JP7208046B2 - Exhaust purification device - Google Patents

Description

The present invention relates to an exhaust purification device.

2. Description of the Related Art Conventionally, there is known an exhaust purification device including a catalyst provided on an exhaust flow path and a reducing agent supply section provided upstream of the catalyst (for example, Patent Document 1). In the conventional exhaust purification device, when the catalyst is regenerated, the time during which the air-fuel ratio of the exhaust gas is made rich and the time during which the air-fuel ratio of the exhaust gas is made lean by the reducing agent supplied by the reducing agent supply unit are set in advance. .

Japanese Unexamined Patent Application Publication No. 2010-203338

In the conventional catalyst regeneration method described above, the addition of a reducing agent to enrich the air-fuel ratio of the exhaust gas may cause excessive heat generation with respect to the target temperature of the catalyst. Therefore, in order to balance the energy in the catalyst, the air-fuel ratio alternates between rich and lean. However, in such a method, the amount of _O2 in the exhaust gas flowing into the catalyst changes greatly, and the catalyst temperature changes greatly and periodically. Difficult to regulate temperature.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust purification system capable of appropriately adjusting the temperature of a catalyst in regeneration control while suppressing temperature fluctuations of the catalyst.

An exhaust purification device according to one aspect of the present invention is an exhaust purification device that includes a catalyst provided on an exhaust flow path of an internal combustion engine and executes regeneration control to regenerate the catalyst by supplying a reducing agent to the catalyst. a reducing agent supply unit that supplies a reducing agent to the catalyst, a catalyst temperature acquisition unit that acquires the temperature of the catalyst, and an air-fuel ratio acquisition unit that acquires the downstream air-fuel ratio that is the air-fuel ratio of the exhaust gas on the downstream side of the catalyst; an air-fuel ratio control unit that sets a target air-fuel ratio, which is a target value of the downstream air-fuel ratio during regeneration control, and controls a reducing agent supply unit so that the downstream air-fuel ratio becomes the target air-fuel ratio; an inflow _O2 amount adjusting unit that adjusts the amount of _O2 in the exhaust gas flowing into the catalyst so that the temperature of the catalyst reaches the target temperature, based on the target temperature, which is the target value of the temperature, and the temperature of the catalyst; The inflow O ₂ amount adjustment unit adjusts the EGR device of the internal combustion engine so that when the temperature of the catalyst is lower than the target temperature, the EGR amount in the internal combustion engine is reduced compared to when the temperature of the catalyst is equal to or higher than the target temperature. to control.

In the exhaust purification device according to the aspect of the present invention, the air-fuel ratio control unit controls the reducing agent supply unit so that the downstream air-fuel ratio becomes the target air-fuel ratio during regeneration control. For example, when the downstream air-fuel ratio is in a reducing atmosphere, the amount of exothermic reaction in the catalyst is governed by the amount of _O2 in the exhaust gas. Therefore, the calorific value in the catalyst can be adjusted by adjusting the amount of _O2 . Therefore, the calorific value of the catalyst can be adjusted by adjusting the amount of O ₂ in the exhaust gas flowing into the catalyst so that the temperature of the catalyst reaches the target temperature by the inflow O ₂ amount adjusting section. As a result, compared to the case where the air-fuel ratio of the exhaust gas alternates between rich and lean, for example, it is possible to appropriately adjust the temperature of the catalyst during regeneration control while suppressing temperature fluctuations of the catalyst. Also, the EGR device can be used to easily adjust the amount of _O2 in the exhaust gas.

An exhaust gas purification device according to another aspect of the present invention is an exhaust gas purification device that includes a catalyst provided in an exhaust flow path of an internal combustion engine and executes regeneration control to regenerate the catalyst by supplying a reducing agent to the catalyst. a reducing agent supply unit that supplies a reducing agent to the catalyst; a catalyst temperature acquisition unit that acquires the temperature of the catalyst; and an air-fuel ratio acquisition unit that acquires the downstream air-fuel ratio that is the air-fuel ratio of the exhaust gas downstream of the catalyst. an air-fuel ratio control unit that sets a target air-fuel ratio, which is a target value of the downstream air-fuel ratio during regeneration control, and controls a reducing agent supply unit so that the downstream air-fuel ratio becomes the target air-fuel ratio; an inflow _O2 amount adjustment unit that adjusts the amount of _O2 in the exhaust gas flowing into the catalyst so that the temperature of the catalyst reaches the target temperature based on the target temperature that is the target value of the temperature of and the temperature of the catalyst; a ratio acquisition unit for acquiring the ratio of _CO and _HC in the _exhaust gas flowing into the catalyst; to adjust.

In the exhaust purification device according to another aspect of the present invention, the reducing agent supply section is controlled by the air-fuel ratio control section so that the downstream air-fuel ratio during regeneration control becomes the target air-fuel ratio. For example, when the downstream air-fuel ratio is in a reducing atmosphere, the amount of exothermic reaction in the catalyst is governed by the amount of _O2 in the exhaust gas. Therefore, the calorific value in the catalyst can be adjusted by adjusting the amount of _O2 . Therefore, the calorific value of the catalyst can be adjusted by adjusting the amount of O ₂ in the exhaust gas flowing into the catalyst so that the temperature of the catalyst reaches the target temperature by the inflow O ₂ amount adjusting section. As a result, compared to the case where the air-fuel ratio of the exhaust gas alternates between rich and lean, for example, it is possible to appropriately adjust the temperature of the catalyst during regeneration control while suppressing temperature fluctuations of the catalyst. In addition, since the calorific value of CO is smaller than that of HC, for example, in order to generate a constant calorific value in the catalyst, the larger the ratio of CO and HC in the exhaust gas, the greater the amount of _O2 to be reacted with CO. becomes larger. Therefore, the temperature of the catalyst in the regeneration control can be more appropriately adjusted by adjusting the _O2 amount with the inflow _O2 amount adjustment unit so that the _O2 amount increases as the ratio of CO and HC increases. can be done.

In one embodiment, an inflow gas temperature acquisition unit that acquires an inflow gas temperature that is the temperature of the exhaust gas that flows into the catalyst, and an exhaust gas flow rate acquisition unit that acquires an exhaust gas flow rate that is the flow rate of the exhaust gas flowing through the catalyst. , the inflow _O2 amount adjusting unit calculates a target _O2 amount, which is a target value of the _O2 amount, based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate, and the _O2 amount is the target _O2 amount. The amount of _O2 may be adjusted so that the amount of In this case, the controllability of adjusting the O ₂ amount can be improved by using the target O ₂ amount calculated based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate, for example, as the prospective control amount.

In one embodiment, the reducing agent supply unit is an injector that injects fuel into a cylinder of the internal combustion engine, and the air-fuel ratio control unit performs fuel injection at an injection timing at which the fuel burns during the expansion stroke of the internal combustion engine. By controlling the injector, the inflow O ₂ amount adjusting unit may retard the injection timing when the temperature of the catalyst is lower than the target temperature compared to when the temperature of the catalyst is equal to or higher than the target temperature. In this case, the fuel whose injection timing is retarded burns in the expansion stroke, thereby increasing the temperature of the exhaust gas. Therefore, the amount of heat generated by the oxidation reaction in the catalyst can be small, and the amount of O ₂ in the exhaust gas to be reacted in the catalyst can be reduced.

