JP2018100615A - Control device for urea scr system and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an addition control device for urea water capable of performing feedback control on an addition amount of the urea water while using a detection value of a NOx sensor even in a case where a concentration of ammonia interferes the detection value, and a control method.SOLUTION: An ECU 30 acquires a detection concentration of a NOx sensor 23 that is installed at a downstream side of a selective reduction type catalyst 18 and calculates an ammonia concentration at the downstream side of the selective reduction type catalyst 18, a basic addition amount of urea water which makes the detection concentration become a target concentration, and a correction value based on a deviation between the target concentration and the detection concentration. In a case where the ammonia concentration is equal to or lower than a threshold and the detection concentration is higher than the target concentration, the ECU 30 then calculates such a correction value that a correction amount to an increase side for the basic addition amount is made greater as the deviation is greater. In a case where the ammonia concentration is higher than the threshold and the detection concentration is higher than the target concentration, the ECU calculates such a correction value that a correction amount to a decrease side for the basic addition amount is made greater as the deviation is greater.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device and a control method for a urea SCR system.

  Conventionally, as an exhaust gas purification system for purifying nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas, an addition valve for adding urea water to exhaust gas and a selective reduction catalyst located downstream of the addition valve are used. Urea SCR (Selective Catalytic Reduction) systems are known. In the urea SCR system, urea water added to the exhaust gas is hydrolyzed into ammonia by the heat of the exhaust gas. When the exhaust gas containing ammonia flows into the selective reduction catalyst, NOx in the exhaust gas is reduced to nitrogen and water using ammonia as a reducing agent. The amount of urea water added by the addition valve is controlled by feedback control based on a detection value of a NOx sensor disposed downstream of the selective catalytic reduction catalyst.

  By the way, the exhaust gas that has passed through the selective catalytic reduction catalyst contains ammonia that has not been consumed by the selective catalytic reduction catalyst. Further, the NOx sensor has a characteristic of reacting not only with NOx but also with ammonia. Therefore, the detection value of the NOx sensor includes a detection value based on NOx and a detection value based on ammonia. In relation to such characteristics of the NOx sensor, for example, in Patent Document 1, a NOx sensor and an ammonia sensor are installed downstream of the selective reduction catalyst, and based on the detected value of the NOx sensor and the detected value of the ammonia sensor. A technique for correcting the amount of urea water added is disclosed.

JP 2002-266627 A

  However, installing an ammonia sensor downstream of the selective catalytic reduction catalyst increases the number of parts. Therefore, there is a demand for a urea SCR system that enables feedback control of the addition amount of urea water using the detected value even if ammonia interferes with the detected value of the NOx sensor.

  The present invention provides a control device and a control method for a urea SCR system capable of performing feedback control of the addition amount of urea water using the detected value even when ammonia interferes with the detected value of the NOx sensor. For the purpose.

  The control device of the urea SCR system that solves the above problems includes an acquisition unit that acquires a detection concentration that is a detection value of a NOx sensor installed downstream of a selective reduction catalyst that reduces NOx using ammonia as a reducing agent, and the selection A concentration calculation unit that calculates the ammonia concentration of the exhaust gas that has passed through the reduction catalyst, a basic addition amount calculation unit that calculates the basic addition amount of urea water at which the detected concentration becomes the target concentration, the detected concentration and the target concentration A correction value calculation unit that calculates a correction value of the basic addition amount based on a deviation from the difference, and the correction value calculation unit holds a threshold value for determining the presence or absence of ammonia interference with the detected concentration, and the concentration When the calculated value of the calculation unit is equal to or less than the threshold value and the detected concentration is larger than the target concentration, the larger the deviation, the more the correction to the increase side with respect to the basic addition amount When the calculated value is larger than the threshold value and the detected concentration is larger than the target concentration, the larger the deviation, the smaller the correction to the basic addition amount. The correction value for increasing the amount is calculated.

  A urea SCR system control method that solves the above problems includes a selective reduction catalyst that reduces NOx using ammonia as a reducing agent, a urea water addition device that adds urea water to exhaust gas upstream of the selective reduction catalyst, A urea SCR system control method comprising a control device for controlling the amount of urea water added by the urea water addition device, wherein the control device is a NOx sensor installed downstream of the selective catalytic reduction catalyst. Obtaining a detected concentration that is a detected value; calculating an ammonia concentration of exhaust gas that has passed through the selective reduction catalyst; calculating a basic addition amount of urea water at which the detected concentration becomes a target concentration; A step of calculating a correction value of the basic addition amount based on a deviation between the detected concentration and the target concentration, and in the step of calculating the correction value, When the calculated value is equal to or less than a threshold for determining the presence or absence of ammonia interference with respect to the detected concentration, and the detected concentration is greater than the target concentration, the larger the deviation, the greater the correction to the basic addition amount. When the correction value for increasing the amount is calculated, the calculated value is larger than the threshold value, and the detected concentration is larger than the target concentration, the larger the deviation, the smaller the amount added to the basic addition amount. The correction value for increasing the correction amount is calculated.

