阅读说明：本技术 滚珠丝杠装置 (Ball screw device ) 是由 山田和也 下村祐二 佐藤宽太 阿部泰明 于 2021-03-10 设计创作，主要内容包括：从负载路(8)的终点向始点返回滚珠(4)的循环路(9)具备返回路径(20)、上提路径(21)以及连接路径(22)。上提路径(21)具有在圆周方向上,越靠近包括丝杠轴(2)的中心轴(O2)和返回路径(20)的中心线的基准假想平面(α),便越向朝向径向外侧的方向弯曲的圆弧状的中心线。连接路径(22)具备具有配置于基准假想平面(α)上且沿与丝杠轴(2)的中心轴(O2)正交的方向延伸的直线状的中心线的直线路径(22a)。在将上提路径(21)的中心线的曲率半径设为R1、将上提角度设为θ、将直线路径(22a)的全长设为S的情况下,R1cos(90°－θ)+S比滚珠(4)的直径(D)大。(A circulation path (9) for returning the balls (4) from the end point to the start point of the load path (8) is provided with a return path (20), a lifting path (21), and a connection path (22). The lifting path (21) has an arc-shaped center line which is curved in a radially outward direction as it approaches a reference virtual plane (alpha) including the center axis (O2) of the screw shaft (2) and the center line of the return path (20) in the circumferential direction. The connection path (22) is provided with a linear path (22a) which is arranged on a reference virtual plane (alpha) and has a linear central line extending along a direction orthogonal to the central axis (O2) of the screw shaft (2). When the curvature radius of the center line of the lifting path (21) is R1, the lifting angle is theta, and the total length of the straight path (22a) is S, R1cos (90 DEG-theta) + S is larger than the diameter (D) of the ball (4).)

1. A ball screw device is characterized by comprising:

a screw shaft having a plurality of spiral shaft-side ball screw grooves on an outer circumferential surface thereof;

a nut having a plurality of spiral nut-side ball screw grooves on an inner circumferential surface thereof;

a helical load path formed by the shaft-side ball thread groove and the nut-side ball thread groove;

a circulation path connecting a start point and an end point of the load path; and

a plurality of balls rolling on the load path and the circulation path,

the circulation path includes:

a return path arranged radially outward of the load path and having a center line parallel to a center axis of the screw shaft;

a lifting path which is respectively arranged at two sides of the long side direction of the return path and lifts the ball from the load path; and

connection paths respectively arranged on both sides of the return path in the longitudinal direction and connecting the return path and the lifting path,

the lifting path has an arc-shaped center line which is curved in a radially outward direction as approaching a reference virtual plane including a center axis of the screw shaft and a center line of the return path in a circumferential direction, and extends from the center line of the load path to the reference virtual plane,

the connection path includes a straight path having a straight center line disposed on the reference virtual plane and extending in a direction orthogonal to the center axis of the screw shaft, and an arc path having an arc-shaped center line disposed on the reference virtual plane and curved in a direction toward the inside in the axial direction toward the outside in the radial direction,

when the lead of the shaft-side ball thread groove and the nut-side ball thread groove is L, the diameter of the ball is D, the curvature radius of the center line of the lifting path is R1, the lifting angle of the lifting path is theta, and the total length of the linear path is S, D/L is not less than 0.6, and R1cos (90 DEG-theta) + S > D is satisfied.

2. The ball screw device according to claim 1,

the radius of curvature of the cross-sectional shape of the outer peripheral portion of the inner wall surface of the upward lifting path on the side away from the center of curvature of the upward lifting path and the radius of curvature of the cross-sectional shape of the outer peripheral portion of the inner wall surface of the circular arc path on the side away from the center of curvature of the circular arc path are both greater than one-half the diameter of the ball.

3. The ball screw device according to claim 1 or 2,

at the connection point between the central line of the load path and the central line of the lifting path, the tangent line relative to the central line of the load path and the tangent line relative to the central line of the lifting path are consistent with each other when viewed along the axial direction.

4. The ball screw device according to any one of claims 1 to 3,

a tangent line to the center line of the lifting path at a connection point between the center line of the lifting path and the center line of the linear path is arranged on the reference virtual plane.

5. The ball screw device according to any one of claims 1 to 4,

the center line of the lift path is inclined by an angle corresponding to the lead angle of the axial ball screw groove when viewed from a direction orthogonal to the reference virtual plane.

6. The ball screw device according to any one of claims 1 to 5,

the circulation member is provided with a part or all of the circulation path inside.

7. The ball screw device according to claim 6,

the circulation path is constituted by the circulation member and the nut.

Technical Field

The present invention relates to a ball screw device.

Background

In order to roll the balls between the screw shaft and the nut, the ball screw device can obtain higher efficiency than a sliding screw device in which the screw shaft and the nut are directly contacted. Therefore, the ball screw device is incorporated into various mechanical devices such as an electric brake device, an Automatic Manual Transmission (AMT), and a positioning device of a machine tool of an automobile in order to convert a rotational motion of a drive source such as an electric motor into a linear motion.

