Coupling structure, rotational linear motion conversion device, and shift actuator

Abstract

[Problem] To achieve a structure that is unlikely to generate wear in a coupling structure having a coupling part formed by screwing a male screw part and a female screw part. [Solution] This coupling structure comprises: a first member having a male screw part on an outer peripheral surface thereof; a second member having a female screw part that is screwed with the male screw part on an inner peripheral surface thereof; a rotation prevention member which is laid between the first member and the second member and prevents relative rotation between the first member and the second member; and an elastic member which imparts axial elasticity between the first member and the second member.

Description

Coupling structure, rotary-to-linear motion conversion device, and shift actuator

[0001] The present disclosure relates to a connection structure of two members that are joined by threading a male threaded portion and a female threaded portion and whose relative rotation is prevented by a rotation-preventing member, a rotary-to-linear motion conversion device that includes the connection structure, and a shift actuator that includes the rotary-to-linear motion conversion device.

[0002] In an outboard motor, switching between forward and reverse drive is achieved by switching the dog clutch to engage with either a forward gear or a reverse gear, each of which is fixed to the propeller shaft, via a wire or rod connected to a lever operated by the operator.

[0003] Japanese Patent Application Laid-Open Publication No. 2008-228557 discloses an outboard motor in which a dog clutch is switched by an actuator that uses an electric motor as a drive source in order to reduce the force required by the operator to operate a lever.

[0004] In the outboard motor actuator disclosed in JP 2008-228557 A, rotation of the output shaft (drive shaft) of the electric motor is converted into linear axial motion of a nut by a ball screw device. The output shaft coupled to the nut is connected to a camshaft via a link member and an operating shaft. As the camshaft moves linearly, a dog clutch, which is supported on the propeller shaft so as to allow relative axial movement but not relative rotation, moves linearly and engages with one of the forward gear and reverse gear.

[0005] Generally, the nut is made of an iron-based alloy such as carbon steel or chromium-molybdenum steel to ensure strength and rigidity, and the output shaft is made of a light alloy such as an aluminum alloy to reduce weight.

[0006] The nut and the output shaft are connected by, for example, the actuator described in JP 2012-063009 A, in which a male threaded portion on the outer peripheral surface of the nut and a female threaded portion on the inner peripheral surface of the output shaft are screwed together, and an anti-rotation member (first output shaft support member) is placed between the nut and the output shaft to prevent relative rotation between the nut and the output shaft.

[0007] JP 2008-228557 A JP 2012-063009 A

[0008] In the actuator described in JP 2012-063009 A, it is difficult to bring the stepped surface facing the axial direction of the nut into contact with the axial end face of the output shaft for the following reasons (1) to (3): (1) To bridge the anti-rotation member, it is necessary to match the circumferential phase of the through hole in the nut with the circumferential phase of the recess in the output shaft. (2) Because a return tube is attached to the outer peripheral surface of the nut, it is necessary to restrict the attachment phase of the nut relative to the housing. (3) To connect to the link member, it is necessary to restrict the circumferential phase of the tip of the output shaft.

[0009] Because the stepped surface facing the axial direction of the nut does not abut against the axial end face of the output shaft, sufficient axial force is not applied to the threaded portion between the male and female threads when the nut and output shaft are not moving linearly. Therefore, when the nut and / or the output shaft vibrate due to engine vibration, the threads of the male thread 101 and the threads of the female thread 102 repeatedly collide with each other, as shown in Figure 8, which may cause wear in the male thread 101 and / or the female thread 102. In particular, the female thread 102 is easily worn because it is provided on an output shaft made of a light alloy that is softer than the iron-based metal that makes up the nut.

[0010] The problem of difficulty in abutting the axially facing step surface of the nut with the axial end face of the output shaft is not limited to structures that satisfy all of (1) to (3), but can also occur in structures that must satisfy one or two of (1) to (3).

[0011] Furthermore, wear at the mating portion between the male and female threads can occur not only in outboard motor actuators, but also in any environment where vibration occurs.

