Threaded spindle for a ball screw drive, ball screw drive comprising same, and method for producing a threaded spindle of a ball screw drive

Abstract

The invention relates to a threaded spindle for a ball screw drive. The outer circumference of the threaded spindle is provided with a ball groove (1) which winds helically about the spindle axis at a pitch angle (a) over a plurality of windings, and a threaded spindle cutout (3), which is open towards the outer circumference, is equipped with a deflecting insert (4) for deflecting balls (5) from one end (E) of a common winding (6) to the start (A) of the common winding (6). The cutout (3) is delimited by side walls (16) which are formed parallel to the pitch angle (a) of the ball groove (1).

Description

[0001] threaded spindle

[0002] The present invention relates to a threaded spindle for a ball screw drive, as well as a ball screw drive with the threaded spindle, and furthermore a method for manufacturing the threaded spindle.

[0003] A ball screw drive according to the features of the preamble of claim 1 is known from DE 10 2022 134 385 A1. The threaded spindle has a ball groove wound helically around the spindle axis on its outer circumference. The ball groove is wound helically around the spindle axis over several turns at a certain helix angle. The threaded spindle is provided with a recess open towards the outer circumference, into which a deflection insert is inserted. The deflection insert is designed to deflect balls from one end of a common turn to the beginning of the common turn. The recess is wider than the ball diameter and crosses a common shoulder of two adjacent turns of the ball groove. The balls are guided in the deflection insert along the deflection channel and cross this common shoulder.

[0004] The recess extends longitudinally along the deflection channel from a first shoulder of the ball groove to a second shoulder of the ball groove, with only the aforementioned common shoulder, which in this case can also be referred to as the middle shoulder, lying between them. The side walls of the recess along the deflection channel are parallel to each other and inclined to the helix angle of the ball groove. The longitudinal extent of the recess is bounded by end run-off surfaces of the recess. The longitudinal extent of the recess does not sever the aforementioned first and / or second shoulder, thus preventing damage to the ball groove in the adjacent turn.

[0005] Particularly with ball screws that have a low pitch-to-ball-diameter ratio, technical problems can arise during the manufacturing of the recess. In these cases, the shoulders become very narrow when viewed in longitudinal section through the threaded spindle. Consequently, there is an increased risk that the aforementioned first shoulder and / or the second shoulder—to which the recess is intended to extend—will be severed by the recess to such an extent that an adjacent ball bearing is damaged.

[0006] The object of the invention was to provide a threaded spindle for a ball screw drive that enables a flawless formation of the recess and that enables reliable operation of the ball screw drive.

[0007] According to the invention, this problem is solved by the threaded spindle according to claim 1 and by a manufacturing method for a threaded spindle according to claim 9. Advantageous embodiments of the threaded spindle according to the invention are specified in claims 2 to 7.

[0008] The threaded spindle according to the invention for a ball screw drive has a spherical groove on its outer circumference, wound helically at a helix angle over several turns around the spindle axis. This spherical groove can have a Gothic profile known per se. In longitudinal section through the threaded spindle, two adjacent turns of the spherical groove are bounded by a common shoulder, as is known.

[0009] The threaded spindle is provided with a recess open towards the outer circumference, in which a deflecting insert is arranged for deflecting balls from one end of a common turn to the beginning of the common turn. The deflecting insert can be formed in a known manner by a deflecting piece having a ball inlet, a ball outlet, and a deflecting section connecting the ball inlet and the ball outlet. This deflecting channel thus formed connects, in a known manner, one end of a common turn of the ball groove to one beginning of the common turn of the ball groove. This deflecting channel can be designed as a groove in the deflecting piece.

[0010] The recess severs this common shoulder of the helically wound ball groove. The balls are moved along the deflection channel through the common shoulder to be returned from the end of the common turn to its beginning. The recess is bounded by side walls that are parallel to the helix angle of the ball groove. This design and position of the recess offers several advantages:

[0011] First, it is ensured that the shoulders on either side of a central shoulder – which is cut to accommodate the deflection insert – are not severed. This is because the side walls of the recess are arranged parallel to the angle of inclination of the ball groove and therefore run parallel to the shoulders of the ball groove.

