Electrically-operated power steering apparatus
AssigneeNsk Ltd.
InventorsIsamu Chikuma, Kenji Someya, Hiroshi Eda
Life of this patent
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Abstract
An electrically-operated power steering apparatus comprises a steering shaft, a rack shaft capable of linear movement for turning a steering running wheel a, rack-pinion gear for coupling the steering shaft with the rack shaft, and a ball screw mechanism including a screw groove formed on the rack shaft, a rotary ball screw nut fitted on the rack shaft, and plural balls positioned in a rolling path. The plural balls are comprised of bulbs of a larger diameter and balls of a smaller diameter, which are alternately arranged, and the smaller diameter is within a defined range.
Claims6
An electrically-operated power steering apparatus comprising:
- a steering shaft to be directly connected to a steering wheel for integral rotation therewith;
- a rack shaft capable of a linear movement for deflecting steerable vehicle wheels;
- rack-pinion gear mechanism including a pinion gear, linked with said steering shaft and said rack shaft, to be rotated by said steering shaft, and a rack gear provided on said rack shaft to be meshed with said pinion gear;
- a ball screw mechanism including a screw portion provided on said rack shaft, a rotary nut portion surrounding at least a part of said screw portion, and plural balls provided in succession in a rolling path formed between said rotary nut portion and said screw portion to transmit power between said rotary nut portion and said screw portion;
- and
- an electric motor unit connected to said rotary nut portion;
- wherein said plural balls include balls of larger diameter and balls of smaller diameter positioned regularly among said larger diameter balls, the diameter Db of said smaller diameter balls satisfying the following condition:
- Da-4Da/1000.ltoreq.Db.ltoreq.Da-Da/1000
- wherein Da is the diameter of said larger diameter balls.
Dependencies are inferred from the claim text.