Screw shaft guide unit and ball screw actuator

Abstract

To reduce energy loss due to movement of a screw shaft, in an actuator that converts rotational motion of a motor, etc., into linear motion.SOLUTION: Two guide members 62 are arranged opposite each other with a screw shaft 30 in between, and their guide surfaces 622 are pressed against a cylindrical planar sliding surface 34 on an outer periphery of the screw shaft by energization from an O-ring 63, to support the screw shaft 30 so that it can rotate around an axial core O and move in a Z direction. A rotation inhibition member 64 has a flat rotation inhibition surface 644, and is fixed at a position where a clearance is provided between the rotation inhibition surface 644 and a flat contact surface 33 on the outer periphery of the screw shaft. When a rotation angle of the screw shaft 30 around the axial core O reaches a predetermined angle, the contact surface 33 and the rotation inhibition surface 644 interfere with each other, preventing further rotation of the screw shaft 30, and on the other hand, when the rotation angle of the screw shaft 30 around the axial core O is made smaller than the predetermined angle, a non-contact state between the contact surface 33 and the rotation inhibition surface 644 is maintained.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a structure of a screw shaft guide unit with low energy loss that supports a screw shaft so as to be movable in the axial direction while preventing rotation of the screw shaft around its axis in an actuator such as a ball screw actuator that converts rotational motion of a motor or the like into linear motion.

Background Art

[0002] In a steer-by-wire system or the like, an electric actuator that converts the rotational motion of a motor into linear motion using a ball screw is used. For example, in the steer-by-wire type steering apparatus described in Patent Document 1, the steering actuator has a nut rotation type ball screw mechanism that converts the rotational motion of an electric motor into the linear motion of a steering shaft connected to a steering wheel via a tie rod and a knuckle arm, and the steering wheel is steered by driving the electric motor according to the detected steering angle.

[0003] In this steering actuator, the steering shaft is slidably supported by the inner peripheral surface of a cylindrical bush fitted into a circumferential groove provided on the inner periphery of the steering housing so that the steering shaft (the screw shaft of the ball screw mechanism) moves in its axial direction in response to the rotation of a nut (the nut of the ball screw mechanism) fixed to the steering housing. Further, the rotation of the steering shaft around its axis with respect to the steering housing is restricted by the following structure.

[0004] The steering housing is provided with a bottomed cylindrical rotation restricting member accommodating portion facing the outer peripheral surface of the steering shaft at a position between the bush and the nut. Inside this rotation restricting member accommodating portion, a cylindrical rotation restricting member is fitted so as to be movable toward the outer peripheral surface of the steering shaft. Further, a compression spring that biases the rotation restricting member toward the steering shaft is disposed between the bottom of this rotation restricting member accommodating portion and the rotation restricting member, and the end surface of the rotation restricting member is pressed against the outer peripheral surface of the steering shaft.

[0005] Within the end face of the rotation restricting member (the face pressed against the outer peripheral surface of the steering shaft), a V-groove into which the outer peripheral surface of the steering shaft is fitted is formed along the axial direction of the steering shaft. On the other hand, on the outer peripheral surface of the steering shaft fitted into the V-groove within the end face of the rotation restricting member, two inclined surfaces (two inclined surfaces facing the inner wall surfaces on both sides of the V-groove) whose intervals gradually become narrower as they approach the groove bottom of this V-groove are provided along the axis of the steering shaft. Due to the biasing of the spring in the compressed state, the inner wall surfaces on both sides of the V-groove of the end face of the rotation restricting member and the two inclined surfaces on the outer periphery of the steering shaft are in slidable surface contact. Therefore, the steering shaft that moves as the nut rotates is guided in the axial direction in a state where its rotation around the axis with respect to the steering housing is restricted by the rotation restricting member.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the above conventional steering actuator, the rotation restricting member is constantly pressed against the steering shaft by the spring in the compressed state, and a large friction acts between the contact surfaces of the rotation restricting member and the steering shaft (between the inner wall surface of the V-groove of the rotation restricting member and the opposing inclined surface on the outer periphery of the steering shaft). Therefore, there is a possibility that the energy loss associated with the movement of the screw shaft increases.

[0008] The present invention has been made in view of the above circumstances, and one of its purposes is to reduce the energy loss associated with the movement of the screw shaft in an actuator that converts the rotational movement of a nut by a motor or the like into the linear movement of the screw shaft.

