JP2016017544A - Top-type ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a top-type ball screw which can utilize a large number of regions as rolling passages more than a conventional top member, and can reduce a size of a nut while securing a sufficient number of the rolling passages, related to a spiral screw groove which is formed at an internal peripheral face of the nut.SOLUTION: In a top-type ball screw having: a screw shaft in which a spiral screw groove is formed at an external peripheral face; a nut 13 which is arranged around the screw shaft, and has a spiral screw groove 14 at an internal peripheral face; a plurality of balls accommodated in a rolling passage 22 which is formed of the opposing two screw grooves; and a circulation path for circulating the balls from one end of the rolling passage 22 to the other end, an outside guide face constituting the circulation path is formed at a top member 16, and an axial guide face is formed at a side face of a top window 15 of the nut 13.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a ball screw used in various machine tools or an electric power steering device or an actuator of an automobile, and more particularly to a piece type ball screw using a piece member as a ball circulation part.

  There are various types of ball circulation mechanisms in the ball screw, and one of them is a method using a piece member. A ball screw using this method is generally called a piece-type ball screw, and many proposals have been made for piece members. For example, the piece-type ball screw described in Patent Documents 1 and 2 has a circulation groove that is curved in a substantially S shape, and a piece member formed in a circle or an ellipse is drilled in the trunk of the nut. It is inserted into the circular or oval piece window formed and fixed to the nut by means such as caulking, press-fitting or adhesion, and forms a circulation path connecting one end and the other end of the rolling path.

JP 2008-244103 A JP 2008-267523 A

  In the conventional piece member, the inner diameter side guide surface of the circulation path and the guide surfaces before and after the axial direction are formed on the piece member. For this reason, the size of the piece member is increased, and in particular, the axial dimension of the piece window has to be increased in accordance with the piece member. Therefore, it is used as a rolling path in the spiral thread groove formed on the inner peripheral surface of the nut. There were many areas that could not be done.

  Since it is necessary to strictly control the accuracy of the thread groove in terms of the cross-sectional shape of the groove, the diameter of the helix, and the lead (advancing amount of the helix per round), the processing conditions from one end of the screw groove to the other end The cutting and grinding are performed while maintaining a constant (change in the processing conditions during the processing may lead to deterioration in accuracy). For this reason, high-precision machining is performed even on the thread groove in the region not used as the rolling path, which increases the manufacturing cost.

  Further, since the size of the piece member is large, the piece window into which the piece member is inserted is also enlarged. As a result, the distance between the piece window and the screw groove adjacent thereto is shortened, so that a thin portion is generated, and there is a possibility that cracking may occur in the heat treatment process.

The object of the present invention is achieved by the following constitution.
(1) a screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut disposed around the screw shaft and having a helical thread groove formed on an inner peripheral surface, a plurality of balls accommodated in a rolling path formed by the two thread grooves facing each other, and the rolling In a piece type ball screw provided with a piece member provided with a circulation path for circulating the ball from one end of the moving path to the other end, an outer diameter side guide surface constituting the circulation path is formed on the piece member. A ball screw characterized in that one nut and the other guide surface in the axial direction constituting the circulation path are formed on the nut.
(2) The ball screw according to (1), wherein a width of the piece member in a direction orthogonal to a ball rolling direction is substantially the same as a width of the rolling path of the nut.
(3) The ball screw according to (1) or (2), wherein the piece member has a substantially S shape when viewed from a radial direction in a state where the piece member is attached to the nut.
(4) The piece member is provided with a convex portion for positioning in the radial direction in a state of being mounted on the nut, and the nut is provided with a concave portion for accommodating the flange. The ball screw according to any one of the above.

  According to the piece type ball screw according to the present invention, the outer diameter side guide surface constituting the circulation path is formed on the piece member, and the axial direction guide surface is formed on the nut, whereby the piece member is reduced in size. The width of the piece member can be reduced. As a result, the thread groove formed on the inner peripheral surface of the nut can use a larger area than the conventional piece member as a rolling path, and the nut can be reduced in size while securing a sufficient number of rolling paths.