  According to the above configuration, even if the detected concentration is larger than the target concentration, if ammonia does not interfere with the detected concentration, a correction value that increases the correction amount to the increase side with respect to the basic addition amount is calculated, and the detected concentration In the case where ammonia interferes, a correction value for increasing the correction amount to the reduction side with respect to the basic addition amount is calculated. As a result, the amount of urea water added can be feedback controlled even when ammonia interferes with the detected concentration. In addition, since the ammonia concentration downstream of the selective catalytic reduction catalyst is obtained by calculation, there is no need to provide an ammonia sensor downstream of the selective catalytic reduction catalyst.

  In the control device for the urea SCR system, the correction value calculation unit is configured such that when the calculated value is less than or equal to the threshold value and the detected concentration is smaller than the target concentration, the basic addition amount decreases as the deviation decreases. When the correction value for increasing the correction amount to the decrease side with respect to is calculated and the calculated value is larger than the threshold value and the detected concentration is smaller than the target concentration, the basic addition becomes smaller as the deviation is smaller It is preferable to calculate the correction value that increases the correction amount to the increase side with respect to the amount.

  According to the above configuration, even when the detected concentration is smaller than the target concentration, if ammonia does not interfere with the detected concentration, a correction value that increases the correction amount on the reduction side with respect to the basic addition amount is calculated, and the detected concentration is calculated. When ammonia interferes, a correction value for increasing the correction amount on the increase side with respect to the basic addition amount is calculated. As a result, feedback control of the urea water addition amount using the detected concentration can be performed according to whether ammonia interferes with the detected concentration.

  In the control device for the urea SCR system, the correction value calculation unit corrects the upper limit value with which the correction amount to the increase side with respect to the basic addition amount becomes maximum and the basic addition amount to the increase side with respect to the correction value. It is preferable that the first reset value is set to the correction value with one of the conditions that the correction value has reached the upper limit value.

  In the control device for the urea SCR system, the correction value calculation unit corrects the lower limit value with which the correction amount to the reduction side with respect to the basic addition amount becomes maximum and the basic addition amount to the reduction side with respect to the correction value. It is preferable that the correction value is set to the second reset value on the condition that the correction value reaches the lower limit value, and the second reset value is a reset value.

  When the correction value reaches the upper limit value or the lower limit value, there is a possibility that feedback control using the detected density is not normally performed. In this regard, according to the above configuration, the first reset value is set as the correction value on the condition that the correction value has reached the upper limit value. Also, the second reset value is set as the correction value on the condition that the correction value has reached the lower limit value. Thereby, the feedback control using the detected concentration can be returned to a normal state.

The figure which shows schematic structure of the urea SCR system carrying one Embodiment of the control apparatus of a urea SCR system. The functional block diagram which shows an example of the various function parts which ECU has. The flowchart which shows an example of the procedure of a calculation process. The graph which shows an example of the relationship between the addition amount of urea water in various conditions, and various density | concentrations. The flowchart which shows an example of the procedure of a reset process. The figure which shows an example of transition of the correction value until it resets to a 1st reset value. The figure which shows an example of transition of the correction value until it resets to a 2nd reset value.

An embodiment of a control device and a control method for a urea SCR system will be described with reference to FIGS.
As shown in FIG. 1, the urea SCR system 10 includes a urea water addition device 15, a selective reduction catalyst 18, and an ECU (Electronic Control Unit) 30 that is a control device for the urea SCR system. The ECU 30 controls the amount of urea water added by the urea water adding device 15.

  The urea water addition device 15 adds urea water to the exhaust passage 11 through which the exhaust gas flows. The urea water addition device 15 includes a urea water supply unit 16 provided with a urea water tank, a mechanical pump, and the like, and an addition valve 17 disposed in the exhaust passage 11. The addition valve 17 adds urea water having a predetermined pressure supplied from the urea water supply unit 16 to the exhaust passage 11.

