JP3515483B2 - Exhaust gas purification system - 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 purification system for temporarily adsorbing automobile exhaust gas with an adsorbent until the exhaust gas treatment catalyst is activated.

[0002]

2. Description of the Related Art Exhaust gas emitted from an automobile is widely targeted as a source of air pollution, and many exhaust gas regulations are fulfilled.

At present, such regulations are cleared by treating exhaust gas with a three-way catalyst using platinum, rhodium or the like, and unburned hydrocarbons and nitrogen in exhaust gas of each vehicle are eliminated. Oxides, etc. are much less than before the regulation.

[0004]

However, in the prior art, the exhaust gas is treated until the temperature of the three-way catalyst rises to the temperature at which it is active (light-off temperature, about 350 ° C.). It wasn't done. In particular, immediately after the engine was started, the unburned hydrocarbons were discharged as they were, although the concentration was very high. For example, the starting temperature is 20
℃, it takes about 100 seconds to reach the light-off temperature (about 350 ℃), 7,000
A very high concentration of unburned hydrocarbons of ˜8000 ppm was in the state of being washed away.

As a measure against this problem, there is a movement to deal with it by heating the catalyst in advance with an electric heater or the like, but since it requires an extremely large amount of electric power, it has a serious problem in practical use. .

On the other hand, due to the increase in the number of vehicles and the increase in size,
The absolute amount of exhaust gas emitted has increased, and in recent years air pollution has become a problem again. Then, as a solution to this, it has been decided that stricter exhaust gas regulations will be implemented. For example, LEV (Low Emission Veh)
It has already been decided that the regulations will be implemented in California, USA since 1997. This will eventually be implemented throughout the United States. It is also clear that similar strict regulations will be implemented in Japan.

An object of the present invention is to provide an exhaust gas purifying system capable of treating exhaust gas discharged while the catalyst is warming up to a temperature at which it activates when the engine is started.

[0008]

The present invention has been made to achieve the above object, and in one aspect thereof, an exhaust gas treatment catalyst disposed in an exhaust gas passage of an engine, and A temperature range for adsorbing fuel hydrocarbons (hereinafter referred to as "adsorption zone") and a temperature range higher than the adsorption zone for desorbing adsorbed unburned hydrocarbons (hereinafter referred to as "adsorption zone"). Desorption zone ") and is disposed upstream of the catalyst in the exhaust gas flow path, and when the catalyst is not functioning, the temperature of the adsorbent is adjusted to the adsorption zone. Unburned hydrocarbons contained in the exhaust gas are temporarily adsorbed by the adsorbent, and when the catalyst starts to function, the temperature of the adsorbent is set to a desorption zone and adsorbed. Temperature control means for desorbing unburned hydrocarbons and supply to the engine And air amount detecting means for detecting an air amount,
A space velocity adjusting means for adjusting the gas velocity of the space inside the adsorbent of the exhaust gas flow path; and a control means for controlling the space velocity adjusting means based on the detection result of the air amount detecting means. An exhaust gas purification system is provided.

As another aspect, a catalyst for exhaust gas treatment arranged in an exhaust gas passage of an engine and a temperature range for adsorbing unburned hydrocarbons (hereinafter referred to as "adsorption zone") And a temperature range (hereinafter referred to as "desorption zone") in which the adsorbed unburned hydrocarbons are desorbed, which is a temperature range higher than the adsorption zone, When the adsorbent disposed on the upstream side of the catalyst and the catalyst are not functioning, the temperature of the adsorbent is kept in the adsorption zone so that the unburned hydrocarbon contained in the exhaust gas is absorbed by the adsorbent. When the catalyst starts functioning, the temperature of the adsorbent is set to a desorption zone and the adsorbed unburned hydrocarbons are desorbed .
And a means for controlling the air-fuel ratio of the exhaust gas, the exhaust gas purifying system being provided.

In this case, the temperature control means is arranged between the portion of the exhaust gas passage upstream of the adsorbent and the portion of the exhaust gas passage between the adsorbent and the catalyst. It is preferably a heat exchanger.

Further, it is preferable to have an air supply means for supplying air to the exhaust gas passage on the upstream side of the catalyst in the exhaust gas passage.

Further, air amount detecting means for detecting the amount of air supplied to the engine, pressure adjusting means for adjusting the pressure in the adsorbent in the exhaust gas flow path, and detection by the air amount detecting means. It is preferable to have control means for controlling the pressure adjusting means based on the result.

Further, pressure detecting means for detecting the pressure of the exhaust gas in the adsorbent, pressure adjusting means provided on the exhaust gas flow path downstream of the adsorbent, and detection results of the pressure detecting means. Based on the above, it is preferable to have a control means for controlling the pressure adjusting means.

In another aspect, an exhaust gas main flow path for exhausting exhaust gas of an engine and a bypass flow path provided in the middle of the exhaust gas main flow path and connecting an upstream part and a downstream part of the exhaust gas main flow path. , A temperature region (hereinafter referred to as "adsorption zone") provided in the bypass passage for adsorbing unburned hydrocarbons, and an unburned hydrocarbon adsorbed in a temperature region higher than the adsorption zone. Temperature range (hereinafter referred to as "desorption zone") at which the adsorbed substances are not completely desorbed in the desorption zone (hereinafter referred to as "regeneration"). An adsorbent having a "zone", a catalyst for exhaust gas treatment provided in a position of the exhaust gas flow path in parallel with the bypass flow path, and a temperature of the adsorbent and / or the catalyst. Temperature detecting means for detecting the In the air supply means disposed on the downstream side of the adsorbent, and a flow that is provided at the outlet of the bypass flow passage and adjusts the exhaust gas flow rate ratio between the exhaust gas main flow passage and the bypass flow passage. When the temperature of the path switching means and the adsorbent is in the adsorption zone, the flow path switching means is controlled to flow the exhaust gas to the bypass flow path side,
On the other hand, when the temperature of the adsorbent is in the desorption zone,
Exhaust gas characterized by having control means for controlling the switching means to flow exhaust gas to the main flow path side by closing the bypass flow path and for supplying air to the bypass flow path by the air supply means. A purification system is provided.

