Exhaust gas purifying apparatus for internal combustion engine

An exhaust gas purifying apparatus for an internal combustion engine is provided to desorb predetermined components contained in exhaust gas from an adsorption device for adsorbing the components and to purify the desorbed components, even during the stop of the internal combustion engine. A main exhaust passage and a bypass passage bypassing the main exhaust passage are provided. An exhaust switching valve is capable of switching a flow target into the exhaust gas flows between the main exhaust passage and the bypass passage. An adsorbent for adsorbing the predetermined components is provided in the bypass passage. An underfloor catalyst including a catalyst with a heater is provided at a downstream side of the bypass passage in the main exhaust passage. A pump and a heater are provided in an air supply passage which branches from the bypass passage at an upstream portion of the adsorbent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application of International Application No. PCT/JP2008/054380, filed Mar. 11, 2008, and claims the priority of Japanese Application No. 2007-105492, filed Apr. 13, 2007, the contents of both of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus including an adsorbent for adsorbing predetermined components that is contained in exhaust gas and cannot be purified by a catalyst before activation of the catalyst.

BACKGROUND ART

A technique concerning an exhaust gas purifying apparatus for a hybrid vehicle has been disclosed in the past, for example, by Patent Document 1. In the technique, a catalyst in an exhaust system is preliminarily heated and put into an active state, and an internal combustion engine is then started. Thus the technique intended to reduce exhaust emission.

Furthermore, an automobile exhaust gas purifying system including an HC adsorber catalyst for adsorbing HC and an NOx adsorber catalyst for adsorbing NOx placed at an upstream side of an exhaust gas purifying catalyst has been disclosed, for example, by Patent Document 2. In the conventional purifying system, exhaust gas is adsorbed by the HC adsorber catalyst and the NOx adsorber catalyst before activation of the exhaust gas purifying catalyst. When exhaust gas passes through the HC adsorber catalyst and the like after the activation of the exhaust gas purifying catalyst, HC and NOx adsorbed by the HC adsorber catalyst and the like are desorbed from the adsorber catalysts and purified by the exhaust gas purifying catalyst.

Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

In the above described hybrid vehicle, an economical running vehicle (a vehicle that has an idling stop function), or the like, an internal combustion engine starts and stops at odd intervals. In a case where the HC adsorber catalyst and the NOx adsorber catalyst are applied to such hybrid vehicle or the like, in order that HC and NOx exhausted at the start can be adsorbed by the HC adsorber catalyst or the like even if the start is performed at odd intervals, it is required to be able to desorb HC or the like adsorbed by the HC adsorber catalyst or the like from the HC adsorber catalyst or the like at the right time and be able to purify HC and the like by the exhaust gas purifying catalyst.

However, there has been a problem that HC or the like cannot be purified after being desorbed from the HC adsorber catalyst or the like in a stop condition of the internal combustion engine by means of only simply combining the technique of Patent Document 1 and the technique of Patent Document 2, that is, by means of just simply applying the HC adsorber catalyst or the like to the hybrid vehicle or the like.

The present invention has been made to solve the above problem. It is an object of the present invention to provide an exhaust gas purifying apparatus which can successfully desorb predetermined components contained in the exhaust gas from adsorption means for adsorbing the components and can successfully purify the desorbed components, even during the stop of the internal combustion engine.

Means for Solving the Problem

A first aspect of the present invention is an exhaust gas purifying apparatus for an internal combustion engine, the apparatus comprising:

adsorption means which is provided in an exhaust passage of the internal combustion engine and adsorbs predetermined components contained in exhaust gas;

a purification catalyst which is provided at a downstream side of the adsorption means in the exhaust passage and purifies the predetermined components;

gas supply means for supplying gas to the adsorption means from an upstream side of the adsorption means during a stop of the internal combustion engine; and

heating means for heating at least the purification catalyst among the adsorption means, the gas supplied to the adsorption means, and the purification catalyst,

wherein the heating means heats the purification catalyst when the gas is supplied by the gas supply means.

