JP4331826B2 - Engine exhaust system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine exhaust system in which an exhaust purifier is disposed on the downstream side of a connection pipe connected to an exhaust pipe for guiding exhaust gas from the engine, and a silencer is disposed on the downstream side of the exhaust purifier. The casing common to the exhaust purifier and the silencer has a cylindrical portion containing the exhaust purifier and the silencer, a large diameter end connected to the upstream end of the cylindrical portion, and a small diameter end connected to the connecting pipe. The exhaust gas purifier includes a catalyst carrier having a circular outer surface larger in diameter than the outer diameter of the connecting pipe and supporting the catalyst in the cylindrical portion , and upstream of the catalyst carrier. at intervals end to the downstream end of the connecting tube an exhaust system of the opposing placement and engine.
[0002]
[Prior art]
Conventionally, such an exhaust purifier is already known, for example, from Japanese Utility Model Laid-Open No. 55-135118. In this case, the downstream end of the connection pipe connected to the exhaust pipe is connected to the small diameter end of the taper portion in the casing. ing.
[0003]
[Problems to be solved by the invention]
By the way, in a small displacement engine mounted on a motorcycle or the like, it is better that the distance from the engine to the catalyst carrier is as short as possible in order to quickly raise the catalyst carried on the catalyst carrier to the activation temperature. If the exhaust gas purifier is arranged as described above in the conventional one, the axial distance between the exhaust pipe and the connection pipe is shortened. However, in the low-speed rotation region of the engine, if the axial distance between the exhaust pipe and the connecting pipe is shortened, the output torque of the engine is reduced. Therefore, it is conceivable to increase the axial distance between the exhaust pipe and the connecting pipe by setting the opening angle of the tapered portion in the casing to be large, but in this case, the downstream end of the exhaust pipe is close to the upstream end of the catalyst carrier. At the same time, the volume occupied by the tapered portion is reduced, which leads to deterioration of the ventilation resistance at the catalyst carrier during high-load operation of the engine.
[0004]
The present invention has been made in view of such circumstances, and enables an early temperature rise of the catalyst while avoiding a reduction in output torque in the low-speed rotation region of the engine, and also in the catalyst carrier during high-load operation of the engine. An object of the present invention is to provide an engine exhaust system that can prevent deterioration of ventilation resistance.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided an exhaust purifier downstream of a connecting pipe connected to an exhaust pipe for guiding exhaust gas from an engine, and a silencer downstream of the exhaust purifier. An exhaust system for each engine, and a casing common to the exhaust purifier and the silencer, a cylindrical portion containing the exhaust purifier and the silencer, and a large diameter end at the upstream end of the cylindrical portion And an exhaust purifier having a circular outer surface larger in diameter than the outer diameter of the connection pipe in the cylindrical part . comprise a catalyst carrier carrying a catalyst and, at the upstream end of the catalyst support that faces placed at intervals in a downstream end of the connecting pipe, the catalyst support, the upstream end of the catalyst support The part projects into the tapered part from the large-diameter end to the small-diameter end. And arranged to, the annular space between the outer peripheral surface and the inner peripheral surface of the casing of the catalyst support, and gradually, characterized in that the throttled toward the upstream side in the tapered portion, such a configuration Therefore, even if the distance from the engine to the catalyst carrier is set to be as short as possible in order to quickly raise the catalyst to the activation temperature, the opening angle of the tapered portion is not set large. Can be made relatively large and used as a buffer chamber during high-load operation of the engine to prevent deterioration of the ventilation resistance in the catalyst carrier.
[0006]
The invention according to claim 2 is characterized in that, in addition to the configuration of the invention according to claim 1, the inner diameter of at least the downstream end of the connection pipe is set smaller than the inner diameter of the exhaust pipe, According to such a configuration, exhaust gas flows from the connecting pipe toward the center of the catalyst carrier, and the temperature of the catalyst supported at the center of the catalyst carrier is quickly raised to the activation temperature when the engine is started. can do.
