JPH10121949A - Engine exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently purify HC in exhaust gas and in transpired gas from a fuel tank by increasing the temperature of catalyst up to an activating temperature at an early time after a start of an engine. SOLUTION: An absorbent 5, an electrically heated oxidizing catalyst 6 and three-way catalyst 7 are arranged in an exhaust pipe 4 in the mentioned order from the upstream side. When the temperature of exhaust gas is low, HC in exhaust gas is adsorbed to the adsorbent 5. When the temperature of the exhaust gas becomes higher, HC released from the adsorbent 5 is purified by the electrically heated oxidizing catalyst 6. At this time, secondary air is fed into the exhaust pipe 4 from an air pump 13 through an atmospheric passage 8a in order to enhance the purifying performance of the electrically heated oxidizing catalyst 6. When HC is completely released from the adsorbent 5, the secondary air is fed into the exhaust pipe 4 from the pump 13 by way of a canister 14 so as to purify HC contained in transpired gas fed together with the secondary air and accumulated in the canister 14.

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 in which a purifying process of an exhaust gas and a purifying process of a vaporized gas from a fuel tank are performed by a catalyst provided in an exhaust system.

[0002]

2. Description of the Related Art Unburned hydrocarbons (hereinafter, referred to as HC) contained in exhaust gas discharged from automobiles are generally purified by using a chemical reaction of an oxidation catalyst, a three-way catalyst, or the like. Has been released into the atmosphere.

However, when the engine is started or the like, the oxidation catalyst, the three-way catalyst, and the like are in a low temperature range, and a sufficient purification action cannot be expected.

[0004] To cope with this, Japanese Patent Laid-Open No. 6-66133 has been proposed.
In the publication, unburned HC contained in the exhaust gas is temporarily adsorbed on an adsorbent until the catalyst reaches an activation temperature, and after the catalyst reaches the activation temperature, the unburned HC is desorbed from the adsorbent. A technique for purifying and a technique for supplying secondary air to the catalyst to efficiently purify unburned HC are disclosed.

[0005]

However, in general, the temperature at which HC starts to be desorbed from the adsorbent is lower than the activation temperature of the catalyst.
According to the technology disclosed in Japanese Patent No. 6133, purification of HC desorbed from the adsorbent and HC in exhaust gas when the adsorbent is at or above the desorption temperature and the catalyst is at or below the activation temperature is insufficient. There is a fear.

Further, in order to improve the catalyst purifying ability at the time of low temperature of the exhaust gas at the time of starting the engine or the like, a technique of electrically heating the catalyst carrier and activating the catalyst carrier early has been widely proposed. However, when the engine is started or the like, the heat of the electrically heated catalyst is taken away by exhaust gas discharged at a low temperature, so that the catalyst heating efficiency is poor, the power consumption is large, and the power supply system including the addition of batteries is increased. May significantly increase the cost.

[0007] HC is also contained in the vaporized gas from the fuel tank. The HC in the vaporized gas is temporarily stored in a canister and then led to a suction pipe for combustion in the engine. Once stored in a canister, there is a means for purifying it with the oxidation catalyst, the three-way catalyst, or the like (JP-A-59-58143, JP-A-5-2636).
No. 38).

In the means for burning the HC stored in the canister in the engine, the air-fuel ratio of the engine is disturbed. Therefore, it is necessary to correct the fuel injection amount and the like to optimize the air-fuel ratio. On the other hand, the means for treating the HC stored in the canister with a catalyst can provide a stable engine air-fuel ratio without having to correct the fuel injection amount or the like for the treatment of the HC, but the purification processing ability of the catalyst is Since there is a time constraint that the catalyst is effective only after the catalyst reaches the activation temperature, if a relatively long time is required from the start to the time when the catalyst is activated, firstly, unreacted gas contained in the exhaust gas is not included. The fuel HC must be processed early, but during that time, the HC in the canister remains accumulated in the canister, and depending on the traveling conditions, the HC in the canister may not be sufficiently processed and may overflow.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. In a means for purifying HC in a vaporized gas with a catalyst, the catalyst temperature is quickly and efficiently raised to an activation temperature after the engine is started, and exhausted from the engine. It is an object of the present invention to provide an engine exhaust gas purifying apparatus capable of efficiently purifying HC and HC in vaporized gas from a fuel tank.

