Threaded shaft guiding unit and ball screw actuator
By using a guide member and rotation limiting device made of resin in the steering actuator, the friction problem between the anti-rotation member and the threaded shaft is solved, and energy conversion with low energy loss is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- OILES CORP
- Filing Date
- 2024-11-20
- Publication Date
- 2026-06-05
Smart Images
Figure CN122162009A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the structure of a threaded shaft guide unit in an actuator, the threaded shaft guide unit having low energy loss and being configured to support the threaded shaft as movable along an axial direction while restricting the rotation of the threaded shaft about the axis. The actuator is an actuator for converting rotary motion from a motor or the like into linear motion, such as a ball screw actuator. Background Technology
[0002] steer-by-wire systems utilize electric actuators, in which a ball screw is configured to convert rotational motion from a motor into linear motion. For example, in the steer-by-wire type steering device disclosed in Patent Document 1, the steering actuator includes a nut-rotating ball screw mechanism configured to convert rotational motion from an electric motor into linear motion of a steering shaft connected to the steering wheel via a tie rod and a steering knuckle arm, thereby driving the electric motor to rotate the steering wheel according to a detected steering angle.
[0003] In this steering actuator, in order to allow the steering shaft (corresponding to the threaded shaft of the ball screw mechanism) to move in either direction along its axis in response to the rotation of the nut (corresponding to the nut of the ball screw mechanism) mounted to the steering housing, the steering shaft is slidably supported on the inner circumferential surface of a cylindrical bushing that fits into a groove formed circumferentially on the inner circumferential surface of the steering housing, and the steering shaft is prevented from rotating about the axis relative to the steering housing by means of the following structure.
[0004] For the steering housing, a cylindrical anti-rotation member receiving portion with a bottom is positioned between the bushing and the nut, extending toward the outer circumferential surface of the steering shaft. The cylindrical anti-rotation member fits within the anti-rotation member receiving portion and is allowed to move toward the outer circumferential surface of the steering shaft. Additionally, a spring, in a compressed state, is located between the bottom of the anti-rotation member receiving portion and the anti-rotation member, thereby elastically biasing the anti-rotation member toward the steering shaft, thereby pressing the end face of the anti-rotation member against the outer circumferential surface of the steering shaft.
[0005] A V-groove is formed in the end face of the anti-rotation member (the surface that presses against the outer circumferential surface of the steering shaft) along the axial direction of the steering shaft, allowing the outer circumferential surface of the steering shaft to fit within it. Simultaneously, two inclined surfaces (two inclined surfaces facing the corresponding inner wall surfaces on either side of the V-groove) are formed along the axis of the steering shaft in the outer circumferential surface of the steering shaft within the V-groove in the end face of the anti-rotation member, thereby narrowing the gap between the two inclined surfaces towards the bottom of the V-groove. Due to the bias of the compressed spring, the inner wall surfaces on both sides of the V-groove in the end face of the anti-rotation member slidably contact each other with the two inclined surfaces on the outer circumference of the steering shaft; thus, the anti-rotation member guides the steering shaft during its interlocked movement with the nut, while preventing the steering shaft from rotating about its axis relative to the steering housing.
[0006] Reference List
[0007] Patent documents
[0008] Patent Document 1: Japanese Patent Publication No. 7208381. Summary of the Invention
[0009] Technical issues
[0010] In the known steering actuators described above, the compressed spring continuously presses the anti-rotation member against the steering shaft, generating significant friction between the contact surfaces of the anti-rotation member and the steering shaft (between the inner wall surfaces of each V-groove of the anti-rotation member and the opposing inclined surfaces in the outer circumference of the steering shaft); this may increase energy loss due to the movement of the threaded shaft.
[0011] The present invention was made in consideration of the above circumstances, and the object of the present invention is to provide reduced energy loss due to the movement of the threaded shaft in an actuator configured to convert the rotational motion of a nut driven by a motor or the like into the linear motion of a threaded shaft.
[0012] Solution to the problem
[0013] To address the aforementioned problems, according to the present invention, a guide surface of a guide member made of resin supports a threaded shaft that can move in an interlocking relationship with the rotation of a nut, allowing the threaded shaft to rotate about its axis and move along the axial direction; and a rotation limiting surface is arranged to define a gap relative to the outer circumference of the threaded shaft, thereby limiting the rotation of the threaded shaft about its axis beyond a rotation angle determined by the thickness of the gap.