[0007]
According to a third aspect of the invention, in addition to the configuration of the first or second aspect of the invention, the downstream end of the connection pipe is projected into the tapered portion from the small-diameter end portion to the large-diameter end portion side. According to such a configuration, even if the distance from the engine to the catalyst carrier is set as short as possible in order to quickly raise the catalyst to the activation temperature, the opening angle of the tapered portion is set large. Since it is possible to avoid a reduction in the axial distance between the exhaust pipe and the connection pipe, it is possible to prevent a reduction in output torque in the low-speed rotation region of the engine, and the volume occupied by the tapered portion is relatively large. In addition, it can be used as a buffer chamber during high-load operation of the engine, and deterioration of the ventilation resistance at the catalyst carrier can be prevented.
[0008]
Furthermore, in the invention of claim 4, in addition to the configuration of the invention of claim 2, 0.05 ≦ {(D2-D1), where D1 is the inner diameter of the connecting pipe and D2 is the inner diameter of the exhaust pipe. ) / D2} ≦ 0.40, and, in addition to the configuration of the invention described in claim 3, the invention according to claim 5 is characterized in that the inner diameter of the connecting pipe is D1. The distance (L) between the downstream end of the connecting pipe and the upstream end of the catalyst carrier is set in a range of 0.5 × D1 to 3 × D1.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below based on one embodiment of the present invention shown in the accompanying drawings.
[0010]
1 to 5 show an embodiment of the present invention. FIG. 1 is a right side view of a motorcycle, FIG. 2 is a longitudinal sectional view of an exhaust purifier and a silencer, and FIG. 3 is a main portion of FIG. FIG. 4 is an enlarged view, FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 3, and FIG. 5 is a diagram showing changes in the catalyst center temperature depending on the drawing ratio in the connecting pipe.
[0011]
First, in FIG. 1, a body frame F of the backbone type motorcycle is composed of a steel pipe backbone 5 inclined downward and a steel plate rear frame 6 welded to the rear end of the backbone 5. A front fork 8 that pivotally supports the front wheel WF is pivotally supported by a head pipe 7 provided at the front end of the backbone 5, and a steering handle 9 is connected to the upper end of the front fork 8. A rear fork 10 that pivotally supports the rear wheel WR is pivotally supported on the rear frame 6, and a rear cushion 11 is provided between the rear fork 10 and the rear frame 6. Further, a saddle 12 is attached to the upper surface of the rear frame 6, and a fuel tank 13 is accommodated and held in the rear frame 6 immediately below the saddle 12. A crankcase 14 of the engine E is attached to the front end portion of the rear frame 6 below the connecting portion with the backbone 5.
[0012]
An air cleaner 15 is attached to the front end portion of the backbone 5. The air cleaner 15 is connected to an intake port (not shown) provided in the cylinder head 16 of the engine E via a horn pipe 17, a throttle body 18 and an intake pipe 19. A fuel injection valve 20 that injects fuel toward the intake port is attached.
[0013]
An exhaust port (not shown) provided at a lower portion of the cylinder head 16 is connected to an upstream end of an exhaust pipe 21 that guides exhaust gas from the engine E. The downstream end of the exhaust pipe 21 is connected to the body frame F. It is connected to a casing 24 that is common to the exhaust purifier 22 and the silencer 23 arranged on the rear right side.
[0014]
2 and 3, a casing 24 is fixed to a cylindrical portion 25, a tapered portion 26 in which one end of the cylindrical portion 25 is connected to a large diameter end, for example, coaxially, and the other end of the cylindrical portion 25. The exhaust purifier 22 includes a terminal wall 27, and a catalyst carrier 28 is disposed coaxially with the cylindrical portion 25 in a portion near one end of the casing 24.
[0015]
With further reference to FIG. 4, the catalyst carrier 28 is a honeycomb having a circular outer surface and extending coaxially with the casing 24 by superimposing a flat plate 29 and a corrugated plate 30 made of stainless steel, for example, and spirally winding them. The catalyst is configured in a cylindrical shape, and a catalyst (not shown) is supported on the catalyst carrier 28.
