Exhaust emission control device

Abstract

An exhaust emission control device includes an adsorbent trapper having an adsorbent for adsorbing and desorbing hydrocarbon in exhaust gas, a catalytic converter, a main exhaust gas passage with a first valve, a bypass exhaust gas passage with a second valve and a control unit. The bypass exhaust gas passage bypassing the first valve is connected with the adsorbent. The control unit controls the first and second valves to desorb the hydrocarbon from the adsorbent when a condition is satisfied. The condition is that the catalyst converter is in active, an oxygen adsorption amount of the catalyst converter is not less than a first predetermined amount and an exhaust gas amount is not more than a second predetermined amount. The first valve is opened and the second valve is closed when the condition is not satisfied during desorption of the hydrocarbon from the adsorbent.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust emission control device that controls exhaust emission discharged from an internal combustion engine.

2. Description of the Related Art

A conventional exhaust emission control device of this kind is disclosed in Japanese Patent Application Laid-Open Publication NO. 06-229235. This conventional exhaust emission control device has a main exhaust gas passage and a bypass exhaust gas passage that are arranged in parallel to each other at an upstream side of an exhaust emission control catalytic converter. The bypass exhaust gas passage is provided with an adsorbent that can adsorb hydrocarbon (HC) contained in an exhaust gas at a low temperature and desorb the HC adsorbed thereon at a high temperature. The conventional exhaust emission control device further has a valve for opening and closing the bypass exhaust gas passage. The valve is controlled by a control unit according to the temperature of the adsorbent.

In this conventional exhaust emission control device, the exhaust gas discharged from an internal combustion engine is introduce into the bypass exhaust gas passage, where harmful components such as the HC is adsorbed on the adsorbent when the temperature of the exhaust gas is low, while the harmful components are desorbed from the adsorbent and this desorbed HC is purified by the catalytic converter when the temperature of the exhaust gas is high.

However, in the above known conventional exhaust emission control device, there are a problem in that the purification performance of the catalytic converter is deteriorated due to lack of the oxygen adsorption amount of the catalytic converter because a large amount of the HC adsorbed on the adsorbent rapidly desorbs from the adsorbent when the exhaust gas flows into the bypass exhaust gas passage when the valve is controlled to open to flow the exhaust gas through the bypass exhaust gas passage.

It is, therefore, an object of the present invention to provide an exhaust emission control device which overcomes the foregoing drawbacks and can suppress the deterioration, in a purifying performance of exhaust emission discharged from an internal combustion engine, due to the excess hydrocarbon emission desorbed from an adsorbent and lack of an oxygen adsorption amount of a catalyst.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an exhaust emission control device including an adsorbent trapper, a catalytic converter, a main exhaust gas passage, a first valve, a bypass exhaust gas passage, a second valve and a control unit. The adsorbent trapper has an adsorbent that can adsorb hydrocarbon in exhaust gas discharged from an internal combustion engine on the adsorbent a low temperature thereof and desorb the hydrocarbon from the adsorbent at a high temperature thereof. The catalytic converter is arranged at a downstream side of the adsorbent trapper and has catalyst for purifying the exhaust gas. The main exhaust gas passage is arranged between the internal combustion engine and the catalytic converter so that the main exhaust passage can flow the exhaust gas discharged from the internal combustion engine to the catalytic converter. The first valve is arranged in the main exhaust gas passage and it is capable of opening and closing to flow the exhaust gas through the main exhaust gas passage and shut the main exhaust gas passage. The bypass exhaust gas passage has an upstream portion connected with an upstream portion of the main exhaust gas passage to bypass the first valve and have the adsorbent trapper in the bypass exhaust gas trapper. The second valve is arranged in the bypass exhaust gas passage and it is capable of opening and closing to flow the exhaust gas through the bypass exhaust gas passage and shut the bypass exhaust gas passage. The control unit controls the first valve and the second valve to open so that the exhaust gas flow through the main exhaust gas passage and the bypass exhaust gas passage so as to desorb the hydrocarbon from the adsorbent when a condition is satisfied, where the condition is that the catalyst converter is in active, an oxygen adsorption amount of the catalyst converter is not less than a first predetermined amount and an exhaust gas amount is not more than a second predetermined amount, while the control unit controls the first valve to open and the second valve to close when the condition is not satisfied during desorption of the hydrocarbon from the adsorbent.

According to a second aspect of the present invention there is provided an exhaust emission control device including an adsorbent trapper, a catalytic converter, a main exhaust gas passage, a first valve, a bypass exhaust gas passage, a second valve and a control unit. The adsorbent trapper has an adsorbent that can adsorb hydrocarbon in exhaust gas discharged from an internal combustion engine on the adsorbent a low temperature thereof and desorb the hydrocarbon from the adsorbent at a high temperature thereof. The catalytic converter is arranged at a downstream side of the adsorbent trapper and has catalyst for purifying the exhaust gas. The main exhaust gas passage is arranged between the internal combustion engine and the catalytic converter so that the main exhaust passage can flow the exhaust gas discharged from the internal combustion engine to the catalytic converter. The first valve is arranged in the main exhaust gas passage and it is capable of opening and closing to flow the exhaust gas through the main exhaust gas passage and shut the main exhaust gas passage. The bypass exhaust gas passage has an upstream portion connected with an upstream portion of the main exhaust gas passage to bypass the first valve and have the adsorbent trapper in the bypass exhaust gas trapper. The second valve is arranged in the bypass exhaust gas passage and it is capable of opening and closing to flow the exhaust gas through the bypass exhaust gas passage and shut the bypass exhaust gas passage. The control unit controls the first valve to close and the second valve to open during from engine start to time where temperature of the adsorbent becomes a desorption temperature of the hydrocarbon, the control unit controlling the first valve to open and the second valve to close during from the time where the temperature of the adsorbent becomes the desorption temperature of the hydrocarbon to time where temperature of the catalyst becomes activation temperature thereof, the control unit controlling the first valve and the second valve to open during from the time where the temperature of the catalyst becomes the activation temperature to time where the hydrocarbon is desorbed from the adsorbent, and the control unit controlling the first valve to open and the second valve to close after the hydrocarbon is desorbed from the adsorbent.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features and advantages of the present invention will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram showing an exhaust emission control device of a first embodiment according to the present invention;

