FR2712923A1 - Motorcycle exhaust valve mechanism. - Google Patents

Abstract

The present invention relates to an exhaust valve mechanism located in a motorcycle having at least an engine (10) and an exhaust pipe assembly (11) for discharging exhaust gases emitted from the engine while damping the noise of exhaust gases. The mechanism comprises a control member (6) for controlling the engine, an exhaust valve device (20) arranged in the exhaust pipe assembly (11) and having an exhaust valve and means for controlling. A control operable in response to actuation of said control member (6) to fully open said exhaust valve from a closed position.

Description

The present invention relates to an exhaust valve mechanism of

  motorcycle, and more particularly an exhaust valve mechanism for use in a motorcycle engine, the exhaust valve mechanism having an exhaust valve which can be actuated by a throttle cable when the motorcycle engine is to be started, the exhaust valve can be temporarily fully opened to reliably start the motorcycle engine.

  There is known an exhaust valve device mounted in the exhaust pipe of a motorcycle powered by a two-stroke engine in order to completely burn the air-fuel mixture of a combustion chamber of the two-stroke engine. by preventing the air-fuel mixture from being subject to reflux when the engine is operating under low load. The exhaust valve device can be actuated by a throttle cable so that when the engine is started, the exhaust valve can be fully opened to reliably start the engine. Until now, no serious consideration has been given to the disposal of the exhaust valve device with respect to the other components of the motorcycle. A problem is constituted by the fact that the device forming the exhaust valve makes it difficult for the motorcycle to take an angle of inclination which is necessary when it takes a curve. According to another problem, since, when the engine is started, the throttle is not actuated over an amplitude (which is 30 to 50% of the total amplitude) such as the valve

  exhaust is fully open, the engine cannot start reliably. The exhaust valve can be fully opened independently by an electric motor when the engine is started. However, such an arrangement has a complex structure and is very expensive because it requires additional mechanical and electrical components. In general, the device forming the exhaust ring is installed at the outlet of the motorcycle exhaust pipe. Consequently, the exhaust valve device is heated to a high temperature when the motorcycle is in operation. Pending Japanese Patent Publication No. 63-141,892, for example, describes a device for

  exhaust system intended for use on a motor vehicle of the scooter type. When the engine of the motor vehicle is rotated at a low speed to have a low output power, the exhaust control device which is described limits the cross-sectional area of an exhaust passage. to remove an undue reduction in torque and power output. Specifically, the exhaust control device comprises an exhaust control valve 0 located at the outlet of the exhaust pipe, and a silencer is mounted on the outlet of the exhaust pipe surrounding the control valve d 'exhaust. The exhaust control valve has an intermediate portion corresponding to a valve body and two shafts extending from opposite sides of the valve body. A pulley is mounted on a first of the shafts to be rotated by a cable, the pulley being received in a pulley housing.

  Since the exhaust control valve is positioned at the outlet of the exhaust pipe, the shafts are heated to a high temperature by the exhaust gases. Since the pulley mounted on one of the shafts is received in the pulley housing, heat from the shaft and therefore from the pulley cannot be dissipated from the pulley housing, and therefore the outer surface of the pulley housing is also heated to an undesirable high temperature.

  Provided that the pulley and pulley housing are located outside the exhaust pipe for reasons of ease of installation and maintenance, it is necessary to take certain measures to thermally protect the pulley and the pulley housing. If the pulley housing is positioned as far as possible from the exhaust pipe, then it is difficult for the motor vehicle to keep its desired inclination angle, and it is necessary to add some arrangement intended to protect the pulley housing against contact with the road when the motor vehicle takes a turn.

  It is therefore an object of the present invention to provide an exhaust valve mechanism having a simple structure, which is suitable for use on a motorcycle.

  According to the present invention there is provided a motorcycle exhaust valve mechanism having at least one engine and an exhaust valve assembly for discharging exhaust gases emitted from the engine while dampening noise exhaust gas, comprising a control element for controlling the engine, an exhaust valve device arranged in the exhaust pipe assembly and comprising an exhaust valve, and actuable control means in response to actuation of the control member to fully open the exhaust valve from a closed position.