[0012] The present disclosure aims to realize a structure for connecting two components that are joined by threading a male threaded portion and a female threaded portion and whose relative rotation is prevented by a rotation-preventing member, in which wear is less likely to occur at the threaded portion, a rotary-to-linear motion conversion device having such a structure, and a shift actuator having such a rotary-to-linear motion conversion device.

[0013] A connection structure according to one embodiment of the present disclosure comprises: a first member having a male threaded portion on its outer circumferential surface; a second member having a female threaded portion on its inner circumferential surface that screws into the male threaded portion; a rotation prevention member that spans between the first member and the second member and prevents relative rotation between the first member and the second member; and an elastic member that imparts axial elasticity between the first member and the second member.

[0014] In the connection structure according to one aspect of the present disclosure, the direction of the elastic force may be a direction that moves the first member and the second member relatively away from each other in the axial direction.

[0015] In this case, the outer peripheral surface of the first member can be configured as a stepped cylindrical surface having a small diameter portion located on one axial side and a large diameter portion located on the other axial side, with a step surface connecting the end of the small diameter portion on the other axial side to the end of the large diameter portion on the one axial side, the male thread portion can be formed on the small diameter portion, and the elastic member can be arranged between the step surface and the end face of the second member on the other axial side.

[0016] The elastic member may be an elastic ring or a wave washer.

[0017] In one embodiment of the connection structure of the present disclosure, the first member may have a first locking portion that opens at least on the outer circumferential surface, the second member may have a second locking portion that penetrates radially, and the anti-rotation member may have a stopper portion that spans between the first locking portion and the second locking portion.

[0018] A rotary-to-linear conversion device according to one aspect of the present disclosure comprises: a housing; a ball screw mechanism including a screw shaft having a spiral shaft-side ball screw groove on its outer peripheral surface; a nut having a spiral nut-side ball screw groove on its inner peripheral surface; and a plurality of balls rollably arranged in a load path formed by the nut-side ball screw groove and the shaft-side ball screw groove; and an output shaft supported so as to be movable axially relative to the housing but not to be rotated relative to the housing.

[0019] In particular, in one aspect of the rotary-linear motion conversion device of the present disclosure, one of the screw shaft and the nut constitutes a linear motion member that moves linearly when in use, and the other of the screw shaft and the nut constitutes a rotating member that moves rotationally when in use, and the linear motion member and the output shaft are connected by a connection structure of one aspect of the present disclosure.

[0020] In the rotary-linear motion device according to one aspect of the present disclosure, the linear motion member may be formed of the first member, and the output shaft may be formed of the second member. In this case, the male threaded portion of the linear motion member and the female threaded portion of the output shaft are threadedly engaged with each other, and the anti-rotation member is engaged between the first engaging portion of the linear motion member and the second engaging portion of the output shaft.

[0021] Alternatively, the linear motion member may be formed of the second member, and the output shaft may be formed of the first member. In this case, the female threaded portion of the linear motion member and the male threaded portion of the output shaft are threadedly engaged with each other, and the anti-rotation member is fitted between the second engaging portion of the linear motion member and the first engaging portion of the output shaft.

[0022] In the rotary-linear motion device according to one aspect of the present disclosure, the linear motion member can be configured by the nut, and the rotating member can be configured by the screw shaft.

[0023] In this case, the nut can include a nut body having the nut-side ball screw groove, and a return tube attached to the nut body for returning the plurality of balls from the start point to the end point of the load path.

[0024] Alternatively, the linear motion member can be formed by the screw shaft, and the rotation member can be formed by the nut.

[0025] A shift actuator according to one aspect of the present disclosure includes: an electric motor having a motor output shaft; a rotary-to-linear motion conversion device that converts rotational motion input to a rotating member into linear motion in the axial direction of the output shaft; and a reduction mechanism that transmits the rotational motion of the motor output shaft to the rotating member.

[0026] In particular, in a shift actuator according to one aspect of the present disclosure, the rotary motion to linear motion converter is configured by the rotary motion to linear motion converter of the present disclosure.

[0027] According to the connection structure and rotary-linear mechanism of one aspect of the present disclosure, it is possible to prevent wear from occurring at the threaded portion between the male thread portion and the female thread portion.