In this case, there is a sub-bypass means for introducing the exhaust gas from the exhaust gas main flow path to the rear side portion of the adsorbent of the bypass flow path, and the control means has the above-mentioned sub-bypass flow path. It is preferable to have a function of causing the exhaust gas to flow into the bypass passage to raise the temperature of the adsorbent to the regeneration zone.

As another aspect, an exhaust gas main flow path for exhausting exhaust gas of an engine, and a bypass flow path provided in the middle of the exhaust gas main flow path and connecting an upstream part and a downstream part of the exhaust gas main flow path , A temperature region (hereinafter referred to as "adsorption zone") provided in the bypass passage for adsorbing unburned hydrocarbons, and an unburned hydrocarbon adsorbed in a temperature region higher than the adsorption zone. Temperature range (hereinafter referred to as "desorption zone") at which the adsorbed substances are not completely desorbed in the desorption zone (hereinafter referred to as "regeneration"). An adsorbent having a "zone", a catalyst for exhaust gas treatment provided in a position of the exhaust gas flow path in parallel with the bypass flow path, and a temperature of the adsorbent and / or the catalyst. Temperature detecting means for detecting the In the air supply means arranged on the upstream side of the adsorbent, and at the outlet of the bypass flow passage, the flow for adjusting the exhaust gas flow rate ratio between the exhaust gas main flow passage and the bypass flow passage. The path switching means, the exhaust gas recirculation means for connecting a downstream portion of the adsorbent in the bypass flow path and the intake system of the engine to return a desired amount of exhaust gas to the intake system, and the temperature of the adsorbent are When in the adsorption zone, the flow passage switching means is controlled to flow the exhaust gas to the bypass flow passage side, while when the temperature of the adsorbent is in the desorption zone, the switching means is controlled. The exhaust gas is flowed to the main flow path side by blocking the bypass flow path, the air is supplied to the bypass flow path by the air supply means, and the gas in the bypass flow path is discharged by using the exhaust gas recirculation means. the above An exhaust gas purification system, characterized in that a control means for recirculating the exhaust system is provided.

In this case, there is a sub-bypass means for introducing the exhaust gas from the exhaust gas main flow path to the front side of the adsorbent in the bypass flow path, and the control means has the bypass flow path through the sub bypass flow path. It is preferable to have a function of causing the exhaust gas to flow into the passage to raise the temperature of the adsorbent to the regeneration zone.

The air amount detection means for detecting the amount of air supplied to the engine and the control means determine the exhaust gas recirculation amount by the exhaust gas recirculation means based on the detection result of the air amount detection means. It is preferable to have a function of controlling.

As still another aspect, an exhaust gas main flow path for exhausting exhaust gas of an engine and a bypass flow path provided in the middle of the exhaust gas main flow path and connecting an upstream part and a downstream part of the exhaust gas main flow path A temperature region (hereinafter referred to as "adsorption zone") provided in the bypass flow path for adsorbing unburned hydrocarbons, and an unburned carbonization adsorbed in a temperature region higher than the adsorption zone. A temperature range in which hydrogen is desorbed (hereinafter, referred to as "desorption zone") and a higher temperature range in which the adsorbed substance which is not completely desorbed in the desorption zone can be removed (hereinafter referred to as "desorption zone"). An adsorbent having a "regeneration zone"), an exhaust gas treatment catalyst provided downstream of the bypass passage in the exhaust gas passage, and a temperature of the adsorbent and / or the catalyst. Temperature detecting means for detecting In the flow path, an air supply means arranged upstream of the bypass flow path, and an exhaust gas flow rate provided between the exhaust gas main flow path and the bypass flow path, which is provided at an inlet portion of the bypass flow path. When the temperature of the flow path switching means for adjusting the ratio and the adsorbent is in the adsorption zone, the flow path switching means is controlled to cause the exhaust gas to flow to the bypass flow path side so that the temperature of the adsorbent is released. When in the remote zone and when the catalyst is not functioning, the switching means is controlled to block the bypass passage to allow the exhaust gas to flow to the main passage side and the air supply means to cause the bypass flow. An exhaust gas purifying system having a function of supplying air to a passage and controlling the switching means to allow the exhaust gas to flow into the bypass passage when the catalyst functions. It is provided.

In this case, it is preferable that the bypass passage has a second catalyst whose activation temperature is lower than that of the catalyst.

[0021]

Function: The temperature of the adsorbent is kept in the adsorption zone until the temperature of the catalyst rises sufficiently to function, and the unburned hydrocarbons are temporarily adsorbed. Then, temperature control is performed so that the catalyst reaches the light-off temperature and the adsorbent reaches the desorption temperature at the same time. As a result, the unburned hydrocarbon that has been once adsorbed is processed by the catalyst.

This temperature control is naturally achieved if the light-off temperature of the catalyst and the desorption zone of the adsorbent are well matched. If they do not match, it is possible, for example, by using a heat exchanger to remove heat from the exhaust gas at the front position of the adsorbent and use it for heating the catalyst.

In the above operation, the pressure in the adsorbent is controlled on the basis of the amount of air supplied to the engine detected by the air amount detecting means and the pressure in the adsorbent detected by the pressure detecting means. The adsorption efficiency can be increased.

The air supply means supplies air from the upstream side of the catalyst to prevent the air-fuel ratio from deviating from the stoichiometric air-fuel ratio due to the presence of desorbed unburned hydrocarbons.

The above-mentioned temperature control and the like can be performed more flexibly by providing a bypass passage in the exhaust gas passage and arranging an adsorbent therein.

Initially, the exhaust gas is caused to flow through the bypass passage by the passage switching means to adsorb unburned hydrocarbons. When the temperature of the adsorbent reaches the desorption zone, the flow path switching means causes the exhaust gas to flow to the main flow path side. On the other hand, air is sent to the bypass flow path by the air supply means so that the desorbed unburned hydrocarbons are caused to flow back through the bypass flow path and return to the main flow path, or the exhaust gas recirculation means is added to the intake system of the engine. return. In this case, the amount of air supplied from the air supply unit is determined based on the detection result of the air amount detection unit.

