WO2017208744A1

WO2017208744A1 - Apparatus for reducing-agent addition control

Info

Publication number: WO2017208744A1
Application number: PCT/JP2017/017506
Authority: WO
Inventors: 浩之成田; 矢羽田　茂人; 祐季樽澤; 佑輔真島
Original assignee: 株式会社デンソー
Priority date: 2016-06-02
Filing date: 2017-05-09
Publication date: 2017-12-07
Also published as: JP6551312B2; JP2017218894A

Abstract

Provided is an apparatus for reducing-agent addition control that controls the operation of a reducing-agent addition device (14). The reducing-agent addition device (14) adds a reducing agent to an upstream side of a catalyst (13) disposed in an exhaust passage (15) where the catalyst adsorbs NO_x contained in the exhaust gas of an internal combustion engine (11) for reduction. The apparatus for reducing-agent addition control comprises: a calculation unit (S1) which calculates the adsorption amount of NO_x adsorbed by the catalyst (13); an acquisition unit (S2) which acquires the catalyst temperature; an estimation unit (S3) which estimates, according to the catalyst temperature acquired by the acquisition unit, the amount of a weak NO_x having a weak adsorption force, such amount being of the absorption amount calculated by the calculation unit; and a control unit (S8) which controls the amount of the reducing agent to be added to the exhaust passage. The control unit performs control such that the reducing agent is added on the condition that the weak NO_x amount estimated by the estimation unit reaches a prescribed threshold.

Description

Reducing agent addition controller

Cross-reference of related applications

This application is based on Japanese Patent Application No. 2016-111204 filed on June 2, 2016, the contents of which are incorporated herein by reference.

The present disclosure relates to a reducing agent addition control device that controls the reducing agent addition device.

In order to purify the exhaust gas of the internal combustion engine, a purification device having a catalyst for adsorbing and reducing NOx (nitrogen oxide) in the exhaust gas is disposed in the exhaust passage of the internal combustion engine. In such a purification device, NOx is adsorbed by the adsorbing component at a low temperature when the catalyst is not activated. On the other hand, when the catalyst has reached the activation temperature, a reducing agent is supplied to the exhaust passage to reduce and purify NOx on the catalyst.

Patent Document 1 estimates the amount of NOx adsorbed on the catalyst in a system including a fuel reformer upstream of the catalyst. When the estimated adsorption amount reaches a predetermined threshold value, the reducing agent species is selected according to the reduction temperature range of the catalyst. For example, a reforming / reducing agent is selected when the catalyst is at a low temperature, and post-injection fuel is selected from the internal combustion engine for reduction when the catalyst is at a high temperature.

Japanese Patent Laying-Open No. 2015-108353

Now, most of NOx adsorbed on the catalyst is NO ₂ or NO ₃ , but NO ₂ has a weaker adsorbing power than NO ₃ . Therefore, NOx adsorbed in the state of NO ₂ (hereinafter referred to as weak NOx) is desorbed from the catalyst at an early timing of low temperature in the process of temperature rise of the catalyst.

In the technique described in Patent Document 1, the reducing agent type and timing are determined based on the catalyst temperature when the estimated NOx adsorption amount reaches a predetermined value. However, NOx adsorbed in a state where the catalyst is at a low temperature is often adsorbed by NO ₂ (nitrogen dioxide) having a weak adsorbing power, and the thermal desorption start temperature of NOx is low. Therefore, if the necessity for reduction and the reducing agent type are determined at the timing when the adsorption amount reaches the threshold value, there is a possibility that weak NOx having a weak adsorption power has already desorbed from the catalyst.

The present disclosure has been made in view of the above-described problems, and an object thereof is to provide a reducing agent addition control device that controls to add a reducing agent before NOx having a weak adsorption power is desorbed from the catalyst. To do.

