JP2010019171A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology using a NOx storage-reduction catalyst for increasing a NOx eliminating rate. <P>SOLUTION: This exhaust emission control device comprises an HC supply means for supplying HC to the NOx catalyst, a reduction component supply means for supplying the NOx catalyst with a reduction component having higher oxidation-reduction reactivity than the HC supplied by the HC supply means, and a NOx reduction means for executing NOx reduction treatment to reduce and eliminate NOx stored in the NOx catalyst by the HC supply means and/or the reduction component supply means supplying the HC and/or the reduction component to the NOx catalyst. During executing NOx reduction treatment, when predetermined conditions of lowering the reactivity of the HC in the NOx catalyst are established and/or when the reactivity of the HC in the NOx catalyst is detected to be lowered, the NOx reduction means sets the rate of the reduction component to the total amount of the HC and the reduction component supplied to the NOx catalyst to be higher than in the other case, or sets the amount of the reduction component supplied to the NOx catalyst to be greater. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

In an exhaust gas purification apparatus for an internal combustion engine equipped with a NOx catalyst for reducing and purifying NOx in exhaust gas, when the catalyst temperature of the NOx catalyst is low, the amount of CO in the exhaust gas is increased, and when the catalyst temperature of the NOx catalyst is high A technique is known in which a high NOx purification rate is obtained in a wide temperature range by increasing the amount of HC in the exhaust (see, for example, Patent Document 1).
JP 2001-164928 A JP 2003-120369 A JP 2007-40241 A JP 2004-346877 A JP 2003-172185 A

  In the above prior art, the amount of CO and HC in the exhaust gas is adjusted only in accordance with the catalyst temperature of the NOx catalyst, and other factors that may affect the NOx purification rate of the NOx catalyst are not considered. In some cases, the NOx purification performance of the catalyst cannot be fully exhibited.

  The present invention has been made in view of such problems, and an object thereof is to provide a technique that makes it possible to further increase the NOx purification rate of the NOx catalyst.

In order to achieve the above object, an exhaust emission control device for an internal combustion engine of the present invention comprises:
A NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
HC supply means for supplying HC to the NOx catalyst;
Reducing component supply means for supplying the NOx catalyst with a reducing component having a higher reactivity of the oxidation-reduction reaction in the NOx catalyst than HC supplied by the HC supply means;
NOx reduction means for performing NOx reduction processing for reducing and purifying NOx occluded in the NOx catalyst by supplying HC and / or the reducing component to the NOx catalyst by the HC supply means and / or the reducing component supply means. When,
With
The NOx reduction means is configured to execute the NOx reduction process.
When a predetermined condition for reducing the reactivity of HC in the NOx catalyst is satisfied, and / or
When it is detected that the reactivity of HC in the NOx catalyst is reduced,
Compared to the case of none of them,
Increasing the ratio of the reducing component to the total amount of HC and the reducing component supplied to the NOx catalyst, or
The amount of the reducing component supplied to the NOx catalyst is increased.

The NOx storage reduction catalyst stores NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and releases the stored NOx when the air-fuel ratio of the inflowing exhaust becomes stoichiometric or rich, and the reducing agent It is a catalyst having a function of reducing the released NOx in the presence to render it harmless to N ₂ . Therefore, in order to reduce and purify NOx by the NOx catalyst, it is necessary to supply the NOx catalyst with a sufficient amount of reducing agent for making the NOx catalyst stoichiometric or rich and reducing NOx to N ₂ .

  In the present invention, HC supply means and reducing component supply means are provided as means for supplying the reducing agent to the NOx catalyst. Examples of the HC supply means include adding unburned fuel to the exhaust passage upstream of the NOx catalyst, and performing sub-injection (post-injection) at the later stage of the expansion stroke. As the reducing component supply means, combustion is performed at a high EGR rate, combustion is performed at a rich air-fuel ratio, low-temperature combustion is performed, the intake air amount is reduced, and sub-injection is performed from the late stage of the exhaust stroke to the early stage of the intake stroke. Examples include performing (bi-rubber injection) and performing sub-injection (after-injection) in the early stage of the expansion stroke.

According to the HC supply means, it is possible to supply a relatively large amount of reducing agent to the NOx catalyst while suppressing deterioration of fuel consumption. However, HC supplied by the HC supply means is relatively heavy, and the oxidation-reduction reaction rate in the NOx catalyst is slow and the reactivity is low. On the other hand, the reducing component supplied by the reducing component supply means is CO, H ₂ and lighter HC, etc., these fast rate of oxidation-reduction reaction in the NOx catalyst, is highly reactive. However, when the reducing component is supplied by the reducing component supply means, it is difficult to supply a large amount of reducing agent while suppressing the influence on fuel consumption and drivability.

  Here, as conditions affecting the reactivity of HC in the NOx catalyst, conditions relating to the reaction environment of HC in the NOx catalyst and conditions relating to the state of the NOx catalyst itself can be considered. Examples of the conditions relating to the former HC reaction environment include the temperature of the NOx catalyst, the flow rate of exhaust gas passing through the NOx catalyst, and the like. For example, when the temperature of the NOx catalyst is low, the reactivity of HC decreases. Further, when the flow rate of the exhaust gas passing through the NOx catalyst is large, the reaction time of HC in the NOx catalyst is shortened, so that the HC having low reactivity cannot sufficiently react in the NOx catalyst. In the present invention, it is determined whether or not the “condition for reducing the reactivity of HC in the NOx catalyst” is satisfied based on the condition relating to the reaction environment of HC in the NOx catalyst.

  Furthermore, examples of the condition relating to the state of the latter NOx catalyst itself include performance deterioration of the NOx catalyst over time. For example, when the oxidation ability of the NOx catalyst is reduced due to deterioration of the NOx catalyst, the amount of NOx in the exhaust gas flowing out from the NOx catalyst and the amount of unreacted HC are larger than expected. In addition, when the HC supplied to the NOx catalyst is not sufficiently reacted due to the deterioration of the NOx catalyst, an air-fuel ratio sensor is arranged downstream of the NOx catalyst and the air-fuel ratio of the exhaust is measured. The value is known to be measured. In the present invention, based on such a phenomenon reflecting the state of the NOx catalyst itself, it is detected that “the reactivity of HC in the NOx catalyst is reduced”.

In the present invention, when it is determined that the condition for reducing the reactivity of HC in the NOx catalyst is satisfied and / or when it is detected that the reactivity of HC in the NOx catalyst is lowered, In the NOx reduction treatment, the ratio of the reducing component to the total amount of HC and reducing components supplied to the NOx catalyst is increased in comparison with the normal time when it is determined that various conditions for reducing the reactivity of HC are not satisfied. Or increasing the amount of reducing component supplied to the NOx catalyst. Here, the amount of HC supplied by the HC supply means in the NOx reduction process under the condition where the reactivity of HC is low may be smaller than that in the normal state or may not be changed. The total amount of reducing agent supplied to the NOx catalyst in the NOx reduction process may not be changed by decreasing the amount of HC according to the increase in the amount of reducing component. In this case, it means that the ratio of the reducing component to the total amount of reducing agent is made higher than usual. Further, in the normal NOx reduction treatment, the total amount of reducing agent may be supplied by HC, and even during normal time, the reducing agent is supplied by both the HC supply means and the reducing component supply means, and the reactivity of HC is improved. You may make it increase the quantity or ratio of a reducing component on low conditions.

As a result, a reducing agent mainly composed of reducing components such as CO, H ₂ and light HC, which can be suitably oxidized / reduced by high reactivity even under low HC reactivity, is supplied to the NOx catalyst. Thus, the NOx reduction process can be suitably executed, and the NOx purification rate of the NOx catalyst can be increased. Further, under a condition where the reactivity of HC is sufficiently high, the NOx reduction process can be executed while suppressing the influence on fuel consumption by supplying a reducing agent mainly composed of HC to the NOx catalyst.

  In the present invention, the NOx reduction means increases the ratio of the reducing component as the degree of decrease in the reactivity of HC in the NOx catalyst due to the establishment of the predetermined condition, or increases the ratio of the reducing component. The amount may be increased. Alternatively, the NOx reduction means increases the ratio of the reducing component or increases the amount of the reducing component as the degree of the decrease in the reactivity of HC in the detected NOx catalyst increases. May be.

