JP3345942B2 - Engine exhaust gas 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 .

[0002]

2. Description of the Related Art In order to purify harmful components (HC, CO, NOx) contained in exhaust gas of automobiles, a catalytic device in which a noble metal such as platinum, rhodium or palladium is conventionally carried on a carrier such as a honeycomb structure. Is used. However, in order for the catalyst device to purify harmful components in the exhaust gas, the catalyst temperature must reach about 300 ° C. or higher. Therefore, when the catalyst temperature is low immediately after the start of the engine, purification cannot be performed. In addition, immediately after the start of the engine, a large amount of HC (hereinafter referred to as cold HC) is discharged, and this HC is released to the atmosphere without being purified.

In order to solve the above problem,
2. Description of the Related Art An exhaust gas purifying apparatus using a catalyst device and an adsorbent for adsorbing cold HC in an exhaust system of an engine has been proposed.

For example, in the exhaust gas purifying apparatus described in Japanese Patent Application Laid-Open No. 2-75327, an adsorbent is provided upstream of a catalyst device in an exhaust pipe to adsorb HC when the engine is cold and adsorbent after the engine is warmed up. The catalyst device purifies HC desorbed from the fuel and HC discharged from the engine.

In an exhaust gas purifying apparatus described in, for example, JP-A-3-194113, a bypass pipe connecting an upstream side and a downstream side of a catalyst device is attached to an exhaust pipe provided with the catalyst device, and the bypass pipe is provided. The adsorbent is arranged in the. Further, a switching valve is provided at a connection portion between the exhaust pipe and the bypass pipe, and at a specific time immediately after the start of the engine, the opening degree of the switching valve is adjusted so that cold HC of the exhaust gas flowing to the bypass pipe is adsorbed by the adsorbent; When the HC is desorbed from the adsorbent, the switching valve is half-opened to flow the high-temperature exhaust gas also to the adsorbent to promote the desorption of the HC and return to the upstream of the catalyst device for purification.

[0006]

Problems to be Solved by the Invention Japanese Patent Laid-Open No. 2-75327
In the exhaust gas purifying system in which the adsorbent is arranged upstream of the catalyst device as shown in (1), the heat energy of the exhaust gas is deprived by the adsorbent when the engine is started, and the catalyst arranged downstream reaches the activation temperature. There is a problem that time is slow. Further, disposing an adsorbent having better adsorption performance as the temperature is lower, upstream of the catalyst device has a problem in terms of adsorption performance.

Further, in an exhaust gas purifying apparatus in which an adsorbent is disposed downstream of a catalyst device as disclosed in Japanese Patent Application Laid-Open No. 3-194113, since HC desorbed from the adsorbent is returned upstream of the catalyst device, Since the air-fuel ratio of the exhaust gas at the position of the device deviates from the stoichiometric air-fuel ratio, oxidation of HC and CO,
Alternatively, there is a problem that the reduction of NOX is deteriorated.

Accordingly, the present invention is to provide an exhaust gas purifying apparatus for an engine in which the adsorbent has a sufficient adsorbing performance, and HC and the like desorbed from the adsorbent can be satisfactorily purified by a catalytic device. This was done as an issue.

[0009]