FIG. 2 is a flowchart of valve open/close control executed by an engine control unit that is used in the exhaust emission control device of the first embodiment;

FIG. 3 is a diagram showing the exhaust emission control device of the first embodiment, with indicating a flow direction of exhaust gas, in a state where a first valve is closed and a second valve is opened when an engine is started;

FIG. 4 is a diagram showing the exhaust emission control device of the first embodiment, with indicating the flow direction of the exhaust gas, in a state where the first valve is opened and the second valve is closed when HC starts to desorb from an adsorbent;

FIG. 5 is a diagram showing the exhaust emission control device of the first embodiment, with indicating the flow directions of the exhaust gas, in a state where the first valve and a second valve are opened when a predetermined condition is satisfied;

FIG. 6 is a flowchart of valve open/close control executed by an engine control unit that is used in an exhaust emission control device of the second embodiment according to the present invention;

FIG. 7 is a diagram of experiment results, of a conventional exhaust emission device and that of the second embodiment, showing a relationship between an amount of HC emission, a vehicle speed and an elapsed time since an engine is started;

FIG. 8 is a diagram of an exhaust emission control device of a third embodiment according to the present invention;

FIG. 9 is a view showing a second catalytic converter with an adsorbent trapper and an engine control unit that are used in the exhaust emission control device of the third embodiment;

FIG. 10 is a view of the second catalytic converter with the adsorbent trapper of the third embodiment, with indicating the flow directions of exhaust gas, in a state where a first valve is closed and a second valve is opened;

FIG. 11 is a view of the second catalytic converter with the adsorbent trapper of the third embodiment, with indicating the flow direction of the exhaust gas, in a state where the first valve is opened and the second valve is closed;

FIG. 12 is a view of the second catalytic converter with the adsorbent trapper of the third embodiment, with indicating the flow directions of the exhaust gas, in a state where the first valve and the second valve are opened;

FIG. 13 is a view of the second catalytic converter with the adsorbent trapper of the third embodiment, with indicating the flow direction of the exhaust gas, in a state where the first valve is opened and the second valve is closed;

FIG. 14 is a diagram showing experimental results of a relationship between the amount of HC emission and elapsed time;

FIG. 15 is a table of a control table for controlling the first valve and the second valve;

FIG. 16 is a view showing a second catalytic converter with an adsorbent trapper that is used in an exhaust emission control device of a fourth embodiment according to the present invention;

FIG. 17 is a view of the second catalytic converter with the adsorbent trapper of fourth embodiment, with indicating a flow direction of exhaust gas, in a state where the first valve is closed and the second valve is opened;

FIG. 18 is a view of the second catalytic converter with the adsorbent trapper of the fourth embodiment, with indicating the flow direction of the exhaust gas, in a state where the first valve is opened and the second valve is closed;

FIG. 19 is view of the second catalytic converter with the adsorbent trapper of the fourth embodiment, with indicating the flow directions of the exhaust gas, in a state where the first valve and the second valve are opened; and

FIG. 20 is a view of the second catalytic converter with the adsorbent trapper of the fourth embodiment, with indicating the flow direction of the exhaust gas, in a state where the first valve is opened and the second valve is closed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Throughout the following detailed description, similar reference characters and numbers refer to similar elements in all figures of the drawings, and their descriptions are omitted for eliminating duplication.

Referring to FIG. 1 of the drawing, there is shown a first preferred embodiment of an exhaust emission control device 1 according to the present invention, which is mounted on a motor vehicle to be connected with an internal combustion engine 2 in this embodiment.

This exhaust emission control device 1 includes a first catalytic converter C1, a main exhaust gas passage 4, a bypass exhaust gas passage 5, an adsorbent trapper 6, a second catalytic converter C2, a first valve V1, a second valve V2 and an engine control unit 8. The main exhaust gas passage 4 and the bypass exhaust gas passage 5 are made of metal pipes. The second catalytic converter C2 corresponds to a catalytic converter of the present invention, and the engine control unit 8 corresponds to a control unit of the present invention.

The first catalytic converter C1 is connected with exhaust ports of the internal combustion engine 2 at its upstream side portion through an exhaust manifold 3, and is connected at its downstream portion with a connecting pipe 3a. The first catalytic converter C1 has a metal catalyst carrier or a ceramic catalyst carrier in a cylindrical case, where the catalyst carrier is constructed by a not-shown honeycomb structural body with catalyst on surfaces of cells thereof so that harmful components such as hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx) in exhaust gas can be changed to harmlessness components such as carbon dioxide (CO₂) and water (H₂O) due to the catalytic activity thereof while the exhaust gas enters from the first catalytic converter C1 and is discharged from the cells of the catalyst carrier.

The connecting pipe 3a is connected with an upstream side portion of the main exhaust gas passage 4

The main exhaust gas passage 4 is provided with the first valve V1 at its intermediate portion. The bypass exhaust gas passage 5 is connected with an upstream portion and a downstream portion of the main exhaust gas passage 4 to bypass the first valve V1. The bypass exhaust gas passage 5 is provided with the adsorbent trapper 6 and the second valve V2.

The adsorbent trapper 6 has a not-shown honeycomb structural body in a cylindrical case, where adsorbent such as zeolite is coated on surfaces of cells thereof so that hydro carbon (HC) in the exhaust gas entering from an upstream side can be adsorbed thereto at a low temperature and be desorbed to be discharged toward a downstream side.

The second catalytic converter C2 is arranged in the main exhaust gas passage 4 at a downstream side of the bypass exhaust gas passage 5. The second catalytic converter C2 is constructed similarly to the first catalytic converter C1, and accordingly its explanation is omitted.

The first valve V1 and the second valve V2 are electromagnetic valves that can be driven by not-shown actuators such electric motors so that they shifts between a close state and an open state to change the exhaust gas to flow through the main exhaust gas passages 4 or the bypass exhaust passage 5, respectively.

