Abstract:
The invention relates to a shaft and hub connection ( 20 ) for transmitting torque, a common longitudinal axis (X-X) comprising the following components: a shaft ( 22 ) which rotates about the longitudinal axis (X-X) and comprises an entraining longitudinal section having an untrue outer contour ( 26 ), and a hub ( 24 ) that is coaxial to the shaft ( 22 ) and encloses the shaft ( 22 ) with its internal contour ( 28 ) at least in the area of the entraining longitudinal section. The invention is characterized in that the outer contour ( 26 ) of the entraining longitudinal section of the shaft ( 22 ) and the inner contour ( 28 ) of the hub ( 24 ) have the shape of a perfect cone to such a degree that, when the shaft ( 22 ) and the hub ( 24 ) are assembled, they automatically self-lock, thereby holding the shaft and hub connection ( 20 ) together. The connection also comprises connecting means which prestress the shaft ( 22 ) and the hub ( 24 ), when assembled, in the direction of the longitudinal axis (X-X).

Description:
This application hereby claims the benefit of the commonly assigned German Patent No. 10 2005 031 832.0 (filed Jul. 6, 2005, in the German Patent Office) and the commonly assigned International Patent Application No. PCT/EP2006/06621 (filed Jul. 6, 2006, in the European Patent Office), both of which are hereby incorporated by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a shaft/hub connection for transmitting torque, comprising the components having a common longitudinal axis:
     a) a shaft, which can be rotated about the longitudinal axis comprising an entraining longitudinal section having an untrue outer contour,   b) a hub, which is coaxial to the shaft and which encloses the shaft with its inner contour at least in the area of the entraining longitudinal section.   

     BACKGROUND 
     In machine construction, such shaft/hub connections are used in many ways for transmitting torques between the shaft and the hub. In addition to many requirements, the basic task of such types of connections is usually the transmission of high torques. The connections should thereby be as compact and light as possible and they should be mountable without extensive installation and adjustment work. On principle, all of the embodiments have in common that the torque transmission loads the shaft/hub connection. Dynamic loads are thereby usually higher than static loads. 
     Due to the fact that, for the most part, a conventional shaft/hub connection is not an interference fit, only a certain portion of the contact surfaces truly participates in torque transmission. This causes high stresses in the components, which must be compensated for or reduced by an appropriately long connection. However, the connection&#39;s enlarged length again causes larger radial run-out and reinforces a relative motion between shaft and hub, during which no transmission of torque occurs (the so-called play). The enlargement of radial run-out also leads to undesired noises and vibrations. A longer connection moreover facilitates sliding of the surfaces upon each other, which again promotes the formation of fretting corrosion. Finally, these effects lead to a reduction in the lifetime of the shaft/hub connection and consequently that of the entire system. 
     DE 198 36 259 A1 shows a tight shaft/hub connection in which, to reduce or prevent the undesired play, a radial pressing device presses the hub toward the rotational axis in such a manner, that the inner contour of the hub engages the shaft free of play. The disadvantage of this embodiment is the need for additional components, which is associated with higher space requirements and costs. 
     Clamping set connections, in which a clamping set is disposed between the shaft and the hub, are known for reducing or preventing the undesired play. Such a clamping set encompasses at least one element, by means of which the annular cross-section of the clamping set can be enlarged and the clamping set is thus, on the one hand, pressed against the jacket surface of the shaft and, on the other hand, against the inner surface of the hub bore and a connection, which is free of play, is created. DE 36 36 393 A1 describes such clamping sets, where the positive fit is achieved in that the shaft as well as the hub are provided with a longitudinal toothing and in that the clamping set encompasses, on the inside as well as on the outside, a longitudinal toothing, which in each case corresponds thereto. Due to the additional components, this embodiment is also associated with correspondingly higher costs having a relatively high space requirement. An additional time-intensive and thus cost-intensive operating step is required for the assembly of the clamping set. 
     EP 1 225 356 B1 describes a shaft/hub connection, where at least one of the components encompasses, in the area of the untrue entraining longitudinal section, at least two holding sections, which are angularly displaced to each other around the longitudinal axis. This can be achieved by means of torsion, for example, which runs across the entire length of the entraining longitudinal section but also by means of two non-twisted longitudinal sections, which are connected with each other via a connecting section and which are offset against each other. A plurality of connecting sections, each of which offsets longitudinal sections in stages or continually against each other, can also be used. It is disadvantageous that the production of the components is possible only with special and very expensive machines. The creation of a twisted inner contour, in particular, is difficult. The assembling or joining of such connections is only possibly with the application of a high axial force, because the sections deform in response to being joined to each other. A joining by hand is thus not possible. 
     The use of wedge-shaped elements, which are inserted between shaft and hub, is also well known. However, these lead to an eccentricity of the shaft and therefore to point contacts or relatively small contact surfaces between shaft and hub. However, this is oftentimes accepted because, as already described above, an increase or an even distribution of the contact surfaces within the entraining longitudinal section only seems to be possible with additional components and with considerably effort. 
     It is the objective of the present invention to create a shaft/hub connection with high functionality and lifetime. In response to a simple construction, the best possible transmission of the torque is to be achieved. The production of the components is to be simple and cost-efficient and the connection is to furthermore be capable of being assembled with little effort. 
     SUMMARY OF THE INVENTION 
     According to the invention, this is achieved by means of a generic shaft/hub connection, which is characterized in that
         the outer contour of the entraining longitudinal section of the shaft and the inner contour of the hub have the shape of a perfect cone to the extent that, when the shaft and the hub are joined, they automatically self-lock, thereby holding the shaft and hub connection together,   a connecting means prestresses the shaft and the hub, when joined, in the direction of the longitudinal axis X-X.       