A reducing agent addition control device according to an aspect of the present disclosure includes a reducing agent addition that adds a reducing agent to an upstream side of a catalyst in an exhaust passage in which a catalyst that adsorbs and reduces NOx in exhaust gas of an internal combustion engine is disposed. Control the operation of the device. The reducing agent addition control device is acquired by the acquisition unit among the calculation unit that calculates the adsorption amount of NOx adsorbed on the catalyst, the acquisition unit that acquires the catalyst temperature, and the adsorption amount calculated by the calculation unit. An estimation unit that estimates the amount of weak NOx having a weak adsorption power according to the catalyst temperature, and a control unit that controls the amount of reducing agent added to the exhaust passage, and the control unit is estimated by the estimation unit Control is performed so that the reducing agent is added on condition that the amount of weak NOx has reached a predetermined threshold value.

According to this disclosure, the amount of weak NOx is estimated using the NOx adsorption amount and the catalyst temperature. Then, the control is performed so that the reducing agent is added on the condition that the amount of weak NOx having a weak adsorption force reaches a predetermined threshold value. Therefore, since the addition timing of the reducing agent is controlled by paying attention to the amount of weak NOx, the reducing agent can be added and the weak NOx can be reduced by the catalyst before the weak NOx having weak adsorption power is desorbed. Therefore, desorption before weak NOx is reduced can be suppressed.

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing
FIG. 1 is a diagram illustrating a combustion system according to a first embodiment. FIG. 2 is a graph showing the relationship between the NOx adsorption amount and the NOx adsorption rate, FIG. 3 is a graph showing the relationship between the catalyst temperature and the NOx thermal desorption amount. FIG. 4 is a flowchart showing the reducing agent addition process. FIG. 5 is a graph showing the relationship between the catalyst temperature and the distribution coefficient, FIG. 6 is a graph showing the relationship between the catalyst temperature and the transfer coefficient, FIG. 7 is a diagram illustrating a combustion system according to the second embodiment.

Hereinafter, modes for carrying out the present disclosure will be described using a plurality of modes with reference to the drawings. In some embodiments, portions corresponding to the matters described in the preceding embodiments may be given the same reference numerals, or one character may be added to the preceding reference numerals, and overlapping descriptions may be omitted. In addition, when a part of the configuration is described in each embodiment, the other parts of the configuration are the same as those of the embodiment described in advance. In addition to the combination of parts specifically described in each embodiment, the embodiments may be partially combined as long as the combination does not hinder the combination.

(First embodiment)
A first embodiment of the present disclosure will be described with reference to FIGS. A combustion system 10 shown in FIG. 1 includes an engine 11 that is an internal combustion engine, a supercharger 12, a NOx purification device 13, and a reducing agent addition device 14. The combustion system 10 is mounted on a vehicle. The vehicle travels using the output of the engine 11 as a drive source. The engine 11 is a compression self-ignition diesel engine. Light oil, which is a hydrocarbon compound, is used as the fuel for combustion. The engine 11 basically operates to burn in a lean state. That is, combustion is performed with the air-fuel ratio, which is the ratio between the fuel injected into the combustion chamber and the air sucked into the combustion chamber, set to an excess of air, that is, lean combustion is performed.

The supercharger 12 includes a turbine 21, a rotating shaft 22 and a compressor 23. The turbine 21 is disposed in the exhaust passage 15 of the engine 11 and rotates by the kinetic energy of the exhaust. The rotary shaft 22 couples the impellers of the turbine 21 and the compressor 23 to transmit the rotational force of the turbine 21 to the compressor 23. The compressor 23 is disposed in the intake passage 16 of the engine 11, compresses intake air, and supercharges the engine 11.

A cooler (not shown) is disposed on the downstream side of the compressor 23 in the intake passage 16. The cooler cools the pressurized air that is the intake air compressed by the compressor 23. The compressed intake air cooled by the cooler is adjusted in flow rate by a throttle valve (not shown) and distributed to a plurality of combustion chambers of the engine 11. A NOx purification device 13 is disposed downstream of the turbine 21 in the exhaust passage 15, and a particulate collection device (hereinafter referred to as DPF) (not shown) is disposed further downstream thereof. The DPF collects fine particles contained in the exhaust.

