Ball screw device

Abstract

The ball screw device of the present disclosure includes a nut, a screw shaft, a plurality of balls, and at least one or more tops for circulating the balls. The outer peripheral surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the top. The inner peripheral surface of the recess is provided with two screw shaft side openings of the outer peripheral raceway surface that open toward the top. The top has a pair of top side openings that open from the outer peripheral surface of the top and connect with the screw shaft side openings, a circulation groove surface that connects with each of the pair of top side openings and whose internal space constitutes a circulation path, and a pair of tongues that are arranged radially outside the circulation groove surface and protrude toward the top side opening. The tip of the tongue is arranged radially outside of the virtual spiral that connects the centers of the plurality of balls that roll on the raceway.

Description

[Technical field]

[0001] The present disclosure relates to a ball screw device. [Background technology]

[0002] The ball screw device includes a nut, a screw shaft inserted into the nut, a plurality of balls arranged between the nut and the screw shaft, and a circulating part. An inner peripheral raceway surface is formed on the inner peripheral surface of the nut. An outer peripheral raceway surface facing the inner peripheral raceway surface is formed on the outer peripheral surface of the screw shaft. A spiral track is formed between the inner peripheral raceway surface and the outer peripheral raceway surface. The plurality of balls are arranged on the track and move in a spiral direction along the track. The circulating part returns the balls that have moved from one end of the track to the other end of the track to one end of the track. One example of the circulating part is a top that returns the balls by one lead.

[0003] In the ball screw device of the following patent document, a recess is formed on the outer circumferential surface of the screw shaft, recessed radially inward. A top is inserted into the recess and attached to the screw shaft. The top has an outer diameter surface facing radially outward and a circulation groove surface recessed radially inward from the outer diameter surface. The circulation groove surface is an S-shaped groove surface that forms an S-shape when viewed from the radial outside. The balls move radially inward within the S-shaped groove surface of the top and ride over the threads of the nut. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2004-225770 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the above-mentioned patent document, when the ball moves radially inward, the ball may be pinched between the S-shaped groove surface (circulation groove surface) and the inner circumferential raceway surface of the nut. Therefore, the smooth rolling of the ball is not ensured. In addition, if the ball is pinched, the groove shoulder of the S-shaped groove surface (circulation groove surface) may be damaged.

[0006] The present disclosure has been made in consideration of the above, and has an object to provide a ball screw device that enables the balls to roll smoothly and prevents damage to the pieces. [Means for solving the problem]

[0007] In order to achieve the above object, a ball screw device according to one aspect of the present disclosure includes a nut having an inner peripheral raceway surface on its inner peripheral surface, a screw shaft inserted into the nut and having an outer peripheral raceway surface on its outer peripheral surface, a plurality of balls arranged on a raceway between the outer peripheral raceway surface and the inner peripheral raceway surface, and at least one or more tops for circulating the balls. The outer peripheral surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the tops. The inner peripheral surface of the recess is provided with two screw shaft side openings of the outer peripheral raceway surface that open toward the tops. The top has a pair of top side openings that open from the outer peripheral surface of the top and connect with the screw shaft side openings, a circulation groove surface that connects with each of the pair of top side openings and whose internal space constitutes a circulation path, and a pair of tongues that are arranged radially outward of the circulation groove surface and protrude toward the top side openings. The tip of the tongue is arranged radially outward of a virtual spiral that connects the centers of the plurality of balls that roll on the raceway.

[0008] According to the present disclosure, the ball that enters the top-side opening from the outer circumferential raceway surface comes into contact with the tip of the tongue. The tip of the tongue also comes into contact with a portion of the ball that is radially outward from the center of the ball. This changes the course of the ball toward the radially inward side, ensuring that the ball moves radially inward. This prevents the ball from being pinched between the circulation groove surface and the inner circumferential raceway surface of the nut, ensuring smooth rolling of the ball. Damage to the groove shoulder of the circulation groove surface is also avoided.

[0009] In a preferred embodiment of the ball screw device, the tang has an inner diameter surface facing inward in the radial direction, the inner diameter surface being inclined so as to be positioned gradually radially inward as it moves away from the tip end portion.

[0010] According to the above-mentioned configuration, after the ball comes into contact with the tip of the tongue, it is guided radially inward along the inclined surface, thereby facilitating the movement of the ball radially inward.

[0011] In a preferred embodiment of the ball screw device, the tip portion is disposed on the inner peripheral raceway surface of the nut.

[0012] According to the above-mentioned configuration, the difference in level between the tip of the tongue and the inner circumferential raceway surface is small, which prevents the ball from getting caught on the tip of the tongue (stopping its movement).

[0013] The circulation groove surface of the ball screw device is an S-shaped groove surface. The S-shaped groove surface is disposed near the top-side opening and has a helical region extending along the helical direction in which the track extends, and a curved region adjacent to the helical region and gradually deviating from the helical direction. The tip portion may be disposed radially outward of the helical region.

[0014] The circulation groove surface of the ball screw device is an S-shaped groove surface. The S-shaped groove surface is disposed near the top-side opening and has a spiral region extending along the spiral direction in which the track extends, and a curved region adjacent to the spiral region and gradually deviating from the spiral direction. The tip portion may be disposed radially outward of the curved region.

[0015] In a preferred embodiment of the ball screw device, the circulation groove surface is an S-shaped groove surface formed in an S-shape. When viewed from the radial outside of the screw shaft, the recess and the piece have a length in a direction intersecting the axial direction that is parallel to the screw shaft that is longer than the length in the axial direction that is parallel to the screw shaft.

[0016] According to the above-mentioned configuration, the ratio of the cross direction in the S-shaped groove surface is increased. In other words, the curvature of the S-shaped groove surface is gentler. As a result, the ball moves smoothly on the S-shaped groove surface.

[0017] Furthermore, the circulation groove surface of the ball screw device may extend in a reverse helical direction that is opposite to the helical direction in which the raceway extends.

[0018] In a preferred embodiment of the ball screw device, the height of the thread on the outer circumferential raceway surface is greater than the height of the thread on the inner circumferential raceway surface.

[0019] According to the above configuration, the height of the thread of the outer peripheral raceway surface is increased, so that the balls are less likely to ride up onto the groove shoulder of the outer peripheral raceway surface. Also, according to the above configuration, the bottom of the outer peripheral raceway surface is deep. Therefore, when the balls move from the outer peripheral raceway surface to the circulation groove surface of the top, the step amount (radial movement amount) between the outer peripheral raceway surface and the circulation groove surface of the top is small. On the other hand, when the top is provided on the nut, the bottom of the inner peripheral raceway surface is shallow, so the step amount (radial movement amount) between the inner peripheral raceway surface and the circulation groove surface of the top is large. Therefore, according to the present disclosure, the radial movement amount of the balls is kept small, and the balls move smoothly on the circulation groove surface.

[0020] In addition, as a preferred embodiment of the ball screw device described above, the circulation groove surface has a pair of inlet / outlet groove surfaces arranged at both ends in the extension direction of the circulation groove surface and extending circumferentially from the frame side opening, and a concave surface arranged between the pair of inlet / outlet groove surfaces and into which the balls sink radially inward.

[0021] According to the above-mentioned configuration, when a radially outward load is applied to the top, the balls rolling on the inlet / outlet groove surface come into contact with the inner peripheral raceway surface of the nut, thereby restricting the top from moving radially outward and preventing the top from coming out of the recess.

[0022] In a preferred embodiment of the ball screw device, the circulation groove surface has a radially inward concave surface into which the balls sink, the concave surface being flat when viewed from the axial direction.

[0023] In a conventional concave surface, when viewed from the axial direction, the center of the S-shaped concave surface is recessed radially inward relative to both ends of the S-shaped concave surface, forming a concave shape. On the other hand, the concave surface of the above configuration is linear when viewed from the axial direction, so the bending angle of the ball when it enters the concave surface is small, and therefore the ball can roll more smoothly.

