EP1703116A2

EP1703116A2 - Exhaust gas recirculation unit for internal combustion engine

Info

Publication number: EP1703116A2
Application number: EP06005000A
Authority: EP
Inventors: Tadashi Toda
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2005-03-15
Filing date: 2006-03-10
Publication date: 2006-09-20
Anticipated expiration: 2026-03-10
Also published as: CN1834440A; JP2006257905A; EP1703116A3; CN100570148C; EP1703116B1; JP4297067B2

Abstract

An exhaust gas recirculation unit (10) has a catalyst portion (14) removing hydrocarbon by oxidation in an exhaust gas recirculation pipe (12) recirculating exhaust gas from an internal combustion engine into an intake pipe. The catalyst portion (14) is provided in contact with an external surface of an exhaust pipe (20) of the internal combustion engine.

Description

This nonprovisional application is based on Japanese Patent Application No. 2005-073080 filed with the Japan Patent Office on March 15, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an exhaust gas recirculation unit for an internal combustion engine.

Description of the Background Art

An exhaust gas recirculation unit (hereinafter referred to as an EGR unit) is a known unit recirculating exhaust gas emitted from a combustion chamber of an internal combustion engine to an exhaust pipe into an intake pipe to suppress an increase in combustion temperature in order to reduce nitrogen oxides in the exhaust gas formed when the internal combustion engine is in operation. When such an EGR unit is employed, the increase in combustion temperature can be suppressed, and formation of nitrogen oxides can be reduced. On the other hand, the amount of unburned hydrocarbon contained in the exhaust gas is increased, and the hydrocarbon deposits on components of the EGR unit, deteriorating the components. Consequently, an EGR unit provided with a catalyst for removing hydrocarbon by oxidation has been proposed as disclosed for example in Japanese Patent Laying-Open No. 11-125148 .
However, when a catalyst has a low temperature and is not activated as in cold start, unburned hydrocarbon cannot fully be removed by oxidation. To cope with such a problem, a technique of increasing the temperature of a catalyst for example by providing a heater for heating the catalyst has been proposed. In this case, however, the number of components is increased, causing new problems such as an increase in the size of the EGR unit and an increase in cost.

