Exhaust gas purification apparatus and exhaust gas purification method

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2007-305368 filed on Nov. 27, 2007 including the specification drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an exhaust gas purification apparatus including, for example, a Hydrocarbon (HC) adsorbent and to an exhaust gas purification method.

2. Description of the Related Art

Some hazardous components (for example, HC and Nitrogen Oxide (NO_x)) contained in the exhaust gas may be discharged without purification by an exhaust gas purification apparatus including an HC adsorbent, thereby decreasing exhaust purification ability of the apparatus. Accordingly, a variety of configurations employing a combination of an Electrically Heated Catalyst (EHC) and an HC adsorbent have been suggested to increase the exhaust purification ability.

Japanese Patent Application Publication No. 6-33747 (JP-A-6-33747) discloses an exhaust gas purification apparatus including an HC adsorbent and an EHC provided downstream thereof.

Japanese Patent Application Publication No. 10-252449 (JP-A-10-252449) discloses an exhaust gas purification apparatus including an HC adsorbent and an EHC provided downstream thereof, wherein the adsorbed HC is purified by the EHC, secondary air is supplied in this process, and the supplied amount of the secondary air is controlled based on the output of an oxygen sensor.

Japanese Patent Application Publication No. 7-63048 (JP-A-7-63048) (FIG. 5) discloses a configuration including an HC adsorbent and an EHC (described as “a catalyst body A” in JP-A-7-63048) provided downstream thereof, wherein the downstream EHC is activated at a temperature at which the desorption of the adsorbed HC is started.

However, in the exhaust gas purification apparatuses disclosed in JP-A-6-33747, JP-A-10-252449, and JP-A-7-63048, the discharge of non-combusted gas components into the atmosphere cannot be suppressed to an almost complete level. More specifically, when the engine is started, the air-fuel ratio feedback control cannot be performed appropriately till the O2 sensor is activated and the Oxygen Storage Capacity (OSC) of the EHC cannot be accurately controlled. As a result, non-purified NOx or HC can be discharged into the atmosphere.

SUMMARY OF THE INVENTION

The invention provides an exhaust gas purification apparatus and an exhaust gas purification method that improve exhaust emission when the engine is started.

The first aspect of the invention relates to exhaust gas purification apparatus installed in an exhaust pipe serving as a flow channel of an exhaust gas discharged from an engine, including: first purification means for purifying at least one component from among a plurality of components contained in the exhaust gas; heating means for heating the first purification means to a predetermined temperature in at least part of a period from before the engine is started to a first point in time that is after the engine is started; and air-fuel ratio control means for controlling an air-fuel ratio of the exhaust gas so as to obtain a first air-fuel ratio suitable for the first purification means to purify the one component in at least part of a period from the time when the engine is started to a second point in time that is on or after a time at which the first purification means is heated to the predetermined temperature; and an adsorption means for communicating with the exhaust pipe and at least partially adsorbs another component from among the plurality of components.

With such a configuration, the heating means preheats the first purification means before the engine is started or immediately after the engine is started. Further, the second point in time is a point in time that is on or after a time at which the first purification means is heated to the predetermined temperature. There is a possibility of the O2 sensor being not activated immediately after the engine is started and the unpurified components can be discharged into the atmosphere, without the OSC of the first purification means being accurately controlled. However, the above-described configuration makes it possible to obtain the temperature and air-fuel ratio that are suitable for reliable purification of one component with the first purification means.

In the exhaust gas purification apparatus according to the present aspect, the adsorption means may communicate with the exhaust pipe downstream of the first purification means.

With the above-described configuration, the adsorption means at least partially adsorbs another component that is other than the one component and has not been adsorbed by the first purification means.

With the above-described configuration, the first purification means is activated by the heating means in advance and the air-fuel ratio is controlled to the first air-fuel ratio. Therefore, the one component can be advantageously purified in the first purification means. On the other hand, the other component passes through the first purification means, but can be adsorbed by the downstream adsorption means. As a result, neither the one component nor the other component is discharged to the outside of the exhaust pipe. The-exhaust emission at the time the engine is started can thus be improved.

In the exhaust gas purification apparatus according to the present aspect, the air-fuel ratio control means may control an air-fuel ratio of the exhaust gas so as to obtain a first air-fuel ratio suitable for purifying one component from among the plurality of components in a period from the time when the first purification means is heated to an activation temperature thereof to the second point in time.

With the above-described configuration, once the first purification means is heated to the activation temperature thereof, the first air-fuel ratio suitable for purifying the one component is set till the second point in time. As a result, the one component can be advantageously purified by the first purification means.

The exhaust gas purification apparatus according to the present aspect may further include air-fuel detection means for detecting an air-fuel ratio of the exhaust gas flowing in the exhaust pipe, and the air-fuel ratio control means may feedback-control the air-fuel ratio of the exhaust gas based at least on the detected air-fuel ratio.

With the above-described configuration, the air-fuel ratio of the exhaust gas flowing in the exhaust pipe is detected by air-fuel ratio detection means. The air-fuel ratio control means can feedback-control the air-fuel ratio of the exhaust gas based at least on the air-fuel ratio that is thus detected.

In the exhaust gas purification apparatus according to the present aspect, the second point in time may be a point in time at which activation of the air-fuel ratio detection means is started, and the air-fuel ratio control means may feedback-control the air-fuel ratio within an active period of the air-fuel ratio detection means that starts at the second point in time.

