Tripod star for a tripod joint

Abstract

A tripod star (10) for a tripod joint comprises an annular body (11, 11') with a through-opening (12, 12') which extends in the direction of a longitudinal axis (A) of the annular body (11, 11') and has an internal toothing (12a, 12a') for coupling to a profiled shaft, pins (13, 13') with a pin axis (Z) for rotatably supporting a respective tripod roller about the pin axis (Z), wherein the pin axis (Z) is radial to the longitudinal axis (A) of the annular body (11, 11'), wherein on the outer circumference of the annular body (11, 11') between the pins (13, 13') vertices of the annular body (11, 11') form a vertex plane (S) perpendicular to the longitudinal axis (A) in the direction of the longitudinal axis (A). A resulting force application point on the journals (13, 13') is offset from the vertex plane (S) of the annular body (12, 12') in the direction of the longitudinal axis (A). Furthermore, a tripod joint with such a tripod star is specified.

Description

[0001] The invention relates to a tripod star for a tripod joint, comprising an annular body with a through-opening which extends in the direction of a longitudinal axis of the annular body and has an internal toothing for coupling to a profiled shaft, as well as pins with a pin axis for rotatably supporting a tripod roller about the pin axis, wherein the pin axis is radial to the longitudinal axis of the annular body, and wherein on the outer circumference of the annular body between the pins, vertices of the annular body in the direction of the longitudinal axis form a vertex plane perpendicular to the longitudinal axis.

[0002] Furthermore, the invention relates to a tripod joint with such a tripod star.

[0003] A generic tripod star and a tripod joint with such a star are known, for example, from DE 102 46 169 A1 and DE 10 2021 210 452 A1.

[0004] Tripod joints are increasingly being operated at their performance limits. The reasons for this are diverse and range from increased drive power and compact installation spaces to weight and cost considerations.

[0005] Due to technical constraints, larger sizes often cannot be used or can only be used in conjunction with other disadvantages.

[0006] There is a need to achieve the highest possible performance in a small installation space while using existing resources as sparingly as possible.

[0007] Dynamic alternating load tests have shown that there is room for improvement, particularly on the tripod star side. A potential cause of premature failure of tripod stars, particularly in DT / AAR joints, has been identified as a tendency toward unfavorable force flow from the tripod star's journal to the profile shaft, which is connected to the tripod star via a toothed system. This toothing is typically hardened.

[0008] The load-bearing capacity of the gearing could be further improved through high dimensional accuracy. However, this is difficult with hardened structures, as this would require expensive manufacturing processes such as hard broaching.

[0009] In today's tripod stars of the type mentioned above, the resulting force introduction point from the tripod roller into the journal lies in a common plane with the vertex plane of the ring body and the central axis of a neck connecting the journal to the ring body.

[0010] Furthermore, it is known to angle the pin axis as well as the center axis of the neck relative to the plane of symmetry of the annular body, as disclosed, for example, in EP 0 453 334 B1, WO 93 / 22577A1, and DE 196 81 477 C2. Furthermore, WO 95 / 23928 A1 discloses angling the pin axes in the circumferential direction around the longitudinal axis, so that the pins no longer extend radially relative to the longitudinal axis of the annular body.

[0011] Furthermore, JP 2015 - 214 995 A shows another tripod joint and a constant velocity joint assembly to which the tripod joint is attached.

[0012] Based on this, the invention is based on the object of demonstrating solutions which allow the component performance to be further improved with a compact design and simple production.

[0013] This object is achieved by a tripod star having the features of patent claim 1. For this purpose, the tripod star according to the invention is provided with a resulting force application point on the pin being offset from the apex plane of the annular body in the direction of the longitudinal axis.

[0014] At high torques, this allows a larger portion of the power transmission to be shifted toward the end of the spline shaft, relieving the primary half of the tripod star and thus protecting it from overload. This improved power flow from the journal to the spline shaft allows higher torque transmission, especially under alternating loads.

[0015] The power transmission can be distributed over a larger area of ​​the internal gearing, resulting in more homogeneous force transmission and a reduction in load peaks. The available gear length is thus better utilized.

[0016] At high torques, a slight twist of the tripod star relative to the spline shaft also occurs, resulting in a higher partial contact force in the desired area of ​​gear engagement. This allows for torque-dependent load distribution.

