JP4367253B2 - Exhaust device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust system for an internal combustion engine that collects exhaust discharged from an exhaust port of each cylinder from a branch pipe to an exhaust merging portion and then introduces the exhaust into an exhaust purification catalyst.

Patent Document 1 discloses a structure in which the inner wall surface of the exhaust manifold is entirely made of a ceramic material in order to reduce the heat release amount of the exhaust gas.
JP-A-6-117244

  However, if the inner wall surface of the exhaust manifold is entirely made of a ceramic material, there is a problem that the cost increases.

  In addition, if the exhaust manifold's inner wall is all made of ceramic material, the exhaust manifold's heat dissipation is small, so exhaust gas at an excessively high temperature is exhausted at the maximum output when the exhaust temperature from the engine is high. A catalyst is introduced, and the exhaust purification catalyst may be thermally deteriorated.

  Therefore, an exhaust system for an internal combustion engine according to the present invention includes a plurality of branch pipes whose upstream side is connected to an exhaust port of each cylinder, and an exhaust merging where exhaust gas from each cylinder joins by connecting the downstream end of each branch pipe. And an exhaust manifold having one end connected to the exhaust merging portion and the other end connected to the exhaust purification catalyst, and only at a portion where the temperature of the exhaust gas in the exhaust collector pipe peaks. A heat insulating material is provided on the inner peripheral surface.

  According to the present invention, by providing a heat insulating material only in a portion where the temperature in the exhaust collecting pipe reaches a peak, it is avoided that the exhaust collecting pipe receives heat from the exhaust locally, and the exhaust collecting pipe with respect to the thermal influence from the exhaust The durability of the exhaust device can generally be improved. Further, since the heat insulating material is provided only in the portion where the exhaust gas temperature reaches a peak, when the engine is operated at the maximum output point or the like and the exhaust gas temperature discharged from the combustion chamber is high, the exhaust gas collection Exhaust gas is not introduced into the exhaust system parts on the downstream side of the exhaust gas collection pipe due to heat radiation from the part where the pipe insulation is not provided or from the part where the exhaust manifold is not insulated. It is possible to prevent the exhaust system parts downstream of the exhaust collecting pipe from being damaged by heat.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an exhaust device according to a first embodiment of the present invention.

  The combustion chamber 2 of each cylinder of the engine 1 is defined by a cylinder head 3, a cylinder 5 formed in the cylinder block 4, and a piston 6 disposed in the cylinder 5.

  In this engine 1, an intake manifold 8 is connected to a combustion chamber 2 of each cylinder via an intake port 7 formed in the cylinder head 3, and a metal is connected via an exhaust port 9 formed in the cylinder head 3. A manufactured exhaust manifold 10 is connected. The exhaust from each cylinder is introduced into a catalytic converter 11 as an exhaust purification catalyst via the exhaust manifold 10 and the exhaust collecting pipe 15.

  Further, a secondary air supply passage 12 is formed in the cylinder head 3 so as to communicate with the exhaust port so as to supply so-called secondary air to the exhaust. Air is introduced into the secondary air supply passage 12 using a pump (not shown) or exhaust pulsation.

  The exhaust manifold 10 is generally composed of a plurality of branch pipes 13 whose upstream sides are connected to the exhaust ports 9 of the respective cylinders, and an exhaust merging section 14 to which downstream end portions of the branch pipes 13 are connected.

  The exhaust collecting pipe 15 has a substantially tubular shape, and has one end connected to the exhaust merging portion 14 and the other end connected to the catalytic converter 11. In FIG. 1, 18 is an intake valve and 19 is an exhaust valve.

  The exhaust collecting pipe 15 is formed so that the exhaust flow path is not linear but is curved at least at one place. A ceramic 17 as a heat insulating material is provided on the inner peripheral surface of the largest curved portion 16 that is the most bent among the curved portions of the exhaust collecting pipe 15 in order to reduce the thermal conductivity. In other words, the ceramic 17 is coated on the inner peripheral surface of the portion where the exhaust temperature in the exhaust collecting pipe 15 has a peak.

