US20090183496A1

US20090183496A1 - Exhaust gas purifying apparatus

Info

Publication number: US20090183496A1
Application number: US12/353,481
Authority: US
Inventors: Miyao Arakawa; Yoshiaki Nishijima; Masatoshi Kuroyanagi
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2008-01-17
Filing date: 2009-01-14
Publication date: 2009-07-23
Also published as: JP2009167941A

Abstract

A throttle unit placed in an exhaust gas passage controls an opening-ratio of each of first and second valve members to control a gas-flow sectional area of the exhaust gas passage. When the temperature of a three-way catalyst is low, the throttle unit introduces the exhaust gas flow into a part of an outer-periphery of the three-way catalyst. This control can rapidly increase the temperature of the three-way catalyst from an early period of starting an internal combustion engine within a short period of time. The throttle unit increases the gas-flow sectional area of the exhaust gas passage according to increasing the temperature of the three-way catalyst. When the three-way catalyst reaches its activation temperature, the throttle unit instructs the first and second valve members to fully open. This decreases a pressure loss of the exhaust gas because the exhaust gas is supplied into the entire of the three-way catalyst.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese Patent Application No. 2008-8305 filed on Jan. 17, 2008, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus using a catalyst such as a three way catalyst capable of purifying an exhaust gas emitted from an internal combustion engine such as a diesel engine under a low temperature of the catalyst in the early period of starting the internal combustion engine.
2. Description of the Related Art
Internal combustion engines such as diesel engines and gasoline engines include a problem of increasing the amount of specified materials such as hydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in an exhaust gas emitted from such an internal combustion engine mounted to a vehicle when the temperature of catalyst placed in an exhaust gas purifying apparatus mounted to the vehicle is low, for example, during early period of starting the internal combustion engine. For this reason, the catalyst placed in the exhaust gas purifying apparatus does not adequately reach its optimum temperature, namely, its activation temperature to activate the function of the catalyst.
In order to solve such a conventional problem, Japanese patent laid open publication No. JP 2004-100481 has proposed an improved structure of an exhaust gas purifying apparatus. In the structure, a low pressure-loss part is formed in a central part in the diameter direction of the exhaust gas purifying apparatus. The exhaust gas is flowing easily through the central part of the exhaust gas purifying apparatus because the central part is lower in pressure than the remaining part of the exhaust gas purifying apparatus. This enables the exhaust gas to be pass easily through the exhaust gas purifying apparatus when the internal combustion engine of the vehicle starts. Thereby, the temperature of the exhaust gas purifying apparatus is increased.
However, from the viewpoint of strength, it is in general difficult to use a usual ceramics support as the exhaust gas purifying apparatus having the low pressure-loss part formed at the central part thereof. Still further, it is hard to concentrate the exhaust gas flow using a pressure difference between the central part and the remaining part of the exhaust gas purifying apparatus. Still furthermore, it is necessary to close the low pressure-loss part after the temperature of the exhaust gas, namely, of the catalyst reaches an optimum temperature such as its activation temperature. As described above, closing the central part of the exhaust gas purifying apparatus will increase the pressure loss of the exhaust gas to the entire of the exhaust gas purifying apparatus. In order to avoid that conventional problem and to keep the capability to adequately purifying the exhaust gas, it is necessary to increase the size of the exhaust gas purifying apparatus. However, such a conventional solution will cause another problem from the viewpoint of miniaturization.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an exhaust gas purifying apparatus capable of rapidly increasing the temperature of a catalyst placed therein for a short period of time without increasing the pressure loss of an exhaust gas and without increasing the size of the exhaust gas purifying apparatus. The catalyst such as a three way catalyst placed in the exhaust gas purifying apparatus according to the present invention is capable of capturing specified materials such as hydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in an exhaust gas emitted from an internal combustion engine such as a diesel engine and a gasoline engine. The purified exhaust gas containing a smaller amount of those specified materials is then discharged from the exhaust gas purifying apparatus to outside.
To achieve the above purposes, the present invention provides an exhaust gas purifying apparatus having an exhaust gas pipe, a catalyst unit, and a throttle unit. The exhaust gas pipe forms an exhaust gas passage in which an exhaust gas emitted from an internal combustion engine flows. The catalyst unit has a catalyst placed in the exhaust gas passage. The catalyst temperature detection means is capable of detecting a temperature of the catalyst placed in the catalyst unit. The throttle unit is placed in at least one of an upstream side and a downstream side thereof. The throttle unit introduces the exhaust gas flowing in the exhaust as passage into a part of the catalyst unit when the temperature of the catalyst detected by the catalyst temperature detection means is lower than an activation temperature of the catalyst.
When observed from the flowing direction of the exhaust gas in the exhaust gas passage formed in the exhaust gas pipe, the throttle unit is placed on at least one of the upstream side and the downstream side thereof. The throttle unit locally introduces the exhaust gas into a part of the catalyst placed in the catalyst unit when the temperature of the catalyst is lower than its activation temperature. That structure allows the exhaust gas emitted from an internal combustion engine to be introduced into the part of the catalyst when the temperature of the catalyst is low, namely, in the early period of starting the internal combustion engine. This allows the temperature of the part of the catalyst to locally and rapidly rise, through which the exhaust gas is concentrated in flow to the part of the catalyst such as the central part or the outer peripheral part of the catalyst. On the other hand, when the temperature of the catalyst reaches or is over its activation temperature, the throttle unit supplies the exhaust gas into the entire of the catalyst without closing the gas-flow sectional area of the exhaust gas passage. Accordingly, without causing the pressure loss of the exhaust gas and without increasing the size of the exhaust gas purifying apparatus, it is possible to rapidly increase the temperature of the catalyst such as a three way catalyst placed in the catalyst unit within a short period of time after the internal combustion engine starts or re-starts. Still further, the structure and function of the exhaust gas purifying apparatus of the present invention can efficiently eliminate specified materials, for example, hydro carbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in the exhaust gas emitted from the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1A is a schematic cross section of a part of an exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 1B is a cross section of the part of the exhaust gas purifying apparatus according to the first embodiment along the B-B line in FIG. 1A;

FIG. 2 shows a schematic diagram of a gasoline engine system (as an internal combustion engine system) equipped with the exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 3A to FIG. 3C, each shows an opening state of a throttle unit (or a valve) assembled into the exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 4 is a flow chart of the operation flow of the exhaust gas purifying apparatus according to the first embodiment of the present invention;

FIG. 5A is a diagram showing a relationship between a temperature of a three way catalyst and an elapsed period of time counted from a gasoline engine start or re-start;

FIG. 5B is a diagram showing a relationship between the elapsed period of time counted from the gasoline engine start or re-start and a concentration of hydro carbon (HC) contained in an exhaust gas emitted from engine main system, one is equipped with the exhaust gas purifying apparatus according to the first embodiment of the present invention and the other (as a comparison example) is equipped with a conventional exhaust gas purifying apparatus;

FIG. 6 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the second embodiment of the present invention;

FIG. 7 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the third embodiment of the present invention;

FIG. 8 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the fourth embodiment of the present invention;

FIG. 9 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the fifth embodiment of the present invention; and

FIG. 10 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the various embodiments, like reference characters or numerals designate like or equivalent component parts throughout the several diagrams.
A description will be given of first to sixth embodiments of an exhaust gas purifying apparatus and an engine system equipped with the exhaust gasp purifying apparatus according to the present invention with reference to FIG. 1A to FIG. 10.

