JP2013181411A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an existing mission control device of an internal combustion engine capable of enhancing the accuracy of a feedback value set for compatibly establishing cleaning NOx and suppressing ammonium from being discharged when feedback controlling an adding quantity of reductant.SOLUTION: An SCR catalyst 41 for cleaning NOx by adding urea water, an urea adding valve 230 for adding the urea water, and a tank 210 for storing the urea water are arranged in an engine 1. A control device 80 calculates a first feedback value renewed based on the output value of a second NOx sensor 140 and calculates a second feedback value renewed based on a disjunction tendency of an estimated urea water remaining quantity in the tank 210 and an actual urea remaining quantity when a changing quantity of an output value of a second NOx sensor 140 is not less than a predetermined value. Further, the control device sets an additional feedback value when feedback controlling a target adding quantity of the urea water adding from the urea adding valve 230 based on the first and second feedback values.

Description

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

  2. Description of the Related Art An exhaust gas purification device for an internal combustion engine that includes a NOx purification catalyst that purifies nitrogen oxide (NOx) in exhaust gas is known. In such an exhaust purification device, for example, a reducing agent such as urea water is injected from the injection valve toward the exhaust passage. When the injected reducing agent reaches the NOx purification catalyst, it is adsorbed on the NOx purification catalyst as ammonia. The NOx is reduced and purified by ammonia adsorbed on the catalyst.

  If the amount of the reducing agent added is too small, NOx cannot be sufficiently purified. Moreover, when there is too much addition amount of a reducing agent, the excess ammonia will be discharged | emitted by NOx purification. Therefore, in order to achieve both NOx purification and ammonia emission suppression, it is necessary to set the amount of reducing agent added appropriately without excess or deficiency as much as possible. Therefore, for example, in the apparatus described in Patent Document 1, the NOx amount is detected by a NOx sensor, and the amount of addition of the reducing agent is feedback controlled based on the detected NOx amount.

JP 2004-517249 A

  When performing feedback control on the amount of reducing agent added as in the apparatus described in the above-mentioned document 1, NOx purification and ammonia emission suppression can be made more compatible by further improving the accuracy of the feedback value. It becomes like this. The conventional apparatus leaves room for further improvement in improving the accuracy of the feedback value.

  The present invention has been made in view of such circumstances, and its purpose is to provide feedback value accuracy that is set to achieve both NOx purification and ammonia emission suppression in feedback control of the amount of reducing agent added. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can improve the engine.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 includes a NOx purification catalyst that purifies NOx by adding a reducing agent, and an addition valve that adds the reducing agent into the exhaust passage, and a target addition amount of the reducing agent that is added from the addition valve In an exhaust gas purification apparatus for an internal combustion engine that is feedback controlled with an addition feedback value, a NOx sensor that detects the amount of NOx in the exhaust gas that has passed through the NOx purification catalyst, and a reducing agent remaining amount in a tank that stores the reducing agent And a first feedback value that is updated based on the output value when the amount of change in the output value of the NOx sensor becomes equal to or less than a predetermined amount. A second feedback that is updated based on a deviation tendency between the estimated reducing agent remaining amount in the tank calculated based on the target addition amount and the remaining reducing agent amount detected by the remaining amount sensor. It calculates a value, as its gist to set the added feedback value based on the first feedback value and the second feedback value.

  According to the configuration, the addition feedback value for correcting the target addition amount is set by the first feedback value and the second feedback value. Here, since the first feedback value is updated based on the output value of the NOx sensor, the first feedback value is calculated as a correction value for the target addition amount according to the actual NOx amount. Therefore, the accuracy of the addition feedback value for achieving both NOx purification and ammonia emission suppression is improved, and the target addition amount setting accuracy is improved.

  Further, the second feedback value is updated based on a deviation tendency between the estimated reducing agent remaining amount in the tank calculated based on the target addition amount and the actual reducing agent remaining amount detected by the remaining amount sensor. The estimated reducing agent remaining amount can be calculated by subtracting the integrated value of the target addition amount from the actual reducing agent remaining amount in the tank detected in advance. The deviation tendency between the estimated reducing agent remaining amount and the actual reducing agent remaining amount indicates the deviation of the actual addition amount from the addition amount command value instructed to the addition valve, that is, the tendency of the addition amount error of the addition valve. Yes, the second feedback value updated based on such a deviation tendency is calculated as a correction value for correcting the addition amount error of the addition valve. As a result, the addition feedback value is set so that the deviation of the actual addition amount with respect to the target addition amount is corrected, and the accuracy of the addition feedback value for achieving both NOx purification and ammonia emission suppression also by this. And the accuracy of the actual addition amount with respect to the target addition amount is improved.

  In general, since the resolution of the NOx sensor is higher than that of the remaining amount sensor, the accuracy of the first feedback value updated by the output value of the NOx sensor is updated using the detection value of the remaining amount sensor. It becomes higher than the feedback value. However, it is desirable to update the first feedback value when the change amount of the output value of the NOx sensor is equal to or less than a predetermined amount and the output value is stable, for example, during steady operation of the engine. During operation, such output values are rarely stabilized. On the other hand, the remaining amount of the reducing agent by the remaining amount sensor can be detected regardless of the steady operation or transient operation of the engine. Therefore, the update frequency of the second feedback value can be higher than the update frequency of the first feedback value. As described above, the first feedback value has a feature that the accuracy is higher than that of the second feedback value, and the second feedback value can ensure a larger update frequency than the first feedback value. There is. Therefore, the addition feedback value set by the first feedback value and the second feedback value is preferably set in terms of accuracy and update frequency.