  The selective catalytic reduction catalyst 18 is disposed downstream of the addition valve 17 in the exhaust passage 11, and reacts the ammonia hydrolyzed by the urea water added by the addition valve 17 with NOx contained in the exhaust gas to produce NOx. Reduce to nitrogen or water. The selective catalytic reduction catalyst 18 is obtained by holding, for example, various catalytic metals such as copper, iron, and vanadium with respect to a flow-through type monolith support made of ceramic or stainless steel having excellent heat resistance. It is. The selective catalytic reduction catalyst 18 has, for example, a temperature range of 150 ° C. to 350 ° C. as an active temperature range.

  The urea SCR system 10 includes an oxygen concentration sensor 21, a temperature sensor 22, a NOx sensor 23, an intake air amount sensor 24, an engine speed sensor 25, and the like as sensors for detecting various state quantities. The oxygen concentration sensor 21 is disposed upstream of the selective reduction catalyst 18 in the exhaust passage 11 and detects the oxygen concentration Cox of the exhaust gas flowing into the selective reduction catalyst 18. The temperature sensor 22 is disposed upstream of the selective reduction catalyst 18 in the exhaust passage 11 and detects the temperature of the exhaust gas flowing into the selective reduction catalyst 18 as the catalyst temperature Temp. The NOx sensor 23 is disposed downstream of the selective reduction catalyst 18 in the exhaust passage 11, and detects the concentration of the NOx concentration and the ammonia concentration in the exhaust gas that has passed through the selective reduction catalyst 18 as the detected concentration Cx. To do. The intake air amount sensor 24 is disposed in the intake passage of the engine and detects an intake air amount Qa that is the amount of air taken in by the engine. The engine speed sensor 25 detects an engine speed Ne that is the speed of the crankshaft of the engine. Each of the sensors 21 to 25 outputs a detection signal indicating the detected detection value to the ECU 30. Further, the ECU 30 receives a detection signal indicating the fuel injection amount Qf from the fuel injection control unit 26 that controls the fuel injection amount to the engine.

  The ECU 30 is mainly configured of a microcontroller in which a processor 31, a memory 32, an input interface 33, an output interface 34, and the like are connected to each other via a bus 35. The ECU 30 calculates a target addition amount Qut that is an addition amount of urea water by the addition valve 17 based on various information acquired via the input interface 33 and various control programs and various data stored in the memory 32. To do. The ECU 30 then outputs a control signal to the addition valve 17 via the output interface 34 so that urea water corresponding to the target addition amount Qut is added to the exhaust gas.

  As shown in FIG. 2, the ECU 30 includes, as various functional units, a target concentration calculation unit 41, a basic addition amount calculation unit 42, a detected concentration acquisition unit 43, a deviation calculation unit 44, a concentration calculation unit 45, a correction value calculation unit 47, A target addition amount calculation unit 48 is provided. The ECU 30 handles the intake air amount Qa as the exhaust flow rate Qe.

  The target density calculation unit 41 calculates the target density Cxt of the detected density Cx. The target concentration calculation unit 41 calculates, for example, a concentration suitable for the engine operating state based on detection signals from various sensors as the target concentration Cxt. In addition, the target density | concentration calculating part 41 is not restricted to the structure which calculates target density | concentration Cxt based on the driving | running state of an engine, The structure which calculates a fixed value as target density | concentration Cxt may be sufficient.

  The basic addition amount calculation unit 42 calculates a basic addition amount Qub of urea water at which the detected concentration Cx becomes the target concentration Cxt. The basic addition amount calculation unit 42 calculates the NOx amount of the exhaust gas discharged from the engine based on, for example, the engine speed Ne, the intake air amount Qa, the fuel injection amount Qf, and the like, and the NOx amount of the NOx amount is reduced. Is calculated as the basic addition amount Qub.

The detected concentration acquisition unit 43 acquires the detected concentration Cx based on the detection signal from the NOx sensor 23 via the input interface 33.
The deviation calculating unit 44 calculates a deviation ΔCx (= Cx−Cxt) between the detected concentration Cx acquired by the detected concentration acquiring unit 43 and the target concentration Cxt calculated by the target concentration calculating unit 41.