[0014] For example, the present invention provides a threaded shaft guiding unit configured to support a threaded shaft in an actuator configured to convert the rotational motion of a nut into the linear motion of the threaded shaft. The threaded shaft guiding unit includes the following structure:
[0015] A guide housing is configured to allow a threaded shaft to be inserted into the guide housing along the direction of the axis of the threaded shaft. The threaded shaft includes a sliding surface and an adjacent surface on its outer circumference. Each sliding surface has a cylindrical surface shape, and the adjacent surface has a different surface shape from the sliding surface.
[0016] Two guide members, made of resin and including guide surfaces, each guide surface configured to contact a corresponding sliding surface of the threaded shaft, are disposed opposite to each other across an axis within a guide housing, such that the guide surfaces support the threaded shaft for rotatability about the axis and movable in the direction of the axis; and
[0017] A rotation limiting device includes a rotation limiting surface configured to face an adjacent surface of a threaded shaft with a gap between the rotation limiting surface and the adjacent surface, and configured to contact the adjacent surface of the threaded shaft when the threaded shaft rotates about an axis by a predetermined rotation angle defined by the thickness of the gap, the rotation limiting device being configured to limit the rotation of the threaded shaft beyond the predetermined rotation angle by the contact occurring between the rotation limiting surface and the adjacent surface of the threaded shaft.
[0018] Furthermore, the present invention provides a ball screw actuator, which includes the following structure:
[0019] The aforementioned threaded shaft guide unit; and
[0020] A ball screw includes a nut and a threaded shaft. The ball screw is configured to convert the rotational motion of the nut into the linear motion of the threaded shaft. The threaded shaft has a sliding surface and an abutting surface on its outer circumference and is supported by the guide surfaces of two guide members so that it is rotatable about an axis and movable in the direction of the axis with a gap provided between the abutting surface and the rotation limiting surface.
[0021] Beneficial effects of the invention
[0022] According to the invention, a gap is provided between a rotation-limiting surface and the outer circumference of the threaded shaft. The rotation-limiting surface is configured to limit the rotation of the threaded shaft about its axis by interfering with the outer circumference of the threaded shaft. Therefore, the outer circumference of the threaded shaft remains in a non-contact state with the rotation-limiting surface for a period of time during which the rotation of the threaded shaft about its axis is maintained below a predetermined angle. This provides reduced energy loss due to the reciprocating motion of the threaded shaft.
[0023] The guide member supports the threaded shaft while allowing it to rotate about its axis, and does not prevent rotation of the threaded shaft about its axis. As a result, it receives relatively low loads from the threaded shaft in either direction of rotation. This allows the guide member to be made of a synthetic resin with a low coefficient of friction to the threaded shaft, eliminating the need to make the guide member from a hard, high-friction material with excessive durability. This provides a further reduction in energy loss due to the reciprocating motion of the threaded shaft. Attached Figure Description
[0024] [ Figure 1 ] Figure 1 This is a cross-sectional view illustrating a portion of the internal configuration of a ball screw actuator according to an embodiment of the present invention.
[0025] [ Figure 2 ] Figure 2 (A) is a view illustrating the internal configuration of a ball screw actuator according to an embodiment of the present invention at the location of the ball screw guide unit, and Figure 2 (B) is Figure 2 (A) AA cross-sectional view.
[0026] [ Figure 3 ] Figure 3 (A) is an external view of the guide housing; Figure 3 (B) to (D) are the front view, right side view, and bottom view of the guide housing 61; and Figure 2 (E) to (F) are respectively Figure 3 (B) BB cross-sectional view and Figure 3 (C) DD cross-sectional view.
[0027] [ Figure 4 ] Figure 4 (A) to (D) are the front view, right side view, rear view, and bottom view of the rotation limiting member 64, respectively; and Figure 4 (E) is Figure 4 (A) EE cross-section diagram.
[0028] [ Figure 5 ] Figure 5 (A) to (D) are the front view, bottom view, rear view and right side view of the guide member 62, respectively; Figure 5 (E) is Figure 5 (A) FF cross-sectional view; and Figure 5 (F) is Figure 5 (A) GG cross-section diagram.
[0029] [ Figure 6 ] Figure 6This is a view illustrating the change in the positional relationship between the adjacent surface of the threaded shaft 30 and the rotation limiting surface 644 of the rotation limiting member 64 as the threaded shaft 30 rotates.