     The invention is based on the knowledge that a reduction of the play between shaft and hub can only diminish or neutralize high stresses in the component, fatigue, true running, and vibrations and can only lead to the objective, if, on the one hand, a self-locking can occur between the shaft and the hub and if, on the other hand, the connection remains permanently prestressed in axial direction. 
     An accurate centricity of the shaft in the hub ensures an even torque transmission. The reduction or neutralization of play in a centered shaft leads to a more favorable distribution of energy during torque transmission, thereby reducing stresses in the component, fatigue, true running, and vibrations. It is easy and quick to join, especially to thread, or to insert the connection together. 
     The shaft/hub connection according to the invention can furthermore be produced and assembled in a very simple manner. In a particularly advantageous embodiment version, provision is made for a prestressing ring as connecting means, which stresses the shaft and the hub in axial direction. For this purpose, the shaft and the hub each have a circumferential ramp-shaped elevation, which is disposed relatively close to each other when the shaft and the hub are joined. During the joining, the prestressing ring is placed above these ramps and is contracted. The contracting leads to the reduction of the diameter of the prestressing ring, thereby causing the lateral flanks of the prestressing ring to come into contact with the ramps and pressing them on top of each other. Once sufficient prestress has been applied, the prestressing ring is fixed and remains in its position. The prestressing ring is made from a resistant material and is advantageously balanced. 
     In addition to the mentioned prestressing ring, other connecting means can also be used as connecting means. Provision can be made, for example, for a coupling nut, which clamps the shaft with the hub via a thread and the contact surface disposed on the other component with each other. 
     According to the invention, the outer contour of the hub and the inner contour of the shaft have the shape of a perfect cone in the area of the entraining longitudinal section. This means that all of the contour lines disposed on the jacket surface and running substantially in longitudinal direction taper towards a single point, which is disposed on the longitudinal axis, and intersect with one another in this point. In other words, the shape of a perfect cone is given if a theoretical extension of all of the essential cone angles intersects the longitudinal axis in a single point. 
     Due to the fact that the shaft as well as the hub has corresponding contours of a perfect cone in the area of the entraining longitudinal section, a so-called positive fitting is the result in response to correspondingly adapted diameters or cross-sections, which leads to a laminar attachment and to a self-locking. 
     With only very little expenditure of energy, the shaft and the hub can be joined in such a manner that they remain in a relatively solid connection due to the self-locking. The shape of a perfect cone furthermore causes the shaft and the hub to be compulsorily centered to each other in response to the joining. The connection is thus completely free of play and avoids all of the disadvantages associated with an undesired play. The transmission of forces takes place across a relatively large surface, thus avoiding load peaks. 
     Polygonally shaped, especially trochoidally shaped cross sections of the shaft and hub have proven to be advantageous. A trochoid arises as the trajectory of a point as the point is carried along when a circle (moving circle) rolls along on or in a circle (rest circle). The number of and embodiment of the trochoidal “indentations and bulges” are variable. It has been shown that it is possible to transmit torque with minimum stress and, at the same time, with minimum relative motion between touching surfaces by using a trochoidal contour that has been optimized with respect to the number of “indentations and bulges” and to their large and small diameters. Small differences in the contour of the touching components enable the properties of the shaft/hub connection to be changed, its lifetime and stability in particular. 