  The concentration calculation unit 45 has a model 46 that calculates the concentration of ammonia in the exhaust gas that has passed through the selective catalytic reduction catalyst 18. The model 46 is a model derived from the results of experiments and simulations performed in advance, and includes exhaust flow rate Qe, oxygen concentration Cox, catalyst temperature Temp, target addition amount Qut, and the like as parameters. In the model 46, the exhaust gas containing ammonia corresponding to the exhaust gas flow rate Qe, the oxygen concentration Cox, and the target addition amount Qut passes downstream of the selective catalytic reduction catalyst 18 when it passes through the selective catalytic reduction catalyst 18 at the catalyst temperature Temp. It is the model comprised so that calculation of the density | concentration of the detected ammonia was possible. The concentration calculation unit 45 outputs the calculated value calculated using the model 46 to the correction value calculation unit 47 as the ammonia concentration Cam.

  The correction value calculation unit 47 calculates a correction value G for feedback control of the addition amount of urea water based on the deviation ΔCx calculated by the deviation calculation unit 44. The correction value calculation unit 47 does not normally perform calculation processing for calculating the correction value G based on the deviation ΔCx, the target concentration Cxt, the detected concentration Cx, the ammonia concentration Cam, and the like, and feedback control using the correction value G. If it is determined, the reset process for resetting the correction value G is repeated. The correction value G includes, for example, a proportional term for performing proportional control based on the deviation ΔCx, an integral term for performing integral control based on the deviation ΔCx, a differential term for performing differential control based on the deviation ΔCx, and the like. It is out. The correction value calculation unit 47 outputs the calculated correction value G to the target addition amount calculation unit 48.

  The correction value calculation unit 47 sets an upper limit Gmax that maximizes the correction amount toward the increase side with respect to the basic addition amount Qub and a lower limit that maximizes the correction amount toward the decrease side with respect to the basic addition amount Qu. The value Gmin is held in a predetermined area of the memory 32. Further, the correction value calculation unit 47 counts a continuation period Tc, which is a period in which the state where the correction value G is the lower limit value Gmin or the upper limit value Gmax continues. In addition, the correction value calculation unit 47 holds a first reset value G1 and a second reset value G2, which will be described later, in a predetermined area of the memory 32.

  The target addition amount calculation unit 48 calculates a value obtained by correcting the basic addition amount Qub calculated by the basic addition amount calculation unit 42 with the correction value G calculated by the correction value calculation unit 47 as the target addition amount Qut. In an example of the target addition amount calculation unit 48, the target addition amount Qut is calculated by multiplying the basic addition amount Qub by the correction value G. The correction amount with respect to the basic addition amount Qub indicates the ratio of the target addition amount Qut to the basic addition amount Qub, and in the configuration in which the basic addition amount Qub is multiplied by the correction value G, it is the correction value G itself. .

With reference to FIG. 3 and FIG. 4, the procedure of the calculation process performed by the correction value calculation unit 47 will be described.
As shown in FIG. 3, in the calculation process, the correction value calculation unit 47 first determines whether or not the ammonia concentration Cam calculated by the concentration calculation unit 45 using the model 46 is equal to or less than a threshold value Camj (step S101). ).

  Here, the threshold value Camj will be described with reference to FIG. FIG. 4 is a graph showing an example of the relationship between the added amount Qu of urea water under a predetermined condition, various concentrations C of the detected concentration Cx, the NOx concentration Cxn, and the ammonia concentration Cxa.

  As shown in FIG. 4, as the urea water addition amount Qu increases, the NOx concentration Cxn decreases while the ammonia concentration Cxa increases. Therefore, in the region where the addition amount Qu of the urea water is small, when the addition amount Qu of the urea water is increased, ammonia corresponding to the increase in the addition amount Qu is consumed for the reduction of NOx. Therefore, the increase rate of the ammonia concentration Cxa However, the decreasing rate of the NOx concentration Cxn increases, and the detected concentration Cx gradually decreases. On the other hand, in the region where the urea water addition amount Qu is large, when the urea water addition amount Qu is increased, ammonia corresponding to the increase in the addition amount Qu is not consumed for the reduction of NOx, so the rate of decrease in the NOx concentration Cxn. The increase rate of the ammonia concentration Cxa becomes larger than that, and the detected concentration Cx gradually increases.

  That is, even if the detected density Cx is the same, there are cases where the value belongs to the non-interference area A1 having the minimum value Cxmin as a boundary and the value belongs to the interference area A2. The non-interference region A1 is a region where the detected concentration Cx decreases as the urea solution addition amount Qu increases, and is a region where it can be determined that ammonia does not interfere with the detected concentration Cx. The interference area A2 is an area where the detected concentration Cx increases as the amount of added aqueous solution Qu increases, and is an area where it can be determined that ammonia interferes with the detected concentration Cx.