[0012] Furthermore, the recess can be produced economically using a disc cutter – for example, a T-slot cutter. The disc cutter has a rotary-driven cutter shank that carries a cutter disc. The cutter disc can be aligned parallel to the helix angle of the ball groove and plunges radially into the threaded spindle.

[0013] Both the side walls of the recess and the end run-out surfaces located longitudinally along the recess – i.e., in the direction of the slope of the ball groove – can easily be produced using the milling cutter. In particular, the milling cutter can form both the run-out surfaces and the recess bottom with its working radius, and the side walls of the recess with its end faces.

[0014] From a manufacturing perspective, it is advantageous if the milling cutter has a thickness that corresponds to the width of the recess. In this case, the recess can be formed simply by plunging the milling cutter radially into the threaded spindle.

[0015] The invention enables a simple shaping of the recess, which can have an approximately rectangular contour when viewed transversely to the longitudinal axis of the threaded spindle on its cylindrical surface. Accordingly, the deflector can also have a simple contour and be rectangular. The contour of the deflector and the contour of the recess can be coordinated so that the insertion of the deflector ensures its secure hold in the threaded spindle. The side walls of the recess can be formed by flat surfaces and arranged parallel to each other. This design facilitates the easy pressing in of the deflector insert. These side walls can be produced with the aforementioned disc cutter simply by radially plunging the cutter disc.

[0016] The length of the recess, extending parallel to the helix angle, can be limited by run-out surfaces that, viewed in a cross-sectional plane parallel to the helix angle of the ball groove, are concavely curved through the threaded spindle and transition into a recess base. The run-out surfaces can transition tangentially into the recess base. This shape enables cost-effective production of the recess using the aforementioned disc cutter.

[0017] It is conceivable and advantageous from a manufacturing perspective if the run-out surfaces have a radius of curvature and extend to the cylindrical surface of the threaded spindle with this radius of curvature. In this case, these run-out surfaces can be produced with the aforementioned disc cutter simply by radially plunging into the threaded spindle.

[0018] The run-out surface can be concave, deviating from a constant radius of curvature, with a changing radius of curvature.

[0019] A particularly cost-effective method for manufacturing the recess and thus the threaded spindle can be achieved if the milling cutter has a thickness corresponding to the axial extent of the recess perpendicular to the helix angle of the ball groove. In this case, it is sufficient for the milling cutter to plunge radially, thereby creating the recess profile, because the radial plunge, and if necessary, a process parallel to the helix angle, can simultaneously produce the side walls, the bottom of the recess, and the run-out surfaces.

[0020] The recess bottom, viewed in a cross-sectional plane parallel to the helix angle of the ball groove through the threaded spindle, can have a flat plateau, at both ends of which the run-out surfaces are located. Here, too, a manufacturing advantage becomes apparent when using the aforementioned disc cutter, which, through relative rotation along the helix angle of the ball groove, provides the sufficient extent of the recess and creates both the plateau and the recess bottom with the plateau.

[0021] A recess width perpendicular to the helix angle preferably corresponds to the axial extent of two adjacent ball grooves. In other words, the recess width perpendicular to the helix angle corresponds approximately to the axial extent of one full turn of the ball groove. This extent is measured from the outer shoulder points of the ball groove. Between these outer shoulder points lies a central shoulder point, which is penetrated by the deflection insert.

[0022] The recess width is limited by the parallel side walls of the recess. This recess width takes into account the requirement that the first and second shoulders – which are immediately adjacent on both sides of the aforementioned central, severed shoulder of the ball groove – are not severed to such an extent that the subsequent ball grooves are damaged.

[0023] The deflection insert can be easily inserted into the recess and secured there by force or material bonding. The possibility of easily shaping the recess contour, as described above, facilitates, for example, pressing in the deflection insert. Another method of securing it involves a material bond using an adhesive.

[0024] Furthermore, it can be advantageous if the deflection insert, designed as a deflecting piece, has two diametrically opposed support arms, each of which engages in a so-called dead-of-play section of the ball groove of the threaded spindle. This dead-of-play section refers to those sections of a ball channel of the ball screw drive that are not traversed by the balls.

