JP2015025434A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of surely purifying exhaust even when a temperature of a catalyst is low.SOLUTION: A lean operation is performed so that an air-fuel ratio becomes a lean air-fuel ratio, when an engine water temperature is 0°C or more, and a multifunctional catalyst temperature Tm is less than a second prescribed temperature. A slightly-rich operation is performed so that the air-fuel ratio becomes slightly rich, when the multifunctional catalyst temperature Tm is the second prescribed temperature or more and less than a third prescribed temperature. A PM combustion operation is performed so that PM accumulated on the multifunctional catalyst is burnt, when a multifunctional catalyst PM accumulation amount is a threshold value or more, and the multifunctional catalyst temperature Tm is a fifth prescribed temperature or more.

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine, and more particularly to control of an air-fuel ratio.

Conventionally, in gasoline engines that operate near the stoichiometric air-fuel ratio, hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc. in the exhaust are exhausted in the engine operating region near the stoichiometric air-fuel ratio. A three-way catalyst that can be purified is provided.
On the other hand, a gasoline lean burn engine in which the air-fuel ratio is a lean air-fuel ratio has been developed as a gasoline engine for the purpose of improving fuel efficiency.

In such a gasoline lean burn engine in which the main operating region is controlled at a lean air-fuel ratio, it is difficult to sufficiently purify NOx in the exhaust gas with a three-way catalyst. This is because the NOx purification capacity of the three-way catalyst is poor at a lean air-fuel ratio.
Therefore, in Patent Document 1, an upstream side three-way catalyst and a downstream side three-way catalyst are provided, and further, platinum (Pt), rhodium (Rh), palladium, between the upstream side three-way catalyst and the downstream side three-way catalyst. Equipped with a catalyst for exhaust purification consisting of a lower layer containing a noble metal such as (Pd) and zeolite and an upper layer containing an alkali metal or alkaline earth metal and a noble metal, and is emitted during engine operation at a lean air-fuel ratio of a gasoline lean burn engine HC, CO and NOx are purified.

JP 2002-273232 A

As described above, in the exhaust gas purification catalyst disclosed in Patent Document 1, an exhaust gas purification catalyst for trapping HC and NOx is provided between the upstream side three-way catalyst and the downstream side three-way catalyst. The engine exhaust is purified.
However, the exhaust purification catalyst of Patent Document 1 is not preferable because the exhaust gas may not be sufficiently purified if the catalyst temperature does not rise immediately after the engine is started.

  The present invention has been made in order to solve such problems mainly in a gasoline engine operated near the stoichiometric air-fuel ratio. The object of the present invention is to ensure exhaust gas even if the temperature of the catalyst is low. It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine that can purify gas.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, HC is adsorbed when disposed in an exhaust passage of the internal combustion engine and the temperature of the catalyst layer is lower than a first predetermined temperature, A first catalyst that desorbs HC when the temperature is equal to or higher than a first predetermined temperature; a second catalyst that is disposed in the exhaust passage and adsorbs NOx when the temperature of the catalyst layer is lower than a second predetermined temperature; A third catalyst disposed in the exhaust passage downstream of the first catalyst and the second catalyst and having a three-way catalyst function that is activated when the temperature of the catalyst layer is equal to or higher than the second predetermined temperature; Air-fuel ratio control means for controlling the fuel ratio, wherein the air-fuel ratio control means makes the air-fuel ratio leaner than the stoichiometric air-fuel ratio until the temperature of the first catalyst reaches the second predetermined temperature. Features.

  In the exhaust gas purification apparatus for an internal combustion engine according to claim 2, in claim 1, the second catalyst is a catalyst that desorbs adsorbed NOx when the temperature of the catalyst layer is equal to or higher than the second predetermined temperature. And the air-fuel ratio control means sets the air-fuel ratio to a slightly rich air-fuel ratio that is slightly richer than the stoichiometric air-fuel ratio when the temperature of the second catalyst is equal to or higher than the second predetermined temperature. And

  According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect, wherein the particulate filter that collects particulate matter discharged from the internal combustion engine in the exhaust passage of the internal combustion engine; A deposition amount detecting means for detecting a deposition amount of the particulate matter collected by the particulate filter, and the air-fuel ratio control means has a function of controlling the temperature of the particulate filter, and the deposition When the accumulation amount detected by the amount detection means is equal to or higher than a threshold value, the temperature of the particulate filter is set to be equal to or higher than a PM combustion temperature that is a temperature at which the particulate matter is combusted.

