Exhaust device for internal combustion engine

An exhaust muffler is made up of a plurality of layers including an exhaust passage pipe and expansion chambers, and includes a front assembly and a rear assembly sub-assembled separately from the front assembly. The front assembly includes a front exhaust passage pipe, a front muffler body disposed in covering relation to the outside of the front exhaust passage pipe and cooperating with the front exhaust passage pipe in making up double-walled pipes, and an exhaust valve disposed in the front exhaust passage pipe. The rear assembly includes a rear exhaust passage pipe and a rear muffler body disposed in covering relation to the outside of the rear exhaust passage pipe and cooperating with the rear exhaust passage pipe in making up double-walled pipes. There is thus provided an exhaust device for an internal combustion engine in which the accuracy of a position where the exhaust valve is installed is high.

TECHNICAL FIELD

The present invention relates to an exhaust device for an internal combustion engine, in which an exhaust valve is provided in an exhaust passage pipe disposed in an exhaust muffler, for opening and closing the exhaust passage pipe to switch between flow passageways for exhaust gases such that when the exhaust valve closes the exhaust passage pipe, one of the flow passageways that is positioned upstream of the exhaust valve is selected for the exhaust gases to flow therethrough.

BACKGROUND ART

Heretofore, there has been an exhaust device for an internal combustion engine, in which an exhaust valve is provided in an exhaust pipe extending through an exhaust muffler (see PATENT DOCUMENT 1). In such an exhaust device for an internal combustion engine, an exhaust valve is provided within an exhaust passage pipe in the vicinity of the center of the exhaust passage pipe that is integrally disposed in and extends through an exhaust muffler. For manufacturing the exhaust device, it is necessary to prepare the exhaust passage pipe with the exhaust valve pre-assembled therein as a sub-assembly and assemble the exhaust muffler in covering relation to the sub-assembly. If the exhaust passage pipe is long in size, then it is difficult to increase the accuracy of a position where the exhaust valve is installed in the exhaust passage pipe.

PRIOR ART DOCUMENT

Patent Document

JP 2006-017124 A

SUMMARY OF THE INVENTION

Underlying Problem to be Solved by the Invention

An exhaust device for an internal combustion engine according to the present invention has been devised in order to overcome the above difficulties. It is an object of the present invention to provide an exhaust device for an internal combustion engine, which includes an exhaust muffler with an exhaust valve provided in an exhaust passage pipe that is integrally disposed in and extends through the exhaust muffler, where the accuracy of a position where the exhaust valve is installed is high.

Means to Solve the Underlying Problem

According to the invention, there is provided an exhaust device for an internal combustion engine, including an exhaust pipe and an exhaust muffler connected to a downstream end of the exhaust pipe, the exhaust muffler extending from a portion thereof connected to the exhaust pipe rearward on a vehicle on which the exhaust muffler is installed, the exhaust device including: a plurality of expansion chambers defined in the exhaust muffler; an exhaust passage pipe extending through the expansion chambers for allowing exhaust gases from the exhaust pipe to flow therethrough; and an exhaust valve provided in the exhaust passage pipe for opening and closing the exhaust passage pipe to switch between flow passageways for exhaust gases,

wherein the exhaust muffler is made up of a plurality of layers including the exhaust passage pipe and the expansion chambers provided around an outer periphery of the exhaust passage pipe;

the exhaust muffler includes a front assembly connected to the exhaust pipe and a rear assembly connected to a rear portion of the front assembly and sub-assembled separately from the front assembly;

the exhaust passage pipe includes a front exhaust passage pipe as part of the front assembly, with the exhaust valve being disposed in the front exhaust passage pipe, and a rear exhaust passage pipe as part of the rear assembly;

the front assembly includes the front exhaust passage pipe41, a front muffler body disposed in covering relation to an outside of the front exhaust passage pipe to cooperate with the front exhaust passage pipe in making up double-walled pipes, and the exhaust valve; and

the rear assembly includes the rear exhaust passage pipe and a rear muffler body disposed in covering relation to an outside of the rear exhaust passage pipe to cooperate with the rear exhaust passage pipe in making up double-walled pipes.

With the above arrangement, the exhaust muffler is made up of a plurality of layers including the exhaust passage pipe and the expansion chambers around the outer periphery of the exhaust passage pipe. Of the exhaust muffler, the front assembly connected to the exhaust pipe serves as a single assembly including the front exhaust passage pipe and the front muffler body that make up double-walled pipes, with the exhaust valve disposed in the front exhaust pipe, and the rear assembly as another assembly. After the front assembly and the rear assembly have been sub-assembled separately, the front assembly and the rear assembly are integrally assembled together into the exhaust device, providing the exhaust device. There is thus provided an exhaust device in which the accuracy of a position where the exhaust valve is installed is high.

In the above arrangement, the front muffler body may be of a circular cross-sectional shape and the rear muffler body may be of a non-circular cross-sectional shape; and a valve actuator coupled to the exhaust valve for opening and closing the exhaust valve may be disposed on an outside of the front muffler body.

With the above arrangement, in a case where the exhaust muffler includes the front muffler body and the rear muffler body that have different cross-sectional shapes, the exhaust valve is disposed in the front assembly that incorporates the front muffler body shaped to a circular cross section, and the valve actuator for opening and closing the exhaust valve is provided on the outer side of the front muffler body. With this arrangement, the layout freedom of the exhaust valve in the circumferential directions of the exhaust muffler can be further increased.

