JP2006022755A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device, most efficiently performing reduction treatment of NOx and oxidation treatment of HC. <P>SOLUTION: This exhaust emission control device includes: the third oxygen sensor 23 disposed on the downstream side in the exhaust emission circulating direction of an HC adsorbing catalyst 13; a temperature sensor 24 for detecting whether or not the HC adsorbing catalyst 13 is equal to or higher than a specified temperature; and an ECU 30 for controlling a fuel injection device 100a so that the air-fuel ratio of exhaust gas from an engine 100 is lean state according to the information of the third oxygen sensor 23 when HC emission from the HC adsorbent catalyst 13 is decided, and then controlling the fuel injection device 100a so that the air-fuel ratio of exhaust gas from the engine 100 is stoichiometric state when the air fuel ratio of the lean state is detected by the third oxygen sensor 23. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

Exhaust gas from internal combustion engines such as automobiles is decomposed into H ₂ O, CO ₂ , and N ₂ by substances such as CO, NOx, and HC (unburned components) in the exhaust gas by a three-way catalyst provided in the exhaust passage. After being purified, it is discharged to the outside. In particular, when the exhaust gas temperature is low (less than about 300 ° C.), such as when starting an internal combustion engine, the HC is not easily oxidized by the three-way catalyst, and may be discharged outside without being purified. For this reason, the HC is adsorbed and held at low temperatures, while the HC (unburned component) adsorption catalyst that oxidizes at the same time as the HC is released at high temperatures is further provided in the exhaust passage so that the HC is reliably purified. It has become.

Japanese Patent No. 3412491

  By the way, since oxygen is required when oxidizing HC released from the HC adsorption catalyst as described above, the air-fuel ratio of the internal combustion engine is made lean (oxygen excess), and the HC adsorption catalyst. The air-fuel ratio of the internal combustion engine is controlled so as to supply oxygen. However, if the air-fuel ratio of the internal combustion engine is made lean (oxygen excess), the ability of NOx to be reduced by the three-way catalyst will be reduced, making it difficult to sufficiently reduce NOx. For this reason, priority must be given to either NOx reduction treatment or HC oxidation treatment. Conventionally, the amount of NOx generated by leaning (oxygen excess) is reduced by the three-way catalyst. The leaning of the air-fuel ratio of the internal combustion engine is terminated so as to suppress the leaning period to oxidize HC to the extent that the processing capacity is not exceeded, and the HC released from the HC adsorption catalyst is discharged only during the leaning period. Oxidation treatment was performed, and sufficient oxidation treatment of HC could not be performed.

  In view of the above, an object of the present invention is to provide an exhaust gas purification apparatus capable of performing both NOx reduction treatment and HC oxidation treatment most efficiently.

  An exhaust gas purification apparatus according to the present invention for solving the above-described problems is disposed in an exhaust passage through which exhaust gas from an internal combustion engine is circulated, and adsorbs unburned components in exhaust gas at low temperatures and adsorbs at high temperatures. It has an unburned component adsorption function that releases unburned components, and adsorbs and holds oxygen in the exhaust gas when the exhaust gas is lean, and stores oxygen that absorbs and holds the oxygen when the exhaust gas is rich. In the exhaust gas purifying apparatus having an exhaust gas purifying catalyst having a function, a downstream air-fuel ratio detecting means that is disposed downstream of the exhaust gas purifying catalyst in the exhaust gas flow direction and detects an air-fuel ratio of the exhaust gas, and the exhaust gas Based on information from the exhaust gas purification catalyst temperature detection means for detecting whether or not the purification catalyst is above a specified temperature, and the exhaust gas purification catalyst temperature detection means, the exhaust gas When it is determined that the unburned component is released from the catalyst, the control means for controlling the air-fuel ratio adjusting means for adjusting the air-fuel ratio of the exhaust gas from the internal combustion engine based on the information from the downstream air-fuel ratio detecting means It is characterized by having.

  The exhaust gas purifying apparatus according to the present invention is characterized in that, in the exhaust gas purifying apparatus described above, the specified temperature is a temperature at which the unburned components adsorbed by the exhaust gas purifying catalyst are released.

