JP2016205619A - Ball Screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw having a long service life even when combined load of thrust load, radial load and moment load is applied.SOLUTION: A ball screw has a screw shaft 1, a nut 2, and a plurality of balls 3, and the screw shaft 1 is penetrated through the nut 2. Spiral grooves 1a, 1b formed on an outer peripheral face of the screw shaft 1 and spiral grooves 2a, 2b formed on an inner peripheral face of the nut 2 are opposed to form ball rolling passages 11A, 11B on which the balls 3 are rolled, and the balls 3 are disposed in the ball rolling passages 11A, 11B. When the screw shaft 1 and the nut 2 are relatively rotated, the screw shaft 1 and the nut 2 are relatively linearly moved in the axial direction through rolling of the balls 3 in the ball rolling passages 11A, 11B. Contact angles of two ball rolling passages 11A, 11B are not uniform, and the ball screw has a plurality of contact angles.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw.

Ball screws used for linear motion actuators are generally subjected to a composite load of thrust load, radial load, and moment load for compactness. Therefore, a ball screw capable of receiving not only a pure thrust load but also a composite load has been proposed (see, for example, Patent Documents 1 and 2).
However, it is difficult for the ball screws disclosed in Patent Documents 1 and 2 to sufficiently receive all of the thrust load, radial load, and moment load. For example, the ball screw disclosed in Patent Document 2 has a low thrust load capacity and a short life against the thrust load.

Japanese Patent No. 4730770 JP 2006-349060 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems of the prior art and to provide a ball screw having a long life even when a combined load of a thrust load, a radial load, and a moment load is applied.

  In order to solve the above problems, a ball screw according to an aspect of the present invention includes a screw shaft, a nut, and a plurality of balls, and the screw shaft passes through the nut and is formed on an outer peripheral surface of the screw shaft. The spiral groove formed on the inner peripheral surface of the nut is opposed to the ball to form a ball rolling path on which the ball rolls, and the ball is disposed in the ball rolling path. By rotating the balls relative to each other, the screw shaft and nut move relative to each other in the axial direction through the rolling of the ball in the ball rolling path, and there are a plurality of ball rolling paths. The contact angles of the ball rolling paths are not all the same, and have a plurality of contact angles.

In the ball screw according to the above aspect, the contact angle of at least one ball rolling path may be 40 ° or less, or 50 ° or more.
Further, in the ball screw according to the above aspect, the contact angle is set by the amount of offset that shifts the axial position of the spiral groove of the opposing screw shaft and the spiral groove of the nut in the axial direction, and the offset amount is different. By assuming that the contact angle may be set to a different angle. Alternatively, the contact angle may be set according to the diameter of the ball, and the contact angle may be set to a different angle by making the diameter of the ball arranged in the ball rolling path different. Alternatively, the contact angles may be set to different angles by making the cross-sectional shapes of the spiral grooves different. Furthermore, the pitch of the spiral groove of the screw shaft and the pitch of the spiral groove of the nut may be different.

  The ball screw of the present invention has a long life even when a combined load of a thrust load, a radial load, and a moment load is applied.

It is sectional drawing of the ball screw which concerns on one Embodiment of this invention. It is a graph which shows the relationship between a contact angle and load capacity. It is a figure explaining the content of the offset of the ball screw of FIG. It is sectional drawing explaining the modification of the ball screw of FIG.

An embodiment of the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view showing a ball screw according to an embodiment of the present invention cut along a plane along the axial direction.
As shown in FIG. 1, the ball screw has a substantially cylindrical screw shaft 1, a substantially cylindrical nut 2, and a plurality of balls 3, and the screw shaft 1 passes through the nut 2. Yes.

  On the outer peripheral surface of the screw shaft 1, two spiral grooves 1a and 1b extending in parallel are formed in a double spiral shape. In addition, two spiral grooves 2 a and 2 b extending in parallel are formed in a double spiral shape on the inner peripheral surface of the nut 2. The cross-sectional shapes of the spiral grooves 1a and 1b and the spiral grooves 2a and 2b (the cross-sectional shapes when cut in a plane perpendicular to the continuous direction of the spiral grooves 1a, 1b, 2a, and 2b that are spirally continuous) are all curved. It is a Gothic arc shape having a substantially V-shape combining two arcs with different centers. However, it may be a curved line consisting of a single arc.

