JP2003278542A - Engine exhausting system structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the exhaust emission control efficiency or the durability of a catalyst, and engine output performance, in an engine exhausting system structure wherein a catalyst converter is arranged in a directly below flow of an exhaust manifold collecting portion, a converter case of the catalyst converter has an extending cylindrical portion extending to an upstream side of the catalyst in the case, and the collecting portion is connected at an upstream end of the extending cylindrical portion. <P>SOLUTION: The collecting portion Md of an exhaust manifold M is shaped in a cylinder tapered off toward a downstream side. At least tip end of the collecting portion Md is projected into the extending cylindrical portion Hu so that an outer peripheral surface thereof is covered with the extending cylindrical portion Hu of the converter case H. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extension cylinder in which a catalytic converter is arranged immediately downstream of a collection portion of an exhaust manifold of an engine, and a converter case of the catalytic converter extends upstream from a catalyst in the case. Has a section,
The present invention relates to an exhaust system structure of an engine in which the collecting portion is connected to an upstream end of the extension cylinder portion.

[0002]

2. Description of the Related Art In the conventional exhaust system structure described above, the extension cylinder portion of the converter case is formed in a tapered conical taper shape on the upstream side of the exhaust gas. This is to diffuse the particles gently inside the extension cylinder and to apply them as evenly as possible to the front surface of the catalyst.

[0003]

By the way, in the above-mentioned conventional structure, in order to sufficiently diffuse the exhaust gas toward the catalyst front surface having a diameter larger than the inlet diameter in the conical tapered extension cylinder portion, the extension is required. It is necessary to lengthen the tubular part in the axial direction, which causes problems such as an increase in the size of the converter case and an increase in weight.

Therefore, in order to efficiently and forcibly diffuse the exhaust gas in the extension cylinder portion, there has been proposed a structure in which a partition wall for guiding gas diffusion is specially provided in the extension cylinder portion. In such a structure, there are other problems such that the partition wall reduces the internal volume of the extension cylinder and the pressure loss increases due to the resistance of the partition wall.

On the other hand, contrary to the above, the diffusion of exhaust gas in the extension cylinder is deteriorated to form a heat spot on a part of the front surface of the catalyst to increase the temperature rising rate of the catalyst and ensure the light-off performance. Although a structure is also proposed, in such a structure, the exhaust gas flows only in a part of the catalyst, and thus there is a problem that the pressure loss also increases. The present invention has been proposed in view of the above circumstances. Therefore, it is an object of the present invention to provide an exhaust system structure of an engine which can solve the above-mentioned conventional problems with a simple structure.

[0006]

In order to achieve the above object, the invention of claim 1 is such that a catalytic converter is arranged immediately downstream of a gathering portion of an exhaust manifold of an engine, and a converter case of the catalytic converter is In the exhaust system structure of the engine, which has an extension cylinder part that extends upstream from the catalyst in the case, and the collection part is connected to the upstream end of this extension cylinder part, the collection part of the exhaust manifold is , Is formed in a tapered tubular shape toward the downstream side, and at least the tip portion of the collecting portion projects into the extension tubular portion such that the outer peripheral surface thereof is covered with the extension tubular portion of the converter case. It is characterized by being

