Technical Field

This invention relates to exhaust systems for internal combustion engines and more particularly to variable exhaust systems for two stroke internal combustion engines.

Background Art

Most two stroke engines have an exhaust system which reflects exhaust pressure waves back towards the engine. A positive pressure wave is reflected as a negative pressure wave and vice versa. A reflected wave of negative pressure, on reaching the exhaust port, aids in scavenging of exhaust gasses from the cylinder. This in turn leads to higher output, since a larger inlet charge may be introduced to the cylinder. Similarly, a reflected positive pressure wave will, on reaching the exhaust port, urge gas back into the cylinder.

The time at which the reflected wave arrives at the exhaust port (relative to piston position) is relatively important as to the effect it has in scavenging exhaust gasses and urging fresh charge back into the cylinder. However, the speed of sound, and hence the speed at which the pressure waves travel along the exhaust system, is relatively independent of engine speed and throttle opening. Thus, the time of arrival at the exhaust port, relative to piston position, varies as engine speed varies.

It has been proposed to provide movable reflectors within the expansion chamber. The reflectors are controlled by means of servomotors which in turn are controlled by a controller sensing, for instance, engine speed and throttle position. The reflector usually comprises a truncated cone arranged to diverge in the upstream direction. The downstream end is slidably received on or in the expansion chamber outlet pipe. Movement of the reflector is usually by means of a simple lever, pivotally connected at one end to the reflector and at the other end joumalled to the output shaft of a servomotor.

The disadvantage of such an arrangement is that the reflector must follow an arc described by the connecting lever which is not necessarily the best path, leading to reduced efficiency and sealing problems. Additionally, the connecting lever is usually securely joumalled to the reflector cone. Thus, when inserting the cone into the expansion chamber, it is necessary to align the connecting lever whilst mounting the reflector on the outlet pipe.

Disclosure of the Invention

In an attempt to overcome at least one the disadvantages of the prior art, the invention, in one broad form, provides an exhaust system comprising:

a) an exhaust pipe;

b) a reflector disposed within the exhaust pipe;

c) an actuator member attached to or engaging the reflector for causing movement of the reflector within the exhaust pipe through movement of the actuator member, the actuator member comprising at least one portion movable between first and second operative positions,

wherein in the first position the at least one portion is engaged with the reflector and in the second position the at least one portion is disengaged from the reflector, thereby allowing removal of the reflector from the exhaust pipe.

The at least one portion is preferably mounted on a shaft, and preferably is slidable along the shaft between the first and second operative positions. The at least one portion may pivot about an axis transverse to the axis of the shaft, either alone or in combination with a sliding action.

Preferably there is a keeper to maintain the at least one portion is in the first operative position. The keeper may move between first and second operative positions to allow or cause the at least one portion is to move between their first and second operative positions. Preferably the keeper is rotatable between its first and second operative positions to move the movable potion(s).

Preferably the actuator pivots to move the reflector.

Preferably, the actuator comprises two arms, one on either side of the reflector and the at least one portion comprises the arms, which are movable relative to each other. The arms or the reflector preferably has upstanding connecting pins received in apertures in the other and preferably each aperture is elongated so as to translate rotary motion of the connecting arms to linear motion of the reflector.

Preferably the apertures or pins are at free end regions of the arms.

Preferably, adjacent to the apertures, are guide means to aid in mounting of the reflector on the arms.

In another broad form, the invention provides an exhaust system comprising:

a) an exhaust pipe

b) a reflector disposed within the exhaust pipe

c) an actuator member attached to the reflector for causing movement of the reflector within the exhaust pipe, through movement of the actuator member,

wherein one of the actuator member and the reflector has at least one pin engaging in at least one elongate aperture in the other.

Preferably the actuator pivots to move the reflector.

Preferably, adjacent to the apertures are guide means to aid in mounting of the reflector on the arms.

Preferably, the actuator member comprises at least one portion movable between first and second operative positions, which in the first position is engaged with the reflector and in the second position is disengaged from the reflector, thereby allowing removal of the reflector from the exhaust pipe.

The at least one portion is preferably mounted on a shaft, and preferably is slidable along the shaft between the first and second operative positions. The at least one portion may pivot about an axis transverse to the axis of the shaft, either alone or in combination with a sliding action.

Preferably there is a keeper to maintain the at least one portion is in the first operative position. The keeper may move between first and second operative positions to allow or cause the at least one portion is to move between their first and second operative positions. Preferably the keeper is rotatable between its first and second operative positions to move the movable potion(s).