[0024] In a preferred embodiment of the ball screw device, the groove shape of the top side opening is larger than the groove shape of the screw shaft side opening.

[0025] According to the above-mentioned configuration, even if the top moves radially outward, the edge of the top-side opening does not move inward of the screw shaft-side opening, thereby preventing the edge of the top-side opening from coming into contact with the balls. Effect of the Invention

[0026] According to the ball screw device of the present disclosure, smooth rolling of the balls is ensured, and damage to the groove shoulder of the circulation groove surface is also avoided. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a cross-sectional view of a brake caliper according to an embodiment. [Diagram 2] FIG. 2 is a perspective view of a top and a recess of the ball screw device according to the embodiment. [Diagram 3] FIG. 3 is an enlarged view of the recess and the piece according to the embodiment, viewed from the radially outer side. [Figure 4]FIG. 4 is a cross-sectional view that shows a schematic cross section taken along the center of the S-shaped groove surface. [Diagram 5] FIG. 5 is a view of an opening (screw shaft side opening) of an outer circumferential raceway surface provided on a second opposing surface of the recess, as viewed from the recess. [Figure 6] FIG. 6 is a diagram showing a state in which the top has moved radially outward from the state shown in FIG. [Figure 7] FIG. 7 is an enlarged view of the recess and the portion of the frame arranged at the lower left in FIG. [Figure 8] FIG. 8 is a cross-sectional view taken along line VIII-VIII in FIG. [Figure 9] FIG. 9 is a cross-sectional view of the ball screw device of Comparative Example 1 taken along the center of the groove width of the S-shaped groove surface. [Figure 10] FIG. 10 is a diagram illustrating an abstract view of a frame of Comparative Example 2. [Figure 11] FIG. 11 is a diagram showing an abstract view of a frame according to an embodiment. [Figure 12] FIG. 12 is a schematic diagram of a top of the first modified example viewed from the outside in the radial direction. [Figure 13] FIG. 13 is a schematic diagram of a cross section of a piece of the second modified example taken along the circulation groove surface. [Figure 14] FIG. 14 is a schematic diagram of a cross section of the piece of the third modified example taken along the circulation groove surface. [Figure 15] FIG. 15 is a schematic diagram of a cross section of a piece according to the fourth modification taken along the circulation groove surface. [Figure 16] FIG. 16 is a schematic diagram of a top of the fifth modified example viewed from the outside in the radial direction. [Figure 17] FIG. 17 is a schematic diagram of a top of the sixth modified example viewed from the outside in the radial direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter, referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be appropriately combined.

[0029] Fig. 1 is a cross-sectional view of a brake caliper according to an embodiment. As shown in Fig. 1, the brake caliper 100 is a device for suppressing the rotational motion of a wheel (not shown) by sandwiching a brake disc 101, which rotates together with the wheel, between two brake pads 102 and 103. The brake caliper 100 includes the brake disc 101, two brake pads 102 and 103, an electric actuator 104 that actuates the brake pad 102, and a housing 120.

[0030] The electric actuator 104 includes a motor (not shown) that generates a rotational motion, a reduction gear 110 that decelerates the rotational motion, and a ball screw device 1 that converts the rotational motion into linear motion. In the following description, a direction parallel to an axis O1 of a screw shaft 2 of the ball screw device 1 is referred to as an axial direction. In addition, within the axial direction, a direction in which the brake disc 101 is disposed as viewed from the ball screw device 1 is referred to as a first direction X1, and a direction opposite to the first direction X1 is referred to as a second direction X2.

[0031] The reduction gear 110 is a planetary gear mechanism and includes an input shaft 111, a sun gear 112, a ring gear 113, a plurality of planetary gears 114, a plurality of transmission shafts 115, and a carrier .

[0032] The rotational motion of the motor is input to the input shaft 111. The input shaft 111 extends in the axial direction. An axis O2 of the input shaft 111 is located on an extension of the axis O1. The sun gear 112 penetrates the input shaft 111 and is fixed to the input shaft 111 so as not to rotate. The ring gear 113 is an internal gear centered on the axis O2. The outer circumferential surface of the ring gear 113 is fitted into the housing 120.

[0033] The planetary gear 114 is disposed between the sun gear 112 and the ring gear 113, and meshes with the sun gear 112 and the ring gear 113. A transmission shaft 115 passes through the planetary gear 114. The planetary gear 114 is supported so as to be rotatable about the transmission shaft 115.

[0034] The carrier 116 is an annular part centered on the axis O1. The outer peripheral surface of the carrier 116 is fitted into a bearing 117. Thus, the carrier 116 is rotatably supported by the housing 120. The connecting portion 10 of the screw shaft 2 is inserted into the center of the carrier 116. Furthermore, the carrier 116 and the connecting portion 10 are spline-fitted. Thus, the carrier 116 and the connecting portion 10 are connected so as not to rotate relative to each other. Furthermore, the transmission shaft 115 penetrates the carrier 116 at a position eccentric radially outward from the center of the carrier 116.

[0035] From the above, when a rotational motion is transmitted from a motor (not shown) to the input shaft 111, the sun gear 112 rotates about the axis O2. The planetary gear 114 rotates (revolves) about the axis O2 while rotating (rotating) about the transmission shaft 115. This causes the carrier 116 and the screw shaft 2 to rotate about the axis O1. The rotational speed of the screw shaft 2 is reduced below the rotational speed of the input shaft 111.

[0036] The ball screw device 1 includes a screw shaft 2, a nut 3, balls 4 (not shown in FIG. 1; see FIG. 4), and a plurality of links 5 (only one shown in FIG. 1). The screw shaft 2 includes a connecting portion 10 that connects to a carrier 116, and a screw shaft body 11 that is disposed in a first direction X1 with respect to the connecting portion 10 and is inserted into the nut 3. The outer circumferential surface of the screw shaft body 11 is provided with an outer circumferential raceway surface 13 that extends in the spiral direction, and a plurality of recesses 14 (only one shown in FIG. 1) that are recessed radially inward.

[0037] The nut 3 is formed in a cylindrical shape with a bottom. Thus, the nut 3 has a cylindrical nut body 6 and a lid portion 7 that closes the opening of the nut body 6. An inner peripheral surface of the nut body 6 is provided with an inner peripheral raceway surface 6a that faces an outer peripheral raceway surface 13. A spiral raceway 8 is formed between the outer peripheral raceway surface 13 and the inner peripheral raceway surface 6a. A plurality of balls 4 are arranged in this raceway 8.

[0038] The outer peripheral surface 6b of the nut body 6 abuts against the support surface 121 of the housing 120. The outer peripheral surface 6b of the nut body 6 and the support surface 121 each have a circular shape centered on the axis O1. A small gap is provided between the support surface 121 and the outer peripheral surface 6b of the nut body 6 so that the nut 3 can slide freely. In other words, the support surface 121 supports the nut 3 so that it can slide freely in the axial direction. In addition, a rotation prevention member (not shown) is provided on the outer peripheral surface 6b of the nut body 6. This rotation prevention member regulates the nut 3 so that it does not rotate around the axis O1.

[0039] The cover portion 7 closes an opening in the first direction X1 of the nut body 6. A surface 7a of the cover portion 7 facing the first direction X1 is in contact with the brake pad 102.

[0040] From the above, when the nut 3 moves in the first direction X1 due to the rotation of the screw shaft 2, the brake pad 102 moves in the first direction X1. The brake pad 102 presses the brake disc 101 in the first direction X1, and the brake disc 101 comes into contact with the brake pad 103. As a result, the brake disc 101 is sandwiched between the brake pads 102 and 103, and the rotation of the wheel (not shown) is restricted.

[0041] The top 5 is a circulation device that returns the ball 4 that has moved one lead on the track 8 by one lead. Also, one top 5 is attached to one recess 14. In this disclosure, there is no particular restriction on the method of fixing the top 5 to the recess 14. In other words, the top 5 may or may not be fixed to the recess 14. Therefore, in this disclosure, the top 5 may be loosely fitted into the recess 14. Alternatively, the top 5 may be fitted into the recess 14 with a tightening margin. Alternatively, the top 5 may be glued to the recess 14. Alternatively, the top 5 may be fixed to the recess 14 by crimping. In this way, there is no particular restriction on whether the top 5 is fixed or not.