The supply passage 31 of the reducing agent addition device 14 is connected to the upstream side of the NOx purification device 13 in the exhaust passage 15. The reformed fuel generated by the reducing agent adding device 14 is added from the supply passage 31 to the exhaust passage 15 as a reducing agent. The reformed fuel is obtained by partially oxidizing a hydrocarbon compound (fuel) used as a reducing agent to reform a partially oxidized hydrocarbon containing aldehyde, olefin, hydrogen, CO and the like.

The NOx purification device 13 has a purification catalyst that is provided in the exhaust passage 15 and purifies nitrogen oxides in the exhaust gas using a reducing agent generated by the reforming catalyst 32. The NOx purification device 13 purifies the exhaust using, for example, a NOx storage reduction catalyst (LNT: Lean NOx Trap) as the purification catalyst. Specifically, the LNT occludes NOx in the exhaust gas by the occlusion material in a lean atmosphere. When the stored amount of NOx becomes a sufficient amount, for example, NOx is reduced to N ₂ (nitrogen molecules) using aldehyde and active HC as a reducing agent and purified. The aldehyde shown here represents a hydrocarbon having an aldehyde group, and the active HC represents an unsaturated hydrocarbon having a double or triple bond. Thus, the exhaust gas is purified by the NOx purification device 13 and the reducing agent addition device 14. Therefore, the NOx purification device 13 and the reducing agent addition device 14 function as an exhaust purification device.

The NOx purification device 13 is configured by housing a honeycomb-shaped carrier in a housing. A coating material is provided on the surface of the carrier, and a NOx adsorbing material and a reduction catalyst are supported on the coating material. The adsorbent is preferably an alkaline earth metal such as K, Li, or Ba, and the reduction catalyst is preferably a platinum group such as Pt, Pd, Rh, Ru, or Ir. Further, this reduction catalyst has a function of adsorbing active oxygen in addition to the NOx adsorption function.

Next, the reducing agent addition device 14 will be described. The reducing agent addition device 14 adds the reformed fuel as a reducing agent to the upstream side of the NOx purification device 13 in the exhaust passage 15. The reducing agent addition device 14 includes a supply passage 31, an injection valve 33, a regulating valve 34, a reforming catalyst 32, and an electronic control unit (Electronic Control Unit: abbreviated ECU) 35. As shown in FIG. 1, the supply passage 31 is supplied with air from the upstream side and connected to the exhaust passage 15 on the downstream side. The reforming catalyst 32, the injection valve 33, and the adjustment valve 34 are provided in the supply passage 31.

The adjustment valve 34 is provided on the most upstream side of the supply passage 31. The opening degree of the adjustment valve 34 is controlled by the ECU 35. Therefore, the amount of air passing through the supply passage 31 is controlled by the adjustment valve 34.

The injection valve 33 is disposed on the downstream side of the adjustment valve 34. The injection valve 33 functions as an addition unit that adds fuel that is a pre-reforming additive before reforming to the supply passage 31. Although not shown, the injection valve 33 includes a body in which an injection hole is formed, an electric actuator, and a valve body. When the electric actuator is energized, the valve element is opened to inject fuel into the supply passage 31 from the nozzle hole. When the electric actuator is deenergized, the valve element is closed to stop the fuel injection. Therefore, the ECU 35 controls the fuel injection amount per unit time to the supply passage 31 by controlling the energization to the electric actuator. The liquid fuel in the fuel tank 36 is supplied to the injection valve 33 by the fuel pump 37. The fuel in the fuel tank 36 is also used as the combustion fuel described above, and the fuel used for the combustion of the engine 11 and the fuel used as the reducing agent are shared. The fuel injected from the injection valve 33 into the supply passage 31 collides with the reforming catalyst 32 together with air. The reforming catalyst 32 reforms the fuel added from the injection valve 33 to generate a reducing agent.

Next, the ECU 35 will be described. The microcomputer included in the ECU 35 includes a storage device that stores a program, and a processor such as a central processing unit that executes arithmetic processing according to the stored program. The storage device is a non-transitional tangible storage medium that stores a computer-readable program and data in a non-temporary manner. The storage medium is realized by a semiconductor memory or a magnetic disk.