It is a perspective view of the piece type ball screw concerning the present invention. (A) is a disassembled perspective view of the nut of the piece type ball screw shown in FIG. 1, (b) is a perspective view which shows the internal peripheral surface of a nut. (A) is a two-plane figure of the piece member concerning the present invention, and (b) is a perspective view of a piece member. It is sectional drawing which shows the circulation path | route of a ball | bowl. It is a figure showing one of the embodiments of the present invention. It is a perspective view of the conventional piece type ball screw. It is a nut sectional view of the conventional piece type ball screw.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIGS. 1 and 2, the piece ball screw 10 has a screw shaft 11 having a spiral thread groove 12a formed on the outer peripheral surface and a spiral screw groove 14 formed on the inner peripheral surface. 11 to the rolling path 22 formed by the nut 13 arranged around the frame 11, the piece member 16 fitted to the piece window 15 of the nut 13, the screw groove 12a of the screw shaft 11, and the screw groove 14 of the nut 13. And a plurality of balls (not shown) that are movably arranged.

  The cross-sectional shapes of the screw shafts 12 and the screw grooves 12a and 14 of the nut 13 are preferably gothic arc shapes having a large allowable axial load and capable of suppressing vibration, but may be circular arc shapes. On the inner peripheral surface of the nut 13, a piece window 15 having the same shape as the piece member 16 and into which the piece member 16 is fitted is formed.

  The piece member 16 has a circulation groove 16a formed on the inner diameter side when fitted to the piece window 15 to return the ball from one end of the rolling path 22 to the other end (see FIG. 3). The circulation groove 16a has a central portion curved in a direction toward the outer diameter when viewed from the radial direction of the nut. When the ball passes through the circulation groove 16a, the ball is returned from one end to the other end of the rolling path 22 beyond the thread of the screw shaft 11, so that the curvature is set so that the ball and the thread do not interfere with each other. ing.

  Further, the piece member 16 is substantially S-shaped when viewed from the radial direction of the nut 13 when fitted to the piece window 15. The substantially S-shaped one end and the other end are smoothly connected in the tangential direction of the thread groove 14 formed on the inner peripheral surface of the nut 13, and when the ball moves from the piece member 16 to the thread groove 14, Or the occurrence of noise in the reverse is suppressed.

  In the conventional piece type ball screw 100 shown in FIGS. 6 and 7, the circulation piece 116 has a shape corresponding to an oval or circular piece window 115 provided on the nut, and is orthogonal to the ball rolling direction of the circulation piece 116. The width W3 in the direction to be larger than the width W2 of the screw groove 114. This is because, in addition to making the piece window 115 larger to some extent, it is easy to process, and in the conventional circulation piece 116, the circulation path 116a and the axial guide surface 116b of the circulation path 122 must be formed in the circulation piece 116. The point where there was. In the sectional view of the nut 113 shown in FIG. 7, the circulation path 122 is provided in two circuits, the piece windows 115 are formed at two positions in the axial direction of the nut 113, and the circulation pieces 116, 116 are provided in the respective piece windows 115, 115. It is mated. In the case of such a configuration, since the piece window 115 is hung on the surrounding screw groove, many regions 116c that cannot be used as rolling paths are generated. Further, if the interval between the nuts 113 in the axial direction of the two piece windows 115 and 115 is reduced in order to increase the number of circuits of the circulation path 112 or shorten the axial dimension of the nut 113, the space between the piece windows 115 and 115 is reduced. Becomes thin and may cause deformation or cracking when the nut 113 is heat treated.

  On the other hand, the piece member 16 according to the present invention is characterized in that the width W1 in the direction orthogonal to the ball rolling direction and the width W4 of the piece window 15 are substantially the same as the width W2 of the screw groove 14 as shown in FIG. To do. That is, only the circulation path 116a is formed in the piece member 16, and the side surface 15a of the piece window 15 serves as an axial guide surface.