  Therefore, when the detected concentration Cx is a detected concentration Cx1 larger than the target concentration Cxt, when the detected concentration Cx belongs to the non-interference area A1 (point P1), the detected concentration Cx is increased by increasing the addition amount Qu of the urea water. It approaches the target density Cxt. On the other hand, when the detected concentration Cx belongs to the interference region A2 (point P2), the detected concentration Cx approaches the target concentration Cxt by reducing the addition amount Qu of the urea water. Further, when the detected concentration Cx is a detected concentration Cx2 smaller than the target concentration Cxt and the detected concentration Cx belongs to the non-interference area A1 (point P3), the detected concentration Cx is reduced by decreasing the addition amount Qu of the urea water. It approaches the target density Cxt. On the other hand, when the detected concentration Cx belongs to the interference region A2 (point P4), the detected concentration Cx approaches the target concentration Cxt by increasing the addition amount Qu of the urea water. The threshold value Camj is a value for determining whether the detected concentration Cx is a value belonging to the non-interference area A1 or a value belonging to the interference area A2, based on the ammonia concentration Cxa, and is set to 10 ppm, for example. The threshold value Camj only needs to be a value at which the detected density Cx indicating the boundary between the non-interference area A1 and the interference area A2 is lower than the target density Cxt, and is not limited to a value at which the detected density Cx becomes the minimum value Cxmin. .

  Returning to FIG. 3, when the ammonia concentration Cam is equal to or less than the threshold value Camj (step S101: YES), the correction value calculation unit 47 sets the value of the flag F indicating the presence or absence of ammonia interference to the detected concentration Cx to 1 (no interference). ) Is set (step S102). Then, the correction value calculation unit 47 determines whether or not the deviation ΔCx is greater than 0 (step S103).

  When the deviation ΔCx is larger than 0 (Cx> Cxt) (step S103: YES), the correction value calculator 47 increases the upper limit of the correction value G that increases the correction amount to the increase side with respect to the basic addition amount Qub as the deviation ΔCx increases. The calculation is performed with the value Gmax as the upper limit (step S104), and the series of processes is temporarily terminated. The upper limit Gmax is a value that is set to the target addition amount Qut that is considerably higher than the basic addition amount Qub, and the target addition amount Qut is calculated by multiplying the basic addition amount Qub by the correction value G. In the configuration, for example, 1.5.

  On the other hand, when the deviation ΔCx is equal to or smaller than 0 (Cx ≦ Cxt) (step S103: NO), the correction value calculating unit 47 increases the correction amount to the decrease side with respect to the basic addition amount Qub as the deviation ΔCx is smaller. G is calculated with the lower limit value Gmin as the lower limit (step S105), and the series of processes is temporarily terminated. The lower limit Gmin is a value that is set to the target addition amount Qut that is considerably lower than the basic addition amount Qub, and the target addition amount Qut is calculated by multiplying the basic addition amount Qub by the correction value G. In the configuration, for example, 0.5.

  On the other hand, when the ammonia concentration Cam is larger than the threshold value Camj (step S101: NO), the correction value calculation unit 47 sets the value of the flag F to 0 (with interference) (step S106), and subsequently the deviation ΔCx is 0. It is determined whether it is larger (step S107).

  When the deviation ΔCx is larger than 0 (Cx> Cxt) (step S107: YES), the correction value calculation unit 47 sets a correction value G that increases the correction amount to the decrease side with respect to the basic addition amount Qub as the deviation ΔCx increases. The lower limit value Gmin is calculated as the lower limit (step S108), and the series of processes is temporarily terminated. On the other hand, when the deviation ΔCx is 0 or less (Cx ≦ Cxt) (step S107: NO), the correction value calculation unit 47 increases the correction amount to the increase side with respect to the basic addition amount Qub as the deviation ΔCx is smaller. G is calculated with the upper limit value Gmax as the upper limit (step S109), and the series of processes is temporarily terminated.

  According to such a configuration, it is determined whether the detected concentration Cx is a value belonging to the non-interference area A1 or a value belonging to the interference area A2, that is, whether ammonia has interfered with the detected concentration Cx. Then, the correction value G based on the deviation ΔCx between the target density Cxt and the detected density Cx can be calculated according to the determination result. As a result, feedback control for the amount of urea water added can be performed based on the detected value of the NOx sensor.

