JP6544207B2 - Ball screw - Google Patents

Description

  The present invention relates to a ball screw.

  The ball screw is formed of a screw shaft having a spiral groove formed on the outer peripheral surface, a nut inserted in the screw shaft and a spiral groove formed on the inner peripheral surface, and a spiral groove of the nut and a spiral groove of the screw shaft Through the track, the return path connecting the end point and the start point of the track to form the circulation path, and a plurality of balls arranged in the track and the return path, and rolling the ball in the loaded state The nut is a device that moves relative to the screw shaft.

Such a ball screw is used not only for positioning devices for general industrial machines, but also for electric actuators mounted on vehicles such as automobiles, two-wheeled vehicles, and ships.
In the return path of the ball screw, there are a circulation tube type and a top type, and in the case of the top type, a top in which a concave portion forming the return path is formed is fitted in the through hole of the nut.
In the cotter type ball screw, the inner diameter of the cotter is formed smaller than the internal diameter of the nut in order to secure a sufficient depth of the circulation groove by the cotter and to improve the scooping property of the ball. Specifically, it is smaller than BCD (Ball Center Diameter, the ball center diameter, the diameter of a circle connecting the centers of a plurality of balls in a track) of a ball screw.

  In Patent Document 1, a recess (circulating groove) forming a return path is provided on the inner peripheral surface of the nut, and a relief groove deeper than the helical groove is provided along the lead angle at the connection portion between the helical groove and the circulating groove of the nut. It is described. In addition, the inner diameter of the nut in the portion where the spiral groove and the circulation groove are formed is set to a size smaller than BCD, that is, the inner peripheral surface position of the nut in the radial direction of the nut, the outer peripheral surface position of the screw shaft and the ball It is described to arrange between the center position (the position of a ball pitch circle which is a circle connecting the centers of balls).

  Patent Document 2 describes a method of directly forming a recess (circulating groove) forming a return path on the inner peripheral surface of a nut material by plastic working (forging). In a ball screw nut having a circulation groove formed on the inner peripheral surface of a cylindrical nut material by a forging process, the inner diameter of the nut is substantially the same in the peripheral portion of the circulation groove and the other portion. Therefore, it is difficult for the ball to scoop into the circulation groove as compared with the top-type ball screw.

  In addition, the outer edge of the circulation groove (the boundary between the circulation groove and the inner circumferential surface of the nut) formed by pressing the punch in the forging process is a portion (sagging) in which the contour is broken due to plastic deformation. Is easy to occur. However, if there is sagging, the contact point between the ball and the circulation groove at the time of scooping up will be on the outer side in the radial direction of the nut than in the case without sagging. descend.

In Patent Document 2, in order to facilitate ball-raising of a nut having a sag in the circulation groove, the boundary position of the return path (linear both end portions which are connection portions to the end point and the start point of the track, It has been described to design the spiral groove of the circulation groove and the screw shaft so that the contact state of the ball at the boundary position with the middle part is within a specific range.
Specifically, the center point of the boundary position ball is O, the straight line connecting the radially outermost point of the sag in contact with the boundary position ball and the point O is A, and the contact point between the boundary position ball and the spiral groove of the screw shaft is Assuming that a straight line connecting Y, O and Y is B, O, and a straight line along the radial direction of the nut is C, an angle between the straight line A and the straight line C rather than an angle θ1 between the straight line B and the straight line C It is designed such that θ2 is larger.

Patent No. 4032901 JP, 2013-76463, A

In the case of a ball screw, in order to increase the contact range between the ball and the spiral groove of the screw shaft (the effective range of the screw shaft spiral groove), the spiral groove of the screw shaft may be formed deep. The described method is not suitable for such a case.
Specifically, in the method of Patent Document 1, when the helical groove of the screw shaft is formed deep, the distance between the outer peripheral surface of the screw shaft and the ball center position in the radial direction of the nut becomes short. It becomes difficult to arrange between the outer peripheral surface of the screw shaft and the ball center position.