The ECU 35 controls the operation of the engine 11 based on various detection values such as the engine speed per unit time and the engine load. The engine speed is detected by a crank angle sensor attached in the vicinity of the output shaft of the engine 11. Examples of the physical quantity representing the engine load include intake pressure, intake air amount, accelerator pedal depression amount, and the like. The intake pressure is detected by an intake pressure sensor attached to the downstream portion of the compressor 23 in the intake passage 16. The intake air amount is detected by an air flow meter attached to an upstream portion of the compressor 23 in the intake passage 16. The accelerator pedal depression amount is detected by an accelerator sensor attached to the accelerator pedal.

ECU35 acquires the physical quantity detected by the reaction chamber temperature sensor, the catalyst temperature sensor 38, the exhaust temperature sensor, the exhaust pressure sensor, etc. in addition to the detected value of the operating state of the engine 11 such as the engine speed and the engine load. Based on these physical quantities, the operation of the reducing agent adding device 14 is controlled.

The catalyst temperature sensor 38 is a temperature detection unit, is attached to the NOx purification device 13, and detects the atmospheric temperature of the catalyst, that is, the catalyst temperature. The exhaust temperature sensor is attached to the exhaust passage 15 and detects the exhaust temperature. The exhaust pressure sensor is attached to the exhaust passage 15 and detects the exhaust pressure. The exhaust temperature sensor and the exhaust pressure sensor are attached to the upstream side of the NOx purification device 13 in the exhaust passage 15.

When the present inventors tested the relationship between the NOx adsorption amount, the NOx adsorption rate, and the catalyst temperature, the results shown in FIG. 2 were obtained. The NOx adsorption amount on the horizontal axis is the amount of NOx adsorbed by the NOx purification device 13 and is the mass of NOx adsorbed per liter volume of the NOx purification device 13. The NOx adsorption rate on the vertical axis is the ratio of the NOx adsorption amount to the NOx amount that has flowed into the NOx purification device 13. In this test, the NOx adsorption amount and the NOx adsorption rate when NOx is flowed into the NOx purification device 13 with the catalyst temperature maintained at a predetermined temperature are measured. When the predetermined temperature is set to 100 ° C., 150 ° C., and 200 ° C., the test is performed to obtain the test results shown in FIG.

The test results in FIG. 2 indicate that the NOx adsorption rate decreases as the NOx adsorption amount increases at any catalyst temperature, and the lower the catalyst temperature, the weaker the NOx adsorption power. It shows that the decrease in the NOx adsorption rate accompanying the increase in the NOx adsorption amount becomes significant. The reason for such a test result is considered that the lower the catalyst temperature, the lower the degree of activation of the catalyst and the lower the oxidizing power of the catalyst.

Next, when the present inventors tested the relationship between the NOx thermal desorption amount and the catalyst temperature, the results shown in FIG. 3 were obtained. The NOx thermal desorption on the vertical axis is a phenomenon in which NOx adsorbed on the catalyst starts desorbing from the catalyst as the temperature of the catalyst rises. FIG. 3 shows the test results of measuring the NOx thermal desorption amount by raising the temperature of the catalyst in a state where a sufficient amount of NOx is adsorbed. The solid line (1) in FIG. 3 is the result of measuring the NOx thermal desorption amount by adsorbing a sufficient amount of NOx while maintaining the catalyst temperature at 100 ° C. The one-dot chain line (2) in FIG. 3 is the result of measuring the NOx thermal desorption amount by adsorbing a sufficient amount of NOx while maintaining the catalyst temperature at 200 ° C.

From the test results shown in (1) and (2) of FIG. 3, the lower the catalyst temperature during NOx adsorption, the lower the NOx thermal desorption start temperature due to the weaker NOx adsorption power. Specifically, thermal adsorption starts at 150 ° C. when adsorbed at 100 ° C., and thermal desorption starts at 225 ° C. when adsorbed at 200 ° C.

Most of NOx adsorbed on the catalyst is NO ₂ or NO ₃ , but NO ₂ has a weaker adsorbing power than NO ₃ . For this reason, weak NOx, which is NOx adsorbed in the state of NO ₂ , starts desorbing from the catalyst at an early timing of low temperature, for example, 150 degrees as shown in FIG. To do. Therefore, the desorbed weak NOx is released to the atmosphere without being reduced. On the other hand, strong NOx, which is NOx adsorbed in the state of NO ₃ , has a strong adsorbing power, and most of it remains adsorbed without being desorbed. Then, strong NOx starts to desorb from, for example, 250 ° C.

