Ball screw device

Abstract

An accommodation groove (10) extending in a straight line in the axial direction and opened at the end faces on both axial outer sides of the nut (3) is provided on the outer peripheral surface of the nut (3). The circulation member (5) is arranged inside the accommodation groove (10). The circulation member (5) is prevented from moving to the radially outer side and the circumferential direction relative to the nut (3) by engaging the engagement protrusions (23) of the fixing portions (17) provided at the respective end portions on both axial outer sides of the circulation member (5) with the engagement recesses provided at the respective end portions on both axial outer sides of the accommodation groove (10).

Description

Technical Field

[0001] The present invention relates to a ball screw device. Background Art

[0002] Ball screws enable balls to roll between the screw shaft and nut, resulting in higher efficiency than sliding screws, which use direct contact between the screw shaft and nut. Therefore, to convert the rotational motion of a drive source such as an electric motor into linear motion, ball screws are incorporated into various mechanical devices, including automotive electric brakes, automatic mechanical transmissions (AMTs), and positioning systems for machine tools.

[0003] A ball screw device comprises a screw shaft having a helical shaft-side ball screw groove on its outer circumference, a nut having a helical nut-side ball screw groove on its inner circumference, a plurality of balls that roll in a load path (loaded ball rolling path) formed by the shaft-side ball screw groove and the nut-side ball screw groove, and a circulation component for returning the balls from the end point of the load path to the starting point. The circulation component internally has a circulation path (unloaded ball rolling path) connecting the starting and end points of the load path.

[0004] Ball screw devices are broadly divided into external circulation ball screw devices, typified by the return tube (tube) type, and internal circulation ball screw devices, typified by the die type. External circulation ball screw devices, which have a portion of the circulation path outside the nut, are widely used because they facilitate the use of large-diameter balls and smooth ball circulation.

[0005] For example, Japanese Patent Application Laid-Open No. 11-351350 discloses an example of an external circulation type ball screw device. Figure 18 A ball screw device 100 of a conventional structure described in Japanese Patent Application Laid-Open No. 11-351350 is shown.

[0006] The ball screw device 100 includes a screw shaft 101, a nut 102, a plurality of balls 103, and a circulation component 104. In this specification, unless otherwise specified, the axial, radial, and circumferential directions refer to the axial, radial, and circumferential directions relative to the screw shaft. Furthermore, with respect to the axial direction, the center side of the nut is referred to as the axial inner side, and the end sides of the nut are referred to as the axial outer side.

[0007] The screw shaft 101 has a helical shaft-side ball screw groove 105 on its outer circumference. The nut 102 has a helical nut-side ball screw groove 106 on its inner circumference. The screw shaft 101 is inserted into the inner side of the nut 102 and is arranged coaxially with the nut 102. The shaft-side ball screw groove 105 and the nut-side ball screw groove 106 are arranged so as to face each other in the radial direction, forming a helical load path.

[0008] The starting point and end point of the load path are connected by a circulation path 107 formed between the nut 102 and the circulation member 104. The balls 103 that have reached the end point of the load path return to the starting point of the load path through the circulation path 107. Furthermore, the starting point and end point of the load path change depending on the direction of relative displacement (relative rotational direction) in the axial direction between the screw shaft 101 and the nut 102.

[0009] The conventional ball screw device 100 has a flat seat portion 108 at a circumferential portion of the outer circumference of the nut 102. The circulation component 104 is mounted on the seat portion 108. A pair of through-holes 109 are formed in the seat portion 108, separated axially. Each through-hole 109 extends radially through the nut 102 and opens at the seat portion 108 and the inner circumferential surface of the nut 102.

[0010] The circulation member 104 includes a partially cylindrical main body 110 having an arcuate end surface, and a pair of legs 111 integrally provided with the main body 110 .

[0011] The main body 110 has a main body-side groove 112 curved into a substantially S-shape on its radially inner surface facing the seating surface 108. The main body-side groove 112 forms a circulation path 107 with the flat seating surface 108. The portion of the radially inner surface of the main body 110 separated from the main body-side groove 112 is seated on the seating surface 108.

[0012] A pair of legs 111 are inserted (pressed) into the inner sides of a pair of through-holes 109 provided in the nut 102 without play. In this state, the tip ends of the pair of legs 111 are positioned inside the shaft-side ball screw groove 105. Each leg 111 has the function of scooping up the balls 103 rolling in the load path and guiding them to the circulation path 107.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: Japanese Patent Application Laid-Open No. 11-351350 Summary of the Invention

[0016] Problems to be solved by the invention

[0017] The ball screw device 100 of the existing structure achieves the positioning of the circulation component 104 relative to the nut 102 by inserting a pair of legs 111 of the circulation component 104 into a pair of through holes 109 of the nut 102. Therefore, in the ball screw device 100 of the existing structure, it is necessary to improve the accuracy of the formation position of the pair of through holes 109. For example, if the formation position of any through hole 109 deviates from the regular position, stress may be applied to the circulation component 104, causing the circulation component 104 to deform. As a result, the balls 103 may be blocked on the inner side of the circulation path 107, hindering the smooth circulation of the balls 103 and causing premature damage to the circulation component 104.

[0018] Furthermore, the conventional ball screw device 100 fixes the circulation member 104 to the nut 102 only by inserting (pressing) the pair of legs 111 into the pair of through holes 109. Therefore, there is a possibility that the fixing force of the circulation member 104 to the nut 102 is insufficient, and the circulation member 104 may float from the seat portion 108 due to the force applied to the circulation member 104 by the balls 103.

