Ball screw assembly with enhanced radial load capacity and method of construction thereof

A linear ball screw assembly, comprising:

• a screw having a helical external groove extending continuously over a plurality of turns with a radially outwardly extending, continuous helical land formed between adjacent turns;
• a ball nut having a through bore extending between opposite ends, said through bore being configured for receipt of said screw therethrough and including a helical internal groove extending over a plurality of turns with a radially inwardly extending helical land formed between adjacent turns, said internal groove having a root diameter and being located generally centrally between said opposite ends and being radially aligned with said external groove of said screw to form a helical raceway;
• a plurality of axial load balls disposed in said helical raceway for simultaneous contact with said helical external groove and said helical internal groove;
• a plurality of internal cylindrical surfaces extending in axially opposite directions from said internal groove, said internal cylindrical surfaces having a diameter different from said root diameter of said internal groove and extending a predetermined length axially along said external groove of said screw to provide outer surfaces of a pair of radial load raceways;
• a plurality of radial load balls disposed in said radial load raceways for simultaneous contact with said helical external groove and said internal cylindrical surfaces;
• and
• wherein said internal cylindrical surfaces are provided by a plurality of sleeve inserts.

A method of constructing a linear ball screw assembly, comprising:

• providing a screw having a helical external groove extending continuously over a plurality of turns with a radially outwardly extending, continuous helical land formed between adjacent turns;
• providing a ball nut having a through bore extending between opposite ends with a helical internal groove having a root diameter and extending over a plurality of turns generally centrally between the opposite ends and including a pair of cylindrical bores extending in axially opposite directions from the helical internal groove toward the opposite ends;
• disposing a plurality of sleeve inserts having internal cylindrical surfaces having a diameter different from the root diameter of the internal groove in the cylindrical bores of the ball nut;
• disposing the screw through the through bore of the ball nut and forming a helical raceway between the helical internal groove of the ball nut and the helical external groove of the screw and a plurality of radial load raceways between the internal cylindrical surfaces of the sleeve inserts and the helical external groove of the screw;
• disposing a plurality of balls in the helical raceway and the radial load raceways;
• and
• further including providing the balls as axial load balls in the helical raceway and as radial load balls in the radial load raceways wherein the helical load balls have a different diameter from the radial load balls.