[0030] [ Figure 7 ] Figure 7 This is an illustration of another connection method between the guide housing 61 and the rotation limiting member 64.
[0031] [ Figure 8 ] Figure 8 This is a cross-sectional view of a modified example of the ball screw guide unit. Detailed Implementation
[0032] In the following description, an embodiment of the invention will be illustrated with reference to the accompanying drawings. This embodiment, as an actuator including a nut-rotating ball screw mechanism, illustrates a ball screw actuator applicable to a steering actuator in a steer-by-wire system.
[0033] Figure 1 This is a cross-sectional view illustrating a portion of the internal configuration of a ball screw actuator according to this embodiment. Figure 2 (A) is a view illustrating the internal arrangement of the ball screw actuator according to this embodiment at the mounting position of the ball screw guide unit, and Figure 2 (B) is Figure 2 (A) AA cross-sectional view. Figure 1 and Figure 2 (A) Each only shows a portion of the slender threaded shaft 30.
[0034] As shown in the figure, the ball screw actuator according to this embodiment includes a nut-rotating ball screw mechanism 10, which includes: a nut 20 rotatably supported by a housing 50 via a bearing 40; a cylindrical threaded shaft 30 inserted into the nut 20; and balls (not shown) configured to recirculate in a rolling groove, which is provided in the outer circumference 31 of the threaded shaft 30 and the inner circumference of the nut 20; thereby, the nut 20 is rotated in two directions about the axis O of the nut by a motor or the like, causing the threaded shaft 30 to reciprocate in the direction of the axis O of the threaded shaft 30. The ball screw actuator also includes at least one ball screw guide unit 60, which is fitted in the inner circumference of the housing and thus inserted between the inner circumference of the housing 50 and the outer circumference 31 of the threaded shaft 30.
[0035] For ease of explanation below, three mutually orthogonal directions are defined in the housing space of the ball screw actuator, including the Z direction along the axis O of the thread shaft 30 (along which the thread shaft 30 can reciprocate), which are defined as the X direction, Y direction and Z direction; each view indicates these X direction, Y direction and Z direction as appropriate.
[0036] As shown in the figure, the threaded shaft 30 has a cylindrical shape. Its outer circumference 31 is not only provided with a helical groove around the axis O of the threaded shaft 30 as a rolling groove 32 for balls, but also, in a section S2 other than the section where the rolling groove 32 is formed (hereinafter referred to as the "rolling groove forming section"), two flat surfaces 33 are provided that are positioned opposite each other across the axis O. Each of these two flat surfaces 33 has a Z-direction length determined by the maximum stroke of the threaded shaft 30. In this embodiment, the two flat surfaces parallel to the XZ plane are formed as two flat surfaces (hereinafter referred to as "adjacent surfaces") 33 that are located opposite each other relative to the axis O and are equidistant from the axis O. Therefore, the outer circumference of the threaded shaft 30 includes two remaining cylindrical surface regions 34 positioned opposite each other across the axis O between the two adjacent surfaces 33. The guide surfaces 622 of the two guide members 62 (described below) provided in the ball screw guide unit 60 are configured to slidably contact the cylindrical surface area (hereinafter referred to as the “sliding surface”) 34, thereby supporting the threaded shaft 30 while allowing the threaded shaft 30 to rotate about the axis O and move in the Z direction.
[0037] Meanwhile, the ball screw guide unit 60 includes: a hollow cylindrical guide housing 61, which fits and is fixed in the inner circumference of the housing 50 of the ball screw actuator; two guide members 62 made of resin, which are disposed opposite to each other in the guide housing 61 and configured to support the threaded shaft 30 for rotatability about axis O and movable in the Z direction; and an O-ring 63, which is inserted between the guide housing 61 and at least one of the two guide members 62 (in this embodiment, between the guide housing 61 and each guide member 62), and is configured to bias the corresponding guide member 62 toward axis O of the threaded shaft 30 in the X direction. Furthermore, in order to restrict the rotation of the threaded shaft 30 and the nut 20 in an interlocking relationship about axis O, two rotation limiting members 64 are disposed and arranged in the ball screw guide unit 60, thereby being opposite to each other.