Next, the control of the ECU 35 will be described. The ECU 35 is a control unit, and controls the reducing agent adding device 14 to control the amount of reducing agent added. Since the control of the addition amount includes control of the addition amount 0, it also includes control of the timing of addition. The ECU 35 controls the timing of adding the reducing agent based on the characteristics such as the NOx adsorption amount of FIGS. 2 and 3.

Specifically, the operation of the reducing agent adding device 14 is controlled by the microcomputer repeatedly executing the program of the procedure shown in FIG. 4 at a predetermined cycle. In S1, the NOx adsorption amount in the catalyst of the NOx purification device 13 is estimated, and the process proceeds to S2. The NOx adsorption amount includes both weak NOx and strong NOx. As an example of the calculation method, estimation according to the operating state of the engine 11 is given. For example, NOx emission amounts with respect to engine 11 operating state values such as engine load, engine speed, EGR rate, supercharging pressure, etc. are obtained by testing in advance, and the test results are mapped and stored. . Then, based on the actually detected value of the engine 11 operating state, the NOx emission amount is calculated with reference to the map. Then, based on the correlation between the NOx emission amount and the NOx adsorption amount, the NOx adsorption amount is calculated from the calculated NOx emission amount. For example, the NOx adsorption amount is calculated by multiplying the NOx adsorption amount by a predetermined coefficient.

In S2, the catalyst temperature is acquired from the catalyst temperature sensor 38, and the process proceeds to S3. By performing the process of S2, it functions as an acquisition unit that acquires the catalyst temperature. In S3, the amount of weak NOx is estimated based on the NOx adsorption state based on the signal from the catalyst temperature sensor 38, and the process proceeds to S4. In order to estimate the amount of weak NOx, for example, the characteristic shown in FIG. 5 is used. In FIG. 5, the distribution coefficient is set based on the catalyst temperature. The distribution coefficient is the ratio of the amount of weak NOx to the NOx adsorption amount. For example, the value of the distribution coefficient with respect to the catalyst temperature is obtained by testing in advance, and the test result is stored as a map shown in FIG. Then, based on the actually detected catalyst temperature, the distribution coefficient is calculated with reference to the map of FIG.

The distribution coefficient is set to a smaller value as the catalyst temperature is higher. However, as shown in the map of FIG. 5, if the catalyst temperature is high, for example, 250 ° C. or higher, the distribution coefficient is set to the minimum value. If the catalyst temperature is low, for example, less than 100 ° C., the distribution coefficient is set to the maximum value.

Therefore, in S3, the amount of weak NOx is calculated by multiplying the NOx adsorption amount calculated in S1 by the distribution coefficient. The amount of weak NOx calculated in S3 is instantaneous and is the amount adsorbed by the catalyst per unit time.

In S4, based on the signal from the catalyst temperature sensor 38, the amount by which the previous accumulated weak NOx amount shifts to the strong adsorption state is estimated, and the process proceeds to S5. The amount of weak NOx because NO ₂ weak adsorption state is strongly reactive to NO ₃ adsorption state proceeds according to the catalyst temperature, it is necessary to consider the amount of shift. Specifically, first, the transfer coefficient is set based on the current catalyst temperature. The movement coefficient is the ratio of the amount of transition from weak NOx to strong NOx with respect to the amount of weak NOx. For example, the value of the transfer coefficient with respect to the catalyst temperature is obtained by testing in advance, and the test result is stored in a map as shown in FIG. Then, based on the actually detected catalyst temperature, the movement coefficient is calculated with reference to the map.

The transfer coefficient is set to a larger value as the catalyst temperature is higher. Therefore, the higher the catalyst temperature is, the smaller the amount of transition to strong NOx is estimated, and the amount of weak NOx is estimated. Then, the shift amount, which is the amount of transition from weak NOx to strong NOx, is calculated by multiplying the amount of the previous integrated weak NOx by the set movement coefficient.

