JP5257332B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust purification device that purifies exhaust exhausted from an internal combustion engine.

Conventionally, as a catalyst for reducing nitrogen oxides contained in exhaust gas discharged from an internal combustion engine, an occlusion reduction catalyst (also known as NOx occlusion catalyst, NOx trap catalyst, NOx Trap Catalyst, etc.) is known. In other words, nitrogen oxide (NOx) is occluded in the form of nitrate in an oxidizing atmosphere during normal operation, and the nitrogen oxide is intermittently reduced to nitrogen (N ₂ ) by receiving a reducing agent. is there.

  As a method for supplying the reducing agent to the storage reduction catalyst, extra fuel is injected into the cylinder of the internal combustion engine to leave unburned fuel in the exhaust, which is used as a nitrogen oxide reducing agent. In some cases, an injector is provided in the middle of the exhaust passage, and a reducing agent (hydrocarbon such as light oil or a hydroxyl group compound such as alcohol) is injected from the injector into the exhaust. In the former method, the exhaust gas passage device configuration can be simplified, but torque correction of the internal combustion engine is required. In the latter method, a reducing agent supply device is required in the exhaust passage, while the exhaust component can be controlled without affecting the torque generated by the internal combustion engine.

  An exhaust purification system in which an oxidation catalyst is provided on the upstream side of the exhaust passage with respect to the storage reduction catalyst is also known. That is, excess oxygen that adversely affects the reduction of nitrogen oxides is removed by reacting with a reducing agent on the oxidation catalyst to improve reduction efficiency. For example, in the technique of Patent Document 1, a reducing agent injector is provided on the upstream side of the oxidation catalyst or on the upstream side of each of the oxidation catalyst and the storage reduction catalyst, and the supply amount of the reducing agent is controlled according to the engine exhaust temperature. Thus, nitrogen oxides in the exhaust are efficiently removed.

JP-A-8-49533

  By the way, not only nitrogen oxides but also sulfur compounds such as sulfur oxides adhere to the storage reduction catalyst. In general, since sulfur compounds inhibit the adsorption performance of nitrogen oxides, an operation for periodically removing sulfur compounds adhering to the storage reduction catalyst is required. On the other hand, the environmental conditions for reducing sulfur compounds and removing them from the storage reduction catalyst are different from those for nitrogen oxides. For example, highly reactive reducing components are not required, but the exhaust temperature must be high. I must. Therefore, when each reduction operation of nitrogen oxides and sulfur compounds is performed in the same storage reduction catalyst, it is desirable to generate an environment suitable for each chemical reaction.

One of the purposes of the present invention was devised in view of such problems, and is to increase the regeneration efficiency by improving the reactivity during the reduction operation of nitrogen oxides and sulfur compounds in the occlusion reduction catalyst. .
In addition, the present invention is not limited to the above-mentioned object, and is an operational effect derived from each configuration shown in the embodiment for carrying out the invention, which will be described later. Can be positioned.

The disclosed exhaust purification device is provided in an exhaust passage of an internal combustion engine, and has an oxidation catalyst having an oxidizing ability for components in exhaust gas, and is provided in the exhaust passage downstream of the oxidation catalyst, and the exhaust gas is exhausted in an oxidizing atmosphere. A first storage agent that stores the nitrogen oxide therein and reduces the nitrogen oxide in a reducing atmosphere; and a first reducing agent that is oxidized by the oxidation catalyst is supplied to the exhaust gas flowing into the oxidation catalyst. supply means, provided in the exhaust passage between the oxidizing catalyst and the absorbent storage reduction catalyst, a second supply means for supplying a second reducing agent for reducing nitrogen oxides in absorbent storage reduction catalyst during the exhaust A first purge control for releasing the nitrogen oxide stored in the storage reduction catalyst when a predetermined first purge start condition is satisfied, and when the first purge start condition is not satisfied and a predetermined first When the double purge start condition is satisfied Reducing agent control means for performing second purge control for removing sulfur compounds as one of the components adhering to the storage reduction catalyst, and the reducing agent control means is supplied from the first supply means. Each supply amount of the first reducing agent and the second reducing agent supplied from the second supply means is individually controlled by the first purge control and the second purge control, and the first purge When the control is performed, the first reducing agent is injected from the first supply unit, and the second reducing agent is also injected from the second supply unit. When the second purge control is performed, the first reducing agent is injected. The first reducing agent is injected from the supply means, and the injection of the second reducing agent from the second supply means is suspended .

In the disclosed exhaust purification device, each of the first supply unit and the second supply unit injects unburned fuel as the first reducing agent and the second reducing agent.
In the disclosed exhaust purification device, the reducing agent control means injects an amount of the unburned fuel from the first supply means so that the exhaust air-fuel ratio in the oxidation catalyst is stoichiometric when the first purge control is performed. It is characterized by letting.

In the disclosed exhaust purification apparatus, the reducing agent control means causes the first supply means to supply the unburned fuel in an amount that makes the exhaust air-fuel ratio in the oxidation catalyst richer than the stoichiometry when the second purge control is performed. It is characterized by being sprayed from.
The disclosed exhaust purification device further includes catalyst inlet exhaust temperature detecting means for detecting a catalyst inlet exhaust temperature at the inlet of the storage reduction catalyst, and the reducing agent control means is configured to perform the second purge control, and The second purge control is terminated when a predetermined time elapses after the catalyst inlet exhaust temperature detected by the catalyst inlet exhaust temperature detection means becomes equal to or higher than a predetermined temperature.

  Further, in the disclosed exhaust purification apparatus, the catalyst inlet exhaust temperature detected by the catalyst inlet exhaust temperature detecting means when the reducing agent control means performs the second purge control is less than the predetermined temperature. Sometimes, the first reducing agent is injected from the first supply means and the second reducing agent is also injected from the second supply means, and the supply amount of the second reducing agent is determined by the catalyst inlet. It is an amount required for raising the exhaust temperature to the predetermined temperature.

  Further, in the disclosed exhaust purification apparatus, the reducing agent control means performs the second purge control, and the catalyst inlet exhaust temperature detected by the catalyst inlet exhaust temperature detection means is equal to or higher than the predetermined temperature. Sometimes, the first reducing agent is injected from the first supply means and the second reducing agent is also injected from the second supply means, and the supply amount of the second reducing agent is determined by the catalyst inlet. It is an amount required to maintain the exhaust temperature at the predetermined temperature.

  According to the disclosed exhaust purification apparatus, the exhaust gas temperature upstream of the storage reduction catalyst can be changed to an arbitrary value by individually controlling the supply amounts of the first reducing agent and the second reducing agent. It is possible to generate a reduction field corresponding to the reduction target in the storage reduction catalyst. Thereby, the reactivity at the time of each reduction operation of a nitrogen oxide and a sulfur compound can be improved, and regeneration efficiency can be improved.

It is a mimetic diagram showing the composition of the exhaust-air-purification device concerning one embodiment. FIG. 3 is a flowchart (main flow) for explaining the control contents of the exhaust purification device of FIG. 1. FIG. FIG. 3 is a flowchart (first purge control flow) for explaining the control content of the exhaust purification device of FIG. 1. FIG. FIG. 3 is a flowchart (second purge control flow) for explaining the control contents of the exhaust purification device of FIG. 1. FIG. FIG. 2 is a flowchart (filter combustion control flow) for explaining the control contents of the exhaust purification device of FIG. 1. FIG. 2 is a time chart for explaining the control action of the exhaust gas purification apparatus of FIG. 1, (a) shows the state of execution of the first purge control, (b) shows the state of execution of the second purge control, (c) Shows the fluctuation of the oxygen concentration C, (d) shows the injection state of unburned fuel from the second injector, and (e) shows the fluctuation of the air-fuel ratio on the outlet side of the storage reduction catalyst. It is a schematic diagram which shows the structure of the exhaust gas purification apparatus which concerns on a modification. FIG. 8 is a flowchart (filter combustion control flow) for explaining the control contents of the exhaust emission control device of FIG. 7. FIG.

  Hereinafter, an embodiment of an exhaust emission control device will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not clearly shown in the embodiment described below. That is, the present embodiment may be variously modified and implemented without departing from the spirit of the invention.

[1. overall structure]
An engine 12 (internal combustion engine) shown in FIG. 1 is a diesel engine that uses light oil containing hydrocarbons (HC) having various carbon amounts as fuel. An exhaust passage 11 and an intake passage 14 are connected to the engine 12. Intake air is introduced into the combustion chamber of the cylinder of the engine 12 via the intake passage 14, and exhaust gas after combustion (hereinafter simply referred to as exhaust) is discharged to the outside of the vehicle via the exhaust passage 11.