  Then, the spiral grooves 1a and 2a face each other to form a spiral rolling ball path 11A, and the spiral grooves 1b and 2b face each other to form a spiral continuous ball rolling path 11B. Has been. That is, the ball screw of this embodiment has two ball rolling paths 11A and 11B. A plurality of balls 3 are movably disposed in the two ball rolling paths 11A and 11B having a double spiral shape.

  Although not shown in FIG. 1, the ball screw of the present embodiment has a ball return path for circulating the ball 3 from the end point of the ball rolling path 11A to the starting point, and the ball 3 for the ball rolling path 11B. Each has a ball return path that circulates from the end point to the start point. These ball return paths are constituted by, for example, a return tube, a circulation piece, an end cap, or an end deflector. An endless circulation path is formed by the ball rolling paths 11A and 11B and the ball return paths.

  In the ball screw of the present embodiment, the ball 3 moves around the screw shaft 1 while moving in the ball rolling paths 11A and 11B to reach the end points of the ball rolling paths 11A and 11B, where the ball rolling path 11A. , 11B and enters one end of each ball return path. The ball 3 that has entered the ball return path passes through the ball return path, reaches the other end of the ball return path, and returns from there to the starting points of the ball rolling paths 11A and 11B.

  Therefore, in the ball screw of this embodiment, when the screw shaft 1 and the nut 2 are relatively rotated, the screw shaft 1 and the nut 2 are connected to each other through the rolling of the ball 3 in the ball rolling paths 11A and 11B. Relative linear movement is made in the axial direction. Since the ball 3 circulates infinitely in each endless circulation path, the screw shaft 1 and the nut 2 can continuously move relative to each other.

Further, in the ball screw of the present embodiment, the contact angles of the two ball rolling paths 11A and 11B are not the same angle but different angles. That is, the ball screw of this embodiment has two contact angles.
The contact angle of one of the two ball rolling paths 11A and 11B is set to a large angle (for example, 50 ° or more) so as to receive a thrust load, and the other contact angle is set to a radial load and If the angle is set to a small angle (for example, 40 ° or less) so that a moment load can be received, the ball screw of this embodiment can receive a composite load. In the example of FIG. 1, the contact angle of the ball rolling path 11A is set to 30 °, and the contact angle of the ball rolling path 11B is set to 60 °.

  The relationship between the contact angle and the load capacity is shown in the graph of FIG. As can be seen from the graph of FIG. 2, when the contact angle is 40 ° or less, the load capacity of the radial load is larger than the load capacity of the thrust load. As the contact angle increases, the load capacity of the radial load gradually decreases and the load capacity of the thrust load gradually increases. When the contact angle is 50 ° or more, the load capacity of the thrust load is larger than the load capacity of the radial load.

  The method for setting the contact angle is not particularly limited, but is set according to the amount of offset by which the axial positions of the spiral grooves 1a and 1b of the opposing screw shaft 1 and the spiral grooves 2a and 2b of the nut 2 are shifted in the axial direction. can do. That is, by making the offset amounts of the opposing spiral grooves 1a and 2a different from the offset amounts of the opposing spiral grooves 1b and 2b, the contact angles of the ball rolling paths 11A and 11B are different angles. Can be set to

For example, in the example of FIG. 1, if the offset amount of the spiral groove 1b and the spiral groove 2b is set larger than the offset amount of the spiral groove 1a and the spiral groove 2a, the contact angle of the ball rolling path 11B is set to the ball rolling. It can be set larger than the contact angle of the path 11A.
The diameter of the ball 3 arranged in the ball rolling path 11A is the same as the diameter of the ball 3 arranged in the ball rolling path 11B, but the diameter of the ball 3 in the ball rolling path 11A, 11B is the same. By changing the diameter, the contact angle set by the offset amount as described above can be finely adjusted. In the case of a double ball screw, the load capacity of the thrust load and radial load can be adjusted by the diameter of the ball 3 disposed in the ball rolling paths 11A and 11B. Further, the contact angle may be adjusted by using the ball 3 having a size slightly larger than the size of the internal space of the ball rolling paths 11A and 11B. The contact angle increases as the size of the ball 3 increases.