  Here, “the degree of reduction in the reactivity of HC in the NOx catalyst due to the establishment of the predetermined condition is large” means that the condition relating to the reaction environment of HC in the NOx catalyst described above is the reaction of HC in the NOx catalyst. It means that it is satisfied as a condition that lowers the performance. For example, the lower the temperature of the NOx catalyst, the lower the reactivity of HC in the NOx catalyst. Further, as the flow rate of the exhaust gas passing through the NOx catalyst increases, the reaction time of HC in the NOx catalyst becomes shorter, and HC becomes more difficult to react in the NOx catalyst. Therefore, in these examples, the lower the temperature of the NOx catalyst or the higher the flow rate of the exhaust gas passing through the NOx catalyst, the more the ratio or amount of the reducing component is increased.

  In addition, “the degree of decrease in the reactivity of HC in the detected NOx catalyst is large” means that the condition relating to the state of the NOx catalyst itself further reduces the reactivity of HC in the NOx catalyst. It means that it is satisfied as a condition. As described above, the reactivity of HC decreases as the NOx catalyst decreases in its redox capacity due to deterioration. As described above, the deterioration of the NOx catalyst can be detected based on the NOx amount in the NOx catalyst output gas and the unreacted HC amount. Therefore, in this example, as the amount of NOx and the amount of unreacted HC in the NOx catalyst output gas is larger than expected, the ratio or amount of the reducing component is further increased.

  As a result, the NOx reduction treatment can be suitably executed even under conditions where the reactivity of HC in the NOx catalyst is lower, and the NOx purification rate of the NOx catalyst can be increased.

  In the present invention, it further comprises catalyst temperature acquisition means for acquiring the temperature of the NOx catalyst, and the NOx reduction means is provided when the temperature of the NOx catalyst acquired by the catalyst temperature acquisition means is lower than a predetermined reference temperature. Therefore, it can be determined that a condition for reducing the reactivity of HC in the NOx catalyst is satisfied.

  As described above, the temperature of the NOx catalyst affects the reactivity of HC in the NOx catalyst, and the reactivity of HC tends to decrease as the temperature of the NOx catalyst decreases. According to the above configuration, when the temperature of the NOx catalyst is lower than the predetermined reference temperature, the amount or ratio of the reducing component supplied by the reducing component supply means increases. The reducing component supplied by the reducing component supply means is HC lighter than the gas or HC supplied by the HC supply means, and can perform oxidation-reduction reaction with high reactivity even under conditions where the catalyst temperature is low. Therefore, the NOx reduction treatment can be suitably executed even under conditions where the catalyst temperature is low.

  Here, the reference temperature refers to the amount or ratio of the reducing component supplied by the reducing component supply means at the time of execution of the NOx reduction process, set to a normal amount or ratio, supplies the reducing agent to the NOx catalyst, It is determined based on the lower limit value of the temperature of the NOx catalyst that can achieve the target NOx purification rate.

  In the above configuration, most simply, when supplying the reducing agent in the NOx reduction treatment, two supply patterns having different amounts or ratios of reducing components may be switched depending on whether or not the temperature of the NOx catalyst is lower than the reference temperature. it can.

  In the above configuration, the NOx reduction means reduces the reactivity of HC in the NOx catalyst due to the establishment of the predetermined condition as the temperature of the NOx catalyst acquired by the catalyst temperature acquisition means decreases. It may be determined that the degree is large, and the ratio of the reducing component may be increased, or the amount of the reducing component may be increased.

  In this case, the amount or ratio of the reducing component may be continuously changed with respect to the temperature of the NOx catalyst, or may be changed stepwise. As a result, it is possible to supply a reducing agent that more accurately reflects the relationship between the temperature of the NOx catalyst and the reactivity of HC in the NOx catalyst, and the NOx reduction treatment is suitably performed even under conditions where the reactivity of HC is low. Can be executed.

  The present invention further includes a catalyst passing gas amount acquisition means for acquiring a flow rate of the exhaust gas passing through the NOx catalyst, and the NOx reduction means passes through the NOx catalyst acquired by the catalyst passage gas amount acquisition means. When the exhaust gas flow rate is higher than a predetermined reference flow rate, it can be determined that the condition for reducing the reactivity of HC in the NOx catalyst is satisfied.

  As described above, the flow rate of exhaust gas that passes through the NOx catalyst affects the reactivity of HC in the NOx catalyst, and the reactivity of HC tends to decrease as the flow rate of exhaust gas that passes through the NOx catalyst increases. According to the above configuration, when the flow rate of the exhaust gas passing through the NOx catalyst is higher than the predetermined reference flow rate, the amount or ratio of the reducing component supplied by the reducing component supply means increases. The reducing component supplied by the reducing component supply means is HC lighter than the gas or HC supplied by the HC supply means, and can sufficiently perform a redox reaction even if the reaction time in the NOx catalyst is short. . Therefore, the NOx reduction process can be suitably executed even under conditions where the catalyst passage exhaust amount is large.

  Here, the reference flow rate means that when the NOx reduction process is performed, the amount or ratio of the reducing component by the reducing component supply means is set to the normal amount or ratio, the reducing agent is supplied to the NOx catalyst, It is determined based on the upper limit value of the flow rate of the exhaust gas that passes through the NOx catalyst so that the target NOx purification rate can be achieved.

  In the above configuration, most simply, when supplying the reducing agent in the NOx reduction treatment, there are two supply patterns in which the amount or ratio of the reducing component differs depending on whether or not the flow rate of the exhaust gas passing through the NOx catalyst is larger than the reference flow rate. Can be switched.

  In the above-described configuration, the NOx reduction means has a lower degree of HC reactivity in the NOx catalyst due to the predetermined condition as the intake air quantity acquired by the intake air quantity acquisition means is larger. It may be determined that the ratio is large and the ratio of the reducing component is increased or the amount of the reducing component is increased.

In this case, the amount or ratio of the reducing component may be continuously changed with respect to the flow rate of the exhaust gas passing through the NOx catalyst, or may be changed stepwise. As a result, it is possible to supply a reducing agent that more accurately reflects the relationship between the flow rate of exhaust gas passing through the NOx catalyst and the reactivity of HC in the NOx catalyst, which is also suitable under conditions where the reactivity of HC is low. In addition, the NOx reduction process can be executed.

  The present invention further includes NOx amount acquisition means for acquiring the amount of NOx in the exhaust gas flowing out from the NOx catalyst, wherein the NOx reduction means is configured such that the NOx amount acquired by the NOx amount acquisition means is a predetermined reference amount. It may be detected that the reactivity of HC in the NOx catalyst is reduced.

  As described above, if the oxidation / reduction ability of the NOx catalyst itself is deteriorated, even if the reaction environment of HC in the NOx catalyst is good, it becomes difficult for HC to react appropriately. The NOx purification rate decreases. Therefore, when the performance of the NOx catalyst is deteriorated, the amount of NOx in the exhaust gas flowing out from the NOx catalyst becomes larger than expected. According to the above configuration, when the amount of NOx in the exhaust gas flowing out from the NOx catalyst is larger than the predetermined reference amount, the amount or ratio of the reducing component supplied by the reducing component supply means increases. Since the reducing component supplied by the reducing component supply means is more reactive than the HC supplied by the HC supply means, even if the NOx catalyst is deteriorated, it can react suitably in the NOx catalyst. Therefore, the NOx reduction process can be suitably executed even under conditions where the NOx catalyst is deteriorated.

  Here, the reference amount is determined based on the amount of NOx in the NOx catalyst exit gas assumed when the NOx catalyst is assumed to have no performance deterioration. This reference amount may be determined for each operating condition.

  In the above configuration, in the simplest case, when the reducing agent is supplied in the NOx reduction treatment, the amount or ratio of the reducing component varies depending on whether the amount of NOx in the exhaust gas flowing out from the NOx catalyst is larger than the reference amount. The supply pattern can be switched.

  Further, in the above configuration, the NOx reduction means determines that the greater the amount of NOx acquired by the NOx amount acquisition means, the greater the degree of decrease in HC reactivity in the detected NOx catalyst, The ratio of the reducing component may be increased, or the amount of the reducing component may be increased.

  In this case, the amount or ratio of the reducing component may be continuously changed with respect to the NOx amount in the exhaust gas flowing out from the NOx catalyst, or may be changed stepwise. As a result, it is possible to supply a reducing agent that more accurately reflects the relationship between the degree of deterioration of the NOx catalyst and the reactivity of HC in the NOx catalyst, and it is possible to reduce NOx suitably even under conditions where the reactivity of HC is low. Processing can be executed.