  The exhaust valve assembly includes an exhaust pipe, the exhaust valve being arranged in the exhaust pipe and capable of angular movement to substantially close the exhaust pipe in a cross section of that here, the exhaust valve device further comprising a drive shaft supporting the exhaust valve to angularly move the exhaust valve around the drive shaft, the drive shaft having end portions projecting from the exhaust pipe. One of the end parts is positioned farther from the geometric center of the motorcycle than the other end part. Preferably, the drive shaft is inclined with respect to the line of the ground so that one of the end parts is positioned upwards with respect to the other of the end parts. With this arrangement, the motorcycle can maintain the desired angle of inclination when it is inclined, without damaging the exhaust valve device in contact with the ground.

  The control element may include a throttle control element and a throttle cable connected to the throttle control element, and the control means may include a drum attached to a first of the end portions of the 'drive shaft, the throttle cable having a part wound around the drum. The control element may alternatively comprise an engine control element, such as a foot starter, which can be actuated to start the engine, and the control means may be sensitive to the actuation of the engine control element to fully open the exhaust valve from the closed position when starting the engine.

  Preferably, the exhaust valve mechanism may further include a protector covering the exhaust valve device. The motorcycle has a support which can be lowered for parking the motorcycle, and the protector is positioned so that the protector and the exhaust valve device are protected by the support when it is raised and that the motorcycle is tilted. The protector preferably has openings connected to the atmosphere to prevent the protector and the exhaust valve device from being heated to an elevated temperature.

  The exhaust valve device may include a valve housing connected to the exhaust pipe assembly and receiving the exhaust valve, and a drive shaft extending substantially horizontally through the valve housing and connected to the exhaust valve to angularly move the exhaust valve, the drive shaft having end portions projecting from the valve housing, the control means comprising a pulley arranged on a first of the portions d end protruding from the valve housing. The motorcycle has a rear wheel and a support which can be lowered for parking the motorcycle, the exhaust valve device and the guard being positioned inwardly in a straight line, intersecting one side of the rear wheel on which the exhaust valve device is located as well as the outermost end of the support when it is lifted, as seen from the rear.

  The above objects, details and advantages, as well as others, of the present invention will appear on reading the detailed description which will follow in preferred embodiments thereof, made with reference to the drawings. attached in which: - Figure 1 is a schematic side view of a motorcycle equipped with an exhaust valve mechanism according to a first embodiment of the present invention, - Figure 2 is a sectional view taken along line II-II of FIG. 1, FIG. 3 is an enlarged sectional view of an exhaust valve mechanism according to a second embodiment of the present invention, which can be used on the motorcycle shown in Figure 1, - Figure 4 is a sectional view taken along the line IV-IV of Figure 3, - Figure 5 is a partial view of a set-

  ble starting at the foot of the motorcycle which can actuate the exhaust valve mechanism shown in Figure 3, - Figure 6 is a partial perspective view of the motorcycle, representing the positional relationship between the valve mechanism shown in FIG. 3 and a handle of the gases, FIG. 7 is a schematic side view of a motorcycle of the scooter type equipped with an exhaust valve mechanism according to a third embodiment of the present invention, - Figure 8 is a schematic top view of the scooter type motorcycle shown in Figure 7, - Figure 9 is a partial side view on a larger scale of the motorcycle, representing the exhaust valve mechanism according to the third embodiment, which is mounted in an assembly forming an exhaust pipe, - Figure 10 is a rear view of the motorcycle of the scooter type shown in Figure 7, representing in section the exhaust valve mechanism, - Figure 11 is a schematic side view of the scooter type motorcycle shown in Figure 7, having a modified exhaust pipe, and - Figure 12 is a partial side view & more large scale of the scooter type motorcycle shown in FIG. 7, a connection box being arranged in a modified arrangement with respect to the