[0016]
The catalyst carrier 28 is accommodated and held in a catalyst case 31 made of the same material as the catalyst carrier 28, for example, stainless steel. That is, the catalyst case 31 is formed in a cylindrical shape longer than the catalyst carrier 28, and the catalyst carrier 28 is fitted in the catalyst case 31 so that both ends thereof are located inward of both ends of the catalyst case 31. The catalyst carrier 28 is welded to the catalyst case 31 in the fitted state. The catalyst case 31 is disposed, for example, concentrically in the cylindrical portion 25 so that one end in the longitudinal direction thereof protrudes into the tapered portion 26, and is supported by the cylindrical portion 25 by a support member 32.
[0017]
The support member 32 includes a support cylindrical portion 32a that fits from one end in the longitudinal direction of the catalyst case 31 to a middle portion in the longitudinal direction so as to be relatively slidable, and a flange that protrudes radially outward from the other end of the support cylindrical portion 32a. The part 32b and the mounting cylindrical part 32c that are connected to the outer peripheral edge of the flange part 32b and are fitted to the inner surface of the cylindrical part 25 are integrally formed, and the same material as the catalyst carrier 28 and the catalyst case 31, for example, stainless steel Formed of steel.
[0018]
One end of the support cylindrical portion 32 a is welded and fixed to one end of the catalyst case 31. At this time, one end of the support cylindrical portion 32 a is welded to one end of the catalyst case 31 protruding from one end of the catalyst carrier 28, thereby avoiding as much as possible the influence of heat during welding on the catalyst supported on the catalyst carrier 28. can do. Further, the outer peripheral edge of the mounting cylindrical portion 32 c, that is, the flange portion 32 b is welded and fixed to the inner surface of the cylindrical portion 25 in the casing 24.
[0019]
By the way, one end of the support cylindrical portion 32a and the catalyst case 31 that are welded and fixed to each other may be set at the upstream end as in this embodiment when the temperature of the exhaust gas is relatively high. On the other hand, when the temperature of the exhaust gas is relatively low enough to slightly exceed the activation temperature of the catalyst, it is desirable to set it at the downstream end. That is, when exhaust gas discharged from the engine E flows from the upstream side to the downstream side with the start of the engine E, the temperature of the catalyst carrier 28 is increased by the catalytic reaction when the catalyst reaches the activation temperature. The temperature gradually increases from the upstream end side, and the catalyst case 31 also gradually increases from the upstream end side. At this time, one end of the support cylindrical portion 32 a of the support member 32 is welded and fixed to the upstream end of the catalyst case 31, so that excessive stress due to the difference in thermal expansion does not act on the welded and fixed portion. can do. Therefore, when the exhaust gas is relatively hot, one end of the support cylindrical portion 32 a is welded and fixed to the upstream end of the catalyst case 31. On the other hand, since the heat transfer action from the catalyst case 31 to the casing 24 is generated by the support member 32, one end of the support cylindrical portion 32a is formed when the temperature of the exhaust gas is only a relatively low temperature that slightly exceeds the activation temperature. If the upstream end of the catalyst case 31 is welded and fixed, heat transfer to the casing 24 side by the support member 32 delays the temperature rise of the catalyst and the start of the catalytic reaction is delayed, so one end of the support cylindrical portion 32a. Is preferably welded and fixed to the downstream end of the catalyst case 31.
[0020]
A cap 33 is provided at the small diameter end of the taper portion 26 in the casing 24, and the connection pipe 34 is connected to the small diameter end portion of the taper portion 26 via the cap 33, for example, coaxially. Thus, the downstream end of the exhaust pipe 21 is coaxially connected to the connection pipe 34.
[0021]
The cap 33 has a small-diameter cylindrical portion 33a and is formed in a stepped cylindrical shape, and is coaxially welded to the small-diameter end of the tapered portion 26 so that the small-diameter cylindrical portion 33a protrudes outward from the tapered portion 26. It is fixed.
[0022]
The connecting pipe 34 is formed by welding and fixing an outer pipe 35 and an inner pipe 36 inserted into the outer pipe 35 so that both ends protrude outward from both ends of the outer pipe 35. . Thus, the downstream end of the connecting pipe 34, that is, the downstream end of the inner pipe 36 is inserted into the casing 24 from the small diameter end portion of the tapered portion 26 to a position facing the upstream end of the catalyst carrier 28 with a gap L. In this way, the connecting pipe 34 penetrates the small diameter cylindrical portion 33 a of the cap 33, and the intermediate portion of the outer pipe 35 is welded and fixed to the cap 33.
