JP4784132B2 - Ball screw mechanism - Google Patents

Description

  The present invention relates to a ball screw mechanism that is assembled to a general industrial machine or used in an automobile.

  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.

However, normally, the ball screw mechanism is composed of a screw shaft, a nut, and a ball that rolls in a rolling path formed between them. In order to return the ball to the other end, a top is attached to the nut (see Patent Document 1).
JP 11-270648 A

  Here, the frame will be described. In the ball screw mechanism, a mechanism for circulating the ball when the screw shaft and the nut relatively move in the axial direction is inherently necessary. In the top type ball screw mechanism, the top attached to the nut has one end of a rolling path extending about 340 degrees around the axis to compensate for the deviation of the rolling path in the axial direction corresponding to one lead of the ball screw. And a circulation groove meandering in an S shape connecting the other end. Accordingly, after rolling along the rolling path, the ball is guided from one end of the rolling path into the circulation groove of the coma so as to get over the land portion of the screw shaft, and then from the circulation groove to the other end of the rolling path. It is supposed to be returned.

However, in the ball screw mechanism, it is important to make the ball roll as smoothly as possible to suppress the generation of noise and vibration, and to ensure the efficiency and durability of the ball screw. . For this reason, in the prior art as in Patent Document 1, when viewed from the inside in the radial direction of the nut, the circulation groove of the top is S-shaped, and its center line is smoothly bent from the end of the circulation groove. . However, in the prior art, due to the problems described below, the connection between the rolling path and the circulation groove is not smooth, causing abnormal noise and vibration of the passing ball.
(1) In the top type ball screw mechanism, usually, a through hole is formed on the outer periphery of the nut, and the top is inserted into the through hole. In this case, the through hole of the nut is generally made into an arc-shaped oval shape or a simple circular arc at both ends due to processing limitations. For this reason, when the center of the rolling path and the center of the circulation groove of the frame are connected by the edge of the circulation frame, there is a problem that the connection is not smoothly and smoothly performed.
(2) Further, it is essential that the circulation groove of the top has a groove width that is somewhat large with respect to the ball diameter because the ball needs to pass smoothly. If the cutter is moved in such a way that the radius center of the cutter having a groove width (groove radius) that is somewhat larger than the ball diameter is aligned with the center of the ball rolling path and the circulation groove center of the top, There is a possibility that a large step is generated between the bottom of the female screw groove and the circulation groove of the top, thereby increasing noise and vibration when passing the ball.

  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 suppress abnormal noise and vibration and ensure a smooth operation.

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 piece that is inserted into the mounting hole of the nut and has a circulation groove for rolling the ball that circulates from one end to the other end of the rolling path, and
When the nut is viewed from the inside in the radial direction, an introduction portion having a central axis coincident with the central axis of the rolling path is formed at the end of the circulation groove connected to one end of the rolling path,
When taking the axial orthogonal direction cross section of the nut, the end portion of the circulation grooves have a linear shape,
There is a step between the female thread groove of the nut and the circulation groove .

  In the case of the ball screw mechanism of the prior art, as shown in Patent Document 1, since the circulation groove of the piece has an S shape, when the ball moves from the rolling path on the nut side to the circulation groove of the piece, Thus, a force in the axial direction of the nut is applied to the ball, so that the ball is easily caught. If measures such as increasing the width of the circulation groove are taken in order to prevent the ball from being caught, the ball will come into contact with the groove wall, and noise and vibration are likely to occur.

  On the other hand, according to the present invention, when the nut is viewed from the inside in the radial direction, the end of the circulation groove connected to one end of the rolling path matches the center axis of the rolling path. Since the introduction portion having the axis is formed, since the force in the axial direction of the nut is not applied to the ball when the ball moves from the rolling path to the introduction portion, there is little possibility that the ball will be caught. Therefore, since it is not necessary to significantly increase the width of the circulation groove with respect to the width of the rolling path, the contact of the ball with the groove wall is suppressed, and abnormal noise and vibration can be suppressed. In addition, in the circulation groove of the same member, the shape with respect to the ball can be finished with high accuracy, so that there is little risk of catching the ball even if the circulation groove is S-shaped.

Further, when taking the axial orthogonal direction cross section of the nut, the end of the previous SL circulation groove has a linear shape, by reducing the step, when the ball possess to the circulation groove from the rolling path, The collision is suppressed, and abnormal noise and vibration can be suppressed.

  Furthermore, the top is preferably manufactured by metal sintering.

  The top is preferably manufactured by forging.

  The top is preferably produced by injection molding a resin.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a side view of the ball screw mechanism according to the present embodiment, FIG. 2 is a view of the configuration of FIG. 1 taken along line II-II and viewed in the direction of the arrow, and FIG. Fig. 4 is a view of the configuration of Fig. 1 taken along the line III-III and viewed in the direction of the arrow, Fig. 4 is a view of the configuration of Fig. 2 viewed in the direction of the arrow IV, and Fig. 5 is an arrow of the configuration of Fig. 2. It is an enlarged view of the V section.

  In FIG. 1, a male screw groove 1a (partially simplified) 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 arranged so as to surround the screw shaft 1 and forms a female screw groove 2a (see FIG. 2) on an inner peripheral surface thereof. A plurality of balls 3 (see FIG. 2) are arranged so as to be able to roll in a spiral rolling path formed between the opposing screw grooves.