[0042] When viewed from the axial direction, the multiple pieces 5 (multiple recesses 14) are arranged in different directions from the axis O1. This allows the load acting on the screw shaft 2 from the nut 3 via the balls 4 to be evenly distributed in the circumferential direction. It is more preferable that the multiple pieces 5 are arranged at equal intervals in the circumferential direction.

[0043] Fig. 2 is a perspective view of the top and recess of the ball screw device of the embodiment. As shown in Fig. 2, the top 5 has an S-shaped groove surface 21, a pair of top-side openings 32, 32 opening from the S-shaped groove surface 21, and a pair of tangs 40, 40 protruding toward the top-side opening 32. The recess 14 and the top 5 will be described in detail below.

[0044] Fig. 3 is an enlarged view of the recess and the piece of the embodiment viewed from the radial outside. Hereinafter, as shown in Fig. 3, a direction perpendicular to the axis O1 viewed from the radial outside is referred to as a cross direction Y. Also, a direction parallel to a virtual line Z extending along the track 8 is referred to as a spiral direction. As shown in Fig. 3, the recess 14 has an inner peripheral surface 14b. The inner peripheral surface 14b has a pair of first opposing surfaces 15, 15 and a pair of second opposing surfaces 16, 16.

[0045] The first opposing surfaces 15 are surfaces extending in the intersecting direction Y when viewed from the radial outside. The pair of first opposing surfaces 15, 15 oppose each other in the axial direction. The first opposing surfaces 15 extend linearly when viewed from the radial outside.

[0046] The second opposing surfaces 16 are surfaces extending in the axial direction. The pair of second opposing surfaces 16, 16 face each other in the transverse direction Y. The pair of second opposing surfaces 16 are parallel to the axial direction (see the axis O1). The length from one end to the other end of the first opposing surface 15 in the transverse direction Y is greater than the length from one end to the other end of the second opposing surface 16 in the axial direction.

[0047] The piece 5 is formed point symmetrically with respect to a center C (see FIG. 3). The piece 5 has an outer peripheral surface 24 that is annular with the center C as the center. The outer peripheral surface 24 has a pair of first side surfaces 25, 25 that face the pair of first opposing surfaces 15, 15, and a pair of second side surfaces 26, 26 that face the pair of second opposing surfaces 16, 16.

[0048] The outer shape (outer peripheral surface 24) of the top 5 has the same shape as the inner shape (inner peripheral surface 14b) of the recess 14. Thus, the first side surface 25 extends linearly in the intersecting direction Y, similar to the first opposing surface 15. The second side surface 26 extends linearly in the axial direction, similar to the second opposing surface 16. The length from one end to the other end of the first side surface 25 in the intersecting direction Y is greater than the length from one end to the other end of the second side surface 26 in the axial direction. In addition, the bottom surface 5a of the top 5 abuts against the bottom surface 14a of the recess 14 (see FIG. 4). The bottom surfaces 5a and 14a are flat surfaces.

[0049] From the above, when viewed from the radially outer side, the recess 14 and the link 5 are rectangular. Furthermore, the recess 14 and the link 5 have a longer length in the cross direction Y than in the axial direction.

[0050] The shapes of the recess 14 and the link 5 will be described in more detail. The first opposing surface 15 of the recess 14 is inclined with respect to the intersecting direction Y and is parallel to the helical direction (see imaginary line Z). Similarly, the first side surface 25 of the link 5 is also parallel to the helical direction. In other words, the first opposing surface 15 and the first side surface 25 are parallel to the thread 13a. When viewed from the radially outside, the recess 14 and the link 5 are parallelograms.

[0051] Moreover, the thread 13a of the outer peripheral raceway surface 13 of the screw shaft 2 is cut out in an area overlapping with the recess 14. Therefore, a part of the thread 13a constitutes a thin portion 18 having a small thickness H. Note that the thickness H is the thickness in a direction perpendicular to the spiral direction.

[0052] Here, if the first opposing surface 15 extends in the cross direction Y, the thin portion 18 will have a portion with a large thickness H and a portion with a small thickness H. The portion with the small thickness H has a relatively small strength, and the thread 13a is easily deformed. On the other hand, according to this embodiment, the first opposing surface 15 and the first side surface 25 are parallel to the thread 13a. That is, the thickness H of the thin portion 18 is uniform over the entire direction in which the thin portion 18 extends. Therefore, the thin portion 18 of this embodiment does not have a relatively weak portion, and deformation of the thread 13a (thin portion 18) is suppressed. In addition, the second opposing surface 16 and the second side surface 26 of this embodiment are inclined with respect to the axial direction and are parallel to the orthogonal direction perpendicular to the helical direction (see the virtual line Z).

[0053] Next, the S-shaped groove surface 21 will be described. The extension direction of the S-shaped groove surface 21 (the direction along the imaginary line W passing through the center of the groove width of the S-shaped groove surface 21 in FIG. 3) is referred to as the S-shaped direction. The S-shaped groove surface 21 is a circulation groove surface whose internal space forms a circulation path. Therefore, when the ball 4 moves on the S-shaped groove surface 21, it returns one lead. Also, the S-shaped groove surface 21 is formed in an S-shape when viewed from the outside in the radial direction. In other words, the S-shaped groove surface 21 has a central groove surface 30 arranged in the center of the S-shaped direction of the S-shaped groove surface 21, two inlet / outlet groove surfaces 31 arranged at both ends of the S-shaped direction of the S-shaped groove surface 21, and a bent groove surface 33 connecting the central groove surface 30 and the inlet / outlet groove surface 31. Also, a top-side opening 32 that opens the inlet / outlet groove surface 31 in the cross direction is provided on the second side surface 26 of the top 5.

[0054] The central groove surface 30 and the inlet / outlet groove surface 31 are formed in a straight line, allowing the balls 4 to roll smoothly. The inlet / outlet groove surface 31 is continuous with the outer peripheral raceway surface 13 of the screw shaft 2 via a top-side opening 32. The inlet / outlet groove surface 31 extends in a spiral direction and is parallel (straight) to the outer peripheral raceway surface 13. Therefore, the balls 4 smoothly enter the inlet / outlet groove surface 31 from the outer peripheral raceway surface 13. Since the inlet / outlet groove surface 31 extends in a spiral direction, it is sometimes referred to as a spiral region.

[0055] The bent groove surface 33 (see the imaginary line W1 of the imaginary line W in FIG. 3) is curved and formed in an arc shape when viewed from the radial direction. In other words, the center of the groove width of the bent groove surface 33 deviates significantly from the spiral direction (see imaginary line Z) as it approaches the central groove surface 30. Therefore, the ball 4 rolling on the bent groove surface 33 deviates from the spiral direction as it moves. Since the bent groove surface 33 is curved, it is sometimes referred to as a curved region.

[0056] Here, as described above, the length of the top 5 in the transverse direction Y is greater than its length in the axial direction. Therefore, the length of the central groove surface 30 in the transverse direction Y is also relatively long. As a result, the S-shaped curvature of the S-shaped groove surface 21 (bent groove surface 33) when viewed from the radially outer side (see the portion of the imaginary line W1 of the imaginary line W in FIG. 3) is gentle (the curvature is small). Therefore, the balls 4 roll smoothly on the S-shaped groove surface 21 (bent groove surface 33).

[0057] In addition, one groove shoulder 31a in the axial direction of the entrance / exit groove surface 31 is largely cut out. Note that one groove shoulder 31a in the axial direction is a groove shoulder that is arranged in the direction in which the center C of the piece 5 is arranged, as viewed from the center part (imaginary line W) of the groove width of the entrance / exit groove surface 31. For this reason, one groove shoulder 31a in the axial direction is recessed radially inward from the other groove shoulder 31b in the axial direction (see FIG. 8).