According to the present invention, it is possible to appropriately adjust the temperature of the catalyst during regeneration control while suppressing temperature fluctuations of the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram which shows the engine system provided with the exhaust gas purification device which concerns on embodiment. It is a figure which shows an example of the relationship between a COHC ratio and a correction coefficient. 4 is a flowchart illustrating a catalyst temperature control process; FIG. 4 is a flowchart illustrating a target O ₂ amount calculation process of FIG. 3; FIG. FIG. 4 is a flowchart illustrating an O ₂ amount adjustment process of FIG. 3; FIG. 2 is a timing chart showing an operation example of the exhaust purification system of FIG. 1; FIG. 7 is a timing chart showing the catalyst temperature in the operation example of FIG. 6; FIG. 4 is a timing chart showing an operation example of a conventional exhaust purification device; FIG. 9 is a timing chart showing the catalyst temperature in the operation example of FIG. 8; FIG. FIG. 10 is a diagram for explaining a modification of the O ₂ amount adjustment process; FIG. 11 is a flowchart illustrating an O ₂ amount adjustment process of FIG. 10; FIG. FIG. 11 is a diagram for explaining another modification of the O ₂ amount adjustment process;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same reference numerals are used for the same or corresponding elements, and overlapping descriptions are omitted.

[Overview of exhaust purification device]
FIG. 1 is a block diagram showing an engine system provided with an exhaust purification device according to an embodiment. In FIG. 1, an exhaust purification device 1 according to the present embodiment is mounted on a vehicle, for example, and constitutes part of an engine system 100 having an engine (internal combustion engine) 2 . The engine 2 is, for example, a diesel engine having multiple cylinders (not shown).

The exhaust purification device 1 includes an NSR (NOx Storage Reduction) 4 provided on an exhaust passage 3 for discharging exhaust gas after combustion in the engine 2 . The NSR 4 is a catalyst that adsorbs NOx (nitrogen oxides) contained in the exhaust gas discharged from the engine 2 to purify the exhaust gas. A DPF (Diesel Particulate Filter) 5 is provided downstream of the NSR 4 in the exhaust flow path 3 . The DPF 5 collects PM (particulate matter such as soot) contained in the exhaust gas and purifies the exhaust gas.

The exhaust purification device 1 is configured to be able to execute regeneration control (so-called S regeneration) of the NSR 4 for reducing SOx adsorbed on the NSR 4 by supplying a reducing agent to the NSR 4 . In regeneration control, a reducing agent is supplied to the NSR 4 which has a temperature equal to or higher than a predetermined temperature. The reducing agent here means CO (carbon monoxide), H2 (hydrogen), and HC (hydrocarbon, that is, unburned fuel). By supplying the reducing agent to the NSR4, the SOx is reduced in the NSR4 and released from the NSR4. The details of the playback control process will be described later.

[Configuration of exhaust gas purification device]
The exhaust purification device 1 has, as an example, an engine 2 functioning as an O ₂ supply section that supplies O ₂ to the NSR 4 and a reducing agent supply section that supplies a reducing agent to the NSR 4 .

The engine 2 has an intake device 2a for supplying fresh air to the combustion chamber of each cylinder. The intake device 2a adjusts the amount of fresh air to be supplied into the combustion chamber (hereinafter simply referred to as the in-cylinder fresh air amount).

The intake device 2a includes, for example, a throttle valve and a variable displacement turbocharger compressor (not shown). The throttle valve is, for example, an electronically controlled butterfly valve. The operation of the throttle valve is controlled by an ECU [Electronic Control Unit] 10, which will be described later. A variable displacement turbocharger is a supercharger that has a compressor and a turbine. This turbine has a variable nozzle capable of changing the variable nozzle opening (hereinafter simply referred to as VN opening [Variable Nozzle]) by driving a plurality of vanes. The VN opening of the variable capacity turbocharger is controlled by the ECU 10 .

By adjusting the in-cylinder fresh air amount, the intake device 2 a can adjust the amount of O ₂ remaining in the exhaust gas that has been burned in the combustion chamber and discharged to the exhaust passage 3 . In other words, the intake device 2a functions as an O ₂ supply section that supplies O ₂ to the NSR 4 .

The engine 2 has a plurality of injectors 2b for injecting fuel into the combustion chamber of each cylinder. The injector 2b supplies fuel into the combustion chamber by injecting fuel at an amount of fuel set by the ECU 10 (hereinafter simply referred to as an injection fuel amount) and an injection timing. A common rail (not shown) is connected to each injector 2b. The common rail stores high pressure fuel supplied to each injector 2b. The injection fuel amount of the injector 2b is controlled by the ECU10.

The injector 2b performs main injection, pilot injection that injects a small amount of fuel before the main injection, after-injection that injects a small amount of fuel after the main injection, and post-injection that injects after the after-injection. and can be done.

The injector 2b can adjust the amount of reducing agent in the exhaust gas discharged to the exhaust passage 3 by adjusting the amount of injected fuel. In other words, the injector 2b functions as a reducing agent supply unit that supplies the reducing agent to the NSR4.

The engine 2 has an EGR device 2c for recirculating part of the exhaust gas as exhaust gas recirculation (EGR) gas into the combustion chamber. The EGR device 2c includes an EGR valve (not shown) that adjusts the amount of recirculated EGR gas. The recirculated amount of EGR gas may be represented, for example, by an EGR rate (hereinafter simply referred to as the EGR amount) corresponding to the ratio of the recirculated amount of EGR gas to the amount of fresh air in the cylinder. The EGR amount of the EGR device 2c is adjusted by the ECU 10 controlling an EGR valve drive section (not shown) that opens and closes the EGR valve.

By adjusting the EGR amount, the EGR device 2c can adjust the amount of O ₂ remaining in the exhaust gas that has been burned in the combustion chamber and discharged to the exhaust passage 3 . In other words, the EGR device 2c functions as an _O2 supply unit that supplies _O2 to the NSR4.

Subsequently, the exhaust purification device 1 includes an upstream temperature sensor (inflow gas temperature acquisition unit) 6 provided upstream of the NSR 4 in the exhaust passage 3 and a downstream temperature sensor provided downstream of the NSR 4 in the exhaust passage 3. A sensor 7, a NOx sensor 8 and an air-fuel ratio sensor (air-fuel ratio acquisition unit) 9 provided downstream of the DPF 5 in the exhaust passage 3, and an ECU 10 connected to each of the sensors 6-9.

The upstream temperature sensor 6 is a detector that detects (acquires) the upstream temperature (hereinafter referred to as the inflow gas temperature) that is the temperature of the exhaust gas flowing into the NSR 4 . The upstream temperature sensor 6 transmits a detection signal of the detected inflow gas temperature to the ECU 10 . The downstream temperature sensor 7 is a detector that detects the temperature of the exhaust gas on the downstream side of the NSR 4 (hereinafter simply referred to as downstream temperature). The downstream temperature sensor 7 transmits a detection signal of the detected downstream temperature to the ECU 10 .

The NOx sensor 8 is a detector that detects the downstream NOx concentration, which is the NOx concentration of the exhaust gas on the downstream side of the DPF 5 . The NOx sensor 8 transmits a detection signal of the detected NOx concentration to the ECU 10 . The air-fuel ratio sensor 9 is a detector that detects the air-fuel ratio of exhaust gas on the downstream side of the DPF 5 . That is, the air-fuel ratio sensor 9 acquires the downstream air-fuel ratio, which is the air-fuel ratio of the exhaust gas on the downstream side of the NSR 4 . The air-fuel ratio sensor 9 transmits a detection signal of the detected downstream air-fuel ratio to the ECU 10 .