  Further, the exhaust gas purification apparatus according to the present invention is the above-described exhaust gas purification apparatus, wherein the control means releases unburned components from the exhaust gas purification catalyst based on information from the exhaust gas purification catalyst temperature detection means. When the air-fuel ratio adjusting means is controlled to bring the air-fuel ratio of the exhaust gas from the internal combustion engine into a lean state, and the lean air-fuel ratio is detected by the downstream air-fuel ratio detecting means, the internal combustion engine The air-fuel ratio adjusting means is controlled so that the air-fuel ratio of the exhaust gas from the engine is in a stoichiometric state.

  Further, the exhaust gas purifying apparatus according to the present invention is the above exhaust gas purifying apparatus, wherein the control means controls the air-fuel ratio adjusting means so that the air-fuel ratio of the exhaust gas from the internal combustion engine is in a stoichiometric state. When the air-fuel ratio in the rich state is detected within a predetermined time by the downstream air-fuel ratio detecting means, the air-fuel ratio adjusting means is controlled so that the air-fuel ratio of the exhaust gas from the internal combustion engine becomes lean. Features.

  Further, the exhaust gas purifying apparatus according to the present invention is the above-described exhaust gas purifying apparatus, further comprising an upstream side air-fuel ratio detecting means that is disposed upstream of the exhaust gas purifying catalyst in the exhaust gas circulation direction and detects the air-fuel ratio of the exhaust gas. And the control means determines the air-fuel ratio of the internal combustion engine based on information from the downstream air-fuel ratio detection means, and outputs the determined air-fuel ratio from the upstream air-fuel ratio detection means. The air-fuel ratio adjusting means is controlled based on the information.

  According to the exhaust gas purification apparatus of the present invention, the exhaust gas purification catalyst is first operated in the minimum lean state necessary for adsorbing oxygen to the saturated state, and then operated in the stoichiometric state. As a result, it is possible to oxidize almost all the unburned components adsorbed by the exhaust gas purification catalyst while minimizing the operation in the lean state. Can be performed most efficiently.

  An embodiment of an exhaust gas purifying apparatus according to the present invention will be described below based on FIGS. FIG. 1 is a schematic configuration diagram of an exhaust gas purification device, FIG. 2 is a flow chart relating to exhaust gas purification, and FIG. 3 is an explanatory diagram of the operation of exhaust gas purification.

As shown in FIG. 1, an exhaust gas purification catalyst device 10 is provided in the middle of an exhaust passage 101 connected to an engine 100 that is an internal combustion engine. On the upstream side in the exhaust gas flow direction in the casing 11 of the exhaust gas purification catalyst 10, substances such as CO, NOx and HC (unburned components) in the exhaust gas are decomposed into H ₂ O, CO ₂ and N _2. A three-way catalyst 12 for purification treatment is provided. On the downstream side in the exhaust gas flow direction in the casing 11, while adsorbing and holding HC at a low temperature, the adsorbed HC is released at a high temperature (for example, about 150 ° C. or more) and simultaneously oxidized, and the exhaust gas is lean. Oxygen Storage Capability (OSC) that adsorbs and holds oxygen in exhaust gas when exhausted (excess oxygen), and releases oxygen that is adsorbed and retained when exhaust gas is rich (oxygen deficient) An HC (unburned component) adsorption catalyst 13 which is an exhaust gas purification catalyst according to the present invention is provided.

