fig1 shows a prior art constant velocity universal joint which comprises an outer joint part 11 , and inner joint part 12 , torque transmitting balls 13 and a ball cage 14 . at one end , the outer joint part 11 is closed by a base 15 which is followed by a joint journal 16 . an aperture 17 of the outer joint part 11 is provided axially opposite the base 15 . in the outer joint part 11 , there is shown one of a plurality of circumferentially distributed outer ball tracks 18 which , if viewed from the open end 17 , is undercut - free and has a center line s a . the inner joint part 12 is provided with a central aperture 19 into which there is inserted a connecting shaft 20 which is axially secured by a securing ring 32 . in the inner joint part 12 , there is shown one of a plurality of circumferentially distributed inner ball tracks 22 which is also undercut - free if viewed from the open end 17 and has a center line s i . outer ball tracks 18 and inner ball tracks 22 are associated with one another in pairs and jointly accommodate in pairs the torque transmitting balls 13 . the balls 13 are jointly held in one plane by the ball cage 14 in that the balls are inserted into the cage windows 23 in the central cage plane which coincides with the central joint plane e . the ball track center lines s i , s a are parallel to the respective ball track ground lines . both center lines s i , s a are symmetrical to one another with respect to plane e . the central joint plane e also contains the joint center c which is defined by the point of intersection of the axes a a , a i of the outer joint part and inner joint part when the joint is articulated . at the open end 17 of the outer joint part l , there is provided an inner cone 24 which forms a stop for the connecting shaft 20 of the inner joint part 12 when the joint is articulated and thus limits the articulation angle β of the joint , as described below . fig2 shows the outer joint part 11 with an outer ball track 18 in a broken - away manner . said inner cone 24 which cuts off the outer ball track 18 at the open end 17 is still visible . furthermore , there is shown a ball 13 in the ball track 18 in a position which is assumed by the ball 13 when the inner joint part is articulated by its maximum amount relative to the outer joint part . in this case , the maximum articulation angle β between the axes , which will again be referred to below , leads to an articulation angle of the cage relative to the outer joint part of β / 2 which is shown in the drawing . by correspondingly articulating the central plane of the cage relative to the central joint plane e , the ball 13 , too , is moved out of the central joint plane e by the angle β / 2 . the center m of the balls follows the dash - dotted central line of the outer ball track 18 which is defined by a circular arc s a with the radius r 1 whose center z on the axis a a is offset by the offset o 1 relative to the central joint plane e , and by a straight lien g following same tangentially and extending parallel to the axis a a . in the ball position as illustrated , the contact point b of the ball in the outer ball track 18 is positioned in a radial plane through the ball center m . relative to the track end edge defined by the inner cone 24 , the contact point b is at a minimum axial distance l which , in view of possible edge breakages at the track end , must not be allowed to be reduced . the distance between the contact point b and the central joint plane e has been given the reference number n . fig3 shows the above - mentioned joint articulation angle β between the axis a a of the outer joint part 11 and the axis a i of the inner joint part 11 in the joint center c . in this case , the connecting shaft 20 replaces the inner joint part ; in this position , it comes to rest against the inner cone 24 . by thus limiting the degree of articulation to the angle β , the minimum distance l between the contact point b and the track end edge of the ball track 18 is ensured . fig4 shows an inventive constant velocity universal joint which comprises an outer joint part 31 , an inner joint part 32 , torque transmitting balls 33 and a ball cage 34 . at one end , the outer joint part 31 is closed by a base 35 which is followed by a joint journal 36 . an aperture 37 of the outer joint part 31 is provided axially opposite the base 35 . in the outer joint part 31 , there is shown one of a plurality of circumferentially distributed outer ball tracks 38 which , if viewed from the open end 37 , are undercut - free , without this being absolutely essential . the inner joint part 32 is provided with a central aperture 39 into which there is inserted a connecting shaft 40 which is axially secured by a securing ring 41 . in the inner joint part 32 , there is shown one of a plurality of circumferentially distributed inner ball tracks 42 which , with reference to the central joint plane e , extends symmetrically relative to the outer ball track and — if viewed from the open end 37 — is undercut - free . outer ball tracks 38 having center lines s a and inner ball tracks 42 having