Abstract:
A constant velocity fixed joint has an outer part  1,  an inner part  9,  a cage  18  and balls  23  which are guided by the cage  18  in the outer running grooves  5  of the outer part  1  and in the inner running grooves  14  of the inner part  9.  The inner part  9  is held relative to the outer part  1  entirely by the balls  23  in the radial direction and by the ball  23  on the one hand and by a control element  24  on the other hand, which control element  24  is supported on the inner part  9  and on a supporting element  35  associated with the outer part  1.  Beyond the advantageous supporting conditions achieved by said assembly, it is possible to achieve a further reduction in friction by friction-reducing means which are provided in the form of lubricating grooves  31, 33  for example, thus achieving hydro-dynamic lubrication conditions which are advantageously affected in that the control element  24  achieves high sliding speeds relative to the supporting element  35.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a constant velocity fixed joint which comprises an outer part, an inner part, a cage, balls and a control element. The outer part comprises a first longitudinal axis and a cavity centered on the axis. The inner face of the outer part is provided with outer running grooves which are circumferentially distributed around the first longitudinal axis. The inner part comprises a second longitudinal axis and, in its outer face, is provided with inner running grooves which are distributed around said second longitudinal axis. The number of inner running grooves corresponds to the number of outer running grooves, with the inner running grooves being arranged opposite the outer running grooves. Furthermore, the inner part is provided with an outer spherical face. The outer running grooves and inner running grooves are positioned opposite one another in pairs, and arranged in meridian planes relative to the associated longitudinal axis and extend in an undercut-free way from a first joint end. 
     The cage is provided with a hollow spherical partial face by means of which it is guided on the outer spherical face of the inner part. The cage is provided with windows which are circumferentially distributed in accordance with the outer running grooves and inner running grooves. The windows accommodate balls which engage the opposed running grooves for the purpose of transmitting torque. For this purpose they project radially outwardly and inwardly from the cage. The control element is supported on the inner part on the one hand and on a supporting element on the other hand. 
     U.S. Pat No. 5,376,052 describes such a constant velocity fixed joint wherein the control element comprises a spherical control face which engages a cavity of the inner part, which cavity is centered on the second longitudinal axis. The cavity forms a hollow spherical contact face, with the spherical control face resting thereagainst. Furthermore, the control element comprises a face which extends at a right angle relative to the first longitudinal axis and which supports the control element against a correspondingly extending face of the outer part in a way so as to be radially adjustable relative to the first longitudinal axis. Between the outer face of the cage and the inner face of the cavity of the outer part there is no area contact. In this way, any heat introduced into the inner part while the balls are transmitting torque only has to travel a short distance to reach the sliding region between the control element and the inner part. 
     U.S. Pat No. 5,453,052 describes a constant velocity fixed joint wherein the outer part and the inner part are provided with running grooves for receiving torque transmitting balls, which running grooves extend in an undercut-free way from one opening end. By means of its spherical outer face, the cage is supported in one direction against supporting elements fixed to the outer part in the region of the opening end. The supporting element is arranged in the region between two circumferentially adjoining outer running grooves. They extend wedge-like into the gap between the cylindrical part of the inner face of the cavity of the outer part and the spherical outer face of the cage. The inner part is supported in the direction opposed to the above-mentioned direction against a spherical dish-like holding element which rests against a spherical outer face of a ball cup in the cavity of the outer part. Otherwise, there is no contact between the outer face of the cage and the outer part. Contact is limited to the supporting elements secured to the outer part. There is no contact between the cage and the outer face of the inner part. Therefore, under torque, the cage is not supported on the inner part in the direction of the longitudinal axis of the outer part, but only on the small supporting elements and, via the holding element, on the outer part, because the outer part and inner part are loaded in opposite directions in the sense of being moved apart. This design leads to high loads and—because of the design of the supporting elements—to considerable friction. 
