SPRING ELEMENT FOR A REDUCTION GEAR OF AN ELECTROMECHANICAL STEERING SYSTEM

Abstract

An electromechanical steering system may include a reduction gearbox where a worm gear is mounted in first and second bearings rotatably about a longitudinal axis. Rolling elements are disposed between inner and outer rings of the bearings. The inner rings are rotationally fixed on a shaft driven by the worm gear. A spring element is disposed between the inner ring of the second bearing and the worm gear. The spring element has an at least partially annular main body that when installed extends coaxially with the longitudinal axis. Spring arms in a circumferential direction are spaced apart from the longitudinal axis emanating from an external circumferential side of the main body. A first spring arm has a first leg that points away from the longitudinal axis and a second leg on which a free end is disposed, with the second leg running at least partially parallel to the longitudinal axis.

Claims

1.-19. (canceled).

20. An electromechanical steering system for a motor vehicle, the electromechanical steering system comprising: a reduction gearbox comprising a worm and a worm gear, wherein the worm gear in a gearbox housing is mounted in a first bearing at a first end side and in a second bearing at a second end side so as to be rotatable about a longitudinal axis, wherein the first and second bearings include an outer ring and an inner ring between which rolling elements are disposed, wherein the inner rings are rotationally fixed on a shaft that is driven by the worm gear, wherein the outer rings sit in the gearbox housing; and a spring element, wherein when viewed in a direction of the longitudinal axis the spring element is disposed between the inner ring of the second bearing and the worm gear, wherein the spring element has an at least partially annular main body that in an installed state extends coaxially with the longitudinal axis, wherein the spring element includes spring arms that in a circumferential direction are spaced apart from the longitudinal axis emanating from an external circumferential side of the at least partially annular main body, wherein a first spring arm of the spring arms has a free end, with a first leg of the first spring arm pointing away from the longitudinal axis, with a second leg of the first spring arm running at least partially parallel to the longitudinal axis, wherein the free end is configured on the second leg.

21. The electromechanical steering system of claim 20 wherein the at least partially annular main body in the installed state lies against an end side of the inner ring of the second bearing that is proximal to the worm gear.

22. The electromechanical steering system of claim 20 wherein the spring arms in the installed state lie against the end side of the worm gear that faces the second bearing.

23. The electromechanical steering system of claim 20 wherein the at least partially annular main body is entirely annular.

24. The electromechanical steering system of claim 20 wherein the spring arms lie against a clearance of the worm gear that is disposed in the end side that faces the second bearing, preloading the worm gear in the longitudinal direction and a radial direction.

25. The electromechanical steering system of claim 20 wherein the first spring arm includes a third leg that points toward the longitudinal axis and forms another free end.

26. The electromechanical steering system of claim 25 wherein the free ends of the spring arms on a common side of the spring element extend in the direction of the longitudinal axis.

27. The electromechanical steering system of claim 25 wherein the free ends of the spring arms lie against the worm gear.

28. The electromechanical steering system of claim 25 wherein the free ends of the spring arms have a plastics material coating.

29. The electromechanical steering system of claim 20 wherein the spring arms are uniformly spaced apart in a circumferential direction.

30. The electromechanical steering system of claim 20 comprising cams that are oriented in a longitudinal direction and that center the spring element on the shaft, wherein the cams are disposed on an internal circumferential side of the at least partially annular main body.

31. The electromechanical steering system of claim 20 wherein the spring element is integral and comprised of sheet metal.

32. The electromechanical steering system of claim 20 wherein the spring arms have a U-shaped profile when viewed in a longitudinal section along the longitudinal axis.

33. The electromechanical steering system of claim 20 wherein the first leg of the first spring arm extends from the at least partially annular main body and is substantially planar, wherein the first leg encloses an angle in a range from 10° to 30° relative to a plane of the at least partially annular main body.

34. The electromechanical steering system of claim 20 wherein in a longitudinal direction the at least partially annular main body has a thickness in a range from 0.3 mm to 1.0 mm.

35. The electromechanical steering system of claim 20 wherein the spring element with the spring arms has an external thickness in a range from 6.5 mm to 11 mm.

36. The electromechanical steering system of claim 20 wherein the spring arms in a circumferential direction have a maximum width in a range between 5 mm and 12 mm.

37. The electromechanical steering system of claim 20 wherein in terms of width the spring arms taper towards the longitudinal axis.