When the catalyst is provided in a position parallel to the bypass flow passage, exhaust gas is caused to flow through the sub bypass flow passage to heat the catalyst during adsorption. On the other hand, during desorption and regeneration, the adsorbent is heated.

A mode in which the catalyst is arranged on the rear side of the bypass channel will be described.

In a state where the adsorbent is in the desorption zone and the catalyst has not reached the light-off temperature, the exhaust gas is made to flow by the air supply means provided upstream of the catalyst while flowing the exhaust gas in the main passage. Supply air to the main flow path. As a result, unburned hydrocarbons are burned in the main flow path.

[0030]

An embodiment of the present invention will be described with reference to the drawings.

The basic idea of the present invention is that the unburned hydrocarbon is temporarily adsorbed by the adsorbent until the catalyst reaches a temperature at which it becomes active, in other words, until it can be treated by the exhaust gas catalyst. It does not allow it to be discharged. Then, when the catalyst becomes active, the adsorbed unburned hydrocarbon is desorbed and released, and the final treatment is performed by the catalyst.

The adsorbent, which is a prerequisite for the establishment of the present invention, will first be described.

As the adsorbent, of course, it is necessary to use an adsorbent having a characteristic of adsorbing the target substance, in this embodiment, unburned hydrocarbon, but the characteristic varies depending on the temperature.

When the temperature is low, as shown in FIG.
Adsorb unburned hydrocarbons (indicated as "adsorption zone QZ" in the figure). Further, when the temperature rises, the adsorbed unburned hydrocarbons are desorbed (in the figure, "desorption zone D
Z ”. ). However, once adsorbed unburned hydrocarbon is not completely desorbed even when the desorption temperature is reached, and remains adsorbed to some extent. In order to remove such unburned hydrocarbons, it is possible to remove the unburned hydrocarbons by burning them at a higher temperature (indicated as "regenerated zone SZ" in the figure).

The limit at which the catalyst or the like is destroyed (indicated as "heat-resistant limit zone TNZ" in the figure) must be at least in a higher temperature region.

In the present invention, such a temperature characteristic of the adsorbent is used. That is, until the catalyst is activated, the temperature of the adsorbent is kept in the adsorption zone to adsorb unburned hydrocarbons. After the catalyst is activated, the temperature of the adsorbent is raised to the desorption zone to desorb and release the adsorbed unburned hydrocarbons. When a large amount of undesorbed unburned hydrocarbon remains and the adsorption capacity of the adsorbent decreases, the temperature is raised to the regeneration zone for regeneration, and the adsorption amount is increased again.

Such an adsorption system itself is completely independent of the exhaust gas treatment by the catalyst, and it is necessary to independently control the temperature. Further, the temperature of the adsorption zone or the like varies depending on the type of adsorbent.

Therefore, if the characteristics of the adsorbent are well matched with those of the catalyst to be used, it is not necessary to control the temperature of the adsorbent independently, and the temperature can be controlled together with the catalyst. However, if it does not fit well, it is necessary to control the temperature separately from the catalyst. In other words, the configuration of the pipe or the like required for practical use differs depending on the temperature characteristics of the adsorbent and the catalyst.
This point will be described later in the description using some specific configuration examples.

In the above description of the adsorption characteristics, only the influence of temperature has been explained, but other influences such as pressure and space velocity are also present. In this case, the higher the pressure, the faster the adsorption, but the lower the pressure, on the contrary, the faster the desorption.
In addition, space velocity (SV: Space Velocity)
The smaller y), the higher the adsorption rate.

Hereinafter, a specific configuration of the exhaust gas purification system will be described with some examples.

FIG. 2 shows a structural example in which an adsorbent is arranged in front of the catalyst in one exhaust gas flow path.

In this embodiment, the adsorbent 4 is first provided in the exhaust gas flow path connected to the engine 1. The main catalyst 8 is arranged on the rear side.

A secondary air pump 9 and a secondary air amount control valve 10 are provided on the upstream side of the adsorbent 4. Further, a pressure control valve 6 is provided between the adsorbent 4 and the main catalyst 8.

The adsorbent 4 of this embodiment is optimally one in which the above-mentioned desorption zone is in the temperature range above the light-off temperature of the main catalyst 8. In other words, when the temperature characteristics of the main catalyst 8 are matched and only the temperature of the adsorbent 4 does not need to be independently controlled, the configuration of this embodiment can be adopted.
Specifically, the desorption zone and the regeneration zone are preferably in the temperature range achieved by the exhaust gas during traveling. In this case, desorption and regeneration are naturally performed by normal traveling. If the desorption characteristic is good, the regeneration zone may be omitted. Further, even during normal traveling, the exhaust gas passes through the adsorbent 4 as it is, and therefore sufficient heat resistance equal to or higher than that of the main catalyst 8 is required (the adsorbent 4 is located in front of the main catalyst 8). Therefore, the temperature may be higher than that of the main catalyst 8). Needless to say, it is necessary to adsorb unburned hydrocarbons in the temperature range at the time of starting.

The adsorbent 4 is provided with an exhaust gas temperature sensor 2, an adsorbent temperature sensor 3, and an exhaust gas temperature sensor 5 in order to detect the temperature accurately. The method of detecting the temperature using these temperature sensors will be described later together with the case of the other configuration examples, and will not be described here in detail.

A three-way catalyst is used as the main catalyst 8.
The main catalyst 8 is provided with a catalyst temperature sensor 7 for detecting the temperature. Although not described here in detail, the valves and the like are controlled by using the detection result of the catalyst temperature sensor 7.

The secondary air pump 9 and the secondary air amount control valve 10 are for maintaining the air-fuel ratio of the exhaust gas flowing into the main catalyst 8 at the stoichiometric air-fuel ratio. This is because even if the air-fuel ratio supplied to the engine 1 is the stoichiometric air-fuel ratio, the adsorbent 4
This is because the presence of unburned hydrocarbons desorbed from the exhaust gas causes the exhaust gas reaching the main catalyst 8 to deviate from the theoretical air-fuel ratio.