First Embodiment

FIG. 2 shows a schematic diagram of an gasoline engine system as an internal combustion engine system equipped with an exhaust gas purifying apparatus according to the first embodiment of the present invention. As shown in FIG. 2, the engine system 10 has a gasoline engine 11 and an exhaust gas purifying apparatus 12. The gasoline engine 11 is comprised of an engine main system 13, an intake air system 14, an exhaust gas system 15, a gasoline supply system 16, and a control unit 17 (or an electronic control unit (ECU)).
The engine main system 13 has pistons which are located in cylinders. Each piston 13 performs reciprocating motion in the corresponding cylinder. Each cylinder 18 is equipped with an injector 21 to inject a fuel. The gasoline engine 18 uses gasoline as fuel. It is possible to use liquefied petroleum gas (LPG), liquefied natural gas (LNG), and alcohol such as ethanol instead of gasoline as fuel.
It is also possible for the engine system 10 to incorporate a diesel engine instead of the gasoline engine 11. Through the specification of the present invention, the engine system 10 is a gasoline engine system.
The injector 21 injects gasoline as fuel into a combustion chamber 22 formed between the cylinder 18 and the piston 19. In the first embodiment, the gasoline engine 11 is a direct injection type gasoline engine to inject gasoline from the injector 21 into the combustion chamber 22. However, the present invention is not limited by this structure. It is possible to apply the exhaust gas purifying apparatus into a gasoline engine system of pre-mixed combustion type.
The intake air system 14 has an intake air pipe 23 that forms an intake air passage. One end part of the intake air pipe 23 communicates with the engine main system 13. The intake air pipe 23 is equipped with an air filter placed at the end part of the air atmosphere side thereof. After eliminating foreign materials such as dust by the air filter, the air is introduced into the engine main system 13 through the intake air passage in the intake air pipe 23.
The air intake system 14 has a throttle 25. The throttle 25 opens and closes the intake air passage in order to adjust the amount of the intake air flowing in the intake air passage.
An intake air valve (not shown) is placed at the end part of the intake air passage at the combustion chamber 22 side. Opening and closing the intake air valve (not shown) permits and interrupts the air introduction from the intake air passage into the combustion chamber 22.
The exhaust gas system 15 has an exhaust gas pipe 26 that forms an exhaust gas passage. One end part of the exhaust gas pipe 26 communicates with the engine main system 13. The exhaust gas pipe 26 has a muffler 27 placed at the end part of the exhaust gas pipe 26 at the air atmosphere side, namely, opposing the engine main system 13 side.
The exhaust gas emitted from the engine main system 13 is discharged to the outside atmosphere through the exhaust gas passage.
An exhaust gas valve (not shown) is placed at one end part of the exhaust gas passage at the combustion chamber 22 side. Opening and closing the exhaust gas valve permits and interrupts the exhaust gas flow from the combustion chamber 22.
The gasoline supply system 16 is equipped with a gasoline tank 28, a supply pipe 29, a pump 31, and an injector 21. The gasoline tank 28 stores gasoline. The gasoline stored in the gasoline tank 28 is injected through the injector 21 into the combustion chamber 22. The supply unit 29 connects the gasoline tank 28 and the injector 21. The pump 31 is placed in the supply unit 29 which is placed between the gasoline tank 28 and the injector 21.
The pump 31 sucks the gasoline stored in the gasoline tank 28, and pressurizes and supplies the gasoline into the injector 21. The injector 21 injects the gasoline pumped by the pump 31 as fuel into the combustion chamber 22.
The control unit 17 is an electronic control unit (ECU) capable of controlling the entire of the engine system 10. The engine system 10 comprises the gasoline engine 11 and the exhaust gas purifying apparatus 12 according to the first embodiment of the present invention.
The control unit 17 comprises a microcomputer having a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM) which are omitted from FIG. 2. The control unit 17 communicates with other control units (not shown) incorporated to the engine system 10 through a vehicle local area network (or a vehicle LAN for short, not shown).
The control unit 17 generates drive signals or control signals based on the amount of depression of the accelerator pedal of the vehicle. The control unit 17 then transfers the drive signals to the injector 21 and the throttle 25. The control unit 17 transfers the drive signal to the injector 21 in order to obtain an optimum opening period of time of the injector 21, namely, to obtain an optimum injection amount of the gasoline as the fuel. The control unit 17 transfers the drive signal to the throttle 25 in order to obtain an optimum opening ratio of the throttle 25.
The exhaust gas purifying apparatus 12 is equipped with a three way catalyst unit 32, a temperature sensor 33 (or a catalyst temperature detection means), and a throttle unit 40. In the three way catalyst unit 32, a three way catalyst unit 32 is placed. The control unit 17 in the engine system 10 forms the part of the exhaust gas purifying apparatus 12.
The three way catalyst unit 32, the temperature sensor 33, and the throttle unit 40 are placed in the exhaust gas system 15.
When reaching its activation temperature, the three way catalyst in the three way catalyst unit 32 oxidizes hydro carbon (HC) contained in the exhaust gas into water (H₂O) and carbon dioxide (CO₂). Further, the three way catalyst oxidizes carbon monoxide (CO) contained in the exhaust gas into carbon dioxide (CO₂). Still further, the three way catalyst reduces nitrogen oxide (NOx) contained in the exhaust gas into nitrogen (N₂).
Although the first embodiment uses such a three way catalyst, it is possible to use other catalysts such as ammonia oxidizing catalyst, NOx selective reduction catalyst, or NOx adsorbing catalyst.
The temperature sensor 33 is placed in the exhaust gas pipe 26 in which the three way catalyst unit 32 is also placed. The temperature sensor 33 is comprised of a temperature detection element such as a thermistor. The temperature sensor 33 outputs a detection signal corresponding to the temperature of the three way catalyst unit 32 to the control unit 17.
When receiving the detection signal transferred from the temperature sensor 33, the control unit 17 detects the temperature of the three way catalyst unit 32. Thus, the temperature sensor 33 and the control unit 17 form a catalyst temperature detection means which is used in the claims according to the present invention.
The present invention is not limited by the above structure to detect the temperature of the three way catalyst unit 32 by the temperature sensor 33 mounted to the exhaust gas pipe 26, and the three way catalyst unit 32 is placed in the exhaust gas pipe 26. For example, it is acceptable to place the temperature sensor 33 in the exhaust gas pipe 26, which forms the exhaust gas passage, in order to detect the temperature of the three way catalyst unit 32 based on the detected temperature of the exhaust gas. Still further, it is also acceptable to indirectly detect the temperature of the three way catalyst unit 32 based on the temperature of a cooling water for the engine main system 13.
It is possible to indirectly detect or estimate the temperature of the three way catalyst unit 32 based on the injection amount of gasoline from the injector 21 or based on a correlation between the injection amount of gasoline and the temperature of the exhaust gas.
FIG. 1A is a schematic cross section of a part of the exhaust gas purifying apparatus according to the first embodiment of the present invention. FIG. 1B is a cross section of the part of the exhaust gas purifying apparatus according to the first embodiment along the B-B line in FIG. 1A.
As shown in FIG. 1, the throttle unit 40 is placed at the upstream side of the exhaust gas flowing in the exhaust gas passage 41 which is formed in the exhaust gas pipe 26. The throttle unit 40 has rotary shafts 42 and 43 which penetrate through the exhaust gas pipe 26 in which the exhaust gas passage 41 is formed.
The rotary shafts 42 and 43 penetrate the exhaust gas pipe 26 toward the diameter direction thereof, and further toward the vertical direction of the central axis of the exhaust gas passage 41.
The rotary shafts 42 and 43 form coaxial shafts of a double structure. One rotary shaft 42 and a first valve member 44 are assembled together. The first valve member 44 rotates around the rotary shaft 42. The first valve member 44 opens and closes the exhaust gas passage 41 in the exhaust gas pipe 26 at the engine main body 13 side, opposing to the exhaust gas passage 41 at the three way catalyst unit 32 side.
