JPH05231136A - Exhaust emission control device for automobile - Google Patents

Abstract

(57) Abstract: [Purpose] The present invention, at least one of the front catalyst and the rear catalyst of the rear of the exhaust path, is to not disposed lowering the purification efficiency and durability of the lean NO _X catalyst .. [Structure] A front catalyst 9 and a rear catalyst 10 behind the combustion chamber 101 of the internal combustion engine 1 are sequentially provided, and the front catalyst 9 is configured to perform exhaust gas purification at the initial stage of engine operation. The second stage catalyst 1 is bypassed to the passage 2 by bypassing the first stage catalyst 9.
A bypass passage 202 that joins the exhaust passage 2 is provided on the upstream side of 0, and a switching valve 11 that controls increase / decrease of the flow rate of exhaust gas that flows into the bypass passage 202 and the pre-catalyst 9 is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is arranged in an exhaust passage of an internal combustion engine, and more particularly, an automobile equipped with a front catalyst located adjacent to a combustion chamber on the exhaust passage of the internal combustion engine and a rear catalyst arranged behind the front catalyst. The exhaust gas purifying device of.

[0002]

2. Description of the Related Art Conventionally, an automobile exhaust gas purifying apparatus detoxifies exhaust gas generated by an internal combustion engine of an automobile and discharges it into the atmosphere, and has an important role in protecting the natural environment. This exhaust gas purifying device, for example, a three-way catalyst, is equipped with both redox catalysts, and the air-fuel ratio is maintained in a narrow window region including stoichio, so that the oxidation catalyst can remove C
The reducing catalyst acts on O and HC so as to convert NO _X in the exhaust gas into harmless components.

By the way, it is widely known that lean burn (lean combustion) is an effective means for reducing fuel consumption of a gasoline engine, and many automobiles equipped with a lean burn engine have been announced. However, the three-way catalyst, which is effective as an exhaust gas purifying means during combustion at the stoichiometric air-fuel ratio, cannot perform an appropriate catalytic action during lean combustion under an excess of oxygen (lean air-fuel ratio) and must meet various exhaust gas regulations. Has become difficult. As a technique for solving this problem, the nitrogen oxides in the exhaust gas during lean-burn (NO _X) have been proposed that can lean NO _X catalyst to purify, discloses an example of which in JP 60 over 125,250 Publication Has been done.

[0004] The lean NO _X catalyst, in particular, has left and that a large deterioration at high temperatures, the problems in the actual vehicle equipped in that they require a HC component to purify NO _X.
That is, as shown in FIG. 4, unless the HC / CO ratio in the exhaust gas exceeds a predetermined value, the NO _x purification rate (η _NOx ) does not rise sufficiently and normal operation cannot be performed. Therefore, when sequentially arranged and the lean NO _X catalyst and the three-way catalyst in an exhaust passage, the lean NO _X
It is necessary to arrange the catalyst upstream of the three-way catalyst.

Further, in order to improve the exhaust gas purification rate in the early stage of starting the vehicle at an early stage, it is necessary to shorten the time to reach the activation completion temperature of the catalyst (light off earlier). For this reason, a conventional pre-catalyst (warm-up catalyst) having a relatively small capacity is installed near the exhaust port of the combustion chamber of the engine, and the main post-catalyst is arranged behind it. As a result, the pre-stage catalyst composed of the three-way catalyst is heated early near the exhaust port, and because the capacity is small, the activation completion temperature is reached relatively quickly, and the exhaust gas purification rate at the initial stage of engine startup is increased in a short time. I try to rationalize.

[0006]

By the way, exhaust gas regulations are being strengthened, and it is considered that the need for a pre-stage catalyst (warm-up catalyst) will rapidly increase in the future. However, since the HC component is required for purification of NO _x , when the three-way catalyst is used as it is as the front catalyst, the lean N of the rear stage is used.
O _X catalyst can not be normal operation by HC shortage. On the other hand,
The use of a lean NO _X catalyst in the pre-catalyst is lean N
O _X catalyst than is large deterioration at high temperatures, it can not be used as is, and has a problem.

An object of the present invention, when deploying lean NO _X catalyst in at least part of the post-catalyst exhaust path, without arrangement can exhaust of an automobile to reduce the lean NO _X catalyst purification efficiency and durability To provide a purification device.

