JP2012172765A - Ball screw device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw device, which is improved in durability life by reducing impact loads on a ball or a boundary portion between a ball rolling groove and a circulation path constituting a rolling path which is formed on the inner periphery of a nut.SOLUTION: The ball screw device 1 includes: a screw shaft 2 having a spiral first ball rolling groove 5 formed on the outer periphery; the nut 3 fitted onto the screw shaft 2 and having a second ball rolling groove 6 formed on the inner periphery to face the first ball rolling groove 5; a plurality of balls 4 filled in the rolling path 7 formed by the first ball rolling groove 5 and the second ball rolling groove 6 so as to be rollable; and the circulation path 8 formed on the inner periphery of the nut 3 to return the balls 4 to the rolling path 7 in front thereof. The boundary portion 9 between the second ball rolling groove 6 and the circulation path 8 constituting the rolling path 7 is subjected to crowing 10.

Description

  The present invention relates to a ball screw device that circulates a plurality of balls interposed between a screw shaft and a nut.

Conventionally, as this type of ball screw device, for example, the one shown in FIG. 7 is known (see Patent Document 1).
A ball screw device 100 shown in FIG. 7 includes a screw shaft 101, nuts 102, and a plurality of balls 103.
The screw shaft 101 has a spiral ball rolling groove 104 having a predetermined lead formed on the outer peripheral surface thereof. The nut 102 has a substantially cylindrical shape, and an inner diameter thereof is formed larger than an outer diameter of the screw shaft 101, and is externally mounted on the screw shaft 101 with a predetermined gap. A spiral ball rolling groove 105 having a lead equal to the lead of the screw shaft 101 is formed on the inner peripheral surface of the nut 102. A rolling path 106 having a substantially circular cross section is formed by the ball rolling groove 105 and the ball rolling groove 104 of the screw shaft 101 facing the ball rolling groove 105. A plurality of balls 103 are filled in the rolling path 106 so as to roll. Then, one end and the other end of the rolling path 106 are connected to the inner peripheral surface of the nut 102 so that the ball 103 can circulate, and a plurality of circulation paths returning the ball 103 rolling on the rolling path 106 from one end to the other end. 107 is formed.

  With these circulation paths 107, the balls 103 rolling on the rolling paths 106 toward the circulation path 107 are scooped up in the radial direction of the screw shaft 101, overcoming the thread of the screw shaft 101, and one roll before (one lead). By returning to the rolling path 106, the ball 103 can be circulated. A substantially annular endless circulation path is formed outside the screw shaft 101 by the passage formed by the circulation path 107 and the rolling path 106. Accordingly, the ball 103 rolls between the ball rolling groove 104 and the ball rolling groove 105 with the relative rotation of the screw shaft 101 with respect to the nut 102, so that the nut 102 moves with respect to the screw shaft 101. Thus, it is possible to linearly move in the axial direction of the screw shaft 101.

  By the way, in the ball screw device 101 shown in FIG. 7, the cross section of the boundary portion between the circulation path 107 and the ball rolling groove 105 formed on the inner peripheral surface of the nut 102 constituting the rolling path 106 has an edge shape. It has become. For this reason, when the ball 103 passes through the circulation path 107 and is returned to the rolling path 106, or when the ball 103 is introduced from the rolling path 106 into the circulation path 107, the ball 103 may collide with the boundary portion. For this reason, when the screw shaft 101 or the nut 102 is rotated at a high speed, an excessive impact load is applied to the boundary portion or the ball 103, and the durability life of the ball screw device 101 may be reduced.

In order to solve such problems, for example, a ball screw device shown in FIGS. 8 and 9 (see Patent Document 2) and a spindle nut for the ball screw device shown in FIG. 10 (see Patent Document 3) have been proposed. Yes.
A ball screw device 201 shown in FIG. 8 is provided with recessed portions 203 for assembling a circulating top at both ends of an inner peripheral surface of a nut 202, and a gap between a screw shaft (not shown) and the ball rolling groove 204 of the nut 202. A rolling ball (see FIG. 9) 207 is introduced into a ball return path (not shown) formed in the nut 202 by a circulation top 205 fitted in the recessed portion 203 so as to be circulated. 9, the boundary 206 between the ball rolling groove 204 and the recessed portion 203 formed on the inner peripheral surface of the nut 202 has a curvature of R = 0.05 Dw or more with respect to the diameter Dw of the ball 207. It is formed into a curved surface with a radius.

