on the detection value by the sensor 50 (detection apparatus). The change adsorption amount estimation unit estimates the change adsorption amounts M2x and M3x based on the change purification rates R2y and R3y detected by the change index detection unit.

  Here, the change purification rates R2y and R3y have a high correlation with the actual characteristic line Ma. Therefore, if the change purification rates R2y and R3y can be grasped, the adsorption amount at that time (change adsorption amount) can be grasped with high accuracy. In this embodiment focusing on this point, the gradual change control is executed to detect the on-change purification rates R2y and R3y, and the on-change adsorption amounts M2x and M3x are estimated based on the detected on-change purification rates R2y and R3y. .

  For this reason, the adsorption amounts M2x and M3x at the time of change can be estimated with high accuracy. In particular, even when the characteristic line Ma changes as the purification device 30 deteriorates over time, the adsorption amounts M2x and M3x at the time of change can be estimated with high accuracy. Moreover, since the on-change purification rates R2y and R3y used for the correction can be calculated by gradually changing the addition amount, it is possible to change while eliminating the need to control the adsorption amount to be zero (known amount). Estimation of the hourly adsorption amounts M2x and M3x (known amounts) can be realized.

  Furthermore, in this embodiment, the adsorption amount estimation part by step S1 is provided. The adsorption amount estimation unit estimates the adsorption amount during the execution stop period of the gradual change control based on the addition amount of the reducing agent from the addition valve 20, the catalyst temperature, and the adsorption amounts M2x and M3x at the time of change. Specifically, in the sequential estimation, the adsorption amount is estimated based on the reducing agent addition amount, the catalyst temperature, etc. without using the change-time adsorption amounts M2x and M3x. The estimated adsorption amount is corrected to the known adsorption amounts which are the adsorption amounts M2x and M3x. Here, contrary to the present embodiment, when the adsorption amount is estimated from the addition amount of the reducing agent and the catalyst temperature without using the adsorption amounts M2x and M3x at the time of change, the estimation error is accumulated and sufficient estimation is performed. There is a concern that accuracy cannot be secured. On the other hand, in this embodiment, since the adsorption amount is estimated using the adsorption amounts M2x and M3x at the time of change in addition to the addition amount and the catalyst temperature, the above concerns can be suppressed.

  Furthermore, in this embodiment, the addition valve control unit in step S2 and the target adsorption amount setting unit in step S10 are provided, and the addition valve control unit is configured so that the adsorption amount estimated by the adsorption amount estimation unit becomes the target adsorption amount. The operation of the addition valve 20 is controlled. The target adsorption amount setting unit sets the target adsorption amount to a value in a range narrower than the appropriate range W1.

  Here, if the catalyst temperature or the exhaust gas flow rate changes, the appropriate range W1 also changes. Therefore, contrary to the above setting, when the adsorption amount at the boundary between the underrange W2 or the excess range W3 and the appropriate range W1 is set to the target adsorption amount, the actual adsorption is performed only by slightly changing the catalyst temperature or the exhaust flow rate. There is concern that the amount deviates from the appropriate range W1. On the other hand, in this embodiment, since the target adsorption amount is set to a value in a range narrower than the appropriate range W1 as described above, the above concern can be suppressed. In particular, in this embodiment, since the median value A1 of the appropriate range W1 is set as the target adsorption amount, the above concerns can be further suppressed.

  Furthermore, in the present embodiment, a range identifying unit is provided in step S5 that identifies whether the current adsorption amount is the appropriate range W1, the under range W2, or the over range W3. Then, the gradual change control unit in step S7 gradually increases and changes the addition amount in step S21 when the range identification unit identifies the underrange W2, and in the case where it is identified as the excessive range W3. In step S22, the addition amount is gradually decreased. Further, the change amount adsorption amount estimation unit in step S9 determines whether the change amount adsorption amounts M2x and M3x are increased or decreased when estimating the change amount adsorption amounts M2x and M3x based on the correlation with the change purification rates R2y and R3y. Differentiate the correlation. Specifically, the adsorption amounts M2x and M3x at the time of change are estimated by using different characteristic maps M for the time of increase change and for the decrease change time.