Means for Solving the Problems

[0009] In order to solve the above problems, in the present invention, a screw shaft that moves in the axial direction by the rotation of a nut is supported by a guide surface of a resin guide member so as to be rotatable about the axis and movable in the axial direction, and a rotation prevention surface is disposed with a clearance from the outer periphery of the screw shaft, and rotation of the screw shaft about the axis by an angle of rotation or more corresponding to the thickness of the clearance is prevented by interference between the rotation prevention surface and the outer periphery of the screw shaft.

[0010] For example, the present invention is a screw shaft guide unit for supporting the screw shaft in an actuator that converts the rotational motion of a nut into the linear motion of the screw shaft, wherein the screw shaft having a sliding surface in the shape of a cylindrical surface and a contact surface having a surface shape different from that of the sliding surface on the outer periphery is inserted into a guide housing in the direction of the axis of the screw shaft, and two resin guide members arranged opposite to each other across the axis are provided in the guide housing so as to have a guide surface for contacting the sliding surface of the screw shaft and support the screw shaft so as to be rotatable about the axis and movable in the direction of the axis by the guide surface, and a rotation prevention means that is arranged opposite to the contact surface of the screw shaft with a clearance therebetween and has a rotation prevention surface that contacts the contact surface of the screw shaft when the screw shaft rotates about the axis by a predetermined rotation angle or more determined by the thickness of the clearance, and prevents rotation of the screw shaft by an angle of rotation or more by contact between the rotation prevention surface and the contact surface of the screw shaft, and provides a screw shaft guide unit characterized by comprising the above. Further, the present invention comprises the above screw shaft guide unit, a ball screw that has the nut and the screw shaft and converts the rotational motion of the nut into the linear motion of the screw shaft, wherein the screw shaft Provided is a ball screw actuator having the sliding surface and the contact surface on the outer periphery, and being supported by the guide surfaces of the two guide members so as to be rotatable about the axis and movable in the direction of the axis with the clearance provided between the contact surface and the rotation prevention surface.

Advantages of the Invention

[0011] According to the present invention, since a clearance is provided between the rotation prevention surface that prevents rotation about the axis of the screw shaft due to interference with the outer periphery of the screw shaft and the outer periphery of the screw shaft, when the rotation about the axis of the screw shaft remains less than a predetermined angle, a non-contact state between the outer periphery of the screw shaft and the rotation prevention surface is maintained. For this reason, it is possible to reduce the energy loss associated with the reciprocating movement of the screw shaft.

[0012] Further, since the guide member rotatably holds the screw shaft and does not bear the function of preventing rotation about the axis of the screw shaft, the load in the rotational direction received from the screw shaft is relatively small. For this reason, the guide member does not need to be made of a hard high-friction material having more durability than necessary, and can be made of a synthetic resin having a small friction coefficient with respect to the screw shaft. For this reason, it is possible to further reduce the energy loss associated with the reciprocating movement of the screw shaft.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In this embodiment, as an example of an actuator having a nut-rotating type ball screw mechanism, a ball screw actuator applicable as a steering actuator of a steer-by-wire system will be cited.

[0015] Fig. 1 is a cross-sectional view showing a partial internal structure of the ball screw actuator according to this embodiment. Fig. 2(A) is a diagram showing the internal structure of the ball screw actuator according to this embodiment at the arrangement position of the ball screw guide unit, and Fig. 2(B) is a cross-sectional view taken along line A-A of Fig. 2(A). Note that Figs. 1 and 2(A) show only a partial section of the long screw shaft 30.

[0016] As shown in the figure, the ball screw actuator according to this embodiment includes a nut 20 rotatably supported by a housing 50 via a bearing 40, a cylindrical screw shaft 30 inserted into the nut 20, and balls (not shown) that circulate in rolling grooves provided on the outer periphery 31 of the screw shaft 30 and the inner periphery of the nut 20. It has a nut-rotation type ball screw mechanism 10 that reciprocates the screw shaft 30 in the direction of its axis O by rotating the nut 20 bidirectionally around its axis O by a motor or the like. Further, this ball screw actuator has one or more ball screw guide units 60 attached to the inner periphery of the housing so as to be interposed between the inner periphery of the housing 50 and the outer periphery 31 of the screw shaft 30.

[0017] For the convenience of the following description, three mutually perpendicular directions (X direction, Y direction, Z direction) including the Z direction (the direction in which the screw shaft 30 reciprocates) along the axis O of the screw shaft 30 are defined in the arrangement space of the ball screw actuator, and these directions XYZ are appropriately shown in each figure.