  scooter type tocycle. We will now describe an exhaust valve mechanism according to a first embodiment of the present invention, with reference to Figures 1 and 2. As shown in Figure 1, a motorcycle comprises a body 1 of motorcycle, supporting a front wheel 2 using a front fork 3 located under a front part of the body 1 of the motorcycle. The front fork 3 has an upper part supported in an angular manner by a front tube 4 of the body 1 of the motorcycle. A handlebar 5 is mounted in the form of an upper cross member located on the upper end of the front fork 3, and two handles 6, one of which serves as a throttle grip, are mounted on the respective opposite ends of the handlebar 5. A front headlight 7 which is directed towards the front and two indicators (not shown) positioned laterally with respect to the front headlight 7 are arranged towards the front of the handlebar 5. The upper part of the front wheel 2 is covered a mudguard 8 which is fixed on the front fork 3.

  The body 1 of the motorcycle comprises a body frame 9 extending rearwards from a front part thereof, and a power assembly 10 comprising an internal combustion engine is mounted on a lower part. practically central of the frame 9 of the body. An assembly 11 forming an exhaust pipe comprising a silencer intended to discharge the exhaust gases while damping the noise is mounted on the right side of the body 1 of the motorcycle, parallel to this. The exhaust pipe assembly 11 comprises an upstream exhaust pipe 11a, a downstream exhaust pipe 11b and a silencer lic. As shown in FIG. 2, a pair of footrests 12 is fixed to the lower end of the frame 9 of the body, the footrests 12 being positioned on each side of the frame 9 of the body. As shown in FIG. 1, a tilting arm 14, on which the rear wheel 13 is supported, is angularly supported on the lower end of the frame 9 of the body.

  The frame 9 of the body is covered with a cover 15 for protecting the motor and a cover 16 for the body extending from the latter towards the rear towards a position situated above the rear wheel. 13. A driver's seat 17 is mounted on the body cover 16. The body frame 9 is also covered with a lower cover 18 extending downwards from the engine protection cover 15. The exhaust valve mechanism according to the first embodiment of the present invention comprises an exhaust valve device 20 connected between the upstream exhaust pipe 11a and the downstream exhaust pipe llb of the assembly 11 forming exhaust pipe. As shown in Figure 2, the exhaust valve device 20 includes a pipe 21, a shaft 22 extending transversely through the pipe 21 and having opposite end portions projecting from the pipe 21 perpendicularly at the axis of the pipe 21, an exhaust valve 23 fixed on the shaft 22 in the pipe 21, and a drum 24 fixed on a first of the end parts of the shaft 22 forming

  protrusion from the pipe 21. On the drum 24, is rolled up part of a throttle cable 25 which can be actuated by the throttle grip 6, forming a gas control element, to rotate the shaft 22 as a drive shaft for selectively opening and closing the exhaust valve 23. The exhaust valve device 20 is covered with a protective casing 20a intended to protect the components of the valve device 20 exhaust. As shown in FIG. 1, the device 20 forming the exhaust valve is arranged inside the lower cover 18 which protects the device 20 forming the exhaust valve from pebbles directly striking it, muddy water, curves, and others

  foreign matter when the motorcycle is in motion. As shown in Figure 2, the device 20 forming the exhaust valve can be oriented so that its central axis is inclined relative to the ground line GL at an angle 01 preferably located in the range from 0 to 45 . The device 20 forming the exhaust valve is arranged in its entirety towards the inside of a plane defined by an imaginary line S which intersects the side of the front wheel 2 o the device 20 forming the exhaust valve is positioned and the outer end of the corresponding footrest 12. Consequently, the motorcycle can take an angle of inclination 02 which is formed between the ground line GL and the imaginary line S.