  Here, as described above, the on-change purification rate R2y of the under-side change point R2 has a correlation with the characteristic line Ma, and the on-change purification rate R3y of the over-side change point R3 has a correlation with the characteristic line Ma. However, in the portion of the characteristic line Ma in the underrange W2, the change purification rate R2y has a higher correlation than the change purification rate R3y. Further, in the characteristic line Ma, in the excessive range W3, the change purification rate R3y has a higher correlation than the change purification rate R2y. In the present embodiment in view of this point, as described above, when the change purification rate R2y is calculated from the increase change and when the change purification rate R3y is calculated from the decrease change, the change adsorption amounts M2x and M3x Different correlations are used for estimation. Therefore, it is possible to estimate using the purification rate having a high correlation among the two types of change purification rates R2y and R3y, and the estimation accuracy of the change adsorption amounts M2x and M3x can be improved.

  Further, in the present embodiment, the gradual change control unit in step S7 executes gradual change control on the condition that the purification index detected based on the detection value by the NOx sensor 50 (detection device) is less than the target index. For example, if it is not determined in step S4 that the purification index is less than the target index, the gradual change control in step S7 is not executed. Here, if the purification index is greater than or equal to the target index, there is a high probability that the actual adsorption amount can be controlled within the appropriate range W1, and the need for correction is low. In this embodiment in view of this point, since the gradual change control is executed on condition that the purification index is less than the target index, it is possible to suppress the gradual change control from being executed more than necessary.

  Further, in the present embodiment, the gradual change control unit in step S7 gradually changes on the condition that the change amount per unit time is a steady state that is less than a predetermined amount for at least one of the catalyst temperature and the exhaust gas flow rate. Execute control. For example, if it is not determined in step S6 that both the catalyst temperature and the exhaust gas flow rate are in the steady state, the gradual change control in step S7 is not executed. Here, the correlation between the change purification rates R2y, R3y and the characteristic line Ma varies depending on the catalyst temperature and the exhaust gas flow rate. For this reason, if the characteristic map M is corrected by executing the gradual change control during a transition in which the catalyst temperature or the exhaust gas flow rate is changing, there is a concern that the correction accuracy may deteriorate. In the present embodiment in view of this point, since the gradual change control is executed on the condition that it is in a steady state, the above-mentioned concern can be suppressed.

  Further, in the present embodiment, in consideration of the fact that the correlation varies depending on the catalyst temperature and the exhaust gas flow rate, the change amount adsorption amount estimation unit in step S9 determines the catalyst temperature and the exhaust gas flow rate when performing the gradual change control. The adsorption amounts M2x and M3x at the time of change are estimated according to at least one. Therefore, the estimation accuracy of the adsorption amounts M2x and M3x at the time of change can be improved.

  Furthermore, in this embodiment, the effect that the deterioration degree can be estimated with high accuracy based on the purification rates R2y and R3y during change detected by the gradual change control or the adsorption amounts M2x and M3x during change is exhibited. By using this, it is determined whether or not the purification capacity is abnormally low. Specifically, the deviation of the current value from the initial value of the change purification rates R2y, R3y or the change adsorption amounts M2x, M3x is calculated. And when the calculated deviation value is greater than or equal to a predetermined value, an abnormality determination unit in step S12 is provided that determines that the NOx purification device 30 is in an abnormal state in which the purification ability is abnormally low. As described above, according to the present embodiment, the degree of deterioration can be estimated with high accuracy. Therefore, it is possible to determine with high accuracy whether or not the state is abnormal using the estimation result.

