Abstract:
An inner joint part of a tripod constant velocity joint comprises a hub having an axis of rotation. Three projections extend radially outwardly. There is an adjoining transition region and a bearing region. A spherical circumferential surface of each projection forms a first surface line extending in a first plane. A resulting inner sphere contacts opposite points of the first surface line extending at least in first angle ranges adjacent to a respective point outside the inner sphere. A second surface line in a second plane touches the inner sphere at touch points only at the height of the largest diameter of the projection and extends at least in second angle ranges adjacent to the respective touch point within the inner sphere. A roller element has a convex inner circumferential surface, an extension line forming a radius having a maximum magnitude in a central region, less in an adjacent region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage of, and claims priority to, Patent Cooperation Treaty Patent Application No. PCT/EP2014/062897, filed on Jun. 18, 2014, which claims priority to German Application No. DE 10 2013 106 86835 filed on Jul. 1, 2013, each of which applications are hereby incorporated herein by reference in their entireties. 
     
    
     BACKGROUND 
       [0002]    Tripod constant velocity joints are employed in particular for transmitting torques by shafts when axial displacement and deflection of the shafts in relation to one another is to be (simultaneously) enabled. 
         [0003]    A tripod joint is disclosed in EP 1 008 777 A2, for example. There, inter alia, a projection which has a crowned circumferential face having a surface line which is assembled from a plurality of part-portions is disclosed, wherein the surface line in the region of the maximum diameter of the projection has a larger radius than in the adjacent portions of the surface line. The surface line here is embodied so as to be constant across the circumference of the crowned circumferential face, that is to say that the crowned circumferential face is embodied so as to be rotationally symmetrical in relation to the longitudinal axis of the respective projection. The projection of this tripod constant velocity joint thus deviates from the otherwise known spherical shape. 
         [0004]    Proceeding therefrom, there is a need for a lightweight and cost-effective tripod constant velocity joint which moreover has a very good load capacity. Furthermore, said tripod constant velocity joint is to be employable also with comparatively large angles of deflection. For a tripod constant velocity joint of this type an inner joint part and a roller element are proposed. 
       SUMMARY 
       [0005]    Disclosed herein is an inner joint part of a tripod constant velocity joint and an (adapted) roller element for disposal on a projection of an inner joint part of a tripod constant velocity joint. The tripod constant velocity joint is lightweight, cost-effective, has a very good load capacity, and is employable with comparatively large angles of deflection. For a tripod constant velocity joint of this type an inner joint part and a roller element are proposed. 
         [0006]    This is achieved by an inner joint part of a tripod constant velocity joint according to the features of claim  1 . This is furthermore achieved by a roller element for an inner joint part (according to the invention) according to claim  9 . Further advantageous design embodiments are stated in the dependent claims and this disclosure. The features which are individually listed in the claims may be intercombined in any technologically meaningful manner and may be complemented by explanatory facts of cases from the description, wherein further variants of embodiments of the invention will be demonstrated. 
         [0007]    To this end an inner joint part of a tripod constant velocity joint, comprising a hub having a rotation axis and three projections, which outwardly extend from the hub in a radial direction, and have a transition region, which adjoins the hub, and a bearing region, is proposed. Each projection has a longitudinal axis and in the bearing region a crowned circumferential face. The inner joint part has a first plane which comprises all longitudinal axes of the projections and is defined so as to be perpendicular to the rotation axis. The crowned circumferential face of each projection forms a first surface line which runs in the first plane, wherein at a height along the longitudinal axis, at which a maximum diameter of the projection is present, an inner sphere having an inner sphere radius is predefined, the midpoint of said inner sphere lying on the longitudinal axis at the point of the height, and said inner sphere contacting the opposite contact points of the first surface line. The first surface line of each projection runs at least in first angular ranges which in each case are adjacent to the respective contact point and which are outside the inner sphere, wherein the first angular range emanates from the midpoint of the inner sphere and in each case extends to at maximum 20 angular degrees, in particular in each case to at maximum 10 angular degrees, to both sides of the respective contact point. A second surface line of the crowned circumferential face of each projection is present in a second plane, wherein the second plane is disposed so as to be perpendicular to the first plane and contains the longitudinal axis of the respective projection. Furthermore, the second surface line touches the inner sphere only at the height of the maximum diameter of the projection in the touch points, and runs at least in second angular ranges which in each case are adjacent to the respective touch point and which are within the inner sphere, wherein the second angular range emanates from the midpoint of the inner sphere and in each case extends to at maximum 30 angular degrees, in particular in each case to at maximum 20 angular degrees, to both sides of the respective touch point. 
         [0008]    It may be assumed that the in-principle construction of an inner joint part of a tripod constant velocity joint is known, wherein the hub may in particular receive a shaft (rotating about the rotation axis) and thus may transmit an input torque via the projections to an outer joint part, or vice versa, respectively. The projections have functional regions which are readily apparent to a person skilled in the art, wherein typically a transition region which extends from the hub in a radial direction is provided, prior to being adjoined farther out by a bearing region of which the crowned circumferential face represents the sliding contact face for the roller element which is to be fitted thereonto. The circumferential face is embodied so as to be crowned, wherein the circumferential face is most often not spherically shaped. An end face, which is in particular characterized in that it is shaped so as to be perpendicular to the longitudinal axis or that the vectoral curvature radius of the end face is disposed in a cone which is disposed about the longitudinal axis and has an opening angle of 30 to 60 angular degrees, may form a radial terminal of the projection. 
         [0009]    The longitudinal axes of the projections lie in a common plane which is positioned so as to be perpendicular to the rotation axis of the inner joint part and here is referred to as the “first plane”. When a section through the projection in the first plane is now viewed, the contour of the circumferential face configures a “first surface line” (surface line of the projection in the first plane). This first surface line in the bearing region is functionally important, since a transmission of force in the circumferential direction of the inner joint part is performed by way of the former. Therefore, this surface line is also referred to for defining an inner sphere having an unequivocally determined inner sphere radius. To this end, the height of the projection having the maximum diameter (in terms of value) which is perpendicular to the longitudinal axis has to be identified first in the bearing region. Here, the maximum height is to be assumed, that is to say for the maximum diameter of the projection which lies farthest to the outside in the radial direction. The points of the opposite portions of the first surface line, which define the maximum diameter at this height, therefore are contact points of the imaginary, i.e., mathematically defined, inner sphere, wherein the midpoint of the inner sphere is positioned on the longitudinal axis, and the inner sphere radius corresponds to half the maximum diameter of the projection at the height of the longitudinal axis. The inner sphere which is referred to here for describing the contour of the projection serves in the comparison with a spherical shape of the projection from which the presently proposed embodiment correspondingly deviates. 
         [0010]    In particular, the maximum diameter in the first plane may deviate from the maximum diameter of the projection in the second plane by a minor dimension (in the range from 0.01 to 0.1 millimeters), such that a cross section through the projection in a third plane is shaped in a slightly elliptical manner, wherein the third plane is oriented so as to be perpendicular to both the longitudinal axis of the respective projection as well as to the first plane. 
         [0011]    Comparing the profile of the contour of the inner sphere in the first plane and of the first surface line adjacent to these contact points here results in that the first surface line is curved to a lesser extent, or runs outside the inner sphere (having a larger distance from the longitudinal axis), respectively. This determination should be present for corresponding first angular ranges (angular ranges referring to the first surface line), wherein the values of the first angular ranges may also be dissimilar, in particular with a view to the design embodiment below and above the height having the maximum diameter in the direction of the longitudinal axis (in the radial direction). In this way, the first angular range below the height may be embodied so as to be larger than, equal to, or smaller than the first angular range above the height. In the case of both first angular ranges being at maximum, both in each case encompass 20 angular degrees, such that in total 40 angular degrees are comprised. In the case of a first angular range being at minimum and another being at maximum, a first angular range (above or below the one contact point) then extends only across 20 angular degrees, while toward the other side (accordingly below or above the same contact point) the above condition does not have to be met. However, it is clear that the first surface line is to lie farther outside at least on one side, in particular across a (minimum) first angular range of 2 angular degrees on both sides of the contact point, in particular of at least 5 angular degrees. 
         [0012]    The profile of the first surface line thus deviates from a spherical shape and in particular in the first plane extends in a flatter manner than the profile of the sectional circle of the inner sphere in the first plane. The circumferential forces between the inner joint part and the outer joint part of a tripod constant velocity joint are transmitted primarily in this first plane. As a result of the first surface line running in a flatter manner, the osculation between the projection surface in the bearing region and the inner circumferential face of a roller element becomes tighter. As a result of the first surface line running in a flatter manner, the Hertzian contact stress in the primary direction of force of the tripod constant velocity joint (in the first plane) may thus be considerably reduced. In this way, comparatively high forces may be transmitted by this tripod constant velocity joint, so that the projections may also be embodied having a maximum diameter which in terms of value is significantly smaller than is the case in known tripod constant velocity joints. On account thereof, comparatively small roller elements may be used, so that in consequence a reduction of the external dimensions of an outer joint part may be achieved. As a result of the tighter osculation between the roller element and the projection the NVH (noise, vibration, harshness) properties of the constant velocity joint are also improved, in particular in the case of angles of deflection of the inner joint part in relation to the outer joint part of in excess of 16 angular degrees. It is precisely in the case of such large angles of deflection that so-called “shuddering” or “start-up wobbling” which is attributable to the cyclical axial force of the 3 rd  order arises in known joints during operation. 