  Thus, by forming the boundary portion 206 between the ball rolling groove 204 and the recessed portion 203 formed on the inner peripheral surface of the nut 202 into a curved surface, the ball can be rotated even if the screw shaft or the nut 202 is rotated at high speed. When the ball 207 rolled on the return path collides with the boundary portion 206, the surface pressure of the impact load applied to the boundary portion 206 and the ball 207 can be reduced, and the durable life of the ball screw can be improved.

  A spiral ball rolling groove 303 for the ball 307 is formed on the inner peripheral surface of the spindle nut 302 for the ball screw device 301 shown in FIG. Further, in the ball screw device 301, there is provided a turning device 305 having a turning passage 306 for turning the ball 307 from the terminal portion of one ball rolling groove 303 to the starting end portion of one ball rolling groove 303. Is provided. On the inner peripheral surface of the spindle nut 302, a ball run-in path 304 that is connected to the ball rolling groove 303 on the one hand and to the turning path 306 on the other hand is formed. Both the ball rolling groove 303 and the ball entry path 304 have the same cross-sectional shape. The cross-sectional shape of the ball rolling groove 303 has a Gothic shape, and the ball running path 304 also has the same Gothic shape. This enables the transition of the ball 307 without catching from the ball rolling groove 303 to the ball entry path 304 and from the ball entry path 304 to the turning path 306 of the turning device 305.

JP 2008-281063 A JP 2003-336715 A Special table 2008-500500 gazette

However, the ball screw device 201 shown in FIGS. 8 and 9 and the spindle nut 302 for the ball screw device 301 shown in FIG. 10 have the following problems.
That is, the ball screw device 201 shown in FIGS. 8 and 9 is a so-called top type ball screw device, and depending on the dimensional difference due to processing of the circulating top 205 and the recessed portion 203, the ball rolling groove 204 and the recessed portion 203 Even if the boundary portion 206 is formed in a curved shape, the ball return path and the ball rolling groove 204 may not be smoothly connected. This may require further processing. If the ball return path and the ball rolling groove 204 are not smoothly connected, the ball 103 passes through the ball return path and returns to the ball rolling groove 204 or is introduced from the ball rolling groove 204 to the ball return path. May impact the boundary between the ball return path and the ball rolling groove 204, and an excessive impact load may be applied to the boundary or the ball 207, possibly reducing the durability life of the ball screw device 201. there were.

Further, the spindle nut 302 for the ball screw device 301 shown in FIG. 10 is also a so-called top-type ball screw device, and has the same problem as the ball screw device 201 shown in FIG.
Therefore, the present invention has been made in view of these problems, and the object thereof is to the boundary portion between the ball rolling groove and the circulation path that constitute the rolling path formed on the inner peripheral surface of the nut and the ball. An object of the present invention is to provide a ball screw device capable of reducing the applied impact load and improving the durability life.

  In order to solve the above problems, a ball screw device according to claim 1 of the present invention includes a screw shaft having a spiral first ball rolling groove on an outer peripheral surface, and an inner peripheral surface that is externally fitted to the screw shaft. And can be rolled into a rolling path formed by a nut having a second ball rolling groove facing the first ball rolling groove, and the first ball rolling groove and the second ball rolling groove. In a ball screw device comprising a plurality of filled balls and a circulation path formed on the inner peripheral surface of the nut for returning the balls to the preceding rolling path, a second ball rolling that constitutes the rolling path is provided. It is characterized in that a crowning is applied to the boundary between the moving groove and the circulation path.

A ball screw device according to claim 2 of the present invention is the ball screw device according to claim 1, wherein the crowning is a convex arc.
Furthermore, the ball screw device according to claim 3 of the present invention is the ball screw device according to claim 1, characterized in that the crowning is a slope.
A ball screw device according to a fourth aspect of the present invention is the ball screw device according to any one of the first to third aspects, wherein the crowning is performed by planet tapping. .

