JPH0821233A - Exhaust manifold of internal combustion engine - Google Patents

Abstract

PURPOSE:To realize early activation of a catalyst to purify exhaust gas by decreasing the temperature drop of exhaust gas on an exhaust port part through a process of restraining the heat transferring amount from exhaust gas. CONSTITUTION:A double pipe structure is provided with an outer pipe 101, an inner pipe 102 thinner than the outer pipe 101, and a heat insulating layer formed by a clearance 106 between the inner pipe 102 and the outer pipe 101, and an exhaust manifold is inserted into an exhaust port part 109 for insertion of a cylinder head, and the diameter on the tip of the inner pipe 102 of the inserted exhaust manifold is so formed as to be larger than or equal to the diameter of the exhaust port 109, moreover, the part other than the tip of the inner pipe 102 is arranged through a heat insulating material 107.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust manifold of an internal combustion engine which is directly connected to exhaust holes of each cylinder head and collects exhaust gas to guide it to a muffler.

[0002]

2. Description of the Related Art Directly connected to an engine exhaust manifold,
An exhaust manifold of an internal combustion engine that collects exhaust gas and guides it to a muffler has two problems in its structure. First
First, to reduce the amount of heat released from the exhaust manifold into the engine room as much as possible to suppress the influence of heat, and secondly, to activate the catalyst early in order to speedily purify the exhaust gas. Is.

For the above first problem, the exhaust manifold has a double pipe structure of an outer pipe and an inner pipe so as to reduce the amount of heat radiated from the exhaust manifold into the engine room. Has been done to prevent the rise.

In order to solve the above-mentioned second problem, in order to purify the exhaust gas, it is necessary to raise the temperature of the exhaust gas flowing into the catalyst to a temperature at which the catalyst is activated at an early stage. For this purpose, the inner pipe of the double-piped exhaust manifold has been made thinner. That is, by reducing the wall thickness of the inner pipe in the exhaust manifold, the heat capacity is lowered and the inner pipe wall temperature is raised at an early stage. As the temperature of the inner pipe wall rises, the amount of heat transferred from the exhaust gas to the inner pipe decreases, the decrease in the temperature of the exhaust gas flowing into the catalyst is suppressed, and the catalyst is activated early.

For the purpose of early activation of the above-mentioned catalyst, a double-piped exhaust manifold for an internal combustion engine is, for example, one in which an inner pipe made of steel is cast by an outer pipe made of cast iron. It is disclosed in Japanese Patent Laid-Open No. 63-215809 and Japanese Patent Laid-Open No. 2-112864. Further, Japanese Patent Laid-Open No. 56-96114 discloses that both the inner pipe and the outer pipe are formed of semi-circular pipes and are formed in a hollow shape. further,
Japanese Utility Model Laid-Open No. 56-97515 discloses a structure in which a part of an exhaust manifold is inserted into the engine and a gap is provided between the exhaust manifold and the exhaust port wall.

[0006]

However, the conventional exhaust manifold of the internal combustion engine as described above has the following problems due to its structure.

In the exhaust manifold disclosed in Japanese Patent Laid-Open No. 63-215809, both ends are only outer pipes, and the heat of the exhaust gas flowing inside the exhaust manifold is absorbed by the exhaust manifold itself. Moreover, since the heat is absorbed by the cooling water in the water jacket of the double structure, the temperature of the exhaust gas lowers, which hinders the early activation of the catalyst. In addition, the temperature of the cooling water in the water jacket, which received heat in the exhaust manifold, rises, so the radiator and cooling fan had to be enlarged.

Further, in the exhaust manifold disclosed in Japanese Patent Laid-Open No. 2-112864, an integrated structure is adopted by casting an inner pipe, an outer pipe and a flange, and the heat quantity of the exhaust gas is It will escape to the flange and the outer pipe, and the temperature of the exhaust gas will drop, hindering the early activation of the catalyst.

Further, in the exhaust manifold disclosed in Japanese Patent Laid-Open No. 56-96114, the inner pipe and the outer pipe are in contact with each other over the entire exhaust manifold, and the heat of the exhaust gas is removed from the inner pipe. It is transmitted to the pipe, and the temperature of the exhaust gas drops, impeding the early activation of the catalyst.

Further, in the exhaust manifold disclosed in Japanese Utility Model Laid-Open No. 56-97515, the tip end of the exhaust manifold inserted into the engine is the largest heat receiving portion, so that the exhaust manifold is doubled. When made into a tube, the heat capacity of the tip part where the inner tube and the outer tube contact increases,
The heat of the exhaust gas escapes from the tip to the outer pipe, which lowers the temperature of the exhaust gas and hinders early activation of the catalyst.

The present invention has been made in view of the above, and suppresses the amount of heat transfer from the exhaust gas and reduces the temperature decrease of the exhaust gas at the exhaust port,
The purpose is to achieve early activation of the catalyst for purifying exhaust gas.