According to the above feature, at least the front end of the exhaust manifold assembly formed in the tapered cylindrical shape cooperates with the extension cylindrical portion covering the outer peripheral surface thereof to form a double pipe. The exhaust gas that has passed through can be poured into the converter case with almost no escape to the outside, and this effectively suppresses the temperature drop of the exhaust gas discharged toward the catalyst in the extension cylinder portion. ， The catalyst temperature rise characteristics and eventually the exhaust purification performance are improved. Moreover, when the engine is running at a low speed, the relatively slow exhaust gas flow can be efficiently collected at the center of the front surface of the catalyst to form a heat spot by the tapered cylindrical gathering section. Even when the engine is running at a low engine speed such as a cold start when the engine temperature is low (that is, the gas flow rate is small and the gas holding heat amount is small), the temperature rise characteristics can be further improved by the heat spot, and the exhaust gas purification efficiency by the catalyst is further improved. On the other hand, when the engine temperature is relatively high (that is, the gas flow rate is large and the amount of heat of gas retained is large), the gas diffusivity from the tapered cylindrical assembly increases, and a large amount of exhaust gas is sufficiently diffused. Since it is possible to apply it evenly over the entire front surface of the catalyst,
Not only can the purification volume of the catalyst be used effectively as a whole to improve the exhaust purification efficiency, but also the temperature of the entire catalyst can be raised almost uniformly to reduce the heat load on the catalyst and thus improve its durability. In addition, there is no need to specially install a gas diffusion guide partition wall that causes an increase in pressure loss in the extension cylinder part between the downstream opening end of the exhaust manifold assembly and the catalyst front surface. The characteristics can be improved.

According to the invention of claim 2, in addition to the above-mentioned features, the downstream end of the collecting portion is provided with an opening end so as to guide the diffusion of exhaust gas ejected from the opening end toward the catalyst. It is characterized in that a guide portion which is bent to the radially enlarged side is formed immediately before, and according to this feature, the tapered tubular collecting portion of the exhaust manifold is thrust into the extension cylindrical portion, so that the downstream portion of the collecting portion is reduced. Even if the distance between the side open end and the front of the catalyst becomes short,
The guide portion enhances the gas diffusivity from the collecting portion at the time of high engine speed, and allows the exhaust gas to be sufficiently diffused and evenly applied to the entire front surface of the catalyst, thus improving the exhaust gas purification efficiency as described above. The effects of improving the durability of the catalyst and improving the output characteristics of the engine can be further enhanced.

According to the invention of claim 3, in addition to the above features, the engine body of the engine is mounted on a vehicle body, and the exhaust manifold and the catalytic converter are arranged on the rear side of the engine body. According to this feature, the temperature rise characteristics of the catalyst at low engine speed are further improved, and the exhaust gas purification efficiency thereof is further enhanced.

Further, in addition to the above respective features, a second aspect of the present invention is provided below the floor of the vehicle, on the downstream side of the catalytic converter disposed immediately downstream of the collecting portion of the exhaust manifold.
The exhaust gas that has been sufficiently heated in the catalytic converter located immediately downstream of the exhaust manifold assembly is connected to the downstream catalytic converter. Since it is guided to the catalytic converter, the exhaust gas purification efficiency is further enhanced.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below based on the embodiments of the present invention illustrated in the accompanying drawings.

1 to 4 show an embodiment of the present invention, and FIG. 1 is a schematic perspective view showing an engine and its exhaust system in an engine room. Is an enlarged cross-sectional view of a main part of the exhaust manifold and the catalytic converter (cross-sectional view taken along line 2-2 of FIG. 1), FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 2, and FIG. It is explanatory drawing which shows simply the diffusion mode of the gas in the extension cylinder part at the time of rotation.

In a vehicle engine room ER, a horizontal multi-cylinder engine E in which a plurality of cylinders are arranged in the lateral direction of the vehicle body is housed, and the engine E is mounted and supported by a vehicle body frame (not shown). A transmission T is integrally provided on the left and right sides of the engine body 1 of the engine E, and the rear side surface of the engine body 1 in the front-rear direction of the vehicle body is connected to each cylinder and merges with each other on the downstream side to form an integral body. The upstream end Mu of the exhaust manifold M having the plurality of exhaust manifolds 2 ...

A downstream collecting portion M of the exhaust manifold M
Immediately downstream of d, a first catalytic converter C1 arranged upright on the rear side of the engine body 1 is arranged.
A downstream side of the catalytic converter C1 is connected to a second catalytic converter C2 under the floor of the vehicle body via an exhaust pipe 3 which is bent rearward of the vehicle body in an L shape, and is not shown downstream of the second catalytic converter C2. An exhaust muffler is connected.