In the above arrangement, one of the expansion chambers may be provided between the front exhaust passage pipe and the front muffler body; others of the expansion chambers may be provided between the rear exhaust passage pipe and the rear muffler body; the front muffler body may have an outside diameter smaller than an outside diameter of the rear muffler body and may have a constricted shape; and the front exhaust passage pipe and the rear exhaust passage pipe may be generally of the same diameter as each other.

With the above arrangement, the front exhaust passage pipe of the exhaust muffler is generally of the same diameter as the rear exhaust passage pipe, and the outside diameter of the first expansion chamber around the outer periphery of the front exhaust passage pipe is smaller than the outside diameter of the expansion chambers in the rear exhaust muffler. Therefore, the length of the exhaust valve shaft that connects the exhaust valve and the valve actuator to each other is reduced, minimizing twisting of the exhaust valve shaft to minimize an operational delay of the exhaust valve.

In the above arrangement, the exhaust muffler may have a front end connected to the downstream end of the exhaust pipe; the exhaust passage pipe may have an upstream end positioned upstream of the exhaust valve and connected to the exhaust pipe in the exhaust muffler; and the exhaust passage pipe may have fluid communication holes defined therein between an area where the upstream end of the exhaust muffler is connected and an area where the exhaust valve is provided, the through holes being held in fluid communication with the expansion chamber.

With the above arrangement, where the front end of the exhaust muffler is connected to the exhaust pipe, the upstream end of the exhaust passage pipe is connected to the downstream end of the exhaust pipe, and the exhaust passage pipe is held in fluid communication with the expansion chamber through the through holes on the upstream side of the exhaust valve. Consequently, when the exhaust valve is closed, exhaust gases are caused to flow into the expansion chamber by a simple structure.

In the above arrangement, the exhaust muffler may have a front end connected to the downstream end of the exhaust pipe; the exhaust passage pipe may have an upstream end positioned upstream of the exhaust valve and spaced an interval from the exhaust pipe in the exhaust muffler; and the exhaust pipe may be held in fluid communication with the expansion chamber through a gap between the exhaust pipe and the upstream end of the exhaust passage pipe.

With the above arrangement, where the upstream end of the exhaust muffler is connected to the exhaust pipe, the front end of the exhaust passage pipe is spaced from the downstream end of the exhaust pipe. When the exhaust valve is closed, exhaust gases from the exhaust pipe is caused to flow into the expansion chamber through the gap between the exhaust pipe and the exhaust passage pipe. The junction between the exhaust pipe and the exhaust passage pipe is thus reduced, providing a simpler structure.

In the above arrangement, at least either upstream portions or downstream portions of the front muffler body and the front exhaust passage pipe may be integrally connected to each other respectively by annular plate members; and the annular plate members may have fluid communication holes defined therein through which exhaust gases flow.

With the above arrangement, the portion of the front exhaust passage pipe where the exhaust valve is disposed is covered with the front muffler body having inner and outer double-walled pipes, and the upstream and downstream ends of the double-walled tubular members are connected by the annular plate members. The space of the expansion chamber can thus simply be created using the annular plate members, and the plural members can easily be integrated.

In the above arrangement, the communication holes defined in the annular plate members may be provided as a plurality of fluid communication holes spaced at circumferential intervals.

With the above arrangement, as the fluid communication holes in the annular members are disposed at circumferentially spaced intervals, exhaust gases that are flowing in is diffused in outer circumferential directions through the fluid communication holes for a balanced flow of exhaust gases.

In the above arrangement, the fluid communication holes defined in the annular plate members may be provided such that the number of the fluid communication holes defined in the annular plate member disposed on an upstream side may be larger than the number of the fluid communication holes defined in the annular plate member disposed on a downstream side.

With the above arrangement, the larger number of the fluid communication holes on the upstream side promotes diffusion of exhaust gases, and the smaller number of the fluid communication holes on the downstream side permits each of the fluid communication holes to be increased in size, thereby making it easy to discharge exhaust gases from the front assembly and hence to prevent exhaust gases from staying stagnant in the front assembly.

In the above arrangement, the exhaust pipe may have a downstream end fitted over or in and held by a front end of the exhaust passage pipe, and only the annular plate member may be disposed downstream of the exhaust valve.

With the above arrangement, inasmuch as the downstream end of the exhaust pipe is fitted in or over and held by the front end of the exhaust passage pipe, one of the annular plate members can be dispensed with, and the cross-sectional area of the flow passageway for exhaust gases is maximized, so that the resistance to a flow of exhaust gases is reduced and the number of parts used is reduced for a cost reduction.

In the above arrangement, the annular plate member may include radial extensions separating adjacent ones of the fluid communication holes and disposed radially; and one of the radial extensions may be positioned in overlapping relation to an exhaust valve shaft of the exhaust valve in the direction of a flow passage.

With the above arrangement, one of the radial extensions is positioned in overlapping relation to the exhaust valve shaft. Consequently, the resistance of the flow passage is prevented from increasing without an increase in the areas of closures provided by the valve shaft and the radial pieces.

In the above arrangement, the exhaust muffler may include an exhaust device mount member by which the exhaust device is mounted on the vehicle; the exhaust device mount member may include a front mount and a rear mount that are fixed respectively to the front muffler body and the rear muffler body, a front mount piece extending from the front mount upwardly of the front muffler body, and a rear mount piece extending from the rear mount and joining the rear mount to an upper end of the front mount piece; and a vehicle mount to be mounted on the vehicle may be provided on a junction between the front mount piece and the rear mount piece.

With the above arrangement, the exhaust muffler is suspended by the front mount and the rear mount of the exhaust device mount member, the front mount piece and the rear mount piece extending respectively from the front mount and the rear mount, and the vehicle mount provided on the junction between the front mount piece and the rear mount piece that are arranged in a triangular layout, and hence the rigidity with which the exhaust muffler is suspended is increased.

