Patent ID: 12247613

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a ball spline having reinforcement bush parts according to the present invention will be described in detail with reference to the accompanying drawings.

FIG.3is a partially omitted perspective view showing a ball spline having reinforcement bush parts according to the present invention,FIG.4is a perspective view showing a nut included in the ball spline according to the present invention,FIG.5is a perspective view showing a retainer included in the ball spline according to the present invention,FIG.6is a partially cut-away perspective view showing a modified example of a ball spline according to the present invention, andFIG.7is a cross-sectional view showing a spline shaft and balls in the ball spline according to the present invention.

Hereinafter, the extension direction of a spline shaft110inFIG.3is described as “longitudinal direction”.

As shown inFIG.3, the ball spline100having reinforcement bush parts according to the present invention includes a rod-shaped spline shaft110, a nut part into which the spline shaft110is inserted so that the nut part can move in the longitudinal direction of the spline shaft110, and a plurality of balls150provided between the nut part and the spline shaft110so as to circulate.

The nut part includes a nut120which is a hollow body into which the spline shaft110is inserted, and retainers130, which are hollow bodies and provided at both sides of the nut120in the longitudinal direction of the nut120and into which the spline shaft110is inserted. The nut part may further include ring-shaped seals between the nut120and the retainers130, as indicated by reference numeral7inFIG.1.

The nut120is made of high carbon steel such as bearing steel. InFIG.4, reference numeral123indicates a flange protruding radially outward from one or both end portions of the nut120in the longitudinal direction of the nut120.

The retainer130has a doughnut shape in which an inner diameter portion is removed from a disk. The retainer130may be made of engineering plastics (nylon 6, nylon 66, or glass fibers included therein), and may be made of a metal such as bearing steel like the nut120. A seal that is a hollow body (not shown) may be provided between the nut120and the retainer130. The retainer130may be coupled to the nut120by means of bolts as shown inFIG.1.

The spline shaft110is formed with at least one concave track groove111that extends in the longitudinal direction thereof. The spline shaft110may be manufactured by processing the concave track groove111on the outer surface of a rod having a circular cross section. A plurality of the track grooves111are formed to be spaced apart from each other in the circumferential direction. As shown inFIG.2, two track grooves111may be provided at positions opposite to each other. The spline shaft110may include a shaft mounting part113having a reduced diameter at an end thereof. The shaft mounting portion113is formed with a key groove (not shown) and mounted with a pinion or the like.

The nut part is provided with two spline parts and two reinforcement bush parts, respectively.

The spline part includes at least one concave load track groove125formed in the longitudinal direction on the inner surface part121of the nut120, which is a hollow part into which the spline shaft110is inserted, and at least one no-load circulation part127formed in parallel to the load track groove125in the longitudinal direction. The load track groove125and the no-load circulation part127are provided in the same number as the track groove111provided on the spline shaft110. The no-load circulation part127may be formed as a through hole formed in the nut120in the longitudinal direction of the nut120. The load track groove125is formed at a position facing the track groove111.

A curvedly concave spline circulation groove133is formed on the inner surface of each of the retainers130, which faces the nut120. At least one spline circulation groove133is formed. The spline circulation groove133is formed in the same number as the track groove111. One side of the spline circulation groove133faces the end portion of the load track groove125and the other side faces the end portion of the no-load circulation part127.

Some of the balls150are diverted in the spline circulation grooves133of the retainers130, which are provided on both sides in the longitudinal direction, and roll between the track groove111and the load track groove125and circulate and move along the no-load circulation part127. Since the circulation of the balls150is a known technique, a description thereof will be omitted.

The balls150may come into contact with the track groove111at two points and come into contact with the load track groove125at two points, thereby rolling in a four-point contact. The track groove111and the load track groove125may be formed in the shape of an arc having a radius of curvature larger than the radius of the balls150, so that the balls150can roll in a two-point contact, which is a conventionally known technique, so a detailed description thereof will be omitted.

As shown inFIG.4, extended track extension parts125aare formed at both end portions of the load track groove125in the longitudinal direction. When the balls150move and reach the track extension parts125a, a clearance for the balls150between the track extension parts125aand the track groove111increases so that the balls150can smoothly move to the spline circulation grooves133of the retainers130and, accordingly, damage to the track groove111and the load track groove125caused by the balls150can be suppressed or prevented.

