BALL SCREW DRIVE WITH FORCE TRANSMISSION ELEMENT AND IMBALANCE COMPENSATION

Abstract

A ball screw drive having a threaded spindle and a spindle nut which coaxially encloses at least partially the threaded spindle. The spindle nut receives a ball deflector and therefore has an imbalance caused by the structure. A force transmission element is positively connected to the spindle nut. Here, the outer surface of the spindle nut has at least one recess which is dimensioned and arranged to serve as a stop or groove for the force transmission element and at the same time contributes to the imbalance compensation of the spindle nut. An imbalance compensation method is also provided by fixing the action surface as a surface recess such that the smallest width b of the recess is at least 3 times as large as the maximum radial indentation t thereof. The filling up of at least parts of the recess by the force transmission element is then taken into account and the recess is lengthened along the spindle nut for imbalance reduction.

Claims

1. A ball screw drive, comprising: a threaded spindle; a spindle nut which coaxially encloses at least partially the threaded spindle; a plurality of balls which may circulate in the intermediate space between the threaded spindle and the spindle nut; a ball deflector which is arranged in an opening in the outer surface of the spindle nut; a force transmission element which is positively connected to the spindle nut; and an outer surface of the spindle nut has at least one recess dimensioned and arranged such that the at least one recess serves as a stop or groove for the force transmission element and simultaneously provides imbalance compensation for the spindle nut.

2. The ball screw drive according to claim 1, wherein the recess has a shape of at least one of: a rectangle with rounded corners, a flat slot, a circle, an oval, or a square recess.

3. The ball screw drive according to claim 1, wherein the recess has a planar base with a peripheral, at least partially recessed, edge toward the outer surface of a nut body of the spindle nut or without a stepped edge leads into a cylindrical outer surface of the nut body.

4. The ball screw drive according to claim 1, wherein a radially measured depth of the recess ranges from a few tenths of a millimetre to a few millimetres.

5. The ball screw drive according to claim 1, wherein the recess includes a plurality of stepped portions or planes in a depth direction, forming a stepped funnel shape.

6. The ball screw drive according to claim 1, wherein the outer surface of the spindle nut has at least one further recess which is dimensioned such that the at least one further recess contributes to the imbalance compensation.

7. The ball screw drive according to claim 1, wherein the recess is formed by material-removal, grinding, or cold forming.

8. A method for the imbalance compensation of an assembly including at least one ball screw drive and a force transmission element, the ball screw drive comprising a spindle nut and a threaded spindle, the method comprising: i. fixing an action surface as a surface portion of the surface of the spindle nut for transmission of a required torque between the force transmission element and the spindle nut; ii. forming the action surface as a surface recess such that a smallest width b of the recess is at least 3 times as large as a maximum radial indentation t thereof, wherein b is measured in a cross-sectional plane to a rotational axis; iii. aligning the surface recess on a periphery such that the imbalance produced by the ball deflectors reduces or limits an increase vi. taking into account a filling up of at least parts of the surface recess, which is carried out by the force transmission element and by material of the force transmission element; v. subsequently increasing the surface recess along a longitudinal axis of the spindle nut until no further reduction of the imbalance is achievable; and vi. providing at least one further recess on the surface of the spindle nut according to steps ii, iii and v if the surface recess formed according to an initial carrying out of steps i-v are insufficient in order to achieve a predetermined imbalance compensation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 shows a ball screw drive according to the prior art.

[0037] FIG. 2 shows perspective views of a spindle nut body.

[0038] FIG. 3 shows a side view of a ball screw drive.

[0039] FIG. 4 shows a cross-sectional view through the ball screw drive of FIG. 3.

[0040] FIGS. 5 to 9 show cross-sectional views through different embodiments of the ball screw drive in the overlapping region of the force transmission element which encloses the spindle nut.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a ball screw drive 10 as known in the prior art and as has been described above in the paragraph technical background.

[0042] FIG. 2 shows a spindle nut body 20 in two views. To the left are shown recesses 24, 25 are shown and openings provided for ball return channels. Ball deflectors may be inserted therein.

