Abstract:
Tripod joints have a joint outer part and a joint inner part which are in driving connection to each other with cylindrical rolling bodies being connected in between and axial displacement and pivotability being ensured. The longitudinal axes of adjacent rolling bodies are arranged at an acute angle to one another. This may result in an improved mechanical behavior of the tripod joint particularly during pivoting. The tripod joints may be suitable for the displaceable and pivotable driving connection of two shaft ends, in particular in conjunction with drive trains or side shafts of motor vehicles.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims priority to Application No. 101 41 440.4, filed in the Federal Republic of Germany on Aug. 23, 2001, which is expressly incorporated herein in its entirety by reference thereto. 
   FIELD OF THE INVENTION 
   The present invention relates to a tripod joint. 
   BACKGROUND INFORMATION 
   Tripod joints are used, for example, as side shafts of motor vehicles. In this case, the tripod joints are used for transmitting driving torques between two driving elements of a drive train. The tripod joints permit a relative displacement and a relative pivoting of the driving elements to be compensated for. For the use in the case of side shafts of a motor vehicle, relative movements of this type are caused by spring deflections of the vehicle wheels. 
   Conventional tripod joints have a joint outer part and a joint inner part held therein. Rolling bodies are inserted in the force flux between the joint outer part and joint inner part. With a rolling movement of the rolling bodies, the joint outer part is axially displaceable and/or pivotable with respect to the joint inner part about an axis transverse to the plane defined by the longitudinal axes of the joint outer part and of the joint inner part with the transmission of a driving torque being ensured. Use is made of cylindrical rolling bodies which, for the purpose of transmitting large driving torques, may be advantageous in comparison with spherical rolling bodies due to the linear contact formed by the adjacent components. 
   In the case of components configured in such a manner, it may be disadvantageous that mechanical impairments of the transmission function may occur in the case of three-dimensional movements of a tripod joint, which, in the worst case, may result in the drive train vibrating and/or producing noise and in resultant impairments of comfort. 
   It is an object of the present invention to provide a tripod joint which is improved with regard to the mechanical transmission properties. 
   SUMMARY 
   The above and other beneficial objects of the present invention are achieved by providing a tripod joint as described herein. 
   In accordance with one example embodiment of the present invention, longitudinal axes of adjacent rolling bodies are orientated at an acute angle with respect to one another. 
   The investigations on which the present invention is based have shown that in the case of an axial, translatory displacement of the joint inner part with respect to the joint outer part, a pure rolling movement of the rolling bodies with optimized frictional conditions arises for cylindrical rolling bodies. When the joint parts pivot, which is unavoidable (additional) in practice with rotating driving elements, a kinematically necessary, two-dimensional movement of the pin with respect to the joint outer part is produced. This gives rise to a movement component in the longitudinal direction of the rolling bodies, which component may be compensated only by a sliding movement of the rolling bodies with respect to the adjacent components. These sliding movements cause (sliding) frictional forces which constitute the cause of the undesirable mechanical impairments. The frictional forces form non-linear forces and result, in particular, in a third-order excitation of vibration. The orientation according to the present invention of the longitudinal axes of adjacent rolling bodies with respect to one another enables the rolling bodies to have different, preferred rolling directions, as a result of which the sliding fractions do not compulsorily occur at all rolling bodies, but rather occur in a minimized manner only for individual rolling bodies or do not occur at all for particular, three-dimensional forms of movement. In addition to avoiding the abovementioned disadvantages, the reduced sliding fraction may have a positive effect on the wear or the service life of the joint, the rolling bodies or the running paths of the rolling bodies. In the case of a skillful, kinematic configuration of the transmission elements, self-centering of cages, which hold the rolling bodies, with respect to the pins of the tripod joint may be obtained, and so centering devices, such as springs, etc. may be omitted or may be constructed more simply or cost-effectively. The components are not required to have any play in the circumferential direction. The components may even be built over with a lightweight covering. The freedom from play may result in improved comfort in the vehicle, e.g., in the case of load-change processes. 