[0038] Figure 3 (A) is an external view of the guide housing 61; Figure 3 (B) to (D) are respectively the front view, right side view (symmetrical to the left side view), and bottom view (symmetrical to the plan view) of the guide housing 61; and Figure 3 (E) to (F) are respectively Figure 3 (B) BB cross-sectional view (symmetrical to CC cross-sectional view) and Figure 3 (C) DD cross-sectional view.
[0039] As shown in the figure, the guide housing 61 is a block having a hollow cylindrical shape, configured to receive a threaded shaft 30 inserted therein along the Z direction. The threaded shaft 30 is supported by two guide members 62 and is axially aligned with the guide housing 61, and thus the axis of the guide housing 61 is similarly referred to as axis O. The guide housing 61 includes an inner surface that defines two pairs of inner wall surfaces disposed opposite each other across axis O: namely, two inner wall surfaces (hereinafter referred to as "rotation limiting member mounting surfaces") 612A, 612B, on which the rotation limiting member 64 will be disposed; and two inner surfaces (hereinafter referred to as "guide member mounting surfaces") 613A, 613B, on which the guide member 62 will be disposed.
[0040] The two rotation limiting member mounting surfaces 612A and 612B are flat surfaces arranged parallel to each other along the XZ plane, and are formed at positions opposite each other across axis O, with equal distances D1 from axis O. The distance D1 between axis O and each rotation limiting member mounting surface 612A and 612B is designed to be greater than the distance d between axis O and the adjacent surface 33 of threaded shaft 30 and the plate thickness t of plate 641 (described below) included in rotation limiting member 64 (see [reference]). Figure 4 The sum of these components, therefore, provides a predetermined thickness G (see [reference needed]) between the rotation-limiting surface 644 of plate 641 (described below) and each adjacent surface 33 of threaded shaft 30. Figure 6 The plate 641 includes a rotation limiting member 64 disposed on the corresponding rotation limiting member mounting surfaces 612A, 612B, with a gap 70.
[0041] For each of the two rotation-limiting member mounting surfaces 612A and 612B, a through hole (hereinafter referred to as a "boss press-fit hole") 614 is formed at its substantially central location through the mounting surface 612A and 612B. This through hole 614 is used for press-fitting a boss 643 (described below) provided on the corresponding rotation-limiting member 64. Meanwhile, the two guide member mounting surfaces 613A and 613B are flat surfaces parallel to each other and arranged along the YZ plane. They are formed at positions opposite each other across axis O and are equidistant from axis O by a distance D2. The distance (2×D2) between the guide member mounting surfaces 613A and 613B is designed to be greater than the diameter of the threaded shaft 30.
[0042] For the two guide member mounting surfaces 613A and 613B, a stepped through-hole (hereinafter referred to as a "snap-fit insertion hole") 615 is formed through the guide member mounting surfaces 613A and 613B at their substantially central location. This through-hole 615 is used to insert a snap-fit insertion portion 624 (described below) provided on the corresponding guide member 62. Each snap-fit insertion hole 615 includes two sections with different inner diameters and arranged continuously in the X direction: a first section opening at the corresponding guide member mounting surfaces 613A and 613B, and a second section with a diameter larger than that of the first section and positioned closer to the outer circumference of the guide housing 61 than the first section. This allows a latch (described below) provided on the snap-fit insertion portion 624 of the corresponding guide member 62 to engage with a stepped surface 616 formed between the inner circumferential surfaces of the first and second sections.
[0043] At least one of the two guide member mounting surfaces 613A and 613B defines a circumferential O-ring mounting groove 617, which surrounds a snap-fit insertion hole 615 and allows an O-ring 63 to be mounted therein. In this embodiment, the two guide member mounting surfaces 613A and 613B define their respective circumferential O-ring mounting grooves 617 such that each O-ring 63 is biased against a corresponding one of the two guide members 62.
[0044] For example, the guide housing 61 of this form can be formed as an assembly of two semi-cylindrical parts that are symmetrical to each other.
[0045] Each O-ring 63 has a cross-sectional diameter greater than the sum of the following: the thickness of the gap created between the corresponding guide member mounting surfaces 613A, 613B and the bottom surface of the corresponding guide member 62, and the groove depth of the corresponding O-ring mounting groove 617. This causes each O-ring 63 to be compressed between the rear surface of the corresponding guide member 62 and the bottom surface of the corresponding O-ring mounting groove 617, thereby biasing each O-ring 63 in the compressed state toward the corresponding sliding surface 34 of the threaded shaft 30 toward the corresponding guide member 62 in the X direction.
