HELICAL GEAR TRANSMISSION COMPRISING A PIVOT BEARING WITH A DEFINED PIVOT AXIS

Abstract

A helical gear transmission for an electromechanical servo steering mechanism may include a shaft that meshes with a helical gear. The shaft may be arranged in a transmission housing and, at its first end, may be mounted in a drive-side bearing arrangement so as to be rotatable about an axis of rotation. At its second end, the shaft may be mounted in a drive-remote bearing arrangement in the transmission housing. The drive-side bearing arrangement may have a rolling bearing, an outer ring of which is spherical. The rolling bearing may be enclosed by two bearing shells. The outer side of the outer ring may have two flat points that are opposite one another and form a pivot axis about which the shaft is pivotable in a direction of the helical gear.

Claims

1.-16. (canceled)

17. A helical gear transmission for an electromechanical servo steering mechanism, the helical gear transmission comprising: a shaft that meshes with a helical gear, wherein the shaft is disposed in a transmission housing, wherein a first end of the shaft is mounted in a first bearing arrangement so as to be rotatable about an axis of rotation, wherein a second end of the shaft is mounted in a second bearing arrangement in the transmission housing, wherein the first bearing arrangement includes a rolling bearing, an outer ring of which is spherical, wherein the rolling bearing is enclosed by two bearing shells, wherein an outer side of the outer ring of the rolling bearing has two flat points that lie opposite each other in a circumferential direction and form a pivot axis about which the shaft is pivotable in a direction of the helical gear.

18. The helical gear transmission of claim 17 wherein an inner side of the two bearing shells has two flat surfaces that lie opposite each other in the circumferential direction and are in contact with the two flat points of the outer ring.

19. The helical gear transmission of claim 18 wherein the outer ring of the rolling bearing is in contact with the inner side of the two bearing shells at two further limited contact surfaces.

20. The helical gear transmission of claim 19 wherein the two further limited contact surfaces are shaped in a diametrically opposed manner to the spherical outer side of the outer ring.

21. The helical gear transmission of claim 19 wherein the two further limited contact surfaces are offset by 90 in the circumferential direction with respect to the two flat surfaces.

22. The helical gear transmission of claim 17 wherein the outer ring of the rolling bearing is in contact with an inner side of one of the two bearing shells at exactly four locations.

23. The helical gear transmission of claim 17 wherein the two bearing shells have lateral elevations that define a position of the rolling bearing in a direction of the axis of rotation.

24. The helical gear transmission of claim 23 wherein the lateral elevations are disposed along a circumference at least partially in regions of the two flat surfaces.

25. The helical gear transmission of claim 23 wherein the lateral elevations extend over an angular range of 45 to 135 and, opposite thereto, in an angular range of 225 to 315.

26. The helical gear transmission of claim 23 wherein the lateral elevations are disposed on end sides of the two bearing shells, wherein inner sides of the lateral elevations are in contact with end sides of the outer ring of the rolling bearing.

27. The helical gear transmission of claim 17 wherein the two bearing shells are identical.

28. The helical gear transmission of claim 17 wherein an outer side of the two bearing shells has projections configured for securing against rotation, wherein the projections are configured to engage in recesses of the transmission housing.

29. The helical gear transmission of claim 17 wherein the second bearing arrangement includes a prestressing device by way of which a position of the shaft is adjustable with respect to the helical gear.

30. The helical gear transmission of claim 17 wherein the helical gear is a worm gear and the shaft is a worm shaft.

31. An electromechanical servo steering mechanism comprising: an electric motor with a motor shaft; and the helical gear transmission recited in claim 17, wherein the motor shaft drives the shaft of the helical gear transmission.

32. The electromechanical servo steering mechanism of claim 31 wherein the helical gear is configured to conjoint rotation on a steering shaft of a motor vehicle.

Description

[0024] An exemplary embodiment of the present invention is described below with reference to the drawings. Identical components or components having identical functions bear the same reference signs. In the drawings:

[0025] FIG. 1: shows a three-dimensional illustration of a worm transmission of an electromechanical servo steering mechanism,

[0026] FIG. 2: shows a detailed illustration of the transmission of FIG. 1 reduced to an electric motor and a worm shaft in engagement with a worm gear,

[0027] FIG. 3: shows a three-dimensional view of the engagement of worm shaft and worm gear,

[0028] FIG. 4: shows a longitudinal section through the worm shaft with a bearing arrangement according to the invention,

[0029] FIG. 5: shows an exploded drawing of the bearing arrangement according to the invention, and

[0030] FIG. 6: shows a side view of the bearing arrangement according to the invention.

[0031] FIG. 1 shows a power-assisted steering mechanism 1 which is attached to a steering shaft 6 which is mounted rotatably about its longitudinal axis L, the steering shaft axis. The steering shaft 6 is rotationally fixed in a rear steering shaft part 61, but is adjustable in the direction of the longitudinal axis L, as indicated by the double arrow, in order to adjust a steering wheel (not illustrated here), which is attached to a fastening portion 62, in the longitudinal direction.

[0032] The power-assisted steering mechanism has a transmission housing 7 which has been omitted in the exploded illustration of FIG. 2. In the transmission housing 7, a worm gear 5, which is connected to the steering shaft 6 for conjoint rotation, is mounted rotatably about the longitudinal axis L. A worm shaft 4 is in toothing engagement with the worm gear 5 in order to form a worm transmission.

[0033] An electric motor or a servo motor 3 drives the worm shaft 4 via a motor shaft which is coupled for conjoint rotation to the worm shaft 4 via a clutch 30 consisting of two clutch parts. The worm shaft 4 is in engagement by means of its worm 40 with a worm gear 5, which is connected for conjoint rotation to a pinion or, as illustrated here, to the lower steering shaft 6. During operation of the electric motor 3, the worm shaft 4 is driven and the worm gear 5 correspondingly rotates in order to provide rotational assistance for the lower steering shaft 6.