  In the method of Patent Document 2, when the boundary position ball contacts the outer peripheral surface side end (the boundary position with the chamfered portion) of the spiral groove of the screw shaft, if the spiral groove of the screw shaft is formed deep, It becomes difficult to design the spiral groove of the circulation groove and the screw shaft so as to satisfy the relationship of θ1 <θ2. In addition, Patent Document 2 does not describe how to satisfy the relationship of θ1 <θ2. Further, the method of Patent Document 2 is specified when the nut has a sagging.

As described above, the methods described in Patent Literatures 1 and 2 have room for improvement in that, when the spiral groove of the screw shaft is deeply formed, the balls can be smoothly scooped in the circulation groove.
An object of the present invention is to provide a ball screw capable of smoothly scooping the ball in the circulation groove even when the contact range between the ball and the spiral groove of the screw shaft is large.

In order to solve the above-mentioned subject, the first mode of the present invention provides a ball screw which has the following composition (a) (b).
(a) A screw shaft having a spiral groove formed on the outer peripheral surface, a nut having the spiral shaft formed on the inner peripheral surface, and a screw groove on the nut and a spiral groove on the screw shaft A track to be formed, a return path connecting the end point and the start point of the track to form a circulation path, and the track and the return path are disposed to roll in a loaded state in the track to form the circulation path It has a plurality of circulating balls, and a recessed portion formed directly on the inner peripheral surface of the nut, and has a circulating groove that constitutes the return path.

(b) The diameter of the ball is Dw, the radius of the arc forming the groove perpendicular section of the helical groove of the screw shaft is Ri, the contact angle of the ball with the helical groove of the screw shaft is α, the helical groove of the screw shaft The angle θ at the groove right-angle section indicating the effective range, and the distance between the position of the circle connecting the centers of the balls in the track and the ball-raising contact point of the circulation groove in the radial direction of the nut , And satisfy the following equation (1).
P <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (1)
A second aspect of the present invention is a ball screw having the above configuration (a) and the following configuration (c).

(c) The diameter of the ball is Dw, the radius of the arc forming the groove perpendicular section of the helical groove of the screw shaft is Ri, the contact angle of the ball with the helical groove of the screw shaft is α, the helical groove of the screw shaft Assuming that the angle at the groove right-angle section indicating the effective range is θ, the diameter of a circle connecting the centers of the plurality of balls in the orbit is Dm, and the diameter of the inner peripheral surface of the nut is Dn, (2) The equation is satisfied.
(Dn−Dm) / 2 <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (2)
A third aspect of the present invention is a ball screw having the above configuration (a) and the following configuration (d) (e).

(d) Rounding is present at the boundary between the circulation groove and the inner circumferential surface of the nut.
(e) The diameter of the ball is Dw, the radius of the arc forming the groove perpendicular cross section of the spiral groove of the screw shaft is Ri, the contact angle of the ball with the screw groove of the screw shaft is α, the spiral groove of the screw shaft An angle at a groove right-angled cross section showing an effective range is θ, and a distance between a position of a circle connecting centers of the plurality of balls in the orbit and a outermost point of the roundness of the nut in the radial direction of the nut When Q is satisfied, the following equation (3) is satisfied.
Q <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (3)

  According to the present invention, it is possible to provide a ball screw capable of smoothly scooping the ball in the circulation groove even when the contact range between the ball and the spiral groove of the screw shaft is large.

It is a sectional view showing a ball screw of an embodiment. It is a figure which shows the opening surface shape of the circulation groove of the ball screw of 1st embodiment. It is sectional drawing which shows the relationship between the circulation groove of the ball screw of 1st embodiment, a ball | bowl, and the helical groove of a screw shaft. It is the elements on larger scale of FIG. FIG. 5 is a further enlarged view of FIG. 4, showing the center of a ball and the center of an arc forming a spiral groove of a screw shaft; It is a figure which shows the example in which effective range angle (theta) of the helical groove of a screw shaft is small. It is a figure which shows the example in which effective range angle (theta) of the helical groove of a screw shaft is large. It is a figure which shows the opening surface shape of the circulation groove of the ball screw of 2nd embodiment. It is sectional drawing which shows the relationship between the circulation groove of the ball screw of 2nd embodiment, a ball | bowl, and the helical groove of a screw shaft.