The ECU 10 is a control unit that controls the _O2 supply unit and the reducing agent supply unit based on the temperature of the NSR 4 and the downstream air-fuel ratio. The ECU 10 is an electronic control unit having a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a CAN [Controller Area Network] communication circuit, and the like. The ECU 10 implements various functions by loading programs stored in the ROM into the RAM and executing the programs loaded into the RAM by the CPU. The ECU 10 may be composed of a plurality of electronic control units.

The ECU 10 includes, as a functional configuration, an engine state acquisition unit 11, a catalyst temperature acquisition unit 12, an exhaust gas flow rate acquisition unit 13, a ratio acquisition unit 14, a regeneration control execution unit 15, an air-fuel ratio control unit 16, and an inflow O ₂ amount adjusting unit 17 .

The engine state acquisition unit 11 acquires the engine state. The engine state acquisition unit 11 detects, for example, an accelerator opening detected by an accelerator opening sensor (not shown), an intake air amount detected by an airflow sensor (not shown), and an engine speed sensor (not shown). 1) is acquired as the engine state. The engine state acquisition unit 11 acquires the basic injection fuel amount corresponding to the required torque of the engine 2 as the engine state, for example, based on the detected accelerator opening and engine speed. The engine state acquisition unit 11 acquires, as an engine state, a cylinder air-fuel ratio correction coefficient for correcting the cylinder air-fuel ratio with respect to the basic injection fuel amount, based on the detected accelerator opening and engine speed, for example. . The engine state acquisition unit 11 may calculate the injection timing of fuel injection based on the engine speed, the required torque, and the like, for example, by a known method. The injection timing means the timing for causing the injector 2b to start injecting fuel. The engine state acquisition unit 11 may calculate the estimated deposition amount of sulfur in the NSR 4 based on the amount of exhaust gas passing through the NSR 4, the amount of intake air, and the amount of injected fuel. The estimated deposit amount may be calculated, for example, by multiplying the time integrated value of the fuel consumption calculated based on the injected fuel amount by the concentration of sulfur per unit weight. The estimated accumulated amount is used by the later-described regeneration control execution unit 15 to determine whether regeneration of the NSR 4 is necessary. The engine state acquisition unit 11 calculates the basic EGR amount when the regeneration control is not executed, for example, based on the detected accelerator opening and engine speed. The engine state acquisition unit 11 may also acquire environmental parameters (for example, atmospheric pressure) for correcting the injected fuel amount, the in-cylinder fresh air amount, and the EGR amount as the engine state.

A catalyst temperature acquisition unit 12 acquires the temperature T of the NSR 4 . The catalyst temperature acquisition unit 12 estimates the temperature T of the NSR 4 based on, for example, the inflow gas temperature detected by the upstream temperature sensor 6, the downstream temperature detected by the downstream temperature sensor 7, and the engine state. The catalyst temperature acquisition unit 12 can estimate the temperature T of the NSR 4 by a known estimation method. The temperature T of the NSR 4 is the floor temperature of the NSR 4.

Here, as an example of the temperature T, the catalyst temperature acquisition unit 12 estimates the temperature T of the NSR 4 as the upper temperature of the upper stage of the NSR 4 and the lower temperature of the lower stage of the NSR 4 . The upper stage side of the NSR 4 means a portion of the NSR 4 on the upstream side in the flow direction of the exhaust gas of the exhaust passage 3 . The lower stage side of the NSR 4 means a portion of the NSR 4 on the downstream side of the exhaust passage 3 in the flow direction of the exhaust gas. The catalyst temperature acquisition unit 12 may further estimate the middle stage temperature of the NSR 4 instead of or in addition to the lower stage temperature. The middle stage of the NSR4 means a portion between the upper stage side and the lower stage side of the NSR4.

The exhaust gas flow rate acquisition unit 13 acquires the exhaust gas flow rate, which is the flow rate of the exhaust gas flowing through the NSR 4 . The exhaust gas flow rate acquisition unit 13 may, for example, calculate the exhaust gas flow rate based on the amount of intake air. The exhaust gas flow rate acquisition unit 13 can calculate the exhaust gas flow rate by a known method using the intake air amount.

The ratio acquisition unit 14 acquires the ratio of CO and HC in the exhaust gas flowing into the NSR 4 (hereinafter simply referred to as the COHC ratio). The COHC ratio may be, for example, a ratio obtained by dividing the CO concentration (g/s) in the exhaust gas flowing into the NSR 4 by the HC concentration (g/s) in the exhaust gas flowing into the NSR 4 . The ratio acquisition unit 14 may calculate the COHC ratio, for example, according to combustion characteristics (characteristics of exhaust gas components) determined according to the in-cylinder air-fuel ratio and the in-cylinder temperature (combustion temperature).

Specifically, the ratio acquisition unit 14 calculates the basic COHC ratio using a map defined according to the engine speed and the basic injection fuel amount. The basic COHC ratio means the COHC ratio corresponding to the in-cylinder temperature when the in-cylinder air-fuel ratio corresponds to the basic injection fuel amount. The ratio acquisition unit 14 calculates a COHC ratio correction coefficient for correcting the in-cylinder air-fuel ratio with respect to the basic COHC ratio, for example, using a map defined according to the in-cylinder air-fuel ratio correction coefficient. The ratio acquisition unit 14 calculates the COHC ratio by multiplying the basic COHC ratio by the COHC ratio correction coefficient. The basic COHC ratio and the COHC ratio correction coefficient can be set in advance by, for example, an actual machine test or simulation of the engine 2 .

Alternatively, the ratio acquiring unit 14 may calculate the COHC ratio using a map defined according to the estimated in-cylinder temperature and the in-cylinder air-fuel ratio. In this case, the ratio acquisition unit 14 may calculate the estimated in-cylinder temperature based on, for example, the compression ratio of the engine 2, the charging efficiency, the intake air temperature, the water temperature, and the like. For example, the ratio acquisition unit 14 may use the downstream air-fuel ratio as the cylinder air-fuel ratio, or estimate the cylinder air-fuel ratio based on the intake air amount, the basic injection fuel amount, the cylinder air-fuel ratio correction coefficient, and the like. good too.

The regeneration control execution unit 15 executes regeneration control to regenerate the NSR 4 by supplying a reducing agent to the NSR 4 . The regeneration control execution unit 15 executes regeneration control, for example, when the estimated deposit amount exceeds a predetermined deposit amount threshold. The deposition amount threshold is an estimated deposition amount threshold for determining whether or not to execute regeneration control. The deposition amount threshold is set according to, for example, the required exhaust gas purification capability.

In the regeneration control, for example, the engine 2 as an _O2 supply unit and a reducing agent supply unit is controlled such that the temperature T of the NSR 4 is equal to or higher than a target temperature. The target temperature is the target value of the temperature T of the NSR 4 during regeneration control. The target temperature can be a preset temperature T1 within the regeneration activation temperature range of the NSR4. The regeneration activation temperature range means the range of the temperature T of the NSR4 in which the regeneration of the NSR4 can be favorably progressed in the regeneration control. The temperature T1 may be the lower limit temperature (for example, 640° C.) of the regeneration activation temperature range. The temperature T1 may change over time, for example, it may change stepwise according to the elapsed time from the start of regeneration control.