     Optionally, provision can be made for an additional sealing element between the shaft and the hub. To avoid corrosion, a sealing of the polygon section is sensible under sustained loading. Such a sealing can also be sensible if the shaft/hub is used in all-terrain vehicles or in construction machinery. 
     The shaft/hub connection according to invention is particularly suited for a use in automotive technology, for example for braking systems, wheel suspensions or as connections for joint and prop shafts of motor vehicles. It is advantageous hereby that a hub according to the invention having a polygonal inner contour must not be machined during the production process. It is consequently unnecessary to manufacture it out of steel; the hub could also be produced from cast iron, for example. The shaft/hub connection according to the invention is thus also particularly well suited for such a use, because brake systems, for example, are subjected to high thermal loads. 
     Further advantageous embodiment characteristics of the invention are included in the subclaims as well as in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention shall be explained in more detail below based on preferred embodiments illustrated in the drawings. 
         FIG. 1  shows a perspective view of a shaft/hub connection having the shape of a perfect cone, 
         FIG. 2  shows a cross section of the shaft/hub connection from  FIG. 1  along a longitudinal axis, 
         FIG. 3  shows a prestressing ring according to the invention in a perspective view, closed, 
         FIG. 4  shows a prestressing ring according to the invention in a perspective view, closed, opened, partially cut, 
         FIG. 5  shows a shaft according to the invention in side view, wherein the contour in the shape of a perfect cone is clarified by means of artificial lines, 
         FIG. 6  shows a perspective view of an embodiment version of a shaft/hub connection according to the invention having a profiled prestressing ring as connecting means. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 6  clarify the function and the configuration of a shaft/hub connection  20  as claimed in the invention. The shaft/hub connection  20  has a shaft  22  and a hub  24 , wherein the shaft  22  with its outer contour  26  rests against an inner contour  28  of the hub  24 . This area, in which a torque can be transmitted, will be referred to hereinbelow as entraining longitudinal section. 
     The shaft  22  and the hub  24  are disposed so as to be concentric to a longitudinal axis X-X and rotate around said longitudinal axis during the torque transmission. The shaft  22  has trochoidal bulges and the hub  24  has trochoidal indentations relative to its cross section. However, all other out-of-round cross sectional shapes are also fundamentally suitable for implementing the invention. A six-sided polygon in particular has proven to be particularly suitable for transmitting the torque. It has likewise been shown for a six-sided polygon that a relative eccentricity E of between 2% and 10%, preferably between approximately 3% and 5% should be specified. The relative eccentricity E describes the eccentricity of the polygon relative to the non-physical average diameter Dm expressed in percent, that is, it describes a relation between an outer diameter Do and an inner diameter D i  of the polygon. D m  is the diameter of a circular disk having the same surface content as the polygon. The term polygon is not to be understood here within its strictest meaning, but rather as an approximate, polygon-like shape. The relative eccentricity E can be computed according to the following formula:
 