[0019] An object of the present invention is to provide a ball screw device having a structure capable of relaxing the accuracy of the formation position of a through-hole and improving the fixing force of a circulation member with respect to a nut.

[0020] Solutions for solving problems

[0021] A ball screw device according to one aspect of the present invention includes a screw shaft, a nut, a circulation member, and a plurality of balls.

[0022] The screw shaft has a spiral shaft-side ball screw groove on its outer peripheral surface.

[0023] The nut has a spiral nut-side ball screw groove on the inner peripheral surface.

[0024] The shaft-side ball screw groove and the nut-side ball screw groove form a spiral load path having a starting point and an end point.

[0025] The circulation member is mounted on the outer peripheral surface of the nut and forms a circulation path connecting the starting point and the end point of the load path between the circulation member and the nut.

[0026] The plurality of balls are rollably arranged in the load path and the circulation path.

[0027] In a ball screw device according to one aspect of the present invention, the nut has a receiving groove formed on the outer peripheral surface of the nut, extending linearly in the axial direction, and opening at both axially outer end surfaces of the nut.

[0028] The accommodating groove includes a flat groove bottom surface and a pair of groove wall surfaces facing each other in the circumferential direction.

[0029] The nut has a pair of through holes that are open separately from each other in the bottom surface of the groove and penetrate the nut in the radial direction.

[0030] The pair of groove wall surfaces have engaging recesses at respective ends on both outer sides in the axial direction.

[0031] The circulation member is arranged inside the accommodating groove and includes a pair of leg portions inserted into the pair of through holes and a pair of fixing portions provided at both outer ends in the axial direction.

[0032] Each of the pair of fixing portions includes an engaging protrusion that engages with the engaging recess to prevent the circulation member from being displaced radially outward and circumferentially relative to the nut.

[0033] In the ball screw device according to one aspect of the present invention, the circulation member can be made of metal, and the engaging protrusion can be formed as a caulking portion that is pressed against the engaging recess by plastic deformation.

[0034] When the circulation component is made of metal, it can be formed as an injection molded product using metal powder as a raw material. In other words, it can be formed as a component manufactured by metal powder injection molding.

[0035] Alternatively, the circulation member may be made of synthetic resin.

[0036] When the circulation member is made of synthetic resin, the engagement projection can be engaged with the engagement recess by snapping.

[0037] In the ball screw device according to one aspect of the present invention, the engagement recess can be opened at the axially outer end surface of the nut.

[0038] In the ball screw device according to one aspect of the present invention, the pair of fixing portions can be arranged at positions separated axially outward from the pair of leg portions.

[0039] In the ball screw device according to one aspect of the present invention, the fixing portion may include a pair of side plate portions that are arranged to face the pair of groove wall surfaces and each include the engagement projection.

[0040] In this case, the fixing portion may include a base plate portion placed on the groove bottom surface and having both ends in the circumferential direction connected to radially inner ends of the pair of side plate portions.

[0041] In the ball screw device according to one aspect of the present invention, the circulation member can be arranged inside the accommodating groove so as not to protrude radially outward from the accommodating groove.

[0042] In the ball screw device according to one aspect of the present invention, the circulation member may have a rotationally symmetrical shape centered at a central portion in an axial direction (in the longitudinal direction of the circulation member).

[0043] Effects of the Invention

[0044] According to one aspect of the present invention, a structure of a ball screw device can be realized in which the accuracy of the formation position of the through-hole can be relaxed and the fixing force of the circulation member with respect to the nut can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a perspective view of a ball screw device according to a first example of an embodiment of the present invention.

[0046] Figure 2 It is a top view of the ball screw device of the first example.

[0047] Figure 3 yes Figure 2 I-I line cross-sectional view.

[0048] Figure 4 yes Figure 3 A partial enlarged view of .

[0049] Figure 5 yes Figure 2 Sectional view along line II-II.

[0050] Figure 6 yes Figure 5 A partial enlarged view of .

[0051] Figure 7 yes Figure 1 A partial enlarged view of .

[0052] Figure 8 yes Figure 2 Schematic diagram of the III-III line cross-section.

[0053] Figure 9 This is a perspective view of a nut constituting the ball screw device of the first example.

[0054] Figure 10 yes Figure 9 A partial enlarged view of .

[0055] Figure 11 The ball screw device according to the first example is a schematic diagram for explaining the operation of forming engaging recesses on a pair of groove wall surfaces constituting the accommodating groove.

[0056] Figure 12 The ball screw device according to the first example is a perspective view of the circulation member as viewed from the radially outer side before the engagement projection is formed.

[0057] Figure 13 The ball screw device according to the first example is a perspective view of the circulation member as viewed from the radially inner side before the engagement protrusion is formed.

[0058] Figure 14 It is a perspective view of a ball screw device according to a second example of an embodiment of the present invention.

[0059] Figure 15 yes Figure 14 A partial enlarged view of .

[0060] Figure 16 The ball screw device of the second example is equivalent to Figure 12 Picture.

[0061] Figure 17 The ball screw device of the second example is equivalent to Figure 13 Picture.

[0062] Figure 18 This is an exploded perspective view of a conventional ball screw device. DETAILED DESCRIPTION

[0063] [First example]

[0064] use Figures 1 to 13 , a first example of an embodiment of the present invention is described.

