JP6631469B2 - Adsorption amount estimation device - Google Patents

Description

  The present invention relates to an adsorption amount estimating device for estimating the amount of a reducing agent adsorbed on a purification device.

  A purification device disposed in an exhaust passage of the internal combustion engine; and an addition valve for adding a reducing agent upstream of the purification device in the exhaust passage, wherein NOx in the exhaust gas is reduced by a reducing agent on a catalyst of the purification device. 2. Description of the Related Art A purification system for reducing and purifying has been conventionally known (see Patent Document 1). Most of the added reducing agent is adsorbed on the catalyst, and then chemically reacts with NOx in the exhaust gas on the catalyst to reduce NOx.

  If the amount of adsorption of the reducing agent is too small relative to the amount of NOx flowing into the purification device, the amount of NOx that passes through the purification device without being reduced (NOx slip amount) increases. On the other hand, if the adsorption amount of the reducing agent is excessive, the amount of the reducing agent flowing out of the purification device (the amount of the reducing agent slip) increases. In order to reduce these slip amounts, it is necessary to control the supply amount of the reducing agent so that the amount of adsorption of the reducing agent is in 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 addition of the reducing agent may be controlled so that the estimated amount of adsorption falls within an appropriate range. Then, the estimation errors are accumulated, and it becomes impossible to secure sufficient estimation accuracy. To cope with this problem, the adsorption amount estimating apparatus described in Patent Document 1 resets the estimation error by forcibly stopping the addition of the reducing agent so that the actual adsorption amount matches a known amount (zero). , Etc. are periodically executed.

US Patent Application Publication No. 2005/0282285

  However, during the execution period of the above-described calibration control, the adsorption amount becomes too small or zero, so that the NOx slip amount 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 estimating apparatus capable of estimating 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. The reference numerals in the claims and parentheses in this section indicate the correspondence with specific means described in the embodiments described later, and do not limit the technical scope of the invention. .

The disclosed invention is
A purifying 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 an exhaust passage (11a) of the internal combustion engine upstream of the purifying device. The present invention is applied to a purification system including a valve (20) and a detection device (50) that is disposed downstream of the purification device in the exhaust passage and detects at least one of the NOx amount and the reducing agent amount. In the adsorption amount estimating device for estimating the adsorption amount of the agent,
A gradual change control unit (S7) for performing 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 device is defined as a purification index, and a purification index when the amount of change (ΔR) of the purification index that changes every time the addition amount is gradually changed by the gradual change control changes by a predetermined amount or more is a change index ( R2y, R3y), a change index detection unit (S8) for detecting a change index based on a value detected by the detection device;
A change-time adsorption amount estimating unit (S9) for estimating a change-time adsorption amount (M2x, M3x) that 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. When,
It is an adsorption amount estimating device provided with:

  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 index of time (index of change) has a high correlation 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-described invention, the change-time index is detected by executing the gradual change control, and the change-time adsorption amount is estimated based on the detected change-time index. become able to. Moreover, since the change index used for the estimation can be calculated by gradually changing the addition amount, it is unnecessary to control to force the adsorption amount to zero (known amount), and the change adsorption amount ( (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. FIG. 4 is a schematic diagram showing an internal state of the NOx purification device when a NOx slip has occurred. FIG. 3 is a schematic diagram showing an internal state of the NOx purification device when a reducing agent slip has occurred. The figure which shows the characteristic line showing the relationship between the adsorption amount and the purification rate. The figure which shows an example of a state change of the characteristic line showing the relationship between the adsorption amount and the purification rate. 5 is a flowchart illustrating a procedure of a process executed by a processor of the adsorption amount estimation device according to the first embodiment. 7 is a flowchart showing a processing procedure of the gradual change control shown in FIG. 6. FIG. 7 is a diagram illustrating a characteristic line representing a relationship between an adsorption amount and a purification rate, and is a diagram illustrating an outline of a gradual change control according to a second embodiment of the present invention. 9 is a flowchart illustrating a procedure of a process executed by a processor of the adsorption amount estimation device according to the second embodiment.

  Hereinafter, a plurality of embodiments for carrying out the invention will be described with reference to the drawings. In each embodiment, portions corresponding to the items described in the preceding embodiment are 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 part of the configuration can be applied with reference to the other embodiments described earlier.

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

  The NOx purifying device 30 includes a carrier 31 having a selective reduction type reduction catalyst, and a case that holds the carrier 31 inside and is connected to the exhaust pipe 11. This reduction catalyst has a reduction function of accelerating a reaction of the reducing agent to reduce NOx and an adsorption function of adsorbing the reducing agent, and specific examples of the reduction catalyst include zeolite.

  The addition valve 20 adds urea water to the exhaust passage 11a on the upstream side of the NOx purification device 30. 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 an injection 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 the energization of the electromagnetic coil 22 is started, the valve body 21 operates to open the valve, urea water is injected from the injection hole, and urea water is added to the exhaust passage 11a. When the energization of the electromagnetic coil 22 ends, the valve body 21 operates to close the valve, and the addition of the urea water to the exhaust passage 11a ends.