  As shown in FIG. 1, the device 20 forming the exhaust valve is positioned in front of the lowest part 11d of the assembly 11 forming the exhaust pipe. Therefore, the exhaust valve device 20 is not subject to valve malfunctions due to the unburnt fuel. With the exhaust valve mechanism according to the first embodiment, as described above, the central axis of the device 20 forming the exhaust valve, that is to say the axis of the shaft 22 around from which the exhaust valve 23 is angularly mobile, is inclined relative to the ground line GL so that the outer end of the shaft 22, which is further from the geometric center of the body 1 of the motorcycle, is positioned upwards with respect to the inner end of the shaft 22 which is closer to the geometric center of the body 1 of the motorcycle. The motorcycle can therefore maintain its angle of inclination 02 when it makes a turn. An exhaust valve mechanism according to a second embodiment of the present invention will now be described below with reference to Figures 3 to 6.

  In the exhaust valve mechanism according to the first embodiment, when the throttle grip 6 to which the throttle cable 25 is connected, as an engine control element, is rotated, the control cable butterfly 25 is actuated to rotate the drum 24, forming valve control means, to fully open the exhaust valve 23 from a closed position, for example. The exhaust valve mechanism according to the second embodiment uses a different engine control element. As shown in FIG. 3, the exhaust valve mechanism according to the second embodiment comprises a device 200 forming an exhaust valve comprising a pipe 221, a shaft 222 extending transversely through the pipe 221 and having opposite end portions projecting from the pipe 221 at a right angle to the axis of the pipe 221, an exhaust valve 223 fixed to the shaft 222 in the pipe 221, and a drum 224 fixed on a first of the end portions of the shaft 222 projecting from the pipe 221. As shown in FIG. 6, the device 200 forming the exhaust valve is mounted in an assembly forming a pipe d 'escape

  ment, extending rearward from engine 210 and having a silencer (not shown) at its rearmost end. As shown in FIG. 3, the shaft 222, as a drive shaft, is rotatably mounted in stirrups 242, 243 by means of a pair of bearings 241, the stirrups 242, 243 being arranged in lateral parts of the pipe 221. The exhaust valve 223 has a dimension which is practically equal to the oblique transverse surface of the pipe 221 inclined at an angle 0 of 30 degrees, for example, with respect to port to the axis of the pipe 221. The exhaust valve 223 is fixed on the shaft 222 so that it forms the angle 0 relative to the axis of the pipe 221 when the exhaust valve 223 is fully closed.

  On a first of the end parts of the shaft 222, the drum 224, a spacer 244, a pulley 245 and an end plate 246 are successively arranged. The pulley 245 is rotatably mounted on the shaft 222, and the end plate 246 is fixed on the shaft 222. A finger 247 is fixed on the end surface of the pulley 245 which is opposite the end plate 246, and the end plate 246 comprises a slot 246a in an arc of a circle (see FIG. 4) defined inside of it, which receives the finger 247. On the other part of the end of the shaft 222, is arranged a pair of spaced apart spring supports 249a, 249b which support a return spring 248 between them around the shaft 222 to normally return the shaft 222 in a direction intended to reset the valve 223 in the fully closed position. The return spring 248 has one end engaged with a spring hook 243a which is fixed to the bracket 243, and the other end engaged with a hook located on the spring support 249a. The spring supports 249a, 249b are fixed to the shaft 222 by a nut 249c screwed onto the shaft 222. The spring support 249b is held against the bearing 241.

  A stop finger 222a is fixed on the shaft 222 perpendicularly to the axis thereof. When the stop finger 222 abuts against a predetermined part of the stirrup 242, the exhaust valve 223 is held in the fully closed position. A washer W arranged on the shaft 222 is held against the bearing 241 and is retained in position by an E-shaped ring E arranged on the shaft 222. A butterfly cable 225a has a part wound around the drum 224. The throttle cable 225a can be actuated, to rotate the shaft 222, by means of a throttle grip 206 (see FIG. 6). As shown in Figure 6, a throttle cable 225 extending from a throttle cable housing 250 connected to the throttle grip 206, to a junction box 251, and the throttle cable 225a is branched from the throttle cable 225 by the connection box 251. A throttle cable 225b intended to actuate an oil pump 252 is also branched from the throttle cable 225 by the connection box 251 , and a throttle cable 225c intended to actuate a carburetor 253 is also connected to the throttle cable 225 by the connection box 251.