  According to the ball screw device according to claim 1 of the present invention, the crowning is applied to the boundary portion between the second ball rolling groove and the circulation path constituting the rolling path formed on the inner peripheral surface of the nut. The circulation path and the second ball rolling groove are smoothly connected, and the rolling path is configured when the ball passes through the circulation path and is returned to the rolling path or when the ball is introduced from the rolling path to the circulation path. The boundary between the second ball rolling groove and the circulation path passes smoothly, and the impact load applied to the boundary and the ball is reduced. For this reason, the durable life of the ball screw device can be improved.

  Moreover, according to the ball screw device according to claim 2 of the present invention, in the ball screw device according to claim 1, since the crowning is a convex arc, the second ball rolling which constitutes a rolling path. The smoothness effect when passing through the boundary between the moving groove and the circulation path is considerably large, and the impact load applied to the boundary and the ball is considerably reduced. In addition, it is relatively easy to process the crowning into a convex arc.

  Further, according to the ball screw device according to claim 3 of the present invention, in the ball screw device according to claim 1, since the crowning is an inclined surface, the second ball rolling groove in which the ball forms a rolling path. The smoothness effect at the time of passing through the boundary portion between the boundary and the circulation path is large, and the impact load applied to the boundary portion and the ball is effectively reduced. Moreover, the process which makes a crowning a slope is easy.

  Moreover, the ball screw device according to claim 4 of the present invention is the ball screw device according to any one of claims 1 to 3, wherein the crowning is performed by planet tapping. Crowning can be accurately applied to the boundary between the second ball rolling groove and the circulation path.

It is sectional drawing of embodiment of the ball screw apparatus which concerns on this invention. In the ball screw device shown in FIG. 1, it is a schematic diagram showing the vicinity of the boundary between the second ball rolling groove and the circulation path constituting the transfer path. It is sectional drawing which follows the 3-3 line in FIG. In the ball screw device shown in FIG. 1, it is a schematic diagram showing a contact state between the ball, the second ball rolling groove and the circulation path at the boundary between the second ball rolling groove and the circulation path constituting the transfer path. It is a figure which shows the relationship between the various crowning shape, the processability in each crowning shape, and the effect by crowning. It is a figure which shows the mode of a planet tap process, (A) is a perspective view which shows the state of the planet tap process of a to-be-processed object, (B) is the figure seen in the arrow VB direction in (A). It is sectional drawing of the ball screw apparatus of a prior art example. It is a perspective view which shows some conventional ball screw apparatuses of another example. It is sectional drawing of the state which cut | disconnected the ball rolling groove and recessed part of the nut in the ball screw apparatus shown in FIG. It is a partial cross section figure of the spindle nut for the ball screw devices of other conventional examples.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of an embodiment of a ball screw device according to the present invention. FIG. 2 is a schematic diagram showing the vicinity of the boundary between the second ball rolling groove and the circulation path constituting the transfer path in the ball screw device shown in FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. FIG. 4 is a schematic diagram showing a contact state between a ball and the second ball rolling groove and the circulation path at a boundary portion between the second ball rolling groove and the circulation path constituting the transfer path in the ball screw device shown in FIG. 1. FIG.

A ball screw device 1 shown in FIG. 1 includes a screw shaft 2, a nut 3, and a plurality of balls 4.
The screw shaft 2 has a cylindrical shape centered on the central axis CL, and a spiral first ball rolling groove 5 having a predetermined lead is formed on the outer peripheral surface thereof.
The nut 3 has a substantially cylindrical shape, and an inner diameter thereof is formed larger than an outer diameter of the screw shaft 2 and is externally fitted to the screw shaft 2 with a predetermined gap. A second ball rolling groove 6 that has a lead equal to the first ball rolling groove 5 of the screw shaft 2 and faces the first ball rolling groove 5 is formed on the inner peripheral surface of the nut 3. A rolling path 7 having a substantially circular cross section is formed by the first ball rolling groove 5 of the screw shaft 2 and the second ball rolling groove 6 of the nut 3. A plurality of balls 4 are filled in the rolling path 7 so as to roll.

