JP3113099B2 - Engine exhaust purification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly, to an apparatus having two branched exhaust passages.

[0002]

2. Description of the Related Art Conventionally, as one example of this type of exhaust gas purifying apparatus, as disclosed in Japanese Patent Application Laid-Open No. 3-141816, HC (hydrocarbon) in exhaust gas is adsorbed in an exhaust passage of an engine. An HC adsorbing member and an exhaust gas purifying catalyst are provided downstream of the HC adsorbing member, and a bypass passage is provided to bypass the HC adsorbing catalyst. Is H
It is known that the gas flows toward the C adsorbing member and flows into the bypass passage when the exhaust gas temperature increases.

[0003]

SUMMARY OF THE INVENTION In the above prior art,
When the exhaust gas temperature is low, a large amount of HC generated particularly during cranking of the engine can be adsorbed by the HC adsorbing member, and the emission performance can be improved. However, when the exhaust gas temperature is high, the exhaust gas flows by bypassing the HC adsorbing member, so that the HC adsorbed by the HC adsorbing member at a low temperature is retained as it is, and in terms of overall improvement in emission performance. There's a problem.

[0004] The present invention has been made in view of the above points, and an object of the present invention is to provide a method for controlling the emission of HC when the temperature of exhaust gas is high.
An object of the present invention is to improve the emission performance as a whole by positively purifying HC stored in a storage unit with a catalyst.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, a catalyst having a smaller capacity than the original catalyst and being easily warmed up is provided in the bypass passage. Then, the exhaust gas is passed through the catalyst to purify the exhaust gas while warming it up at an early stage. At a high temperature, the exhaust gas flows into the HC storage unit in the same manner as at a low temperature, and is trapped in the HC storage unit at a low temperature. HC was passed through the original catalyst for purification.

That is, in the present invention, as described above,
An HC storage portion for storing HC in the exhaust gas is provided in the exhaust passage, and a main catalyst means for purifying exhaust gas is provided downstream of the HC storage portion. The exhaust passage upstream of the HC storage portion and the HC storage portion are provided. An exhaust gas purifying device for an engine in which the exhaust passage on the part downstream side and the exhaust passage on the upstream side of the main catalyst means are connected by a bypass passage is premised.

The sub-catalyst having a smaller capacity than the main catalyst is disposed in the bypass passage, so that the heat resistance of the HC storage section is higher than that of the sub-catalyst.

When the exhaust gas temperature is low (for example, 1
When the temperature of the exhaust gas is in a middle temperature state (eg, 100 to 300 ° C.), the exhaust gas flows into the secondary catalyst when the temperature of the exhaust gas is in a middle temperature state (eg, 100 to 300 ° C.). A control means for switching the exhaust gas flow path so as to flow to the means is provided.

According to the second aspect of the present invention, there is provided means for reducing the minimum cross-sectional area of the exhaust passage on the HC storage portion side, that is, the exhaust passage between the portions where the upstream and downstream ends of the bypass passage are connected.

[0010] The control means is provided with a switching valve for closing the bypass passage when the exhaust gas temperature is low.

According to the third aspect of the present invention, H
The length of the exhaust passage to the C storage section is made longer than the length of the passage to the sub-catalyst means.

[0012]

According to the above construction, according to the first aspect of the present invention, the control means switches the exhaust gas flow path according to the exhaust gas temperature, and switches the exhaust gas to flow to the HC storage section when the exhaust gas temperature is low. Can be For this reason,
In particular, a large amount of HC generated during cranking of the engine
Flows into the HC storage section and is stored there, so that it is possible to prevent the HC from being discharged to the outside as it is, even when the main catalyst means is not activated during the cold period.

When the temperature of the exhaust gas rises to a medium temperature state, the exhaust gas is switched to flow to the sub-catalyst means in the bypass passage. In other words, the exhaust gas that has been heated to a medium temperature flows to the sub-catalyst means at a stretch, and the exhaust gas purification performance can be secured by quickly warming up the exhaust gas, and the HC can be efficiently purified. During this time, since the exhaust gas does not flow into the HC storage section, the HC stored therein is not released.

When the temperature of the exhaust gas further rises to a high temperature range, the control means switches the exhaust gas to flow again into the HC storage section. Therefore, at low temperatures, the HC stored in the HC storage section flows to the activated main catalyst means and is purified there. Thus, HC can be reliably purified, and emission performance can be improved as a whole. In addition, since the high-temperature exhaust gas does not flow to the sub-catalyst means, the heat damage can be avoided.

