JP6197994B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine equipped with a particulate matter collecting filter.

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 due to the 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 purifying exhaust gas comprising 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 exhausted in a lean air-fuel ratio engine operation of a gasoline lean burn engine HC, CO and NOx are purified.

JP 2002-273232 A

As described above, in the exhaust purification catalyst disclosed in Patent Document 1, the exhaust purification catalyst for trapping HC and NOx is provided between the upstream side three-way catalyst and the downstream side three-way catalyst, so that each catalyst temperature is increased. Purifies the exhaust when the temperature is low.
On the other hand, some gasoline lean burn engines are equipped with a gasoline particulate filter that collects particulate matter (PM) in the exhaust gas generated by changing the lean air-fuel ratio to further improve fuel efficiency, and burns and removes it. is there.

  However, applying the technology of Patent Document 1 to a gasoline lean burn engine having such a gasoline particulate filter for the purpose of purifying HC, CO, and NOx has a plurality of catalysts and filters disposed on the exhaust passage. As a result, the exhaust pressure may increase, leading to a decrease in engine performance and an increase in cost due to an increase in catalyst, which is not preferable.

  The present invention has been made in order to solve such problems mainly in gasoline engines that are operated near the stoichiometric air-fuel ratio. The object of the present invention is to provide a simple structure with a low catalyst temperature. Another object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can reliably purify exhaust gas.

In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, the HC is adsorbed when the temperature of the catalyst layer is less than a first predetermined temperature. A first catalyst layer that desorbs HC when the temperature is equal to or higher than a first predetermined temperature; and NOx is adsorbed when the temperature of the catalyst layer is lower than a second predetermined temperature that is higher than the first predetermined temperature and is equal to or higher than the second predetermined temperature. A second catalyst layer that desorbs NOx at the time, and the temperature of the catalyst layer is less than the second predetermined temperature on the downstream side in the exhaust flow direction of the first catalyst layer and the second catalyst layer. A particulate filter having a third catalyst layer including a three-way catalyst function that performs HC purification and becomes active at a temperature equal to or higher than the second predetermined temperature, and an empty space of the internal combustion engine in accordance with the temperature of the first or second catalyst layer And an air-fuel ratio control means for controlling the fuel ratio.

In the exhaust gas purification apparatus for an internal combustion engine according to claim 2, in claim 1, the third catalyst layer is formed to have a larger contact area with the exhaust than the first catalyst layer and the second catalyst layer. It is characterized by being.
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 air-fuel ratio control means sets the air-fuel ratio when the temperature of the first catalyst layer is lower than the second predetermined temperature. It is characterized by leaner than the stoichiometric air-fuel ratio.

  According to a fourth aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to any one of the first to third aspects, wherein the air-fuel ratio control means is configured such that the temperature of the second catalyst layer is equal to or higher than the second predetermined temperature. The air-fuel ratio is characterized by being a rich rich air-fuel ratio that is slightly richer than the stoichiometric air-fuel ratio.

  According to the first aspect of the present invention, the air-fuel ratio of the internal combustion engine is controlled according to the temperature of the first catalyst layer or the second catalyst layer. When the temperature is lower than the second predetermined temperature, NOx discharged from the internal combustion engine can be adsorbed to the second catalyst layer. When the temperature of the second catalyst layer is equal to or higher than the second predetermined temperature at which the desorption of NOx starts, the air-fuel ratio is made to be a rich rich gas that facilitates the reduction reaction of NOx, so that the downstream third catalyst NOx desorbed in the layer can be efficiently purified. Further, when the temperature of the first catalyst layer is lower than the first predetermined temperature lower than the second predetermined temperature, hydrocarbons (HC) discharged from the internal combustion engine can be trapped in the first catalyst layer. When the temperature of the first catalyst layer is equal to or higher than the first predetermined temperature, the HC desorbed in the downstream third catalyst layer can be purified with higher efficiency by making the air-fuel ratio lean. it can. Moreover, the particulate matter (PM) discharged from the internal combustion engine can be collected by a particulate filter.

