Actuator

Abstract

This actuator provides a nut that can be slidably supported even when fitted with a sleeve, and further reduces the labor involved in manufacturing. [Solution] The actuator of this disclosure comprises a ball screw device having a screw shaft, a nut, a plurality of balls and a circulation section, a sleeve that fits the outer circumference of the nut, a sliding bearing that fits the outer circumference of the nut, and a housing. The screw shaft is oriented in a direction parallel to the central axis and in the axial direction. The housing extends in the axial direction and has a housing space that accommodates the ball screw device, the sleeve and the sliding bearing. The nut has a through hole that penetrates in the radial direction. The circulation section is inserted into the through hole. The sleeve covers at least a portion of the circulation section from the radially outer side. The sliding bearing is positioned on one side in the axial direction relative to the sleeve. The outer diameter of the sliding bearing is larger than the outer diameter of the sleeve. The sliding bearing is supported so as to be axially slidable on the inner circumferential surface of the housing space.

Description

Technical Field

[0001] The present disclosure relates to an actuator.

Background Art

[0002] An actuator includes a ball screw device that converts rotational motion into linear motion or converts linear motion into rotational motion. The ball screw device has a screw shaft, a nut, a plurality of balls disposed in an orbit between the screw shaft and the nut, and a circulation part. The circulation part circulates the balls that have moved from one end of the orbit to the other end back to the one end of the orbit. In Patent Document 1 below, a cam that circulates the balls by about one lead is used as the circulation part.

[0003] Also, when a cam is used as the circulation part, a through-hole penetrating in the radial direction is formed in the nut. Then, the cam is attached to the nut by inserting the cam into the through-hole from the outside in the radial direction. In Patent Document 1 below, in order to prevent the cam from falling off to the outside in the radial direction, after inserting the cam into the through-hole, a metal sleeve formed in a cylindrical shape is fitted to the outer peripheral side of the nut. Further, after fitting the sleeve, the end portion of the sleeve is caulked. Thereby, the caulked portion is caught by the groove on the outer peripheral surface of the nut, and the sleeve does not fall off from the nut.

[0004] Also, in the actuator of Patent Document 2 below, a ball screw device is used so that the torque generated by the motor is transmitted to the screw shaft. That is, in Patent Document 2 below, the screw shaft rotates and the nut moves linearly. Also, in Patent Document 2 below, the outer peripheral surface of the nut is supported by the housing so as to be slidable in the axial direction.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In recent years, there has been consideration of supporting a nut fitted with a sleeve in a housing so that it can slide freely. However, metal sleeves are formed by press-forming metal materials, and the processing accuracy is not high. In other words, it is difficult to manufacture a sleeve with sufficient thickness to slide freely against the housing with high precision. Also, metal sleeves have low hardness and require special surface treatment. On the other hand, it is also difficult to manufacture resin sleeves with high precision. Furthermore, resin sleeves wear down due to sliding. For these reasons, it is difficult to support a nut fitted with a sleeve in a housing so that it can slide freely, regardless of whether it is made of metal or resin. In addition, according to the above-mentioned Patent Document 1, it is necessary to crimp the sleeve. Therefore, there is a desire to reduce the labor involved in manufacturing.

[0007] This disclosure has been made in view of the above, and aims to provide an actuator that can slidably support a nut fitted with a sleeve, and further reduces the labor involved in manufacturing. [Means for solving the problem]

[0008] To achieve the above objective, an actuator according to one aspect of the present disclosure comprises a ball screw device, a sleeve that fits the outer circumference of a nut of the ball screw device, a sliding bearing that fits the outer circumference of the nut, and a housing. The ball screw device has a screw shaft, a nut, a plurality of balls, and at least one circulation part. The screw shaft is oriented in a direction parallel to the central axis and in the axial direction. The housing extends in the axial direction and has a housing space that accommodates the ball screw device, the sleeve, and the sliding bearing. The nut has a through hole that penetrates radially. The circulation part is inserted into the through hole. The sleeve covers at least a portion of the circulation part from the radially outside. The sliding bearing is positioned relative to the sleeve in one axial direction. The outer diameter of the sliding bearing is larger than the outer diameter of the sleeve. The sliding bearing is slidably supported in the axial direction on the inner circumferential surface of the housing space.

