Ball screw device

Abstract

To provide a mechanism that holds a position of a liner motion member without causing complication and radial increase of a structure, on a ball screw device.SOLUTION: An end cap 10 can move axially relative to a nut 3. When a ball screw device is not driven, the end cap 10 is brought closer to the nut 3 to narrow a width t1 of a direction change path 23 and regulate the circulation of balls 4 within a circulation path 20. This increases a rotational resistance of the nut 3, thereby making it more difficult for the nut 3 to rotate, so that an axial position of a screw shaft 2 can be maintained.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In recent years, electrification has progressed with the aim of reducing labor and improving fuel consumption in vehicles, etc., and systems have been developed and introduced to the market that use the power of electric motors to operate, for example, automatic transmissions, brakes, steering, etc. of automobiles. As actuators used for such purposes, electric actuators equipped with a ball screw device that converts the rotational motion of an electric motor into linear motion are known.

[0003] A ball screw device has a screw shaft with a helical screw groove formed on its outer circumferential surface, a nut with a helical screw groove formed on its inner circumferential surface, and a large number of balls arranged in a rolling path formed by the screw groove of the screw shaft and the screw groove of the nut. The ball screw device can transmit power efficiently because the balls roll in the rolling path, reducing the rotational resistance. However, because the rotational resistance is small, when a reverse axial input load is applied to a linear moving member (e.g., a screw shaft), the rotating member (e.g., a nut) may rotate, causing the axial position of the linear moving member to shift.

[0004] Therefore, a ball screw device having a mechanism for preventing the rotation of the rotating member and holding the position of the linear moving member has been proposed. For example, in the ball screw device shown in the following Patent Document 1, a bridge member provided on the nut is rotated by a plunger of an electromagnetic solenoid to restrict the circulation of the balls through the bridge member, thereby preventing the rotation of the nut. In addition, in the ball screw device shown in the following Patent Document 2, a protruding member is protruded into a rolling path formed by the screw groove of the screw shaft and the screw groove of the nut, and the protruding member is engaged with the balls to restrict the circulation of the balls, thereby preventing the rotation of the nut. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-032085 A [Patent Document 2] JP 2017-032109 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the ball screw device of Patent Document 1, an electromagnetic solenoid needs to be provided on the nut, which is a rotating member, and this makes the structure of the ball screw device complex.

[0007] Furthermore, in the ball screw device of Patent Document 2, it is necessary to provide a protruding member and a drive mechanism for driving the protruding member (a pressing member in the document) on the outer diameter side of the rolling path, which leads to an increase in size in the radial direction.

[0008] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a ball screw device with a mechanism for maintaining the position of a linear motion member without complicating the structure or increasing the radial size. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a ball screw device comprising: a threaded shaft having a helical thread groove formed on its outer peripheral surface; a nut having a helical thread groove formed on its inner peripheral surface; an end cap attached to an axial end of the nut; a circulation path having a rolling path formed radially between the thread groove of the threaded shaft and the thread groove of the nut, a direction change path at least a portion of which is formed axially between the end cap and the nut, and a return path penetrating the nut in the axial direction; and a number of balls arranged in the circulation path, The ball screw device is provided such that the end cap is axially movable relative to the nut between a position that restricts passage of the ball through the direction changing path and a position that allows passage of the ball through the direction changing path.

[0010] In this way, in the present invention, the end cap is made axially movable with respect to the nut between a position that restricts the passage of the balls in the direction change path and a position that allows it. When the ball screw device is driven, the end cap is disposed in a position that allows the passage of the balls in the direction change path. When the rotating member is rotated in this state, the balls circulate in the circulation path, suppressing the rotational resistance of the rotating member, thereby improving power transmission efficiency. On the other hand, when the ball screw device is not driven, the end cap is disposed in a position that restricts the passage of the balls in the direction change path. When a reverse input load is input to the linear motion member in this state, the circulation of the balls in the circulation path is restricted, causing the balls to come into sliding contact with the screw groove, increasing the rotational resistance, and thus suppressing the rotation of the rotating member.

[0011] By making the end cap movable in the axial direction relative to the nut, the width of the direction change path formed between them can be changed. Specifically, the end cap can be made movable in the axial direction between a position where the width of at least a part of the direction change path is smaller than the diameter of the ball and a position where the width of the entire direction change path is equal to or larger than the diameter of the ball. The "width" of the direction change path refers to the diameter of the largest imaginary sphere inscribed in the direction change path.

