【０００１】
【発明の属する技術分野】本発明は、自動二輪車に搭載したエンジンから排出される排気ガスの排気音を規制値に適正維持させるとともに排気サウンドとして所謂「いい音」、「心地よい音」を得る事の出来たマフラ構造に関する。
【０００２】
【従来の技術】従来の自動二輪車用のマフラ構造としては例えば特開２００２−８９２３１号公報で知られているように、筒状マフラ内を複数の隔壁で複数の消音室に仕切りそれら消音室内を適宜３本以上の並列した複数の挿入管で連結して音圧レベルを下げて排気音を消音していた。又特開平７−２５３０１７号公報で知られているように筒状マフラ内を複数の隔壁で複数の消音室に仕切り、各隔壁にそれぞれ挿入管を軸方向に直列に配置固定し、しかも最下流の挿入管の軸心を車体外方に傾斜させた自動二輪車のマフラ構造も知られている。
【０００３】
【発明が解決しようとする課題】上記従来例の前者のように３本以上の複数の挿入管を軸方向で並列オーバーラップさせることによって排気ガスを膨張収縮させこの繰り返しで音圧レベルを下げ効果的に消音していた。しかし排気ガスは紆余曲折して流れるのでその分排気抵抗となりエンジン性能は十二分発揮されない懸念があった。
【０００４】又上記従来例の後者のように直列に配置された２本の挿入管を備えたマフラ構造では排気ガスの排気抵抗は少なくエンジン性能上では有利であるが、隔壁に排気ガス流が断続的に衝突し運転者にとって不快な「叩き音」が発生し、しかも最後尾の挿入管の軸心を車体外方に向けていたので周りの人には音圧レベルが高く排気騒音として伝わっていた。また排気音も規制値をクリアするためだけの画一的な音に制限されていてユーザがエンジン排気音をサウンドとして人間の聴覚に心地よいあるいはいい音として表現できるマフラとしては十二分機能していなかった。
【０００５】即ち、一般にエンジンの爆発による鼓動、サウンドは排気ガス流れの一部または全部が紆余曲折せずに直線的に後方に流れることに因って強力に発生する。例えば消音装置が内蔵されていない直管は充分な鼓動感はあるが音圧レベルが高く騒音規制値を満足する事はできない。
【０００６】そこで本発明は以上のような課題を解決するためのもので、自動二輪車用エンジンのマフラ構造において、エンジン性能を低下させることなく、しかも排気騒音規制値を満足させ且つ人間の聴覚に心地よいあるいはいい音としての排気鼓動音を作り出すマフラ構造を得たものでしかもコストダウンにも貢献することをも目的としたものである。
【０００７】
【課題を解決するための手段】本発明の請求項１記載のマフラ構造は、筒状マフラを車両側面に略並行に配置し、車両前方に搭載したエンジンの排気口から排出された排気ガスを、該筒状マフラ内で適宜間隔を置いて固定された複数の隔壁と、隔壁に支持された複数の挿入管によって排気音を消音する自動二輪車用エンジンのマフラ構造において、該筒状マフラ内に固定した少なくとも２つの隔壁のそれぞれに一定長さの管状挿入管を支持させるとともに上流側挿入管後端の横断面積を下流側挿入管前端の横断面積より大きく設定し、且つ上流側挿入管後端の投影断面積と下流側挿入管前端の投影断面積とを投影断面において一部をオーバーラップさせ、更にマフラ前端に装着したエキゾーストパイプの横断面積を最上流挿入管の前端の横断面積より大きく設定し且つエキゾーストパイプの投影断面積と最上流挿入管前端の投影断面積とを投影断面において一部をオーバーラップさせるとともに、少なくとも最後部の挿入管の軸心を、車両平面視において車体中心線に対して後方内側に少しの角度で傾斜させて固定し、更に又該筒状マフラ内に固定した隔壁のうち最後部の隔壁よりも後方のマフラ外筒に後方に適宜長さに亘って延びた延長部を形成し、この延長部と該最後部の隔壁後面部との間に大気開放の空間を設けたもの。
【０００８】本発明の請求項２記載のマフラ構造は、最後部の挿入管の大気開放後端の横断面積を同管の前端の横断面積より大きくなるように末広がり状に形成し、且つその挿入管の一部に低周波域の消音に効果のある共鳴構造としての挿入管壁を貫通する複数の小さな穴を設けたもの。