[0012]

In order to achieve the above object, the invention according to claim 1 uses an outer pipe, an inner pipe thinner than the outer pipe, and a gap between the inner pipe and the outer pipe. In an exhaust manifold of an internal combustion engine having a double-pipe structure having a heat insulating layer formed, an end portion of the exhaust manifold on a cylinder head side is inserted into an exhaust port portion of the cylinder head, and the inner portion of the exhaust port portion includes the inner portion. The heat insulating layer is formed by the pipe and the outer pipe, and the diameter of the inner pipe of the exhaust manifold is formed larger than that of the exhaust port portion in contact with the exhaust gas at the portion where the exhaust gas flows from the exhaust port portion to the exhaust manifold, and the outer pipe is formed. The inner pipe is in non-contact with the outer pipe and the flange in the flange portion fixed to the cylinder head.

According to the second aspect of the present invention, the tip of the inner pipe of the exhaust manifold inserted into the exhaust port is curved outward.

Further, in the invention according to claim 3, as the heat insulating layer, a heat insulating material is inserted into a gap formed by the inner pipe and the outer pipe, and the inner pipe is provided at a tip end portion on the exhaust port side of an exhaust manifold. And the outer tube is fixed.

In the invention according to claim 4, the inner pipe and the outer pipe of the exhaust manifold inserted into the exhaust port portion are fixed to each other, and the inner pipe has the same thermal expansion characteristics as the inner pipe, or An auxiliary member having a thermal expansion characteristic larger than that of the inner pipe is provided.

According to a fifth aspect of the present invention, in the exhaust manifold insertion portion of the exhaust port portion, a projection portion protruding toward the exhaust manifold side is provided in a part of the exhaust port portion, and the projection portion and the exhaust port portion are provided. A space is formed between the inner tube and the outer tube, and the distal ends of the inner tube and the outer tube are arranged in a non-contact state in the space.

Further, in the invention according to claim 6, the tip of the inner pipe of the exhaust manifold inserted into the exhaust port is curved outward from the vicinity of the tip of the protrusion.

In the invention according to claim 7, the tip portion of the inner pipe has a shape in which a dead water area is formed.

The invention according to claim 8 is of a double-pipe structure having an outer pipe, an inner pipe thinner than the outer pipe, and a heat insulating layer formed by a gap between the inner pipe and the outer pipe. In an exhaust manifold of an internal combustion engine, a protrusion protruding toward the exhaust manifold is provided in a part of the exhaust port portion, a space is formed between the protrusion and the exhaust port portion, and the inner pipe is The outer tube is arranged so that the tip portion of the outer tube does not come into contact with it.

In the invention according to claim 9, the tip of the inner pipe of the exhaust manifold inserted into the exhaust port is curved so as to be curved from the vicinity of the tip of the protrusion toward the outer pipe. It is what

Further, in the invention according to claim 10, as the heat insulating layer, air is interposed in a gap formed between the inner pipe and the outer pipe, and the air is provided on the side opposite to the exhaust port portion and from the flange portion. A heat conductive spacer is arranged at a distant portion.

[0022]

In the exhaust manifold for an internal combustion engine according to the present invention (claim 1), the inner pipe is thinned to form a double pipe, and
By inserting the double-piped inner pipe and outer pipe into the exhaust port of the engine, and making the diameter of the inner pipe larger than that of the exhaust port at the portion connecting the exhaust port to the inner pipe of the exhaust manifold, In the exhaust port section, a heat insulating layer is formed by the gap between the inner tube and the outer tube of the exhaust manifold, and a heat insulating section is formed from the exhaust gas to the cooling water in the water jacket of the exhaust port section. In addition, by reducing the heat transfer coefficient at the exhaust port side end where the heat capacity of the exhaust manifold increases, heat transfer from the exhaust gas to the outer pipe, cooling water, etc. is suppressed, and the temperature of the exhaust gas at the exhaust port decreases. Suppress.

Further, the exhaust manifold of the internal combustion engine according to the present invention (claim 2) is characterized in that the inner pipe is curved toward the exhaust port portion at the tip end of the exhaust manifold, so It absorbs the difference in thermal expansion due to the temperature difference between the inner and outer pipes that occurs when the exhaust manifold is sufficiently warm, and prevents the outer and inner pipes from separating. Prevents flow into the gap.

In the exhaust manifold for an internal combustion engine according to the present invention (claim 3), the surface temperature of the exhaust manifold is further lowered by inserting a heat insulating material into the gap formed by the inner pipe and the outer pipe. Further, since the inner pipe and the outer pipe are fixed to each other at the end portion on the exhaust port side of the exhaust manifold, the fibers constituting the heat insulating material are suppressed from jumping out, and the occurrence of seizure of the piston or valve due to the fibers is prevented.

