EP1331388A2

EP1331388A2 - Exhaust gas recirculation device for engines

Info

Publication number: EP1331388A2
Application number: EP03001389A
Authority: EP
Inventors: Tomohiro Ohashi; Kazuo Koga
Original assignee: Mitsubishi Motors Corp
Current assignee: Mitsubishi Motors Corp
Priority date: 2002-01-28
Filing date: 2003-01-27
Publication date: 2003-07-30
Anticipated expiration: 2023-01-27
Also published as: EP1331388A3; JP2003214261A; KR20030064630A; DE60302258T2; EP1331388B1; KR100549979B1; JP3988028B2; DE60302258D1

Abstract

An EGR device for engines, capable of recirculating a SOF-removed EGR gas irrespective of the set condition of a catalyst in an exhaust system and without needing to extend an EGR conduit (7) and provide a universal joint; reducing the manufacturing cost in consequence; and preventing the deposition of SOF in an intake air system. The EGR conduit (7) is connected at one end thereof to an exhaust pipe (2C) collected portion of an exhaust manifold (2), and at the other end thereof to an engine-side fixing flange, and a catalyst (6) used exclusively for EGR is provided in the EGR conduit (7). A part of an exhaust gas flowing in the exhaust manifold (2) is recirculated as an EGR gas into the intake air system for an engine via the EGR conduit (7), and, during this time, the SOF contained in the EGR gas is removed by the catalyst (6).

Description

This invention relates to an EGR (EXHAUST GAS RECIRCULATION) device for engines, and more particularly to an EGR device capable of preventing the occurrence of the deposition of SOF (SOLUBLE ORGANIC FRACTION) contained in an EGR gas.