An in-cylinder injector 16 for fuel injection is provided in the cylinder of the engine 12. The amount of fuel injected from the in-cylinder injector 16 is controlled by the engine ECU 15. The engine ECU 15 is an electronic control device in which a known microprocessor, ROM, RAM, and the like are integrated. The engine ECU 15 calculates the intake air mass flow rate M _air and the fuel mass flow rate M _fuel using various sensor information (not shown), and controls the in-cylinder injector 16 so that fuel corresponding to the calculated mass is injected. is there. The specific calculation method of the intake air mass flow rate M _air and the fuel mass flow rate M _fuel is arbitrary. The intake air mass flow rate M _air and the fuel mass flow rate M _fuel calculated here are input to the regeneration control device 9 described later.

On the exhaust passage 11, a turbocharger 13, an oxidation catalyst 1, an occlusion reduction catalyst 2, and a filter 3 are interposed in order from the upstream side of the exhaust flow.
The turbocharger 13 is a supercharger interposed so as to straddle the exhaust passage 11 and the intake passage 14. The turbocharger 13 rotates the turbine with the exhaust pressure in the exhaust passage 11 and drives the compressor using the rotational force, thereby compressing the intake air from the intake passage 14 and supercharging the engine 12. .

  The oxidation catalyst 1 is a catalyst that contains a catalytic noble metal on its surface and has an ability to oxidize components in exhaust gas. The components in the exhaust gas oxidized by the oxidation catalyst 1 include nitrogen oxide (NO), hydrocarbons in unburned fuel, and the like. The hydrocarbon referred to here includes saturated hydrocarbons whose carbon skeleton is composed of only single bonds, or unsaturated hydrocarbons having double or triple bonds. In general, unsaturated hydrocarbons are chemically more unstable than saturated hydrocarbons and have higher reactivity on the oxidation catalyst 1.

For example, when nitrogen oxide is oxidized on the oxidation catalyst 1, it becomes nitrogen dioxide (NO ₂ ). Further, when the hydrocarbon is oxidized on the oxidation catalyst 1, it becomes carbon dioxide (CO ₂ ) or water (H ₂ O) with heat generation.
The storage reduction catalyst 2 is a catalyst in which a nitrogen oxide storage material (trap agent) such as potassium (K) or barium (Ba) is supported on the catalyst surface, and stores nitrogen dioxide in the form of nitrate (NO ₃ ⁻ ). It has a function. On the surface of the occlusion reduction catalyst 2, not only the above-described nitrogen oxide occlusion material, but also catalyst noble metal fine particles similar to the oxidation catalyst 1 are supported. Thereby, the occlusion reduction catalyst 2 occludes the nitrogen dioxide produced by the occlusion reduction catalyst 2 itself in an oxidizing atmosphere. On the other hand, the occlusion reduction catalyst 2 reduces the occluded nitrate to nitrogen dioxide and releases it from the nitrogen oxide occlusion material when the environment around the catalyst becomes a reducing atmosphere.

The oxidizing atmosphere here means a state in which the oxygen concentration in the exhaust gas is relatively high with respect to the concentration of the reducing component (hydrocarbon, carbon monoxide, etc.). The reducing atmosphere is a state in which the concentration of the reducing component in the exhaust gas is relatively high with respect to the oxygen concentration, and the oxygen concentration (absolute concentration) is a predetermined concentration or less (eg, 1.0 [%] or less). It means a certain state.
Under a reducing atmosphere, the storage reduction catalyst 2 oxidizes both the nitrogen dioxide released by itself and the carbon monoxide and hydrocarbons in the exhaust to produce carbon dioxide, nitrogen and water. That is, the occlusion reduction catalyst 2 functions as a three-way catalyst that occludes nitrogen oxides in exhaust gas under an oxidizing atmosphere and reduces nitrogen oxides under a reducing atmosphere. Note that the hydrocarbon oxidation process in the storage reduction catalyst 2 also generates heat.

In addition, not only nitrogen dioxide but also a sulfur component contained in exhaust gas may adhere to the nitrogen oxide storage material of the storage reduction catalyst 2 in the form of sulfate (SO ₄ ²⁻ ). The adhesion of sulfur compounds to the storage reduction catalyst 2 is called sulfur poisoning. As the sulfur poisoning progresses, the ability to store nitrogen dioxide decreases, and therefore it is necessary to periodically remove the sulfur compound from the storage reduction catalyst 2. In the exhaust purification apparatus 10, a temperature of about 650 [° C.] is assumed as an atmospheric temperature for desorbing the sulfate from the storage reduction catalyst 2.

  The filter 3 is a porous filter (for example, a ceramic filter) that collects particulate matter (PM, particulate matter, soot) mainly containing carbon contained in exhaust gas. The interior of the filter 3 is divided into a plurality along the flow direction of the exhaust by the wall, and when the exhaust passes through the wall, particulate matter is collected on the wall and the surface of the wall, and the exhaust is Filtered. Similar to the occlusion reduction catalyst 2, the filter 3 is also required to periodically remove the particulate matter collected on the surface thereof. In the present exhaust purification apparatus 10, a temperature of about 550 [° C.] is assumed as an atmospheric temperature for removing particulate matter from the filter 3.

  A first injector 4 (first supply means) is interposed in the exhaust passage 11 upstream of the oxidation catalyst 1. The first injector 4 injects unburned fuel as a first reducing agent that is oxidized by the oxidation catalyst 1 into exhaust gas. The unburned fuel is the same fuel that is injected from the in-cylinder injector 16 into the cylinder of the engine 12. When the unburned fuel injected here is combined with oxygen in the exhaust gas and oxidized on the surfaces of the oxidation catalyst 1 and the occlusion reduction catalyst 2, the exhaust temperature rises.

  A second injector 5 (second supply means) is interposed in the exhaust passage 11 between the oxidation catalyst 1 and the storage reduction catalyst 2. The second injector 5 injects and supplies unburned fuel into the exhaust as a second reducing agent for reducing nitrogen dioxide to nitrogen in the storage reduction catalyst 2. The unburned fuel injected from the first injector 4 and the second injector 5 is the same type, and is the same type as the unburned fuel injected into the cylinder of the engine 12.

An oxygen concentration sensor 6 (oxygen concentration detection means) and a catalyst inlet temperature sensor 7 (catalyst inlet exhaust temperature detection means) are interposed in the exhaust passage 11 between the oxidation catalyst 1 and the storage reduction catalyst 2. The oxygen concentration sensor 6 detects the oxygen concentration C in the exhaust gas in the exhaust passage 11 between the oxidation catalyst 1 and the storage reduction catalyst 2. The catalyst inlet temperature sensor 7 detects the exhaust gas temperature T ₁ flowing into the storage reduction catalyst 2. Both the oxygen concentration C and the exhaust temperature T ₁ are input to the regeneration control device 9 described later.

A filter inlet temperature sensor 8 (filter inlet temperature detection means) is interposed in the exhaust passage 11 between the storage reduction catalyst 2 and the filter 3. The filter inlet temperature sensor 8 detects the exhaust gas temperature T ₂ flowing into the filter 3. Hereinafter, in order to distinguish the two types of exhaust temperatures, they are referred to as catalyst inlet exhaust temperature T ₁ and filter inlet exhaust temperature T ₂ , respectively.

[2. Control type]
The exhaust purification device 10 is provided with a regeneration control device 9 (reducing agent control means). The regeneration control device 9 is an electronic control device that controls the amount of unburned fuel injected from the first injector 4 and the second injector 5, and is provided as an LSI device in which a known microprocessor, ROM, RAM, and the like are integrated. Yes. Reproduction control apparatus 9, the oxygen was detected in the oxygen concentration sensor 6 concentration C, the catalyst inlet temperature sensor 7 and the catalyst inlet exhaust temperature T ₁ of which is detected by the filter inlet temperature sensor 8, another filter inlet exhaust gas temperature T _2, the engine The first injector 4 and the second injector 5 are controlled using the intake air mass flow rate M _air and the fuel mass flow rate M _fuel input from the ECU 15.

The intake air mass flow rate M _air is the mass flow rate of the intake air into the cylinder of the engine 12. The regeneration control device 9 uses the value of the intake air mass flow rate M _air as the exhaust flow rate flowing through the exhaust passage 11. The fuel mass flow rate M _fuel is the mass flow rate of the fuel injected in the cylinder of the engine 12. The regeneration control device 9 calculates the injection amount of unburned fuel from the first injector 4 and the second injector 5 by diverting the fuel amount injected into the cylinder by the in-cylinder injector 16.

The reproduction control device 9 performs the following three types of control.
[A] First purge control [B] Second purge control [C] Filter combustion control The first purge control is a purge control for releasing the nitrogen dioxide stored in the storage reduction catalyst 2. The start conditions for the first purge control are as follows.

[A-1] A predetermined cycle time T (for example, 20 [s]) has elapsed since the end of the previous first purge control. Further, the environmental conditions necessary for obtaining a predetermined purge efficiency in the first purge control are set. Listed below. It is assumed that the end condition of the first purge control is satisfied because all of the following environmental conditions are satisfied.