Preferably the actuator comprises two arms, one on either side of the reflector. Preferably the at least one portion comprises the arms, which are movable relative to each other. The arms or the reflector preferably has upstanding connecting pins received in apertures in the other and preferably each aperture is elongated so as to translate rotary motion of the connecting arms to linear motion of the reflector.

Preferably the apertures or pins are at free end regions of the arms.

Preferably, adjacent to the apertures, are guide means to aid in mounting of the reflector on the arms.

Preferably the arms are biased to the first operative position.

Brief Description of the Drawings Figure 1 shows an axial cross section of an embodiment of the invention.

Figure 2 shows an exploded perspective of a second embodiment of the invention.

Figure 3 shows in perspective, a detail of part of the embodiment of Figure 1.

Figures 4 & 5 show, in cross-section, details of the embodiment of Figure 2.

Figures 6, 15 and 17 show variations of the invention.

Figure 16 shows the embodiment of Figures. 1 to 5 in the disengaged position.

Best Mode of Carrying out the Invention

The invention shall be better understood from the following description of non-limiting embodiments.

Referring to Figure 1 , there is provided an exhaust system generally indicated by the numeral 10. The exhaust system 10 includes an expansion chamber 12, the upstream end of which is not shown. The expansion chamber 12 tapers at its downstream end to a relatively small diameter exit pipe 14.

Located within the exhaust system 10, mainly in the expansion chamber 12, there is provided a movable reflector member 16. The reflector member 16 comprises a frusto- conical reflector 18 and a transfer pipe 20. The frusto-conical reflector 18 has its larger end upstream and its smaller end downstream and communicates with the transfer pipe 20. The transfer pipe 20 is received in the exit pipe 14. Preferably, the outside diameter of the transfer pipe 20 is slightly less than the inside diameter of the exit pipe 14 so as to allow slidable movement but relatively good sealing. Similarly the larger end of the reflector 18 is preferably of slightly less size than the expansion chamber 12.

Located on the reflector member 16, preferably near the junction of the reflector 18 and exit pipe 20, there are provided two outwardly extending pins 22. Preferably, the pins are located diametrically opposite each other. The pins 22 each engage an arm 24 of an actuator member 26. The actuator member 26 is generally Y shaped with the arms 24 straddling the reflector member 16 and an upwardly directed leg 28 extending through an aperture 30 in the wall of the expansion chamber 12. The leg 28 is pivotally mounted on a shaft 32 and at its free end has an eye 34 for connection to an actuating rod or wire, not shown.

By virtue of the relatively snug fit of the exit and transfer pipes 12 and 20 respectively and the reflector 10 and expansion chamber 12, the reflector member 16 is constrained to follow a linear path. Accordingly, it is necessary for the pins 22 engage in elongate apertures 36 in the arms 24. Preferably, the width of the apertures 36 is only slightly greater than the diameter of the pins 22, but the length is much greater.

Thus as the actuator member 26 is caused to rock about shaft 32 and cause linear motion of reflector member 16, the pins 22 travel along the elongate slots 36 relative to the arms 24. It will, however, be appreciated that the slots 36 allow the reflector path to follow other, non linear, paths, depending on the particular configuration of the expansion chamber 12 and exit pipe 20 whilst still maintaining a snug fit.

It will be appreciated that the arrangement of pins and apertures may be reversed so that the arms 24 have inwardly directed pins engaging with apertures in the reflector member. Similarly, the actuator member 26 may be mounted directly on an output shaft of a servomotor or mounted on a shaft in turn joumalled on the exhaust chamber.

Referring to Figure 2 there is shown another embodiment of the invention.

The exhaust system 100 includes an expansion chamber 112, the downstream end of which is only shown. The chamber 112 tapers to a relatively small outlet 113. An exhaust pipe 114 is sealingly located in the outlet 113 such that a free end portion 116 extends into the chamber.

The reflector member 118 is frusto-conical in shape with its larger size upstream. The downstream end forms an opening 120 that slidably passes over the free end 116 of exhaust pipe 114 located within the expansion chamber 112. Again the larger end is a snug fit within the expansion chamber 112.

Adjacent the opening 120, there are two diametrically opposed, outwardly extending pins 122. Each pin 122 engages an actuator arm 124. More specifically, each pin 122 is received in an elongate opening 126 located at a free end 127 in each arm 124. Adjacent each elongate opening 126, each arm has an inwardly directed flange 128, best seen in Figure 3. The flange 128 is positioned downstream of the opening, as will be explained later.