Hereinafter, although the embodiment of this invention is described, this invention is not limited to the embodiment shown below. In the embodiments shown below, technically preferable limitations are made to carry out the present invention, but this limitation is not a requirement of the present invention.
As shown in FIG. 1, the ball screw 10 of the embodiment includes a screw shaft 1, a nut 2 and a plurality of balls 3. A spiral groove 12 is formed on the outer peripheral surface 11 of the screw shaft 1. A spiral groove 22 is formed on the inner circumferential surface 21 of the nut 2. The nut 2 has a flange 23. The screw shaft 1 is inserted into the nut 2.

The ball screw 10 has four circulation paths. Each circulation path is composed of a track formed by the spiral groove 22 of the nut 2 and the spiral groove 12 of the screw shaft 1 facing each other, and a return path 4 connecting the end point and the start point of the track. The return path 4 is composed of a circulation groove 5 consisting of a recess directly formed on the inner circumferential surface 21 of the nut 2 and a portion facing the circulation groove 5 of the outer circumferential surface 11 of the screw shaft 1.
As shown in FIG. 2, the circulation groove 5 is composed of a pair of end portions 51 which are connection portions with the track formed of the spiral grooves 12 and 22 and an intermediate portion 52 connecting the both end portions 51. The end 51 is straight, the middle 52 is curved, and both ends 51 and the middle 52 are smoothly connected. That is, the shape of the opening surface (the surface along the inner peripheral surface of the nut) of the circulation groove 5 is substantially S-shaped.

  When driving the ball screw 10, for example, one of the screw shaft 1 and the nut 2 is rotated relative to the other. As a result, the balls 3 roll in the raceway in a loaded state for each circulation path, then enter the circulation groove 5 from the end point of the raceway, and the scooping portion (the end 51 and the middle portion 52) of the circulation groove 5 (3) move up the return path 4 and move back to the starting point of the orbit and circulate. Along with this, one of the screw shaft 1 and the nut 2 moves continuously in the axial direction relative to the other.

First Embodiment
As shown in FIG. 2, the ball screw 10 of the first embodiment does not have a roundness such as sagging on the outer edge portion (the boundary portion with the inner circumferential surface of the nut 2) of the circulation groove 5. Accordingly, a cross-sectional view of the ball screw 10 at the scoop portion of the circulation groove 5 is as shown in FIG.
The cross-sectional view of FIG. 3 corresponds to the groove-perpendicular cross section of the spiral groove 12 of the screw shaft 1. The spiral groove 12 of the screw shaft 1 has a gothic arc shape. A chamfered portion 13 is formed between the outer peripheral surface 11 of the screw shaft 1 and the spiral groove 12 .
The ball screw 10 of the first embodiment satisfies the following equations (1) and (2).
P <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (1)
(Dn−Dm) / 2 <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (2)

In the equations (1) and (2), P is the distance between the ball center position (the position of the circle connecting the center points O of the plurality of balls 3) T and the ball scooping contact point a of the circulation groove 5. Dw is the diameter of the ball 3 Ri is a radius of an arc forming a groove perpendicular section of the spiral groove 12 of the screw shaft 1. α is the contact angle of the screw shaft 1 of the ball 3 with the spiral groove 12. θ is an angle at a groove perpendicular cross-section indicating the effective range of the helical groove 12 of the screw shaft 1 (effective range angle of the screw axial helical groove). Dm is a diameter (BCD) of a circle connecting center points O of a plurality of balls 3 in the orbit. Dn is the inner diameter (diameter of the inner peripheral surface) of the nut 2.
By satisfying the equations (1) and (2), the ball screw 10 according to the first embodiment smoothly scoops the ball even when the effective range angle θ of the screw shaft spiral groove is large. be able to. The reason will be described below.