[0012] The above-mentioned ball screw device may have a housing, an electromagnetic coil fixed to the housing, a rotor rotatably provided with respect to the housing, and a biasing member disposed between the rotor and the end cap in the axial direction and biasing the end cap in a direction pressing the end cap against the nut. When the ball screw device is driven, the electromagnetic coil is energized, and the end cap is moved away from the nut against the biasing force of the biasing member by the attraction force of the electromagnetic coil, thereby widening the width of the direction change path. On the other hand, when the ball screw device is not driven, the electromagnetic coil is not energized, and the end cap is moved closer to the nut by the biasing force of the biasing member, thereby narrowing the width of the direction change path. Effect of the Invention

[0013] As described above, in the ball screw device of the present invention, by making the end cap axially movable, the axial position of the linear motion member can be maintained without complicating the structure or increasing the radial size. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a ball screw device according to an embodiment of the present invention, showing a state in which the circulation of balls is restricted. [Diagram 2] 4 is a cross-sectional view of the above-mentioned ball screw device, showing a state in which balls are allowed to circulate. FIG. [Diagram 3] FIG. 11 is a cross-sectional view of a ball screw device according to another embodiment, illustrating a state in which the circulation of the balls is restricted. [Figure 4] FIG. 11 is a cross-sectional view of a ball screw device according to still another embodiment, illustrating a state in which the circulation of the balls is restricted. [Diagram 5] 2 is a plan view of a retaining ring provided in the ball screw device of FIG. 1. [Figure 6] 6 is a cross-sectional view of the retaining ring taken along line X-O1-X in FIG. 5. [Figure 7] FIG. 11 is an enlarged cross-sectional view of the vicinity of a properly assembled retaining ring. [Figure 8] FIG. 11 is an enlarged cross-sectional view of the vicinity of a retaining ring that is assembled in an abnormal state. [Figure 9] FIG. 11 is an enlarged cross-sectional view of the vicinity of a retaining ring that is assembled in an abnormal state. [Figure 10] FIG. 13 is a plan view of a retaining ring according to another example. [Figure 11] 11 is a cross-sectional view of the retaining ring taken along line YOY in FIG. 10. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] FIG. 1 shows a ball screw device 1 according to an embodiment of the present invention, which is incorporated in a linear motion type electric actuator (linear actuator). The ball screw device 1 has a linear motion member including a screw shaft 2, a rotating member including a nut 3, a large number of balls 4 arranged between the screw shaft 2 and the nut 3, and a housing 5 that accommodates them. The nut 3 is rotatably attached to the housing 5 via a bearing 6. The bearing 6 is a rolling bearing having an outer ring, an inner ring, and rolling elements arranged between them, and in the illustrated example, is a ball bearing using steel balls as the rolling elements. The nut 3 is rotated by an electric motor provided in the electric actuator. In this embodiment, a drive gear 8 is fixed to the rotating shaft of the electric motor, and a driven gear 7 that meshes with the drive gear 8 is attached to the outer periphery of the nut 3 via a key 40 so as to be able to transmit torque.

[0017] A helical screw groove 2a is formed on the outer peripheral surface of the screw shaft 2. A helical screw groove 3a is formed on the inner peripheral surface of the nut 3, radially opposing the screw groove 2a of the screw shaft 2. These screw grooves 2a, 3a form a rolling path 21 along which the balls 4 travel under load. In this embodiment, two screw grooves 2a, 3a are formed in the screw shaft 2 and the nut 3, respectively, and these form two rolling paths 21. The number of screw grooves 2a, 3a (rolling paths 21) is not limited, and may be one, or three or more.

[0018] The nut 3 is provided with a through hole 3b penetrating in the axial direction at a position offset from the axis. This through hole 3b forms a return path 22 that returns the ball 4 that has reached the end point of the rolling path 21 to the starting point. The number of through holes 3b (return paths 22) is the same as the number of rolling paths 21, and two are provided in this embodiment.

[0019] End caps 9, 10 are attached to both axial ends of the nut 3. The end caps 9, 10 are provided to form a direction change path 23 that sends the ball 4 from the rolling path 21 to the return path 22 or from the return path 22 to the rolling path 21. One end of the direction change path 23 is connected to the rolling path 21, and the other end of the direction change path 23 is connected to the return path 22. In this embodiment, direction change grooves 9a, 10a are formed on the end faces of the end caps 9, 10, and the direction change path 23 is formed by these direction change grooves 9a, 10a. The number of direction change paths 23 is the same as the number of the rolling path 21 and the return path 22. In this embodiment, two direction change grooves 9a, 10a are formed in each of the end caps 9, 10, and the direction change path 23 is formed by each of the direction change grooves 9a, 10a.