The ball screw device is provided with: a screw shaft having a spiral shaft-side ball screw groove on an outer peripheral surface thereof; a nut having a spiral nut-side ball thread groove on an inner peripheral surface; a plurality of balls that roll on a load path (load ball rolling path) formed by a shaft-side ball thread groove and a nut-side ball thread groove; and a circulation unit for returning the balls from the end point to the start point of the load path. The circulation member has therein a circulation path (unloaded ball rolling path) for joining the start point and the end point of the load path.

The ball screw device is classified into a return pipe (conduit) type, a guide plate type, an end cap type, a die type, and the like according to the circulation system of the balls, and when any circulation system is adopted, the circulation path for circulating the balls greatly affects various performances of the ball screw device such as smooth circulation of the balls. Therefore, the path of the circulation path has been improved.

For example, international publication No. 2010/013706 discloses the following invention: in order to make the number of turns of the load path close to an integer and to realize smooth circulation of the balls, the path of the circulation path is improved. Fig. 16 to 20 show a ball screw device 100 of a conventional structure described in international publication No. 2010/013706.

The ball screw device 100 includes a screw shaft 101, a nut 102, a plurality of balls 103, and a circulating member 104. In the specification, the axial direction, the radial direction, and the circumferential direction refer to the axial direction, the radial direction, and the circumferential direction in relation to the screw shaft unless otherwise specified. In the axial direction, the center side of the nut is referred to as the axially inner side, and the both sides of the nut are referred to as the axially outer sides.

The screw shaft 101 has a spiral shaft-side ball screw groove 105 on the outer circumferential surface. The nut 102 has a spiral nut-side ball screw groove 106 on the inner peripheral surface. The threaded shaft 101 is inserted through the inside of the nut 102 and is disposed coaxially with the nut 102. The shaft-side ball screw groove 105 and the nut-side ball screw groove 106 are arranged to face each other in the radial direction, and constitute a helical load path 107.

The circulation member 104 is attached to the outer peripheral surface of the nut 102. The start point P1 and the end point P2 of the load path 107 are connected by a circulation path 108 provided inside the circulation unit 104. Fig. 18 shows the center lines of the load path 107 and the circulation path 108 (center tracks of the balls 103). The balls 103 having reached the end point P2 of the load path 107 return to the start point P1 of the load path 107 through the circulation path 108. The start point and the end point of the load path 107 are replaced by the direction of relative displacement in the axial direction of the screw shaft 101 and the nut 102 (relative rotation direction). That is, when the nut 102 is displaced to the right side of fig. 17 with respect to the threaded shaft 101, P1 is a start point and P2 is an end point. On the other hand, when the nut 102 is displaced to the left side of fig. 17 with respect to the threaded shaft 101, P2 is a start point and P1 is an end point. The number of the circulating members 104 is an arbitrary number, and is two in the illustrated example.

The circulation path 108 is divided into a plurality of paths (sections) according to its operation. In the ball screw device 100 having the conventional structure, the circulation path 108 can be divided into a return path 109, a lift path 110, and a connection path 111.

The return path 109 has a function of returning the ball 103 from the end point side to the start point side of the load path 107 in the axial direction. The return path 109 is disposed radially outward of the load path 107 and has a center line parallel to the center axis O101 of the threaded shaft 101.

The lifting path 110 has a function of lifting the balls 103 from the load path 107. As shown in fig. 19, the center line of the lifting path 110 is curved in an arc shape when viewed from the axial direction, and extends from the center line of the load path 107 to the center axis O including the screw shaft 101₁₀₁And a reference imaginary plane alpha of the center line of the return path 109. In the ball screw device 100 having the conventional structure, the lifting path 110 includes an inner diameter side lifting path 110a disposed on the radially inner side and an outer diameter side lifting path 110b disposed on the radially outer side.

As shown in fig. 20, the center line of the inner diameter side lift path 110a is arranged parallel to an orthogonal virtual plane orthogonal to the central axis O101 of the screw shaft 101, as viewed from the direction orthogonal to the reference virtual plane α (the side of the nut 102).

In contrast, the center line of the outer diameter side raising path 110b is curved not only in an arc shape as viewed from the axial direction but also in an arc shape as viewed from a direction orthogonal to the reference virtual plane α. That is, the center line of the outer diameter side rising path 110b is curved in the direction toward the axially inner side while being curved in the direction toward the radially outer side as it approaches the reference virtual plane α in the circumferential direction.

The connection path 111 connects the lifting path 110 (outer diameter side lifting path 110b) and the return path 109, and has a function of converting the moving direction of the ball 103. The center line of the connection path 111 is arranged on the reference virtual plane α, and curves in a direction toward the inside in the axial direction (toward the return path 109) as it goes toward the radially outer side. Accordingly, the connection path 111 is also curved in an arc shape when viewed from the direction orthogonal to the reference virtual plane α, as in the case of the outer diameter side raising path 110 b.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2010/013706

Disclosure of Invention

Problems to be solved by the invention

The ball screw device is different in required performance and size (physical constitution) depending on its use. In a ball screw device for an automobile incorporated in an electric brake booster device or the like, in order to improve fuel performance and traveling performance of the automobile, (1) downsizing, (2) obtaining a large generated thrust with a small driving torque, and (3) a large load capacity are particularly important.

