JP2007064095A - Exhaust manifold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust manifold capable of reducing the turbulence of exhaust flow which is the backflow to a branch pipe through a collective chamber and of suppressing the occurrence of vibrations without resulting in the increase of weight thereby. <P>SOLUTION: The exhaust manifold 1 is provided with a plurality of branch pipes 3 including a double pipe part formed by coaxially inserting an inner pipe 3b into an outer pipe 3a, and whose upstream sides are connected with exhaust ports of a multi-cylinder engine; and a collective chamber 4 connected with downstream sides of the branch pipes, wherein a small diameter part 7 which is extended to the downstream side farther than the downstream end of the inner pipe and which has the inner diameter size D2 made not larger than the inner diameter size D1 of the inner pipe. In particular, it is preferable that a damping member 9 is interposed between the outer peripheral surface of a downstream end in the inner pipe and inner peripheral surface of the outer pipe. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust manifold of a multi-cylinder engine, and more particularly to an exhaust manifold formed by connecting a plurality of branch pipes formed of double pipes to one collective chamber.

  In a multi-cylinder engine of an automobile, as shown in FIG. 5, a plurality of branch pipes 103 connected to each of exhaust ports opened in a cylinder head are connected to one collective chamber 104, so that a catalytic converter and a muffler In general, exhaust gas from each combustion chamber is concentrated on one exhaust pipe in which a vessel is connected in series (see Patent Document 1).

On the other hand, each branch pipe 103 is composed of a double pipe in which steel pipes having different diameters are coaxially fitted to suppress exhaust heat from being dissipated into the atmosphere and to lower the temperature to activate the catalytic converter. An exhaust manifold is also known. In such an exhaust manifold, as shown in FIG. 5, the outer peripheral surface of the outer pipe 103a constituting the double pipe is fixed to the end wall 105 on the upstream side of the collecting chamber 104, and is fitted into the outer pipe 103a. The outer peripheral surface of the annular convex portion 111 formed at the end of the inserted inner pipe 103b is fitted and fixed to the inner peripheral surface of the outer pipe 103a, and between the inner peripheral surface of the outer pipe 103a and the outer peripheral surface of the inner pipe 103b. The heat insulation layer G of closed space is formed (refer patent document 2).
JP 2000-240450 A Japanese Utility Model Publication No. 7-17775

  However, according to the conventional structure as described in Patent Document 2, the open end surfaces of the outer pipe and the inner pipe that constitute the branch pipe face the inside of the assembly chamber on substantially the same plane, and the outer peripheral surface of the outer pipe Since the gap between the inner peripheral surface of the inner pipe also faces the collecting chamber, for example, the exhaust port of the engine is depressurized and the exhaust gas in the collecting chamber flows into the inner pipe during combustion stop control during deceleration. When the reverse flow phenomenon occurs, an exhaust flow vortex is generated around the open end of the branch pipe, which may cause the exhaust manifold to vibrate.

  Such vibrations not only cause noise, but can also cause unnecessary stresses in the welded parts of the members constituting the exhaust manifold to induce cracks and the like and impair durability.

  Although it is effective to increase the thickness of the branch pipe for such a problem, an increase in the thickness is not preferable because it causes an increase in weight and an increase in manufacturing cost.

  The present invention has been devised to eliminate such drawbacks of the prior art, and its main purpose is to reduce the turbulence of the exhaust gas flowing back from the collecting chamber to the branch pipe, thereby increasing the weight. It is an object of the present invention to provide an exhaust manifold that can suppress the occurrence of vibrations without incurring such problems.

In order to solve such a problem, the present invention provides a plurality of branches each having a double pipe portion formed by coaxially inserting an inner pipe 3b into an outer pipe 3a and connected upstream to an exhaust port of a multi-cylinder engine. In the exhaust manifold 1 having a pipe 3 and a collecting chamber 4 in which the downstream sides of the plurality of branch pipes are connected, the outer pipe extends further downstream from the downstream end of the inner pipe to the connecting portion of the outer pipe to the collecting chamber. Further, a reduced diameter portion (small diameter portion 7) is provided in which the inner diameter dimension D2 of the inner pipe is equal to or smaller than the inner diameter dimension D1 of the inner pipe.
In particular, a damping member 9 may be provided between the outermost peripheral surface of the most downstream end of the inner pipe and the inner peripheral surface of the outer pipe.