The pressure control valve 6 is for adjusting the space velocity, in other words, the flow rate of exhaust gas. As a result, the space velocity can be reduced and the adsorption rate of unburned hydrocarbons can be increased within a range permitted by conditions such as temperature. The control of the pressure control valve 6 requires data on the amount of exhaust gas, which is detected by the air flow rate detector 16 to detect the amount of air taken in through the air cleaner 17 and is used as the amount of intake air. Emissions are calculated. In this example, it is approximated that the intake amount and the exhaust gas amount are equal. Although not described in detail, the air amount detector 1
The air intake amount detected by 6 is used as data not only for controlling the pressure control valve 6 but also for controlling various valves used in other configuration examples described later.

Adjusting the space velocity also adjusts the pressure in the adsorbent 4. In this case, the temperature changes, but this change is almost negligible, and the space velocity can be controlled almost independently of the temperature.

The operation will be described.

Since the temperature is low when the engine 1 is started,
The main catalyst 8 is not functioning. However, even in such a low case, the adsorbent 4 adsorbs unburned hydrocarbons in the exhaust gas and is not discharged as it is.

When the temperature of the main catalyst 8 rises and reaches the light-off temperature, unburned hydrocarbons and the like are processed. On the other hand, almost simultaneously with this, the adsorbent 4 enters the desorption zone,
The unburned hydrocarbons that have been adsorbed are released. In this state, the exhaust gas newly discharged from the engine 1 and the unburned hydrocarbons discharged from the adsorbent 4 are contained in the main catalyst 8
Is processed by. In this case, the main catalyst 8 may deviate from the stoichiometric air-fuel ratio, but this can be adjusted by separately supplying air from the secondary air pump 9. It is possible to more accurately control the air-fuel ratio by providing an air-fuel ratio detecting means immediately in front of the main catalyst 8 and controlling the secondary air pump 9 and the like based on the detection result.

The regeneration is naturally performed as it is if the adsorbent 4 has a regeneration zone at the temperature achieved by the exhaust gas as described above.

All the operations described above are performed based on the instruction from the control control unit 23 shown in FIG. This control unit 2
The third item will be collectively described at the end.

An example in which the precatalyst 11 and the pressure detector 12 are provided in the system of this embodiment is shown in FIG.

In this example, since the pressure detector 12 is provided, the pressure control valve 6 can be controlled more accurately and the capacity of the adsorbent can be maximized.

On the upstream side of the adsorbent 4, in other words,
Since the temperature of the pre-catalyst 11 directly attached to a position closer to the exhaust hole of the engine 1, for example, directly attached to the exhaust manifold, increases in temperature, it is possible to further shorten the time until the catalyst activity is obtained. The catalyst used for the pre-catalyst 11 may be the same as the main catalyst 8, but since it is arranged at a position close to the engine 1, it is necessary to use a catalyst having higher heat resistance.

Another configuration example will be described with reference to FIG.

In this example, the bypass exhaust pipe 13 is provided in the exhaust gas flow path, and the adsorbent 4 is placed therein. A secondary air pump 9 and a secondary air amount control valve 10 for adjusting the air-fuel ratio are provided on the downstream side of the adsorbent 4 in the bypass exhaust pipe 13. An exhaust passage switching valve 18 that controls the inflow of exhaust gas into the bypass exhaust pipe 13 is provided on the outlet side of the bypass exhaust pipe 13. By operating this, it is possible to switch whether the exhaust gas emitted from the engine 1 passes through the main flow path side where the main catalyst 8 is present or the bypass exhaust pipe 13. Further, the exhaust passage switching valve 18 is capable of adjusting the opening, and a part of the exhaust gas is bypassed by the bypass exhaust pipe 13.
It is also possible to flush it to

The secondary air pump 9 and the secondary air amount control valve 10 are arranged on the downstream side of the adsorbent 4, and the exhaust passage switching valve 18 is arranged on the outlet side. This is because when desorbing hydrogen, the gas will flow backward in the bypass exhaust pipe 13 as described later.

Further, the main catalyst 8 is provided between the inlet and the outlet of the bypass exhaust pipe 13 on the main flow passage side of the exhaust gas flow passage.
That is, it is arranged in parallel with the adsorbent 4. Therefore, when the exhaust gas is flowing to the bypass exhaust pipe 13 side, the exhaust gas does not directly pass through the main catalyst 8,
The temperature rise of the main catalyst 8 becomes gentle, but this can be sufficiently compensated by devising the pipe shape and the like. For example, shortening the distance from the branch point between the bypass exhaust pipe 13 and the main flow path to the main catalyst 8 or the bypass exhaust pipe 1
It is conceivable to arrange 3 so that the main catalyst 8 is wound around it. The exhaust passage switching valve 18 is arranged on the downstream side of the bypass exhaust pipe 13 because the flow passage itself is provided at the inlet portion of the bypass exhaust pipe 13 even when the exhaust gas is flowing to the bypass exhaust pipe 13 side. This is also because the heat of the exhaust gas is easily transferred to the main catalyst 8 without shutting off.

Branch point with bypass exhaust pipe 13 and main catalyst 8
An A / F detection sensor 21 is provided between and.
This is to monitor that the air-fuel ratio of the exhaust gas flowing into the main catalyst 8 changes due to unburned hydrocarbons desorbed from the adsorbent 4. The detection result of the A / F detection sensor 21 is reflected in the control of the secondary air pump 9 and the secondary air amount control valve 10 described above, and the stoichiometric air-fuel ratio is maintained.

In this configuration example, since the temperature control can be independently performed by disposing the adsorbent 4 in the bypass exhaust pipe 13, is the desorption zone compatible with the characteristics of the main catalyst 8? Whether or not it does not matter. Also, the playback zone,
The heat-resistant zone is likewise not subject to any restrictions. However, as for the adsorption zone, which is a prerequisite for adsorbing unburned hydrocarbons, it is necessary to adsorb unburned hydrocarbons even in the starting temperature range of the engine 1 as in the above embodiment.

The exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, and the catalyst temperature sensor 7 are the same as those in the above embodiment. The temperature detection will be described in detail later.

The operation will be described.

When the engine 1 is started, the exhaust passage switching valve 18 is set at an angle a that closes the main passage side of the exhaust gas passage. In this state, unburned hydrocarbons in the exhaust gas are adsorbed by the adsorbent 4 and are not discharged to the outside.

At this time, the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, the catalyst temperature sensor 7
The temperatures of the adsorbent 4 and the main catalyst 8 are monitored based on the output of Then, when the temperature of the adsorbent 4 approaches the desorption zone, the exhaust passage switching valve 18 is gradually opened so that part of the exhaust gas passes through the main catalyst 8. The main catalyst 8 has already been warmed to some extent, and the temperature of the exhaust gas itself is higher than immediately after the engine is started.
Quickly reaches the light-off temperature.

When the catalyst temperature sensor 7 confirms that the temperature of the main catalyst 8 has risen sufficiently, the exhaust passage switching valve 18 is set to the angle b so that all the exhaust gas passes through the main catalyst 8. Therefore, after that, the exhaust gas newly discharged from the engine 1 is directly processed by the main catalyst 8.

On the other hand, when the exhaust passage switching valve 18 is completely set to the angle b, the temperature of the adsorbent 4 reaches the desorption zone. Therefore, in this state, the secondary air pump 9 and the secondary air amount control valve 10 are operated to cause the unburned hydrocarbon desorbed from the adsorbent 4 to flow back through the bypass exhaust pipe 13 and to pass through the main catalyst 8. , Process. In this case, the inflow of the desorbed unburned hydrocarbon does not cause the exhaust gas passing through the main catalyst 8 to deviate from the theoretical air-fuel ratio (14.7).
The secondary air pump 9, which is monitored by the / F detection sensor 21,
The amount of air sent by the secondary air amount control valve 10 is adjusted.

The temperature rise required for the regeneration of the adsorbent 4 is caused by heat transfer from the exhaust gas passing through the main catalyst 8 if the layout and shape of the bypass exhaust pipe 13 are devised, as in the case of the main catalyst 8. You can get enough.

In the state where the gas is allowed to flow backward in the bypass exhaust pipe 13, unburned hydrocarbons and the like are discharged to the outside without being processed until the main catalyst 8 reaches the light-off temperature. . However, some time has passed since the engine was started, and the content of unburned hydrocarbons in the exhaust gas is lower than immediately after the engine is started. Almost no problem. Therefore, as described above, the desorption temperature of the adsorbent 4 and the light-off temperature of the main catalyst 8 do not necessarily match. However, the temperature of the adsorbent 4 reaches the desorption zone until the main catalyst 8 reaches the light-off temperature by separately providing the bypass exhaust pipe 13 with a structure in which air is introduced from the upstream side of the adsorbent 4. By controlling not to do so, this problem can be easily solved.

All the operations described above are performed based on the instruction from the control control unit 23 shown in FIG. This control unit 2
The third item will be collectively described at the end.

Another configuration example will be described.

As shown in FIG. 5, the configuration of this example is basically the same as that of the embodiment shown in FIG. However, the desorbed unburned hydrocarbons are not allowed to flow back through the bypass exhaust pipe 13 and pass through the main catalyst 8, but to the bypass exhaust pipe 1
It is configured to return to the intake system of the engine 1 through the EGR valve 15 provided in the downstream region of the adsorbent 4 of No. 3. Therefore, the secondary air pump 9 and the secondary air amount control valve 10 are arranged upstream of the adsorbent 4.

The operation is almost the same as that of the above embodiment. EG
The R valve 15 is controlled to open when desorbing the adsorbed unburned hydrocarbons, that is, when the exhaust passage switching valve 18 is set to the angle b. The control in this case is performed corresponding to the intake air amount detected by the air amount detector 16.

Similarly, the heat source required for reproduction can be obtained by devising the layout configuration. Alternatively,
The exhaust passage switching valve 18 or the EGR valve 15 may be opened slightly and the exhaust gas may be introduced into the bypass exhaust pipe 13 to heat the exhaust gas. In this configuration example, gas does not flow back through the bypass exhaust pipe 13, and smoother control can be performed.

Still another configuration example will be described with reference to FIG.

This example is basically the same as the configuration example shown in FIG. 5, but in order to regenerate the adsorbent 4 more smoothly, the temperature of the adsorbent 4 is heated to the regeneration zone. As a heat source for this, the gas is introduced from the mainstream side of the exhaust gas flow path.

In this example, an exhaust gas introduction valve 25 is provided on the rear side of the main catalyst 8 in the main flow of the exhaust gas flow path which is present in parallel with the bypass exhaust pipe 13. Further, a sub-bypass exhaust pipe 22 is provided to allow the exhaust gas flowing in from the exhaust gas introduction valve 25 to flow into the bypass exhaust pipe 13 upstream of the adsorbent 4.

The opening degree of the exhaust gas introduction valve 25 can be adjusted based on the detection results of the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, and the catalyst temperature sensor 7.

The operation will be described.

The operation is basically the same as the example shown in FIG.

Immediately after the engine 1 is started, when the unburned hydrocarbon is adsorbed by the adsorbent 4, the exhaust passage switching valve 1
The exhaust gas is passed through the bypass exhaust pipe 13 at an angle a of 8. In this example, in this state, the exhaust gas introduction valve 25 is slightly opened to allow the exhaust gas to flow to the main catalyst 8 to some extent. As a result, the temperature rise of the main catalyst 8 can be accelerated.

Regeneration is carried out during normal running, that is, in a state where the temperature of the main catalyst 8 has risen sufficiently and the exhaust gas is being treated by the main catalyst 8. At the time of regeneration, the exhaust gas introduction valve 25 is slightly opened to allow the high-temperature exhaust gas passing through the main catalyst 8 to flow to the upstream side of the adsorbent 4. As a result, the adsorbent 4 can be heated and the temperature can be raised to a sufficient temperature. In this case, the degree of opening of the exhaust gas introduction valve 25 depends on the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3,
The optimum temperature for regeneration can be obtained by adjusting based on the temperatures of the exhaust gas temperature sensor 5 and the catalyst temperature sensor 7.