[0028] FIG. 1 is a cross-sectional view showing a rotary-linear motion device according to an embodiment of the present disclosure. FIG. 2 is a perspective view showing the rotary-linear motion device shown in FIG. 1 with the housing removed. FIG. 3 is an enlarged perspective view showing a coupling portion between a nut and an output shaft. FIG. 4(A) is a perspective view showing a state before the nut and the output shaft are coupled, with the nut, output shaft, anti-rotation member, and elastic member removed, and FIG. 4(B) is a perspective view seen from the opposite side of FIG. 4(A) in the axial direction. FIG. 5 is a perspective view of the housing seen from the left side of FIG. 1. FIG. 6 is a cross-sectional view schematically showing a coupling portion between a nut and an output shaft. FIG. 7(A) is an enlarged view of portion X in FIG. 6 when the nut and the output shaft move toward one axial side, and FIG. 7(B) is an enlarged view of portion X in FIG. 6 when the nut and the output shaft move toward the other axial side. FIG. 8 is a schematic diagram for explaining problems with the conventional structure.

[0029] A connection structure according to one embodiment of the present disclosure comprises a first member having a male threaded portion on its outer circumferential surface, a second member having a female threaded portion on its inner circumferential surface that screws into the male threaded portion, a rotation prevention member that spans between the first member and the second member and prevents relative rotation between the first member and the second member, and an elastic member that imparts axial elasticity between the first member and the second member.

[0030] As an example of an embodiment of the present disclosure, an example in which the connection structure of one embodiment of the present disclosure is applied to a connection structure between a nut 15 and an output shaft 4 that constitutes a rotary-to-linear motion conversion device 1 used in a shift actuator of an outboard motor will be described with reference to Figures 1 to 7(B).

[0031] In this example, the nut 15 constitutes the linearly moving member and also constitutes the first member, the screw shaft 14 constitutes the rotating member, and the output shaft 4 constitutes the second member.

[0032] However, when the connection structure of one embodiment of the present disclosure is applied to a connection structure between a nut and an output shaft, the output shaft can also constitute the first member and the nut can constitute the second member.

[0033] The coupling structure according to an embodiment of the present disclosure can also be applied to a coupling structure between a screw shaft and an output shaft that constitute a rotary-to-linear motion converter, in which the screw shaft constitutes a linear motion member and the nut constitutes a rotating member.

[0034] Furthermore, the connection structure of one embodiment of the present disclosure is not limited to the connection structure between the linear motion member and output shaft of the rotary-to-linear motion conversion device that constitutes the shift actuator of an outboard motor, but can be applied to any connection structure of two members that are connected by threaded engagement of a male threaded portion and a female threaded portion and in which relative rotation between them is prevented by a rotation prevention member.

[0035] For example, the coupling structure of one embodiment of the present disclosure can be applied to a rotary-to-linear motion conversion device used in a shift actuator of an automobile transmission or the like.

[0036] [Rotary-to-linear motion converter] The rotary-to-linear motion converter 1 of this example includes a housing 2, a ball screw mechanism 3, and an output shaft 4. The coupling structure is applied to a coupling structure between a nut 15 constituting the ball screw mechanism 3 and the output shaft 4. In this example, the nut 15 constitutes the first member, and the output shaft 4 constitutes the second member.

[0037] In the following description, unless otherwise specified, the axial, radial, and circumferential directions refer to the axial, radial, and circumferential directions of the rotary motion converter 1. The axial, radial, and circumferential directions of the rotary motion converter 1 coincide with the axial, radial, and circumferential directions of the screw shaft 14, the axial, radial, and circumferential directions of the nut 15, and the axial, radial, and circumferential directions of the output shaft 4, respectively.

[0038] Moreover, one axial side refers to the output shaft 4 side (the right side in FIG. 1), and the other axial side refers to the nut 15 side (the left side in FIG. 1).

[0039] In this example, the housing 2 is formed in a cylindrical shape with both axial ends open, that is, the housing 2 has a center hole 5 that passes through the center of the housing 2 in the axial direction.