[0020] At least a part of the direction change path 23 is formed between the end caps 9, 10 and the nut 3 in the axial direction. In the illustrated example, one end (the end on the rolling path 21 side) of the direction change grooves 9a, 10a and an end of the screw groove 3a of the nut 3 face each other in the axial direction, and these form one end of the direction change path 23. In addition, an intermediate portion of the direction change grooves 9a, 10a excluding one end and the other end faces the end face of the nut 3 in the axial direction, and these form an intermediate portion of the direction change path 23. The other end of the direction change grooves 9a, 10a (i.e., the other end of the direction change path 23) is connected to the return path 22.

[0021] Two circulation paths 20 are formed by the rolling path 21, the return path 22, and a pair of direction change paths 23 connecting the axial ends of these paths, and a large number of balls 4 are packed in each circulation path 20.

[0022] The end cap 9 on one axial side (left side in FIG. 1) is fixed to one axial end face of the nut 3 with a bolt or the like. The end cap 10 on the other axial side (right side in FIG. 1) is attached to the other axial end face of the nut 3 in a state in which it can move in the axial direction (hereinafter, this end cap 10 is also referred to as the "movable end cap 10"). In the illustrated example, a guide pin 11 is provided protruding from the other axial end face of the nut 3 to the other axial side, and this guide pin 11 is fitted and inserted into an axial hole 10b provided in the movable end cap 10. The guide pins 11 are provided at multiple locations (for example, three locations) in the circumferential direction, and axial holes 10b are provided at multiple locations in the circumferential direction of the movable end cap 10 corresponding to the guide pins 11. This allows the movable end cap 10 to move in the axial direction while sliding on the guide pins 11.

[0023] The ball screw device 1 is provided with an electromagnetic clutch mechanism as a drive means for driving the movable end cap 10 in the axial direction. The electromagnetic clutch mechanism has an electromagnetic coil 12 arranged on the other axial side of the movable end cap 10 (the side opposite to the nut 3). In this embodiment, a plurality of electromagnetic coils 12 are attached to an annular coil holder 13 at equal intervals in the circumferential direction, and this coil holder 13 is fixed to the housing 5 with bolts 14. Electric power is supplied to the electromagnetic coils 12 from the outside via a power supply line 15.

[0024] A rotor 16 is disposed between the electromagnetic coil 12 and the movable end cap 10 in the axial direction. The rotor 16 in the illustrated example has a disk portion 16a disposed between the electromagnetic coil 12 and the movable end cap 10, and cylindrical portions 16b and 16c extending from the inner diameter end and the outer diameter end of the disk portion 16a toward the other axial direction side (the opposite side to the nut 3), and has a substantially C-shaped cross section opening toward the other axial direction side. The electromagnetic coil 12 and the coil holder 13 are disposed in a space surrounded by the disk portion 16a and the cylindrical portions 16b and 16c. The rotor 16 is attached to the housing 5 via a bearing 17 in a rotatable state but immovable in the axial direction. The rotor 16 and the movable end cap 10 are formed of a magnetic material, for example, a steel material. The disk portion 16a of the rotor 16 is provided with an axial through hole 16d. In this embodiment, a plurality of arc-shaped slits are provided as the through hole 16d. This through hole 16d allows the magnetic force generated by the electromagnetic coil 12 to be easily transmitted to the movable end cap 10.

[0025] An elastic member 18 is provided between the rotor 16 and the movable end cap 10 in the axial direction as an urging member for urging the movable end cap 10 toward one axial side (the nut 3 side) with respect to the rotor 16. The elastic member 18 is, for example, a spring, specifically a wave spring (wave washer). The elastic member 18 is disposed between the movable end cap 10 and the rotor 16 in a state where it is elastically compressed in the axial direction. The elastic member 18 is slidable in the circumferential direction with at least one of the rotor 16 and the movable end cap 10. In this embodiment, the elastic member 18 is disposed in an annular groove provided on the end face of the rotor 16, and is slidable in the circumferential direction with both the annular groove of the rotor 16 and the end face of the movable end cap 10.

