Rotational-linear motion conversion device and shift actuator

Abstract

A structure that is less susceptible to wear is achieved in a connection structure having a connection portion formed by threading a male thread portion and a female thread portion together. [Solution] The connecting structure comprises 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 that screws into the male threaded portion, a rotation prevention member that spans 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.

Description

Technical Field

[0001] The present disclosure relates to a coupling structure of two members that are coupled by screwing a male screw portion and a female screw portion and whose relative rotation is prevented by a rotation prevention member, a rotary linear motion conversion device including the coupling structure, and a shift actuator including the rotary linear motion conversion device.

Background Art

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

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

[0004] In the actuator of the outboard motor described in Japanese Patent Application Laid-Open No. 2008-228557, the rotation of the output shaft (drive shaft) of the electric motor is converted into a linear motion in the axial direction of a nut by a ball screw device. The output shaft coupled to the nut is connected to a cam shaft via a link member and an operation shaft. As the cam shaft moves linearly, a dog clutch supported to allow axial relative movement and prevent relative rotation on the propeller shaft moves linearly and meshes with one of a forward gear and a 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 achieve weight reduction.

[0006] The nut and the output shaft are connected, for example, as in the actuator described in Japanese Patent Publication No. 2012-063009, by screwing together a male threaded portion on the outer circumferential surface of the nut and a female threaded portion on the inner circumferential surface of the output shaft, and by having an anti-rotation member (first output shaft support member) stretched between the nut and the output shaft to prevent relative rotation between the nut and the output shaft. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2008-228557 [Patent Document 2] Japanese Patent Publication No. 2012-063009 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In the actuator described in Japanese Patent Publication No. 2012-063009, it is difficult to bring the axially oriented stepped surface of the nut into contact with the axial end face of the output shaft for the following reasons (1) to (3). (1) In order to secure the anti-rotation member, the circumferential phase of the through-hole in the nut and the circumferential phase of the recess in the output shaft must be aligned. (2) Because a return tube is attached to the outer surface of the nut, it is necessary to restrict the mounting phase of the nut relative to the housing. (3) In order 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 of the nut facing axially does not come into contact with the axial end face of the output shaft, sufficient axial force is not acting on the threaded portion between the male and female threads when the nut and output shaft are not moving in a linear motion. Therefore, when the nut and / or output shaft vibrate due to engine vibration, repeated collisions occur between the threads of the male thread 101 and the threads of the female thread 102, as shown in Figure 8, which can cause wear on the male thread 101 and / or female thread 102. In particular, the female thread 102 is provided on the output shaft, which is made of a light alloy that is softer than the iron-based metal that makes up the nut, making it particularly susceptible to wear.

[0010] Furthermore, the problem of difficulty in bringing the axially oriented stepped surface of the nut into contact with the axial end face of the output shaft can occur not only in structures that satisfy all of (1) to (3), but also in structures that need to satisfy one or two of (1) to (3).

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

[0012] This disclosure aims to provide a coupling structure for two members, where a male threaded portion and a female threaded portion are joined by screwing them together, and relative rotation between them is prevented by an anti-rotation member, in which wear is less likely to occur at the screwed portion, a rotary-to-linear motion converter equipped with this structure, and a shift actuator equipped with this rotary-to-linear motion converter. [Means for solving the problem]

[0013] One aspect of the bonding structure of this disclosure is, The outer surface of the first member has a male threaded portion, A second member having a female threaded portion that engages with the male threaded portion on its inner circumferential surface, A rotation-preventing member is provided that spans between the first member and the second member and prevents relative rotation between the first member and the second member, An elastic member that provides axial elasticity between the first member and the second member, comprises.

[0014] In the coupling structure according to one aspect of the present disclosure, the direction of the elastic force can be a direction in which the first member and the second member are relatively moved away from each other in the axial direction.

[0015] In this case, the outer peripheral surface of the first member can be constituted by a stepped cylindrical surface including a small-diameter portion disposed on one axial side and a large-diameter portion disposed on the other axial side, the stepped surface connecting an end portion on the other axial side of the small-diameter portion and an end portion on the one axial side of the large-diameter portion. The male screw portion can be formed on the small-diameter portion, and the elastic member can be disposed between the stepped surface and an end surface on the other axial side of the second member.

[0016] The elastic member can be constituted by an elastic ring or a wave washer.