[0065] [Overall structure of the ball screw unit]

[0066] The ball screw device 1 in this example is an external circulation type ball screw device for automobiles, and is used, for example, for the following purposes: being installed in an electric brake booster device to convert the rotational motion of an electric motor serving as a driving source into linear motion to move the piston of a hydraulic cylinder, etc.

[0067] The ball screw device 1 includes a screw shaft 2 , a nut 3 , a plurality of balls 4 , and a circulation member 5 .

[0068] The screw shaft 2 is inserted into the inner side of the nut 3 and is arranged coaxially with the nut 3. A spiral load path 8 is provided between the outer peripheral surface of the screw shaft 2 and the inner peripheral surface of the nut 3. A plurality of balls 4 are rollably arranged in the load path 8. When the screw shaft 2 and the nut 3 are rotated relative to each other, the balls 4 that reach the end of the load path 8 return to the starting point of the load path 8 through the circulation path 9 formed between the nut 3 and the circulation component 5. The ball screw device 1 is used, for example, in a manner such that the screw shaft 2 is linearly moved relative to the nut 3 by causing the nut 3 to rotate relative to the screw shaft 2. The structure of each structural component of the ball screw device 1 is described below.

[0069] Screw shaft

[0070] The screw shaft 2 is made of metal and has a spiral shaft-side ball screw groove 6 on its outer circumference. The shaft-side ball screw groove 6 has a constant lead. The shaft-side ball screw groove 6 is formed by grinding, cutting, or rolling the outer circumference of the screw shaft 2. The number of shaft-side ball screw grooves 6 is, for example, one. The cross-sectional groove shape (groove bottom shape) of the shaft-side ball screw groove 6 is a Gothic groove shape or a circular arc groove shape.

[0071] Nut

[0072] The nut 3 is made of metal and is generally cylindrical in shape. The nut 3 has a spiral nut-side ball screw groove 7 on the inner circumference. The nut-side ball screw groove 7 is formed by grinding, cutting, rolling tapping, or cutting tapping on the inner circumference of the nut 3, and has the same lead as the shaft-side ball screw 6. Therefore, when the screw shaft 2 is inserted and arranged on the inner side of the nut 3, the shaft-side ball screw groove 6 and the nut-side ball screw groove 7 are arranged in a radially opposed manner to form a spiral load path 8. The number of nut-side ball screw grooves 7 is, for example, one, similar to the number of shaft-side ball screw grooves 6. The groove shape (groove bottom shape) of the cross section of the nut-side ball screw groove 7 is also a Gothic groove shape or an arc groove shape, similar to the shaft-side ball screw groove 6.

[0073] The nut 3 has a receiving groove 10 at a point in the circumferential direction of the outer peripheral surface. The receiving groove 10 extends in a straight line along the axial direction, which is the direction along the center axis O2 of the screw shaft 2. In other words, the receiving groove 10 extends in a direction perpendicular to the end faces on both axial outer sides of the nut 3. In addition, the receiving groove 10 is open at either of the end faces on both axial outer sides of the nut 3. The radial depth dimension R and the circumferential width dimension H of the receiving groove 10 are constant throughout the entire axial length. In this case, as Figure 6As shown, the radial depth dimension R of the receiving groove 10 is smaller than the circumferential width dimension H of the receiving groove 10. The depth dimension R of the receiving groove 10 is approximately 1.0 to 1.2 times the diameter D of the ball 4, and the width dimension H of the receiving groove 10 is approximately 1.4 to 3.0 times the diameter D of the ball 4.

[0074] The accommodating groove 10 has a roughly rectangular (rectangular) cross-sectional shape, and has a flat groove bottom surface 11 and a pair of flat groove wall surfaces 12. The groove bottom surface 11 is arranged parallel to the center axis O2 of the screw shaft 2. The pair of groove wall surfaces 12 are arranged at roughly right angles relative to the groove bottom surface 11. The groove wall surfaces 12 are arranged parallel to each other and opposite to each other in the circumferential direction. In this example, the accommodating groove 10 is formed by cutting using a cutting tool such as an end mill. As described above, the accommodating groove 10 has a roughly rectangular cross-sectional shape and extends in a straight line along the axial direction. Since the shape is not complicated, it can be easily and accurately processed by cutting.

[0075] like Figure 9 As shown, a pair of through holes 13 are provided in the groove bottom surface 11, separated in the axial direction. Each through hole 13 of the pair of through holes 13 is formed to penetrate the nut 3 in the radial direction, and is opened not only in the groove bottom surface 11 but also in the inner peripheral surface of the nut 3. Specifically, the pair of through holes 13 is opened in the nut side ball screw groove 7 in the inner peripheral surface of the nut 3. In addition, each through hole 13 is composed of a long hole (rectangular hole) extending along the nut side ball screw groove 7. A pair of legs 16 described later, which are provided on the circulation component 5, are inserted into the pair of through holes 13.