[0026] When the electric motor stops, that is, when the ball screw device 1 stops, the electromagnetic coil 12 is not energized. In this state, as shown in Fig. 1, the movable end cap 10 is biased axially to one side (the left side in the figure) by the biasing force of the elastic member 18 and pressed against the end face on the other axial side (the right side in the figure) of the nut 3. In this state, the width of at least a part of the direction-changing path 23, specifically, the width t1 at one end of the direction-changing path 23 (the end on the transfer path 21 side) is smaller than the diameter Db of the ball 4 (t1 < Db). As a result, since the ball 4 cannot pass through the direction-changing path 23, the circulation of the ball 4 in the circulation path 20 is restricted. In this state, when an external axial load is applied to the screw shaft 2, this load is transmitted to the nut 3 via the ball 4, and the nut 3 tries to rotate. At this time, since the circulation of the ball 4 in the circulation path 20 is restricted, the ball 4 and the screw grooves 2a, 3a are in sliding contact, and the rotational resistance of the nut 3 increases due to these frictional resistances. As a result, it becomes difficult for the nut 3 to rotate, so the axial movement of the screw shaft 2 is suppressed and the axial position of the screw shaft 2 is maintained.

[0027] On the other hand, when the electric motor is rotationally driven, the nut 3 is rotationally driven via the drive gear 8 and the driven gear 7, and its rotational motion is converted into the linear motion of the screw shaft 2 via the ball 4. While the electric motor is energized in this way, by energizing the electromagnetic coil 12, as shown in Fig. 2, by the attracting force of the electromagnetic coil 12, the movable end cap 10 moves axially to the other side (the right side in the figure) against the biasing force of the elastic member 18 and is attracted to the rotor 16. In this way, by separating the movable end cap 10 from the nut 3, the width t2 over the entire area of the direction-changing path 23 becomes equal to or greater than the diameter Db of the ball 4 (t2 ≧ Db). As a result, the ball 4 can pass through the direction-changing path 23, and the circulation of the ball 4 in the circulation path 20 is allowed. When the nut 3 is rotationally driven by the electric motor, the ball 4 circulates in the circulation path 20, so the frictional resistance between the ball 4 and the screw grooves 2a, 3a, and thus the rotational resistance of the nut 3 is reduced, improving the power transmission efficiency.

[0028] The present invention is not limited to the above embodiment. Other embodiments of the present invention will be described below, but redundant description of the same points as the above embodiment will be omitted.

[0029] The embodiment shown in FIG. 3 differs from the above embodiment in that the rotor 16 is fixed to the nut 3. Specifically, a cylindrical portion 19 is provided as an extension portion extending beyond the movable end cap 10 to the other axial side at the end of the nut 3 on the other axial side (the right side in the figure), and the rotor 16 is fixed to the cylindrical portion 19 by, for example, press fitting. In the illustrated example, the nut 3 and the cylindrical portion 19 are provided integrally as one component. In this case, regardless of whether or not the electromagnetic coil 12 is energized, that is, regardless of the axial position of the movable end cap 10, the nut 3 and the rotor 16 always rotate together. In this embodiment, the bearing 17 (see FIG. 1) that supports the rotor 16 with respect to the housing 5 is not required.

[0030] The embodiment shown in FIG. 4 differs from the embodiment shown in FIG. 3 in that the cylindrical portion 19 is formed separately from the nut 3. Specifically, a flange portion 3c protruding outward is provided at the end of the outer peripheral surface of the nut 3 on the other axial side (right side in the figure), and a flange portion 19a protruding inward is provided at the end of the cylindrical portion 19 on one axial side (left side in the figure). The flange portion 19a of the cylindrical portion 19 is then sandwiched between the flange portion 3c of the nut 3 and the inner ring of the bearing 6 from both axial sides, whereby the cylindrical portion 19 is fixed to the nut 3. As a result, the rotor 16 is fixed to the nut 3 via the cylindrical portion 19.

[0031] Incidentally, the ball screw device 1 shown in FIG. 1 is provided with a retaining ring 30 for axially positioning the inner ring of the bearing 6 supporting the nut 3. More specifically, the bearings 6 are provided on both sides of the driven gear 7 in the axial direction, and the inner rings of these bearings 6 are fitted to the outer peripheral surface of the nut 3. A protruding portion 3e protruding to the outer diameter side is provided at an end portion on one axial side (left side in the figure) of the outer peripheral surface of the nut 3. An annular groove 3f is provided near an end portion on the other axial side (right side in the figure) of the outer peripheral surface of the nut 3, and a retaining ring 30 is attached to this annular groove 3f. The driven gear 7 and the inner rings of the bearings 6 provided on both sides thereof are sandwiched from both axial sides between the protruding portions 3e of the nut 3 and the retaining ring 30, so that the bearings 6 and the driven gear 7 are positioned in the axial direction with respect to the nut 3.