[0017] In the coupling structure according to one aspect of the present disclosure, the first member can have a first locking portion that opens at least on the outer peripheral surface, the second member can have a second locking portion that penetrates in the radial direction, and the anti-rotation member can have a stopper portion that spans the first locking portion and the second locking portion.

[0018] A rotary-linear motion conversion device according to one aspect of the present disclosure includes a housing, 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 that are rotatably disposed in a load path formed by the nut-side ball screw groove and the shaft-side ball screw groove, an output shaft that is supported so as to be axially movable with respect to the housing and non-rotatable relative to the housing, comprises.

[0019] In particular, in the rotary-linear motion conversion device according to one aspect of the present disclosure, One of the members of the screw shaft and the nut constitutes a linear motion member that linearly moves during use, and the other member of the screw shaft and the nut constitutes a rotary member that rotates during use. The linear motion member and the output shaft are coupled by a coupling structure according to 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 can be constituted by the first member, and the output shaft can be constituted by the second member. In this case, the male screw portion provided on the linear motion member and the female screw portion provided on the output shaft are screwed together, and the rotation prevention member is stretched between the first engagement portion provided on the linear motion member and the second engagement portion provided on the output shaft.

[0021] Alternatively, the linear motion member can be constituted by the second member, and the output shaft can be constituted by the first member. In this case, the female screw portion provided on the linear motion member and the male screw portion provided on the output shaft are screwed together, and the rotation prevention member is stretched between the second engagement portion provided on the linear motion member and the first engagement portion provided on the output shaft.

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

[0023] In this case, the nut can include a nut body having a 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 constituted by the screw shaft, and the rotary member can be constituted by the nut.

[0025] A shift actuator in one aspect of this disclosure is An electric motor having a motor output shaft, A rotation-to-linear motion converter that converts rotational motion input to a rotating member into linear motion in the axial direction of the output shaft, A reduction mechanism that transmits the rotational motion of the motor output shaft to the rotating member, It is equipped with.

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

[0027] According to one aspect of the coupling structure and rotary linear motion mechanism of this disclosure, wear can be prevented at the threaded portion between the male screw portion and the female screw portion. [Brief explanation of the drawing]

[0028] [Figure 1] Figure 1 is a cross-sectional view showing a rotary linear motion device as an example of an embodiment of the present disclosure. [Figure 2] Figure 2 is a perspective view of the rotary linear motion device shown in Figure 1, with the housing removed. [Figure 3] Figure 3 is an enlarged perspective view showing the connection between the nut and the output shaft. [Figure 4] Figure 4(A) is a perspective view showing the nut, output shaft, anti-rotation member, and elastic member removed, before the nut and output shaft are joined together, and Figure 4(B) is a perspective view from the opposite side in the axial direction to Figure 4(A). [Figure 5] Figure 5 is a perspective view of the housing, seen from the left side of Figure 1. [Figure 6] Figure 6 is a schematic cross-sectional view showing the connection between the nut and the output shaft. [Figure 7] Figure 7(A) is an enlarged view of section X in Figure 6 when the nut and output shaft move in one axial direction, and Figure 7(B) is an enlarged view of section X in Figure 6 when the nut and output shaft move in the other axial direction. [Figure 8] Figure 8 is a schematic diagram illustrating the problems with the conventional structure. [Modes for carrying out the invention]

[0029] A coupling 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, an anti-rotation member spanning between the first member and the second member to prevent relative rotation between the first member and the second member, and an elastic member providing 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 coupling structure of one embodiment of the present disclosure is applied to the coupling structure between a nut 15 and an output shaft 4 that constitute a rotary-to-linear motion converter 1 used in the 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 a linear motion member and also constitutes the first member. The screw shaft 14 constitutes a rotating member, and the output shaft 4 constitutes the second member.

[0032] However, when applying the coupling structure of one embodiment of this disclosure to the coupling structure between a nut and an output shaft, the output shaft may constitute a first member and the nut may constitute a second member.

[0033] The coupling structure of one embodiment of the present disclosure can also be applied to the coupling structure between a screw shaft and an output shaft constituting a rotary-to-linear motion converter. In this case, the screw shaft constitutes the linear motion member, and the nut constitutes the rotary motion member.