  As described above, according to the same configuration, when feedback control is performed on the addition amount of the reducing agent, the accuracy of the addition feedback value that is set in order to achieve both NOx purification and ammonia emission suppression can be increased.

  According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, a reflection degree of the first feedback value with respect to the addition feedback value is larger than a reflection degree of the second feedback value. The main point is to make it larger.

  As described above, the accuracy of the first feedback value updated by the output value of the NOx sensor is higher than the second feedback value updated by using the detection value of the remaining amount sensor. Therefore, in the same configuration, the reflection degree of the first feedback value with respect to the addition feedback value is made larger than the reflection degree of the second feedback value, thereby improving the accuracy of the addition feedback value.

  According to a third aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect, the degree of reflection of the first feedback value with respect to the addition feedback value increases as the temperature of the NOx purification catalyst increases. The gist is to be done.

  The higher the temperature of the NOx purification catalyst, the more quickly the output value of the NOx sensor reacts, so the time until the output value stabilizes becomes shorter. Accordingly, the higher the temperature of the NOx purification catalyst, the more frequently the first feedback value is updated, and the higher the accuracy of the first feedback value is. Therefore, in this configuration, the degree of reflection of the first feedback value is increased as the temperature of the NOx purification catalyst is higher, and thereby the accuracy of the addition feedback value can be further increased.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to third aspects, when the update frequency of the first feedback value is lower than a predetermined value, the update frequency is the same. The gist of the invention is that the degree of reflection of the first feedback value with respect to the additive feedback value is smaller than when the value is higher than the predetermined value.

  When the update frequency of the first feedback value is lower than the predetermined value, the number of updates of the first feedback value is small, and the reliability of the value is also low. Therefore, in the same configuration, when the update frequency of the first feedback value is lower than the predetermined value, the reflection degree of the first feedback value with respect to the addition feedback value is reduced. Therefore, it becomes possible to suppress the setting of the addition feedback value by the feedback value having low reliability.

  According to a fifth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fourth aspects, after the processing for increasing the amount of addition of the reducing agent is performed, the detected value of the NOx sensor When the NOx sensor increases, the first feedback value is updated to reduce the target addition amount, and after the process of increasing the reducing agent addition amount is performed, the target addition amount is detected when the detected value of the NOx sensor decreases. The gist of the invention is that the first feedback value is updated on the side of increasing the amount.

  Some NOx sensors detect not only NOx but also ammonia. Therefore, in this configuration, first, the amount of reducing agent added is increased. When the detected value of the NOx sensor increases due to the increase in the reducing agent, it can be considered that the NOx sensor detects ammonia due to excessive addition of the reducing agent. In this case, in order to suppress excessive addition of the reducing agent, the first feedback value is updated to reduce the target addition amount. On the other hand, when the detected value of the NOx sensor decreases due to the increase of the reducing agent, it can be considered that the NOx amount is decreased due to the addition of the reducing agent. In this case, NOx can be further purified by correcting the reducing agent in an increased amount. Therefore, the first feedback value is updated to the side for correcting the target addition amount to be increased. As described above, according to the same configuration, even if the NOx sensor detects not only NOx but also ammonia, the first feedback value that can achieve both NOx purification and ammonia emission suppression can be calculated. Become.

  According to a sixth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, the target addition is performed when the remaining reducing agent amount is smaller than the estimated remaining reducing agent amount. The second feedback value is updated on the side for correcting the amount to be decreased, and the second feedback value is updated on the side for increasing the target addition amount when the remaining amount of the reducing agent is larger than the estimated remaining amount of reducing agent. The gist is to be done.

  As described above, the deviation tendency between the estimated reducing agent remaining amount in the tank calculated based on the target addition amount and the actual reducing agent remaining amount detected by the remaining amount sensor is determined by the addition amount instructed to the addition valve. It shows the tendency of the actual addition amount with respect to the command value, that is, the addition amount error of the addition valve. Therefore, in the same configuration, when the actual reducing agent remaining amount is small with respect to the estimated reducing agent remaining amount, the actual addition amount is excessive with respect to the target addition amount. The feedback value is updated. On the other hand, when the remaining amount of the actual reducing agent is larger than the estimated remaining amount of the reducing agent, the actual addition amount is too small with respect to the target addition amount, so the second feedback value is updated on the side to increase the target addition amount. Like to do. Therefore, according to the configuration, it is possible to appropriately calculate the second feedback value for correcting the deviation of the actual addition amount with respect to the target addition amount.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about one Embodiment of the exhaust gas purification device of the internal combustion engine concerning this invention. The flowchart which shows the procedure about the calculation process of the urea addition amount in the embodiment. The flowchart which shows the procedure about the setting process of the 1st feedback value in the embodiment. The flowchart which shows the procedure about the setting process of the 2nd feedback value in the embodiment. The flowchart which shows the procedure about the setting process of the addition feedback value in the embodiment. The graph which shows the relationship between 2nd exhaust temperature and the reflection coefficient K. FIG.

  Hereinafter, an embodiment of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to FIGS. Note that “upstream” and “downstream” described in this specification are based on the flow direction of the exhaust gas in the exhaust system.

FIG. 1 is a schematic configuration diagram showing a diesel engine (hereinafter simply referred to as “engine”) to which the exhaust emission control device according to the present embodiment is applied, and a peripheral configuration thereof.
The engine 1 is provided with a plurality of cylinders # 1 to # 4. A plurality of fuel injection valves 4 a to 4 d are attached to the cylinder head 2. These fuel injection valves 4a to 4d inject fuel into the combustion chambers of the cylinders # 1 to # 4. Also, the cylinder head 2 is provided with intake ports for introducing fresh air into the cylinders and exhaust ports 6a to 6d for discharging combustion gas to the outside of the cylinders corresponding to the respective cylinders # 1 to # 4. It has been.