With the above-described configuration, the second point in time is a point in time at which the activation of the air-fuel ratio detection means is started and the active period of the air-fuel ratio detection means that starts at the second point in time can be recognized with a comparatively high reliability of detection results. Therefore, the air-fuel ratio can be feedback-controlled within the active period. Conversely, the first air-fuel ratio can be maintained so that the one component can be reliably purified with the first purification means till the reliability of the feedback control is ensured.

The exhaust gas purification apparatus according to the present aspect may further include desorption state specifying means for specifying a desorption state of the other component from the adsorption means, and the second point in time may be established according to the specified desorption state of the other component.

With the above-described configuration, the desorption state of the other component from the adsorption means is specified by the desorption state specifying means, and the second point in time (that is, the start of a period in which it is undesirable to set the air-fuel ratio to the first air-fuel ratio) is established correspondingly thereto. Accordingly, on or after the second point in time, it is possible to switch from the first air-fuel ratio, which is useful only for the one component and at which the other component is assumed to be adsorbed, to the air-fuel ratio that is useful to a certain degree for both components. Therefore, the case in which the other component is discharged without being purified by some means can be avoided.

The exhaust gas purification apparatus according to the present aspect may further include second purification means for purifying another component adsorbed by the adsorption means.

With the above-described configuration, the second purification means purifies another component adsorbed by the adsorption means. The adsorbed other component is thus purified in some form. As a result, the adsorption capacity of the adsorption means can be ensured prior to the arrival of the new other component.

In the exhaust gas purification apparatus according to the present aspect, the first purification means may also function as the second purification means and may further include restricting means for restricting the release of the exhaust gas from the exhaust pipe downstream of the first purification means and the adsorption means in the exhaust pipe, and recirculation means for desorbing the adsorbed other component and recirculating the other component via a recirculation channel to a zone upstream of the first purification means, while the release of the exhaust gas is restricted by the restricting means.

With the above-described configuration, the exhaust pipe can be shut off by the restricting means such as a shut valve in the zone of the exhaust pipe that is downstream of the first purification means. Therefore, the discharge of exhaust gas from the exhaust pipe can be appropriately restricted. Within this interval, the adsorbed other component is desorbed and recirculated via the recirculation channel to the zone upstream of the first purification means by the recirculation means configured by a combination of a recirculation channel and a pneumatic pump installed in the channel or motoring of the engine. Here, the first purification means also functions as the second purification means. As a result, the first purification means purifies the recirculated other component, while purifying the one component. Therefore, each component can be purified.

The exhaust gas purification apparatus according to the present aspect may further include supply means for supplying secondary air to the first purification means via the recirculation channel.

With the above-described configuration, the supply means supplies the secondary air to the first purification means via the recirculation channel. As a result, the OSC state of the first purification means can be restored and the purification capacity thereof can be ensured.

The exhaust gas purification apparatus according to the present aspect may further include desorption state specifying means for specifying a desorption state of the other component from the adsorption means, wherein the supply means may supply the secondary air according to the specified desorption state of the other component.

With the above-described configuration, the supply means supplies the secondary air according to the desorption state of the other component specified by the desorption state specifying means. Where it is detected that the temperature of the desorption means has risen close to the desorption temperature, it is possible that the other component will start desorbing from the adsorption means in the nearest future. In such case, it is possible to prepare for the arrival of the desorbed other component by supplying the secondary air in advance, thereby supplying oxygen to the first purification means and restoring the OSC state of the first purification means.

Alternatively, the exhaust gas purification apparatus according to the present aspect may further include OSC state specifying means for specifying an OSC state of the first purification means that also functions as the second purification means, wherein the supply means may supply the secondary air according to the specified OSC state.

With the above-described configuration, the OSC state of the first purification means that also functions as the second purification means is specified by the OSC state specifying means, and the supply means supplies the secondary air corresponding to the OSC state thereof. When the amount of the stored oxygen is extremely small and the OSC state is specified as poor, it is possible to prepare for the arrival of the desorbed other component by appropriately restoring the OSC state of the first purification means as necessary.

Alternatively, the exhaust gas purification apparatus according to the present aspect may further include internal pressure specifying means for specifying a pressure inside the exhaust pipe in a state in which the release of the exhaust gas is restricted by the restriction means, wherein the supply means may regulate the supplied amount of the secondary air according to the specified internal pressure.

With the above-described configuration, the supply means regulates the supplied amount of the secondary air according to the pressure inside the exhaust pipe specified by the internal pressure specifying means. As a result, when the internal pressure can be too high and can exceed the pressure resistance of the restricting means, it is possible to suppress the supply of the secondary air, thereby making it possible to avoid the leak of exhaust gas from the restricting means.

In the exhaust gas purification apparatus according to the present aspect, the heating means may heat the first purification means according to the amount of the secondary air supplied by the supply means.

With the above-described configuration, the temperature of the first purification means can decrease with the increase in the amount of secondary air supplied by the supply means. Therefore, the first purification means is heated accordingly. As a result, the first purification means can be maintained in the active state even as the secondary air is supplied.

In the exhaust gas purification apparatus according to the present aspect, the second purification means may purify the other component in a period during which the engine is stopped.

