Abstract:
A joint arrangement includes an outer joint component, an inner joint component, a cage and at least two balls located between the outer and inner joint component and in openings of the cage. The balls run in ball recesses, while at least two are in a mechanical contact with pressing devices, which are adapted for holding the respective balls in a radially flexible position relative to one of the inner joint component, the outer joint component and the cage and for pressing the respective balls into the corresponding recesses. Such a joint arrangement is based on a homokinetic joint and allows a homogenous transfer of torque without alternating acceleration and deceleration due to the action of the joint itself. Furthermore, a reliable and effective torque limitation may be accomplished.

Description:
TECHNICAL FIELD 
       [0001]    The invention relates to a joint arrangement, a drive system for driving control surfaces of an aircraft and an aircraft with such a drive system. 
       BACKGROUND OF THE INVENTION 
       [0002]    For transferring torque and rotational motion between two components that may comprise a variable angular relationship in view of their rotational axes it is known to use flexible joints that are able to compensate the relative angle. Besides cardan joints with inhomogeneous torque and speed characteristics it is known to use homokinetic joints. These comprise two joint components surrounding each other such that two spherical surfaces are arranged at a distance to and facing each other, wherein a number of balls is supported in a cage between these two surfaces. The balls are resting in grooves that allow the transfer of torque between the two components along their individual longitudinal or central axes and also allow the alteration of their relative angle to each other. 
         [0003]    Typically, high lift systems of commercial and military aircraft are powered by a centralized power control unit (PCU) positioned in the fuselage of the aircraft and connected to a transmission shaft arrangement providing mechanical power to geared actuators at flap or slat panel drive stations. The transmission shaft arrangement comprises at least two transmission shafts, each extending from the PCU into a wing of the aircraft. Commonly, the transmission arrangement may also comprise several gearboxes, universal joints, spline joints and other components for compensating manufacturing tolerances, deflections of the wing structure during flight and changes in the extension direction of the transmission shaft from the PCU to the individual drive stations. 
         [0004]    U.S. Pat. No. 1,916,442 discloses a homokinetic universal joint in which a driving and a driven member have the same angular velocity without angular acceleration or deceleration of a driving shaft due to a universal joint action. The universal joint comprises an outer joint component with ball grooves, an inner joint component with corresponding ball grooves, the inner joint component positioned in a hollow space of the outer joint component and a ball supporting cage located therebetween. 
         [0005]    EP 1 462 361 B1 and U.S. Pat. No. 7,048,234 B2 disclose an adaptive flap and slat drive system for an aircraft comprising a central power control unit. 
         [0006]    DE 3 620 886 C2 and U.S. Pat. No. 4,786,013 disclose a drive arrangement for a landing flap on an aircraft wing which includes a structure for variable torque limiting and position fixing. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    There may be a need to provide an apparatus that enables the harmonic transfer of torque between two shafts at an angle to each other and, at the same time, provide a simple, yet reliable limitation of torque resulting in a least possible weight, particularly for the use in an aircraft. 
         [0008]    A joint arrangement is proposed, comprising an outer joint component having a spherical inner surface surrounding a hollow space and a first interface section, the inner surface comprising at least two outer ball recesses; an inner joint component positioned inside the hollow space of the outer joint component, the inner joint component having a spherical outer surface and a second interface section, the outer surface comprising at least two inner ball recesses; a spherical cage arranged in the hollow space between the inner surface of the outer joint component and the outer surface of the inner joint component, the cage comprising at least two openings extending from a side facing the outer joint component to a side facing the inner joint component; at least two balls and at least two pressing devices. Each of the outer ball recesses constitutes a ball recess pair with an inner ball recess and corresponds to an opening in the cage. The at least two balls are arranged in the outer ball recesses, the inner ball recesses and openings of the cage for transferring a torque from the first interface section to the second interface section. The at least two pressing devices are arranged in one of the inner joint component, the outer joint component and the cage, each in mechanical contact with one of the at least two balls. Furthermore, the at least two pressing devices are adapted for holding the at least two balls in a respective recess with a predetermined maximum pressing force for limiting a transferable torque of the joint arrangement. 
         [0009]    Such a joint arrangement according to an embodiment of the invention is based on a homokinetic joint that allows a homogenous transfer of torque without alternating acceleration and deceleration due to the action of the joint itself. The outer joint component may comprise any suitable shape as long as a spherical inner surface may be provided. The spherical surface corresponds to a surface that is a part or a section of a sphere in order to allow for a relative motion of the inner joint component inside the outer joint component such as a joint head in a joint socket, while maintaining a predetermined distance between the inner and outer joint components. The inner joint component, which is positioned inside the hollow space of the outer joint component, therefore has an outer surface that is spherical as well and that corresponds to the inner surface of the outer joint component. Furthermore, the cage that holds the at least two balls, e.g. such as in a ball bearing device, is positioned between the inner surface and the outer surface in the joint arrangement. Other forms than spheres may be provided, e.g. countertracks like in WO 2008/080709 A1. 