         [0013]    In a section through the longitudinal axis of each individual projection which is offset by 90 angular degrees in relation to the first plane, a corresponding contour of the crowned circumferential face, here is referred to as the “second surface line” (surface line in the second plane), becomes identifiable. Hereby, the profile is now compared again with the same inner sphere, that is to say with the sectional line of the inner sphere in the second plane (in particular at the same height of the longitudinal axis). Here, the inner sphere also touches the second surface line at two points which are opposite one another in relation to the longitudinal axis and which here are referred to as touch points. Thus (only) the touch points of the second surface line and the contact points of the first surface line lie on a common circle of the inner sphere. Comparing the profile of the contour of the inner sphere in the second plane with the second surface line adjacent to these touch points results in that the second surface line is more heavily curved, or runs within the inner sphere (having a smaller distance from the longitudinal axis). This determination should be present for corresponding second angular ranges (angular ranges referring to the second surface line), wherein the values of the second angular ranges may also be dissimilar, in particular with a view to the design embodiment above and below the height with the maximum diameter in the direction of the longitudinal axis. To this extent reference is made to the corresponding narrative relating to the first angular range, which here is to equally apply to the second angular range. 
         [0014]    The profile of the second surface line in the second plane, which therefore now runs within the inner sphere, in particular enables a minor play to be adjusted between the roller element and the projection, so that the center of the roller element in the second plane is displaceable in relation to the projection when the joint is deflected. As a result of this potential displacement it may be avoided that jamming between the projection and the roller element in the region of the first surface line arises when the joint is deflected and a tilt movement of the roller element in relation to the projection is performed. This potential jamming is a result of the profile of the first surface line which here is formed by the large first curvature radius (or by a straight line, respectively). Accordingly, a plurality of contact points with the inner circumferential face of the roller element may be configured on one side of the projection in the region of the first surface line, so that jamming would be possible. The profile of the second surface line now ensures that displacement between the projection and the roller element is possible, so that jamming is positively prevented. 
         [0015]    In particular, it is now enabled by the profile of the second surface line that contact between the second surface line of the projection and the roller element arises only on one side of the projection when the joint is deflected. This may be traced back in particular to the projection radius in this contact region with the roller element being smaller than the inner sphere radius. In this way the center of the roller element (the center point of the roller element) in the case of large angles of deflection may be displaced in relation to the midpoint of the projection and along the second plane. On account thereof, the play between the roller element and the projection (in the region of the first surface line) may be minimized without jamming arising at large angles of deflection. 
         [0016]    In particular, the transition between the second surface line and the first surface line in the circumferential direction about the longitudinal axis of each of the projections runs in a continuous manner. “Continuous” here means that no abrupt changes in the contour of the surface lines or on the circumferential face, respectively, are provided. 
         [0017]    In particular, the projection has no circumferential face which is rotationally symmetrical about the longitudinal axis. The profile of the first surface lines in the first plane (primary direction of force) differs from the profile of the second surface lines in the second plane, in particular adjacent to the contact points or to the touch points with the inner sphere, respectively. The first surface lines and the second surface lines are in each case adapted to the various stresses during operation. During operation circumferential forces are largely transmitted by those regions of the circumferential face of the projection that are disposed in the region of the first plane. The (significantly lower) forces which act in the axial direction of the constant velocity joint are transmitted by way of those regions of the circumferential face of the projection that are disposed in the second plane. On account of these axially acting forces the inner joint part is displaced in relation to the outer joint part in the axial direction. 
         [0018]    In particular, the first surface line in the bearing region has a first curvature radius which is at maximum at least at the contact point. By way of this maximum first curvature radius (in terms of value) the (deviating) profile of the first surface line in relation to the inner sphere will now be defined. The inner sphere has the maximum diameter of the projection or of an inner sphere radius, respectively, which is (considerably) smaller than the first curvature radius of the first surface line. This applies in particular at least to the first angular range adjacent to the contact point and/or to the contact point per se. 
         [0019]    In particular, a ratio (V1) of the value of the first curvature radius (eKRmax) in the contact point to the value of the inner sphere radius (IKR) is at least 50 (V1=eKRmax/IKR≧50). Preferably, the ratio is in a range from 100 to 1000 (100≦V1≦1000). In this case, the osculation which has already been described above is particularly well achieved. 
         [0020]    Enlarging the first curvature radius reduces the contact pressure between the roller element and the projection in a corresponding manner (good osculation). Here, values in a range from 50 to 1000 permit a good compromise between a necessary play without jamming and the resulting lower contact pressure (Hertzian contact stress). 
         [0021]    According to one example the first surface line of each projection at the contact points and in first angular ranges which are in each case adjacent thereto is embodied as a straight line, wherein the first angular range emanates from the midpoint of the inner sphere and at least on one side extends so as to be adjacent to the contact point by 2 to 20 angular degrees. 
         [0022]    In particular, the first surface line thus extends in the manner of a portion of a straight line (i.e., first curvature radius is infinitely large) across a portion which lies within the first angular range, wherein the portion of the straight line does not inevitably have to be configured on both sides of the contact point and/or uniformly on both sides of the contact point. Rather, it is sufficient that a portion of 2 to 20 angular degrees is encompassed, wherein the portion of the straight line very particularly preferably extends across 5 to 20 (very particularly preferably 5 to 10) angular degrees and beyond the contact point. It is furthermore preferable that the portion of the straight line, or the first angular range, respectively, here is configured so as to be (predominantly or indeed only) above the contact point (that is to say toward the end face of the projection). In particular, it is possible for the first surface line to intersect the inner sphere outside the first angular range and to then run within the inner sphere. 
         [0023]    In particular, the circumferential face of each projection in the third plane in the region of the first surface line is formed by the first curvature radius. Furthermore, the circumferential face of each projection in the third plane and in a fourth angular range between the first plane and the respective second plane of the projection is formed by a second curvature radius which is continuously varied. 
         [0024]    According to a further example, each projection in the transition region configures a transition radius the value of which in a circumferential direction about the longitudinal axis of the projection is varied, wherein the values of the transition radius in the first plane are at maximum and in the circumferential direction are at minimum and offset thereto by 90 angular degrees. The transition region in relation to the bearing region is typically configured so as to taper off, wherein it is predefined here in which regions of the transition region more or less material may be removed, respectively, such that a better result in terms of weight savings while at the same time providing high load transmission and durability is enabled. In particular, the transition radius between the maximum value and the minimum value is varied in a continuous manner, that is to say that no abrupt transitions in the circumferential direction are provided. On account of this design embodiment of the transition radius across the circumference of the projection, in particular having the minimum value in the second plane of each projection, a relief groove and/or a cut-out in the projection into which part of the roller element may also plunge in the case of deflection of the tripod constant velocity joint may be provided, so that a collision between the roller element and the inner joint part may be avoided even in the case of large angles of deflection. On account thereof, comparatively large angles of deflection of the inner joint part in relation to the outer joint part may also be enabled without the outer diameter of the tripod joint having to be enlarged (that is to say the outer diameter of the outer joint part). 
         [0025]    In particular, the described cut-outs permit the outer diameter of a tripod joint having a comparable function to be able to be reduced by up to 5%. 
         [0026]    Optionally, the profile of this transition in the second plane of each projection is only approximately defined by the transition radius. The contour of the projection in this transition region may optionally run in a jerky manner and/or have a plurality of dissimilar radii. A person skilled in the art may readily apply this teaching here in a corresponding manner. 
         [0027]    In particular, a ratio (V2) of the maximum value of the transition radius (URmax) to the minimum value of the transition radius (URmin) is in a range from 5 to 10 (V2=URmax/URmin; 5≦V2≦10). In particular, this ratio is in a range from 8 to 10 (8≦V2≦10). 
         [0028]    In particular, the maximum possible transition radius is to be disposed at that point where the highest bending stress arises. A comparatively large transition radius minimizes notch stressing. The upper limit results from optimizing the construction size, the maximum angle of deflection of the joint, and the strength of the roller element. 
         [0029]    In particular, in order for a minimum height of the transition region and thus of a maximum functional region to be implemented on the projection for the roller element to be tilted, the smallest transition radius is disposed so as to be orthogonal to the region of force introduction, this means here in the region of the second plane. 
         [0030]    It is further proposed that the first surface line of each projection in a region between the contact point and the hub has a spacing from the longitudinal axis of the projection which corresponds to at least the inner sphere radius. In other words, this means in particular that the first surface line of the projection in a region between the contact point and the hub (in particular at least partially [only] in the transition region) has a spacing from the longitudinal axis of the projection which substantially corresponds to the inner sphere radius. In particular, the first surface line, emanating from the contact point and toward the hub, thus continues in the form of a straight line which runs parallel with the longitudinal axis of the projection. 
