Abstract:
A suction tube with a switching element for longitudinal adjustment of different tube sections ( 16 ), particularly a suction tube having a drum switch ( 12 ). The invention provides for sealing strips ( 29 ) or sealing rings ( 17 ) which are supported inside the suction tube casing ( 14 ). This results in a relative movement between the drum switch ( 12 ) and the sealing elements fixed to the casing. The positioning of the sealing elements in the suction tube casing ( 14 ) is advantageous for assembly and allows for better compensation of tolerances in the sealing gap between the drum switch ( 12 ) and the suction tube casing ( 14 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a suction tube with a switching element, particularly for adjusting the length of different segments of the suction tube. 
     Suction tubes are generally known. The employed switching elements primarily adjust the length of the intake ports connecting the plenum to the cylinder intakes. To this end, the switching elements must be movable. In most cases, they are therefore cylindrical, and the desired adjustment in the suction tube length is obtained by rotating the switching element. 
     To adjust the length, the switching elements communicate with the walls of the suction tube. To be able to use the acoustic or flow effects of the adjustment in the suction tube length, the gaps created between the suction tube wall and the switching element must be sealed as tightly as possible, even though an absolute seal is not necessary since these are seals between ducts that carry filtered air. This may be achieved by a high dimensional accuracy of the switching elements and the suction tube walls and may be enhanced by providing sealing rings. One technical solution is indicated in DE 44 23 427 A1. This document proposes seating rings, which can be inserted into grooves in the cylindrical switching element and which have a larger diameter than the mounting opening for the switching element. As a result, when the switching element is installed, the sealing rings are elastically deformed to provide a seal against the suction tube wall. The aforementioned sealing options for switching elements in the suction tube are, however, associated with high production or assembly costs. Particularly in suction tubes that are made of synthetic resin material, due to material shrinkage after molding, sufficient dimensional accuracy of the switching element and the suction tube to ensure a satisfactory seal can be obtained only by costly finish-machining. Although the sealing rings arranged in the drum switch are capable of compensating such tolerances, they make it more difficult to mount the switching element in the associated opening. For in many cases, the mounting opening has abrupt diameter differences to form curved intake cross sections. The switching element, after installation, forms a wall segment of said curved intake cross sections. For assembly, the drum equipped with the sealing rings must be pushed through the hollow spaces, which invariably causes the sealing rings to re-expand to their original diameter. They must then be brought back to their installation diameter in places where the sealing gap is located between the mounting opening and the switching element, which are extremely difficult to access. Furthermore, if the mounting opening is out of round, it is impossible to obtain a complete seal even with the use of sealing rings supported in the switching element, since the sealing rings cannot completely adapt to the out-of-round inside contour of the mounting opening without the adjusting forces of the switching drum assuming excessively high values. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to create a suction tube provided with sealing means between the switching element and the associated mounting opening, which is easy to install and at the same time provides an optimal seal between the suction tube segments. This seal should be largely independent of the tolerances that occur in the suction tube and the switching element. 
     This object is attained by the invention as described and claimed hereinafter. 
     The suction tube according to the invention has at least one switching element, which is movably arranged inside the suction tube. Between the walls of the suction tube and the switching element, gaps are created. These gaps are sealed by sealing means supported inside the suction tube so that, as the switching element moves, there is a relative movement between the sealing means and the switching element. The sealing means are at least partially elastic and are made in such a way that the elastic parts or the entire sealing means are elastically deformed when installed. This can be used to create a surface pressure, which is used either to fix the sealing means inside the suction tube or to obtain a sealing effect between the switching element and the sealing means. Alternatively, the sealing means may be fixed inside the suction tube by a form-fit connection, particularly a groove. Important is that the form-fit connection does not prevent the sealing effect of the sealing means, i.e., that it allows, for instance, the sealing means to be pressed against the switching element. If the sealing means are pressed against the switching element, i.e., if there is contact between these components, the contact pressure must be low enough that a relative movement between the sealing means and the switching element is still possible. Alternatively, a contact-free seal, particularly a labyrinth seal, may be provided. As an alternative to the aforementioned form-fit and frictional connection options, the sealing means may also be fixed inside the suction tube by material coupling, particularly by gluing. 