In this way, with a simple configuration comprising the particulate filter having the first catalyst layer, the second catalyst layer, and the third catalyst layer, and the air-fuel ratio control means, the performance deterioration of the internal combustion engine due to the increase in exhaust pressure is suppressed. However, exhaust gas can be reliably purified even if the temperature of the catalyst is low.
According to the invention of claim 2, the third catalyst layer is formed so that the contact area with the exhaust is larger than that of the first catalyst layer and the second catalyst layer. For example, the contact area is increased. Further, the length of the noble metal layer in the exhaust flow direction is longer than the length of the first catalyst layer and the second catalyst layer in the exhaust flow direction, so that the HC desorbed from the first catalyst layer and the second catalyst layer The desorbed NOx can be reliably purified by the third catalyst layer.

  According to the invention of claim 3, when the temperature of the first catalyst layer is lower than the second predetermined temperature, the air-fuel ratio is made lean, and is discharged from the start of the internal combustion engine in the second catalyst layer. NOx can be adsorbed. In addition, when the temperature of the first catalyst layer is lower than the second predetermined temperature, HC is desorbed from the first catalyst layer. Therefore, even if the temperature of the catalyst is low, the first catalyst is reduced by making the air-fuel ratio lean. The desorbed HC can be purified by the third catalyst layer provided on the downstream side of the bed in the exhaust flow direction.

  According to a fourth aspect of the present invention, when the temperature of the second catalyst layer is equal to or higher than the second predetermined temperature, the air-fuel ratio is made rich at the downstream side of the second catalyst layer in the exhaust flow direction. NOx desorbed from the second catalyst layer can be purified by the third catalyst layer.

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 an enlarged view of the A section of FIG. It is an enlarged view of the cross section BB of FIG. It is an enlarged view of the cross section CC of FIG. 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 an enlarged view of part A in FIG. 4 is an enlarged view of a cross section BB in FIG. 3, and FIG. 5 is an enlarged view of a cross section CC in FIG. FIG. 6 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. 6 indicates 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 layer of the multifunctional catalyst, and the multifunctional catalyst temperature Tm from the top. . Note that the HC, CO, NOx purification range and the state of each catalyst layer of the multifunction catalyst in the three-way catalyst and multifunctional catalyst in FIG. 6 are the three-way catalyst temperature or the three-way catalyst temperature Tm. This shows the purifiable range of HC, CO, NOx in the catalyst and the multifunctional catalyst and the state of each catalyst layer of the multifunctional catalyst. FIG. 7 is a diagram showing details of the air-fuel ratio control in the light rich operation in time series. The vertical axis in FIG. 7 indicates the air-fuel ratio. In this embodiment, the low-temperature HC trap catalyst layer (corresponding to the first catalyst layer of the present invention) 26c, the low-temperature NOx adsorption catalyst layer (corresponding to the second catalyst layer of the present invention) 26d, and the three-way catalyst function Since the PM combustion catalyst layer (equivalent to the third catalyst layer of the present invention) 26e is integrally formed in the casing 26a of the multifunctional catalyst 26, the multifunctional catalyst temperature Tm is set to the temperature of each catalyst layer. It is said.

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. The exhaust pipe 24 upstream of the multi-function catalyst 26 is provided with an exhaust pressure sensor 27 that detects the pressure of the exhaust upstream of the multi-function catalyst 26 and an air-fuel ratio sensor 28 that detects the air-fuel ratio of the exhaust. ing. Further, an exhaust pressure sensor 29 that detects the pressure of the exhaust downstream of the multifunctional catalyst 26 and an exhaust temperature sensor 30 that detects the temperature of the exhaust are provided in the exhaust pipe 24 downstream of the multifunctional catalyst 26. .