  As shown in FIGS. 3 and 5, a cable 255 has a part wound around the pulley 245 for actuating the valve 223 in response to the actuation of a foot starter 254 (see FIG. 5) which serves as motor control element which it is necessary to actuate to start the motor 210. The displacement of the starter to the foot 254 is transmitted by means of a cam 257 arranged on a spindle 256 of the - foot feeder as valve control means and then to an arm 259 which is in contact with the cam 257 and arranged angularly movable on a shaft 258, then towards the cable 255 having a first end connected to one end 259a of the arm 259. The device 200 forming the exhaust valve, which is designed in particular to reliably start the engine 210, acts as follows: when the exhaust valve 223 is completely closed, the finger 247 fixed on the pulley 245 is held in abutment against e one end 246b (see FIG. 4) of the slot 246a in an arc defined in the end plate 246 under the effect of the return exerted by the

  return spring 248, when the motorcycle driver presses the starter motor 254 while turning the throttle grip 206 to start the engine 210, the cam 257 rotates in the direction indicated by the arrow B in FIG. 5, driving the arm 259 to rotate anti-clockwise around the shaft 258 so as to pull the cable 255 in the direction indicated by the arrow C. The pulley 245 is now rotated around the 'shaft 222, pressing finger 247 against the end 246b of the slot 246a in an arc. The end plate 246 fixed on the shaft 222 is then rotated in the direction indicated by the arrow A in FIG. 4. When the end plate 246 is rotated, the shaft 222 is also put in rotation until the stop finger 222a located on the shaft 222 abuts against the stirrup 242, after which the exhaust valve 223 is fully open.

  Consequently, the exhaust gases produced in the engine cylinder by the combustion of the air-fuel mixture are efficiently discharged from the engine 210, and a mixture of fresh air-fuel can easily be introduced and ignited in the engine cylinder, allowing the engine to start easily and reliably. When the foot starter 254 returns to its rest position, the shaft 222 is rotated 5 in the direction opposite to the direction A (see FIG. 4) under the effect of the return of the spring 248, by closing the valve d exhaust 223. After the engine 210 has started, when the drum 224 is rotated by the control handle 206 via the throttle cables 225, 225a, the shaft 222 can be rotated to fully open the exhaust valve 223. At this time the end plate 226 is also rotated in direction A (see Figure 4). Since the pulley 245 can rotate relative to the shaft 222, the pulley 245 is not controlled by the shaft 222. More specifically, the end 246b of the arcuate slot 246a is spaced from the finger 247 which can therefore move in the slot 246a in an arc. Consequently, the finger 20 247 is not moved by the end plate 246 and the lie 245 is not affected by the end plate 246.

  Although the foot starter 254 serves as the engine control element necessary to start the engine 210 in the second embodiment, a clutch lever, a brake lever, or the like, which is actuated when starting the engine can also be used as an engine control element. In the second embodiment, as described above, since the exhaust valve 223 is fully open when the engine 210 is to be started, the sweeping efficiency of the engine 210 is increased and the air mixture fuel in the engine cylinder can easily be ignited to easily and reliably start the engine. Since the exhaust valve mechanism has a relatively simple mechanical nature, it can be produced inexpensively.

  An exhaust valve mechanism according to a third embodiment of the present invention will now be described below with reference to Figures 7 to 12. As shown in Figure 7, the exhaust valve mechanism according to the third embodiment is incorporated in a motorcycle of the scooter type. The scooter-type motorcycle has a body 301 of a motorcycle comprising a post 304 for handlebars, a handlebar 305, a body frame 306, a driver's seat 307, and a bodywork 308, and an engine assembly capable of tilting 310 mounted on the body 301 of the motorcycle. A wheel nt 303 is rotatably supported by the handlebar post 304. The engine assembly 310 includes an engine 311, an exhaust pipe 312, an exhaust valve device 313 of the exhaust valve mechanism, a silencer 314, and an air filter device 315, a device 316 carburetor valve, and a speed reducer housing 317.