[0023]
In addition, the outer diameter of the inner pipe 36 is set so as to fit into the exhaust pipe 21, and the upstream end of the inner pipe 36 is fitted to the downstream end of the exhaust pipe 21, and the exhaust pipe 21. And the upstream end of the outer pipe 35 are welded and fixed to each other.
[0024]
By the way, at least the downstream end of the connecting pipe 34, in this embodiment, the inner diameter D1 over the entire length of the connecting pipe 34, that is, the inner diameter D1 of the inner pipe 36 is set smaller than the inner diameter D2 of the exhaust pipe 21. The exhaust gas is throttled by the connecting pipe 34 and introduced into the casing 24.
[0025]
As described above, when at least the downstream end of the connection pipe 34 is throttled, exhaust gas flows from the connection pipe 34 toward the center of the catalyst carrier 28, and is supported at the center of the catalyst carrier 28 when the engine E is started. The temperature of the prepared catalyst can be quickly raised. At this time, the catalyst temperature at the center of the catalyst carrier 28 when {(D2-D1) / D2} is changed is as shown in FIG. 5, and {(D2-D1) / D2} is less than 0.05. Then, the effect of intensively directing the flow of the exhaust gas toward the center of the catalyst carrier 28 is not obtained, and the temperature rise of the catalyst center is insufficient, and {(D2-D1) / D2} is 0.40. If exceeded, the exhaust gas is excessively throttled and the amount of exhaust gas is reduced, so that the temperature of the catalyst center temperature is not sufficiently raised. Therefore, it is desirable to set 0.05 ≦ {(D2−D1) / D2} ≦ 0.40.
[0026]
Further, if the distance L between the downstream end of the connecting pipe 34 and the upstream end of the catalyst carrier 28 is too small, it causes a local deterioration of the catalyst, and if it is too large, it is carried at the center of the catalyst carrier 28 when the engine E is started. Since the effect of quickly raising the temperature of the catalyst thus obtained cannot be obtained, practically, the interval L is set to 0.5 × D1 to 5 × D1, more preferably 0.5 × D1 to 3 × D1. It is desirable.
[0027]
In FIG. 2 again, the silencer 23 is disposed in the casing 24 in the order of the first expansion chamber 37, the second expansion chamber 38, the fourth expansion chamber 40, and the third expansion chamber 39 from the upstream side along the axial direction. The first expansion chamber 37 is formed in the casing 24 between the taper portion 26 and the flange portion 32b of the support member 32 so as to face the upstream end of the catalyst carrier 28. .
[0028]
A cylindrical body 41 is inserted in a downstream rear half portion of the cylindrical portion 25 in the casing 24 so as to form a slight gap with the inner surface of the cylindrical portion 25. A plurality of protrusions 41 a, 41 b, and a plurality of protrusions are provided on the inner surface of the cylindrical portion 25.
[0029]
The second expansion chamber 38 includes a partition wall 42 whose outer periphery is fixed to an inner surface of a substantially central portion of the cylindrical body 41 so as to partition the inside of the cylindrical body 41 into an upstream half and a downstream half, and the support member 32. The downstream end of the catalyst carrier 28 faces the second expansion chamber 38, and the flange portion 32 b of the support member 32 is between the first and second expansion chambers 37, 38. It also functions as a partition wall.
[0030]
The third expansion chamber 39 is formed in the casing 24 between the partition wall 43 whose outer periphery is fixed to the inner surface near the downstream end of the cylindrical body 41 and the terminal wall 27, and the fourth expansion chamber 40 is formed of the partition walls 42, 43. Formed in the cylindrical body 41.
[0031]
The second and third expansion chambers 38 and 39 are communicated with each other by a pair of communication pipes 44, both ends of which are supported by the partition walls 42 and 43, and the third and fourth expansion chambers 39 and 40 are supported by the partition wall 43. Are communicated by a pair of communicating pipes 45. In addition, a single discharge pipe 46 having an upstream end opened to the fourth expansion chamber 40 and a downstream end opened to the outside penetrates the central portion of the partition wall 43 and the terminal wall 27 to the partition wall 43 and the terminal wall 27. The exhaust gas is finally exhausted from the exhaust pipe 46.