  A top 4 is arranged in a through hole (attachment hole) 2b having an elliptical cross section formed on the outer periphery of the nut 2. The top 4 is formed with a circulation groove 4a on the inner side in a state of being attached to the through hole 2b (see FIG. 4). As seen from the direction shown in FIG. 4, the circulation groove 4a is point-symmetric with a phase of 180 degrees with respect to the center.

  Referring to FIGS. 3 and 4, the rolling path formed by male thread groove 1a and female thread groove 2a is divided by frame 4 when it is wound slightly around the circumference of screw shaft 1, and each end thereof is cut. The circulation groove 4a of the top 4 is connected to the other end. A land portion 1c is formed between adjacent male screw grooves 1a.

  The operation of the ball screw mechanism of the present embodiment will be described. When the nut 2 is rotationally driven by an electric motor (not shown), the rotational movement of the screw shaft 1 is caused by the ball 3 rolling on the rolling path. The driven member (not shown) connected thereto can be moved in the axial direction. At this time, as shown in FIG. 3, the ball 3 that has entered the circulation groove 4a from the rolling road rolls along the circulation groove 4a, gets over the land portion 1c, and moves from one end to the other end of the rolling path. And can be moved.

  According to this embodiment, as shown in FIG. 4, when the nut 2 and the piece 4 are viewed from the inside in the radial direction, both ends of the circulation groove 4a connected to one end of the female screw groove 2a forming the rolling path. An introduction portion 4b having a center axis X2 (between points A and B) coinciding with the center axis X1 of the rolling path, that is, the female thread groove 2a is formed in the portion. That is, the center P of the circular arc having the radius Rf drawn by the center line of the circulation groove 4a is a position overlapping with the point B in the axial direction. This means that during the period from point A to point B, the ball 3 discharged from the rolling path cannot be applied with a force in the axial direction of the nut 2, so that the ball 3 may be caught. Since there is little and it is not necessary to make the width | variety of the introducing | transducing part 4b so large with respect to the width of a rolling path, the contact of the ball | bowl 3 with a groove wall is suppressed, and abnormal noise and a vibration can be suppressed.

  On the other hand, as shown in FIG. 6, in the case of the top 4 ′ having the circulation groove 4a ′ having the same shape as the prior art, there is no introduction portion as in the present embodiment, that is, the center line of the circulation groove 4a ′ is The center P of the circular arc having the radius Rf to be drawn is a position overlapping with the end of the circulation groove 4a ′ in the axial direction. Accordingly, the ball 3 discharged from the rolling path to the circulation groove 4a ′ is immediately applied with a force in the axial direction of the nut 2 and is forced to bend its traveling direction, so that the ball 3 is positioned between the nut 2 and the top 4 ′. There is a risk that the ball 3 may be caught due to the difference in level. In the present embodiment, such a problem can be avoided.

  Furthermore, in the prior art, as shown by the dotted line in FIG. 5, the bottom of the circulation groove is drawn to the end, and therefore, the step difference between the nut 2 and the female thread groove 2a is Δ2. In other words, the circulation groove of the top is formed larger than the ball diameter in the width direction so that the ball can pass smoothly, but for the convenience of cutting, it is formed slightly larger than the ball diameter in the radial direction. Will be. This is because when a tool (not shown) having a hemispherical rotary cutting part is moved so as to draw an ideal trajectory of the circulation groove, the arc center of the rotary cutting part coincides with the ball center trajectory. Therefore, it is due to excessive cutting in the radial direction by the amount expanded in the width direction. When the piece with the circulation groove processed in this manner is attached to the nut, a step Δ2 is generated between the female screw groove of the nut and the circulation groove of the piece, which may cause abnormal noise or vibration when the ball passes. .

  On the other hand, according to the present embodiment, as shown by the solid line in FIG. 5, since the groove bottom of the introduction portion 4b is linear from point B to point A, the difference Δ1 between the nut 2 and the female thread groove 2a. Can be made smaller (Δ1 <Δ2). Here, the difference (Δ1−Δ2) is the correction amount.

  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. The coma is preferably formed by sintering or forging when a metal is used as a raw material, and preferably formed by injection molding when a resin is used as a raw material. There is no limit.

It is a side view of the ball screw mechanism which is this Embodiment. It is the figure which cut | disconnected the structure of FIG. 1 by the II-II line | wire, and looked at the arrow direction. It is the figure which cut | disconnected the structure of FIG. 1 by the III-III line | wire, and looked at the arrow direction. FIG. 4 is a diagram when the configuration of FIG. 2 is viewed in the direction of arrow IV. FIG. 3 is an enlarged view of an arrow V part in the configuration of FIG. 2. It is a figure similar to FIG. 4 concerning a comparative example.

Explanation of symbols

1 Screw shaft 2 Nut 3 Ball 4 Top

Claims (4)

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 piece that is inserted into the mounting hole of the nut and has a circulation groove for rolling the ball that circulates from one end to the other end of the rolling path, and
When the nut is viewed from the inside in the radial direction, an introduction portion having a central axis coincident with the central axis of the rolling path is formed at the end of the circulation groove connected to one end of the rolling path,
When taking the axial orthogonal direction cross section of the nut, the end portion of the circulation grooves have a linear shape,
A ball screw mechanism having a step between the female screw groove of the nut and the circulation groove .   The ball screw mechanism according to claim 1, wherein the piece is manufactured by metal sintering.   The ball screw mechanism according to claim 1, wherein the top is manufactured by forging.   The ball screw mechanism according to claim 1, wherein the top is manufactured by injection molding a resin.

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