   According to an example embodiment of the present invention, the longitudinal axes of a plurality of rolling bodies assigned to a running path have a common intersecting point. For pivoting the joint inner part about the common intersecting point, an optimized rolling and sliding behavior of the tripod joint arises, since all of the rolling bodies move on a circular path for which the pure rolling movement of the rolling bodies is orientated tangentially to the circular path, with the result that no sliding movement occurs. For a pure translatory movement, i.e., a pure axial displacement of the joint inner part with respect to the joint outer part, the intersecting point ideally lies in infinity®=∞), while for a pure pivoting movement the intersecting point may be in the region of the central point of the tripod star at the distance R=R G . For complex three-dimensional forms of movement, an ideal distance 0&lt;R&lt;∞ is to be defined. The ideal distance, from which the acute angle, which is to be selected, between adjacent longitudinal axes results, may be determined according to the rolling bodies selected, the component dimensions, the forces to be transmitted and the relative displacements and pivotings occurring during operation. For example, a typical movement profile may be taken as a basis here, based on which the sliding movements occurring during operation are determined and, by varying the acute angle, are minimized. In this manner, relatively large sliding frictional forces may be displaced into operating ranges which rarely occur while relatively low sliding frictional forces are to be accumulated in operating ranges which occur frequently. 
   According to an example embodiment of the present invention, a tripod joint for transmitting a driving torque between two driving elements of a drive train includes: a joint inner part having a tripod star with a pin; a joint outer part holding the joint inner part; and rolling bodies inserted in a force flux between the joint outer part and the joint inner part, the rolling bodies having a cylindrical lateral surface. The joint outer part and the joint inner part may be at least one of axially displaceable and pivotable with respect to each other in accordance with rolling movement of the rolling bodies. The longitudinal axes of adjacent rolling bodies may be orientated at an acute angle with respect to one other. 
   According to an example embodiment of the present invention, the longitudinal axes of a plurality of rolling bodies may have a common intersecting point. The intersecting point may be located in a region of a central point of the tripod star. 
   According to an example embodiment of the present invention, the tripod joint may include a cage and a plurality of rolling bodies accommodated in the cage. The longitudinal centers of the rolling bodies of the cage may be located on a straight line or arranged on a curved, planar curve. Further, the longitudinal center of the rolling bodies of the cage may be located on one of a circular arc and a cutout of an ellipse. 
   Exemplary embodiments of the tripod joint according to the present invention are explained in greater detail below with reference to the Figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is longitudinal cross-sectional view of a tripod joint according to the present invention. 
       FIG. 2  is a cross-sectional view of a tripod joint according to the present invention. 
       FIG. 3  is a cross-sectional view of a joint pin according to the present invention with pressure element, moving cage, rolling bodies and centering elements taken along the line A—A illustrated in  FIG. 2 . 
       FIG. 4  illustrates a moving cage according to the present invention with rolling bodies. 
       FIG. 5  illustrates a moving cage according to the present invention with rolling bodies and a pressure element illustrated by dashed lines. 
       FIG. 6  illustrates a moving cage according to the present invention with rolling bodies and a pressure element illustrated by dashed lines. 
       FIG. 7  is a cross-sectional view of a joint pin according to the present invention with pressure element, moving cage, rolling bodies and centering elements, taken along the line A—A illustrated in  FIG. 2 . 
       FIG. 8  is a cross-sectional view of a tripod joint according to the present invention. 
   

   DETAILED DESCRIPTION 
   A tripod joint  10  has a joint inner part  11  and a joint outer part  12  holding the latter. The joint inner part  11  and the joint outer part  12  are in each case connected, at least in a rotationally fixed manner, to a driving element of a drive train of a motor vehicle, for example, to a drive shaft and a vehicle wheel. The tripod joint  10  is used for transmitting a driving torque between the joint inner part  11  and the joint outer part  12  while ensuring a relative displacement along the longitudinal axis  13 — 13  of the joint inner part  11  and along the longitudinal axis  14 — 14  of the joint outer part  12 , a relative pivoting of the joint inner part  11  with respect to the joint outer part  12 , which pivoting is associated with a change in the angle  15  between the longitudinal axes  13 — 13  and  14 — 14 , and a three-dimensional movement which arises from a combination of the above-mentioned forms of movement. 
