Internal combustion engine having an elastic connector and method of producing same

An internal combustion engine having a cylinder, a fuel-supply mechanism, and an elastic connector for connecting the fuel supply mechanism to the cylinder. The connector has a first channel for fuel/air mixture and a second channel for combustion air. The connector has a first connection end and a second connection end at which the two channels open out. The two channels are separated from one another by a partition that extends in the longitudinal direction of the channels. The partition is twisted about its longitudinal central axis between the first and second connection ends to achieve a great elasticity of the connector. To produce the elastic connector, a respective core is used for each channel, and the cores are moved relative to one another to enable removal of the connector from a mold.

The instant application should be granted the priority date of Jan. 30, 2008, the filing date of the corresponding German patent application 10 2008 006 681.8

BACKGROUND OF THE INVENTION

The present invention relates to an internal combustion engine having an elastic connector, and also relates to a method of producing an elastic connector for an internal combustion engine.

US 2005/0045138 A1 discloses an internal combustion engine having an elastic connecting duct. The elastic connecting duct has two conduits, and in particular a conduit for fuel/air mixture and a second conduit for largely fuel-free air. The connecting duct is made of an elastic material; an adequate elasticity of the connecting duct is achieved by the fact that the two conduits are embodied separately from one another, so that relative movements that occur between the mixture supply mechanism and the internal combustion engine during operation can be compensated for.

EP 1 221 545 A2 discloses an internal combustion engine where downstream of a carburetor, the inlet duct is divided into two passages by a partition wall. One of the passages conveys fuel/air mixture and the other passage conveys combustion air, which depending upon the operating state can contain different quantities of fuel.

It is an object of the present invention to provide an internal combustion engine having an elastic connector, according to which the elastic connector has an adequately great elasticity and at the same time has a high stability. A further object of the invention is to provide a method of producing an elastic connector.

SUMMARY OF THE INVENTION

The object of the present application is realized by an internal combustion engine having an elastic connector that connects a fuel supply mechanism with a cylinder of the engine, wherein the elastic connector has a first mixture channel for fuel/air mixture and a second supply channel for combustion air, further wherein the elastic connector has a first connection end and a second connection end, and wherein the first and second channels open out at the first and second connection ends; and having a partition that is disposed in the elastic connector and separates the mixture channel and the supply channel from one another, wherein the partition extends in the longitudinal direction of the channels, and wherein the partition is twisted about its longitudinal central axis between the first connection end and the second connection end.

The object of the present application is also realized by a method of producing an elastic connector for an internal combustion engine, wherein the elastic connector is provided with two channels that are separated from one another by a partition that extends in the longitudinal direction of the channels, and wherein the method includes the steps of using a respective core for each of the channels, and moving the cores relative to one another to enable removal of the elastic connector from a mold.

To achieve a straightforward construction of the internal combustion engine, a first channel for fuel/air mixture and a second channel for combustion air are formed in the elastic connector. The two channels are separated from one another by a partition. The partition, which extends in the longitudinal direction of the connector, increases the stability of the connector in the longitudinal direction, thus making the connector less elastic. However, this greater rigidity cannot arbitrarily be compensated for by a different material or thinner wall thicknesses, since thinner wall thicknesses or the selection of a softer material for the elastic connector could, under certain operating conditions, promote collapse of the channel walls of the connector. In such a case, the connector bends, so that the channels can temporarily be at least partially closed off. This can lead to disruptions in running conditions and even stalling of the internal combustion engine. In order to nonetheless achieve an adequately high elasticity of the connector, the partition is twisted about its longitudinal central axis between the first and the second connection ends. The twisting of the partition about its longitudinal central axis reduces the rigidity of the connector in its longitudinal direction. In this way, an adequate thickness and rigidity of the partition can be ensured, thus ensuring the function of the connector.

The end edge of the partition at the first connection end advantageously forms an angle of approximately 10° to approximately 180° with the end edge of the partition at the second connection end as viewed perpendicular to the plane of the first connection end. The angle is advantageously from approximately 25° to approximately 60°, in particular to approximately 45°. The partition is thus twisted about its longitudinal central axis between the first and the second connection ends by about 10° to about 180°. Consequently, it is possible to achieve an adequately high elasticity of the connector. At the same time, it is still possible to remove the connector from a mold when being manufactured in an injection molding process, or when manufacturing by vulcanization. It has furthermore been shown that due to the twisting of the partition, favorable installation conditions result since also the fuel supply mechanism can be installed twisted about an appropriate angle. As a result, the installation space that is available can be better utilized.