A first temperature sensor SE1 is provided at an upstream side of the adsorbent trapper 6 to detect the surface temperature of the adsorbent or the ambient temperature thereof, and a second temperature sensor SE2 is provided at an upstream side of the second catalytic converter C2 to detect the surface temperature of the catalyst or the ambient temperature thereof. In addition, a first oxygen sensor SE3 is provided at an upstream side of the second catalytic converter C2 to detect an oxygen concentration of the exhaust gas passing through the upstream side, and a second oxygen sensor SE4 is provided at a downstream side of the second catalytic converter C2 to detect an oxygen concentration of the exhaust gas passing through the downstream side.

Further, an airflow sensor SE5 is provided in an intake manifold 7of the engine 2 to detect an amount of intake air.

The first temperature sensor SE1, the second temperature sensor SE2, the first oxygen sensor SE3, the second oxygen sensor SE4 and the airflow sensor SE5 are electrically connected to the engine control unit 8 to send their detection signals thereto.

The engine control unit 8 is further electrically connected to no-shown various sensors to receive an engine coolant temperature signal, an engine speed signal, an accelerator opening-degree signal, a vehicle speed signal, an ignition signal, a fuel injection amount signal and others so as to control the engine 2, the first valve V1 and the second valve V2.

The operation and effects of the exhaust emission control device 1 of the first embodiment will be described.

In the exhaust emission control device 1 of the first embodiment, the engine control unit 8 controls the first valve V1 and the second valve V2 to open and close according to a flowchart shown in FIG. 2 of valve open/close control executed by the engine control unit 8.

At step S1, the engine control unit 8 starts the open/close control when it detects a start of the engine 1, and then the flow goes to step S2.

At the step S2, the first valve V1 is closed to shut the main exhaust passage 4, the second valve V2 being opened to flow the full amount of the exhaust gas discharged from the engine 2 through the bypass exhaust gas passage 5, and then flow goes to step S3.

At the step S3, the engine control unit 8 judges whether or not the adsorbent in the adsorbent trapper 6 begins to desorb the exhaust gas therefrom based on the temperature signal outputted from the first temperature sensor SE1. If YES, the flow goes to step S4, while, if NO, the flow returns to the step S2. The start of HC desorption is judged when the temperature detected by the first temperature sensor SE1 reaches a predetermined temperature, where the HC desorption temperature of the adsorbent is 250° C. in general.

At the step S4, the first valve V1 is opened to flow the full amount of the exhaust gas discharged from the engine 2 through the main exhaust gas passage 4, the second valve V2 being closed to shut the bypass exhaust passage 5, and then the flow goes to step S5.

At the step S5, the engine control unit 8 judges, based on the detection signals of the second temperature sensor SE2, the first and the second oxygen sensors SE3 and SE4 and the airflow sensor SE5, whether or not the catalyst in the second catalytic converter C2 is activated, an oxygen adsorption amount of the second catalytic converter C2 is equal to or larger than a first predetermined amount, and the amount of the exhaust gas is equal to or smaller than a second predetermined amount. If Yes, the flow goes to step S6, while, if NO, the flow returns to the step S4. The activation of the second catalytic converter C2 is judged based on whether or not the temperature detected by the second temperature sensor SE2 reaches a predetermined temperature, where the activation temperature of the second catalytic converter C2 is equal to or higher than 350° C. in general. The first predetermined amount may be set appropriately, and it is set to be a value corresponding to approximately 50% of the maximum oxygen adsorption amount of the second catalytic converter C2 in this embodiment. The second predetermined amount may be set appropriately, and it is set to be a value corresponding to an amount of the exhaust gas discharged from the engine 2 that is running at a low speed in this embodiment.

Incidentally, in FIG. 2, the oxygen adsorption amount is indicated by “OA”, the first predetermined amount is indicated by “A1”, the exhaust gas amount is indicated by “EA”, and the second predetermined amount is indicated by “A2”.

Instead of this judgment, the activation of the second catalytic converter C2 may be judged based on whether or not the elapsed time has passed since the engine 2 is started. In this case, the elapsed time may be set to change according to the temperature of the engine coolant detected when the engine 2 is started.

Further, instead of the above-described judgments, the activation of the second catalytic converter C2 may be judged based on an integrated value of the engine speed and the fuel injection amount.

The oxygen adsorption amount of the second catalytic converter C2 is estimated based on the detection signals outputted from the first oxygen sensor SE3 and the second oxygen sensor SE4 or from the airflow sensor SE5.

Instead of this estimate, the oxygen adsorption amount of the second catalytic converter C2 may be estimated based on the detection signal outputted from the airflow sensor SE5 and a fuel cut signal.

The amount of the exhaust gas is estimated based on an airflow amount signal outputted from the airflow sensor SE5.

At the step S6, both of the first valve V1 and the second valve V2 are opened to flow the exhaust gas through the main exhaust gas passage 4 and the bypass exhaust gas passage 5, and then the flow goes to the step S7.

At the step S7, the engine control unit 8 judges whether or not the detection signals newly detected can satisfy the same condition at the step S5. If YES, the flow goes to step S8, while, if NO, the flow returns to the step S4.

At the step S8, the engine control unit 8 judges whether or not the adsorbent ends desorption of the hydrocarbon therefrom. If YES, the flow goes to step S9, while, if NO, the flow returns to the step S7.

The end of the HC desorption from the adsorbent is set to be time after a predetermined time has passed the engine 2 is started.

Instead of this setting, the end of the HC desorption from the adsorbent may be estimated by adding a sensor for detecting an HC concentration to the adsorbent trapper 6, or it may be judged by estimating a residual volume of HC on the adsorbent based on the signals of the engine control unit 8.

At the step S9, the first valve V1 is opened to flow the full amount of the exhaust gas through the main exhaust gas passage 4, the second valve V2 being closed to shut the bypass exhaust passage 5, and then the flow ends.