  Further, in the present embodiment, the predetermined amount ΔM2 for increasing the adsorption amount by gradual change control is variably set according to the catalyst temperature and the exhaust gas flow rate. Specifically, the predetermined amount ΔM2 to be increased is decreased as the catalyst temperature is higher and the exhaust gas flow rate is higher. As the catalyst temperature is higher and the exhaust gas flow rate is higher, the slope of the characteristic line Ma in the underrange W2 becomes larger. Therefore, the point that greatly exceeds the actual underside change point R2 to the appropriate range W1 side is the underside change point. Can be suppressed by reducing the predetermined amount ΔM2. Therefore, the detection accuracy of the on-change purification rate R2y can be improved, and as a result, the estimation accuracy of the on-change adsorption amount M2x can be improved.

  Further, in the present embodiment, the predetermined amount ΔM3 for decreasing the adsorption amount by the gradual change control is variably set according to the catalyst temperature and the exhaust gas flow rate. Specifically, the predetermined amount ΔM3 to be reduced is reduced as the catalyst temperature is higher and the exhaust gas flow rate is higher. Since the absolute value of the slope of the characteristic line Ma in the excessive range W3 increases as the catalyst temperature is higher and the exhaust gas flow rate is higher, a point that greatly exceeds the actual excessive side change point R3 to the appropriate range W1 side is set as the excessive side change point. Detection can be suppressed by reducing the predetermined amount ΔM2. Therefore, the detection accuracy of the on-change purification rate R3y can be improved, and as a result, the estimation accuracy of the on-change adsorption amount M3x can be improved.

(Second Embodiment)
In the gradual change control according to the first embodiment, the adsorption amount is changed in one direction, and the purification rate when the change amount of the purification index changes by a predetermined amount or more is detected as the on-change purification rates R2y and R3y. Yes. In contrast, in this embodiment, the amount of adsorption is changed in one direction, the amount of change in the purification index is changed by a predetermined amount or more, and then the amount of adsorption is changed in the reverse direction. The purification rates when the change amount changes by a predetermined amount or more are detected as the change-time purification rates R2y and R3y.

  For example, when it is identified as the underrange W2 in step S5, the gradual change control is executed as follows. First, as shown in FIG. 8, control (first gradual change control) is performed in which the adsorption amount is increased by a predetermined amount ΔM21 from the under range W2 to the appropriate range W1. The first gradual change control is ended when the purification rate change amount changes by a predetermined amount or more due to exceeding the underside change point R2 toward the appropriate range W1 by the first gradual change control. Thereafter, control (second gradual change control) is performed in which the adsorption amount is decreased by a predetermined amount ΔM22 from the appropriate range W1 toward the underrange W2.

  The second gradual change control is terminated when the purification rate change amount changes by a predetermined amount or more due to exceeding the underside change point R2 toward the underrange W2 by the second gradual change control. And the purification rate at the time of complete | finishing 2nd gradual change control is detected as purification rate R2y at the time of a change. The predetermined amount ΔM21 that is increased by the first gradual change control is set larger than the predetermined amount ΔM22 that is decreased by the second gradual change control.

  For example, when the excessive range W3 is identified in step S5, the gradual change control is executed as follows. First, as shown in FIG. 8, a control (first gradual change control) is performed in which the adsorption amount is decreased by a predetermined amount ΔM31 from the excessive range W3 to the appropriate range W1. The first gradual change control is terminated when the purification rate change amount changes by a predetermined amount or more due to exceeding the excessive side change point R3 toward the appropriate range W1 by the first gradual change control. Thereafter, control (second gradual change control) is performed in which the adsorption amount is increased by a predetermined amount ΔM32 from the appropriate range W1 to the excessive range W3. The second gradual change control ends when the purification rate change amount changes by a predetermined amount or more due to exceeding the excessive side change point R3 toward the excessive range W3 by the second gradual change control. And the purification rate at the time of complete | finishing 2nd gradual change control is detected as the purification rate R3y at the time of a change. The predetermined amount ΔM31 that is decreased by the first gradual change control is set to be larger than the predetermined amount ΔM32 that is increased by the second gradual change control.