[0046] This embodiment uses O-rings 63 disposed between the guide housing 61 and the corresponding guide member 62, such that each guide member 62 can be biased toward the sliding surface 34 of the threaded shaft 30 in the X direction, but is not limited thereto; other types of elastic members can be used as alternatives to the O-rings 63. For example, elastic members with non-circular cross-sections, such as X-rings, D-rings, or T-rings, can be applied. Plate-shaped elastic members made of an elastomer with rubber elasticity (such as polyurethane rubber or silicone rubber) can be arranged in a suitable layout, for example, arranged at equal angular intervals around the snap-fit insertion hole 615.
[0047] Figure 4 (A) to (C) are the front view, right side view (symmetrical to the left side view), rear view, and bottom view (symmetrical to the plan view) of the rotation limiting member 64; and Figure 4 (E) is Figure 4 (A) EE cross-section diagram.
[0048] As shown, each rotation limiting member 64 is made of a material with high durability and wear resistance, such as iron, composite materials, or sintered alloys, and includes a plate 641 and a boss 643. The boss 643 is disposed on the plate 641 and protrudes in the Y direction from one surface (rear surface) 642 of the plate 641. The other surface of the plate 641 (the surface opposite the rear surface, hereinafter referred to as the "front surface") includes a rotation limiting surface 644 configured to limit the rotation of the threaded shaft 30 about axis O. The outer diameter of the boss 643 is designed to be larger than the inner diameter of the boss press-fit hole 614 of the guide housing 61 by a predetermined interference. Each of the two rotation limiting members 64 is secured to the guide housing 61 by press-fitting the boss 643 into the corresponding boss press-fit hole 614 until the entire rear surface 642 of the plate 641 contacts the corresponding rotation limiting member mounting surfaces 612A, 612B of the guide housing 61. To ensure that the spacing between the rotation-limiting surfaces 644 of the plates 641 of the two rotation-limiting members 64 is greater than the width of the transverse flat portion of the threaded shaft 30 (the distance between the two adjacent surfaces 33) in this state, the plate thickness t of the plates 641 is less than the difference (D1-d) between the distance D1 in the guide housing 61 from the axis O to the rotation-limiting member mounting surfaces 612A, 612B and the distance d in the threaded shaft 30 from the axis O to the adjacent surface 33. This creates a gap 70 with a predetermined thickness G (D1-dt) between the rotation-limiting surfaces 644 of each of the two rotation-limiting members 64 fixed to the guide housing 61 and the corresponding one of the two adjacent surfaces 33 of the threaded shaft 30 supported by the two guide members 62 (see...). Figure 6 ).
[0049] Figure 5 (A) to (D) are the front view, bottom view, rear view (symmetrical to the plan view), and right side view (symmetrical to the left side view) of the guide component 62, respectively. Figure 5 (E) is Figure 5 (A) FF cross-sectional view; and Figure 5 (F) is Figure 5 (A) GG cross-section diagram.
[0050] As shown in the figure, the guide member 621 includes a guide body 621 and a snap-fit insertion portion 624, which is disposed on the guide body 621 and protrudes from one surface (rear surface) 623 of the guide body 62 in the X direction. The guide member 62 thus configured can be integrally made of a resin with high sliding properties (such as polyethylene terephthalate, polybutylene terephthalate, polyamide, polyphenylene sulfide, or polyacetal), which can be reinforced with fibers (including but not limited to glass).
[0051] The snap-fit insertion portion 624 includes a cylindrical portion 624A protruding from the rear surface 623 of the guide body 621 and a latch 624B disposed on the end face of the cylindrical portion 624A. The cylindrical portion 624A has an outer diameter smaller than the inner diameter of the first section of the snap-fit insertion hole 615, and is thus disposed in the first section. Furthermore, the length of the cylindrical portion 624A (the distance between the rear surface 623 of the corresponding guide member 62 and the end face of the cylindrical portion 624A) is longer than the length of the first section in the snap-fit insertion hole 615 in the corresponding guide member mounting surfaces 613A, 613B. Meanwhile, the latch 624B has a maximum diameter greater than the inner diameter of the first section in the snap-fit insertion hole 615 but smaller than the inner diameter of the second section, and the latch 624B has a tapered shape (e.g., a conical shape or a truncated conical shape) such that it becomes smaller than the first section of the snap-fit insertion hole 615 at its distal end.
