METHOD FOR MANUFACTURING A SCREW GEAR, WHICH IS IN PARTICULARLY ASSOCIATED ON AN ANCHOR SHAFT

Description

State of the art

[0001] The invention relates to a method for manufacturing a gear worm, which is arranged in particular on an armature shaft.

[0002] German patent DE 102 011 006 276 A1 discloses a gear with axial grooves on its tooth flanks that serve as lubricant reservoirs. These grooves allow lubricant to be directed to the friction-critical areas of the gear teeth during operation without displacing the lubricant completely. Such a gear can, for example, also be designed as a worm gear for a worm drive. While this design ensures reliable lubrication of the gear teeth, there is a tendency for the self-locking of such a drive to be reduced by the continuous lubrication. However, there are applications, such as actuators in motor vehicles that adjust windows, sunroofs, or seat components, where a higher degree of self-locking is desirable when the electric drive is stationary in order to hold the adjusted component in its final position.Therefore, the object of the invention is, on the one hand, to produce a gearbox with reliable lubrication, in which the self-locking can be specifically adjusted at the same time.

[0003] The JP 2003 207031 A is a geared worm gear in which two helical grooves are formed on the tooth flanks over the entire length of the worm gearing, which serve as lubricant reservoirs.

[0004] EP 1 780 446 A1 describes a worm gear in which lubricant reservoirs are formed within a plastic worm gear. These lubricant reservoirs are formed by means of a corresponding manufacturing screw that has an abrasive surface. Disclosure of the invention Advantages of the invention

[0005] In contrast, the inventive method with the features of the independent claim has the advantage that, by forming a groove structure extending circumferentially with the worm flanks, a lubricant reservoir is provided on the highly stressed worm flanks, and the self-locking of such a gear worm can be specifically influenced. First, the gear geometry, which has a defined smooth surface, is produced by rolling. Then, grooves extending concentrically to the longitudinal axis of the gear worm are formed into the smooth surface. This has the decisive advantage that the entire surface of the worm flanks is constantly supplied with sufficient lubricant, and at the same time, there is direct contact between the tips of the groove structure and the mating teeth.This direct contact between the tips of the groove structure and the mating teeth can be used to adjust the self-locking of the gearing. The depth of the grooves determines the degree of lubrication of the gearing and simultaneously the contact area between the tips of the groove structure and the mating teeth.

[0006] According to the invention, the concentric groove structure in the rolled surface of the worm gear flanks can be formed very precisely by belt grinding. This allows the worm gear flanks of the gear worm to be roughened selectively with the grinding belt by grinding circular grooves in the circumferential direction. The depth and radial spacing of the grooves can be easily determined by selecting the grinding belt and the contact pressure.

[0007] The measures listed in the dependent claims enable advantageous further developments of the manufacturing process and the devices according to the dependent claims.

[0008] For this purpose, the flexible abrasive belt with a profiled contact piece can be pressed directly against the surface of the worm gear flanks, which is particularly advantageous. The profile of the contact piece corresponds to the shape of the worm gear teeth, so that the flexible abrasive belt lies flat against the worm gear flank in a specific angular segment of the gear worm.

[0009] The belt finishing process is suitable for forming concentric, regular grooves in the surface of the worm gear flanks. In this process, the abrasive belt lies directly against the worm gear flanks in a tangential direction to the gear worm, so that circular grooves can be ground into the worm gear flanks in the radially outer area of ​​the gear worm.

[0010] The worm gear with its rolled worm flanks is preferably set in rotation, causing the grinding belt to move along the helical pitch of the worm flanks, thus grinding the tooth flanks across the entire axial range of the worm gear. Due to the formation of such concentric grooves, the circumferential roughness of this groove structure is relatively low. This minimizes wear on the grooves. In the radial direction, perpendicular to the grooves, the roughness can be precisely controlled. When the gearbox is stationary, the lubricant can retreat into the grooves, so that the crests of the groove structure are in direct contact with the mating teeth, thereby improving self-locking.

[0011] In belt grinding, the rolled threaded worm is set in rotation, and simultaneously the grinding belt has its own feed speed. The profile of the groove structure can be influenced by the ratio of these two movements.