According to the second aspect of the present invention, since the minimum cross-sectional area of the HC storage section side exhaust passage is smaller than that of the bypass passage, the bypass passage is closed by the switching valve of the control means when the exhaust gas temperature is low. Then, the exhaust pressure increases due to the exhaust gas throttle loss, the engine load is increased, and the internal EGR in the engine is increased, so that the engine can be warmed up early. Therefore, the temperature of the exhaust gas can be quickly increased to activate the main catalyst means at an early stage. As a result, in the high temperature region where the stored HC is released from the HC storage section, the sufficiently activated main catalyst means is activated. Released by
C can be reliably purified.

According to the third aspect of the present invention, H
Since the passage length of the exhaust passage to the C storage unit is longer than the passage length to the sub-catalyst means, the heat resistance of the HC storage unit and the HC
Storage efficiency can be increased.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 shows an embodiment 1 of the present invention, in which 1 is an in-line four-cylinder engine having four cylinders 2, 2,..., And 3 is an exhaust gas from a combustion chamber in each cylinder 2. This is an exhaust passage for discharging. This exhaust passage 3 contains HC in the exhaust gas.
An HC adsorption catalyst 4 which constitutes an HC storage section for adsorbing and storing the gas, and an exhaust passage 3 downstream of the HC adsorption catalyst 4 are provided with a main catalyzer 5 as a main catalyst means for purifying exhaust gas. I have.

An upstream end of a bypass passage 6 is branched and connected to the exhaust passage 3 upstream of the HC adsorption catalyst 4, and a downstream end of the bypass passage 6 is an exhaust gas downstream of the HC adsorption catalyst 4 and upstream of the main catalyst 5. The exhaust gas is bypassed to the HC adsorption catalyst 4 by a bypass passage 6 and communicates with the passage 3.

The bypass passage 6 is provided with a pre-catalyst 7 as a sub-catalyst having a smaller capacity than the main catalyzer 5 near the upstream side thereof. It is set higher than the pre-cat 7. Further, the passage length LH of the exhaust passage 3 from the main body of the engine 1 to the HC adsorption catalyst 4 is longer than the passage length LP to the precatalyst 7 (LH> LP).

Further, a switching valve 8 for switching exhaust gas from the engine 1 so as to flow to one of the HC adsorption catalyst 4 and the precatalyst 7 (bypass passage 6) is provided at an upstream end of the bypass passage 6. The switching valve 8 is driven by an actuator 9 that operates upon receiving a control signal from a controller 17. An output signal of a temperature sensor 18 for detecting an exhaust gas temperature is input to the controller 17. In this embodiment, the controller 17, the actuator 9, and the switching valve 8 constitute a control unit according to the present invention, and when the exhaust gas temperature is low (for example, 100 ° C. or lower) and high (for example, (300 ° C. or more), the switching valve 8 closes the bypass passage 6 to flow the exhaust gas to the HC adsorption catalyst 4, while the exhaust gas temperature is in a middle temperature state (for example, 100 to 300).
(° C.), the exhaust gas flow path is switched so that the bypass passage 6 is opened by the switching valve 8 and the exhaust gas flows to the pre-catalyst 7.

Next, the operation of the above embodiment will be described. An exhaust gas temperature of the engine 1 is detected by a temperature sensor 18, and a signal from the temperature sensor 18 is input to the controller 17. And this controller 17
Is output to the actuator 9, the switching valve 8 is controlled to open and close, and the exhaust gas flow path in the exhaust passage 3 is switched according to the exhaust gas temperature. Specifically, when the exhaust gas temperature is low, for example, at 100 ° C. or lower, the switching valve 8 closes the bypass passage 6 and opens the original exhaust passage 3 on the HC adsorption catalyst 4 side.
It flows to the main cater 5 through the C adsorption catalyst 4. Therefore, even if a large amount of HC is generated during cranking of the engine 1, the HC flows into the HC adsorption catalyst 4 and is adsorbed there. As a result, HC can be prevented from being released to the outside even when the main cater 5 is not activated during the cold period.

At this time, since the passage length LH of the exhaust passage 3 from the main body of the engine 1 to the HC adsorbing catalyst 4 is longer than the passage length LP to the precatalyst 7, the lower the exhaust gas temperature, the more the HC is adsorbed. Therefore, the temperature of the HC adsorption catalyst 4 having a low temperature can be maintained at a low temperature at which the HC is easily adsorbed, and the HC storage efficiency can be increased.