With the above-described configuration, by contrast with the first purification means, the second purification means purifies the other component in a period during which the engine is stopped. As a result, the other component adsorbed when the engine is started can be reliably purified by shutting off the exhaust pipe with the restricting means and recirculating the other component several times in a period during which the engine is stopped.

In the exhaust gas purification apparatus according to the present aspect, the first point in time may be a point in time at which the exhaust gas is practically not discharged from the engine. Further, in the exhaust gas purification apparatus according to the present aspect, the one component may be nitrogen oxide, and the first air-fuel ratio may be an air-fuel ratio on a rich side from a theoretical air-fuel ratio of the engine.

The second aspect of the invention relates to an exhaust gas purification method in purification means for purifying at least one component from among a plurality of components contained in an exhaust gas discharged from an engine. The exhaust gas purification method includes: heating the purification means to a predetermined temperature in a period that is at least part of a period from before the engine is started to a first point in time that is after the engine is started; controlling an air-fuel ratio of the exhaust gas so as to obtain a first air-fuel ratio suitable for the purification means to purify the one component in at least part of a period from the time when the engine is started to a second point in time that is on or after a time at which the purification means is heated to the predetermined temperature; and at least partially adsorbing another component from among the plurality of components.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a schematic plan view illustrating an exhaust gas purification apparatus of the first embodiment of the invention;

FIG. 2 is a flowchart illustrating the operation of the exhaust gas purification apparatus of the first embodiment;

FIG. 3 is a schematic plan view illustrating the exhaust gas purification apparatus of the second embodiment;

FIG. 4 is a flowchart illustrating the operation of the exhaust gas purification apparatus of the second embodiment;

FIGS. 5A and 5B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the third embodiment;

FIG. 6 is a schematic plan view illustrating the exhaust gas purification apparatus of the fourth embodiment;

FIGS. 7A and 7B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the fourth embodiment;

FIG. 8 is a schematic plan view illustrating the exhaust gas purification apparatus of the fifth embodiment;

FIGS. 9A and 9B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the fifth embodiment;

FIG. 10 is a schematic plan view illustrating the exhaust gas purification apparatus of the sixth embodiment; and

FIGS. 11A and 11B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the sixth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the invention will be described below in greater details with reference to the appended drawings.

First, a basic configuration of the exhaust gas purification apparatus of the first embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic plan view illustrating an exhaust gas purification apparatus of the first embodiment of the invention.

As shown in FIG. 1, the exhaust gas purification apparatus of the first embodiment is installed, for example, on a hybrid vehicle and has an intake pipe 206 equipped with a throttle valve 214, an engine 200, and an exhaust pipe 210 configured on a base. In a well-known process, an air-fuel mixture obtained by mixing a fuel with intake air from the intake pipe 206 is combusted in the engine 200 and exhaust gases generated by the combustion are discharged via the exhaust pipe 210. The configuration of the present embodiment will be described below. In the present embodiment, “downstream” refers to a zone that is closer to the outlet port of the exhaust pipe 210. Conversely, “upstream” refers to a zone closer to the inlet port of the intake port 206.

An EHC 222 is a three-way catalyst equipped with a heater that is installed in a tube of the exhaust pipe 210 and can be heated to a desired temperature, for example, under the control by a control device 100. For example, the EHC 222 reduces NOx and oxidizes HC with the stored oxygen. The EHC 222 assumes an active state or a passive state depending on whether the temperature thereof is higher than an active temperature inherent thereto and demonstrates good purification ability only in the active state.

An O2 sensor 221 is provided downstream of the EHC 222 and detects the concentration of oxygen contained in the exhaust gas that passed through the EHC 222. As a result, the OSC state of the EHC 222 is detected. The O2 sensor 221 also assumes an active state or a passive state depending on whether the temperature thereof is higher than an active temperature inherent thereto and can detect oxygen concentration accurately only in the active state.

A recirculation channel 310 communicates with portions of the exhaust pipe 210 that are upstream and downstream of the EHC 222 and recirculates the exhaust gas from the zone downstream of the EHC 222 to the zone upstream thereof.

An HC adsorbent 340 is formed from a material (active carbon or zeolite) having an HC adsorption capacity and installed in a portion of the recirculation channel 310 that is downstream of the EHC 222.

A bypass flow channel 311 links a portion of the exhaust 210 that is downstream of the EHC 222 with a portion of the recirculation channel 310 that is upstream of the HC adsorbent 340. As a result, HC contained in the exhaust gas which has not been purified by the EHC 222 is adsorbed by the HC adsorbent 340 in a temperature range below a predetermined HC desorption temperature. On the other hand, the adsorbed HC is desorbed in a temperature range above the predetermined HC desorption temperature.

A three-way valve 320 electromagnetically or mechanically switches a flow channel between a flow channel a passing to the HC adsorbent 340 via the bypass flow channel 311 and a flow channel b through which the exhaust gas flows directly, without passing through the bypass flow channel 311, in the exhaust pipe 210.

A gas circulation pump 350 is installed in a portion of the recirculation channel 310 upstream of the HC adsorbent 340. Where the gas circulation pump 350 is driven, the exhaust gas located in the recirculation channel 310 is recirculated from the downstream zone to the upstream zone by the suction force thereof.