[A-2] The oxygen concentration C at the inlet of the storage reduction catalyst 2 is less than the first predetermined concentration C _T1. [A-3] A highly reactive hydrocarbon exists in the vicinity of the storage reduction catalyst 2 [A-4] ] The above conditions [A-2] and [A-3] continue for a predetermined duration X _T1 (for example, 1.0 [s]). The first predetermined concentration C _T1 here is the oxygen necessary for the reducing atmosphere described above. The concentration is the same as 1.0 [%]. It should be noted that the specific value of the first predetermined concentration C _T1 may be set to a different value depending on the characteristics of the storage reduction catalyst 2, the shape of the exhaust passage 11, and the like. In the first purge control, the atmospheric temperature of the storage reduction catalyst 2 is arbitrary.

  The second purge control is purge control that removes sulfur compounds adhering to the storage reduction catalyst 2. The start conditions for the second purge control are as follows.

[B-1] The travel distance has exceeded a predetermined distance (for example, 1000 [km]) after the end of the previous second purge control. Also, environmental conditions necessary for obtaining a predetermined purge efficiency in the second purge control are set. Listed below. It is assumed that the end condition of the second purge control is satisfied because all of the following environmental conditions are satisfied.

[B-2] The oxygen concentration C in the vicinity of the storage reduction catalyst 2 is less than the second predetermined concentration C _T2. [B-3] The ambient temperature of the storage reduction catalyst 2 is _{equal to} or higher than the first predetermined temperature T _T1. 4] The above conditions [B-2] and [B-3] continue for a predetermined duration X _T2 (for example, 120 [s]) The second predetermined concentration C _T2 here is, for example, 1.0 [%] Alternatively, it may be a value corresponding to the oxygen concentration in the exhaust gas after the premixed gas having an air-fuel ratio of 14.5 or less is burned by the engine 12. In addition, the first predetermined temperature T _T1 here may be, for example, 650 [° C.] which is a desorption temperature of the sulfur compound from the storage reduction catalyst 2. The second purge control does not require a highly active reducing agent.
The filter combustion control is control for burning the particulate matter collected by the filter 3.

[C-1] The travel distance has exceeded a second predetermined distance (for example, 500 [km]) after the end of the previous filter combustion control. Also, environmental conditions necessary for obtaining a predetermined combustion efficiency in the filter combustion control are as follows. Listed below. It is assumed that the end condition of the filter combustion control is satisfied because all of the following environmental conditions are satisfied.

[C-2] The filter 3 is in an oxidizing atmosphere [C-3] The exhaust gas temperature T ₂ flowing into the filter 3 is equal to or higher than the second predetermined temperature T _T2 [C-4] The above conditions [C-2] and [C-3] continues for a predetermined duration X _T3 (for example, 600 [s]) The second predetermined temperature T _T2 here is, for example, 550 [° C.] at which the combustion state of the particulate matter is good. It is possible. In the filter combustion control, the more oxygen related to the combustion of the particulate matter, the better.

  The contents of control performed by the exhaust gas purification apparatus 10 are classified as shown in Table 1 below. That is, the regeneration control of the exhaust purification device 10 is mainly divided into purge control and filter combustion control, and the purge control includes the first purge control and the second purge control. Here, the purge control start condition [A-1] or [B-1] is called a first regeneration start condition, and the filter combustion control start condition [C-1] is also called a second regeneration start condition. Also, the first purge control start condition [A-1] is referred to as a first purge start condition, and the second purge control start condition [B-1] is referred to as a second purge start condition.

  The first purge control, the second purge control, and the filter combustion control are not performed simultaneously with other controls, and priority is set for each control. The priority order in the exhaust purification apparatus 10 is the order of the second purge control, the filter combustion control, and the first purge control in order from the highest priority.

[3. Configuration of control device]
As a software configuration for performing each control described above, the regeneration control device 9 includes a determination unit 9a, a supply amount calculation unit 9b, and a reducing agent control unit 9c. Each software shown here is recorded in a memory or a storage device (not shown), and implements the functions described below by being read by the CPU as needed.

The determination unit 9a determines a start condition and an end condition of each control described above, and includes a purge control determination unit 21 and a filter combustion control determination unit 24 corresponding to each control described above. Further, the purge control determination unit 21 includes a first purge control determination unit 22 and a second purge control determination unit 23.
The first purge control determination unit 22 determines a start condition and an end condition of the first purge control, and determines the above-described conditions [A-1] to [A-4]. The second purge control determination unit 23 determines a start condition and an end condition of the second purge control, and determines the above-described conditions [B-1] to [B-4]. Further, the filter combustion control determination unit 24 determines a start condition and an end condition of the filter combustion control, and determines the above-described conditions [C-1] to [C-4]. The determination result of each condition is transmitted to the supply amount calculation unit 9b and the reducing agent control unit 9c.

[3-1. Supply amount calculation unit]
The supply amount calculation unit 9b calculates the supply amount (injection amount) of unburned fuel injected from the first injector 4 and the second injector 5 in each control described above. For example, the supply amount calculation unit 9b individually calculates an unburned fuel supply amount in the purge control and an unburned fuel supply amount in the filter combustion control. In the first purge control and the second purge control, the unburned fuel supply amount (injection amount) is individually calculated as part of each purge control according to the oxygen concentration upstream of the storage reduction catalyst 2.

[A. Calculation during first purge control]
The supply amount calculation unit 9b calculates the supply amount M _ex1 from the first injector 4 using the following expression 1 when the condition [A-1] is satisfied. In Formula 1, M _air is an intake air mass flow rate [g / s], and M _fuel is a fuel mass flow rate [g / s].

Equation 1 subtracts the amount of fuel actually injected into the cylinder by the in-cylinder injector 16 from the amount of fuel required to make the air-fuel ratio stoichiometric (the air-fuel ratio is 14.5, where the coal oil ratio of light oil is 1.8). Value. In other words, in order to make the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 1 stoichiometric in addition to the amount of fuel injected into the cylinder of the engine 12 in the combustion cycle at the time of calculation of the supply amount M _ex1 , the first injector 4 This is an equation that gives an added value of the amount of fuel to be injected.

Next, when the condition [A-2] is satisfied, the supply amount M _ex2 from the second injector 5 is calculated using the following Expression 2.

Equation 2 subtracts the amount of fuel actually injected into the cylinder by the in-cylinder injector 16 from the amount of fuel required to bring the air-fuel ratio to the target first purge air-fuel ratio, and then injects from the first injector 1 A value obtained by subtracting the amount of fuel used is given. In other words, in addition to the amount of fuel injected into the cylinder of the engine 12 and the amount of fuel injected from the first injector 1 in the combustion cycle when the supply amount M _ex2 is calculated, the exhaust gas flowing into the storage reduction catalyst 2 This is an equation for giving an added value of the amount of fuel to be injected from the second injector in order to set the air / fuel ratio of the fuel to the target first purge air / fuel ratio.

  Note that the target first purge air-fuel ratio here is an air-fuel ratio suitable for desorbing nitrogen dioxide from the storage reduction catalyst 2, and may be a preset fixed value, or any method may be used. It is good also as a fluctuation value computed in this way. In this embodiment, the target first purge air-fuel ratio is set as a value [(target first purge air-fuel ratio) <14.5] that is even smaller than the stoichiometric value (14.5) described in Equation 1.

The supply amount calculation unit 9b stops the calculation of the supply amounts M _ex1 and M _ex2 when all the conditions [A-2] to [A-4] are satisfied.
[B. Calculation during second purge control]
The supply amount calculation unit 9b calculates the supply amount M _ex3 from the first injector 4 using the following expression 3 when the condition [B-1] is satisfied.

Equation 3 gives a value obtained by subtracting the amount of fuel actually injected into the cylinder by the in-cylinder injector 16 from the amount of fuel necessary to make the air-fuel ratio the target second purge air-fuel ratio. In other words, in addition to the amount of fuel injected into the cylinder of the engine 12 in the combustion cycle when calculating the supply amount M _ex2 , the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 1 is set to the target second purge air-fuel ratio. This is an expression that gives an added value of the amount of fuel to be injected from the first injector 4.

  Note that the target second purge air-fuel ratio here is an air-fuel ratio suitable for desorbing sulfur compounds from the storage reduction catalyst 2, and may be a fixed value set in advance, or any method may be used. It is good also as a fluctuation value computed in this way. Here, the target second purge air-fuel ratio is set to a fixed value set in a range of less than 14.0 (so-called over-rich air-fuel ratio richer than stoichiometry).

In addition, the supply amount calculation unit 9b determines that the second condition is satisfied when both the conditions [B-2] and [B-3] are satisfied and there is a concern that the fuel sticks to the injection port of the second injector 5. The supply amount M _ex4 from the injector 5 is calculated. The supply amount M _ex4 is a _{very small} amount that does not affect the air-fuel ratio and exhaust temperature of the exhaust gas flowing into the storage reduction catalyst 2, and is preferably the minimum amount that can be injected by the second injector 5. That is, the supply amount _Mex4 calculated here is a fuel amount intended only to prevent the fuel from sticking in the vicinity of the injection port of the second injector 5, and does not contribute to exhaust purification. Note that conditions for determining the state where fuel sticking is a concern will be described later.