In S5, the current weak NOx amount obtained in S3 is added to the previous accumulated weak NOx amount, and the shift amount obtained in S4 is subtracted to obtain the accumulated weak NOx amount, and the process proceeds to S6. . As a result, the amount of NO ₂ that has been adsorbed on the catalyst since the reduction has been estimated.

In S6, it is determined whether or not the amount of accumulated weak NOx is larger than a predetermined threshold value. If it is larger, the process proceeds to S7, and if it is not larger, this flow is terminated. The threshold is set to an amount that can suppress the desorption of weak NOx.

In S7, it is determined whether or not the catalyst temperature is higher than the reformable temperature. If so, the process proceeds to S8, and if not, the flow ends. This is because when the catalyst temperature is lower than the reformable temperature, for example, 200 ° C., it cannot be reduced even if a reducing agent is added. In S8, the reducing agent adding device 14 is controlled to add the reducing agent, and this flow is finished. By S8, the weak NOx and the strong NOx adsorbed on the catalyst are reduced.

In this way, the ECU 35 functions as a calculation unit that calculates the adsorption amount of NOx adsorbed on the catalyst. Further, the ECU 35 functions as an estimation unit that estimates the amount of weak NOx that is the amount of adsorption adsorbed as NO ₂ when the catalyst temperature is equal to or lower than a predetermined temperature, using the adsorption amount and the catalyst temperature. As described above, attention is paid to the fact that the adsorption force of NOx adsorbed differs depending on the catalyst temperature during adsorption, and NO ₂ having a weak adsorption force is desorbed from a low temperature and the catalyst cannot hold NOx. Then, the adsorption amount of strong NOx and weak NOx is estimated as the adsorption state according to the catalyst temperature, and the timing of adding the reducing agent is controlled based on the amount of integrated weak NOx.

As described above, the ECU 35 of the present embodiment functions as a reducing agent addition control device, and estimates the amount of weak NOx using the adsorption amount and the catalyst temperature. NO ₂ and NO ₃ are present in NOx adsorbed on the catalyst. As described above, the adsorption power of NO ₂ is weaker than the adsorption power of NO _3. As the catalyst temperature at the time of adsorption is lower, the adsorption is more difficult in the state of NO ₃ , and the amount of weak NOx with respect to the strong adsorption amount The ratio of becomes higher. Control is performed so that the reducing agent is added on the condition that the amount of such weak NOx having a weak adsorption force reaches a predetermined threshold value. Therefore, since the addition timing of the reducing agent is controlled by paying attention to the amount of weak NOx, the reducing agent can be added and weak NOx can be reduced by the catalyst before the weak NOx is desorbed. Therefore, it is possible to suppress weak NOx from desorbing.

The threshold value is preferably set so that the amount of reducing agent added is reduced while suppressing the desorption of weak NOx. This is because, as the reducing agent addition interval is shorter, the desorption of weak NOx can be suppressed, but the consumption of the reducing agent increases. Therefore, the threshold value is preferably set so as to satisfy the target purification rate.

In this embodiment, the value obtained by integrating the instantaneous adsorption amount of NO _{2 on} the catalyst is estimated as the weak NOx amount. The higher the catalyst temperature during adsorption, the instantaneous adsorption of NO ₂ with respect to the instantaneous adsorption amount of NOx. The instantaneous adsorption amount of NO ₂ is estimated by estimating the amount ratio to be small. Here, the most of NOx adsorbed in the catalyst is adsorbed in the state of NO ₂ and NO ₃ are as described above, the lower the catalyst temperature at the time of adsorption, less likely to be adsorbed in the form of NO _3, The ratio of weak NOx to strong NOx increases. Therefore, even if the amount of NOx flowing into the catalyst is the same and the proportion of NO ₂ contained in the NOx is the same, the proportion of weak NOx increases as the catalyst temperature at that time decreases. In the present embodiment taking this point into account, as the catalyst temperature at the time of NOx adsorbed is high as described above, since the estimated small percentage of the instantaneous amount of adsorption of NO ₂ with respect to the instantaneous amount of adsorbed NOx, high catalyst temperature during adsorption It is estimated that the amount of weak NOx is small. Therefore, since the amount of weak NOx is estimated in consideration of the catalyst temperature during adsorption, the amount of weak NOx can be estimated with high accuracy.