         [0031]    According to one further aspect of the invention, a roller element of a tripod constant velocity joint which is optionally also combinable with the inner joint part which has been discussed here, is proposed. 
         [0032]    The roller element of a tripod constant velocity joint has a center and an outer circumferential face and a convex-shaped inner circumferential face which are configured so as to be rotationally symmetrical about a central axis. Furthermore, a median plane which includes a central axis of the roller element and defines a profile line of the convex inner circumferential face is present. The profile line configures a profile line radius of which the value is at maximum in a central region about a central plane which is disposed so as to go through the center and to be perpendicular to the median plane, wherein the value of the profile line radius is smaller in an adjacent region. 
         [0033]    The in-principle construction of such roller elements is known to a person skilled in the art. Typically, such a roller element comprises an inner bearing ring and an outer bearing ring, wherein needle-shaped rolling elements are interdisposed therebetween. The convex-shaped inner circumferential face here is typically formed by the inner bearing ring, and the outer circumferential face is formed by the outer bearing ring. The inner bearing ring has an opening which is designed such that the roller element may be push-fitted on the projection of the associated tripod constant velocity joint and may interact with the bearing face provided thereon. Typically, the center axis here represents the rotation axis for the roller element, the center thus also lying on said rotation axis. A central plane which intersects the roller element centrically and perpendicularly to a median plane (which encloses the central axis) runs through the center. 
         [0034]    In particular, the inner circumferential face or the profile line, respectively, continues outside this convex portion by way of a concave or straight portion (or a combination thereof). 
         [0035]    During operation of the tripod constant velocity joint in particular both regions of the convex-shaped inner circumferential face (that is to say the central region and the adjacent region having a comparatively small profile line radius) may come into contact with the circumferential face of the projection. The shape of the inner circumferential face of the roller element permits in particular that the high loads which generally arise frequently in the case of small angles of deflection are transmitted via the central region, having a good osculation. The minor loads which usually arise in the case of comparatively large angles of deflection may be transmitted via a somewhat poorer osculation in the adjacent region. On account of this special shape of the convex inner circumferential face, it is now possible in particular for the osculation between the roller element and the projection to be adapted to the respective loading situation and at the same time for a slight play between the roller element and the projection to be implemented, so that the risk of the roller element jamming on the projection does not exist. 
         [0036]    In particular, a ratio (V3) of the maximum value of the profile line radius (VLRmax) to the smaller value of the profile line radius (VLRred) is at least 2 (V3=VLRmax/VLRred; V3≧2). Very particularly preferably, the ratio is in a range from 3 to 6 (3≦V3≦6). 
         [0037]    It has been demonstrated here that a good compromise between contact pressure, play and tilting capability of the roller element on the projection results here within these limits. 
         [0038]    According to one further example, the central region comprises a third angular range which emanating from the center extends beyond the central plane to both sides thereof by at minimum 1 angular degree and at maximum 6 angular degrees. Very particularly preferred limits of the third angular range are: ±1.5 angular degrees to ±2.5 angular degrees (that is to say symmetrical above and below the central plane). Overall, the third angular range should thus preferably comprise 2 to 12 angular degrees, in particular 3 to 5 angular degrees. In particular, the profile line of the inner circumferential face, which is in each case formed by the smaller profile radius, extends in each case across a (wider) angular range, so as to emanate from the center and on both sides (that is to say symmetrical above and below the central plane) so as to in each case adjoin the third angular range, said angular range being from ±1 to ±6 angular degrees, in particular from ±1.5 to ±2.5 angular degrees. 
         [0039]    The mentioned values for the third angular range and the further angular range are in particular advantageous for joint angles of deflection of up to 6 or 10 angular degrees (Hertzian contact stress in the loading range which is relevant to the service life of the tripod constant velocity joint), respectively, at the same time considering the tilting capability of the roller element, that is to say the tilt angle range of up to 10 angular degrees (in relation to the centric plane of the clearance in the outer joint part). 
         [0040]    The roller element in particular has a convex-shaped and crowned outer circumferential face, wherein tilting of the roller element in relation to the outer joint part is enabled therewith within a guide track (clearance) of the outer joint part. 
         [0041]    The invention furthermore relates to a tripod constant velocity joint which comprises at least an inner joint part as described herein, a rotatably mounted roller element according to the invention on each projection, and an outer joint part having axially running clearances for guiding in each case one roller element along an axial direction. It is provided here that opposite regions of the second surface lines of each projection, which during operation are in contact with the convex inner circumferential faces of the roller elements, in each case form one segment of a contour circle, the circle centers of said segments in each case being disposed at a distance from the longitudinal axis of the projection, wherein a ratio of the distance to the inner sphere radius having a value of 0.02 to 0.38 applies. 
         [0042]    In other words, this means that the opposite portions of the second surface lines (in particular going beyond the contact points) are shaped in the manner of an arc segment, wherein the arc segments here are configured so as to be mirror symmetrical in particular in relation to the longitudinal axis of the projection. Superimposed thereon, so-called contour circles may be formed in the second plane, the circle center of said contour circles not being positioned on the longitudinal axis but distanced therefrom somewhat so as to be perpendicular to the longitudinal axis, such that a type of “offset” is formed. Here, the ratio (V4) of the distance (D) from the inner sphere radius (IKR) having a value of 0.02 to 0.38 (V4=D/IKR; 0.02≦V4≦0.38) applies. This is to say that it applies in particular for the second surface line that the two contour circles in each case have a smaller contour circle radius than the inner sphere has an inner sphere radius. 
         [0043]    Establishing a lower limit (here V4=0.02) serves to ensure that no jamming arises when the tripod constant velocity joint is deflected and there is minor play between the roller element and the projection (in the region of the first surface line). Establishing the upper limit limits the play between the roller element and the projection (in the region of the second surface line) to a low value, said play arising in a cyclical manner when the tripod constant velocity joint is deflected. On account thereof, NVH issues during load alternation are avoided. 
         [0044]    Further, to this end, the first surface lines can be in each case formed in portions which are in each case offset by 90 angular degrees in the circumferential direction and which come into contact with the convex inner circumferential faces of the roller elements, such that contour circles having a considerably larger contour circle radius or even an infinitely large contour circle diameter (in the manner of a portion of a straight line) may be formed there. 
         [0045]    Furthermore, an embodiment of a tripod constant velocity joint comprising at least an inner joint part as described herein, a rotatably mounted roller element according to the invention on each projection, and an outer joint part having axially running clearances for guiding in each case one roller element along an axial direction is proposed. It is provided here that the clearances have a pair of axially running guide faces on which the roller elements are supported in a circumferential direction, wherein at least one support face which limits a tilt movement of the roller elements about a tilt axis is disposed between the pair of guide faces, and wherein the tilt axis of the roller elements is formed by the intersection line of the central plane of the roller element and the centric plane of the guide faces which runs parallel with the joint axis of the outer joint part. 
         [0046]    In particular, two supporting faces which in each case are disposed so as to be adjacent to the guide faces are provided. In particular, the support faces here are configured so as to be eccentric between the guide faces. 
         [0047]    The in particular crowned outer circumferential face of the roller elements enables that the roller element may perform a (low-friction) tilt movement in the axially running clearances of the outer joint part. The guide faces in the clearances of the outer joint part are adapted to this shape of the roller elements. In this way, the tilt angle of the projection that is required for the respective angle of deflection of the tripod constant velocity joint in relation to the roller element may be reduced, because the roller element conjointly with the inner joint part in relation to the outer joint part performs a tilt movement in the identical direction. This reduction in the tilt movement may avoid contact between the roller element and the inner joint part, in particular in the region of the transition radius having a minimum value, such that comparatively large angles of deflection between the inner joint part and the outer joint part may be implemented. Limiting the tilt movement of the roller element by way of the support face is provided also in particular so that the roller element does not become wedged in the axially running clearances of the outer joint part when the inner joint part is heavily deflected in relation to the outer joint part. 
         [0048]    The support faces which run in the axial direction extend across a predefined depth of the clearance (in the circumferential direction) and in each case in the radial direction inwardly toward the inner joint part of the tripod constant velocity joint. In particular, the support faces are formed by the material of the outer joint part, and are thus integrated in the outer joint part. 
         [0049]    The at least one support face may be disposed such that the roller elements are tiltable about the tilt axis by a tilt angle range of at maximum 10 angular degrees. In particular, the tilt angle range is at maximum ±10 angular degrees (about a normal position), in particular at maximum ±6 angular degrees about the tilt axis. 
         [0050]    These limits for the tilt angle range result in an advantageous compromise for maximum angles of deflection and good NVH properties. Thus, cyclical axial forces of the 3 rd  order and high-frequency displacement forces may be minimized. 
         [0051]    The following advantageous (approximate) values may be stated in an exemplary manner for a tripod constant velocity joint having a nominal torque of 3300 Nm [Newton meters]:
       Outer diameter of outer joint part: 82 mm   PCR (pitch circle radius—spacing of the median plane of the respective guide faces from the joint axis of the outer joint part): 24 to 25 mm   Height: 23 to 26 mm   Transition radius (maximum value): 9 mm   Transition radius (minimum value): 1.5 mm   First curvature radius in the contact point (eKRmax): 4831.40 mm   Inner sphere radius (IKR): 9.59 mm   Distance: 2.02 mm   Radius of contour circle (IKR distance): 7.57 mm       
 