  The present invention further includes an air-fuel ratio sensor for measuring an air-fuel ratio of the exhaust gas flowing out from the NOx catalyst, wherein the NOx reduction means is configured such that the air-fuel ratio of the exhaust gas measured by the air-fuel ratio sensor is leaner than a predetermined reference value. If the value is on the side, it may be detected that the reactivity of HC in the NOx catalyst is reduced.

  As described above, when the performance of the NOx catalyst is deteriorated, HC hardly reacts in the NOx catalyst, so that HC supplied to the NOx catalyst may flow out of the NOx catalyst without being reacted. In such a case, it is known that the air-fuel ratio sensor arranged on the downstream side of the NOx catalyst shows a leaner value than expected. For example, when a rich spike is executed in the normal NOx reduction process, the measured value by the air-fuel ratio sensor should be an air-fuel ratio that is richer than stoichiometric. However, if the NOx catalyst is deteriorated, even if the rich spike is performed, Even lean air-fuel ratios may be measured.

  According to the above configuration, when the air-fuel ratio of the exhaust gas measured by the air-fuel ratio sensor downstream of the NOx catalyst is a value leaner than the predetermined reference value, the amount or ratio of the reducing component supplied by the reducing component supply means Will increase. Since the reducing component supplied by the reducing component supply means is more reactive than the HC supplied by the HC supply means, even if the NOx catalyst is deteriorated, it can react suitably in the NOx catalyst. Therefore, the NOx reduction process can be suitably executed even under conditions where the NOx catalyst is deteriorated.

  Here, the reference value is determined based on the measured value of the air-fuel ratio of the exhaust gas on the downstream side of the NOx catalyst, which is assumed when the NOx catalyst is assumed to have no performance deterioration.

  In the above configuration, most simply, when supplying the reducing agent in the NOx reduction treatment, the amount of reducing component depends on whether the measured value of the air-fuel ratio of the exhaust downstream of the NOx catalyst is a value leaner than the reference value. Alternatively, two supply patterns having different ratios can be switched.

  In the above configuration, the NOx reduction means determines that the leaner the air-fuel ratio acquired by the air-fuel ratio sensor, the greater the degree of decrease in HC reactivity in the detected NOx catalyst. The ratio of the reducing component may be increased, or the amount of the reducing component may be increased.

  In this case, the amount or ratio of the reducing component may be continuously changed with respect to the air-fuel ratio of the exhaust measured by the air-fuel ratio sensor downstream of the NOx catalyst, or may be changed stepwise. As a result, it is possible to supply a reducing agent that more accurately reflects the relationship between the degree of deterioration of the NOx catalyst and the reactivity of HC in the NOx catalyst, and it is possible to reduce NOx suitably even under conditions where the reactivity of HC is low. Processing can be executed.

  Here, the exhaust gas temperature acquisition means for acquiring the temperature of the exhaust gas flowing into the NOx catalyst is further provided, and the NOx reduction means is configured such that the exhaust gas temperature acquired by the exhaust gas temperature acquisition means is higher than a predetermined reference exhaust gas temperature. The supply of HC by the HC supply unit and the supply of the reducing component by the reducing component supply unit may not be performed.

  This is because, when the temperature of the inflowing exhaust gas is high, the NOx catalyst is difficult to store NOx. Therefore, it is necessary to perform NOx reduction treatment for releasing and storing the stored NOx from the NOx catalyst in the first place. Low. Therefore, in such a case, even if the air-fuel ratio measured by the air-fuel ratio sensor downstream of the NOx catalyst is leaner than expected, it is necessary to increase the supply amount or ratio of the reducing component by the reducing component supply means. It may not be performed. Even if it does in this way, there is little possibility that a NOx purification rate will fall. Further, since an increase in the supply amount of the reducing component may affect the fuel consumption performance, the deterioration of the fuel consumption can be suppressed by suppressing the increase in the useless reducing component.

  According to the present invention, the NOx reduction treatment can be suitably executed even under conditions where the HC reactivity in the NOx catalyst is low, and the NOx purification rate of the NOx catalyst can be increased.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the present embodiment are not intended to limit the technical scope of the invention only to those unless otherwise specified.

  FIG. 1 is a conceptual diagram schematically showing the schematic configuration of an internal combustion engine to which the exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied, and its intake system and exhaust system. The internal combustion engine 1 is a diesel engine having four cylinders 49. Each cylinder 49 is provided with an injector 29 for injecting and supplying fuel into the cylinder. Each cylinder 49 communicates with the intake manifold 17 via an intake port (not shown). An intake passage 42 is connected to the intake manifold 17. Each cylinder 49 communicates with the exhaust manifold 18 through an exhaust port (not shown). An exhaust passage 43 is connected to the exhaust manifold 18. The exhaust manifold 18 is provided with a fuel addition valve 19 that adds fuel to the exhaust.

The exhaust passage 43 and the intake passage 42 communicate with each other through the EGR passage 15. A part of the exhaust gas from the internal combustion engine 1 flows into the intake passage 42 as EGR gas via the EGR passage 15. An EGR valve 14 that adjusts the amount of EGR gas is disposed in the EGR passage 15. The intake passage 42 is provided with an intake throttle valve 22 for adjusting the intake air amount and an air flow meter 7 for measuring the intake air amount. The exhaust passage 43 is provided with a NOx storage reduction catalyst 41. The NOx catalyst 41 occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and releases NOx when the air-fuel ratio of the inflowing exhaust is stoichiometric or rich. Then, if there is a reducing agent around the NOx catalyst to reduce and purify the released was NOx to N _2. The NOx catalyst 41 may be supported on a filter that collects particulate matter in the exhaust gas. An exhaust gas temperature sensor 52 that measures the temperature of the exhaust gas flowing into the NOx catalyst 41 is provided in the exhaust passage 43 upstream of the NOx catalyst 41. In the exhaust passage 43 on the downstream side of the NOx catalyst 41, an air-fuel ratio sensor 50 that measures the air-fuel ratio of the exhaust gas that flows out from the NOx catalyst 41, and an exhaust sensor 51 that measures the amount of NOx in the exhaust gas that flows out from the NOx catalyst 41. Is provided.

  The internal combustion engine 1 is provided with an ECU 26 that is a computer that controls the operation of the internal combustion engine 1. In addition to the air flow meter 7, the air-fuel ratio sensor 50, the exhaust sensor 51, the exhaust temperature sensor 52, sensors such as a crank angle sensor and an accelerator opening sensor are connected to the ECU 26, and measurement data of these sensors are input. The ECU 26 is connected to an injector 29, a fuel addition valve 19, an intake throttle valve 22, an EGR valve 14 and other devices, and a control signal for controlling the operation of each device is output from the ECU 26.

To reduce and purify NOx by the NOx catalyst 41, the NOx catalyst 41 with a stoichiometric or rich atmosphere, it is necessary to supply a sufficient amount of reducing agent for reducing NOx to _{N 2} in the NOx catalyst 41 . In this embodiment, as means for supplying the reducing agent to the NOx catalyst 41, means for supplying unburned fuel (hereinafter referred to as HC) in the exhaust (hereinafter referred to as HC supply means) and means for supplying HC such as CO in the exhaust gas. Means for supplying a reducing component having a higher reactivity in the NOx catalyst 41 than the supplied HC (hereinafter referred to as CO supply means).

  The HC supply means of the present embodiment is at least one of adding HC to the exhaust passage 43 upstream of the NOx catalyst 41 by the fuel addition valve 19 and performing sub-injection (post-injection) at the later stage of the expansion stroke. is there.

  The HC supplied into the exhaust gas by the HC supply means flows into the NOx catalyst 41 together with the exhaust gas. The HC that has flowed into the NOx catalyst 41 is adsorbed by the NOx catalyst 41 and vaporizes, and then undergoes an oxidation-reduction reaction. This HC is relatively heavy because decomposition has not progressed, the speed of the adsorption and vaporization process in the NOx catalyst 41 is slow, and the reactivity in the NOx catalyst 41 is low.

Therefore, in the case where the temperature of the NOx catalyst 41 is low and the catalytic activity is low, or in the case where the flow rate of exhaust gas passing through the NOx catalyst 41 is large and the reaction time of HC in the NOx catalyst 41 cannot be sufficiently secured, etc. The NOx catalyst 4 is used as in the case where an environmental condition that lowers the reactivity of HC is satisfied or the oxidation-reduction performance of the NOx catalyst 41 is deteriorated.
When the state of 1 itself is such that the oxidation-reduction reaction of HC does not occur well, HC hardly undergoes the oxidation-reduction reaction in the NOx catalyst 41, and it becomes difficult to suitably perform the NOx reduction process.

