JPS6347948B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ball screw without a ball return tube.

Conventional ball screws usually have a ball screw shaft and a ball nut that is screwed together via a large number of balls that are inserted into the thread groove of the screw shaft and roll and circulate, and the nut is provided with a return tube for the balls. The disadvantage was that the structure was extremely complex. For this reason, as shown in FIG. 1, there is also a structure in which a nut combined with a screw shaft 1 is formed by fixing three ball bearings 3 in a hollow cylinder 2 to simplify the structure. With this structure, the inner race 4 has a convex inner surface, and the inner race 4 is fitted into the thread groove 5 with the inner race 4 inclined with respect to the axis by the lead angle. The outer race 7 is fixed in the hollow cylinder 2 by a suitable fixing fitting 6 so that the bearing 3b is eccentric in the opposite direction. However, in order to fix the bearing 3 at an angle with respect to the shaft center as described above, it is necessary to make the inner diameter of the inner race 4 extremely large with respect to the screw shaft 1. It has the disadvantage of being large in size.

SUMMARY OF THE INVENTION An object of the present invention is to provide a ball screw with a new structure that eliminates the above-mentioned drawbacks of conventional ball screws.

In the present invention, the bearing is fixed to the housing such that the screw shaft has a thread having a flank angle and a cylindrical thread groove, and the inner race of the rolling bearing is perpendicular to the screw shaft and eccentrically in contact with the screw groove. It is characterized by having a ball nut,
In order to hold the ball nut on the screw shaft, three rolling bearings are alternately eccentric in opposite directions, and one
The housing is supported on the threaded shaft by journal bearings that are slidable in the axial direction on both sides of the rolling bearings.

The following describes the embodiments of the present invention.
3, the screw shaft 8 has a thread 9 and a cylinder having a flank angle α and a lead angle β (where β=tan ⁻¹ P/πd, where P is the pitch and d is the effective diameter). The ball nut has three rolling bearings 12 in a housing 11.
The inner surface of the inner race 13 of the rolling bearing 12 has an inner diameter larger than the diameter of the thread groove 10 by at least the height of the thread 9, and the outer race 14 is arranged eccentrically in a plane perpendicular to the axis and in contact with the thread groove 10. It is fixed to the housing 11 via a spacer 15.
The center bearing 12a and the left and right bearings 12b are fixed to the housing 11 eccentrically in opposite directions, so that the housing 11 moves in the axial direction without moving in the radial direction due to the rotation of the screw shaft 8.
In this case, since the inner race 13 rolls into contact with the thread groove 10, the friction between the two is extremely small.

The axial width of the thread groove 10 is set slightly larger than the width of the inner race 13 according to the lead angle β, so that the inner race 13
0 closely fits between the threads 9 without any free movement in the axial direction, but as the inner surface of the inner race 13 moves away from the thread groove 10 (Fig. 3), both ends of the inner surface of the inner race 13 become threaded. Due to the flank angle α, the thread 9 can be removed without interfering with the thread 9.
Go beyond the exterior of. Therefore, inner lace 1
3 is arranged perpendicularly to the screw shaft 8, and the housing 1 is
1 can be made smaller. When the lead angle β is large, the axial width of the thread groove 10 is increased to improve contact with the inner race 13.

Although the distance between the bearings 12a and 12b is (Λ+0.5)P (P is pitch) in FIG. 2, it can generally be (n+0.5)P (n is 0 or an integer). Therefore, as illustrated in Figure 4, the pitch is
For both screw shafts P ₁ and P ₂ , a nut with n set so that 0.5P ₁ =(n+0.5)P ₂ can be used in common for both screw shafts.

FIG. 5 shows an embodiment in which a journal bearing 16 that fits into the thread 9 is fixed to the housing 11 instead of the rolling bearing 12b shown in FIG. This is an example. In this embodiment, the bearing 16 comes into pressure contact with the thread 9 on the side opposite to the contact portion of the inner race 13, but the frictional force thereof is small compared to the entire frictional force in the axial direction, so this embodiment It can also be seen as a type of ball screw. In the case of this embodiment, the nut can be shared by screw shafts with different leads.

The present invention is as described above, and since the ball nut does not have a ball return tube and is attached to the screw shaft by an eccentric rolling bearing perpendicular to the ball nut, the structure is extremely simple and can be manufactured at low cost. This has the effect of reducing the axial length of the ball nut to form a thin nut, which is particularly advantageous for ball nuts used in large lead screw shafts. Furthermore, since there is no thread on the nut side, the same nut can be used for different screw shafts or can be used for different screw shafts by changing the mutual spacing of the rolling bearings.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of a conventional example, Fig. 2 is a longitudinal cross-sectional view of an embodiment of the present invention, Fig. 3 is a cross-sectional view taken along line A-A in Fig. 2, and Fig. 4 is a cross-sectional view of a ball nut that can be used in common. An explanatory diagram of the screw shaft, FIG. 5 is a longitudinal sectional view of another embodiment of the present invention. 8...Screw shaft, 9...Thread thread, 10...Thread groove, 11...Housing, 12...Rolling bearing, 13...Inner race, 14...Outer race, 16...Bearing.

Claims (1)

[Claims] 1. Three rolling bearings each having an inner race whose inner diameter is larger than the thread groove diameter by more than the thread height in the thread groove of a screw shaft having a thread having a flank angle and a cylindrical thread groove. A ball screw in which an outer race is fixed to a housing such that the inner race is perpendicular to the shaft center and spaced apart from each other in the axial direction, and the central bearing and the bearings on both sides are in contact with each other eccentrically in the reaction direction. 2 The inner race of one rolling bearing has an inner race whose inner diameter is larger than the thread groove diameter by more than the thread height, in the thread groove of a screw shaft having a thread with a flank angle and a cylindrical thread groove. A ball screw in which an outer race is fixed to a housing so as to be in contact eccentrically at right angles to the outer race, and bearings are provided on both sides of the housing to slidably support a screw shaft in the axial direction.