Ball screw nut and method for manufacturing a spindle nut

Abstract

During the forming process of manufacturing a spindle nut (1) of a ball screw drive (10), an external functional contour (6) is produced by displacing material from the inside to the outside. An insert (11) is inserted into the area of ​​displaced material on the inside of the spindle nut (1).

Description

[0001] The invention relates to a method for manufacturing a spindle nut of a ball screw drive, designed according to the preamble of claim 1. Furthermore, the invention relates to a ball screw nut for use in a ball screw drive, according to the preamble of claim 3. A spindle nut is understood to be the nut of any ball screw drive – whether with or without rolling elements. The term ball screw nut, however, is used exclusively for the nut of a ball screw drive, which comprises balls as rolling elements.

[0002] US Patent 2012 / 0325036 A1 describes a generic process for manufacturing a lead screw nut. In this process, an S-shaped recess is formed on the inner surface of a tubular workpiece from which the lead screw nut is to be manufactured. This recess serves as a guide for the rolling elements within the final product, the lead screw nut. The material displacement during the forming process of the S-shaped recess on the inner circumferential surface of the lead screw nut creates a material accumulation on the outer circumferential surface. This accumulation of material is then shaped by a suitable tool, in which the lead screw nut is held during the forming process, into the form of a so-called stop, i.e., a functional contour of the final lead screw.

[0003] Other forming processes for manufacturing spindle nuts for ball screw drives are described, for example, in documents US 2012 / 0325036 A1 and US 2013 / 0008275 A1. In these cases, curved contours for ball deflection are also created on the inner circumferential surface of a spindle nut by displacing material from a sleeve-shaped workpiece.

[0004] DE 10 2023 107 423 A1 discloses a method for manufacturing a spindle nut of a ball screw drive. The method according to DE 10 2023 107 423 A1 provides that a nut body of a spindle nut is machined exclusively without chips on its outer circumferential surface and by machining on its end faces and its inner circumferential surface, wherein the machining without chips on the outer circumferential surface includes the formation of return grooves for the rolling element return.

[0005] A ball screw drive described in DE 10 2015 214 856 B4 has a threaded nut, i.e., a spindle nut, with an internal ball groove into which several pockets are formed, each containing a deflecting element for deflecting balls running in the ball groove from one channel section to an adjacent channel section. On the outside of the spindle nut according to DE 10 2015 214 856 B4, an integral bearing geometry serving for the rotary bearing of the spindle nut or a drive geometry serving for the drive of the spindle nut is provided.

[0006] DE 10 2015 214 859 B4 relates to a ball screw drive whose spindle nut has a deflection element designed as a single deflection element. An external deflection device is axially positioned in front of this deflection element. The external deflection device engages in two openings in the spindle nut.

[0007] A ball screw drive disclosed in DE 199 44 875 A1 comprises a spindle and an associated nut, which is designed as a one-piece sleeve with a circular cylindrical outer shell. Deflection pieces are arranged in through-holes of the nut within the outer shell.

[0008] DE 10 2019 107 684 A1 shows a ball screw drive with a spindle having an external thread and a nut having an internal thread, wherein a form element is arranged between the external thread and the internal thread which is designed to be complementary to the external thread in order to receive an impulse from the threaded nut and to dissipate it via the spindle.

[0009] The invention is based on the objective of further developing spindle nuts for threaded drives, including ball screw drives or other rolling screw drives, compared to the aforementioned prior art with regard to manufacturing aspects, while at the same time striving for a particularly good ratio between installation space requirement and mechanical load capacity.

[0010] This problem is solved according to the invention by a method for manufacturing a spindle nut of a threaded drive as designed according to claim 1. The threaded drive can, in principle, be a simple linear screw or a rolling screw drive, in particular a ball screw drive. Furthermore, the problem is solved by a ball screw nut according to claim 3. The embodiments and advantages of the invention explained below in connection with the devices, i.e., the ball screw nut or other spindle nut and the threaded drive equipped therewith, also apply mutatis mutandis to the manufacturing method, and vice versa.

[0011] The manufacturing process is generally characterized by the displacement of material from the inside of the spindle nut to the outside. This creates a recess on the inner circumferential surface of the spindle nut, interrupting the area of ​​the future thread, and simultaneously forms a functional contour on the outer circumferential surface of the spindle nut during the forming process. An insert is then placed into the free volume created by the displacement of material on the inner circumferential surface of the spindle nut.