Description of the Related Art

An EGR device adapted to lower a combustion temperature by recirculating a part of an exhaust gas discharged from an engine into an intake air system, and thereby reduce a discharge of NOx (nitrogen oxide) is being used widely in practice. As known well, an exhaust gas contains SOF formed of unburnt fuel and oil as main components, and the SOF recirculated with the EGR gas into the intake air system becomes a factor of the deposition thereof. Therefore, as in the EGR device disclosed in, for example, JP-A-2000-356134, an EGR gas introduction portion of an EGR conduit is connected to a downstream side portion of a proximity catalyst provided in an exhaust manifold-side portion of an exhaust pipe connected to the exhaust manifold, and an exhaust gas introduced into the EGR conduit via this EGR gas introduction portion, i.e. an EGR gas is recirculated into the intake air system via the EGR conduit. In this EGR device, the SOF contained in the EGR gas is removed therefrom by the proximity catalyst, so that the proximity catalyst is needed.
There is a vehicle in which a proximity catalyst is omitted in view of the cost and an engine output. In an EGR device for such a vehicle, an EGR gas is introduced from a downstream side of an underfloor catalyst provided in an underfloor portion of an exhaust pipe and recirculated as disclosed in, for example, JA-P-2000-249003.
However, since the underfloor catalyst is considerably distant from an engine, the extending of an EGR conduit greatly is inevitably needed. Moreover, it becomes necessary that a universal joint, such as bellows and a spherical joint be provided on the EGR conduit so as to avoid the influence of the rolling and vibration of the engine upon the EGR conduit. As a result, the manufacturing cost increases.
An object of the present invention is to provide an EGR device for engines, capable of recirculating a SOF-removed EGR gas irrespective of the set condition of a catalyst in an exhaust system and without needing to extend an EGR conduit and provide a universal joint; reducing the manufacturing cost in consequence; and preventing the SOF from being deposited in an intake air system.
This object can be achieved by the features defined in the claims. Particularly, in order to attain this and other objects, the invention provides an EGR device for engines, adapted to recirculate a part of an exhaust gas discharged from an engine into an intake air system through an EGR conduit, the EGR device having an introduction portion for introducing a part of the exhaust gas into the EGR conduit, and a catalyst provided in the portion of the EGR conduit which is on the downstream side of the introduction portion, and adapted to purify the exhaust gas introduced from the introduction portion into the EGR conduit.
The nature of this invention as well as the objects and advantages thereof will be explained in the following with reference to the accompanying drawings in which like reference characters designate the same or similar parts throughout the figures wherein:
Fig. 1 is a front view showing a mode of embodiment of the EGR device for engines according to the present invention; and
Fig. 2 is a perspective view showing the same mode of embodiment of the EGR device for engines according to the present invention.
A mode of embodiment of the EGR device for engines in which the present invention is actualized will now be described.
In this mode of embodiment, the EGR device according to the present invention is applied to a four-cylinder gasoline engine.
Fig. 1 is a front view showing a mode of embodiment of the EGR device for engines, and Fig. 2 a perspective view showing the same EGR device. Referring to the drawings, a reference numeral 1 denotes a cylinder head of an engine. An exhaust manifold 2 is fixed to an exhaust-side side surface of the cylinder head 1. The exhaust manifold 2 has an engine-side fixing flange 2a secured to the cylinder head 1 by bolts 3, exhaust pipes 2c provided correspondingly to cylinders and adapted to circulate therein an exhaust gas discharged from the cylinders, and an exhaust-side connecting flange 2b joined to an exhaust pipe member (not shown). The exhaust pipes 2c are welded at the upper ends thereof to the engine-side fixing flange 2a, and at the lower ends thereof to the exhaust-side connecting flange 2b. The exhaust pipes 2c are collected at the downstream side thereof by units each of which includes two exhaust pipes. The exhaust pipe member is provided at an underfloor portion of a vehicle with an underfloor catalyst, and a silencer on the downstream side. This mode of embodiment is not provided with such a proximity catalyst as is set in a related art apparatus in the portion of an exhaust pipe which is close to an exhaust manifold 2 of exhaust pipes.
An annular bracket 4 as a support member is fixed by a bolt 5 to an intermediate portion of one exhaust pipe 2c out of the plural exhaust pipes 2c. This annular bracket 4 supports at an inner circumferential portion thereof a cylindrically formed catalyst 6. This catalyst 6 does not demand to have an action of purifying an exhaust gas as a whole but demands as will be described later to have only an action of cutting off a bond of SOF containing an unburnt fuel and oil as main components . Therefore, a supporting catalyst seedy is not limited to Pt (platinum), Pd (palladium) and Rh (rhodium) which are utilized as general oxide catalysts, and a catalyst seed having a lower degree oxidation action, for example, zeolite utilized as, for example, a HC trap and a selective reducing type Nox catalyst may also be carried.
A lower-side EGR conduit 7a is extended from a lower portion of the catalyst 6, and a lower end 8a of the lower-side EGR conduit 7a is welded to one exhaust pipe collected portion of the exhaust pipes 2c. This connected portion constitutes an EGR gas introduction portion 10a. Similarly, an upper-side EGR conduit 7b is extended from an upper portion of the catalyst 6, and an upper end 8b of the upper-side conduit 7b is welded to one side of the engine-side fixing flange 2a. This connected portion constitutes an EGR gas discharge portion 10b. Thus, the lower-side EGR conduit 7a and upper-side EGR conduit 10b form an EGR conduit 7, which is provided with the catalyst 6 on the downstream side of the EGR gas introduction portion 10a.