[0032]
Next, this embodiment will be described. The connecting pipe 34 connected to the exhaust pipe 21 that guides the exhaust gas from the engine E reaches a position where the downstream end of the connecting pipe 34 faces the upstream end of the catalyst carrier 28 with a space therebetween. Since the taper portion 26 of the casing 24 is inserted into the casing 24 from the small-diameter end portion, even if the distance from the engine E to the catalyst carrier is set to be as short as possible in order to quickly raise the catalyst to the activation temperature, the taper It is possible to avoid the axial distance between the exhaust pipe 21 and the connection pipe 34 from being shortened without setting the opening angle of the portion 26 large. Therefore, it is possible to prevent the output torque from being reduced in the low speed rotation region of the engine E, and the volume occupied by the taper portion 26, that is, the volume of the first expansion chamber 37 is made relatively large, so It is possible to prevent the deterioration of the ventilation resistance in the catalyst carrier 28 by using it as a buffer chamber.
[0033]
Further, since the inner diameter D1 of at least the downstream end of the connection pipe 34 is set smaller than the inner diameter D2 of the exhaust pipe 21, the exhaust gas flows from the connection pipe 34 toward the center of the catalyst carrier 28, and the engine At the start of E, the temperature of the catalyst supported on the central portion of the catalyst carrier 28 can be quickly raised to the activation temperature.
[0034]
Further, a cylindrical catalyst case 31 that holds a catalyst carrier 28 that supports a catalyst is disposed, for example, concentrically in a cylindrical portion 25 provided in the casing 24, and a support member 32 that supports the catalyst case 31 on the cylindrical portion 25 includes a catalyst. A support cylindrical portion 32a in which one end in the longitudinal direction of the case 31 is fitted to a middle portion in the longitudinal direction so as to be relatively slidable, and one end is fixed to one end of the catalyst case 31, and a radial direction from the other end of the support cylindrical portion 32a The outer peripheral edge of the flange portion 32b (in this embodiment, the mounting cylindrical portion 32c) is fixed to the inner surface of the cylindrical portion 25. Therefore, the catalyst case 31 can be supported on the cylindrical portion 25 of the casing 24 by the single support member 32 while allowing the catalyst case 31 to be deformed due to thermal expansion, and the support member 32 has a simple shape. In addition, the number of parts for supporting the catalyst case 31 can be reduced, and the cost can be reduced.
[0035]
Further, the outer peripheral edge of the flange portion 32b that projects radially outward from the other end of the support cylindrical portion 32a at a position corresponding to the intermediate portion in the longitudinal direction of the catalyst case 31 is fixed to the cylindrical portion 25 of the casing 24. The support member 32 is fixed to the cylindrical portion 25 at a location near the center of gravity of the 28 and the catalyst case 31, and the influence of the stress on the support member 32 due to the vibration of the catalyst carrier 28 and the catalyst case 31 is minimized. Can be suppressed.
[0036]
Furthermore, since the heat transfer area of the heat transfer path between the cylindrical portion 25 of the casing 24 and the catalyst case 31 is smaller than that of the conventional one using a plurality of support members, the catalyst is hardly affected by the ambient temperature, The influence of the external temperature on the catalyst supported on the catalyst carrier 28 in the portion of the catalyst case 31 that is not fitted to the support cylindrical portion 32a of the support member 32 becomes smaller, and the catalyst temperature can be further stabilized. it can.
[0037]
Moreover, the silencer 23 is configured by partitioning the inside of the casing 24 into a plurality of expansion chambers 37 to 40 in the axial direction thereof, and the flange portion 32b of the support member 32 faces the upstream end of the catalyst carrier 28. Since the first expansion chamber 37 and the second expansion chamber 38 facing the downstream end of the catalyst carrier 28 are partitioned, the exhaust purifier 22 forms a part of the silencer 23 with the casing 24 in common. The number of parts of the silencer 23 can be reduced, and the size and weight can be reduced.
[0038]
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design changes can be made without departing from the present invention described in the claims. Is possible.
