JP2008281161A - Ball screw mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw mechanism preventing erroneous combination of a ball in assembly. <P>SOLUTION: A groove part 2B in which the ball 3 does not roll is a simple circular arc shape including a radius of curvature R2 (<Sϕ1/2+Δ) smaller than quantity of a radius (Sϕ1/2) of the ball 3 from which a clearance quantity in the radial direction Δ is deducted in a cross-section shape orthogonal to an axis of a female screw groove 2a, or BCD (BCDn') of the ball rolling along the groove part 2B in which the ball does not roll is smaller than BCDs of the ball 3 rolling along a male screw groove 1a as seen in the axial direction of a nut 2. The ball thereby cannot physically intrude between the groove part 2B not rolling and the male screw groove 1a, and erroneous combination of the ball 3 is prevented and locking of the ball screw mechanism is also prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is applied to a deflector-type ball screw mechanism suitable for mechanical devices, automobile parts (including motorcycles), and marine applications.

  In recent years, labor saving of vehicles and the like has progressed, and for example, a system has been developed in which a transmission, a parking brake, and the like of an automobile are performed not by hand but by the power of an electric motor. An electric actuator used for such an application may use a ball screw mechanism in order to convert the rotational motion transmitted from the electric motor into the axial motion with high efficiency.

As one form of the ball screw mechanism, a deflector type ball screw mechanism as shown in Patent Document 1 is known.
Japanese Patent No. 3736912

  Usually, in the assembly work of the deflector type ball screw mechanism, the deflector is assembled to a nut for each circuit, the nut is attached to a dedicated assembly jig, and the ball is interposed in the nut. By sequentially performing such intervention work, a set number of circuits corresponding to the number of deflectors can be formed. Here, if the clearance between the nut inner diameter and the assembly jig is larger than the ball diameter due to the bias of the nut in the ball interposing operation, the ball may be accidentally inserted outside the circulation circuit. During the operation of the mechanism, the ball hits the deflector outside the circulation circuit, causing clogging and locking.

  The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a ball screw mechanism that can prevent erroneous assembly of balls during assembly.

The ball screw mechanism of the present invention is
A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a rolling path formed between opposing screw grooves;
A circulation groove connected to one end and the other end of the rolling path, and a deflector attached to an attachment hole of the nut,
The female screw groove is characterized in that a shape of a groove portion that is connected to the circulation groove and the ball rolls is different from a shape of a groove portion that is not connected to the circulation groove and the ball does not roll.

  According to the present invention, the female screw groove is different from the shape of the groove portion that is connected to the circulation groove and the ball rolls, and the shape of the groove portion that is not connected to the circulation groove and the ball does not roll. Therefore, for example, by reducing the cross-sectional shape of the groove portion where the ball does not roll, there is no possibility that the ball is mistakenly assembled at the time of assembly, and the ball screw mechanism can be prevented from being locked by the misassembled ball.

  The groove portion where the ball rolls has a curvature radius larger than the radius of the ball in a cross-sectional shape perpendicular to the axis line of the female screw groove, and the groove portion where the ball rolls when viewed in the axial direction of the nut. It is preferable that the BCD (Ball Circle Diameter) of the ball rolling along the ball is larger than the BCD of the ball rolling along the male screw groove.

  It is preferable that the groove portion where the ball rolls has a radius of curvature larger than an amount obtained by adding a radial clearance to the radius of the ball in a cross-sectional shape perpendicular to the axis of the female screw groove.

  The groove portion where the ball does not roll includes a radius of curvature smaller than the radius of the ball in a cross-sectional shape perpendicular to the axis of the female screw groove, or the groove portion where the ball does not roll when viewed in the axial direction of the nut. It is preferable that the BCD (Ball Circle Diameter) of the ball rolling along the ball is smaller than the BCD of the ball rolling along the male screw groove.