According to a first aspect of the present invention, a catalyst device provided in an exhaust pipe of an engine and a bypass pipe branched from the exhaust pipe on the downstream side of the catalyst device are provided. An adsorbent for adsorbing harmful components in the exhaust gas, a valve means for selectively switching an exhaust gas flow path between the exhaust pipe and the bypass pipe, and a valve between the adsorbent and the exhaust pipe upstream of the catalyst device. And a circulation channel pipe for refluxing the harmful component desorbed from the adsorbent upstream of the catalyst device,
Secondary air supply means for supplying secondary air to the harmful components to be recirculated, and controlling the valve means so as to switch the exhaust gas flow path to the bypass pipe when the engine is cold, and for recirculating the harmful components. Control means for controlling the air-fuel ratio of the exhaust gas containing the recirculating harmful component at the position of the catalyst device to a stoichiometric air-fuel ratio, and a one-way valve is disposed in the circulation flow pipe; Directional valve is en
The gin is opened by the control means when the gin is warmed up. According to a second aspect of the present invention, there is provided a catalyst device provided in an exhaust pipe of an engine, an adsorbent provided in a bypass pipe branched from the exhaust pipe on a downstream side of the catalyst device to adsorb harmful components in exhaust gas, A valve means for selectively switching a passage between the exhaust pipe and the bypass pipe, and a communication between the adsorbent and the upstream side of the catalyst device of the exhaust pipe, wherein the harmful component desorbed from the adsorbent is removed from the catalyst device. A circulation flow pipe for recirculating upstream, secondary air supply means for supplying secondary air to the harmful components to be recirculated, and the valve means for switching the exhaust gas flow path to the bypass pipe when the engine is cold. Control means for controlling the air-fuel ratio of the exhaust gas containing the recirculated harmful component at the position of the catalyst device to the stoichiometric air-fuel ratio at the time of the recirculation of the harmful component. Concentration When the air-fuel ratio of the exhaust gas containing the recirculated gas detected by the oxygen concentration sensor during the recirculation of the harmful component shifts to the lean side, the exhaust gas is adjusted to the stoichiometric air-fuel ratio. Thus, the air-fuel ratio control means of the engine is controlled via the control means.
According to a third aspect of the present invention, in the configuration of the first aspect, an oxygen concentration sensor is disposed at an upstream position of the catalyst device, and detects an air-fuel ratio of exhaust gas reaching the catalyst device at the time of recirculation. When the engine shifts to the lean side, the air-fuel ratio control means of the engine may be controlled by the control means to adjust the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio. According to a fourth aspect of the present invention, there is provided a catalyst device provided in an exhaust pipe of an engine, an adsorbent provided in a bypass pipe branched from the exhaust pipe on a downstream side of the catalyst device to adsorb harmful components in exhaust gas, A valve means for selectively switching a passage between the exhaust pipe and the bypass pipe, and a communication between the adsorbent and the upstream side of the catalyst device of the exhaust pipe, wherein the harmful component desorbed from the adsorbent is removed from the catalyst device. A circulation flow pipe for refluxing upstream,
Secondary air supply means for supplying secondary air to the harmful components to be recirculated, and controlling the valve means so as to switch the exhaust gas flow path to the bypass pipe when the engine is cold, and for recirculating the harmful components. Control means for controlling the air-fuel ratio of the exhaust gas containing the recirculating harmful component at the catalyst device position to a stoichiometric air-fuel ratio, and an oxygen concentration sensor is arranged upstream of the catalyst device, A flow control valve is disposed in the flow pipe, and when the harmful component is refluxed, the air-fuel ratio of the exhaust gas containing the recirculated gas detected by the oxygen concentration sensor shifts to the lean side. The flow rate of the flow control valve is reduced through the control means so that the exhaust gas has a stoichiometric air-fuel ratio. Furthermore, as in the fifth aspect, in the configuration of the first aspect of the present invention, when a flow rate adjusting valve is disposed in the circulation flow pipe, the exhaust gas air-fuel ratio detected by the oxygen concentration sensor shifts to the lean side. The control means may throttle the flow rate control valve to adjust the exhaust gas air-fuel ratio to the stoichiometric air-fuel ratio.