[0040] The inner peripheral surface of the central hole 5 has, in order from one axial side, a first housing large-diameter cylindrical surface portion 6 , a housing small-diameter cylindrical surface portion 7 , and a second housing large-diameter cylindrical surface portion 8 .

[0041] The first housing large-diameter cylindrical surface portion 6 has an inner diameter larger than the inner diameter of the housing small-diameter cylindrical surface portion 7. The second housing large-diameter cylindrical surface portion 8 has an inner diameter smaller than the inner diameter of the first housing large-diameter cylindrical surface portion 6 and larger than the inner diameter of the housing small-diameter cylindrical surface portion 7. However, the inner diameter of the second housing large-diameter cylindrical surface portion 8 can be the same as the inner diameter of the first housing large-diameter cylindrical surface portion 6, or can be larger than the inner diameter of the first housing large-diameter cylindrical surface portion 6.

[0042] The other axial end of the first housing large-diameter cylindrical surface portion 6 and the one axial end of the housing small-diameter cylindrical surface portion 7 are connected by a first housing step surface 9 facing one axial side. The one axial end of the second housing large-diameter cylindrical surface portion 8 and the other axial end of the housing small-diameter cylindrical surface portion 7 are connected by a second housing step surface 10 facing the other axial side.

[0043] The housing 2 has a tube receiving recess 11 recessed radially outward at one location in the circumferential direction of the housing small diameter cylindrical surface portion 7 .

[0044] In this example, the tube accommodating recess 11 is formed axially in the housing small-diameter cylindrical surface portion 7. That is, one axial end of the tube accommodating recess 11 opens to the first housing step surface 9, and the other axial end of the tube accommodating recess 11 opens to the second housing step surface 10. However, it is also possible for the one axial end of the tube accommodating recess 11 to open only to the first housing step surface 9, and for the other axial end of the tube accommodating recess 11 to not open to the second housing step surface 10.

[0045] The housing 2 is supported and fixed to a fixed part such as the hull of a ship by bolts inserted through mounting holes 13 in a mounting flange portion 12 provided at a plurality of locations, and does not rotate or move during use.

[0046] The ball screw mechanism 3 includes a screw shaft 14, a nut 15, and a plurality of balls (not shown).

[0047] The screw shaft 14 has a spiral ball screw groove 16 on its outer circumferential surface. In this example, the ball screw groove 16 is provided on one axial side of the outer circumferential surface. The ball screw groove 16 has a Gothic arch or circular arc cross section.

[0048] The screw shaft 14 is supported so as to be unable to move axially but to be rotatable relative to the housing 2. In this example, an axially intermediate portion of the screw shaft 14 is supported by the second housing large-diameter cylindrical surface portion 8 of the housing 2 via a radial bearing 17.

[0049] In this example, the screw shaft 14 is configured to be rotatable by a motor output shaft of an electric motor 19 via a reduction mechanism 18 .

[0050] The nut 15 has on its inner peripheral surface a spiral nut-side ball screw groove 20. In this example, the nut-side ball screw groove 20 has a cross-sectional shape of a gothic arch or a circular arc.

[0051] The nut 15 is arranged so as to be movable in the axial direction relative to the housing 2 but not to be rotatable relative to the housing 2 .

[0052] In this example, the nut 15 includes a nut body 21 and a return tube 22 .

[0053] The nut body 21 is made of an iron-based metal such as carbon steel or chrome-molybdenum steel, and has a substantially cylindrical shape.

[0054] The nut-side ball screw groove 20 is provided on the inner peripheral surface of the nut body 21 .

[0055] The return tube 22 has a circulation path inside that connects the start point and end point of the load path formed by the shaft-side ball screw groove 16 and the nut-side ball screw groove 20. For this purpose, both ends of the return tube 22 are connected to the radially outer ends of two through holes that radially penetrate the nut body 21. The radially inner ends of the through holes each open to both ends of the nut-side ball screw groove 20.

[0056] Each of the balls is rotatably disposed in the load path and the circulation path.

[0057] In this example, when the screw shaft 14 is rotationally driven based on the energization of the electric motor 19, the nut 15 moves linearly in the axial direction. At this time, each of the balls rolls in the load path while circulating through the circulation path.