For example, the regeneration control execution unit 15 estimates the amount of sulfur poisoning of the NSR 4 during execution of the regeneration control, and terminates the regeneration control when the estimated amount of sulfur poisoning falls below a predetermined threshold value. The regeneration control execution unit 15 can estimate the amount of sulfur poisoning based on, for example, a map having the temperature T of the NSR 4 and the downstream air-fuel ratio as arguments. Note that the regeneration control execution unit 15 may end the regeneration control when the execution time of the regeneration control reaches a predetermined time threshold.

The air-fuel ratio control unit 16 acquires the downstream air-fuel ratio based on the detection signal from the air-fuel ratio sensor 9, for example. The air-fuel ratio control unit 16 sets a target air-fuel ratio, which is a target value of the downstream air-fuel ratio during regeneration control. The target air-fuel ratio is a target value of the downstream air-fuel ratio for making the exhaust gas in the regeneration control into a reducing atmosphere in which the regeneration of the NSR 4 can be favorably progressed. The target air-fuel ratio is set in advance so as to be richer than the downstream air-fuel ratio when the regeneration control is not executed. The target air-fuel ratio is set according to the specifications of the engine 2 and the specifications of the NSR 4, for example. The target air-fuel ratio is not particularly limited, but can be, for example, an A/F (air-fuel ratio) of 15 or less. The target air-fuel ratio is, for example, substantially constant during regeneration control.

As an example of the target air-fuel ratio, as shown in FIG. 6, the air-fuel ratio control unit 16 may set the target air-fuel ratio during regeneration control to AF2. FIG. 6 is a timing chart showing an operation example of the exhaust purification device 1. FIG. In FIG. 6, the horizontal axis indicates time, and the solid line indicates the downstream air-fuel ratio. The right vertical axis indicates the A/F of the downstream air-fuel ratio, and the left vertical axis indicates the amount of SOx released from the NSR 4 (the amount of SOx released will be described later). In the example of FIG. 6, regeneration control is started at time t1. The air-fuel ratio control unit 16 sets the target air-fuel ratio AF2 during the regeneration control to an air-fuel ratio richer than the air-fuel ratio AF1 when the regeneration control is not executed.

For example, when the engine 2 is idling, the air-fuel ratio control unit 16 may further correct the target air-fuel ratio to the rich side by a predetermined value. The predetermined value can be set, for example, according to the combustion stability of the engine 2 during idling. Further, the predetermined value may be a value that increases as the exhaust gas flow rate decreases.

The air-fuel ratio control unit 16 controls the injector 2b, for example, so that the downstream air-fuel ratio becomes the target air-fuel ratio. As the control of the injector 2b, the air-fuel ratio control unit 16 may adjust the downstream air-fuel ratio by, for example, adjusting the injection fuel amount of the post-injection that contributes less to the output torque. Based on the downstream air-fuel ratio detected by the air-fuel ratio sensor 9, the air-fuel ratio control unit 16 performs fuel feedback control with the target air-fuel ratio as a target value so that the downstream air-fuel ratio becomes the target air-fuel ratio. You may control the injection fuel quantity of a post-injection. A known method can be used for fuel feedback control.

The inflow O ₂ amount adjustment unit 17 sets the target temperature of the NSR 4 during regeneration control, and based on the temperature T of the NSR 4 and the target temperature, the exhaust gas flowing into the NSR 4 so that the temperature T of the NSR 4 becomes the target temperature. Adjust the amount of _O2 in the gas. By _O2 amount is meant the amount of _O2 that is available for the oxidation reaction of the reducing agent in NSR4 due to the increase in temperature T of NSR4. The O ₂ amount is represented by the concentration of O ₂ contained in the exhaust gas, and may be, for example, the mass flow rate (g/sec) of O ₂ contained in the exhaust gas.

More specifically, the inflow _O2 amount adjustment unit 17 calculates the temperature deviation based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate during the regeneration control, for example, and calculates the _O2 amount target value. Calculate a certain target _O2 amount. The inflow O ₂ amount adjustment unit 17 acquires the inflow gas temperature based on the detection signal from the upstream temperature sensor 6, for example. The inflow O ₂ amount adjusting unit 17 calculates the basic target O ₂ amount using, for example, the following equations (1) to (3). The basic target O ₂ amount is a target value of the O ₂ amount to be made to flow into the NSR 4, for example, when the COHC ratio is 0 (that is, when CO is not contained in the exhaust gas). The target _O2 amount is the target value of the _O2 amount according to the COHC ratio.
Basic target _O2 amount = exhaust gas flow rate x specific heat x temperature deviation x coefficient K/calorific value (1)
Coefficient K = O ₂ molecular weight/molecular weight of reducing agent (2)
Target _O2 amount = basic target _O2 amount x correction coefficient (3)

In equation (1), “exhaust gas flow rate” is the exhaust gas flow rate acquired by the exhaust gas flow rate acquisition unit 13 . "Specific heat" is the specific heat of the exhaust gas, for example, the specific heat of the exhaust gas having predetermined components that are typical during regeneration control. The typical predetermined component can be, for example, a component of the exhaust gas when the downstream air-fuel ratio is the target air-fuel ratio and the EGR amount is not reduced as described above. "Temperature deviation" is the deviation between the inflow gas temperature and the target temperature, and is a positive value when the inflow gas temperature is lower than the target temperature. The "calorific value" is the calorific value of the reducing agent in NSR4, and for example, combustion heat per unit mass of HC in the exhaust gas can be used. The combustion heat of HC in the exhaust gas may be represented by, for example, the value of a compound selected in advance, or may be an average value according to the composition of HC components in the fuel. The "calorific value" may take into consideration the combustion heat per unit mass of CO in the exhaust gas, depending on the properties of the fuel, for example.

In equation (2), " _O2 molecular weight" is the molecular weight of _O2 in the exhaust gas. "Reducing agent molecular weight" is the molecular weight of HC and CO in the exhaust gas. The molecular weights of HC and CO in the exhaust gas may be represented, for example, by the molecular weights of compounds selected in advance, or may be the average molecular weights according to the composition of the HC components in the fuel. " _O2 molecular weight" and "reducing agent molecular weight" are not given a particular coefficient, but may be multiplied by a coefficient according to the reaction molar ratio in the oxidation reaction of the reducing agent, which is determined in advance by a compatibility test. A factor may be multiplied.

In formulas (1) and (2), the "specific heat", "target temperature", "calorific value", " _O2 molecular weight", and "reducing agent molecular weight" are parameters stored in advance in the ROM of the ECU 10, for example. may be

The inflow O ₂ amount adjustment unit 17 adjusts the O ₂ amount so that, for example, the O ₂ amount increases as the COHC ratio increases. The inflow O ₂ amount adjustment unit 17 here may calculate a correction coefficient for correcting the basic target O ₂ amount based on the COHC ratio, as shown in FIG. 2, for example. FIG. 2 is a diagram showing an example of the relationship between the COHC ratio and the correction coefficient. In FIG. 2, the horizontal axis indicates the COHC ratio, and the vertical axis indicates the correction coefficient. The correction coefficient is a positive value, and is "1", for example, when the COHC ratio is 0 (that is, when the exhaust gas does not contain CO). The correction coefficient becomes larger than "1" as the COHC ratio increases. Therefore, the inflow _O2 amount adjustment unit 17 multiplies the basic target _O2 amount by the correction coefficient as shown in the above equation (3), thereby adjusting the target O2 amount so that the _O2 amount increases as the COHC ratio increases. ₂ Calculate the amount.