 E=ε/D   m *100
         where   ε=polygon&#39;s out-of-roundness       

     The relative eccentricity E should be advantageously derived from the following formula:
 
 E =( D   o   −D   i   /D   o   +D   i )×50
 
     Particularly advantageous polygonal shapes arise from the use of IPROTEC process and can in particular be computed according to the following formulas (deviation +/−10%):
 
 x (γ)=( D   m /2)×cos(γ)+ε×cos(( n− 1)×γ)
 
 y (γ)=( D   m /2)×sin(γ)−ε×sin(( n− 1)×γ)
         where   γ=0 to 360°, continuous parameter   n=number of sides of the polygon   ε=polygon&#39;s out-of-roundness       

       FIGS. 1 and 2  clarify how the shaft  22  can be inserted into the hub  24 . As can be seen in particular from  FIG. 3 , the outer contour  26  and the inner contour  28  have the shape of a perfect cone. This means that the relative eccentricity E across the length of the entraining longitudinal section is constant. 
     As results in particular from  FIG. 2 , the entraining longitudinal section is very short towards the longitudinal axis X-X. It has been shown that the entraining longitudinal section can be shortened by up to 60% with comparable torques, which are to be transmitted, as compared to conventional connections. On the one hand, the production costs are reduced with this shortening and, on the other hand, the overall size of the shaft/hub connection  20  is reduced as well. Vibrations and unintentional fretting corrosion are also minimized. The minimally possible length of the entraining longitudinal section is the length that allows for the safe transmission of the desired torque. 
     Advantageously, the length of the entraining longitudinal section is only up to 40%, in particular only up to 33% of the average cone diameter of the cross section of the untrue entraining longitudinal section. On principle, however, other aspect ratios can also be used, depending on the embodiment of the connection. 
     Two circumferential ramps  30  as claimed in the invention, each of which are provided at the shaft  22  and at the hub  24  and which run coaxially around the longitudinal axis X-X, become apparent from  FIG. 2 . In the illustrated exemplary embodiment, each of the ramps  30  has a slope  32  approaching each other in the direction away from the shaft/hub connection  20 . The ramps  30  comprising the slopes  32  serve the purpose of attaching the connecting means shown in  FIG. 4 , which is embodied as a prestressing ring  34  in the illustrated exemplary embodiment. 
     To be able to apply sufficient prestress, the prestressing ring  34  is placed above the ramps  30  after joining the shaft  22  and the hub  24  and the inner side of said prestressing ring  24  comes into contact with the slopes  32 . Due to the reduction of the diameter of the prestressing ring  34 , said prestressing ring  34  pushes against the slopes  32  and presses the ramps  30  towards one another. 
     The prestressing ring  34  is clearly shown in particular in  FIGS. 3 and 4 , wherein, for an improved illustration, the prestressing ring  34  in  FIG. 4  is illustrated in two parts, wherein the two parts are offset to one another to a certain extent. The reduction of the diameter of the prestressing ring can be carried out by means of a so-called ear  36 , which is compressed by means of a suitable tool. This method can be carried out in a rapid and simple manner and leads to a very even and constant prestressing force across the entire periphery of the ramps  30 . Nonetheless, there are also other possibilities, for example connecting means, which are joined by means of screws. It has been shown that the connecting means is to be balanced, because it rotates in response to the torque transmission. However, the balancing is not necessary for applications with low speeds. The inner side of the prestressing ring  34  has a profile, which is adapted to the ramps  30  or the slopes  32  in such a manner that a reduction of the diameter causes a prestressing force to act on the slopes  32 . The connecting means creates a prestressing force, which is sufficient for maintaining the shaft/hub connection  20  in a self-locking state. In the instant exemplary embodiment, the prestressing ring  34  has side walls  38 , the inner sides of which each come into contact with the slopes  32 . The side walls  38  can be embodied so as to be continuous, but they can also be interrupted by means of indentations  39  so that a plurality of side walls sections  40  is embodied. It is important that the side walls  38  are embodied in such a manner that the force, which is summoned up by said side walls  38 , acts as evenly as possibly across the periphery of the ramps  30  in axial direction. In the illustrated exemplary embodiment, four side wall sections  40  are shown for each side. However, up to twenty side wall sections are also possible. 
