WO2010022760A1

WO2010022760A1 - Inner joint part of constant velocity universal joint

Info

Publication number: WO2010022760A1
Application number: PCT/EP2008/010191
Authority: WO
Inventors: Rolf Cremerius
Original assignee: Gkn Driveline International Gmbh
Priority date: 2008-08-28
Filing date: 2008-12-02
Publication date: 2010-03-04
Also published as: DE102008044723B4; CN102203446B; DE102008044723A1; CN102203446A

Abstract

The invention relates to an inner joint part for a constant velocity universal joint with an axis of rotation A. The inner joint part comprises a plurality of circumferentially distributed ball tracks (4) for receiving torque transmitting balls (23), and a plurality of circumferentially distributed webs (3) which are each formed between two circumferentially adjoining ball tracks (4), each of said webs (5) comprising an outer face (5), wherein an enveloping spherical face (K) of the inner joint part (2) comprises a diameter (D), wherein the outer faces (5) of at least some of the webs (3), if viewed in at least one cross-section, each comprise a first portion (9) for guiding a ball cage (14) and at least one second portion (10) which is arranged at a distance from the enveloping spherical face (K) of the inner joint part (2). The invention also relates to a constant velocity universal joint with such an inner joint part.

Description

Inner joint part of constant velocity universal joint

Description

The invention relates to an inner joint part for a constant velocity universal joint, which inner joint part has a plurality of circumferentially distributed ball tracks for guiding torque transmitting balls. Furthermore, the invention relates to a constant velocity universal joint which, in addition to such an inner joint part, comprises an outer joint part with outer ball tracks, also torque transmitting balls which are each held in a pair of outer and inner ball tracks, as well as a ball cage in which the balls are held.

Such constant velocity universal joints serve to transmit torque between the inner joint part and the outer joint part, with angular movements of the inner joint part being permitted relative to the outer joint part. Generally, there is differentiated between constant velocity fixed joints wherein the inner joint part is substantially axially fixed relative to the outer joint part, as well as constant velocity plunging joints wherein the inner joint part is able to carry out axial plunging movements relative to the outer joint part. Furthermore, constant velocity joints can comprise different track shapes, such as straight ball tracks or curved ball tracks.

From DE 10 2005 023 045 A1 there is known a constant velocity universal joint which comprises an outer joint part, an inner joint part, torque transmitting balls as well as a cage in which the balls are held. The ball tracks are unevenly spaced around the circumference, so that between adjoining ball tracks there are provided webs of different widths. At the inner joint part, the webs of a smaller width at one axial end are reduced in height relative to a spherical face enveloping the webs in order to reduce the risk of fracture.

From DE 195 14 868 C1 there is known a further constant velocity universal joint with an outer joint part, an inner joint part, torque transmitting balls and a ball cage. A first group of guiding webs is delimited along the entire axial length of the inner joint part by a spherical surface. A second group of guiding webs, at its axial end with the greater track depth, is reduced to a contour below the respective spherical surface. It is intended, in this way, to achieve improved mounting conditions and, related thereto, an increased strength of the ball cage.

From DE 10 2005 063 006 A1 there is known an inner joint part for a constant velocity universal joint in the form of a plunging joint, as well as a method of producing an inner joint part. The inner joint part comprises a plurality of circumferentially distributed webs which form spherical guiding faces for a ball cage. The ball tracks each comprise a hard-machined first track portion and an unmachined second track portion.

WO 2006/058556 A1 proposes a method of machining an inner joint part of a constant velocity universal joint wherein at least one ball track and at least one guiding web are machined simultaneously.

It is the object of the present invention to propose an inner joint part for a constant velocity universal joint, which ensures a reduction in the friction forces acting on the ball cage, which permits improved guiding conditions for the ball cage and which can be produced easily and cost-effectively. A further object consists in proposing a constant velocity universal joint which comprises such an inner joint part.