[0058] The output shaft 4 is fixedly coupled to the nut 15. In this example, the output shaft 4 is disposed inside the housing 2 so as to be movable in the axial direction, and is fixedly coupled to one axial side of the nut 15.

[0059] In this example, the output shaft 4 is made of a light alloy such as an aluminum alloy in order to reduce weight.

[0060] When implementing the present disclosure, the nut constituting the first member and the output shaft constituting the second member can be made of the same material, but when the nut constituting the first member and the output shaft constituting the second member are made of different materials, the effects of the present disclosure can be obtained more significantly than when they are made of the same material.

[0061] [Joint Structure] The joint structure of this example includes the nut 15 constituting the first member, the output shaft 4 constituting the second member, a rotation prevention member 38, and an elastic member 41.

[0062] The nut 15 has a male thread portion 26 on its outer circumferential surface.

[0063] The outer peripheral surface of the nut body 21 that constitutes the nut 15 is configured as a stepped cylindrical surface that includes a small diameter portion 23 located on one axial side, a large diameter portion 24 located on the other axial side, and a step surface 25 that connects the other axial end of the small diameter portion 23 to the one axial end of the large diameter portion 24. The large diameter portion 24 has an outer diameter that is slightly smaller than the inner diameter of the housing small diameter cylindrical surface portion 7 of the housing 2.

[0064] In this example, the male screw portion 26 is provided on the small diameter portion 23. Note that the threads of the male screw portion 26 are omitted in Figures 4(A) and 4(B).

[0065] The nut 15 has a first locking portion 27 that opens at least on the outer circumferential surface.

[0066] In this example, the first locking portion 27 is provided so as to open at one location in the circumferential direction of the small diameter portion 23. Specifically, the first locking portion 27 is configured as a recess that opens at one end face in the axial direction of the nut body 21 and extends in the axial direction.

[0067] However, the first locking portion may also be configured as a recess that does not open to one axial end face of the nut body, or as a notch that penetrates radially through the nut and opens to one axial end face of the nut, or as a through-hole that penetrates radially through the nut and does not open to one axial end face of the nut.

[0068] In this example, the return tube 22 is supported and fixed at one circumferential position on the large diameter portion 24 of the nut body 21 by means of a retaining metal fitting 42 and a screw 43 .

[0069] The nut 15 is positioned inside the housing small diameter cylindrical surface portion 7 so as to position the return tube 22 inside the tube accommodating recess 11, allowing axial movement relative to the housing 2 and without any radial play.

[0070] The nut 15 is prevented from rotating relative to the housing 2 by connecting the tip of the output shaft 4, which is connected to one axial side of the nut 15 in a manner that prevents relative rotation via a locking member 38, to a link member or the like.

[0071] The output shaft 4 has, on its inner peripheral surface, a female thread portion 28 that screws into the male thread portion 26 of the nut 15 .

[0072] In this example, the output shaft 4 has, in order from one axial end, a connecting shaft portion 30, a small diameter shaft portion 31, and a large diameter shaft portion 32.

[0073] The connecting shaft portion 30 has a generally oval end face shape when viewed in the axial direction. In this example, the connecting shaft portion 30 has a circular hole 33 penetrating therethrough in the minor axis direction. The connecting shaft portion 30 is connected to the end of the link member by a connecting member inserted through the circular hole 33.

[0074] The small diameter shaft portion 31 is formed in a cylindrical shape and has an outer diameter larger than the diameter of the circumscribing circle of the connecting shaft portion 30. In this example, the portion between the first housing large diameter cylindrical surface portion 6 of the housing 2 and the small diameter shaft portion 31 of the output shaft 4 is sealed by a seal member 44 made of an elastomer such as rubber.

[0075] The large diameter shaft portion 32 has an outer diameter that is larger than the outer diameter of the small diameter shaft portion 31 and is the same as the outer diameter of the large diameter portion 24 of the nut 15. The large diameter shaft portion 32 has a recess 34 that opens to the other end face in the axial direction and has a circular opening shape when viewed from the axial direction.