Advantageous Effect of the Invention

An exhaust device for an internal combustion engine according to the present invention includes an exhaust muffler incorporating an exhaust valve therein and disposed in the vicinity of the center of an exhaust passage pipe that is disposed integrally with and extending through the exhaust muffler, the exhaust muffler including a front assembly connected to an exhaust pipe and serving as a single assembly that includes a front exhaust passage pipe and a front muffler body that make up double-walled pipes, and a rear assembly as another assembly, the exhaust valve being disposed in the front assembly. Therefore, the accuracy of a position where the exhaust valve is installed is high.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An exhaust device20for an internal combustion engine according to a first embodiment of the present invention for use on a saddle-type vehicle will be described below with reference toFIGS. 1 through 14.

FIG. 1is a right-hand side elevational view of a two-wheel motorcycle1as an example of a saddle-type vehicle incorporating the exhaust device20according to the present embodiment. In the present description, forward, rearward, leftward, and rightward directions are defined with respect to the posture of the motorcycle1that is oriented in a forward direction along which the motorcycle1moves ahead.

The two-wheel motorcycle1includes a vehicle body frame2constructed as follows. A pair of left and right main frames2bfixed to a head pipe2aextends rearward on a central line of the vehicle body and is bent downward in surrounding relation relative to a cylinder head13of an internal combustion engine E of the motorcycle1. Seat rails2care mounted on upper rear portions of the main frames2band extend rearward while spreading to the left and right.

In the vehicle body frame2, a front fork3is pivotally supported on the head pipe2a, and a handle4extending to the left and right is mounted on an upper end of the front fork3. A front wheel5is rotatably supported on a lower end of the front fork3. A swing arm6has a front end pivotally supported by a swing arm pivot2dmounted on lower portions of the main frames2band extends rearward, and a rear wheel7is rotatably supported on a rear end of the swing arm6. A rear cushion8is interposed between the swing arm6and a lower portion of the vehicle body frame2. A fuel tank9is mounted on the main frames2band the seat rails2c, and a rider's seat10is supported on the seat rails2cbehind the fuel tank9.

The internal combustion engine E supported on the vehicle body frame2includes an in-line four-cylinder, four-stroke internal combustion engine, for example, and includes a cylinder block12and the cylinder head13that are stacked successively on a crankcase11and fastened integrally together by bolts (not depicted), with the cylinder head13being covered with a cylinder head cover14disposed on its upper portion. The internal combustion engine E has a crankshaft15oriented in the widthwise directions of the vehicle body, is surrounded by the vehicle body frame2, and has cylinders16slightly inclined forwardly.

To the cylinders16of the internal combustion engine E, there are connected an intake manifold (not depicted) having a fuel injection valve (not depicted), a throttle body17, a connecting tube (not depicted), and an air cleaner18arranged in succession. Ambient air that is drawn in from the air cleaner18is mixed with a fuel injected from the fuel injection valve, producing an air-fuel mixture that is delivered to the cylinders16in which the air-fuel mixture is burned.

An exhaust manifold19is connected to the cylinders16of the internal combustion engine E. The exhaust manifold19includes header pipes19aconnected to the respective cylinders16, extending downward, and then bent rearward, and a collecting pipe19bconnected to rear ends of the header pipes19a. The collecting pipe19bhas a rear end connected to the exhaust device20. Exhaust gases discharged from the cylinders16of the internal combustion engine E are delivered from the exhaust manifold19to the exhaust device20, from which the exhaust gases are discharged into the atmosphere. The exhaust device20includes an exhaust device mount member38by which the exhaust device20is mounted on the vehicle body frame2in a manner to extend obliquely rearward and upward at a position on the right-hand side of the motorcycle1.

As shown inFIG. 2, the exhaust device mount member38includes a front mount38aand a rear mount38cthat are fixed respectively to a front muffler body24and a rear muffler body31, to be described later, a front mount piece38bextending from the front mount38aupward of the front muffler body24, and a rear mount piece38dextending from the rear mount38cand joining the rear mount38cto an upper end of the front mount piece38b. A mount boss38eas a vehicle mount to be mounted on the motorcycle1is provided on the junction between the front mount piece38band the rear mount piece38d. The exhaust device mount member38also has through holes38f, one in the front mount piece38band three in the rear mount piece38d, for making itself lightweight. As depicted inFIG. 1, a mounting bolt39is inserted through the mount boss38eof the exhaust device mount member38and fastened to the motorcycle1, thereby mounting the exhaust device20to the motorcycle1.

As depicted inFIGS. 1 and 2, the exhaust device20includes an exhaust pipe21connected to a rear end of the collecting pipe19bof the exhaust manifold19for receiving burned exhaust gases from the internal combustion engine E, and an exhaust muffler22for silencing exhaust gases delivered from the exhaust pipe21. As illustrated inFIGS. 2 through 4, the exhaust pipe21has a downstream end21aconnected to a front end22aof the exhaust muffler22. As depicted inFIG. 1, the exhaust muffler22is in an attitude extending obliquely rearward and upward with respect to the motorcycle1on which the exhaust muffler22is mounted.

As depicted inFIG. 3, the exhaust muffler22has its interior divided by a first partition wall34and a second partition wall35into a first expansion chamber45, a third expansion chamber47, and a second expansion chamber46that are arranged successively from the front. To the downstream end21aof the exhaust pipe21, there is connected an exhaust passage pipe40through which exhaust gases from the exhaust pipe21flow. The exhaust passage pipe40is of a hollow cylindrical shape extending through the expansion chambers45,46, and47in the exhaust muffler22to a rear end of the exhaust device20, and has a diameter that remains essentially the same from its front end to rear end. The exhaust muffler22is thus made up of a plurality of layers as the exhaust passage pipe40and the expansion chambers45,46, and47provided around the outer periphery of the exhaust passage pipe40. Furthermore, in the exhaust passage pipe40is disposed an exhaust valve50for switching between flow passageways for exhaust gases by opening and closing the exhaust passage pipe40.