Therefore, in the ball screw device for the automobile, the number of the thread grooves is set to one, and the lead of the thread groove is set to be small with respect to the diameter of the ball. Specifically, the ratio of the lead of the thread groove to the diameter of the ball is set to 0.6 or more. In addition, in order to increase the number of balls that can be accommodated in the load path, it is also conceivable to set the lift angle to be large.

In order to use the ball screw device 100 having the above-described conventional structure of the circulation passage 108 for an automobile, when the number of the shaft-side ball screw grooves 105 and the nut-side ball screw grooves 106 is one, the ratio of the lead to the diameter of the balls 103 is 0.6 or more, and the lift angle is increased, a part of the circulation passage 108 may interfere with the load passage 107. Specifically, as shown in fig. 21, the outer diameter side raising path 110b or the connection path 111 in the circulation path 108 may cross the groove portion (symbol G portion in fig. 21) in the second row from the axial outside in the nut-side ball screw groove 106. Therefore, it is difficult to use the ball screw device 100 of the conventional structure as a ball screw device for an automobile.

The present invention has been made to solve the above problems, and an object thereof is to provide a ball screw device suitable for automotive use.

Means for solving the problems

A ball screw device according to an aspect of the present invention includes a screw shaft, a nut, a load path, a circulation path, and a plurality of balls.

The screw shaft has a plurality of spiral shaft-side ball screw grooves on an outer peripheral surface.

The nut has a plurality of spiral nut-side ball screw grooves on an inner peripheral surface.

The load path is formed in a spiral shape and includes the shaft-side ball screw groove and the nut-side ball screw groove.

The circulation path connects the start point and the end point of the load path.

The plurality of balls roll on the load path and the circulation path.

In the ball screw device according to an aspect of the present invention, the circulation path includes:

a return path arranged radially outward of the load path and having a center line parallel to a center axis of the screw shaft;

a lifting path which is respectively arranged at both sides of the long side direction of the return path and lifts the ball from the load path; and

and connection paths respectively arranged on both sides of the return path in the longitudinal direction and connecting the return path and the lifting path.

The lifting path has an arc-shaped center line which is curved in a radially outward direction as it approaches a reference virtual plane including a center axis of the screw shaft and a center line of the return path in a circumferential direction, and extends from the center line of the load path to the reference virtual plane.

The connection path includes a straight line path having a straight center line disposed on the reference virtual plane and extending in a direction orthogonal to the central axis of the screw shaft, and an arc path having an arc-shaped center line disposed on the reference virtual plane and curved in a direction toward the inside in the axial direction toward the outside in the radial direction.

When the lead of the shaft-side ball thread groove and the nut-side ball thread groove is L, the diameter of the ball is D, the curvature radius of the center line of the lifting path is R1, the lifting angle of the lifting path is theta, and the total length of the linear path is S, D/L is not less than 0.6, and R1cos (90 DEG-theta) + S > D is satisfied.

In the ball screw device according to one aspect of the present invention, the radius of curvature of the cross-sectional shape of the outer peripheral portion of the inner wall surface of the lift path on the side away from the center of curvature of the lift path and the radius of curvature of the cross-sectional shape of the outer peripheral portion of the inner wall surface of the circular arc path on the side away from the center of curvature of the circular arc path can be made larger than half the diameter of the ball.

In the ball screw device according to one aspect of the present invention, at a connection point between the center line of the load path and the center line of the lift path, a tangent to the center line of the load path and a tangent to the center line of the lift path may be aligned with each other when viewed in the axial direction.

In the ball screw device according to one aspect of the present invention, a tangent line to the center line of the lift path at a connection point between the center line of the lift path and the center line of the linear path may be arranged on the reference virtual plane.

In the ball screw device according to one aspect of the present invention, the center line of the lift path may be inclined by an angle corresponding to the lead angle of the axial ball screw groove when viewed from a direction orthogonal to the reference virtual plane.

The ball screw device according to an aspect of the present invention may further include a circulation member having a part or all of the circulation passage therein.

In this case, the circulation path may be constituted by the circulation member and the nut.

ADVANTAGEOUS EFFECTS OF INVENTION

The ball screw device according to one aspect of the present invention includes a path of a circulation path suitable for an automobile application.

Drawings

Fig. 1 is a perspective view of a ball screw device 1 example of the embodiment of the present invention.

Fig. 2 is a plan view of the ball screw device.

Fig. 3 is a sectional view taken along line I-I of fig. 2.

Fig. 4 is a partially enlarged view of fig. 3.

Fig. 5 is a sectional perspective view of line II-II of fig. 2.

Fig. 6 is a plan view of the ball screw device with circulation components omitted.

Fig. 7 is a sectional view taken along line III-III of fig. 2.

Fig. 8 is a bottom view of the circulating member constituting the ball screw device as viewed from the radially inner side.

Fig. 9 is a schematic view of a part of the center line of the circulation path as viewed from the axial direction of the ball screw device.

Fig. 10 is a schematic view of a part of the center line of the circulation passage of the ball screw device as viewed from the side of the nut.

