JP2018178774A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of highly accurately estimating poisoning amount of substances poisoning an NOx catalyst.SOLUTION: An exhaust emission control system 1 for purifying exhaust gas from an engine 10 includes an NOx catalyst 21, a hydrocarbon supply section 31 and a poisoning amount estimation section 41. The NOx catalyst 21 is provided in an exhaust passage 12 of the engine 10. The hydrocarbon supply section 31 supplies hydrocarbon to the NOx catalyst 21. Based on a temperature and flow rate of exhaust gas flowing into the NOx catalyst 21 and concentrations of two types of poisoning substances included in the exhaust gas out of poisoning substances that are substances causing poisoning through adsorption to the NOx catalyst 21, the poisoning amount estimation section 41 estimates poisoning amount that is the amount of poisoning substances poisoning the NOx catalyst 21.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification system.

  2. Description of the Related Art An exhaust gas purification system is known which estimates a poisoning amount, which is the amount of poisoned substance poisoned to the NOx catalyst, based on the amount of hydrocarbons flowing into the NOx catalyst. For example, in the exhaust gas purification system of Patent Document 1, the higher the exhaust gas temperature, the higher the poisoning ratio of poisoned hydrocarbons contained in the exhaust gas flowing into the NOx catalyst, and The quantity is estimated.

Patent No. 3712314

  By the way, the exhaust flowing into the NOx catalyst contains various poisoning substances such as nitrogen oxides and sulfur oxides in addition to hydrocarbons. In the exhaust gas purification system of Patent Document 1, the poisoning amount is estimated independently of other poisoning substances based on the amount of only hydrocarbons flowing into the NOx catalyst. Therefore, in the exhaust gas purification system of Patent Document 1, it is difficult to accurately estimate the amounts of various poisoning substances which are actually poisoned to the NOx catalyst. As a result, the fuel efficiency may be deteriorated due to the excessive regeneration control for reducing the poisoning amount of the NOx catalyst, or the performance of the NOx catalyst may be deteriorated due to the insufficient regeneration.

  An object of the present invention is to provide an exhaust gas purification system capable of accurately estimating the poisoning amount of the poisoning substance to the NOx catalyst.

The present invention is an exhaust gas purification system (1) for purifying exhaust gas from an internal combustion engine (10), comprising a NOx catalyst (21), a hydrocarbon supply unit (31), and a poisoning amount estimation unit (41) ing.
The NOx catalyst is provided in the exhaust passage (12) of the internal combustion engine.
The hydrocarbon supply unit supplies hydrocarbons to the NOx catalyst.
The poisoning amount estimating unit includes two or more types of poisoning substances contained in the exhaust gas among the poisoning substances that are poisoning substances that cause poisoning by adsorbing to the NOx catalyst. Based on the concentration of the substance, the poisoning amount which is the amount of poisoning substance poisoned to the NOx catalyst is estimated. Therefore, the poisoning amount estimating unit can estimate the poisoning amount of the poisoning substance to the NOx catalyst with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows the exhaust gas purification system by 1st Embodiment. (A) shows the initial state of the NOx catalyst, (B) shows the poisoned state of the NOx catalyst, (C) shows the poisoned catalyst of the NOx catalyst estimated according to the comparative example FIG. (A) is a figure which shows the occupancy rate of the site by the poisoning substance in the initial state of the catalyst of NOx catalyst and the state after poisoning, (B) is the initial state of catalyst of NOx catalyst and to be covered estimated by a comparative example. The figure which shows the occupancy rate of the site by the poisoning substance in the state after poisoning. (A) is a diagram showing the occupancy of the site by the poisoning substance in the initial state of the catalyst of the NOx catalyst at low temperature and the state after poisoning; (B) is the NOx catalyst at low temperature estimated by the comparative example The figure which shows the occupancy rate of the site by the poisoning substance in the initial state of a catalyst, and the state after poisoning. FIG. 7 is a flow chart showing processing concerning estimation of the poisoning amount of the poisoning substance to the NOx catalyst and the like by the exhaust gas purification system of the first embodiment. The map which shows the adsorption coefficient used when the exhaust gas purification system of 1st Embodiment estimates poisoning amount. The map which shows the desorption coefficient used when the exhaust gas purification system of 1st Embodiment estimates the amount of poisonings. FIG. 7 is a flow chart showing processing concerning regeneration control by the exhaust gas purification system of the first embodiment. The schematic diagram which shows the exhaust gas purification system by 2nd Embodiment. FIG. 7 is a flow chart showing processing concerning estimation of the poisoning amount of a poisoning substance to the NOx catalyst, etc. by the exhaust gas purification system of the second embodiment. The map which shows the adsorption coefficient used when the exhaust gas purification system of 2nd Embodiment estimates poisoning amount. The map which shows the desorption coefficient used when the exhaust gas purification system of a 2nd embodiment estimates the amount of poisoning. FIG. 7 is a flow chart showing processing concerning regeneration control by the exhaust gas purification system of the second embodiment. The flowchart which shows the process regarding the target temperature setting by the exhaust gas purification system of 2nd Embodiment. The map which shows the poisoning substance list which is used when the exhaust gas purification system of a 2nd embodiment sets up target temperature. The schematic diagram which shows the exhaust gas purification system by 3rd Embodiment. The schematic diagram which shows the exhaust gas purification system by 4th Embodiment. The map which shows the adsorption coefficient used when the exhaust gas purification system of 5th Embodiment estimates poisoning amount. The map which shows the adsorption coefficient used when the exhaust gas purification system of 5th Embodiment estimates poisoning amount.

Hereinafter, exhaust purification systems according to a plurality of embodiments of the present invention will be described based on the drawings. In addition, the same code | symbol is attached | subjected to a substantially the same structure site | part in several embodiment, and description is abbreviate | omitted. In addition, substantially the same components in the plurality of embodiments exhibit the same or similar effects.
First Embodiment
An exhaust gas purification system according to a first embodiment is shown in FIG.
The exhaust gas purification system 1 is provided in a vehicle (not shown) and is used to purify the exhaust gas discharged from an internal combustion engine (hereinafter referred to as "engine") 10 of the vehicle.

The vehicle includes an engine 10, a fuel tank 2, an intake passage 11, an exhaust passage 12, a fuel injection valve 30, an electronic control unit (hereinafter referred to as "ECU") 40, and the like.
In the fuel tank 2, light oil as fuel is stored. The fuel injection valve 30 is provided in the engine 10. The fuel injection valve 30 injects and supplies light oil stored in the fuel tank 2 to the combustion chamber of the engine 10. That is, in the present embodiment, the engine 10 is a diesel engine.

  The intake passage 11 is provided such that one end is open to the atmosphere and the other end is connected to the engine 10. The intake passage 11 guides intake air to the engine 10. One end of the exhaust passage 12 is connected to the engine 10, and the other end is open to the atmosphere. The exhaust passage 12 guides the exhaust generated by the combustion of fuel in the combustion chamber of the engine 10 from the engine 10 to the atmosphere side.

  The intake passage 11 is provided with a throttle valve (not shown). The throttle valve opens and closes the intake passage 11, and can control the amount of intake flowing through the intake passage 11, that is, the amount of intake.

  The ECU 40 is a small computer having a CPU as an operation means, a ROM as a storage means, a RAM, an EEPROM, an I / O as an input / output means, and the like. The ECU 40 executes an operation according to a program stored in the ROM or the like based on information such as signals from various sensors provided in each part of the vehicle, and controls the operation of various devices and devices of the vehicle. Thus, the ECU 40 executes the program stored in the non-transitional tangible storage medium. By executing this program, a method corresponding to the program is executed.