SUMMARY OF THE INVENTION

The present invention has been made in view of these circumstances, and one object of the present invention is to provide an exhaust gas recirculation unit capable of quickly increasing the temperature of a catalyst with a simple structure.
The present invention is an exhaust gas recirculation unit having a catalyst portion removing hydrocarbon by oxidation in an exhaust gas recirculation pipe recirculating exhaust gas from an internal combustion engine into an intake pipe, the catalyst portion being provided in contact with an external surface of an exhaust pipe of the internal combustion engine.
With this structure, the catalyst portion removing hydrocarbon by oxidation is in contact with the external surface of the exhaust pipe of the internal combustion engine. Accordingly, the catalyst portion directly receives heat from the external surface of the hot exhaust pipe heated by hot exhaust gas emitted from a combustion chamber. Therefore, the temperature of a catalyst can be increased quickly with a simple structure.
Preferably, the catalyst portion is provided in contact with an upper portion of the external surface of the exhaust pipe.
With this structure, since the catalyst portion is attached to the upper portion of the external surface of the exhaust pipe, that is, the portion releasing the greatest amount of heat in the external surface of the exhaust pipe, the temperature of a catalyst can be increased efficiently.
More preferably, the catalyst portion is provided in contact with an external surface of an exhaust manifold of the internal combustion engine.
With this structure, the catalyst portion is in contact with the external surface of the exhaust manifold located at the uppermost stream of the exhaust pipe of the internal combustion engine. In other words, the catalyst portion is in contact with a portion of the exhaust pipe having the greatest temperature. Consequently, the temperature of a catalyst can be increased more quickly.
When a catalyst portion is provided in contact with an external surface of an exhaust manifold of an internal combustion engine, if the catalyst portion is disposed at a position where branch pipes constituting the exhaust manifold are independently provided, some section of the catalyst portion is in contact with the exhaust manifold, and some section of the catalyst portion is not in contact with the exhaust manifold. In this case, the section of the catalyst portion not in contact with the exhaust manifold is hard to heat in comparison with the section in contact with the exhaust manifold, and thus it becomes difficult to heat the entire catalyst portion uniformly.
Consequently, more preferably, the catalyst portion is provided in contact with an external surface of a connected portion where branch pipes constituting the exhaust manifold are connected. As a result, the catalyst portion is in contact with the exhaust manifold evenly, and thus the entire catalyst portion can be heated uniformly.
More preferably, the catalyst portion is disposed with its longitudinal direction oriented substantially perpendicular to a direction in which the branch pipes extend.
With this structure, a larger contact area between the catalyst portion and the exhaust manifold can be obtained, and the entire exhaust gas recirculation unit can be designed compactly.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a plan view of an exhaust gas recirculation unit in accordance with the present invention.
Fig. 2 is a side view of the exhaust gas recirculation unit seen from a direction A in Fig. 1.
Fig. 3 is a plan view showing a modification of the exhaust gas recirculation unit in accordance with the present invention.
Fig. 4 is a plan view showing another modification of the exhaust gas recirculation unit in accordance with the present invention.
Fig. 5 is a side view showing another modification of the exhaust gas recirculation unit in accordance with the present invention.
Fig. 6 is a side view showing another modification of the exhaust gas recirculation unit in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, an exhaust gas recirculation unit (hereinafter referred to as an EGR unit) 10 in accordance with an embodiment of the present invention will be described with reference to Figs. 1 and 2.
As shown in Fig. 1, an exhaust pipe 20 includes an exhaust manifold 22.
Exhaust manifold 22 is a manifold having a branch pipe portion 22a including branch pipes 22a1 to 22a4, and a connected portion 22b where branch pipes 22a1 to 22a4 are connected. Exhaust manifold 22 guides exhaust gas from a combustion chamber of an internal combustion engine not shown to the downstream side of exhaust pipe 20. In the present embodiment, exhaust manifold 22 is made of an iron-based material. A turbo charger now shown is connected to a position downstream of exhaust pipe 22.
As shown in Fig. 1, EGR unit 10 includes an exhaust gas recirculation pipe (hereinafter referred to as an EGR pipe) 12, a catalyst portion 14, an EGR cooler not shown, and the like.
One end of EGR pipe 12 on the upstream side of the exhaust gas is connected to exhaust manifold 22, and the other end of EGR pipe 12 on the downstream side of the exhaust gas is connected to an intake pipe not shown. Consequently, exhaust manifold 22 is connected to the intake pipe.
EGR pipe 12 is provided with catalyst portion 14 for removing unburned hydrocarbon emitted from the combustion chamber by oxidation. As shown in Fig. 1, catalyst portion 14 has a cylindrical shape extending in a direction of an axis of EGR pipe 12 (in a direction indicated by an arrow C), and is provided in contact with an external surface of connected portion 22b of exhaust manifold 22 with its longitudinal direction (the direction indicated by arrow C) oriented perpendicular to a direction in which branch pipes 22a1 to 22a4 of exhaust manifold 22 extend (a direction indicated by an arrow M). Catalyst portion 14 includes a cylindrical cover 14a containing a noble metal catalyst not shown, a bracket 14b for securing cover 14a to exhaust manifold 22, and a bolt 14c for securing bracket 14b to exhaust manifold 22. Cover 14a is secured to exhaust manifold 22 via bracket 14b by fastening bolt 14c into a bolt hole not shown formed in exhaust manifold 22.
Specifically, as shown in Fig. 2, bracket 14b has a semicircular concave shape to fit with the shape of a lower portion of cylindrical cover 14a. With this structure, cover 14a of catalyst portion 14 is attached in contact with an upper portion of the external surface of exhaust manifold 22. Cover 14a, bracket 14b, and bolt 14c constituting catalyst portion 14 and EGR pipe 12 are all made of an iron-based material. In the present embodiment, a noble metal catalyst which is activated at a high temperature and has an improved capability of removing hydrocarbon by oxidation is employed as a catalyst provided within catalyst portion 14.
A description will now be given on a function of exhaust gas recirculation unit 10 in accordance with the present invention.
When the internal combustion engine starts operation, hot exhaust gas emitted from the combustion chamber is discharged to exhaust manifold 22. The hot exhaust gas heats exhaust manifold 22 to increase its temperature. In particular, because of heat transfer within exhaust manifold 22, the upper portion of the external surface of exhaust manifold 22 releases more heat than the other portion thereof. Since catalyst portion 14 is in contact with the upper portion of the external surface of exhaust manifold 22, the temperature of catalyst portion 14 also increases quickly with an increase in the temperature of exhaust manifold 22.
According to the present embodiment described above, the following effects can be obtained.