[0017] The invention thus describes an asymmetrical tripod star whose geometry is designed in such a way that increased torques lead to a change in the force flow from the tripod star to the profile shaft and thus the load capacity is increased.

[0018] In contrast to tripod stars with angled pins, the solution according to the invention can be integrated into the production of conventional, symmetrical tripod stars on existing equipment without great additional effort.

[0019] The resulting force application point is the point at which the force is transferred between a roller and the pin of the tripod star. This ultimately depends on the pin contour with which the roller engages. With a single-point contact, usually realized via a ball head shape on the pin, the resulting force application point coincides with the single-point contact. However, pin geometries are also possible in which the roller has two or more contact points with the pin, for example, through a spline contour or similar. In this case, the resulting force application point represents the center of gravity of the contact points.

[0020] Particular embodiments of the invention are the subject of further patent claims.

[0021] In particular, the pin axis can be offset from the apex plane in the direction of the longitudinal axis in order to achieve the improved force flow.

[0022] According to another particular embodiment of the invention, the annular body can be designed asymmetrically between the pins in the direction of the longitudinal axis. Such an asymmetric design of the annular body enables homogenization of the force flow through different torsional stiffnesses of the annular body in the direction of its longitudinal axis.

[0023] According to a further particular embodiment of the invention, the pin axis can be axially offset from the center plane of the annular body in the direction of the longitudinal axis of the same.

[0024] According to a further particular embodiment of the invention, alternatively or additionally, the apex plane can be axially offset from the center plane of the annular body in order to achieve an axial offset between the pin axis and the apex plane.

[0025] The pin axis and vertex plane can be located on opposite sides of the center plane of the ring body. However, the pin axis and vertex plane can also be located in a common half of the ring body with respect to the center plane.

[0026] Furthermore, the vertex plane can coincide with the center plane of the ring body in the direction of its longitudinal axis, whereas the pin axes are offset from the center plane. In this case, the ring body can be designed symmetrically with respect to the center plane, for example, in a conventional construction. The offset is then primarily achieved via the pins.

[0027] According to a further alternative particular embodiment of the invention, however, the vertex plane is axially offset from the center plane of the annular body, while the pin axis coincides with the center plane of the annular body.

[0028] Furthermore, as already mentioned, it is possible to offset both the vertex plane and the pin axis relative to the center plane of the ring body in the direction of the longitudinal axis of the same.

[0029] According to a further particular embodiment of the invention, the pins can each be coupled to the annular body via a tapered neck, wherein the neck has a center that is asymmetrical to the pin axis and / or asymmetrical to the apex plane. Such an asymmetrical pin neck geometry can further enhance the effect explained above.

[0030] Furthermore, in this sense, additional weakening and / or reinforcing structures can be provided on the outer circumference of the ring body in areas between the pins.

[0031] In particular, according to another particular embodiment of the invention, the annular body can have at least one recess on its outer circumference between the pins, which is recessed into a flat or convexly curved wall section, preferably forming an edge with the latter, wherein the arrangement of the at least one recess on the annular body is asymmetrical in the direction of the longitudinal axis. By designing such recesses, the loading in the toothing can be further influenced. The term "edge" in this case includes conventional radii of curvature in the transition from the recess to the surrounding areas.

[0032] In one embodiment, the depth of the at least one recess in the wall section can be provided to decrease toward the apex plane. This can, for example, achieve a decidedly higher degree of compliance in an axial end section of the annular body.

[0033] In a further embodiment, which can be combined with the aforementioned embodiment, the annular body can have at least one axial rib on its outer circumference between the pins, which rises above a flat or convexly outwardly curved wall section, wherein the ribbing by the at least one axial rib on the annular body is asymmetrical in the direction of the longitudinal axis.

[0034] The formation of at least one recess and / or at least one axial rib can, in particular, already occur during the production of the basic shape of the ring body, for example, through a forming process such as cold extrusion. Recesses can also be subsequently introduced into an already manufactured ring body in order to fine-tune the torsional stiffness along the longitudinal axis if necessary. Reworking of recesses and / or axial ribs prefabricated by forming or casting is also possible.