  The ceramic 17 is not provided on the entire circumference in the circumferential direction of the inner circumferential surface of the maximum bending portion 16, but is a portion of the inner circumferential surface of the maximum bending portion 16 on the outer peripheral side of the bending of the maximum bending portion 16. It is provided only in. Further, the exhaust collecting pipe 15 in the first embodiment has a relatively short pipe length between the maximum curved portion 16 and the exhaust merging portion 14, and is a catalyst in the catalytic converter 11 when the engine is cold. The portion where the exhaust gas temperature reaches a peak due to the introduction of secondary air in a state where is not activated substantially coincides with the maximum curved portion 16. That is, in the first embodiment, the ceramic 17 is provided on the inner peripheral surface of the portion where the temperature of the exhaust gas in the exhaust collecting pipe 15 reaches a peak. The portion where the exhaust temperature peaks due to the introduction of secondary air is determined by the operating conditions, the length of the exhaust path from the exhaust valve 19, the connection position of the secondary air supply passage 12 to the exhaust port 9, etc. The position can be specified in advance by experimental adaptation or the like.

  When the exhaust flow path through which the exhaust flows is curved, there is a characteristic that the temperature at the curved portion (for example, the surface temperature of the exhaust manifold 10) increases due to the exhaust flow, and the heat radiation amount at the curved portion also increases. .

  FIG. 2 is an explanatory view schematically showing the temperature change of the exhaust gas at the time of cold start in the exhaust device in the first embodiment described above.

  A solid line A in FIG. 2 indicates a change in the exhaust temperature when the secondary air is supplied from the secondary air supply passage 12 to the maximum bent portion 16 of the exhaust collecting pipe 15 where the ceramic 17 is not provided. The exhaust temperature that has risen due to the action of the secondary air increases the amount of heat dissipated in the maximum bending portion 16, so that the exhaust temperature greatly decreases from the middle of the maximum bending portion 16.

  On the other hand, when the secondary air is supplied from the secondary air supply passage 12 in the exhaust device of the first embodiment described above, the discharge from the maximum bending portion 16 is caused by the action of the ceramic 17 provided in the maximum bending portion 16. Since the amount of heat decreases, as shown by the thick dotted line B in FIG. 2, the exhaust gas temperature that has risen due to the action of the secondary air is greatly suppressed from decreasing at the maximum bending portion 16.

  A thin dotted line C in FIG. 2 shows a case where secondary air is not supplied from the secondary air supply passage 12 to the largest curved portion 16 of the exhaust collecting pipe 15 where the ceramic 17 is not provided. In this case, the exhaust temperature gradually decreases as it proceeds through the exhaust path.

  In such an exhaust device in the first embodiment, the ceramic 17 is provided on the maximum curved portion 16 where the exhaust temperature reaches a peak, so that the heat dissipation in the maximum curved portion 16 is mitigated by the heat retaining property of the ceramic 17, and secondary air is introduced. Since the exhaust gas whose temperature has been raised by the above can be introduced into the catalytic converter 11 in a high temperature state, the catalyst in the catalytic converter 11 can be used when the engine in the low temperature is not activated. It is possible to shorten the time until the temperature reaches the activation temperature. Further, since the ceramic 17 is provided only on the inner peripheral surface of the maximum curved portion 16 where the exhaust temperature reaches a peak, the exhaust temperature discharged from the combustion chamber 2 when the engine 1 is operated at the maximum output point or the like is high. In this case, excessively high-temperature exhaust is not introduced into the catalytic converter 11 due to heat radiation from the portion where the ceramics 17 are not provided, and the catalytic converter 11 can be prevented from being damaged by heat. . That is, excessively high-temperature exhaust is not introduced into the exhaust system parts downstream of the exhaust collecting pipe 15, and damage to the exhaust system parts downstream of the exhaust collecting pipe 15 can be prevented.

  Then, the action of the ceramic 17 having low thermal conductivity prevents the maximum bending portion 16 from receiving heat locally from the exhaust, and the durability of the maximum bending portion 16 against the heat effect from the exhaust can be improved. That is, the overall durability of the exhaust device can be improved as a whole.

Next, although the comparative example of this invention is demonstrated, the same code | symbol is attached | subjected to the part which becomes the same structure as 1st Embodiment mentioned above, and the overlapping description is abbreviate | omitted.

The exhaust system in the comparative example has substantially the same configuration as the exhaust system of the first embodiment described above, but as shown in FIG. 3, the exhaust collecting pipe 32 in this comparative example is an exhaust group in the first embodiment. With respect to the pipe 15, the pipe length on the upstream side of the maximum bending portion 16 is formed to be relatively long. In this comparative example , ceramics 34 as a heat insulating material is provided only on the inner peripheral surface of the exhaust temperature peak portion 33 where the exhaust temperature of the exhaust collecting pipe 32 peaks. That is, the exhaust temperature peak portion 33 is located upstream of the maximum curved portion 16 and is introduced by secondary air when the engine is started and the catalyst in the catalytic converter 11 is not activated. This is the part where the exhaust temperature reaches its peak.