  The motor assembly 310 is mounted by a link 318 so as to pivot vertically on the frame 306 of the body. The exhaust pipe 312, the device 313 forming the exhaust valve, and the associated silencer 314 constitute an assembly forming the exhaust pipe. A rear wheel 320 is operatively connected to the engine assembly 310 and is supported by a rear suspension 319. The motorcycle of the scooter type also includes an oil pump 321, a fuel tank 322 (see also FIG. 8), a support 323, gas throttle cable 325, junction box 326, exhaust valve cable 327, carburetor cable 328 and oil pump cable 329. The device 313 forming an exhaust valve, the device 316 forming a carburetor valve, and the oil pump 321 can be controlled by a handle through the mechanisms which will be described below.

  As shown in Figure 8, the fuel tank 322 is positioned within a substantially elliptical configuration of the frame 306 of the body. The engine 311, the exhaust pipe 312, the device 313 forming the exhaust valve, the silencer 314, the device 315 forming the air filter, the device 316 forming the carburetor valve, the housing 317 speed reducer, and the rear wheel. 320 are positioned below the frame 306 of the body, as shown in FIG. 7, and are positioned inside the practically elliptical configuration of the frame 306 of the body as shown in FIG. 8. The box 326 is mounted on the frame 306 of the body, and is connected to the cable 327 of the exhaust valve, to the cable 328 of the carburetor, and to the cable 329 of the oil pump.

  FIG. 9 shows the device 313 forming an exhaust valve installed in the assembly forming the exhaust pipe. The exhaust pipe 312 extends forward from the engine 311, then curves down below the engine 311 and runs backward. The exhaust pipe 312 comprises an outlet flange 312a to which is fixed a flange 313a of the device 313 forming an exhaust valve by means of bolts 332 passing through an elastic seal 331. The silencer 314 is connected to the device 313 forming exhaust valve. The device 313 forming an exhaust valve comprises a butterfly valve mechanism comprising a circular valve 313b fixedly supported by a drive shaft 313c which can be rotated about its own axis by the cable 327 of valve d 'exhaust.

  FIG. 10 represents a rear view of the scooter-type motorcycle, the device 313 forming an exhaust valve being shown in section. As shown in FIG. 10, the engine assembly 310 and the rear suspension 319 are positioned on the left side of the rear wheel 320, and the silencer 314 and the device 313 forming an exhaust valve are positioned on the right side of the rear wheel 320. The drive shaft 313c of the device 313 forming the exhaust valve extends practically horizontally through a cylindrical valve casing 313d.

  The drive shaft 313c has a left end portion 313f projecting from the valve housing 313d and covered with a left guard 335, and a right end portion 313e projecting from the housing valve ter 313d and supporting a pulley 313g as control means of the device 313 forming an exhaust valve. The right end portion 313e and the pulley 313g are covered with a right protector 334. The right protector 334 is fixed to tabs 334c mounted on the valve housing 313d by means of spacers 334d d adapted thickness, by defining an air inlet space 334a located in the lower left part of the right protector 334 and an air outlet space 334b located in the upper left part of the right protector 334 These air inlet and outlet spaces 334a, 334b are connected to the atmosphere.

  The left protector 335 has an air inlet hole 335a defined in the lower wall thereof and an air outlet hole 335b defined in the upper wall thereof. These air inlet and outlet holes 335a, 335b are connected to the atmosphere. The support 323 includes a right bar 323a for contact with the ground and a left bar 323b for contact with the ground which are shown raised in FIG. 10 to allow the motorcycle to roll. The support 323 is shown lowered in FIG. 7 for parking the motorcycle. When the support 323 is raised, it abuts against the motor assembly 313 so that the bars 323a, 323b thereof are not raised beyond the position shown in Figure 10. Even when the ground level is positioned in relation to the motorcycle as indicated in figure 10 by the line L in dashed line by a point, when the motorcycle is tilted, the straight bar 323a of contact with the ground will be first in contact with the ground, preventing the right protector 334 of the device 313 forming an exhaust valve from coming into contact with the ground.