In this embodiment, bellows 9b as a movable member obtained by forming a metal pipe to a bellows-like shape are provided in the upper-side EGR conduit 7b. The annular bracket 4 is formed by setting an inner diameter thereof slightly larger than an outer diameter of the catalyst 6, and allows a relative movement of the catalyst 6. Accordingly, even when thermal expansion occurs on the exhaust manifold 2 to cause the catalyst 6 to be displaced, the catalyst 6 is retained by the annular bracket 4.
The lower-side EGR conduit 7a is formed to as smallest a length as possible. As a result, the catalyst 6 is provided in a position in the vicinity of the exhaust pipe collected portion of the exhaust manifold 2 as is clear from Fig. 1, i.e., in a position in a dead space not utilized in a related art apparatus of this kind and close to the EGR gas introduction portion 10a. Therefore, a high-temperature EGR gas which has just entered the EGR gas introduction portion 10a is introduced into an inner portion of the catalyst.
As shown by a broken line in Fig. 2, one end of a downstream side EGR passage 11 is opened in an exhaust-side side wall of the cylinder head 1 so that this end of the EGR passage 11 is opposed to an opened portion of the upper side EGR conduit 7b formed in the engine-side fixing flange 2a. This downstream side EGR passage 11 is provided in an engine through the cylinder head 1, and the other end thereof is opened in a suction-side side wall of the cylinder head 1 and connected to an intake air passage of the engine via an EGR valve (not shown).
In the EGR device formed as described above, an exhaust gas discharged in accordance with an operation of the engine is sent out from the exhaust manifold 2 to the outside via the exhaust pipe member and an underfloor catalyst and silencer which are provided in the exhaust pipe member. On the other hand, a part of the exhaust gas is introduced as an EGR gas from the EGR gas introduction portion 10a, which is connected to the exhaust pipe collected portion of the exhaust manifold 2, into the lower side EGR conduit 7a. This gas is then recirculated into the intake air passage via the catalyst 6, upper-side EGR conduit 7b, downstream side EGR passage 11 and EGR valve. During this time, a recirculation rate is regulated in accordance with the degree of opening of the EGR valve, and a discharge rate of NOx from the engine is thereby reduced.
The EGR gas passing through the catalyst 6 is subjected to the removal of SOF contained in the gas owing to the action of the catalyst seed, and the resultant SOF is recirculated into the intake air passage. Owing to the removal of the SOF, the occurrence of deposition of SOF in members constituting the intake air system which include, for example, a throttle valve and intake air valve is prevented. Since the temperature of the catalyst 6 provided in the portion of the EGR conduit 7 which is close to the EGR gas introduction portion 10a as mentioned above is increased speedily by the high-temperature EGR gas, the removal of the SOF can be started speedily even at the cold mode engine starting time.
Since the catalyst 6 used exclusively for an EGR gas is thus provided in the EGR conduit 7 connected to the exhaust manifold 2, the SOF contained in the EGR gas can be removed without being influenced at all by the condition of installation of a primary exhaust gas purification catalyst in the exhaust pipe. To be concrete, even in a case where a proximity catalyst is not provided in the portion of the exhaust pipe which is close to the exhaust manifold as in this mode of embodiment, it is not necessary to recirculate the EGR gas from a downstream side of an underfloor catalyst away from the engine. This enables the manufacturing cost to decrease without needing to provide a long EGR conduit and a universal joint incidental thereto, such as bellows and a spherical joint.
Since the quantity of the EGR gas passing through the catalyst 6 is substantially small as compared with that of an exhaust gas as a whole, the catalyst 6 can be miniaturized. Moreover, the EGR is executed mainly in low and intermediate load regions, and the EGR gas passing through the catalyst 6 does not reach so high a level of temperature, so that the catalyst 6 has a comparatively large margin with respect to the heat deterioration of the catalyst 6. Therefore, the catalyst 6 can be manufactured inexpensively, and the influence of the addition of the catalyst 6 upon the manufacturing cost is small, so that a sufficient decrease in the cost of the apparatus as a whole can be attained. Moreover, since the catalyst 6 is provided in a dead space as mentioned above, the influence of the addition of the catalyst 6 upon the circumferential machines is also small, so that the EGR can be executed without lowering a space efficiency in an engine room.
In addition, the EGR conduit 7 and catalyst 6 are formed in one body with respect to the exhaust manifold 2 as mentioned above, these members including the exhaust manifold 2 can be provided in the engine on an engine assembling stage. Namely, when an underfloor catalyst and engine are connected together by an EGR conduit as disclosed in JP-A-2000-249003 referred to as a publication for describing a related art apparatus of this kind, the EGR conduit cannot be provided on an engine assembling stage. It becomes possible to provide the EGR conduit for the first time on a stage for mounting a completely assembled engine on a chassis, so that the engine mounting operation becomes complicated.
Therefore, the EGR device in this mode of embodiment is advantageous in that an engine mounting operation can be rationalized.
As known well, the exhaust pipes 2c of the exhaust manifold 2 expand due to the exhaust heat every time the engine is operated, so that a variation of a distance between the upper and lower ends 8a, 8b of the EGR conduit 7 and a variation in angle of the upper and lower ends 8a, 8b in the circumferential direction (twisting direction) occur. However, the bellows 9b absorb the thermal expansion of the exhaust pipes 2c mentioned above, and the catalyst 6 is moved axially with respect to the annular bracket 4. Therefore, the catalyst 6 can be supported without being influenced by this thermal expansion. This enables the catalyst 6 from being broken due to the stress occurring during this time, and in its return the durability thereof to be improved.