[0034] Furthermore, the coupling structure of one embodiment of this disclosure is not limited to the coupling structure between the linear motion member of a rotary-to-linear motion converter constituting the shift actuator of an outboard motor and the output shaft, but can be applied to any coupling structure of two members that are coupled by screwing a male screw portion and a female screw portion, and whose relative rotation to each other is prevented by an anti-rotation member.

[0035] For example, the coupling structure of one embodiment of the present disclosure can be applied to a rotary-to-linear converter used in a shift actuator such as a transmission in an automobile.

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

[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-to-linear converter 1. The axial, radial, and circumferential directions of the rotary-to-linear 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] Furthermore, "one axial side" refers to the output shaft 4 side (right side in Figure 1), and "the other axial side" refers to the nut 15 side (left side in Figure 1).

[0039] In this example, the housing 2 is configured as a cylindrical shape with openings on both axial sides. That is, the housing 2 has a central hole 5 that penetrates through its center in the axial direction.

[0040] The inner circumferential surface of the central hole 5 has, in order from one side in the axial direction, 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 it can be larger than the inner diameter of the first housing large-diameter cylindrical surface portion 6.

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

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

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

[0045] The housing 2 is supported and fixed to a fixed part such as the hull by bolts inserted through mounting holes 13 of mounting flange portions 12, which are provided in multiple locations, and does not rotate or displace during use.

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

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

[0048] The screw shaft 14 is supported relative to the housing 2 in a way that prevents axial movement but allows for relative rotation. In this example, the axial middle portion of the screw shaft 14 is supported by the second 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 rotatably driven by the motor output shaft of the electric motor 19 via a reduction mechanism 18.

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

[0051] The nut 15 is positioned to allow axial movement relative to the housing 2, but to prevent relative rotation.

[0052] In this example, the nut 15 comprises 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 chromium-molybdenum steel and has a roughly cylindrical shape.

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

[0055] The return tube 22 has a circulation path on its inside that connects the start and end points of the load path, which consists of a shaft-side ball screw groove 16 and a 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 penetrate the nut body 21 radially. Each of the radially inner ends of the through holes opens to both ends of the nut-side ball screw groove 20.

[0056] Each of the balls is arranged to be rotatable in the load path and the circulation path.

[0057] In this example, when the screw shaft 14 is rotated 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 along the load path while circulating through the circulation path.

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

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

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

[0061] [Bond structure] The coupling structure in this example comprises a nut 15 constituting the first member, an output shaft 4 constituting the second member, an anti-rotation member 38, and an elastic member 41.

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

[0063] The outer circumferential surface of the nut body 21 constituting the nut 15 is composed of a stepped cylindrical surface comprising a small-diameter portion 23 located on one axial side, a large-diameter portion 24 located on the other axial side, and a stepped surface 25 connecting the end of the small-diameter portion 23 on the other axial side and the end of the large-diameter portion 24 on one axial side. 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 threaded portion 26 is provided on the small diameter portion 23. Note that the threads of the male threaded 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 its outer circumferential surface.

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

[0067] However, the first locking portion may also be formed by a recess that does not open to one end face on the axial side of the nut body. Alternatively, the first locking portion may be formed by a notch that penetrates the nut radially and opens to one end face on the axial side of the nut, or by a through hole that penetrates the nut radially and does not open to one end face on the axial side 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 using a retaining bracket 42 and a screw 43.

[0069] The nut 15 is positioned inside the small-diameter cylindrical surface portion 7 of the housing, such that the return tube 22 is positioned inside the tube housing recess 11, allowing for axial movement relative to the housing 2 and without 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 coupled to it via an anti-rotation member 38 on one axial side, to a link member or the like.

[0071] The output shaft 4 has a female threaded portion 28 on its inner circumferential surface that engages with the male threaded portion 26 of the nut 15.

[0072] In this example, the output shaft 4 has, in order from one axial side, 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 substantially oval end face shape when viewed from the axial direction. In this example, the connecting shaft portion 30 has a circular hole 33 that penetrates in the direction of the short axis. The connecting shaft portion 30 is connected to the end of the link member by a connecting member that passes through the circular hole 33.

[0074] The small-diameter shaft portion 31 is cylindrical in shape and has an outer diameter larger than the diameter of the circumscribed circle of the connecting shaft portion 30. In this example, the portion between the first 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 sealing member 44 made of an elastomer such as rubber.