Thereafter, when the warm-up of the engine 1 is promoted and the temperature of the exhaust gas rises to a medium temperature of 100 to 300 ° C., the switching valve 8 opens the bypass passage 6 contrary to the low temperature. The original exhaust passage 3 is closed, and the exhaust gas flows through the pre-cat 7 to the main cat 5. For this reason, the precatalyst 7 is not heated slowly over a long period of time from the state where the exhaust gas temperature is low, but is heated at a stretch by the exhaust gas which has risen to a somewhat high temperature. As a result, the exhaust gas purification performance is ensured, and the purification of HC by the precatalyst 7 can be performed efficiently. Also, during this time, the original exhaust passage 3 is closed, and the exhaust gas does not flow to the HC adsorption catalyst 4, so that the adsorbed HC can be prevented from being released from the HC adsorption catalyst 4. Incidentally, when the exhaust gas is introduced into the precatalyst 7, the ignition timing of the engine 1 may be retarded to increase the exhaust gas temperature, so that the purification performance of the precatalyst 7 can be further enhanced.

When the exhaust gas temperature further rises to a high temperature range of 300 ° C. or higher, the switching valve 8 is switched again so as to close the bypass passage 6 and open the original exhaust passage 3, and the exhaust gas is transferred to the HC adsorption catalyst 4. Through the main caterer 5. Therefore, the HC adsorbed by the HC adsorbing catalyst 4 at the time of the low temperature flows into the activated main caterter 5 which is heated and heated, and is surely purified there.

At this time, the high-temperature exhaust gas is
The heat damage can be avoided.

Also, the HC adsorption catalyst 4
The length LH of the exhaust passage 3 to the pre-catalyst 7 is longer than the length LP of the exhaust passage 3 to
The adsorption catalyst 4 can be kept at a relatively low temperature, and its heat resistance can be ensured.

Therefore, in this embodiment, as described above, HC is reliably purified from a low exhaust gas temperature to a high exhaust gas temperature, and the improvement of emission performance can be effectively achieved as a whole.

(Embodiment 2) FIG. 2 shows Embodiment 2 of the present invention (in the following embodiments, the same parts as those in FIG. 1 are denoted by the same reference numerals and detailed description thereof is omitted). , The configuration of the control means is changed.

That is, in this embodiment, the pre-cat
An on-off valve 10 composed of a butterfly valve is provided in the bypass passage 6 on the downstream side. The on-off valve 10 is closed when the exhaust gas temperature is low and high by an actuator 11 which has received a control signal from a controller 17, and is closed when the exhaust gas temperature is high. Sometimes driven to open.

In the exhaust passage 3, the bypass passage 6
A guide member 12 that guides exhaust gas from the engine 1 preferentially to the bypass passage 6 protrudes immediately upstream of the branch portion at the upstream end, and the on-off valve 10 is opened to open the bypass passage 6. When opened, the guide member 12 prevents the exhaust gas from flowing to the HC adsorption catalyst 4.

Therefore, in this embodiment, the same operation and effect as those of the first embodiment can be obtained with a relatively simple configuration using the on-off valve 10 composed of a butterfly valve.

Third Embodiment FIG. 3 shows a third embodiment. In this embodiment, in the configuration of the first embodiment, the downstream side of the HC adsorption catalyst 4 and the downstream end of the bypass passage 6 just upstream of the branch portion. The exhaust passage 3 is formed with a throttle portion 13 having a smaller passage cross-sectional area than other portions. The throttle portion 13 connects the exhaust passage 3 on the HC adsorption catalyst 4 side (upstream and downstream ends of the bypass passage 6 are connected). The minimum cross-sectional area of the exhaust passage between the divided portions is smaller than that of the bypass passage 6.

Therefore, in this embodiment, the same operation and effect as those of the first embodiment can be obtained. Also, HC
Since the minimum cross-sectional area of the exhaust passage 3 in which the adsorption catalyst 4 is arranged is smaller than that of the bypass passage 6, when the exhaust gas temperature is low, the bypass passage 6 is closed by the switching valve 8 and the side of the HC adsorption catalyst 4 is closed. With the exhaust passage 3 opened,
The exhaust gas pressure rises due to the exhaust gas throttle loss caused by the throttle unit 13 in the exhaust passage 3, increasing the load on the engine 1 and increasing the internal EGR in the engine 1 to warm up the engine 1 early. Can be. For this reason, the exhaust gas temperature rises quickly and the main caterter 5 is activated earlier, and in the high temperature range where HC adsorbed by the HC adsorbing catalyst 4 is released, the sufficiently activated main caterer 5 releases HC. There is an advantage that can be reliably purified.

(Embodiment 4) FIG. 4 shows Embodiment 4, in which the HC adsorbing catalyst 4
Is provided with a throttle control valve 14 capable of adjusting the opening degree of the exhaust passage 3 in which is disposed. The control valve 14 is provided with the switching valve 8
In the same manner as described above, the actuator is driven by an actuator 15 which operates in response to a control signal from a controller 17. The minimum cross-sectional area of the exhaust passage 3 on the side of the HC adsorption catalyst 4 is variably adjusted by the throttle control valve 14 so as to adjust the rising speed of the exhaust gas temperature and the like. Therefore, in this embodiment, the same operation and effect as those of the third embodiment can be obtained.