         [0010]    By placing the balls into the ball recesses, a mechanical shearing force may be transferred between the inner joint component and the outer joint component. Depending on the size and depth of the recesses, the size of the balls and the achievable forces of the pressing devices, a maximum shearing force to be transferred between these joint components is adjustable, such that a maximum transferable torque is definable, comparable to a ball ramp mechanism. 
         [0011]    By providing such a radially flexible position support, the respective balls are not necessarily always placed in the corresponding ball recesses. By exceeding a predetermined maximum shearing force between the joint components acting on the respective balls, their radially flexible support may not be able to maintain the position. Consequently, they move radially and therefore leave the corresponding ball recesses. Due to the limited size of the recesses in the inner or outer surface of the joint components, the joint components may rotate relative to each other such that the inner ball recesses are not aligned with the outer ball recesses or any intermediate recess or torque transferring device. Hence, the transfer of torque ends. 
         [0012]    The design principle of the joint arrangement according to an embodiment of the invention therefore combines a very homogeneous transfer of torque between two components at an angular relative position as well as an efficient limitation of transferable torque. The joint arrangement is reliable and substantially maintenance-free. 
         [0013]    The joint arrangement may be connected to two rotating components by means of the first interface section and the second interface section, which may be flanges, shaft-hub-connections, indentations or recesses with a suitable torque transferring profile etc. The interface sections may preferably be realized by means of profiled surfaces e.g. inside the inner joint component to receive a correspondingly shaped shaft section, and e.g. at a side face of the outer joint component. 
         [0014]    Due to the distinct reliability, the low complexity and the low weight, the joint arrangement according to an embodiment of the invention is predestined for a use in an aircraft, for example in a drive train of a high lift system. As described further below, the joint arrangement may be used for connecting transmission shaft sections of a transmission shaft system for a trailing edge flap arrangement or a leading edge slat arrangement. 
         [0015]    Exemplarily, each of the outer ball recesses constitutes a ball recess pair with an inner ball recess and corresponds to an opening in the cage, wherein at least two first balls are arranged in the ball recess pairs and a corresponding opening of the cage. The setup of the joint arrangement is rather simple, yet extremely reliable and allows a compact installation space and a safe operation. 
         [0016]    In an exemplary embodiment, the outer ball recesses are realized as outer ball grooves comprising a radius of curvature exceeding the radius of curvature of the respective balls, wherein the center of curvature of the outer ball grooves is distanced from a geometrical center of the outer joint component. Due to the different radii of curvature, the respective balls contact the outer ball recesses, i.e. the outer ball grooves, only at a single point. During normal operation, the pressing devices press the respective balls into the outer ball recesses. Due to the curvature of the outer ball recesses and the distance of the center of curvature and the geometrical center of the outer joint component, the balls only roll on the outer ball recesses if a pressing force and a corresponding counterforce are present. By providing a torque to be transferred that exceeds a predetermined maximum torque, the pressing devices are forced to radially move the respective balls such that the joint arrangement is released. 
         [0017]    The radius of curvature of the ball grooves may be at least twice the radius of curvature of the respective balls, which allows a rather distinct degree of freedom for the first balls. 
         [0018]    In a still further embodiment, the outer ball recesses are realized as outer ball grooves comprising a radius of curvature, which equals the radius of curvature of the respective balls. A central angle of a cross-section of the inner ball recess exceeds a central angle of a cross-section of the outer ball recess. Together with a suitably determined central angle of a cross-section of the outer ball recess on the inner joint component it is maintained that all respective balls begin with their rolling motion simultaneously. For example, the central angle of a cross-section of the outer ball recess may be determined by the following equation for an angle ψ between an outer and an inner joint component and a related cage position ψ/2: 
         [0000]    
       
         
           
             
               tan 
                
               
                   
               
                
               
                 α 
                  
                 
                   ( 
                   ψ 
                   ) 
                 
               
             
             = 
             
               T 
               
                 
                   F 
                   S 
                 
                  
                 
                   n 
                   K 
                 
                  
                 r 
                  
                 
                     
                 
                  
                 
                   cos 
                   2 
                 
                  
                 
                   ψ 
                   2 
                 
               
             
           
         
       
     
         [0000]    wherein
       T: torsional moment of the drive shaft   n k : number of respective balls,   α: central angle of a cross section of the outer ball grooves,   ψ: angle between the central axes of the joint components,   r: distance between the centre of the joint and the centre of the balls,   F S  cos (ψ/2): preload force by each pressing device on each ball.       
 