The ECU 40 can control the operation of the throttle valve, the fuel injection valve 30, and the like based on information such as signals from various sensors.
The ECU 40 can control the amount of intake air supplied to the engine 10 by controlling the operation of the throttle valve. Further, the ECU 40 can control the amount of fuel injected and supplied to the combustion chamber of the engine 10 by controlling the operation of the fuel injection valve 30.

The exhaust purification system 1 includes an NOx catalyst 21, a hydrocarbon supply unit 31, a poisoning amount estimation unit 41, a regeneration control unit 42, an NOx concentration acquisition unit 43, a temperature sensor 51, a flow sensor 52, a concentration sensor 53, and the like. .
The NOx catalyst 21 is provided in the exhaust passage 12. The NOx catalyst 21 has a carrier made of alumina, for example, and a metal catalyst carried on the carrier. For example, the metal catalyst includes Ag ₂ O (silver oxide). The metal catalyst is provided on the surface of the carrier in the form of fine powder. The NOx catalyst 21 can reduce and purify NOx (nitrogen oxide) contained in the exhaust gas flowing through the exhaust passage 12.

  The hydrocarbon supply unit 31 is provided between the engine 10 and the NOx catalyst 21 in the exhaust passage 12, that is, on the upstream side of the exhaust flow with respect to the NOx catalyst 21. The hydrocarbon supply unit 31 can inject fuel, ie, hydrocarbon (HC) stored in the fuel tank 2 into the exhaust passage 12 and supply it to the NOx catalyst 21.

  The hydrocarbon supplied from the hydrocarbon supply unit 31 to the NOx catalyst 21 acts as a reducing agent, and promotes the NOx purification action of the NOx catalyst 21. The ECU 40 can control the amount of hydrocarbons supplied to the NOx catalyst 21 by controlling the operation of the hydrocarbon supply unit 31.

  As shown in FIG. 2A, in the initial state of the NOx catalyst 21, no substance is adsorbed on the site of the catalyst (Cat.) And the catalyst is empty. Purification of the exhaust by the NOx catalyst 21 is started, and after a predetermined period, poisoning of the catalyst site is achieved by adsorbing hydrocarbon (HC), nitrogen oxide (NOx), sulfur (S), etc. to the catalyst. It will be in the state which the poisoning substance which is a substance made to produce adsorb | suck (refer FIG. 2 (B)). As shown in FIG. 3A, after the NOx catalyst 21 is poisoned, the performance of the NOx catalyst 21 is greatly reduced by filling the sites of the catalyst with hydrocarbons and other substances.

Further, as shown in FIG. 4A, at the low temperature where there is no catalytic activity, nitrogen oxide (NOx) is adsorbed (occluded) on the site of the catalyst. Therefore, even if the catalyst is in the initial state, a certain amount of nitrogen oxides may be adsorbed on the catalyst site. Thereafter, when the temperature of the NOx catalyst 21 shifts from a low temperature state without catalytic activity to a high temperature state which is a reduction region, nitrogen oxides and hydrocarbons (HC) are adsorbed at the sites of the catalyst. If the catalyst site is filled with hydrocarbons or nitrogen oxides after the NOx catalyst 21 is poisoned, the performance of the NOx catalyst 21 is greatly reduced.
In addition, the NOx catalyst 21 may be thermally deteriorated by being placed in a high temperature environment for a long time. The performance of the NOx catalyst 21 is also degraded by thermal degradation.

  As shown in FIG. 1, the poisoning amount estimation unit 41, the regeneration control unit 42, and the NOx concentration acquisition unit 43 are provided in the ECU 40 as a functional unit. Here, part or all (functional parts) of the functions executed by the ECU 40 may be configured as hardware by one or a plurality of ICs or the like. That is, the functions provided by the ECU 40 can be provided by software stored in a substantial memory device and a computer that executes the software, only software, only hardware, or a combination thereof.

The temperature sensor 51 is provided to the NOx catalyst 21. The temperature sensor 51 can detect the temperature of the exhaust flowing into the NOx catalyst 21. The temperature sensor 51 transmits a signal corresponding to the detected temperature to the ECU 40.
The flow rate sensor 52 is provided in the intake passage 11. The flow rate sensor 52 can detect the flow rate of intake air taken into the engine 10. The flow rate sensor 52 transmits a signal corresponding to the detected flow rate to the ECU 40. The flow rate of intake air taken into the engine 10 and the flow rate of exhaust gas flowing into the NOx catalyst 21 are substantially the same.

  The concentration sensor 53 is provided on the exhaust passage 12 on the opposite side of the NOx catalyst 21 to the engine 10, that is, on the downstream side of the exhaust gas flow to the NOx catalyst 21. The concentration sensor 53 can detect the concentration of nitrogen oxides (NOx) in the exhaust gas flowing out of the NOx catalyst 21. The concentration sensor 53 transmits a signal corresponding to the detected concentration of nitrogen oxide to the ECU 40.

The poisoning amount estimating unit 41 can estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 based on the signals transmitted from the temperature sensor 51 and the flow rate sensor 52. The process of the poisoning amount estimating unit 41 will be described in detail later.
The regeneration control unit 42 reduces the poisoning amount of the NOx catalyst 21 based on the poisoning amount estimated by the poisoning amount estimating unit 41 and performs regeneration control capable of regenerating the NOx catalyst 21.
The NOx concentration acquisition unit 43 acquires the concentration of nitrogen oxide on the downstream side of the exhaust gas flow with respect to the NOx catalyst 21 based on the signal transmitted from the concentration sensor 53.

Next, processing relating to the estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 by the ECU 40 will be described based on FIG.
For example, when the ignition key of the vehicle is turned on and the ECU 40 is activated and the concentration of nitrogen oxides on the downstream side of the NOx catalyst 21 acquired by the NOx concentration acquisition unit 43 becomes equal to or higher than a predetermined concentration, a series of processes S100 shown in FIG. , Is executed. The process S100 estimates the poisoning amount of the poisoning substance to the NOx catalyst 21, and reduces the poisoning amount of the NOx catalyst 21 to restore the performance of the NOx catalyst 21, that is, the poisoning regeneration that regenerates the NOx catalyst 21. It is a process related to control.

  In S101, the ECU 40 acquires the state of the NOx catalyst 21. Specifically, the ECU 40 obtains the temperature (T) and the space velocity (SV) of the exhaust flowing into the NOx catalyst 21 based on the signals transmitted from the temperature sensor 51 and the flow rate sensor 52. The space velocity (SV: Space Velocity) is a value calculated from the flow rate (Q1). After S101, the process proceeds to S102.

  In S102, the ECU 40 acquires the previous value of the poisoned state of the NOx catalyst 21. Specifically, the ECU 40 acquires the adsorption amount (ΣNOx) of nitrogen oxides to the NOx catalyst 21 calculated in the previous processing S100 and the adsorption amount (ΣHC) of hydrocarbons. The previous value of the poisoning state of the NOx catalyst 21 is stored in, for example, the RAM or the EEPROM of the ECU 40. After S102, the process proceeds to S103.

  In S103, the ECU 40 acquires the gas concentration in the exhaust flowing into the NOx catalyst 21. Specifically, the ECU 40 controls the concentration of nitrogen oxides in the exhaust flowing into the NOx catalyst 21 (NOx) based on control information of the engine 10, that is, a map for each operating condition of the engine 10, a theoretical formula, a model, etc. Calculate and obtain the concentration of hydrocarbons (HC). After S103, the process proceeds to S104.