【０００９】
【発明の実施の形態】本発明を以下図について説明する。図は何れも本発明を示すもので、図１は本発明のマフラ構造を採用した自動二輪車の全体概略側面図、図２乃至図４はそれぞれ本件発明の実施例を表すもので図２は車両平面視における要部水平縦断面図、図３は図２のＡ−Ａ線垂直縦断面図、図４は概略投影図で、（ａ）は挿入管同士の横断面概略投影図を表し、（ｂ）は挿入管とエキゾーストパイプの横断面概略投影図を表す、図５は他の変形例を表す要部水平縦断面である。
【００１０】図１において、１は自動二輪車の車体に搭載されたエンジンを示し、このエンジンからの排気ガスは、エンジン排気口に連結したエキゾーストパイプ２を介し車体下側方に車体と略並行に配置された筒状マフラ３に導かれる。そしてこの筒状マフラ３内で排気音が消音され後部から大気に放出される。
【００１１】図２は本発明の請求項１を表す第一実施例を示すもので、筒状マフラ３の内部を上流から下流の前後方向に複数の室に仕切る適宜間隔を置いて固定された複数の隔壁４、５と、これら各隔壁４、５とで仕切られた各室を順次連通させたそれぞれの挿入管６，７を装着している。尚、筒状マフラ３の内部には通常グラスウール等の断熱材が備えられている。
【００１２】本発明は、それぞれの隔壁４，５に固定したそれぞれの挿入管６、７とその上流のエキゾーストパイプ２とを次の関連をもって構成したものである。即ち上流側挿入管６の後端１４の横断面積を下流側挿入管７の前端１２の横断面積より大きく設定し、且つ上流側挿入管６後端１４の投影断面積と下流側挿入管７の前端１２の投影断面積とを投影断面において一部をオーバーラップ１５させ（図４（ａ）参照、オーバーラップ率１０％から４０％）、更にエキゾーストパイプ２のマフラとの接続部１６の横断面積を上流側挿入管６の前端１７の横断面積より大きく設定し、且つエキゾーストパイプ２のマフラとの接続部１６の投影断面積と上流側挿入管６の前端１７の投影断面積を投影断面において一部をオーバーラップ１８させた（図４（ｂ）参照、オーバーラップ率１０％から４０％）ものである。即ち各挿入管６，７とエキゾーストパイプ２の断面積の大きさは、マフラとの接続部１６＞挿入管６の前端１７＞挿入管７の前端１２の如く下流に行くに従い小さくなるように構成した。
【００１３】本発明は又、最後部の隔壁５を横断する状態で固定した管状の挿入管７の軸心を、車両平面視において車体中心線１０に対して後方内側（車体中心側）に少しの角度α（具体的には略３度から１０度の範囲）で傾斜させて固定し、更にその挿入管７の大気開放後端１１の横断面積を前端１２の横断面積より大きくなるように末広がり状に形成し、且つその挿入管７の一部、例えば挿入管７の後方径大部７１と前方径細部７２にそれぞれ低周波域の消音に効果のある共鳴構造としての管壁を貫通する複数の小さな穴１３１、１３２を設けたものである。
【００１４】本発明は又、上記マフラ構造において、最後部の隔壁５後面部よりも後方下流に向けてマフラ筒を延長させた延長部８を設け、この延長部８と最後部の隔壁５後面部との間に大気開放の空間部９を形成する。尚この延長部８の後端面の形状は図２に示す如く車両平面視側方前広がり傾斜面形状（角度θ＝略４５度）とするが図５に示す如く車両平面視進行方向と直角な面としてもよい。
【００１５】本発明は、又前記上流挿入管６と下流挿入管７のそれぞれの軸心を、車両平面視において車体中心線１０に対して後方内側（車体中心側）に少しの角度α（略３度から１０度の範囲）、β（略３度から１０度の範囲）でそれぞれ傾斜させて固定して構成してもよい。
【００１６】尚、上流挿入管６と下流挿入管７は図３に見られるように垂直断面図示ではその軸心がそれぞれ水平面上にあるがこれをそれぞれ前方上がり傾斜又は後方上がり傾斜でもよい。即ち挿入管６，７は水平面上では車体中心側にそれぞれ傾斜しているが鉛直線上では水平でも前後に傾いていても良い。