[0010]

To achieve the above object, an exhaust gas purifying apparatus for an engine according to the present invention comprises an adsorbent for adsorbing hydrocarbons at a low temperature from an upstream side to an exhaust system of an engine body, an electric heating oxidation catalyst, A three-way catalyst is provided, and a passage switching means is provided between the adsorbent and the electrically heated oxidation catalyst, between a secondary air supply passage and a canister purge passage communicating with a canister storing evaporative fuel in a fuel tank. The adsorbent is connected to the secondary air supply passage via the switching means during the desorption of the adsorbed hydrocarbons when the adsorbent is heated to a high temperature. After the completion of the desorption of the hydrocarbons, the canister is connected to the purge passage.

In the present invention having the above-described structure, the adsorbent adsorbs and holds hydrocarbons in the exhaust gas discharged from the engine body at a low temperature. Thereafter, when the temperature of the exhaust gas rises and the temperature of the adsorbent rises, the adsorbed hydrocarbons begin to desorb, and the electrically heated oxidation catalyst purifies the desorbed hydrocarbons. At this time, the secondary air supplied from the secondary air supply passage between the adsorbent and the electrically heated oxidation catalyst improves the purification ability of the electrically heated oxidation catalyst.

After the completion of the desorption of the hydrocarbon adsorbed by the adsorbent, the secondary air supply passage is switched by the switching means.
Switching to the canister purge passage, the electric heating oxidation catalyst purifies the vaporized fuel stored in the canister supplied with secondary air from the canister purge passage between the adsorbent and the electric heating oxidation catalyst together with the secondary air.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show an embodiment of the present invention. FIG. 1 is a configuration diagram of an exhaust gas purifying apparatus for an engine when evaporative gas is supplied to an exhaust pipe, and FIG. 2 is an illustration of an engine when secondary air is supplied to an exhaust pipe. FIG. 3 is a flowchart showing a power supply control routine of an electric heating oxidation catalyst 6 described later, and FIG. 4 is a flowchart showing a secondary air supply passage control routine.

In FIG. 1, reference numeral 1 denotes an engine body, and an exhaust pipe 4 is connected to an exhaust port of the engine body 1 via an exhaust manifold 3.

An adsorbent 5, an electrically heated oxidation catalyst 6, and a well-known three-way catalyst 7 are interposed from the upstream side in the middle of the exhaust pipe 4, and are interposed by the electrically heated oxidation catalyst 6 and the three-way catalyst 7. HC in the exhaust gas and the evaporated gas is purified.

The adsorbent 5 adsorbs and retains unburned hydrocarbons (HC) in the exhaust gas discharged from the engine body 1 at a low temperature, and desorbs the hydrocarbons at a predetermined temperature or higher.

An air pump 13 is connected to the exhaust pipe 4 between the adsorbent 5 and the electrically heated oxidation catalyst 6 via an atmosphere passage 8a.

In the middle of the air passage 8a, switching valves 12a and 12b which are operated by a solenoid or the like in order from the air pump 13 are interposed.

One end of a bypass passage 8b is connected to the switching valve 12a, and the other end of the bypass passage 8b is connected to a secondary air inlet 14a of the canister 14. Further, the purge port 14b of the canister 14 is provided.
Is connected to one end of a bypass passage 8c, and the other end of the bypass passage 8c is connected to the switching valve 12b. Further, the vaporized gas inlet 14c of the canister 14 is connected to the fuel tank 16 via the vaporized gas passage 15.
Is linked to

The adsorbent 5 and the electrically heated oxidation catalyst 6
Are provided with temperature sensors 9 and 10, respectively.
These temperature sensors 9 and 10 are connected to a control device 11 and output signals to the control device 11 according to the temperatures of the adsorbent 5 and the electrically heated oxidation catalyst 6.