[0008]

In order to achieve the above-mentioned object, a first aspect of the present invention is directed to a pre-catalyst which is located close to a combustion chamber of an internal combustion engine, and lean NO _X which is arranged behind the pre-catalyst.
A downstream catalyst including a catalyst is sequentially provided on the exhaust passage, and the upstream catalyst is mainly configured to perform exhaust gas purification at the initial stage of engine operation.In particular, the exhaust passage bypasses the upstream catalyst and the downstream catalyst. By providing a bypass passage that joins the exhaust passage on the upstream side of the catalyst, a switching valve that controls the exhaust gas flow rates respectively flowing into the bypass passage and the pre-catalyst according to the operating information of the internal combustion engine is provided. To do.

[0009] The second invention sequentially comprises a pre-catalyst that is close to the combustion chamber of an internal combustion engine, a lean NO _X catalyst is deployed in the rear of the front catalyst and Fukumuru stage catalyst in an exhaust path,
The pre-stage catalyst is mainly configured to perform exhaust gas purification at the initial stage of engine operation, and in particular, a bypass passage that bypasses the pre-stage catalyst and joins the exhaust passage upstream of the post-stage catalyst is provided in the exhaust passage. A valve for controlling a flow rate of exhaust gas flowing into each of the bypass passage and the front catalyst, and a valve for outputting a switching control signal corresponding to a predetermined opening degree to an actuator of the switching valve according to operation information of the internal combustion engine. A control means is provided, and the valve control means switches the switching valve to a position where the bypass passage is opened when the engine is stopped.

[0010]

In the first aspect of the invention, since the switching valve controls the flow rate of the exhaust gas flowing into the bypass passage and the pre-catalyst in accordance with the operating information of the internal combustion engine, the exhaust gas is allowed to flow into the pre-catalyst only at a predetermined time for purification. You can

In the second aspect of the invention, the switching valve increases or decreases the flow rate of the exhaust gas flowing into the bypass passage and the front catalyst, respectively, and the valve control means causes the actuator of the switching valve to perform switching control corresponding to a predetermined opening degree according to the operation information of the internal combustion engine. Since a signal is output and the switching valve is switched to the position where the bypass passage is opened when the engine is stopped, exhaust gas can be purified by the pre-catalyst at the beginning of engine operation, and the switching valve is switched to the position where the bypass passage is opened when the engine is stopped. A fail-safe function can be added when the valve sticks.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The automobile exhaust gas purification apparatus shown in FIGS. 1 and 2A is mounted on an exhaust passage 2 of a gasoline engine E. In this engine E, the fuel supply amount is controlled by an engine control unit (hereinafter simply referred to as ECU) 3, and the current air-fuel ratio is adjusted and controlled to a target air-fuel ratio corresponding to load information and engine speed information at each time point. It is configured. The exhaust passage 2 is connected to an exhaust branch pipe 4 connected to the engine body 1, a continuous connection to a confluent portion thereof, an upstream exhaust pipe 5 having a warm-up catalyst 9 as a pre-stage catalyst, and a downstream end thereof. Downstream exhaust pipe 6 equipped with a post-catalyst 10
And a muffler (not shown).

The upstream exhaust pipe 5 is branched between the upstream bifurcating portion 7 and the downstream merging portion 8 to bypass the upstream main passage 201 equipped with the warm-up catalyst 9 which is the upstream catalyst and the upstream catalyst. The bypass path 202 is formed in parallel. Particularly, here, the upstream main road 20 is connected to the bifurcated branch portion 7.
1 and a switching valve 11 that controls the increase / decrease of the flow rate of exhaust gas that can flow into the bypass passage 202. This switching valve 11 is a rotary shaft 1 that is pivotally supported by a bifurcated portion 7 of an upstream exhaust pipe.
2, the lever 13 integrated with the rotary shaft 12 is rotated by the air actuator 14 to switch and hold the valve body 111 to a predetermined opening degree.

