JPH06235320A - Automobile exhaust gas purifier - Google Patents

Abstract

PURPOSE:To completely purify, by means of an absorbent, harmful ingredients contained in exhaust gas and harmfull ingredients disengaged after being absorbed in the absorbent by using an automobile exhaust gas purifier which uses a catalyzing device and the absorbent jointly together. CONSTITUTION:A catalyzing device 4 is arranged on an exhaust pipe 4 of an engine 1, an absorbent 6 is arranged on a bypass pipe 5 on the upstream of the catalyzing device 4, switchover valves 7a, 7b, 7c, which switch the exhaust gas passage, the absorbent 6 and the upper stream of the catalyzing device are connected together through an one-way valve 9, and a circulation passage pipe 8, which makes harmful ingredients disengaged from the absorbent 6 to flow back to the catalyzing device 43, and a secondary air supply means 10, which supplies air to the back flow harmful ingredients, are provided. It is made to run exhaust gas through the bypass pipe 5 when the engine is cold by controlling the switchover valves 7a, 7b, 7c with a control means 13 and correcting the air-fuel ratio of the exhaust gas, containing back flow harmful ingredients, in the catalyzing device 4 position, when the harmful ingredients are flowing back, to a theoretical air-fuel ratio by the control means 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle exhaust gas purifying device, and more particularly to the above device using a catalyst device.

[0002]

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

Therefore, as a solution to the above problems,
An exhaust gas purification apparatus has been proposed in which a catalyst device and an adsorbent for adsorbing cold HC are used together in an exhaust system of an engine.

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

Further, for example, in the exhaust gas purifying apparatus described in JP-A-3-194113, a bypass pipe connecting the upstream side and the downstream side of the catalyst device is attached to the exhaust pipe in which the catalyst device is arranged, The adsorbent is installed in the. Further, a switching valve is provided at the connecting portion between the exhaust pipe and the bypass pipe, and the opening degree of the switching valve is adjusted at a specific time immediately after the engine is started to adsorb the cold HC of the exhaust gas flowing to the bypass pipe to the adsorbent. When desorbing HC from the adsorbent, the switching valve is half-opened to allow high-temperature exhaust gas to flow through the adsorbent to promote desorption of HC and return it to the upstream side of the catalyst device for purification.

[0006]

[Patent Document 1] Japanese Patent Application Laid-Open No. 2-75327
In the exhaust gas purifying device in which the adsorbent is arranged on the upstream side of the catalyst device as shown in No. 5, the heat energy of the exhaust gas is deprived by the adsorbent at the time of engine start, and the catalyst arranged on the downstream side reaches the activation temperature. There is a problem that time will be late. Further, if the temperature is lower, it is disadvantageous in terms of adsorption performance to dispose an adsorbent having better adsorption performance upstream of the catalyst device.

Further, in the exhaust gas purifying apparatus in which the adsorbent is disposed on the downstream side of the catalyst device as in JP-A-3-194113, the HC desorbed from the adsorbent is returned to the upstream side of the catalyst device. Since the air-fuel ratio of exhaust gas at the position of the device deviates from the stoichiometric air-fuel ratio, oxidation of HC and CO,
Alternatively, there arises a problem that the reduction of NOX deteriorates.

[0008] Therefore, an object of the present invention is to provide an exhaust gas purifying apparatus capable of sufficiently adsorbing the adsorbent and capable of completely purifying HC and the like desorbed from the adsorbent with a catalyst device. It was made.

[0009]

According to the present invention, as shown in FIG. 1, a catalyst device 4 is arranged in an exhaust pipe 3 of an engine 1, and a bypass pipe 5 branched from the exhaust pipe 3 in the downstream of the catalyst device 4. An adsorbent 6 is provided in the exhaust gas flow path and the exhaust pipe 3 and the bypass pipe 5
Switching valves 7a, 7b, 7c for selectively switching between and are provided. Further, a circulation flow path pipe 8 is provided which connects the adsorbent 6 of the bypass pipe 5 and the upstream side of the catalyst device 4 to recirculate the exhaust gas harmful component adsorbed by the adsorbent 6 to the catalyst device 4. A one-way valve 9 is provided in the middle of the circulation passage pipe 8. In addition, a secondary air supply means 10 is provided for supplying secondary air to the harmful components refluxed to the bypass pipe 5. Then, when the engine is cold, the switching valve 7a, so as to switch the exhaust gas flow path to the bypass pipe 5,
A control means is provided for controlling the operations of 7b and 7c and for controlling the air-fuel ratio of the exhaust gas containing the reflux harmful component at the position of the catalyst device 4 to the stoichiometric air-fuel ratio when the harmful component is refluxed.

[0010]

When the engine 1 is cold immediately after starting, the exhaust gas flows through the bypass pipe 5, and harmful components such as HC are adsorbed and removed by the adsorbent 6 and released. After the engine is warmed up, the exhaust gas from which harmful components have been purified by the catalyst device 4 flows through the exhaust pipe 3 and is discharged. At this time, the harmful components desorbed from the adsorption device 6 pass through the circulation flow path pipe 8, are supplied with the air supplied by the secondary air supply means 10, and are recirculated to the catalyst device 4,
It is purified by the catalyst device 4 together with harmful components in the exhaust gas. At this time, the exhaust gas added with the reflux harmful component is controlled to the stoichiometric air-fuel ratio, and the purification is completely performed.