Fig. 11(a) is a schematic sectional view of the lifting path and the connection path of the ball screw device as viewed from the axial direction, and fig. 11(B) is a schematic sectional view taken along line IV-IV of fig. 11 (a).

Fig. 12(a) is a schematic cross-sectional view of the ball screw device as viewed from the side of the nut, and fig. 12(B) is a schematic cross-sectional view taken along line V-V of fig. 12 (a).

Fig. 13 is a plan view of the ball screw device, in which only the screw shaft and the balls are shown, with the nuts and the circulating members omitted.

Fig. 14 is a side view of the ball screw device, in which only the screw shaft and the balls are shown, with the nuts and the circulating members omitted.

Fig. 15 is a view corresponding to fig. 1, showing a modification of the ball screw device using the circulating member integrally formed.

Fig. 16 is a perspective view showing a ball screw device of a conventional structure.

Fig. 17 is a perspective view showing a conventional ball screw device.

Fig. 18 is a schematic view showing the center lines of a load path and a circulation path of a ball screw device of a conventional structure.

Fig. 19 is a schematic view of a part of the center line of the circulation path as viewed from the axial direction of the ball screw device of the conventional structure.

Fig. 20 is a schematic view of a part of the center line of the circulation passage as viewed from the side of the nut in the ball screw device of the conventional structure.

Fig. 21 is a partial sectional view of the ball screw device shown to explain a problem of the conventional structure.

Detailed Description

Example 1 of the embodiment of the present invention will be described with reference to fig. 1 to 5.

[ integral Structure of ball screw device ]

The ball screw device 1 of the present example can be applied to an automobile. For example, the ball screw device 1 is not limited to this, and may be incorporated into an electric brake booster device, and convert the rotational motion of an electric motor as a drive source into linear motion to actuate a piston of a hydraulic cylinder.

The ball screw device 1 of the present example includes a screw shaft 2, a nut 3, and a plurality of balls 4 as constituent members. The ball screw device 1 of the present example includes a circulating member 5.

The threaded shaft 2 is inserted through the inside of the nut 3 and is disposed coaxially with the nut 3. A spiral load path 8 constituting the ball screw device 1 of this example is provided between the outer peripheral surface of the screw shaft 2 and the inner peripheral surface of the nut 3. A circulation path 9 constituting the ball screw device 1 of the present example is provided between the outer peripheral surface of the nut 3 and the circulation member 5. The circulation path 9 is connected to the start point and the end point of the load path 8. A plurality of balls 4 are rollably disposed in the load path 8 and the circulation path 9. When the screw shaft 2 and the nut 3 are relatively rotated, the balls 4 reaching the end point of the load path 8 are returned to the start point of the load path 8 through the circulation path 9. The ball screw device 1 can be used to convert linear motion into rotational motion or to convert rotational motion into linear motion, and specifically, for example, to rotate the nut 3 relative to the screw shaft 2 to linearly move the screw shaft 2 relative to the nut 3. The path of the circulation path 9 will be described in detail below after the structures of the components and elements of the ball screw device 1 are described.

Screw shaft

The screw shaft 2 is made of metal and has a spiral shaft-side ball screw groove 6 having a constant lead L on the outer peripheral surface. The shaft-side ball screw groove 6 is formed by grinding, cutting, or rolling the outer peripheral surface of the screw shaft 2. The number of the shaft-side ball screw grooves 6 is one. The groove shape (groove bottom shape) of the cross section of the shaft-side ball screw groove 6 is a gothic arch groove or a circular arch groove.

Nut

The nut 3 is made of metal and is formed in a substantially cylindrical shape as a whole. The nut 3 has a spiral nut-side ball screw groove 7 on the inner peripheral surface. The nut-side ball screw groove 7 is formed by performing grinding, cutting, or rolling on the inner peripheral surface of the nut 3, or by performing machining using a rolling tap or a cutting tap. The nut-side ball screw groove 7 has the same lead L as the shaft-side ball screw groove 6. The number of the nut-side ball screw grooves 7 is one in the same manner as the shaft-side ball screw grooves 6. The groove shape of the cross section of the nut-side ball screw groove 7 is also a gothic arch groove or a circular arch groove, similarly to the shaft-side ball screw groove 6.

In a state where the screw shaft 2 is inserted and arranged inside the nut 3, the shaft-side ball screw groove 6 and the nut-side ball screw groove 7 are arranged to face each other in the radial direction, and constitute a helical load path 8.

The nut 3 has a flat seat surface portion 10 at one circumferential position on the outer circumferential surface. The seat surface portion 10 includes a nut-side recessed groove 11 and through holes 12 disposed on both axial sides of the nut-side recessed groove 11. The circulation member 5 is mounted on the seat surface portion 10.

The nut-side groove 11 extends linearly in the axial direction and is aligned with the central axis O of the threaded shaft 2₂Are arranged in parallel. The groove shape of the cross section of the nut-side recess 11 is an arc shape having a diameter larger than one-half of the diameter D of the ball 4. The depth dimension of the nut-side recess 11 from the seat surface portion 10 is constant in the axial direction at the middle portion in the axial direction, but becomes larger as the distance becomes closer to the through hole 12 at the end portions on both sides in the axial direction.