  It is preferable that the groove portion where the ball does not roll includes a radius of curvature smaller than an amount obtained by subtracting a radial clearance from the radius of the ball in a cross-sectional shape perpendicular to the axis of the female screw groove.

  The groove part where the ball rolls preferably has a Gothic arc shape in a cross-sectional shape perpendicular to the axis of the female screw groove.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the ball screw mechanism according to the present embodiment, FIG. 2 is a view of the ball screw mechanism according to the present embodiment as viewed in the axial direction, and FIG. 3 is the present embodiment. FIG. 4 is a partial cross-sectional view of the ball screw mechanism as viewed in the direction orthogonal to the axis, and FIG. 4 is a view showing the male screw groove and the female screw groove cut and enlarged in the direction orthogonal to the axis. FIG. 5 is a diagram illustrating a state in which the deflector is incorporated in the nut.

  1 and 3, a male screw groove 1a is formed on the outer peripheral surface of a screw shaft 1 connected to a driven member and supported so as not to rotate but to move only in the axial direction. A cylindrical nut 2 supported so as to be rotatable only with respect to a housing (not shown) is disposed so as to surround the screw shaft 1 and has a female screw groove 2a formed on an inner peripheral surface thereof. A plurality of balls 3 are arranged so as to be able to roll in a spiral rolling path formed between the opposing screw grooves.

  As shown in FIG. 5, on the outer periphery of the nut 2, a cylindrical mounting hole 2b penetrating in the radial direction, and a positioning extending linearly opposite to the mounting hole 2b in both circumferential directions of the nut 2. A groove 2c is formed. At least a part of the positioning groove 2 c is provided with a so-called dovetail groove in which the width of the side wall increases toward the bottom, and has a function of positioning the phase when the deflector 4 is attached.

  As shown in FIGS. 3 and 4, the deflector 4 mounted in the mounting hole 2 b includes a cylindrical main body 4 b formed with a circulation groove 4 a connected to one end and the other end of the rolling path, and an outer periphery of the main body 4 b. A flange portion 4c having a rectangular cross section is formed so as to extend symmetrically in the circumferential direction of the nut 2 and not to protrude from the outer diameter of the nut 2 when attached to the nut 2. Such a deflector 4 can be formed by metal powder injection molding or press sintering.

  The operation of the present embodiment will be described. When the nut 2 is rotationally driven by an electric motor (not shown), the rolling path rolls and from one end of the rolling path to the other end via the circulation path 4a of the deflector 4. The rotating ball 3 efficiently converts the rotational motion into the axial motion of the screw shaft 1, and a driven member (not shown) connected thereto can be moved in the axial direction.

  The shape of the female thread groove 2a of the nut 2 according to this embodiment will be described. In FIG. 4, a central groove 2A, which is a part of the female screw groove 2a, is connected to a circulation path 4a (not shown in FIG. 4) of the deflector 4 and is a groove on which the ball 3 rolls. On the other hand, the groove portions 2B on both sides, which are different parts of the female screw groove 2a, are not connected to the circulation path 4a of the deflector 4 and are the grooves on which the ball 3 does not roll, and the groove portions 2A and 2B have different groove shapes. . Such a shape can be formed by an NC-controlled precision lathe or the like.

  More specifically, as shown in FIG. 4, the groove portion 2A on which the ball 3 rolls has a radial clearance amount Δ on the radius (Sφ1 / 2) of the ball 3 in a cross-sectional shape perpendicular to the axis of the female screw groove 2a. Of the ball 3 which has a gothic arc shape including a radius of curvature R1 (> Sφ1 / 2 + Δ) larger than the amount of the ball 3 and rolls along the groove 2A where the ball 3 rolls when viewed in the axial direction of the nut 2. BCD (BCDn) is larger than the BCD (BCDs) of the ball 3 rolling along the male screw groove 1a. Thereby, the ball | bowl 3 can be filled between the groove part 2A and the external thread groove 1a which roll, and the inside of a rolling path can be rolled smoothly. In the same cross-sectional shape, the male screw groove 1a preferably has a curvature radius R1.