[0018] As shown in the figure, the screw shaft 30 has a cylindrical shape, and on its outer periphery 31, in addition to a spiral groove around the axis O formed as a rolling groove 32 for the balls, two flat surfaces 33 having a Z-direction length corresponding to the maximum stroke of the screw shaft 30 are formed in a section S2 other than the section S1 where the rolling groove 32 is formed (hereinafter referred to as the rolling groove formation section) so as to face each other with the axis O in between. In this embodiment, as such two flat surfaces (hereinafter referred to as contact surfaces) 33, two flat surfaces parallel to the XZ plane are formed at positions equidistant d from the axis O in opposite directions from each other. For this reason, on the outer periphery of the screw shaft 30, between these two contact surfaces 33, two cylindrical surface regions 34 with a predetermined width facing each other with the axis O in between are left. The guide surfaces 622 of the two guide members 62 (described later) provided in the ball screw guide unit 60 slidably contact these cylindrical surface regions (hereinafter referred to as sliding surfaces) 34 to support the screw shaft 30 so as to be rotatable around the axis O and movable in the Z direction.

[0019] On one hand, the ball screw guide unit 60 includes a cylindrical guide housing 61 that is fitted and fixed to the inner periphery of the housing 50 of the ball screw actuator, two resin guide members 62 that are arranged opposite to each other within the guide housing 61 and support the screw shaft 30 so as to be rotatable about the axis O and movable in the Z direction, and an O-ring 63 that is arranged between at least one of the guide housing 61 and the two guide members 62 (in this embodiment, between the guide housing 61 and each guide member 62) and biases the guide member 62 in the X direction toward the axis O of the screw shaft 30. Further, in order to restrain the rotation of the screw shaft 30 about the axis O accompanying the rotation of the nut 20, two rotation restraining members 64 that are arranged opposite to each other within the guide housing 61 are provided in the ball screw guide unit 60.

[0020] FIG. 3(A) is an external view of the guide housing 61, FIGS. 3(B) to (D) are a front view, a right side view (symmetrical to the left side view), and a bottom view (symmetrical to the plan view) of the guide housing 61, and FIGS. 3(E) to (F) are a B-B cross-sectional view of FIG. 3(B) (symmetrical to the C-C cross-sectional view) and a D-D cross-sectional view of FIG. 3(C).

[0021] As shown in the figure, the guide housing 61 is a block having a hollow cylindrical shape into which the screw shaft 30 can be inserted in the Z direction. Since the screw shaft 30 is supported by the two guide members 62 in a state of being aligned with the guide housing 61, hereinafter, the axis of the guide housing 61 is also denoted as the axis O. On the inner surface of the guide housing 61, there are included two sets of inner wall surfaces that face each other with the axis O interposed therebetween, that is, two inner wall surfaces (hereinafter, rotation restraining member mounting surfaces) 612A and 612B on which the rotation restraining members 64 are arranged, and two inner wall surfaces (hereinafter, guide member mounting surfaces) 613A and 613B on which the guide members 62 are arranged.

[0022] The two rotation prevention member mounting surfaces 612A and 612B are flat surfaces that are provided along the XZ plane and parallel to each other, and are formed at positions equidistant D1 from the axis O in opposite directions from each other. A clearance 70 (see FIG. 6) with a predetermined thickness G is formed between the rotation prevention surface 644 of the plate 641 (described later) provided in the rotation prevention member 64 disposed on the rotation prevention member mounting surfaces 612A and 612B and the contact surface 33 of the screw shaft 30. The distance D1 from the axis O to each of the rotation prevention member mounting surfaces 612A and 612B is set to be larger than the sum of the distance d from the axis O to the contact surface 33 of the screw shaft 30 and the plate thickness t (see FIG. 4) of the plate 641 (described later) provided in the rotation prevention member 64.

[0023] In each of the two rotation prevention member mounting surfaces 612A and 612B, at substantially the central position, a through hole (hereinafter, boss press-fitting hole) 614 for press-fitting a boss 643 (described later) provided in the rotation prevention member 64 is formed. On the other hand, the two guide member mounting surfaces 613A and 613B are flat surfaces that are provided along the YZ plane and parallel to each other, and are formed at positions equidistant D2 from the axis O in opposite directions from each other. The distance 2×D2 between the guide member mounting surfaces 613A and 613B is set to be larger than the diameter of the screw shaft 30.