The longitudinal central axis of the partition at the first connection end advantageously has a spacing relative to the longitudinal central axis of the partition at the second connection end that is measured perpendicular to the longitudinal central axis in the first connection end and perpendicular to the longitudinal axis of the cylinder of the internal combustion engine. The second connection end is thus laterally offset relative to the first connection end and relative to the longitudinal cylinder axis. Due to the lateral offset of the two connection ends relative to one another, a further increase of the elasticity is achieved without noticeably adversely affecting the stability of the connector. The lateral offset also enables a better utilization of the installation space that is available, so that on the whole the internal combustion engine requires a smaller installation space. The spacing is advantageously approximately 2 mm to approximately 15 mm, in particular approximately 4 mm to approximately 10 mm. This offset is sufficient to achieve a greater elasticity of the connector. Since the spacing is relatively small, a removal of the connector from a mold is still possible, even if the connector is produced in a vulcanization process or in an injection molding process with only two cores.

The first connection end is advantageously inclined relative to the second connection end. This inclination of the two connection ends relative to one another leads to different lengths of the two channels. By means of the inclination, the desired ratio of the channel lengths relative to one another can be established. At the same time, the inclination of the connection ends relative to one another can also lead to a better utilization of the installation space that is available. The mounting flange at the cylinder can be shorter, and the connector can in contrast be longer. Due to the fact that a greater channel length is formed in the connector, which is made of polymeric material, in particular rubber, and a shorter channel portion is formed in the metallic cylinder flange, the overall weight of the internal combustion engine is reduced. The angle between the first and second connection ends is advantageously approximately 15° to approximately 60°, in particular approximately 25° to approximately 45°. The angle between the two connection ends advantageously opens toward that side of the connector that faces the mixture channel. This results in a greater length of the mixture channel and a shorter length for the air channel. This leads to an improved running condition of the internal combustion engine.

The first connection end advantageously faces the cylinder, while the second connection end faces the mixture supply mechanism. The end edge of the partition at the first connection end is advantageously disposed in a plane that is disposed perpendicular to the cylinder axis. As a result, the mixture channel and the air channel open out one above the other at the cylinder flange. As a result, a symmetrical supply of scavenging air to both sides of the cylinder is made possible. The first connection end is advantageously inclined relative to the longitudinal axis of the cylinder by an angle of approximately 3° to approximately 30°. The inclination of the cylinder flange provides adequate installation space for the mounting of the connector. At the same time, the cylinder flange can be made relatively short. The angle between the first connection end and the longitudinal axis of the cylinder advantageously opens toward that side that faces the mixture channel. The angle between the first connection end and the longitudinal cylinder axis advantageously opens toward that side that faces the crankcase.

With channels that supply fuel/air mixture to the internal combustion engine, fuel can deposit on the walls of the channel and, upon pivoting of the internal combustion engine, can pass in a surging manner to the internal combustion engine and can adversely affect the running condition of the engine. To avoid this, at least one channel that is formed in the connector can be provided with a structured inner surface. The inner surface is advantageously provided with a plurality of raised portions having the shape of pyramids. The fuel can accumulate between the raised portions. Thus, the formation of drops or pools of fuel in the channel can be prevented. The raised portions advantageously have side surfaces that are oriented in the longitudinal direction of the channel. Since in some operating states fuel/air mixture is supplied not only via the air channel but also via the mixture channel, both of the channels can be provided with a structured inner surface. Due to the orientation of the raised portions in the longitudinal direction of the channel, it is possible despite the raised portions on both sides of the partition to remove the connector from a mold during production in an injection molding process.

The first connection end is advantageously formed on a first mounting flange and the second connection end is advantageously formed on a second connection flange. As a result, the connector can be easily secured to adjoining components. However, it would also be possible to secure one or both of the connection ends to a separate mounting flange.

As indicated previously, for a method for producing an elastic connector for an internal combustion engine, whereby the connector has two channels that are separated from one another by a partition that extends in the longitudinal direction of the channels, for each channel a core is used, and the two cores are moved relative to one another to enable removal of the connector from a mold.