  Figure 11 shows the scooter type motorcycle shown in Figure 7, having a modified exhaust pipe 312 '. The exhaust pipe 312 'is not curved downward from the engine 311 but extends laterally with respect to the engine 311 backward along one side of the motorcycle body. The exhaust valve device 313 connected to the exhaust pipe 312 'is therefore located in an elevated position to be reliably protected against contact with the ground when the motorcycle is tilted. . Figure 12 shows the scooter type motorcycle shown in Figure 7, having a connection box 326 'arranged in a modified arrangement. The connection box 326 'is positioned in close proximity to the motor 311. From the connection box 326', extends an exhaust valve cable 327 'going to the device 313 forming an exhaust valve. ment, a carburetor cable 328 'going to the device 316 forming a carburetor valve, and an oil pump cable 329' going to the oil pump 321.

  With the arrangement shown in FIG. 12, although a throttle cable 325 'extending from the throttle grip to the connection box 326' is relatively long, the valve cable 327 ' exhaust, the carburetor cable 328 ', and the oil pump cable 329' are relatively short so that the total length of the cables is reduced. The device 313 forming an exhaust valve and its protectors 334, 335 according to the third embodiment act as follows: in FIG. 7, when the engine 311 which has been started acts at low speed for a low output power while the the motorcycle is moving, the valves of the device 316 forming the carburetor valve and of the device 313 forming the exhaust valve are restricted, and the oil pump 21 rotates at a low speed of rotation. Specifically, the throttle grip is pulled back to release the throttle cable 325 and therefore the three cables 327, 328, 329 through the junction box 326.

  When the throttle is turned so as to increase the output power of the engine 311, the valves of the device 316 forming the carburetor valve and of the device 313 forming the exhaust valve are open, and the oil pump 321 rotates at a higher speed. The valve of the device 313 forming an exhaust valve is fully open when the output power of the engine 311 reaches a medium level, and remains fully open until the output power 311 reaches a maximum level. In FIG. 10, the exhaust valve 313b of the device 313 forming the exhaust valve is heated by the exhaust gases and consequently the shaft 313c is also heated to an elevated temperature. Although the right guard 334 is also heated, since the cold ambient air flows successively through the air inlet space 334a, the right end portion 313e of the shaft 313c, and l 'air outlet space 334b intended to expel hot air outside the right protector 334, the inside of the right protector 334 cannot be heated to a too high temperature. As a result, the temperature of the outer surface of the right protector 334 is relatively low.

  Similarly, since the cold ambient air successively flows through the air inlet hole 335a and the air outlet hole 335b, the temperature of the outer surface of the left guard 335 remains relatively low. . In the third embodiment, the device 313 forming an exhaust valve is positioned between the exhaust pipe 312 and the muffler 314. However, the device 313 forming an exhaust valve can be positioned elsewhere in the exhaust pipe 312 or in the silencer 314 provided that the device 313 forming the exhaust valve is positioned somewhere in the assembly forming the exhaust pipe. The exhaust valve 313b and the shaft 313c can be mounted directly in the exhaust pipe 312 or the muffler 314, and the valve housing 313d can be omitted.

  The air inlet and outlet spaces or holes of the protectors 334, 335 can have the form of any openings having any shape as long as they can introduce air and allow air to escape. As described above, the end portions 313e, 313f of the shaft 313c are covered with respective protectors 334, 335 which are mounted on the valve housing 313d, the inlet or outlet spaces or holes' air being defined in the protectors 334, 335. Since the cold ambient air can flow through the protectors 334, 335, no undue heat is trapped in the protectors 334, 335, which are therefore maintained relatively cold.