[0012] This method is very suitable for the mass production of worm gears, in which long metal rods are first formed into a worm using continuous rolling, and then the concentric grooves are cut into the worm flanks using belt grinding. This allows for the production of virtually meter-long lengths of finished threaded rods with a concentric groove structure, which can then be cut to the desired length.

[0013] Preferably, such a worm gear has a central longitudinal bore by means of which the threaded worm is pushed onto a transmission shaft. The transmission shaft can preferably be the armature shaft of the electric motor. From a manufacturing perspective, it is particularly advantageous if the worm gear is pressed directly onto the shaft, preferably onto a previously profiled area of ​​the shaft to create an interference fit. Alternatively, the threaded sleeve can also be fixed to the shaft by bonding or other material forming.

[0014] For the mass production of threaded rods, belt grinding can be directly combined with burnishing. The grinding belt can, for example, be positioned axially directly behind the burnishing wheels, so that when forming the helical thread onto the metal rod, the rod is moved axially towards the grinding belt immediately after passing axially through the burnishing wheels. This allows a long metal rod to be first axially pushed through the burnishing tools and, in the same feed, immediately afterwards through the grinding device in a single operation.

[0015] Rolling allows for the simple creation of a high-quality, highly compacted surface with a roughness of less than 1 µm, ensuring a long service life. Subsequent belt finishing allows circumferential grooves to be ground into this smooth surface of the worm flanks, roughening the radial surface of the grooved structure to a roughness of Rz = 0.2 µm to 20 µm. This grooved structure reliably prevents the worm flanks from being continuously connected to the mating teeth via an uninterrupted lubricating film when the gearbox is stationary. Because the groove tips now rest directly against the mating teeth, a desired self-locking effect can be achieved.

[0016] The depth and profile of the grooves can be adjusted via the properties of the abrasive belt as well as the contact pressure of the belt or the contact piece. This allows for easy variation of the groove structure in the rolled worm flank to accommodate changing self-locking requirements for the intended application of the worm gear, without incurring significant tooling costs. Such a process, combining rolling and belt finishing, is considerably more cost-effective than machining processes such as milling or turning.

[0017] A gear worm produced according to the invention can be manufactured with a concentric groove structure that is specifically adapted to the lubricant used and to the surface of the mating teeth.

[0018] The raw material for the worm gear is preferably a metal bar, especially made of steel, which is plastically deformed using rolling discs to provide a very smooth surface on the worm flanks. A defined groove structure can then be engraved into this rolled metal surface by belt grinding, with the grooves being very regular and uniform in the circumferential direction to the longitudinal axis of the worm.

[0019] The use of the worm gear according to the invention is particularly advantageous in an electric motor drive unit in which a gearbox housing is directly flanged axially to an electric motor. The torque from the electric motor is transmitted via an armature shaft to a worm gear, which, in addition to the worm gear according to the invention, has a worm wheel with worm gear teeth that mesh with the worm flanks. It is particularly advantageous to arrange the worm gear directly on the armature shaft, which preferably projects axially into the gearbox housing. The worm wheel is preferably made of plastic – for example, as an injection-molded part – and is rotatably mounted directly in the gearbox housing. The worm wheel has, for example, an output element that then transmits the reduced torque of the electric motor to a part to be adjusted or driven.In an alternative embodiment, the gear worm can also be wound directly onto the armature shaft of the electric motor and subsequently machined by belt grinding. Such a drive unit according to the invention, with high efficiency and adjustable self-locking, is particularly suitable as a window regulator, sunroof or seat adjustment drive in motor vehicles. Brief description of the drawings

[0020] Exemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. They show Fig. 1 a manufacturing method according to the invention for a gear worm, Fig. 2 a schematic representation of a worm flank according to the invention, and Fig. 3 a gear drive unit according to the invention.