[0012] In addition to the external functional contour, provided this is not to be removed in one of the subsequent manufacturing steps, the insert placed inside the spindle nut also has a function within the later threaded drive, which is completed by the threaded spindle and the optional rolling elements. This applies both to embodiments in which the spindle nut functions as the drive element of the threaded drive and to embodiments in which the spindle nut is part of the output side of the threaded drive. Generally, the drive element of the threaded drive is a rotating machine element, while the output element is displaceable and protected against rotation.

[0013] Regarding the technology for manufacturing the spindle nut, forming processes are used in all cases. In particular, it may be possible to first create the outer functional contour using forming techniques and then, using this functional contour as a reference, to produce the thread by machining. Machining of the functional contour is also possible.

[0014] In principle, in addition to the external functional contour, the thread of the spindle nut, intended for interaction with a threaded spindle of the screw drive, can also be manufactured using forming techniques. During the forming process of the external functional contour, previously formed structures may be partially affected, necessitating post-processing.

[0015] The ball screw nut according to the application generally comprises an inner thread, which interacts with a spindle of a screw drive via rolling elements, namely balls, and an outer functional contour projecting from an outer surface, formed by material displaced from the inside to the outside. Apart from the functional contour, the outer surface has, for example, at least a partially cylindrical shape. The outwardly displaced material forms, in particular, pockets which, from a manufacturing perspective, are related to features on the outer diameter. These pockets also have a function within the ball screw drive, as will be explained below.

[0016] Regarding the external functional contour, it can fulfill various tasks in different configurations. For example, in cases where the ball screw nut represents a displaceable output element of a threaded drive, the functional contour serves as an anti-rotation device. Conversely, in cases where the ball screw nut is located on the drive side of a threaded drive, a rotationally fixed connection between the functional contour of the ball screw nut and a drive element may be provided. The functional contour itself can also be designed as the drive element of the ball screw drive.

[0017] Regardless of the ball screw nut's function within a threaded drive, the material displaced from the inside out by the ball screw nut can interrupt the rolling element raceway. A bridging element, made of plastic or metal, for example, can be inserted into this interruption. This bridging element, or insert, in its various possible designs, does not serve a deflecting function but simply bridges two load-bearing sections of the ball screw nut's threaded raceway. Thus, the inner recess into which the insert is placed can be positioned independently of any deflecting contour, depending on the position of the outer functional contour. This means that the outer functional contour, created by the radial displacement of material by the ball screw nut, is freely positionable.

[0018] The thread of the spindle nut can be a single-start or multi-start thread. Optionally, at least one formed feature, i.e., an internal recess, is located outside or between the raceways for the balls of the screw drive. In these cases, each internal feature is also associated with an external functional contour that serves a purpose during the manufacturing process and / or in the subsequent operation of the screw drive.

[0019] Regarding the external shape of the spindle nut, numerous design variations also exist. For example, the outer contour of the spindle nut can be circular or any polygon, such as a hexagon or an octagon. The outer contour of the spindle nut can vary along its length.

[0020] The ball screw nut is, in particular, a component of a ball screw drive with individual deflection. This means that the balls of the screw drive are lifted from their raceway and guided into an adjacent thread without entering a space outside the outer circumferential surface of the ball screw nut. To achieve individual deflection, a deflection element, i.e., an insert, is used, which is inserted into an internal recess, i.e., a pocket, created during the forming process. The functional contour formed by the displaced material is located radially outside the recess. The ball screw nut can have multiple deflection elements and associated functional contours, which are used during the manufacturing process and / or in the subsequent operation of the ball screw drive.

[0021] Due to the fact that the functional contour is pressed out of the original contour of the workpiece from which the ball screw nut is manufactured using forming processes, the machining volume can be drastically reduced or even completely eliminated compared to non-stressed manufacturing processes that are predominantly or exclusively based on machining.

[0022] With regard to the mechanical strength of the final product, the forming process used to manufacture the various internal and external contours of the spindle nut offers advantages compared to contours produced solely by machining. In particular, even after hardening, visible flow lines extend continuously in a multiply curved form, following the contour of a pocket formed by material displacement, beyond the pocket of the spindle nut.

[0023] If the forming process from the inside out, which creates pockets on the inside of the ball screw nut, results in protrusions on the outside of the ball screw nut that are not needed in later manufacturing phases or in the operation of the ball screw drive, these protrusions can be easily removed by machining.

[0024] The features, that is, the functional contours that remain on the ball screw nut, can have any shape. For example, the features may have a circular or polygonal cross-section. In the case of an elongated cross-section, for example elliptical or rectangular, this can be oriented tangentially to the ball screw nut, axially, or in any other direction, in particular with a slight inclination to the tangential direction, corresponding to the pitch of the thread of the ball screw nut.

