CONSTANT VELOCITY JOINT

Abstract

The present disclosure relates to a constant-velocity joint for torque-transmission, in which a first type of track pairs of ball tracks is configured in such a manner that the centers of curvature of the center lines of the ball tracks are situated in the joint center plane when the joint is straight. A second type of track pairs of ball tracks is configured in such a manner that their center lines have at least two portions. The respective center line of the outer ball tracks of the second type of track pairs has at least one inner portion and one outer portion, wherein the inner portion is situated on the connection side of the outer joint portion, while the outer portion is situated on the opening side of the outer joint portion, and the inner portion is curved.

Claims

1. A constant-velocity rotary joint for torque transmission, comprising: an outer joint portion with several outer ball tracks, an inner joint portion with several inner ball tracks, torque-transmitting balls, which are each guided in track pairs of outer ball tracks and inner ball tracks, and a cage, which accommodates the torque-transmitting balls in circumferentially distributed cage windows and retains them in a common joint center plane when the constant-velocity rotary joint is straight, wherein the outer joint portion has a longitudinal axis and, situated axially opposite each other, an opening side and a connecting part, and the paths of the centers of the torque-transmitting balls is in each case defined as a center line of the respective ball track, and a first type of track pairs of ball tracks is configured so that the centers of curvature of the center lines of the ball tracks are situated in the joint center plane when the joint is straight, while a second type of track pairs of ball tracks is configured so that their center lines have at least two portions, and the respective center line of the outer ball tracks of the second type of track pairs has at least one inner portion and one outer portion, wherein the inner portion is situated on a connection side of the outer joint portion, while the outer portion is situated on a opening side of the outer joint portion, and the inner portion is curved and a center of curvature of the inner portion, when the joint is straight, is situated within a hollow volume of the outer joint portion, offset from the joint center plane towards the opening side, while the center line widens through the outer portion towards the opening side.

2. The constant-velocity rotary joint of claim 1, wherein the center line widens in a linear manner through the outer portion.

3. The constant-velocity rotary joint of claim 1, wherein the at least two portions are curved in opposite directions and the center of curvature of the outer portion is situated outside the hollow volume of the outer joint part.

4. The constant-velocity rotary joint of claim 3, wherein the ratio of a curvature radius of the inner portion to the diameter of an associated ball between 1.5 and 2.5.

5. The constant-velocity rotary joint of claim 3, wherein the ratio of a curvature radius of the outer portion to the diameter of an associated ball is between 1.0 and 10.

6. The constant-velocity rotary joint of claim 3, wherein the center of curvature of the outer portion is offset from the joint center plane towards the opening side.

7. The constant-velocity rotary joint of claim 1, wherein the ratio of a curvature radius of the center lines of the first type of track pairs to the diameter of an associated ball is between 1.5 and 2.5.

8. The constant-velocity rotary joint of claim 1, wherein the at least two portions of the center lines of the ball tracks of the second type of track pairs are at least two first portions, wherein at least two second portions follow the at least two first portions of the center lines of the ball tracks of the second type of track pairs.

9. The constant-velocity rotary joint of claim 8, wherein the at least two second portions are formed in a linear or a curved manner.

10. The constant-velocity rotary joint claim 1, that wherein an equal number of track pairs of both first type and second type is provided and the track pairs of the first type and the second type alternate.

11. The constant-velocity rotary joint of claim 1, wherein the number of torque-transmitting balls is at least eight.

12. The constant-velocity rotary joint of claim 1, wherein the first type of track pairs of ball tracks is configured in such a manner that the respective center line of the outer ball tracks of the first type of track pairs has at least one inner portion and one outer portion, wherein the inner portion is situated on the connection side of the outer joint portion, while the outer portion is situated on the opening side of the outer joint portion, and the center of curvature of the inner portion is situated in the joint center plane, while the center of curvature of the outer portion is situated outside the outer joint part.

Description

[0021] In the drawings:

[0022] FIG. 1 shows a front view onto the opening side of an embodiment of the constant-velocity rotary joint according to the embodiment in the straight position;

[0023] FIG. 2 shows a sectional view of the embodiment of FIG. 1 along the section line E-E;

[0024] FIG. 3 shows a schematic representation of the configuration of center lines of two types of track pairs in a constant-velocity rotary joint according to FIG. 2;

[0025] FIG. 4 shows a front view onto the opening side of the constant-velocity rotary joint of FIG. 1 in the bent position;

[0026] FIG. 5 shows a sectional view of the constant-velocity rotary joint according to FIG. 4 along section line A-A;

[0027] FIG. 6 shows a sectional view of the constant-velocity rotary joint according to FIG. 4 along section line C-C.