  For example, if the appropriate range W1 is identified in step S5, the gradual change control is executed as follows. First, control (first gradual change control) is performed in which the adsorption amount is changed by a predetermined amount from the appropriate range W1 toward the underrange W2 or the overrange W3. The first gradual change control is terminated when the purification rate change amount changes by a predetermined amount or more due to exceeding the change points R2 and R3 from the appropriate range W1 side by the first gradual change control. Thereafter, control (second gradual change control) is performed in which the adsorption amount is changed by a predetermined amount from the underrange W2 or the overrange W3 toward the appropriate range W1. The second gradual change control is terminated when the purification rate change amount changes by a predetermined amount or more due to exceeding the change points R2 and R3 by the second gradual change control. And the purification rate at the time of complete | finishing 2nd gradual change control is detected as change purification rate R2y and R3y. The predetermined amount that is changed by the first gradual change control is set larger than the predetermined amount that is changed by the second gradual change control.

  The first gradual change control and the second gradual change control described above are realized by being repeatedly executed at a predetermined cycle by the processor 61a according to the processing procedure shown in FIG. 9, and the processor when executing the processing of FIG. 61a corresponds to the gradual change control unit described in the claims. In the process of FIG. 9, the processes of steps S26 and S27 are added to the process of FIG. 7 according to the first embodiment.

  Steps S20 to S25 in FIG. 9 are the same processes as in FIG. 7, and the control when the adsorption amount is increased or decreased by a predetermined amount in steps S21, S22, and S24 is the first gradual change control described above. Equivalent to. Then, when an affirmative determination is made in steps S23 and S25, the first gradual change control is terminated, and in the subsequent step S26, the aforementioned second gradual change control is executed. In step S26, the increase or decrease in the first gradual change control is reversed, and the adsorption amount is further changed by a predetermined amount.

  Specifically, when the second gradual change control is executed after increasing by the predetermined amount ΔM21 in step S21, the amount is decreased by the predetermined amount ΔM22 in step S26. When the second gradual change control is executed after the amount is decreased by the predetermined amount ΔM31 in step S22, the amount is increased by the predetermined amount ΔM32 in step S26. In the case where the second gradual change control is executed after being increased by a predetermined amount in step S24, the second gradual change control is executed after being decreased by a predetermined amount in step S26 and decreased by the predetermined amount in step S24. In step S26, the amount is increased by a predetermined amount.

  As described above, according to the present embodiment, the gradual change control unit executes the first gradual change control for increasing or decreasing the addition amount of the reducing agent by a predetermined amount until the change amount of the purification index changes by a predetermined amount or more. To do. Thereafter, the second gradual change control is executed in which the increase and decrease in the first gradual change control is reversed to increase or decrease the addition amount by a predetermined amount. Then, the change index detection unit detects, as the change index, the purification index when the amount of change in the purification index that occurs due to the change in the addition amount by the second gradual change control changes by a predetermined amount or more. According to this, in addition to the first gradual change control, the second gradual change control in which the increase / decrease direction is changed is executed, so that it is possible to reduce the fear of failing to detect the change time index, and the certainty of detection of the change time index. Can be improved.

  Further, in the present embodiment, the predetermined amounts ΔM21 and ΔM31 that are increased or decreased by the first gradual change control are set larger than the predetermined amounts ΔM22 and ΔM32 that are increased or decreased by the second gradual change control. Therefore, it is possible to detect the change index with high accuracy and complete the gradual change control required for the detection in a short time.

(Other embodiments)
The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made as illustrated below. Not only combinations of parts that clearly show that combinations are possible in each embodiment, but also combinations of the embodiments even if they are not explicitly stated unless there is a problem with the combination. Is also possible.

  In the gradual change control shown in FIG. 4, when the adsorption amount is gradually changed, the amount is increased or decreased by the same amount. On the other hand, the predetermined amount ΔM2 to be increased or the predetermined amount ΔM3 to be decreased may be gradually increased or decreased. Similarly, in the gradual change control shown in FIG. 8, the predetermined amounts ΔM21, ΔM32 to be increased or the predetermined amounts ΔM22, ΔM31 to be decreased may be gradually increased or decreased.