The exhaust manifold for an internal combustion engine according to the present invention (claim 4) has the same thermal expansion characteristics as the inner pipe inside the inner pipe at the connecting portion between the inner pipe and the outer pipe inserted into the exhaust port. Or, since an auxiliary member having a thermal expansion characteristic larger than that of the inner pipe is provided, it is possible to further prevent peeling of the inner pipe and the outer pipe due to repeated absorption of thermal expansion due to a temperature difference between the inner pipe and the outer pipe. You can

Further, the exhaust manifold of the internal combustion engine according to the present invention (claim 5) is provided with a projection protruding toward the exhaust manifold on a part of the exhaust port, and a space is provided between the projection and the exhaust port. Since the inner pipe and the outer pipe are arranged in the space in a state where the tips of the inner pipe and the outer pipe do not contact each other, the heat quantity of the exhaust gas is less likely to be transmitted to the outer pipe and the exhaust port, and the temperature drop of the exhaust gas can be suppressed. it can.

Further, in the exhaust manifold for an internal combustion engine according to the present invention (claim 6), since the tip of the inner pipe is curved outward from the vicinity of the tip of the projection, the projection and the exhaust manifold. The leading edge overlaps, making it difficult for gas to flow into the gap.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 7), since the end portion of the inner pipe has a shape in which a dead water region is formed, the channel transmission from the exhaust gas to the exhaust manifold is large. As a result, the amount of heat transferred from the exhaust gas to the exhaust manifold tip is greatly reduced.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 8), since the tip of the inner pipe is curved outward from the vicinity of the tip of the protrusion, the protrusion and the exhaust manifold. The leading edge overlaps, making it difficult for gas to flow into the gap.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 9), the dead water region of the exhaust gas is not formed, but since the inner pipe and the outer pipe are not in contact with each other, the heat quantity of the exhaust gas from the inner pipe It is difficult to reach the outer pipe and further to the exhaust port, and the temperature drop of the exhaust gas is suppressed.

In the exhaust manifold of the internal combustion engine according to the present invention (claim 10), air is interposed as a heat insulating layer in the gap formed by the inner pipe and the outer pipe, and the air is provided on the side opposite to the exhaust port portion. In addition, since the heat conductive spacer is arranged at the portion away from the flange portion, the number of parts is reduced and the manufacturing is facilitated. Further, since the spacer is arranged apart from the flange, heat transfer from the inner pipe to the flange via the outer pipe due to the spacer is also suppressed.

[0032]

【Example】

[Embodiment 1] An embodiment of an exhaust manifold for an internal combustion engine according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory view showing a schematic configuration from an internal combustion engine including an exhaust manifold to a muffler portion, 10 is an engine as an internal combustion engine, 11 is directly connected to an exhaust hole of a cylinder head of the engine 10, and exhaust gas is discharged. An exhaust manifold that collects and guides to the muffler 12 is a catalytic converter that is disposed in the preceding stage of the muffler 12 and purifies the exhaust gas by a catalyst. The exhaust gas generated in the engine 10 part is directly connected to the exhaust hole of the cylinder head. Through the exhaust manifold 11 that is connected to the catalytic converter 13
And is purified in the catalytic converter 13.
The purified exhaust gas is then guided to the muffler and discharged to the outside.

FIG. 2 is an explanatory view showing the structure of the exhaust manifold according to the first embodiment and the mounting state of the exhaust manifold on the engine. In FIG. 2, 101 is an outer pipe forming the exhaust manifold 11, and 102 is the exhaust manifold 11. , 103 is a flange for fixing the exhaust manifold 11 to the engine 10 (corresponding to the flange portion in the claims), 104 is an exhaust port portion for inserting the exhaust manifold 11 in the cylinder head (claim 105 is a water jacket, 106 is a gap provided between the inner pipe 102 and the outer pipe 101 (corresponding to a heat insulating layer in the claims), and 107 is an inner pipe. The heat insulation material 108 filled in the gap 106 between the outer pipe 102 and the outer pipe 101 is discharged. Manifold leading end, 109 (corresponding to the exhaust port portion in contact with the exhaust gas in the claims) the exhaust port unit, 110 is a dead water generated by the shape of the inner tube 102 in the insertion exhaust port 104.

Next, the structure of each element and the relationship between parts will be described in detail. The outer pipe 101 is formed thicker so as to be a reinforcing member for the entire exhaust manifold 11, while the inner pipe 102 is formed thinner than the outer pipe 101, for example, about 0.5 mm. Has been done. An exhaust manifold 11 is coupled to the main body of the engine 10 and a flange 103 having a sufficient thickness is welded to the outer pipe 101 to suppress deformation of the exhaust manifold 11 due to exhaust gas pressure and high temperature. Also, the inner pipe 10
The distal end portion of the second member inserted into the insertion exhaust port portion 104 is curved from the inside of the inner pipe 102 toward the outer pipe 101 side, and is crimped with the outer pipe 101 at the exhaust manifold front-end portion 108. It is fixed by welding.