As shown inFIG. 2, the exhaust muffler22includes a front assembly23positioned forward and connected to the exhaust pipe21and a rear assembly30connected to a rear portion of the front assembly23. The rear assembly30is sub-assembled separately from the front assembly23, and then assembled integrally with the front assembly23.

As depicted inFIG. 3, the exhaust passage pipe40includes a front exhaust passage pipe41as part of the front assembly23and a rear exhaust passage pipe42as part of the rear assembly30. The front exhaust passage pipe41includes a first exhaust passage pipe41apositioned forward and a second exhaust passage pipe41bpositioned rearward. The rear exhaust passage pipe42includes a third exhaust passage pipe42apositioned forward and a fourth exhaust passage pipe42bpositioned rearward. The exhaust valve50is provided in the first exhaust passage pipe41aof the front exhaust passage pipe41.

As shown inFIGS. 3 and 4, the front assembly23includes the front exhaust passage pipe41and the front muffler body24disposed in covering relation to the outside of the front exhaust passage pipe41and cooperating with the front exhaust passage pipe41in making up double-walled pipes. The front exhaust passage pipe41is made up of the first exhaust passage pipe41aand the second exhaust passage pipe41b. The front assembly23further includes a first annular plate member25fixed to an upstream portion41a1of the first exhaust passage pipe41aand an upstream portion24b1of the front muffler body24and closing the gap between the upstream portion41a1and the upstream portion24b1, a second annular plate member26fixed to a downstream portion41a2of the first exhaust passage pipe41aand a downstream portion24b2of the front muffler body24and closing the gap between the downstream portion41a2and the downstream portion24b2, and the exhaust valve50disposed in the first exhaust passage pipe41afor opening and closing the first exhaust passage pipe41a.

As depicted inFIG. 3, the rear assembly30includes the rear exhaust passage pipe42, the rear muffler body31disposed in covering relation to the outside of the rear exhaust passage pipe42and cooperating with the rear exhaust passage pipe42in making up double-walled pipes, the first partition wall34and the second partition wall35that divide the interior of the rear muffler body31, and a fluid communication pipe37that provides fluid communication between the first expansion chamber45and the second expansion chamber46.

The front assembly23is of a substantially circular cross-sectional shape, as depicted inFIGS. 3 and 5, and the rear assembly30is of a non-circular cross-sectional shape that is longer vertically and narrower horizontally, as will be noted fromFIGS. 11 and 12. As depicted inFIG. 3, the front assembly23has an outside diameter smaller than the outside diameter of the rear assembly30and has a constricted shape. The front assembly23and the rear assembly30are connected to each other by a connector28whose cross-sectional area is progressively larger from its front end toward its rear end. The first expansion chamber45in the front assembly23has an outside diameter smaller than the outside diameters of the second expansion chamber46and the third expansion chamber47in the rear assembly30.

The front muffler body24includes a front cover24aconnected to the exhaust pipe21, a first tubular member24bconnected to a rear end of the front cover24a, and a second tubular member24chaving a front end connected to a rear end of the first tubular member24band a rear end connected to the connector28. The first tubular member24band the second tubular member24care of substantially the same diameter. The first tubular member24bextends straight, while the second tubular member24cis of a gradually curved shape.

The front exhaust passage pipe41is provided within the front muffler body24. As depicted inFIG. 4, the first exhaust passage pipe41ahas an upstream end connected to the downstream end21aof the exhaust pipe21. The first exhaust passage pipe41ais disposed within the front cover24aand the first tubular member24bconcentrically with the first tubular member24b, providing inner and outer double-walled pipes. The second exhaust passage pipe41bis of substantially the same diameter as the outside diameter of the first exhaust passage pipe41a, and is connected to a downstream end of the first exhaust passage pipe41a. As depicted inFIG. 3, the second exhaust passage pipe41bis curved to a shape along the curvature of the second tubular member24c, and disposed within the second tubular member24cconcentrically therewith.

As depicted inFIG. 4, the first annular plate member25and the second annular plate member26are disposed between the first tubular member24band the front exhaust passage pipe41disposed therein, and attached to the first tubular member24band the front exhaust passage pipe41such that planes of the first annular plate member25and the second annular plate member26lie perpendicularly to the longitudinal directions of the first tubular member24b. The first annular plate member25is disposed closely to a front end of the first tubular member24b, while the second annular plate member26is disposed closely to a rear end of the first tubular member24b.

As depicted inFIG. 6, the first annular plate member25includes a ring-shaped annular plate25ahaving an outside diameter that is the same as the inside diameter of the first tubular member24band an inside diameter that is the same as the outside diameter of the first exhaust passage pipe41ainserted in the annular plate25a. The annular plate25ahas a plurality of (four in the present embodiment) fluid communication holes25bdefined therein that provide fluid communication between a first compartment45aand a second compartment45b, to be described later, of the first expansion chamber45. The fluid communication holes25bare shaped as oblong holes along the circumferential directions of the annular plate25a, are of identical shapes, and are spaced at equal circumferential intervals. As depicted inFIG. 4, the first annular plate member25includes a fixing flange25cextending rearward from an outer circumferential edge of the annular plate25aperpendicularly to the annular plate25aand having a predetermined width, and a fixing flange25dextending forward from an inner circumferential edge of the annular plate25aperpendicularly to the annular plate25aand having a predetermined width.