[0076] like Figure 9 and Figure 10 As shown, in this example, each of the pair of groove wall surfaces 12 has a snap-fitting recess 14 at the end portions on both axially outer sides. That is, a pair of snap-fitting recesses 14 are respectively provided at the end portions on both axially outer sides of the accommodating groove 10. Each snap-fitting recess 14 constituting a pair of snap-fitting recesses 14 has a roughly triangular cross-sectional shape and is arranged at the radial middle portion or the radially outer portion of the groove wall surface 12. Thus, the snap-fitting recess 14 has no opening on the outer peripheral surface of the nut 3. However, the snap-fitting recess 14 is open at the end face on the axial outer side of the nut 3. In addition, as Figure 10 As shown, the axially inner portion (deep portion) of the engaging recess 14 has a triangular pyramid shape, and the circumferential depth and radial width of the engaging recess 14 decrease axially inward. Therefore, the circumferential widths of the groove bottoms (vertices of the triangular cross-section) of a pair of circumferentially opposed engaging recesses 14 decrease axially inward in the axially inner portions of the pair of engaging recesses 14.

[0077] In the example shown in the figure, the axially inner end of the engaging recess 14 is located at approximately the same axial position as the axially inner end of the opening of the through hole 13. However, when the present invention is implemented, the axially inner end of the engaging recess 14 can be located further axially outward than the position shown in the figure, or further axially inward. In addition, the grooves constituting the engaging recess 14 provided at the axially outer ends of each groove wall surface 12 can be axially continuous with each other. In other words, it is also possible to form a groove over the entire length of each groove wall surface 12, with the engaging recess 14 being constituted by the axially outer portions of the groove. As Figure 11 As shown, a pair of engaging recesses 14 provided at each of the axially outer ends of the accommodating groove 10 can be simultaneously formed on a pair of groove wall surfaces 12 by moving a cutting tool 27 having, for example, a prismatic cross-sectional shape (such as the cross-sectional shape of an abacus bead) from the axial opening side of the accommodating groove 10 toward the axial inner side.

[0078] Rollerball

[0079] The balls 4 are straight steel balls with a predetermined diameter and are rollably arranged in the load path 8 and the circulation path 9. The balls 4 arranged in the load path 8 roll while receiving a compressive load, while the balls 4 arranged in the circulation path 9 do not receive a compressive load and roll due to being pushed by the balls 4 described later.

[0080] Circulation parts

[0081] The circulation member 5 is an injection-molded part made of metal powder using metal injection molding (MIM) and is positioned inside the receiving recess 10 of the nut 3. Examples of the metal powder (MIM alloy) constituting the circulation member 5 include Fe-Ni-C (1-8% Ni-0.8% C), Fe-Cr-C (0.5-2% Cr-0.4-0.8% C), SCM415, and SUS630.

[0082] like Figure 12 and Figure 13 As shown, the circulation member 5 includes a main body 15, a pair of leg portions 16, and a pair of fixing portions 17. The circulation member 5 has a rotationally symmetrical shape centered at the center in the longitudinal direction (axial direction).

[0083] The main body 15 is configured as a long plate, and is arranged on the inner side of the receiving groove 10 of the nut 3 with a gap (a small gap) to the extent that no load is applied to the main body 15, with the long side direction aligned with the axial direction. Therefore, when the circulation component 5 is arranged on the inner side of the receiving groove 10, the two side surfaces of the main body 15 in the circumferential direction are opposed to each other with a gap relative to the pair of groove wall surfaces 12. The main body 15 has a width dimension that is slightly smaller than the width dimension H of the receiving groove 10 in the circumferential direction. In addition, when the present invention is implemented, by arranging (embedding) the main body on the inner side of the receiving groove without shaking in the circumferential direction, the positioning of the circulation component in the circumferential direction relative to the nut can also be achieved.

[0084] The main body portion 15 has a main body side groove 18 extending linearly in the axial direction on the radially inner side surface (lower surface) opposite to the groove bottom surface 11. The main body side groove 18 forms a part of the circulation path 9 (the return path 24 described later) between the main body side groove 18 and the axial middle portion of the groove bottom surface 11 (the flat surface between the openings of the pair of through holes 13). Figure 6 As shown, the groove shape of the cross section of the main body side groove 18 is a semi-circular shape. The main body side groove 18 has a groove width slightly larger than the diameter D of the ball 4, and has a groove depth slightly larger than the diameter D of the ball 4. The groove depth of the main body side groove 18 on the radial inner side surface of the main body 15 does not change in the axial direction in the axial middle part, but at the ends on both axial outer sides, it decreases in a curved manner as it moves toward the axial outer side. The portion of the radial inner side surface of the main body 15 that is separated from the main body side groove 18 in the circumferential direction is seated on the groove bottom surface 11. In this example, the main body 15 is arranged on the inner side of the accommodating groove 10 so that a portion of the radial inner side surface of the main body 15 abuts against the groove bottom surface 11, thereby realizing the radial positioning of the circulation component 5 relative to the nut 3.

[0085] The radially outer side surface (upper surface) of the main body portion 15 is formed as a flat surface substantially parallel to the groove bottom surface 11 so as to protrude radially outward from the outer peripheral surface of the nut 3. However, the radially outer side surface of the main body portion 15 may also be formed as a partially cylindrical surface having a curvature radius substantially the same as that of the outer peripheral surface of the nut 3.