         [0061]    In particular, it is proposed that the height of the maximum diameter of each projection in relation to the PCR is offset by +1 mm to −1 mm. On account of this offset the profile of the axial force of the 3 rd  order may likewise be influenced. In particular, the height of the maximum and of the minimum as well as the position of the maximum and of the minimum may be influenced in the profile of the axial force of the 3 rd  order so as to depend on the angle of deflection (cf.  FIG. 15 : maximum at 7.5 angular degrees and minimum between 15 and 17.5 angular degrees of angle of deflection). 
         [0062]    A fourth angular range of in each case 90° extends in the third plane of each projection, in each case between the first plane and the second plane. The profile of the circumferential face of the projection, emanating from the rotation axis along the radial direction, is in each case formed by a surface line. This surface line, at least in the intersection point between the third plane, the circumferential face of the projection, and an angular value within the fourth angular range, is in each case formed by a second curvature radius (KR), and the profile of the surface line of the circumferential face along the radial direction is thus defined. The value of this second curvature radius, along the fourth angular range emanating from the first curvature radius of the first surface line in the region of the first plane, is continuously varied. The respective curvature radius is referred to as KR. An angular value of 0° is in each case present in the second plane. An angular value of 90° is in each case present in the first plane. This means that at an angular value of 0° the curvature radius of the second surface line defines the profile of the circumferential face of the projection along the radial direction. This (second) curvature radius of the second surface line substantially corresponds to the inner sphere radius minus the distance. In the case of an angular value of 90° the profile of the circumferential face is defined by the first curvature radius of the first surface line. The following values for the (second) curvature radii may be assumed for the exemplary tripod constant velocity joint having the nominal torque of 3300 Nm, as stated above (see Table 1): 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Angular 
                 (second) 
                   