  According to the invention of claim 1, until the temperature of the catalyst layer reaches the first predetermined temperature, the hydrocarbons (HC) and nitrogen oxides (NOx) in the exhaust discharged from the internal combustion engine are the first It is adsorbed by the catalyst and the second catalyst. Further, until the temperature of the catalyst layer of the first catalyst reaches the second predetermined temperature, the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio, so that HC desorbed from the first catalyst is located downstream of the first catalyst. The third catalyst having the three-way catalyst function provided can be purified with higher efficiency. Further, since the second catalyst can adsorb NOx if the temperature of the catalyst layer is lower than the second predetermined temperature, the NOx emission can be suppressed even if the air-fuel ratio is controlled to be lean.

Therefore, even if the temperature of each catalyst is a low temperature (less than 200 ° C.) at which the function of the three-way catalyst cannot be fully exhibited, the exhaust purification efficiency can be improved.
According to the second aspect of the present invention, even if NOx adsorbed by the second catalyst is desorbed, the air-fuel ratio is adjusted to be slightly rich in which the NOx reduction reaction easily proceeds, so that it is provided downstream of the second catalyst. In addition, NOx can be efficiently purified by the third catalyst having a three-way catalyst function.

  Therefore, when the temperature of the third catalyst having the three-way catalyst function is lower than the second predetermined temperature at which NOx cannot be purified, NOx is adsorbed to the second catalyst, and the third catalyst having the three-way catalyst function is used. When the temperature is equal to or higher than a second predetermined temperature at which NOx can be purified, NOx is purified by a third catalyst having a three-way catalyst function, thereby reliably purifying exhaust gas even if the temperature of each catalyst is low. be able to.

  According to the invention of claim 3, the particulate filter is provided in the exhaust passage, and when the amount of particulate matter (PM) collected in the particulate filter exceeds a threshold value, the temperature of the particulate filter is increased. The exhaust temperature can be reliably purified by collecting and burning PM discharged from the internal combustion engine.

1 is a schematic configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied. It is a figure which shows the schematic structure of a multifunctional catalyst. It is a figure which shows an example of the driving | running state of an engine, the temperature of a multifunctional catalyst, and the state of each catalyst layer in time series. It is a figure which shows the detail of the air fuel ratio control in a light rich operation in a time series. It is a part of flowchart of the air fuel ratio and temperature control of a multifunctional catalyst which an electronic control unit performs. It is the remainder of the flowchart of the air-fuel ratio and temperature control of the multifunction catalyst which an electronic control unit performs.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied. FIG. 2 is a diagram showing a schematic configuration of the multifunctional catalyst. The arrows in FIG. 2 indicate the flow direction of the exhaust gas. FIG. 3 is a diagram showing an example of the operating state of the engine, the temperature of the multifunctional catalyst, and the state of each catalyst layer in time series. The vertical axis in FIG. 3 shows, from the top, the air-fuel ratio, the purification range of HC, CO, and NOx in the three-way catalyst and the multifunctional catalyst, the state of each catalyst in the multifunctional catalyst, and the multifunctional catalyst temperature Tm. The HC, CO, NOx purification range and the state of each catalyst of the multifunctional catalyst in the three-way catalyst and multifunctional catalyst in FIG. 3 are the three-way catalyst temperature or the multifunctional catalyst temperature Tm. In addition, the purifying range of HC, CO and NOx in the multifunctional catalyst and the state of each catalyst layer of the multifunctional catalyst are shown. FIG. 4 is a diagram showing details of the air-fuel ratio control in the light rich operation in time series. The vertical axis in FIG. 4 indicates the air-fuel ratio. In this embodiment, a low temperature HC trap catalyst (corresponding to the first catalyst of the present invention) 27, a low temperature NOx adsorption catalyst (corresponding to the second catalyst of the present invention) 28, and a PM combustion catalyst having a three-way catalyst function. (Corresponding to the third catalyst of the present invention) 29 is integrally formed in the casing 26a of the multifunctional catalyst 26, so that the multifunctional catalyst temperature Tm is the temperature of the catalyst layer supported by each catalyst. Yes.