Each through hole 12 is formed to penetrate the nut 3 in the radial direction and open to the inner circumferential surfaces of the seat surface portion 10 and the nut 3. Specifically, the through hole 12 opens in the nut-side ball screw groove 7 in the inner peripheral surface of the nut 3. The through-hole 12 is an elongated hole (rectangular hole) extending along the nut-side ball screw groove 7. The end portions (leg portions 14 described later) of the circulation member 5 on both sides in the longitudinal direction are inserted into the through holes 12 without rattling. Thereby, the positioning of the circulating member 5 with respect to the nut 3 can be realized.

Ball bearing

The balls 4 are steel balls having a predetermined diameter D, and are arranged rollably on the load path 8 and the circulation path 9. The balls 4 arranged in the load path 8 roll while receiving a compression load, whereas the balls 4 arranged in the circulation path 9 roll while being pushed by the following balls 4 without receiving a compression load. Since the ball screw device 1 of the present example is applicable to automotive applications, a ratio (D/L) of the lead L of the shaft-side ball screw groove 6 and the nut-side ball screw groove 7 to the diameter D of the balls 4 is set to 0.6 or more (D/L ≧ 0.6) so that a large generated thrust can be obtained with a small driving torque.

Circulation parts

The circulating member 5 is formed of an injection-molded article of synthetic resin or metal powder, and includes a main body 13 and leg portions 14 provided at both ends of the main body 13 in the longitudinal direction. The circulating member 5 has a rotationally symmetric shape with a center in the longitudinal direction as a center. The circulating member 5 is fixed to the seat surface portion 10 of the nut 3 by the pressing member 15 so as not to fall off. The ball screw device 1 of this example employs a circulation system of a so-called return pipe type (external circulation type). In the illustrated example, a pin-shaped member is used as the pressing member 15. However, a plate-like member may be used as the pressing member 15.

The body portion 13 is formed in an elongated plate shape (substantially semi-cylindrical shape), and is disposed so as to cover the nut-side recess 11 provided in the seat surface portion 10 from the radially outer side. A main body side recessed groove 16 extending linearly in the axial direction is provided in a widthwise intermediate portion of the radially inner surface of the main body 13, the intermediate portion facing the nut side recessed groove 11. The groove shape of the cross section of the main body-side concave groove 16 is an arc shape having a curvature radius larger than one-half of the diameter D of the ball 4. The depth dimension of the main body side recessed groove 16 from the radially inner side surface of the main body 13 is constant in the axial direction at the axial direction middle portion, but becomes smaller in a curve toward the axial direction outer side at the axial direction both end portions.

Both width-direction side portions of the radially inner surface of the body portion 13, which are separated from the body-side concave grooves 16, are seated on the seat surface portion 10. The radially outer surface of the body 13 is configured as a partial cylindrical surface having a radius of curvature substantially equal to that of the outer peripheral surface of the nut 3 so as not to protrude radially outward from the outer peripheral surface of the nut 3. In the case of implementing the present invention, although not shown, the radially outer surface of the body may be configured as follows: the seat cushion portion 10 has a flat surface portion parallel to the seat cushion portion 10 at a center portion in the width direction, and a pair of tapered surface portions inclined with respect to the seat cushion portion 10 are provided on both sides in the width direction of the flat surface portion.

Each leg 14 is formed in a substantially semi-cylindrical shape, and extends radially inward from both ends of the body 13 in the longitudinal direction. The leg portion 14 is inserted into the through hole 12 formed in the nut 3 from the radially outer side without rattling. The leg 14 has a tongue-shaped lifting portion 17 at a front end (radially inner end) thereof for lifting the balls 4 rolling on the load path 8 and guiding the balls to the circulation path 9. The lifting portion 17 is disposed inside the shaft-side ball screw groove 6. The leg portion 14 includes a leg-side groove 18 smoothly connected to an axial end portion of a main-body-side groove 16 provided in the main body portion 13. The foot-side concave groove 18 is open to a portion facing axially outward in the inner peripheral surface of the through-hole 12.

In this example, in a state where the circulating member 5 is attached to the nut 3, the circulating path 9 is formed in a portion between the circulating member 5 and the nut 3. That is, the circulation path 9 is constituted not only by the circulation member 5 but by the circulation member 5 and the nut 3. Therefore, the inner wall surface of the circulation passage 9 is provided not only in the circulation member 5 but also in the nut 3. In this example, the circulation path 9 is constituted by a space having a substantially circular cross section formed between the body-side recessed groove 16 and the nut-side recessed groove 11, and a space having a substantially circular cross section formed between the leg-side recessed groove 18 and the inner peripheral surface of the through hole 12. The circulation path 9 is connected to the start point and the end point of the load path 8. In other words, the start point and the end point of the load path 8 are the connection points (boundaries) between the load path 8 and the circulation path 9, and are the scooping points of the raising section 17. Further, the direction of the relative displacement in the axial direction (relative rotation direction) between the screw shaft 2 and the nut 3 is changed, the moving direction of the balls 4 is changed, and the start point and the end point of the load path 8 are changed accordingly.