  The exhaust temperature peak portion 33 is determined by the length of the exhaust path from the exhaust valve 19 and the connection position of the secondary air supply passage 12 to the exhaust port 9. Is.

Further, the ceramics 34 is not provided on the entire circumference in the circumferential direction of the inner peripheral surface of the exhaust temperature peak portion 33, and the exhaust gas flows relative to the exhaust path leading to the exhaust temperature peak portion 33 depending on the shape (bending condition, etc.). Is provided only in the upper portion in FIG. 3 in this comparative example .

FIG. 4 is an explanatory view schematically showing the temperature change of the exhaust in the exhaust system of the comparative example described above.

  The solid line D in FIG. 4 shows the change in the exhaust temperature when the secondary air is supplied from the secondary air supply passage 12 with respect to the ceramics provided only on the maximum curved portion 16 of the exhaust collecting pipe 32 described above. The exhaust temperature increased by the action of the secondary air is greatly decreased after reaching the maximum temperature at the exhaust temperature peak portion 33, but no significant temperature decrease is observed at the maximum curved portion 16 due to the action of ceramics.

On the other hand, when secondary air is supplied from the secondary air supply passage 12 in the exhaust device of the comparative example described above, the discharge from the exhaust temperature peak portion 33 is caused by the action of the ceramics 34 provided in the exhaust temperature peak portion 33. Since the amount of heat decreases, as shown by the thick dotted line E in FIG. 4, the exhaust temperature that has increased due to the action of the secondary air is greatly suppressed from decreasing at the exhaust temperature peak portion 33.

  4 indicates the case where secondary air is supplied from the secondary air supply passage to the exhaust temperature peak portion 33 of the exhaust collecting pipe 32 where the ceramic 34 is not provided. In this case, the exhaust temperature decreases at both the exhaust temperature peak portion 33 and the maximum curved portion 16.

  A thin dotted line G in FIG. 4 shows a case where secondary air is not supplied from the secondary air supply passage to the exhaust temperature peak portion 33 of the exhaust collecting pipe 32 where the ceramic 34 is not provided. In this case, the exhaust temperature gradually decreases as it proceeds through the exhaust path.

In this way, even in the exhaust device in the comparative example in which the exhaust path between the exhaust confluence portion 14 and the maximum curved portion 16 is long, the ceramic 34 is provided on the inner peripheral surface of the exhaust temperature peak portion 33. The exhaust gas temperature rise caused by the action of the secondary air can be significantly suppressed, and the catalyst in the catalytic converter 11 can be used when the engine at a low temperature when the catalyst in the catalytic converter 11 is not activated. It is possible to shorten the time until the temperature reaches the activation temperature. Further, since ceramics are not provided on all inner peripheral surfaces of the exhaust collecting pipe 32 constituting the exhaust passage, the exhaust temperature discharged from the combustion chamber 2 when the engine 1 is operated at the maximum output point or the like is high. In this case, excessively high temperature exhaust is not introduced into the catalytic converter 11 due to heat radiation from the portions of the exhaust manifold 10 and the exhaust collecting pipe 32 where ceramics are not provided. Damage to the exhaust system parts downstream of the exhaust collecting pipe 32 due to heat can be prevented.

  Then, the action of the ceramic 34 having low thermal conductivity prevents the exhaust temperature peak portion 33 from receiving heat locally from the exhaust, and improves the durability of the exhaust temperature peak portion 33 with respect to the heat effect from the exhaust. it can. That is, the overall durability of the exhaust device can be improved as a whole.

In the implementation described above, but ceramics 17 and 34 are not provided on the entire circumference in the circumferential direction of the inner peripheral surface of the maximum bending portion 16 and the exhaust temperature peak 33, the maximum bending portion of the ceramic 17 and 34 16 and the exhaust temperature peak 33 may be provided on the entire circumference in the circumferential direction of the inner circumferential surface.