A second aspect of the present invention is the exhaust gas purifying apparatus for the internal combustion engine according to the first aspect of the present invention,

wherein the gas is air.

A third aspect of the present invention is the exhaust gas purifying apparatus for the internal combustion engine according to the first or second aspect of the present invention,

wherein the exhaust passage includes a main exhaust passage through which the exhaust gas exhausted from the internal combustion engine flows, and a bypass passage which bypasses the main exhaust passage;

wherein the exhaust gas purifying apparatus for the internal combustion engine further includes flow path switching means that is capable of switching a flow target into which the exhaust gas flows between the main exhaust passage and the bypass passage, and control means for controlling the flow path switching means;

wherein the adsorption means is disposed in the bypass passage;

wherein the gas supply means is disposed in the bypass passage; and

wherein the purification catalyst is disposed at a downstream side of the bypass passage in the main exhaust passage.

A fourth aspect of the present invention is the exhaust gas purifying apparatus for the internal combustion engine according to any one of the first to third aspects of the present invention,

wherein the heating means heats at least one of the gas and the adsorption means, besides the purification catalyst; and

wherein the exhaust gas purifying apparatus for the internal combustion engine further includes desorbing-operation judgment means for judging whether a desorbing operation for desorbing the predetermined components contained in the exhaust gas from the adsorption means during the stop of the internal combustion engine is terminated, wherein the apparatus continues to operate the gas supply means and stops the heating performed by the heating means if it is determined that the desorbing operation is terminated.

A fifth aspect of the present invention is the exhaust gas purifying apparatus for the internal combustion engine according to the fourth aspect of the present invention,

wherein the exhaust gas purifying apparatus for the internal combustion engine further includes temperature detection means for detecting a temperature of the adsorption means; and

wherein the desorbing-operation judgment means judges whether the desorbing operation is terminated based on the detected temperature of the adsorption means.

A sixth aspect of the present invention is the exhaust gas purifying apparatus for the internal combustion engine according to any one of the first to fifth aspects of the present invention,

wherein the exhaust gas purifying apparatus for the internal combustion engine is mounted in a hybrid vehicle including the internal combustion engine and an other power source; and

wherein the internal combustion engine starts and stops automatically based on predetermined conditions.

ADVANTAGES OF THE INVENTION

The first aspect of the present invention makes it possible to successfully desorb the predetermined components of the exhaust gas from the adsorption means and successfully purify the desorbed components, even in the stop condition of the internal combustion engine.

The second aspect of the present invention makes it possible to rapidly desorb the components from the adsorption means without decreasing the adsorption ability of the adsorption means, while using the air whose moisture concentration is lower than the exhaust gas.

The third aspect of the present invention makes it possible to prevent the adsorption means and gas supply means from inhibiting the exhaust gas stream during the normal operation of the internal combustion engine, and to use the purification catalyst heated by the heating means either during the adsorbing operation or the normal operation of the internal combustion engine. Further, according to the present invention, the advantages of the first or the second aspect of the present invention are achieved, providing that the exhaust gas purifying apparatus for the internal combustion engine is equipped with such a proper configuration.

The fourth aspect of the present invention makes it possible to cool down the adsorption means being put in a high-temperature state by desorbing the predetermined components of the exhaust gas from the adsorption means in the stop condition of the internal combustion engine, thereby securing the adsorption ability of the adsorption means at the next restart of the internal combustion engine.

The fifth aspect of the present invention makes it possible to judge a termination time point of the desorbing operation based on the temperature of the adsorption means.

The sixth aspect of the present invention makes it possible to successfully reduce exhaust emission at the cold start of the internal combustion engine, while successfully suppressing electric power consumption, in the hybrid vehicle in which the start and the stop of the internal combustion engine are performed at odd intervals.