During the removal of an elastic connector from a mold, the channels must be expanded or spread apart, so that the connector can be withdrawn from the cores. However, the partition cannot shift since a core is disposed on both sides of the partition. Due to the fact that the two cores are moved relative to one another for the removal from a mold, the spacing of the core in the region of the partition can be increased, thus making removal of the connector from a mold very possible. The connector is advantageously made of a polymeric material, including rubber, and is produced in an injection molding process or, when produced from rubber, in a vulcanization process.

For the removal from a mold, the cores are advantageously moved relative to one another in a direction of pulling that is inclined relative to the longitudinal central axis of the partition of the connector. Due to the fact that the direction of pulling is inclined relative to the partition of the connector, an excessive stretching of the connector toward the outside is avoided. Due to the movement transverse to the partition of the connector, the spacing of the cores in the region of the partition can be easily increased.

At least one of the channels is provided with a structured inner surface, which includes pyramid-shaped raised portions. To ensure that the pyramid-shaped raised portions can be removed from a mold, the raised portions, especially the side surfaces of the raised portions that are disposed in the longitudinal direction of the channel, are oriented approximately parallel to the direction of pulling. As a result, a tearing-off of the raised portions during the movement of the cores relative to one another is avoided. The surfaces of the pyramid-shaped raised portions that are oriented parallel to the direction of pulling can furthermore be readily removed from the mold in the pulling direction. For the removal from a mold, the two cores can be moved relative to one another by a displacement amount that corresponds at least to the height of the raised portions as measured in the pulling direction. In this connection, advantageously only one of the cores is moved, while the other core can be stationary.

Further specific features of the present application will be described in detail subsequently.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Referring now to the drawings in detail, the internal combustion engine1shown inFIG. 1is a single-cylinder engine, and in particular a two-cycle engine that operates with scavenging. The internal combustion engine1can serve, for example, for driving the tool of a manually-guided implement such as a power saw, a cut-off machine or the like. The internal combustion engine1has a cylinder2in which is formed a combustion chamber3. The combustion chamber3is delimited by a piston5that is reciprocably mounted in the cylinder2and that, via a connecting rod6, rotatingly drives a crankshaft7that is rotatably mounted in a crankcase4. A supply channel8for air, and a mixture channel10, open out at the cylinder2. The supply channel8opens out at the cylinder2via an air inlet9. Two air inlet openings are advantageously provided on either side of the section plane shown inFIG. 1. The mixture channel10opens out at the cylinder2via a mixture inlet11that is port-controlled by the piston5.

The internal combustion engine1has total of four transfer channels12,15, which are disposed symmetrically relative to the section plane shown inFIG. 1. The transfer channels12that are close to the inlet open into the combustion chamber3via transfer windows13, and the transfer channels15that are disposed remote from the mixture inlet10open into the combustion chamber3via transfer windows16. An outlet17leads out of the combustion chamber3. The piston has at least one piston pocket14. Two piston pockets14are advantageously disposed on either side of the plane of symmetry shown inFIG. 1as the section plane. In the region of the upper dead center position of the piston5, the air inlet9is connected via the piston pocket14with the transfer windows13and16of the transfer channels12and15, so that by means of the piston pocket14scavenging air can be temporarily stored in the transfer channels12and15.

The cylinder2has a cylinder flange19, to which is secured a connector20. The connector20is essentially comprised of an elastic material, advantageously of a polymeric material, in particular of a rubber or an elastomer. In the elastic connector20, the air or supply channel8and the mixture channel10are guided as channels that are completely separated from one another. The connector20has a first mounting flange34, which is fixed to the cylinder flange19. At the opposite end, the connector20has a second mounting flange35, which is secured to a carburetor21, which in turn is connected to an air filter22. The air filter22has filter material23that separates a clean chamber24from the atmosphere. An intake channel25, which is guided in the carburetor21, opens into the clean chamber24. Pivotably mounted in the carburetor21are a choke valve28, and downstream thereof a throttle valve29. The butterfly valve29is disposed downstream of the choke valve28relative to a direction of flow26from the air filter22to the cylinder2. In the completely opened position shown inFIG. 1, the choke valve28is oriented in the direction of the longitudinal axis27of the intake channel25. The butterfly valve29is shown in a largely closed position. In the completely opened position, the butterfly valve29is also oriented in the direction of the longitudinal intake channel axis27. Thus, the butterfly valve29and the choke valve28are disposed in a plane, so that when the valves28,29are both completely opened, the intake channel25is largely divided by them into two channel portions.