  The fuel injection valves 4a to 4d are connected to a common rail 9 that accumulates high-pressure fuel. The common rail 9 is connected to the supply pump 10. The supply pump 10 sucks fuel in the fuel tank and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected into the cylinder from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened.

  An intake manifold 7 is connected to the intake port. The intake manifold 7 is connected to the intake passage 3. An intake throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3.

An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. The exhaust manifold 8 is connected to the exhaust passage 26.
In the middle of the exhaust passage 26, there is provided a turbocharger 11 that supercharges intake air introduced into the cylinder using exhaust pressure. An intercooler 18 is provided in the intake passage 3 between the intake side compressor of the turbocharger 11 and the intake throttle valve 16. The intercooler 18 cools the intake air whose temperature has risen due to supercharging of the turbocharger 11.

  A first purification member 30 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the exhaust side turbine of the turbocharger 11. Inside the first purification member 30, an oxidation catalyst 31 and a DPF catalyst 32 are arranged in series with respect to the flow direction of the exhaust gas.

  The oxidation catalyst 31 carries a catalyst for oxidizing HC in the exhaust. The DPF catalyst 32 is a filter that collects PM (particulate matter) in the exhaust gas and is composed of a porous ceramic, and further supports a catalyst for promoting oxidation of PM. . The PM in the exhaust gas is collected when it passes through the porous wall of the DPF catalyst 32. The DPF catalyst 32 constitutes the exhaust purification member.

  Further, a fuel addition valve 5 for supplying fuel as an additive to the oxidation catalyst 31 and the DPF catalyst 32 is provided in the vicinity of the collecting portion of the exhaust manifold 8. The fuel addition valve 5 is connected to the supply pump 10 through a fuel supply pipe 27. The position of the fuel addition valve 5 can be changed as appropriate as long as it is in the exhaust system and upstream of the first purification member 30.

  When the amount of PM collected by the DPF catalyst 32 exceeds a predetermined value, regeneration processing of the DPF catalyst 32 is started, and fuel is injected from the fuel addition valve 5 into the exhaust manifold 8. The fuel injected from the fuel addition valve 5 is combusted when it reaches the oxidation catalyst 31, thereby increasing the exhaust temperature. The exhaust gas heated by the oxidation catalyst 31 flows into the DPF catalyst 32, whereby the DPF catalyst 32 is heated, whereby the PM deposited on the DPF catalyst 32 is oxidized to regenerate the DPF catalyst 32. Is planned.

  A second purification member 40 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the first purification member 30. Inside the second purification member 40, a selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) 41 is disposed as a NOx purification catalyst that reduces and purifies NOx in the exhaust using a reducing agent.

  Further, a third purification member 50 for purifying exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the second purification member 40. Inside the third purification member 50, an ammonia oxidation catalyst 51 for purifying ammonia in the exhaust is disposed.

  The engine 1 is provided with a urea water supply mechanism 200 as a reducing agent supply mechanism that supplies a reducing agent to the SCR catalyst 41. The urea water supply mechanism 200 includes a tank 210 that stores urea water, a urea addition valve 230 that injects urea water into the exhaust passage 26, a supply passage 240 that connects the urea addition valve 230 and the tank 210, and a supply passage 240. A pump 220 provided in the middle, a remaining amount sensor 250 for detecting the amount of urea water stored in the tank 210 (urea remaining amount NR), and the like.

  The urea addition valve 230 is provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40, and the injection hole is opened toward the SCR catalyst 41. When the urea addition valve 230 is opened, urea water is injected and supplied into the exhaust passage 26 via the supply passage 240. The urea addition valve 230 constitutes the reducing agent injection valve.

  The pump 220 is an electric pump, and at the time of forward rotation, the urea water is fed from the tank 210 toward the urea addition valve 230. On the other hand, during reverse rotation, urea water is sent from the urea addition valve 230 toward the tank 210. In other words, during the reverse rotation of the pump 220, urea water is recovered from the urea addition valve 230 and the supply passage 240 and returned to the tank 210.

  A dispersion plate 60 is provided in the exhaust passage 26 between the urea addition valve 230 and the SCR catalyst 41 to promote atomization of the urea water by dispersing the urea water injected from the urea addition valve 230. It has been.

  When urea water injected from the urea addition valve 230 reaches the SCR catalyst 41, it is adsorbed as ammonia. Then, NOx is reduced and purified by the ammonia adsorbed on the SCR catalyst 41.

  In addition, the engine 1 is provided with an exhaust gas recirculation device (hereinafter referred to as an EGR device). This EGR device is a device that reduces the combustion temperature in the cylinder by introducing a part of the exhaust gas into the intake air, thereby reducing the amount of NOx generated. This exhaust gas recirculation device includes an EGR passage 13 that communicates the intake passage 3 and the exhaust manifold 8, an EGR valve 15 provided in the EGR passage 13, an EGR cooler 14, and the like. By adjusting the opening degree of the EGR valve 15, the exhaust gas recirculation amount introduced into the intake passage 3 from the exhaust passage 26, that is, the so-called external EGR amount is adjusted. Further, the temperature of the exhaust gas flowing through the EGR passage 13 is lowered by the EGR cooler 14.

  Various sensors for detecting the engine operation state are attached to the engine 1. For example, the air flow meter 19 detects the intake air amount GA in the intake passage 3. The throttle valve opening sensor 20 detects the opening of the intake throttle valve 16. The engine rotation speed sensor 21 detects the rotation speed of the crankshaft, that is, the engine rotation speed NE. The accelerator sensor 22 detects an accelerator pedal depression amount, that is, an accelerator operation amount ACCP. The outside air temperature sensor 23 detects the outside air temperature THout. The vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle on which the engine 1 is mounted.