As shown in FIG. 1, an engine (internal combustion engine) 1 includes an in-cylinder injector (air-fuel ratio control) disposed in a cylinder head 3 so as to face a combustion chamber 10 formed by a cylinder head 3 and a piston 6. Means) A four-cycle in-line four-cylinder gasoline engine performing in-cylinder injection in which fuel is directly injected from the fuel 21 into the combustion chamber 10.
FIG. 1 shows a longitudinal section of one cylinder of the engine 1. In addition, illustration and description are abbreviate | omitted as what has the same structure also about another cylinder.

As shown in FIG. 1, the engine 1 is configured by mounting a cylinder head 3 on a cylinder block 2.
The cylinder block 2 is provided with a water temperature sensor 4 that detects the temperature of cooling water that cools the engine 1. A piston 6 is provided in the cylinder 5 formed in the cylinder block 2 so as to be slidable up and down. The piston 6 is connected to a crankshaft 8 via a connecting rod 7. The cylinder block 2 is provided with a crank angle sensor 9 that detects the rotational speed of the engine 1 and the phase of the crankshaft 8. The combustion chamber 10 is formed by the cylinder head 3, the cylinder 5, and the piston 6.

  The cylinder head 3 is provided with a spark plug 11 so as to face the combustion chamber 10. Further, an intake port 12 is formed in the cylinder head 3 from the combustion chamber 10 toward one side surface of the cylinder head 3, and an exhaust port 13 is formed from the combustion chamber 10 toward the other side surface of the cylinder head 3. Yes. The cylinder head 3 is provided with an intake valve 14 for communicating and blocking the combustion chamber 10 and the intake port 12 and an exhaust valve 15 for communicating and blocking the combustion chamber 10 and the exhaust port 13. Further, an intake camshaft 18 having an intake cam 16 for driving the intake valve 14 and an exhaust camshaft 19 having an exhaust cam 17 for driving the exhaust valve 15 are respectively provided on the upper portion of the cylinder head 3. . An intake manifold 20 is connected to one side surface of the cylinder head 3 so as to communicate with the intake port 12. Further, an in-cylinder injector 21 is provided on the side surface of the cylinder head 3 to which the intake manifold 20 is connected so as to face the combustion chamber 10. On the other hand, an exhaust manifold 23 is connected to the side of the cylinder head 3 opposite to the side connected to the intake manifold 20 so as to communicate with the exhaust port 13.

The in-cylinder injector 21 has a fuel supply pressure variable via a fuel pipe (not shown), a high-pressure pump for supplying high-pressure fuel, and a feed pump for supplying fuel in the fuel tank to the high-pressure pump. Is connected. The in-cylinder injector 21 injects high-pressure fuel into the combustion chamber 10.
An intake pipe (not shown) and an electronic control throttle valve (not shown) for adjusting the intake air flow rate are provided at the intake upstream end of the intake manifold 20. The electronically controlled throttle valve is provided with a throttle position sensor (not shown) that detects the opening degree of the throttle valve. An air flow sensor (not shown) for detecting the intake air flow rate is provided in the intake pipe upstream of the electronic control throttle valve, and an air cleaner (not shown) is provided at the intake upstream end of the intake pipe.

  Further, a three-way catalyst 25 and a multifunctional catalyst 26 are provided at the exhaust downstream end of the exhaust manifold 23 from the upstream side through an exhaust pipe (exhaust passage) 24. An exhaust pipe 24 upstream of the multifunctional catalyst 26 includes an exhaust pressure sensor (deposition amount detection means) 30 that detects the pressure of the exhaust upstream of the multifunctional catalyst 26, and an air-fuel ratio that detects the air-fuel ratio of the exhaust. A sensor 31 is provided. Further, in the exhaust pipe 24 downstream of the multifunctional catalyst 26, an exhaust pressure sensor (deposition amount detecting means) 32 for detecting the pressure of the exhaust downstream of the multifunctional catalyst 26 and an exhaust temperature sensor 33 for detecting the temperature of the exhaust. And are provided.

  The three-way catalyst 25 has a noble metal such as platinum (Pt), rhodium (Rh), palladium (Pd) or the like as a noble metal catalyst on a carrier, an air-fuel ratio is in the vicinity of stoichiometric, and a hydrocarbon when the catalyst is in an active state. It has a function of removing (HC), carbon monoxide (CO), and nitrogen oxide (NOx). In the present invention, when the three-way catalyst is about 300 ° C. to about 400 ° C., it is assumed that the three-way catalyst is in an active start state in which a practically effective exhaust purification performance can be obtained, and the temperature is referred to as the activation temperature. .

