Differential device and method of manufacturing the device

A differential apparatus comprising (a) a casing having an opening on each side wall;

• (b) a pair of disc plates rotatably received in said casing and having connecting portions each connectable to a shaft rotatably supported by each opening of said casing, an opposing surface of each disc plate being formed with a circumferentially continuous groove winding such that a radial position changes at a constant period;
• (c) a plurality of balls rolling in winding continuous grooves of a pair of disc plates;
• and (d) a ball holder disposed between a pair of disc plates and engaging said casing, said ball holder having radially elongated guide holes each holding one ball circumferentially at an equal interval, wherein said winding continuous groove has first guide regions each extending from a radially outer position to a radially inner position and second guide regions each extending from a radially inner position to a radially outer position, inflected regions each connecting said first guide region and said second guide region being larger in width and/or depth than said first guide regions and said second guide regions, whereby a contact stress between said balls and said winding continuous groove is decreased in said inflected regions.

A differential apparatus comprising (a) a casing rotated by a driving force from outside;

• (b) a pair of opposing disc plates coaxially disposed in said casing, an opposing surface of each disc plate being formed with a circumferentially continuous groove winding such that a radial position changes at a constant period;
• (c) a plurality of balls rolling in opposing winding continuous grooves of both disc plates;
• and (d) a ball holder rotating integrally with said casing and having a plurality of radially extending guide holes, each guide hole movably receiving each ball, wherein said winding continuous groove has a plastically worked surface.

A differential apparatus comprising (a) a casing rotated by a driving force from outside;

• (b) a pair of opposing disc plates coaxially disposed in said casing, an opposing surface of each disc plate being formed with a circumferentially continuous groove winding such that a radial position changes at a constant period;
• (c) a plurality of balls rolling in opposing winding continuous grooves of both disc plates;
• and (d) a ball holder rotating integrally with said casing and having a plurality of radially extending guide holes, each guide hole movably receiving each ball, wherein said winding continuous groove has a small groove extending along a bottom thereof.

A differential apparatus comprising (a) a casing rotated by a driving force from outside;

• (b) a pair of opposing disc plates coaxially disposed in said casing, an opposing surface of each disc plate being formed with a circumferentially continuous groove winding such that a radial position changes at a constant period;
• (c) a plurality of balls rolling in opposing winding continuous grooves of both disc plates;
• and (d) a ball holder rotating integrally with said casing and having a plurality of radially extending guide holes, each guide hole movably receiving each ball, wherein said winding continuous groove has a rolling-formed surface having a shape error of 100 μm or less and a surface roughness Rz of 30 μm or less.

An apparatus for producing a ball holder for a differential apparatus, said ball holder having a pair of radial guide holes for holding balls circumferentially at an equal interval, said apparatus comprising (1) rolling-forming balls received in guide holes formed in advance in said ball holder with a plastic deformation margin left;

• (2) a pair of rolling-forming discs each having on an opposing surface a guide groove for rotatably holding and guiding said rolling-forming balls;
• (3) a means for relatively rotating a pair of rolling-forming discs in a state that they are disposed on both sides of said ball holder holding said rolling-forming balls in said guide holes, said rolling-forming balls being forced to move along the inner walls of said guide holes by the relative rotation of a pair of rolling-forming discs, thereby rolling-forming curved surface portions corresponding to said rolling-forming balls on said inner walls of said guide holes.

A method for producing a ball holder for a differential apparatus, said ball holder having a pair of radial guide holes for holding balls circumferentially at an equal interval, said method comprising the steps of (a) forming guide holes in said ball holder with a plastic deformation margin left in advance;

• (b) sandwiching said ball holder coaxial with a pair of rolling-forming discs having a guide groove for rotatably holding and guiding said rolling-forming balls on opposing surfaces with said rolling-forming balls held in the guide groove of said ball holder;
• (c) relatively rotating a pair of rolling-forming discs to force said rolling-forming balls to move along the inner walls of said guide holes, thereby rolling-forming curved surface portions corresponding to said rolling-forming balls on the inner walls of said guide holes.

A differential apparatus comprising (a) a casing rotated by a driving force from outside;

• (b) a pair of opposing disc plates coaxially disposed in said casing, an opposing surface of each disc plate being formed with a circumferentially continuous groove winding such that a radial position changes at a constant period;
• (c) a plurality of balls rolling in opposing winding continuous grooves of both disc plates;
• and (d) a ball holder rotating integrally with said casing and having a plurality of radially extending guide holes, each guide hole movably receiving each ball, wherein said casing has a pressure chamber connected to a controlling operating fluid supply system, to supply the operating fluid to the pressure chamber with pressure variable depending on the driving conditions of a vehicle, whereby said disc plate is pressed to said casing to control a differential-limiting force.