                   
               
               
                 value 
                 Curvature radius 
               
               
                 ° [Angular 
                 (KR) 
                 V1 = 
               
               
                 degrees] 
                 mm [millimeter] 
                 KR/IKR 
                 Remarks 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 0 
                 7.59 
                 0.79 
                 approx. IKR 
               
               
                   
                   
                   
                 distance 
               
               
                 5 
                 7.81 
                 0.81 
               
               
                 10 
                 8.03 
                 0.84 
               
               
                 15 
                 8.25 
                 0.86 
               
               
                 20 
                 8.47 
                 0.88 
               
               
                 25 
                 8.70 
                 0.91 
               
               
                 30 
                 8.92 
                 0.93 
               
               
                 35 
                 9.14 
                 0.95 
               
               
                 40 
                 9.36 
                 0.98 
               
               
                 45 
                 9.59 
                 1.00 
                 IKR 
               
               
                 50 
                 9.86 
                 1.03 
               
               
                 55 
                 10.27 
                 1.07 
               
               
                 60 
                 11.16 
                 1.16 
               
               
                 65 
                 13.16 
                 1.37 
               
               
                 70 
                 17.89 
                 1.87 
               
               
                 75 
                 30.98 
                 3.23 
               
               
                 80 
                 79.68 
                 8.31 
               
               
                 85 
                 383.17 
                 39.98 
               
               
                 90 
                 4831.40 
                 504.06 
                 eKRmax 
               
               
                   
               
             
          
         
       
     
         [0063]    In particular, it is proposed that the inner joint part, the roller element, and/or the tripod constant velocity joint are/is employable in a motor vehicle. These components serve in particular for connection purposes and for transmitting torques from a drive unit to the wheels of a motor vehicle. This is performed either in combination with a longitudinal shaft or with shafts which are disposed so as to be transverse to a vehicle axis, that is to say with side shafts. 
     