[0058] Fig. 4 is a cross-sectional view showing a schematic cross section taken along the center of the S-shaped groove surface. The imaginary line K1 shown in Fig. 4 is a line extending in the circumferential direction from the outer circumferential raceway surface 13 of the screw shaft 2. In Fig. 4, only a portion of the multiple balls 4 is shown in order to make the S-shaped groove surface 21 easier to see.

[0059] As shown in Fig. 4, the central groove surface 30 and the bent groove surface 33 are disposed radially inward from the imaginary line K1. The two bent groove surfaces 33 are inclined so as to be gradually positioned radially inward from the center of the S-shaped direction of the central groove surface 30. In other words, the cross-sectional shape of the central groove surface 30 and the bent groove surface 33 cut along the S-shaped direction is concave. Therefore, the central groove surface 30 and the bent groove surface 33 are concave surfaces, and the balls 4 rolling on the central groove surface 30 and the bent groove surface 33 sink radially inward.

[0060] To explain the movement of the balls 4 in detail, the balls 4 move radially inward as they approach the center of the S-shaped direction of the central groove surface 30 from one of the two bent groove surfaces 33 (see ball 4A among the balls 4 shown in FIG. 4). Also, the ball 4A moves radially outward as it approaches the other bent groove surface 33 from the center of the S-shaped direction of the central groove surface 30. This causes the balls 4 to ride over the thread 6c of the inner peripheral raceway surface 6a. In this embodiment, the radial movement amount when the balls 4 roll on the S-shaped groove surface 21 (the central groove surface 30 and the bent groove surface 33) is defined as R1.

[0061] In the nut 3 of this embodiment, the height of the thread 6c of the inner peripheral raceway surface 6a is L1. The height of the thread 13a of the outer peripheral raceway surface 13 is L2. The height L2 of the thread 13a of the outer peripheral raceway surface 13 is greater than the height L1 of the thread 6c (L2>L1). Therefore, the ball 4 is less likely to ride up onto the groove shoulder 13c of the outer peripheral raceway surface 13. The height is the distance (depth) from the groove bottom to the groove shoulder.

[0062] As shown in FIG. 4, the inlet / outlet groove surface 31 extends in the circumferential direction from the top-side opening 32. In other words, the groove bottom of the inlet / outlet groove surface 31 has a constant distance from the axis O1. That is, unlike the concave surface (the central groove surface 30 and the bent groove surface 33), the inlet / outlet groove surface 31 of this embodiment is not inclined so as to be located radially inward as it approaches the center of the S-shape. Therefore, the ball 4 rolling on the inlet / outlet groove surface 31 does not move radially inward even when it approaches the center of the S-shape of the central groove surface 30 (see ball 4B among the balls 4 shown in FIG. 4). According to this inlet / outlet groove surface 31, when a radially outward load acts on the top 5, the ball 4B rolling on the inlet / outlet groove surface 31 abuts against the inner peripheral raceway surface 6a of the nut 3. Therefore, the radially outward movement of the top 5 is restricted, and the top 5 does not come off the recess 14.

[0063] In this embodiment, the groove bottom of the inlet / outlet groove surface 31 is located radially inward from the imaginary line K1. Therefore, when a radially outward load acts on the top 5, the top 5 moves slightly radially outward. And the ball 4B rolling on the inlet / outlet groove surface 31 also moves slightly radially outward and abuts against the inner circumferential raceway surface 6a of the nut 3. Therefore, the amount of radially outward movement of the top 5 is restricted to a small amount, and the top 5 does not come out of the recess 14.

[0064] Fig. 5 is a view of the opening (screw shaft side opening) of the outer circumferential raceway surface provided on the second opposing surface of the recess, viewed from the recess. As shown in Fig. 5, the screw shaft side opening 13b of the outer circumferential raceway surface 13 is provided on the second opposing surface 16 of the inner circumferential surface 14b of the recess 14. This screw shaft side opening 13b is adjacent to the top side opening 32 of the top 5 (see Figs. 2 to 4) in the rolling direction of the balls 4 (S-shaped direction).

[0065] 5, when viewed from the rolling direction of the balls 4, the groove shape of the inlet / outlet groove surface 31 of the S-shaped groove surface 21 is larger than the groove shape of the outer circumferential raceway surface 13. In other words, when viewed from the rolling direction of the balls 4, the groove shape of the top side opening 32 is also larger than the groove shape of the screw shaft side opening 13b. In other words, the screw shaft side opening 13b is disposed inside the top side opening 32. Therefore, the top side opening 32 is deeper and has a larger groove width than the screw shaft side opening 13b.

[0066] For this reason, the inlet / outlet groove surface 31 is disposed radially inward of the imaginary line K1 (the outer peripheral raceway surface 13) as shown in Fig. 4. Since the inlet / outlet groove surface 31 is disposed radially inward of the imaginary line K1, the load from the nut 3 acting on the inlet / outlet groove surface 31 via the balls 4 is reduced, and deformation of the top 5 is suppressed.

[0067] Fig. 6 is a diagram showing a state in which the top has moved radially outward from the state shown in Fig. 5. As shown in Fig. 6, the groove shape of the top-side opening 32 is larger than that of the screw shaft-side opening 13b, so that even if the top 5 is displaced radially outward, the top-side opening 32 does not move toward the inside of the screw shaft-side opening 13b. In other words, the ball 4 moving from the outer circumferential raceway surface 13 to the inlet / outlet groove surface 31 is prevented from getting caught on the edge of the top-side opening 32.

[0068] Next, the tongue 40 will be described in detail. As shown in FIG. 2, the top 5 has an outer diameter surface 20 facing radially outward. The outer diameter surface 20 is disposed radially outward from the groove shoulder 13c of the outer circumferential raceway surface 13. The tongue 40 has a semi-cylindrical base portion 41 that protrudes radially outward from the outer diameter surface 20, and a tongue body 42 that protrudes from the base portion 41 toward the top side opening 32. The two tongues 40 are spaced apart from each other in the axial direction. The thread 6c of the nut 3 is disposed between the two tongues 40.

[0069] 3, the tongue 40 extends in the spiral direction. Although not particularly shown, the tongue 40 is housed inside the inner circumferential raceway surface 6a of the nut 3. In addition, the tongue 40 is spaced apart from the inner circumferential raceway surface 6a of the nut 3 so as not to come into contact with it.

[0070] The center of the tongue body 42 in the width direction (orthogonal direction) overlaps with the imaginary line Z. The length H2 of the tongue body 42 in the width direction (orthogonal direction) becomes smaller toward the frame side opening 32, and is tapered. The tip 43 of the tongue body 42 is disposed radially outward from the entrance / exit groove surface 31 (more specifically, disposed radially outward from the portion of the entrance / exit groove surface 31 closer to the bent groove surface 33). The center of the tongue body 42 in the spiral direction is disposed radially outward from the bent groove surface 33. The base 44 of the tongue body 42 is disposed radially outward from the central groove surface 30 (more specifically, disposed radially outward from the portion of the central groove surface 30 closer to the bent groove surface 33).

[0071] As shown in Fig. 4, the tip portion 43 of the tongue body 42 is disposed radially outward of the groove shoulder 6e of the inner circumferential raceway surface 6a. Therefore, the step amount L3 between the groove bottom of the inner circumferential raceway surface 6a and the tip portion 43 is small. The tongue body 42 also has an inner diameter surface 45 facing radially inward. The inner diameter surface 45 is inclined so as to be positioned radially inward as it approaches the base portion 44 from the tip portion 43.

[0072] According to the tongue 40 described above, the ball 4 that enters the S-shaped groove surface 21 from the top-side opening 32 comes into contact with the tip 43 of the tongue body 42 at the inlet / outlet groove surface 31. As a result, the ball 4, which had been moving in a spiral direction, changes direction toward the radially inward side (see arrow A1 in FIG. 4). The ball 4 then moves along the radially inner side of the tongue body 42. Therefore, the path of the ball 4 is closer to the radially inward side than when there is no tongue 40. In addition, since the step amount L3 of the tip 43 is small, the ball 4 moves smoothly without getting caught when it comes into contact with the tip 43.