[0086] Each foot 16 constituting a pair of feet 16 is configured to be roughly semi-cylindrical. A pair of feet 16 extends radially inward from the radial inner side surfaces of the ends on both axial outer sides of the main body 15. Each foot 16 is inserted into the inner side of each through hole 13 formed in the nut 3 from the radial outer side. In this example, the foot 16 is inserted into the inner side of the through hole 13 with a gap (a small gap) to the extent that no load is applied to the foot 16. The front end portion (the radial inner end portion) of the foot 16 has a tongue-shaped scooping portion 19 for scooping up the balls 4 rolling on the load path 8 and guiding them to the circulation path 9. The scooping portion 19 is arranged on the inner side of the shaft-side ball screw groove 6. The foot 16 is provided with a foot-side groove 20, which is smoothly connected to the axially outer end portion of the main body-side groove 18 provided on the main body 15. The foot-side groove 20 is open to the axially outer portion of the inner circumferential surface of the through hole 13.

[0087] In this example, each of the pair of fixing portions 17 has a substantially U-shaped cross-sectional shape. The pair of fixing portions 17 are arranged on both axially outer sides of the main body 15. Figure 3 and Figure 4 As shown, the pair of fixing portions 17 are disposed at both axially outer ends of the circulation member 5 separated axially outward from the pair of leg portions 16. Each fixing portion 17 includes a thin-walled flat plate-shaped base portion 21 and a pair of side plate portions 22.

[0088] The base plate portion 21 is placed on the groove bottom surface 11 without a gap. A pair of side plate portions 22 are arranged on both sides of the base plate portion 21 in the circumferential direction (width direction), and are bent at a substantially right angle toward the radial outside relative to the base plate portion 21. That is, the pair of side plate portions 22 are arranged to be opposite (overlap) to the pair of groove wall surfaces 12. In addition, the end portions on both sides of the base plate portion 21 in the circumferential direction are respectively connected to the radially inner end portions of the pair of side plate portions 22. The pair of side plate portions 22 are in a state before forming a pair of engaging protrusions 23 described later, as shown in FIG. Figure 12 and Figure 13 As shown, each is formed into a thin-walled flat plate shape, having the same width dimension as the width dimension of the main body 15. However, when the circulation component 5 is fixed to the nut 3, as shown in FIG. Figure 8 As shown, the pair of side plate portions 22 includes a pair of engaging protrusions 23 constituted by caulking portions obtained by being pressed by the respective engaging recesses 14 through plastic deformation.

[0089] With the circulation component 5 arranged on the inner side of the accommodating groove 10, the punch (not shown) arranged on the radial outer side of the fixing portion 17 is moved radially inward, so that the radial outer side portions of the pair of side plate portions 22 are plastically deformed in the circumferential direction (plate thickness direction), thereby forming a pair of engaging protrusions 23. That is, by using the above-mentioned punch, the radial outer side portions of the pair of side plate portions 22 are opened in the circumferential direction, thereby forming each engaging protrusion 23 at the same time. The pair of engaging protrusions 23 enter the inner side of the pair of engaging recesses 14 provided on the groove wall surface 12 and are squeezed into the pair of engaging recesses 14. As a result, the pair of engaging protrusions 23 are engaged with respect to the pair of engaging recesses 14 so as to be unable to displace radially outward. Specifically, the circumferential end portions of each engaging protrusion 23 engage with the radial outer end portions of each engaging recess 14, thereby preventing the pair of engaging protrusions 23 from being displaced radially outward relative to the pair of engaging recesses 14. In this example, for each fixing portion 17 provided at the ends of both axially outer sides of the circulation component 5, a pair of engaging protrusions 23 are engaged with a pair of engaging recesses 14, and the pair of fixing portions 17 are riveted and fixed relative to the nut 3 so as not to fall off (displace) radially outward. In addition, this achieves radial positioning of the circulation component 5 relative to the nut 3. Furthermore, for each fixing portion 17, a pair of engaging protrusions 23 are pressed against a pair of engaging recesses 14, thereby preventing the circulation component 5 from being displaced in the circumferential direction relative to the nut 3, thereby achieving circumferential positioning of the circulation component 5 relative to the nut 3.

[0090] In this example, only the axially intermediate portion of the radially outer portion of each side plate portion 22 is plastically deformed in the circumferential direction to form the engaging protrusion 23 in this portion. Furthermore, by forming the engaging protrusion 23 on the radially outer portion of each side plate portion 22, the portion of the side plate portion 22 separated from the engaging protrusion 23 is pressed against the groove wall surface 12 of the receiving groove 10.

[0091] In this example, when the circulation component 5 is installed on the nut 3, a circulation path 9 is formed in the portion between the circulation component 5 and the nut 3. That is, the circulation path 9 is composed not only of the circulation component 5, but also of the circulation component 5 and the nut 3. Specifically, the circulation path 9 is composed of a space with a semi-elliptical cross-section formed between the main body side groove 18 and the groove bottom surface 11 of the accommodating groove 10, and a space with a roughly circular cross-section formed between the foot side groove 20 and the inner peripheral surface of the through hole 13. The circulation path 9 is connected to the starting point and end point of the load path 8, respectively. In other words, the starting point and end point of the load path 8 are the connection points (boundaries) between the load path 8 and the circulation path 9, and are scooping points based on the scooping portion 19. In addition, the starting point and end point of the load path 8 are changed as the relative displacement direction (relative rotation direction) of the screw shaft 2 and the nut 3 in the axial direction changes and the moving direction of the ball 4 changes.

[0092] In this example, the circulation path 9 has a path that avoids interference with the load path 8 and includes a return path 24, a pair of scoop paths 25, and a pair of connecting paths 26. More specifically, the circulation path 9 comprises the scoop path 25, the connecting path 26, the return path 24, the connecting path 26, and the scoop path 25, arranged in this order from the end point to the starting point of the load path 8. Specifically, the scoop path 25 is connected to the load path 8 and the connecting path 26. The connecting path 26 is connected to the scoop path 25 and the return path 24. The return path 24 is connected to each of the connecting paths 26.