[0052] By inserting the snap-fit insertion portion 624 configured as such into the snap-fit insertion hole 615 of the corresponding guide member mounting surfaces 613A, 613B, the latch 624B passes through the first section while elastically deforming due to contact with the inner circumferential surface of the first section, and then is accommodated in the second section in a state of returning to its original shape, engaging with the stepped surface 616 formed at the boundary between the first and second sections. Each guide member 62 is elastically supported on the corresponding guide member mounting surfaces 613A, 613B by an O-ring 63, and is movable by a distance corresponding to the difference between the length of the first section and the length of the cylindrical portion 624A in the corresponding snap-fit insertion hole 615.
[0053] Another surface of the guide body 621 (the surface on the opposite side of the rear surface: the "front surface") defines a guide groove 625 extending in the Z direction to receive the outer circumference of the threaded shaft 30 therein. The guide groove 625 has an inner wall defining a guide surface 622, which is curved and configured to support the sliding surface 34 of the threaded shaft 30 in a slidable manner. The guide groove 625 may have a shape opposite to a corresponding one of the sliding surfaces 34 of the threaded shaft 30, thereby making slidable surface contact with that corresponding one of the sliding surfaces 34 of the threaded shaft 30, or the guide groove 625 may include two cylindrical surface regions (each cylindrical surface region having a diameter larger than the diameter of the threaded shaft 30) configured to make line contact with a corresponding one of the sliding surfaces 34 of the threaded shaft 30 at a position symmetrical with respect to the XZ plane containing the axis O. The guide groove 625 may be formed as a V-shaped groove extending along the Z direction, and its inner wall surfaces (two sidewalls facing each other) may define respective flat guide surfaces, each flat guide surface being configured to make line contact with a corresponding one of the sliding surfaces 34 of the threaded shaft 30 at a position symmetrical with respect to the XZ plane containing the axis O.
[0054] In this configuration, the threaded shaft 30 is rotatably supported, thus allowing it to move in the Z direction while being restricted from rotating about axis O by a predetermined angle, as described below.
[0055] Figure 6 This is a view illustrating the change in the positional relationship between the adjacent surface 33 of the threaded shaft 30 and the rotation limiting surface 644 of the rotation limiting member 64 as the threaded shaft 30 rotates.
[0056] Although Figure 6 The guide surfaces 622 of the two guide members 62, which are arranged opposite each other across the threaded shaft 30, are each configured to be pressed against a corresponding one of the sliding surfaces 34 of the threaded shaft 30 due to the bias of the corresponding O-ring 63, thereby supporting the threaded shaft 30 as rotatable about axis O and movable in the Z direction.
[0057] A gap 70 is formed between the rotation limiting surface 644 of each of the two rotation limiting members 64 arranged opposite to each other across the threaded shaft 30 and the corresponding one of the adjacent surfaces 33 of the threaded shaft 30.
[0058] As described above, although the threaded shaft 30 is supported by the guide surfaces 622 of the two guide members 62 to rotate about the axis O, when the threaded shaft 30 rotates about the axis O by a predetermined angle defined by the thickness G of the gap 70, as Figure 6As shown by the dashed lines, further rotation about axis O is restricted due to interference between the adjacent surface 33 of the threaded shaft 30 and the rotation-restricting surface 644 of the corresponding rotation-restricting member 64. This prevents the threaded shaft 30 from rotating beyond a predetermined angle when subjected to a large torque about axis O due to the rotation of the nut 20.
[0059] At the same time, such as Figure 6 As shown by the dashed line, when the rotation angle of the threaded shaft 30 about the axis O remains less than a predetermined angle, there is no interference between any adjacent surface 33 of the threaded shaft 30 and the rotation limiting surface 644 of the corresponding rotation limiting member 64. Therefore, when the threaded shaft 30 is subjected to a relatively small torque about the axis O due to the rotation of the nut 20, a non-contact state is maintained between each adjacent surface 33 of the threaded shaft 30 and the rotation limiting surface 644 of the corresponding rotation limiting member 64, thereby providing a further reduction in energy loss caused by the reciprocating motion of the threaded shaft 30.