[0073] Moreover, the ball 4 moving radially inward of the tongue body 42 is guided by the inner diameter surface 45 so as to be gradually positioned radially inward. Therefore, the ball 4 moves along the concave surface (the central groove surface 30 and the bent groove surface 33). This reliably prevents the ball 4 from contacting the thread 6c of the inner circumferential raceway surface 6a.

[0074] Next, effects of the ball screw device 1 of the embodiment will be described. The effects of the ball screw device 1 include a first effect, a second effect, and a third effect. The second effect and the third effect will be described using comparative examples.

[0075] The first effect is exerted when the ball 4 changes its course on the S-shaped groove surface 21. In addition, in this explanation, a case where the ball 4 enters the frame side opening 32 from the screw shaft side opening 13b located at the lower left of Fig. 3 will be explained as an example.

[0076] Fig. 7 is an enlarged view of the recess and the part of the frame arranged at the lower left in Fig. 3. Fig. 8 is a cross-sectional view taken along the line VIII-VIII in Fig. 7. As shown in Fig. 7, the ball 4 that enters the S-shaped groove surface 21 from the frame side opening 32 moves in a spiral direction (imaginary line Z) along the entrance / exit groove surface 31. Then, the ball 4 starts to bend from the imaginary line Z to the second direction X2 at the bent groove surface 33 (see W1 of the imaginary lines W in Fig. 7). Then, the ball 4 moves in a direction inclined by θ1 degrees in the second direction X2 with respect to the spiral direction in the central groove surface 30.

[0077] As a result, the ball 4 receives a pressing load in the second direction X2 while rolling on the bent groove surface 33 and the central groove surface 30 (see arrow A3 in FIG. 7). The portion of the S-shaped groove surface 21 that presses the ball 4 in the second direction X2 is a one-side groove surface (hereinafter referred to as "guide surface 28") that is disposed in the first direction X1 relative to the imaginary line W.

[0078] Also, the amount of recession in the radially inward direction is small at both ends in the S-shape direction of the bent groove surface 33 and the central groove surface 30 (see FIG. 4). If the tang 40 were not present, a part of the ball 4D would be disposed inside the inner raceway surface 6a of the nut 3 and come into contact with the inner raceway surface 6a, as in the case of the ball 4D shown in FIG. 8. The part of the inner raceway surface 6a that is in contact with the ball 4D becomes a one-side groove surface (hereinafter referred to as the opposing surface 6d) that is located in the second direction X2 further than the center of the groove width of the inner raceway surface 6a.

[0079] Therefore, the ball 4D is likely to be sandwiched between a portion of the guide surface 28 close to the groove shoulder 31b of the S-shaped groove surface 21 (hereinafter referred to as the "guide-side contact portion 29") and a portion of the opposing surface 6d close to the groove shoulder 6e (opposing-side contact portion 6f). In other words, there is a high possibility that the rolling of the ball 4 will be hindered and the groove shoulder 31b or the groove shoulder 6e will be damaged.

[0080] On the other hand, according to this embodiment, as shown in Fig. 8, the ball 4E comes into contact with the tip portion 43 of the tongue body 42, and the course of the ball 4E becomes radially inward. Therefore, the ball 4E does not come into contact with the opposing surface 6d (opposing side abutment portion 6f), and the ball 4E is prevented from being sandwiched between the guide side abutment portion 29 and the opposing side abutment portion 6f. From the above, according to the embodiment, a first effect is achieved in that the smooth rolling of the ball 4 is ensured and damage to the groove shoulder 31b is avoided.

[0081] The second effect is due to the fact that the top 5 is provided on the screw shaft 2. Therefore, in Comparative Example 1, a case in which the top 5 is provided on the nut 3 will be given.

[0082] Fig. 9 is a cross-sectional view of the ball screw device of Comparative Example 1 taken along the center of the groove width of the S-shaped groove surface. As shown in Fig. 9, a ball screw device 1001 of Comparative Example 1 includes a screw shaft 1002 and a nut 1003. This ball screw device 1001 differs from the embodiment in that a top 1005 is provided on the nut 1003.

[0083] In addition, the height L11 of the thread 1006c of the inner peripheral raceway surface 1006a of the nut 1003 is L1, which is the same as the embodiment. The height L12 of the thread 1013a of the outer peripheral raceway surface 1013 of the screw shaft 1002 is L2, which is the same as the embodiment. Note that the imaginary line K2 in Fig. 9 is a line extending the inner peripheral raceway surface 1006a in the circumferential direction.

[0084] When the ball 1004 moves on the S-shaped groove surface 1021 of the top 1005, the radial movement amount of the ball 1004 is R2. This radial movement amount R2 is a movement amount that exceeds the height amount L12 of the thread 1013a of the outer peripheral raceway surface 1013 in order to avoid contact with the thread 1013a. In addition, in the inner peripheral raceway surface 1006a of Comparative Example 1, the thread 1006c has a small height amount L11. Therefore, the bottom of the inner peripheral raceway surface 1006a is shallow, and the step amount between the bottom of the inner peripheral raceway surface 1006a and the deepest part of the S-shaped groove surface 1021 is large. In other words, according to Comparative Example 1, the radial movement amount R2 of the ball 1004 is large.

[0085] 4, on the outer circumferential raceway surface 13 of the embodiment, the screw thread 13a has a large height L2. Therefore, the bottom of the outer circumferential raceway surface 13 is deep, and the step between the bottom of the outer circumferential raceway surface 13 and the deepest part of the S-groove surface 21 is small. In other words, according to the embodiment, the radial movement amount R1 of the ball 4 is smaller than the movement amount R2 of the comparative example 1.

[0086] From the above, the step amount (amount of radial movement) of the S-shaped groove surface 1021 of Comparative Example 1 is large. On the other hand, the step amount of the S-shaped groove surface 21 of the embodiment is small. Therefore, according to the embodiment, the inclination in the depth direction (radial direction) of the S-shaped groove surface 21 is gentle, and flatness is ensured. In other words, the embodiment achieves a second effect that the balls 4 rolling on the S-shaped groove surface 21 move smoothly.

[0087] The third effect is due to the fact that the length of the piece 5 (recess 14) in the cross direction Y is longer than the length in the axial direction. Therefore, in Comparative Example 2, a circular piece whose length in the cross direction Y is equal to the length in the axial direction is used.

[0088] FIG. 10 is a diagram showing an abstract of a top of Comparative Example 2. FIG. 11 is a diagram showing an abstract of a top of an embodiment. As shown in FIG. 10, the top 2005 of Comparative Example 2 has a circular outer shape. According to the top 2005 of Comparative Example 2, the angle at which the ball bends in the axial direction along the S-shaped groove surface 2021 is θ11, which is relatively large. Also, according to the top 2005 of Comparative Example 2, the angle at which the ball bends in the radial direction along the S-shaped groove surface 2021 is θ12, which is relatively large.

[0089] 11, the piece 5 of the embodiment is longer in the transverse direction than in the axial direction. Therefore, the angle θ13 at which the ball bends in the axial direction along the S-shaped groove surface 21 is small, and the inclination is gentler than that of Comparative Example 2. In addition, the angle θ14 at which the ball bends in the radial direction along the S-shaped groove surface 21 is also small, and the inclination is gentler than that of Comparative Example 2. Therefore, according to the embodiment, a third effect is achieved in which the ball 4 rolls on the S-shaped groove surface 21 more smoothly.

[0090] In addition, according to the top 2005 of Comparative Example 2 shown in FIG. 10, after the top 2005 is assembled in the recess, it is necessary to rotate the top 2005 to connect the S-shaped groove surface 2021 and the outer circumferential raceway surface (not shown). On the other hand, the recess 14 and the top 5 of the embodiment are parallelograms (rectangles) when viewed from the radially outer side. In other words, the recess 14 and the top 5 are non-circular. Therefore, the S-shaped groove surface 21 and the outer circumferential raceway surface 13 are connected by simply inserting the top 5 into the recess 14. Therefore, it is not necessary to rotate the top 5 to set the orientation of the top 5 after assembling the top 5 in the recess 14.