  On the other hand, the supply of HC by the HC supply means, in particular, the addition of fuel into the exhaust gas by the fuel addition valve 19 can be performed without being subjected to quantitative and timing restrictions depending on the operating state of the internal combustion engine 1. A large amount of HC can be supplied to the NOx catalyst 41 in response to a request for NOx reduction treatment. Further, even if such a large amount of HC is supplied, the influence on the operating state and fuel consumption performance of the internal combustion engine 1 is small.

  The CO supply means of the present embodiment opens the EGR valve 14 and burns it at a high EGR rate, increases the injection amount by the injector 29 and burns it at a rich air-fuel ratio, or introduces a large amount of EGR gas. Performing low temperature combustion, reducing the intake air amount by restricting the intake throttle valve 22, performing sub-injection (bi-rubber injection) from the late stage of the exhaust stroke to the early stage of the intake stroke, Injection).

In this embodiment, for convenience, it is referred to as “CO supply means”. However, by the above-mentioned CO supply means, in addition to CO, H ₂ , HC lighter than HC supplied by the HC supply means, etc. A reducing component having higher reactivity than HC is also supplied.

Since the reducing component supplied into the exhaust gas by the CO supply means is gas molecules or light, when it flows into the NOx catalyst 41, it can quickly undergo a redox reaction, and the NOx catalyst 41 has high reactivity. Therefore, even in a situation where HC does not react well in the NOx catalyst 41, such as when the conditions for reducing the reactivity of HC as described above are satisfied or when the NOx catalyst 41 is deteriorated. Further, a highly reactive reducing component such as CO or H ₂ supplied by the CO supply means can be suitably oxidized and reduced.

  On the other hand, when the reducing component is supplied into the exhaust gas by the CO supply means, it is necessary to perform control related to engine combustion, such as rich combustion or high EGR rate combustion, and the influence on the operating state of the internal combustion engine 1 is affected. It is difficult to supply a large amount of reducing components while suppressing the influence on fuel efficiency.

  Here, the reactivity of HC in the NOx catalyst 41 is affected by the reaction environment of HC in the NOx catalyst 41 and the state of the NOx catalyst 41 itself.

  Examples of the HC reaction environment that affects the reactivity of HC in the NOx catalyst 41 include the temperature of the NOx catalyst 41, the flow rate of exhaust gas passing through the NOx catalyst 41, and the like. For example, when the temperature of the NOx catalyst 41 is low, the NOx catalyst 41 is not sufficiently activated, and HC is difficult to vaporize, so that the reactivity of HC decreases. Further, when the flow rate of the exhaust gas passing through the NOx catalyst 41 is large, the reaction time of HC in the NOx catalyst 41 is shortened, so that the HC having low reactivity cannot sufficiently react in the NOx catalyst 41.

  Examples of the state of the NOx catalyst 41 itself that affects the reactivity of HC in the NOx catalyst 41 include performance deterioration of the NOx catalyst 41 over time. When the oxidation / reduction ability of the NOx catalyst 41 is reduced due to the deterioration of the performance of the NOx catalyst 41, HC having low reactivity cannot react well in the NOx catalyst 41.

However, since the reducing component supplied by the CO supply means is more reactive than the HC supplied by the HC supply means, the NOx catalyst 41 is excellent even under the condition that the reactivity of HC is reduced as described above. In some cases, a redox reaction is possible. Therefore, even when the conditions for reducing the HC reactivity as described above are satisfied during the execution of the NOx reduction process, the reducing agent necessary for the NOx reduction process is supplied to the NOx catalyst 41 by the CO supply unit. If it supplies, it will become possible to perform a NOx reduction process suitably.

  Therefore, in the exhaust purification system of this embodiment, when it is determined that the condition for reducing the reactivity of HC is satisfied during the execution of the NOx reduction process, the condition for reducing the reactivity of HC is satisfied. The ratio of the reducing component supplied by the CO supply means out of the total amount of reducing agent to be supplied to the NOx catalyst 41 in the NOx reduction treatment is made higher than in the normal time when it is determined that there is no. Further, when it is judged that the reactivity of HC in the NOx catalyst 41 is further lowered, the ratio of the reducing component supplied by the CO supply means is made higher.

  FIG. 2 shows the degree of decrease in the reactivity of HC in the NOx catalyst 41 and the amount of reducing agent supplied to the NOx catalyst 41, supplied by the HC and CO supply means supplied by the HC supply means. It is a figure which represents typically the relationship with a ratio with a reducing component. As shown in FIG. 2, the amount of reducing agent supplied to the NOx catalyst 41 is constant, but as the degree of decrease in the reactivity of HC in the NOx catalyst 41 increases, it is supplied by the CO supply means out of the total amount of reducing agent. The ratio of the reducing component (denoted as CO in FIG. 2) is increased.

  As a result, even when the reactivity of HC in the NOx catalyst 41 is reduced, a reduction component having a higher reactivity than HC is supplied to the NOx catalyst 41 more than usual. It is possible to satisfactorily carry out the oxidation-reduction reaction of the reducing agent and to suitably execute the NOx reduction treatment.

  In FIG. 2, the total amount of the reducing agent supplied to the NOx catalyst 41 is HC when the decrease in the reactivity of HC is the smallest, but the CO supply means is also used when the decrease in the reactivity of HC is the smallest. The reducing component may be supplied by In the example shown in FIG. 2, the total amount of reducing agent supplied to the NOx catalyst 41 is constant, and the ratio of reducing components by the CO supply means is increased as the reactivity of HC decreases. As shown in FIG. 3, the supply amount of the reducing component by the CO supply means may be increased as the reactivity of HC decreases. In this case, as shown in FIG. 3, even if the reactivity of HC decreases, the amount of HC supplied by the HC supply means may be kept constant. More simply, the two reducing agent supply patterns are switched between a normal time when it is determined that the HC reactivity in the NOx catalyst 41 has not decreased and a case where it is determined that the NOx catalyst 41 has decreased. Anyway. In that case, for example, only HC from the HC supply unit may be supplied to the NOx catalyst 41 as a reducing agent during normal operation, and only CO from the CO supply unit may be supplied to the NOx catalyst 41 as a reducing agent when the reactivity decreases. Further, only HC may be supplied during normal operation, and HC and CO may be supplied when reactivity decreases. In addition, HC and CO are supplied both at the normal time and at the time of a decrease in reactivity, but the CO ratio may be set higher than that at the normal time at the time of a decrease in reactivity. In short, when it is determined that the reactivity of HC in the NOx catalyst 41 is lowered, if the reducing component having high reactivity by the CO supply means is supplied to the NOx catalyst 41 more than usual, this The effects of the invention can be obtained.

  In the present embodiment, whether or not the HC reactivity in the NOx catalyst 41 is reduced is determined based on the conditions that can affect the HC reactivity as described above, that is, the conditions related to the HC reaction environment in the NOx catalyst 41, Judgment is made based on conditions relating to the state of the NOx catalyst itself.

  Specifically, as a condition relating to the reactivity of HC in the NOx catalyst 41, a decrease in the reactivity of HC in the NOx catalyst 41 is determined based on the temperature of the NOx catalyst 41 and the flow rate of exhaust gas passing through the NOx catalyst 41. To do.

The conditions relating to the state of the NOx catalyst itself include the reaction of HC in the NOx catalyst 41 based on the amount of NOx in the exhaust flowing out from the NOx catalyst 41 and the measured value of the air-fuel ratio of the exhaust flowing out from the NOx catalyst 41. Determining gender decline.

  In the first embodiment, an example in which a decrease in the reactivity of HC in the NOx catalyst 41 is determined based on the amount of NOx in the exhaust gas flowing out from the NOx catalyst 41 will be described.

  When the oxidation-reduction capability is reduced due to the performance deterioration of the NOx catalyst 41, the emission deteriorates and the amount of NOx in the exhaust gas flowing out from the NOx catalyst 41 tends to increase. Therefore, the amount of NOx flowing out of the NOx catalyst 41 is measured by the exhaust sensor 51, and when the measured amount of NOx in the catalyst output gas exceeds a predetermined reference amount mN0, the redox of the NOx catalyst 41 is measured. It is determined that the capacity has deteriorated due to factors such as changes over time, and it is determined that the reactivity of HC in the NOx catalyst 41 has decreased. Here, the predetermined reference amount mN0 is determined based on the amount of NOx in the exhaust gas of the NOx catalyst 41 that is assumed when there is no deterioration in the oxidation-reduction capability of the NOx catalyst 41.