The first valve member 44 rotates from a first state to a second state, where in the first state, the outer peripheral part 45 of the first valve member 44 is in contacts with the inner wall 46 of the exhaust gas pipe 26 around the rotary shaft 42, and in the second state, the outer peripheral part 45 of the first valve member 44 is approximately in parallel to the central axis of the exhaust gas passage 41. Under the first state of the first valve member 44 where the outer peripheral part 45 of the first valve member 44 is in contact with the inner wall 46 of the exhaust gas pipe 26, a part of the exhaust gas passage 41 at the engine main system 13 side observed from the rotary shaft 42 is closed.
On the other hand, under the second state of the first valve member 44 where the first valve member 44 becomes in parallel to the exhaust gas flow, namely, is positioned approximately in parallel to the central axis of the exhaust gas passage 41, the exhaust gas passage 41 is fully opened, namely, is not closed by the first valve member 44.
The second valve member 47 and the other rotary shaft 43 are assembled together. The second valve member 47 rotates around the rotary shaft 43. The first valve member 44 and the second valve member 47 are independently driven by the control unit 17.
The second valve member 47 rotates from a first state to a second state, where in the first state, the outer peripheral part 48 of the second valve member 47 is closed to the inner wall 46 of the exhaust gas pipe 26 around the rotary shaft 43. In the second state, the outer peripheral part 48 of the second valve member 47 is approximately in parallel to the central axis of the exhaust gas passage 41. Under the first state of the second valve member 47 where the outer peripheral part 48 of the second valve member 47 is closed to the inner wall 46 of the exhaust gas pipe 26, the exhaust gas flows into the outside of the three way catalyst unit 32 in the diameter direction of the exhaust gas pipe 26, namely, the upper stream side in FIG. 1A, through between the inner wall 46 of the exhaust gas pipe 26 and the outer peripheral part 48 of the second valve member 47. In this state, the second valve member 47 becomes in a semi-opening condition to open a part of the exhaust gas passage 41.
On the other hand, under the second state of the second valve member 47 where the outer peripheral part 48 of the second valve member 47 is approximately in parallel to the central axis of the exhaust gas passage 41, the second valve member 47 makes a fully opening condition not to close any part of the exhaust gas passage 41.
The throttle unit 40 has a drive unit 49 (or a throttle drive means shown in FIG. 1B) for driving the first valve member 44 and the second valve member 47.
The drive unit 49 is comprised of an electric motor, for example. This electric motor receives a control signal as an instruction transferred from the control unit 17, and controls the opening condition (namely, between the semi-opening state and the fully opening state) of the first valve member 44 and the second valve member 47 based on the received control signals.
The first valve member 44 and the second valve member 47 are driven independently of each other. That is, the opening state of the first valve member 44 is controlled independently of the opening state of the second valve member 47.
FIG. 3A to FIG. 3C, each shows the opening state of the throttle unit (or the valve) assembled in the exhaust gas purifying apparatus according to the first embodiment of the present invention.
As shown in FIG. 3A, when the first valve member 44 is in the semi-opening state and the second valve member 47 is also in the semi-opening state, the opening state of the throttle unit 40, namely, the inclination of the throttle unit 40 to the central axis of the exhaust gas passage 41 decreases the gas-flow sectional area of the exhaust gas passage 41.
At this time, the first valve member 44 and the second valve member 47 guide the exhaust gas flowing in the exhaust gas passage 41 toward the outer peripheral side in the diameter direction of the three way catalyst unit 32.
The exhaust gas is thereby introduced into a part of the outer end part of the three way catalyst unit 32 in the diameter direction.
As shown in FIG. 3B, when the first valve member 44 is in the semi-opening state, and on the other hand, the second valve member 47 is in the fully opening state, the throttle unit 40 decreases the gas-flow sectional area of the exhaust gas passage 41, but increases the gas-flow sectional area rather than that of the state shown in FIG. 3A where both the first valve member 44 and the second valve member 47 are in the semi-opening state.
In this case, the first valve member 44 and the second valve member 47 guide the exhaust gas flowing in the exhaust gas passage 41 into the upper half area of the three way catalyst unit 32. That is, the exhaust gas is introduced into the upper half area of the three way catalyst unit 32.
Still further, as shown in FIG. 3C, when the first valve member 44 and the second valve member 47 are in the fully opening state, the throttle unit 40 does not decrease the gas-flow sectional area of the exhaust gas passage 41. The exhaust gas flowing through the exhaust gas passage 41 is introduced into the three way catalyst unit 32 along the exhaust gas passage 41 without being obstructed by the first valve member 44 and the second valve member 47. The exhaust gas is therefore introduced into the entire of the three way catalyst unit 32.
Next, a description will now be given of the operation of the exhaust gas purifying apparatus 12 having the above structure with reference to FIG. 4. FIG. 4 is a flow chart of the operation flow of the exhaust gas purifying apparatus according to the first embodiment of the present invention.
When an ignition switch is turned on (step S101), the operation flow goes to step S102. The control unit 17 judges whether or not the gasoline engine 11 is in its starting operation (step S102). By the way, the ignition switch is omitted from the drawings.
When the judgment result in step S102 indicates that the gasoline engine 11 is not in the starting operation, the operation flow goes to step S103. In step S103, the control unit 17 judges whether or not the gasoline engine 11 is now rotating. That is, the control unit 17 judges whether the gasoline engine 11 is in the starting operation which is in an early period of starting the gasoline engine 11, namely, within a predetermined period of time counted from the start of the gasoline engine 11, or the gasoline engine 11 is in a normal operation which has been adequately elapsed after the predetermined period of time has been elapsed after the gasoline engine 11 starts.
When the judgment result in step S103 indicates that the gasoline engine 11 is not rotating, namely, the gasoline engine 11 is not in the normal operation condition, the control unit 17 completes the routine shown in FIG. 4. When the judgment result in step S103 indicates that the gasoline engine 11 is not rotating, the gasoline engine 11 is not in the normal operation although the ignition switch is turned on. Accordingly, this condition indicates that the gasoline engine 11 is not operating and no exhaust gas is emitted from the engine main system 13. The control unit 17 therefore completes the routine shown in FIG. 4.
When the judgment results in step S102 and step S103 indicate that the gasoline engine 11 is in the start operation and the gasoline engine 11 is now rotating, the operation flow goes to step S104. In step S104, the control unit 17 judges whether or not the temperature of the three way catalyst placed in the three way catalyst unit 32 is lower than a predetermined temperature “t”, where the control unit 17 obtains the temperature of the three way catalyst based on a detection signal transferred from the temperature sensor 33.
The predetermined temperature “t” which the control unit 17 uses when the above judgment regarding the temperature of the three way catalyst is an activation temperature of the three way catalyst in the three way catalyst unit 32, for example. That is, the control unit 17 judges in step S104 whether or not the temperature of the three way catalyst is lower than its activation temperature. By the way, when the temperature of the three way catalyst in the three way catalyst unit 32 is detected based on the temperature of the exhaust gas which flows in the exhaust gas passage 41, it is acceptable that the predetermined temperature “t” has a different value of the activation temperature of the three way catalyst in the three way catalyst unit 32. In this case, the predetermined temperature “t” is set in advance based on a relationship between the temperature of the three way catalyst unit 32 and the temperature of the exhaust gas.
The judgment result in step S104 indicates that the temperature of the three way catalyst in the three way catalyst unit 32 is lower than the predetermined temperature “t”, the control unit 17 instructs the first valve member 44 to close (step S105). The control unit 17 then generates and transfers the drive signal to the drive unit 49 in order to drive the first valve member 44. The first valve member 44 is thereby driven so that the outer peripheral part 45 of the first valve member 44 is in contact with the inner wall 46 of the exhaust gas pipe 26 around the rotary shaft 42. As a result, as shown in FIG. 3A, the exhaust gas passage 41 is entered into the semi-opening state where a part of the cross section of exhaust gas passage 41 in the exhaust gas pipe 26 is closed by the first valve member 44.