  The urea water added to the exhaust passage 11a is heated and hydrolyzed in a path 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 on the reduction catalyst of the carrier 31, as shown in FIGS. Thereafter, NOx contained in the exhaust gas is chemically reacted with NOx on 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 device 40 includes a carrier having an oxidation catalyst, and a case that holds the carrier inside and is connected to the exhaust pipe 11. Among the ammonia supplied to the NOx purification device 30, the ammonia flowing 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 amount of NOx and the amount of ammonia contained in the exhaust gas. Specifically, the NOx sensor 50 outputs a signal of a voltage value corresponding to the NOx concentration in the exhaust to the electronic control unit (ECU 60). The NOx sensor 50 also outputs a signal in response to the ammonia in the exhaust gas, and detects both the ammonia amount (reducing agent amount) and the NOx amount. Note that the NOx sensor 50 corresponds to a 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 above 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 is input to the ECU 60. Further, a signal including information indicating an operation state of the internal combustion engine 10, such as a rotation speed of an output shaft of the internal combustion engine 10, a load of the internal combustion engine 10, an exhaust temperature, and the like, is input to the ECU 60. The ECU 60 controls the energization state of the electromagnetic coil 22 based on these signals, thereby controlling the opening and closing operation of the valve body 21 to control 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 above-mentioned 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 adsorbed amount) is controlled.

  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 purification device 30 is NOx. The temperature of the reduction catalyst is defined as the catalyst temperature. The NOx inflow amount is estimated by the microcomputer 61 based on the above-described rotation speed, load, and the like. The catalyst temperature is estimated by the microcomputer 61 based on the above-described exhaust gas temperature and the like. The method of calculating the target adsorption amount and the estimated adsorption amount will be described later in detail with reference to FIG.

  The microcomputer 61 sets a 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 the symbol A in FIG. 2 increases. On the other hand, if the amount of the reducing agent added to the current amount of adsorption is excessive, the amount of the reducing agent that passes through the NOx purification device 30 without being adsorbed, that is, the amount of the reducing agent slip indicated by reference symbol B in FIG. 3 increases. Therefore, it is required to control the supply amount of the reducing agent so that the amount of the adsorbed reducing agent 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 referred to here is a ratio of the detection value of the NOx sensor 50 to the NOx inflow amount, and corresponds to a purification index indicating 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 purification rate decreases as the NOx slip amount increases, and the purification rate decreases as the reducing agent slip amount increases. That is, when both the NOx slip amount and the reducing agent slip amount decrease, the purification rate shown on the vertical axis in FIG. 4 increases.

  Estimating the purification rate based on the detection value of the NOx sensor 50 can be more accurately estimated than estimating the adsorption amount of the reducing agent to the reduction catalyst based on the detection value of the NOx sensor 50. Then, 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 amount of adsorption and the purification rate as correlation information. For example, a specific example of the correlation information is a characteristic map M (see FIG. 4) indicating the value of the adsorption amount with respect to the purification rate, or a mathematical expression representing the adsorption amount with the purification rate as a variable. In the example of FIG. 4, the value of the characteristic line Ma matches the value of the characteristic map M.

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

  The ECU 60 calculates the purification rate based on the detection 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 estimating 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 underrange W3 is referred to as the change point. This is referred to as an excessive change point R3. Further, the purification rates at these change points correspond to the change time index.

  The correlation between the adsorption amount and the purification rate, that is, the characteristic line Ma changes according to the aging of the NOx purification device 30, the poisoning state of the reduction catalyst, and 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 in FIG. 5, the actual characteristic line Ma changes as shown by the solid line, and the characteristic map M And the characteristic line Ma do not coincide with each other, and the accuracy of estimating the amount of adsorption decreases. Therefore, in the present embodiment, the characteristic map M stored in the ECU 60 is corrected so as to be closer to 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 the reducing agent adsorbed on the reduction catalyst (hereinafter referred to as the adsorbed amount) is estimated as follows. The processor 61a when executing the process of step S1 corresponds to an adsorption amount estimating unit described in the claims. In this estimation process, first, an adsorption speed, a desorption speed, an oxidation speed, and a reduction speed described below are calculated.

  The adsorption speed is a rate at which the amount of adsorption generated by the reduction agent being adsorbed by the reduction catalyst is increased, and is calculated using the previous value of the amount of urea water added, the hydrolysis ratio, the catalyst temperature, and the exhaust gas flow rate as parameters. In general, the larger the values of these parameters, the larger the adsorption speed is calculated. For example, a suction speed corresponding to these parameters is mapped and stored in advance, and the suction speed is calculated by referring 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 of ammonia (a reducing agent) generated by hydrolysis of the added urea water, and is calculated based on the exhaust gas temperature. The exhaust gas temperature may be detected by an unillustrated exhaust gas temperature sensor or may be estimated based on the operating state of the internal combustion engine. The catalyst temperature is estimated based on the exhaust gas 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 flow rate per unit volume. The exhaust flow rate defined in this way is estimated based on the operating state of the internal combustion engine.