  In addition, a plurality of circulation paths 8 for returning the balls 4 to the rolling path 7 on the near side are formed on the inner peripheral surface of the nut 3. With this circulation path 8, the ball 4 rolling on the rolling path 7 toward each circulation path 8 is scooped up in the radial direction of the screw shaft 2, and further over the thread of the screw shaft 2. The ball 4 can be circulated by returning to the rolling path 7 on the front side. The circulation path 8 and the rolling path 7 form a substantially annular infinite circulation path outside the screw shaft 2. As a result, the plurality of balls 4 endlessly circulate in the endless circulation path with the relative rotation of the screw shaft 2 with respect to the nut 3, so that the nut 3 moves in the axial direction of the screw shaft 2 relative to the screw shaft 2. It becomes possible to move linearly.

Here, the boundary 9 between the second ball rolling groove 6 constituting the rolling path 7 and the introduction part 8a of the circulation path 8 formed on the inner peripheral surface of the nut 3 is shown in FIGS. Thus, crowning 10 (shown by hatching in FIG. 2) is applied.
By applying a crowning 10 to the boundary portion 9, a ball locus that is a locus of contact between the ball 4 and the second ball rolling groove 6 (gothic shape, see FIG. 4) constituting the rolling path 7, The ball bottom locus which is the locus of contact with the circulation path 8 (semicircle, see FIG. 4) is smoothly connected. Thus, when the ball 4 passes through the circulation path 8 and is returned to the rolling path 7 or when the ball 4 is introduced from the rolling path 7 to the circulation path 8, the second ball rolling groove 6 constituting the rolling path 7 and Passing smoothly through the boundary portion 9 with the circulation path 8, the impact load applied to the boundary portion 9 and the ball 4 is reduced. For this reason, the durable life of the ball screw device 1 can be improved.

Further, since the circulation path 8 is not a top type but formed on the inner peripheral surface of the nut 3, the boundary portion 9 between the direct circulation path 8 and the second ball rolling groove 6 constituting the rolling path 7 can be directly processed. Therefore, unlike the Koma type, it is unlikely that the ball return path and the ball rolling groove are smoothly connected, and the boundary portion between the second ball rolling groove 6 and the circulation path 8 that reliably constitutes the rolling path 7. 9 can be smoothed. Moreover, since the boundary part 9 can be processed directly, processing efficiency is also good.
Further, at the boundary portion 9 between the second ball rolling groove 6 constituting the rolling path 7 and the introduction portion 8a of the circulation path 8, the ball 4 and the second ball rolling groove 6 are formed as shown in FIG. The two points A and B are in contact, and the ball 4 and the circulation path 8 are in contact at one point C.

  Here, as shown in FIG. 3, the crowning 10 is formed in a convex arc whose upper side is convex with respect to the groove bottom 6 a of the second ball rolling groove 6. The radius of curvature R1 of the convex arc is preferably 0.5 to 18 times the diameter of the ball 4. The reason is that if the radius of curvature R1 is smaller than 0.5 times the diameter of the ball 4, the effect of the curvature cannot be obtained and the ball 4 cannot pass smoothly, and the radius of curvature R1 is smaller than the diameter of the ball 4. This is because when the ratio is larger than 18 times, the rated load of the ball screw is lowered. By making the crowning 10 a convex arc, the smoothness effect when the ball 4 passes through the boundary portion 9 between the second ball rolling groove 6 and the circulation path 8 constituting the rolling path 7 is considerably large. The impact load applied to the part 9 and the ball 4 is considerably reduced. Further, it is relatively easy to process the crowning 10 into a convex arc.

Here, FIG. 5 shows the relationship between various crowning shapes, processability in each crowning shape, and the effect of crowning.
FIG. 5 exemplifies a crowning shape that is not subjected to conventional crowning, a concave arc, a slope, a convex arc, and a plurality of arcs connected together.
Referring to FIG. 5, a conventional product not subjected to crowning is most easily processed but has no effect of crowning. Thereafter, it becomes difficult to process in the order of a concave arc, a slope, a convex arc, and a series of arcs, but the effect of crowning gradually increases.

  Considering both the ease of processing and the effect of crowning, it is preferable that the crowning 10 as shown in FIG. When the crowning 10 is an inclined surface, the smoothness effect when the ball 4 passes through the boundary part 9 between the second ball rolling groove 6 and the circulation path 8 constituting the rolling path 7 is large. And the impact load applied to the ball 4 is effectively reduced. Moreover, the process which makes the crowning 10 a slope is easy. When the crowning 10 is a slope, the slope is preferably 7 ° to 19 ° with respect to the tangential direction of the boundary portion 9. The reason is that if the inclination is smaller than 7 ° with respect to the tangential direction of the boundary portion 9, the effect of the inclination cannot be obtained and the ball 4 cannot pass smoothly, and the inclination is 19 ° with respect to the tangential direction of the boundary portion 9. It is because the rated load of a ball screw will fall when larger.