DESCRIPTION OF SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

FIG. 1is a diagram for showing a schematic configuration of a drive system for a plug-in hybrid vehicle to which the present invention is applied. The drive system10includes an internal combustion engine12and a vehicle driving motor (hereinafter simply referred to as a “motor”)14as power sources of the vehicle. The drive system10also includes a generator16that receives a supply of a drive force and generates electric power. The internal combustion engine12, the motor14, and the generator16are mutually connected via a power dividing mechanism18. A reducer20is connected to a rotating shaft of the motor connected to the power dividing mechanism18. The reducer20connects the rotating shaft of the motor14with a drive shaft24connected to drive wheels22. The power dividing mechanism18divides and distributes a drive force of the internal combustion engine12into the generator16and the reducer20. The distribution rate of the drive force by the power dividing mechanism18can be freely changed.

The drive system10further includes an inverter26, a converter28, and a high voltage battery30. The inverter26is connected to the generator16and the motor14, and also connected to the high voltage battery30via the converter28. The electric power generated by the generator16may be supplied to the motor14via the inverter26, or charged into the high voltage battery30via the inverter26and the converter28. The electric power charged into the high voltage battery30can be supplied to the motor14via the converter28and the inverter26.

The drive system10described above can rotate the drive wheels22only by the drive force of the internal combustion engine12while stopping the motor14, and, conversely, can rotate the drive wheels22only by the drive force of the motor14while stopping the internal combustion engine12, according to predetermined conditions. The system can also rotate the drive wheels22by the drive forces of both the motor14and the internal combustion engine12while operating both of them. Further, according to the drive system10, the motor14can function as a starter for the internal combustion engine12. More specifically, by inputting part or all of the drive force of the motor14to the internal combustion engine12via the power dividing mechanism18at the start timing of the internal combustion engine12, it is possible to crank the internal combustion engine12.

The drive system10of the present embodiment is controlled by an electronic control unit (ECU)40. The ECU40comprehensively controls the drive system10including the internal combustion engine12, the motor14, the generator16, the power dividing mechanism18, the inverter26, the converter28, and the like. The above described high voltage battery30is configured to receive a supply of electric power from outside the vehicle (domestic power supply or the like). More specifically, the drive system10of the present embodiment is configured as a drive system for a so-called plug-in hybrid vehicle.

[Configuration of Exhaust Gas Purifying Apparatus]

FIG. 2is a diagram illustrating a configuration of an exhaust gas purifying apparatus mounted in the internal combustion engine system inFIG. 1. The internal combustion engine12shown inFIG. 2includes an intake passage (not shown) for taking air into a cylinder, and an exhaust passage through which exhaust gas exhausted from the cylinder flows.

The exhaust passage of the present embodiment includes a main exhaust passage42for exhausting the exhaust gas from the cylinder, and a bypass passage46described later. A front stage catalyst (SC)44that can purify the exhaust gas is disposed at an upstream portion in the main exhaust passage42.

The bypass passage46is configured as a passage bypassing the main exhaust passage42on a downstream side of the front stage catalyst44in the main exhaust passage42. More specifically, the bypass passage46is configured to branch off from the main exhaust passage42at an upstream connecting portion48aplaced downstream of the front stage catalyst44, and merge again with the main exhaust passage42at a downstream connecting portion48bplaced downstream of the upstream connecting portion48a.

In the upstream connecting portion48a, an exhaust switching valve50is placed for switching a flow target into which the exhaust gas flows between the main exhaust passage42and the bypass passage46. In the middle of the bypass passage46, an adsorbent52is placed having a function of adsorbing predetermined components such as the HC components and the NOx components contained in the exhaust gas. Into the adsorbent52, an adsorbent temperature sensor54for detecting a temperature of the adsorbent52is integrated.

An underfloor catalyst (UF)56that can purify the exhaust gas is placed downstream of the downstream connecting portion48bin the main exhaust passage42. An upstream part of the underfloor catalyst56is configured as a catalyst with an electric heater (hereinafter referred to as an EHC (Electric Heated Catalyst))58. The heater included in the EHC58receives a supply of electric power from the high voltage battery30, and is capable of heating the EHC58when the energization is appropriately controlled by the ECU40. By such an energization control, the EHC58can keep a predetermined activation temperature. A catalyst temperature sensor60for detecting the temperature of the EHC58is integrated into the EHC58. In the main exhaust passage42provided downstream of the underfloor catalyst56, a sub muffler62and a main muffler64are placed in series in order from the upstream side.