    
     
       SUMMARY OF THE DRAWINGS 
         [0064]    The invention as well as the general technical field will be discussed in more detail below by the figures. The figures show exemplary embodiments to which the invention is not limited, however. In particular, it is to be pointed out that the figures and in particular the proportions illustrated are only schematic. Same reference signs refer to same items in the figures in which: 
           [0065]      FIG. 1  shows a motor vehicle; 
           [0066]      FIG. 2  shows an inner joint part; 
           [0067]      FIG. 3  shows an inner joint part in a side view; 
           [0068]      FIG. 4  shows an inner joint part according to  FIG. 3 , in a sectional view; 
           [0069]      FIG. 5  shows an inner joint part in a view along the rotation axis; 
           [0070]      FIG. 6  shows a detail A of  FIG. 5 ; 
           [0071]      FIG. 7  shows an inner joint part according to  FIG. 5 , in the cross section; 
           [0072]      FIG. 8  shows a roller element; 
           [0073]      FIG. 9  shows a component of the roller element according to  FIG. 8 ; 
           [0074]      FIG. 10  shows a tripod constant velocity joint in a perspective view; 
           [0075]      FIG. 11  shows a detail of a tripod constant velocity joint in a perspective view; 
           [0076]      FIG. 12  shows a tripod constant velocity joint in a sectional side view; 
           [0077]      FIG. 13  shows the tripod constant velocity joint according to  FIG. 12 , likewise in a sectional side view; 
           [0078]      FIG. 14  shows the inner joint part in a plan view, in order to illustrate the second curvature radius; and 
           [0079]      FIG. 15  shows a diagram for illustrating the profile of the cyclical axial force of the 3 rd  order, depending on the angle of deflection. 
       
    
    