[0093] The return path 24 has the function of returning the ball 4 to the starting point side of the load path 8 in the axial direction. The return path 24 is composed of a flat surface portion between the axial middle portion of the main body side groove 18 and the opening portion of a pair of through holes 13 in the groove bottom surface 11. The return path 24 is arranged on the radial outside of the load path 8 (outside the nut 3). The return path 24 has a center line parallel to the center axis O2 of the screw shaft 2 and extending in a straight line in the axial direction. Thus, in this example, the phase of the starting point and the end point of the load path 8 in the circumferential direction can be close, and it is preferred to make the phase of the starting point and the end point in the circumferential direction consistent so that the number of turns of the load path 8 is close to an integer.

[0094] The scooping path 25 scoops up the balls 4 at the end of the load path 8 and supplies them to the starting point of the load path 8. The scooping path 25 is formed by the radially inner portion of the leg-side groove 20 and the radially inner portion of the inner circumferential surface of the through-hole 13. The centerline of the scooping path 25 is curved in an arc shape when viewed axially.

[0095] Connecting path 26 connects scooping path 25 and return path 24. Connecting path 26 is formed by the radially outer portion of foot-side groove 20, the radially outer portion of the inner circumferential surface of through-hole 13, the axially outer end of body-side groove 18, and the axially inner portion of the opening edge of through-hole 13 that opens into groove bottom 11. The centerline of connecting path 26 is at least partially curved in an arc shape when viewed circumferentially.

[0096] In the ball screw device 1 of this example, the accuracy of the formation positions of the pair of through holes 13 can be relaxed, and the fixing force of the circulation member 5 with respect to the nut 3 can be improved.

[0097] Specifically, in this example, for each of the fixing portions 17 provided at the axially outer ends of the circulation member 5, a pair of engaging protrusions 23 engages with a pair of engaging recesses 14. This prevents radial outward and circumferential displacement of the circulation member 5 relative to the nut 3, thereby achieving radial and circumferential positioning of the circulation member 5 relative to the nut 3. Therefore, unlike conventional ball screw devices, the ball screw device 1 of this example does not require positioning of the circulation member 5 relative to the nut 3 by inserting the pair of legs 16 constituting the circulation member 5 into the pair of through-holes 13 provided in the nut 3. This allows for less precise positioning of the through-holes 13 that constitute the pair of through-holes 13. Consequently, even if the position of any of the through-holes 13 deviates from its intended position, deformation of the circulation member 5 can be suppressed. This prevents clogging of the balls 4 within the circulation path 9 due to deformation of the circulation member 5, enabling smooth circulation of the balls 4. In addition, the processing cost of the through-hole 13 can also be reduced.

[0098] In this example, the portions of the pair of side plates 22 separated from the pair of engaging protrusions 23 are pressed against the pair of groove wall surfaces 12 , thereby effectively suppressing the circumferential displacement of the circulation member 5 relative to the nut 3 .

[0099] In this example, the circumferential widths of the groove bottoms of the pair of circumferentially opposed engaging recesses 14 provided in the accommodating groove 10 are narrowed toward the axially inner side of the pair of engaging recesses 14. This prevents the pair of engaging protrusions 23 engaged with the pair of engaging recesses 14 from axially displacing inward. Consequently, axial displacement of the circulation component 5 relative to the nut 3 is also suppressed.

[0100] In this example, for each fixing portion 17 provided at the ends of the two axially outer sides of the circulation component 5, a pair of engaging protrusions 23 are engaged with a pair of engaging recesses 14, and the fixing portion 17 is riveted and fixed relative to the nut 3 so as not to fall off radially outward. Therefore, in this example, compared with the situation where the fixing force is obtained only by inserting (pressing) the foot into the through hole as in the existing structure, the fixing force of the circulation component 5 relative to the nut 3 can be fully improved. Thus, the circulation component 5 can be effectively prevented from being pulled out (floating) radially outward from the accommodating groove 10. In addition, in order to fix the circulation component 5 to the nut 3, it is completed without using fixing members such as screws, thereby preventing the number of parts from increasing and achieving a reduction in manufacturing costs.

[0101] In this example, the fixing portion 17 is arranged at a position axially separated from the leg 16, so that the force applied from the punch to the pair of side plate portions 22 constituting each fixing portion 17 can be limited from being transmitted to each leg 16. Therefore, when the pair of engaging protrusions 23 are formed on the pair of side plate portions 22, deformation of the leg 16 can be suppressed. In addition, the pair of engaging protrusions 23 are formed on the radially outer portions of the pair of side plate portions 22, so that the protrusion amount (protrusion amount) of the pair of engaging protrusions 23 in the circumferential direction can be ensured. Furthermore, only the axial middle portion in the radially outer portions of the pair of side plate portions 22 is plastically deformed in the circumferential direction to form a pair of engaging protrusions 23 in this portion, so that a large force can be prevented from being applied to the nut 3 as the pair of engaging protrusions 23 are formed, thereby suppressing deformation of the nut 3.