In the bypass passage46, one end of an air supply passage66is connected to an upstream portion of the adsorbent52, that is, a portion between the upstream connecting portion48aand the adsorbent52. The other end of the air supply passage66is open to the atmosphere. A motor-driven pump68for supplying the air toward the adsorbent52, a heater70for heating the air force-fed by the pump68, and a check valve72for preventing the exhaust gas in the bypass passage46from being released into the atmosphere via the air supply passage66are arranged in the air supply passage66, respectively, in that order from the open end thereof. The pump68and the heater (dryer)70are connected to the ECU40, respectively. Electric power for the heater70is supplied by the high voltage battery30.

[Operation of Exhaust Gas Purifying Apparatus]

FIG. 3is a diagram illustrating an operation of the exhaust gas purifying apparatus according to the first embodiment of the present invention.

First, with reference toFIG. 3(A), an operation for causing the adsorbent52to adsorb the predetermined components (such as HC and NOx) contained in the exhaust gas exhausted from the cylinder at the cold start of the internal combustion engine12will be described.

The adsorbing operation is started at the cold start timing of the internal combustion engine12in a state where the exhaust switching valve50blocks the main exhaust passage42as shown inFIG. 3(A). When the exhaust switching valves50is thus controlled, all of the exhaust gas exhausted from the internal combustion engine12is supplied into the bypass passage46from the main exhaust passage42via the upstream connecting portion48a. The exhaust gas supplied into the bypass passage46passes through the adsorbent52and is then returned to the main exhaust passage42. Then, the exhaust gas is released into the atmosphere.

By the above described adsorbing operation, HC and NOx contained in the exhaust gas are adsorbed by the adsorbent52so as to be removed. This can prevent HC and NOx from being released into the atmosphere at the cold start when the front stage catalyst44and the EHC58, or the like have not yet been activated.

In the system of the present embodiment, a flow path pattern shown inFIG. 3(A)is also selected when an exhaust purging operation for desorbing HC and the like from the adsorbent52is performed during operation of the internal combustion engine12. More specifically, a flow path pattern is switched to a state shown inFIG. 3(A)when a predetermined timing for purging comes during the operation of the internal combustion engine12, so that exhaust gas being heated to some extent after start-up is supplied to the adsorbent52. This allows HC and the like to be desorbed from the adsorbent52, and allows desorbed HC and the like to be purified by the underfloor catalyst56.

Next, with reference toFIG. 3(B), a forced purging operation for forcedly desorbing HC and the like from the adsorbent52during the stop of the internal combustion engine12will be described. More specifically, the forced purging operation is a purging operation performed when the internal combustion engine12is stopped in a state where the adsorbing operation for HC and the like using the adsorbent52is partly or completely performed at the cold start timing of the internal combustion engine12and thus HC and the like is adsorbed by the adsorbent52, or a state where the exhaust purging operation is not completed after the adsorbing operation and thus HC and the like are being adsorbed by the adsorbent52.

In the forced purging operation, as shown inFIG. 3(B), the exhaust switching valve50is controlled to block the bypass passage46, and the energization control of the EHC58is performed, so that the EHC58is controlled to be in an active state. In the forced purging operation, the pump68and the heater70are operated under such conditions and thus air (high-temperature air) heated to such a level that facilitates the desorption of HC and the like from the adsorbent52is supplied to the adsorbent52via the air supply passage66.

The forced purging operation described above can desorb HC and the like from the adsorbent52by supplying the adsorbent52with the high-temperature air heated by the heater70. Then, the forced purging operation can purify HC and the like desorbed from the adsorbent52using the underfloor catalyst56including the active EHC58.

Next, with reference toFIG. 3(C), a forced cooling operation that is performed for cooling the adsorbent52being put in a high-temperature state due to the execution of the above forced purging operation during the stop of the internal combustion engine12will be described.