A gap 1 is provided between the inner pipe 102 and the outer pipe 101.
06 is formed, and the heat insulating material 107 made of ceramic fiber, glass fiber or the like is inserted into the gap 106. Further, in the exhaust manifold portion (not shown) on the side opposite to the portion inserted into the insertion exhaust port portion 104, the inner pipe 102 and the outer pipe 101 are fitted or braided by a heat resistant metal wire. The inner pipe 102 is held by the outer pipe 101 via the elastic spacers.

The insertion exhaust port portion 104 inside the engine 10 has a larger inner diameter than the exhaust port portion 109 so that the outer pipe 101 of the exhaust manifold 11 can be inserted into the insertion exhaust port portion 104. Has been formed. Further, the curved portion of the tip end of the inner pipe 102 inserted into the insertion exhaust port portion 104 is located inside the exhaust port portion 109 and the flange 103 which are directly exposed to the exhaust gas in the exhaust manifold front end portion 108. The pipe 102 is smoothly connected to the pipe 102 and has a shape that spreads outward as shown in FIG.

That is, the end portion of the exhaust manifold 11 on the cylinder head side is inserted into the cylinder head insertion exhaust port portion 104, and the insertion exhaust port portion 10 is inserted.
In the inside of 4, the heat insulating material 10 is formed by the inner pipe 102 and the outer pipe 101.
7 is formed, the diameter of the inner pipe 102 of the exhaust manifold 11 is larger than that of the exhaust port portion 109 which is in contact with the exhaust gas at the portion where the exhaust gas flows from the exhaust port portion 109 to the exhaust manifold 11, Flange 103 for fixing the pipe 101 to the cylinder head
In, the inner pipe 102 is the outer pipe 101 and the flange 103
It does not come into direct contact with or through the heat transfer body, that is, it has a non-contact structure.

Next, the operation will be described. First, the temperature rise of the exhaust gas temperature at the start will be described. Except immediately after the engine 10 is stopped, the temperatures of the exhaust port portion 104 for insertion of the cylinder head and the outer pipe 101 and the inner pipe 102 of the exhaust manifold 11 before starting the engine 10 are substantially the same as the outside air temperature. After the engine 10 is started, in the exhaust manifold 11, the inner pipe 102
The inner pipe 102 is first warmed by the exhaust gas flowing inside. As a result, the wall temperature in the inner pipe 102 rises,
The temperature of the exhaust gas decreases by the amount of heat given to the inner pipe 102. Therefore, by reducing the wall thickness of the inner pipe 102, the heat capacity is reduced, the wall temperature of the inner pipe 102 is quickly raised, and the heat transfer amount from the exhaust gas to the inner pipe 102 is suppressed, and the temperature of the exhaust gas is lowered. The exhaust manifold 1
It is intended to suppress the decrease in the temperature of the exhaust gas at the inlet of the catalytic converter 13 installed in the rear part of No.

In the exhaust port portion 109 near the combustion chamber which is directly exposed to the exhaust gas, the cylinder head itself has a heat capacity much larger than that of the exhaust manifold 11,
In addition, the water jacket 10 in the cylinder head
Since 5 serves as a heat absorber, the heat quantity of the exhaust gas is absorbed by the cooling water in the water jacket 105 via the exhaust port portion 109.

That is, in the insertion exhaust port portion 104 in which the exhaust manifold 11 is inserted, the inner pipe 102 is warmed by the exhaust gas as in the exhaust manifold 11, and the gap 106 between the inner pipe 102 and the outer pipe 101 is generated. The heat transfer from the inner pipe 102 to the outer pipe 101 is suppressed by the air layer, and the amount of heat transfer from the exhaust gas to the cooling water in the water jacket 105 via the inner pipe 102 and the outer pipe 101 is reduced.

Further, in the exhaust manifold most front end portion 108 inserted in the insertion exhaust port portion 104, the inner pipe 1
02, the curved portion of the tip end of 02 is directly exposed to exhaust gas, and the inner pipe 102 near the flange 103.
The shape of the exhaust manifold is such that the diameter of the exhaust manifold tip end portion 108 becomes larger than the diameter of the exhaust port portion 109, and the pipe expands rapidly due to the increase in the pipe cross-sectional area. As a result, as shown in FIG. 2, separation of the gas flow occurs, and exhaust gas dead water area 11
0 occurs. In the dead water region 110, the heat transfer from the exhaust gas to the exhaust manifold tip end portion 108 is greatly reduced, so the amount of heat transfer is greatly reduced, and therefore, the temperature drop of the exhaust gas can be reduced and the exhaust gas purification Early activation of the catalyst for can be realized.