[0102] In this example, when forming the pair of engaging protrusions 23 on the pair of side plates 22, the base plate 21 is placed on the groove bottom surface 11 and a punch (not shown) is moved radially inward. This allows the groove bottom surface 11 to serve as a receiving surface. This allows force to be efficiently transmitted from the punch to the pair of side plates 22, causing each side plate 22 to fully plastically deform. Consequently, the engaging protrusions 23 can be securely pressed against the engaging recesses 14, engaging them.

[0103] In this example, the circulation member 5 is entirely disposed inside the receiving groove 10. Therefore, as the receiving groove 10 is formed on the outer peripheral surface of the nut 3, a decrease in the rigidity of the nut 3 can be suppressed. Furthermore, by disposing the circulation member 5 inside the receiving groove 10 so as not to protrude radially outward from the receiving groove 10, an increase in the size of the ball screw device 1 can be suppressed.

[0104] In this example, the circulation member 5 has a rotationally symmetrical shape centered at the axial center, thereby alleviating restrictions on the assembly direction of the circulation member 5. This reduces assembly man-hours and is advantageous in reducing assembly costs.

[0105] In addition, in this example, a pair of engaging recesses 14 are provided at the respective ends of the axially outer sides of a pair of groove wall surfaces 12, a pair of engaging protrusions 23 are provided at the pair of fixing portions 17, and the pair of engaging recesses 14 and the pair of engaging protrusions 23 are engaged at the respective ends of the axially outer sides of the accommodating groove 10. However, the displacement of the circulation component in the radial direction outward and in the circumferential direction relative to the nut can be prevented mainly by the engagement of the engaging recesses and the engaging protrusions, and the present invention is not limited to the illustrated example. For example, it is also possible to provide a engaging recess 14 at the respective ends of the axially outer sides of a pair of groove wall surfaces 12, a engaging protrusion 23 is provided at the pair of fixing portions 17, and each engaging recess 14 and the engaging protrusion 23 are engaged at the respective ends of the axially outer sides of the accommodating groove 10. More specifically, an engaging recess may be provided at an end portion on one axial side of one groove wall surface, and an engaging recess may be provided at an end portion on the other axial side of the other groove wall surface; the engaging protrusion may be formed only on a portion of the side plate portion on the groove wall surface side of a pair of side plates of a fixing portion disposed on one axial side that corresponds to the engaging recess on one axial side; and the engaging protrusion may be formed only on a portion of the side plate portion on the groove wall surface side of a pair of side plates of a fixing portion disposed on the other axial side that corresponds to the engaging recess on the other axial side. Such a structure also falls within the scope of the present invention.

[0106] [Second example]

[0107] use Figures 14 to 17 A second example of the embodiment of the present invention will be described.

[0108] In the ball screw device 1a of this embodiment, the structure of the pair of fixed portions 17a included in the circulation component 5a is modified from that of the first embodiment. Specifically, each of the fixed portions 17a is composed solely of a pair of side plates 22 arranged to oppose (overlap) the pair of groove wall surfaces 12 of the accommodating groove 10. In other words, each fixed portion 17a does not include a base plate portion that rests on the groove bottom surface 11 of the accommodating groove 10.

[0109] In the ball screw device 1a of this example, the pair of side plates 22 can be strongly pressed against the pair of groove wall surfaces 12, thereby more effectively suppressing circumferential displacement of the circulation member 5a relative to the nut 3. Furthermore, compared to the structure of the first example, the two base plates are omitted, thereby reducing the weight of the circulation member 5a. The remaining structure and effects are the same as those of the first example.

[0110] When implementing the present invention, the structures of the respective examples of the above-described embodiments can be appropriately combined and implemented as long as no contradiction occurs.

[0111] When implementing the present invention, the pair of groove wall surfaces constituting the receiving groove are not limited to being parallel to each other. For example, a structure can be adopted in which the groove wall surfaces are inclined in a direction that becomes increasingly separated from each other in the circumferential direction as they move radially outward. When such a structure is adopted, the cross-sectional shape of the receiving groove is a trapezoid.

[0112] When the present invention is implemented, the circulation component can be made of a synthetic resin. In this case, as the synthetic resin, a fiber-reinforced polyamide resin material, for example, obtained by appropriately adding glass fiber to a polyamide 66 resin can be used. In addition, as needed, water resistance can be further improved by appropriately adding an amorphous aromatic polyamide resin (modified polyamide 6T / 6I) or a low-water-absorbing aliphatic polyamide resin (polyamide 11 resin, polyamide 12 resin, polyamide 610 resin, polyamide 612 resin) to the polyamide resin. When the circulation component is made of a synthetic resin, the engaging protrusion provided on the fixing portion can be engaged with the engaging recess provided on the receiving groove of the nut by snapping.

[0113] Explanation of symbols

[0114] 1, 1a—ball screw device, 2—screw shaft, 3—nut, 4—ball, 5, 5a—circulation component, 6—shaft-side ball screw groove, 7—nut-side ball screw groove, 8—load path, 9—circulation path, 10—accommodation groove, 11—groove bottom surface, 12—groove wall surface, 13—through hole, 14—engaging recess, 15—main body, 16—leg, 17, 17a—fixing part, 18—main body side groove, 19—lifting part, 20—leg side groove, 21—base plate , 22—side plate portion, 23—engaging protrusion, 24—return path, 25—lifting path, 26—connecting path, 27—cutting tool, 100—ball screw device, 101—screw shaft, 102—nut, 103—ball, 104—circulation component, 105—shaft side ball screw groove, 106—nut side ball screw groove, 107—circulation path, 108—seat portion, 109—through hole, 110—main body, 111—foot, 112—main body side groove.

