US 11,680,628 B2
Ball screw device
Kazuya Yamada, Kanagawa (JP); Yuji Shimomura, Kanagawa (JP); Kanta Sato, Kanagawa (JP); and Yasuaki Abe, Kanagawa (JP)
Assigned to NSK LTD., Tokyo (KR)
Appl. No. 17/439,254
Filed by NSK LTD., Tokyo (JP)
PCT Filed Mar. 10, 2021, PCT No. PCT/JP2021/009489
§ 371(c)(1), (2) Date Sep. 14, 2021,
PCT Pub. No. WO2021/199989, PCT Pub. Date Oct. 7, 2021.
Claims priority of application No. JP2020-066567 (JP), filed on Apr. 2, 2020.
Prior Publication US 2023/0087898 A1, Mar. 23, 2023
Int. Cl. F16H 25/22 (2006.01)
CPC F16H 25/2214 (2013.01) 7 Claims
OG exemplary drawing
 
1. A ball screw device comprising:
a screw shaft having a spiral shaft-side ball screw groove with a number of threads of one on an outer-circumferential surface thereof;
a nut having a spiral nut-side ball screw groove with a number of threads of one on an inner-circumferential surface thereof;
a spiral load path composed of the shaft-side ball screw groove and the nut-side ball screw groove;
a circulation path connecting a start point and an end point of the load path; and
a plurality of balls rolling on the load path and the circulation path;
wherein the circulation path has:
a return path arranged on an outside in a radial direction of the load path and having a center line parallel to a center axis of the screw shaft;
scooping paths respectively arranged on both sides in a length direction of the return path and scooping up the balls from the load path; and
connecting paths respectively arranged on the both sides in the length direction of the return path and connecting the return path and the scooping paths; wherein each of the scooping paths has an arc-shaped center line which is curved toward outside in the radial direction as approaching a reference imaginary flat plane including the center axis of the screw shaft and the center line of the return path in a circumferential direction and extends from a center line of the load path to the reference imaginary flat plane;
each of the connecting paths has a straight path having a linear center line that is arranged on the reference imaginary flat plane and extends in a direction orthogonal to the center axis of the screw shaft, and an arc path having an arc-shaped center line that is arranged on the reference imaginary flat plane and is curved inward in an axial direction as going toward outside in the radial direction; and
when a lead of the shaft-side ball screw groove and the nut-side ball screw groove is L, a diameter of the balls is D, a radius of curvature of the center line of each of the scooping paths is R1, a scooping angle of the balls by each of the scooping paths is θ, and an entire length of the straight path is S, D/L≥0.6 is satisfied and R1 cos(90°−θ)+S>D is satisfied.