The control unit 17 drives the first valve member 44 (step S105), and further adjusts the opening ratio of the second valve member 47 in the exhaust gas pipe 26 (step S106).
The control unit 17 outputs the drive signal to the drive unit 49 in order to drive the second valve member 47. The control unit 17 determines the opening ratio of the second valve member 47 according to the temperature of the three way catalyst unit 32 detected in step S104.
For example, when the temperature of the three way catalyst unit 32 is adequately lower than its activation temperature during the period, like the state immediately after the engine main system 13 starts, as shown in FIG. 3A, the control unit 17 instructs the drive unit 49 to rotate the second valve member 47 so that the outer peripheral part 48 of the second valve member 47 is closed to the inner wall 46 of the exhaust gas pipe 26.
On the other hand, the control unit 17 controls the second valve member 47 so that the second valve member 47 rotates from the position shown in FIG. 3A to the position shown in FIG. 3B based on increasing the temperature of the three way catalyst unit 32. In particular, FIG. 3A shows the position of the second valve member 47, in which the outer peripheral part 48 of the second valve member 47 is closed at the inner wall 46 of the exhaust gas pipe 26. FIG. 3B shows the position of the second valve member 47, in which the outer peripheral part 48 of the second valve member 47 reaches the central axis of the exhaust gas passage 41 in the exhaust gas pipe 26.
That is, according to the temperature rise of the three way catalyst in the three way catalyst unit 32, the outer peripheral part 48 of the second valve member 47 is moved from the inner wall 46 side to the central axis of the exhaust gas passage 41. As a result, the gas-flow sectional area of the exhaust gas passage 41 is switched from the state shown in FIG. 3A to the state shown in FIG. 3B. The state shown in FIG. 3A indicates the semi-opening state in which the exhaust gas is introduced into a part of the outer periphery of the three way catalyst unit 32. The state shown in FIG. 3B indicates the half-opening state in which the exhaust gas is introduced into the upper half of the three way catalyst unit 32.
As described above, according to the exhaust gas purifying apparatus of the first embodiment, through the drive unit 49 the control unit 17 controls the first valve member 44 to close the lower half area of the exhaust gas passage 41 shown in FIG. 3A, and further controls the second valve member 47 to close a large part of the exhaust gas passage 41 shown in FIG. 3A.
The exhaust gas flowing in the exhaust gas passage 41 is thereby introduced into a part of the outer periphery of, namely, the upper end part of the three way catalyst unit 32 shown in FIG. 3A. According to increasing the temperature of the three way catalyst unit 32, the control unit 17 drives the second valve member 47 to increase the gas-flow sectional area of the exhaust gas passage 41, without driving the first valve member 44. That is, the first valve member 44 maintains the state to close the lower half part of the exhaust gas passage 41. It is thereby possible to gradually increase the gas-flow sectional area of the exhaust gas passage 41 by shifting the outer peripheral part 48 of the second valve member 47 from the inner wall 26 side to the central axis side of the exhaust gas passage 41 in the exhaust gas pipe 26. As a result, the exhaust gas flowing in the exhaust gas passage 41 is introduced into the three way catalyst in the three way catalyst unit 32 from a part of the upper side to the upper half of the three way catalyst unit 32 according to rotating the second valve member 47.
When the judgment result in step S104 indicates that the temperature of the three way catalyst unit 32 is not less than the predetermined temperature “t”, namely, than its activation temperature, the control unit 17 instructs the drive unit 49 to drive the first valve member 44 and the second valve member 47 to be fully opened (step S109). The control unit 17 outputs the drive signal to the drive unit 49 in order to drive the first valve member 44. The second valve member 47 is positioned on the central axis of the exhaust gas passage 41 because of the temperature rise of the catalyst in the three way catalyst unit 32. The control unit 17 instructs the drive unit 49 to move the first valve member 44 onto the central axis of the exhaust gas passage 41. This control of the control unit 17 makes the state in which the first valve member 44 and the second valve member 47 are positioned on the central axis of the exhaust gas passage 41. As a result, the exhaust gas passage 41 enters the fully-opened state in which the exhaust gas passage 41 is not closed by the first valve member 44 and the second valve member 47. This makes it possible to introduce of the exhaust gas in the exhaust gas passage 41 into the three way catalyst in the three way catalyst unit 32 without any obstacles
After adjusting the opening condition of the first valve member 44 and the second valve member 47 in step S105, step S106, or step S109 according to the temperature of the three way catalyst unit 32, the control unit 17 instructs the injector 21 in the engine main system 13 to inject the gasoline as fuel into the combustion chamber 22 (step S107). Thus, the control unit 17 transfers the drive signal to the injector 21 in order to inject the fuel. When the injector 21 injects the fuel into the combustion chamber 22, the control unit 17 instructs an ignition plug (not shown, or a spark plug) to ignite the fuel in the combustion chamber 22 (step S108).
As described above in detail, the exhaust gas purifying apparatus of the first embodiment has the throttle unit 40 comprised of the first valve member 44 and the second valve member 47. The throttle unit 40 controls the opening state of the first valve member 44 and the second valve member 47 so as to adjust the gas-flow sectional area of the exhaust gas passage 41 and to control the amount of the exhaust gas flowing in the exhaust gas passage 41. In particular, when the temperature of the three way catalyst unit 32 is low, the throttle unit 40 introduces the exhaust gas into a part of the outer periphery side of the three way catalyst unit 32. The throttle unit 40 gradually increases the gas-flow sectional area of the exhaust gas passage 41 according to the temperature rise of three way catalyst unit 32. When the temperature of the three way catalyst unit 32 reaches its activation temperature, the throttle unit 40 fully opens the gas-flow sectional area of the exhaust gas passage 41. That is, the control unit 17 instructs the drive unit 49 to fully open both the first valve member 44 and the second valve member 47 in the exhaust gas passage 41.
FIG. 5A is a diagram showing a relationship between the temperature of the three way catalyst unit 32 and the elapsed period of time counted from the start or re-start of the gasoline engine in the engine main system 13 shown in FIG. 2. FIG. 5B is a diagram showing a relationship between the elapsed period of time counted from the start of the gasoline engine and a concentration of hydro carbon (HC) contained in the exhaust gas emitted from the engine main system 13, one which is equipped with the exhaust gas purifying apparatus according to the first embodiment of the present invention and the other, as a comparison example, is equipped with a conventional exhaust gas purifying apparatus.
According to the exhaust gas purifying apparatus of the first embodiment, the exhaust gas is introduced into a part of the three way catalyst unit 32 when the temperature of the three way catalyst in the three way catalyst unit 32 is low. As a result, as shown in FIG. 5A, when compared with the conventional exhaust gas apparatus which is equipped with no throttle unit 40, the temperature of the three way catalyst in the three way catalyst unit 32 in the exhaust gas purifying apparatus rapidly rises after the engine main system 13 starts. When the temperature of the three way catalyst of the three way catalyst unit 32 reaches the activation temperature, the control unit 17 controls the throttle unit 40 so as to fully open the exhaust gas passage 41, so that the exhaust gas is introduced into the entire of the three way catalyst unit 32. This control decreases the pressure loss of the exhaust gas in the exhaust gas passage 41. The exhaust gas purifying apparatus according to the first embodiment of the present invention provides the function to rapidly rise the temperature of the three way catalyst in the three way catalyst unit 32, and also provides the pressure loss of the exhaust gas without increasing the size of the exhaust gas purifying apparatus. Still further, as shown in FIG. 5B, when compared with the conventional exhaust gas purifying apparatus equipped with no throttle unit, the structure of the exhaust gas purifying apparatus of the first embodiment can decrease the concentration of hydro carbon (HC) contained in the exhaust gas passing through the exhaust gas purifying apparatus even though the gasoline engine in the engine main system 13 is in the initial stage to start.