As depicted inFIGS. 4 and 7, the second annular plate member26also includes a ring-shaped annular plate26a, as with the first annular plate member25, and fixing flanges26cand26dextending forward and rearward from outer and inner circumferential edges of the annular plate26aperpendicularly thereto and having predetermined widths. The annular plate26ahas an outside diameter that is the same as the inside diameter of the first tubular member24band an inside diameter that is the same as the outside diameter of the first exhaust passage pipe41ainserted in the annular plate26a. As depicted inFIG. 7, the annular plate26ahas a plurality of (four in the present embodiment) fluid communication holes26bdefined therein that provide fluid communication between the second compartment45band a third compartment45c, to be described later, of the first expansion chamber45. The fluid communication holes26bare shaped as oblong holes along the circumferential directions of the annular plate26a, are of identical shapes, and are spaced at equal circumferential intervals. The fluid communication holes26bare angularly spaced 45 degrees from the fluid communication holes25bdefined in the first annular plate member25about the central axis of the first exhaust passage pipe41a.

As depicted inFIG. 4, the fixing flange25cof the first annular plate member25is held in abutment against and fixed to an inner circumferential surface of the upstream portion24b1of the first tubular member24b, and the fixing flange25dthereof is held in abutment against and fixed to an outer circumferential surface of the upstream portion41a1of the first exhaust passage pipe41a. The upstream portions24b1and41a1of the first tubular member24band the first exhaust passage pipe41a, which are provided as the inner and outer double-walled pipes, are integrally connected to each other by the first annular plate member25in a manner to close the gap therebetween.

The fixing flange26cof the second annular plate member26is held in abutment against and fixed to an inner circumferential surface of the downstream portion24b2of the first tubular member24b, and the fixing flange26dthereof is held in abutment against and fixed to an outer circumferential surface of the downstream portion41a2of the first exhaust passage pipe41a. The downstream portions24b2and41a2of the first tubular member24band the first exhaust passage pipe41a, which are provided as the inner and outer double-walled pipes, are integrally connected to each other by the second annular plate member26in a manner to close the gap therebetween. The first expansion chamber45is divided by the first annular plate member25and the second annular plate member26into the first compartment45a, the second compartment45b, and the third compartment45cthat are successively arranged from the front.

As depicted inFIGS. 4 and 5, the exhaust valve50for opening and closing the exhaust passage pipe40is provided in the first exhaust passage pipe41athereof that is positioned upstream. The exhaust valve50is controlled for its opening and closing operation depending on the output power of the internal combustion engine E. The exhaust valve50serves as a device for silencing exhaust gases by changing flow passageways for the exhaust gases thereto to expand the exhaust gases, and also for adjusting the characteristics of the internal combustion engine E by applying a back pressure to the exhaust gases. The exhaust valve50is disposed in a region of the exhaust muffler22where the first tubular member24band the first exhaust passage pipe41aare provided as the inner and outer double-walled pipes, and is positioned between the first annular plate member25and the second annular plate member26with respect to the direction along which the exhaust gases flow. The exhaust valve50is of a disk shape whose outer edge extends along an inner circumferential surface of the first exhaust passage pipe41a. As depicted inFIG. 4, the exhaust valve50has an outside diameter d2smaller than an inside diameter d1of the first exhaust passage pipe41a, allowing a very small amount of exhaust gases to pass through the gap between the exhaust valve50and the first exhaust passage pipe41a.

As depicted inFIGS. 5 through 8, the exhaust valve50includes an exhaust valve shaft51fastened thereto by a pair of screws52with a washer57interposed therebetween. The exhaust valve shaft51is coupled to a valve actuator60that opens and closes the exhaust valve50. As depicted inFIG. 3, the exhaust valve shaft51extends through outer surfaces of the first exhaust passage pipe41aand the first tubular member24bof the front assembly23of the exhaust muffler22, and the valve actuator60is disposed on an outer side surface of the exhaust muffler22. As depicted inFIG. 5, the exhaust valve shaft51is angularly movably supported by bearings53on an upper support member54mounted on an upper portion of the first exhaust passage pipe41aand a lower support member55mounted on a lower portion of the first exhaust passage pipe41a. A cap56for preventing the exhaust valve shaft51from coming off is attached to a lower surface of the lower support member55.

As depicted inFIGS. 5 and 8, the exhaust valve shaft51has an upper portion51aextending upward through upper portions of the first exhaust passage pipe41aand the first tubular member24bof the front muffler body24. A pulley62is mounted on the upper portion51aof the exhaust valve shaft51for angular movement in unison therewith, and a drive wire63is trained around the pulley62. When the drive wire63is pulled by a drive device, not shown, the exhaust valve shaft51is angularly moved about its own axis, opening and closing the exhaust valve50in the exhaust passage pipe40. The pulley62has its peripheral area covered with a case65that is made up of an upper case body65aand a lower case body65bwhich are integrally fastened to each other by a pair of bolts66. The case65is supported on a base64welded to an outer surface of the first tubular member24b.

As depicted inFIG. 4, the first exhaust passage pipe41aof the front exhaust passage pipe41of the exhaust passage pipe40has a plurality of through holes40bformed therein between an area where the front end22aof the exhaust muffler22is connected and an area where the exhaust valve50is provided, the through holes40bproviding fluid communication between the inside of the exhaust passage pipe40and the first expansion chamber45. When the exhaust valve50closes the exhaust passage pipe40, exhaust gases flowing from the exhaust pipe21into the exhaust passage pipe40pass through the through holes40band flow into the first compartment45aof the first expansion chamber45.

