Planetary screw drive with lubricant distribution recess

Abstract

Planetary screw drive (10) with a nut (20) and a spindle (30), wherein the spindle (30) extends along a longitudinal axis (11) and is provided with an outer profile (31), wherein the nut (20) surrounds the spindle (30) and is provided with an inner profile (21), wherein at least one planet (40) is provided, which extends parallel to the longitudinal axis (11) and is provided with an outer profile (42), wherein the at least one planet (40) is arranged between the nut (20) and the spindle (30) such that its outer profile (42) engages both in the outer profile (31) of the spindle (30) and in the inner profile (21) of the nut (20), wherein a lubrication channel (60) is provided on the nut (20), which has an opening (63) in the region of the inner profile (21) of the nut, characterized in that at the opening (63) a recess (64) is provided,which is formed deeper than the inner profiling (21) of the nut (20), so that a cutting edge of a turning tool for producing the inner profiling (21) on the nut (30) merges into the recess (64) during the cutting process, wherein said cutting edge does not come into contact with the lubrication channel (60) at all during the cutting process, wherein a surface of the recess (64) is formed as a section of a circular ring, wherein a circular ring is understood to mean a body which is produced by rotating a circle around an axis of rotation lying in the plane of the circle and not intersecting the circle.

Description

[0001] The invention relates to a planetary screw drive according to the preamble of claim 1.

[0002] A planetary screw drive is known from DE 92 14 062 U1. The planetary screw drive comprises a spindle and a nut. The spindle extends along a longitudinal axis and is provided with an external profile. In this case, the external profile is designed as a multi-start V-thread, i.e. there are several grooves running helically around the longitudinal axis which are V-shaped when viewed in cross-section. The nut surrounds the spindle and is provided with an internal profile. The pitch and profile shape of the internal profile of the nut and the external profile of the spindle match. Furthermore, several planets are provided which extend parallel to the longitudinal axis and are arranged between the spindle and the nut. The planets are provided with an external profile which engages with the external profile of the spindle and the internal profile of the nut.The outer profile of the planets, in turn, has the same pitch and profile shape as the outer profile of the spindle. As usual, pitch is defined as the pitch of the helical grooves divided by the number of helical grooves or thread turns.

[0003] The nut is provided with a lubrication channel with an opening in the area of ​​the inner profile. The nut is typically made of steel, and is hardened at least in the area of ​​the inner profile. The inner profile of the nut can be produced either by grinding or by turning the hardened nut body.

[0004] Since the lubrication channel can only be created before the nut is hardened, the problem arises that the turning tool used to create the internal profile of the nut passes over the opening of the lubrication channel. This creates very harsh, impact-like loads on the cutting edge of the turning tool, as it is completely relieved of load in the area of ​​the opening, and is also subjected to the high cutting forces during hard turning. The cutting edge of this turning tool therefore has a short service life.

[0005] Another planetary screw drive with a lubrication channel is known from DE 102 49 762 A1.

[0006] DE 10 2007 038 740 B4 discloses a device for lubricating a screw gear. The corresponding nut is provided with at least one axial bore through which lubricant can be introduced into the recess(es).

[0007] The object of the invention is to provide a planetary screw drive in which the aforementioned turning tool can be used for a longer period of time for hard turning the inner profile of the nut. In particular, the impact loads in the area of ​​the opening are to be minimized.

[0008] According to the independent claim, this object is achieved by providing a recess at the mouth opening that is deeper than the internal profile of the nut. As will be explained below, the recess according to the invention can easily be designed such that the forces acting on the cutting edge gradually decrease and then increase again as they transition into the recess. The recess is deeper than the internal profile of the nut so that the cutting edge of the turning tool no longer comes into contact with the lubrication channel at all. The applicant's experience has shown that the service life of the cutting edge of the turning tool typically increases by a factor of eight thanks to the recess according to the invention.

[0009] Advantageous further developments and improvements of the invention are specified in the dependent claims.

[0010] The recess can be elongated, extending transversely to the longitudinal axis or in the pitch direction of the nut's internal profile. The elongated shape ensures that the cutting edge of the turning tool meets the edge of the recess at an acute angle, rather than at a nearly right angle as in the prior art. This results in the cutting forces no longer rising and falling suddenly, but rather gradually. The elongated shape of the recess also has the advantage that lubricant can be supplied even if a planet is located directly above the opening of the lubrication channel when the planetary screw drive is at a standstill.