[0024] In each of the two guide member mounting surfaces 613A and 613B, at substantially the central position, a stepped through hole (hereinafter, snap-fit insertion hole) 615 into which a snap-fit insertion portion 624 (described later) provided in the guide member 62 is inserted is formed. Each snap-fit insertion hole 615 has two sections with different inner diameters, that is, a first section that opens in the guide member mounting surfaces 613A and 613B, and a second section that is located on the outer peripheral side of the guide housing 61 and has an inner diameter larger than that of the first section, and the two sections are provided continuously in the X direction. A latch portion (described later) provided in the snap-fit insertion portion 624 of the guide member 62 engages with a stepped surface 616 formed between the inner peripheral surface of the first section and the inner peripheral surface of the second section.

[0025] Further, an annular O-ring mounting groove 617 for mounting the O-ring 63 is formed around the snap-fit type insertion hole 615 on at least one of the two guide member mounting surfaces 613A and 613B. In the present embodiment, in order to bias each of the two guide members 62 with the O-ring 63, annular mounting grooves 617 are formed on the two guide member mounting surfaces 613A and 613B, respectively.

[0026] The guide housing 61 having such a shape can be formed, for example, as an assembly of two symmetric semi-cylindrical parts.

[0027] The O-ring 63 has a wire diameter larger than the sum of the thickness of the clearance provided between the guide member mounting surfaces 613A and 613B and the bottom surface of the guide member 62 and the groove depth of the O-ring mounting groove 617. For this reason, the O-ring 63 is compressed between the back surface of the guide member 62 and the groove bottom of the O-ring mounting groove 617, and the guide member 62 is biased in the X direction toward the sliding surface 34 of the screw shaft 30 by the compressed O-ring 63.

[0028] In the present embodiment, the O-ring 63 is interposed between the guide housing 61 and the guide member 62 in order to bias the guide member 62 in the X direction toward the sliding surface 34 of the screw shaft 30. However, other elastic members may be used instead of the O-ring 63. For example, an annular elastic member having a non-circular cross-sectional shape such as an X-ring, a D-ring, a T-ring, etc. may be used. Also, a plate-shaped elastic member formed of an elastomer having rubber elasticity such as urethane rubber or silicone rubber may be arranged around the snap-fit type insertion hole 615 in an appropriate layout such as at equal angular intervals.

[0029] Figs. 4(A) to (C) are a front view, a right side view (symmetric to the left side view), a rear view, and a bottom view (symmetric to the plan view) of the rotation prevention member 64, and Fig. 4(E) is a cross-sectional view taken along the line E-E of Fig. 4(A).

[0030] As shown in the figure, the rotation prevention member 64 is formed of a material excellent in durability and wear resistance, such as iron, a multilayer material, a sintered alloy, etc., and has a plate 641 and a boss 643 provided on the plate 641 so as to protrude in the Y direction from one surface (back surface) 642 of the plate 641. On the other surface of the plate 641 (the surface opposite to the back surface: the front surface), a rotation prevention surface 644 for preventing rotation around the axis O of the screw shaft 30 is included. The outer diameter of the boss 643 is set to be larger than the inner diameter of the boss press-fitting hole 614 of the guide housing 61 by a predetermined tightening allowance. The two rotation prevention members 64 are fixed to the guide housing 61 by press-fitting the boss 643 into the boss press-fitting hole 614 until the entire back surface 642 of the plate 641 contacts the rotation prevention member mounting surfaces 612A and 612B of the guide housing 61. In this state, the plate 641 has a plate thickness t smaller than the difference (D1 - d) between the distance D1 from the axis O of the guide housing 61 to the rotation prevention member mounting surfaces 612A and 612B and the distance d from the axis O of the screw shaft 30 to the contact surface 33, so that a gap larger than the two-sided width of the screw shaft 30 (the distance between the two contact surfaces 33) is formed between the rotation prevention surfaces 644 of the plates 641 of the two rotation prevention members 64. For this reason, a clearance 70 (see Fig. 6) with a predetermined thickness G (D1 - d - t) is formed between the rotation prevention surfaces 644 of the two rotation prevention members 64 fixed to the guide housing 61 and the two contact surfaces 33 of the screw shaft 30 supported by the two guide members 62, respectively.

