JPH05231138A - Exhaust emission control device for automobile - Google Patents

Abstract

PURPOSE:To improve the purification efficiency and durability of a lean NOx catalyst for each operation condition of an engine, when a forestage catalyst and a rearstage catalyst containing the lean NOx catalyst at least at a part behind the forestage catalyst are arranged on an exhaust passage. CONSTITUTION:A forestage catalyst 9 in close to the combustion chamber 10 of an internal combustion engine E and a rear stage catalyst 10 including a lean NOx catalyst 22 behind are provide. The forestage catalyst 9 is constituted so as to carry out the exhaust gas purification in the initial stage of the start of the engine operation, and in particular, in an exhaust passage 2, the first bypass passage 202 which makes a detour around only the forestage catalyst 9 and converges with the exhaust passage 2 and the second bypass passage which makes a detour only around the lean NOx catalyst 22 in the rear stage catalyst and converges with the exhaust passage 2 are formed. The first selector valve 11 for controlling the exhaust gas flow rate which flows into the first bypass passage 202 or the forestage catalyst 9 is installed. The second selector valve 27 for controlling the exhaust gas flow rate which flows into the second bypass passage 32 or the lean NOx catalyst 22 is installed.

Description

Detailed Description of the Invention

[0001]

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

[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 exhibit an appropriate catalytic action during lean combustion under excess oxygen (lean air-fuel ratio) and satisfies various exhaust gas regulations. It 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, one example in JP 60 over 125,250 that It is disclosed.

[0004] The lean NO _X catalyst, in particular, and that a large deterioration at high temperatures, the deterioration in terms and rich atmosphere or stoichiometric atmosphere that requires HC component to purification of the NO _X is large, the actual vehicle equipped Leaving the problem above.
As shown in FIG. 3, 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, conventionally, a pre-stage 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-stage 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, moreover, the engine is not resolved even point Okiki degradation of the lean NO _X catalyst in was operated rich or stoichiometric, lean NO The problem of durability of the _X catalyst 22 has not been sufficiently solved.

An object of the present invention, when deployed and the rear stage catalyst having a lean NO _X catalyst in at least a portion precatalyst and its rear exhaust path, the lean NO _X catalyst for each operating condition of the engine An object of the present invention is to provide an exhaust gas purifying apparatus for automobiles, which can ensure the purification efficiency of the above with good durability.

[0008]

Means for Solving the Problems In order to achieve the above object, a rear catalyst This invention containing lean NO _X catalyst is deployed behind the front catalyst and the pre-stage catalyst that is close to the combustion chamber of an internal combustion engine Is provided on the exhaust passage, and the pre-stage catalyst is mainly configured to purify exhaust gas at the initial stage of engine operation. In particular, the first bypass bypasses only the pre-stage catalyst in the exhaust passage and joins the exhaust passage. The second passage that bypasses only the lean NO _x catalyst in the latter-stage catalyst and joins the exhaust passage
A bypass passage is provided, the first bypass passage or flow rate of the exhaust gas flowing into said precatalyst is provided a first switching valve for controlling in accordance with the operation information of the internal combustion engine, the second bypass passage or said lean NO _X Second control for controlling the flow rate of exhaust gas flowing into the catalyst according to the operation information of the internal combustion engine
A vehicle characterized by being provided with a switching valve.

[0009]

[Action] The first switching valve is controlled in accordance with the operation information of the engine exhaust gas flow rate flowing into the first bypass passage or pre-catalyst, an exhaust gas second switching valve flows into the second bypass passage or lean NO _X catalyst since controlled according to flow rate operation information of the internal combustion engine, the exhaust gas only a predetermined time to flow into the pre-catalyst, the lean NO _X catalyst 2 of the exhaust gas only a predetermined time
The catalyst can purify the exhaust gas properly by allowing the exhaust gas to flow into the exhaust gas.

[0010]

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 provided with an exhaust branch pipe 4 connected to the engine body 1, a warm-up catalyst 9 as a pre-catalyst, and a first bypass passage 202 that bypasses the warm-up catalyst 9, which is continuously connected to a merging portion thereof. The pipe 5, the downstream catalyst 10 connected to the downstream end thereof, and the lean NO _X catalyst 2 in the latter catalyst 10
The downstream exhaust pipe 6 is provided with a second bypass passage 32 that bypasses only 2 and a muffler (not shown).