[0011] The surface of the recess is formed as a section of a circular ring. In particular, the idea is to produce the recess using a side milling cutter whose cutting edge is shaped like a semicircle, the diameter of which corresponds to the cross-sectional diameter of the circular ring. With this shape of the recess, the applicant achieved particularly long service lives for the cutting edge of the turning tool. This is due not only to the elongated shape proposed above, but also to the continuously increasing and decreasing depth of the recess, which also causes a gradual decrease and increase in the cutting forces on the turning tool.

[0012] The cross-sectional diameter of the circular ring can be between 1 and 5 times the pitch of the nut's internal profile. These dimensions ensure particularly long tool life for the aforementioned turning tool.

[0013] The outer diameter of the circular ring can be between 3 and 8 times the cross-sectional diameter of the circular ring. These dimensions result in an elongated recess with a particularly favorable length-to-width ratio, thus extending the tool life of the turning tool. If a side milling cutter is used to create the recess, the specified outer diameter must not be larger than the diameter of the inner profile of the nut, otherwise the side milling cutter cannot be inserted into the nut.

[0014] The lubrication channel can be designed in the form of a stepped bore with a first and a second diameter, with the first diameter being smaller than the second diameter in the area of ​​the orifice. The large second diameter offers little flow resistance to the supplied lubricant. The smaller first diameter is selected at the transition to the recess according to the invention so that it does not have to be excessively wide. This would unnecessarily reduce the load-bearing capacity of the planetary screw drive.

[0015] The invention is explained in more detail below with reference to the accompanying drawings. It shows: Fig. 1 shows a longitudinal section of a planetary screw drive according to the invention; Fig. 2 a perspective view of the main body of the nut before the internal profiling is produced; Fig. 3 a partial sectional view of the finished main body of the nut in the area of ​​the mouth opening of the lubrication channel; Fig. 4 a front view of a side milling cutter for producing the recess according to the invention; and Fig. 5 a top view of the side milling cutter according to Fig. 4.

[0016] Fig. 1 shows a longitudinal section of a planetary screw drive 10 according to the invention. The planetary screw drive 10 comprises a spindle 30 extending along a longitudinal axis 11. The spindle 30 is made of steel and has an external profile 31 produced using the thread rolling process, wherein it was hardened after the thread rolling. The external profile 31 is in the form of a pointed thread, which may, for example, have five starts. Accordingly, a total of five V-shaped grooves are provided, viewed in cross-section, which run helically with respect to the longitudinal axis 11. The spacing of these grooves in the direction of the longitudinal axis 11 is referred to as the pitch, wherein the pitch is equal to the lead of the individual groove divided by the number of grooves.

[0017] The spindle 30 is surrounded by a nut 20, which comprises a sleeve-like main body 25 made of steel. The main body 25 is provided with an internal profile 21 on its inner circumferential surface. This profile corresponds to the outer profile 31 of the spindle 30 in terms of pitch and profile shape. However, the pitch of the individual grooves of the internal profile 21 does not necessarily correspond to that of the spindle 30. The internal profile 21 can even be provided with grooves that encircle the longitudinal axis 11 in a circle, so that one could speak of a thread with a zero pitch.

[0018] Between the spindle 30 and the nut 20, several identical planets 40 are arranged, the number of which can be, for example, seven. The planets 40 are made of hardened steel and are provided with an outer profile 42, which corresponds to that of the spindle 30 in terms of profile shape and pitch. The outer profile 42 of the planets 40 engages both the outer profile 31 of the spindle 30 and the inner profile 21 of the nut 20. The pitch angle of the outer profile 42 of the planets 40 is identical to the pitch angle of the inner profile 21 of the nut 20, with the pitch directions being opposite. As a result, there is no relative movement between the planets 40 and the main body 25 of the nut 20 with respect to the longitudinal axis 11. Only the entire nut 20 with the planets 40 moves in the direction of the longitudinal axis 11 with respect to the spindle 30.

[0019] The planets 40 have a central axis 41 that extends parallel to the longitudinal axis 11. To ensure this alignment, the planets 40 are provided at both ends with external teeth 43, which mesh with a separate, associated gear ring 50 with a matching internal toothing. The gear ring 50 is firmly connected to the main body 25 of the nut 20 via several threaded pins 51. It should be noted that the internal toothing can also be formed directly on the main body 25 of the nut 20.