With reference to FIGS. 5-7, the procedure of the reset process which the correction value calculating part 47 performs is demonstrated.
As shown in FIG. 5, in the reset process, the correction value calculator 47 first determines whether or not the value of the flag F is 1 (step S201). When the value of the flag F is 1 (step S201: YES), that is, when there is no ammonia interference with respect to the detected concentration Cx, the correction value calculation unit 47 determines whether or not the correction value G is the upper limit value Gmax. (Step S202). When the correction value G is the upper limit value Gmax (step S202: YES), the correction value calculation unit 47 determines whether or not the continuation period Tc has reached the determination period Tcj (step S203). When the continuation period Tc has reached the determination period Tcj (step S203: YES), the correction value calculation unit 47 corrects that the feedback control of the target addition amount Qut using the detected concentration Cx does not function normally. The value G is reset to the first reset value G1 (step S204), and a series of processes is once ended.

  The first reset value G1 is a value at which a value slightly higher than the basic addition amount Qub is set as the target addition amount Qut, and is a reset value when the basic addition amount Qub is corrected to the increase side. The first reset value G1 is, for example, 1.05 in the configuration in which the target addition amount Qut is calculated by multiplying the basic addition amount Qub by the correction value G. Further, when the correction value G is reset, if the correction value G includes an integral term, the integral term is also reset.

  On the other hand, when the correction value G has not reached the upper limit value Gmax (step S202: NO), or when the continuation period Tc has not reached the determination period Tcj (step S203: NO), the correction value calculation unit 47 remains unchanged. A series of processing is once ended.

  That is, as shown in FIG. 6, for example, when the deviation ΔCx (> 0) between the detected concentration Cx and the target concentration Cxt gradually increases when there is no ammonia interference with the detected concentration Cx, the correction value G gradually increases. And eventually reaches the upper limit Gmax. Then, when the state in which the correction value G is the upper limit value Gmax continues for the determination period Tcj, the correction value calculation unit 47 resets the correction value G to the first reset value G1.

  When the value of the flag F is 0 (step S201: NO), that is, when there is ammonia interference with the detected concentration Cx, the correction value calculation unit 47 determines whether or not the correction value G is the lower limit value Gmin. Judgment is made (step S205). When the correction value G is the lower limit value Gmin (step S205: YES), the correction value calculation unit 47 determines whether or not the continuation period Tc has reached the determination period Tcj (step S206). When the continuation period Tc has reached the determination period Tcj (step S206: YES), the correction value calculation unit 47 assumes that the feedback control of the target addition amount Qut by the correction value G is not functioning normally, and the correction value G Is reset to the second reset value G2 (step S207), and a series of processing is once ended. The second reset value G2 is a value smaller than the first reset value G1. The second reset value G2 is a value that is set to the target addition amount Qut that is slightly lower than the basic addition amount Qub, and the target addition amount Qut is obtained by multiplying the basic addition amount Qub by the correction value G. In the calculated configuration, for example, 0.95. Further, when the correction value G is reset, if the correction value G includes an integral term, the integral term is also reset.

  On the other hand, when the correction value G is not the lower limit value Gmin (step S205: NO), and when the continuation period Tc has not reached the determination period Tcj (step S206: NO), the correction value calculation unit 47 performs a series of processing as it is. Exit once.

  That is, as shown in FIG. 7, for example, when the deviation ΔCx (> 0) between the detected concentration Cx and the target concentration Cxt gradually increases when there is ammonia interference with the detected concentration Cx, the correction value G gradually increases. It becomes smaller and eventually reaches the lower limit Gmin. Then, when the state where the correction value G is the lower limit value Gmin continues for the determination period Tcj, the correction value calculation unit 47 resets the correction value G to the second reset value G2.

According to the control device and the control method of the urea SCR system of the above embodiment, the following effects can be obtained.
(1) When there is no interference of ammonia in the detected concentration Cx and the detected concentration Cx is larger than the target concentration Cxt, the ECU 30 increases the correction amount on the increase side with respect to the basic addition amount Qub as the deviation ΔCx (> 0) increases. A correction value G to be increased is calculated. In addition, when there is ammonia interference in the detected concentration Cx and the detected concentration Cx is larger than the target concentration Cxt, the ECU 30 increases the correction amount on the decrease side with respect to the basic addition amount Qub as the deviation ΔCx (> 0) increases. A correction value G is calculated. Thus, by calculating the correction value G according to the presence or absence of ammonia interference with the detected concentration Cx, feedback control using the detected concentration Cx can be performed for the amount of urea water added. Moreover, since the ammonia concentration Cam is obtained by calculation, it is not necessary to provide an ammonia sensor downstream of the selective catalytic reduction catalyst 18.