A shut valve 330 is provided in the lowermost stage (more specifically, even downstream of the downstream portion of the exhaust pipe 210 that communicates with the recirculation channel 310) of the exhaust system, and the discharge amount of exhaust gas is regulated by the opening degree of the shut valve 330. For example, when the shut valve 330 is completely closed, the exhaust gas is shut down and a closed-loop circulation channel is formed.

The control device 100 is the so-called ECU (Engine Control Unit) configured as a logic computation circuit constituted mainly by a central processing unit (CPU), a read only memory (ROM) storing a control program, and a random access memory (RAM) storing a variety of data. The control device 100 is connected via a bus to an intake port receiving input signals from the O2 sensor 221 and a variety of sensors that indicate the revolution speed of the engine 200. Further, the control device 100 is also connected via a bus to an output port that sends control signals to actuators of an opening drive unit of the throttle valve 214, an ignition unit of the engine 200, a current supply unit of the EHC 222, a drive unit of the gas circulation pump 350, a drive unit of the three-way valve 320, and a drive unit of the shut valve 330. As a result, it is possible to control the air-fuel ratio by controlling current supply to the EHC 222 or by adjusting the opening degree of the throttle valve 214 or adjusting the fuel injection amount in the engine 200.

Basic operation of the exhaust gas purification apparatus of the first embodiment will be described below with reference to FIG. 2. FIG. 2 is a flowchart illustrating the operation of the exhaust gas purification apparatus of the first embodiment.

As indicated hereinabove in the section relating to the problems associated with the related art, untreated NOx or HC can be discharged into the atmosphere after the engine 200 is started and before the O2 sensor 221 is activated.

Accordingly, in the exhaust gas purification apparatus of the first embodiment, The following treatment is performed to purify NOx almost completely at least with the EHC 222 after the engine 200 is started and before the O2 sensor 221 is activated. Thus, the EHC 222 is activated (step S100) by preheating before the engine 200 is started. The engine 200 is then started (step S101). The air-fuel ratio (more specifically, “slight rich”) is controlled to a value optimum for NOx purification by the air-fuel control performed with the control device 100 (step S102). As a result, the EHC 222 can purify almost entirely the NOx contained in the exhaust gas discharged when the engine is started. The “slight rich” as referred to in the present embodiment, represents an air-fuel ratio slightly to a rich side from the stoichiometric ratio and is, for example, an air-fuel ratio from 14.2 to a stoichiometric ratio. This is an air-fuel ratio at which the reduction of NOx can be effectively performed at predetermined operation conditions.

On the other hand, in this interval, the three-way valve 320 is switched to the flow channel a on the side of the HC adsorbent 340 (step S103). As a result, HC that could not be purified by the EHC 222 during the operation of the EHC 222 at an air-fuel ratio (more specifically, “slight rich”) optimum for NOx purification can be adsorbed by the HC adsorbent 340.

The O2 sensor 221 located downstream of the EHC 222 is then activated, the OSC state of the EHC 222 is accurately detected, and the slight rich operation is continued in order to maintain an NOx purification ratio at an almost complete level till it becomes possible to control the air-fuel ratio according to the OSC state of the EHC 222. Whether the O2 sensor 221 has been activated can be determined, for example, based on whether the amplitude of the output current of the O2 sensor 221 is higher than a predetermined value.

It is then determined whether the O2 sensor 221 has been activated, or whether the temperature of the HC adsorbent 340 has reached the predetermined HC desorption temperature (more specifically, an upper limit value of a temperature at which the HC adsorption ability can be advantageously demonstrated) (step S104). When it is determined that the O2 sensor 221 has been activated (step S104: Yes), the air-fuel feedback control is adequately performed. Therefore, the slight rich operation is interrupted (step S10) to switch from the slight rich operation to a stoichiometric operation. Alternatively, when it is determined that the temperature of the HC adsorbent 340 has reached the predetermined HC desorption temperature (step S104: Yes), the slight rich operation is interrupted to avoid the decrease in HC adsorption ability (step S10).

The control device 100 then performs switching from the slight rich operation to stoichiometric operation (step S106). As a result, not only NOx, but also HC can be almost completely purified in the EHC 222. In this case, because it is not necessary to cause the adsorption of HC in the HC adsorbent 340, the three-way valve 320 is switched to the flow channel b at the side of the bypass flow channel 311 of the HC adsorbent 340 and the purified gas is discharged (step S107). In this case, the HC that has already been adsorbed by the HC adsorbent 340 is retained without discharging.

The processing then waits till the engine 200 stops (step S108: No), and once the engine 200 stops (step S108: Yes), the control device 100 closes the shut valve 330 (step S109), switches the three-way valve 320 to the flow channel b (step S110), and drives the pump 350 (step S111) to cause the closed-loop circulation of the gas present in the system. In such closed-loop circulation, an electric current may be supplied to the EHC 222 (step S112). In this case, the active state of the EHC 222 can be maintained. In addition, the circulating gas is heated, the desorption of the HC adsorbed at the HC adsorbent 340 is enhanced, and the desorbed HC is recirculated to the EHC 222, thereby making it possible to purify the desorbed HC in the EHC 222.