  The desorption speed is a rate of decrease in the amount of adsorption caused by the desorption of the reducing agent adsorbed on the reduction catalyst from the reduction catalyst, and is calculated using the previous value of the estimated adsorption amount and the catalyst temperature as parameters. The desorption speed is generally calculated to be a larger value as the values of these parameters are larger. For example, desorption velocities corresponding to these parameters are mapped and stored in advance, and the desorption velocities are calculated with reference to the map based on these parameters.

  The oxidation rate is a rate at which the reducing agent adsorbed on the reduction catalyst is oxidized by oxygen in the exhaust gas without reducing NOx, and the amount of adsorption is reduced. The temperature and the exhaust flow rate are calculated as parameters. Generally, the larger the values of these parameters, the larger the oxidation rate is calculated. For example, the oxidation rate corresponding to these parameters is mapped and stored in advance, and the oxidation rate is calculated based on these parameters with reference to the map.

The reduction rate is a rate at which the amount of adsorption is reduced by the reduction agent adsorbed on the reduction catalyst reducing NOx, and is the previous value of the estimated amount of adsorption, the catalyst temperature, the exhaust gas flow rate, NOx inflow, and is calculated _NO 2 / NO ratio as a parameter. NOx inflow amount and _NO 2 / NO ratio is estimated based on the operating state of the internal combustion engine. In general, the larger the values of these parameters, the larger the reduction rate is calculated. For example, the reduction speed corresponding to these parameters is mapped and stored in advance, and the reduction speed is calculated by referring to the map based on these parameters.

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

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

  In the following step S3, it is determined whether or not the estimated amount of adsorption estimated in step S1 matches the target amount of adsorption. 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 the values match. If it is determined that they match, the process proceeds to step S4.

  In the next step S4, the purification rate described with reference to 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 into the purification device 30. Then, the ratio of the NOx purification amount to the NOx inflow amount is calculated as the purification ratio. In addition, even when the NOx sensor 50 detects the reducing agent slip amount, the NOx slip amount is replaced with the reducing agent slip amount, and the purification rate is similarly calculated.

  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, the error of the estimated amount of adsorption with respect to the actual amount of adsorption is checked by the purification rate. That is, as shown by the characteristic line Ma in FIG. 4, if the actual amount of adsorption matches the target amount of adsorption, there is a high probability that a sufficient purification rate can be obtained. Therefore, when the purification rate is not less than the target purification rate even though the estimated adsorption amount matches the target adsorption amount, 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. If it is determined in step S4 that the detected purification rate is not less than the target purification rate, the processes in steps S1 to S3 are continued until the purification rate becomes less than the target purification rate, and the processing is less than the target purification rate. If the determination is made, the process proceeds to step S5.

  In the next step S5, it is determined whether the current adsorption amount falls into any of the appropriate range W1, the underrange W2, and the overrange W3. Specifically, the operation of the addition valve 20 is controlled such that the addition amount is increased by a predetermined amount with respect to the target adsorption amount set in step S2, and then the addition amount is reduced by a predetermined amount (dither control). I do. These increase and decrease are performed for a predetermined time (for example, several seconds). Then, the above identification is performed based on a change in the detection value of the NOx sensor 50 caused by changing the adsorption amount by executing the dither control. Note that the processor 61a when executing the processing of step S5 corresponds to a range identification 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 the execution of the dither control, the purification rate based on the detection value of the NOx sensor 50 should hardly change. is there. Further, when the actual adsorption amount exists in the under-range W2, the purification rate should decrease with the decrease in dither control, and should not change depending on the increase. If the actual adsorption amount exists in the excessive range W3, the purification rate should decrease with the increase in the dither control, and the purification rate should not change depending on the decrease. As described above, the above-described identification is performed by detecting how the purification rate changes with the execution of the dither control.

  In the following step S6, it is determined whether or not both the catalyst temperature and the exhaust 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 per unit time is less than a predetermined threshold, the exhaust flow is considered to be in a steady state. When it is determined that the state is not the steady state, the processing in FIG. 6 is terminated without executing the processing in step S7 and subsequent steps. If it is determined that the vehicle is in the steady state, the process proceeds to step S7.