         [0025]    The cross-sections are given in a plane that is perpendicular to a local extension of the ball recess in case the recess is a groove that extends over a certain length, which clearly exceeds its width. The cross-section may also extend through the geometrical center of the recess at least in case the recess is a mere spherical indentation. Hence, the recess in question may have a contour that is a segment of a circle. The angle ψ depends on the actual alignment of the central axes of the joint components relative to each other. 
         [0026]    In another exemplary embodiment, the pressing devices are arranged in the cage and support at least two first balls in a radially flexible position relative to the cage. The cage comprises an inner cage surface having at least two rotatably supported second balls. The at least two second balls are arranged in corresponding inner recesses of the inner joint component. This leads to the fact that the first balls are directly acted upon a pressing force of the at least two pressing devices such that the pressing devices may be designed more conservatively, e.g. as cylindrical ball cups. Further, the preload is completely independent from the alignment angle between the rotational axes of the first and second joint components. Hence, it is possible to reduce the diversity of produced joint arrangements, which reduces the total manufacturing costs. Due to the independent pressing force on the first balls the central angle of a cross-section of the outer ball recess may be determined by the following equation: 
         [0000]    
       
         
           
             
               tan 
                
               
                   
               
                
               
                 α 
                  
                 
                   ( 
                   ψ 
                   ) 
                 
               
             
             = 
             
               T 
               
                 
                   F 
                   S 
                 
                  
                 
                   n 
                   K 
                 
                  
                 r 
                  
                 
                     
                 
                  
                 cos 
                  
                 
                   ψ 
                   2 
                 
               
             
           
         
       
     