[0032] As such a retaining ring 30, for example, a known bevel-type retaining ring as shown in Figs. 5 and 6 can be used. This retaining ring 30 has a C-shape with a circumferentially divided portion (see Fig. 5). The retaining ring 30 has a radial width that varies in the circumferential direction. Specifically, the center O1 of the inner peripheral surface of the retaining ring 30 and the center O2 of the outer peripheral surface are offset, so that the radial width gradually increases with increasing distance from the circumferential end (divided portion) of the retaining ring 30 (W1>W2). One side surface 31 of the retaining ring 30 (the side surface on the right side in Fig. 6) is a flat surface perpendicular to the axial direction. The inner diameter end of the other side surface 32 (the side surface on the left side in Fig. 6) of the retaining ring 30 is provided with a tapered surface 32a that is inclined toward the one side surface 31 toward the inner diameter side. As shown in FIG. 7, in the annular groove 3f of the nut 3, a side surface facing the tapered surface 32a of the other side surface 32 of the retaining ring 30 is provided with a tapered surface 3g having the same angle as the tapered surface 32a.

[0033] The driven gear 7 and the bearing 6 are assembled to the nut 3 in the following procedure. First, one bearing 6, the driven gear 7, and the other bearing 6 are fitted to the outer circumferential surface of the nut 3 in that order. Then, in a state in which the snap ring 30 is elastically expanded in diameter, one side surface 31 of the snap ring 30 is pressed against the end surface of the inner ring of the other bearing 6 and placed on the outer circumferential surface of the annular groove 3f. By elastically restoring the snap ring 30 to a reduced diameter in this position, as shown in FIG. 7, the tapered surface 32a of the snap ring 30 is pressed against the tapered surface 3g of the annular groove 3f, and the snap ring 30 presses the inner ring of the other bearing 6 to one axial side (the left side in the figure). As a result, the inner rings of the pair of bearings 6 and the driven gear 7 are sandwiched from both axial sides between the snap ring 30 and the protruding portion 3e of the nut 3, and these can be fixed without any backlash in the axial direction. At this time, a radial gap δ is provided between the inner diameter end of the retaining ring 30 and the groove bottom of the annular groove 3f, so that the retaining ring 30 can reliably press the inner ring of the bearing 6 to one side in the axial direction.

[0034] At this time, if the inner diameter end of the retaining ring 30 contacts the groove bottom of the annular groove 3f as shown in FIG. 8, or if the retaining ring 30 is assembled in a state where it is inverted in the axial direction as shown in FIG. 9, the retaining ring 30 will be improperly assembled. In this case, the protruding amount H1 (see FIG. 8) and H2 (see FIG. 9) of the retaining ring 30 from the outer peripheral surface 3h of the nut 3 to the outer diameter side is different from the protruding amount H0 (see FIG. 7) during normal assembly, so that the assembly abnormality of the retaining ring 30 can be confirmed by checking this protruding amount. However, since the conventional bevel-type retaining ring 30 has a radial width that differs in the circumferential direction as shown in FIGS. 5 and 6, even if it is normally attached to the annular groove 3f as shown in FIG. 7, the protruding amount of the retaining ring 30 from the outer peripheral surface 3h of the nut 3 differs in the circumferential direction, so that it is difficult to quantitatively judge the assembly abnormality from this protruding amount. Therefore, in practice, the confirmation is made visually, and there is a problem that the assembly abnormality is inevitably overlooked.

[0035] In addition, as shown in FIGS. 5 and 6, a retaining ring 30 whose radial width gradually varies in the circumferential direction is generally manufactured by press molding. However, in the case of press molding, the portion of the plate material remaining after the retaining ring 30 is punched out is discarded as scrap, resulting in problems of poor material yield and high manufacturing costs.