<Method of Deriving Formula (1) and Formula (2)>
The derivation method of (1) Formula and (2) Formula is demonstrated using FIGS. 3-5.
In FIG. 3 to FIG. 5, the distance between the ball center position T in the radial direction of the nut 2 and the center point e of the arc of the spiral groove 12 is indicated by b. As can be seen from FIG. 4, the distance between the center point O of the ball 3 and the point e is Ri−Dw / 2. In FIG. 5, Z is inserted between point O and point e. That is, Z = Ri−Dw / 2. As can be seen from FIG. 5, the distance b is expressed as b = Z cos α using the distance Z. Therefore, the following equation (11) is established.

b = (Ri-Dw / 2) cos α (11)
Also, assuming that the distance between the ball center position T and the point f indicating the boundary position between the screw groove 1 and the chamfered portion 13 of the screw shaft 1 is c, “b + c” is b + c =, as can be seen from FIG. Since it is represented by Ri · cos β and β = θ, the following equation (12) is established.
b + c = Ri · cos β = Ri · cos θ (12)
Further, when a distance between a ball center position T and a point g where a straight line extending from the point e and a line connecting the point f and the point e intersects the ball 3 is d, it can be seen from FIGS. Since the straight line y connecting point f and point g is approximately equal to Dw, and the internal angle γ at point g of a right triangle with the straight line y as the oblique side is equal to angle θ, the following equation (13) holds.
d + c = y · cos γ ≒ Dw · cos θ (13)

From equation (13), the distance d is expressed by d = Dw · cos θ−c,
Substituting c = Ri · cos θ−b obtained from the equation (12), d = Dw · cos θ− (Ri · cos θ−b) is obtained.
Substituting b = (Ri-Dw / 2) cos α of the equation (11), d = Dw · cos θ-Ri · cos θ + (Ri-Dw / 2) cos α,
Finally, the distance d is expressed by the following equation (14).
d = (Dw-Ri) cos θ + (Ri-Dw / 2) cos α (14)

  Here, if the position of point g is outside the inner circumferential surface 21 of the nut 2 in the radial direction of the nut 2 (if it is θ <δ as in FIG. 3), the ball 3 is in the track and the circulation groove 5 of the nut 2 It is smoothly scooped up at the boundary between the two, and is led into the return path (a space formed by the circulation groove 5 of the nut 2 and the outer peripheral surface 11 of the screw shaft 1). On the other hand, as shown in FIG. 7, when the position of the point g is on the inner side than the nut inner circumferential surface 21 in the radial direction of the nut 2, scooping up of the ball 3 becomes difficult.

The angle δ is defined by a straight line L connecting the ball scooping contact point a of the circulation groove 5 to the point e and a straight line M passing the center point O of the ball 3 and extending in the radial direction of the nut 2 in the state of FIG. It is an angle. The straight line M is also a bisector of a circular arc forming the groove-perpendicular cross section of the helical groove 12 of the screw shaft 1, that is, a reference line of the effective range angle θ.
In the case of θ = δ, the distance P between the ball center position T and the ball raising contact a is equal to the distance d between the point g and the ball center position T, and in the case of θ <δ, P <d. Therefore, the ball 3 is scooped up smoothly at the boundary between the track and the circulation groove 5 of the nut 2 by satisfying the following equation (1) where “d =” in the above equation (14) is “P <”. Lead into the return path. That is, the scooping performance of the ball 3 in the circulation groove 5 is improved.
P <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (1)

And since the ball screw 10 of 1st embodiment does not have roundness, such as a sag, in the outer edge part of the circulation groove 5, it is set to P = (Dn-Dm) / 2 so that FIG. 3 may show. Therefore, the ball screw 10 of the first embodiment satisfies both of the equations (1) and (2).
(Dn−Dm) / 2 <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (2)
That is, a nut for ball screw in which a circulation groove is formed by a forging process on an inner peripheral surface of a cylindrical nut material, which has no sagging (in the case where sagging occurs in the forging process, sagging is removed) Can satisfy the equation (2) to improve the scooping performance of the ball 3 in the circulation groove 5.