Here, the air actuator 14 is provided with a negative pressure chamber 141, which faces the negative pressure chamber 141 and is linked to the lever 13 by a link 1.
A diaphragm 142 connected via 7 and a return spring 143 that presses the diaphragm 142 are provided. The negative pressure chamber 141 has an intake passage 16 downstream of a throttle valve 18 as a negative pressure source via an opening / closing valve 15. It is connected. In addition,
The actuator for driving the switching valve may be replaced with the air actuator 14 described above, and for example, a well-known rotation transmission means including a step motor and a gear train for transmitting the rotation of the motor to the rotary shaft 12 may be used.

The on-off valve 15 is a duty valve and has an EC
It is switched to U3 and driven. The on-off valve 15 completely releases the negative pressure chamber 141 to the atmosphere when the duty ratio is 0% off, strengthens the negative pressure of the negative pressure chamber 141 according to the increase of the duty ratio, and resists the return spring 143. It is configured to pull the lever 13 more greatly. That is, the switching valve 1
When the duty ratio of the on-off valve 15 is equal to or lower than a predetermined level, the first valve body 111 receives the elastic force of the return spring 143 to fully open the bypass passage 202 and close the upstream main passage 201 (the position shown by the solid line in FIG. 1). The first position P1 is held.

On the contrary, the valve body 111 has a diaphragm 142 when the duty ratio of the on-off valve 15 exceeds a predetermined level.
By this action, the bypass passage 202 starts to close against the return spring 143, and the upstream main passage 201 starts to open. When the duty ratio exceeds the fully open level, the upstream main path 201 is opened and the bypass path 202 is closed at the second position P2 (the position shown by the chain double-dashed line in FIG. 1). Here, a valve opening sensor 19 is provided opposite to the link 17, and the sensor 19 outputs an analog output corresponding to the opening of the switching valve 11 to an A / D converter (not shown), and the digital output of the A / D converter. Output is ECU3
It is configured to be output to.

The warm-up catalyst 9 in the upstream main path 201 is arranged relatively close to the exhaust port 102 of the combustion chamber 101 on the engine body 1 side, and the latter-stage catalyst 10 described later is arranged relatively distant from the exhaust port 102. The warm-up catalyst 9 is composed of a three-way catalyst and has a sufficiently small capacity as compared with the post-stage catalyst 10. The warm-up catalyst 9 has a monolithic carrier, and a well-known three-way catalytically active component is attached to the inner wall surface of the carrier. Therefore, when the exhaust gas passing through the carrier has an air-fuel ratio at that time in the vicinity of stoichiometry and is at the activation temperature, HC, CO, and NO _x redox treatment can be performed, and the detoxified exhaust gas can be discharged. I can. It should be noted that instead of the three-way catalyst, an oxidation catalyst may be used as the pre-stage catalyst to reduce the cost. As this oxidation catalyst, a palladium (Pd) -based catalyst having a low light-off temperature can be used.

The post-catalyst 10 is arranged on the downstream exhaust pipe 6 which is downstream of the confluent portion 8 of the upstream exhaust pipe 5. The latter-stage catalyst 10 is housed in a single cylindrical catalyst case 21, and the lean NO _x catalyst 22 and the three-way catalyst 23 are arranged along the exhaust passage direction.
Is adopted in this order. In addition, this lean NO
_{The X} catalyst 22 and the three-way catalyst 23 were housed in a single catalyst case 21 for compactness, but in some cases,
A configuration may be adopted in which the catalysts are housed in individual catalyst cases (not shown) and both cases are sequentially connected. Here, the lean NO _x catalyst 22 has a monolithic carrier, and the catalytically active component is attached to the entire inner wall surface thereof. The catalytically active component here is capable of reducing NO _x by excess oxygen (lean air-fuel ratio), and as shown in FIG. 4, when the HC / CO ratio is above a predetermined value, the NO _x purification rate (η _NOX ) shows high level characteristics.
That is, when the air-fuel ratio of the exhaust gas at that time is in a lean atmosphere and at the activation temperature, NO _x is reduced by HC as a reducing agent to render it harmless.

The three-way catalyst 23 on the rear side is formed to have a sufficiently large capacity as compared with the warm-up catalyst 9 on the front stage, and the stoichiometric catalyst is formed on the entire inner wall surface of the monolith-type carrier like the warm-up catalyst 9 on the front stage. It adopts a well-known structure to which a catalytically active component that can be subjected to redox treatment in an atmosphere is attached. In this way, the post-stage catalyst 10 is constituted by the lean NO _X catalyst 22 and the three-way catalyst 23 downstream thereof, so that the exhaust gas purification performance of both catalysts is improved.