Therefore, the exhaust manifold frontmost part 1
The increase in the heat capacity at 08 and the temperature decrease of the exhaust gas due to the heat transfer from the inner pipe 102 to the outer pipe 101 are suppressed. Also, the engine 10 and the exhaust manifold 1
Since the inner pipe 102 does not directly contact the outer pipe 101 and the flange 103 at the mounting portion of No. 1, direct heat transfer from the inner pipe 102 to the outer pipe 101 and the flange 103 can be prevented. it can.

Further, in the present embodiment, the inner pipe 102 and the outer pipe 1
The exhaust gas is prevented from flowing into the gap 106 by fixing 01 at the leading edge 108. This is because when the exhaust gas flows into the gap 106 between the inner pipe 102 and the outer pipe 101 from the exhaust manifold leading end portion 108, the flowing-in exhaust gas gives the outer pipe 101 its heat quantity, and the exhaust gas temperature lowers. This is because Further, a part of the exhaust gas flowing in the inner pipe 102 is deprived by the gap 106, so that the heat quantity of the exhaust gas in the inner pipe 102 becomes low and the exhaust gas temperature lowers. In addition, when the exhaust gas flows into the gap 106,
The exhaust gas temperature in the inner pipe 102 decreases at the flow-in portion, and a larger exhaust gas temperature is obtained at the portion where the exhaust gas flowing in the inner pipe 102 at the rear of the exhaust manifold 11 and the exhaust gas flowing into the gap 106 merge. This is because the decrease is promoted.

Further, the exhaust manifold according to the present embodiment is provided with the inner pipe 10 at the tip end portion 108 of the exhaust manifold.
2 is curved toward the outer pipe 101 side, the exhaust gas and the exhaust manifold 11 at the time of steady running etc.
When the tube is sufficiently warm, the curved shape is
2 and the difference in thermal expansion due to the temperature difference between the outer tube 101 can be absorbed. That is, since the inner tube 102 is thinner than the outer tube 101, the coefficient of thermal expansion is high, but the shape of the curved portion can absorb the difference in coefficient of thermal expansion. As a result, the outer pipe 101 and the inner pipe 102 are not separated from each other, and the exhaust gas does not flow into the gap 106 between the inner pipe 102 and the outer pipe 101.

In terms of the amount of heat dissipation from the cooling water of the engine 10, the amount of heat transfer from the exhaust gas to the cooling water and the amount of heat transfer from the exhaust manifold 11 at the exhaust port portion 109 are It reaches about 1/3 or more, and most of the heat transfer from the exhaust manifold 11 is
It goes from 03 through a gasket.

Therefore, according to the exhaust manifold 11 of the present embodiment, as described above, the amount of heat transferred from the insertion exhaust port portion 104 and the exhaust manifold 11 to the cooling water is the inner pipe 102 and the outer pipe 101. Also, since there is no contact with the flange 103 directly or through the heat transfer body, it becomes extremely small, and the heat radiation amount of the cooling water from the flange 103 via the gasket is reduced, and the radiator capacity and the air flow rate of the radiator are reduced. It is possible to reduce the drive amount of the fan for securing, that is, to save space by downsizing the cooling fan.

As described above, it is generally known that the surface temperature of the exhaust manifold 11 is lowered and the atmosphere temperature in the engine room is lowered by duplicating the exhaust manifold 11. At this time,
As shown in FIG. 2, the gap 10 between the inner pipe 102 and the outer pipe 101 is
When the heat insulating material 107 is inserted into the valve 6, the surface temperature of the exhaust manifold 11 can be further lowered and the temperature drop of the exhaust gas can be suppressed.

As the heat insulating material 107 in the above, a fibrous material having elasticity is generally often used because of its workability and absorption of deformation of the inner tube 102. However, at the tip of the exhaust manifold 11, there is a gap 10 between the inner pipe 102 and the outer pipe 101.
If 6 is present, a part of the fibers forming the heat insulating material 107 may be sucked into the cylinder by the suction force from the engine 10, and seizure of the piston or the valve may occur. Tip 1
At 08, the inner pipe 102 and the outer pipe 101 are fixed to each other. Further, since the tip portion of the inner pipe 102 is curved toward the outer pipe 101, as described above, the inner pipe 102 and the outer pipe 10 are
It is possible to absorb the difference in thermal expansion due to the temperature difference between the inner tube 102 and the outer tube 101, the separation of the inner tube 102 and the outer tube 101 does not occur, and the ejection of the fibers constituting the heat insulating material 107 is suppressed, and the pistons formed by the fibers It is possible to prevent the seizure of the valve and the valve.

Further, in a state where the exhaust gas and the exhaust pipe are sufficiently warmed due to traveling in the city, etc., as described above, the heat capacity and the surface temperature due to the difference in wall thickness between the inner pipe 102 and the outer pipe 101 are different from each other. There is a difference in expansion. Outer tube 101
Is not directly exposed to exhaust gas and has a low surface temperature and a large wall thickness, so that the heat capacity is large and its thermal expansion is
Less than.

