Slide rail device for vehicle seat

Abstract

A slide rail device which includes a lower rail, an upper rail which is freely slidably engaged with the lower rail, and balls which are installed between the lower and upper rails. The lower rail includes a lower-rail bottom wall, a pair of lower-rail side walls, a pair of lower-rail upper walls, a pair of lower-rail lower-ball contact R-portions, and a pair of lower-rail upper-ball contact R-portions. The upper rail includes an upper-rail top wall, a pair of upper-rail side walls, and a pair of upper-rail ball-bearing walls. Each upper-rail ball-bearing wall includes an upper-rail lower-ball contact portion and an upper-rail upper-ball contact portion. A radius of curvature of the lower-rail lower-ball contact R-portion of the lower rail is greater than that of the lower ball, and a radius of curvature of the lower-rail upper-ball contact R-portion of the lower rail is greater than that of the upper ball.

1 . A slide rail device which includes a lower rail having a uniform cross section, an upper rail having a uniform cross section which is freely slidably engaged with said lower rail, and balls which are installed between said lower rail and said upper rail,
 wherein said lower rail comprises:   a lower-rail bottom wall;   a pair of lower-rail side walls which extend upward from both ends of said lower-rail bottom wall, with respect to a lateral direction, respectively;   a pair of lower-rail upper walls which extend toward a center of said lower rail in the lateral direction from upper ends of said pair of lower-rail side walls, respectively;   a pair of lower-rail lower-ball contact R-portions via which said pair of lower-rail side walls are connected to said lower-rail bottom wall, respectively; and   a pair of lower-rail upper-ball contact R-portions via which said pair of lower-rail upper walls are connected to said pair of lower-rail side walls, respectively,   wherein said upper rail comprises:   an upper-rail top wall;   a pair of upper-rail side walls which are continuous with said upper-rail top wall and extend downward between said pair of lower-rail upper walls into said lower rail from both sides of said upper-rail top wall, with respect to said lateral direction, respectively; and   a pair of upper-rail ball-bearing walls which extend outwardly upwards from lower ends of said pair of upper-rail side walls, respectively,   wherein each of said pair of upper-rail ball-bearing walls includes an upper-rail lower-ball contact portion which is formed to face an adjacent lower-rail lower-ball contact R-portion of said pair of lower-rail lower-ball contact R-portions of said lower rail, and an upper-rail upper-ball contact portion which is formed to face an adjacent lower-rail upper-ball contact R-portion of said pair of lower-rail upper-ball contact R-portions of said lower rail,   wherein said balls comprise a pair of upper balls which are installed between said pair of lower-rail upper-ball contact R-portions of said lower rail and said upper-rail upper-ball contact portions of said pair of upper-rail ball-bearing walls of said upper rail, respectively; and a pair of lower balls which are installed between said pair of lower-rail lower-ball contact R-portions of said lower rail and said upper-rail lower-ball contact portions of said pair of upper-rail ball-bearing walls of said upper rail, respectively,   wherein a radius of curvature of said lower-rail lower-ball contact R-portion of said lower rail is greater than a radius of said lower ball, and   wherein a radius of curvature of said lower-rail upper-ball contact R-portion of said lower rail is greater than a radius of said upper ball.   
     
     
         2 . The slide rail device according to  claim 1 , wherein, out of said upper-rail lower-ball contact portion and said upper-rail upper-ball contact portion of each of said pair of upper-rail ball-bearing walls of said upper rail, at least said upper-rail upper-ball contact portion is formed as an upper-rail upper-ball contact R-portion that is formed into a circular arc shape with a specific curvature in cross section. 
     
     
         3 . The slide rail device according to  claim 2 , wherein a radius of curvature of said upper-rail upper-ball contact R-portion of the upper rail is greater than said radius of said upper ball. 
     
     
         4 . The slide rail device according to  claim 2 , wherein said upper-rail lower-ball contact portion of each of said pair of upper-rail ball-bearing walls of said upper rail is formed as an upper-rail lower-ball contact R-portion that is formed into a circular arc shape with a specific curvature in cross section, a radius of curvature of said upper-rail lower-ball contact R-portion being greater than said radius of said lower ball. 
     
     
         5 . The slide rail device according to  claim 1 , wherein the following conditions are satisfied:
   R1≧1.1r1,
     and     R2≧1.1r2,
   wherein r 1  designates said radius of said lower ball,   r 2  designates said radius of said upper ball,   R 1  designates said radius of curvature of said lower-rail lower-ball contact R-portion, and   R 2  designates said radius of curvature of said lower-rail upper-ball contact R-portion.   
     
     
         6 . The slide rail device according to  claim 1 , wherein each inner surface of two connecting corners between said upper-rail top wall of said upper rail and said pair of upper-rail side walls of said upper rail serves as an assumed deformation rotational center when said upper rail is resiliently deformed upon a normal load being applied thereto, and
 wherein a cross sectional shape of said upper rail is determined so as to define an outward crossing angle between a line segment which connects said assumed deformation rotational center and a center of associated one of said pair of lower balls and a line segment which is tangent to both said associated one of said pair of lower balls and said upper-rail lower-ball contact R-portion at an angle in a range from 80 degrees to less than 90 degrees.   
     
     
         7 . The slide rail device according to  claim 1 , wherein said lower rail further comprises a pair of lower-rail inner side walls which are positioned between said pair of lower-rail side walls and extend downward from inner ends of said pair of lower-rail upper walls, respectively. 
     
     
         8 . The slide rail device according to  claim 1 , wherein each of said pair of upper-rail ball-bearing walls further comprises a vertical connecting wall via which said upper-rail lower-ball contact portion and said upper-rail upper-ball contact portion are connected.