A main fuel opening30as well a number of secondary fuel openings31open out into the intake channel25. In this connection, the fuel openings30and31open out into the intake channel25on that side of the choke valve28and the butterfly valve29that is disposed upstream of the mixture channel10. The opposite side of the intake channel25is disposed upstream of the supply channel8for air. The fuel openings30and31are supplied from a fuel chamber32, which is advantageously the regulation chamber of the carburetor21, which is embodied as a diaphragm carburetor.

The connector20has a partition33against which the butterfly valve29, in the completely open position, can partially rest. In the region of the mounting flange35, there is provided on the connector20an intermediate ring47, which can, for example, be comprised of an inherently stable polymeric material or of metal, and against which the butterfly valve29can also rest. The intermediate ring47can have a partitioned portion that supports the partition33of the connector20.

As schematically indicated inFIG. 1, the inner upper surfaces of the supply channel8and of the mixture channel10have a structured configuration. The supply channel8has a knurling42, and the mixture channel10has a knurling43. In each case, the knurling is shown only schematically, and can respectively extend over a portion of the length of the channels8,10or can extend over their entire lengths. Furthermore, a structuring or texturing, in particular a knurling42,43, can also be provided only in the supply channel8or advantageously only in the mixture channel10.

As shown inFIG. 1, the cylinder flange19is inclined relative to the longitudinal axis18of the cylinder1by an angle α that can advantageously be approximately 1° to approximately 15°. The angle α opens out in the direction toward the crankcase4and toward the mixture channel10.

When the internal combustion engine1is in operation, during an upward stroke of the piston5fuel/air mixture is drawn into the crankcase4through the mixture channel10. By means of the piston pocket14, combustion air from the supply channel8is temporarily stored in the transfer channels12,15. During partial throttle or during idling, the combustion air, which is supplied by the supply channel8, can contain fuel. During full throttle operation, when the butterfly valve29is oriented parallel to the longitudinal axis27of the intake channel25, the combustion air supplied by the supply channel8is advantageously largely free of fuel.

During the downward stroke of the piston5, the fuel/air mixture in the crankcase4is compressed. As soon as the transfer windows13and16are opened by the downward traveling piston5, first the temporarily stored scavenging air flows into the combustion chamber3. Subsequently, fuel/air mixture flows in from the crankcase4. During the upward stroke of the piston5, the mixture is compressed in the combustion chamber3and is ignited in the region of the upper dead center position of the piston5. In this connection, the piston5moves in the direction of the longitudinal axis18of the cylinder2. During the downward stroke of the piston5, first the outlet17is opened, so that exhaust gases can escape from the combustion chamber3. The transfer windows13and16are subsequently opened. The scavenging air that flows into the combustion chamber3through the transfer windows13and16displaces or expels the remaining exhaust gases from the combustion chamber3and scavenges them through the outlet17. This achieves a good separation of the exhaust gases from the fresh mixture that subsequently flows in from the crankcase4.

When the internal combustion engine1is installed in a manually-guided implement such as a power saw, a cut-off machine, a brush cutter, a trimmer or the like, the internal combustion engine1is mounted so as to be vibration-isolated from the handles or grips of the implement in order to keep the strain on the operator low. Advantageously, the carburetor21is also vibration-isolated from the internal combustion engine1, so that also at the carburetor21only slight vibration stresses occur. The connector20must bridge the relative movements that during operation occur between the carburetor21and the cylinder2of the internal combustion engine1. For this purpose, the connector20must have an adequate elasticity. At the same time, the connector20must also have an adequate stability.

FIGS. 2 to 7show the configuration of the connector20in detail. AsFIGS. 2 and 3show, the first mounting flange34has three mounting openings36for the fixation of the connector20to the cylinder2. The mounting openings36are formed in a core37, which is also shown in the cross-sectional view ofFIG. 5. The core37is comprised of an inherently stable material, advantageously of a light metal such as aluminum or the like. The core37itself can be comprised of a plurality of components, for example a harder and a softer component, in order to achieve good strength characteristics, a good bonding to the elastic material46of the connector, and a long service life during operation. The elastic material46of the connector20is sprayed about the cores37. In the region of the mounting openings36, the elastic material46is recessed, thus enabling a good fixation of the connector20to the cylinder flange19. High contact pressures can be achieved, so that an adequate sealing is obtained.