In the exhaust emission control device 1 of the first embodiment, for a while after the engine 2 is started, as shown in FIG. 3, the first valve V1 is closed to shut the main exhaust gas passage 4, the second valve V2 being opened to flow the exhaust gas discharged from the engine 2, according to the operation at the steps 1 to 3, because it takes a while for the temperature of the exhaust gas to reach to the desorption temperature of the adsorbent. As a result, the full amount of the exhaust gas discharged from the engine 2 passes through the adsorbent trapper 6 and then enters the second catalytic converter C2 as indicated dashed line arrow in FIG. 3. In this operation, the adsorbent adsorbs the HC contained in the exhaust gas while it passes through the adsorbent, while the catalysts of the first and second catalytic converter C1 and C2 does not work because the temperature of the exhaust gas is low. Thus, the adsorbent trapper 6 can prevent the HC in the exhaust gas from being discharged in the air during no catalytic activities of the first and second catalytic converters C1 and C2.

Then when the temperature of the exhaust gas rises to reach the desorption temperature of the adsorbent, as shown in FIG. 4, the first valve V1 is opened to flow the full amount of the exhaust gas through the main exhaust gas passage 4, the second valve V2 being closed to shut the bypass exhaust gas passage 5, according to the operation at the step S4. As a result, the full amount of the exhaust gas discharged from the engine 2 enters the main exhaust gas passage 4 and the second catalytic converter C2 arranged therein as indicated by a dashed line arrow in FIG. 4. In this operation, the catalyst of the first catalytic converter C1 purifies the HC in the exhaust gas since the catalyst thereof is activated.

In addition, the engine control unit 8 judges whether or not the catalyst in the second catalytic converter C2 is activated, an oxygen adsorption amount of the second catalytic converter C2 is equal to or larger than the first predetermined amount, and the amount of the exhaust gas is equal to or smaller than the second predetermined amount, according to the operation at the step S5. If the above condition is do not satisfied, the first and second valves V1 and V2 are kept being opened and closed, respectively.

On the other hand, if the above condition is satisfied, both of the first and second valves V1 and V2 are opened to flow the exhaust gas through the main exhaust gas passage 4 and the bypass exhaust gas passage 5 as shown in FIG. 5, according to the operation at the step S6.

As a result, the exhaust gas discharged from the engine 2 flows through the main exhaust gas passage 4 and the bypass exhaust gas passage 5 as indicated by dashed line arrows in FIG. 5. In this operation, the harmful components such as the HC are purified by the second catalytic converter C2 in addition to the first catalytic converter C1.

After opening both the first and second valves V1 and V2, the engine control unit 8 judges again whether or not the above condition is satisfied, according to the operation at the step S7. If the above condition is not satisfied, the first valve V1 is opened to flow the full amount of the exhaust gas through the main exhaust gas passage 4 and the second valve V2 is closed to shut the bypass exhaust gas passage 5.

On the other hand, if the above condition is satisfied, the engine control unit 8 judges whether or not the desorption of the HC from the adsorbent ends, according to the operation at the step S8. If the desorption does not end, the first and second valves V1 and V2 are maintained to open, while if it ends, the first valve V1 is opened to flow the full amount of the exhaust gas through the main exhaust passage 4 and the second valve V2 is closed to shut the bypass exhaust gas passage 5, according to the operation at the step S9. In the latter case, a part of the exhaust gas can be prevented from flowing through the bypass exhaust gas passage 5, so that the durability of the adsorbent trapper 6 can be improved.

As described above, in the exhaust emission control device 1 of the first embodiment, the second valve V2 is opened and closed according to the condition at the steps S5 and S7 during time between the beginning of the desorption of the HC from the adsorbent and the end thereof.

Only when the oxygen adsorption amount is equal to or larger than the predetermined amount and the exhaust gas amount is equal to or smaller than the second determined amount, in other words, only when the second catalytic converter C2 stores sufficient oxygen and the amount of the exhaust gas passing through the adsorbent is small, the second valve V2 is opened to flow the HC desorbed from the adsorbent into the second catalytic converter C2.

Accordingly, in the exhaust emission control device 1 of the first embodiment, the HC that is adsorbed on the adsorbent can be prevented from being rapidly and in large quantities desorbed from the adsorbent to enter the second catalytic converter C2, and its purification performance can be prevented from being deteriorated due to lack in the oxygen adsorption amount of the second catalytic converter C2.

Next, an exhaust gas emission control device of a second embodiment according to the second embodiment will be described with reference to the accompanying drawings.

The exhaust gas emission control device 1 of the second embodiment is constructed similarly to that of the first embodiment shown in FIG. 1. In the exhaust gas emission control device 1 of the second embodiment, an engine control unit 8 executes valve open/close control according to a flowchart shown in FIG. 6 which is different from that in FIG. 2 of the first embodiment.

As shown in FIG. 6, its steps S1 to S4, S6, S8 and S9 are similar to those of the first embodiment except steps S50, S70 and S71, and accordingly the explanations of the similar steps are omitted.

At the step S50, the engine control unit 8 judges whether or not a second catalytic converter C2 is activated, fuel injection is halted (or a motor vehicle is slowing down), and an amount of the exhaust gas discharged from the engine 2 is equal to or smaller than a second predetermined amount corresponding to the second predetermined amount of the first embodiment. If YES, the flow goes to the step S6 where both of a first valve V1 and a second valve V2 are opened to flow the exhaust gas through the main exhaust gas passage 4 and the bypass exhaust gas passage 5, while, if NO, the flow returns to the step S4 where the first valve is opened to flow the full amount of the exhaust gas through the main exhaust gas passage 4 and the second valve V2 is closed to shut the bypass exhaust gas passage 5.

At the step S70 after the step S6, the engine control unit 8 judges again whether or not the second catalytic converter C2 is activated, the fuel injection is halted (or the motor vehicle is slowing down), and the amount of the exhaust gas discharged from the engine 2 is equal to or smaller than the second predetermined amount. If YES, the flow goes to the step S8 where the engine control unit 8 judges whether or not HC desorption from an adsorbent ends, while, if NO, the flow goes to the step S71.