  On the other hand, the groove 2B on which the ball 3 does not roll has a radius of curvature R2 (<< smaller than the amount obtained by subtracting the radial clearance amount Δ from the radius (Sφ1 / 2) of the ball 3 in the cross-sectional shape perpendicular to the axis of the female screw groove 2a. (Sφ1 / 2−Δ) or a BCD (BCDn ′) of the ball rolling along the groove 2B where the ball 3 does not roll when viewed in the axial direction of the nut 2 is the male screw groove 1a. It is smaller than the BCDs of the ball 3 rolling along. Thereby, since the ball 3 cannot physically enter between the groove portion 2B that does not roll and the male screw groove 1a, it is possible to prevent the balls 3 from being mistakenly assembled and to prevent the ball screw mechanism from being locked. According to the present embodiment, in addition to the advantage that the ball 3 is not interposed in the non-rolling groove 2B, the number of the balls 3 can be reduced even when a small number of balls 3 are interposed in the rolling groove 2A. Since it can be easily managed, it has an effect of avoiding problems such as a decrease in load capacity and a decrease in life of the ball screw mechanism due to a shortage of interposed balls.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. In the female thread groove 2a, the groove portion where the ball 3 rolls may have a circular arc shape, and the groove portion where the ball 3 does not roll may have a Gothic arc shape.

It is a perspective view of the ball screw mechanism which is this Embodiment. It is the figure which looked at the ball screw mechanism which is this Embodiment in the axial direction. It is the partial sectional view which looked at the ball screw mechanism which is this embodiment in the direction orthogonal to an axis. It is a figure which cut | disconnects and expands to a male thread groove, a female thread groove, and the axis orthogonal direction. It is a figure which shows the state which incorporates a deflector in a nut.

Explanation of symbols

1 Screw shaft 1a Male thread groove 2 Nut 2a Female thread groove 2b Mounting hole 2c Positioning groove 3 Ball 4 Deflector 4a Circulation groove 4b Body 4c Flange

Claims (6)

A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a rolling path formed between opposing screw grooves;
A circulation groove connected to one end and the other end of the rolling path, and a deflector attached to an attachment hole of the nut,
The female screw groove is characterized in that a shape of a groove portion that is connected to the circulation groove and the ball rolls is different from a shape of a groove portion that is not connected to the circulation groove and the ball does not roll. Screw mechanism.   The groove portion where the ball rolls has a curvature radius larger than the radius of the ball in a cross-sectional shape perpendicular to the axis line of the female screw groove, and the groove portion where the ball rolls when viewed in the axial direction of the nut. 2. The ball screw mechanism according to claim 1, wherein a BCD (Ball Circle Diameter) of the ball rolling along the ball is larger than a BCD of the ball rolling along the male screw groove. 3.   The groove portion in which the ball rolls includes a radius of curvature larger than an amount obtained by adding a radial clearance to the radius of the ball in a cross-sectional shape perpendicular to the axis of the female screw groove. Ball screw mechanism.   The groove portion where the ball does not roll includes a radius of curvature smaller than the radius of the ball in a cross-sectional shape perpendicular to the axis of the female screw groove, or the groove portion where the ball does not roll when viewed in the axial direction of the nut. The ball screw mechanism according to any one of claims 1 to 3, wherein a BCD (Ball Circle Diameter) of the ball rolling along the ball is smaller than a BCD of the ball rolling along the male screw groove. .   5. The groove portion where the ball does not roll includes a curvature radius smaller than an amount obtained by subtracting a radial clearance amount from the radius of the ball in a cross-sectional shape perpendicular to the axis of the female screw groove. Ball screw mechanism.   The ball screw mechanism according to any one of claims 1 to 5, wherein the groove portion on which the ball rolls has a Gothic arc shape in a cross-sectional shape perpendicular to the axis of the female screw groove.

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