[0009] A sliding bearing with a larger outer diameter than the sleeve is fitted into the nut. Therefore, there is no need to slide the sleeve on the inner surface of the housing space. Thus, according to this disclosure, even a nut with a fitted sleeve can be slidably supported in the housing. Furthermore, when the sleeve moves to one side in the axial direction, it comes into contact with the sliding bearing. Therefore, the sleeve is prevented from moving to one side in the axial direction and falling off the nut. As a result, according to this disclosure, the crimping work of the sleeve is unnecessary, and the labor required to manufacture the actuator is reduced.

[0010] Furthermore, in the actuator described above, a recess is formed on the outer circumferential surface of the nut, which is recessed radially inward and extends circumferentially. The sliding bearing is formed in a C-shape when viewed from the axial direction. The inner diameter of the sliding bearing before it is attached to the nut is smaller than the outer diameter of the nut. By expanding the diameter of the sliding bearing, the nut is inserted into the circumferential side of the sliding bearing, and the sliding bearing is fitted into the recess.

[0011] According to the above configuration, the sliding bearing catches on the inner surface of the recess and does not move in the axial direction. Therefore, the sliding bearing is prevented from falling out.

[0012] Furthermore, in the actuator described above, when the sliding bearing is fitted into the recess, a gap is formed between one end in the circumferential direction and the other end in the circumferential direction.

[0013] The sliding bearing may expand due to thermal stress due to sliding against the housing. If the sliding bearing expands radially outward, the minute gap between it and the inner circumferential surface of the housing will decrease, impairing its sliding performance. On the other hand, with the above configuration, even if the sliding bearing expands due to thermal stress, this expansion is absorbed by the gap between one end and the other end in the circumferential direction. Therefore, the impairment of the sliding performance of the sliding bearing due to thermal stress is avoided.

[0014] Furthermore, in the actuator described above, the gap in the sliding bearing is inclined with respect to the axial direction.

[0015] The inner surface of the housing wears down due to sliding by the sliding bearing. If the gap of the sliding bearing extends in the axial direction, a portion of the inner surface of the housing will not wear down because it is opposite the gap, and this portion will become a protrusion that extends in the axial direction. On the other hand, with the above configuration, the entire circumference of the inner surface of the housing slides and wears down with the sliding bearing. Therefore, no protrusion is formed.

[0016] Furthermore, in the actuator described above, the inner diameter of the sliding bearing before it is attached to the nut is smaller than the outer diameter of the nut. The sliding bearing is press-fitted onto the outer circumference of the nut, thereby creating a tight fit on the outer surface of the nut.

[0017] According to the above configuration, the sliding bearing does not move in the axial direction. Therefore, the sliding bearing is prevented from falling out.

[0018] In addition, in the actuator described above, a retaining ring that abuts against the sliding bearing from one side in the axial direction is provided. A groove into which the retaining ring fits is formed on the outer peripheral surface of the nut.

[0019] According to the above configuration, movement of the sliding bearing in one direction in the axial direction is restricted by the retaining ring. Therefore, the sliding bearing is prevented from falling off.

[0020] In addition, in the actuator described above, the accommodation space has a first accommodation space disposed on one side in the axial direction in the accommodation space and a second accommodation space disposed on the other side in the axial direction in the accommodation space. The first accommodation space and the second accommodation space are formed in a circular shape centered on the central axis when viewed from the axial direction. The second accommodation space is formed to have a larger diameter than the first accommodation space. The nut and the sleeve are disposed across the first accommodation space and the second accommodation space. A first inner peripheral surface of the first accommodation space slidably supports the sliding bearing. The other end portion of the nut in the axial direction is movable in the axial direction and non-rotatable around the central axis with respect to a second inner peripheral surface of the second accommodation space.

[0021] According to the above configuration, when the screw shaft rotates, the nut moves in the axial direction without rotating together with the screw shaft.

Advantages of the Invention

[0022] According to the present disclosure, it is possible to slidably support even a nut fitted with a sleeve. In addition, the labor required for manufacturing the actuator can be reduced.