As shown inFIG. 2, at the second mounting flange35the partition33has an end edge45, which in the illustrated embodiment extends approximately perpendicular to the longitudinal central axis41(FIG. 5) of the partition33. The end edge45need not have a linear configuration, but rather can also be provided with a circular recess, for example for the butterfly valve29. The second mounting flange35of the connector20has a receiving means48for the intermediate ring47.

The first mounting flange34is shown inFIG. 3. The supply channel8opens out at the first mounting flange34via an outlet opening39, and the mixture channel10opens out via an outlet opening40. As shown inFIG. 3, a sealing means38, which is comprised of the elastic material46of the elastic connector20, is sprayed or extruded onto the first mounting flange34. The sealing means or seal38surrounds both of the outlet openings39and40. At the first mounting flange34, the partition33has an end edge44, on which also the sealing means38is sprayed or extruded, so that the two channels8,10are entirely separated from one another at the first mounting flange34by the sealing means38. InFIG. 3, in the direction of viewing, also the position of the longitudinal axis18of the cylinder2is schematically shown perpendicular to the first mounting flange34. As shown inFIG. 3, the end edge44of the partition33is perpendicular to the longitudinal cylinder axis18.

As shown inFIG. 4, the supply channel8opens out at the second mounting flange35via an outlet opening49, and the mixture channel10opens out via an outlet opening50. The two outlet openings49and50are separated from one another by the planar, relatively thin partition33. In a projection into the plane of the first mounting flange34, the end edge45is inclined relative to the end edge44by an angle β. The angle β is advantageously approximately 10° to approximately 180°, expediently approximately 10° to approximately 60°, and in particular approximately 25° to approximately 45°. Particularly advantageous is an angle β of approximately 30°. Due to the inclination of the two end edges44,45relative to one another, the partition33is twisted about its longitudinal central axis41over its entire length (see alsoFIG. 5). This reduces the rigidity of the connector20in the longitudinal direction. If the end edges44or45are not linear, but rather, for example, have a curved or similar configuration, the specifications for the angle β relate to the extension of the partition33into the planes of the mounting flanges34and35.

Due to the twisting of the partition33, there results in the cross-sectional illustration ofFIG. 7a section edge that is inclined relative to the longitudinal central axis41of the partition33. The sprayed or injected-in core37and sealing means38are also very visible inFIG. 7. The knurling43is only indicated inFIG. 7.

As shown inFIG. 5, the first mounting flange34is inclined relative to the second mounting flange35by an angle γ that is approximately 15° to approximately 60°, in particular approximately 25° to approximately 45°. An angle γ of approximately 35° to approximately 40° is advantageous. The angle γ opens toward the mixture channel10. The angle γ is measured in a plane that is disposed transverse to the partition33, advantageously perpendicular to the end edge44of the partition33. Due to the angle γ, the mixture channel10in the connector20is longer than the supply channel8. Due to the inclination of the mounting flanges34and35relative to one another, a suitable channel length ratio of supply channel8and mixture channel10can be established.

FIGS. 8 to 14show a further embodiment of a connector60. The same reference numerals designate the same elements as in the embodiment ofFIGS. 1 to 7. A supply channel8and a mixture channel are also formed in the connector60, and are separated from one another by a partition33. The connector60has a first mounting flange34with mounting openings36and core37, as well as a second mounting flange35.

As shown inFIGS. 10 and 11, the end edge44of the partition33at the first mounting flange34extends perpendicular to the longitudinal axis18of the cylinder2. As furthermore shown inFIGS. 10 and 11, the longitudinal central axis41of the partition33at the first mounting flange34has a lateral offset a relative to the longitudinal central axis41at the second mounting flange35. The offset a is measured from a projection of the longitudinal central axis41into the plane of the first mounting flange34and perpendicular to the longitudinal cylinder axis18. The offset a exists relative to a plane that is defined by the longitudinal central axis41at the first mounting flange34and the longitudinal cylinder axis18. This plane extends perpendicular to the plane of the drawing sheet inFIGS. 10 and 11. The distance or spacing a is advantageously approximately 2 mm to approximately 15 mm, in particular approximately 4 mm to approximately 10 mm.

As shown inFIG. 11, the end edge45of the partition33at the second mounting flange35is inclined relative to the end edge44at the first mounting flange34by an angle β. The angle β is advantageously approximately 10° to approximately 180°, in particular approximately 25° to approximately 45°.