  The first exhaust temperature sensor 100 provided upstream of the oxidation catalyst 31 detects the first exhaust temperature TH1 that is the exhaust temperature before flowing into the oxidation catalyst 31. The differential pressure sensor 110 detects the pressure difference ΔP between the exhaust pressure upstream and downstream of the DPF catalyst 32.

  A second exhaust temperature sensor 120 and a first NOx sensor 130 are provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40 and upstream of the urea addition valve 230. The second exhaust temperature sensor 120 detects a second exhaust temperature TH2, which is the exhaust temperature before flowing into the SCR catalyst 41. The first NOx sensor 130 detects a first NOx concentration N1, which is the NOx concentration in the exhaust before flowing into the SCR catalyst 41.

  The exhaust passage 26 downstream of the third purification member 50 is provided with a second NOx sensor 140 that detects a second NOx concentration N2 that is the NOx concentration in the exhaust gas that has passed through the SCR catalyst 41. The first NOx sensor 130 and the second NOx sensor 140 are sensors that react not only to NOx in the exhaust but also to ammonia, and the output value increases as the amount of NOx and the amount of ammonia in the exhaust increases.

  Outputs from these various sensors are input to the control device 80. The control device 80 includes a central processing control device (CPU), a read-only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, a timer counter, an input The microcomputer is mainly configured with an interface, an output interface, and the like.

  Then, the controller 80 controls, for example, the fuel injection amount control / fuel injection timing control of the fuel injection valves 4a to 4d and the fuel addition valve 5, the discharge pressure control of the supply pump 10, and the drive amount of the actuator 17 that opens and closes the intake throttle valve 16. Various controls of the engine 1 such as control and opening control of the EGR valve 15 are performed.

The exhaust gas purification control such as the regeneration process for burning the PM collected by the DPF catalyst 32 is also performed by the controller 80.
The control device 80 also performs urea water addition control by the urea addition valve 230 as one of such exhaust gas purification controls. In this addition control, a urea addition amount QE, which is a target addition amount of urea water necessary for reducing NOx discharged from the engine 1, is calculated based on the engine operating state and the like. Then, the open state of the urea addition valve 230 is controlled so that the calculated urea addition amount QE is injected from the urea addition valve 230.

FIG. 2 shows a procedure for calculating the urea addition amount QE. This process is executed by the control device 80.
When this process is started, first, the equivalence ratio TT is calculated based on the intake air amount GA and the second exhaust temperature TH2 (S100). This equivalence ratio TT is an addition amount of urea water that is sufficient for reducing NOx, and is necessary for the unit concentration of NOx (for example, to completely reduce 1 ppm of NOx). Necessary addition amount). Then, as the intake air amount GA increases (that is, the exhaust flow rate increases) or as the second exhaust temperature TH2 increases, the amount of addition required per unit concentration of NOx tends to increase. The equivalence ratio TT is variably set so that the value of the equivalence ratio TT increases as the amount of exhaust gas increases or as the second exhaust temperature TH2 increases.

  Next, the equivalence ratio TT is multiplied by the first NOx concentration N1 and the addition feedback value (hereinafter referred to as the addition FB value) F, thereby calculating the urea addition amount QE (S110), and this processing is completed. Is done. The added FB value F is set by a first feedback value (hereinafter referred to as a first FB value) F1 and a second feedback value (hereinafter referred to as a second FB value) F2.

  First, the setting of the first FB value F1 will be described. The first FB value F1 is a value set through the setting process shown in FIG. The setting process is executed by the control device 80.

  When this process is executed, first, it is determined whether or not the second NOx output value S2 that is the output value of the second NOx sensor 140 is greater than or equal to the determination value A (S200). When the second NOx output value S2 is less than the determination value A (S200: NO), it is determined that the NOx and ammonia in the exhaust gas are sufficiently small, and the present process is terminated.

  On the other hand, when the second NOx output value S2 is greater than or equal to the determination value A (S200: YES), it is determined that NOx or ammonia in the exhaust gas is relatively large, and then the urea addition amount is increased (S210). In step S210, the urea addition amount is increased by adding a predetermined urea increase amount to the currently set urea addition amount QE.

  Next, it is determined whether or not the second NOx output value S2 is stable (S220). In step S220, it is determined that the second NOx output value S2 is stable when the amount of change in the second NOx output value S2 is equal to or smaller than a predetermined amount. When the second NOx output value S2 is not stable (S220: NO), the determination process of step S210 is repeatedly executed until the second NOx output value S2 is stabilized.

  When it is determined in step S220 that the second NOx output value S2 is stable (S220: YES), it is determined whether or not the second NOx output value S2 has decreased after the urea addition amount has increased in step S210 ( S230).

  When the second NOx output value S2 is decreasing (S230: YES), it can be considered that the NOx amount has decreased due to the increase in the urea addition amount in step S210. In this case, NOx can be further purified by increasing the urea addition amount QE. Therefore, in this case, the first FB value F1 is corrected to increase in order to increase the urea addition amount QE (S240), and this process is terminated. In this step S240, by adding a predetermined value α to the currently set first FB value F1, the first FB value F1 is updated to a larger value, whereby the first FB value F1 increases the urea addition amount QE. Updated to the correction side.