  In step S12 of FIG. 6, the cumulative value of the correction amount in step S9 is calculated as the degree of deterioration, but the purification rate in the characteristic map M corresponding to the predetermined adsorption amount is set as the deterioration index purification rate, and the deterioration index. The deviation between the current value of the purification rate and the initial value may be calculated as the degree of deterioration. As a specific example of the deterioration index purification rate, the purification rate at the excessive change point R2, the purification rate at the excessive change point R3, and the median value A1 of the appropriate range W1 in the characteristic map M corrected in step S9. The purification rate at

  In the example shown in FIG. 7, the gradual change control is performed so as to detect one of the underside change point R2 and the overside change point R3, and the estimated adsorption amount is corrected based on the purification rate related to the detected one change point. Yes. In contrast, the gradual change control may be performed so as to detect both the underside change point R2 and the overside change point R3, and the estimated adsorption amount may be corrected based on both of the detected change purification rates R2y and R3y. .

  For example, when it is identified as the excessive range W2, the adsorption amount is increased toward the appropriate range W1, and after the change purification rate R2y is acquired, the adsorption amount is increased toward the excessive range W3 side. The change purification rate R3y is also acquired. The change amount of adsorption M3x corresponding to the change time purification rate R3y may be corrected based on the change time purification rate R2y.

  For example, when the excessive range W3 is identified, the adsorption amount is decreased toward the appropriate range W1, and after the change purification rate R3y is acquired, the adsorption amount is decreased toward the under range W2 side. The change purification rate R2y is also acquired. The change amount of adsorption M2x corresponding to the change time purification rate R2y may be corrected based on the change time purification rate R3y.

  In the example illustrated in FIG. 1, the adsorption amount estimation device (ECU 60) is applied to the purification system including the oxidation device 40, but the adsorption amount estimation device is also applicable to a purification system that does not include the oxidation device 40. . Further, the adsorption amount estimation device is applicable not only to a purification system that adds urea water to the exhaust passage 11a but also to a purification system that adds fuel (hydrocarbon compound) used for combustion of the internal combustion engine 10 to the exhaust passage 11a. is there.

  In the gradual change control shown in FIGS. 7 and 9, even when the appropriate range W1 is identified, the amount of adsorption is gradually changed in step S24 to detect the change purification rate. On the other hand, when it is identified as the appropriate range W1, the gradual change control is prohibited, and when it is identified as the underrange W2 or the overrange W3, the adsorption amount is gradually changed to change the purification rate at the time of change. May be detected.

  Steps S1, S2, and S3 shown in FIG. 6 may be eliminated. In this case, the estimated adsorption amounts M2x and M3x at the time of change are not used for correcting the value of the adsorption amount estimated sequentially, but are used for the abnormal state determination in step S12.

  Means and / or functions provided by the control device of the ECU 60 can be provided by software recorded in a substantial storage medium and a computer that executes the software, only software, only hardware, or a combination thereof. For example, if the controller is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a number of logic circuits, or an analog circuit.

  20 ... Addition valve, 30 ... NOx purification device, 50 ... NOx sensor (detection device), 60 ... ECU (adsorption amount estimation device), M2x, M3x ... Adsorption amount during change, R2y, R3y ... Purification rate during change (during change) Index), S7: gradual change control unit, S8: change index detection unit, S9: change adsorption amount estimation unit.

Claims (10)