[0025] Regardless of the overall shape of the external functional contours, indentations may be present in areas of the functional contours not intended for torque or force transmission. These indentations, i.e., additional depressions created by the contours of a forming tool, ensure that during the forming process, material from the workpiece is directed towards the flanks of the functional contour. This gives the flanks a precisely defined shape, providing them as force- and torque-transmitting surfaces for the threaded drive component, i.e., the spindle nut.

[0026] Low-alloy carbon steels are particularly suitable as materials for manufacturing the spindle nut. One example of such a steel, which can be used as a case-hardening steel, is 16MnCr5 (material number 1.7131).

[0027] Several embodiments of the invention are explained in more detail below with reference to a drawing. This drawing shows: Fig. 1 a first embodiment of a ball screw nut of a screw drive, Fig. 2 a detail Y from Fig. 1, Fig. 3. the ball screw nut Fig. 1 in another cutaway view, Fig. 4 a detail X out Fig. 3, Fig. 5. the ball screw nut Fig. 1 in perspective view, Fig. 6 and Fig. 7 an intermediate product from which the ball screw nut is made Fig. 1 is manufactured, Fig. 8 another intermediate product from which a ball screw nut is manufactured, Fig. 9 a detail Y2 from Fig. 8, Fig. 10 the intermediate product after Fig. 8 in another cutaway view, Fig. 11 a detail X2 from Fig. 10, Fig. 12 the intermediate product after Fig. 8 in a sectional perspective view, Fig. 13 compared to the variant after Fig. 8 modified intermediate in top view, Fig. 14 the intermediate product after Fig. 13 in cutaway view, Fig. 15 a pre-product of a ball screw nut with hexagonal internal geometry in cutaway view, Fig. 16 the ball screw nut after Fig. 15 in another sectional view, Fig. 17, Fig. 18 flow lines created by forming within the ball screw nut according to Fig. 1, Fig. 19 a ball screw nut with single deflection in cutaway view, Fig. 20 the ball screw nut after Fig. 19 in another cutaway view.

[0028] Unless otherwise stated, the following explanations apply to all embodiments. Corresponding or essentially equivalent parts are marked with the same reference numerals in all figures.

[0029] A ball screw nut 1, also referred to as a spindle nut, is part of a ball screw drive 10, i.e., a threaded drive, which is used in an electromechanical actuator (not shown), for example, in a motor vehicle or a stationary machine. Inside the spindle nut 1, a thread 2 is formed in which balls 3 roll as rolling elements. The balls 3, which roll on the thread 2 as a raceway, simultaneously roll in an external thread of an associated threaded spindle (not shown). A single deflection 4 is provided for the return of the balls 3 within the threaded drive 10. Regarding the basic design and function of ball screw drives with single deflection, reference is made to the prior art cited above.

[0030] The outer circumferential surface of the spindle nut 1, designated 5, is predominantly cylindrical in the exemplary embodiments. In contrast to this basic cylindrical shape, outwardly projecting functional contours 6 are present, which will be discussed in more detail below. In all cases, the functional contours 6 are predominantly or exclusively formed. Each outer functional contour 6 corresponds to a pocket 7 on the inside of the spindle nut 1, generally referred to as a recess. In the exemplary embodiment according to Fig. 1. The pockets 7 are in the form of deflection pockets 8 and a further pocket 9. When each pocket 7, 8, 9 is created by forming, i.e., material displacement from the inside to the outside, the corresponding functional contour 6 is inevitably created, which protrudes from the otherwise cylindrical outer circumferential surface 5.

[0031] In the case of Fig. 1 are in the pockets 8 deflection parts 11 not shown here (see Fig. 19 and Fig. 20) are used, with which the individual deflection 4 within the threaded drive 10 is accomplished. The deflection elements 11 generally represent insert elements 11, irrespective of their function. The further pocket 9 is only provided to create one of the cam-shaped functional contours 6, which in this case is slightly inclined relative to the tangential direction of the essentially cylindrical spindle nut 1 in adaptation to the pitch of the thread 2.

[0032] The functional contours 6 are used in the manufacturing process, in particular, to align the spindle nut 1 or an intermediate product 12, i.e., a pre-product from which the spindle nut 1 is produced, during machining. After the spindle nut 1 has been manufactured, the functional contours 6 can function as contours for an anti-rotation device, as contours for holding a drive element (not shown), or as the drive element itself. Functional contours 6 that are not required after manufacturing can be removed by machining.

[0033] The Fig. 6 and Fig. Figure 7 shows an intermediate product 12 in which the thread 2 is still missing. Like the existing external functional contours 6, the thread 2 can be produced without machining. Machining or post-processing of the thread 2 is also possible.