   The joint inner part  11  has, at the end arranged on the inside, three pins  16  which are formed as a single piece of a number of pieces together with the latter, are orientated radially and are distributed in each case at 120° in the circumferential direction and form a tripod star. The pins  16  have in each case a partially spherical ball body  17 . In order to transmit forces in both circumferential directions, the ball body  17  bears, in each case in the region of the spherical lateral surface, against a correspondingly configured recess  18  of a pressure element  19 . On the opposite side of the pressure element  19 , which side faces a flat mating surface  20  of the joint outer part  12 , the pressure element is of flat configuration with a running surface  21 . The mating surface  20  may be formed by a relatively large, flat surface or else may be provided in a path or groove  22  of the joint outer part  12 . The running surface  21  and the mating surface  20  are orientated parallel to each other. Cylindrical rolling bodies  23 , e.g., rollers or needles, are held between the latter forming a linear contact. That is, cylindrical rolling bodies  23  are inserted in a force flux between the joint outer part  12  and the joint inner part  11 . A plurality of rolling bodies are guided in a cage  24 . In order to transmit circumferential forces in the opposite direction, each pin  16  is configured with the associated pressure elements  19 , the rolling bodies  23  and the surfaces  20 ,  21  symmetrically to a pin central plane accommodating the longitudinal axis  13 — 13 . 
   The running surface  21  of a pressure element  19  may have a rectangular form, with the result that as many rolling bodies  23  as possible form a load-bearing contact with the surface pressure being reduced. However, circular or oval pressure elements  19  are also possible. 
   The joint outer part  12  has a recess  25  orientated in the direction of the longitudinal axis  14 — 14  with an essentially circular, central hole  26  and three receiving spaces  27  which are orientated radially and are distributed in each case at 120° in the circumferential direction and are used in each case for receiving and supporting a pin  16 , two pressure elements  19  and rolling bodies  23 . In the section illustrated in  FIG. 2 , the receiving spaces  27  have an essentially U-shaped contour open in the direction of the hole  26 , the side limbs of the U-shaped contour being formed by the mating surfaces  20 . In the exemplary embodiment illustrated in  FIG. 1 , the side limbs are of rectilinear configuration without a transitional region to the mating surfaces  20 . An additional or sole guidance of the rolling bodies  23  and cages  24  by the joint outer part may be achieved if grooves  28 , as shown in  FIG. 8 , are introduced into the side limbs, the mating surfaces  20  forming the base of the groove and the cages  24  being guided in the radial direction by the side surfaces of the grooves  28 . 
   Two pressure elements  19 , as shown in  FIG. 2 , and two cages  24 , as shown in  FIG. 2 , may be used per pin  16 . As an alternative, the two pressure elements  19  may be connected to each other via connecting regions or webs  34  to form a pressure body  35 , as shown in  FIG. 3 , and/or the two cages  24  may be configured as a single-piece cage  30 , as shown in  FIG. 7 . 
   As illustrated in  FIG. 2 , the rolling bodies  23  are guided in a cage  24 . The rolling bodies  23  are guided in the cages  24  with the relative position of the longitudinal axes  31  of the rolling bodies  23  with respect to each other being ensured. The cages  24  are guided in the radial direction with respect to the pressure element  19  via shoulders  32  engaging around and enclosing the pressure element  19 . The cages  24  may be “clipped” via the shoulders  32  onto the pressure element  19 , as illustrated. The cages  24  may furthermore be centered in the running direction of the rolling bodies  23  via spring elements  33 . Two cages  24  of a pin  16  may be guided and centered via a common spring element  33 . 