  In S104, the ECU 40 calculates the amount of change in the amount of adsorption of hydrocarbons and nitrogen oxides on the NOx catalyst 21. Specifically, the ECU 40 calculates the amount of change (ΔHC, ΔNOx) of the adsorption amount of hydrocarbon and nitrogen oxide on the NOx catalyst 21 based on the adsorption coefficients α1 and α2, the desorption coefficients β1 and β2, and the like. Here, the adsorption coefficient α1 is a coefficient that correlates with the ease of adsorption of hydrocarbons on the NOx catalyst 21. The adsorption coefficient α2 is a coefficient that correlates with the ease of adsorption of nitrogen oxides on the NOx catalyst 21. The adsorption coefficients α1 and α2 are space velocities (flow rates) of exhaust flowing into the NOx catalyst 21 and map values stored for each gas composition, and the values from 0 to 1 decrease as the temperature increases. (See FIG. 6). The desorption coefficient β1 is a coefficient correlating to the ease of desorption of hydrocarbons from the NOx catalyst 21. The desorption coefficient β2 is a coefficient that correlates with the ease of nitrogen oxide desorption from the NOx catalyst 21. The desorption coefficients β1 and β2 are space velocities (flow rates) of exhaust flowing into the NOx catalyst 21 and map values stored for each gas composition, and become larger values as the temperature is higher, from 0 to 1. It is a value (see FIG. 7). The ECU 40 sets the adsorption coefficients α1 and α2 and the desorption coefficients β1 and β2 based on the above map and the temperature (T) and space velocity (SV) or flow rate (Q1) acquired in S101.

The ECU 40 calculates the amount of change (ΔHC, ΔNOx) of the amount of adsorption of hydrocarbons and nitrogen oxides on the NOx catalyst 21 according to the following formulas 1 and 2.
ΔHC = α1 * HC−β1 * ΣHC formula 1
ΔNOx = α2 * NOx-β2 * ΣNOx Formula 2
Note that ΔHC and ΔNOx can take negative values depending on the balance of the adsorption of the substance to the NOx catalyst 21 and the desorption of the substance from the NOx catalyst 21. After S104, the process proceeds to S105.

At S105, the ECU 40 calculates the present amount of adsorption of hydrocarbon and nitrogen oxide on the NOx catalyst 21. Specifically, the ECU 40 calculates the present amounts of adsorption of hydrocarbons and nitrogen oxides to the NOx catalyst 21 (ΣHC, NOxNOx) according to the following formulas 3 and 4.
HCHC = ΣHC + ΔHC formula 3
NOxNOx = ΣNOx + ΔNOx Equation 4
Here, ΣHC on the right side of Formula 3 is the previous value of the amount of adsorption (ΣHC) of hydrocarbons to the NOx catalyst 21 acquired in S102. Further, ΔHC on the right side of Formula 3 is a change amount (ΔHC) of the amount of adsorption of hydrocarbons to the NOx catalyst 21 calculated in S104. Further, ΣNOx on the right side of Formula 4 is the previous value of the adsorption amount (ΣNOx) of the nitrogen oxide to the NOx catalyst 21 acquired in S102. Further, ΔNOx on the right side of the equation 4 is the change amount (ΔNOx) of the adsorption amount of nitrogen oxide to the NOx catalyst 21 calculated in S104.
The present amounts of adsorption of hydrocarbons and nitrogen oxides to the NOx catalyst 21 calculated in S105 (ΣHC, NOxNOx) are stored in the RAM, EEPROM or the like of the ECU 40 and used in S102 in the next processing S100. After S105, the process proceeds to S106.

In S106, the ECU 40 determines whether the NOx catalyst 21 has been poisoned by a predetermined amount or more. Specifically, the ECU 40 first functions as the poisoning amount estimating unit 41, and estimates the poisoning amount of the poisoning substance (hydrocarbon, nitrogen oxide) to the NOx catalyst 21 according to the following equation 5.
HCHC + γ * ΣNOx Equation 5
Here, HCHC and ΣNOx in the equation 5 are the present adsorption amounts of hydrocarbon and nitrogen oxide on the NOx catalyst 21 calculated in S105. Further, γ in Equation 5 is an arbitrary constant larger than 0, for example. Since the influence of the amount of adsorption of hydrocarbons and the amount of adsorption of nitrogen oxides on the purification of exhaust gas by the NOx catalyst 21 is not limited to 1: 1, poisoning of the NOx catalyst 21 is performed using γ as shown in equation 5. Estimate the quantity.

  Subsequently, the ECU 40 determines whether the estimated poisoning amount of the NOx catalyst 21 is equal to or greater than a predetermined poisoning threshold value Pt. If it is determined that the poisoning amount of the NOx catalyst 21 is the poisoning threshold Pt or more (S106: YES), the process proceeds to S120. On the other hand, when it is determined that the poisoning amount of the NOx catalyst 21 is smaller than the poisoning threshold value Pt (S106: NO), the ECU 40 ends the series of processing S100.

In S120, the ECU 40 functions as the regeneration control unit 42 and performs poisoned regeneration control. A series of processes S120 related to the poisoning regeneration control is shown in FIG.
In S121, the ECU 40 determines whether the temperature of the NOx catalyst 21 is currently being increased, that is, whether the temperature of the NOx catalyst 21 is being controlled. If it is determined that the temperature of the NOx catalyst 21 is rising (S121: YES), the process proceeds to S123. On the other hand, when it is determined that the temperature of the NOx catalyst 21 is not rising (S121: NO), the process proceeds to S122.

  In S122, the ECU 40 starts temperature increase control of the NOx catalyst 21. Specifically, the ECU 40 increases, for example, the amount of fuel supplied from the fuel injection valve 30 to the engine 10 as compared to that during normal operation, and increases the combustion heat in the engine 10. Thereby, the temperature of the exhaust gas discharged from the engine 10 rises. As a result, the temperature of the NOx catalyst 21 rises. After S122, the ECU 40 ends a series of processing S120.

  In S123, the ECU 40 acquires the present poisoning amount X of the NOx catalyst 21. Specifically, the poisoning amount (ΣHC + γ * ΣNOx) of the NOx catalyst 21 estimated in S106 is acquired as the poisoning amount X of the current NOx catalyst 21. After S123, the process proceeds to S124.

  In S124, the ECU 40 determines whether the present poisoning amount of the NOx catalyst 21 is equal to or greater than a predetermined regeneration threshold. Specifically, the ECU 40 determines whether the poisoning amount X acquired in S123 is equal to or greater than the regeneration threshold value X1. Here, the regeneration threshold value X1 is set to, for example, the maximum value that can be tolerated as the poisoning amount of the poisoning substance to the NOx catalyst 21. If it is determined that the poisoning amount X is equal to or greater than the regeneration threshold value X1, that is, the poisoning regeneration of the NOx catalyst 21 is not completed (S124: YES), the ECU 40 ends a series of processes S120. On the other hand, when it is determined that the poisoning amount X is smaller than the regeneration threshold value X1, that is, it is determined that the poisoning regeneration of the NOx catalyst 21 is completed (S124: NO), the process proceeds to S125.

  In S125, the ECU 40 stops the temperature increase control of the NOx catalyst 21. Specifically, the amount of fuel supplied from the fuel injection valve 30 to the engine 10 is returned to the amount at normal operation. As a result, the temperature rise of the NOx catalyst 21 is stopped. After S125, the ECU 40 ends the series of processing S120.

  The ECU 40 determines NO at S106, and after S122 determines YES at S124 after S122 or ends S125 of a series of processes after S125, and the downstream of the NOx catalyst 21 acquired by the NOx concentration acquisition unit 43. If the concentration of nitrogen oxides on the side is equal to or higher than the predetermined concentration, the process S100 is started again. Thus, the processes S100 and S120 are processes that are repeatedly executed when the concentration of nitrogen oxide on the downstream side of the NOx catalyst 21 is equal to or higher than a predetermined concentration.