38. The electromechanical steering system of claim 20 wherein the at least partially annular main body is planar.

Description

[0023] Preferred embodiments of the invention will be explained in more detail hereunder by means of the drawings. Components of identical type or equivalent function are identified with the same reference signs in the figures in which:

[0024] FIG. 1: shows an isometric illustration of a worm gearbox in an electromechanical power-assisted steering system;

[0025] FIG. 2: shows a further isometric illustration of a worm gearbox of a power-assisted steering system according to FIG. 1;

[0026] FIG. 3: shows a longitudinal section through the worm gearbox, FIGS. 4,4A,4B,4C: show views of a spring element;

[0027] FIG. 4d: shows an enlarged fragment X to FIG. 4C;

[0028] FIGS. 5,5A,5B,5C: show views of the second embodiment of a spring element;

[0029] FIGS. 6,6A,6B: show views of a third embodiment of a spring element;

[0030] FIG. 7: shows a plan view of a spring element of a further embodiment;

[0031] FIG. 8: shows a plan view of a spring element of a further embodiment;

[0032] FIG. 9: shows a rear view of a spring element of a further embodiment;

[0033] FIG. 10: shows a rear view of a spring element of a further embodiment;

[0034] FIG. 11: shows an isometric view of a spring element of a further embodiment; and

[0035] FIG. 11a: shows a lateral view of a spring element of a further embodiment.

[0036] FIGS. 1 to 3 show a worm gearbox 1 as part of an electromechanical power-assisted steering system which transmits an auxiliary torque from an electric motor 42 to a lower steering shaft 2. A worm gear 3 which is connected in a rotationally fixed manner to the lower steering shaft 2 is provided. A rotation of the worm gear 3 about the rotation axis 100 thereof causes an auxiliary force, or an additional force, respectively, to be applied to the steering shaft 2 so as to accordingly incorporate an auxiliary force, or an additional steering angle, respectively, into the steering train.

[0037] The worm gear 3 is driven by way of a worm 4 which in turn is driven by the electric motor 40, wherein the output of the electric motor for transmitting torque is correspondingly coupled to the worm 4. An integral functional unit 5 having a torque sensor unit 6 and a steering angle sensor unit 7 is furthermore provided in FIG. 2. The torque sensor unit 6 detects the rotation of an upper steering shaft 8 in relation to the lower steering shaft 2 as a measure of the torque manually exerted on the upper steering shaft 8. In contrast, the steering angle sensor unit 7 measures the current steering angle of the lower steering shaft 2. The torque sensor unit 6 has an annular magnet 9 (permanent magnet) which is connected in a rotationally fixed manner to the upper steering shaft 8, and a magnetic flux conductor 10. An associated sensor unit 11 is held so as to be stationary in space. The upper steering shaft 8 in a rear steering shaft part 81 is rotationally fixed yet adjustable in the direction of the longitudinal axis 100, as is indicated by the double arrow in FIG. 1, so as to adjust in the longitudinal direction a steering wheel which is not illustrated here and is attached to a fastening portion 82.

[0038] As is illustrated in FIG. 3, the worm gear 3 at both end sides thereof is mounted in a gearbox housing 12 so as to be rotatable by means of a ball bearing 13. The ball bearings 13 have an inner ring 14, 140 which is connected to the lower steering shaft 2, and an outer ring 15 which sits in the gearbox housing 12, and rolling elements 16. The rolling elements 16 run in grooves between the inner ring 14, 140 and the outer ring 15. The inner rings 14, 140 have an inner cylindrical shell face for a tight fit on the lower steering shaft 2. The outer rings 15 are in each case received in a seat 17 in the gearbox housing 12. The seat 17 is in each case formed by an annular shoulder 18 which in the gearbox housing 12 encircles the longitudinal axis 100 in the circumferential direction. The shoulders 18 serve as a contact face which extends in the radial direction to the longitudinal direction 100 and thus defines the orientation of the ball bearing 13 in the longitudinal direction 100. The outer rings 15 by way of the end sides 19 thereof that are proximal to the worm gear and by way of the shell face 20 thereof thus lie against the gearbox housing 12. The outer rings 15 are not in contact with the worm gear 3. In contrast, the inner rings 14, 140 by way of the end sides 21 thereof that are proximal to the worm gear are supported on the worm gear 3. A first inner ring 140 of a first bearing, by way of the end side 21 of the former that is proximal to the worm gear, directly lies against a first end side of the worm gear 3. In contrast, a spring element 22 which applies a constant preload on the encircling/annular face of the second inner ring 14 is provided between a second inner ring 14 of a second bearing and a second end side of the worm gear. The spring element 22 lies against the end side of the second inner ring 14 that is proximal to the worm gear and engages in a clearance 23 in the second end side of the worm gear 3 that encircles the longitudinal axis 100 in the circumferential direction.