The control device 11 detects the temperatures of the adsorbent 5 and the electrically heated oxidation catalyst 6 based on signals output from the temperature sensors 9 and 10, and detects the temperature of the adsorbent 5
The on / off control of the drive signal for the switching valves 12a and 12b is performed based on the temperature of the electric heating oxidation catalyst 6, and the energization control for the electric heating oxidation catalyst 6 is performed based on the temperature of the electric heating oxidation catalyst 6.

In the present embodiment, when the drive signals applied to the switching valves 12a and 12b are off,
The air pump 13 and the exhaust pipe 4 are communicated with each other by the atmosphere passage 8a (see FIG. 2). On the other hand, when the drive signal applied to the switching valves 12a and 12b is on, the air pump 13 and the exhaust pipe 4 are turned on. 4 is communicated with the atmosphere passage 8a via the bypass passage 8b, the canister 14, and the bypass passage 8c halfway (see FIG. 1).

The temperature of the adsorbent 5 and the temperature of the electrically heated oxidation catalyst 6 are detected by the temperature sensors 9 and 10. However, the temperature of the adsorbent 5 and the electric heating oxidation catalyst 6 are indirectly detected based on, for example, the temperature of the cooling water. The temperature of the electric heating oxidation catalyst 5 and the temperature of the electrically heated oxidation catalyst 6 may be estimated, or the temperature rise may be determined based on the elapsed time after starting the engine.

In the exhaust gas purifying apparatus 2 for an engine having the above-described structure, HC is purified by the electrically heated oxidation catalyst 6 and the three-way catalyst 7, and the harmful gas nitrogen contained in the exhaust gas. Oxide (NOX) and carbon monoxide (CO) are purified by the three-way catalyst 7, but when the engine is started, a large amount of HC contained in unburned exhaust gas and a large amount in the canister 14 are present. HC in the evaporated gas stored in the tank is difficult to purify. Therefore, the following operation is performed to efficiently purify these HCs at an early stage.

The controller 11 controls the energization of the electrically heated oxidation catalyst 6 and the supply of the secondary air and the vaporized gas stored in the canister 14 to the electrically heated oxidation catalyst 6 and the three-way catalyst 7. Is done.

Hereinafter, the control of the energization of the electric heating oxidation catalyst 6 and the switching valve 1 by the control device 11 will be described.
The switching control between 2a and 12b will be described with reference to the flowcharts in FIGS.

When an ignition switch (not shown) is turned on and power is supplied to the control device 11, the control device 11 receives the adsorbent 5 output from the temperature sensors 9, 10.
A signal indicating the temperature of the electrically heated oxidation catalyst 6 is input. The controller 11 calculates the temperature of the electrically heated oxidation catalyst 6 based on the output signal from the temperature sensor 10, and calculates the temperature of the adsorbent 5 based on the output signal from the temperature sensor 9.

The temperature of the electrically heated oxidation catalyst 6 is read in an electrically heated oxidation catalyst energization control routine shown in FIG. The temperature of the adsorbent 5 is read in a switching valve operation routine shown in FIG.

In the electric heating oxidation catalyst energization control routine shown in FIG. 3, in step S1, the temperature of the electric heating oxidation catalyst 6 is read and compared with a preset reference value. If the catalyst temperature is equal to or lower than the activation temperature, the process proceeds to step S2 to turn on the power supply to the electrically heated oxidation catalyst 6, and exits the routine.

On the other hand, if the catalyst temperature is equal to or higher than the activation temperature in step S1, the process proceeds to step S3, in which the power supply to the electrically heated oxidation catalyst 6 is turned off, and the routine exits.

When the power supply to the electrically heated oxidation catalyst 6 is turned on, the electrically heated oxidation catalyst 6 is electrically heated, and the catalyst temperature rises. On the other hand, when turned off, the electrically heated oxidation catalyst 6 is not electrically heated.