As described hereinabove, with the exhaust gas purification apparatus of the first embodiment, the discharge of HC and NOx can be actively avoided or suppressed within an interval after the engine 200 is started and before the air-fuel ratio feedback control can be executed appropriately. Further, in the intermittent mode in which the engine 200 stops, the desorption of the adsorbed HC and purification of the desorbed HC can be performed in an exhaustless state. In this case, because the gas containing the desorbed HC is circulated and passed through the EHC 222 repeatedly, the desorbed HC can be thoroughly purified. In addition, because it is not necessary to operate the engine 200 to cause the desorption of the material adsorbed by the HC adsorbent 340 during circulation, the increase in fuel consumption can be avoided. Moreover, because only the gas having a volume within the close loop may be heated during circulation, the consumption of energy required for HC desorption can be significantly reduced.

The basic configuration of the exhaust gas purification apparatus of the second embodiment will be described below with reference to FIG. 3. FIG. 3 is a schematic plan view of the exhaust gas purification apparatus of the second embodiment. In FIG. 3, components identical to those shown in the above-described FIG. 1 are assigned with identical reference symbols and detailed explanation therefor is herein omitted.

As shown in FIG. 3, the configuration of the exhaust gas purification apparatus, of the second embodiment is different from that of the first embodiment as follows. More specifically, the recirculation channel 310 links the intake pipe 206 to the zone of the exhaust pipe 210 that is downstream of the EHC 222 and recirculates the exhaust gas from the zone downstream of the EHC 222 to the zone upstream thereof. In other words, in the first embodiment, the exhaust gas is recirculated completely in the exhaust system, whereas in the second embodiment, the exhaust gas is recirculated to the intake system.

Further, a motor 44 used for motoring the engine 200 is provided instead of the gas circulation-pump 350. The motor 44 is a motor generator or a starter motor and is so configured that even when the engine 200 is in an intermittent mode, the drive power is supplied from the battery (not shown in the figure) and the output thereof can be transmitted to the output shaft of the engine 200, for example, via a pulley.

The basic operation of the exhaust gas purification apparatus of the second embodiment will be described below with reference to FIG. 4. FIG. 4 is a flowchart illustrating the operation of the exhaust gas purification apparatus of the second embodiment.

As shown in FIG. 4, the exhaust gas purification apparatus of the second embodiment operates in the following manner. More specifically, in the desorption treatment process (steps S109 to S112) of the adsorbed HC that is implemented when the engine 200 assumes a stop state (intermittent mode of the engine), the shut valve is closed (step S109), the motor 44 is then driven, and motoring of the engine 200 is performed (step S211). As a result, the desorbed HC is recirculated to the intake pipe 206 via the recirculation channel 310 and is introduced in the EHC 222 via the engine 200. Therefore, the desorbed HC can be purified in the EHC 222.

As described hereinabove, in the exhaust gas purification apparatus of the second embodiment, the desorption treatment of the adsorbed HC can be performed, without adding the gas circulation pump 350 such as used in the first embodiment. As a result, the amount of energy consumed for the desorption treatment of the adsorbed HC can be greatly reduced and the increase in fuel consumption can be effectively prevented.

The basic configuration of the exhaust gas purification apparatus of the third embodiment may be identical to that of the second embodiment and detailed explanation thereof is herein omitted. This configuration can be represented by FIG. 3.

The basic operation of the exhaust gas purification apparatus of the third embodiment will be described below with reference to FIGS. 5A and 5B. FIGS. 5A and 5B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the third embodiment.

As shown in FIGS. 5A and 5B, the exhaust gas purification apparatus of the third embodiment operates in the following manner. More specifically, the processing of throttling the shut valve 330 and desorbing the adsorbed HC (steps S3071 to S3073) is performed in the idling mode of the engine 200 (that is, before the result of determination in step S108 is Yes), rather than in the stop state of the engine 200. As a result, part of the exhaust gas is recirculated to the HC adsorbent 340, and this gas enhances the desorption of the adsorbed HC and can be introduced as an exhaust gas recirculation (EGR) gas into the intake system.

In this case, the larger is the throttling of the opening of the shut valve 330, the larger is the amount of the desorbed HC contained in the EGR introduced to the intake. This is because where a large amount of exhaust gas is recirculated to the HC adsorbent 340, the temperature of the adsorbent 340 rises and the desorption of the adsorbed HC is enhanced.

Accordingly, the opening degree of the shut valve 330 may be variably controlled according to the output of the O2 sensor 221 disposed behind the EHC 222 (step S3071).

More specifically, when the output of the O2 sensor 221 disposed behind the EHC 222 is a stoichiometric voltage (more specifically, close to 0.5 V) (S3071: STOICH), the opening degree of the shut valve 330 may be maintained. However, when the output of the O2 sensor 221 shifts from the stoichiometric voltage to the rich side (S3071: RICH), the opening degree of the shut valve 330 is increased, the amount of gas recirculated to the HC adsorbent 340 is reduced, the desorption of the adsorbed HC is reduced, and the amount of rich EGR containing the desorbed HC is decreased.

On the other hand, when the output of the O2 sensor 221 shifts from the stoichiometric voltage to the lean side (S3071: LEAN), the opening degree of the shut valve 330 is decreased, the amount of gas recirculated to the HC adsorbent 340 is increased, the desorption of the adsorbed HC is enhanced, and the amount of rich EGR containing the desorbed HC is increased.

