External ball screw

Abstract

Externally mounted ball screw, featuring: • a spindle shaft (10), • a screw nut (20) which can be placed on the spindle shaft (10) and is provided with a through hole (24) with an opening edge (241) which is continuously connected by a ball path (T1) which is arranged between the screw nut (20) and the spindle shaft (10), • several bearing balls (30) which can roll along the ball path (T1), wherein the diameters of the bearing balls (30) are defined as ball diameters (BD), and • a rotating component (40) connected to the screw nut (20) and provided with a running groove (41) which is continuously connected to the through hole (24) and is formed with a pivot segment (411) connected thereto, wherein the end of the pivot segment (411) connected to the through hole (24) is formed with a coupling edge (411A) which presses against the opening edge (241), wherein the connection of the opening edge (241) to the coupling edge (411A) is not arranged tangentially, wherein the pivot segment (411) can rotate about a reference point (A) and the outer wall surface (411B) of the pivot segment (411) is arc-shaped with this reference point (A) as the center of a circle, which is located away from the outer wall surface (411B) by a radius of curvature (R), wherein the radius of curvature (R) is greater than or equal to the 1.2 times the diameter of a sphere (BD) or less than or equal to 1.5 times the diameter of a sphere (BD).

Description

[0001] The invention relates to ball screw spindles, in particular an externally mounted ball screw spindle.

[0002] To adapt to modern electronic automotive and entertainment products, current ball screw designs tend towards miniaturization. However, with the existing design of the inner contact plate, there is a height difference between the screw nut and the contact plate, resulting in a noticeable jerk due to the smaller ball diameter.

[0003] In Fig. Figure 1 shows a known tangential external rotary ball screw with reference to Taiwanese patents TW M485984 U and TW M519199 U, while the experimental data in Fig. Figure 5 shows a schematic diagram of the impact force of the bearing balls 90 on the orbital path 81 as it passes through the conventional top cover 80, which has a screw nut 70, a top cover 80 connectable to the screw nut 70, and several bearing balls 90 orbiting between the screw nut 70 and the top cover 80. The screw nut 70 is provided with two through holes 71, the direction of which is defined as a direction of movement Z. The top cover 80 has an orbital path 81 which is continuously connected to the through holes 71, allowing the bearing balls 90 to orbit. The orbital path 81 is tangentially connected to the through holes 71 and has a pivot segment 811 and an additional segment 812. Thanks to the tangential connection of the orbital path 81 to the through holes 71, the pivot segment 811 has a large range of rotation.If the bearing balls 90 enter the pivot segment 811 from the through holes 71, they will, due to inertia, impact the upper edge of the wall surface 811A of the pivot segment 811. The opposing force components of the bearing balls 90 in the direction of movement Z will increase, causing the rear bearing balls 90 to push against the front bearing balls 90. This results in problems such as ball jamming and high impact forces.

[0004] The invention is based on the objective of providing an externally rotating ball screw with a smoothly rotating bearing ball without bearing ball jamming.

[0005] To solve the problem, an external ball screw is provided, consisting of: a spindle shaft a screw nut which can be placed on the spindle shaft and is provided with at least one through hole with an opening edge which is continuously connected to a ball path arranged between the screw nut and the spindle shaft, several bearing balls which can roll along the ball path, where the diameters of the bearing balls are defined as ball diameters, a rotating component connected to the screw nut and provided with a running groove which is continuously connected to the through hole and is formed with a pivot segment connected thereto, wherein the end of the pivot segment connected to the through hole is formed with a coupling edge which presses against the opening edge, wherein the connection of the opening edge to the coupling edge is not arranged tangentially, wherein the pivot segment can rotate about a reference point and the outer wall surface of the pivot segment is arc-shaped with this reference point as the center of a circle which is located away from the outer wall surface by a radius of curvature, wherein the radius of curvature is greater than or equal to 1.2 times a sphere diameter or less than or equal to 1.5 times the sphere diameter.