As shown inFIG. 12, the first mounting flange34is inclined relative to the second mounting flange35by an angle γ that corresponds to the angle γ of the first connector20. InFIGS. 13 and 14, the angle β and the distance a are shown in a projection into the second mounting flange35.

FIGS. 15 to 17show the intermediate ring47. Formed on the intermediate ring47is a partition portion53that extends on both sides of the intermediate ring47. Also disposed on the intermediate ring47is a pin54that projects toward the carburetor21and can serve for position securement.

FIG. 18shows the intermediate ring47on the connector60. As shown inFIG. 18, a partition portion53rests against that side of the partition33that faces the mixture channel10. The partition33is supported by the partition portion53. The partition portion53can also be disposed on that side of the partition33that faces the supply channel8, or can extend around the partition33. On that side that faces the carburetor21, the partition portion53has an abutment surface55for the butterfly valve29against which the butterfly valve rests in the completely opened position.

On the elastic connector60no seal38is shown at the first mounting flange34; advantageously, however, here also a seal38is provided. Also the connector60advantageously has knurlings42and43in both of the channels8,10.

The connectors20,60can be produced by vulcanization out of rubber, or in an injection molding process from other polymeric materials such as elastomers or thermoplastic elastomers. During the manufacture, at the same time also the core37is encased with elastic material. In order to form the two channels8and10, the cores61and62shown inFIG. 19are provided. Each core61,62forms the inner wall of a channel8,10. In this connection, the first core61projects into the supply channel8, and the second core62projects into the mixture channel10. In particular if the connectors20,60are provided with knurlings42and43in the channels8and10, a removal of the connector20,60from a mold is very difficult, since there is the danger that the knurlings42,43will be torn off in the region of the partition33during the removal from the mold.

However, in order to permit the manufacture of the connector20,60in a vulcanization or injection molding process, the two cores61and62are movable relative to one another. Advantageously, the first core61is stationary and the second core62can, in the direction of pulling63shown inFIG. 20, be moved downwardly by a displacement amount b, in other words, can be moved out of the connector20,60. The direction of pulling63is oriented perpendicular to the first mounting flange34. Thus, the direction of pulling63is inclined relative to the longitudinal central axis41of the partition33by an angle of between 0° and 90°, advantageously between 20° and 70°. Due to the inclination of the direction of pulling63relative to the longitudinal central axis41, the spacing c between the two cores61and62is increased during the movement of the core62in the direction of pulling63. Thus, the partition33, with knurlings42and43disposed on both sides of the partition33, can be removed from a mold. A corresponding movement of the core62is also advantageous if only one of the channels8,10is provided with a knurling.

FIGS. 21 to 23show the configuration of the knurlings42and43in order to enable an easy removal of the connector20from a mold. The knurlings42,53on the connector60are correspondingly designed. In each case, the knurlings42and43are comprised of a plurality of elevations or raised portions56, each of which has the shape of a pyramid. Each raised portion56has a first surface57, which is disposed in the direction of pulling63, in particular approximately parallel to the direction of puling63, as well as a second surface58that is disposed transverse, and in particular approximately perpendicular, to the direction of pulling63. Each raised portion56has a height d that at the most corresponds to the displacement b. In this connection, the height d is not measured perpendicular to the partition33, but rather is measured in the direction of pulling63and corresponds to the spacing between two surfaces58of the raised portions56that are disposed adjacent to one another in the longitudinal direction.

As shown inFIG. 23, the raised portions56are disposed one after the other in the longitudinal channel direction64. Thus, the raised portion56are oriented parallel to the longitudinal channel direction64and in the direction of pulling63. The side surfaces59of the raised portions56are disposed parallel to the longitudinal channel direction64and thereby in the direction of pulling63form no undercuts, so that they can be removed from a mold without any problems. The side surfaces57can be inclined slightly relative to the direction of pulling63in order to realize a mold removal angle. The direction of the inclination of the surfaces57is to be selected such that no undercut results. The second surfaces58can be provided with a different orientation since they are disposed transverse to the direction of pulling63and can thus be removed from a mold without any problems. As shown inFIG. 23, the raised portions56are aligned relative to the direction of pulling63and parallel to the longitudinal channel direction64.