As shown in FIG. 2, the multi-functional catalyst 26 is formed by including a low-temperature HC trap catalyst 27, a low-temperature NOx adsorption catalyst 28, and a PM combustion catalyst 29 having a three-way catalyst function in a cylindrical casing 26a. ing.
The low temperature HC trap catalyst 27 is formed by supporting a low temperature HC trap catalyst layer 27d on a gasoline particulate filter (particulate filter) 27a.

The gasoline particulate filter 27a is a so-called wall flow filter in which the upstream side and the downstream side of the passage 27b through which the exhaust gas formed by the porous wall 27c passes are alternately closed by plugs. The gasoline particulate filter 27a has a function of collecting particulate matter (PM) in the exhaust gas.
The low temperature HC trap catalyst layer 27d is a catalyst layer containing an HC trap agent such as zeolite that can trap HC at a low temperature lower than the first predetermined temperature (about 200 ° C.). Note that the zeolite may be a material modified with a transition metal (such as iron (Fe) or silver (Ag)). The low temperature HC trap catalyst layer 27d contains zeolite as an HC trap agent in the catalyst layer, and as shown in FIG. 3, the temperature of the low temperature HC trap catalyst 27, that is, the temperature of the multifunction catalyst 26 is the multifunction catalyst temperature. HC in the exhaust is trapped when Tm is a low temperature lower than a first predetermined temperature (about 200 ° C.), and the temperature of the low-temperature HC trap catalyst 27 is equal to or higher than the first predetermined temperature and lower than the activation temperature of the three-way catalyst. 2 Has a function of desorbing trapped HC when the temperature is lower than a predetermined temperature (about 300 ° C.).

The low temperature NOx adsorption catalyst 28 is formed by supporting a low temperature NOx adsorption catalyst layer 28d on a gasoline particulate filter (particulate filter) 28a.
The gasoline particulate filter 28a has the same configuration as the gasoline particulate filter 27a and has the same function, and therefore detailed description thereof is omitted.
The low temperature NOx adsorption catalyst layer 28d is made of iron (Fe), which is a transition metal capable of adsorbing NOx on a base material such as alumina (Al ₂ O ₃ ) at a low temperature lower than a second predetermined temperature (about 300 ° C.) or It is a catalyst layer containing a NOx adsorbent such as silver (Ag) and a promoter such as cerium oxide (CeO ₂ ) and titanium oxide (TiO ₂ ). The low temperature NOx adsorption catalyst layer 28d contains a transition metal such as Fe or Ag as a NOx adsorbent in the catalyst layer, and as shown in FIG. 3, the temperature of the low temperature NOx adsorption catalyst 28, that is, the temperature of the multifunctional catalyst 26. NOx in the exhaust gas is adsorbed when the multifunctional catalyst temperature Tm is a low temperature lower than a second predetermined temperature (about 300 ° C.), and the temperature of the low-temperature NOx adsorption catalyst 28 is equal to or higher than the second predetermined temperature and a third predetermined temperature ( It has a function of desorbing adsorbed NOx when the temperature is less than about 400 ° C., that is, at a temperature at which NOx purification performance can be obtained in the three-way catalyst.

The PM combustion catalyst 29 having a three-way catalyst function is formed by supporting a PM combustion catalyst layer 29d on a gasoline particulate filter (particulate filter) 29a.
The gasoline particulate filter 29a has the same configuration as the gasoline particulate filters 27a and 28a and has the same function, and therefore detailed description thereof is omitted.
The PM combustion catalyst layer 29d includes a base material such as alumina (Al ₂ O ₃ ), a noble metal such as rhodium (Rh), and a promoter layer such as cerium oxide (CeO ₂ ) and zirconia (ZrO ₂ ). It is. The PM combustion catalyst layer 29d contains a noble metal in the catalyst layer. That is, it functions as a three-way catalyst. Like the three-way catalyst 25, when the air-fuel ratio is in the vicinity of stoichiometric and the catalyst is in an active state, hydrocarbon (HC), carbon monoxide (CO ) And nitrogen oxide (NOx). Furthermore, as shown in FIG. 3, even when the temperature of the PM combustion catalyst layer 29d, that is, the multifunction catalyst temperature Tm, which is the temperature of the multifunction catalyst 26, does not reach the activation temperature (when it is lower than the second predetermined temperature). The air-fuel ratio has a function of purifying HC desorbed from the low-temperature HC trap catalyst 27 by making the air-fuel ratio leaner than stoichiometric. Further, the PM combustion catalyst layer 29d is configured such that the temperature of the low-temperature HC trap catalyst 27, the low-temperature NOx adsorption catalyst 28, and the PM combustion catalyst 29, that is, the multi-function catalyst temperature Tm, which is the temperature of the multi-function catalyst 26, is the three-way catalyst PM combustion. The temperature was set at a fifth predetermined temperature (about 650 ° C.) that easily progressed in a short time, and was collected and deposited by the gasoline particulate filters 27a, 28a, 29a of the low temperature HC trap catalyst 27, the low temperature NOx adsorption catalyst 28, and the PM combustion catalyst 29. It also has a function of purifying CO and the like generated when PM is burned.