[0010]

According to the first aspect of the invention, when the engine is cold immediately after the start of the engine, the exhaust gas flows through the bypass pipe, and harmful components such as HC are adsorbed and removed by the adsorbent and released. After the engine is warmed up, the exhaust gas whose harmful components have been purified by the catalyst device flows through the exhaust pipe and is released. At this time, the harmful components desorbed from the adsorbent pass through the circulation channel pipe, are supplied with air supplied by the secondary air supply means, are returned to the catalyst device, and are purified by the catalyst device together with the harmful components in the exhaust gas. Is done. When recirculating exhaust gas to the catalyst device,
Exhaust gas containing reflux harmful components at the catalyst device position
In order to control the gas air-fuel ratio to the stoichiometric air-fuel ratio,
Exhaust gas containing harmful components released from the adsorbent in the catalytic device
The exhaust gas is set to the stoichiometric air-fuel ratio even if
In this way, harmful components can be effectively purified by the catalyst device.
Will be. In addition, since the one-way valve that is opened via the control means when the engine is warmed up is arranged in the circulation flow pipe, exhaust gas passes through the circulation flow pipe when the engine is cold, and the exhaust gas of the catalyst device is removed. It does not reach the upstream side. In addition, since the exhaust gas is a one-way valve at the time of opening, the exhaust gas on the upstream side of the catalyst device does not flow back to the adsorbent through the circulation flow pipe. According to the second aspect, in a cold state immediately after the start of the engine, the exhaust gas flows through the bypass pipe, and harmful components such as HC are adsorbed and removed by the adsorbent and released. After the engine is warmed up, the exhaust gas whose harmful components have been purified by the catalyst device flows through the exhaust pipe and is released. At this time, the harmful components desorbed from the adsorbent pass through the circulation channel pipe, are supplied with air supplied by the secondary air supply means, are returned to the catalyst device, and are purified by the catalyst device together with the harmful components in the exhaust gas. Is done. At this time, the exhaust gas to which the recirculating harmful component is added is controlled to the stoichiometric air-fuel ratio, and the harmful component is purified. Further, when circulating the exhaust gas through the circulation passage pipe, by controlling the air-fuel ratio control means of the engine, the exhaust air-fuel ratio on the upstream side of the catalyst device is controlled to be the stoichiometric air-fuel ratio. Even if exhaust gas containing a harmful component desorbed from the adsorbent flows into the exhaust gas, the exhaust gas is set to the stoichiometric air-fuel ratio, so that the harmful component is successfully purified by the catalyst device. According to the third aspect, in addition to the effect of the first aspect, when the exhaust gas is circulated through the circulation flow pipe, the exhaust air on the upstream side of the catalyst device is controlled by controlling the air-fuel ratio control means of the engine. Since the fuel ratio is controlled to be the stoichiometric air-fuel ratio, the exhaust gas is set to the stoichiometric air-fuel ratio even if exhaust gas containing a harmful component released from the adsorbent flows into the catalyst device. The purification of harmful components will be performed well. According to the fourth aspect, in a cold state immediately after the start of the engine, the exhaust gas flows through the bypass pipe, and harmful components such as HC are adsorbed and removed by the adsorbent and released. After the engine is warmed up, the exhaust gas whose harmful components have been purified by the catalyst device flows through the exhaust pipe and is released. At this time, the harmful components desorbed from the adsorbent pass through the circulation channel pipe, are supplied with air supplied by the secondary air supply means, are returned to the catalyst device, and are purified by the catalyst device together with the harmful components in the exhaust gas. Is done. At this time, the exhaust gas to which the recirculating harmful component is added is controlled to the stoichiometric air-fuel ratio, and the harmful component is purified. Further, when circulating the exhaust gas through the circulation flow pipe, the exhaust gas air-fuel ratio on the upstream side of the catalyst device is controlled to be the stoichiometric air-fuel ratio by adjusting the flow rate of the flow control valve. Even if an exhaust gas containing a harmful component desorbed from the adsorbent flows in, the exhaust gas is set to the stoichiometric air-fuel ratio, so that the harmful component is successfully purified by the catalyst device. Moreover, since the air-fuel ratio on the engine side is not changed, there is no effect on fuel efficiency and drivability. According to claim 5, claim 1
In addition to the effects of the invention, when circulating the exhaust gas through the circulation flow pipe, the exhaust air-fuel ratio on the upstream side of the catalyst device is controlled to be the stoichiometric air-fuel ratio by adjusting the flow rate of the flow control valve. Therefore, even if exhaust gas containing harmful components desorbed from the adsorbent flows into the catalytic device, the exhaust gas is set to the stoichiometric air-fuel ratio, so that the catalytic device can purify harmful components satisfactorily. Become. Moreover, since the air-fuel ratio on the engine side is not changed, there is no effect on fuel efficiency and drivability.