In this example, the circulating member 5 is formed by axially connecting two segment members 19a and 19 b. The segment members 19a and 19b are each provided with one half of the main body 13 and one leg portion 14. However, as the circulation member, a member integrally configured as a whole may be used as in a modification shown in fig. 15. Alternatively, three or more segment members may be connected to constitute the circulating member.

When an injection-molded article using a metal powder as a raw material is used as the circulating member 5, the circulating member 5 can be manufactured by a metal powder injection molding (MIM). In this case, as the metal powder (MIN alloy) constituting the circulating member 5, for example, Fe-Ni-C (1 to 8% Ni, 0.8% C), Fe-Cr-C (0.5 to 2% Cr, 0.4 to 0.8% C), SCM415, SUS630, or the like can be used.

Description of the path of the circulation Path

The circulation path 9 has a path that avoids interference with the load path 8, and includes a return path 20, lift paths 21 that are respectively disposed on both sides of the return path 20 in the longitudinal direction, and connection paths 22 that are respectively disposed on both sides of the return path 20 in the longitudinal direction and connect the return path 20 and the lift paths 21. The path of the circulation path 9 of the present example will be described below with reference to fig. 9 to 12. Fig. 9 shows a part of the center line of the circulation path 9 (the center trajectory of the balls 4) as viewed from the axial direction, and fig. 10 shows a part (half) of the center line of the circulation path 9 as viewed from the side of the nut 3 (the direction orthogonal to the reference virtual plane α described later).

In the circulation path 9, a lifting path 21, a connection path 22, a return path 20, a connection path 22, and a lifting path 21 are arranged in this order from the end point to the start point of the load path 8. Both sides of the lifting path 21 in the longitudinal direction are connected to the load path 8 and the connection path 22. Both sides of the connection path 22 in the longitudinal direction are connected to the lifting path 21 and the return path 20. Both sides of the return path 20 in the longitudinal direction are connected to the connection paths 22.

Return Path

The return path 20 has a function of returning the balls 4 from the end point side to the start point side of the load path 8 in the axial direction. The return path 20 is formed by an axial intermediate portion of the main body-side groove 16 and an axial intermediate portion of the nut-side groove 11, and is disposed radially outward of the load path 8. The return path 20 has a center line extending linearly in the axial direction and parallel to the central axis O2 of the screw shaft 2. Therefore, in this example, the phases of the start point and the end point of the load path 8 can be made close to each other, and the number of turns of the load path 8 can be made close to an integer.

In the following description, the center axis O of the screw shaft 2 will be included₂And the center line of the return path 20 is referred to as a reference imaginary plane α. Will be connected with the central axis O of the screw shaft 2₂The orthogonal imaginary plane is referred to as an orthogonal imaginary plane β. In addition, the center axis O of the screw shaft 2 is aligned with the center axis₂And the direction in which the center lines of the return paths 20 are orthogonal to each other are referred to as X-direction. The lifting path 21 and the connection path 22 are disposed on both sides of the return path in the longitudinal direction, but are disposed in rotational symmetry about the center portion in the longitudinal direction, and the shapes thereof are the same on both sides.

Lifting Path

The lifting path 21 has a function of lifting the balls 4 at the end point of the load path 8 and supplying the balls 4 to the start point of the load path 8. The lift path 21 is formed by the inner peripheral surfaces of the leg-side groove 18 and the through hole 12. As shown in fig. 9, the center line of the lifting path 21 is curved in an arc shape as viewed in the axial direction, and extends from the center line of the load path 8 to the reference virtual plane α. Specifically, the center line of the lifting path 21 is formed by an arc having a curvature radius R1, and is curved in a radially outward direction as it approaches the reference virtual plane α in the circumferential direction.

Particularly in this example, at a connection point C1 between the center line of the load path 8 and the center line of the upward movement path 21, a tangent T1 to the center line of the load path 8 and a tangent T2 to the center line of the upward movement path 21 are made to coincide with each other as viewed from the axial direction, so that the balls 4 can smoothly move from the load path 8 to the upward movement path 21. In order to move the balls 4 from the load path 8 to the lifting path 21 more smoothly, as shown in fig. 10, the center line of the lifting path 21 is inclined at an angle corresponding to the lead angle of the axial ball screw groove 6 with respect to the orthogonal virtual plane β when viewed from the direction orthogonal to the reference virtual plane α (the side of the nut 3). However, in the case of implementing the present invention, the center line of the lifting path may be arranged parallel to the orthogonal virtual plane β.

Further, a tangent line to the center line of the lifting path 21 at a connection point C2 between the center line of the lifting path 21 and the center line of the connection path 22 (a straight path 22a described later) is arranged on the reference virtual plane α so that the ball 4 can smoothly move between the lifting path 21 and the connection path 22.

As shown in fig. 11, the radius of curvature R18 of the cross-sectional shape of the leg-side groove 18 constituting the outer peripheral side portion on the side away from the center of curvature a1 of the upward path 21 in the inner wall surface of the upward path 21 is larger than half the diameter D of the ball 4 (R18)₁₈> D/2) so that the balls 4 can smoothly move inside the uplift path 21. Thereby, the balls 4 are brought into contact with a portion of the inner wall surface of the lift path 21, which is strongly pressed by the centrifugal force by the balls 4, only at one point.