[0039]
For example, in the above embodiment, the exhaust purifier 22 and the silencer 23 are configured in the common casing 24, but the present invention can also be applied to an exhaust purifier configured independently of the silencer 23. .
[0040]
【The invention's effect】
As described above, according to the first aspect of the present invention, even if the distance from the engine to the catalyst carrier is set as short as possible in order to quickly raise the catalyst to the activation temperature, the opening angle of the tapered portion is set large. it is not, therefore, a relatively large volume of the tapered portion occupies, the ventilation resistance deterioration of the catalyst carrier can be prevented so as to use as a buffer chamber for a high-load operation of the engine.
[0041]
According to the second aspect of the present invention, the temperature of the catalyst supported on the center of the catalyst carrier can be quickly raised to the activation temperature when the engine is started.
[0042]
According to the invention of claim 3, even if the distance from the engine to the catalyst carrier is set as short as possible so that the catalyst is quickly heated to the activation temperature, the opening angle of the tapered portion is not set large, A reduction in the axial distance between the exhaust pipe and the connecting pipe can be avoided, and it is possible to prevent a reduction in output torque in the low-speed rotation region of the engine, and a relatively large volume is occupied by the tapered portion. Further, it can be used as a buffer chamber during high-load operation of the engine, and deterioration of the ventilation resistance at the catalyst carrier can be prevented.
[Brief description of the drawings]
FIG. 1 is a right side view of a motorcycle.
FIG. 2 is a longitudinal sectional view of an exhaust purifier and a silencer.
FIG. 3 is an enlarged view of a main part of FIG.
4 is a cross-sectional view taken along line 4-4 of FIG.
FIG. 5 is a diagram showing a change in catalyst center temperature depending on a drawing ratio in a connecting pipe.
[Explanation of symbols]
21 ... Exhaust pipe 22 ... Exhaust gas purifier
23 ... silencer 24 ... casing 25 ... cylindrical part 26 ... taper part 28 ... catalyst carrier 34 ... connecting pipe E ... engine

Claims (5)

An exhaust purifier (22) is provided downstream of the connecting pipe (34) connected to the exhaust pipe (21) for introducing exhaust gas from the engine (E), and a silencer (23) is provided downstream of the exhaust purifier (22). ) Are the exhaust systems of the engine respectively disposed,
A casing (24) common to the exhaust purifier (22) and the silencer (23) includes a cylindrical portion (25) in which the exhaust purifier (22) and the silencer (23) are incorporated, and a cylindrical portion (25 ) And a tapered portion (26) having a small diameter end connected to the connecting pipe (34), and the exhaust purifier (22) is connected to the cylindrical portion (22). 25) , a catalyst carrier (28) having a circular outer surface larger than the outer diameter of the connection pipe (34) and carrying the catalyst is provided, and the upstream end of the catalyst carrier (28) is connected to the upstream end of the catalyst carrier (28). in those opposed placed spaced downstream end of the connecting tube (34),
The catalyst carrier (28) is arranged such that the upstream end portion of the catalyst carrier (28) projects into the tapered portion (26) from the large diameter end portion to the small diameter end portion side. 28) The exhaust system of the engine , wherein an annular space between the outer peripheral surface of 28) and the inner peripheral surface of the casing (24) is gradually narrowed toward the upstream side by the tapered portion (26) .   The engine exhaust gas purifier according to claim 1, wherein the inner diameter of at least the downstream end of the connection pipe (34) is set smaller than the inner diameter of the exhaust pipe (21). 3. The engine exhaust system according to claim 1, wherein a downstream end of the connection pipe (34) projects into the taper portion (26) from the small diameter end portion toward the large diameter end portion. 4. . When the inner diameter of the connecting pipe (34) is D1 and the inner diameter of the exhaust pipe (21) is D2, 0.05 ≦ {(D2−D1) / D2} ≦ 0.40 is set. The engine exhaust system according to claim 2. When the inner diameter of the connection pipe (34) is D1, an interval (L) between the downstream end of the connection pipe (34) and the upstream end of the catalyst carrier (28) is 0.5 × D1-3 × D1. The engine exhaust system according to claim 3, wherein the engine exhaust system is set within a range.

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