<About the difference of effective range angle θ>
According to the effective range angle θ of the screw shaft spiral groove, the inner diameter Dn of the nut which can smoothly perform the scooping of the ball differs. As shown in FIG. 6, when the effective range angle θ is smaller than δ, the point g is present radially outward of the nut from the ball-raising contact point a, so that the ball can be smoothly raised.
However, as shown in FIG. 7, when the inside diameter Dn of the nut is the same as that of FIG. 6 when the effective range angle θ is larger than δ, the point g exists radially inward of the inner circumferential surface of the nut. Therefore, the ball can not be scooped up smoothly.

<Summary>
The ball screw of the first embodiment satisfies the equations (1) and (2), and the point g is located radially outward of the nut from the ball-clad raised contact point a. Even if you take a large, you can smoothly perform the crawling of the ball.
In addition, since the ball screw 10 of the first embodiment does not have roundness at the boundary between the circulation groove 5 and the inner circumferential surface 21 of the nut 2, P = (Dn−Dm) / 2. Therefore, by setting the BCD and the inner diameter Dn of the nut so as to satisfy the equation (2), it is possible to smoothly raise the ball even when the effective range angle θ of the screw shaft spiral groove is large.
In the case where a rounding (larger rounding than a small rounding) is provided at the boundary between the circulation groove 5 and the inner circumferential surface 21 of the nut 2, P ≠ (Dn−Dm) / 2, and the diameter of the nut Since the position of the outermost point of the rounding in the direction is the ball-raising contact point a, the size of the rounding and the BCD and the inner diameter Dn of the nut are set so as to satisfy the equation (1).

Second Embodiment
The ball screw 10 of the second embodiment has a drip 55 at the outer edge of the circulation groove 5 as shown in FIG. Therefore, a cross-sectional view of the ball screw 10 at the scoop portion of the circulation groove 5 is as shown in FIG.
The ball screw 10 of the second embodiment satisfies the following equation (3).
Q <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (3)

  In the equation (3), Dw is the diameter of the ball 3. Ri is a radius of an arc forming a groove perpendicular section of the spiral groove 12 of the screw shaft 1. α is the contact angle of the screw shaft 1 of the ball 3 with the spiral groove 12. θ is an angle at a groove perpendicular cross-section indicating the effective range of the helical groove 12 of the screw shaft 1 (effective range angle of the screw axial helical groove). Dm is a diameter (BCD) of a circle connecting center points O of a plurality of balls 3 in the orbit. Dn is the inner diameter (diameter of the inner peripheral surface) of the nut 2. Q is the distance between the outermost point s of the sag 55 in the radial direction of the nut 2 and the ball center position T.

Since the outermost point s of the nut 2 of the sag 55 in the radial direction of the sag 55 is the ball scooping contact point a, the concept of the distance Q is the distance P in FIG. 3 (ball center position T and ball scooping contact point (3) is the same as equation (1) above.
That is, a nut for ball screw in which a circulation groove is formed by a forging process on the inner peripheral surface of a cylindrical nut material, and which does not remove the sagging produced in the forging process, as shown in FIG. Since (Dn-Dm) / 2, by satisfying the expression (3), it is possible to improve the scooping performance of the ball 3 in the circulation groove 5.

<Summary>
The ball screw of the second embodiment satisfies the equation (3) (the same as the equation (1)), and the point g is located radially outside the nut from the ball-raising contact point a. Even when the range angle θ is made large, it is possible to smoothly raise the ball.
That is, the effective range angle θ of the screw shaft spiral groove is made large by setting the outermost point s (ball-raising contact point a) in the radial direction of the nut 2 of the sag 55 so as to satisfy formula (3) Even in this case, the ball can be scooped up smoothly.
In addition, regardless of the presence or absence of sagging, according to the depth of the spiral groove of the screw shaft, the above equation (1) is satisfied (point g is disposed outside in the radial direction of the nut than the ball contact) By designing, it is possible to improve the scooping performance of the ball 3 in the circulation groove 5.