         [0000]    wherein F S  is the preload force by each pressing device on each first ball independent of ψ. 
         [0027]    In another exemplary embodiment, the cage is at least partially divided in a radial direction into a first cage part and a second cage part. The second cage part surrounds the first cage part at least partially, each of the first and second cage part having at least two cage part recesses arranged in corresponding positions. The pressing devices are arranged in one of the first cage part and the second cage part and support at least two first balls in a radially flexible position relative to one of the first cage part and the second cage part. The cage comprises an inner cage surface having at least two rotatably supported second balls and wherein the at least two second balls are arranged in corresponding outer recesses of the inner joint component. The cage comprises an outer cage surface having at least two rotatably supported third balls and the at least two third balls are arranged in corresponding inner ball recesses of the outer joint component. Again, the pressing force directly acts upon the first balls independent of the relative alignment angle between the first joint component and the second joint component in view of their rotational axes. Once a predetermined maximum torque is exceeded, the first balls are pressed into one of the first cage part and the second cage part. Consequently, the two cage parts may rotate relative to each other. The requirements for supporting the first balls are less strict for this arrangement as, for example, the inner cage part may be guided inside the second cage part and the first balls merely need to provide a linear motion between two substantially longitudinal, i.e. cylindric, indentations. Also, the pressing devices may be designed in a more conservative manner as in the previous embodiment, e.g. as cylindrical ball cups. 
         [0028]    Preferably, the pressing devices may be realized as springs arranged in a pressing device recess, wherein each spring is in a mechanical contact with an end face of the pressing device recess and the respective first ball. The mechanical design of such a pressing device is simple and reliable. Further, the achievable pressing or preload force of the pressing device may easily be adjusted by replacing the spring, without having to alter the whole setup of the joint arrangement. 
         [0029]    Furthermore, each first ball may be supported on a ball cup. In the ball cup, an appropriate ball recess may be arranged. If the pressing device comprises a spring, the spring may extend from an end face of a pressing device recess to an end face of the ball cup. Consequently, an even and harmonic introduction of the pressing force is achieved. 
         [0030]    In an embodiment with swept wings the rotational vectors of the outer joint component, the cage and the inner joint components have the same length, but different directions. This may be used to integrate an electric generator into the joint arrangement. With the electric power produced by this electric generator a control device, actuator devices and sensors may be operated. Instead of springs, force sensors connectable to a control device may be installed. If the sensors detect an overload, the control device may initiate actuators, coupled to the ball cups, to pull the ball cups inwardly and to uncouple the outer joint component from the inner joint component. 
         [0031]    The invention further relates to a drive system for control surfaces of an aircraft, comprising a power control unit, at least one transmission shaft having a plurality of transmission shaft sections and at least one drive station coupled with the drive system, wherein the transmission shaft sections are coupled by means of the joint arrangement described above. 
         [0032]    Also, the invention relates to an aircraft having such a drive system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Further characteristics, advantages and application options of the present invention are disclosed in the following description of the exemplary embodiments in the figures. All the described and/or illustrated characteristics per se and in any combination form the subject of the invention, even irrespective of their composition in the individual claims or their interrelationships. Furthermore, identical or similar components in the figures have the same reference characters. 
           [0034]      FIGS. 1   a  and  1   b  show a first exemplary embodiment of the joint arrangement in two perpendicular sectional views. 
           [0035]      FIGS. 2   a  and  2   b  show a second exemplary embodiment of the joint arrangement with first balls and pressing devices in the cage in two perpendicular sectional views. 
           [0036]      FIGS. 3   a  and  3   b  show a third exemplary embodiment of the joint arrangement with first balls, second balls and pressing devices in the cage in two perpendicular sectional views. 
           [0037]      FIGS. 4   a  to  4   f  show fourth exemplary embodiments of the joint arrangement with first balls, second balls, third balls, a divided cage and pressing devices in the cage in sectional views. 
           [0038]      FIGS. 5   a  to  5   d  show fifth exemplary embodiments of the joint arrangement with first balls, second balls, a divided cage and pressing devices in the cage in sectional views. 
           [0039]      FIG. 6  shows a drive system for a high lift system of an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]      FIG. 1   a  shows a joint arrangement  2  comprising an outer joint component  4 , an inner joint component  6 , a spherical cage  8 , four first balls  10  as well as four corresponding pressing devices  12 . The outer joint component  4  comprises a hollow space  16 , in which the inner joint component  6  and the cage  8  are arranged. 
         [0041]    The cage  8  comprises openings  14  that are adapted for guiding the first balls  10  between the inner joint component  6  and the outer joint component  4 . Exemplarily, the pressing devices  12  are arranged at the inner joint component  6  and comprise a recess  16  into which recess  16 , e.g. a bushing, ball cups  18  may be moved. The crescent-shaped ball cups  18  are guided by means of linear guides  20  located at the side faces of the recess  16  and comprise an inner ball recess  19 . The first balls  10  contact the inner ball recesses  19  by means of a circular contact line. The guides  20  run parallel to a sectional plane marked as “AA” and vertically to a sectional plane marked “BB”. The outward motion of the ball cups  18  may be limited by end stops  31  engaging correspondingly shaped steps of the ball cups  18 . Between an underside of the ball cups  18  and the interior end face of the recess  16 , springs  22  are located. By a force acting upon the first balls  10  into the direction of the recess  16 , the ball cups  18  move inwardly, i.e. into the direction of a central axis  24 . The inner ball recess  19  is a meridional groove, in which the first balls  10  may roll, clearly visible in  FIG. 1   b . In contrast, the recess  16  is a groove with a ground, comparable to a stud hole, extending parallel to the axis  24  of the inner joint component and exemplarily comprising a substantially rectangular or another non-circular or circular cross-section suitable to allow the ball-cup  18  to move inwardly. 