As a result, the EGR can be appropriately implemented so that the output of the O2 sensor 221 becomes a stoichiometric voltage.

Further, when the output of the O2 sensor 221 shifts from the stoichiometric voltage to the rich side, the amount of fuel supplied to the engine 200 may be decreased and the air-fuel ratio may be controlled to the lean side.

Furthermore, the HC amount in the EGR gas may be calculated from the amount of gas recirculated to the HC adsorbent 340, air-fuel ratio, initial HC adsorption amount of the HC adsorbent 340, temperature of the HC adsorbent 340, and the like, and the fuel injection amount may be reduced in advance to match the calculated HC amount.

Moreover, it is also possible to calculate the HC amount that can be purified in the EHC 222 from the present OSC state of the EHC 222, then calculate the desorbed HC amount corresponding to the recirculation gas amount from the initial HC adsorption amount of the HC adsorbent 340, temperature of the HC adsorbent 340, and the like, and adjust the degree of opening of the shut valve 330 and control the amount of gas recirculated to the HC adsorbent 340 so as to obtain the, HC amount that can be purified in the EHC 222.

As described hereinabove, with the exhaust gas purification apparatus of the third embodiment, the EGR with a rich gas including the desorbed HC from the HC adsorbent 340 can be appropriately implemented and the deterioration of the purification capacity of the EHC 222 caused by implementation of the EGR with an excessively rich gas and worsening of combustion in the engine 200 can be effectively prevented. Furthermore, the desorption efficiency of the adsorbent 340 can be increased, without degrading the purification capacity of the EHC 222.

The basic configuration of the exhaust gas purification apparatus of the fourth embodiment will be described below with reference to FIG. 6. FIG. 6 is a schematic plan view of the exhaust gas purification apparatus of the fourth embodiment. In FIG. 6, components identical to those shown in the above-described FIG. 1 are assigned with identical reference symbols and detailed explanation thereof is herein omitted.

As shown in FIG. 6, the configuration of the exhaust gas purification apparatus of the fourth embodiment is different from that of the first embodiment as follows. More specifically, a system in which purging circulation is performed by the gas circulation pump 350 includes an Air introducing pipe 370 that communicates with the atmosphere for introducing Air (that is, secondary air) to the gas circulation pump 350 and an Air introducing valve 371 that adjusts the amount of introduced Air according to the degree of opening. In addition, an internal pressure sensor 360 that detects the pressure inside the system is provided to monitor the increase in the internal pressure of the system caused the by introduction of Air. The internal pressure sensor 360 is installed in the tube of the exhaust pipe 210, preferably close to the shut valve 330.

The Air may be also introduced from the intake side by motoring the engine 200, instead of using the Air introducing valve 371.

The basic operation of the exhaust gas purification apparatus of the fourth embodiment will be described below with reference to FIGS. 7A and 7B. FIGS. 7A and 7B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the fourth embodiment.

As shown in FIGS. 7A and 7B, the exhaust gas purification apparatus of the fourth embodiment operates in the following manner. More specifically, in the desorption treatment process (steps S109 to S112) of the adsorbed HC that is implemented when the engine 200 assumes a stop state, the O2 sensor 221 disposed downstream of the EHC 222 is used to determine whether the OSC state of the EHC 222 is periodic or a periodic (step S400). In this case, when it is not determined that the output of the O2 sensor 221 is larger than the predetermined rich determination value (for example, close to 0.8 V) (step S400: No), the Air introducing valve 371 remains closed. On the other hand, when it is determined that the output of the O2 sensor 221 is larger than the predetermined rich determination value (step S400: Yes), it is determined that a completely rich state is assumed and the oxygen contained in the system is almost completely consumed, and the Air introducing valve 371 is opened and oxygen is introduced-in the system to restore the OSC of the EHC 222 (step S401). Because it is possible that the temperature inside the system will be decreased by the introduction of Air, an electric current is passed to the EHC 222 to prevent the decrease in purification capacity (step S112). In addition, when the internal pressure in the system becomes too high because the Air is introduced, it is possible that the gas contained in the system will leak to the atmosphere. Therefore, it is periodically or a periodically determined whether the output of the internal pressure sensor 360 exceeds a predetermined leak determination value (step S402). In this case, when the output of the internal pressure sensor 360 exceeds the predetermined leak determination value (step S402: Yes), the gas circulation pump 350 is temporarily stopped (step S403), the shut valve 330 is opened, and the pressure is released till the output of the internal pressure sensor 360 somewhat decreases (step S404). On the other hand, when the output of the internal pressure sensor 360 does not exceed the predetermined leak determination value (step S402: No), there is some space for introducing Air. Therefore, the Air introducing valve 371 is opened till the output of the O2 sensor 221 located downstream of the EHC 222 becomes below a predetermined lean determination value (for example, close to 0.2 V) (step S405: No) and a completely lean state is assumed. Once the output of the O2 sensor 221 becomes below a predetermined lean determination value (step S405: Yes) and a completely lean state is assumed, subsequent Air introduction becomes unnecessary. Therefore, the Air introducing valve 371 is closed (step S406).

Alternatively, the Air may be also successively introduced into the system so as to maintain the output of the O2 sensor 221, which is disposed downstream of the EHC 222, close to 0 V. In this case, the amount of Air introduced into the system may be controlled by performing F/B control of the opening degree of the Air introducing valve 371 according to the variation of the output of the O2 sensor 221. More specifically, at a predetermined amount of introduced Air, the introduced amount may be increased when the rich output is maintained.