FIGS. 24 to 26show an embodiment of a connector70. Here again elements that correspond to one another have the same reference numerals as in the previous embodiments. The connector70is disposed between a carburetor21and a cylinder flange19. A mixture channel10and a supply channel8for combustion air are guided in the connector70. The two channels8,10are separated from one another by a partition33. The connector70is secured to the cylinder flange19via a mounting flange34, and is secured to the carburetor21via a mounting flange35. The mounting flange34includes a flange plate71, which can be made of an inherently stable material such as an inherently stable polymeric material or of metal. The flange plate71does not have the elastic material46of the connector70sprayed or injected about it, but rather is sprayed or injected onto the material of the connector.

As shown inFIG. 25, the flange plate71of the mounting flange34is provided with mounting openings36, by means of which the connector70can be secured to the flange19via mounting screws72. As also shown inFIG. 25, the supply channel8opens out at the mounting flange34via an outlet opening39, and at the mounting flange35via an outlet opening49. The mixture channel10opens out at the mounting flange34via an outlet opening40, and at the mounting flange35via an outlet opening50. As shown inFIG. 25, the supply channel8at the cylinder2is disposed on that side of the mixture channel10that faces the combustion chamber3, and at the carburetor21the supply channel18is disposed on that side of the mixture channel10that faces away from the combustion chamber3and faces the crankcase, which is not shown inFIG. 25.

InFIG. 26, the contour of the partition33is clearly schematically indicated. The partition33is embodied as a thin plate that is twisted about its central longitudinal axis41. At the mounting flange35, the partition33has an end edge45that projects up to the carburetor21. At the opposite end, the partition33has an end edge44that is formed on the flange plate71, which is not shown inFIG. 26. The end edges44and45are rotated relative to one another about an angle β, which can be up to 180°. In the embodiment illustrated inFIGS. 24 to 26, the angle β is advantageously between approximately 120° and approximately 180°. As a result, the rigidity in the longitudinal direction of the channel can be greatly reduced.

As shown inFIGS. 24 to 26, the surfaces of the mounting flanges34and35of the connector70are disposed parallel to one another and, as viewed in the longitudinal channel direction, are aligned with one another, so that no lateral offset results.

FIGS. 27 to 29show a further embodiment of a connector80. The connector80essentially corresponds to the connector70. The same reference numerals here also represent the same elements. The connector80has a mounting flange35for the connection with the carburetor21. At its opposite end, the connector80has a connection rim81that is secured to a separate mounting flange82. The mounting flange82is secured to the cylinder flange19via the mounting screws87, which are shown inFIG. 28. For this purpose, a total of four mounting openings86are provided in the mounting-flange82.

The mounting flange82has a securement rim85, over which extends the connection rim81of the connector80. The connection rim81is fixed on the securement rim85via a clamp strap83.

As shown inFIG. 28, the connection rim81has a circumferential raised element88on an inner surface thereof that projects into a circumferential groove89on the securement rim85, thus enabling a form-fitting fixation of the connector80on the mounting flange82. As also shown inFIG. 28, formed on the mounting flange82is a partition portion84against which the partition33abuts, as shown inFIG. 27.

As shown inFIG. 28, the mixture channel8opens out at the connecting rim81via an outlet opening40, and at the mounting flange35via an outlet opening50. The supply channel8opens out at the connection rim81via an outlet opening39, and at the mounting flange35via an outlet opening49.

FIG. 29schematically shows the contour of the partition33in the connector80. The partition33has an end edge45at the mounting flange35as well as an end edge44at the connection rim81. The partition33is twisted about its longitudinal central axis41and in particular between the mounting-flange35and the connection rim81by an angle β, which is advantageously between approximately 120° and 180°. The two ends of the connector80are not offset relative to one another. The mounting flange35and the connection rim also extend parallel to one another. Due to the very large angle β, there results an adequate elasticity of the connector80in its longitudinal direction.

The connectors70and80can also be provided with a structured inner surface in one or in both of the channels. For this purpose, knurlings can be provided that correspond to the knurlings of the connectors20and60.

With both of the connectors70and80, the end edge44of the partition33is disposed in a plane perpendicular to the longitudinal axis18of the cylinder2. The manufacture of the connectors70,80is effected in the manner described in conjunction with the connectors20and60.

The specification incorporates by reference the disclosure of German priority document 10 2008 006 681.8 filed Jan. 30, 2008.