[0021] In Fig. 1 A schematic representation of a method for manufacturing a gear worm 12 is shown, in which a gear worm 12 is first formed from a metal rod using a rolling tool. Such a threaded rod 11 with formed worm flanks 22 of a worm gear 20 is shown in Fig. 1 The tool holder 16 is rotatably mounted in a tool holder 16. Subsequently, a groove structure 24 is formed into the worm flanks 22 of the worm gear 20. For this purpose, a flexible abrasive belt 30 is positioned radially 19 against the threaded rod 11 by means of a profiled contact piece 32 and pressed against the worm flanks 22. The profiled contact piece 32 is in Fig. 1 The contact element 32 is designed as an elastic contact roller – e.g., made of rubber. In an alternative embodiment, the contact element 32 is designed as a rigid guide rail – e.g., made of aluminum – extending in the direction of the sandpaper, over which the sanding belt is drawn. The worm flanks 20 run helically around a longitudinal axis 18 of the gear worm 12. Therefore, the sanding belt 30 is pressed against the worm flanks 22 in the longitudinal direction 18, while at the same time the gear worm 12 is set into rotation in the tool holder 16. This rotation of the gear worm 12 moves the sanding belt 30 together with the contact element 32 along the worm flank 22 over the entire length of the threaded worm 12. Simultaneously, the sanding belt 30 is also set into relative motion by a separate drive 31. This causes concentric grooves 25 to be ground into the surface of the worm flanks 22.Additionally, the grinding belt 30 can be lubricated during the grinding process by means of a lubrication device 34. During belt grinding, the grinding belt is guided tangentially to the gear worm 12 in the area of ​​the worm flanks 22 and pressed axially against the worm flanks 22 by the profiled contact piece 32. For example, the length of such a threaded rod can be up to 1.5 m, and then cut to the desired length after the grinding process.

[0022] Fig.2 Figure 1 shows a detailed view of a section of a worm flank 22, which extends helically around a cylindrical base body of the gear worm 12. The worm flank 22 has a pitch, or lead height, which determines the transmission ratio of a worm gear 50. The worm flank 22 was first formed by roller burnishing to a very smooth surface with a roughness Rz of up to 0.2 µm. Subsequently, circular grooves 25 were ground into the worm flanks 22, preferably extending over the entire circumference of the gear worm 12 in the circumferential direction 17. The roughness Rz of the grooves in the radial direction 19 is now in the range of 0.5 µm to 5 µm. Alternatively, the roughness Rz can also be in the range of 0.2 µm to 20 µm. In the operating state, lubricant is arranged in the grooves 25 as a grease reservoir, which increases the efficiency in the moving state.When the worm gear 12 is stationary, the tips 44 of the groove structure 24 are in direct contact with the teeth of the worm wheel 52, and the lubricant can retract into the grooves 25. Therefore, such a worm gear 50 exhibits a relatively high self-locking effect to prevent the worm gear 50 from rotating backwards when a torque is applied on the load side.

[0023] A gear drive unit 10 according to the invention is in Fig. 3An electric motor 48 has an armature shaft 14 that projects into a gearbox housing 56, which is axially connected to the electric motor 48. The worm gear 12 is arranged on the armature shaft 14, in the exemplary embodiment, in particular, pressed axially onto a material deformation 58 of the armature shaft 14. For this purpose, the worm gear 12 has a bore 26, which extends, for example, as a through-hole over the entire axial length of the worm gear 12. The worm teeth 20 engage with a corresponding mating tooth 53 of the worm wheel 52, which is rotatably mounted in the gearbox housing. The tooth flanks 22 of the worm gear 12 bear against the teeth of the worm wheel 52. The worm wheel 52 is made of plastic, preferably as an injection-molded part. The surface of the teeth of the worm gear 52 can optionally have a certain surface structure at specific points, which can be designed as a lubricant reservoir.Circumferential grooves 25 are ground into the tooth flanks 22 of the worm gear 12, which also act as lubricant reservoirs. Depending on the direction of rotation of the electric motor 48, either a worm flank 22 of a first axial side of the worm teeth 20, or, in the opposite direction of rotation, the axially opposite worm flank 22 of the worm teeth 20, bears force against the teeth 53 of the worm wheel 52. The free end of the armature shaft 14 is radially supported in the gearbox housing 56 so that the worm teeth 20 remain reliably engaged with the teeth 53 of the worm wheel 52 even under heavy load. In the longitudinal direction, the armature shaft 14 is supported by a damping element 62 to prevent disruptive noise when moving against a stop 60. A driven element 64 is arranged on the worm gear 52, which transmits the torque, for example, to a part to be adjusted in the motor vehicle.Preferably, such a gear drive unit 10 is designed as a window lift drive or sunroof drive or as a seat adjuster.