  As described above, the ECU 40 functions as the poisoning amount estimating unit 41 in S106 and adsorbs the temperature (T) and the flow rate (Q1) of the exhaust flowing into the NOx catalyst 21 and the NOx catalyst 21 by adsorbing the poison. The amount of poisoned substances poisoned to the NOx catalyst 21 based on the concentrations (HC, NOx) of two kinds of poisoned substances (hydrocarbons and nitrogen oxides) contained in the exhaust among the poisoned substances which are substances to be produced The poisoning amount (ΣHC + γ * ΣNOx), which is

  Further, the ECU 40 functions as the regeneration control unit 42 in S120, and can regenerate the catalyst by reducing the poisoning amount of the NOx catalyst 21 based on the poisoning amount (ΣHC + γ * ΣNOx) estimated by the poisoning amount estimating unit 41. Control playback. In the regeneration control, when the temperature of the NOx catalyst 21 reaches a predetermined temperature or more, hydrocarbons and nitrogen oxides adsorbed to the NOx catalyst 21 are desorbed from the NOx catalyst 21. Thereby, the poisoning amount of the NOx catalyst 21 is reduced. The temperature required for nitrogen oxides to desorb from the catalyst is lower than the temperature required for hydrocarbons to desorb from the catalyst.

Next, the effect of the present embodiment will be clarified by explaining how to estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 according to the comparative example.
In the comparative example, as in the exhaust gas purification system of Patent Document 1 (Japanese Patent No. 3712314) described above, it is estimated that only the hydrocarbon is adsorbed to the catalyst of the NOx catalyst 21 (see FIG. 2C). The poisoning amount is estimated based on the amount of hydrocarbons flowing into 21 only. Therefore, originally, if the catalyst site is filled with hydrocarbons or other substances, the performance of the NOx catalyst 21 is greatly reduced (see FIG. 3A), and as shown in FIG. Since only the poisoning amount of hydrocarbon is estimated, it may take time to determine that the catalyst site has been filled up with a predetermined amount or more. Therefore, the poisoning regeneration control can not be performed at a necessary timing, and the performance of the NOx catalyst 21 may be degraded. On the other hand, in the present embodiment, as described above, the poisoning substance may be poisoned on the NOx catalyst 21 based on the concentrations (HC, NOx) of the two kinds of poisoning substances (hydrocarbons and nitrogen oxides) contained in the exhaust gas. Since the poisoning amount can be estimated, the poisoning amount can be estimated with high accuracy (see FIG. 3A), and it can be accurately determined that the catalyst site is filled with the poisoning substance by a predetermined amount or more. Therefore, in the present embodiment, the poisoning regeneration control can be performed at an appropriate timing as compared with the comparative example, and the deterioration of the performance of the NOx catalyst 21 can be suppressed.

  Also, originally, when the temperature of the NOx catalyst 21 shifts from a low temperature state where nitrogen oxides are adsorbed to a certain degree to a high temperature state which is a reduction region, nitrogen oxides and hydrocarbons are adsorbed at the sites of the catalyst, and the sites of the catalyst When the catalyst is filled with hydrocarbons or nitrogen oxides, the performance of the NOx catalyst 21 is greatly reduced (see FIG. 4A). As shown in FIG. 4B, the poisoning amount of hydrocarbons is shown in the comparative example. In order to judge only that the catalyst site is filled with only hydrocarbons, there is a possibility that the poisoning regeneration control may be performed more than necessary. If the poisoning regeneration control is performed more than necessary, fuel consumption may be deteriorated. On the other hand, in the present embodiment, as described above, the poisoning substance may be poisoned on the NOx catalyst 21 based on the concentrations (HC, NOx) of the two kinds of poisoning substances (hydrocarbons and nitrogen oxides) contained in the exhaust gas. Since the poisoning amount can be estimated, the poisoning amount can be estimated with high accuracy (see FIG. 4A), and it is possible to suppress performing the poisoning regeneration control more than necessary. Therefore, compared with the comparative example, the present embodiment can suppress the deterioration of the fuel efficiency caused by the poisoning regeneration control.

As described above, (1) the present embodiment is the exhaust gas purification system 1 for purifying the exhaust gas from the engine 10, including the NOx catalyst 21, the hydrocarbon supply unit 31, and the poisoning amount estimation unit 41. There is.
The NOx catalyst 21 is provided in the exhaust passage 12 of the engine 10.
The hydrocarbon supply unit 31 supplies hydrocarbons to the NOx catalyst 21.
The poisoning amount estimation unit 41 includes two types of temperature and flow rate of exhaust flowing into the NOx catalyst 21 and two types of exhaust gases contained in the exhaust that are poisoning substances that cause poisoning by adsorbing to the NOx catalyst 21. The poisoning amount which is the amount of the poisoning substance poisoned to the NOx catalyst 21 is estimated based on the concentration of the poisoning substance (hydrocarbon, nitrogen oxide). Therefore, the poisoning amount estimating unit 41 can estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 with high accuracy.

  (2) In the present embodiment, the poisoning amount estimation unit 41 estimates the poisoning amount based on the concentrations of hydrocarbons and nitrogen oxides among poisoning substances contained in the exhaust gas.

  (8) The present embodiment further includes a reproduction control unit 42. The regeneration control unit 42 performs regeneration control that can reduce the poisoning amount of the NOx catalyst 21 based on the poisoning amount estimated by the poisoning amount estimating unit 41. As described above, the poisoning amount estimating unit 41 can estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 with high accuracy. Therefore, the regeneration control unit 42 can perform regeneration control at an appropriate timing, and can suppress the deterioration of the performance of the NOx catalyst 21. In addition, it is possible to suppress that the regeneration control unit 42 performs regeneration control more than necessary, and it is possible to suppress the deterioration of the fuel efficiency caused by the regeneration control.

  (10) The present embodiment further includes the NOx concentration acquisition unit 43. The NOx concentration acquisition unit 43 acquires the concentration of nitrogen oxide on the downstream side of the exhaust gas flow with respect to the NOx catalyst 21. The regeneration control unit 42 controls the regeneration control (S106: YES) when the concentration acquired by the NOx concentration acquisition unit 43 is a predetermined concentration or more and the poisoning amount estimated by the poisoning amount estimation unit 41 is a predetermined amount or more (S106: YES). Perform S120). By the way, when the performance (exhaust gas purification rate) of the NOx catalyst 21 is reduced due to factors such as thermal deterioration and the like other than poisoning, the regeneration of the NOx catalyst 21 is difficult even if regeneration control is performed. In the present embodiment, when the performance (exhaust gas purification rate) of the NOx catalyst 21 decreases due to factors other than poisoning, such as thermal deterioration, the concentration of nitrogen oxides on the downstream side of the NOx catalyst 21 becomes equal to or higher than a predetermined concentration. Although S100 is executed, it is determined that the poisoning amount to the NOx catalyst 21 is smaller than the predetermined value in S106 (S106: NO), the poisoning regeneration control (S120) by the regeneration control unit 42 is not executed. As described above, in the present embodiment, it is determined whether the cause of the performance degradation of the NOx catalyst 21 is due to poisoning or other factors, and regeneration is performed only when the performance of the NOx catalyst 21 is degraded due to poisoning. Take control. Therefore, it is possible to suppress wasteful regeneration control, and to suppress deterioration in fuel consumption associated with the regeneration control.

Second Embodiment
An exhaust gas purification system according to a second embodiment is shown in FIG. The second embodiment differs from the first embodiment in the configuration and the like of the exhaust gas purification system 1.
In the second embodiment, the exhaust gas purification system 1 further includes a reformer 25, a heater 26, a concentration information acquisition unit 44, a temperature sensor 54, a concentration sensor 55, and the like.