     DESCRIPTION 
       [0080]      FIG. 1  shows a motor vehicle  51  having a drive unit  65  and wheels  57 . Torques which are generated by the drive unit  65  are transmitted via shafts  50  and tripod constant velocity joints  2  or other types of joint to the wheels  57 . In particular, the tripod constant velocity joints  2  which are described herein are employable in side shaft assemblies  49  in which comparatively large angles of deflection typically arise. 
         [0081]      FIG. 2  shows an inner joint part  1  of a tripod constant velocity joint  2 , comprising a hub  3  having a rotation axis  4  and three projections  5 , which outwardly extend from the hub  3  in a radial direction  6 , including first a transition region  58 , then a bearing region  59 , and finally an end face  32 . Each projection  5  has a longitudinal axis  7  and a crowned circumferential face  9  in the bearing region  59 . The longitudinal axes  7  collectively define a first plane  8  which is perpendicular to the rotation axis  4 . A second plane  16  is disposed so as to be perpendicular to the first plane  8  and comprises in each case the longitudinal axis  7  of a single projection  5 . A third plane  18  runs perpendicularly to the first plane  8  and to the second plane  16 , wherein a maximum diameter  12  of the projection  5  is disposed in this third plane  18 . 
         [0082]      FIG. 3  shows an inner joint part  1  in a side view, wherein emanating from the hub  3 , three projections  5  outwardly extend in the radial direction  6 . The crowned circumferential face  9  of the projection  5  in the second plane  16  (here parallel with the plane of the illustration) is formed by a second surface line  15 . The projection  5  has a maximum diameter  12  which emanating from the rotation axis  4  in the radial direction  6  is disposed at a height  11 . A transition radius  25  which here is embodied at a minimum value in the second plane  16  is provided between the projection  5  and the hub  3 . It can be seen that the projection  5  in the second plane  16  and emanating from the maximum diameter  12  (along the second surface line  15 ) tapers off further toward the hub  3 . The transition region  58  adjoins this taper toward the hub  3 . A relief groove, into which a roller element  28  (not illustrated here) which is disposed on the projection  5  can plunge without contacting the inner joint part  1  in the case of a tilt movement of the roller element  28 , is configured below the transition radius  25  in the direction of the rotation axis  4  of the inner joint part  1 . 
         [0083]      FIG. 4  shows the inner joint part  1  according to  FIG. 3  in the cross section. The projection  5  at the height  11  has a maximum diameter  12  which corresponds to the diameter of an inner sphere  13  (illustrated with dotted lines). In the second plane  16  which is shown here, the circumferential face  9  of the projection  5  is formed by a second surface line  15 . This second surface line  15  emanating from the maximum diameter  12  at the height  11  extends outwardly in the radial direction  6 , within the inner sphere  13 . The profile of the second surface line  15  may be approximated by the segments  40  of two contour circles (illustrated with dashed lines), the circle centers  43  of which are disposed at the height  11 , in each case at a distance  39  from the longitudinal axis  7 . The circle centers  43  are thus at a distance  39  from the midpoint  14  of the inner sphere  13 . While the inner sphere  13  has a maximum diameter  12  and thus an inner sphere radius  19 , the second surface line  15  is at least partially generated by the segments  40  of the contour circles  42 , so as to have a relatively small radius, the latter corresponding to the inner sphere radius  19  minus the distance  39 . 
         [0084]    In particular, the second surface line  15  also runs in a region between the height  11  and the hub  3 , at least partially within the inner sphere  13 . 
         [0085]      FIG. 5  shows an inner joint part  1  in a plan view along the rotation axis  4 . Emanating from the hub  3 , three projections  5  in each case extend along a longitudinal axis  7  in the radial direction  6 . In the first plane  8  (parallel with the plane of illustration) the circumferential face  9  of the projections  5  is formed by the first surface line  10 . In the bearing region  59  at the height  11 , emanating from the rotation axis  4  along the longitudinal axis  7  of each of the projections  5  in radial direction  6 , the projection  5  has a maximum diameter  12 . Emanating from this maximum diameter  12 , the projection  5  tapers off outwardly along the first surface line  10  in the radial direction  6 . A maximum transition radius  25  is provided between the projection  5  and the hub  3 , in the transition region  58 . It can be seen here that the first surface line  10 , emanating from the height  11  and in the direction of the hub  3 , has an almost constant spacing  27  from the longitudinal axis  7 , which spacing  27  substantially corresponds to the inner sphere radius  19  (not shown here) and thus to half the maximum diameter  12 . Emanating from this spacing  27 , the projection  5  exclusively widens in the transition region  58  and up to the hub  3 . A relief groove or a cut-out, as is shown in the second plane  16  in  FIGS. 2 and 3 , has not been implemented here. In this first plane  8  the tilt movement of the roller element  28  (not shown here) in relation to the projection  5  is performed to a far lesser extent than in the second plane  16 . The transition region  58  having the maximum transition radius  25  now enables the projection  5  to have no (or only a very minor) taper between the hub  3  and the height  11  in this first plane  8 . In this way, high circumferential forces and thus high torques may be transmitted, wherein also smaller construction sizes of the tripod constant velocity joints  2  than previously usual may be employed, which then likewise achieve a long service life. 
         [0086]      FIG. 6  shows a detail A of  FIG. 5 . The projection  5  is shown in the first plane  8  (plane of illustration). The first surface line  10  in the first plane  8  runs outside the indicated inner sphere  13  and contacts this inner sphere  13  by way of the inner sphere radius  19  in the region of the contact point  52 . The projection  5  has its maximum diameter  12  in this contact point  52 . The third plane  18  extends so as to be transverse to the first plane  8  and through the contact point  52  and across the maximum diameter  12 . The midpoint  14  of the inner sphere  13  lies on the third plane  18  and in the intersection point with the second plane  16  as well as with the first plane  8 . The first surface line  10  in the region of the contact point  52  has a maximum first curvature radius  17  which is present in the first angular ranges  20  which lie on both sides adjacent to the contact point  52 . 
         [0087]      FIG. 7  shows the inner joint part  1  according to  FIG. 5  in a sectional view. The projection  5  in the first plane  8  (plane of illustration) is limited by the first surface line  10 . The latter in the region of the maximum diameter  12  has a straight line  21  which extends across first angular ranges  20 . The angular ranges  20  enclose the contact point  52 . The regions of the first surface line  10 , which during operation of the tripod constant velocity joint  2  contact the inner circumferential face  29  of a roller element  28 , here are formed by opposite portions of straight lines (contour circles having an infinitely large radius). The dashed lines on the upper projection  5  highlight that the portions of the straight line are mutually opposite and highlight the extent of the straight line  21  along the first surface line  10 . 
         [0088]    The transition region  58  is disposed between the contact point  5  and the hub. The first surface line  10  now continues between the contact point  52  toward the hub  3  at a (constant) spacing  27  and so as to be substantially parallel with the longitudinal axis  7 . The transition region  58  is formed by the maximum transition radius  25 , wherein there is no tapering of the projection  5  here, in particular. 
         [0089]      FIG. 8  shows a roller element  28  which is disposed on one of the projections  5  (not shown here). The roller element  28  here is formed by a plurality of individual components, wherein the roller element  28  has an outer circumferential face and an inner circumferential face  29 . The outer circumferential face  38  is in contact with the outer joint part (not shown here), and the inner circumferential face  29  is in contact with the crowned circumferential face  9  of the projection  5 . A median plane  31  (plane of illustration) which encompasses the central axis  30 , as well as a central plane  22  which is disposed centrically thereto, may be fixed in relation to the roller element  28 , wherein the intersection point  35 , composed of the central axis  30  and of the central plane  22 , forms the center  61  of the roller element  28 . The roller element  28  has a shape which is rotationally symmetrical about the central axis  30  and is embodied so as to be substantially mirror symmetrical about the central plane  22 . 