  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 includes a cylindrical casing 26a, a gasoline particulate filter (particulate filter) 26b provided in the casing 26a, and a low temperature HC trap catalyst layer (first catalyst layer) 26c. And a low temperature NOx adsorption catalyst layer (second catalyst layer) 26d and a PM combustion catalyst layer (third catalyst layer) 26e.
The gasoline particulate filter 26b is a wall flow filter that is a honeycomb carrier in which the upstream side and the downstream side of the passage 26f through which exhaust passes are alternately closed by plugs. The passage 26f is formed of a porous wall 26g. The gasoline particulate filter 26b has a function of collecting particulate matter (PM) in the exhaust gas.

  The low temperature HC trap catalyst layer 26c is a catalyst layer including an HC trap agent such as zeolite that can trap HC at a low temperature lower than a 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 26c is carried on the upstream side in the exhaust flow direction of the gasoline particulate filter 26b as shown in FIGS. Note that the low temperature HC trap catalyst layer 26c contains zeolite as an HC trap agent in the catalyst layer, and as shown in FIG. 6, the temperature of the low temperature HC trap catalyst layer 26c, that is, the temperature of the multifunctional catalyst 26. HC in the exhaust is trapped when the functional catalyst temperature Tm is lower than the first predetermined temperature (about 200 ° C.), the temperature of the low temperature HC trap catalyst layer 26c is equal to or higher than the first predetermined temperature, and the second predetermined temperature ( When the temperature is less than about 300 ° C., it has a function of desorbing trapped HC.

The low-temperature NOx adsorption catalyst layer 26d is a second predetermined temperature (about 300) that is an activation temperature of the three-way catalyst 25 and starts desorption of adsorbed NOx on a base material such as alumina (Al ₂ O ₃ ). NOx adsorbent such as iron (Fe) or silver (Ag), which is a transition metal capable of adsorbing NOx at a low temperature of less than ° C.), and a promoter such as cerium oxide (CeO ₂ ) and titanium oxide (TiO ₂ ). Is a catalyst layer. The low temperature NOx adsorption catalyst layer 26d is supported on the low temperature HC trap catalyst layer 26c as shown in FIGS. That is, the low temperature HC trap catalyst layer 26c and the low temperature NOx adsorption catalyst layer 26d are stacked and supported on the upstream side in the exhaust flow direction of the gasoline particulate filter 26b. The low temperature NOx adsorption catalyst layer 26d contains a transition metal such as Fe or Ag as a NOx adsorbent in the catalyst layer, and as shown in FIG. 6, the temperature of the low temperature NOx adsorption catalyst layer 26d, that is, a multifunctional catalyst. NOx in the exhaust gas is adsorbed when the multifunctional catalyst temperature Tm, which is 26, is lower than a second predetermined temperature (about 300 ° C.), and the temperature of the low-temperature NOx adsorption catalyst layer 26d is higher than the second predetermined temperature. 3. It has a function of desorbing adsorbed NOx when it is lower than a predetermined temperature (about 400 ° C.), that is, at a temperature at which the three-way catalyst can obtain NOx purification performance.

The PM combustion catalyst layer 26e having a three-way catalytic function is formed by supporting a noble metal such as rhodium (Rh), cerium oxide (CeO ₂ ), zirconia (ZrO ₂ ), etc. on a base material such as alumina (Al ₂ O ₃ ). It is a catalyst layer containing a catalyst. As shown in FIGS. 2, 3 and 5, the PM combustion catalyst layer 26e is carried on the gasoline particulate filter 26b on the downstream side in the exhaust flow direction of the low temperature HC trap catalyst layer 26c and the low temperature NOx adsorption catalyst layer 26d. Has been. Note that the length L2 of the PM combustion catalyst layer 26e in the exhaust flow direction is greater than the carrying length L1 of the catalyst layer formed by stacking the low temperature HC trap catalyst layer 26c and the low temperature NOx adsorption catalyst layer 26d in the exhaust flow direction. It is carried so as to be long. The PM combustion catalyst layer 26e includes 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. 6, even when the temperature of the PM combustion catalyst layer 26e, that is, the multifunctional catalyst temperature Tm that is the temperature of the multifunctional 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 layer 26c by making the air-fuel ratio leaner than stoichiometric. Further, the PM combustion catalyst layer 26e has the temperature of the PM combustion catalyst layer 26e, that is, the multifunction catalyst temperature Tm, which is the temperature of the multifunction catalyst 26, at a fifth predetermined temperature at which PM combustion of the three-way catalyst easily proceeds in a short time ( About 650 ° C.), and has a function of purifying CO or the like generated when burning PM collected and deposited by the gasoline particulate filter 26b.