[0006] The solution is that the conventional problem of non-running bearing balls or bearing ball jams is solved by limiting the radius of curvature to greater than or equal to 1.2 times the ball diameter or less than or equal to 1.5 times the ball diameter, and by ensuring that the connection of the opening edge to the coupling edge is not tangential. Fig. 1 View of a conventional ball screw whose orbital path is tangentially connected to the through hole. Fig. 2 Exploded view of the externally rotating ball screw according to the invention. Fig. 3 Top view of the externally spherical ball screw according to the invention. Fig. 4 View of the embodiment according to the invention, wherein the through hole is not tangentially connected to the running groove. Fig. 5A Impact force data graph for a conventional ball screw with a recirculating path tangentially connected to the through hole, provided that the radius of curvature is 0.7 mm, where each broken line in the coordinate system represents an impact force generated by a bearing ball at different times, the horizontal axis represents the time (unit: S) and the vertical axis represents the impact forces (unit: Newton (N)). Fig. 5B Impact force data graph for a conventional ball screw with a recirculation path tangentially connected to the through hole, provided that the radius of curvature is 0.8 mm. Fig. 5C Impact force data graph for a conventional ball screw with a recirculation path tangentially connected to the through hole, provided that the radius of curvature is 0.9 mm. Fig. 5D impact force data graph for the ball screw according to the invention with a running groove not tangentially connected to the through hole, provided that the radius of curvature is 0.8 mm. Fig. 5E Impact force data graph for the ball screw according to the invention with a running groove not tangentially connected to the through hole, provided that the radius of curvature is 0.85 mm. Fig. 5F Impact force data graph for the ball screw according to the invention with a running groove not tangentially connected to the through hole, provided that the radius of curvature is 0.9 mm. Fig. 5G impact force data graph for a ball screw according to the invention with a circulation path not tangentially connected to the through hole, provided that the radius of curvature is 1.0 mm.

[0007] In Fig. 2 to Fig. Figure 4 shows an embodiment of the externally rotating ball screw according to the invention.

[0008] The spindle shaft 10 extends along an axis L, from which an axial direction X is derived. The outer circumferential surface of the spindle shaft 10 is formed with an external threaded groove 11.

[0009] The nut 20 is mounted on the spindle shaft 10 and is provided with a through-hole 20A for receiving the inserted spindle shaft 10, an inner wall 21, and an outer wall 22. The outer wall 22 is formed as a plane, while the inner wall 21 is the side formed by the through-hole (20A) and faces the through-hole 20A. The inner wall 21 has an internal thread groove 211, which is complementary to the external thread groove 11. A ball path T1 is thus formed between the internal thread groove 211 and the external thread groove 11. The nut 20 is further provided with two threaded bores 23 and two through-holes 24. Both the threaded bores 23 and the two through-holes 24 extend through the outer wall 22. The ball path T1 is continuously connected to the two through-holes 24.The point on the outer wall 22 where the two through holes 24 pass through is formed as an opening edge 241. The direction of the through holes 24 is defined as a vertical direction Y.

[0010] The bearing balls 30 can roll along the ball path T1. The diameter of each bearing ball 30 is defined as the ball diameter BD, which in one embodiment is between 0.4 mm and 1.0 mm.

[0011] The circulation block 40 is connected to the outer wall 22 of the screw nut 20 and is provided with a contact surface 40A opposite the outer wall 22. The contact surface 40A is provided as a plane with a running groove 41, the running groove 41 together with the two through holes 24 forming a return path T2, which is continuously connected to the ball path T1. The running groove 41 has a sequentially connected pivot segment 411, an additional segment 412, and a drain segment 413. The pivot segment 411 is continuously connected to one through hole 24, while the drain segment 413 is continuously connected to the other through hole 24. The end of the pivot segment 411 connected to the through-hole 24 is formed with a coupling edge 411A which presses against the opening edge 241, while the other end of the pivot segment 411 is connected to the additional segment 412.The direction of travel of the pivot segment 411 includes components of the axial direction X and the vertical direction Y, such that the outer wall surface 411B, which is complementary to the pivot segment 411, is arc-shaped and can rotate the pivot segment 411 about a reference point A. The outer wall surface 411B incorporates the reference point A as the center of a circle. Between the outer wall surface 411B and the reference point A, there exists a radius of curvature R, the length of which is greater than or equal to 1.2 times the sphere diameter BD or less than or equal to 1.5 times the sphere diameter BD.