On the other hand, when the condition [B-2] is satisfied and the condition [B-3] is not satisfied, the supply amount M _ex5 from the second injector 5 for increasing the exhaust temperature in the vicinity of the storage reduction catalyst 2 is set. Calculate. The specific calculation method of the supply amount M _ex5 is arbitrary. For example, the exhaust temperature T ₁ (or the deviation between the exhaust temperature T ₁ and the first predetermined temperature T _T1 ) detected by the catalyst inlet temperature sensor 7 and The supply amount M _ex5 may be calculated based on the intake air mass flow rate M _air corresponding to the exhaust flow rate.

The supply amount calculation unit 9b stops the calculation of the supply amounts M _{ex3 to} M _ex5 when all the conditions [B-2] to [B-4] are satisfied.

[C. Calculation during filter combustion control]
The supply amount calculation unit 9b calculates the supply amount M _ex6 from the second injector 5 when the condition [C-1] is satisfied. The supply amount M _ex6 is a fuel amount necessary for setting the exhaust temperature T ₂ flowing into the filter 3 to be _{equal to} or higher than the second predetermined temperature T _T2 , that is, required for _{satisfying the} condition [C-3]. . Specific computation method of the supply amount M _ex6 is arbitrary, for example, (deviation or the exhaust gas temperature _T2 and the second predetermined temperature T _T2) filter inlet temperature sensor 8 is detected by the exhaust temperature T ₂ and an exhaust The supply amount M _ex6 may be calculated based on the intake air mass flow rate M _air corresponding to the flow rate.

The supply amount calculation unit 9b stops the calculation of the supply amount M _ex6 when all of the conditions [C-2] to [C-4] are satisfied.

[3-2. Reducing agent control unit]
The reducing agent control unit 9c is configured so that the unburned fuel of the supply amount calculated by the supply amount calculation unit 9b is injected from the first injector 4 and the second injector 5 according to the determination result of the determination unit 9a. The injectors 4 and 5 are individually controlled. That is, the reducing agent control unit 9c performs fuel injection in the exhaust passage 11 in a manner different between the purge control and the filter combustion control. Also, the amount of unburned fuel supplied is different between the first purge control and the second purge control.

[A. Control during first purge control]
When the condition [A-1] is satisfied, the reducing agent control unit 9c is configured so that unburned fuel of the supply amount M _ex1 calculated by the supply amount calculation unit 9b is injected into the exhaust gas from the first injector 4. One injector 4 is controlled. The fuel injection from the first injector 4 is continued until the first purge control is completed.

Further, when the condition [A-2] is satisfied, the second injector 5 is controlled so that unburned fuel of the supply amount M _ex2 calculated by the supply amount calculation unit 9b is injected into the exhaust gas from the second injector 5. To do. As a result, unburned fuel is supplied immediately upstream of the storage reduction catalyst 2, and the condition [A-3] is satisfied. Fuel injection from the second injector 5 is continued until the first purge control is completed, as in the case of the first injector 4. Moreover, the reducing agent control part 9c complete | finishes control of the 1st injector 4 and the 2nd injector 5, if all the conditions [A-2]-[A-4] are satisfied.

Thus, focusing on the fuel injection amounts from the first injector 4 and the second injector 5, the first purge control includes a control state in which unburned fuel is supplied only to the oxidation catalyst 1, the oxidation catalyst 1 and the occlusion. A control state in which unburned fuel is supplied to both of the reduction catalysts 2 is provided.
That is, when the oxygen concentration C according to the above condition [A-2] is less than the first predetermined concentration C _T1 , the reducing agent control means 9c injects the unburned fuel of the supply amount M _ex1 from the first injector 4. And the supply of unburned fuel from the second injector 5 is suspended. On the other hand, when the oxygen concentration C is equal to or higher than the first predetermined concentration C _T1 , the reducing agent control means 9 c injects the unburned fuel with the supply amount M _ex1 from the first injector 4 and the supply amount from the second injector 5. _Mex2 unburned fuel is injected.

Therefore, when the oxygen concentration C is equal to or higher than the first predetermined concentration C _T1 , unburned fuel is preferentially supplied to the oxidation catalyst 1 over the storage reduction catalyst 2.

[B. Control during second purge control]
When the condition [B-1] is satisfied, the reducing agent control unit 9c is configured so that unburned fuel of the supply amount M _ex3 calculated by the supply amount calculation unit 9b is injected into the exhaust gas from the first injector 4. One injector 4 is controlled. The fuel injection from the first injector 4 is continued until the second purge control is completed.

Further, when the condition [B-2] is satisfied, one of the following three types of control is performed. (A) Subsequently, control for injecting fuel only from the first injector 4 (b) No. (C) Control in which fuel injection for preventing sticking is performed by the second injector 5 in addition to fuel injection by one injector (c) Control in which fuel injection for temperature increase is performed by the second injector 5 in addition to fuel injection by the first injector In (b), the unburned fuel with the supply amount M _ex4 is injected from the second injector 5, and the unburned fuel with the supply amount M _ex5 is injected from the second injector 5 in (c) above. is there. The above (c) is performed when the condition [B-3] is not satisfied. The above (b) is carried out only when the condition [B-3] is satisfied and there is a concern that fuel sticks to the injection port of the second injector 5.

  Specific conditions for determining whether or not fuel sticking is a concern include, for example, measuring the accumulated time k during which the second purge control is performed, and the shape of the tip sack portion of the second injector 5, It is conceivable to determine whether or not the fixing durability time K set according to the material or the like has elapsed. In this case, when the cumulative time k ≧ the sticking durability time K, it is determined that the fuel sticking is a concern. The above (a) is a control when the above (b) and (c) are not performed, the condition [B-3] is satisfied, and the fuel is fixed to the injection port of the second injector 5. Implemented when there is no concern.

Moreover, the reducing agent control part 9c will complete | finish control of the 1st injector 4 and the 2nd injector 5, if all the conditions [B-2]-[B-4] are satisfied.
If attention is paid to the fuel injection amounts from the first injector 4 and the second injector 5 in this way, unburned fuel is supplied only to the oxidation catalyst 1 in the second purge control, and the storage reduction catalyst 2 is basically in the state. Unburned fuel supply is suspended. That is, fuel injection from the second injector 5 is performed under the second purge control only when the condition [B-3] is not satisfied or when there is a risk of fuel sticking to the second injector 5.

  Here, “suspending the supply of unburned fuel” refers to stopping the supply of unburned fuel from the second injector 5 (that is, fuel injection from the second injector 5) unless other conditions are satisfied. Means 0).

[C. Control during filter combustion control]
When the condition [C-1] is satisfied, the reducing agent control unit 9c is configured so that unburned fuel of the supply amount _Mex6 calculated by the supply amount calculation unit 9b is injected into the exhaust gas from the second injector 5. The two injectors 5 are controlled. At this time, the first injector 4 is held in a stopped state (the fuel injection amount from the first injector 4 is 0), and the supply of unburned fuel to the oxidation catalyst 1 is suspended. The fuel injection from the second injector 5 is continued until the filter combustion control ends. That is, the reducing agent control unit 9c ends the control of the second injector 5 when all the conditions [C-2] to [C-4] are satisfied.

  Table 2 below summarizes the relationship between the control condition determined by the determination unit 9a of the exhaust emission control device 10 and the injector to be controlled.

[4. flowchart]
2 to 5 are flowcharts for explaining an example of control in the exhaust purification device 10. The flow in FIG. 2 is a main flow for selecting any one of three types of control, and the flows in FIGS. 3 to 5 are subflows subordinate to the flow in FIG.

[4-1. Main flow]
In step A10 in the main flow of FIG. 2, the second purge control determination unit 23 determines whether or not the second purge control start condition [B-1] is satisfied. If the condition [B-1] is satisfied, the process proceeds to the second purge control flow of FIG. On the other hand, if the condition [B-1] is not satisfied, the process proceeds to Step A20.

In step A20, the filter combustion control determination unit 24 determines whether or not the filter combustion control start condition [C-1] is satisfied. Here, when the condition [C-1] is satisfied, the flow proceeds to the filter combustion flow of FIG. If the condition [C-1] is not satisfied, the process proceeds to step A30.
In step A30, the first purge control determination unit 22 determines whether or not the first purge control start condition [A-1] is satisfied. If the condition [A-1] is satisfied, the process proceeds to the first purge control flow of FIG. On the other hand, when the condition [A-1] is not satisfied, the process proceeds to step A10 again, and this flow is repeated at a predetermined cycle.

