JP2008281064A - Ball screw mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw mechanism avoiding abrasion of a ball or damage of a nut, and ensuring smooth movement. <P>SOLUTION: Shot-peeling work is applied to at least a part of a female screw groove 2a of a nut adjacent to an attachment hole 2b, and thereby, damage of the nut 2 near the piece attachment hole 2b by stress concentration when the ball 3 enters a load region (the region where the load is applied) from a no-load region (the region where the load is not applied), is prevented. By applying shot-peeling work to a straight line introduction part 4b of the piece 4, damage of a circulation groove 4a is prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ball screw mechanism used for an electric actuator for automobiles, for example, an automatic transmission control device (shift-by-wire), an electric brake, an automatic control device (AMT) for a manual transmission, and the like.

  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 the two. In the so-called top-type ball screw mechanism, the ball screw mechanism starts from one end of the rolling path. In order to return the ball to the other end, a top is attached to the nut (see Patent Document 1).

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 to connect the other end. Therefore, after rolling along the rolling path, the ball is guided from one end of the rolling path into the circulation groove of the top 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.
JP 11-270648 A JP 2004-138179 A

  By the way, when a ball rolls from a top, which is an unloaded area, to a nut side, which is a loaded area, the ball is pushed by a subsequent ball and enters a rolling path between the nut and the screw shaft. As a result, the balls collide in the vicinity of the inlet of the nut, and stress concentrates on the corner mounting hole corner of the nut, and there is a possibility that separation or the like may occur from that point.

  In Patent Document 1, it is disclosed that the stepped portion is chamfered after the piece is assembled into the nut. In this prior art, the stepped portion of the connecting portion with the nut is chamfered in a state in which the piece is incorporated, so that even the processed ball groove may be removed. Further, since it is a manual work or a grinding process by a machine, a considerable processing time is required to process all the connecting portions. Furthermore, there is a risk that cutting powder during processing enters the gap between the top and the top mounting hole of the nut.

  The top is generally formed by metal sintering or forging, but a resin injection molding may be used for weight reduction and cost reduction. In the case of a resin, 6-6 nylon, 6 nylon, 4-6 nylon, POM (polyacetal), or the like is used as a material, and glass fibers are often contained from several percent to several tens percent for reinforcement. In this case, as in the prior art of Patent Document 1, if the step is cut after the piece is assembled in the nut, the glass fiber may come out on the surface of the piece and the glass fiber may promote the wear of the ball.

  On the other hand, Patent Document 2 discloses a technique in which an elastic member is attached to a doorway of a frame. According to this technique, it is possible to eliminate the level difference between the top and the nut, but there is a risk that the elastic member may fall off and prevent the ball from rolling. Further, such an elastic member cannot effectively prevent damage caused by stress concentration near the top of the nut where the ball is inserted from the top into the nut.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide a ball screw mechanism that can avoid wear of a ball and damage to a nut and ensure smooth operation.

The ball screw mechanism according to the first aspect of the present invention comprises:
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,
A shot peening process is performed on at least a portion adjacent to the mounting hole in the female screw groove of the nut.

The ball screw mechanism of the second 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 roll along a rolling path formed between both opposing screw grooves, and
The nut is formed with a circulation groove for rolling the ball circulating from one end to the other end of the rolling path,
A shot peening process is performed on a portion of the female screw groove of the nut adjacent to the circulation groove.

  According to the first aspect of the present invention, since the shot peening process is performed on at least a portion adjacent to the mounting hole in the female thread groove of the nut, the ball is changed from a no-load region (a region where no load is received) to a load region (a load). The area near the top mounting hole of the nut due to stress concentration when entering the receiving area) can be prevented.

  It is preferable to perform shot peening on at least the straight line introduction portion in the circulation groove of the top. Shot peening is preferably performed on the ball groove in the vicinity of the nut mounting hole, particularly in the corner of the mounting hole, using the mounting hole from the outer diameter side of the nut. Shot peening may be performed on the entire circulation groove of the top, which is a separate body from the nut.

  The shot peening process is preferably performed before the frame is attached to the attachment hole. This is because if shot peening is performed after the top is assembled into the nut mounting hole, shot peening particles may be clogged in the top and nut mounting holes.

  It is preferable that the portion adjacent to the mounting hole in the female screw groove of the nut is crowned before shot peening.

