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MANUFACTURING TECHNIQUE TO REDUCE RACK ELECTRIC POWER STEERING GEAR'S WEIGHT, COST, AND IMPROVE PERFORMANCE

IP.com Disclosure Number: IPCOM000248670D
Publication Date: 2016-Dec-23
Document File: 2 page(s) / 342K

Publishing Venue

The IP.com Prior Art Database

Abstract

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This is the abbreviated version, containing approximately 57% of the total text.

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MANUFACTURING TECHNIQUE TO REDUCE RACK ELECTRIC POWER STEERING GEAR'S WEIGHT, COST,

AND IMPROVE PERFORMANCE

For REPAS gears, the Ball Nut Assembly is used as linear actuation mechanism. It is the most critical

mechanical component in the REPAS gear. Performance of the BNA is very susceptible to manufacturing

errors. The ball track on the rack bar must have accurate gothic-arch profiles, helix angle, run out and

concentricity, and can cause steering gears to exhibit stick-slip, rattle, clatter and produce friction

variation.

One major source for manufacturing inaccuracies comes from induction hardening process that distorts

the ball screw. New Method of selective laser hardening is proposed to reduce the distortion. Laser

hardening causes very

little distortion, which

may eliminate need for

straightening and re-

grinding. Also, by

installing the laser beam

output device in the ball

screw processing machine,

further material handling

and processing can be

eliminated.

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Currently, BNA accuracy requirements are met with expensive manufacturing processes, where

tolerances are in the order of few microns. With strength and wear requirement, the Ball screw rack bar

must be case hardened by induction hardening process, which introduces large distortion. In order to

meet the hardness and accuracy requirement, ball screw rack bars must undergo several steps of

grinding, rolling, machining and straightening, finish grinding and polishing.

By utilizing a 3KW laser with 6mm diameter be...