[0020] To determine the distance between the planets 40 in the circumferential direction relative to the longitudinal axis 11, a guide disk is provided at each end of the planets 40, with the planets 40 engaging with a pin in a matched bore of the guide disk 13 for rotation. The guide disk 13 is held in the main body 25 of the nut 20 by means of an associated retaining ring 14, and can be rotated relative to the main body 25 with respect to the longitudinal axis 11 so that the planets 40 have the required mobility. Furthermore, a rubber end seal is fixedly provided at each end of the main body 25, the sealing lip of which slides against the outer profile 31 of the spindle 30. Accordingly, lubricating grease inside the nut 20 can essentially not escape from it.

[0021] The main body 25 of the nut 20 is provided with a one-piece flange 24, via which the nut 20 can be attached to a higher-level assembly, for example, the carriage of a machine tool. A lubrication channel 60 is provided in the flange 24, which leads to the inner profile 21 of the nut 20. The lubrication channel 60 is composed of several bores on the outer surface of the main body 25, which can be connected to a lubricant supply, for example, a grease nipple (not shown). The unused opening of the lubrication channel 60 on the outer surface of the nut is tightly closed with a plug (not shown).

[0022] Fig. Figure 2 shows a perspective view of the main body 25 of the nut before the internal profiling is produced. Fig. The state shown in Figure 2 is produced in the unhardened state, i.e., only the inner profiling of the nut is produced after the main body has been hardened in the area of ​​the inner profiling. The inner profiling is produced by hard turning, with the individual helical grooves of the inner profiling being produced one after the other with respect to the longitudinal axis.

[0023] In doing so, the turning tool (not shown) also passes over the opening 63 of the lubrication channel, resulting in a very sharp change in load. In the area of ​​the opening 63, the turning tool is completely unloaded, while in the area of ​​the internal profiling it is subjected to the full cutting force, which is very high during hard turning. The recess 64 according to the invention in the area of ​​the opening 63 is intended to achieve a smoother transition between the fully loaded and unloaded state of the turning tool. It has been shown that in the present exemplary embodiment, the service life of the turning tool is eight times longer when manufacturing a main body 25 with the recess 64 according to the invention than when manufacturing an identical main body 25 without the recess 64.

[0024] The recess 64 is, for example, filled with the Fig. 4 and Fig. 5 is manufactured. The axis of rotation of the disc milling cutter is aligned parallel to the longitudinal axis 11, whereby it is also conceivable to incline the axis of rotation of the disc milling cutter relative to the longitudinal axis 11 in accordance with the pitch angle of the internal profiling. The result is a recess 64 that is elongated, with the surface of the recess 64 being shaped like a section of the surface of a circular ring. During the production of the recess 64, the disc milling cutter is moved radially outward with respect to the longitudinal axis 11 until the recess 64 is so deep that the internal profiling of the nut no longer overlaps with the opening of the lubrication channel.

[0025] Fig. 3 shows a partial sectional view of the finished main body 25 of the nut in the area of ​​the mouth opening 63 of the lubrication channel 60. The sectional plane runs through the longitudinal axis (No. 11 in Fig. 1) of the planetary screw drive and the central axis 66 of the lubrication channel 60.

[0026] The inner profile 21 of the main body 25 is formed by several with respect to the longitudinal axis (No. 11 in Fig. 1) helical grooves 26, which, viewed in cross-section, are V-shaped, resulting in a multi-start V-shaped thread. The pitch 23 of the internal profile is, for example, 2 mm.

[0027] The lubrication channel 60 is formed in the region of the orifice 63 in the form of a stepped bore with a first and a second diameter 61; 62. The first diameter 61, which simultaneously defines the orifice 63, is approximately as large as the pitch 23 of the internal profile 21, so that the orifice 63 is small. The length of the section with the first diameter 61 is approximately as large as the first diameter 61 itself. The second diameter 62 is, for example, 2.5 times as large as the first diameter 61, so that the lubricant, in particular lubricating grease, faces little flow resistance there.

[0028] The depth 65 of the recess 64 according to the invention is approximately 20% deeper than the depth 22 of the inner profile 21, so that the inner profile 21 does not intersect the mouth opening 63. The surface of the recess 64, viewed in the present section, is circular, as would be expected for a section of a circular ring surface.