         [0042]    The joint arrangement  2  is designed for transferring torque between the inner joint component  6  and the outer joint component  4 . For the sake of clarifying the general setup the inner joint component  6  and the outer joint component  4  are arranged parallel to each other in the drawing of  FIG. 1   a . For the purpose of transferring torque, the outer joint component  4  comprises four outer ball recesses  28  on an inner surface of the outer joint component  4 . By providing a rotation of the inner joint component  6  or the outer joint component  4 , the first balls  10  transfer a shearing force due to the pressing action of the pressing devices  12 , which may be realized by pre-loaded springs. Due to the shearing force acting upon the outer recesses  28 , the outer joint component  4  rotates with the same speed as the inner joint component  6 , unless the shearing force exceeds a predetermined limit. 
         [0043]    If this is the case, the pressing force upon the first balls  10  is insufficient to maintain their position in the outer recesses, such that the first balls  10  are moving in a radial direction onto an inner surface  29  of the outer joint component located between the outer recesses  28 , which inner surface  29  does not allow the transfer of a shearing force, which leads to the interruption of the transfer of torque. The inner surfaces  29  separate the outer recesses  28  from each other and comprise a smaller distance to the central axis  24  than the outer recesses  28 . To prevent the loss of the ball cups  18 , the pressing devices  12  include end stops  30  that are adapted to hold the ball cups  18  in an outermost position. As the transition between the outer recesses  28  and the inner surfaces  29  may be smooth, the first balls  10  may conduct a slight lateral motion in the outer recesses  28 , which may slightly damp harsh changes in the torque to be transferred. 
         [0044]    The outer ball recesses  28  comprise a radius of curvature which clearly exceeds the radius of curvature of the first balls  10 , but which may be lower than the radius of curvature of the inner surfaces  29  between the outer ball recesses  28  in a circumferential direction. Furthermore, the center of curvature of the outer ball recesses  28  is located in a distance to the central axis  24 . For example, the center of curvature may be positioned between the central axis  24  and the corresponding end face of the ball cup  18 . Exemplarily, four centres  30   a - 30   d  of curvature of the outer recesses  28  are indicated in  FIG. 1   a . This has the effect that the first balls  10  may only start to roll on the inner surface  28  when they are moved into the direction of the central axis  24 . However, such an inward motion of the ball cups  18  is prevented in normal operation by the pressing devices  12 . 
         [0045]      FIG. 1   b  shows a sectional view perpendicular to the sectional view shown in  FIG. 1   a . The sectional plane for the view in  FIG. 1   b  is indicated by “AA” in  FIG. 1   a . However,  FIG. 1   a  shows parallelly arranged first and second interface sections  33  and  32 , while  FIG. 1   b  shows angular first and second interface sections  33  and  32 . The same applies for  FIGS. 2   b ,  3   b ,  4   b ,  4   d ,  4   f ,  5   b  and  5   d.    
         [0046]    In  FIG. 1   b  the outer joint component  4  and the inner joint component  6  are aligned in an angle to each other. A first interface section  33 , which is realized as a recess, allows receiving a drive shaft, is arranged in the outer joint component  4  and is situated around a longitudinal axis  25  of the outer joint component  4 . In analogy, a second interface section  32 , realized as a recess, is arranged in the inner joint component  6 , allows receiving a drive shaft and is situated around a longitudinal axis  24  of the inner joint component  24 . The recesses  32  and  33  may be of a pinion type. 
         [0047]    On introduction of a torque through one of the interface sections  32  or  33  into the inner joint component  6  or outer joint component  4 , the first balls  10  transfer a shearing force through the inner recess  19  and the outer recess  28 , while conducting a balancing motion along the inner recess  19  and the outer recess  28  while the cage  8  maintains the relative positions of the first balls  10 . End stops  88  limit the radial motion of the cage  8  in the direction of an angle between the axes  24  and  25  in the drawing plane of  FIG. 1   b , which is referred to as the alignment angle ψ in the following. 
         [0048]    The basic design and setup of the joint arrangement according to  FIGS. 1   a  and  1   b  is rather simple and of a light weight, yet a reliable operation may be accomplished. 
         [0049]      FIG. 2   a  shows a slight modification in form of a joint arrangement  35  with an outer joint component  34 , an inner joint component  36  and a cage  38 . Here, also four first balls  10  are arranged between ball cups  18  having inner ball recesses  41  and the outer joint component  34 . The outer joint component  34  comprises outer ball recesses  40  that have the same radius of curvature compared to the first balls  10 . Hence, the first balls  10  contact the outer joint component  34  by means of a circle. 
         [0050]    A central angle α of a cross-section of the inner ball recesses  40  is less than a central angle β of a cross-section of the inner ball recesses  41  for maintaining a simultaneous rolling motion of the first balls  10  once the predetermined maximum torque is exceeded. An angle β exceeding 90° prevents the first balls  10  from leaving the ball cups  18 . As the pressing force onto the first balls  10  depends on an alignment angle ψ the necessary central angle α depends on the angle ψ as well and may be calculated by the previously mentioned equation: 
         [0000]    
       