  Here, the details of the offset of the ball screw of the present embodiment will be described in detail with reference to FIG. The ball screw shown in FIG. 3 is a double ball screw having two ball rolling paths 11A and 11B, and the pitch of both the two ball rolling paths 11A and 11B is L. However, the pitches at all axial positions are not the same (L), but some of the pitches are different as shown in FIG. That is, the distance (axial distance) between the cross sections of the ball rolling paths 11A and 11B seen in the sectional view cut along the plane along the axial direction is the same (L) at all axial positions. Rather, some axial positions are different.

More specifically, in the case of one ball rolling path 11A, only one pitch at the substantially center in the axial direction is offset by ε and becomes L-ε, and the other pitch is L. In the case of the other ball rolling path 11B, only one pitch at the substantially axial center is offset by β to L-β, and the other pitches are L.
In this way, by making the offset amounts different between the ball rolling paths 11A and 11B, the contact angles of the ball rolling paths 11A and 11B can be set to different angles, and a preload is applied. Therefore, as can be seen from FIG. 3, the contact angles of the ball rolling paths 11A and 11B are symmetrical with respect to the center in the axial direction. In addition, since a preload can be applied to each of the strips (ball rolling paths 11A and 11B), it is possible to apply a preload to only some of the strips.

  Alternatively, the content of the offset of the ball screw of the present embodiment may be as in the following modification. A modification of the ball screw of the present embodiment will be described with reference to FIG. The ball screw shown in FIG. 4 is a double ball screw having two ball rolling paths 11A and 11B, similar to the ball screw shown in FIGS. 1 and 3, and the pitch of both the two ball rolling paths 11A and 11B is the same. Is L. However, the pitches at all axial positions are not the same (L), but some pitches are different as shown in FIG. That is, the distance (axial distance) between the cross sections of the ball rolling paths 11A and 11B seen in the sectional view cut along the plane along the axial direction is the same (L) at all axial positions. Rather, some axial positions are different.

  Specifically, in the case of the other ball rolling path 11B, the pitches at all axial positions are the same (L). On the other hand, in the case of one ball rolling path 11A, the pitches at all the axial positions are offset by α to L−α or L + α. In the example of FIG. 4, the pitch on one axial end side (left side in FIG. 4) is L−α, and the pitch on the other axial end side (right side in FIG. 4) is L + α. . However, it may be offset by a pitch of a part of the ball rolling path 11A in the axial direction (for example, near the center in the axial direction), and the other pitch may be L.

For example, when the offset is performed by changing the pitch of the spiral groove 2a of the nut 2, the pitch of the spiral groove 1a of the screw shaft 1 is L / 2. α or L / 2 + α may be used. As shown in FIG. 4, if one of the pitches of the spiral groove 2a of the nut 2 is L / 2−α and the pitch adjacent to the axial direction is L / 2 + α, the pitch of the ball rolling path 11A is L−α or L + α.
As a result, preload is applied in opposite directions in the two ball rolling paths 11A and 11B (as shown in FIG. 4, the contact angle direction is reversed in the two ball rolling paths 11A and 11B. Since the spiral grooves 1a, 1b, 2a, 2b and the ball 3 are in a two-point contact state, the rigidity of the ball screw is excellent.

Note that the offset in the ball screw of the present embodiment and the ball screw of the modified example is performed by changing the pitch of the spiral grooves 2 a and 2 b of the nut 2.
In addition, the diameter of the ball 3 disposed in the ball rolling path 11A and the diameter of the ball 3 disposed in the ball rolling path 11B may be the same or different. Furthermore, the cross-sectional shape of the spiral grooves 1a and 2a and the cross-sectional shape of the spiral grooves 1b and 2b may be the same or different.

  Such a ball screw of this embodiment has a high load capacity with respect to any of thrust load, radial load, and moment load, and has a long life even when combined with thrust load, radial load, and moment load. It is. Therefore, the ball screw of this embodiment can be used suitably for a linear actuator, and contributes to the compactness and long life of the linear actuator for automobiles and the linear actuator for general industries.

  The ball screw used for the linear motion actuator is required to have a high load capacity, and a multi-threaded ball screw is often adopted. Therefore, the ball screw of this embodiment is suitable for the linear motion actuator. If the lead is set large and the relative linear movement between the screw shaft 1 and the nut 2 is accelerated, a ball screw suitable for a high-speed linear motion actuator can be obtained.