  (2) Since the addition amount of urea water can be controlled even when the detected concentration Cx belongs to the interference region A2, the degree of freedom of the addition amount of urea water is greatly improved. As a result, the degree of freedom regarding the reduction amount of NOx is also greatly improved. For example, the detected concentration Cx can be controlled to the target concentration Cxt after setting the detected concentration Cx to a value belonging to the interference region A2. As a result, the amount of NOx emission can be further reduced.

  (3) When there is no interference of ammonia in the detected concentration Cx and the detected concentration Cx is smaller than the target concentration Cxt, the ECU 30 decreases the correction amount on the decrease side with respect to the basic addition amount Qub as the deviation ΔCx (<0) is smaller. A correction value G to be increased is calculated. Further, when there is ammonia interference in the detected concentration Cx and the detected concentration Cx is smaller than the target concentration Cxt, the ECU 30 increases the correction amount on the increase side with respect to the basic addition amount Qub as the deviation ΔCx (<0) is smaller. The correction value G to be calculated is calculated. Thereby, even when the detected concentration Cx is smaller than the target concentration Cxt, feedback control using the detected concentration Cx can be performed according to the presence or absence of ammonia interference with the detected concentration Cx.

  (4) The ECU 30 resets the correction value G to the first reset value G1 on condition that the correction value G has reached the upper limit value Gmax. That is, the ECU 30 resets the correction value G when it is determined that the correction value G is maintained at the upper limit value Gmax and feedback control using the detected concentration Cx is not functioning normally. Thereby, the ECU 30 can return the feedback control using the detected concentration Cx to a normal state.

  (5) The ECU 30 resets the correction value G to the second reset value G2 on condition that the correction value G has reached the lower limit value Gmin. That is, the ECU 30 resets the correction value G when it is determined that the correction value G is maintained at the lower limit value Gmin and feedback control using the detected concentration Cx is not functioning normally. Thereby, the ECU 30 can return the feedback control using the detected concentration Cx to a normal state.

  (6) The reset to the first reset value G1 is performed when the ammonia concentration Cam is equal to or less than the threshold value Camj (F = 1), and the second reset value when the ammonia concentration Cam is greater than the threshold value Camj (F = 0). A reset to G2 is performed. That is, the correction value G is reset when the ratio of the NOx concentration or the ammonia concentration to the detected concentration Cx is extremely high. As a result, the correction value G can be reset after increasing the probability that the feedback control using the detected concentration Cx is not normally performed.

  (7) Moreover, the correction value G is reset after the continuation period Tc reaches the determination period Tcj. For this reason, since the correction value G is reset after further increasing the probability that the feedback control using the detected density Cx is not normally performed, unnecessary resetting of the correction value G can be avoided.

In addition, the said embodiment can also be suitably changed and implemented as follows.
The ECU 30 may be configured not to perform at least one of resetting the correction value G to the first reset value G1 and resetting the correction value G to the second reset value G2. Further, regardless of the value of the flag F, the ECU 30 may reset the correction value G to the first reset value G1 and reset the correction value G to the second reset value G2. Further, the ECU 30 may reset the correction value G on condition that the correction value G has reached the upper limit value Gmax or the lower limit value Gmin.

  The ECU 30 may be configured to calculate a value larger than the upper limit value Gmax as the correction value G when correcting the basic addition amount Qub to the increase side. Further, the ECU 30 may be configured to calculate a correction value G that is smaller than the lower limit value Gmin when correcting the basic addition amount Qub to the decrease side.

  The ECU 30 calculates a correction value G that increases the correction amount to the increase side with respect to the basic addition amount Qub when the ammonia concentration Cam is equal to or less than the threshold value Camj and the detected concentration Cx is smaller than the target concentration Cxt. Also good. That is, a correction value G that changes the detected density Cx from a value belonging to the non-interference area A1 to a value belonging to the interference area A2 may be calculated.

  The ECU 30 calculates a correction value G that increases the correction amount to the decrease side with respect to the basic addition amount Qub when the ammonia concentration Cam is larger than the threshold value Camj and the detected concentration Cx is smaller than the target concentration Cxt. Also good. That is, a correction value G that changes the detected density Cx from a value belonging to the interference area A2 to a value belonging to the non-interference area A1 may be calculated.

  The urea SCR system 10 may have a configuration including, for example, an oxidation catalyst that oxidizes ammonia downstream of the selective reduction catalyst 18 in addition to the urea water addition device 15, the selective reduction catalyst 18, and the ECU 30. When the NOx sensor 23 is disposed downstream of the oxidation catalyst, the model 46 is a model that takes into account the consumption of ammonia in the selective reduction catalyst 18 and the oxidation catalyst.