The compressive residual stress by shot peening is about 2 × 10 ^{8 to} 7 × 10 ⁸ N / m ² , preferably about 1 × 10 ⁹ N / m ² from 20 to 100 μm from the outermost surface. It is desirable to give it to the depth.

  If the nut is a non-ground ball screw, that is, if the groove is processed before the heat treatment and the screw groove is not processed after the heat treatment, the deterioration of the roughness of the groove surface due to the shot peening does not matter so much.

  On the other hand, in the case of a grinding screw in which the ball groove is ground after the heat treatment, it is preferable to perform shot peening after the heat treatment and then perform the grinding because there is no influence of surface roughness deterioration due to the shot peening. Here, the heat treatment refers to a carburizing treatment using a carburizing material or a high-frequency heat treatment using a high-frequency material.

  Shot peening may be performed only in the vicinity of the entrance of the nut mounting hole, and it is sufficient for the ball diameter from the end of the top mounting hole. The thread groove in the vicinity of the nut mounting hole may be cut into a gentle arc shape by crowning using a polishing means such as a grindstone. In this case, shot peening may be performed only on the crowning portion.

  According to the second aspect of the present invention, since the shot peening process is performed on the portion of the female thread groove of the nut adjacent to the circulation groove, the ball is moved from the no-load region (the region not receiving the load) to the load region (the load is reduced). It is possible to prevent damage in the vicinity of the boundary between the male screw groove and the circulation groove due to stress concentration when entering the receiving region.

  The thread groove of the nut may be processed by rolling as disclosed in Japanese Patent Application Laid-Open No. 2000-88072, but when performing shot peening, it is better to form the thread groove by cutting. This is because, as shown in Japanese Patent Application Laid-Open No. 2005-99721, a concave portion is formed in the land portion by rolling. Furthermore, in order to prevent particles used for shot peening from being caught in the recesses, it is better to form thread grooves by cutting.

  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 top view of the ball screw mechanism according to the present embodiment, and FIG. 3 is an enlarged view of the nut. 4 is a view of the configuration of FIG. 3 cut along the line IV-IV and viewed in the direction of the arrow, and FIG. 5 is a view of the configuration of FIG. 3 cut along the line VV and viewed in the direction of the arrow. 6 is a view of the configuration of FIG. 4 as viewed in the direction of the arrow VI, and FIG. 7 is an enlarged view of an arrow VII portion of the configuration of FIG.

  1 and 2, a screw shaft 1 attached to a housing H by means of bearings B1 and B2 so as to be rotatable and immovable in the axial direction is provided with a gear G that transmits power from a motor (not shown) near one end. ing. A male screw groove 1 a is formed on the outer peripheral surface of the screw shaft 1.

  A cylindrical nut 2 that is pin-coupled to a shaft S as a driven member via link members L1 and L2 and supported so as not to rotate with respect to the housing H and to move only in the axial direction surrounds the screw shaft 1. The female screw groove 2a (see FIG. 4) is formed on the inner peripheral surface. A plurality of balls 3 (see FIG. 4) are arranged so as to roll freely in a spiral rolling path formed between the opposing screw grooves.

  In FIG. 3, a piece 4 is disposed in a through hole (mounting hole) 2 b having an oval 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). In addition, seeing from the direction shown in FIG. 6, the S-shaped circulation groove 4a is point-symmetric with a phase of 180 degrees with respect to the center.

  4 to 6, the rolling path formed by the male screw groove 1 a and the female screw groove 2 a is divided by the frame 4 when the circumference of the screw shaft 1 is wound slightly less than one turn. 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 according to the present embodiment will be described. When the screw shaft 1 is rotationally driven through a gear G by an electric motor (not shown), the rotational motion is caused by the ball 3 rolling on the rolling path. The shaft S that is efficiently converted into two axial movements and connected via the links L1 and L2 can be rotated. At this time, as shown in FIG. 5, the ball 3 that has entered the circulation groove 4a from the rolling path 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.

  In this embodiment, as shown in FIG. 6, when the nut 2 and the piece 4 are viewed from the inside in the radial direction, both end portions of the circulation groove 4a connected to one end of the female screw groove 2a forming the rolling path. In addition, a straight line 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. 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.

  Furthermore, in the prior art, as shown by the dotted line in FIG. 7, the bottom of the circulation groove is curved 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. 7, since the groove bottom of the introduction portion 4b is linear from point B to point A, the step 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.