[0075] The large-diameter shaft portion 32 has an outer diameter larger than that of the small-diameter shaft portion 31 and the same outer diameter as 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 on the axial side 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 that is located radially outward from 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 penetrate radially through one circumferential position of the cylindrical portion 35. Specifically, the second locking portion 29 is formed by a notch that opens onto the other end face of the cylindrical portion 35 on the axial side and extends in the axial direction.

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

[0080] In this example, the output shaft 4 has a groove 36 extending around the entire circumference of the outer surface of the cylindrical portion 35. The 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 portion of the screw shaft 14. In this example, the bottomed hole 37 is provided in the output shaft 4, in the range from the axial middle portion of the large diameter shaft portion 32 to the other axial 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 comprises a stopper portion 39 and a base portion 40, and the entire structure is integrally constructed from synthetic resin.

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

[0084] In this example, with the stopper portion 39 positioned inside the second locking portion 29, the dimensions and shape of the stopper portion 39 are restricted so that the axial end of the stopper portion 39 does not protrude further axially than the axial end face of the output shaft 4. This prevents the force gripping 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 stepped surface 25 of the nut 15 and the other end face on the axial side of the output shaft 4 do not come into direct contact.

[0086] The base portion 40 is configured as a cylindrical section with a discontinuity at one location in the circumferential direction, and extends circumferentially so as to cross the radially outer end of the stopper portion 39. The base portion 40 is elastically fitted onto the bottom surface of the groove 36. This prevents the stopper portion 39 from falling out of 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 adopted as long as it can prevent relative rotation between the nut and the output shaft. For example, an anti-rotation member made of an elastic material, which is columnar or cylindrical overall, can be stretched between the first and second locking parts, provided that it can prevent detachment from the first and second locking parts. Alternatively, the anti-rotation member can be made of a cotter pin stretched between the first and second locking parts, which are each through holes. Alternatively, a claw-shaped anti-rotation member provided on one of the nut and the output shaft can be locked into a recess provided on the other of the nut and the output shaft.

[0088] The elastic member 41 provides axial elasticity between the nut 15 and the output shaft 4.

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

[0090] In this example, the elastic member 41 attempts to elastically restore itself between the stepped surface 25 of the nut 15 and the other end face of the output shaft 4 on the axial side, thereby applying a force to the nut 15 and the output shaft 4 that causes them to move relative to each other in the axial direction.

[0091] Therefore, even when the nut 15 is not moving in a linear motion, as shown in Figure 7(B), the flank surface of the threads constituting the male thread portion 26 that faces the other axial direction and the flank surface of the threads constituting the female thread portion 28 that faces the one axial direction can be brought into elastic contact. Consequently, even if the nut 15 and / or the output shaft 4 vibrate due to engine vibration or the like, wear on the male thread portion 26 and / or the female thread portion 28, especially the female thread portion 28 provided on the output shaft 4 made of light alloy, can be prevented.

[0092] The elastic member can be made of any material, as long as it can impart axial elasticity 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 rectangle.

[0093] Alternatively, the elastic member can be made of a disc spring.

[0094] However, disc springs have a larger spring constant and a larger change in elastic force with respect to compression compared to elastic rings and wave washers.

[0095] In the coupling structure of this example, it is difficult to precisely control the axial distance between the stepped surface 25 of the nut 15 and the other end face of the output shaft 4 for the following reasons (1) to (3). (1) In order to secure the anti-rotation member 38, the circumferential phase of the first locking portion 27 of the nut 15 and the circumferential phase of the second locking portion 29 of the output shaft 4 must be aligned. (2) The circumferential phase of the return tube 22 of the nut 15 must be matched with the circumferential phase of the tube housing recess 11 of the housing 2. (3) In order to connect to the link member, it is necessary to restrict 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 distance between the stepped surface 25 of the nut 15 and the other end face 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 elastic member can be made up of a washer.

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

[0099] In the rotary-to-linear motion converter 1 of this example, the screw shaft 14 is rotationally driven based on the energization of the electric motor 19, causing the nut 15 to move linearly in the axial direction. Along with the nut 15, the output shaft 4 also moves linearly in the axial direction. The linear motion of the nut 15 is transmitted to the output shaft 4 through the threaded portion between the male threaded portion 26 and the female threaded portion 28. As the output shaft 4 moves linearly, the link member is pushed and pulled, and the direction of travel and / or the gears of the multi-speed transmission are switched.