(1) As shown in Figs. 1 and 2, cover 14a of catalyst portion 14 removing hydrocarbon by oxidation is provided in contact with the external surface of exhaust manifold 22 of the internal combustion engine. Accordingly, cover 14a directly receives heat from the external surface of exhaust manifold 22 having the highest temperature in the hot exhaust pipe heated by the hot exhaust gas emitted from the combustion chamber. Therefore, the temperature of a catalyst can be increased quickly with a simple structure.
(2) Since catalyst portion 14 is attached to the upper portion of the external surface of exhaust manifold 22, that is, the portion releasing the greatest amount of heat in the external surface of exhaust manifold 22, the temperature of a catalyst can be increased effectively.
(3) When a catalyst portion is provided in contact with an external surface of an exhaust manifold of an internal combustion engine, if the catalyst portion is disposed at a position where branch pipes constituting the exhaust manifold are independently provided, some section of the catalyst portion is in contact with the exhaust manifold, and some section of the catalyst portion is not in contact with the exhaust manifold. In this case, the section of the catalyst portion not in contact with the exhaust manifold is hard to heat in comparison with the section in contact with the exhaust manifold, and thus it becomes difficult to heat the entire catalyst portion uniformly.
In contrast, according to the present embodiment, catalyst portion 14 is in contact with the external surface of connected portion 22b where branch pipes 22a1 to 22a4 constituting exhaust manifold 22 are connected, as shown in Figs. 1 and 2. Accordingly, catalyst portion 14 is in contact with exhaust manifold 22 evenly, and thus entire catalyst portion 14 can be heated uniformly.
(4) Catalyst portion 14 is disposed with its longitudinal direction oriented substantially perpendicular to the direction in which branch pipes 22a1 to 22a4 extend. With this structure, a larger contact area between catalyst portion 14 and exhaust manifold 22 can be obtained, and entire exhaust gas recirculation unit 10 can be designed compactly.
(5) Since the external surface of exhaust manifold 22, which becomes hot when the internal combustion engine is in operation, is in contact with catalyst portion 14, which also becomes hot, these hot portions are located in one place. This can simplify a countermeasure for preventing surrounding components from being damaged by heat, for example by means of a heat shield.

It is to be noted that the present embodiment described above can be modified as will be described below.
The manner in which catalyst portion 14 is attached is not limited to the manner illustrated in the above embodiment, specifically, the manner in which cover 14a is secured to exhaust manifold 22 via bracket 14b. Cover 14a may be provided in contact with the external surface of exhaust manifold 22 without a bracket, for example by securing bracket 14b attached to cover 14a to a position other than exhaust manifold 22 such as a cylinder head. In this case, heat transfer from the external surface of exhaust manifold 22 to the catalyst within cover 14a is more directly performed, increasing the temperature of the catalyst more quickly.
The direction in which catalyst portion 14 is attached is not limited to the direction illustrated in the above embodiment, specifically, the direction such that catalyst portion 14 is disposed with its longitudinal direction oriented substantially perpendicular to the direction in which branch pipes 22a1 to 22a4 extend. For example, catalyst portion 14 may be disposed with its longitudinal direction oriented along the direction in which branch pipes 22a1 to 22a4 extend.
The position to which catalyst portion 14 is attached is not limited to the position illustrated in the above embodiment, specifically, connected portion 22b where branch pipes 22a1 to 22a4 constituting exhaust manifold 22 are connected. For example, as shown in Fig. 3, catalyst portion 14 may be attached to a position closer to the upstream side of the exhaust gas than connected portion 22b and having independently provided branch pipes 22a1 to 22a4 constituting an exhaust manifold 22A. Further, as shown in Fig. 4, catalyst portion 14 may partially be deviated from an upper portion of an external surface of an exhaust manifold 22B. The temperature of a catalyst can also be increased in these cases, via a portion in contact with exhaust manifolds 22A and 22B.
The position to which catalyst portion 14 is attached is not limited to the position illustrated in the above embodiment, specifically, the upper portion of the external surface of exhaust manifold 22. The position to which catalyst portion 14 is attached may be altered as described below, depending on the layout of an internal combustion engine or the like. For example, as shown in Fig. 5, catalyst portion 14 may be attached in contact with a lower portion of an external surface of an exhaust manifold 22C. Further, as shown in Fig. 6, catalyst portion 14 may be attached in contact with a side portion of an external surface of an exhaust manifold 22D. It is desirable to attach catalyst portion 14 to the most appropriate position on an external surface of an exhaust manifold, taking the amount of heat that catalyst portion 14 receives from exhaust manifold 22, a restriction on the layout of an internal combustion engine, and the like into consideration.
The position to which catalyst portion 14 is attached is not limited to the position illustrated in the above embodiment, specifically, the external surface of exhaust manifold 22. For example, it may be attached to a position in exhaust pipe 20 other than exhaust manifold 22. In short, catalyst portion 14 can be any portion as long as it is provided in contact with the external surface of exhaust pipe 20 of the internal combustion engine.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

An exhaust gas recirculation unit having a catalyst portion removing hydrocarbon by oxidation in an exhaust gas recirculation pipe recirculating exhaust gas from an internal combustion engine into an intake pipe,
characterized in that
said catalyst portion is provided in contact with an external surface of an exhaust pipe of said internal combustion engine.
The exhaust gas recirculation unit according to claim 1, wherein said catalyst portion is provided in contact with an upper portion of the external surface of said exhaust pipe.
The exhaust gas recirculation unit according to claim 1, wherein said catalyst portion is provided in contact with an external surface of an exhaust manifold of said internal combustion engine.
The exhaust gas recirculation unit according to claim 3, wherein said catalyst portion is provided in contact with an external surface of a connected portion where branch pipes constituting said exhaust manifold are connected.
The exhaust gas recirculation unit according to claim 3 or 4, wherein said catalyst portion is disposed with its longitudinal direction oriented substantially perpendicular to a direction in which said branch pipes extend.