Therefore, for example, at the time of a cold start, the electrically heated oxidation catalyst 6 is electrically heated until it reaches the activation temperature. As a result, the electrically heated oxidation catalyst 6 can be quickly heated to the activation temperature. it can. Needless to say, even when the temperature of the electrically heated oxidation catalyst 6 once becomes higher than the activation temperature and then becomes lower than the activation temperature, the electrically heated oxidation catalyst 6 is electrically heated again. Can always be maintained.

In the switching valve operation routine shown in FIG. 4, the temperature of the adsorbent 5 is read in step S11,
The temperature is compared with a reference temperature indicating a preset temperature of desorption of HC from the adsorbent 5. If the temperature of the adsorbent 5 is equal to or lower than the reference temperature, the process proceeds to step S12, in which the drive signal for the switching valves 12a and 12b is turned off, and the routine exits.

When the operating voltage is not applied (turned off) to the switching valves 12a and 12b, the switching valves 12a and 12b
The air passage 8a for supplying the secondary air directly to the exhaust pipe 4 is opened, and the air passage 8a is isolated from the bypasses 8b and 8c (see FIG. 2). Then, the secondary air from the air pump 13 is supplied to the atmosphere passage 8a.
Through the exhaust pipe 4.

On the other hand, if the temperature of the adsorbent 5 is equal to or higher than the reference temperature, the process proceeds to step S13. In step S13,
The elapsed time from when the adsorbent 5 becomes higher than the reference temperature is measured and compared with a preset set time. The set time is, for example, a time from the start of desorption of the adsorbent 5 to the start of desorption of HC adsorbed on the adsorbent 5 until the desorption is completed, and is set in advance by an experiment or the like. Is required by:

If it is determined in step S13 that the elapsed time is equal to or shorter than the set time, the process exits the routine with the operating voltage kept off. That is, when the elapsed time after the adsorbent 5 has reached or exceeded the desorption temperature is equal to or less than the set time, the secondary air from the air pump 13 is supplied to the exhaust pipe 4 through the atmosphere passage 8a. You. Then, the HC desorbed from the adsorbent by the secondary air is efficiently purified by the electric heating oxidation catalyst 6.

On the other hand, if the elapsed time is equal to or longer than the set time in step S13, the process proceeds to step S14, where the drive signal to the solenoid valves 12a and 12b is turned on, and the routine exits.

When a drive signal is applied (turned on) to the switching valves 12a and 12b, the switching valves 12a and 12b are turned on.
a closes the middle of the atmosphere passage 8a and communicates the air pump 13 with the bypass passage 8b. The switching valve 12b closes the middle of the atmosphere passage 8a and connects the air passage 8a to the bypass passage 8b. It communicates with the bypass passage 8c (see FIG. 1). Then, the secondary air from the air pump 13 is supplied to the exhaust pipe 4 through the path through the canister 14 in the middle of the air path 8a.

The secondary air from the air pump 13 passes through the canister 14 while passing through the atmosphere passage 8a, and is accompanied by vaporized gas containing a large amount of HC from the fuel tank 16 stored in the canister 14. To the exhaust pipe 4. Then, HC contained in the vaporized gas supplied to the exhaust pipe 4 is purified by the electric heating oxidation catalyst 6.

According to the above operation, for example, when the exhaust gas temperature immediately after the start of the engine is low, the electrically heated oxidation catalyst 6 is in a low temperature state, and the ability to purify the unburned HC discharged from the engine body 1 is not sufficient. However, until the electrically heated oxidation catalyst 6 is sufficiently activated, the unburned HC is temporarily retained in the adsorbent 5 and is not discharged to the atmosphere. Since there is no need to purify the unburned HC during the heating, the heating is performed efficiently and early.

Therefore, when the exhaust gas temperature rises and the HC retained in the adsorbent 5 starts to be desorbed, the electric heating oxidation catalyst 6 is heated to the activation temperature by electric heating, and the electric heating oxidation catalyst 6 is heated. Since the secondary air from the air pump 13 is directly supplied to the catalyst 6 through the air passage 8a, the desorbed HC from the adsorbent 5 and the HC in the exhaust gas are efficiently purified. .