  When the NOx reduction process is performed, it is detected that the NOx amount mN in the catalyst output gas is equal to or less than the reference amount mN0 (mN ≦ mN0), and it is determined that the reactivity of HC in the NOx catalyst 41 has not decreased. (Hereinafter, normal time), the total reducing agent amount to be supplied to the NOx catalyst 41 is supplied by the fuel addition valve 19.

Further, when the NOx reduction process is executed, it is detected that the NOx amount mN in the catalyst output gas exceeds the reference amount mN0 (mN> mN0), and it is determined that the reactivity of HC in the NOx catalyst 41 is reduced. In this case, the amount of HC supplied by the fuel addition valve 19 is set to an amount ma ′ smaller than the normal addition amount ma (ma ′ <ma), and the injector 29 is controlled to perform after injection. Execute. By performing the after injection, the amount of highly reactive reducing components such as CO contained in the exhaust gas from the combustion chamber is increased. Thereby, the ratio of reducing components (CO, H ₂ , light HC, etc.) having higher reactivity than HC in the total amount of reducing agent supplied to the NOx catalyst 41 is increased. By supplying these highly reactive reducing components to the NOx catalyst 41, it is possible to execute the NOx reduction process satisfactorily even when the oxidation-reduction ability of the NOx catalyst 41 is deteriorated.

  The reducing agent supply control in the NOx reduction process described above will be described with reference to FIG. FIG. 4 is a flowchart showing the execution procedure of the reducing agent supply control routine of this embodiment. This routine is periodically executed by the ECU 26 while the internal combustion engine 1 is operating.

  In step S101, the ECU 26 determines whether or not an execution condition for the NOx reduction process is satisfied. Specifically, the NOx amount stored in the NOx catalyst 41 is estimated based on the operation history of the internal combustion engine 1 and the NOx reduction process is executed when it is determined that the NOx storage amount exceeds a predetermined reference amount. It is determined that the condition is met. In this embodiment, when it is determined that the temperature of the exhaust gas flowing into the NOx catalyst 41 is higher than a predetermined reference temperature, for example, when the internal combustion engine 1 is in a high load operation state, the execution condition of the NOx reduction process is It is determined that it is not established. This is because, when the temperature of the exhaust gas flowing into the NOx catalyst 41 is high, the NOx catalyst 41 is difficult to store NOx. That is, when the temperature of the exhaust gas flowing into the NOx catalyst 41 is high, it is considered that NOx that needs to be reduced and purified by performing NOx reduction processing is not stored in the NOx catalyst 41. NOx reduction processing is not executed. By doing so, it is possible to suppress deterioration in fuel consumption due to the execution of unnecessary NOx reduction processing. If it is determined in step S101 that the execution condition for the NOx reduction process is satisfied (Yes), the ECU 26 proceeds to step S102. If it is determined in step S101 that the execution condition for the NOx reduction process is not satisfied (No), the ECU 26 temporarily exits this routine.

  In step S102, the ECU 26 acquires the NOx amount mN in the catalyst exhaust gas of the NOx catalyst 41. In this embodiment, the NOx amount mN in the catalyst output gas is measured by the exhaust sensor 51 as described above.

  In step S103, the ECU 26 determines whether or not the NOx amount mN in the catalyst output gas acquired in step S102 is larger than the reference amount mN0. When the measured value mN of the NOx amount in the catalyst output gas is equal to or less than the reference amount mN0 (mN ≦ mN0, Step S103: No), the ECU 26 proceeds to Step S104. When the measured value mN of the NOx amount in the catalyst output gas is larger than the reference amount mN0 (mN> mN0, Step S103: Yes), the ECU 26 proceeds to Step S105.

  In step S104, the ECU 26 adds the exhaust fuel by the fuel addition valve 19 by the addition amount ma.

  In step S105, the ECU 26 adds the exhaust fuel by the fuel addition valve 19 by the addition amount ma '(<ma) and performs after injection.

  FIG. 5 schematically shows temporal changes in the NOx amount in the catalyst exhaust gas of the NOx catalyst 41, the amount of exhaust fuel added by the fuel addition valve 19, and the state of after-injection when the above reducing agent supply control is executed. It is a represented time chart. As shown in FIG. 5A, when the NOx amount mN in the catalyst output gas increases and exceeds the reference amount mN0, the exhaust fuel addition amount ma by the fuel addition valve 19 is increased as shown in FIG. The amount is reduced to ma ′, and the amount of HC supplied to the NOx catalyst 41 is reduced. Further, as shown in FIG. 5C, after injection is executed, the amount of CO supplied to the NOx catalyst 41 increases.

  Thus, in a situation where the performance of the NOx catalyst 41 is not deteriorated, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed only by adding the exhaust fuel by the fuel addition valve 19. Thereby, NOx reduction processing can be performed while suppressing deterioration of fuel consumption as much as possible. Further, in a situation where the performance of the NOx catalyst 41 is deteriorated, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed by addition of exhaust fuel by the fuel addition valve 19 and after injection. Thereby, since a highly reactive reducing component is supplied to the NOx catalyst 41, the NOx reduction treatment can be suitably executed even if the NOx catalyst 41 has deteriorated in performance, and a high NOx purification rate can be maintained. It becomes possible.

  In the second embodiment, an example in which a decrease in the reactivity of HC in the NOx catalyst 41 is determined based on the temperature of the NOx catalyst 41 will be described.

  When the temperature of the NOx catalyst 41 decreases, the activity of the NOx catalyst 41 decreases, so that the reactivity of HC in the NOx catalyst 41 tends to decrease. Therefore, the temperature of the exhaust gas flowing into the NOx catalyst 41 is measured by the exhaust temperature sensor 52, and when the measured catalyst input gas temperature T is lower than a predetermined reference temperature T0, the temperature of the NOx catalyst 41 is low and the catalytic activity is lowered. Therefore, it is determined that the reactivity of HC in the NOx catalyst 41 is reduced. Here, the predetermined reference temperature T0 sets the amount or ratio of the reducing component by the CO supply means to the normal amount or ratio at which it is determined that the reactivity of HC is not lowered during the execution of the NOx reduction process. Then, the reducing agent is supplied to the NOx catalyst 41 and determined based on the lower limit value of the temperature of the NOx catalyst 41 so that a predetermined target NOx purification rate can be achieved.

When the NOx reduction process is performed, it is detected that the input gas temperature T of the NOx catalyst 41 is equal to or higher than the reference temperature T0 (T ≧ T0), and it is determined that the reactivity of HC in the NOx catalyst 41 has not decreased. During normal operation, the fuel addition valve 19 adds the exhaust amount ma to the exhaust gas and controls the opening of the EGR valve 14 so that the EGR rate becomes Re.

Further, when the NOx reduction process is executed, it is detected that the input gas temperature T of the NOx catalyst 41 is lower than the reference temperature T0 (T <T0), and it is determined that the reactivity of HC in the NOx catalyst 41 is reduced. In this case, the addition amount of the exhaust fuel by the fuel addition valve 19 is set to a small amount ma ′ (ma ′ <ma) as compared with the normal addition amount ma, and the opening degree of the EGR valve 14 is set to the normal time. Further, the EGR rate is controlled to be higher than the normal time by setting the EGR rate to be more open. By increasing the EGR rate, the amount of highly reactive reducing components such as CO contained in the exhaust gas from the combustion chamber increases. Thereby, the ratio of reducing components (CO, H ₂ , light HC, etc.) having higher reactivity than HC in the total amount of reducing agent supplied to the NOx catalyst 41 is increased. By supplying these highly reactive reducing components to the NOx catalyst 41, even when the temperature of the NOx catalyst 41 is low, it is possible to execute the NOx reduction process satisfactorily.

  The reducing agent supply control in the NOx reduction process described above will be described with reference to FIG. FIG. 6 is a flowchart showing the execution procedure of the reducing agent supply control routine of this embodiment. This routine is periodically executed by the ECU 26 while the internal combustion engine 1 is operating.

  In step S201, the ECU 26 determines whether an execution condition for the NOx reduction process is satisfied. Since this is the same as the content of step S101 described in FIG. 4 of the first embodiment, a detailed description is omitted. If it is determined in step S201 that the execution condition for the NOx reduction process is satisfied (Yes), the ECU 26 proceeds to step S202. If it is determined in step S201 that the execution condition for the NOx reduction process is not satisfied (No), the ECU 26 temporarily exits this routine.