         
           
             
               tan 
                
               
                   
               
                
               
                 α 
                  
                 
                   ( 
                   ψ 
                   ) 
                 
               
             
             = 
             
               T 
               
                 
                   F 
                   S 
                 
                  
                 
                   n 
                   K 
                 
                  
                 
                   r 
                   06 
                 
                  
                 
                     
                 
                  
                 
                   cos 
                   2 
                 
                  
                 
                   ψ 
                   2 
                 
               
             
           
         
       
     
         [0000]    wherein
       T: torsional moment of a drive shaft,   n k : number of first balls  10 ,   r 06  cos (ψ/2): distance between a joint centre  0  and centres  6  of first balls  10 ,   F S  cos (ψ/2): preload force of ball cup  18 ,   ψ: angle between the central axes of the joint components, bordered by body stops  88 .       
 
         [0056]    Hence, the relationship between the torque limit and the preload force of the ball cups  18  depends on the alignment angle ψ. The drive shaft mentioned above may be a shaft which is introduced into the second interface section  32 . 
         [0057]    As rendered clear by  FIG. 2   b  the outer ball recesses  40  are realized as a circle segment inside the outer joint component  34 . The distance between the joint centre  0  and the ground of the outer ball recess  40  is r 06 +r 67 , where r 67  is the radius of the first balls  10 . Correspondingly, the inner ball recesses  41  are circle segments at an outer surface of the crescent-shaped ball cups  18 . This allows for different alignment angles ψ, which may be measured in various spatial directions. The edge between the surface  29  and the recess  40  is labelled as  7 . To maintain a simultaneous initiation of moving of the first balls  10  in case of overload the depth of the outer ball recesses  40  at a cage position ψ/2 is 
         [0000]        r   67 (1−cos α(ψ)).
 
         [0058]    The distance r 029  between the joint centre  0  and the surface  29  of the first balls  10  at a cage position ψ/2 follows to 
         [0000]        r   029   =r   06   +r   67  cos α((ψ)).
 
         [0059]    The surface  29  is not part of a spherical shape. 
         [0060]      FIGS. 3   a  and  3   b  show a further joint arrangement  42  with an outer joint component  44 , an inner joint component  46  and a cage  48  situated between the inner joint component  46  and the outer joint component  44 . Here, first balls  10  reside in substantially cylindrical ball cups  50  that comprise a ball recess  51  extending over more than one half of the first balls  10  such that they may not exit the ball cups  50  without large force. The first balls  10  are also slidably supported by outer ball recesses  52  arranged in the outer joint component  44  and pressed outwardly in a radial direction by pressing devices  54 . 
         [0061]    By placing the pressing devices  54  inside the cage  48 , the pressing devices  54  directly act upon the first balls  10  such that the necessary preload force for maintaining a predetermined torque limit is completely independent from the alignment angle ψ between the first joint component  44  and the second joint component  46 . 
         [0062]    The central angle α of the cross-section of the outer ball recesses  52  may therefore be calculated by the previously mentioned equation, in which the force F s  does not need to be divided into separate force fractions for different directions, according to following equation: 
         [0000]    
       
         
           
             
               tan 
                
               
                   
               
                
               
                 α 
                  
                 
                   ( 
                   ψ 
                   ) 
                 
               
             
             = 
             
               T 
               
                 
                   F 
                   S 
                 
                  
                 
                   n 
                   K 
                 
                  
                 
                   r 
                   06 
                 
                  
                 
                     
                 
                  
                 cos 
                  
                 
                   ψ 
                   2 
                 
               
             
           
         
       
     
         [0000]    wherein
       T: torsional moment of the drive shaft,   n k : number of first balls  10 ,   r 06  cos (ψ/2): distance between the joint centre  0  and centres  6  of first balls  10 ,   F s : preload force of the ball cup  50 ,   ψ: angle between drive shaft and driven shaft, bordered by the body stop  88 .       
 
         [0068]    The edge between an inner surface  29  of the outer joint component  44  and the outer recess  52  is labelled as  7 . To maintain a simultaneous initiation of motion of the first balls  10  in case of overload, the depth of the outer recess  52  at a cage position ψ/2 follows to: 
         [0000]        r   67 (1−cos α(ψ)).
 
         [0069]    The distance r 029  between the joint centre  0  and the inner surface  29  at a cage position ψ/2 follows to: 
         [0000]        r   029   =r   06   +r   67  cos α((ψ)).
 