[0031] Figs. 5(A) to (D) are the front view, bottom view, rear view (symmetrical to the plan view), and right side view (the left side view is symmetrical) of the guide member 62, Fig. 5(E) is the F-F cross-sectional view of Fig. 5(A), and Fig. 5(F) is the G-G cross-sectional view of Fig. 5(A).

[0032] As shown in the figure, it has a guide body 621 and a snap-fit insertion part 624 provided on the guide body 621 so as to protrude in the X direction from one surface (rear surface) 623 of the guide body 621. Such a guide member 62 can be integrally formed of a resin excellent in slidability, such as polyethylene terephthalate, polybutylene terephthalate, polyamide, polyphenylene sulfide, polyacetal, etc. fiber-reinforced with glass or the like.

[0033] The snap-fit insertion part 624 has a cylindrical part 624A protruding from the rear surface 623 of the guide body 621 and a latch part 624B provided on the end face of the cylindrical part 624A. The cylindrical part 624A has an outer diameter smaller than the inner diameter of the first section so as to be arranged in the first section of the snap-fit insertion hole 615. Also, the length of the cylindrical part 624A (the distance from the rear surface 623 of the guide member 62 to the end face of the cylindrical part 624A) is larger than the length of the first section in the snap-fit insertion hole 615 of the guide member mounting surfaces 613A, 613B. On the other hand, the latch part 624B has a maximum diameter larger than the inner diameter of the first section and smaller than the inner diameter of the second section in the snap-fit insertion hole 615, and has a shape (for example, a conical shape, a frustum of a cone shape) tapered so that the tip becomes thinner than the first section of the snap-fit insertion hole 615.

[0034] When such a snap-fit insertion part 624 is inserted into the snap-fit insertion hole 615 of the guide member mounting surfaces 613A, 613B, the latch part 624B passes through the first section while elastically deforming by contact with the inner peripheral surface of the first section, and then is accommodated in the second section in a state of restoring to its original shape and engages with a step surface 616 formed at the boundary between the first and second sections. The guide member 62 is elastically supported by an O-ring 63 on the guide member mounting surfaces 613A, 613B in a state where movement by a distance corresponding to the difference between the length of the first section in the snap-fit insertion hole 615 and the length of the cylindrical part 624A is allowed.

[0035] On the other surface of the guide body 621 (the surface opposite to the back surface: the front surface), a guide groove 625 into which the outer periphery of the screw shaft 30 is fitted is formed in the Z direction. On the inner wall of the guide groove 625, a curved guide surface 622 that slidably supports the sliding surface 34 of the screw shaft 30 is formed. This guide surface 622 may have an inverted shape of the sliding surface 34 of the screw shaft 30 so as to be in surface contact with the sliding surface 34 of the screw shaft 30, or may include two cylindrical surface regions (cylindrical surface regions having a larger diameter than the screw shaft 30) that are in line contact with the sliding surface 34 of the screw shaft 30 at positions symmetric with respect to the XZ plane including the axis O. Also, a V-groove may be formed as the guide groove 625 in the Z direction, and a flat guide surface that is in line contact with the sliding surface 34 of the screw shaft 30 may be formed on the inner wall (two opposing side walls) thereof at positions symmetric with respect to the XZ plane including the axis O.

[0036] In such a configuration, the screw shaft 30 is supported so as to be movable in the Z direction in a state where rotation around the axis O by a predetermined angle or more is blocked, as described below.

[0037] FIG. 6 is a diagram showing changes in the positional relationship between the contact surface 33 of the screw shaft 30 and the rotation blocking surface 644 of the rotation blocking member 64 in response to the rotation of the screw shaft 30.

[0038] Although omitted in FIG. 6, the guide surfaces 622 of the two guide members 62 arranged to face each other with the screw shaft 30 interposed therebetween are pressed against the sliding surface 34 of the screw shaft 30 by the biasing of the O-ring 63, and support the screw shaft 30 so as to be rotatable around the axis O and movable in the Z direction.

[0039] Clearances 70 are respectively formed between the rotation blocking surfaces 644 of the two rotation blocking members 64 arranged to face each other with the screw shaft 30 interposed therebetween and the contact surface 33 of the screw shaft 30.