The object is achieved by providing an inner joint part for a constant velocity universal joint, comprising a plurality of circumferentially distributed ball tracks for receiving torque transmitting balls, and a plurality of circumferentially distributed webs which are formed between two circumferentially adjoining ball tracks and comprise an outer face, wherein an imaginary enveloping spherical face of the inner joint part comprises a diameter D, wherein the outer face of at least some of the webs, if viewed in at least one cross-section, comprises a first portion for guiding a ball cage and at least one second portion which is arranged at a distance from the enveloping spherical face K radially inwardly.

"At least one of the webs" in this context means that either all the webs can be designed as mentioned or only some of the webs. In the latter case, at least one further web can be designed differently, for example for mounting purposes. The webs are preferably of the above-mentioned type whose outer faces, while reduced to a contour below the enveloping spherical face, are distributed around the circumference in such a way that the ball cage is coaxially centred relative to the inner joint part when the joint is in the aligned condition.

The advantage of the inventive inner joint part is that the guiding face of the inner joint part is small relative to the entire outer face, so that the face of contact with the ball cage is correspondingly small. This, in turn, is advantageous in that the friction forces acting between the guiding face of the inner joint part and the inner face of the ball cage are reduced, which results in improved guiding conditions for the ball cage relative to the inner joint part. The second portions which are set back relative to the enveloping spherical face assist in reducing the friction forces because there are thus formed gaps between the second portions and the inner face of the ball cage, which gaps can be entered by the lubricants. Depending on the contour of the outer face, the lubricant can enter deeply into the gap in order to lubricate the contact faces between the first portions of the webs and the inner face of the ball cage. The first portions which, in the mounted condition, serve to guide the ball cage - taking into account the surface pressure existing between the inner joint part and the ball cage - can, in principle, be as small as desired; the smaller the first portion and, respectively, the larger the second portion freed by the inner face of the ball cage, the lower the friction forces and the better the supply of lubricant and the better the guiding conditions for the ball cage.

A further advantage consists in that the outer faces of the webs can be produced with the workpiece being fixed, i. e. non-rotating, and by a rotating tool, which applies both to the milling and grinding operations. When machining the outer faces of the webs, the respective tool, i.e. the grinding and milling disc, are guided so as to extend parallel to the axis of the inner joint part and fed in radially. The surface structure thus produced by machining, for instance by grinding marks, is also aligned axially, which further intensified the friction-reducing effect between the inner joint part and the ball cage. Overall, depending on existing requirements to be met by the joint, the outer faces of the webs can have axial and radial contours. By providing the webs with first portions for guiding purposes and second portions which are reduced inwardly relative to the imaginary spherical face, there is achieved a defined web contour, which, in turn, leads to an improved supporting pattern.

In principle, the outer faces of the webs, in a cross-sectional view, can be designed in any way, but it is advantageous to provide the smallest possible face for guiding the ball cage to achieve low friction values. The ratio of the extension Bi of the first portion in the circumferential direction to the entire extension B of the outer face in the circumferential direction is preferably smaller than two thirds, i.e. Bi/B < 2/3, more particularly smaller than one third, i.e. B₁ZB < 1/3. According to a preferred embodiment, the at least one web, in a cross-sectional view, is symmetric, with the first portion being arranged centrally and with a second portion being arranged in each circumferential direction so as to laterally adjoin the first portion. The maximum M of the first portion is preferably arranged in the plane of symmetry, approximately on the enveloping spherical face. The outer face of the webs, in a cross-sectional view, is preferably formed by radii, but in principle, the outer contour can also be formed by curves of a higher order. According to a first embodiment, it is proposed that the first portion for guiding the ball cage and the second portion which is set back relative to the spherical face, in a cross-sectional view, are formed by one circular arch with a radius R_A which remains constant along the width of the web. Regarding this embodiment with a constant radius of the outer face over the circumference, it is proposed that the radius R_A is smaller than half die diameter D/2 of the enveloping spherical face. In a cross-sectional view, this results in a point contact and, because of the surface pressure, in a minimum surface contact between the outer face of the inner joint part and the inner face of the ball cage. The first radius R_A is preferably greater than/equal to one quarter of the diameter D, i.e. R_A > D/4. The advantage of the present embodiment with a constant radius R_A is that the gap between the outer face of the inner joint part and the inner face of the ball cage is maximised, so that lubricant is able to penetrate particularly deeply as far as the central region of the web. In an advantageous way, the continuous transition of the first and second portions because of the constant radius, also assists the lubricant in entering deeply into the gap. The good lubrication conditions result in low friction values between the inner joint part and the ball cage.