  On the other hand, if it is determined in step S230 that the second NOx output value S2 has not decreased (S230: NO), whether or not the second NOx output value S2 has increased after the urea addition amount has increased in step S210. Is determined (S250). When the second NOx output value S2 is increasing (S250: YES), it can be considered that the second NOx sensor 140 detects ammonia due to excessive urea addition. Therefore, in this case, the first FB value F1 is corrected to decrease in order to suppress excessive urea addition (S260), and this process is terminated. In this step S260, the predetermined value α is subtracted from the currently set first FB value F1, so that the first FB value F1 is updated to a smaller value, whereby the first FB value F1 decreases the urea addition amount QE. Updated to the correction side.

On the other hand, when it is determined in step 250 that the second NOx output value S2 has not increased (S250: NO), this process ends.
Incidentally, when the difference between the first FB value F1 before update and the first FB value F1 after update is very large, it is determined that the reliability of the first FB value F1 after update is low, and the first FB value F1 before update is determined. You may make it maintain.

  By performing the setting process of the first FB value F1, even if the second NOx sensor 140 is a sensor that detects not only NOx but also ammonia, the first FB value that can achieve both NOx purification and ammonia emission suppression. F1 can be calculated.

  In the setting process of the first FB value F1, the first FB value F1 is updated based on the output value of the second NOx sensor 140. Therefore, the first FB value F1 is corrected for the urea addition amount QE according to the actual NOx amount. Calculated as a value. Accordingly, the accuracy of the added FB value F for achieving both NOx purification and ammonia emission suppression is improved, and when setting the urea addition amount QE intended to achieve both NOx purification and ammonia emission suppression, Setting accuracy is improved. That is, the first FB value F1 is a feedback value for increasing the setting accuracy of the urea addition amount QE.

  Next, the setting of the second FB value F2 will be described. The second FB value F2 is a value set through the setting process shown in FIG. The setting process is repeatedly executed by the control device 80 at predetermined intervals.

  When this process is started, it is first determined whether or not it is immediately after the urea water is replenished to the tank 210 (S300). Here, for example, when the urea water remaining amount RN detected by the remaining amount sensor 250 is greater than a predetermined value by the previous detection value, it can be determined that the urea water has just been replenished. It is. If it is immediately after the urea water is replenished (S300: YES), the integrated urea addition amount QES is reset in step S390, and this process is temporarily ended. The integrated urea addition amount QES is an integrated value of the urea addition amount QE, and the calculation of the integrated value is started immediately after urea water is replenished to the tank 210. If there is no injection error in the urea addition valve 230, the total amount of actual urea water injected from the tank 210 after the urea water is replenished and the integrated urea addition amount QES match.

  On the other hand, when it is determined in step S300 that it is not immediately after the urea water is replenished (S300: YES), the current accumulated urea addition amount QES is read (S310), and the current urea water remaining amount RN is also read. (S320).

  Next, it is determined whether or not the remaining amount change amount RNH is equal to or greater than a determination value H1 (S330). This remaining amount change amount RNH is the remaining amount change amount of the urea water stored in the tank 210. More specifically, the remaining amount of urea water remaining RN from when the second FB value F2 is updated to the present time is updated. The amount of change. The urea water remaining amount RN detected by the remaining amount sensor 250 is affected by the urea water shaking in the tank 210. Therefore, when the remaining amount change amount RNH is very small, the remaining amount change amount RNH calculated based on the sensor detection value may include a large detection error with respect to the actual remaining amount change amount. Conversely, if the remaining amount change amount RNH is large to some extent, the influence of such a detection error is reduced. Therefore, as the determination value H1, a value that can determine whether or not the value of the remaining amount change amount RNH is large enough to sufficiently reduce the influence of the detection error described above is set.

When the remaining amount change amount RNH is less than the determination value H1 (S330: NO), this process is temporarily terminated.
On the other hand, when the remaining amount change amount RNH is greater than or equal to the determination value H1 (S330: YES), the estimated remaining amount RS is calculated based on the following equation (1) (S340).

Estimated remaining amount RS = urea remaining amount RN immediately after urea solution replenishment RN−integrated urea addition amount QES (1)

As can be seen from the equation (1), the estimated remaining amount RS is obtained by subtracting the integrated value of the urea addition amount QE from the urea water remaining amount RN immediately after the urea water replenishment, and the addition amount command to the urea addition valve 230 If the urea addition amount QE, which is the value, and the urea water amount actually added from the urea addition valve 230 match, the urea water remaining amount RN detected by the remaining amount sensor 250 matches the estimated remaining amount RS. To do. On the other hand, when there is an addition amount error in the urea addition valve 230, the amount of urea water actually added from the urea addition valve 230 is deviated from the urea addition amount QE. It is reflected in the divergence tendency with estimated remaining amount RS. Therefore, in the processing after step S350, the second FB value F2 for correcting the addition amount error of the urea addition valve 230 is updated based on such a tendency to deviate.

  First, in step S350, it is determined whether the urea water remaining amount RN is smaller than the estimated remaining amount RS. When the urea water remaining amount RN is smaller than the estimated remaining amount RS (S350: YES), it can be considered that the actual addition amount is too large with respect to the urea addition amount QE that is the target addition amount. Therefore, in this case, the second FB value F2 is corrected to decrease in order to suppress the actual urea addition amount (S360), and this process is temporarily terminated. In this step S360, the predetermined value β is subtracted from the currently set second FB value F2, so that the second FB value F2 is updated to a smaller value, whereby the second FB value F2 reduces the urea addition amount QE. Updated to the correction side.