  Next, the processing aspect of a nut is demonstrated. FIG. 8 is a perspective view of a single nut subjected to shot peening, and FIG. 9 is a cross-sectional view of a nut in which a piece is incorporated in a mounting hole. As shown in FIGS. 8 and 9, the shot peening process is performed on at least a portion of the female screw groove 2 a of the nut 2 adjacent to the mounting hole 2 b (region C indicated by cross-hatching, range from the mounting hole 2 b to the diameter of the ball 3). On the other hand, it is performed by spraying particles from the mounting hole 2b. As shown in FIG. 9, the shot peening process is performed on the straight line introduction portion (region D indicated by cross-hatching) in the circulation groove 4 a of the top 4. The shot peening process is performed separately for the nut 2 and the top 4. Further, the portion adjacent to the mounting hole 2b in the female thread groove 2a of the nut 2 is crowned before the shot peening process to form a smooth curved surface. Shot peening may be applied to the entire circulation groove 4a of the top 4.

  According to the present embodiment, since shot peening is performed on at least a portion of the female screw groove 2a of the nut 2 adjacent to the mounting hole 2b, the ball 3 is moved from the no-load region (the region where no load is applied) to the load region (the region where no load is received). It is possible to prevent damage in the vicinity of the top mounting hole 2b of the nut 2 due to stress concentration when entering the load receiving region. Further, by performing shot peening on the straight line introduction portion 4b of the top 4, damage to the circulation groove 4a can be prevented.

  10 is a cross-sectional view of a nut according to another embodiment, and FIG. 11 is a view of the nut of FIG. 9 as viewed in the direction of arrow XI. Such a nut is disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-194174. On the inner periphery of the nut 2 ′, the same shape as the circulation groove of the top (circulation groove 2c) is formed by plastic working such as forging or cutting. Directly formed.

  Also in this embodiment, since the thread groove 2a of the nut and the circulation groove 2c that connects both ends of the thread groove 2a are different processing steps, a step is likely to remain at the joint. Therefore, the ball 3 is removed by subjecting the portion C adjacent to the circulating groove 2c in the female thread groove 2a of the nut 2 'and the portion D (straight line introduction portion) adjacent to the female thread groove 2a in the circulating groove 2c to the shot 3 by shot peening. It is possible to prevent damage in the vicinity of the boundary between the male screw groove 2a and the circulation groove 2c due to stress concentration when entering the load region (region receiving the load) from the load region (region not receiving the load).

  Here, when the circulation groove 2c is formed integrally with the nut 2 ', since the nut 2 does not have a coma mounting hole inherently, shot peening particles cannot be sprayed therethrough. Therefore, shot peening particles may be sprayed from both ends of the nut 2 ', or if there is a pin fitting hole 2d with the link member, shot peening particles may be sprayed from the fitting hole 2d.

  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 a top view of the ball screw mechanism which is this Embodiment. It is a figure which expands and shows a nut. It is the figure which cut | disconnected the structure of FIG. 3 by the IV-IV line and looked at the arrow direction. It is the figure which cut | disconnected the structure of FIG. 3 by the VV line and looked at the arrow direction. It is the figure which looked at the structure of FIG. 4 in the arrow VI direction. It is an enlarged view of the arrow VII part of the structure of FIG. It is a perspective view of the nut single-piece | unit which performed the shot peening process. It is sectional drawing of the nut which built the top in the attachment hole. It is sectional drawing of the nut concerning another embodiment. It is the figure which looked at the nut of Drawing 9 in the direction of arrow XI.

Explanation of symbols

1 Screw shaft 2, 2 'Nut 3 Ball 4 Top

Claims (5)

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,
A ball screw mechanism characterized in that shot peening is performed on at least a portion of the female screw groove of the nut adjacent to the mounting hole.   The ball screw mechanism according to claim 1, wherein the shot peening is performed before the top is attached to the attachment hole.   The ball screw mechanism according to claim 1 or 2, wherein shot peening is applied to at least the straight line introduction portion in the circulation groove of the top.   The ball screw mechanism according to any one of claims 1 to 3, wherein a portion of the female screw groove of the nut adjacent to the mounting hole is crowned before shot peening. 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 roll along a rolling path formed between both opposing screw grooves, and
The nut is formed with a circulation groove for rolling the ball circulating from one end to the other end of the rolling path,
A ball screw mechanism wherein shot peening is performed on a portion of the female screw groove of the nut adjacent to the circulation groove.

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