[0039] A first example of a spring element 22 is illustrated in FIGS. 4 to 4C. The spring element 22 is formed by an annular main body 220, spring arms 222 emanating at a uniform spacing from the external circumferential side 221 of said main body 220. The spring arms 222 have in each case a free end 223. Proceeding from the main body 220, a first leg 222a of the spring arm 222 points outward, away from the longitudinal axis 100. The first leg 222a transitions to a second leg 222b which in this embodiment assumes a bent shape. The second leg at the highest point thereof or in the center thereof is approximately parallel to the longitudinal axis 100. The second leg transitions to a third leg 222c of the spring arm 222, said third leg 222c pointing toward the longitudinal axis 100. Proceeding from the main body 220, the spring arms 222 widen in the circumferential direction to the longitudinal axis up to a maximum width b1, and in an end region toward the free end 223 then taper down to a minimum width b2. The main body 220 in the installed state lies against the inner ring, and the free ends of the spring arms 223 are supported on the worm gear in the clearance.

[0040] This spring arms 222 project from the annular main body 220 outward in the radial direction to the longitudinal axis 100, wherein the spring arms 222 are bent or canted back inward toward the center of the main body such that said spring arms 222 by way of the free ends 223 thereof face one another toward the center. The spring arms 222, when viewed in the longitudinal section along the longitudinal axis, thus have an approximately U-shaped profile. The first leg 222a of the spring arms 222, that extends from the main body 220 and is substantially planar, in relation to the plane of the main body encloses an angle α. The region having the maximum width b1 in terms of the radial direction lies so as to be at the extreme outside and in the second leg 222b. The free ends 223 of the spring arms 222 emanate from the third leg 222c and, when viewed from the center in the direction of the main body or in the direction of the longitudinal axis 100, respectively, are bent inward in such a manner that in the end region a contact face 225 having the minimum width b2 by way of which the spring arms can be supported on the worm gear is configured on the upper side of the spring arms 222. The seat of the spring can be readily controlled as the contact face 225 is relatively large. The spring arms 222 are preferably pulled inward so far that a radial movement/preload is possible. The annular main body 220 in the longitudinal direction has a thickness d1. The entire spring element having the spring arms has an external thickness d2 which in this exemplary embodiment comprises the first, second and third legs 222a-c. The maximum width b1 of the spring arms preferably assumes a value between 5 mm and 12 mm. the external thickness d2 preferably assumes a value between 6.5 and 11 mm. The angle α preferably assumes a value between 10° and 30°. The sheet-metal thickness d1 preferably assumes a value between 0.3 and 1 mm. The spring arms 222 are mutually spaced apart and are connected to one another exclusively by way of the main body. The spring arms are preferably linked to the main body in an integral manner.

[0041] FIG. 4d represents a partial view from FIG. 4C. It is illustrated herein that the second leg 222b runs so as to be almost parallel to the longitudinal axis. The second leg has an internal circumferential face and an external circumferential face, wherein the external circumferential face is disposed so as to be further apart from the longitudinal axis than the internal circumferential face and on the external circumferential face is touched by a tangent 222b-1 which is parallel to the longitudinal axis. A secant 222b-2 which is parallel to this tangent 222b-1 is formed by the internal circumferential face of the second leg 222b, wherein the internal circumferential face is disposed so as to be closer to the longitudinal axis 100 than the external circumferential face. The secant 222b-2 and the tangent 222b-1 run so as to be parallel to the longitudinal axis 100 and are mutually spaced apart by a spacing Dx, where Dx≤10.Math.d1≥d1, preferably Dx≤7.Math.d1≥5.Math.d1. It is furthermore illustrated that one tangent that diverges from the longitudinal axis is in each case formed by the first leg 222a and by the third leg 222c. The second, bent, leg 222b lies between these two tangents. A right angle is formed at the point where these two tangents intersect. In terms of the right angle, the two tangents form the adjacent sides to the angle. The opposite side to the angle is formed by the tangent 222b-1 or by the secant 222b-2 such that two isosceles right-angled triangles are defined.

[0042] FIGS. 5 to 5C show a further exemplary embodiment of a spring element 22 which corresponds substantially to the previously described spring element but in which the free ends 223 of the spring arms 222 are not additionally bent inward. The end faces of the free ends 223 in the installed state thus lie against the worm gear 3. The free ends 223 of the spring arms 222 taper sharply down to the minimum width b2, on account of which stresses during compression can be uniformly distributed. The free ends 223 have a plastics material covering 226 in order to prevent wear on the spring arms 222.