Second Embodiment

A description will be given of the exhaust gas purifying apparatus according to the second embodiment of the present invention with reference to FIG. 6.
FIG. 6 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the second embodiment of the present invention. As shown in FIG. 6, the exhaust gas purifying apparatus 12 of the second embodiment has a throttle unit 50 instead of the throttle unit 40 according to the first embodiment. The throttle unit 50 of the second embodiment has a pair of the throttle valve members 51 and a pair of valve drive units 52. Each throttle valve member 51 is a plate shape. One end of each throttle valve member 51 is rotatably fixed to the inner wall of the exhaust gas pipe 26. That is, each exhaust gas pipe 26 rotates around a rotary shaft 53. As shown in FIG. 6, each throttle valve member 51 has a movable end part 54 which is extended toward the three way catalyst unit 32 side. According to the rotation of the throttle valve member 51 around the rotary shaft 53, the movable end part 54 moves from the inner side toward the outer side in the diameter of the three way catalyst unit 32.
The valve drive unit 52 rotatably drives the throttle valve member 51 around the rotary shaft 53. The valve drive units 52 serve as the valve drive means which is used in the claims according to the present invention.
As shown in FIG. 6, when the movable end part 54 of the throttle valve member 51 is positioned at the inner side in the diameter direction of the three way catalyst unit 32, the sectional area of the exhaust gas passage 41 is more decreased according to approaching the three way catalyst unit 32.
When the movable end part 54 of the throttle valve member 51 is positioned at the inner side in the diameter direction of the three way catalyst unit 32, the exhaust gas in the exhaust gas passage 41 is introduced into the central part in the diameter direction of the three way catalyst unit 32.
On the other hand, when the movable end part 54 of the throttle valve member 51 is positioned at the outer side in the diameter direction of the three way catalyst unit 32, the movable end part 54 is positioned at the inner wall 46 side of the exhaust gas pipe 26 in which the three way catalyst unit 32 is placed. In this case, the gas-flow sectional area of the exhaust gas passage 41 is more increased according to approaching the three way catalyst unit 32, and the exhaust gas in the exhaust gas passage 41 is introduced into the entire of the three way catalyst unit 32.
In the structure of the exhaust gas purifying apparatus according to the second embodiment of the present invention, the temperature sensor 33 is placed at the upstream side of the throttle unit 50, as shown in FIG. 6, namely, placed at the engine main system 13 side.
When receiving the detection signal transferred from the temperature sensor 33, the control unit 17 estimates the temperature of the three way catalyst in the three way catalyst unit 32 based on the temperature of the exhaust gas flowing in the exhaust gas passage 41 at the upstream side of the throttle unit 50. It is possible to have a structure in which the temperature sensor 33 directly detects the temperature of the three way catalyst in the three way catalyst unit 32, like the structure of the first embodiment.
In the structure of the exhaust gas purifying apparatus according to the second embodiment of the present invention, when the temperature of the three way catalyst in the three way catalyst unit 32 is low, the control unit 17 controls the valve drive unit 52 to move the movable end part 54 of the throttle valve member 51 toward the central part of the three way catalyst unit 32. The exhaust gas flowing in the exhaust gas passage 41 is introduced into a part of the central part of the three way catalyst unit 32 in the diameter direction of the three way catalyst unit 32. According to the temperature rise of the three way catalyst unit 32, the control unit 17 controls the valve drive unit 52 to drive the movable end part 54 of the throttle valve member 51 toward the outer part of the three way catalyst unit 32 in its diameter direction. Therefore the sectional area of the three way catalyst unit 32 to introduce the exhaust gas is increased according to the temperature rise of the three way catalyst unit 32.
In the structure of the exhaust gas purifying apparatus according to the second embodiment of the present invention, when the temperature of the three way catalyst in the three way catalyst unit 32 is low, the exhaust gas is introduced into the central part of the three way catalyst unit 32 by the throttle valve member 51. The central part of the three way catalyst unit 32 is heated by the introduced exhaust gas. This promotes a partial heating of the three way catalyst in the three way catalyst unit 32. As a result, specified materials such as HC, CO, and NOx contained in the exhaust gas are oxidized or reduced at the central part of the three way catalyst unit 32. Introducing the exhaust gas into the central part of the three way catalyst in the three way catalyst unit 32 decreases the amount of thermal discharge from the outer peripheral wall of the exhaust gas pipe 26. For example, the exhaust gas pipe 26 is made of stainless steel having a relatively high thermal conductivity. On the other hand, the three way catalyst unit 32 is supported in a filter made of ceramics. In general, ceramics have a low thermal conductivity. For this reason, the central part of the three way catalyst unit 32 has a high heat insulating capability when compared with the outer peripheral part thereof. As a result, the exhaust gas introduced into the three way catalyst unit 32 rapidly heats the three way catalyst in the three way catalyst unit 32. Accordingly, it is hard to decrease the temperature at the central part of the three way catalyst unit 32. This provides the rapid increase of the temperature of the three way catalyst in the three way catalyst unit 32 to its activation temperature. This enables the specified materials such as HC, CO, and NOx contained in the exhaust gas to be eliminated. The specified materials are generally contained in the exhaust gas from early period of starting the gasoline engine 11 in the engine main system 13.
The throttle valve member 51 moves toward the inner wall 46 side of the exhaust gas pipe 26 according to increasing the temperature of the three way catalyst unit 32 in order to expand the gas-flow sectional area of the exhaust gas passage 41. The exhaust gas flowing in the exhaust gas passage 41 is introduced into the entire part of the three way catalyst unit 32 when the temperature of the three way catalyst unit 32 reaches its activation temperature. This can decrease the pressure loss of the exhaust gas, like the structure of the exhaust gas purifying apparatus according to the first embodiment.