Brief Description of the Drawings

[0023] [Figure 1] [[ID=Z7]]FIG. 1 is a view of the actuator of Embodiment 1 as viewed from a direction orthogonal to the central axis. [Figure 2] FIG. 2 is a view of the actuator of Embodiment 1 in a state where the nut, the sleeve, and the sliding bearing are cut in the axial direction as viewed from a direction orthogonal to the central axis. [Figure 3] Figure 3 is an enlarged view of the concave portion in Figure 2. [Figure 4] Figure 4 is an enlarged view of the concave portion in Figure 3. [Figure 5] Figure 5 is a cross-sectional view of the sliding bearing of Modification 1 cut in the axial direction. [Figure 6] Figure 6 is a view of the actuator of Modification 2 as seen from a direction orthogonal to the central axis. [Figure 7] Figure 7 is a cross-sectional view of the sliding bearing of Modification 2 cut in the axial direction. [Figure 8] Figure 8 is a cross-sectional view of the sliding bearing of Modification 3 cut in the axial direction.

MODE FOR CARRYING OUT THE INVENTION

[0024] Hereinafter, the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited by the following mode for carrying out the invention (hereinafter referred to as the embodiment). Also, the constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, substantially the same ones, and those within a so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate.

[0025] (Embodiment 1) Figure 1 is a view of the actuator of Embodiment 1 as seen from a direction orthogonal to the central axis. As shown in Figure 1, the actuator 100 of Embodiment 1 includes a housing 110, a motor (not shown), a ball screw device 1, a sleeve 5, and a sliding bearing 6. The ball screw device 1 includes a screw shaft 2, a nut 3, a plurality of balls (not shown), and a collar 4 which is a circulation part (not shown in Figure 1, see Figure 2). Hereinafter, the direction parallel to the central axis O of the screw shaft 2 is referred to as the axial direction. Also, the direction orthogonal to the central axis O is referred to as the radial direction.

[0026] The housing 110 is a component that houses each component. The housing 110 has a housing space 111 that extends in the axial direction. The housing space 111 has a first housing space 112 located on one side in the axial direction and a second housing space 113 located on the other side in the axial direction. In the following, the direction in the axial direction where the first housing space 112 is located, as viewed from the second housing space 113, will be referred to as the first direction X1, and the opposite direction will be referred to as the second direction X2.

[0027] The first and second containment spaces 112 and 113 are formed in a circular shape around the central axis O when viewed from the axial direction. The diameter R1 of the first containment space 112 (see Figure 1) is smaller than the diameter R2 of the second containment space 113 (see Figure 1).

[0028] The inner circumferential surface 114 surrounding the housing space 111 has a first inner circumferential surface 115 surrounding the first housing space 112 and a second inner circumferential surface 116 surrounding the second housing space 113. The first inner circumferential surface 115 is a sliding surface that supports the nut 3 so that it can slide freely in the axial direction. The second inner circumferential surface 116 has a plurality of grooves 117 (only one is shown in Figures 1 and 2) that are recessed radially outward and extend in the axial direction. A key 118 that extends in the axial direction is fitted into the grooves 117. A part of the key 118 protrudes radially inward from the second inner circumferential surface 116. The key 118 is restricted by a retaining ring 119 from moving in the second direction X2.

[0029] Figure 2 is a view of the actuator of Embodiment 1, with the nut, sleeve, and sliding bearing cut in the axial direction, as seen from a direction perpendicular to the central axis. As shown in Figure 2, the screw shaft 2 comprises a connecting portion 20 and a screw shaft body 21 arranged sequentially in the first direction X1. The connecting portion 20 is located in the first housing space 112. The screw shaft body 21 is located across the first housing space 112 and the second housing space 113. An outer circumferential raceway surface 22 extending in the helical direction is formed on the outer circumferential surface of the screw shaft body 21.

[0030] The connecting portion 20 is a part that connects to other components. The other components that connect to the connecting portion 20 are rotatably arranged in the second housing space 113 of the housing 110 by rolling bearings. When the connecting portion 20 connects to the other components, the screw shaft 2 rotates integrally with the other components around the central axis O. Torque generated by the motor is transmitted to the other components, causing the screw shaft 2 to perform rotational motion. Examples of other components that connect to the connecting portion 20 include carriers of a planetary gear mechanism and driven pulleys of a pulley mechanism, which are components of a reduction gear; however, this disclosure may also refer to components of devices other than reduction gears. Furthermore, the connecting portion 20 in this disclosure may be directly supported by rolling bearings. Additionally, this disclosure may also refer to the connecting portion 20 being directly connected to the output shaft of a motor.