As described hereinabove, with the exhaust gas purification apparatus of the fourth embodiment, by appropriately introducing oxygen into the system with the Air introducing valve 371 in the desorption treatment process of the adsorbed HC, the OSC insufficiency of the EHC 222 is eliminated, thereby making it possible to avoid the decrease in purification capacity of the desorbed HC. By passing an electric current to the EHC 222, it is possible to avoid the decrease in temperature when the Air is introduced and prevent the purification capacity of the EHC 222 from decreasing. In addition, by monitoring the internal pressure in the system with the internal pressure sensor 360, it is possible to prevent reliably the release of the gas contained in the system to the atmosphere caused by the rise in internal pressure.

The basic configuration of the exhaust gas purification apparatus of the fifth embodiment will be described below with reference to FIG. 8. FIG. 8 is a schematic plan view of the exhaust gas purification apparatus of the fifth embodiment. In FIG. 8, components identical to those shown in the above-described FIG. 6 are assigned with identical reference symbols and detailed explanation thereof is herein omitted.

As shown in FIG. 8, the configuration of the exhaust gas purification apparatus of the fifth embodiment is different from that of the fourth embodiment as follows. More specifically, the exhaust gas purification apparatus of the fifth embodiment further includes a temperature sensor 380 that detects the temperature of the HC adsorbent 340. The temperature sensor 380 may directly detect the temperature of the HC adsorbent 340, or may indirectly evaluate the temperature by the conditions of the exhaust gas introduced into the HC adsorbent 340.

The basic operation of the exhaust gas purification apparatus of the fifth embodiment will be described below with reference to FIGS. 9A and 9B. FIGS. 9A and 9B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the fifth embodiment.

As shown in FIGS. 9A and 9B, the exhaust gas purification apparatus of the fifth embodiment operates as follows. More specifically, after the engine 200 has assumes a stop state (step S108: Yes), the shut valve 330 is opened or closed, or the Air introducing valve 371 is opened or closed according to whether or not the temperature of the HC adsorbent 340 has reached the predetermined HC desorption temperature (that is, the temperature at which the desorption of the HC adsorbed by the HC adsorbent 340 is enhanced), which is determined based on the output of the temperature sensor 380 (step S500).

Here, when the temperature of the HC adsorbent 340 has not reached the HC desorption temperature (step S500: Yes), the amount of HC desorbed from the HC adsorbent 340 is extremely small. Therefore, where a purge gas is passed one time to the EHC 222, it will apparently be possible to purify practically the entire desorbed HC contained therein. Accordingly, the purging treatment is performed by opening the shut valve 330 (step S501) and driving the pump 350 in this state (step S502), thereby circulating the gas contained in the system in an open loop. The Air introducing valve 371 of the pump 350 is then opened (step S503), the Air is introduced in the system, and a state with a maximum OSC of the EHC 222 is maintained.

On the other hand, after the temperature of the HC adsorbent 340 has reached the HC desorption temperature (step S500: No), the amount of desorbed HC in the purge gas increases. Therefore, by passing the purge gas once through the EHC 222, it will apparently be impossible to purify the desorbed HC contained therein. Accordingly, the purging treatment is performed by closing the shut valve 330 (step S511) and driving the pump 350 in this state (step S512), thereby circulating the gas contained in the system in a closed loop. In the course of circulation purging in the closed loop, the Air introducing valve 371 of the pump 350 is closed so as to prevent an excess increase in the internal pressure in the system (step S513).

In these processes, the conduction control of the EHC 222 is implemented so that the temperature of the EHC 222 is constantly maintained at a level equal to or higher than the active temperature (step S504) (step S514).

As described hereinabove, with the exhaust gas purification apparatus of the fifth embodiment, the Air is introduced in advance, prior to the desorption of HC. Therefore, the desorbed HC can be purified almost completely from the very start of HC desorption and the time required for the purification can be shortened. In addition, because no Air is introduced during circulation purging in the closed loop, the internal pressure increase in the system can be avoided.

The basic configuration of the exhaust gas purification apparatus of the sixth embodiment will be described below with reference to FIG. 10. FIG. 10 is a schematic plan view of the exhaust gas purification apparatus of the sixth embodiment. In FIG. 10, components identical to those shown in the above-described FIG. 8 are assigned with identical reference symbols and detailed explanation thereof is herein omitted.

As shown in FIG. 10, the configuration of the exhaust gas purification apparatus of the sixth embodiment is different from that of the fifth embodiment as follows. More specifically, the exhaust gas purification apparatus of the sixth embodiment includes a flow rate sensor 380 that detects the gas flow rate in the system. The flow rate sensor 380 serves to determine, as will be described below, that gas circulation in the system has stopped, that is, serves to confirm that the gas contained in the system is not released although the shut valve 330 is opened. Therefore, it is preferred that the flow rate sensor be disposed close to the shut valve 330 in a location in which the gas flow rate during circulation purging in the closed loop is comparatively large. For example, as shown in FIG. 10, the flow rate sensor 380 is disposed in a zone where the recirculation channel 310 and exhaust pipe 210 communicate before the shut valve 330.