Third Embodiment

A description will be given of the exhaust gas purifying apparatus according to the third embodiment of the present invention with reference to FIG. 7.
FIG. 7 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the third embodiment of the present invention. As shown in FIG. 7, the exhaust gas purifying apparatus of the third embodiment has a throttle unit 60 instead of the throttle units 40 and 50 of the first and second embodiments.
The throttle unit 60 has a pair of throttle valve members 61. Each throttle valve member 61 has a bimetal 62. The bimetal 62 drives the corresponding throttle valve member 61. The bimetal 62 is deformed according to the temperature change of the exhaust gas. That is, the deformation of the bimetal 62 drives a movable end part 64 of the throttle valve member 61 from the central part toward the outer part of the three way catalyst unit 32. That is, the bimetal 62 serves as a valve drive member which will be used in the claims according to the present invention.
The throttle valve member 61 is driven by the bimetal 62. The temperature of the three way catalyst unit 32 correlates with the temperature of the exhaust gas. That is, the temperature of the three way catalyst of the three way catalyst unit 32 is low when the temperature of the exhaust gas is low in early period of starting the engine main system 13. On the other hand, the temperature of the three way catalyst of the three way catalyst unit 32 and the temperature of the exhaust gas become high when the engine main system 13 is stably operating.
Because of deforming the bimetal 62 according to the temperature change of the exhaust gas, the movable end part 64 of the throttle valve member 61 is positioned at the central part side of the three way catalyst unit 32 when the temperature of the exhaust gas is low, and positioned at the outer peripheral side of the three way catalyst unit 32 when the temperature of the exhaust gas is high.
In the structure of the exhaust gas purifying apparatus of the third embodiment, the temperature sensor 33 is placed at the upstream side (or at the gasoline engine side) of the throttle unit 60, like the structure of the second embodiment. It is also possible to have another structure in which the temperature sensor is placed in the three way catalyst unit 32 in order to directly detect the temperature of the three way catalyst unit 32.
In the structure of the third embodiment, the deformation of the bimetal 62 drives the throttle valve member 61. The structure of the third embodiment can eliminate the power source to drive the throttle valve member 61 such as a throttle valve drive unit.

Fourth Embodiment

A description will be given of the exhaust gas purifying apparatus according to the fourth embodiment of the present invention with reference to FIG. 8.
FIG. 8 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the fourth embodiment of the present invention. As shown in FIG. 8, the exhaust gas purifying apparatus of the fourth embodiment has a throttle unit 70 instead of the throttle units 40, 50, 60 of the first to third embodiments. As shown in FIG. 8, the throttle unit 70 has a pair of elastic members 72. Each elastic member 72 supports a corresponding throttle valve member 71. The elastic member 72 is made of a spring, for example. One end of the elastic member 72 is fixed to the throttle valve member 71, and the other end of the elastic member 72 is connected to the inner wall of the exhaust gas pipe 26. The elastic member 72 gently presses the throttle valve member 71 to the inner wall of the exhaust gas pipe 26. One end of the throttle valve member 71 is fixed to the exhaust gas pipe 26 through a rotary shaft 73. The throttle valve member 71 rotates around the rotary shaft 73.
When the amount of the exhaust gas flowing in the exhaust gas passage 41 is low, a movable end part 74 of the throttle valve member 71 is positioned at the central side of the three way catalyst unit 32 by the pressing force of the elastic member 72. Because the pressing force of the elastic member 72 is relatively small, the movable end part 74 of the throttle valve member 71 is moved from the central side toward the outer peripheral side of the three way catalyst unit 32 when the amount of the exhaust gas flowing in the exhaust gas passage 41 is increased. That is, the elastic member 72 serves as the valve drive means which is used in the claims according to the present invention.
The amount of the exhaust gas is changed according to the load of the engine main system 13. The more the load of the engine main system 13 increases, the more the amount of the exhaust gas increases. In addition, the more the load of the engine main system 13 increases, the more the temperature of the exhaust gas rises. As a result, the more the load of the engine main system 13 increases, the more the temperature of the three way catalyst in the three way catalyst unit 32 rises. That is, the flow rate of the exhaust gas correlates with the temperature of the three way catalyst in the three way catalyst unit 32. Accordingly, when the gas flow rate of the exhaust gas is low, the temperature of the three way catalyst unit 32 is also low.
In the structure of the exhaust gas purifying apparatus of the fourth embodiment, the temperature sensor 33 is placed at the upstream side of the throttle unit 70, like the structure of the second embodiment. It is acceptable to place the temperature sensor 33 to the three way catalyst unit 32 in order to directly detect the temperature of the three way catalyst unit 32.
In the structure of the exhaust gas purifying apparatus of the fourth embodiment, when the gas flow rate of the exhaust gas is low, namely, when the temperature of the three way catalyst in the three way catalyst unit 32 is low, the movable end part 74 of the throttle valve member 71 in the throttle unit 70 is moved toward the central side of the three way catalyst unit 32.
When the temperature of the three way catalyst unit 32 is low, the exhaust gas is introduced into the central part of the three way catalyst unit 32 by the throttle unit 70. According to increasing the flow rate of the exhaust gas, the movable end part 74 of the throttle valve member 71 is gradually moved from the central side toward the outer peripheral side of the three way catalyst unit 32. This operation of the movable end part 74 of the throttle valve member 71 expands the gas-flow sectional area in the exhaust gas passage 41. Thus, the structure of the exhaust gas purifying apparatus of the fourth embodiment changes the gas-flow sectional area in the exhaust gas passage 41 according to the gas flow rate of the exhaust gas without using any power source to drive the throttle unit 70 such as a valve drive unit. The adjustment of the gas-flow sectional area of the exhaust gas passage 41 can promote heating of the central part of the three way catalyst unit 32 when the gas flow rate of the exhaust gas in the exhaust gas passage 41 is low.