[0035] The tripod star explained above is preferably part of a tripod joint, which in addition to this further comprises: tripod rollers arranged on the journals, which are either mounted by means of rolling bearings directly on a cylindrical outer surface of the journal or which each additionally have an inner ring which is mounted on a spherical journal outer peripheral surface, as well as an outer joint part with mutually parallel raceway pairs, wherein a tripod roller is guided axially in each raceway pair, and furthermore a profile shaft with an external toothing which engages with the internal toothing of the ring body.

[0036] Such a tripod joint is characterized by a higher torque transmission capacity than conventional tripod joints of the same size. Nevertheless, the manufacturing effort remains comparable, as expensive technologies such as hard broaching of the toothing structure between the tripod star and the profiled shaft are avoided. Furthermore, such a tripod joint better meets the requirements of electric vehicles with regard to high alternating loads. The system can act as a damping element during severe load changes.

[0037] In the following, ways of implementing the invention are explained in more detail using exemplary embodiments illustrated in the drawing. The drawing shows: Fig. 1 a spatial view of a tripod star according to a first embodiment of the invention for a double roller tripod joint, in particular of the DT / AAR type, Fig. 2 a front view of the tripod star from Fig. 1 seen in the direction of its longitudinal axis, Fig. 3 a sectional view of the tripod star from Fig. 1 with additionally indicated profile wave, Fig. 4 a schematic representation to illustrate the offset of the force application point on the pin relative to the vertex plane of the ring body, Fig. 5 a schematic representation to illustrate another possibility of offsetting the force application point on the pin relative to the vertex plane of the ring body, Fig. 6 a spatial view of a tripod star according to a second embodiment of the invention for a single tripod joint, in particular of the TG / Gl type, Fig. 7 a schematic representation to illustrate the offset of the force application point on the journal relative to the vertex plane of the ring body for a tripod star according to Fig. 6, Fig. 8 a schematic representation to illustrate a further possibility of offsetting the force application point on the pin relative to the vertex plane of the ring body, Fig. 9 a representation to illustrate a recess / axial rib on the outer circumference of the ring body between the pins, Fig. 10 a further illustration of recesses / axial ribs on the outer circumference of the ring body between the pins, Fig. 11 is a diagram illustrating a single-point contact on the pin, and in Fig. 12 a diagram illustrating a two-point contact on the pin.

[0038] Fig. 1 shows a tripod star 10 for a tripod joint, which is particularly suitable for use in a sideshaft of a passenger car or light commercial vehicle, but can also be used for other purposes.

[0039] The Fig. The tripod star 10 shown in Figure 1 for a tripod joint of the DT / AAR type is merely exemplary and serves to illustrate the inventive principle in a broader context. However, the inventive principle can also be applied to tripod stars in other types of tripod joints. Expressly mentioned here are so-called single tripods of the TG / GI type, for which Fig. 6 shows an example of a tripod star according to the invention, without the invention being limited to this specific individual case.

[0040] The tripod star 10 has an annular body 11 with a through-opening 12. The through-opening 12 extends in the direction of a longitudinal axis A of the annular body 11.

[0041] The through-hole 12 is provided with an internal toothing 12a, which enables coupling with a Fig. 3 serves as the profiled shaft, which is only indicated. The internal toothing 12a can, for example, be a serrated toothing. However, other profiles of the internal toothing 12a are also possible.

[0042] The tripod star 10 further comprises several, preferably three, pins 13, each with a pin axis Z, which project radially from the annular body 11. The pin sections 13 are preferably equally spaced in the circumferential direction.

[0043] The pin axes Z of the pin sections 13 fall into a common plane perpendicular to the center plane M of the ring body 11. In the present case, the center plane M is understood to be the plane which represents the geometric center between the axial ends of the ring body 11 and extends perpendicular to its longitudinal axis A.

[0044] Each pin 13 of the Fig. 1 to 4 has a journal outer peripheral surface 13a for supporting a tripod roller (not shown in detail). The journal outer peripheral surfaces 13a are rotationally symmetrical to the respective journal axis Z and preferably curved outward. The apex of the curvature can be located approximately at the level of the center of the respective journal outer peripheral surface 13a, viewed in the direction of the journal axis Z.

[0045] For a tripod star 10' for a single tripod joint as in Fig. 6, the curvature on the outer peripheral section 13a is omitted.