     The above-described sealing means are suitable for roughly toleranced synthetic resin tubes and their synthetic resin switching elements. In particular, sealing rings that are completely elastic can be adapted to the wall of a cylindrical mounting opening to receive the switching element if these are out of round. This is made possible in that the sealing means are fixed inside the cylindrical mounting opening and thus do not need to rotate as the switching element is adjusted. The suction tube according to the invention may of course also be made of other materials besides synthetic resin, e.g., aluminum or magnesium or a combination of these materials. 
     For the aforementioned reasons it is particularly advantageous to design the switching element as a cylindrical body, particularly as a drum switch. Due to out-of-roundness of the drum switch or the cylindrical mounting opening, differently sized gaps are created along the circumference, which may be compensated by sealing means. This may be accomplished, in particular, by providing grooves in the drum switch, so that the sealing means in conjunction with these grooves form a labyrinth seal. What has been said above regarding drum switches is also true for rotary slide valves. 
     According to another embodiment of the invention, the sealing means may also be configured as sealing strips. Sealing strips make it possible to seal the gap formed by the suction tube wall and the switching element along a straight line. Depending on the elasticity of the sealing strip, it is also possible to realize a slightly winding or curved shape of the sealing gap. Sealing through sealing strips is possible, for instance, in slide valves. Sealing gaps along the end faces of cylindrical switching elements may also be sealed in this manner. Alternatively, the sealing strip may be arranged in a cylindrical mounting opening parallel to the axis of rotation of a cylindrical switching element. 
     In cylindrical mounting openings, according to an advantageous embodiment of the idea underlying the invention, the sealing ring takes the shape of a circular ring. The sealing ring may be advantageously provided with an elastic layer along its outer circumference, which after installation contacts the walls of the suction tube and thus ensures fixation. The elastic layer is preferably made of silicon or sponge rubber. To increase the contact pressure to fix the sealing ring against the suction tube wall, the ring may be provided with a larger diameter than that available in the mounting opening. In this case it must be slit, so that it can be elastically deformed for installation. The slit may be configured in such a way that the ends of the sealing ring overlap to obtain an optimal sealing effect in the slit area. The slit may also comprise a recess that is wide enough so that a sealing strip may be provided in the cylindrical mounting opening, which crosses the sealing rings. 
     If the suction tube casing is longitudinally split, the slit in the sealing rings may be eliminated. In this case, the sealing rings may be inserted into the mounting opening before the casing shells are assembled. The sealing rings may, for instance, comprise a rigid ring, the outer circumference of which is provided with a groove to receive a sealing ring. The sealing ring is the elastic layer. 
     An advantageous embodiment of the sealing ring provides for a garter spring to be placed along the ring&#39;s inner surface. When the sealing ring is installed this garter spring is compressed and thus exerts an outwardly directed radial force on the sealing ring, which further presses the sealing ring against the suction tube wall. In this case, the sealing ring may be very soft, so that it can particularly well adapt to out-of-roundness in the cylindrical mounting opening. This type of sealing ring is best combined with the above-described labyrinth seal, which interacts with grooves in the switching element. The flexibility of the sealing ring can be influenced not only by a corresponding material selection but also by changing the ring cross section. 
     In contrast, if the sealing means are supported in grooves of the suction tube wall for a form-fit connection and if they are to be supported against the switching element to produce a seal, it is advantageous to produce the contact pressure by an elastic element, which is located in the grooves inside the suction tube wall and which should be understood as part of the sealing means. This may be accomplished, for instance, by a waved spiral spring. Such an arrangement is particularly suitable for sealing strips, but may also be realized in sealing rings. 