[0034] In the exemplary embodiment according to the Fig. 8, Fig. 9, Fig. 10, Fig. 11 to Fig. 12 is located in the outer surface of each cam, which is raised from the outer circumferential surface 5 and through which a functional contour 6 is formed, an indentation 13. In the case of the Fig. 13 and Fig. 14 are the same as in the exemplary embodiment according to Fig. 1. The functional contours 6, designed as cam-shaped elevations, are slightly inclined to match the thread pitch. The same applies to the elongated indentations 13. The indentations 13 are additional recesses located on a surface of a cam that is practically not subjected to forces or moments when the spindle nut 1 is used in the ball screw drive 10. In contrast, the flanks of the cam-shaped functional contour 6 are surfaces that must absorb forces and torques. The indentations 13 ensure that material is directed to these flanks during the forming process used to create the functional contours 6.

[0035] The exemplary embodiment according to the Fig. 15 and Fig. 16 differs from the other embodiments in that the pockets 7, as well as the associated external functional contours 6, are located in a section of the ball screw nut 1 without threads 2. Instead, a hexagonal internal profile 14 is formed in the relevant section. The internal profile 14 can, for example, be used for the torque-transmitting connection of the spindle nut 1 to another machine element, not shown.

[0036] The Fig. 17 and Fig. Figure 18 shows flow lines 15 resulting from the forming process of the pockets 7, 8, 9, which exist in every embodiment and extend beyond the area of ​​the pockets 7, 8, 9. The simultaneous forming process of the pockets 7, 8, 9 and the associated external functional contours 6 significantly increases the mechanical strength compared to contours produced by machining.

[0037] In the Fig. 19 and Fig. Figure 20 shows the steel balls 3, i.e., the rolling elements of the ball screw drive 10. The previously mentioned deflection elements 11 guide the balls 3 from one turn of the thread 2 to an adjacent turn. The individual deflection 4 is implemented in the same way in each of the other embodiments. Reference symbol list 1 ball screw nut, spindle nut 2 threads, raceway 3 rolling elements, ball 4 single deflection 5 External perimeter area 6 Functional contour 7 Pocket, general, indentation 8 pockets, for rolling element deflection 9 additional pockets interrupting the rolling element track 10. Screw drive, ball screw drive 11 Deflection part, insert part 12 Intermediate product, preliminary product 13. Imprinting 14 Inner profile 15 Flow line QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2012 / 0325036 A1 [0002, 0003] US 2013 / 0008275 A1

[0003] DE 10 2023 107 423 A1

[0004] DE 10 2015 214 856 B4

[0005] DE 10 2015 214 859 B4

[0006] DE 199 44 875 A1

[0007] DE 10 2019 107 684 A1

[0008]

Claims

Method for manufacturing a spindle nut (1) of a threaded drive (10), wherein an outer functional contour (6) is produced by displacing material from the inside to the outside, interrupting the area of ​​a subsequent thread (2), characterized in that an insert (11) is inserted into the area of ​​displaced material. Method according to claim 1, characterized in that the outer functional contour (6) is first produced by forming technology and then the thread (2) is produced using this functional contour (6) as a reference contour. Ball screw nut (1), with an inner thread (2) designed as a raceway for rolling elements (3) and an outer functional contour (6) formed by material displaced from the inside to the outside and projecting from an outer circumferential surface (5), characterized by an insert (11) placed in the area of ​​displaced material. Ball screw nut (1) according to claim 3, characterized in that the functional contour (6) is attributable to an anti-rotation device. Ball screw nut (1) according to claim 3, characterized in that the functional contour (6) is provided for a rotationally fixed connection with a drive element. Ball screw nut (1) according to one of claims 3 to 5, characterized in that an indentation (13) is located in a surface of the functional contour (6) which is not intended for torque or force transmission. Ball screw nut (1) according to one of claims 3 to 6, characterized in that flow lines (15) extend in a multiply curved form uninterrupted beyond a pocket (7, 8, 9) formed by material displacement, following the contour of the pocket (7, 8, 9). Ball screw nut (1) according to one of claims 3 to 7, characterized in that a pocket (9) interrupting the thread (2) is formed by the outwardly displaced material, wherein an insert (11) without a deflecting function is inserted into the pocket (9). Ball screw nut (1) according to one of claims 3 to 8, characterized in that it is designed as a component of a ball screw drive with single deflection (4). Ball screw nut (1) according to claim 9, characterized in that a deflecting part (11) provided for accomplishing the individual deflection (4) is inserted into an inner recess (8) as an insert part (11), wherein the functional contour (6) formed by displaced material is located radially outside the recess (8).

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