  The water temperature sensor 4, the crank angle sensor 9, the exhaust pressure sensor 30, the air-fuel ratio sensor 31, the exhaust pressure sensor 32, the exhaust temperature sensor 33, the intake pressure sensor, the throttle position sensor, the air flow sensor, and the vehicle speed are detected. Various sensors such as a vehicle speed sensor that is not connected are electrically connected to the input side of an electronic control unit (air-fuel ratio control means, accumulation amount detection means) 40 mounted on the vehicle, and detection information from these sensors. Is input to the electronic control unit 40.

On the other hand, various devices such as the spark plug 11, in-cylinder injector 21, and electronically controlled throttle valve are electrically connected to the output side of the electronic control unit 40. These various devices include various sensors. The ignition timing, fuel injection amount, fuel injection timing, throttle opening, etc. calculated based on the detected information are output.
The electronic control unit 40 calculates a multifunctional catalyst temperature (corresponding to the temperature of each catalyst layer of the present invention) Tm, which is the temperature in the multifunctional catalyst 26, from the exhaust temperature detected by the exhaust temperature sensor 33. The electronic control unit 40 controls the fuel injection amount from the in-cylinder injector 21 based on the multifunction catalyst temperature Tm so that the desired multifunction catalyst temperature Tm and the desired air-fuel ratio are obtained. 26 air-fuel ratio and temperature control. Specifically, the electronic control unit 40 controls the operation of the in-cylinder injector 21 so that the air-fuel ratio becomes lean when the multifunctional catalyst temperature Tm is lower than the second predetermined temperature (lean operation in FIG. 3). . Further, when the multifunctional catalyst temperature Tm is equal to or higher than the second predetermined temperature and lower than the third predetermined temperature, the operation of the in-cylinder injector 21 is controlled so that the air-fuel ratio becomes slightly rich (slight rich operation in FIG. 3). ). In the light rich operation of FIG. 3, as shown in FIG. 4, a cycle in which the air fuel ratio is changed between rich and lean within a predetermined time (for example, about 1 sec) so that the average value of the air fuel ratio becomes light rich. This is performed a plurality of times to make the average air-fuel ratio slightly rich (for example, the average air-fuel ratio is 0.3% to 3.0% richer than the theoretical air-fuel ratio). Here, if the average air-fuel ratio is set to an excessively rich setting (rich setting exceeding 3.0% of the theoretical air-fuel ratio), the NOx reduction performance increases, but the oxidation performance of HC and CO decreases, which is not preferable. Further, if the average air-fuel ratio is set to an excessively rich setting (rich setting lower than the theoretical air-fuel ratio by 0.3%), the NOx reduction performance is lowered, which is not preferable. Furthermore, by making the average air-fuel ratio slightly rich and then changing the air-fuel ratio alternately between rich and lean, not only the reduction performance of NOx but also the reduction of the oxidation performance of HC and CO can be suppressed. When the multifunctional catalyst temperature Tm is equal to or higher than the third predetermined temperature, the operation of the in-cylinder injector 21 is controlled so that the air-fuel ratio detected by the air-fuel ratio sensor 31 becomes stoichiometric (FIG. 3). Stoichiometric feedback operation).