【００１７】更に又本発明の実施例は２つの隔壁と２つの挿入管を備えたマフラ構造としたが、本発明の思想を持った３つ以上の隔壁と挿入管を備えてもいいことは明らかである。
【００１８】上記構成の作用を説明すると、エンジンから排出された排気ガスは、基本的にはエキゾーストパイプ２からマフラ３に入り各隔壁４，５で仕切られた室を挿入管６，７を介して拡散膨張干渉作用をして音圧レベルを下げて消音された後、大気に放出される。
【００１９】そして本発明は、エキゾーストパイプ２と上流挿入管６と下流挿入管７とを投影断面でそれぞれオーバーラップさせるとともに排気ガスの流れの一部を直線的に後方に流すことによってエンジン爆発の鼓動をいろいろ変化させる事ができた。即ちオーバーラップ率が大変重要な要素となり種々実験の結果、オーバーラップ率が１０％以下ではエンジン爆発の鼓動が聴覚的に劣り、オーバーラップ率が４０％以上では充分な鼓動が感じられるが音圧が高く騒音規制値の対処に困難が伴う。結局排気鼓動音として規制値をもクリアして聴覚的にも「心地よい、いい音」を両立させるには上記オーバーラップ率は１０％〜４０％が最適であることが判明した。
【００２０】更に本発明は、各挿入管６，７とエキゾーストパイプ２の断面積の大きさをマフラとの接続部１６＞挿入管６の前端１７＞挿入管７の前端１２の如く下流に行くに従い小さくなるように構成したので音圧を少しずつ低下させ排気抵抗を減じているのでエンジン鼓動の減衰を押さえ高い音圧レベルを低下させる事が出来た。
【００２１】更に又本発明は、最後部の挿入管７の軸心を、車体中心線１０に対して後方内側に少しの角度αで傾斜させ、更にその挿入管７の大気開放後端１１の横断面積を前端１２の横断面積より大きくなるように末広がり状に形成し、且つその挿入管７にそれぞれ低周波域の消音に効果のある共鳴構造としての管壁を貫通する複数の小さな穴１３１、１３２を設けるとともに、マフラ筒を延長させた延長部８内側に大気開放の空間部９を形成したので、排気ガスがマフラ内から大気に開放される時に上記空間が変性可能な空間として利用されるため、音質をより「心地よい、いい音」とすることが出来た。尚、穴１３１、１３２は減衰させたい周波数、音圧によって穴の大きさ数、位置は適宜変更可能である。
【００２２】
【発明の効果】本発明の自動二輪車用エンジンのマフラ構造によれば、エンジン性能を低下させることなく、しかも排気騒音規制値を満足させ且つ人間の聴覚に心地よいあるいは「心地よい、いい音」としての排気鼓動音を作り出すマフラ構造を得たものでしかも価格の廉価な筒状マフラを備えた自動二輪車に好適である。
【図面の簡単な説明】
【図１】本発明のマフラ構造を備えた自動二輪車の全体概略側面図。
【図２】本発明の実施例を表すもので車両平面視における要部水平縦断面図。
【図３】図２のＡ−Ａ線垂直縦断面図。
【図４】本発明の要部概略投影図で、（ａ）は挿入管同士の横断面概略投影図を表し、（ｂ）は挿入管とエキゾーストパイプの横断面概略投影図を表す。
【図５】他の変形例を表す要部水平縦断面。
【符号の説明】
２． エキゾーストパイプ
３． 筒状マフラ
４． 隔壁（上流側）
５． 隔壁（下流側）
６． 挿入管（上流側）
７． 挿入管（下流側）
８． 延長部
９． 空間
１０．車両平面視における車体中心線
１１．後端
１２．前端
１３１．穴
１４．後端
１５．オーバーラップ部
１６．接続部
１７．前端
１８．オーバーラップ部[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for maintaining the exhaust sound of exhaust gas emitted from an engine mounted on a motorcycle at a regulated value and obtaining so-called "good sound" and "comfortable sound" as the exhaust sound. On the muffler structure made.