The mode of the present invention is not limited to this mode of embodiment. Although the apparatus in, for example, the above mode of embodiment is actualized as an EGR device for a four-cylinder gasoline engine, the type of the engine is not limited to this. The number of the cylinders of the engine may be varied, or the apparatus may be actualized as an EGR device for a diesel engine. Moreover, the existence or non-existence of a proximity catalyst is not limited either, and the EGR device may be applied to an engine provided with a proximity catalyst. Even in this case, the advantage of the capability of rationalizing an engine mounting operation can be obtained.
Although the engine-side fixing flange for the EGR conduit 7 is formed in one body with respect to the engine-side fixing flange 2a of the exhaust mani fold 2 in the above mode of embodiment, the engine-side fixing flange exclusively used for the EGR conduit 7 may be formed separately from the engine-side fixing flange 2a. Furthermore, the EGR conduit 7 is not limited to an EGR conduit connected to the downstream side EGR passage 11 provided in the interior of the cylinder head 1, and the EGR conduit may be connected to an EGR passage provided outside the cylinder head 1. The EGR gas may be recirculated from the EGR conduit to the intake air passage by omitting the EGR passage, and, in this case, an EGR valve is necessarily provided in the EGR conduit.
Although an axial movement of the catalyst 6 in the above-described mode of embodiment is allowed by setting the diameter of the bracket 4 larger than the outer diameter of the catalyst 6, the structure is not limitative. The annular bracket 4 may allow an axial movement of the catalyst 6, for example, by forming the annular bracket 4 so that the annular bracket retains the catalyst 6 immovably and is swung around the fixing bolt 5. In other case, a movement of the catalyst 6 maybe allowed by the flexure of the annular bracket 4 itself.
In the EGR device for engines according to the present invention described above, an exhaust gas from an engine is discharged to the outside via the exhaust manifold and exhaust passage, and a part of the exhaust gas is recirculated as an EGR gas from the exhaust manifold into the intake air system of the engine via the EGR conduit, so that a discharge of NOx is reduced. The EGR gas is purified with the catalyst provided in the EGR conduit, and SOF is removed therefrom. This can prevent the deposition of SOF on each member constituting the intake air system.
Thus, owing to the structure in which the EGR conduit is connected to the exhaust manifold, it becomes unnecessary to recirculate the EGR gas from the downstream side of the underfloor catalyst spaced from the engine. Therefore, the manufacturing cost can be reduced without needing to provide a long EGR conduit for the recirculation of the EGR gas and an incidental universal joint, such as bellows and a spherical joint. The catalyst used exclusively for an EGR gas provided in the EGR conduit executes the removal of the SOF contained in the EGR gas.
Since the quantity of the EGR gas passing through the catalyst is substantially small as compared with a flow rate of the total discharge gas, the catalyst,itself can be miniaturized. Moreover, the temperature of the EGR gas is comparatively lower than that of the general discharge gas, and the EGR gas does not demand a high thermal resistance on the catalyst. This enables an inexpensive catalyst seed to be utilized, and a sufficient SOF removing effect to be obtained in consequence by the inexpensive catalyst.
Therefore, a SOF-removed EGR gas can be recirculated irrespective of the set condition of the catalyst in the exhaust system without needing to extend the EGR conduit and provide a universal joint. As a result, themanufacturing cost is reduced, and the deposition of SOF in the intake air system can be prevented.
The EGR conduit has a discharge portion from which an exhaust gas purified with a catalyst is discharged into the EGR passage provided in an engine, and this discharge portion has the engine-side fixing flange fixed to the engine. The EGR device can be set on the engine in an engine assembling step by fixing the engine-side fixing flange to the engine, and the engine mounting operation can be rationalized.
Furthermore, forming the engine-side fixing flange for the EGR conduit in one body with a fixing portion of the exhaust manifold for the engine enables these members including the exhaust manifold to be set in the engine in an engine assembling step, and an engine mounting operation to be more rationalized.
Since the catalyst is provided in the portion of the EGR conduit which is close to the EGR gas introduction portion of the EGR conduit, the high-temperature EGR gas which has just been introduced into the EGR conduit passes through the catalyst, so that the temperature of the catalyst increases speedily. Therefore, the removal of SOF is started speedily even at the cold mode engine starting time. This enables the deposition of SOF in the intake air system to be prevented more reliably.
Since the EGR gas introduction portion is connected to the exhaust pipe collected portion of the exhaust manifold, the catalyst is provided in a position in the vicinity of the exhaust pipe collected portion of the exhaust manifold, i.e., in a position in a dead space not utilized in a related art apparatus of this kind. Therefore, the additional provision of the catalyst does not have influence upon the circumferential machines, so that the EGR can be executed without causing a space efficiency in the engine room to lower.
The EGR conduit has an axially expansible/contractible or circumferentially movable member. Therefore, even when the exhaust manifold is thermally expanded, the thermal expansion is absorbed in this member owing to the axial expansion and contraction and circumferential movement thereof. This enables the breakage of the catalyst due to the stress occurring during this time to be prevented, and the durability of the catalyst to be improved.
The catalyst is supported on the exhaust manifold via a support member allowing a relative movement thereof. Therefore, even when the exhaust manifold is thermally expanded to cause the catalyst to be displaced, the catalyst is supported on the support member, so that the breakage of the catalyst ascribed to the stress occurring due to the thermal expansion of the exhaust manifold is prevented.