[0031] As shown in Figure 2, the nut 3 has a nut body 30, a flange portion 31 formed at the end of the nut body 30 in the second direction X2, and a recess 32 formed near the end of the nut body 30 in the first direction X1. The nut body 30 is arranged across the first housing space 112 and the second housing space 113. The flange portion 31 is located in the second housing space 113. The recess 32 is located in the first housing space 112.

[0032] The nut body 30 is formed in a cylindrical shape with respect to a central axis O. Therefore, the inner circumferential surface 33 and outer circumferential surface 34 of the nut body 30 are circular when viewed from the axial direction. Multiple inner circumferential raceway surfaces 35 are formed on the inner circumferential surface 33 of the nut body 30.

[0033] The inner circumferential raceway surface 35 faces the outer circumferential raceway surface 22 of the screw shaft 2. The space between the inner circumferential raceway surface 35 and the outer circumferential raceway surface 22 constitutes the raceway. Multiple balls (not shown) are arranged in the raceway. Furthermore, the inner circumferential raceway surface 35 extends in a spiral shape for approximately one turn (approximately 1 lead). Therefore, the raceway also extends in a spiral shape for approximately one turn (approximately 1 lead).

[0034] The nut body 30 has multiple through holes 36 that penetrate radially. A ball 4 is inserted into each through hole 36. An S-shaped circulation groove 4a is formed on the radially inward-facing surface of the ball 4. As a result, a ball that has moved from one end of the track to the other passes through the circulation groove 4a and circulates back to the one end of the track.

[0035] Hereinafter, the portion of the outer circumferential surface 34 of the nut 3 between the flange portion 31 and the recess 32 will be referred to as the covering portion 37. The multiple through holes 36 are positioned in a second direction X2 from the recess 32 and in a first direction X1 from the flange portion 31. Therefore, the through holes 36 open radially outward from the covering portion 37.

[0036] The flange portion 31 protrudes radially outward from the outer circumferential surface 34 of the nut body 30. The outer circumferential surface 31a of the flange portion 31 is formed in a circular shape when viewed from the axial direction. The flange portion 31 has multiple notches 31b (only one is shown in Figures 1 and 2) that cut out the radially outward end of the flange portion 31. The notches 31b open radially outward and in the axial direction. The key 118 of the housing 110 is inserted into the notches 31b. As a result, the end of the nut 3 in the second direction X2 is supported by the housing 110 so that it is movable in the axial direction but not rotatable around the central axis O. The flange portion 31 also has a first end face 31c facing the first direction X1.

[0037] Figure 3 is an enlarged view of the recess in Figure 2. The recess 32 is recessed radially inward from the outer circumferential surface 34 of the nut body 30. The recess 32 extends in the circumferential direction and is annular in shape. The inner surface of the recess 32 has a bottom surface 40, a first side surface 41 positioned in a first direction X1 of the bottom surface 40, and a second side surface 42 positioned in a second direction X2 of the bottom surface 40.

[0038] As shown in Figures 1 and 2, the sleeve 5 is a cylindrical metal part. Pressing (forging) is one possible manufacturing method for the sleeve 5, but this disclosure is not particularly limited to any specific manufacturing method for the sleeve 5. Furthermore, although a metal sleeve 5 is used in the embodiment, this disclosure may also use a resin sleeve. The sleeve 5 is fitted to the outer circumference of the nut body 30. In detail, the sleeve 5 is fitted to the covering portion 37 of the nut body 30 and covers the nut 4 from the radially outer side. As a result, the movement of the nut 4 radially outward is restricted and it does not fall out of the through hole 36.

[0039] The sleeve 5 is installed by inserting the end of the nut 3 in the first direction X1 into the sleeve 5 before fitting the sliding bearing 6 onto the nut 3, thereby fitting the sleeve 5 to the outer circumference of the nut 3. Furthermore, the inner diameter of the sleeve 5 is slightly larger than the outer diameter of the nut 3. Therefore, the nut 3 can be easily inserted into the sleeve 5.