According to a second embodiment, it is proposed that the first portion comprises a radius R_Ai which is smaller than/equal to half the diameter D of the enveloping ball face, i.e. R_AI < D/2 and that the second portion of the outer face comprises a radius RA2 which is smaller than the first radius R_Ai , i.e. RA2 £ R_AI - In a preferred embodiment, the ratio of the extension B₁ of the first portion in the circumferential direction to the entire extension B of the outer face in the circumferential direction amounts to one third to two thirds, i.e. 1/3 < Bi/B < 2/3. As compared to the webs of the first embodiment, the webs of the second embodiment comprise enlarged guiding faces and a higher load bearing capacity. This is particularly advantageous for constant velocity joints in which the surface pressure between the inner joint part and the ball cage is greater. According to a preferred embodiment which applies to both the above-mentioned designs, the webs, in a cross-sectional view, comprise chamfers in the region of transition between the outer face and the adjoining ball tracks. The chamfers are provided more particularly for such webs wherein the gap dimension between the second portions and the inner face of the ball cage and, respectively, the enveloping spherical face is small. The chamfers prevent any material which, during the operation of the joint is rolled out as a result of the rolling movement of the balls in the ball tracks, from moving radially outwardly, which would lead to an increase in friction and wear. In the inventive inner joint part, the chamfers can be produced at the same time as the outer contour. A separate production operation especially for producing the chamfers is therefore not necessary.

As mentioned above, also in the longitudinal direction, the webs of the inventive inner joint part can generally have any design inside the enveloping spherical face.

According to a first possibility which applies to all the above-mentioned embodiments, the outer face, in a longitudinal section through the web, is formed by a circular arch whose radius R_L is smaller than/equal to half the diameter D of the enveloping spherical face, i.e. R_L < D/2, with the guiding face of the web extending over the entire length of the inner joint part, so that it is also able to support the ball cage along the entire length.

According to a second possibility which also applies to all the above-mentioned embodiments, the guiding face is designed in such a way that the ball cage, if viewed in a longitudinal section, is guided on two end regions of the web. This is achieved in that the first portion, in a central region, comprises a flattened portion, so that, in an axial view, two end regions for guiding the ball cage are formed and arranged so as to axially adjoin the flattened portion. In this case, too, it applies that the first portion, in a longitudinal section through the web, is formed by a circular arch, whose radius R_L is smaller than or equal to half the diameter D of the enveloping ball face, i.e. R_L < D/2. The smaller the radius R_L, the smaller the contact face between the inner joint part and the ball cage. Said embodiment with two side end regions which guide the ball cage, can also be referred to as roof-shaped.

Further possibilities for providing the guiding face in the longitudinal direction are not excluded. For example, the supporting end regions can also be formed by conical faces instead of by radii.

According to a possible further design which an be applied to any of the above- mentioned embodiments, one web or a plurality of webs can be designed in such a way as to simplify the operation of mounting the inner joint part in the ball cage. For this purpose, the at least one web, according to a first solution, can comprise a flattened portion at one axial end, which flattened portion extends from the guiding face to the end face of the inner joint part. According to a second solution, the at least one web can be flattened completely along its entire length, so that it no longer has a guiding function relative to the ball cage. In a preferred embodiment, two opposed webs are provided with such flattened assembly portions.

Furthermore, the above-mentioned object is achieved by providing a constant velocity universal joint comprising an outer joint part with outer ball tracks; an inner joint part with inner ball tracks; torque transmitting balls which are guided in pairs of tracks, each pair consisting of an outer ball track and an inner ball track; a ball cage with windows in which there are received the torque transmitting balls; wherein the inner joint part is designed in accordance with any one of the above embodiments. The main advantage of the inventive constant velocity universal joint consists in that the guiding faces of the inner joint part and thus the contact faces between the webs and the ball cage are reduced in size, which leads to less friction in the entire joint. According to a preferred embodiment, half the diameter D of the enveloping ball face of the inner joint part is smaller than/equal to a spherical inner face of the ball cage. This measure, too, leads to a reduction in friction.