[0028] An embodiment of the constant-velocity rotary joint 10 according to the embodiment is shown in FIG. 1 and the associated longitudinal section E-E along the two longitudinal axes La, Li of the joint of FIG. 2. It has a cup-shaped outer joint portion 11 and an inner joint portion 12. A number of eight balls with an identical diameter, of which two balls are denoted with the reference numerals 30 and 31 by way of example, are disposed between the outer joint portion 11 and the inner joint portion 12. These balls are, on the one hand, guided in outer ball tracks 20a, 20b and, on the other hand, in inner ball tracks 40a, 40b, wherein, also, only the associated ball tracks are given reference numerals. The outer ball tracks 20a, 20b are formed on an inner circumferential surface of the outer joint portion 11 and extend from an opening side 60 towards a connection side 61 of the outer joint portion 11. The outer joint portion 11 forms a shaft journal (not shown), for example, at its connection side 61.

[0029] The inner joint portion 12 inserted into the hollow volume formed by the outer joint portion 11 respectively forms inner ball tracks 40a, 40b, which are opposite, in pairs, to the outer ball tracks 20a, 20b, accommodating one ball 30, 31 in each case. The inner joint portion 12 forms an axle-accommodating portion 13, for example, which is not shown in FIGS. 2, 5, 6, however, for the purpose of simplification. If used as intended, the outer joint portion 11 rotates about a first longitudinal axis La, and the inner joint portion 12 correspondingly rotates about a second inner joint portion Li. Due to the ball tracks being shaped differently, particularly in the axial direction, all pairings of an outer ball track 20a, 20b and an inner ball track 40a, 40b formed by their being situated opposite each other in space can be divided into two types of track pairs, which are hereinafter referred to as the first type of track pairs 20a, 40a and as the second type of track pairs 20b, 40b. The balls disposed in the respective type of track pairs are referred to in a different manner only due to this association, and not due to a difference in design, wherein the ball associated with the first type of track pairs 20a, 40a is denoted 30, and the ball associated with the second type of track pair 20b, 40b is denoted 31.

[0030] The balls 30 are neutral balls in track pairs whose ball tracks have a center of curvature situated in the joint center plane EM when the joint is straight. The balls 31 are controlled balls in track pairs whose ball tracks consist of at least two portions curved in opposite directions, wherein the inner portion of an outer ball track 20b is situated offset from the joint center plane EM towards the opening side 60. Another portion widens towards the opening side 60 with a radius running in the opposite direction.

[0031] The track pairs of one type do not differ, and, per type, are uniformly distributed in the circumferential direction; in this case, they are arranged offset from each other by 90° on the inner circumferential surface of the outer joint portion 11 or the outer circumferential surface of the inner joint portion 12. The types of track pairs are disposed in an alternating manner across the circumference. Therefore, there is an angle of 45° between track pairs of different types. Thus, the section E-E extends through a neutral ball 30 and a controlled ball 31.

[0032] The balls 30, 31 are retained in a common ball cage 50, wherein the centers of the balls 30, 31 are retained in a common plane, the so-called joint center plane EM, which, when the joint is straight, is perpendicular to the first longitudinal axis La and the second longitudinal axis Li (see FIG. 2). If the joint 10 is bent, as shown in FIG. 5, the joint center plane EM corresponds to an angle-bisecting plane between the first longitudinal axis La and second longitudinal axis Li. In this case, a spherical outer surface 50 of the cage rests, with clearance, against a spherical inner surface of the outer joint portion 11, while a spherical inner surface of the cage 50 rests, with clearance, against a spherical outer surface of the inner joint portion 12, in order thus to enable the cage 50 to pivot freely between the two joint portions 11, 12.

[0033] The difference in design substantially characterizing the type of track pairs is to be illustrated based on the sectional view of FIG. 2 and the schematic depiction of FIG. 3, wherein the joint is in the straight position in each case, in which the first longitudinal axis La and the second longitudinal axis Li are aligned. For the sake of simplicity, but without limiting the disclosed embodiments thereto, it was assumed here that the balls 30, 31 in each case roll on a bottom line of the respective ball track and that thus, in the Figures, the course of the center lines MN, MS of the outer ball tracks determined by the ball center, offset by the ball radius in a parallel direction, corresponds to that of the respective track bottom line.