[0040] In this embodiment, the inner diameter of the sleeve 5 is larger than the outer diameter of the nut 3, but in this disclosure, the inner diameter of the sleeve 5 may be the same as the outer diameter of the nut 3, or it may be smaller than the outer diameter of the nut 3.

[0041] The inner diameter of the sleeve 5 is smaller than the outer diameter of the flange portion 31. As shown in Figure 2, one end 50 of the sleeve 5 in the second direction X2 is in contact with the first end face 31c of the flange portion 31. Therefore, the movement (detachment) of the sleeve 5 in the second direction X2 is restricted by the flange portion 31.

[0042] The sliding bearing 6 is fitted into the recess 32. As shown in Figure 1, the sliding bearing 6 is formed in a C-shape when viewed from the axial direction. That is, the sliding bearing 6 has one end 64 and the other end 65 in the circumferential direction. With this C-shaped sliding bearing 6, applying force to the sliding bearing 6 can cause it to deform so that its diameter expands.

[0043] Before being attached to the nut 3, the inner diameter of the sliding bearing 6 is smaller than the outer diameter of the nut 3. The method of attaching the sliding bearing 6 involves deforming the sliding bearing 6 to expand its diameter and inserting the nut 3 inside the sliding bearing 6. Then, when the force applied to the sliding bearing 6 is removed, the sliding bearing 6 shrinks in diameter. As a result, the sliding bearing 6 fits into the recess 32.

[0044] A gap 70 extending in the axial direction exists between one end 64 and the other end 65 of the sliding bearing 6. Both end 64 and end 65 are inclined with respect to the axial direction. Therefore, the gap 70 is also inclined with respect to the axial direction.

[0045] As shown in Figure 3, the axial length of the sliding bearing 6 is the same as the axial length of the recess 32. Therefore, the end face 61 of the sliding bearing 6 in the first direction is in contact with the first side surface 41. Also, the end face 62 of the sliding bearing 6 in the second direction X2 is in contact with the second side surface 42. Therefore, the axial movement of the sliding bearing 6 is restricted.

[0046] The outer diameter R3 (see Figure 3) of the sliding bearing 6 when fitted into the recess 32 is larger than the outer diameter R4 (see Figure 3) of the sleeve 5. Therefore, the sliding bearing 6 protrudes radially outward from the sleeve 5. Furthermore, the other end 51 of the sleeve 5 in the first direction X1 abuts against the end face 62 of the sliding bearing 6. As a result, the movement of the sleeve 5 in the first direction X1 is restricted.

[0047] Furthermore, the outer diameter R3 of the sliding bearing 6 when fitted into the recess 32 is slightly smaller than the diameter R1 of the first inner circumferential surface 115 (see Figure 1). Therefore, a small gap S1 (see Figure 4) is provided between the outer circumferential surface 63 of the sliding bearing 6 and the first inner circumferential surface 115. As a result, the sliding bearing 6 is slidable relative to the first inner circumferential surface 115.

[0048] Furthermore, the inner diameter of the sliding bearing 6 before it is attached to the nut 3 is smaller than the diameter of the bottom surface 40 of the recess 32. Therefore, when the force that expands the diameter of the sliding bearing 6 during installation is removed, the inner circumferential surface 60 of the sliding bearing 6 comes into contact with the bottom surface 40 of the recess 32. This prevents the nut 3 from rattling radially relative to the sliding bearing 6. In this embodiment, the inner diameter of the sliding bearing 6 before it is attached to the nut 3 is smaller than the bottom surface 40 of the recess 32, but in this disclosure, it may be the same as the bottom surface 40 of the recess 32.

[0049] Figure 4 is an enlarged view of the recess in Figure 3. As shown in Figure 4, the radial size R10 of the minute gap S1 provided between the outer circumferential surface 63 and the first inner circumferential surface 115 of the sliding bearing 6 is smaller than the step amount R11 of the recess 32. Note that the radial size R10 of the minute gap S1 is the value obtained by subtracting the value obtained by halving the diameter R12 of the bottom surface 40 of the recess 32 and the radial thickness R13 of the sliding bearing from the value obtained by halving the diameter R1 of the first inner circumferential surface 115. In other words, in this embodiment, the following holds true: (Diameter R1 of the first inner circumferential surface 115) × 1 / 2 - (Diameter R12 of the bottom surface 40) × 1 / 2 - (Radial thickness R13 of the sliding bearing 6) < (Step amount R11 of the recess 32).