  The water temperature sensor 4, the crank angle sensor 9, the exhaust pressure sensor 27, the air-fuel ratio sensor 28, the exhaust pressure sensor 29, the exhaust temperature sensor 30, the intake pressure sensor, the throttle position sensor, the air flow sensor, and the vehicle speed of the vehicle 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) 40 mounted on the vehicle, and detection information from these sensors is electronic control unit 40. Is input.

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 30. 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. 6). . 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. 6). ). 6, the 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 slightly rich, as shown in FIG. This is performed a plurality of times, and the average air-fuel ratio is set to be rich 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 28 becomes stoichiometric (FIG. 6). Stoichiometric feedback operation).

  In addition, the electronic control unit 40 is configured such that the upstream exhaust pressure of the multifunctional catalyst 26 detected by the exhaust pressure sensor 27 and the downstream exhaust pressure of the multifunctional catalyst 26 detected by the exhaust pressure sensor 29. 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. 6). 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 the PM in the multifunctional catalyst 26 is combusted (PM combustion operation in FIG. 6).

Next, the air-fuel ratio and temperature control of the multifunctional catalyst 26 in the electronic control unit 40 will be described.
FIG. 8 is a part of a flowchart of air-fuel ratio and temperature control of the multi-functional catalyst 26 executed by the electronic control unit 40. FIG. 9 shows air-fuel ratio and temperature control of the multi-functional catalyst 26 executed by the electronic control unit 40. It is the remainder of the flowchart.

As shown in FIGS. 8 and 9, 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 multifunction catalyst temperature Tm that is the temperature of the multifunction catalyst 26 is calculated from the exhaust temperature downstream of the multifunction catalyst 26 detected by the exhaust temperature sensor 30. 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. 6). 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. 6). In the light rich operation, as shown in FIG. 7, 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 28 becomes stoichiometric (the stoichiometric feedback operation in FIG. 6). 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 27 and the exhaust pressure downstream of the multifunction catalyst 26 detected by the exhaust pressure sensor 29, 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. 6). 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. 6). Then, this routine is returned.

  Thus, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, as shown in FIG. 6, when the multifunctional catalyst temperature Tm is lower than the second predetermined temperature at the time of starting the engine 1, the exhaust gas is discharged from the engine 1. NOx to be adsorbed can be adsorbed to the low temperature NOx adsorption catalyst layer 26d. If the multifunctional catalyst temperature Tm is equal to or higher than the second predetermined temperature, the air-fuel ratio is made to be rich, so that the NOx desorbed from the low temperature NOx adsorption catalyst layer 26d in the downstream PM combustion catalyst layer 26e can be reduced. It can be purified efficiently. Further, when the multifunctional catalyst temperature Tm is lower than the first predetermined temperature, hydrocarbons (HC) discharged from the engine 1 can be trapped in the low temperature HC trap catalyst layer 26c. When the multifunctional catalyst temperature Tm is equal to or higher than the first predetermined temperature, the air-fuel ratio is made lean so that the HC desorbed from the low-temperature HC trap catalyst layer 26c in the downstream PM combustion catalyst layer 26e is higher. It can be purified with efficiency. Moreover, the particulate matter (PM) discharged from the engine 1 can be collected by the gasoline particulate filter 26b.