At the step S71, the engine 2 is controlled to be driven at a rich mixture where an air fuel ratio (the mass ratio of air to fuel present during combustion) is set less than the stoichiometric air-fuel mixture 14.7 for gasoline fuel, and then the flow returns to the step S4.

As described above, the exhaust emission control device 1 of the second embodiment has the effects similar to those of the first embodiment.

In addition, when the fuel injection is halted or the motor vehicle is slowing down, the oxygen amount in the exhaust gas increases to a maximum of approximately 21% thereof, thereby generating a lean mixture (the air fuel ratio is more than the stoichiometric air-fuel mixture) state. This can skip an arithmetic processing for estimating the oxygen adsorption amount of a second catalytic converter C2.

In a case where at least any one of the condition at the step S71 during the desorption of HC when the first and second valves V1 and V2 are opened at the step S6, the mixture to be supplied to the engine 2 is controlled to be rich so that the oxygen amount in the exhaust gas is decreased for to exert the catalytic activity of the second catalytic converter C2 earlier. Thus, the catalyst of the second catalytic converter C2 can be prevented from being not activated for a short time because of the lean mixture state due to the excess oxygen absorption mount of the second catalytic converter C2.

In addition, although the NOx amount in the exhaust gas increases only in a case where the engine 2 is driven merely at the lean mixture, the exhaust emission control device 1 of the second embodiment uses the lean mixture control with the fuel injection cut-off, so that the oxygen can be supplied to the second catalytic converter C2 without increase in NOx because the air fuel ratio is not changed.

FIG. 7 shows experiment results, of a conventional exhaust emission device and that of the second embodiment, showing a relationship between the amount of HC emission, a vehicle speed and an elapsed time since the engine 2 is started. The vehicle speed is set according to a speed model that is used for experiments. The conventional exhaust emission control device is constructed in such a way that a first valve V1 and a second valve V2 are opened to flow the exhaust gas through the main exhaust gas passage 4 and the bypass exhaust gas passage 5 immediately after a second catalytic converter C2 is activated and they are controlled to be maintained to open afterward.

As shown in FIG. 7, compared to the exhaust emission control device of the second embodiment and the conventional one, they need the almost same time from engine start to the time where the first catalytic converter C1 is activated to decrease the amount of HC emission, and the HC emission amount can be largely decreased during the declaration of the vehicle speed with the fuel injection cut-off in the exhaust emission control device of the second embodiment, while it largely increases after the second catalytic converter C2 is activated in the conventional one.

Next, an exhaust emission control device of a third embodiment according to the present invention will be described with the accompanying drawings.

As shown in FIG. 8, the exhaust emission control device 11 includes a first catalytic converter C1, a main exhaust gas passage 4, a bypass exhaust gas passage 5, a second catalytic converter C2 with an adsorbent trapper, a first valve V1, a second valve V2, a center muffler MF, a rear muffler MR and an emission control unit 12. The emission control unit corresponds to the control unit of the present invention.

The first catalytic converter C1 is constructed similarly to that of the first embodiment, and is connected with an engine 2 at its upstream portion through an exhaust manifold 3 and with a connecting pipe 3a at its downstream portion.

A downstream side end portion of the connecting pipe 3a is provided with a flange that is joined with a flange 25 of an upstream side end portion of the main exhaust gas passage 4.

The second catalytic converter C2 with an adsorbent trapper includes a main case 20, an adsorbent part 21 and a catalyst part 23. The adsorbent part 21 has a metal external cylinder 21a and an adsorbent 21b that is formed in a cylindrical shape and is contained in the external cylinder 21a. The adsorbent 21b has cells that is penetrated in its axial direction and is coated with zeolite on their surfaces. The adsorbent part 21 is formed at a center thereof with a hole to be penetrated through by a downstream portion of the main exhaust passage 4.

The main case 20 includes an end plate 23a, a first cylinder 23b, a second cylinder 23 and a diffuser 24, which are made of metal material.

An upstream portion of the external cylinder 21a of the second catalytic converter C2 is connected with the first cylindrical part 23b, which is blocked off by the end plate part 23a at its upstream portion. The end portion plate 23a is provided with two opening portions, so that a downstream side end portion of the bypass exhaust gas passage 5 is connected with one of the opening portion and an intermediate portion of the main exhaust gas passage 4 penetrates the other opening portion. A first chamber R1 is formed among the end plate 23a, the first cylinder 23b and the adsorbent part 21, so that the first chamber R1 is arranged at an upstream side of the adsorbent part 21. A downstream portion of the external cylinder 21a of adsorbent part 21 is connected with the second cylinder 23b, which is connected at its downstream portion with an external cylinder 22a of the catalyst part 22.

The catalyst part 22 includes the external cylinder 22a and a catalyst carrier 22b that is formed like a cylindrical shape and is contained in the external cylinder 22a. The catalyst carrier 22b is a metal catalyst carrier or a ceramic catalyst carrier. The downstream side end portion of the main exhaust gas passage 4 and an upstream side end portion of the catalyst part 22 are connected with each other through a partition part 29 that is shaped like a funnel with a plurality of communicating holes 29a. The diameter of the partition part 29 increases toward its downstream side.

A second chamber R2 is formed among the adsorbent part 21, the second external cylinder 23c and the catalyst part 22, so that the second chamber R2 is arranged at a downstream side of the adsorbent part 21 and at an upstream side of the catalyst part 22.

Incidentally, the second catalytic converter C2 may have an external cylinder that contains the adsorbent 21b and the catalyst carrier 22b, instead of first cylinder 23b, the second cylinder 23, the external cylinder 21a and the external cylinder 22a.

A downstream end portion of the catalyst part 22 is connected with the diffuser 24 that decreases its diameter toward the downstream side and is provided with a flange 26.

The flange 26 is connected with a flange of an exhaust pipe 9a, which is further connected with the center muffler MF. The center muffler MF is connected with the rear muffler MR through an exhaust pipe 9b.