  In the next step S7, the operation of the addition valve 20 is controlled (gradual change control) so as to gradually change the addition amount of the reducing agent by executing a subroutine process shown in FIG. In the subsequent step S8, the change-time purification rates R2y and R3y (see FIG. 5), which are the purification rates when the amount of change in 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 by the NOx sensor 50. Is detected based on the detection value of 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 process of the gradual change control shown in FIG. 7, first, in step S20, the identification result by the dither control in step S5 is obtained. If it is determined that the range is too small, in step S21, the operation of the addition valve 20 is controlled to increase the current adsorption amount by a predetermined amount ΔM2 (see FIG. 4), 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, as the catalyst temperature is higher and the exhaust gas flow rate is higher, the predetermined amount ΔM2 to be increased is reduced.

  If it is determined that the excess range W3 is detected, in step S22, the operation of the addition valve 20 is controlled so that the current adsorption amount is reduced 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 higher the catalyst temperature and the larger the exhaust flow rate, the smaller the predetermined amount ΔM3 to be reduced.

  In the following 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 detection value should be sharply smaller than the previous purification rate change amount ΔR. Therefore, when the purification rate change amount ΔR has changed by a predetermined amount or more from the previous value, it can be considered that the change points R2 and R3 have been exceeded toward the appropriate range W1.

  In consideration of this point, in step S23, it is determined whether or not the amount of change in the detection value of the NOx sensor 50 caused by performing the increase in amount in step S21 or the decrease in amount 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 adsorption amount after the increase or decrease is continuously the amount in the under range W2 or the over range W3, the purification rate change amount ΔR becomes equal to or more than a predetermined value, and when the amount changes in 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, the adsorption amount after the increase is considered to be continuously in the under-range W2, or the adsorption amount after the decrease is continued to be in the excessive range W3. And the process returns to step S20. Therefore, the current adsorption amount 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 ended.

  On the other hand, if it is determined in step S20 that it is identified as the appropriate range W1, 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 the following 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 be sharply larger than the previous purification rate change amount ΔR. Therefore, when the purification rate change amount ΔR has changed by a predetermined amount or more from 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 detection value of the NOx sensor 50 caused by performing 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 equal to or greater than a predetermined value. When the amount of adsorption is reduced in step S24 and the amount of adsorption after the amount of reduction continues to be in the appropriate range W1, the change in the purification rate becomes less than the predetermined value, and The predetermined value is set so that the amount of change in the purification rate is equal to or more than the predetermined value. Further, when the amount of adsorption is increased in step S24 and the amount of adsorption after the amount of increase continues to be in the appropriate range W1, the amount of change in the purification rate becomes less than the predetermined value, and the amount of change in the purification rate changes to the amount of the excessive range W3. The predetermined value is set so that the amount of change in the purification rate is equal to or more 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 amount of change in the purification rate is not equal to or more than the predetermined value, the adsorption amount after the decrease or increase is considered to be continuously within the appropriate range W1, or the adsorption amount after the decrease continues to be in the excessive range. It is assumed that it is W3, and the process returns to step S20. Therefore, the current adsorption amount is further increased or decreased. If it is determined in step S23 that the purification rate change amount is equal to or more than the predetermined value, the gradual change control in FIG. 7 is terminated.

  Returning to the description of FIG. 6, after performing the gradual change control in step S7, in step S8, the above-described change-time purification rates R2y and R3y are detected. That is, of the change points R2 and R3 at which 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 The change point located at the boundary with is referred to as an excessive change point R3. Then, the purification rate at the underside change point R2 is detected as the underside change-time purification rate R2y, and the purification rate at the excessive side change point R3 is detected as the excess side purification rate R3y.

  Specifically, the purification rate at the time when the gradual change control in step S7 ends, that is, when the affirmative determination is made in steps S23 and S25 is calculated based on the detection value of the NOx sensor 50. In the gradual change control, when the amount of adsorption is increased in step S21 or when the amount of adsorption is decreased in step S24, the purification rate detected in step S8 is changed at the time of the change at the underside change point R2. The purification rate is R2y. In short, the amount of adsorption in the under range W2 gradually approaches the underside change point R2 by repeating the increase in step S21, and when the amount of adsorption exceeds the underside change point R2, the slope of the purification rate becomes greater than or equal to the predetermined value. It changes below a predetermined value. Further, when the amount of adsorption in the appropriate range W1 exceeds the underside change point R2 by repeating the reduction in step S24, the gradient of the purification rate changes from less than the predetermined value to more than the predetermined value. The purification rate at this point is detected as the change-time purification rate R2y at the under-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 time of the change at the excessive side change point R3. The purification rate is R3y. In short, when the amount of adsorption in the excess range W3 exceeds the excess-side change point R3 by repeating the reduction in step S22, the absolute value of the gradient of the purification rate changes from a predetermined value or more to less than the predetermined value. Further, the amount of adsorption in the appropriate range W1 gradually approaches the excessive side change point R3 by repeating the increase in step S24, and when the amount exceeds the excessive side change point R3, the absolute value of the gradient of the purification rate becomes a predetermined value. It changes from less than the value to more than the predetermined value. The purification rate at this point is detected as a change-time purification rate R3y at the excessive change point R3.