The collecting portion Md of the exhaust manifold M is
The inner peripheral surface of the upstream large-diameter end portion and the inner peripheral surface of the downstream small-diameter end portion (opening O described later) are formed in a tapered shape toward the downstream side. Is smoothly continuous (that is, without interposing stepped portions, recessed portions, or discontinuous portions) across the intermediate tapered portion. Further, the downstream ends of the plurality of exhaust manifolds 2 ... Are integrally connected to the upstream side closed end wall W of the collecting portion Md having a gentle mountain shape and open to the internal space of the collecting portion Md. There is.

The first catalytic converter C1 comprises a cylindrical converter case H and a catalyst 4 housed and held in the case H. Incidentally, in this embodiment,
The catalyst 4 is held by the catalyst carrier and formed into a predetermined columnar shape. The whole formed body including the catalyst carrier is called a catalyst for convenience.

The converter case H is integrally connected to a cylindrical case body Hm in which the catalyst 4 is fitted and held on the inner periphery thereof, and an upstream end of the case body Hm, and the front surface of the catalyst 4, that is, the upstream end surface. A first extension cylinder Hu extending further upstream,
The catalyst 4 is integrally connected to the downstream end of the case body Hm.
The second extension cylindrical portion Hd extends downstream from the rear surface, that is, the downstream end surface.

The first extension cylinder portion Hu is formed in a conical taper shape tapering toward the upstream side and having a relatively gentle gradient, and its upstream end is integrated with the collecting portion Md of the exhaust manifold M. Connected to. Further, the second extension cylinder portion Hd is formed in a conical taper shape which is tapered toward the downstream side and has a relatively steep gradient, and the downstream end thereof is integrally connected to the exhaust pipe 3.

In the exhaust manifold M, at least the front portion (most of the portion excluding the base end portion in the illustrated example) of the collecting portion Md formed in the tapered tubular shape is inside the first extension tubular portion Hu of the converter case H. And the outer peripheral surface of the protruding portion is covered by the extension cylindrical portion Hu with an annular space S, and the base end outer peripheral surface of the collecting portion Md is the first extension cylindrical portion Hu. Is airtightly fitted to the inner circumference of the upstream end of the.

The opening O of the exhaust manifold M on the tip side (downstream side) of the collecting section Md formed in a tapered cylinder shape.
Faces the front surface of the catalyst 4 with the internal space of the first extension tube portion Hu interposed therebetween, and the opening 4 is provided with the catalyst 4 from there.
A diffusion guide portion G having a divergent shape which is gently curved on the diameter-increasing side immediately before the opening end is integrally formed so as to guide the diffusion of the exhaust gas ejected toward the.

Next, the operation of the above embodiment will be described. During operation of the engine E, the high-temperature exhaust gas passes through the exhaust manifold M and flows from the collecting portion Md to the first catalytic converter C1.
And the harmful components in the exhaust gas are primarily purified when passing through the catalyst 4 in the first catalytic converter C1.
Further, the relatively high-temperature exhaust gas purified by the first catalytic converter C1 passes through the exhaust pipe 3 and then the second catalytic converter C2.
The harmful components in the exhaust gas are secondarily purified when flowing into the exhaust gas and passing through the catalyst in the converter C2.

By the way, the collecting portion Md of the exhaust manifold M is formed in a tapered cylindrical shape toward the downstream side, and at least the tip portion (most of the illustrated example) of the collecting portion Md has an outer peripheral surface having a converter. It projects into the extension cylinder Hu so as to be covered by the first extension cylinder Hu of the case H, and functions as an inner pipe of a double pipe structure. Therefore, the exhaust gas that has passed through the exhaust manifold M is hardly released from the collecting portion Md to the outside of the converter case H.
Since it can be poured into the inside of the case H, the temperature drop of the exhaust gas discharged toward the catalyst 4 in the extension cylindrical portion Hu of the case H can be effectively suppressed, so that the temperature rising characteristic of the catalyst and the exhaust purification can be achieved. Performance is improved.