     It is the object of the invention to provide a low-friction constant velocity fixed joint wherein the losses during operation are correspondingly low. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, the objective is achieved by providing a constant velocity fixed joint wherein the outer tracks and inner tracks extend from a common first joint end in meridian planes in an undercut-free way and wherein the balls are supported on the window faces of the windows which are arranged near the first joint end. The outer face of the cage is arranged relative to the inner face of the cavity of the outer part in such a way that there exists a distance therebetween over the entire articulation range. Furthermore, the control element is provided with a spherical control face and with a guiding face. The proposed supporting element comprises a hollow spherical contact face against which the control element is supported by means of its control face. Furthermore, the control element is supported by means of its guiding face on a supporting face of the inner part, which supporting face is arranged in such a way that the second longitudinal axis of the inner part is positioned perpendicularly thereon. The supporting element is secured to the outer part or to a component connected to the outer part. The control element and the supporting element are arranged towards the first joint end from which the outer running grooves and inner running grooves extend in an undercut-free way. 
     The advantage of such a design is that the forces resulting from the transmission of torque at all angles of articulation are advantageously supported via the control element and the supporting element. There exists a further advantage in that, as compared to an assembly wherein the control element is supported against a hollow spherical face of the inner part, it is possible to reduce the number of faces which have to be produced accurately on the inner part. Furthermore, as compared to such a low-friction joint, the amount of friction is reduced even further. 
     Clear guidance is obtained because support is provided in one direction only and there is no expansion effect, so that there is no risk of jamming. In consequence, the components can be set advantageously relative to one another in the radial direction, taking into account the construction tolerances occurring. The shape of the outer ruing grooves and inner running grooves, and in particular, the way in which they extend from the first joint end towards the second joint end, is selected in such a way that, in all joint angle situations, the balls, when under torque, apply a force to the cage in the sense of applying a load to the window faces close to the first joint end, on which window faces the balls are supported. In this way it is ensured that the cage, by means of its hollow spherical face, is always held in contact with the outer spherical face of the inner part. Centering relative to the outer part in the radial direction is effected entirely by the balls, and in the axial direction, the unit of inner cage part and control element relative to the outer part is achieved by supporting same on the supporting element secured to the outer part. By classifying and dimensioning the components relative to the theoretical articulation center it is thus possible to ensure that all components match one another in such a way that they come as close as possible to the optimum alignment of their operating faces relative to the theoretical joint articulation center. 
     According to a further embodiment of the invention it is proposed that the control element is dish-shaped. In this way it is possible to achieve a component which can be produced cost-effectively by a non-chip-forming method with a high degree of repeat accuracy. 
     The supporting element, too, can be provided as a part formed from sheet metal. It is preferably firmly connected to the outer part, so that a pre-assembled unit is achieved. 
     In addition to the advantageous supporting conditions achievable, it is also possible to provide friction-reducing means between the control face and the contact face. 
     For a first embodiment it is proposed that the friction-reducing means comprise lubricating grooves which are annular in shape and are connected to a lubricant reservoir by means of lubricating bores. The dish-shaped chamber of the control element can be used as the lubricant reservoir. 
     The advantage of this embodiment is that it is possible to achieve high sliding speeds between the control face and the contact face when the joint rotates in an articulated condition. By selecting a suitable surface ratio between the lubricating grooves and the area of surface contact which occurs between the control face and the contact face when the outer part and inner part are in an aligned condition relative to one another, the high sliding speeds lead to a hydrodynamic condition of lubrication. The amount of friction thus becomes negligibly small, which means that overall, it is possible to achieve a long service life and reduce any transmission losses to a minimum. This also ensures a high degree of efficiency which, in turn, means that less heat is generated, so that it is possible to lubricate the constant velocity fixed joint with cheaper greases such as used for rolling contact bearings, for example. 