In principle, the inventive constant velocity joint can have any design, with RF joints, UF joints, counter track joints and DO joints being particularly suitable.

Preferred embodiments will be explained below with reference to the drawings wherein

Figure 1 shows an inventive inner joint part in a first embodiment a) in an axial view; b) in a side view; c) in a longitudinal section; d) a first web according to Figure 1a in the form of a detail in a cross- sectional view, with the ball cage drawn in.

Figure 2 shows an inventive inner joint part in a second embodiment a) in a side view; b) a web according to Figure 2a in the form of a detail in a cross-sectional view along sectional line M-Il.

Figure 3 shows an inventive inner joint part in a third embodiment a) in a side view; b) a web according to Figure 3a in the form of a detail in a cross-sectional view according to sectional line Ill-Ill.

Figure 4 shows an inventive inner joint part in a fourth embodiment a) in a side view; b) in a longitudinal section along sectional line IVb-IVb of Figure 4a); c) a web according to Figure 4a in the form of a detail in a cross-sectional view according to sectional line IVc-IVc.

Figure 5 shows an inner joint part in a fifth embodiment a) in a longitudinal section b) in an axial view.

Figure 6 shows an inventive inner joint part in a sixth embodiment a) in a longitudinal section b) in an axial view.

Figure 7 shows an inventive inner joint part in a modified seventh embodiment a) in an axial view b) in a side view; and

Figure 8 shows a constant velocity universal joint in the form of a fixed joint with an inventive inner joint part a) in a longitudinal section, wherein the sectional line in the upper half of the Figure extends through a ball track and in the lower half of the Figure through a web; b) a web according to Figure 8a in the form of a detail in a cross-sectional view with the ball cage.

Figures 1 to 4 will be described jointly below as far as the features are concerned which they have in common, with identical components having been given the same reference numbers and the reference numbers of modified components having been provided with subscripts corresponding to the respective Figures.

There is shown an inner joint part 2 for a constant velocity universal joint described in greater detail below. In addition to having the inner joint part 2, the constant velocity universal joint comprises an outer joint part, a ball cage and torque transmitting balls which are held in windows of the ball cage.

The inner joint part 2 comprises a plurality of circumferentially distributed webs 3, as well as ball tracks 4 each being arranged between two circumferentially adjoining webs 3. The ball tracks 4 serve to receive and guide the torque transmitting balls of the constant velocity universal joint. At the axial outer ends, the webs 3 each comprise an outer face 5 which will be described in greater detail below. Furthermore, the inner joint part 2 comprises a first end face 6, a second end face 7 which is positioned axially opposite thereto, as well as a central through-aperture 8. The through-aperture 8 comprises inner teeth (not illustrated) into which, for torque transmitting purposes, there can be inserted a shaft or a journal in a rotationally fixed way.

The maxima of the outer faces 5 of the webs 3 comprise an imaginary spherical face K which envelopes the inner joint part 2 and which is also referred to as an enveloping spherical face K. The inner joint part is asymmetric in a longitudinal section in so far as a plane E, which in the centre of curvature O of the spherical ball face is positioned perpendicularly relative to the longitudinal axis A, divides the inner joint part 2 into two portions of different axial lengths.

The ball tracks 4 extend parallel to the longitudinal axis A. The number of ball tracks 4 depends on the number of torque transmitting balls to be used. Normally, constant velocity universal joints for the driveline of motor vehicles are provided with six or eight balls, but different numbers of balls are also conceivable. Between each two ball tracks 4, there is formed a web 3, so that, overall, the number of webs corresponds to the number of ball tracks.