   According to an example embodiment of the present invention, the longitudinal axes  31  of a plurality of rolling bodies  23  assigned to a running path have a common intersecting point  39 . For pivoting the joint inner part  11  about the common intersecting point  39 , an optimized rolling and sliding behavior of the tripod joint arises, since all of the rolling bodies  23  move on a circular path for which the pure rolling movement of the rolling bodies  23  is orientated tangentially to the circular path, with the result that no sliding movement occurs. For a pure translatory movement, i.e., a pure axial displacement of the joint inner part  11  with respect to the joint outer part  12 , the intersecting point  39  ideally lies in infinity (R=∞), while for a pure pivoting movement the intersecting point  39  may be in the region of the central point of the tripod star at the distance R=RG. For complex three-dimensional forms of movement, an ideal distance 0&lt;R&lt;∞ is to be defined. The ideal distance, from which the acute angle, which is to be selected, between adjacent longitudinal axes  31  results, may be determined according to the rolling bodies  23  selected, the component dimensions, the forces to be transmitted and the relative displacements and pivotings occurring during operation. For example, a typical movement profile may be taken as a basis here, based on which the sliding movements occurring during operation are determined and, by varying the acute angle, are minimized. In this manner, relatively large sliding frictional forces may be displaced into operating ranges which rarely occur while relatively low sliding frictional forces are to be accumulated in operating ranges which occur frequently. 
   According to the exemplary embodiment illustrated in  FIG. 2  and  FIG. 3 , two spring elements  33  are connected to the pressure element  19 , the pressure body  35  or the ball body  17  via a respective fastening arrangement  36 . The spring elements  33  in each case have two elastic fingers  37  which bear against the opposite cages  24  or are connected thereto, for the purpose of supporting them. 
   As illustrated in  FIG. 4 , the longitudinal axes  31  of the cylindrical rolling bodies  23  are inclined with respect to each other at an acute angle  38  in an essentially rectangular cage  24 ,  30  and intersect at a common intersecting point  39 . The longitudinal centers  40  of the rolling bodies  23  are on a straight line  41  which is spaced apart from the central point  42  of the tripod star at a distance R. The intersecting point  39  may be located in a region of the central point  42  of the tripod star. 
   As illustrated in  FIG. 5 , the longitudinal centers  40 ′ may be on a circular path having the radius R, the cage  24 ′,  30 ′ in this case being configured in the form of a segment of a circle and, e.g., the central point of the segments of a circle bounding the cage  24 ′,  30 ′ corresponds to the intersecting point  39 . The contour  43  of the pressure element  19 ′, which has an outer contour in the form of a segment of a circle and, on the side arranged opposite the rolling bodies, has the partially spherical recess  18  for receiving the ball body  17 ,is illustrated by dashed lines in  FIG. 5 . 
   As a departure from this, as illustrated in FIG.  6 —with the cage  24 ″,  30 ″ and the rolling bodies  23  configured according to FIG.  5 —the pressure element  19 ″,  20  may have a circular outer contour  44  arranged concentrically to the outer contour of the recess  18 . 
   According to the exemplary embodiment illustrated in  FIG. 7 , the cages  24 ′″, which are arranged on the opposite sides of the ball body  17 , are connected to each other via connecting regions  45  to form a single-piece cage  30 ′″. In this case, it may be ensured that the position of the cages  24 ′″ in the running direction coincides. The cage  30 ′″ may be centered with respect to pressure elements  19 ′″, pressure body  29  or the ball body  17  via one or two spring elements  33  of simplified configuration. In the exemplary embodiment illustrated in  FIG. 7 , two compression springs  46  are arranged in the running direction on both sides of the pressure elements  19 ′″. The compression springs  46  are configured as leaf springs having a central bulge  47 , the end regions of which are supported on the pressure elements  19 ′″ and which bear in the region of the bulge  47  against a connecting region  45 . 
   In the exemplary embodiment illustrated in  FIG. 8 , the mating surfaces are formed in grooves  28  in receiving space  27 ′ of a joint outer part  12 ′. In these grooves  28 , the rolling bodies  23  are guided together with the cages  24  in the radial direction. In this case, the radial guidance of the cages  24  with respect to the pressure elements  19  via the shoulders  32  as illustrated in  FIG. 2  may be omitted. 