  On the other hand, when the urea water remaining amount RN is not smaller than the estimated remaining amount RS (S350: NO), it is determined in step S370 whether the urea water remaining amount RN is larger than the estimated remaining amount RS. When the urea water remaining amount RN is larger than the estimated remaining amount RS (S370: YES), it can be considered that the actual addition amount is too small with respect to the urea addition amount QE that is the target addition amount. Therefore, in this case, the second FB value F2 is corrected to increase in order to increase the actual urea addition amount (S380), and this process is temporarily terminated. In this step S380, by adding a predetermined value β to the currently set second FB value F2, the second FB value F2 is updated to a larger value, whereby the second FB value F2 increases the urea addition amount QE. Updated to the correction side.

  On the other hand, when it is determined in step 370 that the urea water remaining amount RN is not larger than the estimated remaining amount RS (S370: NO), this process is temporarily ended. Therefore, in this case, the second FB value F2 is not substantially updated.

  Incidentally, when the difference between the second FB value F2 before the update and the second FB value F2 after the update is very large, it is determined that the reliability of the second FB value F2 after the update is low, and the second FB value F2 before the update is determined. You may make it maintain.

  Further, in the setting process of the second FB value F2, when it is determined in step S330 that the remaining amount change amount RNH is equal to or larger than the determination value H1, the processes after step S340 are performed. Therefore, the second FB value F2 is updated each time it is determined that the remaining amount change amount RNH is greater than or equal to the determination value H1 in the process of gradually consuming the urea water in the tank 210.

  By performing the setting process of the second FB value F2, the second FB value F2 that corrects the deviation of the actual addition amount with respect to the urea addition amount QE is appropriately calculated. Then, the added FB value F is set so as to correct the deviation of the actual added amount with respect to the urea added amount QE, and this also makes it possible to achieve both NOx purification and ammonia emission suppression. The accuracy of the FB value F is increased, and the accuracy of the actual addition amount with respect to the urea addition amount QE is improved.

Next, the setting of the added FB value F will be described.
First, since the resolution of the NOx sensor is generally higher than that of the remaining amount sensor 250, the accuracy of the first FB value F1 updated by the output value of the second NOx sensor 140 is updated using the detection value of the remaining amount sensor 250. Higher than the second FB value of 2. However, the update of the first FB value F1 is performed when the change amount of the second NOx output value S2 is equal to or less than a predetermined amount and the output value S2 is stable, for example, during steady operation of the engine. The frequency with which the second NOx output value S2 stabilizes during operation is low. On the other hand, the urea water remaining amount RN can be detected by the remaining amount sensor 250 regardless of the steady operation or transient operation of the engine. Therefore, the update frequency of the second FB value F2 is higher than the update frequency of the first FB value F1. As described above, the first FB value F1 has a feature that the accuracy is higher than that of the second FB value F2, and the second FB value F2 can secure a larger update frequency than the first FB value F1. There is. Therefore, the added FB value F set by the first FB value F1 and the second FB value F2 is preferably set in terms of accuracy and update frequency.

  Here, since the first FB value F1 and the second FB value F2 have the characteristics as described above, the degree of reflection of the first FB value F1 with respect to the added FB value F and the By setting the reflection degree of the 2FB value F2, the accuracy of the added FB value F can be further increased. Therefore, in the present embodiment, when the addition FB value F is set by the first FB value F1 and the second FB value F2, a reflection coefficient K indicating such a reflection degree is set.

FIG. 5 shows the procedure for setting the additive FB value F. This process is repeatedly executed by the control device 80 at predetermined intervals.
When this process is started, a reflection coefficient K is first set (S400). The reflection coefficient K is a value indicating the degree of reflection of the first FB value F1 with respect to the added FB value F, and is variably set within a range of “0 ≦ K ≦ 1”. The reflection degree of the second FB value F2 with respect to the added FB value F is (1-K).

The reflection coefficient K is set as follows.
First, the reflection coefficient K is set so that the reflection degree of the first FB value F1 with respect to the added FB value F is larger than the reflection degree of the second FB value F2. For example, the reflection coefficient K is basically a value in the range of “0.5 <K ≦ 1”.

Further, as shown in FIG. 6, the reflection coefficient K is variably set so as to increase as the second exhaust temperature TH2 correlated with the temperature of the SCR catalyst 41 increases.
Further, when the update frequency of the first FB value F1 is lower than a predetermined value N, the reflection coefficient K is reduced by the decrease value KM compared to when the update frequency is higher than the predetermined value N. Thus, the reflection coefficient K is corrected.

When the reflection coefficient K is set in this way, the added FB value F is calculated by the following equation (2) and S410), and this process is temporarily ended.

F = K × F1 + (1−K) × F2 (2)
F: Added FB value F1: First FB value F2: Second FB value K: Reflection coefficient

Next, the effect | action of the setting process of the said addition FB value F is demonstrated.

  First, the first FB value F1 has a feature that the accuracy is higher than that of the second FB value F2, and the second FB value F2 has a feature that a larger update frequency can be secured than the first FB value F1. is there. Therefore, in the setting process, the addition FB value F is set by the first FB value F1 and the second FB value F2, and the addition FB value F is suitably set in terms of accuracy and update frequency. .

  Further, as described above, the accuracy of the first FB value F1 updated by the output value of the second NOx sensor 140 is higher than the second FB value F2 updated using the detection value of the remaining amount sensor 250. Therefore, the reflection coefficient K is set so that the reflection degree of the first FB value F1 with respect to the added FB value F is larger than the reflection degree of the second FB value F2. As a result, the accuracy of the added FB value F is increased.