On the contrary, the inner pipe 102 is directly exposed to high-temperature exhaust gas and has a small heat capacity due to its thin wall, so that the inner pipe 102 becomes hot and thermal expansion occurs. Therefore, the difference in thermal expansion of the exhaust manifold 11 as a whole is absorbed by fitting the inner pipe 102 and the outer pipe 101 at the end portion which is not on the engine mounting portion (not shown) side, or by using a spacer.
It is possible to prevent damage due to thermal expansion of the inner pipe 102.

Further, in the present embodiment, the outer pipe 101 is long at the tip of the exhaust manifold 11 so as to cover the outer pipe 101 and the inner pipe 102. By protecting the inner pipe 102, it is possible to prevent an external force from being applied to the inner pipe 102 and prevent its deformation or damage.

[Embodiment 2] FIG. 3 is an explanatory view showing the structure of an exhaust manifold according to the second embodiment and its engine mounting state.
A heat insulating material 107 is provided in the gap 106 between the inner pipe 102 and the outer pipe 101.
A heat insulating layer is formed by air without inserting. further,
The exhaust manifold 11 according to this embodiment includes a flange 10
3 is held by the inner tube 102 and the outer tube 101 by a spacer 201 having elasticity and braided with a heat-resistant metal wire. In addition, in the exhaust manifold most front end portion 108, the inner pipe 102 and the outer pipe 101
The joining may be performed by fitting without welding.

In the second embodiment constructed as described above, the surface of the exhaust manifold 11 during high load running is slightly higher than that of the first embodiment, but the surface of the exhaust manifold 11 is higher than that of the double manifold exhaust manifold. Since the rising margin is smaller than the margin, the impact is small and the number of parts is reduced.
Manufacturing is also easy. Further, since the holding of the inner pipe 102 is separated from the vicinity of the flange 103, heat transfer from the inner pipe 102 to the flange 103 via the outer pipe 101 by the spacer 201 which is a heat transfer body is also suppressed.

[Third Embodiment] FIG. 4 is an explanatory view showing the structure of an exhaust manifold according to a third embodiment, and is different from the structure of FIG.
At the connecting portion of the inner pipe 102 and the outer pipe 101 in
A structure in which a ring-shaped auxiliary member 301 (corresponding to the auxiliary member in the claims) made of the same material as the inner tube 102 or a material having the same or greater thermal expansion characteristics as the inner tube 102 is provided inside the inner tube 102. It is adopted.

Further, in the exhaust manifold according to the third embodiment, when the divided inner pipes 102 are combined to form a tubular shape, the ring-shaped auxiliary member 301 is used to form the curved portion 3 of the inner pipe 102.
No. 02, the outer pipe 101 is installed outside the inner pipe 102, and then the ring-shaped auxiliary member 301 is pushed to the tip side, whereby the manufacturing can be easily performed. In addition, the inner pipe 102 and the outer pipe 101 at the tip 108 of the exhaust manifold
And are joined by welding or welded.

In the third embodiment configured as described above, peeling of the inner tube 102 and the outer tube 101 by repeating absorption of thermal expansion due to the temperature difference between the inner tube 102 and the outer tube 101,
It can be further prevented.

[Embodiment 4] FIG. 5 is an explanatory diagram showing a structure of an exhaust manifold according to Embodiment 4 and a mounting state of the exhaust manifold 11 to the engine 10. Here, in the insertion exhaust port portion 104, a part of the exhaust port portion 109 forms a protrusion portion 401 protruding toward the exhaust manifold 11, and between the protrusion portion 401 and the exhaust port portion 109, A space portion 402 (corresponding to the space in the claims) is formed. Further, the exhaust manifold 11 is inserted into the space portion 402 so that the ends of the inner pipe 102 and the outer pipe 101 do not come into contact with each other to form end portions. Further, the exhaust manifold frontmost portion 108 of the inner pipe 102 is curved toward the outer pipe 101.

In the above structure, a part of the inner pipe 102 is curved toward the outer pipe 101, and the inner pipe 102 and the protrusion 401
The dead water area of the exhaust gas is formed between and. In this embodiment, the inner pipe 102 and the outer pipe 101 are not in contact with each other, and
Since the heat transfer efficiency of the exhaust gas in the dead water region is low, the amount of heat of the exhaust gas is less likely to be transferred to the outer pipe 101 and the insertion exhaust port portion 104, and the temperature drop of the exhaust gas can be suppressed. Further, since the protrusion 401 and the exhaust manifold front-most portion 108 overlap, the gap 1
The outflow of gas to 06 is less likely to occur.