[0011]

Embodiment 1 In the first embodiment of the present invention shown in FIG. 1, a catalyst device 4 is provided at a connection portion between an exhaust manifold 2 of an engine 1 and an exhaust pipe 3. A bypass pipe 5 branched from the exhaust pipe 3 is provided downstream of the catalyst device 4.
An adsorbent 6 is interposed in the bypass pipe 5. The type of the adsorbent 6 may be any of a pellet type, a foam type and a honeycomb type.

The exhaust pipe 3 is provided with a switching valve 7a at a portion where the bypass pipe 5 is arranged in parallel. The bypass pipe 5 is provided with switching valves 7b and 7c upstream and downstream of the adsorbent 6, respectively.

From the bypass pipe 5 , a circulating flow pipe 8 branches between the adsorbent 6 and a switching valve 7c downstream thereof. The circulating flow pipe 8 is connected to the exhaust manifold 2 upstream of the catalyst device 4. A one-way valve 9 is interposed in the circulation flow pipe 8.

The bypass pipe 5 is provided with a secondary air supply means 10 between the adsorbent 6 and the upstream switching valve 7b.
The secondary air supply means 10 is provided with a one-way valve 10b which opens at a weak negative pressure at an air inlet 10a.

Immediately above the catalyst device 4, the exhaust manifold 2 is provided.
O ₂ sensor 11a to the exhaust pipe 3 immediately after the catalytic converter 4
O ₂ sensor 11b is, it is provided with respectively, so as to monitor the oxygen concentration of the exhaust gas. The exhaust pipe 3 has an exhaust gas temperature sensor 12 downstream of the O ₂ sensor 11b.
Is provided to monitor the exhaust gas temperature.

Numeral 13 denotes control means incorporating a microcomputer, a water temperature sensor 14 provided in the engine 1,
_In response to signals from the _two sensors 11a and 11b and the exhaust temperature sensor 12, the on / off valves 7a, 7b and 7c and the one-way valve 9 are controlled to open and close via an actuator (not shown).
It is set to control the air-fuel ratio of the exhaust gas at the position.

Hereinafter, further details of this embodiment will be described with reference to the flowchart of FIG.

After the engine 1 is started, before the feedback control of the air-fuel ratio (F / B) is started, or when the temperature of the exhaust gas does not exceed the adsorbable temperature of the adsorbent 6, the switching valve 7 is used.
The valves b and 7c are opened and the switching valve 7a is closed. Then, the exhaust gas flows through the bypass pipe 5. At this time, since the temperature of the catalyst device 4 is low and has not reached the activation temperature (300 ° C. to 350 ° C.), harmful components such as cold HC (hereinafter, collectively referred to as HC) pass through the catalyst device 4 without being purified. Adsorbed on the adsorbent 6.

When the feedback control is started or when it is determined that the exhaust gas temperature exceeds the adsorbable temperature of the adsorbent, the control means 13 controls the switching valves 7b and 7c.
Is closed, and the switching valve 7a is opened.

When the exhaust gas temperature becomes high, the adsorbent 6 is heated by the heat transfer, and the desorption of HC is promoted. When the warm-up of the engine 1 is completed, the one-way valve 9 is operated by the control means 13, and HC and the like desorbed from the adsorbent 6 are returned to the catalyst device 4 by the circulation flow pipe 8 using the exhaust pulsation. The warm-up state is determined, for example, when the engine coolant temperature is 7
A temperature of 0 ° C or higher is set to a warm-up state.