[0076] In this example, the female thread portion 28 is provided on the inner circumferential surface of the recess 34. In other words, the female thread portion 28 is provided on the inner circumferential surface of the cylindrical portion 35 of the large diameter shaft portion 32, which is located radially outside the recess 34.

[0077] The output shaft 4 has a second locking portion 29 that penetrates radially.

[0078] In this example, the second locking portion 29 is provided so as to radially penetrate one circumferential position of the cylindrical portion 35. Specifically, the second locking portion 29 is configured as a notch that opens on the other axial end face of the cylindrical portion 35 and extends in the axial direction.

[0079] However, the second locking portion may also be configured as a through hole that does not open to the end face on the other axial side of the cylindrical portion 35 .

[0080] In this example, the output shaft 4 has a recessed groove 36 formed around the entire periphery on the outer circumferential surface of the cylindrical portion 35. The recessed groove 36 has a rectangular cross-sectional shape.

[0081] The output shaft 4 further has a bottomed hole 37 that opens to the bottom surface of the recess 34. The bottomed hole 37 is provided for inserting one axial side portion of the screw shaft 14. In this example, the bottomed hole 37 is provided in the output shaft 4 in a range from the axial middle portion of the large diameter shaft portion 32 to the other axial side portion of the small diameter shaft portion 31.

[0082] The anti-rotation member 38 prevents relative rotation between the output shaft 4 and the nut 15. In this example, the anti-rotation member 38 includes a stopper portion 39 and a base portion 40, and is made of synthetic resin as a whole.

[0083] The stopper portion 39 spans between the first locking portion 27 and the second locking portion 29. Specifically, the stopper portion 39 is inserted from the radially outer side into the first locking portion 27 and the second locking portion 29. In this example, the stopper portion 39 has a substantially oval end face shape when viewed from the radial direction.

[0084] In this example, the dimensions and shape of the stopper portion 39 are restricted so that, with the stopper portion 39 disposed inside the second locking portion 29, the other axial end of the stopper portion 39 does not protrude further in the axial direction than the other axial end face of the output shaft 4. This prevents the force that clamps the elastic member 41 between the nut 15 and the output shaft 4 from becoming uneven in the circumferential direction.

[0085] In order to insert the stopper portion 39 of the anti-rotation member 38, the male threaded portion 26 and the female threaded portion 28 are screwed together, and when the circumferential phase of the first locking portion 27 and the circumferential phase of the second locking portion 29 are aligned, the step surface 25 of the nut 15 and the end face on the other axial side of the output shaft 4 do not come into direct contact with each other.

[0086] The base 40 is configured as a notched cylinder having a discontinuous portion at one circumferential position, and extends circumferentially across the radially outer end of the stopper portion 39. The base 40 is elastically fitted onto the bottom surface of the recessed groove 36, thereby preventing the stopper portion 39 from falling off the first locking portion 27 and the second locking portion 29.

[0087] However, the anti-rotation member is not limited to the structure of this example, and any structure can be used as long as it can prevent relative rotation between the nut and the output shaft. For example, if it can prevent the anti-rotation member from falling off the first and second locking portions, a columnar or tubular anti-rotation member made of an elastic material can be fitted between the first and second locking portions. Alternatively, the anti-rotation member can be a split pin fitted between the first and second locking portions, each of which is a through hole. Alternatively, a claw-shaped anti-rotation member provided on one of the nut and the output shaft can be fitted into a recess provided on the other of the nut and the output shaft.

[0088] The elastic member 41 applies elastic force in the axial direction between the nut 15 and the output shaft 4 .

[0089] In this example, the elastic member 41 is composed of a rubber elastic ring called an O-ring, which has a circular cross-sectional shape in a free state, and is elastically clamped between the step surface 25 of the nut 15 and the other axial end face of the output shaft 4.

[0090] In this example, the elastic member 41 attempts to elastically restore its original shape between the step surface 25 of the nut 15 and the other axial end face of the output shaft 4, thereby applying a force to the nut 15 and the output shaft 4 in a direction that moves the nut 15 and the output shaft 4 relative to each other in the axial direction.