It can be seen that the outer faces 5 in a cross-sectional view each comprise a first portion 9 for guiding the ball cage of the constant velocity universal joint, as well as two laterally adjoining second portions 10, 10' which are spaced inwardly from the enveloping spherical face. As a result of this design, the guiding face 12 between the inner joint part 2 and the ball face (not illustrated here), which guiding face 12 is defined by the first portions 9, is small relative to the entire outer face 5, so that the friction forces acting between said two components are low. In a cross-sectional view, the outer face 5 of the webs 3 can, in principle, have any contour. It is important in the sense of the invention that the first portion 9 which is positioned on the spherical face K is clearly reduced, more particularly by a multiple, relative to the entire length of the outer face 5 in the circumferential direction.

The special characteristics of the individual embodiments according to Figures 1 to 4 will be explained blow.

In the embodiment according to Figure 1 , the first portion 9 and the laterally adjoining second portions 10, 10' are formed by a common constant radius R_A. To that extent, there is achieved, as is particularly obvious in Figure 1b, a substantially linear guiding face 12 between the outer face 5 of the inner joint part 2 and the inner face 13 of the outer joint part 14. "Substantially linear" in this context means that, as a result of the surface pressure, there does not occur a pure line contact, but a surface contact extending narrowly in the circumferential direction. In the present embodiment, the radius R_A of the outer face amounts to approximately one quarter of the diameter D of the enveloping ball face, i.e. R_A = D/4. It goes without saying that the radius R_A can also be greater than one quarter of the diameter D, but in any case it is smaller than half the diameter D of the enveloping ball face, i.e. D/4 < R_A < D/2.

In the embodiment shown in Figure 2, the first portion 9₂ of the webs comprises a first radius R_Ai which approximately corresponds to half the diameter D of the enveloping ball, i.e. R_Ai = D/2. The second portions IO2, IO₂' which, in the circumferential direction, on opposed sides, continuously adjoin the first portion 9₂ comprise a second radius RA₂' which is smaller than the first radius R_Ai of the first portion 9₂. The guiding face 12₂ formed by the first portion 9₂, if viewed in the longitudinal direction, is approximately strip-like, which is particularly obvious from Fig. 2a. It can be seen that the circumferential width B1 of the guiding face 12₂ is approximately half the size of the entire extension B of the outer face 5₂ in the circumferential direction in the region of the side face of the inner joint part. To that extent, the surface pressure between the webs 3₂ of the inner joint art 2₂ and the ball cage 14 is reduced as compared to the above embodiment.

The embodiment shown in Figure 3 largely corresponds to that according to Figure 2, so that, as far as the common features are concerned, reference is made to the description of Figure 2. The only difference is that the webs 3₃ at their edges positioned opposite one another in the circumferential direction each comprise a chamfer 15, which chambers 15 form a transition from the respective ball track 4 to the second portion 1O₃, 1O₃' at the outer face 5₃. The chamfers 15 prevent any material being rolled out by the rolling movement of the balls in the ball tracks 4 from being moved radially outwardly. This could lead to the gap 16 between the respective web 3₃ and the inner face 13 of the ball cage 14 being clogged up. To that extent, the chamfer 15 ensures that even after a long period of operation, lubricant is able to enter the gap 16 and lubricate the surfaces which contact one another. This has a particularly advantageous effect on the service life of the joint.

The embodiment according to Figure 4 largely corresponds to that according to Figure 2, so that, as far as the common features are concerned, reference is made to the description of Figure 2. The only difference is that in an axially central region, the outer face 5₄ of the webs 3₄ of the present embodiment comprises flattened portions 17. In said flattened portions 17, the webs 3₄ are not in contact with the inner face 13 of the ball cage 14. On the contrary, if viewed in a longitudinal section, there takes place a two-surface contact, which is particularly obvious in Figure 4b, with the supporting first portions 9₄ of the webs 3₄ being positioned in axial end regions of the inner joint part 2₄. As a result of the flattened portions 17, the contact face between the outer face 5₄ of the inner joint part 2₄ and the inner face 13 of the ball cage 14 is reduced once more, which has an advantageous effect on friction. A further advantage consists in that the inner joint part 2₄ is well supported relative to any tilting movements around the axis of articulation of the joint.