As depicted inFIG. 3, the rear assembly30is connected to the downstream side of the front assembly23through the connector28. The rear assembly30includes the rear muffler body31, the first partition wall34and the second partition wall35that divide the interior of the rear muffler body31, a downstream end wall36that closes a downstream end of the rear muffler body31, the rear exhaust passage pipe42, and the fluid communication pipe37. The rear exhaust passage pipe42is connected to a downstream end of the front exhaust passage pipe41, extends through the first partition wall34, the second partition wall35, and the downstream end wall36, and is held in fluid communication with the ambient air. The fluid communication pipe37extends through the first partition wall34and the second partition wall35, and is held in fluid communication with the first expansion chamber45and the second expansion chamber46.

As depicted inFIGS. 9 and 10, the rear muffler body31includes a tubular outer body31aand an inner body31bdisposed in the outer body31awith a predetermined gap therebetween. The gap between the outer body31aand the inner body31bis filled up with a filling material32such as glass wool or the like for heat insulation and sound absorption. A tail cover31cis mounted on a downstream end of the outer body31aand has an exhaust passage pipe insertion hole31ddefined therein. As depicted inFIGS. 11 and 12, the rear muffler body31is of a noncircular cross-sectional shape perpendicular to the flow of exhaust gases, which is vertically elongate, widest at a portion slightly above its center, and progressively narrower in a downward direction.

As shown inFIG. 9, the rear exhaust passage pipe42is made up of a third exhaust passage pipe42aconnected to the downstream end of the second exhaust passage pipe41bof the front exhaust passage pipe41and a fourth exhaust passage pipe42bconnected to the downstream end of the third exhaust passage pipe42a. The fourth exhaust passage pipe42bhas a downstream end inserted in the exhaust passage pipe insertion hole31din the tail cover31c, and the exhaust passage pipe40has a downstream end40cheld in fluid communication with the ambient air. The third exhaust passage pipe42aof the rear exhaust passage pipe42has a plurality of through holes42cdefined therein which provides fluid communication between the inside of the rear exhaust passage pipe42and the third expansion chamber47. The through holes42care provided to allow exhaust gases that have passed successively through the first expansion chamber45, the second expansion chamber46, and the third expansion chamber47to pass through the through holes42cand flow into the rear exhaust passage pipe42, from which the exhaust gases are discharged through the downstream end40cof the exhaust passage pipe40.

As depicted inFIGS. 3, 9, and 13, the interior of the exhaust muffler22is divided by the first partition wall34and the second partition wall35into the first expansion chamber45, the third expansion chamber47, and the second expansion chamber46that are arranged successively from the front. As depicted inFIG. 11, the first partition wall34has an exhaust passage pipe insertion hole34bdefined in an upper portion of a wall34athereof for insertion of the third exhaust passage pipe42atherein, and a fluid communication pipe insertion hole34cdefined in a lower portion of the wall34afor insertion of the fluid communication pipe37therein. As depicted inFIG. 12, the second partition wall35has an exhaust passage pipe insertion hole35bdefined in an upper portion of a wall35athereof for insertion of the third exhaust passage pipe42atherein, a fluid communication pipe insertion hole35cdefined in a lower portion of the wall35afor insertion of the fluid communication pipe37therein, and a pair of left and right fluid communication holes35ddefined therein in a region between the exhaust passage pipe insertion hole35band the fluid communication pipe insertion hole35cfor providing fluid communication between the second expansion chamber46and the third expansion chamber47. AsFIG. 9shows, the first partition wall34and the second partition wall35are fixedly mounted in the rear muffler body31.

The rear exhaust passage pipe42is inserted in the exhaust passage pipe insertion holes34b,35b, and36bin the first partition wall34, the second partition wall35, and the downstream end wall36and supported by the first partition wall34, the second partition wall35, and the downstream end wall36. The fluid communication pipe37is inserted in the fluid communication pipe insertion holes34cand35cin the first and second partition walls34and35and supported by the first and second partition walls34and35.

According to the present embodiment, the number of the fluid communication holes25bin the first annular plate member25and the number of the fluid communication holes26bin the second annular plate member26are the same as each other, i.e., four. However, the number of the fluid communication holes25bin the first annular plate member25may be larger than the number of the fluid communication holes26bin the second annular plate member26. The larger number of the fluid communication holes25bon the upstream side promotes diffusion of exhaust gases, and the smaller number of the fluid communication holes26bon the downstream side permits each of the fluid communication holes26bto be increased in size, thereby making it easy to discharge exhaust gases from the front assembly23and hence to prevent exhaust gases from staying stagnant in the front assembly23.

Flows of exhaust gases in the exhaust device20in the present embodiment of the invention will be described below with reference toFIGS. 13 and 14.FIG. 13schematically shows a flow of exhaust gases while the exhaust valve50is open. When the valve actuator60is operated to open the exhaust valve50, exhaust gases emitted from the internal combustion engine E pass through the exhaust pipe21, flow from the downstream end21aof the exhaust pipe21through the upstream end of the exhaust passage pipe40into the exhaust passage pipe40, and most of them then are discharged into the ambient air from the downstream end40cof the exhaust passage pipe40. Though some of the exhaust gases in the exhaust passage pipe40pass through the through holes40binto the first compartment45aof the first expansion chamber45, most of the exhaust gases are discharged from the downstream end40cof the exhaust passage pipe40. While the exhaust valve50is open, therefore, the exhaust gases are discharged directly from the exhaust passage pipe40into the ambient air, and do not reduce the output power of the internal combustion engine E.