     The prestressing ring  34  has two free ends. Starting from the free ends, an overlapping section  50  results, above which end regions of the prestressing ring  34  overlap in the closed state. The overlapping section  50  has a length of from approximately 10 to 20% of the outer periphery of the prestressing ring  34  and is limited by the free ends. In the region of the overlapping section  50 , the two end regions each have a clamp  52  and an opening  54 , which are disposed in such a manner that the two clamps  52  can be hooked into the corresponding opening  54  of the other end region. If the ear  36  is crimped or compressed, the clamps  52  contract the prestressing ring  34  via the attachment on an edge of the corresponding opening  54 . 
     An important advantage of the invention is also that the same or different materials can be used for the production of the shaft  22  and/or the hub  24 . The hub  24  can be made from cast iron, for example, while the shaft  22  is made from steel. Further materials, which are suitable for manufacturing, include ceramics, aluminum, MMC as well as globular or laminar cast iron. Combinations of the different types of materials can also be used. 
     As can be seen from  FIG. 5 , contour lines of the outer contour  26  running approximately in longitudinal direction X-X intersect in a single point on the longitudinal axis X-X, if they are theoretically extended. Shown is a cone angle A, which is included by the longitudinal axis X-X and by a line attached at a maximum diameter of the shaft  22  and a cone angle B, which is included by the longitudinal axis X-X and by a line attached at a minimal diameter of the shaft  22 . The cone angle A can also be referred to as outer cone angle A; the cone angle B can also be referred to as inner cone angle B. It has been shown that the desired self-locking is made possible in a reliably manner by means of an outer cone angle of between 0.5° and 7°. If the inner contour  28  of the shaft  22  is embodied in a corresponding manner, the result of the joining of the shaft  22  and of the hub  24  is a laminar contact, which provides for an optimal torque transmission. However, it is also important therein that the state of the self-locking is reached in response to a joining, that is, when the outer contour  26  attaches on the inner contour. 
       FIG. 6  shows a preferred field of application of the shaft/hub connection  20 , that is, as connection of a drive shaft  42  with a constant velocity joint  44 . For this purpose, the shaft/hub connection  20  can also be integrated with a slip joint. In the end region, the drive shaft has splines  48  for the torque transmission. 
     Preferably, the side walls  38  have an angle of between 20° and 28°, wherein the angle describes the deviation from a plumb line to the longitudinal axis X-X. Even though this angle region has proven to be advantageous, other angles can also be used, depending on the field of application. 
     The prestressing ring  34  creates the prestressing in that the side walls  38  or the side wall sections  40  deform elastically. To ensure a sufficiently sound deformation of the side walls  38 , the side walls  38  or the side wall sections  40  should have a smaller angle than the slopes  32 . It has been shown that an angle of between 14° to 22° in combination with the above-mentioned angles works very well for the slopes  32 . 
     To simplify assembly, the prestressing ring  34  is embodied so as to be open in a preassembly state, wherein the free ends of the prestressing ring  34  overlap in sections. In the overlapping area, in the area of the one free end, a recess is disposed, into which a clamp, which is disposed in the area of the other free end, can be hooked. The ear  36  merges into the normal periphery of the prestressing ring  34  via two journals and thus has the approximate shape of an omega. After the hooking and the plastic deformation of the ear  36 , the diameter of the prestressing ring is reduced, so that the journals of the ear  36  can be pressed towards one another and the side walls elastically deform at the ramps  30  and hold the shaft  22  and the hub  24  together under prestress. 
     The use of an ear  36  is very cost-efficient and permits a simple and rapid tightening of the connection. Needless to say, other devices, such as a knee lever, screw connections or the like, are also possible, instead of an ear  36 . 
     The prestressing ring  34  is able to cover a gap distance between the two ramps  30  of the shaft  22  and of the hub  24  and can nonetheless create sufficient prestress. 
     Advantageously, the prestressing ring  34  can be connected with the shaft  22  or with the hub  24  already prior to the joining of the shaft/hub connection  20 . This clearly simplifies the assembling once more. 
     In the illustrated exemplary embodiment, an additional sealing element  46 , which is designed as an O-ring, is disposed between the shaft  22  and the hub  24 . 
     The foregoing description only serves for comprehending the invention and is not to be understood to be limiting. Instead, the described exemplary embodiment represents only a very advantageous realization of the invention.