[0060] As described above, according to this embodiment, since the gaps 70 are each formed between the adjacent surface 33 of the threaded shaft 30 and the rotation limiting surface 644 of the corresponding rotation limiting member 64, the following situation occurs:
[0061] When the threaded shaft 30 is subjected to a large torque about axis O due to the rotation of nut 20, the threaded shaft 30 is restricted from rotating beyond a predetermined angle; and
[0062] When the rotation angle of the threaded shaft 30 about the axis O is kept less than a predetermined angle, during the movement of the threaded shaft 30, each adjacent surface 33 of the threaded shaft 30 remains in a non-contact state with the rotation limiting surface 644 of the corresponding rotation limiting member 64, thereby providing reduced energy loss due to the movement of the threaded shaft 30.
[0063] The guide surface 622 of the guide member 62 supports the threaded shaft 30 for rotatability about axis O, but does not prevent the threaded shaft from rotating about the axis, resulting in relatively low loads received from the threaded shaft 30 in either direction of rotation. This allows the guide member 62 to be made of a synthetic resin with a low coefficient of friction to the threaded shaft 30, eliminating the need to make the guide member 62 from a hard, high-friction material with excessive durability. This provides a further reduction in energy loss due to the reciprocating motion of the threaded shaft 30.
[0064] In the related technologies described above, since a gap is provided between each inner wall surface of the anti-rotation member receiving portion of the steering housing and the anti-rotation member, thus serving as a space in which the anti-rotation member can move, the anti-rotation member vibrates due to the extension or contraction of the spring biasing the anti-rotation member, causing a change in the permissible range of rotation of the steering shaft about its axis. In contrast, according to this embodiment, each rotation limiting member 64 is fixed to the guide housing 61, and the entire bottom surface (rear surface of plate 641) 642 of the rotation limiting member 64 is in close contact with the corresponding rotation limiting member mounting surfaces 612A, 612B, thereby limiting vibration relative to the guide housing 61. Therefore, this embodiment prevents a change in the permissible range of rotation of the threaded shaft 30.
[0065] The present invention may include, but is not limited to, the above embodiments; it will be apparent to those skilled in the art that various changes or modifications can be made without departing from the scope of the present invention.
[0066] In the above embodiments, the boss 643 of the rotation limiting member 64 is press-fitted into the boss press-fit hole 614 of the guide housing 61, thereby connecting the rotation limiting member 64 to the guide housing 61; however, it is not limited to this, and the rotation limiting member 64 and the guide housing 61 can be connected to each other by another connection method. For example, as Figure 7 As shown, when a rotation limiting member 64A without a boss is used and the width of the rotation limiting member 64A in the X direction is greater than the corresponding rotation limiting member mounting surfaces 612A, 612B, the slit 618 can be formed at the corresponding boundary position between the rotation limiting member mounting surfaces 612A, 612B and the guide member mounting surfaces 613A, 613B of the guide housing 61A, thus parallel to the rotation limiting member 64A, thereby allowing both sides of each rotation limiting member 64A to be inserted into the corresponding slit 618. In this case, the boss press-fit hole 614 can be omitted. For each slit 618, the thickness (width in the Y direction) of the slit 618 is greater than the plate thickness of the corresponding rotation limiting member 64A, and the two opposing wall surfaces 618A, 618B include a wall surface 618A oriented toward the corresponding rotation limiting member mounting surfaces 612A, 612B, the distance between the wall surface 618A and the corresponding rotation limiting member mounting surfaces 612A, 612B is set to be slightly less than the plate thickness of the rotation limiting member 64A. Therefore, press-fitting both sides of the rotation limiting member 64A along the Z direction into the two slits 618 that are arranged facing each other across the YZ plane containing the axis O will cause the rotation limiting member 64A to be connected to the guide housing 61A.
[0067] In the above embodiments, rotation limiting members 64, 64A having rotation limiting surfaces 644 are attached to guide housings 61, 61A; however, not limited thereto, as an alternative to using rotation limiting members 64, a pair of opposing inner wall surfaces 612A, 612B of the guide housing may each be provided with a rotation limiting layer made of a material with high durability and wear resistance, such as a sintered metal layer or a metal coating layer, thereby allowing the surface of each rotation limiting layer to act as a rotation limiting surface.
[0068] In the above embodiments, a flat surface is formed as an adjacent surface on the outer circumference of the threaded shaft 30; however, each adjacent surface is not limited to being flat, and can be curved, such as... Figure 8 As shown, the adjacent surface can interfere with the corresponding rotation-limiting surface 644 as long as the threaded shaft 30 rotates about the axis O by a predetermined angle. In this case, each rotation-limiting surface 644 can be flat or curved, following the shape of the corresponding adjacent surface of the threaded shaft 30.