   The longitudinal centers  40 ,  40 ′ of adjacent rolling bodies  23  may be on a curve, a straight line or a circular arc. 
   The cages  24 ,  30  may execute purely translatory movements with respect to the mating surfaces  20 . According to the exemplary embodiment illustrated in  FIG. 8 , the cages  24  are guided in rectilinear grooves  28  of the joint outer part  12 ′. In this case, the shoulders  32  of the cages  24  are omitted, with the result that there is no radial guidance of the cages  24  with respect to the pressure elements  19 ,  19 ′ and the pressure elements  19 ,  19 ′ may execute relative movements and pivotings in the radial direction with respect to the cages  24 . 
   In the exemplary embodiment illustrated in  FIG. 2 , the cages  24  are pivoted with the radial distance from the pin  16  remaining the same. In this case, the cage  24  does not execute a rectilinear movement with respect to the joint outer part  12 , but rather a curved pivoting movement. For this purpose, coordinated, curved grooves  28  or else—as illustrated in FIG.  1 —mating surfaces  20  which are not arranged in grooves are to be provided in the joint outer part  12 . 
   The kinematic limits of the pivoting movement are formed by the geometry of the cage  24  and of the joint outer part  12 . During operation of the tripod joint  10 , in borderline situations controlling contact of the pressure elements  19 ,  19 ′ by the end stops of the cage  24  or else radial contact of cage  24  and joint outer part  12  may occur. These contacts do not have a negative effect on the operating comfort because the forces occur stochastically only in borderline situations and therefore do not lead to periodic excitation. 
   The abovementioned arrangements of guiding the cages  24  with respect to the joint outer part  12  and the pressure elements  19  or  19 ′ may also be entirely omitted or may be of elastic configuration. In this case, an undefined form of movement of the cage  24  with respect to the adjacent components arises, which may result in a minimization of wear. As an alternative, the movement may occur in a self-centering manner, in particular by the arrangement according to the present invention of the longitudinal axes  31  of the rolling bodies  23  at an acute angle  38 , the rolling path of the cage  24  being automatically established on the mating surface  20  on account of the effective outer and inner rolling-body guiding forces. 
   Without departing from the principle on which the present invention is based, it is possible to form groups of adjacent or non-adjacent rolling bodies  23 , rolling bodies  23  of one group having longitudinal axes  31  orientated parallel to one another, and these longitudinal axes  31  forming a second, acute angle  38  with respect to the longitudinal axes  31  of the rolling bodies  23  of other groups. As an alternative or in addition, the longitudinal axes  31  of adjacent rolling bodies  23  of one group may be inclined with respect to one another at a first angle  38  while the rolling bodies  23  of a second group are inclined with respect to one another at a second angle  38 . Different angles  38  for adjacent longitudinal axes  31 , for example angles  38  which rise or fall in the running direction from the center of the cage  24 , are possible. 
   The arrangements according to the present invention may be used in conjunction with any desired tripod-joint configurations, for example tripod joints corresponding to those described in U.S. Pat. Nos. 4,619,828 or 4,708,693. 
   The essentially cylindrical rolling bodies  23  may have a contour which is slightly curved in the longitudinal direction of the lateral surface, as a result of which the sliding fraction in the case of a movement component in the direction of the longitudinal axis  31  of the rolling bodies  23  or in the case of rotational movements of the rolling bodies transversely with respect to the longitudinal axis  31  may be further reduced. 
   Furthermore, the use of tapered rollers (with a small tapered opening angle) is possible as rolling bodies  23 , for which the pivoting may be further simplified. In this case, in order to ensure a translatory displacement, a further degree of freedom of the joint may be provided. 
   The example embodiments described involve configurations only given by way of example. A combination of the described features for different embodiments is possible. Further features, in particular features which have not been described, of the device parts belonging to the invention are to be taken from the device-part geometries illustrated in the drawings.