In the forced cooling operation, as shown inFIG. 3(C), the exhaust switching valve50is also controlled to block the bypass passage46. In the forced cooling operation, only the pump68is operated without operating the heater70under such conditions, air at ordinary temperatures is supplied to the adsorbent52via the air supply passage66. By supplying the adsorbent52with the air at ordinary temperatures, the forced cooling operation can cool down the adsorbent52that is in the high-temperature state due to the execution of the above described forced purging operation, thereby preparing for the next adsorbing operation properly.

Next, with reference toFIG. 3(D), a flow path pattern used at the normal start of the internal combustion engine12will be described.

The exhaust switching valve50is also controlled to block the bypass passage46during the normal operation of the internal combustion engine12as shown inFIG. 3(D). With such a flow path pattern, the exhaust gas exhausted from the internal combustion engine12passes through the main exhaust passage42without passing through the adsorbent52, and is then released into the atmosphere.

[Detailed Processes in First Embodiment]

FIG. 4is a flowchart of a routine performed by the ECU40for reducing exhaust emission at the cold start of the internal combustion engine12in the first embodiment of the present invention. This routine is started when a switch for starting the plug-in hybrid vehicle is turned on (ignition is on).

In the routine inFIG. 4, when the ignition is on, the HV system becomes ready (step100). Then, according to a vehicle driver's demand, EV running using only the motor14as a power source is started (step102).

Then, a load demand from the driver is detected based on an accelerator press-down degree, and it is determined whether the load demand is equal to or higher than a predetermined value A1(step104). When it is determined that the load demand is equal to or higher than A1, then the internal combustion engine12is started, and the exhaust switching valve50is controlled so that the exhaust gas is supplied into the adsorbent52(step106). Thus, the adsorbing operation is started. (seeFIG. 3(A)).

When the adsorbing operation is started, processes in steps108to112and processes in steps114to122described below are concurrently performed.

More specifically, when the adsorbing operation is started, first, the EHC58is energized so that the electric power supplied to the EHC58is maximized in order to immediately activate the EHC58(step108). Then, it is determined whether the floor temperature of the EHC58becomes equal to or higher than the predetermined temperature B (step110). The temperature B is a threshold for determining whether the EHC58is active. When it is determined that the floor temperature of the EHC58is increased to the value equal to or higher than the temperature B, the electric power supplied to the EHC58is reduced, and the energization of the EHC58is controlled so that the floor temperature of the EHC58keeps a predetermined activation temperature (step112).

When the adsorbing operation is started, then, it is determined whether a temperature of the adsorbent52is equal to or lower than a predetermined temperature C1(step114). The temperature C1is an upper limit value of a temperature that allows the adsorbing operation by the adsorbent52. When it is determined that the adsorbent temperature is higher than C1, that is, when it can be determined that the adsorbing operation cannot be continued any longer, the exhaust switching valve50is controlled so that the exhaust gas flows through the main exhaust passage42without passing through the adsorbent52(step116). Thus, the adsorbing operation is terminated.

Next, it is determined whether the load demand from the driver is equal to or lower than a predetermined value A2(<A1) (step118). When it is determined that the load demand is equal to or lower than A2, that is, when it can be determined that a high load demand from the driver is dissolved, the internal combustion engine12is stopped. Also in this case, the exhaust switching valve50is controlled so that the exhaust gas flows through the main exhaust passage42without passing through the adsorbent52(step120).

On the other hand, when it is determined in step114that the adsorbent temperature is equal to or lower than C1(that is, when it can be determined that the adsorbing operation can be still continued) and that the load demand is equal to or lower than A2, similarly, the internal combustion engine12is stopped and the exhaust switching valve50is controlled (step120). In such a case, that is, in a case where the high load demand to the vehicle is dissolved even during the adsorbing operation, the internal combustion engine12is stopped to return to the EV running. Thus, the adsorbing operation is terminated.

In a case where the internal combustion engine12is stopped and the exhaust switching valve50is controlled due to the above described step120, then the pump68is operated with an operation of the heater50(step122). Thus, the forced purging operation is started (seeFIG. 3(B)).