It goes without saying that the modification to the inventive inner joint part with flattened portions can be applied to any outer surface contour. More particularly, the embodiments according to Figure 1 and also according to Figure 3 are conceivable which can comprise flattened portions according to the embodiment shown in Figure 4.

Figure 5 shows an inventive inner joint part 2₅ in a modified form. In respect of the design of the webs 3, the inner joint part 2₅ can be designed in accordance with any one of the individual above-described embodiments according to Figures 1 to 4. The special feature of the present variant consists in that two opposed webs 3₅' comprise recesses 18 on the same axial side of the inner joint part. The recesses 18 which are provided in the form of edge fractures of the end edge permit an easy assembly without reducing the strength of the cage, as described in the above-mentioned DE 195 14 868 C1. The remaining webs 3₅ do not comprise any recesses 18 and can all have the same design as referred to in one of the above embodiments.

Figure 6 shows a further variant of an inventive inner joint part 2₆ wherein the webs 3₆ can also be designed according to one of the above-mentioned embodiments according to Figures 1 to 4. The special feature of the present variant is that two opposed webs 3₆ comprise recesses 18₆ which are provided in the form of central flattened portions. The present embodiment with central flattened portions, too, is advantageous in that it permits a simplified assembly procedure for mounting the inner joint part 2₆ in the associated ball cage, without losing any of its strength. The remaining webs 3β which do not contain any flattened portions can be designed according to any one of the above-mentioned embodiments.

Figure 7 shows an inventive inner joint part in a further embodiment which is slightly modified relative to the embodiments according to Figures 1 to 4. To that extent, as far as the common features are concerned, reference is made to the above descriptions wherein identical components have been given the same reference numbers. The outer face 5 of the webs 3 of the present inner joint part 2, as far as details are concerned, can be designed in accordance of any one of the embodiments shown in Figures 1 to 4, i.e., in a cross-sectional view, they can be provided with continuous constant radii according to Figure 1 or with different radii of the first and second portion according to Figure 2, and additionally optionally with chamfers according to Figure 3 or with central flattened portions according to Figure 4.

The special feature of the present embodiment is that the inner joint part 2₇ comprises two groups of webs 3', 3" whose webs differ from one another, because there is provided a first group of webs 3' whose outer faces 5', in a cross-sectional view, at least by means of a partial portion, radially extend as far as the enveloping spherical face. In the mounted condition of the inner joint part 2₇, the webs of said first group of webs 3' are in contact with the ball cage (not illustrated) to be able to guide same.

The webs of a second group of webs 3", on the other hand, are radially inwardly set back relative to the enveloping spherical face, so that the outer faces 5" are arranged along the entire length of the respective web 3" at a radial distance from the enveloping spherical face. In consequence, in the mounted condition of the inner joint part, between outer faces 5" of the second group of webs 3" and the spherical inner face of the ball cage (not shown here), there are formed radial gaps, i.e. the second webs 3" are normally not in contact with the ball cage. This is advantageous in that the friction forces acting between the inner joint part and the ball cage have been reduced once again, which has an advantageous effect on the service life and performance losses of the joint.

More particularly, it is proposed that the outer contours of the first webs 3' and of the second webs 3", if viewed in a cross-section and a longitudinal section, are identical in design, the advantage being that - if due to the production tolerances or hardness distortions, the ball cage, if deviating from an ideally round shape when under torque load - nevertheless comes into contact with one or several of the second webs 3", there occurs a uniform load bearing pattern between the inner face of the ball cage and the first webs 3' and second webs 3" respectively. In principle, however, it is also conceivable for the outer contours of the second webs to deviate from the outer contours of the first webs.

It can be seen that the inner joint part in the present embodiment comprises six ball tracks 4 and, accordingly, six webs 3, wherein the webs of the first group and the webs of the second group are arranged so as to alternate around the circumference. This measure ensures in an advantageous way that the ball cage is supported in three regions around the circumference, which ensures accurate centring of the ball cage coaxially relative to the inner joint part. However, it goes without saying that the inner joint part can also comprise any other number of ball tracks and webs, more particularly eight. Furthermore, the arrangement of the webs can also differ from an alternating arrangement. For example, it is also possible for two first webs to be arranged adjacent and which, in the circumferential direction, are followed by a second web.