[0012] The opening edge 241 is not tangentially connected to the coupling edge 411A, so that the return path T2 is not tangential.

[0013] Since the coupling edge 411A of the pivot segment 411 of the running groove 41 is not tangentially connected to the opening edge 241 of the through hole 24, the rotational clearance of the pivot segment 411 according to the invention is relatively smaller compared to the conventional tangential design due to the same radius of curvature R. This means that the point of impact of the bearing balls 30 against the outer wall surface 411B of the pivot segment 411 is closer to the coupling edge 411A, and the counterforce component of the bearing balls 30 when impacting the outer wall surface 411B in the axial direction X is greater. As a result, the front bearing balls 30 are less forced by the rear bearing balls 30 as they move from the pivot segment 411 into the additional segment 412. This generates a lower impact force and enables smooth rotation of the bearing balls.

[0014] The rotating component 40 is further provided with two corresponding bores 43 and two locking pieces 50. The positions of the two corresponding threaded bores 43 remain complementary to the positions of the first two threaded bores 23. The two locking pieces 50 are inserted through the first threaded bores 23 and the second threaded bores 43 to lock the rotating component 40 to the nut 20.

[0015] It is preferred that the rotating component 40 is further formed with two extension segments 42 extending from the contact surface 40A. One extension segment 42 is adjacent to the pivot segment 411, and the other extension segment 42 is adjacent to the drain segment 413. Both extension segments 42 project into the through-hole 24.

[0016] The arrangement of the important components of the embodiment according to the invention is described in the section above. The functional performance of the embodiment according to the invention is explained accordingly.

[0017] In relation to Fig. 5A to Fig. 5C is the computer-simulated impact force of the bearing balls 90 as they pass through the conventional top cover 80 against the orbital path 81. Because the conventional orbital path 81 is tangentially connected to the through-hole 71 and the ball diameter is 0.6 mm, the bearing balls 90 generate a specific impact force as they travel along the orbital path 81. Each individual broken line in the coordinate system represents an impact force generated by a bearing ball 90 at different times as it travels along the orbital path 81, with the horizontal axis representing the time (unit: S) and the vertical axis representing the impact force (unit: Newton (N)). If the radius of curvature is 0.7 mm, the average impact force of the bearing ball 90 with respect to Fig. 5A 13 N and the maximum impact force of the bearing ball 90 is 35.37 N. If the radius of curvature is 0.8 mm, the average impact force of the bearing ball 90 in relation to Fig. 5B 1.5 N and the maximum impact force of the bearing ball 90 is 3.09 N. If the radius of curvature is 0.9 mm, the average impact force of the bearing ball 90 in relation to Fig. 5C 3.7 N and the maximum impact force of the bearing ball 90 6.47 N.

[0018] In relation to Fig. 5D to Fig. 5F is the impact force of the bearing balls 30 as they pass through the rotating component 40 according to the invention against the running groove 41, simulated by computer. Due to the fact that the through holes 24 according to the invention are not tangentially connected to the running groove 41 and the ball diameter BD is 0.6 mm, the bearing balls 30 generate a specific impact force as they run along the running groove 41. Each individual broken line in the coordinate system represents an impact force generated by a bearing ball 30 in the running groove 41 at different times, with the horizontal axis representing the time and the vertical axis representing the impact force. If the radius of curvature R is 0.8 mm, the average impact force of the bearing balls 30 with respect to Fig. 5D 0.29 N and the maximum impact force of the bearing ball 30 0.75 N. If the radius of curvature R is 0.85 mm, the average impact force of the bearing balls 30 with respect to Fig. 5E 0.26 N and the maximum impact force of the bearing ball 30 0.89 N. If the radius of curvature R is 0.9 mm, the average impact force of the bearing balls 30 with respect to Fig. 5F 0.38 N and the maximum impact force of the bearing ball 30 0.66 N.