  A first oxygen sensor 21 for detecting an air-fuel ratio in the exhaust gas is disposed on the inlet side of the exhaust gas purification catalyst device 10, that is, on the upstream side of the three-way catalyst 12 and the HC adsorption catalyst 13 in the exhaust gas flow direction. Yes. Between the three-way catalyst 12 and the HC adsorption catalyst 13 in the exhaust gas purification catalyst device 10, that is, upstream of the HC adsorption catalyst 13 in the exhaust gas flow direction, the upstream side according to the present invention that detects the air-fuel ratio in the exhaust gas. A second oxygen sensor 22 serving as air-fuel ratio detection means is provided. A third oxygen sensor which is a downstream air-fuel ratio detecting means according to the present invention for detecting an air-fuel ratio in the exhaust gas at the outlet side of the exhaust gas purification catalyst device 10, that is, downstream of the HC adsorption catalyst 13 in the exhaust gas flow direction. 23 is arranged. These oxygen sensors 21 to 23 are provided with heaters (not shown) for activating the sensors 21 to 23. Further, on the downstream side in the exhaust gas flow direction of the HC adsorption catalyst 13, there is an exhaust gas purification catalyst temperature detection means according to the present invention for detecting whether the temperature of the HC adsorption catalyst 13 is higher than a specified temperature. A temperature sensor 24 is attached.

  The sensors 21 to 24 are electrically connected to an input unit of an electronic control unit (ECU) 30 that is a control unit according to the present invention. The output portion of the ECU 30 is electrically connected to a fuel injection device 100a that is an air-fuel ratio adjusting means for adjusting the air-fuel ratio (A / F) of the engine 100. The ECU 30 is connected to the sensors 21 to 24 and the like. Based on the above information, the fuel injection device 100a is controlled to adjust the air-fuel ratio of the engine 100 (details will be described later). In addition, the heater is electrically connected to the output portion of the ECU 30.

  Next, the operation of the exhaust gas purifying apparatus according to this embodiment will be described with reference to FIG.

  When the ignition switch is operated to start the engine 100 (S1), the ECU 30 operates the heater to activate the oxygen sensors 21 to 23 (S2), and the air-fuel ratio in the engine 100 (from the engine 100). The fuel injection device 100a of the engine 100 is based on the information from the first and second oxygen sensors 21 and 22, so that the air-fuel ratio of the exhaust gas of the exhaust gas becomes a target stoichiometric state (theoretical air-fuel ratio). Is stoichiometric feedback controlled (S3).

  Subsequently, the ECU 30 determines whether or not the HC adsorption catalyst 13 of the exhaust gas purification catalyst device 10 is equal to or higher than a specified temperature (150 ° C.) based on information from the temperature sensor 24 (S4). When the temperature is lower than 150 ° C. (for example, at a low temperature such as the start of operation), that is, when the HC adsorption catalyst 13 adsorbs and removes HC in the exhaust gas, the stoichiometric feedback control is continued as it is.

  When the HC adsorption catalyst 13 of the exhaust gas purifying catalyst device 10 reaches a specified temperature (150 ° C.) or higher, the ECU 30 determines that HC is released from the HC adsorption catalyst 13, and the air-fuel ratio in the engine 100 (engine Based on the information from the first and second oxygen sensors 21, 22, the fuel injection device of the engine 100 is set so that the air-fuel ratio of the exhaust gas from 100 becomes a target lean state (oxygen excess). 100a is lean-controlled (S5).

  Then, because the oxygen in the exhaust gas is excessive, the HC adsorption catalyst 13 adsorbs and holds the oxygen, so that the exhaust gas on the inlet side is in a lean state (oxygen excess) as shown in FIG. Then, the exhaust gas on the outlet side becomes stoichiometric (theoretical air-fuel ratio) (A region in FIG. 3).

  When the HC adsorption catalyst 13 is saturated by adsorbing oxygen in this way, the exhaust gas on the outlet side of the HC adsorption catalyst 13 is also in a lean state (oxygen excess) (region B in FIG. 3). Here, the ECU 30 determines whether the air-fuel ratio detected by the third oxygen sensor 23 is in a lean state (S6), and detects the lean air-fuel ratio by the third oxygen sensor 23. Information from the first and second oxygen sensors 21 and 22 so that the air-fuel ratio in the engine 100 (the air-fuel ratio of the exhaust gas from the engine 100) becomes the target state (the stoichiometric air-fuel ratio). Based on the above, the fuel injection device 100a of the engine 100 is subjected to stoichiometric feedback control (S7).