         [0090]      FIG. 9  shows a component of the roller element  28  according to  FIG. 8 , in a sectional view in the median plane  31  (plane of illustration), wherein the inner circumferential face here is shown in detail. The convex-shaped inner circumferential face  29  is configured so as to be rotationally symmetrical about a central axis  30 , wherein the roller element is constructed so as to be substantially symmetrical in relation to the central plane  22  which runs perpendicularly to the central axis  30 . The profile line  33  of the convex-shaped inner circumferential face  29  has variable profile radii  23  and in the region of the central plane  22  (central region  26 ) and within a third angular range  41 , which emanating from the center  61  extends on both sides beyond the central plane  22 , is formed by a maximum profile line radius  63  and, in continuation thereof (in the adjacent region  62 ), by in each case at least one profile line radius  64  which in terms of value is comparatively small. In continuation of the respective comparatively small profile line radius  64 , a portion having a concave-shaped profile line  33  of the inner circumferential face  29 , which is adjoined again by a convex-shaped portion, can be seen here. 
         [0091]    That part of the inner circumferential face  29  that during operation of a tripod constant velocity joint  2  is now in contact with the projection  5  of a inner joint part  1  (according to the invention) is formed by the convex inner circumferential face  29  having the maximum profile line radius  63  and the respective adjoining comparatively small profile line radii  64 . 
         [0092]    The inner circumferential face  29  which is formed by the maximum profile line radius  63  extends across a third angular range  41 , emanating from the center  61  over the central plane  22  by ±1 angular degree to ±6 angular degrees, in particular by ±1.5 to ±2.5 angular degrees. In particular, the third angular range  41  also has a range from 2 to 12, in particular from 3 to 5 angular degrees. Furthermore, the profile line  33  of the inner circumferential face  29 , which is in each case formed having the comparatively small profile radii  64 , emanating from the center  61  and on both sides (that is to say symmetrically above and below the central plane  22 ) and in each case adjoining the third angular range  41 , extends across in each case one (further) angular range by ±1 to ±6 angular degrees, in particular ±1.5 to ±2.5 angular degrees. 
         [0093]      FIG. 10  shows a tripod constant velocity joint  2  in a perspective view. An outer joint part  36  has three clearances  37  which run in the axial direction  56  (into the plane of illustration) and in which the roller elements  28  are disposed so as to be displaceable in the axial direction  56 . The roller elements  28  are disposed on projections  5  of an inner joint part  1 . In the extended (not deflected) state of the tripod constant velocity joint  2  the height  11 , the third plane  18 , the maximum diameter  12 , and the central plane  22  are substantially in mutual alignment. Emanating here for example from the outer joint part  36 , a torque is transmitted in the circumferential direction  24  via the guide faces  44  and the outer circumferential face  38  of the roller element  28  and further via the inner circumferential face  29  of the roller element  28  to the crowned circumferential face  9  of the projections  5 , such that the inner joint part  1  conjointly rotates with the outer joint part  36  in the circumferential direction  24 . A support face  45  which here is disposed so as to be centric in relation to the guide faces  44  in the outer joint part  36  and in this way limits a tilt movement of the roller element  28  is provided in the respective clearance  37 . 
         [0094]      FIG. 11  shows a further variant of embodiment of the design of an outer joint part  36 , wherein two support faces  45  for the roller elements  28  are provided in the clearance  37 . Said support faces  44  are identifiably disposed so as to be eccentric and in each case adjacent to the guide faces  44 . 
         [0095]      FIG. 12  shows a tripod constant velocity joint  2  in a sectional side view, wherein an outer joint part  36  having clearances  37  and guide faces  44  disposed in the latter receives a roller element  28  which is disposed so as to be displaceable in the axial direction  56 . The roller elements  28  are disposed on projections  5 , wherein it can be seen here that the inner joint part  1  in relation to the outer joint part  36  is deflected about an angle of deflection  55 . Accordingly, an angle of deflection  55  is configured between the rotation axis  4  and the joint axis  54 . The guide faces  44  have a centric plane  66  which extends so as to be parallel with the joint axis  54  of the outer joint part  36 . It can be seen that the roller element  28  plunges into the cut-out/relief groove in the region of the transition  58  having the minimum transition radius  25 , such that the maximum possible angle of deflection  55  is enlarged (cf. also  FIG. 13 ). 
         [0096]      FIG. 13  shows a tripod constant velocity joint  2  in a sectional side view, wherein the inner joint part  1  in relation to the outer joint part  36  is disposed so as to be deflected about an angle of deflection  55  (cf.  FIG. 12 ). Roller elements  28  are disposed on the projection  5 , wherein the roller element  28  in relation to the joint axis  54  and in relation to the third plane  18  of the projection  5  is disposed so as to be tilted. On account of its specially shaped and crowned outer circumferential face  38  and of the correspondingly shaped guide faces  44 , the roller element  28  may perform a tilt movement  46  about a tilt axis  47 . This tilt axis  47  of the roller element  28  is the sectional line of the central plane  22  of the roller element  28  having the centric plane  66  of the guide faces  44  which runs parallel with the joint axis  54  of the outer joint part  36 . 
         [0097]    The tilt axis  47  runs parallel with the axis  53  which is formed by the third plane  18  of the projection  5  and by the longitudinal axis  7  of the projection. It can be seen that the roller element  28  in relation to the centric plane  66  of the clearance  37  tilts about the tilt angle  48 . 
         [0098]    On account of the tilt movement  46  about the tilt axis  47 , the angle of deflection  55  between the inner joint part  1  and the outer joint part  66  may be further enlarged, since the roller element  28  together with the inner joint part  1  tilts up to a tilt angle  48 , and limiting the angle of deflection  55  by way of impact of the roller element  28  on the inner joint part  1  only arises in the case of very large angles of deflection  55 . 
         [0099]    The tilt movement  46  of the roller element  28  is limited by the support faces  45  in the clearance  37  of the outer joint part  36 . In this way, wedging of the roller element  28  in the guide faces  44  of the clearance  37  is prevented. 
         [0100]      FIG. 14  shows the inner joint part  1  in a plan view, in order to illustrate the second curvature radius  67 . A fourth angular range  68  extends in the third plane  18  of each projection  5 , in each case between the first plane  8  and the second plane  16 . The profile of the circumferential face  9  of the projection  5  along the radial direction  6 , emanating from the rotation axis (not illustrated here) is in each case formed by a surface line. This surface line in the intersection point between the third plane, the circumferential face  9  of the projection  5 , and an angular value  69  within the fourth angular range  68 , is in each case formed by a second curvature radius  67 . The value of this second curvature radius  67 , emanating from the first curvature radius  17  of the first surface line  10  in the region of the first plane  8  (KR(angular value  69 =90°=eKRmax) up to the (second) curvature radius of the second surface line  15  in the region of the second plane  16  (KR(angular value  69 =0°=IKR-distance), continuously varies along the fourth angular range  68 . This (second) curvature radius of the second surface line  15 , according to the description of  FIG. 4 , corresponds to the inner sphere radius  19  minus the distance  39 . In the case of an angular value  69  of 45°, the second curvature radius  67  corresponds to the inner sphere radius  19  (KR(angular value  69 =45°=IKR). 
         [0101]      FIG. 15  shows a diagram in order to illustrate the profile of the cyclical axial force of the 3 rd  order  70 , depending on the angle of deflection  55  of the tripod constant velocity joint  2 . The cyclical axial force of the 3 rd  order  70  is that variable of the tripod constant velocity joint  2  that determines the NVH (noise, vibration, harshness) behavior. The particular embodiment of the projection  5  and of the roller element  28  has the effect that the cyclical axial force of the 3 rd  order  70  has only minor values, even in the case of comparatively large angles of deflection  55 . The advantage of the tripod constant velocity joint  2  in comparison with a joint of the prior art  72  (for example according to DE 101 06 727 B4, or to EP 1 505 308 A1) becomes apparent specifically in the case of comparatively large angles of deflection  55 . The profile of the cyclical axial force of the 3 rd  order  70  remains considerably below the acceptance limit which is defined for such joints. The tripod constant velocity joint  2  which is being proposed here is thus specifically suitable for employment in cases where primarily comparatively large angles of deflection  55  are present during operation. 
         [0102]    In a preemptive manner it should finally be pointed out that the combinations of technical features as shown in the figures are not generally mandatory. In this way, technical features of one figure may be combined with other technical features of a further figure and/or with those of the general description, unless the combination of features has in a particular instance been explicitly stated and/or a person skilled in the art realizes that the basic functions of the device would no longer be provided.