     Alternatively, the friction reducing means can be provided in the form of a rolling contact bearing which comprises a bearing cage for guiding bearing balls which, by the bearing cage, are rollingly held between the control face and the contact face. In this way it is possible to achieve supporting conditions and friction conditions which are similar to those of rolling contact bearings. 
     Particularly advantageous conditions can be achieved if the bearing cage is connected to the cage, so that the bearing cage controlled by the cage necessarily follows the movement of the latter. Two preferred embodiments of the invention are diagrammatically illustrated in the drawing wherein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal section through a first embodiment of an inventive constant velocity fixed joint in an aligned position, with friction bearing means between the control element and the supporting element. 
     FIG. 2 is a longitudinal section through a further embodiment of an inventive constant velocity fixed joint, with rolling contact bearing means between the control element and the supporting element. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a first embodiment of an inventive constant velocity fixed joint having an outer part  1  which is provided in the form of a sheet metal part and which comprises a cavity  2  whose largest opening width is provided towards the first joint end  7 . The cavity  2  is delimited by the inner face  3  and the circumferentially distributed outer running grooves  5  starting from the first joint end  7 . The outer running grooves  5  extend from first joint end  7  in an undercut-free way and are arranged in meridian planes relative to the first longitudinal axis  4  of the outer joint part  1 . Furthermore, the outer joint part, towards the first joint end  7 , comprises an outwardly extending flange  6 . Towards the second joint end  8 , the outer joint part  1  comprises a reduced cross-section, with its outer face being provided with a seat face  11  for fixing the large diameter of a convoluted boot whose small diameter is intended to be fixed on a shaft  12  which is indicated by dashed lines and which extends out of the second joint end  8 . The cavity  2  of the outer part  1  accommodates an inner part  9  which is illustrated in the drawing in such a way that the second longitudinal axis  10  of the inner part  9  coincides with the first longitudinal axis  4 . The joint is in the aligned condition, i.e. the articulation angle is 0°. Towards the first joint end  7 , the inner part  9  comprises the end face which serves as a supporting face  13  and which is arranged in such a way that the second longitudinal axis  10  is positioned perpendicularly on a plane formed by the supporting face  13 . In the outer face of the inner part  9 , there are arranged circumferentially distributed inner running grooves  14  in such way that always one inner running groove  9  is positioned opposite an outer running groove  5 , so that they form pairs. The inner running grooves  14  are also arranged in meridian planes, with their track base being designed to be undercut-free, starting from the first joint end  7 . Furthermore, the inner part  9 , on its outer face extending towards the second joint end  8 , comprises an outer spherical face  15  whose center is centered on the theoretical joint articulation center O. The inner part  9  is also provided with a toothed bore  16  which is centered on the second longitudinal axis  10  and whose purpose it is to receive a correspondingly toothed shaft  12 . Furthermore, there is provided a retaining element  17  which stores the lubricant required for lubricating the outer spherical face  15 . 