The outline of the automobile exhaust gas purifying apparatus of FIG. 1 is shown in FIG. 2 (a). Here, the front exhaust passage length L1 between the combustion chamber 101 of the engine 1 and the warm-up catalyst 9 is set. On the other hand, the warm-up catalyst 9 and the post-stage catalyst 10
The rear exhaust passage length L2 between the two is set to a large value, which improves the performance of the warm-up catalyst 9 and increases the lean N
Thereby achieving a secure durability of the O _X catalyst 22. A main part of the ECU 3 is formed by a microcomputer, and performs well-known control processing such as fuel supply control to the engine E, ignition timing control, throttle valve drive control, and switching valve control. Therefore, the ECU 3 is provided with the above-mentioned valve opening sensor 1
9, a pre-stage catalyst temperature sensor 24 provided in the warm-up catalyst 9, a post-stage catalyst temperature sensor 25 provided in the lean NO _X catalyst 22, a water temperature sensor 26 attached to the engine body 1, an engine rotation sensor 27. , Etc. are connected and the respective detection signals are respectively fetched from these.

Here, the ECU 3 particularly has a function as a valve control means, and outputs a switching control signal corresponding to a predetermined opening degree to the air actuator 14 of the switching valve 11 according to the operation information of the engine E. The operation of the exhaust gas purifying apparatus for automobiles of FIG. 1 will be described below with reference to the control program of the ECU 3 (see FIG. 5) and the waiting time calculation map of FIG. When the engine key is turned on, the ECU 3 enters a well-known main routine, and the switching valve control process is reached during the process.

As shown in FIG. 5, in the switching valve control processing, first, data from each sensor is read and stored in a predetermined area. Then, it is determined whether or not the engine speed Ne is below the engine stop determination value Ne1, and if it is below that, it is considered that the engine is stopped, and the process proceeds to step a3, and the switching valve 11 (the switching valve 11 in FIGS. 5 and 6 is selected. Are all referred to as bypass valves) so that the output to the on-off valve 15 has a duty ratio of 0% in order to maintain the upstream main path 201 at the first position P1.
Hold on. As a result, the opening / closing valve 15 is closed, the negative pressure chamber is released to the atmosphere, and the process of switching the switching valve 11 to the first position P1 is performed. Thereafter, in steps a4 and a5, waiting for the switching valve 11 to reach the first position P1 and detecting that the switching valve 11 reaches the first position P1 from the output of the valve opening sensor 19,
If the first position P1 is not reached even after the elapse of the predetermined elapsed time T1, the fault display is output in step a6 and the process returns.

On the other hand, if it is determined that the engine is not stopped in step a2 and the process proceeds to step a7, the output of the water temperature sensor 26 as the engine temperature is read and it is determined whether the same value exceeds the warm-up completion determination value T2 of the engine. Is step a
If it is higher than 8, proceed to step a9. Warm-up completion judgment value T2
If it is lower, in step a8, the waiting time H1 that is relatively longer than the waiting time calculation map of FIG. 3 is read, and while the waiting time H1 has elapsed, the process proceeds to step a10 and the upstream main road 20
1 is opened and the switching valve 11 is switched to the second position P2 where the bypass passage 202 is closed and the waiting time H1 elapses before proceeding to step a13.

Steps a11 and a after step a10
12 waits for the switching valve 11 to reach the second position P2, and when it is detected from the output of the valve opening sensor 19 that the switching valve 11 reaches the second position P2, it returns as it is, and even if a predetermined elapsed time T1 elapses, 2 If the position P1 is not reached, step a
Proceed to step 6, issue a fault output, and return. Step a9, assuming that the engine temperature exceeds the warm-up completion determination value T2
When the process proceeds to step 2, here, a relatively short waiting time H2 is read from the waiting time calculation map, and while the waiting time H2 is elapsed, the process proceeds to step a10 to switch to the second position P2 where the upstream main road 201 is opened and the bypass road 202 is closed. When the valve 11 is switched and it is determined that the waiting time H2 has elapsed, step a13
Proceed to.