The inflow _O2 amount adjustment unit 17 adjusts the _O2 amount so that the _O2 amount in the exhaust gas flowing into the NSR 4 during regeneration control reaches the calculated target _O2 amount. The inflow _O.sub.2 amount adjusting unit 17 adjusts the _O.sub.2 amount by controlling the EGR device 2c so that the _O.sub.2 amount in the regeneration control becomes the target _O.sub.2 amount, for example. More specifically, the inflow _O2 amount adjustment unit 17 adjusts the actual _O2 amount in the cylinder during regeneration control based on the intake air amount, the EGR amount (EGR rate), the fuel injection amount into the cylinder, and the estimated combustion fuel amount. amount may be calculated. The estimated combustion fuel amount means the amount of fuel that is estimated to have burned out of the fuel injection amount injected into the cylinder. The estimated combustion fuel amount can be calculated, for example, based on a map or the like using the estimated in-cylinder temperature (described above) and the estimated in-cylinder pressure as arguments. In this case, the inflow O ₂ amount adjustment unit 17 calculates the estimated in-cylinder pressure based on, for example, the injection timing calculated by the engine state acquisition unit 11, the compression ratio of the engine 2, the charging efficiency, the intake air temperature, the water temperature, etc. You may For example, when the NSR 4 is provided with a temperature sensor, learning of the parameter related to the calculation of the estimated combustion fuel amount may be performed according to the actual temperature change of the NSR 4 based on the detection result of the temperature sensor. . The inflow _O2 amount adjusting unit 17 adjusts the control amount of the EGR device 2c (for example, the opening degree of the EGR valve or the driving amount of the EGR valve driving unit) so that the actual _O2 amount becomes the target _O2 amount, and the EGR The amount (EGR rate) may be adjusted.

The inflow O ₂ amount adjustment unit 17 reduces the amount of EGR in the engine 2 when the temperature T of the NSR 4 is lower than the target temperature during regeneration control, compared to when the temperature T of the NSR 4 is equal to or higher than the target temperature. It controls the EGR device 2c. As an example, when the operating conditions of the engine 2 are the same, the basic EGR amount when the regeneration control is not executed is used as the EGR amount when the temperature T of the NSR 4 is equal to or higher than the target temperature during the regeneration control. may be In this case, if the temperature T of the NSR 4 is lower than the target temperature during the regeneration control, the inflow O ₂ amount adjusting unit 17 may control the EGR device 2c so that the EGR amount is reduced below the basic EGR amount. good. As a result, the in-cylinder fresh air amount increases in accordance with the decrease in the in-cylinder EGR amount, so the amount of _O2 in the exhaust gas flowing into the NSR 4 increases. As a result, the temperature T of the NSR 4 rises due to an increase in oxidation heat generation in the NSR 4 .

Note that the inflow O ₂ amount adjusting unit 17 may control the EGR device 2c so as to return the EGR amount to the basic EGR amount (EGR amount cancellation of weight loss).

[Example of arithmetic processing by ECU 10]
Next, an example of arithmetic processing by the ECU 10 will be described. FIG. 3 is a flowchart illustrating a catalyst temperature control process. The processing shown in FIG. 3 is repeatedly executed, for example, at predetermined calculation cycles during regeneration control.

As shown in FIG. 3, in S01, the ECU 10 acquires the engine state using the engine state acquisition unit 11. FIG. The engine state acquisition unit 11 acquires, for example, the intake air amount, the engine speed, the basic injection fuel amount, the in-cylinder air-fuel ratio correction coefficient, the estimated deposition amount, and the basic EGR amount as the engine state.

In S<b>02 , the ECU 10 uses the inflow O ₂ amount adjusting section 17 to set the target temperature. The inflow O ₂ amount adjusting unit 17 sets the target temperature to, for example, the lower limit temperature of the regeneration activation temperature range. In S<b>03 , the ECU 10 uses the air-fuel ratio control section 16 to set the target air-fuel ratio. The air-fuel ratio control unit 16 sets the target air-fuel ratio, for example, so that the air-fuel ratio is richer than the downstream air-fuel ratio when the regeneration control is not executed. In S<b>04 , the ECU 10 uses the air-fuel ratio control section 16 to adjust the downstream air-fuel ratio. The air-fuel ratio control unit 16 adjusts the downstream air-fuel ratio acquired based on the detection signal from the air-fuel ratio sensor 9, for example, by adjusting the injected fuel amount of the post injection.

In S<b>05 , the ECU 10 mainly uses the inflow O ₂ amount adjusting section 17 to calculate the target O ₂ amount. Specifically, the ECU 10 performs the processing of FIG. FIG. 4 is a flowchart illustrating the target _O2 amount calculation process of FIG.

As shown in FIG. 4, in S11, the ECU 10 acquires the inflow gas temperature by means of the inflow _O2 amount adjusting section 17. As shown in FIG. The inflow O ₂ amount adjustment unit 17 acquires the inflow gas temperature based on the detection signal from the upstream temperature sensor 6, for example. In S<b>12 , the ECU 10 acquires the exhaust gas flow rate using the exhaust gas flow rate acquiring section 13 . The exhaust gas flow rate acquisition unit 13 calculates the exhaust gas flow rate based on the amount of intake air, for example. At S<b>13 , the ECU 10 uses the inflow O ₂ amount adjusting section 17 to calculate the temperature deviation. The inflow O ₂ amount adjustment unit 17 calculates the temperature deviation based on the inflow gas temperature and the target temperature. In S14, the ECU 10 uses the inflow _O2 amount adjusting section 17 to calculate the basic target _O2 amount. The inflow O ₂ amount adjustment unit 17 calculates the basic target O ₂ amount using, for example, the above equations (1) and (2).

In S<b>15 , the ECU 10 acquires the COHC ratio using the ratio acquisition unit 14 . The ratio acquisition unit 14 calculates the basic COHC ratio and the COHC ratio calculated using, for example, a map defined according to the engine speed and the basic injection fuel amount and a map defined according to the in-cylinder air-fuel ratio correction coefficient. The COHC ratio is calculated by multiplying by the correction coefficient. In S16, the ECU 10 causes the inflow _O2 amount adjusting section 17 to calculate a correction coefficient for correcting the basic target _O2 amount. The inflow O ₂ amount adjustment unit 17 calculates a correction coefficient based on, for example, the COHC ratio. In S<b>17 , the ECU 10 uses the inflow O ₂ amount adjusting section 17 to calculate the target O ₂ amount. The inflow O ₂ amount adjustment unit 17 calculates the target O ₂ amount using, for example, the above equation (3). After that, the ECU 10 ends the processing of FIG. 4 and proceeds to S06 of FIG.

In S<b>06 , the ECU 10 mainly uses the inflow O ₂ amount adjusting section 17 to adjust the O ₂ amount. Specifically, the ECU 10 performs the process of FIG. FIG. 5 is a flowchart illustrating the _O2 amount adjustment process of FIG.