         [0070]    The inner surface  29  is not part of a spherical shape. 
         [0071]    For coupling the cage  48  with the inner joint component  46 , second balls  58  are provided that sit in the cage  48  and extend into inner ball recesses  60  located on the inner joint component  46 . Consequently, when a predetermined maximum torque is exceeded, the first balls  10  and the ball cups  50  are pressed towards the central axis  24  under compression of the pressing devices  54  such that the cage  48  may freely rotate relative to the outer joint component  44 . The recess  51  of the ball cup  50  for the first balls  10  has a spherical shape, the ball cup  50  has a cylindrical form, the ball cup sits in a cylindrical recess  36 . An angle β exceeding 90° prevents the first balls  10  from leaving their ball cups. 
         [0072]    In  FIG. 3   b , it is shown in more detail how the inner joint component  46 , the cage  48  and the outer joint component  44  are coupled. For example, the inner joint component  46  comprises two inner ball recesses  60  parallel to the drawing plane in  FIG. 3   b  that join each other such that a single substantially circular inner ball recess  60 , which extends over the whole circumference of the inner joint component  46  in the drawing plane of  FIG. 3   b , is created. Therefore, the inner joint component  46  may freely rotate around an axis perpendicular to the drawing plane. It is clear that another inner ball recesses  60  shown in  FIG. 3   a  parallel to the axis  25  may also extend over a whole circumference in the plane vertical to the drawing plane of  FIG. 3   a . The cage  48  comprises spherical ball recess  56  for holding the second balls  58 . 
         [0073]    In analogy, the outer ball recesses  52  extend over a circular segment over exemplarily approximately 70° of the inner surface of the outer joint component  44 . Since the pressing force is applied directly within the cage  48  onto the first balls  10 , the alignment of the central axis  24  of the inner joint component  46  and a central axis  25  of the outer joint component  44  is not relevant for the pressing force onto the first balls  10 . 
         [0074]      FIGS. 4   a  and  4   b  show a further exemplary embodiment in form of a joint arrangement  62  having an outer joint component  64 , an inner joint component  66  as well as a cage with an outer cage part  68  and an inner cage part  70 , which resides in a correspondingly formed annular cut-out  72  of the outer cage part  68 . Third balls  80  are arranged in the outer cage part  68  and run in outer ball recesses  57 . Second balls  58  are arranged in the inner cage part  70  and run in inner recesses  60  in order to introduce the rotational motion from the inner joint component  66  to the cage parts  68  and  70 . 
         [0075]    Additionally, first balls  10  are arranged between the outer cage part  68  and the inner cage part  70  and reside in substantially cylindrical ball cups  74  that are slidably arranged in the inner cage part  70 . The first balls  10  are in contact with a cage part recess  71  of the outer cage part  68 . In the embodiment of  FIGS. 4   a  and  4   b  the simultaneous initiation of motion of the first balls  10  in case of overload cannot be maintained by varying the angle α and the distance r 029  in ψ-direction. 
         [0076]    Therefore in  FIGS. 4   c  and  4   d  for a fixed angle α the preload force F s  is varied by an variable ground of a recess  36  (as introduced in  FIG. 3   a ), which is connected over a lever  136  to a radial cam  236 . The second balls  58  are arranged by 45° relative to the radial cams  236  and the radial cam  236  is part of the inner joint component  66 . 
         [0077]    By means of the radial cams  236  the preload force acting upon the first balls  10  is adjusted due to the variable ground of the recess. With a rising angle ψ the preload force is increased, since the lever  136  is pushed to increase the compression of the springs  22  by a rising local height s of the cams. 
         [0078]    With a preload F s =c s  s(ψ) the form of the radial cam is defined over 
         [0000]    
       
         
           
             
               s 
                
               
                 ( 
                 ψ 
                 ) 
               
             
             = 
             
               T 
               
                 
                   c 
                   s 
                 
                  
                 
                   n 
                   K 
                 
                  
                 
                   r 
                   06 
                 
                  
                 
                     
                 
                  
                 cos 
                  
                 
                   ψ 
                   2 
                 
                  
                 tan 
                  
                 
                     
                 
                  
                 α 
               
             
           
         
       
     
         [0000]    wherein
       T: torsional moment of the drive shaft,   n k : number of first balls  10 ,   r 06  cos(ψ/2): distance between joint centre  0  and centres  6  of first balls  10 ,   c s : spring constant of spring  22 ,   s(ψ) height of the radial cam at a cage position ψ/2   ψ: angle between drive shaft and driven shaft, bordered by body stops  88 .       
 