The upstream exhaust pipe 5 is branched between the upstream bifurcating portion 7 and the downstream merging portion 8 so as to bypass the upstream main passage 201 equipped with the warm-up catalyst 9 as the pre-catalyst and the pre-catalyst. The first bypass passage 202 is arranged in parallel. In particular, here, the bifurcating part 7 is provided with the first switching valve 11 for increasing / decreasing the exhaust gas flow rate that can flow into the upstream main path 201 or the first bypass path 202.
The first switching valve 11 includes a rotary shaft 12 pivotally supported by the bifurcated portion 7 of the upstream exhaust pipe, and the lever 1 integrated with the rotary shaft 12.
By rotating 3 by the air actuator 14, the valve body 111 is switched to a predetermined opening degree and held.

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 first switching valve may be replaced by the air actuator 14 described above, and for example, a well-known rotation transmitting means including a step motor and a gear train for transmitting the rotation of the motor to the rotating shaft 12 may be used.

The on-off valve 15 is a duty valve and is 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 valve body 111 of the first switching valve 11 receives the elastic force of the return spring 143 and fully opens the first bypass passage 202 and closes the upstream main passage 201 when the duty ratio of the opening / closing valve 15 is equal to or lower than a predetermined level. The position indicated by the solid line 1) is held at the first position P1.

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.
Of the first bypass passage 202 against the return spring 143.
Is started, and the upstream main path 201 is not opened until the exhaust gas starts flowing into the warm-up catalyst 9. When the duty ratio exceeds the fully open level, the upstream main road 2
The second position P2 which opens 01 and closes the first bypass passage 202
(The position indicated 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 first switching valve 11 to an A / D converter (not shown), and a digital output of the A / D converter. Is output to the ECU 3.

The warm-up catalyst 9 has a monolith-type 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 downstream exhaust pipe 6 bypasses only the lean NO _x catalyst 22 and the rear stage catalyst 10 in which the lean NO _x catalyst 22 and the three-way catalyst 23 are arranged in this order along the flow direction of the exhaust passage 2. 2 bypass passage 32. A part of the downstream exhaust pipe 6 lean NO _X catalyst 22 and the three way catalyst 2
3 is a single cylindrical catalyst case 21,
33 and are connected to each other in sequence. In addition,
The lean NO _X catalyst 22 and the three way catalyst 23 housed in a single catalyst case 21 may be compactified.

Here, the second bypass passage 32 has its branch portion 3
4 and the merging portion 35 (upstream position of the three-way catalyst 23 on the rear side) are communicated with the exhaust passage 2, and a second switching valve 27 is provided in the middle thereof, which opens and closes the second bypass passage 32. .. The valve body 271 of the second switching valve 27 is a butterfly valve, and the link 29 of the air actuator 26 is pin-coupled to the valve body 271 via a lever 30 integral with the butterfly valve.

Here, the air actuator 26 is formed similarly to the air actuator 14 of FIG.
A diaphragm 36 to which one end of the diaphragm 9 is connected, a negative pressure chamber 28 facing the diaphragm, and a return spring 37 for pressing the diaphragm 36 are provided, and the negative pressure chamber 28 is provided with an intake valve downstream of the throttle valve 18 via an opening / closing valve 31. The passage 16 is connected. Here, a valve opening sensor 38 is provided opposite to the link 29, and the sensor outputs an analog output corresponding to the opening of the second switching valve 27 to an A / D converter (not shown), and the analog output of the A / D converter is not shown. The digital output is configured to be output to the ECU 3.

The on-off valve 31 is an on / off valve, and the ECU
It is switched to 3 and driven. The on-off valve 31 is configured to completely open the negative pressure chamber 28 to the atmosphere when it is off, and strengthen the negative pressure of the negative pressure chamber 28 when it is on. That is, the second switching valve 27 is held at the first position Q1 by fully closing the second bypass passage 202 (the position shown by the solid line in FIG. 1) when the opening / closing valve 31 is on, and the exhaust gas flows into the lean NO _x catalyst 22. It can be done. On the contrary, when the on-off valve 31 is off, the second bypass passage 202
Is held in the second position Q2 where the exhaust gas is fully opened
Bypassing the O _X catalyst 22 can be supplied directly to the three-way catalyst 23.

The lean NO _x catalyst 22 has a monolith type 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. 3, when the HC / CO ratio is above a predetermined value, the NO _x purification rate (η _NOX )
Shows a high level characteristic. 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 on the entire inner wall surface of the monolith-type carrier in the same stoichiometric atmosphere as the warm-up catalyst 9 on the front stage. It adopts a well-known structure to which a catalytically active component capable of redox treatment is attached. In this way, the rear catalyst 10 is the lean NO _X catalyst 22.
And the three-way catalyst 23 downstream thereof,
We are trying to improve the exhaust gas purification performance of both catalysts.