     The retaining element  17  partially overlaps a cage  18  which, in its interior, comprises a hollow spherical partial face  21 . Cage  18  is guided on the outer spherical face  15  by the hollow spherical partial face  21 . Furthermore, the cage  18  is provided with windows  19  which are circumferentially distributed in accordance with the pairs of inner running grooves  14  and outer running grooves  5  and which serve to receive balls  23  which project radially inwardly and outwardly beyond the cage  18  and engage the outer running grooves  5  and inner running grooves  14 . When the balls  23  transmit torque, the cage  18 , by means of its hollow spherical partial face  21 , is held in contact with the outer spherical face  15  of the inner part  9 . This is true because the balls  23  are supported on the window faces  20  of the windows  19 , which window faces are near the first joint end  7 , and, because of the undercut-free track shape starting from the first joint end  7 , the balls  23  load the cage  18  towards the right in the direction of the first joint end  7 . Over the entire articulation range, i.e. under all positions of articulation which can be assumed between the inner part  9  and the outer part  1  relative to one another, there always exists a distance between the outer face  22  of the cage  18  and the inner face  3  of the outer part  1 . This means that the unit consisting of the inner part  9  and the cage  18  is radially centered relative to the outer part  1  by means of the balls  23 . The inner part  9 , by means of its supporting face  13 , is supported on an annular guiding face  27  of a dish-shaped control element  24  which comprises a ball cup portion  25  and a cylindrical portion  26 . Between the inner part  9  and the control element  24 , a radial adjustment is possible on the faces mutually supporting one another, i.e. on the supporting face  13  and the guiding face  27 . The spherical control face  28  of the control element  24  is provided with annular lubricating grooves  32 ,  33  which, by means of circumferentially distributed lubricating bores  30 ,  31 , are connected to a lubricant reservoir  29  formed by the cup shape inside the control element  24  and filled with lubricant. In the case of the illustrated embodiment, two annular lubricating grooves  32 ,  33  are pressed into the control face  28 . The control element  24  is provided with a central aperture  34  opposite which, in the aligned condition of the joint, there is arranged a corresponding recess  37  of a ball-cup-shaped contact face  36  of a supporting element  35 . Contact face  36 , otherwise, is contacted by the control element  24  by means of its spherical control face  28 . The supporting element  35  is secured to the flange  6  of the outer part  1  by means of a flange  38 . The centers of the spherical control face  28  and of the hollow spherical contact face  36  of the supporting element  35  are also centered on the theoretical articulation center O of the constant velocity fixed joint. By selecting a suitable ratio of area surface of the annular lubricant grooves  32 ,  33  and of the radii of the control face  28  and the contact face  36  relative to one another and taking into account the fact that, when the joint is articulated and rotates, it is possible to achieve high sliding speeds, because the control element  24  passes through the entire articulation range relative to the supporting element  35 , the condition of hydro-dynamic lubrication can be achieved. Furthermore, by providing the recess  37  and the aperture  34  it is ensured that self-inhibition in the region of contact between the control face  28  and the contact face  36  cannot occur. 
     FIG. 2 shows the longitudinal section through a further embodiment of an inventive constant velocity universal joint having the outer part  1 ′ in which a cavity  2 ′ with the inner face  3 ′ is formed. The outer part  1 ′ comprises the first longitudinal axis  4 ′ around which the outer running grooves  5 ′ are distributed in the inner face  3 ′ of the cavity  2 ′. The outer running grooves  5 ′ extend in an undercut-free way from the first joint end  7 ′. Furthermore, at the first joint end  7 ′, the outer part  1 ′ is provided with a flange  6 ′ which serves to connect the outer part  1 ′ to a driving or driven component. As in the case of the embodiment according to FIG. 1, the outer part  1 ′ is provided as a formed sheet metal part. It also comprises a seat face  11  for securing a convoluted boot. The second joint end  8 ′ serves to introduce the shaft  12 ′ which is indicated by dashed lines. The inner part  9 ′ is received in the cavity  2 ′ and comprises the second longitudinal axis  10 ′, with the outer part  1 ′ and the inner part  9 ′ being illustrated in such a way that their longitudinal axes  4 ′ and  10 ′ coincide with one another. Towards the first joint end  7 ′, the inner part  9 ′ comprises a supporting face  13 ′ which is arranged in such a way that the second longitudinal