In addition, in order to increase the number of balls 4 that can be accommodated in the load path 8 and increase the load capacity of the ball screw device 1, the lifting angle θ of the lifting portion 17 (lifting path 21) with respect to the balls 4 is set large. Specifically, the upward-lifting angle θ can be set in the range of 45 ° to 79 ° when the diameter of the ball 4 is 2.381mm, and can be set in the range of 45 ° to 80 ° when the diameter of the ball 4 is 2 mm. The lifting angle θ is from the center axis O of the screw shaft 2 with respect to the reference virtual plane α₂The angle of the orthogonal reference line Z to the connection point C1.

The balls 4 move inside the lift path 21 in an arc-shaped curve toward the radially outer side while approaching the reference virtual plane α in the circumferential direction. The ball 4 moves R1cos (90 ° - θ) (═ R1sin θ) in the X direction (radial direction) while moving on the lift path 21. In the ball screw device 1 of this example, unlike the conventional structure described in international publication No. 2010/013706 (see reference numeral 110b in fig. 19 and 20), the balls 4 do not move inward in the axial direction while moving in the lift-up path 21.

Connection Path

The connection path 22 has a function of connecting the uplift path 21 and the return path 20. The connection path 22 is formed by the inner circumferential surfaces of the leg-side recess 18 and the through hole 12, and the axial end portions of the body-side recess 16 and the nut-side recess 11. The connection path 22 includes a straight path 22a disposed on the radially inner side and an arc path 22b disposed on the radially outer side.

Straight-line route

The linear path 22a is formed by the inner peripheral surfaces of the leg-side groove 18 and the through hole 12. The linear path 22a has a linear center line disposed on the reference virtual plane α and extending in a direction (X direction) orthogonal to the central axis O2 of the threaded shaft 2. Therefore, the ball 4 moving on the linear path 22a does not move in the axial direction but moves only in the X direction. In this example, the entire length (radial dimension) of the linear path 22a is S, and therefore the ball 4 moves by S in the X direction while moving on the linear path 23.

Circular arc path

The circular arc path 22b is constituted by an axial end portion of the body-side groove 16 and an axial end portion of the nut-side groove 11. The center line of the circular-arc path 22b is curved in a circular-arc shape as viewed from a direction (a side of the nut 3) orthogonal to the reference virtual plane α. Specifically, the center line of the circular arc path 22b is formed of a circular arc having a curvature radius R2, and is arranged on the reference virtual plane α, and is curved in a direction toward the inside in the axial direction (toward the return path 20) as it goes toward the radially outer side.

In this example, a tangent line to the center line of the circular arc path 22b at a connection point C3 between the center line of the linear path 22a and the center line of the circular arc path 22b is made to coincide with the center line of the linear path 22a, so that the ball 4 can smoothly move between the linear path 22a and the circular arc path 22 b.

Further, a tangent line to the center line of the circular-arc path 22b at a connection point C4 between the center line of the circular-arc path 22b and the center line of the return path 20 is made to coincide with the center line of the return path 20, so that the ball 4 can smoothly move between the circular-arc path 22b and the return path 20.

As shown in fig. 12, the inner wall surface of the circular path 22b is positioned away from the center a of curvature of the circular path 22b₂The curvature radius R16 of the cross-sectional shape of the axial end of the main body side groove 16 of the side outer peripheral side portion is larger than half the diameter D of the ball 4 (R16 > D/2) so that the ball 4 can smoothly move inside the circular arc path 22 b. Thereby, the ball 4 is brought into contact with only a little with the portion of the inner wall surface of the circular arc path 22b that is strongly pressed by the centrifugal force by the ball 4.

The balls 4 lifted from the load path 8 move inside the circulation path 9 in the order of the lifting path 21, the straight path 22a and the circular path 22b of the connection path 22, the return path 20, the circular path 22b and the straight path 22a of the connection path 22, and the lifting path 21, and are returned to the load path 8 again. In the circulation path 9 of this example, only the circular arc path 22b is curved inward in the axial direction so as to be closer to the load path 8 when viewed from the direction orthogonal to the reference virtual plane α. Therefore, only the circular arc path 22b may interfere with the load path 8.

In this example, in order to prevent the arc path 22b from interfering with the load path 8, the installation height of the arc path 22b (height from the connection point C1, radial position) is limited. More specifically, the sum of the dimension in the X direction of the uplift path 21 corresponding to the set height of the circular-arc path 22b and the dimension in the X direction of the straight path 22a, i.e., the value of R1cos (90 ° - θ) + S, is set to be larger than the diameter D of the ball 4 (R1cos (90 ° - θ) + S > D). Further, since the dimension in the X direction of the uplift path 21 can be approximated to the curvature radius R1, the sum of the curvature radius R1 of the uplift path 21 and the dimension in the X direction of the straight path 22a, that is, the value of R1+ S can be set to be larger than the diameter D of the ball 4 (R1+ S > D).

The ball screw device 1 of the present example as described above can have a path of the circulation path 9 suitable for an automobile application.