  In step S202, the ECU 26 acquires the temperature T of the catalyst input gas of the NOx catalyst 41. In this embodiment, the temperature T of the catalyst-containing gas is measured by the exhaust temperature sensor 52 as described above.

  In step S203, the ECU 26 determines whether or not the catalyst input gas temperature T acquired in step S202 is lower than the reference temperature T0. When the measured value T of the catalyst input gas temperature is equal to or higher than the reference temperature T0 (T ≧ T0, Step S203: No), the ECU 26 proceeds to Step S204. When the measured value T of the catalyst input gas temperature is lower than the reference temperature T0 (T <T0, Step S203: Yes), the ECU 26 proceeds to Step S205.

  In step S204, the ECU 26 adds the exhaust fuel by the addition amount ma by the fuel addition valve 19, and controls the opening degree of the EGR valve 14 so that the EGR rate becomes Re.

  In step S205, the ECU 26 adds the exhaust fuel by the addition amount ma ′ (<ma) by the fuel addition valve 19 and controls the opening degree of the EGR valve 14 so that the EGR rate becomes Re ′ (> Re). .

FIG. 7 is a time chart schematically showing the time variation of the catalyst inlet gas temperature of the NOx catalyst 41, the amount of exhaust fuel added by the fuel addition valve 19, and the EGR rate when the above reducing agent supply control is executed. . As shown in FIG. 7A, when the catalyst input gas temperature T decreases and becomes lower than the reference temperature T0, the exhaust fuel addition amount ma by the fuel addition valve 19 is reduced as shown in FIG. 7B. The amount of HC supplied to the NOx catalyst 41 is reduced. Further, as shown in FIG. 7C, the EGR rate Re is increased to Re ′, and the amount of CO supplied to the NOx catalyst 41 is increased.

  Thus, in a situation where the temperature of the NOx catalyst 41 is sufficiently high, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed mainly by adding the exhaust fuel by the fuel addition valve 19. Thereby, NOx reduction processing can be performed while suppressing deterioration of fuel consumption as much as possible. Further, in a situation where the temperature of the NOx catalyst 41 is low, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed by reducing components such as CO discharged from the combustion chamber when the combustion gas has a high EGR rate. Performed as the subject. As a result, since a highly reactive reducing component is supplied to the NOx catalyst 41, the NOx catalyst 41 can be suitably used even when the temperature of the NOx catalyst 41 is low and the catalytic activity is so low that it is difficult for HC to react suitably. Reduction processing can be executed, and a high NOx purification rate can be maintained.

  In the third embodiment, an example in which a decrease in the reactivity of HC in the NOx catalyst 41 is determined based on the flow rate of exhaust gas passing through the NOx catalyst 41 will be described.

  When the flow rate of the exhaust gas passing through the NOx catalyst 41 is increased, the reaction time of the reducing agent in the NOx catalyst 41 is shortened, so that the reactivity of HC having a particularly slow reaction rate tends to decrease. Therefore, when the intake air amount Ga is measured by the air flow meter 7 and the measured intake air amount Ga is larger than the predetermined reference amount Ga0, the flow rate of the exhaust gas passing through the NOx catalyst 41 is large, and HC undergoes an oxidation-reduction reaction. Therefore, it is determined that a sufficient reaction time cannot be secured, and it is determined that the reactivity of HC in the NOx catalyst 41 is reduced. Here, the predetermined reference amount Ga0 sets the amount or ratio of the reducing component by the CO supply means to the normal amount or ratio at which it is determined that the reactivity of HC is not lowered during the execution of the NOx reduction process. Then, the reducing agent is supplied to the NOx catalyst 41 and determined based on the upper limit value of the intake air amount that can achieve a predetermined target NOx purification rate.

  When the NOx reduction process is performed, it is detected that the intake air amount Ga is equal to or less than the reference amount Ga0 (Ga ≦ Ga0), and at the normal time when it is determined that the reactivity of HC in the NOx catalyst 41 is not lowered. The total reducing agent amount to be supplied to the NOx catalyst 41 is supplied by the fuel addition valve 19.

Further, when the NOx reduction process is performed, when it is detected that the intake air amount Ga is larger than the reference amount Ga0 (Ga> Ga0) and it is determined that the reactivity of HC in the NOx catalyst 41 is reduced, The addition amount of the exhaust fuel by the fuel addition valve 19 is set to a small amount ma ′ (ma ′ <ma) compared with the normal addition amount ma, and a large amount of EGR is introduced to reduce the combustion mode of the internal combustion engine 1 at a low temperature. Switch to combustion. By performing low temperature combustion, the amount of highly reactive reducing components such as CO contained in the exhaust gas from the combustion chamber increases. Thereby, the ratio of reducing components (CO, H ₂ , light HC, etc.) having higher reactivity than HC in the total amount of reducing agent supplied to the NOx catalyst 41 is increased. By supplying these highly reactive reducing components to the NOx catalyst 41, even when the flow rate of the exhaust gas passing through the NOx catalyst 41 is large, the NOx reduction process can be performed satisfactorily.

  The reducing agent supply control in the NOx reduction process described above will be described with reference to FIG. FIG. 8 is a flowchart showing the execution procedure of the reducing agent supply control routine of this embodiment. This routine is periodically executed by the ECU 26 while the internal combustion engine 1 is operating.

In step S301, the ECU 26 determines whether an execution condition for the NOx reduction process is satisfied. Since this is the same as the content of step S101 described in FIG. 4 of the first embodiment, a detailed description is omitted. If it is determined in step S301 that the execution condition for the NOx reduction process is satisfied (Yes), the ECU 26 proceeds to step S302. When it is determined in step S301 that the execution condition for the NOx reduction process is not satisfied (No), the ECU 26 temporarily exits this routine.

  In step S302, the ECU 26 acquires the intake air amount Ga. In the present embodiment, the intake air amount is measured by the air flow meter 7 as described above.

  In step S303, the ECU 26 determines whether or not the intake air amount Ga acquired in step S302 is larger than the reference amount Ga0. When the measured value Ga of the intake air amount is equal to or less than the reference amount Ga0 (Ga ≦ Ga0, step S303: No), the ECU 26 proceeds to step S304. When the measured value Ga of the intake air amount is larger than the reference amount Ga0 (Ga> Ga0, step S303: Yes), the ECU 26 proceeds to step S305.

  In step S <b> 304, the ECU 26 adds the exhaust fuel by the fuel addition valve 19 by the addition amount ma.

  In step S305, the ECU 26 adds the exhaust fuel by the fuel addition valve 19 by the addition amount ma '(<ma) and switches the combustion mode to low-temperature combustion.

  FIG. 9 is a time chart schematically showing the time variation of the intake air amount, the exhaust fuel addition amount by the fuel addition valve 19, and the low temperature combustion implementation state when the above reducing agent supply control is executed. As shown in FIG. 9A, when the intake air amount Ga increases and becomes larger than the reference amount Ga0, as shown in FIG. 9B, the exhaust fuel addition amount ma by the fuel addition valve 19 is reduced to ma. The amount of HC supplied to the NOx catalyst 41 decreases. Further, as shown in FIG. 9C, low temperature combustion is performed, and the amount of CO supplied to the NOx catalyst 41 increases.

  Thus, in a situation where the flow rate of the exhaust gas passing through the NOx catalyst 41 is not so high, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed only by adding the exhaust fuel by the fuel addition valve 19. Thereby, NOx reduction processing can be performed while suppressing deterioration of fuel consumption as much as possible. Further, in a situation where the flow rate of the exhaust gas passing through the NOx catalyst 41 is large, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed by addition of exhaust fuel by the fuel addition valve 19 and low-temperature combustion. Accordingly, since a highly reactive reducing component is supplied to the NOx catalyst 41, the flow rate of the exhaust gas passing through the NOx catalyst 41 is large, and it is preferable even when the reaction time of the reducing agent in the NOx catalyst 41 cannot be sufficiently secured. In addition, the NOx reduction process can be executed, and a high NOx purification rate can be maintained.

  In the fourth embodiment, an example in which a decrease in the reactivity of HC in the NOx catalyst 41 is determined based on the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst 41 will be described.

  When the oxidation-reduction capability is reduced due to the performance deterioration of the NOx catalyst 41, it is assumed that the exhaust air-fuel ratio when the rich spike is executed on the NOx catalyst 41 is measured by the air-fuel ratio sensor 50 installed downstream of the NOx catalyst. It is known that the value on the lean side is measured. Therefore, the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst 41 when the rich spike is executed on the NOx catalyst 41 is measured by the air-fuel ratio sensor 50, and the measured air-fuel ratio A / F is leaner than the stoichiometric ratio. In this case, it is determined that the oxidation-reduction ability of the NOx catalyst 41 has deteriorated due to factors such as a change over time, and it is determined that the reactivity of HC in the NOx catalyst 41 has decreased.