[0043] In contrast, the plastics material covering is dispensed with in the exemplary embodiment of FIGS. 6 to 6B. Here, bending cams 228 which are oriented in the longitudinal direction and serve for centering the spring element 22 on the outer steering shaft as well as an anti-rotation safeguard are provided on an internal circumferential side 227 of the annular main body 220.

[0044] It is also conceivable for the spring arms 222 of the spring element 22 to be only in part disposed at regular spacings in the circumferential direction of the main body 220, as is illustrated in FIGS. 7 and 8. The disposal herein can, for example, take place so as to be symmetrical to a plane which is defined by the longitudinal axis 100, as is illustrated in FIG. 7, or in the circumferential direction about the longitudinal axis 100 so as to be offset by a defined angle about the center of the spring, as is illustrated in FIG. 8.

[0045] It can also be provided that the main body 220 is inclined, or has a bent shape, respectively, so as to likewise contribute toward the spring travel. Such a main body 220 is illustrated in FIG. 9. In the exemplary embodiment shown, substantially triangular, planar spring arms 222 extend from both sides of the main body 220 in the direction of the longitudinal axis 100. In this exemplary embodiment, the spring arms of the one side lie against the worm gear, and the spring arms of the other side lie against the inner ring of the bearing.

[0046] FIG. 10 shows a further exemplary embodiment in which the annular main body 220 is designed so as to be almost wire-shaped and spring arms 222 which in the profile are U-shaped at one of the legs 222a-c thereof, in this example the first leg 222a, on the external side are connected to the main body 220. The main body 220 herein lies in the central region of the first leg 222a, between the free end of the latter and between the second leg 222b. The spring arm 222 herein protrudes beyond the main body 220 in the direction of the longitudinal axis 100. As in the other embodiments, the spring arms 222 extend in the direction of the center of the spring.

[0047] It is furthermore preferable that the spring element 22 is composed of only the first leg 222a and the second leg 222b, as is illustrated in FIGS. 11 and 11a, so as to enable a contact face in which force is distributed and tension is thus low in the longitudinal direction. The first leg 222a herein runs away from the main body 220 and extends so as to be substantially planar and in relation to the plane of the main body 220 encloses an angle α. The second leg 222b emanates from the first leg 222a and forms the free and 223. The second leg herein is planar, as is illustrated in FIG. 11a, and is thus configured so as to be parallel to the longitudinal axis. The first leg 222a and the second leg 222b herein define an angle β which is smaller than or equal to 180° and is larger than α. The first leg 222a and the second leg 222b preferably assume a V-shape, as is illustrated in FIG. 11a. The second leg 222b may also assume a bent shape, as is illustrated in FIG. 11. The second leg herein forms a U-shape and is bent in such a manner that the second leg 222b is approximately parallel to the longitudinal axis. The spring element is preferably configured so as to be integral, this simplifying the assembling and preventing friction between the components of the part and an associated generation of noise. The spring element can however also be configured in multiple parts. The spring element moreover has a symmetrical distribution of load (even when the load may not be constant across the circumference). The production can take place by way of a bending process of a single sheet-metal part. In comparison to disk springs, less tension in the tangential direction can be implemented in the basic concept of a beam-in-bending. Any movement in the radial direction of the spring on the seat of the spring is suppressed, this leading to a positive NVH behavior.

[0048] It is also conceivable for the annular main body not to have a mechanically closed connecting ring. In this case, the spring arms and potential bending cams emanate from a linear main body. The main body is bent so as to form a ring during production. The spring arms in a manner similar to beams-in-bending are bent from the sheet-metal part so as to form U-shaped spring elements which are connected to one another by way of the main body.

[0049] The main body can be configured so as to be flat or undulated in order for the spring travel to be increased. The spring element by means of a metal spinning method or a press/bending method can be configured as a sheet-metal element and be covered with plastics material. The use of a lubricant varnish is also conceivable and possible. The spring element is particularly preferably configured so as to be integral; it is however conceivable and possible for said spring element to be configured in multiple parts.

[0050] It is furthermore conceivable and possible for the free ends of the spring arms to be closed so as to thus guarantee simplified assembling, since no bulk material can be trapped on account thereof, for example.

[0051] Play in the axial direction, tolerances and thermal expansions can be compensated for on account of the spring according to the invention.