  In this way, the exhaust pressure can be reduced by adopting a simple configuration including the gasoline particulate filter 26b carrying the low temperature HC trap catalyst layer 26c, the low temperature NOx adsorption catalyst layer 26d, and the PM combustion catalyst layer 26e and the electronic control unit 40. The exhaust gas can be reliably purified even if the temperature of each catalyst is low, while suppressing the deterioration of the performance of the engine 1 due to the rise of the engine.

  Further, the length L2 of the PM combustion catalyst layer 26e in the exhaust flow direction is longer than the carrying length L1 of the catalyst layer formed by stacking the low temperature HC trap catalyst layer 26c and the low temperature NOx adsorption catalyst layer 26d in the exhaust flow direction. That is, by increasing the contact area of the PM combustion catalyst layer 26e with the exhaust gas, the NOx desorbed from the low-temperature NOx adsorption layer 26d and the HC desorbed from the low-temperature HC trap layer 26c are reliably PM burned. It can be purified by the catalyst layer 26e.

This is the end of the description of the embodiment of the invention, but the invention is not limited to this embodiment.
In this embodiment, the low-temperature NOx adsorption layer 26d is supported on the low-temperature HC trap layer 26c. However, the present invention is not limited to this, and the low-temperature HC trap layer 26c is not limited to this. You may make it carry | support on.

  Further, the PM combustion catalyst layer 26e is supported only on the gasoline particulate filter 26b on the downstream side in the exhaust flow direction of the catalyst layer formed by stacking the low temperature HC trap catalyst layer 26c and the low temperature NOx adsorption catalyst layer 26d. However, the present invention is not limited to this, and the low temperature HC trap catalyst layer 26c and the low temperature NOx adsorption catalyst layer 26d, together with the downstream side in the exhaust flow direction of the catalyst layer formed by stacking the low temperature NOx adsorption catalyst layer 26d, May be carried on the upper side of the catalyst layer formed by laminating.

1 engine (internal combustion engine)
21 In-cylinder injector (air-fuel ratio control means)
24 Exhaust pipe (exhaust passage)
25 Three-way catalyst 26 Multifunctional catalyst 26b Gasoline particulate filter (particulate filter)
26c Low temperature HC trap catalyst layer (first catalyst layer)
26d Low temperature NOx adsorption catalyst layer (second catalyst layer)
26e PM combustion catalyst layer (third catalyst layer)
30 Exhaust temperature sensor 40 Electronic control unit (air-fuel ratio control means)

Claims (4)

A first catalyst layer 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; And a second catalyst layer that adsorbs NOx when the temperature is lower than a second predetermined temperature higher than the first predetermined temperature and desorbs NOx when the temperature is equal to or higher than the second predetermined temperature. Including a three-way catalyst function on the downstream side in the exhaust flow direction between the catalyst layer and the second catalyst layer, wherein the catalyst layer is HC purified when the temperature of the catalyst layer is lower than the second predetermined temperature and becomes active when the temperature exceeds the second predetermined temperature. An exhaust gas for an internal combustion engine comprising: a particulate filter having a third catalyst layer; and air-fuel ratio control means for controlling an air-fuel ratio of the internal combustion engine in accordance with a temperature of the first or second catalyst layer. Purification equipment.   2. The exhaust gas purification of an internal combustion engine according to claim 1, wherein the third catalyst layer is formed to have a larger contact area with the exhaust gas than the first catalyst layer and the second catalyst layer. apparatus.   3. The air-fuel ratio control means according to claim 1, wherein the air-fuel ratio is made leaner than the stoichiometric air-fuel ratio when the temperature of the first catalyst layer is lower than the second predetermined temperature. An exhaust purification device for an internal combustion engine.   The air-fuel ratio control means is characterized in that when the temperature of the second catalyst layer is equal to or higher than the second predetermined temperature, the air-fuel ratio is made slightly rich that is an air-fuel ratio slightly richer than the stoichiometric air-fuel ratio. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3.

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