[0046] The pins 13 can each be connected to the annular body 11 via a tapered neck 14. In particular, the pins 13 and the annular body 11, including the necks 14, can be formed integrally with one another.

[0047] For the design of the tripod rollers and the outer joint part of the tripod joint that guides them, reference is made to DE 10 2021 210 452 A1 as an example.

[0048] A tripod joint according to the invention accordingly comprises a tripod star 10 of the aforementioned type, tripod rollers arranged on the pin 13, which are either mounted directly on a cylindrical outer surface of the pin by means of rolling bearings or which each additionally have an inner ring which is mounted on a spherical pin outer peripheral surface, an outer joint part with mutually parallel raceway pairs, wherein a tripod roller is guided axially in each of the raceway pairs, and a profile shaft with an external toothing which engages with the internal toothing of the ring body.

[0049] The ring body 11 has a torus shape between the pins with a profile whose outer contour is in the Fig. 3, a vertex is formed in the direction of the longitudinal axis, at which the outer contour between the pins is furthest from the longitudinal axis A. The corresponding vertices can, in particular, be connected to one another to form an annular line. However, smaller interruptions in the circumferential direction are also possible. In this case, the majority of the vertices lie in a common plane perpendicular to the longitudinal axis A. This common plane of the vertices is also referred to below as the vertex plane S.

[0050] According to the invention, when a torque is applied, a resulting force application point on the pin 13 is offset relative to the apex plane S of the annular body 11 in the direction of the longitudinal axis A. The corresponding axial offset is designated by x in the drawing.

[0051] This offset x results in a larger portion of the force transmission being shifted toward the corresponding end of the ring body 12 when a high torque is applied, preferably toward the end closest to the free end of the profile shaft. This results in a more even force distribution in the area of ​​the tooth engagement between the internal toothing 12a of the ring body 11 and the corresponding external toothing of the profile shaft, since a larger axial length of the toothing is effectively utilized for torque transmission.

[0052] At high torques, the offset x also causes a slight twist of the tripod star 10 relative to the splined shaft. This tends to increase the contact force in the gearing in the desired area.

[0053] In this way, a torque-dependent load distribution in the gearing can be achieved.

[0054] To explain the resulting force application point, please refer to the Fig. 11 and Fig. 12.

[0055] In Fig. Figure 11 shows a tripod star 10 with a single-point contact P1 on the pin 13. During operation of a tripod joint, the force is transmitted between a tripod roller inner ring and the pin 13. In this case, the single-point contact P1 represents the resulting force application point.

[0056] Fig. Figure 12 shows an example of a multi-point contact using a two-point contact as an example. In this case, the force is transmitted at the two contact points P2 due to the contour of the pin 13. For this purpose, the pin 13 can be slightly flattened in the direction of rotation of the tripod star 10 and the longitudinal axis A, for example, by a spline contour, so that two contact points P2 are created with the tripod roller inner ring in the direction around the pin axis Z. In this case, the resulting force application point represents the center of gravity of the two contact points P2, i.e., the resulting force application point lies midway between the two actual contact points P2.

[0057] The offset x can be realized in various ways, as explained in more detail below using non-limiting examples. In the drawing, the offset x is not shown to scale.

[0058] In the Fig. 4 and Fig. 5, the tenon axis Z is offset from the vertex plane S in the direction of the longitudinal axis A. Such an offset x can in principle be made independently of the center plane M, ie neither the tenon axes Z nor the vertex plane S must coincide with the center plane. The variants in the Fig. 4 and Fig. 5 therefore represent only selected variants in the form of non-limiting embodiments.

[0059] In principle, as in Fig. 3, the ring body 11 between the pins 13 can be designed asymmetrically in the direction of the longitudinal axis A in order to specifically adjust the torsional stiffness of the tripod star along the longitudinal axis A.

[0060] Fig. 4 illustrates a corresponding example in which the vertex plane S is axially offset from the center plane M of the ring body 12, whereas the pin axes Z of the pins 13 coincide with the center plane M of the ring body 11.

[0061] Fig. Figure 5 shows another example in which the vertex plane S coincides with a center plane M of the ring body 11 in the direction of its longitudinal axis A. In contrast, the pin axes Z of the pins 13 are each axially offset from the center plane M.