     A further variant of the invention provides that the sealing ring be constructed of two disks. These disks are provided with an elastic connection along their outer edges. The disks may be made of steel. In this case, a tube is particularly used as the elastic connection, which is glued to the outer edges of the disks. Alternatively, the disks may also be made of synthetic resin material, in which case the elastic connection, for instance made of rubber, is injection molded onto the outer edges of the disk in a multi-component technique. The sealing rings are installed by inserting them into the cylindrical mounting opening. In their undeformed state, they may be slightly undersized or oversized in relation to the inside diameter of the mounting opening, so that the installation forces are small. As soon as the sealing ring is positioned at the intended installation site, the distance between the disks is reduced, which causes the elastic connection to expand radially outwardly until it reaches the wall of the mounting opening. A further approach of the disks will then increase the contact pressure of the sealing ring inside the mounting opening. The distance between the disks may be reduced, for instance, with the aid of a corresponding assembly tool. As an alternative, the switching element may be constructed of different switching disks, which are introduced into the mounting opening alternately with the sealing rings. The seal can then be pressed against the tube wall by pushing the switching disks together. To this end, the disks must have a limit stop that defines the distance between the disks. This can, for instance, be a disk hub. In this case the switching disks are mounted by placing them on a shaft. Along the outside circumference of the switching disks, groove-like notches must remain free to interact with the sealing rings. Pushing them together creates a sealing effect between the sealing ring disks and the adjacent groove flanks of the switching disks. 
     A special embodiment of the sealing rings constructed in the form of disks provides for a snap connection between the disks to fix the sealing ring in its mounted state. This has the advantage of minimizing the friction that occurs between the above-described groove flanks and the sealing ring. A contact-free labyrinth seal between these components is also possible. 
     The friction between the sealing means and the switching element, if contact is provided between these components, can be advantageously reduced by providing beads on the sealing means, which are in contact with the switching elements. The beads may also be arranged on the switching element in such a way that they engage with the sealing means. These beads can also enhance the action of labyrinth seals as a flow obstacle. 
     These and other features of preferred further developments of the invention are set forth in the claims as well as in the description and the drawings. The individual features may be implemented either alone or in combination in the embodiment of the invention or in other fields of application and may represent advantageous embodiments that are protectable per se, for which protection is herewith claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details will now be described by way of example, with reference to schematic embodiments shown in the drawings in which 
     FIG. 1 is a cross-section through a suction tube with a drum switch, which is mounted in one piece inside the suction tube and has a sealing strip as well as four sealing rings along the axis of rotation of the drum switch, 
     FIG. 2 is a section along line B—B according to FIG. 1, 
     FIG. 3 shows detail X of FIG. 2 in cross section illustrating a sealing strip with a waved spring as the elastic element, 
     FIG. 4 shows detail Y of FIG. 1 in cross section illustrating a sealing ring with elastic layer and garter spring, 
     FIG. 5 shows a detail of a suction tube with a drum switch constructed in the form of disks and sealing rings in accordance with detail Z of FIG. 1, and 
     FIG. 6 is a sealing ring constructed in the form of disks with an elastic connection of the disks and a snap connection. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The adjustable suction tube shown in FIG. 1 is substantially cylindrical. An inlet  10  for the filtered intake air is provided on the one end face and a cover  11  for a mounting opening for a drum switch  12  on the other end face. When the cover is removed, drum switch  12  can be inserted into the interior of the suction tube. In its mounted state, this drum switch has two mounting points  13  by which it is supported in a suction tube casing  14  and in the cover  11 . The mounting point on the cover side further has a recess  15  for a drive (not shown) of the drum switch  12 . 
     The suction tube is intended for the operation of a three-cylinder internal combustion engine. The intake ports  16  to the cylinders are formed by parts of the inner wall of suction tube casing  14  and the outer wall of drum switch  12 . The intake ports thus extend annularly around drum switch  12 . Intake ports  16  are sealed with respect to one another and against the remaining suction tube volume by sealing rings  17 , which are supported inside cylinder segments  18  of the inner suction tube wall and are inserted in annular grooves  19  in drum switch  12 . 
     Drum switch  12  comprises a drum  20 , which is provided with an end disk  21  and thus forms a plenum. The drum bottom is not closed but is made of spoke-like ribs  23 . These ribs ensure that the intake air from inlet  10  can reach the plenum  22  irrespective of the angular position of drum switch  12 . Screwed connections  24  serve to fasten end disk  21  to drum  20 , cover  11  to suction tube casing  14 , and one of the supports  13  to end disk  21 . 