axis  10 ′ is arranged perpendicularly on a plane formed by said supporting face  13 ′. From the supporting face  13 ′, i.e. also from the first joint end  7 ′, there extend the inner running grooves  14 ′ worked into the outer face of the inner part  9 ′. The inner running grooves  14 ′, like the outer running grooves  5 ′, extend in meridian planes relative to the associated longitudinal axes  4 ′ and  10 ′. Being undercut-free means that, starting from the supporting face  13 ′, the track base of the inner running grooves  14 ′ extends towards the second joint end  8 ′ away from the associated longitudinal axis  10 ′. As compared thereto, the track base of the outer running grooves  5 ′, starting from the first joint end  7 ′, extends towards the second joint end  8 ′ progressively approaching the associated first longitudinal axis  4 ′. Whereas the outer part  1 ′ is provided as a formed sheet metal part, the inner part  9 ′ is a solid part which can also be produced by a non-chip-forming method. On its outer face, the inner part  9 ′ comprises an outer spherical face  15 ′ which is arranged towards the second joint end  8 ′. Furthermore, the inner part  9 ′ comprises a toothed bore  16 ′ which is centered on its second longitudinal axis  10 ′ and which serves to connect the shaft  12 ′ in a rotationally fast way. Furthermore, there is provided a retaining element  17 ′ for concentrating a lubricant reservoir in the vicinity of the outer spherical face  15 ′ to ensure adequate lubrication of same. The divided retaining element  17 ′ is secured to the shaft  12 ′. It extends over the outer face  22 ′ of the cage  18 ′ which, by means of a hollow spherical partial face  21 ′, is slidingly guided on the outer spherical face  15 ′. The cage  18 ′ is provided with windows  19 ′ which are circumferentially distributed in accordance with the pairs of outer running grooves  5 ′ and inner running grooves  14 ′ which serve to receive the torque transmitting balls  23 ′ which engage an outer running groove  5 ′ and inner running groove  14 ′ each and which, in all positions of articulation, are supported against window faces  20 ′ arranged towards the first joint end  7 ′ in order to hold the cage  18 ′ by means of its hollow spherical partial face  21 ′ in contact with the outer spherical face  15 ′ of the inner part  9 ′. Between the outer face  22 ′ of the cage  18 ′ and the inner face  3 ′ of the outer part  1 ′, there is provided a space, so that, independently of the joint articulation, no contact can occur between the outer part  1 ′ and the cage  18 ′. The inner part  9 ′, by means of its supporting face  13 ′, is supported against a guiding face  27 ′ of a cylindrical portion  26 ′ of a control element  24 ′, which guiding face  27 ′ is designed as an annular face. The dish-shaped control element  24 ′ produced from sheet metal otherwise comprises a ball-cup-shaped spherical dish portion  25 ′ whose control face  28 ′ constitutes a spherical face whose center is centered on the theoretical joint articulation center O′. The windows  19 ′ of the cage  18 ′ and the window faces  20 ′ are arranged in such a way that the centers of the balls  23 ′ are also located in a plane containing the theoretical articulation center O′. The control face  28 ′ serves as a running face for bearing balls  40  which are held in a bearing cage  39 . The bearing cage  39  comprises a centering projection  41  by means of which it is held on a centering face  42  of the cage  18 ′ in the region extending towards the first joint end  7 ′, so that the bearing cage  39  carries out half the articulation angle carried out by the cage  18 ′, when the outer part  1 ′ and the inner part  9 ′ are articulated relative to one another. The bearing balls  40  are supported against a ball-cup-shaped contact face  36 ′ of a supporting element  35 ′ which, by means of a flange  38 ′, is connected to the flange  6 ′ of the outer part  1 ′. The center of the contact face  36 ′ in the shape of a hollow sphere is also centered on the theoretical articulation center O′. During assembly, the parts to be assembled and their respective functional faces can be selected in such a way that they ensure a combination wherein the balls  23 ′ permit articulation of the constant velocity fixed joint around a center which is as close as possible to the theoretical articulation center O′. By selecting rolling contact bearing means it is also possible to achieve a considerable reduction in friction because the forces resulting from the transmission of torque and to be introduced by the control element  24 ′ into the supporting element  35 ′ can also be transmitted while being supported by a rolling contact bearing. 
     The above-described joints are preferably used in a drive line of a motor vehicle, i.e. they can be used both in the propeller shaft between the front drive unit and the rear axle and in the sideshafts which lead from the differential to the driven wheels. The joints are characterized by a long service life and low friction losses.