Endless ball spline

Claim 1

An endless ball spline comprising: a spline bearing including an outer casing, a pair of cages fitted inside said outer casing and each having a ball recirculating groove, a pair of end covers respectively fitted on projections formed at both axial ends of said cages and secured to both axial ends, respectively, of said outer casing, and a multiplicity of balls disposed in ball recirculating endless track bores defined by said outer casing, said cages and said end covers; and a spline shaft supported through the multiplicity of balls in said spline bearing, said outer casing including: grooves with a U-shaped cross-section provided in the inner peripheral surface thereof, said U-shaped grooves extending over the whole length of said outer casing in parallel with the axis thereof and in bisymmetry with each other; loaded ball guide grooves provided in both side surfaces, respectively, of the bottom of each of said U-shaped grooves; ridges with a triangular cross-section provided on the inner peripheral surface of said outer casing in such a manner that said triangular ridges extend axially over the whole length of said outer casing in parallel to each other and in symmetry with each other with respect to the plane which intersects the respective centers of said U-shaped grooves; cage securing grooves with a substantially trapezoidal cross-section provided on both sides, respectively, of each of said triangular ridges; and annullar slanted surfaces formed at both axial ends, respectively, of the inner periphery of said outer casing, each slanted surface expanding or diverging outward, said cages having an inner peripheral surface with a substantially V-shaped cross-section, and each cage including: cage securing pieces provided at both longitudinal ends, respectively, of said cage; a plurality of annular grooves provided in the outer peripheral surface of said cage, said annular grooves including loaded ball grooves corresponding to the loaded ball guide grooves on said outer casing, said loaded ball grooves being formed in the substantially central portion of said cage and each having a slot with a diameter slightly smaller than the diameter of said balls; and non-loaded ball grooves formed on both lateral end surfaces of said cage, said non-loaded ball grooves being communicated with the corresponding loaded ball grooves through ball turning grooves which are provided at both ends, respectively, of each of said loaded ball grooves, said end covers having a substantially U-shaped cross-section and each end cover including: a through-hole provided in its center and having a diameter slightly larger than the outer diameter of said spline shaft; ball turning grooves respectively corresponding to the ball turning grooves provided in said cages; a pair of axially extending ridges with a triangular cross-section provided on the inner peripheral surface of said end cover so that said triangular ridges can be respectively aligned with the corresponding triangular ridges formed inside said outer casing; and grooves with a substantially trapezoidal cross-section provided on both sides, respectively of each of said triangular ridges, and said spline shaft having a substantially square cross-section and including loaded ball rolling grooves formed on both sides, respectively, of each of one pair of diagonally opposing corners thereof.