[0069] In the above embodiments, two adjacent surfaces 33 are each formed on the outer circumference of the threaded shaft 30, thereby interfering with the corresponding rotation limiting surface 644 when the threaded shaft 30 is rotated about the axis O by a predetermined angle; however, it is sufficient for at least one adjacent surface 33 thus configured to be formed on the outer circumference of the threaded shaft 30.
[0070] The above embodiments illustrate an application to a ball screw actuator that can be used as a steering actuator in a steer-by-wire system; however, the invention is not limited to steering actuators in steer-by-wire systems, but can be widely applied to any feed mechanism configured to convert the rotational motion of a nut into the linear motion of a threaded shaft, such as a nut-rotating ball screw mechanism.
[0071] List of reference numerals
[0072] 10: Ball screw mechanism; 20: Nut; 30: Threaded shaft; 31: Outer circumference of threaded shaft; 32: Rolling groove; 33: Adjacent surface; 34: Sliding surface; 40: Bearing; 50: Housing; 60: Ball screw guide unit; 61, 61A: Guide housing; 62: Guide member; 63: O-ring; 64, 64A: Rotation limiting member; 70: Clearance between the rotation limiting surface of the rotation limiting member and the adjacent surface of the threaded shaft; 612A, 612B: Mounting surface of the rotation limiting member; 61 3A, 613B: Guide member mounting surface; 614: Boss press-fit hole; 615: Snap-fit insertion hole; 616: Stepped surface; 617: O-ring mounting groove; 618: Slit; 621: Guide member body; 622: Guide surface; 623: Rear surface of guide member body; 624: Snap-fit insertion part; 624A: Cylindrical part; 624B: Latch; 625: Guide groove; 641: Plate; 642: Rear surface of plate; 643: Boss; 644: Rotation limiting surface.
Claims
1. A threaded shaft guiding unit configured to support a threaded shaft in an actuator configured to convert rotational motion of a nut into linear motion of the threaded shaft, the threaded shaft guiding unit comprising: A guide housing configured to allow the threaded shaft to be inserted into the guide housing in the direction of the axis of the threaded shaft, the threaded shaft including a sliding surface and an adjacent surface on the outer circumference of the threaded shaft, each sliding surface having a cylindrical surface shape, and the adjacent surface having a different surface shape from the sliding surface; Two guide members, made of resin and including guide surfaces, each guide surface being configured to contact a corresponding sliding surface of the threaded shaft, the guide members being disposed opposite to each other across the axis in the guide housing such that the guide surfaces support the threaded shaft so that it can rotate about the axis and move in the direction of the axis; as well as A rotation limiting device includes a rotation limiting surface configured to face an adjacent surface of a threaded shaft with a gap between the adjacent surface and the rotation limiting surface, and configured to contact the adjacent surface of the threaded shaft when the threaded shaft rotates about the axis by a predetermined rotation angle defined by the thickness of the gap, the rotation limiting device being configured to limit rotation of the threaded shaft beyond the predetermined rotation angle by contact occurring between the rotation limiting surface and the adjacent surface of the threaded shaft.
2. The threaded shaft guide unit according to claim 1, in, The rotation limiting device includes a rotation limiting member, the rotation limiting member including surfaces, one of the surfaces facing the adjacent surface of the threaded shaft and including the rotation limiting surface, the other surface being disposed on the opposite side of the rotation limiting member opposite to the rotation limiting surface, and the rotation limiting member being fixed to the guide housing while the other surface is in surface contact with the guide housing.
3. The threaded shaft guide unit according to claim 1, in, The rotation limiting device includes a rotation limiting layer formed on the inner wall surface of the guide housing, the rotation limiting layer including a surface facing the adjacent surface of the threaded shaft, and the surface including the rotation limiting surface.
4. A ball screw actuator, comprising: Threaded shaft guide unit according to any one of claims 1 to 3; as well as A ball screw includes the nut and the threaded shaft, the ball screw being configured to convert the rotational motion of the nut into the linear motion of the threaded shaft, the threaded shaft having the sliding surface and the abutting surface on the outer circumference of the threaded shaft, and being supported by the guide surfaces of the two guide members so as to be able to rotate about the axis and move in the direction of the axis with the gap provided between the abutting surface and the rotation limiting surface.