[0025] In an alternative embodiment, it may be advantageous for the deflection piece to be provided with support surfaces on its side facing the threaded spindle, which are supported on shoulders of the threaded spindle. In this way, a perfect alignment of the deflection piece with the thread of the threaded spindle can also be achieved.

[0026] An inventive method for manufacturing a threaded spindle of a ball screw drive enables a particularly economical production of the recess in the threaded spindle. This method relates to the threaded spindle, which has a ball groove on its outer circumference wound helically over several turns around the spindle axis at a helix angle, wherein the threaded spindle is to be provided with a recess open towards the outer circumference, which is suitable for receiving a deflection insert for deflecting balls from one end of a common turn to one beginning of the common turn.

[0027] The method involves machining the recess using a milling cutter whose end faces are parallel to the helix angle and whose axis of rotation is perpendicular to the helix angle, and which has a working radius. The milling cutter cuts radially into the threaded spindle to a depth of [missing information] and forms concave run-out surfaces of the recess between a recess bottom and a cylindrical surface of the threaded spindle. In a preferred embodiment, the end run-out surfaces can have a radius of curvature corresponding to the working radius of the milling cutter.

[0028] The concavely curved run-out surfaces at the ends can have different radii of curvature along their length, the smallest of which is greater than or equal to the working radius of the milling disc. This allows the disc cutter to follow a milling curve and mill the contour of the run-out surfaces.

[0029] For this process, it can be advantageous if the milling cutter has a working radius that is matched to the ball diameter of the balls to be accommodated in the ball groove. The working radius of the milling cutter is therefore greater than or equal to the ball diameter and less than or equal to five times the ball diameter. The larger the ball diameter, the deeper the recesses in the threaded spindle must be machined. A ball screw drive with this threaded spindle requires that the balls in the deflection channel of the deflection insert cross the shoulder of the threaded nut; therefore, the deflection section in the threaded spindle must be sufficiently radially recessed. This recess can be readily achieved with the milling cutter described.

[0030] This method of creating the recess according to the invention is very economically advantageous. It allows the use of disc milling cutters with cutter discs in the form of, for example, T-slot cutters. The cutter disc plunges radially into the threaded spindle at the helix angle, creating the recess by machining. Ideally, the cutter disc can be formed by simply plunging radially into the material of the threaded spindle, completely forming the contour of the recess.

[0031] Alternatively, a disc cutter with a small working radius can be used to mill the concavely curved contour of the run-out surface. This run-out surface can have any desired curvature along its path from the recess bottom to the outer surface of the threaded spindle, forming the run-out surface, with the smallest radius of curvature of the run-out surface being greater than or equal to the working radius of the disc cutter.

[0032] The plunge depth of the disc cutter into the lead screw is limited by the radius of the rotating cutter shank, which carries the cutter disc. The maximum plunge depth of the cutter disc is determined by the difference between the working radius of the cutter disc and the radius of the cutter shank. The cutter shank lies in a plane parallel to the plane containing the spindle axis. When the maximum plunge depth is reached, the spindle shank rests on the outer diameter of the lead screw, i.e., on the tooth tips of the ball groove.

[0033] Surprisingly, it has been shown that good milling results are achieved when, at the desired plunge depth of the milling cutter, a distance of between 0.05 mm and 0.25 mm is maintained between the cutter shank and the outer diameter of the threaded spindle. Maintaining this distance reliably prevents unwanted deflection of the milling cutter.

[0034] The working radius of the milling cutter and the radius of the cutter shank can be matched to ensure both sufficient plunge depth and the shortest possible longitudinal extent of the recess – i.e., along the thread pitch. If the working radius of the milling cutter is too large, a large plunge depth and a large distance between the cutter shank and the outer diameter of the threaded spindle can be achieved. However, the longitudinal extent of the recess will also be correspondingly large, potentially leading to undesirable breakout of the shoulders adjacent to the common or central shoulder being cut. Conversely, if the working radius of the milling cutter is too small, the required plunge depth may not be achieved because, in the worst-case scenario, the cutter shank will come into contact with the outer diameter.