When HC starts to be desorbed from the adsorbent 5, the temperature of the exhaust gas has risen to some extent, so that the activation temperature of the electrically heated oxidation catalyst 6 is sufficiently maintained.

When the HC adsorbed by the adsorbent 5 is completely desorbed, secondary air from the air pump 13 is supplied to the exhaust pipe 4 through the canister 14. At this time, when the secondary air passes through the canister 14, the secondary air reaches the exhaust pipe 4 with the vaporized gas containing a large amount of HC from the fuel tank 16 accumulated in the canister 14, and reaches the exhaust pipe 4. When passing through, the HC in the vaporized gas is purified.

The HC adsorbed on the adsorbent 5
By the time exhaust gas is completely desorbed, the three-way catalyst 7 is also activated by the exhaust gas.
And the three-way catalyst 77 synergistically purify the HC and exhaust gas components in the vaporized gas with high efficiency.

As described above, in the embodiment of the present invention, when the temperature of the electrically heated oxidation catalyst 6 is lower than the activation temperature, the unburned HC discharged from the engine main body 1 is temporarily held by the adsorbent 5. Even if the electrically heated oxidation catalyst 6 is at or below the activation temperature, unburned HC is not discharged out of the vehicle. After that, the treatment of HC after the temperature of the electrically heated oxidation catalyst 6 becomes equal to or higher than the activation temperature is not performed at once, but first, the treatment of HC desorbed from the adsorbent 5 is performed. Of HC in the vaporized gas from the plant. For this reason, both the desorbed HC from the adsorbent 5 and the HC in the vaporized gas from the canister 14 can be reliably processed without a large amount of HC being supplied to the electrically heated oxidation catalyst 6 at one time. . Further, since the electric heating oxidation catalyst 6 is heated early by electric heating and the secondary air is supplied, the desorbed HC from the adsorbent 5 is efficiently treated at an early stage. Treatment of HC in the vaporized gas of the adsorbent 5
Even after the HC treatment desorbed from the canister 14
The treatment of HC in the vaporized gas from the canister can be started early, and the canister 14 does not exceed the saturated amount of the vaporized gas.

[0046]

As described above, according to the present invention, after the engine is started, the catalyst temperature is quickly and efficiently raised to the activation temperature, and the HC discharged from the engine body and the vaporized gas from the fuel tank are removed. HC can be efficiently purified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an exhaust gas purifying apparatus for an engine when evaporative gas is supplied to an exhaust pipe.

FIG. 2 is a configuration diagram of an engine exhaust gas purifying apparatus when secondary air is supplied to an exhaust pipe.

FIG. 3 is a flowchart showing an electric heating oxidation catalyst energization control routine.

FIG. 4 is a flowchart showing a switching valve operation control routine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 4 Exhaust pipe 5 Adsorbent 6 Electric heating oxidation catalyst 7 Three-way catalyst 8a Atmospheric passage 8b Bypass passage 8c Bypass passage 12a Switching valve 12b Switching valve 14 Canister 16 Fuel tank

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/08 ZAB F01N 3/20 ZABK 3/20 ZAB 3/22 ZAB 3/22 ZAB 301B 301 3/36 ZABJ 3/36 ZAB F02M 25/08 ZAB F02M 25/08 ZAB 301V 301 B01D 53/36 ZABB

Claims (1)

[Claims] 1. An adsorbent for adsorbing hydrocarbons at a low temperature from an upstream side in an exhaust system of an engine body, an electrically heated oxidation catalyst, and a three-way catalyst are disposed, and between the adsorbent and the electrically heated oxidation catalyst. A secondary air supply passage and a canister purge passage communicating with a canister storing evaporative fuel in a fuel tank are selectively selectively connected to each other through a passage switching means. During the desorption of hydrogen, the secondary air supply passage is communicated via the switching means, and after the desorption of the hydrocarbons adsorbed by the adsorbent is completed, the canister purge passage is communicated. Engine exhaust gas purification device.