  In the present embodiment, the vehicle further includes the reforming passage 13. One end of the reforming passage 13 is connected to the exhaust passage 12 and the other end is connected to the exhaust passage 12 on the downstream side of the one end. Here, the other end of the reforming passage 13 is located upstream of the NOx catalyst 21. Therefore, part of the exhaust flowing through the exhaust passage 12 flows again into the exhaust passage 12 via one end and the other end of the reforming passage 13 and flows into the NOx catalyst 21.

  The reformer 25 is provided in the reforming passage 13. The heater 26 is provided to the reformer 25. The heater 26 can heat the reformer 25. The ECU 40 can control the operation of the heater 26. The hydrocarbon supply unit 31 is provided on the upstream side of the exhaust flow with respect to the reformer 25 in the reforming passage 13. Therefore, the hydrocarbon (HC) injected from the hydrocarbon supply unit 31 flows into the reformer 25.

  When the hydrocarbon injected from the hydrocarbon supply unit 31 passes through the reformer 25 heated by the heater 26, the hydrocarbon as the reducing agent is reformed into a highly active reducing agent such as an aldehyde. By supplying the hydrocarbon reformed by the reformer 25 to the NOx catalyst 21, the performance of the NOx catalyst 21 can be improved. The ECU 40 can adjust the amount and type of reformed hydrocarbon supplied to the NOx catalyst 21 by controlling the operation of the hydrocarbon supply unit 31 and the heater 26.

  The concentration information acquisition unit 44 is provided in the ECU 40 as a functional unit. The concentration information acquisition unit 44 is based on control information of the hydrocarbon supply unit 31 and the heater 26 by the ECU 40, that is, information on the concentration of the main hydrocarbon species to be reformed by the reformer 25 based on the reformer control information. get.

  In the present embodiment, the flow rate sensor 52 is provided on the upstream side of the exhaust flow with respect to one end of the reforming passage 13 in the exhaust passage 12. The flow rate sensor 52 can detect the flow rate of the exhaust gas discharged from the engine 10. The flow rate sensor 52 transmits a signal corresponding to the detected flow rate to the ECU 40. The flow rate of the exhaust gas discharged from the engine 10 and the flow rate of the exhaust gas flowing into the NOx catalyst 21 are substantially the same.

  The temperature sensor 54 is provided on the upstream side of the exhaust flow with respect to one end of the reforming passage 13 in the exhaust passage 12 as in the case of the flow rate sensor 52. The temperature sensor 54 can detect the temperature of the exhaust gas discharged from the engine 10. The temperature sensor 54 transmits a signal corresponding to the detected temperature to the ECU 40.

  The concentration sensor 55 is provided on the upstream side of the exhaust flow with respect to one end of the reforming passage 13 in the exhaust passage 12, similarly to the flow rate sensor 52. The concentration sensor 55 can detect the oxygen concentration of the exhaust gas discharged from the engine 10. The concentration sensor 55 transmits a signal corresponding to the detected oxygen concentration to the ECU 40.

Next, processing relating to the estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 by the ECU 40 will be described based on FIG.
In the series of processes S200 shown in FIG. 10, for example, when the ignition key of the vehicle is turned on and the ECU 40 is activated, the concentration of nitrogen oxides downstream of the NOx catalyst 21 acquired by the NOx concentration acquisition unit 43 becomes a predetermined concentration or more , Is executed. The process S200 is a process related to the estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 and the poisoning regeneration control for regenerating the NOx catalyst 21.

  In S201, the ECU 40 acquires the state of the NOx catalyst 21. Specifically, the ECU 40 obtains the temperature (T) and the flow rate (Q1) of the exhaust flowing into the NOx catalyst 21 based on the signals transmitted from the temperature sensor 51 and the flow rate sensor 52. After S201, the process proceeds to S202.

  In S202, the ECU 40 acquires the previous value of the poisoned state of the NOx catalyst 21. Specifically, the ECU 40 acquires the adsorption amount (ΣPn) of each poisoning substance to the NOx catalyst 21 calculated in the previous processing S200. Here, each poisoning substance which acquires the adsorption amount is, for example, hydrocarbon (HC), nitrogen oxide (NOx), sulfur oxide (SOx). After S202, the process proceeds to S203.

  In S203, the ECU 40 acquires the concentration of each poisoning substance in the exhaust flowing into the NOx catalyst 21. Specifically, the ECU 40 controls the NOx catalyst based on control information of the engine 10, that is, a map for each operating condition of the engine 10, a theoretical formula, a model, signals from the flow sensor 52, the temperature sensor 54, the concentration sensor 55, etc. The concentration (Pn) of each poisoning substance in the exhaust flowing into 21 is calculated and acquired. After S203, the process proceeds to S204.

  In S204, the ECU 40 functions as the concentration information acquisition unit 44, and acquires information on the concentration of the main hydrocarbon species to be reformed by the reformer 25 based on the reformer control information. Specifically, the ECU 40 obtains the concentration (Pn, HCn) for each hydrocarbon type having the same carbon number and functional group, such as aldehyde. After S204, the process proceeds to S205.

  In S205, the ECU 40 calculates the amount of change in the amount of adsorption of each poisoning substance to the NOx catalyst 21. Specifically, the ECU 40 determines the adsorption coefficient α n (n = 1, 2, 3...) Correlating with the ease of adsorption of each poisoning substance to the NOx catalyst 21, and poisoning from the NOx catalyst 21. The amount of change (ΔPn) in the amount of adsorption of each poisoning substance to the NOx catalyst 21 is calculated based on the desorption coefficient βn (n = 1, 2, 3...) Which correlates to the ease of substance desorption. calculate. Here, the adsorption coefficient α n is a space velocity (flow rate) of exhaust flowing into the NOx catalyst 21 and a map value stored for each gas composition, and is a value from 0 to 1, which becomes smaller as the temperature is higher. (See FIG. 11). The desorption coefficient β n is a space value (flow rate) of the exhaust flowing into the NOx catalyst 21 and a map value stored for each gas composition, and is a value from 0 to 1 which becomes larger as the temperature is higher ( See Figure 12). The ECU 40 sets the adsorption coefficient α n and the desorption coefficient β n based on the map and the temperature (T) and flow rate (Q1) acquired in S201.

The ECU 40 calculates the change amount (ΔPn) of the adsorption amount of each poisoning substance to the NOx catalyst 21 by the following equation 6.
ΔPn = αn * Pn−βn * ΣPn equation 6
Note that ΔPn can take a negative value depending on the balance of the adsorption of the substance to the NOx catalyst 21 and the desorption of the substance from the NOx catalyst 21. After S205, the process proceeds to S206.

At S206, the ECU 40 calculates the present adsorption amount of each poisoning substance to the NOx catalyst 21. Specifically, the ECU 40 calculates the present adsorption amount (ΣPn) of each poisoning substance on the NOx catalyst 21 by the following equation 7.
Σ P n = P P n + Δ P n Expression 7
Here, ΣPn on the right side of Formula 7 is the previous value of the amount of adsorption (PPn) of each poisoning substance to the NOx catalyst 21 acquired in S202. Further, ΔPn on the right side of Formula 7 is a change amount (ΔPn) of the adsorption amount of each poisoning substance to the NOx catalyst 21 calculated in S205.
The present adsorption amount (量 Pn) of each poisoning substance to the NOx catalyst 21 calculated in S206 is stored in the RAM, EEPROM or the like of the ECU 40, and is used in S202 in the next processing S200. After S206, the process proceeds to S207.