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

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

  Further, since the underside change point R2 and the excessive side change point R3 have a high correlation, the coordinates of the excessive side change point R3 can be estimated from the coordinates of the underside change point R2 estimated as described above. It is also possible to estimate the underside change point R2 from the excessive side change point R3. Therefore, if either the underside change point R2 or the overside change point R3 can be estimated, the shape of the entire characteristic line Ma can also be estimated. In other words, the actual characteristic line Ma shape is obtained based on at least one of the detected values of the purification rate at the underside change point R2 (purification rate at change R2y) and the purification rate at the excessive side change point R3 (purification rate at change R3y). Can be estimated.

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

  Then, when the purification rate detected in step S8 is the purification rate R2y at the time of change on the underside, the characteristic map M for the underside corresponding to the purification rate is acquired from the memory. On the other hand, when the purification rate detected in step S8 is the excess-time change-time purification rate R3y, the excess-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 change-time adsorption amounts M2x and M3x corresponding to the change-time purification rates R2y and R3y in the characteristic map M are estimated. Further, the change-time adsorption amounts M2x and M3x estimated in this way are corrected by replacing the estimated adsorption amounts estimated in step S1.

  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 adsorption amount 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 cycle. In short, by detecting the change-time purification rates R2y and R3y by executing the gradual change control, the change-time adsorption amounts M2x and M3x based on the characteristic map M can be estimated with high accuracy. Further, the accumulated amount of estimation error of the estimated adsorption amount is reset by correcting the estimated adsorption amount estimated in step S1 to the change-time adsorption amounts M2x and M3x.

  Further, in step S9, the characteristic map M obtained 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 estimating unit described in the claims, and calculates the adsorption amount estimated by step S1 (adsorption amount estimating unit). It also functions as a correction unit for correcting.

  In the following 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 smaller the detected purification rate, the smaller the target adsorption amount. Alternatively, the central value A1 of the appropriate range W1 in the corrected characteristic map M is set to the target suction amount. Also, the higher the catalyst temperature, the smaller the target adsorption amount. In the following 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 reduced as the detected purification rate is smaller.

  In the following step S12, the cumulative value of the correction amount for the estimated adsorption amount in step S9 or the cumulative value of the correction amount for 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 more than a predetermined value. If the accumulated value is less than the predetermined value, the process of FIG. 6 is terminated. Set the warning flag on. When the warning flag is set to ON, it is considered that the reduction performance of the reduction catalyst due to sulfur poisoning or the like is progressing beyond the allowable range, and the fact is notified to the vehicle user by a warning display or a warning sound. Notify.

  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. Note that the processor 61a when executing the processing of step S12 corresponds to the abnormality determination unit described in the claims.

  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-time index detector detects the change-time index that is a purification index when the change amount of the purification index caused by the change of the addition amount by the gradual change control changes by a predetermined amount or more, that is, the change-time purification rates R2y and R3y, Detection is performed based on the detection value of the sensor 50 (detection device). The change-time adsorption amount estimation unit estimates the change-time adsorption amounts M2x and M3x based on the change-time purification rates R2y and R3y detected by the change-time index detection unit.

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

  Therefore, the change-time adsorption amounts M2x and M3x can be estimated with high accuracy. In particular, even when the characteristic line Ma changes due to the aging of the purification device 30, the change-time adsorption amounts M2x and M3x can be estimated with high accuracy. In addition, the change-time purification rates R2y and R3y used for the correction can be calculated by gradually changing the addition amount, so that the control for forcibly reducing the amount of adsorption to zero (known amount) is not required, and the change is not required. It is possible to realize estimation of the time adsorption amounts M2x and M3x (known amounts).

  Further, in the present embodiment, an adsorption amount estimating unit in step S1 is provided. The adsorption amount estimating 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 change-time adsorption amounts M2x and M3x. Specifically, in the successive estimation, the amount of adsorption is estimated based on the amount of the reducing agent added and the catalyst temperature without using the amounts of adsorption M2x and M3x at the time of change. The estimated adsorption amount is corrected to a known adsorption amount that is 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 change adsorption amounts M2x and M3x, estimation errors are accumulated and sufficient estimation is performed. There is a concern that accuracy cannot be ensured. On the other hand, in the present embodiment, since the adsorption amount is estimated using the change-time adsorption amounts M2x and M3x in addition to the addition amount and the catalyst temperature, the above concern can be suppressed.

  Further, in the present embodiment, an addition valve control unit in step S2 and a target adsorption amount setting unit in step S10 are provided, and the addition valve control unit controls the adsorption amount estimated by the adsorption amount estimation unit to be the target adsorption amount. , The operation of the addition valve 20 is controlled. The target suction amount setting unit sets the target suction amount to a value in a range narrower than the appropriate range W1.