[0019] In Fig. Figure 5G shows that the through hole 24 is not tangentially connected to the raceway 41 and that the ball diameter BD is 0.6 mm. However, if the radius of curvature R is 1.0 mm, the condition that the radius of curvature R is less than or equal to 1.5 times the ball diameter BD cannot be met. This results in a measurement finding that the bearing balls 30 do not rotate freely and can become jammed.

[0020] Based on the description above, the average impact force of the bearing balls 30 is only 0.29 N, even though the radii of curvature R are all 0.8 mm, when the through-hole 24 is not tangentially connected to the raceway 41. However, if the orbital path 81 is tangentially connected to the through-hole 71, the average impact force of the bearing balls 90 increases to 1.5 N. Furthermore, the average impact force of the bearing balls 30 is only 0.38 N, even though the radii of curvature R are all 0.9 mm, when the through-hole 24 is not tangentially connected to the raceway 41. However, if the orbital path 81 is tangentially connected to the through-hole 71, the average impact force of the bearing balls 90 increases to 3.7 N.

[0021] It then turns out that the conventional problem with regard to non-running bearing balls 30 or bearing ball jams is solved by limiting the radius of curvature R to greater than or equal to 1.2 times a ball diameter BD or less than or equal to 1.5 times the ball diameter BD and by not arranging the connection of the opening edge 241 to the coupling edge 411A tangentially.

Claims

[1] External ball screw, comprising: • a spindle shaft (10), • a screw nut (20) which can be placed on the spindle shaft (10) and is provided with a through hole (24) with an opening edge (241) which is continuously connected by a ball path (T1) which is arranged between the screw nut (20) and the spindle shaft (10), • several bearing balls (30) which can roll along the ball path (T1), wherein the diameters of the bearing balls (30) are defined as ball diameters (BD), and • a rotating component (40) connected to the screw nut (20) and provided with a running groove (41) which is continuously connected to the through hole (24) and is formed with a pivot segment (411) connected thereto, wherein the end of the pivot segment (411) connected to the through hole (24) is formed with a coupling edge (411A) which presses against the opening edge (241), wherein the connection of the opening edge (241) to the coupling edge (411A) is not arranged tangentially, wherein the pivot segment (411) can rotate about a reference point (A) and the outer wall surface (411B) of the pivot segment (411) is arc-shaped with this reference point (A) as the center of a circle, which is located away from the outer wall surface (411B) by a radius of curvature (R), wherein the radius of curvature (R) is greater than or equal to the 1.2 times the diameter of a sphere (BD) or less than or equal to 1.5 times the diameter of a sphere (BD). [2] External ball screw according to claim 1, characterized by , that the ball diameter (BD) is between 1.0 mm and 0.4 mm. [3] Externally rotating ball screw according to claim 1, characterized by , that the running groove (41) further comprises an additional segment (412), a drain segment (413), wherein one end of the pivot segment (411) is connected to a through hole (24) and the other end is connected to the additional segment (412), wherein the additional segment (412) is connected to the drain segment (413), while the drain segment (413) is continuously connected to the second through hole (24). [4] Externally rotating ball screw according to claim 1, characterized by, that the screw nut (20) is provided with a through hole (20A) receiving the spindle shaft (10), an inner wall (21) and an outer wall (22), and the spindle shaft (10) is formed with an external thread groove (11), wherein the inner wall (21) is formed by the through hole (20A) and is formed with an internal thread groove (211), wherein a ball path (T1) is formed between this and the complementary external thread groove (11), wherein the recirculating block (40) is connected to the screw nut (20) at the outer wall (22), and the opening edge (241) is a place where the through hole (24) passes through the outer wall (22). [5] External ball screw according to claim 1, characterized by, that the screw nut (20) is formed with two first threaded bores (23), while the rotating component (40) is provided with two corresponding bores (43) and two locking pieces (50), wherein the positions of the two corresponding bores (43) remain complementary to the positions of the two first threaded bores (23) and the two locking pieces (50) are inserted through the first threaded bores (23) and the corresponding bores (43).

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