Fifth Embodiment

A description will be given of the exhaust gas purifying apparatus according to the fifth embodiment of the present invention with reference to FIG. 9.
FIG. 9 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the fifth embodiment of the present invention. As shown in FIG. 9, a throttle unit 80 is placed, at the downstream side of the three way catalyst unit 32, in the flow direction of the exhaust gas in the exhaust gas passage 41. Closing a part of the gas-flow sectional area in the exhaust gas passage 41 by the throttle unit 80 generates a pressure difference in the gas-flow sectional area of the exhaust gas passage 41. This pressure difference allows the exhaust gas to mainly flow the part of the three way catalyst unit 32, which is not closed by the throttle unit 80. Thus, the structure of the exhaust gas purifying apparatus of the fifth embodiment, in which the throttle unit 80 is placed at the downstream side of the three way catalyst unit 32, controls the flow of the exhaust gas in the three way catalyst unit 32.
In the structure of the exhaust gas purifying apparatus of the fifth embodiment, the throttle unit 80 has a first valve member 81 and a second valve member 82. The first valve member 81 and the second valve member 82 are independently driven around rotary shafts 83 and 84.
When both the first valve member 81 and the second valve member 82 are positioned at the central axis along the longitudinal direction of the exhaust gas passage 41, namely, positioned in parallel to the exhaust gas flow, the throttle unit 80 enters the fully opening state in which both the first valve member 81 and the second valve member 82 do not close the gas-flow sectional area of the exhaust gas passage 41. In that case, the exhaust gas is introduced into the entire of the three way catalyst unit 32.
It is so designed that the outer diameter of the first valve member 81 is smaller than the inner diameter of the exhaust gas passage 41. This structure forms a gas-flow passage between an end part 85 of the first valve member 81 and the inner wall 46 of the exhaust gas pipe 26 when the first valve member 81 is positioned to be approximately perpendicular to the central axis of the exhaust gas passage 41.
When both the first valve member 81 and the second valve member 82 are positioned to be approximately perpendicular to the central axis of the exhaust gas passage 41, the exhaust gas flowing in the exhaust gas passage 41 is introduced into a part of the outer peripheral side of the three way catalyst unit 32, namely, into the upper side of the exhaust gas passage 41 shown in FIG. 9. As a result, this can promote heating of the outer peripheral part of the three way catalyst unit 32 through which the exhaust gas mainly flows.
In the structure of the exhaust gas purifying apparatus of the fifth embodiment, as shown in FIG. 9, the temperature sensor is placed at the downstream side of the throttle unit 80, namely, at the opposite side of the engine main system 13. The control unit 17 receives the detection signal transferred from the temperature sensor 33, and estimates the temperature of the three way catalyst in the three way catalyst unit 32 based on the received detection signal which indicates the temperature of the exhaust gas flowing in the exhaust gas passage 41 at the downstream side of the throttle unit 80.
It is also possible to have a structure in which the temperature sensor 33 directly detects the temperature of the three way catalyst in the three way catalyst unit 32, like the structure of the first embodiment.
The structure of the exhaust gas purifying apparatus of the fifth embodiment controls the gas-flow sectional area in the exhaust gas passage 41 for the exhaust gas at the downstream side of the three way catalyst unit 32. The structure of the exhaust gas purifying apparatus of the fifth embodiment enables the exhaust gas to be introduced into the entire surface of the three way catalyst unit 32 at the upstream side of the three way catalyst unit 32. Because the structure of the fifth embodiment increases the contact area of the exhaust gas with the three way catalyst in the three way catalyst unit 32, it is possible to increase the function to purify specified materials such as HC, CO, and NOx contained in the exhaust gas even if the flow rate of the exhaust gas is low.

Sixth Embodiment

A description will be given of the exhaust gas purifying apparatus according to the sixth embodiment of the present invention with reference to FIG. 10.
FIG. 10 is a schematic cross section of a part of the exhaust gas purifying apparatus according to the sixth embodiment of the present invention. The structure of the sixth embodiment is a modification of the structure of the first embodiment.
As shown in FIG. 10, an exhaust gas heating unit 90 is placed at the upstream side of the three way catalyst unit 32 in the exhaust gas purifying apparatus, namely, at the engine main system 13 side. The exhaust gas heating unit 90 has an electrical heater unit or a burner The control unit 17 instructs the exhaust gas heating unit 90 to heat the exhaust gas when the temperature of the three way catalyst unit 32 is low. Thus, the exhaust gas heating unit 90 heats the exhaust gas to be introduced into the three way catalyst in the three way catalyst unit 32.
Thus, supplying the high-temperature exhaust gas heated by the exhaust gas heating unit 90 into the three way catalyst unit 32 can rapidly increase the temperature of the three way catalyst in the three way catalyst unit 32. Because the exhaust gas purifying apparatus of the sixth embodiment has the exhaust gas heating unit 90 to directly heat the exhaust gas in the exhaust gas passage 41, the exhaust gas heated by the exhaust gas heating unit 90 is introduced into the three way catalyst unit 32. Because this structure can provide rapidly increasing the temperature of the three way catalyst in the three way catalyst unit 32 from early period of starting the engine main system 13, it is possible to purify specified materials such as HC, CO, and NOx contained in the exhaust gas from early period of starting the engine main system 13.
In the structure of the exhaust gas purifying apparatus of the sixth embodiment, the exhaust gas heating unit 90 is added into the structure of the first embodiment. The present invention is not limited by this case, for example, it is possible to add the exhaust gas heating unit 90 into each of the structure of the exhaust gas purifying apparatus of each of the second to fifth embodiments.

(Other Modifications)

The present invention is not limited by the structures of the exhaust gas purifying apparatus according to the first to sixth embodiments described before. For example, it is acceptable to place a plurality of the temperature sensors 33 at the upstream side and downstream side observed from the three way catalyst unit 32 along the exhaust gas flow in the exhaust gas passage 41 in the exhaust gas pipe 26. In this structure, the control unit 17 estimates the temperature of the three way catalyst in the three way catalyst unit 32 based on the correlation between the temperature of each temperature sensor and the temperature of the three way catalyst in the three way catalyst unit 32.