  As described above, any one of the three types of control in the exhaust control device 10 is selectively performed. For example, even if the conditions [A-1], [B-1], and [C-1] are satisfied at the same time depending on the running state of the vehicle, the second purge control is performed first, and then the filter combustion control is performed. Finally, the first purge control is performed.

[4-2. First purge control flow]
In step B1 in the first purge control flow of FIG. 3, the intake air mass flow rate M _air and the fuel mass flow rate M _fuel calculated by the engine ECU 15 are input to the supply amount calculation unit 9b of the regeneration control device 9. In the subsequent step B2, the supply amount M _{ex1 of} unburned fuel from the first injector 4 is calculated according to Equation 1. In the subsequent step B3, the first injector 4 is controlled by the reducing agent controller 9c, and the unburned fuel of the supply amount M _ex1 is injected upstream of the oxidation catalyst 1.

Here, the oxidation reaction of the unburned fuel in the oxidation catalyst 1 consumes oxygen contained in the exhaust gas and raises the exhaust temperature. In the subsequent step B4, the oxygen concentration C at the inlet of the storage reduction catalyst 2 immediately downstream of the oxidation catalyst 1 is detected by the oxygen concentration sensor 6 and input to the first purge control determination unit 22 of the regeneration control device 9. .
In Step B5, the first purge control determination unit 22 determines the condition [A-2]. Here, the process proceeds oxygen concentration C is to step B1 again when it is first predetermined concentration C _T1 or higher, if it is less than the first predetermined concentration C _T1 proceeds to step B6. That is, until the oxygen concentration C at the inlet of the storage reduction catalyst 2 becomes less than the first predetermined concentration C _T1, unburned fuel is supplied only from the first injector 4 and oxygen consumption in the oxidation catalyst 1 is continued. .

When the condition [A-2] is satisfied and the process proceeds to step B6, the supply amount calculation unit 9b calculates the supply amount M _{ex2 of} unburned fuel from the second injector 5 according to Equation 2. Then, in the subsequent step B7, the second injector 5 is controlled by the reducing agent control unit 9c, and the unburned fuel of the supply amount M _ex2 is injected to the upstream side of the storage reduction catalyst 2.
At this time, there is almost no oxygen in the vicinity of the occlusion reduction catalyst 2 (less than the first predetermined concentration C _T1 ), and unburned containing highly reactive hydrocarbons supplied from the second injector 5. Since the fuel is in an abundant state, nitrogen dioxide stored in the storage reduction catalyst 2 is easily desorbed, and the reduction action of nitrogen dioxide is promoted.

In subsequent step B8, the first purge control determination unit 22 determines whether or not a condition [A-4] which is one of the conditions for ending the first purge control is satisfied. Note that the condition [A-2] is satisfied in Step B5, and the condition [A-3] can be regarded as being satisfied in Step B7.
If the condition [A-4] is satisfied, the process proceeds to step B9, and the first purge control is finished. That is, the supply of unburned fuel from the first injector 4 and the second injector 5 by the reducing agent control unit 9c is stopped, and the control returns to the main flow. On the other hand, if the condition [A-4] is not satisfied, the process proceeds to step B1, and this subflow is repeated.

The approximate total duration of the first purge control is a predetermined duration X _T1 (for example, 1.0 [s]) defined in the condition [A-4], and the repeated cycle in which the first purge control is performed is A predetermined cycle time T (for example, 20 [s]) defined by the condition [A-1] is obtained.

[4-3. Second purge control flow]
In step C1 in the second purge control flow of FIG. 4, the intake air mass flow rate M _air and the fuel mass flow rate M _fuel calculated by the engine ECU 15 are input to the supply amount calculation unit 9b of the regeneration control device 9. In the subsequent step C2, the unburned fuel supply amount M _ex3 from the first injector 4 is calculated according to Equation 3. Then, in the subsequent step C3, the first injector 4 is controlled by the reducing agent control unit 9c, and the unburned fuel of the supply amount M _ex3 is injected upstream of the oxidation catalyst 1.

Here, similarly to the case where the first purge control is performed, the unburned fuel is oxidized by the oxidation catalyst 1, and the exhaust temperature rises. In the subsequent step C4, the oxygen concentration C at the inlet of the storage reduction catalyst 2, which is immediately downstream of the oxidation catalyst 1, is detected by the oxygen concentration sensor 6 and input to the second purge control determination unit 23 of the regeneration control device 9. .
In Step C5, the second purge control determination unit 23 determines the condition [B-2]. Here, the process proceeds oxygen concentration C is to step C1 again if it is the second predetermined concentration C _T2 above, if it is less than the second predetermined concentration C _T2 proceeds to step C6. In other words, the inlet of the oxygen concentration C of storage-reduction catalyst 2 Until less than the second predetermined concentration C _T2 is unburned fuel supplied from only the first injectors 4, it is continued oxygen consumption in the oxidation catalyst 1 .

If the condition [B-2] proceeds satisfied to step C6, the exhaust temperatures T ₁ flowing into the storage-reduction catalyst 2 is detected by the catalyst inlet temperature sensor 7. In step C7, based on the exhaust temperatures T ₁ detected in the previous step, the condition [B-3] it is determined in the second purge control determination unit 23. Here, if the exhaust temperature T ₁ is equal to or higher than the first predetermined temperature T _T1 , the process proceeds to Step C8. On the other hand, when the exhaust temperature T ₁ is _lower than the first predetermined temperature T _T1 , the process proceeds to Step C21 for increasing the exhaust temperature.

In order to increase the exhaust temperature T ₁ of the repetition of the control of step C1 to C5, usually never exhaust temperatures T ₁ less than the first predetermined temperature T _T1 in step C7. Step C21 subsequent steps, which corresponds to the control of the (c), a control flow which is provided as a fail-safe when for some reason the exhaust temperatures T ₁ has not sufficiently increased.

First, in step C21, the supply amount _Mex5 of the fuel from the second injector 5 is calculated in the supply amount calculation unit 9b. Here, for example, the supply amount M _ex5 is calculated based on the deviation between the exhaust temperature T ₁ and the first predetermined temperature T _T1 and the intake air mass flow rate M _air . In the subsequent step C22, the second injector 5 is controlled by the reducing agent control unit 9c, and the unburned fuel of the supply amount M _ex5 is injected upstream of the storage reduction catalyst 2. Further, in the subsequent step C23, the control of the first injector 4 by the reducing agent control unit 9c is continued, and the unburned fuel of the supply amount M _ex3 is injected upstream of the oxidation catalyst 1. Thereafter, the flow proceeds to step C7 again, proceeds when the exhaust temperatures T ₁ becomes equal to or higher than the first predetermined temperature T _T1 to Step C8 later.

  In step C8, the second purge control determination unit 23 determines whether or not there is a concern about fuel sticking to the injection port of the second injector 5. For example, when the accumulated time k of the second purge control is equal to or longer than the sticking durability time K of the second injector 5, the process proceeds to Step C10 because fuel sticking is a concern. On the other hand, if the accumulated time k is less than the sticking durability time K, it is determined that there is no concern about fuel sticking, and the process proceeds to step C9.

In step C9, the fuel injection from the second injector 5 is suspended by the reducing agent controller 9c, and then the process proceeds to step C11. On the other hand, in step C10, the reducing agent control unit 9c injects fuel of the supply amount M _ex4 from the second injector 5 and proceeds to step C11.
In the subsequent step C11, the supply amount M _ex3 of fuel is injected from the first injector 4. The supply amount M _ex3 injected here may be the value calculated in the above steps C1 to C3, or the intake air mass flow rate M _air and the fuel mass flow rate M _fuel input from the engine ECU 15 are used, and the step C11 is performed. You may calculate it again in. The control in steps C9 and C11 corresponds to the control (a) described above. The control in steps C10 and C11 corresponds to the control in (b) above. As a result, the injection port of the second injector 5 is not left in a state where it is exposed to high-temperature exhaust gas having a temperature _{equal to} or higher than the first predetermined temperature T _T1 , and fuel sticking is prevented.

In addition, even when any of the controls (a) and (b) is performed, there is almost no oxygen in the vicinity of the storage reduction catalyst 2 (less than the second predetermined concentration C _T2 ). In addition, since the exhaust temperature T flowing into the storage reduction catalyst 2 is in a state _{equal to} or higher than the first predetermined temperature T _T1 , the sulfur compound adhering to the storage reduction catalyst 2 is easily detached, and the reduction action of the sulfur compound is promoted. Is done.
In the subsequent step C12, the second purge control determination unit 23 starts counting the duration related to the condition [B-4] which is one of the end conditions of the second purge control. If counting of the duration of the second purge control has already been started, step C12 is skipped and only counting is continued. In the subsequent step C13, it is determined whether or not the duration time of the second purge control is _{equal to} or longer than a predetermined duration time _XT2 . The condition [B-2] is satisfied at step C5, and the condition [B-3] can be regarded as being satisfied at step C7.