  In addition, when the addition amount increasing process in step S210 shown in FIG. 3 is performed, the higher the temperature of the SCR catalyst 41, the faster the output value of the second NOx sensor 140 reacts. The time until the value S2 is stabilized is shortened. Therefore, as the temperature of the SCR catalyst 41 is higher, the update frequency of the first FB value F1 is increased, and the accuracy of the first FB value F1 is further increased. Therefore, as shown in FIG. 6, the reflection coefficient K is variably set so as to increase as the second exhaust temperature TH2 correlated with the temperature of the SCR catalyst 41 increases. As a result, the higher the temperature of the SCR catalyst 41, the greater the degree of reflection of the first FB value F1 with respect to the added FB value F, thereby further increasing the accuracy of the added FB value F.

  When the update frequency of the first FB value F1 is lower than the predetermined value, the number of updates of the first FB value F1 is small and the reliability of the first FB value F1 is also low. Therefore, when the update frequency of the first FB value F1 is lower than a predetermined value N, the reflection coefficient K is decreased by the decrease value KM compared to when the update frequency is higher than the predetermined value N. I am trying to correct it. The decrease value KM is determined to be a suitable value by a prior experiment or the like. By reducing the reflection coefficient K by the decrease value KM in this manner, the degree of reflection of the first FB value F1 with respect to the added FB value F is reduced when the update frequency of the first FB value F1 is low. Therefore, the setting of the added FB value F with a feedback value with low reliability can be suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The target addition amount (urea addition amount QE) of urea water added from the urea addition valve 230 is feedback controlled by the addition FB value F.

  In addition, when the amount of change in the output value of the second NOx sensor 140 becomes equal to or less than a predetermined amount, that is, when the amount of change is stable, the first FB value F1 that is updated based on the output value is calculated. . Further, it is updated based on a deviation tendency between the estimated remaining amount RS in the tank 210 calculated based on the urea addition amount QE that is the addition amount command value and the urea water remaining amount RN detected by the remaining amount sensor 250. The second FB value F2 is calculated.

  The first FB value F1 has a feature that the accuracy is higher than that of the second FB value F2, and the second FB value F2 has a feature that a larger update frequency can be ensured than the first FB value F1. Therefore, the added FB value F is set based on the first FB value F1 and the second FB value F2. Therefore, the added FB value F is suitably set in terms of accuracy and update frequency. Therefore, when feedback control is performed on the amount of urea water added, the accuracy of the added FB value F set to achieve both NOx purification and ammonia emission suppression can be increased.

(2) The reflection degree of the first FB value F1 with respect to the added FB value F is set larger than the reflection degree of the second FB value F2. As a result, the accuracy of the added FB value F is increased.
(3) The degree of reflection of the first FB value F1 with respect to the added FB value F is increased as the second exhaust temperature TH2 is higher, that is, as the temperature of the SCR catalyst 41 is higher. Therefore, the accuracy of the added FB value can be further increased.

  (4) When the update frequency of the first FB value F1 is lower than the predetermined value N, the degree of reflection of the first FB value F1 with respect to the added FB value F is made smaller than when the update frequency is higher than the predetermined value N. I have to. Therefore, it becomes possible to suppress the setting of the added FB value F by a feedback value with low reliability.

  (5) When the detected value of the second NOx sensor 140 increases after the process of increasing the amount of urea water added, the first FB value F1 is updated to the side on which the urea addition amount QE is corrected to decrease. . When the detected value of the second NOx sensor 140 decreases after the process of increasing the amount of urea water added, the first FB value F1 is updated so that the urea addition amount QE is corrected to increase. Therefore, even if the second NOx sensor 140 is a sensor that detects not only NOx but also ammonia, the first FB value F1 that can achieve both NOx purification and ammonia emission suppression can be calculated.

  (6) When the urea aqueous solution remaining amount RN is smaller than the estimated remaining amount RS, the second FB value F2 is updated to the side for correcting the decrease in the urea addition amount QE. In addition, when the urea water remaining amount RN is larger than the estimated remaining amount RS, the second FB value F2 is updated so as to correct the increase in the urea addition amount QE. Therefore, the second FB value F2 for correcting the deviation of the actual addition amount with respect to the urea addition amount QE can be appropriately calculated.

In addition, the said embodiment can also be changed and implemented as follows.
-By basically setting the reflection coefficient K to a value within the range of "0.5 <K≤1," the reflection degree of the first FB value F1 with respect to the added FB value F is compared with the reflection degree of the second FB value F2. To make it bigger. In addition, when the second FB value F2 is more accurate than the first FB value F1, for example, the reflection coefficient K is basically set to a value in the range of “0 ≦ K <0.5”. Thus, the reflection degree of the second FB value F2 with respect to the added FB value F may be larger than the reflection degree of the first FB value F1. Further, the setting of the reflection degree related to such accuracy may be omitted.

  The reflection coefficient K increases as the second exhaust temperature TH2 correlated with the temperature of the SCR catalyst 41 increases. However, the variable setting of the reflection coefficient K may be omitted. Even in this case, effects other than the above (3) can be obtained.

  When the update frequency of the first FB value F1 is lower than a predetermined value N, the reflection coefficient K is made smaller by the decrease value KM than when the update frequency is higher than the predetermined value N. However, the correction of the reflection coefficient K may be omitted. Even in this case, effects other than the above (4) can be obtained.

  When the update frequency of the second FB value F2 is lower than a predetermined value M, the degree of reflection of the second FB value F2 with respect to the added FB value F is set compared to when the update frequency is higher than the predetermined value M. It may be made smaller. In this case, the setting of the added FB value F by the second FB value F2 having low reliability can be suppressed. In this modification, when the update frequency of the second FB value F2 is lower than a predetermined value M, the reflection coefficient K is corrected so that, for example, the reflection coefficient K is increased by the increase value KP. This can be implemented.