  In addition, the electronic control unit 40 determines the exhaust pressure upstream of the multifunctional catalyst 26 detected by the exhaust pressure sensor 30 and the exhaust pressure downstream of the multifunctional catalyst 26 detected by the exhaust pressure sensor 32. Based on the difference, the PM accumulation amount in the multi-functional catalyst 26 is estimated. When the PM deposition amount exceeds the threshold value, the multifunctional catalyst temperature Tm is equal to or higher than the fourth predetermined temperature (about 500 ° C.) and lower than the fifth predetermined temperature (about 650 ° C.). 5 The operation of the in-cylinder injector 21 is controlled so as to be equal to or higher than the predetermined temperature (catalyst temperature raising operation in FIG. 3). Further, if the multifunctional catalyst temperature Tm is equal to or higher than the fifth predetermined temperature, the operation of the in-cylinder injector 21 is controlled so that PM in the multifunctional catalyst 26 is combusted (PM combustion operation in FIG. 3).

Next, the air-fuel ratio and temperature control of the multifunctional catalyst 26 in the electronic control unit 40 will be described.
FIG. 5 is a part of a flowchart of the air-fuel ratio and temperature control of the multifunctional catalyst 26 executed by the electronic control unit 40. FIG. 6 shows the air-fuel ratio and temperature control of the multifunctional catalyst 26 executed by the electronic control unit 40. It is the remainder of the flowchart.

As shown in FIGS. 5 and 6, in step S10, the operating condition of the engine 1 is detected. Specifically, the operating condition of the engine 1 is detected from detection results of various sensors such as a crank angle sensor 9, an intake pressure sensor, a throttle position sensor, an air flow sensor, and a vehicle speed sensor. Then, the process proceeds to step S12.
In step S12, the engine coolant temperature Tc is detected. Specifically, the water temperature sensor 4 detects the engine water temperature Tc which is the temperature of the cooling water of the engine 1. Then, the process proceeds to step S14.

In step S14, it is determined whether or not the engine water temperature Tc is 0 ° C. or higher. If the determination result is true (Yes) and the engine water temperature Tc is 0 ° C. or higher, the process proceeds to step S16. If the determination result is negative (No) and the engine water temperature Tc is not 0 ° C. or higher, this routine is returned.
In step S16, the multifunctional catalyst temperature Tm is detected. Specifically, the multifunctional catalyst temperature Tm that is the temperature of the multifunctional catalyst 26 is calculated from the exhaust temperature downstream of the multifunctional catalyst 26 detected by the exhaust temperature sensor 33. Then, the process proceeds to step S18.

In step S18, it is determined whether or not the multifunctional catalyst temperature Tm is lower than a second predetermined temperature. If the determination result is true (Yes) and the multifunctional catalyst temperature Tm is less than the second predetermined temperature, the process proceeds to step S20. If the determination result is negative (No) and the multifunctional catalyst temperature Tm is not less than the second predetermined temperature, the process proceeds to step S22.
In step S20, a lean operation is performed. Specifically, the lean operation for controlling the operation of the in-cylinder injector 21 is performed so that the air-fuel ratio becomes the lean air-fuel ratio (lean operation in FIG. 3). Then, this routine is returned.

On the other hand, in step S22, it is determined whether or not the multifunctional catalyst temperature Tm is lower than a third predetermined temperature. If the determination result is true (Yes) and the multifunctional catalyst temperature Tm is less than the third predetermined temperature, the process proceeds to step S24. If the determination result is negative (No) and the multifunctional catalyst temperature Tm is not less than the third predetermined temperature, the process proceeds to step S26.
In step S24, a light rich operation is performed. Specifically, a light rich operation is performed in which the operation of the in-cylinder injector 21 is controlled so that the air-fuel ratio becomes light rich (the light rich operation in FIG. 3). In the light rich operation, as shown in FIG. 4, a cycle for changing the air fuel ratio to rich and lean within a predetermined time (about 1 sec) is performed a plurality of times so that the average value of the air fuel ratio becomes light rich. The air / fuel ratio is made to be slightly rich. Then, this routine is returned.

On the other hand, in step S26, stoichiometric feedback operation is performed. Specifically, the stoichiometric feedback operation for controlling the operation of the in-cylinder injector 21 is performed so that the air-fuel ratio detected by the air-fuel ratio sensor 31 becomes stoichiometric (the stoichiometric feedback operation in FIG. 3). Then, the process proceeds to step S28.
In step S28, the PM accumulation amount is estimated. Specifically, based on the difference between the exhaust pressure upstream of the multifunction catalyst 26 detected by the exhaust pressure sensor 30 and the exhaust pressure downstream of the multifunction catalyst 26 detected by the exhaust pressure sensor 32, Estimate the amount of PM deposition. Then, the process proceeds to step S30.