[0035] The invention is explained in more detail below with reference to an embodiment illustrated in a total of six figures. These show:

[0036] Figure 1 shows a threaded spindle with deflection insert in one view.

[0037] Figure 2 shows the threaded spindle from Figure 1 in perspective view with individual parts.

[0038] Figure 3 shows the threaded spindle as in Figure 1, but without a deflection insert.

[0039] Figure 4 shows a section along the section line AA through the threaded spindle in Figure 1 ,

[0040] Figure 5 shows a schematic representation of a tool for manufacturing a schematically depicted threaded spindle.

[0041] Figure 6 shows another schematic representation of the tool from Figure 5, and Figure 7 shows a longitudinal section through a ball screw drive with the threaded spindle from Figure 1.

[0042] Figures 1 to 4 show a threaded spindle for a ball screw drive, on the outer circumference of which a ball groove 1 is formed helically wound around the spindle axis over several turns at a helix angle α (Figure 3). The threaded spindle is hollow cylindrical and fixedly connected at one end face to a shaft 2.

[0043] Figure 2 clearly shows several recesses 3 distributed around the circumference of the threaded spindle. The recesses 3 are open towards the outer circumference of the threaded spindle. A deflecting insert 4 is arranged in each recess 3 to deflect balls 5 from an end “E” of a common turn 6 to a beginning “A” of the common turn 6. In the exemplary embodiment, three deflecting inserts 4 are provided, each connecting an end “E” of a turn of the common ball groove 1 with a beginning “A” of the common turn 6 of the ball groove 1.

[0044] In the exemplary embodiment, the deflection insert 4 is formed by a deflection piece 7 injection-molded from plastic. A groove-shaped deflection channel 8 is formed on the deflection piece 7 on its side facing away from the threaded spindle. The deflection channel 8 has a ball inlet 9, a ball outlet 10, and a deflection section 11 connecting the ball inlet and the ball outlet. Furthermore, two diametrically opposed support arms 12 are formed on opposite end faces of the deflection piece 7, each engaging in the ball groove 1 in a so-called dead-space section 13 of the ball groove 1, in which no balls 5 circulate.

[0045] Figures 2 and 3 clearly show that the recess 3 is bounded by side walls 16 formed parallel to the angle of inclination α of the ball groove 1. The side walls 16 are formed by flat surfaces and are arranged parallel to each other.

[0046] A recess width “b” of the recess 3 transverse to the slope angle a corresponds approximately to the axial extent of two adjacent spherical grooves 1 .

[0047] Figure 3 clearly shows the side walls 16 of the recess 3, which are parallel to the shoulders 20 of the ball groove 1 and lie in front of the apex of the shoulders 20. These side walls ensure that the shoulders 20 have the ball groove profile on their shoulder sides facing away from the recess, meaning that these shoulders 20 are not penetrated. Figure 4 clearly shows the length of the recess 3, which extends parallel to the angle of inclination α and is bounded by run-off surfaces 17. The depicted section plane lies parallel to the angle of inclination α of the ball groove 1. It is clearly visible that the run-off surfaces 17 transition into a recess bottom 18 of the recess 3 via a radius of curvature R1. In the exemplary embodiment, the run-off surface has this radius of curvature R1.

[0048] In one variant, this run-out surface 17 can be concavely curved along its extension from the recess bottom 18 to the outer surface of the threaded spindle and change its radius of curvature along this extension.

[0049] In other embodiments, it may be advantageous if the run-out surface, as seen in this section, is straight and radially aligned with the spindle axis.

[0050] Figure 4 further shows that the recess base 18 forms a flat plateau 19, at whose two ends, located in the longitudinal direction of the recess 3, the radius of curvature R adjoins, connecting tangentially to the plateau. The length “a” of the plateau 19 between the run-out surfaces 17 is adapted to the required length of the deflection piece and provides for the length of the ball entry and ball exit each to be half the ball diameter, and for the deflection section an amount that depends on the thread pitch and the ball diameter.