At the time of HC recirculation, H is introduced from the secondary air inlet 10a.
Secondary air for oxidizing C is introduced, and HC is mixed with the secondary air and refluxed.

At the start of the desorption of HC from the adsorbent 6, the amount of desorption is large and secondary air is required, but the desorption amount decreases as the desorption time elapses. Therefore, the oxygen contained in the recirculated gas becomes excessive, and the recirculated gas is added, so that the air-fuel ratio of the exhaust gas passing through the catalyst device 4 shifts to the lean side. This shift is determined by the O ₂ sensors 11a and 11b.

When this shift is determined, the control means 13
Controls the air-fuel ratio control means of the engine 1 to shift the air-fuel ratio of the exhaust gas to the rich side, and adjusts the air-fuel ratio of the exhaust gas at the position of the catalyst device 4 to the stoichiometric air-fuel ratio. Thus,
HC and recirculated HC in the exhaust gas discharged from the engine 1 are completely purified by the catalyst device 4.

When a predetermined time has elapsed with the one-way valve 9 open, HC
Is determined, the one-way valve 9 is closed.

[0025]

Embodiment 2 FIG. 3 shows the configuration of a second embodiment of the present invention, and FIG. 4 shows a flowchart of its operation.

In the above embodiment, the correction of the air-fuel ratio at the position of the catalyst 4 during the recirculation of HC was performed by controlling the air-fuel ratio of the exhaust gas on the engine side. In this case, there is a limit to the effect of increasing the air-fuel ratio on the engine side to the rich side due to the influence on fuel efficiency and drivability. Therefore, in the present embodiment, the correction of the air-fuel ratio is performed by adjusting the amount of the recirculated gas containing HC desorbed from the adsorbent.

That is, as shown in FIG. 3, a flow regulating valve 15 is provided in the circulation flow pipe 8. At the start of the reflux of the HC desorbed from the adsorbent 6, the flow control valve 15 is fully opened. Secondary amount of HC refluxed with air gradually decreases and oxygen becomes excessive, the catalytic converter 4 the air-fuel ratio of the exhaust gas at a position that is shifted to the lean side O ₂ sensor 11a, 11b
Is determined, the flow control valve 15 is controlled by the control means 12 to reduce the flow. By adjusting the amount of recirculated air in this way, the air-fuel ratio of the exhaust gas containing the recirculated gas at the position of the catalyst device 4 is controlled to the stoichiometric air-fuel ratio.

The other structure and operation are substantially the same as those of the first embodiment, and the description is omitted.

[0029]

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing the operation of the first embodiment.

FIG. 3 is an overall configuration diagram of an apparatus according to a second embodiment of the present invention.

FIG. 4 is a flowchart showing an operation of the second embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust manifold 3 Exhaust pipe 4 Catalytic device 5 Bypass pipe 6 Adsorbent 7a, 7b, 7c Switching valve 8 Circulating flow pipe 9 One-way valve 10 Secondary air supply means 11a, 11b O ₂ sensor 12 Exhaust temperature sensor 13 Control means 14 Water temperature sensor 15 Flow control valve

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yuji Mori 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-6-74020 (JP, A) JP-A-6-740 200748 (JP, A) JP-A-3-194113 (JP, A) JP-A-4-231616 (JP, A) JP-A-6-173662 (JP, A) JP-A-6-66134 (JP, A) JP-A-4-31618 (JP, A) JP-A-62-162715 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9/00 -11/00

Claims (5)