In S207, the ECU 40 determines whether the NOx catalyst 21 has been poisoned by a predetermined amount or more. Specifically, the ECU 40 first functions as the poisoning amount estimating unit 41, and according to the following equation 8, the poisoning amount of each poisoning substance (hydrocarbon, nitrogen oxide, sulfur oxide) to the NOx catalyst 21 Estimate
Σ (γ n * P P n) equation 8
Here, PPn of the equation 8 is the present adsorption amount of each poisoning substance to the NOx catalyst 21 calculated in S206. Further, γ n (n = 1, 2, 3...) In Expression 8 is an arbitrary constant larger than 0, for example. The amount of adsorption of hydrocarbons having different carbon numbers and functional groups, the amount of adsorption of nitrogen oxides, and the amount of adsorption of sulfur oxides have an effect on purification of exhaust gas by the NOx catalyst 21 is not necessarily 1: 1. As described above, the poisoning amount of the NOx catalyst 21 is estimated using γn. More specifically, the poisoning amount of each poisoning substance (hydrocarbon, nitrogen oxide, sulfur oxide) to the NOx catalyst 21 is estimated by the following equation 9.
(Γn * Σ (HCn)) + γn * ΣNOx + γn * ΣSOx equation 9
Σ (HCn) of the equation 9 is the present amount of adsorption of hydrocarbons on the NOx catalyst 21. The ΣNOx of the equation 9 is the present adsorption amount of nitrogen oxide on the NOx catalyst 21. ΣSO x of the equation 9 is the present adsorption amount of sulfur oxide on the NOx catalyst 21.

  Subsequently, the ECU 40 determines whether the estimated poisoning amount of the NOx catalyst 21 is equal to or greater than a predetermined poisoning threshold value Pt. If it is determined that the poisoning amount of the NOx catalyst 21 is equal to or greater than the poisoning threshold Pt (S207: YES), the process proceeds to S220. On the other hand, when it is determined that the poisoning amount of the NOx catalyst 21 is smaller than the poisoning threshold value Pt (S207: NO), the ECU 40 ends the series of processing S200.

In S220, the ECU 40 functions as the regeneration control unit 42 and performs poisoned regeneration control. A series of processes S220 related to the poisoning regeneration control is shown in FIG.
In S221, the ECU 40 determines whether the temperature of the NOx catalyst 21 is currently rising. If it is determined that the temperature of the NOx catalyst 21 is rising (S221: YES), the process proceeds to S223. On the other hand, when it is determined that the temperature of the NOx catalyst 21 is not rising (S221: NO), the process proceeds to S240.

At S240, the ECU 40 sets a target temperature for temperature increase control. A series of processes S240 relating to setting of a target temperature for temperature increase control are shown in FIG.
In S241, the ECU 40 calculates the minimum value n_min of n when the poisoning amount (ΣMn) of the NOx catalyst 21 when the temperature is raised to a certain temperature Tn becomes larger than the poisoning allowable amount Y. Here, the poisoning allowable amount Y is a poisoning amount that is acceptable as the poisoning amount of the NOx catalyst 21 that can exhibit the performance of the NOx catalyst 21 with respect to exhaust gas purification.

  Specifically, the ECU 40 calculates the minimum value n_min based on the poisoning substance list shown in FIG. P 1, P 2, P 3... P n in the poisoning substance list shown in FIG. 15 correspond to the respective poisoning substances. The poisoning substance list T1, T2, T3... Tn is necessary for desorbing the respective poisoning substances (P1, P2, P3... Pn) from the NOx catalyst 21, ie, regenerating them. It corresponds to the temperature. The poisoning substance list M1, M2, M3... Mn are respectively added to the current poisoning amounts Σ (γn * nPn) of the poisoning substances (P1, P2, P3... Pn) estimated in S207. It corresponds.

  In the poisoning substance list shown in FIG. 15, each item is organized such that T1> T2> T3>...> Tn. The ECU 40 adds the poisoning amount from the left side of the list, as in M1 and M2, for example, and calculates n as the minimum value n_min when MnMn becomes larger than the poisoning allowable amount Y. After S241, the process proceeds to S242.

  In S242, the ECU 40 sets the target temperature of the temperature increase control to Tn_min. Specifically, the ECU 40 sets the temperature Tn_min corresponding to n_min calculated in S241 as the target temperature. For example, when n_min calculated in S241 is 3, the target temperature is T3. After S242, the ECU 40 ends the process S240 and proceeds to S222 of S220.

  In S222, the ECU 40 starts temperature increase control of the NOx catalyst 21. Specifically, the ECU 40 increases, for example, the amount of fuel supplied from the fuel injection valve 30 to the engine 10 as compared to that during normal operation, and increases the combustion heat in the engine 10. Thereby, the temperature of the exhaust gas discharged from the engine 10 rises. As a result, the temperature of the NOx catalyst 21 rises. Here, the ECU 40 raises the temperature of the NOx catalyst 21 until the target temperature Tn_min set in S242 is reached. After S222, the ECU 40 ends a series of processing S220.

  In S223, the ECU 40 acquires the present poisoning amount X of the NOx catalyst 21. Specifically, the poisoning amount Σ (γn * ΣPn) of the NOx catalyst 21 estimated in S207 is acquired as the poisoning amount X of the current NOx catalyst 21. After S223, the process proceeds to S224.

  In S224, the ECU 40 determines whether the present poisoning amount of the NOx catalyst 21 is equal to or greater than a predetermined regeneration threshold. Specifically, the ECU 40 determines whether the poisoning amount X acquired in S223 is equal to or greater than the regeneration threshold X1. If it is determined that the poisoning amount X is equal to or greater than the regeneration threshold value X1, that is, the poisoning regeneration of the NOx catalyst 21 is not completed (S224: YES), the ECU 40 ends a series of process S220. On the other hand, when it is determined that the poisoning amount X is smaller than the regeneration threshold value X1, that is, it is determined that the poisoning regeneration of the NOx catalyst 21 is completed (S224: NO), the process proceeds to S225.

  In S225, the ECU 40 stops the temperature increase control of the NOx catalyst 21. Specifically, the amount of fuel supplied from the fuel injection valve 30 to the engine 10 is returned to the amount at normal operation. As a result, the temperature rise of the NOx catalyst 21 is stopped. After S225, the ECU 40 ends a series of processing S220.

  The ECU 40 determines NO at S207, and after S222 determines YES at S224 after S222, or ends S200 of a series of processes after S225, and the downstream of the NOx catalyst 21 acquired by the NOx concentration acquisition unit 43. If the concentration of nitrogen oxides on the side is equal to or higher than the predetermined concentration, the process S200 is started again. As described above, the processes S200 and S220 are processes that are repeatedly executed when the concentration of nitrogen oxide on the downstream side of the NOx catalyst 21 is equal to or higher than a predetermined concentration.

  As described above, the ECU 40 functions as the poisoning amount estimating unit 41 in S207, and adsorbs the temperature (T) and the flow rate (Q1) of the exhaust flowing into the NOx catalyst 21 and the NOx catalyst 21 thereby adsorbing the poison. Among the poisoning substances which are substances to be produced, the NOx catalyst 21 is subjected to the poisoning based on the concentration (HC, NOx, SOx) of two or more kinds of poisoning substances (hydrocarbons, nitrogen oxides, sulfur oxides) contained in exhaust gas. The poisoning amount (Σ (γn * ΣPn)), which is the amount of poisoned poison, is estimated.