As shown in FIG. 5, in S21, the ECU 10 determines whether or not the temperature T of the NSR 4 is lower than the target temperature using the catalyst temperature acquiring section 12 and the inflow _O2 amount adjusting section 17. The catalyst temperature acquisition unit 12 estimates the temperature T of the NSR 4 (for example, the upper stage temperature of the NSR 4) based on, for example, the inflow gas temperature detected by the upstream temperature sensor 6, the downstream temperature detected by the downstream temperature sensor 7, and the engine state. do. The inflow O ₂ amount adjustment unit 17 determines, for example, whether or not the temperature T of the NSR 4 estimated by the catalyst temperature acquisition unit 12 is lower than the target temperature.

If the inflow _O2 amount adjusting unit 17 determines that the temperature T of the NSR 4 is lower than the target temperature (S21: YES), the ECU 10 causes the inflow _O2 amount adjusting unit 17 to reduce the EGR amount in S22. . The inflow O ₂ amount adjusting section 17 controls the EGR device 2c, for example, so that the EGR amount is reduced from the basic EGR amount. After that, the ECU 10 terminates the processing of FIG. 5 and the processing of FIG.

On the other hand, if the inflow _O2 amount adjusting unit 17 determines that the temperature T of the NSR 4 is equal to or higher than the target temperature (S21: NO), the ECU 10 causes the inflow _O2 amount adjusting unit 17 to reduce the EGR amount in S23. is canceled. The inflow O ₂ amount adjusting section 17 controls the EGR device 2c, for example, so as to return the EGR amount to the basic EGR amount. After that, the ECU 10 terminates the processing of FIG. 5 and the processing of FIG.

[Example of operation of exhaust purification device 1]
As an example, the temperature T of the NSR 4 changes as shown in FIG. 7 by the exhaust purification device 1 described above. FIG. 7 is a timing chart showing catalyst temperatures in the operation example of FIG. In FIG. 7, the horizontal axis is time and the vertical axis is temperature T of NSR4. In FIG. 7, the solid line indicates the upper temperature of the NSR4, and the dashed line indicates the lower temperature of the NSR4.

In the example of FIG. 7, the regeneration control is started at time t1, and the injector 2b is controlled by the air-fuel ratio control section 16 so that the downstream air-fuel ratio becomes the target air-fuel ratio. As a result, the downstream air-fuel ratio is maintained near the target air-fuel ratio AF2 (see FIG. 6). At time t1, the upper stage temperature of the NSR 4 is lower than the target temperature T1 (640° C.), so the inflow O ₂ amount adjusting section 17 reduces the EGR amount. As a result, heat generated by oxidation increases in the NSR 4, so that the temperature T of the NSR 4 rises (t1 to t2 in FIG. 7). At time t2 in FIG. 7, the temperature T of the NSR 4 reaches approximately 640° C., and the temperature T of the NSR 4 exceeds the target temperature, so the reduction of the EGR amount is canceled. The target air-fuel ratio (AF2 in FIG. 6) in the exhaust purification device 1 may be on the richer side than the rich air-fuel ratio (AF0 in FIG. 8) of the conventional method.

Here, conventional methods are shown in FIGS. 8 and 9. FIG. FIG. 8 is a timing chart showing an operation example of a conventional exhaust purification device. In FIG. 8, the horizontal axis indicates time, and the solid line indicates the downstream air-fuel ratio. The right vertical axis indicates A/F of the downstream air-fuel ratio, and the left vertical axis indicates the amount of SOx released from the catalyst. FIG. 9 is a timing chart showing the catalyst temperature in the operation example of FIG. In FIG. 9, the horizontal axis is time and the vertical axis is temperature of the catalyst. In FIG. 9, the solid line indicates the temperature at the upper stage of the catalyst, and the dashed line indicates the temperature at the lower stage of the catalyst.

As shown in FIG. 8, in the case of the conventional method, a rich air-fuel ratio in regeneration control may cause excessive heat generation relative to the target temperature of the catalyst. Therefore, in order to balance the energy in the catalyst, the air-fuel ratio alternates between rich and lean. Lean in the conventional method means, for example, A/F of 20 or more. When the air-fuel ratio is changed in this way, as shown in FIG. 9, the amount of _O2 in the exhaust gas flowing into the catalyst changes greatly, and the catalyst temperature changes greatly and periodically. It is difficult to adjust the temperature of the catalyst so that the temperature is suitable for

In particular, since the amplitude of change in catalyst temperature tends to be larger on the front-stage side of the catalyst than on the rear-stage side, the temperature on the front-stage side of the catalyst drops too much and the catalyst temperature required for regeneration of the catalyst (example in FIG. 9) 640° C.). As a result, the amount of SOx emitted from the catalyst (broken line in FIG. 8) periodically decreases as the catalyst temperature periodically decreases. In other words, the large temperature variation between the front-stage side and the rear-stage side of the catalyst reduces the regeneration efficiency of the catalyst as a whole, and it takes a long time to sufficiently regenerate the catalyst.

In this respect, according to the exhaust purification system 1, the temperature T of the NSR 4 is increased as shown in FIG. Further, since the target air-fuel ratio in regeneration control is not alternately rich and lean (see FIG. 6), the temperature T of the NSR 4 in FIG. , the temperature continues to be above the target temperature. As a result, the SOx reduction reaction can be continuously caused in the NSR4, so that the SOx can be efficiently released from the NSR4. For example, it is possible to achieve a SOx release amount (broken line in FIG. 6) that monotonically increases up to a certain peak value and transitions like a first-order lag attenuation curve after the peak value.

[Action and effect of the exhaust purification device 1]
In the exhaust purification device 1 described above, the injector 2b is controlled by the air-fuel ratio control section 16 so that the downstream air-fuel ratio becomes the target air-fuel ratio during regeneration control. For example, when the downstream air-fuel ratio is in a reducing atmosphere, the amount of exothermic reaction in NSR4 is controlled by the amount of _O2 in the exhaust gas. Therefore, the amount of heat generated by NSR4 can be adjusted by adjusting the amount of _O2 . Therefore, by adjusting the amount of O ₂ in the exhaust gas flowing into the NSR 4 so that the temperature T of the NSR 4 becomes the target temperature, the amount of heat generated in the NSR ₄ can be adjusted. . As a result, the temperature T of the NSR 4 in the regeneration control can be appropriately adjusted while suppressing the temperature fluctuation of the NSR 4, as compared with the case where the rich and lean air-fuel ratios of the exhaust gas are alternately repeated, for example. Also, the EGR device 2c can be used to easily adjust the amount of O ₂ in the exhaust gas.

In addition, since the calorific value of CO is smaller than the calorific value of HC, for example, in order to generate a constant calorific value in the NSR4, the larger the ratio of CO and HC in the exhaust gas, the more the amount of _O2 to be reacted with CO. becomes larger. Therefore, in the exhaust purification device 1, the O ₂ amount is adjusted by the inflow O ₂ amount adjustment unit 17 so that the O ₂ amount increases as the ratio of CO and HC increases, so that the temperature of the NSR 4 in regeneration control T can be adjusted more appropriately.