  The device 313 forming an exhaust valve and the protectors 334, 335 are positioned relative to the support 323 so that the support 323 always comes first into contact with the ground when the motorcycle is tilted. Consequently, the device 313 15 forming an exhaust valve and the protectors 334, 335 are protected from coming into contact with the ground and consequently from deterioration or rupture.

  Although the embodiments of the present invention which are currently considered to be preferred have been described, it can be understood that the invention can be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments must therefore be considered from all points of view as representative and not restrictive.

Claims (9)

  1. Exhaust valve mechanism located in a motorcycle having at least one engine (10; 210; 312, 311) and an assembly (11; 211; 312, 312 ') forming an exhaust pipe intended to discharge the exhaust gases. exhaust emitted from the engine while dampening the noise of exhaust gases, characterized in that it comprises: a control element (6; 206) intended to control the engine; an exhaust valve device (20; 200; 213) arranged in the exhaust pipe assembly and comprising an exhaust valve (23; 223; 313b), and control means (22, 24 , 25; 222, 224, 225a; 313c, 313g, 327) operable in response to actuation of said control member to fully open said exhaust valve (23; 223; 313b) from a closed position .   2. Exhaust valve mechanism according to claim 1, characterized in that said exhaust pipe assembly comprises an exhaust pipe (11), said exhaust valve (23) being arranged in said pipe d exhaust and angularly movable to substantially close said exhaust pipe through a cross section thereof, said exhaust valve device (20) further comprising a drive shaft (22) supporting said valve exhaust (23) for angularly displacing the exhaust valve around the drive shaft, said drive shaft (22) having end portions projecting from said exhaust pipe (11 ), a first of said end parts being positioned further from the geometric center of the motorcycle than the other of said end parts, said drive shaft being inclined (01) relative to the line of ground (GL) so that said first part of the ends is positioned towards the top of said other of the end parts.   3. Exhaust valve mechanism according to claim 2, characterized in that said control means (22, 24, 25) consist of a throttle valve control element (22) and a throttle cable (25) connected to said throttle valve control element, and said control means consist of a drum (24) fixed on a first of said end portions of said drive shaft (22), said butterfly cable having a part wound around the drum (24).   4. Exhaust valve mechanism according to claim 1, characterized in that said control element (254) consists of an engine control element which can be actuated to start the engine, and said control means ( 222, 224, 225a) are constituted by means sensitive to the actuation of said engine control element to fully open said exhaust valve from the closed position when the engine is started.   5. Exhaust valve mechanism according to claim 4, characterized in that said engine control element (254) consists of a foot starter intended for starting the engine.   6. Exhaust valve mechanism according to claim 1, characterized in that it further comprises a protector (334, 335) covering said device forming an exhaust valve.   7. Exhaust valve mechanism according to claim 6, characterized in that said motorcycle comprises a support (323) which can be lowered for parking the motorcycle, said protector (334, 335) being positioned so that the protector and said device (313) forming an exhaust valve are protected by said support (323) when it is lifted, the motorcycle being inclined.   8. Exhaust valve mechanism according to claim 5, characterized in that said protector (334, 335) has openings (335a, 335b) connected to the atmosphere.   9. exhaust valve mechanism according to claim 6, characterized in that said device 313) forming exhaust valve comprises a valve housing (313d) connected to said assembly (312 ') forming exhaust pipe and receiving said valve exhaust (313b) therein, and a drive shaft (313c) extending horizontally through said valve arter and connected to said exhaust valve (313b) to angularly move the exhaust valve, said drive shaft (313c) having end portions projecting from said valve housing (313d), said control means (313g) being constituted by a pulley arranged on a first of said end ties protruding from said valve housing, and in that said motorcycle has a rear wheel (320) and a support (323) which can be lowered for parking the motorcycle, said device (313) for - mant exhaust valve and said protector (334, 335) being positioned towards the inside of a straight line (L) intersecting the side of said rear wheel (320) where said valve device is located and the outermost end of said support when it is raised, as seen from the rear.