In this configuration example, the heat required for regeneration can be reliably ensured, and the degree of freedom in the shape and layout of the bypass exhaust pipe 13 and the like increases. In addition, since the gas that is treated by the main catalyst 8 and does not contain unburned hydrocarbons is used for the heating during the regeneration, the regeneration can be performed more completely.

Still another configuration example will be described with reference to FIG.

This configuration example is basically the same as that shown in FIG. However, an exhaust gas introduction valve 27 is provided on the rear side of the main catalyst 8, and the exhaust gas introduced from the exhaust gas introduction valve 27 is introduced to the rear side of the adsorbent 4 of the bypass exhaust pipe 13 by the sub bypass exhaust pipe 29. The difference is. As a result, the heat required to regenerate the adsorbent 4 is to be obtained from the exhaust gas. The exhaust gas introduction valve 27 is configured so that its opening degree can be adjusted based on the detection results of the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, and the like. Further, in this figure, the sub bypass exhaust pipe 29 communicates with the bypass exhaust pipe 13 at the rear side of the secondary air amount control valve 10 of the bypass exhaust pipe 13, but the adsorbent 4 and the secondary air amount control valve A configuration in which 10 and 10 communicate with the bypass exhaust pipe 13 may be used.

The operation will be described.

The basic operation is the same as the example shown in FIG.

However, at the time of regeneration, the exhaust gas introduction valve 27 is opened and high-temperature exhaust gas is passed through the adsorbent 4, whereby the temperature of the adsorbent 4 can be easily raised to the regeneration zone. The degree of opening of the exhaust gas introduction valve 27 is adjusted based on the detection results of the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, and the catalyst temperature sensor 7 so that the optimum temperature can be obtained. .

In this example, the heat required for regeneration can be easily obtained. Further, there is less restriction on the shape and layout of the bypass exhaust pipe 13 for obtaining heat required for regeneration, and the degree of freedom in design is increased. In addition,
Even when desorbing unburned hydrocarbons, it is possible to introduce exhaust gas from the sub-bypass exhaust pipe 29 and heat it so that sufficient desorption can be performed.

The next structural example will be described with reference to FIG.

This example is similar to the example shown in FIG.
There is only one exhaust flow path and no bypass is provided. The same applies to the fact that the adsorbent 4 and the main catalyst 8 are arranged in series in the exhaust passage.

However, this example is different from the example of FIG. 1 in that the heat exchanger 19 is provided on the upstream side of the adsorbent 4. That is, in this example, the temperature of the adsorbent 4 was controlled.
2 is an embodiment showing a part of the configuration for the purpose.

In the exhaust gas passage, the upstream side portion of the adsorbent 4 and the portion between the adsorbent 4 and the main catalyst 8 are heat exchangers 19.
It is configured to exchange heat via. This allows
While arranging the adsorbent 4 and the main catalyst 8 in series, the main catalyst 8
The temperature of the adsorbent 4 can be adjusted independently to some extent without hindering the temperature rise. Therefore, the desorption zone of the adsorbent 4 used in this example may be lower than the light-off temperature of the main catalyst 8 as long as it is within the range adjustable by the heat exchanger 19. Further, its heat resistance may be weaker than that in the case without the heat exchanger 19.

The operation will be described.

Immediately after the engine 1 is started, the exhaust gas exhausted is deprived of heat by the heat exchanger 19 and its temperature is lowered to some extent, so that the adsorbent 4 is not directly subjected to high heat. However, the unburned hydrocarbons in the exhaust gas are not affected by the existence of the heat exchanger 19 itself,
It passes through as it is and is adsorbed by the adsorbent 4.

On the other hand, since the heat taken by the heat exchanger 19 is returned to the exhaust gas flow path again on the upstream side of the main catalyst 8,
Since the temperature of the adsorbent 4 is not raised, the time required for the main catalyst 8 to reach the light-off temperature is shortened. Conversely, it is possible to delay the adsorbent 4 from entering the desorption zone until the main catalyst 8 reaches the light-off temperature.

At the time of regeneration, the temperature of the adsorbent 4 can be easily raised to a regeneration zone by adjusting the capacity of the heat exchanger 19.

Although not described in detail here, the capacity adjustment of the heat exchanger 19 is based on the detection results of the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, the catalyst temperature sensor 7, and the like. This enables accurate control.

In this structural example, the heat exchanger 19 and the main catalyst 8 are separate, but it is of course possible to integrate both.

Description will be made using another configuration example.

In this example, during the transitional period of switching from the adsorbent to the catalyst, the unburned hydrocarbons are burned in the exhaust gas passage to prevent the unburned hydrocarbons from being directly discharged to the outside. It is characterized by points.

As shown in FIG. 9, the specific structure is such that a bypass exhaust pipe 13 is provided in the exhaust gas flow path, and the adsorbent 4 is provided therein. On the other hand, the main catalyst 8 is arranged on the rear side of the bypass exhaust pipe 13 in the main flow portion of the exhaust gas flow path, and all the exhaust gas always passes through the main catalyst 8.

An exhaust passage switching valve 31 whose opening can be adjusted to a desired angle is provided at the inlet of the bypass exhaust pipe 13. A flow rate control valve 14 that controls the flow rate of the exhaust gas to the bypass exhaust pipe 13 is provided on the outlet side of the bypass exhaust pipe 13. Therefore, by controlling these, it is possible to switch whether the exhaust gas reaches the main catalyst 8 after passing through the adsorbent 4 or directly reaches the main catalyst 8 without passing through the adsorbent 4. It is configured to be able to. Therefore, in the adsorbent 4 used in this example, the desorption zone is higher than the light-off temperature of the catalyst.
It may be in a low area. Also, the heat resistance does not necessarily have to be as high as that of the catalyst.