According to the present invention, the opening end surface of the inner pipe is arranged in the assembly chamber by providing a reduced diameter portion having a diameter equal to or smaller than the diameter of the inner pipe at the end of the outer pipe formed longer than the inner pipe. Therefore, the backflow gas can be prevented from entering the gap between the outer pipe and the inner pipe, and the flow of the backflow gas to the inner pipe can be smoothed. That is, according to the present invention, since the backflow gas flow can be smoothed, vibrations of the exhaust manifold can be suppressed at the time of combustion stop control at the time of deceleration, and a great effect can be achieved in reducing noise.
In addition, if a damping member is interposed between the outermost peripheral surface of the innermost pipe of the inner pipe and the inner peripheral surface of the outer pipe, the gap between the open end surface of the inner pipe and the outer pipe can be eliminated. Further, smoothing of the backflow gas flow can be further enhanced. This, combined with the fact that the downstream end of the inner pipe is non-rigidly supported by the outer pipe, combined with the fact that the heat expansion / contraction difference between the two pipes and the vibration absorbing action are obtained, improve the vibration suppressing action of the exhaust manifold. It is a great place to contribute.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an exhaust manifold to which the present invention is applied. The exhaust manifold 1 is used, for example, in an in-line four-cylinder engine, and is connected to a flange 2 coupled to a cylinder head (not shown) and an upstream end of each exhaust port opened in the cylinder head. Exhaust gas from each combustion chamber into four branch pipes 3 integrally connected to the flange 2 by welding or the like and one exhaust pipe (not shown) in which a catalytic converter, a silencer, etc. are connected in series. And a collecting chamber 4 in which the downstream ends of the branch pipes 3 are coupled to each other.

  As shown in FIG. 2, the four branch pipes 3 coupled to the collecting chamber 4 are each composed of an outer pipe 3a made of, for example, a stainless steel pipe having a relatively large diameter and a thick wall (t = 1.5 mm), and a relatively small diameter. The inner pipe 3b is made of, for example, a stainless steel pipe having a thin wall (t = 0.4 mm). The inner pipe 3b is inserted into the outer pipe 3a substantially coaxially, and the inner peripheral surface of the outer pipe 3a and the outer peripheral surface of the inner pipe 3b. A gap (air layer) G having an appropriate dimension continuous in the circumferential direction and the axial direction is formed between the two. The heat insulation function of the gap G and the reduction of the heat capacity by making the inner pipe 3b thinner than the outer pipe 3a are intended to suppress the temperature drop of the exhaust gas.

  The assembly chamber 4 is formed by integrally joining a cap 5 to which each downstream end portion of the four branch pipes 3 is connected and a case body 6 that is tapered in a funnel shape by welding or the like. 6 has a double structure with an outer case 6a and an inner case 6b in the same manner as the branch pipe 3, and one exhaust pipe is connected to the lower end side thereof.

  Next, a connection portion between the downstream end portion of each branch pipe 3 and the cap 5 of the collecting chamber 4 will be described.

  At the downstream end of each branch pipe 3, the outer pipe 3a is gradually reduced in diameter, and the predetermined axial length portion of the downstream end is a small diameter portion 7 having a substantially constant diameter. Each outer pipe 3a is integrally coupled to the cap 5 by tightly fitting and welding the small diameter portion 7 to the coupling hole 8 formed in the cap 5 by burring or the like.

  The inner pipe 3b fitted into the outer pipe 3a has a uniform thickness that is substantially equal to or slightly larger than the diameter of the small diameter portion 7 of the outer pipe 3a (D1 ≧ D2), and has its end on the most downstream side. The outer peripheral surface is supported on the inner peripheral surface of the large-diameter general portion of the outer pipe 3a via an annular damping member 9 made of, for example, stainless mesh. Here, the downstream end face of the inner pipe 3b and the small-diameter portion 7 of the outer pipe 3a are separated by an appropriate dimension (g) in the axial direction. That is, the outer pipe 3a and the inner pipe 3b are substantially non-contact with a radial gap of an appropriate dimension between them, and the downstream end of the inner pipe 3b is provided on the downstream side of the outer pipe 3a. It can be said that it is supported non-rigidly only by the damping member 9.

  The difference (D1-D2) between the inner diameter D1 of the inner pipe 3b and the inner diameter D2 of the small diameter portion of the outer pipe 3a is preferably 4 mm or less, and particularly preferably 2.5 mm or less.