[0051] Furthermore, Figure 4 shows that the contours of the recess 3 and the deflection piece 7 are aligned so that simply inserting the deflection piece 7 into the recess 3 ensures its correct positioning. The deflection piece 7 can be pressed in and / or fixed in the recess 3 using an adhesive.

[0052] Figures 6 and 7 show a schematic representation of a tool arrangement with which the recess 3 can be machined into the threaded spindle. This tool arrangement comprises a disc cutter 21 with a cutter disk 22, which is mounted on a rotary-driven cutter shank 24. This disc cutter 21 enables the process steps described below for producing the recess in the threaded spindle.

[0053] The disk cutter 21, shown only schematically, has in the exemplary embodiment the cutter disc 22 with a working radius R2 and flat and parallel end faces 23 (not shown further), as well as a cutter shaft 24 with a shaft radius R3, which is driven by a rotation axis 28 of the disk cutter 21.

[0054] The cutter shank 24 and the cutter disc 22 are arranged coaxially and perpendicular to each other. The axis of rotation 28 of the disc cutter and the spindle axis 29 of the threaded spindle each lie in a plane that is parallel to each other. In a viewing direction perpendicular to these planes, the axes 28 and 29 are inclined to each other at the helix angle α (see Figure 3).

[0055] The recess 3 described and illustrated above is milled using this disc cutter 21. The milling process involves aligning the end faces 23 of the cutter disc 22 parallel to the helix angle α of the ball groove 1, and aligning the rotation axis FA of the disc cutter 21 perpendicular to the helix angle α. The rotation axis A of the disc cutter 21 and the spindle axis of the threaded spindle each lie in a plane that is parallel to each other.

[0056] The milling disc 22 is advanced radially towards the threaded spindle to a depth "t" and mills into the threaded spindle. Upon reaching the depth of cut "t", at least one of the two run-out surfaces 17 of the recess is immediately formed. The disc cutter 21 is then moved along a straight line parallel to the helix angle α, milling the recess bottom 18 of the recess 3. In the described embodiment, the plateau 19 is formed by this process along the straight line. The milling disc 22 can now be moved radially away, forming the other run-out surface 17. If the extent of the recess 3 perpendicular to the helix angle α is wider than the thickness of the milling disc 22, the further part of the recess 3 with the other side wall 16 can be formed by relative displacement between the threaded spindle and the cutter shank 24 along the axis of rotation 28 of the disc cutter 21.In the exemplary embodiment, the working radius R2 of the milling disc 22 and the radius of curvature R1 of the recess 3 coincide; the milling disc 22 mills the radius of curvature R1 with the working radius R2, which forms the run-out surface 17 of the recess 3 and transitions tangentially into the recess bottom 18.

[0057] The recess base 18 can also be formed with the radius of curvature R1 in a modified variant without the plateau 19 described above.

[0058] Figure 7 shows a line “T” tangent to the outer diameter of the threaded spindle. The radial feed of the milling cutter 22 continues until the intended depth for forming the recess 3 is reached. In this situation, it is ensured that the milling cutter shank 24 maintains a minimum distance “s” from this line “T”, which is at least 0.25 mm. Maintaining this distance “s” prevents the milling cutter 22 from being pushed away unintentionally.

[0059] Figure 7 shows a ball screw drive with the threaded spindle described in the exemplary embodiment, on which a threaded nut 25 is arranged, on the inner circumference of which a helically wound ball groove 26 is formed around the spindle axis, which together with the spindle-side ball groove 1 and the spindle-side deflection inserts 4 forms three endless ball channels 27 in which the balls 5 circulate endlessly.