[0062] Due to the radial alignment of the pins Z to the longitudinal axis A, such tripod stars can be integrated into a production process in which symmetrical tripod stars are also manufactured, ie tripod stars in which the pin axes Z and the vertex plane S coincide.

[0063] In a modification of the illustrated embodiments, it is also possible to slightly angle the pin axes Z in the direction of the longitudinal axis A, so that the pin axes no longer run radially to the longitudinal axis A. Alternatively or additionally, an angle in the circumferential direction can also be performed. However, both of these options will complicate any machining of the pins 13.

[0064] As already mentioned, the pins 13 can each be connected to the annular body 11 via a tapered neck 14. The above-explained effect of equalizing the load in the toothing between the annular body 11 and the profile shaft can be influenced, in particular further enhanced, by an asymmetric cross-sectional geometry of the neck 14. In particular, the neck 14 can have a center that is arranged asymmetrically to the pin axis Z and / or asymmetrically to the apex plane S. In this case, the center of the neck is related to a cross-sectional area that is orthogonal to the radial direction of the longitudinal axis A.

[0065] Alternatively or additionally, the cross-section of the neck 14 perpendicular to the pin axis Z may deviate from a circular shape, for example, be oval.

[0066] Fig. Figure 6 shows another embodiment of a tripod star 10', which, as already mentioned above, is designed as a tripod star for a single tripod joint. Accordingly, the outer circumference of the pins 13' around the pin axes Z is not spherical, but cylindrical. A pin neck is not shown in this embodiment, but can be optionally provided, as in the first embodiment.

[0067] Here again, as in Fig. 6, the ring body 11' between the pins 13' may be formed asymmetrically in the direction of the longitudinal axis A, wherein the vertex plane S has an offset x relative to the center plane M.

[0068] Fig. 7 illustrates this by way of example in a variant in which the vertex plane S is axially offset from the center plane M of the ring body 11', whereas the pin axes Z of the pins 13' coincide with the center plane M of the ring body 11'.

[0069] Fig. Figure 8 shows a further embodiment in which the vertex plane S coincides with a center plane M of the annular body 11' in the direction of its longitudinal axis A. In contrast, the pin axes Z of the pins 13' are each axially offset by x relative to the center plane M.

[0070] In a modification of the illustrated embodiments, it is again possible to additionally angle the pin axes Z slightly in the direction of the longitudinal axis A, so that the pin axes Z no longer run radially to the longitudinal axis A. Likewise, alternatively or additionally, an angle can also be carried out in the circumferential direction around the longitudinal axis A.

[0071] Furthermore, it is possible to further influence the load distribution in the toothing by intervening in the outer contour of the ring body 11 or 11' between the pins 13 or 13' in order to even out the force transmission and to attenuate local force peaks.

[0072] For this purpose, the annular body 11 of the tripod star 10 (analogously also for the tripod star 10') can have at least one recess 15 on its outer circumference between the pins 13. Preferably, similar recesses 15 are provided between adjacent pairs of pins 13.

[0073] The recess 15 can be recessed into a flat or convexly curved wall section 16 of the outer circumference of the annular body 11, preferably forming an edge with this wall section 16 that delimits the recess 15. The recess 15 can be concavely curved inward. In the case of a convexly curved wall section 16, the recess 15 can also be a flattened portion, in particular a flat flattened portion or a convex curvature with a larger radius of curvature.

[0074] Preferably, the arrangement of the at least one recess 15 on the annular body 11 is asymmetrical in the direction of the longitudinal axis A, so that different torsional stiffnesses result along the longitudinal axis.

[0075] For example, a recess 15 can extend from a frontal axial end of the annular body 11 parallel to the longitudinal axis A in the direction of the vertex plane S. The recess 15 can end before reaching the vertex plane S, but can also slightly penetrate the vertex towards the other side.

[0076] Furthermore, it can be provided that the deepening of the recess 15 into the wall section 16 decreases towards the apex plane S.

[0077] Furthermore, in a further embodiment, the annular body 11 may have at least one axial rib 17 on its outer circumference between the pins 13. Preferably, similar axial ribs 17 are provided between adjacent pairs of pins 13.