[0091] 7(B), even when the nut 15 is not moving linearly, the surface of the flank surface of the thread that constitutes the male thread portion 26 facing the other axial side and the surface of the flank surface of the thread that constitutes the female thread portion 28 facing the one axial side can be brought into elastic contact with each other. Therefore, even when the nut 15 and / or the output shaft 4 vibrate due to engine vibration or the like, wear can be prevented from occurring in the male thread portion 26 and / or the female thread portion 28, particularly in the female thread portion 28 provided on the output shaft 4 made of light alloy.

[0092] The elastic member can be made of any material as long as it can apply axial elastic force to the nut and the output shaft. For example, the elastic member can be made of a rubber elastic ring or wave washer having a non-circular cross-sectional shape, such as a rectangular shape.

[0093] Alternatively, the elastic member may be constituted by a disc spring.

[0094] However, the disc spring has a larger spring constant than the elastic ring or wave washer, and the amount of change in elastic force relative to the amount of compression is large.

[0095] In the coupling structure of this example, it is difficult to regulate with high precision the axial distance between the stepped surface 25 of the nut 15 and the other axial end face of the output shaft 4 for the following reasons (1) to (3): (1) In order to span the anti-rotation member 38, it is necessary to match the circumferential phase of the first locking portion 27 of the nut 15 with the circumferential phase of the second locking portion 29 of the output shaft 4. (2) It is necessary to match the circumferential phase of the return tube 22 of the nut 15 with the circumferential phase of the tube accommodating recess 11 of the housing 2. (3) In order to connect to the link member, it is necessary to regulate the circumferential phase of the connecting shaft portion 30 of the output shaft 4.

[0096] Therefore, in order to minimize the influence of changes in elastic force due to errors in the axial spacing between the step surface 25 of the nut 15 and the end face on the other axial side of the output shaft 4, it is preferable that the elastic member be composed of an elastic ring or a wave washer.

[0097] Alternatively, the resilient member may be constituted by a washer.

[0098] However, in order to press the stepped surface 25 of the nut 15 and the other axial end face of the output shaft 4 in a balanced manner in the circumferential direction, it is preferable that the elastic member be composed of an elastic ring or a wave washer.

[0099] In the rotary-to-linear motion converter 1 of this example, when the screw shaft 14 is rotationally driven based on the energization of the electric motor 19, the nut 15 moves linearly in the axial direction, and the output shaft 4 moves linearly in the axial direction together with the nut 15. The linear motion of the nut 15 is transmitted to the output shaft 4 through the engagement portion between the male thread portion 26 and the female thread portion 28. As the output shaft 4 moves linearly, the link member is pushed and pulled, changing the traveling direction and / or the gear of the multi-speed transmission.

[0100] 7A, when the nut 15 moves linearly toward one axial side, the flank surfaces of the threads constituting the male thread portion 26 that face one axial side press the flank surfaces of the threads constituting the female thread portion 28 that face the other axial side toward one axial side. This causes the output shaft 4 to also move linearly toward one axial side.

[0101] However, if the elastic force of the elastic member 41 is large, even when the nut 15 moves linearly toward one axial side, the end face on the other axial side of the output shaft 4 is pressed toward one axial side by the step surface 25 of the nut 15 via the elastic member 41, causing the output shaft 4 to move linearly toward one axial side. In this case, as shown in Figure 7(B) , the surface of the flank surface of the thread that constitutes the male thread portion 26 facing toward the other axial side and the surface of the flank surface of the thread that constitutes the female thread portion 28 facing toward one axial side remain in contact.

[0102] 7(B), when the nut 15 moves linearly toward the other axial side, the surface of the flank surface of the thread that constitutes the male thread portion 26 that faces the other axial side presses the surface of the flank surface of the thread that constitutes the female thread portion 28 that faces one axial side toward the other axial side. As a result, the output shaft 4 also moves linearly toward the other axial side.

[0103] In this example, an example has been described in which the coupling structure of the present disclosure is applied to a structure in which the nut 15 and the output shaft 4 are coupled together by threading the male thread portion 26 of the nut 15 and the female thread portion 28 of the output shaft 4. However, the coupling structure of the present disclosure can also be applied to a structure in which the nut and the output shaft are coupled together by threading the female thread portion provided on the nut and the female thread portion provided on the output shaft.