DESCRIPTION OF SYMBOLS 10 ball screw 1 screw shaft 11 outer peripheral surface of screw shaft 12 spiral groove of screw shaft 13 chamfered portion 2 nut 21 inner peripheral surface of nut 22 spiral groove of nut 23 flange 3 ball 4 return path 5 circulation groove (inner peripheral surface of nut Directly formed recess)
51 end 52 middle part 55 drip (roundness)
a Ball scooping contact point s Dall's outermost point (roundness outermost point)
T ball center position (the position of the circle connecting the center points of multiple balls)

Claims (3)

A screw shaft having a spiral groove formed on the outer peripheral surface,
A nut into which the screw shaft is inserted and a spiral groove is formed on the inner circumferential surface;
A track formed by a helical groove of the nut and a helical groove of the screw shaft;
A return path connecting the end point and the start point of the track to form a circulation path;
A plurality of balls disposed in the track and the return path, rolling under load in the track and circulating in the circulation path;
And a circulation groove which is formed of a recess directly formed on the inner peripheral surface of the nut, and which constitutes the return path,
The diameter of the ball is Dw,
The radius of the arc forming the groove-perpendicular cross section of the spiral groove of the screw shaft is Ri,
The contact angle of the ball with the spiral groove of the screw shaft is α,
An angle at a groove perpendicular section showing the effective range of the helical groove of the screw shaft, θ,
A distance between a position of a circle connecting centers of the plurality of balls in the track and a ball-raising contact point of the circulation groove in a radial direction of the nut,
And a ball screw that satisfies the following equation (1).
P <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (1) A screw shaft having a spiral groove formed on the outer peripheral surface,
A nut into which the screw shaft is inserted and a spiral groove is formed on the inner circumferential surface;
A track formed by a helical groove of the nut and a helical groove of the screw shaft;
A return path connecting the end point and the start point of the track to form a circulation path;
A plurality of balls disposed in the track and the return path, rolling under load in the track and circulating in the circulation path;
And a circulation groove which is formed of a recess directly formed on the inner peripheral surface of the nut, and which constitutes the return path,
The diameter of the ball is Dw,
The radius of the arc forming the groove-perpendicular cross section of the spiral groove of the screw shaft is Ri,
The contact angle of the ball with the spiral groove of the screw shaft is α,
An angle at a groove perpendicular section showing the effective range of the helical groove of the screw shaft, θ,
A diameter of a circle connecting centers of the plurality of balls in the orbit is Dm,
The diameter of the inner circumferential surface of the nut is Dn,
And a ball screw that satisfies the following equation (2).
(Dn−Dm) / 2 <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (2) A screw shaft having a spiral groove formed on the outer peripheral surface,
A nut into which the screw shaft is inserted and a spiral groove is formed on the inner circumferential surface;
A track formed by a helical groove of the nut and a helical groove of the screw shaft;
A return path connecting the end point and the start point of the track to form a circulation path;
A plurality of balls disposed in the track and the return path, rolling under load in the track and circulating in the circulation path;
And a circulation groove which is formed of a recess directly formed on the inner peripheral surface of the nut, and which constitutes the return path,
Rounding is present at the boundary between the circulation groove and the inner circumferential surface of the nut,
The diameter of the ball is Dw,
The radius of the arc forming the groove-perpendicular cross section of the spiral groove of the screw shaft is Ri,
The contact angle of the ball with the spiral groove of the screw shaft is α,
An angle at a groove perpendicular section showing the effective range of the helical groove of the screw shaft, θ,
A distance Q between a position of a circle connecting centers of the plurality of balls in the orbit and a outermost point of the roundness of the nut in a radial direction of the nut,
And a ball screw that satisfies the following equation (3).
Q <(Dw−Ri) cos θ + (Ri−Dw / 2) cos α (3)

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