Further, in the present embodiment, among NOx adsorbed on the catalyst, the amount of transition from NO ₂ to NO ₃ as the temperature rises is taken as the shift amount that is the NO ₃ transition amount, and the value obtained by integrating the instantaneous adsorption amount of NO ₂ The amount of weak NOx is estimated using the value obtained by subtracting the shift amount from. Here, if the catalyst temperature is equal to or higher than a predetermined temperature (for example, 100 ° C.), a phenomenon in which weak NOx transitions to strong NOx occurs. In this embodiment in view of this point, the amount of weak NOx is estimated in consideration of the shift amount thus shifted, that is, the amount of strong NOx transition, so that the amount of weak NOx can be accurately estimated.

Further, in the present embodiment, the temperature at which the reducing agent exhibits the reduction effect by the catalyst is defined as the reformable temperature, the estimated amount of weak NOx reaches the threshold value, and the catalyst temperature is equal to or higher than the reformable temperature. As described above, control is performed so that a reducing agent is added. When the catalyst temperature is lower than the reformable temperature, the additive is wasted without being reduced even if the reducing agent is added. Therefore, the adsorbed NOx can be reliably reduced by adding a reducing agent when the temperature is higher than the reformable temperature.

Furthermore, in this embodiment, the reducing agent addition device 14 modifies the pre-reforming additive added from the injection valve 33 and the injection valve 33 that adds the pre-reforming additive before reforming, and reduces the reducing agent. And a reforming catalyst 32 to be generated. The pre-reform additive is a fuel used for the engine 11. As a result, the fuel used for the engine 11 and the additive before reforming can be shared. Therefore, the configuration can be simplified as compared with the case of separately preparing an additive.

(Second Embodiment)
Next, a second embodiment of the present disclosure will be described with reference to FIG. In the present embodiment, the configuration of the supply passage 312 of the reducing agent addition device 14 is different. As shown in FIG. 7, the supply passage 312 is a passage that branches off from the branch portion 41 of the exhaust passage 15 and joins at the joining portion 42 of the exhaust passage 15 that is located downstream of the branch portion 41. Accordingly, a part of the exhaust gas flowing through the exhaust passage 15 flows into the supply passage 312.

An adjustment valve 34 is provided in the supply passage 312 on the upstream side of the reforming catalyst 32. The adjustment valve 34 adjusts the flow rate of the exhaust gas that passes through the supply passage 312. The regulating valve 34 is constituted by, for example, a cantilever door and a butterfly door, and the supply passage 312 is opened and closed when the door is angularly displaced. The adjustment valve 34 may be provided on the downstream side of the reforming catalyst 32.

Thus, since the exhaust gas passes through the supply passage 312, the reforming catalyst 32 can be heated by the heat of the exhaust gas. Therefore, exhaust gas can be used to increase the temperature of the reforming catalyst 32.

(Other embodiments)
The preferred embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure.

The structure of the above-described embodiment is merely an example, and the scope of the present disclosure is not limited to the scope of these descriptions. The scope of the present disclosure is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

In the first embodiment described above, the additive added from the reducing agent addition device 14 is fuel, but is not limited to fuel, and may be a dedicated additive for the reducing agent.

In the first embodiment described above, the reducing agent addition device 14 is applied to a compression self-ignition diesel engine, and light oil used as a fuel for combustion is used as the reducing agent. On the other hand, gasoline used as a fuel for combustion may be used as a reducing agent by applying the reducing agent addition device 14 to an ignition ignition type gasoline engine.

In the above-described first embodiment, the reducing agent adding device 14 includes the reforming catalyst 32, but is not limited to such a configuration. For example, fuel may be supplied to the exhaust passage 15 by post injection, and the fuel may be reformed by the heat of the exhaust.