Moreover, when the engine is running at low speed, the relatively slow exhaust gas flow can be efficiently collected at the central portion of the front surface of the catalyst 4 by the tapered cylindrical collecting portion Md of the exhaust manifold M to form the heat spot hs. Therefore, for example, even when the engine is running at a low engine speed such as a cold start when the gas temperature is relatively low, the temperature rise characteristics can be further improved by the heat spot hs, and the exhaust gas purification efficiency by the catalyst 4 is further improved. On the other hand, when the engine temperature is relatively high and the gas temperature is relatively high, the gas diffusivity from the tapered cylindrical collecting portion Md of the exhaust manifold M is increased, and a large amount of exhaust gas is sufficiently diffused to be substantially even over the entire front surface of the catalyst 4. Therefore, not only can the purification volume of the catalyst 4 be used effectively as a whole to improve exhaust gas purification efficiency, but also the temperature of the entire catalyst 4 can be raised almost uniformly and the heat load of the catalyst can be increased. Gas that reduces the pressure, and thus improves the durability, and further causes an increase in pressure loss in the internal space of the extension cylinder portion Hu between the downstream opening end of the exhaust manifold collecting portion Md and the front surface of the catalyst 4. Since it is not necessary to install a partition wall for diffusion guidance, the output characteristics of the engine can be improved.

Further, in the downstream side opening O of the collecting portion Md formed in the tapered cylindrical shape of the exhaust manifold M, a diffusion guide portion G in the shape of a taper which is gently curved on the diameter expansion side immediately before the opening end thereof. Are integrally formed, and the guide portion G smoothly guides the diffusion of the exhaust gas ejected from the opening O toward the catalyst 4. Therefore, even if the distance between the opening end of the collecting portion Md and the catalyst front surface is shortened by making the tapered cylindrical collecting portion Md project into the first extension cylindrical portion Hu, the diffusion guide portion G causes The gas diffusivity from the collecting portion Md at the time of high engine rotation is further enhanced, and exhaust gas can be sufficiently diffused and evenly applied to the entire front surface of the catalyst 4. The effects of improving efficiency, durability and engine output characteristics are further enhanced.

Further, the catalyst 4 in the first catalytic converter C1
Since the exhaust gas having a sufficiently raised temperature-raising characteristic is guided to the second under-floor second catalytic converter C2 on the downstream side, the exhaust gas purification efficiency by the catalytic converter C2 is also improved.

Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various design changes can be made.

For example, in the above embodiment, the first catalytic converter C located immediately downstream of the exhaust manifold collecting section Md.
In the present invention, the first catalytic converter C1 does not necessarily have to be placed upright. Further, in the above-described embodiment, the exhaust manifold collecting portion Md formed in a tapered cylindrical shape is provided with the diverging guide portion G for guiding the gas diffusion in the opening O on the front end side. In 1), such a guide part G can be omitted.

[0028]

As described above, according to the invention of claim 1,
At least the tip of the tapered tubular assembly of the exhaust manifold projects into the extension cylinder so that its outer peripheral surface is covered by the extension cylinder of the converter case, and the inner pipe of the double pipe structure is formed. As a result, the exhaust gas from the exhaust manifold can be poured into the converter case with almost no escape to the outside, and therefore the temperature drop of the exhaust gas in the case extension cylinder is effectively suppressed and the catalyst rises. The temperature characteristics are improved. Moreover, when the engine is running at a low speed, the relatively slow exhaust gas flow can be efficiently collected at the center of the front surface of the catalyst by the tapered cylindrical assembly of the exhaust manifold to form a heat spot. Even when the engine is running at low engine speed, such as during start-up, the temperature rise characteristics are further improved, and the exhaust gas purification efficiency by the catalyst is improved. Due to the increase in the gas diffusivity of the catalyst, it becomes possible to diffuse a large amount of exhaust gas sufficiently and evenly apply it to the entire front surface of the catalyst. Since the temperature can be raised uniformly and its durability is improved, and it is not necessary to provide a special partition wall for gas diffusion guide in the extension cylinder, which causes pressure loss. Which can contribute to the output characteristic improvement gin.