[0091] As described above, the ball screw device 1 of the embodiment includes the nut 3 having an inner peripheral raceway surface 6a on its inner peripheral surface, the screw shaft 2 inserted into the nut 3 and having an outer peripheral raceway surface 13 on its outer peripheral surface, a plurality of balls 4 arranged in a raceway 8 between the outer peripheral raceway surface 13 and the inner peripheral raceway surface 6a, and at least one or more tops 5 for circulating the balls 4. The outer peripheral surface of the screw shaft 2 is provided with at least one recess 14 that is recessed radially inward and accommodates the tops 5. The inner peripheral surface 14b of the recess 14 is provided with two screw shaft side openings 13b of the outer peripheral raceway surface 13 that open toward the tops 5. The top 5 has a pair of top-side openings 32, 32 that open from the outer circumferential surface 24 of the top 5 and connect to the screw shaft-side opening 13b, a circulation groove surface (S-shaped groove surface 21) that connects to each of the pair of top-side openings 32, 32 and whose internal space constitutes a circulation path, and a pair of tongues 40, 40 that are arranged radially outward of the circulation groove surface (S-shaped groove surface 21) and protrude toward the top-side opening 32. A tip portion 43 of the tongue 40 is arranged radially outward of an imaginary spiral E (see FIG. 4) that connects the centers of the multiple balls 4 that roll on the raceway 8.

[0092] According to the above-described ball screw device 1, it is possible to prevent the balls 4 from being pinched between the circulation groove surface (S-shaped groove surface 21) and the inner peripheral raceway surface 6a. This allows the balls 4 to roll smoothly and prevents the top 5 from being damaged.

[0093] Moreover, the tongue 40 of the embodiment has an inner diameter surface 45 facing inward in the radial direction. The inner diameter surface 45 is inclined so as to be positioned gradually inward in the radial direction as it moves away from the tip portion 43.

[0094] This allows the balls 4 to move smoothly inward in the radial direction.

[0095] Further, the tip portion 43 of the embodiment is disposed on the inner peripheral raceway surface 6 a of the nut 3 .

[0096] According to this, when the ball 4 moves from the entrance / exit groove surface 31 to the radially inward direction of the tongue body 42 , it rolls smoothly without being caught by the tip portion 43 .

[0097] The circulation groove surface in the embodiment is an S-shaped groove surface 21. The S-shaped groove surface 21 is disposed near the top-side opening 32 and has a spiral region extending along the spiral direction in which the track 8 extends, and a bent region adjacent to the spiral region and gradually deviating from the spiral direction. The tip portion 43 is disposed radially outward from the spiral region.

[0098] In addition, the circulation groove surface in the embodiment is an S-shaped groove surface 21 formed in an S-shape. When viewed from the radial outside of the screw shaft 2, the recess 14 and the piece 5 have a length in a cross direction Y that crosses the axial direction longer than the length in the axial direction parallel to the screw shaft 2.

[0099] According to this, the ratio of the S-shaped groove surface 21 in the intersecting direction Y becomes large, and the movement of the ball 4 on the S-shaped groove surface 21 becomes smoother.

[0100] In the embodiment, the height L2 of the thread 13a on the outer circumferential raceway surface 13 is greater than the height L1 of the thread 6c on the inner circumferential raceway surface 6a.

[0101] This makes it difficult for the balls 4 to ride up onto the groove shoulder 13c of the outer circumferential raceway surface 13. Also, the radial inclination of the S-shaped groove surface 21 becomes gentle, so that the movement of the balls 4 on the S-shaped groove surface 21 becomes smooth.

[0102] In addition, the circulation groove surface (S-shaped groove surface 21) in this embodiment has a pair of inlet / outlet groove surfaces 31, 31 arranged at both ends in the extension direction in which the circulation groove surface (S-shaped groove surface 21) extends, extending circumferentially from the frame side opening 32, and a concave surface (central groove surface 30 and bent groove surface 33) arranged between the pair of inlet / outlet groove surfaces 31, 31, into which the ball 4 sinks radially inward.

[0103] With this, even if a radially outward load acts on the top 5, the balls 4 rolling on the inlet / outlet groove surface 31 come into contact with the inner circumferential raceway surface 6a. Therefore, the top 5 is restricted from moving radially outward and does not come out of the recess 14.

[0104] In the embodiment, the outer peripheral surface 24 of the top 5 is provided with a top-side opening 32 of the S-shaped groove surface 21. The inner peripheral surface 14b of the recess 14 is provided with a screw shaft-side opening 13b of the outer peripheral raceway surface 13 that is continuous with the top-side opening 32. The groove shape of the top-side opening 32 is larger than the groove shape of the screw shaft-side opening 13b.

[0105] Even if the top 5 moves radially outward, the edge of the top-side opening 32 does not enter the inside of the screw shaft-side opening 13b.

[0106] Although the ball screw device of the embodiment has been described above, the present disclosure is not limited to the ball screw device exemplified in the embodiment. For example, the ball screw device of the present disclosure may be applied to devices other than the electric actuator 104 and the brake caliper 100.

[0107] In the embodiment, the inner peripheral surface 14b of the recess 14 and the outer peripheral surface 24 of the piece 5 are parallelograms, but the present disclosure may have shapes other than parallelograms. Therefore, in the present disclosure, the inner peripheral surface 14b of the recess 14 and the outer peripheral surface 24 of the piece 5 may be, for example, rectangular or elliptical. In addition, the pair of first opposing surfaces 15, 15 and the pair of first side surfaces 25, 25 extend in the spiral direction, but may extend in the cross direction Y. In addition, the second opposing surface 16 and the second side surface 26 extend in a direction perpendicular to the spiral direction (see virtual line Z), but may extend in the axial direction. In addition, when the recess 14 and the piece 5 are quadrangular, the shape includes a rectangle, a square, a parallelogram, a rhombus, a trapezoid, and the like. In addition, the corners of the quadrangular shape may be rounded, and are not particularly limited.

[0108] In addition, although the circulation groove surface in the embodiment is exemplified as an S-shaped S-shaped groove surface 21, the present disclosure is not limited to this shape. Fig. 12 is a schematic diagram of a frame of modified example 1 viewed from the radial outside. In the present disclosure, the circulation groove surface 221 may extend in a reverse spiral direction Z1 direction that is reverse to the spiral direction Z, as in the frame 205 of modified example 1 shown in Fig. 12. In addition, according to modified example 1, the inlet / outlet groove surface 231 of the circulation groove surface 221 also extends in the reverse spiral direction Z1.

[0109] In addition, the S-shaped groove surface 21 of the embodiment has a central groove surface 30 and an entrance / exit groove surface 31 that are linear, but may have a curved portion in part. In addition, in the embodiment, the center of the groove width of the top side opening 32 (see the imaginary line W in FIG. 3) and the center of the groove width of the outer peripheral raceway surface 13 are arranged so as to coincide with the spiral direction, but in the present disclosure, the center of the groove width of the top side opening 32 and the center of the groove width of the outer peripheral raceway surface 13 may not coincide with the spiral direction (may be shifted in the axial direction). In addition, the entrance / exit groove surface 31 of the embodiment extends in the spiral direction, but the entrance / exit groove surface of the present disclosure may not extend in the spiral direction. In other words, the entrance / exit groove surface may extend in the cross direction Y or in the reverse spiral direction Z1 (see the entrance / exit groove surface 231 in FIG. 12).