The outline of the automobile exhaust gas purifying apparatus of FIG. 1 is shown in FIG. 2 (a), but here, in the front exhaust passage length L1 between the combustion chamber 101 of the engine 1 and the warm-up catalyst 9, 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
In addition to 9, the linear air-fuel ratio sensor 24 that outputs over the whole area of the air-fuel ratio (A / F) information of the exhaust gas while being mounted on the exhaust passage 2, the rear stage to output the exhaust gas temperature information of the lean NO _X catalyst 22 position A catalyst temperature sensor 25, 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 is provided with a function as a valve control means, in particular, according to the operating information of the engine E.
Air actuator 1 for each second switching valve 11, 27
A switching control signal corresponding to a predetermined opening is output to 4, 26. The operation of the exhaust gas purifying apparatus for automobiles shown in FIG.
The control program of the CU 3 (see FIGS. 6 and 7) and the waiting time calculation map of FIG. 3 will be described. 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.

In the switching valve control process as shown in FIGS. 6 and 7, 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 a4, where the first switching valve 11 closes the upstream main path 201 at the first position. The duty ratio of the output to the on-off valve 15 should be 0% to maintain P1.
Hold on. As a result, the opening / closing valve 15 is closed, the negative pressure chamber is released to the atmosphere, and the first switching valve 11 is switched to the first position P1. At the same time, an ON output is issued to keep the second switching valve 27 at the first position Q1. As a result, the on-off valve 31 is turned on, the negative pressure chamber 28 is made negative, and the second switching valve 27
To the first position Q1 (indicated by a symbol e in FIG. 5 to indicate a stopped state).

Thereafter, at step a6, the first switching valve 11 waits for the first position P1 and the second switching valve 27 for the first position Q1, respectively, and the valve opening sensors 19, 3 are detected.
When it is detected from the output of No. 7 that the first position P1 and the first position Q1 are reached, the process directly returns and a predetermined elapsed time T1
If the first position P1 and the first position Q1 are not reached even after the passage of, the fault display is output in step a7 and the process returns.

On the other hand, assuming that the engine is not stopped at step a2, the process proceeds to step a3, at which the output of the water temperature sensor 26 as the engine temperature is read, and the same value is used as the engine warm-up completion determination value T.
If it is higher than 2, it is determined that it is lower, step a9.
If it is higher, the process proceeds to step a8. Assuming that the warm-up completion determination value T2 is lower than the warm-up completion determination value T2, a relatively long waiting time H1 is read from the waiting time calculation map of FIG. 3, and while the waiting time H1 is elapsed, the process proceeds to step a11 and the upstream main road 201
Is opened and the bypass valve 202 is closed to switch the switching valve 11 to the second position P2, and after the waiting time H1, the process proceeds to step a10.

Steps a12 and a after step a11
At 13, when waiting for the switching valve 11 to reach the second position P2 and detecting that it reaches the second position P2 from the output of the valve opening sensor 19, the process proceeds to step a14, and even if a predetermined elapsed time T1 elapses. If the second position P1 is not reached, the process proceeds to step a6, a fault output is issued, and the process returns. Step a assuming that the engine temperature exceeds the warm-up completion determination value T2.
8, the waiting time H2, which is relatively shorter than the waiting time calculation map, is read here, and while the waiting time H2 has elapsed, the process proceeds to step a11, where the upstream main road 201 is opened and the bypass 202 is closed to the second position P2. When the switching valve 11 is switched and it is determined that the waiting time H2 has elapsed, step a1
Go to 0. Here, the exhaust gas temperature T3 of the post-catalyst is taken in from the post-catalyst temperature sensor 25, and while the same value is lower than the activation completion temperature Tr of the post-catalyst, the process proceeds to step a15, and when it exceeds, the process proceeds to step a16 described above.

At step a15, the differential value ΔT (= ΔT _n-1 -ΔT _n ) of the exhaust gas temperature T3 of the latter stage catalyst is calculated, and the level of the differential value ΔT indicates that the warm-up catalyst 9 has reached the activation completion temperature Tf. Judgment value ΔTα corresponding to the temperature gradient that can be considered
Or not. Here, while falling below the temperature, the routine proceeds to step a11, where the first switching valve 11 is held at the second position P2 that opens the upstream main path 201, the temperature of the warm-up catalyst 9 is increased, and if it exceeds, the routine proceeds to step a19 and the first The switching valve 11 is held at the intermediate opening degree P3 (for example, the case where this state is reached at the time point t1 in the stoichio region is shown by the symbol n in FIG. 5), and the heating of the bypass passage 202 is started.

