Ball Screw Device

Abstract

There is provided a ball screw device capable of allowing interference to be easily elastically deformable and decreasing friction resistance of a seal member with respect to a screw shaft without damaging seal properties of the seal member. A predetermined section of a land sliding-contact portion ( 46 ) of a sliding-contact portion ( 40 ) and a section of a seal piece ( 37 ) of a lip portion ( 31 ) corresponding to the predetermined section are bent to protrude in one side in the axial direction of a nut ( 7 ) so that a protrusion ( 55 ) is formed, the bent section of the land sliding-contact portion ( 46 ) and the bent section of the seal piece ( 37 ) configure a pair of side surface portions ( 58, 58 ) of the protrusion ( 55 ) and a bottom portion ( 61 ) connecting the one side ends of the pair of side surface portions ( 58, 58 ).

1 . A ball screw device comprising:
 a screw shaft linearly extending and including a helical rolling groove formed on an outer circumferential surface;   a cylindrical nut including a rolling groove opposing the helical rolling groove on an inner circumferential surface, and screwed to the screw shaft via a plurality of balls which disposed between the rolling groove and the helical rolling groove of the screw shaft;   balls disposed between track grooves formed of the rolling groove of the nut and the rolling groove of the screw shaft;   an annular sealing device provided on an inner diameter side of the nut and sealing a gap between the nut and the screw shaft; and   a tip portion of a lip portion externally fitted to the screw shaft and including an inner circumferential edge portion coming into sliding-contact with an outer circumferential surface of the screw shaft,   wherein the tip portion of the lip portion includes an easily deformable portion elastically deformed so that a shape of the inner circumferential edge portion is matched to a shape of the outer circumferential surface of the screw shaft when the tip portion of the lip portion is assembled to the screw shaft.   
     
     
         2 . The ball screw device according to  claim 1 ,
 wherein the helical rolling groove of the screw shaft includes a grinding clearance groove, and a depth of the grinding clearance groove is set to be smaller than interference of the tip portion of the lip portion with respect to the screw shaft.   
     
     
         3 . The ball screw device according to  claim 1 ,
 wherein the sealing device includes a fitting portion on which at least one or more convex portions protruding in an axial direction of the sealing device are provided, and   wherein, when an axial direction of the nut and an axial direction of the sealing device are approximately the same direction as each other, at least one or more concave portions are provided on an end of an inner circumferential surface of the nut depending on disposition of the convex portion in the fitting portion, a direction in which the convex portion protrudes opposes a direction in which the concave portion is opened, the convex portion and the concave portion are fitted to each other, the lip portion protrudes inwardly toward the helical rolling groove of the screw shaft, and the sealing device is fitted to the inner circumferential surface of the nut.   
     
     
         4 . The ball screw device according to  claim 2 ,
 wherein an angle at which the grinding clearance groove and the rolling groove come into contact with each other is equal to or more than 155°.   
     
     
         5 . The ball screw device according to  claim 2 ,
 wherein the interference of a section in which the sealing device comes into contact with the vicinity of the grinding clearance groove is larger than the interference of a section in which the sealing device comes into contact with sections other than the grinding clearance groove.   
     
     
         6 . The ball screw device according to  claim 2 ,
 wherein the shape of the grinding clearance groove is a gothic arc shape.   
     
     
         7 . The ball screw device according to  claim 2 ,
 wherein the rolling groove of the screw shaft and the grinding clearance groove have a smooth cross-sectional shape formed with a curved surface portion.   
     
     
         8 . The ball screw device according to  claim 3 ,
 wherein a tip portion of the convex portion is chamfered or curved-surface processed, and a bottom surface of the concave portion is also chamfered or curved-surface processed.   
     
     
         9 . The ball screw device according to  claim 3 ,
 wherein the convex portion has elasticity in the axial direction.   
     
     
         10 . The ball screw device according to  claim 2 ,
 wherein a gap C 3  between the convex portion and the concave portion in the radial direction is larger than a gap C 1  between the outer circumferential surface of the sealing device and the inner circumferential surface of the nut, or than a gap C 2  between the lip portion of the sealing device and the outer circumferential surface of the screw shaft.   
     
     
         11 . The ball screw device according to  claim 1 ,
 wherein the easily deformable portion is a protrusion formed in an approximately U shape in which a section of the inner circumferential edge is bent to protrude to one side in the axial direction of the nut and is opened to the other side in the axial direction, and is more easily deformed elastically than the sections of the sealing device other than the easily deformable portion.   
     
     
         12 . The ball screw device according to  claim 11 ,
 wherein the protrusion is elastically deformed so that the opening is enlarged.   
     
     
         13 . The ball screw device according to  claim 1 ,
 wherein the inner circumferential edge includes a groove sliding-contact portion which comes into sliding-contact with a groove surface of the rolling groove of the screw shaft, and an outer circumferential sliding-contact portion which comes into sliding-contact with the outer circumferential surface portion between the rolling grooves adjacent in the axial direction, and the easily deformable portion is formed on the outer circumferential sliding-contact portion.   
     
     
         14 . The ball screw device according to  claim 1 ,
 wherein the inner circumferential edge includes a groove sliding-contact portion which comes into sliding-contact with a groove surface of the rolling groove of the screw shaft, and an outer circumferential sliding-contact portion which comes into sliding-contact with the outer circumferential surface portion between the grooves adjacent in the axial direction, a cross-sectional area of the outer circumferential sliding-contact portion is formed to be smaller than a cross-sectional area of the groove sliding-contact portion, and the easily deformable portion is the outer circumferential sliding-contact portion.   
     
     
         15 . The ball screw device according to  claim 14 ,
 wherein the outer circumferential sliding-contact portion is elastically deformed to extend in the circumferential direction of the inner circumferential edge.   
     
     
         16 . The ball screw device according to  claim 1 ,
 wherein the inner circumferential edge includes a large diameter portion having a large cross-sectional diameter, and a small diameter portion having a smaller cross-sectional diameter than that of the large diameter portion, and the easily deformable portion is the small diameter portion.   
     
     
         17 . The ball screw device according to  claim 16 ,
 wherein the small diameter portion is elastically deformed to extend in the circumferential direction of the inner circumferential edge.   
     
     
         18 . The ball screw device according to  claim 4 ,
 wherein the interference of a section in which the sealing device comes into contact with the vicinity of the grinding clearance groove is larger than the interference of a section in which the sealing device comes into contact with sections other than the grinding clearance groove.   
     
     
         19 . The ball screw device according to  claim 8 ,
 wherein the convex portion has elasticity in the axial direction.