Claims

An EGR device for engine, adapted to recirculate a part of an exhaust gas discharged from an engine into an intake air system through an EGR conduit, comprising:

an introduction portion (10a) provided at one end of the EGR conduit (7), connected to an exhaust manifold (2) of an engine and adapted to introduce a part of an exhaust gas into the EGR conduit, and

a catalyst(6) provided in the portion of the EGR conduit which is on a downstream side of the introduction portion, and adapted to purify the exhaust gas introduced from the introduction portion into the catalyst.
An EGR device for engine according to Claim 1, wherein the EGR conduit further includes a discharge portion (10b) adapted to discharge an exhaust gas purified with the catalyst into an EGR passage(11) provided in the engine,
the discharge portion having an engine-side fixing flange(2a) fixed to the engine.
An EGR device for engine according to Claim 2, wherein the exhaust manifold has a fixing portion (2a) fixed to the engine,
the engine-side fixing flange of the EGR conduit being formed in one body with the fixing portion of the exhaust manifold.
An EGR device for engine according to any of claims 1 to 3, wherein:

the catalyst is provided in the portion of the EGR conduit which is close to the introduction portion.
An EGR device for engine according to any of claims 1 to 4, wherein:

the exhaust manifold is formed by collecting a plurality of exhaust pipes(2c),

the introduction portion being connected to an exhaust pipe collected portion of the exhaust manifold.
An EGR device for engine according to any of claims 1 to 5, wherein:

the EGR conduit has an axially expansible/contractible or circumferentially pivotable member (9b).
An EGR device for engine according to any of claims 1 to 6, wherein the catalyst is supported on the exhaust manifold via a support member(4) allowing a relative movement of the catalyst.