If the condition [B-4] is satisfied, the process proceeds to step C14, and the second purge control is finished. That is, the supply of unburned fuel from the first injector 4 and the second injector 5 by the reducing agent control unit 9c is stopped, and the control returns to the main flow. On the other hand, if the condition [B-4] is not satisfied, the process proceeds to step C8, and the second purge control is continued.
The approximate total duration of the second purge control is defined by the time required for the exhaust temperature T ₁ flowing into the storage reduction catalyst 2 to be equal to or higher than the first predetermined temperature T _T1 and the condition [B-4]. This is a time obtained by adding a predetermined duration X _T2 (for example, 120 [s]). The second purge control is periodically performed every time the vehicle travels a predetermined distance (for example, 1000 [km]) defined in the condition [B-1].

[4-4. Filter combustion control flow]
In step D1 in the filter combustion control flow of FIG. 5, the exhaust gas temperature T ₂ detected by the filter inlet temperature sensor 8 and the intake air mass flow rate M _air calculated by the engine ECU 15 are used as the supply amount calculation unit 9b of the regeneration control device 9. Is input. In the subsequent step D2, the unburned fuel supply amount M _ex6 from the second injector 5 is calculated. In the subsequent step D3, the second injector 5 is controlled by the reduction calculation control unit 9c, and the unburned fuel of the supply amount M _ex6 is injected upstream of the storage reduction catalyst 2.

As a result, the exhaust gas temperature T ₂ flowing into the filter 3 increases. Further, since unburned fuel is supplied from the second injector 5 disposed closer to the filter 3 than the first injector 4, the exhaust gas flowing into the filter 3 quickly becomes an oxidizing atmosphere.
On the other hand, in the subsequent step D4, the fuel injection from the first injector 4 is suspended by the reduction control unit 9c. That is, unburned fuel is not supplied to the oxidation catalyst 1.

In step D5, on the basis of the exhaust temperature T ₂ detected in step D1, the condition [C-3] it is determined in the filter combustion control determination unit 24. Here, if the exhaust temperature T ₂ is equal to or higher than the second predetermined temperature T _T2 , the process proceeds to Step D6. On the other hand, the exhaust temperature T ₂ within is less than the second predetermined temperature T _T2 returns to step D1 to further raise the exhaust gas temperature T _2, the fuel injection from the second injector 5 is repeated.

In step D6, the filter combustion control determination unit 24 starts counting the duration related to the condition [C-4], which is one of the end conditions of the filter combustion control. If counting of the duration of filter combustion control has already been started, step D6 is skipped and only counting is continued. In the subsequent step D7, it is determined whether or not the duration of the filter combustion control is _{equal to} or longer than a predetermined duration _XT3 . The condition [C-2] is satisfied at step D3, and the condition [C-3] can be regarded as being satisfied at step D5.

Here, when the condition [C-4] is satisfied, the process proceeds to step D8, and the filter combustion control ends. That is, the supply of unburned fuel from the second injector 5 is stopped, and the control returns to the main flow. On the other hand, when the condition [C-4] is not satisfied, the routine proceeds to step D1, and the filter combustion control is continued.
The approximate total duration of the filter combustion control is the time required for the exhaust gas temperature T ₂ flowing into the filter 3 to be equal to or higher than the second predetermined temperature T _T2 and the predetermined duration defined in the condition [C-4]. This is a time obtained by adding the time X _T3 (for example, 600 [s]). The filter combustion control is repeatedly performed every time the vehicle travels a predetermined distance (for example, 500 [km]) defined in the condition [C-1].

[5. Action, effect]
[5-1. During first purge control]
The control action of the exhaust emission control device 10 during vehicle travel will be described.
As shown in FIG. 6A, until the time t ₁ , none of the start conditions of the first purge control, the second purge control, and the filter combustion control is satisfied, and the condition [A-1] is satisfied at the time t _1. It is assumed that the first purge control start condition is satisfied. The reproduction control unit 9, until the time t ₁ the main flow is performed as shown in FIG. 2, the time t ₁ after the first purge control flow shown in FIG. 3 is performed.

First, immediately after time t ₁ , the oxygen concentration C at the inlet of the storage reduction catalyst 2 is not sufficiently lowered and is still higher than the first predetermined concentration C _T1 . That is, since the condition [A-2] is not satisfied, the supply amount calculation unit 9b calculates the supply amount _Mex1 of the first injector 4, and the reducing agent control unit 9c _does not set the upstream side of the oxidation catalyst 1. _Fuel is injected at a supply rate M _ex1 . At this time, as shown in FIGS. 6B and 6D, unburned fuel is supplied into the exhaust gas only from the first injector 4, and the second injector 5 is stopped.

The unburned fuel injected from the first injector 4 consumes oxygen on the oxidation catalyst 1 to be oxidized and raises the exhaust temperature. As shown in FIG. 6C, the oxygen concentration C at the inlet of the storage reduction catalyst 2 gradually decreases. Further, as shown in FIG. 6 (e), the air-fuel ratio on the outlet side of the storage reduction catalyst 2 also decreases and gradually approaches the stoichiometric value (for example, 14.5).
When the oxygen concentration C decreases to less than the first predetermined concentration C _{T1 at} time t ₂ , the condition [A-2] is satisfied, and the supply amount calculation unit 9b calculates the supply amount M _ex2 of the second injector 5, The reducing agent control unit 9c also injects unburned fuel at the supply amount M _ex2 upstream of the storage reduction catalyst 2. That is, as shown in FIGS. 6B and 6D, unburned fuel is injected from both the first injector 4 and the second injector 5.

Here, by injection of unburned fuel from the second injector 5, highly reactive hydrocarbons are supplied in the vicinity of the storage reduction catalyst 2, and the condition [A-3] is satisfied. Further, the oxygen concentration C becomes a predetermined value lower than the first predetermined concentration _CT1 (a minute predetermined value that is almost 0%), and the condition [A-3] is maintained. As shown in FIG. 6E, the air-fuel ratio on the outlet side of the storage reduction catalyst 2 further decreases slightly later than time t ₂ and gradually approaches the target first purge air-fuel ratio. The area of a region S1 in FIG. 6 (e) corresponds to the supply amount M _ex1 of fuel injected from the first injector 4, the area of the region S2 in the supply amount M _ex2 of fuel injected from the second injector 5 Correspond.

When the time t ₂ predefined duration from X _T1 is the time t ₃ when passed, satisfied conditions [A-4], the first purge control is completed. Thereby, as shown in FIG.6 (c), the oxygen concentration C increases gradually. Further, as shown in FIG. 6 (e), the air-fuel ratio on the outlet side of the storage reduction catalyst 2 also increases and gradually approaches the combustion air-fuel ratio.
As described above, according to the disclosed exhaust purification device 10, by supplying unburned fuel only to the upstream side of the oxidation catalyst 1 at the start of the first purge control, oxygen in the exhaust flowing into the storage reduction catalyst 2 is reduced. It can be greatly reduced and can provide an advantageous environment for the reduction of nitrogen dioxide.

  In addition, the hydrocarbons contained in the exhaust gas that has passed through the oxidation catalyst 1 are mostly lower hydrocarbons (hydrocarbons with low reactivity), and there are cases where the reducing ability of nitrogen dioxide is poor. On the other hand, in the disclosed exhaust purification device 10, after reducing the oxygen concentration C, unburned fuel is supplied to the upstream side of the storage reduction catalyst 2, whereby highly reactive hydrocarbons are brought into the vicinity of the storage reduction catalyst 2. It is possible to improve the reducibility of nitrogen dioxide.

In addition, in a state where the oxygen concentration C is not sufficiently lowered, the unburned fuel is not supplied to the upstream side of the storage reduction catalyst 2, so that the fuel consumption can be improved.
Further, since the supply amount M _ex1 from the first injector 4 is set to an amount that makes the air-fuel ratio stoichiometric, the oxygen concentration on the upstream side of the storage reduction catalyst 2 can be rapidly reduced, and nitrogen dioxide The reproduction efficiency can be further improved.

[5-2. During second purge control]
Further, in the disclosed exhaust purification device 10, unburned fuel is supplied only to the upstream side of the oxidation catalyst 1 even during the second purge control. Thereby, the reducing atmosphere in the vicinity of the occlusion reduction catalyst 2 can be reliably formed, and an environment advantageous for the reduction of the sulfur compound can be provided. At this time, since the supply amount M _ex3 from the first injector 4 is set to an amount that makes the air-fuel ratio _overrich (target second purge air-fuel ratio), the reduction reaction of the sulfur compound can be promoted, The regeneration efficiency of the storage reduction catalyst 2 can be improved.