A secondary air pump 9 for burning unburned hydrocarbons and adjusting the air-fuel ratio is provided upstream of the branch point between the main flow passage side of the exhaust gas flow passage and the bypass exhaust pipe 13. A secondary air amount control valve 10 is provided.

The exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, and the catalyst temperature sensor 7 are the same as in the above example. Details will be described later.

The operation will be described.

At the time of starting, the exhaust passage switching valve 31 is controlled to the angle a, that is, the main flow path side is completely closed and the exhaust gas is flown into the bypass exhaust pipe 13 side. in this case,
To reduce the resistance, the flow control valve 14 is fully opened. However, in order to improve the adsorption efficiency, the space velocity may be reduced by closing the flow rate control valve 14 within a range that does not hinder the gas discharge. In this case, the flow rate control valve 14 is controlled by using the exhaust gas amount calculated by using the detection result of the air amount detector 16 for optimization. The secondary air pump 9 and the secondary air amount control valve 1
0 does not need to be activated. In this state, the unburned hydrocarbons in the exhaust gas are adsorbed by the adsorbent 4. Also,
As described above, all the exhaust gas passes through the main catalyst 8, so the temperature of the main catalyst 8 is raised.

At this time, the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, the exhaust gas temperature sensor 5, the catalyst temperature sensor 7
The temperatures of the adsorbent 4 and the main catalyst 8 are monitored based on the output of When the temperature of the adsorbent 4 approaches the desorption zone, the exhaust passage switching valve 31 is once set to the angle b and the flow rate control valve 14 is closed to bypass the bypass exhaust pipe 13.
Stop the flow of gas inside. On the other hand, in parallel with this, the secondary air pump 9 and the secondary air amount control valve 10 are operated,
Inject fresh air into the exhaust gas flowing through the main flow path. Then, the unburned hydrocarbons in the exhaust gas are burned by the fresh air before they reach the main catalyst 8. Therefore, when the exhaust gas flow path is switched from the bypass exhaust pipe 13 to the main flow path side by the exhaust passage switching valve 31, the main catalyst 8
Even if the temperature does not reach the light-off temperature, the unburned hydrocarbons are not directly discharged to the outside.

When the main catalyst 8 reaches the light-off temperature, the exhaust passage switching valve 31 is opened to the middle, that is, the angle between the angle a and the angle b is set, and the exhaust gas is caused to flow into the bypass exhaust pipe 13 to some extent. As a result, the temperature of the adsorbent 4 is raised to the desorption zone, and the adsorbed unburned hydrocarbons are desorbed. In this case, the flow rate control valve 14 is fully opened to reduce the resistance.

Incidentally, when the main catalyst 8 reaches the light-off temperature, the unburned hydrocarbon treatment itself can be performed only by the ability of the main catalyst 8, but the presence of unburned hydrocarbons desorbed from the adsorbent 4 exists. To prevent deviation from the stoichiometric air-fuel ratio due to
The secondary air pump 9 and the secondary air amount control valve 10 feed air to some extent.

Regeneration of the adsorbent 4 is carried out under normal running conditions. In this case, as in the case of desorption, the exhaust passage switching valve 31 is opened to allow the exhaust gas to flow into the bypass exhaust pipe 13 to some extent, and the adsorbent 4 is heated to the regeneration zone. However, unlike the case of desorption, it is not necessary to operate the secondary air pump 9 and the secondary air amount control valve 10. Also in this case, the flow rate control valve 14 is fully opened to reduce the resistance.

During running, especially when a high load is applied, the temperature of the exhaust gas may rise and the heat resistance limit of the adsorbent 4 may be exceeded. Therefore, prevent the exhaust gas from flowing into the bypass exhaust pipe 13. The flow passage control valve 14 is closed while controlling the exhaust passage switching valve 31.

Another configuration example will be described.

As shown in FIG. 10, this example is almost the same as the example of FIG. 9, but a low temperature active catalyst 20 is provided between the adsorbent 4 of the bypass exhaust pipe 13 and the flow rate control valve 14. It is characterized by

With such a structure, even if the adsorbent 4 is saturated, it is possible to prevent the unburned hydrocarbons from flowing out. Further, when desorbing the adsorbed unburned hydrocarbons, the unburned hydrocarbons can be treated by the low temperature active catalyst 20 even if the main catalyst 8 does not reach the light-off temperature. Therefore, it is not necessary to close the exhaust passage switching valve 31 and the flow rate control valve 14 until the main catalyst 8 reaches the light-off temperature, and the exhaust gas can be treated more quickly. This is particularly effective in the case where the engine start / stop is repeated in a short time for maintenance or the like, and an extremely large amount of unburned hydrocarbon is generated without sufficiently increasing the temperature of the main catalyst 8.

The temperature control of some of the configuration examples described above will be collectively described below.

It is necessary for the adsorbent 4 to secure a sufficient adsorption capacity, and it is difficult to reduce the size to a certain extent or more.
Moreover, in order to increase the adsorption rate, it is necessary to increase the surface area, and a large amount of space exists in the adsorbent 4. Therefore, it is difficult to make the temperature inside the adsorbent 4 constant anywhere. Therefore, the temperature distribution of the adsorbent 4 is reliably detected by using a plurality of temperature sensors.

At the time of adsorption, various valves and the like are controlled based on the maximum temperature in the adsorbent 4.
In addition, the judgment of whether or not the heat resistance limit is reached is naturally made based on the maximum temperature. On the other hand, desorption and regeneration need to be sufficiently performed for the entire adsorbent 4, so the determination is made using the lowest temperature and each part is controlled.

The temperature detection of the above configuration example will be specifically described.

In each of the above configuration examples, the temperature of the adsorbent 4 is measured by the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, and the exhaust gas temperature sensor 5, that is, at a total of three locations.

Normally, the temperature becomes higher on the side where the exhaust gas flows in, so the adsorption time and the heat resistance limit are judged using the detection results of the exhaust gas temperature sensor 2. on the other hand,
Since it is considered that the minimum temperature is detected on the outlet side, the determination is made using the detection result of the exhaust gas temperature sensor 5 during desorption and regeneration.