center lines s i are associated with one another in pairs and jointly accommodate the torque transmitting balls 33 , wherein each ball is held in the point of intersection of the associated center lines s a , s i . the balls 33 are inserted into cage windows 43 in the central plane of a ball cage 34 , which coincides with the central plane e of the joint , and are jointly held in one plane by the ball cage 34 . the central joint plane e also contains the joint center c which is defined by the point of intersection of the axes a a , a i of the outer joint part and inner joint part when the joint is articulated . in the outer joint part , on the side of the open end 37 , there is provided an inner cone 44 which can form a stop for the connecting shaft 40 when the joint is articulated . the center lines s a , s i of the ball tracks 38 , 42 which extend parallel to the respective track base and which intersect one another in the center of the ball 33 comprise turning points t 1 , t 2 . it is an important aspect that the outer ball tracks 38 , towards the open end 37 , move away from the longitudinal axis a a , for example in that a center of curvature of the end portion of the center line s a of the outer ball track 38 is positioned outside the outer joint part 31 and said center line s a respectively . accordingly , the inner ball tracks 42 , towards the base end 35 , move away from the longitudinal axis a i in that the center of curvature of the end portion of the center line s i of the inner ball track 42 is positioned outside the inner joint part 32 and said center line s i respectively . the center lines s a , s i are each composed of at least two differently curved portions adjoining one another , to be described more detailed with reference to fig5 and 6 . fig5 shows the outer joint part 31 with the outer ball tracks 38 in a broken away manner . it is possible to see said inner cone 44 which cuts off the outer track base 38 at the open end 38 . furthermore , the ball 33 of the ball track 38 is shown in the position which it assumes when the inner joint part is articulated relative to the outer joint part by the unchanged joint articulation angle β . the joint articulation angle β between the axes , which will be referred to below , leads to an articulation angle of the cage relative to the outer joint part of β / 2 which is shown in the drawing . with the central plane of the cage being articulated accordingly relative to the central joint plane e , the ball 33 , too , is moved out of the central joint plane e by the angle β / 2 into the angle bisecting plane w . the center m of the ball follows the dash - dotted central line s a of the outer ball track 38 which is defined by a first circular arc s 1 with the radius r 1 whose center z 1 on the axis a a is offset by the offset o z1 relative tot eh central joint plane e , and by an adjoining second circular arc s 2 with the radius r 2 which is less than the radius r 1 and whose center z 2 on a straight line extending outside the joint at a distance o y2 from the longitudinal axis a a is offset by the offset o z2 relative to the central joint plane e . the first end portion s 2 of the center line s a continuously adjoins the inner portion s 1 of the center line s a in a turning point t 1 . 2 respectively . tangents on the center line s a are axis - parallel in the respective turning points t 1 . 2 . the inner portion s 1 of the ball tracks 38 in the outer joint part 31 extend by 10 ° beyond the central joint plane e towards the open end 37 of the outer joint part 31 . with the articulation angle β assumed to be unchanged , the ball center m is slightly displaced towards the central joint plane e . on the other hand , the contact point b of the ball 33 at the outer ball track has moved behind the ball center m back to the central joint plane e and also radially outwards . as a result , the distance n * of the contact point b from the central joint plane becomes smaller as compared to the earlier distance n , as shown in fig6 . this means that by maintaining the minimum axial distance l of the contact point from the track and edge , the position of the inner cone 44 can be displaced towards the base 15 , i . e . the outer joint part has been shortened . fig6 shows the above - mentioned joint articulation angle β between the axis a a of the outer joint part 31 and the axis a i of the inner joint part 32 . in fig6 the inner joint part is replaced by the connecting shaft 40 which , in this position , as already mentioned , is positioned at a distance from the inner cone 44 as a result of the displacement of the latter . in consquence , it becomes possible , without changing the articulation angle β , to increase the thickness of the connecting shaft 40 in order to increase the torque transmitting capacity . if , in deviating from the illustration , the position of the inner cone is slightly changed while retaining the thickness of the connecting shaft , and while maintaining an adequate safety distance l of the contact point b from the end of the ball track , the articulation angle β can be increased .