[0002]
2. Description of the Related Art As a conventional muffler structure for a motorcycle, for example, as disclosed in Japanese Patent Application Laid-Open No. 2002-89231, a cylindrical muffler is divided into a plurality of muffling chambers by a plurality of partition walls, and the muffling chambers are divided into a plurality of mufflers. The exhaust sound is muted by lowering the sound pressure level by appropriately connecting a plurality of parallel insertion pipes of three or more. Further, as is known from Japanese Patent Application Laid-Open No. 7-253017, the inside of the cylindrical muffler is partitioned into a plurality of muffling chambers by a plurality of partitions, and an insertion tube is arranged and fixed in each partition in the axial direction in series with each other. There is also known a muffler structure of a motorcycle in which the axis of an insertion pipe is inclined outwardly of a vehicle body.
[0003]
The exhaust gas is expanded and contracted by overlapping three or more insertion tubes in parallel in the axial direction as in the former case of the above-mentioned conventional example, thereby reducing the sound pressure level by repeating this operation. Was silent. However, since the exhaust gas flows in twists and turns, there is a concern that the exhaust resistance will be reduced accordingly and the engine performance will not be sufficiently exhibited.
A muffler structure having two insertion tubes arranged in series like the latter of the prior art described above has a low exhaust gas exhaust resistance and is advantageous in terms of engine performance. Intermittent collisions caused an unpleasant "slap" sound for the driver, and since the axis of the last insertion tube was directed toward the outside of the vehicle body, the sound pressure level was high to surrounding people and transmitted as exhaust noise. I was Exhaust sound is also limited to a uniform sound just to clear the regulation value, and it functions more than enough as a muffler that allows the user to express the engine exhaust sound as a sound that is comfortable or good for human hearing. Did not.
That is, in general, the beating and sound due to the explosion of the engine are generated strongly because part or all of the flow of the exhaust gas flows straight backward without twisting. For example, a straight pipe without a built-in silencer has a sufficient pulsation but has a high sound pressure level and cannot satisfy the noise regulation value.
SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-described problems. In a muffler structure for a motorcycle engine, the engine noise is not reduced, the exhaust noise regulation value is satisfied, and human hearing is reduced. It is a muffler structure that produces a pleasant or good exhaust beating sound, and is also intended to contribute to cost reduction.
[0007]
According to a first aspect of the present invention, there is provided a muffler structure in which a cylindrical muffler is disposed substantially parallel to a side surface of a vehicle, and exhaust gas discharged from an exhaust port of an engine mounted in front of the vehicle is provided. In a muffler structure of a motorcycle engine that silences exhaust sound by a plurality of partition walls fixed at appropriate intervals in the cylindrical muffler and a plurality of insertion pipes supported by the partition wall, A fixed-length tubular insertion tube is supported on each of the at least two fixed partition walls, a cross-sectional area of the rear end of the upstream insertion tube is set to be larger than a cross-sectional area of the front end of the downstream insertion tube, and the rear end of the upstream insertion tube The projected cross section of the front end of the downstream insertion pipe is partially overlapped with the projected cross section of the front end of the downstream insertion pipe, and the cross sectional area of the exhaust pipe attached to the front end of the muffler is traversed by the front end of the most upstream insertion pipe. The projection cross section of the exhaust pipe and the projection cross section of the front end of the most upstream insertion pipe are partially overlapped in the projection cross section, and at least the axial center of the rearmost insertion pipe is set in the plan view of the vehicle. It is fixed at a slight angle to the rear inside with respect to the vehicle body center line, and furthermore, the partition wall fixed inside the cylindrical muffler has a suitable length to the rear of the muffler outer cylinder behind the rearmost partition. An extended portion that extends over the space, and a space open to the atmosphere is provided between the extended portion and the rear surface of the last partition wall.
In the muffler structure according to the second aspect of the present invention, the cross section of the rear end of the insertion tube at the rear end, which is open to the atmosphere, is larger than the cross section of the front end of the tube, and is formed so as to expand. A tube with a plurality of small holes that penetrate the insertion tube wall as a resonance structure that is effective in silencing low-frequency regions.