[0060] List of reference signs

[0061] ball groove

[0062] 2nd wave

[0063] 3 Exclusion

[0064] 4 deflection insert

[0065] 5 balls

[0066] 6 turns

[0067] 7 Deflection piece

[0068] 8 Deflection channel

[0069] 9 Ball entry

[0070] 10 Ball discharge

[0071] 11 Deflection section

[0072] 12 Support arm

[0073] 13 Dead Man's Walk section

[0074] 14

[0075] 15

[0076] 16 side wall

[0077] 17 Run-off area

[0078] 18 Extraction floor

[0079] 19 flat plateau

[0080] 20 Shoulder

[0081] 21 disc cutters

[0082] 22 milling disc

[0083] 23 Front surface

[0084] 24 milling cutter shank

[0085] 25 threaded nut

[0086] 26 ball groove

[0087] 27 endless ball channel

[0088] 28 Rotation axis of the disc cutter

[0089] 29 Spindle axis

[0090] “a” angle of inclination

[0091] “a” length of the plateau “A” beginning of the common bend

[0092] “b” recess width

[0093] “D” ball diameter

[0094] “E” End of the common loop

[0095] “R1” radius of curvature

[0096] "R2" working radius

[0097] “R3” radius of the milling cutter shank

[0098] “s” distance of the milling cutter shank to the outer circumference of the threaded spindle

[0099] "t" depth of the recess

[0100] "T" line that is tangent to the outer diameter of the threaded spindle

Claims

Patent claims 1. Threaded spindle for a ball screw drive, on the outer circumference of which a ball groove (1 ) is formed helically wound over several turns around the spindle axis at a helix angle (a), and in the recess (3) of which open towards the outer circumference a deflecting insert (4) is arranged for deflecting balls (5) from an end (E ) of a common turn (6) to a beginning (A) of the common turn (6), characterized in that the recess (3) is bounded by side walls (16) formed parallel to the helix angle (a) of the ball groove (1 ).

2. Threaded spindle according to claim 1, the side walls (16) of which are formed by flat surfaces and arranged parallel to each other.

3. Threaded spindle according to claim 1 or 2, the threads of which are parallel to the helix angle (a) the extended length of the recess (3) is limited by run-out surfaces (17) which, viewed in a section plane parallel to the helix angle (a) of the ball groove (1), are concavely curved and transition into a recess bottom (18) of the recess (3).

4. Threaded spindle according to claim 3, the recess bottom (18) of which, viewed in the section plane through the threaded spindle, has a flat plateau (19) at both ends of which the run-out surfaces (17) connect.

5. Threaded spindle according to one of claims 1 to 4, having a recess width (b) the recess (3) transverse to the angle of inclination (a) which corresponds to an axial extent of approximately one full turn (6) of the ball groove (1 ).

6. Ball screw drive with a threaded spindle according to one of claims 1 to 5, with a threaded nut (25) arranged on the threaded spindle, wherein the balls (5) circulate in endless ball channels (27), and wherein the deflection insert (4) is fixed in the recess (3) of the threaded spindle by force and / or material interlock.

7. Method for manufacturing a threaded spindle of a ball screw drive, on the outer circumference of which a ball groove (1) is formed helically wound over several turns (6) around the spindle axis with a helix angle (a), and which is provided with a recess (3) open towards the outer circumference, which is suitable for receiving a deflecting insert (4) for deflecting balls (5) from an end (E) of a common turn (6) to a beginning (A) of the common turn (6), characterized in that the recess (3) is milled by means of a milling cutter (22), the end face (23) of which is aligned parallel to the helix angle (a) and the axis of rotation (28) is oriented transversely to the helix angle (a) and which has a working radius (R2), wherein the milling cutter (22) mills radially into the threaded spindle with a depth (t) and a run-out surface (17) trains,which extends between a recess bottom (18) of the recess (3) and a cylindrical surface of the threaded spindle, wherein the run-out surface (17) is milled with a concave curve.

8. Method according to claim 7, wherein the run-out surface (17) is concavely curved with a radius of curvature (R1) corresponding to the working radius (R2) of the milling disc (22).

9. Method according to claim 7, wherein the concavely curved run-out surface (17) has different radii of curvature along its extent, the smallest radius of curvature of which is greater than or equal to the working radius (R2) of the milling disc (22).

10. Method according to one of claims 7 to 9, wherein the ball groove (1 ) is designed to receive balls (5) with a ball diameter (D), wherein the working radius (R2) of the milling disc (22) is greater than or equal to the ball diameter (D) and less than or equal to five times the ball diameter (D).

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