The first valve V1 is provided in the main exhaust gas passage 4 at the upstream side of the partition part 29, and the second valve V2 is provided in the bypass exhaust gas passage 5 which is connected with the upstream portion of the main exhaust gas passage 4 at an upstream side of the first valve V1. The first valve V1 and the second valve V2 employ butterfly valves, which are controlled to open and close by not-shown actuators such as electric motors, respectively. The actuators are electrically connected to and controlled by the emission control unit 12, which is further electrically connected to a third temperature sensor 27, a fourth temperature sensor 28 and an engine control unit 14.

The third temperature sensor 27 is arranged in the second chamber R2 near the downstream end portion of the adsorbent part 21 to detect a temperature of the adsorbent 21b of the adsorbent part 21 or an ambient temperature thereof, while the fourth temperature sensor 28 is arranged in the diffuser 24 near the downstream end portion of the catalyst part 22 to detect a temperature of the catalyst carrier 22b of the catalyst part 22 or an ambient temperature thereof.

The engine control unit 14 is electrically connected to not-shown various sensors to receive an engine coolant temperature signal, an engine speed signal, an accelerator opening-degree signal, an airflow amount signal, a vehicle speed signal, an ignition signal, a fuel injection amount signal and others so as to control the engine 2.

The other parts are constructed similarly to those of the first embodiment.

The operation and effects of the exhaust emission control device 10 of the third embodiment will be described.

In the exhaust emission control device 10 of the third embodiment, the emission control unit 12 receives the various signals outputted from the engine 2 and temperature signals outputted from the first and second temperature sensors 27 and 28 so that the emission control unit 12 controls the first valve V1 and the second valve V2 to open and close according to a control table shown in FIG. 15.

While the temperature of the exhaust gas is lower than the desorption temperature of the HC from the adsorbent 21b after the engine 2 is started, the first valve V1 is closed to shut the main exhaust gas passage 4, while the second valve V2 is opened to flow the full amount of the exhaust gas through the bypass exhaust gas passage 5 as shown in FIG. 10. The flow directions of the exhaust gas are indicated by dashed line arrows.

In this operation, the full amount of the exhaust gas discharged from the engine 2 in introduced into the first chamber R1 through the bypass exhaust gas passage 5, and then it passes through the adsorbent part 21, where the HC in the exhaust gas is adsorbed on the adsorbent 21b. The exhaust gas that has passed through the adsorbent part 21 is introduced into the second chamber R2, and then to the catalyst part 22 through the communicating holes 29a of the partition plate 29.

The exhaust gas passes through the catalyst carrier 22b, and then through the center muffler MC and the rear muffler MR to be discharged in the air.

In this operation, although the first catalytic converter C1 and the catalyst part 21, functioning as a second the second catalyst converter of the first and second embodiments, because the temperature of the exhaust gas is low, the HC is trapped by the adsorbent part 21b, so that the HC is prevented from being emitted in the air.

While the temperature of the adsorbent 21b is equal to or higher than the desorption temperature thereof and the temperature of the catalyst carrier 22b being lower than the activation temperature thereof, the first valve V1 is opened to flow the full amount of the exhaust gas through the main exhaust gas passage 4 and the second valve V2 is closed to shut the bypass exhaust gas passage 5 as shown in FIG. 11. The flow direction of the exhaust gas is indicated by a dashed line arrow.

In this operation, the temperature of the first catalytic converter C1 has reached to the activation temperature thereof, so that the HC in the exhaust gas discharged from the engine 2 is purified by the catalyst of the first catalytic converter C2, although the catalyst of the catalyst carrier 22b cannot purify the exhaust gas.

The partition part 29 prevents a part of the exhaust gas from being blown back to the adsorbent 21b.

While the adsorbent 21b are desorbing the HC therefrom and the temperature of the catalyst carrier 22b is equal to or higher than the activation temperature thereof, the first valve V1 and the second valve V2 are opened to flow the exhaust gas through the main exhaust gas passage 4 and the bypass exhaust gas passage 5 as shown in FIG. 12. The flow directions of the exhaust gas are indicated by dashed line arrows.

The end of the HC desorption from the adsorbent 21b is estimated to be a predetermined time after the second valve V2 is opened. Instead of this estimation, a sensor for detecting an HC concentration may be provided in the second chamber R2, or the HC residual amount on the adsorbent 21b may be estimated based on signals outputted from the engine control unit 13 by using one of the conventional estimation methods.

In this operation, the adsorbent 21b desorbs the HC adsorbed on the adsorbent 21b to flow downstream side. The catalyst of the catalyst carrier 22b purifies the harmful components including the HC in the exhaust gas. This purified exhaust gas flows into the center muffler MC and the rear muffler MR, then being discharged in the air.

After the HC desorption from the adsorbent 21b ends, the first valve V1 is opened to flow the full amount of the exhaust gas through the main exhaust gas passage 4 and the second valve V2 is closed to shut the bypass exhaust gas passage 5 as shown in FIG. 13. The flow direction of the exhaust gas is indicated by a dashed line arrow.

In this operation, the adsorbent 21b becomes to be in an initial state where the HC is completely desorbed from the adsorbent 21b. The catalyst of the catalyst carrier 22b purifies the exhaust gas to change the harmful components in the exhaust gas into the harmless components. This purified exhaust gas flows into the center muffler MC and the rear muffler MR, then being discharged in the air.

Therefore, the exhaust mission control device 10 of the third embodiment has the following effects in addition to those of the first and second embodiments.

In the exhaust mission control device 10 of the third embodiment, after the substantially full amount of the HC is desorbed from the adsorbent 21b, the second valve V2 closes to shut the bypass exhaust gas passage 5. As a result, the exhaust gas does not pass through the adsorbent 22b, so that the durability of the adsorbent 22b can be improved compared to a conventional exhaust emission control device described in Japanese Patent Application Laid-Open No. 2006-194231 where a part of the exhaust gas passes through an adsorbent after the HC is desorbed from the adsorbent.

In addition, in the exhaust mission control device 10 of the third embodiment, the coating amount of zeolite and/or others on the adsorbent can be deceased, and the amount of catalyst can be also decreased. Therefore, costs of an adsorbent trapper and a catalytic converter can be decreased.