  The portion corresponding to the projection surface of the opening end face of each small diameter portion 7 between the outer case 6a and the inner case 6b that constitute the case body 6 in a double structure (four locations / see FIG. 3) includes an inner pipe 3a. Similar to the indirect support structure of the inner pipe 3b with respect to the peripheral surface, a damping member 10 made of, for example, stainless mesh is interposed. As a result, the outer case 6a and the inner case 6b are substantially non-contact with a gap (air layer) G having an appropriate dimension between the outer case 6a and the inner pipe 3b, and the inner case 6b. It can be said that the case 6b is supported non-rigidly only by the damping member 10 with respect to the outer case 6a.

  Next, the function of the exhaust manifold 1 will be described. Hot exhaust gas intermittently discharged from a plurality of exhaust ports of the multi-cylinder engine flows through the inner pipe 3b. At this time, the heat of the exhaust gas is transmitted to the outer pipe 3a through an air layer formed in the gap G between the inner pipe 3b and the outer pipe 3a. Here, since the thermal conductivity of air is overwhelmingly lower than that of metal, the temperature increase of the outer pipe 3a is suppressed, and the temperature decrease of the exhaust gas is suppressed. Thereby, the catalyst arrange | positioned downstream of the exhaust manifold 1 can be activated at an early stage.

  Further, the downstream ends of the inner pipe 3b and the inner case 6b are substantially non-rigid, and the lengthwise direction thereof is a free end that can be easily expanded and contracted. At that time, vibration and thermal expansion and contraction are absorbed. Further, the exhaust gas flowing into the collecting chamber 4 from each branch pipe 3 collides with the inner surface of the inner case 6b. Since the vibration damping member 10 is interposed at the colliding portion, this serves as a buffer material and serves as an inner member. The vibration of the case 6b is suppressed, and the generation of noise is suppressed.

  As described above, in the present invention, by providing the small diameter portion 7 at the downstream end portion of the outer pipe 3a, the inner peripheral surface of the small diameter portion 7 and the inner peripheral surface of the inner pipe 3b are connected to each other on substantially the same surface. It is composed. In addition, in the present invention, the damping member 9 is provided at the most downstream end of the inner pipe 3b, so that no depression (gap) is formed between the open end surface of the inner pipe 3b and the outer pipe 3a.

  As a result, the inflow resistance of the backflow gas at the opening end face of the inner pipe 3b can be reduced and the smoothness of the backflow gas flow can be further increased, so that the exhaust port of the engine is depressurized during the combustion stop control during deceleration. Even when the exhaust backflow phenomenon occurs, the exhaust gas flowing back to the engine side can smoothly flow into the inner pipe 3b from the collecting chamber 4.

  In this way, according to the present invention, the downstream end of the inner pipe 3b is supported non-rigidly on the outer pipe 3a, so that a thermal expansion difference and vibration absorbing action between the two pipes can be obtained. This greatly contributes to the improvement of the vibration suppressing action of the exhaust manifold 1, and by these actions, it is avoided that unnecessary stress is generated in the connecting portions of the branch pipes 3 and the collecting chamber 4, and the durability is also improved. .

  In addition, as shown in FIG. 4, the boundary of the small diameter part 7 and the downstream end of the inner pipe 3b are made as close as possible, and the gap c between the downstream end of the inner pipe 3b and the starting end of the small diameter part of the outer pipe 3a is as small as possible. Then, the inner pipe 3b can be fitted and fixed to the outer pipe 3a with the annular convex portion 11a formed on the outer peripheral surface of the inner pipe 3b or the annular convex portion 11b formed on the inner peripheral surface of the outer pipe 3a.

1 is an overall perspective view of the device of the present invention. It is principal part side sectional drawing of this invention apparatus. It is a bottom view of the device of the present invention. It is principal part sectional drawing which shows another aspect of the fitting part of the inner pipe with respect to an outer pipe. It is a conceptual principal part structure figure of the exhaust manifold by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust manifold 3 Several branch pipe 3a Outer pipe 3b Inner pipe 4 Collecting chamber 7 Small diameter part 9 Damping member

Claims (2)

A plurality of branch pipes having a double pipe portion formed by coaxially inserting an inner pipe into an outer pipe and connected to the exhaust port of a multi-cylinder engine, and downstream sides of the plurality of branch pipes are connected. An exhaust manifold having a collection chamber,
Exhaust gas characterized in that the outer pipe has a reduced diameter portion that extends further downstream from the downstream end of the inner pipe and has an inner diameter dimension equal to or smaller than the inner diameter dimension of the inner pipe. Manifold.   2. The exhaust manifold according to claim 1, wherein a damping member is interposed between an outer peripheral surface of the most downstream end of the inner pipe and an inner peripheral surface of the outer pipe.

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