In the routine inFIG. 4, the processes in steps108to112and the processes in steps114to122described above are concurrently performed, and then it is determined whether the temperature of the adsorbent52is equal to or higher than a predetermined temperature C2(step124). The temperature C2is a value preset as a temperature of the adsorbent52that allows determination that the purging operation is completed. By such a process, a termination time point of the purging operation (desorbing operation) can be precisely determined based on the temperature of the adsorbent52.

When it is determined that the adsorbent temperature is equal to or higher than C2, that is, when it is determined that purging using the forced purging operation is completed, the operation of the heater70is stopped while the operation of the pump68is continued, and the energization of the EHC58is stopped (step126).

Next, it is determined whether the temperature of the adsorbent52is equal to or lower than a predetermined temperature C3(step128). The temperature C3is a value for judging whether the temperature of the adsorbent52reaches (that is, is lower than) a temperature that allows the adsorbing operation to be performed once again. When it is judged that the adsorbent temperature is equal to or lower than the temperature C3, the operation of the dryer pump68is stopped (step130). For the purpose of supplying the exhaust gas to the adsorbent52, next, the exhaust switching valve50is controlled so as to become the state shown inFIG. 3(A)(step132). In other words, step132is performed to allow the system to go into standby state, in order that the adsorbent52can adsorb HC and the like contained in the exhaust gas even if the cold start of the internal combustion engine12is performed once again afterward. Then, the process in Step104and thereafter are repeatedly performed until the vehicle system (HV system) is stopped.

Cruising distance by EV running using only the motor as a power source is longer in a plug-in hybrid vehicle such as the system according to the present embodiment, than in a hybrid vehicle which does not have a charging function from outside the vehicle. As a result, the start-up of the internal combustion engine while the vehicle is running occurs mainly in a case where a high load demand is given by the driver. This means that the catalyst becomes apt to be cooled down in the plug-in hybrid vehicle since the chance that the internal combustion engine is started up becomes rare.

In the plug-in hybrid vehicle, therefore, it is conceivable to always activate the EHC by means of the high voltage battery during the EV running. Such a method can purify HC and NOx contained in the exhaust gas by means of the active EHC even if the internal combustion engine is cold started following receipt of a high load demand, thereby reducing the exhaust emission.

In a hybrid vehicle (or, for example, an economical running vehicle that has an idling stop function), regardless of whether it is a plug-in-type, however, the internal combustion engine12starts and stops at odd intervals. In order to perform the above described method, therefore, it is necessary for the EHC to be always energized and be always high temperature. Due to such consumption of an electrical energy, however, there is a possibility that the cruising distance at the EV running becomes short. Alternatively, it becomes not necessary to keep the EHC always in high temperature, provided that the internal combustion engine is not allowed to be started even if the high load demand is issued and the internal combustion engine is allowed to be started only when SOC (State Of Charge) of the high voltage battery becomes low. However, there is a possibility that the demands from the driver cannot be met properly because using only the EV running may not be able to give a sufficient vehicle torque.

In contrast, according to the routine shown inFIG. 4described above, the energization to the EHC58is not performed during the EV running, and the energization to the EHC58is just started when the internal combustion engine12is started following the receipt of the high load demand during the EV running. Besides, the adsorbing operation to adsorb HC and the like exhausted from the cylinder to the adsorbent52is performed. Therefore, it is possible to successfully reduce the exhaust emission at the cold start, while reducing the consumption of the electrical energy.

Particularly, in the case of the hybrid vehicle which is the plug-in-type, even if HC and the like exhausted when the internal combustion engine is cold started following the receipt of the high load demand is adsorbed by the adsorbent52, the internal combustion engine is immediately stopped to return the EV running after termination of the high load demand. For this reason, it becomes difficult to obtain enough occasions for performing the exhaust purging operation using the exhaust gas contrary to a case where the operation of the internal combustion engine is continued.

In contrast, according to the routine described above, the forced purging operation that supplies air heated by the heater70to the adsorbent52by means of the pump68is performed, if the internal combustion engine12is stopped to return to the EV running after termination of the adsorbing operation, or if the internal combustion engine12is stopped to return to the EV running during the adsorbing operation. As a result, heated air whose moisture concentration is quite lower than that of the exhaust gas whose moisture concentration is approximately fourteen percent is supplied to the adsorbent52, and thus the adsorbent52can be purged more rapidly without decreasing the adsorption ability of the adsorbent.