FIG. 14schematically depicts a flow of exhaust gases while the exhaust valve50is closed. Providing the output power of the internal combustion engine E is very small, when the valve actuator60is operated to close the exhaust valve50, and the exhaust gases emitted from the exhaust pipe21are blocked as the first exhaust passage pipe41ais closed by the exhaust valve50. Since the amount of exhaust gases emitted from the internal combustion engine E is small in this state, most of the exhaust gases pass through the gap between the outer circumferential edge of the exhaust valve50and the inner circumferential surface of the first exhaust passage pipe41a. The pressure wave generated by the exhaust gases, which causes exhaust sounds, passes through the through holes40bin the front exhaust passage pipe41upstream of the exhaust valve50and is transmitted into the first compartment45aof the first expansion chamber45.

Thereafter, the pressure wave passes from the first compartment45athrough the fluid communication holes25bin the first annular plate member25into the second compartment45b, then from the second compartment45bthrough the fluid communication holes26bin the second annular plate member26into the third compartment45c. Then, the pressure wave passes through the fluid communication pipe37that is open into the third compartment into the second expansion chamber46. Thereafter, the pressure wave passes from the second expansion chamber46through the fluid communication holes35din the second partition wall35into the third expansion chamber47, then from the third expansion chamber47through the fluid communication holes42cin the rear exhaust passage pipe42into the exhaust passage pipe40, and is discharged into the ambient air from the downstream end40cof the exhaust passage pipe40. While the exhaust valve50is closed, therefore, the exhaust gases emitted from the internal combustion engine E pass through the exhaust passage pipe40, while the pressure wave of the exhaust gases passes through the expansion chambers45,46, and47, so that the exhaust sounds are reduced.

The exhaust valve50is controlled so as to be opened in proportion to the output power of the internal combustion engine E. The opening of the exhaust valve50is adjusted to cause the exhaust gases to flow in a manner to match the characteristics of the internal combustion engine E, thereby adjusting the flow rate of the exhaust gases. As the pressure wave is caused to pass into the expansion chambers (first expansion chamber45) upstream of the exhaust valve50, the noise of the exhaust gases that increases in proportion to the output power is effectively silenced. The exhaust muffler structure described above is able to separate an exhaust output route and a sound route from each other, so that the output power can be adjusted by a simple structure while a satisfactory silencing capability is achieved. Since the exhaust valve50is of the butterfly type, the output power of the internal combustion engine E can be set to a desired level and the silencing capability for the exhaust sounds can be set to a desired level by changing the opening of the exhaust valve50.

Inasmuch as the exhaust device20for the internal combustion engine according to the embodiment of the present invention is of the above structure, it offers the following advantages.

With the exhaust device20according to the present embodiment, the exhaust muffler22is made up of a plurality of layers as the exhaust passage pipe40and the expansion chambers around the outer periphery of the exhaust passage pipe40. Of the exhaust muffler22, the front assembly23connected to the exhaust pipe21serves as a single assembly including the front exhaust passage pipe41and the front muffler body24that make up double-walled pipes, with the exhaust valve50disposed in the front exhaust passage pipe41, and the rear assembly30as another assembly. After the front assembly23and the rear assembly30have been sub-assembled separately, the front assembly23and the rear assembly30are integrally assembled together into the exhaust device20, providing the exhaust device. The accuracy of a position where the exhaust valve50is installed is therefore increased.

Furthermore, in a case where the exhaust muffler22includes the front muffler body24and the rear muffler body31that have different cross-sectional shapes, the exhaust valve50is disposed in the front assembly23that incorporates the front muffler body24shaped to have a circular cross section, and the valve actuator60for opening and closing the exhaust valve50is provided on the outer side of the front muffler body24. With this arrangement, the layout freedom of the exhaust valve50in the circumferential directions of the exhaust muffler22can be increased.

Of the expansion chambers45,46, and47, the first expansion chamber45is provided between the front exhaust passage pipe41and the front muffler body24, the front exhaust passage pipe41of the exhaust muffler is generally of the same diameter as the rear exhaust passage pipe42, and the outside diameter of the first expansion chamber45around the front exhaust passage pipe41is smaller than the outside diameters of the second expansion chamber46and the third expansion chamber47in the rear muffler body31. Therefore, the length of the exhaust valve shaft51that connects the exhaust valve50and the valve actuator60to each other is reduced, thus minimizing twisting of the exhaust valve shaft51to minimize an operational delay of the exhaust valve50.

Furthermore, the front end22aof the exhaust muffler22is connected to the downstream end21aof the exhaust pipe21, the upstream end40aof the exhaust passage pipe40positioned upstream of the exhaust valve50is connected to the exhaust pipe21in the exhaust muffler22, and the exhaust passage pipe40has the through holes40bformed therein between the area where the front end22aof the exhaust muffler22is connected and the area where the exhaust valve50is provided, the through holes40bbeing held in fluid communication with the first expansion chamber45. Consequently, when the exhaust valve50is closed, exhaust gases are caused to flow into the first expansion chamber45by a simple structure.

The portion of the exhaust muffler22where the exhaust valve50is disposed includes the first tubular member24bof the front muffler body24and the first exhaust passage pipe41aas a plurality of tubular members providing inner and outer double-walled pipes, the upstream portions24b1and41a1of the first tubular member24band the first exhaust passage pipe41aand the downstream portions24b2and41a2thereof are integrally connected to each other respectively by the first annular plate member25and the second annular plate member26that close the gap therebetween, and the first annular plate member25and the second annular plate member26have the fluid communication holes25band26bformed therein through which exhaust gases flow. The space of the first expansion chamber45can simply be created using the first annular plate member25and the second annular plate member26, and the plural members can easily be integrated.