Then, during the rich spike execution of the NOx reduction process, the air-fuel ratio sensor 50 measures the stoichiometric or the catalyst exhaust gas air-fuel ratio on the richer side than the stoichiometric (A / F ≦ stoichiometric), and the reactivity of HC in the NOx catalyst 41 decreases. In normal times when it is determined that the fuel is not present, the fuel addition valve 19 adds the exhaust amount of the exhaust gas ma and controls the injector 29 so as to inject the fuel at the fuel injection amount Qm.

In addition, when the rich spike of the NOx reduction process is executed, the air-fuel ratio of the catalyst output gas leaner than the stoichiometry is measured by the air-fuel ratio sensor 50 (A / F> stoichi), and the reactivity of HC in the NOx catalyst 41 decreases. If it is determined that the amount of exhaust fuel added by the fuel addition valve 19 is smaller than the normal addition amount ma (ma ′ <ma), the fuel injection amount is set to normal. An amount Qm ′ larger than the current fuel injection amount Qm is assumed (Qm ′> Qm). By increasing the fuel injection amount, the amount of highly reactive reducing components such as CO contained in the exhaust gas from the combustion chamber increases. Thereby, the ratio of reducing components (CO, H ₂ , light HC, etc.) having higher reactivity than HC in the total amount of reducing agent supplied to the NOx catalyst 41 is increased. By supplying these highly reactive reducing components to the NOx catalyst 41, it is possible to execute the NOx reduction process satisfactorily even when the oxidation-reduction ability of the NOx catalyst 41 is deteriorated.

  The reducing agent supply control in the NOx reduction process described above will be described with reference to FIG. FIG. 10 is a flowchart showing the execution procedure of the reducing agent supply control routine of this embodiment. This routine is periodically executed by the ECU 26 while the internal combustion engine 1 is operating.

  In step S401, the ECU 26 determines whether an execution condition for the NOx reduction process is satisfied. Since this is the same as the content of step S101 described in FIG. 4 of the first embodiment, a detailed description is omitted. If it is determined in step S401 that the execution condition for the NOx reduction process is satisfied (Yes), the ECU 26 proceeds to step S402. If it is determined in step S401 that the execution condition for the NOx reduction process is not satisfied (No), the ECU 26 once exits this routine.

  In step S402, the ECU 26 executes rich spike. Specifically, the reducing agent is supplied at the normal time when it is determined that the reactivity of HC in the NOx catalyst 41 is not lowered, that is, the fuel addition valve 19 adds the added amount of exhaust fuel and the fuel injection. The injector 29 is controlled to perform fuel injection with the amount Qm.

  In step S403, the ECU 26 acquires the air-fuel ratio of the catalyst output gas corresponding to the rich spike executed in step S402. In this embodiment, the air-fuel ratio of the catalyst output gas is measured by the air-fuel ratio sensor 50 as described above.

  In step S404, the ECU 26 determines whether or not the catalyst output gas air-fuel ratio A / F acquired in step S403 is a leaner value than the stoichiometric value. When the measured value A / F of the catalyst output air / fuel ratio is stoichiometric or a richer value than stoichiometric (A / F ≦ stoichiometric, step S404: No), the ECU 26 proceeds to step S405. If the measured value A / F of the catalyst output air-fuel ratio is a value on the lean side of the stoichiometric value (A / F> stoichiometric, step S404: Yes), the ECU 26 proceeds to step S406.

  In step S405, the ECU 26 adds the exhaust fuel by the addition amount ma by the fuel addition valve 19, and performs the fuel injection by the fuel injection amount Qm by the injector 29.

In step S406, the ECU 26 adds the exhaust fuel by the addition amount ma '(<ma) by the fuel addition valve 19, and also by the injector 29, the fuel injection amount Qm' (
> Qm) fuel injection is performed.

  FIG. 11 schematically shows changes in the measured value of the catalyst output gas air-fuel ratio of the NOx catalyst 41, the amount of exhaust fuel added by the fuel addition valve 19, and the fuel injection amount over time when the above reducing agent supply control is executed. It is a time chart. As shown in FIG. 11A, when the catalyst outgas air-fuel ratio A / F measured when the rich spike is executed is a value on the lean side from the stoichiometry, as shown in FIG. The amount of exhaust fuel added by the fuel addition valve 19 is reduced from ma to ma ′, and the amount of HC supplied to the NOx catalyst 41 is reduced. Further, as shown in FIG. 11C, the fuel injection amount is increased from Qm to Qm ′, and the amount of CO supplied to the NOx catalyst 41 increases. As a result, since the CO undergoes a good oxidation-reduction reaction in the NOx catalyst 41, as shown in FIG. 11 (A), the value becomes richer than the catalyst outgas air-fuel ratio stoichiometry measured when the rich spike is executed.

  Thus, in a situation where the performance of the NOx catalyst 41 is not deteriorated, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is performed mainly by adding the exhaust fuel by the fuel addition valve 19. Thereby, NOx reduction processing can be performed while suppressing deterioration of fuel consumption as much as possible. Further, in a situation where the performance of the NOx catalyst 41 is deteriorated, the supply of the reducing agent to the NOx catalyst 41 in the NOx reduction process is such as CO discharged from the combustion chamber when the fuel injection amount is increased and rich combustion is performed. The reduction component is mainly used. Thereby, since a highly reactive reducing component is supplied to the NOx catalyst 41, the NOx reduction treatment can be suitably executed even if the NOx catalyst 41 has deteriorated in performance, and a high NOx purification rate can be maintained. It becomes possible.

  In each of the embodiments described above, a decrease in HC reactivity in the NOx catalyst 41 is determined based on individual conditions related to the HC reaction environment in the NOx catalyst 41 and individual conditions related to the state of the NOx catalyst 41 itself. However, the determination of the decrease in HC reactivity may be made by combining these conditions. For example, the reduction degree of the reactivity of HC in the NOx catalyst 41 is determined in consideration of both the temperature of the NOx catalyst 41 and the deterioration degree of the NOx catalyst 41, and the supply of the reducing component by the CO supply means is controlled based on the judgment. You may do it.

  In each of the above embodiments, when the NOx reduction process is performed, it is determined whether or not the reactivity of HC in the NOx catalyst 41 is decreased, and when the reactivity is determined not to decrease, However, as shown in FIG. 2 and FIG. 3, according to the degree of decrease in reactivity, The amount or ratio of reducing agent supplied by the CO supply means may be changed stepwise or continuously. For example, in the second embodiment, the amount of addition by the fuel addition valve 19 may be reduced and the EGR rate may be increased as the catalyst input gas temperature T measured by the exhaust temperature sensor 52 becomes lower. By doing so, when the reactivity of HC in the NOx catalyst 41 is further lowered, the ratio or amount of the reducing component having high reactivity among the reducing agents supplied to the NOx catalyst 41 is increased. The NOx reduction process can be more suitably executed. Such a modification can be similarly applied to the first, third, and fourth embodiments.

Further, in each of the above-described embodiments, the configuration in which unburned HC is supplied to the exhaust gas by the fuel addition valve 19 as the HC supply unit is illustrated, but the HC supply unit is not limited thereto. For example, HC can be supplied also by post injection. Further, the conditions for determining the decrease in the reactivity of HC in each of the above embodiments (the amount of catalyst output NOx, the catalyst temperature, the amount of gas passing through the catalyst, the catalyst output gas air-fuel ratio) and the reactivity of HC are reduced. The combination with the means (after injection, EGR rate increase, low temperature combustion, rich combustion) for increasing the highly reactive reducing component when judged is not limited to the combinations exemplified in the above embodiments. Any combination is possible within the possible range.

  In the second embodiment, the example in which the catalyst temperature of the NOx catalyst 41 is determined based on the catalyst inlet gas temperature measured by the exhaust temperature sensor 52 has been described. However, a sensor for measuring the catalyst outlet gas temperature is provided. The temperature of the NOx catalyst 41 may be determined based on the measured value by the sensor, or a sensor for directly measuring the temperature of the NOx catalyst 41 is provided to acquire the temperature of the NOx catalyst 41 based on the measured value by the sensor. May be. Further, the temperature of the NOx catalyst 41 may be estimated based on information related to the operating state such as the rotational speed and load of the internal combustion engine 1.