When step a13 is reached assuming that the waiting time H1 or H2 has elapsed, the post-catalyst temperature T3 is fetched from the output of the post-catalyst temperature sensor 25, and it is determined whether the same value exceeds the activation completion temperature Tr of the post-catalyst. If it is lower, the process proceeds to step a14, and if it is higher, the process proceeds to step a3. In step a14, the pre-catalyst temperature T4 is taken in from the pre-catalyst temperature sensor 24, and it is determined whether or not this value exceeds the activation completion temperature Tf of the pre-catalyst. If the value is lower, the process proceeds to step a10, and the upstream main path 201 is opened. The switching valve 11 is held at the position P2 to increase the temperature of the warm-up catalyst 9, and when it exceeds the temperature, the process proceeds to step a15. It should be noted that here, the rear catalyst temperature T3 is detected by the rear catalyst temperature sensor 25.
In addition, although the front catalyst temperature T4 is fetched from the front catalyst temperature sensor 24, the exhaust gas temperatures near the rear catalyst and near the front catalyst may be fetched in some cases, and the same temperature determination may be performed.

In step a15, the warm-up catalyst 9
Has reached the activation completion temperature Tf, and the post-catalyst has reached the activation completion temperature Tf.
Since it has not reached r, the switching valve 11 is held at the intermediate opening degree P3. By this processing, a part of the exhaust gas is caused to flow into the bypass passage 202 in advance to heat the same, and the temperature of the exhaust gas is increased by the passage of the bypass passage 202 at the time of switching to the first position P1 where the bypass passage 202 is fully opened thereafter. By suppressing the decrease, the purification efficiency is prevented from decreasing due to the lower temperature of the post-catalyst. The intermediate opening P3 regulates the amount of exhaust gas flowing into the upstream main path 201,
The opening value is experimentally set in advance so that a part of exhaust gas can be supplied to 02. Further, this intermediate opening P
3 may be set to keep the switching valve 11 held for a predetermined time Tw to sufficiently heat the bypass passage 202. In this case, the bypass valve 202 may be set for a predetermined time Tw while returning from step a16. The step of waiting processing may be added.

Steps a16 and a after step a15
At 17, waiting for the switching valve 11 to reach the intermediate opening P3, and when it is detected from the output of the valve opening sensor 19 that it reaches the intermediate opening P3, the routine returns and the intermediate time is reached even if a predetermined waiting time T1 has elapsed. If the opening P3 is not reached, step a
At 6, a fault output is issued and the process returns. In the above description, for example, when the duty ratio of the on-off valve 15 is turned off by 0% due to the disconnection of the control system and the negative pressure chamber 141 is released to the atmosphere, the return spring 143 operates and the switching valve 11 is moved to the first position P1. It will be retained. In the event of such a control system failure or when closing the upstream main path 201, the first position P
When the switching valve 11 is held at 1 for a long time, the switching valve 11 may stick to the inner wall of the exhaust pipe. However, at this first position P1, the bypass passage 202 opens,
Since the supply of HC to the lean NO _x catalyst 22 is secured, the NO _x purification rate can be prevented from lowering, and further, the upstream main path 201 can be closed to prevent the heat deterioration of the warm-up catalyst 9, and fail safe at the time of market shipment. It can have a function.

In the above description, FIG. 1 and FIG.
Stage catalyst temperature sensor 24 is an exhaust gas purifying apparatus for an automobile of warming up the catalyst 9 (a) and the lean NO _X catalyst 22
The middle-stage catalyst temperature sensor 25 is used to detect when the warm-up catalyst 9 has reached the activation completion temperature Tf and the latter catalyst has not reached the activation completion temperature Tr, and the switching valve 11 is held at the intermediate opening degree P3. However, instead of this, FIG.
As shown in (b), the warm-up catalyst 9 reaches the activation completion temperature Tf and the latter catalyst does not reach the activation completion temperature Tr only with the latter-stage catalyst temperature sensor 25 in the lean NO _X catalyst 22, and Set the switching valve 11 to the intermediate opening P3.
The exhaust gas purifying apparatus for automobiles may be configured to hold the above.