As the fluid communication holes25band26bin the first annular plate member25and the second annular plate member26are disposed at circumferentially spaced intervals, exhaust gases that are flowing in are diffused in outer circumferential directions through the fluid communication holes25band26bfor a balanced flow of exhaust gases.

Moreover, the first annular plate member25and the second annular plate member26have radial extensions25eand26eseparating adjacent ones of the fluid communication holes25band26band disposed radially, and one of the radial extensions25eand26eis positioned in overlapping relation to the exhaust valve shaft51of the exhaust valve50in the direction of the flow passage. Consequently, the resistance of the flow passage is prevented from increasing without an increase in the areas of closures provided by the exhaust valve shaft51and the radial extensions25eand26e.

The exhaust muffler22includes the exhaust device mount member38by which the exhaust device20is mounted on the vehicle. The exhaust device mount member38includes the front mount38aand the rear mount38c, the front mount piece38bextending from the front mount38aupward of the front muffler body24, and the rear mount piece38dextending from the rear mount38cand joining the rear mount38cto the upper end of the front mount piece38b. Further, the mount boss38eto be mounted on the motorcycle1is provided on the junction between the front mount piece38band the rear mount piece38d. Therefore, the exhaust muffler is suspended by the front mount38aand the rear mount38cby way of the front mount piece and the rear mount piece in a triangular layout on the vehicle mount, and hence the rigidity with which the exhaust muffler is suspended is increased.

Since the number of the fluid communication holes25bin the first annular plate member25disposed on the upstream side may be larger than the number of the fluid communication holes26bin the second annular plate member26disposed on the downstream side, the larger number of the fluid communication holes25bon the upstream side may promote diffusion of exhaust gases, and the smaller number of the fluid communication holes26bon the downstream side may permit each of the fluid communication holes26bto be increased in size, thereby making it easy to discharge exhaust gases from the front assembly23and hence to prevent exhaust gases from staying stagnant in the front assembly23.

An exhaust device120for an internal combustion engine according to a second embodiment of the present invention will be described below with reference toFIG. 15. Those structural details that are identical to those of the first embodiment will be described using the reference symbols of the first embodiment. In the exhaust device20according to the first embodiment, the upstream end40aof the exhaust passage pipe40is connected to the downstream end21aof the exhaust pipe21. In the exhaust device120according to the second embodiment, an upstream end140aof an exhaust passage pipe140m, serving as an exhaust passage to which exhaust gases are delivered from the exhaust pipe21, is not connected to the downstream end21aof the exhaust pipe21, but spaced a predetermined interval from the downstream end21aof the exhaust pipe21. The exhaust pipe21and the first expansion chamber45are held in fluid communication with each other through a gap143between the downstream end21aof the exhaust pipe21and the upstream end140aof the exhaust passage pipe140. When the exhaust valve50is closed, exhaust gases flowing from the exhaust pipe21flow from the gap143into the first expansion chamber45. When the exhaust valve50is open, exhaust gases flow from the exhaust pipe21into the exhaust passage pipe140and are discharged into the ambient air from a downstream end140cof the exhaust passage pipe140.

According to the second embodiment, therefore, since the exhaust pipe21and the exhaust passage pipe140are not connected to each other, and exhaust gases from the exhaust pipe21flow into the first expansion chamber45through the gap143between the exhaust pipe21and the exhaust passage pipe140, no connection is necessary between the exhaust pipe21and the exhaust passage pipe140, and the exhaust passage pipe140does not need to have fluid communication holes for fluid communication with the first expansion chamber, resulting in a much simpler structure.

An exhaust device220for an internal combustion engine according to a third embodiment of the present invention will be described below with reference toFIGS. 16 and 17. Those structural details that are identical to those of the first embodiment will be described using the reference symbols of the first embodiment. In the exhaust device220according to the third embodiment, a downstream end221aof an exhaust pipe221is fitted in and held by a front end241cof a front exhaust passage pipe241aof an exhaust passage pipe241. The first annular plate member25is dispensed with, but only a second annular plate member226is provided downstream of the exhaust valve50. According to the present embodiment, though the downstream end221aof the exhaust pipe221is fitted in and held by the front end241cof the front exhaust passage pipe241aof the exhaust passage pipe241, the downstream end221aof the exhaust pipe221may be fitted over and held by the front end241cof the front exhaust passage pipe241aof the exhaust passage pipe241. According to the present embodiment, since the first annular plate member25according to the first embodiment is dispensed with, the first expansion chamber45is divided into two compartments, i.e., the first compartment45apositioned on a front side and the second compartment45bpositioned on a rear side. According to the present embodiment, furthermore, the second annular plate member226has fluid communication holes226bwhich, as depicted inFIG. 17, have radial widths that are in agreement with the maximum width of an annular plate226athat serves as the width of a flow passageway for exhaust gases, making exhaust gases in the first expansion chamber45likely to be discharged and preventing exhaust gases from staying stagnant therein.

In the exhaust device220according to the third embodiment, inasmuch as the downstream end221aof the exhaust pipe221is fitted in or over and held by the front end241cof the front exhaust passage pipe241a, the first annular plate member25is dispensed with, and the radial width of the fluid communication holes226bin the second annular plate member226is maximized to maximize the cross-sectional area of the flow passageway for exhaust gases, so that the resistance to flow of exhaust gases is reduced and the number of parts used is reduced for a cost reduction.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, but various other changes and modifications may be made therein. The exhaust device20according to the present invention is not limited to use on the motorcycle1, but is also widely applicable to other types of saddle-type vehicles.

REFERENCE SIGNS LIST