[0110] Furthermore, the S-shaped groove surface (circulation groove surface) 21 in the embodiment has an inlet / outlet groove surface 31 that is at a constant distance from the axis O1, but the circulation groove surface of the present disclosure does not need to have an inlet / outlet groove surface 31. Fig. 13 is a schematic diagram of a cross section of a piece of modified example 2 cut along the circulation groove surface. In the present disclosure, as in the piece 305 of modified example 2 shown in Fig. 13, the circulation groove surface 321 may have only a concave surface on the radially inward side into which the balls 4 sink.

[0111] In addition, the concave surface in the present disclosure includes a concave surface 321A (see the imaginary line in FIG. 13) that is flat (linear) when viewed from the axial direction, in addition to the concave surface recessed toward the axis O1 as shown in the modified example 2. Even this flat concave surface 321A is disposed radially inward of the imaginary line K1 (extension of the outer circumferential raceway surface 13). In other words, the ball 4 can ride over the thread 6c (see FIG. 4) of the nut 3. The imaginary line K321 shown in FIG. 13 is the trajectory of the center of the ball 4 rolling on the outer circumferential raceway surface 13 and the circulation groove surface 321. The imaginary line K321A shown in FIG. 13 is the trajectory of the center of the ball 4 rolling on the outer circumferential raceway surface 13 and the concave surface 321A. The imaginary line K8 shown in FIG. 13 is an extension of the trajectory of the center of the ball 4 rolling on the outer circumferential raceway surface 13 (raceway 8). 13, the bending angle θ321A when entering the concave surface 321A from the outer circumferential raceway surface 13 is smaller than the bending angle θ321 when entering the circulation groove surface 321 from the outer circumferential raceway surface 13. Therefore, the concave surface 321A allows the balls 4 to roll (enter) smoothly.

[0112] In addition, in the present disclosure, the height L1 of the thread 6c of the inner peripheral raceway surface 6a may be the same as or greater than the height L2 of the thread 13a of the outer peripheral raceway surface 13. In addition, the link 5 in the embodiment is longer in the transverse direction Y than in the axial direction, but in the present disclosure, the link 5 may be longer in the axial direction.

[0113] In addition, in the present disclosure, there is no particular limitation on the material and manufacturing method of the top. For example, the top may be manufactured from a resin material such as nylon 66 resin. The top may also be manufactured by a metal powder injection molding method. The top of this embodiment is formed from one part, but may be composed of two or more parts. When the top is composed of two or more parts, there is no particular limitation on the dividing surface. It may be divided into two parts, an inner circumference side and an outer circumference side, or a first direction X1 and a second direction X2.

[0114] In addition, with regard to the radial position of the tip portion 43 of the tongue 40, the tip portion 43 in the embodiment is disposed within the inner peripheral raceway surface 6a of the nut 3, but the present disclosure is not limited thereto as long as it can guide the balls 4 radially inward. In other words, it is sufficient that the tip portion 43 is disposed radially outward of the imaginary spiral E (see FIG. 4) connecting the centers D of the balls 4 rolling on the raceway 8. If disposed radially outward of the imaginary spiral E, the tip portion 43 comes into contact with the radially outer side of the center D of the balls 4. This is because the course of the balls 4 can be changed radially inward.

[0115] In addition, although the two tongues 40 in this embodiment are spaced apart from each other, in the present disclosure, the distance Q (see FIG. 12) between the tongue bodies 42 may be smaller than the diameter of the ball 4. This prevents the ball 4 from falling (getting caught) in the gap between the tongue bodies 42. In other words, the ball 4 moves smoothly from the inner diameter surface 45 of one tongue body 42 along the inner diameter surface 45 of the other tongue body 42.

[0116] In addition, regarding the position of the tip 43 of the tongue body 42, the tip 43 of this embodiment is disposed radially outward of the spiral region (entrance / exit groove surface 31), but the present disclosure is not limited thereto. The position at which the ball 4 is sandwiched in the S-shaped groove surface 21 is not fixed. Therefore, the tip 43 of the present disclosure may be disposed closer to the top side opening 32 than the predetermined position at which the ball 4 is sandwiched in the S-shaped groove surface 21. In other words, the present disclosure is not particularly limited, and the tip 43 of the tongue 40 may be disposed radially outward of the bent region (bent groove surface 33) or may be disposed at the end of the S-shaped direction of the central groove surface 30. Modified examples will be described below.

[0117] FIG. 14 is a schematic diagram of a cross section of the top of the third modification cut along the circulation groove surface. The top 405 of the third modification has a pair of tongues 440. The tip 443 of the tongue body 442 of the tongue 440 is in contact with the imaginary line N1. This imaginary line N1 is a straight line passing through the axis O1 of the screw shaft 2 and the groove bottom 432N of the top-side opening 432. According to this tongue 440, the ball 4 that enters the top-side opening 432 is immediately guided radially inward. Therefore, the possibility of the ball 4 being pinched is extremely small. In addition, if the tip 443 exceeds the imaginary line N1, the ball 4 is prevented from abutting against the inner circumferential raceway surface 6a, and the load capacity of the ball screw device is reduced. Therefore, according to the third modification, there is no risk of the load capacity of the ball screw device being reduced. From the above, in the present disclosure, it is preferable that the tip 443 does not exceed the imaginary line N1.

[0118] 15 is a schematic diagram of a cross section of a top of Modification 4 cut along the circulation groove surface. A top 505 of Modification 4 has a pair of tongues 540. A tip 543 of a tongue body 542 of the tongue 540 is in contact with an imaginary line N2. This imaginary line N2 extends linearly along the second side surface 526 of the top 505. Even in the tongue 540 according to Modification 4, the position of the tip 543 is closer to the top-side opening 532 than in the embodiment. This reduces the possibility of the ball 4 being caught.

[0119] FIG. 16 is a schematic diagram of a top of the fifth modification viewed from the radial outside. As shown in FIG. 16, the top 605 of the fifth modification has a pair of tongues 640 (only one is shown). In addition, the top 605 has a circumferential (spiral) length N3 from the axis O1 to the second side surface 626 viewed from the radial outside. The imaginary line N4 shown in FIG. 16 extends linearly in the axial direction and is disposed at a position where the distance from the axis O1 in the circumferential (spiral) direction is half of N3. In the fifth modification, the tip 643 of the tongue body 642 is in contact with the imaginary line N3 viewed from the radial outside. Thus, the tip 643 of the fifth modification is farther away from the top-side opening 632 than the tip 443 of the third modification and the tip 543 of the fourth modification, but the present disclosure may be such a tongue 640.

[0120] Modifications 3 to 5 have been described above, but in the present disclosure, the tip of the tongue may be disposed between imaginary line N1 (see FIG. 14) and imaginary line N2 (see FIG. 15), or between imaginary line N2 (see FIG. 15) and imaginary line N4 (see FIG. 16). Even with such a tongue, smooth rolling of the balls can be ensured, and damage to the groove shoulder of the circulation groove surface can be avoided.

[0121] According to the embodiment, the pair of tangs 40, 40 are arranged to be spaced apart from each other in the axial direction (see FIG. 2, FIG. 3, etc.). That is, a space is provided between the pair of tangs 40, 40, but in the present disclosure, the pair of tangs 40, 40 may be connected to each other. FIG. 17 is a schematic diagram of a block of the sixth modification seen from the radial outside. More specifically, as shown in FIG. 17, the present disclosure may be a block 705 having a wall portion 750 connecting the pair of tangs 740, 740 to each other. According to the block 705 of the sixth modification, the ball 4 is prevented from falling (moving radially outward) between the pair of tangs 740, 740. Therefore, the ball 4 is prevented from contacting the groove shoulder 6e (see FIG. 8) of the nut 3.

[0122] 17, in the present disclosure, in the bent groove surface 733 (bent region W1) of the S-shaped groove surface 721, an inner circumferential side surface 733a disposed on the inner circumferential side may be arc-shaped (R-shaped) when viewed from the radially outer side. This makes it difficult for the ball 4 to get caught on the inner circumferential side surface 733a, ensuring smooth rolling of the ball 4.