[0104] REFERENCE SIGNS LIST 1 rotary-to-linear motion converter 2 housing 3 ball screw mechanism 4 output shaft 5 center hole 6 first housing large-diameter cylindrical surface portion 7 housing small-diameter cylindrical surface portion 8 second housing large-diameter cylindrical surface portion 9 first housing stepped surface 10 second housing stepped surface 11 tube accommodating recess 12 mounting flange portion 13 mounting hole 14 screw shaft 15 nut 16 shaft-side ball screw groove 17 radial bearing 18 reduction mechanism 19 electric motor 20 nut-side ball screw groove 21 nut body 22 return tube 23 small diameter portion 24 large diameter portion 25 stepped surface 26 male thread portion 27 first locking portion 28 female thread portion 29 second locking portion 30 connecting shaft portion 31 small diameter shaft portion 32 large diameter shaft portion 33 circular hole 34 recess 35 cylindrical portion 36 Groove 37: Bottomed hole 38: Anti-rotation member 39: Stopper portion 40: Base portion 41: Elastic member 42: Retaining metal fitting 43: Screw 44: Sealing member

Claims

1. A connection structure comprising: a first member having a male threaded portion on its outer peripheral surface; a second member having a female threaded portion on its inner peripheral surface which screws into the male threaded portion; a rotation prevention member that spans between the first member and the second member and prevents relative rotation between the first member and the second member; and an elastic member that imparts axial elasticity between the first member and the second member.

2. The connection structure according to claim 1, wherein the direction of the elastic force is a direction that moves the first member and the second member relatively away from each other in the axial direction.

3. The connection structure described in claim 2, wherein the outer peripheral surface of the first member is configured as a stepped cylindrical surface having a small diameter portion located on one axial side, a large diameter portion located on the other axial side, and a step surface connecting the end of the small diameter portion on the other axial side and the end of the large diameter portion on the one axial side, the male threaded portion is formed on the small diameter portion, and the elastic member is sandwiched between the step surface and the end face of the second member on the other axial side.

4. The coupling structure according to claim 3, wherein the elastic member is constituted by an elastic ring.

5. The coupling structure according to claim 3, wherein the elastic member is a wave washer.

6. A connection structure as claimed in any one of claims 1 to 5, wherein the first member has at least a first locking portion opening onto the outer circumferential surface, the second member has a second locking portion penetrating in the radial direction, and the anti-rotation member has a stopper portion spanning the first locking portion and the second locking portion.

7. A rotary-linear conversion device comprising: a housing; a ball screw mechanism including a screw shaft having a helical shaft-side ball screw groove on its outer peripheral surface, a nut having a helical nut-side ball screw groove on its inner peripheral surface, and a plurality of balls arranged to roll in a load path consisting of the nut-side ball screw groove and the shaft-side ball screw groove; and an output shaft supported to allow axial movement relative to the housing but not allow relative rotation, wherein one of the screw shaft and the nut constitutes a linear motion member which moves linearly in use, and the other of the screw shaft and the nut constitutes a rotating member which rotates in use, and the linear motion member and the output shaft are connected by a connection structure described in any one of claims 1 to 6.

8. The device for converting rotary motion into linear motion as set forth in claim 7, wherein the linear motion member is formed of the first member, and the output shaft is formed of the second member.

9. A rotary-linear conversion device as set forth in claim 7 or 8, wherein the linear motion member is constituted by the nut, and the rotating member is constituted by the screw shaft.

10. A rotary-to-linear conversion device as described in claim 9, wherein the nut comprises a nut body having the nut-side ball screw groove, and a return tube attached to the nut body for returning the plurality of balls from the start point of the load path to the end point thereof.

11. A shift actuator comprising: an electric motor having a motor output shaft; a rotary-to-linear motion conversion device that converts rotational motion input to a rotating member into linear motion in the axial direction of the output shaft; and a speed reduction mechanism that transmits the rotational motion of the motor output shaft to the rotating member, wherein the rotary-to-linear motion conversion device is constituted by the rotary-to-linear motion conversion device described in any one of claims 7 to 10.

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