Each arm 124 is approximately arcuate and subtends an angle of about 90 degrees, such that the two arms 124 meet at the top of the expansion chamber. The other free end portion 130 of each arm 124 is provided with an upstanding boss 132, best seen in Figure 4. This boss 132 extends through an opening 134 in the wall of the expansion chamber 112.

The two bosses 132 have opposing faces comprised of abutting faces 136 and diverging faces 137. The diverging faces 137 thus define a V-shaped space therebetween. Passing through each boss 132, so as to exit through the diverging face 137, there is a bore 140. The bore 140 has a non-circular shape, such as a square or rectangle.

Passing through the bores 140, is a drive shaft 142. The drive shaft has a middle section

144, which engages in bores 140, and circular end sections 145, 146. The end sections

145, 146 are joumalled for rotation in bosses 148 upstanding from the wall of the expansion chamber 112.

The square section of shaft 142 has similar dimensions to the bores 140 in the bosses 132. Thus the arms 124 may slide axially on the shaft 142. However, rotation of the shaft 142 will cause rotation of the arms 124, and hence linear motion of the reflector 118.

Springs 152 are mounted on the shaft 142 between adjacent bosses 132, 148 and urge the two flanges together until faces 136 bear against each other. A lock member 150 is located between the two diverging faces 137. The lock member 150 is U-shaped so as to slide over the shaft 140 but each leg is tapered so as to bear on all of each face 137.

The free end 146 of shaft 142 extends through its respective boss and may be connected to a suitable drive means. It may be mounted directly on a servomotor or, as in Figure 2, driven indirectly by a cable system. In the embodiment of Figure 2, drive is from a cable system via bevel gears 152, 153, best seen in Figure 5. Bevel gear 152 is mounted on shaft 142 and gear 153 is mounted for rotation on the expansion chamber 112. Integral with gear 153 is a pulley to which push and pull cables 154, 155 are attached.

A cover 160 extends over the opening so as to prevent leakage of exhaust gasses. This may be a rigid metal or plastics cover or a flexible rubber boot. If a flexible boot is used, the mechanism may be operated without removal of the boot.

When the locking member 150 is in position of Figure 4, the free ends 127 of the arms are urged toward each other by springs 152. Thus the pins 122 are securely engaged in the openings 126. If the locking member 150 is urged downwards as in Figure 16, the two arms 124 are urged apart as the lock member bears on the faces 137. In this position the free ends 127 will have moved outwardly, disengaging the pins 122 from the openings 126.

The reflector 118 is thus free to be removed in an upstream direction, for maintenance, cleaning or replacement.

The dimensions of the arms 124 and the pins 122 are such that the pins 122 and inwardly directed flanges 128 overlap, even when the arms are fully separated. Thus, when inserting the reflector 118, it is merely a matter of mounting the reflector on the exit pipe 116. The reflector 118 is then moved towards the pipe 116, until the pins 122 bear on the flanges 128. The arms 124 may then be slid along shaft 142 to bring the pins 122 into engagement with the openings 126. The locking member 150 may then be retracted between faces 137 to allow the springs 152 to retain the arms 124 in that position against themselves and lock member 150.

The flanges 128 may also be used to limit rotation of the reflector member 118 relative to the arms 124. The reflector member 118 may be provided with shoulders against which the flanges locate. Obviously, the shoulders must have sufficient clearance to allow some movement of the reflector 118 relative to the arms 124.

As an alternative to sliding the two arms apart, the invention also includes rocking the arms apart. In such a case the bores through the flanges will need to be higher than the shaft. Thus, for instance a square action shaft may be received in a rectangular bore. Alternatively the arms may be mounted on a second shaft which in turn is mounted on the primary actuator shaft.

It will be appreciated that there are many ways of achieving the rocking of the arms to allow release of the reflector member. Figures 6 to 11 show various embodiments to achieve this. For clarity the reflector is not shown.

In Figure 6 the two arms 224 have rectangular bores 226 which receive square section shaft 228. An actuator lever 230 mounted between arms 224 controls rotation of arms 224. Movement of the arms 224 is achieved merely by squeezing free end portions 232 together.

In Figure 7 arms 324 have rectangular bores 326 through which shaft 328 passes. A spacer 330 is mounted between arms 324 and a spring is located between free end portions 332. Again squeezing the end portions 332 together will release the reflector.

Figure 8 shows an arrangement in which the arms 424 are otherwise identical to those of Figs. 6 and 7, but are joined together by a flexible bridge 440.