In the automobile exhaust gas purification apparatus shown in FIG. 1, only the rear catalyst temperature sensor 25 is used for the first switching valve 11
However, conversely, it is possible to adopt a configuration in which a pre-catalyst temperature sensor (not shown) is provided in the warm-up catalyst 9 and the switching valve 11 is switched only by the output of the sensor. Step a2 after step a19
At 0 and a21, the switching valve 11 waits until it reaches 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, it returns as it is and even after a predetermined elapsed time T1 elapses. If the intermediate opening P3 is not reached, the process proceeds to step a7, a fault output is issued, and the process returns.

When the subsequent stage catalyst temperature T3 exceeds the activation completion temperature Tr from step a10 and the process reaches step a16, the first switching valve 11 is set to the first opening degree P1 as shown by the chain double-dashed line m in FIG. Switching, the subsequent step a1
7 and a18, the switching valve 11 waits for the first opening P1 to reach the first opening P1, and when it is detected from the output of the valve opening sensor 19 that the first opening P1 is reached, the process proceeds to step a22, and the predetermined elapsed time T1 is passed. If the first opening P1 has not been reached even after the lapse of time, the routine proceeds to step a7, where a failure output is issued and the routine returns.

When step a22 is reached, here, the air-fuel ratio information is taken in based on the output of the linear air-fuel ratio sensor 24, it is judged whether or not the air-fuel ratio is in the lean range, and if lean, the process proceeds to step a23, otherwise, that is, If it is the time point (for example, time point t2 in FIG. 5) when switching to the stoichio area or the rich area, the process proceeds to step a24, the second switching valve 27 is switched to the second position Q2 that opens the second bypass passage 32, and is held. Go to a25, 26. Here, it waits for the second switching valve 27 to reach the second position Q2, and when it is detected from the output of the valve opening sensor 19 that the second switching valve 27 reaches the second position Q2, the process returns without further processing, and a predetermined elapsed time T1 elapses. Also does not reach the second position Q2, the process proceeds to step a7, where a failure display is issued and the process returns. In this way, the second switching valve 27 is set to the second position in the region other than the lean operation.
Lean NO _x catalyst 2 by holding at position Q2
Stoichiometric range to 2, reducing the exhaust gas in the rich region to flow, it is possible to improve the durability of the lean NO _X catalyst 22.

On the other hand, when a23 is reached as the lean operating range from step a22, the rear catalyst temperature sensor 2 is detected here.
The exhaust temperature information at the position of the lean NO _X catalyst 22 is fetched by 5, and it is judged whether or not this value exceeds a fixed value allowed by the post-catalyst, that is, the upper limit value T _MAX on the high temperature side. 2 Open the bypass 32 (Fig. 5
It indicated by the two-dot chain line b in) to prevent high-temperature degradation of the lean NO _X catalyst 22. On the other hand, if it is below step a14
Then, in step a14, the second switching valve 27 is set to the first
By switching to the opening degree Q1 and closing the second bypass passage 32, the exhaust gas in a lean atmosphere is supplied to the lean NO _x catalyst 22. When the process proceeds from step a14 to steps a27 and 28, here, the second switching valve 27 waits until it reaches the first position Q1, and the output of the valve opening sensor 19 determines the first position Q1.
When it is detected that the number reaches 1, the process returns as it is, and if the first position Q1 is not reached even after the lapse of a predetermined elapsed time T1, the process proceeds to step a7, where a failure display is output and the process returns.

Thus, in the lean operation range, step a
At 16, the first switching valve 11 is switched to the first position P1 to prevent the warm-up catalyst 9 from consuming HC,
Since directing exhaust gas from the combustion chamber 101 including the HC closes the second bypass passage 32 as it is lean NO _X catalyst 22, as long as the lean NO _X catalyst 22 is not excessively heated,
That is, unless the upper limit T _MAX on the high temperature side is exceeded, lean NO _x
It is possible to avoid a decrease in NO _x purification efficiency in the lean region of the catalyst 22. In FIG. 5, the solid line a shows a state in which the first switching valve 11 is held at the first position P1 and the second switching valve 27 is kept at the first position Q1 at time t3.