  Further, the ECU 40 functions as the regeneration control unit 42 in S220, and reduces the poisoning amount of the NOx catalyst 21 based on the poisoning amount (Σ (γn * ΣPn)) estimated by the poisoning amount estimating unit 41, 21. Reproducible playback control is performed. In the regeneration control, when the temperature of the NOx catalyst 21 reaches the target temperature Tn_min, the poisoned substances from Pn_min to Pn adsorbed to the NOx catalyst 21 are desorbed from the NOx catalyst 21. As a result, the poisoning amount of the NOx catalyst 21, that is, the poisoning amount after regeneration 量 Mn, which is the poisoning amount after regeneration, is reduced until the poisoning allowable amount Y becomes equal to or less than the poisoning allowable amount Y.

  As described above, (3) In the present embodiment, the poisoning amount estimating unit 41 determines the poisoning amount based on the concentrations of hydrocarbon, nitrogen oxide, and sulfur oxide among poisoning substances contained in the exhaust gas. presume. Therefore, the poisoning amount estimation unit 41 can estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 with higher accuracy.

(6) The present embodiment further includes a reformer 25 and a concentration information acquisition unit 44.
The reformer 25 can reform the hydrocarbon supplied to the NOx catalyst 21. Thereby, the exhaust gas purification rate by the NOx catalyst 21 can be improved. The concentration information acquisition unit 44 acquires information on the concentration of the main hydrocarbon species to be reformed by the reformer 25. The poisoning amount estimating unit 41 estimates the poisoning amount based on the information acquired by the concentration information acquiring unit 44. Therefore, the poisoning amount estimating unit 41 can estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 with higher accuracy.

  (7) In the present embodiment, the poisoning amount estimating unit 41 calculates the poisoning amount for each hydrocarbon type having the same carbon number and the same functional group, and estimates the poisoning amount to the NOx catalyst 21. Therefore, the poisoning amount estimating unit 41 can estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 with higher accuracy.

  (11) In the present embodiment, the regeneration control unit 42 can regenerate the NOx catalyst 21 by reducing the poisoning amount by raising the temperature of the NOx catalyst 21. Further, the regeneration control unit 42 sets the lowest temperature Tn_min among the temperatures estimated to be the poisoning allowable amount Y or less, which is the poisoning amount after regeneration, as the target temperature Tn_min. Then, the regeneration control unit 42 raises the temperature of the NOx catalyst 21 until the target temperature Tn_min is reached. Thereby, in the regeneration control, when the temperature of the NOx catalyst 21 reaches the target temperature Tn_min, the poisoning substances from Pn_min to Pn adsorbed to the NOx catalyst 21 are desorbed from the NOx catalyst 21. As a result, the post-regeneration poisoning amount MnMn of the NOx catalyst 21 is reduced to the poisoning allowable amount Y or less. Thus, the regeneration control unit 42 can regenerate the NOx catalyst 21 without raising the temperature of the NOx catalyst 21 more than necessary. Therefore, it is possible to suppress the deterioration of the fuel consumption caused by the regeneration control.

Third Embodiment
An exhaust gas purification system according to a third embodiment is shown in FIG. The third embodiment differs from the second embodiment in the configuration and the like of the exhaust gas purification system 1.
In the third embodiment, the vehicle does not include the reforming passage 13. The reformer 25 is provided between the engine 10 and the NOx catalyst 21 in the exhaust passage 12, that is, on the upstream side of the exhaust flow with respect to the NOx catalyst 21 in the exhaust passage 12. The heater 26 is provided to the reformer 25.

The hydrocarbon supply unit 31 is provided between the engine 10 and the reformer 25 of the exhaust passage 12, that is, on the upstream side of the exhaust flow with respect to the reformer 25 in the exhaust passage 12. Therefore, the hydrocarbon (HC) injected from the hydrocarbon supply unit 31 flows into the reformer 25. The hydrocarbon reformed by the reformer 25 is supplied to the NOx catalyst 21 downstream.
The third embodiment is the same as the second embodiment in the configuration other than the above-described point and processing regarding estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 and the like.

Fourth Embodiment
An exhaust gas purification system according to a fourth embodiment is shown in FIG. The fourth embodiment differs from the second embodiment in the configuration and the like of the exhaust gas purification system 1.
In the fourth embodiment, the vehicle is provided with a fresh air passage 14 instead of the reforming passage 13. One end of the fresh air passage 14 is open to the atmosphere, and the other end is connected to the exhaust passage 12. Here, the other end of the fresh air passage 14 is located upstream of the NOx catalyst 21. Therefore, fresh air flowing in from one end of the fresh air passage 14 flows through the fresh air passage 14, joins with the exhaust gas in the exhaust passage 12, and flows into the NOx catalyst 21.

The reformer 25 is provided in the fresh air passage 14. The heater 26 is provided to the reformer 25. The hydrocarbon supply unit 31 is provided upstream of the fresh air flow with respect to the reformer 25 in the fresh air passage 14. Therefore, the hydrocarbon (HC) injected from the hydrocarbon supply unit 31 flows into the reformer 25. The hydrocarbon reformed by the reformer 25 is supplied to the NOx catalyst 21 downstream.
The fourth embodiment is the same as the second embodiment in the configuration other than the above-described point and the processing regarding estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 and the like.

Fifth Embodiment
An exhaust gas purification system according to a fifth embodiment will be described based on FIG. The fifth embodiment is different from the first embodiment in the method of estimating the poisoning amount by the poisoning amount estimating unit 41.
In the fifth embodiment, the ECU 40 sets the adsorption coefficients α1 and α2 as follows when calculating the amount of change in the adsorption amount of hydrocarbon and nitrogen oxide on the NOx catalyst 21 in S104. That is, at this time, as the adsorption coefficients α1 and α2 increase as the poisoning amount of the poisoning substance to the NOx catalyst 21 (previous value of the poisoning state of the NOx catalyst 21) increases, as shown by the broken line in FIG. The amount is set smaller than in the case where the poisoning amount of the poisoning substance to the NOx catalyst 21 is small (solid line). The adsorption coefficient α1 is a coefficient that correlates with the ease of adsorption of hydrocarbons on the NOx catalyst 21. The adsorption coefficient α2 is a coefficient that correlates with the ease of adsorption of nitrogen oxides on the NOx catalyst 21.
The fifth embodiment is the same as the first embodiment in the configuration and processing regarding estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 other than the points described above.

  As described above, (4) In the present embodiment, the poisoning amount estimating unit 41 sets the adsorption coefficients α1 and α2 correlated with the ease of adsorption of the poisoning substance to the NOx catalyst 21 to the NOx catalyst 21. The larger the poisoning amount of the poisoning substance, the smaller the poisoning amount of the poisoning substance to the NOx catalyst 21 than in the case where the poisoning amount of the poisoning substance is small. Therefore, it is possible to estimate the poisoning amount of the poisoning substance to the NOx catalyst 21 with higher accuracy, in consideration of the change in the contact probability of the poisoning substance to the NOx catalyst 21.

Sixth Embodiment
An exhaust gas purification system according to a sixth embodiment will be described based on FIG. The sixth embodiment is different from the first embodiment in the method of estimating the poisoning amount by the poisoning amount estimating unit 41.
In the sixth embodiment, when the ECU 40 calculates the amount of change in the adsorption amount of hydrocarbon and nitrogen oxide on the NOx catalyst 21 in S104, if the hydrocarbon and nitrogen oxide coexist in the exhaust gas, As shown by the broken line in FIG. 18, as the NOx adsorption coefficient α2 correlated with the ease of adsorption of nitrogen oxides to the NOx catalyst 21 becomes higher at high temperatures, hydrocarbons and nitrogen oxides coexist in the exhaust gas. If not set (solid line), set larger.
The sixth embodiment is the same as the first embodiment in the configuration and processing regarding estimation of the poisoning amount of the poisoning substance to the NOx catalyst 21 other than the points described above.