[0024] It should be noted that, with regard to the embodiments shown in the figures and in the description, numerous combinations of the individual features are possible. For example, the electric motor 48 can be combined with different gear designs of the worm gear 50. Likewise, the worm gear 12 can be rolled directly onto the armature shaft 14 instead of being manufactured separately, and the concentric grooves 25 can then be formed by belt grinding. The worm gear 12 can also be manufactured with a blind hole 26, through which it is pushed onto a shaft. Instead of being pressed on, the worm gear 12 can also be glued or otherwise attached to a gear shaft. The manufacturing method according to the invention is also suitable for applications of worm gears 12 outside of actuators in motor vehicles.

Claims

1. Method for producing a gear worm (12) which is arranged, in particular, on an armature shaft (14) of an electromotive drive unit (10), wherein a worm toothing system (20) with worm flanks (22) lying axially opposite one another on a longitudinal axis (18) is formed first by means of a roller burnishing tool, and subsequently a groove structure (24) which is concentric around the longitudinal axis (18) is formed on the worm flanks (22) by means of a further process step, wherein the concentric groove structure (24) is produced by belt grinding.

2. Method according to Claim 1, characterized in that a flexible sanding belt (30) - in particular a sanding paper - is used for the belt grinding, which is pressed against the worm flanks (22) by means of a profiled contact piece (32) - preferably simultaneously against two worm flanks (22) lying opposite one another in a thread groove.

3. Method according to either of Claims 1 or 2, characterized in that the worm flanks (22) of the gear worm (12) are roughened in a targeted manner by way of the sanding belt (30).

4. Method according to Claim 1, characterized in that the concentric groove structure (24) is produced by means of a fixed grinding block, which comprises, in particular, pumice stone or diamond.

5. Method according to any one of Claims 2 to 4, characterized in that, during the belt grinding, the gear worm (12) is rotated, and the sanding belt (30) is pulled with the contact piece (32) along the worm flanks (22) by the lead of the worm toothing system (20).

6. Method according to any one of Claims 2 to 5, characterized in that the sanding belt (30) is moved at a lower relative speed than the circumferential speed of the worm toothing system (20) by the rotation of the gear worm (12) in order to form the concentric groove structure (24) on the worm flanks (22).

7. Method according to any one of the preceding claims, characterized in that the gear worm (12) is manufactured as a separate component with a central bore (26) along the longitudinal axis (18), and is subsequently pressed onto a shaft of the drive unit (10) - in particular onto the armature shaft (14).

8. Method according to any one of the preceding claims, characterized in that the roller burnishing tool forms an endless worm thread in the throughfeed method with a belt grinding method which is directly linked to the latter, which endless worm thread is then cut to the desired length (13) of the gear worm (12).

9. Method according to any one of the preceding claims, characterized in that a surface roughness of the worm flanks (22) Rz of up to 0.5 µm - in particular up to 0.1 µm - is produced during rolling, and the subsequently formed concentric groove structure (24) has a structured roughness Rz of from 0.2 µm to 10 µm.

10. Method according to any one of Claims 2 to 9, characterized in that the depth and the profile of the groove structure (24) can be adjusted both via the properties of the sanding belt (30) and via the contact pressure of the sanding belt (30) or the contact piece (32).

11. Method according to any one of the preceding claims, characterized in that the gear worm (12) is made of metal and interacts with a worm wheel (52) which is made of plastic and is produced by injection moulding.

12. Method according to any one of the preceding claims, characterized in that the gear worm (12) is arranged on an armature shaft (14) of an electric motor (48) which is preferably directly flange-connected to a gear housing (56) of a worm gear (50) which comprises the gear worm (12).