  DESCRIPTION OF SYMBOLS 10 ... Urea SCR system, 11 ... Exhaust passage, 15 ... Urea water addition apparatus, 16 ... Urea water supply part, 17 ... Addition valve, 18 ... Selective reduction type catalyst, 21 ... Oxygen concentration sensor, 22 ... Temperature sensor, 23 ... NOx sensor, 24 ... intake air amount sensor, 25 ... engine speed sensor, 26 ... fuel injection control unit, 30 ... ECU, 31 ... processor, 32 ... memory, 33 ... input interface, 34 ... output interface, 35 ... bus, DESCRIPTION OF SYMBOLS 41 ... Target density | concentration calculation part, 42 ... Basic addition amount calculation part, 43 ... Detection density acquisition part, 44 ... Deviation calculation part, 45 ... Concentration calculation part, 46 ... Model, 47 ... Correction value calculation part, 48 ... Target addition amount Arithmetic unit.

Claims (5)

An acquisition unit that acquires a detection concentration that is a detection value of a NOx sensor installed downstream of a selective reduction catalyst that reduces NOx using ammonia as a reducing agent;
A concentration calculator that calculates the ammonia concentration of the exhaust gas that has passed through the selective catalytic reduction catalyst;
A basic addition amount calculation unit for calculating a basic addition amount of urea water at which the detected concentration becomes a target concentration;
A correction value calculation unit that calculates a correction value of the basic addition amount based on a deviation between the detected concentration and the target concentration;
The correction value calculator is
Holding a threshold for determining the presence or absence of ammonia interference with the detected concentration;
When the calculated value of the concentration calculation unit is equal to or less than the threshold value and the detected concentration is greater than the target concentration, the correction increases the correction amount to the increase side with respect to the basic addition amount as the deviation increases. Calculate the value
When the calculated value is larger than the threshold value and the detected concentration is larger than the target concentration, the correction value for increasing the correction amount to the decrease side with respect to the basic addition amount is calculated as the deviation is larger. Urea SCR system controller. The correction value calculator is
When the calculated value is less than or equal to the threshold value and the detected concentration is smaller than the target concentration, the correction value is calculated to increase the correction amount to the decrease side with respect to the basic addition amount as the deviation is smaller. ,
When the calculated value is larger than the threshold value and the detected concentration is smaller than the target concentration, the correction value that increases the correction amount to the increase side with respect to the basic addition amount is calculated as the deviation is smaller. The urea SCR system control device according to claim 1. The correction value calculator is
About the correction value, an upper limit value at which the correction amount to the increase side with respect to the basic addition amount is maximized and a first reset value that is a reset value when correcting the basic addition amount to the increase side are held,
3. The urea SCR system control device according to claim 1, wherein the first reset value is set to the correction value on the condition that the correction value has reached the upper limit value. 4. The correction value calculator is
About the correction value, a lower limit value at which the correction amount to the reduction side with respect to the basic addition amount is maximized and a second reset value that is a reset value when correcting the basic addition amount to the reduction side are held,
The urea SCR system control device according to any one of claims 1 to 3, wherein the correction value is set as the second reset value on the condition that the correction value has reached the lower limit value. A selective reduction catalyst that reduces NOx using ammonia as a reducing agent; a urea water addition device that adds urea water to exhaust gas upstream of the selective reduction catalyst; and an addition amount of the urea water by the urea water addition device. A control method for a urea SCR system comprising a control device for controlling,
The controller is
Obtaining a detection concentration which is a detection value of a NOx sensor installed downstream of the selective catalytic reduction catalyst;
Calculating the ammonia concentration of the exhaust gas that has passed through the selective catalytic reduction catalyst;
Calculating a basic addition amount of urea water at which the detected concentration becomes a target concentration;
A step of calculating a correction value of the basic addition amount based on a deviation between the detected concentration and the target concentration,
In the step of calculating the correction value, the deviation is calculated when the calculated value of the ammonia concentration is equal to or less than a threshold value for determining the presence or absence of ammonia interference with the detected concentration, and the detected concentration is larger than the target concentration. When the correction value for increasing the correction amount to the increase side with respect to the basic addition amount is calculated as the value is larger, the calculated value is greater than the threshold value, and the detected concentration is greater than the target concentration, The urea SCR system control method in which the correction value is calculated such that the larger the deviation is, the larger the correction amount to the reduction side with respect to the basic addition amount is.