[0050] As described above, according to Embodiment 1, the sleeve 5 is fitted onto the nut 3, but the sliding bearing 6 allows the nut 3 to be slidably supported. Furthermore, the sliding bearing 6 is positioned in the first direction X1 of the sleeve 5. Therefore, the sleeve 5 does not move in the first direction X1 and fall off the nut 3. Thus, according to this embodiment, the work of crimping the sleeve 5 is unnecessary, and the labor required to manufacture the actuator 100 is reduced.

[0051] Furthermore, the sliding bearing 6 is hooked onto the first side surface 41 of the recess 32. Therefore, the sliding bearing 6 will not fall off the nut 3.

[0052] Furthermore, the sliding bearing 6 may expand due to thermal expansion caused by friction with the first inner circumferential surface 115. If it expands radially outward, the minute gap S1 with the first inner circumferential surface 115 will decrease, potentially impairing its sliding performance. On the other hand, in the sliding bearing 6 of this embodiment, a gap 70 is generated between one end 64 and the other end 65. Therefore, even if the circumferential length of the sliding bearing 6 increases due to thermal expansion, it is absorbed by the gap 70. Thus, the impairment of the sliding performance of the sliding bearing 6 due to thermal expansion is avoided.

[0053] Furthermore, the gap 70 of the sliding bearing 6 is inclined with respect to the axial direction. If the gap 70 of the sliding bearing 6 were to extend in the axial direction, the first inner surface 115 would be divided into a portion that is worn by the sliding bearing 6 and a portion that does not wear because it is opposite the gap 70. The portion that does not wear would then become a protrusion that extends in the axial direction. On the other hand, in this embodiment, the gap 70 is inclined, and the entire circumference of the first inner surface 115 slides with the sliding bearing 6. Therefore, no protrusion is formed on the first inner surface 115.

[0054] Furthermore, the radial size R10 of the minute gap S1 is smaller than the step amount R11 of the recess 32. Therefore, even if the sliding bearing 6 expands in diameter, the inner circumference of the sliding bearing 6 remains positioned inside the recess 32. In other words, the sliding bearing 6 remains fitted into the recess 32.

[0055] Next, a modified example in which a part of the actuator 100 of Embodiment 1 is changed will be described. Furthermore, in the modified example, the explanation will focus on the differences from the actuator described earlier.

[0056] (Variation 1) Figure 5 is a cross-sectional view of the sliding bearing of Modified Example 1, cut in the axial direction. As shown in Figure 5, the recess 32A of the actuator 100A of Modified Example 1 differs from Embodiment 1 in that its axial length is greater than that of the sliding bearing 6. This allows the sliding bearing 6 to be fitted into the recess 32A even if its axial length is manufactured to be greater than a predetermined length due to manufacturing tolerances. Although the gap between the second side surface 42 and the end face 62 shown in Figure 5 is depicted as relatively large, this disclosure also allows the recess 32A to be slightly longer in the axial direction than the sliding bearing 6, resulting in a very small gap between the second side surface 42 and the end face 62.

[0057] (Modification 2) Figure 6 is a view of the actuator of Modified Example 2 from a direction perpendicular to the central axis. Figure 7 is a cross-sectional view of the sliding bearing of Modified Example 2 cut in the axial direction. As shown in Figure 6, the sliding bearing 6B of the actuator 100B of Modified Example 1 differs from that of Embodiment 1 in that it is formed in an annular shape. As shown in Figure 7, the nut 3B of the actuator 100B of Modified Example 2 differs from that of Embodiment 1 in that a recess 32 is not formed on the outer circumferential surface 34.

[0058] In Modification 2, the inner diameter of the sliding bearing 6B before attachment to the nut 3B is smaller than the outer diameter of the nut 3B. In other words, the sliding bearing 6B has an overlap on the outer surface of the nut. When attaching the sliding bearing 6A to the nut 3, the end of the nut 3B in the first direction X1 is press-fitted into the interior of the sliding bearing 6A, so that the sliding bearing 6B is fitted to the outer surface of the nut 3B. In other words, the sliding bearing 6B is tightly fitted to the nut 3B. For this reason, the sliding bearing 6B is difficult to move axially and will not fall off the nut 3B.