         [0085]    The central angle α of the cross-section of the cage part recesses  71  may therefore be calculated as in the previous exemplary embodiment, as the force F s  directly acts upon the first balls  10  and independent from alignment angle ψ. 
         [0086]    Hence, by exceeding a predetermined maximum torque, the inner cage part  70  and the outer cage part  68  start to rotate relative to each other as the first balls  10  are displaced in a radial direction towards the central axis  24 ,  25  and their intersection, respectively. 
         [0087]      FIGS. 4   e  and  4   f  show an embodiment of a joint arrangement  262 , which is a modification of the joint arrangement  162  according to  FIGS. 4   c  and  4   d . Here, the ball cups  74  and the movement of the first balls  10  are substantially parallel to the axis  24 , similar to a common ramp mechanism. 
         [0088]      FIGS. 5   a  to  5   d  show still further joint arrangements.  FIGS. 5   a  and  5   b  show a joint arrangement  82 , comprising an outer joint component  84 , an inner joint component  86  as well as an outer cage part  88  and an inner cage part  90 , constituting a cage. Different than in  FIGS. 4   a  and  4   b , the inner cage part  90  has an outer diameter slightly below the outer diameter of the outer cage part  88  and therefore dominates the cage. Instead of using third balls, the first balls  10  reside in ball cups  92  slidably located in the inner cage part  90  and extending from the inner cage part  90  through the outer cage part  88  into the outer joint component  84 . While exceeding a predetermined maximum torque, the ball cups  92  are displaced towards the rotational axis  24  and  25 , respectively, such that the inner cage part  90  and the outer cage part  88  start to rotate relative to each other. In contrast to  FIG. 1   a ,  1   b ,  2   a ,  2   b ,  3   a ,  3   b ,  4   a  and  4   b  the first balls  10  remains in the cage  88  meanwhile the ball cups  92  glides under the cage  88  without the first balls  10 . 
         [0089]    In the embodiment of  FIGS. 5   a  and  5   b  the simultaneous initiation of motion of the first balls  10  in case of overload cannot be maintained by varying the angle α and the distance r 029  in ψ-direction. Therefore in  FIGS. 5   c  and  5   d  for a fixed angle α the preload force F s  is varied by an alterable ground  118  of the recess  36 , which is connected over a lever  136  to the radial cam  236 . The second balls  58  are arranged by 45° and the radial cam  236  is part of the inner joint component  66 . 
         [0090]    With the preload F s =c s s(ψ) the form of the radial cam is defined over 
         [0000]    
       
         
           
             
               s 
                
               
                 ( 
                 ψ 
                 ) 
               
             
             = 
             
               T 
               
                 
                   c 
                   s 
                 
                  
                 
                   n 
                   K 
                 
                  
                 
                   r 
                   06 
                 
                  
                 
                     
                 
                  
                 cos 
                  
                 
                   ψ 
                   2 
                 
                  
                 tan 
                  
                 
                     
                 
                  
                 α 
               
             
           
         
       
     
         [0000]    wherein
       T: torsional moment of the drive shaft,   n k : number of balls,   r 06  cos(ψ/2): distance between joint centre  0  and centre  6  of first balls  10 ,   c s : spring constant of spring  22 ,   s(ψ): height of the radial cam at a cage position ψ/2,   ψ: angle between drive shaft and driven shaft, bordered by body stops  88 .       
 
         [0097]      FIG. 6  shows a general overview of a drive system  94  of an aircraft for driving control surfaces  96 , which may be trailing edge flaps or leading edge slats. The drive system  94  comprises a first transmission shaft  98  on a left side as well as a second transmission shaft  100  on a right side of the drive system  94 , in order to provide rotational power to drive stations  102  coupled with the control surfaces  96 . Several of these drive stations  102  are exemplarily distributed along a trailing and/or leading edge of each wing and are designed for converting rotary power into a translational movement of the control surfaces  96 . The transmission shaft  32  and  34  are driven by a PCU  104 , comprising a speed summing differential  106 , two pressure or power off brakes  108  and two motor units  110 . The PCU  104  is exemplarily located inside a fuselage of the aircraft. The PCU  104  is connected by the shaft  198  to the joint arrangement  2 ,  32 ,  42 ,  62 ,  162  and  82 , which is connected by the shaft  200  to the T-gearbox  111 . The Wing Tip Break (WTB) is labelled as  112 . 
         [0098]    The transmission shafts  98  and  100  each may comprise joint arrangements  2 ,  32 ,  42 ,  62 ,  162  and  82  for compensation alignment alterations in the wing, which may also be effected by wing flexing. Due to the use of the joint arrangement  2 ,  32 ,  42 ,  62 ,  162  and  82  according to embodiments of the invention, the transferred torque is harmonic and the rotational speed does not accelerate or decelerate due to immanent characteristics of the joints. With a homokinetic joint  2 ,  32 ,  42 ,  62 ,  162  and  82  it is easier to change the wing sweepback over the wing span. Also a wing with a pivoting sweepback, comparable to the TORNADO or F14, may become simpler to design. 
         [0099]    In addition, it should be pointed out that “comprising” does not exclude other elements or steps, and “a” or “an” does not exclude a plural number. Furthermore, it should be pointed out that characteristics or steps which have been described with reference to one of the above exemplary embodiments can also be used in combination with other characteristics or steps of other exemplary embodiments described above. Reference characters in the claims are not to be interpreted as limitations.