In addition, this embodiment shows an example of this invention and this invention is not limited to this embodiment. In addition, various changes or improvements can be added to the present embodiment, and forms to which such changes or improvements are added can also be included in the present invention.
For example, in the present embodiment, the contact angles of the ball rolling paths 11A and 11B are set to different angles by making the offset amounts different, but the contact angles of the ball rolling paths 11A and 11B are set by other means. Different angles may be set.

  Another means is the diameter of the ball 3. That is, the offset amount of the spiral groove 1a and the spiral groove 2a is the same as the offset amount of the spiral groove 1b and the spiral groove 2b, and the diameter of the ball 3 disposed in the ball rolling path 11A and the ball rolling path 11B By making the diameters of the balls 3 arranged different, the contact angles of the ball rolling paths 11A and 11B can be set to different angles.

Furthermore, as another means, the cross-sectional shape of the spiral grooves 1a, 1b, 2a, 2b can be mentioned. That is, the offset amount of the spiral groove 1a and the spiral groove 2a is the same as that of the spiral groove 1b and the spiral groove 2b, and the diameter of the ball 3 disposed in the ball rolling path 11A and the ball rolling path 11B The diameters of the balls 3 arranged inside are the same, and the cross-sectional shapes of the spiral grooves 1a and 2a are different from the cross-sectional shapes of the spiral grooves 1b and 2b, so that the contact angles of the ball rolling paths 11A and 11B are increased. Different angles can be set.
Of course, the contact angles of the ball rolling paths 11A and 11B may be set to different angles by combining two or three of these three means.

  Furthermore, in the present embodiment, the description has been given by exemplifying the two-row ball screw having two ball rolling paths. However, the number of the ball rolling paths is not particularly limited as long as it is plural. It may be more than an article. In the case of having three or more ball rolling paths, not all of the contact angles of each ball rolling path are the same angle, and there are two or more contact angles. That is, at least one of the three or more ball rolling paths has a contact angle different from that of the other ball rolling paths.

  For example, in the case of a triple ball screw having three ball rolling paths, the contact angles of all three ball rolling paths may be different and may have three contact angles. The contact angle of the two ball rolling paths is the same, and the contact angle of the remaining one ball rolling path is different from the contact angle of the other two ball rolling paths. You may have. Moreover, if it is a 4-way ball screw which has a 4-way ball rolling path, the number of contact angles which it has may be any of two, three, or four.

  Furthermore, the magnitudes of the thrust load and the radial load applied to the ball screw are not limited to the same level, and one load may be larger than the other load. In such a case, the number of ball rolling paths is preferably 3 or more, and the number of ball rolling paths that receive a large load is preferably larger than the number of ball rolling paths that receive a small load. Then, since a large load is received by many ball rolling paths, the load capacity becomes high.

1 Screw shaft 1a Spiral groove 1b Spiral groove 2 Nut 2a Spiral groove 2b Spiral groove 3 Ball 11A Ball rolling path 11B Ball rolling path

Claims (7)

A screw shaft, a nut, and a plurality of balls;
The screw shaft passes through the nut;
The spiral groove formed on the outer peripheral surface of the screw shaft and the spiral groove formed on the inner peripheral surface of the nut face each other to form a ball rolling path on which the ball rolls.
The ball is disposed in the ball rolling path;
By relatively rotating the screw shaft and the nut, the screw shaft and the nut are relatively moved in the axial direction through rolling of the ball in the ball rolling path. And
A ball screw having a plurality of ball rolling paths, the contact angles of the respective ball rolling paths being not the same angle, and having a plurality of contact angles.   The ball screw according to claim 1, wherein a contact angle of at least one of the ball rolling paths is 40 ° or less.   The ball screw according to claim 1 or 2, wherein a contact angle of at least one of the ball rolling paths is 50 ° or more.   The contact angle is set according to the amount of offset that shifts the axial position of the spiral groove of the screw shaft and the spiral groove of the nut in the axial direction, and the contact angle differs by making the offset amount different. The ball screw according to any one of claims 1 to 3, wherein the ball screw is set to an angle.   The contact angle is set according to the diameter of the ball, and the contact angle is set to a different angle by changing the diameter of the ball arranged in the ball rolling path. The ball screw according to any one of the above.   The ball screw according to any one of claims 1 to 4, wherein the contact angles are set to different angles by making the cross-sectional shapes of the spiral grooves different.   The ball screw according to any one of claims 1 to 6, wherein a pitch of the spiral groove of the screw shaft is different from a pitch of the spiral groove of the nut.

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