[0059] (Variation 3) Figure 8 is a cross-sectional view of the sliding bearing of Modified Example 3, cut in the axial direction. As shown in Figure 8, the sliding bearing 6C of the actuator 100C of Modified Example 3 is similar to that of Modified Example 2 in that it is formed in an annular shape. However, it differs from Modified Example 2 in that the inner diameter of the sliding bearing 6C of Modified Example 3 before being attached to the nut 3C is the same as the outer diameter of the nut 3. Also, the nut 3C of Modified Example 3 differs from that of Modified Example 2 in that it has a groove 80 that extends in the circumferential direction. Furthermore, the groove 80 of the nut 3C differs from that of Modified Example 2 in that a C-shaped retaining ring 81 is provided in the groove 80 of the nut 3C when viewed from the axial direction.

[0060] The outer diameter of the retaining ring 81 is smaller than the outer diameter of the sliding bearing 6C. Therefore, the retaining ring 81 does not contact the first inner circumferential surface 115. Also, the retaining ring 81 is in contact with the end face 61 of the sliding bearing 6C from the first direction X1. As a result, the sliding bearing 6C does not move in the first direction X1 and does not fall off the nut 3C.

[0061] In Modification 3, the inner diameter of the sliding bearing 6C of Modification 3 before attachment to the nut 3C is the same as the outer diameter of the nut 3, but it may be smaller than the outer diameter of the nut 3. Alternatively, the inner diameter of the sliding bearing 6C of Modification 3 may be slightly larger than the outer diameter of the nut 3C.

[0062] Although Embodiment 1 and its modifications have been described above, this disclosure is not limited to the examples shown in Embodiment 1, etc. For example, in this embodiment, both ends of the sleeve 5 (one end 50 and the other end 51) abut against the flange portion 31 and the sliding bearing 6, and the sleeve 5 covers the entire covering portion 37, but in this disclosure, the sleeve 5 may cover only a part of the covering portion 37. Also, if the sleeve 5 covers at least a part of the link 4 from the radially outward direction, the link 4 will not fall out radially outward. Therefore, in this disclosure, the sleeve 5 may cover at least a part of the link 4.

[0063] Furthermore, while a 4-ring circulator is used as the circulation unit in Embodiment 1, this disclosure may also use a tube-type circulation unit, and there are no particular limitations on the type of circulation unit.

[0064] Furthermore, although the gap 70 of the sliding bearing 6 in Embodiment 1 is inclined with respect to the axial direction, the present disclosure indicates that the gap 70 of the sliding bearing 6 may extend in the axial direction.

[0065] In Embodiment 1 and others, the flange portion 31 restricts the movement of the sleeve 5 in the second direction X2, but in this disclosure, the movement of the sleeve 5 in the second direction X2 may be restricted by other configurations. In other words, in this disclosure, the nut may not have a flange portion 31 formed thereon. Other configurations that allow the sleeve 5 to move in the second direction X2 include, for example, a sliding bearing or retaining ring fitted near the end of the nut 3 in the second direction X2, but in this disclosure, this disclosure is not limited to these. Furthermore, when a sliding bearing is fitted near the end of the nut 3 in the second direction X2, the configuration shown in Embodiment 1 and others may be applied to the sliding bearing. Also, in Embodiment 1 and others, the first inner circumferential surface 115 of the housing 110 supports the sliding bearing 6 so that it can slide axially, but in this disclosure, it may be used to support it so that it can rotate around a central axis. Furthermore, in this disclosure, the nut 3 may rotate while moving axially. In other words, the present disclosure may be such that the sliding bearing 6 slides axially against the first inner circumferential surface 115 of the housing 110 while rotating around its central axis.