Further, until the exhaust gas temperature T ₁ flowing into the storage reduction catalyst 2 becomes equal to or higher than the first predetermined temperature T _T1 , the exhaust temperature raising operation is repeated without starting the counting of the duration of the second purge control. The atmospheric temperature of the catalyst 2 can be reliably raised to a temperature at which the sulfur compound can be efficiently reduced, and the reducibility of the sulfur compound can be improved.
Further, when there is a concern about fuel sticking, since the minimum amount of unburned fuel is injected from the second injector 5, the performance of the second injector 5 hardly affects the air-fuel ratio and fuel consumption of the exhaust gas. Can be secured.

Further, even if the exhaust gas temperature T ₁ has not risen to the first predetermined temperature T _T1 or more when the oxygen concentration C becomes less than the second predetermined concentration C _T2 , the fuel injection is controlled to be in the hold state. By additionally injecting the fuel of the supply amount M _ex5 from the second injector 5, the exhaust temperature T ₁ can be reliably set to the first predetermined temperature T _T1 or more.
Further, in the second purge control, the state in which the atmospheric temperature of the storage reduction catalyst 2 is _{equal to} or higher than the first predetermined temperature T _T1 is maintained for a predetermined duration X _T2, so that the sulfur compound is reliably removed from the surface of the storage reduction catalyst 2. Can be removed.

[5-3. During filter combustion control]
Further, according to the disclosed exhaust purification device 10, fuel injection from the first injector 4 is suspended and fuel is supplied only from the second injector 5 during filter combustion control. As a result, the amount of heat generated in the vicinity of the filter 3 (ie, the amount of heat generated by the storage reduction catalyst 2) can be increased, and heat loss to the filter 3 can be reduced to improve fuel efficiency. In addition, unburned fuel is not supplied to the oxidation catalyst 1, that is, it is not necessary to expect the temperature increase in the oxidation catalyst 1 in consideration of heat loss on the exhaust pipe, thereby suppressing thermal deterioration of the oxidation catalyst 1. As a result, the cost of the catalyst noble metal can be reduced.

In the filter combustion control, the state where the atmospheric temperature of the filter 3 is _{equal to} or higher than the second predetermined temperature T _T2 is maintained for a predetermined duration X _T3, so that the particulate matter collected by the filter 3 is reliably burned. Can be removed.

[5-4. Synergy, synergy]
Furthermore, according to the disclosed exhaust emission control device 10, the supply amounts M _ex1 , M _ex2 , M _ex3 , M of unburned fuel injected from the first injector 4 and the second injector 5 based on the oxygen concentration C in the exhaust gas. _By controlling _ex4 respectively, the reduction field can be controlled freely as shown in FIGS. _6C and _6E , and the reduction reactivity and regeneration efficiency in the vicinity of the occlusion reduction catalyst 2 are improved. Can do.

In particular, paying attention to the first purge control and the second purge control, unburned fuel depends on the type of purge (that is, whether the purge target from the storage reduction catalyst 2 is nitrogen dioxide or sulfur compound). Therefore, the exhaust temperature T ₁ upstream of the storage reduction catalyst 2 can be set to a temperature suitable for each control, and the regeneration efficiency in each control can be increased.

  If attention is paid to purge control and filter combustion control, the supply mode and supply amount of unburned fuel are changed according to the regeneration target (that is, whether it is the storage reduction catalyst 2 or the filter 3). In addition, while ensuring the regeneration efficiency of the filter 3, it is possible to suppress thermal deterioration of the oxidation catalyst 1 and the occlusion reduction catalyst 2 disposed on the upstream side, and it is possible to realize an optimum state for each control. .

  Further, since both the first injector 4 and the second injector 5 inject the unburned fuel as a reducing agent, the exhaust purification device 10 has a simple configuration. For example, the same fuel pipe material is connected to each injector. Cost can be reduced.

[6. Modified example]
FIG. 7 illustrates an exhaust purification device 30 as a modification of the above-described embodiment. This exhaust purification device 30 differs from the above-described exhaust purification device 10 in the arrangement positions of the respective components interposed on the exhaust passage 11. In addition, about the same structure, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  On the exhaust passage 11, a turbocharger 13, an oxidation catalyst 1, a filter 3, and an occlusion reduction catalyst 2 are interposed in order from the upstream side of the exhaust flow. That is, the arrangement positions of the storage reduction catalyst 2 and the filter 3 in the exhaust purification device 10 are exchanged. The second injector 5, the oxygen concentration sensor 6, and the catalyst inlet temperature sensor 7 are disposed on the downstream side of the oxidation catalyst 1 that is immediately upstream of the storage reduction catalyst 2, and the filter inlet temperature sensor 8 is immediately upstream of the filter 3. It is arranged downstream of the oxidation catalyst 1.

  The first injector 4 has a function of supplying unburned fuel to the oxidation catalyst 1, and the second injector 5 has a function of supplying unburned fuel to the storage reduction catalyst 2. Therefore, the first purge control and the second purge control in the exhaust purification device 30 are performed in the same manner as the first purge control and the second purge control in the exhaust purification device 10 described above. On the other hand, as shown in FIG. 7, the closest injector disposed upstream of the filter 3 is not the second injector 5 but the first injector 4. Therefore, in the filter combustion control, unburned fuel is discharged from the first injector 4. Supplied.

[6-1. Configuration of Modification]
For example, the supply amount calculation unit 9d calculates the supply amount M _ex7 from the first injector 4 when the condition [C-1] is satisfied. The supply amount M _ex7 is a fuel amount necessary for setting the exhaust temperature T ₂ flowing into the filter 3 to be _equal to or higher than the second predetermined temperature T _T2 , similarly to the above-described supply amount M _ex6 , that is, the condition [C-3 ] Is required to establish Specific computation method of feed amount M _ex7 is optional, the filter inlet temperature sensor 8 is detected by the exhaust temperature T ₂ (deviation or the exhaust gas temperature _T2 and the second predetermined temperature T _T2) and corresponding to the exhaust flow rate It is conceivable to calculate based on the intake air mass flow rate M _air to be performed.

In this case, when the conditions [C-2] and [C-3] are satisfied and the fuel injection sticking of the second injector 5 is concerned, the supply amount calculation unit 9d A supply amount M _ex8 from the injector 5 is calculated. Similarly to the supply amount M _ex4 , the supply amount M _ex8 is a _{very small} amount that does not affect the air-fuel ratio and exhaust temperature of the exhaust gas flowing into the storage reduction catalyst 2, and preferably the second injector 5 can inject. Minimum amount.

On the other hand, when the condition [C-1] is satisfied, the reducing agent control unit 9e causes the unburned fuel of the supply amount M _ex7 calculated by the supply amount calculation unit 9d to be injected into the exhaust gas from the first injector 4. The first injector 4 is controlled. At this time, the second injector 5 is held in a stopped state (the fuel injection amount from the second injector 5 is 0), and the supply of unburned fuel to the storage reduction catalyst 2 is suspended.

In addition, the reducing agent control unit 9e determines that the second injector is in a state where the conditions [C-2] and [C-3] are satisfied and there is a concern about fuel sticking to the injection port of the second injector 5. Release the 5 stop state. That is, the second injector 5 is controlled so that unburned fuel of the supply amount M _ex8 is injected into the exhaust gas from the second injector 5 while continuing the control of the first injector 4.

[6-2. Action and effect of modification]
As an example of control in the exhaust purification device 30, a flow of filter combustion control is shown in FIG.
In step E1, the exhaust gas temperature T ₂ detected by the filter inlet temperature sensor 8 and the intake air mass flow rate M _air calculated by the engine ECU 15 are input to the supply amount calculation unit 9d of the regeneration control device 9. In the subsequent step E2, the unburned fuel supply amount M _ex7 from the first injector 4 is calculated. In the subsequent step E3, the first injector 4 is controlled by the reduction control unit 9e, and the unburned fuel of the supply amount M _ex7 is injected upstream of the oxidation catalyst 1.

As a result, the exhaust gas temperature T ₂ flowing into the filter 3 rises, and the exhaust gas flowing into the filter 3 quickly becomes an oxidizing atmosphere. On the other hand, in the subsequent step E4, the fuel injection from the second injector 5 is suspended by the reduction calculation control unit 9e.
In step E5, based on the exhaust temperature T ₂ detected in step E1, the condition [C-3] is determined in the filter combustion control determination unit 24. Here, if the exhaust temperature T ₂ is equal to or higher than the second predetermined temperature T _T2 , the process proceeds to Step E6. On the other hand, when the exhaust temperature T ₂ is _lower than the second predetermined temperature T _T2 , the process returns to step E1 to further increase the exhaust temperature T ₂ and the fuel injection from the second injector 5 is repeated.

In step E6, it is determined in the reducing agent control unit 9e whether or not fuel sticking to the injection port of the second injector 5 is a concern. If it is determined that fuel sticking is concerned, the process proceeds to step E7. If not, step E7 is skipped and the process proceeds to step E9.
In step E7, the reducing agent control unit 9e injects fuel of the supply amount M _ex8 from the second injector 5. As a result, the second injector 5 is not left in a state where it is exposed to high-temperature exhaust gas that is equal to or higher than the second predetermined temperature T _{T2, and} fuel sticking is prevented.