When the engine 100 is subjected to stoichiometric feedback control and the air-fuel ratio of the exhaust gas from the engine 100 is in a stoichiometric state (theoretical air-fuel ratio), the oxygen adsorbed and held by the HC adsorption catalyst 13 is adsorbed and held by the HC adsorption catalyst 13. The HC is released together with the HC, and the HC and oxygen undergo an oxidation reaction, and the HC is purified (region C in FIG. 3).
Here, the principle of the exhaust gas purifying apparatus will be described.

  When oxidizing the HC adsorbed and held by the HC adsorption catalyst 13 at a specified temperature or higher by making the exhaust gas from the engine 100 lean (oxygen excess), conventionally, the HC released from the HC adsorption catalyst 13 is used. However, since it was considered that the oxidation reaction proceeds during the operation in the lean state, all the HC adsorbed and held by the HC adsorption catalyst 13 is removed. It was thought that it was necessary to operate in a lean state until it was oxidized.

  However, when the inventors of the present application have conducted intensive research, HC adsorbed and held on the HC adsorption catalyst 13 does not have a large amount of oxidation reaction during the operation in the lean state, and the operation from the lean state is not performed. It was newly found that the oxidation reaction proceeds significantly after shifting to the stoichiometric operation.

  The reason for this is not clear, but if the HC adsorption catalyst 13 is in a lean state, it absorbs and retains oxygen, so that the activity ability as a catalyst is hindered, and the HC oxidation treatment ability decreases. However, in the stoichiometric state, the active ability as a catalyst can be fully exerted to release the adsorbed and retained oxygen at the time of change to the rich state at the time of feedback control. It is presumed that oxygen may be efficiently oxidized using oxygen.

  Accordingly, the inventors of the present application first operate the HC adsorption catalyst 13 in a lean state that is the minimum necessary to adsorb oxygen to a saturated state, and then perform an operation in a stoichiometric state. In this way, when almost all the HC adsorbed by the HC adsorption catalyst 13 is oxidized, the lean operation can be minimized, that is, the NOx reduction treatment and the HC oxidation treatment are most efficiently performed. The present invention has been completed by thinking that it can be performed.

  As described above, after performing the stoichiometric feedback control in step S7, the control device 30 determines whether or not the air-fuel ratio detected by the third oxygen sensor 23 has become rich (oxygen shortage) within a predetermined time. Determination (S8), and when the third oxygen sensor 23 detects the rich air (oxygen deficient) air-fuel ratio within a predetermined time, that is, even if all the oxygen adsorbed and held by the HC adsorption catalyst 13 is released. When the HC is still adsorbed and held on the HC adsorption catalyst 13 (D region in FIG. 3), the ECU 30 returns to the above-described step S5, and the air-fuel ratio in the engine 100 (the exhaust gas from the engine 100). Based on the information from the first and second oxygen sensors 21 and 22, the fuel injection of the engine 100 is performed so that the air-fuel ratio becomes a target lean state (oxygen excess). The device 100a again lean control.

  On the other hand, when the third oxygen sensor 23 does not detect the rich (oxygen-deficient) air-fuel ratio within a predetermined time, the ECU 30 determines that all the HC adsorbed and held by the HC adsorption catalyst 13 has been oxidized. Then, control is shifted to normal mode control (S9).

  That is, in the present embodiment, as described above, the HC adsorption catalyst 13 is first operated in the minimum lean state necessary for adsorbing oxygen to the saturated state, and then stoichiometric. By performing the operation in the state, almost all the HC adsorbed by the HC adsorption catalyst 13 can be oxidized while the operation in the lean state is minimized.

  Therefore, according to the exhaust gas purifying apparatus according to the present embodiment, NOx reduction treatment and HC oxidation treatment can be performed most efficiently.

  Further, since the operation in the lean state when oxidizing almost all the HC adsorbed by the HC adsorption catalyst 13 can be minimized, the output reduction of the engine 100 can be greatly suppressed.

  In this embodiment, the oxygen sensors 21 to 23 are applied to the air-fuel ratio detection means. However, as another embodiment, an air-fuel ratio (A / F) sensor can be applied to the air-fuel ratio detection means. is there.

  In this embodiment, the temperature sensor 24 is applied to the exhaust gas purification catalyst temperature detection means. However, as another embodiment, a timer can be applied to the exhaust gas purification catalyst temperature detection means.