[0100] When the nut 15 moves linearly in one axial direction, as shown in Figure 7(A), the flank surface of the threads constituting the male thread portion 26 that faces one axial direction presses against the flank surface of the threads constituting the female thread portion 28 that faces the other axial direction. As a result, the output shaft 4 also moves linearly in one axial direction.

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

[0102] When the nut 15 moves linearly in the other axial direction, as shown in Figure 7(B), the flank surface of the threads constituting the male thread portion 26 that faces the other axial direction presses against the flank surface of the threads constituting the female thread portion 28 that faces one axial direction. As a result, the output shaft 4 also moves linearly in the other axial direction.

[0103] In this example, the coupling structure of the present disclosure is described in an example in which the nut 15 and the output shaft 4 are coupled by screwing the male threaded portion 26 of the nut 15 and the female threaded portion 28 of the output shaft 4 together. 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 by screwing the female threaded portion provided on the nut and the female threaded portion provided on the output shaft together. [Explanation of symbols]

[0104] 1. Rotary-to-linear motion converter 2 Housing 3. Ball screw mechanism 4 Output shafts 5 Center hole 6. First housing large diameter cylindrical surface 7. Small diameter cylindrical surface of the housing 8. Second housing large diameter cylindrical surface 9. First housing stepped surface 10. Second housing step surface 11 Tube housing recess 12 Mounting flange section 13 mounting holes 14 Screw shaft 15 nuts 16. Ball screw groove on the shaft side 17 Radial bearings 18 Reduction mechanism 19 Electric motor 20 Ball screw groove on the nut side 21 Nut body 22 Return Tube 23 Small diameter section 24 Large diameter section 25 Step surface 26 Male threaded section 27 First locking section 28 Female thread section 29 Second locking section 30 Connecting shaft 31 Small diameter shaft section 32 Large diameter shaft section 33 Round hole 34 recess 35 Cylindrical part 36 grooves 37 Bottomed hole 38 Anti-rotation member 39 Stopper section 40 base 41 Elastic members 42 Retaining clip 43 screws 44 sealing member

Claims

1. a first member having a male thread portion on its outer peripheral surface; a second member having a female thread portion on its inner peripheral surface that engages with the male thread portion; a detent member spanning between the first member and the second member to prevent relative rotation between the first member and the second member; an elastic member that applies an axial elastic force between the first member and the second member; A coupling structure comprising:

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

3. The outer peripheral surface of the first member is constituted by a stepped cylindrical surface including a small-diameter portion disposed on one side in the axial direction, a large-diameter portion disposed on the other side in the axial direction, and a stepped surface connecting an end portion on the other side in the axial direction of the small-diameter portion and an end portion on the one side in the axial direction of the large-diameter portion, The male thread portion is formed on the small-diameter portion, and The elastic member is sandwiched between the stepped surface and an end surface on the other side in the axial direction of the second member. The coupling structure according to claim 2.

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 constituted by a wave washer.

6. The first member has at least a first locking portion that opens to the outer peripheral surface, The second member has a second locking portion that penetrates in the radial direction, and The detent member has a stopper portion spanning between the first locking portion and the second locking portion. The coupling structure according to claim 1.

7. a housing; a ball screw mechanism including a screw shaft having a helical axial 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 rotatably disposed in a load path formed by the nut-side ball screw groove and the axial ball screw groove; an output shaft supported to be axially movable and non-rotatable relative to the housing; Comprising: One of the screw shaft and the nut constitutes a linear motion member that moves linearly during use, and the other of the screw shaft and the nut constitutes a rotary member that rotates during use, A rotary-linear motion conversion device, wherein the linear motion member and the output shaft are coupled by the coupling structure according to claim 1.

8. The rotary-linear motion conversion device according to claim 7, wherein the linear motion member is constituted by the first member, and the output shaft is constituted by the second member.

9. The rotary-linear motion conversion device according to claim 7, wherein the linear motion member is constituted by the nut, and the rotary member is constituted by the screw shaft.

10. The nut according to claim 9, comprising a nut body having a 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.

11. An electric motor having a motor output shaft, A rotary-linear motion conversion device that converts the rotary motion input to the rotary member into a linear motion in the axial direction of the output shaft, A speed reduction mechanism that transmits the rotary motion of the motor output shaft to the rotary member, Comprising, A shift actuator, wherein the rotary-linear motion conversion device is constituted by the rotary-linear motion conversion device according to any one of claims 7 to 10.

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