The exhaust purification device 1 includes an upstream temperature sensor 6 that acquires the inflow gas temperature, which is the temperature of the exhaust gas that flows into the NSR 4, and an exhaust gas flow rate acquisition unit 13 that acquires the exhaust gas flow rate, which is the flow rate of the exhaust gas flowing through the NSR 4. and further comprising: The inflow _O2 amount adjustment unit 17 calculates a target _O2 amount, which is a target value of the _O2 amount, based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate, and adjusts the O2 amount so that the _O2 amount becomes the target _O2 amount. to adjust the amount of _O2 . Thus, by using the target _O2 amount calculated based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate, for example, as a prospective control amount, it is possible to improve the controllability of the adjustment of the _O2 amount.

In addition, in the exhaust emission control device 1, since the regeneration efficiency of the NSR 4 as a whole can be improved, the regeneration time of the NSR 4 can be shortened. As a result of being able to shorten the regeneration control time, it is possible to suppress the time during which the temperature T of the NSR 4 is high (suppress the increase in thermal history), so that the deterioration (sintering) of the noble metal supported on the NSR 4 can be suppressed. can.

[Modification]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. The present invention can be embodied in various forms with various modifications and improvements based on the knowledge of those skilled in the art, including the embodiment described above.

In the above embodiment, the inflow O ₂ amount adjusting section 17 controls the EGR device 2c to adjust the O ₂ amount, but the O ₂ amount may be adjusted by controlling the injector 2b. For example, when the temperature T of the NSR 4 is lower than the target temperature, the inflow O ₂ amount adjusting section 17 may retard the injection timing compared to when the temperature T of the NSR 4 is equal to or higher than the target temperature. In this case, the air-fuel ratio control unit 16 controls the injector 2b so that the post-injection is performed at the retarded injection timing at which the fuel is combusted in the expansion stroke of the engine 2 . Specifically, the injection timing at which fuel burns during the expansion stroke of the engine 2 is, as shown in FIG. It means an injection timing that is more advanced than the injection timing that takes the maximum value. Within such an injection timing range, the fuel is burned during the expansion stroke of the engine 2, so the more retarded the injection timing, the higher the inflow gas temperature.

The O ₂ amount adjustment process corresponding to S06 in FIG. 3 in the modification will be described in detail. FIG. 11 is a flowchart illustrating the _O2 amount adjustment process of FIG. As shown in FIG. 11, in S31, the ECU 10 determines whether or not the temperature T of the NSR 4 is lower than the target temperature using the catalyst temperature acquiring section 12 and the inflow _O2 amount adjusting section 17. The inflow O ₂ amount adjustment unit 17 determines, for example, whether or not the temperature T of the NSR 4 estimated by the catalyst temperature acquisition unit 12 is lower than the target temperature.

If the inflow _O2 amount adjusting section 17 determines that the temperature T of the NSR 4 is lower than the target temperature (S31: YES), the ECU 10 causes the inflow _O2 amount adjusting section 17 to retard the injection timing in S32. conduct. The inflow O ₂ amount adjusting unit 17 controls the injector 2b so that the post-injection is performed at an injection timing that is retarded from the injection timing when the temperature T of the NSR 4 is equal to or higher than the target temperature, for example. After that, the ECU 10 terminates the processing of FIG. 11 and the processing of FIG.

On the other hand, if the inflow _O2 amount adjusting section 17 determines that the temperature T of the NSR 4 is equal to or higher than the target temperature (S31: NO), the ECU 10 causes the inflow _O2 amount adjusting section 17 to retard the injection timing in S33. Release the angle (advance the retarded injection timing). The inflow O ₂ amount adjusting unit 17 controls the injector 2b, for example, so as to return the injection timing of the post injection to the injection timing when the temperature T of the NSR 4 is equal to or higher than the target temperature. After that, the ECU 10 terminates the processing of FIG. 11 and the processing of FIG.

In such adjustment of the O ₂ amount by retarding the injection timing, the fuel with the retarded injection timing is burned in the expansion stroke, thereby increasing the inflow gas temperature (exhaust temperature). Therefore, the amount of heat generated by the oxidation reaction in the NSR 4 is small, so the amount of O ₂ in the exhaust gas to be reacted in the NSR 4 can be reduced. Note that the control of the injector 2b may be used together with the control of the _O2 supply unit to adjust the _O2 amount, or may not be used together.

Note that, when the temperature T of the NSR 4 is lower than the target temperature, the inflow O ₂ amount adjusting section 17 may reduce the injection fuel amount compared to when the temperature T of the NSR 4 is equal to or higher than the target temperature. In this case, as shown in FIG. 12, as the amount of injected fuel (in-cylinder injection amount) is reduced, the in _- cylinder fresh air amount used for combustion in the cylinder is reduced. ( _O2 concentration) increases. In this case, the air-fuel ratio control unit 16 may control the injector 2b to additionally inject fuel that does not burn during the expansion stroke of the engine 2 so that the downstream air-fuel ratio becomes the target air-fuel ratio.

_In the above embodiment, the EGR device 2c is controlled to adjust the _O2 amount. good. For example, when the temperature T of the NSR 4 is lower than the target temperature during regeneration control, the inflow O ₂ amount adjusting unit 17 increases the in-cylinder fresh air amount compared to when the temperature T of the NSR 4 is equal to or higher than the target temperature. The intake device 2a may be controlled as follows. Other configurations may function as the O ₂ supply unit as long as the O ₂ amount can be changed. For example, a variable valve timing mechanism, a variable valve lift mechanism, a secondary air device provided in the exhaust passage 3, or the like may function as the _O2 supply unit.

In the above embodiment, the inflow O ₂ amount adjustment unit 17 uses the COHC ratio calculated by the ratio acquisition unit 14 to adjust the O ₂ amount so that the O ₂ amount increases as the COHC ratio increases. , but not limited to. When using the COHC ratio, the inflow O ₂ amount adjustment unit 17 does not necessarily have to increase the O ₂ amount as the COHC ratio increases. For example, the COHC ratio may be the reciprocal of the above embodiment example. Specifically, the COHC ratio is a ratio obtained by dividing the HC concentration (g/s) in the exhaust gas flowing into the NSR 4 by the CO concentration (g/s) in the exhaust gas flowing into the NSR 4. good. In this case, the inflow O ₂ amount adjustment unit 17 may adjust the O ₂ amount so that the O ₂ amount increases as the COHC ratio decreases. Alternatively, the numerator or denominator of the COHC ratio may include parameters other than the HC concentration or the CO concentration (eg correction factor, proportionality constant, etc.). Note that the inflow O ₂ amount adjustment unit 17 may adjust the O ₂ amount without using the COHC ratio.

_In the above embodiment, the inflow _O2 amount adjustment unit 17 calculates the target _O2 amount and adjusts the _O2 amount so as to achieve the calculated target _O2 amount. good too. In this case, the inflow O ₂ amount adjustment unit 17 adjusts the intake device 2a, the EGR device 2c, the injectors, and the like based on a parameter or a map in which the control amount corresponding to the temperature deviation between the inflow gas temperature and the target temperature is stored in advance, for example. The amount of O ₂ may be adjusted by controlling 2b and the like.

In the above embodiment, the upstream temperature sensor 6 is used as an example of the inflow gas temperature acquisition unit, but the inflow gas temperature may be acquired using the estimation process in the ECU 10 as the inflow gas temperature acquisition unit.

In the above embodiment, the air-fuel ratio sensor 9 is used as the air-fuel ratio acquisition unit, but the estimated downstream air-fuel ratio may be acquired using the estimation processing in the ECU 10 as the air-fuel ratio acquisition unit.