[Embodiment 5] FIG. 6 is an explanatory view showing a structure of an exhaust manifold according to a fifth embodiment and a mounting state of the exhaust manifold 11 to the engine 10. Here, in the insertion exhaust port portion 104, a part of the exhaust port portion 109 forms a protrusion 401 protruding toward the exhaust manifold 11, and a space is provided between the protrusion 401 and the exhaust port portion 109. 402 is formed. Also,
The exhaust manifold 11 is inserted into the space 402 so that the ends of the inner pipe 102 and the outer pipe 101 do not come into contact with each other to form end portions. Further, the most distal end portion of the exhaust manifold (the tip portion of the inner pipe 102) 108a is curved so as to be curved from the vicinity of the tip of the protrusion 401 toward the outer pipe 101 side.

In the structure shown in FIG. 6, the dead water region of the exhaust gas is not formed, but the inner pipe 102 and the outer pipe 101 are not formed.
Are not in contact with each other, the heat quantity of the exhaust gas is hard to be transmitted from the inner pipe 102 to the outer pipe 101, and further to the insertion exhaust port portion 104, and the temperature decrease of the exhaust gas can be suppressed.

The configuration shown in FIGS. 5 and 6 has a simpler shape as compared with the configurations shown in FIGS. 2 to 4. Therefore, the effect of facilitating the manufacture of the exhaust manifold 11 is added. It

[0062]

As described above, in the exhaust manifold for an internal combustion engine according to the present invention (claim 1), the inner pipe is thinned to be a double pipe, and The exhaust gas at the engine exhaust port by inserting the outer pipe and the outer pipe into the exhaust port of the engine and making the diameter of the inner pipe larger than the exhaust port at the part connecting the exhaust port to the inner pipe of the exhaust manifold. To the cooling water in the water jacket of the exhaust port, a heat insulating layer is formed by the gap between the inner pipe and the outer pipe of the exhaust manifold, and the heat transfer coefficient is reduced at the exhaust port end where the heat capacity of the exhaust manifold increases. Therefore, the heat transfer from the exhaust gas to the cooling water can be suppressed, and the temperature decrease of the exhaust gas at the exhaust port can be suppressed.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 2), since the inner pipe is bent toward the exhaust port portion side at the tip end of the exhaust manifold, the exhaust gas during steady running etc. It absorbs the difference in thermal expansion due to the temperature difference between the inner and outer pipes that occurs when the gas and exhaust manifolds are sufficiently warm, and prevents the outer and inner pipes from separating. It is possible to prevent the flow into the gap between and.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 3), since the heat insulating material is inserted into the gap formed by the inner pipe and the outer pipe, the surface temperature of the exhaust manifold is further lowered. Can be made. Also,
Since the inner pipe and the outer pipe are fixed to each other at the end portion on the exhaust port side of the exhaust manifold, the fibers constituting the heat insulating material are prevented from protruding, and the piston and the valve can be prevented from being burned by the fibers.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 4), the same portion as the inner pipe is provided inside the inner pipe at the connecting portion between the inner pipe and the outer pipe inserted into the exhaust port portion. Since a ring-shaped auxiliary member having a thermal expansion characteristic or a thermal expansion characteristic larger than that of the inner tube is provided, separation of the inner tube and the outer tube due to repeated absorption of thermal expansion due to the temperature difference between the inner tube and the outer tube, It can be further prevented.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 5), a protrusion projecting to the exhaust manifold side is provided in a part of the exhaust port portion, and the protrusion portion is provided between the exhaust port and the exhaust port. Since a space is formed in the space and the tips of the inner and outer pipes do not contact each other in the space, the heat quantity of the exhaust gas is less likely to be transferred to the outer pipe and exhaust port, and the temperature drop of the exhaust gas is suppressed. can do.

Further, in the exhaust manifold for an internal combustion engine according to the present invention (claim 6), since the tip of the inner pipe is curved outward from the vicinity of the tip of the protrusion, the protrusion is And the leading edge of the exhaust manifold overlap, gas does not easily flow into the gap, and the temperature drop of the exhaust gas can be suppressed.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 7), since the end portion of the inner pipe has a shape in which a dead water region is formed, the heat from the exhaust gas to the exhaust manifold is reduced. Since the transfer is greatly reduced, the amount of heat transferred from the exhaust gas to the tip of the exhaust manifold is greatly reduced, and the temperature drop of the exhaust gas can be suppressed.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 8), since the tip end portion of the inner pipe is curved outward from the vicinity of the tip end of the protrusion portion, the protrusion portion is formed. And the leading edge of the exhaust manifold overlap, gas does not easily flow into the gap, and the temperature drop of the exhaust gas can be suppressed.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 9), the dead water region of the exhaust gas is not formed, but since the inner pipe and the outer pipe are not in contact with each other, the heat quantity of the exhaust gas is It is difficult for the inner pipe to reach the outer pipe and further to the exhaust port portion, and it is possible to suppress the temperature drop of the exhaust gas.