[0040] As described above, the screw shaft 30 is rotatably supported around the axis O by the guide surfaces 622 of the two guide members 62. However, as shown by the dotted line in FIG. 6, when the screw shaft 30 rotates around the axis O by a predetermined angle determined according to the thickness G of the clearance 70, the rotation of the screw shaft 30 around the axis O is further prevented due to the interference between the contact surface 33 of the screw shaft 30 and the rotation prevention surface 644 of the rotation prevention member 64. Therefore, when a large moment acts on the screw shaft 30 around the axis O due to the rotation of the nut 20, the rotation of the screw shaft 30 by a predetermined angle or more can be prevented.

[0041] On the other hand, when the rotation angle of the screw shaft 30 around the axis O remains less than the predetermined angle, as shown by the dashed-dotted line in FIG. 6, there is no interference between the contact surface 33 of the screw shaft 30 and the rotation prevention surface 644 of the rotation prevention member 64. Therefore, when a relatively small moment acts on the screw shaft 30 around the axis O due to the rotation of the nut 20, the non-contact state between the contact surface 33 of the screw shaft 30 and the rotation prevention surface 644 of the rotation prevention member 64 is maintained, so that the energy loss associated with the movement of the screw shaft 30 can be reduced.

[0042] As described above, according to the present embodiment, since the clearance 70 is provided between the contact surface 33 of the screw shaft 30 and the rotation prevention surface 644 of the rotation prevention member 64, when a large moment acts on the screw shaft 30 around the axis O due to the rotation of the nut 20, the rotation of the screw shaft 30 by a predetermined angle or more can be prevented. At the same time, when the rotation angle of the screw shaft 30 around the axis O remains less than the predetermined angle, during the movement of the screw shaft 30, the non-contact state between the contact surface 33 of the screw shaft 30 and the rotation prevention surface 644 of the rotation prevention member 64 is maintained, and the energy loss associated with the movement of the screw shaft 30 can be reduced.

[0043] Further, since the guide surface 622 of the guide member 62 supports the screw shaft 30 so as to be rotatable about the axis O and does not bear the function of preventing rotation about the axis of the screw shaft, the rotational load received from the screw shaft 30 is relatively small. Therefore, the guide member 62 does not need to be made of a hard high-friction material with more durability than necessary, and can be made of a synthetic resin with a small friction coefficient with respect to the screw shaft 30. Accordingly, the energy loss associated with the reciprocating movement of the screw shaft 30 can be further reduced.

[0044] Also, in the above prior art, a gap serving as a movable space for the rotation prevention member is provided between the inner wall surface of the rotation regulation member housing portion of the steering housing and the rotation prevention member, and the rotation prevention member swings due to the expansion and contraction of the spring that biases the rotation prevention member. Therefore, the allowable rotation angle range about the axis of the steering shaft fluctuates. In contrast, the rotation prevention member 64 according to the present embodiment is fixed to the guide housing 61 in a state where the entire bottom surface (the back surface of the plate 641) 642 is in close contact with the rotation prevention member mounting surfaces 612A and 612B, and the swinging with respect to the guide housing 61 is restricted. Therefore, according to the present embodiment, it is possible to prevent fluctuations in the allowable rotation angle range of the screw shaft 30.

[0045] Note that the present invention is not limited to the above-described embodiment, and numerous modifications are possible within the scope of the gist thereof.

[0046] In the above-described embodiment, the rotation prevention member 64 is coupled to the guide housing 61 by press-fitting the boss 643 of the rotation prevention member 64 into the boss press-fitting hole 614 of the guide housing 61. However, the rotation prevention member 64 and the guide housing 61 may be coupled by other coupling methods. For example, as shown in FIG. 7, when using a rotation prevention member 64A without a boss that is wider in the X direction than the rotation prevention member mounting surfaces 612A and 612B, slits 618 for inserting both sides of the rotation prevention member 64A may be provided in parallel with the rotation prevention member 64A at the boundary positions between the rotation prevention member mounting surfaces 612A and 612B and the guide member mounting surfaces 613A and 613B of the guide housing 61A. In this case, the boss press-fitting hole 614 may be omitted. Each slit 618 has a thickness (Y-direction width) larger than the plate thickness of the rotation prevention member 64A. However, the distance between one wall surface 618A facing the rotation prevention member mounting surfaces 612A and 612B and the rotation prevention member mounting surfaces 612A and 612B among the two opposing wall surfaces 618A and 618B is set to be slightly smaller than the plate thickness of the rotation prevention member 64A. For this reason, the rotation prevention member 64 can be coupled to the guide housing 61A by press-fitting both sides of the rotation prevention member 64A in the Z direction into the two slits 618 facing each other across the YZ plane including the axis O.