[0009]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the present invention, FIG. 1 is an overall schematic side view of a motorcycle employing a muffler structure of the present invention, FIGS. 2 to 4 each show an embodiment of the present invention, and FIG. FIG. 3 is a vertical sectional view taken along line AA in FIG. 2, FIG. 4 is a schematic projection view, and FIG. b) is a schematic cross-sectional projection view of the insertion pipe and the exhaust pipe, and FIG. 5 is a main part horizontal vertical cross-section showing another modification.
In FIG. 1, reference numeral 1 denotes an engine mounted on the body of a motorcycle. Exhaust gas from this engine is substantially in parallel with the body in a lower side of the body through an exhaust pipe 2 connected to an engine exhaust port. It is guided to the arranged cylindrical muffler 3. Then, the exhaust sound is silenced in the cylindrical muffler 3 and released from the rear into the atmosphere.
FIG. 2 shows a first embodiment of the present invention. The inside of the cylindrical muffler 3 is fixed at appropriate intervals to partition the inside of the cylindrical muffler 3 into a plurality of chambers from upstream to downstream in the front-rear direction. A plurality of partition walls 4 and 5 and respective insertion tubes 6 and 7 in which chambers partitioned by the partition walls 4 and 5 are sequentially communicated are mounted. Note that a heat insulating material such as glass wool is usually provided inside the cylindrical muffler 3.
In the present invention, the respective insertion pipes 6, 7 fixed to the respective partition walls 4, 5 and the exhaust pipe 2 upstream thereof are constituted as follows. That is, the cross-sectional area of the rear end 14 of the upstream insertion pipe 6 is set to be larger than the cross-sectional area of the front end 12 of the downstream insertion pipe 7, and the projected sectional area of the rear end 14 of the upstream insertion pipe 6 and the cross-sectional area of the downstream insertion pipe 7. The projection cross section of the front end 12 is partially overlapped 15 in the projection cross section (see FIG. 4A, the overlap ratio is 10% to 40%), and further, the cross-sectional area of the connection portion 16 of the exhaust pipe 2 with the muffler Is set larger than the cross-sectional area of the front end 17 of the upstream insertion pipe 6, and the projected cross-sectional area of the connecting portion 16 of the exhaust pipe 2 with the muffler and the projected cross-sectional area of the front end 17 of the upstream insertion pipe 6 are one in the projected cross section. The portions are overlapped 18 (see FIG. 4B, the overlap ratio is 10% to 40%). That is, the size of the cross-sectional area of each of the insertion pipes 6, 7 and the exhaust pipe 2 becomes smaller as going to the downstream, such as the connecting portion 16 with the muffler> the front end 17 of the insertion pipe 6> the front end 12 of the insertion pipe 7. did.
In the present invention, the axial center of the tubular insertion tube 7 fixed so as to cross the rearmost partition wall 5 is slightly inwardly rearward (in the center of the vehicle body) with respect to the vehicle body center line 10 in a plan view of the vehicle. (Specifically, in the range of about 3 to 10 degrees), and furthermore, the insertion pipe 7 has a cross-sectional area of the rear end 11 which is open to the atmosphere and is widened so as to be larger than the cross-sectional area of the front end 12. And a part of the insertion tube 7, for example, a large rear portion 71 and a small front diameter portion 72 of the insertion tube 7, each penetrating through a tube wall as a resonance structure effective for silencing low-frequency regions. Are provided with small holes 131 and 132.
According to the present invention, in the above-mentioned muffler structure, there is provided an extension 8 which is formed by extending a muffler cylinder toward the downstream downstream from the rear surface of the rearmost partition 5, and the extension 8 and the rear of the rearmost partition 5 are provided. A space portion 9 open to the atmosphere is formed between the surface portion. The shape of the rear end surface of the extension portion 8 is an inclined front surface shape (angle θ = approximately 45 degrees) as shown in FIG. 2, but is perpendicular to the traveling direction of the vehicle as shown in FIG. It may be a surface.
According to the present invention, the respective axes of the upstream insertion pipe 6 and the downstream insertion pipe 7 are set at a slight angle α (substantially inward of the vehicle body center) with respect to the vehicle body center line 10 in plan view of the vehicle. The angle may be fixed at an angle of 3 degrees to 10 degrees) and β (range of about 3 degrees to 10 degrees).