Although the adsorbent temperature sensor 3 is not used in concrete control, it has a self-diagnosis function of whether or not the exhaust gas temperature sensor 2 and the exhaust gas temperature sensor 5 are functioning normally. I am using it to have. That is, the results detected by the exhaust gas temperature sensor 2, the adsorbent temperature sensor 3, and the exhaust gas temperature sensor 5 are compared, and if the temperature distribution is as shown in FIG. 11, it is determined that it is functioning normally. To do. It should be noted that a certain amount of margin (indicated by "α" in the figure) is provided in the determination of acceptability.

The control of each valve and the like in each of the above configuration examples is a control calculated by the control control unit 23 performing a predetermined calculation based on the data obtained by the sensor and the like described in the above description. It is based on the value. That is, in the examples shown in FIGS.
The temperature control means for opening each temperature sensor 2, 3, 5 and each temperature
Control controller to which the output from the degree sensors 2, 3 and 5 is input
And the control unit 23
With each valve operating based on the control value from
It FIG. 12 shows a part of the input / output to / from the control controller 23.
It was shown to.

As described above, according to the above embodiment,
When the exhaust gas treatment catalyst is not functioning, for example, unburned hydrocarbons are not directly discharged to the outside even immediately after the engine is started. Further, in the above embodiment, only the example of adsorbing unburned hydrocarbons has been described, but it is also applicable to the removal of other harmful substances such as NOx.

[0127]

As described above, in the present invention,
Even when the catalyst is not warm enough immediately after the engine is started, it is possible to prevent unburned hydrocarbons from being adsorbed by the adsorbent and flowing out to the outside as they are.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing characteristics of an adsorbent.

FIG. 2 is a configuration diagram showing an embodiment of the present invention.

FIG. 3 is a configuration diagram showing an embodiment of the present invention.

FIG. 4 is a configuration diagram showing an embodiment of the present invention.

FIG. 5 is a configuration diagram showing an embodiment of the present invention.

FIG. 6 is a configuration diagram showing an embodiment of the present invention.

FIG. 7 is a configuration diagram showing an embodiment of the present invention.

FIG. 8 is a configuration diagram showing an embodiment of the present invention.

FIG. 9 is a configuration diagram showing an embodiment of the present invention.

FIG. 10 is a configuration diagram showing an embodiment of the present invention.

FIG. 11 is a graph showing a rule of temperature control.

FIG. 12 is an explanatory diagram showing inputs and outputs of the entire control system.

[Explanation of symbols]

1: Engine, 2: Exhaust gas temperature sensor, 3: Adsorbent temperature sensor, 4: Adsorbent, 5: Exhaust gas temperature sensor, 6:
Pressure control valve, 7: catalyst temperature sensor, 8: main catalyst,
9: Secondary air pump, 10: Secondary air amount control valve, 1
1: front catalyst, 12: pressure detector, 13: bypass exhaust pipe, 14: flow control valve, 15: EGR valve, 1
6: Air flow rate detector, 17: Air cleaner, 18: Exhaust passage switching valve, 19: Heat exchanger, 20: Low temperature active catalyst, 21: A / F detection sensor, 22: Sub bypass exhaust pipe, 23: Control Control unit, 25: exhaust gas introduction valve, 27: exhaust gas introduction valve, 29: sub-bypass exhaust pipe, 31: exhaust passage switching valve, a: angle,
b: angle

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kuroda 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Hitachi, Ltd., Hitachi Research Laboratory (72) Toshio Ogawa 4026 Kuji Town, Hitachi City, Ibaraki Hitachi Research Co., Ltd. In-house (72) Noriko Watanabe 4026 Kuji-cho, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. (72) Minor Osuga 4026, Kuji-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (56) References JP 62-159714 (JP, A) JP 55-101715 (JP, A) Jitsukaihei 3-82824 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/24

Claims (3)

(57) [Claims] 1. A catalyst for exhaust gas treatment, which is arranged in an exhaust gas flow path of an engine, and a temperature range for adsorbing unburned hydrocarbons (hereinafter referred to as "adsorption zone").
And a temperature range higher than the adsorption zone and in which adsorbed unburned hydrocarbons are desorbed (hereinafter referred to as "desorption zone"). When the catalyst is not functioning with the adsorbent disposed upstream of the catalyst in the gas flow path, the temperature of the adsorbent is kept in the adsorption zone so that the unburned hydrocarbons contained in the exhaust gas. Is temporarily adsorbed by the adsorbent, and when the catalyst starts to function, the temperature of the adsorbent is set to a desorption zone to desorb adsorbed unburned hydrocarbons, and the engine is used. An air amount detecting means for detecting the amount of air supplied to the space, a space velocity adjusting means for adjusting the gas velocity of the adsorbent internal space of the exhaust gas flow path, based on the detection result of the air amount detecting means, Control means for controlling the space velocity adjusting means, An exhaust gas purification system, characterized in that. 2. A catalyst for treating exhaust gas arranged in an exhaust gas passage of an engine, and a temperature range for adsorbing unburned hydrocarbons (hereinafter referred to as "adsorption zone").
And a temperature range higher than the adsorption zone and in which adsorbed unburned hydrocarbons are desorbed (hereinafter referred to as "desorption zone"). When the catalyst is not functioning with the adsorbent disposed upstream of the catalyst in the gas flow path, the temperature of the adsorbent is kept in the adsorption zone so that the unburned hydrocarbons contained in the exhaust gas. Is temporarily adsorbed by the adsorbent, and when the catalyst begins to function, the temperature of the adsorbent is set to a desorption zone to desorb adsorbed unburned hydrocarbons, and the catalyst. An exhaust gas purification system comprising: means for controlling an air-fuel ratio of exhaust gas flowing into the exhaust gas . 3. The temperature control means comprises heat disposed between a portion of the exhaust gas flow passage upstream of the adsorbent and a portion of the exhaust gas flow passage between the adsorbent and the catalyst. The exhaust gas purification system according to any one of claims 1 and 2, further comprising an exchanger.