The basic operation of the exhaust gas purification apparatus of the sixth embodiment will be described below with reference to FIGS. 11A and 11B. FIGS. 11A and 11B are a flowchart illustrating the operation of the exhaust gas purification apparatus of the sixth embodiment.

As shown in FIGS. 11A and 11B, the exhaust gas purification apparatus of the sixth embodiment operates as follows. More specifically, in the very middle of the circulation purging, it is periodically or a periodically determined based on the output of the O2 sensor 221 as to whether the OSC of the EHC 222 has to be restored (step S600). When it is necessary to restore the OSC of the EHC 222 (step S600: Yes), gas circulation in the system is stopped prior to introducing the Air for restoration (step S601). For example, the drive of the gas circulation pump 350 is stopped. Alternatively, the intake recirculation by the monitoring of the engine 200 is stopped. Then, it is determined with the flow rate sensor 380 as to whether gas circulation in the system has stopped (step S602).

In this case, when it is determined that gas circulation in the system has stopped (step S602: Yes), the shut valve 330 is opened (step S603) and the Air introducing valve 371 is opened (step S604). As a result, the Air is introduced into the EHC 222 and the OSC of the EHC 222 is restored. Alternatively, monitoring of the engine 200 may be performed and the Air may be introduced into the EHC 222 from the intake side. Such Air introduction is implemented till the OSC of the EHC 222 is completely restored, for example, till the output of the O2 sensor 221 assumes an almost entirely lean state (close to 0 V). Alternatively, the amount of Air matching the OSC of the EHC 222 that has been found in advance may be determined and the introduced amount may be adjusted accordingly. In the case of the Air introducing valve 371, the adjustment of the amount of introduced Air can be performed by regulating the opening degree of the Air introducing valve 371, and when motoring of the engine 200 is performed, the adjustment can be performed based on the revolution speed of the motor and the opening degree of the throttle 214.

Once the OSC of the EHC 222 is restored as a result of Air introduction 'step S600: No), the Air introduction is stopped (step S611). Then, the temperature of the EHC 222 is detected and where the temperature of the EHC 222 is lower than the active temperature due to the Air introduction, an electric current is passed to the EHC 222 (step S612). Once the temperature of the EHC 222 reaches the active temperature, the shut valve 330 is closed again (step S613) and the circulation purge is restarted (step S614).

As described hereinabove, with the exhaust gas purification apparatus of the sixth embodiment, the shut valve 330 is opened prior to the introduction of Air into the system with the object of restoring the OSC of the EHC 222 in the course of circulation purging. Therefore, the increase in internal pressure caused by the Air introduction can be inhibited. Moreover, because the shut valve 330 is opened after the circulation of gas in the system has been stopped, the release of HC into the external atmosphere via the shut valve 330 can be effectively prevented even when the Air is introduced.

In the above-described embodiments, the exhaust gas purification apparatus is an example of the “exhaust gas purification apparatus” according to the invention, NOx is an example of the “one component” according to the invention, the HC is an example of the “other component” according to the invention, the EHC 222 is an example of the “first purification means”, “second purification means”, and “heating means” according to the invention, the control device 100 is an example of the “air-fuel ratio control means” according to the invention, the HC adsorbent 340 is an example of the “adsorption means” according to the invention, the O2 sensor 221 is an example of the “air-fuel ratio detection means” according to the invention, the temperature sensor 380 is an example of the “desorption state specifying means” according to the invention, the shut vale 330 is an example of the “restricting means” according to the invention, the recirculation channel 310 and the gas circulation pump 350 or motor 44 are examples of the “recirculation means” according to the invention, the Air introducing pipe 370 and Air introducing valve 371 are examples of the “supply means” according to the invention, the O2 sensor 221 is an example of the “OSC state specifying means” according to the invention, and the internal pressure sensor 360 is an example of the “internal pressure specifying means” according to the invention.

A resistance heater or a burner-type heater may be used as the first purification means or second purification means in accordance with the invention.

The “first point in time” after the start of the engine in accordance with the invention may be a point in time equivalent to that immediately after the engine is started, preferably a point in time at which practically no exhaust gas is discharged from the engine.

The “predetermined temperature” in accordance with the invention may be a temperature within an interval from the temperature close to the right-off of the first purification means to the active temperature. The “right-off” as referred to herein is a temperature obtained by adding a certain margin to a temperature established empirically or by simulation as a temperature at which the first purification means starts reacting with the one component or the active temperature of the first purification means at which the first purification means can demonstrate the purification capacity inherent thereto.

The state of desorption of the other component from the adsorption means, which is specified by the desorption state specifying means in accordance with the invention, may be a state in which the amount of the other component adsorbed by the adsorption means is saturated, or a state in which the other component is easily desorbed from the adsorption means.

When the temperature of the adsorption means is detected and this temperature exceeds the desorption temperature of the other component (that is, the temperature at which the desorption of the other component that has been adsorbed by the adsorption means is started), because the adsorption means cannot adsorb other component, this time may be established as the second point in time.

The invention is not limited to the above-described embodiments and can be changed appropriately without departing from the scope or essence of the invention as summarized in all the claims and the entire detailed description thereof, and an exhaust gas purification apparatus incorporating such changes is also included in the technical scope of the invention.

Exhaust gas purification apparatus and exhaust gas purification method

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CPC

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