  As described above, (5) In the present embodiment, the poisoning amount estimating unit 41 determines that nitrogen oxide is adsorbed to the NOx catalyst 21 when hydrocarbon and nitrogen oxide coexist in the exhaust gas. The NOx adsorption coefficient α2 correlating to ease is set larger as the temperature is higher, as compared with the case where hydrocarbon and nitrogen oxide do not coexist in the exhaust gas. As described above, the temperature range (high temperature range) where nitrogen oxides are easily adsorbed to the catalyst by coexistence with hydrocarbon is reflected in the process of estimation of the poisoning amount, whereby the poisoning substance to the NOx catalyst 21 can be The poisoning amount can be estimated with higher accuracy.

(Other embodiments)
In the above-mentioned embodiment, ECU40 showed the example which performs regeneration control, when the poisoning amount of NOx catalyst 21 presumed is more than predetermined poisoning threshold value Pt. On the other hand, in another embodiment of the present invention, the poisoning threshold value Pt may be set smaller as the thermal deterioration of the NOx catalyst 21 progresses. That is, (9) In this embodiment, the regeneration control unit 42 starts regeneration control when the poisoning amount estimated by the poisoning amount estimating unit 41 becomes equal to or larger than a predetermined poisoning threshold value Pt. As the thermal deterioration progresses, the poisoning threshold value Pt is set smaller. Therefore, even when the thermal deterioration of the NOx catalyst 21 progresses and the poisoning allowance decreases, the regeneration control can be started at an appropriate timing.

  In the above embodiment, the poisoning amount of the poisoning substance to the NOx catalyst 21 is limited only when the concentration of nitrogen oxide on the downstream side of the NOx catalyst 21 acquired by the NOx concentration acquisition unit 43 is equal to or higher than the predetermined concentration. In the example, the process related to the poisoning regeneration control to regenerate the NOx catalyst 21 is performed. On the other hand, in another embodiment of the present invention, regardless of the concentration of nitrogen oxide on the downstream side of the NOx catalyst 21 acquired by the NOx concentration acquisition unit 43, the poisoning amount of the poisoning substance to the NOx catalyst 21 is It is also possible to perform the estimation and the process related to the poisoning regeneration control to regenerate the NOx catalyst 21. In this case, the concentration sensor 53 downstream of the NOx catalyst 21 may be omitted.

Further, in the above embodiment, when the regeneration control unit 42 performs temperature increase control, the amount of fuel supplied from the fuel injection valve 30 to the engine 10 is increased compared to that during normal operation, and the combustion heat in the engine 10 is increased. In the example, the temperature of the NOx catalyst 21 is increased. On the other hand, in another embodiment of the present invention, the regeneration control unit 42 raises the temperature of the NOx catalyst 21 by, for example, changing the EGR rate and raising the exhaust temperature of the engine 10 when performing the temperature increase control. May be Further, at this time, the temperature of the NOx catalyst 21 may be raised by the heat of reaction caused by the injection of the fuel into the oxidation catalyst (DOC) provided upstream of the NOx catalyst 21. Further, at this time, the temperature of the NOx catalyst 21 may be raised by a heater, a burner or the like provided in the NOx catalyst 21.
Further, in the embodiment described above, the Ag ₂ O as a catalyst an example to be supported on a carrier. On the other hand, in another embodiment of the present invention, for example, zeolite or the like may be used as a carrier, and an active metal such as platinum may be used as a catalyst.
Thus, this invention is not limited to the said embodiment, It can implement with various forms in the range which does not deviate from the summary.

1 exhaust purification system, 10 internal combustion engine, 12 exhaust passage, 21 NOx catalyst, 31 hydrocarbon supply unit, 41 poisoning amount estimation unit

Claims (11)

An exhaust gas purification system (1) for purifying exhaust gas from an internal combustion engine (10), comprising
An NOx catalyst (21) provided in an exhaust passage (12) of the internal combustion engine;
A hydrocarbon supply unit (31) for supplying a hydrocarbon to the NOx catalyst;
The temperature and flow rate of the exhaust flowing into the NOx catalyst, and the concentration of two or more poisoning substances contained in the exhaust among the poisoning substances that are poisoning substances that cause the NOx catalyst to adsorb. A poisoning amount estimating unit (41) for estimating a poisoning amount which is an amount of the poisoning substance poisoned to the NOx catalyst;
Exhaust purification system comprising.   The exhaust gas purification system according to claim 1, wherein the poisoning amount estimation unit estimates the poisoning amount based on the concentration of hydrocarbon and nitrogen oxide among poisoning substances contained in the exhaust gas.   The exhaust gas purification system according to claim 1, wherein the poisoning amount estimating unit estimates the poisoning amount based on concentrations of hydrocarbon, nitrogen oxide and sulfur oxide among poisoning substances contained in the exhaust gas.   The poisoning amount estimating unit has an adsorption coefficient (α1, α2) correlating with the ease of adsorption of the poisoning substance on the NOx catalyst as the poisoning amount of the poisoning substance on the NOx catalyst is larger. The exhaust gas purification system according to any one of claims 1 to 3, wherein the exhaust gas purification system is set smaller than the case where the poisoning amount of the poisoning substance to the NOx catalyst is small.   When the hydrocarbon and the nitrogen oxide coexist in the exhaust gas, the poisoning amount estimation unit correlates the NOx adsorption coefficient (α2) with the ease of nitrogen oxide adsorption to the NOx catalyst, The exhaust gas purification system according to any one of claims 1 to 4, wherein the temperature is set larger as the temperature is higher than in the case where hydrocarbon and nitrogen oxide do not coexist in the exhaust gas. A reformer (25) capable of reforming hydrocarbons supplied to the NOx catalyst;
The concentration information acquisition unit (44) for acquiring information on the concentration of the main hydrocarbon species to be reformed by the reformer,
The exhaust gas purification system according to any one of claims 1 to 5, wherein the poisoning amount estimating unit estimates the poisoning amount based on the information acquired by the concentration information acquiring unit.   The exhaust purification system according to claim 6, wherein the poisoning amount estimation unit calculates the poisoning amount for each hydrocarbon type having the same carbon number and functional group, and estimates the poisoning amount to the NOx catalyst.   The regeneration control unit (42) for performing regeneration control capable of reducing the poisoning amount of the NOx catalyst and regenerating the NOx catalyst based on the poisoning amount estimated by the poisoning amount estimating unit. The exhaust gas purification system according to any one of the preceding claims.   The regeneration control unit starts the regeneration control when the poisoning amount estimated by the poisoning amount estimating unit becomes equal to or more than a predetermined poisoning threshold, and the poisoning threshold is started as the thermal deterioration of the NOx catalyst progresses. The exhaust gas purification system according to claim 8, wherein the It further comprises a NOx concentration acquisition unit (43) for acquiring the concentration of nitrogen oxide on the downstream side of the exhaust flow relative to the NOx catalyst,
The regeneration control unit performs the regeneration control when the concentration acquired by the NOx concentration acquisition unit is a predetermined concentration or more and the poisoning amount estimated by the poisoning amount estimation unit is a predetermined amount or more. Or 9 exhaust purification system.   The regeneration control unit reduces the poisoning amount by raising the temperature of the NOx catalyst and can regenerate the NOx catalyst, and the poisoning amount after regeneration, which is the poisoning amount after regeneration, is less than the poisoning allowable amount. The exhaust gas purification system according to any one of claims 8 to 10, wherein the lowest temperature among the temperatures estimated to be set as a target temperature, and the temperature of the NOx catalyst is raised until the target temperature is reached.

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