In Figure 9 the two arms 524 are mounted on a shaft 530. The shaft 530 is in turn mounted on a drive shaft 528 at substantially 90 degrees thereto. The arms 524 may be mounted on either side of shaft 528 or on the same side. A spring 529 mounted between the arms 524 retains them in position.

Figure 10 shows a variation of Figure 9 in which the free end portions 660 cross, so that disengagement requires the end portions 660 to be separated, rather than pressed together.

In Figure 11 the arms 720 each has an upstanding flange 722. Each flange has a rectangular passageway receiving a square section shaft 724, as previously described. Intermediate the two flanges there are two L-shaped fingers 726. The fingers 726 are mounted to either side of the shaft 724 on a common shaft 728 for rotation thereabout. Each finger abuts a flange 722 below the shaft 724. By squeezing legs 730 of fingers 726 together, the arms 720 are caused to rotate outward and disengage from the reflector member.

Figure 12 shows an arrangement in which the arms 820 each has upstanding flanges 822 a, b, through which the actuator shaft 824 passes. In this case the bores in the flanges are of the same shape as the shaft and the flanges can only slide along the shaft as in the embodiment Figs. 1 to 5 and 16. One of the flanges 822 a, is provided with a threaded bore in which a complementary threaded screw or bolt 830 is received. The bolt 830 bears against the other flange 822 b, and by suitable rotation of the bolt the two flanges and arms may be forced apart. Springs 832 urge the two flanges and arms together.

Figure 13 shows a variation of the embodiment of Figure 12. Both flanges 850a & 850b have threaded bores therein. A bolt 852 having two threaded sections, of opposite direction to each other, is received in the bores. By suitable rotation of the bolt, the flanges and hence arms are drawn together or urged apart.

Figure 14 shows a further variation of the invention. As with the embodiments of Figures 12 and 13, the flanges 860 a, 860 b, can only slide along the shaft 862. The cover 864 is rigid and has mounted therein a release member 866. The member 866 is rotatable in the cover and has two legs 868 a, 868 b, which extend downwards between the flanges 860 a, 860 b. Rotation of the release member 866 causes the legs 868 to bear against the flanges 860, thereby separating the arms.

In the embodiment of Figure 15, the arms 920 are mounted via flanges 921 on a shaft 922. The shaft 922 has a non-circular cross-section and the arms 920 are mounted so as to be only slidable on the shaft 922. The arms may not otherwise move relative to the shaft. A spring 923 is mounted between the flanges 921 upon the shaft 922 and urges the flanges 921 and arms 920 apart. A lock member 924 passes around the flanges 921 and maintains them together. Removal of the lock member 924 allows the spring 923 to urge the flanges 921 apart. The top surfaces 925 of the flanges converge in an upward direction and the shape of the lock member 924 is complementary to the flanges.

When the lock member 924 is about to be installed, the lower legs 926 of the lock member 924 bear against the angled surfaces 925. Pushing downwards on the member 924 urges the two flanges together until legs 926 may pass on either side of the flanges 921.

As an alternative, the tool 945 may be removed from the exhaust and only inserted when changing of the cone is required. In such a case, the boot may have an aperture for insertion of the tool, which preferably will have a handle.

Figure 17 shows, schematically, the invention in a curved exhaust chamber 972 and utilising an arm arrangement as in Figures 4 and 16. In this case the release tool 959 is permanently mounted on the chamber 972 and biased by a spring 960 to a disengaged position. The spring 960 bears against a push button 961. Pushing the push button 961 toward the right, to engage the arms 970, releases the cone 965. As will be seen in Figure 17, the exhaust chamber 972 and outlet pipe 973 are curved. Despite this, movement of the reflector 980 between its various positions is possible whilst maintaining sliding contact with the exhaust chamber 972.

In a further embodiment, not shown, the connector member may comprise a single U- shaped member mounted on an actuator shaft that straddles the reflector cone. The connector member has two arms straddling the cone and at the free end of each arm there is provided an elongate slot. However, rather than being a closed slot, each slot is open at the free end. Thus the pins on the cone can then be slid into the slots.

Obviously the connector member must be configured such that in use the cone cannot become accidentally disengaged. Removal of the cone may be achieved by rotation of the connector member outside the normal working range such that the pins can be slid out of the open ended elongate slots.

It will be apparent that many modifications and variations may be made to the embodiments described herein without departing from the spirit or scope of the invention.

Industrial Applicability

The invention has applicability to two stroke power plants.