  Here, if the catalyst temperature or the exhaust flow rate changes, the appropriate range W1 also changes. Therefore, contrary to the above setting, when the adsorption amount at the boundary between the under-range W2 or the over-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 and the exhaust flow rate. It is feared that the amount deviates from the appropriate range W1. On the other hand, in the present embodiment, since the target amount of adsorption 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 the present embodiment, since the median value A1 of the appropriate range W1 is set as the target adsorption amount, the above-mentioned concern can be further suppressed.

  Further, in the present embodiment, a range identification unit in step S5 is provided for identifying whether the current amount of adsorption is in the appropriate range W1, the underrange W2, or the overrange 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 under-range W2, and determines in the case where the range W3 is identified as the excessive range W3. In step S22, the addition amount is gradually reduced. In addition, the change-time adsorption amount estimating unit in step S9 estimates the change-time adsorption amounts M2x and M3x based on the correlation with the change-time purification rates R2y and R3y. The above correlation is made different. Specifically, the change-time adsorption amounts M2x and M3x are estimated by using different characteristic maps M for the time of increase change and the time of decrease change.

  Here, as described above, the purification rate R2y at the time of the change in the underside change point R2 has a correlation with the characteristic line Ma, and the purification rate R3y at the time of the change in the excessive side change point R3 has a correlation with the characteristic line Ma as described above. However, in the portion of the characteristic line Ma in the underrange W2, the change-time purification rate R2y has a higher correlation than the change-time purification rate R3y. Further, in the portion of the characteristic line Ma in the excessive range W3, the change-time purification rate R3y has a higher correlation than the change-time purification rate R2y. In the present embodiment in consideration of this point, as described above, the change-time adsorption amounts M2x and M3x are calculated when the change-time purification rate R2y is calculated from the increase change and when the change-time purification rate R3y is calculated from the decrease change. The correlation used for estimating is made different. Therefore, it is possible to estimate using the purification rate having a high correlation among the two types of the purification rates R2y and R3y at the time of change, and it is possible to improve the estimation accuracy of the adsorption amounts M2x and M3x at the time of change.

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

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

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

  Further, in the present embodiment, there is an effect that the degree of deterioration can be estimated with high accuracy based on the change-time purification rates R2y and R3y or the change-time adsorption amounts M2x and M3x detected by the gradual change control. Utilizing this, it is determined whether or not the purifying ability is abnormally low. Specifically, the deviation of the current value from the initial value of the change-time purification rates R2y, R3y or the change-time adsorption amounts M2x, M3x is calculated. Then, when the calculated value of the deviation is equal to or more than a predetermined value, an abnormality determination unit in step S12 is provided for determining that the NOx purification device 30 is in an abnormal state in which the purification capability is abnormally low. As described above, according to the present embodiment, the degree of deterioration can be estimated with high accuracy, and it is possible to determine with high accuracy whether or not an abnormal state is present by using the estimation result.

  Further, in the present embodiment, the predetermined amount ΔM2 for increasing the adsorption amount by the gradual change control is variably set according to the catalyst temperature and the exhaust gas flow rate. Specifically, as the catalyst temperature increases and the exhaust gas flow rate increases, the predetermined amount ΔM2 to be increased is reduced. As the catalyst temperature increases and the exhaust gas flow rate increases, the slope of the characteristic line Ma in the under-range W2 increases. Therefore, the point at which the actual under-side change point R2 greatly exceeds the appropriate range W1 is determined as the under-side change point. Can be suppressed by reducing the predetermined amount ΔM2. Therefore, the detection accuracy of the change-time purification rate R2y can be improved, and thus the change-time adsorption amount M2x can be estimated more accurately.

  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 flow rate. Specifically, the higher the catalyst temperature and the larger the exhaust flow rate, the smaller the predetermined amount ΔM3 to be reduced. As the catalyst temperature increases and the exhaust gas flow rate increases, the absolute value of the slope of the characteristic line Ma in the excess range W3 increases, so a point that greatly exceeds the actual excess side change point R3 to the appropriate range W1 side is defined as an excess side change point. Detection can be suppressed by reducing the predetermined amount ΔM2. Therefore, the detection accuracy of the change-time purification rate R3y can be improved, and the estimation accuracy of the change-time adsorption amount M3x can be improved.

(2nd Embodiment)
In the gradual change control according to the first embodiment, the amount of adsorption is changed in one direction, and the purification rates when the amount of change of the purification index changes by a predetermined amount or more are detected as change-time purification rates R2y and R3y. I have. On the other hand, in the present embodiment, the adsorption amount is changed in one direction, and after the change amount of the purification index changes by a predetermined amount or more, the adsorption amount is changed in the opposite direction, and the purification index is changed in accordance with the change. The purifying rate when the amount of change has changed by a predetermined amount or more is detected as the purifying rates at change R2y and R3y.