[0043] Relative to this figure, details have also been provided above in the paragraph technical background.

[0044] FIG. 3 shows an assembly consisting of a ball screw drive 30 consisting of a threaded spindle 32 and a spindle nut 34, and the possible position for a force transmission element 39 (marked in dashed lines). It may be seen that in this embodiment both the openings 36, 37 for the ball deflector(s) would be covered by the force transmission element 39, as well as the recess 38.

[0045] In FIG. 4 an embodiment according to the invention is shown in cross section. The assembly made up of a ball screw drive 40, formed of a threaded spindle 42 and a spindle nut 44 may be seen. Balls 43 are shown in the space between the threaded spindle and the spindle nut, and the ball deflector is located outside the cutting plane. As may be seen on the lower edge of the spindle nut 44, the recess 48 (equivalent to the aperture 38 in FIG. 3) is covered by the force transmission element 49. At this point, therefore, the force transmission element 49 fills a gap (partially, depending on the design) and thus partially compensates for the loss of material produced. Also illustrated is the cutting plane E which is used in FIGS. 5-9.

[0046] FIGS. 5 to 9 show in cross section specifically the overlapping region of the force transmission element 49 which encloses the spindle nut 44 positively and non-positively. The position of a threaded spindle 42 is indicated. The proportions of the threaded spindle 42, spindle nut 44 and force transmission element 49 are not to scale and the view is to be understood as a sketch.

[0047] In FIG. 5 the recess (corresponding to features 22, 23, 38, 48) is designed as a flat, planar flattened portion identifiable in cross section as a circular segment. This embodiment may be achieved, for example, by flat grinding or milling, by a material-removing treatment process or cold forming. The width b is determined by the deviation from the original outer contour. The maximum depth t of the material removal is measured radially outwardly from the central axis as a maximum difference between the radius of the original outer contour and the actual outer contour.

[0048] In FIG. 6 the secant is not designed as a straight line but as a radially inwardly curved base. The width is measured as in FIG. 5, and the depth t in turn is defined as the maximum radial deviation from the original outer contour.

[0049] Alternatively, as shown in FIG. 7, the material removal may also be implemented as a broad channel with vertically radially sloping walls and a uniform depth t, whereby the base of the channel describes a circular arc at a uniform distance from the central axis.

[0050] FIG. 8 shows a variant thereof where in comparison the base is also flattened, so as to be designed to be flat.

[0051] FIG. 9, however, shows a polygonal profile (in this case a hexagon) which on one side deviates from a symmetrical shape. This should not have to be carried out parallel to a polygonal side but could also be carried out across the corner which would lead to an irregular seven-sided shape.

[0052] Preferably, this recess may have a planar base which, depending on the technical design, may form a peripheral recessed edge toward the outer surface of the nut body (FIG. 8) or at certain points may lead in a flat manner, i.e. without a stepped edge, into the cylindrical outer surface of the nut body (as in FIG. 5).

[0053] The depth of the recess is intended to be selected such that the fatigue strength of the spindle nut body is not impaired. Depending on the wall thickness of the spindle nut body, the depth of the recess will thus range from a few tenths of a millimetre to a few millimetres.

[0054] The features of the invention disclosed in the above description, in the drawings and in the claims may be essential for the implementation of the invention both individually and in any combination which is, however, technically expedient and/or advantageous.

REFERENCE LIST

[0055] 10, 30, 40 Ball screw drive

[0056] 12, 42 Threaded spindle

[0057] 13 Nut body

[0058] 14, 34, 44 Spindle nut

[0059] 15 Ball deflector

[0060] 17 Opening

[0061] 20 Spindle nut body

[0062] 22, 23 Recesses (for imbalance compensation)

[0063] 24, 25 Recesses (openings provided for ball return channels)

[0064] 43 Balls

[0065] 36, 37 Opening(s)

[0066] 38, 48 Recess(es)

[0067] 39, 49 Force transmission element