The entire structure of the exhaust gas purifying apparatus for an automobile in this case is different from the exhaust gas purifying apparatus for automobiles shown in FIG. 1 in that the pre-catalyst temperature sensor 24 is eliminated, and the duplicated description will be omitted. Further, FIG. 6 shows a switching valve control processing routine performed by the exhaust gas purifying apparatus for automobiles of FIG. 2 (b). Here, only step a14 ′ is different from step a14 of FIG. 5, and duplicate description of other parts is omitted.

That is, in the switching valve control processing routine of FIG. 2B, the processing from step a8 or step a9 to step a13 is performed in the same manner as in FIG. The exhaust gas temperature T3 of the catalyst is taken in, and while the same value is lower than the activation completion temperature Tr of the post-catalyst, the process proceeds to step a14 ', and when it exceeds the same, the process proceeds to step a3 described above. At step a14 ′, the differential value ΔT (= ΔT _n-1 −Δ of the exhaust gas temperature T3 of the latter-stage catalyst is obtained.
T _n ) is calculated, and it is determined whether or not the level of the differential value ΔT exceeds a determination value ΔTα corresponding to a temperature gradient at which it can be considered that the pre-catalyst has reached the activation completion temperature Tf. Here, while the temperature is below the lower limit, the process proceeds to step a10, the switching valve 11 is held at the second position P2 that opens the upstream main path 201, and the warm-up catalyst 9
The temperature of the bypass passage 20 is maintained at the intermediate opening degree P3 when the temperature of the bypass passage 20 exceeds the temperature of the bypass valve 20.
2 is performed, and thereafter, the same processing as the switching valve control processing routine of FIG. 5 is performed.

In this case, in particular, the front catalyst temperature sensor 24
There is an advantage that can be eliminated. In the automobile exhaust gas purifying apparatus shown in FIG. 2B, the switching valve 11 is switched only by the rear catalyst temperature sensor 25. On the contrary, the switching valve 11 is switched only by the output of the front catalyst temperature sensor 24. It is also possible to adopt various configurations. In the exhaust gas purifying apparatus for automobiles shown in FIG. 1, the switching valve 11 is attached to the bifurcated branch portion 7 of the upstream exhaust pipe 5, but instead of this, a switching valve 11 ′ may be provided in the merging portion 8 on the downstream side. Well, the schematic configuration in this case is shown in FIG. 7, and an example of the switching valve 11 'is shown in FIG.

The exhaust gas purifying apparatus for an automobile shown in FIG. 8 has the same structure as that of the exhaust gas purifying apparatus for an automobile shown in FIG. 1, except that the mounting position of the switching valve 11 'is different, and a duplicated description thereof will be omitted. Here, in particular, a rotary shaft 12 is pivotally supported at a connecting portion between the merging portion 8 on the downstream side of the upstream exhaust pipe 5 and the downstream exhaust pipe 6, and a switching valve 11 ′ integrated with the rotary shaft 12 has an air flow similar to that described above. It is configured to be rotated by the actuator 14. Also in this case, the valve main body 111 closes the upstream main path 201 (the position shown by the solid line in FIG. 8) at the first position P1 and the second position P2 that opens the upstream main path 201 and closes the bypass path 202 (indicated by the broken line in FIG. 8). (The position shown) and the intermediate opening P3 (not shown) are switched and maintained, and the exhaust gas purifying apparatus for an automobile shown in FIG. 8 can obtain the same effect as that of the apparatus shown in FIG.

Although the exhaust gas purifying apparatus for automobiles of FIG. 1 employs the output of the water temperature sensor 26 as the temperature of the engine body 1, instead of this, the oil temperature of the engine or the wall temperature of the cylinder block may be used. good. In the exhaust gas purifying apparatus for automobiles of FIG. 1, the ECU 3 as the valve control means controls the opening / closing of the switching valve 11 in accordance with the front and rear catalyst temperatures, but instead of this, the elapsed time after the start of the engine is started. According to the first opening P1, the intermediate opening P3 and the second opening P2.
It is also possible to adopt a configuration in which it is more selectively obtained and sequentially switched. In this case, each temperature sensor can be eliminated. Furthermore, FIG.
As a valve control means of an automobile exhaust gas purification apparatus
3 sets the opening degree of the switching valve 11 to the first opening degree P1, according to the catalyst temperature before and after and the elapsed time after the start of engine start.
A configuration may be adopted in which the intermediate opening P3 and the second opening P2 are selectively obtained and sequentially switched. In this case, the opening degree of the switching valve 11 can be controlled more accurately according to the warm-up of the engine and each catalyst.