A purification device (30) having a catalyst for reducing and purifying NOx contained in the exhaust gas of the internal combustion engine (10), and a reducing agent added to the upstream side of the purification device in the exhaust passage (11a) of the internal combustion engine And an addition valve (20) that is disposed downstream of the purification device in the exhaust passage and a detection device (50) that detects at least one of the amount of NOx and the amount of reducing agent. In the adsorption amount estimation device for estimating the adsorption amount of the reducing agent to the purification device,
A gradual change control unit (S7) for executing a gradual change control for controlling the operation of the addition valve so as to gradually change the addition amount of the reducing agent;
The purification index when the amount of change (ΔR) of the purification index that occurs each time the addition amount is gradually changed by the gradual change control is changed by a predetermined amount or more, and the purification index when the purification performance by the purification device is used as the purification index. A change time index detection unit (S8) for detecting a change time index based on a detection value by the detection device, and a change time index (R2y, R3y);
Based on the change time index detected by the change time index detection unit, a change time adsorption amount estimation unit that estimates an adsorption amount at change (M2x, M3x) that is an adsorption amount when the change time index is detected. (S9).   An adsorption amount estimation unit that estimates an adsorption amount during an execution stop period of the gradual change control based on the addition amount of the reducing agent from the addition valve, the temperature of the catalyst, and the adsorption amount estimated by the adsorption amount estimation unit during change The adsorption amount estimation apparatus according to claim 1, comprising (S1). An addition valve control unit (S2) for controlling the operation of the addition valve so that the adsorption amount estimated by the adsorption amount estimation unit becomes a target adsorption amount;
The range of the adsorption amount in which the amount of change is less than a predetermined value, the range having the upper limit or the lower limit of the adsorption amount at the time of change as an appropriate range (W1), and the target adsorption to a value in a range narrower than the appropriate range A target adsorption amount setting unit (S10) for setting the amount;
The adsorption amount estimation apparatus according to claim 2, comprising: The range of the adsorption amount in which the amount of change is less than a predetermined range, the range having the upper limit or the lower limit of the adsorption amount at the time of change as an appropriate range (W1), and the range of the adsorption amount on the side smaller than the appropriate range Is the excessive range (W2), the adsorption amount range on the side larger than the appropriate range is the excessive range (W3), and the current adsorption amount is any of the appropriate range, the underrange and the excessive range. A range identification unit (S5) for identifying
The gradual change control unit gradually increases and changes the amount of addition when the range identifying unit identifies the excessive range, and when the range identifying unit identifies the excessive range, The amount added is gradually decreased and changed
The change-time adsorption amount estimation unit estimates the change-time adsorption amount based on the correlation with the change-time index by estimating the correlation between the increase change and the decrease change. The adsorption amount estimation apparatus according to claim 2 or 3.   The said gradual change control part performs the said gradual change control on condition that the said purification | cleaning parameter | index detected based on the detected value by the said detection apparatus is less than a target parameter | index. Adsorption amount estimation device. The gradual change control unit executes the gradual change control on the condition that at least one of the temperature of the catalyst and the exhaust gas flow rate is a steady state in which a change amount per unit time is less than a predetermined amount. The adsorption amount estimation apparatus according to any one of Items 1 to 5.

The gradual change control unit executes the gradual change control on the condition that at least one of the temperature of the catalyst and the exhaust gas flow rate is a steady state in which a change amount per unit time is less than a predetermined amount. The adsorption amount estimation apparatus according to any one of Items 1 to 5.   The change-time adsorption amount estimation unit estimates the change-time adsorption amount according to at least one of a temperature of the catalyst and an exhaust flow rate when the gradual change control is executed. The adsorption amount estimation apparatus according to one.   An abnormality determination unit that determines that the purification device is in an abnormal state in which the purification capability of the purification device is abnormally low when the deviation of the current value from the change time index or the initial value of the adsorption amount at the time of change is a predetermined value or more. The adsorption amount estimation apparatus according to any one of claims 1 to 7, comprising (S12). The gradual change control includes a first gradual change control in which the amount of addition of the reducing agent is increased or decreased by a predetermined amount until the change amount changes by a predetermined amount or more, and after the gradual change control. A second gradual change control in which the addition amount is changed by a predetermined amount in a direction opposite to the first gradual change control,
The change index detection unit detects, as the change index, the purification index when the amount of change in the purification index that occurs each time the addition amount is gradually changed by the second gradual change control changes by a predetermined amount or more. The adsorption amount estimation apparatus according to any one of claims 1 to 8.   The adsorption amount estimation apparatus according to claim 9, wherein the predetermined amount that is increased or decreased by the first gradual change control is set larger than the predetermined amount that is increased or decreased by the second gradual change control.

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