The reinforcement bush part is provided between the track grooves111of the spline shaft110. A plurality of reinforcement bush parts is provided. The reinforcement bush parts are provided alternately with the spline parts.

Hereinafter, an example will be described, in which two track grooves111are formed so as to be opposite to each other and spaced apart from each other at an angle of 180°, two spline parts are provided, and two reinforcement bush parts are positioned between the spline parts.

The reinforcement bush part includes at least one concave bush track groove125-1formed in the longitudinal direction on the inner surface part121of the nut120, and at least one bush circulation part127-1formed in parallel to the bush track groove125-1at a position spaced apart from the bush track groove125-1in the longitudinal direction. The bush track groove125-1is provided so as to face the outer surface of the spline shaft110. The bush circulation part127-1may be formed as a through hole formed in the nut120in the longitudinal direction of the nut120.

A curvedly concave bush circulation groove133-1is formed on the inner surface of each of the retainers130, which faces the nut120. At least one bush circulation groove133-1is formed. The bush circulation groove133-1is formed between the spline circulation grooves133. One side of the bush circulation groove133-1faces the end portion of the bush track groove125-1and the other side faces the end portion of the bush circulation part127-1.

The others of the balls150are diverted in the bush circulation grooves133-1of the retainers130, which are provided on both sides in the longitudinal direction, roll between the outer surface of the spline shaft110and the bush track groove125-1, are diverted in the bush circulation grooves133-1so as to be guided into the bush circulation part127-1, thereby moving along the bush circulation grooves133-1and circulating.

As shown inFIG.4, extended track extension parts are formed at both end portions of the bush track groove125-1in the longitudinal direction. When the balls150move and reach the track extension parts, the clearance for the balls150increases in the track extension parts125aso that the balls150can smoothly move to the bush circulation grooves133-1of the retainers130and, accordingly, damage to the bush track groove125-1caused by the balls150can be suppressed or prevented.

As shown inFIG.5, an inner surface part131of the retainer is formed in a cylindrical shape, and the spline circulation groove133and the bush circulation groove133-1are opened to the retainer inner surface part131so as to have an inner surface opening135opened to the retainer inner surface part131from an inner diameter side. Therefore, the retainer130does not have any element that is provided on the radially inner side of the retainer130so as to protrude inward from the retainer inner surface part131, and interference with the track groove111does not occur while the retainer130moves, so that damage to the retainer130does not occur due to the interference with the track groove111.

The diameter of the balls150provided in the ball spline100having reinforcement bush parts according to the present invention is provided to be greater than a gap between the load track groove125of the nut120and the track groove111and than a gap between the bush track groove125-1and the outer surface of the spline shaft110. Accordingly, preload is generated between the load track groove125and the track groove111and between the bush track groove125-1and the outer surface of the spline shaft110.

The gap between the bush track groove125-1and the outer surface of the spline shaft110is formed to be larger than the gap between the load track groove125and the track groove111, and assembly is carried out such that the preload acting on the balls150between the outer surface of the spline shaft110and the bush track groove125-1is smaller than the preload acting on the balls150between the track part111and the load track groove125. The reinforcement bush part is assembled with a smaller preload than the spline part but has a phase of 90° with respect to the spline part, as shown inFIG.7, so that the load bearing capacity in the right angle direction is maximized. In addition, the reinforcement bush part is provided and supported without the formation of the track groove111in the right angle direction, thereby preventing decrease in the rigidity of the spline shaft110due to the processing of the track groove111.

Therefore, the ball spline100according to the present invention is provided with reinforcement bush parts, so that the rigidity against the radial load acting on the nut120(“A” direction inFIG.7) is improved, thereby improving the lifespan of the ball spline.

Hereinabove, the ball spline having reinforcement bush parts according to the present invention has been described with reference to the embodiments shown in the drawings, which are only exemplary, and it will be understood by those skilled in the art that various modifications and equivalent other embodiments may be made thereto. Accordingly, the true technical protection scope should be determined by the technical spirit of the appended claims.

INDUSTRIAL APPLICABILITY

The ball spline having reinforcement bush parts according to the present invention has high rigidity and thus the lifespan thereof is extended.