Further, when a motor vehicle is running after the HC is desorbed from the adsorbent, the exhaust gas does not pass through the adsorbent, so that the flow resistance of the exhaust gas is reduced, thereby increasing output power of the engine 2.

FIG. 14 shows experimental results of a relationship between the HC emission amount and an elapsed time. In FIG. 14, operation areas (1) to (4) correspond to the operation cases (1) to (4) where the first valve V1 and the second valve V2 are opened and/or closed in the control table in FIG. 15. As understood from the experimental results in FIG. 14, the exhaust emission control device 10 of the third embodiment can decrease the emission amount of the HC that is discharged in the air before the catalyst of the catalyst carrier 22b becomes to be active.

Next, an exhaust emission control device of a fourth embodiment according to the present invention will be described with reference to the accompanying drawings.

The exhaust emission control device of the fourth embodiment is constructed similarly to that of the third embodiment shown in FIG. 8.

A second catalytic converter C2 with an adsorbent trapper includes a main case 23, an adsorbent part 21, a catalyst part 22 and a diffuser 24. The catalyst part 22 is arranged between a downstream side of the adsorbent 21 at an upstream side thereof and the diffuser 24 at a downstream side thereof.

The adsorbent part 21 includes an external cylinder 21a and an adsorbent 21b arranged in the external cylinder 21a, which has a diameter smaller than that of the third embodiment. The external cylinder 21a is fixed to and supported by a first baffle pate 30 and a second baffle plate 31.

The first baffle plate 30 and the second baffle plate 31 are fixed on an inner surface of a first cylinder 23b of the main case 23, being away from each other in an axial direction of the second catalytic converter C2.

A main exhaust gas passage 4 penetrates through a hole formed in the first baffle plate 30 with a clearance 30a therebetween, and it is fixed to and supported by the second baffle plate 31 so that a downstream side opening of the main exhaust gas passage 4 opens in a second chamber R2 that is formed by the second baffle plate 31, an upstream side end portion of a catalyst carrier 22b and a second cylinder 23b of the main case 23. The diameter of second cylinder 23b is formed to be smaller toward its downstream side. On the other hand, a third chamber R3 is formed by the first cylinder 23a, the external cylinder 21a of the adsorbent part 21 and a pipe forming the main exhaust gas passage 4. The third chamber R3 communicates only with a first chamber R1 through the clearance 30a formed in the first baffle plate 30. The third chamber R3 corresponds to a sound attenuation means of the present invention.

The diffuser 24 is formed like a cup and is connected with a downstream end portion of the catalyst part 22.

The other parts of the exhaust emission control device of the fourth embodiment are constructed similarly to those of the third embodiment except that it has not the partition part 29 of the third embodiment.

A first valve V1 and a second valve V2 are controlled by an emission control unit 12 according to a control table shown in FIG. 15.

The operation of the exhaust emission control device of the fourth embodiment is similar to that of the third embodiment. The exhaust emission control device of the fourth embodiment can obtain the effects similar to those of the first to third embodiments.

In addition, in the exhaust emission control device of the fourth embodiment, the first chamber R1 and the third chamber R3 are communicated with each other through the clearance 30a. When the second valve V2 is opened and the exhaust gas flows through the bypass exhaust gas passage 5 (corresponding to the cases (1) and (3) in the control table in FIG. 15), a part of the exhaust gas in the first chamber R1 is introduced into the third chamber R3 through the clearance 30a to resonate therein so that the third chamber R3 can function as a resonant chamber. Therefore, the noise of the exhaust gas can be decreased.

The resonance frequency of the third chamber R3 may be set appropriately according to a volume of the third chamber R3 and others.

For example, it may be set according to a frequency of noise that might generate by confluence of the exhaust gasses that have passed through the main exhaust gas passage 4 and the bypass exhaust gas passage 5 when the first valve V1 and the second valve V2 are opened (corresponding to case (3) in the control table in FIG. 15).

Alternatively, it may be set to decrease a noise, what is called, a muffled sound that generates at a low engine speed, equal to or less than 2000 r.p.m. of the engine speed obtained immediately after the engine starts and when the engine is driven at idle speed. This case corresponds to the case (1) in the control table in FIG. 15.

In addition, the exhaust emission control device of the fourth embodiment can decrease the noise generated when the exhaust gas enters the first chamber R1 through the bypass exhaust gas passage 5 and when the exhaust gas enters the second chamber R2 through the main exhaust gas passage 4, because of expansion effect of volumes thereof to reduce noise energy.

While there have been particularly shown and described with reference to preferred embodiments thereof, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

The control unit for controlling the first valve V1 and the second valve V2 may be separated from the engine control unit for controlling an engine, or it may be integrated with the engine control unit.

The judging methods for estimating the activation of the catalytic converter, the oxygen adsorption amount of the catalytic converter and the emission amount may be employed appropriately.

The temperature of the adsorbent and the temperature of the catalyst may be detected by appropriate various sensor and/or information instead of using the temperature sensors.

The entire contents of Japanese Patent Applications No. 2008-038322 filed Feb. 20, 2008, No. 2008-011458 filed Jan. 22, 2008 and No. 2008-011459 filed Jan. 22, 2008 are incorporated herein by reference.