[0047] Also, in the above-described embodiment, the rotation prevention members 64 and 64A having the rotation prevention surfaces 644 are attached to the guide housings 61 and 61A. However, instead of using the rotation prevention member 64, a rotation prevention layer formed of a material excellent in durability and wear resistance, such as a sintered metal layer or a metal coating layer, may be provided on a pair of opposing inner wall surfaces 612A and 612B of the guide housing, and the surface of this rotation prevention layer may be made to function as the rotation prevention surface.

[0048] Further, in the above embodiment, a flat surface is formed as the contact surface on the outer periphery of the screw shaft 30. However, such a contact surface does not have to be flat as long as it can interfere with the rotation prevention surface 644 when the screw shaft 30 rotates by a predetermined angle around the axis O, and it may be curved as shown in FIG. 8. In this case, the rotation prevention surface 644 may be flat or may be curved following the shape of the contact surface of the screw shaft 30.

[0049] Further, in the above embodiment, two contact surfaces 33 that interfere with the rotation prevention surface 644 when the screw shaft 30 rotates by a predetermined angle around the axis O are formed on the outer periphery of the screw shaft 30. However, such a contact surface 33 only needs to be provided at least one on the outer periphery of the screw shaft 30.

[0050] In the above embodiment, an application example to a ball screw actuator applicable as a steering actuator of a steer-by-wire system is given. However, the present invention is not limited to the steering actuator of the steer-by-wire system, and can be widely applied to devices that utilize a feed mechanism such as a nut rotation type ball screw mechanism that converts the rotational motion of the nut into the linear motion of the screw shaft.

Explanation of Signs

[0051] 10: Ball screw mechanism; 20: Nut; 30: Screw shaft; 31: Outer circumference of the screw shaft; 32: Rolling groove; 33: Contact 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 prevention member; 70: Clearance between the rotation prevention surface of the rotation prevention member and the contact surface of the screw shaft; 612A, 612B: Rotation prevention member mounting surface; 613A, 613B: Guide member mounting surface: 614: Hole for boss press-fitting; 615: Snap-fit insertion hole; 616: Step surface; 617: O-ring mounting groove; 618: Slit; 621: Guide member body; 622: Guide surface; 623: Back surface of the guide member body; 624: Snap-fit insertion part; 624A: Cylindrical part; 624B: Latch part; 625: Guide groove; 641: Plate; 642: Back surface of the plate; 643: Boss; 644: Rotation prevention surface

Claims

1. A screw shaft guide unit for supporting a screw shaft in an actuator that converts the rotational movement of a nut into the linear movement of the screw shaft, wherein a guide housing into which the screw shaft having a cylindrical sliding surface and a contact surface having a surface shape different from that of the sliding surface on its outer periphery is inserted in the direction of the axis of the screw shaft, two resin guide members disposed opposite each other across the axis in the guide housing, having a guide surface for contacting the sliding surface of the screw shaft, and supporting the screw shaft so as to be rotatable about the axis and movable in the direction of the axis by the guide surface, a rotation prevention means disposed opposite the contact surface of the screw shaft with a clearance therebetween, and having a rotation prevention surface that contacts the contact surface of the screw shaft when the screw shaft rotates about the axis by a predetermined rotation angle or more determined by the thickness of the clearance, and preventing the rotation of the screw shaft by the contact between the rotation prevention surface and the contact surface of the screw shaft by the rotation prevention surface; A screw shaft guide unit characterized by comprising the above.

2. The screw shaft guide unit according to claim 1, wherein the rotation prevention means comprises a rotation prevention member having the rotation prevention surface on one surface facing the contact surface of the screw shaft and fixed to the guide housing in a state where the other surface located on the opposite side of the rotation prevention surface is in surface contact with the guide housing.

3. The screw shaft guide unit according to claim 1, wherein the rotation prevention means comprises a rotation prevention layer formed on the inner wall surface of the guide housing and having the rotation prevention surface on the surface facing the contact surface of the screw shaft.

4. The screw shaft guide unit according to any one of claims 1 to 3, and having the nut and the screw shaft, and a ball screw that converts the rotational motion of the nut into the linear motion of the screw shaft, The screw shaft has a sliding surface and a contact surface on the outer periphery, and is supported by the guide surfaces of the two guide members so as to be rotatable around the axis and movable in the direction of the axis with the clearance provided between the contact surface and the rotation prevention surface. A ball screw actuator characterized by that.

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