  In the fourth embodiment, the air-fuel ratio at the time of rich spike execution, which is a criterion for determining whether or not the NOx catalyst 41 is deteriorated, is set to stoichiometric, but the reference value is not limited to stoichiometric. An air-fuel ratio that can more appropriately determine the deterioration state of the NOx catalyst 41 can be obtained by experiments or the like and used as a determination criterion.

  The HC supply means (exhaust fuel addition by the fuel addition valve 19) in the present embodiment corresponds to the HC supply means in the present invention. CO supply means in this embodiment (ECU 26 for controlling the injector 29 to perform after injection, ECU 26 for increasing the opening degree of the EGR valve 14 to increase the EGR rate, low temperature combustion by increasing the EGR gas amount) The ECU 26 and the ECU 26 which controls the injector 29 to increase the fuel injection amount to perform rich combustion correspond to the reducing component supply means in the present invention. The ECU 26 that executes the NOx reduction process for reducing and purifying NOx stored in the NOx catalyst 41 by executing the above-described flows in the present embodiment corresponds to the NOx reduction means in the present invention. The exhaust temperature sensor 52 in this embodiment corresponds to the catalyst temperature acquisition means in the present invention. The air flow meter 7 in the present embodiment corresponds to the catalyst passing gas amount acquisition means in the present invention. The exhaust sensor 51 in the present invention corresponds to the NOx amount acquisition means in the present invention. The air-fuel ratio sensor 50 in the present invention corresponds to the air-fuel ratio sensor in the present invention.

It is a figure which shows schematic structure of the internal combustion engine in the Example, its intake system, and an exhaust system. It is a figure which shows the relationship between the degree of the HC reactivity fall in the NOx catalyst in an Example, and the ratio of HC and CO of the reducing agents supplied to a NOx catalyst in a NOx reduction process. It is a figure which shows the relationship between the degree of the HC reactivity fall in the NOx catalyst in an Example, and the quantity of HC and CO of the reducing agents supplied to a NOx catalyst in a NOx reduction process. 6 is a flowchart illustrating an execution procedure of a reducing agent supply control routine when executing NOx reduction processing in the first embodiment. 4 is a time chart showing an example of a temporal change in the NOx amount in the catalyst exhaust gas of the NOx catalyst, the amount of exhaust fuel added by the fuel addition valve, and the after-injection implementation state when the reducing agent supply control of Example 1 is executed. . 7 is a flowchart illustrating an execution procedure of a reducing agent supply control routine when executing NOx reduction processing in the second embodiment. 7 is a time chart showing an example of a change over time of the catalyst input gas temperature of the NOx catalyst, the amount of exhaust fuel added by the fuel addition valve, and the EGR rate when the reducing agent supply control of Example 2 is executed. 12 is a flowchart illustrating an execution procedure of a reducing agent supply control routine when executing NOx reduction processing in the third embodiment. 10 is a time chart showing an example of a time change of an intake air amount, an exhaust fuel addition amount by a fuel addition valve, and an implementation state of low-temperature combustion when reducing agent supply control of Example 3 is executed. 14 is a flowchart illustrating an execution procedure of a reducing agent supply control routine when executing NOx reduction processing in the fourth embodiment. 10 is a time chart showing an example of temporal changes in the air-fuel ratio of catalyst output gas of the NOx catalyst, the amount of exhaust fuel added by a fuel addition valve, and the amount of fuel injection when the reducing agent supply control of Example 4 is executed.

Explanation of symbols

1 Internal combustion engine 7 Air flow meter 14 EGR valve 15 EGR passage 17 Intake manifold 18 Exhaust manifold 19 Fuel addition valve 22 Inlet throttle valve 26 ECU
29 Injector 41 NOx catalyst 42 Intake passage 43 Exhaust passage 49 Cylinder 50 Air-fuel ratio sensor 51 Exhaust sensor 52 Exhaust temperature sensor

Claims (12)

A NOx storage reduction catalyst provided in the exhaust passage of the internal combustion engine;
HC supply means for supplying HC to the NOx catalyst;
Reducing component supply means for supplying the NOx catalyst with a reducing component having a higher reactivity of the oxidation-reduction reaction in the NOx catalyst than HC supplied by the HC supply means;
NOx reduction means for performing NOx reduction processing for reducing and purifying NOx occluded in the NOx catalyst by supplying HC and / or the reducing component to the NOx catalyst by the HC supply means and / or the reducing component supply means. When,
With
The NOx reduction means is configured to execute the NOx reduction process.
When a predetermined condition for reducing the HC reactivity in the NOx catalyst is satisfied, and / or when it is detected that the HC reactivity in the NOx catalyst is reduced,
Compared to the case of none of them,
Increasing the ratio of the reducing component to the total amount of HC and the reducing component supplied to the NOx catalyst, or
An exhaust gas purification apparatus for an internal combustion engine, wherein the amount of the reducing component supplied to the NOx catalyst is increased. In claim 1,
The NOx reduction means includes
The greater the degree of decrease in HC reactivity in the NOx catalyst due to the establishment of the predetermined condition,
An exhaust emission control device for an internal combustion engine, wherein the ratio of the reducing component is increased or the amount of the reducing component is increased. In claim 1 or 2,
The NOx reduction means includes
The greater the degree of decrease in HC reactivity in the detected NOx catalyst,
An exhaust emission control device for an internal combustion engine, wherein the ratio of the reducing component is increased or the amount of the reducing component is increased. In any one of Claims 1-3,
A catalyst temperature acquisition means for acquiring the temperature of the NOx catalyst;
The NOx reduction means includes
An internal combustion engine characterized in that, when the temperature of the NOx catalyst acquired by the catalyst temperature acquisition means is lower than a predetermined reference temperature, it is determined that a condition for reducing the reactivity of HC in the NOx catalyst is satisfied. Engine exhaust purification system. In claim 4,
The NOx reduction means has a lower temperature of the NOx catalyst acquired by the catalyst temperature acquisition means,
An exhaust emission control device for an internal combustion engine, wherein the ratio of the reducing component is increased or the amount of the reducing component is increased. In any one of Claims 1-5,
A catalyst passage gas amount acquisition means for acquiring a flow rate of exhaust gas passing through the NOx catalyst;
The NOx reduction means satisfies a condition for reducing the HC reactivity in the NOx catalyst when the flow rate of the exhaust gas passing through the NOx catalyst acquired by the catalyst passing gas amount acquisition means is greater than a predetermined reference flow rate. An exhaust emission control device for an internal combustion engine, characterized in that it is determined that the engine is operating. In claim 6,
The NOx reduction means has a larger intake air amount acquired by the intake air amount acquisition means,
Increasing the ratio of the reducing component, or
An exhaust emission control device for an internal combustion engine, wherein the amount of the reducing component is increased. In any one of Claims 1-7,
A NOx amount acquisition means for acquiring the amount of NOx in the exhaust gas flowing out from the NOx catalyst;
The NOx reduction means detects that the reactivity of HC in the NOx catalyst is reduced when the NOx amount acquired by the NOx amount acquisition means exceeds a predetermined reference amount. An exhaust purification device for an internal combustion engine. In claim 8,
The NOx reduction means has a larger NOx amount acquired by the NOx amount acquisition means,
Increase the ratio of the reducing component, or
An exhaust emission control device for an internal combustion engine, wherein the amount of the reducing component is increased. In any one of Claims 1-9,
An air-fuel ratio sensor for measuring an air-fuel ratio of the exhaust gas flowing out from the NOx catalyst;
The NOx reduction means detects that the reactivity of HC in the NOx catalyst is lowered when the air-fuel ratio of the exhaust gas measured by the air-fuel ratio sensor is a value leaner than a predetermined reference value. An exhaust emission control device for an internal combustion engine. In claim 10,
As the air-fuel ratio acquired by the air-fuel ratio sensor is leaner, the NOx reduction means
An exhaust emission control device for an internal combustion engine, wherein the ratio of the reducing component is increased or the amount of the reducing component is increased. In claim 10 or 11,
Exhaust temperature acquisition means for acquiring the temperature of the exhaust gas flowing into the NOx catalyst;
The NOx reduction means performs supply of HC by the HC supply means and supply of the reducing component by the reducing component supply means when the temperature of the exhaust gas acquired by the exhaust temperature acquisition means is higher than a predetermined reference exhaust temperature. An exhaust purification device for an internal combustion engine, characterized in that there is no exhaust gas.

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