The positions of the throttle section 13 and the throttle control valve 14 are not limited to the downstream end of the exhaust passage 3 in which the HC adsorption catalyst 4 is disposed, but are connected to the upstream and downstream ends of the bypass passage 6. Any location may be used as long as the exhaust passage 3 is between them.

In each of the above embodiments, the HC adsorption catalyst 4
However, instead of the HC adsorbing catalyst 4, a simple chamber-shaped storage unit for storing HC may be provided, and the same effect can be obtained.

[0038]

As described above, according to the first aspect of the present invention, the HC storage portion and the main catalyst means for purifying the exhaust gas are arranged in the exhaust passage of the engine in order from the upstream side.
In an exhaust gas purifying apparatus for an engine having a bypass passage that bypasses a C storage unit, a sub-catalyst having a smaller capacity than the main catalyst is disposed in the bypass, and the heat resistance of the HC storage is more than that of the sub-catalyst. The exhaust gas flows to the HC storage section when the exhaust gas temperature is low and high, while the exhaust gas flows to the sub-catalyst means when the exhaust gas temperature is in a medium temperature state. HC can be trapped in the HC storage at low temperature and the trapped HC can be positively released at high temperature to purify with the main catalyst while the sub-catalyst means and the HC storage are arranged in a compact and simple layout. As a whole, emission performance can be improved. Further, when the exhaust gas is at a medium temperature, the warm-up performance can be improved by quickly warming up the sub-catalyst means with the middle-temperature exhaust gas, and the high-temperature exhaust gas flows to the sub-catalyst means. Can be avoided and the heat damage can be prevented.

According to the second aspect of the present invention, the minimum cross-sectional area of the HC storage section side exhaust passage is made smaller than that of the bypass passage, and the bypass passage is closed by the switching valve when the exhaust gas temperature is low. Thus, when the exhaust gas temperature is low, the load on the engine is increased due to exhaust gas throttling loss, and the internal EGR in the engine is increased, so that the engine is quickly warmed up, the exhaust gas temperature is increased quickly, and the main catalyst is accelerated. The means can be activated at an early stage, and the stored HC released from the HC storage section in a high temperature range can be reliably purified.

According to the third aspect of the present invention, since the length of the exhaust passage from the engine body to the HC storage portion is set longer than the length of the passage to the sub-catalyst means, the heat resistance of the HC storage portion and the HC storage thereof are improved. Efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a first embodiment of the present invention.

FIG. 2 is a view corresponding to FIG. 1 showing a second embodiment.

FIG. 3 is a view corresponding to FIG. 1 showing a third embodiment.

FIG. 4 is a diagram corresponding to FIG. 1 showing a fourth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 3 Exhaust passage 4 HC adsorption catalyst (HC storage part) 5 Main catalyzer (main catalyst means) 6 Bypass passage 7 Precatalyst (sub-catalyst means) 8 Switching valve 9 Actuator 13 Throttle part (minimum cut of HC storage part side exhaust passage) Means for reducing the area) 14 Throttle control valve (means for reducing the minimum cross-sectional area of the HC storage section side exhaust passage) 17 Controller 18 Temperature sensor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-141816 (JP, A) JP-A-63-68713 (JP, A) JP-A-2-1733312 (JP, A) JP-A 62-1987 174522 (JP, A) JP-A 2-90315 (JP, U) JP-A 63-87212 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08 F01N 3 / 20 F01N 3/24

Claims (3)

(57) [Claims] An HC storage section for storing HC in exhaust gas is provided in an exhaust passage, and a main catalyst means for purifying exhaust gas is provided downstream of the HC storage section. In an exhaust gas purifying apparatus for an engine in which an exhaust passage and an exhaust passage downstream of an HC storage section and upstream of a main catalyst unit are communicated by a bypass passage, a sub-catalyst having a smaller capacity than the main catalyst is provided in the bypass passage. The exhaust gas flows into the HC storage portion while the exhaust gas temperature is low and high, and the exhaust gas temperature is in a medium temperature state when the exhaust gas temperature is low and high. An exhaust gas purifying apparatus for an engine, further comprising control means for switching an exhaust gas flow path so that the exhaust gas flows to the auxiliary catalyst means. 2. The exhaust gas purifying apparatus for an engine according to claim 1, further comprising means for reducing the minimum cross-sectional area of the HC storage section side exhaust passage to be smaller than that of the bypass passage, and wherein the control means bypasses when the exhaust gas temperature is low. An exhaust gas purification device for an engine, comprising a switching valve for closing a passage. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein a length of an exhaust passage from the engine body to the HC storage portion is longer than a length of a passage to the sub-catalyst means. Engine exhaust purification device.