As described above, here, when the engine is stopped, the first
The switching valve 11 is opened to the first position P1 and the second switching valve 27 is held at the first position Q1. For this reason, since the exhaust gas does not flow through the warm-up catalyst 9, even if the first switching valve 11 remains held at the first position P1 for a long time and sticks to the inner wall of the exhaust pipe, this first position P1
Then, the first bypass passage 202 opens, and the lean NO _X catalyst 2 is opened.
It becomes possible to supply HC to No. 2. Therefore, lean NO
The NO _x purification rate of the _X catalyst 22 is prevented from lowering, the upstream main path 201 is closed, the heat deterioration of the warm-up catalyst 9 is also prevented, and the fail safe function at the time of market shipment can be maintained. The second switching valve 27 shown in FIG.
When the switch valve 31 is turned on, the first opening degree Q1 is switched to, but instead of this, when the on-off valve 31 is turned off, the second switch valve 27 is switched to the first opening degree Q1.
The configuration may be such that the opening degree is switched to Q1. In this case, when the engine is stopped, the first bypass passage 202 is opened and the second bypass passage 202 is opened.
Since the bypass passage 32 is closed, the fail-safe function when both valves are stuck together can be further strengthened.

In the exhaust gas purifying apparatus for automobiles shown in FIGS. 1 and 2, the first switching valve 11 is provided at the bifurcated branch portion 7 of the upstream exhaust pipe 5, and the second switching valve 27 is provided at the middle portion of the second bypass passage 32.
However, instead of this, as shown in FIG. 2 (b), a first switching valve 11 is provided at the merging portion 8 on the downstream side,
The merging portion 35 of the second bypass passage 32 may be used. Even with such a configuration, it is possible to obtain the same operational effects as the device of FIG.

In the vehicle exhaust gas purifying apparatus shown in FIG. 1, the ECU 3 as the valve control means controls the opening / closing of the first switching valve 11 according to the temperature of the rear catalyst. The opening degree is the first opening degree P1 and the intermediate opening degree P3 according to the time (the opening degree between the first position and the second position where the exhaust gas can flow into the upstream main path 201 and the first bypass path 202). Alternatively, a configuration may be adopted in which the second opening P2 is selectively and sequentially switched. In this case, the exhaust gas purification efficiency at the time of starting can be improved at an early stage, and after warming up, the same operational effects as the device of FIG. 1 can be obtained. Further, the first switching valve 11 may be controlled to be opened / closed by using both the elapsed time after the start and the temperature of the latter stage catalyst. Further, the second switching valve 27 was switched depending on the air-fuel ratio and the post-catalyst temperature, but it may be switched only by the air-fuel ratio, instead of the post-catalyst temperature,
The switching may be controlled by the temperature of the exhaust gas near the rear catalyst.

[0036]

As described above, according to the present invention, the first switching valve controls the exhaust gas flow rate of the first bypass passage or the front stage catalyst, and the second switching valve controls the exhaust gas flow rate of the second bypass passage or the lean NO _x catalyst. and controls, the exhaust gas flowing into the front catalyst and the lean NO _X catalyst in accordance with the operation information of the internal combustion engine can be purified to accurately, particularly, the lean on at least a portion precatalyst and its rear exhaust path NO in the case _{where X} catalyst deployed and the rear stage catalyst having a purification efficiency and durability of the lean NO _X catalyst sufficiently be secured.

[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 layout diagram of the exhaust gas purifying apparatus of FIG. 1,
(B) is a schematic layout drawing 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 an operation explanatory view of each switching valve of the exhaust gas purifying apparatus of FIG. 1. FIG.

6 is a front part flowchart of a switching valve control routine executed by an ECU of the exhaust gas purifying apparatus of FIG.

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

[Explanation of symbols]

1 Engine Main Body 2 Exhaust Path 3 ECU 5 Upstream Exhaust Pipe 8 Merging Section 9 Warm-up Catalyst 10 Rear Catalyst 11 Switching Valve 14 Air Actuator 15 Solenoid Valve 22 Lean NO _X Catalyst 23 Three-way Catalyst 24 Air-fuel Ratio Sensor 26 Air Actuator 27 2nd Switching valve 31 Open / close valve 32 Second bypass passage 101 Combustion chamber 201 Upstream main passage 202 Bypass passage 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 (1)

[Claims] 1. A and a rear stage catalyst comprising a pre-catalyst and the deployed behind 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 initial In an exhaust gas purifying apparatus for an automobile configured to purify exhaust gas, a first bypass passage that bypasses only the front catalyst and joins the exhaust passage in the exhaust passage, and a lean NO _x catalyst in the rear catalyst. And a second bypass passage that joins the exhaust passage by bypassing only the first bypass passage.
A first switching valve for controlling the flow rate of the exhaust gas flowing into the bypass passage or the pre-stage catalyst according to the operation information of the internal combustion engine is provided, and the second bypass passage or the lean NO.
An exhaust gas purifying apparatus for an automobile, comprising a second switching valve for controlling the flow rate of exhaust gas flowing into the _X catalyst in accordance with the operation information of the internal combustion engine.