[0029] Fig. 4 shows a front view of a side milling cutter 70 for producing the recess according to the invention (No. 64 in Fig. 2), where Fig. 5 shows the corresponding top view.

[0030] The side milling cutter 70 is made of hardened tool steel and has three teeth 74 that are rotationally symmetrical with respect to its rotational axis 73, each arranged at a distance of 120°. Each tooth 74 has a semicircular cutting edge 75, so that the geometry produced by the rotating side milling cutter has the shape of a surface section of a circular ring. The cross-sectional diameter of the circular ring is defined by the diameter 71 of the semicircular cutting edge 75, which is, for example, 5 mm. The outer diameter of the circular ring is defined by the outer diameter 72 of the side milling cutter 70, which is, for example, 21.7 mm. List of reference symbols 10 planetary screw drive 11 Longitudinal axis 12 End seal 13 Guide disc 14 Retaining ring 20 mother 21 Internal profiling of the nut 22 Depth of the internal profiling of the nut 23 Division of the inner profile of the nut 24 flange 25 Main body of the mother 26 Groove of the inner profile of the nut 30 spindle 31 External profiling of the spindle 40 Planet 41 Central axis of the planet 42 External profile of the planet 43 External gearing 50 sprocket 51 threaded pin 60 lubrication channel 61 first diameter 62 second diameter 63 Muzzle opening 64 recess 65 Depth of the recess 66 Central axis of the lubrication channel 70 disc milling cutters 71 diameter of the cutting edge 72 outer diameter of the side milling cutter 73 axis of rotation 74 tooth 75 cutting edge

Claims

[1] Planetary screw drive (10) with a nut (20) and a spindle (30), wherein the spindle (30) extends along a longitudinal axis (11) and is provided with an external profile (31), wherein the nut (20) surrounds the spindle (30) and is provided with an internal profile (21), wherein at least one planet (40) is provided which extends parallel to the longitudinal axis (11) and is provided with an external profile (42), wherein the at least one planet (40) is arranged between the nut (20) and the spindle (30) so that its external profile (42) engages both in the external profile (31) of the spindle (30) and in the internal profile (21) of the nut (20), wherein a lubrication channel (60) is provided on the nut (20), which has an opening (63) in the region of the internal profile (21) of the nut, characterized bythat a recess (64) is provided on the mouth opening (63), which is deeper than the inner profiling (21) of the nut (20), so that a cutting edge of a turning tool for producing the inner profiling (21) on the nut (30) merges into the recess (64) during the cutting process, wherein the said cutting edge does not come into contact with the lubrication channel (60) at all during the cutting process, wherein a surface of the recess (64) is designed as a section of a circular ring, wherein a circular ring is to be understood as a body which is produced by rotating a circle around an axis of rotation lying in the plane of the circle and not intersecting the circle. [2] Planetary screw drive according to claim 1, characterized by that the recess (64) is elongated, extending transversely to the longitudinal axis (11) or in the pitch direction of the inner profile (21) of the nut (20). [3] Planetary screw drive according to claim 2, characterized by that the cross-sectional diameter (71) of the circular ring is between 1 and 5 times as large as the pitch (23) of the inner profile (21) of the nut (20). [4] Planetary screw drive according to claim 2 or 3, characterized by that the outer diameter (72) of the circular ring is between 3 and 8 times the cross-sectional diameter (71) of the circular ring. [5] Planetary screw drive according to one of the preceding claims, characterized by that the outer profile (31) of the spindle has at least one groove which is helical with respect to the longitudinal axis (11). [6] Planetary screw drive according to one of the preceding claims, characterized by that the inner profile (21) of the nut (20) has at least one groove (26) which is helical with respect to the longitudinal axis or circularly endlessly encircling the longitudinal axis (11). [7] Planetary screw drive according to one of the preceding claims, characterized by that the outer profile (43) of the at least one planet (40) has at least one groove which is helical with respect to the central axis (41) of the planet (40) or circularly endlessly encircling said central axis (41). [8] Planetary screw drive according to one of the preceding claims, characterized by that the lubrication channel (60) is designed in the form of a stepped bore with a first and a second diameter (61; 62), wherein the first diameter (61) in the region of the mouth opening (63) is smaller than the second diameter (62). [9] Planetary screw drive according to one of the preceding claims, characterized by that the nut (20) is made of steel, being hardened at least in the area of ​​the inner profiling (21).

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