(57) [Claims] A catalyst device provided in an exhaust pipe of the engine;
An adsorbent provided in a bypass pipe branched from the exhaust pipe on the downstream side of the catalyst device to adsorb harmful components in exhaust gas;
Valve means for selectively switching the exhaust gas flow path between the exhaust pipe and the bypass pipe, and communicating between the adsorbent and the upstream side of the catalyst device of the exhaust pipe to remove the harmful component desorbed from the adsorbent; A circulating flow pipe for refluxing upstream of the catalyst device, a secondary air supply means for supplying secondary air to the harmful components to be refluxed, and an exhaust gas flow path switched to the bypass pipe when the engine is cold. Control means for controlling the valve means, and controlling the air-fuel ratio of the exhaust gas containing the recirculated harmful component at the position of the catalyst device to the stoichiometric air-fuel ratio when the harmful component is recirculated, and , A one-way valve is disposed, and the one-way valve is opened by the control means when the engine is warmed up. 2. A catalyst device provided in an exhaust pipe of an engine,
A bypass branched from the exhaust pipe on the downstream side of the catalyst device;
An adsorbent provided in a pipe to adsorb harmful components in exhaust gas,
The exhaust gas flow path is selectively switched between the exhaust pipe and the bypass pipe.
Valve means for changing, the adsorbent and the exhaust pipe on the catalyst device
The above-mentioned harmful components that are released from the adsorbent by communicating with the flow side
A circulation flow pipe for refluxing the upstream of the catalyst device,
Secondary air supply to supply secondary air to the above harmful components
Means and the above-mentioned bypass in the exhaust gas passage when the engine is cold
While controlling the above valve means to switch to the pipe,
When the harmful components are refluxed, the
Controlling air-fuel ratio of exhaust gas containing harmful components to stoichiometric air-fuel ratio
And control means for controlling
An oxygen concentration sensor is located on the upstream side,
The reflux detected by the oxygen concentration sensor at the time of reflux
If the air-fuel ratio of exhaust gas containing gas shifts to the lean side
In this case, the exhaust gas is adjusted to the stoichiometric air-fuel ratio.
Controlling the air-fuel ratio control means of the engine through the control means.
An engine exhaust gas purifying device characterized by controlling . 3. An oxygen concentration sensor is disposed upstream of the catalyst device, and the air-fuel ratio of the exhaust gas containing the recirculated gas, detected by the oxygen concentration sensor when the harmful component is recirculated, becomes leaner. when shifting the exhaust gas of an engine according to claim 1, characterized in that the exhaust gas control the air-fuel ratio control means of the engine via the control means so as to be adjusted to the stoichiometric air-fuel ratio Purification device. 4. A catalyst device provided in an exhaust pipe of an engine,
A bypass branched from the exhaust pipe on the downstream side of the catalyst device;
An adsorbent provided in a pipe to adsorb harmful components in exhaust gas,
The exhaust gas flow path is selectively switched between the exhaust pipe and the bypass pipe.
Valve means for changing, the adsorbent and the exhaust pipe on the catalyst device
The above-mentioned harmful components that are released from the adsorbent by communicating with the flow side
A circulation flow pipe for refluxing the upstream of the catalyst device,
Secondary air supply to supply secondary air to the above harmful components
Means and the above-mentioned bypass in the exhaust gas passage when the engine is cold
While controlling the above valve means to switch to the pipe,
When the harmful components are refluxed, the
Controlling air-fuel ratio of exhaust gas containing harmful components to stoichiometric air-fuel ratio
And an oxygen concentration sensor is disposed upstream of the catalyst device , and a flow regulating valve is disposed in the circulating flow pipe. When the air-fuel ratio of the exhaust gas including the recirculated gas detected by the concentration sensor shifts to the lean side, the flow rate of the flow control valve is controlled via the control means so that the exhaust gas becomes the stoichiometric air-fuel ratio. be characterized in that the squeeze
Exhaust gas purifying apparatus that engine. 5. An oxygen concentration sensor upstream of the catalyst device.
The circulation flow pipe is provided with a flow control valve.
The oxygen concentration sensor is
Air-fuel of exhaust gas containing the recirculated gas detected by
If the ratio shifts to the lean side, the exhaust gas
The flow rate adjustment via the control means so as to obtain the stoichiometric air-fuel ratio.
2. The method according to claim 1, wherein the flow rate of the valve is reduced.
Engine exhaust gas purification equipment.