  With such a configuration, the plurality of balls rolling in the rolling path 22 are introduced into the circulation groove 16a when reaching one end of the circulation groove 16a, and the nut 13 is axially connected to the piece member 16 with respect to the radial direction. As for the direction, it rolls while being guided by the side surface 15a of the piece window 15 and reaches the other end of the circulation groove 16a over the thread 12b of the screw shaft 11 along the curve of the circulation groove 16a. It returns and rolls along the rolling path 22 again.

  The piece member 16 is integrally formed by a mold (not shown). When the piece member 16 is made of metal, for example, it can be formed by so-called MIM (Metal Injection Molding) in which metal powder and a binder are heated and melted and injected into a mold by an injection molding machine. Thus, by integrally molding the piece member 16 using a mold, the outer diameter side guide surface and the curved portion can be formed with high dimensional accuracy. The piece member 16 is not limited to the MIM as long as it is manufactured by a mold, and may be formed by injection molding a sintered alloy obtained by press-molding metal powder and firing, or synthetic resin.

  The nut 13 is formed with a piece window 15 for fitting the piece member 16 therein. The piece window is a through hole having the same shape as the piece member 16 when viewed from the radial direction of the nut 13 and can be formed by punching or end milling with a press. After the piece window is formed in the nut 13, the piece member 16 is inserted and fixed by crimping or bonding.

  As described above, according to the piece type ball screw 10 according to the present invention, the circulation path 16a is formed in the piece member 16, and the side face 15a of the piece window 15 is used as an axial guide surface. Compared to the ball screw, the width of the piece window can be reduced. Therefore, the thread groove 14 formed on the inner peripheral surface of the nut 13 can use a larger area than the conventional piece member as a rolling path, and the nut 13 can be downsized while ensuring a sufficient number of rolling paths. Can do. Further, since the piece window can be made smaller than the conventional piece type ball screw, a thin portion is not generated between the adjacent screw grooves 14, and cracking can be prevented in the heat treatment step.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. For example, in the piece-type ball screw 10, when the piece member 16 is fixed at an inappropriate position, a step is generated between the circulation path 16a and the screw groove 14, and abnormal noise or vibration is generated when the ball rolls. There is a risk of generating. Therefore, when the piece member 16 is fitted to the piece window 15, the fixed position of the piece member 16 in the piece window 15 is set so that the circulation path 16 a and the screw groove 14 are in the same position in the radial direction of the nut 13. Must be set.

  Therefore, as shown in FIG. 5, flange-shaped projections 26b are provided at both ends of the piece member 26 and on the outer diameter side in the radial direction of the nut 13, and the piece window 25 has a seating surface 25b (on the projection). A correspondingly shaped recess) may be provided. The positions and thicknesses of the protrusions 26b and the seating surface 25b are set so that no step is generated between the circulation path 26a and the screw groove 14 when the piece member 26 is fitted into the piece window 25.

  With such a configuration, the piece member 26 can be set to an appropriate position only by the work of abutting the protrusion 26b against the seating surface 25b, and the work of fitting the piece member 26 to the piece window 25 is easy. In addition, variations in the position of the piece member 26 can be suppressed.

10 piece type ball screw 11 screw shaft 12a (screw shaft) screw groove 13 nut 14 (nut) screw groove 15 piece window 16 piece 16a circulation groove 22 rolling path

Claims (4)

  Formed by a screw shaft having a spiral thread groove formed on the outer peripheral surface, a nut disposed around the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and the two thread grooves facing each other. In the piece type ball screw comprising a plurality of balls accommodated in the rolling path, and a piece member provided with a circulation member for circulating the ball from one end of the rolling path to the other end, A ball screw characterized in that an outer side guide surface constituting the circulation path is formed on the piece member, and one axial guide surface and the other axial guide surface constituting the circulation path are formed on the nut.   The ball screw according to claim 1, wherein a width of the piece member in a direction orthogonal to a ball rolling direction is substantially the same as a width of the rolling path of the nut.   The ball screw according to claim 1, wherein the piece member has a substantially S shape when viewed from a radial direction in a state where the piece member is attached to the nut.   4. The projection according to claim 1, wherein the piece member is provided with a convex portion for positioning in a radial direction in a state where the nut is attached to the nut, and the nut is provided with a concave portion for accommodating the flange. The ball screw described.

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