In the above embodiment, the injector 2b of the engine 2 functions as a reducing agent supply unit, but an addition valve that functions as a reducing agent supply unit may be arranged in the exhaust flow path 3, for example. In this case, the reducing agent can be supplied to the NSR 4 while suppressing changes in the combustion state in the cylinder, which is advantageous during idling, for example. Alternatively, CO, _H2 , or the like may be supplied as a reducing agent instead of supplying fuel. Also, although the post-injection was exemplified as the fuel injection of the injector 2b for adjusting the _O2 amount, it is not limited to this.

In the above embodiment, the process of calculating the target O ₂ amount based on the COHC ratio is performed by the inflow O ₂ amount adjustment unit 17 by feedforward, but may be performed by feedback. For example, based on the deviation between the downstream temperature detected by the downstream temperature sensor 7 and the target temperature, the difference between the COHC ratio calculated by the ratio acquisition unit 14 and the actual COHC ratio of the exhaust gas flowing into the NSR 4 is compensated. , the COHC ratio calculated by the ratio acquisition unit 14 may be corrected. In this case, for example, when the downstream temperature is higher than the target temperature by a predetermined temperature or more, the actual COHC ratio is assumed to be smaller than the COHC ratio calculated by the ratio acquisition unit 14, and the target _O2 amount is calculated. The COHC ratio to be used may be smaller than the COHC ratio calculated by the ratio acquisition unit 14 . Thereby, the controllability of adjusting the O ₂ amount can be further improved.

In the above embodiment, the regeneration control execution unit 15 executes regeneration control when the estimated deposit amount exceeds the predetermined deposit amount threshold value. It may be determined whether or not to execute the control.

In the above embodiment, no other catalyst is provided upstream of the NSR4, but for example, a DOC [Diesel Oxidation Catalyst] may be provided upstream of the NSR4. In this case, the upstream temperature sensor 6 may be provided upstream of the DOC. Also, the influence of heat generated by the DOC and heat dissipation from the DOC to the NSR4 may be taken into consideration, and correction can be made using a known technique.

In the above embodiment, the catalyst temperature acquisition unit 12 acquires the temperature T of the NSR 4 by estimation, but the temperature of the NSR 4 may be acquired directly using a temperature sensor provided on the carrier of the NSR 4, for example.

In the above embodiment, the upper temperature of the NSR4 is used as the temperature T of the NSR4, but it is not limited to this. As the temperature T of the NSR 4, the middle stage temperature or the lower stage temperature may be used, or at least two average values of the upper stage temperature, the middle stage temperature and the lower stage temperature may be used. The average value may take into account the weighting of the upper, middle and lower temperatures.

Although the engine 2 is a diesel engine in the above embodiment, it may be another internal combustion engine such as a gasoline engine.

Reference Signs List 1 Exhaust purification device 2 Engine (internal combustion engine) 2b Injector (reducing agent supply unit) 2c EGR device 3 Exhaust flow path 4 NSR (catalyst) 6 Upstream temperature sensor (inflow gas temperature acquisition unit) 9 air-fuel ratio sensor (air-fuel ratio acquisition unit) 10 ECU 11 engine state acquisition unit 12 catalyst temperature acquisition unit 13 exhaust gas flow rate acquisition unit 14 ratio acquisition unit 16 ... air-fuel ratio control section, 17 ... inflow _O2 amount adjustment section.

Claims (4)

An exhaust purification device comprising a catalyst provided on an exhaust flow path of an internal combustion engine and executing regeneration control for regenerating the catalyst by supplying a reducing agent to the catalyst,
a reducing agent supply unit that supplies a reducing agent to the catalyst;
a catalyst temperature acquisition unit that acquires the temperature of the catalyst;
an air-fuel ratio acquisition unit that acquires a downstream air-fuel ratio, which is the air-fuel ratio of the exhaust gas on the downstream side of the catalyst;
an air-fuel ratio control unit that sets a target air-fuel ratio, which is a target value of the downstream air-fuel ratio during the regeneration control, and controls the reducing agent supply unit so that the downstream air-fuel ratio becomes the target air-fuel ratio;
Based on a target temperature, which is a target value of the temperature of the catalyst during the regeneration control, and the temperature of the catalyst, the amount of _O2 in the exhaust gas flowing into the catalyst so that the temperature of the catalyst reaches the target temperature. an inflow O ₂ amount adjustment unit that adjusts the
an inflow gas temperature acquisition unit that acquires an inflow gas temperature, which is the temperature of the exhaust gas flowing into the catalyst;
an exhaust gas flow rate acquisition unit that acquires an exhaust gas flow rate that is the flow rate of the exhaust gas flowing through the catalyst;
with
The inflow _O2 amount adjustment unit
controlling an EGR device of the internal combustion engine so that when the temperature of the catalyst is lower than the target temperature, compared to when the temperature of the catalyst is equal to or higher than the target temperature, the amount of EGR in the internal combustion engine is reduced ;
A target _O2 amount , which is a target value of the O2 _amount , is calculated based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate, and the O2 amount is adjusted so that the _O2 amount becomes the target O2 _amount . Exhaust purification device that adjusts the amount of ₂ . An exhaust purification device comprising a catalyst provided on an exhaust flow path of an internal combustion engine and executing regeneration control for regenerating the catalyst by supplying a reducing agent to the catalyst,
a reducing agent supply unit that supplies a reducing agent to the catalyst;
a catalyst temperature acquisition unit that acquires the temperature of the catalyst;
an air-fuel ratio acquisition unit that acquires a downstream air-fuel ratio, which is the air-fuel ratio of the exhaust gas on the downstream side of the catalyst;
an air-fuel ratio control unit that sets a target air-fuel ratio, which is a target value of the downstream air-fuel ratio during the regeneration control, and controls the reducing agent supply unit so that the downstream air-fuel ratio becomes the target air-fuel ratio;
Based on a target temperature, which is a target value of the temperature of the catalyst during the regeneration control, and the temperature of the catalyst, the amount of _O2 in the exhaust gas flowing into the catalyst so that the temperature of the catalyst reaches the target temperature. an inflow O ₂ amount adjustment unit that adjusts the
a ratio acquisition unit that acquires the ratio of CO and HC in the exhaust gas flowing into the catalyst;
with
The inflow O ₂ amount adjustment unit adjusts the O ₂ amount so that the O ₂ amount increases as the ratio increases. an inflow gas temperature acquisition unit that acquires an inflow gas temperature, which is the temperature of the exhaust gas flowing into the catalyst;
an exhaust gas flow rate acquisition unit that acquires an exhaust gas flow rate that is the flow rate of the exhaust gas flowing through the catalyst,
_The inflow _O2 amount adjustment unit calculates a target _O2 amount, which is a target value of the _O2 amount, based on the target temperature, the inflow gas temperature, and the exhaust gas flow rate. The exhaust emission control system according to claim ₂ , wherein the _O2 amount is adjusted so as to be the O2 amount. The reducing agent supply unit is an injector that injects fuel into a cylinder of the internal combustion engine,
The air-fuel ratio control unit controls the injector so as to perform fuel injection at an injection timing at which the fuel burns in an expansion stroke of the internal combustion engine,
The inflow O ₂ amount adjusting unit retards the injection timing when the temperature of the catalyst is lower than the target temperature compared to when the temperature of the catalyst is equal to or higher than the target temperature. 4. The exhaust purification device according to any one of 3.

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