Figure 8 shows an inventive constant velocity joint with an inventive inner joint part in the embodiment according to Figure 1. The constant velocity universal joint is provided in the form of a Rzeppa fixed joint which, therefore, is also referred to as a RF joint. The Rzeppa joint serves to transmit torque between two rotating components, with angular movements being possible between the two components. The constant velocity fixed joint comprises an outer joint part 21 with outer ball tracks 22, an inner joint part 2 with inner ball tracks 4, torque transmitting balls 23 which are guided in pairs of tracks each pair consisting of one outer and one inner ball track 22, 4, as well as a ball cage 14 with circumferentially distributed cage windows 24 receiving the balls 23. The balls 23 are held by the ball cage 24 in a common central plane E and when the joint is articulated they are guided on to the angle-bisecting plane between the outer joint part 21 and the inner joint part 2.

In Rzeppa fixed joints, the outer and inner ball tracks 22, 4, if viewed in a longitudinal section, extend arch-like around a centre over their length. The special feature of the present Rzeppa fixed joint consists in that the outer contours of the webs 3 of the inner joint part 2 are designed according to the embodiment shown in Figure 1. In other words, in a cross-sectional view the webs 3 each comprise first portions for guiding the ball cage and circumferentially adjoining second portions which are radially inwardly set back relative to the inner face 13 of the ball cage 14. To complete the picture, it should be mentioned that the inner joint part of the Rzeppa fixed joint as illustrated can, of course, also comprise webs with outer contours as shown in any of Figures 2 to 7.

The inventive constant velocity universal joint as illustrated in Figure 8 is mentioned by way of example in order to show in which types of joint the inventive inner joint 2 can be used. Generally speaking, the teaching of the invention regarding the reduced guiding face of the inner joint part 2 can be transferred to all those constant velocity universal joints wherein the ball cage is guided on the preferably spherical guiding face of the inner joint part 2. This applies to fixed joints, for example joints with undercut-free tracks, which are also referred to as UF joints (undercut-free joints) or to counter track joints with first and second pairs of tracks which open in opposite directions, as well as to plunging joints such as they are shown in the above-mentioned DE 10 2005 063 006 A1 which are also referred to as DO joints. All the above-mentioned constant velocity universal joints with an inventive inner joint part are advantageous in that the guiding faces of the inner joint part and, respectively, the contact faces between the webs and the ball cage have been reduced in size, which leads to an improved lubricant supply to the contact faces and to less friction in the entire joint and thus to a reduction in performance losses.

List of reference numbers

2 inner joint part

3 web

4 ball track

5 outer face

6 end face

7 end face

8 through-aperture

9 first portion

10 second portion

11 free face

12 guiding face

13 inner face

14 ball cage

15 chamfer

16 gap

17 flattened portion

18 reduced portion

19 —

20 constant velocity universal joint

21 outer joint part

22 outer ball track

23 ball

24 cage window

A longitudinal axis

B width

D diameter

E plane

K spherical face

R radius

S plane of symmetry

O centre of curvature

Claims

1. An inner joint part for a constant velocity universal joint with an axis of rotation A, comprising a plurality of circumferentially distributed ball tracks (4) for receiving torque transmitting balls (23), and a plurality of circumferentially distributed webs (3) which are formed between two circumferentially adjoining ball tracks (4), said webs (5) each comprising an outer face (5),

wherein an enveloping spherical face (K) of the inner joint part (2) comprises a diameter (D),

wherein the outer faces (5) of at least some of the webs (3) - if viewed in at least one cross-section - each comprise a first portion (9) for guiding a ball cage (14) and at least one second portion (10) which is arranged at a distance from the enveloping spherical face (K) of the inner joint part (2).