The technical ideas of the present invention that can be grasped from the above-described embodiments will be listed together with their effects.
(1) An exhaust system for an internal combustion engine includes a plurality of branch pipes whose upstream side is connected to an exhaust port of each cylinder, and an exhaust merging part to which the downstream end of each branch pipe is connected and exhaust from each cylinder merges , And an exhaust collecting pipe having one end connected to the exhaust merging portion and the other end connected to the exhaust purification catalyst, and a portion where the temperature of the exhaust gas in the exhaust collecting pipe reaches a peak Only, the heat insulating material is provided on the inner peripheral surface. As a result, by providing a heat insulating material only in a portion where the temperature in the exhaust collecting pipe reaches a peak, the exhaust collecting pipe is prevented from receiving heat locally from the exhaust, and the durability of the exhaust collecting pipe against the heat effect from the exhaust is avoided. And the durability of the exhaust device can be improved as a whole. In addition, since the heat insulating material is provided only in the portion where the exhaust gas temperature reaches a peak, when the engine is operated at the maximum output point or the like and the exhaust gas temperature discharged from the combustion chamber is high, the exhaust gas collection Exhaust gas from the excessively high temperature is not introduced into the exhaust system parts on the downstream side of the exhaust collecting pipe due to heat radiation from the part of the pipe not provided with the heat insulating material or the part of the exhaust manifold that is not insulated. It is possible to prevent the exhaust system parts downstream of the exhaust collecting pipe from being damaged by heat.

  (2) In the exhaust system for an internal combustion engine described in (1) above, the portion where the temperature of the exhaust gas in the exhaust collecting pipe reaches a peak is the largest curved portion having the largest curvature among the curved portions of the exhaust collecting pipe.

  (3) In the exhaust system for an internal combustion engine according to (2), the portion where the temperature of the exhaust gas in the exhaust collecting pipe reaches a peak is a portion on the outer peripheral side of the inner peripheral surface of the maximum curved portion.

  (4) In the exhaust system for an internal combustion engine according to the above (1), the portion where the exhaust gas temperature in the exhaust collecting pipe reaches a peak is when the engine is started and the exhaust purification catalyst is not activated. This is a portion where the temperature rise of the exhaust gas in the exhaust gas collection pipe reaches a peak when the secondary air is supplied upstream from the collection pipe. As a result, the exhaust gas whose temperature has been raised by the introduction of the secondary air can be introduced into the exhaust gas purification catalyst in a high temperature state, so the exhaust gas purification catalyst can be used when the engine is started at a low temperature when the exhaust gas purification catalyst is not activated. The time until the catalyst reaches the activation temperature can be shortened.

Explanatory drawing which shows the structure in 1st Embodiment of the exhaust manifold which concerns on this invention. Explanatory drawing which showed typically the temperature change of the exhaust_gas | exhaustion at the time of the cold start in the exhaust system to which the exhaust manifold in 1st Embodiment was applied. Explanatory view showing a configuration of an exhaust manifold according to a comparative example of the present invention. Explanatory drawing which showed typically the temperature change of the exhaust_gas | exhaustion at the time of the cold start in the exhaust system to which the exhaust manifold in the comparative example was applied.

Explanation of symbols

9 ... Exhaust port 10 ... Exhaust manifold 11 ... Catalytic converter (exhaust purification catalyst)
DESCRIPTION OF SYMBOLS 12 ... Secondary air supply passage 13 ... Branch pipe 14 ... Exhaust merge part 15 ... Exhaust collecting pipe 16 ... Maximum bending part 17 ... Ceramics

Claims (2)

An exhaust manifold having a plurality of branch pipes whose upstream side is connected to an exhaust port of each cylinder, an exhaust merging part to which the downstream end of each branch pipe is connected, and exhaust from each cylinder merges, and one end of which is exhausted In the exhaust device of the internal combustion engine, comprising an exhaust collecting pipe connected to the merging portion and connected to the exhaust purification catalyst at the other end,
The largest curved portion of the curved portion of the exhaust collecting pipe and the largest curved portion and the two-letter air upstream from the exhaust collecting pipe when the engine is started and the exhaust purification catalyst is not activated. An exhaust system for an internal combustion engine, characterized in that when supplied, a portion where the exhaust temperature in the exhaust collecting pipe reaches a peak is matched, and a heat insulating material is provided only on the inner peripheral surface of the portion . 2. The exhaust system for an internal combustion engine according to claim 1 , wherein the portion where the exhaust gas temperature in the exhaust collecting pipe reaches a peak is a portion on the outer peripheral side of the inner peripheral surface of the maximum curved portion.

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