In subsequent step E8, the filter combustion control determination unit 24 starts counting the duration related to the condition [C-4], which is one of the end conditions of the filter combustion control. If counting of the duration of filter combustion control has already been started, step E8 is skipped. In subsequent step E9, it is determined whether or not the duration of the filter combustion control is _{equal to} or longer than a predetermined duration _XT3 . The condition [C-2] is satisfied at step E3, and the condition [C-3] can be regarded as being satisfied at step E5.

  Here, when the condition [C-4] is satisfied, the process proceeds to step E10, and the filter combustion control ends. That is, the supply of unburned fuel from the first injector 4 is stopped, and the control returns to the main flow. If unburned fuel for preventing sticking is also supplied from the second injector 5, this is also stopped. On the other hand, if the condition [C-4] is not satisfied, the process proceeds to step E1, and the filter combustion control is continued.

The approximate total duration of the filter combustion control is the time required for the exhaust gas temperature T ₂ flowing into the filter 3 to be equal to or higher than the second predetermined temperature T _T2 and the predetermined duration defined in the condition [C-4]. This is a time obtained by adding the time X _T3 (for example, 600 [s]). The filter combustion control is repeatedly performed every time the vehicle travels a predetermined distance (for example, 500 [km]) defined in the condition [C-1].

Thus, the exhaust emission control device 30 shown in FIG. 7 has the same effects as those of the above-described embodiment.
Furthermore, the disclosed exhaust purification device 30 can prevent the fuel sticking of the downstream second injector 5 that can be caused by operating only the upstream first injector 4 during filter combustion control, and can reduce the air-fuel ratio of the exhaust. In addition, the performance of the second injector 5 can be ensured without substantially affecting the fuel consumption.

[6-3. Others]
In the above-described embodiment and modification, the example in which unburned fuel is used as the reducing agent for the catalytic reaction in the oxidation catalyst 1 and the storage reduction catalyst 2 is illustrated, but the type of the reducing agent is not limited thereto. For example, instead of unburned fuel, a reducing agent solution obtained by extracting only highly reactive unsaturated hydrocarbons (olefins) may be used, or a solution containing various olefinic hydrocarbons (alkenes) or alkanes. May be used. Or it is possible to use the reducing agent of the component according to the kind of the oxidation catalyst 1 and the occlusion reduction catalyst 2.

It is also possible to use arithmetic expressions other than those exemplified in the above embodiment. For example, in the above equation 1, the intake air mass flow rate M _air and the fuel mass flow rate M _fuel are used in calculating the supply amount M _ex1 supplied from the first injector 4 during the first purge control. It is also conceivable to calculate the supply amount M _ex1 using parameters. Further, a means for calculating or detecting the exhaust flow rate may be provided on the exhaust passage 11, and this may be substituted for the intake air mass flow rate M _air .

  Further, the start conditions and end conditions of the first purge control, the second purge control, and the filter combustion control described in the above-described embodiment are not limited to this. For example, as the starting condition for the first purge control, the amount of nitrogen dioxide stored in the storage reduction catalyst 2 or the cumulative value of the exhaust flow rate flowing through the exhaust passage 11 may be considered. In addition, as a starting condition for the second purge control, it is conceivable to consider the exhaust gas flow rate and the total amount of fuel components that have passed through the storage reduction catalyst 2. Further, as a start condition of the filter combustion control, it can be considered that the upstream side and downstream side differential pressure and the flow path resistance value of the filter 3 are taken into consideration. Various conditions can be similarly set for the end conditions of each control.

As a specific example of the oxygen concentration sensor 6, an oxygen gas sensor or a laser analysis sensor that directly detects the oxygen concentration may be used, or the oxygen oxide concentration sensor 6 or ammonia sensor may be used to detect oxygen concentration from the detection result. The concentration may be estimated.
Further, in the above-described embodiment and modification, the first injector 4 provided in the exhaust passage upstream of the oxidation catalyst 1 is exemplified as the first supply means. It is not limited to. For example, an in-cylinder injector 16 may be used instead of the first injector 4 provided in the exhaust passage, and additional fuel injection (so-called late post injection) or the like may be performed in the exhaust stroke after the main combustion.

  Moreover, although what applied this invention to the exhaust system of the diesel engine 12 is illustrated in the above-mentioned embodiment, the application to the vehicle provided with the gasoline engine is also possible.

DESCRIPTION OF SYMBOLS 1 Oxidation catalyst 2 Occlusion reduction catalyst 3 Filter 4 1st injector (1st supply means)
5 Second injector (second supply means)
6 Oxygen concentration sensor (oxygen concentration detection means)
7 Catalyst inlet temperature sensor (catalyst inlet exhaust temperature detection means)
8 Filter inlet temperature sensor (filter inlet temperature detection means)
9 Regeneration control device (reducing agent control means)
9a Determination unit 9b, 9d Supply amount calculation unit 9c, 9e Reductant control unit 10 Exhaust purification device 11 Exhaust passage 12 Engine (internal combustion engine)
13 Turbocharger 14 Air intake passage 15 Engine ECU
16 In-cylinder injector 21 Purge control determination unit 22 First purge control determination unit 23 Second purge control determination unit 24 Filter combustion control determination unit C Oxygen concentration T ₁ Catalyst inlet exhaust temperature T ₂ Filter inlet exhaust temperature

Claims (7)

An oxidation catalyst provided in the exhaust passage of the internal combustion engine and having an oxidizing ability for components in the exhaust;
An occlusion reduction catalyst that is provided in the exhaust passage downstream of the oxidation catalyst and occludes nitrogen oxides in the exhaust gas under an oxidizing atmosphere and reduces the nitrogen oxides under a reducing atmosphere;
First supply means for supplying, to the exhaust gas flowing into the oxidation catalyst, a first reducing agent that is oxidized by the oxidation catalyst;
It provided the exhaust passage between the oxidizing catalyst and the absorbent storage reduction catalyst, a second supply means for supplying a second reducing agent for reducing nitrogen oxides in absorbent storage reduction catalyst during the exhaust,
The first purge control is performed to release the nitrogen oxide stored in the storage reduction catalyst when the predetermined first purge start condition is satisfied, and when the first purge start condition is not satisfied and the predetermined second purge is performed. A reducing agent control means for performing a second purge control for removing a sulfur compound that is one of the components adhering to the storage reduction catalyst when a start condition is satisfied,
The reducing agent control means comprises:
Respective supply amounts of the first reducing agent supplied from the first supply unit and the second reducing agent supplied from the second supply unit are set as the first purge control and the second purge control, respectively. Individually controlled by
When the first purge control is performed, the first reducing agent is injected from the first supply unit and the second reducing agent is also injected from the second supply unit,
When the second purge control is performed, the first reducing agent is injected from the first supply unit, and the injection of the second reducing agent from the second supply unit is suspended. Exhaust gas purification device. Each of the first supply means and said second supply means, characterized by injecting the unburned fuel as said first reducing agent and said second reducing agent, the exhaust gas purification apparatus according to claim 1. The reducing agent control means, when performing the first purge control, injects an amount of the unburned fuel from the first supply means so that the exhaust air-fuel ratio in the oxidation catalyst is stoichiometric. 2. An exhaust emission control device according to 2 . The reducing agent control means injects, from the first supply means, an amount of the unburned fuel that makes the exhaust air / fuel ratio in the oxidation catalyst richer than stoichiometric when the second purge control is performed. The exhaust emission control device according to claim 2 or 3 . A catalyst inlet exhaust temperature detecting means for detecting a catalyst inlet exhaust temperature at the inlet of the storage reduction catalyst;
When the reducing agent control means performs the second purge control, and when a predetermined time has elapsed since the catalyst inlet exhaust temperature detected by the catalyst inlet exhaust temperature detection means exceeds a predetermined temperature, The exhaust emission control device according to claim 4 , wherein the second purge control is terminated. When the reducing agent control means performs the second purge control and the catalyst inlet exhaust temperature detected by the catalyst inlet exhaust temperature detection means is less than the predetermined temperature, the first supply means Injecting the first reducing agent and also injecting the second reducing agent from the second supply means;
6. The exhaust emission control device according to claim 5 , wherein the supply amount of the second reducing agent is an amount required to raise the exhaust gas temperature at the catalyst inlet to the predetermined temperature. When the reducing agent control means performs the second purge control and when the catalyst inlet exhaust temperature detected by the catalyst inlet exhaust temperature detection means is equal to or higher than the predetermined temperature, the first supply means Injecting the first reducing agent and also injecting the second reducing agent from the second supply means;
The exhaust gas purification apparatus according to claim 5 or 6 , wherein the supply amount of the second reducing agent is an amount required to maintain the catalyst inlet exhaust temperature at the predetermined temperature.

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