[0034] FIGS. 2 to 4 show the worm shaft 4 with a drive-side bearing arrangement 8 and a drive-remote bearing arrangement 9 and the worm gear 5 meshing with the worm shaft 4.

[0035] The worm shaft 4 meshes with the worm gear 5 via the worm toothing 40. The worm gear 5 is in turn connected for conjoint rotation to the steering shaft 6, which runs between a steering wheel (not illustrated) and the actual steering gear of the motor vehicle. The constructional elements mentioned are mounted in the common transmission housing 7.

[0036] The worm shaft 4 is mounted here in the transmission housing 7 by means of the drive-side bearing arrangement 8 and the drive-remote bearing arrangement 9 so as to be rotatable about a longitudinal axis 100. The drive-remote bearing arrangement 9 is a rolling bearing which is in the form of a movable bearing. The position of the worm shaft 4 is adjustable with respect to the worm gear 5 by means of a pretensioning device 10 in the region of the drive-remote bearing arrangement 9. The drive-side bearing arrangement 8 has a rolling bearing 11 which permits pivoting movements about a pivot axis 110, which is oriented perpendicularly to the longitudinal axis 100, in the transmission housing 7.

[0037] The drive-side bearing arrangement 8 is illustrated in detail in FIGS. 5 and 6. As illustrated in FIG. 4, the drive-side bearing arrangement 8 has a rolling bearing 11 with an inner ring 12, rolling bodies 111 and an outer ring 13. The rolling bodies 111 run in grooves between the inner ring 12 and the outer ring 13. The inner ring 12 has an inner cylindrical casing surface for a firm seat on the worm shaft. The outer ring 13, as illustrated in FIG. 5, is formed spherically on the outer side and, on the outer side, has two flat points 14 lying opposite each other in the circumferential direction of the outer ring. The two flat points 14 are flat surfaces which are preferably circular and the circle diameter of which is smaller than the width of the outer ring 13. The flat points 14 are arranged centrally on the outer side of the outer ring 13 in the direction of the longitudinal axis 100 and define the pivot axis 110, about which the drive-side bearing arrangement 8 can be tilted. The rolling bearing 11 is surrounded in the direction of the longitudinal axis 100 by two bearing shells 15 which are of substantially circular-cylindrical shape and concentrically surround the rolling bearing 11 in the unloaded state. The bearing shells 15 are half shells which are preferably formed identically. The inner side of the bearing shells 15 has two flat surfaces 16 which are in the shape of squares or are in the shape of rectangles and are matched to the flat points 14 of the outer ring 13 and against which the outer ring 13 lies. The length a of the flat surface 16 is greater with respect to the circumferential direction of the bearing shells 15 than the diameter d of the flat points 14 of the outer ring 13. The flat points 14 and the flat inner surfaces 16 are formed so as to define the pivot axis 110 perpendicularly thereto.

[0038] The bearing shells 15 furthermore lie against the outer ring 13 of the rolling bearing 11 within two contact surfaces 17 that are limited in the circumferential direction. These contact surfaces 17 are arranged offset by 90 with respect to the flat surfaces 16. The contact surfaces 17 lie opposite each other in the circumferential direction. The contact surfaces 17 are shaped in a diametrically opposed manner to the spherical outer side of the outer ring 13 and are inclined toward the rolling bearing center point. They extend, for example, along the inner circumference over an angular range of between 20 and 60. The contact surfaces 17 permit radial positioning of the bearing 11 and of the longitudinal axis 100 thereof.

[0039] The inside diameter of the bearing shells 15 is greater in the regions outside the contact surfaces 17 and the flat surfaces 16 than the outside diameter of the outer ring 13 of the rolling bearing 11. The bearing 11 is therefore in contact with the bearing shells 15 exclusively at the contact surfaces 17 and the flat surfaces 16. In a top view from the side, the bearing shells 15 have a cloverleaf-shaped recess which forms the inner side.

[0040] In addition, the bearing shells 15 each have an elevation 18 on an end side 150 in both regions of the flat surfaces 16, said elevation extending radially from the inner side in the direction of the longitudinal axis 100. Said elevations 18 on the inner side of the bearing shell form a contact for the bearing 11 in the direction of the longitudinal axis 100. In the installed state, the bearing 11 is clamped between the lateral elevations 18 and is thus fixed in the interior of the bearing shells axially level with the pivot axis 110. Axial forces acting on the bearing 11 are absorbed by the clamping. The lateral elevations 18 are dimensioned in such a manner that they permit pivoting of the worm shaft. They therefore lie only against the outer ring 13 of the bearing 11, and the inner ring 12 is free. In the circumferential direction, the elevations 18 can extend over an angular range which is greater than the flat surfaces.

[0041] In order to ensure the orientation of the bearing arrangement 8 or of the bearing shells 15 in the transmission housing 7, the outer side of each bearing shell 15 has a projection 19. The projection 19 preferably lies in the circumferential direction in the region of one of the flat surfaces 16 located on the inner side. The transmission housing 7 has a seat for the bearing arrangement 8 with a corresponding recess for the projections 19 of the bearing shells. It is thus ensured that the bearing shells or the drive-side bearing arrangement 8 can be installed only with the correct orientation in the transmission housing 7.

[0042] The geometry of the bearing shells and of the outer ring of the rolling bearing define a pivot bearing which can tilt about the pivot axis with a small torque, as a result of which zero backlash is ensured over the service life. The pivoting movement of the worm shaft here is approximately 0.5.