[0034] The configuration of the outer ball track 20a and the inner ball track 40a associated with the first type of track pairs is explained in more detail hereinafter with reference to FIGS. 2 and 3. The contact line associated with the outer ball track 20a of the first type and the center line MN extending parallel thereto are described by concentric circular trajectories whose circle center 0 is situated on the joint center plane EM in their intersection point with the first longitudinal axis Li and with the second longitudinal axis Li. For the track pairs of the first type, the opening angle β consequently is 0°. Due to the concentric circular course of the center line MN, this angle remains at an absolute value of 0° across the pivoting range. In other words, due to the curvature of the associated ball tracks 20a, 40a, balls 30 associated with this first type of track pairing are not subjected to axial forces, neither in the straight position, nor in the bent position of the joint 10.

[0035] Depending on the deflection of the joint, these balls 30 may also be subject to axial forces which, however, are caused by the structural shape of the joint and not by the specific curvature of their ball tracks and the resulting opening angle β. In the case of a bent joint, for example, axial forces act on balls in positions in which the outer and inner ball tracks intertwine.

[0036] FIG. 2 shows the radius R3a of the outer ball track 20a and the radius R3i of the inner ball track 40a of such a neutral track pairing with a concentric radius of curvature. In contrast, FIG. 3 only shows the center line MN of the outer ball track 20a and specifies its radius R3 towards the joint center point 0. In this embodiment, the neutral tracks are produced by a single radius R3 (R3i, R3a) disposed concentrically to the center 0 of the joint.

[0037] In the case of controlling track pairs of the second type with balls 31, the inner and outer ball tracks 20b, 40b, or their center lines, which describe the path of the balls, consist of at least two portions curved in opposite directions in this embodiment. However, the radius of curvature of the outer portion MSa may also be infinite, i.e. the center line MS widens in a linear manner through the outer portion MSa. In the embodiment of FIG. 3, the center of curvature OT′ of an inner portion MSi of the center line MS of the outer ball track 20b is offset from the joint center plane EM, i.e. it is offset towards the opening side 60, preferably on the longitudinal axis La. The resulting radius R1 is specified. The center of curvature X of an outer portion MSa of the center line MS of the outer ball track 20b is situated outside the hollow volume of the outer joint part 11. In this case, it is also situated offset from the joint center plane EM, i.e. offset towards the opening side 60. The resulting radius R2 is specified.

[0038] FIG. 2 examines this with respect to the outer and inner ball tracks 20b, 40b, wherein the radius R1a and the radius R2a with the associated centers of curvature OT′ and Xa are specified for the outer ball track 20b. This also applies to the inner ball track 40b with the radius R1i, the radius R2i and the associated centers of curvature OT″ and Xi.

[0039] The opening angle a of the ball tracks for the controlled balls 31 and the opening angle β of the ball tracks for the neutral balls 30 are also apparent from FIG. 3. Moreover, FIGS. 2 and 3 illustrate that the tangential transition 70 between the curvature of the inner portion MSi and the curvature of the outer portion MSa is preferably relatively close to the opening 60. The angle δ between the joint center plane EM and a line between the joint center point 0 and this tangential transition or transition point 70 is preferably greater than 8°. In particular, it is between 16° and 18°, particularly preferably about 17°. The radii R1 and R2 are selected accordingly in order to cause as late a transition as possible.

[0040] In one embodiment, the ratio of a curvature radius R1 of the inner portion MSi to the diameter D.sub.Kugel of an associated ball 31 is between 1.5 and 2.5, for instance. The ratio of a curvature radius R2 of the outer portion MSa to the diameter D.sub.Kugel of an associated ball 31 is between 1.0 and 10, for instance. Furthermore, the ratio of a curvature radius R3 of the center lines MN of the first type of track pairs to the diameter D.sub.Kugel of an associated ball 30 is between 1.5 and 2.5, for instance.

[0041] FIG. 4 shows a constant-velocity rotary joint according to FIG. 1 in a bent state. FIG. 5 shows the section A-A through the center of two neutral balls 30 situated opposite each other, while FIG. 6 shows the section C-C slightly offset through two neutral balls 30 situated opposite each other. In this case, it becomes clear that the neutral balls 30 are released early when the joint is bent to a great extent. However, this is acceptable due to the high number of balls remaining in engagement.