  In step S30, it is determined whether or not the PM regeneration condition is satisfied. Specifically, it is determined whether or not a PM regeneration condition in which the PM accumulation amount is equal to or greater than a threshold value and the engine operation condition detected in step S10 is a predetermined condition is satisfied. If the determination result is true (Yes), the PM accumulation amount exceeds the threshold value, and the engine operating condition satisfies the predetermined condition, it is determined that the PM regeneration condition is satisfied, and the process proceeds to step S32. If the determination result is NO (No) and either the PM accumulation amount or the engine operating condition does not satisfy the condition, it is determined that the PM regeneration condition is not satisfied, and this routine is returned.

  In step S32, it is determined whether or not the multifunctional catalyst temperature Tm is equal to or higher than the fourth predetermined temperature and lower than the fifth predetermined temperature. If the determination result is true (Yes) and the multifunctional catalyst temperature Tm is equal to or higher than the fourth predetermined temperature and lower than the fifth predetermined temperature, the process proceeds to step S34. If the determination result is NO (No) and the multifunctional catalyst temperature Tm is not lower than the fourth predetermined temperature and lower than the fifth predetermined temperature, the process proceeds to step S38.

In step S34, it is determined whether or not the temperature raising condition is satisfied. If the determination result is true (Yes) and the temperature raising condition is satisfied, the process proceeds to step S36. If the determination result is negative (No) and the temperature raising condition is not satisfied, the routine is returned.
In step S36, a catalyst temperature raising operation is performed. Specifically, the catalyst temperature increasing operation for controlling the operation of the in-cylinder injector 21 is performed so that the multifunctional catalyst temperature Tm is equal to or higher than the fifth predetermined temperature (catalyst temperature increasing operation in FIG. 3). Then, this routine is returned.

On the other hand, in step S38, it is determined whether or not the multifunctional catalyst temperature Tm is equal to or higher than a fifth predetermined temperature. If the determination result is true (Yes) and the multifunctional catalyst temperature Tm is equal to or higher than the fifth predetermined temperature, the process proceeds to step S40. If the determination result is negative (No) and the multifunctional catalyst temperature Tm is not equal to or higher than the fifth predetermined temperature, the present routine is returned.
In step S40, a PM combustion operation is performed. Specifically, the PM combustion operation for controlling the operation of the in-cylinder injector 21 is performed so that the PM deposited on the multifunctional catalyst 26 is combusted (PM combustion operation in FIG. 3). Then, this routine is returned.

  In this way, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, as shown in FIG. 3, the low temperature NOx is maintained until the multifunctional catalyst temperature Tm reaches the second predetermined temperature (about 300 ° C.) at the start of the engine 1 or the like. The low temperature NOx adsorption catalyst layer 28 d of the adsorption catalyst 28 adsorbs NOx discharged from the engine 1. Thereafter, when the multifunctional catalyst temperature Tm reaches the second predetermined temperature, the desorption of NOx from the low-temperature NOx adsorption catalyst layer 28d of the low-temperature NOx adsorption catalyst 28 starts and reaches the third predetermined temperature (about 400 ° C.). NOx desorption is completed. At this time, NOx can be purified with higher efficiency in the PM combustion catalyst layer 29d of the PM combustion catalyst 29 having the three-way catalyst function by making the air-fuel ratio to be rich. In addition, the low temperature HC trap catalyst layer 27d of the low temperature HC trap catalyst 27 traps hydrocarbons (HC) discharged from the engine 1 until the multifunctional catalyst temperature Tm reaches the first predetermined temperature (about 200 ° C.). Thereafter, when the multifunctional catalyst temperature Tm reaches the first predetermined temperature, desorption of HC from the low temperature HC trap catalyst layer 27d of the low temperature HC trap catalyst 27 starts, and when the second predetermined temperature is reached, the HC desorption ends. . As described above, since the three-way catalyst becomes active at the second predetermined temperature or higher, the HC can be sufficiently purified if the air-fuel ratio is stoichiometric with a relatively low oxygen concentration until the second predetermined temperature is reached. Can not. Therefore, by making the air-fuel ratio lean and increasing the oxygen concentration in the exhaust gas, HC is not completely in the PM combustion catalyst layer 29d of the PM combustion catalyst 29 even when the activity of the three-way catalyst is relatively low. However, it can be purified at a level where a practical effect can be obtained. Each gasoline particulate filter 27a, 28a, 29a collects particulate matter (PM) discharged from the engine 1. The PM accumulated on the gasoline particulate filters 27a, 28a, and 29a can be combusted and purified by raising the multifunctional catalyst temperature Tm to a fifth predetermined temperature or higher.