As shown in FIG. 3, the upstream insertion pipe 6 and the downstream insertion pipe 7 have their respective axial centers on a horizontal plane in a vertical cross-sectional view, but they may be inclined forward and backward, respectively. That is, the insertion tubes 6 and 7 are inclined toward the center of the vehicle body on the horizontal plane, but may be horizontal or inclined forward and backward on the vertical line.
Further, although the embodiment of the present invention has a muffler structure having two partition walls and two insertion tubes, three or more partition walls and an insertion tube having the concept of the present invention may be provided. it is obvious.
Explaining the operation of the above construction, the exhaust gas discharged from the engine basically enters the muffler 3 from the exhaust pipe 2 and passes through the chambers separated by the partitions 4 and 5 through the insertion pipes 6 and 7. The sound is reduced by the sound of the sound pressure level due to the diffusion-expansion interference effect, and then released to the atmosphere.
According to the present invention, the exhaust pipe 2, the upstream insertion pipe 6, and the downstream insertion pipe 7 are overlapped with each other in a projected cross section, and a part of the flow of the exhaust gas is caused to flow linearly rearward. I was able to change my heartbeat in various ways. That is, the overlap ratio is a very important factor. As a result of various experiments, when the overlap ratio is 10% or less, the pulsation of the engine explosion is inferior in hearing, and when the overlap ratio is 40% or more, a sufficient pulsation is felt, but the sound pressure is felt. And it is difficult to deal with noise regulation values. In the end, it has been found that the above-mentioned overlap ratio is optimally 10% to 40% in order to clear the regulation value as the exhaust beating sound and to make the sound both pleasant and pleasant.
Further, according to the present invention, the size of the cross-sectional area of each of the insertion pipes 6, 7 and the exhaust pipe 2 goes downstream as in the connection portion 16 with the muffler> the front end 17 of the insertion pipe 6> the front end 12 of the insertion pipe 7. The sound pressure was reduced little by little and the exhaust resistance was reduced, so that the engine pulsation was suppressed and the high sound pressure level could be reduced.
Further, in the present invention, the axial center of the rearmost insertion pipe 7 is inclined rearward and inward with respect to the vehicle body center line 10 at a slight angle α, and the rear end 11 of the insertion pipe 7 is opened to the atmosphere. A plurality of small holes 131 formed in a divergent shape so that the cross-sectional area is larger than the cross-sectional area of the front end 12, and penetrating through the pipe wall as a resonance structure effective for noise reduction in a low frequency range in the insertion pipe 7; In addition to providing the space 132, the air opening space 9 is formed inside the extension 8 that extends the muffler cylinder, so that when the exhaust gas is released from the muffler to the atmosphere, the space is used as a deformable space. Therefore, the sound quality could be made more "comfortable, good sound". The size and position of the holes 131 and 132 can be appropriately changed depending on the frequency and sound pressure to be attenuated.
[0022]
According to the muffler structure of the motorcycle engine of the present invention, it is possible to satisfy the exhaust noise regulation value without deteriorating the engine performance and to be comfortable to human hearing or as a "comfortable, good sound". It is suitable for a motorcycle having a muffler structure for producing an exhaust beating sound and having a low-priced cylindrical muffler.
[Brief description of the drawings]
FIG. 1 is an overall schematic side view of a motorcycle having a muffler structure according to the present invention.
FIG. 2 is a horizontal vertical sectional view of a main part of the embodiment of the present invention, as viewed in a plan view of the vehicle.
FIG. 3 is a vertical sectional view taken along line AA of FIG. 2;
4A and 4B are schematic projections of main parts of the present invention, in which FIG. 4A is a schematic projection of a cross section between insertion pipes, and FIG. 4B is a schematic projection of a cross section of an insertion pipe and an exhaust pipe.
FIG. 5 is a main part horizontal vertical cross section showing another modification.
[Explanation of symbols]
2. 2. Exhaust pipe 3. cylindrical muffler Partition wall (upstream side)
5. Partition wall (downstream side)
6. Insertion tube (upstream side)
7. Insertion tube (downstream side)
8. Extension 9. Space 10. 10. Vehicle center line in plan view of vehicle Rear end 12. Front end 131. Hole 14. Rear end 15. Overlap portion 16. Connection part 17. Front end 18. Overlap section