In the first embodiment described above, the NOx emission amount of the internal combustion engine is estimated according to the operating state of the engine 11, but is not limited to such an estimation method. For example, a NOx sensor may be mounted upstream of the catalyst and the NOx emission amount may be directly detected.

In the first embodiment described above, the amount of adsorption that includes weak NOx and strong NOx is first estimated, but the present invention is not limited to such a configuration. The amount of weak NOx may be estimated using the catalyst temperature from a map or the like without using the NOx adsorption amount.

In the first embodiment described above, the reducing agent addition control device is realized by the ECU 35, but is not limited to such a configuration. The means and / or function provided by the ECU 35 as the reducing agent addition control device is provided by software recorded in a substantial storage medium and a computer that executes the software, software only, hardware only, or a combination thereof. Can do. For example, if the controller is provided by a circuit that is hardware, it can be provided by a digital circuit including a number of logic circuits, or an analog circuit. Moreover, it replaces with ECU35 and a microcomputer may provide an ozone supply control apparatus, and the processor which a microcomputer has may provide a reducing agent addition control apparatus.

In the first embodiment described above, the exhaust gas discharged from the in-vehicle internal combustion engine is purified. However, the exhaust gas is not limited to the in-vehicle internal combustion engine, and may be an internal combustion engine mounted on a ship, a railway vehicle, an aircraft, or the like. The present invention can also be applied to an exhaust purification system that purifies the exhaust of a fuel engine. Furthermore, the present invention is also applicable to an exhaust purification system that purifies exhaust from internal combustion engines and external combustion engines installed for power generation.

Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments and structures. The present disclosure includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, as well as other combinations and forms including only one element, more or less, are within the scope and spirit of the present disclosure.

Claims

Of the exhaust passage (15) in which the catalyst (13) for adsorbing and reducing NOx in the exhaust gas of the internal combustion engine (11) is arranged, a reducing agent addition device (14) for adding a reducing agent to the upstream side of the catalyst. ) Of the reducing agent addition control device (35) for controlling the operation of
A calculation unit (S1) for calculating an adsorption amount of NOx adsorbed on the catalyst;
An acquisition unit (S2) for acquiring a catalyst temperature which is the temperature of the catalyst;
An estimation unit (S3) that estimates the amount of weak NOx having a weak adsorption force according to the catalyst temperature acquired by the acquisition unit among the adsorption amounts calculated by the calculation unit;
A control unit (S8) for controlling the amount of the reducing agent added to the exhaust passage,
The said control part is a reducing agent addition control apparatus which controls to add the said reducing agent on condition that the quantity of the said weak NOx estimated by the said estimation part has reached the predetermined threshold value.
The estimation unit estimates a value obtained by integrating the instantaneous NO 2 adsorption amount to the catalyst as the weak NOx amount, and the higher the catalyst temperature at the time of adsorption, the higher the NO 2 instantaneous adsorption amount of NO 2 . The reducing agent addition control apparatus according to claim 1, wherein the instantaneous adsorption amount of NO 2 is estimated by estimating a ratio of the instantaneous adsorption amount to be small.
Of the NOx adsorbed on the catalyst, the amount of transition from NO 2 to NO 3 as the temperature rises is the NO 3 transition amount,
The estimating unit, the reducing agent addition control device according to claim 1 or 2 to estimate the amount of the weak NOx by using a value obtained by subtracting the NO 3 transition amount from the value obtained by integrating the instantaneous amount of adsorbed NO 2.
The temperature at which the reducing agent exhibits a reducing effect by the catalyst is defined as a reformable temperature,
The control unit controls to add the reducing agent on the condition that the amount of the weak NOx estimated by the estimation unit reaches the threshold and the catalyst temperature is equal to or higher than the reformable temperature. The reducing agent addition control device according to any one of claims 1 to 3.
The reducing agent adding device is:
An addition section (33) for adding the fuel used in the internal combustion engine as a pre-reforming additive before reforming;
A reforming catalyst (32) for reforming the pre-reforming additive added from the addition unit to produce the reducing agent,
The reducing agent addition control device according to any one of claims 1 to 4, wherein the control unit controls an addition amount of the pre-modification additive.