[0034]

As described above, according to the first aspect of the present invention, the exhaust gas can be made to flow into the pre-catalyst only at a predetermined time by the opening / closing process of the switching valve, and the lean NO _X catalyst can be provided in at least a part of the post-catalyst on the exhaust passage. Even if it is deployed, it does not reduce its purification efficiency and durability.

In the second aspect of the invention, since the valve control means controls the opening / closing of the switching valve in accordance with the operating information of the internal combustion engine, for example, the exhaust gas is purified by the pre-catalyst at the beginning of engine operation,
Engine operation start early after direct exhaust gases to flow into the post-catalyst can purify, can improve at least the purification efficiency of some of the lean NO _X catalyst in the subsequent stage catalyst, in particular, fail-safe during fixation of the switching valve It can have a function.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an automobile exhaust gas purifying apparatus as an embodiment of the present invention.

2 (a) is a schematic view of the exhaust gas purifying apparatus of FIG. 1,
(B) is a schematic view of an exhaust gas purifying apparatus as another embodiment of the present invention.

3 is a characteristic diagram of a waiting time calculation map used by the ECU of the exhaust gas purification apparatus of FIG.

FIG. 4 is a purification characteristic diagram of a lean NO _x catalyst.

5 is a flow chart of a switching valve control routine executed by the ECU of the exhaust gas purification apparatus of FIG.

FIG. 6 is a flowchart of a switching valve control routine executed by the ECU of the exhaust gas purification apparatus of FIG. 2 (b).

FIG. 7 is a schematic diagram of an exhaust gas purifying apparatus as another embodiment of the present invention.

8 is an enlarged partial sectional view of a switching valve and an exhaust passage used in the exhaust gas purifying apparatus of FIG.

[Explanation of symbols]

1 Engine Main Body 2 Exhaust Path 3 ECU 5 Upstream Exhaust Pipe 7 Bifurcated Section 8 Confluence Section 9 Warm-up Catalyst 10 Rear Catalyst 11 Switching Valve 14 Air Actuator 22 Lean NO _X Catalyst 23 Three-way Catalyst 101 Combustion Chamber 201 Upstream Main Path 202 Bypass E engine

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location F01N 3/24 B 9150-3G 3/28 301 F 9150-3G (72) Inventor Kazuo Koga Tokyo 5-33-8 Shiba, Minato-ku, Mitsubishi Motors Corporation

Claims (2)

[Claims] 1. A and precatalyst that is close to the combustion chamber of an internal combustion engine, and a rear stage catalyst comprising a lean NO _X catalyst is deployed in the rear of the front catalyst sequentially provided in an exhaust path, the pre-catalyst mainly engine operation In an exhaust gas purifying apparatus for an automobile configured to perform exhaust gas purification in an initial stage, the exhaust passage is provided with a bypass passage that bypasses the front catalyst and joins the exhaust passage upstream of the rear catalyst. An exhaust gas purifying apparatus for an automobile, comprising: a switching valve for controlling an exhaust gas flow rate flowing into each of the bypass passage and the pre-stage catalyst according to operation information of the internal combustion engine. 2. A sequence and a rear stage catalyst comprising a pre-catalyst and are deployed at the rear of the front catalyst lean NO _X catalyst proximate to the combustion chamber of an internal combustion engine in the exhaust path, the pre-catalyst mainly engine operation start In an exhaust gas purifying apparatus for an automobile configured to perform initial exhaust gas purification, a bypass passage is provided in the exhaust passage that bypasses the front catalyst and joins the exhaust passage upstream of the rear catalyst. A switching valve for controlling the flow rate of exhaust gas flowing into the passage and the front catalyst, and valve control means for outputting a switching control signal corresponding to a predetermined opening degree to the actuator of the switching valve according to the operation information of the internal combustion engine. The exhaust gas purifying apparatus for an automobile, wherein the valve control means switches the switching valve to a position where the bypass passage is opened when the engine is stopped.