In this example, in order to apply the ball screw device 1 to an automobile application, the number of the shaft-side ball screw grooves 6 and the nut-side ball screw grooves 7 is set to one, and the ratio (D/L) of the lead L of the shaft-side ball screw grooves 6 and the nut-side ball screw grooves 7 to the diameter D of the balls 4 is set to 0.6 or more, so that the pitch (groove interval) of the nut-side ball screw grooves 7 becomes small. Therefore, if the circular arc path 22b is arranged at a position where the height from the scooping point (the height in the X direction of the distance C1) is insufficient, the circular arc path 22b easily interferes with the load path 8, as in the case of the above-described conventional structure.

Therefore, in this example, a linear path 22a that moves only in the X direction (radial direction ) without moving the ball 4 to the inside in the axial direction is provided on the radially inner side of the circular arc path 22b, and the sum of the X direction dimension of the uplift path 21 and the X direction dimension of the linear path 22a, that is, the value of R1cos (90 ° - θ) + S, is set to be larger than the diameter D of the ball 4. Therefore, the installation height of the arc path 22b can be secured sufficiently, and interference between the arc path 22b and the load path 8 can be effectively prevented. Specifically, the axial end portion of the nut-side recessed groove 11 constituting the circular arc path 22b can be prevented from crossing the second row groove portion (symbol G1 portion in fig. 4) of the nut-side ball screw grooves 7 located axially outward. In addition, a sufficient thickness of the portion between the axial end portion of the nut-side recessed groove 11 and the groove portion of the nut-side ball screw groove 7 can be ensured. Therefore, the reduction of the load capacity due to the reduction of the rigidity of the nut 3 can be prevented.

At a connection point C1 between the center line of the load path 8 and the center line of the lifting path 21, a tangent T1 to the center line of the load path 8 and a tangent T2 to the center line of the lifting path 21 are made to coincide with each other as viewed in the axial direction. Therefore, the balls 4 can be smoothly moved from the load path 8 to the lift path 21. Further, since the center line of the lift path 21 is inclined with respect to the orthogonal virtual plane β by an angle corresponding to the lead angle of the axial ball screw groove 6 as viewed in the direction orthogonal to the reference virtual plane α, the balls 4 can be smoothly moved from the load path 8 to the lift path 21 from this aspect as well.

Since the tangent line to the center line of the lifting path 21 at the connection point C2 between the center line of the lifting path 21 and the center line of the linear path 22a is arranged on the reference virtual plane α, the ball 4 can be smoothly moved from the lifting path 21 to the linear path 22 a.

Since a tangent line to the center line of the circular arc path 22b at a connection point C3 between the center line of the linear path 22a and the center line of the circular arc path 22b is made to coincide with the center line of the linear path 22a, the ball 4 can be smoothly moved between the linear path 22a and the circular arc path 22 b.

Since a tangent line to the center line of the circular-arc path 22b at the connection point C4 between the center line of the circular-arc path 22b and the center line of the return path 20 is aligned with the center line of the return path 20, the ball 4 can be moved smoothly between the circular-arc path 22b and the return path 20.

Further, the constitution in the inner wall surface of the uplift path 21 is located away from the curvature center a of the uplift path 21₁The radius of curvature R of the cross-sectional shape of the foot-side groove 18 of the outer peripheral side portion of the side (3)₁₈Is larger than half the diameter D of the ball 4 (R)₁₈> D/2). In addition, the inner wall surface of the circular path 22b is positioned away from the curvature center a of the circular path 22b₂The outer peripheral side portion of (3) has a radius of curvature R of the cross-sectional shape of the axial end of the main body side groove 16₁₆Is larger than half the diameter D of the ball 4 (R)₁₆> D/2). Therefore, the ball 4 can be brought into contact with the inner wall surface tangent line of the lift path 21 and the circular arc path 22b, and therefore the ball 4 can be moved smoothly.

In the case of implementing the present invention, the circulation path constituting the ball screw device may instead be constituted by only the circulation member. It is also conceivable to omit the circulating member, or to form the circulating member and the nut integrally, and form the circulating passage inside the nut. In the case where the circulation path is constituted by the circulation path member and the nut, the shape of each groove (inner wall surface) constituting the circulation path is not limited to the above shape. In addition, various shapes and methods known in the art can be used for the shape and fixing method of each part of the circulating member.

Description of the symbols

1-a ball screw device, 2-a screw shaft, 3-a nut, 4-a ball, 5-a circulating member, 6-a shaft-side ball screw groove, 7-a nut-side ball screw groove, 8-a load path, 9-a circulating path, 10-a seat surface portion, 11-a nut-side groove, 12-a through hole, 13-a body portion, 14-a foot portion, 15-a pressing member, 16-a body-side groove, 17-a lifting portion, 18-a foot-side groove, 19a, 19 b-a segment member, 20-a return path, 21-a lifting path, 22-a connecting path, 22 a-a straight path, 22 b-an arc path, 100-a ball screw device, 101-a screw shaft, 102-a nut, 103-a ball, 104-a circulating member, 105-a shaft-side ball screw groove, 106-a nut-side ball screw groove, 107-a load path, 108-a circulating path, 109-a return path, 110-a lifting path, 110a inner diameter-side lifting path, 110 b-the outer diameter side lifting path, 111-the connecting path.