[0066] Furthermore, while multiple grooves 117 are formed on the second inner circumferential surface 116 in Embodiment 1 and the like, this disclosure only requires at least one groove 117. Also, regarding the structure for preventing rotation of the nut 3, in this embodiment, a key 118 is fitted into the groove 117, and the inner surface of the notch 31b catches on the key 118, but this disclosure is not limited to this. For example, a key may be fixed to the flange portion 31, and a part of the key may be placed in the groove 117. In this case, the key moves axially along the groove 117, and the key catches on the inner surface of the groove 117, restricting the rotation of the nut 3. Alternatively, a projection protruding radially outward may be formed on the outer circumferential surface 31a of the flange portion 31, and the projection may be placed in the groove 117. In addition, if the nut 3 does not have a flange portion 31, a pin protruding radially outward from the outer circumferential surface 32 of the nut 3 may be provided on the nut 3, and the radially outward end of the pin may be placed in the groove 117. Thus, in this disclosure, the end of the nut 3 in the second direction X2 only needs to be movable in the axial direction with respect to the second inner circumferential surface 116 of the second accommodation space 113, and not rotatable about the central axis O, and there are no particular limitations.

[0067] Furthermore, in Embodiment 1, the radial size R10 of the minute gap S1 is smaller than the step amount R11 of the recess 32. However, in this disclosure, the radial size R10 of the minute gap S1 and the step amount R11 of the recess 32 may be equal, or the radial size R10 of the minute gap S1 may be larger than the step amount R11 of the recess 32. [Explanation of Symbols]

[0068] 1. Ball screw device 2 Screw shaft 3, 3B, 3C nuts 4 panels 5 sleeves 6, 6A, 6B, 6C Plain bearings 20 Connection part 21 Screw shaft body 22 Outer raceway surface 30 Nut body 31 Flange section 32, 32A recess 34 Outer surface 35 Inner raceway surface 36 Through holes 37 Covering part 40 Bottom 100, 100A, 100B, 100C actuators 110 Housing 111 Containment Space 112 First Containment Space 113 Second Containment Space 114 Inner surface 115 1st inner surface 116 Second inner surface

Claims

1. A ball screw device having a screw shaft, a nut, multiple balls and at least one circulation part, A sleeve that fits onto the outer circumference of the nut, A sliding bearing fitted to the outer circumference of the nut, Housing and Equipped with, The direction is parallel to the central axis of the screw shaft and the axial direction. The housing extends in the axial direction and has a housing space in which the ball screw device, the sleeve, and the sliding bearing are housed. The nut has a through hole that penetrates in the radial direction. The circulation unit is inserted into the through hole. The sleeve covers at least a portion of the circulation section from the radially outer side, The sliding bearing is positioned on one side in the axial direction relative to the sleeve, The outer diameter of the sliding bearing is larger than the outer diameter of the sleeve. The sliding bearing is supported on the inner circumferential surface of the housing space so as to be slidable in the axial direction. Actuator.

2. The outer surface of the nut has a recess formed therein, which is recessed radially inward and extends circumferentially. The sliding bearing is formed in a C-shape when viewed from the axial direction, The inner diameter of the sliding bearing before it is attached to the nut is smaller than the outer diameter of the nut. By enlarging the diameter of the sliding bearing, the nut is inserted inside the sliding bearing, and the sliding bearing is fitted into the recess. The actuator according to claim 1.

3. When the sliding bearing is fitted into the recess, a gap is formed between one end in the circumferential direction and the other end in the circumferential direction. The actuator according to claim 2.

4. The gap is inclined with respect to the axial direction. The actuator according to claim 3.

5. The inner diameter of the sliding bearing before it is attached to the nut is smaller than the outer diameter of the nut. The sliding bearing is press-fitted onto the outer circumference of the nut, thereby interlocking it with the outer surface of the nut. The actuator according to claim 1.

6. The sliding bearing has a retaining ring that contacts it from one side in the axial direction, A groove is formed on the outer surface of the nut, into which the retaining ring engages. The actuator according to claim 1.

7. The aforementioned accommodation space is A first accommodation space is located in one of the aforementioned accommodation spaces in the axial direction, A second accommodation space located in the other axial direction of the aforementioned accommodation space, It has, The first and second storage spaces are formed in a circular shape around the central axis when viewed from the axial direction. The second accommodation space is formed to have a larger diameter than the first accommodation space. The nut and the sleeve are arranged to span the first housing space and the second housing space. The first inner surface of the first housing space slidably supports the sliding bearing, The other end of the nut in the axial direction is movable in the axial direction relative to the second inner circumferential surface of the second housing space, but is not rotatable about the central axis. The actuator according to any one of claims 1 to 6.

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