  For example, if it is determined in step S5 that the range is the under-range W2, the gradual change control is executed as follows. First, as shown in FIG. 8, a control (first gradual change control) of increasing the adsorption amount by a predetermined amount ΔM21 from the under range W2 to the appropriate range W1 is executed. The first gradual change control ends when the amount of change in the purification rate 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, a control (second gradual change control) of decreasing the adsorption amount by a predetermined amount ΔM22 from the appropriate range W1 to the underrange W2 is executed.

  The second gradual change control is terminated when the amount of change in the purification rate has changed by a predetermined amount or more due to exceeding the underside change point R2 toward the underrange W2 side by the second gradual change control. Then, the purification rate at the time when the second gradual change control is completed is detected as the change-time purification rate R2y. The predetermined amount ΔM21 that is increased by the first gradual change control is set to be larger than the predetermined amount ΔM22 that is reduced by the second gradual change control.

  For example, if it is determined in step S5 that the range is the excessive range W3, the gradual change control is executed as follows. First, as shown in FIG. 8, a control (first gradual change control) of decreasing the adsorption amount by a predetermined amount ΔM31 from the excessive range W3 to the appropriate range W1 is executed. The first 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 appropriate range W1 by the first gradual change control. Thereafter, control (second gradual change control) of increasing the adsorption amount by a predetermined amount ΔM32 from the appropriate range W1 to the excess range W3 is executed. 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 side by the second gradual change control. Then, the purification rate at the time when the second gradual change control is completed is detected as the change-time purification rate R3y. 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 it is determined in step S5 that the range is the appropriate range W1, the gradual change control is executed as follows. First, a control (first gradual change control) of changing the adsorption amount by a predetermined amount from the appropriate range W1 to the under-range W2 or the over-range W3 is executed. The first gradual change control is ended when the amount of change in the purification rate 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, a control (second gradual change control) of changing the adsorption amount by a predetermined amount from the under range W2 or the over range W3 to the appropriate range W1 is executed. The second gradual change control ends when the amount of change in the purification rate changes by a predetermined amount or more due to exceeding the change points R2 and R3 by the second gradual change control. Then, the purification rate at the time when the second gradual change control is completed is detected as the change-time purification rates R2y and R3y. The predetermined amount changed in the first gradual change control is set to be larger than the predetermined amount changed in 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 predetermined intervals by the processor 61a according to the processing procedure shown in FIG. 61a corresponds to the gradual change control unit described in the claims. In the process of FIG. 9, 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 as those 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 replaced with the first gradual change control described above. Equivalent to. Then, the first gradual change control is terminated at the time when the affirmative determination is made in steps S23 and S25, and the aforementioned second gradual change control is executed in the subsequent step S26. 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, in the case where the second gradual change control is performed after the amount is increased 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 performed 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. When executing the second gradual change control after increasing the amount by a predetermined amount in step S24, reducing the amount by a predetermined amount in step S26, and executing the second gradual change control after decreasing the amount by a 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 of 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. I do. Thereafter, a second gradual change control is executed in which the increase / 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, a purification index when the amount of change of the purification index caused by 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 increasing / decreasing direction is made different is executed, so that the concern of failing to detect the change index can be reduced, and the detection of the change index can be reliably performed. Can be improved.

  Further, in the present embodiment, the predetermined amounts ΔM21 and ΔM31 to be increased or decreased in the first gradual change control are set to be larger than the predetermined amounts ΔM22 and ΔM32 to be increased or decreased in the second gradual change control. Therefore, the change index can be detected with high accuracy, and the gradual change control required for the detection can be completed in a short time.

(Other embodiments)
As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and can be variously modified and implemented as exemplified below. Not only the combination of the parts that clearly indicate that the combination is possible in each embodiment, but also the embodiments are partially combined without being specified unless there is a particular problem with the combination. Is also possible.

  In the gradual change control shown in FIG. 4, when gradually changing the adsorption amount, 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 and ΔM32 to be increased or the predetermined amounts ΔM22 and 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. 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 is calculated. The difference between the current value and the initial value of the purification rate may be calculated as the degree of deterioration. Specific examples of the deterioration index purification rate include, in the characteristic map M corrected in step S9, the purification rate at the excessively small change point R2, the purification rate at the excessively changed point R3, and the median A1 of the appropriate range W1. Purification rate.

  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. I have. On the other hand, 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-time purification rates R2y and R3y. .

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

  For example, when it is identified as the excessive range W3, the adsorption amount is reduced toward the appropriate range W1 side, and after the change-time purification rate R3y is obtained, the adsorption amount is reduced toward the underrange W2 side. Then, the change-time purification rate R2y is also acquired. Then, the change-time adsorption amount M2x corresponding to the change-time purification rate R2y may be corrected based on the change-time purification rate R3y.