[0123] The present disclosure may also be implemented in the following combinations: (1) A nut having an inner raceway on its inner circumferential surface; A screw shaft that is inserted into the nut and has an outer circumferential raceway on its outer circumferential surface; a plurality of balls disposed in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface; At least one piece for circulating the ball; Equipped with The outer circumferential surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the piece, The inner peripheral surface of the recess is provided with two screw shaft side openings of the outer peripheral raceway surface that open toward the top, The frame is: A pair of top-side openings that open from the outer peripheral surface of the top and connect to the screw shaft-side opening; a circulation groove surface connected to each of the pair of frame side openings and having an internal space that constitutes a circulation path; A pair of tongues are disposed radially outward of the circulation groove surface and protrude toward the top side opening; having The tip of the tongue is disposed radially outward of an imaginary spiral connecting the centers of the balls rolling on the raceway. Ball screw device. (2) The tang has an inner diameter surface facing radially inward, The inner diameter surface is inclined so as to be positioned gradually radially inward as it moves away from the tip end. A ball screw device as described in (1). (3) The tip portion is disposed on the inner peripheral raceway surface of the nut. A ball screw device as described in (1) or (2). (4) The circulation groove surface is an S-shaped groove surface formed in an S-shape, The S-shaped groove surface is a spiral region disposed near the top opening and extending along the spiral direction in which the track extends; a bend region adjacent to the helical region and gradually deviating from the helical direction; having The tip portion is disposed radially outward from the helical region. A ball screw device according to any one of (1) to (3). (5) The circulation groove surface is an S-shaped groove surface formed in an S-shape, The S-shaped groove surface is a spiral region disposed near the top opening and extending along the spiral direction in which the track extends; a bend region adjacent to the helical region and gradually deviating from the helical direction; having The tip portion is disposed radially outward from the bending region. A ball screw device according to any one of (1) to (3). (6) The circulation groove surface is an S-shaped groove surface formed in an S-shape, When viewed from the radial outside of the screw shaft, the recess and the piece have a length in a direction intersecting the axial direction that is parallel to the screw shaft that is longer than the length in the axial direction. A ball screw device according to any one of (1) to (5). (7) The circulation groove surface extends in a reverse helical direction opposite to the helical direction in which the raceway extends. A ball screw device according to any one of (1) to (3). (8) The height of the thread on the outer circumferential raceway surface is greater than the height of the thread on the inner circumferential raceway surface. A ball screw device according to any one of (1) to (7). (9) The circulation groove surface is A pair of inlet / outlet groove surfaces are disposed at both ends of the extension direction of the circulation groove surface and extend in a circumferential direction from the frame side opening; a concave surface disposed between the pair of inlet / outlet groove surfaces and into which the ball sinks radially inward; Possesses A ball screw device according to any one of (1) to (8). (10) the circulation groove surface has a concave surface on the radially inner side into which the balls sink, The concave surface is linear when viewed in the axial direction. A ball screw device according to any one of (1) to (8). (11) The groove shape of the frame side opening is larger than the groove shape of the screw shaft side opening A ball screw device according to any one of (1) to (10). [Explanation of symbols]

[0124] 1, 1001 Ball screw device 2, 1002 Screw shaft 3, 1003 Nut 4. 1004 balls 5, 205, 305, 405, 505, 605, 705, 1005, 2005 frames 6 Nut body 6a, 1006a Inner raceway surface 6c, 1006c thread 6e groove shoulder 6f Opposite side contact part 8 orbits 11 Screw shaft body 13 Outer raceway surface 13a thread 13b Screw shaft side opening 13c groove shoulder 14 Recess 15 First opposing surface 16 Second opposing surface 18 Thin Section 20 Outer diameter surface 21, 1021, 2021 S-shaped groove surface (circulation groove surface) 25 First aspect 26 Second aspect 29 Guide side contact part 30 Central groove surface 31 Entrance / exit groove surface 32 Frame side opening 33 Bend groove surface 40 Tongue 100 Brake Caliper 104 Electric Actuator 120 Housing

Claims

1. A nut having an inner raceway on its inner circumferential surface; A screw shaft that is inserted into the nut and has an outer circumferential raceway on its outer circumferential surface; a plurality of balls disposed in a raceway between the outer circumferential raceway surface and the inner circumferential raceway surface; At least one or more pieces for circulating the ball; Equipped with The outer circumferential surface of the screw shaft is provided with at least one recess that is recessed radially inward and accommodates the piece, The inner peripheral surface of the recess is provided with two screw shaft side openings of the outer peripheral raceway surface that open toward the top, The frame is: A pair of top-side openings that open from the outer peripheral surface of the top and connect to the screw shaft-side opening; a circulation groove surface connected to each of the pair of frame side openings and having an internal space that constitutes a circulation path; A pair of tongues are disposed radially outward of the circulation groove surface and protrude toward the top side opening; having The tip of the tongue is disposed radially outward of an imaginary spiral connecting the centers of the balls rolling on the raceway. Ball screw device.

2. The tang has an inner diameter surface facing radially inward, The inner diameter surface is inclined so as to be positioned gradually radially inward as it moves away from the tip end. The ball screw device according to claim 1 .

3. The tip portion is disposed on the inner peripheral raceway surface of the nut. The ball screw device according to claim 1 .

4. The circulation groove surface is an S-shaped groove surface formed in an S-shape, The S-groove surface is a spiral region disposed near the top opening and extending along the spiral direction in which the track extends; a bend region adjacent to the helical region and gradually deviating from the helical direction; having The tip portion is disposed radially outward from the helical region. The ball screw device according to claim 1 .

5. The circulation groove surface is an S-shaped groove surface formed in an S-shape, The S-groove surface is a spiral region disposed near the top opening and extending along the spiral direction in which the track extends; a bend region adjacent to the helical region and gradually deviating from the helical direction; having The tip portion is disposed radially outward from the bending region. The ball screw device according to claim 1 .

6. When viewed from the radial outside of the top, a direction perpendicular to the axis of the screw shaft is defined as a cross direction, In the intersecting direction, a direction away from the axis is defined as an outer side of the intersecting direction, The tip portion is disposed on the outer side of the recess portion in the intersecting direction. The ball screw device according to claim 1 .

7. The circulation groove surface is an S-shaped groove surface formed in an S-shape, When viewed from the radial outside of the screw shaft, the recess and the piece have a length in a direction intersecting the axial direction that is parallel to the screw shaft that is longer than the length in the axial direction. The ball screw device according to claim 1 .

8. The circulation groove surface extends in a reverse helical direction opposite to the helical direction in which the raceway extends. The ball screw device according to claim 1 .

9. The entire portion of the circulation groove surface extending from one end to the other end in the extension direction extends in the reverse spiral direction. The ball screw device according to claim 8.

10. The height of the thread on the outer circumferential raceway surface is greater than the height of the thread on the inner circumferential raceway surface. The ball screw device according to claim 1 .

11. The circulation groove surface is A pair of inlet / outlet groove surfaces are disposed at both ends of the extension direction of the circulation groove surface and extend in a circumferential direction from the frame side opening; a concave surface disposed between the pair of inlet / outlet groove surfaces and into which the ball sinks radially inward; Possesses The ball screw device according to claim 1 .

12. The groove bottom of the inlet / outlet groove surface has a constant distance from the axis of the screw shaft. The ball screw device according to claim 11.

13. the circulation groove surface is constituted only by a concave surface into which the balls sink radially inward, The concave surface is linear when viewed in the axial direction. The ball screw device according to claim 1 .

14. The groove shape of the frame side opening is larger than the groove shape of the screw shaft side opening The ball screw device according to claim 1 .

15. The circulation groove surface is composed only of a concave surface into which the balls sink radially inward, The concave surface is arc-shaped when viewed in the axial direction. The ball screw device according to claim 1 .

16. The pair of tangs are spaced apart from each other in the axial direction, Between the pair of tongues, an opening is formed that opens the circulation path radially outward. The ball screw device according to claim 1 .

17. The maximum radial movement of the ball moving on the circulation groove surface is smaller than the diameter of the ball. The ball screw device according to claim 1 .

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