     The path of the intake air from plenum  22  to the cylinder-side outlets may be seen in FIG.  2 . Outlet branches  26  projecting into plenum  22  each form a passage through drum  20  and open out into the intake ports  16 . These outlet branches end in tongues  27 , which are supported inside the wall segments of the suction tube casing  14 , forming intake ports  16 . Thus, rotating drum switch  12  steplessly adjusts the length of intake ports  16 . These intake ports taper toward their ends where they are sealed with respect to outlets  25  by a sealing strip  28  to prevent a short circuit flow. The sealing strip is located in a longitudinal groove  29  inside suction tube casing  14  extending parallel to the axis of rotation of drum switch  12  and is pressed against drum switch  12  by several waved springs  30  (see FIG.  1 ). Waved springs  30  are located in grooves  31 , which are separated from one another by separation blocks  32  (see FIG.  1 ). 
     FIG. 3 illustrates the functioning of sealing strip  28 . This sealing strip is guided by longitudinal groove  29  and pressed against drum switch  12  by waved springs  30  accommodated in groove  31  and supported against the bottom of longitudinal groove  29 . Drum switch  12  can rotate under the sealing strip in either direction as indicated by the arrows. To minimize friction between sealing strip  28  and drum switch  12 , the sealing strip has two sealing beads  33 , so that the support surface on the drum switch corresponds to two tracks. 
     FIG. 4 illustrates the functioning of sealing ring  17 . This sealing ring has an elastic layer  34  forming a seal in a cylinder segment  18  of suction tube casing  14 . To increase the contact pressure of sealing ring  17 , a garter spring  36  is accommodated in an interior ring groove  35 . This garter spring comprises a helical spring  37 , which is formed into a ring with the aid of a tube  38  and is inserted into interior ring groove  35  in a compressed state. This enhances the radially outwardly directed contact pressure of sealing ring  17 . Further, two sealing beads  33  are applied to the lateral edges of the sealing ring. These sealing beads interact with groove  19  in drum switch  12  and thereby form a labyrinth seal. If sealing beads  33  unintentionally contact the groove flanks, e.g., as a result of tolerances, friction is low due to the small bead surface. 
     An alternative construction of sealing rings  17  is illustrated in FIG.  5 . These sealing rings comprise two disks  39 , which are interconnected along their outer circumference by an elastic connection  40 . In this type of construction, drum switch  12  is made up of a plurality of switching disks  41 . During assembly in suction tube casing  14 , sealing rings  17  and switching disks  41  are alternately mounted on a drive shaft  42 . The distance between switching disks  41  in the area of sealing rings  17  is determined by their axial hub length. The switching disks are secured against axial displacement on drive shaft  42  by a retaining ring  43 . Drive shaft  42  is driven at the end which is not shown. 
     The exterior of the switching disks is connected with hubs  44  by ribs  23   a . The interior of switching disks  41  is used as a plenum  22 . Every second switching disk is radially fixed on drive shaft  43  by a feather key connection  47 . The switching disks are provided with bevel gearing  45  so that a radially fixed switching disk communicates with the adjacent radially non-fixed switching disk via a bevel gear fixed to the casing (not shown) in such a way that they rotate in opposite direction. In other respects, suction tube casing  14  is constructed as described in FIG.  1 . 
     When switching disks  41  and sealing rings  17  are assembled, the sealing rings are compressed by the switching disks in such a way that the tube-like elastic connections  40  located between disks  39  are pressed against the cylinder segments  18  of suction tube casing  14 . This causes them to be fixed inside the suction tube casing, so that when the suction tube is being adjusted there is a relative movement between the counter-rotating switching disks  41  and sealing rings  17 . Sealing ring  17   a  on the last switching disk, which is not inserted between two switching disks, may be configured as shown in FIG.  4 . 
     FIG. 6 shows an alternative embodiment of a sealing ring  17  according to FIG.  5 . This sealing ring comprises synthetic resin disks produced in a creative forming process, which are connected by a second elastic component acting as elastic connection  40 . As disks  39  approach one another, the elastic connection  40  is curved outwardly to provide fixation within the suction tube casing. In their mounted state, disks  39  are held together by a snap connection  46 . In addition, the synthetic resin disks are each provided with an annular sealing bead  33 , which in the mounted state engages with switching disks  41  (not shown).