Further, in the exhaust manifold of the internal combustion engine according to the present invention (claim 10), air is interposed in the gap formed by the inner pipe and the outer pipe as a heat insulating layer, and is opposed to the exhaust port portion. Since the heat-conducting spacer is arranged on the side and away from the flange portion, the number of parts is reduced and the manufacturing is facilitated. Further, since the spacer is arranged apart from the flange, heat transfer from the inner pipe to the flange via the outer pipe due to the spacer can be suppressed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration from an internal combustion engine including an exhaust manifold to a muffler portion.

FIG. 2 is an explanatory diagram showing a configuration of an exhaust manifold according to the first embodiment and a state in which the exhaust manifold is mounted on an engine.

FIG. 3 is an explanatory diagram showing a configuration of an exhaust manifold according to a second embodiment and an engine mounting state thereof.

FIG. 4 is an explanatory diagram showing a configuration of an exhaust manifold according to a third embodiment.

FIG. 5 is an explanatory diagram showing a structure of an exhaust manifold according to a fourth embodiment and a state where the exhaust manifold is mounted on an engine.

FIG. 6 is an explanatory diagram showing a configuration of an exhaust manifold according to a fifth embodiment and a state where the exhaust manifold is attached to an engine.

[Explanation of symbols]

 101 Outer Pipe 102 Inner Pipe 103 Flange 104 Insertion Exhaust Port Portion 106 Gap 107 Thermal Insulation Material 108 Exhaust Manifold Tip 109 Exhaust Port Portion 401 Projection 402 Space

Claims (10)

[Claims] 1. An exhaust manifold of an internal combustion engine having a double pipe structure, comprising an outer pipe, an inner pipe thinner than the outer pipe, and a heat insulating layer formed by a gap between the inner pipe and the outer pipe,
The end of the exhaust manifold on the cylinder head side is
An exhaust port that is inserted into the exhaust port of the cylinder head, forms the heat insulating layer by the inner pipe and the outer pipe in the exhaust port, and contacts the exhaust gas at a portion where the exhaust gas flows from the exhaust port to the exhaust manifold. The inner pipe of the exhaust manifold is formed to have a diameter larger than that of the outer pipe, and the inner pipe is not in contact with the outer pipe and the flange at the flange portion for fixing the outer pipe to the cylinder head. . 2. The exhaust manifold for an internal combustion engine according to claim 1, wherein a tip end portion of an inner pipe of the exhaust manifold inserted into the exhaust port portion is curved outward. 3. The heat insulating layer, wherein a heat insulating material is inserted into a gap formed by the inner pipe and the outer pipe, and the inner pipe and the outer pipe are fixed to each other at a tip end portion on an exhaust port side of an exhaust manifold. An exhaust manifold for an internal combustion engine according to claim 1, wherein the exhaust manifold is an exhaust manifold. 4. The same expansion coefficient as the inner tube or a larger thermal expansion characteristic than the inner tube is provided inside the inner tube in the fixed portion of the inner tube and the outer tube of the exhaust manifold inserted in the exhaust port section. An exhaust manifold for an internal combustion engine according to claim 3, further comprising: an auxiliary member having the auxiliary member. 5. An exhaust manifold insertion portion in the exhaust port portion is provided with a protrusion protruding toward the exhaust manifold side at a part of the exhaust port portion, and a space is formed between the protrusion and the exhaust port portion. 2. The exhaust manifold for an internal combustion engine according to claim 1, wherein the inner pipe and the outer pipe are arranged such that the end portions of the inner pipe and the outer pipe are not in contact with each other in the space. 6. The internal combustion engine according to claim 5, wherein the tip of the inner pipe of the exhaust manifold inserted into the exhaust port is curved outward from the vicinity of the tip of the protrusion. Exhaust manifold of the engine. 7. The exhaust manifold for an internal combustion engine according to claim 1, wherein a tip portion of the inner pipe has a shape in which a dead water region is formed. 8. An exhaust manifold of an internal combustion engine having a double pipe structure, comprising an outer pipe, an inner pipe thinner than the outer pipe, and a heat insulating layer formed by a gap between the inner pipe and the outer pipe,
A protrusion protruding toward the exhaust manifold side is provided in a part of the exhaust port, a space is formed between the protrusion and the exhaust port, and the inner pipe and the tip of the outer pipe contact each other in the space. An exhaust manifold for an internal combustion engine, wherein the exhaust manifold is arranged in a non-operating state. 9. The end portion of the inner pipe of the exhaust manifold inserted into the exhaust port portion is curved so as to warp toward the outer pipe side from the vicinity of the front end of the projection portion. Item 9. An exhaust manifold for an internal combustion engine according to item 8. 10. The heat insulating layer, wherein air is interposed in a gap formed by the inner pipe and the outer pipe, and a heat conductive spacer is provided on a side opposite to the exhaust port portion and away from the flange portion. 9. The exhaust manifold for an internal combustion engine according to claim 1, wherein the exhaust manifold is arranged.