2. An inner joint part according to claim 1,

characterised in that the first portion (9) is arranged centrally and that the at least one second portion (10) is arranged so as to laterally adjoin the first portion (9).

3. An inner joint part according to claim 1 or 2,

characterised in

that the outer face (5) in a cross-sectional view is designed to be symmetric relative to the plane of symmetry (S), wherein a maximum of the first portion is positioned in the region of the plane of symmetry (S).

4. An inner joint part according to any one of claims 1 to 3,

characterised in

that the first portion (9) and the at least one second portion (10) continuously change into one another.

5. An inner joint part according to any one of claims 1 to 4,

characterised in

that the first portion (9) of the outer face (5) extends substantially line-like in the longitudinal direction. (Figure 1)

6. An inner joint part according to any one of claims 1 to 5,

characterised in that the first portion (9) and the at least one second portion (10) in a cross-sectional view comprise a common radius (R_A) which is smaller than half die diameter (D) of the enveloping spherical face (K), i.e. R_A < D/2. (Figure 1).

7. An inner joint part according to claim 6,

characterised in

that the first radius (R_A) is greater than/equal to one quarter of the diameter (D) of the enveloping spherical face, i.e. R_A > D/4.

8. An inner joint part according to any one of claims 1 to 4,

characterised in

that the first portion (9) of the outer face (5) extends substantially surface-like in the longitudinal direction. (Figures 2-4)

9. An inner joint part according to any one of claims 1 to 8,

characterised in

that the first portion (9) comprises a first radius (R_A1) which is smaller than/equal to half the diameter (D/2) of the enveloping ball face (K), i.e.

that the second portion (10) of the outer face (5) comprises a second radius (R_A2) which is smaller than the first radius (R_Ai) of the first portion (9), i.e. R_Λ2 < R_AL (Figures 2-4)

10. An inner joint part according to any one of claims 1 to 9,

characterised in

that the ratio of the extension (B1) of the first portion (9) in the circumferential direction to the entire extension (B) of the outer face (5) in the circumferential direction is smaller than two thirds, i.e. B1/B < 2/3.

11. An inner joint part according to any one of claims 1 to 10,

characterised in

that the outer face (5) of at least one of the webs (3) comprises at least one flattened portion (17) which is arranged more particularly in an axially central region of the first portion (9) of said at least one web (3). (Figure 4)

12. An inner joint part according to any one of claims 1 to 11 ,

characterised in

that the at least one web (3), if viewed in a cross-section, comprises chamfers (15) in the region of transition between the outer face (5) and the adjoining ball tracks (4). (Figure 3)

13. An inner joint part according to any one of claims 1 to 12,

characterised in that, if viewed in a longitudinal section, at least one of the webs (3) comprises a reduced portion (18) for mounting the ball cage (14). (Figures 5, 6)

14. An inner joint part according to any one of claims 1 to 13,

characterised in

that the outer faces (5), if viewed in a longitudinal section, each comprise at least one portion with a radius (R_L) which is smaller than/equal to half the diameter (D) of the enveloping ball face (K), i.e. R_L < D/2.

15. An inner joint part according to any one of claims 1 to 14,

characterised in

that there are provided second webs (3") which are designed in such a way that outer faces (5) of the second webs (3") are reduced along their entire length relative to the enveloping spherical face (K). (Figure 7)

16. An inner joint part according to claim 15,

characterised in

that the second webs (3") and the first webs (3') which comprise the portions (9) for guiding the ball cage (14) are arranged alternately around the circumference.

17. A constant velocity universal joint comprising an outer joint part (21) with outer ball tracks (22); an inner joint part (2) with inner ball tracks (4); torque transmitting balls (23) which are guided in pairs of tracks, each consisting of an outer ball track (22) and an inner ball track (4); a ball cage (14) with windows (24) in which there are received the torque transmitting balls (23);

characterised in that the inner joint part (2) is designed in accordance with any one of claims 1 to 16.

18. A constant velocity universal joint according to claim 17,

characterised in

that a spherical inner face (13) of the ball cage (14) is greater than the diameter (D) of the enveloping spherical face (K) of the inner joint part (2).