[0011]

First Embodiment In the first embodiment of the present invention shown in FIG. 1, a catalyst device 4 is provided at a connecting portion between an exhaust manifold 2 and an exhaust pipe 3 of an engine 1. A bypass pipe 5 that branches from the exhaust pipe 3 is attached to the downstream of the catalyst device 4.
An adsorbent 6 is provided in the bypass pipe 5. The adsorbent 6 type may be pellet, foam, honeycomb type or the like.

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.

A circulation passage pipe 8 branches from the bypass pipe 6 between the adsorbent 6 and the switching valve 7c of the subsequent flow, and the circulation passage pipe 8 is connected to the exhaust manifold 2 upstream of the catalyst device 4. A one-way valve 9 is provided in the middle of the circulation flow pipe 8.

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

An exhaust manifold 2 is provided directly above the catalyst device 4.
The O ₂ sensor 11a is connected to the exhaust pipe 3 immediately after the catalyst device 4.
An O ₂ sensor 11b is provided in each of the above to monitor the oxygen concentration of the exhaust gas. The exhaust temperature sensor 12 on the downstream of the O ₂ sensor 11b in the exhaust pipe 3
Is provided to monitor the exhaust gas temperature.

Reference numeral 13 is a control means having a built-in microcomputer, which is a water temperature sensor 14 provided in the engine 1, and the above-mentioned O.
_{2 In} response to signals from the sensors 11a and 11b and the exhaust gas temperature sensor 12, the on-off valves 7a, 7b and 7c and the one-way valve 9 are controlled to be opened and closed via an actuator (not shown), and the catalyst device 4
It is set to control the air-fuel ratio of the exhaust gas at the position.

The operation of this embodiment will be described below in more detail with reference to the flow chart of FIG.

After the engine 1 is started, before the feedback (F / B) control of the air-fuel ratio is started, or when the exhaust gas temperature is low enough not to exceed the adsorbable temperature of the adsorbent 6, the switching valve 7
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 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, heat transfer heats the adsorbent 6 and promotes desorption of HC. When the engine 1 is warmed up, the control means 13 operates the one-way valve 9 to utilize the exhaust pulsation to circulate the HC and the like desorbed from the adsorbent 6 by the circulation flow pipe 8 to the catalyst device 4. For example, when the engine cooling water temperature is 7
Warm up above 0 ° C.

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

At the start of desorption of HC from the adsorbent 6, the desorption amount is large and secondary air is required, but the desorption amount decreases as the desorption time elapses. Therefore, the oxygen contained in the recirculation gas becomes excessive, the recirculation gas is added, and 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 exhaust gas to the rich side, and adjusts the air-fuel ratio of 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 the one-way valve 9 is open for a predetermined time, the HC
When it is judged that the desorption is completed, the one-way valve 9 is closed.

[0025]

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

In the previous embodiment, the correction of the air-fuel ratio at the position of the catalyst 4 at the time of HC recirculation was performed by controlling the air-fuel ratio of the exhaust gas on the engine side. In this case, there is a limit to making the air-fuel ratio on the engine side rich, because of 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 reflux gas containing HC desorbed from the adsorbent.

That is, as shown in FIG. 3, the circulation flow path pipe 8 is provided with a flow rate adjusting valve 15. At the start of the reflux of the HC desorbed from the adsorbent 6, the flow rate adjusting valve 12 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
If it is determined by, the flow rate adjusting valve 15 is controlled by the control means 12 to throttle the flow rate. 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 thereof will be omitted.

[0029]

According to the present invention, however, the adsorbent of the exhaust gas purifying device is arranged on the downstream side of the catalyst device, so that the adsorbing performance of the adsorbent can be satisfactorily exhibited. Particularly, in the present invention, when the harmful components of the exhaust gas desorbed from the adsorbent are recirculated to the catalyst device, the air-fuel ratio of the exhaust gas to which the reflux harmful components are added at the catalyst device position is corrected to the theoretical air-fuel ratio. By doing so, the purification of harmful components by the catalytic device is almost completely performed.

[Brief description of drawings]

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

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

FIG. 3 is an overall configuration diagram of a second embodiment device of the present invention.

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

[Explanation 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 rate adjusting valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location F01N 3/08 ZAB A 3/20 ZAB P 3/24 ZAB E (72) Inventor Yuji Mori Aichi Prefecture 1-1, Showa-cho, Kariya City, Nippon Denso Co., Ltd.

Claims (1)

[Claims] 1. A catalyst device provided in an exhaust pipe of an engine,
An adsorbent provided on a bypass pipe branched from the exhaust pipe on the downstream side of the catalyst device to adsorb harmful components in the exhaust gas, and a switching valve for selectively switching the exhaust gas flow path between the exhaust pipe and the bypass pipe. And a circulation passage pipe for communicating the adsorbent and the exhaust pipe upstream of the catalyst device via a one-way valve, and for circulating the harmful component desorbed from the adsorbent to the upstream of the catalyst device; Secondary air supply means for supplying secondary air to the harmful components, and opening / closing control of each valve so as to switch the exhaust gas flow path to the bypass pipe when the engine is cold, and at the catalyst device position during the circulation of the harmful components. A vehicle exhaust gas purifying apparatus, comprising: a control means for controlling the air-fuel ratio of the exhaust gas containing the harmful components of reflux to the stoichiometric air-fuel ratio.