Claims

1. A ball screw device, characterized in that: have: A screw shaft having a spiral shaft-side ball screw groove on its outer peripheral surface; a nut having a spiral nut-side ball screw groove on its inner circumferential surface, which forms a spiral load path together with the shaft-side ball screw groove; a circulation member mounted on the outer peripheral surface of the nut and forming a circulation path connecting the starting point and the end point of the load path between the nut and the nut; and A plurality of balls are rollably arranged in the load path and the circulation path, The above nut has: an accommodating groove formed on the outer peripheral surface of the nut, extending linearly in the axial direction, opening at both axially outer end surfaces of the nut, and having a flat groove bottom surface and a pair of groove wall surfaces opposed in the circumferential direction; and A pair of through holes are opened separately on the bottom surface of the groove and penetrate the nut in the radial direction. The pair of groove wall surfaces have engaging recesses at their respective ends on both outer sides in the axial direction. The circulation component is arranged inside the accommodating groove and has a pair of legs inserted into the pair of through holes and a pair of fixing portions provided at both ends on the axially outer sides. Each of the pair of fixing parts has an engaging protrusion, which engages with the engaging recess, thereby preventing the circulation component from being displaced radially outward and circumferentially relative to the nut. The fixing portion includes a pair of side plates, which are arranged to face the pair of groove walls and each of which includes the engagement protrusion. The above-mentioned circulation parts are made of metal. The above-mentioned engaging protrusion is composed of a rivet portion which is pressed against the above-mentioned engaging concave portion by plastic deformation. The fixing portion includes a base plate portion placed on the bottom surface of the groove and having both ends in the circumferential direction connected to the radially inner ends of the pair of side plate portions.

2. The ball screw device according to claim 1, wherein: The engagement recess opens at an axially outer end surface of the nut.

3. A ball screw device, characterized in that: have: A screw shaft having a spiral shaft-side ball screw groove on its outer peripheral surface; a nut having a spiral nut-side ball screw groove on its inner circumferential surface, which forms a spiral load path together with the shaft-side ball screw groove; a circulation member mounted on the outer peripheral surface of the nut and forming a circulation path connecting the starting point and the end point of the load path between the nut and the nut; and A plurality of balls are rollably arranged in the load path and the circulation path, The above nut has: an accommodating groove formed on the outer peripheral surface of the nut, extending linearly in the axial direction, opening at both axially outer end surfaces of the nut, and having a flat groove bottom surface and a pair of groove wall surfaces opposed in the circumferential direction; and A pair of through holes are opened separately on the bottom surface of the groove and penetrate the nut in the radial direction. The pair of groove wall surfaces have engaging recesses at their respective ends on both outer sides in the axial direction. The circulation component is arranged inside the accommodating groove and has a pair of legs inserted into the pair of through holes and a pair of fixing portions provided at both ends on the axially outer sides. Each of the pair of fixing parts has an engaging protrusion, which engages with the engaging recess, thereby preventing the circulation component from being displaced radially outward and circumferentially relative to the nut. The fixing portion includes a pair of side plates, which are arranged to face the pair of groove walls and each of which includes the engagement protrusion. The engaging recess opens at the end surface on the axial outer side of the nut. The fixing portion includes a base plate portion placed on the bottom surface of the groove and having both ends in the circumferential direction connected to the radially inner ends of the pair of side plate portions.

4. A ball screw device, characterized in that: have: A screw shaft having a spiral shaft-side ball screw groove on its outer peripheral surface; a nut having a spiral nut-side ball screw groove on its inner circumferential surface, which forms a spiral load path together with the shaft-side ball screw groove; a circulation member mounted on the outer peripheral surface of the nut and forming a circulation path connecting the starting point and the end point of the load path between the nut and the nut; and A plurality of balls are rollably arranged in the load path and the circulation path, The above nut has: an accommodating groove formed on the outer peripheral surface of the nut, extending linearly in the axial direction, opening at both axially outer end surfaces of the nut, and having a flat groove bottom surface and a pair of groove wall surfaces opposed in the circumferential direction; and A pair of through holes are opened separately on the bottom surface of the groove and penetrate the nut in the radial direction. The pair of groove wall surfaces have engaging recesses at their respective ends on both outer sides in the axial direction. The circulation component is arranged inside the accommodating groove and has a pair of legs inserted into the pair of through holes and a pair of fixing portions provided at both ends on the axially outer sides. Each of the pair of fixing parts has an engaging protrusion, which engages with the engaging recess, thereby preventing the circulation component from being displaced radially outward and circumferentially relative to the nut. The fixing portion includes a pair of side plates, which are arranged to face the pair of groove walls and each of which includes the engagement protrusion. The engaging protrusion is formed on the radially outer side of each of the pair of side plates. The pair of fixing portions are arranged at positions separated axially outward from the pair of legs. The fixing portion includes a base plate portion placed on the bottom surface of the groove and having both ends in the circumferential direction connected to the radially inner ends of the pair of side plate portions.

5. The ball screw device according to any one of claims 1 to 4, characterized in that: The circulation member is disposed inside the accommodating groove so as not to protrude radially outward from the accommodating groove.

6. The ball screw device according to any one of claims 1 to 4, characterized in that: The circulation member has a rotationally symmetrical shape centered at the axial center.

Images