  In the example shown in FIG. 1, the adsorption amount estimation device (ECU 60) is applied to the purification system including the oxidizing device 40, but the adsorption amount estimation device is also applicable to a purification system not including the oxidizing device 40. . Further, the adsorption amount estimating apparatus 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 FIG. 7 and FIG. 9, even when the appropriate range W1 is identified, the amount of adsorption is gradually changed in step S24 to detect the change-time 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 under range W2 or the over range 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 omitted. In this case, the estimated change-time adsorption amounts M2x and M3x are not used for correcting the sequentially estimated adsorption amount values, but are used for the abnormal state determination in step S12.

  The means and / or functions provided by the control device by the ECU 60 can be provided by software recorded on a substantial storage medium and a computer executing the software, only software, only hardware, or a combination thereof. For example, if the control device is provided by electronic circuits that are hardware, it can be provided by digital circuits that include multiple logic circuits, or by analog circuits.

  20: addition valve, 30: NOx purification device, 50: NOx sensor (detection device), 60: ECU (adsorption amount estimation device), M2x, M3x: adsorption amount at the time of change, R2y, R3y: purification rate at the time of change (at the time of change) Index), S7: Slow change control section, S8: Change index detection section, S9: Change adsorption amount estimation section.

Claims (10)

A purifying 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 an exhaust passage (11a) of the internal combustion engine upstream of the purifying device. And a detection device (50) disposed downstream of the purification device in the exhaust passage and configured to detect at least one of the NOx amount and the reducing agent amount. In the adsorption amount estimating device for estimating the adsorption amount of the reducing agent to the purification device,
A gradual change control unit (S7) for performing 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 device is defined as a purification index, and the purification index when a change amount (ΔR) of the purification index that changes every time the addition amount is gradually changed by the gradual change control is changed by a predetermined amount or more. A change-time index detection unit (S8) that detects the change-time index based on a value detected by the detection device as a change-time index (R2y, R3y)
A change-time adsorption amount estimating unit that estimates a change-time adsorption amount (M2x, M3x), 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. (S9).   An adsorption amount estimating unit for estimating an adsorbed amount in the execution stop period of the gradual change control based on the amount of the reducing agent added from the addition valve, the temperature of the catalyst, and the adsorbed amount estimated by the adsorbing amount estimating unit when changing The adsorption amount estimating device according to claim 1, further comprising (S1). An addition valve control unit (S2) that controls the operation of the addition valve so that the adsorption amount estimated by the adsorption amount estimation unit becomes the target adsorption amount;
A range in which the amount of change is less than a predetermined amount, in which the upper limit or lower limit of the amount of change is set as an appropriate range (W1), and the target amount of suction is set to a value smaller than the appropriate range. A target adsorption amount setting unit (S10) for setting an amount;
The adsorption amount estimating device according to claim 2, comprising: A range in which the amount of change is less than a predetermined amount, in which the upper limit or lower limit of the amount of change is set as an appropriate range (W1), and a range of the amount of suction that is smaller than the appropriate range. Is defined as an under-range (W2), and the range of the amount of adsorption on the side larger than the appropriate range is defined as an over-range (W3), and the current amount of adsorption is any of the appropriate range, the under-range, and the over-range. A range identification unit (S5) for identifying
The gradual change control unit gradually increases and changes the addition amount when the range identification unit identifies the underrange, and when the range identification unit identifies the excess range, Gradually decrease the amount of addition,
The change-time adsorption amount estimating unit estimates the change-time adsorption amount based on the correlation with the change-time index, by estimating the correlation by making the correlation different between the case of the increase change and the case of the decrease change. The adsorption amount estimating device according to claim 2 or 3, wherein the adsorption amount is estimated.   5. The gradual change control unit according to claim 1, wherein the gradual change control is performed on a condition that the purification index detected based on a value detected by the detection device is less than a target index. 6. 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 in a steady state in which the amount of change per unit time is less than a predetermined amount. Item 6. The adsorption amount estimating apparatus according to any one of Items 1 to 5 .   The change-time adsorption amount estimating unit estimates the change-time adsorption amount according to at least one of the catalyst temperature and the exhaust gas flow rate when the gradual change control is being performed. The adsorption amount estimation device according to one of the above aspects.   An abnormality determining unit that determines that the purifying device is in an abnormal state in which the purifying capability is abnormally low when a deviation of a current value from an initial value of the changing index or the initial value of the changing adsorption amount is a predetermined value or more. The adsorption amount estimation device according to any one of claims 1 to 7, further comprising (S12). The gradual change control includes a first gradual change control in which the amount of the reducing agent added is increased or decreased by a predetermined amount in a direction of increasing or decreasing 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 amount of addition is changed by a predetermined amount in a direction opposite to the first gradual change control,
The change index detection unit detects the purification index when the amount of change of the purification index that changes every time the addition amount is gradually changed by the second gradual change control is changed by a predetermined amount or more, as the change index. The adsorption amount estimating device according to claim 1.   The adsorption amount estimating device according to claim 9, wherein the predetermined amount to be increased or decreased in the first gradual change control is set to be larger than the predetermined amount to be increased or decreased in the second gradual change control.

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