  Further, in the present embodiment, the case of the exhaust gas purification catalyst device 10 in which the three-way catalyst 12 and the HC adsorption catalyst 13 are housed in the casing 11 has been described, but a single exhaust gas in which the functions of these catalysts 12 and 13 are integrated. Even an exhaust gas purification catalyst device in which a purification catalyst is housed in a casing can be applied in the same manner as in this embodiment. In such a case, the second oxygen sensor 22 is omitted and the first oxygen sensor 21 is used.

  The exhaust gas purifying apparatus according to the present invention can perform the NOx reduction treatment and the HC oxidation treatment in the exhaust gas from an internal combustion engine such as an automobile most efficiently, and therefore can be used extremely beneficially in the automobile industry and the like. it can.

It is a schematic block diagram of embodiment of the exhaust gas purification apparatus which concerns on this invention. It is a flowchart of the exhaust gas purification which concerns on embodiment of the exhaust gas purification apparatus which concerns on this invention. It is operation | movement explanatory drawing of the exhaust gas purification of the exhaust gas purification apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification catalyst device 11 Casing 12 Three-way catalyst 13 HC (unburned component) adsorption catalyst 21 First oxygen sensor 22 Second oxygen sensor 23 Third oxygen sensor 24 Temperature sensor 30 Electronic control unit (ECU)
DESCRIPTION OF SYMBOLS 100 Engine 100a Fuel injection apparatus 101 Exhaust passage

Claims (5)

An exhaust passage through which the exhaust gas from the internal combustion engine is circulated has an unburned component adsorption function that adsorbs unburned components in the exhaust gas at low temperatures and releases the adsorbed unburned components at high temperatures. In a lean state, in an exhaust gas purification apparatus equipped with an exhaust gas purification catalyst having an oxygen storage function that adsorbs and holds oxygen in exhaust gas, and releases exhausted oxygen when the exhaust gas is rich,
A downstream air-fuel ratio detection means that is disposed downstream of the exhaust gas purification catalyst in the exhaust gas flow direction and detects the air-fuel ratio of the exhaust gas;
Exhaust gas purification catalyst temperature detection means for detecting whether or not the exhaust gas purification catalyst is above a specified temperature;
Based on the information from the exhaust gas purification catalyst temperature detection means, if it is determined that the unburned component is released from the exhaust gas purification catalyst, based on the information from the downstream air-fuel ratio detection means, And a control means for controlling an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the exhaust gas. In claim 1,
The specified temperature is a temperature at which an unburned component adsorbed by the exhaust gas purification catalyst is released. In claim 1 or claim 2,
When the control means determines that unburned components are released from the exhaust gas purification catalyst based on information from the exhaust gas purification catalyst temperature detection means, the air-fuel ratio of the exhaust gas from the internal combustion engine is made lean. After controlling the air-fuel ratio adjustment means, when the lean air-fuel ratio is detected by the downstream air-fuel ratio detection means, the air-fuel ratio adjustment is performed so that the air-fuel ratio of the exhaust gas from the internal combustion engine is stoichiometric. An exhaust gas purifying apparatus characterized by controlling the means. In claim 3,
After the control means controls the air-fuel ratio adjustment means so that the air-fuel ratio of the exhaust gas from the internal combustion engine is in a stoichiometric state, the downstream air-fuel ratio detection means detects the rich air-fuel ratio within a predetermined time. When this is done, the air-fuel ratio adjusting means is controlled so that the air-fuel ratio of the exhaust gas from the internal combustion engine is in a lean state. In any one of Claims 1-4,
An upstream air-fuel ratio detection means that is disposed upstream of the exhaust gas purification catalyst in the exhaust gas flow direction and detects the air-fuel ratio of the exhaust gas;
The control means determines the air-fuel ratio of the internal combustion engine based on information from the downstream air-fuel ratio detection means, and uses the information from the upstream air-fuel ratio detection means so as to be the determined air-fuel ratio. Based on this, the exhaust gas purifying apparatus controls the air-fuel ratio adjusting means.

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