  In setting the second FB value F2, the second FB value F2 is set based on the amount of urea water remaining in the tank 210. In addition, since the amount of urea water remaining in the tank 210 and the amount of urea water consumed from the tank 210 are complementary to each other, it is based on the amount of urea water consumed from the tank 210. The second FB value F2 may be set. In this modification, after an affirmative determination is made in the process of step S330 shown in FIG. 4, the actual consumption amount of urea water is calculated instead of the estimated remaining amount RS. More specifically, by subtracting the current urea water remaining amount RN from the urea water remaining amount RN immediately after the urea water replenishment, the actual amount of urea water consumed up to the present after the urea water replenishment is calculated. When the actual amount of urea water consumption is larger than the cumulative urea addition amount QES, the second FB value F2 is corrected to decrease in step S360. On the other hand, when the actual consumption amount of urea water is smaller than the cumulative urea addition amount QES, it can be implemented by performing an increase correction of the second FB value F2 in step S380.

-Setting of the addition FB value F by the 1st FB value F1 and the 2nd FB value F2 can be changed suitably.
For example, when one of the first FB value F1 and the second FB value F2 is updated, the added FB value F may be set using one updated FB value and the other FB value not updated. .

  Further, in the above embodiment, the reflection coefficient K is obtained in order to make the reflection degree of the first FB value F1 and the reflection degree of the second FB value F2 different from the addition FB value F. In the equation (2), the first FB value F1 is multiplied by the reflection coefficient K, and the second FB value F2 is multiplied by the value of (1−reflection coefficient K). However, the reflection degree of the first FB value F1 and the reflection degree of the second FB value F2 with respect to the added FB value F may be made different in this other mode. For example, the first reflection coefficient K1 indicating the reflection degree of the first FB value F1 with respect to the addition FB value F is set, and the second reflection coefficient K2 indicating the reflection degree of the second FB value F2 with respect to the addition FB value F is set. Then, the added FB value F may be set by adding a value obtained by multiplying the first FB value F1 by the first reflection coefficient K1 and a value obtained by multiplying the second FB value F2 by the second reflection coefficient K2.

  Although the second exhaust temperature TH2 is used as a substitute value for the temperature of the SCR catalyst 41, the temperature of the SCR catalyst 41 may be directly detected. Further, the temperature of the SCR catalyst 41 may be estimated based on the engine operating state.

  Although urea water is used as the reducing agent, other reducing agents may be used.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Fuel addition valve, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail, DESCRIPTION OF SYMBOLS 10 ... Supply pump, 11 ... Turbocharger, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... Intake throttle valve, 17 ... Actuator, 18 ... Intercooler, 19 ... Air flow meter, 20 ... Throttle valve opening Degree sensor, 21 ... Engine rotation speed sensor, 22 ... Accelerator sensor, 23 ... Outside air temperature sensor, 24 ... Vehicle speed sensor, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... First purification member, 31 ... Oxidation catalyst, 32 ... Filter, 40 ... Second purification member, 41 ... NOx purification catalyst (selective reduction type NOx catalyst: SCR catalyst), 50 ... Third purification member, 5 DESCRIPTION OF SYMBOLS ... Ammonia oxidation catalyst, 60 ... Dispersion plate, 80 ... Control apparatus, 100 ... First exhaust temperature sensor, 110 ... Differential pressure sensor, 120 ... Second exhaust temperature sensor, 130 ... First NOx sensor, 140 ... Second NOx sensor, 200 ... urea water supply mechanism, 210 ... tank, 220 ... pump, 230 ... urea addition valve, 240 ... supply passage, 250 ... remaining amount sensor.

Claims (6)

A NOx purification catalyst that purifies NOx by adding a reducing agent, and an addition valve that adds the reducing agent into the exhaust passage, and a target addition amount of the reducing agent that is added from the addition valve is feedback-controlled by an addition feedback value. In an exhaust gas purification device for an internal combustion engine,
A NOx sensor that detects the amount of NOx in the exhaust gas that has passed through the NOx purification catalyst;
A remaining amount sensor for detecting the remaining amount of the reducing agent in a tank for storing the reducing agent;
Calculating a first feedback value that is updated based on the output value when the amount of change in the output value of the NOx sensor falls below a predetermined amount;
A second feedback value that is updated is calculated based on a divergence tendency between the estimated reducing agent remaining amount in the tank calculated based on the target addition amount and the reducing agent remaining amount detected by the remaining amount sensor. And
The exhaust gas purification apparatus for an internal combustion engine, wherein the addition feedback value is set based on the first feedback value and the second feedback value. The exhaust emission control device for an internal combustion engine according to claim 1, wherein a reflection degree of the first feedback value with respect to the addition feedback value is made larger than a reflection degree of the second feedback value. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the degree of reflection of the first feedback value with respect to the addition feedback value is increased as the temperature of the NOx purification catalyst is higher. The degree of reflection of the first feedback value with respect to the addition feedback value is reduced when the update frequency of the first feedback value is lower than a predetermined value, compared to when the update frequency is higher than the predetermined value. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3. After performing the process of increasing the addition amount of the reducing agent, when the detection value of the NOx sensor increases, the first feedback value is updated to the side for correcting the decrease of the target addition amount,
5. The first feedback value is updated to increase correction of the target addition amount when the detected value of the NOx sensor decreases after performing the process of increasing the addition amount of the reducing agent. 5. An exhaust purification device for an internal combustion engine according to claim 1. When the remaining amount of the reducing agent is less than the estimated remaining amount of the reducing agent, the second feedback value is updated on the side for correcting the target addition amount to decrease,
6. The internal combustion engine according to claim 1, wherein the second feedback value is updated to increase correction of the target addition amount when the remaining amount of the reducing agent is larger than the estimated remaining amount of reducing agent. Engine exhaust purification system.