Claims

1. An exhaust emission control device comprising:

an adsorbent trapper having an adsorbent that can adsorb hydrocarbon in exhaust gas discharged from an internal combustion engine on the adsorbent a low temperature thereof and desorb the hydrocarbon from the adsorbent at a high temperature thereof;

a catalytic converter that is arranged at a downstream side of the adsorbent trapper and has catalyst for purifying the exhaust gas;

a main exhaust gas passage arranged between the internal combustion engine and the catalytic converter so that the main exhaust passage can flow the exhaust gas discharged from the internal combustion engine to the catalytic converter;

a first valve that is arranged in the main exhaust gas passage and is capable of opening and closing to flow the exhaust gas through the main exhaust gas passage and shut the main exhaust gas passage;

a bypass exhaust gas passage that has an upstream portion connected with an upstream portion of the main exhaust gas passage to bypass the first valve and have the adsorbent trapper in the bypass exhaust gas trapper;

a second valve that is arranged in the bypass exhaust gas passage and is capable of opening and closing to flow the exhaust gas through the bypass exhaust gas passage and shut the bypass exhaust gas passage; and

a control unit that controls the first valve and the second valve, wherein

the control unit controls the first valve and the second valve to open so that the exhaust gas flow through the main exhaust gas passage and the bypass exhaust gas passage so as to desorb the hydrocarbon from the adsorbent when a condition is satisfied, where the condition is that the catalyst converter is in active, an oxygen adsorption amount of the catalyst converter is not less than a first predetermined amount and an exhaust gas amount is not more than a second predetermined amount, wherein

the control unit controls the first valve to open and the second valve to close when the condition is not satisfied during desorption of the hydrocarbon from the adsorbent.

2. The exhaust emission control device according to claim 1, wherein

the control unit controls the second valve to open to flow the exhaust gas through the bypass exhaust gas passage so as to desorb the hydrocarbon from the adsorbent while a fuel injection is halted, a motor vehicle is slowing down and the exhaust gas amount is not more than a second predetermined amount after the catalytic converter becomes in an activation state.

3. The exhaust emission control device according to claim 1, wherein

the internal combustion engine is supplied with rich mixture of fuel/air ratio when the second valve is closed to shut the bypass exhaust gas passage during a valve open/close control where the exhaust gas flows through the bypass exhaust gas passage.

4. The exhaust emission control device according to claim 1, wherein

the first predetermined amount may be set appropriately, and it is set to be a value corresponding to approximately 50% of the maximum oxygen adsorption amount of the catalytic converter.

5. The exhaust emission control device according to claim 1, wherein

The second predetermined amount is set to be an amount of the exhaust gas discharged from the internal combustion engine at a low engine speed.

6. The exhaust emission control device according to claim 1, wherein

the adsorbent trapper and the catalytic converter are contained in a main case, and wherein

the main case is provided with a sound attenuation means for suppressing noise of the exhaust gas.

7. The exhaust emission control device according to claim 6, wherein

the sound attenuation means is a resonant chamber.

8. The exhaust emission control device according to claim 6, wherein

a resonance frequency of the sound attenuation means is set to suppresses the noise caused by the exhaust gas entering the bypass exhaust gas passage.

9. The exhaust emission control device according to claim 6, wherein

a resonance frequency of the sound attenuation means is set to suppresses the noise caused by confluence of the exhaust gasses that have passed through the main exhaust gas passage and the bypass exhaust gas passage.

10. An exhaust emission control device including:

an adsorbent trapper having an adsorbent that can adsorb hydrocarbon in exhaust gas discharged from an internal combustion engine on the adsorbent a low temperature thereof and desorb the hydrocarbon from the adsorbent at a high temperature thereof;

a catalytic converter that is arranged at a downstream side of the adsorbent trapper to purify exhaust gas;

a main exhaust gas passage arranged between the internal combustion engine and the catalytic converter so that the main exhaust passage can flow the exhaust gas discharged from the internal combustion engine to the catalytic converter;

a first valve that is arranged in the main exhaust gas passage and is capable of opening and closing to flow the exhaust gas through the main exhaust gas passage and shut the main exhaust gas passage;

a bypass exhaust gas passage that has an upstream portion connected with an upstream portion of the main exhaust gas passage to bypass the first valve and have the adsorbent trapper in the bypass exhaust gas trapper;

a second valve that is arranged in the bypass exhaust gas passage and is capable of opening and closing to flow the exhaust gas through the bypass exhaust gas passage and shut the bypass exhaust gas passage; and

a control unit that controls the first valve and the second valve, wherein

the control unit controls the first valve to close and the second valve to open during from engine start to time where temperature of the adsorbent becomes a desorption temperature of the hydrocarbon, the control unit controlling the first valve to open and the second valve to close during from the time where the temperature of the adsorbent becomes the desorption temperature of the hydrocarbon to time where temperature of the catalyst becomes activation temperature thereof, the control unit controlling the first valve and the second valve to open during from the time where the temperature of the catalyst becomes the activation temperature to time where the hydrocarbon is desorbed from the adsorbent, and the control unit controlling the first valve to open and the second valve to close after the hydrocarbon is desorbed from the adsorbent.

11. The exhaust emission control device according to claim 10, wherein

the control unit controls the second valve to open to flow the exhaust gas through the bypass exhaust gas passage so as to desorb the hydrocarbon from the adsorbent while a fuel injection is halted, a motor vehicle is slowing down and the exhaust gas amount is not more than a second predetermined amount after the catalytic converter becomes in an activation state.

12. The exhaust emission control device according to claim 10, wherein

the internal combustion engine is supplied with rich mixture of fuel/air ratio when the second valve is closed to shut the bypass exhaust gas passage during a valve open/close control where the exhaust gas flows through the bypass exhaust gas passage.

13. The exhaust emission control device according to claim 10, wherein

the end of the desorption of the hydrocarbon from the adsorbent is set to be a predetermined time after the engine starts.

14. The exhaust emission control device according to claim 10, wherein

the end of the desorption of the hydrocarbon from the adsorbent is judged based on a signal outputted from a sensor for detecting a hydrocarbon concentration.

15. The exhaust emission control device according to claim 10, wherein

the adsorbent trapper and the catalytic converter are contained in a main case, and wherein

the main case is provided with a sound attenuation means for suppressing noise of the exhaust gas.

16. The exhaust emission control device according to claim 15, wherein

the sound attenuation means is a resonant chamber.

17. The exhaust emission control device according to claim 15, wherein

a resonance frequency of the sound attenuation means is set to suppresses the noise caused by the exhaust gas entering the bypass exhaust gas passage.

18. The exhaust emission control device according to claim 15, wherein

a resonance frequency of the sound attenuation means is set to suppresses the noise caused by confluence of the exhaust gasses that have passed through the main exhaust gas passage and the bypass exhaust gas passage.