Features and Effects of the Present Invention

In the exhaust gas purifying apparatus as another aspect of the present invention, the throttle unit decreases a gas-flow sectional area of the exhaust gas passage in the exhaust gas pipe. The throttle unit introduces the exhaust gas flowing in the exhaust gas passage into the part of the catalyst. This structure enables the temperature of the catalyst to rapidly rise within a short period of time counted from the internal combustion engine start.
In the exhaust gas purifying apparatus as another aspect of the present invention, the throttle unit increases the gas-flow sectional area of the exhaust gas passage according to the temperature rise of the catalyst detected by the catalyst temperature detection means. This structure enables the catalyst to receive a large amount of the exhaust gas from the internal combustion engine according to the temperature rise of the internal combustion engine after this engine starts or re-start, and the temperature rise of the catalyst. The exhaust gas adequately warms the catalyst until the temperature of the catalyst reaches its activation temperature. Therefore it is not necessary to have a large size of the catalyst unit for a large amount of the catalyst in order to completely purify the exhaust gas. This structure can decrease specified materials such as HC, CO, and NOx contained in the exhaust gas emitted from the internal combustion engine without increasing the pressure loss of the exhaust gas and also without increasing the size of the exhaust gas purifying apparatus.
In the exhaust gas purifying apparatus as another aspect of the present invention, the throttle unit gradually increases the gas-flow cross section of the exhaust gas passage from the outer peripheral side toward the inner side of the catalyst unit along a diameter direction of the catalyst unit according to the temperature rise of the catalyst in the catalyst unit. Still further, the throttle unit has a rotary shaft, a first valve member, a second valve member, a throttle drive means. The rotary shaft is placed in the diameter direction of the exhaust gas passage in the exhaust gas pipe. The first valve member rotates around the rotary shaft to open and close the exhaust gas passage at the upstream side of the rotary shaft in the upstream side of the catalyst unit. The second valve member rotates around the rotary shaft to open and close the exhaust gas passage at the downstream side of the rotary shaft in the upstream side of the catalyst unit. The throttle drive means independently drives the first valve member and the second valve member. The above simple structure of the exhaust gas purifying apparatus makes the exhaust gas flow in the outer peripheral side of the catalyst in the diameter direction. Thus, it is possible to forcedly introduce the exhaust gas into the part of the catalyst with the simple structure of thee exhaust gas purifying apparatus, and possible to increase the temperature of the catalyst within a short period of time counted from the internal combustion engine start.
In the exhaust gas purifying apparatus as another aspect of the present invention, the throttle unit expands the gas-flow sectional area of the exhaust gas passage from the central side toward the outer peripheral side in the diameter direction of the catalyst unit according to increasing the temperature of the catalyst. Still further, the throttle unit has a throttle member and a valve drive means. The throttle member expands from the inner wall of the exhaust gas pipe toward the catalyst unit side. The valve drive means drives the throttle member between the central side and the outer peripheral side in the diameter direction of the catalyst unit.
In the structure of the exhaust gas purifying apparatus, the throttle unit expands the gas-flow sectional area of the exhaust gas passage from the central side toward the outer peripheral side of the catalyst in the diameter direction of the catalyst unit according to the temperature rise of the catalyst. That is, during the low temperature of the catalyst, the throttle unit introduces the exhaust gas into the central part in the diameter direction of the catalyst unit. A large part of the exhaust gas is mainly supplied into the central part of the catalyst in the catalyst unit. The heat energy of the exhaust gas is transmitted to the central part of the catalyst. Therefore, it is difficult to discharge the heat energy of the central part of the catalyst toward the outside of the catalyst unit through the outer peripheral side of the catalyst unit. As a result, this structure of the exhaust gas purifying apparatus according to the present invention promotes the temperature rise of the catalyst. It is therefore possible to increase the temperature of the catalyst within a short period of time counted from the re-start or start of the internal combustion engine.
The exhaust gas purifying apparatus as another aspect of the present invention, further has an exhaust gas heating means that is placed at the upstream side of the catalyst unit in order to heat the exhaust gas before it reaches the catalyst unit. This exhaust gas heating means heats the exhaust gas before the supply to the catalyst. The heated exhaust gas flowing into the catalyst further promotes to increase the temperature of the catalyst. Therefore it is possible to increase the temperature of the catalyst within a short period of time counted from the internal combustion engine start.
While specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limited to the scope of the present invention which is to be given the full breadth of the following claims and all equivalent thereof.

Claims

1. An exhaust gas purifying apparatus comprising:

an exhaust gas pipe that forms an exhaust gas passage in which an exhaust gas emitted from an internal combustion engine flows;

a catalyst unit having a catalyst placed in the exhaust gas passage;

catalyst temperature detection means capable of detecting a temperature of the catalyst placed in the catalyst unit; and

a throttle unit, placed in at least one of an upstream side and an downstream side of the catalyst unit, capable of introducing the exhaust gas flowing in the exhaust gas passage into a part of the catalyst unit when the temperature of the catalyst detected by the catalyst temperature detection means is lower than an activation temperature of the catalyst.

2. The exhaust gas purifying apparatus according to claim 1, wherein the throttle unit decreases a gas-flow sectional area of the exhaust gas passage in the exhaust gas pipe.

3. The exhaust gas purifying apparatus according to claim 2, wherein the throttle unit increases the gas-flow sectional area of the exhaust gas passage according to the temperature rise of the catalyst detected by the catalyst temperature detection means.

4. The exhaust gas purifying apparatus according to claim 3, wherein the throttle unit gradually increases the gas-flow cross section of the exhaust gas passage from the outer peripheral side toward the inner side of the catalyst unit along a diameter direction of the catalyst unit according to the temperature rise of the catalyst in the catalyst unit.

5. The exhaust gas purifying apparatus according to claim 4, wherein the throttle unit comprises:

a rotary shaft placed in the diameter direction of the exhaust gas passage in the exhaust gas pipe;

a first valve member that rotates around the rotary shaft to open and close the exhaust gas passage at the upstream side of the rotary shaft in the upstream side of the catalyst unit;

a second valve member that rotates around the rotary shaft to open and close the exhaust gas passage at the downstream side of the rotary shaft in the upstream side of the catalyst unit; and

a throttle drive means that independently drives the first valve member and the second valve member.

6. The exhaust gas purifying apparatus according to claim 3, wherein the throttle unit expands the gas-flow sectional area of the exhaust gas passage from the central side toward the outer peripheral side in the diameter direction of the catalyst unit according to the temperature rise of the catalyst.

7. The exhaust gas purifying apparatus according to claim 6, wherein the throttle unit comprises:

a throttle member that expands from the inner wall of the exhaust gas pipe toward the catalyst unit side; and

a valve drive means that drives the throttle member between the central side and the outer peripheral side in the diameter direction of the catalyst unit.

8. The exhaust gas purifying apparatus according to claim 1, further comprising an exhaust gas heating means that is placed at the upstream side of the catalyst unit in order to heat the exhaust gas before it reaches the catalyst unit.

9. The exhaust gas purifying apparatus according to claim 1, further comprising a control means capable of controlling the operation of the throttle unit, wherein the control means is an electronic control unit composed a microcomputer that comprises a central control unit, a read only memory, and a random access memory.

10. The exhaust gas purifying apparatus according to claim 1, wherein the catalyst is a three way catalyst placed in the catalyst unit.