Particularly, in the plug-in hybrid vehicle, there is a possibility that the cold start is performed several times per trip as described above. Under the above circumstances, when the internal combustion engine is started without anytime lag after the forced purge operation, which is performed for the adsorbent by means of methods such as supplying the adsorbent with the heated air described above, the adsorbing operation becomes unable to be satisfactorily performed for the adsorbent being put in a high-temperature state due to the execution of such forced purging operation.

In contrast, the routine described above continues the operation of the pump68after the forced purge operation is terminated while stopping the operation of the heater70. This can supply air at an ordinary temperature to the adsorbent52whose purge is completed, thereby cooling down the adsorbent52promptly. Therefore, the adsorbent52can be returned to a state where the adsorption ability is sufficiently secured, even if the next high load demand is issued in a short period of time.

In the system according to the present embodiment that has described above, the pump68and the heater70are provided at the upstream side of the adsorbent52, and the EHC58is provided at the downstream side of the adsorbent52. Therefore, HC and the like can be forcibly purged from the adsorbent52, and the adsorbent52becomes able to be cooled down promptly, even during the stop of the internal combustion engine12. This makes it possible to prepare for the next adsorbing operation promptly, thereby drastically shortening a time necessary to the energization of the EHC58.

The first embodiment, which has been described above, assumes that the pump68and the heater70are provided at the upstream side of the adsorbent52, as a means for forcibly performing the purge during the stop of the internal combustion engine12. However, the present invention is not limited to the use of such a configuration. For example, the present invention can also be applied to a configuration shown inFIG. 5.

FIG. 5is a diagram illustrating a modified embodiment of the exhaust gas purifying apparatus according to the first embodiment of the present invention. As regards the elements inFIG. 5that are the same as those inFIG. 2, their description is omitted or abridged with the same reference numerals assigned.

The configuration shown inFIG. 5is characterized in that an adsorbent82including an electric heated adsorber (hereinafter referred to as an “EHad”)82as an upstream part thereof is provided instead of the pump68and the heater70. Incidentally, the whole of the adsorbent82may be configured by the EHad82.

In the configuration shown inFIG. 5, the forced purge operation can be performed by means of the following method. More specifically, according to the method, the EHad82is heated by an electric heater which the EHad82has, while in the above described first embodiment, the air supplied to the adsorbent52is heated by the heater70. Then, the internal combustion engine12during the stop is driven by the motor14to allow the internal combustion engine12to function as a pump for supplying the air to the adsorbent80, while in the above described first embodiment, the air is supplied by the pump68from outside. The above described method is also able to perform the forced purge operation, while putting the adsorbent80into the high-temperature state during the stop of the internal combustion engine12.

After the forced purge operation is completed, according to the above described method, the electric heater of the EHad82is stopped operating when the internal combustion engine12is driven by the motor14, while in the above described first embodiment, the pump68is driven in a state where the heater70is stopped. The above described method is also able to supply the adsorbent80with the air at ordinary temperatures promptly, thereby cooling down the adsorbent80including the EHad82.

Incidentally, in the first embodiment, which has been described above, the underfloor catalyst56including the EHC58corresponds to the “purification catalyst” according to the first aspect of the present invention; the air supply passage66and the pump68correspond to the “gas supply means” according to the first aspect of the present invention; and the heater70and the heater of the EHC58correspond to the “heating means” according to the first aspect of the present invention.

Further, the exhaust switching valve50corresponds to the “flow path switching means” according to the third aspect of the present invention. In addition, the “control means” according to the third aspect of the present invention is implemented when the ECU40performs steps106,116,120, and132.

Further, the “desorbing-operation judgment means” according to the fourth aspect of the present invention is implemented when the ECU40performs step124.

Further, the adsorbent temperature sensor54corresponds to the “temperature detection means” according to the fifth aspect of the present invention.