Next, a method for manufacturing the nut 3 will be described.
First, the circulation path 8 is formed on the inner peripheral surface of the flanged hollow cylindrical member N (see FIG. 6), which is the material of the nut 3. When the heat treatment after forming the second ball rolling groove 6 and the circulation path 8 is carburizing, the material of the nut 3 is chromium steel or molybdenum steel having a carbon content of 0.10 to 0.25% by mass ( For example, when the heat treatment is induction hardening, carbon steel having a carbon content of 0.4 to 0.6% by mass (for example, S53C, SAE4150) is preferable. The circulation path 8 is formed by forging using a mold having a predetermined shape.

  Next, the second ball rolling groove 6 is formed on the inner peripheral surface of the hollow cylindrical member N in which the circulation path 8 is formed. The second ball rolling groove 6 is formed by planet tapping as shown in FIG. In planet tap processing, cutting is performed using a cutting tool T as shown in FIG. The cutting tool T forms a blade Tb on the outer periphery of the rotation axis Ta. The cutting surface (surface facing the circumferential direction) of the blade Tb matches the shape of the second ball rolling groove 6. The rotation axis Ta rotates around its axis (in the direction of arrow A in FIG. 6A), but independently revolves around the eccentric shaft (in the direction of arrow B in FIG. 6B).

  Further, as shown in FIG. 6 (A), the rotational axis Ta of the cutting tool T is shifted radially outward at a predetermined axial position, and revolved while being fed in the axial direction at the pitch of the second ball rolling groove 6. In addition, the spiral second ball rolling groove 6 of less than 360 degrees can be cut and formed on the inner peripheral surface of the hollow cylindrical member N by rotating at a higher speed. At this time, each circulation path 8 can be formed to be connected to both ends of the second ball rolling groove 6 by matching the position and phase in the axial direction with the circulation path 8.

  In the hollow cylindrical member N in which the circulation path 8 and the second ball rolling groove 6 are formed, the crowning 10 is applied to the boundary portion 9 between the circulation path 8 and the second ball rolling groove 6. The crowning 10 is performed by the planet tap process shown in FIG. By performing the crowning 10 by planet tap processing, the crowning 10 can be accurately applied to the boundary portion 9 between the second ball rolling groove 6 and the circulation path 8 constituting the rolling path.

Finally, a quenching process is performed on the inner peripheral surface of the hollow cylindrical member N. Thereby, the nut 3 is manufactured.
As mentioned above, although embodiment of this invention has been described, this invention is not limited to this, A various change and improvement can be performed.
For example, the shape of the crowning 10 may not be the convex arc or slope shown in FIG. 3, but may be a series of concave arcs or a plurality of arcs shown in FIG.
Further, the processing of the second ball rolling groove 6 and the crowning 10 is not limited to planet tap processing.

DESCRIPTION OF SYMBOLS 1 Ball screw apparatus 2 Screw shaft 3 Nut 4 Ball 5 1st ball rolling groove 6 2nd ball rolling groove 6a Groove bottom 7 Rolling path 8 Circulation path 8a Introduction part 9 Boundary part 10 Crowning

Claims (4)

A screw shaft having a spiral first ball rolling groove on the outer peripheral surface; and a nut having a second ball rolling groove which is fitted on the screw shaft and faces the first ball rolling groove on the inner peripheral surface; A plurality of balls filled in a rolling path formed by the first ball rolling groove and the second ball rolling groove, and formed on an inner peripheral surface of the nut; In the ball screw device having a circulation path for returning to the previous rolling path,
A ball screw device, wherein a crowning is applied to a boundary portion between the second ball rolling groove constituting the rolling path and the circulation path.   The ball screw device according to claim 1, wherein the crowning is a convex arc.   The ball screw device according to claim 1, wherein the crowning is a slope.   The ball screw device according to any one of claims 1 to 3, wherein the crowning is performed by planet tapping.

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