[0078] The axial rib 17 can rise above a flat or convexly outwardly curved wall section 16 of the outer circumference of the annular body 11, wherein the ribbing of the annular body 11 by the axial ribs 17 in the direction of the longitudinal axis is preferably again asymmetrical.

[0079] The axial rib 17 may end before reaching the apex plane S, but may also slightly exceed the apex towards the other side.

[0080] The invention has been explained in more detail above with reference to exemplary embodiments and further modifications. In particular, individual technical features explained above in the context of further individual features can be implemented independently of these and in combination with further individual features, even if not expressly described, as long as this is technically feasible. The invention is therefore expressly not limited to the described exemplary embodiments and modifications, but encompasses all configurations defined by the patent claims. List of reference symbols 10, 10' tripod star 11, 11' ring body 12, 12' passage opening 12a, 12a' internal gearing 13, 13' cones 13a Pin outer peripheral surface 14 Neck 15 Recess 16 Wall section on the outer circumference of the ring body between the pins 17 Axial rib on the outer circumference of the ring body between the pins A Longitudinal axis M Middle level P1 single-point contact P2 two-point contact S vertex plane Z pin axis x offset

Claims

[1] Tripod star for a tripod joint, comprising an annular body (11, 11') with a through-opening (12, 12') which extends in the direction of a longitudinal axis (A) of the annular body (11, 11') and has an internal toothing (12a, 12a') for coupling to a profile shaft, Pin (13, 13') with a pin axis (Z) for rotatably supporting a tripod roller around the pin axis (Z), wherein the pin axis (Z) is radial to the longitudinal axis (A) of the annular body (11, 11'), wherein on the outer circumference of the annular body (11, 11') between the pins (13, 13') vertices of the annular body (11, 11') form a vertex plane (S) perpendicular to the longitudinal axis (A) in the direction of the longitudinal axis (A), characterized by , that a resulting force application point on the pins (13, 13') is offset from the vertex plane (S) of the ring body (12, 12') in the direction of the longitudinal axis (A). [2] Tripod star according to claim 1, characterized by that the tenon axis (Z) is offset from the vertex plane (S) in the direction of the longitudinal axis (A). [3] Tripod star according to claim 1 or 2, characterized by that the annular body (11, 11') is formed asymmetrically between the pins (13, 13') in the direction of the longitudinal axis (A). [4] Tripod star according to one of claims 1 to 3, characterized by that the pin axis (Z) is axially offset from a center plane (M) of the annular body (12, 12') in the direction of the longitudinal axis (A) thereof. [5] Tripod star according to one of claims 1 to 4, characterized by that the vertex plane (S) is axially offset from the center plane (M) of the ring body (11, 11'). [6] Tripod star according to one of claims 1 to 5, characterized bythat the pins (13) are each coupled to the annular body (11) via a tapered neck (14) and the neck (14) has a center which is asymmetrical to the pin axis (Z) and / or asymmetrical to the vertex plane (S). [7] Tripod star according to one of claims 1 to 6, characterized by that the annular body (11) has at least one recess (15) on its outer circumference between the pins (13), which is recessed into a flat or convexly outwardly curved wall section (16), wherein the arrangement of the at least one recess (15) on the annular body (11) is asymmetrical in the direction of the longitudinal axis (A). [8] Tripod star according to claim 7, characterized by that the deepening of the at least one recess (15) in the wall section (16) decreases towards the apex plane (S). [9] Tripod star according to one of claims 1 to 8, characterized bythat the annular body (11) has at least one axial rib (17) on its outer circumference between the pins (13), which rises above a flat or convexly outwardly curved wall section (16), wherein the ribbing by the at least one axial rib (17) on the annular body (11) is asymmetrical in the direction of the longitudinal axis (A). [10] Tripod joint, comprising a tripod star (10, 10') according to one of the preceding claims, tripod rollers arranged on the journals (13, 13'), which are either mounted directly on a cylindrical outer surface of the journal (13') by means of rolling bearings or which (13) each additionally have an inner ring which is mounted on a spherical journal outer peripheral surface, an outer joint part with parallel pairs of raceways, with a tripod roller being guided axially in each pair of raceways, and a profile shaft with an external toothing which engages with the internal toothing (12a, 12a') of the annular body (11, 11').

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