Therefore, even if the temperature of the three-way catalyst 25 and the PM combustion catalyst 29 is not a low temperature at which HC or NOx cannot be purified, that is, the activation temperature, the HC, NOx and PM can be reliably purified.
This is the end of the description of the embodiment of the invention, but the invention is not limited to this embodiment.

In the present embodiment, the low-temperature HC trap catalyst 27, the low-temperature NOx adsorption catalyst 28, and the PM combustion catalyst 29 are provided in the casing 26a of the multifunctional catalyst 26. However, the present invention is not limited to this. Each catalyst may be housed in a separate casing and provided in the exhaust pipe 24.
Further, the low-temperature HC trap catalyst layer 27d and the low-temperature NOx adsorption catalyst layer 28d are supported on separate gasoline particulate filters 27a and 28a to form the respective catalysts. However, the present invention is not limited to this. For example, it may be formed so as to be integrally formed by being stacked on a single gasoline particulate filter. In this case, either the low temperature HC trap catalyst layer 27d or the low temperature NOx adsorption catalyst layer 28d may be the upper layer.

  Further, the low temperature HC trap catalyst layer 27d, the low temperature NOx adsorption catalyst layer 28d, and the PM combustion catalyst layer 29d are supported on the gasoline particulate filters 27a, 28a, and 29a. However, the present invention is not limited to this. In an engine that emits less PM and does not require PM removal, the engine may be supported on an open flow honeycomb.

1 engine (internal combustion engine)
21 In-cylinder injector (air-fuel ratio control means)
24 Exhaust pipe (exhaust passage)
26 Multifunctional catalyst 27 Low temperature HC trap catalyst (first catalyst)
28 Low temperature NOx adsorption catalyst (second catalyst)
29 PM combustion catalyst (third catalyst)
30 Exhaust pressure sensor (accumulation amount detection means)
32 Exhaust pressure sensor (deposition amount detection means)
40 Electronic control unit (air-fuel ratio control means, accumulation amount detection means)

Claims (3)

A first catalyst that is disposed in an exhaust passage of the internal combustion engine, adsorbs HC when the temperature of the catalyst layer is lower than a first predetermined temperature, and desorbs HC when the temperature is equal to or higher than the first predetermined temperature;
A second catalyst disposed in the exhaust passage and adsorbing NOx when the temperature of the catalyst layer is lower than a second predetermined temperature;
A third catalyst that is disposed in the exhaust passage downstream of the first catalyst and the second catalyst and has a three-way catalyst function that is activated when the temperature of the catalyst layer is equal to or higher than the second predetermined temperature;
Air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine,
The exhaust gas purification apparatus for an internal combustion engine, wherein the air-fuel ratio control means makes the air-fuel ratio leaner than a stoichiometric air-fuel ratio until the temperature of the first catalyst reaches the second predetermined temperature. The second catalyst is a catalyst that desorbs adsorbed NOx when the temperature of the catalyst layer is equal to or higher than the second predetermined temperature,
When the temperature of the second catalyst is equal to or higher than the second predetermined temperature, the air-fuel ratio control means sets the air-fuel ratio to a slightly rich air-fuel ratio that is slightly richer than the stoichiometric air-fuel ratio. The exhaust emission control device for an internal combustion engine according to claim 1. A particulate filter that collects particulate matter discharged from the internal combustion engine in the exhaust passage of the internal combustion engine;
A deposition amount detecting means for detecting a deposition amount of the particulate matter collected by the particulate filter,
The air-fuel ratio control means has a function of controlling the temperature of the particulate filter, and when the accumulation amount detected by the accumulation amount detection means is greater than or equal to a threshold value, the temperature of the particulate filter is set to the particulates. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas purification temperature is equal to or higher than a PM combustion temperature, which is a temperature at which the particulate matter is combusted.

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