[0036] Therefore, a retaining ring 30 as shown in Figs. 10 and 11 may be used. This retaining ring 30 differs from the retaining ring 30 shown in Fig. 5 in that the radial width is uniform in the circumferential direction. Specifically, the centers of curvature O of the outer peripheral surface and the inner peripheral surface of the retaining ring 30 coincide with each other, and this makes the radial width of the retaining ring 30 constant (W1 = W2). When this retaining ring 30 is properly attached to the annular groove 3f, the outer diameter of the retaining ring 30 and the amount of protrusion of the retaining ring 30 from the outer peripheral surface 3h of the nut 3 to the outer diameter side are constant in the circumferential direction. On the other hand, if there is an abnormality in the attachment of the retaining ring 30 to the annular groove 3f (see Figs. 8 and 9), the outer diameter of the retaining ring 30 and the amount of protrusion of the retaining ring 30 from the outer peripheral surface 3h of the nut 3 to the outer diameter side differ in the circumferential direction. Therefore, after the retaining ring 30 is assembled into the annular groove 3f, the outer diameter of the retaining ring 30 and the amount of protrusion of the retaining ring 30 from the annular groove 3f are measured at multiple points in the circumferential direction, thereby making it possible to quantitatively determine whether or not there is an assembly error in the retaining ring 30. This makes it possible to reliably detect an assembly error in the retaining ring 30 and to increase the reliability of the quality.

[0037] Furthermore, since the width of the retaining ring 30 is constant, it can be formed by bending, not by punching, as in press molding. Specifically, a metal wire is first formed into a strip of a predetermined cross-sectional shape by drawing. This strip-shaped member is then formed into a circle by bending (e.g., coiling), and cut to a predetermined length, thereby manufacturing a retaining ring 30 with a constant width as shown in Figures 10 and 11. This improves material yield and reduces manufacturing costs.

[0038] The present invention is not limited to the above embodiment. Other embodiments of the present invention will be described below, but redundant description of points similar to the above embodiment will be omitted.

[0039] In the above embodiment, the entire area of ​​the direction change path 23 is formed between the movable end cap 10 and the nut 3 in the axial direction, but this is not limited to the above. For example, the middle part of the direction change path 23 may be formed by a hole provided inside the movable end cap 10.

[0040] In the above embodiment, the present invention is applied to a so-called nut rotation type ball screw device 1 in which the nut 3 is rotated to linearly move the screw shaft 2, but the present invention may be applied to a so-called screw shaft rotation type ball screw device in which the nut 3 is linearly moved by rotating the screw shaft 2. In this case, the nut 3 does not rotate, so the rotor 16 can be omitted. However, it is necessary to provide a mechanism for sliding the electromagnetic coil 12 in the axial direction together with the nut 3. [Explanation of symbols]

[0041] 1. Ball screw device 2 Screw shaft 2a Thread groove 3 Nut 3a Thread groove 4. Ball 5. Housing 6 Bearings 7 Driven gear 8 Drive Gear 9 End Cap 9a Direction change groove 10 End cap (movable end cap) 10a Direction change groove 10b Axial hole 11 Guide pin 12 Electromagnetic coil 16 Rotor 18 Elastic member (biasing member) 20 Circulation Route 21 Turnaround 22 Return Route 23 Turning Point 30 Retaining ring

Claims

1. A screw shaft having a helical thread groove formed on an outer circumferential surface thereof; A nut having a helical thread groove formed on its inner circumferential surface; an end cap attached to an axial end of the nut; A circulation path having a rolling path formed radially between the screw groove of the screw shaft and the screw groove of the nut, a direction change path at least a portion of which is formed axially between the end cap and the nut, and a return path axially penetrating the nut; A ball screw device including a plurality of balls arranged in the circulation path, A ball screw device, wherein the end cap is axially movable relative to the nut between a position that restricts passage of the ball through the direction change path and a position that allows passage of the ball through the direction change path.

2. 2. The ball screw device according to claim 1, wherein the end cap is axially movable between a position where the width of at least a portion of the direction change path is smaller than the diameter of the ball and a position where the width of the entire direction change path is equal to or greater than the diameter of the ball.

3. 2. The ball screw device according to claim 1, further comprising: a housing; an electromagnetic coil fixed to the housing; a rotor rotatably arranged relative to the housing; and a biasing member disposed axially between the rotor and the end cap, biasing the end cap in a direction pressing the end cap against the nut.

4. A bearing is attached to the outer peripheral surface of the nut, and a retaining ring is attached to an annular groove provided on the outer peripheral surface of the nut and positions the bearing in the axial direction, a tapered surface inclined toward the other axial side toward the inner diameter side is provided at an inner diameter end of one axial side surface of the retaining ring, a tapered surface that fits with the tapered surface is provided on a side surface of the annular groove that faces the tapered surface on one side surface of the retaining ring in the axial direction, 2. The ball screw device according to claim 1, wherein the radial width of the retaining ring is constant.

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