Further, according to the invention of claim 2, in particular, in the downstream side opening of the tapered cylindrical collecting portion of the exhaust manifold,
A guide part is formed on the expanded side immediately before the opening end so as to guide the diffusion of the exhaust gas ejected from there toward the catalyst. Even if the distance between the opening end of the part and the front surface of the catalyst becomes short, the guide part enhances the gas diffusivity from the collecting part at the time of high engine rotation, and diffuses exhaust gas sufficiently to cover the entire front surface of the catalyst. Because you can apply it evenly,
The exhaust gas purification efficiency and durability of the catalyst and engine output characteristics can be further improved.

According to the third aspect of the invention, since the exhaust manifold and the catalytic converter are disposed on the rear side of the engine body, the catalyst temperature rising characteristics at a low engine speed are further improved. Exhaust gas purification efficiency is further enhanced.

Further, according to the invention of claim 4, the exhaust gas sufficiently heated by the catalytic converter located immediately downstream of the exhaust manifold collecting portion is guided to the downstream underfloor catalytic converter. The exhaust gas purification efficiency can be further enhanced.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an essential part of an engine and its exhaust system in an engine room.

FIG. 2 is an enlarged sectional view of an essential part of an exhaust manifold and a catalytic converter (a sectional view taken along line 2-2 of FIG. 1).

3 is a sectional view taken along line 3-3 of FIG.

FIG. 4 is an explanatory view schematically showing a gas diffusion mode in the extension cylinder portion at low engine speed and high engine speed.

[Explanation of symbols]

1 engine body 4 catalyst E engine C1 first catalytic converter (catalytic converter) C2 second catalytic converter (second catalytic converter) G guide H converter case Hu first extension cylinder (extension cylinder) M exhaust manifold Md assembly section O opening

Claims (4)

[Claims] 1. A catalytic converter (C) is provided immediately downstream of a collecting portion (Md) of an exhaust manifold (M) of an engine (E).
1) is arranged, and the converter case (H) of the catalytic converter (C1) has an extension cylinder portion (Hu) extending upstream from the catalyst (4) in the case (H). In the exhaust system structure of the engine in which the collecting portion (Md) is connected to the upstream end of the extension cylinder portion (Hu), the collecting portion (Md) of the exhaust manifold (M) is tapered toward the downstream side. The extension cylinder portion (Hu) is formed in a tubular shape, and at least the front end of the collecting portion (Md) is covered with the extension cylinder portion (Hu) of the converter case (H) so that the outer peripheral surface thereof is covered. The exhaust system structure of the engine, which is characterized in that it rushes inside. 2. The downstream opening (O) of the collecting portion (Md) is provided immediately before the opening end so as to guide the diffusion of exhaust gas ejected from the opening (O) toward the catalyst (4). The exhaust system structure of the engine according to claim 1, wherein a guide portion (G) is formed that is bent toward the radially enlarged side. 3. The engine body (1) of the engine (E) is mounted on a vehicle body, and the exhaust manifold (M).
3. The engine exhaust system structure according to claim 1, wherein the catalytic converter (C1) and the catalytic converter (C1) are disposed on the rear side of the vehicle body of the engine body (1). 4. The collecting portion (M) of the exhaust manifold (M)
The second catalytic converter (C2) arranged under the floor of the vehicle is connected to the downstream side of the catalytic converter (C1) arranged immediately downstream of d).
Or, the exhaust system structure of the engine according to item 3.